Abstract:
Methods include direct and indirect communication of a lifting force to the middle slide of each drawer slide that counteracts the effects of gravity and maintains the maximum elevated position of the middle slide, where said methods cooperating with over-length drawer slides enable further improvement in rigidity.

Description:
[0001]    This application claims priority to U.S. 62/231,362 
     
    
     BACKGROUND 
       [0002]    Work surfaces exist for a great many purposes, and it appears a common characteristic that is important and valued is how stable it is. A work surface that wiggles or wobbles is not suitable for many tasks. Preventing this condition in a variable height work surface that is elevated 18 or 21 inches is regarded as very important to persuading customers that it will meet their needs. 
         [0003]    In 2014, medical researchers published findings that excessive sitting is significantly detrimental to one&#39;s health. This news has boosted new product offerings, and none offer these drawer slide mechanisms. Weakness in the stability of these drawer slides in a variable height work surface application or any vertical application may be the reason. 
         [0004]    This weakness is the middle slide assembly including the arrays of ball bearings that is susceptible to gravity in a vertical orientation. After a bit of use, normal human interactions while in an elevated position communicate lateral and torsional forces to the extended slides, relieving the lateral tension of the guide rails on the ball bearings long enough for the middle slide assembly to continue slipping down from the not fully elevated position it may have attained during lifting. A worst case condition also occurs, where from the sitting or starting position, the inner slide extends by itself half of the total travel distance, or phase 1 of the travel before engaging and lifting the middle slide assembly for the remaining phase 2 distance. This minimizes the drawer slide&#39;s resistance to lateral and torsional forces. 
       SUMMARY 
       [0005]    Alternatively, if a sufficient lifting force is communicating with the middle slide it will extend along with the inner slide during phase 1 travel, thereby providing the maximum available support resulting in maximum available rigidity of the drawer slide. From this location the phase 2 extension of the unsupported inner slide is the travel distance remaining, where this maximum available support and rigidity drops to the same low level of support at full travel extension as does the drawer slides without this lifting force. 
         [0006]    This support and resulting improvement in rigidity of the drawer slides contributes to the rigidity of the work surface. At nearly all elevations excepting the start and end points, this rigidity is significantly greater than without the lifting force applied. 
         [0007]    Further improvement in this rigidity is attained when this lifting force cooperates with over—length drawer slides. 
       Benefits 
       [0008]    This recovery and gain in stiffness is significant and believed to be essential to sustaining the quality feel of a variable height work surface for the long term. 
         [0009]    Additional support and rigidity is gained by applying this lifting force to over-length slides that further increases the middle slide extension. 
         [0010]    The improved stiffness enables drawer slides to compete in vertically oriented applications where they offer low cost ball bearing movements. 
         [0011]    Drawer slides that further comprise the features to enable implementing this method are neither difficult nor costly to produce. 
       Limitations 
       [0012]    Drawer slide bearings are exposed to the elements and intended for indoor use. 
         [0013]    Suitable for light and moderate load applications. 
         [0014]    Requires heavy duty drawer slides for superior results. 
     
    
     
       DESCRIPTION OF DRAWINGS 
         [0015]      FIG. 1  is a left side view of an extended drawer slide cooperating with a work surface underframe vertical object. 
           [0016]      FIG. 2  is a left front isometric partial view of an underframe with a smaller diameter constant force spring applying a lifting force to a middle slide of a drawer slide. 
           [0017]      FIG. 3  is a left front isometric partial view of an underframe with a larger diameter constant force spring applying a lifting force to a middle slide of a drawer slide. 
           [0018]      FIG. 4  is a right side isometric view of an underframe with a constant force spring cooperating with flexible cable manipulated by a pulley to communicate a lifting force to middle slide of a drawer slide. 
       
    
    
