Motion Profiling

[flameout]

Originally Posted by winchymatt

So on a side note, if you were sending just position information to the PID controller, and did not have velocity and acceleration data, could one derive the velocity and acceleration by differentiating the position data with the previous position.. I guess this would not produce a true goal velocity, but may give some feed forward gain??

Matt.

You can, if and only if that signal is twice differentiable. If not, then you'll get bad spikes in your data -- if you have spots that are not twice differentiable, you'll need to differentiate on each side then use each section as a separate input, essentially "cutting out" the bad spots. This is much more useful if the position trajectory is derived via some analytical or numerical process -- you'll likely have a ton of noise if you try to do this with real sensor data.

Also, with full PID, having a feedforward on the velocity target will cause overshoot, just FYI.* If you're doing PID for position control, then having an acceleration feedforward should be fine; a velocity feedforward would be beneficial if you're doing PD.

If anyone disagrees with any of the statements in this post, please correct me -- this is operating at the edge of my knowledge of control theory.

* This statement is incorrect, please see AustinSchuh's post below.