Abstract:
A fluid-driven actuator includes a chamber having a first stop and a second stop, a member that is extendable and retractable from the chamber, and a piston that is moveable toward the first stop to extend the member from the chamber and toward the second stop to retract the member into the chamber. The first stop is adjustable to vary a distance between the first stop and the second stop.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    This invention generally relates to automated handling equipment. More particularly, this invention relates to an actuated gripper device. 
         [0002]    Automated handling equipment is typically employed in industrial settings for transferring work pieces between work stations. Typically, the equipment includes a fluid-actuated gripper that clamps the work pieces while moving them between the stations. 
         [0003]    Conventional fluid-actuated grippers include a fluid actuator, such as a pneumatic or hydraulic cylinder, that linearly reciprocates a piston. The piston is coupled to a cam pin that is received through cam slots of two opposed gripper jaws. Each gripper jaw is pivotable about a pivot pin that extends into side walls that extend from the fluid actuator. As the piston reciprocates, the cam pin slides along the cam slots to selectively pivot the jaws about the pivot pins between open and closed jaw positions. 
         [0004]    The jaws of typical fluid-actuated grippers are removable and replaceable with different jaws to accommodate work pieces of varying shapes and sizes or to provide different open jaw positions. For example, jaws having different cam slot lengths and shapes (i.e., slot angles) may be substituted. The cam slot length and shape defines the open position of the jaws. Alternatively, adjustable stops on the jaws are used to limit the degree to which the jaws open, for example. 
         [0005]    Although conventional grippers are effective for clamping and transferring work pieces or other objects, using replaceable jaws or stops to change the size of the gripper opening adds complexity and is time consuming. Additionally, jaws and stops that are not in use require storage space and may become lost. 
         [0006]    Accordingly, there is a need for an actuator and a gripper assembly that provides adjustment of the degree to which the jaws open without having to replace the jaws or use adjustable stops on the jaws. This invention addresses those needs and provides enhanced capabilities while avoiding the shortcomings and drawbacks of the prior art. 
       SUMMARY OF THE INVENTION 
       [0007]    An example fluid-driven actuator includes a chamber having a first stop and a second stop, a member that is extendable and retractable from the chamber, and a piston that is moveable toward the first stop to extend the member from the chamber and toward the second stop to retract the member into the chamber. The first stop is adjustable to vary a distance between the first stop and the second stop. 
         [0008]    An example fluid-driven gripper assembly includes at least one gripper jaw, and a chamber having a proximal stop and a distal stop relative to the at least one gripper jaw for defining a range of movement of a piston within the chamber. The proximal stop is adjustable to vary the range of movement. 
         [0009]    An example method of controlling a fluid-driven gripper assembly includes the steps of reciprocally moving the piston within the chamber over a distance between the proximal stop and the distal stop relative to the at least one gripper jaw to reciprocally move the at least one gripper jaw through the range of movement, and adjusting the proximal stop to vary the distance between the proximal stop and the distal stop to thereby vary the range of movement. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]      FIG. 1  illustrates example gripper assemblies in an example industrial setting. 
           [0011]      FIG. 2  is a perspective view of an example gripper assembly. 
           [0012]      FIG. 3  is an exploded view of the example gripper assembly. 
           [0013]      FIG. 4  is a cross-sectional view of a portion of the example gripper assembly. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0014]      FIG. 1  illustrates selected portions of several gripper assemblies  10  used in an example industrial setting to grip and move a work piece  12  (shown schematically). The gripper assemblies  10  may be used in a variety of different configurations from that shown. In this example, the gripper assemblies  10  are coupled to extended arms  14 , which are each secured to a rail  16 . An adapter arm  18  is secured to the rail  16 . An automated machine  20 , such as a robot, moves the adapter arm  18 , the extended arms  14 , and the gripper assemblies  10  to desired positions to retrieve and deposit the work pieces  12 , such as between work stations. 
