Abstract:
A gripping device including a main body, a first elongate actuator, a second elongate actuator, a first jaw, a second jaw, a first pin, a second pin, a pair of pulleys, and a cable. The elongate actuators are both disposed in respective actuator bores within the main body and translate opposingly to each other. The jaws are both driven by a respective elongate actuator. The pins both include respective pin bodies defining a channel and are configured to drive their respective jaw by a respective elongate actuator and are disposed through transverse holes formed in the respective elongate actuator and a respective pin slot formed in the main body. The pulleys are attached to the main body. The cable forms a closed loop around the pulleys through the channels and is affixed to the first channel to inhibit relative movement between the first channel and the cable.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a gripping device, and, more particularly, to a gripper that includes synchronized movable jaws. 
     2. Description of the Related Art 
     Grippers are mechanical devices characterized by one or more jaws that are moved together or apart by motive means such as an electric motor or pneumatic piston. Once moved into a position of contact with the gripped workpiece, the jaws produce a gripping force against the workpiece so that the position of the workpiece might be subsequently translated or rotated. It is often desirable for the movements of the jaws to be synchronized together so that the gripped workpiece is always moved to a repeatable position coincident with the middle of the gripper, irrespective of which jaw might contact the surface of the workpiece first. Methods used in prior art to synchronize jaw motion include racks driving a common pinion, such as is disclosed by Null, et al, in U.S. Pat. No. 7,490,881 or pinned linkages, as taught by Null, et al, in U.S. Pat. No. 6,598,918. Methods used in prior art to synchronize the jaws typically result in an undesirable increase in the physical size, weight, and manufacturing cost of the gripper. 
     What is needed in the art is a gripper with a synchronizing mechanism that is smaller, lighter, and less expensive than those known in the art. 
     SUMMARY OF THE INVENTION 
     The present invention provides an improved gripper incorporating a cable synchronizing mechanism. 
     The invention in one form is directed to a gripper including a main body that contains a first actuator bore, a second actuator bore, a first pin slot located transversely to the first actuator bore, and a second pin slot located transversely to the second actuator bore. Within the first actuator bore and second actuator bore there is a first elongate actuator with a first transverse hole and a second elongate actuator with a second transverse hole, respectively. The first elongate actuator and the second elongate actuator are configured to translate opposingly to one another within their respective first actuator bore and second actuator bore. The first elongate actuator drives a first jaw and the second elongate actuator drives a second jaw. A first pin including a first pin body defining a first channel and configured to drive the first jaw by the first elongate actuator is disposed through the first transverse hole and the first pin slot. A second pin including a second pin body defining a second channel and configured to drive the second jaw by the second elongate actuator is disposed through the first transverse hole and the second pin slot. The device further includes a pair of pulleys that are attached to the main body and a cable forming a closed loop around the pair of pulleys through the first channel and the second channel. The cable is affixed to the first channel to inhibit relative movement between the cable and the first channel. 
     An advantage of the present invention is the gripper uses a polymer cable, which offers advantages over traditional steel cable. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above-mentioned and other features and advantages of this invention, and the manner of attaining them, will become more apparent and the invention will be better understood by reference to the following description of an embodiments of the invention taken in conjunction with the accompanying drawings, wherein: 
         FIG. 1  is an exploded perspective view of an embodiment of the gripper of the present invention; 
         FIG. 2A  is an assembled perspective view of an embodiment of a synchronizing mechanism of the present invention; 
         FIG. 2B  is an exploded view showing multiple examples of how the ends of a cable can be configured as a first end termination and a second end termination; 
         FIG. 2C  is an exploded perspective view showing how the first end termination and the second end termination can be configured to affix the cable to a first pin to inhibit relative movement between the cable and the first pin; 
         FIG. 2D  is an exploded perspective view showing how the cable can be wound around a pin to add a pretension to the cable; and 
         FIG. 2E  is an exploded perspective view of one embodiment of a pin and how the cable can be configured within a channel of the pin. 
