U.S. patent number 3,608,743 [Application Number 05/034,159] was granted by the patent office on 1971-09-28 for material-handling apparatus.
This patent grant is currently assigned to General Electric Company. Invention is credited to Donald A. Kugath, Ralph S. Mosher.
United States Patent |
3,608,743 |
Mosher , et al. |
September 28, 1971 |
MATERIAL-HANDLING APPARATUS
Abstract
An articulated boom having a single joint intermediate the ends
thereof is pivoted at one end about a horizontal axis of a support
member. The other end of the boom has end effectors and end
effector positioning elements located thereon. A control member
smaller in size but similar in form to the articulated boom having
a single joint intermediate the ends thereof is also pivoted at one
end about another horizontal axis of another support member and a
handle is provided at the other end thereof. Means are provided to
cause each of the two parts of the articulated boom to follow in
orientation a respective one of the two parts of the control member
in response to movement of the handle by an operator. Additional
means are provided so that forces encountered by the articulated
boom are reflected back, reduced in magnitude however, to the
handle held by the operator. A pair of assemblies of levers and
springs are provided each in cooperative association with a
respective part of the control member to counterbalance completely
the weight of the unloaded control member and the weight of
unloaded boom as reflected by force feedback to the control
member.
Inventors: |
Mosher; Ralph S. (Schenectady,
NY), Kugath; Donald A. (Schenectady, NY) |
Assignee: |
General Electric Company
(N/A)
|
Family
ID: |
21874670 |
Appl.
No.: |
05/034,159 |
Filed: |
May 4, 1970 |
Current U.S.
Class: |
414/5; 901/9;
901/13; 901/21; 901/22; 901/29; 901/40; 901/48 |
Current CPC
Class: |
B25J
9/046 (20130101); B25J 19/0016 (20130101); B25J
15/0616 (20130101); B25J 9/101 (20130101) |
Current International
Class: |
B25J
19/00 (20060101); B25J 9/10 (20060101); B25J
9/02 (20060101); B25J 15/06 (20060101); B25J
9/04 (20060101); B25j 003/04 () |
Field of
Search: |
;214/1CM,1BV,1BD,147R
;212/35,59 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Forlenza; Gerald M.
Assistant Examiner: Abraham; George F.
Claims
What we claim as new and desire to secure by Letters Patent of the
United States is:
1. In combination,
a slave support member,
a slave member, one end of said slave member pivotally connected to
said slave support member and pivotal about one horizontal
axis,
a master support member,
a master member, one end of said master member connected to said
master support member and pivotable about another horizontal
axis,
a servo loop means responsive to displacements of said master
member to maintain alignment of the longitudinal axis of said slave
member with the longitudinal axis of said master member,
a force feedback means responsive to torque of said slave member
about said one horizontal axis for applying a corresponding torque
reduced in magnitude to said master member about said other
horizontal axis in a direction in opposition to the direction of
movement of said master member producing the torque in said slave
member,
a lever arm member having a pair of ends, one end of which is in
fixed relationship to said master member and movable about said
other horizontal axis therewith,
a bearing member,
a flexible tension member,
a spring member,
one end of said flexible tension member connected to said other end
of said lever arm member and the other end of said tension member
connected to one end of said spring member, the other end of said
spring member connected to said master support member,
an intermediate portion of said tension member bearing on a support
point of said bearing member on a side thereof remote from said
other horizontal axis,
the angle less than 180.degree. formed between a line extending
from said other end of said lever arm member to said third
horizontal axis and a line extending from said support point to
said third horizontal axis being equal to the angle less than
180.degree. between the longitudinal axis of said master member and
an axis extending vertically upward from said third horizontal
axis,
the spring constant of said spring member being equal to M/ar,
where M is the moment of said master member, and the moment of said
slave member as reflected to said master member,
a is the length of the line from said support point to said third
horizontal axis, and
r is the length of the line from said other end of said lever arm
to said third horizontal axis.
2. The combination of claim 1 in which the length of said tension
member being such that the end thereof remote from the end
connected to said spring member when unattached and said spring
member is in its unstressed condition extends to said support
point.
3. In combination,
a slave support member,
a slave member including an upper arm element and a lower arm
element, one end of said upper arm element pivotally connected to
said slave support member and pivotal about a first horizontal
axis, the other end of said upper arm element pivotally connected
to one end of said lower arm element and pivotal about a second
horizontal axis,
a master support member,
a master control member including an upper arm element and a lower
arm element, one end of said upper arm element connected to said
master support member and pivotable about a third horizontal axis,
the other end of said upper arm element pivotally connected to said
lower arm element and pivotal about a fourth horizontal axis,
first servo loop means responsive to the displacements of said
lower slave arm element to maintain alignment of the longitudinal
axis of said lower slave arm element with the longitudinal axis of
said lower master arm element,
second servo loop means responsive to the displacements of said
upper slave arm element to maintain alignment of the longitudinal
axis of said upper slave arm element with the longitudinal axis of
said upper master arm element,
a first force feedback means responsive to torque of said upper
slave arm element about said first horizontal axis for applying a
corresponding torque reduced in magnitude to said upper master arm
element about said third horizontal axis in a direction in
opposition to the direction of movement of said upper master arm
element producing the torque in said upper slave arm element,
a second force feedback means responsive to torque of said lower
slave arm element about said second horizontal axis for applying a
corresponding torque reduced in magnitude to said lower master arm
element about said forth horizontal axis in a direction in
opposition to direction of movement of said lower master arm
element producing the torque in said lower slave arm element,
a first lever arm having a pair of ends, one end of which is in
fixed relationship to said upper master arm element and movable
about said third horizontal axis therewith,
a first support point,
a first flexible tension member,
a first spring member,
one end of said first flexible tension member connected to said
other end of said first lever arm and the other end of said first
tension member connected to one end of said first spring member,
the other end of said first spring member connected to said master
support member,
an intermediate portion of said first tension member bearing on
said first support point,
the angle less than 180.degree. formed between the a line extending
from said other end from said first lever arm member said third
horizontal axis and a line extending from and said first support
point to said third horizontal axis being equal to the angle less
than 180.degree. between the longitudinal axis of said upper arm
element and an axis extending vertically upward from said third
horizontal axis,
the spring constant of said first spring member being equal to
M.sub.SM / a.sub.1 r.sub.1, where M.sub.SM is the moment of the
upper master arm element with said lower master arm attached, and
the moment of said upper slave arm element with said lower slave
arm attached as reflected to said lower master arm element,
a.sub.1 is the length of the line from said first support point to
said third horizontal axis, and
r is the length of said normal from said other end of said first
lever arm to said third horizontal axis,
the length of said first tension member being such that the end
thereof remote from the end connected to said first spring member
when unattached and said first spring member is in its unstressed
condition extends to said first support point,
a second lever arm having a pair of ends, one end of which is
coincidental with said third horizontal axis and the other end of
which is pivotable thereabout,
means for transferring an angular displacement of said lower master
arm element with respect to said upper master arm element about
said forth horizontal axis to an equal angular displacement of said
lever arm about said third horizontal axis,
a second support point,
a second flexible tension member,
a second spring member,
one end of said second flexible tension member connected to said
other end of said second lever arm and the other end of said second
tension member connected to one end of said second spring member,
the other end of said second spring member connected to said master
support member,
an intermediate portion of said second tension member bearing on
said second support point,
the angle less than 180.degree. formed between a line extending
from said other end of said lever arm member to said third
horizontal axis and a line extending from said second support point
to said third horizontal axis being equal to the angle less than
180.degree. between the longitudinal axis of said lower arm element
and an axis extending vertically upward from said fourth horizontal
axis,
the spring constant of said second spring member being equal to
M.sub.EM /a.sub.2 r.sub.2, where M.sub.EM is the moment of the
lower master arm element and the moment of said lower slave arm
element as reflected to said lower master arm element,
a.sub. 2 is length of the line from said second support point to
said third horizontal axis, and
r.sub.2 is the length of the line from said other end of said
second lever arm to said third horizontal axis,
the length of said second tension member being such that the end
thereof remote from the end connected to said second spring member
when unattached and said second spring member is in its unstressed
condition extends to said second support point.
