Note: Descriptions are shown in the official language in which they were submitted.
WO9S/11780 ~ PCT/CA94/00~83
Title: M~ NT~M~ FOR ORl~'L.~ AND PI~CII~G ARTIC~B~
Field of the Invention
This invention relates to the field of
mechAnicms and particularly to me~h~nicms suited for use
in the field of robotics. The described mechAnicms are
not, however, limited to that field but are suited to
applications wherever an article is to be oriented or
displaced within a given workspace. The described
mechAn;sms can also be used as sensors to detect both
rotational and translational motions.
Back~l oulld to the Invention
~ech~ni~ms are mechAnical structures
synthesized with assemblages of joints and links designed
to provide them with predictable structural, kinematic
and dynamic properties. They are the basis for vast
numbers of applications including cars, aircraft, optical
instruments, manipulation devices, etc. and as such are
particularly important elements of most technological
systems.
M~rhAn;sms are synthesized by constraining
joints or articulations to fixed relationships by means
of links. A kinematic analysis assumes links to be
ideally rigid. Most mech~n;~ms can be described by
selecting one ouL~uL link and one ground link and
defining the elements there-between.
WO95/11780 2 ~ ~ 5 2 a 6 PCT/CAg~/00583
Parallel mech~n;fims, a vast sub-class of all
m~ n;~ -, offer an opportunity for improved structural
properties with rigidity, light weight and improved
dynamic properties. Parallel me~h~n;sms used in drives
allow actuators to be placed at locations where they
contribute the least to an increase of inertia. Further,
improved accuracy can be achieved by eliminating the
accumulation of errors.
Unfortunately, most known parallel m~rh~n;e~c
with more than two or three degrees of freedom suffer
from a reduced usable workspace. The invention reported
herein achieves a significant improvement in this areaO
If a chain of links and joints forms loops,
then the merh~n;~m is termed parallel. If a mech~n;~em
requires exact geometrical properties to poeeeee mobility
(degrees of freedom), it is termed over-constrained. If
a ~?^hAn;em has no mobility, it is called a 'structure'.
(The term 'structure' may apply to other notions but
should be clear by context). If there are no loops the
me~-h~n;em is called serial.
As joints play a central role in mechAn;ems and
are needed to describe the invention, they are defined
herein. The joints needed to describe the invention
belong to the class of lower pairs because they can be
defined by specifying certain pairs of surfaces which
have the property of allowing relative motion without the
W O 95/11780 ~ PCT/CA94/00583
surface contact being lost. Two surfaces of revolution
form the revolute joint which has one angular degree of
freedom. Two cylindrical surfaces define the cylindrical
joint which has two degrees of freedom, one angular about
the axis of the cylinder and one translational along the
same axis. Two surfaces Ch~r~ as parallel prisms form
the prismatic joint which has one freedom of
translational motion. The modes of realization of these
basic joints include a variety of t~chn; ques, e.g.
rolling elements of locally deforming members, but these
do not change the definition.
A "universal" joint is composed of two non-
collinear, preferably orthogonal revolute joints with a
centre of rotation at the intersection of their axes.
The spherical joint has three degrees of
angular freedom of motion. A spherical joint may be
composed of spherical surfaces in contact, vis, a
ball-in-socket; or can be created by three orthogonal
revolute joints with a centre of rotation at the
intersection of their aXes.
A "gimbal" joint has three revolute joints
positioned to rotate about a common centre of rotation.
Actuated joints are equipped to provide
mechanical power derived from an external source.
25 Passive joints are left free to move by virtue of the
WO9~/11780 PCT/CA9~/00583
2 ~ ~5206
forces present in the links. Joints may be actuated to
provide rotational or translational motion.
Any joint can be instrumented with sensors to
measure position or velocity of the relative motion of
links. MechAn;cms can, therefore, be reversed in their
functions. Rather than controlling a driven link through
actuators placed at joints, the actuators may be replaced
by sensors which detect the position and/or orientation
of the former "driven" but now "sensing" link. In such
cases it is particularly important for the mec-h~nicm to
have reduced inertia in order to permit it to track
higher frequency oscillations to which the sensing link
may be exposed. Meçh~n;sms which are both instrumented
and actuated are amenable to feedback control as applied
to most drive systems.
As a further variant on the application of such
mech~n;cms, actuators may be placed by locking devices
such as "brakes". In this configuration, a mechAn;sm can
be positioned to provide support as a jig, and then
become locked in place. In such application, it is
desirable for the locked m~çh~n;cm to remain precisely
positioned after being locked.
Four bar mech~n;cms having four links and four
joints are used in a bewildering number of applications.
Many functions can be accomplished by changing the four
kinematic design parameters (link lengths). If the axes
WO95/11780 2 1 7 5 ~ 3 6 PCT/CA94/00583
of joints are not exactly parallel, the "m~ch~n;cm"
becomes a structure with rare exceptions.
In a four-bar planar mech~n;sm, if one link is
grounded as a "base" link, then the link opposite the
ground link - the output or driven link - can be
displaced along a curve in a plane through the
manipulation of the links proximate to the base line -
the "proximal" links. The driven link may carry an
object or a further mech~n;sm, such as a claw, tool or
"end effector".
A five-bar m~-h~n;cm has five links and five
joints. If one link is grounded as a "base" link, then
the joint opposite the grounded link - the "driven joint"
- can be displaced in a plane through the manipulation of
the links proximate to the base link - the "proximal"
links. The remaining two links next to the driven joint
may be classified as "distal links".
Prior Art
Two backyLo~sld papers of interest to the
present invention are:
- Pierrot F., Dombre, E. l99l. "Parallel
Structures for Robot Wrists~. In Advances in
Robot Kinematics. Stifter, S., Lenarcic
(eds.). Sprinter-Verlag. pp. 476-484; and
WO9~/11780 2 t ~ ~ Q 6 PCT/CA9~/OOS83
- Inoue, H., Tsukasa, Y., Fukuizumi, T. 1986.
"Parallel Manipulator." In The Third
International Symposium on Robotics Rece~rch.
Faugeras, O.E., Giralt, G. (eds). MIT Press.
pp. 321-327.
The Pierrot/Dombre paper describes a series of
parallel structures commencing with the basic Stewart
platform. One structure, "P4" in this paper, introduces
a constraint for the upper platform which includes a
universal and prismatic joint. In this P4 structure,
three symmetrically placed, two-link supports extend
between the lower and upper platforms. The joints for
these supports are variously spherical and universal and
actuation is effected through rotary actuators. In the
Inoue/Fukuizumi paper an upper platform is supported by
three symmetrically placed 5-bar linkages called
"pantograph" links in the paper. The upper platform is
otherwise unconstrained and actuation is effected through
rotary actuators.
Nhile both provide interesting designs, these
papers do not suggest the configuration proposed herein
to provide a "wrist" type orienting mechAn;~m of the type
hereinafter described.
