Why do some servo motors oscillate around the target position?
In most cases it is because the characteristics of the load are not compatible with the PID filter settings. Generally, oscillation can be eliminated by: • 1) Verifying / optimizing load mechanics • 2) Adjusting PID filter parameters Even if these two steps do not solve the problem, they should provide sufficient information to help determine why the oscillation remains. Often, oscillation is caused by a combination of factors, and a successful resolution may require the user to prioritize between competing application requirements. For example, an X-Y table application that couples the servo motor to a lead screw via a belt-and-pulley system will tend to induce some phase lag into the servo loop. As the belt stretches over time, the axis might begin to oscillate around the target position. It may be possible to reduce the oscillation by reducing the gain of the PID filter, but this might result in reduced position repeatability. Tightening the belt may be a more satisfactory solution.
