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An electric motor actuated vice

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Michael Gilligan02/01/2019 20:36:08
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Posted by Robert Atkinson 2 on 02/01/2019 20:23:08:
 
... That is a different situation your system did not stall, it was slowed to a halt. The drive signal was stopped and the motor is still in sync. < etc. >

.

The situation I described [whatever you choose to call it] is the one that I believe would apply to the Vice.

MichaelG.

.

Perhaps we could use this as a common point of reference:

https://www.motioncontroltips.com/faq-whats-the-difference-between-detent-torque-and-holding-torque/

Edited By Michael Gilligan on 02/01/2019 20:42:09

Nick Clarke 302/01/2019 20:48:21
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Posted by Michael Gilligan on 02/01/2019 14:06:03:.

May not be quite the same as an electric window ...

.

Yes, Nick ... I realise that it may not be 'quite the same'

But the control principle [threshold load triggers stop and retract slightly] is still worth a look.

Hi Michael -

The point I was thinking about was that while an electric window works as you suggest a vice would surely need to stop at a threshold load but NOT retract slightly or it would not grip.

Dunno - Just thinking aloud online.

Take care

Nick

Edited By Nick Clarke 3 on 02/01/2019 20:51:03

Edited By Nick Clarke 3 on 02/01/2019 20:55:27

Robert Atkinson 202/01/2019 20:49:31
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Posted by Michael Gilligan on 02/01/2019 20:36:08:
Posted by Robert Atkinson 2 on 02/01/2019 20:23:08:
... That is a different situation your system did not stall, it was slowed to a halt. The drive signal was stopped and the motor is still in sync. < etc. >

.

The situation I described [whatever you choose to call it] is the one that I believe would apply to the Vice.

MichaelG.

Not really, you don't know when to stop the motor on a vice, unless there is a sensor which has not been mentioned. In simple terms a stepper motor has good static holding force i.e it resists counter torque. but they are very bad at producing a constant torque output. I guess one option would be to put a spring between the motor and load but you still need a sensor to stop the motor drive. A microswitch activated by the spring movement would work. A DC motor and current limit circuit seems much easier.

Robert G8RPI.

Michael Gilligan02/01/2019 20:55:45
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19599 forum posts
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Posted by Nick Clarke 3 on 02/01/2019 20:48:21:
Posted by Michael Gilligan on 02/01/2019 14:06:03:.

May not be quite the same as an electric window ...

.

Yes, Nick ... I realise that it may not be 'quite the same'

But the control principle [threshold load triggers stop and retract slightly] is still worth a look.

Hi Michael -

The point I was thinking about was that while an electric window works as you suggest a vice would need to stop at a threshold load but NOT retract slightly.

Dunno - Just thinking aloud online.

Take care

Nick

.

No problem, Nick ... very reasonable thinking yes

How much, if any, retraction would be appropriate to the Vice would probably depend on the speed and force of operation and the response time of the detector.

MichaelG.

Robin Graham02/01/2019 23:51:15
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Thanks for replies - as MichaelG rightly remembered it is indeed to do with a woodworking vice, I was just surprised that anyone would remember that I'd mentioned this possibility earlier!

I'll re-read the discussion later with more attention to detail, but for now it looks like it it could be done with either a stepper and associated control electronics, a DC motor with current control, or a simple slipping clutch as in Hacksaw's link.

I now have enough info to get back to my friend with some possibilities and see if he thinks it's worth pursuing - personally I can't yet see why one would construct such a thing outside a production environment, but it would be a fun project.

Robin.

 

Edited By Robin Graham on 02/01/2019 23:51:47

Hopper03/01/2019 00:10:35
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Alternatively, a pneumatically operated vice running off a common-a-garden workshop compressor might be simpler to make? A double acting cylinder, commonly available from commercial suppliers, could be either manually controlled by valves or electrically via a solenoid valve. Just don't leave your finger in the way when you hit the button/valve!

Tim Chambers03/01/2019 00:20:21
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You could incorporate a loadcell to control the clamping load.


duncan webster03/01/2019 00:32:32
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Taking Tim's suggestion but making it a bit simpler, incorporate a preloaded axial spring in the drive mechanism, and detect when the preload is overcome to stop the motor. I'd be tempted to use a braked motor so it won't vibrate loose, but I suppose with this system the 'preload overcome' detector would just re-energise and tighten it up again

John McNamara03/01/2019 01:57:37
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I am guessing that the force needed to clamp the work is more than the force that would cause injury to a person.

When an individual builds a machine alone for personal use that person has to accept all responsibility for the safety of the mechanism.

Apart from pointing out the possible risks. I would be hesitant offering advice to another person on how such a device may be constructed unless it was made safe by the installation of guards that stopped all access while the device is switched on or working.

Safety systems have to be robust. Electronic means of protection have to have built in redundancy, they have to be duplicated, better still they should be backed up by a physical guard barrier.

This paper is a useful guide.
**LINK**

Regards
John

Edited By John McNamara on 03/01/2019 02:01:45

Edited By John McNamara on 03/01/2019 02:02:55

Hopper03/01/2019 04:08:34
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Posted by John McNamara on 03/01/2019 01:57:37:...

....

Safety systems have to be robust.....

As we used to say in the car factory, it's no good making safety guards foolproof; they need to be idiotproof.

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