Abstract:
The present invention relates to a position adjustment mechanism, comprising two cylindrical portions, a first one of the portions being slidably disposed inside a second one of the portions. One of the portions has at least three detents and the other portion has at least three members for engaging in respective the detents to hold the portions in a first position, the members being removable from the detents to allow the portions to move into a second position; wherein the detents and members are equi-spaced around the first and second portions.

Description:
This application is a continuation-in-part of PCT/GB02/04175 filed 13 Sep. 2002. 

   BACKGROUND OF THE INVENTION 
   The present invention relates to a position adjustment mechanism, and more particularly to an adjustment mechanism for use in raising and lowering the height of the bed of a snooker table, billiards table, pool table or the like. 
   Snooker tables, and tables for playing related games such as billiards and pool, are of course well known. Such tables can be used as dining tables, by resting a cover on the cushions of the table, but the dining table formed by doing this is generally not at a convenient height for dining, as the surface of the dining table is normally too high. The height difference is normally around 75 mm (3 inches). 
   BRIEF DESCRIPTION OF THE PRIOR ART 
   Mechanisms are known for adjusting the height of the surface of the table, thus allowing the table to used both as a snooker table (or a billiards or pool table) and as a dining table. When it is desired to convert the table to a dining table, the height of the bed of the table is lowered, and a cover is laid across the cushions. 
   A prior art height adjusting mechanism  110 , which has been known for many years, is shown in  FIG. 1 . 
   This prior art mechanism includes a first part  112 , which is connected to the frame of the table, and a second part  130  which is connected to the bed. The parts are shown separated for clarity. As can be seen, the first part  112  comprises a generally flat member  114 , which is normally formed from a metal such as brass. A number of grooves  116  are formed on a face of the flat member. The member is also formed with holes  118  for screws or the like, allowing it to be attached to a support frame of the table. 
   The second part  130  is formed to engage with the first member so that it can slide relative to the first member in the direction A-A. The second part also comprises a peg  132  for engaging in the grooves  116  on the first part  112 . The peg  132  can slide in a slot  134  formed in the second part, the slot extending transverse to the direction A-A. The second part  130  also has a part  136  allowing it to be connected to the underside of a bed of a snooker table. 
   The operation of the prior art height adjusting mechanism  110  will now be briefly discussed. When the bed is in its lifted (playing) position, the peg  132  of the second part  130  engages in a detent  120 , and is retained therein by the weight of the bed urging it downwardly. 
   When it is desired to move the bed to its lowered (dining) position, it is necessary to lift the bed, so that the peg  132  is lifted from the detent  120 . The peg  132  comes into contact with a rib  122 , which urges it sideways in the slot  134 . The bed is then lowered, and the peg moves downwardly in groove  124  to the side of the detent  120 . This movement of the peg  132  past the detent  120  allows the bed of the table to be lowered. 
   When it is desired to move the bed back to its lifted (playing) position, the bed is again lifted. The peg  132  now moves along groove  126 , and at the top of the groove is urged sideways in the slot by rib  128 . The bed is then lowered, so that the peg  132  enters detent  120 . 
   One problem with the prior art height adjusting mechanism  110  is that the peg  132  is moved in the slot  134  purely by contact with the grooves and ribs of the first part. It is possible for the peg to “jam” during the lifting or lowering process; for example, it can come into direct contact with the lowermost part of rib  122 , and now be moved sideways as a result of this contact. If this occurs, it is necessary to move the bed laterally with respect to the frame, to attempt to dislodge the peg, which can be difficult as the beds of snooker tables normally have a considerable mass. 
   Further, the prior art height adjusting mechanism must be mounted directly between the support frame of the table, to which the legs of the table are attached and the bed. This can cause problems if the bed is particularly thick, as is the case if the table is used for playing pool and includes a ball-return mechanism. 
   SUMMARY OF THE INVENTION 
   According to the invention, there is provided a position adjustment mechanism, the mechanism comprising: —two cylindrical portions, a first one of the portions being slidably disposed inside a second one of the portions, wherein one of the portions has at least three detents and the other portion has at least three members for engaging in respective the detents to hold the portions in a first position, the members being removable from the detents to allow the portions to move into a second position; wherein the detents and members are equi-spaced around the first and second portions. Having three such equi-spaced detents and members affords enhanced stability and solidity. In this regard, being equi-spaced, the detents and members are provided at substantially 120° intervals around the circumference of the portions and hence are not diametrically opposite one another. This avoids the possibility that the members will effectively form an axle about which the portions would tend to rock in relation to one another. 
