Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
668
FIELD OF INVENTION
. _ _
This invention relates to an improved technique
for co-ordinating the extend/retract motions of a manipulator
arm assembly. In particular this invention relates to an
anthropornorphic manipulator arm assembly in which first and
second arm men~ers are connected to one another in a manner
such that the distal end of one member may be moved relative
to the proximal end of the other arm in a straight line.
PRIOR ART
_
In order to achieve maximum extend/retract motion
for a given maximum reach, spot mounted manipulator arms
commonly incorporate an elbow and discrete upper and lower
arm members. There are many applications in which the
operator must be able to control the motion of such a
manipulator arm while looking along the arm as for ex~ample
in submersible vehicles or when viewing is from a camera
mounted at the proximal end of the arm. In order to
facilitate the manipulation of such arms there should be
no apparent wrist an~le change due to an elbow movement
-20 as elbow movements are primarily commandecl in order to pro-
vide extend/retract motion. Furthermore, there should be
no apparent shoulder pitch or jaw movement due to an elbow
movement. There should be no cross-coupling between the
locator (shoulder and elbow) and orientor (wrist) movements
defined relative to an operator looking down the arm from -'
a point close to the spot mounting.
Considerable difficulty has been experienced in
attempting to meet these practical requirements in a simple
inexpensive manipulator arm assembly.
--1--
In a manipulator arm assembly described hereinafter
with reference to a prefe~red embodiment there is provided
a method of achieving non-coupled easily controlled arm
motion on a manipulator arm assembly where the radial reach
envelope has been maximised by incorporation of an elbow
between equal length upper and lower arm members. The
mechanism provides the control simplicity which is inherent
in a telescoping arm without many of the structural dis-
advantages of a conventional telescoping arm.
An important feature of the structure of the mani-
pulator arm assembly described hereinafter is that the
required non-cross coupled arm motions are each powered by
; discrete actuators with the result that all electrical and
hydraulic control channels can also be discrete. This serves
to maximise the simiplicity of the control system and
simplifies servicing.
SUMMARY OF INVENTION
According to one aspect of the present invention
a manipulator arm assembly comprises a first arm member
having a proximal end and a distal end, a second arm
member having a proximal end and a distal end, the length
of said second arm member from its proximal end to its
distal end being equal to that of said first arm member,
a shoulder joint at said proximal end of said first arm
member for supporting said first arm for extend/retract
rotation about a first axis, an elbow joint connecting
the distal end of said first arm to the proximal end of
said second arm for extend/retract rotation about a second
axis which extends parallel to said first axis, actuator
means drivingly connected to said first arm for rotatably
driving said first arm about said first axis at a first
angular velocity, first power transmission means drivingly
connecting said actuator means and said second arm to
6~8
rotatably drive said second arm about said axis, at a
second angu].ar velocity which is twice said first angular
velocity, but in the opposite direction to that in which
the first arm is driven about said first axis, as said
actuator means drives the first arm about said first axis
whereby said distal end of said second arm is driven in
a straight path which extends radially from said first axis
during both extension and retraction.
According to a further aspect oft~e present
inven~ion, a manipulator arm assembly comprises a first
arm member having a proximal end and a distal end, a
second arm member having a proximal end and a distal end,
a wrist member having a proximal end and a distal end, a
shoulder joint at said proximal end of said first arm mem-
ber for supporting said first arm member for extend/retract
rotation about a first axis, an elbow joint connecting the
distal end of said first arm member to the proximal end of
said second arm member for extend/retract rotation about
a second axis which extends parallel to said first axis,
a wrist joint connecting said distal end of said second
arm member to said proximal end of said wrist member for
extend/retract rotation about a third axis, at the distal
end of said arm member, said first and third axes being
equally spaced from said second axis, said wrist member pro-
jecting outwardly from said third axis in a first radial
direction with respect to said third axis, actuator means
drivingly connected to said first arm member for rotatably
driving sai.d first arm member about said first axis at a
first angular velocity, first power transmission means
drivingly connecting said actuator means and said second arm
member to rotatably drive said second arm about said
second axis, at a second angular velocity which is twice
said first angular velocity but in the opposite direction
to that in which said first arm member is driven about
said first axis, as said actua~or means drives said first
arm member about said first axis, second power trans-
mission means drivingly connecting said extend/retract
actuator means and said wrist member to rotatably drive
said wrist member about said third axis at an angular
velocity equal to said first angular velocity and in the same
angular direction as said first direction, as said first
power transmission means drives said second arm about said
second axis whereby the wrist joint at the distal end
of said second arm member is driven in a straight path which
extends radially from said first axis during both extension
and retraction of said arm assembly and said wrist ntember
is driven relative to said second arm member so as to be
retained in a position extending in said first radlal direc-
tion relative to said third axis as said arm assembly is
extended and retracted in use.
