In a robot having a gripper including a pair of fingers and a drive motor for driving the fingers toward and away from one another while the fingers remain parallel to each other, the fingers consist of finger pads, which interface with a handle on an object to be grasped, and a shank, which attaches the fingers to the robot gripper. The double-V finger has two orthogonal V-grooves forming in the center of the finger pads and recessed cruciform. The double-V finger is used with a handle on the object to be grasped which is the negative of the finger pads. The handle face consists of V-shaped pads capped with a rectangular cruciform. As the gripper is brought into place near the handle, the finger pads are lined up facing the handle pads. When the finger pad and the handle pad are in proper alignment, the rectangular ridges on the handle fall inside the rectangular grooves on the finger, and the grip is complete

Voellmer, George M.

English

NASA Technical Reports Server

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United States Patent 
US005178431A 
[ i l l  Patent Number: 5,178,431 
Voellmer [45] Date of Patent: Jan. 12, 1993 
DOUBLE-V BLOCK FINGERS WITH 
CRUCIFORM RECESS 
Inventor: George M. Voellmer, Takoma Park, 
Md. 
[73] Assignee: The United States of America as 
represented by the Administrator of 
the National Aeronautics and Space 
Administration, Washington, D.C. 
[21] Appl. No.: 899,145 
1221 Filed: Jun. 17, 1992 
Related U.S. Application Data 
[63] Continuation of Ser. No. 760,634, Sep. 16, 1991, aban- 
doned. 
[51] Int. C l . 5  .............................................. B25J 15/08 
[52] U.S. Cl. ................................... 294/86.4; 294/902; 
901/39; 269/270 
[58] Field of Search ................. 294/86.4, 902; 901/39; 
269/265, 266, 268, 270; 8V424.5, 426, 426.5 
~561 References Cited 
U.S. PATENT DOCUMENTS 
D. 294,174 2/1988 Radocy ................................ D24/33 
3,848,753 11/1974 Borg et al. .......................... 214/1 B 
4,505,636 3/1985 Sugino et al. ....................... 414/736 
4,530,536 7/1985 Williams ........................ 294/86.4 X 
4,565,400 VI986 Nakashima et al. ........... 294D6.4 X 
4,708,383 11/1987 Deringer ............................ 294/86.4 
4,740,025 4/1988 Nelson ............................... 294/99.1 
4,819,978 4/1989 Scheinmen et al. ............. 294A19.1 
4,822,091 4/1989 Vermeer et al. ................... 294/86.4 
4,944,765 7/1990 Keith ..................................... 623/65 
Primary Examiner-Charles A. Marmor 
Assistant Examiner-Joseph D. Pape 
Attorney, Agent, or Firm-R. Dennis Marchant; Guy M. 
Miller; Paul S. Clohan 
[571 ABSTRACT 
In a robot having a gripper including a pair of fingers 
and a drive motor for driving the fingers toward and 
away from one another while the fingers remain parallel 
to each other, the fingers consist of finger pads, which 
interface with a handle on an object to be grasped, and 
a shank, which attaches the fingers to the robot gripper. 
The double-V finger has two orthogonal V-grooves 
forming in the center of the finger pads a recessed cruci- 
form. The double-V finger is used with a handle on the 
object to be grasped which is the negative of the finger 
pads. The handle face consists of v-shaped pads capped 
with a rectangular cruciform. As the gripper is brought 
into place near the handle, the finger pads are lined up 
facing the handle pads. When the finger pad and the 
handle pad are in proper alignment, the rectangular 
ridges on the handle fall inside the rectangular grooves 
on the finger, and the grip is complete. 
4 Claims, 3 Drawing Sheets 
58 29 51 
\ I 
57 
56 
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U.S. Patent Jan. 12, 1993 Sheet 1 of 3 5,178,431 
FIG. 1 
FIG. 2 
U.S. Patent Jan. 12, 1993 Sheet 2 of 3 
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FIG. 3 
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FIG. 4 
U.S. Patent Jan. 12, 1993 Sheet 3 of 3 5,178,431 
5,178,43 1 
1 2 
present within the grasped object to force sensors asso- 
ciated with the gripper mechanism. 
It is another object of this invention to provide an 
improved robot gripper that is reliable and durable in 
5 operation and that is also easily and inexpensively con- 
DOUBLE-V BLOCK FINGERS WITH CRUCIFORM 
RECESS 
ORIGIN OF THE INVENTION 
siructed relative to other robot grippers utilized in outer 
space applications. 
The foregoing objects and others are achieved by 
10 finger pad, which interface with a handle on an object 
to be moved, and a shank, which attaches the finger to 
the robot gripper. The finger pads are v-shaped and 
used to cradle obiects to be moved. The single-V finger 
The invention described herein was made by an em- 
ployee of the U.S. Government, and may be manufac- 
mental purposes without the payment of any royalties 
thereon or therefor. 
