Close-loop torque control

[alanambrose]

Hi,

Re: closed-loop steppers & torque (as opposed to position) control. Viz:

https://en.nanotec.com/knowledge-base-article/closed-loop-technology

"In torque mode, the closed-loop stepper motor functions analogously to a spring, whereby the spring tension characteristic curve can be set via a potentiometer. Thus, the motor delivers a stable force, even when the motor counteracts a force while at a standstill. When the force declines, the motor begins to turn proportionally to the declining force up to the set current and torque values. Thus, closed-loop stepper motors prove ideal for any type of winding, stretching and pressing applications."

I think ClearPath have support for this application:

https://www.youtube.com/watch?v=fHPZ0lqU-80

Anyone know of any others?

Ta, Alan

[m_c]

Not any that take a pulse input. There are possibly some servo drives that can do it, but it's not a feature I've ever looked for.
Pretty much any modern servo drive that supports analogue +/-10V input, will support torque mode.

[JAZZCNC]

Nope, I've not seen any closed-loop stepper system other than the Clear path which can do it, and to be honest at the money they want you could get an AC brushless servo which would be much stronger. Thou I'm still not sure they could use a pulse signal to control torque, torque is usually and easily done with +/-10v as MC says. (that said I have some Adtec servos which are pulse only and I think they have torque mode.?, will check that.!)

[Muzzer]

The Lichuan, DMM and Yaskawa AC servos all support torque mode although the Lichuan seems to only support analogue (+/-10V) inputs. The others seem to support serial / digital comms etc as well. Step/dir isn't an obvious mode for controlling torque but I suppose the pulse frequency would indicate the torque demand.

My Leadshine closed loop servo only supports position control with step/dir inputs, so I'm guessing this "closed loop stepper in torque mode" function seems to be a bit of a minority sport. I suspect the norm is just to use servos for torque control.

Unless you need true 4 quadrant operation, there are iron powder clutches and brakes that generate a (drag) torque that is proportional to control current. For things like coil winders and tensioners, this may be a much simpler solution but it's not clear what the OP is actually after. https://www.aliexpress.com/w/wholesale-magnetic-powder-brake.html

[alanambrose]

>>> "closed loop stepper in torque mode" function seems to be a bit of a minority sport.

Yeah, I think so. And I didn't realise the preference for servos for this application although that makes sense, so thanks everyone for that.

>>> it's not clear what the OP is actually after

I should have said: the application is a clamping one - needing to produce a given clamping force in the 1-5Kg (~10-50 Nm) range and constant over a variable distance of ~5mm or so. There is a requirement to start at a particular distance (hence my 'stepper thinking') but after that it's a 'closed-loop clamping application'.

Alan