Using OMROM Incremental Rotary Encoder

[Blacknight_81]

Hi,

I am working on a project to upgrade a control cabinet for assembly machine. We are thinking also to replace some CAM_SWITCHES with OMRON Incremental Rotary Encoder E6C2-6. I just to know if someone knows how to program this encoder with OMRON CJ1 modular plc?

Thanks

 

[LadderLogic]

Blacknight:

Are you sure you want an incremental encoder for your application? You will need a special high-speed counter card in your PLC. You will have to provide a way to safely home your machine upon power-up, since an incremental encoder does not initally know where it is.

If this is a cam switch type of application, my preference would be to use an absolute encoder; it can be connected to a regular input module and it always knows its true position - power-up or not. A lot of advantages for a bit of price (a decent one can pe bought for about $250)

 

[BobB]

One thing you can do to remember where you are is use data memories for counting. They a memory retentive.
Yes, you will need a high speed counter card suitable for incremental encoders.
Yes, absolute is much much better.
Is the positioning at high speed and high pulse rate?
If not and a slight delay time will not worry you I would suggest an absolute encoder on Device Net. Pepperl & Fuchs make a good on that is quite well priced compared to AB, Sick, Danaher etc.
beerchug

 

[ArikBY]

Hi
I almost sure CJ1 have High Speed Counter build in.
like all Omron PLCs which I know.
I used it some times but it depend on your application.
you need to use CTBL command.
You dont have memory retentive.
Pay attention what you doing when the power shut off and what happen
when it go on.in that case you need to go home position.
Is it possibale?.
If you dont create any damage when you go home position.

You can do it by Useing CTBL command in Range mode it more safe.

For assembly machine absolute encoder is more common.
My personal preference go with absolute encoder.
You can get absolute encoder unit or you can use input unit and write
the ledder by your self.it work in grey code.
Omron encoders have 2 types for absolute encoders 8 bit and 12 bit
if you need higher resolution then go to incremental encoder.
If you need example of program let me know I will send you.

 

[Blacknight_81]

Yes please send me some example program for absolute encoder, as i was unaware of it before! and please explain in simple words that what is difference in them? i just want to get position info of the assembly track and according to that position info i`ll plc to force some other work such us glass loading etc.
And i think absolute encoder will use about 8-10 inputs of my plc, which could cost alot in case of CJ1 plc, so isnt it better to use just 3 inputs and one could get resolution of 360 per revolution i.e 1 position for each degree? and could get to zero position from Z-output of encoder?

thanx

 

[BobB]

If you are looking for fairly accurate position, use an absolute encoder, unless you can home the machine regularly to reset your count from an incremental encoder. If you follow this forum, you will find that Paul Lucas homes the cranes, regularly at his place of employment, to reset the count. THIS IS ONLY CRANES, NOT A MACHINE THAT WILL BE DOING MANY MORE OPERATIONS PER DAY.
Don't be lousy. If you are using the CJ1, the cost of I/O cards is chicken feed, particularly the 64 bit input and output cards I normally use. 32 inputs is a small number with this baby. I would use 8 inputs up very quickly. Can use up to 192 inputs and 192 outputs to control a municipal swimming pool, plus analogues.
For what this PLC can do, the cost really is low.
beerchug

 

[Blacknight_81]

So could any one please explain how to use absolute encoder?? and how one should get to zero position?

 

[Peter Nachtwey]

There are two ways to zero the absolute encoder. The simple an obvious way is to turn the encoder until it provides the correct reading before fixing it to the shaft. The second way is to have a smart encoder where you give it a pulse and it resets the position to zero and stores an offset into its internal flash.

Oh, there is a third. Some motion controllers like ours have the ability to store the encoder offset in the controller flash so a cheaper encoder can be electronically zeroed.


Running parallel lines for any distance is asking for trouble. You would also need to latch all those lines at the same time. There for
these lines should go into the same card.


I would check for a SSI (synchronous serial inteface) card for the Omron. SSI allows the absolute encoder to send 24 bits of absolute position data over two wires at about 400K bps.

Check out Stegmann Absolute Encoders


Blacknight, you don't really need to zero the encoder. You just need to keep track of the encoder direction and offset. We do something like this when we read an encoder.

Modified counts = ( actual counts XOR EncDir ) + EncOff.

The EncDir is normall 0 and has no effect. If the encoder is counting down when we want it to count up we set the EncDir to -1 or 0FFFFFFFFH. This toggle every bit so the result will count in the desired direction. We jog the machine to the desired zero point and save the current negative counts in the EncOff. This way the modified counts will read zero. I would rather zero the encoder with an offset the fuss with moving it and worrying it I got it attached tightly and in alignment.

 

[Antipathy]

Blacknight

I don't know if you are aware of it, but Omron do dedicated cam positioner units which are excellent for replacing existing cam systems.

I've had cause to use a couple of these and I found them very easy to install and use. In fact, if you need to be able to make regular angle adjustments but don't have a HMI they are perfect!

If you are interseted, info can be found here...

http://www.europe.omron.com/UK_en/c...atalog/Counters/Cam_Positioners/auto_H8PR.asp

Regards

Anthony

 

[ArikBY]

Blacknight_81


I will send you ledder diagram with absolute encoder next time I will be in my office. I am out of the office in the next few days.
Arik

 

[Sleepy Wombat]

Blacknight_81

See attached file for an example of connecting up a Abs Enc to a CPM1 PLC. It would be the same principal for the CJ PLC. This inof can be found in the Absolute Encoder Data Sheets.

BTW, the CJ1M PLC comes with built I/O namely 10 digital inputs and 6 digital outputs. They can be configured as High Speed Counters, Quick Response, Interupt Inputs. I will also attach the specs..

In the program for the CJ PLC after doing the ABS Grey Scale to Dec number converion logic I would use the BCMP or the BCMP2 funciton, each giving a 16pt and 256pt range each respectively. Don't include the BCD(24) function though and substitue the SUB(31) instruction for the -(410) instruciton.

Hope it helps.

 

[Sleepy Wombat]

CJ1M CPU22 / CPU23 Inpuilt I/O Specs.....

 

[Blacknight_81]

thank you all for ur help, but well i dont know why my boss wants me to use incremental encoder only well so i have to do so. still i dont know what is the diff in between. As i have discussed with him about zero position. We have Z-output from encoder which tells that. and whenever the machine is started we could have a one full circle to determine its origin position and thats it?