     
    
    
     Corresponding reference characters indicate corresponding parts throughout the several views. The exemplification set out herein illustrates one embodiment of the invention and such exemplification is to be construed as limiting the scope of the invention in any manner. 
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring now to the drawings, and more particularly to  FIG. 1 , a main body  3  includes a first actuator bore  2 A and a second actuator bore  2 B formed within the main body  3  going in the longitudinal direction of the main body  3 . The first actuator bore  2 A and second actuator bore  2 B are configured to hold a first elongate actuator  1 A and a second elongate actuator  1 B, respectively, such that the first elongate actuator  1 A and second elongate actuator  1 B are free to translate unencumbered along the longitudinal axis of the bores, but are prevented from translating radially by the walls of the bores. Although first elongate actuator  1 A and second elongate actuator  1 B are shown as pistons in  FIG. 1 , those skilled in the art will appreciate that the first elongate actuator  1 A and the second elongate actuator  1 B can be any type of actuator capable of providing a motive force in a linear direction such as an electric motor, pneumatic actuator, or hydraulic actuator. 
     In a preferred embodiment using pistons as the first elongate actuator  1 A and second elongate actuator  1 B, a plurality of seals  4 A,  5 A,  4 B, and  5 B is included to seal the peripheries of first elongate actuator  1 A and second elongate actuator  1 B against the first actuator bore  2 A and the second actuator bore  2 B, respectively, to prevent the flow of motive compressed air around the pistons. A first gasket  6 A and a second gasket  6 B seal a first end cap  7 A and a second end cap  7 B, respectively, against the ends of the main body  3  to form a closed cavity at either end of the first elongate actuator  1 A and the second elongate actuator  1 B. A threaded fastener  8  attaches the first end cap  7 A and the second end cap  7 B to the main body  3 . 
     A first pin  9 A passes through a first transverse hole  23 A in the first elongate actuator  1 A and a first pin slot  28 A formed in the main body  3 . The first pin slot  28 A should preferably have a width slightly greater than the first pin  9 A and a length equal to or greater than the distance between opposing gripping elements of the gripper. The first pin  9 A is attached to a first driver bar  10 A with a threaded fastener  11 A. A first jaw  12 A is attached to the driver bar  10 A with threaded fasteners  13 A. In this manner, the motive force generated by compressed air acting upon the first elongate actuator  1 A is transmitted to the first jaw  12 A through the pin  9 A and the driver bar  10 A. A rib  24  protruding from the sides of the first jaw  12 A is disposed into a first jaw slot  25 A in the main body  3  so as to prevent the rotation of the first jaw  12 A and limit the translation of the first jaw  12 A in all directions except along the longitudinal axis of the main body  3 . In an analogous manner, a second pin  9 B passes through a second transverse hole  23 B in the second elongate actuator  1 B and a second pin slot  28 B. The second pin slot  28 B is configured similarly to the first pin slot  28 A. The second pin  9 B is attached to a second driver bar  10 B with a threaded fastener  11 B. A second jaw  12 B is attached to the second driver bar  10 B with threaded fasteners  13 B so that the motive force generated by compressed air acting upon the second elongate actuator  1 B is transmitted to the second jaw  12 B through the second pin  9 B and the second driver bar  10 B. Similarly, a rib  24  protruding from the sides of second jaw  12 B engage a second jaw slot  25 B in the main body  3  to prevent the rotation of, and guide the translation of, the second jaw  12 B. Those skilled in the art will recognize that the configuration of the first jaw  12 A and the second jaw  12 B can be suitably altered to engage various workpieces. 
