Abstract:
A powered clamp includes a pair of moveable members which engage one another to maintain, at least temporarily, a locking position of an arm when actuating fluid pressures have been decreased or lost. In another aspect of the present invention, the apparatus is simplified by engaging a slide rod with a rotatable hub. Furthermore, the overall packaging envelope required by the clamp is reduced by aligning the transverse axis of the rotatable hub with a longitudinal axis of an actuator.

Description:
BACKGROUND AND SUMMARY OF THE INVENTION  
         [0001]    The invention relates generally to clamping devices and particularly to a powered clamp having a toggle action with a self-locking feature.  
           [0002]    Powered clamps are commonly used in industrial applications for holding work pieces of many sizes and shapes during forming, welding and/or machining operations. Such devices typically include a pneumatically, hydraulically or electrically actuated cylinder which causes one or more arms to move through a desired range of rotational motion. Furthermore, the user may wish to actuate the arms in a contaminated environment having weld splatter, saw chips, coolants, dust, dirt and the like. One such conventional powered clamp is disclosed in U.S. Pat. No. 5,171,001 entitled “Sealed Power Clamp” which issued on Dec. 15, 1992 and is hereby incorporated herein by reference.  
           [0003]    Other traditional clamps have arms which typically move or release pressure upon the work piece when the actuating force is reduced or lost. Furthermore, the machining tolerances of the majority of the internal clamp components must be accurately controlled in order to achieve desired component part motions and to achieve satisfactory clamping forces.  
           [0004]    Another powered clamp disclosed in U.S. Pat. No. 5,884,903 entitled “Powered Clamp and Engaging Apparatus” issued on Mar. 23, 1999 and is hereby incorporated by reference. This clamp incorporates a variety of components including a slide, a link, a crank and a hub. The components also combine to provide a lost linear motion device to maximize arm unlocking forces. While the above-mentioned clamps have satisfactorily performed a desired function, it is desirable to provide a clamp having a reduced number of components. Also, it is desirable to provide a powered clamp that will not release its grip when actuating pressure is removed.  
           [0005]    In accordance with the present invention, an embodiment of the apparatus performs as a clamp with a moveable member or members which perform a clamping function. The clamp includes a pair of moveable members which mechanically butt against each other to maintain, at least temporarily, a locking position of an arm when actuating forces have been decreased or lost.  
           [0006]    The powered clamp apparatus of the present invention is highly advantageous over conventional clamps because the present invention includes a tapered self-locking feature for holding a rotated arm in a desired position even after loss of actuating force occurs. Thus, work pieces will not fall from their locked or engaged positions, thereby preventing work piece and equipment damage. Another advantage of the present invention apparatus is that the overall packaging envelope required by the clamp is reduced by aligning the transverse axis of a rotating hub with a longitudinal axis of a piston. The present invention is further advantageous by employing a slide rod including an angled surface which selectively engages a seat on the hub when the actuator is in a fully extended position. The slide rod and hub mating surfaces function to restrict movement of the actuator away from the fully extended position regardless of the presence of actuating fluid pressure. The present invention apparatus includes presence of actuating fluid pressure. The present invention apparatus includes an end cap having a pair of fluid ports. The end cap is rotatable about a longitudinal axis of the clamp to allow the user to easily connect the clamp to a fluid power source. Furthermore, the present invention advantageously includes a position sensor operable to indicate the presence or absence of an actuator at a predetermined location. A position sensor may be configured to accommodate electrical connections at twelve different orientations. The present invention apparatus is fully sealed and permanently lubricated and is therefore suitable for use in even the most contaminated environments. The power clamp apparatus is also very compact and lightweight, and may have its clamping or engaging arm easily preset to any one of a number of positions. The total rotational angle of the arm is also adjustable. Additional advantages and features of the present invention will become apparent from the following description and dependent claims, taking in conjunction with the accompanying drawings. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0007]    The present invention will become more fully understood from the detailed description and the accompanying drawings, wherein:  
         [0008]    [0008]FIG. 1 is a perspective view showing the preferred embodiment of a powered clamp apparatus of the present invention;  
         [0009]    [0009]FIG. 2 is an exploded perspective view depicting the present invention;  
         [0010]    [0010]FIG. 3 is a cross-sectional side view of the powered clamp of the present invention;  
         [0011]    [0011]FIG. 4 is a perspective view of an end cap constructed in accordance with the teachings of the present invention;  
         [0012]    [0012]FIG. 5 is a cross-sectional view taken along line  5 - 5  as shown in FIG. 4;  
         [0013]    [0013]FIG. 6 is a perspective view of a hub constructed in accordance with the teachings of the present invention;  
         [0014]    [0014]FIG. 7 is a top view depicting an alternate embodiment clamp having a single straight arm;  
         [0015]    [0015]FIG. 8 is a top view of an alternate embodiment clamp having a yoke arm;  
         [0016]    [0016]FIG. 9 is a top view of another alternate embodiment clamp having dual straight arms;  
         [0017]    [0017]FIG. 10 is a side view of a clamp constructed in accordance with the teachings of the present invention having an arm positioned at 90 degrees to the body when located in its fully rotated position;  
         [0018]    [0018]FIG. 11 is a side view of a clamp having an arm positioned substantially in-line with the body when the arm is in a fully rotated position;  
         [0019]    [0019]FIG. 12 is a partial perspective view of the clamp of the present invention having a position sensor oriented at an exemplary first position;  
         [0020]    [0020]FIG. 13 is a partial perspective view of a clamp of the present invention having the position sensor oriented at an alternate exemplary second position; and  
         [0021]    [0021]FIGS. 14-17 depict a slide rod, link and hub assembly at various positions during operation. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0022]    The following description of the preferred embodiment is merely exemplary in nature and is in no way intended to limit the invention, its application, or uses.  
