CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims priority to EP Patent Application No. EP 13155480.0 filed Feb. 15, 2013, the contents thereof to be incorporated herein by reference in its entirety. 
       FIELD OF THE INVENTION 
       [0002]    The present invention relates to portable work benches or tables which include an integral clamping table or vise. More particularly, the present invention relates to a work table with a clamping table or vise where the vise may be operated with one hand. 
       BACKGROUND OF THE INVENTION 
       [0003]    Carpenters, woodworkers and handymen who work with wood as well as other materials, often need a work bench or table which may be utilized to hold workpieces. Ordinarily, these work benches include a frame and a table surface connected to the frame, the table surface including at least two substantially flat members. One of the members is movably coupled with said frame in order to enable clamping of a workpiece between said members. These tables may be versatile, may provide for secure clamping, and may be compact and adjustable. 
         [0004]    Such work benches ordinarily includes two vise screws with handles on each one. The vise screws, via the handles, may be operated by the user with the user using both hands. Both handles must be rotated in order to clamp a workpiece between the clamping table members. A transmission belt or chain connecting the two screws may be provided, such that both of the screws may be cranked using only one hand. One handed cranking of the vise to clamp the workpiece allows the user to hold the workpiece in place with his other hand. 
         [0005]    However, such mechanisms can be difficult to operate or stiff to turn, since the turning force for both screws must be applied via one handle. It is also desirable to increase the ease and convenience of the clamping operation. 
       BRIEF SUMMARY OF THE INVENTION 
       [0006]    Accordingly, it is an object of the present invention to provide an improved vise for a work bench which enables the vise to be easily and quickly tightened using one hand. 
         [0007]    In accordance with the invention, there is provided a work bench comprising a frame and a table surface connected to the frame. The table surface includes at least two members, one of which is movably coupled with the frame to enable clamping of a workpiece between the two table surface members. A drive mechanism moves one of the table members with respect to the other table member. The drive mechanism comprises a first screw coupled with the movable member, a second screw coupled with the movable member and spaced apart from the first screw, a first screw sprocket coupled with the first screw, a second screw sprocket coupled with the second screw and an intermediate shaft carrying a first and second intermediate sprocket, wherein each intermediate sprocket has a larger diameter than the respective screw sprocket. The drive mechanism also comprises a first transmission belt or chain coupling the first screw sprocket to the first intermediate sprocket and a second transmission belt or chain coupling the second screw sprocket to the second intermediate sprocket, and the drive mechanism is arranged such that the movable member may be moved by turning the intermediate shaft. The drive mechanism reduces the time required to drive the screws. 
         [0008]    One or both screws may further include a screw handle. The intermediate shaft may be provided with a drive handle which is activatable to turn the intermediate shaft. The drive handle may be a crank-type handle. The work bench may be provided with a drive motor which is activatable to turn the intermediate shaft. The drive motor may be activatable by a switch, and the unit may be cordless (battery powered) or corded (mains powered). If both a drive handle and a drive motor are provided, the user may be able to choose which means to use each time the drive mechanism is actuated. 
         [0009]    The intermediate shaft may be approximately equidistant from the first and second screws, and may extend parallel to the first and second screws in or close to the plane defined by the axes of the first and second screws. The intermediate shaft and drive handle or drive motor switch may be located near the front centre of the work bench, allowing the drive handle to be operated conveniently and maximising the stability of the work bench during use. 
         [0010]    At least one clutch may be coupled with at least one screw to limit clamping pressures on the workpiece, and to limit stress and load on the transmission belt. The clutch or clutches may be arranged as in EP0921911, for example. The clutch enables rotation of one screw with respect to the other screw so that irregular workpieces may be clamped between the table members and clamping of the workpiece may be accomplished by rotation of the handle by one hand of the operator. Both first and second screws may include a separate clutch. 
         [0011]    One or more of the clutches may comprise a spring and a pin removably coupled within notches of the screw sprocket, and may be self-actuating. 
         [0012]    The frame may include a guard in order to protect at least a part of the first or second transmission belt or chain by preventing access from one or more directions. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0013]    The invention is herein described, by way of example only, with reference to the accompanying drawings, wherein: 
           [0014]      FIG. 1  is a perspective view of a work bench in accordance with the present invention. 
           [0015]      FIG. 2  is a cutaway partial view of the table surface and drive mechanism of the work bench of  FIG. 1 , in which the frame legs are truncated. 
           [0016]      FIG. 3  is a close-up view of the drive mechanism of  FIG. 2 . 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0017]    The preferred embodiment of the present invention is a work bench which is identified with the reference numeral  10 . The work bench includes a frame structure  12  which has two sides, the two sides connected to each other with one or more crossbars  18 . Each side of the frame  12  includes a front leg  14 , a rear leg  16  and a bracket  20 , the bracket providing support for the table surface. The table surface comprises two members  24  and  26 , one of which is movable with respect to the frame. As shown in  FIG. 1 , the brackets  18  may be spaced apart from each other, and are preferably positioned close to opposing outer side edges of the two table surface members  24  and  26 , so that the brackets do not unnecessarily prevent sections of clamped workpieces from being able to protrude down in-between the two table surface members. 