     A first port  14 A and a second port  14 B allow compressed air to fill the volumes between the sealed caps  4 A,  4 B,  5 A,  5 B and the first elongate actuator  1 A and the second elongate actuator  1 B. Passageways are so arranged in the main body  3  and the end caps  7 A,  7 B to allow compressed air applied through a first port  14 A or a second port  14 B to produce motive pressure against opposed ends of each elongate actuator  1 A,  1 B. In this manner, compressed air applied to the first port  14 A causes the pistons, and the jaws attached to the pistons, to move towards one another. Compressed air applied to port  14 B causes the pistons and the attached jaws to move away from one another. 
     A first pivot pin  15 A and a second pivot pin  15 B are press-fit into complementary bores in the main body  3 . A first pulley  16 A and a second pulley  16 B are disposed on top of the first pivot pin  15 A and the second pivot pin  15 B, respectively, so that both pulleys  16 A, 16 B are free to rotate around the corresponding pivot pin  15 A,  15 B. A cable  17  is joined to the first pin  9 A and the second pin  9 B to form a continuous loop around the pulleys  16  such that translation of the first pin  9 A causes a corresponding opposed translation of the second pin  9 B. A cover  18  is attached to the main body  3  with a plurality of fasteners  19  to retain the pulleys  16  upon the first pivot pin  15 A and the second pivot pin  15 B. 
     In one embodiment, a first end termination  26 A and a second end termination  26 B are added to a single length of cable  17  prior to installing the cable  17  into the synchronizing mechanism. Several possibilities exist to create suitable end terminations  26 A,  26 B, a few examples being shown in  FIG. 2B , with the choice of termination commensurate with the material from which the cable  17  is constructed. Knotted or heat-bloomed terminations are particularly well suited to polymer cables, while crimped or externally clamped terminations are typically limited to metal cables, because of the stress relaxation associated with polymers.  FIG. 2E  shows the construction of the end of the second pin  9 B that receives the cable  17 . A second channel  21 B spans the length of a second pin body  20 . A pair of dowel pins  22  is located on either end of the second channel  21 B with the gap between the diameters of the opposing dowel pins  22  chosen to allow the diameter of the cable  17  to pass unencumbered through the second channel  21 B, while restricting the end terminations  26 A, 26 B of the cable  17  from passing through. The cylindrical body of the dowel pins  22  provides a smooth geometric transition between the portion of the cable  17  passing through the second channel  21  and the portion of the cable  17  exiting the second channel  21 B to preclude cutting of the cable surface as the cable  17  is subjected to tensile loading. Although the dowel pins  22  are used to provide a smooth geometric transition, it will be understood by one skilled in the art that such a transition could also be affected by appropriately chosen blend radii between the walls of the second channel  21 B and the diameter of the pin body  20 , substituted for the dowel pins  22 . The cable-receiving end of the first pin  9 A is constructed in an analogous manner to that of the second pin  9 B. 
     In an embodiment of the present invention, a slot  27  is provided within the main body  3  to hold the gripper synchronizing mechanism described. The slot  27  can be configured as any shape capable of substantially holding the pair of pulleys  16 A, 16 B, cable  17 , and first and second channels  21 A, 21 B during operation. Ideally, the slot  27  is cylindrically shaped with a diameter greater than the diameter of both pulleys  16 A, 16 B and a length greater than the distance between the centers of the pulleys  16 A, 16 B plus the radii of the pulleys  16 A, 16 B. The slot  27  should be arranged transversely to the pin slots  28 A, 28 B of the main body  3  and the transverse holes  23 A, 23 B of the elongate actuators  1 A, 1 B. 
     The length of the cable  17  is chosen to exceed the perimeter distance formed by the radii of the pulleys  16  and the distance between the pulley centers. FIG. C shows, in left to right progression, the preferred steps used to attach the opposing, suitably terminated ends  26 A, 26 B of the cable  17  to the first pin  9 A (see also  FIG. 1 ) to form a closed loop about the pulleys  16 . Each end of the cable  17  exiting the first channel  21  of the first pin  9 A is wrapped about the first pin body  20  and the dowel pins  22  to reduce the force transmitted to the end terminations  26 A, 26 B of the cable  17  as the cable  17  is subjected to tensile loading. Such a reduction in transmitted tensile force by wrapping a cable about a cylinder is commonly known as “capstan effect”. 
