Drive assembly with dynamic tensioning device

1. A drive assembly for a closed loop cable system in which a cable drives a moveable structure back and forth and in which the cable is wrapped around and driven by a drive pulley, the drive assembly comprising:

the drive pulley,

a motor unit having a motor shaft that rotates around a drive axis for rotating the drive pulley around a drive pulley axis, and

a tensioning mechanism that adjusts the position of the drive pulley axis with respect to the drive axis responsive to tension in the cable.

2. The cable drive assembly as defined in claim 1 wherein the pulley axis moves in a circular orbit about the drive axis and the tensioning mechanism adjusts the position of the drive pulley axis with respect to the drive axis in the circular orbit.

3. The cable drive system as defined in claim 1 wherein the pulley axis is transverse to the drive axis and moves in a path parallel to the drive axis and wherein the tensioning mechanism adjusts the position of the pulley axis with respect to the drive axis in the path parallel to the drive axis.

4. The drive assembly as defined in claim 1 wherein the flexible drive member is a cable.

5. The drive assembly as defined in claim 1 wherein the flexible drive member is a beaded cable.

6. A drive assembly for a closed loop system in which a cable drives a moveable structure back and forth and in which the cable is wrapped around and driven by a drive pulley the drive assembly comprising:

a motor unit having an output shaft rotatable about a drive axis for rotating the drive pulley about a pulley axis, and

a tensioning mechanism for adjusting the position of the pulley axis of the drive pulley with respect to the drive axis of the output shaft of the motor responsive to tension in the cable,

the tensioning mechanism including a first gear driven by the motor about the drive axis, and a second gear meshing with the first gear and driven about the pulley axis of the drive pulley.

7. The drive assembly as defined in claim 6 wherein the tensioning mechanism includes a moveable carrier that is spring biased in one direction, and wherein the second gear is mounted on the carrier rotationally.

8. The drive assembly as defined in claim 7 wherein the moveable carrier is spring biased in one direction by a tension spring.

9. The drive assembly as defined in claim 8 wherein the tension spring has one end attached to the carrier and an opposite end attached to a fixed reaction member.

10. The cable drive assembly as defined in claim 6 wherein the pulley axis moves in a circular orbit about the drive axis and the tensioning mechanism adjusts the position of the pulley axis with respect to the drive axis in the circular orbit.

11. The cable drive system as defined in claim 6 wherein the pulley axis is transverse to the drive axis and moves in a path parallel to the drive axis and wherein the tensioning mechanism adjusts the position of the pulley axis with respect to the drive axis in the path parallel to the drive axis.

12. A cable drive assembly for a closed loop system in which a cable drives a moveable structure back and forth and in which the cable is wrapped around a drive pulley and an idler pulley that is spaced from the drive pulley, the cable drive system comprising:

the drive pulley being rotatable about a pulley axis,

a motor unit having an output shaft rotatable about a drive axis for rotating the drive pulley about the pulley axis, and

a tensioning mechanism for adjusting the position of the pulley axis of the drive pulley with respect to the drive axis of the output shaft of the motor unit,

the tensioning mechanism including a first gear driven by the motor unit about the drive axis, and a second gear meshing with the first gear and driven about the pulley axis of the drive pulley by the first gear.

13. The cable drive assembly as defined in claim 12 wherein the tensioning mechanism further includes a carrier that is rotatable concentrically with respect to the first gear, the second gear being journalled in the carrier in an offset location so that the pulley axis moves in a circular orbit with respect to the drive axis when the rotor is rotated with respect to the first gear, and spring means to rotate the rotor with respect to the first gear in one direction.

14. The cable drive assembly as defined in claim 12 wherein the tensioning mechanism includes a worm gear driven by the motor unit about the drive axis, and a helical gear meshing with the worm gear and driven about the pulley axis of the drive pulley by the worm gear.

15. The cable drive assembly as defined in claim 14 wherein the tensioning mechanism further includes a carrier that is moveable in a direction that is parallel to the axis of the worm gear, the helical gear being journalled in the carrier so that the pulley axis is transverse to the drive axis and moves in a path that is parallel to the drive axis and wherein the tensioning mechanism includes spring means to move the carrier with respect to the worm gear in one direction.

16. The cable drive assembly as defined in claim 12 wherein the pulley axis moves in a circular orbit about the drive axis and the tensioning mechanism adjusts the position of the pulley axis with respect to the drive axis in the circular orbit.

17. The cable drive system as defined in claim 12 wherein the pulley axis is transverse to the drive axis and moves in a path parallel to the drive axis and wherein the tensioning mechanism adjusts the position of the pulley axis with respect to the drive axis in the path parallel to the drive axis.

18. A drive assembly for a closed loop cable system in which a cable is wrapped around and driven by a drive pulley, the drive assembly comprising:

the drive pulley,

a motor unit having a motor shaft that rotates about a drive axis for rotating the drive pulley about a drive pulley axis, and

a tensioning mechanism for adjusting the position of the drive pulley axis with respect to the drive axis responsive to tension in the cable,

the tensioning mechanism including a first gear driven by the motor about the drive axis, and a second gear meshing with the first gear and driven about the drive pulley axis of the drive pulley.