encoders on motors and conveyors!!!!!!!!!!

[raybird]

I am in the industrial field....I have a good knowledge of plcs and can program the I/Os and know the ladder diagrams of allen bradley. I was asking a question of how does the encoders on the conveyors work? I see the plc has an HSC card...and when i go online im not sure how to go in and see the logic for the encoder! I know an encoder counts pulses....but how does it work in the plc? How does it control position of other things? like timing....retarding or advancing a conveyor? or a pin positioner? are there any good books that explain and show diagrams? please help!

Ray

 

[Skogsgurra]

I did a presentation for SKF people once upon a time. Some basic facts about encoders are given in this pdf (free to download):

http://www.gke.org/presentationer/SKF Sensor Bearing 1a.pdf

There is also a glossary that describes some fundamental components and techniques at:

http://www.gke.org/rapporter/Glossary for the encoder world.pdf

(also public)



Gunnar Englund

http://www.gke.org

 

[Barry1961]

In most encoder applications the encoder pulses are scaled to some user unit. An example would be a 1000 ppr encoder with 3" wheel riding on a belt conveyor.

Each rev of the wheel is 3" x pi = 9.4247"
One pulse is 9.4247"/1000ppr = .00942 inch per pulse
One inch is 1/.00942 = 106.157 pulse per inch

So if you want the conveyor to stop after moving 8.50" you would have the operator enter 8.50 with HMI then you would multiply it by 106.157 = 902.33. Once you have the target, 902, you would then compare it to the register that has the encoder counts.

There are many ways to do the logic with the encoder. Two common ways are, reset count to zero each time there is a move(incremental move), always keep count from a home point(absolute move).

You could load the target then subtract some amount for a slow down point. You could have a math formula so the move slows down in porportion to the distance away from target(algorithm).

There are too many ways to do the program to list. But I would advise you to keep a common user unit across all machines. Each machine will probably have to have a different scale factor to convert pulses to "inches".

Barry1961

 

[blacksea]

The encoder's count is PLC unit. But I hope that HSC definition of used PLC has opportunity to count of encoder pulses (two channels A and B) with x1, x2 or x4 evaluation also.