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The classification of the CNC machine tool servo system

by:SNK     2020-08-25
The classification of the CNC machine tool servo system release date: 2019 - 07 - 12 author: small make up click: servo system including 2 most servo drive and servo drive circuit. Servo system according to the control methods are divided into open loop servo system, a closed-loop servo system and half closed loop servo system; According to the use of drive can be divided into electro-hydraulic servo system and the electrical servo system; According to the use of motor can be divided into dc servo system and ac servo system; According to the feedback comparison can be divided into pulse digital servo system, servo system, the phase comparison amplitude comparison of servo system and the digital servo system. Introduce the main according to control methods of the classification of the type. Open loop servo system of the open loop servo system is primarily a stepper motor driving element or electric hydraulic motor, it does not need to position and velocity detecting element, also have no feedback circuit, pulse work under the direction of a numerical control system, is the result of the execution of the moving parts of the actual displacement is not for testing and feedback. The system is characterized by simple structure, debugging, maintenance, use convenient, reliable operation, low cost, but its precision is poor, not stable at low speed, high torque is small. So generally used for light load, load changed or economical nc machine tools. Closed-loop servo system closed-loop servo system is error control servo system, it is mainly composed of position compare link, servo amplifier, the closed loop motor, mechanical transmission device and the displacement detection device. Closed-loop servo system working principle is that, after sending the displacement instructions when the numerical control system, through the servo motor and mechanical transmission device to drive the moving parts, linear position detection device to detect the displacement feedback to the position of the comparison, comparing with the input signal, the error compensation to the control instruction to control the servo motor. The precision of the system depends largely on the precision of the position detection device, so the system of high precision. However, due to mechanical transmission device, the stiffness of friction damping characteristics, the reverse clearance has a great influence on the stability of nonlinear factors such as closed loop of the servo system caused by installation is more complex. Moreover, the price of the straight line position detection device is higher, so many used for high precision nc machine tools and large nc machine tools. Half closed loop servo system with detecting element is the difference between a closed loop system for angular displacement detection device, the working principle of two identical, the rotary type measuring element in a screw or servo motor shaft end, through testing the screw or the rotation Angle of the motor, indirectly measure the displacement of the machine moving parts by the feedback loop back to the control system and servo system, and compared with the control instruction value. If there is a deviation between them, and the differential signal is amplified, continues to control the motor drives the moving parts to reduce the deviation direction, until the deviation is zero. Because only to feedback control of the intermediate links, screw and nut vice part is outside of the control links, therefore calls a half closed loop servo control. Due to the reverse gap of screw and screw pitch error of mechanical transmission parts such as limiting the location accuracy, so it is worse than the accuracy of the closed loop system; On the other hand, due to the moving parts of nc machine tool, rigidity and the ball screw nut pair clearance outside the feedback control loop, its stiffness, nonlinear factors such as clearance has no effect on system stability, convenient debugging, although compared with the closed loop system precision is low, but for most applications, has enough precision, so the application is very broad.
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