Jaw Assembly

This invention relates to a jaw assembly for gripping and releasing objects and is of the type which is used in a machine having a movable arm which operates to grip workpieces at one station, by means of said jaw assembly, transfer the workpieces to another station, and release the workpieces at the latter station.

In order to promote productivity in manufacturing operations, it is often desirable to employ machines which can repetitively execute a cycle of operation to move parts, or workpieces, from one station to another station. These devices are today commonly referred to as robots. As such they may comprise a movable arm mounted on the robot device which is operable to grip a workpiece at one station, move the workpiece to another station, and release it at the latter station.

The actual work-engaging means which is used on a work arm may be either passive (no moving parts in of itself), or it may be active (moving parts). Active work-engaging means of this type are commonly referred to as jaw assemblies. When the arm is in the correct position at one station the jaw assembly is operated to grasp a workpiece or workpieces. It maintains its grasp on the workpiece or workpieces while the work arm transfers it or them to another station. Upon arrival at the other station, the jaw assembly releases the workpiece or workpieces and then returns to the first station to conclude a cycle. This cycle is repeated either continuously or in response to a particular stimulus, depending on the operation involved.

It is important that jaw assemblies be capable of reliably gripping workpieces so that they are not inadvertently or accidentally dropped. Disruptions of this type can defeat the purpose of using robots.

It is also important that the jaw assemblies be operable to provide a suitable gripping force upon workpieces in accordance with the particular nature of the workpieces involved. An especially difficult problem is in gripping workpieces from the side (either an inside or an outside diameter, for example) and then lifting and/or lowering such workpieces by means of the work arm. Prior devices have been beset by different problems, for example, having excessive weight, limited stroke, and being not useful with different shaped workpieces.

The present invention is directed to a jaw assembly which is particularly well suited for application where workpieces are gripped from the side and moved with motion which includes a vertical component. It is effective for use in gripping workpieces at either inside or outside diameters, and it is capable of use with a range of varying diameters. Of particular advantage is that the jaw elements of the jaw assembly which grip a workpiece are mounted in such a manner that increased surface gripping area of the jaw elements with a workpiece is obtainable even though the radial motion which is imparted to the jaw elements is along a component which is arcuate rather than truly linearly radial. In other words, the invention is effective, in the case of gripping a vertical surface of a workpiece, to maintain the work gripping surface of the jaw vertical so as to maximize the surface area at which gripping occurs, yet with the use of a linear actuator (i.e. fluid cylinder) which operates axially of the jaw assembly. The invention can be fabricated with relatively simple mechanism, and provide increased surface gripping area for gripping workpieces of various diameters over a range of diameters within the confines of a dimensionally compact envelope. The invention is also susceptible to various embodiments depending upon the particular requirements for gripping and releasing particular workpieces.

The foregoing features, advantages and benefits of the invention along with additional ones, will be seen in the ensuing description and claims which should be considered in conjunction with the accompanying drawings. The drawings disclose a preferred embodiment of the invention according to the best mode contemplated at the present time in carrying out the invention.

FIG. 1 is a front vertical elevational view having a portion sectioned away illustrating a jaw assembly embodying principles of the present invention.

FIG. 2 is a horizontal sectional view taken substantially in the direction of arrows 2--2 in FIG. 1.

FIG. 3 is a view similar to FIG. 1 illustrating another embodiment of the invention.

FIG. 4 is a view of FIG. 3 illustrating one operative position.

FIG. 5 is a view of FIG. 3 illustrating another operative position.

FIG. 1 illustrates a first embodiment of jaw assembly 10 in accordance with principles of the present invention. It comprises a head designated by the general reference numeral 12 to which various additional components are assembled. The head itself is adapted to be mounted by means (not shown) on a work arm of a robot type device. In the preferred application the jaw assembly is mounted with its axis 14 vertically disposed.

The illustrated head 12 may be considered of multiple element construction including a first head element 16 and a second head element 18 suitably assembled together along mating surfaces indicated by the general reference number 20. The two elements 16 and 18 are constructed to cooperatively define a cylinder space 22 coaxial with axis 14 and within which a piston 24 is disposed. The piston 24 is operable vertically along axis 14. A circular hole 26 is centrally provided through head element 18 coaxial with axis 14. Suitable seals and/or liners may also be used in the construction and these are conventional details involved in the design of fluid cylinders and will not be expounded upon here.

A rod 28 affixed to piston 24 passes through hole 26 to the exterior and is suitably sealed with respect to the hole. Ports (not shown) to cylinder space 22 on opposite sides of piston 24 and suitable external controls (not shown) are also provided such that the rod 28 may be caused to be displaced axially of the jaw assembly on the head in accordance with operation of the controls. FIG. 1 illustrates a position which is at the midpoint of the rod's vertical travel relative to the head.

