Patent Publication Number: US-10329822-B2

Title: Door latch with opening and closing mechanical advantage

Description:
BACKGROUND OF THE INVENTION 
     This invention generally relates to a simple door latch which provides leverage to the door in both the closing and opening operations of the latch&#39;s door handle which is particularly desirable for ultra-low temperature (ULT) freezers. The latching handle of the invention, when rotated by a user, applies a closing force to compress a door gasket and an opening force to unseat a frozen gasket or some other resisting force. Doors that have frozen onto their gaskets and therefore make the door difficult to open are a particular problem associated with ULT Freezers. 
     ULT freezers generally operate at temperatures from −70° C. to below −145° C. The door gasket seal may account for 30% or more of the heat leak into the cabinet. Proper compression of the gasket seal is imperative to obtain a seal that exhibits good thermal resistance to the relatively warm ambient air. It is desirable that this be accomplished by a latch that requires an operating effort no more than can be offered by a person of minimum strength. This implies that the door latch should not require the application of a substantial force against the door in order to get the latch engaged and that the door be closable and latchable by a one hand operation. 
     When a ULT freezer cabinet door is opened, ambient moisture tends to condense onto the door gasket and the cabinet&#39;s thermal breaker assembly. Under certain conditions, when the door is subsequently closed, the condensed moisture will freeze and bond the door gasket to the frame of the cabinet and thus require a large force to break the bond and re-open the door. In the prior art, heating has been provided in the door frame either electrically or by a warm refrigerant line. This works most of the time but occasionally doors become frozen to the door frame and therefore require applying an external opening force of substantial magnitude often through application of a prying bar. 
     A similar problem arises when the door needs to be opened shortly after being closed. In this situation, the ambient air that entered the freezer when the door was open becomes cold. The reduced air temperature in the freezer cabinet reduces the pressure within the cabinet causing a force of considerable magnitude across the door that tends to hold the door closed. A vacuum breaker is generally provided to ameliorate this problem of differential pressure. However, the equalization of pressure afforded by the vacuum breaker takes a little time, perhaps up to 10 minutes. Anyone who needs access to a recently opened and closed freezer must therefore wait until the internal pressure has been equalized with the ambient pressure. It would be of great utility if a simple door latch were provided to assist in opening the door in cases where it is frozen shut or is held closed by differential pressure or both. 
     During closing, the door gasket must be properly compressed to obtain good thermal resistance to the ambient air. The compression force applied by the gasket against the door is large and therefore substantial leverage is needed to allow a person of minimum strength to apply the necessary force. This leveraged force should also be reversible in order to more easily open the door in the event that the door is adhered to the gasket by condensed water that has frozen or in the event that the internal cabinet pressure has dropped to a low level thereby creating a large force that resists opening. 
     Another desirable feature of a latch for a ULT freezer is that the freezer door latch can be moved by a simple single handed operation to unlatch and pull open the door and similarly to push closed and latch the door. The reason is that commonly a user has an object in one hand when opening or closing the freezer door such as a container of vials to be placed in or just removed from the freezer. 
     It is therefore an object and purpose of the invention to provide a door latching mechanism that applies a sufficient gasket compression force without requiring more effort than can be provided by one handed operation of a person of minimum strength and also can be leveraged open by the same one handed effort as is available from such a person. 
     BRIEF SUMMARY OF THE INVENTION 
     The latch of the invention not only latches or releases the cabinet door but also acts as a lever to apply a force with a mechanical advantage for both opening and closing the door. That mechanical advantage changes as a function of the rotational angle of the latch handle in order to change the door closing or opening force applied by a user who is opening or closing the door and in order to change the rate at which the door is pushed open or closed. The latch is designed so that the force applied as a result of the mechanical advantage and the rate of change of the mechanical advantage both vary as the latch handle is rotated. They vary to values that are desirable for the changing position of the door with respect to the cabinet as the door is being opened or closed. 
