Patent Publication Number: US-7909563-B2

Title: Fork positioner

Description:
BACKGROUND OF THE INVENTION 
     This invention relates to a fork positioner for moving the load-lifting forks of a lift truck carriage selectively toward or away from each other so as to change their transverse separation. More particularly, the invention relates to a fork positioner which can be attached to an existing lift truck carriage, or incorporated as original equipment in a newly-manufactured carriage. 
     Fork positioners actuated by pairs of hydraulic cylinders, motor-driven screws, or the like have been used extensively on fork-supporting lift truck carriages. Most of these fork positioners are furnished as integral components of a carriage, often in combination with a side-shifting function which enables the carriage to be moved transversely so as to side-shift the forks in unison. Some detachably-mountable fork positioners have been provided in the past, such as those shown in U.S. Pat. Nos. 4,756,661, 4,902,190 and 6,672,823, to enable existing lift truck carriages without fork-positioning capability to be provided with such capability. However such detachably-mounted side-shifters have in the past increased the dimensions of the lift truck carriage, either horizontally as shown in U.S. Pat. No. 4,756,661 which reduces the load-carrying capacity of a counterbalanced lift truck by moving the load forward, or vertically as shown in U.S. Pat. Nos. 4,902,190 and 6,672,823 which impairs the lift truck operator&#39;s visibility over the top of the carriage. 
     BRIEF SUMMARY OF THE INVENTION 
     A need therefore exists for a highly-compact fork positioner which does not require such increased dimensions, does not significantly impair operator visibility, and is easy to mount on existing carriages or newly-manufactured carriages. 
     The foregoing and other objectives, features, and advantages of the invention will be more readily understood upon consideration of the following detailed description taken in conjunction with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL DRAWINGS 
         FIG. 1  is a perspective view of an exemplary embodiment of a fork positioner in accordance with the present invention, shown prior to mounting on a load-lifting carriage. 
         FIG. 2  is a front view of an exemplary load-lifting carriage mounting the fork positioner of  FIG. 1 . 
         FIG. 3  is a rear view of the carriage of  FIG. 2 . 
         FIG. 4  is a partially sectional side view of the carriage of  FIG. 2 , taken along line  44 . 
         FIG. 5  is an enlarged rear detail view of a center portion of the fork positioner of  FIG. 1  showing interior hydraulic conduits. 
         FIG. 6  is an enlarged rear detail view of a center portion of the fork positioner of  FIG. 1  showing other interior hydraulic conduits. 
         FIG. 7  is an enlarged rear detail view of a base portion of one of the piston and cylinder assemblies of the fork positioner of  FIG. 1 . 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
       FIGS. 2-4  show an exemplary embodiment of a load-lifting carriage  10  mountable for vertical movement on the mast of an industrial lift truck (not shown). The carriage  10  can be any of numerous different types, usually having an upper transverse fork-supporting member such as  14  and a lower transverse member such as  16  mounting two or more load-lifting forks such as  18  by means of fork hooks  20 ,  21  ( FIG. 4 ) slidably engaged for transverse movement by hook portions  14   a  and  16   a , respectively, of upper member  14  and lower member  16 . The hook portions  14   a  and  16   a  may be integral parts of the upper member  14  and lower member  16  respectively if the carriage  10  is of a simple standard type. Alternatively, the hook portions  14   a  and  16   a  may be transversely movable relative to the remainder of the upper member  14  and lower member  16  on slide bushings such as  22 ,  23  ( FIG. 4 ) under the control of a bidirectional side-shifting hydraulic piston and cylinder assembly  24  interacting between a side-shifting frame  25  containing the hook portions  14   a ,  16   a , and the remainder of the carriage  10 . Such a side-shifting frame  25  enables the forks  18  to be moved transversely in unison if desired. 
     As shown in  FIG. 2 , the upper hook portion  14   a  and lower hook portion  16   a  of the carriage  10  are joined by respective end members  26  of the frame  25  which side-shift transversely in unison with the hook portions  14   a ,  16   a  and the forks  18 . Alternatively, if the carriage  10  is not of the side-shifting type, such end members  26  can join the upper member  14  and lower member  16  of a standard carriage. 
     If the carriage  10  is of the side-shifting type, its side-shifting piston and cylinder assembly  24  is preferably located immediately beneath, rather than above, the upper member  14  to maximize the operator&#39;s visibility over the top of the carriage when the carriage is lowered, and to leave an open space between the side-shifting piston and cylinder assembly  24  and the lower member  16  for enhanced operator visibility through the center of the carriage. 
     It is often desirable that the carriage  10 , whether or not of the side-shifting type, be provided with a fork positioner for enabling the forks  18  to be selectively moved toward or away from each other so as to adjust the transverse spacing between them. To provide this function, a unique fork positioner indicated generally as  28  is disclosed in  FIG. 1 . The fork positioner  28  may either be conveniently mounted to an existing carriage  10  having no fork-positioning capability or, alternatively, included as part of a carriage  10  as originally manufactured. The fork positioner  28  includes a pair of elongate, bidirectional hydraulic piston and cylinder assemblies  30  and  32  having respective longitudinal axes  30   a ,  32   a  ( FIG. 1 ) and each having a respective cylinder  30   b ,  32   b  with a respective base portion  30   c ,  32   c  at one end and a respective rod end portion  30   d ,  32   d  at the other end from which a respective piston rod  30   e ,  32   e  is extensible along a respective axis  30   a ,  32   a . A cylinder connector  34  is adapted to threadably interconnect the rod end portion  30   d  of one cylinder rigidly to the rod end portion  32   d  of the other cylinder so that the axes  30   a  and  32   a  are parallel to each other. When the cylinders are interconnected in this manner, the piston rod  30   e ,  32   e  of each of the pair of piston and cylinder assemblies is extensible into longitudinally-overlapping relationship to the cylinder of the other piston and cylinder assembly as shown in  FIG. 1 . 
