Gripper mechanism having spring-loaded jaws

A gripper for grasping articles in an automatic or semi-automatic handling system includes spring-loaded jaws. No fasteners such as screws, pins, or the like are required to hold the jaws to the gripper assembly. The jaws are moved by way of motor-driven cams. During a grip mode, the cams do not contact the jaws, and the grip is achieved by way of the springs acting against rollers contacting the outside of the jaws. A worm on the motor shaft compresses a spring to buffer the deceleration of the motor. The spring applies a moment to worm gears which mate with the worm on the motor shaft. The gear shaft of each worm gear is operatively coupled to a respective camshaft. In this manner, the cams are locked.

BACKGROUND OF THE INVENTION 
The present invention relates to the grasping of articles, and more 
particularly to a gripper having spring-loaded jaws, for quickly and 
reliably grasping and releasing articles compatible with the jaws, e.g., 
box-like articles. This type of gripper is used, for example, in an 
automated handling system. In general, the present invention relates to 
the grasping of articles compatible with the jaws of the gripper. However, 
for ease of discussion, reference to tape cassettes will be made herein. 
Automated handling systems commonly are used to move an article from one 
point to another. For example, it commonly is desired to retrieve a 
particular cassette from among a library of cassettes, obtain information 
from the cassette, and then return the cassette to its designated position 
in the library. Sometimes the constant retrieval and return of cassettes 
is required; thousands of consecutive load and unload operations may be 
required to be performed in a single day. Thus, a gripper assembly for an 
automated handling system must be capable of quickly and reliably grasping 
and releasing cassettes. 
One recently developed gripper grasps a box-like article between a 
stationary plate and a movable flat spring. This gripper is disclosed in 
U.S. Pat. No. 4,846,619 assigned to the same assignee as the present 
invention. The gripper is attached to an accesser which moves the gripper 
toward a targeted article contained in a storage bin or toward a 
destination point, e.g., a tape transport device. This gripper has many 
advantages in the handling of video cassettes. However, due to its 
construction, the gripper has a low degree of freedom with respect to the 
targeted article and to the destination point, and the gripper must be 
extremely accurately positioned before the article can be loaded or 
unloaded. Thus, the accesser has the burden of very accurately aligning 
the gripper with respect to a targeted article or destination point. 
It is, of course, important that information on tape be protected. Thus, 
care must be taken to limit wear on the cassette housing. Physical rubbing 
and other touching of the cassette by the gripper should be minimized. 
Also, it is desirable for the gripper to have a high degree of freedom, so 
that even if a cassette is misaligned in its storage bin, the gripper is 
still able to function quickly and reliably. 
SUMMARY OF THE INVENTION 
The present invention is directed to a system for quickly and reliably 
grasping and releasing articles in an automatic or semi-automatic handling 
system. 
The gripper of the present invention has two spring-loaded jaws for 
grasping an article. No fasteners, such as screws, pins, or the like, are 
required to hold the jaws to the remainder of the gripper assembly. The 
springs extend between a support member and the jaws and push the jaws 
against stationary members, e.g., rollers, fixed to the remainder of the 
gripper assembly. Motor-driven cams are used to open and close the jaws. 
The cams do not contact the jaws when the jaws are in the closed position; 
the grip is achieved solely by the springs acting against the stationary 
members, and there is no concern that the article will fly loose from the 
jaws due to a loss of motor power. 
Additionally, the gripper is moved toward a targeted article by way of an 
accesser so that the article is situated between, but not in contact with, 
the jaws of the gripper. In the case where the accesser situates the 
gripper so that the cassette is located below a vertical registration 
surface on the gripper, the jaws are moved toward one another and into 
contact with the article, and the springs pull the article into the grasp 
of the jaws.. In this manner, the gripper draws the article into its 
grasp. If the accesser situates the gripper so that the vertical 
registration surface bears down on the cassette, then the springs pull the 
jaws so as to achieve accurate alignment between the cassette and the 
vertical registration surface. Thus, it is not necessary that the accesser 
accurately position the gripper with respect to the article to enable 
proper grasping to be achieved. Rather, the gripper has a high degree of 
freedom and precisely registers the article with respect to a vertical 
registration surface located on the gripper in a very short period of 
time. In this manner, even an article which is in a misaligned position 
can be quickly and reliably grasped. Furthermore, physical touching of the 
article is limited and thus wear on the article is minimized. 
