Motion profile generator.

[richard]

the idea was easier to implement than I expected. when the setpoint to target distance is less than the ramp_length + the constant velocity increment , rather than any fancy math I just set the setpoint to the target-ramp_length value. I just let the pid work the mechanics out for its self. after that its just a matter or playing the array back backwards to arrive dead on target .
I have included a poorly annotated sketch of my c routine,
the motor I want to use can only achieve 300 counts/sec (accel 2000 counts /s/s) and needs to not have a count for at least 30mS to guarantee 0 vel , therefore the pid loop is run @40mS intervals and the profile input is applied on every second pid loop. this works pretty well (motor inertia gives smooth motion) and it stops on target _+ 1 count (pid might need better tuning).
seems to me that motor/load characteristics really change the entire nature of the problem.
I'm yet to try this on a real servo motor my pid loops are taking 50-300 uS to run so hopefully a 1mS pid rate is possible , I think I will get some pic18f2431's and have a play with thev qei module

[richard]

I forgot to add that in my application the accel and max v will never change only the direction and distance therefore the ramp array will never need recalculating , for "short" moves i just reduce the number of elements played out. the pid tolerance seems pretty accommodating.
I want no overshoot no stalling and no hunting +- 4 counts is accurate enough . its controlling the really stiff and jerky air slide on the pid controlled wood heater in the lounge (its a matter of principle)