GEAR PACKAGING FOR ROBOT ARMS
BACKGROUND
5 This invention relates to drive arrangements for robot joints, with particular relevance
to robot wrists.
Robots that are required to manipulate objects, which may for example be industrial
or surgical robots, frequently have an arm composed of rigid elements which are linked
10 together in series by a number of flexible joints. The joints could be of any type but
are typically revolute joints, or a combination of revolute and prismatic joints. The arm
extends from a base, whose location might be fixed or moveable, and terminates in a
tool or an attachment for a tool. The tool could, for example be a gripping, cutting,
illuminating, irradiating or imaging tool. The final joint in the arm may be termed the
15 wrist. The wrist may permit motion about only a single axis, or it may be a complex or
compound articulation, which permits rotation about multiple axes. As disclosed in our
co-pending patent application PCT/GB2014/053523, the wrist may provide two roll
joints whose axes are generally longitudinal to the arm, separated by two pitch/yaw
joints, whose axes are generally transverse to the arm.
20
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
25 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.
30 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
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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
5 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
10 sensors. It is desirable for the arm to include a path for such cables to pass in the
interior of the arm.
15
The number of important criteria makes it difficult to design an arm that best balances
all the requirements.
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.
20 There is a need for an improved drive arrangement for a joint of a robot arm.
25
Another particular problem is how to fit the torque sensors into the wrist of a robot arm.
The arrangement should be compact but also allow for high accuracy in torque
measurement.
There is a need for an improved torque sensor arrangement for a joint of a robot arm.
Another particular problem is how to fit position sensors motors into the wrist of a robot
arm. The arrangement should be compact but also allow for a high degree of
30 accuracy.
There is a need for an improved position sensor arrangement for a joint of a robot arm
and for other applications.
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SUMMARY OF THE INVENTION
According to the present invention there is provided 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
5 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 and fast with the carrier,
whereby rotation of the carrier relative to the first limb about the first rotation axis can
be driven; a second drive gear disposed about the second rotation axis and fast with
10 the second one of the limbs, whereby rotation of the second one of the limbs about
the second rotation axis relative to the carrier can be driven; at least one of the first
and second drive gears being a sector gear.
The first one of the first and second drive gears may be a sector gear. It may be that
15 only one of the first and second drive gears is a sector gear. That may be the first or
the second drive gear.
The or each sector gear may be a toothed gear.
20 The or each sector gear may be a bevel gear: i.e. a gear whose pitch surface is a
straight-sided or curved cone and/or whose teeth are arranged on such a cone.
The operative sector of the or each sector gear may be less than 180°.
25 At least part of one of the drive gears may intersect a circle about the axis of the other
one of the drive gears that is coincident with the radially outermost part of said other
one of the drive gears.
The carrier may carry an intermediate linkage for conveying drive to one of the drive
30 gears, and at least part of that linkage intersects a circle about the axis of the other
one of the drive gears that is coincident with the radially outermost part of said other
one of the drive gears.
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One or both of the first drive gears may be bevel gear(s).
One or both of the first drive gears may be skew axis gear(s).
5 The first and second axes may be orthogonal. The first and second axes may intersect
each other.
10
The or each sector gear may have a smaller outer radius in its non-operative sector
than in its operative sector.
The arm may comprise: a third limb adjacent the first limb and on the opposite side of
the first limb to the coupler; a fourth limb adjacent the second limb and on the opposite
side of the second limb to the coupler; a third revolute joint whereby the third limb and
the first limb are attached together, the third revolute joint having a third rotation axis
15 orthogonal to the first rotation axis; and a fourth revolute joint whereby the fourth limb
and the second limb are attached together, the fourth revolute joint having a fourth
rotation axis orthogonal to the second rotation axis.
20
25
The first and third axes may be orthogonal for all configurations of the joints.
The second and fourth axes may be orthogonal for all configurations of the joints.
The more distal one of the third and fourth limbs may comprise a tool or a tool
attachment.
One of the third and fourth limbs may be the most distal limb of the arm.
The third and fourth axes may be coincident for at least one configuration of the joints.
30 According to another aspect of the present invention there is provided a torque sensor
arrangement for attachment between a first part and a second part to sense torque
therebetween, the torque sensor arrangement comprising: an interface member
having on its exterior an engagement configuration for rotationally engaging the first
part; a torsion member comprising a deflectable body attached at one end thereof to
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the interface member and comprising, at the other end of the deflectable body, an
engagement configuration for rotationally engaging the second part; and a deflection
sensor attached to the deflectable body; wherein the interface member defines a rigid
sleeve extending around the deflectable body and the torque sensor arrangement
5 further comprises a bushing located between and in contact with both the sleeve and
the deflectable body.
10
15
20
25
The bushing may be a solid bushing. The bushing may be a unitary tube of material.
The bushing may be formed of plastics material.
The first part and the second part may be configured for mutual rotation about a
rotation axis. The bushing may surround the deflectable body about that axis.
The bushing may be a rigid bushing.
The first part and the second part may be configured for mutual rotation about a
rotation axis and the material of the bushing may be such as to substantially transfer
shear load about that axis from the deflectable body to the sleeve and such as to
substantially isolate torsion of the deflectable body from the sleeve.
The interface member may comprise a shoulder on the opposite side of the sleeve
from that at which the torsion member is attached to the interface member. The torsion
member may be configured to hold the bushing captive against the shoulder when the
torsion member is attached to the interface member.
The deflectable body is a hollow body. The deflectable body may be a hollow cylinder.
The deflectable body may be deflectable in torsion and/or bending about the axis of
the cylinder.
30 The deflection sensor may be a strain gauge.
The engagement configuration for rotationally engaging the first part may be a set of
gear teeth. The gear teeth may be of a bevel gear: i.e. a gear whose pitch surface is
a straight-sided or curved cone and/or whose teeth are arranged on such a cone.
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The engagement configuration for rotationally engaging the second part may be a
spline coupling.
5 The interface member may be rotationally engaged with the first part. The torsion
member may be rotationally engaged with the second part.
10
The torque sensor may be arranged for sensing torque between two limbs of a robot
arm.
According to another aspect of the present invention there is provided a rotary position
sensor arrangement for sensing rotary motion about a first rotation axis between a first
part and a second part, the arrangement comprising: a first ring defining a plurality of
magnetic poles, the first ring being attached to the first part; a second ring defining a
15 plurality of magnetic poles, the second ring being attached to the first part; a first
sensor attached to the second part for sensing motion of the magnetic poles of the
first ring past that sensor; and a second sensor attached to the second part for sensing
motion of the magnetic poles of the second ring past that sensor; the first ring and the
second ring being spaced apart along the rotation axis.
