1 Overview Numerical control transformation generally refers to a certain transformation of some parts of ordinary machine tools, equipped with numerical control devices, so that the machine tool has the ability of numerical control processing. There are about 3 million ordinary machine tools in our country. The CNC transformation of these equipment has become an important technical policy of the country to implement in production. Use MCS-51 series 8031 single-chip microcomputer to carry out the numerical control transformation of the ordinary machine tool C620 lathe, use the microcomputer to carry out the open-loop control of the longitudinal and transverse feed system, the driving element adopts a stepping motor, and the transmission system adopts a ball screw pair. The system block diagram is as follows.
2 Repair and treatment before machine tool reconstruction. Because the machine tool modified by microcomputer can only improve the consistency of the machining quality of the parts, the machining accuracy of the parts is guaranteed by the transmission accuracy of the machine tool itself and the stepping accuracy of the stepping motor. Therefore, the machine tool must be repaired before the machine tool modification.
(1 For machine tools with an actual service age of less than 5 years, the parts and components are still in good condition and the accuracy has not been reduced, and the scratches on the guide rails are basically visible, and no overhaul is required. This type of machine tools can be equipped with both microcomputer control and manual operation. The dual function of the machine tool is to ensure the processing of individual single-piece and small-batch parts. When it is not necessary to use CNC cutting, it can still be operated manually to give full play to the potential of the machine tool and increase the utilization rate of the machine tool.
(It is good for the basic parts of the machine tool with a service age of 5:10 years. Only some vulnerable parts need to be overhauled and replaced, and the transformation can be carried out after passing the inspection of the lathe overhaul standard.
3 Modification process 3.1 Modification of the lathe transmission system For ordinary lathes, the main transmission system and the feed system are all driven by the main axis motor, and the modified CNC lathe, the main transmission system and the feed system are separated into two unrelated systems .
Three-phase motor-belt pulley-main shaft gearbox-main shaft (feed system longitudinal and horizontal are indicated by! “Direction respectively) transmission route plate box tool post) after the transformation, see the transmission diagram of the activation control lathe.
3.2 Connection of stepper motor and ball screw The connection method of stepper motor and ball screw is an important issue in machine tool modification, and reliable connection is required.
In order to facilitate programming and ensure machining accuracy, the lathe is generally required to be longitudinal! The pulse equivalent is 0.01mm, and the pulse equivalent is 0.05mm, and the diameter value is 0.01mm. Since the dimensions of the drawings of the rotary workpiece are expressed in diameter, the horizontal “experience exchange” machine 丨 electricity I work time I technology I (Technical direction) The pulse equivalent of 0 is not only intuitive, but also can improve the accuracy of repeated positioning.
Select the step angle pulse equivalent of the stepping motor and the ball screw pitch! After that, the connection between the stepping motor and the ball screw may not be exactly 11. At this time, two gears “1,” 2 must be used. Transmission. The transmission ratio of “1” and “2” is: the number of teeth A-the basic lead of the feed screw, equivalent to one pulse! One step pitch angle.
“Toward the ball screw pitch! = 8mm, the step angle of the 110BF type stepping motor! =0.75., =0.01mm, then)=5/3=the number of screw gear teeth/the number of stepping motor gear teeth)=25/ 12=The number of screw gear teeth/the number of stepper motor gear teeth In order to achieve the above transmission ratio and ensure the pulse equivalent, the ball screw of the CNC lathe is connected with the stepper motor by gear connection. For example, the 110BF003 type stepper motor is used for the transformation of the C620 lathe , Then other lathe refitting can be calculated according to the above formula, and the design and calculation parameters of the gear are determined according to the structure size.
3.3 The connection form of stepping motor and machine tool adopts gearbox connection. The stepping motor shaft and the screw shaft are connected with a box body, and the center distance of the shaft hole can be more accurately guaranteed, so that the gear meshes well, the transmission is stable, the noise is low, and it is easy to prevent dust. It is suitable for refitting lathes with better accuracy.