In a preferred embodiment of the present invention, a worm is splined to 
the shaft of a drive motor and mates with worm gears which are attached to 
shafts operatively coupled to the camshafts. The motor-driven worm drives 
the worm gears and thus the camshafts and associated cams. In this manner, 
the jaws are opened and closed. 
The motor is de-energized when a sensor detects that the camshafts have 
rotated a predetermined amount. When cam rotation is stopped, e.g., when 
the worm gears contact associated hard stops, the action of the worm 
changes in that the worm moves up or down the motor shaft depending on the 
rotational direction of the motor shaft. A spring is located on the motor 
shaft and is compressed by the worm moving along the shaft. Thus, the 
deceleration of the motor is buffered by the spring acting against the 
worm. Also, the cams are locked by way of a moment applied to each of the 
worm gears through the spring acting on the worm. If motor deceleration is 
required to be buffered in both directions, two springs are situated on 
the motor shaft, one on either side of the worm. Each spring is seated on 
a slidable sleeve which is restricted in its motion along the motor shaft. 
Restriction may be by way of, for instance, a shoulder on the shaft or a 
retaining ring. In this manner, the springs are decoupled. That is, when 
the worm has moved from the neutral position, i.e., when the worm has 
moved up or down the motor shaft after cam rotation has been stopped, only 
one spring can axially impart force on the worm at any one time. 
The gripper of the present invention achieves extremely precise 
registration within a very short period of time. It limits physical 
contact of the article by the gripper so that wear on the article is 
minimized. Additionally, the grip is achieved by way of springs acting 
against stationary members, and there is no danger of the grip being lost 
even if motor power is lost. Also, the gripping force is applied primarily 
in a shear plane (i.e., the most rigid plane) of an article to further 
minimize possible damage to the article. Furthermore, the deceleration of 
the motor is buffered by using a simple, compact arrangement of reliable, 
long-lasting components.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
The following description is of the best presently contemplated mode of 
carrying out the invention. This description is made to illustrate the 
general principles of the invention, and is not to be viewed in a limiting 
sense. In particular, although the invention is described with reference 
to a cassette handling system, the invention may be used in other 
applications where other articles compatible with the jaws of the gripper 
are handled. The scope of the invention is best determined by reference to 
the accompanying claims. 
First, a general overview of the operation of the gripper 10 of the present 
invention will be given. FIG. 1 shows an example of an automated cassette 
handling system incorporating the gripper 10 of the present invention. A 
library of magnetic tape cassettes 12 is stored in rows of storage bins 
14. Each cassette 12 is horizontally situated in an assigned storage bin 
14 so that the tape-side is facing down. A number of tape transport 
devices 16 for playing cassettes are located below the storage bins 14. 
Each tape transport device 16 has a slot 18 into which a cassette 12 is 
inserted. When a targeted cassette 12 is to be retrieved from its storage 
bin 14, an accesser 20, controlled by a microcomputer (not shown), moves 
the gripper 10 toward the cassette 12. The accesser 20 has a relatively 
high degree of freedom with respect to the alignment of the gripper 10 
with the cassette 12. For example, the gripper 10 can approach the 
cassette 12 from 3/16" from the top of the cassette 12. 
FIG. 8 shows the gripper 10 positioned adjacent a cassette 12. The gripper 
10 is designed to position a cassette 12 with respect to a surface 106 
(FIG. 3) for achieving horizontal registration and a surface 114 (FIG. 8) 
for achieving vertical registration. The gripper 10 is situated so that 
the cassette 12 is between, but not in contact with, jaws 22A-B. Also, the 
cassette 12 is situated below the vertical registration surface 114. 
Actuation of a drive motor 23 (discussed in connection with FIGS. 12-15) 
is controlled by a microcomputer (not shown) based on detection signals 
received from various sensors. When the motor 23 is actuated, cams 28A-D 
(FIG.5) are driven so that the jaws 22A-B move toward each other. As the 
jaws 22A-B close, claws 60 of the jaws 22A-B engage in grooves 64 in the 
cassette 12 and the cassette 12 is pulled by the forces of the springs 
24A-H so that the cassette 12 is drawn into the grasp of the jaws 22A-B. 