20
The first part may comprises material interposed between the poles of the first and
second rings. The said material may be metallic material. The said material may be
non-magnetically susceptible material.
25 The first and second part may be attached by a pair of bearings defining a revolute
joint about the rotation axis. The bearings may be located at the extremities of the
interface between the first and second parts along the rotation axis. The first ring may
be located at one of the bearings and the other ring may be located at the other of the
bearings.
30
The first ring may be located so as to lie in a common plane perpendicular to the
rotation axis with the said one of the bearings. The second ring may be located so as
to lie in a common plane perpendicular to the rotation axis with the said other of the
bearings.
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The first ring may be located around the said one of the bearings. The second ring
may be located around the said other of the bearings.
5 The spacing along the rotation axis between the first and second rings may be greater
than 5 times the thickness of the rings in the direction along the rotation axis. If the
rings are of different thicknesses, the spacing may be greater than 5 times the
thickness of the thinner of the rings.
10 The second part may be a first limb of a robot arm. The first part may be a coupler
whereby the first limb is attached to a second limb of the robot arm. The coupler may
be a rigid element.
The coupler may be attached to the second limb by a revolute joint having a second
15 rotation axis oblique, or more particularly orthogonal, to the first rotation axis.
20
25
The first and second sensors may be capable of sensing the relative position of poles
of the rings thereto to a resolution of two bits or more than two bits. The rings may
have different numbers of poles. The numbers may be co-prime.
BRIEF DESCRIPTION OF THE FIGURES
The present invention will now be described by way of example with reference to the
accompanying drawings. In the drawings:
Figure 1 is a general representation of a surgical robot arm.
Figure 2 shows in more detail the rotation axes at the wrist of the arm of figure 1.
30 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.
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Figure 5 shows part of a second wrist mechanism from proximally and one side.
Figure 6 shows part of the second wrist mechanism from distally and one side.
5 Figure 7 shows a third wrist mechanism from distally and one side.
Figure 8 shows the third wrist mechanism from distally and the other side.
Figure 9 shows the third wrist mechanism in section on a central longitudinal plane
10 viewed from one side.
Figure 10 shows the third wrist mechanism in section on a central longitudinal plane
viewed from the other side.
15 Figure 11 illustrates communication paths in a robot arm.
Figure 12 shows a terminal module for a robot arm in longitudinal cross-section.
DETAILED DESCRIPTION
20 The wrist mechanisms to be described below have been found to provide compact
and mechanically advantageous arrangements for at least some of the joints of a robot
wrist, or for other applications.
Figure 1 shows a surgical robot having an arm 1 which extends from a base 2. The
25 arm comprises a number of rigid limbs 3. The limbs are coupled by revolute joints 4.
The most proximal limb 3a is coupled to the base by joint 4a. It and the other limbs
are coupled in series by further ones of the joints 4. A wrist 5 is made up of four
individual revolute joints. The wrist 5 couples one limb (3b) to the most distal limb (3c)
of the arm. The most distal limb 3c carries an attachment 8 for a surgical instrument
30 or tool 9. Each joint 4 of the arm has one or more motors 6 which can be operated to
cause rotational motion at the respective joint, and one or more position and/or torque
sensors 7 which provide information regarding the current configuration and/or load at
that joint. For clarity, only some of the motors and sensors are shown in figure 1. The
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arm may be generally as described in our co-pending patent application
PCT/GB2014/053523. The attachment point 8 for a tool can suitably comprise any
one or more of: (i) a formation permitting a tool to be mechanically attached to the arm,
(ii) an interface for communicating electrical and/or optical power and/or data to and/or
5 from the tool, and (iii) a mechanical drive for driving motion of a part of a tool. In
general it is preferred that the motors are arranged proximally of the joints whose
motion they drive, so as to improve weight distribution. As discussed below,
controllers for the motors, torque sensors and encoders are distributed with the arm.
The controllers are connected via a communication bus to control unit 10.
10
A control unit 1 0 comprises a processor 11 and a memory 12. Memory 12 stores in a
non-transient way software that is executable by the processor to control the operation
of the motors 6 to cause the arm 1 to operate in the manner described herein. In
particular, the software can control the processor 11 to cause the motors (for example
15 via distributed controllers) to drive in dependence on inputs from the sensors 7 and
from a surgeon command interface 13. The control unit 1 0 is coupled to the motors 6
for driving them in accordance with outputs generated by execution of the software.
The control unit 10 is coupled to the sensors 7 for receiving sensed input from the
sensors, and to the command interface 13 for receiving input from it. The respective
20 couplings may, for example, each be electrical or optical cables, or may be provided
by a wireless connection. The command interface 13 comprises one or more input
devices whereby a user can request motion of the arm in a desired way. The input
devices could, for example, be manually operable mechanical input devices such as
control handles or joysticks, or contactless input devices such as optical gesture
25 sensors. The software stored in memory 12 is configured to respond to those inputs
and cause the joints of the arm to move accordingly, in compliance with a predetermined
control strategy. The control strategy may include safety features which
moderate the motion of the arm in response to command inputs. Thus, in summary,
a surgeon at the command interface 13 can control the robot arm 1 to move in such a
30 way as to perform a desired surgical procedure. The control unit 1 0 and/or the
command interface 13 may be remote from the arm 1.
Figure 2 shows the wrist 5 of the robot in more detail. The wrist comprises four
revolute joints 300, 301, 302, 303. The joints are arranged in series, with a rigid part
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of the arm extending from each joint to the next. The most proximal joint 300 of the
wrist joins arm part 4b to arm part 310. Joint 300 has a "roll" rotation axis 304, which
is directed generally along the extent of the limb 4b of the arm that is immediately
proximal of the articulations of the wrist. The next most distal joint 301 of the wrist
5 joins arm part 310 to arm part 311. Joint 301 has a "pitch" rotation axis 305 which is
perpendicular to axis 304 in all configurations of joints 300 and 301. The next most
distal joint 302 of the wrist joins arm part 310 to arm part 311. Joint 302 has a "yaw"
rotation axis 306 which is perpendicular to axis 305 in all configurations of joints 301
and 302. In some configurations of the wrist, axis 306 is also perpendicular to axis
10 304. The next most distal joint of the wrist 303 joins arm part 311 to arm part 4c. Joint
303 has a "roll" rotation axis 307 which is perpendicular to axis 306 in all configurations
of joints 302 and 303. In some configurations of the wrist, axis 307 is also
perpendicular to axis 305 and parallel with (and preferably collinear with) axis 304. It
is preferable for axes 305 and 306 to intersect each other, since this gives a particularly
15 compact configuration. Joints 300 and 303 may be positioned so that axes 304 and
307 can pass through the intersection of axes 305, 306 for some configurations of the
wrist.
