Abstract:
A keyboard support mechanism containing a novel articulating arm mechanism for permitting vertical movement of the keyboard shelf. The articulating arm mechanism has six major components: (1) a mounting bracket, (2) a mounting bracket support in combination with a swivel bracket, (3) a shelf bracket, (4) an upper arm, (5) at least one side arm, and (6) at least one stopping means. The upper arm links the shelf bracket and the mounting bracket; the side arm and the stopping means cooperate to keep the shelf bracket (and hence the keyboard shelf) at a constant angle relative to the ground.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of Ser. No. 10/689,955 filed Oct. 21, 2003, now U.S. Pat. No. 7,198,239, which in turn is a continuation of Ser. No. 09/357,175 filed Jul. 17, 1999, now U.S. Pat. No. 6,883,764, which in turn is a continuation of Ser. No. 08/995,889, filed Dec. 22, 1997, now U.S. Pat. No. 5,924,664, which in turn is a continuation-in-part of Provisional U.S. application Ser. No. 60/040,972, filed Mar. 12, 1997 in the name of the same inventors and bearing the same title. 
    
    
     FIELD OF THE INVENTION 
     This invention relates to improved adjustable support mechanisms for keyboards and other items. 
     BACKGROUND OF THE INVENTION 
     The use of computers for both personal and business use has become so common that it is fair to say that almost all businesses, and many homes, have at least one computer or computer terminal. Computers are particularly prevalent in the office environment. Among the health issues which have become increasingly important as the use of computers has become more common is the need to promote proper posture while using the computer so as to both maintain working efficiency and minimize the occurrence of repetitive stress injuries. One basic principal which has been developed to address these issues is that the computer keyboard should be used while at a level considerably below the level of most desktops, so the user&#39;s wrists, when the keyboard is in use, are a “neutral” position; that is, the surface defined by the user&#39;s forearms and the top of his or her hands is fiat. In addition to regulating the height at which the keyboard is used, it is also important for ergonomic purposes to control the angle which the keyboard shelf makes with the ground. 
     There have been a number of devices which have been developed for use in supporting keyboards (and associated computer accessories, such as a computer mouse) at a level below the surface of a desk while in use and underneath the desk when not in use. One such device is described in Smeenge, et al., U.S. Pat. No. 4,616,798, which discloses the use of a parallelogram linkage to connect a shelf for holding a keyboard to the underside of the desk surface. The overall system described by Smeenge permits a fair degree of flexibility in positioning the keyboard relative to the user and the desk. One disadvantage of Smeenge&#39;s system is that the parallelogram linkage used by the system is attached to the underside of the keyboard support shelf Therefore, when the keyboard is positioned underneath the desk, the leg room available to the user between the bottom of the mechanism and the floor is limited. 
     McConnell, U.S. Pat. No. 5,257,767 attempted to address this deficiency of the Smeenge mechanism by using a non-parallelogram linkage to connect the keyboard shelf to the underside of the desk. This non-parallelogram linkage causes the front of the keyboard shelf to be angled upwards when the shelf is lowered relative to the desk top, marginally increasing the leg room available to the user when the keyboard is positioned beneath the desk. Like the Smeenge mechanism, the McConnell mechanism has its linkage attached to the bottom of the keyboard shelf which limits the total leg room available to the user. 
     SUMMARY OF THE INVENTION 
     In one aspect, this invention improves upon the prior art mechanisms by the use of a novel linkage between the underside of the desk and the keyboard shelf which novel linkage increases the leg room available to the user. The improved mechanism of this invention permits the adjustment of the angle of the keyboard shelf relative to the ground within certain parameters so that the angle is ergonomically correct for the vast majority of users. 
     The mechanism according to this aspect of the invention comprises a novel articulating arm mechanism for permitting vertical movement of the keyboard shelf. The articulating arm mechanism has six major components: (1) a mounting bracket, (2) a mounting bracket support in combination with a swivel bracket, (3) a shelf bracket, (4) an upper arm, (5) at least one side arm, and (6) at least one stopping means. The upper arm links the shelf bracket and the mounting bracket; the side arm and the stopping means cooperate to keep the shelf bracket at a constant angle relative to the ground. 