     The door latch has a door axle attached to an edge of the door for pivotally mounting a latch pivoting component. A striker is attached to the cabinet in a juxtaposition with the door axle that permits the pivoting component to be rotated into and out of engagement with the striker. The latch pivoting component has a base bearing journaled to the door axle and a handle is attached to the base bearing for manually rotating the base bearing about the door axle. A cam is attached to the base bearing and is engageable with the striker by rotation of the base bearing. The cam has a cam surface defining a striker harbor with a peripherally outwardly opening mouth for receiving the striker into the striker harbor. The striker harbor extends from the striker harbor mouth progressively closer to the base bearing. The cam surface includes a closing cam surface on a side of the striker harbor and an opening cam surface on the opposite side of the striker harbor. The opening cam surface is positioned a radial distance from the base bearing to engage and slide along the striker as the latch pivoting component is rotated in an opening direction of rotation. The closing cam surface is positioned a radial distance from the base bearing to engage and slide along the striker as the latch pivoting component is rotated in a closing direction of rotation. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
         FIG. 1  is a view in perspective of an ultra-low temperature freezer to which is mounted a latch embodying the invention. 
         FIG. 2  is a view in frontal perspective of the latch pivoting component of the invention. 
         FIG. 3  is a top view of the latch pivoting component. 
         FIG. 4  is a side view of the latch pivoting component. 
         FIG. 5  is a rear view of the latch pivoting component. 
         FIG. 6  is a rear perspective view of the latch pivoting component with the striker also shown. 
         FIG. 7  is a rear perspective view of the latch. 
         FIG. 8  is a rear perspective view of the latch pivoting component from a different perspective. 
         FIG. 9  is a front view of the installed latch with hidden lines shown. 
         FIG. 10  is a greatly enlarged view of a segment of the latch illustrating the striker seated against the retaining cam segment of the cam. 
         FIG. 11  is a view in exploded perspective of the door axle and the door axle attachment bracket of the latch. 
         FIG. 12  is a view in perspective of the striker and the striker attachment bracket of the latch. 
         FIG. 13  is an enlarged front view of the cam and striker of the latch. 
         FIG. 14  is a diagrammatic view illustrating the operation of the latch in a series of positions during the opening and closing of the latch. 
     
    
    
     In describing the preferred embodiment of the invention which is illustrated in the drawings, specific terminology will be resorted to for the sake of clarity. However, it is not intended that the invention be limited to the specific term so selected and it is to be understood that each specific term includes all technical equivalents which operate in a similar manner to accomplish a similar purpose. 
     DETAILED DESCRIPTION OF THE INVENTION 
     Structure 
     The major components of a ULT freezer cabinet are shown in  FIG. 1 . A vacuum insulated cabinet  10  is closed off by a vacuum insulated door  12  and has a door latch  14 . A double (sometimes triple) gasket  16  is attached to the door  12  for sealing the interior of the cabinet against heat and moisture from the surrounding environment. A door latch embodying the invention has three main component parts with the third component part having several subcomponents. 
     Referring to  FIG. 11 , the first main component is a door axle  18  that, when installed on a ULT freezer, is attached to an edge of the door  12  for pivotally mounting a latch pivoting component to the door edge. The door axle  18  is preferably fixed to a flat plate attachment bracket  20  that is bolted, screwed or otherwise fixed to the door  12  and preferably extends horizontally from the door edge. 
     Referring to  FIG. 12 , the second main component is a striker  22  that, when installed on a ULT freezer, is attached to a sidewall of the cabinet  10  in a juxtaposition with the door axle  18  that permits the pivoting component to be rotated into and out of engagement with the striker  22 . The striker  22  is preferably also fixed to an attachment bracket  24  which is attached to the sidewall of the cabinet  10  so that the striker preferably extends horizontally from the sidewall and parallel to the door axle  18 . The preferred striker comprises a striker axle  26  which is fixed to its attachment bracket  24  and has a rotatable striker roller  28  journaled to the striker axle  26 . 
