Multiple Prehension Manipulator

Abstract

A multiple prehension manipulator 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.

Description

BACKGROUND OF THE INVENTION

Many attempts known 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 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 be 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 may individually or collectively pivot the fingers about their finger axes. Also, the planes of movement of the fingers may be rotated so that the positioning axis substantially intersects the finger axes.

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 a side view of the manipulator of FIG. 1 shown partly in cross-section with the fingers in tip prehensile mode and the finger drive mechanism omitted for clarity;

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

FIG. 4 is an operating end view of the manipulator of FIG. 1; and,

FIG. 5 is a cross-sectional view of the finger mechanism taken along line 5--5 in FIG. 4.

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. 1-5, it will be seen that the first embodiment of the manipulator is designated by the numeral 10. Generally, the manipulator 10 includes a base 11, a plurality of finger assemblies 12 mounted on base 11, a finger driving mechanism 14 carried by each finger assembly 12, and a positioning mechanism 15 carried in base 11 for positioning the finger assemblies 12.

Basically, the manipulator is an assembly of drives and mechanisms intended for prehension. These mechanisms, called fingers, can have one or more bending sections. Externally, a finger with its bending sections resembles an open linkage. Each finger link is a component of a closed linkage which can pivot or rotate the link. The fingers do not translate and 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 either in the base or finger assemblies. 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 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 optimum when it is estimated that the manipulator 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 10 is able to generate all of the above four equivalent prehensile patterns.

Referring now to FIGS. 2-4, it will be seen that the base 11 is hollow with an equilateral triangular shaped top palmar plate 21 and bottom base plate 22. A tubular side wall 24 also having a general equilateral triangular cross-sectional shape connects the plates 21 and 22 so that the plates are substantially parallel to each other and in vertical alignment. Generally speaking, the palmar plate 21 corresponds to the palm of the human hand. A cavity 25 is defined within the plates 21 and 22 and side wall 24. requires velocity

A finger assembly 12 is rotatably journalled between plates 21 and 22 at each of their three corners and extends outwardly from the palm plate 21. The finger assemblies 12 are individually designated 12.sub.a -12.sub.c to distinguish each. The finger driving mechanism 14 of each assembly 12 is positioned in cavity 25 and rotatable with its associated assembly 12 as will become more apparent. The positioning mechanism 15 is also mounted within cavity 25.

FINGER ASSEMBLY

Finger assemblies 12.sub.a -12.sub.c are all identical in construction and therefore only one assembly which is designated generally 12 as seen in FIG. 5 will be described in detail with like reference numbers applied to each. The assembly 12 includes a frame 31 which is rotatably journalled about a positioning axis PA between palmar plate 21 and base plate 22 as seen in FIG. 2. A mounting bracket 32 on frame 31 projects through an appropriate opening 26 in palmar plate 21. A finger 34 is connected to bracket 32 through a single revolute joint 35 so the entire finger 34 is pivotal through a single curling plane CP as best seen in FIG. 1 about a curling axis CA passing through the joint 35. It will be noted that the positioning axis PA is parallel to the curling axis CA passing through the joint 35. It will be noted that the positioning axis PA is parallel to the curling plane CP while the curling axis CA is perpendicular to the curling plane CP. In this embodiment, it will be noted that the positioning axis PA substantially intersects the curling axis CA and lies within the curling plane CP.

While fingers 34 may be a single rigid member, those illustrated have multiple links joined by revolute joints to increase the ability of the finger to constrain an object and thus its versatility. The fingers 34 may have any number of links, however, three links are illustrated and have been found sufficient when used in combination with other like fingers to approximate the human hand. The links illustrated are a base link 40, an intermediate link 41 and a distal link 42. The base link 40 is connected at one end to the bracket 32 through the revolute joint 35. One end of the intermediate link 41 is connected to the other end of the base link 40 through a revolute joint 44 so that link 41 is pivoted to link 40 about a second curling axis CA-2 parallel to the axis CA of joint 35. One end of the distal link 42 is connected to the other end of the intermediate link 41 through a third revolute joint 45 so that link 42 is pivoted to link 41 about a third curling axis CA-3 parallel to the second axis CA-2 and base axis CA.

