Multiple prehension mechanism

Abstract

A multiple prehension mechanism including a base; a plurality of finger assemblies mounted on the base; finger drive means for selectively opening and closing the fingers so that each finger moves in a single curling plane; and positioning drive means for selectively positioning the finger assemblies so that different prehensile modes can be achieved. The disclosure also contemplates the method of operation of the mechanism.

Parent Case Text

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of my co-pending application Ser. No. 360,022, filed May 14, 1973 entitled "Multiple Prehension Manipulator Mechanism", now abandoned.

Description

BACKGROUND OF THE INVENTION

Many attempts have been made to produce a manipulator having substantially the same capabilities as the human hand. Because the human hand has many motor and control systems, such prior art manipulators have been very complicated and therefore prohibitively expensive to manufacture and maintain. Because of the complexity of the human hand, many of these prior art manipulators attempted to combine several motor functions of the human hand with the attendant loss of capability.

SUMMARY OF THE INVENTION

The invention disclosed herein overcomes these and other problems associated with the prior art by providing a manipulator mechanism which has virtually all of the basic capabilities associated with the human hand. The construction of the invention is relatively simple thereby reducing the manufacturing cost and maintenance cost.

The invention comprises generally a plurality of finger assemblies, each including a finger pivoted about at least one finger axis through a single plane normal to the finger axis, a base mounting the finger assemblies so that the plane of each finger can e rotated about a positioning axis through the plane and normal to the finger axes, finger drive means for pivoting the fingers about the respective finger axes, and positioning means for moving the finger assemblies so that at least two of the planes will be rotated about their respective positioning axes. The finger drive means collectively pivots the fingers about their finger axis.

These and other features and advantages will become more apparent upon consideration of the following specification and accompanying drawings wherein like characters of reference designate corresponding parts throughout the various views and in which:

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of one embodiment of the invention;

FIG. 2 is an operating end view of the invention of FIG. 1;

FIG. 3 is a cross-sectional view taken along line 3--3 in FIG. 2 showing the finger assemblies in wrap-spread prehensile mode;

FIG. 4 is a cross-sectional view taken along line 4--4 in FIG. 3;

FIG. 5 is a side view illustrating a second embodiment of the invention;

FIG. 6 is a longitudinal cross-sectional view of FIG. 5;

FIG. 7 is a cross-sectional view taken along line 7--7 in FIG. 5;

FIG. 7A is a cross-sectional view taken along line 7A--7A in FIG. 5;

FIG. 8 is an enlarged side view of one of the tips of that embodiment of FIG. 5;

FIG. 9 is an edge view taken along line 9--9 in FIG. 8;

FIG. 10 is a cross-sectional view taken along line 10--10 in FIG. 9; and,

FIGS. 11-18 illustrate the embodiment of FIG. 5 in operation.

These figures and the following detailed description disclose specific embodiments of the invention, however, it is to be understood that the inventive concept is not limited thereto since it may be embodied in other forms.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

Referring to FIGS. 1-4, it will be seen that the first embodiment of the manipulator is designated by the numeral 110. Generally, the manipulator mechanism 110 includes a base 111, a plurality of finger assemblies 112 mounted on base 111, a firger driving mechanism 114 carried by the base 111, and a positioning mechanism 115 carried by base 111 for positioning the finger assemblies 112.

Basically, the manipulator mechanism is an assembly of drive and mechanisms intended for prehension. These mechanisms, called fingers, are attached to a base. Three fingers are considered necessary and sufficient in the construction of the manipulator. Fingers can approach, contact, or pass one another during prehensile operation. The manipulator contains all of the drives below the palmar surface of base 111. A multiple degree-of-freedom wrist mechanism (not shown) may be used to connect to and move the manipulator so that it can approach an object from any direction.

The objective of the manipulator mechanism is to produce a highly versatile hand with a minimum number of moving parts, a dependable drive system, and an optimum number of degrees of freedom. The number of degrees of freedom is considered uptimum when it is estimated that the manipulator mechanism can grasp all of the basic geometrical shapes from any aspect with the minimum number of external control inputs. These basic shapes are rectangular and triangular prisms, spheres, and cylinders.