Description
The present invention relates in general to material handling
apparatus of the kind in which the movements of a control or master
member produces corresponding movements amplified in respect to the
force exerted thereby of a controlled or slave member and in which
a portion of the force exerted by the slave member is reflected
back to the master to provide a sense of feel for the force being
applied by the slave member and in particular relates to such a
manipulator in which means are provided for counterbalancing the
unloaded weight of the master and slave members to improve the
performance per se thereof as well as to facilitate operator use
thereof.
This application is an improvement in the material handling
apparatus described and claimed in a copending patent application,
Ser. No. 33,442, filed Apr. 30, 1970, and assigned to the assignee
of the present application.
An object of the present invention is to provide a manipulator of
relatively simple construction and high performance capability.
Another object of the present invention is to provide means for
simply counterbalancing the unloaded weight of a manipulator having
a slave arm member with bilateral interconnection to the end that
the mental and physical capability of an operator can be used to
the fullest in fast, efficient, effective control of the slave
member of the manipulator to duplicate the motions of the arm of
the operator.
In carrying out the present invention in accordance with an
illustrative embodiment thereof there is provided an articulated
boom having a single joint intermediate the ends thereof and
pivoted at one end about a horizontal axis of a support member. The
other end of the boom has end effectors and end effector
positioning elements located thereon. A control member smaller in
size but similar in form to the articulated boom having a single
joint intermediate the ends thereof is also pivoted at one end
about another horizontal axis of another support member and a
handle is provided at the other end thereof. Means are provided to
cause each of the two parts of the articulated boom to follow in
orientation a respective one of the two parts of the control member
in response to movement of the handle by an operator. Additional
means are provided so that forces encountered by the articulated
boom are reflected back, reduced in magnitude however to the handle
held by the operator.
A pair of assemblies of levers and springs are provided, each in
cooperative association with a respective part of the control
member to counterbalance completely the weight of the unloaded
control member and the weight of unloaded boom as reflected by
force feedback to the control member for all positions thereof. A
spring constant is provided for each assembly which is a function
of movement to be balanced and fixed geometric factors. The force
applied by the spring of an assembly is made a particular function
of geometry and particularly applied to make possible utilization
of a fixed spring constant.
The novel features which are believed to be characteristic of the
present invention are set forth in the appended claims.
The invention itself, however, together with further objects and
advantages thereof may best be understood by reference to the
following description taken in connection with the accompanying
drawings wherein:
FIG. 1 is a perspective view of a manipulator to which the
invention of the present application will be applied.
FIG. 2 is an enlarged perspective view of a portion of the
apparatus of FIG. 1 showing the slave or controlled member and the
master or control member and the interconnections thereof.
FIG. 3 is a schematic diagram of the hydraulic and electrical
systems of the manipulator of FIGS. 1 and 2.
FIG. 4 is an enlarged perspective view similar to the enlarged
perspective view of FIG. 2 particularly showing the spring
counterbalance assemblies for the upper and lower arm elements of
the controlled member.
FIG. 5 is a line diagram of the control member and the slave member
of FIG. 1 with the forces acting thereon when unloaded.
FIG. 6 is a line diagram of the spring counterbalance assembly for
the upper control arm element of the control member useful in
explaining the operation of the counterbalance assembly as applied
in FIG. 4.
FIG. 7 is a line diagram of the spring counterbalance assembly as
applied to counterbalancing the forces on the lower arm element of
the control member also useful in explaining the application of the
spring counterbalance assembly shown in FIG. 4.
The subject matter described in connection with FIGS. 1, 2 and 3 is
also described and claimed in a copending application Ser. No.
33,442, filed Apr. 30 1970 and assigned to the assignee of the
present invention. FIGS. 1, 2 and 3 and the description thereof are
provided to set forth the apparatus to which the counterbalance
assemblies of the present application are applied and the manner of
application thereto.
Referring now to FIG. 1, there is shown a manipulator 10 having an
articulated boom or slave member 11 including an upper arm element
12 and a lower arm element 13. A control or master member 15
including an upper arm element 16 and a lower arm element 17 is
also provided. One end of the upper arm element 12 of the slave
member is pivotally connected to a stanchion or slave support
member 20 about a horizontal axis 21 to form a shoulder joint. The
slave support member 20 is supported in the bearing member 22 which
is connected to a base or mount member 23. The support member 20 is
pivotal on mount member 23 about a vertical axis 24 thereof. The
other end of the upper arm element 12 is pivotally connected to one
end of the lower arm element 13 to form an elbow joint and is
pivotal about a second horizontal axis 14. The other end of the
lower arm element 13 has connected thereto end-effector-positioning
apparatus 25 and an end effector 26. The end-effector-positioning
apparatus 25 comprises three rotary elements 27, 28 and 29,
connected in series so as to permit movement of the end effector 26
about any one of three mutually perpendicular axes. The end
effector 26 shown is one in which suction cups 31-34 are provided
for interfacing and securing thereto objects to be moved by the
manipulator.
The upper arm element 16 of the master control member is pivotally
connected to a master support member 40 and is pivotal about a
third horizontal axis 41. The master support member 40 in turn is
pivotally mounted to the slave support member 20 and is displaced
horizontally therefrom so as to be pivotal with respect thereto
about a second vertical axis 42. The other end of the upper arm
element 16 is pivotally connected to one end of the lower arm
element 17 and pivotal about a fourth horizontal axis 43. A handle
45 is provided on the other end of the lower master arm element 17.
