High-frequency (inaudible by humans) acoustic noise from stepper motor

In summary, the high-frequency noise coming from the motor is caused by the driver, which is being driven at a frequency that is high enough for humans to not hear, but rats can. Stepper motors are always noisy when they are rotating, because the driving force is a series of pulses, not a continuous torque. However, a PWM drive may reduce this noise.
  • #1
aalnaif
6
0
Hello,

I am using stepper motors for some neuroscience experiments on rats. The problem is that our experiments are being corrupted by high-frequency noise. The acoustic frequency of the noise is high enough that humans can't hear it, but rats can (humans can hear up to 20 kHz, whereas rats can hear up to 80 kHz). Using a microphone, I measured the acoustic frequencies of the noise coming from the motor, and I observed peaks at 22.5 kHz, 43.25 kHz, 88 kHz, 110 kHz (note that the larger frequencies are harmonics of 22.5 kHz, with the exception of 65 kHz which is missing for some reason). The weird thing is that the motor does not need to be moving for this sound to happen; simply supplying idle current to the motor generates this sound. I checked to make sure that this sound was not present when no current was supplied to the motor, and I also ensured that the sound is indeed coming from the motor and not another piece of equipment.

The stepper motor we are using is the 2-phase Vexta PK223PA (http://www.orientalmotor.com/products/pdfs/2009-2010/C/usa_st_2pk_pv.pdf), and the driver is Applied Motion Products Si3540 (although I don't think the driver matters since no movement is necessary for this sound to occur).

My questions are:

1. Why would simply supplying idle current cause such high-frequency noise, regardless of whether the motor is moving?

2. Would a 5-phase motor also produce this sound?

3. Are there any quieter options? How do servo-motors, linear motors, and solenoids compare to stepper motors, in terms of acoustic noise levels?
 
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  • #2
I think the driver does matter. Most likely it is not producing a DC output when the motor is stopped. The first thing I would do would be put an oscilloscope across the motor input terminals. My guess is you will see some sort of pulse waveform, with no 3rd harmonic content.

You should be able to hold the motor in a fixed position with a DC current and no noise. Stepper motors are always noisy when they are rotating, because the driving force is a series of pulses, not a continuous torque.
 
  • #3
AlephZero said:
I think the driver does matter. Most likely it is not producing a DC output when the motor is stopped. The first thing I would do would be put an oscilloscope across the motor input terminals. My guess is you will see some sort of pulse waveform, with no 3rd harmonic content.

You should be able to hold the motor in a fixed position with a DC current and no noise. Stepper motors are always noisy when they are rotating, because the driving force is a series of pulses, not a continuous torque.

From the Applied website:
•Dual MOSFET H-bridge, 3 state, pulse width modulated amplifier switching at 20-30 kHz

The PWM circuit is running at 20-30kHz, so the primary drive frequency and harmonics are what you are picking up. Maybe the output could be filtered to reduce this?

Any type of PWM drive will probably exhibit this characteristic regardless of type of motor. I use an Aerotech motion controller with a linear motor, the drive output has an adjustable filter presumably to reduce this effect. I cannot hear anything, but I have not measured with a mic. Maybe you could look into a linear drive for your stepper instead of a PWM drive?
 
  • #4
MRFMengineer, AlephZero,

Thanks for your help. Both of your posts were enlightening.
 

What is high-frequency acoustic noise from stepper motor?

High-frequency acoustic noise from stepper motor refers to the sound produced by the motor while it is in operation. This sound is typically inaudible to humans, as it falls outside of the range of frequencies that the human ear can detect.

Why does stepper motor produce high-frequency acoustic noise?

Stepper motors produce high-frequency acoustic noise due to the rapid switching of electrical currents within the motor. This switching action creates vibrations that result in audible sound waves.

Can high-frequency acoustic noise from stepper motor be harmful?

In most cases, high-frequency acoustic noise from stepper motor is not harmful to humans. However, prolonged exposure to high levels of noise can potentially cause hearing damage. It is important to take necessary precautions, such as wearing ear protection, when working with stepper motors.

How can high-frequency acoustic noise from stepper motor be reduced?

There are several methods that can be used to reduce high-frequency acoustic noise from stepper motor. These include using dampening materials, adjusting the motor's current and voltage levels, and using anti-vibration mounts. Proper maintenance and lubrication of the motor can also help reduce noise levels.

Are there any benefits to high-frequency acoustic noise from stepper motor?

High-frequency acoustic noise from stepper motor can be beneficial in some applications. For example, it can be used to detect the movement and position of the motor, which is important in precision machinery. It can also be used as a diagnostic tool to identify any potential issues with the motor.

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