FIELD OF THE INVENTION This invention is related to a folding table construction, and more specifically a table leg locking mechanism for securing at least one table leg in an erect supportive position from a folded position against and parallel to the underside of the table.

BACKGROUND ART Numerous technical solutions are known in the field of folding tables. From patent US 4 064 815 is known a table leg locking mechanism, which locks joined pairs of table legs in either their supportive or their folded positions at their cross member. The locking mechanism includes a pivot mount situated within a rectangular housing attached to the underside of the table. This locking mechanism consists of a pair of sleeves mounted on a tubular cross member, such that one sleeve is welded, or in some other manner securely united to its associated housing, and the other sleeve is rigidly united to the tubular cross member. A spring is connected to the tubular cross member whereby constant pressure is exerted between the two sleeves, one against the other, to insure locking of the table legs into position. The sleeves are interlocked together by virtue of their shape, in which one of the sleeves has wedge-shaped protrusions on its end, conforming to matching wedge shaped notches in the adjoining end of the other sleeve. There is one lock for each united pair of legs at each end of the table. The resulting table construction does not achieve the elegant slimness and light weight preferred in folding tables, since the rotating tube locking force is concentrated at a short wedge which requires a fairly large overall radius for the circular locking mechanism to achieve its necessary strength, resulting in a relatively bulky mechanism, shrouded by a bulky frame. The long term strength of such a design is questionable, due to its complete reliance on the table top for support of the legs and locking mechanism, with the frame giving no direct support to the legs and locking mechanism. The given solution is not an optimal design for the best universal table utility, in which a leg is near each corner of a rectangular table.

The current state of the art of folding tables is fundamentally limited by the tradeoff achieved between strength and rigidity, and the aesthetic execution of the locking mechanism. Today's most popular folding tables generally continue a half century practice of using interfering, unaesthetic, visible angled braces for the legs. In addition, legs are paired in such a way that it is impossible to sit between such legs at the table end. Due to the impossibility of sitting at the table end, between the legs of the shorter models of the most popular type of folding table, which continues to dominate the state of the art, the only pro ' ~sed solution to enable end seating at these types of tables is to increase leg J room distance between the end of the table and the legs, which generally requires making the table longer. In attempts to attain these features, excessively expensive or flimsy tables have been developed. This limits the utility of tables based on the state of the art.

SUMMARY An objective of the present invention is to overcome the limitations mentioned above in a compact, light, simple and economical, strong, rigid, safe, and mechanically and aesthetically optimal folding table, whose execution in metal (the top may be other than metal) is practically indistinguishable from the clean lines of a nonfolding welded frame metal table. A further objective of this invention is to present a solution for automatically locking and unlocking of the hinged legs in their erect position. In other words, the operator simply and obviously, by grasping and pulling or pushing a leg, extends, or folds the legs, without any separate thought or action to actually lock or unlock the legs, which automatically "snap" into or out of their "locked" erect position by applying force on a table leg. Another object is to ensure table leg rigidity and security in the working, erect position by the overall design.

This invention is applicable to a broad variety of embodiments, depending on the choice of materials, the chosen technologies, the aesthetic and functional executions, various levels of quality and price. Two obviously differing embodiments are the one of 100% plastic, and the sheet steel frame and structure with particleboard top version, reflecting the most popular common construction. The following overview for a preferred embodiment of this invention approximates the most popular prior art folding table attributes. Such a preferred embodiment consists of a particleboard (plastic, wooden, combination, or similar) table top supported by an open "U" profile sheet steel frame and a pair of rotational leg assemblies, which can include a single leg or pair of legs, achieved through a construction in which a leg (one or more) is rigidly joined to a hinged, lockable horizontal cross member (typically tubular), of preferably square cross section, such that by rotating a leg, two rigidly joined legs at a time are automatically locked into or out of the erect position. Such a tubular cross member is rotationally attached to the table at a pivot. The preferred embodiment of this pivot is a continuous ("piano") hinge attached to an intermediate steel plate which rigidly unites into a self-supporting unit the entire hinged leg assembly and table frame combination, independent of (without) the table top. By appropriate bonding and fastening to the frame and intermediate plate, the table top can enhance the strength and rigidity of both the frame and intermediate plate. The intermediate plate's resistance to deformation, through numerous means of stiffening and strengthening well known to the art, is the foundation of the strength and rigidity of the legs in their erect working position.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 illustrates a front view of a preferred embodiment of the table with legs unfolded according to the present invention.