The human hand is generally accepted as being capable of the six basic prehensile patterns: lateral, hook, tip, palmar, spherical, and cylindrical. These six basic prehensile patterns, because of similarities, can be reduced to the three basic mechanical equivalents of wrap, three-jaw and tip prehension that very nearly duplicate the basic human hand prehensile patterns. Additionally, in order to grip large objects that the fingers can not surround, spread prehension is created which consists of inserting the fingers into an opening in the object and then bending them outward to engage the object within the opening. The manipulator mechanism 110 is able to generate all of the above four equivalent prehensile patterns.

The base 111 seen in FIGS. 1-4 includes generally a top palmar plate 121, which corresponds to the palm of the human hand, a base plate 122 and a plurality of spacer supports 124 which connect plates 121 and 122 so that they are generally parallel with palmar plate 121 providing a working surface 125. Appropriate cutouts 126 are provided in palmar plate 121 for the finger assemblies 112 to operate as will become more apparent.

Three finger assemblies 112 designated 112.sub.a -112.sub.c are mounted between plates 121 and 122 at equally spaced points about the circle defined by radius R from the common centerline CL of plates 121 and 122.

FINGER ASSEMBLY

Finger assemblies 112.sub.a -112.sub.c are virtually identical in construction and therefore only one will be described in detail with like numerals applied to each. Each assembly 112 includes a support arm 130 having a pair of spaced apart mounting ears 131. The finger 134 is pivotally mounted between ears 131 through a base revolute joint 135 about a curl axis CA. The arm 130 is attached to the back side of palmar plate 121. The arm 130 of assemblies 112.sub.b and 112.sub.c are connected to the plate 121 through revolute joint 136 so that the arm 130 pivots about a positioning axis PA which intersects the circle of radius R and is normal to the working surface 125 of plate 121 whereas the curl axis CA is normal to axis PA and spaced outwardly therefrom a distance D. The arm 130 of assembly 112.sub.a is fixed to the back of plate 121 so that it extends radially, however, the distance from the circle of radius R to axis CA is the distance D and the orientation of axis CA is like that described above for assemblies 112.sub.b and 112.sub.c. Thus, it will be seen that the finger 134 is pivotal through a single curling plane CP as best seen in FIG. 1 about the curling axis CA perpendicular to the plane. The planes CP.sub.b and CP.sub.c of assemblies 112.sub.b and 112.sub.c are pivoted about the positioning axis PA which is parallel to the curling plane CP. In the example shown, the axis PA lies within the curling plane CP.

The fingers 134 may have multiple joints and links as fingers 34, however, those illustrated are single elongate members 140 pivoted at joint 135 and projecting out over the working surface 125 of plate 121. A driving leg 141 is integral with member 130 and extends below arm 130 for use in driving finger 134 as will be explained. It will be noted that fingers 134 have a normal open position so that the longitudinal axis of finger 134 lies along a path P substantially perpendicular to working surface 125. The finger 134 is designed to be double acting so that it can pivot both inwardly and outwardly from path P as will become more apparent.

FINGER DRIVE MECHANISM

While separate drive mechanism may be used for each finger assembly 112, a simplified common drive mechanism is illustrated. Mechanism 114 includes a tubular drive rod 150 slidably journalled in base plate 122 for sliding movement along the centerline CL of base 111. The operating end 151 of rod 150 projects into space 152 between plates 121 and 122 and its other end is connected to a drive unit 154 such as the fluid cylinder shown in FIG. 3. A power adapter 155 is attached to the operating end 151 of rod 150 in space 152. The outwardly extending power arms 156.sub.a -156.sub.c are attached to adapter 155 so that they are aligned with the arm 130 each associated finger assembly 112.sub.a -112.sub.c. The power arms 156.sub.b and 156.sub.c are pivoted along the respective positioning axes PA of assemblies 112.sub.b and 112.sub.c so that arms 156.sub.b and 156.sub.c pivot in tandem with arms 130 of assemblies 112.sub.b and 112.sub.c respectively. A drive link 158 connects each arm 156 with its associated finger 134 so that as rod 150 moves adapter 155 and power arms 156 toward the back of palmar plate 121, the fingers 134 will be simultaneously closed and as rod 150 and adapter 155 moves toward base plate 122, the fingers 134 will be opened to their normal position. Further movement of rod 150 toward base plate 122 cause the fingers 134 to continue to spread outwardly past the paths P into the spread prehensile mode.