   Moreover, where only a single detent and member is provided, there is a greater possibility that the cylindrical portions will be misaligned, such that excess forces are exerted on the member causing it to shear. Providing two detents and members also can be problematic as indicated above, since if one of the cylindrical portions has rocked to one side it will be misaligned and forces on the two members will not be equally shared. This can lead to the one bearing the excess forces failing, following which the remaining one will fail. 
   Preferably, the portions are biassed away from each other by a resilient device. The use of cylindrical portions allows the provision of such a resilient device-positioned between the portions. These resilient device tend to urge the positions apart, and this helps prevent the mechanism from jamming. 
   Preferably, the detents are upwardly open. The members can then be retained in the detents by gravity. 
   In a preferred form, the detents are formed on the first portion, and the members are formed on the second portion. It is preferred for each detent to form part of a groove formed on the first portion, with the members engaging in respective grooves. 
   In a preferred form, the grooves each form a circuit, and the members move around their respective circuit as the portions move from their first position to their second position and back to their first position. 
   It is further preferred for there to be an odd number of grooves, and a corresponding number of members, greater than one. This reduces the chance of the mechanism jamming. 
   Preferably, one of the portions is in contact with a first body and the other of the portions is in contact with a second body, with motion of the portions between the first position and the second position serving to adjust the vertical distance between the bodies. 
   Conveniently, the detents are aligned in the longitudinal axis of the cylindrical portions. In other words, a lower detent is vertically below an upper detent. This means that the process of moving the member from one detent to another does not leave the cylindrical portions relatively twisted. 
   In a preferred embodiment, a chamber is formed between the cylindrical portions, relative movement of the cylindrical portions being effected through pressurizing or depressurizing the chamber. 
   According to a further aspect of the present invention there is provided apparatus for holding two elements at two longitudinally spaced positions, the apparatus comprising: —a cam circuit provided for a first one of the elements; a cam follower provided for a second one of the elements; wherein the cam circuit directs the cam follower around the circuit as a result of alternating relative longitudinal movements of the first and second elements, relative longitudinal movements between the elements in one direction being effected through pressurizing or depressurizing a chamber formed between the elements. 
   With such an arrangement, the need to manually lift an object being supported by the apparatus is avoided. Preferably, the first and second elements comprise respective first and second cylindrical portions, the first one of which is disposed inside the second. In this manner, the first and second cylindrical portions can function as a piston/cylinder arrangement. 
   Preferably, an end of the first cylindrical portion together with an internal bore of the second cylindrical portion form the chamber between the elements. 
   The chamber conveniently has a combined fluid inlet/outlet. Multiple inlet/outlets may provided where suitable. 
   The apparatus preferably has a plurality of cam circuit/cam follower combinations positioned non-diametrically opposite around the circumference of the cylindrical portions. Conveniently, three such cam circuit/cam follower combinations are provided at equal intervals around the circumference of the cylindrical portions. 

   
     BRIEF DESCRIPTION OF THE FIGURES 
     A preferred embodiment of the invention will now be described by way of example only and with reference to the accompanying drawings, in which: 
       FIG. 1  is a view of a prior art height adjustment mechanism; 
       FIG. 2  is a perspective view of an embodiment of the height adjustment mechanism of the invention; 
       FIGS. 3   a  to  3   c  are perspective views of parts of the mechanism shown in  FIG. 2 ; 
       FIG. 4  shows a cut away perspective view of a height adjustment mechanism of the present invention; 
       FIG. 5  shows a cut away perspective view of a height adjustment mechanism of a second embodiment of the present invention; 
       FIG. 6  shows a partial cross-sectional view of a height adjustment mechanism of a third embodiment of the present invention; and 
       FIG. 7  shows a further embodiment of a cam circuit. 