In this manner, the gripper 10 achieves extremely precise registration, 
e.g., 0.001", with respect to the vertical registration surface 114 within 
a very short period of time, e.g., 50 milliseconds. Thus, the gripper 10 
has a high response time and can quickly and reliably perform thousands of 
consecutive load and unload operations. Also, other than the contact with 
the registration surfaces 106, 114, physical touching of the cassette 12 
by the gripper 10 is limited to the claws 60 contacting the grooves 64 of 
the cassette 12. Moreover, when the jaws 22A-B are closed, the cams 28A-D 
do not contact the jaws 22A-B, and the grip is achieved solely by the 
force of springs 24A-H acting against rollers 90A-D situated on the 
outside of the jaws 22A-B. 
When the cassette 12 is to be released, the motor 23 is energized, thereby 
driving the cams 28A-D. The cams 28A-D contact the jaws 22A-B and move the 
jaws 22A-B away from one another. The gripper 10 then releases the 
cassette 12 into the slot 18 of one of the tape transport devices 16. The 
accesser 20 is only required to position the cassette 12 within, for 
example, 3/16" above the slot 18 of the tape transport device 16. The 
downward and outward motions of the jaws 22A-B smoothly transport the 
cassette 12 down to the surface of the tape transport device 16. That is, 
the dynamics of the jaw movements prevent the cassette 12 from merely 
falling to the surface when the jaws 22A-B are opened. The gripper 10 
returns the cassette 12 to a storage bin 14 in a similar manner. 
As shown in FIGS. 2-4, two jaws 22A-B are held against external rollers 
90A-D seated on shafts 92A-D, respectively. The shafts 92A, 92C and the 
shafts 92B, 92D are seated in bores in front endplate 86 and rear endplate 
96, respectively. The rollers 90A, 90C are seated on the shafts 92A, 92C 
situated in bores in the endplate 86 so that the rollers 90A, 90C contact 
the outside of a first substantially vertical portion 46 of the jaws 
22A-B, respectively. The endplate 86 is held to the assembly by collars 
88A-B. Similarly, the endplate 96 located at the rear end 72 of the jaws 
22A-B and attached to the support 98 has shafts 92B, 92D upon which 
rollers 90B, 90D are seated so that the rollers 90B, 90D contact the 
outside of the first substantially vertical portion 46 of the jaws 22A-B, 
respectively. Motor-driven cams 28A-D are eccentrically mounted to 
camshafts 30A-B. A Worm 32 (FIGS. 3 and 13) is mounted to the motor shaft 
34. The worm 32 mates with worm gears 36A-B which are seated on 
corresponding gear shafts 38A-B. Each of the gear shafts 38A-B is linked 
by an associated coupler 40A-B to a corresponding one of the camshafts 
30A-B. When the motor 23 is actuated, the motor shaft 34 drives the worm 
32 which in turn drives the gears 36A-B and thus the gear shafts 38A-B. In 
this manner, the cams 28A- D are rotated, and the jaws 22A-B are opened 
and closed. 
For ease of reference, detailed description of each of the jaws 22A-B will 
be made with reference to the jaw 22A only. However, the jaw 22B is the 
identical, obverse mate to the jaw 22A. As shown in FIG. 6, the jaw 22A 
has a first section 42 defined generally by a horizontal top portion 44, a 
first substantially vertical portion 46 extending downwardly from the top 
portion 44, and an inclined portion 48 extending outwardly from the base 
of the first substantially vertical portion 46. The second section 50 of 
the jaw 22A is defined generally by a second substantially vertical 
portion 52 extending downwardly from the inclined portion 48, and a 
substantially horizontal shelf 54 extending inwardly from the base of the 
second substantially vertical portion 52. The third section 56 is defined 
generally by a third substantially vertical portion 58 extending outwardly 
and downwardly from the second substantially vertical portion 52, and a 
claw 60 attached at the bottom of the third substantially vertical portion 
58. The claw 60 has a slightly inclined upper surface 62 which contacts 
the groove 64 in the cassette 12 and also an inclined portion 66. A pad of 
rubber or a like material may be secured to inclined upper surface 62 of 
the jaw 22A to facilitate gripping and to absorb shock. Alternatively, as 
shown in FIG. 7, if a cassette 12 does not have a groove 64 for gripping, 
the jaw 22A need not have a claw 60, and a material for increasing the 
coefficient of friction of the jaw 22A may be mounted to that part of the 
jaw 22A which contacts a cassette 12. The material is selected so that 
when the jaws 22A-B are closed, the cassette 12 is firmly grasped. For 
example, a pad 67 of a suitable type of rubber may be secured along the 
inside of a part of the third substantially vertical portion 58 of each 
jaw 22A-B. 
