Source: https://patents.google.com/patent/GB2541369A/en
Timestamp: 2019-12-15 01:16:01
Document Index: 635921284

Matched Legal Cases: ['arts 310', 'art 310', 'arts 4', 'art 311', 'art 310', 'art 310', 'art 310', 'art 311', 'art 310', 'art 310', 'art 311']

GB2541369A - Drive mechanisms for robot arms - Google Patents
GB2541369A
GB2541369A GB1512959.6A GB201512959A GB2541369A GB 2541369 A GB2541369 A GB 2541369A GB 201512959 A GB201512959 A GB 201512959A GB 2541369 A GB2541369 A GB 2541369A
GB1512959.6A
GB201512959D0 (en
2015-07-22 Priority to GB1512959.6A priority Critical patent/GB2541369A/en
2015-09-02 Publication of GB201512959D0 publication Critical patent/GB201512959D0/en
2017-02-22 Publication of GB2541369A publication Critical patent/GB2541369A/en
A robot arm comprises a joint mechanism for articulating one limb of the arm relative to another limb of the arm about two non-parallel rotation axes, the mechanism comprising: an intermediate carrier 64, 104 attached to a first one of the limbs by a first revolute joint having a first rotation axis 62, 102 and to a second one of the limbs by a second revolute joint having a second rotation axis 63, 103; a first drive gear 74, 107 disposed about the first rotation axis 62, 102, the first drive gear 74, 107 being fast with the carrier 64, 104: a second drive gear 75, 108 disposed about the second rotation axis 63, 103, the second drive gear 75, 108 being fast with the second one of the limbs; a first drive shaft 76 for driving the first drive gear 74, 107 to rotate about the first rotation axis 62, 102, the first drive shaft 76, 111 extending along the first one of the limbs and having a first shaft gear 78, 118 thereon, the first shaft gear 78, 118 being arranged to engage the first drive gear 74, 107; a second drive shaft 77 for driving the second drive gear 75, 108 to rotate about the second rotation axis 63, 103, the second drive shaft 77, 112 extending along the first one of the limbs and having a second shaft gear 79, 113 thereon. The joint mechanism may comprise an intermediate gear train 80, 81 borne by the carrier 64 and coupling the second shaft gear 79 to the second drive gear 75. The joint mechanism may comprise an intermediate mechanism (82 fig. 5) that meshes with the second drive shaft 77. The joint mechanism may comprise a prismatic joint 116 allowing the length of the second drive shaft 112 to vary.
In the case of a surgical robot there are a number of important criteria that influence the design of the distal joint(s) of the arm. 1. It is desirable for the arm, and particularly its distal portion where the wrist is located, to be small in size. That allows multiple such robot arms to work in close proximity and hence opens up a wider range of surgical procedures that the arm can perform. 2. It is desirable for the outer profile of the distal portion of the arm to be circularly symmetrical about the length of the arm. This allows the distal portion to be rotated longitudinally without having to be repositioned if it is close to another robot, to some other equipment or to the patient. 3. It is desirably for the joints to be capable of delivering a high torque, so that they can carry heavier tools and deliver high acceleration to the tool tip. 4. It is desirable for the joints to be stiff, with little or no backlash or elasticity, so that when a tool tip has been positioned it will be fixed in position. A conventional approach to minimising backlash is to designate one or more gear elements as sacrificial, but this requires a high level of maintenance, and can result in worn gear particles being liberated within the arm. 5. It is desirable for all articulations to have position and force/torque sensors, so that the control mechanism can take data from those sensors. 6. It is desirable for the distal portion of the robot arm to be as light as possible, to reduce the force that must be exerted by more proximal joints of the robot arm. 7. A typical robot arm carries cables that provide power to its drive motors and perhaps to a tool, and carry signals back from sensors such as position, torque and imaging sensors. It is desirable for the arm to include a path for such cables to pass in the interior of the arm. 8. It is desirable for there to be a method of cooling for the motors driving the distal joints of the robot arm and payload or tool.
One particular problem is how to fit the motors and gearing into the wrist of a robot arm. The arrangement should be compact but also allow for high stiffness and torque transfer. Many existing designs compromise one of these criteria.