Mounted on rod 28 on the exterior of the cylinder space is a coupling 30. The coupling comprises a pair of axially spaced apart elements 32 and 34. The elements 32 and 34 are identical and each comprises a central circular aperture. The two elements 32 and 34 are suitably secured to the rod 28 in a predetermined axially spaced apart relation provided by an annular spacer 31. The shank of a screw 33 passes through the two elements and the spacer and into a tapped hole in the end of rod 28, and the screw head is effective to secure them in place. As can be seen in FIG. 2, element 32 has three radial flanges 32a, 32b, 32c, disposed 120.degree. apart about the axis 14. Element 34 is identical to element 32 and has its three flanges circumferentially aligned with those of element 32. Each pair of axially spaced apart flanges axially captures with a close fit a circular cylindrical pin 38 which is disposed generally tangentially to the OD of spacer 31.

Each pin 38 in turn is operatively coupled with a corresponding crank 40 mounted on the head of the jaw assembly. The illustrated crank on the right in FIGS. 1 and 2 comprises a pair of angularly related crank arms 42 and 44, with the latter being the longer one. Arm 42 is disposed in generally the radial sense while arm 44 is disposed in generally the axial sense.

There is also a pivotal mounting via which the crank is pivotally mounted about a crank axis 46. This crank axis is spaced radially from axis 14 at a given radial distance, and it is tangential to an imaginary circle defined by that radius. The pivotal mounting of the crank is provided by a mounting structure, generally 48, including a clevis 50 which projects vertically downwardly from a clevis block 58. Crank 40 is provided with a suitable recess within which the clevis 50 is received, and a pivot shaft 52 passes through suitable circular holes in both the clevis and the crank to provide for the pivotal mounting about axis 46. Means are provided on shaft 52 on opposite sides of the crank so that shaft 52 is suitably retained.

The mounting structure 48 which includes clevis block 58 also serves to mount resilient elements 60 and 62 which form a part of the jaw assembly mechanism. These resilient elements 60 and 62 are in the form of flat resilient strips which in the position illustrated in FIG. 1 are disposed in vertical planes parallel with each other. For the illustrated mounting structure 48, the upper end of one strip 60 is disposed within a vertical slot 64 formed in the radially outer wall of head member 18. The clevis block 58 fits in the slot and against strip 60. Strip 62 is disposed against the outer surface of block 58, and a keeper 66 fits over strip 62. Thus, the two resilient elements, the clevis block and the keeper are disposed in a stacked relationship, and all are held in place on the head by means of a pair of screws 68 whose shanks pass through suitable clearance holes in the four stacked pieces and thread into suitable tapped holes 70 formed in head member 18 within slot 64. Suitable countersinking of the heads of the screws into the keeper is preferable, as shown.

The vertical dimension between coupling elements 32 and 34 is preferably such as to forcefully clamp onto the diameter of pin 38 when screw 33 is tightened. As can be seen in FIGS. 1 and 2, the distal end of crank arm 42 includes a recess 71 which allows the crank arm to fit closely over the side edges of flange 32a. Pin 38 passes through suitable holes in the sides of the crank arm to provide a pivotal connection of the distal end of the crank arm on the ends of the pin. The pin is retained in place by suitable means 72, 74. With this arrangement, the crank 40 is operatively coupled with rod 28 such that in response to the vertical displacement of the rod along axis 14, there is a corresponding rocking arcuate motion imparted to the crank about axis 46.

The distal end of crank arm 44 includes a recess 75 to receive mounting structure 76 for the mounting of a jaw element 82. The mounting structure 76 includes a mounting block 77 and a keeper 80. Circular holes are provided through crank arm 44 at its distal end and a slot 79 through block 76. A circular pin 78 passes through these holes and slot and is suitably retained in place. The width of the slot is preferably just large enough for pin 78. In the FIG. 1 position, the slot is vertical. The mounting block 77 therefore has a pivotal mounting with respect to the distal end of crank arm 44 about pin 78, but it is also capable of limited axial (i.e. vertical) movement because of slot 79. Block 77 is preferably dimensioned to fit closely between the lower ends of the two resilient strips 60 and 62 so as to maintain them parallel and unstressed in the FIG. 1 position. Additional elements are also provided to keep the assembled relationship. This is done by means of the keeper 80 on one side, the jaw element 82 on the opposite side, and screws 88. As can be seen in FIG. 2, block 77 is provided on opposite sides with vertical grooves 84, 86 within which the lower ends of strips 60 and 62 are respectively disposed. The keeper 80 fits into groove 84 and against strap 60 while jaw element 82 fits into groove 86 and against strap element 62. These are all held in assembled relationship by means of the screws 88. For example, the screws may pass through suitable clearance holes in jaw element 82, strip 62, block 77, strip 60, and into tapped holes in keeper 80, with the screw heads preferably being countersunk.

