Note: Descriptions are shown in the official language in which they were submitted.
~8~
FIELD pF THE INVENTION
The present invention is in the field of air-inElatable
tension actuators which decrease in length as they are inflated
and conversely which elongate as they are deflated, for example
as shown in U.S. Patent No. 3,645,173 of John M. Yarlott, and as
shown in my U.S. Patent No. 4,751,8~9 issued June 21, 1988. More
particularly, this invention relates to a method and system
employing elongated strings of such pneumatic tension actuators
arranged and operated in opposed relationship in jointed arms,
legs, beams and columns for controlling their movements, Eor
example for controlling the movements of arms, legs, elephant
trunks or flexible antennae in robots and for controlling the
deflections of beams and columns in frames and structures.
BACKGROUND OF THE DISCLOSURE
Small-size robots performing precise but rapid light
assembly tasks, have often utilized electric and/or hydraulic
drive operators. The mass and weight of such conventional
operators have tended to limit the dynamic response of prior
robots and to dominate the total cost of such robots.
SUMMARY OF THE DISCLOSURE
The present invention provides a method and a system,
wherein pneumatic tension actuators are interconnect~d in s~ries
to form strings arranged for controLling elongated jointed arms
and the like. Such strings of tension actuators extend along
opposite sides of the elongated jointed arms and they act in
opposition to each other for controlling its motions or
deflections.
.c ~.. ~
~ iJ
The term "el~ngated jointed arm" i~ intended to be
interpreted broadly to include various types o~ elongated jointec
members, for example such as arms, legs, ele~hant trunks,
flexible antennae, and the like, in robots and including beams
and columns in chasses and carriages, all haviny a plurality of
joints, with the joints being located at spaced p~sitions along
the length of the jointed member.
The opposed tension actuators are inflated with con-
trolled air pressures which are oppositely varied from a prede-
termined common-mode pressure PO (initial fluid pressure level
PO). In other words, as one string of tension actuators is beinc
inflated with pressure increasing above PO, the opposed string
is ~upplied with pressure decreasing below PO, for producing
motion or deflection of the jointed arm in one direction, and
conversely for producing motion or deflection in the other direc-
tion~ The jointed arm includes elongated links arranyed in
sequence in end-to-end relationship along the length or longi-
tudinal axis of the arm. The first link in sequence is position-
ed near a supporting structure or support body, for example such
as the body of a robot, and has a pivotal mounting to this sup-
port body, and the last link in the sequence is positioned and
rigidly attached near the remote (or outer) end of the arm. Each
successive link in the sequence has a single pivotal mounting to
the preceding link for enabling the arm to bend and swing into
various angular positions. Thus, the arm can curve or straighter ,
can swing up or down.
Fastened rigidly to the above-described rigid links,
thexe are rigid elements for controlling the movements of the
arm, with a respective one of these rigid elements being located
at each pivotal mounting and projecting out on opposite sides of
the longitudinal axis of the arm. The strings of pneumatic
-3-
~.ZE3~'78~
tension actuat~rs which h~ve been de~cribed ~8 extending along
opposite sides of the jointed arm are off6et from, i.e. ~paced
away from, the longitudinal axis of the arm. These ~trings
are fastened to the respective rigid elements at fastening
positions which are located at points located between tension
actuators in the respective strings.
A controllable source of pressurized air communicates
with the first tension actuator in each of the respective strings
for controllably inflating the strings on opposite sides of the
arm for producing arm motion, like muscles in the arm. By virtue
of controlling the opposed strings of actuators with a common-
mode pressure level PO, they are always exerting a net compress-
ive force on each pivotal mounting, i.e. each joint, so
advantageously permitting usage of simple, inexpensive, light-
weight, non-capturing joints as shown. Moreover, the use of a
common-mode pressure automatically causes the jointed arm to
return to a prPdetermined mid-range rest position whenever air
pressures are returned to PO. A nearly uniform stiffness (or
mechanical output impedance) is provided at all arm positions by
controlling the opposed pressures to be PO ~ ~ P and PO - ~P,
where ~ P is a correspondin~ increment above and below the
initial (common-mode) level PO.
The terms "air" and "pneumatic" and "gaseous fluid"
are intended to be interpreted broadly to include the various
appropriate gaseous media capable of being economically employed
to inflate tension actuators, for example air, mixtures of gases
or individual gases, nitrogen, carbon dioxide, and the like.
