Stepper jogging

[Joel Moore]

I've implemented a jog feature in our 888 program by sending large values to STEPMOVE and issuing a STEPSTOP when the jogging is done.  However we recently uncovered a problem with this technique that somehow escaped our notice before.  If the speeds are too high suddenly stopping the motor with STEPSTOP results in the motor skipping a number of steps (due to momentum) which knocks the position off.

One solution is to limit jog speeds but this is very unsatisfactory since the speeds would be too slow to be useful in our application.

So consider this post an enhancement request for future versions of the Triplc firmware.  I'd like to either see some jog functions added (maybe even simplifying the use of an analog input for speed control) or at the least add a deceleration parameter to the STEPSTOP command where obviously a decel of "0" would make it work as it does now.

[dan]

Hi,

You can make an acceleration and a decceleration phase using a custom function.
The deceleration function will between your max speed
and your low speed. From the "low speed" to Stop you can use the program you allready made.
Problem is that you need an extra control for this function.

Dan.

PS. When you find a better solution please let me know. I'm not 100% happy with this solution.

[Joel Moore]

This is an interesting idea.  I've occasionally had problems changing step speeds while the axis is running (motor stalls) but maybe if I'm careful this could work.

Another issue to consider is overtravel.  Depending on how fast I can step down the speeds to simulate deceleration there could be some significant overtravel (significant is a relative term here).

[support]

Will submit this suggestion to the product development for consideration.

[evanh]

Not having used it yet but doesn't SETSPEED configure acceleration for you?  By experimenting, you should be able to arrive at a reliable acceleration for your setup.


Evan

[Joel Moore]

Not having used it yet but doesn't SETSPEED configure acceleration for you?  By experimenting, you should be able to arrive at a reliable acceleration for your setup.

I don't have a problem with acceleration -- it deceleration.  Specifically when interrupting a jog.

I've done some initial experimenting with Dan's suggestion and so far it seems promising.  In the custom function where I normally STEPSTOP the motor when jogging I now check to see if my speed exceeds some threshold.  If so I proceed to issue STEPSPEED's that cut the speed down by 10% every 20ms until I'm below the threshold at which point I issue a STEPSTOP.

Initial tests have been encouraging.  At speeds above some configurable threshold I can come smoothly to a stop with a little overtravel.  Below the threshold I am still able to stop on a dime by issuing an immediate STEPSTOP.