Voice Coil Motor Magnets
Voice coil motors are a special form of linear motion motor, and also famous for its working principle which similar to the loudspeaker. Voice coil motor has a simple structure, low volume and noise, in the meanwhile, its specific thrust, acceleration, response speed and accuracy are also excellent. Besides, voice coil motor is also reliable and easy to maintain. Therefore, voice coil motors are widely applied to hard disk drive (HDD), optical disk drive (ODD), scanner, lens focusing, laser cutting, vibrating motor of mobile phone, medical equipment and spaceflight apparatus. Even to this day, a great deal of Neodymium magnets is still serving as voice coil motor magnets which utilized as servo drive of seeking and focusing mechanism in hard disk drive (HDD) and the optical disk drive (ODD).
About Voice Coil Motor Magnets
The magnetization pattern of ring-shaped voice coil motor magnets in cylindrical voice motor should via radial direction, and most of them are built by several pieces of diametrically magnetized arc magnet. By comparison with arc magnet array, radially oriented ring magnets will exhibit more uniformly distribution in the magnetic field.
HSMAG team can not only provide sintered radially oriented magnet, but also manufacture hot-pressed/hot-deformed magnets which have more superior magnetic field distribution and consistency.
What is a Voice Coil Motor? Characteristics and Selection of Voice Coil Motors
Voice Coil Motors are highly controllable electrical actuators suitable for applications needing only limited displacement. They offer the following features:
• 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
• Controll ability – 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
• Low hysteresis – The magnetic be haviour is free of hysteresis over typical operating areas, depending on the type of bearings used, very low hysteresis can be realised Voice Coil Motor coil diagram
• Reliability – side forces developed are negligible, so bearing loading can be very low to enable long life operation
• 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
• Flexible Configuration – the principle of operation lends itself to many different mechanical layouts allowing great flexibility in design of associated systems
• 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
Working Principle of Voice Coil Motor
According to Ampere’s force law, force F suffered by current-carrying wires in the magnetic field is determined by magnetic induction B, current I and included angle θ between magnetic field and current direction. When the length of current-carrying wire and magnetic induction being kept constant, the force is directly proportional to the current, and voice coil motor is right based on this principle. Place a conducting coil into the magnetic field, and magnetic conduction cylinder which inside the coil and external permanent magnets will form a magnetic circuit. Coil will be subjected to the magnetic field after energized the coil, therefore generate an axial force on the coil. It should be noted that the direction of force is affected by the current direction in coil.
Custom designs can incorporate many different features including the following:
• Flexible circuit termination of the coil provides reliable electrical connection with repeatable low resistance to movement and low friction (hysteresis). Body is extended with end cover providing a sealed unit with easy electrical termination
• Flat coil design allows pivoting motion and tolerance to some variation in position of the coil relative to magnet assembly.
• Flex circuit is used for easy termination
• End cover and flex circuit allow sealed unit with reliable, low-friction electrical connection. Connector allows easy installation and replacement.
• Special tip fitted to shaft
Voice Coil Motor End cover and flex circuit• Steel flexure guidance provides repeatable, friction-free guidance of the shaft with unlimited life expectancy
• Multiple poles for higher force and efficiency with reduced size and mass, use of multipole designs may be inappropriate to applications requiring large displacement
• Aluminium coil windings enable reduced moving mass for high acceleration, the flat design illustrated uses multiple poles and aluminium coil winding to achieve force capability >50N peak with coil mass <12g for acceleration capability >400G
Voice Coil Motor Rolling element bearings • Rolling element bearings provide more precise guidance, and more repeatable friction behaviour when subjected to variable side loading, the part shown also employs flexible circuit termination and a focused radial magnet assembly for higher force / mass and better dynamic performance
• Position encoder with resolution to <1µm for closed loop (servo) control
• Multiple coil and lightweight titanium shaft for high force / mass ratio
• Rolling element bearings for high precision, long life linear guidance
• Flex termination integrated within compact design