Characterizing Sources of Small DC Motor Noise and Vibration

Abstract

Small direct current (DC) motors are widely used due to their low cost and compact structure. Small DC motors of various designs are available on the market in different sizes. The smaller the motor, the more closely it may be used by individuals. Contrary to the size and simplicity of these motors in terms of structural design, sources of motor noise and vibration can be quite diverse and complicated. In this study, the source of motor noise and vibration was visualized over a very wide range of frequencies. The particle velocity of the motor was reconstructed from nearfield sound pressure measurements of motor noise. In addition to noncontact measurements conducted on a motor running at constant speed, the particle velocity of a stationary motor due to the impulse of an impact hammer was measured with an accelerometer. Furthermore, motor noise was measured under motor run-up conditions with different rotational speeds. As a result, by combination of these three methods, the sources of motor noise were accurately identified over a wide range of frequencies.

Noise Source Visualization for Small DC Motors Using Current Reference without a Reference Microphone

“…To derive an optimal design for low noise motors, sources of motor noise and vibration should be accurately visualized. Such sources were clearly visualized for a small direct current (DC) motor, and the results were confirmed with structural excitation tests using an impact hammer and motor run-up tests for different motor rotational speeds [ 6 ]. For accurate visualization of motor noise sources, relatively good reference measurements at optimal locations close to the sources is required [ 7 , 8 ].…”

“…In this study, cylindrical SONAH was implemented to identify noise sources in a small DC motor with motor current used as a reference signal and sound pressure measurements used as both scanning and moving reference signals. A more detailed derivation of cylindrical SONAH has been provided in a previous work [ 6 , 15 ], so SONAH is described relatively briefly here.…”

“…Sound pressure and current for a motor rotating at constant speed were measured on a cylindrical surface to enable reconstruction of the particle velocity of a source surface. The measurement of sound pressure was achieved in a way similar to in previous work, where it is described in detail [ 6 ]. The same motor and scanning microphones were used for measurement, but reference signals were taken from motor current.…”

“…For accurate visualization of motor noise sources, relatively good reference measurements at optimal locations close to the sources is required [ 7 , 8 ]. In previous work, a reference microphone was located above the motor shaft to avoid physical interference with scanning microphones [ 6 ]. However, as motors are constructed to be increasingly smaller, the optimal position for a stationary reference microphone may not be accessible for actual measurement.…”

Short Transient Parameter-Varying IIR Filter Based on Analog Oscillatory System

“…Unfortunately, voltage measurements can be easily noised by other electrical equipment around the sensors. The noise source is often an integral part of the measured object itself [3]. For example, the measurement of DC motor speed is conducted by magnetic encoders which are usually placed at the end of the motor shaft.…”