Servo Motor Brake


Thread Starter

Alvin Goh

Dear List Members,

We are using a servo motor with brake. The specification of the motor says the brake release power supply should be strictly 24VDC or a little
bit higher, but not lower. Has anyone heard of such strict requirement of power supply? Does the brake really need such accurate power supply?
Any suggestion or experience to share?

Alvin Goh

Steve Bailey

My guess would be that the release solenoid needs a minimum voltage to reliably release the brake. You don't say how much is 'a little higher', but you probably have a pretty reasonable range. You certainly should not need a precision supply accurate to millivolts.

Most of my experience has been with 90 VDC brakes rather than 24 volt. These are typically +/- 10% or sometimes +10%, -5%.
I don't know what kind of servo motor /drive system used in your application. I used a lot of BOSCH servo system in motion control. The brake release function was seperately evaluated by controller, and the brake voltage was not critical for application. Maybe your servo system brake release function has to be evaluated thru. special electronic component that I never heard.

Shantanu Apte

I have used such number of servo motors with brake. These brakes are FAIL SAFE in nature . Meaning that movement the supply to the brake is turned on the brake gets released . In case of power failure the brakes get engaged .

Some careful thought must be given to the power supply for such brakes . If the power supply for the brake goes off momentarily (and the servo motor power supply is ON) then motor gives jerk and goes into the following error (If the drive and master controller is programmed such) .

This is the reason to follow the power requirement(at defined voltage levels) of such brakes as specified by the manufacturer , unless you know the exact construction and design aspects of such brakes .

As per my experience +/- 10 % of 24 V DC is still a safe level but it needs to be STABLE !

Shantanu Apte.
Brakes coils are inductive loads and unless the servo brake manufacturer did a poor design and is worried about over heating, 24Volts +/-15% is
typical for a brake power supply. We routinely run as high as 28Volts when using an unregulated "Black Power" power supply without problems on
both domestically produced and off-shore brakes.

Ken Brown
Applied Motion Systems, Inc.

Harlow G. Ahlstrom, Jr.

We have experience of brakes not pulling in due to line voltage drop. Brakes are a high inductive load and thus have high in-rush currents. Our
brakes are 120 Vac. (a little larger than the one your dealing with) If the line drops more than 10% during actuation, the brake will not release fully. Ken's solution is good. It provides the required power, without a lot of cost. You do not need a highly regulated supply, just one with enough power.
Hal Ahlstrom
Standard disclaimer... Views are mine, not those of my employer

David Leese Dresser Valve Div., Hallibur

I've worked on a few custom brake designs with a couple of vendors of servo brakes. It is possible that this vendor has pushed the limit of the holding force for one of their standard brake housings. This could mean a couple of things:

1) They put a 24VDC coil in a brake originally designed for rectified 115VAC (90 or 108 VDC), and there isn't enough physical space to fit a proper 24VDC coil; or

2) To increase the holding force of the brake, the holding spring was increased so much that voltage less than 24VDC can't overcome it.

Either way, it is possible that the 24VDC (+10%/-0) is real, even though it is unusual.

D. Leese

Cameron Anderson

The specs I have seen for one motor manufacturer with a 24VDC brake is: 21.6 to 27.6 VDC . The reason for the tolerance spec is to make sure your not lacking when the brake needs to be energized. Make sure that you are using a seperate supply for the brake.

Typicall brakes on servo motors are holding brakes, not fail safe or stopping brakes. Most holding brakes can withstand occasional use as a stopping brake for main power failures. It is most recommended that you decelerate the motor to 0 RPM before engaging the brake. Repeat use of a servo brake (holding brake) can result in increased wear of the pad and reduce the life.

Cameron Anderson
Power/mation division
Senior Motion Control Specialist

Jeff Richards

Why do you recommend a separate power supply for 24VDC brake? If your power supply is large enough does it matter?

Cameron Anderson

It is typically recomended that you use a seperate supply for the brake because the brake is energized (released) with the DC power. If you are running other devices and you over load your supply, your brake will then denergize (engage) and either slam your load to a stop or break the brake.

Other reason is that in a safety situation, you may remove power from sensors and solenoids. Typically you are doing a Category 1 stop; decel the motor to stop, engage the brake, and kill drive power. If you were sharing the DC supply and had to kill it, your brake will enguage before you have the chance to do the controlled stop.

If you are confident your supply can handle the load and you do not need to meet a saftey need, then you can get away with using 1 supply.

Hope this helps answer your questions.