Abstract:
A linkage mechanism for mounting a movable support to a fixed member for movement between a first position and a second position. The mechanism includes a first linkage arm respectively connected at each end to the fixed member and the movable support and second linkage arm having one end connected to the movable support and the other to a connector located intermediate the ends of the first linkage arm. A third linkage arm extends between the movable support and the connector. The connector controls the movable support during the movement between the first and second positions. A two link arrangement is also disclosed having a pair of linkage arms extending between a movable support and a fixed member. The linkage arms being linked by a connector intermediate their respective ends.

Description:
FIELD OF THE INVENTION  
         [0001]    The present invention relates to a linkage mechanism and in particular to a linkage mechanism for mounting a movable support to a fixed support for movement between a first raised position and a second lowered position.  
           [0002]    The invention has been developed primarily for adjustably mounting a keyboard support platform to a desk and will be described hereinafter with reference to that application. However, the invention is not limited to that particular field of use. The mechanism could equally be used in a variety of applications requiring a movable support adjustable relative to a fixed member, for example, a support for a VDU, television monitor or surveillance camera.  
         BACKGROUND TO THE INVENTION  
         [0003]    In general, a workstation or other desk includes a fixed platform for supporting the variety of tools, books, stationery and other implements utilised by a user of the workstation to achieve the task at hand. In circumstances where use is made of a computer it is desirable to ensure that the user&#39;s posture is favourably maintained to protect against unnecessary physical strains and the development of long-term medical conditions as a result of those strains. This is particularly important for those users who have to spend long periods operating the computer on a regular basis.  
           [0004]    To this end, it is known to provide a height adjustable support for a keyboard that is utilised by the user to operate the computer. To achieve the height adjustment, the keyboard support is connected to the fixed platform by a linkage mechanism. In essence, the more common prior art linkage mechanisms comprise a pantographic or parallelogram linkage that allows some degree of height adjustment of the keyboard support. The pantographic linkage maintains the keyboard support substantially parallel to the platform throughout the movement, while the parallelogram linkage results in some tilting of the keyboard support during that same movement.  
           [0005]    Examples of such known linkages are described in U.S. Pat. No. 4,616,798 (Smeenge), U.S. Pat. No. 5,037, 054 (McConnell), U.S. Pat. No. 5,292,097 (Russell) and) U.S. Pat. No. 5,707,034 (Cotterill).  
           [0006]    For the prior art linkages to provide the necessary strength for the desired application, there must be sufficient vertical distance between the arms that comprise the pantograph or parallelogram. This results in a bulky arrangement that extends downwardly from the underside of the platform and the keyboard support. Accordingly, while height adjustment of the keyboard is achieved, an additional hazard is created in that the user is increasingly likely to inadvertently contact the linkage mechanism with their legs. This can be painful and injurious and is particularly undesirable. This problem is exacerbated due to the sharp edges that are often included in prior art linkage application. These prior art arrangements are also subject to support instability and reduced options for design flexibility. It will be appreciated that any reduction in the bulkiness of the linkage provides advantages in a variety of other applications to which such linkages may be applied.  
         SUMMARY OF THE INVENTION  
         [0007]    It is an object of the present invention to overcome or ameliorate at least one of the disadvantages of the prior art, or to provide a useful alternative.  
           [0008]    According to a first aspect of the invention there is provided a linkage mechanism for mounting a movable support to a fixed member for movement between a first position and a second position, the mechanism including:  
           [0009]    a first linkage arm that extends between a first end and a second end that are respectively connected to the fixed member and the movable support;  
           [0010]    a second linkage arm that extends between a third end and a fourth end, wherein the third end is connected to the fixed support;  
           [0011]    a third linkage arm that extends between a fifth end and a sixth end, wherein the sixth end is connected to the movable support; and  
           [0012]    a connector for connecting the fourth end and the fifth end to the first linkage arm intermediate the first end and the second end for controlling the movable support during the movement between the first and second positions.  
           [0013]    Preferably, the connector also controls the attitude of the movable support during the movement of between the first and second positions.  