     The third main component of the preferred embodiment of the invention is the latch pivoting component  30  illustrated in  FIGS. 2-8 . Some of those figures reveal a cam  36  and other structures formed as part of the pivoting component  30 .  FIGS. 5-8  are views showing the pivoting component  30  from its back which is not visible when the pivoting component  30  is installed in its operable orientation because the back lies nearly against the sidewall of the cabinet  10 . However, in order to better illustrate the functional operation of the invention,  FIGS. 9, 10, 13 and 14  illustrate the preferred embodiment from a different perspective. In  FIGS. 9, 10, 13 and 14  the arrangement of the parts of the pivoting component  30  appear flipped like mirror images from the arrangement as viewed in  FIGS. 2-8 . That is because  FIGS. 9, 10, 13 and 14  are views from outwardly beside the latch looking horizontally toward the latch when the latch is mounted in its operable position. In other words,  FIGS. 9, 10, 13 and 14  are views looking through the subsequently described decorative outer surface  40  ( FIG. 2 ) of the base  38  as if it were transparent to reveal the working structures from the perspective of a user looking at the side of the installed latch. 
     The latch pivoting component  30  is pivotable around the door axle  18  for opening and closing the door  12 . The principal subcomponents of the latch pivoting component  30  are a base bearing  32 , a handle  34  and a cam  36 . These components are fixed together to operate as a unitary body. Preferably, the entire latch pivoting component  30  is cast as a unitary casting having its principal components all cast in attachment to a base  38 . The casting is preferably machined to form a smooth surface on the cam  36  and bored through a boss to form the base bearing  32 . The base  38  is essentially a plate that extends to the periphery of the latch pivoting component  30 , has a planar interior surface and has an aesthetically contoured and decorative outer surface  40 . Preferably a conventional key lock mechanism  39  is mounted to the base  38  with a mating lock striker mounted to the door  12  for securing a closed door  12  to the cabinet  10 . The cam  36  can be a raised railing, ridge or fence as is illustrated but alternatively could be a shoulder or a slot machined into a sufficiently thick base. 
     When mounted in its operable position to a ULT freezer, the base bearing  32  is journaled to the door axle  18  and has a pivot axis for rotation of the entire latch pivoting component  30  about the door axle  18 . As can be seen from  FIGS. 2 and 11 , the pivoting component  30  is retained on the door axle  18  ( FIG. 11 ) by a washer  29  that is fixed to the door axle  18  by a fastener  31  and seats ( FIG. 2 ) against the bottom of a counterbore  37 . The counterbore  37  is closed by a decorative cover  33  that is press fit into the counterbore  37 . 
     The handle  34  is attached to the base bearing  32  by way of their common attachment to the base  38  and extends outward from the periphery of the base  38 . In use, the handle  34  is grasped by the user for manually rotating the base bearing and the entire latch pivoting component  30  about the door axle  18 . Preferably, in the operable orientation of the installed latch, the handle  34  extends close to vertically upward when the door is latched closed so that the user pulls the handle  34  horizontally directly away from the cabinet to rotate the pivoting component  30  approximately 90° in an opening direction to open the door. The user pushes the handle  34  horizontally toward the cabinet and rotates the latch pivoting component  30  in the opposite closing direction in order to close and latch the door in the closed position. As will be seen, the latch pivoting component  30  should be positioned so that the striker harbor mouth (described subsequently) opens toward the striker  22  when the handle  34  is rotated to the fully open position in which it extends horizontally away from the front of the door  12 . That positioning assures that the user is able to pull the handle  34  horizontally away from the cabinet  10  to open the door  12  and to push the handle  34  toward the cabinet  10  to close the door  12 . That direction of user motion is the most ergonomically natural motion for opening and closing the door  12  and also enables the user to most comfortably apply an opening or closing force to the door handle  34 . 
     The most important and unique subcomponent of the latch pivoting component  30  is the cam  36  and its interaction with the striker  22 . The cam  36  is attached to the base bearing  32  by way of their common attachment to the base  38  and is engageable with the striker  22 . The cam  36  has a cam surface defining a striker harbor  42  with a peripherally outwardly opening mouth  44  for receiving the striker  22  into the striker harbor  42 . The striker harbor  42  extends from its mouth  44  progressively closer to the base bearing  32  at an acute angle to a radial from the pivot axis of the base bearing  32 . When the entire latch pivoting component  30  is rotated, the cam surface moves along the striker  22 . On both opening and closing the door  12 , rotation by the user varies the position along the cam surface that is contacted by the striker  22 . 
