Abstract:
A clamp having a lock is provided. In another aspect, a fail safe lock maintains the position of a clamping member when fluid pressure or other actuating power is undesirably reduced. Another aspect employs teeth on a locking structure which engage matching teeth on a shaft where engagement of the teeth prevent unclamping of a workpiece. In still another aspect, a manual override member disengages a lock in order to unclamp a workpiece.

Description:
BACKGROUND 
     The disclosure pertains generally to powered clamps and more particularly to a powered clamp having a fail safe lock. 
     It is well known to employ powered clamps to retain sheet metal panels during welding or other assembly plant operations. Examples of such powered clamps include U.S. Pat. No. 5,165,670 entitled “Retracting Power Clamp” issued to Sawdon on Nov. 24, 1992, and U.S. Pat. No. 5,118,088 entitled “Power Clamp” which issued to Sawdon on Jun. 2, 1992; both of which are incorporated by reference herein. Traditional power clamps, however, are prone to unclamping the panel if the fluid pressure is lost. This can lead to damaged or misaligned parts. 
     More recently, detent and plunger arrangements, and offset piston mechanisms have been provided in an effort to overcome the traditional pressure lost concerns. For example, reference should be made to U.S. Pat. No. 6,378,855 entitled “Locking Pin Clamp” which issued to Sawdon et al. on Apr. 30, 2002, and U.S. Pat. No. 6,059,277 entitled “Retracting Power Clamp” which issued to Sawdon et al. on May 9, 2000; both of which are incorporated by reference herein. Notwithstanding, while the above-identified patents disclose significant inventions, there is still room for further improvement. 
     SUMMARY 
     In accordance with the present invention, a clamp having a lock is provided. In another aspect of the present invention, a fail safe lock maintains the position of a clamping member when fluid pressure or other actuating power is undesirably reduced. Another aspect of the present invention employs teeth on a locking structure which engage matching teeth on a rod or shaft where engagement of the teeth prevent unclamping of a workpiece. In still another aspect of the present invention, a manual override member disengages a lock in order to unclamp a workpiece. Yet another aspect of the present invention includes a cam and pin arrangement for a rotating pin clamp and a method of manufacturing same. A further aspect employs a clamp with longitudinal fluid flow paths through a housing with at least one of the paths extending internally through a piston. A method of using a locating pin clamp with a fail safe lock is also provided. 
     The present clamp is advantageous over conventional devices in that the present clamp achieves a more precise and secure locking function in order to maintain a clamping member in its workpiece-clamping position. Another advantageous aspect of the present clamp uses fluid pressure to disengage the lock from a movable member rather than prior camming or mechanical detent interfaces; in other words, the use of fluid pressure to retract the lock in the present clamp directly corresponds to clamping fluid pressure loss, rather than the mechanically indirect actions in some prior devices. The present clamp further employs a modularized body or housing, requires a minimal amount of parts, is easier and less costly to manufacture, and is easier to assemble as compared to certain conventional devices. Additional advantages and features of the present invention will become apparent from the following description and appended claims taken in conjunction with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The drawings described herein are for illustrative purposes only of selected embodiments and not all possible implementations, and are not intended to limit the scope of the present disclosure. 
