LDmicro Forum - I need clarity on quadrature encoder

I need clarity on quadrature encoder (by Ziggy)

OK I need clarity on quadrature encoder

Here is the task

A lead screw of 4mm pitch needs to transport a bracket over a distance of 500mm in a time of 7 seconds.
The distance is therefore equivalent to 125 revolutions of the screw.
The distance is traversed in 7 seconds therefore the screw runs at 125 revolutions per 7 seconds or 1071 RPM.

The screw will be driven by a DC motor which has a quadrature encoder on motor shaft of 13 pulses per phase or four times this rate 52 pulses out of the quadrature encoder.

The motor drives the screw through a 5: 1 reduction gearbox which means motor will run at 1071 * 5 =5355 RPM

So in operation the quadrature decoder will have to feed 5355 * 52 pulses / min.

This translates to 4641 pulses per second.

What should the PLC loop time be?

A bit better than 1/4641 seconds? =0.2mS

OR four times quicker? = 0.05mS

Looking forward to Your comments

Wed Oct 24 2018, 21:40:00

(no subject) (by MGP)

4641Hz and you need at least 2 cycles to detect a high and a low signal, that means 9282cycles/sec minimum.
For not missing one puls you have to scan it faster, minimum X3.

As you can see it's not possible with LDmicro.
Why not 1 puls/rev?

Thu Oct 25 2018, 03:09:24

(no subject) (by Ziggy)

These are small brush dc motors with a gearbox.

The encoders are 13 pulses per revolution quadrature outputs.
I could select to use only a single channel and operate at reduced resolution.

This would mean going away from 0.077 mm resolution to 0.31mm resolution.
0.31 is not going to be too bad.

1 Pulse per revolution would be too coarse.

Thu Oct 25 2018, 04:03:08

(no subject) (by Ziggy)

The project has been deferred indefinitely although just today the interest has been revived... i will be seeing the fellow who needed this solution in a few days ( january 15th after Christmas ),

Will know more what to think about this issue.

Fri Jan 3 2020, 06:31:14