This design of wrist is advantageous in that it allows a wide range of movement from
20 a tool attached to the attachment point 8 at the distal end of arm part 4c, but with the
wrist being capable of being assembled in a relatively compact form and without there
being singularities at certain parts of the range of motion that could demand
excessively high rates of motion at individual joints.
25 Figures 3 and 4 show one example of a mechanism suitable for implementing part of
the wrist 5 of the arm 1 of figure 1. Figures 3 and 4 concentrate (as to figures 5 to 1 0)
on the mechanism associated with the joints designated 301 and 302 in figure 2.
In the region of the wrist 5 the rigid arm parts 310, 311 have hollow outer shells or
30 casings 31 0', 31 0", 311 '. 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
5
10
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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: 31 0' and
31 0", 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 '.
The shell of arm part 310 (constituted by shell parts 31 0' and 31 0") and the shell of
arm part 311 (which extends from spur 311 ')are movable with respect to each other
about two rotation axes, shown at 20 and 21. These correspond to axes 305, 306 of
figure 2. Axes 20 and 21 are orthogonal. Axes 20 and 21 intersect. A central coupler
15 28 is mounted to arm part 310 by bearings 29, 30. The coupler extends between the
bearings 29, 30. The bearings 29, 30 hold the coupler fast with arm part 310 except
that they permit relative rotation of the coupler and that arm part about axis 20, thus
defining a revolute joint corresponding to joint 301 of figure 2. A further bearing 31
attaches the distal shell connector spur 311' to the coupler 28. Bearing 31 holds the
20 distal shell connector spur 311' fast with the coupler 28 except for permitting relative
motion of the spur and the coupler about axis 21, thus defining a revolute joint
corresponding to joint 302 of figure 2.
Two electric motors 24, 25 (see figure 4) are mounted in arm part 310. The motors
25 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
30 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 311 '.
Gear 33 is formed as a sector gear: that is its operative arc (defined in the example of
figures 3 and 4 by the arc of its teeth) is less than 360°.
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The gear train 35 is borne by the coupler 28. The gear train comprises an input gear
38 which engages the worm 34. Input gear 38 is located with its rotation axis relative
to the coupler 28 being coincident with axis 20. That means that the input gear can
5 continue to engage the worm 34 irrespective of the configuration of the coupler 28
relative to arm part 310 about axis 20. A series of further gears whose axes are
parallel with axis 20 transfer drive from the input gear 38 to an output gear 39 on a
shaft 40 whose rotation axis relative to the carrier 28 is parallel with but offset from
axis 20. Shaft 40 terminates in the worm 36. Shaft 40 extends parallel to axis 20.
10 The gears of gear train 35, together with shaft 40, are borne by the coupler 28.
The operation of the wrist mechanism will now be described. For motion about axis
20, motor 24 is operated to drive shaft 26 to rotate relative to arm part 310. This drives
the bevel gear 33 and hence coupler 28 and distal shell spur 311' to rotate about axis
15 20 relative to arm part 310. For motion about axis 21, motor 25 is operated to drive
shaft 27 to rotate relative to arm part 310. This drives the bevel gear 37 and hence
distal shell connector 311' to rotate about axis 21 relative to arm part 310. It will be
observed that if drive shaft 26 is rotated, driving the coupler 28 to rotate, whilst drive
shaft 27 remains stationary then gear 38 will also rotate relative to the coupler 28,
20 causing parasitic motion of the distal shell connector spur 311' about axis 21. To
prevent this, the control system 1 0 of the arm is configured so that when required there
is compensatory motion of drive shaft 27 in tandem with motion of drive shaft 26 so as
to isolate motion about axis 21 from motion about axis 20. For example, if it is required
to cause relative motion of shells 310, 311 about only axis 20 then motor 24 is operated
25 to cause that motion whilst motor 25 is simultaneously operated in such a way as to
prevent input gear 38 from rotating relative to carrier 28.
Various aspects of the mechanism shown in figures 3 and 4 are advantageous in
helping to make the mechanism particularly compact.
30 1. It is convenient for bevel gear 33 to be of part-circular form: i.e. its teeth do not
encompass a full circle. For example, gear 33 may encompass less than 270° or less
than 180° or less than 90°. This allows at least part of the other bevel gear 37 to be
located in such a way that it intersects a circle coincident with gear 33, about the axis
of gear 33 and having the same radius as the outermost part of gear 33. Whilst this
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feature can be of assistance in reducing the size of a range of compound joints, it is
of particular significance in a wrist of the type shown in figure 2, comprising a pair of
roll joints with a pair of pitch/yaw joints between them, since in a joint of that type there
is a degree of redundancy among the pitch/yaw joints and hence a wide range of
5 positions of the distal end of the arm can be reached even if motion about axis 20 is
restricted.
2. It is convenient if the part gear 33 serves rotation about the axis 20 by which the
carrier 28 is pivoted to the next-most-proximal arm part 310, as opposed to rotation
about axis 21, since the part gear can also be cut away to accommodate shaft 40
10 intersecting the said circle. That saves space by permitting the worm 36 to be located
on the opposite side of bevel gear 33 to the gear train 35. However, in other designs
the part gear could serve rotation about axis 21, so gear 37 could be of part-circular
form.
3. It is convenient if the worms 32, 34 are located on the opposite side of axis 20 to
15 bevel gear 37: i.e. that there is a plane containing axis 20 on one side of which are the
worms 32, 34 and on the other side of which is the bevel gear 37. This helps to provide
a compact packaging arrangement.
4. It is convenient if the worm 34 is located on the opposite side of bevel gear 33 from
worm 36 and/or that the gear train 35 is located exclusively on the opposite side of
20 bevel gear 33 from worm 36. This again helps to provide a compact packaging
arrangement.
5. The gears 33 and/or 37 are conveniently provided as bevel gears since that permits
them to be driven from worms located within the plan of their respective external radii.
