Recommended way to EStop (Disconnect?) Servo Motor


Thread Starter

Peter Elliot

I have a servo motor driven actuator, mounted on a robot arm, which I currently EStop using a dual contactors between the servo drive amplifier and the actuator (interlocked by a safety relay so drive is already disabled at time contactors break).

This solution is a little costly/bulky and I would like to know what other people to in similar situations. I was wondering if a single contactor along with the internal drive disable would meet global safety applications (for use under automatic control in a robot cell).

NB: The product is being designed for a global market place.

Thanks in advance,
For the global marketplace (and domestic as well) you must assure that a failure of a single component will not permit an unsafe condition to exist. The failure of the component must be detected and a second machine cycle prevented, videlicet, you need two contactors and those contactors must be monitored contactors with guided contacts and they are interconnected to a safety relay. It is costly and bulky, but that is how it is.

shantanu apte

In the case of Emergency Stop Situation, following points need to be considered

1) The reflected moment of inertia on the motor shaft.
2) The load, coupled to motor: is it moving against gravity?
3) The Kind of motor. DC Servo / AC Servo.
4) The worst case speed and torque conditions.

In case of nominal load moving along linear axes, parallel to the horizontal plane, the method suggested by you is okay.

But if load is heavy, speed is higher and load movement is along verticle axes, you will need to clamp down the +/- Ananlog voltage command to drive faster (Experiments have no substitues). Command drive in Disable mode . (Apply fail safe brake , if need be) . Disconnect the POWER SUPPLY to drive .

It is always better to keep a tap on FOLLOWING ERROR by writing a loop with high scanning rate to anticipate trouble sooner.

In case of further doubts please contact me.

Best Regards
Shantanu Apte

Thompson, Tommy

On many of our servo applications we remove the high voltage feeding the servo drive during an estop condition by opening a contactor. When
available, we also break the hardwired enable signal to the drive. We leave the control voltage connected to the servo drive so it can still monitor feedback signals from the motor and communicate with the control system.

Cameron Anderson

Cost should never be an issue when your talking about machine safety or people safety. For your application, it is typical to do a Category 2 stop. You will want a safety controller with a time delayed module. What this will allow you to do and still meet safety guidelines is do a controlled stop before killing drive power. When the e-stop is hit, a set of contacts will open or close immediately. This will be your signal to your servo drive to stop. Not disable the drive, but stop the drive in a controlled deceleration. Then after a set time, the next set of contacts will open and kill AC power to the drive.

Check out "": for all your safety information. Banner will have all the guidelines and safety equipment you will need.

Cameron Anderson
Advanced Products Specialist - Motion Control
Power/mation - St. Paul, MN