     A second aspect of the invention comprises the attachment of a linkage between a desk and a keyboard shelf so that nothing extends beneath the bottom of the keyboard shelf. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an exploded, perspective view of the auxiliary shelf mechanism of the invention. 
         FIG. 2  is a side elevational view of the auxiliary shelf mechanism in its downward and retracted position. Those parts of the mechanism which would not ordinarily be seen from this angle are shown in dotted lines; a keyboard is also shown in dotted lines, but does not form part of the invention. 
         FIG. 3  is a top plan view of an adjustable stopping means for use in the auxiliary shelf mechanism of the invention. 
         FIG. 4  is a side elevational view, similar to the view in  FIG. 2 , showing the auxiliary shelf mechanism in an extended and upward position. 
         FIG. 5  is a top plan view showing the auxiliary shelf mechanism as attached to a desk. The dotted lines show how the auxiliary shelf mechanism may be rotated relative to the desk, which is also shown in dotted lines. 
         FIG. 6  is a front elevational view of the auxiliary shelf mechanism, showing the means by which the mechanism can be made to rotate as shown in  FIG. 4 . 
         FIG. 7  is a side elevational view of a portion of a different embodiment of the invention, showing a movable stopping means. The dotted lines show the stopping means in a different position. 
         FIG. 8  is a side elevational view of the portion of the invention shown in  FIG. 7 , showing slightly different details of the movable stopping means. 
         FIG. 9  is a top view of an embodiment of the invention, showing a movable stopping means. 
         FIG. 10  is a top view of a portion of an embodiment of the invention, showing a stopping means with a chamfer in combination with a section of the mounting bracket. 
         FIG. 11  shows the same view as shown in  FIG. 10 , with the stopping means with a chamfer and a portion of the mounting bracket, with the additional showing of the side arm. 
         FIG. 12  shows a side view of an alternate embodiment of the side arm in combination with the stopping means. 
         FIG. 13  is a bottom elevational view of a different movable stopping means. 
         FIG. 14  is a bottom view of the embodiment shown in  FIG. 13 . 
         FIG. 15  is a top elevational view of element of the mechanism used to allow the stopping means to move as shown in  FIG. 13 . 
         FIG. 16  is a top elevational view of a different element of the mechanism used to allow the stopping means to move as shown in  FIG. 13 . 
         FIG. 17  is a bottom elevational view of a different movable stopping means. 
         FIG. 18  is a bottom view of the embodiment shown in  FIG. 17 . 
         FIG. 19  is a top plan view showing an auxiliary shelf mounted on an auxiliary shelf mechanism according to a preferred embodiment of the present invention attached to a desk. 
     
    
    
     DETAILED DESCRIPTION 
     As used in this specification and the appended claims, the term “desk” means any desk, table, shelf or other suitable work surface. The term “desk top” means the working surface of a desk (i.e. the surface facing upwards). The term “front” when applied to any component of the auxiliary shelf mechanism means the end closest to the user; the term “back” means the part farthest away from the user. 
     Referring to  FIG. 1 , there is illustrated an exploded view of an auxiliary shelf mechanism  1  according to the invention. Auxiliary shelf mechanism  1  includes an upper arm  2 , a mounting bracket  3 , a shelf bracket  4 , and a pair of side arms  5 . Though two side arms  5  are shown in  FIG. 1  and constitute the preferred embodiment, only one side arm is required. Attached to mounting bracket  3  is a mounting bracket support  6  (shown in  FIG. 6 ) in combination with swivel bracket  32  and swivel bracket support  33 . The combination of the swivel bracket  32  and the mounting bracket support is illustrated in further detail in  FIG. 6 . A first pivot rod  7  connects mounting bracket  3  to upper arm  2  at paired pivot points  8 , secured by washers  9  and push nuts  10 . Upper arm  2  is attached to shelf bracket  4  by means of second pivot rod  11  through holes  12  (one such hole is not shown). 