Figure 2 illustrates an end view of the preferred embodiment of the table with legs unfolded according to the present invention.

Figures 3a illustrates a bottom view of the preferred embodiment of the table with legs folded according to the present invention.

Figure 3b illustrates a front view of the preferred embodiment of the table with legs folded according to the present invention.

Figure 4 illustrates a bottom view of a preferred embodiment of the table with legs unfolded according to the present invention.

Figure 5 illustrates an enlarged corner view of Fig. 4.

Figure 6 illustrates table leg locking mechanism with legs folded according to the present invention.

Figure 7 illustrates the table leg locking mechanism in the process of unfolding the legs, at the point that the crossmember supporting the legs is pressing into the spring, forcing it against the backing plate in order to force the end of the spring in contact with the crossmember to ride up and over the corner of the crossmember to establish the locked condition of Figure 8 according to the present invention. The two arcs in the drawing are circles centered on the pivot of the hinge of leg assembly rotation, showing the locus of movement of the two vital corners of the leg cross member in relation to the cross member locking spring, which is designed and contoured to ride up the first surface with which it comes in contact, ride over the corner with the next surface, and establish a firm lock or grip on the second surface, as described in the sequence of Figures.

Figure 8 illustrates table leg locking mechanism with legs erect and in their fully locked condition according to the present invention.

Figure 9 illustrates table leg locking mechanism in the process of folding the legs, at the point of breaking the grip of the spring at its contact with the bottom surface of the cross member, as the spring is stretched into a more flattened contour, and is forced to ride over the corner of the crossmember to establish the unlocked condition of Figure 6 according to the present invention.

Figure 10 illustrates the full cycle of motion of the locking spring by superimposing the previously illustrated different positions of the locking spring when engaging and disengaging the cross member according to the present invention.

Figure 11 illustrates an alternate embodiment of the invention.

Figure 12 illustrates the profile of an alternate metal locking spring, which is readily adaptable to a plastic version executed in thicker material.

Figure 13 shows a rotational stop reinforcing bracket in a vertical side view with leg unfolded, shaded with hash lines, placed (welded or brazed) at the four corners of the table frame to provide a second rigid stop applied directly to the four legs, at the point of greatest mechanical stress. If the tubular cross member were perfectly rigid, this would be less necessary, but due to torsional twisting, such reinforcements would help relieve stress near the ends of the hinge in heavy duty applications. Figure 14 shows the reinforcing bracket of Figure 13 in full detail, in horizontal view, crosshatched, and also in the sheetmetal layout prior to bending into the bracket configuration.

Figure 15 shows a horizontal table view with legs unfolded of the reinforcing brackets at all four corners of the table.

Figure 16 shows the table of Figure 15 with the legs folded, revealing an additional stiffening crossmember, which is not necessary for common use, but for certain grades of tables, of certain sizes and applications, may prove advantageous to add, as an option.

Figure 17 shows the appearance of the optional stiffening crossmember of Figure 16 with the legs in their working position.

Figure 18 shows an alternative embodiment of a table, wherein the table is modified to adapt to a magnetic strips, instead of a spring latch.

Figure 19 shows matched, oppositely polarized attracting magnetic strips in use, attached to both the cross member and the table.

Figure 20 shows the magnetic strips attached only to the cross member.

Figure 21 shows an embodiment of the present invention having an optional non- releasably engaging spring and a spring lock disengaging device.

Figure 22 shows a cross-sectional view of the embodiment of Figure 21.

Figure 23 shows a bottom left-hand view of a table leg locking mechanism having an optional spring lock disengaging device according to the invention.

Figure 24 shows a bottom right-hand view similar to Figure 23 (mirror image view).

Figure 25 shows an alternate spring lock disengagement device. Figure 26 shows a cross-sectional view of the embodiment of Figure 25.

Figure 27 shows a bottom view of a table leg locking mechanism having an optional spring lock disengaging device according to the invention.

DETAILED DESCRIPTION OF THE INVENTION The present invention is more particularly described in the following exemplary embodiments that are intended as illustrative only since numerous modifications and variations therein will be apparent to those skilled in the art. The preferred embodiments are now described with reference to the figures, in which like reference characters indicate like parts throughout the several views.

In Figs. 1 and 2 is illustrated a preferred embodiment of the folding table according to the invention. The table comprises table top 1, table frame 2 and legs 3. The metal embodiment of the table unfolded (the top may be other than metal) is practically indistinguishable from the clean lines of a nonfolding welded frame metal table.

