Shape-memory alloy micro-actuator

• US 5,061,914 A
• Filed: 06/27/1989
• Issued: 10/29/1991
• Est. Priority Date: 06/27/1989
• Status: Expired due to Term

• Current Assignee: TiNi Alloy Company
• Original Assignee: TiNi Alloy Company
• Inventors: Busch, John D., Johnson, Alfred D.
• Primary Examiner(s): Broome, H.
• Application Number:
  US07/373,030
• Time in Patent Office: 854 Days
• Field of Search: 337/140, 60/527, 60/528, 427/295
• US Class Current: 337/140
• CPC Class Codes: F03G 7/065 using a shape memory element
• CPC Class Codes: F16F 2224/0258 Shape-memory metals, e.g. Ni-Ti alloys
• CPC Class Codes: H01H 1/0036 Switches making use of microelectromechanical systems [MEMS] for electromagnetic relays H01H50/005; for electrostatic relays H01H59/0009
• CPC Class Codes: H01H 2001/0042 Bistable switches, i.e. having two stable positions requiring only actuating energy for switching between them, e.g. with snap membrane or by permanent magnet
• CPC Class Codes: H01H 2037/008 Micromechanical switches operated thermally
• CPC Class Codes: H01H 2061/0122 Two SMA actuators, e.g. one for closing or resetting contacts and one for opening them
• CPC Class Codes: H01H 37/323 making use of shape memory materials in thermal relays H01H61/0107; release mechanism H01H71/145; treatment of SMF alloys C22F1/006; for control of temperature G05D23/024

Abstract

A method of producing an integral piece of thermo-sensitive material, which is responsive to a shift in temperature from below to above a phase transformation temperature range to alter the material'"'"'s condition to a shape-memory condition and move from one position to another. The method is characterized by depositing a thin film of shape-memory material, such as Nickel titanium (Ni-Ti) onto a substrate by vacuum deposition process such that the alloy exhibits an amorphous non-crystalline structure. The coated substrate is then annealed in a vacuum or in the presence of an inert atmosphere at a selected temperature, time and cool down rate to produce an ordered, partially disordered or fully disordered BCC structure such that the alloy undergoes thermoelastic, martinsetic phase transformation in response to alteration in temperature to pass from a martinsetic phase when at a temperature below a phase transformation range and capable of a high level of recoverable strain to a parent austenitic phase in a memory shape when at a temperature above the phase transformation range.

Also disclosed are actuator devices employing "shape-memory material" actuators that deform from a set shape toward an original shape when subjected to a critical temperature level after having been initially deformed from the original shape into the set shape while at a lower temperature. The actuators are mechanically coupled to one or more movable elements such that the temperature-induce deformation of the actuators exerts a force or generates a motion of the mechanical element(s).

Claims

1. A mechanical device comprising:

a support element;

a movable element displaceable with respect to said support element between a first position and a second position;

and a temperature-sensitive actuating element linking said support element to said movable element and displaceable between a first position wherein said movable element is in said first position thereof and a second position wherein said movable element is in said second position thereof;

said actuating element comprising a film of a shape-memory alloy having a phase transformation temperature range below which said alloy exhibits a martensitic crystal structure and is in a ductile condition and above which said alloy exhibits a parent austenitic crystal structure and approximates its undistorted shape;

and means for positioning said actuating element in said first position when said alloy is in a ductile condition;

said actuating element being responsive to a shift in its temperature from below to above said phase transformation temperature range to alter its condition to a parent austenitic condition and thereby move from said first position to said second position.

2. The mechanical device of claim 1 wherein said actuating element is less than 50 microns thick.

3. The mechanical device of claim 1 wherein said alloy comprises an ordered, partially disordered or fully disordered austenitic BCC crystal structure when heated above said phase transformation temperature range and exhibiting characteristics of mechanical shape-memory.

4. A two-state mechanical device comprising:

support means;

a movable element displaceable with respect to said support means between a first position and a second position;

a pair of temperature-sensitive actuating elements linking said support means to said movable element and displaceable between a first position wherein said movable element is in said first position thereof and a second position wherein said movable element is in second position thereof;

said temperature-sensitive actuating elements each comprising a film of shape-memory alloy which comprises an austenitic crystal structure above a phase transformation temperature range and exhibits characteristics of mechanical shape-memory due to thermoelastic, martensitic phase transformation in response to a shift in temperature from below to above said phase transformation temperature range to alter its condition and thereby move between said first and second positions;

said temperature-sensitive actuating elements being arranged such that when one of said actuating elements is in a parent austenitic condition and the other of said actuating elements is in ductile condition, said actuating elements assume said first position, and arranged such that reversing said conditions said actuating elements will assume said second position displaced from said first position;

control means for selectively heating said actuating elements to control the amount of shape change thereby controlling the position of said movable elements.

5. The mechanical device of claim 4 wherein said actuating elements are both in a ductile condition in a third position of said movable element.

6. The mechanical device of claim 4 wherein said alloy comprises an ordered, partially disordered or fully disordered austenitic BCC crystal structure when heated above said phase transformation temperature range and exhibiting characteristics of mechanical shape-memory.

7. A mechanical device having an actuating element linked to other elements for relative movement thereof, said actuating element being comprised of a shape-memory alloy responsive to temperature change to produce said relative movement, wherein said actuating element comprises a film of a shape-memory alloy having a phase transformation temperature range above which said alloy exhibits an austenitic crystal structure.

8. A method for producing a thin film exhibiting characteristics of mechanical shape-memory comprising:

depositing a film of shape-memory alloy onto a substrate by means of a vacuum deposition process such that said alloy, either after annealing in a vacuum or in the presence of an inert atmosphere at a selected temperature, time and cool down rate, or after deposition on a heated substrate and cooling at a selected time and cool down rate,

exhibits an ordered, partially disordered or fully disordered austenitic BCC crystal structure, said alloy undergoing thermoelastic, martensitic phase transformation in response to alterations in temperature to pass from a martensitic phase when at a temperature below a phase transformation temperature range and capable of a high level of recoverable strain to a parent austenitic phase and a memory shape when at a temperature above the phase transformation range.

9. A method for producing a two-state mechanical device comprising:

etching side one of a substrate whereby windows covered by thin substrate membranes are created in the substrate;

depositing at least two film actuator elements of shape-memory alloy onto side two of said substrate by means of a vacuum deposition process such that said alloy exhibits an amorphous crystalline structure;

applying a force through a medium such as inert gas pressure to said substrate such that said substrate and said alloy films are deformed to a predetermined shape;

annealing said alloy films in a vacuum or in the presence of an inert atmosphere at a selected temperature, time and cool down rate to produce an ordered, partially disordered or fully disordered austenitic BCC crystal structure when heated above a phase transformation temperature range and exhibiting characteristics of mechanical shape-memory;

relieving said pressure such that said substrate membrane imposes a strain on said alloy films resulting in plastic deformation of one or both of said films at a temperature below said phase transformation temperature range; and

etching the periphery of said thin substrate membranes of said substrate such that an island of substrate membrane is operably connected to said original substrate by said alloy films.