Application characteristics of CNC technology in machine tools

The multi-axis AC servo drive control card and two sets of servo amplifiers, servo motors and encoders respectively form two semi-closed loop servo control systems. Its main task is to complete the control of starting, accelerating, decelerating and stopping the servo motor according to the commands sent by the industrial computer, and to generate 6 interrupt signals according to the motion status of the two servo axes: position error exceeds limit, transmission midway speed change point Arrived, the position counter value is full foldback, the encoder index positioning mark and illegal control command.

Optical isolation digital output card and 1 SSR relay module port board to complete the grinding head motor, headstock motor, cooling valve, loading and unloading mechanism, receiving mechanism, fixture cleaning device, X-axis, Z-axis servo amplifier output Output control of switch control signals such as enable and alarm.

The digital signal input card and a light-isolated input port board jointly complete the monitoring of the loading, unloading, receiving mechanism and the X-axis and Z-axis 5 pairs of limit signals and the status signals of the machine tool cooling and lubrication system. Any one of the limit signals can cause a hard interrupt to ensure that it does not cause damage to the mechanical system.

The characteristics of the control system are as follows. Servo control accuracy analysis In order to ensure that the servo drive output device has a certain mechanical strength, the transmission part of the worktable adopts a ball screw with a pitch of 6mm, and the encoder installed at the tail of the servo motor generates 4096 pulses every time the servo motor rotates. And output to the pulse counter on the servo control board. Therefore, each pulse theoretically corresponds to the displacement of the worktable of 1.4m, which is less than 1/5 of the allowable error of the design requirements. Usually in high-precision control systems, the theoretical design error is generally 1/3 to 1/ of the allowable error. 2. From the point of view of signal resolution, it can fully meet the design requirements of the system, and the test results have confirmed the correctness of this selection.

Servo control mode and signal transmission mode In order to ensure that the computer has enough time to respond and process the user's special commands, while meeting the requirements of control accuracy, a PID servo control board with adjustable PID parameters is adopted. Before the industrial computer sends a control command to the control board, it only needs to select reasonable PID coefficients according to the displacement, speed and acceleration parameters, calculate the theoretical pulse count value corresponding to the displacement and the speed count value and acceleration count value obtained by the difference principle, and After passing the above values to the servo control board, the industrial computer completes one servo control output operation. Therefore, the industrial computer has a lot of time to process external requests and status display. Even in the case of two-axis linkage control, the start-up time difference between the two axes is only 1.2×10-7s according to the machine code. In the case of 3000r/min, the resulting displacement error is about 0.03m, so it can be ignored.

There is a Hall element sensor for each controlled mechanical device to detect whether it reaches the limit position, which can protect each movement mechanism from being damaged, and is used to specify the coordinate origin of the servo axis. These detection signals contact the industrial computer by means of interrupt request.

The control signal input from the laminated keyboard during the cycle processing is also connected with the industrial computer in an interrupt mode, and the industrial computer makes corresponding processing through key value analysis. Special machine tool failure and protection control In order to prevent accidents, the control system is equipped with 3 kinds of safety protection to stop the processing operation. The first type is the emergency stop button on the main control cabinet. When it is pressed, it will send a low-level signal to the servo amplifier and the industrial computer at the same time. Its function is to make the servo amplifier output enable signal position zero and stop the servo part output. , And after receiving the signal, the industrial computer releases all outputs and re-directs to the initial preparation state for processing. The second type is to enable the control software to enter a specific interrupt service through the red stop button on the film key, to retract the two servo axes to the origin in time, release other external outputs, and then be in a waiting state. The third type is the power control button on the main control board. Pressing this button will cut off the power supply of the industrial computer and the servo amplifier. It is the control and protection button for emergency shutdown.