The handle 45 is provided with buttons, switches and the like
responsive to finger action to effect through appropriate
electrical and hydraulic control elements the operation of the
end-effector-positioning effector elements 27-29 and the end
effector 26. Also connected to the slave support member 20 and
displaced horizontally from the slave support member so that the
control member 15 is positioned between an operator of the
manipulator apparatus and the slave member is a platform or
operator support member 50 shown in the form of a seat for the
operator and a foot rest so that the operator is oriented in the
direction in which the end of the slave member 11 is oriented and
the operator moves in azimuth so as to maintain such orientation.
The control arm member 15 is provided with elements 16 and 17 which
are comparable in length with the corresponding portions of the
adjacent arm of an operator so that motions of the arm of the
operator when grasping the handle produces motions in the elements
of the control member 15 which correspond to the motions of the arm
of the operator. Also, the ratio of the length of the lower arm
element of the master member to the length of the lower arm element
of the slave member is made substantially equal to the ratio of the
length of the upper arm element of the master member to the length
of the lower arm element of the slave member to provide a good
sense of position correspondence between handle 45 and end effector
26. Hydraulic actuators, control valves, and control linkages are
interconnected with the slave member 11 and the control member 15
in a manner which will be fully described in connection with FIGS.
2 and 3 so that as an operator moves the handle 45 of the control
member 15, the elements of the slave member 11 mimic the motion of
the elements of the control member 15. Accordingly, the position of
the hand of the operator produces a corresponding position of the
end effector 26 and, in addition, force exerted by the end effector
on an object is reflected back to the handle 45 reduced in
magnitude so that the operator has a feel for the force being
applied by the slave member.
Reference is now made to FIG. 2 in which elements corresponding to
the elements of FIG. 1 are denoted by the same reference symbol.
The slave support member 20 is a stanchion generally U-shaped to
the base of which is connected to a vertically extending shaft 51
which extends vertically downward and is supported in the
manipulator mount member 23 by bearing 22 and a thrust bearing (not
shown) located below the member 20. To the lower end of the shaft
51 is connected a sprocket 52 the teeth of which are engaged by a
chain 53. One end of the chain 53 is connected to the piston of a
hydraulic actuator 54 and the other end thereof is connected to the
piston of another hydraulic actuator 55. The cylinders of the
actuators 54 and 55 are secured to the support 23. Accordingly, by
appropriate energization of the actuators with hydraulic fluid the
slave support member 20 can be made to move about the first
vertical axis 24. Bearing surfaces are provided in the opposed
regions of the legs of the slave support member 20 and journals are
provided in one end of the upper slave arm element 12 for enabling
movement of the upper arm element about the horizontal axis 21. The
upper arm element may be a structural element rectangular in cross
section or of other columnar design to provide the desired strength
thereto. In this figure the element 12 is shown open for the
purposes of illustrating the embodiment of the invention. To the
other end of the upper arm element 12 is pivotally connected one
end of the bearing elements located in lower arm element 13 by
means of the elements 12 and 13. The lower arm element is pivoted
about the second horizontal axis 14 with respect to the upper arm
element. The upper arm element and the lower arm element have
longitudinal axes which intersect and lie in a vertical plane which
is perpendicular to the aforementioned first horizontal axis 21 and
the second horizontal axis 14.
The master control member 15 includes an upper arm element 16 and a
lower arm element 17. One end of the upper arm element 16 is
connected to master support member 40 and is pivotal with respect
thereto about a third horizontal axis 41. Master support member 40
is connected to a slave support extension member 56 so as to be
pivotal about the second vertical axis 42 to a limited extent. The
second vertical axis 42 is horizontally displaced along extension
member 56 from the first vertical axis 24. The first vertical axis
24, the first horizontal axis 21 and the second vertical axis 42
lie in a vertical plane. The other end of said upper arm element 16
is pivotally connected to one end of the lower arm element 17 of
bearing elements by means located in elements 16 and 17 and is
pivotal about a fourth horizontal axis 43. The other end of the
lower arm element 17 has secured thereto a handle 45 for
manipulation of the control member 15. The longitudinal axes of the
upper arm element 16 and the lower arm element 17, respectively,
intersect and lie in a second vertical plane perpendicular to the
aforementioned third horizontal axis 41 and fourth horizontal axis
43 and intersecting the aforementioned vertical plane including the
first and second vertical axes.
A first linkage means 60 is provided for transferring angular
displacement of the lower master arm element 17 with respect to the
upper master arm element 16 about the fourth horizontal axis 43 to
a corresponding angular displacement of a first reference arm
element 61 about the first horizontal axis 21 and includes a
sprocket 62 mounted to a shaft 63 which is pivotally supported in
the sidewalls of the master support member 40, and which pivotally
supports upper arm element 16, a lever arm 64 at one end pivotally
connected to an intermediate point on the lower arm element 17 and
at the other end pivotally connected to a side of the sprocket 62.
Accordingly, movement of the lower arm element 17 about the upper
arm element 16 causes a corresponding movement of the sprocket 62.
The angular displacement of the sprocket 62 about the third
horizontal axis 41 which is coincident with the axis of the shaft
63 is transferred to angular displacement about the first
horizontal axis 21 by means of another sprocket 65 fixedly mounted
to one end of tubular member 66 having its longitudinal axis
coincident with the first horizontal axis 21 and rotatable
thereabout. The tubular member 66 is rotatably supported in the
tubular slave support extension member 56. An endless chain 67 with
a small amount of slack engages the teeth of the sprockets 62 and
65 and interconnects them. The reference arm element 61 is
connected to the other end of the tubular member 66. Accordingly,
the movement of the sprocket 62 about the third horizontal axis is
transferred through the second sprocket 65 and through the tubular
member 66 is transferred to the tab 61 to produce a rotation of the
longitudinal axis thereof about the first horizontal axis 21.
Second linkage means 70 are provided for transferring angular
displacements of the upper master arm element 16 with respect to
the third horizontal axis 41 to a corresponding angular
displacement of a second reference arm element 17 about the first
horizontal axis 21 and includes a second lever arm 72 which at one
end is universally pivotal about a shaft 73 rigidly connected to a
point on the upper master arm element 16 and at the other end is
universally pivotal about a shaft 74 rigidly connected to an offset
75 member rigidly mounted on shaft 76. Shaft 76 has an axis of
rotation coincident with the first horizontal axis 21. The shaft 76
is rotatably supported within extension member 56 and connects to
reference arm 71 at the other end thereof. The socket 78 is
provided at one end of lever arm 72 which engages a ball 79 fixedly
secured to shaft to provide a universal joint. Similarly, a socket
80 is provided at the other end of lever arm 72 which engages a
ball 81 fixedly secured to shaft 73 to provide another universal
joint. Enough play is provided in the aforementioned universal
joints so that small angular displacements, for example less than
10.degree., of the support member 40 about axis 42 with respect to
extension member 56 on which member 40 is pivotally mounted does
not bind the universal joints yet allows the indicated
displacements to take place. Accordingly, movement of the upper
master arm element 16 about the third horizontal axis 41 causes a
movement of the shaft 76 about the first horizontal axis 21 which
in turn causes the second reference arm 71 to execute a
corresponding movement about the first horizontal axis.
