| Title of Invention | A SHAPE MEMORY ALLOY STEP DRIVE MECHANISM |
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| Abstract | A shape memory alloy step drive mechanism includes at least one shape memory alloy element with a fixed end, the other end being connected to one end of a lever. The lever is provided with a pawl which is located to move on the teeth of a ratchet wheel mounted on a main shaft along with the lever. A stopper pin is provided which also guides the pawl on the ratchet wheel. A bias spring is provided on a mandril on the main shaft for returning the lever to its original position. A detent wheel with at least one detent lever is mounted on the main shaft to provide the detent torque required to hold the main shaft in po.sition when the lever returns to its original position. A pair of support brackets are provided for supporting and holding the various components together in an assembly. |
| Full Text | The invention provides a shape memory alloy step drive mechanism for providing step motion to a system. Many step drive mechanisms are known in the art. Almost all of them uses electromagnetic components. In certain precise applications such as in space applications it is desirable to have non-magnetic components in such step drive mechanism. The invention provides a step drive mechanism which does not use any magnetic component. The step drive mechanism according to the invention uses a shape memory alloy element. Shape memory alloy is an alloy which is plastically deformed at a suitable temperature recovers fully or partially its original shape on subsequent heating, by solid state phase changes in the alloy. The shape memory alloy element is heated by passing electric current using pulses in order to actuate the step motion. The invention provides a step drive mechanism comprising at least one shape memory alloy element with a fixed end, the other end of the shape memory alloy element being connected to one end of a lever, lever being provided with a pawl which is located to move on the teeth of a ratchet wheel mounted on a main shaft along with the lever, a stopper pin which also guides the pawl on the ratchet wheel, a bias spring provided on a mandril on the main shaft for returning the lever to its original position, a detent wheel with at least one detent lever mounted on the main shaft to provide the detent torque required to hold the main shaft in position when the lever returns to its original position and a pair of support brackets for supporting and holding the said components together in an assembly. The desirable step movement of the main shaft is achieved by pulse width modulated heating of the shape memory alloy element which ensures uniform heating and long life of the shape memory alloy element. In a prefered embodiment two shape memory alloy elements are used one for the step movement in clock wise direction and the other for step movement in the anti-clock wise direction. The invention will now be described with reference to the accompanying drawings : Fig, 1 shows the step drive mechanism according to the invention. Fig. 2 shows the sectional view of the step drive mechanism shown in fig. 1 along the sectional line X-X. Fig. 3 shows the exploded view of a prefered step drive mechanism according to the invention. The step drive mechanism comprises at least one shape memory alloy element (1> with one of its end fixed. The fixed end is preferably fixed to a spring loaded mandril alloy element (1) is connected to one end of a lever (2) through an insulator and a flexible cord (3) passing over guided pullies (13). The lever is mounted on a main shaft (6) along with a rachet wheel (5), The other end of the lever (2) is provided with a pawl (4> located to move over the teeth of the ratchet wheel (5), A stoper pin (7) with guides for guiding the pawl (4) is provided for stoping the movement of the lever (2) and disengaging the pawl (4) from the ratchet wheel (5), allowing the lever to come back to the original position due to the action of a bias spring (9) provided on a mandril on the main shaft (8) on the side of the lever (1) are provided with end terminals (20) and electrical connecting terminals (16) at both ends for passing current through the shape memory alloy elements and heating them. The whole assembly may be provided with a protection cover (17) if desired, Typical composition of shape memory alloy used in a prototype and its specification are given below : The step drive mechanism according to the invention can be adapted for various applications where a simple accurate and non-magnetic step drive mechanism is required. The control of step motion is accurate and simple. Pulse width modulation can be used for electrical heating of the shape memory alloy element to obtain an improved operation life cycle for the shape memory alloy element. WE CLAIM : 1. A shape memory alloy step drive mechanism comprising at least one shape memory alloy element (1) with a fixed end, the other end of the shape memory alloy element being connected to one end of a lever (2), said lever (2) being provided with a pawl (4> which is located to move on the teeth of a ratchet wheel (5) mounted on a main shaft (6> along with the lever (2>, a stopper pin , a bias spring (9) provided on a mandril on the main shaft (6) for returning the lever (2) to its original position, a detent wheel (8) with a least one detent lever (10) mounted on the main shaft (6) to provide the detent torque required to hold the main shaft (6> in position when the lever (2) returns to its original position and a pair of support brackets (11) for supporting and holding the said components together in an assembly. 2. The step drive mechanism as claimed in claim 1, wherein two shape memory alloy elements are provided with fixed ends, the other end of the second memory element also being connected to a similar mechanism as that provided with the first memory element for providing step movement in the reverse direction. 3. The step drive mechanism as claimed in claims 1 or 2, wherein the fixed end of the shape memory alloy element is provided with a load limiting spring (12). 4. The step drive mechanism as claimed in any one of the previous claims, wherein the flexible cord (3) connecting one end of the shape memory alloy element (1) to the lever (2) is passed through guide pullies (13). 5. The step drive mechanism as claimed in any one of the previous claims, wherein an output shaft (14) is provided which is coupled through a reduction gear (15) to the main shaft (6), 6. The step drive mechanism as claimed in any one of the previous claims, wherein the shape memory alloy element is provided with electrical connecting terminals (16) for passing current through it. 7. The step drive mechanism as claimed in any one of the previous claims, wherein a protection cover (17) is provided for the step drive mechanism. 8. A shape memory alloy step drive mechanism, substantially as hereinabove described and illustrated with reference to the accompanying drawings. |
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121-mas-2000- claims duplicate.pdf
121-mas-2000- claims original.pdf
121-mas-2000- correspondence others.pdf
121-mas-2000- correspondence po.pdf
121-mas-2000- descripition complete duplicate.pdf
121-mas-2000- descripition complete original.pdf
| Patent Number | 206763 | |||||||||
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| Indian Patent Application Number | 121/MAS/2000 | |||||||||
| PG Journal Number | 26/2007 | |||||||||
| Publication Date | 29-Jun-2007 | |||||||||
| Grant Date | 11-May-2007 | |||||||||
| Date of Filing | 17-Feb-2000 | |||||||||
| Name of Patentee | M/S. INDIAN SPACE RESEARCH ORGANISATION | |||||||||
| Applicant Address | ANTHARIKSH BHAVAN, NEW BEL ROAD, BANGALORE 560094. | |||||||||
Inventors:
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| PCT International Classification Number | F 16 K 11/04 | |||||||||
| PCT International Application Number | N/A | |||||||||
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