Internet PLC Forum
General => Technical support => Topic started by: dutch_CAT on September 04, 2004, 02:50:35 PM
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Hi,
I need to jog my stepper motor at a certain speed for an "indefinite" time, that is I can not define the number of steps beforehand.
Imagine moving the system in and out of the region were normal positioning would happen.
Is there any way this can be realizied?
- merge a next move to an ongoing move?
- reset the pulses to go?
- ???
please advice,
Another solution for me would be to use another output to jog BUT how do I get something like 4kHz out of any of the other outputs (since it is a variable frequency I cannot use the PWM output for this)
Thanks in advance
Martin :-[
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Based on advice I've received from support here in the past, I simply use a very large number as the move to position when I want to jog. Then I issue a STEPSTOP when I want the jogging to stop.
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Thanks for your reaction,
unfortunately I will run out of counts when I run for prolonged time
see it like I have 2 modes with one motor; positioning and jogging/running for prolonged time
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Ah, I see now. This controller could use a mode where the stepper just continuously spins. It'd be useful for things like conveyor belts, spindles, and anything else that has no absolute position. It could also be used for jogging as well.
The only other options I can think of are the PWM output (which gives you only a few options for speed control) or else getting a seperate stepper controller. Applied Motion (http://www.applied-motion.com/) has a model that has an onboard oscillator that is controlled via an analog input to control the speed. The one we used before (3540MO) was around $200 which kind of hurts if you're only paying $200 for the PLC. They may have other models with the oscillator that are cheaper or maybe another company can offer something similar for less.
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Hi Joel,
Thank you for helping to answer this question by dutch_CAT! Your suggestions are exactly what I would have suggested too.
Hi dutch_CAT
I am a bit curious: if a motor is to run continuously then why use a stepper motor? Stepper motors are typically used for positioning and not to be used to drive a fan, for example.
In any case, if you set 2 x 10^9 counts and the motor turns at 5000 pps, it will run continuously for 400000 seconds, or 4.6 days. Once the motor stop running, have it trigger a relay to restart itself for 2 x 10^9 counts again and it will run on forever. Is a brief stop and restart every 4 days intolerable for your application?
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Thanks for the replies;
The stepper motor was selected for size and cost of drive unit (unfortunately without on-board oscillator)
Also I have tha ability to switch to accurate positioning and speed control in a different mode, like killing two birds with one stone
I think I could get away with 4 days since the longest operation is likely to be 12 hours but I will have to scale back on pulses per rev, microstepping that is
is stepper control realizd in hardware or purely in firmware?
IF hardware then my question would be if the two channels run syncrhonized or not
IF firmware then my question is why the HOME command can not reset the actual position thus creating eternal running capabilities
thanks again