       FIG. 2D  shows, in left to right progression, the steps used to attach the cable  17  to the second pin  9 B. The attachment of the cable  17  to the second pin  9 B also provides a means of taking up any extra cable length present due to cut-length variation and variation of the relative positions of the end terminations  26 A,  26 B. After insertion of the cable  17  into the second channel  21 , the second pin  9 B is rotated (shown by the arrows in  FIG. 2D ) so as to wind the cable  17  about the second pin  9 B. During the progressive winding of the cable  17  about the second pin  9 B, the cable  17  remains free to translate along the longitudinal axis of the second channel  21 B so as to equalize the tension of the two portions of the cable  17  exiting the second pin  9 B. Once the extra cable length has been completely removed from the closed loop of the cable  17  formed around the pulleys  16 , additional rotation of the second pin  9 B will serve to elongate the cable  17 , imparting a tension to the cable  17  in a manner analogous to stretching an extension spring. The magnitude of this tension is directly proportional to the torque applied to rotate the second pin  9 B. This proportionality allows a chosen pretension to be applied to the entire cable loop by applying an appropriate torque to the second pin  9 B. 
     It is desirable to pretension the cable loop to limit the force excursions that the cable  17  experiences during operation of the gripper, as large amplitude excursions promote fatigue of the cable material. Should one jaw contact the surface of the gripped workpiece prior to the other jaw contacting the workpiece, the force generated by the elongate actuator attached to the non-contacting jaw will be transmitted to the contacting jaw through the cable loop. Cables are limited to transmitting force only by tension due to the flexible nature of the cable  17  preventing the transmission of compressive force. If the cable loop is not pretensioned, the entire force generated by the non-contacting elongate actuator will be carried as a tensile load by only one of the two portions of the cable loop that connect the first pin  9 A to the second pin  9 B. The other portion of the loop cannot transmit any of the force, as doing so would place the cable  17  in compression. In an adequately pretensioned cable loop system, the elongate actuator force will be equally divided between the two portions of the cable loop, with one portion of the loop experiencing an increase in tension, while the other portion experiences a corresponding decrease in tension. The total tension in one portion of the loop will therefore be equal to the pretension load plus one-half of the elongate actuator force, while the total tension in the other portion of the loop will be equal to the pretension load minus one-half of the elongate actuator force. Neither portion of the loop will therefore experience a force excursion amplitude greater than one-half of the elongate actuator force. 
     Pretensioning also provides the advantage of increasing the effective stiffness of the cable  17  by removing the air spaces present between the individual strands comprising the cable  17 . The increased effective stiffness reduces the undesirable relative movement of one jaw with respect to the other jaw, which compromises the ability of the jaws to center the gripped workpiece. 
     The cable  17  can be comprised of any material suitable to handle the tensile loads that the cable  17  will experience during operation. Polymer cable offers the advantages of improved resistance to fatigue and corrosion, greater flexibility, improved dissipation of mechanical shock, and lower cost compared to traditional steel cable. Polymer cable suffers from lower stiffness and increased stress relaxation (loss of load while under sustained material deformation) when compared to steel cable. The lower comparative stiffness results in the polymer cable elongating more than steel cable under the same tensile load. The increased comparative stress relaxation makes it difficult to attach the polymer cable to other structures by mechanical crimping, as is typically done to attach steel cable. 
     A fastener  11 B is tightened to retain the position of the second pin  9 B, once the appropriate pretension has been established in the cable loop system. 
     While this invention has been described with respect to at least one embodiment, the present invention can be further modified within the spirit and scope of this disclosure. This application is therefore intended to cover any variations, uses, or adaptations of the invention using its general principles. Further, this application is intended to cover such departures from the present disclosure as come within known or customary practice in the art to which this invention pertains and which fall within the limits of the appended claims.