Need Help!- Stall Sensor for Steppers?

[basskitcase]

I have run into a few instances with my machine where i had a motor stall that could have been disasterous if i had not been right by the machine (caused the router to plunge collet deep into the work).

Is anyone familiar with a way to monitor the motor current of a stepper (unipolar or bipolar) to cut the machine off in case of a detected stall?

I was wondreing about using a low amperage circuit breaker in series with the motor windings (assumption: current spikes when motor stall?) tied into a relay that feeds back into the limit switch connections?

[tpworks]

encoders

[CarveOne]

You mean something like this?

Been there, done that....


CarveOne

[ger21]

http://rogersmachine.net/encoderinterface.html

But, it's cheaper and easier to just run them within their capabilities. They only stall if you try to go faster than they're capable of.

[neilw20]

Why do want to push the speed too close to the limits?
Use bigger motors or back off.
Cutting too much air at high speed? Optimize tool cutting paths.
Run within the proper limits steppers NEVER stall.
For reliability I have reduced 2500mm/min to 1500, and with expensive tooling and material have never had a problem in over 1000 hours, but might have saved 10 hours and lost $$$$$s of time and expensive materials. 80000++ parts and no stuffups, all on a syil SX3.
If you want a rocket ship use a servo based system and pay the money.

[basskitcase]

I don't want to push the steppers faster than they are capable of, but it would be nice to have the extra peice of mind of stall protection, as you never know when something might go wrong. Something mechanically could fail (timing belt break, screw vibrate loose, etc) and then you could stall the machine, even if you are not running the steppers faster than they are normally capable of. I don't want to overengineer, but I like safeguards just in case. I had thought about encoders but was hoping for something a little less pricy. Does anyone know if my assumption about power spiking when steppers stall is wrong?

[cyclestart]

Originally Posted by basskitcase Does anyone know if my assumption about power spiking when steppers stall is wrong?

Don't know, interesting idea.

Digikey has some nice rotary encoders for ~$30, maybe more than you want to spend. A resourceful electronics guy can probably salvage something functional for $0. Being neither resourceful or electron literate I paid Digikey. An encoder reading directly off the screw (not the motor) would cover +90% of the common failures. That said, if there's a cheaper way than encoders let's hear it

edit/ well +90% of the mechanical failures. The nut behind the wheel is usually the weak link

[neilw20]

Do the protection mechanically. eg belt.
Sense failure, by belt tension or similar
It is emergency stop dropping out a safety relay (you should already have).
Keep the protection SIMPLE. Never rely on anything electronic.

[basskitcase]

Originally Posted by cyclestart Don't know, interesting idea. Digikey has some nice rotary encoders for ~$30, maybe more than you want to spend. A resourceful electronics guy can probably salvage something functional for $0. Being neither resourceful or electron literate I paid Digikey. An encoder reading directly off the screw (not the motor) would cover +90% of the common failures. That said, if there's a cheaper way than encoders let's hear it edit/ well +90% of the mechanical failures. The nut behind the wheel is usually the weak link

So the encoders themselves seem reasonable, but don't i need an additional interface board, or can I tie them directly into Mach3 somehow?

[cyclestart]

Originally Posted by basskitcase So the encoders themselves seem reasonable, but don't i need an additional interface board, or can I tie them directly into Mach3 somehow?

Sounds like a question for Mach support ?

Here's something from the guy at candcnc
http://www.cnczone.com/forums/showpo...41&postcount=4
He suggests it's possible(?) although you might want use a relatively low count encoder if counting in software. The CUI amt encoders can be set within a range of counts/rev.

[ger21]

You can wire them to a parallel port. But, if you want them to stop your machine, you'll need to write a plugin or macropump to do it.

The encoder interface I linked comes with a plugin to stop the machine when it loses position.

[Drools]

This is more what I was looking at when I asked about encoders on steppers a while ago. I to would just like to stop my machine if a certain (x) resolution threshold has been reached or compromised. I’m not looking at having Mach3 control the steppers. I also was thinking about having some sort of sensor on the work piece to tell me if it has moved. I do a lot of PCB/Plastic routing where I hold the material down with double sided tape so it would be nice to know if the work piece has moved even slightly.