     Referring to several figures but particularly to  FIG. 13 , the striker harbor  42  is a region between, and partially enclosed by, the surfaces of the cam  36 . The cam surfaces lie along a path that is analogous to the shoreline of a harbor. The striker harbor  42  has a peripherally outwardly opening mouth  44  for receiving the striker  22  into the striker harbor  42  so that the surface of the cam  36  can apply a force against the striker  22  as the cam  36  is rotated about the pivot axis of the base bearing  32 . The striker harbor  42  extends from the mouth  44  progressively closer to the base bearing  32 . The term “progressively closer to the base bearing” means that, as the striker harbor  42  progresses away from the mouth  44 , it progresses in a direction that becomes radially closer to the base bearing  32 . 
     Preferably, as the cam surfaces that begin at the sides  46  and  48  of the mouth  44  progress away from the mouth  44 , they both progress generally and principally in a direction that brings them radially closer to the base bearing  32  and they converge. However, as subsequently described, the cam  36  comprises a series of different cam segments and it is not necessary that all portions of all segments progress radially closer to the base bearing  32 . As will be seen from a description of the operation of the latch, there can be discontinuities in the cam  36  because some parts of the cam  36  in the preferred embodiment are never contacted by the striker  22  and therefore could be absent. However, even though there may be segments of the cam  36  that are never contacted by the striker  22 , it is preferred that the cam  36  extends smoothly and continuously to define the striker harbor  42  from one side  46  of the mouth  44 , around the striker harbor  42  to the opposite side  48  of the mouth  44 . 
     Additionally, for aesthetics, strength and simplicity and to provide a protective barrier against the infiltration of dust particles or other contamination from the ambient air, the cam  36  is preferably extended as an outer wall  50  extending continuously from one side  46  of the mouth  44  around the periphery of base  38  to the other side  48  of the mouth  44  in order to enclose the parts and protect them. This extension of the cam  36  never engages the striker  22  and does not function as a cam but only serves as a housing wall blended to join the cam  36 . 
     An important feature of the invention is that the cam  36 , and therefore its active cam surface, has two principal cam segments which are preferably subdivided into multiple cam segments. Each of the cam segment subdivisions varies in its functional operation. One principal cam segment is an opening cam segment  52  on one side of the striker harbor  42  and the other principal cam segment is a closing cam segment  54  on the opposite side of the striker harbor  42 . The closing cam segment  54  is spaced radially farther from the base bearing  32  than the opening cam segment  52 . The opening cam segment  52  is positioned a radial distance from the base bearing  32  to engage and slide along the striker  22  as the latch pivoting component  30  is rotated in an opening direction  49  of rotation. The closing cam segment  54  is positioned a radial distance from the base bearing  32  to engage and slide along the striker  22  as the latch pivoting component  30  is rotated in a closing direction  51  of rotation. However, it is not necessary that, in embodiments of the invention, the entire length of the cam  36  slides along in contact with the striker  22  during opening or closing rotations of the latch pivoting component  30 . 
     Referring to  FIG. 13 , the opening cam segment  52  includes a push open cam segment  56  that is adjacent the harbor mouth  44  of the striker harbor  42  and extends along the side of the harbor  42  away from the mouth  44 . The push open cam segment  56  is positioned to engage and slide along the striker  22  as the latch pivoting component  30  is rotated in an opening direction  49  of rotation. The push open cam segment  56  is constructed so it progresses radially closer to the pivot axis of the base bearing  32  as it progresses away from the mouth  44  of the striker harbor  42 . As will be seen from the subsequent description of the operation of the preferred embodiment, the distance that the push open cam segment  56  extends inward along the opening cam segment  52  and away from the harbor mouth  44  can vary depending upon the dimensions of a particular design, including the width of the striker harbor  42  and the thickness of the gasket  16 . In the normal operation of the preferred embodiment, the striker  22  only contacts the illustrated push open cam segment  56 . Consequently, although not preferred, the remainder of the opening cam segment  52  that lies inward beyond the push open cam segment  56  can be eliminated. Preferably, the push open cam segment  56  at the side  48  of the striker harbor mouth  44  is gradually arcuately blended to the protective peripheral outer wall  50 . 
