1. Field of the Invention
The present invention relates to a piezoelectric actuator and an apparatus for driving a lens applied to an optical device using the piezoelectric actuator, and more particularly, to a piezoelectric actuator which is simplified in a driving mechanism to achieve a smaller size, minimized in loss of a driving force for driving a lens and ensures more accurate and stable transport of the lens.
2. Description of the Related Art
In general, an optical apparatus includes a lens driving device for driving a lens. This lens driving device employs an actuator such as an electromagnetic motor or a piezoelectric actuator to generate a driving force, and a cam or a screw to transmit the driving force generated from the actuator.
Therefore, the lens driving device drives the lens in an optical axis direction using the driving force generated from the actuator. At this time, the lens driving device changes a relative distance between a lens and an adjacent lens thereof to perform zooming or focusing.
Meanwhile, recently, a piezoelectric actuator utilizing a piezoelectric body has been highlighted as a new motor to substitute an electromagnetic motor.
This piezoelectric actuator generates high frequency vibration of minute amplitudes in a piezoelectric vibrator and transfers these minute vibrations by contact friction between a friction member and a slider (rotor) attached to the piezoelectric vibrator, thereby enabling the slider (rotor) to perform minute motion. This piezoelectric actuator is smaller in size, higher in driving resolution and less noise-causing than the conventional electromagnetic motor.
FIG. 1 is a schematic view illustrating a structure of a conventional piezoelectric actuator. The piezoelectric actuator includes a piezoelectric body 10, and a friction member 30 attached to one side thereof.
The piezoelectric body 10 is structured such that a plurality of piezoelectric ceramic sheets formed of a plurality of ceramics are stacked, and each of the piezoelectric ceramic sheets has an internal electrode formed thereon to define the piezoelectric body into a plurality of vibrators.
These internal electrodes can be configured variously on a surface of the piezoelectric sheet considering type and direction of vibration generated from the piezoelectric body 10, and number and location of the friction member 30.
Also, wires or the external electrodes 21 and 22 are formed on the piezoelectric body 10 to connect the internal electrodes together so as to supply alternating currents of an identical phase to the two vibrators 11 and 14, and 12 and 13 located diagonally. Also, the friction member 30 is disposed on the one side surface of the piezoelectric body 10 to transfer vibration generated from the piezoelectric body 10 to the outside. The friction member 30 is made of a ceramic material or a hard metal.
Accordingly, the alternating voltages of an identical phase are applied to the two rotators 11 and 14, and 12 and 13 located diagonally through the wires or external electrodes 21 and 22 of the piezoelectric body 10 which is divided into the vibrators 11, 12, 13 and 14. Then, the piezoelectric body 10 generates vibrations of two modes.
That is, the piezoelectric body 10 generates a dilation mode of vibration for enabling dilation along a longitudinal direction and a bending mode of vibration for enabling bending in a thickness direction thereof.
With simultaneous occurrence of the vibrations of these two modes, the friction member performs elliptical motion and this elliptical motion of the friction member 30 is transferred to the slider or rotor to enable linear motion for the slider and rotational movement for the rotor.
However, the conventional piezoelectric actuator entails a complicated process of forming the external electrodes connected to the internal electrode, thus requiring high precision. This hinders simplification of a manufacturing process for saving manufacturing costs and reduction of the bulk of the piezoelectric actuator.
U.S. Pat. No. 5,768,038 discloses a device for moving a lens including a lens frame, a signal generator, a piezoelectric vibrator, a supporter, a pressure surface and a pressure member. The guiding member guides a lens frame. The signal generator generates an electrical signal. The piezoelectric vibrator moves the lens frame along the guiding member by vibration according to the electrical signal. The supporter supports the piezoelectric vibrator. The pressure surface is in pressure contact with the piezoelectric vibrator. The pressure member brings the piezoelectric vibrator into pressure contact with the pressure surface.
However, this conventional device requires the guiding member to be additionally assembled so that the lens frame is moved along an optical axis direction. This complicates an assembling structure and a process, and hinders miniaturization of the product.
Moreover, U.S. Pat. No. 6,215,605 discloses a driving device. In the driving device, piezoelectric devices are fixed to a base block and a driving force is transferred to driving rods. Then, a lens is moved by a pressure generated from a slide part, an inertial force of a lens frame and acceleration effects. The lens frame is transferred along with the driving rods according to a waveform of an input voltage or performs slidable relative motion, thereby enabling the driving device to reciprocally move the lens.
However, in this conventional device, the driving rods are fixed so that a length of barrel cannot be changed. This accordingly is an impediment to reduction in size. Also, a driving signal of the device is an asymmetrical wave signal, not a sine wave signal, thereby complicating a driving circuit.
Therefore, there is a need for a lens driving device which can be mounted in a small volume, controlled precisely due to high driving resolution, while operating with a small driving power and achieving a sufficient driving distance.