           [0014]    Preferably also, the first arm includes a control formation and the connector slideably connects the fourth end and the fifth end to the control formation. More preferably, the control formation is a slot in the first linkage arm and the connector is a pin that connects the fourth and the fifth ends and which is slideably received in the slot. In other embodiments, the connector is a fourth linkage that extends between a seventh end and an eighth end that are respectively connected to the fourth end and the fifth end by respective pins, wherein the control formation includes two slots that are spaced apart in the first linkage arm and which receive respective one of the pins. In further embodiments the two slots are joined to form a single slot.  
           [0015]    In a preferred form, the first, second, third and sixth ends are pivotally connected to the respective fixed member and movable support. More preferably, the first, second, third and sixth ends are pivotally fixed or attached to the respective fixed member and movable support. That is, the ends are connected for pivotal movement only. In other embodiments one of the first, second, third and sixth ends are pivotally and slideably connected to the respective fixed member and movable support. More preferably, the pivotal and slideable connection allows selective locking of the support against relative movement. Even more preferably, the pivotal and slideable connection allows selective locking at one of a plurality of discrete further positions between the first and second positions.  
           [0016]    According to a second aspect of the invention there is provided a movable support for a load, the movable support being mounted to a fixed support by a linkage mechanism for movement between a raised position and a lowered position, the support including:  
           [0017]    a platform having an upper surface for supporting the load, the upper surface extending substantially along a plane; and  
           [0018]    a mount extending upwardly from the platform for engaging with the linkage mechanism at an upper mounting point and a lower mounting point that is spaced apart from the upper mounting point, the mounting points being on opposite sides of the plane.  
           [0019]    Preferably, the lower mounting point is immediately adjacent to the plane. In other embodiments the mounting points are equally spaced from the plane.  
           [0020]    Preferably also, the mount extends below the platform for providing additional load bearing capacity. More preferably, the mount includes two spaced apart support formations that each extend from one end that is connected to the linkage mechanism to another end that is disposed beneath the platform. Even more preferably, the support formations are mechanically linked by a cross member.  
           [0021]    In a preferred form, the platform includes a front edge, a rear edge spaced apart from the front edge, and two side edges joining the front edge and the rear edge. More preferably, the mount extends normally from the platform and defines the front edge. Even more preferably, the rear edge is bevelled or otherwise rounded to reduce the risk of inadvertent contact with the rear edge causing injury to a user of the support.  
           [0022]    Preferably, the linkage mechanism includes a lock for selectively preventing and allowing the movement between the raised and the lowered positions.  
           [0023]    According to a third aspect of the invention there is provided an adjustable support for a load, the adjustable support being mountable to a fixed support by a linkage and including:  
           [0024]    a base extending from the linkage and providing two spaced apart guide formations;  
           [0025]    a platform for supporting the load, wherein the platform is mounted to the base for movement between a first position and a second position; and  
           [0026]    two spaced apart control formations being associated with the platform for respectively inter-engaging with the guide formations such that the movement of the platform between the first position and the second position results in a change of inclination of the platform with respect to the base.  
           [0027]    Preferably, guide formations are respective slots formed in the base and the control formations are respective sliders that extend from the platform and which are received within the corresponding slots. More preferably, the platform includes a platen having a substantially planar upper surface upon which the load is supported and a lower surface to which the sliders are mounted.  
           [0028]    Preferably also, the guide formations are inclined with respect to each other to allow the application of an automatic locking force to lock the platform at one of a plurality of positions intermediate the first and the second positions. More preferably, the locking force is increased with the weight of the load.  
           [0029]    In a preferred form, the platform, during movement between the first and second positions, follows a predetermined path due to the inter-engagement between the guide formations and the control formations. More preferably, the predetermined path includes both transverse and rotational components.  
           [0030]    According to a fourth aspect of the invention there is provided an adjustable support for a load, the adjustable support being mountable to a fixed support and including:  
           [0031]    a base for mounting to fixed support and having two spaced apart guide formations;  
           [0032]    a platform for supporting the load, wherein the platform is mounted to the base for movement between a first position and a second position; and  
           [0033]    two spaced apart control formations being associated with the platform for respectively inter-engaging with the guide formations such that the movement of the platform between the first position and the second position results in a change of inclination of the platform with respect to the base.  