This application is a continuation application Ser. No. 
07/760,634, filed Sep. 16, 1991, now abandoned. 
tured and by Or for the Government for govern- providing single- and doub1e-V fingers consisting of a 
TECHNICAL FIELD has one groove, -perpendicular to the shank. The d&- 
15 ble-V finger also has v-shaped pads, and in the center of This invention relates to an object gripping device for the finger pads there is a recessed cruciform. robotic applications and more specifically relates to a The double-V finger is used with a handle on the device to eliminate the backdriving of robotic grippers object to be moved which is the negative of the finger. 
under twisting or side loads experienced in robotic end The handle face consists of v-shaped pads capped with 
20 a protruding rectangular cruciform. As the gripper is effectors. 
BACKGROUNDART brought into place near the handle, the finger pads are 
lined up facing the handle pads. Great efforts have been made to make improvements between 
in the design of robotic grippers; however, end effec- the finger pads and the handle pads. As the gripper 
tors, or hands, for robotic arms continue to be a limiting 25 fingers are,closed down upon the handle, the protruding 
Invariably, there will be 
ekment for efficient use of the robotic grippers. Many 
different types of grippers have been used in the past, 
wide Opening grippers, heavy load grippers, jaw grip- 
Prs? 
for outer space use employ finger elements containing 
“V” grooves to grip an object. These ‘‘V” grooves are 
ridges on the handle d] Contact 
the sloped portion ofthe v-shaped finger pads. This sets 
into a more correct orientation. This force is sensed 
Frequently, robot grippers 30 either by the teleoperator via force feedback, or by a 
force-torque Ensor in an autonomous robot’s wrist, 
allowing corrective realignments of the manipulator to 
such as general purpose grippers* grippers9 up a force vector on the finger pads pushing the finger 
grippers, 
used to both guide the object into place within the robot 
finger mechanism and to grasp and lock the object in When the finger pads and the handle pads are in 
that position once the object is securely in place. The 35 proper alignment, the protruding rectangular cruciform 
“V” groove grippers have a frictional component at the ridges on the handle will fall inside the 
interface between the object being grasped and the gular cruciform grooves in the finger, and the grip is 
gripper finger. complete. The protruding rectangular cruciform ridges 
In ‘V’ groove grippers, since the Parts contact each on the handle have a loose fit inside the finger recessed 
other with sloped faces, twisting of the object being 40 rectangular crucifom grooves, so the actual contact 
grasped in the gripper Will tend to Pry the fingers apart, between the finger and the handle is made by the sloped 
with large forces. This results in the backdriving of ‘‘V” faces of the finger pads contacting the sloped faces of 
groove grippers; i.e., large moments Or forces tend to the handle pads. This ensures that the mechanical inter- 
force the grippers open, requiring the drivetrain to face between the two parts is highly reptable;  the 
resist this overload, or drop the object. 45 handle returns to exactly the same orientation with 
The apparatus disclosed in the instant invention Over- respect to the gijpper each time the handle is grasped. 
comes the shortcomings of the “V” groove grippers by The rectangular ridges of the protruding cruciform 
providing an end effector gripper that will, with very on the handle come into play when large forces are to 
low frictional forces, effectively guide, align and seat an be transmitted across the interface. Since the parts 
object in a desired position without experiencing back- 50 contact each other with sloped faces, twisting of the 
driving during twisting or side loads. handles in the fingers would tend to pry the fingers 
apart with large forces. With the rectangular ridges, 
small deflections of the finger are allowed before the 
It is therefore an object of the present invention to sides of the rectangular ridge (protruding cruciform) 
provide a set of fingers for a robot gripper that will 55 contact the sides of the grooves (recessed cruciform). 
improve the gripper’s ability to more effectively grasp The sides of the groove are orthogonal to the direction 
an object. of force, hence there is no component of the force pry- 
It is another object of the present invention to pro- ing the fingers open, only one pushing them sideways. 
vide a robot gripper that eliminates backdriving during Thus the gripper drivetrain does not need to take these 
twisting or side loads. 
It is still a further object of this invention to provide The single-V finger operates on a similar principle 
an improved robot gripper that smoothly and efficiently except the capture range is only large in the direction of 
guides, aligns and securely seats an object in the desired the finger shank. This simplifies the design of the handle 
position within the end effector apparatus despite large needed on cylinders, such as a truss element. All that is 
misalignments. 65 needed is a circumferential, rectangular ridge, with 
It is an additional object of this invention to provide several longitudinal ridges. These will then form raised 
an improved robot gripper that will more accurately cruciforms around the perimeter of the cylinder, which 
transmit the magnitude of vector component forces fit into the recesses in the finger pad. 
be 
STATEMENT OF THE INVENTION 
60 overloads into account. 