     The closing cam segment  54  includes a rapid closing segment  58  adjacent the mouth  44  of the striker harbor  42  and a slow closing cam segment  60  spaced inward from the mouth  44  of the striker harbor  42  and radially nearer the pivot axis of the base bearing  32  than the rapid closing segment  58 . The rapid closing segment  58  is constructed so its contact point with the striker  22  progresses toward the pivot axis of the base bearing  32  at a higher rate per degree of rotation of the pivoting component  30  than the slow closing segment  60 . The significance of that is described in the description of the operation. 
     The initial, most outward segment of the rapid closing cam segment  58  is formed to have a capture valley  64  at a peripherally outer end of the closing cam segment  54 . The outer part of the capture valley  64  hooks around toward the harbor mouth  44  to form a valley that captures the striker  22  and draws the striker into the striker harbor  42  when the latch pivoting component  30  is rotated in the closing direction  51 . The capture valley  64  includes a cam surface that curves in a manner that a tangent to the valley cam surface makes a progressively greater acute angle with a radial from the door axle  18  through the intersection of the tangent and the cam surface as the valley cam surface progresses outwardly away from the door axle. Consequently, that cam surface engages the striker and applies a force against the striker that has a force component radially inwardly toward the door axle  18 . That inward force component draws the striker into the striker harbor  42 . 
     The closing cam segment  54  also has a retaining cam segment  62  in the form of an indentation. The indentation of the retaining cam segment  62  is best observed in  FIG. 10  which is greatly enlarged because of the shallow depth of the indentation, which is preferably 0.5 mm to 1.0 mm deep. The retaining cam segment  62  is positioned at the end portion of the closing cam segment  54  contiguous to the side of the slow closing cam segment  60 . The indentation of the retaining cam segment  62  extends away from the pivot axis of the base bearing  32  to provide a valley that receives the striker  22  and resists rotation of the pivoting component  30  in an opening direction of rotation when the door is fully closed. Most preferred is a retaining cam segment  62  that is a segment of a cylindrical surface having substantially the same radius as the peripheral surface of the striker  22 . 
     Preferably the closing cam segment  54  extends through an angular interval greater than 45° and most preferably it extends through an angular interval of substantially 90° as illustrated for the preferred embodiment. This angular interval takes full advantage of the ergonomic and intuitive rotation of the pivoting component  30  by 90° by distributing the action of the closing cam segment  54  over a broader angular range of rotation thereby allowing the mechanical advantage to be varied at a smaller rate of change per degree of rotation. 
     Operation 
       FIG. 14  shows the operational progression of the illustrated latch of the invention in degrees of rotation of the latch pivoting component  30  during closing and opening operations. The user pulls the handle  34  toward the user and downward to rotate the latch pivoting component  30  and open the door  12  of the ULT freezer cabinet  10 . The operator raises and pushes on the handle  34  to rotate the latch pivoting component  30  and close the door  12 . 
     The closing operation is illustrated along the upper row of symbolic images and starts at position A and ends at position F. The opening operation is illustrated along the lower row of symbolic images and starts at position G and ends at position L. The angle of rotation in degrees for each position is shown above each position. The opening and closing distance between the axis of the striker  22  and the pivot axis of the base bearing  32  is shown as a dimension in millimeters for representational rotational positions from the cam&#39;s first engagement against the striker  22  in position B through the position at which the cam  36  is about to disengage from the striker  22  in position L. 
     The operation of an embodiment of the invention is first described in a general overview and then described in increased detail. 
