Actuator device and method for setting a position of a linearly movable element

1. A hydraulic actuator device for producing a linear movement, the device comprising:

a first piston element disposed in a first working chamber;

a second piston element disposed in a second working chamber;

the first and second working chambers having respective volumes which are changed by movement of the first and second piston elements, respectively;

two oppositely oriented check valves fluidically connecting the first and second working chambers along separate fluid lines, the oppositely oriented check valves each associated with a different opening force;

wherein an isolated reservoir is only directly connected to the first working chamber by a third fluid line which includes a single restrictor element; wherein the restrictor element allows fluid flow in to the reservoir and out of the reservoir to the second working chamber via one of the two oppositely oriented check valves; and

a piezoelectric actuator to exert an input force on the first piston element, and thereby transmit an output force on the second piston through the two fluid lines.

2. The actuator device as claimed in claim 1 , wherein the first and second working chambers are formed by respective cylinders, in which the first and second pistons are respectively movably accommodated.

3. The actuator device as claimed in claim 1 , wherein the first and second working chambers are formed by respective bellows.

4. The actuator device as claimed in claim 1 , wherein the second piston element has a larger cross sectional area than the first piston element.

5. A method for setting a position of a linearly movable element, the method comprising:

exerting a force on a first piston element disposed in a first working chamber by actuating a piezoelectric actuator;

changing a volume of the first working chamber by a movement of the first piston element in response to the force exerted on the first piston element; and

transferring a working fluid between the first working chamber and a second working chamber assigned to the second piston element through two separate fluid lines, each fluid line including a check valve, the two check valves oppositely oriented and associated with a different opening force;

wherein to produce a movement in a predetermined direction, the piezoelectric actuator is moved at a first speed in the predetermined direction in a first phase of movement resulting in a pressure produced in the first working chamber by the first phase of movement overcoming a closing force of a first check valve fluidically connecting the first and second working chambers in the predetermined direction of movement,

wherein, in a second phase of movement, the piezoelectric actuator is moved at a second speed slower than the first speed counter to the predetermined direction resulting in a pressure produced in the first working chamber by the second phase of movement does not overcome a closing force of a second check valve fluidically connecting the first and second working chambers counter to the predetermined direction of movement; and

exchanging the working fluid between the first working chamber and an isolated reservoir through a single restrictor element to compensate for a change in volume in the first working chamber during the second phase of movement; wherein the isolated reservoir is only directly connected to the first working chamber by a third fluid line which includes the single restrictor element; wherein the restrictor element allows fluid flow in to the reservoir and out of the reservoir to the second working chamber via one of the two oppositely oriented check valves.

6. The method as claimed in claim 5 , wherein the first and second phases of movement are repeated alternately until the second piston element is in a predetermined setpoint position.

7. A method for setting a position of a linearly movable element, comprising:

exerting a force on a first piston element by a piezoelectric actuator;

changing a volume of a first working chamber assigned to the first piston element by the force exerted on the first piston element; and

transmitting the force exerted on the first piston element, to a second piston element by transferring fluid between the first working chamber and a second working chamber assigned to the second piston element, and

exchanging the working fluid between the first working chamber and an isolated reservoir through a single restrictor element in communication only with the first working chamber to compensate for a change in volume in the first working; wherein the isolated reservoir is only directly connected to the first working chamber by a third fluid line which includes the single restrictor element; wherein the restrictor element allows fluid flow in to the reservoir and out of the reservoir to the second working chamber via one of the two oppositely oriented check valves; wherein

decreasing the volume of the first working chamber with the piezoelectric actuator moving at a first speed overcomes a closing force of a first check valve allowing fluid to move from the first working chamber to the second working chamber,

increasing the volume of the first working chamber with the piezoelectric actuator moving at the first speed overcomes a closing force of a second check valve allowing fluid to move from the second working chamber to the first working chamber,

increasing the volume of the first working chamber at a second speed slower than the first speed moves fluid to the first working chamber from the reservoir, and

decreasing the volume of the first working chamber at the second speed moves fluid from the first working chamber to the reservoir.

8. The method as claimed in claim 7 , wherein to move the second piston element in a first direction, the volume of the first working chamber is repetitively increased at the first speed then decreased at the second speed, and to move the second piston element in a second direction opposite the first direction, the volume of the first working chamber is repetitively increased at the second speed then decreased at the first speed.

9. The method as claimed in claim 7 , wherein the second piston element has a larger cross sectional area than the first piston element.