However, they could be externally toothed gears engaged on their outer surfaces by
25 the worms 32, 34 or by radially toothed gears.
6. The bevel gear 33 is conveniently located so as to be interposed between worms
32 and 34. This helps the packaging of the motors 24, 25.
7. The bevel gears and the worm gears that mate with them can conveniently be of
hypoid or skew axis, e.g. Spiroid®, form. These gears allow for relatively high torque
30 capacity in a relatively compact form.
Figures 5 and 6 show a second form of wrist mechanism suitable for providing joints
301, 302 in a wrist of the type shown in figure 2.
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As shown in figure 5 the wrist comprises a pair of rigid external shells 31 0', 311' which
define the exterior surfaces of arm parts 310, 311 respectively of figure 2. 31 0' is the
more proximal of the shells. The arm parts formed of the shells 31 0', 311' can pivot
relative to each other about axes 62, 63, which correspond respectively to axes 305,
5 306 of figure 2. Axes 62, 63 are orthogonal. Axes 62, 63 intersect. The shells 31 0',
311' define the exterior of the arm in the region of the wrist and are hollow, to
accommodate a rotation mechanism and space for passing cables etc., as will be
described in more detail below. 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
10 composite such as resin-reinforced carbon fibre. The shells constitute the principal
rigid structure of the arm parts that attaches between the respective joints.
15
Figure 6 shows the same mechanism from distally and one side, with the shell 311'
removed for clarity.
Shell 31 0' 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 31 0', 311' is attached to the coupler 64 by a revolute joint: i.e. in such a
20 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 31 0' by bearings 70, 71 which permit
rotation between those first arms and the shell 31 0' 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 7 4 is concentric with
25 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 31 0'. 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.
30 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 31 0'. 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 31 0'.
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In this way the shafts 76, 77 can be driven by the motors to rotate with respect to the
proximal shell310'.
Shaft 76 and its associated motor operate motion about axis 62. Shaft 76 terminates
5 at its distal end in a worm gear 78 which engages bevel gear 7 4. Rotation of shaft 76
causes rotation of the bevel gear 7 4 relative to shell 31 0' about axis 62. Bevel gear
7 4 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 31 0', 311' about axis 62.
10 Shaft 77 and its associated motor operate motion about axis 63. In order to do that it
has ultimately to drive bevel gear 75 by means of a worm gear 79 carried by the
coupler 64. Rotation of that worm gear can cause relative rotation of the coupler and
the distal shell 311 '. To achieve this, drive is transmitted from the shaft 77 through a
pair of gears 80, 81 borne by the carrier 64 to a shaft bearing the worm gear 79. Shaft
15 77 approaches the carrier 64 from the proximal side. The gears 80, 81 are located on
the distal side of the coupler. The shaft 77 passes through the duct defined by tube
65 in the centre of the coupler. To accommodate motion of the coupler 64 relative to
the first shell 31 0' the shaft 77 has a universal or Hooke's joint 82 along its length. The
universal joint 82 lies on axis 62. Instead of a Hooke's joint the shaft could have
20 another form of flexible coupling, for example an elastic coupling (which could be
integral with the shaft) or a form of constant velocity joint.
This mechanism has been found to be capable of providing a particularly compact,
light and rigid drive arrangement for rotation about axes 62 and 63 without the
25 components of the mechanism unduly restricting motion of the shells. It permits both
motors to be housed in the proximal shell which reduces distal weight.
Various aspects of the mechanism shown in figures 5 and 6 are advantageous in
helping to make the mechanism particularly compact.
30 1. It is convenient for bevel gear 7 4 to be of part-circular form: i.e. its teeth do not
encompass a full circle. For example, gear 7 4 may encompass less than 270° or less
than 180° or less than 90°. This allows at least part of the other bevel gear 75 to be
located in such a way that it intersects a circle coincident with gear 7 4, about the axis
of gear 7 4 and having the same radius as the outermost part of gear 7 4. Whilst this
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feature can be of assistance in reducing the size of a range of compound joints, it is
of particular significance in a wrist of the type shown in figure 2, comprising a pair of
roll joints with a pair of pitch/yaw joints between them, since in a joint of that type there
is a degree of redundancy among the pitch/yaw joints and hence a wide range of
5 positions of the distal end of the arm can be reached even if motion about axis 62 is
restricted. As shown in figure 6, the bevel gear 7 4 is of reduced radius in the region
not encompassed by its teeth. Part-circular bevel gears of the other embodiments
may be formed in the same manner.
2. The gears 74 and/or75 are conveniently provided as bevel gears since that permits
10 them to be driven from worms located within the plan of their respective external radii.
However, they could be externally toothed gears engaged on their outer surfaces by
the worms 76, 79, or by radially toothed gears.
4. The bevel gears and the worm gears that mate with them can conveniently be of
skew axis, e.g. Spiroid®, form. These allow for relatively high torque capacity in a
15 relatively compact form.
Figures 7 to 10 illustrate another form of wrist mechanism. In these figures the shells
of arm parts 310, 311 are omitted, exposing the structure within the arm parts.
Proximal arm part 310 has a structural framework 100, which is shown in outline in
20 some of the figures. Distal arm part 311 has a structural framework 101. Arm parts
310 and 311 are rotatable relative to each other about axes 102, 103, which
correspond to axes 305, 306 respectively of figure 2. A carrier 1 04 couples the arm
parts 310, 311 together. Carrier 104 is attached by bearings 105, 190 to arm part 310.
Those bearings define a revolute joint about axis 102 between arm part 310 and the
25 carrier 104. Carrier 104 is attached by bearing 106 to arm part 311. Those bearings
define a revolute joint about axis 103 between arm part 311 and the carrier 104. A
first bevel gear 1 07 about axis 1 02 is fast with the carrier 1 04. A second bevel gear
1 08 about axis 1 03 is fast with arm part 311 .
30 As with the other mechanisms described herein, the carrier 104 is located inboard of
the limbs 310, 311.
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
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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
5 motion of bevel gear 1 08 relative to motor 11 0 when the coupler 1 04 moves about axis
1 02 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 1 04 by bearing 117.
10 It is convenient for bevel gear 107 to be of part-circular form: i.e. its teeth do not
encompass a full circle. For example, gear 107 may encompass less than 270° or
less than 180° or less than 90°. This allows at least part of the other bevel gear 108
to be located in such a way that it intersects a circle coincident with gear 107, about
the axis of gear 107 and having the same radius as the outermost part of gear 107.
