Types of program control systems. Typical block diagram of a cnc system
Mechanical engineering is the basis for the successful development of all industries National economy. The efficiency of machine-building production and the quality of manufactured products are largely determined by the level of its automation. The main direction in the automation of machine-building production is currently based on the widespread introduction of digital computing devices and machines.
To control universal machines and other technological equipment, numerical control systems(CNC).
The CNC controls the movement of the working bodies of machine tools and equipment, their speed during the shaping of parts, installation movements, as well as the sequence of processing modes and auxiliary functions.
The part programs of the control system contain two types of information needed to automatic operation machine tools (equipment): geometric and technological. Geometric information includes data on the shape, dimensions of the elements of the part and tool, as well as their relative position in space.
Technological information is instructions on the sequence of putting tools into operation, changing cutting conditions, changing tools, turning on the coolant supply, etc.
Technological information is also used for control in other software devices, for example, in cyclic program control systems (SCP). The geometric information in the SCPU is implemented by reconfigurable stops placed directly on the machine (equipment). The advantages of the SCPA are in their great versatility, the possibility of quick readjustment, program correction and inclusion in more complex integrated systems. automated production. CNCs are complex multi-loop automatic control systems, since they simultaneously control several independent or related object parameters (coordinates). Accordingly, there are several control loops (channels) in the structure of the control system. So, for example, in machine tools The CNC simultaneously controls the main shaping movement, the feed movement and auxiliary movements: transport, clamping, retraction and approach, tool change, etc.
CNCs are classified according to the following features: structure and principle (algorithm) of control, purpose, type of drive, nature of drive movement, method of program definition.
According to the structure, CNCs are divided into open, closed and combined.
The principle of control of open-loop CNCs is based on the use of only the master action embedded in the control program (principle of rigid control). In closed control systems, in addition to the master influence - control program information about the actual values of the controlled parameters is used, i.e. control principle based on the deviation of the controlled parameter (flexible control).
IN combined The CNC control of the main parameters (main motion and feed motion) is carried out by closed control loops operating on the principle of deviation, and the control of auxiliary parameters (workpiece clamping, tool approach, tool change, turning on of the coolant, etc.) can be carried out by open control loops.
IN adaptive The CNC has additional sensors for information about the parameters of the machining process: cutting force, temperature, tool wear, etc. This information is used in the CNC to correct the technological parameters set by the control program, depending on the change in the machining allowance, the hardness and rigidity of the workpieces, the condition of the tool, etc.
Depending on the purpose of the equipment equipped with CNC devices, control systems are divided into positional, contour and universal.
IN positional control systems programmed coordinates (x, y) individual discrete points (Fig. 13.4, but), determining the position (position) of the tool or workpiece. Such systems are used to control drilling and boring machines.
A variety of positional control systems are rectangular systems that control movement along the segments (indicated in Fig. 13.4, b numbers 7 ... b), parallel to the guides of the machine. Rectangular systems are designed for sequential control of one of two mutually perpendicular coordinates. Such systems are used on turning
a B C
Rice. 13.4. To the definition of the type of control in the control:
but - positional; b- rectangular; in- contour
machines to control the processing of parts such as stepped rollers, and on milling parts with a rectangular contour.
IN contour The control system performs simultaneous interconnected control along several coordinates along segments and sections of curves, in fig. 13.4, in labeled 1... 6 And r 1 , r 2 , to obtain parts with a complex profile. Such systems are used to control turning, milling, electroerosive machines, as well as welding machines.
In multi-operational machines designed for processing complex parts (such as a body) with several tools at the same time, universal (positional-contour) control systems.
Depending on the number of simultaneously controlled coordinates, CNCs are distinguished with control over one, two, three, four, five or more coordinates.
Depending on the type of energy used in the motors of the drive devices, there are CNCs with an electric drive, electro-hydraulic and electro-pneumatic drives.
In the CNC, various servo drives are mainly used, built on the principle of closed (servo) automatic control systems. Less often, open-loop drives are used using only stepper motors that allow direct software control of both the displacement value and its speed.
In devices with a servo drive, DC and motors can be used. alternating current, as well as stepper hydraulic and pneumatic motors. The frequency of rotation of the motors in the servo drive must vary over a wide range (by 1000 or more times).
Drives use displacement sensors that generate a feedback signal that is sent to the CNC, where it is compared with the command signal received from the control program. Selsyns, rotating transformers, inductosyns, multi-turn potentiometers are used as displacement sensors in analog devices of the servo drive of the CNC. In addition, various types of movement-to-code converters are used in the analogue devices of the CNC servo drive.
Depending on the structure of the CNC device, all systems are divided into two main types: built on the principle of a digital model and built on the structure of a computer.
In systems where the CNC device is built according to the principle digital model, all operations are performed by the corresponding specialized electronic units with strictly defined functions, and the connections between these units are unchanged. The principle of building a CNC device based on the use of blocks - units with clearly defined functions is called aggregate. Such a control device operates according to an unchanged algorithm, while all blocks work in parallel, performing the information conversion operations assigned to them.
In systems where the CNC device (CNC) is built according to computer structure, blocks are universal and the links between them can be changed in accordance with a given program. Control operations in this case are performed sequentially using the central arithmetic unit. As part of the CNC there are storage devices: operational (RAM) and permanent (ROM).
The functioning of RAM and ROM is carried out according to the algorithm for processing information received in the form of a control program, i.e. these devices require special software. Moreover, the software can be stored in ROM if frequent changes in operation algorithms are not required, or it can be entered through an input device as part of a control program. Such a construction makes it easy to correct the CNC device operation algorithm and improve it as statistical information about the quality of manufactured parts is accumulated.
It is promising to create CNC devices based on the use of one or more microprocessors built on large integrated circuits (LSI), i.e. the use of the aggregate principle of building a CNC based on microprocessors programmed on specific tasks. It is possible to build a CNC device on the basis of a microcomputer, supplementing it with a microprocessor or controllers - programmable logic devices for processing information. In the future, as the element base improves, it may become rational to build a CNC based on a mini-computer. This will expand the functionality of the CNC and facilitate their inclusion in more complex integrated automated production systems: automatic lines, sections, workshops, flexible automated production systems. Generalized functional diagram CNC lathe, built on the principle of an open system, is shown in Fig. 13.5. Here, the actuators of the main movement (M1), feed movement (M2, MZ), auxiliary movement - rotation and feed of the turret with tools (M4, M5) receive control signals from the drive control unit (BUP).
The input-output device (I/O) receives the control program from the central computer (with group control, when the control system operates as part of a flexible production system) or reads it from a punched tape (with autonomous control). At the same time, the control program, intermediate results of calculations, the necessary constants are stored in a memory device (memory) and, as necessary, are used by a computing device (CD) to generate control actions on the TCU. The latter contains electronic control units for stepper motors or error signal amplifiers (in servo drive devices), thyristor converters for controlling the speed of the main movement (in this circuit, the spindle speed), etc.
The control panel (CP) has buttons and a keyboard for controlling individual blocks or manual control of the drive, as well as for full or partial (during setup) manual entry of the control program into the memory and processing the first part using it, followed by editing the program (in the CNC with direct input programs). The control panel allows you to display
to indicate (on the display) any block of the program or other information processed by the system, and signal the occurrence of malfunctions.
In positional CNCs that work according to a rigid algorithm, the VU may be absent. In contour CNCs built on the principle of a digital model, VU is used as interpolator, which is a specialized block-unit that controls the processing speed simultaneously in two coordinates. Interpolators can be linear, circular, parabolic.
Linear interpolators are used if the contour of the workpiece can be represented as straight line segments located at any angle to the coordinate axes. Curvilinear sections are approximated in this case by line segments. Linear-circular interpolators are used when processing parts with a complex contour, made up of various arcs of circles and line segments. The arc of a circle in such interpolators is specified by one block of the program, and the general curvilinear contour is approximated by several straight lines and arcs of circles of different radii. Parabolic interpolators are used in the processing of very complex parts (propeller blades, turbines, etc.).
In the CNC, built on the principle of the structure of a computer, microprocessors, as well as micro- and mini-computers, are used as a VU. Mini-computer-based CNCs are most promising when creating complex integrated systems for automatic production, such as technological modules, automatic lines, sections, workshops and flexible production systems.
The technological module is an automated multi-operational machine and an automatic manipulator united by a common ACS.
Technological complex is an automatic production complex, consisting of a group of CNC machines, an automatic manipulator, transport and storage devices, united by a common ACS, operating from a central computer, and providing full or partial processing of a certain type of part.
