Abstract:
A fluid device includes a rotationally oscillating piston within a sector-shaped chamber, a reciprocating ram for performing work and a link pivotally connected to both the piston and the ram. The piston moves the ram through the link to an extended position and a retracted position. When the ram is in its extended position, the link is moved to an over-center position locking the ram in the extended position. A manually operated unlocking device is provided for moving the piston to eliminate the over-center condition of the link.

Description:
FIELD OF THE INVENTION 
     The present invention relates to fluid motors for use in the machine tool field. More particularly, the present invention relates to fluid motors which utilize a simple air driven toggle mechanism for activating the shot pin units. 
     BACKGROUND OF THE INVENTION 
     Pneumatic piston and cylinder units are used in a great many different ways for many different functions in connection with the machine tool field. These functions include advancing and retracting tools of various types, advancing and retracting fixtures and the like, advancing and retracting work pieces, ejecting work pieces, work piece locating and work piece clamping, just to name a few. Often it is necessary for these pneumatic cylinder units to provide work functions at closely adjacent points on a work piece or machine. Because of the generally bulky configuration of these piston and cylinder units, it is often necessary in such cases to provide external linkages or levers extending from the piston rod to these closely adjacent points where the application of force is required. The existence of such external levers or other mechanisms presents not only a safety hazard, but it greatly complicates the apparatus necessary to accomplish a given function. In addition, the initial costs and the maintenance costs involved with this complex system are excessive. A good example of where it is often necessary to apply a force on closely spaced centers is in the automobile industry where sheet metal parts need to be precisely located while the parts are assembled, usually by welding. 
     Prior art devices which are narrow and do not sacrifice output force capacity have been developed. These devices include a rotationally oscillating piston located within a generally sector-shaped chamber, a reciprocating ram element for performing work, internal linkage means interconnecting the ram element and the piston, and means for supplying a fluid under pressure to the chamber. The device is designed to allow the pressurized fluid to be supplied to opposite sides of the piston in order to actuate and de-actuate the piston. 
     While the prior art devices have performed satisfactorily in the machine tool industry, the continued development of these devices has been directed towards improving their function, their performance and their durability. 
     SUMMARY OF THE INVENTION 
     The present invention provides the art with a shot pin which includes a rotary oscillating piston located in a sector-shaped chamber, a reciprocating ram for performing work, and an internal linkage assembly interconnecting the piston and the ram. The shot pin of the present invention includes a mechanism for preventing unlocking of the shot pin from its extended position, a manual unlocking device, a rectangular ram, a hardened scraper and seals which protect the ram as well as numerous other improvement over the systems disclosed in the prior art. 
     Other advantages and objects of the present invention will become apparent to those skilled in the art from the subsequent detailed description, appended claims and drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In the drawings which illustrate the best mode presently contemplated for carrying out the present invention: 
     FIG. 1 is a perspective view of an assembled shot pin in accordance with the present invention with the ram in the retracted position; 
     FIG. 2 is a top plan view of the shot pin shown in FIG. 1 with the ram in the retracted position; 
     FIG. 3 is a top plan view of the shot pin shown in FIG. 1 with the ram in the extended position; and 
     FIG. 4 is an exploded perspective view of the shot pin shown in FIG.  1 . 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring now to the drawings in which like reference numerals designate like or corresponding parts throughout the several views, there is shown in FIGS. 1-4, an improved shot pin in accordance with the present invention which is designated generally by the reference numeral  10 . Shot pin  10  comprises a body  12 , a cover plate  14 , a piston  16 , a ram  18  and a link  20 . Body  12  is preferably manufactured from aluminum and it defines an internal chamber  22 . Chamber  22  includes a generally rectangular section  24  for accepting ram  18 , a generally sector-shaped section  26  for accepting piston  16  and a generally circular section  28  for providing a pivot point for piston  16 . 
     Piston  16  is preferably manufactured from steel which is plated to prevent corrosion. Piston  16  includes a generally circular section  32  and a piston body  34 . Circular section  32  of piston  16  is positioned within circular section  28  of chamber  22  which simultaneously positions piston body  34  of piston  16  within sector-shaped section  26  of chamber  22 . Piston  16  pivots within chamber  22  guided by circular section  32  of piston  16  and circular section  28  of chamber  22 . A pair of rectangular U-shaped seals  36  seal the interface between piston  16  and body  12  and the interface between piston  16  and cover plate  14  after installation of cover plate  14  as detailed below. Seals  36  are preferably made from Carboxylated Nitrile which does not typically require lubrication. 
