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Author Topic: Step pulse duty cycle  (Read 5800 times)

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Re: Step pulse duty cycle
« Reply #20 on: May 04, 2019, 04:15:19 PM »
Hi,
I am of the opinion that closed loop stepper drivers offer too few advantages over open loop drives to justify the extra expense.

It is my opinion that the manufacturers of these things play on the insecurity of customers with phrases like 'never lose steps'.
If an open loop stepper loses steps because of overload (too high accel or too high velocity or too high inertia) then a closed loop
stepper will lose steps as well, and for exactly the same reason. A closed loop stepper is still a stepper, it has the same torque/speed
characteristics as an open loop stepper. Its true that the closed loop stepper will try to recover....but if its overloaded it will
fail. If it gets too far behind its commanded position it will fault 'following error', ie warning you that its lost steps. That is an
advantage over an open loop stepper.

The better path is to select a stepper, it matters not whether its open loop or closed loop, that can do the job required
WITHOUT losing steps, ie operate WITHIN its torque/speed area. This requires a certain minimum holding torque but more
importantly places an upper limit on the inductance of the stepper.

In experienced stepper buyers look at the holding torque only reasoning that the higher the torque the better the motor.
What they don't realize is that a high inductance motor will lose all its torque at speed whereas a low inductance stepper
retains more of its holding torque.

If a manufacturer or supplier cannot provide you with an inductance specification or torque/speed diagram.....walk away,
they are trying to hoodwink gullible buyers.

The second issue is the voltage of the supply/driver driving the stepper, the higher the voltage the faster the stepper will go
without undue loss of torque. Gecko drives are typically capable of 72V-80V and Leadshine AM882' are 80V capable.
Leadshine AM882's are pretty good value. Pair that with a low inductance (2mh or less) stepper and 80V power supply
and that stepper will sing!

The other alternative is genuine servos. Over recent times the price of genuine, good quality AC servos have come down in price.
Have a look at DMM:

http://www.dmm-tech.com/

They are a Canadian company but manufacture in China. Good quality at a very good price. There are cheaper 'no brand'
Chinese servos...don't go there!

Servos still command a premium over steppers (open or closed loop) but they are EXCEPTIONALLY CAPABLE.
Once you have used them you'll never go back to steppers.

Craig
My wife left with my best friend...
     and I miss him!
Re: Step pulse duty cycle
« Reply #21 on: May 05, 2019, 02:40:41 AM »
Craig,

Thanks again for the reply.
I'll have an experiment with power supplies I think and see how good I can get my current motors working.

I've also asked DMM for a quote to replace my X and Y axis motors, might be a bit to pricey for me though.

regards

Carl.
Re: Step pulse duty cycle
« Reply #22 on: July 27, 2019, 09:26:51 AM »
Got servo's from DMM only to find the same issue with those ?
Finally found it was my laptop that was a bit to old for the job, used my new laptop and they work fine, even the closed loop one.

Can't believe how good the servo's are, quiet, cool and can go way faster than I could use :-)
Re: Step pulse duty cycle
« Reply #23 on: July 27, 2019, 07:45:19 PM »
Hi,

Quote
Can't believe how good the servo's are, quiet, cool and can go way faster than I could use :-)

That sums up my experience also. It was not until I tried using a servo to realize just how much superior thay are.

Craig
My wife left with my best friend...
     and I miss him!