Under which circumstances can servo motor vibration occur? How can these issues caused by servo motor vibration be resolved? And how are they resolved respectively?
Below is a curated selection on the causes of servo motor vibration, for your understanding and reference:
For example, when the acceleration and deceleration times are set too short, the servo motor will produce high-inertia vibration during sudden starts or stops... Increasing the acceleration and deceleration times can resolve this issue.
Viewpoint 1
When a servo motor experiences vibration at zero speed, it is likely due to excessively high gain, which can be resolved by reducing the gain value. If the motor vibrates briefly upon startup and then alarms and stops, the most likely cause is incorrect motor phase sequence.
Viewpoint 2
When the PID gain is adjusted too high, it can easily cause motor vibration, especially when D is added, making the issue more severe. Therefore, it is advisable to increase P as much as possible, reduce I, and ideally avoid adding D.
Incorrect wiring of the encoder can also lead to vibration.
If the load inertia is too large, consider replacing the motor and drive with larger ones.
Interference at the analog input port can cause vibration. To mitigate this, add ferrite cores to the motor input cables and servo drive power input cables, and keep the signal cables away from power cables.
Additionally, for motors with a rotary encoder interface, poor grounding can easily cause vibration.
Viewpoint 3
Servo Wiring:
a. Use standard power cables, encoder cables, and control cables, and check for any damage to the cables.
b. Inspect the vicinity of the control cables for interference sources and ensure they are not parallel or too close to nearby high-current power cables.
c. Check for any fluctuations in the potential of the grounding terminal and ensure proper grounding.
Servo Parameters:
a. If the servo gain is set too high, it is recommended to manually or automatically readjust the servo parameters.
b. Confirm the setting of the time constant for the speed feedback filter, which is initially set to 0, and try increasing the setting value.
c. If the electronic gear ratio is set too high, it is recommended to reset it to the factory default.
d. For resonance between the servo system and the mechanical system, try adjusting the frequency and amplitude of the harmonic filter.
Mechanical System:
a. The coupling connecting the motor shaft to the equipment system may be misaligned, or the mounting screws may not be tightened properly.
b. Poor meshing of pulleys or gears can also cause fluctuations in load torque. Try running the system under no-load conditions. If it operates normally under no-load, check for abnormalities in the coupling parts of the mechanical system.
c. Confirm whether the load inertia, torque, and rotational speed are excessive. Try running the system under no-load conditions. If it operates normally under no-load, consider reducing the load or replacing the drive and motor with higher capacity ones.
Viewpoint 4
Servo motor vibration can be caused by faults in the mechanical structure, speed loop, compensation board and servo amplifier of the servo system, load inertia, and electrical components.
Summary
I. Vibrations Caused by Mechanical Structures can be Divided into Two Scenarios:
- No-Load Vibrations:
a. The motor base is not secure, lacks stiffness, or is not tightly fixed.
b. Damage to fan blades disrupts the mechanical balance of the rotor.
c. The shaft is bent or has cracks. These issues can be resolved by tightening screws, replacing fan blades, or replacing the shaft.
- Vibrations Under Load: Typically caused by faults in the transmission device. Possible defects include:
a. Unbalanced rotation of the pulley or coupling.
b. Misalignment of the coupling centerline, causing the motor and driven machinery axes to not coincide.
c. Unbalanced transmission belt joints. These issues can be resolved by aligning the transmission device for balance.
II. Vibrations Caused by Speed Loop Issues:
Improper parameters such as speed loop integral gain, speed loop proportional gain, and acceleration feedback gain. Larger gains result in higher speeds, greater inertial forces, smaller deviations, and a higher likelihood of vibrations. Setting smaller gains can maintain speed response while reducing the likelihood of vibrations.
III. Vibrations Caused by Faults in the Servo System's Compensation Board and Servo Amplifier:
Sudden power loss during motor operation causes significant vibrations, related to improper wiring of the servo amplifier's BRK terminal and incorrect parameter settings. Increasing the acceleration and deceleration time constants and using a PLC to start or stop the motor slowly can prevent vibrations.
IV. Vibrations Caused by Load Inertia:
Issues with guide rails and lead screws increase load inertia. The rotational inertia of guide rails and lead screws significantly affects the rigidity of the servo motor drive system. At a fixed gain, larger rotational inertia leads to greater rigidity and a higher likelihood of motor vibrations; smaller rotational inertia leads to less rigidity and reduced motor vibrations. Reducing the rotational inertia by replacing guide rails and lead screws with smaller diameters can reduce load inertia and prevent motor vibrations.
V. Vibrations Caused by Electrical Components:
a. Factors such as a brake not being released or unstable feedback voltage can cause vibrations. Check if the brake is released and use encoder vector control with zero servo function to output a certain torque in a torque-reducing manner to resolve vibrations. If the feedback voltage is abnormal, first check if the vibration period is related to speed. If related, inspect the connection between the spindle and spindle motor, and check for damage to the spindle and pulse generator mounted at the rear of the AC spindle motor. If unrelated, check for faults on the printed circuit board, which may require inspection or adjustment.
b. Sudden vibrations during motor operation are mostly caused by phase loss. Focus on checking if the fuse has blown, if switch contacts are good, and measuring the presence of power in each phase of the grid.
With these viewpoints, do you now have a general understanding of the causes of vibrations during servo motor operation? In such cases, you can troubleshoot based on the causes analyzed in these viewpoints. Additionally, being aware of these issues can help prevent vibrations during servo motor operation.