4 
5,178,431 
3 
they are outwardly pointed finger pads formed by pads 
51-58; Le., finger pads 51 and 52 form a first outwardly 
FIG. 1 is a perspective view of prior art “V-groove” pointed pad, finger pads 53 and 54 form a second out- 
wardly pointed pad, etc. This combination of outwardly 
FIG. 2 is a perspective view of a single-V finger 5 pointed pads thus forms a double-V finger in which the 
v-shaped pads are orthogonal to one another. 
FIG. 3 is a side view of the single-V gripper about to The double-V finger 27 shown in FIG. 4 is used with 
a handle which is the negative of the finger, shown in 
FIG. 4 is a perspective view of a double-V finger FIG. 5. Handle 72, a pair of which are attached to an 
10 object to be moved (not shown), consists of four in- 
FIG. 5 is a perspective view of the mating interface wardly sloped handle pads, formed by pads 61-68, 
capped with a protruding rectangular cruciform 70 
FIG. 6 is a perspective view of an alternate embodi- consisting of intersecting ridges 48 and 49. Handle pads 
61-68 mate with finger pads 51-58 respectively. AS a 
15 pair of fingers 27 is brought into place near a pair of 
handles 72, the finger pads 51-58 are lined up facing the 
FIG. 1 depicts a prior art robotic hand assembly 1 Invariably, there will be some misalignment between 
including a pair of identical and opposing single-V fin- the finger pads 51-58 and the handle pads 61-68. AS the 
gers 4 and 5. Fingers 4 and 5 are adapted to move closer 20 fingers are closed down upon the handles, the raised 
to or further apart from each other in response to any rectangular cruciform 70 on handle 72 will contact a 
well known gear motor combination. As shown in FIG. sloped portion of the pointed pads on finger 27. This 
1, motor 2 rotates a beveled drive gear 3. A mating sets up a force vector on the finger pads, pushing finger 
drive gear 7 is mounted on and secured to a threaded 27 into a more correct orientation. This force is sensed 
shaft 8. Shaft 8, upon rotation, moves fingers 4 and 5 25 either by the teleoperator via a force feedback, or by a 
either closer together or further apart depending upon force-torque sensor in an autonomous robot’s wrist, 
the direction of rotation. allowing corrective realignments of the manipulator to 
Shaft 8 turns within inner threaded openings 9 and 10 be performed. 
in a pair of guide pieces 14 and 15. Guide pieces 14 and When the finger pads 51-58 and the handle pads 
15 slide in a channel frame 20, which frame holds a pair 30 61-68 are in proper alignment, protruding cruciform 70 
of double slide rods 21, 22. Fingers 4 and 5 are thus on handle 72 falls inside recessed cruciform 71 in finger 
adapted to move together or apart in a smooth non- 27, and the grip is complete. Cruciform 70 on handle 72 
binding motion under control of any suitable computer has a loose fit inside finger cruciform 71, so the actual 
or control system (not shown) which energizes motor 2. contact between finger 27 and handle 72 is made by the 
On the flat outer faces of guides 14 and 15 are 35 sloped faces of the finger pads contacting the sloped 
mounted a pair of flexible base members 25 and 30. faces of the handle pads. This ensures that the mechani- 
Each base member is I shaped and has a central elon- cal interface between the two parts is highly repeatable; 
gated hollow rectangular cylinder with extending the handle returns to exactly the same orientation with 
mounting ears integrally formed therewith. Threaded respect to the gripper each time the handle is grasped. 
bolts, such as 23, 24 and 33, 34 holds the upper and 40 The two mating cruciforms 70 and 71 come into play 
lower edges of the outwardly extending ears of base when large forces are to be transmitted across their 
block 25 respectively to guide 14 and finger 4. Compa- interface. Since the fingers and handles contact each 
rable bolts 35,36 and 37,38 secure finger 5 to guide 15. other with sloped faces, twisting of handle 72 in finger 
In this prior art embodiment, fingers 4 and 5 move 27 would tend to pry the fingers apart, with relatively 
parallel to one another. When a force F1 or F2 is applied 45 large forces. With the two cruciforms 70 and 71 present 
to cylinder 45, a reactive force shown by arrows 46 will however, small deflections of the fingers are allowed 
cause fingers 4 and 5 to open and to backdrive the gear before the sides of the cruciforms contact each other. 
