Voice coil motor (VCM) belongs to the linear DC motor, with a compact size and simple structure. Its function is to adjust the position of the lens so that the object in focus presents a clear image and realizes autofocus. The voice coil motor (VCM) has become the core component of the cell phone camera.
Principle of Voice Coil Motor
The principle of the voice coil motor is simple. According to the Lorentz law, When the coil is in a magnetic field, the current through the coil cuts the magnetic lines of force, which creates a force that adjusts the position of the lens.
Lorentz force formula: F = B * L * I
B is the magnetic field strength, L is the coil length, and I is the coil current. For a VCM, B and L are fixed and only I is adjustable. By controlling the magnitude and direction of the current, you can control the precise movement of the lens driven by the coil.
The thrust produced by the voice coil motor is directly proportional to the current flowing through the coil, the stronger the current, the greater the thrust. The voice coil motor is matched with a Driver IC, which controls the amount of current flowing through the coil, thus generating different amounts of thrust to push the lens to the appropriate position to complete focusing.
Voice Coil Motor Market Analysis
The global demand for VCM is 1,781 million, 1,793 million, and 1,803 million from 2017 to 2019, respectively. With the popularity of dual-camera phones and multi-camera phones, it further boosts the demand for VCMs. Global VCM consumption is expected to reach 3.94 billion pieces by 2025.
Key Parameters of Voice Coil Motor
Rated Current | The current when the lens reaches the rated stroke, generally set at 80mA, is also defined as 90mA or 100mA.
Voltage Range | The voltage range supplied to the drive motor, generally below 3.0V.
Terminal Resistance | The resistance value of the motor.
Rated Stroke | The stroke of the motor at rated current.
Slope | The slope of the curve in the stroke.
Hysteresis | The deviation between the forward and backward stroke of the lens at the same current, this deviation is the hysteresis error.
Tilt | The angle of deviation between the optical axis of the lens and the vertical axis of the sensor.
Voice Coil Motor Magnets
Materials | Since the VCM has strict requirements on the performance and size of the magnets, NdFeB magnets are the first choice.
Grade | The main magnet grades are 42M, 45M, 45H, 45SH, 48M, 50M, 50SH, 52M, 48H, 48SH, etc.
Magnetization Direction | The magnetization direction of ring-shaped voice coil motor magnets should be via radial direction. If the voice coil motor magnets are arc-shaped, they are diametrically magnetized. Radially magnetized ring magnets generate a more uniform magnetic field distribution than arc magnets.
Shape | The arc or ring shape is the main shape and the thickness of the magnet is no more than 1mm.
Basic Structure of Voice Coil Motor
The most important components of a voice coil motor are the coil, magnet, and springs. There are also some other auxiliary parts.
Yoke | It is a magnetic conductor and works with the magnet to create a magnetic field circuit.
Magnets | Different designs have different magnet styles and magnetization directions.
Coils | Generates propulsion when energized.
Springs | One is at the top and one at the bottom, which produces a pulling force opposite to the magnetic force
Carrier | It serves to hold the coil and has internal threads for screwing into the lens.
Other Applications of Voice Coil Motor
Due to the high precision and fast response of voice coil motors, VCM motors have a wide range of applications. In addition to cell phone cameras, voice coil motors have been used in laptops, webcams, video monitors, scanners, hard disks, and more.
The future development of autofocus technology will mainly focus on improving focusing speed and increasing image stability. The voice coil motor will also gradually evolve from the traditional motor to the OIS (Optical Image Stabilization) motor, solving the problem of image blurring and improving the stability of photographic images
* Images for the article are from Mpcomagnetics, Semanticscholar, and Cnstamping
