Everything You Need to Know About Voice Coil Motor
What is voice coil motor?
Voice Coil Motors (VCM) are the simplest type of electric motors, which consist of two separate parts; the magnetic housing and the coil.
Voice coil motors are brushless and do not utilize commutation. Their structural stability can support high positioning resolutions presented by external position sensors and motion controllers.
1. Reliability – side forces developed are negligible, so bearing loading can be very low to enable long life operation; 2. Simplicity – the voice coil motor is a single pole device requiring no commutation. Both the device itself, and the associated controller can be very simple and robust; 3. Flexible Configuration – the principle of operation lends itself to many different mechanical layouts allowing great flexibility in the design of associated systems; 4. Fast operation – Low electrical inductance, and low moving mass enable fast inflow of current and high acceleration. Acceleration of >500G is possible with custom devices; 5. Controllability – Force is proportional to applied current, and is uniform through a displacement that can be several 10’s of mm or several 10’s of degrees rotation; 6. Low hysteresis – The magnetic behavior is free of hysteresis over typical operating areas, depending on the type of bearings used, very low hysteresis can be realized; 7. Flexible Production – Most product configurations can be produced without requiring tooling for prototypes, or for limited production volumes – product design needs to allow for manufacturing methods appropriate to customer volume requirements.
A simple linear voice coil motor consists of a tubular coil of wire. The wire is situated within a magnetic field. The magnetic field is produced by permanent magnets embedded on the inside diameter of a ferromagnetic cylinder.
The cylinder is arranged such that the side of the magnets that faces the ferromagnetic cylinder has the same polarity as the cylinder. The opposite side of the magnets facing the coil has the opposite polarity. An inner core of ferromagnetic material set along the axial centreline of the coil, joined at one end to the permanent magnet assembly, is used to complete the magnetic circuit.
Why are the linear voice coil motors widely used?
The linear voice coil motor (VCM) is a direct drive and hysteresis-free device used for providing highly accurate linear motion. The linear VCMs utilize a magnetic field generated by permanent magnets in connection with a coil of wires to produce an electric driving force for high precision position control. Since the mass of the moving coil is typically low, the speed and acceleration of the VCM are very high and the settling time is very short. Moreover, because the inductance of a VCM is typically low, the resulting low electrical time constant enables the VCM to have a very fast response and bandwidth. Besides, the direct drive features benefits for the VCM such as zero cogging, zero backlash, smooth motion at low speeds, and limitless resolution. Therefore, VCMs have been widely applied to various small range positioning applications
What are the applications of voice coil motors?
For slow speed operation, it is preferable if the coil assembly is mounted to a fixed component, and the field assembly to the moving component in the customer assembly so as to prevent flexing of lead wires to the coil assembly.
For fast operation, it may be necessary to attach the field assembly to the fixed point, and the lighter coil assembly to the moving part – care should be taken with the connection to allow unimpeded movement and avoid failure due to fatigue of the electrical termination to the moving coil assembly.
The voice coil actuator is inherently a bidirectional device and can drive in either direction, if force is required in one direction only, the actuator can be biased in this direction with a spring to allow twice as much peak usable force to be produced in this direction with the same peak input power.