         [0023]    Referring to FIGS. 1-5, the preferred embodiment of a powered clamp  20  includes a body  22 , an actuator  24 , a link  26 , a hub  28 , an end cap  30  and a yoke arm  32 . Yoke arm  32  is located externally to body  22  while the other previously referenced components are at least partially internally disposed within body  22 .  
         [0024]    Body  22  is forged or extruded and then machined from 6061-T651 aluminum as a unitary, substantially hollow, part. End cap  30  is coupled to the proximal end of body  22 . End cap  30  includes a substantially cylindrical portion  34  and a flange portion  36 . Cylindrical portion  34  includes a pair of annular seal grooves  38 . Elastomeric seals  40  are positioned within grooves  38  to sealingly engage a bore  42  extending through body  22 . Bore  42  extends along a longitudinal axis  44 . End cap  30  includes another annular groove  46  axially spaced apart from seal grooves  38 . Roll pins  48  extend through body  22  and are positioned within groove  46  to couple end cap  30  to body  22 . It should be appreciated that this method of attachment axially restrains end cap  30  from movement while allowing the end cap to rotate 360 degrees about longitudinal axis  44 .  
         [0025]    A first fluid port  50  and a second fluid port  52  are positioned on an end face  54  of flange portion  36 . First fluid port  50  is in fluid communication with a proximal end of bore  42 . Second fluid port  52  exits at an aperture  56  located between elastomeric seals  40 . Aperture  56  fluidly communicates with a passageway  58  extending substantially parallel to bore  42  within body  22 . Passageway  58  is in fluid communication with a distal end of bore  42 . A plug  60  is coupled to end cap  30  to assure that pressurized fluid entering second fluid port  52  exits at aperture  56  and supplies pressure to the distal end of bore  42 .  
         [0026]    Actuator  24  includes a piston  62  and a slide rod  64 . A stroke spacer  66  may be coupled to piston  62  to adjust the total range of rotation of yoke arm  32 . A set of stroke spacers is available to the user to vary the arm rotation range in increments of 15 degrees. It will be appreciated that any number of stroke spacers having varying thicknesses can be provided to achieve a desired total stroke range. Piston  62  is linearly moveable within bore  42 . Piston  62  is axially moved in response to pneumatic or hydraulic fluid pressures forcing the piston in either longitudinal direction. Slide rod  64  is coupled to piston  62  via a threaded fastener  68 . Slide rod  64  is axially translatable within a bore  70 . Bore  70  extends substantially parallel to but offset from longitudinal axis  44 . An annular piston seal  72  is provided between piston  62  and bore  42 . An annular slide rod seal  74  is positioned between slide rod  64  and bore  70 .  
         [0027]    Piston  62  includes a generally cylindrical body  75  having a flat  76  for use in conjunction with a sensor assembly  78  as will be described in greater detail hereinafter. Piston  62  includes a first end face  82  and a second end face  84 . Stroke spacer  66 , if necessary, is coupled to first end face  82  via a spacer fastener  86 . A shim pack  88  is coupled to second end face  84  of piston  62  by a shim fastener  90 . The thickness of shim pack  88  may be varied at final assembly to assure proper operation of clamp  20 . Specifically, the thickness of shim pack  88  accounts for variance in machining and assures that yoke arm  32  continues to exert a clamping force on a work piece even if supply pressure is reduced or lost. Shim pack  88  also functions to assure that slide rod  64  is not overly forced into contact with hub  28 . It is desirable for actuator  24  to be returned using available pressurized fluid acting on second end face  84  of piston  62  without additional assistance.  
