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Cross coupled Gantry problem


kmonroe023
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We are utilizing the cross-coupled gantry algorithm for one of our machines running the Power Pmac. We hare having a sporadic problem I would like your opinion on.

 

Occasionally, when the gantry is holding position the two gantry motors appear to start fighting each other. I've observed that the I2t sum on one of the motors will gradually accumulate to the point were it exceeds the limit, causing an I2t fault on that motor. When that happens the motor will disable, but then the gantry will run away making a howling sound (sorry for the low tech description, but I don't know how to describe it any other way).

 

Disabling, then re-enabling both motors generally gets things back to normal and the machine will run fine for a significant period of time (several days) without problems.

 

There does not seem to be any identifiable precursors to the motor problem, it seems to 'just happen'. The gantry structure itself is very rigid so I don't believe that is the cause.

 

Any ideas as to what could be causing this? I thought I might have a problem with the way the motors are homed, but it runs normally the vast majority of the time so I basically ruled that out.

 

Thanks,

Kevin Monroe

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According to your description and assuming I2t settings are correct, my guess is this may be related to the accumulated error in integral registers, can you please check Motor[x].Servo.Integrator and

Motor[x].Servo.Xint before the fault happens.Although the servo algorithm llimits saturates both these values with Servo.Maxint value for integral anti-windup, (and the servooutput will be limited also)

this still may cause an I2t fault if it is saturated for a while. You may

test this hypothesis by either decreasing your integral gains or the integrator limit.

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