Encoder for data count

[roxtech]

Hi Dears,
I am stuck at one point. I am useing incremantal encoder 600 p/r. with mitsubishi PLC FX2n. I am useing x0 for A channel and use high speed counter C235. Now problem is when we start motor in forword direction it count pulses incremantally then i want to reverse motor and deincrement count pulses in forword direction, but how? encoder always give me increment pulses.
My target to set motor on specific length for example 950000 pulses.
Best Regards,

 

[Eric Nelson]

I am useing x0 for A channel

That's the problem. The PLC cannot know which way the encoder is rotating when there is only 1 pulse. You need 2 pulses in quadrature if you want to sense direction.

http://en.wikipedia.org/wiki/Rotary_encoder#Incremental_rotary_encoder



-Eric

 

[iant]

Just a thought Eric,
If you have the reverse Status in the PLC cant you cause the HSC to use the pulse as a Decrement instead

(Of course you are right with the Quadrature A-B pulse)

 

[Ajinkya24]

Dear Zahid,

To deincrement the pulses in reverse direction of motor, you need to use it in quadrature mode. I think your's is a cut-to-length application. Use your A channel to read the number of pulses and channel B to sense the direction of rotation, needless to say that you configure your controller for quadrature mode.

 

[Eric Nelson]

Just a thought Eric,
If you have the reverse Status in the PLC cant you cause the HSC to use the pulse as a Decrement instead

Good point, Ian. He could tell the counter to decrement by turning on bit M8235 while reversing. I don't know his specific application, so this may be good enough...



-Eric

 

[Peter Nachtwey]

NO! Do it right. Use two phases

Good point, Ian. He could tell the counter to decrement by turning on bit M8235 while reversing. I don't know his specific application, so this may be good enough...



-Eric

Often the encoder will stop where it rocks back and forth between two counts. A PLC won't know about this.

 

[iant]

Thats ok Peter - it will only dammage the machine and send it to oblivion - But it will work - ONCE