1. Field of the Invention
The invention generally relates to a casement defining an opening in a structure, such as a wall, in combination with a closure element that is movable with respect to the casement for opening or closing at least a portion of the casement opening; and, more particularly, to a latch mechanism for fixing the relative position of the closure element with respect to the casement, preferably in the closed position.
2. Related Art
A casement assembly comprising a combination of a casement frame and a closure element is well known and finds common examples in security screens, sliding glass doors, or double hung windows, to name a few examples. Generally, the casement frame is positioned within a wall or similar structural element to define a passage therethrough. The closure element (generally a window, screen or door) is movable (generally slidable or pivotal) with respect to the casement frame for alternatively opening or closing the passageway.
For safety, it is common to provide a latch mechanism for locking the closure element in a fixed position relative to the casement frame, preferably in the closed position. Previous latch mechanisms typically include one or more locking rods mounted to the closure element and laterally movable between a retracted and extended position for inserting and removing an outer end of the bar into and out of engagement with the casement frame to prevent the movement of the closure element with respect to the casement frame. A laterally movable or rotatable handle or knob was directly mechanically coupled to the inner end of the rod for moving the rod between the extended and retracted positions as the handle is slid or rotated. The direct mechanical coupling between the rod inner end and the knob or handle typically included rotatably pinning the end of the rod to the handle or providing an intermediate link having one end pinned to the rod and the other end pinned to the handle or knob. Examples of such latch mechanisms with direct mechanical links are illustrated in U.S. Pat. No. 2,708,478, filed May 17, 1955, U.S. Pat. No. 2,883,225, filed Oct. 16, 1953, U.S. Pat. No. 4,362,328, issued Dec. 7, 1982, U.S. Pat. No. 4,803,808, issued Feb. 14, 1989, U.S. Pat. No. 5,090,750, issued Feb. 25, 1992, U.S. Pat. No. 5,595,408, issued Jan. 21, 1997, and U.S. Pat. No. 5,806,353, issued Sep. 15, 1998 to name a few.
A disadvantage of the prior art latches lies in the direct mechanical linkage, which can often be difficult to extend and retract because of the inherent friction or resistance in the mechanical linkages. Many of the mechanical linkages change angular orientation with respect to the handle or knob as it is rotated, resulting in quickly varying relatively small lever arms that require applying relatively large and varying rotational forces to the handle or knob to effect the extension or retraction. The magnitude and varying nature of the operational force results in jerky operation and sometimes a very high initial force. The combination of these effects can often lead to the user having to apply a relatively very large initial force until the inherent friction or resistance is overcome, resulting in the user feeling as if the latch mechanism has broken away. An additional problem lies in that the various components are typically metal and the linkages can rust, increasing the force necessary to overcome the additional resistance and exacerbating the initial force problem.