An automatic line is a complex of automated working machines located in the sequence of technological operations connected by means of transportation and auxiliary equipment, united by a common ACS, operating from a central computer, and providing a full cycle of processing a part or a group of parts of the same type.
An automated section is a complex of several automated machines or modules, combined with the help of a transport system, and manipulators, auxiliary
powerful devices, a single system of group control from the central computer, providing complex processing of the same type of parts with different sequences of operations.
Flexible production systems(GPS) are designed for automated design and manufacture of new products in the conditions of small-scale multi-product production.
The transfer of the State Fire Service to the production of new products is provided by software without manual restructuring of equipment. The GPS unites several complexes, each of which uses a local computer for control. For general management The GPS complex uses a powerful main computer, and the entire management structure is based on a hierarchical principle.
On fig. 13.6 shown structural scheme GPS control, which includes the following subsystems:
Design CAD - system automatic design designs of new products, consisting of automatic workstations of the designer (ARM-K);
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CAD technology - automatic design system technological processes manufacturing of new products, consisting of automatic workstations of a technologist (ARM-T);
OKP system - a system of operational scheduling, connected via a computer with automatic system production management (APCS);
SAP - a system for automatic preparation of control programs for CNC machines and automatic manipulators;
SAC is a system of automatic control and diagnostics that controls the operation of all systems included in the GPS, as well as fixing and classifying faults in all subsystems.
In addition, the automated production system includes subsystems 7 ... 7, shown in Fig. 13.6.
The class of computers used in each system and subsystem depends on the complexity of the tasks performed. In general, the management of the GPS is a computer complex associated with the automated control system.
Industrial robots
Robot is called an automatic machine physical work instead of a person. The scope of robots is very extensive. Exploration of space and the depths of the oceans, Agriculture, transport and industrial production, construction - everywhere there is an urgent need for such machines. Robots can replace a person when working in conditions dangerous to life and health, free him from monotonous, tedious, unpleasant work. Greatest development currently received industrial robots, which are the most important component of complex automation production processes. Industrial robots differ from traditional automation tools in the versatility of reproducible movements and the ability to quickly change them to new operations, as well as the ability to combine them into complexes along with process equipment.
Robots are mainly used in mechanical engineering to replace workers, employed in servicing machine tools, presses, furnaces and other technological equipment, as well as to perform such basic technological operations as welding, simple assembly, transportation, etc. The use of industrial robots makes it possible not only to comprehensively automate the operation of individual machines, but also to switch to the automation of individual sections, such as machining, stamping, spot welding, by creating robotic complexes. Such complexes are mandatory integral part GPS - higher systems (achievable for modern technology) level of production automation.
The main task performed by industrial robots is manipulative actions in the production process.
Manipulative actions- this is the movement and orientation in space of objects (blanks, finished parts) and tools (tools). Based on the main task of an industrial robot, it can be defined as a set mechanical hands- manipulators and control device. In the general case, the robot can also have vehicles.
The simplest robots, the main task of which is to perform certain movements(manipulations) given by the program are called automatic manipulators. Depending on the complexity of the work performed, there are three types of automatic manipulators - three generations.
robotic arms first generation work according to a strict program, and their interaction with the environment is limited by elementary feedbacks. First generation robots can be sentient, i.e. have touch sensors (in particular, touch sensors - tactile, allowing you to adjust the force of compression of the grip). The environment in which such robots operate must be organized in a certain way. This means that all items (blanks and finished parts, tools, structural elements, machine tools, equipment, etc.) must be in certain places and have a certain orientation in space. This requirement imposes some restrictions on the use of first-generation robotic arms.
robotic arms second generation have elements of adaptation to environmental conditions and are able to solve more complex problems. These are sentient robots that have sensory sensors that allow them to coordinate movements based on perceived state signals. environment. In particular, these can be tactile sensors that allow you to change the developed force, location sensors (light, ultrasonic, television, gamma-ray, etc.) that allow you to change the trajectory of the manipulator when an obstacle appears, the need to combine parts that are not clearly oriented in space , etc.
robotic arms third generation are able to logically process incoming information, i.e. have artificial intelligence. These robots are capable of learning and adapting, can carry on a dialogue with a human operator, recognize and analyze difficult situations, form concepts and create a model of the environment, plan behavior in the form of an action program (taking into account previous experience), etc. Oshu work on such complex algorithm only possible with a computer.
The basis of the park in the industry is currently made up of first-generation robots as the most simple, reliable and economical.
On fig. 13.7 schematically shows the device of an automatic robotic arm, and in fig. 13.8 shows a functional diagram of its control. Structurally, such a robot consists of two main parts: an executive one, which includes a manipulator or manipulators (M) and a movement device (PM), and a control one, i.e. a robot control device (CU).
The robot arm has a horizontal arm 3, which can move both horizontally (along the x-axis) and vertically (along the x-axis). T) directions relative to the rack 2. In this case, the stand can be rotated through an angle a around the vertical axis 2 relative to the fixed base 1. Hand mechanism fixed at the end of the arm 4, additionally providing two degrees of freedom to grip 5: rotation around the longitudinal axis of the arm at an angle p and rotation (swing) relative to the perpendicular axis at at the corner at To fix the part, grip 5 can be automatically closed (movement in the direction of the arrow BUT).
(rectangular, cylindrical, spherical, combined) for the implementation of the portable movement of the working body (movement of the actual arm of the manipulator), the working area of the manipulator can be in the form of a parallelepiped, cylinder, ball and more complex spatial bodies. Since the arm of the manipulator shown in Fig. 13.7, has one rotational and two translational degrees of freedom (mobility): movement along the axes X And at and rotation around axis 2, its working area looks like a cylinder. Brush movement - rotation around an axis X and swing around the axis at are orienting. Automatic robotic manipulators can have from three to seven degrees of mobility, and the device of their working body depends on the purpose of the robot.
In robots that perform loading and unloading operations, transportation, tool change, they use and different kinds captures, providing the capture, orientation and retention of the object of manipulation. In robots that perform technological operations, the working body can be a spray gun, welding head, wrench or other tool.
The principles of operation and designs of grippers are very diverse, since the dimensions, shape and physiochemical properties objects of manipulation can vary widely. According to the method of capturing and holding the object of manipulation, gripping devices are divided into mechanical, vacuum, electromagnetic and combined.
The actuators of the manipulator are driven by motors, the number of which depends on the number of degrees of its mobility. There are manipulators that have one engine for several degrees of freedom, equipped with clutches for distributing movement. The type of drive motor depends on the purpose of the manipulator and its parameters. Currently, pneumatic, hydraulic and electric motors are used approximately equally.
Mobile robots can have various devices movements - from well-known rolling devices to walking mechanisms (pedipulators), which have been developed recently.
The robotic manipulator control device can be made as an independent (structurally isolated) unit or be built into the body of its executive part. Usually, the control device (see Fig. 13.8) includes: a control panel (CP), which allows you to enter and control the task; a memory device (memory) storing the work program; servo drive mechanisms of the manipulator and movement device; amplifiers; converters; power supplies; control elements (relays, contactors, spools, jet pipes, motion distributors, solenoid valves, etc.).
The number of feedback sensors in the control circuit (DOS1, DOS2) is determined by the number of degrees of freedom of the manipulator and the number of coordinates of its movement executive device. They are used in the follower drive to control the movement of the working body of the manipulator and, in general, its entire actuator (DA).
Potentiometers, selsyns, rotating transformers, inductosyns, coding converters, etc. are used as motion feedback sensors in robotic manipulators.
Sensed and adaptive robots can have touch sensors to receive additional information about the actual situation in the zone of action of their manipulators. As touch sensors included in the sensing system, in addition to tactile and location sensors, any other sensors can be used in robotic manipulators: temperature, pressure, magnetic field, colors, etc. Sensory information is entered into a computing device (CD) to correct the robot's action.
The robot arm creates the main work force Y x on technological equipment or an object of manipulation (workpiece, part, tool). In addition, control actions can be applied to technological equipment. (U 1 , U 2) and technology teams 2 directly from the process control unit (PCU) - to block the operation of the equipment during the working movements of the manipulator, change the operating mode of the equipment, etc. In turn, information and control actions on this robot can come from technological equipment or other robots (conditionally from remote sensing sensors).
In robotic systems and GPS systems, the robot can receive inputs G1 from control devices of a higher rank (level).
So, from the main computer, management work complex or GPS, new work programs may arrive, as well as commands that correct a given program or coordinate the action of a robotic arm with the actions of other robots or with the process of operation of technological equipment.
