Abstract:
An adjustable table is easily moved from coffee table height to dining table. The weight of the table top is supported by a pneumatic cylinder, preferably exerting a force slightly greater than the weight of the table top. The cylinder connects to a much larger air tank, so that essentially constant lifting force is exerted. For stability of the table top a guide mechanism firmly retains the table against rotation, side movement or tilting. A unique locking mechanism retains the table at a selected height and is easily released with a finger lever.

Description:
This application claims benefit from provisional application Ser. No. 60/984,668, filed Nov. 1, 2007. 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention relates to a design of a table which serves multiple purposes as a coffee table and/or dinner table. For this purpose the table is vertically adjustable from a low coffee table height, such as 18 inches, continuously up to a dining table height, such as 29 inches. Other height ranges can also be encompassed, such as a table height for standing use. 
     In the majority of motor homes and other recreational vehicles currently produced the design focus is on providing a social gathering area which must double as a dining area because of limited space. This gives rise to the need for a table which can serve the dual purpose of a coffee table and a dining table. The present invention addresses this need by providing a table that can be easily raised from coffee table height to dining table height. 
     Other areas where this present invention is useful are in efficiency and studio apartments and in boats where space is also at a premium. Still other potential areas of use are in child care and elder care where a table easily adjustable can satisfy the need for a specific height. 
     Prior art includes several designs intended to fill this need. Although these designs currently on the market can fill the basic requirement of coffee table height and dining table height, they are universally difficult to change from one height to another and are generally limited to two specific predetermined heights. They continue to generate dissatisfaction among those who use them. Most require skill and/or physical strength to change the subject table from one height to another height. 
     The following patents have some relevance to adjustable-height tables or other adjustable-height devices: U.S. Pat. Nos. 7,246,779, 7,182,323, 6,997,116, 6,874,432, 6,840,582, 6,578,501, 6,571,720, 6,536,357, 6,435,110, 6,378,671, 6,343,556, 6,283,047, 6,227,357, 6,101,956, 5,553,550, 5,513,825, 5,438,939, 5,322,025, 5,313,892, 5,197,393, 4,436,007, 3,710,735 and 3,080,835. Of these patents, U.S. Pat. No. 6,283,047 discloses an adjustable-height table that can work on a pneumatic principle, i.e. an air spring. In the principal embodiment a double pivot is involved, with the table top swung upward or downward on an arm, thus displacing the horizontal position of the table as it is raised or lowered. In a second embodiment the movement of the table top is vertical, with a “bellows cylinder” or bellows type spring acting against gravity exerted on the table top and associated frame. A reservoir separate from the bellows cylinder is included. That table did not provide for a guiding assembly to provide stability of the table against lateral, tipping or rotating motion, through all the range of height adjustment, as in the present invention described below. Moreover, that patent involved a separate and spaced apart air reservoir connected by a fluid line to the pneumatic cylinder or bellows cylinder that exerted upward force on the table top. 
     U.S. Pat. No. 7,182,323 also employs a type of pneumatic spring, but in a much different arrangement from that of the present invention. Several of the other patents in the above list employ mechanical lifting devices, motorized or hand-rotated. Some use hydraulic cylinders, not necessarily for table tops as in the current invention. 
     SUMMARY OF THE INVENTION 
     In its several embodiments this invention is a system which includes a base designed to rest on the floor or other supporting surface, a table top and a relatively frictionless means to raise and guide the table top from a coffee table height, such as 18 inches, to a dining table height, such as 29 inches. Other possible height ranges include table height to a height appropriate for standing. A means is also included to provide a lifting force sufficient to support slightly more than the weight of the table top assembly, preferably with a net light lifting force. This lifting force is such that little or no effort is required from the user to raise the table and only light downward pressure is required to return the table to a lower position. A means of locking and unlocking the vertical movement of the table in an infinite plurality of vertical positions is also included. A relatively frictionless guiding mechanism maintains vertical alignment and a stable relationship between the table top and the base. 
