Abstract:
A lift truck fork positioner for respective inner and outer pairs of load-handling forks includes power actuators for selectively extending and retracting the outer pair of forks and latch assemblies for selectively detachably connecting an inner fork fixedly to a respective adjacent outer fork in spaced relation thereto automatically in response to the extension of the outer forks beyond a predetermined inner range of extension. Each latch assembly, when connecting the inner fork to the outer fork, fixedly prevents any narrowing of the spacing between the interconnected inner and outer forks, as well as fixedly preventing any widening of such spacing.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to positioners for multiple pairs of load-handling forks mounted on a lift truck, such multiple pairs including at least an outer pair of forks and an inner pair located between the outer pair. Multiple-pair fork positioners enable a lift truck to selectively carry either a single palletized load or multiple palletized loads in side-by-side relation, depending upon the adjustable positions of the forks. 
     Some types of multiple-pair fork positioners have required a separate powered actuator for each fork in order to adjust the positions of the forks. However, such a multiplicity of actuators adds unnecessary weight and expense to the lift truck&#39;s load-handling assembly. In order to limit the number of powered actuators required, other multiple-pair fork positioners have provided powered actuators only for the outer pair of forks, while the inner pair of forks are selectively moved in unison with the outer pair of forks over a limited range of movement. For example, U.S. Pat. No. 4,533,290 and Austrian Patent No. 342500 disclose positioners which provide limited extension and retraction of the inner forks in unison with the extension and retraction of the outer forks. However, neither discloses a structure capable of fixedly maintaining a constant spacing between the adjacent inner and outer forks in the outer range of extension of the outer forks. Likewise, German published patent application No. DE 3702918, although disclosing stops on the outer fork slides which pull the inner forks outwardly with the outer forks to the full extension of the outer forks, provides only a tension spring to prevent any narrowing of the spacing between the adjacent inner and outer forks. Therefore, obstacles or frictional binding of the inner forks during retraction of the outer forks can cause inadvertent narrowing of such spacing merely by overcoming the spring force. 
     Any fork positioner which does not fixedly prevent both widening and narrowing of the spacing between the adjacent inner and outer forks, during extension or retraction of the outer forks in their outer range of extension, can cause severe load handling problems. For example, if the forks are supporting a palletized load, a widening of the spacing during extension, caused by an obstacle or frictional binding impeding the extension of the inner fork, may pull the pallet apart and cause the load to fall off of the forks. Conversely, a narrowing of the spacing during retraction may destabilize the support of the load by the forks, likewise causing the load to fall off of the forks. Alternatively, if the forks are unloaded during such extension or retraction, the positioning of adjacent inner and outer forks to engage a pallet may be rendered difficult or impossible if the fork spacing is varied by obstacles or frictional binding impeding the movement of the inner fork, since the spacing of the adjacent forks may then not match the spacing of the pallet fork pockets. 
     A multiple-pair fork positioner has been previously marketed by Cascade Corporation of Portland, OR which provides a hinged linkage between adjacent inner and outer forks. The hinged linkage, in response to extension of the outer forks, extends to a locked position which, upon locking, bidirectionally maintains a fixed spacing between the inner and outer forks during their subsequent extension and retraction within the outer range of extension of the outer forks. However, such linkage does not provide a detachable connection between the adjacent inner and outer forks and therefore has substantial length which is susceptible to bending or other damage by contact with loads or other obstacles. Moreover, the linkage does not permit any adjustment in the fixed spacing between the adjacent inner and outer forks to accommodate different spacings of pallet fork pockets or different sized loads. 
     SUMMARY OF THE INVENTION 
     The present invention overcomes the foregoing deficiencies of the prior art by providing a powerextensible outer pair of forks, together with an inner pair of forks having respective latch mechanisms which detachably fixedly connect each inner fork to a respective adjacent outer fork automatically in response to the extension of the outer forks from an inner range of extension into an outer range of extension. Conversely, when the outer forks are retracted inwardly within the inner range of extension, the latch mechanisms automatically detach the inner forks from the outer forks. When connecting the inner forks to the outer forks, the latch mechanisms fixedly prevent any narrowing of the spacing between each inner fork and the adjacent outer fork, as well as fixedly preventing any widening of such spacing. 
     Thus, within the outer range of extension of the outer forks, and regardless of whether the outer forks are being extended or retracted in such outer range, the spacing between each interconnected inner fork and outer fork is bidirectionally fixedly maintained at a constant spacing by the latch mechanism. Accordingly, no frictional binding or other obstacle tending to impede the movement of the inner fork during the extension or retraction of the outer fork within the outer range of extension can change the spacing between the interconnected inner fork and outer fork, either in a direction tending to narrow the spacing or widen it. This result is obtained without the need for any other interconnecting linkage between the outer and inner forks which could be susceptible to damage Rather, the detachable connection provided by the latch mechanism eliminates any need for such linkage while also providing adjustability of the fixed spacing. 
