Abstract:
A fork positioner for a forklift truck has power-actuated yokes, each having a base from which a pair of transversely spaced legs depend, for engaging respective load lifting forks and adjusting their spacing transversely along a fork-supporting member. Each of the yokes is selectively movable between a fork-engaging position and a fork-disengaging position, the latter position permitting the fork to be lifted upwardly off of the fork-supporting member for easy replacement of the fork.

Description:
RELATED APPLICATIONS 
   This application is a continuation of U.S. patent application Ser. No. 09/952,256, filed Sep. 11, 2001, now U.S. Pat. No. 6,672,823. 

   BACKGROUND OF THE INVENTION 
   This invention relates to a fork positioner for adjusting the transverse spacing between load-lifting forks of a lift truck. More particularly, the invention is an improvement of a previous fork positioner disclosed in U.S. Pat. No. 4,902,190, which is hereby incorporated by reference. 
   It is a common occurrence for one or more of the load-lifting forks of a lift truck to require replacement for any of a number of reasons, such as damage to the fork or the need to change the type of fork. Normally, such replacement is relatively easy because standard forks with hook-type mounting hardware can simply be moved transversely along a fork-supporting member to a disengagement position and then lifted vertically off of the fork-supporting member to detach the fork therefrom. However the presence of a fork positioner usually hinders such easy detachment. For example, the downwardly depending U-shaped fork positioning yokes utilized in the aforementioned U.S. Pat. No. 4,902,190 prevent the fork from being lifted upwardly off of the fork-supporting member. Accordingly, each yoke must be disassembled and moved out of the way to enable the fork to be replaced. 
   BRIEF SUMMARY OF THE INVENTION 
   The present invention solves the foregoing problem by providing a fork positioner having multiple fork-engaging yokes, each having a base from which a pair of transversely-spaced legs depend to detachably engage a respective fork such that the base of the yoke is positioned above an upper portion of the respective fork, and the legs of the yoke depend downwardly along the transversely-opposite sides of the respective fork. A power actuator assembly selectively moves the yokes transversely, and thereby moves the forks along a transverse fork-supporting member to adjust their transverse spacing. Each of the yokes has a fork-engaging position preventing a respective fork from being lifted upwardly off of the fork-supporting member, and a fork-disengaging position permitting the fork to be lifted upwardly off of the fork-supporting member, each of the yokes being selectively movable between its fork-engaging position and its fork-disengaging position. 
   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 VIEWS OF THE DRAWINGS 
       FIG. 1  is a side view of an exemplary embodiment of a fork positioner in accordance with the present invention, shown mounted on a side-shifting carriage in relation to a forklift truck indicated in phantom. 
       FIG. 2  is a perspective view of the fork positioner of  FIG. 1 , shown mounted on the side-shifting carriage. 
       FIG. 3  is a front view of the fork positioner of  FIG. 1 , showing a pair of forks at minimum transverse spacing and the yokes in their fork engaging positions. 
       FIG. 4  is a cross section taken along line  4 — 4  of  FIG. 3 . 
       FIG. 5  is a front view of the fork positioner of  FIG. 1 , with the yoke of  FIG. 4  detached from its power actuator and moved away from the actuator preparatory to disengagement from the fork. 
       FIG. 6  is a cross-sectional view showing the detached yoke of  FIG. 5  in its fork disengaging position. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     FIG. 1  shows the forward end of a typical counterbalanced lift truck  10  having a front axle  11  and a mast  12  upon which is mounted a vertically-reciprocating standard load carriage  13 . Preferably, but not necessarily, a side-shifting carriage  14  is connected to the standard carriage  13  by upper and lower hooks  15   a  and  15   b  which slidably engage upper and lower fork-supporting members  13   a ,  13   b , respectively, of the standard carriage  13 . These hooks are slidable transversely relative to the carriage  13  by actuation of a double-acting side-shift hydraulic cylinder  17  interposed between a hook-type bracket  19  affixed to the carriage  13  and lugs  21  ( FIG. 2 ) on the side-shifting carriage  14 , utilizing a principle similar to that shown in U.S. Pat. No. 4,406,575 which is incorporated herein by reference. The side-shifting carriage  14  includes an elongate, transversely-extending upper fork-supporting member  16  having an upwardly-facing fork-supporting surface  18  adjacent to an upwardly-protruding lip  20 . The surface  18  and lip  20  matingly engage downwardly-opening hooks such as  22  on the upstanding portions  24  of a pair of standard load-lifting forks  26  having forwardly-protruding load-lifting portions  25 . The hooks  22 , which normally are connectable to the upper fork-supporting member  13   a  of the standard carriage  13  in the absence of the side-shifting carriage  14 , are slidable transversely along the fork-supporting surface  18  of the fork-supporting member  16 . The forks  26  are further connected to the carriage  14  by means of upwardly-opening hooks  28  at the bottom of the upstanding portions  24  of the forks which slidably engage a downwardly-protruding lip  30  of a bottom fork-supporting member  32  on the carriage  14 . 