The preferred embodiment in Fig. 3A comprises a particleboard (or similar) table top 1 supported by a table frame 2 and legs 3, achieved through a construction in which each pair of legs 3 are rigidly joined to a rotating lockable cross member 5 (typically tubular), of nearly square cross section, such that by rotating a leg, two legs at a time are automatically locked into or out of the erect position. Figure 3b illustrates that according to the present invention the folded rotating leg assembly and the locking mechanism can be hidden behind an ordinary table frame 2. Such a rotating leg assembly 3 and 5 is rotationally attached to the table at a robust pivot 6 as illustrated in Figs. 4 and 5. The preferred embodiment of this pivot is a continuous ("piano") hinge 7 attached robustly to an intermediate plate 8, which rigidly interconnects into a self-supporting unit the entire hinged leg assembly and table frame combination, independent of (without) the table top 1. By appropriate bonding and fastening to the frame 2 and intermediate plate 8, the table top 1 enhances the strength and rigidity of both the frame 2 and intermediate plate 8. The intermediate plate's 8 resistance to deformation determines the strength and rigidity of the legs in their erect working position. The intermediate plate 8 is for the support, through rigid connection with the frame and firm bonding with the table top, of the high leverage stresses exerted by the tubular cross member and legs combination 3 and 5 in conjunction with the hinge 7, and to a small extent the locking forces on the locking spring 9 through combined bracket 10 and frame 2. Therefore the intermediate plate 8 can be welded or brazed along its continuous contact with all three sides of the frame 2, and the frame in this area, although an open "U" profile, or channel, should be closed to form a rigid tube by channel 10, as drawn, adjacent to the rotational legs and cross member unit, and for highest heavy duty rigidity, closed around the curves unto the end of the intermediate plate (not shown in the drawings, which reflect a medium quality version). As seen by comparing Figure 7 with Figure 8, a leg stopping surface 11 of Figure 7, prevents the leg assembly 3,5 from rotating beyond substantially 90 degrees (so that stopping surface 11 is substantially parallel to leg assembly surface 12).

A preferred inexpensive enhancement to the basic design discussed thus far, including the three-legged round version of this table, is the second leg stop bracket 15 illustrated in Figures 13 and 14. Such an optional bracket 15 at each leg, located near each corner of the table frame in the case of a rectangular table frame as shown unfolded and folded in Figures 15 and 16, respectively (which would fit nicely also underneath a round table having four legs), adds a second stopping surface at each of the legs, which is exactly the point of greatest stress on the piano hinge due to leverage, and reduces that leverage ratio at least by a factor of one to the square root of 2. In other words the stress on the hinge is reduced to no more than 0.707 times what it was without this bracket. Because the bracket 15 can contact the leg at a point beyond the spring-engaging corner of the cross member, this stress reduction is even greater, giving a ratio number even smaller than 0.707. Figure 15 also shows two support blocks 20 in the center of the table whose purpose is to support the table legs while the table is being carried with the legs folded. A long table would of course have four such support blocks instead of two, one for the foot of each leg.

The leg stopping surfaces of the intermediate plate 8 and the optional leg stopping bracket 15 can be protected from corrosion with either suitable metal plating, or special thin plastic films, with possible adhesive backing, instead of paint which can crack or chip under the high stress of high-leverage contact. The corresponding contact surfaces of the rotating horizontal cross member can likewise be protected from possible corrosion. A higher quality, heavy duty table can also feature brazing or welding some of the links in the continuous hinge located nearest to the legs both to the intermediate plate, as well as to the hinge plate itself, to prevent the rolled hinge from unrolling under stress which may be somewhat more concentrated at the legs 2, due to the imperfect rigidity of the cross member 5. On the contrary, for a cheap table, the floor plate could be of more deformable steel, unconnected to the frame, or entirely eliminated (preferably compensated through the use of a hinge with a wider leaf for greater adhesive bonding surface to the underside of the table), and the construction less robust, with a lowering of quality. For plastic top tables, including blow molded tables, the top of the intermediate plate 8 would likely need to be reinforced to be made highly rigid, which can be done as simply as bonding a strong wooden board to this area. Or the complete metal table structural unit, reinforced by a rigid stiffening panel on top of intermediate plate 8, could be molded directly into a suitably reinforced plastic table top matrix in a single molding operation.

