Numerical control transformation of machine tools

3 Research work on machine tool numerical control transformation and other aspects.
The vast majority of the production and processing equipment of most manufacturing industries and enterprises in China is a traditional machine tool. The products processed with this equipment generally have poor quality, low variety, low grade, high cost and long delivery period, so they lack competitiveness in the international and domestic markets, directly affecting a company's products, markets, benefits, and influence. The survival and development of enterprises. Only by doing a numerical control transformation of the machine tool can these problems be solved, so as to cope with the inevitable trend of the world manufacturing center transplanting China.
2 The advantages of CNC machine tools can process complex parts such as curves and curved surfaces that cannot be processed by traditional machine tools.
It is possible to automate the processing, and it is flexible automation and programming of parts processing. The program controls the machining accuracy, not the artificial level of technology, so that the efficiency can be increased by 3 to 7 times compared with the traditional machine tool.
The precision of the machined parts is high, the dimensional dispersion is small, and the assembly is easy. It is no longer necessary to "repair and realize the concentration of multiple processes, and reduce the frequent handling of parts between machine tools.
With automatic alarm, automatic monitoring, automatic compensation and other self-discipline functions, it can achieve long-term unattended processing.
3.1 Control principle of CNC machine tools For traditional ordinary machine tools, the electrical part mainly controls the rotation speed of the spindle motor, the start and stop of the cooling pump, etc., and the control of the feed axis is mainly the thread.
In addition to the requirements for speed regulation of the spindle, CNC machine tools have higher requirements for the speed and position control of the spindle. The overall electrical control system of a typical CNC machine tool is shown.
CNC machine tool electrical control system consists of 1 data input device to input command information and various application data into the necessary installation of the CNC system. At present, commonly used input devices include a 3.5-inch floppy disk drive, a CNC keyboard (general input operation), a hard disk and a drive device (for large-scale data storage protection), a PC computer, and the like.
3.1.2 The numerical control system is the backbone of the CNC machine tool. It decodes and calculates all the functional commands received, and then sequentially issues various required motion commands and control commands for various machine functions until the end of motion and function.
3.1.3 Programmable Logic Controller is the logical control center for all functions of the machine tool. It logically sorts the various motion and function commands from the CNC, enabling them to operate safely and in an orderly and safe manner. At the same time, it transmits various information and working status from the machine tool to the CNC so that the CNC can issue further and timely and accurately. The control instructions thus achieve control of the entire machine.
4 The spindle drive system accepts the drive command from the CNC, and the output drive signal is driven by the speed and torque (power) to drive the main motor to rotate, and the speed feedback is implemented to implement the speed closed loop control.
It also informs the CNC of various real-world working states of the spindle through the PLC to complete the function control of the spindle.
5 The feed servo system accepts the speed command provided by the CNC for each motion coordinate axis, and drives the servo motor rotation through the speed and current (torque) adjustment output drive signal to realize the movement of the machine coordinate axis and accept the speed feedback signal implementation speed. Closed-loop control. It also communicates with the CNC through the PLC to inform the current working status and accept the control of the CNC.
3.1.6 Speed ​​measurement is usually done by a tachometer that is housed in the main shaft and the feed motor. It matches the actual motor speed to a voltage value and sends it back to the servo drive system as a speed feedback signal, which is compared with the commanded speed voltage value to achieve precise speed control.
3.1.7 Position measurement Earlier machines used linear or circular synchronous sensors or resolvers, while modern machine tools mostly used grating scales and digital pulse encoders as position measuring components. They measure the actual position of the machine axis in operation directly or indirectly, and feed back the measured value to the CNC and compare it with the commanded displacement until the axis reaches the command position, thus achieving precise control of the position.
1 Open loop system for motor drag The servo drive system of this system is mainly stepper motor, power stepper motor, electro-hydraulic pulse motor and so on. The feed command pulse sent by the numerical control system is controlled by the drive circuit and the power is amplified, so that the stepping motor rotates, and the actuator is driven by the gear pair and the ball screw pair.
As long as the number, frequency, and energization sequence of the command pulses are controlled, the amount of displacement, speed, and direction of motion of the actuator movement can be controlled. Such a system does not need to feed back the measured actual position and speed to the input end, so it is called an open loop system. The displacement accuracy of the system is mainly determined by the angular displacement accuracy of the stepping motor, the transmission components of the gear screw and the like. Pitch accuracy, so the system's displacement accuracy is low.