A patent of interest is U.S. 5,219,266 issued
15 June, 1993 on an invention by Claude Reboulet and
Claude Lambert. This references three five bar linkages
WO9S/11780 2 1 7 ~ PCT/CA94/00583
constrained to elevate a platform so that it can be
laterally displaced at a predetermined altitude.
A further reference prepared by the present
inventor is an article - Borrowing some Ideas from
Biological Manipulators to Design an Artificial One -
published in "Robots and Biological systems", Nato
Series, R. Dario, P. Aebisher and G. SAn~;ni (Eds.),
Springer Verlag pp 139-151. (1993). Figure 12 of this
reference depicts a platform type m~chAni~m with the
platform constrained to rotate around a central spherical
joint and actuated by four piston type actuators attached
at both ends by spherical joints.
While the text of this reference refers to this
arrangement as having a useful range of motion, with no
self-interference, the fact that all joints are depicted
as spherical, and that multiple links are attached to
such joints means that a proper mec-hAnism, with the
capacity for structural integrity has not been described.
Accordingly, this reference does not suggest the
invention hereinafter disclosed.
The present invention addresses the need for
providing an advantageous dual-five bar merhAnicm to
effect, or track, rotational motion in two or three
degrees of rotational freedom plus one optional degree of
25 translational motion. This dual-five bar mechAni! can
be combined advantageously with a linkage that serves as
W O 95/11780 2 t ~ ~ ~ a-~ PC~r/CA94/00583
a positional me~h~n;c~ and provides further degrees of
translational freedom.
This simple positional mechAn;~m can perform
either as a actuated or sensing device in its own right.
It employs a parallel arrangement that is akin to that of
the forearm of a human. In doing so, it benefits from
the intrinsic characteristics of a parallel mech~n;~m.
That invention in its general form will now
first be described, and then its implementation in terms
of specific embodiments will be detailed with reference
to the drawings following hereafter. These embodiments
are intended ~o demonstrate the principle of the
invention, and the manner of its implementation. The
invention in its broadest and more specific forms will
then be further described, and defined, in each of the
individual claims which conclude this Specification.
Summary of the Invention
"Orienting M~chAn;~m~'
This invention relates to an orienting assembly
for effecting the rotational displacement about a fixed
point of an end member supported by a rotational support
joint hàving two or three degrees of rotational freedom
that is carried to a base. Additionally, translational
displacements of the end member from that fixed point may
also be effected by provision of a cylindrical joint
~ WO95/11780 ~ 6. PCT/CA94/00583
which is located in the path of the support provided to
the end member by the rotational support joint. This
includes, for example, locating the cylindrical joint
between the end member and the support joint within the
support joint, or between the support joint and the base.
In order to control the orientation of the
manipulated end member with either two or three degrees
of rotational freedom, two, paired "5-bar" linkage
assemblies are employed, each equipped with actuators.
The 5-bar linkages are each supported by a revolute joint
connected between the base link of the 5-bar assembly the
base which serves as a llylOul~d". The opposed, "driven"
joint of each 5-bar linkage is coupled by universal or
spherical joints to the end member which is to be
oriented. The actuators employed may either be
translational or rotary.
In one variant of the invention employing
rotary actuation this mechAn;~m relies upon two pairs of
rotational actuators positioned at two of the joints of
each 5-bar linkage. Preferably the rotary actuators are
positioned at the two joints located at the ends of the
base link that connect to the two "proximal" links. In
another variant of the invention, linear actuators are
placed between the ends of the base link and the driven
joint in each 5-bar linkage. In both cases, actuation
means are used to control the position of the driven
WO95111780 PCT1CA9~100583
21 75Z~ ~
joint with respect to the base link, and thereby the
orientation of the end member.
In the case of the use of linear actuators
these elements may only be positioned between the
proximal links and the "distal" links which join the
proximal links to the driven joint.
The driven joint of the 5-bar linkage, opposite
the base link, may be connected to the end member through
either a universal or spherical joint. If this joint is
universal, then the end member may be manipulated by the
actuator to effect pitch and yaw motions. If the
connecting joints between the driven joint and end member
are spherical, then roll motions may also be achieved.
All these rotations occur within a large workspace due to
limited interference from the 5-bar linkages.
In the case where couplings between the driven
joints of each 5-bar assembly and the end member are
universal, providing only two rotational degrees of
freedom, then the mech~n;Rm in this degenerate form will
still function usefully as a "pointing" mech~n;~m.
Applications for such a device include supporting
microwave antennae, telescopes and directional laser
mounts, rocket engines and boring heads.
When the support joint for the end member has
only two degrees of rotational freedom then the end
member may only be pointed.
WO95/11780 ~ ~ 7 ~ ~ O 6 PCT/CA94/00583
11
In either case, an advantage of this
configuration is that the full weight of the pointed
element is carried by the pivotal mount at the center of
rotation of the rotational joint supporting the end
member. Thus the actuators associated with the 5-bar
linkages never need to carry any of the load of the
apparatus which is being oriented.
In the rotary variant of the invention where
three degrees of rotational freedom are desired, four
rotational actuators are preferably provided. These are
preferably mounted, in pairs, at the ends of the base
link of the respective 5-bar linkages, just above the
grounded revolute joint to apply a positioning force
between their respective proximal linkages and the base
lS link. This may be effected by employing a common shaft
for the revolute joints which these proximal links then
share.
The mechAn;~m is inherently light and has low
inertia. Rotational positioning may be provided by
tendons. The mechAn;cm may be utilized in either input
or output mode and may be inverted. In telerobotic
applications it will provide a high band-width level of
sensory feed-back to an operator.
More generally, the invention may be described
as an actuable me~hAni~m for orienting an end member with
respect to a base, the end member being constrained by
wos~ 78o PCTICA9~100~83
~ ~ 7~206; 12
a support joint with is grounded to the base, such
support joint having two or three rotational degrees of
freedom and a centre of rotation for said two or three
of said degrees of rotational freedom, such meçh~n;~m
comprising two 5-bar linkages each defining a closed loop
and having:
(a) a base link with two ends, such base link
being connected to the base through a revolute
joi~t;
(b) first and second proximal links connected
respectively to the ends of the base link;
(c) a driven joint positioned opposite to said
base link and joined thereto by first and
second distal links which are respectively
coupled through said proximal links to said
base link; and
(d) first and second actuated joints positioned
within said closed loop between said base link
and said driven joint for displacing the
driven joint with respect to the base link,
wherein the driven joints of each of said 5-bar linkages
are each respectively connected to the end member at
connection points through twinned joints which are either
twinned spherical joints or twinned universal joints,
being twinned with respect to the two distal links, said
connection points being non-coincident with the centre of
WO95/11780 ~ a 6 PCT/CA94/00583
rotation for the support joint, thereby to provide
mobility to the end member with respect to said base in
response to said actuators. A twinned universal joint is
defined as a single universal joint with an additional
third joint mounted co-axially on an extension to the
axle of one of the original joints, thus adding a
coupling for another link having two degrees of
rotational freedom.
