Abstract:
A gripper having a housing containing a piston and cylinder assembly and a pair of pinion gears rotatably journalled therein to oscillate in opposite directions. The housing is provided with a cruciform shaped guide way for accommodating a pair of finger carriers having a complementary cruciform shaped cross section slidably disposed within the guide way. A toggle arrangement including a cross-link connected to the piston and opposed connecting links interconnects the piston rod to the corresponding pinion gears so that, as the connecting links distend and extend upon the actuating of the piston, it results in reciprocation of the finger carriers to impart an enhanced closing force on the finger carriers in moving toward the closed position. Guide pins connected to the cross link and riding in slots on a cover plate enhance repeatability.

Description:
FIELD OF THE INVENTION 
     This invention relates generally to a gripper for use with robotic type tooling and more specifically to a parallel gripper having enhanced gripping power, accuracy and repeatability. 
     BACKGROUND OF THE INVENTION 
     Various types of grippers for use with-robotic type tooling or machines are known. Variations of the known grippers are disclosed in the following U.S. Pat. Nos. 4,593,948; 4,741,568; 4,874,194; 5,125,708; 5,163,729; 5,529,359; 5,572,915; 5,976,581 and 6,003,431. While the known grippers are operative for their intended purposes, efforts persist to obviate certain noted problems and/or to improve the operation thereof so as to enhance the accuracy and/or to provide for a more positive and/or enhanced gripping action while maintaining the parameters of the known grippers, i.e. in keeping within the physical limitations of the known grippers. 
     SUMMARY OF THE INVENTION 
     An object of this invention is to provide a gripper for use with robotic type tooling or machines capable of having an enhanced gripper force for positively retaining a workpiece. 
     Another object of this invention is to provide a gripper having means for enhancing repeatability of the movable finger carriers. 
     Another object of this invention is to provide a gripper with a relatively inexpensive and positive means for minimizing any play of the movable finger carriers to enhance the accuracy thereof. 
     The foregoing objects and other features and advantages, as will be apparent, are attained by a gripper having a housing provided with a piston or cylinder chamber having a piston reciprocally mounted therein, which is driven by means of a fluid medium imparting a fluid pressure on said piston to effect the reciprocation thereof. Connected to the piston is a piston rod having its free end operatively connected to a pair of pinion gears which are rotatably mounted within a gear chamber disposed adjacent. to the piston chamber. The arrangement is such that the piston rod extends through an opening formed in a partition or wall which separates the piston chamber from the gear chamber. 
     Journalled within the gear chamber are a pair of pinion gears which are operatively connected to the piston rod so as to oscillate in one direction or the other as the piston is displaced within the piston chamber in accordance with the direction in which the piston is being displaced by the pressure of the actuating fluid medium acting thereon. The connection between the piston rod and the pair of pinion gears is in the form of a toggle type linkage. The arrangement comprises a cross link fixed to the free end of the piston rod which extends into the gear recess. A connecting link pivotally connected to each end of the cross link is pivotally connected to the adjacent pinion gear so that when the piston rod is projected into the gear housing, the respective pinion gears are oppositely rotated in one direction and when the piston rod is shifted in the opposite direction, the pinion gears are oppositely rotated in the other or opposite direction. 
     Formed in the end of the housing is a cruciform transversely extending, guide way for accommodating a pair of finger carriers which are slidably mounted therein for reciprocal movement between an open and closed position. The respective finger carriers are provided with a rack disposed in meshing relationship with a corresponding pinion gear whereby the respective finger carriers are shifted between open and closed positions within the guide way in accordance to the direction of rotation of the pinion gears. 
     The cruciform guide way is formed so that the tolerance between the respective finger carriers and guide way are maintained to an absolute minimum on at least three contacting surfaces to minimize any play therebetween relative to the X, Y and Z axes thereof. 
     A cover plate having a pair of guide slots formed on the inner side thereof is provided to seal the gear housing. The cross link in turn is provided with a pair of guide pins arranged to be received in the respective guide slots of the cover plate so as to prohibit any flexing or deviation of the respective finger carriers so as to enhance the repeatability thereof. 
    
    
     IN THE DRAWINGS 
     FIG. 1 is a perspective view of a gripper embodying the invention. 
     FIG. 2 is a perspective exploded view of the gripper of FIG. 1 having parts shown in section. 
     FIG. 3 is a detail side view of a finger carrier component. 
     FIG. 4 is a side elevation view of the gripper of FIG. 1 illustrating the component parts in a finger carrier closed position. 
