Rotary table indexer - Page 67

1. ## Re: Rotary table indexer

I've been using this excellent design from one of the supplied kits for a couple of years now with no problems. But just got a question stimulated by discussion over on the ME forum. When dividing by a number "N" which isn't an integer divisor of the number of steps per rev, how does the controller deal with the resulting error? Does it use something like the Bresenham algorithm to minimise the error.

Thanks, John.

2. ## Re: Rotary table indexer

Originally Posted by JohnHaine
I've been using this excellent design from one of the supplied kits for a couple of years now with no problems. But just got a question stimulated by discussion over on the ME forum. When dividing by a number "N" which isn't an integer divisor of the number of steps per rev, how does the controller deal with the resulting error? Does it use something like the Bresenham algorithm to minimise the error.

Thanks, John.

Hi John,
that's exactly how it works.

So basically internally it multiplies the number of divisions by the actual division its on then divides the result by the number of steps for a full circle - this gives it the nearest number of steps it needs to get to that division (doing the multiply first prevents loss of resolution although it means it needs 32 bit maths which is why the max steps per rev is 16 bit).
Internally it knows exactly how many steps it's currently taken so simply adds (or subtracts) that from the answer above to get the number of steps to take.

This means there isn't a constant number of steps since it may need to take an extra step (or lose one to be accurate).

In practice the accuracy of the maths is half the single step resolution, so a 400 step driver on a 90:1 worm gives you 0.01 degrees per step so the accuracy is 0.005 degrees. (Mechanical accuracy not withstanding).

Cheers,
Steve.

3. ## Re: Rotary table indexer

Brilliant, many thanks Steve.

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