         FIG. 1  is a side elevational view showing a first embodiment of a pin clamp shown in a workpiece-clamping position and with a lock in a retracted position; 
         FIG. 2  is a longitudinal, cross-sectional view, taken along line  2 - 2  of  FIG. 1 , showing the first embodiment pin clamp in the workpiece-clamping position with the lock in the retracted position; 
         FIG. 3  is an exploded perspective view showing various components of the first embodiment pin clamp; 
         FIG. 4  is a longitudinal, cross-sectional view showing the components of the first embodiment pin clamp in the workpiece-clamping position and the lock in an advanced and locking position; 
         FIG. 5  is a longitudinal, cross-sectional view showing the components of the first embodiment pin clamp in the workpiece-clamping position and the lock in the retracted position; 
         FIG. 6  is an enlarged longitudinal, sectional view, similar to that of  FIG. 5 , showing the first embodiment pin clamp with the lock in the retracted position; 
         FIG. 7  is a cross-sectional view, taken along line  7 - 7  of  FIG. 4 , showing the first embodiment pin clamp with the lock in the advanced and locking position; 
         FIG. 8  is a cross-sectional view, like that of  FIG. 7 , showing the first embodiment pin clamp with the lock in the retracted position; 
         FIG. 9  is a perspective view showing a second embodiment of the pin clamp in a releasing and unclamping position; 
         FIG. 10  is a longitudinal, sectional view showing the second embodiment of the pin clamp in a workpiece-clamping position and with a lock in an advanced and locking position; 
         FIG. 11  is a longitudinal, sectional view, like that of  FIG. 9 , showing the second embodiment pin clamp in an unclamping position and with the lock in a retracted position; 
         FIG. 12  is a longitudinal, sectional view taken  90 ° to that of  FIG. 11 , showing the second embodiment pin clamp in the releasing and unclamping position; 
         FIG. 13  is a perspective view, with the housing removed, showing the second embodiment pin clamp in the clamping position; 
         FIG. 14  is a perspective view, like that of  FIG. 13 , showing the second embodiment pin clamp in the released and unclamping position; 
         FIG. 15  is a top elevational view showing the second embodiment pin clamp in the clamping position; 
         FIG. 16  is a cross-sectional view, taken along line  16 - 16  of  FIG. 10 , showing the second embodiment pin clamp with the lock in the advanced and locking position; and 
         FIG. 17  is a partially schematic bottom elevational view showing the second embodiment pin clamp. 
     
    
    
     DETAILED DESCRIPTION 
     A locating pin clamp assembly  21  is shown in  FIGS. 1-4 . Clamp assembly  21  includes a pair of generally cylindrical housings or bodies  23  and  25  upon which is affixed a support cap  27 . A tapered locating pin  29  is mounted to and projects from cap  27 . A longitudinally elongated slot  31  is open along one lateral side of and through the center of locating pin  29 . A clamping arm or member  33  is longitudinally and laterally movable within slot  31  of locating pin  29  such that a hook shaped distal end  35  of clamping arm  33  can be moved from a retracted and releasing position hidden within locating pin  29  to an advanced and clamping position (shown in  FIG. 1 ) where the distal end contacts against and clamps a workpiece  37  against cap  27  after a hole within workpiece  37  has been aligned with and circumferentially surrounds locating pin  29 . This is ideally suited for locating and holding the workpiece, which is preferably but not limited to a sheet metal, automotive vehicular body panel, during welding or other manufacturing plant operations. 
     Clamp assembly  21  further includes a piston  51 , a piston rod or shaft  53 , a locking rod or shaft  55 , a locking mechanism  57 , and multiple elastomeric O-rings or generally V-shaped seals  59 . A pivot pin  61  located adjacent the first end of piston rod  53  is movable within a camming slot  63  of clamping arm  33 . Furthermore, piston rod  53  is affixed within the center of piston  51 . Thus, fluid, preferably pneumatic, pressure actuates piston  51  to advance and retract piston rod  53  and locking rod  55  in a longitudinal direction along a central axis  65  of clamp assembly  21 . This piston and rod movement concurrently drive clamping arm  33  between its clamping and releasing positions which include longitudinally linear movement along axis  65  and rotational movement toward and away from axis  65 . Piston  51  is movable within a piston chamber  67  which is in fluid communication with an inlet retraction port  81 , an inlet advancing port  83 , an outlet advancing port  85  and an outlet retracting port  87 . The inlet ports are connected to an air compressor or other pressurized fluid source. Internal passageways connect the port to the piston chamber  67 . 
