Title of Invention

"A NOVEL ACTUATOR DEVICE FOR CONTROLLING SWIVELING MOVEMENT OF AN OBJECT OR MECHNICAL PART".

Abstract A novel actuator device for controlling swiveling movement of a mechanical part, comprising a mechanical part (1) fixed onto a hinged mounted plate(7) in a housing (2), one edge(6) of the said movable plate(7) being connected to one end of one or more shape memory alloy actuating element(s) (5) such as herein described, the other edge(6A) of the said plate(7) being connected to one end of one or more super-elastic alloy biasing and sensory element(s) (8) such as herein described, the said super-elastic biasing and sensory element(s) (8) being anchored at the other end(s) to a body(ll), the said shape memory alloy actuating element(s)(5) and the super-elastic alloy biasing and sensory elements(s)(8) being provided at their ends with electrical connections through bus-bars (10,12) and (9,13) .
Full Text This invention relates to a device for effecting and controlling swiveling movement of an object or part. The present invention particularly relates to a novel actuator device using shape memory alloys and super-elastic shape memory alloys for effecting and controlling swiveling movement of an object or part.
The present invention is useful for holding, imparting and controlling rotary/swiveling movement of an object or part, such as a baffle, the rotating arm of a pulley, a louver, a robotic arm, an aircraft control surface such as a flap and such other objects or devices.
The novel actuator device of the present invention has both sensory and actuation features and has a much lower weight as compared to hitherto known rotary actuators. Further, since it has a low resisting force biasing characteristics, the device of the present invention is particularly efficient in effecting and controlling swiveling movement of objects or parts.
The term shape memory alloy refers to a class of materials which remember the past state or condition. Hence, in the case of a shape memory alloy when external stimulus such as heat or stress is applied, physical change does occur due to this as in the case of other materials, but on removal of the external stimulus the shape memory alloy material reverts back to the original shape and state.
In the present invention the actuation is imparted by a shape memory alloy actuator and is based on thermally induced shape memory effect in the shape memory alloy. The sensing feature is based on the stress induced
transformation which strains the material when the stress is applied and takes the material back to the original condition on removal of stress.
Conventional rotary arm actuators which give swiveling movements to an object or part based on hydraulic or electric actuators have been used in several areas such as robotics and other automated systems in automobile and aircraft industry. One such conventional rotary arm actuator is shown in figure 1 of the drawings accompanying this specification, wherein the movement of the rotary part is by a conventional hydraulic actuator. Figure 1 shows a rotary arm (1) mounted on a hinged / movably mounted plate (7) in housing (2) and the said movable plate (7) being connected to a conventional hydraulic actuator (3) which is fixed to a rigid part (11). The linear movement of the actuator (3) is transmitted via the hinged / movably mounted plate in housing (2) to impart a rotary motion to the arm (1). These conventional systems using hydraulic and electric actuators, suffer from inherent drawbacks such as low power output to weight ratios, absence of sensory function, the need for frequent maintenance and are not corrosion resistant.
Presently Ni-Ti based shape memory alloy actuators are known and can be used in place of the conventional hydraulic and electric actuators. These Ni-Ti based actuators are much simpler in operation as compared to the conventional hydraulic and electric actuators and are characterized by high power to weight ratios, improved corrosion resistance and strength.
Rotary actuator device is an example using nickel-titanium shape memory alloy. Reference may be made to the book: Engineering Aspects of Shape
Memory Alloys by T.W.Duerig, K.N.Melton, D.Stockel, C.M.Wayman, published by Butterworth - Hieneman, pages 338-340. In this device the nickel-titanium wire is connected to one side of a rotary arm, while the other side is connected by a conventional biasing spring. The change in temperature in the Ni-Ti shape memory alloy actuating element which is obtained by electrical energization, causes the forward and backward rotational movement of the rotary arm. This presently known rotary shape memory alloy actuator with thermally activated shape memory alloy wire on one side is biased by a conventional helical steel spring whose force deflection characteristics are linear and therefore the resisting force increases linearly with the movement. One such presently known rotary arm actuator is shown in figure 2 of the drawings accompanying this specification wherein the movement of the rotary part is by a shape memory alloy actuator and the biasing element is a conventional helical steel spring. In figure 2 is shown a rotary arm (1) mounted on a hinged / movably mounted plate (7) in housing (2). The said movable plate (7) being connected at one end (6) to one end of a shape memory alloy actuating element (5) and the other end of the plate (7) being connected to one end of a conventional helical steel spring biasing element (4). Both the actuating element (5) and the spring (4) being anchored at the other end(s) to rigid part (11). The shape memory alloy actuating element (5) being provided at the ends with electrical connections through bus-bars (10,12). The conventional steel spring does not perform any sensory function and therefore other devices to sense the rotational movement are required. The drawbacks of this device is that it offers a linear increase in resisting force as the arm rotates thereby loading the shape memory alloy actuator. It cannot perform any sensory function and therefore a separate sensing unit such as potentiometer or linear variable
differential transformer (LVDT) is required to sense the rotary movement. Further, due to the bulky helical spring the power output to weight ratio though improved is still low and needs to be improved.
Another reference may be made to the article titled " Shape Memory Alloy Consortium" part of SPIE conference on Industrial & Commercial Applications of Smart Structures Technologies - New Port Beach, California, March 1999, SPIE Vol. 3674, in which a shape memory alloy based actuator concept has been described for obtaining the rotary movement of an object. In this concept a nickel titanium shape memory alloy torque tube is used as an actuating element and a super elastic alloy tube is used as a biasing return spring element.
The drawbacks of the hitherto known prior art as given above are:
i) Mode of deformation is shear in which does not allow generation
of large forces, ii) The sensing feature has not been exploited and hence it does not
obviate the need for a separate sensing device.
On making a patents search it is seen that U.S. patents no.06129181 and no.6069419 have some relevance to the present invention.
In U.S. patent no.06129181, titled "Constant force spring actuator" there is described an actuator which can provide the rotary motion. The draw backs of this invention are:
