Help with ladder logic determining direction with quadrature
Help with ladder logic determining direction with quadrature
(OP)
Hello all,
I am trying to program a PLC (Idec) to determine direction from two impulse proxs arranged in a quadrature formation. Searching around on the net has shown that a D-latch device can be used to determine direction, but the PLC doesn't have a D-latch device, just contacts, timers, counters and coils. I guess I could program a D-latch with contacts in an "and" formation, but it would be a messy design.
Any help out there?
Thanks
I am trying to program a PLC (Idec) to determine direction from two impulse proxs arranged in a quadrature formation. Searching around on the net has shown that a D-latch device can be used to determine direction, but the PLC doesn't have a D-latch device, just contacts, timers, counters and coils. I guess I could program a D-latch with contacts in an "and" formation, but it would be a messy design.
Any help out there?
Thanks





RE: Help with ladder logic determining direction with quadrature
Question: you may need to look at timing. Can your PLC handle the pulses at highest speed? Also, if your proximity switches are arranged so that they do not overlap, you will have a problem telling direction when movement starts after power on. If that is not a problem, then go ahead.
Gunnar Englund
www.gke.org
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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...
RE: Help with ladder logic determining direction with quadrature
You might want to look at set/reset or latching coils
in programming. The quadrature leading lagging can
determine the direction.
Alternatively, if the quadrature is spaced correctly,
one of the prox is the data input to the D latch, the
other is the clock.
Hope this helps!
Cheers,
Rich S.
RE: Help with ladder logic determining direction with quadrature
The PLC is fast enough to catch each rising edge of a pulse so I can precisely determine speed. I've thought the logic through and here is what the logic should be doing.
Definition
A - First rising edge pulse in the forward direction
B - Second rising edge pulse in the forward direction shifted 90° after the rising edge pulse in A.
If the rising edge of B is after the rising edge of A and before the falling edge of A, that is a "forward".
If the rising edge of A is after the rising edge of B and before the falling edge of B, that is a "reverse".
RE: Help with ladder logic determining direction with quadrature
Gunnar Englund
www.gke.org
--------------------------------------
100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...
RE: Help with ladder logic determining direction with quadrature
I further added ladder logic to look at every rising and falling event on A and B for greater rollback detection.
Thanks for all the help/hints!
Mike
RE: Help with ladder logic determining direction with quadrature
If yes, it must be a bit in the PLC for counting direction indication.
RE: Help with ladder logic determining direction with quadrature
RE: Help with ladder logic determining direction with quadrature
My application had a 10'circumference drum with 6 steel plate prox targets. These were arranged to provide equal on/off time to the prox switches. (22.5 degrees on, 22.5 off) The sensors were offset about 11 degrees, or 1/2 the pulse duration to set up the directional detection. Since the drum max speed was only just over 3 linear FPS, scans consideration was not a problem as the program scan maxed at 30 ms and the pulse duration was 200 plus ms max.
If you would like a copy of the logic I will be glad to forward. Notify me at bgoodwin@pinnoakresources.com. I will send an RSLogix file which contains it.
RE: Help with ladder logic determining direction with quadrature
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RE: Help with ladder logic determining direction with quadrature