Each link is provided with a gripping surface 46 to engage an object as is apparent. While only one gripping surface 46 is provided on one side of each link, it is to be understood that such surfaces may be provided on both sides if the finger is to be double acting as will become more apparent.

To limit the amount of movement between links 40-42 and with bracket 32, a stop 48 may be provided on each end of base link 40 at the revolute joints 35 and 44 as well as on the distal link 42 at the revolute joint 45. The stops 48 may be configurated differently depending on the movement to be controlled, however, the stops 48 illustrated limit the opening movement of the links to a position in which the links are longitudinally aligned in a substantially straight path P as seen in FIGS. 2 and 5 and the entire finger 34 so that the path P is substantially normal to the working surface 23 of the palmar plate 21 when the finger assembly 12 is in its normal open position.

It will also be understood that while the fingers 34 could be curled away from path P in either direction in a plane CP, the embodiment shown curls the fingers 34 away from path P in only one direction and that is in the direction toward the surface 46 as indicated by arrow C in FIGS. 2 and 5. The finger 12 is shown in a first curled position in FIG. 2 by dashed lines and in another curled position by phantom lines in FIG. 5.

FINGER DRIVE MECHANISM

Any of many systems may be used to pivot links 40-42 with respect to each other and the finger 12 with respect to bracket 32 and the working surface of palmar plate 21. For instance, the links 40-42 may be pivoted independently at each revolute joint 35,44 and 45 or the pivoting at the joints may be coupled in any desired fashion. Several systems which can be used are cross four-bar chains, miniature compound pulleys, four-bar chains with an expanding link and tension cables. Cross four-bar chains are dependable, easily built, and can transmit an angular displacement to the finger links in a continuously compounding manner. Miniature compound pulleys develop a high mechanical advantage and allow the finger links to bend through large angles. Expanding link four-bar chains can be used to drive the links easily with a high mechanical advantage and reasonable losses. Tension cables rotate the links by simple direct contact and require very little space. The finger driving mechanism 14 is shown by way of example only and is a tension cable-pulley system.

The mechanism 14 is mounted in frame 31 and rotatable therewith so that the relative positions are maintained between the finger 34 and driving mechanism 14 as the finger assembly 12 is rotated about its positioning axis PA. Because the motion of the finger 34 is attempting to duplicate that of the human finger, the base revolute joint 35 is independently rotated while the second and third revolute joints 44 and 45 are concurrently rotated in this illustration.

The mechanism 14 includes a curl drive unit 50 and a pinch drive unit 51 as best seen in FIG. 5. Unit 50 includes a reversible drive motor 52 drivingly connected to a first multiple sheave winding drum 54. A third cable drive 55 is operatively connected to one sheave of drum 54 and serves to selectively close the third revolute joint 45. Third cable drive 55 includes a pair of pulleys 56, one being rotatably journalled in the distal link 42 on the opposite side from the revolute joint 45 and one being rotatably journalled in the intermediate link 41 on the opposite side from joint 45. A flexible cable 58 is wound around pulleys 56 and attached to drum 54 in such a way that when cable 58 is wound upon drum 54 as drum 54 is rotated in a first direction, the cable 58 forces the pulleys 56 toward each other to force the link 45 to pivot toward link 44 about the third curl axis CA-3. A second cable drive 60 similar to drive 55 is operatively connected to another sheave of the winding drum 54 to selectively close the second revolute joint 44. The second drive 60 includes a pair of pulleys 61 journalled in links 41 and 40 across joint 44 and drive cable 62 wound therearound and connected to drum 55 so that, as the drum rotates in the first direction, the pulleys 61 will be drawn together to pivot link 41 toward link 40 about the second curl axis CA-2.

