How to carry out numerical control transformation

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How to carry out numerical control transformation of ordinary lathe

numerical control processing is the development trend of the machining industry towards high quality, high precision, high yield and high efficiency. Combined with the actual situation of our country, economic CNC lathe is an important step in the development of our country from ordinary lathe to CNC lathe. It is a low-cost and high-efficiency way to use the existing ordinary lathe to carry out numerical control transformation

I. overall scheme:

Figure 1 is the digital control voltage normal? The maintenance method can refer to the overall framework configuration of the system in Section 1 of nixie tube maintenance in Chapter 1.

description of the overall framework:

1. PC can adopt industrial PC, which can meet the control requirements of the control system

2. Motion control card. We use the PCL motion control card produced by Advantech company. The card is a high-speed three-axis stepping motor motion control card without automatic return. It has 16 bit digital input and output ports, which can realize three-axis linkage. Therefore, it can meet the x-axis and z-axis linkage of lathe and realize linear and circular interpolation

3. The photoelectric coupling circuit is designed by ourselves. Its function is to isolate the signal impact of external interference signals on the motion control card and improve the stability of the system

4. The machine tool body is transformed from c613. Remove the screw rod, slide box, gearbox, etc. from the identification problem of raw material testing machine, and retain the original three jaw chuck, etc

5. The stepper motor and its driver are from Nanjing stone company. The input voltage of the driver is 45V. Considering the step angle of the stepping motor and the screw pitch of the screw, the pulse equivalent of the x-axis and the z-axis of the system is 0.00125 and 0.0025 respectively. It can fully meet the machining accuracy requirements of 0.005mm

6. All kinds of limit switches, deceleration switches and zero return switches are installed on the machine body. The limit switch plays the role of hardware hard limit. When the workpiece processed by the lathe exceeds the processing range, the lathe automatically stops processing. The function of the deceleration switch is that when the lathe tool rest returns to zero and moves near the lathe zero point, the deceleration switch is turned on and informs the lathe to decelerate to zero position

second, the design of the feed system

considering that the CNC system is open-loop control, there is no position feedback, so the feed system should reduce the intermediate transmission links as much as possible. The x-axis and z-axis feeding system of this lathe removes the intermediate transmission link of the original feeding system and directly adopts the transmission scheme of stepper motor + rigid coupling + ball screw. Remove the original screw and add a small amount of mechanical accessories to install the stepping motor and ball screw nut pair. According to the calculation, the torque of the stepping motor is required to be 5 nm. The stepping motor we choose is 86byg250c-safrbc-0302 of Nanjing stone company, with a step angle of 0.9/1.8 and a torque of 7.5nm. The model of the driver is sh20806, and the input voltage is 45V

III. software part of the control system

the software part of the lathe control system is written in VC + + 6.0. The processing interface of the software is shown in Figure 2. Its functions mainly include reading the machining G code of parts and compiling G code, Simulation processing (including pre machining simulation and synchronous simulation with machining, return to reference point, manual tool setting, machining interruption, overtravel soft limit and other functions. It can process a variety of machining information such as feed speed, spindle speed and speed direction, tool information, m function and so on. The operating platform of the software is Windows98. The operating process of the software is to first read in the G code file of *.nc or *.txt; then compile it, and the compiler can give the language that does not conform to the software Method error prompt; If there are errors, they can be corrected immediately; Then according to the actual size of the wool embryo input, the software carries out pre-processing simulation. After confirming that there is no processing error caused by G code, the machine tool processing can be started. Before machining, the tool should be set first. The significance of tool setting is to establish the relationship between workpiece coordinates and lathe coordinates. During processing, the status bar of the software interface also displays the current coordinates of the tool, processing status, processing time and other information

Figure 2 software interface of this CNC lathe system

IV. transformation of spindle system

the original spindle gearbox is removed, and frequency converter + BELT + spindle + encoder are adopted. The spindle speed of the system is also regulated in seven levels, and the speed can be from 40rpm to 1200rpm, but the speed of each gear can be achieved by setting the frequency converter as needed. Using the five terminals of the frequency converter, the forward, reverse, stop and speed of each gear of the motor can be controlled by digital quantity. This frequency converter is a Panasonic product, in which the seven gear frequency is set in a20~a26, and the port should be controlled by the port controller (A1). This system does not adopt manual mechanical speed regulation, and all speeds are controlled by s command in G code. The software can read the G code and automatically control the speed of the spindle motor

v. tool rest structure

after the modification of the tool rest of this lathe, only two tools can be installed, one for Turning Ordinary columns, the cone and end face are graded according to the combustion performance of building materials, and one for processing threads, so the rotary tool rest is not used. The tools are installed at the front and rear ends of the tool rest, and the x-axis forward and backward tool walking is used to realize automatic tool change. (end)

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