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Current Mode Control Of Linear Drive


jimmyNI

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Im having trouble with a linear motor drive application. Im using a motor/servo drive to power a linear drive. The drive is running in torque/current mode so that the output current/force is proportional to an analog input which is sent to it. For this particular application, I would like to send it a sinusoidal voltage waveform and would expect a sinusoidal force out. Yet, using a load cell, I can see that the sin wave is being truncated on the top and bottom, being that it rises to fast in response to the voltage and then plateaus while the reciprocal happens during unloading and it reaches low load and then levels off where as it should be a gradual change where the sin wave changes direction. This is not a saturation effect though as I can raise the magnitude of the input voltage, and the force will follow the same type of waveform but at new load levels. Where it gets even more confusing is that I can look at the output current/voltage levels from the servo drive which feed the linear drive and they are perfect sinusoids, just like the input, so the truncation is some type of effect caused by the motor itself. If it matters, it is a EC4 series linear drive from kollmorgran powered by an AKM42 servo motor. Im not really sure how the motor works, but this has been really troubling for me and any help is appreciated.

 

There are no tuning parameters for the current mode of the servo drive although there are for position mode. The force should be 100% proportional to the input voltage. Also, I've tried different types of waveforms like a sin^3 without luck as it creates an even larger low force period.

 

thanks

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The effective inertia of a linear servo system is higher than a rotational servo system.

The servo drive system needs to be set up differently when used on a linear motor.

 

Best regads,

Mark.

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