There is a need for an improved drive arrangement for a joint of a robot arm.
One or both of the first drive gears may be bevel gear(s): i.e. gears whose pitch surface is a straight-sided or curved cone and/or whose teeth are arranged on such a cone.
The tooth lines may be straight or curved. One or both of the first drive gears may be skew axis gear(s).
Figure 2 shows in more detail the rotation axes at the wrist of the arm of figure 1. Figure 3 shows part of a first wrist mechanism from distally and one side.
Figure 4 shows part of the first wrist mechanism from distally and the other side. Figure 5 shows part of a second wrist mechanism from proximally and one side.
In the region of the wrist 5 the rigid arm parts 310, 311 have hollow outer shells or casings 310’, 310”, 31T. The shells define the majority of the exterior surface of the arm, and include a void which is partly or fully encircled by the exterior wall of the respective shell and within which the motors, sensors, cables and other components of the arm can be housed. The shells could be formed of a metal, for example an aluminium alloy or steel, or from a composite, for example a fibre-reinforced resin composite such as resin-reinforced carbon fibre. The shells constitute part of the rigid structure of the arm parts that attaches between the respective joints. The shells may contain a structural framework as shown later in relation to the embodiment of figure 7.
In figures 3 and 4, for clarity the shell of arm part 310 is shown in two parts: 310’ and 310”, both of which are drawn in outline and exploded from each other. The shells of arm parts 4b and 4c are omitted, as is the mechanism associated with joints 300 and 303. The shell of arm part 311 is shown in part, the majority extending from spur 311 ’.
Two electric motors 24, 25 (see figure 4) are mounted in arm part 310. The motors drive respective drive shafts 26,27 which extend into the midst of the wrist mechanism. Shaft 26 drives rotation about axis 20. Shaft 27 drives rotation about axis 21. Drive shaft 26 terminates at its distal end in a worm gear 32. The worm gear 32 engages a bevel gear 33 which is fast with the coupler 28. Drive shaft 27 terminates at its distal end in a worm gear 34. The worm gear 34 engages a gear train shown generally at 35 which terminates in a further worm gear 36. Worm-form pinion gear 36 engages a hypoid-toothed bevel gear 37 which is fast with the distal shell connector 31T.
Figure 6 shows the same mechanism from distally and one side, with the shell 311 ’ removed for clarity.
Shell 310’ is coupled to shell 311’ by a cruciform coupler 64. The coupler has a central tube 65 which defines a duct through its centre, running generally along the length of the arm. Extending from the tube are first arms 66, 67 and second arms 68, 69. Each of the shells 310’, 311’ is attached to the coupler 64 by a revolute joint: i.e. in such a way that it is confined to be able to move relative to the coupler only by rotation about a single axis. The first arms 66, 67 attach to shell 310’ by bearings 70, 71 which permit rotation between those first arms and the shell 310’ about axis 62. The second arms 68, 69 attach to shell 311’ by bearings 72, 73 which permit rotation between those second arms and the shell 311’ about axis 63. A first bevel gear 74 is concentric with the first arms 66, 67. The first bevel gear is fast with the coupler 64 and rotationally free with respect to the proximal one of the two shells 310’. A second bevel gear 75 is concentric with the second arms 68, 69. The second bevel gear is fast with the distal one of the two shells 311’ and rotationally free with respect to the coupler 64.
Two shafts 76, 77 operate the motion of the compound joint. The shafts extend into the central region of the joint from within the proximal one of the shells 310’. Each shaft is attached at its proximal end to the shaft of a respective electric motor (not shown), the housings of the motors being fixed to the interior of the proximal shell 310’.
In this way the shafts 76, 77 can be driven by the motors to rotate with respect to the proximal shell 310’.
Shaft 76 and its associated motor operate motion about axis 62. Shaft 76 terminates at its distal end in a worm gear 78 which engages bevel gear 74. Rotation of shaft 76 causes rotation of the bevel gear 74 relative to shell 310’ about axis 62. Bevel gear 74 is fast with the coupler 64, which in turn carries the distal shell 311’. Thus rotation of shaft 76 causes relative rotation of the shells 310’, 311’ about axis 62.