     On rotation in the closing direction  51 , the closing cam segment  54  forces the door  12  and cabinet  10  toward each other as the cam  36  slides along the striker  22 . This initially pushes the door  12  and gasket  16  toward the cabinet opening. When the gasket  16  contacts the side of the cabinet opening, further rotation compresses the gasket and tightens the door against the cabinet 
     On rotation in the opening direction  49 , the closing segment  54  first releases the compressed gasket  16  and allows it to elastically expand. During the release operation, the striker  22  travels back along the closing segment  54  of the cam  36  until gasket compression is released (the gasket stops elastically expanding). Further rotation of the handle  34  toward the user (away from the cabinet  10  pulling the door open) moves the opening segment  52  of the cam  36  against the striker  22 . If the cabinet  10  is not adhered to the door  12  at the gasket  16  and the door  12  is not held closed by a pressure differential, the door  12  can be pulled open by the user. But if the door  12  is held closed by either, the application of a downward force by the user causes the opening segment  52  of the cam  36  to push against the striker  22  and push the striker  22  away from the door axle  18  to force apart the door  12  and the cabinet  10 . 
     However, the operation is more complicated than simply explained above. The cam and the cam surface have important different cam segments each of which is designed to provide an optimum function for the state of the door position while the particular cam surface segment is in contact with the striker. 
     In order to describe the operation of the cam segments, it is desirable to describe some mechanical principles that are applied in the operation of the latch by these cam segments. The mechanical principles are based upon an analysis of the forces applied between the cam  36  and the striker  22  and how those forces affect both the mechanical advantage gained by the latch  14  at different rotational positions of the latch pivoting component  30  and how the rate of change of those forces as the handle  34  is rotated affects the rate at which the door  12  is moved closer or farther from the cabinet. 
     The first principle is the mechanical advantage gained from the latch  14  of the invention. Whenever the cam  36  engages the striker  22 , the cam  36  applies a force against the striker  22  and the striker  22  applies an equal and opposite force against the cam  36 . In the closing direction  51  of rotation, the striker  22  applies a force against the cam  36  which forces the door  12  toward a more closed position and eventually against the gasket  16  and finally compressing the gasket  16 . Rotation in the closing direction causes the contact point of the striker  22  against the cam surface to move along the cam surface away from the mouth  44  of the striker harbor  42 . At any point of contact, there is a mechanical advantage that multiplies the force applied to the hand grip  35  to a greater force applied by the striker  22  against the cam  36 . The mechanical advantage is expressed as a ratio. The numerator of the ratio is the radius from the center of the door axle  18  to the hand grip  35  of the handle  34 . The denominator of the ratio is the radius from the center of the door axle  18  to the point of contact of the cam  36  with the striker  22 . So the mechanical advantage increases as the striker  22  point of contact against the cam  36  moves closer to the door axle  18  center thereby making the denominator of the mechanical advantage ratio smaller and the mechanical advantage greater. In other words, the mechanical advantage ratio becomes greater as the radius from the center of the door axle  18  to the point of contact of the cam surface with the striker  22  become less. This increases the mechanical advantage as the door  12  becomes closed further and tighter. An important feature of the present invention is that the same principles of mechanical advantage are also applied to opening the door  12 . 
     The second principle is the change in the speed that the door  12  moves toward or away from the cabinet  10  as the latch  14  is rotated. The rate at which the door  12  is moved closer to or farther from the cabinet  10  is the rate at which the door axle  18  moves closer to or farther from the striker  22  per degree of handle rotation. That rate is a ratio. The numerator of that ratio is the distance [ΔD] that the door  12  moves over an interval of movement of the striker  22  along the cam  36  as the handle  34  is rotated. That distance [ΔD] is the amount of change of the radius from the pivot center of the door axle  18  to the point of contact of the striker  22  against the cam  36 . The denominator of that ratio is the angle [Δα] through which the handle  34  is rotated to cause the door to move by a distance [ΔD]. However, because the cam  36  has a smoothly continuous curved cam surface, the rate at which the door  12  is moved closer or farther from the cabinet continuously changes as the cam  36  moves along the striker  22 . Therefore, except for any cam surface that is linear, it is more mathematically accurate to designate the rate at which the door  12  is moved closer or farther from the cabinet  10  as the differential [dD]/[dα]. 