POSITIONING MECHANISM

Referring to FIG. 2, it will be seen that finger assemblies 112.sub.b and 112.sub.c can be moved from a three-jaw prehensile mode shown in solid lines to a wrap prehensile mode shown in dashed lines. It will be noted that the spread prehensile mode can be achieved in either position and that the tip prehensile mode could be easily provided for with very little modification. Stops 159 may be provided on plate 121 as seen in FIG. 4 to limit the movement of the finger assemblies about axes PA.

The positioning of the assemblies 112 may be accomplished in a number of different ways, however, the mechanism 115 includes a drive gear 160 on drive shaft 161 journalled for rotation about the centerline CL of base 111. An appropriate power source 162 such as the motor shown in FIG. 3 is used to selectively rotate gear 160. Shaft 161 passes through rod 150 but is rotatable independently thereof. Gear 160 meshes directly with driven gear 164 attached to arm 130 of finger assembly 112.sub.b and is connected to driven gear 165 attached to arm 130 of finger assembly 112.sub.c through reversing idler gear 166. When gear 160 is rotated clockwise as seen in FIG. 9, the finger assemblies 112.sub.b and 112.sub.c will be simultaneously rotated toward the wrap mode position, and when gear 16 is rotated counterclockwise, assemblies 112.sub.b and 112.sub.c will be rotated toward their three-jaw mode position.

SECOND EMBODIMENT OF THE INVENTION

The second embodiment of the invention shown in FIGS. 5-18 is a refinement of the manipulator mechanism 110 and is designated generally 210 with finger assemblies 212 mounted on base 211 with finger driving mechanism 214 and positioning mechanism 215.

The base 211 seen in FIGS. 5-10 includes generally a top palmar plate 221, which corresponds to the palm of the human hand, a base plate 222 and a plurality of spacer supports 224 which connect plates 221 and 222 so that they are generally parallel with palmar plate 221 providing a working surface 225. Appropriate cutouts 226 are provided in plates 221 and 222 for the finger assemblies 212 to operate as will become more apparent.

Three finger assemblies 212 designated 212.sub.a -212.sub.c are mounted between plates 221 and 222 at equally spaced points about the circle defined by radius R from the common centerline CL of plates 221 and 222 as seen in FIG. 7.

FINGER ASSEMBLY

Finger assemblies 212.sub.a -212.sub.c are similar to assemblies 112, virtually identical in construction and therefore only one will be described in detail with like numerals applied to each. Each assembly 212 includes a support arm 230 having a pair of spaced apart mounting ears 231. The finger 234 is pivotally mounted between ears 231 through a base revolute joint 235 about a curl axis CA. The arm 230 is attached to the back side of palmar plate 221. The arm 230 of assemblies 212.sub.b and 212.sub.c are connected to the plate 221 and spacer 233 through revolute joint 236 so that the arms 230 pivot about a positioning axes PA which intersect the circle of radius R and are normal to the working surface 225 of plate 221 whereas the curl axes CA are normal to axes PA and spaced outwardly therefrom a distance D. The arm 230 of assembly 212.sub.a is fixed to the back of plate 221 so that it extends radially, however, the distance from the circle of radius R to axis CA is the distance D and the orientation of axis CA is like that described above for assemblies 212.sub.b and 212.sub.c. Thus, it will be seen that each finger 234 is pivotal through a single curling plane CP about the curling axis CA perpendicular to the plane. The planes CP.sub.b and CP.sub.c of assemblies 212.sub.b and 212.sub.c are pivoted about the positioning axes PA which are parallel to the curling plane CP. In the example shown, the axis PA lies within the curling plane CP.

The fingers 234 illustrated are single elongate members 240 pivoted at joint 235 and projecting out over the working surface 225 of plate 221. A driving leg 241 is integral with member 240 and extends below arm 230 for use in driving finger 234 as will be explained. It will be noted that fingers 234 have a normal open position so that the longitudinal axis of finger 234 lies along a path P substantially perpendicular to working surface 225. The finger 234 is designed to be double acting so that it can pivot both inwardly and outwardly from path P as will become more apparent.

Each finger assembly 212 mounts a tip assembly 300 at the projecting end of member 240 as best seen in FIGS. 8-10. Each tip assembly 300 includes a tip 301 and an initial positioner unit 302. The projecting end 242 of member 240 defines a slot 244 therethrough oriented generally parallel to the curling plane CP of assembly 212. The tip 301 is a generally rectilinear plate defining a V-shaped notch 304 at its inner and outer ends to define a pair of spaced apart contact points 305 at opposite ends of tip 301. The points 305 define contact surfaces 307 thereon to engage the object to be grasped. The tip 301 is pivoted at its center between the ears 245 in the end 242 of member 240 on opposite sides of slot 244 on a support pin 306 carried between ears 245. The tip 301 is free to pivot about the axis TA of pin 305 within slot 244.