15 Whilst this feature can be of assistance in reducing the size of a range of compound
joints, it is of particular significance in a wrist of the type shown in figure 2, comprising
a pair of roll joints with a pair of pitch/yaw joints between them, since in a joint of that
type there is a degree of redundancy among the pitch/yaw joints and hence a wide
range of positions of the distal end of the arm can be reached even if motion about
20 axis 102 is restricted.
The gears 107 and/or 108 are conveniently provided as bevel gears since that permits
them to be driven from worms located within the plan of their respective external radii.
However, they could be externally toothed gears engaged on their outer surfaces by
25 the worms attached to shafts 111, 112, or by externally toothed gears.
30
The bevel gears and the worm gears that mate with them can conveniently be of skew
axis, e.g. Spiroid®, form. These allow for relatively high torque capacity in a relatively
compact form.
Various changes can be made to the mechanisms described above. For example,
and without limitation:
- The axes corresponding to axes 305, 306 need not intersect and need not be
orthogonal.
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- The bevel gears or their outer toothed gear equivalents need not be driven by worms.
They could be driven by other gears.
- Either or both bevel gears could be part gears.
- In the examples given above, the mechanisms form part of a wrist for a robot arm.
5 The mechanisms could be used for other applications, for example for other parts of
robot arms, for robot tools, and for non-robotic applications such as control heads for
cameras.
As discussed above with reference to figure 1, each joint is provided with a torque
10 sensor which senses the torque applied about the axis of that joint. Data from the
torque sensors is provided to the control unit 1 0 for use in controlling the operation of
the arm.
Figures 9 and 1 0 shows one of the torque sensors and its mounting arrangement in
15 cross-section. Torque sensor 150 measures the torque applied about axis 103: that
is from carrier 1 04 to distal arm frame 1 01 . As described above, bevel gear 1 08 is fast
with frame 1 01 and rotatable about axis 1 03 with respect to the carrier 1 04. Bevel
gear 108 comprises a radially extending gear portion 151, from which its gear teeth
152 extend in an axial direction, and an axially extending neck 153. The neck, the
20 radially extending gear portion and the teeth are integral with each other. The interior
and exterior walls of the neck 153 are of circularly cylindrical profile. A pair of roller or
ball bearing races 1 06, 154 fit snugly around the exterior of the neck. The bearings
sit in cups in the carrier 1 04 and hold the neck 153 in position relative to the carrier
whilst permitting rotation of the bevel gear 108 relative to the carrier about axis 103.
25
The torque sensor 150 has a radially extending top flange 155, an axially elongate
torsion tube 156 which extends from the top flange, and an internally threaded base
157 at the end of the torsion tube opposite the flange. The top flange 155 abuts the
gear portion 151 of the bevel gear 108. The top flange is held fast with the gear portion
30 by bolts 158. The torsion tube 156 extends inside the neck 153 of the bevel gear 1 08.
The exterior wall of the torsion tube is of circularly cylindrical profile. The exterior of
the base 157 is configured with a splined structure which makes positive engagement
with a corresponding structure in the frame 1 01 so as to hold the two in fixed
relationship about axis 103. A bolt 159 extends through the frame 101 and into the
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base 157 to clamp them together. Thus, it is the torque sensor 150 that attaches the
bevel gear 1 08 to the arm frame 1 01, and the torque applied about axis 1 03 is applied
through the torque sensor. The torsion tube has a hollow interior and a relatively thin
wall to its torsion tube 150. When torque is applied through the torque sensor there is
5 slight torsional distortion of the torsion tube. The deflection of the torsion tube is
measured by strain gauges 160 fixed to the interior wall of the torsion tube. The strain
gauges form an electrical output indicative of the torsion, which provides a
representation of the torque about axis 1 03. The strain gauges could be of another
form: for example optical interference strain gauges which provide an optical output.
10
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 1 08 and the base 157 of the torque sensor. One possibility is to provide
15 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 1 03, 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
20 gear 1 08 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 1 08. The sleeve is sized so that it makes continuous contact with the
25 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
30 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
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a plastics material such as nylon, polytetrafluoroethylene (PTFE), polyethylene (PE)
or acetal (e.g. Delrin®), or of graphite or a metal impregnated with lubricant.
For easy assembly of the mechanism, and to hold the sleeve 161 in place, the interior
5 wall of the neck 153 of the bevel gear 108 is stepped inwards at 162, near its end
remote from the radially extending gear portion 151. When the sleeve 161 is located
between the neck 153 and the torsion tube 156, and the head 155 of the torque sensor
is bolted to the gear portion 151 the sleeve is held captive both radially (between the
torsion tube and the neck) and axially (between the head 155 of the torque sensor and
10 the step 162 of the interior surface of the neck 153 of the bevel gear). It is preferred
that the internal radius of the neck 153 in the region 163 beyond the step 162 is such
that the internal surface of the neck in that region is spaced from the torque sensor
150, preventing frictional torque transfer between the two.
15 Similar arrangements can be used for the torque sensor about the other axis 102 of
the embodiment of figures 7 to 10, and for the torque sensors of the embodiments of
the other figures.
Hall effect sensors are used to sense the rotational position of the joints. Each position
20 sensor comprises a ring of material arranged around one of the rotation axes. The
ring has a series of regularly spaced alternating north and south magnetic poles.
Adjacent to the ring is a sensor chip with a sensor array comprising multiple Hall effect
devices which can detect the magnetic field and measure the position of the magnetic
poles on the ring relative to the sensor array so as to provide a multi-bit output
25 indicative of that relative position. The rings of magnetic poles are arranged such that
each position of the respective joint within a 360° range is associated with a unique
set of outputs from the pair of magnetic sensors. This may be achieved by providing
different numbers of poles on each ring and making the numbers of poles the rings coprime
to each other. Hall effect position sensors employing this general principle are
30 known for use in robotics and for other applications.
More specifically, associated with each joint is a pair of alternatingly magnetised rings,
and associated sensors. Each ring is arranged concentrically about the axis of its
respective joint. The rings are fast with an element on one side of the joint and the
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sensors are fast with an element on the other side of the joint, with the result that there
is relative rotational motion of each ring and its respective sensor when there is rotation
of the robot arm about the respective joint. Each individual sensor measures where
between a pair of poles the associated ring is positioned relative to the sensor. It
5 cannot be determined from the output of an individual sensor which of the pole pairs
on the ring is above the sensor. Thus the individual sensors can only be used in a
relative fashion and would require calibration at power up to know the absolute position
of the joint. However by using a pair of rings designed so that the numbers of pole
pairs in each ring has no common factors it is possible to combine the inter-pole pair
10 measurement from both sensors and work out the absolute position of the joint without
calibration.