The invention will be more clearly understood
after reference to the following detailed specification
read in conjunction with the drawings wherein,
Figure 1 is a diagrammatic plan view of a ~:
manipulator arm constructed in accordance with an embodi-
ment of the present invention;
Figure 2 is a diagrar,tmatic plan view of a
manipulator arm constructed in accordance with a further
embodiment of the present invention;
Figure 3, 3a, 3b, 3c, 3d, 3e, and 3f are
diagrammatic side views showing various positions which
6~
the arm will assume in response to discrete operation of
the arm's pitch joint actuators (shoulder pitch, extend/
retract, wri~t pitch);
Figure 4 is a diagrammatic illustration of a
manipulator arm and a portion of its actuator mechanism;
Figure 5 is a vector diagram which provides
an analysis of the structure illustrated in Figure 4;
Figure 6 is a view similar to Figure 4 which
includes the power transmission means for operating the
distal end of the outer arm;
Figure 7 is an exploded pictorial view of an
underwater manipulator arm assembly incorporating a
pitch joint arrangement.
With reference to Figure 1 of the drawings, the
reference numeral 10 refers generally to a manipulator
arm assembly which comprises a first arm member 12 and a
second arm member 14. The first arm member 12 has its
proximal end mounted and fixed on the housing of extend/
retract actuator 24. The drive shaft 16 of the extend/
retrac~ actuator is coupled to the output drive shaft of
a shoulder pitch actuator 22 which is in turn mounted on
a support structure 20. A sprocket 26 is keyed to the
shaft 16 for rotation therewith. A second sprocket 28 is
mounted on a second drive shaft 30 which is located at .
the distal end of the first arm 12. The shaft 30 is
secured with respect to the proximal end of the arm 14
for rotation therewith relative to the distal end of the
arm 12. A sprocket 32 is secured against movement relative
to the distal end of the arm 12 and has its central axis
co-incident with the axis of the shaft 30. A second shaft
34 is mounted for rotation about its longitudinal axis
68
at the distal end of the arm 14. A sprocket 36 is keyed
to and rotatably drives the shaft 34 about its longitudinal
axis. A wrist pitch actuator 38 is drivingly rotatable
on the shaft 34 to control the pitch of the wrist member
40 with respect to the distal end of the arm 14. A first
drive chain 42 extends between sprocket 26 and 28 and
a second drive chain 44 extends between sprocket 32 and
36.
As will be described hereinafter in order to
obtain ~he required straight line motion of the distal
end of the arm 14, the arms 12 and 14 are of equal length
between shafts 16, 30 and 34. Furthermore, the sprockets
26 and 36 must have twice as many teeth as sprockets 28
and 32 respectively.
Figure 2 shows an equivalent arrangement where
wrist pitch actuator 38 has been moved up to the elbow
where it is fixed with respect to the distal end of
first arm member 12. In tllis arrangement the output
shaft 35 of the wrist pitch actuator 38 drives wrist
member 40 through the transmission comprising sprockets
32a and 36b and chain 44.
The operation of the manipulator arm of Figure
1 can thus be understood with reference to an analysis
of the relative motion which occurs as a result of
activating the extend/retract actuator 24 with reference
to Figures 3, 4 and 5 of the drawings.
With reference to Figures 1 and 4 of the drawings
consider what happens when the proximal end of the arm
12 is driven about the shoulder pitch axis 50 at an
angular velocity w~R by activating the extend/retract
actuator 24. Thus, with reference to Figure 3 of the
8~8
drawings, it will be seen that
C VB (VC) relB .L
where
B _ER ~ 1 _ 2
( c)relB WBC ~ A2
Where WBC Efl (~ C)relAB
_ER 2~ER
_ ~R . _ 4
Substituting 4 in 3
( c)relB _E~ ~ _2 _ 3 A :~
Substituting 3 A and 2 in 1
Vc = __ER A _1 W~R ~ 2
_E~ ~ (Al A2)
With reference to Figure 5 of the drawings, it
will be seen that since
Al A2 ~ the construction in the figure
shows Al- A2 is perpendicular to Al + A2 (the
_
vector along the line joining the shoulder and
wrist pitch axis) and since ~E~ iS perpendicular
to the plane containing Aland A2 and therefore
also perpendicular to Al - A2 ~ it fo~lows from
the definition of a vector product that Vc
lies along Al + A2
i.e. along the line AC. Thus actuation of the
extend/retract actuator results in pure extend/
retract motion.
If the sprockets 32 and 36 and their associated
chain 44 are added to the system as shown in Figure 5,
a symmetry argument becomes apparent in that the mechanism
appears identical when viewed from either side. It follows
that the shoulder connection at the proximal end of the
arm member 12 and the wrist connection at the distal end
of the arm member 14 are mirrored and there is therefore
no change in the orientation of the wrist member 40 as
the arm is extended or retracted.
Referring once again to Figures 1 and 2 of the
drawings, it will be seen that operation of the shoulder
pitch actuator 22 to rotatably drive the shaft 16 will
cause simultaneous rotation of the sprocket 26 and extend/
retract actuator 24 about the axis of the shaft 16 with
the result that the power transmission means associated with
the sprocket 26 will not move relative to the first arm
member 12 and consequently the pitch of the arm may be
varied without extending or retracting the arms by rotatably
driving the shoulder pitch actuator 22.
