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Common faults and troubleshooting of CNC machine tool feed servo system
Release time:
Oct 17,2023
The servo system is the communication link between CNC equipment and the machine tool host. It is used to receive feed pulse or feed displacement information announced by the CNC equipment interpolator. After a certain signal conversion and voltage and power amplification, the servo motor drives the transmission mechanism, and Z is ultimately converted into the linear or rotational displacement of the machine tool workbench relative to the tool.
In order to improve the functionality of CNC machine tools, high requirements have been put forward for the feed servo system used in machine tools. Due to the different processing tasks completed by various CNC machine tools, the requirements for the feed servo system are also different. The following are common faults and troubleshooting methods for Mo Mo servo systems.
When the feed motion exceeds the soft limit set by the software or the hard limit set by the limit switch, an over travel alarm will occur. Usually, the alarm content will be displayed on the CRT. According to the CNC system manual, the problem can be eliminated and the alarm can be cleared.
Overload: When the load of the feed motion is too large, frequent forward and reverse movements, and the smoothness of the transmission chain is poor, it will cause an overload alarm. Usually, CRT displays alarm information such as servo motor overload, overheating, or overcurrent. At the same time, on the feed drive unit in the high-voltage cabinet, indicator lights or digital tubes will indicate the overload and overcurrent information of the drive unit.
During feeding, there is a phenomenon of movement: the speed measurement signal is unstable, such as speed measurement equipment failure, speed response signal disturbance, etc; The speed control signal is unstable or disturbed; Poor contact of wiring terminals, such as loose screws. When the motion occurs at the moment of reversal from forward motion to reverse motion, it is generally caused by the reverse clearance of the feed transmission chain or excessive gain in the servo system.
Crawling during low-speed feed during acceleration or start-up is usually caused by factors such as poor smoothness of the feed transmission chain, low servo system gain, and excessive external load. Special attention should be paid to the coupling used for connecting servo motors and ball screws. Due to loose connections or defects in the coupling itself, such as cracks, asynchronous rolling of ball screws and servo motors, the feed motion fluctuates rapidly and slowly, resulting in crawling phenomenon.
When the machine tool is running at high speed, oscillation may occur and overcurrent alarms may occur. The problem of machine tool oscillation is generally reduced to a speed problem, so it is necessary to find a speed loop; The entire process of adjusting the speed of the machine tool is completed by a speed regulator, which means that for any speed related problems, a speed regulator should be sought. Therefore, for oscillation problems, a speed regulator should be sought. Mainly search for faults from three aspects: given signal, response signal, and speed regulator itself.
In addition to the speed control signal, there is also an enable control signal from the CNC system to the feed drive unit, usually the DC24V relay coil voltage. The servo motor does not rotate.