In accordance with the present invention in one of
its embodiments there is provided a gaseous-fluid-pressure
actuated, elongated jointed arm having a longitudinal axis and
~L28~
capable Df being moved about in variou~ controlled directions,
comprising: a plurality of rigid elements located at re~pective
positions spaced along the axis of the arm, each o these
elements extending across the axis and having first and cecond
projections protruding outwardly on opposite sides of the axis,
all of the first projections being on a first side of said
axis and all of the 6econd projections being on the second ~ide
of said axis. Each of these elements is oriented generally
perpendicular to the neighboring portion of the longitudinal
axis at the respective position where the element crosses the
axis. mere are a plurality of elongated rigid links extending
longitudinally along the axis, with respective ones of these
links extending along the axis between successive elements, and
with one end of each link having a pivoted relationship with the
adjacent element. There are first and second pluralities of
fluid-inflatable tension actuators, and each of these tension
actuators has an inlet end and an outlet end. The tension
actuators of the first plurality are joined end-to-end, forming
a first inflatable string with the outlet end of each actuator
communicating with the inlet end of the next actuator in the
first string, and with the outlet end of the last actuator in the
first string being blocked. The tension actuators of the second
plurality are joined end-to-end forming a second inflatable
string with the outlet end of each actuator communicating with
the inlet end of the next actuator in the second string, and
with the outlet end of the last actuator in the second string
being blocked. The first string of tension actuators extends
generally parallel with the axis of the arm and is offset f~om
the axis on the first side of the axis, while the second string
of tension actuators extends generally parallel with the axis
and is offset from the axis on the second side thereof. The
1 ~28~17~
fir~t string cf tension actuatsr6 is anchored t~ the fir6t
projection~ of said elements, with respective anchoring
connections bein~ located at the ends of tension actuators in
said first string, and the ~econd string of tension actuators
is anchored to the ~econd projecti~ns of 6aid elements with each
respective anchoring connection being located at the ends
of tension actuators in the second string. Pressurized gaseous
fluid control means communicate with the inlet ends of the first
and second strings for controllably inflating these ~rings with
pressurized fluid controllably varying in opposite directions
from a common pressure level PO for causing the jointed arm to
move and bend in various directions.
BRIEF DESCRIPTION OF THE DRAWINGS
The various features, objects, aspects and advantages
of the present invention will become more fully understood
from a consiaeration of the following-detailed description
in conjunction with the accompanying drawings, which are not
drawn to scale but are arranged for clarity of illustration.
In these drawings:
FIGURE 1 is a longitudinal sectional view of a jointed
arm including a plurality of strings of air-inflated tension
actuators acting in opposition to each other for producing
controlled movements through controlled curvature and bending of the
arm. FIG. 1 is a section taken along the line 1-1 in FIG. 2.
FIG. 2 is a cross-sectional view of the jointed arm
of FIG. 1, being a section taken along the plane 2-2 in FIG. 1.
FIG. 3 is a schematic diagram of a controllable source
oi pressurized gaseous fluid, for example air at various
pressures for controlling contraction and elongation of the
-G-
~2~
strlng~ oi ten~ion a~tuator6. For ~larity ~ ~llu~trati~n,
electrical re~istance 6ymbol6 and variable re~i~tance 6ymbol6
are shown in ~IG. 3 for explaining oper~tion o~ the control-
lable air source.
~ IG. 4 is an enlargement of a portion of the dia-
gram of FIG. 3 in which mechanical ~ymbol~ replace the
electrical symbols for further explanation of the illustrative
embodiments, and showing the control system.
~ IG. ~ illustrates movement of the various embodiments
of the jointed arm shown in FIGS. 1-4 and in ~IGS. 6-12.
FIG. 6 is an enlargement of a portion of FIG. 1
included within the dashed and dotted circle for illustratin~
one embodiment of the pivotal joints in the arm.
FIG. 7 is a view similar to FIG. 6 and illustrating
another embodiment of the pivotal joints in the arm.
FIG. 8 is a longitudinal sectional view of a portion of a jointe~
arm similar to FIG. 1, except that the pivotal joints have
line contact, and therefore they act like hinges for allowing
swinging movement of the arm back and forth along predetermined
arcs of movement in a predetermined plane.
FIG. 9 is a cross-sectional view of the jointed arm
of FIG. 8, being a section taken along the plane 9-9 in FIG. 8.
FIG. 10 is a perspective view of one of the links
of the arm of FIGS. 8 and 9.
FIG. 11 illustrates a further embodiment of a pivotal
joint for use in the arm of FIGS. 8 and 9.
FIG. 12 is a perspective view of the type of link used
with the joints of FIG. 11.
FIG. 13 shows a further embodiment of an elongated
jointed arm operated by opposed pairs of pneumatic tension
actuators.
FIG. 1~ is an enlarged sectional view showiny the
I couplings between successive tension actuators in a jointed arm.
30785
~ IG. 15 is an enlarged ~ectional view showing in
greater detail the ball-and-socket pivotal joint corre~ponding
to the embodiment depicted in FIG. 5.
FIG. 16 illustrates a further embodiment of the
compression-carrying link in the form of a compression element
constructed as a pressurized chamber sealed by a fiber-rein-
forced elastomeric oblate surface of revolution.
