Actuator for an optical-mechanical scanner and a method of using the actuator
In an actuator for an optical mechanical scanner comprising a positioning element for an optical mirror wherein the positioning element is an electrically heatable flexible element consisting of a shape memory alloy having a Curie temperature and a transformation temperature, and wherein the flexible element is ferromagnetic when cold and can be bent in a first position by a magnet but is heated to exceed the Curie temperature and the transformation temperature so as to become paramagnetic whereby the flexible element becomes deformed in the opposite direction.
1. An actuator for an optical-mechanical scanner with an operating element for an optical mirror, said operating element being a flexible member consisting of a shape memory alloy having a Curie temperature and a transition temperature from a martensite to an austenite phase above an operating temperature wherein, above the Curie temperature and the transition temperature, said flexible member has a pre-imposed memory shape and paramagnetic properties, and below the Curie temperature, the flexible member has ferromagnetic properties, the flexible member being so formed that a return force into a previously imposed memory shape and a force generated by the magnetic field in opposite direction are effective on the flexible element.
2. An actuator according to claim 1 , wherein said operating element is one of a bending and torsion element.
3. An actuator according to claim 1 , wherein:
a) the flexible member comprises a U-shaped metal strip of an NiMnGa alloy having spaced legs whose first ends are mounted on said support structure in an electrically insulated manner and at whose free joined ends a mirror is disposed for a beam deflection,
b) electrical connectors are attached to the free ends of the legs of the flexible member for electrically heating the flexible element directly by passing an electric current therethrough, and
c) permanent magnet is arranged on said support structure opposite the end of said legs of said flexible member for generating a magnetic field.
4. An actuator according to claim 3 , wherein said support structure is a U-shaped metal structure comprising one of a bent structure and a structure assembled of several components, said metal structure having two parallel legs, one supporting said flexible member and the other supporting said permanent magnet.
5. An actuator according to claim 4 , wherein
a) said support structure consists of a soft magnetic material and forms with the flexible member and the permanent magnet a magnetic circuit, and
b) an electric insulation is provided between the flexible member and the support structure.
6. An actuator according to claim 1 , wherein said Curie temperature and said transition temperature are in a temperature window of 30° C.
7. An actuator according to claim 1 , wherein said shape memory alloy consists of 50–54 at % Ni, 23–25 at % Mn and 21–25 at % Ga.