   The fork positioner comprises a frame  34  which mounts to the side-shifting carriage  14  by means of side members  34   a  which abut the opposite transversely-facing ends of the carriage  14  and are fastened thereto by means of bolts (not shown) or, alternatively, by welding. As seen in  FIG. 1 , the frame  34  and its side members  34   a  overlap the upstanding portions  24  of the forks  26  in a rearward direction, but do not protrude forwardly beyond the forward extremities  24   a  of the upstanding portions  24  of the forks. 
   Alternatively, the side-shifting carriage  14  could be eliminated so that the hooks  22 ,  28  of the load-lifting forks  26  are instead slidably connected directly to the fork-supporting members  13   a  and  13   b  respectively of the standard load carriage  13 , with the side members  34   a  of the fork positioner being fastened to the opposite transversely-facing ends of the fork-supporting members  13   a  and  13   b.    
   The side members  34   a  of the frame  34 , as well as an intermediate frame member  34   b , support a pair of oppositely-facing double-acting hydraulic cylinders  40  and  42  whose piston rods  43  are detachably connected by threaded nuts  44  to respective yokes  50  and  52 . The hydraulic cylinders  40  and  42  are connected in parallel to a source of pressurized fluid through a conventional flow divider (not shown) causing the two cylinders to extend and retract substantially equally in unison in response to a conventional operator-controlled valve (not shown). Each yoke  50  and  52  has a respective base  50   a ,  52   a , each base containing a cylindrical bushing  50   b ,  52   b  which slides transversely and supportably along the exterior of one of the cylinders  40  and  42  in response to the extension and retraction of the cylinders  40  and  42 . Depending from each base  50   a ,  52   a  is a pair of downwardly-protruding legs  50   c ,  50   d  and  52   c ,  52   d , respectively. Each pair of legs extends downwardly alongside the respective opposite transverse sides of the upstanding portions  24  of a respective fork  26  in rearwardly-overlapping relationship thereto when the yokes are in fork-engaging positions as shown in all of the figures except  FIG. 6 . The base of each yoke, when in its fork-engaging position, extends over the top of each upstanding portion  24  of the forks in rearwardly-overlapping relationship thereto. Like the frame  34 , the yokes in their fork-engaging positions do not extend forwardly of the forward extremities  24   a  of the upstanding portions  24  of the forks. 
   At least one depending leg of each yoke, such as  50   c  and  52   c , has one or more adjusters, such as cap screws  54 , so that the legs of the yokes can be adjusted to closely fit the opposite transverse sides of forks having different widths. Also, the legs of the yokes preferably extend downwardly sufficiently to engage the sides of the forks at locations below the fork-supporting surface  18  of the fork-supporting member  16 . These features help to prevent the yokes from tilting the upstanding portions of the forks sideways, which would cause binding of the hooks  22  relative to the surface  18  and thereby impede sliding adjustment of the forks along the fork-supporting member  16 . 
   When it is desired to remove one of the forks  26  for replacement or repair, it is necessary to lift the fork upwardly off of the fork-supporting member  16  so that the respective hook  22  of the fork is lifted above the lip  20  of the member  16 . However the base  50   a  or  52   a  of each yoke prevents the fork from being lifted upwardly off of the fork-supporting member  16  when the yoke is in its fork-engaging position. Accordingly, to enable the fork to be lifted off of the fork-supporting member  16 , the yoke must first be moved to a fork-disengaging position. As shown with respect to yoke  52  in  FIG. 5 , this is accomplished by removing the respective threaded nut  44  on the piston rod  43  connected to the yoke  52 , and moving the yoke away from the piston rod (or retracting the piston rod from the yoke) so that they are no longer engaged with each other. If necessary, the cap screw adjusters  54  may also be loosened somewhat. Then the yoke  52  is pivoted about the cylinder  42  in a generally forwardly and upwardly direction to a fork-disengaging position as shown in  FIG. 6 . Thereafter the fork is moved manually along the fork-supporting member  16  into alignment with a conventional detachment slot  56  formed in the bottom fork-mounting member  32  on the carriage  14 , so that the hook  28  at the bottom of the fork can be disengaged from the downwardly-protruding lip  30  by pulling the bottom of the fork forwardly. Thereafter the fork can be lifted upwardly off of the fork-supporting member  16  and replaced or repaired. 
   Although a power actuator assembly consisting of fluid-power cylinders such as  40  and  42  is preferable, other types of power actuator assemblies may alternatively be used in the present invention, such as a screw-type assembly as shown in U.S. Pat. No. 4,902,190 which is incorporated herein by reference. Other alternatives include electrical, rather than fluid-power, actuators. 
   As alternatives to the above-described pivotal motion of the yokes between their fork-engaging and fork-disengaging positions, other motions are also within the scope of the invention. For example, the motion of the yokes between the two positions could be forwardly and/or upwardly along variously curved or straight paths, utilizing multiple pivots and/or sliding structures. 
   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.