The magnetic rings and sensors are shown in figures 7 to 10. For the joint that
15 provides rotation about axis 1 02 position is sensed by means of magnetic rings 200
and 201 and sensors 202 and 203. For the joint that provides rotation about axis 103
position is sensed by means of magnetic rings 210, 211, sensor 212 and a further
sensor that is not shown. Magnetic ring 200 is fast with carrier 1 04 and mounted on
one side of the carrier. Magnetic ring 201 is fast with carrier 1 04 and mounted on the
20 other side of the carrier to magnetic ring 200. The magnetic rings 200, 201 are planar,
and arranged perpendicular to and centred on axis 1 02. Sensors 202 and 203 are
fast with the frame 100 of the arm part 310. Sensor 202 is mounted so as to be
adjacent to a side of ring 200. Sensor 203 is mounted so as to be adjacent to a side
of ring 201. Cables 204, 205 carry the signals from the sensors 202, 203. Magnetic
25 ring 210 is fast with carrier 104 and mounted on one side of a flange 220 of the carrier.
Magnetic ring 211 is fast with carrier 104 and mounted on the other side of the flange
220 to magnetic ring 200. The magnetic rings 210, 211 are planar, and arranged
perpendicular to and centred on axis 103. Sensor 212 and the other sensor for rotation
about axis 103 are fast with the frame 101 of the arm part 311. Sensor 212 is mounted
30 so as to be adjacent to a side of ring 210. The other sensor is mounted so as to be
adjacent to a side of ring 211.
Thus, in the arrangement of figures 7 to 1 0, rotation about each of the axes 1 02, 1 03
is sensed by means of two multi pole magnetic rings, each with a respective associated
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sensor. Each sensor generates a multi-bit signal representing the relative position of
the nearest poles on the respective ring to the sensor. By arranging for the numbers
of poles on the two rings to be co-prime the outputs of the sensors are in combination
indicative of the configuration of the joint within a 360° range. This permits the rotation
5 position of the joint to be detected within that range. Furthermore, in the arrangement
of figures 7 to 10 the two rings associated with each joint (i.e. rings 200, 201 on the
one hand and rings 210, 211 on the other hand) are located so as to be substantially
offset from each other along the axis of the respective joint. Ring 200 is located near
the bearing 190 on one side of the body of carrier 1 04 whereas ring 201 is located
10 near bearing 105 on the opposite side of the carrier 104. Ring 210 is located on one
side of the flange 220 whereas ring 211 is located on the other side of the flange 220.
Each ring is made of a sheet of material which is flat in a plane perpendicular to the
axis about which the ring is disposed. The magnetic rings of each pair (i.e. rings 200,
201 on the one hand and rings 210, 211 on the other hand) are spaced from each
15 other in the direction along their respective axes by a distance greater than 5 and more
preferably greater than 1 0 or greater than 20 times the thickness of the rings of the
pair. Conveniently, the rings of a pair can be on opposite sides of the respective joint,
as with rings 200, 201. Conveniently the carrier 104 to which the both rings of a pair
are attached extends radially outwardly so as to lie at a radial location that is between
20 the rings when viewed in a plane containing the respective rotation axis. Thus, for
example, flange 220 lies radially between rings 210 and 211. Conveniently the
respective joint can be supported or defined by two bearings, one on either side of the
joint along the respective axis, and at extreme locations on the joint, and the or each
ring for that joint can overlap a respective one of the bearings in a plane perpendicular
25 to the axis. Conveniently the sensors for the rings can be mounted on an arm part
that is articulated by the joint. The sensors can be mounted on opposite sides of the
arm part.
By spacing the rings apart the packaging of the joint and/or of the arm part where the
30 associated sensors are mounted can be greatly improved. Spacing the rings apart
allows for more opportunities to locate the rings at a convenient location, and allows
the sensors to be spaced apart, which can itself provide packaging advantages. It is
preferred that the joint is sufficiently stiff in comparison to the number of magnetic
poles on the rings that torsion of the joint under load will not adversely affect
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measurement. For example it is preferred that the joint is sufficiently stiff that under
its maximum rated operating load the elements of the joint cannot twist so much that
it can cause a change in the order of magnetic transitions at the sensors, even though
they are spaced apart. That permits direction to be detected, in addition to motion, for
5 all load conditions.
Arm part 311 is distal of arm part 310. Arm part 310 is proximal of the joint about axes
1 02 and 1 03 shown in figure 7 to 1 0. As discussed with reference to figure 1, data
from the torque sensors and the position sensors to be fed back to the control unit 1 0.
10 It is desirable for that data to be passed by wired connections that run through the arm
itself.
Each arm part comprises a circuit board. Figures 7 to 1 0 show a circuit board 250
carried by arm part 311. Each circuit board includes a data encoder/decoder (e.g.
15 integrated circuit 251 ). The encoder/decoder converts signals between formats used
locally to the respective arm part and a format used for data transmission along the
arm. For example: (a) locally to the arm part the position sensors may return position
readings as they are passed by magnetic pole transitions, the torque sensor may
return an analogue or digital signal indicative of the currently sensed torque and the
20 drive motors may require a pulse width modulated drive signal; whereas (b) for data
transmission along the arm a generic data transmission protocol, which may be a
packet data protocol such as Ethernet, can be used. Thus the encoders/decoders can
receive data packets conveyed along the arm from the control unit 1 0 and interpret
their data to form control signals for any local motor, and can receive locally sensed
25 data and convert it into packetised form for transmission to the control unit. The circuit
boards along the arm can be chained together by communication cables, so that
communications from a relatively distal board go via the more proximal boards.
In general it is desirable not to feed data from one component of the arm to a more
30 distal component of the arm. Doing so would involve cables running unnecessarily
distally in the arm, increasing distally distributed weight; and since the circuit boards
are chained together once data has been sent to a relatively distal board the next most
proximal board will handle the data anyway in order to forward it.
