The benefits of quiet motor systems

Dave Walsha explores some applications where motors must keep the noise down

The world’s loudest sound was the eruption of the Krakatoa volcano in 1883, which was clearly heard 3,000 miles away — that’s more than the width of the United States.

While micromotors won’t reach this extreme volume, their noise can still be problematic, such as in loud medical equipment that triggers patient anxiety. 

When designing a motor, engineers must rightly prioritise performance and precision. While it’s less important for your vacuum cleaner and blender to be silent, it’s essential that medical equipment puts patients at ease, and that the sunroof in a luxury car gives the user a sense of opulence. 

Quiet comfort

Motors power many everyday items and normally go unnoticed, unless you hear them. A noisy fridge fan can give the impression that the appliance is working poorly, and a harsh noise when the TV comes up from the end of the bed will dampen any relaxing evening. In home disability aids, such as stair lifts and bath lifts, a noisy motor may cause the user to think the equipment is struggling. 

Going beyond the home, many luxury car add-ons, such as motorised sun roof shades and automatic passenger assistance steps, require minimal sound to convey high quality. 

Additionally, motor noise is an important consideration in offices, where there are rooms filled with motorised equipment, such as computer fans, air conditioning units and printers. 

Prolonged noise from office equipment can cause an uncomfortable and distracting atmosphere for employees.

Another area where quietness brings comfort is in the medical industry. Many people share the same nightmare of a dentist approaching them with a noisy drill — and this is a large cause of patient anxiety. Medical equipment powered by quiet motors puts patients at ease by creating a calm atmosphere. 

Similarly, quiet motors can be used in medical and industrial ventilators, which enable the user to wear the equipment comfortably for a long period of time.

The key to quiet

Keeping a motorised appliance quiet requires careful consideration of the motor system as a whole, including the motor and associated gearbox. Within the motor, changing the bearing material and shape can be beneficial, such as upgrading to a high-quality steel, deep groove ball bearing. 

Ensuring the internal rotor is well-balanced, by aligning the centre of mass as close to the geometric centre as possible, can also significantly lower noise by reducing vibration. Motor noise is kinetic energy wasted as sound energy, so using a high efficiency motor will also lower sound levels.

Engineers must carefully consider noise during the whole design process of a gearbox in order for it to produce minimal sound. 

Adjusting the tolerancing of the gearbox to minimise pitch, tooth profile, lead and runout errors ensures precise alignment of teeth for lower vibration. Reinforcing gearbox housing to increase stability can also alter noise levels by minimising vibration. 

Trialling a more viscous lubricant can reduce friction, but it’s important to ensure the lubricant is compatible with the motor.

Once the motor system has been built using a considered design process, it must be analysed for sound using an accelerometer, with repeated prototype testing and refinement. 

An accelerometer measures vibration and correlates it to a frequency of noise, allowing identification of the noise source. 

EMS manufactures and supplies a range of motor systems, and also offers a bespoke design service. EMS’s team of design, test, procurement and manufacturing experts, along with an in-house accelerometer, allows motor systems to be catered to low noise requirements from concept to production.

While micromotors won’t produce volcanic levels of noise, they can still be problematic. Lowering motor system noise provides comfort to the user, and gives the impression of a quality, high performance device. By taking a considered approach to the design process, and using an accelerometer for refinement, motors can keep the noise down.

Dave Walsha is commercial development officer at precision drive system supplier EMS Ltd.