A system of levers is provided responsive to the orientation of the
longitudinal axis of the first reference arm 61 to the orientation
of the longitudinal axis of the lower slave arm element 13 to
produce a displacement in a differential lever arm 85. The
direction of such displacement of the lever arm 85 from a neutral
position and the magnitude of such displacement corresponds to the
direction and magnitude of misalignment of the lower slave arm
element 13 and the lower master arm element 17. To this end a lever
86 is provided connected between the remote end of the first
reference arm 61 and one end of the differential lever arm 85.
Another lever 87 is provided connected between an extension of the
lower slave arm beyond the horizontal pivotal axis 14 thereof and
the other end of the differential lever arm 85. An intermediate
point 88 on the differential lever arm 85 is connected to one end
of an actuating arm 89, the other end of which is pivotally secured
to the upper slave arm element 12. The longitudinal axis of the
first reference arm 61 is aligned to correspond with the
longitudinal axis of the lower master arm element 17. Accordingly,
a movement of the lower master arm element provides a corresponding
angular displacement of the reference arm which produces a movement
in one direction of the differential arm 85. If the other end of
the differential arm is maintained fixed the movement of the
differential arm is in the same direction. To maintain the
actuating arm 89 fixed in position, it is necessary to move the
other end of the differential arm 85. Accordingly, the magnitude
and direction of the movement of the actuating arm 89 corresponds
to the magnitude and direction of movement of the longitudinal axis
of the lower master arm 17. Such movement is sensed by a control
valve 90 connected to the upper slave arm element 12. The control
valve has a button which is moved in one direction or the other
from a neutral position to cause fluid to flow from one side to the
other or vice versa of a slave hydraulic linear actuator 91
connected between the upper slave arm element 12 and the lower
slave arm element 13. The control system is polarized so that the
flow of fluid causes the actuator 91 to bring the lower slave arm
13 into correspondence with the lower master control arm 17. Such
action causes the differential lever arm to be moved so as to
maintain the actuating arm 89 in a neutral position.
A second servo loop means is provided responsive to the
displacement of the second reference arm 71 to maintain alignment
of the longitudinal axis of the upper slave arm element 12 with the
longitudinal axis of the upper master arm element 16. Connected to
the upper slave arm element 12 is another control valve 92 having a
button 93 which bears against the second reference arm 71. Movement
of the reference arm 71 in one direction or the other corresponding
to movement of the upper control arm 16 in one direction or the
other about the third horizontal axis 41 causes a displacement of
the button 93 inward or outward, and accordingly directs hydraulic
fluid to flow in one direction between the ends of the linear
actuator 94 or in the other direction to cause the slave arm
element 12 to move in one direction or the other to maintain
correspondence in the direction of the longitudinal axis thereof
with respect to the longitudinal axis of the upper control arm
element 16.
A third servo loop means is provided responsive to the displacement
of the second vertical plane, that is the plane of the longitudinal
axes of the elements 16 and 17 of the control member 15 about the
second vertical axis 42 from a position in which it is parallel to
the first vertical plane, that is the plane including the
longitudinal axes of the elements 12 and 13 of the slave arm member
11, for maintaining the planes in parallel. To this end the slave
support extension member 56, one end of which is secured to the
stanchion 20 is provided at the other end thereof with a U-shaped
member 95, the base 96 of which is attached to the tubular member
56. A pair of bearing elements are provided, one in each of legs 97
and 98 of the U-shaped member 95 in opposed relationship and
aligned along the second vertical axis 42. The bearing element
associated with leg 97 includes a shaft 99 secured to the leg 97.
To the upper end of the shaft 99 is secured a cam 100 having a
peripheral surface 101 which is eccentric with respect to the
second vertical axis 42. A bracket 102 having an upper horizontal
portion 103, a lower horizontal portion 104 and a side portion 105
is connected between opposed walls of the support 40. The upper
horizontal portion 103 is connected to the wall of the support 40
adjacent the slave member 11, the side portion 105 is connected to
the opposed wall of the support 40 and the lower horizontal portion
104 is provided with a bearing which engages a journal in leg 98 of
the U-shaped member 95. As mentioned above, a bearing element is
provided in the upper horizontal portion 103 so as to permit
pivoting of the support 40 with respect to member 95 about the
second vertical axis 42. A servo valve 106 having an actuating
button 107 is mounted to a wall of the support 40. The button 107
bears against the peripheral surface 101 of the cam 100. When the
aforementioned second vertical plane is aligned with the
aforementioned first vertical plane, the button 107 of valve 106 is
in a neutral position on the cam 100. When the control arm member
15 is moved in one azimuth direction, the support 40 is displaced
about the vertical axis 42 in one direction and the cam displaces
the button in one direction to produce a flow of hydraulic fluid
through the actuators 54 and 55 to cause the shaft 51 to move in a
direction to align the first vertical plane with a second vertical
plane. Conversely, when the control arm member 15 is moved in the
opposite azimuth direction the cam 100 displaces the button 107 in
the opposite direction from neutral to cause actuators 54 and 55 to
move shaft 51 in the opposite direction to align the first and
second vertical planes. The movements of the control arm member 15
in one direction or the other about the second vertical axis 42
need not be large, i.e., less than a degree, since it need be
sufficient only to produce sufficient error signal in the servo
loop to cause the slave arm member 11 to move in correspondence
therewith. The provision of a chain 67 linking the first sprocket
62 and second sprocket 65 which is slightly slack enables such
limited movement to be performed without binding the mechanism.
Similarly, the lever arm 72 having ball and socket joints on the
ends thereof with a small tolerance is provided to avoid binding of
the lever arm yet permitting the error signal in the servo loop to
be produced.
Limit switches 110 and 111 are provided responsive respectively to
engagement of cams 112 and 113, therewith in the azimuth limit
positions of the support member 20 to block flow of fluid to the
actuators 54 and 55 and thereby limit the azimuth excursion of the
support member 20 to those limits. The circuit connections and
operation of the limit switches 110 and 111 will be further
described in connection with FIG. 3.