The advantages to be derived by employing the
technique for coordinating the extend/retract motion
according to the structures illustrated in Figures 1 and
2 of the drawings are readily apparent with reference to
Figures 3 to 3f inclusive.
With reference to these figures, it will be seen
that the proximal end of the arm member 12 is mounted for
rotation about the shoulder pitch axis 16a, the distal
end of the arm member 12 is pivotally connected to the
proximal end of the arm mem~er 14 for rotation about
elbow axis 30a and the wrist member 40 is connected at
the distal end of the arm member 14 for rotation about
-
~ ~t~ 8
wrist pitch axis 34a.
By activating the wrist pitch actuator 38 (Fig. 1)
the wrist member 40 may be progressively driven about the
wrist axis 34a as shown in Figures 3a and 3b of the drawings.
It will be noted that the wrist member 40 may be moved
independently of any movement of the arms 12 and 14. By
activating the shoulder pitch actuator 22 (Fig. 1) the
arm members 12 and 14 may be rotated about the shoulder
axis 16a as shown in Figures 3c and 3d without any resultant
change in the relative positions of the axm mcmbers 12, 14
and wrist member 40. By activating the extend/retract
actuator 24, the arm members 12 and 14 are caused to move
progressively from the extended position shown in Figure
3 to the intermediate position shown in Figure 3e and the
retracted position shown in Figure 3f, it will be noted
that the wrist member 40 remains in the same plane in
all positions of the arms during the extend/retract motion.
By incorporating this pitch coordinating mechanism
and actuator arrangement in an arm having the morphology
shown in Figure 7 an arm with both the control advantages
of a telescoping arm and the reach envelope advantages of an
articulated arm is achieved. A further advantage of the
apparatus of the invention described above is that it
permits the extend/retract actuator and wrist pitch actuator
to be located closer to the proximal end of the arm than
can be achieved with the conventional arm joint actuation
arrangements. This serves to reduce the arm dead weight
contribution to actuator loading for a given arm lift
capability and minimises wrist length.
Various modifications of the present invention
will be apparent to those skilled in the art. For example,
the mounting at the shoulder may be varied so as to provide
a single actuator which will selectively effect a shoulder
pitch movement or the extend/retract movement. ,This
structure may be used to advantage in order to provide
a minimum weight arm for application where a simultaneous
actuation of the arm extend/retract and shoulder pitch (or
yaw) is not required. In a further modified structure, the
wrist pitch actuator may be located at the shoulder with a
sprocket mounted for free rotation on the shaft 30 drivingly
engaging a further sprocket keyed to the shaft 34, each of
these sprockets having a one to one ratio. The second
design variation will provide a spatially stable wrist
pitch axis, i.e. the wrist side of the wrist pitch joint
will ~main at the same fixed orientation in space regardless
of shoulder pitcll and extend/retract tions. This may
be desirable in situations where, for example, an inspection
probe held by the arm is being scanned vertically up the
leg of an offshore structure.
Figure 7 illustrates a modular underwater arm of
a type which may incorporate the pitch jointarrangement
described above. The arm includes an interface mounting
plate 100 upon which a support member 102 is coupled by
means of an arm jettison assembly 104. A shoulder yaw
actuator has a splined shaft 108 mounted in a splined passage
110 in the support 102. The shoulder yaw actuator 106
is rotatable about the axis of the shaft 108. A shoulder
pitch actuator 113 is mounted on the shoulder yaw actuator.
The output shaft of this actuator is connected through
; 30 couplers 115 and 117 to the output shaft of the extend/retract
-- 10 --
~86~8
actuator 124 which is located at the proximal end of the
first arm 112. The proximal end of the second arm memher
114 is pivotally connected to the distal end of the first
arm 112 for rotation about shaft 130. A sprocket 126 is
drivingly connected to the extend/retract actuator shaft
coupling and a chain 142 drivingly connacts the sprocket
126 to a sprocket 128 which is fixed with respect to the
shaft 130 which in turn is fixed with respect to arm
member 114. ~ sprocket 132 is drivingly connected to a
wrist pitch actuator mounted within the distal end of the
arm member 112 and is connected to a sprocket 136 at the
- distal end of the arm member 114 by means of a chain 145
A wrist member 138 is mounted for rotation about the
wrist axis and is drivingly engaged by the sprocket 136.
The wrist memher 138 is in the form of a wrist yaw
actuator which supports a wrist extend/retract mechanism
140 which in turn supports a wrist roll actuator 142, a
rotary union 143, a tool engage/disengage mechanism
144, and a hook hand 146. By activating the extend/retract
actuator 124 of Figure 7, the arm of Figure 7 may be
caused to operate in the manner previously described with
reference to Figures 3, 3e and 3f. By operating the
wrist pitch actuator (not shown) which is located within
the distal end of the first arm 112 the wrist member 140
may be moved as shown with reference to Figure 3, 3a and 3b
of the drawings. By operating the shoulder pitch actuator
113 the arm assembly may be moved as shown in Figure 3,
3c and 3d of the drawings.
From the foregoing it will be apparent that the
present invention provides a simple and efficient mechanism
for achieving a coordinated extend/retract motion of a
manipulator arm.
-- 11 --