         [0028]    Slide rod  64  is a substantially cylindrical member having a first end  92  and a bifurcated second end  94 . First end  92  is coupled to piston  62  as previously described. An aperture  96  extends through bifurcated second end  94 . Slide rod  64  includes a flat  98  to assure that the slide rod does not trigger sensor assembly  78  during actuation. Slide rod  64  further includes an angled surface  100  (FIGS. 3 and 14- 17 ) extending at a 5 degree angle. Angled surface  100  is positioned near second end  94 . Slide rod  64  is preferably constructed from ASTMA311 Class B chrome material. Angled surface  100  includes a Titanium Nitride treatment or is otherwise hardened to improve the longevity of slide rod  64 .  
         [0029]    Link  26  includes a first aperture  102  aligned with aperture  96  extending through bifurcated second end  94  from slide rod  64 . A pin  104  rotatably interconnects link  26  to slide rod  64 . Preferably, pin  104  is slip fit within aperture  96  for easy assembly.  
         [0030]    As shown in FIGS. 2 and 6, hub  28  has a cylindrically shaped peripheral surface  106  partially split by a laterally extending channel  108 . Peripheral surface  106  of hub  28  is rotatably received within a matching cross-bore  110  extending through the side walls of body  22 . Cross-bore  110  defines a transverse axis  111  substantially orthogonally intersecting longitudinal axis  44 . End portions  112  of hub  28  extend beyond and project outwardly from the side walls of body  22 . Each of end portions  112  include a pair of orthogonally oriented slots  114 . A threaded aperture  116  is also positioned in each of end portions  112 . Hub  28  also includes a pair of axially spaced apart annular grooves  118 . Elastomeric O-rings  120  are positioned within grooves  118  to sealingly engage cross-bore  110 . Within channel  108 , a seat  122  is formed or machined at a 5 degree self-locking angle. A recess  124  is formed within seat  122  to assure clearance is maintained between second end  94  of slide rod  64  and hub  28 . An aperture  126  extends through hub  28 . Link  26  includes a second aperture  128  aligned with aperture  126  of hub  28 . A pin  130  rotatably interconnects link  26  and hub  28 . A pair of set screws  132  capture pin  130  within aperture  126 . Hub  28  is formed from 4150HT HRS.  
         [0031]    With reference to FIG. 1, yoke arm  32  includes a pair of bifurcated legs  134  coupled to hub  28 . Each bifurcated leg  134  is positioned within one of slots  114  and is coupled to hub  28  with a threaded fastener  136 . Threaded fastener  136  extends through a counter bore  138  formed in leg  134  and threadingly engages threaded aperture  116 . Alternately, a singular arm  139  or pair of straight arms may be coupled to the faces of hub  28  as shown in FIGS. 7-9.  
         [0032]    As shown in FIGS. 10 and 11, the user may vary the final position of yoke arm  32  by choosing the appropriate slot  114 . Yoke arm  32  may be positioned substantially in line with longitudinal axis  44  as shown in FIG. 11. Alternatively, yoke arm  32  may be rotated to a position extending 90 degrees to longitudinal axis  44  when the arm is in the fully rotated or closed position as depicted in FIG. 10.  
         [0033]    As shown in FIGS. 2, 12 and  13 , sensor assembly  78  includes a first sensor head  140 , a second sensor head  142 , a cover  144  and a controller switch  146 . First sensor head  140  and second sensor head  142  are proximity sensors which sense the presence or absence of a component within a given distance of the sensor head. First and second sensor heads  140  and  142  are substantially identical to one another. Accordingly, only first sensor head  140  will be described in detail. First sensor head  140  includes a cylindrical body  147  having a first end face  148  and a second end face  150 . An annular elastomeric seal  152  is positioned between body  147  and a first sensor bore  154  extending from an outer surface of body  22  to bore  42 . Body  22  includes a second sensor bore  156  axially offset from first sensor bore  154 .  
         [0034]    First sensor head  140  is positioned within first sensor bore  154  such that first end face  148  is adjacent bore  42 . Second sensor head  142  is similarly positioned within second sensor bore  156 . Cover  144  is coupled to body  22  to restrict the sensor heads from being axially pushed out of their respective bores during pressurization of bore  42 . For example, second end face  150  of first sensor head  140  contacts cover  144  when bore  42  is pressurized. Controller switch  146  is mounted to cover  144 . Wires (not shown) interconnect first sensor head  140  and controller switch  146  as well as second sensor head  142  and controller switch  146 . The wires are at least partially positioned within a cavity  157  and concealed by cover  144 . Controller switch  146  includes a pivotable plug  158  selectively positionable in one of three locations. Plug  158  may extend generally parallel to the mounting plane defined by cover  144 , at 45 degrees thereto or at 90 degrees thereto. Furthermore, control switch  146  may be mounted to body  22  in one of four orientations relative to the body. Two such orientations are depicted at FIGS. 12 and 13. Accordingly, it should be appreciated that twelve plug position permutations are available to allow a user to easily couple sensor assembly  78  to a data collection device or programmable controller.  
