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Following Error


amitkumar
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we use Turbo Pmac as an integrator of two motors (with current loop amplifiers) into axis 1 and 2 providing a common speed loop which sums the speed of the two motors averages them and which acts as velocity feedback to a dummy axis 5th.

The 5th axis is given an analog input which comes from an external position loop and made to position follow it.

The speed of the motors change with the following error of the 5th axis.At the maximum analog input the following error is 190 the speeds of the motor are what is the speed required for the system. But if The Following error increases to 215 or 220 due to some reasons the current loop amplifiers go into overspeed.

Is there a way to limit the following error value to 190 ?

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In a closed loop servo system, limiting the following error is directly tied to the following:

 

- Motor Phasing:

If you are performing commutation in PMAC, you want to make sure that you have performed the best phasing search method.

 

- Tuning (both current loop and position loop):

Tighten up your tuning.

 

- Mechanics:

Make sure the mechanics are rigid.

 

- Size of Motor and/or Drive:

Make sure you are not exceeding the motor or drive capabilities.

 

I don't fully understand your implementation, but a couple of other things you might want to look at:

 

-Averaging "desired-commanded" velocities instead of "actual". This eliminates calculation quantization noise.

 

-Filtering (tracking or low pass) the analog input.

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Thank you for the reply.

In a closed loop servo system, limiting the following error is directly tied to the following:

 

- Motor Phasing:

If you are performing commutation in PMAC, you want to make sure that you have performed the best phasing search method.

 

We are not commutating with PMAC. The drives are doing it.

- Tuning (both current loop and position loop):

Tighten up your tuning.

Yes we want to tighten the tuning

 

- Mechanics:

Make sure the mechanics are rigid.

Mechanics are more or less rigid.

 

- Size of Motor and/or Drive:

Make sure you are not exceeding the motor or drive capabilities.

The drive speeds are limited to a value much higher than the one set by PLC.Yet the amplifiers go into overspeed

I don't fully understand your implementation, but a couple of other things you might want to look at:

 

-Averaging "desired-commanded" velocities instead of "actual". This eliminates calculation quantization noise.

How do we do it ?

-Filtering (tracking or low pass) the analog input.

How do we do it ?

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Thank you for the reply.

Unless I am misunderstanding your question, could you not simply set Ixx20 (for jog moves) or Ixx16 (for programmed moves) to limit the speed of the motor?

 

Ixx20 values are 0

 

Ixx16 values are 32

 

We use two motors in one axis Say motor 1 and motor 2 and a dummy axis to integrate the two say motor 5. we close the 5th axis loop by giving #5j/ and run motor 1 and 2 in open loop #1o0 #2o0. A plc is wriiten which feed the command output of fifth into motor 1 and 2 output.

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Thank you for the reply.

Unless I am misunderstanding your question, could you not simply set Ixx20 (for jog moves) or Ixx16 (for programmed moves) to limit the speed of the motor?

 

Ixx20 values are 0

 

Ixx16 values are 32

 

We use two motors in one axis Say motor 1 and motor 2 and a dummy axis to integrate the two say motor 5. we close the 5th axis loop by giving #5j/ and run motor 1 and 2 in open loop #1o0 #2o0. A plc is wriiten which feed the command output of fifth into motor 1 and 2 output.

 

Did you try setting Ixx67 of your dummy axis to 190*16? This should limit the servo output command of the virtual motor.

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