     Side arms  5  are attached to shelf bracket  4  by means of third pivot rod  13 . The use of two side arms  5  is preferred and illustrated because this arrangement enhances stability of shelf bracket  4 , but only one is necessary. Side arms  5  are attached to mounting bracket  3  by means of bolt  14 , which extends through holes  15  in the mounting bracket  3  (one not shown) and through first openings  16  in the side arms. Spacer  41  is wrapped around bolt  14  and is wider than first openings  16 , so as to prevent it from sliding out from between side arms  5  via first openings  16 . Spacer  41  provides assistance in locking the mechanism in place, as described more fully below. One end of bolt  14  is square (this end is not shown in drawing). The square end can either be part of bolt  14  as manufactured or can be a cover which is slipped onto the round end. The square end prevents bolt  14  from rotating due to the interaction of the square end with first opening  16 . 
     A curved end  21  of each side arm projects behind first openings  16  away from shelf bracket  4 . Lower arm  17  is not required, but is included in the preferred embodiments shown in the drawings. Lower arm  17  is attached to upper arm  2  by means of fourth pivot rod  18  through holes  19  (one not shown) in upper arm  2 . Lower arm  17  is also attached to both side arms  5  and mounting bracket  3  by means of bolt  14 . Bolt  14  passes through lower arm  17  through second openings  20  (one not shown). 
     As shown in  FIG. 2 , auxiliary shelf mechanism  1  may be attached to the underside of a desk top  36  by means of mounting track  22 . Mounting track  22  is affixed to the underside of desk top  36  by conventional means, such as nails or screws. Swivel bracket support  33  cooperates with mounting track  22  as is more fully shown in  FIG. 6  to permit auxiliary shelf mechanism to slide back and forth relative to mounting track  22 . Also shown in  FIG. 2  is stopping means  23 , which is attached to mounting bracket  3 . Stopping means  23  has a first side  24  which faces towards the curved end  21  of the side arm. There is one first side  24  for each side arm  5 . Preferably, though not necessarily, first side  24  is concave in shape, as shown in the different figures. 
     In an embodiment where the stopping means is adjustable and when two side arms are used, the two first sides  24  can form part of a single stopping means, which consequently has a C-shaped top profile, as shown in  FIG. 3  (the first sides  24  representing the ends of the short parts of the “C”  37 ), with the open side of the “C” facing towards the front. The center piece  38  connecting the two sides of the stopping means  23  can have its lateral position relative to mounting bracket  3  adjusted by means of knob  27 , as described more fully below, or by any other means. When two side arms are used, but stopping means  23  is not adjustable, two stopping means may be used, each of which may be attached in a fixed manner by spot-welding or flat riveting (or other conventional means) to the side of mounting bracket  3 . 
     Keyboard  25  (not part of this invention) can rest directly on shelf bracket  4 , as shown in the drawing. Preferably, however, an additional, wider keyboard shelf (not shown) is attached to shelf bracket  4  through attachment holes  26  (as shown in  FIG. 1 ), on which can rest the keyboard. Additional components, such as a supplemental shelf for a computer mouse or pad of paper may be attached to the keyboard shelf (or directly to shelf bracket  4 ). 
     In the preferred embodiment, upper arm  2 , lower arm  17 , and mounting bracket  3  thereby form a wedge-shaped box whose surfaces are made up of the top of upper arm  2 , the base of lower arm  17 , and the overlapping sides of upper arm  2  and lower arm  17 , and whose edges are defined by first pivot rod  7 , fourth pivot rod  18 , and bolt  14 . From the side, as shown in  FIG. 2 , the system resembles a triangle, which can be pivoted to permit the raising or lowering of shelf bracket  4  relative to mounting bracket  3 , and hence the top of the desk  36 . As upper arm  2  pivots about first pivot rod  7 , lower arm  17  both pivots about bolt  14  and slides forward or backward relative to it, via first and second openings  16  and  20 . 
     Curved ends  21  of side arms  5  contact first sides  24  of stopping means  23 . This prevents side arms  5  from sliding rearwards, relative to bolt  14 , past the point where side arms  5  contact the first sides  24  of the stopping means  23 . When first sides  24  have a concave shape, this point varies as side arms  5  are pivoted around bolt  14 . By positioning stopping means  23  at a specific distance behind bolt  14 , and giving first sides  24  of stopping means  23  a particular degree of curvature (which may be easily determined by one of ordinary skill in the art), shelf bracket  4  can be kept at a consistent angle relative to the ground, regardless of the height of shelf bracket  4  relative to mounting bracket  3 . 
