Piezo actuator device and motor

1. A piezo actuator comprising:

a piezo material having

a top surface,

a bottom surface, and

a circumference surface,

the piezo material having a polarity and the piezo material comprising one or more mounting holes in the piezo material, the one or more mounting holes being positioned substantially central in at least the top surface or the bottom surface of the piezo material,

at least one contact point for contacting a load to be actuated, the at least one contact point being positioned on the circumference surface of the piezo material, and

a set of electrodes being positioned on the top surface of the piezo material and at least one electrode being positioned at the bottom surface of the piezo material;

wherein the electrodes are electrically connected and configured such that, taking into account the polarity of the piezo material, driving of the electrodes induces an in-plane bending mode and/or an in-plane expansion mode, wherein the in-plane bending mode is an oscillation mode wherein adjacent corners move in opposite sense and wherein the in-plane expansion mode is an oscillation mode wherein different corners of the top surface move in a same direction being synchronously outward or inward.

2. The piezo actuator according to claim 1 , wherein the electrodes are electrically connected and configured such that, taking into account the polarity of the piezo material, the driving of the electrodes induces alternatingly the in-plane bending mode and the in-plane expansion mode.

3. The piezo actuator according to claim 1 , wherein the set of electrodes being positioned on the top surface of the piezo material comprises four electrodes, the four electrodes being paired two by two and the paired electrodes being positioned diametrically opposite with respect to the one or more mounting holes.

4. The piezo actuator according to claim 1 , wherein the paired electrodes are configured such that they are energized two by two, symmetrically opposite to each other with respect to a center of a motor.

5. The piezo actuator according to claim 1 , wherein the at least one electrode positioned at the bottom surface is used as a reference electrode.

6. The piezo actuator according to claim 1 , wherein the piezo actuator comprises four electrodes at the top surface and four electrodes at the bottom surface, the four electrodes at the bottom surface each covering substantially a same area as their corresponding electrode at the top surface, and

wherein corresponding electrodes are electrically connected and configured such that corresponding electrodes are polarized inversely.

7. The piezo actuator according to claim 1 , wherein the one or more central mounting holes are positioned in a knot of excited or excitable vibration modes.

8. The piezo actuator according to claim 1 , wherein the one or more mounting holes have a non-circular cross-section.

9. The piezo actuator according to claim 1 , wherein the at least one contact point is positioned at a corner edge of the circumference surface and/or wherein the piezo actuator has a substantially quadrangular shape.

10. The piezo actuator according to claim 1 , wherein the piezo actuator material comprises a balancing mass integrated in the piezo actuator material.

11. The piezo actuator according to claim 1 , wherein the piezo actuator is a piezo actuator plate having an average dimension in the plane with respect to thickness ratio larger than 1, for example larger than 2 to 1.

12. A motor for actuating a load, the motor comprising the piezo actuator according to claim 1 .

13. The motor according to claim 12 , wherein the piezo actuator is mounted using at least one mounting bar mounted in the at least one mounting hole.

14. The motor according to claim 13 , wherein the at least one mounting bar is obtained by a bar having at least one slit along at least part of its length as well as an insertable element in the at least one slit and pushing, when positioned in the slit, different parts of the at least one mounting bar radially outward.

15. The motor according to claim 12 , wherein the motor comprises a stack of piezo actuators for driving the same load, the stack of piezo actuators being stacked on top of each other.

16. The motor according to claim 12 , the motor furthermore comprising a driver for providing driving signals to the electrodes of the piezo actuator wherein the driver and the piezo actuator material are adapted for inducing in the piezo actuator material an in-plane bending mode and/or an in-plane expansion mode.