On Wed, Oct 31, 2012, at 10:28 PM, Peter C. Wallace wrote:
>
> After spending some forum time trying to help a customer with tuning a
> torque
> mode drive, I have noticed that ferror is calculated incorrectly and if
> minimized will result in less than optimum actual error.
>
> The error appears to be that ferror is calculated before the trajectory
> is
> calculated so it always compares the previous waypoint with the current
> (encoder) position.
The PID loop was asked to go to the previous waypoint, and comparing
it with the current position tells you how well it was able to achieve
that goal.
If we were to compare the encoder position with the new waypoint
we would be evaluating the PID loop on how well it hit a target it
hasn't even seen yet.
This is easily see by the difference in ferror from
> the
> PID error (they should be the same)
>
> This causes a value equal to the velocity in machine units per
> second*servo
> thread_period to be added to the ferror.
>
>
>
> Peter Wallace
> Mesa Electronics
>
> (\__/)
> (='.'=) This is Bunny. Copy and paste bunny into your
> (")_(") signature to help him gain world domination.
>
>
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