     In the preferred embodiment frictionless linear bearings sliding vertically on one or more suitable shafts provide the required guidance and stabilization and one or more air cylinders connected to one or more pressurized air reservoirs provide a lifting force. A further aspect of the preferred embodiment uses a large sealed tubular tank member into which an air cylinder is directly mounted with the rod end of the cylinder projecting out of the tank. The tank end is sealed around the body of the air cylinder by means such as multiple o-rings and the air cylinder is held in place, preferably down in the tank so as to be integral with the tank, by means of a suitable bracket fastened securely to the tank. The rod end of the air cylinder is open to the atmosphere and the other end is in and open to the interior of the tank. This end of the air cylinder is therefore pressurized to the amount of pressure established in the tank. A suitable means, such as an automotive type air valve assembly, is provided for introducing air into the tank to bring the pressure to the desired amount. The integral mounting of the air cylinder into the tank eliminates numerous pipe fittings and pipes and/or hoses which would otherwise be required to connect the cylinder to the tank to form a closed system as taught by Haller in U.S. Pat. No. 6,283,047. The benefits include reduced chances of air leakage and reduced manufacturing costs. 
     The preferably integral air tank and air cylinder assembly is mounted in such fashion as to oppose the downward weight force of the table top assembly. When the cylinder rod is pushed back into the cylinder air is returned to the tank maintaining the pressure and therefore no external air pressure source is required once the tank has been charged to the required pressure. Since the combined volume of the air cylinder and the tank is substantially greater than the displacement volume generated by the air cylinder movement (in a ratio such as at least about 4 or 5 to 1), the lifting force applied to the table top by the air cylinder remains essentially constant (in contrast, U.S. Pat. No. 7,182,323 described above allows a 2 to 1 tank to cylinder ratio, which would not provide an essentially constant lifting force). As a result the air system can be pressurized to a pressure slightly higher than the pressure required to raise the table top assembly to its full height without external assistance when the locking mechanism is released, but still require only a light downward external force applied to the table top with the locking mechanism released to lower the table to the coffee table configuration or an intermediate level. 
     This type of integrated modular tank and air cylinder unit, especially in the integrated form described, has in any other potential applications essentially constant force without external power or air source connections as needed in a self contained unit. 
     Another feature of the preferred embodiment of the present invention is the design of the locking mechanism which allows for an infinite number of vertical height positions at which the table top assembly can be set and locked in place. This locking mechanism is actuated by a bell crank pivotally mounted to the upper table top assembly with its horizontal arm preferably recessed into the underside of the table top in a narrow slot such that it can be easily moved by upward finger pressure but not by accidental pressure from a person&#39;s knee, etc. The end of this arm is conveniently located near the edge under the table top. The other, vertical arm of the bell crank locking mechanism depends downwardly and is positioned to release the locking mechanism allowing free vertical table top movement when the horizontal arm is raised. This locking mechanism consists of a body which contains a slot through which one of the supporting shafts passes and which contains two eccentric circular clamping units brought to bear on the subject supporting shaft by a spring. The clamping units or cam lock units are arranged in an opposed or up/down mirror image fashion so that one is made to tighten with upward motion while the other clamps tighter with downward motion. As a result, until released, the subject shaft cannot move in either direction until released by the bell crank mechanism. This design of clamp has many potential applications wherever two-directional infinitely adjustable clamping is needed. 
     Also in the preferred embodiment of the invention the air cylinder or cylinders are oriented to provide the lifting force by upward cylinder rod extension. By this orientation cylinder rod seals are eliminated from the sealed pressurized system and rod seal leakage cannot affect the pressurization of the system. Since in this orientation the rod end of the cylinder or cylinders face upward and the upper end of the cylinder or cylinders are left open to the atmosphere, appropriate lubrication can be introduced into the open port on the rod end. Also in this embodiment of the invention a plug having a hole of appropriate size drilled through it is inserted into the open port on the rod end to control the rate of air flow in and out of the atmospheric end of the air cylinder or cylinders and thus to control the rate of vertical movement of the table top assembly. 
     Additionally in the preferred embodiment of the invention a shroud system consisting of upper and lower telescoping sheet metal members hide the mechanism between the table top assembly and the base assembly for aesthetic reasons. 
     In other embodiments of the invention a sealed tank or bladder unit or units can be substituted for the integrated modular tank employed in the preferred embodiment to supply air pressure to the air cylinder or cylinders. These and other objects, advantages and features of the invention will be apparent from the following description of a preferred embodiment, considered along with the accompanying drawings. 
    
    
     
       DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a drawing showing the present invention, a pneumatically adjustable height table, illustrating the table in two vertical positions. 
         FIG. 2  is a drawing showing the present invention, a pneumatically adjustable height table, illustrating in a cutaway view format the various parts and features of the present invention in its preferred embodiment. 