Force feedback is applied to the handle 45 by means of linear
actuators 114, 115 and 116. The linear actuator 114 pivotally is
connected between the elements 16 and 17 to provide torque about
the fourth horizontal axis 43. The linear actuator 115 is pivotally
connected between element 16 and master support member 40 to
provide torque on the third horizontal axis 41. The linear actuator
116 is pivotally connected between members 40 and 95 to provide a
torque about the second vertical axis 42. As mentioned above,
actuator 91 is connected between elements 12 and 13 and is used for
applying torque about the second horizontal axis 14. Actuator 94 is
connected between element 12 and member 20 and is used for applying
a torque about the first horizontal axis 21. The actuators 54 and
55 are connected to a chain 53 which moves the element 20 about the
first vertical axis 24.
Each of the slave actuators 91, 94 and 54, and 55, and also each of
master actuators 114, 115 and 116 is in an assembly of a cylinder
with a piston therein and has a pair of fluid ports, one at each
end of the cylinder. The application of a pressure differential
between one side and the other side of the piston produces a net
force thereon. The magnitude of such force and the direction of
such force being dependent upon the magnitude and direction of
pressure differential and, of course, on the active cross-sectional
area of the piston. The active area of each of the pistons of
actuators 114, 115 and 116 is substantially smaller by a
predetermined ratio than the active area of each of the pistons of
actuators 91, 94, 54 and 55. The pressure differential applied to
each of actuators 114, 115 and 116 is substantially the same as
appearing across respective actuators 91, 91 and one of the pair of
actuators 54 and 55. The actuators 114, 115 and 116 are
mechanically connected to provide torque lever arms about
horizontal axes 43, 41 and vertical axis 42, respectively which are
substantially smaller than lever arms provided to actuators 91, 94
and one of a pair of actuators 54 and 55, respectively. Each of the
actuators 114, 115 and 116 are situated in respect to the
corresponding actuator or pair of actuators on the slave member in
a kinematically similar position so that the ratio of slave torque
to master torque for a pair of corresponding horizontal axes is the
same for any location of the handle 45. Preferably such ratio is
made the same for each of the three sets of axes so that force fed
back to the handle is a faithful replica of the force encountered
by the end effector 26. Also, of course, actuators 114, 115 and 116
are connected in circuit so that pressure differential existing
thereacross is opposite in direction to the pressure differential
existing at actuators 91, 94 and at pair of actuators 54 and 52,
respectively, to provide a restraining force to the movement of the
handle 45 which produced the force in the slave member.
The magnitude and direction of pressure applied to each of the
actuators 91, 94, and 54 and 55 is controlled by a hydromechanical
servo valves 90, 92 and 106. As mentioned above, servo valve 90
controls the pressure applied to actuator 91, valve 92 controls the
pressure applied to actuator 94 and valve 106 controls the pressure
applied to actuators 54 and 55.
The structure of each of the control valves 90, 92 and 106 and the
manner of their connection to respective slave actuators 91, 94 and
a pair of linear actuators 54, 55 as well as the operation thereof
will be explained in detail in connection with FIG. 3. Also in
connection with FIG. 3, the manner of applying pressure
differential appearing across each of the slave linear actuators
91, 92 and the azimuth set 54 and 55 to the force feedback linear
actuators 114, 115 and 116, respectively, will also be
described.
Reference is now made to FIG. 3 in which elements identical with
the elements of FIG. 2 are denoted by the same reference symbols.
Specifically, in this figure are shown mechanical servo valves 92,
90 and 106 for controlling fluid flow to respective linear
actuators 91, 94 and pairs of linear actuators 54 and 55. Each of
the servo valves 92, 90 and 106 is a four-way proportional control
pressure flow valve to which a mechanical input on a button thereof
produces a flow at a pair of output ports P.sub.1 and P.sub.2 the
magnitude and direction of which is proportional to the magnitude
and direction of movement of the button about a neutral position.
In addition to the output ports P.sub.1 and P.sub.2, each of the
valves is provided with a source port S for the application of
fluid pressure from a reservoir or a pressure generator and a
return port R therefor. Each of the control valves is a valve such
as a type 50- 346 hydromechanical servo valve manufactured by Moog
Inc. of Proner Airport, East Aurora, New York.
As mentioned above, each of the linear actuators 91, 94 and 54 and
55 include a cylinder and a piston movable therein. The cylinder is
provided with a port at one end and another port at the other end
thereof. The application of a pressure differential between the
ports of the cylinder provides a force between the piston and
cylinder thereof. Coupling members are connected to the piston and
the cylinder which in turn are connected to appropriate elements
between which it is desired to apply the force. As shown in this
figure, the linear actuator 94 is connected between elements 12 and
20. Linear actuator 91 is connected between elements 12 and 13. The
piston of linear actuator 54 is connected to one end of chain 53,
the other end of which is connected to the piston of actuator
55.
The hydraulic fluid source line 118 of a source of pressurized
hydraulic fluid is connected to each of the source ports of the
valves 92, 90 and 106 and the return ports of each of the control
valves 92, 90 and 106 are connected to the return line 119 of the
hydraulic fluid source. The output ports P.sub.1 and P.sub.2 of
control valve 92 are connected over lines 120 and 121,
respectively, to respective ports on the linear actuator 94. Line
120 includes fluid pathway of a two-way directional control valve
122 which is open when electrically energized and closed when
deenergized. The valve 122 provides a means to lock the actuator 94
in the event of electric power failure. The output ports of the
valve 90 each are connected to respective ports of the linear
actuator 91 along lines 124 and 125. Line 124 includes another
fluid pathway of valve 122 which is open when energized and closed
when deenergized. Valve 122 also provides a means to lock actuators
91 as well as 94 in the event of power failure. Each of the output
ports P.sub.1 and P.sub.2 of valve 106 is connected to a respective
port linear actuator the ports at the same end of the linear
actuators 54 and 55 over lines 126 and 127. The other ports of the
linear actuators 54 and 55 are connected together and are connected
to the return line 119 of the fluid source. A lock valve 128 is
connected in line 126 to block fluid flow therein when electrically
deenergized by limit switch 110 electrically connected thereto.
Similarly, lock valve 129 is connected in line 127 to block fluid
flow therein when electricity deenergized by limit switch 111
electrically connected thereto.
Force feedback to the elements 16 and 17 are provided by linear
actuators 115 and 114 which as mentioned are connected between
elements 16 and 40 and 16 and 17, respectively. While the pressure
difference appearing across the slave actuator 94 and the slave
actuator 91 could be applied respectively to the linear actuators
115 and 114, because of the large difference in masses of the
master and slave circuits instabilities are produced in such
circuits. Accordingly, in order to stabilize the master loop,
isolation is provided which makes the master control circuit
relatively independent of the slave circuit. The isolation is
achieved by actuator 94 and actuator 115, a pair of pressure
sensors 130 and 131, a differential amplifier 132 and a control
valve 133 and similarly for actuator 91 and actuator 114 providing
a pair of pressure sensors 135 and 136, a differential amplifier
137 and a control valve 138.
