SCOPE OF THE INVENTION 
     The present invention relates to a height adjustable table. 
     BACKGROUND OF THE INVENTION 
     Height adjustable tables are known which can be adjusted to different levels for different purposes. 
     Many known height adjustable tables suffer the disadvantages that they are limited as to the different heights to which they can be positioned and frequently can only assume two or more pre-set heights. Such tables suffer the disadvantage that they cannot have incremental heights as may be desired. 
     Many known height adjustable tables suffer the disadvantage that they are difficult to adjust to different levels. 
     SUMMARY OF THE INVENTION 
     To at least partially overcome these disadvantages of the previous known devices, the present invention provides an improved height adjustable table that can be easily adjusted to assume different heights. 
     It is an object of the present invention to provide a height adjustable table that can be adjusted to any desired height to suit different individuals or for different purposes. 
     It is another object of the present invention to provide a height adjustable table that is simple in construction and easy to adjust. 
     The present invention provides a height adjustable table, preferably with a circular tabletop which includes a vertically telescoping column to support the tabletop and with the column telescoping between extended and retracted positions. A base supports lower end of the column vertically upright. A locking mechanism is provided within the telescoping column adapted to lock the column against telescoping when the tabletop is rotated in one direction relative the base and to unlock the column when rotated in the other direction. When the table is unlocked, a user may adjust the height of the table either by manually lifting alone or assisted by a lifting mechanism to bias the tabletop upwardly and at least partially bear the weight of the tabletop. A stop mechanism is preferably provided to ensure the table is not extended so far as to disengage the tabletop structure. The base of the table is adapted to be engaged by a user&#39;s feet to prevent rotation relative to the tabletop when locking or unlocking. 
     According to one aspect of the invention, there is provided a height adjustable table comprising: 
     a vertically telescoping column to support a tabletop having an upper end and a lower end and a longitudinal axis, the column telescoping between an extended position and a retracted position, 
     the column being attached to the tabletop at its upper end, 
     a base receiving the lower end of the column and supporting the column generally vertically upright, 
     a locking mechanism within the telescoping column adapted to lock the column against telescoping when the tabletop is rotated in a first direction relative the base and adapted to unlock the column for telescoping extension or retraction when the tabletop is rotated relative to the base in a second direction opposite to the first direction. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Further aspects and advantages of the present invention will become apparent from the following description taken together with the accompanying drawings in which: 
     FIG. 1 is a perspective view of a height adjustable table in accordance with a first embodiment of the present invention; 
     FIG. 2 is a perspective view of the height adjustable table of FIG. 1 with a top structure being detached from a base structure showing the position of a locking mechanism; 
     FIG. 3 is a partial cutaway longitudinal cross section of a pair of telescopic columns of the height adjustable table of FIG. 1; 
     FIG. 4 is an exploded view of a locking mechanism in accordance with a preferred embodiment of FIG. 1; 
     FIG. 5 is a cross sectional view of the locking mechanism of FIG. 3 along section line  5 — 5 ′ in FIG. 3 however showing the locking mechanism in an unlocked position and without showing the lower column; 
     FIG. 6 is a cross sectional view of the locking mechanism which is the same as that of FIG. 5 but showing the locking mechanism in a locked position; 
     FIG. 7 is a partial cutaway longitudinal cross section of a height adjustable table in accordance with a second embodiment of the present invention; and 
     FIG. 8 is a perspective view of a table in accordance with a third embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring now in more detail to the drawings, in which like reference numerals represent like parts throughout the several views, FIGS. 1 and 2 show a height adjustable table in accordance with a first embodiment of the present invention. The height adjustable table, generally designated by reference numeral  10 , comprises a top structure  12  and a base structure  14  with a locking mechanism  30  carried on the top structure  12 . 
     The top structure  12  comprises a support  16  for a tabletop  18  and an upper tubular member  20 . The upper tubular member  20  is fixedly attached to the tabletop support  16 . The base structure  14  comprises a base  22  and a lower tubular member  24 . The lower tubular member  24  is fixedly attached to the base  22 . The upper tubular member  20  is telescopically slidable within the lower tubular member  24  and together form a vertically telescoping column. 
     The height of the table  10  can be adjusted to any level between a retracted position and an extended position. Adjustment is achieved by turning the top structure  12  clockwise or counter-clockwise relative the base structure  14 , clockwise in order to lock and counterclockwise in order to unlock the upper and lower tubular members  20 ,  24  and by sliding the top structure  12  vertically relative the base structure  14  in order to raise or lower the top structure  12  relative the base structure  14  when the upper and lower tubular members  20 ,  24  are unlocked. 
