Alignment jitter suppression

[trueninjalo]

Ok so I now have a new issue. I have about 12 feet from where the web sensor is to where the knife is. I thought I would use Time over distance instead of distance over time to set my cycle time to move the knife when needed. well if the rotation speed goes to zero then the PLC faults out because we all know (or should know) that you can't divide by zero. so how can i set up a delay system that is dependent on the belt speed?
I have YPM from the motor. I calculate to inches per second and then try to calculate seconds per inch and use this solution to feed the timer preset dint. Again, when the drive stops the time goes to 0 and the PLC faults. I can add a compare speed>0 to enable the calculation but i am wondering if you can convert it another way.

for example : (10/5)=(10*.2)=2
I cant figure out how to use this or some other method to get the desired delay from when the sensor sees the shift to when the knives react.
Thanks in advance.

 

[JRoss]

If you're happy with the calculation otherwise, use the comparator. You won't need to move the knife if the material speed is zero.

 

[Geoff White]

Use a shift register with the knife setpoint being loaded into it. Move she shift register each time the belt moves the shift register resolution. Read the knife setpoint at the other end of the shift register that corresponds to the knife offset from the sensor.