Recesses 68A-H are formed in the underside of the horizontal top portion 44 
of each jaw 22A-B to accommodate the springs 24A-H, respectively (FIGS. 
3-4). Two recesses 68A-B toward the front end 70 of the jaw 22A 
accommodate the springs 24A-B, and two recesses 68C-D toward the rear end 
72 of the jaw 22A accommodate the springs 24C, 24D. Similarly, recesses 
68E-H are formed in the jaw 22B to accommodate the forward springs 24E, 
24F and the rear springs 24G, 24H. When the jaws 22A-B are in the closed 
position, each of the springs 24A-H is situated substantially vertically, 
and the bottom of each of the springs 24A-H is situated in a corresponding 
recess in the support member 26. The support member 26 is situated between 
the two spaced jaws 22A-B and has a front portion 76 (FIG. 5) to 
accommodate the springs 24A-B, 24E-F and a rear portion 78 to accommodate 
the springs 24C-D, 24G-H. A connecting portion 80 extends from the front 
portion 76 of the support member 26 to the rear portion 78 of the support 
member 26. Bearings 84A-B and 84E-F are located in the front portion 76 of 
the support member 26 and bearings 84C-D and 84G-H are located in the rear 
portion 78 of the support member 26, respectively. 
The configuration of the camshafts 30A-B and associated parts is shown in 
FIG. 5. For ease of discussion, only reference to the camshaft 30B will be 
made. However, the camshafts 30A-B are similarly configured. The bearings 
84E, 84F are seated on the front end of the camshaft 30B, and the bearings 
84G, 84H are seated on the rear end of the camshaft 30B. The forward cam 
28C is eccentrically mounted behind the front end portion 76 of the 
support member 26, and the rearward cam 28D is eccentrically mounted 
forward of the rear portion 78 of the support member 26. The cams 28C-D 
are connected by an inter-connect 85 attached to each of the cams 28C-D by 
way, for example, of a nut-plate. The camshaft 30B extends past the front 
end 70 of the gripper jaw 22B, through the endplate 86, and a collar 88B 
is attached at the end. 
The camshaft 30B is operatively coupled at its rearward end to a 
corresponding gear shaft 38B. Each gear shaft 38A-B is equipped with a 
corresponding gear 36A-B (FIG. 13). The gears 36A-B mate with a worm 32 
splined to the motor shaft 34. The motor shaft 34 has a shoulder 100A 
above the worm 32 upon which a first slidable sleeve 102A sits. Also, the 
motor shaft 34 has a shoulder 100B located below the worm 32 upon which a 
second slidable sleeve 102B sits. A spring 104A is seated on the first 
slidable sleeve 102A, and a spring 104B is seated on the second slidable 
sleeve 102B. In this manner, the springs 104A-B are decoupled. At the end 
opposite the slidable sleeves 102A-B, each of the springs 104A-B 
respectively seats on a shoulder of a block or the like. When the motor 
shaft 34 rotates, for example, in a clockwise direction, the gear 36A 
rotates in one direction, e.g., a counterclockwise direction, and the gear 
36B rotates in the opposite direction, e.g., in a clockwise direction. The 
gear shafts 38A-B rotate in the counterclockwise and clockwise directions, 
respectively, and camshafts 30A-B and corresponding cams 28A, 28C and 28B, 
28D are rotated in the counterclockwise and clockwise directions, 
respectively. In this manner, the jaws 22A-B are opened and closed. 