           [0034]    Preferably, the guide formations are slots and the control formation are sliders that are received within the respective slots, wherein the slots are inclined with respect to each other so that the platform is gravitationally biased into locking engagement with the base. More preferably, the locking engagement is overcome by a force that is applied by a user such that, upon the removal of that force the platform returns into locking engagement with the base.  
           [0035]    According to a fifth aspect of the invention there is provided a linkage mechanism for mounting a movable support to a fixed member for movement between a first position and a second position, the mechanism including:  
           [0036]    an arm that extends between a first end and a second end that are respectively connected to the fixed member and the movable support;  
           [0037]    a linkage that extends between a third end and a fourth end that are respectively connected to the fixed member and the movable support, the linkage also being connected, intermediate the third end and the fourth end, to the arm intermediate the first end and the second end for controlling the attitude of the movable support during the movement between the first and second positions.  
           [0038]    Preferably, the movement of the movable support between the first and second positions is along a predetermined path. More preferably, the attitude of the movable platform remains substantially constant throughout the movement between the first and the second positions.  
           [0039]    Preferably also, the linkage includes a first linkage member and a second linkage member that are respectively connected to the fixed and the movable support, the members being rotatably mounted to each other at a mounting point. More preferably, the mounting point corresponds to the connection between the arm and the linkage.  
           [0040]    In other embodiments, the linkage includes a first, second and third linkage members, where the first and the second members are respectively connected to the fixed and the movable support and the third element extends between and is connected to the first and the second members.  
           [0041]    Preferably, the arm includes a guide formation intermediate the first and second ends and the linkage includes a control formation intermediate the third and fourth ends wherein the guide and control formations define the connection between the arm and the linkage. More preferably, the control formation is mounted for relative movement with respect to the guide formation during the movement of the movable support between the first and the second positions. Even more preferably, the guide formation is a slot formed in the arm and the control formation is a slider that extends from the linkage and which is received in the slot for slideable progression along the slot during the movement of the movable support between the first and the second positions. Preferably, the slot has two ends that are abutted by the slider when the movable support is in the first and second positions respectively.  
           [0042]    Preferably also, the linkage mechanism includes a lock for selectively preventing and allowing the movement between the first and second positions.  
           [0043]    According to a sixth aspect of the invention there is provided a linkage mechanism for mounting a movable support to a fixed member for movement between a first position and a second position, the mechanism including:  
           [0044]    a first linkage that extends longitudinally between a first end and a second end that are respectively connected to the fixed member and the movable support;  
           [0045]    a second linkage arm that extends longitudinally between a third end and a fourth end that are respectively connected to the fixed member and the movable support;  
           [0046]    a first connection element disposed intermediate the first end and the second end; and  
           [0047]    a second connection element disposed intermediate the third and the fourth end and being mechanically linked with the first connection element during movement between the first and second positions for ensuring that a transverse load applied to any one of the arms is shared by both arms.  
           [0048]    Preferably also, the first connection element includes a slot in the first arm and the second connection element includes a pin that travels along the slot during the movement between the first and second positions. More preferably, the second linkage arm includes a first link that extends between the third end and a fifth end and a second link that extends between the fourth end and the  5  fifth end. Even more preferably, the pin extends from the fifth end.  
           [0049]    Further embodiments and exemplifications of the invention will become apparent from the following detailed description. 
       
    
    
     BRIEF DESCRIPTION OF DRAWINGS  
       [0050]    Preferred embodiments of the various aspects of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which:  
         [0051]    [0051]FIG. 1 shows a side elevation view of one embodiment of the present invention;  
         [0052]    [0052]FIG. 2 shows a side elevation view of a second embodiment of the present invention;  
         [0053]    [0053]FIG. 3 shows a side elevation view of a third embodiment of the present invention;  
         [0054]    [0054]FIG. 4 shows a side elevation view of a fourth embodiment of the present invention;  
         [0055]    [0055]FIG. 5 shows an enlarged side elevation view of the platen arrangement of FIG. 4;  
         [0056]    [0056]FIG. 6 shows a side elevation view of fifth embodiment of the present invention;  
         [0057]    [0057]FIG. 7 shows a side elevation view of one embodiment of the present invention with the linkage in a first position;  
         [0058]    [0058]FIG. 8 shows the embodiment of FIG. 7 with the linkage in a second position;  
         [0059]    [0059]FIG. 9 shows an enlarged side elevation view of the movable support of FIG. 7;  
         [0060]    [0060]FIG. 10 shows a side elevation of a further embodiment of the present invention;  
         [0061]    [0061]FIGS. 11A and 11B show a side view of the locking key of FIG. 10 in an unlocked and locked position, respectively;  
         [0062]    [0062]FIGS. 12A and 12B show a plan view of the locking key of FIG. 10 in an unlocked and locked position, respectively, with the slot path shown in dotted outline;  
         [0063]    [0063]FIG. 13 shows a side elevation of a further embodiment of the first aspect of the invention; and  
         [0064]    [0064]FIG. 14 shows a side elevation of a further embodiment of the present invention; and  
         [0065]    [0065]FIG. 15 shows a plan view of the embodiment of FIG. 14. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0066]    Referring to the drawings, the various preferred embodiments of the invention will now be described. The same numbering will be used to indicate the same or similar features of each of the embodiments.  