Offline master influence G2 created by a program stored in memory. In the setup or training mode, the master influence G3 created by the operator through the PU. In this case, the computing device of the robot can be different levels(in robots with cyclic program management WU is absent). The more versatile the robot and the more complex the tasks solved with its help, the higher the level of CS: microprocessor, micro- or mini-computer. In robotic complexes and GPS, computers of medium and high power, as well as complexes of several computers, are used.
Industrial robots-manipulators are classified according to a number of the following main features included in the symbol of their type:
number of manipulators (1M, 2M, 3M, ...);
the number of degrees of mobility, taking into account the device of movement (2; 3 or more);
type of working area (flat - Pl, surface - Pv, in the form of a parallelepiped - Pr, spherical - Sh, combined - PrTsl, TslSh, PrSh);
load capacity;
Type of manipulator drives (pneumatic - Pn, hydraulic - G, electromechanical - E, combined - GPn, GE, EPn);
type of control system (cyclic - C, positional - P, contour - K, sensible robot - O, with artificial intelligence - I);
accuracy class (0; 1; 2; 3).
For example, a robotic arm with symbol 1M4Tsl-5EK1 has one manipulator with four degrees of freedom, working area cylindrical shape, load capacity 5 kg, electromechanical drive, contour control system, first class accuracy (trajectory reproduction error from 0.01 to 0.05%). Part of the information characterizing the robot is indicated verbally (the presence of a movement device, separate or common drive according to the degrees of freedom, adaptive or non-adaptive control, type of execution - heat-protective, explosion-proof, normal, etc.).
The figure shows a general enlarged block diagram of the CNC system. It includes the following main elements: CNC device; feed drives of the working bodies of the machine and feedback sensors (DOS) installed for each controlled coordinate. The CNC device is designed to issue control actions by the working body of the machine in accordance with the control program entered on the punched tape. The control program is read sequentially within one frame with storage in the memory block, from where it is fed into the blocks of technological commands, interpolation and feed rates. Interpolation block - a specialized computing device (interpolator) - formulates a partial trajectory of the tool between two or more points specified in the control program. The output information from this block enters the feed drive control unit, usually presented as a sequence of pulses for each coordinate, the frequency of which determines the feed rate, and the number determines the amount of movement.
The information input and reading block is intended for input and reading of the control program. Reading is performed sequentially line by line within one frame.
Memory block. Since the information is read sequentially, and is used all at once within one frame, when reading it, it is stored in the memory block. Here, it is also monitored and a signal is generated when an error is detected in the punched tape. Since the processing of information proceeds sequentially by frames, and the time for reading information from one frame is approximately 0.1 - 0.2 s, a gap in the transmission of information is obtained, which is unacceptable. Therefore, two blocks of memory are used. While the information of one frame from the first memory block is being processed, the second frame is read and stored in the second block. The time for introducing information from the memory block into the interpolation block is negligible. In many CNC systems, the memory block can receive information bypassing the input block and reading directly from the computer.
interpolation block. This is a specialized computing device that forms a partial tool path between two or more points specified in the control program. This is the most important block in CNC contouring systems. The basis of the block is the interpolator, which, according to the numerical parameters of the contour section specified by the control program, restores the function f (x, y). In the intervals of X and Y coordinate values, the interpolator calculates the coordinate values of the intermediate points of this function.
At the outputs of the interpolator, control pulses strictly synchronized in time are generated to move the working body of the machine along the corresponding coordinate axes.
Linear and linear-circular interpolators are used. In accordance with this, the former perform linear interpolation, and the latter linear and circular.
The linear interpolator provides, for example, the movement of the working body with a cutter with a diameter between two reference points in a straight line with a deviation from the given contour by .
In this case, the initial information for the interpolator is the magnitude of increments in coordinates and and the processing time of moving along a straight line, i.e. , where S is the set tool feed rate.
The operation of a linear-circular interpolator can be carried out according to the method of the evaluation function F. The method lies in the fact that when the next control pulse is generated, the logic circuit evaluates on which coordinate this pulse should be issued so that the total movement of the working body of the machine tool brings it as close as possible to the specified contour.
The interpolated line (see Fig. a) divides the plane in which it is located into two regions: above the line, where the evaluation function F>0, and below the line, where F<0. Все точки, лежащие теоретически заданной линии, имеют F=0.
The interpolation trajectory is a certain sequence of elementary displacements along the coordinate axes from the starting point with coordinates to the end point with coordinates , .
If the intermediate point of the trajectory is in the region F>0, then the next step is taken along the X axis. If the intermediate point is in the region F<0, шаг делается по оси Y. Аналогично происходит работа интерполятора при круговой интерполяции (см. рис. б).
Feed drive control unit. From the interpolation block, the information is fed to the feed drive control unit, which converts it into a form suitable for controlling feed drives. The latter is done so that upon receipt of each pulse, the working body of the machine moves by a certain amount, characterizing the discreteness of the CNC system. When each impulse arrives, the controlled object moves by a certain amount, called the impulse price, which is usually 0.01 - 0.02 mm. Depending on the type of drive (closed or open, phase or amplitude) used on machines, control units differ significantly. In closed-loop phase-type drives using feedback sensors in the form of rotating transformers operating in the phase shifter mode, control units are pulse-to-phase AC converters and phase discriminators that compare the phase of the signal at the output of the phase converter with the phase of the feedback sensor and output a difference error signal to the drive power amplifier.
Feed rate block - provides a given feed rate along the contour, as well as acceleration and deceleration processes at the beginning and end of processing sections according to a given law, most often linear, sometimes exponential. In addition to working feeds (0.5 - 3000 mm / min), this block, as a rule, also provides idling with an increased speed (5000 - 20000 mm / min).
Control and indication panel. The operator communicates with the CNC system through the control and display panel. With the help of this console, the CNC system is started and stopped, switching the operating mode from automatic to manual, etc., as well as correcting the feed rate and tool sizes and changing the initial position of the tool in all or some coordinates. This console contains a light signaling and digital indication.
The program correction block is used to change the programmed processing parameters: feed rate and tool dimensions (length and diameter).
The block of canned cycles is used to simplify the programming process when processing repeating elements of a part (for example, drilling and boring holes, threading, etc.), a block of canned cycles is used. For example, such movements as fast withdrawal from a finished hole are not programmed on a punched tape - this is incorporated in the corresponding cycle (G81).
The block of technological commands provides control of the cycle of the machine (its cyclic automation), including the search and analysis of the cutting tool, switching the spindle speed, clamping and unclamping the moving working bodies of the machine, and various interlocks.
The power supply unit supplies the necessary constant voltages and currents to all CNC units from a conventional three-phase network. A feature of this block is the presence of voltage stabilizers and filters that protect the CNC electronic circuits from interference that always occurs in industrial power networks.
Feedback sensors (DOS)
DOS are designed to convert the linear movements of the working body of the machine into electrical signals containing information about the direction and magnitude of movements.
The whole variety of DOS can be conditionally divided into angular (circular) and linear. Circular DOS usually convert the angle of rotation of the lead screw or the movement of the working body of the machine through a rack and pinion gear. The advantage of circular DOS is their independence from the length of movement of the working body of the machine, ease of installation on the machine and ease of operation. The disadvantages include the principle of indirect measurement of the displacement of the working body, and therefore the measurement error.
Topic 1.6. CNC tasks
The CNC device is the control device in relation to the machine. At the same time, it is itself an object of control when interacting with the environment, which is the operator, upper-level computer, etc. If we consider from these positions the tasks that it should solve, then the following tasks can be distinguished:
A geometric task is the interaction of the CNC with the machine to control the shaping of the part. The solution to this problem is to display the geometric information of the drawing in a set of such movements of the working bodies of the machine, which materialize the drawing into a product.
The logical task is to control discrete electroautomatics, i.e. automation of auxiliary operations on the machine (tool clamping, tool change, etc.).
The technological challenge is to manage the workflow and achieve the required quality of parts processing at a lower cost.
The terminal task is the interaction of the CNC with the environment.
geometric problem
The essence of the geometric task can be defined as follows: to display the geometric information of the drawing in the aggregate of such shaping movements of the machine tool that materialize the drawing in the final product. Each machine has its own set of electric drives located according to the coordinate system. The electric drives are located in such a way as to ensure the processing of parts of the corresponding class, i.e. moving the tool (or workpiece) along the guides.
For example, on machines of the turning group, the profile of the part is formed by moving the tool in one plane, so the machines of this group are equipped with a set of two drives that move the tool along the longitudinal and transverse guides.