     Side arms  5  are kept in contact with the first sides  24  of stopping means  23  by means of the arrangement of shelf bracket  4 , upper arm  2 , and side arms  5 . Upper arm  2  is pivotally connected to shelf bracket  4  by means of second pivot rod  11 . Therefore, the weight of shelf bracket  4  (Plus the weight of anything else attached to it or resting on it) will tend to force shelf bracket  4  to pivot around second pivot rod  11 . This pivoting action forces third pivot rod  13  backwards, in turn forcing side arm  5  (attached to shelf bracket  4  by means of third pivot rod  13 ) back into the first sides  24  of stopping means  23 . Thus, side arms  5  will always be in contact with stopping means  23 , keeping shelf bracket  4  at a consistent horizontal orientation. 
     Among things,  FIG. 3  shows knob  27  connected to bolt  28 . 
     The relative movements of the various components of the mechanism as shelf bracket  4  is moved in a vertical direction can best be appreciated by comparing their positions as shown in  FIGS. 2 and 4 , which depict auxiliary shelf mechanism  1  in a retracted, downward position and in an extended, forward position respectively. 
     It is preferable to upwardly bias auxiliary shelf mechanism  1  slightly, by means of a torsion spring  39 , or other types of springs (e.g., leaf springs) or other conventional mechanisms, such as a compressible fluid cylinder. 
     Stopping means  23  can be fixed in position during the manufacturing process by any conventional means. Among the means for fixing it are spot welding or flat riveting. Fixing the stopping means in position ensures that the horizontal orientation of shelf bracket  4  remains constant. 
     Alternatively, the position of stopping means  23  can be adjustable. By adjusting the position of the stopping means, the angle of shelf bracket  4  relative to the ground can be changed. This is because a change in position of stopping means  23  changes the amount by which the side arms  5  can be pushed back, which in turn changes the angle of shelf bracket  4  to the ground. Preferably the position of stopping means  23  can only be adjusted within certain parameters, the limits of which ensure that the angle of shelf bracket  4  is always within an ergonomically acceptable range. 
     If stopping means  23  is movable, its position may be adjusted by a variety of means, such as with a sliding track with a locking mechanism, or with a rack and pinion mechanism, or with a pneumatic cylinder. One preferred means, however, is by way of a screw-type mechanism, as shown in  FIGS. 7-9 . Knob  27 , which passes through support  30 , is connected by threaded bolt  28  to stopping means  23 . Threaded bolt  28  is attached to stopping means  23  by being screwed into threaded aperture  29  in stopping means  23 . As knob  27  is turned in one direction, threaded bolt  28  is also turned; because stopping means  23  and threaded aperture  29  cannot also turn (because of geometric constraints within mounting bracket  3 ), the turning of threaded bolt  28  in one direction forces it to unscrew from threaded aperture  29 , pushing stopping means  23  towards the front of mounting bracket  3 . The turning of knob  27  in the other direction has the opposite effect. The degree to which threaded bolt  28  can be screwed or unscrewed from the threaded aperture  29  (and hence the degree to which stopping means  23  may be moved) may be governed by the use of mechanical stopping means as shown in  FIGS. 8 and 9 .  FIG. 9  shows a top view of the mechanism. As may be seen from the drawing, stop rod  42  runs parallel to center piece  38  of stopping means  23 .  FIG. 8  shows a side view of mounting bracket  3  with stopping means  23 . Stop rod  42  is fixed in place and is vertically positioned in the middle of ends  37  of stopping means  23 , running through ends  37  via third openings  43  (only one shown). As stopping means  23  moves back and forth relative to mounting bracket  3  from the turning of knob  27 , third openings  43  move relative to stop rod  42 . Once stop rod  42  reaches an end of third openings  43 , stopping means  23  cannot move any further in that direction. The dotted lines in  FIG. 7  show stopping means  23  in a forwardly displaced position compared to the position shown in the solid lines. 
     Other simple mechanical means may also be used to limit the amount by which stopping means  23  can be moved. 