The m~ch~nicm of the invention may have first
and second actuated joints within each 5-bar linkage
which are rotational joints, positioned respectively
between the ends of the base link and the driven joint.
More preferably, such first and second actuated
rotational joints are positioned respectively at the ends
of the base link, between such ends and the respective
proximal links.
Alternately, a me~hAn;~m of the invention may
have first and second actuated joints which are sliding
joints, positioned respectively between the proximal and
distal links.
If the rotational freedom of the end member is
to be limited to that suited for a pointing mech~n;sm,
the said twinned universal joints in each 5-bar linkage
may comprise three revolute joints, the first and second
of which joints having coinciding axes and being
connected to the distal links; the third of such joints
_
WO95/11780 ~ 1 7 5 2 0 6 PCT/CA94/00583
14
being positioned between the first and second joints and
the end member, all of said joints having a common centre
of rotation. In the fully spherical embodiment, the
twinned spherical joints respectively connecting the dual
5-bar linkages to the end member may each comprise four
revolute joints, the first and second of which are
respectively co~nected to distal links and have
coinciding axes, all of the axes of said joints having a
common centre of rotation.
As an additional option, the me~-h~n;cm of the
invention may further incorporate a cylindrical joint
positioned between the end member and the base, in the
path carrying the support provided by the support joint
as, for example, within the support joint, to permit the
end member to be translationally displaced with respect
to the centre of rotation for the end member.
Some of the features of the embodiments of the
invention may be summarized as follows:
(l) The m~ch~nism of the present invention may
have four degrees of freedom: three in
angular motions and one in translational
motion. If the translational motion is not
used it reduces to a spherical mechAn;sm. If
one selected rotational degree of freedom is
suppressed, it becomes a pointing mech~nism.
WO9Stll780 ~ Q~61 PCT/CA94/00583
(2) If one of the four freedoms is restricted to a
small range, or totally suppressed, the
remaining workspace---the range of motion free
of interferences and inside which the
mech~nical advantage of the actuators is kept
approximately constant---becomes large, a
property which is extremely unusual in
parallel mech~nifims. This is particularly
remarkable if additional motion is suppressed.
A constructed m~c-h~nical model has shown that
a workspace in excess of 180 degrees of roll
motion combined with 90 degrees of pitch and
yaw motion can be achieved.
(3) In the case where the needed range of motion
is small, the mech~nical advantage of the
actuators with respect to the output link can
be selected over a wide range of values for
each principal direction of motion.
(4) Again in the case of small motions, control is
facilitated by the fact that each direction of
motion corresponds exactly to the sums and
differences of actuator motions, taken two by
two.
(5) In cases where a large range of motion in the
angular workspace is needed, the mech~n;cal
advantage of the actuators taken as a group
-
woss/11780 2 ~ ~ 5 ~ ~ 6 PCT/CA94/00~83 ~
16
can be made approximately constant and equal
for each direction of motion, possibly
approaching or even reaching a condition
known as isotropy.
(6) The special organization of the arrangement
makes it particularly easy .to achieve high
structural stiffness and accuracy in many
designs as the majority of structural members
are in a position to undergo well defined
stresses: either compression-tension, or
bending in a single plane.
(7) Parallel m~çhAni~ms with more than one or two
degrees of freedom are often plagued by the
necessity of numerous passive joints. This
increases the cost of fabrication and if
exacting specifications are not respected,
this can defeat the claimed advantages of
parallel me~h~n;sms. The present invention
achieves a significant reduction of the number
of passive joints while ret~;ning the required
mobility.
(8) In the case where the meçh~nicm is restricted
to three degrees of freedom, to become
spherical for example, it can be made to
create bias forces within its structure to
2 1 75236
W O 9S/11780 PCT/C~94/00583
17
eliminate backlash in the joints even in the
presence of wear or fabrication imprecision.
(9) Certain versions of the mechAn;-cm can be made
to exhibit advantageous dynamic properties,
minimizing the reaction forces at the ground
link in conditions of high accelerations.
(lO) The mec-hAniem can be easily instrumented and
the sensors can be placed to provide accurate
measurements of the position of the o~L~uL
link. In fact if more sensors than strictly
needed are used, the redundant information can
be used to increase accuracy or perform such
functions as self-calibration or self-testing.
(ll) The mechAni~m is power efficient as compared
to many conventional mechAniems, in particular
as compared to its serial counter-parts.
(12) The mech~nifim is advantageous from a
fabrication viewpoint as it introduces
simplifications which make it simpler to
achieve mobility and rigidity with a reduced
number of parts, some of them being replicated
four times.
(13) The mechAniem is particularly suited to tendon
control arrangements as wire routing need not
be made to run throughout the entire
structure.
WO95/11780 PCT/CA94/00583
2 t ~
18
(14) Fabrication is made easy because of the simple
type of stress supported by each joint. In
addition, contrary to serial mech~n;~ms, all
joints are involved in any stress thus sharing
the load.
The foregoing description has been made in
respect of a primarily orienting assembly. This
orienting assembly can be rendered more useful by
combining it with a further positioning mechAn;~m. The
positioning me~h~n;sm hereinafter disclosed is believed
to be itself novel and constitutes a separate invention
as well as comprising part of the present invention.
~Positioning Mech~n;Fm"
In one of its broad aspects, the positioning
m~c-h~n; ~m of the in~ention may be used for effecting
displacement of an end member to be positioned. It
broadly comprises a linkage having four joints and four
main positional links wherein:
(a) three of the four links comprise:
(i) one base link having two ends with first and
second joints mounted on such ends
respectively; and
(ii) first and second oriented links each having
base and elevated ends and being coupled at
their base ends to the respective ends of the
WO9S/11780 2 ~ ~23~ PCT/CA94/00583
.
19
base link through the first and second joints
respectively;
(b) the first joint permitting orientation of the
first oriented link about a centre of
rotation;
(c) third and fourth joints are located at the
elevated end of the first and second oriented
links respectively;
(d) the second and third joints being revolute,
each permitting rotation about one axis with
respective axes which are non-orthogonal to
each other;
(e) the fourth link comprises an elevated link
supported at its two ends respectively through
said third and fourth joints by the two
oriented links
whereby the end of the elevated link at the third joint
is constrained to move in a path which lies on a sphere
centered at the first joint, and the end of the elevated
link at the fourth joint is constrained to move in a path
which is circular about the second joint.
In one variant, the first and fourth joints may
be spherical. In another variant the second and fourth
joints provide two degrees of rotational freedom. In yet
another variant, all four joints may provide two degrees
of freedom.
