This example shows a VCA driven motion control loop that is acting through an equivalent model of a flexible mechanical structure. This model is shown on the right side of the schematic. It was calibrated to match a physical structure, based purely on its frequency response data and using the HyperLynx complex-pole fitting technology. The original mechanical model can be seen here: https://www.systemvision.com/design/spring-mass-structural-model-and-fitted-equivalent

The top net in this schematic represents the displacement of an ideal position sensor, which provides the actual target position feedback. The loop compensation was designed by using "AC" or frequency-domain analysis of the open loop transfer function. The results are shown in the Magnitude and Phase difference plots (sensor_displacement - feedback). The loop crossover is seen to be at approximately 100 Hz, and the phase margin is just over 44 degrees. The corresponding time-domain step response is shown in the left-most waveform plot.

You can see this same design and analysis using the original mechanical structural model for the "plant" here:

https://www.systemvision.com/design/motion-control-voice-coil-actuator-vca-physical-plant

You can see a more detailed model of this system, that includes the Power Electronics section (i.e. a PWM controlled MOSFET H-Bridge used to drive the VCA), here: https://www.systemvision.com/design/motion-control-vca-pwm-drive