Evaluating the oscilloscope pattern
While the axis reverses, observe the behavior with the oscilloscope. The following oscilloscope pattern shows the velocity command value and actual velocity value in the upper diagram and the current or torque ("torque feedback value") in the lower diagram. The red line is based on an increased value for Kp. The next motion shows that an oscillation occurs, which continues for the whole motion. | |
Depending on the mechanical system, the value that was reached can be regarded as Kpcrit, or Kp can be increased further, until the oscillation also shows up in the velocity value. It will then also be more audible. In the sample application with a ball screw, the oscillation in the current signal starts at Kp = 0.22. Only a soft "squeaking" can be heard, which is inaudible in a noisy environment. At Kp = 0.25 the oscillation also shows up in the speed signal. |