     Another screw-type mechanism for adjusting the position of the stopping means is shown in  FIGS. 13-16 . As shown in  FIG. 13 , sliding bracket  46  is adjacent to mounting bracket  3 . Sliding bracket  46  is shown in more detail in  FIG. 15 . Stopping means  23  are attached to sliding bracket  46  by conventional means, such as rivets or screws. Sliding bracket  46  has, near to where stopping means  23  are attached to it, fourth openings  53 , through which passes stop rod  42 , which is attached to mounting bracket  3 . As was discussed above in connection with  FIGS. 7 and 8 , the interaction between stop rod  42  and fourth openings  53  limits the amount of possible back and forth movement by the mechanism. 
     Sliding bracket  46  is attached to setting bracket  47  (shown in more detail in  FIG. 16 ) by means of attachment pin  48  which passes through opening  49  in setting bracket  47  and openings  63  in sliding bracket  46  (shown in  FIG. 15 ). Setting bracket  47  is attached to mounting bracket  3  by means of attachment rods  50  and  51 , which pass through holes  52  (see  FIG. 16 ). Opening  49  in angled so that as setting bracket  47  is moved from side to side relative to mounting bracket  3 , attachment pin  48 , which must slide within the confines of opening  49  is forced to move either forward or backward, which in turn forces sliding bracket  46  and stopping means  23  to also move forward or backward. 
     For example, looking at  FIG. 14 , if setting bracket  47  is pushed to the left, it is easy to see that attachment pin  48  will be forced along opening  49  towards the front of mounting bracket  3 , forcing sliding bracket  46  to also move forward, carrying stopping means  23  forward also. By varying the angle of opening  49  it is possible to control how much sideways movement of setting bracket  47  will force forward movement of sliding bracket  46 . 
     In the embodiment shown in  FIGS. 13 and 14 , the lateral position of setting bracket  47  (and hence sliding bracket  46  and stopping means  23 ) is adjusted by means of knob  54  in combination with threaded attachment rod  50  and threaded fastener  55 . Threaded fastener  55  is attached to setting bracket  47  adjacent to one of the holes  52 . Threaded attachment rod  50  passes through one hole  52  and threaded fastener  55 . One end of threaded attachment rod  50  is attached to knob  54  (which is positioned on the outside of mounting bracket  3 ), while the other is rotatably fixed to the opposite side of mounting bracket  3 . When knob  54  is turned by the user, it turns threaded attachment rod  50  and causes it to interact with threaded fastener  55 . Because threaded attachment rod  50  is rotatably fixed, threaded fastener  55  is forced to “migrate” up and down threaded attachment rod  50 , causing setting bracket  46  to move laterally, and the test of the mechanism to move forwards and backwards as described above. 
     A related mechanism for adjusting the position of the stopping means  23  is shown in  FIGS. 17-19 . In this embodiment, the position of the stopping means  23  is adjusted by means of sliding bracket  46  in combination with setting bracket  47   a . However, the lateral position of setting bracket  47   a  is not adjusted by means of threaded screw mechanism as described above, but rather by means of adjustment lever  56 . Setting bracket  47   a  differs from setting bracket  47  in that it includes a laterally protruding wing  59 , which has within it a hole  60 . Position bracket  57  is fixedly attached to mounting bracket  3 . Adjustment lever  56  is pivotally attached to position bracket  57  by pin  58 . Adjustment lever  56  is attached to setting bracket  47   a  by means of pin  61  which passes through hole  60  in setting bracket  47   a  and through slot  62  in adjustment lever  56 . 
     A related mechanism for adjusting the position of the stopping means  23  is shown in  FIGS. 17-19 . In this embodiment, the position of the stopping means  23  is adjusted by means of sliding bracket  46  in combination with setting bracket  47   a . However, the lateral position of setting bracket  47   a  is not adjusted by means of threaded screw mechanism as described above, but rather by means of adjustment lever  56 . Setting bracket  47   a  differs from setting bracket  47  in that it includes a laterally protruding wing  59 , which has within it a hole  60 . Position bracket  57  is fixedly attached to mounting bracket  3 . Adjustment lever  56  is pivotally attached to position bracket  57  by pin  58 . Adjustment lever  56  is attached to setting bracket  4  by means of pin  61  which passes through hole  60  in setting bracket  47   a  and through slot  62  in adjustment lever  56 . 