Two motors 109, 110 are fixed to the framework 100 of arm part 310. Motor 109 drives a shaft 111. Shaft 111 is rigid and terminates in a worm 118 which engages bevel gear 107. When motor 109 is operated, shaft 111 rotates relative to the proximal arm part 310, driving bevel gear 107 and hence coupler 104 and arm part 311 to rotate relative to arm part 310 about axis 102. Motor 110 drives a shaft 112. Shaft 112 has a worm 113 near its distal end which engages bevel gear 108. To accommodate motion of bevel gear 108 relative to motor 110 when the coupler 104 moves about axis 102 shaft 112 includes a pair of universal joints 114, 115 and a splined coupler 116 which accommodates axial extension and retraction of shaft 112. The final part of shaft 112 is mounted to the coupler 104 by bearing 117.
In order to get the most accurate output from the torque sensor, torque transfer from the bevel gear 108 to the frame 101 in a way that bypasses the torsion tube 156 should be avoided. For that reason, it is preferred to reduce friction between the neck 153 of the bevel gear 108 and the base 157 of the torque sensor. One possibility is to provide a gap between the neck of the bevel gear and both the base of the torque sensor and the torsion tube. However, that could permit shear forces to be applied to the torsion tube in a direction transverse to axis 103, which would itself reduce the accuracy of the torque sensor by exposing the strain gauges 160 to other than torsional forces. Another option is to introduce a bearing race between the interior of the neck of bevel gear 108 and the exterior of the base 157 of the torque sensor. However, that would substantially increase the volume occupied by the mechanism. Instead, the arrangement shown in figure 8 has been shown to give good results. A sleeve or bushing 161 is provided around the torsion tube 156 and within the neck 153 of the bevel gear 108. The sleeve is sized so that it makes continuous contact with the interior wall of the neck 153 and with the exterior wall of the torsion tube 156, which is also of circularly cylindrical profile. The whole of the interior surface of the sleeve makes contact with the exterior of the torsion tube 156. The whole of the exterior surface of the sleeve makes contact with the interior surface of the neck 153. The sleeve is constructed so that it applies relatively little friction between the neck and the torsion tube: for instance the sleeve may be formed of or coated with a low-friction or self-lubricating material. The sleeve is formed of a substantially incompressible material so that it can prevent deformation of the torque sensor under shear forces transverse to the axis 103. For example, the sleeve may be formed of or coated with a plastics material such as nylon, polytetrafluoroethylene (PTFE), polyethylene (PE) or acetal (e.g. Delrin®), or of graphite or a metal impregnated with lubricant.
This arrangement is illustrated in figure 11. Arm part 310 comprises circuit board 195 which receives data from position sensor 202 and provides command data to motors 109, 110. Arm part 311 comprises circuit board 250 which receives data from position sensor 212 and torque sensors 150, 191. Circuit board 250 encodes that sensed data and passes it over a data bus 196 to circuit board 195, which forwards it on towards control unit 10 via a link 197. Position sensor 202 is connected directly by a cable to circuit board 195. Position sensor 212 and torque sensors 150, 191 are connected directly by cables to circuit board 195.
1. A robot arm comprising a joint mechanism for articulating one limb of the arm relative to another limb of the arm about two non-parallel rotation axes, the mechanism comprising: an intermediate carrier attached to a first one of the limbs by a first revolute joint having a first rotation axis and to a second one of the limbs by a second revolute joint having a second rotation axis; a first drive gear disposed about the first rotation axis, the first drive gear being fast with the carrier; a second drive gear disposed about the second rotation axis, the second drive gear being fast with the second one of the limbs; a first drive shaft for driving the first drive gear to rotate about the first rotation axis, the first drive shaft extending along the first one of the limbs and having a first shaft gear thereon, the first shaft gear being arranged to engage the first drive gear; a second drive shaft for driving the second drive gear to rotate about the second rotation axis, the second drive shaft extending along the first one of the limbs and having a second shaft gear thereon; and an intermediate gear train borne by the carrier and coupling the second shaft gear to the second drive gear.
2. A robot arm as claimed in claim 1, wherein the intermediate gear train comprises a first intermediate gear disposed about the first rotation axis, the first intermediate gear being arranged to engage the second shaft gear.