-
WO9Stll780 2 ~ 7 5 ~ Q ~ PCT/CA91/00583 ~
The positional m~Gh~n;Rr of the invention also
comprises first, second and third actuators for orienting
the first and second orient links and the elevated link:
(a) the first actuator being coupled on one side
thereof to the base link, and coupled on its
other side to the first oriented link in order
to effect orientation of the first link about
an axis which is non-orthogonal to the axis of
rotation of the second joint;
(b) the second actuator being coupled on one side
thereof to the base link and coupled on its
other side to the second oriented link to
effect orientation of such second link;
(c) the third actuator being connected between the
second and elevated links to orient the
elevated link with respect to the R~Co~ link
about an axis that is non-orthogonal to the
axis of rotation of the third joint;
whereby the actuators may collectively position and
orient the elevated member within a work space in which
the elevated member may serve as the end ~-^r. This
elevated member may also carry the orienting mech~n;cm
described above, thus combining the work-spaces of the
two individual mech~n;~ms in a combined mech~n;sm.
By a further feature of this positional
mech~n;Rm an extension member may be coupled at one of
WO95/11780 ~ ? ~52~6 PCT/CA94/00583
21
its ends to the elevated link, providing at its other end
a free end whereby such free end may be positioned within
a work space in response to said actuators.
Preferably, the axis of the second joint is
aligned to intersect the centre of rotational of the
first joint and the axis of the 3rd joint may intersect
the centre of rotation of the 4th joint.
In a preferred configuration, the distance from
the centre of rotation of the first joint to the axis of
the third joint is substantially egual to the distance
from the centre of rotation of the fourth joint to the
axis of rotation of the second joint, rendering the
m~chAn;sm capable of assuming a rectangular form.
A positional mech~nism in accordance with the
invention can provide three degrees of freedom which
permit the elevated member to serve as an end member that
can be positioned anywhere with its workspace. A
restricted variant can provide two degrees of freedom to
serve as a pointing mechAn;~m.
Because two actuators are yroul~ded~ the
supported mass of the system is minimized, reducing its
inertia and improving its dynamic response
characteristics. Similarly, as the first and second
oriented links are supported at grounded links, they may
be shaped to minimize their inertia while achieving a
desired level of structural supporting capacity.
WO95/11780 PCT/CA9~/00583
2~7~06 ~
22
An efficient characteristic of the mech~nicm of
the invention is that two of the three positional motions
can be achieved through differential motion of the two
grounded actuators. By providing a locking
characteristic to the third, elevated actuator, force-
demanding activities, such as lifting heaving loads, can
be achieved through activation of the grounded actuators
only. By selecting various lengths for the links, a
range of mech~n;cal gains can be achieved.
one particularly attractive mode of operation
of the positional mechAn;~m of the invention is to
activate the joints through use of cables or tendons.
Because the oriented links are grounded at one end and
can be placed generally upright in their position, they
are favourably positioned to support the stresses
generated by tensioning control cables. Loads can be
supported and cables rigged so that each joint i8 exposed
only to simple stresses.
The operation of the positional mech~n;~m of
the invention in accordance with these variants requires
co-ordination of the actions of the three actuators.
This is readily effected through modern micro-electronic
circuitry, an option not available in the past at the
cost and performance levels available.
The foregoing summarizes the principal features
of the invention and some of its optional aspects. The
W O 95/11780 2 1 7 ~ ~ ~6 PCT/CA94/00583
23
invention may be further understood by the description of
the preferred embodiments, in conjunction with the
drawings, which now follow.
SummarY of the Fiqures
Figure 1 is a symbolic depiction of the rotary
actuated form of orienting m~ch~n;cm~ identifying the
links and joints therein.
Figure 2 is a schematic of the links of the
orienting mechAn;cm when rotary actuators are employed
labelled to show important dimensions.
Figure 3 is a schematic of a five-bar linkage.
Figure 4 is a schematic of a constrained
six-bar linkage that functions as a five-bar linkage and
is considered to be as such for the purposes of this
Specification.
Figure 5 is a pictorial depiction of the
linear-actuated form of the orienting me~hAn;fim,
identifying the links, joints and actuators (in the form
of prismatic cylinders).
Figure 6 is a schematic of the links of the
orienting merhAn;cm when linear actuators are employed
showing important dimensions.
Figure 7 is a depiction of a robot manipulator
shoulder mechAnicm equipped with linear actuators.
~ 'f ! - t ~ r j,~ ,t ,- .
~ (showing cha~es ~ei~ -
~ i' 7i52~ mOcle to text)
24
Figure 8 is a depiction of a rotary cutting
head mounted on a structure according to the orienting
mechanism of the invention and suited for boring
operations.
Figure 9 is a depiction of a support suited for
orienting optical gratings and the like utilizing the
orienting mechanism of the invention.
Figure 10 is a depiction of an orienting
mechanism based on the invention for supporting a joy
stick.
Figure 11 is a depiction of an inverted
configuration (to the orientation of Figure 7) of the
orienting mechanism to provide a levelling platform for
a turret.
Figure 12 is a pictorial depiction of the dual
5-bar linkages of the orienting mechanism used to support
and point an antenna.
Figure 13 is a symbolic depiction of the links
and joints of the positional mechanism of the invention,
wherein the elevated link supports an end effector.
Figure 14 is a further pictorial depiction of
the positional mechanism of Figure 13 wherein the details
of optional actuator joint arrangements employing
[cylindrical] revolute couplings are depicted.
Figure 15 is an enlarged detail of an alternate
joint and actuator arrangement to that of Figure 14.
AMENDED SHEET
WO95/11780 2 ~ ; PCT/CA94/00583
Figure 16 is a perspective view of the
positional meçhAnicm of the invention employed as a crane
for lifting a heavy load.
Figure 17 is a depiction of the positional
mechanism of the invention e~uipped with a compartment to
contain a person as, for example, to pick fruit.
Figure 18 is a pictorial view of the tendon
activated mechAn;cm wherein a handle or writing
instrument is the end element within the orienting dual
5-bar me~hAn;cm of the invention being, in turn, carried
by the positional me~-h~n;sm of the invention and equipped
with tendons linked to sensors and actuators.
Figure l9 is a depiction of the combined
mech~n;cms of Figure l and a variant of Figure 14 with
transposed spherical joints.
Figure 20 is a pictorial depiction of a
prototype of the combined positional and orientational
mechAn;cm portions of the mechAn;~m built to evaluate its
characteristics.
Description of the Preferred Embodiment
"Operation of Orienting MechAn;sm with Rotary Actuators"
The main links which play a structural role are
labelled in Figures l and 2 as follows: Lo (ouL~L
link), Lg (ground link), Lb (base link), Lp (proximal
link), Ld (distal link). Five link lengths Ll, L2, L3,
3~ f~ $r~
2 1 7520G
L4 and L5 shown in Figure 2 describe the basic geometry, they
are --- kinematic design parameters. In Figure 2 the
principal directions of motion for the output link Lo are
labelled R (roll), P (pitch), Y (yaw) and S (slide). Joints
labelled Ml, M2, M3, M4 in Fiqure 1 are rotary joints
actuated by motors. By convention a positive direction of
motion is indicated. Joints labelled J1, J2, J3, form a
passive spherical joint (or gimbal). Jl, is optionally a
cylindrical joint allowing the output link Lo to slide in and
out, as indicated by [5] S in Fi~ure 2.