     With these principles in mind, the operation of the different cam segments can be described. Each cam segment provides a mechanical advantage and a rate of door movement toward or away from the cabinet  10  that is most desirable for the state of the door  12  when a particular cam segment is engaged against the striker  22 . The states of the door include: (1) the door  12  being fully latched closed with the striker  22  seated in the valley of the retaining cam segment  62  and the gasket  16  compressed; (2) the gasket  16  partially compressed; (3) the gasket  16  relaxed but seated against the cabinet  10  and possibly adhered to the cabinet  10 ; and (4) the gasket  16  freed from contact with the cabinet  10 . 
     The operation is described in association mainly with  FIGS. 13 and 14 . The different cam segments are shown in the greatly enlarged  FIG. 13  because the drawings in  FIG. 14  are so small scale that there is insufficient space to show them. 
     Referring to  FIG. 14 , as the pivoting component  30  rotates counterclockwise in the closing direction  51 , the closing segment  54  of the cam  36  eventually engages the striker  22  and pulls it towards the axis of the base bearing  32 . The closing distance can be seen to diminish as the latching handle progresses from position B to position E. The final closed position is at F. 
     Looking at the closing operation in more detail, the striker  22  first engages the rapid closing cam segment  58  near the closing side  46  of the striker harbor mouth  44 . The rapid closing cam segment  58  then slides along the striker  22  to the end of the rapid closing cam segment  58  which ends at the peak  59  of a hump in the cam  22 . Because of the curvature of the cam segment  58  as it approaches the peak  59 , the surface of the cam segment  58  pushes the striker  22  more rapidly toward the base bearing  32  than does any other part of the cam  36 . That causes the rate of increase of the mechanical advantage and the rate of movement of the door  12  toward the cabinet  10  to be relatively large. That is appropriate because while the rapid closing cam segment  58  is engaged against the striker  22 , the gasket  16  of the door  12  has not yet engaged the cabinet  10  so the door  12  should be closed more rapidly and is easier to close because no force is yet applied for compressing the gasket  16 . 
     Further rotation of the latch pivoting component  30  in the closing direction causes the striker  22  to slide across the slow closing cam segment  60  beginning at the peak  59  of the hump and continuing to the edge of the retaining cam segment  62 . Although the slow closing cam segment  60  continues to progress closer to the base bearing  32 , it does so at a lower rate per degree of rotation. Consequently, the mechanical advantage is near its maximum but is increased at a smaller rate per degree of rotation. That is appropriate because the state of the door  12  during engagement of the striker  22  with the slow closing cam segment  60  is that the gasket  16  is being compressed. Consequently, the rotation of the latch pivoting component  30  is distributed over a greater arc of rotation thereby requiring the application of less force by the user per degree of rotation. This is analogous to walking up a hill along a less steep but longer path. 
     Finally, the user rotates the latch pivoting component  30  in the closing direction  51  until the striker  22  falls into the valley of the retaining cam segment  62 . As seen at position F, the spring-like force applied by the gasket  16  pushes the door  12  a slight distance in the opening direction so that the cam  36  is prevented from rotating in an opening direction except upon application by a user of a sufficient force in the opening direction of rotation. This is appropriate because the state of the door  12  is closed and the retaining cam segment  62  prevents rotation in the opening direction from vibration. 
     As an alternative, the hump in the cam  36  that extends over adjoining parts of the rapid closing cam segment  58  and the slow closing cam segment  60  can be eliminated. Instead a linear segment of the cam can be substituted for the hump as illustrated by the phantom lines in  FIG. 13 . With this alternative, the cam segments  58  and  60  continue to progress closer to the base bearing  32  but a linear progression is substituted for progression over a hump. 
