extruder vfd question
extruder vfd question
(OP)
We purchased a used extrusion machine a year or so ago that extrudes plastic tubing and at that time we found it had a bad variable speed drive. We redesigned the control system somewhat and added a new plc ( which the machine didn't have) and a new Allen-Bradley vfd( not sure of exact model). This machine has a 25 hp motor with encoder feedback. The speed is controlled via potentiometers on the operator panel. The drive was tuned and it has been running great for a year or so. However, now the operators are complaining that the speed fluctuates via the rpm gauge on the operator panel which makes the screw in the machine pulsate. There could be mechanical issues at work here however, I am not that familiar with vfd's so I am wondering if this could be a tuning issue for the drive or something? We actually have one other simliar extrusion line in the facility that has the same control scheme ( vfd and potentiometer) but have never really had an issue with fluctuating speed with it. That one we purchased new. Any thoughts if this could be a motor/vfd issue.





RE: extruder vfd question
2. If it is a digital drive you can go to the display and monitor speed error.
3. In addition I would monitor the motor current to see if the speed is fluctuating as a result of the load rapily changing.
4. Or simply a bad potentiometer/dirty spot ect..
5.. How much is the speed fluctuating? Is the meter just driven off an analog output of the drive or directly from the encoder?
RE: extruder vfd question
RE: extruder vfd question
respectfully
RE: extruder vfd question
RE: extruder vfd question
----------------------------------
Sometimes I only open my mouth to swap feet...
RE: extruder vfd question
If the speed readout is from the analog output of the drive, the problem can't very well be slipping belts or such, can it?
If the speed reference is changing, then you don't really have a drive problem. The problem is in your speed signal. The pot has already been changed so check your wiring and shielding. Remember, a noisy speed reference or a vibrating potentiometer can produce irratic speed input signals.
RE: extruder vfd question
RE: extruder vfd question
RE: extruder vfd question