Joints J10, Jll, J12, J13, J14, J15, J16 and J17 forming
the driven, twinned spherical joints (as explained further
below). The common axes of joints Ml, M2, and M3, M4 (resp.
J10, Jll, J12, J13) do not need to be coincidental. They are
represented or constructed this way for simplicity of
depiction. Jb is the base joint supporting each 5-bar
linkage.
Joints labelled J6, J7, J8, J9 within the dual 5-bar
linkages, joining the proximal and distal links Lp, Ld are
revoluté; There are several ways to implement the four-joint
substructures J10, J11, J14, J16 and J12, J13, J15, J17 in a
manner which is similar to ordinary universal joints for
example, using forks.
In the above Figures, several features are optional.
F~f]or example, the centre of rotation of the support joint
constituted by joints Jl, J2, J3 need not be coincident
~EIYDED St~EEr
~ 2175~06
27
with the axes of the joints Ml, M2, M3, M4.
S~s]ymmetries have been introduced to simplify analysis
and fabrication.
Referring to Figures l and 2, the principles of
operation of this rotary-activated embodiment may be
summarized as follows:
- Let joints Ml, M2, M3, M4, rotate in the
positive direction: the output link
undergoes a pitch motion.
- Let joints Ml, M2, rotate in the positive
direction and joints M3, M4, in the negative
one: the output link undergoes a roll motion.
- Let joints M1, M4 rotate in the positive
direction and joints M2, M3 in the negative
one: the output link undergoes a yaw motion.
- Let joints Ml, M3 rotate in the positive
direction and joints M2, M4 in the negative
one: the output link undergoes a sliding
motion.
"Summary of Features - Rotary Actuators"
1. Feature 1: It must be noticed that the two
actuated 5-bar structures appear as six joint/six link
assemblies. The six joints and six links arise from the
fact that the basic 5-bar linkage - Figures 1-4 -
includes a driven joint Jd which is twinned (being either
DEo S~E
WO95/11780 2 ~ ~ 5~0 ~ PCT/CA94/00583 ~
spherical or universal) as shown in Figure 4 by joints
JlO and Jll (resp. Jl2, Jl3) and is connected to the end
member through an additional link, La. This sixth link La
is, however, outside the 5-bar loop (Figure 4) and the
two revolute joints JlO, Jll (resp. Jl2, Jl3) share a
common axle Lc connected to the additional link La. It
is therefore characterized as a 5-bar linkage for the
purposes of this Specification.
As a six joint/six link assembly, this
structure appears to be an over-constrained chain,
thereby potentially losing mobility. However, this type
of structure is commonly made to function properly by
keeping all axes parallel, which is a simple mac-h; n; ng
operation. In cases of exacting specifications, the
problem can be dealt with by introducing suitable
elasticity in the links.
2. Feature 2: Singularities occur either:
(l) when the ouL~uL can undergo finite
displacements while one of the actuator's
velocity vanishes: or,
(2) when the converse condition occurs.
Condition (l) occurs for example when the
mF~h~n;~m is in a position such that points, C, Bl, Al or
C, B2, A2 align, as shown in Figure 2. By design such
conditions can be avoided for large excursions. In
addition, even in such positions where actuators Ml and
~ ~ 1 75~6.
29
M2 lose their influence on the yaw motion of the output
link, M3 and M4 would be capable of controlling this
motion.
Condition (1) also occurs when points Al and A2
both undergo a motion in a direction exactly orthogonal
to the principal direction of a distal link. Proper
functioning has, however, been verified by constructing
mechanical models and it was impossible to find such
conditions within any workspace free of interferences.
Condition (2) occurs when one 5-bar linkage
stretches completely. This may put a definite bound on
the workspace as a degree of freedom is lost.
Construction of mechanical models has shown that such
condition can be avoided with a proper choice of design
parameters.
3. Feature 3: A wide range of mechanical
amplification gains or attenuations is achievable by
selecting the distance L5 between the central support
joint for the output link Lo and the line joining the
tbase] driven joints Al, A2 (as shown in Figure 2) and
the link-length parameters L2, L3, L4, being the proximal
and distal link lengths and the distance of separation
between the actuated joints. These lengths may be chosen
to vary the angle of incidence of each connecting link in
order to create various lever-arm actions around the
pitch and the yaw directions.
AMrN~ED SHEET
WO95/11780 2 ~ 7 ~ ~ 0 6 PCT/CA9~/00583 ~
4. Feature 4: The m~chAn;~m has the ability to
operate with each effected motion based on the sum and
differences of actuator motion for wide ranges of designs
and in the neighbourhood of any operating point. This
property can be exploited by making use of analog
electronics to control the device, despite its complex
kinematic structure, and thereby achieving very high
control bandwidth. This is because no multiplications
are needed other than by constant quantities, due to the
four way differential nature of the driving actions.
5. Feature 5: The mech~n;cal advantage changes
mildly for yaw motions as one structure extends while the
other contracts. It changes moderately for sliding
motions.
It remains almost constant for pitch motions.
The worse case occurs for retractions combined with a
roll. Depending on the inte~ application, many
designs are possible. For a general ~uLpo-4e device, one
should seek angular isotropy. For example, it is easy to
see that if the point C, the centre of rotation for the
output link, falls on the line joining the points Bl, B2
in Figure 2, then the mer-hAn;cal gain in pitch motions is
exactly l for each actuator. The other design parameters
can be searched for similar conditions for the other
motions. To date, a good general design has been found
~ WO95/11780 2 1 7 5 ~ 0 6 PCT/CA94/00583
for the following length parameters: Ll=4, L2=3, L3=4,
L4=4, L5=4 (spherical case).
6. Feature 6: If we replace cylindrical joint Jl
in Figure 2 by a revolute joint, eliminating the sliding
motion, the angular workspace can then be made to reach
its maximum. In this case, we are in the presence of a
redundantly actuated mechAn;sm. For a given output
torque, an infinite set of actuator torques can be chosen
by control. This effect can be applied to fulfil a
number of functions. For example, the set of torques can
be selected to create minimum stress in the structure.
Another example is to select those torques required to
minimize the maximum torque in the actuators for a given
output, thereby maximizing efficiency. Yet another
example is to create given bias forces in the joints,
thereby c~ncelling backlash if any.
This particular effect can be appreciated by
inspection of Figure l. If a positive torque is created
in actuators Ml, M3 while a negative one is created in
M2, M4 (corresponA;nq to the eliminated sliding motion),
the resulting forces cancel out and all the passive
joints are bias-loaded in one well defined direction.
Thus, accuracy can be upheld even in the presence of
wear.
