Graduation design of numerical control

Numerical control research and transformation design of common lathe

Chinese Abstract: Aiming at the shortcomings of the existing conventional CA6140 common lathe puts forward the CNC modification program and the design of single-chip computer system, to improve the machining accuracy and expand the scope of use of the machine tool, and to improve the productivity. This thesis explains the design process of CNC retrofitting of the general lathe, and describes in more detail the design of the CA6140 mechanical retrofit part and the design of the CNC system part. The control system with 8031 as CPU is used to process the signals, and the stepping pulses are output from the I/O interface, which are decelerated by a first-stage gear drive and then drive the rolling screw to rotate, so as to realize the longitudinal and transverse feeding motion.

Keywords: CNC machine tools, single-chip CNC system, retrofit design

I. Introduction

Machine tools, as an important basic equipment for the machinery manufacturing industry, its development has always attracted people's attention, due to the rise of computer technology, prompting a qualitative breakthrough in the machine tool control information, leading to a new generation of machine tools for the application of digital technology to carry out flexible automation control -The birth and development of CNC machine tools. The emergence and application of computers, for human beings to provide an ideal means of realizing the automation of machining processes. With the development of computers, CNC machine tools have also been the rapid development and wide application, at the same time make people on the traditional machine tool transmission and structure of the concept of a fundamental change.

Overview

Working CNC machine tools with its excellent performance and accuracy, nimble and diverse functions to attract the world's attention, and create mechanical products to the development of mechatronics precedent. CNC machine tool is to digitalize the information to achieve the machine control of mechatronics products, it is the relative position between the tool and the workpiece, the machine motor start and stop, spindle speed, workpiece loosening and clamping, tool selection, cooling pump start and stop a variety of operations and sequential actions and other information with the code of the digital record in the control medium, and then send the digital information into the numerical control devices or computers, through the translation, operation, and issue a variety of instructions to control the machine tool. After decoding, arithmetic, issued a variety of instructions to control the machine tool servo system or other executive elements, plus the required workpiece.

CNC machine tools and ordinary machine tools, compared to its main advantages are as follows:

1. adaptable, suitable for processing a single piece or a small batch of complex workpieces; in the CNC machine tools to change the processing of workpieces, only need to re-programming of new workpieces of the machining process, you can realize the new workpieces processing.

2. High machining accuracy;

3. High productivity;

4. Reduced labor intensity, improve labor conditions;

5. Good economic efficiency;

6. Good for the modernization of production management.

CNC machine tools have become the mainstream of China's market demand for products, demand surged year by year. China's CNC machine tools in recent years in industrialization and product development has made significant progress, especially in the high-speed machine tools, multi-axis, composite, precision progress. However, domestic CNC machine tools and similar products in advanced countries, there is still a gap, can not meet the needs of national construction. China is a large machine tool country, there are more than three million ordinary machine tools. But the quality of machine tools is poor, backward performance, the average value of a single machine tool is only about 1/10 of the advanced industrial countries, the gap is too wide, the urgent need for transformation. CNC transformation of old machine tools, as the name suggests, is to increase the ordinary machine tools on the microcomputer control devices, so that it has a certain degree of automation capabilities to achieve the intended processing technology goals. With the increasing popularization and application of CNC machine tools, the technical and economic benefits of CNC machine tools for everyone to understand. In the technical transformation of domestic factories, machine tools of microcomputer numerical control transformation has become an important aspect. Many factories on one side of the purchase of CNC machine tools on the one side of the use of numerical control, digital display, PC technology to transform ordinary machine tools, and has achieved good economic benefits.

China's limited economic resources, the country's large, large machine tool needs, so it is not possible to come up with a considerable amount of money to buy a new type of CNC machine tools, and a lot of China's old machine tools, the use of economical CNC system to transform ordinary machine tools, in the case of less investment, so that it can meet the needs of processing, but also to improve the degree of automation of machine tools, more in line with China's national conditions. 1984, China began to In 1984, China began to produce economic CNC systems, and used to retrofit old machine tools. So far, there are many manufacturers of economic CNC systems. It can be expected that in the future, the economic CNC transformation of machine tools will be rapidly developed and popularized. Therefore, this graduation design example is typical and practical.

Three, the design of the overall program

3.1 design task

The design task is to carry out CNC transformation of CA6140 ordinary lathe. The use of microcomputer open-loop control of longitudinal and transverse feeding system, longitudinal (Z direction) pulse equivalent to 0.01mm/pulse, transverse (X direction) pulse equivalent to 0.005mm/pulse, the drive element adopts stepping motors, the transmission system adopts the ball screw sub-system, and the tool holder adopts the automatic indexing tool holder.