     FIG. 5 is a side elevation view similar to FIG. 4 illustrating the component parts in a finger carrier open position. 
     FIG. 6 is an end view of FIG.  1 . 
     FIG. 7 is a sectional view taken along line  7 — 7  on FIG.  5 . 
     FIG. 8 is a sectional view taken along line  8 — 8  on FIG.  5 . 
    
    
     DETAILED DESCRIPTION 
     Referring to the drawings, there is illustrated in FIG. 1 an embodiment of the invention. As shown, the gripper  10  includes a housing  11  having a piston or cylinder chamber  12  in which a displaceable piston  13  is slidably mounted. The outer end  12 A of the piston or cylinder chamber  12  is closed or sealed by an end closure  14 . A sealing ring  15  is disposed between the end  12 A of the piston or cylinder chamber  12  and closure  14 , and retainer ring  16  maintains the end closure  14  in sealing relationship relative to the cylinder chamber  12 . 
     In the illustrated embodiment, the housing  11  is also provided with a chamber or recessed portion  17  for accommodating a pair of pinion gears  18  and  19 . The respective pinion gears  18  and  19  are rotatably journalled within the gear recess or chamber  17  about their respective axle pins  18 A,  19 A. As best seen in FIGS. 7 and 8, the opposed ends of the axle pins  18 A,  19 A are suitably journalled in corresponding spaced apart bearing holes  20  and  21  formed in the end wall  11 A of the housing and an opposed end closure plate  22 . The end closure plate  22  is detachably connected to the housing  11  by means of screw type fasteners or bolts  23 . 
     In accordance with this invention, a piston rod  24  is connected to the piston  13  and has its free end extending through an opening  25  formed in the partition portion separating the cylinder chamber  12  from the pinion gear recess or chamber  17 . Thus, the free end of the piston rod  24  extends into the pinion gear recess  17 . 
     As best seen in FIGS. 2,  4  and  5 , the respective pinion gears  18 ,  19  are provided with a cutaway portion as indicated at  18 B,  19 B, respectively, which are oppositely disposed. A segmental portion of the pinion gears  18 ,  19  is provided with a series of circumferential teeth  18 C and  19 C respectively. As will be hereinafter described, the respective series of teeth  18 C and  19 C of pinion gears  18  and  19  are disposed in meshing relationship with the rack portion  26 A,  27 A of finger carriers  26  and  27  respectively. It will be understood that the respective finger carriers  26  and  27  are adapted to be fitted with suitable fingers  26 B,  27 B respectively to shift between open and closed positions for gripping a workpiece as will be hereinafter described. 
     In accordance with this invention, the free end of the piston rod  24  is operatively connected to the respective pinion gears  18  to  19  to effect the drive thereof as the piston  13  is displaced within the cylinder chamber by the action of an actuating fluid medium, e.g. compressed air or hydraulic fluid. In the illustrated embodiment, the connection comprises a toggle like means that includes a cross link  28  connected to the free end of piston rod  24 . To each end of the cross link  28  there is pivotally connected about respective pivot pins  29  and  30 , a connecting link  31  and  32 . The other ends of connecting links  31  and  32  are pivotally connected to the pinion gears  18  and  19  by pivot pins  33  and  34  respectively. In the illustrated embodiment, it will be noted that the respective pinion gears  18  and  19  are provided with a bifurcated portion or recess for receiving the ends of the connecting links  31  and  32  which are journalled or pivotally connected by pivot pins  33 ,  34  respectively. 
     From the foregoing and as best noted in FIGS. 4 and 5, it will be apparent that as the piston  13  is displaced in the direction of the arrow A′ as noted in FIG. 5, the piston rod  24  is projected into the pinion gear recess or chamber  17  to elevate the cross link  28 , as viewed in FIG. 5, causing the respective connecting links  31  and  32  to effect counter-rotation of the respective pin gears in a direction to shift the respective finger carriers  26  and  27  in meshing relationship therewith to an open position as shown in FIG.  5 . When the piston  13  is displaced in the opposite direction to withdraw the piston rod  24 , as viewed in FIG. 4, the toggle connection described causes the respective pinion gears  18 ,  19  to counter-rotate in the opposite direction to shift the respective finger carriers  26 ,  27  to their closed position shown in FIG.  4 . It is important that the throw or travel of the piston and connected piston rod for actuating the finger carriers toward the closed position, as seen in FIG. 4, is such that the cross link  28  and the respective connecting links extend only short of a dead center position of the toggle connection described, and do not go beyond or through the dead center position of the described toggle connection. Thus, maximum closing force is imparted to the closing fingers  26 B,  27 B without overstressing the same. 
