We are having packing machines in which we have mechanical cams & micro switches for contolling the machine operations .
I am planning to replace mechanical cams by absolute encoders . Hence request the forum members to explain how we should connect the absolute encoders output to Micrologix1500 / slc .
Also request the members how should we program it for grey code to absolte value in decimals conversion .

Regards

Prashant

 

normally it requires an specific card for encoders, this kind of cards give to you absolute position and so on, look for this kind of card in rockwell site.

but i think that there isn't this kind of card to micro logix.

 

Visit http://www.electrocam.com

 

This could be a problem. Most encoder outputs are TTL. You could use a conventional IO card to connect the absoulte encoder, but the 1769 IO family has only 24VDC or AC input modules. So unless your absoute encoder has 24v lines instead of TTL you cannot connect it. You could use a 1769-HSC module and an incremental encoder, but this complicates your programming. If you go that route, upgrade to the compact logix processor, it still uses 1769 IO, but gives you a better motion instruction set. Another reason to consider the compact logix is that the Logix1500 may not be fast enough if your rotation speed is high.

If you can connect it, to find the angle of rotation you simply divide 360 by encoder resolution, then multiply by the value input by the encoder. For example if your encoder resolution is 12 bit and it is connected to input card 1, you divide 360/2^12 (4095) and multiply by I:1.0. You may be tempted to use the extra IO points on the card to which the encoder is connected. Dont.

If you do not need blinding speed you can use device-net absolute encoders. AB and Dynapar make these.

 

You can use standard PLC inputs and code to do this but you must be wary of the encoder pulse rate. Typical PLc inputs (Digital) are usually only capable of around 100Hz.

Another option is incremental encoders and feed this it to high speed inputs most micro plc's have a few of these.

depending on number of cams, Omron offer a CAM position module (standalone). It has an absolute encoder connected to it and you program each output for a on/off range in deg (typically 8/16 points). This may also help you.

Any questions, let me know!

[email protected]

 

You can hook an absolute encoder up to a regular digital input module. get yourself a 1769-IB16 (assuming your encoder puts out 24Vdc) and hook each of the wires to one of the input points. You can look at the value of the whole word (ie. I:2.0) to see the value of the position. You will want a natural binary output type. And NO don't use the latch control wire... tie it low.

The specialty encoder cards are for quadrature type encoders which don't report actual coded position but rather just pulses. They are High Speed Counter cards.

Tech_guru

 

for a ttl encoder, use a -ig16.

you still supply the endoder with 24v but it returns 5v, then use logic to convert the grey code to binary (then to some usable dec number if you need it).

 

We have use several absolute encoder with the 1769-IQ16 for slow rotating applications. Automation Direct makes an economical and reliable unit with 24vdc output. It takes 20 rungs of code to convert the gray code back into decimal. If you still need help, feel free to contact me at [email protected]