How to make single turn absolute encoder as multi turn

Hi all.

My question or idea is to use single turn apsolute encoder as multi turn. Whta is that mean?

 If I have encoder with 1000 pulses. For one turn this pseudo code is right.

curr pos = curr pos + (enc position - enc pos old);

enc pos old = enc pos;

// enc pos - reading from encoder

What happens when I want to continue to counting when I move to next turn?

How to handle that?

BR,

Miloš

Hello Miloš;

First, have a look at this article, the basic difference between single-turn and multi-turn absolute encoders is clearly described. 

https://www.motioncontroltips.com/faq-whats-the-difference-between-single-and-multi-turn-rotary-encoder/

You cannot "change" a single-turn absolute encoder into a multi-turn absolute encoder since the construction of the 2 is basically different: single encoder wheel vs multiple geared encoder wheels.

The only way for you to use a single-turn encoder over multiple rotations would be to count the number of revolutions of the encoder (add 1 to your count everytime the encoder resets), multiply this number by the count/revolution parameter of your encoder and add the first read value (captured when your motion begins) to get a full count.

Hope this helps,

Daniel Chartier 

Thanks a lot.

First solution: 

dif = enc pos - enc pos old;

if dif < 500 => dif = dif + 1000;

if dif > 500 => dif = dif - 1000;

cur pos = cur pos + dif;

enc pos old = enc pos;

 Second solution as you proposed:

dif = enc pos - enc pos old;

if dif < 500 => count++;

if dif > 500 => count--;

curr pos = count * 1000 + enc pos;

enc pos old = enc pos;

 1000 - resolution of encoder

 BR,

Miloš

Hi again.

What is your propose to detect new turn of encoder?!

Hello Milosh;

I propose that you make a bench-test with your rotary encoder and find out what happens when it goes from 360 degrees to 1 degree.

The count should reset but how exactly it does that will depend on the encoding numeric scheme that your particular model is built upon. 

Absolute encoders often use gray-scale counting, others use SSI (multi-bit) encoding, some of them work on the "modulo-positioning" principle, others... You could look up the characteristics of your model with the manufacturers' data, or simply setup an experiment as suggested and validate how your PLC reacts to the turnover at 360 degrees (max count of the single-turn encoder). That is the event you must track to add another turn.

Hope this helps,

Daniel Chartier

Thank's a lot for suggestion.

But I would like to know some other solution, in programm code.

Not to use events etc.

So, idea is in main program cycle to detect new turn. In positive or negative direction. 

Sample: Get 900 pulses from encoder, max is 1000. Then, in next cycle I get 40 pulses. It starts to count from begin but I must add pulses maked before. So total pulses will be: 1000+40.

The same thing in negative direction: Get 20 pulses, then continue in negative directin, make turn. In next cycle I get 860 pulses from encoder. So in total it is 860 - 1000 pulses, when make another turn in negative direction I will be (current position - 2*1000)

Thanks a lot in advace to ALL