What are the common faults and elimination methods of the machine feed servo system?

The servo system is the link between the numerical control device and the machine mainframe. It is used to receive the feed pulse or feed displacement information from the numerical control device interpolator. After a certain signal conversion and voltage and power amplification, the servo motor drives the transmission mechanism. Finally, it translates into the linear or rotary displacement of the machine table relative to the tool.

In order to improve the performance of CNC machine tools, high requirements are placed on the feed servo system for machine tools. Due to the different processing tasks performed by various CNC machine tools, the requirements for the feed servo system are not the same. The following are the common faults and remedies for servo systems that have been compiled by Xiaobian.


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


When the load of the feed motion is too large, frequent positive and negative movements and poor lubrication of the drive chain will all cause an overload alarm. Alarms such as servo motor overload, overheating or overcurrent are normally displayed on the CRT. At the same time, the information on the drive unit overload, over-current, etc. will be indicated on the feed drive unit, indicator or digital tube in the power cabinet.


The phenomenon of turbulence occurs when feeding: 1 The speed signal is unstable, such as the speed measuring device is faulty, the speed feedback signal interference, etc.; 2 The speed control signal is unstable or interfered; 3 The contact of the terminal is bad, such as screw loosening. When swaying occurs at the commutation moments from the positive direction movement and the reverse direction movement, it is generally caused by the backlash of the feed transmission chain or the excessive gain of the servo system.


Occurs in the starting acceleration section or low-speed feeding, which is generally caused by factors such as poor lubrication of the feed chain, low gain of the servo system, and excessive applied load. In particular, attention should be paid to the fact that couplings used for the coupling of servomotors and ball screws are not synchronized with the rotation of the ball screw due to loose coupling or defects of the coupling itself, such as cracks. Gives the sport a sudden, slow, and creeping phenomenon.

[machine vibration]

When the machine tool is running at a high speed, vibration may occur and an over-current alarm may occur. The machine tool vibration problem is generally a speed problem, so the speed loop should be looked for; and the entire adjustment process of the machine tool speed is completed by a speed regulator. That is, all speed-related problems should be found in the speed regulator, and therefore the vibration problem. Look for a speed regulator. Mainly from the given signal, feedback signal and speed regulator itself to find the fault.

[Servo motor does not turn]

In addition to the speed control signal, the CNC system feeds the drive unit with an enabling control signal, typically a DC 24V relay coil voltage. Servo motor does not turn,

Common diagnostic methods are:

1 check whether the CNC system has speed control signal output;

2 Check that the enable signal is on. Observe I/O state through CRT, analyze machine tool PLC ladder diagram (or flow diagram), in order to confirm the starting condition of the feed axis, if lubrication, cooling,etc. are satisfied;

3 For servo motor with electromagnetic brake, check whether the electromagnetic brake is released;

4 feed drive unit failure;

5 Servo motor failure.

Functional features:

1. With adoption of gear mechanical transmission systems, the machine is featured with high efficiency and low noise.

2. With braking function, the spindle is flexible and reliable.

3. With adoption of frequency control in electrical system, the machine controls braking using a frequency converter, so start and brake slopes can be preset for optimal winding.

4. The scope of frequency control is wide. Sped regulation is accurate and stable. The insulation level of the motor is level F.

5. Automatic winding displacement, auto-displacement inter layer trapezoid insulation.

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