     Ram  18  is a generally rectangular shaped member preferably manufactured from steel. The rectangular shape of ram  18  prevents rotation of ram  18  and ram  18  is preferably plated to prevent corrosion or prevent the retention of contaminants such as weld spatter. Ram  18  is slidably disposed within rectangular section  24  of chamber  22  and is movable between a retracted position shown in FIG.  2  and an extended position shown in FIG. 3. A pair of rectangular U-shaped seals  40  seal the interface between ram  18  and body  12  and the interface between ram  18  and cover plate  14  after installation of cover plate  14  as detailed below. Seals  40  are preferably made from Carboxylated Nitrile which does not typically require lubrication. 
     Link  20  extends between piston  16  and ram  18  and is pivotally connected to each one. Link  20  is preferably manufactured from steel and is coated to prevent  10  corrosion. Link  20  includes a circular portion at one end which defines a circular aperture  44 . Aperture  44  is designed to mate with an aperture  46  extending through ram  18 . Link  20  is inserted into a slot  48  formed in the inner end of ram  18 . Aperture  44  is aligned with aperture  46  and a link pin  50  is inserted through apertures  44  and  46  to pivotally attach link  20  with ram  18 . Link pin  50  is preferably manufactured from bearing bronze. The opposite end of link  20  includes a circular portion which defines a circular aperture  54 . Aperture  54  is designed to mate with an aperture  56  extending through piston  16 . Link  20  is inserted into a slot  58  formed in piston body  34  of piston  16 . Aperture  54  is aligned with aperture  56  and a link pin  60  is inserted through apertures  54  and  56  to pivotally attach link  20  with piston  16 . Link pin  60  is preferably manufactured from bearing bronze. 
     The pivoting movement of piston  16  within chamber  22  thus causes reciprocating movement of ram  18  within chamber  22  through link  20 . Ram  18  is normally positioned in its retracted position as shown in FIG.  2 . When piston  16  is pivoted clockwise to the position shown in FIG. 3, link  20  moves ram  18  into its extended position. When the full clockwise movement of piston  16  has been reached and ram  18  is fully extended, link  20  is moved to an over-center linkage position to lock ram  18  in its fully extended position. Any axial load exerted on ram  18  towards its retracted position will attempt to move piston  16  further in a clockwise direction urging piston  16  against the wall of body  12 . When in its extended position, pivoting of piston  16  in a counter-clockwise direction will move ram  18  to its retracted position shown in FIG.  2 . Once piston  16 , ram  18  and link  20  are attached to each other and positioned within chamber  22 , cover  14  is sealingly attached to body  12  by a plurality of bolts  62  and a plurality of nuts  64 . Preferably, a non-silicone adhesive/sealant is used between body  12  and cover  14 . During assembly of ram  18 , it is necessary for ram  18  to fit precisely within rectangular section  24  of chamber  22 . Body  12  which forms chamber  22  is preferably made from aluminum and it is hard coated for wear purposes. A coating of Teflon® (Fluorocarbon) on body  12  makes up any tolerances and it produces an excellent ram  18  to body  12  fit with little tolerance and high lubricity. Cover  14  engages seals  36  and  40  to provide a sealed space  66  on one side of piston  16  and a sealed space  68  on the opposite side of piston  16 . 
     Body  12  defines a fluid port  70  which is in communication with sealed space  66  and a fluid port  72  which is in communication with sealed space  68 . When pressurized fluid is provided to sealed space  66  through fluid port  70 , piston  16  is moved in a counter-clockwise direction to the position shown in FIG.  2 . An elastomeric cushion  74  is positioned in a slot formed in body  12  to cushion the contact of piston  16  with body  12  in the counter-clockwise direction. The counter-clockwise movement of piston  16  retracts ram  18 . When pressurized fluid is provided to sealed chamber  68  through fluid port  72 , piston  16  is moved in a clockwise direction to the position shown in FIG.  3 . 
