Abstract:
A safety release for a clamping brake mechanism in which the clamping force increases with increasing loads and the force required to release the clamping brake also increases. The safety release comprises a fixed housing, a cable release coupled to the housing, a pivot link coupling an end of said cable release and constrained to pivot through a predetermined arc. A release rod is coupled to an end of the pivot link remote from the release lever, and a compression spring extends between the end of said pivot link and the release rod, such that the spring will compress in the event the force to move the release rod exceeds the spring constant. This compresses the spring and prevents the release rod from moving to release the clamping brake. The compression spring, in one embodiment, comprises a plurality of stacked Belleville washers.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims priority under 35 U.S.C. § 119(e) and the benefit of U.S. Provisional Application Nos. 61/647,571 entitled SAFETY RELEASE filed May 16, 2012, by Wilkinson et al.; 61/672,925 entitled SAFETY RELEASE filed Jul. 18, 2012, by Wilkinson et al.; 61/647,566 entitled DOUBLE ACTING FLUID CYLINDER LOCK filed May 16, 2012, by Wilkinson et al.; 61/672,920 entitled DOUBLE ACTING FLUID CYLINDER LOCK filed on Jul. 18, 2012, by Wilkinson et al.; and 61/758,997 entitled SELF-ALIGNING AXIAL BEARING, filed on Jan. 31, 2013, by Wilkinson et al., the entire disclosures of which are incorporated herein by reference. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    The present invention relates to a release mechanism for a mechanical brake which will prevent release of the brake in the event of an overload. 
         [0003]    Fluid cylinders used for raising and lowering adjustable tables, such as gas springs, are controlled by a variety of means to allow height adjustment without excessive sudden movement. Several designs exist for the control of gas springs typically used in table and chair height adjustments. Use of such gas springs is commonplace in the furniture industry in which chairs, tables, and other items are desired to be easily adjustable. Typically, the gas spring force is selected to counterbalance a normal weight load expected on a chair or table, and the stroke of the gas spring is selected for the desired amount of movement. To control telescopic support tubes in which gas springs are employed, mechanical locking mechanisms have been employed as well as controlling the flow of fluid on either side of the piston of a gas spring. When a table or chair is overloaded or has no load, the release of the position locking mechanism can result in the undesired sudden movement of the table or chair. This invention provides a safety release preventing such sudden movement. 
       SUMMARY OF THE INVENTION 
       [0004]    The present invention is a safety release for a clamping brake mechanism in which the clamping force increases with increasing loads and the force required to release the clamping brake also increases. The safety release comprises a fixed housing, an actuator coupled to the housing, and a release lever, which is constrained to move through a predetermined distance. A compression spring extends between the end of the release lever and the release rod, such that the spring will compress in the event the force to move the release rod exceeds the spring constant. This compresses the spring and the constrained movement of the release lever prevents the release rod from moving to release the clamping brake. The compression spring, in one embodiment, comprises a plurality of stacked Belleville washers. 
         [0005]    These and other features, objects and advantages of the present invention will become apparent upon reading the following description thereof together with reference to the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0006]      FIG. 1  is a perspective view of two adjustable tables incorporating the system of the present invention; 
           [0007]      FIG. 2  is a side elevational view of a telescopic leg of the table supports shown in  FIG. 1 ; 
           [0008]      FIG. 3  is a vertical cross-sectional view of an adjustable table support embodying the locking and release mechanism of the present invention; 
           [0009]      FIG. 4  is an enlarged fragmentary cross-sectional view of the locking mechanism shown in  FIG. 3 ; 
           [0010]      FIG. 5  is a fragmentary cross-sectional view of the locking mechanism seen in  FIG. 4 ; 
           [0011]      FIG. 6  is a pictorial view of the locking mechanism, shown removed from the telescopic tubes; 
           [0012]      FIG. 7  is a fragmentary perspective view of the release mechanism removed from the telescopic tubes; 
           [0013]      FIG. 8  is a cross-sectional view of the release mechanism shown mounted to the connecting head on the gas spring; and 