Logic task
Numerous auxiliary operations, also called technological ones, are automated on modern CNC machines. These include: tool change, tool clamping/unclamping, feed box switching, chuck control, cooling, guard, lubrication, etc. All these functions are performed by a system of cyclic electroautomatics - a system of automatic control of mechanisms and groups of mechanisms, the behavior of which is determined by a set of discrete operations with the relations of succession and parallelism. Moreover, individual operations are initiated by electrical control signals, and the conditions for their change are formed under the influence of informing signals coming from the control object. All complex cyclic processes performed on a CNC machine can be represented as automation cycles and operations. The automation cycle of a CNC machine is a sequence of actions called by name by one of the following three information words of the control program: “Main movement speed”, “Tool function”, “Auxiliary function”. The automation cycle consists of operations, and an operation can be understood as any independent action of a discrete mechanism performed by one engine, opened by an independent control signal, confirmed or not confirmed when closed by an informing signal.
The information word "Speed of the main movement" begins with the address S, followed by a combination of numbers that determines either the cutting speed or the spindle speed in different cases. To encode the speed of the main movement, the methods of direct designation, geometric and arithmetic progressions, and the symbolic method are used.
The direct designation method is the most obvious: the word S800 means, for example, calling a cycle that sets the speed to 800 min-1. When coding by the geometric progression method, the rotation frequency is designated by the conditional code 00, .... 98, and the true values form a geometric progression: 0; 1.12; 1.25; 1.40; ...; 80,000.
The info word "Tool function" begins with a T address followed by one or two groups of digits. In the first case, the word indicates only the number of the called tool, and the offset number for this tool is determined by another word with address D. In the second case, the second group of digits specifies the number of the tool length, position or diameter offset. For example, in the word Т1218: Т – address, 12 – tool number; 18 - corrector number.
The information word "Auxiliary function" defines various commands to the cyclic mechanisms of the machine and the CNC itself. Auxiliary functions are set with words with the address M and a conditional two-digit code combination 00, ..., 99. Some commonly used auxiliary functions are given in Table. 1.2. Other auxiliary functions are introduced when creating a specific machine and a specific CNC device.
Numerical control metal-cutting machines are called the control of the working bodies of the machine when processing the workpiece according to the control program, which is a sequence of commands in an alphanumeric code (in symbolic form) in a special language. The fundamental difference between CNC systems and previously considered control systems lies in the method of calculating the sequence of control signals and transmitting them to the working bodies of the machine.
In the drawing, technological information is presented in the form of graphic images (contour), numbers (dimensions), symbols (roughness), text, etc. In the previously considered control systems, the processing program is embodied in physical analogues: copiers, cams, travel stops, the position of the patch panel plugs, etc. Their manufacture is a very laborious process and is accompanied by errors in the calculation of the copier profile and errors in their manufacture. When operating atacin copiers wear out, which introduces an additional error.
In CNC systems, the control program includes:
Technological commands similar to PLC commands (tool selection, spindle speed and feed speed setting, coolant supply on/off, etc.);
Geometric commands for moving the working body along a certain trajectory that are not available in the PLC (setting the coordinates of the successive positions of the RO);
Preparatory commands that serve to control the control device itself and set its operating modes.
Each command is a set of symbols and numbers, easily accessible to the understanding of a person (technologist-programmer of CNC devices), which simplifies programming and reduces the number of errors in the program. Below are the main terms used when programming the CNC.
Part zero point(part zero) - a part point whose coordinates are taken as zero in the coordinate system associated with the part. From the zero of the part, the dimensions of the processed surfaces are laid off. Machine zero point(machine zero) - a point in space that has zero coordinates in the coordinate system associated with the machine (usually coincides with the base point of the fixture). The coordinate axes of the machine tool system are usually parallel to the machine guides and the axis of rotation of the spindle
Rice. 6.4. Examples of calculated trajectories
Tool center - fixed point of the tool relative to the holder, for which the trajectory is calculated. For a cutter, this is its top, for a cutter, it is the point of intersection of the cutter axis with its end face.
The machine coordinate system is determined by the machine design, and each part can have one or more of its own coordinate systems, which are determined based on the convenience of describing the surfaces to be machined. The NC geometric commands are specified in the part coordinate system and are transferred to the machine coordinate system during the NC execution.
starting point(machine) - a point in the machine coordinate system, used as the starting point of the NC operation, linking the machine zero and the part zero.
Estimated trajectory - trajectory of the tool center, which is calculated from the geometry of the machined surfaces, taking into account the geometry of the tool. In the simplest case, the calculated trajectory coincides with the contour of the part (for example, when turning, when the tool center is the tool tip). This can be an equidistant curve (Fig. 6.4, a) or a more complex curve (Fig. 6.4, b).
Reference geometric or technological point - this is the point of the calculated trajectory, at which the law describing the trajectory changes, or the processing conditions change.
Below is the simplest program in the universal CNC programming language CLDATA (Catter Location Data - data on the position of the cutting edge) for external turning of a cylindrical surface and trimming the end face (Fig. 6.5) with comments, compiled in accordance with the ISO standard.
The coordinates of the trajectory points are set from the zero point of the part, which in this example is the point of intersection of the part axis with its right end, the Z axis is directed along the part axis to the right, the axis X - along the radius.
Rice. 6.5. The scheme of turning the outer cylindrical surface and trimming the end face on a CNC machine
N10 G90 G95 S670 M4 - coordinates of the path points - absolute (G90), spindle speed setting: set the rotation speed (G95) 670 rpm (S670)), counterclockwise rotation (M4);
N15 GO X50 Z1.5 T1l M8 - rapid tool approach: positioning (GO) of the tool with code 11 (T11) to a point with coordinates X = 50 mm (X50), Z = 1.5 mm (Z1.5), 1, 5 mm - lead-in section, turn on cooling with code 8 (M8);
N20 Gl Z-10 F0.35 - working stroke - turning: linear
interpolation (G1) (trajectory - straight line segment) from the previous point X = 50 mm, Z = 1.5 mm to a point with the same X coordinate and Z coordinate - -10 mm (Z-10) with axial feed S = 0, 35mm/rev (F0.35);
N25 G95 S837 M4 - setting the spindle speed: I set the speed (G95) 837 rpm (S837)), rotation again counterclockwise;
N30 Gl X56 F0.3 - facing up 5+1 mm: linear interpolation (G1) to point X = 56 mm, Z = -10 mm (X56) with radial feed S = 0.3 mm/rev (F0. 3);
N35 GO X70 Z30 - quick retraction of the tool to the right: positioning to point X = 70 mm, Z = 30 mm (Z30);
N40 M02 - end of program.
The program is typed on a punched tape or recorded on a magnetic tape or disk, after which the commands are entered into the CNC, decrypted, the CNC issues orders to the working bodies of the machine, waits for the completion of the current command and proceeds to the next one. Each command provides for the automatic execution of complex actions by the machine control systems related to the movement of the working bodies in time under conditions of disturbances from the external environment (fluctuations in the supply voltage, hardness of the workpiece, friction, etc.) - The commands are executed sequentially, the transition to the next command is possible only after the completion of the current one.
Control program block - part of the UE, performed as a whole (tool supply, passage, etc.). Block or head of the control program - a set of frames performed with one setting of the technological system (the example considered above). Main frame of the control program- the first after stopping the processing sets the new settings of the technological system necessary to continue processing. The remaining frames of the block (chapter) set a sequential change in the settings defined by the main frame.
In the ROM, the CNC is placed in the form of subroutines of the sequence of control signals necessary for the machine to perform the main actions associated with the processing of the workpiece. The CNC is an interpreter that decodes the next NC command and launches the corresponding subroutine for executing this command (for example, the subroutine for controlling the rapid approach of the tool to the desired point G0), leading to the operation of relays, clutches, travel switches, etc. and providing the execution of various technological commands (tool change, spindle speed switching, caliper movement, etc.).
Constant cycle - a frequently occurring sequence of NC commands, designed as a standard CNC subroutine, which is called by a single NC macro instruction (for example, subroutines for turning a cylindrical surface, threading, drilling holes). The use of loops simplifies programming and reduces the length of the NC.
Interpolator- the CNC block responsible for calculating the coordinates of the intermediate points of the trajectory that the tool must pass between the points specified in the NC. The interpolator has as input data a NC command for moving the tool from the start to the end point along the contour in the form of a straight line segment, a circular arc, etc., for example:
N15 G0 X50 Z1.5 T1l M8 - fast approach in a straight line;
N20 Gl Z-10 F0.35 - working stroke in a straight line.