         FIG. 2A  is a drawing showing the present invention, a pneumatically adjustable height table, illustrating the same parts and features shown in  FIG. 2 , but in an exploded view format. 
         FIG. 3  is a cut away drawing the integrated air tank and cylinder unit used in the preferred embodiment of the present invention, with  FIGS. 4B and 4C  omitting a spring, for clarity. 
         FIGS. 4A ,  4 B and  4 C are front, side and top views showing the infinitely adjustable clamping system used in the preferred embodiment of the invention, with  FIGS. 4B and 4C  omitting a spring, for clarity. 
         FIG. 5  is a drawing showing the drop leaves used in the preferred embodiment of the present invention in their fully opened, extended position. 
     
    
    
     DESCRIPTION OF PREFERRED EMBODIMENTS 
     The present invention provides a convenient system for raising a table top  1  as shown in  FIG. 1  from a low position such as an 18 inch coffee table height to a higher position such as a 29 inch dining table height (or with other height limits), relative to a mounting base  2 , by means of a pneumatic system enclosed for cosmetic purposes in a shroud assembly consisting of two telescoping parts  3 . Only the outer shroud component  3  is seen in  FIG. 1 ; an inner component can extend upward from the base  2 , just inside the illustrated component  3 , which is secured to and moves with the table.  FIG. 1  also shows that the base  2  includes a floor-engaging pedestal. The base  2  is removable from the base plate  19  seen in  FIG. 2  and interchangeable via several bolts (not shown) to a different style or configuration or material of floor-engaging element. 
     As shown in  FIG. 2  and in exploded view  FIG. 2A , the invention embodies a system in which an integrated air cylinder and tank assembly  4  supplies a substantially vertical force to a table support frame  5  to counteract the gravitational force exerted on the table top surface  1  and in which substantially frictionless guiding means  8  and  9  (with essentially frictionless linear bearings, not shown) running on vertical shafts  6  and  7  stabilize the vertical movement of the subject table top surface  1  relative to the mounting base  2  or other mounting device. At least one such vertical shaft  6 ,  7  is provided, more preferably two. Vertical support members  10 ,  11  and  12  join the frictionless guide assembly  8  and  9  to the top frame  5 .  FIG. 2A  more clearly shows this upper assembly and indicates the outer shroud component  3   a  that is secured to the table top from 5 and fits over the base shroud component  3   b .  FIG. 2A  also shows that the unit  4  can be removed from the base unit (as by several bolts, not shown). The unit has a cylinder rod  4   a  that engages the table top frame; it need not be secured to the table top but can merely bear upwardly against it. 
       FIG. 2A  also shows, as part of the base components shown on the left, a stabilizing, structural member  17 , which can be a generally horizontal bar or plate as illustrated. This can be firmly anchored by a generally vertical anchoring pedestal or post  18  secured to a base plate  19 . As an alternative, the bar  17  could be anchored to the wall of the base shroud component  3   b , in one or two places, to firmly stabilize the vertical shaft or shafts ( 6 ,  7 ). Any appropriate form of bracing could be used for stabilizing the upper end of the vertical shaft or shafts. 
     A further element of the preferred embodiment of the invention is a clamping unit  13  mounted on the support member  10  and which clamps onto the guide shaft  7  until released by the vertical arm  14  of a bell crank assembly  14 ,  16  (pivotally mounted by a shoulder bolt  15 ) when upward finger pressure is applied to the distal end of the horizontal lever  16  within the notch  29  in the edge of the table top  1  illustrated in  FIG. 1  and  FIG. 5 . 
     An important element of the preferred embodiment of the invention is the integrated air cylinder and tank assembly  4  shown in detail in the cut away drawing of  FIGS. 2 and 3  in the exploded view of  FIG. 2A . The top of the air reservoir or tank  4  is fitted with O-rings  21  that form a static air tight seal around the body of the air cylinder  20  (other types of seal could be provided here). A bracket  22  holds the air cylinder  20  securely in place in the air tank  4 . An air inlet fitting  23  provides an accessible means of pressurizing the air tank  4  and the air cylinder  20 , with an air tight seal. Communication between the cylinder&#39;s displacement volume and the volume of the tank  4  is provided by an opening  20   a , avoiding the need for tubes and fittings to connect the cylinder and tank. No such fittings are needed on either end of the cylinder in this implementation; the upper end, above the piston, is open to the atmosphere. Due to the fact that movement of the piston (not shown) and piston rod in the air cylinder  20  as the table top  1  is raised or lowered displaces only a small volume of air compared to the much larger volume of the air tank  4 , the air pressure remains essentially constant in both the tank  4  and the air cylinder  20  and therefore the vertical force exerted upward on the table top  1  also remains essentially constant throughout vertical adjustments. Additionally, since as the table top  1  is lowered, the air used in the air cylinder  20  to raise it is returned into the air tank  4 , the air pressure charge in it is essentially permanent. In the event that a change in the air cylinder  20  lifting force is desired, air pressure in the tank  4  can easily be altered using the air inlet fitting  23  accessed through a hole provided  12   a  in the base plate  19 . 