         [0018]    The brackets include means to enable the second table portion  26  to be fixed onto the brackets  20 , for example by a nut and bolt connection. The brackets  20  have a hollow portion and include elongated slots  21  in the surface adjacent to the movable table surface member  26 , which enables movement of the movable table surface member  26  with respect to the brackets  20 . A screw  30  is positioned within each bracket  20 . The screws include a threaded portion  32  which carries a threaded nut coupled with the movable table surface member  26 . In  FIG. 2 , part of the near-side bracket  20  is not shown, revealing the screw  30  and other features which would otherwise be hidden. The coupling between the threaded nut and the movable table surface member  26  extends through the slot  21 . Rotation of the screws  30  within the brackets  20  forces the threaded nuts to move along the screws, which causes the movable table surface member  26  to move laterally towards or away from the other table surface member  24 , depending on the direction of rotation of the screws. 
         [0019]    An intermediate shaft  35  is connected to the frame. In the embodiment shown in the Figures, the intermediate shaft  35  is located in between the two screws  30 , approximately equidistant from them. The intermediate shaft  35  carries two intermediate sprockets  36 , and the two screws each carry a smaller diameter screw sprocket  38 . One of the intermediate sprockets  36  is connected to one of the screw sprockets  38  by a first transmission belt  40 , and the other of the intermediate sprockets  36  is connected to the other of the screw sprockets  38  by a second transmission belt  41 . In the embodiment shown in the Figures, each sprocket has a plurality of projections which engage with apertures in the transmission belt  40 ,  41 . Any known alternative mechanism for transmitting rotational movement may be used, for example the transmission belts may be replaced by transmission chains which cause the sprockets to rotate, for example by engaging with recesses of the sprockets. The frame includes a guard  22  at the front, which partially supports the intermediate shaft  35  and which shields the sprockets and transmission belts in order to protect them, for example from being knocked by the user or tangled with other equipment. 
         [0020]    A drive handle  44 , which may be a crank-type handle as shown in the 
         [0021]    Figures, is attached to the intermediate shaft  35 . If a drive motor is provided to turn the intermediate shaft, this may be attached to the frame in any suitable sheltered location, preferably close or adjacent to the intermediate shaft, and a drive motor switch may be provided, for example on the front or top of the frame  12 . Turning the intermediate shaft  35  drives both transmission belts  40 ,  41 , such that the two screws  30  are caused to rotate simultaneously, and the movable table surface member  26  is moved. A workpiece can thereby be clamped between the two table surface members  24 ,  26 , or released. The user can turn intermediate shaft  35  with one hand, which allows the user to hold the workpiece in place with his other hand. Each screw  30  is connected to a handle  50  which can also be used to turn the screws. The handles  50  are suitable for fine-adjustments or final tightening of the vice formed by the two table surface members. The large size of the two intermediate sprockets allows the movable table surface member  26  to be moved a given distance with fewer rotations of a handle than would be possible using handles  50  alone. 
         [0022]    As shown in detail in  FIG. 3 , a clutch mechanism may be provided on the screw  30  to limit the pressure applied to the workpiece when the vice is being tightened. Screw  30  includes a smooth shank portion  31  on which sprocket  38  is positioned. The smooth shank portion  31  also carries a pin  32  and a helical spring  33 . Helical spring  33  urges the sprocket  38  towards the pin  32 , and notches  34  of the sprocket engage with the pin  32 . During normal operation, sprocket  38  is driven by intermediate shaft  35  in order to turn the screw  30 . At high clamping torques, the pin  32  disengages from the respective notch  34  and the sprocket is shifted, compressing the clutch spring  33 . When the high clamping pressure is released, the spring  33  forces the sprocket to reengage with the pin  32  to allow full operation of the screw  30 . 
         [0023]    Preferably both screws carry a similar clutch mechanism, which enables the user to clamp an irregularly shaped workpiece using one hand to turn the intermediate handle to quickly rotate both screws. Once one side of the movable table surface member clamps the workpiece tightly, the clutch on that side will disengage the screw sprocket from the screw on that side, so that continuing to turn the intermediate handle will only cause the other side of the movable table surface member to continue to tighten. Once the irregular workpiece is held by the vice, the handles  50  can be used to fine-tune the clamping forces on both sides of the movable table member. 
         [0024]    The transmission belts may be made of any suitable flexible material, for example plastic, rubber, metal chain or fabric. The table surface may be made of any suitable solid or laminated material, for example wood, bamboo, wood-like material or plastic. The frame structure is preferably made of metal, but could be made of any other suitably rigid material, for example, wood or reinforced plastic. The parts of the frame which contact the surface on which the work bench is supported, including the lower ends of the front and rear legs, may be provided with plastic or rubber feet in order to minimise slippage on the supporting surface on which the work bench is placed. 
         [0025]    It should be understood that although the invention has been described in conjunction with specific embodiments thereof, it is evident that many alternatives, modifications and variations will be apparent to those skilled in the art. Accordingly, it is intended to embrace all such alternatives, modifications and variations that fall within the scope of the claims.
A work bench including a frame and a table surface connected to the frame. The table surface includes first and second table surface members. The first table surface member is movably coupled with the frame and has first and second ends. The work bench also includes a first user-actuatable drive member for moving the first end of the first table surface member, a second user-actuatable drive member for moving the second end of the first table surface member and a third user-actuatable drive member for moving the first end and the second end of the first table surface member concurrently.