The jaw assembly of FIG. 1 comprises three jaw elements 82 and corresponding mechanism as described above, and arranged 120.degree. apart about axis 14. Thus the jaw assembly illustrated in FIGS. 1 and 2 is a three jaw element construction in which all jaw elements are simultaneously movable in unison to grip and release workpieces.

From consideration of FIG. 1 it can be understood that in response to operation of rod 28 in the axial direction, crank 40 is pivoted about axis 46. This will result in the distal end of crank arm 44 moving in an arcuate path having a radius about pivot 46. As such, this motion is generally radial of axis 14, but it is not linearly radial; rather it is along the arc which is centered at 46.

The resilient strips 60 and 62 will interact with the mechanism during operation of the crank in the following manner to produce the following detailed motion of jaw element 82. In explaining the operation of the jaw assembly let it be assumed that jaw element 82 is intended to grip the I.D. surface 90 of a workpiece 92. Hence in order to grip the workpiece, the rod 28 will initially be sufficiently retracted to allow the jaw elements to fit within the I.D. of the workpiece. Once they have been axially positioned by means of vertical downward movement of the workarm on which the jaw assembly mounts, then rod 28 is extended to urge the jaw elements radially outwardly. As the jaw elements move radially outwardly of the position illustrated in FIG. 1, but before contacting the workpiece, the strips 60 and 62 will begin to resiliently deflect in a manner analogous to that of a cantilever. Yet, they deform in a general S-shape so that the radially outer surface of jaw element 82 will remain substantially vertical. If there is a slight departure from vertical, it may be generally anticipated that the jaw elements will first make contact with the I.D. surface 90 of workpiece 92 along their lowermost edges as viewed in FIG. 1. When this contact occurs, the mechanism still allows for a final increment of motion of the crank whereby the jaw element is caused to pivot upon the pin 78 so as to allow the outer surface of the jaw element to finally arrive in a position where it is truly vertically disposed against the vertical surface 90. As this final increment occurs, the resilient elements 60, 62 flex slightly more. The S-shape of the strips will be seen in subsequent FIGS. 4 and 5 to be described. With the invention the work gripping surface of the jaw is caused to assume a maximum contact with the workpiece thereby improving the workgripping capability of the jaw assembly. Advantageously this is done with what is strictly a mechanical mechanism and one which is compact and not complicated. Moreover, where the workpiece is not exactly concentric with the three jaws, the mechanism allows resilient conformance to achieve uniform gripping at each of the three 120.degree. spaced apart points. It is therefore an effective and economical means for reliably gripping workpieces.

Moreover, it can be used for gripping either I.D.'s or O.D.'s. For example, it might be possible to use the surface 94 of jaw element 82 to grip onto the O.D. of a workpiece such as indicated by the reference numeral 96. Gripping would occur by retracting the rod 28 so as to displace the jaw elements radially inwardly. Alternate constructions for the jaw elements themselves and their mountings are also anticipated within the scope of this invention.

Another embodiment 100 of the invention is illustrated in FIGS. 3, 4 and 5. The components of this embodiment correspond to those of the first embodiment and are identified by like but primed reference numerals. Embodiment 100, like the first embodiment has three jaw elements and mechanisms 120.degree. apart around axis 14. One of the differences is that the two resilient strips 60' and 62' in embodiment 100 are disposed side-by-side to one side (the radially inner side) of the crank arm 44' whereas in the FIGS. 1 and 2 embodiment, they were spaced apart on opposite sides of the crank arm 44. Also, the shapes of the various mounting blocks, jaw elements and keepers are slightly different.

FIGS. 4 and 5 illustrate the manner in which the resilient strips 60', 62' warp when a workpiece is being gripped. FIG. 3 illustrates the neutral centered position. FIG. 4 illustrates the condition where a very thin workpiece is being gripped on its outside while FIG. 5 illustrates a condition where a much larger diameter workpiece is being gripped on its inside. Thus in addition to being susceptible to various embodiments, the invention in any given embodiment can be used for gripping workpieces having gripping diameters over a range of diameters. Hence, different workpieces may be gripped by the same jaw assembly so that it may not be necessary to have a unique jaw assembly for each workpiece. Moreover, while the illustrated shape of the jaw assemblies has been illustrated as being generally rectangular, it will be appreciated that other shapes may be used and that workpieces may be gripped along surfaces which are not necessarily parallel with the axis of the jaw assembly. In other words a construction is envisioned in which the work gripping surfaces of the jaw elements may be disposed in other than a vertical plane when gripping a workpiece.

While a preferred embodiment of the invention has been disclosed, it will be appreciated that principles of the invention are applicable to other embodiments.