3.2 Overall program justification

For the economic CNC transformation of ordinary machine tools, in determining the overall design program, should be considered on the premise of meeting the design requirements, the changes to the machine tool should be as little as possible, in order to reduce costs.

1) Determination of CNC system motion

CNC system can be divided into point control system, point linear control system, continuous control system according to the mode of motion. Due to the requirement of CA6140 lathe processing complex contour parts, so this microcomputer numerical control system adopts two-axis linkage continuous control system.

2) servo feed system transformation design

The servo feed system of CNC machine tool has open loop, semi-closed loop and closed loop. Because open-loop control has the advantages of simple structure, easy to design and manufacture, better control accuracy, easy to debug, cheap, easy to use and maintain. Therefore, this design decided to use open-loop control system.

3) Hardware circuit design of the CNC system

Any CNC system consists of two parts: hardware and software. Hardware is the basis of the CNC system, the performance of good and bad directly affects the overall performance of the CNC system. With the hardware, the software can run effectively. In the design of the CNC device, the choice of CPU is the key, the choice of CPU should consider the following elements:

(1) the clock frequency and word length is closely related to the controlled object of the speed and accuracy of the movement;

(2) the capacity of the scalable memory is related to the strength of the CNC function;

(3) the ability to expand the I/O ports is related to the ability of the external device control.

In addition to this, according to the application of the CNC system, the control object and a variety of performance, parameter requirements, and so on, comprehensively consider to determine the CPU. in our country, the common machine tool CNC transformation of the application of the more common is the Z80CPU and MCS-51 series of microcontrollers, mainly because of their supporting chip is cheap, popularity, universality, manufacturing and maintenance is convenient, can meet the economic CNC machine tools, and can be used to meet the needs of the general public. Can meet the needs of economic CNC machine tool transformation. This design is based on the MCS-51 series microcontroller, 51 series relative to the 48 series of instructions are more abundant, relative to the 96 series of cheaper, 51 series, is no ROM 8051, 8751 is an EPROM instead of ROM 8051. at present, the most widely used in the industrial control machine is the 8031 microcontroller. This design is based on the 8031 chip as the core, increase the memory expansion circuit, interface and panel operation switch composed of control system.

3.3 Determination of the overall program

After the demonstration of the overall design program, the CA6140 lathe economic CNC transformation schematic diagram. the spindle speed of the CA6140 lathe partially retains the function of the original machine tool, that is, manual speed change. The longitudinal (Z-axis) and transverse (X-axis) feeding motion of the lathe is driven by stepping motor. The microcomputer composed of 8031 microcontroller is used as the core of the CNC device, and the stepping motor is controlled by the I/O interface, ring distributor and power amplifier together, and the ball screw is driven to rotate after gear deceleration, so as to realize the lathe's longitudinal and transversal feeding motion. The tool holder is changed to a microcomputer-controlled, motor-driven, automatically controlled, automatic indexing tool holder. In order to maintain the function of cutting threads, it is necessary to install the spindle pulse generator, for this reason, the spindle is used to synchronize the rotation of the pulse generator by synchronous toothed belt to send out two signals: the number of pulses issued per revolution and a synchronization signal, through the isolation circuit and the I / O interface to the microcomputer.

Four, microcomputer numerical control system hardware circuit design

4.1 microcomputer numerical control system hardware circuit design

This system uses 8031CPU as the central processor of the numerical control system. A piece of 2764EPROM is connected externally as the program memory for monitoring and storing the machining program of common parts. Then choose a piece of 6264RAM is used to store the part program and work parameters that need to be randomly modified. Using the decoding method to address the expansion chip, using 74LS138 decoder to complete this function. 8279 as the system's input and output port expansion, respectively, connected to the keyboard input, output display, 8255 connected to the stepper motor ring distributor, respectively, parallel control of the X-axis and Z-axis stepper motor. In addition, it is also necessary to consider the optical isolation between the machine tool and the microcontroller, power amplification circuits and so on.

The functions of each pin are briefly described as follows:

1) Source pin VSS: power supply ground terminal. VCC: +5V power supply terminal.