     Locking rod  55  has a generally cylindrical exterior surface  91  and a generally hollow center  93 . A threaded bolt  95  is located within hollow center  93  of the locking rod for fastening locking rod  55  to a proximal hollow end  97  of piston rod  53 . Locking rod  55  and the adjacent end  97  of the piston rod are on an opposite side of piston  51  from clamping arm  33 . Locking rod  55  is linearly and longitudinally movable in a bore  99  within a center of housing  23 . A pair of O-rings  101  seal exterior surface  91  of locking rod  55  adjacent its end, to an internal surface  103  defining bore  99 . At least twenty-five generally circumferentially arranged groove-like teeth  105  are machined into exterior surface  91  of locking rod  55  between O-rings  101 . Teeth  105  are positioned to allow lock engagement anywhere during the entire stroke; small radii are present at the peaks of the one millimeter pitch and sixty degree angled teeth and a 10 micro finish is used. A threaded bolt  111  is optionally enmeshed with internal threads within hollow center  93  of locking rod  55 . Optional bolt  111  provides a manual pulling projection to allow a maintenance technician to manually retract or advance piston  51  and clamping arm  33  when the pneumatic pressure is off, and when a manual override screw is actuated as will be discussed hereinafter. 
     As can best be observed in  FIGS. 3-8 , locking mechanism  57  includes a partially hollow lock structure  151 , a compression spring  153 , a plate  155  and an override screw  157 . A set of fastening screws  159  attach plate  155  to an outside surface of housing  23  after lock  151  and spring  153  are assembled within a laterally oriented and cylindrically shaped passageway  171  extending from the outside surface of housing  23  to a laterally enlarged middle section of bore  99 . An elastomeric O-ring  173  circumferentially seals an exterior of lock  151  to a wall defining passageway  171 . One end of compression spring  153  abuts against an interior of plate  155  while an opposite end of spring  153  compresses and biases against a back side and internal face within the hollow of lock  151 . Lock  151  has at least twenty teeth similar in construction to those on the locking rod, on a partially circular leading surface  175  of the lock. A dowl pin  160  is loosely inserted into a hole of lock  151 , offset from both the hollow spring cavity and a threaded bore for override screw  157 . An opposite end of dowl pin  160  is snuggly received within a tighter hole of end plate  155 . Dowl pin  160  prevents rotation of lock  151  relative to its bore  171 . There is a slight clearance between the dowl and its hole within lock  151  to allow for relative advancing and retracting movement therebetween. 
     When lock is retracted to the unlocking position shown in  FIGS. 5 ,  6  and  8 , a radial gap  177  is laterally created between the external surface of locking rod  55  and the internal surfaces  103  and  175  of housing  23  and lock  151 , respectively, and longitudinally between O-rings  101 . This gap provides a fluid passageway to allow air entering an inlet port  179  to flow around the middle of locking shaft  55  and outwardly push lock  151  into its retracted position. In the lock retracted position, teeth  181  are disengaged from teeth  105  of locking rod  55  such that locking rod  55  and the attached piston rod  53 , piston  51  and clamping arm  33  (see  FIG. 2 ) can freely advance and retract pursuant to the normal and desired pressurized actuation against the piston. However, if pneumatic pressure is undesirably lost or weakened from inlet ports  179  and  81  (see  FIG. 2 ) then the air no longer causes lock  151  retraction and spring  153  therefore pushes lock away from plate  155  so that the teeth of lock  151  and locking rod  55  are engaged. This advantageously prevents unclamping of the clamping arm such that the workpiece is firmly held in position even during a power failure, pressure loss or other such undesirable manufacturing plant situation. 
     Override screw  157  provides a manual lock release function. Override screw  157  is essentially a shoulder screw having an enlarged head suitable for receiving an Allen head wrench or other screwdriver blade, an unthreaded shoulder which allows for movement relative to plate  155 , and a threaded shank which engages an internal threaded hole  187  in lock  151 . Override screw is offset from spring  153 . If lock  151  is advanced to its locking shaft-engaging position, such as shown in  FIGS. 4 and 7 , but it is desired to advance the rods, piston and clamping arm to unclamp the workpiece, then the technician can manually tighten override screw  157  so that it withdraws lock  151  away from locking rod  55  to release their teeth. 