The unit 50 also includes an uncurling cable drive 64 operatively connected to yet another sheave of the first winding drum 54 and serves to concurrently open the second and third revolute joints 44 and 45. The drive 64 includes a pair of pulleys 65, one rotatably journalled in the inboard end of link 42 at the stop 48 and the other rotatably journalled in the outboard end of base link 40 at stop 48. A slack adjustment pulley 66 is rotatably journalled in link 41 intermediate its ends and is spring urged toward the gripping surface 46. A flexible cable 68 is wound around pulleys 65 and 66 and connected to winding drum 54 in such a manner that when drum 54 is rotated oppositely to the first direction, the pulleys 65 will be forced toward pulley 66 to open the links 41 and 42 about the curling axes CA-2 and CA-3. Thus, as the drum 54 is rotated in the first direction (counterclockwise in FIG. 5), the links 41 and 42 will be concurrently curled, and as drum 54 is rotated in the opposite direction (clockwise in FIG. 5) the links 41 and 42 will be uncurled to straighten the finger 34.

Unit 51 includes a reversible drive motor 70 drivingly connected to a second multiple sheave winding drum 71. A first cable drive 72 is operatively connected to one sheave of drum 71 and serves to selectively close the first revolute joint 35. First cable drive 72 includes a pair of pulleys 74, one being rotatably journalled in the base link 40 on the opposite side from the revolute joint 35 and one being rotatably journalled in the bracket 32 on the opposite side from joint 35. A flexible cable 75 is wound around pulleys 74 and attached to drum 71 in such a way that when cable 75 is wound upon drum 71, as the drum 71 is rotated in a first direction, the cable 75 forces the pulleys 74 toward each other to force the link 40 to pivot toward bracket 32 about the first curl axis CA to impart a pinching movement to finger 34.

The unit 51 also includes an unpinching cable drive 76 operatively connected to another sheave of the second winding drum 71 and serves to concurrently open the first revolute joint 35. The drive 76 includes a pulley 78 rotatably journalled in the inboard end of link 40 at the stop 48. Pulley 79 is rotatably journalled in bracket 32 and is spring urged away from revolute joint 35. A flexible cable 80 is wound around pulleys 78 and 79 and connected to winding drum 71 in such a manner that when drum 71 is rotated oppositely to the first direction, the pulley 78 will be forced toward pulley 79 to open the link 40 about the curling axis CA. Thus, as the drum 71 is rotated in the first direction (clockwise in FIG. 5), the link 40 will be rotated to cause the finger 34 to pinch, and as drum 71 is rotated in the opposite direction (counterclockwise in FIG. 5) the link 40 will be unpinched to straighten the finger 34.

POSITIONING MECHANISM

The positioning mechanism 15 uses a single drive motor to drive the finger assemblies 12 into their various prehensile modes. If the fingers 34 can be pinched or curled in both directions in the curling plane CP away from their normal path P, then it is necessary to rotate only two finger assemblies 12 about their positioning axes PA. While various mechanisms may be used to rotate the assemblies 12, the mechanism shown rotates all three finger assemblies 12 to allow the fingers 34 to be pinched or curled in only one direction away from normal path P.

Referring now to FIG. 3, the mechanism 15 includes a positioning drive motor 81 mounted on palmar plate 21 within cavity 25. The drive shaft 82 of motor 81 mounts drive gear 84 on the lower end thereof with a pitch diameter d.sub.1. The drive gear 84 meshes directly with a gear 85 on the pivot shaft 38 of finger assembly and drives a driven gear 86 on shaft 38 of assembly 12.sub.c through idler gear 88. Gears 85, 86 and 88 have pitch diameters d.sub. , d.sub.3 and d.sub.4 respectively. A four-bar link 89 is pinned at one end to 84 by drive pin 90 located from the rotational axis of gear 84 a distance r.sub.1 as will become more apparent. The link 89 has an effective length L and its opposite end is pinned to a four-bar gear 91 through a driven pin 92. The pin 92 is located from the rotational axis of gear 91 a distance r.sub.2 as will become more apparent. The four-bar gear 91 meshes with a driven gear 94 on the pivot shaft 38 of finger assembly 12.sub.a to drive same.