     FIG. 2 shows the locking mechanism  30  secured at the lower end of the upper tubular member  20 . The locking mechanism  30  is adapted to lock the upper and lower telescoping tubular members  20 ,  24  together at any desired position between an extended position and a retracted position. 
     FIG. 3 is a partially cutaway longitudinal cross sectional view of the embodiment of FIG. 1 showing the upper and lower tubular members  20 ,  24  and the locking mechanism  30 . 
     Each of the upper and lower tubular members  20 ,  24  is in the form of a cylindrical tube about their respective axis with each having a circular cross section along its length. The outer diameter of the upper tubular member  20  is slightly less than the inner diameter of the lower tubular member  24  so that the upper tubular member  20  is telescopically received in and axially slidably moveable relative the lower tubular member  24  in a vertical direction. 
     The locking of the upper and lower tubular members  20 ,  24  together is achieved by the locking mechanism  30  which is now described in detail with reference to FIGS. 3 to  6 . 
     As best seen in FIG. 4, the locking mechanism  30  comprises a cam bushing  62  and an eccentric collar or split locking ring  64 . The cam bushing  62  includes a cylindrical stub  66  and a projecting plug  63  comprising an upper annular flange  68 , an eccentric post  70 , and a lower annular flange  72 . 
     The cylindrical stub  66  is coaxially secured inside the lower end of the upper tubular member  20  with the end of the upper tubular member  20  abutted against the axially upper surface of the upper annular flange  68 . As seen in FIG. 3, at least one fastening pin  58  is used to fasten the stub  66  within the lower end of the upper tubular member  20 . Two fastening pins  58  are shown in the present embodiment shown in FIG. 3 each in a radially outer segment of a bore through the stub  66 . 
     The upper annular flange  68 , the eccentric post  70  and the lower annular flange  72  together define the plug  63  as a spool-shaped member having an eccentric groove to receiving the locking ring  64 . 
     The upper and lower flanges  68 ,  72  and the stub  66  are each circular in cross-section and coaxial to each other each being disposed about common axis  67 . They are each coaxially disposed relative the upper tubular member  20 . The upper and lower annular flanges  68 ,  72  each presents outwardly facing bearing surfaces facing the inner surface of the lower tubular member  24 . 
     The eccentric post  70  defines a radially outwardly directed eccentric bearing surface  78 . The eccentric post  70  is cylindrical but about an axis  71  disposed parallel to the axis  67  of the flanges and stub  66  but offset radially from this axis  67 , as best seen in FIGS. 5 and 6. A pin  74  extends radially and outwardly from the eccentric post  70 . 
     The split locking ring  64  is in the form of a C-shape with a slot  76  totally through a circumferential sector of the ring allowing the locking ring  64  to flex to expand or contract radially. The locking ring  64  has an outer surface which when unbiased is generally cylindrical about a first axis. A cylindrical opening  82  extends through the locking ring which is disposed about a second axis parallel to the first axis but displaced from the first axis such that the opening  82  is eccentric relative the outer surface of the locking ring and, for example, as seen in FIG. 4, the locking ring has a radial width which is smallest on the left hand side and greatest on the right hand side near the slot  76 . The eccentric opening  82  is of a diameter marginally greater than that of the eccentric post  70  and is adapted to fit around the eccentric post  70 . 
     The locking ring  64  has a circumferentially extending slot or cutout portion  80  opposite the slot  76 . The locking ring  64  is engaged journalled around the eccentric post  70  between the upper and lower flanges  68 ,  72  with the pin  74  positioned in the cutout portion  80 . The cutout portion  80  has a circumferential extent from a first end  79  to a second end  81 . The cutout portion  80  interacts with the pin  74  so as to limit the rotational positions which the locking ring  64  may assume relative the cam bushing  62  to being between the two positions shown in FIGS. 5 and 6. FIG. 5 illustrates a fully unlocked configuration in which the pin  74  is in engagement with the first end  79  of the cutout portion  80  and the cam bushing is rotated relatively as far as possible counterclockwise relative the locking ring  64 . FIG. 6 illustrates a fully locked configuration in which the pin  74  is in engagement with the second end  81  of the cut out portion  80  and the cam busing is rotated relatively as far as possible clockwise relative the locking ring  64 . 