In many cases, the gripper 10 may be required to perform thousands of 
consecutive load and unload operations. Thus, a high-speed motor 23 is 
used, e.g., a motor which attains a velocity of 8000 rpm in just 80 
milliseconds. In order to achieve greater efficiency, it is desired that 
the motor 23 is operated at maximum speed so that load and unload 
operations may be performed as quickly as possible. The gripper 10 of the 
present invention employs a motor deceleration buffer which permits the 
motor 23 to be operated at maximum speed until a load or unload action of 
the jaws 22A-B is completed, i.e., the motor 23 need not be decelerated 
until after the movement of the jaws 22A-B is completed. Cam rotation is 
stopped by, for example, providing each of the gears 36A-B with a 
corresponding hard stop, e.g., a pin (not shown) carried in the gear 
housing, which stops its rotation. Hard stops can be placed anywhere along 
the camshaft drive system to effectively stop rotation of the cams 28A-D. 
The worm 32 is splined to the motor shaft 34 so that it rotates with the 
shaft 34 and is slidable along the motor shaft 34. When the motor 23 is 
de-energized and the gears 36A-B are stopped by the hard stops, the worm 
32 continues to rotate as the motor decelerates. Since the gears 36A-B are 
stopped, the worm moves either up or down the motor shaft 34 depending on 
the rotational direction of the motor shaft 34. If, for example, as shown 
in FIG. 15, the motor shaft 34 is rotating in a direction so that the worm 
32 moves downward when the gears 36A-B contact their corresponding hard 
stops, then the worm 32 contacts the slidable sleeve 102B and pushes it 
downward in opposition to the spring 104B, thus buffering, or absorbing, 
the deceleration of the motor 23. The spring 104B is selected to have a 
coefficient of spring force such that when the gears 36A-B are stopped, 
the gears 36A-B are locked. That is, the spring 104B applies a moment to 
each of the gears 36A-B, thereby locking the gears 36A-B and thus the cams 
28A-D. The gears 36A-B can therefore rotate only when the motor shaft 34 
(and therefore the worm 32) is rotated. 
As noted previously, the tops of the springs 24A-H contact the horizontal 
top portion 44 of the jaws 22A-B, and the bottoms of the springs 24A-H 
contact the support member 26 as shown in FIG. 6. Each of the springs 
24A-H has a coefficient of spring force such that when the jaws 22A-B are 
closed, the cassette 12 is firmly grasped. Most of the gripping force is 
applied in the shear plane of the cassette 12, i.e., the most rigid plane. 
When the jaws 22A-B are in the closed position as in FIG. 6, the cams 
28A-D do not contact the jaws 22A-B. The grip is achieved by the force of 
the springs 24A-H urging the jaws 22A-B against the rollers 90A-D. 
The movement of the jaws 22A-B from a closed to an opened position and vice 
versa corresponds to a predetermined camshaft rotation. The motor 23 is 
de-energized when a sensor 112 (FIG. 3) detects that the camshafts 30A-B 
have rotated the predetermined amount, e.g., 180.degree.. Thus, the 
rotation of the camshafts 30A-B is used to control the timing of the 
de-energization of the motor 23 during a load operation. 
FIGS. 8-11 show the relationship between various elements as the jaws 22A-B 
move from an opened to a closed position to grip a cassette 12. For ease 
of discussion, reference will be made only to the elements shown in FIGS. 
8-11. However, like elements not shown in these figures operate similarly. 
In the illustrated case, the gripper 10 is not accurately aligned with the 
cassette 12. That is, the gripper 10 has been positioned by the accesser 
20 such that the cassette 12 is located below the vertical registration 
surface 114, by, e.g., 3/16". 
FIG. 8 shows a configuration in the 180.degree. position, i.e., the fully 
opened position. The cams 28B, 28D push down on the substantially 
horizontal shelf 54 and also push outwardly on the second substantially 
vertical portion 52 of each jaw 22A-B, respectively. In this manner, the 
jaws 22A-B are pushed outward, and the springs 24D, 24H are further 
compressed. The rollers 90B, 90D oppose the forces of the cams 28B, 28D. 
