Getting motion from a stepper motor?

[stirling]

Hi Dave

Before I'd suggest a solution I'd question your requirements.

You say at the end of your first post:

User input would just need to be a simple pot for the overall speed - this would set the amount of foil fed in the window provided by the start/stop signals.

No it wouldn't - well not accurately anyway. Consider your mill for a moment. If you want to cut from x=0mm to x=100mm on your mill at a feed of 10mm/s you wouldn't say cut for 10s at 10mm/s. You'd say cut from x=0 to x=100 at 10. If you did the former, you'd be dissapointed. Why? Because it wouldn't actually get to x=100mm. Why? because it's not ALWAYS moving at 10mm/s because of the accel and decel ramps.

If you want to feed a specific amount of foil between the start/stop signal then that is what you should be specifying - plus of course a desired feedrate (which will be maintained during the constant speed period between the accel and decel ramps).

[cropwell]

Dave,

It could be that a DC motor and a 555 timer circuit with a pot to set the time and a button to trigger the process would do the job. Some of the timer circuits on eBay have on board pots, so all you would need then is a trigger and a latching relay. The latch would switch the motor on and after a preset time it all drops out waiting for the next trigger.

As you say, accuracy to CNC standards is not the issue.

I use a similar circuit to hold off a pump for 7 seconds, otherwise the relay would be switching the pump on and off all the time as soon as the reservoir fluid level drops below the float switch.

Cheers,

Rob

[Davek0974]

Hi Dave

Before I'd suggest a solution I'd question your requirements.

You say at the end of your first post:



No it wouldn't - well not accurately anyway. Consider your mill for a moment. If you want to cut from x=0mm to x=100mm on your mill at a feed of 10mm/s you wouldn't say cut for 10s at 10mm/s. You'd say cut from x=0 to x=100 at 10. If you did the former, you'd be dissapointed. Why? Because it wouldn't actually get to x=100mm. Why? because it's not ALWAYS moving at 10mm/s because of the accel and decel ramps.

If you want to feed a specific amount of foil between the start/stop signal then that is what you should be specifying - plus of course a desired feedrate (which will be maintained during the constant speed period between the accel and decel ramps).

Yes but its not that complex - the operator set the machine up, sets the foil feed where he thinks it needs to be, runs a few sheets - not enough? just increase the speed a little, too much? then back it off when running.

Its a simple process, not CNC. :)

[stirling]

OK - looks like I posted at the same time as your #24 so I didn't see that accuracy was not important.

In this case I agree with Rob - a DC motor would be a better fit. A stepper is not appropriate for this. It just introduces unnecessary complexity for no gain.

[Davek0974]

Hmm, ok maybe :)

Simple pwm control would work, Will have a look at some motors, will still need a gearbox reduction though i think.

[Davek0974]

Just wrapping this up, going for a stepper motor at present cheap, cheerful and plenty powerful.

If anyone is interested in moving a stepper without a PC, take a look at the Leadshine DM805-AI drive, it has a built in oscillator and ramp controls, speed input etc, exactly what the doctor ordered, price was £106 inc Vat.