Power plants – Motor operated by expansion and/or contraction of a unit of... – Mass is a solid
Reexamination Certificate
1999-08-06
2001-08-14
Nguyen, Hoang (Department: 3748)
Power plants
Motor operated by expansion and/or contraction of a unit of...
Mass is a solid
Reexamination Certificate
active
06272857
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATION
Not Applicable
FIELD OF THE INVENTION
This invention relates to actuators. More specifically, the invention relates to a high repetition actuator having a large force-to-weight ratio with the use of shape memory alloy.
BACKGROUND OF THE INVENTION
Certain metals, often referred to as shape memory alloys, undergo a phase transformation upon a change in temperature. These alloys are characterized by memory of a mechanical configuration imposed upon the alloy during its austenite phase. At a lower temperature, the alloy's martensite phase allows the alloy to be relatively easily deformed into a particular shape. If, when in that particular shape, the alloy is heated to a temperature in which the alloy undergoes a phase transformation from martensite phase to austenite phase, the memory effect of the alloy is manifested by a return to the shape ordinarily imparted upon the alloy in its austenite phase.
Many different types of actuators have been proposed using shape memory alloys. A typical actuator construction is to use thin wires of the shape memory alloy. The actuation is caused by the elongation and contraction of the wires. Also, these actuators typically use resistive methods for heating the alloys and air/water convection methods to cool the alloys.
An example of an actuator using shape memory alloy is found in U.S. Pat. No. 5,396,769 to Brudniki. Brudniki shows two capstans mounted on a shaft which is supported in a framework with each capstan capable of rotating the shaft. Two separate lengths of shape memory wire are wrapped around each capstan to form a winding around that particular capstan. One wire is wrapped in a pre-stretched state and the other is not. When heated, one wire performs work in one direction, and when the other wire is heated the action is reversed.
Another example is found in U.S. Pat. No. 5,127,228 to Swenson. Swenson shows a rotary actuator using shape memory alloy. The actuator is made of two concentric tubular shape memory alloy members torsioned along their longitudinal axis with ends constrained relative to each other. One end of the actuator is constrained while the other is the output. A heater is located inside the inner shape memory alloy member, and a heater is located on the outside of the outer shape memory alloy member. The unconstrained end is caused to rotate between positions by applying current to the appropriate heater.
A mechanical actuator is taught by U.S. Pat. No. 4,553,393 to Ruoff. The mechanical actuator is constructed using a plurality of shape memory actuator elements in parallel to control the amount of actuating force. The actuating elements may vary in stiffness according to a binary relationship. The cooling time of the actuator elements may be employing Peltier junction cooling assemblies in the actuator.
Still another actuator using shape memory alloy is taught in U.S. Pat. No. 4,700,541 to Gabriel et al. Gabriel shows an electrically controlled shape memory alloy actuator made of a shape memory wire which is torsioned along its longitudinal axis and with its ends constrained against movement. A lever is attached to a wire at a desired point other than at a wire end. Electrical connections spaced along the wire define different sections along the wire. The wire and attached control element are made to rotate by selectively apply voltages to the different sections of the wire to heat the individual sections.
A problem, however, with most types of these actuators is that the frequency of operation is not very high. The frequency being the amount of cycles over a given time that the actuator performs, and a cycle defined as the total of the movement of the actuator from the initial state to an intermediary state and back to the first state. One cause for the low frequency of operation is the length of time required to cool the memory shape alloy.
Another problem associated with these types of actuators is that geometries other than thin wires of the shape memory alloy cause the electrical resistance of the shape memory alloy to be very low. As such, to heat the alloy in such shapes using resistive heating requires a large current. Thus, unless an external heater is employed, a large power system would likely be needed to supply the actuator with enough current to heat the alloy sufficiently to cause a phase transformation.
BRIEF SUMMARY OF THE INVENTION
It is therefore an object of the invention to provide an actuator using plates of shape memory alloy and a method of making same that can produce a very high frequency of operation.
It is another object of the invention to provide an actuator using shape memory alloy and method of making the same that has a large weight to force ratio.
It is yet another object of the invention to provide an actuator using shape memory alloy and method of making the same that uses a thermoelectric/thermoionic material to provide heating and cooling to the shape memory alloy. Also, the thermoelectric/thermoionic material is preferably capable of being operated using battery-supplied current.
It is a further object of the invention to provide an actuator using shape memory alloy and method of making the same that can be effectively used in mesoscopic systems with mesoscopic systems being approximately less than or equal to 5 CM.
It is still another object of the invention to provide an actuator using shape memory alloy and method of making the same that can be embedded within the structure of a mechanism, which enables an elimination of power transmission requirements.
These and other objects of the invention are achieved by the subject device which comprises a first leg, a second leg, and a heating/cooling device. The first and second legs are formed from shape memory alloy material and have respective fixed and opposing free ends. The fixed ends are fixed by a base. The second leg opposes the first leg and is connected to the first leg. The heating/cooling device is preferably disposed between the first and second legs and is thermally connected to the first and second legs.
The preferred heating/cooling device is a thermoelectric element. The thermoelectric element heats the first leg and cools the second leg upon application of a current in a first direction through the thermoelectric element. Also, the thermoelectric element cools the first leg and heats the second leg upon application of the current through the thermoelectric element in a second direction opposite the first direction. The first leg is trained in its austenite phase in the first position, and the second is trained in its austenite phase in the second position. The thermoelectric element can also be disposed adjacent respective stationary portions of the first and second legs. A method of manufacture and use of the actuator is also disclosed.
In a second embodiment of the invention, the actuator comprises legs, a connector, a spring, and a heating/cooling device. The legs are formed from shape memory alloy material and adapted to be connected to a base. The connector connects the legs and is connected to the spring. The spring is also adapted to be connected to the base. The heating/cooling device is thermally connected to each of the legs and has two modes of operation. The heating/cooling device in a first mode causes the legs to expand to a first position, the heating/cooling device in a second mode causes the legs to contract to a second position. By alternating the modes of operation, the actuator can be cycled between the first and second positions.
In a third embodiment of the invention, the actuator comprises first and second elements, a separator, and a heating cooling device. The elements are formed from shape memory alloy metal with each of the elements cyclable between first and second shapes. The separator is disposed between the first and second elements. The heating/cooling device is thermally connected to the elements and has two modes of operation. The heating/cooling device in a first mode heats the first element and cools the second element. The heating/coo
Nguyen Hoang
Senterfitt Akerman
UT-Battelle LLC
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