coupler
coupler
(OP)
Need some help with failing coupler. We have rigid coupler between ball-screw and a stepper motor. The coupler failed four times so far. Two times the clamping screw got loose and the shaft came out of coupler but two times coupler was sheared.
This is a custom coupler made of Aluminum and I do not have any spec for it. I do not know what max allowable torque is.
I created model and run FEA with max torque stepper can develop. The maximum stress was 62 MPa that is almost 50% of the shear strength for the weakest Aluminum alloy (in my model I assumed 2104 Al). I need to add that the stepper needs to deliver only 25% of its max torque during this application.
We are doing a lot of short moves less than 1 mm per 0.15 s. This is stop and go application 24/7.
Both sheared failures happened after few thousands moves.
Is it fatigue? Appreciate any comments/suggestions.
Thanks
This is a custom coupler made of Aluminum and I do not have any spec for it. I do not know what max allowable torque is.
I created model and run FEA with max torque stepper can develop. The maximum stress was 62 MPa that is almost 50% of the shear strength for the weakest Aluminum alloy (in my model I assumed 2104 Al). I need to add that the stepper needs to deliver only 25% of its max torque during this application.
We are doing a lot of short moves less than 1 mm per 0.15 s. This is stop and go application 24/7.
Both sheared failures happened after few thousands moves.
Is it fatigue? Appreciate any comments/suggestions.
Thanks





RE: coupler
Keith Cress
Flamin Systems, Inc.- http://www.flaminsystems.com
RE: coupler
Thanks
RE: coupler
You should be using a flex coupling. I like the Servo Class couplings made by Zero-Max.
RE: coupler
Ordinarily, I like the Heli-Cal spiral beam couplers, but they produce some axial force when loaded... so your stepper would kill either its own bearings or the thrust bearing of whatever you're driving. Have the t-shirt.
If you can stand the positioning error, use a rotationally soft coupling, like the ancient Acushnet K-Coupling.
Mike Halloran
Pembroke Pines, FL, USA
RE: coupler
What type of load?
Keith Cress
Flamin Systems, Inc.- http://www.flaminsystems.com
RE: coupler
itsmoked, the load is 6 lb , the motor size 42 (diameter) has holding torque 140 mNm
RE: coupler
Mike Halloran
Pembroke Pines, FL, USA
RE: coupler
SNAP!
Too bad you can't use a servo motor as this would probably reduce all aspects of the jerking.
Keith Cress
Flamin Systems, Inc.- http://www.flaminsystems.com