How Does SMA OIS Work?
The SMA OIS actuator is placed between the traditional Auto Focus (AF) actuator and the sensor. The OIS has a fixed plate that is mounted to a moving plate which the AF is attached to. Ball bearings separate the plates to ensure low static and dynamic tilt is achieved. SMA wire is attached on each side connecting the fixed and the moving plate. SMA wire is unique compared to most other metals. SMA wire shortens and its diameter increases when it gets hot and lengthens and narrows in diameter when it cools. By passing the correct amount of current through each wire, the wire contracts to pull the actuator to the desired position. Because the diameter changes with respect to temperature and length, resistance of the wire can be measured and used to calculate the position of the actuator. This can be done directly by the drive circuitry and there is no need for additional hall effect sensors, which are commonly used with competing VCM technology to attain closed loop control. CML's engineers and scientists have derived the key relationships and developed the control firmware to accurately position the actuator to sub micron resolution with good linearity and minimal hysteresis using this control methodology.