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Integrated Position Error Output ??


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I am setting two motors one feedback on Power PMAC

because get more motor power.

(Direct PWM and use Gantry Mode Motor[x].ServoCtrl = 8)


however , happen to against force between two motors.

(different direction integrated position error)

after all, happen to I2T amp fault.


Can I use to access integrated position error register on Power PMAC?



I used to access integrated position error register on Turbo PMAC.


Have any advice and ideals?

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I'm sorry, but I am not understanding your configuration. If there is only one feedback for the two motors in a gantry system, both motors will have the same command and feedback, and therefore the same servo command output going into the I2T check. Of course, if there is separate feedback for each motor, the servo output could be different if there is different load on the two motors.


You can read Motor[x].Servo.Integrator at any time, but the servo algorithm will overwrite any value you write to it from outside. Remember that this is the position error integrator, not the command output integrator. The command output integrator value is in Motor[x].I2tSum. This is compared to I2tTrip for the fault calculations.


If your I2T limits are set well, then a fault is a real problem that must be dealt with by figuring out how to reduce the demand on the motor.

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Machine is Gantry system.


Y1 Axis have two motor (Y1-1,Y1-2)

and Y2 Axis have two motor (Y2-1,Y2-2)

Y1 motors connect each PWM drive. (2 pwm drive)

Y2 motors connect each PWM drive. (2 pwm drive)


And Y1-1,Y1-2 motors feedback laser enc1

Y2-1,Y2-2 motors feedback laser enc2


happen to against force between Y1-1,Y1-2

and happen to against force between Y2-1,Y2-2


Stop status increase servo out value

After all, happen to I2T Ampfault.


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Sounds like your gantry system may not be mechanically aligned.


The cross-coupled algorithm will work real hard to make both motor positions the same. If your bearing rails are not straight, and 1 motor travels farther than the other over the Y-axis travel distance, the position difference will increase causing one motor to work against the mechanical system. Depending on the stiffness of the structure and the position difference between the two motors, the motor may not have enough torque to align to the other motor, causing I2T faults.


I speak from experience here; in our gantry one rail had a slight curve to it (our mechanical engineer determined it had a 3 mile radius!). This curve meant one motor basically traveled farther than the other; when the position difference between the motors was large enough...POW!...I2T faults. If the leader motor faults first, this can cause the follower motor to basically run away.


One easy way to test your system: kill all motors then pull your Y-axis gantry against the hard-stop, 'homez' the Y-axis motors, then push the gantry to the opposite hard-stop; note the positions of each motor, they should be basically the same (for us, less than 0.1mm difference). If the positions are different, then there may be a problem with the gantry structure or with the feedback sensors; either the encoder tape or the sensors themselves.


Good luck, this can be tricky to fix. You may need to enlist the help of some good mechanical folks to get your system setup properly.




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Thank you for the diagram. That helps a lot. If I understand you now, the problem is that one of the two motors on one single track is faulting on I2T. Both of these motors are - or should be - getting the exact same torque (quadrature current) command, so why is one failing on overcurrent, and the other is not?


I think the most likely reason is that the coils on the two motors are not installed to the same phasing relative to the magnet common magnet track. The motor that is out of ideal phasing will see less back EMF and therefore permit more current to flow.

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