Each of the valves 133 and 138 are electrohydraulic flow valves
having a source port S and a return port P and a pair of output
ports P.sub.1 and P.sub.2. The valve is provided with solenoids
responsive to current applied thereto to control the flow in the
valve. Input current flow into one solenoid produces a flow in one
direction between the output ports P.sub.1 and P.sub.2, the
magnitude of which depends upon the magnitude of the current.
Similarly, input current flow to the other solenoid produces a
fluid flow in the opposite direction between the output ports
P.sub.1 and P.sub.2, the magnitude of which is dependent upon the
magnitude of such current flow. The electrohydraulic flow valve is
of a type such as type 30 Flow Control servo Valve made by Moog
Inc., Proner Airport, East Aurora, New York. Each of the pressure
transducers 130, 131, 135 and 136 are transducers of the strain
gauge type and have a pair of fluid pressure input ports and a pair
of electrical output terminals from which a voltage is derived
proportional to the pressure differential applied between the input
ports. The magnitude and the direction of the voltage is dependent
upon the magnitude and direction of the pressure applied between
input ports of the strain gauge. The pressure transducers or
sensors such as Model 620-1 manufactured by Standard Controls Inc.,
South Bayview St., Seattle, Washington, may be used. Each of the
differential amplifiers 132 and 137 has a pair of input channels
and a pair of output channels. The amplifier compares the signals
applied to the input channels and develops an output current in one
channel or the other depending on which of the two signals is
larger. The magnitude of the output current depends on the
magnitude of the difference. The pressure input ports of pressure
sensor 130 are connected to the ports of the actuators 94. The
pressure input ports of pressure sensor 131 are connected to the
ports of actuator 115. The electrical outputs of sensors 130 and
131 are applied to respective input channels of the amplifier 132.
Each of the output channels of the amplifier 132 are applied to a
respective solenoid of the control valve assembly 133. Each of the
output ports P.sub.1 and P.sub.2 of control valve assembly 133 are
applied to a respective port of actuator 115. Accordingly, when the
pressure differential between the ends of the actuator 94 and the
actuator 115 are the same, the outputs from the transducers 130 and
131 are the same and no net output would be produced from the
amplifier 132, consequently no fluid flow would appear at the
output ports P.sub.1 and P.sub.2 of the valve assembly 133. Should
the linear actuator 94 be energized by fluid flow or pressure
differential appear between the ends thereof, a signal would be
produced in transducer 130 which would produce a net output from
the amplifier 132 and would accordingly actuate valve assembly 133
to apply fluid pressure to the linear actuator 115 to develop an
output from the transducer 131 and accordingly restore balance to
the system. The elements of the feedback loop are phased in a
manner to produce such restoration.
Similarly, the pressure input ports of pressure sensor 135 are
connected to the ports of the actuator 91. The pressure input ports
of sensor 136 are connected to the ports of actuator 114. The
electrical outputs of sensors 135 and 136 are applied to respective
input channels of the amplifier 137. Each of the output channels of
the amplifier 137 are applied to a respective solenoid of the
control valve assembly 138. Each of the output ports P.sub.1 and
P.sub.2 of the control valve 138 is connected to a respective port
of actuator 114. The circuits described are so phased that the
pressure differential appear across the ends of the actuator 91 are
essentially matched by a pressure differential across actuator 114
in the manner described above in connection with actuators 94 and
115. The linear actuator 116 for azimuth force feedback has a
cylinder thereof connected to the element 40 and the piston
connected to the element 95. One port of actuator 116 is connected
to a port of the actuator 54 and the other port thereof is
connected to a port of the actuator 55, each through respective
orifices 140 and 141. The fluid circuit connections are made so
that actuator provides a force to member 40 counter to the movement
thereof which produced movement of member 95. The actuator 116 not
only provides force feedback but also acts in conjunction with the
orifices 140 and 141 as a dashpot to stabilize the operation of the
master azimuth circuit. The stabilizing circuit is described and
claimed in a copending patent application filed Apr. 30, 1970, Ser.
No. 33,191 and assigned to the assignee of the present
invention.
Reference is now made again to FIGS. 1 and 2 in which is shown a
plurality of rotary actuators 27, 28 and 29. Each of the actuators
has a stator and a rotor. Each of the actuators is fluid operated.
The rotor of actuator 27 is connected to the end of the member 13
and the stator of actuator 27 is connected to the rotor of actuator
28. The stator of actuator 28 is connected to the stator of
actuator 29, the rotor of which is connected to the end effector
26. A plurality of finger operated switches 145, 146 and 147 are
provided on the handle 45. Movement of the switch 145 to the left
or right causes electrical and hydraulic circuits to be actuated to
move the end effector 26 to be moved in yaw by actuator 28 to the
left or right. Moving the switch 145 forward or reverse causes
electrical and hydraulic circuits to be energized to actuate the
rotary actuator 27 to move the end effector 26 up and down in
pitch. Actuation of the trigger switch 146 causes electrical and
hydraulic circuits to energize the rotary actuator 29 to rotate the
end effector 26. Each of the rotary actuators 27, 28 and 29 are
rate actuators in that upon the application of fluid the rotor
thereof moves with respect to the stator until energization is
removed or until appropriate stops are reached for each of the
actuators which limit the movement of the rotors with respect to
the stator thereof. The base of the cups 31, 32, 33 and 34 are
provided with openings each of which are sealed by a cover. The
cover is mechanically opened upon the interfacing of the cups with
a surface of the object to be moved thereby by vacuum forces secure
the object to the end effector. The switch 147 provides a means for
releasing vacuum and hence breaking the seal between the end
effector and the object to be moved.
In operation of the manipulator apparatus of FIGS. 1, 2 and 3, the
operator would initially set on the seat of support member 50 and
grasp handle 45 on the master control member. Upon energization of
the hydraulic and electrical circuits of the system to free the
slave elements from a stowed position, the apparatus would be ready
for operation. Movement of the handle 45 in an arbitrary direction
in space would produce a corresponding movement of the end of the
element 13 and the end effector 26 into a corresponding position.
Such operation would be produced by the servoing action described
above. If such arbitrary movement of hand 45 required that element
17 be moved with respect to 16, tab 61 would be moved to produce a
corresponding movement in the arm 89 which would actuate the
control valve 90 in appropriate direction to energize linear
actuator 91 to bring the element 13 into correspondence with the
orientation of element 17. Similarly, if such arbitrary movement of
the handle 45 required that element 16 be moved about its
horizontal axis 41, the control valve 92 would produce a fluid flow
into linear actuator 94 to cause the spatial orientation of element
16 to line up with the element 12. Similarly, if such arbitrary
movement of handle 45 required that support member 40 be moved in
azimuth direction with respect to the horizontal axis 42, the servo
valve 106 would be actuated to actuate the linear actuators 54 and
55 in the appropriate direction to cause the slave support member
20 to move in azimuth in correspondence with the movement of the
control handle. If now the handle 45 is moved so as to cause the
end effector 26 to abut an object, force applied to the object is
reflected back to the handle 45 reduced in magnitude by a
predetermined ratio as described above by virtue of the fact that
force feedback cylinders 114, 115, and 116 are connected between
elements 17 and 16, between elements 16 and 40, and elements 40 and
95, respectively. Accordingly, the operator has a sense of feel for
the amount of force that his movement of the handle produced. If it
is desired now to life an object, such is accomplished by means of
the end effector 26. The handle now can be retracted to position
the object.
