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Parker 590 speed error

Dear All, 

I have Parker 590P it working with motor very well when working with normal speed as speed demand 8 % and FBK was 8 % and error 0.01 to 0.03 

but when speed demand 0.4% speed error increase to playing from 0.2 to - 0.1 that affect on machine accuracy and motor sound 

any one have an idea why when working on low speed error increase ????????

  • Good morning.  This is actually not that uncommon.  At low speed, it is more difficult to control speed accurately.  There are two reasons for this:

    • Your rate of speed measured in encoder counts per second is very low.  The data from the encoder is therefore very coarse at low speed and the control suffers as a result.
    • Many machines require less torque at low speed.  If the torque requirement is low enough, the drive may slip into the "discontinuous region", where the portions of the waveform cut up by the SCRs no longer overlap.  Current fluctuations in the discontinuous region are naturally higher and there is not much that can be done about it.

    So, what options do you have?  I think the simplest one is to get a higher resolution encoder.  If you are currently using a 1,000 line encoder, try using a 5,000 line encoder.  You will need to alter the encoder resolution parameter, but the change is quite simple.

    Overall, your performance requirements are pushing the boundaries of what a brushed DC motor and drive can be expected to do.  If you never need to go above 10% speed setpoint, consider getting a 10:1 gearbox so that you can run the motor faster.

    If you need to run at high speed and low speed and maintain accurate speed at both ranges, maybe a flywheel will help.  This is not something on which I can provide lots of advice, but perhaps a local machine builder could.

    The only other option I can conceive to handle very high and very low speeds while keeping very close to the speed setpoint is to use a servo motor with a high resolution encoder.  Parker makes servo motors up to about 21 kW.

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