     A pair of fork-positioning guide members  36 ,  38  each connects to a respective piston rod  30   e ,  32   e  by means of a respective rod connector  36   a ,  38   a  ( FIG. 3 ) while also slidably and guidably engaging the respective cylinder  32   b ,  30   b  of the opposite piston and cylinder assembly by a respective slide bushing  36   b ,  38   b . This arrangement enables a recessed fork-engagement surface  36   c ,  38   c  ( FIG. 1 ) of each respective guide member to face away from the respective longitudinal axes  30   a ,  32   a  of the piston and cylinder assemblies in a forward direction substantially perpendicular to an imaginary plane  40  ( FIG. 4 ) containing both of the longitudinal axes  30   a  and  32   a . When the fork positioner  28  is mounted on the carriage  10 , the plane  40  also interconnects the upper transverse member  14  and lower transverse member  16  since the piston and cylinder assemblies  30  and  32  are inserted between the members  14  and  16 . 
     When the fork positioner  28  has been mounted to the carriage in an inserted position between the upper member  14  and the lower member  16  as shown in the figures, the piston and cylinder assemblies  30  and  32  can move the guide members  36  and  38  selectively toward and away from each other. Fork positioning force is applied by the guide members  36 ,  38  to the sides of the respective forks  18  in a substantially direct, nonbinding fashion so that the forks slide easily toward and away from each other along the upper transverse fork-supporting member  14 . To maximize this nonbinding force transmission, the fork-engaging surfaces  36   c ,  38   c  are preferably vertically coextensive with at least a major portion of the distance separating the respective longitudinal axes  30 ,  32   a  of the piston and cylinder assemblies. 
     In order to provide easy mounting of the fork positioner on the carriage  10  in its inserted position between the upper member  14  and lower member  16 , the piston and cylinder assemblies  30  and  32  are preferably mountable on the carriage  10  while interconnected with each other as a unit, for example by the cylinder connector  34  and/or the fork-positioning guide members  36 ,  38 . This unitized insertable fork positioner package requires no unitizing framework other than the piston and cylinder assemblies themselves and, if desired, also the fork-positioning guide members. The resultant rigid, essentially frameless fork positioner unit is thus so compact that it can be mounted in its inserted position centrally on the carriage  10  without significantly impairing the operator&#39;s visibility, or altering the dimensions of the carriage  10  in a way that would push the load forwardly and thereby reduce the load-carrying capacity of the lift truck. Moreover, mounting of the fork positioner on the carriage is greatly simplified by the unitized nature of the fork positioner, and by the fact that only the piston and cylinder assemblies  30 ,  32  must be supportably connected to the carriage  10  since the fork-positioning guide members  36 ,  38  are supportable by the piston and cylinder assemblies  30 ,  32  independently of any engagement by either guide member with a fork  18 . 
     One possible easy mounting arrangement for the piston and cylinder assemblies  30  and  32  is to connect the respective base portions  30   c ,  32   c  of the cylinders to respective end members  26  of the carriage  10  by screws  39  as shown in the drawings or by any other convenient means. If an existing carriage  10  has no such end members, they can easily be added to the carriage as part of the assembly process. Alternatively, the piston and cylinder assemblies  30   a ,  32   a  could be more centrally mounted to the carriage  10  by one or more brackets attached to the carriage upper member  14  or  14   a  in a manner which does not significantly impair operator visibility through the center of the carriage. 
     Preferably, the cylinder connector  34  includes one or more hydraulic fluid line connectors  42 ,  44 ,  46 ,  48  communicating with the interiors of the respective cylinders  30   b ,  32   b . For example, one such connector  44  ( FIG. 5 ) can introduce pressurized fluid simultaneously to the rod end portions  30   d ,  32   d  of the cylinders through internal spiral conduits  50  to retract the piston rods  30   e ,  32   e  simultaneously, while another connector  42  ( FIG. 6 ) communicating with interior conduits  54  and exterior conduits  52  can exhaust hydraulic fluid simultaneously from the base portions  30   c ,  32   c  of the cylinders. Respective conventional flow equalizer valves such as  56  ( FIG. 7 ) in each base portion  30   c ,  32   c  achieve uniform movement of the piston rods. An operator control valve (not shown) can reverse the flows of pressurized fluid and exhaust fluid through connectors  42  and  44  respectively to similarly extend the piston rods. 
     Although the preferred form of the fork positioner utilizes piston and cylinder assemblies wherein each cylinder  30   b ,  32   b  is connected to the carriage  10  so as to prevent the cylinder&#39;s longitudinal movement relative to the carriage, a reversed structure wherein piston rods are connected to the carriage so that their cylinders can move the fork-positioning guide members would also be within the scope of the invention. 
     The terms and expressions which have been employed in the foregoing specification are used therein as terms of description and not of limitation, and there is no intention, in the use of such terms and expressions, of excluding equivalents of the features shown and described or portions thereof, it being recognized that the scope of the invention is defined and limited only by the claims which follow.