Reference is now made to FIGS. 4, 5, 6, and 7 in connection with
which the invention of the present application will be particularly
described. FIG. 4 is similar to FIG. 2 and the elements of FIG. 4
are identical to the elements of FIG. 2 are designated by the same
symbols. The master support member 40 of FIG. 4 is identical to the
master support member 40 of FIG. 2, and also the control member 15
is identical to the control member 15 of FIG. 2. The endless chain
67 of FIG. 4 has been eliminated from FIG. 4 for reasons of clarity
of showing the assembly of the present invention.
The spring counterbalance assembly 150 applied to the upper control
arm element includes a lever arm 151 provided by the extension of
the control arm element 16 beyond the axis of rotation thereof
about the third horizontal axis 41. A support pin 152 is provided
in the end thereof remote from the third horizontal axis 41. The
assembly 150 also includes a bearing support member 153 in the form
of a sprocket of small radius rotatable about a shift 154 extending
horizontally between the side portions of the member 40. The shaft
154 is placed below the third horizontal axis 41 and on the side
thereof away from the side from which the control member 15
extends. A flexible tension member 155 in the form of a chain and a
coil spring member 156 are also provided. One end of the tension
member 155 is connected to the pin 152 attached to the upper arm
element extension 151 and the other end of the tension member 155
is connected to one end of the spring member 156. The other end of
the spring member 156 is connected to a crossbar 157 through an
adjusting bolt 162 for adjusting spring tension. The crossbar 157
is connected between the sidewalls of the master support member 40.
An intermediate portion of the tension member 155 bears on a first
support point 158 (clearly shown in FIG. 6) of the first bearing
member 153 on a side thereof which is remote from a third
horizontal axis 41. Another sprocket 160 is also provided below
sprocket 153 to enable securing of the fixed end of the spring
member 156 to the crossbar 157. The idler sprocket 160 is supported
on a shaft 161 extending between the sidewalls of the master
support member 40. Rotation of the upper arm element 16 in the
bearing about the horizontal axis 41 causes the spring member 156
to be deflected and exert a counterbalancing force on the upper arm
element 16. The geometrical and physical proportioning of the
elements of the upper arm element counterbalance assembly will be
fully described in connection with FIGS. 5 and 6.
Spring counterbalance assembly 170 for the lower control arm
element 17 is similar to the counterbalance assembly for the upper
control arm element 16. The assembly for the lower control arm
element includes a tab 171 providing a lever arm, one end of which
is secured to the shaft 63 and hence is rotatable about the third
horizontal axis 41 and the other end is provided with support
aperture 172 for fastening another tension member 173 thereto. The
assembly also includes bearing support member 174 and spring member
175. The bearing member 174 is also in the form of a sprocket of
small radius free to move about the shaft 154. One end of the
spring member 175 is adjustably attached to the crossmember by
means of nut and bolt assembly 176 and the other end extends
downward. The tension member 173 in the form of a chain, has one
end secured to aperture 172 in arm 171 and has the other end
secured to the downward extending end of the spring member 175. An
intermediate portion of the tension member 176 bears on the
sprocket 174 on a support point 177 thereof which is on a side
remote from the side of the third horizontal axis 41. A second
idler sprocket 178 is provided on the shaft 161 to enable the
spring member 175 to be secured as shown, that is with an
adjustable positioned end up and the other end down. The
geometrical arrangement and the physical characteristics of the
elements of the spring counterbalance assemblies will be described
and explained in greater detail in connection with FIGS. 5, 6, and
7 to which reference is now made.
FIG. 5 includes two line diagrams, one for the control member 15
and the other for the controlled or slave member 11 of FIG. 1 in
which corresponding elements are denoted by the same numerical
designation. FIG. 5 shows the forces acting on elements 16 and 17
of the control arm member 15 and also on the elements of the slave
member 11 and the point of application thereof. As described in
connection with FIGS. 1, 2, and 3 means are provided so that
movement of the control arm member 15 causes the elements of the
slave member 11 to move in a way to be identically oriented with
the corresponding control member elements. Also force feedback
loops are provided from the slave elements to the master elements
to provide an operator of the control member with a sense of feel
for the force being applied by the slave member. In the absence of
any work being done or force being applied by the slave member, the
unloaded or dead weight of the elements of the slave member produce
a corresponding force on the elements of the controlled member.
Accordingly, an operator in operating the manipulator has to apply
force to overcome not only the weight of the control arm elements
but also to overcome the unloaded or dead weight of the slave arm
elements as reflected back to the control arm elements. Such force
or exertion required by the operator considerably limits the ease
and freedom with which he can manually direct the slave member to
perform the functions which he desires it to perform. Also the need
for the operator to counterbalance by his effort the unloaded
weight of the elements of the manipulator distorts the sense of
feel of the force being applied by the slave member.
The torque produced on the lower control arm element about the
elbow joint E is given by the following equation:
T.sub.EM =[F.sub.ME .sup.. R .sub.ME +(1/R )(F.sub.SE .sup..
R.sub.SE) ]cos .alpha. (1)
The torque produced about the shoulder joint S on the upper control
arm element is represented by the following equation:
T.sub.SM =[F.sub.ME .sup.. R.sub.MS +(F.sub.SE /R).sup.. R' .sub.SS
+F.sub. MS .sup.. R.sub. MS +F.sub.SS.sup.. R.sub.SS ]cos .theta.
(2)
Where the symbols in the equations are defined as follows:
T.sub.EM = Torque produced by weight of master lower arm element
and slave lower arm element as reflected to lower master arm
element
F.sub.ME = Weight of lower master arm
R = Torque reflection ration of a slave element to a corresponding
master element
F.sub.SE = Weight of lower slave arm
R.sub.SE = Distance from elbow pivot point E to center of gravity
of lower slave arm
.alpha. = Angle of longitudinal axis of lower master arm element
with respect to a horizontal plane
T.sub.SM = Torque produced by dead weight of master upper arm
element and master lower arm attached thereto, and slave upper arm
element and slave lower arm element attached thereto as reflected
to upper master arm element
R.sub.ME = Distance from elbow pivot E to center of gravity of
lower master arm
R' .sub.MS = Length of upper master arm element
R'.sub.SS = Length of upper slave arm element
F.sub.MS = Weight of upper master arm
R.sub.MS = Distance from shoulder pivot point S to center of
gravity of upper master arm element
F.sub.SS = Weight of upper slave arm
R.sub.SS = Distance from shoulder pivot point S to center of
gravity of upper slave arm element
.theta. = Angle of longitudinal axis of upper master arm element
with respect to a horizontal plane P
Reference is now made to FIG. 6 which shows the line diagram of the
spring counterbalance assembly 150 as applied to the control member
15 of FIG. 4. In this figure elements identical to elements of FIG.
