sound coming from mill

[Black Forest]

When I have the AC closed loop stepper fired up but not actually moving there is a sound coming from the bottom side of the table of the mill almost like the sound of an air leak! It is not an air leak because there is no air involved. This is an AC closed loop stepper with only a 1000line encoder with the drive set to 4000ppr. Could it be the motor is bouncing between increments on the encoder causing a minuscule vibration in the ballscrew? The motor doesn't get warm to the touch and with my ear directly on the motor I don't hear anything.

[polaraligned]

Sounds like the motor is hunting between counts.

[Toolguy]

That's what I was thinking. That can be caused by a looseness in the mechanical system. Maybe the ballscrew bearings aren't adjusted tight enough, or the bearings on the end of the ballscrew have some play, etc. One of mine was doing that, and I was able to fix it by tightening up the seals on the ends of the ballscrew bearing. The bottom line on mine was, something was just loose enough to let the ballscrew oscillate rotationally a small amount. That may or may not be what's going on with yours.

[Black Forest]

Thanks I will check for some play. Just to be clear, this is with the ball screw not turning. That is the table not moving.

[macona]

Are there tuning adjustments for the motors? The gain might be too high.

[MaxHeadRoom]

The issue is I believe in trying to obtain accurate servo action from closed loop steppers, they were not really intended for closed loop.
When this occurs in actual servo motors, it is generally means the PID loop requires tuning.

[Black Forest]

Yes there is a parameter on the drive I can tune. I will go out and see what it is set to now. A little experimenting is in order I guess. Thanks.

[Black Forest]

I just tried lowering and raising the KP parameter. No change in either direction. The option is from 1 - 1000. I tried a lot of values up and down. Zero change. That is the only parameter that is changeable in regards to tuning. I have decided the sound is more like hearing water running through a pipe, not an air leak.

[Toolguy]

Hi BF - The sound on mine was with everything sitting still, table not moving.

[danlb]

It sounds like it's time to trace down source using the hose in the ear trick.

[MaxHeadRoom]

It sounds like the problem is that the loop tuning is aiming for a point between stepper motor steps, which it can never reach or achieve.
This is where a servo has the edge, it can be tuned to what is called The least Increment Input, which is the to the encoder degree of resolution.

[Black Forest]

On this mill the ball screw on the X axis is only supported by the motor shaft on that end. There was a brake mounted in the motor mounting flange but I completely removed all the parts of the brake. The other end has bearings. That doesn't seem right to me. The original motors are DC Brushed servos that are at least twice the size of the AC closed loop stepper. The DC servo has really good bearings in it. I took the one I have taken off apart in order to get the tach off. Do you think this might be contributing to the sound I am hearing?

[Noitoen]

My stepper controllers/motors make a shhhhhh sound from the micro stepping feature. Maybe this is the sound you hear

[psomero]

If it's a stepper and it's not hot or not moving when you don't want it to, you're probably fine. Seems like it's trying to servo to a rotor position between steps. Does the sound change if you spin the leadscrew manually?

[Black Forest]

If it's a stepper and it's not hot or not moving when you don't want it to, you're probably fine. Seems like it's trying to servo to a rotor position between steps. Does the sound change if you spin the leadscrew manually?

No the sound doesn't change when I try to turn the hand wheel.