           [0014]      FIG. 9  is a fragmentary perspective view of the release mechanism, taken from the side opposite that shown in  FIG. 7 . 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0015]      FIG. 1  shows adjustable tables  30  which include a height adjustment assembly  15  ( FIG. 2 ) including telescopic tubes  32  and  34  extending between a floor support  36  and a table surface  38 .  FIG. 2  shows one of the table legs  15  with a support flange  35  at the upper end of telescopic tube  34  and a fitting  33  which extends into a socket in the floor support  36  of  FIG. 1 . The telescopic tube  34  slideably extends within outer tube  32  with polymeric bearings  20  ( FIGS. 2) and 23  ( FIG. 5 ) providing smoothly guided movement between the tubes  32 ,  34 . These bearings and the general construction of the leg  15  are disclosed in U.S. patent application Ser. No. 61/758,997 filed on Jan. 31, 2013, entitled SELF-ALIGNING AXIAL BEARING, the disclosure of which is incorporated herein by reference. Within the telescopic tubes, there is a fluid spring, such as gas spring  10  shown in  FIG. 3 , with an extendable and retractable rod  12  to raise and lower the extruded inner table support tube  34 . For such purpose, the opposite ends of gas spring  10  are conventionally coupled to each of the respective tubes  32 ,  34  so that extension of rod  12  causes the overall length of the tubes to extend. Fixedly coupled to the lower end of extruded tube  34  is the locking mechanism  40  incorporating the safety release  100  (FIGS.  3  and  7 - 9 ) of the present invention. The outer tube  32  is mounted to support member  33  (or  18  in  FIG. 3 ), in turn, coupled to the floor support  36 . The orientation of the telescopic tubes can be reversed depending upon a particular application. 
         [0016]    The leg assembly  15  so-formed also includes a safety release  100  which includes a cable release  120  ( FIG. 3 ) which is coupled to a control handle (not shown) and is limited in its movement, as shown by arrow A, to a few millimeters as described below. A coupling  124 , acting through leg  112 , ( FIG. 8 ) couples the cable release  120  to a release rod  26 , which, when raised in the direction of arrow B in  FIG. 8 , releases the locking mechanism  40  as described below. The locking mechanism  40 , which is secured to telescopic tube  34 , grips the rod  12  extending from gas spring  10  in any desired position selected by the user by moving rod  26  upwardly, as indicated by arrow B in the figures, to release the grip on rod  12  by locking mechanism  40 . The table surface can then be raised manually with gas assist or pushed down until the desired position of the table is reached. The operation of the locking mechanism is best seen in  FIGS. 4-6 . 
         [0017]    The locking mechanism  40  comprises a lock base  42 , which is a generally triangular member having a central aperture  49  ( FIG. 4 ) surrounding piston rod  12 . It includes three lateral flanges  47  with apertures  52  through which three screws  41  extend to securely fix the lock base  42  and hence the locking mechanism  40  to threaded extrusions of the extruded hexagonal inner support tube  34  to secure the locking mechanism to the lower end of tube  34 . The outer tube  32  is fixed and is attached to the table base, while the inner extruded tube  34  moves up and down with the rod  12  sliding through locking mechanism  40 , when in a released position, to raise and lower the table surface  38  attached to the upper end of extruded tube  34 . Associated with the lock base  42  are opposed upper and lower conical cam plates  46 ,  48  with external conical surfaces  43  and  45  ( FIGS. 4 and 6 ). Surfaces  43 ,  45  are engaged by interior conical mating surfaces  61  and  63  of upper and lower movable clamping members  60  and  62  ( FIGS. 4-6 ), respectively. The plates  46 ,  48  have central apertures  50 ,  51  ( FIG. 4 ) which generally align with aperture  49  of lock base  42  and receive rod  12 , which extends through members  60 ,  46 ,  42 ,  48  and  62 , as best seen in  FIG. 4 . Lock base  42  has an upper surface  53  which is slideably engaged by the lower surface  55  ( FIG. 4 ) of conical cam plate  46 . Similarly, the lower surface  56  of lock base  42  is engaged by the upper surface  57  of conical cam plate  48 . This sliding or floating arrangement of the cam plates  46 ,  48  allows the tapered clamping members  60 ,  62  to better engage the offset cam plates to effect locking of the locking member  40  to rod  12 . The construction of the locking mechanism is described in greater detail in the copending patent application entitled DOUBLE ACTING FLUID CYLINDER LOCK, Serial No. (Atty. Docket No. SUS001 P345) filed on even date herewith, the disclosure of which is incorporated herein by reference. 