3.2.2 Step motor or DC motor drag, closed-loop numerical control system for grating measurement feedback The difference between the system and the open-loop system is: the actual position feedback signal measured by the position detecting device such as grating, inductive synchronizer, etc. The values ​​are compared, the difference between the two is amplified and transformed, and the actuator is driven to move at a given speed toward the direction of the deviation until the difference between the given position and the actual position of the feedback is equal to zero. The closed-loop feed system is more complex in structure than the open-loop feed system, and the cost is also high, and the environmental room temperature requirements are strict. Design and commissioning are more difficult than open loop systems. However, it is possible to obtain higher accuracy, faster speed, and higher power consumption characteristics than the open loop feed system. The system can be decided according to the technical requirements of the product.
3.2.3 DC servo motor drag, the semi-closed loop system of the encoder feedback The semi-closed loop system detection component is mounted on the intermediate transmission component to indirectly measure the position of the actuator. It can only compensate for the error of some components inside the system loop. Therefore, its accuracy is lower than that of the closed-loop system, but its structure and debugging are simpler than the closed-loop system. When the angular displacement detecting element is integrated with the speed detecting element and the servo motor, there is no need to consider the mounting problem of the position detecting device. Mechanical repair and electrical modification are combined. In general, mechanical repairs are required for machines that require electrical modifications. It is necessary to determine the requirements, scope and content of the repair; also to determine the requirements and contents of the mechanical structural transformation required for electrical transformation; and to determine the interleaving time requirements between electrical renovation and mechanical repair and transformation. The good mechanical properties are the basis for the successful electrical transformation.
Take the easy to difficult, partial and integral combination. The whole electrical part transformation is first divided into several subsystems, such as numerical control system, measuring system, main shaft, feed system, panel control and high-voltage part, etc., after each system is basically formed, and then interconnected to complete the whole system work.
This can make the renovation work less omissions and errors. In each subsystem work, you should first do a less technical, high-volume work, and then do technically high-level, demanding work, so that people's attention can be concentrated in key areas.
Assign transformation tasks and implement the responsibilities of the participants. According to each divided subsystem, the responsibilities of the personnel are determined, and there are times for the owner to facilitate organization and coordination.
Determine the scope and cycle of the transformation.
2 Technical preparations for the preparation of the mechanical part. The measurement, calculation, design, drawing, and part making of the mechanical modification required to cope with the electrical transformation shall be completed in advance. At the same time, the parts that need to be dismantled, modified and processed after the shutdown should be planned in advance, and clear requirements should be put forward, and the whole transformation work should be properly connected.
Retrofit plan electrical part preparation. The new system has many new functions, new requirements, and new technologies. Therefore, you should be familiar with the technical materials before the transformation, including system principle description, circuit diagram, PLC ladder diagram and text, installation and debugging instructions, user manual, programming manual, etc. It is necessary to have sufficient time to translate the above materials (import system), digest, sort and check, so that the ideas are clear and the layers are clear.
Preparation of the interface device. The conversion design of the interface between the old and new systems is different according to the scope of transformation of each equipment. It is necessary to design the interface part conversion in advance. If all the transformations are made, the electromechanical conversion interface, operation panel control and configuration, interconnection part contacts, parameter measurement points, maintenance positions, etc. should be designed. It is required to be convenient and reasonable for operation and maintenance, the line is smooth, the connection points are small, the interference between strong and weak electricity is minimum, and the appropriate margin is provided.
For partial transformation, it is also necessary to consider the performance matching of new and old systems, voltage polarity and size conversion, installation position, digital-to-analog conversion, etc., if necessary, to make a conversion interface.
The commissioning steps and the determination of the acceptance criteria. After the renovation of the new electrical system, how to debug and determine reasonable acceptance criteria is also an important part of the technical preparation work. The commissioning work involves mechanical, hydraulic, electrical, control, sensing, etc., so it must be carried out by the project leader and other personnel. The debugging steps can be from simple to complex, from small to large, from outside to inside, or first and then global, first subsystem and then complete system. The acceptance criteria are the assessment of the new system. It must be realistic when it is formulated. The standards that are too high or too low will have a negative impact on the transformation work. Once the standard is determined, it cannot be easily modified because it involves all aspects of the entire transformation work.
3.3 Implementation of the machine tool transformation work First of all, the overall maintenance of the old machine tool to be modified. After long-term use of the machine tool, there will be defects in mechanical, hydraulic, lubrication, cleaning, etc., so the first step is to carry out comprehensive maintenance. Secondly, the geometric accuracy and dimensional accuracy of the machine tool should be measured before the change. This can not only guide the transformation work, but also can be used for comparative analysis at the end of the transformation.