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The compound joint about axes 1 02, 1 03 has rotary position sensors 202, 203 (for
rotation about axis 1 02) and 212 (for rotation about axis 1 03). Sensors 202, 203 are
mounted on the frame 100 of the arm part 310 that is proximal of the joint whose
motion is measured by the sensor. Data from position sensors 202, 203 is fed along
5 cables 204, 205 which lead along arm part 310 proximally of the sensors. Sensor 202
is mounted on the frame 101 of the arm part 311. Data from position sensor 202 is
fed along a cable to circuit board 250 on the same arm part. In each case the data is
not passed to a more distal element of the arm than the one where the data was
collected.
10
The compound joint about axes 1 02, 1 03 has torque sensors 150 (for rotation about
axis 1 03) and 191 (for rotation about axis 1 02). Data sensed by torque sensors 150,
191 is carried in native form to circuit board 250 by flexible cables. At circuit board
250 the encoder/decoder 251 encodes the sensed data, e.g. to Ethernet packets, and
15 transmits it to the control unit 10. Thus, rather than being fed to the circuit board of
the more proximal arm part 310 for encoding, the data from the torque sensors is
passed to the circuit board of the more distal arm part for encoding, and then from that
circuit board it is passed by cables in a distal direction along the arm.
20 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
25 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.
As illustrated in figure 2, arm part 4c is borne by arm part 311 and can be rotated
30 relative to arm part 4c about axis 307. Figure 12 shows a cross-section through a
module that comprises arm part 4c. The module has a base 400 and a side-wall 440
which is fast with the base. Base 400 attaches to the end face 401 of the distal end
of arm part 311. (See figure 7). Arm part 4c is indicated generally at 403. Arm part
4c is rotatable relative to the base about an axis 402 corresponding to axis 307 of
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figure 2. To that end, arm part 4c is mounted to the side-wall 440 by bearings 430,
431 which define a revolute joint between side wall 440 and arm part 4c about axis
402.
5 Arm part 4c has a housing 404 which houses its internal components. Those
components include a circuit board 405 and motors 406, 407. Motors 406, 407 are
fixed to the housing 404 so they cannot rotate relative to it. The housing 404 is free
to rotate relative to the base 400 by means of the bearings 430, 431. A channel 408
runs through the interior of the module to accommodate a communication cable (not
10 shown) passing from circuit board 250 to circuit board 405. The communication cable
carries signals which, when decoded by an encoder/decoder of circuit board 405,
cause it to issue control signals to control the operation of motors 406, 407.
Motor 406 drives rotation of arm part 4c relative to arm part 311. Thus, motor 406
15 drives rotation of housing 404 relative to base 400. Base 400 has a central boss 41 0.
A torque sensor generally of the type discussed in relation to figures 9 and 10 is
attached to the boss 410. The torque sensor has an integral member comprising a
base 411, a torsion tube 412 and a radially extending head 413. The base 411 of the
torque sensor is fast with the boss 410 of the base 400. As with the torque sensor of
20 figures 9 and 10, a sleeve 421 extends around the torsion tube of the torque sensor
to protect it from shear forces and to reduce friction between it and the surrounding
component, which is the base 400.
An internally toothed gear 420 is fast with the head 413 of the torque sensor. Motor
25 406 drives a shaft 414 which carries a pinion gear 415. Pinion gear 415 engages the
internal gear 420. Thus, when the motor 406 is operated it drives the pinion gear 415
to rotate and this causes the arm part 4c, of which the motor 406 is part, to rotate
about axis 402. The resulting torque about axis 402 is transmitted to the base 400
through the torsion tube 412 of the torque sensor, allowing that torque to be measured
30 by strain gauges attached to the torsion tube.
The interface 8 for attachment to an instrument is shown in figure 12. The shaft 440
of motor 407 is exposed at the interface for providing drive to an instrument.
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Torque data from the torque sensor 411, 412, 413 is passed to circuit board 250 on
arm part 311 for encoding. The rotational position of arm part 4c can be sensed by a
sensor 445 carried by arm part 4c and which detects transitions between magnetic
poles on rings 446, 447 mounted on the interior of housing 404. Data from sensor 445
5 is passed to circuit board 405 of arm part 4c for encoding.
The motors that drive rotation about joints 1 02 and 1 03 are mounted proximally of
those joints, in arm part 310. As discussed above, this improves weight distribution
by avoiding weight being placed nearer to the distal end of the arm. In contrast, the
10 motor that drives rotation of arm part 4c is mounted in arm part 4c rather than in arm
part 311. Although this might be seen as disadvantageous due to it requiring motor
406 to be mounted more distally, it has been found that this allows for arm part 311 to
be especially compact. Motor 406 can be packaged in arm part 4c in parallel with the
motor(s) (e.g. 407) which provide drive to the instrument: i.e. so that the motors
15 intersect a common plane perpendicular to the axis 402. That means that
incorporation of motor 406 in arm part 4c need not make arm part 4c substantially
longer.
20
Instead of toothed gears, the drive of the joints could be by frictional means.
The applicant hereby discloses in isolation each individual feature described herein
and any combination of two or more such features, to the extent that such features or
combinations are capable of being carried out based on the present specification as a
whole in the light of the common general knowledge of a person skilled in the art,
25 irrespective of whether such features or combinations of features solve any problems
disclosed herein, and without limitation to the scope of the claims. The applicant
indicates that aspects of the present invention may consist of any such individual
feature or combination of features. In view of the foregoing description it will be evident
to a person skilled in the art that various modifications may be made within the scope
30 of the invention.

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 and fast with the carrier,
whereby rotation of the carrier relative to the first limb about the first rotation axis can
be driven;
a second drive gear disposed about the second rotation axis and fast with the
second one of the limbs, whereby rotation of the second one of the limbs about the
second rotation axis relative to the carrier can be driven;
at least one of the first and second drive gears being a sector gear.
2. A robot arm as claimed in claim 1, wherein the first one of the first and second drive
gears is a sector gear.
3. A robot arm as claimed in any preceding claim, wherein only one of the first and
second drive gears is a sector gear.
4. A robot arm as claimed in any preceding claim, wherein the or each sector gear is
a toothed gear.
5. A robot arm as claimed in any preceding claim, wherein the operative sector of the
or each sector gear is less than 180°.
6. A robot arm as claimed in any preceding claim, wherein at least part of one of the
drive gears intersects a circle about the axis of the other one of the drive gears that is
coincident with the radially outermost part of said other one of the drive gears.