7. Feature 7: Consider a fixed inertial load
acting vertically on the ouL~uL link Lo. If its center
WO9S/11780 2 t 7 5 2 Q 6 PCT/CA94/00583 ~
32
of mass lies on the axis of joint Jl, then sliding
motions will not create reaction forces and torques other
than those that are exactly in the direction of motion.
If the combined contribution of the load and links to the
inertial tensor of the total r?ch~n;cm causes the axes of
the corresponding ellipsoid of inertia to coincide with
the principal directions of motion, and this ellipsoid is
centered at the center of rotation, then angular
accelerations will create zero reaction forces at the
ground link, and only reaction torques. This is even
more desirable if all the axes of this ellipsoid are
equal, in which case this effect is obtained for any
direction of rotational acceleration. This feature is
particularly useful for high acceleration, high bandwidth
applications.
8. Feature 8: The most obvious place for sensors
to be located is on the same shaft as the actuators.
However, the joints J6, J7, J8, J9 are also excellent
candidates for instrumentation, as well as joints Jl, J2,
J3. Redundant sensing offers a range of possibilities
including augmentation of accuracy and usage of
self-calibration te~-hn; ques. The spherical case with
co-located actuators and sensors is sensor-redundant too.
This invention does not suffer from
accumulation of errors as a serial me~h~n;cm does. In
fact exactly the opposite occurs, error reduction is
WO95/11780 ~ t ~2~6 PCT/CA94/00583
33
obtained as all sensors are made to measure any motion or
position. In an analogous way all actuators are made to
cause any motion. In the serial case, each sensor and
actuator is dedicated to each principal direction of
motion, and therefore errors accumulate.
9. Feature 9: Consider a sliding motion for
example. In the serial case only joint Jl contributes
power to this motion. The design of the invention will
require the contribution of all four actuators to cause
the same motion. The same argument can be repeated for
all four principal directions of motion, it thus follows
that this design can achieve a factor four in power
efficiency improvement.
"Operation of Orienting Me~hAn;~m with T;neAr Actuators"
Joints labelled Pl, P2, P3, P4 in Figure 5 are
actuated prismatic joints. By convention the positive
direction is taken in the sense of actuator shorten; n~.
As in the prior case, joints labelled Jl, J2, J3 form a
passive gimbal, with Jl optionally being a cylindrical
joint, allowing the output link Lo to slide in and out.
The axes of joints JlO, Jll, (resp. Jl2,Jl3)
whereby the distal links Ld join at the driven joint Jd
do not need to be coincidental. They are represented or
constructed this way for simplicity.
WO9S/11780 2 1 7 ~ ~ 0 ~ PCT/CA9~/00583
34
Again, in Figure 5 as in Figure 1, symmetries
have been introduced to simplify analysis and
fabrication. Figure 6 shows the important kinematic
design parameters of this linear-actuator version of the
invention wherein B3, B4, B5 and B6 are the points at the
intersection of the axes of the joints J4 and base joint
JB2, J5 and base point JB2, J24 base joint and JB3, J25
and base joint JB3. L6 is the distance between the
points B3, B6 (resp. B4, B5); and L7 is the distance
between the points B3, B4 (resp. B5, B6).
Referring to the Figures 5 and 6, the
principles of operation of this linear-activated,
orienting embodiment are as ~ollows:
- Let joints Pl, P2, P3, P4 translate in the positive
direction: the o~L~L link Lo undergoes a sliding
motion.
- Let joints Pl, P2 translate in the positive
direction and joints P3, P4 in the negative one.
The ou~L link Lo undergoes a yaw motion.
- Let joints P1, P4 translate in the positive
direction and joints P2, P3 in the negative one.
The ouL~uL link Lo undergoes a pitch motion.
- Let joints Pl, P3 translate in the positive
direction and joints P2, P4 in the negative one.
The output link Lo undergoes a roll motion.
WO95/11780 ~ 7 5 ~ ~ 6 PCT/CA94/00583
"Summary of Features - Linear Actuators":
1. Feature 1 is analogous to the previous case.
2. Feature 2 is also analogous except that the
algebraic determination of locus of singularities has
been performed in the spherical case and for when the
distance L5, which separates the line joining points Al,
and A2 from the centre of rotation C is not of zero
length. It was found that loss of control condition
occurs only in the case where points Al, A2 as depicted
in Figure 6 falls in the plane B3, B4, B5, B6 which
corresponds to a 90 degrees pitch motion. Condition (2)
of previous case never occurs.
3. Feature 3 is exactly analogous to previous
case.
4. Feature 4 is exactly analogous to previous
case. In fact, the determination of the various
mech~nical gains is simpler.
5. Feature 5 is analogous to the previous case.
With the length L5 chosen arbitrarily as being 10 units
a good design has been found for the following parameters
L1=8, L6=8, L7=12 where L6 and L7 are respectively the
distance between the joints J4, J5 and the distance
between the joints J6, J7 (or J8, J9). One disadvantage
of the linear actuator design is the requirement to
provide room for the actuators to move free of
interference--as their length is by necessity larger than
WO95/11780 Z ~ ~ 5- 2 Q ~ PCTICA9~/00583
twice their stroke on the extended position while their
retracted length must be larger than their stroke.
However a practical design with piston actuators has been
physically realized.
6. Feature 6: By analogy with the previous case,
cylindrical joint Jl can be replaced by a revolute and
the me~h~n; cm becomes spherical with three degrees o~
angular freedom.
7. Feature 7: This is exactly analogous to the
previous case.
8. Feature 8: Even if the actuators are piston
type, thus typically being cylindrical pairs, they are
constrained to undergo strictly translational motions
with no twist. Therefore, position sensors can safely be
strapped on their sides without need for torsion
decoupling joints, simplifying design and construction.
In fact the linear actuator design is even more
advantageous for achieving high rigidity.
9. Feature 9: The m~c-h~n;cal advantage varies
most significantly for roll motions, as both regional 5-
bar actuator structures extend simultaneously, thus
losing their advantage together. It must be remembered
that the effective range of motion around this direction
is in excess of 180 degrees irrespective of other
motions.
WO95/11780 2 1 7 S ~ ~ 6 PCT/CA9~/00583
!-
37
"Applications for the Orienting ~ech~n;-cm -
HIGH PERFORMANCE SHOULDER MECHANISM"
The robot manipulator joint of Figure 7 has
four linear actuators P40 supported off a base 40 by four
revolute joints J40. In pairs the pistons of the
actuators P40 meet at two twinned spherical joints J4l
that support a platform 41. A spherical joint J42
constrains the platform 41 to spherical motions about its
centre. This shoulder me~hAn;cm is designed to support
large loads (up to 150 Nm around any axis at 350 N/cm2
pressure supply and with 22.2mm bore diameter cylinders),
while featuring a large workspace (90 degrees, 90
degrees, 180 degrees) and low weight. Because of the
various properties claimed earlier, a very simple
fabrication process achieves superior performance and the
reduction of parts count. In our laboratory version,
each actuator has been instrumented with position and
force transducers.