~ IG. 17 shows in cross section yet another
embodiment of the compression element in the form of a pres-
surized flexible annular shell, shaped like a laterally-
compressed tire inner-tube.
FIG. 18 depicts an advantageous embodiment of my
invention wherein the compressive load is carried by a pres-
surized cell formed by an air-tight membrane envelope extend-
ing between rigid circular end-plates and completely enclosing
the tension actuators contained within.
FIG. 19 shows a cross-sectional view of the jointed-
arm embodiment illustrated in FIG. 18, being a section taken
along the plane A-A of FIG. 18.
FIG. 20 represents a longitudinal interior view of
the same jointed-arm embodiment shown in FIGS. 18 and 19, being
a cross section taken along the plane B-B of FIG. 19.
FIG. 21 indicates the variation in curvature
and resulting movement of a multi-section embodiment as the
control pressures are varied.
FIG. 22 shows a useful embodiment employing two
jointed-arm sections terminating in a gripper, all of which
have independent open-loop control.
FIG. 23 graphs the proportional variation in
tension actuator spring-rate with actuator supply pressure.
FIG. 24 indicates quantitatively how the push-
pull operation of the opposed actuator strings yields open-
loop proportional con-trol of arm curvature as portrayed in
FIGS. 5, 21 and 22.
~ ~8078~
DETAIL~D DESCRIPTI~N OP PRE~ERRED EMB~DIM~N~S
Inviting attention to ~IGS. 1 ~nd 2, there is ~hown
an elongated jointed arm 20 having an inner end 21 and an
outer or remote end 22. The inner end 21 of the arm i~ mounted
upon a support 24, for example such as the body of a robot
having a ~ase or frame 26. A controllable source 30 of
pressurized gaseous fluid located near the support 24 serves
to control the arm motions, as will be explained later. The
outer end 22 of the arm 20 is shown carrying an article-handling
mechanism 40 for grasping, handling or manipulating objects
or articles, as will be explained later.
In lieu of this article-handling mechanism 40, the
outer end of the elongated jointed member 20 may carry any suit-
able termination, for example in the case vf a jointed leg, a
termination such as a friction foot is used with a wear-
resistant sole for engaging the floor or the ground; in the
case of a jointed antenna or elephant trunk, the termination
40 includes a suitable sensor, which may be a mechanical proxi-
mity or contact or shape sensor or shape tracer; the sensor
may be an optical, thermal, magnetic, electrical or radiation
sensor. The teimination 40 may be a suitable tool, for example
such as a paintspray gun, weldiny tool or grasping or mani-
pulating tool, and this termination may comprise one or more
sensors plus one or more tools in cooperative association with
each other. In cases where the jointed member 10 is
employed as a column or beam in a frame or structure, then the
termination 40 is a mechanical fastening or coupling for attach-
ing the outer end 22 of this column or beam to another frame
member or structural element.
!
~ 8-
Finally, the termination 40 may in turn comprise
an extended additional sequence of elongated jointed-arms,
like 20 itself, joined in various ways, and constructed
with similar or different dimensions and controlled by a
variety of supplied pressures. A particular embodiment with
two arms, 20F and 20G is portrayed in FIG. 22.
In summary, the elongated jointed member 20
may carry any suitable termination means 40 or combinations
thereof on its outer end 22, as appropriate for the instal-
lation and usage of this jointed member 20 in various
o~s
-8~-
I
8078S
Extending along the longitudinal axi6 ~f the arm 20
is a sequence of elongated rigid links 50-1, 50-2, ~0-3,
5~-(n-1) and 50-n, where "n" is the number of jointed sections
in the arm 20. Each of these links 50 is formed of ~trong,
lightweight material, for example aluminum or fiber-reinforced
plastic, and each link is shown having the shape of a round rod,
preferably of tubular configuration for minimizing weight, mass
and inertia while maximizing rigidity, with conically pointed
or tapered ends. It is noted that the links 50 can have any
desired cross-sectional configuration for optimizing strength
and rigidity for resisting deflection under axial compression,
for example such as an extruded H-shape or star shape, or square
rectangular, triangular or hexagonal shape, and so forth; and
in each case, these links 50 are configured for maximizing
strength and rigidity while minimizing weight, mass and inertia.
As shown most clearly in FIG. 6, the pointed or taperl ~d
ends 52 of each link 50 are received in a centrally located
socket indentation 54 ]o~ate~ ,7n, the adiacent face of a
rigid, generally square (See FIG.2) plate element 60. As shown
in FIG. 1, there are a plurality of these plate elements 60-1,
60-2, 60-(n-1) and 60-n, with each of these plate elements 60
being positioned between the adjacent pointed end of the successive
links 50 along the length of the arm 20. The last plate element
60-n is located at the outer or remote end 22 of the arm and
: carries the termination means 40. Thus, each link 50 has a
pivotal mounting 52, 54, 60 at one of its end~.