         [0067]    [0067]FIG. 1 shows a linkage mechanism  5  arranged between a fixed member  6  and a movable support  7 . The linkage mechanism  5  in this embodiment comprises a first bowed linkage arm  8  pivotally attached at one end  9  to a bracket  10  fixed to the member  6  and pivotally attached at a second end  11  to the movable support  7 . A second linkage arm  12  is pivotally attached at one end  13  to the bracket  10  at a connection point  14  which is spaced from and above the connection point  15  of the first linkage arm  8  and at its other end  16  to a connector pin  17 . A third linkage arm  18  is pivotally attached at one end  19  to the movable support  7  at a connection point  20  spaced from and above the connection point  21  of the first linkage arm  8  and at its other end  22  to the connector pin  17 . The connector pin  17  links the respective ends  16  and  22  of the second and third linkage arms to a point  23  intermediate the ends of the first linkage arm  8 . Connector pin  17  passes through the ends  16  and  22  and is slideably received in a slot  24 . The movable support may be raised and lowered between a first and second position defined by the limits of movement of connector pin  17  within slot  24 .  
         [0068]    Each of the pivotal attachments described can be considered fixed in they typically consist of a fixed pin or bush mating with a complementary hole to provide pivotal movement about a fixed axis of the pin. In alternative embodiments, the attachment points may be provided by a movable pivot, typically a pin or bush slideably mating with a slot though other functionally equivalent mechanisms could be used.  
         [0069]    [0069]FIG. 2 shows a second embodiment of the first aspect of the present invention. The linkage mechanism  5  in this embodiment comprises a first linkage arm  8  pivotally attached at one end  9  to a bracket  10  fixed to the member  6  and pivotally attached at a second end  11  to the movable support  7 . A second linkage arm  12  is pivotally attached at one end  13  to the bracket  10  at a connection point  14  which is spaced from and above the connection point  15  of the first linkage arm  8  and at its other end  16  to a connector pin  17 . A third linkage arm  18  is pivotally attached at one end  19  to the movable support  7  at a connection point  20  spaced from and above the connection point  21  of the first linkage arm  8  and at its other end  22  to a connection point  30  intermediate the ends of the second linkage arm  12 . The connector pin  17  links the respective ends  16  and  22  of the second and third linkage arms to a point  23  intermediate the ends of the first linkage arm  8 . Connector pin  17  passes through the ends  16  and  22  and is slideably received in a slot  24 .  
         [0070]    [0070]FIG. 3 shows an embodiment of the second aspect of the invention. The Figure illustrates the first and second positions of the movable support  7  and the corresponding movement of the linkage mechanism  5 . The linkage mechanism  5  in this embodiment comprises a first linkage arm  8  which is reverse-bowed about a central point and pivotally attached at one end  9  to a bracket  10  and pivotally attached at a second end  11  to the movable support  7 . A second linkage arm  12  is pivotally attached at one end  13  to the bracket  10  at a connection point  14  which is spaced from and above and in front of the connection point  15  of the first linkage arm  8  and at its other end  16  to a connector pin  17 . A third linkage arm  18  is pivotally attached at one end  19  to the movable support  7  at a connection point  20  spaced from and above the connection point  21  of the first linkage arm  8  and at its other end  22  to the connector pin  17 . The connector pin  17  links the respective ends  16  and  22  of the second and third linkage arms to a point  23  intermediate the ends of the first linkage arm  8 . Connector pin  17  passes through the ends  16  and  22  and is slideably received in a slot  24 . In this embodiment the movable support  7  includes a platform or surface  35  for supporting a load. Again, as shown in the figures the movable support  7  may be raised and lowered between a first and second position defined by the limits of movement of connector pin  17  within slot  24 .  