     As seen in FIG. 6 in the fully locked configuration, the outer surface of the locking ring extends radially beyond the upper and lower flanges  68  and  72  of the cam bushing  62  to an extent such that the locking ring if inside the lower tubular member  24 , which is not shown in FIGS. 5 and 6, would be urged radially outwardly into frictional engagement with the inside surface of the lower tubular member  24  to lock the upper and lower columns against relative sliding. The lower tubular member  24  is not shown in FIGS. 5 and 6 to assist illustration and teaching of the relative positioning of the locking ring  64  with relative rotation of the cam bushing. 
     In contrast to FIG. 6, as seen in FIG. 5 in the fully unlocked configuration, the outer surface of the locking ring  64  effectively does not extend sufficiently radially beyond the upper and lower flanges  68  and  72  of the cam bushing to prevent relative sliding of the upper and lower tubular members. In FIG. 5, the locking ring  64  is shown to extend marginally outwardly of the upper flange  68 , however with sufficient space radially inwardly of the locking ring  64  between the locking ring  64  and the eccentric post  70  that due to the inherent resiliency of the locking ring  64 , the locking ring will engage the inner surface of the lower tubular member  24  but only with forces generated due to the inherent bias of the locking ring  64  to assume an expanded unbiased condition. 
     FIGS. 5 and 6 show the fully unlocked and fully locked positions. For locking it is not necessary that the cam bushing be rotated to the fully locked position. Locking may be accomplished by rotation of the cam bushing clockwise towards the fully locked position to an extent that the locking ring is expanded radially outwardly to accomplish locking. Similarly, for unlocking it is not necessary that the cam bushing be rotated to the fully unlocked position. Unlocking may be accomplished by rotation of the cam bushing counter-clockwise towards the fully unlocked position to an extent that the locking ring is not urged by the eccentric post  70  outwardly into the inner surface of the lower tubular member  24  sufficiently to lock the upper and lower tubular members against relative sliding. 
     To adjust the height of the table  10  of the present invention, a user preferably first steps on the base  22  with one foot. The base  22  defines stepping surfaces for the user to step on so that the user can with his foot hold the base  22  firmly to the ground and prevent the base from rotating and/or being lifted up during table height adjustment. In the present embodiment shown in FIG. 1, the base  22  comprises a plurality of radially outwardly extending spoke-like legs  32  and an annular base portion  34 . The inner end of each of the legs  32  is connected to a lower portion of the lower tubular member  24 . The outer end of each of the legs  32  is connected to the annular base portion  34 . 
     With the base  22  firmly held to the ground, or at least against rotation, the user then grasps the tabletop support  16  with his hands. The tabletop support  16  defines gripping surfaces for the user to hold onto during table height adjustment. In the present embodiment shown in FIG. 1, the tabletop support  16  comprises a plurality of radially outwardly extending spoke-like arms  36  and an annular top portion  38 . 
     The user rotates the tabletop support  16  counter-clockwise relative to the base  22  which moves cam bushing  62  and its locking pin  74  counter-clockwise relative the locking ring  64  sufficiently towards the fully unlocked position as seen in FIG. 5 to adopt an unlocked configuration. 
     In an unlocked position, a user may either pull up or push down the tabletop support  16  so as to vertically adjust the height of the table  10  by adjusting the extent to which the lower and upper tubular members are telescoped. 
     After the tabletop support is positioned at a desired height, the user then turns the tabletop support  16  clockwise relative the base  22  which moves the cam bushing  62  and its locking pin clockwise relative the locking ring  64  toward the fully locked position as seen in FIG. 6 to adopt a locked configuration with the outer surface of the locking ring urged out beyond the upper and lower annular flanges  68 ,  72  and into friction engagement with the inner wall of the lower tubular member  24 , thereby frictionally engaging and locking the upper and lower tubular members  20 ,  24  in a locked position. 
     A cover  40  is provided at an upper end of the lower tubular member  24 . The cover  40 , preferably made of plastic, is fixedly attached to the upper end of the lower tubular member  24 . The cover  40  includes a cylindrical sleeve  42  covering the outer wall of the lower tubular member  24  and a radially and inwardly extending annular flange  44  covering and extending inwardly from the top annular edge of the lower tubular member  24 . The annular flange  44  defines a circular opening  46  through which the upper tubular member  20  passes. 
     The opening  46  has an inwardly facing annular bearing surface  48  which slidably engages the outer wall of the upper tubular member  20 . The annular bearing surface  48  assists in centering and guiding the upper tubular member  20  as it slides within the lower tubular member  24 , as for example to help prevent the upper tubular member  20  from tilting so as to maintain the tabletop  18  horizontal. 
