Stepmove pause question

[cch1955]

I have a need to load a stepmove distance and then during the execution of that move and prior to completion, to stop the motor and hold position.

I then will continue the move to the original completion point. I would call this a "feed hold" type of function. It looks like I can create this function with the stepcount function and some code. I would like to simply execute a STEPSPEED 1,0 to cause the stepper pulse stream to stop until I give a new STEPSPEED command to resume the move, but it faults out.

Any elegant solutions come to mind? Suggestions of best way to do this?

[support]

Why don't you use a variable to keep the total distance to move, then execute a stepmove once to move to the intermediate location and stop and hold, then later run a stepmove for the remaining value to the final location? You could also do it using STEPMOVEABS.

To stop a stepper motor half way, use a STEPSTOP command instead of changing the speed to zero using STEPSPEED. If you use STEPMOVEABS you could reexecute the STEPMOVEABS with the same absolute location and the stepper motor will complete the move.

[cch1955]

Master of TRI-PLC:

I did try a variation yesterday on what you suggested first and it works well.  As we all know the only potential problem I have is if the motor is running fast, and I hit feed hold, STEPSTOP will not ramp down to a stop so I could loose position by some steps in open loop control.

I can go through the detail of creating a ramp down cycle hold, but I hope in actual operation the problem will not be a big one.

I would suggest to make a great product even better; a STPmovHLD command would be very popular. The function would allow a person to cause a STEPMOVE command to be brought to a stop in a ramp down to a stop manner and then ramp up and resume the unfinished STEPMOVE once a control bit goes high.

How about a place on the forum where we customer could vote for the list of potential software and hardware changes to you product? As a manufacturer with limited resources, it would allow you to make the product more attractive  to your customer - you would sell more and it would cost you less.

Thanks for the help.

[support]

It is possible execute STEPSPEED again while the stepper motor is moving to change the speed to a lower one so that it does not overshoot when the final STEPSTOP is executed. i.e. when it exceed  certain stepcount you start slowing it down before the final stepstop. That should work out better.