Spring-loaded oscillating cam latch
BACKGROUND OF THE INVENTION 
     Many mechanisms have been devised for installation on cabinet doors and the like to provide positive locking of the doors in closed position while permitting convenience in operation of the door. An important feature often sought to be attained is to make it harder to open the door than to close it to discourage unauthorized access. Other objectives are simplicity in operation, manufacture and construction, as well as installation. The closest art to the invention of the applicant is set forth below. 
     Bacon, U.S. Pat. No. 2,552,390 employs a cam faced latch employing a coiled spring which works through a link and lever machanism so that the action of the spring is to hold the latch against the catch when opening the door and aid the operation of the latch when closing the door. 
     Nottingham, U.S. Pat. No. 2,626,170 likewise uses a spring, in this case a leaf spring, operating against a pin in a slot in the cam so that because of the configuration of the latch member, the combined action of the spring and pin against it also requires more force to open and to close. 
     Sealey, U.S. Pat. No. 4,230,352 uses a complicated combination of rollers, latches and cam, the rollers being spring-loaded so that pressure externally on the door is transmitted through the linkage to release the catch and permit the door to open. 
     While applicant also employs a spring, cam, and rollers or pins, he uses them in an entirely different combination and configuration so that the method of operation of his latch differs entirely from that of the prior art as will be evident from the description below. 
     SUMMARY OF THE INVENTION My invention entails the use of a single moving part comprising a body member which includes the housing for spring, stationary pins and cam shaped latch member which is exceedingly simple in construction, offers ease of operation and installation and when installed on a cabinet door or the like makes it harder to open the door than to close it. 
    
    
     DESCRIPTION OF THE FIGURES 
     FIG. 1 is a top view of a cabinet partly in section showing my device installed in a cabinet. 
     FIG. 2 is an upper right frontal exploded perspective of my device. 
     FIG. 3 is a right side view of the assembly. 
     FIG. 4 is a front view of the assembly. 
     FIG. 5 is a top sectional view along lines 5--5 showing the basic mechanism in position in a housing. 
     FIG. 6A shows the position of the mechanism when closing the door. 
     FIG. 6B shows the position of the mechanism when opening the door. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Located through the body are oppositely spaced arcuate slots 2A and 2B. These slots engage stationary pins 3A and 3B respectively upon which the body 1 oscillates back and forth within slots 2A and 2B. 
     Centrally located through the body 1 is circular opening 1C which communicated with milled recesses 1A and 1B. These are provided to receive helical spring 4 with its ends 4A and 4B protruding through the recesses 1A and 1B respectively to engage the stationary pins 3A and 3B mentioned above. 
     The catch unit 6 here shown attached to the door of a cabinet as described below, but such a catch unit may be part of any other mechanical movement which it is desired to latch and unlatch. 
     Forming an integral part of body 1 is tongue 7 having a convex cam surface 7A which operates on opening of the door and flat surface 7B which operates on closing of the door, the surfaces meeting at catch point P as described more fully below. 
     The installation of my device on a cabinet is best seen on FIG. 1 wherein 8 shows the side of the cabinet, 9 the door and 9A the handle. 
     As employed in this embodiment, the body 1 is located within latch housing 10 in which there is a snug sliding fit. The housing is provided with holes 11 through which screws 11A effect fastening of the device to the floor of the cabinet 17. Holes 12 in the housing permit the insertion of pins 3A and 3B which are further held in position by cotter pin 16 after passing through their respective slots in body 1, namely 2A and 2B respectively, all of which may be clearly seen on FIG. 2. There is also shown there, opening 13 in the housing 4 permitting the protrusion of tongue 7 for engagement with catch member 6. The latter is supported by bracket 14 which in turn is fastened to door 9 by screws 15. 
     It should be noted that tongue 7 is located eccentrically to body 1 so that convex surface 7A is closer to pin 3B than flat surface 7B is to pin 3A. The reason for this will be apparent from a description of the operation of my device set forth below. 
     OPERATION 
     Referring again to the figures, at the start of the operation the door 9 is in closed position and catch member 6 is positioned against tongue 7 as shown in FIG. 1, the body of the latch being in a central or normal position as shown in the section view of FIG. 5. When opening door 9, catch member 6 is caused to move against convex surface 7A and rotate the entire body 1 around pin 3B and against the action of spring 4 against pin 3A. This is best seen on FIG. 6B. After catch member 6 passes catch point P, the tongue member is released and the action of spring 4 causes the body to spring back again to its normal central position of FIG. 1 or FIG. 5. Door 9 is then free to swing wide open. When closing, the door is brought back until catch member 6 contacts flat surface 7B of tongue 7. Further movement of the door rotates body 1 around pin 3A and against the action of pin 3B against spring 4. This is best seen on FIG. 6A. Here again, after catch point P is passed, body 1 by the action of spring 4 is caused to spring back so that tongue 7 is again in a neutral or central position, catch member 6 being moved back to its initial closed position shown on FIG. 1. 
     When the door is being opened, catch member 6 has a moment arm of the distance between where it makes contact to convex surface 7A and where spring end 4B contacts pin 3B. This is resisted by the wing 4A of spring 4, having its moment arm from the contact point between pin 3A and the contact point between pin 3B and spring end 4B. When closing, the catch member has a moment arm of the distance from where it contacts flat surface 7B to the contact point between pin 3A and spring end 4A. This is much greater than the corresponding moment arm on closing, mentioned above. Consequently, there will be considerably less force required to move tongue 7 in this direction and consequently to close the door than it took to open it. Moreover, since 7A is convex, the moment arm on opening increases slower since it is not increasing as rapidly as it is when a contact point is moving along the straight line represented by 7B which further increases the difference in amount of force required to open the door in comparison to what it takes to close it. It should now be apparent that all this is accomplished through the use of only one moving part in the latch itself in contrast to the more complicated mechanisms employed in the prior art.