Common faults and troubleshooting methods for CNC machine tool feed servo system

2019-08-28 08:32

Common faults and troubleshooting methods for CNC machine tool feed servo system

Common faults in the feed servo system are as follows:


When the feed motion exceeds the software limit set by the software or the hardware limit set by the limit switch, an overtravel alarm will occur, and the alarm content will be displayed on the CRT. According to the CNC system manual, the alarm can be eliminated. Fault, cancel the alarm.


When the load of the feed motion is too large, frequent positive and negative movements, and poor lubrication of the transmission chain, an overload alarm will be caused. Alarm information such as servo motor overload, overheat or overcurrent is usually displayed on the CRT. At the same time, on the feed drive unit in the power cabinet, the indicator light or the digital tube will prompt the drive unit to overload, over current and other information.


The phenomenon of turbulence occurs during feeding: 1 The speed measurement signal is unstable, such as the speed measuring device failure, the speed feedback signal interference, etc.; 2 The speed control signal is unstable or interfered; 3 The terminal is in poor contact, such as loose screws. When the turbulence occurs in the commutation moment of the forward direction and the reverse motion, it is generally caused by the backlash of the feed chain or the servo system gain being too large.


When it occurs in the starting acceleration section or low-speed feed, it is generally caused by factors such as poor lubrication state of the feed transmission chain, low servo system gain, and excessive load. In particular, the coupling between the servo motor and the ball screw is not synchronized with the rotation of the servo motor due to loose coupling or defects in the coupling itself, such as cracks. Give the movement a flickering and creeping phenomenon.

[Machine vibration]

When the machine is running at high speed, vibration may occur and an overcurrent alarm will occur. Machine vibration problems are generally speed problems, so you should look for the speed loop; and the entire adjustment process of the machine speed is done by the speed regulator, that is, all speed-related problems should be found in the speed regulator, so the vibration problem Look for the speed regulator. Mainly from the given signal, feedback signal and speed regulator itself to find faults.

[Servo motor does not turn]

In addition to the speed control signal, the CNC system to the feed drive unit also has an enable control signal, typically a DC+24V relay coil voltage. The servo motor does not turn,

Common diagnostic methods are:

1 Check if the CNC system has a speed control signal output;

2 Check if the enable signal is on. Observe the I/O status through CRT, analyze the PLC ladder diagram (or flow chart) of the machine tool to determine whether the starting condition of the feed axis, such as lubrication and cooling, is satisfied;

3 pairs of servo motors with electromagnetic brakes should check whether the electromagnetic brake is released;

4 feed drive unit failure;

5 servo motor failure.

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