3. A robot arm as claimed in claim 2, further comprising a control unit arranged to respond to command signals commanding motion of the robot arm by driving the first and second drive shafts to rotate, the control unit being configured to, when the robot arm is commanded to articulate about the first axis without articulating about the second axis, drive the first shaft to rotate to cause articulation about the first axis and also drive the second shaft to rotate in such a way as to negate parasitic articulation about the second axis.
4. A robot arm as claimed in any preceding claim, wherein the intermediate gear train comprises a plurality of interlinked gears arranged to rotate about axes parallel with the first rotation axis.
5. A robot arm as claimed in any preceding claim, wherein the intermediate gear train comprises an intermediate shaft arranged to rotate about an axis parallel with the first rotation axis, the intermediate shaft having a third shaft gear thereon, the third shaft gear being arranged to engage the second drive gear.
6. A robot arm as claimed in claim 5 as dependent on claim 4, wherein the interlinked gears are on one side of a plane perpendicular to the first axis and containing the teeth of the first drive gear, and at least part of the third shaft gear is on the other side of that plane.
7. A robot arm as claimed in claim 5 or 6, wherein the third shaft gear is a worm gear.
8. A robot arm as claimed in any preceding claim, wherein one or both of the first and second shaft gears is/are worm gears.
9. A robot arm as claimed in any preceding claim, wherein one or both of the first drive gears is/are bevel gear(s).
11. A robot arm as claimed in any preceding claim, wherein the first drive gear is a part-circular gear.
12. A robot arm as claimed in claim 11, wherein at least part of the second drive gear intersects a circle about the first axis that is coincident with the radially outermost part of the first drive gear.
13. A robot arm as claimed in claim 11 or 12 as dependent on claim 5, wherein at least part of the intermediate shaft intersects a circle about the first axis that is coincident with the radially outermost part of the first drive gear.
14. A robot arm substantially as herein described with reference to figures 1 to 4 of the accompanying drawings.
14. A robot arm as claimed in any preceding claim, wherein the first and second axes are orthogonal.
15. A robot arm as claimed in any preceding claim, wherein the first and second axes intersect each other.
16. A robot arm comprising a joint mechanism for articulating one limb of the arm relative to another limb of the arm about two non-parallel rotation axes, the mechanism comprising: an intermediate carrier attached to a first one of the limbs by a first revolute joint having a first rotation axis and to a second one of the limbs by a second revolute joint having a second rotation axis; a first drive gear disposed about the first rotation axis, the first drive gear being fast with the carrier; a second drive gear disposed about the second rotation axis, the second drive gear being fast with the second one of the limbs; a first drive shaft for driving the first drive gear to rotate about the first rotation axis, the first drive shaft extending along the first one of the limbs and having a first shaft gear thereon, the first shaft gear being arranged to engage the first drive gear; a second drive shaft for driving the second drive gear to rotate about the second rotation axis, the second drive shaft extending along the first one of the limbs on a first side of a plane containing the second rotation axis and extending through that plane to the second side of that plane; and an intermediate linkage that meshes with the second drive shaft on the second side of the plane and that couples the second shaft gear to the second drive gear.
17. A robot arm as claimed in claim 16, wherein the second shaft comprises a flexible element.
18. A robot arm as claimed in claim 17, wherein the flexible element is located on the first rotation axis.
19. A robot arm as claimed in claim 17 or 18, wherein the flexible element is a universal joint.
20. A robot arm as claimed in any of claims 16 to 19, wherein the second shaft is coupled to the carrier by a revolute joint on the second side of the said plane.
21. A robot arm as claimed in any of claims 16 to 19, wherein the second drive shaft has a second shaft gear on the second side of the said plane and the intermediate linkage comprises an intermediate shaft having a first intermediate gear that meshes with the second shaft gear and a second intermediate gear that meshes with the second drive gear.
22. A robot arm as claimed in claim 21, wherein the second drive shaft is arranged to rotate about an axis perpendicular to the second rotation axis.
