Multi-turn encoder alternative?

[mommus]

We have stepper motor driving a lead screw that requires resilience to power failure and the ability to re-start and still retain its position data.

I've been looking at multi-turn encoders but they're big and expensive.

Is there an alternative way to track the position of a shaft over a max of 10 rotations? I had thought about using a standard 360 degree encoder with a reduction gear to prevent it from turning more than 360 degrees... but we would then need a ROM/capacitor setup of some kind to store the position data until power up

Anyone done anything similar?

 

[cswilson]

I suspect that a commercially available multi-turn encoder, with absolute position retained both within a single revolution and over multiple revolutions, will be your best option.

Newer encoders can maintain turns count without mechanical gearing and without backup supply. It's hard to match that when considering total system and development cost.

I suppose you could roll your own system with two single-turn absolute encoders, one directly on the motor, the other off a gear down of at least 10:1. But by the time you engineer this robustly, I suspect that you would have found a multi-turn encoder a better solution.

Curt Wilson
Omron Delta Tau