2) Input/Output (I/O) Port Lines The 8031 microcontroller has four ports, P0, P1, P2, and P3

, with eight I/O lines per port. When the system expands the external memory, the P0 port is used to output the low 8-bit parallel data, the P2 port is used to output the high 8-bit address, and the P3 port can be used as an 8-bit quasi-bidirectional parallel port, but also has a second function, the second function of each pin is defined as follows: P3.0

RXD: Serial Data Input. P3.1 TXD: Serial Data Output P3.2 INT0: External Interrupt 0 request signal input. P3.3

INT1: external interrupt 1 request signal input. P3.4 T0: Timer/counter 0 external input P3.5 T1: Timer/counter 1 external input P3.6

WR: External data memory write selector.P3.7 RD: External data memory read selector. Before the second function operation, the output latch for the second function must be set to 1 by the program.

3) Signal control line

RST/VPD: RST is the reset signal line input pin, after the clock circuit works, the high level of more than two machine cycles appears on the pin, completing a reset operation.
The 8031 MCU adopts two kinds of reset methods: one is the The 8031 MCU adopts two reset methods: one is automatic reset after power-on, and the other is switch reset. Its role is to send the CPU from the P0 port time-sharing low 8-bit address latch in an external latch.

External program memory read select signal. Valid when it is low.

VPP: The CPU executes the program in internal program memory when EA is high and the PC value is less than 0FFFH. When EA is low, the CPU only executes the program in the external program memory.

4.2 Off-chip three-bus structure

In practical applications, microcontrollers often need to expand the external memory, I/O, and I/O functions. To expand the external memory, I/O ports and so on. Microcontroller pins, in addition to the power supply, reset, clock input and user I/O port, the rest of the pins are set up to achieve the system expansion, these pins constitute a three-bus form:

1) Address bus AB

Address bus width of 16 bits. Therefore, the direct addressing range of external memory is 64KB. The low 8-bit address (A7 to A0) of the 16-bit address bus is provided by the P0 port via an address latch, and the high 8-bit address (A15 to A8) is provided directly by the P2 port.

2) Data bus DB

The data bus width is 8 bits, which is provided by the P0 port.

3)Control Bus CB

The control bus consists of the P3 port in the second function state and four independent control lines RST, EA, ALE and PSEN.8255A Programmable Parallel I/O Port Expansion Chip

The 8255A Programmable Parallel I/O Port Expansion Chip can be directly connected with the system bus of the MCS series MCUs, it It has three 8-bit parallel I/O ports with three operating modes, which can be easily programmed to complete the information exchange between the CPU and peripheral devices by unconditional transmission, query transmission or interrupt transmission.

Structure and Pin Function of the 8255A: Structure of the 8255A

The internal structure of the 8255A consists of three 8-bit parallel data I/O ports, two operating mode control circuits, a read/write control logic circuit and an 8-bit data bus buffer. The functions of each part are described as follows:

(1) Three 8-bit parallel I/O ports A, B, and C

A: has an 8-bit data output latch/buffer and an 8-bit data input latch. Can be programmed as an 8-bit input, or an 8-bit output, or an 8-bit bidirectional register.

B: Has an 8-bit data output latch/buffer and an 8-bit input or output register, but not bi-directional input/output.

C: has an 8-bit data output latch/buffer and an 8-bit data input buffer, and port C can be divided into two 4-bit ports for input or output, and can also be used as a status control signal when working in the selective mode of port A and port B.

(2) Operating mode control circuit

The A and B control circuits divide the three ports into two groups, A and B. Group A controls all the bits of the A port and the high four bits of the C port, while group B controls all the bits of the B port and the low four bits of the C port. Each of the two control circuits has a control command register, which is used to receive the control word written by the CPU to determine the operation mode of the two groups of ports. The C port can also be cleared to "0" or set to "1" by bit according to the requirement of the control word.

(3) Read/Write Control Logic Circuit

It receives address signals and some control signals from the CPU and controls the working status of each port.

(4) Data bus buffer

It is a three-state bi-directional buffer used to connect directly with the system's data bus to realize the transfer of information between the CPU and the 8255A.

V. Summary

Conventional lathe CNC conversion program and microcontroller system design to improve machining accuracy and expand the use of machine tools, and improve productivity. Adopt the control system with 8031 as CPU to process the signal, output the stepping pulse by I/O interface, and then drive the rolling screw to rotate after decelerating by one-stage gear transmission, so as to realize the longitudinal and transverse feeding movement.

Sixth, acknowledgements

The thesis temporarily ended, which also means that my three years of study in Jiujiang Vocational University will end. Looking back, the most valuable time of my life in such a campus, can be in a number of rich and talented teachers to spend under the cultivation, it is a great honor. In these three years, I have benefited greatly in learning and thinking. This is in addition to their own efforts, and teachers, students and friends of the care, support and encouragement is inseparable