The initial positioner unit 302 serves to initially position tip 301 in a known pivotal position with respect to member 240 as will become more apparent. While different mechanisms may be used, the unit 302 illustrated includes a compression coil spring 310 and a plunger 311. An appropriate hole 246 is provided in the end 242 of member 240 at the bottom of slot 244 to slidably receive the spring 310 and plunger 311 therein. The hole 246 is located so that the spring 310 resiliently urges the tip 301 in a predetermined rotational direction, here shown as counterclockwise by the plunger 311 bearing against the tip 301. The rotational direction in which tip 301 is urged can easily be reversed simply by shifting the positioner unit 302 to the opposite side of the slot 244 as shown by dashed lines in FIG. 10.

FINGER DRIVE MECHANISM

While separate drive mechanisms may be used for each finger assembly 212, a simplified common drive mechanism is illustrated. Mechanism 314 includes a drive rod 250 slidably journalled in base plate 222 for sliding movement along the centerline CL of base 211. The operating end 251 of rod 250 projects into space 252 between plates 221 and 222 and its other end is connected to a drive unit 254 such as the piston 255 of a double acting fluid cylinder 256 shown in FIG. 6. A power adapter 258 is attached to the operating end 251 of rod 240 in space 252 so that adapter 258 can be reciprocated in space 252 along the centerline CL. Adapter 258 includes a pair of spaced apart, generally circular, parallel carriage plates 259 joined at their central portions by a boss 260 so that an annular arm mounting recess 261 is defined between plates 259.

Outwardly extending power arms 265.sub.a -265.sub.c of finger drive linkages 263 are mounted within the annular recess 261 in alignment with support arms 230. Each power arm 265 has a generally horizontal leg 266 and an upwardly and outwardly extending bifurcated leg 268. Each leg 266 is slidably received between carriage plates 259 and is rotatably mounted on a pivot pin 269 extending between plates 259 about the positioning axes PA. The leg 266 of positioning arm 265.sub.a is held in a fixed position in alignment with support arm 230.sub.a by a second pin 270 extending through let 266 between carriage plates 259 as seen in FIGS. 6 and 7. Thus, it will be seen that power arms 265.sub.b and 265.sub.c can pivot about axes PA while arm 265.sub.a is held in a fixed position.

Drive links 271 connect each power arm 265 with the driving leg 241 of the finger 234 associated therewith so that fingers 234 will be driven open or closed as the power adapter 258 is moved within space 252 by drive unit 254. Each link 271 has its outer end 272 pinned between the ends of bifurcated leg 268 of arm 265 while its bifurcated inner end 274 has the driving leg 241 of finger 234 pinned therebetween. Thus, as the power adapter 258 is moved toward the palmar plate 221 of base 211, the tips 301 on fingers 234 will be closed and vice versa.

It will further be noted that the mechanical advantage of the drive input to fingers 234 decreases as the fingers close. This is advantageous since the larger objects to be grasped by fingers 234 normally weigh more than smaller objects thereby requiring a greater holding force. Thus, a variation in holding force is provided without a change in the fluid pressure of cylinder 256. It will also be noted that the finger drive linkages 263 are slider crank mechanisms where the slider axis is parallel to the curling plane of the particular finger assembly 212 with which it is associated. This causes the movement of the linkage 263 to be coplanar with the curling plane of its associated finger assembly 212.

POSITIONING MECHANISM

Referring to FIG. 7, it will be seen that finger assemblies 212.sub.b and 212.sub.c can be moved from a three-jaw prehensile mode shown in dashed lines to a wrap prehensile mode shown in solid lines. It will be noted that the spread prehensile mode can be achieved in either position and that the tip prehensile mode is provided in the three-jaw prehensile mode. The positioning mechanism 215 is effective to position the assemblies 212.sub.b and 212.sub.c in their different modal positions.

