Common Failures and Maintenance for Electric Actuators

Electric actuators are vital components in automation control systems, widely used in industrial production to accurately control the opening, closing, and flow rate of valves and other regulating devices. The stability and control precision of electric actuators directly affect the efficiency and safety of production processes. This article provides an in-depth analysis of common electric actuator failures and offers maintenance suggestions to enhance their stability and control precision.

Brake Failure in Electric Actuators

The brake in an electric actuator is designed to eliminate the inertia slide of the rotor and output shaft, as well as the load's reaction torque when power is lost. This ensures that the output shaft stops accurately at the required position. A brake failure can lead to reduced control precision and an inability to stabilize valve positioning.

Solution

Adjust brake torque: Adjust the brake torque based on the load size to ensure effective braking and prevent inaccuracies caused by inertia sliding.
Adjust brake disc and wheel clearance: Ensure the appropriate gap between the brake wheel and brake disc. Both excessive and insufficient gaps can affect braking performance.
Ensure adequate friction coefficient: Keep the brake lining's friction coefficient high. Avoid lubricant leakage that could affect friction performance. Ensure the proper amount of lubricant is used without exceeding the recommended limit.

Output Lag in Electric Actuators

Output lag in electric actuators typically occurs in the connection between the output shaft of the actuator and the adjustment mechanism (such as a butterfly valve). Loose or gapped connections may cause delayed actuator movement, affecting control precision.

Solution

Eliminate looseness or gaps: During installation, ensure all linkages and levers are firmly secured to avoid any looseness or gaps. Loose connections can lead to angular deviation and control lag.
Use dedicated couplings: Use dedicated couplings instead of ordinary linkages to minimize gaps during movement.
Ensure correct angle and feedback signal matching: During installation, ensure that the actuator output angle (90°) matches the valve body angle (90°) and that the valve position feedback signal (4-20mA) is correctly correlated.

Servo Amplifier Sensitivity Issues

Improper sensitivity settings in the servo amplifier can affect the response speed and stability of the electric actuator. Too high a sensitivity can cause actuator oscillation, while too low a sensitivity can lead to slow action and inability to achieve precise adjustments.

Solution

Adjust sensitivity: The sensitivity of the servo amplifier should be set accurately. Too high sensitivity (≤130μA) can cause oscillation, potentially damaging the servo motor or even leading to system failure. Too low sensitivity (≥450μA) causes sluggish response and affects regulation precision.
Optimal range: Sensitivity should generally be set between 180-340μA to accommodate the response time of the controlled object and the characteristics of the control system.

Valve Position Feedback Signal Errors

Feedback signal errors are often caused by vibration, especially when equipment is installed in inappropriate locations. Vibration can disrupt the feedback system's stability, leading to signal deviation.

Solution

Avoid vibration sources: Install the electric actuator away from vibration sources, ensuring it is mounted on a sturdy foundation or fixed to larger process pipelines to minimize vibration interference.
Regular calibration of feedback signals: Regularly calibrate the actual valve position against the feedback signal to ensure accuracy. For differential transformer feedback systems, vibration can cause the core to shift, increasing errors, while potentiometer feedback systems may experience signal distortion due to poor contact.
Ensure feedback accuracy: Ensure the error between the feedback signal and the actual valve position is within 1% to guarantee adjustment precision.

Incorrect Selection of Electric Actuators

Incorrect actuator selection, especially when dealing with high-viscosity or contaminated media, can result in excessive load or valve blockage, severely affecting actuator efficiency and control precision.

Solution

Choose the right actuator: For dirty or high-viscosity fluids, select an electric actuator with a higher output torque to ensure adequate load capacity for challenging operating conditions.
Regular cleaning of valves: Periodically clean the regulating valve to maintain its flexibility and prevent blockages, such as tar buildup, which could reduce actuator control precision.

Regular Maintenance and Inspections

Electric actuators can experience wear and corrosion over time, especially in harsh operating conditions, which can degrade performance.

Solution

Regular inspections and cleaning: Perform regular inspections and cleaning of electric actuators and regulating valves, especially when handling sticky substances. For electric actuators used to control ammonia water or tar in our plant, a steam cleaning system is implemented monthly to ensure the equipment remains flexible and reliable.
Routine checks and maintenance: In addition to scheduled cleanings, regular daily checks are essential, particularly in harsh environments, to detect issues early and perform necessary repairs.

Conclusion

Electric actuators play an essential role in industrial automation, with their performance and control precision directly influencing the stability and efficiency of production processes. By properly adjusting the brake system, addressing output lag, fine-tuning servo amplifier sensitivity, eliminating vibration interference, selecting the right actuator, and maintaining regular inspections, the reliability and accuracy of electric actuators can be significantly improved, ensuring smooth production operations. Regular inspection, adjustment, and maintenance are key to keeping electric actuators running efficiently.