4 are designated by the same reference numerals. The upper arm
element 16 is pivotably about the third horizontal axis 41 and
makes an angle .phi.' with a vertical line extending vertically
upward from the third horizontal axis. FIG. 6 is a representation
of the movement occurring in a plane perpendicular to the third
horizontal axis 41 and will be used for deriving the relationship
between certain geometrical and physical quantities achieving
counterbalancing. The general matter of spring balancing of loads
is described in an article entitled "Spring Mechanisms" by Kurt
Hahn in Product Engineering of Jan. 9, 1961. The following is an
extension of the principles described therein. Nomenclature to be
used in the derivation is as follows:
F = Force or load to be balanced
.rho. = Effective length of force lever arm
M = F.rho. = Torque produced by an equivalent beam in a horizontal
position
r = Spring moment arm
a = Straight line spacing between pivot point or axis 41 and
tangential point 158 on bearing member 153
.phi.' = Angular displacement of element 16 with respect to a
vertical line from axis 41
.phi. = Angular displacement of r with respect to straight line
a
P = Spring force
h = Projection of spring moment arm r onto a line normal to
direction of application of spring force P
d = Distance between end of spring moment arm r to tangent point
158 on bearing member 153
c =P/d = Spring rate or constant
As torque produced by force F about axis 41 is equal to torque
produced by spring force P,
F.rho.sin .phi.'=Ph (3) Since rsin .beta.=d/sin .phi., and sin
.beta.=h/a, then
h =(r a sin .phi.)/d
Substituting equation (4) in equation (3)
F sin .phi.'=(Pr a sin .phi.)/ d (5)
Making .phi. = .phi.' yields
F.rho.=(Pr a)/d (6)
If
P= cd (7)
F.rho.=r ac
Or
c=F.rho. /(r )
Accordingly, it is seen from equation (5) that when the angle
.phi.' is equal to the angle .phi. and the spring force P is made a
function of the distance d, complete counterbalancing over the
range of movement of the upper element 16 may be achieved by use of
a spring having the spring constant or rate set forth in equation
(7). The reflected torque from the slave upper arm element is
counterbalanced as well. It should be observed that in the
unstressed position and the tension member 155 disconnected from
pin 152, the disconnected end extends to the support point 158.
With this requirement met, attachment of the tension member 155 to
the lever arm 151 or r ideally should provide perfect balance for
the upper arm element 16. In view of the physical dimensions of the
tension member and the finite size of support points, friction
factors and the like, the derivation does not produce a perfect
balance but does provide a balance sufficiently close for all
practical purposes to provide counterbalancing. It should be noted
in connected with FIG. 4 that for fine adjustment to accommodate
changes, such as changes in the constants of the slave element end
effectors and torque feedback ratios from lower to master elements,
that the spring constant may be varied by linking a fewer number of
turns of the spring member. Bolt and nut assembly 162 provides for
adjusting the position of the remote end of the tension member to
coincide with point 158 when the spring member is free of stress so
that the relationship P=cd is established. Also, while a spring
member which provides a force when it is deflected in tension has
been shown it will be appreciated that a spring which provides a
force under compression may also be used. It should be noted that
angles .phi.' and .phi. are less than 180.degree. and the angle
.phi. is the angle between the normal from the remote end of the
lever arm r to the third horizontal axis and the normal from the
first support point 158 to the third horizontal axis.
Reference is now made to FIG. 7 which shows a line diagram of the
lower arm element 17 and the counterbalance spring assembly 170 as
applied thereto. In this figure elements identical with the
elements of FIG. 4 are designated by the same symbol. In this
figure, the lower control arm element 17 is pivotable about the
fourth horizontal axis 43 and the longitudinal axis of the lower
arm element makes an angle .phi.' with a vertical line extending
upward from the fourth horizontal axis. A pantograph assembly
including a lever 64 at one end pivotally connected to the lower
control arm element 17 and at the other end pivotally connected to
a point on sprocket 62 which is rotatable about the third
horizontal axis 41. The lever arm 64 is proportioned and so
connected that a given angular displacement of the lower arm
element 17 about the fourth horizontal axis 43 produces a
corresponding angular displacement of the sprocket 62 about the
third horizontal axis 41. Connected to the sprocket 62 is a second
lever arm 171 having a pair of ends, one end of which is connected
to the shaft 63 and has an axis coincidental with the third
horizontal axis 41 and the other end is pivotal about the third
horizontal axis 41. The pantograph arrangement described provides a
means for transferring an angular displacement of the lower arm
element 17 with respect to the upper master arm element about the
fourth horizontal axis 43 to an equal angular displacement of the
lever arm 171 about the third horizontal axis 41. The angle between
the normal from the remote end of the lever arm 171 to the third
horizontal axis 41 and the normal from the second support point 177
to the third horizontal axis 41 is designated .phi. and is made
equal to the angle .phi.'. Both of these angles are less than
180.degree.. The other symbols in the diagram of FIG. 7 are the
same as the symbols in the diagram of FIG. 6 and identical analysis
is applied to derive the formula for the spring constant of the
spring 175. As in the case of the assembly of FIG. 6, using a
spring constant c resulting from the derivation for the lower
control arm element and using a length for the tension member 173
such that when the spring 175 is in an unstressed position the
tension member 173 extends to the second support point 177,
attachment of the tension member 173 to the remote end of the lever
arm 171 or r provides a balance for all positions of the lower
control arm element about the third horizontal axis and as well for
movements of the lower control arm element about the third
horizontal axis resulting from movement of the upper control arm
element. In addition, the reflected torque from the slave lower arm
element is counterbalanced. The same spring constant adjustment and
tension member zero spring force position adjustment capability is
provided in the counterbalance assembly 170 as in counterbalance
assembly 150 by means of nut and bolt assembly 176.
It should be noted that in addition to counterbalancing the master
and slave members of the manipulator, the spring members 156 and
175 also provide dynamic stabilization of the elements (i.e.,
inhibit oscillation thereof) of the master member.
While we have shown a particular embodiment, it will of course be
understood that we do not wish to be limited thereto since many
modifications may be made in the arrangement shown and in the
instrumentalities employed. We contemplate by the appended claims
to cover any such modifications as fall within the true spirit and
scope of our invention.
* * * * *