In the wave of intelligent manufacturing and precision control, the servo motor serves as the power core, and its encoder is like a “neural sensor”, continuously transmitting position and speed feedback in real-time to ensure the stable operation of the system. However, encoder faults under complex working conditions are like “invisible bombs” – they can cause the system to stop running at the least, and at worst, trigger a chain reaction. This article will uncover the “health secrets” of servo motor encoders layer by layer, from fault phenomena and diagnostic logic to maintenance strategies, helping engineers accurately troubleshoot problems and safeguarding the lifeline of the industry.
Common Fault Phenomena and Causes
Signal Loss or Instability
Phenomenon: The motor has positioning deviations and speed fluctuations, and the control system reports an encoder fault.
Causes:
The connection cable is loose, damaged, or the shielding layer is not grounded (accounting for more than 40% of fault cases).
The internal components of the encoder are aging (such as damage to the photoelectric sensor).
The coupling between the motor shaft and the encoder is loose (mechanical transmission error).
Zero Point Offset
Phenomenon: The position of the motor is inaccurate when it starts or stops, and the cumulative error increases.
Causes:
The zero point was not calibrated during installation, or mechanical displacement occurred due to long-term vibration.
The encoder code disc is worn (especially common in high-precision equipment).
Overheating Alarm
Phenomenon: The temperature of the encoder housing exceeds 80°C, and there may be abnormal signals.
Causes:
Poor heat dissipation (such as oil stains blocking the heat dissipation holes).
Overload operation or internal short circuit (which needs to be judged in combination with current detection).
Mechanical Damage
Phenomenon: There are abnormal noises and vibrations, and the output signal jumps.
Causes:
The bearing is worn (common in high-load working conditions).
The code disc is broken due to external impact (such as a collision of an industrial robot).
Diagnostic Steps (with Practical Tools)
Preliminary Inspection
Tools: Multimeter, oscilloscope.
Operations:
Check the cable: Measure the resistance between the encoder cable and the driver to confirm there is no open circuit or short circuit.
Observe the waveform: Use an oscilloscope to detect the pulse signal. The normal waveform should be an equal-amplitude square wave (for example, the phase difference between phases A and B of an incremental encoder is 90°).
Zero Point Calibration Verification
Method: View the encoder feedback value through the driver monitoring interface, and manually rotate the motor to observe whether the counting is continuous. If there is a sudden change, it is necessary to recalibrate.
Environmental Interference Investigation
Key Points:
Electromagnetic interference: Check whether the cable runs parallel to the power cable (a spacing of more than 20 cm should be maintained).
Mechanical vibration: Use a vibration meter to detect the vibration frequency of the motor. If it exceeds the allowable range of the encoder (usually < 10g), it is necessary to reinforce the installation or add a shock-absorbing pad.
Maintenance Methods (with Cases)
Signal Problem Repair
Case: A CNC machine tool experienced intermittent stalling. Inspection found that the shielding layer of the encoder cable was not grounded.
Solution:
Replace the shielded cable and ground it according to the specifications (the grounding resistance ≤ 4Ω).
Install an APF active filter on the driver side (A case in an automobile factory shows that interference is reduced by 70%).
Zero Point Calibration Operation
Steps:
Enter the driver debugging mode and select the “encoder calibration” function.
Rotate the motor to the specified position as prompted, and the system automatically records the zero point (for example, for the Siemens S120 driver, it is necessary to input the calibration parameter P1070 = 1).
Mechanical Fault Handling
Case: The encoder code disc of an industrial robot was broken, resulting in incorrect joint angles.
Solution:
Replace the original encoder (pay attention to the model matching, such as Tamagawa TS5212N).
Improve the mechanical design: Add limit protection to prevent the joints from exceeding the limit.
Overheating Problem Optimization
Measures:
Clean the heat dissipation holes and replace the thermal conductive silicone grease (A case in a textile machine shows a temperature reduction of 15°C).
Adjust the load: Monitor the current through the PLC and limit the instantaneous overload.
Preventive Measures
Regular Maintenance: Clean the inside of the encoder every six months and check the aging condition of the cables.
Anti-interference Design:
Cable Selection: Give priority to using twisted-pair shielded cables (such as MAXWELL HP-100).
Power Isolation: Use a DC/DC module for separate power supply (A practice in a semiconductor factory shows that interference is reduced by 85%).
Operation Training: Standardize the encoder installation process to avoid rough operation.
The faults and maintenance of servo motor encoders are like a “battle” that requires delicate operation, which needs the combination of electrical, mechanical, and software knowledge. We should realize that preventing faults is more important than repairing them after they occur. Regular “check-ups” of the equipment can avoid most potential problems and reduce the risk of faults by 80%. At the same time, technological progress has also provided us with more solutions. For example, the application of digital encoders and wireless transmission technologies is changing the industry rules and bringing us new opportunities.
With the advancement of Industry 4.0, encoder technology will become more and more precise, and its anti-interference ability will also continue to improve. This means that in future work, engineers not only need to continuously learn new technologies but also need cross-disciplinary cooperation to deal with the ever-changing challenges. Only in this way can we truly seize the opportunities of industrial upgrading.