i) That there is no sensing device to indicate the degree of rotation. Therefore, additional sensing devices are required to obtain the
value of the amount of rotation, ii) That the device cannot provide a variable force.
In U.S. patent no.6069419 titled "Micro-actuator assembly", there is described an actuator which can provide rotary motion. The drawbacks of this invention are:
i) The device cannot provide the angle of rotation as there is no sensing device to indicate the degree of rotation. Therefore, additional sensing devices are required to obtain the value of the amount of rotation, ii) There is no low resisting force biasing element.
In view of the prior art rotary actuator devices known at present, as detailed above, there is a definite need for developing an actuator device which overcomes the above noted drawbacks.
The main objective of the present invention is to provide a device for effecting and controlling swiveling movement of an object or part, which obviates the drawbacks of the hitherto known prior art as detailed above.
Another objective of the present invention is to provide a novel actuator device having sensory function which will facilitate superior position controllability of the swiveling object.
Yet another objective of the present invention is to provide a novel actuator device having both biasing and sensory functions using the same element.
Still another objective of the present invention is to provide a non-linear biasing resistance force which will reduce the load due to biasing on the shape memory alloy actuator device.
A further objective of the present invention is to provide a novel rotary actuator device having improved power output to weight ratio in comparison to hitherto known devices.
The present invention relates to a novel device using shape memory and super-elastic alloys for effecting and controlling the swiveling movement of an object or a part. The novelty of the present invention lies in achieving both low resisting bias force and sensing functions in a single unit of the super-elastic element. The super-elastic element is used as a biasing element opposing a shape memory actuating element. This device achieves the low resistance force biasing exploiting the non-linear force-deflection material property of the super-elastic alloy while at the same time performing the function as a sensor. This enables superior position controllability of the swiveling movement of an object or a part. Provides improved power output to weight ratio. It is amenable for interfacing with computer controls. And eliminates the need for additional sensory devices to measure the movement.
The details of an embodiment of the novel actuator device of the present
invention is shown in figures 3, 4 and 5 of the drawings accompanying this
specification.
Figure 3 shows the side view of the rotary part / arm actuated by a shape
memory element and biased by a super-elastic element.
Figure 4 shows the plan view of the drawing shown in figure 3.
Figure 5 shows the extreme position (15) of the rotary part / arm shown in figure 3.
In figures 3, 4 and 5 are shown a rotary part / arm (1) mounted on a hinged / movably mounted plate / shaft (7) in housing (2). The said movable plate / shaft (7) being connected at one edge (6) to one or more shape memory alloy actuating element(s) (5) and the other edge of the plate / shaft (7) being connected to one or more super-elastic alloy biasing and sensory elements) (8). Both the actuating element(s) (5) and the biasing and sensory element(s) (8) being anchored to rigid part (11). The shape memory alloy actuating element(s) (5) and the super-elastic alloy biasing and sensory element(s) (8) being provided at the ends with electrical connections through bus-bars (10,12) and (9,13) respectively, so as to induce electrical resistive heating in actuating element(s) (5) and so as to sufficiently sensitise biasing and sensory element(s) (8) for performing sensory functions, resulting in the required controlled movement of the part / arm (1). The extreme positions of the rotary part / arm (1) are shown as (14) and (15).
Accordingly, the present invention provides a device for effecting and controlling swiveling movement of an object or part, which comprises an object / part (1) fixed onto a hinged / movably mounted plate / shaft (7) in housing (2), the said movable plate / shaft (7) being connected at one edge (6) to one end of one or more shape memory alloy actuating element(s) (5) and the other edge of the plate / shaft (7) being connected to one end of one or more super-elastic alloy biasing and sensory element(s) (8), both the actuating element(s) (5) and the biasing and sensory element(s) (8) being anchored at the other end(s) to a rigid part (11), the said shape memory alloy
actuating element(s) (5) and the super-elastic alloy biasing and sensory elements) (8) being provided at the extremities with electrical connections through bus-bars (10,12) and (9,13) respectively.
In an embodiment of the present invention the shape memory alloy is such as Ni-Ti based alloy, Cu-Zn based alloy or any other alloy having property of shape memory.
In another embodiment of the present invention the super-elastic alloy is such as Ni-Ti based alloy, Cu-Zn based alloy or any other alloy having property of super-elasticity.
In yet another embodiment of the present invention the shape memory alloy actuating element(s) is in the deformed martensite state in the initial neutral position.
In still another embodiment of the present invention the super-elastic alloy biasing and sensory element(s) is in the austenite state in the initial neutral position.
In still yet another embodiment of the present invention the shape memory alloy actuating element(s) is energized by heating means such as electrical, energy from a natural source such as from a hot air stream, solar energy.
In a further embodiment of the present invention the super-elastic alloy biasing and sensory element(s) is energized by passing a constant current.
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In one more embodiment of the present invention the movement of the object or part is such as rotary or any other related movement.
In still one more embodiment of the present invention the actuating elements and biasing and sensory elements are of any geometrical shape such as foils, strips, wires or bars.
In the novel actuator device of the present invention the swiveling, rotary or any other related movement is obtained based on the contraction of the shape memory actuating element when it is heat energized by electrical heating or by other means. The biasing element is the superelastic element which offers a low resisting biasing force while at the same time performing the function of a position sensor. The sensory performance is realized by continuously passing a small constant current and monitoring the voltage changes. The magnitude of the voltage is an indication of the strain in the wire and therefore the position of the element. It also enables superior position controllability of the swiveling object or part and is amenable for interfacing with computer controls. Additional sensory devices to measure the movement are completely eliminated.
