Actuation of a device comprising mechanical arms
Some embodiments of the invention relate to a mechanism for actuating a shaft having two degrees of freedom, comprising: a first actuator configured to rotate the shaft around the shaft axis, and a second actuator configured to bend the shaft using one or more elongated elements attached to the shaft, wherein actuation of the first actuator indirectly manipulates the elongated elements controlled by the second actuator, thereby affecting operation of the second actuator. Some embodiments relate to motorized actuation of a system comprising at least one surgical arm.
1. A mechanism for articulating a surgical arm by linear movement of elongated elements which is driven by rotational movement, comprising:
a first shaft which defines at least a segment of said surgical arm or is formed as a linear extension of said surgical arm, said first shaft including a flexible joint; said shaft configured to rotate around the shaft axis;
a second shaft which is co-axial with said said first shaft and positioned externally to said first shaft, said second shaft being formed with at least a partial first helix in one direction, and at least a partial second helix in an opposite direction;
a right handed rider positioned on said first helix and a left handed rider positioned on said second helix, wherein movement of each of said riders is limited by the respective helix;
a first elongate element extending from said right handed rider to said first shaft, and a second elongate element extending from said left handed rider to said first shaft; said elongate elements being attached to said first shaft at a point distal to said flexible joint;
wherein rotation of said second shaft moves said riders linearly in opposing directions, tensioning one of said elongate elements and releasing tension of the other elongate element, thereby articulating said flexible joint.
2. The mechanism according to claim 1 , further comprising a cylindrical housing formed with radially inward protrusions which limit rotational movement of said riders.
3. The mechanism according to claim 1 , wherein said first and second helixes are configured as a bidirectional screw thread.
4. The mechanism according to claim 1 , wherein said right and left handed riders are half-nuts.
5. The mechanism according to claim 1 , wherein movement of said riders is linearly along a long axis of said second shaft.
6. The mechanism according to claim 1 , wherein each of said elongated elements comprises one of: a wire, cable, ribbon or tape.
7. The mechanism according to claim 1 , wherein a fixed distance between said riders along a width axis of said second shaft maintains said elongated elements at a constant cross-wise distance from each other.
8. The mechanism according to claim 1 , further comprising a motor gear configured to rotate one or both of said first shaft and said second shaft around the shaft axis.
9. The mechanism according to claim 8 , wherein said gear is attached to said second shaft, and the attachment comprises a clutch.
10. The mechanism according to claim 9 , wherein said clutch is in the form of a spring which yields when torque generated by rotation of said second shaft exceeds a predetermined threshold.
11. The mechanism according to claim 1 , wherein one or more springs are linearly attached between at least one of said riders and the respective elongated element such that when said elongated element is tensioned above a predetermined threshold, the spring yields and further movement of said rider is no longer effective to tension said elongate element.
12. The mechanism according to claim 1 , comprising a total of four elongated elements, wherein each of said riders is attached to two elongated elements.
13. The mechanism according to claim 1 , wherein said flexible joint constitutes an elbow joint of said surgical arm.
14. A method for articulating a surgical arm using the mechanism of claim 1 , comprising:
rotating said second shaft to move said rider elements in opposite directions, tensioning said first elongated element and releasing tension of said second elongated element, thereby articulating said flexible joint.
15. The method according to claim 14 , wherein said articulating comprises bending said flexible joint.
16. The method according to claim 14 , wherein said rotating comprises rotating a gear operably attached to said second shaft at a speed selected according to a selected articulation speed of said first shaft.
17. The method according to claim 14 , comprising using said first shaft to operate loads, wherein a pitch of said first and second helixes is constructed according to a size of said load.
18. The method according to claim 14 , comprising stopping rotation of said second shaft when torque generated by rotation of said second shaft exceeds a predetermined threshold.
19. The method according to claim 14 , comprising decoupling said elongated element from the respective rider upon reaching a predetermined tension level.