Automatic takeup and overload protection device for shape memory metal actuator

• US 4,567,549 A
• Filed: 02/21/1985
• Issued: 01/28/1986
• Est. Priority Date: 02/21/1985
• Status: Expired due to Fees

• Current Assignee: Blazer International Corporation
• Original Assignee: Blazer International Corporation
• Inventors: Lemme, Charles D.
• Primary Examiner(s): Feinberg, Craig R.
• Assistant Examiner(s): Okonsky, David A.
• Application Number:
  US06/703,895
• Time in Patent Office: 341 Days
• Field of Search: 337/140, 60/527, 60/528, 60/529, 362/279, 362/325, 362/321, 362/274, 362/277
• US Class Current: 362/279
• CPC Class Codes: F03G 7/065 using a shape memory element

Abstract

A device to provide overload protection for a shape memory metal (SMM) wire of an SMM-type actuator and to automatically compensate for cyclic creep and maintain the tension of the SMM wire. During normal operation, a restraining drum, in cooperation with a biasing spring, maintains the position of one end of the SMM wire so that the other end of the SMM wire can move an actuator. Under excessive loads, the restraining drum permits the first end of the SMM wire to move, thereby reducing the tension and preventing damage to the SMM actuator. When the excessive load is removed, the restraining drum permits the first end of the SMM wire to move under the influence of the biasing spring to its original position. By permitting the first end of the SMM wire to move in dependence upon the tension on the SMM wire, the device automatically takes up any slack caused by cyclic creep and maintains proper tension of the SMM wire.

Claims

1. An automatic takeup and overload protection device for a shape memory metal actuator for the type comprising an actuator mechanism movable between first and second positions, said device comprising:

a biasing element;

a linkage element defining first and second ends and comprising at least one section of shape memory metal material;

said first end fastened to said biasing element and said second end fastened to said actuator mechanism;

said section of shape memory metal material operating to move said actuator mechanism to said second position when said shape memory metal material is placed at a selected temperature; and

a restraining element comprising a friction generating surface in physical contact with said linkage element;

said surface cooperating with said linkage element to generate frictional forces of sufficient magnitude to prevent said first end of said linkage element from moving with respect to said surface during movement of said actuator mechanism to said second position and to protect said linkage element from excessive tension by allowing said first end of said linkage element to move with respect to said surface when excessive forces are applied to said linkage element by said actuator mechanism;

said surface further cooperating with said linkage element to allow said biasing element to move said first end of said linkage element with respect to said surface to substantially maintain a minimum tension of said linkage element between said surface and said actuator mechanism.

2. The device of claim 1 wherein said biasing element comprises a coil spring.

3. The device of claim 1 wherein said section of shape memory metal material comprising a Nitinol wire.

4. The device of claim 1 wherein said restraining element comprises a drum.

5. The device of claim 1 wherein said linkage element is wrapped about said restraining element by at least 180°

.

6. An automatic takeup and overload protection device for a shape memory metal actuator of the type comprising an actuator mechanism capable of traveling between first and second positions, said device comprising:

a biasing element;

a restraining drum; and

a linkage element defining a first end and a second end and comprising at least one section of shape memory metal material;

said first end securely fastened to said biasing element and said second end securely fastened to said actuator mechanism;

said linkage element wrapped about said restraining drum;

said section of shape memory metal material operating to move said actuator mechanism to said second position when said shape memory metal material is brought to a selected temperature;

said restraining drum cooperating with said linkage element to generate frictional forces of magnitude dependent on the tension of said linkage element;

said biasing element, restraining drum and actuator mechanism cooperating to produce tension in said linkage element sufficient to generate frictional forces to prevent said first end of said linkage element from moving with respect to said restraining drum during normal movement of said actuator mechanism to said second position and to protect said linkage element from excessive tension by allowing said first end of said linkage element to move with respect to said restraining drum in response to excessive tension in the linkage element;

said restraining drum further cooperating with said linkage element to allow said biasing element to move said first end of said linkage element with respect to said restraining drum to substantially maintain a minimum tension of said linkage element between said surface and said actuator mechanism.

7. The invention of claim 6 wherein said biasing element comprises a coil spring.

8. The invention of claim 6 wherein said section of shape memory metal material comprises a Nitinol wire.

9. The invention of claim 6 wherein said linkage element is wrapped about said drum by at least 180°

.

10. In a louvered lamp assembly of the type comprising a plurality of louvers and an actuator mechanism capable of moving said louvers between a first position and a second position, the improvement comprising:

a coil spring mounted to the louvered lamp assembly;

a drum mounted to the louvered lamp assembly; and

a length of shape memory metal material wrapped around the drum with a first end fastened to said spring and a second end fastened to said actuator mechanism;

said shape memory metal material operating to move said louvers to said second position when heated;

said drum cooperating with said shape memory metal material to generate frictional forces of sufficient magnitude to prevent sid first end of said shape memory metal material from moving with respect to said drum during normal movement of said louvers to said second position and to protect said shape memory metal material from excessive stress by allowing said first end of said shape memory metal material to move with respect to said restraining element in response to excessive tension in the shape memory metal material;

said restraining element further cooperating with said shape memory metal material to allow said spring to move said first end of said shape memory metal material with respect to said restraining element to substantially maintain a minimum tension of said shape memory metal material between said restraining element and said actuator mechanism.