The actuation of the shape memory alloy actuator elements is based on the thermally induced shape memory effect in shape memory alloy. The term shape memory alloys refer to a class of materials which remember their past. In these shape memory alloys large strains upto about 6% is fully recoverable after heating. The shape memory alloy can undergo large deformations in the cold or the martensite condition and spontaneously recover its original shape when transformed by heating to the hot or the
austenite condition. If fully or partially constrained the shape memory alloy can generate large forces while still undergoing some deformation. The principle of actuation of the shape memory alloy actuator is based on the above phenomena.
The deformation of the super-elastic shape memory alloy biasing and sensing element is based on a distinctly different phenomena in shape memory alloys, where the transformation is stress induced. The super-elasticity in shape memory alloys refers to the property wherein these alloys when subjected to stress can undergo a large elastic strain which can be as high as 6% and then almost completely recover the strain when the stress is removed. In this transformation the material transforms from austenite to the martensite at a constant temperature when the stress reaches a critical level. There is a large deformation while transforming from austenite to stress induced martensite at a constant temperature due to loading which is almost completely recovered when the load is removed. This transformation is completely dependent on stress only. If a small electrical input current is continuously supplied to this super elastic biasing and sensing element it gives an output signal which is directly proportional to the deformation in the super-elastic element both during loading and during unloading. Thus the super-elastic shape memory alloy element has an inbuilt sensory function.
The novelty of the present invention lies in achieving actuation, low resistance biasing and sensory functions thereby effecting and controlling swiveling movement with superior position controllability of the swiveling object. This has been made possible by the non-obvious inventive step of providing a shape memory alloy actuating element in conjunction with a
combined biasing and sensing element in the form of a single unit essentially consisting of super-elastic alloy wire which provides low resisting bias force and sensing functions: This super-elastic alloy wire functions both as a sensing and biasing element opposing the shape memory alloy actuating element. Thus the device of the present invention achieves low resistance force biasing exploiting the non-linear force-deflection material property of the super-elastic alloy wire while at the same time performing the function of a sensor. It also enables superior position controllability of the swiveling object and is amenable to interfacing with computer controls.
The following example is given by way of illustration of the novel device of the present invention and therefore should not be construed to limit the scope of the present invention.
Example -1
This example is described with reference to an embodiment of the novel device of the present invention as depicted in figures 3, 4 and 5 of the drawings. Figures 3 and 5 represent the side view of the device in two extreme positions (14) and (15) respectively, and figure 4 shows the top view of the device. The device comprised of:
A movable flap-arm (1) having length 200mm and width of 50mm is fixed onto a steel shaft (7) mounted in housing (2) such that it swivels about the central axis of the housing (2). An array of 4 nos. of Ni-Ti shape memory alloy actuating elements (5) of length 552 and diameter 0.5mm elements anchored on to the teeth on one edge (6) of the steel shaft (7). These 4 actuating elements were biased by an array of 2 Ni-Ti super-elastic alloy
elements (8) of length 300mm and diameter 0.15mm. The array (8) of super-elastic alloy elements were anchored to the teeth on the other edge of the shaft (7). Both the array of elements (5) and (8) were anchored end to the fixed part (11) as shown in the figures. The elements in array (5) were in the deformed martensite state and the elements in array (8) were in the austenite state before the start of the experiment and the flap-arm was in neutral position. The array (8) was biased using a small electrical current of 20 mA through the electrical connections provided by bus-bars (9) & (13) and a voltmeter was connected across the bus-bars to monitor the voltage. The electrical connections to the array (5) to energize the shape memory alloy was made through bus-bars (10) & (12). When the elements in array (5) were energized due to passage of current, they contracted and simultaneously the stress in this array increased. At the same time the elements in array (8) elongated to match the contraction of the elements in array (5). The force developed in array (5) when it was energized created a rotating moment which overcame the resisting moment offered by the low resisting biasing force of array (8) and therefore there was a swiveling movement of the shaft (7) and consequently of the flap-arm (1). At this point the voltage across bus-bars (9) and (13) peaked, thus sensing the extreme position of the flap-arm, which was 60 degrees from the neutral position.
In the novel device of the present invention, there is a stress build up in the elements in array (8) and a critical stress is reached due to which the austenite starts deforming to the martensite, resulting in large straining, giving rise to the stress induced martensite at a constant value of the critical stress. When the flap-arm (1) moves to the extreme position the contraction in array (5) due to energizing of shape memory alloy actuating elements (5)
is complete. At this position the deformation or elongation in array (8) is maximum and the measured value of sensing voltage signal gives the maximum value indicating the maximum strain. This way the device can be used as a sensory unit also. When the array (5) is de-energized it starts elongating and moves back to the neutral point. So also the stress in the super-elastic array (8) decreases and it regains its initial length. In the experimental set-up used in the example, the total angle of swivel is about 60 degrees from the neutral position, however this should not be construed as a limit for such a device.
In the hitherto known prior art the mode of deformation is shear in which it is not possible to generate large forces. In the present invention the mode of deformation is tension which allows large forces to be generated.
In the hitherto known prior art the sensing feature has not been exploited, thus the device cannot provide the angle of rotation. In the present invention the same super elastic element is used both for sensing and biasing in the tensile mode. This obviates the need for a separate sensing device.
In the hitherto known prior art the device cannot provide a variable force, as there is no low resisting force biasing element. In the present invention the biasing element offers a low resistance biasing force.
The main advantages of the novel device of the present invention are:
1. Is efficient since it has a low resisting force biasing characteristics.
2. Possesses in built sensory features.
3. Is comparatively of much lower weight and thus has improved power
output to weight ratio.
4. The device is particularly efficient in effecting swiveling movement
of objects.
5. Eliminates additional devices to measure movements.
6. It is amenable for interfacing with computer controls.








