Abstract: In view of the existing conventional CA6140 shortcomings generally made CNC lathe conversion program and single-chip system design, to improve machining accuracy and expand the scope of machine use, and increase productivity. This paper describes the general transformation of CNC lathe of the design process, a more detailed description of the transformation part of the CA6140 mechanical design and numerical control system part of the design. 8031 for the CPU to use the control system of the signals are processed by the I / O interface stepper pulse output, with a gear reducer, the drive screw rotating roll in order to achieve vertical and horizontal movement of the feed.

Keywords: CNC machine tools, CNC single-chip system, the design modifications

I. Overview

Machine tool manufacturing industry as an important basis for machinery and equipment, its development has been a source of concern, due to the rise of computer technology, machine control information to a qualitative breakthrough has led to the application of digital technology for flexible automation of a new generation of machine tool control -- the birth of CNC machine tools and development. The emergence of computers and applications, provide humanity with the machining process to achieve the ideal means of process automation. With the development of CNC machine tools have also been rapid development and a wide range of applications, while the traditional tools of transmission and the concept of structure has been a fundamental shift. CNC machine tools for its outstanding performance and precision, agility and functional diversity caused worldwide attention, and to develop mechanical products to the development of the first mechanical-electrical integration. CNC machine tools based on the realization of the digital machine tool control information of the mechanical-electrical integration products, which the tool and workpiece relative position between the machine start and stop the motor, spindle speed, workpiece clamping and release, the tool of choice, the cooling pumps cease operation and a variety of information such as the order of action of using the code in the control of the digital recording medium, and then digital information into digital device or computer, after decoding, computing, control commands issued by a variety of machine tool servo system or the implementation of other components required for processing a workpiece.

CNC machine tools as compared with the general machine tools, its main advantages are as follows:

1. Adaptable for processing single pieces or small batches of complex parts; in CNC machine tool workpiece change, simply re-establishment of the new work processes, we can achieve a new workpiece processing.
2. Processing and high precision;
3. The production of high efficiency;
4. Reduce labor intensity and improve working conditions;
5. Good value for money;
6. Conducive to the modernization of production management.

CNC machine tools has become the mainstream of China's market demand for products, year-on-year surge in demand. CNC machine tools in China in recent years, industrialization and product development has made significant progress, especially in the high-speed machines, multi-axis, and complex, and has made great progress with regard to precision. However, the Chinese-made CNC machine tools and advanced countries compared to similar products, there are still gaps, but also can not meet the needs of national construction. Machine Tool China is a big country, there are more than three million Taiwan general machine tools. However, poor quality machine tools, the performance of backward, a single machine the average value of the advanced industrial countries, only 1 / 10 about the gap too much, need to be modified. CNC machine tool of the old GM, as its name suggests is on the increase in the general computer control machine tool devices, to a certain degree of automation with the ability to achieve a predetermined target processing technology. CNC machine tools with a growing number of universal applications, the technology cost-effective CNC machine tools for everyone to understand. Technological transformation in the domestic plant, the computer numerical control of machine tools has become an important aspect of transformation. While many plants use to purchase a CNC machine tool numerical control, digital display, PC technological transformation of general machine tools, and achieved good economic benefits.

China's limited economic resources, countries, and machine tool requirements, and it is not possible to come up with considerable funds to purchase a new type of CNC machine tools, and a lot of my old machine with a CNC machine tool system common in less investment circumstances, so that it can meet the processing needs, but also to improve the automation of machine tools, more in line with China's national conditions. In 1984, China began production of CNC systems, and for the transformation of the old machine. So far, a lot of manufacturers to produce the economic type CNC system. It can be expected that in the future, numerical control machine tool of economic transformation will be rapid development and popularization. Therefore, the school has a typical design and practicality.