     When the handle of adjustment lever  56  is moved by the user, adjustment lever  56  pivots around pin  58 . This in turn forces movement of slot  62  relative to mounting bracket  3 . Because of the attachment of setting bracket  47   a  to adjustment lever  56  by means of pin  61  through slot  62 , movement of slot  62  forces lateral movement of setting bracket  47   a  along attachment rods  51 . As discussed above, this in turn provides forward and backwards movement of stopping means  23 . 
     Depending upon the exact mechanism used to adjust the stopping means, such adjustment can be easier or more difficult for the user. For example, if the stopping means can only be adjusted using a screwdriver (instead of by the mechanisms described above) it will be less convenient to adjust. This arrangement may be desirable for some applications, where it is sought to minimize the number of adjustments which can be made by the immediate user. 
     The primary purpose behind adjusting the stopping means is to adjust the angle of keyboard shelf  4  relative to the ground. The farther forward stopping means  23  is positioned, the greater the elevation of the front of shelf bracket  4 , and vice-versa. An alternative means for adjusting the horizontal orientation of shelf bracket  4  which is particularly useful when stopping means  23  is not adjustable is by means of conventional locking knob  31 , as shown in  FIG. 1 . Bolt  14  is screwed into locking knob  31 . When locking knob  31  is turned, bolt  14  is prevented from also turning by the interaction of its square end with lateral opening  16 . The threaded connection between locking knob  31  and bolt  14  forces locking knob  31  to move in towards spacer  41 , forcing side arm  5  and lower arm  17  into closer contact with spacer  41 . This eventually tightens the system to the point where neither rotation or lateral movement of lower arm  17  or side arm  5  about bolt  14  is possible. To facilitate the “squeezing” of lower arm  17 , its rearward sections around and adjacent to openings  20  do not have a bottom section connecting them, unlike at its forward sections around and adjacent to fourth pivot rod  18 . 
     When locking knob  31  is used, the angle of shelf bracket  4  can be adjusted by tilting the front of shelf bracket  4  up, pulling side arm  5  away from stopping means  23  and locking shelf bracket  4  into this position by tightening locking knob  31 . By “locking” side arm  5  at a position where it is pulled away from stopping means  23 , the angle of shelf bracket  4  can be altered from what would be permitted by the use of stopping means  23 . The use of locking knob  31  is preferred when only one side arm  5  and one stopping means  23  are used, and when stopping means  23  cannot be moved. Locking knob  31  can also be used in conjunction with a movable stopping means. 
     Other similar, known friction-based systems, such as stopping means with handles, can be used in place of locking knob  31 . 
     The height at which shelf bracket  4  is maintained during use or storage relative to desktop  36  is controlled by the interaction of side arms and stopping means  23 . Each side arm contacts the first side  24  of stopping means  23 , stopping the rearward motion of the side arms  5  and keeping the shelf bracket  4  at a constant angle relative to the ground. By tilting the front of shelf bracket  4  up, each side arm is pulled away from its respective stopping means  23 , permitting vertical movement of the auxiliary shelf mechanism  1 . When the front of shelf bracket  4  is released, each side arm once again contacts its respective stopping means  23 . The curved end  21  of each side arm  5  does not slide relative to its respective stopping means  23  because of friction. Placing additional weight on shelf bracket  4  simply causes the curved ends  21  of the side arms to “dig” into each stopping means  23  even more, further inhibiting vertical movement of auxiliary shelf mechanism  1 . 
     This friction based impediment to movement is enhanced by the use of a preferred configuration of stopping means  23 . In this preferred embodiment, first face  24  of stopping means  23  is concave and has a 45° chamfer directed towards the outside of the mechanism (Us towards the mounting bracket). (One of skill in the art will readily appreciate that the angle of the chamfer can be varied.) This is shown in more detail in  FIG. 10 . This chamfer “funnels” the side arm into a comer created by the stopping means and the mounting bracket, as shown in  FIG. 11 . The increased amount of friction resulting from this arrangement results in greater vertical stability for auxiliary shelf mechanism  1 . 