We claim:
1. A device for effecting and controlling swiveling movement of an object or
part, which comprises an object / part (1) fixed onto a hinged / movably
mounted plate / shaft (7) in housing (2), the said movable plate / shaft (7)
being connected at one edge (6) to one end of one or more shape memory
alloy actuating element(s) (5) and the other edge of the plate / shaft (7) being
connected to one end of one or more super-elastic alloy biasing and sensory
element(s) (8), both the actuating element(s) (5) and the biasing and sensory
element(s) (8) being anchored at the other end(s) to a rigid part (11), the said
shape memory alloy actuating element(s) (5) and the super-elastic alloy
biasing and sensory element(s) (8) being provided at the extremities with
electrical connections through bus-bars (10,12) and (9,1.3) respectively.
2. A device as claimed in claim 1, wherein the shape memory alloy is such
as Ni-Ti based alloy, Cu-Zn based alloy or any other alloy having property
of shape memory.
3. A device as claimed in claim 1-2, wherein the super-elastic alloy is such
as Ni-Ti based alloy, Cu-Zn based alloy or any other alloy having property
of super-elasticity.
4. A device as claimed in claim 1-3, wherein the shape memory alloy
actuating element(s) is in the deformed martensite state in the initial neutral
position.
5. A device as claimed in claim 1-4, wherein the super-elastic alloy biasing
and sensory element(s) is in the austenite state in the initial neutral position.
6. A device as claimed in claim 1-5, wherein the shape memory alloy
actuating element(s) is energized by heating means such as electrical, energy
from a natural source such as from a hot air stream, solar energy.
7. A device as claimed in claim 1-6, wherein the super-elastic alloy biasing
and sensory element(s) is energized by passing a constant current.
8. A device as claimed in claim 1-7, wherein the movement of the object or
part is such as rotary or any other related movement.
9. A novel device as claimed in claim 1-8, wherein the actuating elements
and biasing and sensory elements are of any geometrical shape such as foils,
strips, wires or bars.
10. A device for effecting and controlling swiveling movement of an
object or part substantially as herein described with reference to the
example and figures 3, 4 & 5 of the drawings accompanying this
specification.