     The clockwise movement of piston  16  extends ram  18  and positions link  20  into its over-center position. Thus, by alternately supplying pressurized fluid to ports  70  and  72 , ram  18  can be alternately retracted and extended. 
     One feature of the present invention is its ability to lock ram  18  in its extended position (FIG. 3) in the event that fluid pressure to fluid port  72  is inadvertently lost. For safety reasons, once ram  18  is extended to punch, hold or otherwise engage an object, inadvertent loss of the fluid pressure to fluid port  72  could release the clamping load and possibly present a safety concern. Body  12  defines a retention bore  80  within which is positioned a ball plunger  82  and a sealed pipe plug  84 . Ball plunger  82  includes a ball  85  which is spring biased such that it extends into chamber  22 . Piston body  34  of piston  16  defines a dimpled detent  86  which engages ball  85  of ball plunger  82  when piston  16  is pivoted clockwise which is when ram  18  is extended and link  20  is in its over-center position. By supplying sufficient fluid pressure to chamber  66  through port  70 , ball  85  of ball plunger  82  will be released from detent  86  allowing the counter-clockwise pivoting of piston  16  and the retraction of ram  18 . 
     When fluid pressure has been inadvertently lost and piston  16  is being retained by ball plunger  82  and the over-center position of link  20 , it may be desirable to have the capability of manually retracting ram  18 . Body  12  defines a release aperture  88  through which an unlock pin  90  extends. A seal seals the interface between unlock pin  90  and body  12 . When piston  16  is being retained by ball plunger  82  with ram  18  in its extended position, axial load applied to unlock pin  90  will pivot piston  16  counterclockwise to manually retract ram  18 . Unlock pin  90  is assembled from inside chamber  22  and it includes a head or flange to prevent the possibility of “blow out”. 
     The outer end of ram  18  is protected by a plurality of elastomeric wiper seals  92  which are secured to body  12  through a pair of hardened scrapers  94  using a plurality of bolts  96 . Scrapers  94  and wipers  92  operate to clean ram  18  during its reciprocation motion. The pair of scrapers  94  constitute a single overlapping adjustable scraper. The design of each scraper  94  over the 90° angle of ram  18  produces a metal to metal optimum scraper while at the same time, scrapers  94  compress wipers  92  to further keep ram  18  clean. In addition, the design of wipers  92  and  94  allow for their replacement and adjustment from the outside of shot pin  10 . 
     The outer end of ram  18  defines an axial bore  100  and a transverse bore  102  which intersects bore  100 . Bore  100  is adapted to receive a head or a tool having a bore which aligns with bore  102 . Once assembled, a bolt  104  and nut  106  are used to secure the head or tool within bore  100 . A protective shield  108  is attached to ram  18  to further provide protection for ram  18 . 
     During the retraction and extension of ram  18 , the manufacturing system utilizing shot pin  10  may need to know whether ram  18  is in its extended position or if it is in its retracted position. Shot pin  10  includes a switch package  110  which is mounted to the exterior surface of cover  14 . Switch package  110  comprises a switch cover  112 , a status controller switch  114  and a pair of sleeves  116 . Status controller switch  114  is attached to switch cover  112  and switch cover  112  is attached to body  12  using a plurality of bolts  118 . A slot  120  formed into cover  14  accepts switch  114  and sleeves  116 . A pair of switch targets, not shown, are machined onto piston  16  to allow for the monitoring of the position of piston  16  and thus ram  18  by switch package  110 . Switch package  110  is in communication with the appropriate controller as is well known in the art. 
     The present invention provides a shot pin that has the ability to replace various models and sizes of prior art designs. The amount of stroke for ram  18  can be dictated by the design of piston  16  while still maintaining the advantages of piston  16  such as the over-center stop position, the detent ball locking feature and the manual unlock feature. The pivoting piston design of the present invention uses less air than an equivalent air cylinder of equal stroke and it is able to have withdrawal forces of 4500 pounds at 0.01 inches from the end of the stroke using 80 PSI air pressure. The amount of load exerted by the ram can be controlled by controlling either or both of the pressure of the pressurized fluid and the size of the piston area open to the pressurized fluid. 
     While the above detailed description describes the preferred embodiment of the present invention, it should be understood that the present invention is susceptible to modification, variation and alteration without deviating from the scope and fair meaning of the subjoined claims.