Abstract:
A removable locking plug that is easily inserted and/or removed from the cylinder portion of the locking mechanism. In the preferred embodiment, the plug is enclosed in a case hardened steel housing and contains a tumbler keyed locking mechanism.

Description:
BACKGROUND 
     1. Field of the Invention 
     The present invention relates generally to the field of locks, and more specifically to a removable plug cylinder lock such as may be used in vending machine coin boxes. 
     2. Prior Art 
     Locks and removable plug cylinder locks are well known in prior art. These locks are used in vending machines, cash boxes, parking meters and the like. An excellent discussion of the nature of the coin box used in the machines is found in U.S. Pat. No. 3,871,284, issued on Mar. 18, 1975 to Krise, for a “Coin Box and Lock Mechanism”. As explained in the &#39;284 patent, a coin box is typically securely affixed inside a vending machine with an opening in the vending machine to allow access to the contents of the coin box. A metal plate covers the opening with an appropriate fastening mechanism that requires a special access tool. A smaller aperture located in the cover, designed to allow special access to the fastening mechanism, is blocked by a cylinder plug lock. The current invention relates to improvements in cylinder plug lock technology. 
     The cylinder plug lock includes a locking plug portion that slides in and out of a hollow cylinder portion. The cylinder portion is rigidly affixed to the cover plate. When the plug is properly aligned the cylinder, the plug may be secured and the plug key removed. A problem arises when inserting the plug because prior art devices have made it sometimes difficult to align the plug properly within the cylinder. 
     Prior art lacks a plug that easily and unmistakably seats into a position that easily allows the removal of the plug key without removing the plug as well. Stated slightly differently, prior art devices did not provide a foolproof way to inform the installer that the plug was properly aligned, so that the installer could then remove the key without also removing the plug. Often, when using prior art devices, the installer was left fumbling, sometimes in the dark and sometimes in extreme cold while wearing gloves, trying to get the plug rotationally and/or axially aligned correctly to complete installation of the plug into a locked and secured position. 
     One prior art method of aligning the plug is to use a “c-clip” or spring bar that attaches to the plug and installs into a groove when the plug is inserted into the cylinder. The clip/bar is initially compressed within the cylinder until it aligns with the groove in the inside diameter of the cylinder and then expands into the groove to hold the plug in place while the locking mechanism is actuated. The ease with which the user aligns the plug to the cylinder depends on the flexibility of the clip and the ability of the user to feel and/or hear the clip/bar snap into place. If the clip/bar is too rigid, it will be difficult to remove the plug after it is aligned and seated. If the clip/bar is too flexible, it is harder to know when the groove that aligns and seats the plug within the cylinder is engaged. 
     Another common prior art technology requires two keys for the lock. The first key operates the tumbler mechanism within the lock. The second key is slightly longer and moves a pin that releases the plug and allows it to be removed from the cylinder. The use of the two keys raises the inevitable possibility that at least one of the keys will be lost, rendering the lock useless. 
     Thus, a method and a device are needed that allow a plug to be easily, quickly and unmistakably aligned within a lock cylinder when inserting the plug into the lock cylinder. Further, such a device should not require two keys to operate. 
     Further features and advantages of the present invention will be appreciated by reviewing the following drawings and detailed description of the invention. 
     BRIEF SUMMARY OF THE INVENTION 
     According to the present invention, a removable locking plug is easily inserted and/or removed from the cylinder portion of the locking mechanism. In the preferred embodiment, the plug is enclosed in a case hardened steel housing and contains a tumbler keyed locking mechanism. It has a key activated latch that extends and retracts radially from the sidewall of the plug housing. With the latch in the retracted position, the plug can fit snugly into the cylinder. 
     In the preferred embodiment, the cylinder has an inner flange at the rearward end. An alignment lug or pin extends radially inward from the wall at the inner flange. The plug has an alignment notch to receive the lug/pin when the plug is properly aligned within the cylinder. Cooperation between the alignment notch and the alignment pin acts to prevent rotational movement of the plug within the cylinder. When so aligned, the latch can be extended into a locking notch cut into the cylinder wall at the inner end, preventing the plug from both axial and rotational movement within the cylinder. The plug key may then be removed without removing the plug. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     For a further understanding of the objects and advantages of the present invention, reference should be had to the following detailed description, taken in conjunction with the accompanying drawing, in which like parts are given like reference numbers and wherein: 
     FIG. 1 is perspective of the plug aligned with, but separated from, the cylinder; 
     FIG. 2 is a side view of the plug, with the latch extended; 
     FIG. 3 is a side view of the cylinder; and 
     FIG. 4 is a side view of the cylinder installed on a planar surface. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     In the following description, for the purposes of explanation, specific component arrangements and constructions and other details are set forth in order to provide a more thorough understanding of the present invention. It will be apparent to those skilled in the art, however, that the present invention may be practiced without these specific details. In other instances, well known manufacturing methods and structures have not been described in detail so as not to obscure the present invention unnecessarily. 
     Referring first to FIG. 1, a cylinder with a removable plug lock  10  is shown with the plug  12  withdrawn from the cylinder  14 . The plug  12  includes a tumbler mechanism (not shown) that is operated by a removable key  16 . 