23. A robot arm as claimed in any of claims 16 to 22, wherein the second intermediate gear is a worm gear.
24. A robot arm as claimed in any of claims 16 to 23, wherein the first shaft gear is a worm gear.
25. A robot arm as claimed in of claims 16 to 24, wherein one or both of the first drive gears is/are bevel gear(s).
26. A robot arm as claimed in any of claims 16 to 25, wherein one or both of the first drive gears is/are skew axis gear(s).
27. A robot arm as claimed in any preceding claim, wherein the first drive gear is a part-circular gear.
28. A robot arm as claimed in claim 27, wherein at least part of the second drive gear intersects a circle about the first axis that is coincident with the radially outermost part of the first drive gear.
29. A robot arm as claimed in any preceding claim, wherein the first and second axes are orthogonal.
30. A robot arm as claimed in any preceding claim, wherein the first and second axes intersect each other.
31. A robot arm comprising a joint mechanism for articulating one limb of the arm relative to another limb of the arm about two non-parallel rotation axes, the mechanism comprising: an intermediate carrier attached to a first one of the limbs by a first revolute joint having a first rotation axis and to a second one of the limbs by a second revolute joint having a second rotation axis; a first drive gear disposed about the first rotation axis, the first drive gear being fast with the carrier; a second drive gear disposed about the second rotation axis, the second drive gear being fast with the second one of the limbs; a first drive shaft for driving the first drive gear to rotate about the first rotation axis, the first drive shaft extending along the first one of the limbs and having a first shaft gear thereon, the first shaft gear being arranged to engage the first drive gear; a second drive shaft for driving the second drive gear to rotate about the second rotation axis, the second drive shaft extending along the first one of the limbs and having a second shaft gear thereon, the second shaft gear being arranged to engage the second drive gear; the second drive shaft comprising a prismatic joint whereby the length of the shaft can vary in response to motion of the carrier about the first axis.
32. A robot arm as claimed in claim 31, wherein the prismatic joint is a sliding splined coupling.
33. A robot arm as claimed in claim 31 or 32, wherein the second dive shaft comprises a first flexible joint on one side of the prismatic joint and a second flexible joint on the other side of the prismatic joint.
34. A robot arm as claimed in claim 33, wherein the second drive shaft is connected by a revolute joint to the carrier on the opposite side of the second flexible joint to the prismatic joint.
35. A robot arm as claimed in any of claims 31 to 34, wherein one or both of the first and second shaft gears is/are worm gears.
36. A robot arm as claimed in of claims 31 to 35, wherein one or both of the first drive gears is/are bevel gear(s).
37. A robot arm as claimed in claim 36, wherein one or both of the first drive gears is/are skew axis gear(s).
38. A robot arm as claimed in any of claims 31 to 37, wherein the first drive gear is a part-circular gear.
39. A robot arm as claimed in claim 38, wherein at least part of the second drive gear intersects a circle about the first axis that is coincident with the radially outermost part of the first drive gear.
40. A robot arm as claimed in claim 35 to 39, wherein the first and second axes are orthogonal.
41. A robot arm as claimed in of claims 35 to 40, wherein the first and second axes intersect each other.
42. A robot arm substantially as herein described with reference to figures 1 to 12 of the accompanying drawings. CLAIMS
1. A robot arm comprising a joint mechanism for articulating one limb of the arm relative to another limb of the arm about two non-parallel rotation axes, the mechanism comprising: an intermediate carrier attached to a first one of the limbs by a first revolute joint having a first rotation axis and to a second one of the limbs by a second revolute joint having a second rotation axis; a first drive gear disposed about the first rotation axis, the first drive gear being fast with the carrier; a second drive gear disposed about the second rotation axis, the second drive gear being fast with the second one of the limbs; a first drive shaft for driving the first drive gear to rotate about the first rotation axis, the first drive shaft extending along the first one of the limbs and having a first shaft gear thereon, the first shaft gear being arranged to engage the first drive gear; a second drive shaft for driving the second drive gear to rotate about the second rotation axis, the second drive shaft extending along the first one of the limbs and having a second shaft gear thereon; an intermediate gear train borne by the carrier and coupling the second shaft gear to the second drive gear, the intermediate gear train comprising a first intermediate gear disposed about the first rotation axis, the first intermediate gear being arranged to engage the second shaft gear; and a control unit arranged to respond to command signals commanding motion of the robot arm by driving the first and second drive shafts to rotate, the control unit being configured to, when the robot arm is commanded to articulate about the first axis without articulating about the second axis, drive the first shaft to rotate to cause articulation about the first axis and also drive the second shaft to rotate in such a way as to negate parasitic articulation about the second axis.