At each tubular cross member 5 is a one-piece locking mechanism, a simple spring approximately as illustrated (e.g. Fig. 8), by means of which the tubular cross member 5 is firmly pressed against its rotational limit, in practically full surface contact with the intermediate plate 8 (and possibly also the end surfaces of the legs 3, depending on how they are united with the cross member 5, although a welded splice of the tubes trimmed at 45 degrees joined to form 90 degree comers would seem to produce an optimal joint for square tubing.). The locking spring 9, which is rigidly attached to the adjacent frame element 10 (Figs. 6-10), can engage the cross member 5 near the maximum distance from the cross member pivot 6 for maximum mechanical locking advantage, or counter- leverage (thus minimizing the strength requirement of the locking spring).

The preferred sheet steel support, i.e. frame element 10 for the locking spring 9, performs several functions: it closes the "U" channel frame next to the leg bearing cross member to form a rigid tube, adding necessary strength and rigidity for the intermediate plate 8 to support the high locking stresses due to leg leverage; it provides an appropriate mounting surface for attaching the locking spring 9; it provides a backing surface to limit the rearward yielding motion of the locking spring 9 in the direction of the frame during locking, thereby forcing the locking spring 9 to engage and lock the cross member 5 at the optimum angular position in the turn of the legs for locking (see Fig. 7). The result of such a spring movement limiter, or stop, is assured, "positive" locking action. Also, unlocking is advantageously "delayed" in terms of rotational angle, since there is no stop for the spring 9 in the opposite, forward, or unlocking direction (See Fig. 9). Consequently, the legs 4 must be turned a greater angular distance than for locking before the locking spring 9 will disengage, which is a safety advantage to avoid sudden and unintended collapse of the table under extreme forces on the table.

By virtue of extending the locking spring 9 up to nearly the entire length of the rotating cross member 5 which it engages, the use of an inexpensive light and flexible spring becomes possible due to the unusually high pressure attainable from an unusually wide spring. Thus, a key inventive step is the realization that adequate locking force, without the use of the customary unsightly and interfering diagonal leg braces, is achievable by exploiting the long locking geometry available along the normally extensive length of the cross member (typically the narrow, or "end", width in the case of a rectangular table) by application along the edge diagonally opposite from the hinged corner of this cross member the cumulative pressure of an uncommonly wide spring. The spring needs to be quite yielding (elastic) in order to effectively and durably engage and disengage the cross member (see Fig. 10).

The required flexibility normally, or intuitively, suggests weak locking force, and therefore unsuitability of such a spring for securely holding a table erect in normal use, working against anticipated great leg leverage at the cross member. The wide structural span (from leg to leg in case of a leg at either end) of the cross member is available for application along this width of an unusually long spring whose cumulative pressure by virtue of this width would attain the required locking force.

A corrolary insight was the recognition that to attain secure table stability the locking force applied by the spring 9 need not be great, because the table as a whole is always held rigidly erect by at least one of the two rigidly joined sets of legs. In a traditional completely rigid table, both pairs of legs do this. In this invention, one rotating set of legs is nearly always forced against its rigid mechanical stop, or at right angles to it, which meets with inherently rigid resistance, for any direction of force on the table, resulting in adequate overall table rigidity, in spite of the fact that at the opposite set of legs the locking spring may theoretically yield at a relatively low force applied at the foot of the table leg.

Balancing spring properties against spring length can attain any practical total distributed spring locking force. The greater the spring length, the gentler, more flexible, more durable, and less exotic or expensive can be the spring material. Consequently, the choice of spring materials advantageously grows with the spring length, such as economy, and ability to weld, braze, form, etc. Thus the large available span of the rotating cross member 5 enables a wide choice of materials, not excluding plastic, for an all-plastic table, including a suitable version of the locking spring 9.

The obvious concern regarding the limited, possibly even weak locking force of any such locking spring is answered by the fact that the present invention embodies a robust physical limit to the leg rotation in the direction of extension. Because the opposite pairs of legs 4 open in opposite directions, for any force applied to the table, one set of legs will always be forced against its rigid stop, and hence hold the table rigidly immobile, within the constraints of floor friction, while the locking spring 9 of the opposite pair of legs, which is potentially subject to compression by such a force if the opposite pair of legs slip on the floor, can be designed to be as rigid as necessary, using material or dimensional properties, such as added spring thickness or width, multiple spring layers, or support structures as needed. In other words, great total locking force of the locking spring 9 is consequently not necessary, and locking force which is comfortably modest for snapping the rotational leg assembly (or unit) into lock and snapping out of lock, is very acceptable.

