Common faults and repair methods of electric actuators

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Although electric actuators have advantages such as easy access to energy, fast signal transmission speed, and long transmission distances, their biggest drawbacks are their complex structure, low thrust, higher tendency to fail, and a higher average failure rate compared to pneumatic actuators. They are suitable for applications where explosion protection requirements are not high and where an air supply is unavailable. Furthermore, electric actuators operate slowly; it takes a considerable amount of time for the control valve to respond to a signal sent from the regulator and move to the corresponding position. This is also one of the reasons why electric actuators fail frequently. I. Indicator light failure 1. Symptoms of the failure: When power is supplied to the electric actuator, the power indicator light does not light up; there is no feedback from the control board, and no action is taken in response to the signals sent. 　　Troubleshooting and repair process: Since the power indicator light did not illuminate, the first step was to check whether the fuse was open-circuited. Upon inspection, the fuse appeared to be intact. Based on all the symptoms, it was inferred that the fault might lie in the power supply section of the servo amplifier board. Next, the power indicator light was examined; using a multimeter, it was found to be open-circuited. After replacing the indicator light, the problem was resolved. 　　Conclusion: An open circuit in the power indicator light will cause the entire servo board to stop working. 2. Fault phenomenon: (Discovered during debugging) After the actuator of the electric actuator is powered on, it responds to the open signal, but does not respond to the close signal. 　　Fault diagnosis and repair process: First, carefully inspect the feedback circuit to ensure that there are no faults in the feedback signal. When the open signal is sent, the indicator light should turn on, indicating normal operation; when the close signal is sent, the indicator light should not turn on, suggesting a problem with the thyristor control section. First, check the close indicator light – using a multimeter, it was found that the light was open-circuited. Replacing it resolved the fault. 　　Conclusion: When the on and off indicator lights are not lit (open circuit), the thyristor does not operate. II. Resistance and Capacitance 1. Fault symptoms: When the electric actuator is powered on and a signal is given (e.g., 75%), the actuator will open fully and then return to the specified position (75%). 　　Fault diagnosis and repair process: Based on the above fault symptoms, it is necessary to first determine whether there is a problem with the servo board or the actuator. Remove the control plate from the actuator, and connect the power cable directly to terminals X5/1 and X5/4 to make the actuator move in the closing direction; connect the power cable to terminals X5/1 and X5/2 to make it move in the opening direction. If the actuator does not operate properly, the fault lies with the actuator itself. The motor windings were found to be normal using a multimeter; upon checking the resistances on both sides of the capacitor, an open circuit was detected. Replacing the capacitor resolved the issue. 　　Conclusion: When encountering the above fault symptoms, first determine which part is affected by the fault, and then identify the root cause. 2. Fault phenomenon: When power is supplied to the actuator, a shut-off signal (4mA) is sent, causing the actuator to first open fully and then close fully. 　　Troubleshooting and repair process: First, the servo amplifier board was removed. When power was directly supplied to the actuator, the original fault still persisted. The resistance was checked; its value was normal, indicating that the resistor was fine. The motor windings were then inspected, and their resistance value was also normal, meaning the motor had no issues. Based on this fault, it is likely that the capacitor is damaged; by replacing it, the issue was resolved. 　　Conclusion: When this problem occurs, resistors and capacitors should be suspected first. III. Others 1. Fault symptoms: As long as an AC220V power supply is supplied at the site, the protection switch immediately activates (trips), and the fuse in the actuator blows. 　　Fault diagnosis and repair process: First, use a multimeter to test the motor windings on the actuator; if the resistance of these windings is close to zero, it indicates that the motor is short-circuited. Next, check the resistance between the two ends of the brake – if this resistance is infinite, it means the brake is damaged; the normal value should be around 1.45K. The final solution was to replace the brake and motor with new ones, install the fuse on the servo drive board, and then re-tune the system to restore its normal operation. 　　Conclusion: This situation was likely caused by the brake failing and thus locking the motor, with the issue not being detected in time; as a result, the motor remained in a locked-rotor state and generated heat, eventually leading to the breakdown of the insulation between the motor’s phases. 2. Fault phenomenon: The operating direction of the actuator is not controlled by the input signal. 　　Judgment and troubleshooting process: First, it was verified that both current-limiting resistors and the phase-shifting capacitor showed no abnormalities. A multimeter was used to measure the resistance of the motor windings; the measured value was 1.45 MΩ (and this value changed periodically). This indicated that there was a problem with the motor windings. Ultimately, the only solution was to replace the motor. 3. Fault phenomenon: The operating direction of the actuator is not controlled by the servo control board. 　　Fault diagnosis and repair process: First, the user is asked to use a multimeter to measure the resistance values of the two current-limiting resistors, the phase-shifting capacitor, and the motor windings. The results obtained by the user are consistent with the final data we provide. The three factors that affect the steering of the actuator are ① the windings of the motor itself, ② the current-limiting resistor, and ③ the phase-shifting capacitor; there are no other possibilities apart from these three factors. 4. Symptoms of the fault: No matter what signal is given on-site, the motor does not move at all.
Fault diagnosis and troubleshooting process: Even when voltage was applied directly across the motor windings, the motor still wouldn’t rotate. After removing the brake, the motor still failed to turn upon power application. The resistance values of the motor windings were found to be normal upon measurement. Manually turning the handwheel caused the actuator to operate normally. All test results were normal; however, the motor wouldn’t rotate when powered on. At this point, I suspected there was a problem with the motor’s rotor. After disassembling the motor, I found that the rotor couldn’t be turned at all by hand. It turned out that there was a thick layer of hard dirt between the rotor and the motor end cover. After removing this dirt and applying some lubricating oil, the rotor could finally be turned by hand. Reinstall the motor and fit it together with the actuator; power supply is working properly, so proceed with reconfiguration.