Loudspeakers were used to amplify or create a louder voice, thus the name “voice coil” stuck. Voice coil motor uses similar technology to speakers, but it is designed to produce higher forces over larger distances or “strokes”. Voice coil motors do not have the commutator but use a position sensor. These motors consist of two separate parts: the magnetic housing and the coil.
The current running through the coil creates a magnetic field, which interacts with the field established by the permanent magnet.
The voice coil works because of the force between a static magnetic field and an electric current perpendicular to the field.
Below is a schematic diagram of a current-carrying wire and a magnet.
Arrows indicate the direction of the electric current (to the right) and of the magnetic field (up):
For wear resistance and good surface finish along with required magnetic properties, the shaft material is either stainless steel (hardenable stainless steel may be slightly magnetic and have a slight influence on the force characteristic, nonmagnetic stainless steel is softer and more susceptible to damage) or titanium. The magnet assembly of VM series is designed for good volumetric efficiency and useful linear stroke, these characteristics may be at the expense of some loss of linearity. High energy density magnets drive the material of the voice coil pot (housing) close to magnetic saturation to develop the strongest possible magnetic field.
Stanford Magnets offer custom magnets assemblies to ensure accurate guidance of the coil assembly within the magnet assembly, and to facilitate easy installation in customer applications. Custom designs can demonstrate better linearity at the expense of increased size/weight & cost.
Coils of VCM series are normally designed to use the full depth of the pot assembly. This results in maximum mechanical work output capability but may result in a force characteristic that is not ideally suited to a given application. The portion of the coil which lies outside the airgap field dissipates power (as heat) but develops no useful force.
The linear range of a voice coil (the range within which developed force is >90% of peak force) will normally be roughly equal to the difference between the coil length, and the length of the pole.
For maximum force, the coil length and pole length should be approximately equal in length, but the linear range with this configuration will be small.
For best linearity, one of the coil and polepiece should be longer than the other by the linear range required. It is usually more cost-effective to make the coil longer than the magnet assembly – making the coil shorter than the polepiece results in lower moving mass and faster dynamic response, but this may require a more massive and expensive magnet assembly to produce a required force characteristic.
Thank you for reading our article and we hope it can help you know how a voice coil motor works in a speaker well. If you want to know more about magnet products, we advise you to visit Stanford Magents for more information.
Stanford Magnets is one of the top magnet product suppliers across the world and has rich experience in the manufacture and sale of all kinds of magnet products. We can provide customers with high-quality rare earth permanent magnetic products such as neodymium magnets, and other non-rare earth permanent magnets at a very competitive price.