     The cover  40  also assists in preventing water and other foreign substances, such as water, dust and insects, from entering and contaminating the space between the upper tubular member  20  and the lower tubular member  24  and which may be disadvantageous to smooth telescopic movement of the upper and lower tubular members  20 ,  24 . 
     A circular mounting plate  52  is secured to the inner wall of the lower tubular member  24 . An elongated stop rod  50  is secured to the lower tubular member  24  with a lower end of the stop rod  50  detachably mounted to the mounting plate  52 . The stop rod  50  extends substantially along the length of the lower tubular member  24  along the central axis thereof. The stop rod  50  extends via an elongated central bore  60  through the locking mechanism  30 . The lower end of the stop rod  50  has an upper washer  51  fixedly secured to the rod  50  which engages the upper surface of the mounting plate  52  and limits downward movement of the stop rod  50  in the mounting plate  52 . 
     A detachable locking pin  54  is adapted to be inserted transversely through an aperture in the stop rod  50  below the mounting plate  52  for limiting, with assistance of a removable lower washer  53 , the upward movement of the stop rod  50  relative to the lower tubular member  24  by reason of the lower washer  53  and locking pin  54  engaging the lower surface of the mounting plate. When the locking pin  54  is not installed, the stop rod  50  can be inserted and removed from the lower tubular member  24  and upper tubular member  20  through an upper open end  28  of the upper tubular member  20  of the top structure  12 . 
     The upper end of the stop rod  50  is provided with an enlarged head  56  which is too large to pass through the central bore  60  of the cam bushing  62  such that the enlarged head limits upward movement of the upper tubular member  20  beyond the extended position. The enlarged head  56  effectively provides a stop shoulder directed toward the lower end of the rod  50 . The cam bushing  62  is fixed to the upper tubular member  20  and effectively provides a stop member with stop surfaces to engage the stop shoulders on the enlarged head  56  and prevent extension beyond the fully extended position. 
     The upper tubular member  20  is adapted to slide vertically downwards in the lower tubular member  24  to a fully retracted position where the locking mechanism  30  engages the mounting plate  52  and the tabletop  18  is at its lowest height. The upper tubular member  20  is adapted to slide vertically upwards in the lower tubular member  24  to a fully extended position where the locking mechanism  30  engages the enlarged head  56  of the stop rod  50  and the tabletop  18  is at its highest height. 
     The embodiment of FIG. 1 can be assembled by securing the locking mechanism  30  to the upper tubular member  20 , sliding the upper tubular member  20  into the lower tubular member  24  and then sliding the stop rod  50  down through the open upper end  28  of the upper tubular member  20 , through the central bore  60  in the locking mechanism  30 , and through the mounting plate  52 . Next the lower washer  53  and locking pin  54  are applied to the lower end of the stop rod  50  from the open lower end of the lower tubular member  24 . 
     In the embodiment of FIG. 1, the stop rod  50  is secured to the upper tubular member  20 , it is to be appreciated that the stop rod  50  could be secured to the lower tubular member  24  to engage a stop member secured to the upper tubular member. Other extension stop mechanisms may be provided. 
     FIG. 7 is a longitudinal cross section of a height adjustable table in accordance with a second embodiment of the present invention. The height adjustable table, generally represented by reference numeral  110 , is substantially identical in structure to the height adjustable table  10  of the first embodiment, with the notable exception that the stop rod  50  is replaced by a pressurized gas spring  156 . 
     The gas spring  156  is mounted coaxially within upper and lower tubular members  20 ,  24  and biases the telescoping upper and lower tubular members  20 ,  24  away from each other towards the extended position. 
     The gas spring  156  is of known construction and includes a piston rod  150  which is telescopically received within a gas cylindrical housing cylinder  151  such that gas pressure within the cylinder  151  biases the piston rod  150  outwardly from the gas spring  156 . The gas spring  156  is mounted within the upper tubular member  20  above the locking mechanism  30 . 
     The piston rod  150  passes through the central bore  60  of the locking mechanism  30 . 
     The upper end of the gas spring  156  is detachably attached to the upper end of the upper tubular member  20  by a removable locking pin  84 . The lower end of the piston rod  150  is mounted to the mounting plate  52  by a detachable locking pin  54  adapted to be inserted transversely through an opening in a lower end of the piston rod  150  and openings in the lower tubular member  24  and a mounting tube  88  secured to the mounting plate  52 . 
