Rotational joint assembly for robotic medical system
An example rotational joint assembly for a robotic medical system, the rotational joint assembly comprising at least one arm segment and a rotational joint provided at one end of the arm segment. The rotational joint is to allow the arm segment to rotate about a rotational axis. The rotational joint comprising a brake to lock rotation of the arm segment at the rotational joint and an actuator to selectively engage or disengage the brake. The actuator comprising a cam having two stable regions separated by two transition regions, the two stable regions comprising a first stable region corresponding to engagement of the brake and a second stable region corresponding to disengagement of the brake.
1. A rotational joint assembly for a robotic medical system, the rotational joint assembly, comprising:
at least one arm segment;
a rotational joint provided at one end of the at least one arm segment, the rotational joint configured to allow the at least one arm segment to rotate about a rotational axis, the rotational joint comprising,
a brake to lock rotation of the at least one arm segment at the rotational joint; and
an actuator to selectively engage or disengage the brake, the actuator comprising a cam having two stable regions separated by two transition regions, the two stable regions comprising a first stable region corresponding to engagement of the brake and a second stable region corresponding to disengagement of the brake, the first stable region including a dwell region; and
bellows enclosing at least substantially an entirety of the brake, the bellows providing torsional rigidity during engagement of the brake to cause substantially zero backlash upon engagement or disengagement.
2. The rotational joint assembly of claim 1 , wherein the brake comprises:
a cup having a conical inner perimeter; and
a cone for receiving the conical inner perimeter of the cup when the brake is engaged,
wherein engaging of the brake includes moving the conical inner perimeter of the cup into contact with the cone.
3. The rotational joint assembly of claim 2 , wherein the conical inner perimeter of the cup has a cone angle of between about 15 degrees and about 30 degrees.
4. The rotational joint assembly of claim 3 , wherein the conical inner perimeter of the cup has a cone angle of about 17 degrees.
5. The rotational joint assembly of claim 1 , wherein the brake comprises a plurality of first disc brake portions coupled to an inner housing and a plurality of second disc brake portions coupled to an outer housing, wherein the inner housing rotates relative to the outer housing during rotation of the at least one arm segment about the rotational joint.
6. The rotational joint assembly of claim 5 , wherein frictional surfaces of the first disc brake portions and corresponding frictional surfaces of the second disc brake portions are interleaved circumferentially between the inner housing and the outer housing.
7. The rotational joint assembly of claim 6 , wherein the first disc brake portions include an inner non-planar portion between the inner housing and the corresponding frictional surface,
wherein the inner non-planar portion comprises a first end coupled to the inner housing and a second end coupled to the frictional surface;
wherein the first end of the inner non-planar portion and the second end of the inner non-planar portion are axially offset.
8. The rotational joint assembly of claim 6 , wherein the second disc brake portions include an outer non-planar portion between the outer housing and the corresponding frictional surface; and
wherein the outer non-planar portion comprises a first end coupled to the outer housing and a second end coupled to the corresponding frictional surface;
wherein the first end of the outer non-planar portion and the second end of the outer non-planar portion are axially offset.
9. The rotational joint assembly of claim 1 , wherein the actuator comprises a spring to bias the brake against the cam to a disengaged position.
10. The rotational joint assembly of claim 9 ,
wherein the two stable regions of the cam include:
the first stable region corresponding to a locked position and resulting in exertion of a force causing compression of the spring to engage the brake; and
the second stable region corresponding to an unlocked position and resulting in absence of the force and disengagement of the brake;
wherein the two transition regions of the cam include:
a gradual transition region from the second stable region to the first stable region; and
a rapid transition region from the first stable region to the second stable region.
11. The rotational joint assembly of claim 1 , wherein the rotational joint allows rotation of the arm segment between a left-handed position and a right-handed position.
12. The rotational joint assembly of claim 1 , wherein the cam is positioned on a camshaft driven by a motor.
13. The rotational joint assembly of claim 12 , wherein the camshaft comprises at least one sensor to allow determination of orientation of the cam.
14. The rotational joint assembly of claim 12 , wherein the camshaft is coupled to a manual actuator to allow a user to rotate the camshaft without operation of the motor.
15. The rotational joint assembly of claim 14 , wherein the camshaft comprises a ratchet configured to retain a motor-driven position of the camshaft during operation of the manual actuator, the ratchet being further configured to allow the motor to engage the camshaft at the motor-driven position upon resumption of operation of the motor.
16. The rotational joint assembly of claim 14 , wherein the camshaft comprises a ratchet configured to allow the manual actuator to engage the camshaft when the camshaft is not motor-driven and to disengage the camshaft when the camshaft is motor-driven.
17. The rotational joint assembly of claim 1 , wherein the brake comprises:
a first brake component coupled to an outer housing; and
a second brake component coupled to an inner housing, the inner housing being rotatable relative to the outer housing about a rotational axis,
wherein the first brake component and the second brake component are selectively engageable to each other for engagement of the brake.
18. A robotic medical system comprising:
a brake to lock movement of at least a portion of the robotic medical system;
an actuator to selectively engage or disengage the brake, the actuator including a cam having two stable regions separated by two transition regions, the two stable regions comprising a first stable region corresponding to engagement of the brake and a second stable region corresponding to disengagement of the brake, the first stable region including a dwell region; and
a bellows enclosing at least substantially an entirety of the brake, the bellows providing torsional rigidity during engagement of the brake to cause substantially zero backlash upon engagement or disengagement.
19. The robotic medical system of claim 18 , wherein the dwell region has a lower radius than outer edges of the first stable region.