   

   DETAILED DESCRIPTION 
   As shown in  FIG. 2 , the preferred embodiment of the height adjustment mechanism  10  comprises two main parts, a first portion  12 , which in this embodiment has a foot  18  for engaging a floor, and a second portion  50  for connection to a snooker or pool table. 
   The first portion  12  comprises two parts, a floor-engaging part  14  shown in  FIG. 3   a  and a grooved member shown in  FIG. 3   b.    
   The floor-engaging part comprises a foot  18  for resting on the floor, and a threaded rod  20  extending upwardly from the center of the foot. 
   The grooved member is in the form of a cylinder  22 , with a threaded bore formed  24  in its lower face. The threaded rod  20  engages in the threaded bore  24 , and the rod can be screwed into and out of the bore for fine adjustment purposes. 
   In addition, the central region of the cylinder  22  has an upwardly-open hollow  26  therein to accommodate a spring, which will be described in more detail later. 
   A groove  28  is machined into the outer cylindrical surface of the cylinder  22 , surrounding an “island”  30 . The groove  28  will be described in more detail later with reference to the operation of the height adjusting mechanism. While it is possible to use a single groove, it is preferred that a plurality of identical grooves are formed, equi-spaced around the cylinder, and it is particularly preferred to use three grooves. 
   The second portion  50 , show in  FIG. 3   c , is in the form of a hollow cylinder  52 , whose inner diameter is slightly greater than the outer diameter of the cylinder  22  of the first portion. The hollow cylinder  52  is adapted for connection to a snooker or pool table, and may for example fit into a recess formed on the underside of the support frame of the table. It may also be positioned in the top or bottom of a leg of the table. The embodiment described is intended to fit into the bottom of a leg. 
   In the assembled state of the height adjustment mechanism, the cylinder  22  fits inside the hollow cylinder  52 , as shown in  FIG. 2 . This fit must be tight, to prevent lateral movement of the bed of the table. Additional grooves  44  can be formed on the outside of the cylinder  22  along its length, to allow passage of air into and out of the central part of the hollow cylinder. If these grooves are not provided, and the fit between the cylinders is sufficiently close, then the mechanism may “lock” as a result of pressure difference between the outside and the inside of the mechanism. 
   At least one bore  54  is formed through the hollow cylinder, towards its lower end, and a peg  56  is fitted into the bore. The length of the peg  56  is such that it projects into the hollow central region of the hollow cylinder  52 , the projecting length being slightly less than the depth of the groove  28  machined into the cylinder  22  of the first portion, so that the peg  56  can engage in the groove  28 . The number of bores and pegs is the same as the number of grooves. 
   A spring is positioned between the hollow cylinder  52  of the second portion and the cylinder  22  of the first portion. This spring serves to bias the portions apart, and therefore tends to push the cylinder  22  out of the hollow cylinder  54 . 
   The operation of the height adjusting mechanism will now be described. 
   When the bed is in its lifted (playing) position, the peg  56  engages in a detent  32  formed at the upper end of the “island”  30 . The peg  56  is retained therein by the weight of the bed urging it downwardly, and also by the spring urging the cylinder  22  out of the hollow cylinder  52 . 
   When it is desired to move the bed to its lowered (dining) position, the bed is lifted, and the peg  56  is lifted from the detent  32 . The peg  56  comes into contact with a rib  34 , and exerts a sideways force on it. As a result of this force, the cylinder  22  is forced to rotate in the hollow cylinder  52 . Further, the presence of the spring also serves to urge the cylinder and the hollow cylinder apart, which prevents the peg  56  from jamming in the groove. In addition, the preferred embodiment uses three pegs moving in three grooves, and it is extremely unlikely that all three pegs will jam simultaneously; if one peg jams, the force exerted on the other pegs will tend to unjam it. 
   The peg  56  moves to region  36  of the groove (although it will be appreciated that this movement of the peg is partly achieved by the groove moving relative to the peg as the cylinder  22  rotates). 
   The bed is then lowered, and the peg  56  moves downwardly in groove  38  to the side of the detent  32 . This movement of the peg  56  past the detent  32  allows the bed of the table to be lowered. During this motion, the spring is compressed. 
