Re: [CAD_CAM_EDM_DRO] Re: Closed Loop PC Based CNC

Mariss ........ CAN'T WAIT !!

>
>Mariss Freimanis wrote:
>
>
>
>>This probably doesn't satisfy your immediate needs but I am working
>>on a true closed-loop step motor/encoder system that will be able to
>>use any step motor drive.
>>
>>The "magic" will be in the step/direction controller.
>>
>>Step motors in many ways make ideal CNC motors; they have high torque
>>at low speeds where work is being done and little torque at high
>>speeds (rapids) where little torque is demanded of the motor. The
>>motor stalls when it falls behind by two ordinal steps. Just short of
>>that it is delivering 100% of its available torque for that speed.
>>
>>A step motor's "percentage of available torque demanded" is
>>sinusoidally related to the motor's "lag angle". This simply means
>>the motor's position falls behind from where it should be as torque
>>increases. This "lag angle" can be easily measured with a motor-
>>mounted encoder.
>>
>>The step/direction controller would adaptively react to an impending
>>overload by "backing up" the motor's speed-torque curve by decreasing
>>the step pulse rate sent to the drive until a new stasis point is
>>established, accomodating the new load-point.
>>
>>This would not be a problem in 2-D and 3-D vector motion because the
>>velocity ratios of the 2 or 3 axies would be maintained; only the
>>vector-sum velocity would change.
>>
>>The effect would be an "unstallable" step motor system. It would
>>accelerate at a rate limited only by the mechanicals to speed limited
>>only by the load or controller parameters. As load would change, the
>>motors would slow down or speed up as needed to adapt. An increasing
>>load would ultimately slow the motor down to its holding torque (zero
>>speed). Past that, it would misposition but the encoder would allow
>>it to recover position once the overload was relieved.
>>
>>This past week I cobbled together a strange combination of a G320
>>(encoder inputs, summing junction and a PID loop), a G210 (a VCO and
>>step motor drive) and a G2002 (a motion controller step/direction
>>source). It was enough to demonstrate the feasability of this idea,
>>feeble and limited as it was.
>>
>>I am coding up the G2002 to move the encoder inputs, summing node and
>>PID loop to reside within it. This will allow it to control an
>>ordinary step drive (G201) external to it when the driven motor is
>>encoder mounted. The results should be interesting because of the
>>goal.
>>
>>Mariss
>>
>>
>>

--
Ron Kline

American Precision Ceramics