     A second embodiment of a locating pin clamp  221  is shown in  FIGS. 9-17 . Clamp assembly  221  includes a generally cylindrical housing  223  upon which is affixed a support cap  227 . A generally cylindrical extension  228  integrally extends as a single piece from the lateral portion of cap  227  and a top edge serves as an abutment platform against which sheet metal workpieces  237  are retained by a clamping finger or member ledge  233  of a tapered locating pin  229 . Pin  229  is slightly eccentric relative to an axis  313  to provide the clamping area when rotated; this is shown in  FIG. 15 . A mounting bracket  230  is bolted to an outside of housing  223  for securing clamp assembly  221  to a factory floor-mounted fixture, machine or the like. 
     Clamp assembly  221  further includes a piston  251 , a piston rod or shaft  253 , a locking rod or shaft  255 , a locking assembly  257 , and multiple elastomeric O-rings or generally V-shaped seals  259 . Piston rod  253  is integrally connected to piston  251  as a single piece and locking rod  255  is coaxially attached to piston  251 . Piston  251  and rods  253  and  255  longitudinally advance and retract along axis  313  within a longitudinal bore  260  within cap  227  and a bore  309  in housing  223 . Furthermore, piston  251  longitudinally advances and retracts within a piston chamber  262  defined by internal surfaces of housing  223  and cap  227 . The spring and fluid actuated locking assembly  257  is generally the same as with the aforementioned first embodiment clamp assembly, such that teeth of a lock  252  operably engage matching teeth  205  of locking rod  255  when air pressure is undesirably reduced or lost to both lock  252  and piston  251 . 
     A cam and cam follower mechanism  301  includes a pair of generally spirally-shaped cams  303  longitudinally elongated and oriented on opposite outside surfaces of locking rod  255 . Mechanism  301  further includes a pair of cam followers, more specifically a generally cylindrical dowl pin  305  which interfaces with each cam  303 . Each dowl pin is located within a laterally elongated hole  307  machined completely through opposite exterior surfaces of housing  223  for easy manufacture and assembly. Each hole  307  intersects outboard portions of longitudinally oriented bore  309  of housing  223  such that dowl pins  305  disposed therein ride along and serve to rotate locking rod  255 ; this serves to simultaneously rotate a drive pin  311  and the attached locating pin  229  and clamping finger  233  concurrently therewith about longitudinal advancing and retracting axis  313  from a released and unclamping position (see  FIG. 11 ) to a retracted and clamping position (see  FIGS. 10 and 15 ). Roll pins  321  or the like secure driving pin  311  to locating pin  229  and locking rod  255 . Externally threaded plugs  323  inserted into each end of lateral holes  307  of housing  223  to loosely retain dowl pins  305  therebetween. It may be desirable to apply grease to dowl pins  305  and/or cam surfaces  303 . 
     The camming mechanism provides approximately 45° of rotation to clamping finger  233  between its released and clamping positions. An adjustment screw  241 , however, is provided to add further precision to the exact clamping position and to allow for adjustment of same after the clamp is assembled and used in a manufacturing plant environment. Adjustment screw  241  is threadably enmeshed within an aperture of cap  227  and is rotatable by an Allen head wrench, or alternately a screwdriver. A leading end  243  of adjustment screw  241  protrudes into piston chamber  262 , and operably abuts against an opposing face of piston  251  in order to set and limit the advancing stroke travel of the piston. A supplemental set screw  245  is laterally enmeshed in an associated hole in cap  227 . Set screw  245  is made of a softer brass material such that a leading end thereof is pushed into external threads of adjusting screw  241  to hold it in its desired adjustment position and to prevent loosening or backing out of adjustment screw  241  during normal repeated usage of clamp assembly  221 . Adjustment screw  241  advantageously changes the total stroke distance to allow clamping of different workpiece thicknesses or quantities but in an externally accessible and quick manner. 