   When it is desired to move the bed back to its lifted (playing) position, the bed is again lifted. The peg now moves along groove  40 , and at the top of the groove the peg  56  is moved sideways relative to the groove by rib  42 . Again, it will be appreciated that this sideways movement is achieved by the cylinder  22  rotating in the hollow cylinder  52 . Further, it will also be appreciated that the presence of the spring urging the cylinder and the hollow cylinder away from each other, and the presence of a plurality of pegs and grooves, helps to prevent the peg from jamming. The bed is then lowered, so that the peg  56  enters detent  32 . 
   Fine adjustment of the height, to ensure that the surface of the table is level, can be achieved by rotating the foot  18  relative to the cylinder  22 , thus screwing the threaded rod  20  in and out of the threaded bore  24 . 
   It will be appreciated from the above that at least the preferred embodiment of the height adjustment mechanism is much less prone to jamming than the prior art mechanism. Further, the preferred embodiment of the height adjustment mechanism does not need to be positioned directly between the frame and the bed, thus allowing a greater freedom for the designer. Indeed, the mechanism can be fitted directly between the legs and the bed, thus avoiding the requirement for a frame. Of course, if the mechanism is not fitted into the bottom of the legs of the table, then there is no need for the mechanism to include a fine adjustment mechanism, as described. Instead, a separate fine adjustment mechanism can be installed in the bottom of the leg, to allow the table to be leveled. 
   It will also be appreciated that a number of variations can be made to the height adjusting mechanism. For example, the arrangement of the pegs and grooves could be reversed, so that the pegs are carried on the cylinder and the grooves are formed on the hollow cylinder. Further, although the height adjustment mechanism has been described in the context of snooker, pool and billiard tables, it can of course be used in other situations. 
   As shown in  FIG. 4 , the position adjustment mechanism comprises a first element in the form of an outer cylindrical portion  200  and a second element in the form of an inner cylindrical portion  201  which is slidably received in the outer cylindrical portion. 
   The outer cylindrical portion  200  is provided with one or more cam followers in the form of pegs  202  which are received within a cam circuit  203  provided on an outer face of the inner cylindrical portion  201 . The cam circuit may be cut into the outer surface of the inner cylindrical portion  201 . 
   As is described above, relative longitudinal movement of the inner and outer cylindrical portions causes each peg to move around its cam circuit. In this respect, each cam circuit includes a lower bay or detent  204  and an upper bay or detent  205  in which the pegs can seat. 
   The cam circuit is configured for directing each pegs between these bays. 
   In use, the outer cylindrical portion  200  is attached to an object requiring raising and lowering via bolts or the like in flange  217 . The inner cylindrical portion is attached to a foot  216  for engaging the ground or other support surface. Other forms of attachment means may be provided for supporting the inner cylindrical portion. Hence the pegs  202  are naturally urged downwardly together with the outer cylindrical portion so that they will seat in one of bays  204  or  205 . The mechanism of attachment to the object need not be provided at the top of the outer cylindrical portion but can be provided at any suitable position on the outer cylindrical portion  200 . 
   With the peg positioned in the lower bay  204 , moving the inner and outer cylindrical portions substantially longitudinally away from one another will result in the peg moving upwardly in the cam circuit. Slight deviations in vertical movement will be accommodated by the inclined surface  208 , so that the peg will ultimately engage surface  209  and be directed into detent  214 , above inclined surface  210  of bay  205 . Hence on a further substantially longitudinal relative movement, this time in a direction moving the inner and outer cylindrical portions together, the peg will fall into bay  205 . Movement of the peg from bay  205 , back to bay  204  is conducted in a similar fashion. 
   Hence, in the embodiment shown in  FIG. 4 , in order to raise and then lower the object through one complete cycle of the cam circuit, the inner and outer cylindrical portions are moved in alternating longitudinal directions, i.e. apart then together, then apart and then together. 
   In this connection, a fluid inlet/outlet  211  allows fluid to be introduced into and released from a chamber  212  formed between a top end face  213  of the inner cylindrical portions  201  and an upper internal portion of the outer cylindrical portions  200 . Multiple inlet/outlets may be provided. 
