Abstract:
A mechanism for use in counterbalancing a shelf or the like incident to vertical movement thereof along a trackway featuring a linkage assembly and coupling assemblies for effecting a relatively large displacement of the shelf incident to a relatively small displacement of a shelf counterbalance spring. The shelf is mounted on the trackway by followers carrying a manual brake releasably engageable with the trackway.

Description:
BACKGROUND OF THE INVENTION 
     It is known to provide shelf lifting or counterbalance mechanisms of the type including a frame for mounting a shelf support for vertical movement under the control or influence of a spring device coupled to the shelf support by a cable system. Prior patents disclosing this type of mechanism includes U.S. Pat. Nos. 2,604,996; 2,932,403; 3,436,136; 3,807,821; 3,820,478; 3,871,725; 4,009,915; 4,559,879; 4,605,189; 4,828,119; 4,898,103. Of these patents, U.S. Pat. No. 3,807,821 proposes the use of a lever assembly for connecting a spring to a cable system in such a manner that the extent of travel of shelf support exceeds the extent of travel of the spring. 
     SUMMARY OF THE INVENTION 
     The present invention relates to an improved mechanism for use in counterbalancing a shelf or the like incident to vertical movement thereof and more particularly to a relatively compact mechanism of this type wherein a relatively small spring displacement occurs coincident to a relatively large displacement of the shelf. 
     The mechanism of the present invention features an improved linkage assembly adapted to uniformly apply a spring bias to a pair of coupling assemblies and in turn to opposite sides of a shelf support at the points at which the latter is guided for vertical displacement by a pair of guide tracks, whereby the shelf support is exposed to uniform counterbalancing forces. 
     The mechanism of the present invention additionally features improved follower devices for guiding a shelf for vertical displacement relative to the guide tracks. The follower devices incorporate manually operated brake assemblies constructed so as to allow automatic raising of the shelf, whenever a load of predetermined weight is removed from the shelf mounted on the shelf. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The nature and mode of operation of the present invention will now be more fully described in the following detailed description taken with the accompanying drawings wherein: 
     FIG. 1 is a front elevational view of a counterbalance mechanism formed in accordance with a preferred form of the present invention; 
     FIG. 2 is a sectional view taken generally along the line 2--2 in FIG. 1; 
     FIG. 3 is a sectional view taken generally along the line 3--3 in FIG. 1; and 
     FIG. 4 is a sectional view taken generally along the line 4--4 in FIG. 1. 
    
    
     DETAILED DESCRIPTION 
     A counterbalance mechanism formed in accordance with a preferred form of the present invention is designated as 10 in FIG. 1. As viewed in FIG. 1, mechanism 10 generally includes a frame 12 having a pair of parallel right and left hand guide tracks 14,14; a shelf support 16 having a pair of right and left hand follower devices 18,18 movably associated one with each of the guide tracks for supporting the shelf support for movement lengthwise thereof; a counterbalance spring means 20; spring displacement multiplying linkage assembly 22 operably coupled to the frame by the spring means; and a pair of right and left hand coupling assemblies 24,24 for coupling the linkage assembly to the shelf support. 
     As desired, frame 12 may be suitably fixed to a vertically extending or horizontally disposed support, not shown, in order to arrange guide tracks 14,14 to extend vertically, and a shelf, not shown, may be cantilever or otherwise suitably affixed to shelf support 16, such that the shelf is generally horizontally disposed and supported for vertical movement lengthwise of the guide tracks with the weight of such shelf, any object supported thereon and the shelf support being at least partially counterbalanced by the bias established by counterbalance spring means 20. The structure of the shelf and the mode of attaching frame 12 to its support and the shelf to shelf support 16 may be conventional and form no part of the present invention. 
     The term shelf as used herein is intended to include any fixture adapted to support an art device, such as for example a keyboard, or to provide a work surface, such as for example the top of a drafting table, whose weight is desired to be at least partially counterbalanced throughout a range of vertical travel. 
     Frame 12 is shown in FIGS. 1-3, as having upper and lower generally parallel, U-shaped support channel members 30 and 32 having generally horizontally disposed connecting flanges 30a and 32a and generally vertically disposed and aligned side flanges 30b,30b and 32b,32b. Guide tracks 14,14 are of generally C-shaped configuration and have their upper and lower ends received within and suitably fixed to opposite ends of channel members 30 and 32 to define a generally rectangular open center frame structure, wherein the interiors of the channel members and interiors of guide tracks open towards one another. 