FIG. 7 illustrates an alternative embodiment of the
pivotal mountings at the ends of the respective links 50.
These ends 52 are rounded and are received in axially aligned
socket indentations 54 located in opposite faces of the rigid
plate elements 60.
_g_
.2~3~7E~
It is noted that regardless oE the specific shape of
the tapered link ends 54, as seen in FIGS. 6 and 7, they are
tapered inwardly toward the longitudinal arm axis 28 for causing
the tip of each tapered end 52 to have a small area of contac-t
with the center of each socket 5~, which is aligned with the axis
28 for defining and forming a pivot point 56. Moreover, the
sockets 54 each flare outwardly away from the axis 28 for
providing clearance for enabling the links 50 to move or swlng
into various angular positions relative to these plate elements
60, as illu.strated in FIGS. 5 & 15, where ball and socket joints
are indicated.
Each of the plate elements 60 is formed oE strong,
lightweight material similar to that used to make the links 50
for the same reasons, as before, namely for minimizing weight,
mass and inertia while maximizing strength and rigidity. It is
noted that in order to reduce the weight and mass of the
generally square plate elements 60 they may have cut-outs (not
shown). Such cut-outs are not shown in FIG. 2 for clarity of
illustration, and because the use of weight-reducing cut-outs is
known for inclusion in lightweight but strong, rigid mechanical
elements. In the embodiments indicated in FIGS. 16-20, 22, the
end plates 60 are taken to be circular.
In order to produce controlled motion of the arm 20,
there are four strings 70-1, 70-2, 70-3, and 70-~ (FIG. 2) of
pneumatic, inflatable tension actuators 80. These tension
actuators 80 are constructed as described and shown in U.S.
Patent No. 3,6~5,173 of ~ohn M. Yarlott, or as shown in U.S.
Patent No. ~,751,869. Such tension actuators 80 have the
advantageous operating characteristic that inflation causes them
to lncrease in their enc]osed cross-sectional area and volume
while simultaneously decreasing (contracting) in their axial
length. In other words, as they bulge, they contract in their
axial length. Conversely, when
-- 10 --
~ 7
-~ ~28~7~3~
such ten~icn ~ctu~t~rs ~re ~efl~ted, ~.e. ~ they become m~re
~lim, they elongate. The disclo6ures ~f these two referenceç
are incorporated herein by reference, and the reader i~ invite~
to read them to appreciate more fully the de~irable qualities
of lightweight, low mass, quick respon6e, xeliability, long
life, simplicity and economy, which are provided by cuch ten6ion
actuators 80.
It i6 noted that these tension actuators 80 are 8ym-
metrical end-to-end~ and they each include an inflatable,
elastomeric bladder (envelope or impermeable skin) 81 with a pai
of end fittings 82 and 83 attached to this elastomeric bladder
at each end. These sleeve-like end fitting~ 82 and 33 define
axial passages or ports 84 and 85, respectively, communicating
with theinterior region 86 of the bladder 81 for enabling
the bladder to be inflated or deflated. The two end fittings
82 and 83 in each tension actuator 80 are identical, and their
axial passages or ports 84 and 85 are identical. However, for
clarity of explanation, it is useful to describe that end fittin~
82 a,nd its passage or port 84 of each actuator that is located
nearer to the controlled, pressurized air supply 30 as being the
input end and input passage (input port), while that other end
fitting 83 and its passage or port 85 that is farther from the
controlled air supply 30 is described as being the outlet end ant
outlet passage (outlet port). It will be understood that durin
inflation of the respective actuator strings 70-1, 70-2, 70-3
and 70-4, air flows from the source 30 thr~ugh four respective air
conduits or airlines 39-1, 39-2, 39-3 and 39-4 into the inPut end
82 of the first tension actuator of the respective actuator
strings 70, and through the actuator interior region 86 and
thence through its outlet end fitting 83 into the input end
fitting 82 of the next successive actuator in the respective
string 70, and so forth.
I
lZ8~)71!3~
~ hu , the 6tring6 70-1, 70-2, 70 3 and 70-4 of tensivn
actuator~ 80 are formed by coupling ~ucce~sive tension
actuators together in end-to-end relationship with the passage
or port 85 in the outlet end fitting B3 of each actuator in the
string communicating with the inlet passage or port 84 in the
inlet end fitting 82 of the next successive tension actuator
in the string. The outlet passage 85 in the last tension
actuator 80 in each string 70 is plugged air-tight at 87.
