Worm gear brake selection

[canmecheng]

Hello,

How common is it to damage a worm gear with back driven torque load due to braking from a motor?

I have a slew drive with a 75:2 ratio and a planetary gearbox with an electric motor. The motor has a brake on the back. I need the brake for emergency stops, but when I use the maximum brake torque to calculate the effective torque on the output shaft using the gear ratio & back drive efficiency, I am exceeding the maximum output torque on the slew gear(including service factor). Our motor supplier has already specified their lowest torque brake.

Sorry, I am new to worm gear drives. Is the concern regarding gear damage due to brake torque valid?

 

[tbuelna]

I don't think your 75:2 (37.5:1?) worm gear stage would be efficient enough to back-drive. The motor brake is mostly needed to prevent movement of the slew gear stage under vibration conditions.

While your 37.5:1 worm gear stage is not capable of back-driving, you still need to ensure that the thrust bearing used for the worm is capable of handling the inertia forces created by an E-stop condition.

 

[canmecheng]

Hi tbuelna,

Yes, the worm gear and the gearbox on the motor is back-drivable. We have efficiencies of 65-70% on the worm gear. It has a ratio of 37.5:1 with 2 starts. I am expecting that the thrust bearing will be included in the maximum output torque rating for the slew gear itself, but I will check.

The back driving capability is required in this application so we can manually reposition the driven load during power off failure condition (after manually releasing the brakes).

 

[3DDave]

It'a an energy dissipation and storage problem. When you put on the brake the kinetic energy will be withdrawn from the system under kinetic friction until the motor rotor stops. If that energy withdrawal rate is high enough it will overload the weakest link in the chain. It's possible there will be enough wind-up at the brake to allow the slew to continue to move even after the brake goes static and then the remaining energy will be stored in the deflection of various parts; same as before - if there's too much energy then something will break.

I doubt that it's common, only because no one would want a system that breaks the gearbox when the power is removed.