Rotation sensor for PLC

alanyap · Dec 15, 2014

Hi all,
Please guide me how to implement this idea onto a PLC programming where i needed to detect a 2 dimension movement of a cutting head to move in (x,y) direction.

Selected PLC : SIEMENS S7-300 2PN/DP

These are my problems:
1) The type of rotation sensor i should use is absolute or incremental encoder?
2) How to Link the Encoder with my PLC? Serial or Parallel data transmission?

Serial Data Transmission:
Do i need any Modbus communication for the linking?
Since it is a serial data transmission, which means i need a channel with a pulse detection/generation.

Parallel Data Transmission:
Is there any conversion needed for the position feedback?
Since it is parallel it means i need to use a range of single bits to determine the position of the rotary encoder.

Please feel free to comment.

Thanks alot!!~

shooter · Dec 15, 2014

an absolute encoder will need lots of inputs or a form of communication
an incremental one needs only 2 inputs (24 Volt!!!)

alanyap · Dec 16, 2014

shooter said:
an absolute encoder will need lots of inputs or a form of communication
an incremental one needs only 2 inputs (24 Volt!!!)

Hi can you explain more about the incremental one or provide me an example model of the rotary encoder??

Thanks..

alanyap · Dec 18, 2014

Usually the incremental encoder i can found is with multiple line of signal
for an example such as this type.
http://www.limasoft.cz/omron/pdf/E6C2-C%20(Q109-E1-04)%20DS.pdf

realolman · Dec 21, 2014

Would you explain the necessary operation of the head?

What kind of resolution does it require?

If it only needed one step, you could use a limit switch in each direction of travel. If it always needed to cut the same circular path, you could physically mount it on an mechanically rotating arm of the required radius... I know that these examples are probably ridiculous, but it is important to know what you need to do with this thing.

An absolute encoder will have the position of the encoder on it's leads all the time... that is a very nice thing, until you need higher resolution. to get eight separate positions you would need three lines. I don't know if anyone makes such a thing or not... perhaps you could make one yourself if that's what you wanted with 3 photocells and an opaque pattern on a transparent background

If you need to measure to a millimeter in a meter full travel, it would require a resolution of 1000 ...you would need 10 lines. one advantage of the absolute is that it doesn't require any timing concerns or program overhead ... just read the lines when you want to know where it's at

the incremental has the advantage of only using a few physical lines , but your software has to catch every pulse and count them to know where the encoder is.

JRW · Dec 21, 2014

Alanyap
I would look at the Siemens SM338 module using an SSI encoder

JRW · Dec 21, 2014

Or
https://mall.industry.siemens.com/mall/en/WW/Catalog/Products/10052790

alanyap · Dec 21, 2014

realolman said:
Would you explain the necessary operation of the head?

What kind of resolution does it require?

If it only needed one step, you could use a limit switch in each direction of travel. If it always needed to cut the same circular path, you could physically mount it on an mechanically rotating arm of the required radius... I know that these examples are probably ridiculous, but it is important to know what you need to do with this thing.

An absolute encoder will have the position of the encoder on it's leads all the time... that is a very nice thing, until you need higher resolution. to get eight separate positions you would need three lines. I don't know if anyone makes such a thing or not... perhaps you could make one yourself if that's what you wanted with 3 photocells and an opaque pattern on a transparent background

If you need to measure to a millimeter in a meter full travel, it would require a resolution of 1000 ...you would need 10 lines. one advantage of the absolute is that it doesn't require any timing concerns or program overhead ... just read the lines when you want to know where it's at

the incremental has the advantage of only using a few physical lines , but your software has to catch every pulse and count them to know where the encoder is.

hi, your explanations is great. Now i get some point on how to use this kind of sensor,
My application is to provide a positional feedback for a cutter head to travel in a x,y direction in about 1m square.
The precision is in +/-1mm

realolman · Dec 21, 2014

hi, your explanations is great. Now i get some point on how to use this kind of sensor,
My application is to provide a positional feedback for a cutter head to travel in a x,y direction in about 1m square.

thank you for your kind words, but after following alanyap's link it appears to me that encoders have evolved much more than I was aware.

alanyap · Dec 21, 2014

realolman said:
thank you for your kind words, but after following alanyap's link it appears to me that encoders have evolved much more than I was aware.

yeah, it really does..
Can't wait to study this kind of sensors...

Rotation sensor for PLC

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