| 摘要 |
1. A variable speed drive comprising drive means, an output drive and an endless, extendible member that is driven by the drive means and extends round and drives the output drive, wherein the drive means is operable to drive the endless member at a first speed at a first driving position and means are provided for changing the speed or stopping movement of the endless member at a second position, thereby to cause local expansion or contraction of the endless member round the output drive without extending its overall length. 2. A drive as claimed in Claim 1, wherein the means for changing or stopping the endless member is operable to reduce the speed of the endless member to substantially zero at one of the drive positions, so that the endless member is substantially prevented from moving past that point. 3. A drive as claimed in Claims 1 or 2, wherein the endless, extendible, member is an endless coil or spring or a belt or tube. 4. A variable speed drive as claimed in Claim 3, wherein when the endless member is a spring or coil, the drive means comprises two hollow drive shafts. 5. A variable speed drive as claimed in Claim 4, wherein the hollow drive shafts are driven by the same motor. 6. A variable speed drive as claimed Claim 4 or Claim 5, wherein at least one lug depends from an inner peripheral surface of each hollow drive shaft for locating between adjacent windings of the spring or coil, so that when each hollow drive shaft is rotating the spring is propelled forward by engagement of successive windings with the or each rotating lug. 7. A variable speed drive as claimed in Claim 6, wherein a pair of lugs is provided, each lug of the pair being between adjacent windings of the spring but offset from the other in such a manner that a first one of the pair contacts a forward one of the adjacent windings and the second one of the pair contacts a rearward one of the windings. 8. A variable speed drive as claimed in Claims 6 or 7, wherein at least two lugs are provided opposite each other. 9. A variable speed drive as claimed in any one of Claims 4 to 7, wherein sets of lugs are provided at opposing ends of the hollow drive shaft. 10. A variable speed drive as claimed in any one of Claims 4 to 9, wherein the hollow drive shafts each comprise an inner hollow cylindrical shaft that is releasably coupled to an outer hollow cylindrical shaft, which is driven by an output motor. 11. A variable speed drive as claimed in Claim 10, wherein the means for changing the speed or stopping the endless member is operable to de-couple the inner shaft from the outer shaft. 12. A variable speed drive as claimed in Claim 11, wherein the means for changing the speed or stopping the endless member is hydraulic. 13. A variable speed drive as claimed in Claim 10 or 11 or 12, wherein the means for changing the sped or slowing comprise a braking mechanism for braking movement of at least one of the inner shafts, thereby to de-couple it from the corresponding outer shaft so that the speed of the endless spring through that shaft is reduced or brought to zero. 14. A variable speed drive as claimed in Claim 11, wherein the means for changing the speed or stopping the extendible member comprises a compression spring that is mounted between one end of the inner drive shaft and the same end of the outer shaft, wherein the compression spring is operable to pull the inner shaft into driving engagement with the outer shaft up until a pre-determined tension of the endless spring is reached, at which stage the inner shaft is moved out of engagement with the outer shaft. 15. A variable speed drive as claimed in Claim 14, comprising an actuator that is operable to sense when to switch off the drive and move one of the inner shafts against the action of the spring and out of engagement with the outer shaft, thereby to de-couple that inner shaft from the outer shaft. 16. A variable speed drive as claimed in Claim 15, wherein a detector is provided to detect a loosening of the spring and switch off the motor that drives the outer shaft, thereby to return the drive to a starting position. 17. A variable speed drive as claimed in any one of Claims 10 to 16, wherein the inner shaft has two separate but interlocking parts that can move longitudinally apart from each other, each of the parts being releasably mounted in driving engagement with the outer drive shaft, wherein the means for changing the speed or stopping movement of the endless member past the second point comprise means for moving the parts of the inner shafts from their driven position to a position in which they are de-coupled from the outer shaft. 18. A variable speed drive as claimed in Claim 17, wherein the means for moving the parts of the inner shaft are hydraulic. 19. A variable speed drive as claimed in Claim 17, wherein the means for moving the parts of the inner shaft comprise elliptical wheels that are rotatable into engagement with the parts of the inner shaft, thereby to push the parts of the inner shaft away from each other and out of driving engagement with the outer shaft. 