         [0018]    Compression springs  70  ( FIGS. 5 and 6 ) are mounted on both sides of the lock base  42  and urge members  60 ,  62  in a compressed position against lock base  42 . Members  60 ,  62  have center apertures  65  ( FIG. 4 ) which are offset a distance of about 1 mm from the axis of their conical surfaces  61 ,  63 , as disclosed in greater detail in the above identified patent application entitled DOUBLE ACTING FLUID CYLINDER LOCK. This offset shifts and/or tilts members  60 ,  62  under the forces of springs  70  such that, when compressed to the opposed conical surfaces  43  and  45  of conical cam plates  46 ,  48 , the inner cylindrical surfaces  68  ( FIG. 4 ) of center apertures  65  bind to the outer surface of cylindrical rod  12 , thereby locking the inner extruded tube  34  in a selected adjusted position. A plastic bearing sleeve  23 , shown in  FIG. 5 , facilitates movement of tubes  32  and  34  when the locking mechanism is unlocked. 
         [0019]    The unlocking of mechanism  40  is controlled by the rod  26  of safety release  100 , which rod is coupled to the bracket  64  ( FIG. 4 ) of upper clamping member  60 , which has outwardly extending pins  67  on each side ( FIG. 5 ). Pins  67  extend through apertures in the opposite ends of pivoted levers  90 , which are pivotally mounted to lock base  42  by pivot axles  44  ( FIG. 6 ) integrally extending from opposite sides of the lock base  42 . Springs  70  have ends  71  which fit over tabs  66  in the identical clamping members  60 ,  62  as also illustrated in  FIG. 6 . Springs  70  hold the levers  90  in place on lack base  42 , as best seen in  FIG. 6 . 
         [0020]    When rod  26  is moved upwardly in the direction of arrow B in  FIG. 6 , levers  90  rotate in a counterclockwise direction, as viewed in  FIG. 6 , to raise clamping member  60  away from lock base  42  and associated cam plate  46 , as well as pushing member  62  downwardly away from the lock base  42  and associated cam plate  48 , thereby allowing the apertures  65  of clamping members to move to a coaxial position around rod  12 . This releases the locking force of members  60 ,  62  against rod  12  and permits the table supporting extruded tube  34  to move up and down on rod  12  extending or collapsing the telescopic tubes  32 ,  34 . 
         [0021]    The weight on the table surface is transferred by lock base  42  and conical cam plates  46 ,  48  to one or the other of the clamping members  60 ,  62  of the locking mechanism. When the weight exceeds the force of gas spring  10 , the lower clamping member  62  locks against the rod  12  as the conical surface  45  of cam plate  48  ( FIG. 4 ) pushes against conical surface  63  of clamping member  62 . Thus, the actual weight of the table on members  60 ,  62  offset by the force of gas spring  10  causes the apertures  65  of members  60 ,  62  offset from the central aperture  49  of locking base  42  to increase the effect of the locking action. When the weight on the table surface is less than the force of gas spring  10 , lock base  42  raises and conical surface  43  of plate  46  engages the conical surface  61  of upper clamping member  60  to prevent the undesired raising of the table. Thus, the table surface will remain in a selected adjusted position until such time as the safety release  100  is actuated. The heavier the weight on the table, the more locking force is applied, with the springs  70  positioning locking members  60 ,  62  into a locking position. By providing members  60  and  62  on opposite sides of the locking base  42 , the table is locked against either raising or lowering until the release rod  26  is moved upwardly in the direction of arrow B. 
         [0022]    The locking mechanism  40  ( FIG. 3 ) grips the rod  12  extending from gas spring  10  in any desired position selected by the user until it is desired to change the position of the table. In which case, cable release  120  ( FIGS. 7-9 ) is drawn inwardly (to the left in  FIGS. 3 and 7 ), moving rod  26  upwardly, to release the grip on rod  12  by locking mechanism  40 . Unless overloaded or under loaded, the table can then be lowered or raised under the influence of gas spring  10 . The safety release  100  prevents the release of the locking mechanism when the table is overloaded, such that it will not precipitously drop. If the weight on the table is significantly less than the force provided by the gas spring, the safety release will also prevent the release of the locking mechanism, such that the table surface will not quickly raise. The operation of the release assembly  100  to accomplish these features is best understood by reference to  FIGS. 7-9 . 