7. A robot arm as claimed in any preceding claim, wherein the carrier carries an
intermediate linkage for conveying drive to one of the drive gears, and at least part of
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that linkage intersects a circle about the axis of the other one of the drive gears that is
coincident with the radially outermost part of said other one of the drive gears.
8. A robot arm as claimed in any preceding claim, wherein one or both of the first drive
gears is/are bevel gear(s).
9. A robot arm as claimed in claim 8, wherein one or both of the first drive gears is/are
skew axis gear(s).
10. A robot arm as claimed in any preceding claim, wherein the first and second axes
are orthogonal.
11. A robot arm as claimed in any preceding claim, wherein the first and second axes
intersect each other.
12. A robot arm as claimed in any preceding claim, wherein the or each sector gear
has a smaller outer radius in its non-operative sector than in its operative sector.
13. A robot arm as claimed in any preceding claim, wherein the arm comprises:
a third limb adjacent the first limb and on the opposite side of the first limb to
the coupler;
a fourth limb adjacent the second limb and on the opposite side of the second
limb to the coupler;
a third revolute joint whereby the third limb and the first limb are attached
together, the third revolute joint having a third rotation axis orthogonal to the first
rotation axis; and
a fourth revolute joint whereby the fourth limb and the second limb are attached
together, the fourth revolute joint having a fourth rotation axis orthogonal to the second
rotation axis.
14. A robot arm as claimed in claim 13, wherein the first and third axes are orthogonal
for all configurations of the joints.
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15. A robot arm as claimed in claim 13 or 14, wherein the second and fourth axes are
orthogonal for all configurations of the joints.
16. A robot arm as claimed in any of claims 13 to 15, wherein the more distal one of
the third and fourth limbs comprises a tool or a tool attachment.
17. A robot arm as claimed in any of claims 13 to 16, wherein one of the third and
fourth limbs is the most distal limb of the arm.
18. A robot arm as claimed in any of claims 13 to 17, wherein the third and fourth axes
are coincident for at least one configuration of the joints.
19. A torque sensor arrangement configured to attach between a first part and a
second part to sense torque therebetween, the torque sensor arrangement
comprising:
an interface member having on its exterior an engagement configuration
configured to rotationally engage the first part;
a torsion member comprising a deflectable body attached at one end thereof to
the interface member and comprising, at the other end of the deflectable body, an
engagement configuration configured to rotationally engage the second part; and
a deflection sensor attached to the deflectable body;
wherein the interface member defines a rigid sleeve extending around the deflectable
body and the torque sensor arrangement further comprises a bushing located between
and in contact with both the sleeve and the deflectable body.
20. A torque sensor arrangement as claimed in claim 19, wherein the bushing is a
solid bushing.
21. A torque sensor arrangement as claimed in claim 20, wherein the bushing is a
unitary tube of material.
22. A torque sensor arrangement as claimed in any of claims 19 to 21, wherein the
bushing is formed of plastics material.
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23. A torque sensor arrangement as claimed in any of claims 19 to 22, wherein the
first part and the second part are configured to mutually rotate about a rotation axis
and the bushing surrounds the deflectable body about that axis.
24. A torque sensor arrangement as claimed in any of claims 19 to 23, wherein the
bushing is a rigid bushing.
25. A torque sensor as claimed in any of claims 19 to 24, wherein the interface
member comprises a shoulder on the opposite end of the sleeve from that at which
the torsion member is attached to the interface member, and the torsion member is
configured to hold the bushing captive against the shoulder when the torsion member
is attached to the interface member.
26. A torque sensor as claimed in any of claims 19 to 25, wherein the deflectable body
is a hollow body.
27. A torque sensor as claimed in claim 26, wherein the deflectable body is a hollow
cylinder.
28. A torque sensor as claimed in any of claims 19 to 27, wherein the deflection sensor
is a strain gauge.
29. A torque sensor as claimed in any of claims 19 to 28, wherein the engagement
configuration is configured to rotationally engage the first part is a set of gear teeth.
30. A torque sensor as claimed in any of claims 19 to 29, wherein the engagement
configuration is configured to rotationally engage the second part is a spline coupling.
31. A torque sensor as claimed in any of claims 19 to 30, wherein the interface
member is rotationally engaged with the first part and the torsion member is
rotationally engaged with the second part.
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32. A robot arm comprising two limbs and a torque sensor as claimed in any of claims
19 to 31 configured to sense torque between two limbs of the arm.
33. A robot arm having a first limb and a second limb connected by a revolute joint,
comprising a rotary position sensor arrangement for sensing rotary motion about a first
rotation axis between a first part and a second part, the arrangement comprising:
a first ring defining a plurality of magnetic poles, the first ring being attached to
the first part;
a second ring defining a plurality of magnetic poles, the second ring being
attached to the first part;
a first sensor attached to the second part for sensing motion of the magnetic
poles of the first ring past that sensor; and
a second sensor attached to the second part for sensing motion of the magnetic
poles of the second ring past that sensor;
the first ring and the second ring being spaced apart along the rotation axis and on
opposite sides of the revolute joint.
34. A robot arm as claimed in claim 33, wherein the first part comprises material
interposed between the poles of the first and second rings.
35. A robot arm as claimed in claim 33 or 34, wherein the first and second part are
attached by a pair of bearings defining the revolute joint about the rotation axis, the
bearings being located at the extremities of the interface between the first and second
parts along the rotation axis, and wherein the first ring is located at one of the bearings
and the other ring is located at the other of the bearings.
36. A robot arm as claimed in claim 35, wherein the first ring is located so as to lie in
a common plane perpendicular to the rotation axis with the said one of the bearings
and the second ring is located so as to lie in a common plane perpendicular to the
rotation axis with the said other of the bearings.
37. A robot arm as claimed in claim 35 or 36, wherein the first ring is located around
the said one of the bearings and the second ring is located around the said other of
the bearings.
wo 2017/013451 PCT/GB2016/052262
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38. A robot arm as claimed in any of claims 33 to 37, wherein the spacing along the
rotation axis between the first and second rings is greater than 5 times the thickness
of the rings in the direction along the rotation axis.
39. A robot arm as claimed in any of claims 33 to 38, wherein the first limb comprises
the second part and the first part is a coupler whereby the first limb is attached to a
second limb of the robot arm.
40. A robot arm as claimed in claim 39, wherein the coupler is attached to the second
limb by a revolute joint having a second rotation axis oblique to the first rotation axis.
41. A robot arm substantially as herein described with reference to figures 1 to 12 of
the accompanying drawings.