     Counterbalance spring means 20 may be variously defined, so long as it is capable of producing a force adapted for use in counterbalancing the weight of shelf support 16, the shelf and any art device intended to be supported by the shelf. In the presently preferred construction, spring means 20 is shown as comprising a plurality of parallel, tension type springs, such as coil springs 40--40, whose first or upper ends are fixed to a common hanger bracket 42, which is in turn adjustably fixed to depend from connecting flange 30a of upper channel member 30 by an adjustment bolt 44 having an upper end rotatably supported by the connecting flange and a lower end threadably received within a nut 46 associated with the common hanger bracket. The second or lower ends of springs 40--40 are fixed to linkage assembly 22 in the manner to be described. Alternately, by appropriate rearrangement of the elements of mechanism 10, the tension springs may be replaced by a compression spring, such as may be defined by a gas cylinder. 
     Shelf support 16 is shown in FIGS. 1 and 2 as being in the form of a generally rectangular connecting plate 50 having follower devices 18,18 fixed to its horizontally opposite ends. Follower devices 18,18 are of mirror image construction and, as best shown in FIGS. 3 and 4, each includes a generally L-shaped mounting bracket 52 having a base flange 52a fixed to plate 50 and a bearing flange 52b. As best shown in FIG. 4, bearing flange 52b serves to mount upper and lower bearing pins 54 and 56 for rotatably supporting crowned periphery guide track follower rollers 58 and 60, respectively; an intermediate bearing pin 62 serving to mount on its opposite ends and adjacent opposite sides of the bearing flange, a brake assembly 64 and a brake release link 66; a second bearing pin 62a; and upper and lower spring mounting pins 68 and 70. A second bearing flange 53; shown only in FIGS. 2 and 3, is arranged parallel to bearing flange 52b and is connected to opposite ends of pins 54, 56, 62, 62a, 68, and 70. Preferably, a shelf to be suppported would be affixed to shelf support 16 by bolts 52a carried by base flanges 52a and arranged to freely extend through plate 50. 
     Brake assembly 64 includes a parallelogram linkage defined by pivotably end connected first, second, third, and fourth links 64a, 64b, 64c, and 64d, respectively; a friction brake pad 72 carried by third link 64c to releasably engage with an inner surface of an associated guide track 14; and a pair of springs 76 and 78 having their opposite ends coupled to mounting pin 68 and an upper end of third link 64c and to mounting pin 70 and a lower end of the fourth link 64d, respectively. As will be apparent from viewing FIG. 4, springs 76 and 78 provide a bias tending to maintain the links of brake assembly 64 in their illustrated normal braking position, wherein friction pad 72 is forced into frictional engagement with one side of guide track 14 and rollers 58 and 60 are forced into engagement with an opposite side of the guide track to oppose lowering of shelf support 16 relative to frame 12. The arrangement of links 64a-64d is such that the frictional braking force is automatically increased as downwardly directed force applied to shelf support 16 is increased. The links of brake assembly 64 may be moved from their normal braking position against the bias of springs 76 and 78 by the manual application of a release force to brake release link 66, such as by a release cable or link 80, which serves to pivot the brake release link, and thus bearing pin 62 and first link 64a, in a clockwise direction, as viewed in FIG. 4. As shown in FIGS. 1 and 3, the free ends of brake release links 66,66 freely pass forwardly through slots 50a,50a provided in plate 50. Typically, an upper end of each cable 80, not shown, would be connected to a cable operator, also not shown, carried for movement with the shelf. 
     By again referring to FIG. 4, it will be noted that the point of connection of bearing pin 62 to first link 64a is offset from the center of the first link in a direction relatively towards its pivot connection with fourth link 64d, and that the point of connection of bearing pin 62a to second link 64b is also offset from the center of the second link in a direction relatively towards its pivot connection with the fourth link. This facilitates release of brake pad 72 from frictional engagement with the inner surface of guide track 14 incident to unlocking rotation of brake release link 66. Also, this facilitates sliding of the brake pad upwardly with respect to the inner surface of the guide track when a shelf supported by shelf support 16 is manually lifted or when a heavy load is removed from the shelf and the bias established by springs 40--40 is adjusted/designed such that the weight of the shelf, etc., absent such load, is exceeded by the counterbalance or lifting force established by the springs. 