A practical tradeoff, or optimized balance between the property of ease of locking and unlocking of the legs, and resistance to leg collapse under applied table force is determined experimentally by dragging the table under various loads across floors of various fπctional resistance. Lubrication of the sliding locking spring 9 contact with the cross member 5 may be addressed by plating the cross member 5 with a soft metal such as copper, to form a bearing interface with the hard metal of the spring. Many lubrication techniques are known, and the open and accessible structure of the lock facilitates easy conventional lubrication and cleaning. The preferred implementation of this invention favors popular folding table sheet steel channel (sheetmetal bent in a "U" shape) for the frame, as well as popular fiberboard or unreinforced plastic table material, or the reinforced blow molded plastic table tops coming into popularity. Fiberboard and especially unreinforced plastic tables need supporting frames, since such a table lacking a supporting frame can sooner or later distort or fail. Folded or erect, the simple and simple to use, compact, lightweight, yet robust locking mechanism pertaining to this invention is concealed within the perimeter and shallow depth of the table frame, and when erect, the table is scarcely distinguishable from the optimal lines and configuration of a welded tubular steel frame table, whereby the aesthetic objective of this invention is achieved. In addition, safety is provided for the user, in that the table can be designed so that nothing extends below the table frame to interfere or snag, except the legs in their extended position. A table incorporating the benefits of this invention permits optimal freedom of seating at the ends of even the shortest table because the table legs are at the corners of the table.

Many variations of this invention may be effected, without departing from the scope of the invention. Folding table of the invention can have table top of arbitrary size, shape, structure and composition (see for example Fig. 11). In principle, this invention may be readily implemented totally in plastic. Preferably, reinforced plastic where needed. In addition, the legs 3 can be reinforced as shown in Figure 17 using optional stiffening crossmember 25.

In a much lighter all-plastic version, there may be no apparent frame, and probably bulkier parts, with much internal reinforcement, probably with fibers, and structural parts of the metal version could be only functionally adapted into the plastic embodiment. In other words, the plastic functional equivalent embodiment of this invention may use parts which are very different in appearance from the metal version, may not embody all of those parts, and may have parts or structure which is not at all present in the description of the popular metal frame and legs version described in the preferred embodiment above. Similar comments apply to other materials, and combinations of materials. Even the spring may be plastic.

But having a different design for a plastic spring latch - a flat vertical plastic sheet mounted in a similar position with respect to the square cross member as in the metal version, but having relatively small movement, and having a rigid engaging "catch" on the end, as an angled "tooth", or "shoulder" to engage by spring pressure the corner of the cross member at a wedging angle, so as to yield, break its grip and slide back under unlocking tension. This approach would also work in metal, but less effectively than the presented version, as a simple flat spring with a less than 90 degree bend at the end, either flat or possibly curved round to engage by wedging action the corner of the cross member (Figure 12).

A variety of latch designs is readily conceivable. Instead of the spring the means of holding the cross member in its erect position with firm force against its stop can be a snap-open/snap-locked resilient fastener, which can be magnetic, adhesive, vacuum (e.g. suction cup), spring (e.g. clip), rubber (e.g. clip), mechanical (clip), or similar, enabling automatic engaging of the legs in their erect position, and automatic disengaging of the legs from their fixed erect position. Figure 18 shows a magnetic strip, instead of a latch spring. Obviously, the magnetic strip may be attached to either surface being joined, and work just as well. Or two strips of approximately half the thickness (and magnetic strength) of the preceding single strip can be applied to BOTH surfaces to be locked together, such that the magnetic polarization of the vinyl strips are opposite, so the strips attract. Such paired strips are commercially available, particularly for use in latching together nonmagnetic materials such as plastic or wood. Herein lies the application of such a strip in an all-plastic version of my table. A metal version is shown in Figure 8, but the plastic version can easily be molded such that the magnetic strip is imbedded into the cross member, so as to present a continuous flat surface where the two surfaces come in contact. In Figure 18, the magnetic strip is attached to the table, not the cross member. Figure 19 shows matched, oppositely polarized attracting magnetic strips in use, attached to both the cross member 5 and the table 2. Figure 20 shows the magnetic strips attached only to the cross member.

An all wooden table is possible under this concept, with the obvious exception of the spring, its engaging surface on the wooden cross member, hinges, and similar hardware typically of metal in wooden tables. The invention makes no suggestion of dimensions or relative proportions, as does the ideal embodiment. The spring can thus be long or short, in the horizontal direction parallel to the axis of the horizontal crossmember, and can be of any shape and relationship to the surrounding structures, segmented or continuous, connected in any manner to the table or frame at any suitable location, so long as it accomplishes the same function: automatically (without operator intervention, other than turning the legs as described) engaging and disengaging the table leg cross member with enough force to hold the cross member securely in the erect position. A short table would necessarily have the legs offset in one way or another (legs folded on top of each other (thus having half the thickness shown) or side by side, etc.)