train. This condition has proved to be a serious limita- The sides of the cruciforms are orthogonal to the direc- 
tion of prior art “V” groove grippers and is overcome tions of force, hence there is no longer a component of 
by the present invention as discussed below. 50 the force prying the fingers open, only one pushing 
A new design single-V finger is shown in FIG. 2, and them sideways. Thus the gripper drivetrain does not 
a new design double-V finger is shown in FIG. 4. Refer- need to take these overloads into account. 
ring first to FIGS. 2 and 3, the new design single-V Single-V finger 11 (FIG. 3) operates on a similar 
finger 11 consists of finger pads 12 and 13 which inter- principle except the capture range is only large in the 
face with a handle 17 (FIG. 3) on the object to be 55 direction of the finger shank. This simplifies the design 
moved (not shown), and a shank 6, which attaches fin- of the handle needed on cylinders, such as a truss ele- 
ger 11 to the rob$ gripper in a standard manner. Finger ment. All that is needed is a circumferential, rectangular 
pads 12 and 13 comprise a large V-shaped groove, ma- ridge, with several longitudinal ridges. These will then 
chined into the face of finger 11, to cradle objects to be form raised cruciforms around the perimeter of the 
moved, such as cylinder 45 shown in FIG. ‘1. Single-V 60 cylinder, which fit into the recesses in the finger pad. 
finger 11 also has one recessed groove 16, which is An H-handle fitting can also be provided and is 
perpendicular to shank 6. Recessed groove 16 mates shown in FIG. 6. A typical H-handle compatible finger 
with ridge 26 on handle 17. In addition, finger pads 12 32 consists of pads 41-44, grooves 39 and 40 forming 
and 13 mate with handle pads 18 and 19; this is clearly cruciform 73, a shank 47, and two pairs of tangs 50 and 
shown in FIG. 3. The double-V finger 27, shown in 65 60 on either end. These are particularly useful for work 
FIG. 4, has two orthogonal recessed grooves 28 and 29 with the NASA Module Servicing Tool. The thickened 
forming in the center of the finger pads a recessed cruci- protions of the finger shanks fit with 0.005” clearance 
form 71. The double-V finger also has finger pads, but between the tangs which form an end of the handle. 
DESCRIPT1oN OF THE 
grippers. 
gripper according to the present inventive concepts. 
grip an object to be moved. 
gripper according to the present inventive concepts. 
for the double-V finger gripper. 
ment of the double-V finger gripper. 
DETAILED DESCRIPTION OF THE 
INVENTION handle pads 61-68. 
5,178,43 1 
5 
Additionally, the handle is sandwiched between the 
wider cruciform pad on the top, and a set of tabs on the 
bottom. Generous chamfers assist in the acquisition of 
the handle. As the fingers close completely upon the 
H-handle, inclined surfaces 59 and 69 on the bottom tab 
wedge the handle against the finger pad above, securely 
locking the handle in place. 
To those skilled in the art, many modifications and 
variations of the present invention are possible in light 
of the above teachings. It is therefore to be understood 
that the present invention can be practiced otherwise 
than as specifically described herein and still will be 
within the spirit and scope of the appended claims. 
I claim: 
1. In a robotic system having a gripper to grip an 
object to be moved including a pair of fingers and a 
drive means for driving the fingers toward and away 
from one another while said fingers remain parallel to 
each other, each of said fingers comprises: 
a lower portion comprising a shank for mounting said 
finger to said gripper; 
an upper portion affixed to said lower portion and 
having a plurality of finger pads thereon; 
said plurality of finger pads comprising pairs of sur- 
faces forming outwardly pointed surface pairs and 
5 
10 
15 
20 
._ 
6 
thereby forming v-shaped finger pads on said upper 
portion of said finger; 
said plurality of finger pads having eight said pairs of 
surfaces thereby forming four outwardly pointed 
surface pairs and thereby forming two orthogonal 
v-shaped finger pads on said upper portion of said 
finger, 
two recessed grooves on said upper portion orthogo- 
nal to one another thereby forming a recessed cru- 
ciform at the center of said upper portion of said 
finger; and 
said object to be moved having a pair of complemen- 
tary surfaces to mate with said upper portion of 
said pair of fingers, each said surface comprising a 
like plurality of surface pads, complementary in 
shape to said finger pads, to mate with said plural- 
ity of finger pads and at least one protruding ridge 
to mate with said at least one recessed groove on 
said upper portion of said finger. 
2. The robotic wstem of claim 1 wherein said re- 
cessed grooves are rectangular in cross-section. 
3. The robotic system of claim 1 further including a 
pair of tangs located below said upper portion of said 
fingers. 
4. The robotic system of claim 3 in which said tangs 
include inclined surfaces. 
25 
* * * * *  
30 
35 
45 
50 
55 
60 
65 


Double-V block fingers with cruciform recess

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