Closed(ish) loop stepper control

Projects General Guidance
1

I am working on a project to digitise cine film using a Pi 4b to take and process the images and an Arduino Uno to control the film gate motion, transport, take up spool and tension etc. .

The stepper for the gate motion ( NEMA 23 200 steps/rev) needs to move 20 steps per frame, and is fitted with a 200 slot optical disk. 15fps cine is 27,000 frames per 1/2 hour or ~ 1/2 million steps.

stepper-5

So:

1 Is there any value in trying to implement closed loop control using the optical disk?

2 If so, any suggestions on how to go about it -

               optical sensor

               error detection
               
               error correction

3 is this unnecessary/over complicated?

I have done lots of coding in varied environments and plenty of engineering but this is a first into real time control (and 3D printing). So any reflections will be much valued.

2

Error detection:
You should get one pulse from the enocoder for each step.
If you don't , then you missed a step, so add another step.

1 Like
3

Only if the frames are not integral numbers of steps.

The optical sensor has to be insensitive to ambient light. A narrow light barrier should work. In the best case the sensor switches exactly at the right film/frame position. If not you have to spend some more steps until the begin of the frame.

4

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