Second, the overall design

2.1 Design Task

The design task is to carry out CNC lathe CA6140 transformation. The use of microcomputer for vertical and horizontal feed control system for open-loop, vertical (Z direction) pulse equivalent to 0.01mm / pulse, the horizontal (X to) pulse equivalent to 0.005mm / pulse, the use of stepper motor drive components, drive system used Ball Screws, transposition of the introduction of automatic tool turret.

2.2 The overall program evaluation

For ordinary CNC machine tools transform the program in determining the overall design should be considered to meet the design requirements under the premise of the changes on the machine should be as little as possible in order to reduce costs.

1) CNC system of exercise to determine the numerical control system in accordance with movement points can be divided into control systems, point straight-line control systems, continuous control systems. Due to the complex requirements of the outline of CA6140 lathe parts, so the computer numerical control system for a two-axis control system.

2) Servo System Design of CNC machine tool feed servo system open-loop, semi closed-loop and closed loop of points. Because the open-loop control structure is simple and easy to design and manufacture, the control accuracy is better, easier debugging, cheap, the use of the advantages of easy maintenance. Therefore, the design decided to adopt open-loop control system.

3) CNC system hardware design by a numerical control system hardware and software is composed of two parts. Hardware is the basis of numerical control system, the performance of a direct impact on the overall performance of numerical control system. With hardware, software can be run effectively. In the design of the CNC device, CPU choice is the key, select the CPU should consider the following elements:

(1) clock frequency and word length and the object movement is closely related to the speed and accuracy;
(2) the expansion of memory capacity and the strength of NC-related functions;
(3) I / O port expansion capability and the ability to control related peripherals.

In addition, the numerical control system should be based on applications to control the object as well as various performance parameters of the requirements, consider together to determine the CPU. In China, the general transformation of the application of CNC machine tools more generally Z80CPU and MCS-51 series single-chip, mainly because they are supporting chips cheap, universal, unified, manufacture and maintenance convenience, fully able to meet the economic the transformation of the needs of CNC machine tools. The design is based on MCS-51 series single-chip, 51 Series 48 Series commands a relatively more abundant, relatively cheap price of 96 series, 51 series, there is no ROM is EPROM of 8051,8751 of 8051 instead of ROM. At present, the application of IPC is the largest single-chip 8031. The 8031 chip design at the core, increasing the expansion memory circuit, interface and switch panel, composed of the operation control system.

2.3 Determination of the overall program

By the overall design of the evaluation program to determine the CNC lathe CA6140 Schematic transformation. CA6140 lathe spindle speed of machine parts to retain the original function, that is, manual transmission. Vertical lathe (Z axis) and horizontal (X axis) to the movement into the use of stepper motor driver. Composed by the 8031 single-chip microcomputer as the core of digital devices, from the I / O interface, the annular distributor and the power amplifier control with stepper motor rotation, the ball screw drive gear after the rotation, in order to achieve the vertical lathe, horizontal feed movement. Changed by the microcomputer control tool by the motor-driven automation tool auto-switch. In order to maintain the function of cutting thread, the spindle pulse generator must be installed for the use of synchronous timing belt on the spindle so that rotation synchronous pulse generator, the issue of the two signals: the issue of the pulses per revolution number and a sync signal, the isolation circuit and I / O interface to the computer.


Third, computer numerical control system hardware circuit design

3.1 Computer Numerical Control System Design of the overall hardware

8031CPU selection of the system as a numerical control system of a central processing unit. An external 2764EPROM, as a monitoring program for program memory and storage parts of the processing procedures used. Then choose a random 6264RAM need for storage of spare parts to amend procedures and working parameters. Decoding method used for addressing the expansion of the chip, the 74LS138 decoder to complete this feature. 8279 as a system to expand the input and output port, respectively, then the keyboard input and output show that stepper motor 8255 then the ring distributor, respectively, in parallel to control X-axis and Z-axis stepper motor. In addition, the machine should also be considered with the single-chip opto-electronic isolation between the power amplifier circuit and so on.