The positioning mechanism 215 includes a pair of drive subassemblies 280 carried by the power arm 265.sub.a, one of the subassemblies 280 is operatively connected to the power arm 265.sub.b and one of the subassemblies 280 is operatively connected to power arm 265.sub.c. The subassemblies 280 are mirror images of each other so that only one subassembly will be described in detail while like reference numbers will be applied to the other assembly 280.

Subassembly 280 attached to power arm 265.sub.b includes a fluid cylinder 281 carried by a bracket 282 mounted on the side of the horizontal leg 266 of power arm 265.sub.a. The cylinder 281 is positioned so that its centerline CL.sub.C is generally parallel to the centerline of leg 266 of arm 265.sub.a and generally parallel to the working surface 225 of palmar plate 221 and displaced laterally of leg 266 of arm 265.sub.a a distance d.sub.1.

The piston rod 285 of cylinder 280 has its projecting end connected to the leg 266 of power arm 265.sub.b through a connector 286. One end of connector 286 is pinned to the projecting end of piston rod 285 and its other end is pinned to the leg 266 of arm 265.sub.b in a slot 288 formed in the side of leg 266 by a drive pin 289. Pin 289 is located from the positioning axis PA of arm 265.sub.b a distance d.sub.2. Thus, as the piston rod 285 is extended, the positioning arm 265.sub.b and finger assembly 212.sub.b will be pivoted toward their wrap modal position and toward their three-jaw modal position. The distance d.sub.1 and d.sub.2 are sufficient to insure a sufficient turning moment on arm 265.sub.b and assembly 212.sub.b to position them.

The fluid cylinders 280 illustrated are single action cylinders with a spring return, however, it is to be understood that double acting cylinders may be used. The cylinders 280 may be independently controlled or plumbed in parallel so that they operate sychronously.

OPERATION OF SECOND EMBODIMENT

The operation of the second embodiment of the invention will be best understood by reference to FIGS. 11-18 showing the various modes of operation. It will first of all be noted that the finger assemblies 212 can be selectively rotated to their three-jaw or wrap mode positions by a positioning mechanism 215. The opening and closing of the fingers 234 is effected by the drive unit 254 with the fingers 234 being simultaneously opened and closed.

FIGS. 11-14 illustrate the mechanism 210 picking up a generally rectilinear object O.sub.R. In this operation, the piston rods 285 of cylinders 281 are extended to position finger assemblies 212.sub.b and 212.sub.c so that the wrap mode is accomplished. It will be seen in FIG. 11 that the fingers 234 have closed sufficiently for the innermost contact points 305 to just engage opposed edges of the object O.sub.R. An enlarged portion of FIG. 11 showing the position of the tips 301 in this position is seen in FIG. 12. It will further be noted that as the fingers 234 are closed, the object O.sub.R will be centered therebetween. The object O.sub.R is illustrated as initially adjacent the working surface 225 of the palmar plate 221. As the fingers 234 continue to move inwardly to grip the object O.sub.R, it will be seen that a reaction force F.sub.R will be exerted on that point 305 in contact with the object O.sub.R which causes a moment to be exerted on the tip 301 in opposition to the positioner unit 302 to pivot the tip 301 clockwise as seen in FIG. 12. This in turn causes a holding force F.sub.H to be generated on the object O.sub.R that forces the object toward the palmar plate 221. This insures that the object O.sub.R is clamped against the plate 221. This clamping force is generated as the tip 301 rotates clockwise until the other contact point 305 at the inner end of the tip 301 contacts the side of the object O.sub.R. This position is shown in FIG. 13 and an enlarged portion of FIG. 13 is seen in FIG. 14 showing both of the inner contact points 305 engaging the object O.sub.R. The mechanism 210 has now gripped object O.sub.R sufficiently to allow the object to be picked up.

FIGS. 15 and 16 illustrate the mechanism 210 gripping a spherical object O.sub.S between the tips 301. It will be noted that the fingers 234 center the object O.sub.S with respect to the base 211 and the tips 301 center the object O.sub.S with respect to the tips. Thus, it will be seen that the tips 301 allow the mechanism 210 to grip relatively small objects. The finger assemblies 212.sub.b and 212.sub.c are in their three-jaw modal position in FIGS. 15 and 16.

FIGS. 17 and 18 illustrate the mechanism 210 gripping a large object O.sub.L having an appropriate hole H.sub.L therein sufficient for the fingers 234 to be inserted into the hole H.sub.L. The finger assemblies 212.sub.b and 212.sub.c are illustrated in their three-jaw position so that the fingers 234 can be extended into the hole H.sub.L and opened beyond their normal open position into their spread position to grip the object O.sub.L within the hole H.sub.L.

