Gain can be simply understood as magnification factor.
Servo gain is one of the simplest control methods. Its controller output is proportional to the input error signal.
The structure of the machine itself has a significant impact on the adjustment of the servo gain. If the machine itself has good rigidity (such as a grinding machine lead screw drive), the servo gain can be set higher. If the machine itself has relatively flexible rigidity (such as a feed channel timing belt), the servo gain should not be set too high.
Relationship between servo speed and position gain parameters, and overall debugging approach:
A servo drive consists of three feedback loops: a position loop, a speed loop, and a current loop. The innermost loop (current loop) has the fastest response speed, and the middle loop (speed loop) must have a faster response speed than the outermost loop (position loop). Failure to adhere to this principle will result in motor vibration or poor response. The servo drive is designed to ensure good responsiveness of the current loop, so users only need to adjust the gains of the position and speed loops.
The position loop cannot react faster than the speed loop. Therefore, if the gain of the position loop needs to be increased, the gain of the speed loop must be increased first. If only the gain of the position loop is increased, the motor is likely to vibrate, resulting in an increase in speed command and positioning time, rather than the desired reduction.
Velocity loop gain
Increasing the speed loop proportional gain can reduce the amount of speed pulsation, improve the stiffness of the servo drive system, and ensure the system's performance during steady-state and transient operation. However, in practical systems, the speed loop proportional gain cannot be too large, otherwise it will cause the entire servo drive system to oscillate.
Relationship between speed loop parameter adjustment and load inertia
When the ratio of the moment of inertia of the load to that of the motor is large, and the frictional torque of the load is also large, it is advisable to increase the proportional gain of the speed loop and the integral time constant of the speed loop to meet the requirements of operational stability.
When the ratio of the moment of inertia of the load object to the moment of inertia of the motor is small, and the frictional torque of the load is small, it is advisable to reduce the speed loop proportional gain and the speed transfer integral time constant to ensure the speed control accuracy when running at low speed.
Position loop gain
Position loop gain is closely related to the servo motor and mechanical load. Generally, a higher position loop gain in a servo system reduces the delay in motor speed response to position commands, decreases position tracking error, and shortens positioning time. However, this also requires high rigidity and natural frequency of the corresponding mechanical system. Furthermore, when the input position changes abruptly, the output changes drastically, and the mechanical load must withstand a significant impact. In such cases, the driver must handle acceleration/deceleration or use programming techniques in the host computer to buffer this change.
When the position loop gain of the servo system is relatively small, adjustment is easier because a small position loop gain makes the servo system more stable, and adjustments are simpler for heavy loads. At the same time, a servo system with low position loop gain has a narrow bandwidth and is less sensitive to noise. Therefore, when used for servo feed, the micro-changes in position are small. However, a servo system with low position loop gain has a larger position tracking error, which will create machining errors on the trajectory when performing contour machining.
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