     Air is mentioned as the preferred gas for charging the cylinder and tank, but other gases could be used if desired. 
     Note that the pneumatic cylinder and its relationship to the tank  4  need not be precisely as shown and described above. The cylinder  20  could be threadedly fitted into the top of the tank, with a thread seal. In another form the top portion of the tank  4  could be thickened or it could have a cylindrical collar that itself forms a cylinder wall in which the piston moves up/down. The piston could be long and with a lower end that simply extends down into the tank beyond the end of the cylinder above. All of these configurations are to be understood as within the invention, and within the meaning of “cylinder” in the claims. 
     The clamping unit  13  is an essential element of the preferred embodiment of the invention.  FIGS. 4A-4C  show the details of its function and design. The body part of the clamping unit  13  contains a slot  13   a  configured to fit loosely around the guide shaft  7 , as best seen in  FIG. 4C . This slot also contains two curved cam devices  24  made in a round spool shape pivotally mounted off center as indicated at  27 . Two pin members or cam levers  25  are securely mounted into the cam devices  24 , fixed to the cams. Each end of a tension spring  26  is hooked over one of the pins or levers  25 . The spring  26  pulls on the lower pin  25  causing the lower cam  24  to rotate clockwise which, due to its off-center pivotal mounting, causes it to press against the guide shaft  7  to be forced back against the bottom of the slot  13   a  in the clamp body  13 . Also any downward relative movement of the guide shaft  7  tends to turn the lower cam  24  in the same clockwise locking direction, tightening the grip on the guide shaft  7 . In similar fashion, the upper cam device  24  is turned counterclockwise by the spring  26  causing it to force the guide shaft  7  back against the bottom of the slot in clamping unit  13 ; and further, any relative upward movement of the guide shaft  7  will cause the cam device  24  to turn counterclockwise further tightening the grip on the guide shaft  7 . Therefore, once the spring  26  has tightened the two cam devices  24 , the clamping unit  13  is locked in place and unable to be moved either up or down relative to the vertical shaft  7 . Since the clamp body  13  is securely mounted to the upper table top support members  10 ,  11  and  12  as shown in  FIG. 2  and in exploded view  FIG. 2A , this clamping action effectively locks the table top in position until the clamping action is released. This is done by movement of the bell crank  14 ,  16 . This release is accomplished by the action of the lower end of the generally vertical depending arm  14  of the bell crank, pressing both pins  25  toward guide shaft  7 . As soon as the pressure exerted by the bell crank arm  14  is released, the tension spring  26  reestablishes the clamping action and the table top is again locked in position at the new height. 
     Note that the cam devices  24  need not be fully circular but could only describe an arc or curve of sufficient length to perform the cam function. 
     A final element of the preferred embodiment of the present invention is the use of drop leaves  28  to increase the width of the table top  1 , as shown in  FIGS. 1 and 5 . This allows the table in the mode with the drop leaves  28  folded under on both sides, as shown in  FIG. 1 , to be narrow enough to fit into the limited spaces available in cases such as a motor home with slideouts retracted. The use of special commercially available snap hinges allows the drop leaves  28  to tuck back under the table top  1  creating an esthetically pleasing and practical appearance in the narrow “coffee table” configuration as shown in  FIG. 1  but to be instantly ready to be converted to its “dinner table” or “card table” configuration as shown in  FIG. 5  with the drop leaves  28  open. The table top preferably is configured with recesses as seen in  FIGS. 1 and 5  to receive the drop leaves  28  when folded under, to give an essentially uniform-thickness table edge as shown in  FIG. 1 . 
     The above described preferred embodiments are intended to illustrate the principles of the invention, but not to limit its scope. Other embodiments and variations to these preferred embodiments will be apparent to those skilled in the art and may be made without departing from the spirit and scope of the invention as defined in the following claims.