Servo motor brake

[LARGrizzly]

Hello to all. This is my first post.

I am building a machine tool for a production line we have here in our plant. It is a saw that plunges to cut a slot in a shaft. The saw is mounted vertically on a ballscrew slide and is controlled by a servo motor. The motor has an optional electro-mechanical brake integral to the motor body. The brake is only functional when the servo drive is disabled. The brake is not needed or used when the drive is enabled so my question is do I need the brake? If I just put a line in my PLC program that kept the drive enabled all the time, what would be the drawback? Is it hard on a servo motor to be commanded to hold its position for extended periods of time?

Thanks.

 

[dydt]

hi..
a servo motor has an encoder mounted opposite the shaft..whether its a AC or DC servo it can create thousands of pulses per revolutions...normal pulses is 5000..depending how you commanded the servo where to stop (5000 pulses = 360 degrees ) for certain number of revolutions... i don't see any reason of enabling the brake everytime the motor stops ...this will only create stress on the servo..imagine if the servo enables and the brake is not quick enough to release...i am assumming that we are talking of a mechanical brake...

so my suggestion, don't use the brake..

dydt

 

[jbartos]

Suggestion: Please, would you address any safety issues that may require the mechanical brake to be implemented?

 

Re 'Should I use the Brake' (1st Post)
Having worked in the repair of Servo Drives for a few years.
It is working hardest at trying to maintain zero position.
Thus I suggest using the brake if possible to pro-long the life of the drive.

From
richards31@yahoo.com

 

[LARGrizzly]

Thanks,

That is what I wanted to know "working hardest to hold 0 position."

The drive sets and resets the brake when the drive is enabled and disabled respectively. There is no programming option that allows you to set or reset the brake independent of what the drive is doing. Because of the weight of the motor, saw and associated gearbox, (all mounted on the ballscrew slide) the slide was able to turn the motor when the drive was disabled and the brake was not set.

As an aside, the problem was that the brake was "set" and the slide still moved. Inadequate brake? No. Sent the motor back to Danaher motion for repair (warranty as this was a new motor), the motor (and integral brake) were misaligned during manufacture and it was providing poor braking performance. Post-repair, everyting works great.

 

[jbartos]

Suggestion: The drive may have dry auxiliary contacts that may be used to control the brake.

 

[SERVOCAM]

The brake is there for safety. The problem with ballscrews is that they can backdrive. If you have no brake and the servo is disabled, your load will fall. For safety reasons, keep the brake!

Cameron Anderson
Sales & Applications Engineer

http://www.aerotech.com

"Dedicated to the Science of Motion"

 

[SERVOCAM]

>Is it hard on a servo motor to be commanded to hold its position for extended periods of time?

NO, as long as the servo motor was sized properly, you will not have any problems. I have done a ton of vertical applications. I have done some with acme screw to avoide using a brake and others will ballscrew and always a brake to prevent the load from dropping when the power is off, not to hold the load once in position.

Cameron Anderson
Sales & Applications Engineer

http://www.aerotech.com

"Dedicated to the Science of Motion"

 

[BigSteve]

Exactly! The brake is there for safety only upon power loss. We too have used this many times. Again, there should be no harm to the motor or drive if it is holding 0 position on it's own.