Getting motion from a stepper motor?

[Davek0974]

Yes but inexpensive until it comes to finding a plc capable of stepper control, although i must admit i have only used the larger more expensive units in the past - do you know of a cheaper PLC?

[Gary]

http://www.zappautomation.co.uk/elec...nit-23609.html
Its the last one, so once gone the price goes up.
if you want to set the speed from a 0-10V, you will need another plc, but you can set the speed in the program.
If you have not programmed plcs before you are best getting someone who has to commission the system.
I know an engineer who can do this, but he will charge you.

[Gary]

Also if you want to add a HMI so you can set the speed and move distance from a touch screen you can also do that with one of the HMI we sell.

[Davek0974]

Thanks Gary that looks a nice little unit but yes we will need to vary the speed somehow. The HMI is a good thought but is really not needed here, a simple pot will do the job, especially as the HMI really pushes the cost up.

[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.