     Shown in FIG. 2 is a side elevation of one embodiment of the plug case  18 . In this embodiment, the plug case  18  has two locking notches  28 . The two locking notches  28  are of equal size and are positioned directly opposite of each other at the rearward base of the plug case  18 . The plug case  18  must have at least one locking notch  28 . However, the number of locking notches  28  is not a limiting factor in the invention. The plug  12  is encased in a case  18 , with the key  16  fully inserted into the plug  12 . The plug  12  and plug case  18  are cylindrical in shape. On the side of the plug  12 , at its base, the plug  12  has a latch  20  that is operated by the key  16  and extends or retracts. In FIGS. 1 and 2, the latch  20  is shown in the extended position. Also at the base of the plug  12  is a plug alignment notch  22 . Caps  24  are shown on both ends of the plug  12 . 
     Referring next to FIG. 3, the cylinder  14  is shown. In the preferred embodiment, the cylinder  14  has a forward flange  26  extending radially outwards. At its base, the cylinder has a locking notch  28  that cooperates with the latch  20  to prevent axial and rotational movement of the plug  12  when the latch  20  (not shown in FIG. 3) is extended. Extending below the forward flange  26  is a shaft  30  that has a smaller diameter than the flange. Threads  32  are placed on the outside surface of the shaft to allow a nut (not shown in this figure) to be threaded onto the cylinder  14 . 
     Referring back to FIG. 1, the plug  12  has a keyhole  40  mounted on its forward face  42 . The latch  20 , operated by the rotation of a key  16  inserted into the keyhole  40 , is capable of retracting into or extending beyond the surface of the plug casing  18 . With the latch  20  in its retracted position, the plug  12  may easily slide in and out of the cylinder  14 . When the plug  12  is fully inserted into the cylinder  14  and rotation of the plug  12  is prevented by cooperation between the cylinder alignment lug/pin  44  and the plug alignment notch  22 , the key  16  can be operated to advance or retract the latch  20 . 
     To insert the plug  12  into the cylinder  14  and into a position such that the key  16  can be removed from the keyhole  40 , the plug  12  is placed axially within the cylinder  14 . When the inward axial movement is impeded by the alignment lug/pin  44 , the plug  12  will not fully insert into the cylinder  14 . The plug  12  is then rotated in either direction until the plug alignment notch  22  is aligned, and mates with, the cylinder alignment pin  44 . Cooperation between the alignment notch  22  and the alignment pin  44  prevents further rotational movement of the plug  12  within the cylinder  14 . While the latch  20  is retracted, and the cylinder alignment pin  44  is cooperating with the plug alignment notch  22 , the key  16  within the keyhole  40  is prevented from rotating in one direction, but not in the opposite direction. When further rotational movement is blocked, the key  16  can then operate the latch  20 , extending it fully into the cylinder locking notch  28 . In its extended position, the latch  20  seats in the cut out locking notch  28  (best seen in FIG.  3 ), preventing axial and rotational movement of the plug  12  within the cylinder  14 . With the latch  20  extended into the cut out locking notch  28 , the plug  12  is firmly locked into the cylinder  14  and the key  16  can be withdrawn without removing the plug  12 . 
     In the preferred embodiment, the alignment lug/pin  44  is a small metal pin that protrudes radially inward into the inner surface of the cylinder shaft  30 . When the pin  44  is not mated with the alignment notch  22 , the plug  12  is prevented from being fully inserted into the cylinder  14 . When the pin  44  does align with the alignment notch  22 , the notch  22  slips over the pin  44  and the plug fully inserts into the cylinder  14 . 
     The alignment lug/pin  44  need not be of any particular size. However, it should be large enough to prevent the rotational movement of the plug  12 , when the alignment lug/pin  44  is mated with the alignment notch  22 . Further, the alignment plug/pin  44  need not be made of any specific material, so long as the material that is used is strong enough to prevent the rotation of the plug  12 , when the pin  44  and the notch  22  mate. Also, the pin  44  need not be of any specific shape or configuration, so long as it can successfully mate with the notch  22  when the plug  12  is seated within the cylinder  14 . A rearward flange  46  (seen in FIG. 1 at the base of the cylinder  14 ) extends radially inward on the rearward aperture opening. 
     For ease in operation, a corresponding pair of alignment notches  22  are provided, to correspond to the pair of locking notches  28 . Each alignment notch is positioned to engage the alignment lug/pin  44  when the latch  20  is aligned with an associated locking notch  28 . 
     Referring next to FIG. 4, the cylinder  14  is affixed to a planar surface. The cylinder  14  includes a shaft  30  with threads  32  on the exterior diameter of the shaft and a forward flange  26  extending radially outward on the forward aperture opening  50 . When used in the preferred embodiment, the cylinder  14  is attached to a planar surface with the cylinder&#39;s forward aperture opening  50  and flange  26  adjacent to the exterior surface  52  of a planar surface. The rearward portion of the forward flange  26  is flush with the exterior wall surface  52 . A nut  54  is threaded on the cylinder shaft  30  until it closes onto the interior wall surface  56 . In this manner, the cylinder  14  is firmly affixed onto a flat surface and access to the operating mechanism of the coin box can be restricted through the use of a lockable plug. 
     The description of the present invention has been made with respect to specific arrangements and constructions of a removable plug cylinder lock. It will be apparent to those skilled in the art that the foregoing description is for illustrative purposes only, and that various changes and modifications can be made to the present invention without departing from the overall spirit and scope of the present invention. The full extent of the present invention is defined and limited only by the following claims.