It is also conceivable to attach the spring to the rotating cross member, which could be, for example, an angle ("L" profile) or channel ("U" profile) iron instead of a rectangular tube such that the spring is located within the sides of the L or U, which would then engage a suitable structure fastened to, or part of, the table surface or frame (An example of such a structure is an inverted "L" angle iron along the frame adjacent to the rotating cross member, whose edge engages the locking spring in the cross bar, etc.).

In other words, whereas in the preferred embodiment, the spring was fixed to the table (frame), and the rotating cross member which the spring is to engage was moving, these roles can be easily reversed, by attaching the locking spring to the cross member, to engage a structure analogous in function if not in form to the moving cross member structure in the preferred embodiment described above, without departing from the scope of this invention. The preferred means of holding the legs in the folded position may be replaced by any other means, and likewise, the leg deformation support.

These are nonessential to the invention, and may in fact, be entirely absent, and still meet the scope of this invention. In addition, the described embodiment is a table, however, the concept of the invention would be equally applicable to a chair, a bench or any other structure that could be folded for storage or the like.

Further, the invention has been described in connection with three or four legs. However, the invention would work equal well with two legs. A two legged embodiment would have broad feet to stabilize the legs. Even a one legged embodiment is within the scope of the invention.

In the embodiments described above, by manually applying pressure to a respective leg to cause the fastener to break its grip, the table legs can be moved from the erect position to the folded position. In another embodiment, a disengagement device can be employed. In a preferred embodiment the disengagement device is a spring latch disengagement device.

Figure 21 shows a partial X-Ray view of the latch mechanism in the approximate center of the hinged leg-bearing rotational cross member 5, showing an embodiment of a disengagement device, operator control handle 31. Also shown is the supporting rotational pivot shaft 32 of handle 31 and the surrounding structure. The control handle position is displayed in its normal retracted, or "home" position. This control handle has a spring return 34 as shown in Figure 22 to automatically return the control handle 31 to this home position when the operator releases it.

The view of Figure 21 is from the bottom of the table, or from the floor, looking up at the mechanism against the underside of the table, near the edge of the table. The edge of the table frame 2 is shown. In the operation of the latch, the handle 31 is swung on its shaft 32, 90 degrees outward from the table, crossing the table frame 2 to where it is perpendicular to table frame 2. In this position, the table leg locking spring 9 is forced fully away from and disengages the leg supporting rotational crossmember 5, permitting the legs 3 to be folded. However, the handle 31 need not be turned 90 degrees and can be turned at different angles in order to disengage the locking spring 9.

Figure 21 shows edges of the lower flange of the "U" channel table frame 2 and edges of the square tubular rotational leg bearing cross member 5. Figure 21 also shows the pivot hinge 7, showing the horizontal and vertical leaves and hinge segments, the base plate 8 supporting the folding leg structure, to which the hinge 7 is attached and the latching spring 9, shown in its engaged position, engaging the crossmember 5. Bend lines 10 of frame stiffening channel to which latching spring 9 is attached are also shown.

A cam bearing block 36 is rigidly attached to spring disengagement plate 37. The spring disengagement plate 37, slides in a substantially 90° arc (see Figure 23 & 24) to release spring 9. Control handle return stopping block 38 is rigidly attached to disengagement plate 37. A circular cam 46 is rigidly attached to shaft 32, closely engaging for a sliding fit circular holes in both cam bearing block 36 and spring disengagement plate 37. Note that the spring disengagement plate 37 slides on the surface of crossmember 5 (such that the motion of all points on its surface describe a short substantially 90° arc, the locus of which is depicted in Figures 23 & 24) by means of intermediary blocks 50, 51, and 52; cam bearing block 36, and its own 90° bent edge. Blocks 50 and 51 are rigidly attached to crossmember 5, and block 52 is rigidly attached to disengagement plate 37. The central intermediary block, via which disengagement plate 37 maintains constant sliding contact with crossmember 5, is the cam bearing block 48, in approximately the middle of plate 37, yet positioned (optionally and optimally - not necessary but recommended) such that when maximum disengagement force is applied by plate 37 to spring 9 (at the substantially 90° turn of handle 31), the spring force on plate 37 is balanced around the pivot hole of cam 46.