The inside and outside edges E.sub.I and E.sub.O of each of members 240 of fingers 234 can be used to grip objects as illustrated in FIG. 1. The finger assemblies 212.sub.b and 212.sub.c are in their wrap prehensile mode and are gripping a cylindrical object as shown by dashed lines in FIG. 1.

The finger drive cylinder 256 is connected to an appropriate source fluid under pressure (not shown) so that the rod 250 can be selectively extended and retracted. The positioning cylinders 281 are also connected to an appropriate source of fluid under pressure (not shown) through appropriate valving (not shown) so that the rods 285 can be selectively extended and retracted. The cylinders 281 may be connected in parallel for simultaneous operation only or may be connected so that they operate independently of each other. The cylinders 281 operate independently of cylinder 256.

While specific embodiments of the invention have been disclosed herein, it is to be understood that the full use of modifications, substitutions and equivalents may be made without departing from the scope of the inventive concept.

Claims

I claim:

1. A multiple prehension mechanism adapted to assume different prehensile operational modes to grasp objects comprising:

a palmar base defining a working surface thereon, said base having a centerline generally normal to said working surface;

at least three finger assemblies carried by said base, each of said finger assemblies including a support means mounted on said base, a finger pivotally mounted on each of said support means about a curl revolute axis generally perpendicular to said centerline for movement toward and away from said working surface;

single finger drive means operatively connected to all of said fingers for simultaneously pivoting said fingers about the respective said curl revolute axis of said finger to engage the objects; and,

positioning drive means operatively connected to said support means for selectively positioning said support means so that said fingers close in intersecting curling planes in a first position and in substantially parallel and laterally spaced curling planes in a second position.

2. The mechanism of claim 1 wherein one of said support means is fixedly mounted on said base, wherein two of said support means are pivoted on said base at spaced apart positioning axes generally parallel to said centerline of said base, and wherein said positioning drive means is operatively connected to said two of said support means to selectively pivot said two of said support arms about said positioning axes to selectively move said two of said support arms between said first and second positions.

3. The mechanism of claim 1 wherein said finger drive means includes power means carried by said base, said power means comprising adapter means, a drive unit for selectively moving said adapter means along an operating path generally parallel to said centerline of said base, and connector means operatively connecting each of said fingers to said adapter unit for effecting simultaneous opening and closing of all of said fingers in response to movement of said adapter means.

4. The mechanism of claim 1 wherein said positioning drive means comprises at least one motor means carried by said adapter means and operatively connected to said two of said power arms to selectively pivot said two of said power arms and said two of said support means about said positioning axes.

5. The mechanism of claim 4 wherein said motor means includes fluid cylinder means.

6. The mechanism of claim 5 wherein said fluid cylinder means includes a first fluid cylinder carried by said adapter means having a first piston rod operatively connected to one of said two of said power arms to selectively pivot said one of said two of said power arms about its said positioning axis; and a second fluid cylinder carried by said adapter means having a second piston rod operatively connected to the other of said two of said power arms to selectively pivot said other of said two of said power arms about its said positioning axis.

7. The mechanism of claim 1 wherein each of said fingers of said finger assemblies further includes a projecting end extendable over said base and wherein each of said finger assemblies further includes tip means rotatably mounted in said projecting end of said finger about a tip axis generally parallel to said curl revolute axis of said finger, said tip means constructed and arranged to grasp objects.

8. The mechanism of claim 7 wherein said tip means defines at least two spaced apart contact surfaces thereon on the same side of said finger adapted to engage objects so that said tip means is rotated in response to engagement with the object until said two contact surfaces both engage the object.

9. The mechanism of claim 8 further including initial positioner means construced and arranged to resiliently urge said tip means in a first predetermined rotational direction so that the rotation of said tip means in response to enngagement with the object is in a second predetermined rotational direction opposite to said first direction.

10. The mechanism of claim 1 wherein said finger drive mechanism includes a finger drive linkage operatively associated with each of said finger assemblies and operating substantially coplanar with the curling plane of said finger associated therewith, each of said finger drive linkages defining a slider crank mechanism, the slider axis thereof substantially parallel to said finger curling plane.