The inflatable bladders 81 each includes longitudinally
extending, relatively inextensible filaments or strands of stron~ ~,
flexible high tensile strength material, for example 6uch as
Xevlar plastic, polyester, or polypropylene, as described in
detail in the references above. These longitudinal filaments
or strands are attached to the tubular end fittings 82, 83 for
causing these end fittings to be pulled toward each other as
the ~ladder 81 is inflated for producing axial contraction of
the tension actuator.
In order to control motions of the arm 20, the four
actuator strings, in clockwise (FIG. 2) order around the arm
axis 28, referenced as 70-1, 70-3, 70-2 and 70-4, are offset
from the arm axis 28, as seen most clearly in FIG. 2, and they
are uniformly spaced apart 90 around the axis 28, ~eing
located near the four corners of the square plate elements 60.
The first actuator string 70-1 on a first side of the arm axis
28 operates in opposition to the second actuator string 70-2
spaced 180 away, namely, on the other or second side of the
axis. Similarly, the third actuator string 70-3 on one side
of the axis 28 operates in opposition to the fourth actuator
string 70-4 spaced 180 away on the opposite side of the
axis. In summary, these four actuator strings are operated as
two opposed pairE~.
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11 Z80 7~35
These actuator 6trings 70-1, 7D-3, 70-2 and 70-4 are
fastened ~anchored) to the respective corner~ of the plate
elements 60 by connecting the end fittings 82, 83 to apertures
62 in these plate elements. For example, the respective end
fittings 82,83 are air-tight cemented or bonded in end-to-end
relationship in the respective apertures 62. An alternative
assembly procedure is to use screw-threaded coupling sleeves as
in FIG. 14 for coupling together the respective end fittings
82, 83. Such coupling sleeves are fitted through the apertures
62 in the plate elements 60, shown in FIG. 14.
The gripping mechanism 40 is shown as including a
bracket 41 secured to the outer face of the outer plate
element 60-n. A pair of opposed gripping fingers or jaws
4Z are hinged to the bracket 41 by pivot pins 43. For opening
and closing these grippers 42, there is a double-acting cylinde~
and piston assembly 44 having its piston rod 45 pivotally pinnec
at 46 to one gripper 42. The cylinder has a mounting rod 47
pivotally pinned at 48 to the other gripper 42. A pair of
flexible air lines 49 communicates with the cylinder 44 at
opposite ends. Feeding pressurized air through one of the lin~ ~s
49 into one end of the cylinder 44 causes the grippers 42 to
-13-
128078~i
close toward each other, and conversely to open when pressuriz
ed air is fed through the other line into the other end of
the cylinder 44. These flexible air lines 44 are strung
through holes 64 ~FIG. 2~ in the plate elements 60 located
near the arm axis 28. Air source 30 (FIG. 3) includes line 51
supplying regulated pressurized air to pneumatic controller
53 connected to air lines 49 for operating the article handler
40. There are electrical leads 55 connected from the control-
ler 53 to a control panel 100 (FIG. 4) including a microprocessor
for automatic operation of the article handler 40.
In FIG. 3 is shown the controlled pressurized air
supply 30 comprising an intake air filter 31, communicating
with ambient air and connected into an air compressor 3~, whose
output passes through a moisture eliminator 33, and through a
further filter 34 capable of removing fine particles rom the
compressed air. From the output of filter 34 an air supply
line 35 leads to a pressure regulator 38 whose regulated
output feeds into two branches 36, 37 which feed into two
pneumatic bridge networks 90-1 and 90-2, which are analogous to
electrical Wheatstone bridges.
i223078~
Each bridge network 90 includes a pair of pressure-
dropping flow resistors 92 and 93 and a pair of remotely con-
trollable pressure-dropping flow resistors 94 and 95 whose out-
lets are vented to atmosphere at 96.
As ~hown in FIG. 4, the pressure-dropping flow resist-
ors 92 and 93 are manually adjustable valves each providing a
flow-impeding orifice, for example needle valves. The remotely
controllable pressure-dropping flow resistors 94 and 95 are
needle valves which are controllably adjusted by electric actuator
97 and 98, re ~ ctively, for example solenoids or else reversible stepping mDt~ ~rs.
The output supply line 39-1 is connected to the
bridge 90-1 at the juncture of components 92 and 94, while the
second output supply line 39-2 is connected to the opposite
side of this pneumatic bridge at the juncture of components 93
and 95. Similarly, the third and fourth output supply lines 39-3
and 39-4 are connected to the respective corresponding junctures
located on opposite sides of the other pneumatic bridge 90-2.