3.4 Measures to eliminate gear gaps Since a pair of gears is used for transmission between the stepper motor and the ball screw, a transmission gap is introduced. The stepper motor rotates a step angle and fails to make the ball screw rotate a corresponding angle synchronously. Reduce machining accuracy. If this kind of transmission gap is not compensated, the accumulated error of parts processing may become larger and larger, resulting in dead zone and return error.
The measures to eliminate the gear backlash, on the one hand, use computer software to correct it and on the other hand use a backlash-free gear transmission.
The system adopts a double-gear staggered anti-backlash structure) 2. Two sheets of the same number of teeth mesh with another wide gear at the same time. The two sheet gears are opened to a certain angle by spring force, so that the left and right tooth surfaces of the two sheet gears are in contact with each other. The right and left tooth surface of the wide gear to eliminate backlash. See its structure.
3.5 Hardware circuit overall scheme The hardware circuit of the CNC lathe control system after the transformation is generally composed of the following 4 parts: main controller, memory, bus and interface. The reliability of the hardware circuit directly affects the performance indicators of the numerical control system. The CPU is the heart of the numerical control system. See the hardware block diagram.
Since the 9/:-51 series is widely used in the CNC transformation of machine tools in my country, its supporting chips are cheap and the performance can meet the requirements of economical cnc machine tools, so 8031 is selected as the central processing unit of the CNC system.
6) Memory expansion Because the main controller CPU uses 8031, there are only 128 bytes of RAM in the 031 single-chip microcomputer, no ROM, and the capacity of the program memory and data memory required by the machine tool numerical control system are large, and the program memory must be connected (EPRO9 Xiang data Memory RAM) chip. So choose a piece of 2764 as the program memory, and a piece of 6264 as the data memory. In order to separate and save the address information of the 8031P0 interface, so as to provide the low 8-bit address information for the external memory, the system also uses 74L373 as the address latch. The wiring diagram for the main chip connection.
System expansion, complete keyboard/display input and output.
A series of continuous pulses sent by the numerical control device must be distributed to each phase winding of the stepping motor in a certain order through a ring distributor, so that each phase winding is energized or de-energized according to a predetermined control method. The YB013 ring distributor is used in the system design. At the same time, the power amplifier circuit and photoelectric isolation circuit should also be considered in the drive circuit of the stepper motor.
3.6 Software design This single-chip numerical control system software adopts a modular design method, which includes the main module, subroutine module and interrupt processing module. The function of the main module: 155I/O initialization, microcontroller T0, T1 timer/counter initialization, keyboard data area, display buffer initialization, various software flag initialization, etc. The monitoring in the main module is mainly to judge whether a function key is pressed and if so, then transfer to the corresponding function subroutine module.
The subroutine module is designed according to the function keys.
Three modules are included in the interrupt processing, and the priority queuing sequence is based on the priority of different events in the microcomputer numerical control system. They are: emergency repair processing and travel switch out-of-bounds alarm module; real-time modification of the display buffer data module: disk, display, and timing Scan management module.
3.7 Test machine after completion of the electromechanical installation e Disconnect the power supply of the power amplifier and test the program. If the program is called out and runs correctly, it means that the control system is in good condition; e) The moving direction of the stepper motor must be in accordance with the specified direction with manual function, otherwise the wiring of the motor should be changed; e enter the processing program for no-load operation; e) Trial machining parts; e) Measure the accuracy of the processed parts, adjust the size of each part of the program according to the processing size and error; e) Process a group of parts to check the repeated processing accuracy, if the dispersion of the size distribution of the parts is large, the cause of the error must be analyzed in detail Make improvements until the desired goal is achieved.
4 Conclusion With the development of microelectronics technology, my country’s machine tool numerical control has made great progress in the past ten years, and the numerical control transformation of ordinary machine tools can greatly reduce the technology under the premise of meeting the same processing tasks. The investment funds for the transformation have been widely used in practice.
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