11. The mechanism of claim 1 wherein each of said fingers includes a projecting end which opens and closes within said curling planes and a tip assembly carried by each of said projecting ends, each of said tip assemblies comprising:

a tip member including contact means for engaging the object; and,

pivot means for pivotally mounting said tip member on the projecting end of said finger member about a tip axis generally normal to the curling plane of said finger member for pivotal movement independent of said finger member movement.

12. The mechanism of claim 11 wherein each of said tip assemblies further includes limiting means for limiting the pivotal movement of said tip member in a first direction and in a second direction opposite to said first direction about said tip axis.

13. The mechanism of claim 12 wherein each of said tip assemblies further includes positioner means for resiliently urging said tip means in said first direction.

14. The mechanism of claim 13 wherein each of said tip members defines two spaced apart contact surfaces arranged to urge said tip member in said second direction against the urging of said positioner means as an incident to the engagement of one of said contact points with the object.

15. The mechanism of claim 11 wherein each of said tip members defines a plurality of spaced apart contact surfaces thereon constructed and arranged so that said tip member is inherently shifted to cause at least two of said contact surfaces to engage the object as it is being grasped.

16. A multiple prehension mechanism adapted to assume different prehensile operational modes to grasp objects comprising:

a palmar base defining a working surface thereon, said base having a centerline generally normal to said working surface;

at least three finger assemblies carried by said base, each of said finger assemblies including a support means mounted on said base, a finger pivotally mounted on each of said support means about a curl revolute axis generally perpendicular to said centerline for movement toward and away from said working surface; and,

single finger drive means operatively connected to all of said fingers for simultaneously pivoting said fingers about the respective said curl revolute axis of said finger to engage the objects, said finger drive means including power means carried by said base, said power means comprising adapter means, a drive unit for selectively moving said adapter means along an operating path generally parallel to said centerline of said base, and connector means operatively connecting each of said fingers to said adapter unit for effecting simultaneous opening and closing of all of said fingers in response to movement of said adapter means, said connector means including at least three power arms connected to said adapter means for movement therewith, one of said power arms fixed to said adapter means in alignment with said one of said support means and two of said power arms pivoted to said adapter means about arm positioning axes in alignment with said positioning axes of said two of said positioning means, and link means operatively connecting each of said power arms to said finger associated therewith.

17. The mechanism of claim 16 wherein said drive unit comprises a fluid cylinder carried by said base; said fluid cylinder including a piston rod selectively movable about a path generally parallel to the centerline of said base, said piston rod having a projecting end and said adapter means mounted on said projecting end of said piston rod.

18. A multiple prehension mechanism adapted to assume different prehensile operational modes to grasp objects comprising:

a palmar base defining a working surface thereon, said base having a centerline generally normal to said working surfaces;

at least three finger assemblies carried by said base, each of said finger assemblies including a support means mounted on said base, a finger pivotally mounted on each of said support means about a curl revolute axis generally perpendicular to said centerline for movement toward and away from said working surface, one of said support means fixedly mounted on said base, two of said support means pivoted on said base at spaced apart positioning axes generally parallel to said centerline of said base, said two of said support means selectively movable from a first position in which said fingers move in intersecting curling planes to a second position in which said fingers move in parallel curling planes.

19. A multiple prehension mechanism adapted to assume different prehensile operational modes to grasp objects comprising:

a base defining a centerline;

three finger assemblies carried by said base, each of said finger assemblies including a support arm and a finger pivoted on said support arm about a curl revolute axis generally normal to said centerline, said support arms pinned to said base at three spaced points equally spaced about a circle lying in a plane generally perpendicular to said centerline, said support arm of one of said finger assemblies having a fixed position so that it extends generally radially of said circle and said support arms of the other two of said finger assemblies selectively pivotal about their associated points around positioning axes generally parallel to said centerline so that the curl revolute axes of said other two of said finger assemblies move about arcuate paths centered on said positioning axes.

20. The mechanism of claim 19 further including positioning means for selectively moving said other two of said finger assemblies to a first position in which said support arms extend from said circle in directions not parallel to each other and to a second position in which said support arms are all generally parallel and laterally spaced so that said fingers pivot generally parallel to each other.

21. The mechanism of claim 20 wherein said support arms of said other two of said finger assemblies extend substantially radially with respect to said circle in said first position.

22. The mechanism of claim 21 further including finger drive means for selectively pivoting said fingers about said curl revolute axes to grasp objects.