     The foregoing and other objectives, features, and advantages of the invention will be more readily understood upon consideration of the following detailed description of the invention, taken in conjunction with the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a side view of an exemplary embodiment of a multiple-pair fork positioner constructed in accordance with the present invention, shown mounted on a conventional lift truck. 
     FIG. 2 is a front view of the fork positioner of FIG. 1 with the outer forks shown at their positions of minimum extension. 
     FIG. 3 is a front view of the fork positioner of FIG. 1 with the outer forks shown at the point of transition between their inner range of extension and their outer range of extension. 
     FIG. 4 is a front view of the fork positioner of FIG. 1 with the outer forks shown at their positions of maximum extension. 
     FIG. 5 is an enlarged, partially sectional view of the lower latch mechanism of the fork positioner of FIGS. 1-4, shown in its detached condition. 
     FIG. 6 is a partially sectional view taken along line 6-6 of FIG. 5. 
     FIG. 7 is an enlarged, partially sectional view of the lower latch mechanism of the fork positioner of FIGS. 1-4, shown in its fixedly connected condition. 
     FIG. 8 is a partially sectional view taken along line 8-8 of FIG. 7. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     An exemplary embodiment of the fork positioner of the present invention, designated generally as 10, is shown in FIG. 1 mounted on a vertically-reciprocating load carriage 12 of a mast 14 which is mounted on an industrial forklift truck 16. The fork positioner 10 comprises a fork-supporting frame 18 which may simply be fixedly mounted to fork bars 12a, 12b of the load carriage 12. However, as shown in FIG. 1, the frame 18 is preferably slidably mounted to the fork bars 12a, 12b by upper and lower hooks 18a, 18b respectively, the upper hook 18a slidably engaging a slide bushing 19 to permit the frame 18 to slide transversely along the fork bars. Such slidability of the frame 18 relative to the load carriage 12 enables selective side-shifting of the forks in unison in response to the extension or retraction of a side-shifting hydraulic piston and cylinder assembly 20 interacting between the frame 18, via a lug 22, and the carriage 12 via a bracket 24 hooked fixedly over the top of the upper fork bar 12a in a well-known, conventional manner. 
     The fork-supporting frame 18 has multiple elongate slide guides 26, 28 and 30 extending transversely along its upper portion, and similar slide guides 32, 34 and 36 extending transversely along its lower portion. With reference also to FIGS. 2, 3 and 4, guides 26 and 32 slidably support channel-shaped slides 38 and 40 which are attached to the rear surface of inner fork 42, and also channel-shaped slides 44 and 46 which are attached to the rear surface of inner fork 48. Guides 28 and 36, on the other hand, slidably support elongate I-shaped slides 50 and 52 which are attached to the rear surface of outer fork 54. Finally, guides 30 and 34 slidably support elongate I-shaped slides 56 and 60 attached to the rear surface of outer fork 62. All of the sliding surfaces on the fork-supporting frame 18 are lined with slide bushings such as 21. 
     Each of the forks has an upright portion 42a, 48a, 54a and 62a, respectively, supported by the particular slides to which the fork is attached, and a forwardly-protruding load-supporting portion 42b, 48b, 54b and 62b, respectively, for insertion under a palletized load. Load backrest extensions 42d, 48d, 54d and 62d, respectively, protrude upwardly from the upstanding portions of the respective forks. 
     Outer fork 54 is selectively extended and retracted in response to the extension or retraction of a hydraulic piston and cylinder assembly 64 connected at one end to the frame 18 and at the other end to a bracket 54c protruding from the rear surface of the fork 54. Likewise, outer fork 62 is selectively extended and retracted by a hydraulic piston and cylinder assembly 66 connected between the frame 18 and a bracket 62c protruding from the rear surface of fork 62. The piston and cylinder assemblies 64 and 66 are connected to a conventional hydraulic valve assembly (not shown) which simultaneously extends and retracts them in response to manipulation of the valve by the lift truck operator. Extension of the piston and cylinder assemblies extends the outer forks 54 and 62 from their fully retracted positions shown in FIG. 2 first through a respective inner range of extension, designated as 70 and 72 in FIG. 3, and thereafter through an outer range of extension designated as 74 and 76 in FIG. 4. Alternatively, retraction of the piston and cylinder assemblies retracts the outer forks through the same ranges. 
     The outer forks 54 and 62 interact differently with their respective adjacent inner forks 42 and 48 depending upon whether the outer forks are in their inner range of extension or outer range of extension. These different interactions are determined by respective latch assemblies 78 and 80 which will be described hereafter in detail. In summary, the latch assemblies 78 and 80 operate automatically so that the inner forks 42 and 48 remain stationary during extension or retraction of the outer forks 54 and 62 within their inner range of extension 70, 72 as shown in FIG. 3. However, when the outer forks 54 and 62 are extended or retracted within their outer range of extension 74 and 76 as shown in FIG. 4, the latch assemblies 78 and 80 operate automatically to detachably fixedly connect the inner fork 42 to the outer fork 54, and the inner fork 48 to the outer fork 62, respectively, so that in the outer range of extension the adjacent inner and outer forks move in unison with each other with a predetermined fixed spacing between them. 