If an ideal perfect balance such as just described could be maintained and guaranteed, blocks 50 and 51 (Figure 23 & 24) would not be needed. However, because of imprecision in manufacturing, the latter three blocks at each end of plate 37 enforce perfect balance, or parallel alignment, of plate 37 with crossmember 5 and spring 9, ensuring uniform disengagement of spring 9. Also, when control handle 31 is released, spring 34 (Figure 22) forces the handle 31 and spring disengagement plate 37 to return to their normal positions. This "normal position" is established by the motion limiting contact of blocks 51 and 52 (Figures 23 & 24) at both ends of plate 37. Sliding contact is maintained between the sliding surfaces of blocks 51 and 52 by retaining plates 53 (Figure 23 & 24) and the retaining effect of control handle 31 itself.

A return to rest stopping block 38 to stop the travel of the control handle in its resting position: This stopping block 38 is rigidly attached to the spring release plate 37 at its rear edge. Block 38 is preferably a block of metal brazed, welded, or similarly attached to plate 37.

Figure 22 is a cross sectional view that is virtually identical to the main features of the corresponding cross sectional view shown for the releasably latched version of Figure 7. The basic difference being that the latching spring 9 in the releasable version has a more sloping, releasable bend to it, whereas in this version the bend is sharper, and grabs hold of the cross member 5 with a grip which will not let go by force applied to the table legs. Therefore, the release mechanism 31 is added. This demonstrates that no change in tooling will be necessary to manufacture both versions of this table at one facility.

Figure 22 shows the latch release operating handle 31, which is rigidly attached to a circular cam disc 35, and both of the former are rigidly attached to the pivot shaft 32, supported by bearings 33A and 33B, and tensioned by latch mechanism return spring 34 to automatically return the mechanism to its normal, disengaged position when the control handle 31 is released by the operator. The cam disc 35 slidingly engages identical holes in bearing plate 36 and spring disengagement plate 37. Bearing plate 36 and disengagement plate 37 are rigidly attached to each other, and their combination makes sliding contact with the surface of crossmember 5, in such a manner that all points of the latter two exhibit a motion described by the short 90° arcs shown in Figures 23 and 24. As the control handle is turned 90°, the locus of the motion at all points on the sliding structure is this short 90° arc. Control handle return stopping block 38 is rigidly attached to disengagement plate 37.

Figure 23 shows a bottom left-hand view of a table leg locking mechanism. Figure 24 also shows a bottom view of a table locking mechanism. The two end views are nearly identical, the differences being due to the fact that the motion of all points on the spring unlocking plate 37 describes a short arc of substantially 90° such as depicted in Figure 23; and in Figure 24, the corresponding identical motion of the opposite end of the mechanism. The key to understanding the layout is in viewing the position of locking spring 9: in the fully unlocking position of control handle 31, when it is turned 90° to its terminal unlocking position, the ends of the unlocking plate 37 and the locking spring 9 coincide, so as to produce balanced force on the unlocking plate 37 which has its supporting cam bearing hole in its center. Thus if the construction were perfect, motion stopping blocks 50 on each end of plate 37 would be unnecessary. These latter blocks are in place only to perform an insurance function to insure that in the maximum unlocking position of the control handle 31, the spring 9 is truly pushed evenly back across the entire length of the cross member 5, fully disengaging it. Therefore, this embodiment is shown over engineered for purposes of illustration of the principle involved in order to make alternate embodiments easier for the practitioners of the art. This latter is not necessary for this invention. A main feature of this embodiment is the elements for the control and restriction of the motion of locking spring disengagement plate 37. This motion is described by the two short arcs, drawn with arrows at the ends, describing substantially 90°. Three identical stopping, or motion limiting bars are shown: 50, 51, and 52. Bar 51 is rigidly attached to spring disengagement plate 37; and bars 50 and 52 are rigidly attached to the leg-bearing horizontal crossmember 5, such that bar 51 slides between bars 50 and 52, the latter two bars limiting the motion of bar 51.

Thus, bar 50 insures that when plate 37 is in its maximum disengagement extension, both bars 50 at each end are in contact with both bars 51, insuring that the locking spring 9 is forced back uniformly and precisely to its optimal disengagement position. This position is sensed by the operator, in that he feels the resistance of the blocking, as well as sees the 90° position of the handle; at which point the operator knows that the locking spring is disengaged, and he may begin to rotate the table legs to fold them.