     Referring to  FIG. 14 , the opening operation starts at position G and ends at position L. In this case, as the latch pivoting component  30  with its base  38  rotates clockwise, the striker  22  eventually comes into contact with the push open cam segment  56  at position K. At that point, further rotation of the pivoting component  30  forces the door  12  away from striker  22  with a mechanical advantage according to the above-described principles. Consequently, the user is advantageously able to apply a force in a direction to open the door  12  with the benefit of the mechanical advantage. That is particularly helpful if the door  12  is resisting opening for the reasons explained above. From the initial contact of the opening cam segment  52  at position K against the striker  22 , the push open cam segment  56  slides along the striker  22  around the arcuate opening side  48  of the harbor mouth  44 . As the striker  22  slides along the push open cam segment  56 , the mechanical advantage is reduced but the rate at which the door  12  opens increases. That is appropriate because once the resistance to the door  12  opening is overcome and the gasket  16  releases from the cabinet  10 , the door  12  is moved more quickly open by the user. Of course when the striker harbor mouth  44  is at position L, the door  12  can continue to be opened by the user pulling the handle  34  horizontally away from the cabinet  10  without any further operation of the latch  14  of the invention. 
     From all of the above description, it can be appreciated that the invention involves a latch with an integral latching mechanism. The latching mechanism is based on an over center design. A cam track built into the latch that is mounted on the door engages a striker that functions similarly to a cam follower that is mounted onto the cabinet. The engagement of the striker with the cam occurs before the limit of gasket compression so that the mechanical advantage of the mechanism becomes available to the user immediately on engagement of the latch, well before the latch is fully seated. When the door is open, the latch is in a position of approximately 90° in rotation from its locked position. The latch is thus easily gripped with one hand. As the door is closed, the handle is rotated upward and, by engaging the cam  36  against the striker  22 , draws the door  12  towards the cabinet  10  while compressing the gasket  16 . As the handle approaches the gasket seating position, the cam action applies an over center force to the striker  22  to provide a positive final resting place for the latch  14 . The special attribute of this invention is that a mechanical advantage of this type of mechanism is also applied to opening the freezer. Normally the freezer door can be opened by simply removing the latching force when the handle is rotated to the opening position. In this invention, when the handle is rotated to the open position, the striker will move to the opposite cam track in the latch and that cam track will apply an opening force to the striker that is highly leveraged to the advantage of the user. That means that small handle forces will be amplified as an opening force to the door and, in this way, break any bonding force due to ice and any pressure differential force that may be holding the door shut closed. 
     REFERENCE NUMBER—PARTS LIST 
     
         
         
           
               10  cabinet 
               12  door of cabinet 
               14  latch 
               16  gasket 
               18  door axle 
               20  attachment bracket for door axle 
               22  striker 
               24  attachment bracket for striker 
               26  striker axle 
               28  striker roller 
               29  base bearing retention washer 
               30  latch pivoting component 
               31  fastener to secure washer  29   
               32  base bearing 
               33  decorative cover 
               34  handle 
               35  hand grip of handle 
               36  cam 
               37  base bearing counterbore 
               38  base (plate) 
               39  key lock mechanism 
               40  outer surface of base (of pivoting component) 
               42  striker harbor 
               44  harbor mouth 
               46  closing side of harbor mouth 
               48  opening side of harbor mouth 
               49  opening direction of rotation 
               50  outer wall 
               51  closing direction of rotation 
               52  opening cam segment/surface 
               54  closing cam segment/surface 
               56  push open cam segment/surface 
               58  rapid closing cam segment/surface 
               59  peak of cam hump 
               60  slow closing cam segment/surface 
               62  retaining cam segment/surface 
               64  striker capture valley 
           
         
       
    
     This detailed description in connection with the drawings is intended principally as a description of the presently preferred embodiments of the invention, and is not intended to represent the only form in which the present invention may be constructed or utilized. The description sets forth the designs, functions, means, and methods of implementing the invention in connection with the illustrated embodiments. It is to be understood, however, that the same or equivalent functions and features may be accomplished by different embodiments that are also intended to be encompassed within the spirit and scope of the invention and that various modifications may be adopted without departing from the invention or scope of the following claims.