   With the arrangement shown, the inner cylindrical portion effectively becomes a piston within the outer cylindrical portion. When it is desired to raise the object in question, fluid is introduced under pressure into the chamber  212 , so that the inner cylindrical portion is forced downwardly within the outer cylindrical portion. Hence the peg moves with the outer cylindrical portion from bay  204 , into engagement with surface  209  and then into bay  214 . At this point, pressure is released from the chamber so that the outer cylindrical portion, under the weight of the object being supported, is urged downwardly. The peg thus moves via engagement surface  209  and bay  214  into bay  205 . This represents a high position of the object being supported. 
   The process is repeated to move the peg from bay  205  back to bay  204  and complete one circuit of the cam circuit. In other words, the chamber is again pressurized until the peg is at position  207 , whereupon the pressure is released such that the peg drops down and is directed to bay  204 . 
   Sensors may be positioned at suitable locations such that the position of the peg in detents  207  and  214  is detected for enabling the pressure to be released from chamber  212  at the appropriate time. Also suitable seals, such as an O-ring seal  215  are provided to ensure effectiveness of the pressurized fluid in chamber  212 . The pressure can be released slowly for a controlled lowering of the object. 
   In the context of a table, with such an arrangement all four legs can be raised and lowered at the same time with ease and without any requirement for physical lifting by a user. 
   Three non-diametrically opposed cam circuits and pegs are provided around the circumference of the inner and outer cylindrical portions. Three equi-spaced cam circuits and pegs are particularly preferred as this offers a highly stable support construction. In this respect, not having the pegs diametrically opposite one another is advantageous in that otherwise an axle is effectively formed on which the inner cylindrical portion will tend to rock. 
   The fluid for use in the system may be a liquid or gas or a combination of the two. In this regard, while gases tend to present greater sealing problems, should there be a leakage then less damage is likely to occur, compared with a liquid leak. 
   The mechanism for moving the inner and outer cylindrical portions apart is hence provided in the form of a hydraulic or pneumatic arrangement. Separate inlets and outlets for the fluid may be provided where this is more suitable. 
   In an alternative arrangement, the mechanism for moving the outer cylindrical portion and peg upwardly with respect to the inner cylindrical portion may comprise a vacuum arrangement, as shown in  FIG. 5 , a chamber  220  in this regard being formed by extending the outer cylindrical portion below a base of the inner cylindrical portion, with suitable seals  221  provided around an extended foot section  222 . Alternative forms of mounting devices may be provided for attachment to the inner cylindrical portion. A vent  218  is provided in the upper part of the outer cylindrical portion. 
   The mechanism is not limited to use with tables and may for example be incorporated into other systems which require raising and lowering of a substantial load. Further examples include raising/lowering of scaffolding, or levelling a boat in dry dock. The cam circuit could in this respect have detents or bays at various heights to allow for more variable height adjustment, such that an object could be raised or lowered between more than two positions. 
   The present invention can hence be incorporated, as shown in  FIG. 6 , into for example, a height adjustment system for adjusting the height of a support for a boat in dry dock. 
   As shown, an upper part of a height adjustment assembly  300  for a boat support is attached at one end to a boat support frame  301  and at another end houses a foot post  302 . The assembly includes inner and outer cylindrical portions  303 ,  304  as before with associated cam circuits  305  and pegs  306 . 
   In order to raise the height of the support frame, the pressure of fluid in chamber  307  is increased by introducing fluid through inlet/outlet  309  and then released to direct the peg in a first bay  308  in the cam circuit. To further raise the boat support, the pressure in the chamber is again increased and then released such that the peg is raised to the second bay  310 . To reduce the height of the support frame the pressure in the chamber is again increased and then released. 
   In this regard, it has been calculated that in order to raise the height by around 100 mm, 4 such assemblies (one on each corner of a boat support frame), each having a diameter of around 65 mm would raise a boat and support frame of 3000 Kg in 7.5 seconds, using 0.49 kW or 0.66 Hp rated pump. 
   As shown in  FIG. 7 , the detents or bays in the cam circuit may be aligned in the longitudinal axis of the cylindrical portions. In other words, a lower detent  400  is vertically below an upper detent  401 . This means that the process of moving the cam follower from one bay to another does not leave the cylindrical portions relatively twisted. The cam follower is shown in many positions in  FIG. 7  to illustrate how it moves around the cam circuit.