Piezoelectric actuator and method of measuring motion by using the same

1. A piezoelectric actuator comprising:

a fixed member;

a movable member that is disposed to face the fixed member;

a piezoelectric element that is disposed between the fixed member and the movable member, and configured to operate in a shear mode based on input voltages applied to the piezoelectric element and move the movable member relative to the fixed member; and

a position sensor that is disposed between the piezoelectric element and the movable member, configured to measure a motion of the movable member, and comprising a plurality of substrates that are sequentially stacked,

wherein a first surface of the fixed member and a second surface of the movable member face each other,

wherein a surface of the piezoelectric element which faces the second surface of the movable member contacts a surface of the position sensor which faces the first surface of the fixed member,

wherein the plurality of substrates comprise a first substrate that comprises a first conductive layer that is coated with a conductor; a second substrate that comprises a second conductive layer having one surface coated with a conductor having a linear pattern; a third substrate that comprises a third conductive layer having one surface coated with a conductor having a circular engraved pattern; and a fourth substrate that comprises a fourth conductive layer having one surface divided into regions each being coated with a conductor, and

wherein the first conductive layer, the second conductive layer, and the third conductive layer are disposed to face in a same direction, and the fourth conductive layer is disposed on a surface of the fourth substrate that is spaced apart from the third substrate.

2. The piezoelectric actuator of claim 1 , wherein the position sensor comprises a first electrode and a second electrode,

wherein the first electrode is fixed to a first region of one surface between the piezoelectric element and the movable member, and the second electrode is fixed to a second region of the one surface.

3. The piezoelectric actuator of claim 1 , wherein the position sensor is further configured to measure the motion of the movable member based on a magnitude and a direction of an output voltage that is output from a portion on which the circular engraved pattern is coated.

4. The piezoelectric actuator of claim 1 , wherein the position sensor is further configured to, in response to an output voltage corresponding to 0 being output after the input voltages having different magnitudes and opposite phases are applied, measure the motion of the movable member based on a ratio of the different magnitudes.

5. The piezoelectric actuator of claim 1 , wherein the input voltages have opposite phases and the position sensor is connected to a voltage applier that is configured to adjust magnitudes of the input voltages.

6. The piezoelectric actuator of claim 1 , wherein the second substrate comprises a hole that is filled with a conductive material, and

wherein the second substrate is connected to the third conductive layer of the third substrate through the hole.

7. The piezoelectric actuator of claim 1 , further comprising a driver that is configured to measure a current that is output from the position sensor.

8. The piezoelectric actuator of claim 1 , wherein the piezoelectric element comprises a first piezoelectric layer and a second piezoelectric layer that have different polarization directions.

9. The piezoelectric actuator of claim 1 , further comprising an elastic member having one end that contacts the fixed member and another end that elastically presses the movable member toward the piezoelectric element.

10. A method of measuring a motion, the method comprising:

applying to a position sensor input voltages having a predetermined magnitude and opposite phases;

measuring an output voltage that is generated from a motion of a piezoelectric element that is disposed between a fixed member and a movable member, and is fixed to one surface of the position sensor and output from the position sensor based on the applied input voltages; and

measuring a motion of the movable member based on the measured output voltage,

wherein a first surface of the fixed member and a second surface of the movable member face each other,

wherein a surface of the piezoelectric element which faces the second surface of the movable member contacts a surface of the position sensor which faces the first surface of the fixed member,

wherein the position sensor comprises a plurality of substrates that are sequentially stacked,

wherein the plurality of substrates comprise a first substrate that comprises a first conductive layer that is coated with a conductor; a second substrate that comprises a second conductive layer having one surface coated with a conductor having a linear pattern; a third substrate that comprises a third conductive layer having one surface coated with a conductor having a circular engraved pattern; and a fourth substrate that comprises a fourth conductive layer having one surface divided into regions each being coated with a conductor, and

wherein the first conductive layer, the second conductive layer, and the third conductive layer are disposed to face in a same direction, and the fourth conductive layer is disposed on a surface of the fourth substrate that is spaced apart from the third substrate.

11. The method of claim 10 , wherein the applying the input voltages comprises applying the input voltages having a same magnitude, and

the measuring the motion of the movable member comprises measuring the motion of the movable member based on a magnitude and a direction of the output voltage.

12. The method of claim 10 , wherein the applying the input voltages comprises applying the input voltages having different magnitudes, and the measuring the motion of the movable member comprises measuring a position of the movable member based on a ratio of the input voltages in response to the output voltage, that is output after the input voltages having different magnitudes and opposite phases are applied, corresponding to 0.