The result of the interpolator's operation is a sequence of control pulses for the drive of feeds issued at the right time, providing the required speed and amount of movement of the caliper, or the required laws X(t), Y{ t), Z(t) changes in the coordinates of the working body in time. It is the interpolator that is the master for the automatic control system of the multi-coordinate feed drive, which reproduces the required trajectory.
To ensure the accuracy of trajectory reproduction of the order of 1 µm (the accuracy of the position sensors and the positioning accuracy of the caliper are about 1 µm), the interpolator generates control pulses every 5 ... 10 ms, which requires high speed from it.
In order to simplify the algorithm of the interpolator, a given curvilinear contour is usually formed from segments of straight lines or from arcs of circles, and often the steps of movement along different coordinate axes are performed not simultaneously, but alternately. Nevertheless, due to the high frequency of issuing control actions and the inertia of the mechanical drive units, the broken trajectory is smoothed to a smooth curvilinear contour.
UE is compiled based on some standard tool, the real tool has different dimensions and wears out during operation. The formation of a new version of the UE for each tool is laborious, storing a large number of UE variants is inconvenient. In CNC machines, the possibility of correction is provided: CNC settings manually or by NC commands for a specific tool. When executing NC, each command will be automatically adjusted to take into account the actual tool overhang (by parallel translation) and the radius of the cutting edge (by calculating the equidistance). On fig. 6.5 shows the trajectory of the tool tip specified in the UE and the trajectory of the base point F tool holder, shifted up by L x - cutter offset along the axis X and right to L z - tool overhang along the Z axis
It is possible to automatically correct the trajectory taking into account tool nose (overhang correction) or feed correction with an unacceptable increase in cutting forces, spindle drive torque, vibrations (adaptive control). In this case, a multi-level correction occurs that changes during processing.
CNC systems are divided into position systems, carrying out the installation of the working body at a given point in space, and the trajectory of movement is determined by the CNC itself, and contour systems, ensuring the movement of the working body along the trajectory specified in the UE with a given contour speed.
Positional systems are typical for drilling, spot welding, cutting operations, when the trajectory does not matter, and the movement is usually performed in a straight line with alternate or simultaneous changes in coordinates.
CNC contouring systems are used in surface treatment on turning and milling machines, when the required surface is reproduced by the joint movement of the tool and workpiece. CNC contour systems usually include the functions of positional systems. Thus, the UE considered above was compiled for the contour control device of a lathe (the trajectory of the cutter during the working stroke is set by the G1 command), however, in the UE there is a command for the rapid approach of the working body (CO) typical for positional systems.
For rigid synchronization of movement along the coordinates and rotation of the spindle in the CNC, pulses from the rotation speed sensor of the main drive can be used as a clock generator (instead of a timer in the computer). The machine drives are controlled mainly by pulses, therefore the CNC is a pulse device equipped with a USO with pulse inputs and outputs.
The rapid development of electronics has led to the constant complication of the CNC. The simplest are CNC systems of the NC class (Numeric Control).
The next generation of CNCs were SNC (Stored Numeric Control) class systems built on integrated circuits with greater reliability and capabilities and smaller dimensions, which led to an increase in the power of input language commands, simplification of programming and reduction in the size of the NC. Systems of this class had RAM sufficient to memorize the entire NC; this made possible a single input of the NC into the RAM and its multiple execution when processing a series of parts, the operational characteristics of these systems have improved significantly.
The use of a control minicomputer as a CNC instead of special control units led to the creation of DNC (Direct Numeric Control) class systems. Due to the high cost of the minicomputer of those times and its large dimensions, the computer was located outside the processing area and controlled several machines at the same time.
The use of a universal computer as a CNC allowed:
implement control algorithms in the form of computer programs, which led to the flexibility of the system;
build UE from powerful commands using subprograms-cycles, which simplifies programming and makes UE short;
load UE from a punched tape, magnetic disk or transfer them over the network from an archive.
With the advent of microcomputers, it became possible to place the CNC directly on the machine in relation to this particular machine. Systems of this class are called CNC (Computer Numeric Control) and have the following features:
the same type of computers are used to control a variety of machines, which makes it possible to unify the CNC, reduce their cost, increase reliability and simplify CNC programming;
machine-specific control algorithms are included in the ROM chip, which ensures their storage reliability and the flexibility of the CNC due to the ease of replacing one ROM chip with another.
The connection, using a computer network, of individual CNC systems that control machine tools, robots, transport devices, etc., with a computer that stores NC archives and interconnects the work of individual CNC equipment units, has led to to creation of flexible production systems. In these systems, the central computer synchronizes the operation of all CNCs included in the FMS, monitors the health of the nodes, serves as an operator console, is connected via a network to higher-level control systems: automatic production control systems (APCS), automatic design systems, etc., which ensures uninterrupted supply raw materials, tools, etc.
The growth in the power of computers used as CNC class CNCs has led to the creation of HNC (Handled Numeric Control) class systems equipped with a powerful processor, a magnetic disk and a high-quality display that allow simple manual input and debugging of NC on the machine using auxiliary programming tools.
The more powerful the CNC, the more powerful the operators of its input language (up to CLDATA), the shorter and clearer the NC, the fewer errors, the easier manual and automated programming of the CNC.
Compiling a NC for processing complex parts requires a highly qualified programmer, and errors in it lead to breakdowns of expensive equipment and injuries to people. Therefore, manual programming is replaced by automated one, in which a person, in dialogue with the CNC programming automation system (SAP), installed on a general-purpose computer, solves technological problems, and the CAP performs detailed painstaking execution of commands for the CNC.
On fig. 6.6 shows a diagram of creating and executing a program for the CNC. The geometry of the part and technological information are specified either in the form of operators for describing the initial data for SAP (usually one of the variants of the generally accepted APT language), or in a dialogue with the data preparation program by depicting the geometry of the part in a graphical editor and selecting information from the tables and menus offered by the computer.
Any SAP is a set of programming programs, including programs such as preprocessor, processor and postprocessor.
SAP preprocessor is designed for preliminary analysis of initial data. The SAP processor calculates the trajectory, reference points and forms the NC, usually in CLDATA - the programming language of some abstract CNC, taken as standard. If the real machine CNC requires NC in its input language, the NC is translated into that language in the SAP post-processor. Next, the NC is loaded into the CNC and executed.
The operators are decrypted in turn in the control device (CU), which issues control pulses as needed to the controllers of the main drive drive, tool clamping, etc. Geometric commands are transmitted to the interpolator, which sets the feed drive the required laws for changing the coordinates of the tool center. The corrector takes into account the features of the real geometry of the tool, after which the control pulses are fed to the feed drive.
During processing, the corresponding sensors control the operation of clutches and electric drives, the position of the caliper, the torque of the main drive, cutting forces, vibration levels, etc.
SAP CNC relies on data banks (DBD) containing the following components:
Schemes and adjustments for processing typical surfaces (external/internal turning, threading, grooving, drilling, slot milling, etc.);
A library of simple graphic elements for geometric images (circles, ellipses, rectangles, holes, teeth, gears, etc.);
Technical characteristics of machines, fixtures, tools;
Data for calculating processing modes; archive of previously developed transitions, operations;
Archive of finished UE;
Archive of postprocessors for different CNC.
CNC machines, and hence SAP, are specialized in:
lathes - 2-coordinate in the XZ plane;
milling, drilling machines - 2.5-coordinate, three-dimensional figures are given by a section in the plane XY and height Z; 2.5-axis machines - this means that two coordinates are controlled at the same time (X And Y), after which the processing in the XOU plane stops and the rearrangement is performed along the Z axis into a new plane XOY.
drilling and boring multi-tool machining centers - 3-coordinate.
SAP allows you to simulate and display on the screen the tool trajectory and the metal removal process, which is convenient for NC control. SAP allows correction of UE manually at any stage of preparation.
test questions
1. What forms of representation of the algorithm do you know?
2. What is the purpose of the operating system?
3. What is the purpose of program testing? (Choose the correct answer):
a) demonstration of the program's performance to the customer;
b) identifying errors and shortcomings in the program in "uncomfortable" conditions;
c) checking the operation of the program under typical conditions.
4. What is the difference between a PLC and a control computer?
5. What is the difference between a PLC and a CNC?
Questions for the exam
1. Computer software
2. Algorithms (Block diagram of the algorithm for calculating the average value)
3. Computer operating system
4. Programs (Averaging program)
5. Programmable logic controllers
6. Numerical control systems
Rice. 6.6. Scheme of preparation and execution of the control program of the CNC machine
There are many SAP CNC, the simplest of which provide input of initial data in the input language of the APT type, calculation of trajectories, generation of NC on CLDATA and its translation (if necessary) into the input language of the CNC. More complex SAP are able, in dialogue with the technologist according to the drawing of the part, made on one of the standard machine drawing packages, to form a technological process, design individual operations with the choice of the necessary machine, fixture, tool, calculate the sequence of transitions and passes, calculate processing modes, etc. .
