Mitsubishi FXon

[Guest Guest_Neil]

I have a problem with a piece of plant that has a conveyor controlled by a mitsubishi fxon 40mr es plc. There is a drive unit which is inverter controlled for speed and braking with it feeding approimately 600mm of film though the conveyor before stopping for a set period then re-feeding again in a constant loop. The motor has a rear mounted encoder using the constant pulsed output to feed plc on input X0. This is then used to increment counter 235. When the target is reached the conveyor should stop, and it does but there can be variations of at most 50mm but this is too much of a difference for production to run smoothly. It has to be control but cannot identify where. Is there any plc configurations that can be checked. Are the FXo units susceptable to emc causing rogue pulses? The encoder is fed from the plcs own 24Vdc power supply terminals, could this affect the unit as they seem to float ungrounded? Please help if you can. Any questions neil.robson@btconnect.com

[Guest Guest]

What is the frequency of the pulses? How do you control the inverter? Simple Start/Stop or analog from PLC? When you overshoot your target length, is it counted by C235? What is you maximum amount of pulses read? Besides I can tell you that yes the encoder signal can be messed up by noises especially when you use the high speed input only. Why do you not use the quadrature input C251 (max 2KHz)? This is a simple loop but it has to be setup carefully. You should be able to have the resolution equal to 1 pulse. So it tel us a bit more about load, accel ramp, decel time and precision needed.

[Guest Albert fanakapan]

If it did work correctly but now doesnt, it probably isnt the program (unless you can alter variables by an hmi) Also the problem with monitoring high speed counters (mitsi) is that they DO continue counting past the set point until they are reset. The counter done bit accuates at the set point, but these counters continue counting if pulses are still being recieved. The counter done bit will be the signal to stop the drive, check the drive set-up and any mechanical features that may be worn or have 'play' in them