     An externally threaded and longitudinally elongated bolt  331  is attached adjacent an end of locking rod  255  on an opposite side of piston  251  from clamping finger  233 . Bolt  331  has a metallic sensor flag  333  attached to a leading end thereof by a circlip or the like. Bolt  331  and the attached flag  333  can be longitudinally positioned at various locations within a cavity  335  inside locking rod  255 . The location of flag  333  is sensed by sensors  337  of a proximity switch in order for the proximity switch to determine the stroke position of locking rod  255  and the associated piston and clamping finger which longitudinally advance and retract therewith. Accordingly, bolt  331  and the internal cavity location of flag  333  serve to provide a compactly packaged and protected location while providing essentially infinite adjustment of the sensing flag, with the adjustment being accessible from outside of the clamp after the clamp has been assembled and installed in the manufacturing plant. 
     An air pressure port or inlet  351  for clamping/piston retraction, a port or inlet  353  for loading/unloading and piston advancement, and a constant air port or inlet  355  for retracting lock  252 , are all present on the bottom end of housing  223 . A single pneumatic supply line is connected to a Tee supply from which the constant air has an air dump valve located in a safe area outside of the manufacturing plant working cell. Air conduits  357  and  359  are in communication with inlets  351  and  353 , respectively, and are longitudinally drilled from the bottom of housing  223 . Conduit  359  is directly accessible to the bottom portion of piston chamber  262  between piston  251  and the opposing face of housing  223 . A hollow tube  361  provides a pneumatic flow path between an upper end of conduit  357  and a passageway  363  in cap  227 , which is then accessible to an upper portion of piston chamber  262  between piston  251  and the opposing surface of cap  227 . Tube  361  is firmly and stationarily trapped between housing  223  and cap  227 , and there is a slight lateral clearance between the middle of tube  361  and an adjacent aperture in piston  251  to allow the piston to move relative to the tube. O-rings are provided to seal the exterior of tube  361  to the adjacent portions of the housing and piston. This tube advantageously provides a multi-functional benefit of substantially preventing rotation of piston  251  while also providing a very direct fluid flow path from the bottom end of housing  223  to the opposite and upper end of the piston without requiring the traditional lateral machined apertures and the many expensive to make right angles of conventional clamp flow paths. This direct and longitudinal flow path arrangement internal with the piston advantageously allows lower cost and easier flow path manufacturing while also allowing for thinner housing walls and the associated reduction in material weight. 
     While various features of the present invention have been disclosed, it should be appreciated that modifications can be made. For example, the locking mechanism may engage a piston rod between a piston and clamping arm although certain advantages of the present clamps may not be realized. Furthermore, the locking mechanism disclosed herein may engage shafts or other moveable components used in other types of powered clamps and grippers such as those disclosed in the following U.S. Pat. No. 7,370,856 entitled “Rotating Head Pin Clamp” which issued to Sawdon et al. on May 13, 2008; U.S. Pat. No. 5,884,903 entitled “Powered Clamp and Gauging Apparatus” which issued to Sawdon on Mar. 23, 1999; and U.S. Pat. No. 5,853,211 entitled “Universal Gripper” which issued to Sawdon et al. on Dec. 29, 1998; all of which are incorporated by reference herein, however, all of the advantages of the present clamps may not be obtained. Moreover, different mechanical locking patterns may be utilized between the lock and locking shaft instead of the disclosed teeth to create a firm locking engagement; for example, a knurl pattern, a large array of facing pyramidal projections, multiple tapered pin and hole features, and the like may be used, although such may forego the benefits realized with the present clamps. It is alternately envisioned that differently shaped clamping arms, bodies, rods and locks may be employed, although certain advantages of the present clamps may not be achieved. Alternate acuators, such as hydraulically-powered pistons or electromagnetic drivers, can be used, however, various advantages of the preferred clamps may be forfeited. It is intended by the following claims to cover these and any other departures from the disclosed embodiment which follow in the true spirit of this invention.