2. A robot arm as claimed in any preceding claim, wherein the intermediate gear train comprises a plurality of interlinked gears arranged to rotate about axes parallel with the first rotation axis.
3. A robot arm as claimed in any preceding claim, wherein the intermediate gear train comprises an intermediate shaft arranged to rotate about an axis parallel with the first rotation axis, the intermediate shaft having a third shaft gear thereon, the third shaft gear being arranged to engage the second drive gear.
4. A robot arm as claimed in claim 3 as dependent on claim 2, wherein the interlinked gears are on one side of a plane perpendicular to the first axis and containing the teeth of the first drive gear, and at least part of the third shaft gear is on the other side of that plane.
5. A robot arm as claimed in claim 3 or 4, wherein the third shaft gear is a worm gear.
6. A robot arm as claimed in any preceding claim, wherein one or both of the first and second shaft gears is/are worm gears.
7. A robot arm as claimed in any preceding claim, wherein one or both of the first drive gears is/are bevel gear(s).
8. A robot arm as claimed in claim 7, wherein one or both of the first drive gears is/are skew axis gear(s).
9. A robot arm as claimed in any preceding claim, wherein the first drive gear is a part-circular gear.
10. A robot arm as claimed in claim 9, wherein at least part of the second drive gear intersects a circle about the first axis that is coincident with the radially outermost part of the first drive gear.
11. A robot arm as claimed in claim 9 or 10 as dependent on claim 3, wherein at least part of the intermediate shaft intersects a circle about the first axis that is coincident with the radially outermost part of the first drive gear.
12. A robot arm as claimed in any preceding claim, wherein the first and second axes are orthogonal.
13. A robot arm as claimed in any preceding claim, wherein the first and second axes intersect each other.
GB1512959.6A 2015-07-22 2015-07-22 Drive mechanisms for robot arms Pending GB2541369A (en)
GB1612781.3A GB2542254A (en) 2015-07-22 2016-07-22 Drive mechanisms for robot arms
US15/217,077 US10463436B2 (en) 2015-07-22 2016-07-22 Drive mechanisms for robot arms
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GB1612780.5A GB2541987A (en) 2015-07-22 2016-07-22 Drive mechanisms for robot arms
US15/217,061 US20170021506A1 (en) 2015-07-22 2016-07-22 Drive mechanisms for robot arms
US15/217,035 US10398516B2 (en) 2015-07-22 2016-07-22 Drive mechanisms for robot arms
EP16744496.7A EP3325224A1 (en) 2015-07-22 2016-07-22 Drive mechanisms for robot arms
JP2018074900A JP2018149675A (en) 2015-07-22 2018-04-09 Robot arm
JP2018074902A JP2018134732A (en) 2015-07-22 2018-04-09 Robot arm
GB201512959D0 GB201512959D0 (en) 2015-09-02
GB2541369A true GB2541369A (en) 2017-02-22
GB1512959.6A Pending GB2541369A (en) 2015-07-22 2015-07-22 Drive mechanisms for robot arms
GB1612780.5A Pending GB2541987A (en) 2015-07-22 2016-07-22 Drive mechanisms for robot arms
GB1612781.3A Pending GB2542254A (en) 2015-07-22 2016-07-22 Drive mechanisms for robot arms
US (3) US20170021506A1 (en)
JP6256470B2 (en) 2013-07-04 2018-01-10 株式会社安川電機 Robot, robot arm structure and drive device
US20170014197A1 (en) 2014-03-31 2017-01-19 Covidien Lp Wrist and jaw assemblies for robotic surgical systems
WO2015167808A1 (en) 2014-04-29 2015-11-05 Covidien Lp Surgical instruments, instrument drive units, and surgical assemblies thereof
2016-07-22 US US15/217,061 patent/US20170021506A1/en active Pending