Abstract:
A hydraulic drive system readily adapted for either manual actuation or motor-driven actuation due to the unique design of the hydraulic drive and its coupling to either a hand crank or to a motorized drive to provide hydraulic pressure to lift cylinders that can be attached to table legs for vertical adjustment. The hydraulic drive includes a screw jack having an end extending from one end of a housing and splined or otherwise keyed. A manual crank arm or motorized drive assembly includes a coupling which mates with the end of the screw jack to provide a drive force for the hydraulic cylinder drive. The motorized drive assembly includes a pair of toothed hubs and an intermediate flexible sleeve allowing alignment of the motorized drive to the drive assembly as well as providing sound dampening, a cushioned coupling, and facilitates overcurrent detection.

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 No. 61/483,955 entitled D RIVE  S YSTEM FOR  T ELESCOPIC  L EGS FOR  T ABLES , filed on May 9, 2011, by James E. Doyle and Andrew J. Brouwers, the entire disclosure of which is incorporated herein by reference. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    The present invention relates to an improved manual or motor-driven hydraulic drive system for telescopic legs for a table or other apparatus to be vertically movable. 
         [0003]    Telescopic legs for adjusting the height of a work surface, such as a table, has become increasingly popular as attempts are made to improve the work environment and provide better working conditions for employees. Thus, adjustable height work surfaces accommodate employees that are either standing or sitting and are of different gender and/or stature. U.S. Pat. Nos. 6,705,239 and 7,246,779, both assigned to the present Assignee, disclose adjustable table legs which utilize hydraulic cylinders to provide vertically adjustable work surfaces. Lift systems which include hydraulic cylinders and electrically driven pumps are sold by Suspa Incorporated, the Assignee of the present invention, under the trademark MOVOTEC®. Such systems allow the retrofitting of table legs with attachable cylinders to provide manual or electrical raising and lowering of tables. The MOVOTEC® brand leg systems, however, cannot be easily converted from a manual crank system to an electrically driven system and, thus, require separate and distinct drive systems. 
       SUMMARY OF THE INVENTION 
       [0004]    The system of the present invention, however, utilizes a hydraulic drive system which is readily adapted for either manual actuation or motor-driven actuation due to the unique design of the hydraulic drive and its coupling to either a hand crank or to a motorized drive. With such a system, therefore, a single hydraulic drive can be employed with either a manually actuated crank arm or an electrically driven motor to provide hydraulic pressure to lift cylinders that can be integral with or attached to table legs or other apparatus for vertical adjustment. 
         [0005]    In the preferred embodiment of the invention, the system is a hydraulic drive with a screw jack, having an end extending from one end of a housing and splined or otherwise keyed. In a first embodiment of the invention, a manual crank arm includes a coupling which mates with the end of the screw jack. In another embodiment of the invention, a motorized drive unit includes a motor-driven coupling which likewise mates with the end of the screw jack to provide a drive force for the hydraulic cylinder drive. In a preferred embodiment of the invention, the motorized coupling includes a pair of toothed hubs and an intermediate flexible sleeve coupling allowing alignment of the motorized drive to the drive assembly as well as providing sound dampening and a cushioned coupling. This also facilitates overcurrent detection by preventing sharp overcurrent condition and provides a more gradual current curve with which to operate. Thus, with the system of the present invention, a single hydraulic drive can be provided and universally receives either a hand crank assembly or a motorized drive assembly for the actuation of lift cylinders that can be used for raising and lowering work surfaces or other apparatus. 
         [0006]    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 
         [0007]      FIG. 1  is a perspective view of a motorized leg lift kit including a hydraulic drive and leg assemblies for attaching to legs of a table or work surface; 
           [0008]      FIG. 2  is a perspective view of a work surface, shown with the lift cylinders secured thereto and in a lowered or retracted position; 
           [0009]      FIG. 3  is a perspective view of the structure shown in  FIG. 2 , shown in a raised cylinder extended position; 
           [0010]      FIG. 4  is a perspective view of a hydraulic drive which is mechanically actuated by a crank arm; 
           [0011]      FIG. 5  is an enlarged perspective view of the crank arm and coupler for mechanically attaching the crank arm to the hydraulic drive; 
           [0012]      FIG. 6  is an enlarged cross-sectional view of the crank arm and coupling; 
           [0013]      FIG. 7  is an exploded view of the crank arm coupling and end of the hydraulic drive; 
           [0014]      FIG. 8  is a right end elevational view of the coupling shown in  FIG. 7 ; 
