Five common faults of servo motors

1. Overtravel fault
When the servo motor exceeds the soft limit set by the software or the hard limit set by the limit switch, an overtravel alarm will occur. Generally, the alarm content will be displayed on the CRT. According to the server maintenance manual, the fault can be eliminated and the alarm can be lifted.

2. Overload fault
When the load of the servo motor is too large, frequent forward and reverse movements, and poor lubrication of the transmission chain may cause overload alarms. Generally, alarm information such as servo motor overload, overheating, or overcurrent will be displayed on the CRT. At the same time, maintenance fault information such as overload and overcurrent of the servo drive unit will be displayed on the servo drive, indicator lights or digital tubes in the control cabinet.

3. Movement fault
The phenomenon of servo motor movement can be divided into the following three situations: ① Unstable speed measurement signal, such as speed measurement device failure, speed feedback signal interference, etc.; ② The speed control signal is unstable or interfered with; ③ Poor contact of wiring terminals, such as loose screws. When a bouncing fault occurs at the moment of reversal from forward motion to reverse motion, it is generally caused by the reverse clearance of the servo motor's transmission chain or excessive gain in the servo system.

4. Crawling fault
This type of servo motor maintenance failure occurs during the start-up acceleration stage or low-speed feed, usually due to poor lubrication of the servo motor's transmission chain, low servo system gain, and excessive external load. Special attention should be paid here: the coupling used for connecting the servo motor and the ball screw may not be synchronized with the rotation of the servo motor due to loose connections or defects in the coupling itself, such as cracks, which can cause the servo motor to move rapidly and slowly, resulting in crawling phenomenon.

5. Servo motor not rotating fault
When the CNC system reaches the servo drive unit, in addition to the speed control signal, there is also an enable control signal, usually DC+24V relay coil voltage.

When the servo motor fails to rotate, the commonly used servo motor maintenance methods include:
① Check if the CNC system has speed control signal output;
② Check if the enable signal is connected. By observing the I/O status through CRT, analyze the ladder diagram (or flowchart) of the machine tool PLC to determine whether the starting conditions of the feed shaft, such as lubrication and cooling, are met;
③ For servo motors with electromagnetic braking, it is necessary to check whether the electromagnetic braking is released;
④ Servo drive unit failure;
⑤ The servo motor has malfunctioned.
In addition, when using a servo motor, we should also pay attention to not forcefully pulling the angle of the servo motor when it is powered on, as this will damage the motor. To change the status of the servo machine, it must be powered off for adjustment. The working voltage of the servo motor can only be 5V and cannot be changed. The servo motor operates at a slower speed but with greater force, so there should be no strong resistance to hinder the movement of the servo motor during movement, otherwise it will also cause damage.