Consequently, the pressures of the air being fed through the four
respective output supply lines 39-1 39 2, 39-3 and 39-4 are
controlled by varying the settings of the needle valves 94 and
95 in the two pneumatic bridges 90-1 and 90-2~
The operation of these two pneumatic bridges 90-1 and
90-2 will now be explained. The pressure regulator 38 is set
to supply a regulated air pressure of 2Po through the two branch
lines 36 and 37 into the input junctione 99 of the two bridges
-14-
~L280~78~i
90-1 and 90-2. The four pressure-dropping flow resisting com-
ponents 92, 93, 94 and 95 in each bridge are all initially 6et
the ~ame. Con~equently, one-half of the pre~sure drop occurring
from the input junction 99 to the vent 96 will take place in the
components 92 and 93, and the other half of the pressure drop
will take place in the components 94 and 95. The result is that
the initial output pressure in all four of the output supply
lines 39-1, 39-2, 39-3 and 39-4 will be the same, namely, one-
half of the input pressure of 2Po. Thus, the initial pressure
in lines 39-1, 39-Z, 39-3 and 39-4 is PO' which is called the
initial supply pressure level.
This initial ~upply pressure level of PO may be at any
desired gage pressure, where atmospheric pressure is taken as
zero p.s.i. gage, in the range from 3 p.s.i.g. up to 120
p.s.i.g. depending upon the burst strength limit of the individu~ ll
tension actuators 80.
When the pressure-dropping flow resistance of the
component 94 in the bridge 90-1 i5 increased from its initial
value, more than one-half of the total pressure drop occurring
from the input junction 99 to the vent 96 now occurs across this
component 94. Consequently, the pressure now appearing in the
output line 39-1 is greater than PO. The larger the pressure
drop occurring in the component 94, the nearer the pressure
in the output line 39-1 approaches the 2Po regulated pressure
level at the input junction 99.
Conversely, when the pressure-dropping flow resistan ce
of the component 94 in the bridge 90-1 is decreased from its
initial value, less than one-half of the total pressure drop
now occurs across this component 94. Thus, the pressure now
appearing in the output line 39-1 is less than PO. The smaller
-15-
~ 8~)'78S
the pressure drop occurring ~n the component 94, the nearer the
pressure in the output line 39-1 approaches the ~ero gage
pressure of the atmospheric vent 96.
The motors 97 and 98 are connected for adjusting
the components 94 and 9S in a bridge 90 in opposite directions.
Consequently, the output pressures appearing in the two output
lines 39-1 and 39-2 ~and also in the two output lines 39-3 and
39-4) vary in opposite directions from the initial pressure
level PO. Preferably these controllable pressure-dropping
components 94 and 95 are arranged to produce equal and opposite incrementc
~P above and below the initial pressure level P; so that the
pressures in the two output lines 39-l and 39-2 (and also in the
two output lines 39-3 and 39-4) have values of PO + ~ P.
A nearly uniform stiffnessor mechanical output
impedance of the motions of the arm 20 is advantageously obtained
by controlling the pressures in the bridge output lines 39-l and
39-2 (and also in the other bridge output lines 39-3 and 39-4) to
vary by equal increments ~ P in opposite directions from the
initial common-mode pressure level PO. Moreover, by controlling
the opposed actuator strings with a common mode pressure level PO ,
these actuator strings are always exerting a net compressive
force on each joint, so advantageously permitting usage of simple ,
inexpensive, light-weight, non-capturing joints as shown in
FIGS. 6, 7, 8 and ll.
The jointed arm 20 automatically returns and comes
to rest at an intermediate linear or angular position, for
example it returns to straight, as shown in FIG. l when the
pressures in the four supply lines 39-1, 39-2, 39-3 and 39-4
are returned to their initial equal common-mode values of PO.
As shown in FIG. 5, when the pressure being supplied
to the actuator string 70-1 is decreased below PO' the actuators
-16-
~LZ80785
80 in this ~tring 70-1 become elongated, causing the string 70-1
as a wh~le to elongate, while the pressure being 6upplied to the
opposing actuator string 70-2 is increased above POI causing
this latter ~tring as a whole to contract, thereby producing
bending motion of the jointed arm 20. Thus, it will be under-
stood that by varying the ~ettings of the components 94 and 95
in the two bridges 90-1 and 90-2, the jointed arm 20 can be
caused to bend and move in any desired direction from the
initial straight position shown in FIG~ 1. A sequence of such
positions is shown in FIG. 21. The control motors 97, 98 in the
two pneumatic bridges 90-1 and 90-2 are connected by electrical
leads 101 to the control panel 100 which ~ontains a microproces-
sor for automatically controlling movements of the jointed arm 20.
