Apparatus for applying a cap to and removing the cap from a pin
TECHNICAL FIELD 
     This invention relates to devices for applying caps to, and removing caps from, pins. 
     DISCLOSURE OF INVENTION 
     In many arts, such as the printing art, it is desirable to have a pin, projecting upwardly from a bed, to accurately locate or register a printing plate, sheet of paper or the like on the bed. Since the printing plate, sheet of paper or the like may become inadvertently removed from the bed it is desirable to have a cap on the pin which frictionally engages the pin and, therefore, to a limited degree resists its removal from the pin. The present invention not only provides such a pin and cap, but also employs a cap holding means which may be part of a carrier or elevator that applies paper, printing plates, etc., to, and removes them from, the bed. As a printing plate, for example, is placed on the bed by the elevator, the cap holding means not only holds the cap but presses the cap onto the pin. 
     The cap holding means includes means to operate in either of two modes. In the first of these modes, hereinafter referred to as the &#34;holding mode,&#34; the cap holding means holds the cap with sufficient force that even if the cap is on the pin and the cap holding means is moved away from the pin the cap will be removed from the pin notwithstanding the restraint resulting from the frictional engagement of the cap and pin. In the second mode, hereinafter referred to as the &#34;release mode,&#34; the cap holding means applies little or no force to the cap. Therefore, after the cap has been applied to the pin during said holding mode, the release mode may be selected to thus permit the cap to remain on the pin while the cap holding means is removed from the vicinity of the pin. 
     When the cap holding means is in its holding mode, there is sufficient play to allow the cap to move laterally a substantial distance. Therefore, if the centerline of the cap is not in exact alignment with the centerline of the pin, the cap may move laterally as it is being applied to the pin, whereby the centerlines of the cap and pin are in alignment with each other. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a cross sectional view of the cap holding means (in its release mode) together with a cap. 
     FIG. 2 illustrates a bed from which registration pins 41 and 42 project. 
     FIG. 3 is a side view of the bed of FIG. 2. 
     FIG. 4 is a side view of an elevator 20 with a cap holding means mounted thereon. 
     FIG. 5 illustrates an elevator 20 which is carrying a cap 36 which will subsequently be applied to pin 42. 
     FIG. 6 shows the elevator 20 after it has moved to a position where it may place printing plate 42 onto bed 40. In this position there is at least approximate alignment of the centerlines of the cap and the pin respectively. 
     FIG. 7 illustrates the apparatus of FIG. 6 after the printing plate 43 has been placed on bed 40 and the caps 36 have been placed on the pins 42. 
     FIG. 8 shows the apparatus of FIG. 7 after the elevator 20 has moved away from bed 40 and the cap 36 is on the pin 42. 
    
    
     BEST MODE FOR CARRYING OUT THE INVENTION 
     An elevator 20 has a series of air holes 21 around its periphery. These air holes 21 are used to apply suction so that material such as a printing plate or a sheet of paper may be held onto the bottom flat surface of elevator 20. 
     The bed 40 has registration pins 41 and 42, and the printing plate or sheet of paper 43 (FIGS. 5 to 8) has holes through which the pins 41 and 42 pass when the printing plate or sheet of paper 43 is properly positioned on the bed 40. 
     The cap 36 has a body 33 made of soft iron or other material which will be attracted by a permanent magnet. The cap 36 defines a cylindrical cavity 32 and also has a resilient O ring 34 which projects slightly into the cavity 32 so as to frictionally engage the outer surface of pin 42. This frictional engagement will hold the cap 36 firmly on the pin 42. 
     The cap 36 also has an annular resilient pad 35 which engages the printing plate or sheet of paper 43 and prevents leakage of air around the pin 42. 
     The cap holding means comprises the following: 
     (a) a main body 22, 
     (b) two permanent magnets 23 
     (c) a non-magnetic tube 24 defining a hole 25 
     (d) solenoid 26 
     (e) solenoid armature 28 and pin 29 
     (f) cover 27 with skirt 30. 
