Bosch-Rexroth servo noise.

[jcraft]

We have a small servo motor for a spiral tube cutting machine. the motor drives a 5 to 1 gearbox which is belt connected to a cutting blade assembly and we are controlling the velocity of the motor only . This is a new install and every thing is setup and running. The question is we run the blade above 75 rpm ( 375rpm motor speed) the motor starts to emit an annoying humming sound and increases intensity as you speed it up, This is with only the gear box and cutter load. below this speed it is quite. We ran a test today and we were spiral cutting a 2" tube at 45 rpm cutter speed, Immediately the motor produced and even louder annoying humming noise when it is actually cutting the tube. I went online with the controller and actually reduced the Velocity Pgain from 5 down to about .680 and the noise was elimiated completely and the commanded and actual velocities stayed pretty much identical. Motor current waas at 50% and so was the tourque. MY question is, now that we eliminated the noise while under load when we remove the tube load you stll get the motor hum above the 75 rpm cutter speed. Not sure of what parameter settings would eliminate this. Any thoughts. Thanks

 

[hokie]

Continue to lower the Velocity loop proportional gain(S-0-0100).
You could also lower the integral gain, by raising the velocity loop integral action time (S-0-0101).

 

[jcraft]

That's pretty much what I figured. I tried lowering the Pgain almost to 0 and also increased the Integral quite a bit. Didn't seem to eliminate the noise while not loaded and the motr running above 500 rpm. I'll try again when the machine is running. Thanks

 

[Manglemender]

Also check that the belt, and any other couplings, are tight.

The mass of the cutter assembly will also have a bearing on the stability in respect of the inertia matching - a badly miss-matched servo will be difficult to get stable. For best results the inertia of the load should approximately match the inertia of the motor; bearing in mind the gear ratio as reflectected inertia is multiplied by the square of the gear ratio i.e. if you have a 2:1 gear box then the reflected inertia is 1/4 of the load inertia.

Nick