Brakes on steppers

[JerryFlyGuy]

I'm curious if anyone has put a brake on a stepper. We've been discussing the various options for a counterweight on my Z axis and it was suggested to just use a brake. Anyone want to offer their experiance or knowledge on if or how this could be done w/ a stepper without to much hassel?

Thanks

Jerry

[keyne]

Jerry,

here's a site with brakes on steppers:
http://nanotec.com/page_bremse__en.html

[joecnc2006]

I thought the counter weight is used to help raise the Z, a brake to me just helps stop and hold the motor?

on my 2nd machine i used two springs for couter weight.

Joe

[keebler303]

he doesn't have a lot of space for springs etc. the motor is plenty to move it around when its on he wants it to hold the z up when the machine is turned off. so all you would need is a brake.

jerry
what if you just used an electric clutch and had the other side of the clutch fixed. so instead of being a clutch it would act as a brake. you could probably also machine something like a parking pawl in an automatic transmission that was air or otherwise actuated. it would just be an externally toothed gear and an internally toothed gear that would come together and lock.

Matt

[JerryFlyGuy]

thanks Keyne, looks like it would work in the phyisical sense. However how would one hook that electronically? I'll have to take the time to do some more reading on that site.

Joe, The counterweight would do two things, it would take all static loads off the motor and would stop the head from droping when the power suddenly goes out [ hope that never happens] The down side is its more mass to accell and decell. The motor brake would solve the power outage issue, and the static one is more a question of perfectionizm.. it isn't very high so its really a non-issue other than wanting to build the best machine I can.

Keebler, I think there would probably be many many possible work-arounds. The simplest that I could think of was a spur gear on the ball screw w/ a spring loaded keeper/tab that engages the gear when the power goes out. When the power is on in the system, there is an electromagnetic magnet holding the keeper open. Power goes out... magnet dies.. keeper engages.. ballscrew doesn't move. Down side? If the ball screw is doing 500 rpm when this happens... there might be a big bang.. and parts flying every which way..

I'll think of something yet.. or... someone will have a turn key solution

I've been up and working for 20 hrs.. time for bed.

Jerry

[keyne]

The way you hook this up electonically is simple. The brake is activated when no power is applied. When you power on the machine, first the servo controllers get power and as soon as they are ready, you supply power to the brake (think delay relay) to release it. Now you are ready to move. In the event of a power outage, the brake will activate. Power supply holdup time for the servo controllers should be longer than the brake supply.

[JerryFlyGuy]

Originally Posted by keyne The way you hook this up electonically is simple.

sweet! Ok, now all I need to do is find a brake that fits a 1/2" shaft. Is there going to be room for both my brake and an encoder on the back side of the shaft?


Jerry

[keyne]

I am wondering about mounting an encoder and a brake, too. there are encoders which go on the drive shaft..
I guess i will worry about that after finding a suitable servo with a brake.