Current noise coming from Step Motor

[motor79]

We are currently using the A3959 chip from allegro. But we hear a noise coming from the end cap of the motor. It's sounds like the current circulating through the windings. This noise causes vibration in our machine when it's in holding mode. Does anybody know how to get rid of this noise and where it's coming from. We lowered hold current this helped but we can't lower hold current in our application.

http://www.allegromicro.com/sf/3959/

 

[Skogsgurra]

Hi,

It is something that you can change by adjusting the PWM frequency. You probably have the oscillator running at 4 MHz and your carrier frequency is a small fraction of that - so it is usually in the audible range. It is also possible that mechanical resonance amplifies the sound level. Try to change the Rosc (pin 4 in the DIP version). You can take it down 50 percent or up more than 100 percent by varying the Rosc value from 20 kohm to 100 kohm.



Gunnar Englund

http://www.gke.org

--------------------------------------
100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

 

[motor79]

We are using a 22.1K ohm resistor which is 9.2Mhz, do you think the noise might go away if we lower the PWM frequency. From my PWM frequency how do I find out the carrier frequency?

 

[Skogsgurra]

I cannot say. You have to try it yourself. If you are having mechanical resonance, it is very probable that the sound changes/goes away if you change the Rosc. Standard value is 51 kohms. Try that.

Gunnar Englund

http://www.gke.org

--------------------------------------
100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

 

[OperaHouse]

"vibration in our machine when it's in holding mode."

I was doing some development work on a 3900 pound cast iron EDM machine and that would certainly shake it at different stepper speeds. Haven't seen this when one is "stopped." When you say you are holding, is your position determined by an external encoder? This may be caused by a control loop problem as well as the chopper speed.

 

[motor79]

There is a buzzing noise that comes from the end cap of the motor, this buzzing causes vibration in the equipment when the motor is in holding position.

 

[itsmoked]

Is this an open loop controlled system or are there some kind of encoders?

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com

 

[motor79]

No closed loop controller, it's open loop. I'm going to try to change the Rosc resitor as per recommendation by a user. I don't think it will help get rid of noise since i'll be lowering the operating frequency of the PWM, the lower the frequency we can hear that. But I think it's worth a try.