Continuous determination of medium stiffness and load gain for adaptive actuator control

A method for adaptive control of an actuator of a mechanical testing device, the method comprising:

• generating an actuator current waveform to move an actuator, wherein the actuator current waveform is a periodic waveform;
• moving an actuator through a medium in response to a first current request and the actuator current waveform;
• determining a load gain of the actuator based on a load sensor signal;
• determining a stiffness of the medium based on the load gain of the actuator;
• determining a second current request based on the stiffness of the medium;
• and
• moving the actuator through the medium according to a predefined constant load ramp rate in response to the second current request and the current actuator waveform.

A mechanical testing system comprising:

• a mechanical testing device having an actuator, a load sensor and a displacement sensor;
• and
• a computing system coupled to the mechanical testing device and having a processor, a memory device coupled to the processor, and a computer readable storage device coupled to the processor;
• wherein the computer readable storage device contains program code executable by the processor via the memory device to implement a method for adaptive control of an actuator of a mechanical testing device, the method comprising:
• generating, by the processor, an actuator current waveform to move the actuator;
• controlling, by the processor, a movement of the actuator through a medium in response to a first current request and the actuator current waveform;
• determining, by the processor, a position error by comparing a desired position of the actuator with an actual position of the actuator, and a load error by comparing a desired load of the actuator with an actual load of the actuator;
• calculating, by the processor, a stiffness of the medium based on at least one of the position error and the load error;
• calculating, by the processor, a second current request using the determined stiffness of the medium, the position error, and the load error;
• and
• controlling, by the processor, the movement and the actual load of the actuator using the second current request to achieve the desired position and desired load while maintaining both a uniform velocity and uniform load ramp rate.