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Emergency stop torque vs peak torque

Emergency stop torque vs peak torque

(OP)
When calculating shear Stress from the output of the shaft, should I use the emergency stop torque or peak torque (max acceleration torque)? Hopefully, it would be correct if I were to use peak torque in my calculation. That way I wouldn’t have to increase the size of our spindle, which is mounted to the output of the gearbox….

They state on their website regarding emergency stop torque: “ This torque is actually the design torque of the gearbox without additional safeties. It is recommended not to calculate with this value, but it does give an insight into the safeties applied.”

https://www.apexdyna.nl/en/products/paii-series

RE: Emergency stop torque vs peak torque

Not sure what you are using for your shaft size calculation, most shaft equations are based on fatigue life. If you have a couple of emergency stops in the lifetime of the spindle, it probably won't lead to shaft failure. You could look at how high of a stress level you get with the emergency stopping torque to see that you don't exceed yield strength.

RE: Emergency stop torque vs peak torque

(OP)
I did a hand calc and I came up with a safety factor of 1.4 against the emergency stop torque. Apex gear states: emergency stop torque is 3x the nominal torque. And peak torque is 60% of the emergency torque.

RE: Emergency stop torque vs peak torque

(OP)
Max shear stress is what I used for the calc.

RE: Emergency stop torque vs peak torque

I'd be thinking about yield strength in there somewhere.

RE: Emergency stop torque vs peak torque

Hi aldumoul

I would use the peak torque if it was me.

“Do not worry about your problems with mathematics, I assure you mine are far greater.” Albert Einstein

RE: Emergency stop torque vs peak torque

I guess it depends on how the emergency stop torque is applied, eg brake,

RE: Emergency stop torque vs peak torque

Depending on the driver, the E-stop is either a mechanical means (e.g., brake) or electrical (e.g., reverse power). If it is the brake, then chances are good that the brake does not apply the peak torque capability of the driver - so use the peak torque. For an electrically-powered driver, the most common method is to apply maximum peak current in the reverse direction - which is again the peak torque of the driver. Use this data for your fatigue analysis.

One other thing - for electrically-powered drivers, you not only need to know the motor's peak torque/current capability, but also that of the supply. It is possible the power electronics' "current limit" is lower than the capability of the rotating machine. In that case, using the drive's current to estimate torque is realistic, while using the machine's torque rating is conservative. I would always use the machine's rating, because who knows what the drive may be reconfigured to?

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