Moment of Shaft Direction Change
Moment of Shaft Direction Change
(OP)
I have a machine that has a motor on one end. There is a magnetic coupler between it and an inertia wheel. The inertia wheel is connected to a brake using a ling flexable shaft. The machine spins the inertia wheel to a fixed speed, then the brake is applied. The motor decouples and only the inertia from wheel flexes the shaft. I need to know the exact point that the shaft will change directions and start to unwind. We currently use an encoder for this, but they do not last long because we are constantly slamming the shaft to a stop. This happens in both directions. Does any one have any ideas of another way to accomplish this?





RE: Moment of Shaft Direction Change
RE: Moment of Shaft Direction Change
I recognize that flexible shafts wind up/down but if you are braking the inertia wheel to a stop the shaft would start unwinding once the wheel had stopped? Or just before the wheel has stopped and some balance has been reached where the shaft spring constant equals the inertial wheel torque?
So you want to know when the still rotating system reaches some specific equalization? If this is the case I'm even more confused because why then would you be slamming the system to a stop, you'd rather need a slower smooth reduction so you could find this moving equilibrium point.
Keith Cress
kcress - http://www.flaminsystems.com
RE: Moment of Shaft Direction Change
Thanks for the interest.
RE: Moment of Shaft Direction Change
Or... Automotive Antilock Braking Systems (ABS) need to monitor the realtime rotation (or not) of the car's wheels and they're subject to extreme abuse and survive quite nicely. The ones I've seen are typically a tooth and magnetic sensor system (but there may be other technologies). Your application is very similar to ABS in some ways.
RE: Moment of Shaft Direction Change
RE: Moment of Shaft Direction Change
I'm in with the same solution. Dirt, grit, vibration, ambient temps, all handled with modern automobile wheel sensor tech.
Keith Cress
kcress - http://www.flaminsystems.com
RE: Moment of Shaft Direction Change
http://www.rls.si/default.asp?prod=rm22
RE: Moment of Shaft Direction Change
Placement must be done such that the switches output a quadrature signal (90degs apart).
There's all varieties of COTS stuff that'll take that input and give you a control signal on a direction change.
ed
RE: Moment of Shaft Direction Change
just set the timing down real low.
Ed
RE: Moment of Shaft Direction Change
Only one set of I/Q signals per rotation (off the keyway) isn't likely going to detect rotation reversal within 20ms. I suspect the system will need more pulses per revolution to give the temporal resolution.
RE: Moment of Shaft Direction Change
I was thinking zero speed switches but I doubt that the ones that I am familiar with would be fast enough.
Bill
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Jimmy Carter
RE: Moment of Shaft Direction Change
Ed