"Applications - MINING & CIVIL ENGINEERING APPLICATIONS"
In mining applications, machines with high
structural stiffness and high strength are required. For
example, in a boring machine a simplified version of the
invention as shown in Figure 8 can be applied to produce
three degrees of freedom, all controllable with high
power. A high load-bearing capacity is available for the
woss/11780 2 ~ 7~2~6 PCT/CA9~/00583 ~
38
cutting head 42 since all four hydraulic actuators P41
(seated through revolute joints J43 that are carried by
a vehicle - not shown), can be applied to contribute to
the forward thrust, as well as generating lateral and
vertical orientations.
The general roll motion of the cutter head 42
support is suppressed by means of a prismatic joint J44
replacing the original cylindrical joint that connects to
the supporting universal joint J45. The continuous
rotary motion required by the cutting head 42 can be
produced by a dedicated independent motor (not shown)
that can be placed behind the mech~n;~m. A simplified
kinematic structure results from the reduction of
controlled degrees of freedom but the overall principle
remains identical.
Because of the differential nature of the
principle of operation, suitable control can be achieved
with simplicity through the use of four-way hydraulic
valves and hydraulic circuitry.
"APPLICATIONS - OPTICAL AND MICRO PRECISION APPLICATIONS"
In Figure 9, micro-motion actuators of the
piezo-electric type marked E are used to displace a
central output platform 44 with micro precision in all
four degrees of freedom. In an optical instrument for
~ Wo95/11780 2 1 7 5 2 0 6 PCT/CA94/00583
39
example, a grating can be micro-rotated around the three
principal directions of motion and translated, all in one
single mechanism.
All joints J46 may be realized by means of thin
sections and thin rods for elimination of backlash and
high rigidity. In this example, the entire body of the
mecch~n;cm can be ma~h;~ out of one single block of
material, forming the thin sections first, then the
structure, then the four legs with the actuators E bonded
in place last. Using various geometries, wide ranges of
mech~n;cal gain can be selected for each direction of
motion.
In a micro-surgery application, the platform
44 which serves as the oul~uL link may be extended in one
or the other directions by a cantilevered arm 45, shown
in ghost outline. If this cantilevered arm 45 is long
with respect to the other dimensions, the tip will
approximate closely a manipulator with three degrees of
freedom of translation and one of rotation around its
principal axis.
"APP~ICATIONS - JOYSTICK WITH MOTORIZATION"
In aircraft control, robotics, forestry,
excavation, and more generally in the
operator/computer-assistedcontrolofmachines,joysticks
with multi-degree of freedom are needed. In advanced
2 1 75206
applications joysticks are designed to impart forces in
the operator's hand.
The embodiment of the invention of Figure 10
offers an opportunity to design such joysticks with a
high degree of simplicity. In these applications
electric actuators and sensors are often a prerequisite.
Here four rotary actuator/sensors S1, S2, S3, S4 are
employed mounted two-by-two on coaxial shafts 46 that
respectively connect to the tdistal] proximal links 47 in
each 5-bar linkage 48. Movement of the joystick 49 will
activate the sensors Sl-S4 through the motions as
described above, providing a precise output corresponding
to such movements. Note that other opportunities exist
to place displacement sensors (not shown) in other
favorable joints and introduce numerous improvements to
this basic design.
"APPLICATIONS - EXCAVATION, FORESTRY APPLICATIONS"
Conventional excavators and forestry machines
typicalIy use a turret swivelling around a vertical axis
fixed with respect to the chassis of the vehicle, the
seat of the operator swivelling with the rest of the
machine to provide for visual control. When such
machines are used on uneven terrain, the swivelling axis
will not be vertical. It follows that the operator has
to compensate with bending of ~this] his/her back which
results in
A~E;;`I~ED SHEET
~ ~ ~5~6,
41
injuries. The machine itself must be designed to
accommodate similar stresses.
In the Figure 11 application we employ the
spherical version of the invention to keep a turret
horizontal during swivelling, regardless of the position
of the chassis.
This configuration is "inverted" in that the
output link is the top platform supported (not shown3 by
joints [J47] J48/J49. [These] These joints [is] are
supported through appropriate intermediate joints ~J48,
J49], J50 by hydraulic piston-type cylinders P42 that
seat on a base 50 through spherical joints J51.
Because of the large stroke required from the
pistons P42, the geometry has to be made with a long
vertical dimension. In fact in this case, the roll
motion is m~;r; zed, possibly in excess of 200 degrees
with a corresponding decrease in the mechanical advantage
around the roll motion, but it is precisely the direction
which requires the least (or less) torque for this
application.
"APPLICATIONS - ANTENNA POINTING"
In Figure 12 a rotary-actuated version of the
mechanism suited to pointing an antenna is depicted. The
antenna 51 is carried by end member 52 that is supported
by the spherical support joint 53. The dual 5-bar
AMENDED SHEET
WO95/11780 2 ~ ~ 5 2 ~ 6 PCT/CAg4/00583 ~
42
linkages 54 are connected through the universal (or
spherical) driven joints 55 to the end member 56.
Spherical driven joints S5 would be suitable if the
antenna 51 were to exhibit roll motion, as to allow for
the receipt or transmission of polarized radio signals.
"OPERATION OF POSITIONAL MECHANISM"
In Figure 13 a base link 101 is grounded, as by
attaching it to an immoveable reference 102. At a first
end 103 a first spherical joint 104 is provided. At the
other, second end 105 a second, revolute joint 106 is
provided. First and second oriented links 107, 108 are
coupled to the spherical 104 and revolute 106 joints
respectively. Revolute joint 106 has freedom of motion
in the lateral direction 109 indicated by the arrow. The
first oriented link 107 has a freedom of motion that is
subject to the constraints of the adjacent elements.
The first and s~con~ oriented links 107, 108
terminate in a third, revolute joint 110 and a fourth,
spherical 111 joint respectively. An elevated link 112
extends between and is carried by these latter joints
110, 111. An extension 113 is connected to the elevated
link 112, terminating at its distal end with an end
effector 114.
While the second link 108 is supported by a
revolute joint 106 and is thereby limited to rotational
. ~; "~ $ ~
WO95/11780 ~ PCT/CA94/00583
43
displacement about the axis 115 of that joint, the first
link 107 can only swing in a path that is subject to the
constraint imposed by the presence of the elevated link
112. The first link 107 can follow the displacement of
the second link 108 by rotating in a parallel plane. But
if the second link 108 is fixed, the first link 107 can
only swing in a path that will cause the elevated link
112 to rotate about the spherical joint 111.
The first action permits the end effector 114
to be elevated. And the second motion causes the end
effector 114 to be displaced laterally, as well as
effecting its elevation. By a judicious simultaneous
adjustment of the C~con~ joint 106 in conjunction with
the first 104 and third 110 joints, lateral displacement
of the end effector 114, without a change in elevation,
can be created.