         [0023]    The safety release is pivotally secured to connecting head  25  of the gas spring  10 . Connecting head  25  is threadably secured to a threaded rod  13  at the upper end of gas spring  10 , as seen in  FIG. 8 , and comprises a generally cylindrical member having an aperture  22  therein for receiving a pivot pin  24  ( FIG. 7 ), which pivotally mounts a pivot link  102  to the connecting head  25 . Pivot link  102  includes a circular mount  104  ( FIG. 8 ) having an aperture  105  therein for receiving pivot pin  24 , allowing the pivot lever limited pivoting motion (less than about 10°) which is controlled by a beveled stop surface  21  on connecting head  25 , as best seen in  FIGS. 8 and 9 . Pivot link  102  includes a lower cup-shaped leg  106  with a aperture  108  therein surrounding release control rod  26 . The upper end  27  of rod  26  includes a snap ring  28 . Between the snap ring  28  and the upper surface of leg  106  are a plurality of Belleville washers  110  with, in the preferred embodiment, between about three to about seven Belleville washers typically employed. In some applications, a slightly greater number may be employed. The washers  110  serve as a compression spring in the manner described below. Pivot link  102  also includes an upwardly extending angled leg  112  with a section  114  which engages inclined stop surface  21  of connecting head  25 , thereby limiting the counterclockwise rotation in a direction indicated by arrow C in  FIG. 8  of the lever arm and, therefore, the movement of leg  106  upwardly against Belleville washers  110 . 
         [0024]    Leg  112  extends to an upwardly extending section  114  and then to a circular mount  116  for the pivot link  102 . The connecting head includes a socket  29  for receiving cable release  120 , which has a collar with a mating recess  122  that fits within socket  29  while holding cable release  120  in position on the connecting head  25 . An end of cable release  120  includes a coupling element  124 , which extends within mount  116  in a pivotal fashion, such that actuating of cable release  120  will draw the cable  121  of cable release  120  in the direction indicated by arrow A in  FIG. 8  and will rotate pivot link  102  in the direction indicated by arrow C. Cable release  120  is conventionally coupled to a handle (not shown), which is easily accessible to the user of the table or other device using the telescopic tubes for adjusting the height thereof. In some orientations, the cable release  120  can be oriented in reverse, such that it becomes a foot pedal if the telescopic tubes are reversed. 
         [0025]    Normally, upon actuating cable release  120 , the washers  110  will not significantly compress and will allow the movement of rod  26  upwardly, as indicated by arrow B. If there is an excessive weight on the table or no weight, the locking member  40  will increase the locking force on rod  12 , which, in turn, requires a greater force on rod  26  to release the clamping members  60  and  62 . This compresses washers  110  in a lost motion fashion and rod  26  will not be moved. If, for example, a 200 pound weight is placed on the table, it is desired to prevent the table from slamming down when someone attempts to adjust the table height. Similarly, if there is no load on the table, again the locking mechanism  40  will require a greater release force on rod  26  than the compression force on springs  110 . In either situation, the release rod  26  will require a significant force to release the locking mechanism  40 . In such case, pressing down on cable release  120  will rotate pivot link  102  in a counterclockwise direction. The Belleville washers  110  will compress against snap clip  28  at the upper end  27  of rod  26  due to the excessive force required to move rod  26 . This prevents the movement of rod  26  until the stop limit of pivot link  102  is reached, when surface  114  engages stop  21 , and release rod  26  will not move. Thus, the compressible Belleville washers  110  provide a safety factor preventing the release of the locking mechanism in the event a very heavy object is on the table surface. When a normal load is on the table, actuating cable release  120  will raise rod  26  to release the locking member  40 . 
         [0026]    Other forms of compression springs with limited movement could also be employed in place of the Belleville washer. Also, other forms of actuators can be employed in place of the pivot link  102 . Such actuators may include linear actuators that are constrained in their movement and employ spring(s) to provide the same safety release function as provided by the embodiment described in detail herein. 
         [0027]    These and other modifications will become apparent to those skilled in the art without departing from the spirit or scope of the invention as defined by the appended claims.