         [0035]    Because the linear stroke of actuator  24  is adjusted by coupling spacers  66  of various thickness to piston  62 , sensor assembly  78  may be positioned at one designated location on body  22 . This is advantageous because it is not necessary to machine a plurality of apertures for receipt of sensor heads  140  and  142  for different strokes. Furthermore, the design of the present invention alleviates the need for sensor repositioning which may lead to inaccuracy possibly causing tool or component damage.  
         [0036]    As mentioned earlier, piston  62  includes a generally cylindrical body  75  having a flat  76  positioned thereon. The discontinuity between cylindrical body  75  and flat  76  provides a trigger for second sensor head  142 . When actuator  24  is in the fully extended position shown in FIG. 3, body  75  of piston  62  is positioned closely enough to the distal end of second sensor head  142  to emit a signal indicating the presence of the piston. In similar fashion, spacer  66  includes a body portion  160  and a lead portion  162 . Lead portion  162  has a smaller diameter than body portion  160 . The junction of the different diameters provides a triggering point to signal first sensor head  140 . When actuator  24  is in the fully retracted position, spacer  66  contacts end cap  30 . At this time, enlarged body portion  160  is positioned proximate to first end face  148  of first sensor head  140 .  
         [0037]    The sequence of operational steps may be observed with reference to FIGS. 14-17. Specifically, FIG. 14 shows hub  28  rotated 20 degrees from a location where actuator  24  is in a fully extended position as shown in FIG. 17. When comparing FIGS. 11-14 to one another in numerically ascending order, actuator  24  is moving toward the fully extended position. Yoke arm  32  simultaneously moves toward a clamped position. Movement in this direction is caused by providing a source of pressurized fluid to first fluid port  50 . Pressurized fluid acts on spacer  66  to drive actuator  24  toward the fully extended position. It will be appreciated that each of FIGS. 14-16 show slide rod  64  being spaced apart from hub  28 . Angled surface  100  does not cam or slide on seat  122 . Contact occurs only when actuator  24  is at the fully extended or closed position as shown in FIG. 17. At this time, angled surface  100  frictionally engages seat  122  to cause a self-locking condition. At the same time, link  26  is rotated to a slightly over-center position. The over-center position of link  26  is defined by the center line of pin  104  being positioned closer to the proximal end of clamp  20  than pin  130 . As such, a force applied to yoke arm  32  attempting to rotate hub  28  in a clockwise direction with reference to FIG. 17, would be resisted even if pressure being applied through first port  50  were to be released.  
         [0038]    Actuator  24  may be moved from the fully extended position shown in FIG. 3 into a retracted position by venting pressure from first fluid port  50  and applying pressure through second fluid port  52 . Pressure applied from second fluid port  52  acts on second end face  84  of piston  62  to cause angled surface  100  to disengage from contact with seat  122 . Actuator  24  may be fully returned when spacer  66  contacts end cap  30 . Hub  28  and yoke arm  32  are rotated to an open or returned position at this time.  
         [0039]    The powered clamp of the present invention has further advantageous features. The powered clamp of the present invention has a single hub capable of accommodating left, right or dual arm attachments. The dual slots formed in the end portions of the hub allow for changing the position of the arm without disassembling the internal mechanism of the powered clamp. The arm may be mounted in one of two positions. Additionally, the present invention encourages simplified arm mounting or changeover using a single threaded fastener thereby eliminating pressed-on arms, jack screws or set screw retention. The total angle of arm displacement may be easily adjusted by removal of the end cap and replacement of the spacer.  
         [0040]    While an embodiment of the powered clamp has been disclosed, it will be appreciated that various modifications may be made without departing from the scope of the present invention. For example, the slide rod, link, hub and arm may be partially or totally disposed externally from a body. Also, various other actuating mechanisms may be employed to move the slide rod such as electric motors, internal combustion motors or manual actuation in combination with a rack and pinion mechanism, gears, pulleys, screw drives or the like. Moreover, the moving arm may have many different shapes for engaging or holding a variety of work pieces or instruments. The specific shapes and moving motions of the slide rod, link and hub may be modified or combined while maintaining various of the other novel aspects of the present invention. Various materials and manufacturing processes have been disclosed in exemplary fashion. However, other materials and processes may be employed. It is intended by the following claims to cover these and other departures from the disclosed embodiment which fall within the true spirit of this invention.