Actuators for effecting such motions are
depicted in Figure 14 in the form of pulleys 116, 117,
118, associated with the first 104a, second 106 and third
110 joints respectively. These pulleys 116, 117, 118 can
be rotated by cables or tendons (not shown in Figure 14).
The pulley actuators 116, 117 cause rotation of
the joints 104a, 106 about the grounded axis of the base
link 101. The axes of joints 104a, 106 need not be
n~cecc~rily aligned, or parallel. This effects the
orienting of the oriented links 107, 108.
W095/11780 ~ t ~ ~ ~ a & PCT/CA94/00583
44
The pulley 118 associated with the elevated
link 112 causes rotation of the elevated link 112 about
the axis of the third cylindrical joint 110. While shown
as mounted adjacent to the composite spherical fourth
joint llla, a joint of triple-revolute form composed of
revolute joints 119, 120 and 121, this pulley 118 can
equally be placed adjacent to the revolute joint 110,
where it is shown in ghost outline as 118a. The function
of this pulley 118, 118a in either case is to effect
rotation of the elevated link 112 about the axis of the
third, revolute joint 110.
An optional transposition is possible in the
first spherical joint 104a by constructing it in the form
of a composite Hook joint 104b. As shown in Figure 15,
the pulley 116 may be placed within the internal linkages
joining the revolute joints 122, 123 and 124 to cause
rotation of the third revolute joint 124. Again, the
object is to cau~e the first link 107 to rotate with
respect to the base link 101 (although not necesc~rily
within a plane that is parallel to the alignment of base
link 101).
A practical application of the mec-h~ni~m is
shown in Figure 16 wherein a load 125 is being lifted by
a hook 126 at the end of a cable 127. The cable 127
passes over the outer end 128 of a triangular extension
129 to the elevated link 112. A stand-off strut or
-
wos~/ll780 2 ~ ~ ~ PCT/CA9~/00~83
pulley 130 journalled for rotation about elevated link
112, dresses the cable 127 as it passes back to a cable
capstan 131. This cable capstan 131 is not strictly
required, as a range of motion suited to a crane is
possible by manipulating the hook 126 fixed to the outer
end 128 of the extension 129 by means of orienting
capstans 132, 133, 134 connected by cables 135 to the
appropriate elements of the m~ch~n;Rm. However, its
presence adds versatility to the mech~n;Rm.
In Figure 16, the first spherical joint 104a is
of a modified "transposed" spherical form wherein one of
the contained revolute joints 136 has been displaced to
a position adjacent the cylindrical joint llo creating an
alternate oriented link 107b. The actual oriented link
107a remains present in the juncture between the
displaced revolute joint 136 and the cylindrical joint
110. The operation of the mec-h~n;sm is, however,
unchanged.
The two positional capstans 132, 133 govern the
orientations of the oriented links 107a, 108, and a third
capstan 134 controls the orientation of the elevated link
112 through an elevated a pulley 137 and returning cable
135a. The weight of the load 125 obviates the need for
return cables on the positional capstans 132, 133. If
the cable 127 and cable capstan 131 are present, then the
W095111780 2 ~ 2a;6 PCT/CA9~/00583
46
third capstan 134 and elevated pulley 137 are not
strictly required.
Figure 17 depicts a lifting bucket 145 suited
to carry an individual to an elevated location. In this
variant, electric motors 146 actuate the joints of the
mechAn;~m. An optional pin 147 can be used to lock
joint.
In Figure 17 an improved form of orienting link
108 is shown sitting on a base 141. This improved link
144, shown partially in ghost form is triangular in form
incorporating a diagonal brace 144 extends from the base
link 101 to which i~ is journalled by a cylindrical joint
106 up to the upper end of the second oriented link 108
to which it is affixed. With this diagonal brace present
stiffness is added to link 108 and joint 106.
"COMBINATION OF ORIENTING AND POSITIONAL MECHANISMS"
As a demonstration of how the orienting and
positional mec~An;~ms of the invention can be combined,
Figure 18 depicts a mechAnicm for sensing the position of
a pencil point 151 on a surface 152. A pencil 153 is
seated in a dual 5-bar meC~An;cm 154 of the type
described previously. This orienting me~hAn; fim is, in
turn, carried by the positional me~-hAni cm of the
invention 155 supported by an extension arm 156,
bifurcated for strength. Tendons 157 lead throu~h
~ 1 75206
47
tensioning sensing devices 158 to electrical rotary
~sensors] actuators 159. These tendons all operate on a
returning basis.
Motion of the pencil 153 on the surface 152
therefore, produces an electrical signal from the
~rotary] sensors 15[9]8, and optionally from sensors 160
which may be located within the dual 5-bar assembly 154,
which may be used to drive a suitable remote mechanism
(not shown), possibly identical, wherein it is caused to
track these signals by means of its actuators ~positioned
inplace of the sensors 159~. By this means, the motion
of the pencil point 151 may be duplicated in a remote
location with high precision by a servo-controlled output
pencil. Conversely, torques developed in the
joints at the remote location due to resistance to pencil
movement can be sensed by the remote device. Resistance
developed at the output pencil can be transmitted back
from the remote location to the originating user to
provide feedback through combination actuator/sensors.
Combining these two modes of operation, a bilateral
communication may be established.
Instead of a pencil, a delicate instrument,
such as a scalpel may be substituted. Because of the
light weights and low inertia of the various components
of the over-all invention, a high frequency response can
be achieved.
AMENDED S~IEET
WO95/11780 ~ ~ 7 5 ~ ~ 6 PCT/CAs~/00583
48
Figure 19 shows the combination of a modified
version of positional merhAn;cm of Figure 14 with the
orienting mer-h~n;~m of Figure 1. The positional
mech~n;~m portion is modified by the presence of
transposed revolute joints 150 for the spherical joints
104a, llla. Thus, link 108a serves as a surrogate for
orienting link 108.
In the orienting meçhAn;cm, the joints J50,
J51, J52, J53 are equivalent to Ml, M2, M3, M4 except
they are not activated. Otherwise the elements
correspond as labelled.
A pictorial depiction of a meçhAn;cal model
actually built to verify the actions of the combined
positional and orienting m~h~n;~ms of the invention is
shown in Figure 20O This figure shows a model of the
elements of the combined mech~ni~m used to verify its
workspace and behaviour. It is labelled in the same
manner as Figure 19.
Conclusion
The foregoing has constituted a description of
specific embodiments showing how the invention may be
applied and put into use. These embodiments are only
exemplary. The invention in its broadest, and more
specific aspects, is further described and defined in the
claims which now follow.
WO9S/11780 ~ ~ 5 ~ o ~ PCT/CAg~/C~'83
49
These claims, and the language used therein,
are to be understood in terms of the variants of the
invention which have been described. They are not to be
restricted to such variants, but are to be read as
covering the full scope of the invention as is implicit
within the invention and the disclosure that has been
provided herein.