Documents:

1063-del-2002-abstract.pdf

1063-del-2002-claims.pdf

1063-del-2002-corrspondence-others.pdf

1063-del-2002-corrspondence-po.pdf

1063-del-2002-description (complete).pdf

1063-del-2002-drawings.pdf

1063-del-2002-form-1.pdf

1063-del-2002-form-19.pdf

1063-del-2002-form-2.pdf

1063-del-2002-form-3.pdf


Patent Number 212059
Indian Patent Application Number 1063/DEL/2002
PG Journal Number 50/2007
Publication Date 14-Dec-2007
Grant Date 14-Nov-2007
Date of Filing 22-Oct-2002
Name of Patentee COUNCIL OF SCIENTIFIC AND INDUSTRIAL RESEARCH
Applicant Address RAFI MARG, NEW DELHI-110 001, INDIA.
Inventors:
# Inventor's Name Inventor's Address
1 GIDNAHALLI NARAYANA REDDY DAYANANDA NATIONAL AEROSPACE LABORATORIES, BANGALORE-560 017, INDIA.
2 VENKATANARASIMHAIYA SHANKAR NATIONAL AEROSPACE LABORATORIES, BANGALORE-560 017, INDIA.
3 MADDELA SUBBA RAO NATIONAL AEROSPACE LABORATORIES, BANGALORE-560 017, INDIA.
PCT International Classification Number F16D 31/00
PCT International Application Number N/A
PCT International Filing date
PCT Conventions:
# PCT Application Number Date of Convention Priority Country
1 NA