Den 2021-05-02 kl. 20:00, skrev Chris Albertson:
The below is exactly true. The problem is that PID is widely used and PID
is only "reactive" it can only deal with what has already happened and the
time lag is the source of oscillations. In the past, PID was the only
control option because we had limited computing power. People are
starting to use MPC for motion control now. MPC is predictive and can
account for "spring back", backlash and the time it will take to
decelerate. But it does require modern compute power. If you google,
you find many papers on MPC applied to milling machines starting in about
2010.
So what's the difference between MPC Model Predictive Control and feed
forward? Solve equation analytical instead of using analytical solution?
Read some about it but did not figure out what they are doing but should
not be able to predict something not in the model.
Eventually, this will filter down to the open-source DIY hobby community.
If you have ever seen a machine running with this kind of controller it is
visible even just looking at it by eye, the machine looks "alive" and moves
more like a human or a dog rather than a robot.
A consultant at work my workplace brought two dogs, kept them in a
nearby room during meeting and they pee on the floor. Machine dog eat
oil and shit screw is much better.
The problem is the complexity. It requires some advanced math and the
computer has to be able to run thousands or likely millions of simulations
of the entire machine per second. This is maybe why we don't see
research on this done in the 1990s or 2000s. It is a good use for a
6-core Intel i9 CPU
Read model based control theory at University. Non-linear system may be
linearized around working point while linear system may be stated
directly. In both cases it will be a system on matrix form. There are
standard methods to calculate feed-forward once model have been stated.
For servo motors rather simple calculations give fast dynamic response
though it might be possible to get more accurate control by modeling
more details and improve feed-forward.
Nicklas SB Karlsson
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