It is to be noted that unlike piston-type linear
pneumatic actuators and unlike vane-type rotary pneumatic
actuators, the opposed pneumatic tension actuators 80 provide
the uni~ue and advantageous feature of coming to rest at a
predeterminable intermediate specific position of the jointed an n
20 depending directly upon the opposed fluid pressures supplied
to respective opposed strings 70 of actuators 80. Therefore,
as the source 30 under control of the panel 100 is programmed
to supply pressurized air at PO ~ ~P and PO - ~P, respectively,
to the opposed actuator strings 70-1, 70-2 and 70-3 and 70-4,
the various controlled positions of the arm 20 will vary in a
predeterminable relationship with the various specific values
of the pressure increments ~ P, as shown in FIG. 21. In other
words, the various controlled positions of the arm 20 are pre-
dictable because the curvature is a nearly linear function of variation of
the controlled pressure increments, threby reducing complexity and cost.
Further, this feature of predictable and uniformly curved response
of arm movements as a function of variations in the pressure
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~ 785
alsoincrements ~ P/proYide~ an adv~ntageous nearly unif~rm 6tiffne~,
i.e. a very nearly unif~rm bending stiffness, for all positions o r
the arm 20.
In the elongated arm 20A ~hown in FIGS. 8 and 9
there are peg and groove socket joint~ 58, 54A, thus producing
swinging movement of the jointed arm sections in a plane. As
shown in FI~. lO, the links 50 have transver~e round rigid
rod-like peg elements 58 attached to each end, forming a
generally I-shaped or H-shaped configuration, depending upon
the relative length of the transverse joint elements 58 in
proportion to the length of the axial link 50.
The rigid plate elements 60A have a generally
diamond or rhombus-shape configuration, and there are two
opposed actuator strings 70-l and 70-2 fastened to apertures 62
located near the opposed tip portions of the plate elements
60A. It will be understood that-the controlled pressurized
air supply 30 for this arm 20A includes only one pneumatic
bridge 90-l (FIG. 3~ for operating the two opp~sed tension
actuator strings 70-l and 70-2. The transverse pivot elements
58 are shown oriented perpendicular to a straight line passing
through the centers of the apertures 62. The socket indentation~
54A are grooves extending for the full length of the transverse
elements 58, and these grooves include barriers 59 at each end
for preventing the peg elements 58 from inadvertently sliding
along the grooves 54A in this pivotal mounting 58, 54A, 60A. By
making the groove socket 54A with a larger radius of curvature
than the xounded surface of the pivot element 58, a low-friction
straight-line-contact 66 pivot action is provided.
In lieu of the peg and groove socket type of pivotal
mounting 58, 54A, 50A, shown in FIGS. 8, 9 and lO, a knife-
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~2~ 85
edge S~A and groove 54A pivotal mounting can be used, as 6hown
in FIGS. 11 and 12. The transverse rigid elements 58A have a
triangular cro~s-sectional shape. The apex of this triangular
pivot element 58A engages in the socket groove 54A for providing
a very low-friction, straight-line 66 of pivot contact.
In the ~ointed arm 20B ~FIG. 13) there are opposed
pairs of pneumatic tension actuators 80-1, 80-2 and 80-3, 80-4
which are offset away from opposite sides of the longitudinal
axis 28 of the arm 20B. The inner end 21 of this arm 20B
is pivotally mounted upon a support 24, 26,for example such as a
robot body, and the outer end 22 carries suitable termination
means 40. The rigid links 50B-1 and 50R-2 each includes round
rigid transverse peg elements 58 at their respective inner
ends, which form pivotal joints by seating in non-capturing
groove socket indentations 54A, ~imilar to those shown in FIGS. 8
and 9. These ~rooves 54A extend for the full length of the
transverse pivot elements 58, and these grooves 54A include
barriers at each end for preventing the pivot elements 58 from
inadvertently sliding along the grooves 54A, similar to the
barriers 59 (FIG. 9). Thus, it will be understood that the link
elements 50B-1, 58 and 50B-2, 58 have generally a T-shaped con-
figuration, with the stem ~OB extending axially along the arm axi
28 and constituting the shank of the T and with the transverse
pivot element 58 extending perpendicular to the plane in which
lies the arm axis 28 and consituting the cross bar of the T.
In order to attach the tension actuators 80, there are
rigid attachment or anchoring elements 60~ projecting out
on opposite sides of the arm axis 28 and oriented about the axis
28 at 90 relative to the length of the pivot elements 58. In
other words, these attachment elements 60B lie in the same plane
1~80~85
as the arm axis 28. Near the elbow region 23, one ~f these
attachments 60B' lies on the axis 28 of the inner link 50B-l.
The tension actuators 80 have their inner and outer
end fittings 82, 83 attached by strong flexible tension cords
88 to the respective attachments 60B and 60B'. The passage
or port in the outer end fitting 83 of each actuator i6 plugged
air-tight at 87. The passage (port) in the inner end fittings
82 of the respective actuators 80-1, 80-2, 80-3 and 80-4 communi-
cate with the four respective pressurized air supply lines 39-l,
39-2, 39-3 and 39-4 (FIGS. 3 and 4). Thus, the first pneumatic
bridge 90-1 is employed to control the two opposed tension
actuators 80-1 and 80-2 for controlling movements of the inner
section of the arm 20B, this inner section being the portion
between the shoulder region 21 and the elbow region 23. The
~econd pneumatic bridge 90-2 i~ employed to control the two
opposed tension actuators 80-3 and 80-4 for c~ntrolling movements
of the outer ~ection of this arm 20B, this outer ~ection being
the portion betweèn the elbow region 23 and the wrist region 22.