Bar 52 at both ends of the spring disengagement plate 37 stops the spring 34 driven motion of the entire mechanism at its resting position, where the control handle 31 is parallel to the horizontal crossmember 5, and the spring disengagement plate 37 is resting in its fully retracted position.

Retaining and guide plate 53, in conjunction with its mounting and precision spacing block 54, insure that the ends of the spring disengagement plate 37 cannot be forced out of their normal positions. This is not necessary to the operation of this invention, but is a useful precaution against accident or vandalism.

Figures 23 and 24 also show optional elements such as table leg "glide", or foot 26, assuring an acceptable contact between the table and floor surface. Pop rivets 40, or other suitable fasteners for convenient manufacture are also shown.

As set forth above, Figure 24 is nearly identical to Figure 23, and contains the same identical elements. The embodiment of Figure 24 demonstrates fully the 90° arc in which all of the points on the spring release plate 37 move. The intention of this figure is for the reader to compare the two ends of the mechanism, and referring to the two 90° arcs tipped with arrows, visualize the motion of spring release plate 37, to which are rigidly attached the intermediate stopping bars 51. One can discern the 90° arc motion traversed by stopping bar 51 as it travels from its resting contact with bar 52 (shown) to its limiting contact with bar 50 (not shown, but indicated by the arrows).

Figure 25 is an embodiment that is only a slight modification of the preferred embodiment of the latch unlocking mechanism described above with respect to Figures 21-24, entailing only minor differences, wherein the numbering of the parts common or similar to the two embodiments are exactly the same. Where there is a unique element, it has a unique number.

A primary difference between the two embodiments (of Figures 21-24 and 25-27) is that the cam bearing block 36, which in Figures 21-24 was rigidly attached to spring disengagement plate 37, is in the embodiment of Figures 25-27, free to slide in contact with the latter. And the spring disengagement plate 37 is restrained in its freedom of motion by elongated hole 47 within the latter, through which control handle shaft 32 extends, having a close sliding contact with the latter, such that the hole and the pin comprise the guide for the freedom of motion available for plate 37. Therefore the motion of plate 37 is restricted to motion substantially perpendicular to the axis of crossmember 5, and substantially parallel to its surface, which directly pushes locking spring 9 backwards to its unlocked position. Thus, as the control handle 31 is turned 90° from its rest position, cam bearing block 36 describes exactly the same 90° arc of motion which it did in the embodiment of Figure 21-24, above, but being always in contact with the two surfaces of disengagement plate 37, as it traverses its full arc of motion, it pushes against, and slides along, the 90° flange of plate 37, forcing that flange and plate 37 in the direction of locking spring 9. Since plate 37 is captive in its hole 47 to guide pin 32, plate 37 is thereby constrained to move directly against spring 9, forcing it back to its unlocking position.

Similar to the embodiment of Figures 21-24, at the ends of disengagement plate 37 are stopping blocks 39 and 42 to insure the forward and rearward limits of travel of 37. In this case, there is no intermediate block (corresponding to bar 51 in the embodiment of Figures 21-24). Rather, there are cutouts in the body of plate 37 itself which provide the stopping surfaces analogous to the function of bar 51 previously. A return to rest stopping block 38 is used to stop the travel of the control handle 31 in its resting position. This stopping block 38 is rigidly attached to the spring release plate 37 at its rear edge. The stopping block 38 is preferably an angle bracket that can be brazed or welded (or attached in any suitable manner) to plate 37, at its rear edge. However, note that this bracket is preferably located as near as practical to the center of plate 37. In this central position, the spring driven handle 31 acting on the bracket 38 forces plate 37 backwards to its normal rest position.

Figure 27 further shows a retaining and guide plate 41 for spring release plate 37, insuring that the latter, which is long and easy to bend, can not be forced out of its position and damaged. In addition, a forward stop 42, or motion limit for spring release plate 37, ensures even and precise unlocking of the latching spring 9. A rear stopping surface 43 for plate 37, fixes the rest position of plate 37. Preferably, surface 43 is a notch in plate 37. A forward stopping surface 44 for plate 37, fixes the spring unlocking position of plate 37. Preferably surface 44 is also a notch in plate 37.

In view of the foregoing, the invention resides in the novel selection, arrangement and combination of parts performing clear functional roles of novel choice and combination, as described and claimed, producing a new and advantageous result; it being understood that changes in the precise embodiment of the invention herein disclosed may be made within the scope of what is claimed without departing from the spirit of the invention.