         [0071]    [0071]FIGS. 4 and 5 illustrate the third aspect of the invention and are shown employing a linkage  5  according to the second aspect though it will appreciated other forms of linkage may be used. Referring in particular to FIG. 6, the is movable support  7  is generally L-shaped to provide a support platform  35 . A pair of spaced guide formations in the form of slots  36  and  37  are provided respectively adjacent the apex  38  of the platform  35  and the distal end  39  of the support platform  35 . An adjustable platen  40  having a pair of arms  41  and  42  each of which are provided with a respective control formation  43  and  44  extending normal to the longitudinal axis of the arms. The control formations  43  and  44  are in the form of bushes or pins receivable in an associated guide slot  36  and  37 . The slots and arms are configured relative to one another such that movement of the control formations between the extremities of their associated slots results in movement of the platen  40  between a first and second position, the change in position further resulting in a change of inclination of the platen  40  as illustrated in dotted outline in FIG. 6. The inclination of the guide slots  36  and  37  relative to each other provides for an automatic locking force to be applied to the platen  40  when located at positions intermediate the first and second positions.  
         [0072]    [0072]FIG. 6 illustrates an embodiment of a fourth aspect of the present invention. The embodiment is similar to that of FIG. 5 but does not require the linkage and uses a fixed support bracket  35 ′ in the form of the support platform  35 . The control of the platen  40  operates in a similar manner and the slots  36  and  37  are inclined relative to each other so that the platen is gravitationally biased into locking engagement with the base bracket  35 ′. Translational movement of the platen  40  under a force applied by the user can move it to a second position as illustrated in dotted outline. Once the force is removed the platen  40  will return to the locked position.  
         [0073]    FIGS.  7  to  9  illustrate a further embodiment of the present invention. The  5  linkage mechanism  5  in this embodiment comprises a first bowed linkage arm  8  pivotally attached at one end  9  to a bracket  10  and pivotally attached at its other end  11  to the movable support  7 . A second bowed linkage arm  12  is pivotally attached at one end  13  to the bracket  10  at a connection point  14  which is spaced from and above the connection point  15  of the first linkage arm  8  and at its other end  16  to the movable support  7  at an attachment point  20 . The first linkage arm  8  is pivotally attached at its end  11  to an attachment point  45  which is in the form of a slot  46  which slideably receives a bush or pin  47  to provide a movable pivotable attachment. Attachment point  45  is spaced from and below the connection point  20  of the second linkage arm. The second linkage arm  12  is provided with a slot  24  for slideably receiving a connector pin  17  extending normally from the first linkage arm  8  so as to maintain, in conjunction with movable pivot  45 , a constant attitude of the movable support.  
         [0074]    [0074]FIGS. 10, 11A,  11 B,  12 A and  12 B illustrate a further embodiment of the present invention and in particular a locking mechanism for the linkage mechanism. The linkage mechanism  5  in this embodiment comprises a first bowed linkage arm  8  pivotally attached at one end  9  to a bracket  10  fixed to the member  6  and pivotally attached at a second end  11  to the movable support  7 . A second linkage arm  12  is pivotally attached at one end  13  to the bracket  10  at a connection point  14  which is spaced from and below the connection point  15  of the first linkage arm  8  and at its other end  16  to a connector pin  17 . A third linkage arm  18  is pivotally attached at one end  19  to the movable support  7  at a connection point  20  spaced from and below the connection point  21  of the first linkage arm  8  and at its other end  22  to the connector pin  17 . The connector pin  17  links the respective ends  16  and  22  of the second and third linkage arms to a point  23  intermediate the ends of the first linkage arm  8 . Connector pin  17  passes through the ends  16  and  22  and is slideably received in a slot  24 .  