The use of SAP, created with the participation and on the basis of the experience of qualified technologists-programmers, greatly simplifies CNC programming and improves the quality of programs, which creates the prerequisites for the widespread use of CNC equipment.
MACHINE NUMERICAL PROGRAM CONTROL SYSTEMS
Structure of CNC systems
In general terms, the structure of the CNC machine complex can be represented as three blocks, each of which performs its task: a control program (NC), a CNC device (CNC) and the machine itself (Fig. 1.1).
Rice. 1.1. Functional diagram of CNC machine control
^ COMPLEX "CNC MACHINE"
All blocks of the complex work interconnected in a single structure. Control program contains an enlarged coded description of all stages of the geometric and technological formation of the product. This description should not allow ambiguous interpretations. In the CNC device, control information is transmitted in accordance with the UE, and then used in the computing cycle. The result is the formation of operational commands in real-time machine time.
Machine is the main consumer of control information, the executive part, the object of control, and in a constructive sense - the supporting structure, on which mechanisms with automatic control are mounted, adapted to receive operational commands from the CNC. These mechanisms include, first of all, those that are directly involved in the geometric shaping of the product. Depending on the number of movement coordinates specified by the feed mechanisms, a processing coordinate system is formed. The coordinate system can be flat, spatial three-dimensional, spatial multidimensional. The functionality of a real CNC system (CNC) is determined by the degree of implementation of a number of functions when controlling equipment. Consider a brief description of these functions.
^ Input and storage of system software(SPO). Free software includes a set of programs that reflect the algorithms for the functioning of a particular object. In the CNC of the lower classes, the open source software is structurally embedded and cannot be changed, and the CNC can only control this object (for example, only machines of a turning group with two coordinates). In multi-purpose systems that provide control over a wide class of objects, when setting up the control system for solving a certain range of tasks, the open source software is introduced from the outside. This is necessary because different objects have differences in shaping algorithms in terms of the number of control coordinates, speeds and accelerations of the tool movement. A variety of types of drives and the composition of the technological commands of objects leads to differences in the number and nature of the exchange signals.
In stand-alone multi-purpose control devices, open source software is entered from a punched tape, from a floppy disk, from a compact disk (CD), and in automated devices (as part of an automated process control system, GAP,) - via a communication channel with an upper-level computer. Naturally, the open source software is stored in the system memory until the control object changes. When replacing a control object (for example, instead of a lathe, an industrial robot is connected to the CNC), it is necessary to enter new programs (SPO) into the CNC that would determine the algorithms for the functioning of this new object.
It is necessary to distinguish between open source software and control programs: open source software remains unchanged for a given control object, and UEs change during the manufacture of different parts on the same object. In multi-purpose CNCs, the memory for storing STRs must be non-volatile, i.e. save information in the event of a power failure.
^ Input and storage of UE. The control program can be entered into the CNC from the control panel, from a floppy disk or via communication channels with a higher-level computer. The NC storage memory, which is usually represented in ISO code, must be non-volatile. In higher-class CNCs, the NC is usually entered immediately and in its entirety and stored in the system's RAM. Powerful computer CNCs allow you to record and store a large number of NC programs in the memory of your computer.
^ Frame interpretation. The control program consists of components - frames. The development of the next frame requires a number of preliminary procedures called frame interpretation. For the continuity of the contour control of the interpretation procedure i 1st frame must be implemented during the control of the object by i-th frame. In other words, the control system must be ready for immediate (without interruptions for reading and recognizing frames) issuing control commands in accordance with the commands of the next frame after the execution of the commands embedded in the current frame.
Interpolation. The control system must provide, with the required accuracy, automatic receipt (calculation) of the coordinates of the intermediate points of the trajectory of the elements of the controlled object according to the coordinates of the extreme points and the specified interpolation function.
^ Feed drive control. The complexity of the control depends on the type of drive. In the general case, the problem is reduced to the organization of digital position tracking systems for each coordinate. The input of such a system receives codes (code) corresponding to the results of interpolation. These codes must correspond to the position along the coordinate (linear or angular) of the moving object. Determining the actual position of a moving object and reporting it to the control system are carried out by feedback sensors. In addition to control in the mode of movement along a given trajectory, it is also necessary to organize some auxiliary modes: coordination of the drive control system with the true position of feedback sensors, setting the drive system to a fixed zero of the machine, control of exceeding the permissible values of coordinates, automatic exit of drives into braking mode according to certain laws and etc.
^ Drive control of the main movement. The control provides for enabling and disabling the drive, speed stabilization, and in some cases - controlling the angle of rotation as an additional coordinate.
^ Logic control. This is the control of technological nodes of discrete action, the input signals of which produce operations such as "enable", "disable", and the output signals state "on", "off". Recently, CNCs of the highest level have appeared, possessing the properties of non-standard logic, a kind of high intellectual level.
^ Correction for tool dimensions. NC correction for tool length is reduced to parallel transfer of coordinates, i.e. offset. Taking into account the actual radius of the tool is reduced to the formation of such a trajectory, which is equidistant to the programmed one. In a number of high-level CNCs, it is possible to correct and take into account in the NC up to 15 different tool parameters.
^ Implementation of cycles. The selection of repeating (standard) sections of the program, called cycles, is an effective method of reducing NC. The so-called fixed cycles are typical for certain technological operations (drilling, countersinking, boring, threading, etc.) and are found in the manufacture of many products. When developing a UE, fixed cycles are indicated in the program, and their processing is carried out in accordance with a specific subroutine stored in the memory of the control system by the software system or a structural diagram. In a high-level CNC, up to 500 canned cycles and subroutines can be stored in the memory of the control computer, and, therefore, can be quickly used.
Program technology cycles correspond to the repeating sections of a given workpiece. These cycles in certain control systems can also be selected and entered into the control memory of the control system, and when repeated in accordance with the NC commands, they can be implemented by calling them from the main memory.
^ Tool change. This function is typical for multi-tool and multi-purpose machines. The task of changing a tool generally has two phases: searching for a magazine nest with the required tool and replacing the used tool with a new one. In the GAP with a tool warehouse, there are complex systems for automatic supply (replacement) of tools for machine tool magazines.
^ Correction of mechanical and measuring errors devices. Any specific machining unit (i.e., a control object) can be certified using measuring instruments of a sufficiently high accuracy class. The results of such certification in the form of tables of errors (intra-step error, accumulated error, backlash, temperature errors) are entered into the memory of the control system. When the system is running, the current readings of the sensors of the units are corrected by the data from the error tables. High-level systems have built-in control and measuring complexes that control the main parameters of the machine in the so-called background. The results of the control are immediately used to carry out the necessary corrections.
^ Adaptive processing control. To implement such control, the necessary information is obtained from specially installed sensors, which measure the moment of resistance to cutting or the components of cutting forces, the power of the drive of the main movement, vibration, temperature, tool wear, etc. Most often, adaptation is carried out by changing the contour speed or the speed of the drive of the main movement .
^ Accumulation of statistical information. Statistical information includes fixing the current time and operating time of the system and its individual nodes, determining the equipment load factor, accounting for manufactured products, fixing its individual parameters, etc.
^ Automatic built-in control. The organization of such control in the processing zone is especially relevant for GAP. Continuous control over the formed dimensions of the workpiece is one of the main tasks of improving the quality of processing.
^ Additional features. Additional functions include the following: information exchange with a top-level computer, coordinated control of the technological module equipment, control of elements of an automatic transport and storage system, control of external devices, communication with the operator, technical diagnostics of technological equipment and the CNC system itself, optimization of individual modes and cycles technological process, etc.
^ INFORMATION STRUCTURE OF CNC MACHINES
The CNC includes the means involved in the development of control actions on the executive bodies of the machine and other mechanisms according to a given program, the means for making and controlling the action of external and adaptive corrections, as well as the means for diagnosing and monitoring the performance of the CNC and the machine during the manufacture of the part. The CNC machine tool should include: technical means; software (for programmable control systems); operational documentation.
The technical means of the control system include: the computational-logical part (including storage devices of various types for programmable systems); means of forming influences on the executive bodies of the machine (drives of feeds and the main movement, executive devices of electroautomatics, etc.); means of communication with sources of information about the state of the controlled object (measuring transducers of various types, control devices, adaptation, diagnostics, etc.); means providing interaction with external systems and peripheral devices (communication channels with computers of the highest rank, etc.). Technical means, included in the CNC are usually structurally designed in the form offline device- UCHPU.