           [0015]      FIG. 9  is a top elevational view, partly broken away, of a motorized hydraulic drive assembly; 
           [0016]      FIG. 10  is a fragmentary exploded view of the assembly shown in  FIG. 9 ; 
           [0017]      FIG. 11  is an enlarged assembled fragmentary top elevational view of the drive motor and coupling to the hydraulic drive shown in  FIG. 10 ; 
           [0018]      FIG. 12  is a cross-sectional view of the coupling shown in  FIG. 11 , taken along section line XII-XII; 
           [0019]      FIG. 13  is a cross-sectional view of the drive motor, coupling, and hydraulic drive shown in  FIGS. 10 and 11 ; and 
           [0020]      FIG. 14  is a left end perspective view of the drive block for the hydraulic drive seen in  FIGS. 7 and 9 . 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0021]    Referring initially to  FIG. 1 , there is shown a kit  10  for raising and lowering a work surface, such as  40  illustrated in  FIGS. 2 and 3 . The kit comprises a motorized hydraulic drive unit  20  including a drive motor assembly  30  which controls a screw jack for pressurizing hydraulic cylinders within the hydraulic drive  20  providing hydraulic pressure through tubes  11 - 14  to hydraulically actuated cylinders  21 - 24 , respectively, which form bolt-on legs with extendable foot pads  25 . Cylinders  21 - 24  can be secured to the legs of a work surface, such as fixed legs  42  of work surface  40  as shown in  FIGS. 2 and 3 . The construction of cylinders  21 - 24  can be substantially the same as that disclosed in U.S. Pat. No. 6,711,985, entitled S EALED  G LIDE  A DAPTER , issued Mar. 30, 2004, the disclosure of which is incorporated herein by reference. For the eight-legged work surface  40  shown in  FIGS. 2 and 3 , two kits  10  are employed for moving the work surface  40  from a lowered position, shown in  FIG. 2 , to a raised position, shown in  FIG. 3 , and positions intermediate depending on the desired vertical height of the upper surface  41  of the work surface or table  40 . 
         [0022]    The hydraulic drive  20 , as best seen in  FIGS. 9 and 13 , is the same one used in both the mechanical crank arm version (shown in  FIGS. 4-8 ) as well as the electrically driven version (shown in  FIGS. 9-14 ). Drive unit  20  comprises a generally rectangular extruded aluminum housing  50  for securing in spaced relationship therewith four hydraulic cylinders  52 , which provide pressurized hydraulic fluid at four outlets  54  to tubes  11 - 14  for cylinders  21 - 24 , respectively. The piston rods  56  for hydraulic cylinders  52  have one end anchored into the thrust nut  60  which is slideably mounted within housing  50  and includes an internal thread  62  ( FIG. 14 ) engaging the screw jack  70 , which is supported by a bearing  72  and includes an extended end  74  ( FIGS. 7 and 10 ) which is keyed or splined to engage a coupling for either the mechanically driven system or the electrically driven system as described below. The thrust nut  60  is shown in  FIG. 14  and described in greater detail below. Rotation of screw jack  70  causes thrust nut  60  to move from the left to the right, as illustrated in  FIG. 12 , pushing piston rods  56  (and pistons associated therewith) into cylinders  52 , thereby applying hydraulic pressure to lines  11 - 14  for extending pads  25  and raising the work surface  41  to a raised position, as shown in  FIG. 3 . Rotating the screw jack  70  in the opposite direction reduces the pressure, allowing the cylinders  21 - 24  to contract pads  25  into a lowered position, as shown in  FIG. 2 . Hydraulic drive  20  may be actuated by an electrical motor assembly  30  (FIGS.  1  and  9 - 13 ) or by a manual crank arm assembly  80  as now described in connection with  FIGS. 4-8 . 
         [0023]    Crank arm assembly  80  comprises a crank arm  82  having a foldable handle  84  which folds into the crank arm and a drive hex socket  86  on the end opposite handle  84 . The collapsible handle is pivotally mounted to arm  82  at  85  and pivots into a pocket  83 , as best seen in  FIG. 6 . Socket  86  receives a coupler  90  which has a hex head  92  that fits within the hex socket  86  and is held therein by means of an attachment fastener, such as screw  87  ( FIGS. 6 and 7 ). Coupler  90  has an end opposite hex head  92  with a splined aperture  94  ( FIGS. 5 ,  6 , and  8 ) which mates with and positively engages the splined end  74  of screw jack  70 . Crank arm assembly  80  is assembled onto the hydraulic drive  20 , as illustrated in  FIG. 4 , and held thereon by the fastening screw  87  which, as seen in  FIG. 7 , extends through socket  86 , coupler  90 , and into a threaded aperture  76  ( FIGS. 12 and 13 ) in the extending end  74  of screw jack  70 . Thus, in the embodiment shown in  FIGS. 4-8 , the hydraulic drive  20  is controlled by the crank arm assembly  80 , which is secured to the splined end  74  of screw jack  70  extending from housing  50  of the hydraulic drive  20 . The splined end  74  may otherwise be keyed to the coupler  90  in another manner other than by the spline connection, which, however, is preferable. The handle is held in place to the hydraulic drive  20  by means of the fastener  87  extending axially through the socket  86 , coupler  90 , and into the end  74  of screw jack  70  but can be easily removed and stored when not in use. 