     By again viewing FIGS. 3 and 4, it will be understood that the rotational axes of guide rollers 58 and 60 of the respective follower devices are parallel to each other and generally horizontally disposed, but that the rotational axes of the guide rollers of the left and right hand follower devices, as viewed in FIG. 3, converge in a direction towards plate 50. This canting of the guide rollers 58 and 60 permits the guide rollers to cooperate with guide tracks 14, 14 to constrain horizonal movements of shelf support 16 within a plane disposed normal to the guide tracks. 
     If desired, the lowermost and uppermost adjusted position of shelf support 16 may be defined by engagement of the lower and upper edges 52b&#39; and 52b&#34; of bearing flanges 52b with upper and lower edges 32b&#39; and 30b&#39; of lower and upper 
     Linkage assembly 22 is shown in FIGS. 1 and 3 as including crossed first and second elongated force transmitting arms 86 and 88; having adjacent first ends 86a and 88a and remote second ends 86b and 88b. Pairs of first or right hand and second or left hand links 90 and 92; and a common attachment link or bracket 94. Arms 86 and 88 are preferably pivotably supported by a common horizontally disposed pivot pin 96, which extends through the arms relatively adjacent their first ends 86a and 88a, and has its channel member 32. First and second links 90 and 92 are shown in FIG. 1 as being disposed on opposite sides of pivot pin 96 with their upper or first ends 90a and 92a pivotably connected to opposite or the right and left hand ends of attachment link 94 by pivot pins 100 and 102 and with their lower or second ends 90b and 92b pivotally connected to first ends 88a and 86a of arms 88 and 86 by pivot pins 104 and 106. With this arrangement, arms 86 and 88 are caused to rotate or pivot in opposite directions about common pivot pin 96 incident to vertical displacements of attachment link 94 with their second ends 86b and 88b moving in a common direction opposite to the direction of movement of the attachment link. Moreover, the placement of pivot pin 96 relatively closer to first ends 86a and 88a, than to second ends 86b and 88b results in such second ends undergoing a greater vertical displacement than attachment link 94 incident to any vertical displacement of the latter. 
     Coupling assemblies 24,24 each include a first double sheaved pulley 110 supported for rotation by a bearing pin 112, whose opposite ends are supported by the legs of a U-shaped bracket 114 fixed to depend from connecting flange 30a of upper channel number 30; a second single sheaved pulley 116 supported for rotation by a bearing pin 118, whose opposite ends are supported by the legs of a U-shaped bracket 120; a relatively rigid connecting rod 122 having an upper end 122a connected to bracket 120 and a lower end 122b pivotably connected to the second end of one of arms 86 and 88 by a bearing 122a; and a flexible cable 124 having a first end 124a fixed to connecting flange 30a, a second end 124b fixed to shelf support 16 and an intermediate portion 124c trained about pulleys 110 and 116. 
     In operation, springs 40 tend to exert a bias or lifting force on attachment link 94, which acts through first and second links 90 and 92 and first and second arms 86 and 88 to apply a downwardly directed or tension force to connecting rods 122,122. The tension force applied to connecting rods 122,122 tends to draw second pulleys 116,116 downwardly relative to first pulleys 110,110, thereby tending to increase the length of cable intermediate portion 124c,124c passing between the first and second pulleys and as a result, tends to raise cable second portions 124b,124b together with shelf support 16 and the shelf supported thereby. The lifting or counterbalance force applied to shelf support 16 by springs 40 may be adjusted by rotating bolt 44 for purposes of raising or lowering common hanger bracket 42. 
     The construction of linkage assembly 22 and its mode of attachment to springs 40 and shelf support 16 provides for the uniform application of counterbalancing force to opposite sides of the shelf support. 
     The mechanism is designed for use with a given range of shelf loading conditions, and within this range the shelf tends to reside in any position it is placed by an operator, as by either lifting the shelf with or without first releasing brake assembly 64 or by lowering the shelf after the brake assembly has been released. Moreover, the construction of the brake assembly is intended to allow the shelf to slowly raise automatically without operator intervention, when a load, which is relatively heavy compared to the overall weight of the shelf and movable portions of the mechanisms, is removed from the shelf.