The main classification features of the CNC are the level of complexity of the controlled equipment and the number of axes connected by solving a single interpolation problem in time. On this basis, CNC machines are divided into the following groups:
CNC with rectangular shaping along one coordinate axis;
CNC with contour shaping with a limited set of functions along two or three coordinate axes (information channels);
CNC with extended functionality for equipping multi-purpose machines and machines with complex volumetric shaping along four to five coordinate axes (information channels);
CNC with extended functionality, including special control tasks, for equipping heavy and unique machines and machine modules with 10-12 coordinate axes (information channels).
The complexity of the structure of the control system is determined by information features and is estimated by the number and nature of the information channels used in the operation of the system. Due to the fact that the information purpose of devices and their elements included in the control system is different, they are assigned to different hierarchical ranks. Typically, CNC machines have a two- or three-rank structure, while providing access to higher ranks for working as components of the FMS, automated lines, sections and other production complexes.
In the structural-information analysis of the control system, a certain distribution of levels and information channels is adopted.
Level 0 rank is a combination of factors such as temperature, quality of materials, instrumentation data, etc.
Level 1 rank - these are converters that form channel information:
According to the position of the executive bodies of the machine,
By technological and dimensional parameters characterizing the state of the technological system;
according to the parameters of disturbances introduced into the technological system;
by the accuracy of the part processed on the machine;
on the replacement of fixtures, tools and readiness of the machine;
to monitor the correct course of the cutting process and register the problems that arise, as well as develop ways to eliminate them.
The level of the 2nd rank is a set of executive adjustable drives and actuators of the machine:
basic, carrying out program movement of executive bodies,
auxiliary, performing various kinds of technological commands, including with the help of a robot
additional, intended for adjustment and corrective movements.
Level 3rd rank - the level of technical means of the control system.
Levels 4 and higher ranks go beyond the control and machine. The level of the 4th rank includes, for example, an external computer.
In the most general case, CNC machine tools have a three-rank structure.
Classification of CNC devices
All threads of control of the automatic mechanisms of the machine converge to the CNC. Structurally, the CNC is designed as an autonomous electronic unit with a NC input device, a computing part, an electrical communication channel with the automatic mechanisms of the machine.
The appearance of the CNC is largely determined by the control panel, from which one of the following machine control modes is selected: manual, setup, semi-automatic, automatic; the program is corrected during its debugging period, a correction is introduced, the execution of commands is monitored and the correct operation of the machine and the CNC device itself is monitored, etc. The CNC control panel (remote control), in turn, is determined by the programming system adopted for this device, characteristic signs of the adopted program control system, the CNC class.
In accordance with the international classification, all CNC according to the level of technical capabilities are divided into the following main classes: NC (Numerical Control); SNC(Stored Numerical Control); CNC (Computer Numerical Control); DNC (Direct Numerical Control); HNC (Handled Numerical Control); VNC (Voice Numerical Control).
Structural and informational analysis of these systems is rather complicated, although it makes it possible to single out the presence of certain functional elements and information channels in them. The classification for real CNCs is also conditional, since the implementation of CNC functions can be such that the real version of the control system is a synthesis of individual features of systems of different classes. This is especially true for CNC with class features DNC, which are implemented as class systems DNC-NC, DNC-SNC, DNC-CNC and others to the CNC class CNC, which are implemented as systems VNC, CNC-HNC and etc.
CLASS SYSTEMS NC AND SNC
Machine tools equipped with CNC classes NC And SNC, are currently still available in the practice of enterprises, but the release of systems of these classes has already been discontinued. These are the simplest control systems with a limited number of information channels. As part of these systems, there is no operational computer, and the entire flow of information is usually closed at the level of the 3rd rank. External sign of CNC classes NC And SNC is a way to read and work out the UE.
^ Class systems NC.
In class systems NC frame-by-frame reading of punched tape during the processing cycle of each workpiece. class systems NC operate in the following mode. After turning on the machine and the CNC, the first and second blocks of the program are read. As soon as they finish reading, the machine starts executing the commands of the first frame. At this time, the information of the second program block is in the memory of the CNC. After executing the first frame, the machine begins to work out the second frame, which for this is output from the memory device. In the process of working out the second frame by the machine, the system reads the third frame of the program, which is entered into the storage device freed from the information of the second frame, and so on.
The main disadvantage of the considered mode of operation is that in order to process each next workpiece from a batch, the CNC system has to read all the frames of the punched tape again; in the process of such reading, failures often occur due to insufficiently reliable operation of the CNC readers. As a result, individual parts from a batch may be defective. In addition, with this mode of operation, punched tape quickly wears out and becomes dirty, which further increases the likelihood of reading failures. Finally, if the block contains actions that the machine performs very quickly, then the CNC may not have time to read the next block during this time, which also leads to failures.
Currently CNC class ^NC are no longer issued.
class systems SNC.
These systems retain all the properties of class systems NC, but differ from them in an increased amount of memory. class systems SNC allow you to read all the blocks of the program and place the information in a mass storage device. The punched tape is read only once before processing the entire batch of identical parts and therefore wears out little. All blanks are processed according to signals from the storage device, which dramatically reduces the likelihood of failures, and, consequently, the rejection of parts. Currently CNC class SNC are no longer issued. However, the scheme of operation of these systems is very indicative and determines the essence of program control. When operating a machine controlled by an NC system or SNC, the encoded program is entered on punched tape. In addition, individual commands can be entered from the CNC control panel or from the machine control panel. Information from the punched tape through the input and decoding blocks enters the memory. When the machine is operating in automatic mode, the program commands processed by the interpolator are sent to the drives through the control units. The speed of the drives is controlled according to the data of the feedback system, and the displacements for the feed drives are controlled according to the data of the PD travel sensors.
CLASS SYSTEMS CNC, DNC, HNC
The development of computer technology, the reduction in the size of its elements, the expansion of functionality made it possible to create a CNC based on a computer, installing powerful computer technology directly to the machine tool in production shops. The new systems combined the functions of machine control and the solution of almost all tasks of preparing NC.
^ Class systems CNC
The basis of the CNC class CNC are:
a computer programmed to perform numerical control functions,
communication blocks with coordinate drives, blocks for issuing technological commands in the required logical sequence,
system controls and indications,
data exchange channels with the central computer of the upper level.
In class systems CNC it is possible during the operation period to change and correct both the UE for processing the part and the programs for the functioning of the system itself in order to take into account the features of this machine as much as possible. Each of the functions performed is provided by its own set of subroutines. Subroutines are linked by a common coordinating dispatcher program, which provides flexible interaction of all system blocks.
The software complex of the control system can be built on a modular basis. The main modules of such a system are:
UE loading control program, including subroutines for input and frame decoding;
machine control program, including a subroutine for controlling coordinate movements and a subroutine for executing technological commands.
The coordinate movement control program consists of blocks of interpolation, speed setting, rapid traverse control, and these blocks, in turn, include the following modules:
data preparation program;
organizing manager program;
drivers are standard operators for working with external devices.
To system storage CNC UE can be entered completely not only from a floppy disk or via an external communication channel, but also in separate frames - manually from the CNC control panel. The frames of the program can record not only commands for setting individual movements of the working bodies, but also commands that set entire groups of movements, called constant cycles, which are stored in the storage device of the SPU. A number of systems have a library of standard programs, built-in SAP, etc. This leads to a sharp decrease in the number of PM personnel, to a reduction in the time for its preparation and an increase in the reliability of the machine.
class systems ^ CNC make it possible to simply refine and debug UEs and edit them in a dialogue mode using manual input of information and its display, as well as to obtain an edited and tested program on a magnetic disk (floppy disk), etc. In the process of work, a variety of types of corrections are allowed.
Advantages of class systems CNC:
low cost,
small dimensions,
high reliability,
many CNCs of this class have software that can be used to take into account and automatically correct the constant errors of the machine and thereby influence the set of factors that determine the accuracy of processing,
the use of monitoring and diagnostic systems increases the reliability and performance of CNC machines of the class ^ CNC.
Some CNC class CNC have special test programs to check the performance of all structural parts of the system. These test programs are worked out every time the device is turned on, and if all parts are in good condition, a signal is generated that the system is ready for operation. During the operation of the machine and the CNC, test programs are processed in parts in the so-called background mode, without interfering with the development of the main NC. In the event of a malfunction, its code appears on the light indication board, then, using the code from the table, the location and cause of the malfunction are determined. In addition, the system detects errors associated with improper operation of the device or exceeding the thermal conditions, allows you to find the voltage for the power supply and other parameters.