         [0024]    Coupler  90  can also be assembled directly to splined shaft  74  by means of a fastener  87 . The hex head  92  of assembled coupler  90  can then be driven using a hex socket driven by an electric drill or screwdriver with an integral clutch to prevent pump overdrive. Alternatively, the coupler can be driven utilizing a conventional wrench or ratchet drive with a socket that mates with end  92  of coupler  90 . 
         [0025]    In the electrically driven version, the hydraulic drive  20  is identical, including the splined end  74  of screw jack  70 , but is coupled to the motor assembly  30  utilizing a coupling housing and coupling structure best seen in  FIGS. 10 and 11 . Motor assembly  30  includes a conventional, electrically driven motor  32 , and right angle gear box  34 . Motor  32  is actuated by an electrical control circuit coupled to the motor  32  by means of conductors  36 , which lead to a control circuit sensing the current draw of motor and turning the motor off when an overcurrent is sensed, indicating that the end of travel of the screw jack  70  and piston rods  56  for cylinders  52  has been reached in a conventional manner employed in existing MOVOTEC® brand lift systems. The addition of flexible coupling assembly  110  ( FIG. 11 ) facilitates the overcurrent detection as the flexible coupling prevents a sharp overcurrent condition and provides a more gradual current curve with which to operate. The gear box  34  is mounted to a coupling housing  100 , as best seen in  FIGS. 9-13 , which includes a cover  102  ( FIG. 9 ) for coupling assembly  110  once installed to couple the output shaft of gear box  34  to the screw jack  70 . 
         [0026]    Coupling assembly  110  ( FIGS. 10-12 ) includes a pair of hubs  112 ,  118  which are coupled by a flexible coupling sleeve  116 . Hub  112  is secured to the end of drive shaft from gear box  34  by means of a fastening screw  114 . Hub  112  includes a plurality of arcuately spaced teeth  113  projecting outwardly therefrom around the periphery and which mate within slots  117  formed in a flexible coupling sleeve  116  which has a length L ( FIG. 10 ) greater than the lengths of hubs  112  and  118 . The second or driven hub  118  is mounted to the splined end  74  of hydraulic drive  20  and includes a splined center aperture and is held thereto by means of a similar fastening screw threaded into the threaded aperture  76  of splined end  74  of screw jack  70 . Hub  118  includes teeth  119  similar to teeth  113  of hub  112  and has a thickness or axial length less than half the length L of flexible coupling sleeve  116 , such that, when assembled as shown in  FIGS. 11 and 13 , hubs  112  and  118  do not touch. They lockably engage one another through their engagement with internal slots  117  and adjacent teeth  115  of flexible coupling sleeve  116 . The coupling  110  itself, used for a different purpose in a different environment, can generally be of the type disclosed in U.S. Pat. No. 2,952,143, the disclosure of which is incorporated herein by reference. 
         [0027]    Coupling  110  provides sound damping between the motor and the hydraulic drive, cushioning between motor assembly  30  and hydraulic drive  20 , as well as allow more gradual overcurrent detection for the motor. It also provides easy connection of the motor assembly  30  to the hydraulic drive  20 . Flexible coupling sleeve  116  can be made of a suitable and durable material, such as neoprene, to provide the desired coupling characteristics between the output shaft of gear box  34  and the input of end  74  of screw jack  70 . 
         [0028]    Housing  100  includes mounting tabs  111  for mounting the motor end of the system to a suitable location on a work surface or table while the opposite end includes a similar mounting bracket  120  ( FIG. 9 ) for stabilizing the opposite end and mounting it to the table. The hydraulic drive  20  includes an improved, more robust thrust nut  60 , shown in  FIGS. 13 and 14 , which is made of an acetal, such as Delrin®, and provides a drive block for the four cylinder piston rods  56  associated with four cylinders  52 . The thrust nut or drive block  60  includes central threaded aperture  62 , which is threadably engaged by the threads  75  of screw jack  70 , such that rotation of the screw jack moves the block  60  in the direction indicated by arrow A in  FIG. 13 . Counter rotation of the drive shaft from gear box  34  provides the opposite motion. The four piston rods  56  are inserted in four circular sockets on the side of block  60  opposite that shown in  FIG. 13  and are held therein by means of a press-fit connection to each of the four recessed apertures  64  associated with the piston rods  56 . If it is necessary to replace any one of the cylinders  52 , the piston rods can be pushed from block  60  utilizing the apertures  64  as an access port. Drive block  60  includes a plurality of axially spaced ribs  61 , with grooves  65  between them, which minimizes the friction of the pusher block within the extruded housing  50  of hydraulic unit  20  when motor assembly  30  is actuated to provide a smooth and stable pressurization of cylinders  52  and, subsequently, the hydraulic pressure supplied to lift cylinders  21 - 24  through tubes  11 - 14 . The drive block and extruded housing can be modified to include a greater or fewer number of cylinders and their associated rods. 
         [0029]    It will become apparent to those skilled in the art that various modifications to the preferred embodiment of the invention as described herein can be made without departing from the spirit or scope of the invention as defined by the appended claims.