         [0015]      FIG. 2  shows an example of one of the gripper assemblies  10 .  FIG. 3  illustrates an exploded view of the gripper assembly  10 , and  FIG. 4  illustrates a cross-section through a portion of the gripper assembly  10 . With reference to these figures, the example gripper assembly  10  includes an actuator  30 , such as a pneumatic or hydraulic actuator. It is to be understood that other types of actuators may also be used. The actuator  30  includes a cylinder chamber  32  in which a piston  34  reciprocates. The piston  34  optionally includes bumpers  35   a , such as a resilient polymer, on each side to cushion impact of the piston  34  as it reciprocates within the cylinder chamber  32 . The piston  34  may also include a seal  35   b  such that the piston  34  separates the cylinder chamber  32  into two sealed sections. The piston  34  is coupled to a piston shaft  36  (i.e., a member) that extends from the actuator  30  into a gripper portion  38  of the gripper assembly  10 . Although a shaft is shown, other geometries may alternatively be used. Given this description, one of ordinary skill in the art will recognize the application of the disclosed example actuator  30  to devices other than grippers. 
         [0016]    The actuator  30  of the disclosed example includes two fluid ports  40   a  and  40   b  that fluidly connect to the respective separated sections of the cylinder chamber  32 . In this example, the fluid port  40   b  includes a fluid passage  42  for providing pressurized fluid to the section of the cylinder chamber  32  behind the piston  34  that exerts a force on a back side S 1  of the piston  34  to move the piston  34  and the piston shaft  36  in a forward direction D 1 . The fluid port  40   a  provides pressurized fluid to the section of the cylinder chamber  32  in front of the piston  34  that exerts a force on a front side S 2  the piston  34  to move the piston  34  and the piston shaft  36  in a retract direction D 2 . 
         [0017]    The actuator  30  also includes a first stop  44  near the front of the cylinder chamber  32  (relative to the gripper portion  38 ) and a second stop  46  near the back of the cylinder chamber  32  that define a range of travel  47  of the piston  34 . That is, the range of travel  47  corresponds to a stroke of the piston shaft  36 . 
         [0018]    In one example, the second stop  46  is a rear wall of a housing that forms the cylinder chamber  32 . Alternatively, the second stop  46  may be a separate piece that is secured into the back of the cylinder chamber  32 . 
         [0019]    The first stop  44  includes an opening  50 , such as a central bore, having a seal  52 . The piston shaft  36  extends through the opening  50  of the first stop  44  into the gripper portion  38 . 
         [0020]    The first stop  44  is adjustable relative to the cylinder chamber  32  and the second stop  46  to change the range of travel  47  and thereby change the stroke of the piston shaft  36 . In the illustrated example, the first stop  44  includes a seal  49  for sealing the cylinder chamber  32 , and a periphery having threads  54  that intermesh with corresponding threads  56  within the cylinder chamber  32 . Rotation of the first stop  44  about axis A axially moves the first stop  44  into or out of the cylinder chamber  32  to thereby change the range of travel  47 . The axial length of the threads  54 ,  56  determines a range of adjustability of the first stop  44 . The first stop  44  can thereby provide an infinite number of non-incremental positions between the first stop  44  and the second stop  46 . In other words, the first stop  44  is not limited to incremental preset positions and thereby provides a benefit of greater adjustability than known gripper assemblies. In some examples, acme type threading is used to provide ease of manufacturing and thread strength. 
         [0021]    In this example, the first stop  44  also includes a manual adjustment portion  60  having sockets  62  spaced circumferentially there about for engaging a tool to rotate the first stop  44 . The sockets  62  align with an opening  64  in a side wall  66  of the actuator  30 . In one example, a user inserts the tool into one of the sockets  62  to manually rotate the first stop  44  to achieve a desired range of travel  47 . Side access of the adjustment portion  60  provides the benefit of convenience for a user to adjust the range of travel  47  because the backs and fronts of grippers are not typically easily accessible in an industrial setting. 
         [0022]    Optionally, the side wall  66  of the actuator also includes another opening  68  for receiving a set screw  70  that can be selectively tightened to prevent rotation of the first stop  44  and thereby lock the first stop  44  in a desired position. In the illustrated example, an axial length of a forward surface  71  of the first stop  44  corresponds to the axial length of the threads  54  such that at least a portion of the forward surface  71  aligns with the opening  68  at all axial positions of the first stop  44 . The set screw  70  frictionally engages the forward surface  71  of the first stop  44  to resist rotation of the first stop  44 . 