An integral part of the CNC class CNC is an extensive built-in memory that can be used as a UE archive.
A very important means of optimizing the connection between the CNC and the machine is the introduction of machine parameters or constants into the memory. With the help of these constants, restrictions on the processing zone can be automatically taken into account, requirements for the dynamics of specific drives are set, phase trajectories of acceleration and deceleration are formed, specific features of gearboxes, feed drives are taken into account, systematic errors of these gears are compensated, etc.
The real representation of the high-level CNC CNC assumes the presence of two consoles - an operator panel and a machine console, a combination of CNC blocks with a programmable controller, a separate type of feed and spindle drive control system. The system is distinguished by simple programming and user comfort, provides all kinds of functions of a modern CNC, enhanced correction systems for backlash compensation, measuring system errors, screw stroke errors, NC errors, has a set of standard cycles for programming, a universal interface, etc.
^ Class systems DNC
class systems DNC can be controlled directly by the drives from the central computer, bypassing the reader of the machine. However, the presence of a computer does not mean that the need for a CNC machine tool is completely eliminated. In one of the most common systems DNC each type of equipment on the site retains its CNC classes NC, SNC, CNC. Normal for such a section is the mode of operation with computer control, but in the event of a temporary failure of the computer, such a section remains operational, since each type of equipment can operate using a floppy disk prepared in advance in case of an emergency.
In function DNC includes the management of other equipment of the automated section, for example, an automated warehouse, a transport system and industrial robots, as well as the solution of some organizational and economic tasks of planning and scheduling the work of the site. An integral part of software and mathematical support DNC there may be a specialized system for automating the preparation of UE. Editing UE in DNC it is possible on an external computer on which the automated preparation of the UE is carried out, on a computer that controls a group of machine tools, and on a computer built into the CNC of a particular machine. In all cases, the prepared and edited UEs for the site equipment are stored in the computer memory of the control group of machines, from where they are transmitted to the machines via communication channels.
^ Class systems HNC
Operational CNC class HNC allow manual entry of programs into the electronic memory of the CNC computer directly directly from its console. A program consisting of a sufficiently large number of frames is easily typed and corrected using the keys or switches on the CNC control panel. After debugging, it is fixed until the end of processing a batch of identical workpieces. Originally CNC class HNC, having a simplified scheme, in some cases did not have the ability to make corrections, buffer memory and other elements.
Modern class CNC ^HNC built on the basis of the best CNC-class CNC, only formally differing from the latter by the absence of devices for inputting UE from punched tape. But CNC class HNC have an input device for connecting external devices. The latest CNC class models HNC have an increased memory capacity of the built-in microcomputer. Such devices allow programming from the CNC console in the dialogue mode and using a large archive of standard subroutines stored in the memory of the built-in microcomputer. These subroutines are called up on the display screen by a command from the remote control, both the processing scheme and the text with a list of the necessary data to be entered into the CNC according to the selected subroutine are displayed on the screen.
CNC classes CNC, DNC, HNC they also provide automatic tool selection from those available in the machine shop, determine the processing modes of the selected tool for parts made of various materials, find the optimal sequence of operations, etc. - or special preliminary work of a technological nature. This, of course, imposes increased requirements on the professional preparedness of the CNC machine operator. A number of CNCs of the class under consideration allow programming in parallel with the operation of the machine according to a program previously worked out and stored in the CNC memory, which eliminates machine downtime.
CNC classes CNC, DNC, HNC refer to devices with a variable structure. The main algorithms for the operation of these devices are set by software and can be changed for various conditions, which makes it possible to reduce the number of CNC modifications and speed up their development, including CNC with self-adjusting algorithms. CNCs of these classes have the structure of a computer and have the characteristic features of a computer. The CNC must be properly programmed to operate. For this, such systems have special software and mathematical software, which is a complex of algorithms for processing information received in the form of UE. Mathematical software can be entered into the system through the input device, as well as the main UE. Then the CNC system belongs to the class of freely programmable. In other cases, the software is embedded in the permanent memory of the system at the stage of its manufacture. However, in all cases, there are opportunities for changing, supplementing, enriching this software, so such CNCs have great flexibility and the ability to expand functionally.
Possibilities of modern CNC classes CNC, DNC, HNC unlimited and determined only by the capabilities of the computers used in them.
VNC class systems
VNC class CNCs allow you to enter information directly by voice. The received information is converted into UE and then displayed in the form of graphics and text on the display, which provides visual control of the entered data, their correction and processing. Speech input of information is being introduced into robotics especially actively; In robot control systems, two methods of converting speech signals into commands are used: “synthesis by rules” or “synthesis by samples”.
In the first case, speech input is implemented only if there are rules stored in the memory of the operator's console. It is difficult to obtain high quality here due to the limited storage capacity and the complexity of voice messaging programs. The system contains a storage device for storing message text codes, a text converter and a synthesizer. The text converter translates the audio signals of the text into phonetic characters and performs parsing. The received symbols are used as code signs for the organization of the control program.
With the "synthesis by samples" method, the synthesizer is based on a linear speech production model based on main current generators, a linear filter and a learning model. This expands the scope of speech input commands.
However, the CNC class VNC have not yet been adopted by the industry, but are likely to be widely presented in the near future as the most advanced designs providing the highest level of service capabilities.
^ NEURO-FUZZY (HEYPO-FUZZY) CONTROL SYSTEMS
The beginning of work with computer neural networks dates back to the 40s, but only modern computer technologies have opened the way to their commercial use. Currently, many companies are working on the creation of neural networks for various purposes, but so far only a few have managed to implement NEURO-FUZZY management systems in production practice. By common belief, these systems belong to the future.
Computer neural networks are a special type of computers that imitate the mental processes of the brain to one degree or another. In these computers, data is organized like brain neurons in a network with multilevel connections. These systems quite simply solve not only ordinary standard tasks, but mainly non-standard, non-standard tasks that unexpectedly arise during processing, the solution of which requires non-standard logic, i.e. a certain intelligence. Neural networks solve problems that an ordinary high-speed computer is completely unable to do.
^ Neuro-Fuzzy CNC Generators W(firm SODICK Co.Ltd., Japan) is the world's first industrial control system with artificial intelligence based on a computer neural network. The system is used to control electroerosive jig-piercing machines. In addition to the computer neural network, the neuro-fuzzy also includes a fuzzy control system or control by fuzzy sets using expert fuzzy logic.
The system provides fully automated control of electroerosive machining, providing its optimal conditions and modes. Processing programming is carried out in the operator-CNC dialogue, in which the operator only answers graphically illustrated and intuitive questions of the machine (Fig. 1.2).
To set the initial data, tables of modes and instructions are not required, the operator enters a minimum of data, and the system itself automatically calculates the modes and operating conditions of the machine. At the same time, from positioning to the end of processing, no CNC codes are needed, as well as special experience on this equipment.
Rice. 1.2. Block diagram of the Neuro-fuzzy CNC generator W
Fuzzy control of modes and machining progress with instant response to any deviations optimizes the process for maximum productivity and efficiency. The neural learning system automatically corrects the results and achieves the required quality and performance. The self-learning experience is applied by the system in subsequent processing because the system remembers what it does. The system does not require a long time to master; on machines with such systems, even an inexperienced operator works faster and more efficiently than a qualified operator on a machine with conventional CNC systems.
MANAGEMENT TASKS
Programmable controllers
The controller is a specialized device equipped with a terminal in the form of a personal computer. An increase in the power and level of service of a personal computer makes it possible to combine the terminal, the programmer and the controller itself within a single computer system with an additional module for input-output of electric signals.
There is a preimage called a system ^ PCC (Personal Computer Controller- personal programmable controller). Development RCC goes in the following directions:
use of a single-computer version with a Windows system;
increase in the number of operator interface functions due to multi-mode control and the use of built-in programming tool systems;
maintaining real-time dynamic graphical models of the managed object;
the use of visual programming of electroautomatics (for example, according to the type of graphic language high graph firms Siemens).
The main task of the controller is the simultaneous execution of several commands and parallel processing of external signals. Each controller process that needs to allocate a separate thread runs within the main process. Processor time allocated by the operating system to the main processor must be divided among threads. Processor time is allocated to threads in separate quanta. Only one thread can be implemented in each quantum. All streams are divided into priority groups - the shorter the response time to external influences, the higher the priority of the stream
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