Consider that I have 2 linear actuators that are attached to the 2 free corners of a rectangular hinged frame, so that extension/contraction of the actuators will change the angle that the plane of the frame makes with the local horizontal. In operation, the frame will likely be supporting varying heavy loads (hundreds of pounds), and the objective is to synchronize the actuators so that the frame angle can be varied without "twisting".
At present, I have a microcontroller-based circuit that drives a single actuator via a pair of Infineon BTS-7960 half-bridge chips, and also tracks actuator position using a pair of Hall sensors internal to the actuator. This circuit works perfectly for a single actuator. But now I need to drive two actuators in unison such that the position of one doesn't get ahead or lag behind the other.
One obvious choice is to set up a closed-loop configuration using the respective Hall sensors of the two actuators, and implement a PID algorithm to adjust the actuator speeds based on any difference in measured positions, thus ensuring they move together. Those speeds can easily be controlled by driving the half-bridge chips with PWM. But that begs a couple of questions:
1. How can one select PID gains necessary for stable operation in situations where the load experienced by the actuators will likely vary? I know that there are a variety of tuning algorithms that are based upon "mapping out" the system dynamics in response to step changes in the controlled variable. But that would assume that the system dynamics remains the same throughout the operating regime of the system - which I'm not sure will ever be the case in this situation.
2. Should I use a master-slave configuration, where one actuator is arbitrarily considered a master and dictates the movement, while the other the other (slave) is the one that's controlled to stay in sync with it? If that were the case, I would suspect that the master should be run at some PWM duty factor of, say, 0.7 to that the duty factor of the slave has sufficient latitude to speed up or slow down as needed.
So I'm soliciting any thoughts from folks who might have done something like this. Thanks in advance.
Jim