     The cap holding means has two modes as follows: 
     The &#34;holding mode&#34; continues as long as the solenoid 26 is deenergized. In this mode the permanent magnets 23 attract cap 36 and hold the cap 36 firmly against the magnets 23. In this mode, the holding power of the magnets 23 is so strong that if the cap 36 is on pin 42, and if the elevator 20 is then moved upward the cap 36 will be pulled off of pin 32. In other words the holding power of magnets 23 is sufficient to overcome the frictional engagement between cap 36 and pin 42. 
     The device is in its &#34;release mode&#34; when the solenoid 26 is energized. The force placed on pin 29 when the solenoid is energized is sufficient to push the cap 36 out of contact with the magnets 23. In this mode there is no holding power on cap 36 by the magnets 23. 
     The overall operation is as follows. 
     Assume that it is desired to place the printing plate 42 on the bed 40 and to hold it in place with caps 36. 
     The bed 40 will remain in a fixed location during the following operations. 
     The elevator 20 (FIGS. 1 and 5) has the cap holding means together with a cap 36. Unlike FIG. 1, however, the cap holding means is in its &#34;holding mode&#34;; that is the cap 36 is in physical contact with magnets 23. The printing plate 43 is held against the lower face of elevator 20 by reason of suction. The various holes 21 around the periphery of the elevator 20 have suction applied at their upper ends via a suitable manifold 21a, and the printing plate 43 is held against the lower face of elevator 20 by reason of vacuum in holes 21. 
     As shown in FIG. 5 the elevator 20 is movable, and as shown in FIG. 6, it is moved until the holes in printing plate 43 align with the pins 42, at which time the centerline of cavity 32 is approximately aligned with the centerline of pin 42. 
     The elevator 20 is next lowered to place the printing plate 43 on the bed 40. At the same time the cap 36 moved onto pin 42. If the centerlines of the cap 36 and the pin 42 are not in alignment, the cap 36 moves transverse to its centerline until its centerline is aligned with that of the pin 42. The diameter of cap 36 is smaller than the diameter of the cavity in the cap holding means to allow for the transverse movement just mentioned. 
     Therefore, in FIG. 7 the elevator or carrier 20 has moved the printing plate 42, and the cap 36 (not shown) on pin 42 (not shown). Suction is applied to the lower ends of holes 45 in bed 40 to hold the printing plate firmly against the bed 40. 
     If it is desired to remove the elevator 20 from a position adjacent bed 40, the solenoid 26 is energized. This causes solenoid 26 to attract armature 28 which pushes downwardly on the pin 29 to apply sufficient pressure on cap 36 so that the cap 36 remains on the pin 42 notwithstanding the magnets 23. The elevator 20 may, therefore, be raised, as shown in FIG. 8, leaving cap 36 on the pin 42. The printing plate 43 remains on bed 40 since vacuum is applied to holes 45 but not to holes 21. 
     The bed 40 and the printing plate may now be sent to a scanning device or other processing machinery. During all such operations the plate 43 will be held in place not only by the vacuum in holes 45 but also by the caps 36. 
     After the printing plate 43 has been processed, it is desirable to remove it from the bed 40. To do this, the elevator 20 is moved into the position shown in FIG. 7. The solenoid 26 is now deenergized to place the cap holding means in its &#34;holding mode&#34;, the vacuum is no longer applied to holes 45, and vacuum is applied to holes 21. The elevator 20 is next raised. The holding power of magnets 23 overcomes the frictional engagement between cap 36 and pin 42, and the printing plate is held by the vacuum in holes 21. Therefore, as the elevator 20 is raised, the cap 36 and the printing plate 43 are raised with it. The printing plate 43 can be easily removed from elevator 20 as soon as the vacuum in holes 21 is turned off. 
     As a result, this invention provides means for easily and automatically applying a cap to and removing a cap from, a pin that is on a bed.