Roslyde motors are our low-noise solution
Resonance frequencies in motor-driven devices and drive units can hardly be avoided. However, there are applications where they are especially undesirable. With ROSLYDE, ROTEK succeeded in developing a silent motor, which can be used in noise-critical environments.
Small electric motors are used for a variety of drive tasks. Low-noise plays an important role in addition to the mechanical quality. The motor should run as frictionlessly and silently as possible.
For many years Rotek has been producing synchronous motors and offers a modular system with millions of product variants. Synchronous technology has its advantages in many applications. The motors are particularly energy-efficient and of highly compact construction thanks to their powerful permanent magnet rotors and efficient stator windings – the main difference compared to conventional capacitor start AC motors. They offer constant speed irrespective of load and allow starting and stopping within fractions of a second. The detent torque, which renders brakes superfluous, is also typical.
This is where the often advantageous detent torque of synchronous motors is a disadvantage: noise generation. Magnetic locking of the rotor poles to stator teeth causes oscillations which manifest as structural sound.
The frequency and time characteristics of sound will, among others, determine whether the sound is perceived as disturbing. Certain frequencies are perceived to be louder than they actually are. Penetrating, shrill sounds such as whistling or screeching are perceived as unpleasant. We also perceive sound containing non-harmonising frequencies as annoying. Deep and coarse noises such as buzzing or humming are also deemed disturbing. Specification of the pure acoustic pressure level in dB is therefore of limited use to the customer. This is because acoustic pressure is only one aspect of our perception.
Gentle humming welcomed
What is much more decisive is whether the sound is pleasant and appropriate to the product. The sound of the roaring machine of a heavy motorcycle is generally welcomed. Drives which are used in inhabited areas are not generally desired to generate annoying noises. Steady acoustics without noticeable frequency excursions are optimal in electric motors, with rather subdued high and low frequencies and no prominent individual sounds. The objective is an even, subdued, and hardly audible humming.
The first point of attack to minimise acoustic emission should always be the motor itself as the source of vibrations. To achieve the quietest possible and vibration-free running characteristics, Rotek focused on two aspects in their development of the Roslyde. The alternating magnetic field generated by the stator winding excites vibrations in the drive, this effect could be minimised through optimisation of the winding method. The typical synchronous motor cogging torque was simultaneously minimised through permanent magnet rotor design modifications. Since the rotor is ground between two centres, it is balanced well enough to obviate any additional work steps. The bearings are also a potential source of noise. The more accurate they are, the better.
Since Rotek always uses specially lubricated high-quality ball bearings, these require no modifications either. And the particularly precise machining of the bearing shields ensures symmetrical support. The extremely smooth running motor Roslyde is an in-house development and its design is termed SmoothDrive technology.