     DETAILED DESCRIPTION 
       [0019]    The widespread popularity of drawer slides has supported manufacturers in many countries, and resulted in high volume low cost production of these ball-bearing linear extension mechanisms. Attempting to use these advantages in vertically oriented applications, particularly an adjustable height work surface application, revealed problems that would need cost effective solutions to enable these drawer slides to provide sufficient stability. This exemplary adjustable height work surface application is the first intended application, and the basis of the research herein, where this method improves the rigidity of a purchased component operating in a vertical orientation. 
         [0020]    Different methods of lift assistance including motorized and counterbalanced methods that would cooperate with the underframe to elevate it are not shown. 
         [0021]    Referring to  FIG. 1  showing the left side of an asymmetric work surface  20  cooperating with an underframe comprising vertical components  12  cooperating with the inner slide components  31  attached thereto with just the left side showing. Human interaction such as side impacts to the work surface at location F 1  with the work surface result in lateral and torsional forces applied to these inner slide components or inner slides  31  cooperating arrays of ball bearings  34  to the middle slide component or middle slide  32 , further cooperating with ball bearings  35  to the fixed outer slide component or outer slide  33  further cooperating with the stability of the base objects (not shown). The travel extent of the middle slide  32 , and inner slide  31  are shown as fully extended. The sitting position or starting level  41  for the drawer slides provides the maximum rigidity. The phase 1 of travel extends from  41  to level  51  representing about half of the length of the slide, and the highest level of the middle slide. Phase 2 is the travel distance showing the unsupported inner slide between levels  51  and  61 . 
         [0022]    The arrays of ball bearings  34 ,  35  are retained in cages and frictionally cooperate between slide components and movably cooperate with the movements of the extendable middle and inner slides due to rolling contact of the ball bearings initiated by the movement of one slide in relation to another. This results in vertically extending all of these components in relation to the fixed position of the outer slide  33 , and subjecting them to the force of gravity. The inner slide  31  will extend half its length out of the middle slide  32  before features of the inner slide engage features of the middle slide that insures the middle slide is extended and retains its position when the inner slide is fully extended. Lateral loads in this vertical orientation retain the elevated ball bearings and middle slide. The lateral fraction of a downward load in this vertical orientation is relatively low where human interaction can easily reduce or reverse this lateral load. After a bit of use, normal human interactions producing lateral and torsional forces relieve lateral loads on the ball bearings long enough for gravity to urge the middle slide assembly to continue slipping down from a not fully elevated position it may have attained during lifting. 
         [0023]    A new slide is manufactured to produce slight interference fits between the slides and the ball bearings providing a slight normal force applied to the ball bearings enabling the relative movements between the slides to cause the arrays of ball bearings to appropriately advance and retain their advanced positions. However, with normal use and exposure to loads and forces, this normal force degrades, enabling gravity to retain the middle slide and ball bearing arrays while the inner slide initially extends from the starting level  41  to level  51  before its features begin extending the middle slide. 
         [0024]    Since the loads and forces in this application are initiated at the work surface, and this extended and unsupported half of the inner slide is the least able to communicate loads and forces without distortion, it is described as the providing the minimum stiffness available in this vertical orientation. 
         [0025]    A method to improve the available stiffness of the drawer slides in a vertical orientation is described where minor modifications to the leading ends of the inner and middle slides were required. These modifications enable the leading end of the middle slide to further comprise a feature that cooperates with an object that communicates a sufficient lifting force to the middle slide. 
         [0026]    The lifting force urges the middle slide to remain in contact with its upper stop, enabling it to extend along with the inner slide during phase 1 travel to level  51 , and is retained by the lifting force as the inner slide further extends with the underframe through phase 2 travel to full extension. 
         [0027]    Applying this lifting force maximizes the support provided by the middle slide to the inner slide during the phase 1 travel, and maximizes the proximity of this support as the inner slide further extends in phase 2 travel. Although there is no improvement in stiffness at level  41  or level  61  there is significant improvement in stiffness at the elevated positions between these levels. 
         [0028]    This method further enables the use of over length slides that never reach full extension. Using an over length drawer slides in cooperation with applying a lifting force to the middle slides increases the extended elevation level  51  of the middle slides and the support provided, while also reducing the phase 2 travel distance of the unsupported inner slide. These advantages increase the travel distance providing maximum support, and further maximize the proximity of this support to the further extended inner slide. The available stiffness is further increased primarily in the second half of elevated travel including the level  61  position. 
         [0029]    While features proximate to the leading ends of the inner and middle slides  32  may vary from one manufacturer to the next, a cooperating feature as common as a hole or threaded feature, or other modification has to be added to the middle slide to connect an object providing a lifting force. 
         [0030]    The inner slide  31  leading end features may interfere with a preferred connected object and may also require a modification. Providing drawer slides with the one or more added features described, with or without a lifting force object, and intended for the purpose described herein is considered within the scope of this application. 
         [0031]    Referring to  FIG. 2 , a small diameter constant force spring  10  cooperates with a hub rotationally cooperating with a shaft  14  that cooperates with the under frame vertical object  12  in a cutout  11  above the inner slide. The underframe also comprises a panel object  13  cooperating with a second vertical object  12  (not shown), that further cooperates with a second similarly configured drawer slide further cooperating with a second base object. 
         [0032]    The free end feature  10   b  of each spring cooperates directly or indirectly to the cooperating feature added to the middle slide where a sufficient extended distance of the free end from the spring coil preloads the spring to provide the lifting force. This exemplary view is one of several known arrangements for mounting these springs considered within the scope of this description. 
         [0033]    Referring to  FIG. 3  a larger diameter constant force spring  10  providing very long life cooperates with a hub rotationally cooperating with a shaft  14  that cooperates with brackets  19  connected to the under frame vertical object  12  above the inner slide. Cutout  11  in vertical object  12  is required. The preload distance is greater for the larger diameter, which limits the use of over-length slides. 
         [0034]    Referring to  FIG. 4 , the underframe vertical component  12  cooperates with a panel object  13  that would further cooperate with a second vertical component  12  further cooperating with a second similarly configured drawer slide cooperating with a second base object. 
         [0035]    In this exemplary view, the object connected to the middle slide  32  cooperating feature comprises a cable end fitting  18  connected to a flexible cable  15  that loops over a pulley  16  cooperating with bracket  17  in a cutout of object  12 , and into the underframe. The second end of the cable is connected directly or indirectly to the free end  10   a  of a constant force spring  10  mounted on a hub rotationally cooperating with shaft  24  cooperating with an underframe panel  13 . It is important to add the preload distance and the extended travel distance when locating the spring, and preparing the cable. This configuration enables larger diameter springs to communicate a lifting force to over-length drawer slides. 
         [0036]    In the majority of applications, drawer slides are used in pairs, where the opportunity to further manipulate the orientation of a plurality of lifting cables to cooperate together with one or more springs is within the scope of this method of communicating a lifting force to a plurality of middle slides using springs.