Numerical control transformation of ordinary lathe

1 Overview CNC transformation generally refers to the transformation of certain parts of ordinary machine tools, coupled with numerical control devices, so that the machine tool has the ability of CNC machining. China's existing ordinary machine tools about 3 million units of CNC transformation of these equipment has become an important national technology policy in the implementation of production. The MCS-51 series 8031 ​​single-chip microcomputer is used to carry out numerical control transformation on the ordinary machine tool C620 lathe. The vertical and horizontal feed system is controlled by the microcomputer. The driving component adopts stepping motor and the transmission system adopts ball screw pair. Its system block diagram is as follows.

2 Repair and processing before the machine tool transformation Because the machine tool modified by the microcomputer can only improve the consistency of the part processing quality, the machining accuracy of the part is guaranteed by the transmission precision of the machine tool and the stepping motor step accuracy. Therefore, the machine must be repaired before the machine is modified.

(1) For machine tools with an actual service age of less than 5 years, the components are still in good condition and the accuracy has not been reduced. The guide rails are scratched in a basically visible state and can be overhauled. This type of machine can be equipped with both microcomputer control and manual operation. The dual function is to ensure the processing of individual single-piece small-volume parts. When there is no need to use CNC cutting, manual operation can still be used to fully exploit the potential of the machine and improve the utilization of the machine.

(The basic parts of the machine tool are 5:10 years old, only need to repair and replace some wearing parts, and can be modified according to the standard of lathe overhaul.

3 modification process 3.1 modification of lathe drive system For the ordinary lathe, the main drive system and the feed system are both autonomous shaft motors, and the modified CNC lathe, the main drive system and the feed system are separated into two unrelated systems. .

Three-phase motor - pulley - spindle gearbox - spindle (feeding system longitudinal and horizontal respectively!) to the direction of the transmission path of the box cutter) after the transformation of the excitation of the lathe drive schematic see.

3.2 Stepping motor and ball screw connection The connection method of stepping motor and ball screw is an important problem in machine tool modification, which requires reliable connection.

In order to facilitate programming and ensure machining accuracy, the lathe is generally required to be longitudinal! The pulse equivalent of 0.01mm lateral "direction" pulse equivalent is 0.05mm, the diameter value is 0.01mm. Since the rotary workpiece drawing size is expressed by the diameter value, the horizontal "experience exchange" machine 丨 I I 暇 I technology I The pulse equivalent of 0 is not only intuitive, but also improves 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 does not necessarily have a relationship of 11, in this case, 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, one pulse equivalent! one step angle.

"To ball screw pitch! = 8mm, using 110BF stepping motor with step angle! = 0.75., = 0.01mm, then) = 5 / 3 = screw gear teeth / stepper motor gear teeth = 25 / 12=Number of teeth of the lead screw/number of teeth of the stepping motor To achieve the above transmission ratio and ensure the pulse equivalent, the ball screw of the CNC lathe and the stepping motor are connected by gear. For example, the stepping motor of 110BF003 is adopted for the modification of C620 lathe. Then, other lathe modifications can be calculated according to the above formula, and the design calculation parameters of the gear are determined according to the structural size.

3.3 The connection mode of the stepping motor and the machine tool is connected by a gearbox. The stepping motor shaft and the screw shaft are connected by a box body, and the center distance of the shaft hole can be accurately ensured, the gear meshing is good, the transmission is smooth and low noise and dustproof. Suitable for lathe modification with better precision.

3.4 Measures to eliminate the gear gap Since a pair of gears are used between the stepping motor and the ball screw, the transmission gap is introduced, and the stepping motor turns a step angle to fail to synchronize the ball screw to a corresponding angle. Reduce machining accuracy. If the transmission gap is not compensated, the accumulated error of the part processing may become larger and larger, resulting in dead zone and backhaul error.

The measure to eliminate the gear gap is on the one hand using computer software to correct the other side and using the gapless gear transmission.

The system adopts a double-gear misalignment type anti-backlash structure. 2, two sheets of the same number of teeth are simultaneously meshed with another wide gear, and the two thin-plate gears are opened by a certain angle by a spring force, so that the left and right tooth faces of the two thin-plate gears are respectively contacted. The right and left flank of the wide gear to eliminate the backlash. See its structure.

3.5 Hardware circuit The overall hardware circuit of the CNC lathe control system is composed of the following four parts: main controller, memory, bus and interface. The reliability of the hardware circuit directly affects the performance index of the numerical control system, in which the CPU is the heart of the numerical control system. See the hardware block diagram.

Because the 9/:-51 series is widely used in China's machine tool numerical control transformation, its supporting chips are cheap, and the performance is comparable to the requirements of economical CNC machine tools. Therefore, 8031 ​​is selected as the central processing unit of the numerical control system.

6) Memory expansion Because the main controller CPU selects 8031, 031 has only 128 bytes of RAM in the microcontroller, there is no ROM, and the program memory and data memory required by the machine numerical control system are large. External program memory must be connected (EPRO9 Xiang data) Memory RAM) chip. Therefore, a piece of 2764 is selected as the program memory, and a piece of 6264 is used as the data memory. In order to separate the address information of the 8031P0 interface and save it to provide the lower 8-bit address information for the external memory, the system also uses 74L373 as the address latch. Connect the wiring diagram for the main chip.

System expansion, complete keyboard and display input and output.

A series of continuous pulses sent by the numerical control device must be distributed to the phase windings of the stepping motor in a certain order through the annular distributor, so that the phase windings are energized or de-energized according to a predetermined control mode. The YB013 ring distributor is used in the design of this system. At the same time, the power amplifier circuit and the photoelectric isolation circuit should be considered in the driving circuit of the stepping motor.

3.6 Software Design The single-chip CNC system software adopts a modular design method, that is, a package main module, a subroutine module and an interrupt processing module. Main module functions: 155I/O initialization, MCU T0, T1 timer/counter initialization, keyboard data area, display buffer initialization, various software flag initialization, etc. The main monitoring in the main module is to determine whether there is a function key pressed, if it is, then the corresponding function subroutine module.

The subroutine module is designed according to the function keys.

In the interrupt processing, three modules are packaged, and the priority queuing sequence is based on the priorities of different events in the microcomputer numerical control system. They are: emergency repair processing and trip switch cross-border alarm module; real-time modification of the display buffer data module, display, timing Scan management module.

3.7 Electromechanical installation After the test machine e disconnected the power amplifier power test program. If the program is run accurately, the control system is in good condition; e) the stepping motor with manual function must be in the same direction as the specified direction, otherwise the motor wiring should be replaced; e into the machining program for no-load operation; e) Test the machining parts; e) Measure the precision of the machined parts, adjust the dimensions of each part of the program according to the machining size and error; e) Process the precision of the repeated machining of a set of parts. If the dispersion of the size distribution of the parts is large, the cause of the error must be analyzed. Improve again until the intended purpose is achieved.

4 Conclusion With the development of microelectronics technology, China's machine tool numerical control has been greatly developed 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 transformation have been widely used in practice.

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