A brief introduction of the pin function as follows:

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

2) input / output (I / O) I have a 8031 micro-line P0, P1, P2, P3 4 ports, each port 8 I / O line. When the system when the external memory expansion, P0 I used a low 8-bit parallel output data, P2 I used an 8-bit address output high, P3 in addition to the mouth can be used as an 8-bit quasi-bidirectional parallel extraoral, also has a second function, the pin The second function is defined as follows: P3.0 RXD: serial data input. P3.1 TXD: serial data output P3.2 INT0: external interrupt 0 request input signal. P3.3 INT1: external interrupt request signal input terminal 1. P3.4 T0: Timer / Counter 0 external input P3.5 T1: Timer / Counter 1 external input P3.6 WR: external data memory write strobe. P3.7 RD: external data memory read strobe. Functional operation of the second before the second function of the output latch must be home by the procedure 1.

3) the line of control signal RST / VPD: RST signal to reset input pin, the clock circuit, the pin on the machine cycle two or more high, a reset operation to complete. 8031 micro-reduction using two methods: one is the automatic power-on reset, and the other for the reset switch. ALE / PROG: ALE is the Address Latch signal allowed. Its role is to CPU time from P0 I sent a low 8-bit address of the lock, there is a plus in the latch. Election of the external program memory read signal. When the time being in force for the low level.

VPP: When EA is high and the PC when the CPU is less than 0FFFH internal procedures to implement the program memory. When the EA when low, CPU is only the implementation of external program memory of the procedure. XTAL1: the RP-oscillator amplifier input, the use of an external oscillator must be grounded; XTAL2: the RP-oscillator amplifier output, the use of an external oscillator, the received signal external shocks;

3.2 outside the three-bus architecture

Single-chip in practical applications, often to expand the external memory, I / O port and so on. MCU pin, in addition to power, reset, clock input, and user I / O extraoral, and the rest of the pins are extended in order to achieve the system set up, these pins constitute the form of a three-bus:

1) The address bus AB

Address bus width of 16. Therefore, the external memory for directly addressing the scope of 64KB.

2) data bus DB

Data bus width of 8, provided by the P0 port.

3) control bus CB

Control bus from the second functional state of the mouth and P3 of the four independent control line RST, EA, ALE and PSEN composition. 8255A programmable parallel I / O port expansion 8255A chip programmable parallel I / O port expansion of the chip can be directly related to MCS Series Single-chip system bus connectivity, it has three 8-bit parallel I / O port, with three kinds of work, through the use of programming to facilitate the unconditional transmission, send inquiries or complete interruption of transmission between the CPU and peripheral devices to exchange information.

8255A-pin structure and function: 8255A Structure

8255A of the internal structure consists of three 8-bit parallel data I / O ports, two control circuits work, a read / write control logic circuit and an 8-bit data bus buffers. Function of the various parts as follows:

(1) the three 8-bit parallel I / O ports A, B, C
A I: with an 8-bit data output latch / buffer and an 8-bit data input latch. Programmable 8-bit input, or 8-bit output, or 8-bit bi-directional register.
B I: with an 8-bit data output latch / buffer and an 8-bit input or output registers, but not bi-directional input / output.
C I: with an 8-bit data output latch / buffer and an 8-bit data input buffer, C I can be grouped into two 4-bit port for input or output port can also be used as A and B gated population work the way the state of control signals.
(2) control circuit
A, B two three-port control circuit is divided into A, B group, A group of control you and C I A high population of four, B control group B and C I I I a low of four. Two groups each control circuit a control command register, for receiving from the CPU to write control word to determine the two sets of port work. Can also be controlled in accordance with the requirements of the C bitwise I-ching "0" or home "1."
(3) read / write control logic circuit
It receives signals from the CPU's address and some control signals, control the work of the state of all the mouth.
(4) The data bus buffer
It is a bi-directional tri-state buffers, and systems for the data bus is directly linked to the achievement of information between the CPU and the transmission of 8255A.