The mechanism 15 is known as a "double dwell" mechanism and progressively rotates finger assemblies 12 from the three-jaw prehensile mode (bending direction shown by solid lines in FIGS. 3 and 4) to the wrap prehensile mode (bending direction shown by dashed lines) to the spread prehensile mode (bending direction shown by phantom lines) to the tip prehensile mode (bending direction shown by dot-dash lines). As gear 84 is rotated, the drive pin 90 assumes the solid line position on gear 84 in FIG. 3 labelled P.sub.j for the three-jaw prehensile mode; assumes the dashed line position labelled P.sub.w on gear 84 for the wrap prehensile mode which is displaced from position P.sub.j by angle .alpha.; assumes the phantom line position labelled P.sub.s on gear 84 for the spread prehensile mode which is displaced from position P.sub.w by angle .beta.; and assumes the dot-dash line position labelled P.sub.t on gear 84 for the tip prehensile mode which is displaced from position P.sub.s by angle .theta.. With the initial three-jaw prehensile mode position taken as the zero position and clockwise angular displacement of the finger assemblies 12 as seen in FIG. 3 taken as negative, a comparison of the resulting angular displacement of the finger assemblies 12 is shown in TABLE I attached to the end of this specification.

As seen from TABLE I, finger assembly 12.sub.a is not effectively rotated while assembly 12.sub.b is rotated 60.degree. clockwise and assembly 12.sub.c is rotated 60.degree. counterclockwise when gear 84 moves pin 90 from position P.sub.j to position P.sub.w . As gear 84 rotates pin 90 from position P.sub.j to position P.sub.s , assembly 12.sub.a is effectively rotated 180.degree. counterclockwise, assembly 12.sub.b is rotated 180.degree. clockwise and assembly 12.sub.c is rotated 180.degree. counterclockwise. As gear 84 rotates pin 90 from position P.sub.j to position P.sub.t , assembly 12.sub.a is effectively rotated 180.degree. counterclockwise; assembly 12.sub.b is rotated 330.degree. clockwise, and assembly 12.sub.c is rotated 330.degree. counterclockwise. Thus it will be seen that the various prehensile patterns may be achieved by motor 81 rotating drive shaft 82 counterclockwise from position P.sub.j to position P.sub.t and clockwise from position P.sub.t back to position P.sub.j. Therefore motor 81 is reversible and can stop gear 84 in any of the above positions.

Angles .alpha., .beta. and .theta. are determined by equation:

.alpha./2 + .beta. + .theta./2 = 180.degree.

which produces an angle .alpha. = 48.degree., .beta.= 96.degree. and .theta.= 120.degree.. The ratio of the pitch diameter d.sub.1 of drive gear 84 to each of the pitch diameters d.sub.2 and d.sub.3 of driven gears 85 and 86 is 1.25. To avoid locking mechanism 15, the pitch diameter d.sub.5 of four-bar gear 91 is equal to three times the pitch diameter d.sub.6 of the driven gear 94. The distance r.sub.2 is always less than one-half of the pitch diameter d.sub.5 of four-bar gear 91 and the distance r.sub.1 is always greater than one-half of the pitch diameter d.sub.1 of drive gear 84. Where distance r.sub.1 = r.sub.2 cos 60.degree., the length L of four-bar link 89 can be calculated as follows:

L .gtoreq. [ (.alpha..sub.1 /2 + .alpha..sub.5 /2 + t).sup.2 - (r.sub.2 cos 60.degree.).sup.2 ].sup.1/2

where t = outside diameter -- pitch diameter of four-bar gear 91 or motor gear 84. Thus, it will be seen that assembly 12.sub.a is at the same position P.sub.a during the three-jaw and wrap modes and at the same position P.sub.b during the spherical and tip modes while the finger assemblies 12.sub.b and 12.sub.c change position for each mode. As the pin 90 moves from position P.sub.w to P.sub.s and position P.sub.s to P.sub.t , the pin 92 is moved through angle .pi.. While various sizes of the gears 84, 85, 86, 88, 91 and 94 as well as the length of link 89 may be varied, one representative size is set forth in TABLE II attached to the end of this specification.