     When the locking pins  54  and  84  are removed, the gas spring  156  can be removed from the inside of the upper and lower tubular members  20 ,  24  through the upper opening  28  of the upper tubular member  20 . A cover plate  92  is shown attached to the upper end of the upper tubular member  20  below the tabletop  18 . A cap  94  is used to cover an opening through the cover plate into the upper end of the upper tubular member  24 . 
     Adjustment of the height of the table of the second embodiment is the same as with the first embodiment however the gas spring  156  provides forces which reduce the forces required to raise the top structure  12 . 
     The relative lifting forces developed by the gas spring  156  is preferably proximate to the weight of the top structure  12  such that a person may raise or lower the unlocked top structure  12  with minimal effort. Preferably the lifting forces will be sufficiently great that on unlocking, the top structure  12  will be pushed by the gas cylinder alone to the fully extended position. 
     The gas spring  156  is sized such that maximum extension of the piston rod  150 , represents a fully extended position of the upper tubular member relative the lower tubular member in which the upper and lower tubular members are telescopically engaged and the locking mechanism  30  is within the lower tubular member. The piston rod  150  is retractable into the cylinder such that preferably the locking mechanism  30  engages the mounting plate  52  in a fully retracted position of the upper tubular member relative the lower tubular member. 
     Although it has been shown that the elevation of the tabletop in FIG. 7 is facilitated by a pressurized gas cylinder, it is appreciated that elevation of the tabletop can be achieved by other appropriate mechanisms, such as a compressed spring. 
     Reference is made to FIG. 8 which shows a height adjustable table  10  in accordance with a third embodiment which is identical to that shown in FIG. 1 but for the modification of the base structure  14  to have legs comprising lower leg portion  32  and upper leg portion  33 . Each upper leg portion  33  extends radially outwardly from near the upper end of the lower tubular member  24  and downwardly from a foot portion  35  engaging the floor. Each lower leg portion  32  extends radially outwardly proximate the lower end of the lower tubular member  24  to join a respective upper leg portion  33  above the foot portion. 
     The embodiment of FIG. 8 is particularly adapted for use with a gas spring or other lifting device as described with reference to FIG. 7. A user may place his foot on an appropriate side of any foot portion  35  to prevent rotation of the base or could place his foot on top of the upper leg portion  33 . 
     The preferred embodiments show the upper tubular member  20  being received inside the lower tubular member  24 . This is not necessary. The columns and the locking mechanism could be inverted with the lower tubular member inside the upper tubular member. Locking is described by rotation clockwise, however, locking could be arranged to be accomplished by counter-clockwise rotation. 
     The preferred embodiments preferably have a tabletop of glass, plastic, metal or composites thereof. The columns  20  and  24  and their respective support  16 , base  22  and spoke-like legs  32  and arms  36  are preferably metal such as aluminum or steel and welded together. The cam bushing  62  is preferably of metal or plastic and may comprise one or more elements. The locking ring  64  preferably comprises plastic or metal. 
     In the preferred embodiments, the tabletop is circular. This is not necessary and the tabletop may be square, octagonal, triangular, oval and various other shapes, however, it is generally preferred to be somewhat symmetrical about its base. 
     The preferred embodiments show specific manners of coupling various elements together such as the manner of securing the stop rod  50  to the upper tubular member  20 , securing the gas spring  156  to the upper and lower tubular members and securing the cam bushing to the upper tubular member  20 . 
     It is to be appreciated that many different mechanical coupling mechanisms may be used and substituted without departing from the scope of the invention. 
     While the invention has been described to preferred embodiments, many modifications and variations will now occur to persons skilled in the art. For a definition of the invention, reference is made to the appended claims.
A height adjustable table, preferably with a circular tabletop which includes a vertically telescoping column to support the tabletop and with the column telescoping between extended and retracted positions. A base supports lower end of the column vertically upright. A locking mechanism is provided within the telescoping column adapted to lock the column against telescoping when the tabletop is rotated in one direction relative the base and to unlock the column when rotated in the other direction. When the table is unlocked, a user may adjust the height of the table either by manually lifting alone or assisted by a lifting mechanism to bias the tabletop upwardly and at least partially bear the weight of the tabletop. A stop mechanism is preferably provided to ensure the table is not extended so far as to disengage the tabletop structure. The base of the table is adapted to be engaged by a user's feet to prevent rotation relative to the tabletop when locking or unlocking.