FIG. 9 shows a 167 11' position, i.e., the position after the cams 28B, 
28D have rotated 12.degree. 49' in a clockwise direction from the 
180.degree. position. The springs 24D, 24H pull the jaws 22A-B, and the 
claw 60 of each jaw 22A-B engages the groove 64 in the cassette 12. FIG. 
10 shows a 150.degree. position, i.e., the cams 28B, 28D have rotated 30 
in a clockwise direction from the 180.degree. position. In this position, 
the jaws 22A-B are at their maximum reach, i.e., their maximum downward 
position during an open or close operation. The claw 60 is firmly engaged 
in the groove 64 in the cassette 12 and the cassette 12 is at its lowest 
position. The cams 28B, 28D push down on the substantially horizontal 
shelf 54 but do not contact the second substantially vertical portion 52 
at all. FIG. 11 shows a 0.degree. position, i.e., the cams 28B, 28D have 
rotated 180.degree. in a clockwise direction from the original 180.degree. 
position. In the 0.degree. position, the cams 28B, 28D do not contact the 
jaws 22A-B at any point. The jaws 22A-B are pulled up by the forces of the 
springs 24D, 24H, and the claw 60 is firmly engaged in the groove 64 of 
the cassette 12. As the jaws 22A-B are closed, the jaws 22A-B smoothly 
move upwardly and inwardly against the rollers 90B, 90D and draw the 
cassette 12 up into alignment with the vertical registration surface 114. 
This loading operation takes only a very short period of time, e.g., 80 
milliseconds. 
Of course, if the accesser 20 precisely aligns the gripper 10 with the 
cassette 12, then the jaws 22A-B close laterally so as to engage the 
grooves 64 of the cassette 12; the cassette 12 is not carried downward and 
then pulled up as in the case previously described. Furthermore, the 
accesser 20 may position the gripper 10 such that the vertical 
registration surface 114 bears down on the cassette 12 and the jaws 22A-B 
are located below the grooves 64 in the cassette 12. In this case, the 
jaws 22A-B are closed to contact the cassette 12 below the grooves 64, and 
the springs 24D, 24H pull the jaws 22A-B up into engagement with the 
grooves 64 of the cassette 12. 
As mentioned previously, the cams 28A-D do not contact the jaws 22A-B at 
any point in the closed, i.e., 0.degree., position. The grip is achieved 
by way of the springs 24A-H acting against the rollers 90A-D, and due to 
the nature of springs, the gripper 10 is quite forgiving. Thus, a cassette 
12 need not be perfectly aligned in its storage bin 14 for the gripper 10 
to function effectively, and the accesser 20 is not required to accurately 
align the gripper 10 with the cassette 12. For example, the gripper 10 of 
the present invention, when constructed in accordance with the preferred 
embodiment, registers to 0.001" and has a vertical tolerance of 3/16", a 
widthwise tolerance of .+-.1/16", and a horizontal tolerance of 1/8". 
The best presently contemplated mode of carrying out the present invention 
has been described. Nevertheless, it should be understood that various 
modifications may be made without departing from the spirit and scope of 
the invention. For example, although the present invention has been 
described with reference to cassettes, it is suitable for grasping any 
article compatible with the jaws of the gripper. This includes an article 
adapted to be compatible with the jaws of the gripper, e.g., an article 
with rounded sides having an appropriate receiver attached. Also, it is 
envisioned that elastic devices other than springs may be used as force 
means, and hold means other than rollers may be used. Additionally, the 
gripper is not limited to the orientation described. For example, the 
gripper can be positioned so as to grasp an article from the side rather 
than from the top. Also, the number of elements required, such as springs, 
cams, or bearings, depends on the specific application. Additionally, 
other means for stopping cam rotation may be used. For example, rather 
than at the worm gears, hard stops may be placed at other points along the 
camshaft drive system. Furthermore, the means for buffering the 
deceleration of the motor has use in various applications requiring 
high-response braking. Accordingly, it is to be understood that the 
present invention is not to be limited by the specific illustrated 
embodiment, but only by the scope of the appended claims.