20. A variable speed drive as claimed in any of the preceding Claims, wherein a drive member is provided on the output drive, the endless extendible member being wound around the drive member, which may be circular or "pear" shaped or elliptical. 21. A variable speed drive as claimed in any one of Claims 2 to 20, wherein a detector is provided for detecting the expansion or contraction of the flexible member, and thereby changes in the speed of the output drive. 22. A variable speed drive as claimed in Claim 21, wherein when the flexible member is a spring, the detector is operable to monitor separation of adjacent windings, thereby to gain a measure of the expansion or contraction of the spring and so its speed. 23. A variable speed drive as claimed in Claim 22, comprising two detectors on opposing sides of the output drive and a comparator for comparing the separation of the windings, thereby to calculate the rate of power transmitted. 24. A variable speed drive comprising drive means, an output drive and an endless, extendible member that is driven by the drive means and extends round and drives the output drive, wherein the drive means is operable to drive the endless member at a first speed at a first driving position and means are provided for changing the speed or stopping movement of the endless member at a second point, thereby to cause local expansion or contraction of the endless member round the output drive, wherein the drive means comprises a hollow drive shaft on which is provided means for interacting with the flexible member thereby to move it. 25. A variable speed drive comprising drive means, an output drive and an endless, extendible member that is driven by the drive means and extends round and drives the output drive, wherein the drive means comprise first drive means operable to drive the endless member at a first speed at a first position and second drive means operable to drive the endless member at a second speed at a second position, thereby to cause local expansion or contraction of the endless member round the output drive. 26. A variable speed drive comprising a drive, a movable member, an output drive and an endless extendible member that is driven by the said drive and extends around the output drive and the movable member, wherein movement of the extendible member over the output drive, causes said output drive to move and movement of the moveable member expands or contracts the extendible member, thereby varying its overall length, and so varying the speed at which the output drive is driven, wherein the drive comprises a hollow drive shaft on which is provided drive means for interacting with the flexible member, thereby to move it. 27. A variable speed drive as claimed in Claim 26, comprising two spaced apart moveable locating members are provided the spring being located between them, the two members being fixedly mounted relative to each other and movable relative to the motor, such that when moved in one direction the spring is caused to engage a first one of the movable members and is able to move the second drive shaft in a first direction, and when moved in another direction the spring is caused to engage a second one of the members and is able to move the second drive shaft in a second direction, thereby to provide a reversible drive. 28. A variable speed drive as claimed in Claim 26 or Claim 27, wherein the or each movable member comprises a wheel. 29. A variable speed drive as claimed in any one Claims 26 to 28, wherein the extendible member is a spring or coil. 30. A variable speed drive as claimed in Claim 29, wherein the drive means comprises a lug that depends from an internal wall of the hollow drive shaft for locating between windings of the spring, so that when the hollow drive shaft is rotating the spring is propelled forward by engagement of successive windings with the rotating lug. 31. A variable speed drive as claimed in Claim 30, wherein two or more lugs arc provided. 32. A variable speed drive as claimed in Claim 31, wherein the or each lug is provided with a roller bearing that provides a surface for engagement with the windings of the spring, thereby to reduce the effects of friction. 33. A variable speed drive as claimed in any of Claims 26 to 32, wherein a drive wheel is provided on the output drive, the extendible member being wound around the drive wheel. 34. A variable speed drive as claimed in any of Claims 26 to 33, wherein a detector is provided for detecting any expansion or contraction of the flexible member, and thereby changes the speed of the drive and rate of transmission of power to the output drive. 35. A variable speed drive as claimed in Claim 34 when dependent directly or indirectly on Claim 29, wherein the detector is operable to monitor separation of adjacent windings of the spring or coil, thereby to gain a measure of |