         [0023]    The piston shaft  36  extends from the actuator  30  into the gripper portion  38 . The gripper portion  38  can be any of a variety of different arrangements and is not limited to the illustrated arrangement. In the disclosed example, the gripper portion  38  includes two side walls  80   a  and  80   b . The end of the piston shaft  36  is coupled with a head  82  having a pair of offset cam pins  84 . Other configurations may use a single cam pin. 
         [0024]    The cam pins  84  extend through respective cam slots  86   a  and  86   b  within respective gripper jaws  88   a  and  88   b . Each jaw  88   a  and  88   b  is pivotable about a pivot pin  90 . Depending on the design of the gripper portion  38 , a single pivot pin  90  may be used as shown, or each jaw  88   a  and  88   b  may have its own pivot pin. The ends of each cam pin  84  include a bushing  92  that is received into a slot  94  within each the side walls  80   a  and  80   b . The cam slots  86   a  and  86   b  have a S-shape such that when the actuator  30  extends or retracts the piston  34  and the piston shaft  36 , the jaws  88   a  and  88   b  pivot about the pivot pin  90  between a closed position and an open position as the cam pins  84  slide along the cam slots  86   a  and  86   b.    
         [0025]    In the disclosed example, movement of the piston  34  and piston shaft  36  in the forward direction D 1  opens the jaws  88   a  and  88   b , and movement in the retract direction D 2  closes the jaws  88   a  and  88   b . The range of travel  47  of the piston  34 , i.e., the piston stroke, corresponds to a degree to which the jaws open, represented generally in  FIG. 2  as numeral  96 . In this example, the degree of opening  96  is the angle between jaw faces  98  of the jaws  88   a  and  88   b  relative to axis A of the piston shaft  36 . It is to be understood that the degree  96  of jaw opening can also be expressed relative to other reference axes or to other portions of the jaws  88   a  and  88   b.    
         [0026]    The adjustability of the first stop  44  provides the advantage of allowing a user to limit the degree  96  to which the jaws  88   a  and  88   b  open to provide a desired clearance around machinery (e.g. dies, presses, etc.) in which the gripper assembly  10  operates. For example, the space within a press may be limited such that adjustment of the degree of opening  96  is needed to avoid interference between the jaws  88   a  and  88   b  and the press. 
         [0027]    The actuator  30  of the disclosed example gripper assembly  10  also provides a greater jaw opening force than a jaw closing force. That is, the force that the pressurized fluid exerts on the piston  34  in the forward direction D 1  is greater than the force in the retract direction D 2  because of a difference in the areas of the sides S 1  and S 2  of the piston  34 . The area of side S 2  is smaller than the area of side S 1  by an amount approximately equal to the area of the piston shaft  36  because the coupling between the piston shaft  36  and the side S 2  of the piston  34  reduces the area of the side S 2 . 
         [0028]    The greater amount of opening force provides the benefit of using a peak available force of the actuator  30  to overcome friction in the gripper portion  38 , which is greatest when moving the jaws  88   a  and  88   b  from closed to open (i.e., moving the piston  34  in the forward direction D 1 ). For example, there may be friction between the cam pins  84  and the cam slots  86   a  and  86   b  and friction between the bushings  92  and the slots  94  that must be overcome before the jaws  88   a  and  88   b  are able to open. In the disclosed example, the friction between the cam pins  84  and the cam slots  86   a  and  86   b  is greatest near the back ends  100  of the S-shaped cam slots  86   a  and  86   b.    
         [0029]    The disclosed example gripper assembly  10  therefore provides the advantage of permitting control over the degree to which the jaws  88   a  and  88   b  open without having to substitute different jaws and without using stops on the jaws  88   a  and  88   b . In some examples, this eliminates the need for replacement jaws, which require storage space and are vulnerable to misplacement. 
         [0030]    Although a combination of features is shown in the illustrated examples, not all of them need to be combined to realize the benefits of various embodiments of this disclosure. In other words, a system designed according to an embodiment of this disclosure will not necessarily include all of the features shown in any one of the Figures or all of the portions schematically shown in the Figures. Moreover, selected features of one example embodiment may be combined with selected features of other example embodiments. 
         [0031]    The preceding description is exemplary rather than limiting in nature. Variations and modifications to the disclosed examples may become apparent to those skilled in the art that do not necessarily depart from the essence of this disclosure. The scope of legal protection given to this disclosure can only be determined by studying the following claims.