Adjust and optimize the original electrical part. If the electrical system is partially modified, the maintenance and optimization of the reserved electrical parts should be carried out. Such as the replacement of parts in the strong electric part, the maintenance of the motor, the drying insulation of the transformer, the cleaning of the pollution, the cleaning of the ventilation cooling device, the optimization of the servo drive, the renewal of the aging wire and cable, the fastening of the connector, etc. . Only a fine optimization of the retained electrical parts can ensure that the modified machine has a lower failure rate.
Remove the original system. The removal of the original system must be carried out carefully against the original drawings and marked on the drawings in time to prevent omissions or over-disassembly (under partial modifications). In the process of dismantling, some defects in the design of new systems will also be found. They should be supplemented and corrected in time. The removed systems and parts should be classified and properly kept in case of unsuccessful transformation or partial failure. There are certain use values ​​that can be used as spare parts for other machine tools. Don't be too big and big, throw it away.
Arrange the location and wiring of the new system reasonably. According to the new system design drawings, the new system configuration is rationally carried out, including box fixing, panel placement, line orientation and fixing, adjusting component position, sealing and necessary decoration. The work of connection must be clearly defined, and some people should review and inspect to ensure that the connection process specifications, wire diameter are correct, correct, reliable and beautiful.
debugging. Commissioning must be carried out in accordance with predetermined steps and requirements. The commissioning staff should be calm and record at any time in order to discover and solve problems. In the commissioning, first try to protect the sensitivity of the system to prevent accidents of people and equipment. The debugging site must be cleaned up and free of unnecessary items; each motion coordinate carriage is at the center of the full stroke; it can be loaded with no load test, first loaded after no load; can simulate the test, first simulate and then move; can be manual, first manual After automatic.
3.4 Testing and acceptance of the machine tool after the transformation The test content of the CNC machine tool after the transformation is mainly the confirmation of the power supply voltage, frequency and phase sequence. First, it is necessary to test whether the capacity of the transformer can meet the power consumption of the control unit and the servo system; secondly, the test voltage fluctuation is within the allowable range; for the supply current of the speed control unit and the spindle control unit using the transistor control element, it must be strictly tested. Its phase sequence.
(2) Test whether the DC power output is shorted to ground.
(3) Test whether the voltage on the printed circuit board is normal, and whether the various DC voltages are within the allowable fluctuation range. In general, the +5V power supply requirements are higher, the fluctuation range is *5%. (4) Test various interface signals of the CNC system and the machine side, and whether the output drive voltage of the PLC meets the requirements.
2 After the transformation, the acceptance of the machine tool first accepts the mechanical part of the CNC machine tool after the transformation. After mechanical repair and modification and comprehensive maintenance, the mechanical properties of the machine tool should meet the requirements, and the geometric accuracy should be within the specified range.
Electrical control functions and control accuracy acceptance. The functions of electrical control must be normal, sensitive and reliable. Control accuracy The function of the application itself (such as step size) is checked against standard measuring instruments (such as laser interferometers, coordinate measuring instruments, etc.) to within the accuracy range. At the same time, it should be compared with the functions and precision of the machine tool before the transformation, and the quantitative index difference can be obtained.
The test piece is cut. It can refer to the standards of CNC machine tool cutting test pieces at home and abroad, and carry out trial cutting with the cooperation of qualified operators and programmers. The specimen cutting can accept the machine tool stiffness, cutting force, noise, motion trajectory, associated movements, etc. It is generally not appropriate to use the product parts for the test piece.
Drawings and data acceptance. After the machine tool is rebuilt, the drawings (including schematics, configuration drawings, wiring diagrams, ladder diagrams, etc.), materials (including various specifications), and transformation files (including various records before and after the transformation) should be summarized and organized. Hand over to the file. Keeping the data complete, effective and continuous is very important for the stable operation of the equipment in the future.
4 Conclusion 802S/C numerical control system and stepping drive system perform X, Y and Z three-axis NC transformation on a X53 milling machine; retain the original king shaft system and cooling system; the modified two-axis is mechanically A roller screw and a gear transmission mechanism are used. The entire transformation work includes mechanical design, electrical design, machine tool overhaul, and finally the installation and commissioning of the whole machine. After the milling machine is modified, the effective stroke X/Y/Z axis is 630/240/280mm; the maximum speed X/Y/Z axis is 3000000/600mm/min, and the manual feed speed X/Y/Z axis is 2000/ respectively. The minimum mobile unit of 800/500mm/min is

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