     An alternative means for improving the vertical stability of auxiliary shelf mechanism  1  involves providing curved ends  21  of side arms with a series of “teeth” which can cooperate with a complementary series of “teeth” on the first side  24  of stopping means  23 . The interaction of the teeth on curved end  21  and the first side  24  can prevent vertical movement of auxiliary shelf mechanism  1 . A further alternative, shown in  FIG. 12  is to attach a pivoted side-arm cam  45  to curved end  21  of side arm by means of pin  44 . The curvature of pivoted side-arm cam  45  complements that of first side  24 , thus maximizing the contact area between the surfaces and the amount of friction between them, resulting in greater vertical stability for auxiliary shelf mechanism  1 . 
     Any of the foregoing methods for vertically stabilizing auxiliary shelf mechanism  1  may be used in combination with any of the others (e.g., teeth may be placed on pivoted side-arm cam  45 , and curved face  24  of stopping means  23 ). 
     Regardless of what system (if any), is used to stabilize the vertical positioning of auxiliary shelf mechanism  1 , the use of the stopping means/sidearm mechanism permits the user to adjust the height of the keyboard in a facile, intuitive manner, without the need to reach awkwardly around the keyboard and fuimble for levers or knobs. Moreover, this system is also mechanically quite simple, does not require the complex locking mechanisms of prior art devices, and presents a significant improvement over those devices. 
       FIG. 6  shows the means by which lateral movement of auxiliary shelf mechanism  1  is achieved. Mounting track  22  is attached to the underside of desktop  36 , normally so that it is perpendicular to the front edge of desktop  36 . The outside edges of mounting track  22  are configured so as to form a pair of inwardly facing, C-shaped brackets  34 . Swivel bracket  32  is shaped so that it will fit into the C-shaped brackets  34 . Swivel bracket  32  (and the rest of auxiliary shelf mechanism  1 ) can be moved by simply pushing the mechanism back and forth along the track. Unwanted lateral movement of auxiliary shelf mechanism  1  is controlled by friction between swivel bracket  32  and C-shaped brackets  34 . Moreover, when weight is placed on shelf bracket  4  (for example when a keyboard and/or a pair of hands is resting on it), this will have a tendency to cause swivel bracket  32  to tilt forward, causing the rear of swivel bracket  32  to contact the top of C-shaped brackets  34 , increasing the friction-based resistance of auxiliary shelf mechanism  1  to lateral movement. If desired, an additional locking mechanism may be provided to prevent lateral movement, but such a mechanism is generally unnecessary and makes adjustment of the position of auxiliary shelf mechanism  1  more cumbersome. Mechanical stops (not shown) may be employed at either end of C-shaped brackets  34  to ensure that auxiliary shelf mechanism  1  does not slide off mounting track  22  and fall to the floor. 
     As an alternative to C-shaped brackets  34 , downward facing I-shaped tracks may be used in conjunction with compatible structures on the mounting bracket, such as is set forth in U.S. Pat. No. 4,644,875. Other known means for mounting auxiliary shelf mechanism  1  to the underside of the desk can also be used. 
     Swivel bracket  32  is attached to swivel bracket support  33 , mounting bracket  3 , and mounting bracket support  6  by means of a rivet (not shown). A large washer  35  is fitted between swivel bracket  32  and mounting bracket  3 . The washer may be made of any number of an upwardly extending piece to permit attachment of link means; the vertical profile of the overall mechanism can be shortened, increasing the leg room available to the user when the keyboard is positioned beneath the desk. Thus, another aspect of the present invention is the attachment of an auxiliary shelf (or keyboard shelf) to a desk top, so that the auxiliary shelf can move both horizontally and vertically relative to the desk top, the attachment being made so that nothing extends below the bottom of the auxiliary shelf. This arrangement maximizes the amount of leg room beneath the auxiliary shelf. The attachment between the auxiliary shelf and the desk can be made by either a parallelogram linkage, or by a non-parallelogram linkage, or by a linkage of the type described in detail in this application (i.e. upper arm-side arm-stopping means). 
     One means by which this type of attachment may be accomplished is by using an auxiliary shelf with a vertically oriented piece attached to its rear side. The linkage can be attached to this vertically oriented piece, precluding the need for anything to project beneath the auxiliary shelf. For example, shelf bracket  4  is shaped in such a way that a more conventional parallelogram linkage or non-parallelogram linkage could be used, instead of the upper arm-side arm-stopping means system shown specifically in the drawings. Other attachment means may also be used, as will be readily apparent to those of skill in this area.