     With reference to FIG. 2, each latch assembly 78, 80 comprises a respective housing 78a 80a bolted to the side of a respective inner fork 42, 48, together with a respective spring-biased set of lock plates 78b, 80b within the housing for selectively detachably connecting to a respective slide 52, 56, a respective movable stop 78c, 80c mounted on the respective slide 52, 56, and a respective fixed stop 78d, 80d mounted on the frame 18. The operation of the lower latch assembly 78 will now be described in detail, it being understood that the upper latch assembly 80 operates in exactly the same way simultaneously in the opposite direction. With reference to FIG. 5, as the outer fork 54 is extended through its inner range of extension 70, the front portion of the slide 52 moves freely through a rectangular notch 82 (FIG. 6) formed in the locking plates 78b, thereby permitting the inner fork 42 to remain stationary pursuant to its own natural frictional resistance to movement. Such freedom of movement of the slide 52 relative to the notch 82 is made possible by the fact that the notch is somewhat wider than the front portion of the slide 52 and remains detached from the slide because the locking plates 78b, even though biased to an inclined position by a compression spring 84, remain in a relatively vertical attitude due to their abutment against stop 78d which is fixed to the frame 18. However, upon extension of the outer fork 54 from its inner range of extension into its outer range of extension, the stop 78c on the slide 52 abuts the housing 78a of the latch assembly, thereby pushing the housing and the locking plates 78b away from the fixed stop 78d. When this happens, the compression spring 84 tilts the locking plates 78b into a more inclined position as shown in FIG. 7, but not to the extent that the plates 78b touch the surface 78e of the housing 78a. (Prior to the abutment between stop 78c and the housing 78a, the spring 84 cannot push fork 42 away from stop 78d because the spring is not strong enough to overcome the frictional forces holding fork 42 in place.) The increased inclination of the locking plates 78b as shown in FIG. 7 causes the rectangular notch 82 of the plates to fixedly attach to the front portion of the slide 52 so as to rigidly resist any retraction of the slide 52 relative to the inner fork 42. After the locking plates 78b fixedly attach to the slide 52, outer fork 54 and inner fork 42 proceed outwardly in unison through the outer range of extension, the locking plates 78b fixedly preventing any narrowing of the spacing between the forks 54 and 42, and the abutment of the stop 78c with the housing 78a fixedly preventing any widening of the spacing. Accordingly, such spacing is maintained fixedly throughout extension or retraction of the outer fork 54 within its outer range of extension 74. 
     Upon retraction of the outer fork 54 from its outer range of extension 74 into its inner range of extension 70, locking plates 78b once more come into abutment with the fixed stop 78d thereby moving the plates from their inclined, locked position shown in FIG. 7 to the more vertical, detached position relative to the slide 52 as shown in FIG. 5. At this point the retraction of the inner fork 42 is halted by the stop 78d while the retraction of the outer fork 54 continues due to the detachment of the locking plates 78b from the slide 52. The outer fork 54 may then be brought to its fully-retracted position as shown in FIG. 2. 
     The fixed spacing between the interconnected inner and outer forks in the outer range of extension can be adjusted in any of several different ways. One way is to change the position of the stop 78c relative to the slide 52 by removing bolts 88 (FIG. 5) and repositioning the stop 78c in different bolt holes such as 90. This changes the spacing between the outer fork 54 and the inner fork 42 at the point where locking of the inner fork to the outer fork slide 52 occurs. Another way would be to place removable shims of variable thickness on the exterior of the housing 78a at the point where the stop 78c abuts the housing, thus likewise changing the spacing between the outer and inner forks at the point where locking occurs. Similarly, the position of full retraction of the forks can be adjusted by changing the position of the fixed stop 78d on the frame 18 by removing bolts 92 and repositioning the stop using different bolt holes such as 94. 
     Additional fixed stops 78f, 80f may be mounted on the frame 18 to prevent hyperextension of the forks by abutment with the respective housings 78a, 80a. Preferably, the piston and cylinder assemblies 64, 66 limit extension prior to abutment between the housings 78a, 80a secondary limits. 
     As will be apparent to those skilled in the art from the foregoing description, many alternative forms of detachable latch or clutch assemblies, other than that specifically shown in the preferred embodiment, would be suitable for the purpose. Also, although the inner forks 42 and 48 in the preferred embodiment are movably supported directly on the frame 18, it would be within the scope of the invention to movably support them indirectly on the frame, such as by slidably mounting them on the slides 50, 56 and selectively detachably latching them alternatively either to the frame or to their respective slides automatically in response to the movement of the outer forks. 
     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.