The motions of the whole arm 20B are thereby advantageously con-
trolled automatically in accordance with the programmin~ of the
microprocessor in the control panel 100. Consequently, the
advantageous common-mode pressure control method is achieved for
this arm 20B with all of the resulting desirable features as
explained before, namely: (1) the arm comes to rest, i.e.
it always assumes predeterminable (predictable) intermediate
specific portions depending directly upon the differences in the
opposed fluid pressures being supplied to the opposed pairs of
actuators 80-1 and 80-2, 80-3 and 80-4; in other words, depending
directly up~n the various ~pecific values (magnitudes) of the
pressure increments ~ P; (2) the various controlled positions
~2 !30~8~;
of the arm will vary in a nearly linear relationship as a
function of, i.e. in response to, the various specific values,
i.e. the magnitudes, of the present increments ~ P; (3) a nearly
uniform stiffness of the arm is achieved at all of its positions;
and (4~ a nearly uniform output impedance is achieved for all
positions of the arm.
It is noted that the various pivotal mountings as
described above advantageously involve simple, non-capturing,
inexpensive, lightweight, low-friction types of pivot mounts
having low-friction point contact or line contact pivot action.
This ability to utilize these non-capturing type of pivot mounts
is provided because the opposed pneumatic actuators 80 operated
in the method, as described, always produce a net compressive
force on the pivots, as described above.
It is to be understood that capturing types of pivotal
socket joints can be employed in the jointed arm 20, 20A and 20B,
if desired. Such capturing types of pivotal mountings are, for
example, ball and socket joints where the ball is captured in
the socket, and hingepin joints, where the hirge pin is captured
within encircling portions of the hinged elements, for example,
as in cupboard door hinaes.
It will be understood from FIG. 5 that when the
end fittings 82 and 83 are fastened into the apertures 62 of the
plate elements 60 or 60A, then bending of the jointed arm 20 or
20A is accommodated by flexibing of the bladders 81 in the
respective pneumatic tension actuators 80.
The ball-and-socket joints shown in FIGS. 5 and 15
could be either the capturing or non-capturing type.
One final comment about advantages in the use of
pneumatic tension actuators 8~ they operate in accordance with
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lZ80785
the ~irst Law of thermodynamics ~energy conservation), namely,
tension force "F" times differential change in length, i.e.
differential contraction, "dx" equals inflation pressure "P"
times differ~ntial volume "dv":
(1) F dx = P dv
Solving for tension force gives:
(2) F = PdX
Therefore, the tension force F is directly proportional to the
inflation pressure P within the interior region 86 of each
bladder 81 multiplied by the incremental rate of change of
volume dv with respect to incremental rate of change in length
dx of the actuator. When the bladder Bl and its longitudinal
strands or filaments are architectured for maintaining dv
substantially constant throughout the range of contraction, then
the tension force F is directly proportional to the inflation
pressure P as shown in FIG. 23. In other words, the tension
actuators act like linear tension springs in accordance with
Hooke's Law; when fully extended the tension force is maximum,
and when fully contracted the tension force is minimum. The
values of X are shown in FIG. 23 as negative, because a con-
traction is produced.
When according to my invention, as disclosed above
and claimed below, the tension actuators and actuator strings
are used in opposition, the relation between control pressure
(+ ~P) and resulting curvature (+ K) follows necessarily from
the geometric constraints:
(3) Curvature K = l/R -- A/L = L~X/D,
where R,A,L, and D are as indicated
in FIG. 5 and ~ X is as shown in
FIG. 23.
1'~8~
Also ~IGS. 16 through 20 show useEul embodiments
where the compression-carrying links 50 are embodied in suitable
oblate or toroidal compressive air-springs (or air-actuators).
Jointed -arms in this form have particular value if the arms
must be compactly stowed when not in use.
Correspondin~ reference numbers are used throughout
the various FIGURES for indicating the same elements and for
indicating elements which perform corresponding functions even
though their physical structures or shapes may be somewhat
different.
While the novel features of the invention have
been illustrated and described in connection with specific
embodiments of the invention, it is beieved that these embodi-
ments will enable others skilled inthe art to apply the
principles of the invention in forms departing from the exemplary
embodiments herein, and such departures are contempled by the
~e~e2 L~ y~ e~e~ ~- eb~ e~e~e~
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