     To insure repeatability of the movable finger carriers  26 ,  27  and the fingers  26 B,  27 B carried thereby, the cross link  28  is provided with a pair of projecting spaced apart guide pins  29 A,  30 A, which may be extensions of pivot pins  29 ,  30 . As best seen in FIGS. 2 and 7, the end closure plate  22  on the inner surface thereof is provided with a pair of grooves  35 ,  36  to define a guide way for the projecting pins  29 A,  30 A, as best seen in FIG.  7 . The guide pins  29 A,  30 A are in close tolerance with the grooves  35 ,  36  and in sliding relationship therewith so as to prohibit any undue play or flexing of the piston rod  24  so that the repeatability of the finger carriers is not adversely affected. 
     In accordance with this invention, the gripper housing  11  is provided with a cruciform guide way  37  in which the finger carriers  26  and  27  are slidably disposed for movement toward and away from one another. As best seen in FIGS. 1 and 2, the guide way  37  is in the shape of a cross having a lateral portion  37 A and a vertical portion  37 B. The respective finger carriers  26  and  27  are also cruciform in cross section that complement the cross section of the guide way  37 . As best seen in FIG. 6, the vertical surfaces  37 C and  37 D of the lower end of the vertical portion  37  are machined to a very close tolerance to the complementary vertical surfaces of the finger carrier so as to provide for a minimum clearance tolerance therebetween. Likewise, the complementary upper and lower surfaces  37 E,  37 F of lateral portion  37 A of the guide way  37  are machined to very close tolerances of the complementary lateral surfaces  27 D and  27 E of the finger carrier  27 . Thus, as seen in FIG. 6, the complementary surfaces  37 C,  37 D;  37 E,  37 F are in close sliding relationship with the complementary surfaces  27 B,  27 C and  27 D,  27 E respectively of the corresponding finger carrier  27  so as to provide virtually zero tolerance therebetween. The arrangement is such that the respective finger carriers  26  and  27  are slidably mounted within the guide way  37  in a manner whereby any play therebetween is maintained to an absolute minimum or nil in the X, Y and Z axes thereof in a relatively simple and expedient manner. As a result, the accuracy and durability of the gripper can be maintained over a considerable period of use. 
     The cylinder chamber  12  of the gripper is provided with fluid inlet-outlet ports  40  and  41  to which the supply conduit (not shown) of a fluid activating medium is connected. As seen in FIG. 5, the ports  40  and  41  are in communication with the piston chamber  12  on opposite sides of the piston  13 . It will be understood that the actuating fluid medium may be either a gas or liquid, e.g. compressed air or a hydraulic liquid. 
     In operation, when a fluid activating medium is introduced into port  41 , e.g. compressed air, the piston  13  is displaced toward its upper position as viewed in FIG.  5 . The displacement of the piston and connected piston rod  24  causes the pinion gears to be oppositely rotated to move the respective finger carriers  26 ,  27 , in meshing relationship with the respective pinion gears  18  and  19 , toward the open position. In doing so, the actuating fluid on the opposite side of the piston  13  is being exhausted through port  40 . 
     When the flow of actuating medium is reversed, i.e. introduced into port  40 , the operation is reversed. That is, the piston  13  is forced to its downward position as viewed in FIG. 4, causing the cross link  28  to be lower. In doing so, the connecting links  31  and  32  are caused to be extended to impart a large closing force on the finger carriers  26 ,  27 , disposed in meshing relationship with the respective pinion gears  18 ,  19 . The stroke of the piston rod  24  is such that the cross link merely approaches the dead center position of the toggle linkage, i.e. stops short of dead center and does not pass through the dead center position. The arrangement provides for a much greater closing force to be imparted to the respective gripping fingers  26 B,  27 B in the closed position to more positively grip a workpiece therebetween. 
     From the foregoing, it will be apparent that the described gripper is rugged in construction, yet rendered very accurate in operation and repeatability. The actuation of the respective pinion gears by means of a toggle like connection  28 ,  29  and  30 , interposed between the piston rod  24  and the respective pinion gears  18 ,  19 , imparts an enhanced closing force on the respective associated finger carriers  26 ,  27  to result in a greater and more positive gripping force being imparted to the gripping fingers  26 B,  27 B. 
     While the present invention has been described with respect to a particular embodiment, modifications and variations may be made without departing from the spirit or scope of this invention.