Mechanical actuators, by which lenses are made to move linearly using gears by rotation of motors have been widely used as actuators for automatically controlling the focal point of cameras. However, when such mechanical actuators are used, it is impossible to avoid static and dynamic errors caused by the friction, mechanical modification or backlash resulting from driving motors and gears, so it is also impossible to precisely control such mechanical actuators. Accordingly, it is difficult to precisely control the focal point, and to make cameras compact due to the space required for motors and gears.
In order to solve the above problems arising from mechanical actuators, voice coil actuators have been developed. Voice coil actuators are used to control the linear motion using the Lorentz force generated by the induced magnetic force of coils in the static magnetic field produced by permanent magnets, and are suitable for precise linear motion for relatively short distances. Such voice coil actuators have been utilized in ultra-precise linear motion systems, for example, for moving pickup heads inside hard disks or optical discs. Such conventional voice coil actuators move lens barrels mounted inside housings linearly back and forth in order to automatically control the focal point of lenses.
However, since such conventional lens barrels inside housings are elastically supported only by leaf springs disposed on upper or lower portions of lens barrels without additional support members, axes of lenses are twisted when lens barrels move back and forth during the automatic focal point control operation. Additionally, it is difficult to maintain horizontal balance regardless of the movement of the lens barrels, and tilting to the left and right occurs, so that the precision of the focal point control is reduced. Furthermore, power needs to be continuously supplied when lens barrels move, so power consumption increases and coils become disconnected.