         [0075]    The pivotal attachment at end  9  of the linkage arm  8  is a movable pivot comprising a horizontal slot  50  in the end  9  slideably receiving a pin or bush  49  extending from the bracket  10 . This enables translational to and fro movement of the movable support  7  and associated linkage  5  relative to the bracket  10  and fixed member  6 . The translational movement being between a locked position and an unlocked position.  
         [0076]    The bracket  10  is provided with an arcuate slot  51  slideably receiving a locking key  52  which is pivotally attached to linkage arm  8 . The locking key  52  shown in detail in FIG. 11 has a tapered groove  53  in one side  54  which slideably receives one edge  55  of the slot  51 . In said unlocked position the locking key  52  slides freely along the slot edge  55 , however, when linkage is moved horizontally by the user to a locked position, the key groove engages with the edge of the slot  55  to lock the linkage mechanism in any desired position between the normal extremities of movement set by slot  24 .  
         [0077]    A further embodiment of the first aspect of the invention is illustrated in FIG. 13. The linkage mechanism  60  in this embodiment comprises a first linkage arm  8  pivotally attached at one end  9  to a bracket  10  fixed to the member  6 . A second linkage arm  12  is pivotally attached at one end  13  to the bracket  10  at a connection point  14  which is spaced from and above the connection point  15  of the first linkage arm  8  and at its other end  16  to a connector pin  17 . A third linkage arm  18  is pivotally attached at one end  19  to the movable support  7  at a connection point  20  and at its other end  22  to a fourth linkage arm  61  at one end  62 . A further connector pin  63  is provided at the other end  64  of the fourth linkage arm  61 .  
         [0078]    The other end  11  of first linkage arm  8  is pivotally attached to one end  65  of a first link  66  . The other end  67  of the first link  66  is provided with a connector pin  68  which pivotally connects to one end  69  of a second link  70  and is slideably received in a slot  71  provided intermediate the ends  19  and  22  of the third linkage arm  18 . The other end  72  of the second link  70  is pivotally attached to the movable support  7  at a connection point  21  spaced from and below connection point  20 . A third link  76  connects the pivotal connection point  77  of third and fourth linkage arms  18 ,  61  and the pivotal connection point  78  of the first linkage arm  8  and the first link  66 .  
         [0079]    The connector pin  17  links end  16  of the second linkage arm to a point  23  intermediate the ends of the first linkage arm  8 . Connector pin  17  passes through the end  16  and is slideably received in a slot  24  formed in linkage arm. The connector pin  63  links end  64  of of the fourth linkage arm to a point  73  spaced from and adjacent point  23 . Connector pin  63  passes through the end  64  and is slideably received in a slot  74  formed in linkage arm.  8 . Slots  24  and  74  may be constituted by a single slot. In this example, the movable support  7  is shown supporting a VDU  75 .  
         [0080]    [0080]FIGS. 14 and 15 illustrate an embodiment of the invention where the disposition of the various linkage arms relative to one another serve to provide torsional rigidity to the linkage mechanism.  
         [0081]    The linkage mechanism  5  in this embodiment comprises a first bowed linkage arm  8  pivotally attached at one end  9  to a bracket  10  fixed to the member  6  and pivotally attached at a second end  11  to the movable support  7 . A second linkage arm  12  is pivotally attached at one end  13  to the bracket  10  at a connection point  14  which is spaced from and above the connection point  15  of the first linkage arm  8  and at its other end  16  to a connector pin  17 . A third linkage arm  18  is pivotally attached at one end  19  to the movable support  7  at a connection point  20  spaced from and above the connection point  21  of the first linkage arm  8  and at its other end  22  to the connector pin  17 . The connector pin  17  links the respective ends  16  and  22  of the second and third linkage arms which are located on opposite sides of the linkage arm  8  to a point  23  intermediate the ends of the first linkage arm  8 . Connector pin  17  passes through the end  16 , slot  24  and then end  22 . Linkage arm  8  is effectively sandwiched between arms  12  and  18 .  
         [0082]    The sandwich arrangement of the various arms provides for uniform distribution of the load and resists torsional and compressive forces applied to the linkage mechanism.  
         [0083]    It will be appreciated that further embodiments and exemplifications of the invention are possible without departing from the spirit or scope of the invention described.