While the positioning axes PA are illustrated parallel to each other it is to be understood that these axes may be skewed with respect to each other without departing from the scope of the invention. Likewise, while each axis PA is also illustrated as parallel to its respective curling plane CP, it is to be understood that it may be skewed with respect to the plane CP without departing from the scope of the invention. In the same manner it is to be understood that the curlling axes CA of each finger assembly 12 may be skewed with respect to each other.

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

TABLE 1 ______________________________________ COMPARISON OF ANGULAR DISPLACEMENT OF FINGERS Prehensile Finger Finger Finger Mode Assembly 12.sub.a Assembly 12.sub.b Assembly 12.sub.c ______________________________________ Three-Jaw 0.degree. 0.degree. 0.degree. Wrap 0.degree. -60.degree. +60.degree. Spread +180.degree. -180.degree. +180.degree. Tip +180.degree. -330.degree. +330.degree. ______________________________________

TABLE II ______________________________________ REPRESENTATIVE SIZES COMPONENT DIMENSION SIZE ______________________________________ d.sub.1 2.10" d.sub.2 1.80" d.sub.3 1.80" d.sub.4 Practical d.sub.5 1.50" d.sub.6 .50" r.sub.1 .419" r.sub.2 .65" L 1.83" ______________________________________

Claims

1. A multiple prehension manipulator mechanism comprising:

a plurality of finger means;

finger drive means for selectively opening and closing said finger means to grasp; and,

positioning drive means for selectively positioning said finger means so that at least two of said finger means are aligned along a common path in direct opposition to each other at a first position, and are parallel to

2. The mechanism of claim 1 wherein said positioning drive means further positions said at least two finger means so that said finger means are directed toward a common point displaced laterally from the common path in

3. The mechanism of claim 2 wherein said positioning drive means includes a

4. The mechanism of claim 3 wherein each of said finger means includes a finger bendable in a single curling plane about a revolute axis substantially normal to said curling plane and rotatable about a

5. The mechanism of claim 4 wherein each of said fingers has a normal substantially straight open position in which said finger lies along a prescribed substantially straight path in said curling plane substantially

6. The mechanism of claim 5 wherein there are three finger means and further including a palmar member rotatably mounting each of said finger means for rotation about said positioning axes, said palmar member defining a planar working surface and said finger means located so that said fingers project over said surface from spaced points and said

7. The mechanism of claim 6 wherein said finger means are positioned so that said positioning axis of each of said finger means lies in said curling plane of said finger in substantial alignment with said prescribed

8. The mechanism of claim 7 wherein said positioning means further includes a four-bar linkage mechanism operatively connecting said motor with said other of said finger means so that other finger means is substantially parallel to and in opposition to said at least two finger means in said second position, and is directed toward said common point in said third

9. The mechanism of claim 8 wherein said four-bar linkage mechanism includes a drive gear having a first prescribed pitch diameter d.sub.1 operatively connected to said motor for selected rotation by said motor; a first driven gear having a second prescribed pitch diameter d.sub.2 operatively connected to one of said at least two finger means for rotating said finger means about its positioning axis and drivingly meshing with said drive gear; a four-bar gear rotatably mounted in said base having a third pitch diameter d.sub.5 ; a second driven gear having a fourth pitch diameter d.sub.6 operatively connected to said other finger means for rotating said other finger means about its positioning axis and drivingly meshing with said four-bar gear; and a four-bar link pinned to said drive gear a prescribed distance r.sub.1 from its center of rotation and pinned to said four-bar gear a prescribed distance r.sub.2 from its center of rotation and having a prescribed length L according to the following relationships:

d.sub.1 /d.sub.2 = 1.25

d.sub.5 = 3 d.sub.6

r.sub.2 = d.sub.5 /2

r.sub.1 > d.sub.1 /2

r.sub.1 = r.sub.2 cos 60.degree.

L .gtoreq. [ (.alpha..sub.1 /2 + .alpha..sub.5 /2 + t).sup.2 - (r.sub.2 cos 60.degree.).sup.2 ] .sup.1/2

where t = outside diameter of said driven gear - d.sub.1 .