Abstract:
For minimizing the height of the load-measuring attachment for a lift-truck, the cover is made of thin sheet metal. The side-walls of the channel-section of the cover are folded into double thickness, to stabilize the side-walls of the cover.

Description:
[0001]    This invention relates to a loadcell system, of the kind used to indicate the weight of a load resting on the load-platform (herein termed the forks) of a pallet-truck (motorized or manual), fork-lift truck, and the like, herein collectively termed lift-trucks. The system is especially applicable in the case of an add-on loadcell weight-measurement system, i.e a system that can be added to the lift-truck as a post-purchase installation. 
         [0002]    Attention is directed to patent publication WO-2009/143613. This present specification is concerned with a development to the technology disclosed therein. 
         [0003]    FIGS. 6,7,8 of the said WO-2009/143613 are a plan view, a front view, and a side-view of a pallet walkie-truck. There, fork-covers have been placed over the forks of the lift-truck. The fork-covers carry loadcells, for measuring and indicating the weight of a load carried by the forks, the load resting directly on the fork-covers. The left and right fork-covers are joined at their back ends by a cross-bar. 
         [0004]    Except as indicated herein, the apparatus and the layout of the components are the same, in the examples described herein, as in the apparatus depicted in the said FIGS.  6 , 7 , 8 . 
         [0005]    One of the problems, when adding a capability to measure a load resting on the forks of an existing lift-truck, is the lack of available space above the forks. The lift-truck was designed to enable the forks to be entered into the fork-receiving fork-pockets of a standard pallet; the designers of the lift-truck were motivated to provide such clearance as would ensure the fork would enter the fork-pocket of a standard pallet, but they were not motivated to leave a large allowance to accommodate a cover that might later be placed over the fork. That is to say: so long as the fork could actually enter the pocket, the designers did not provide a large clearance between the upper surface of the fork and the top of the fork-pocket. The space available above the upper surface of the fork, within which the load-measuring cover must be accommodated, therefore, is, or might be, severely limited. 
         [0006]    Consequently, it might happen that, when a load-measuring cover is placed on top of the fork, and the combined cover-plus-fork enters the fork-pocket, the cover might actually touch the top of the fork-pocket of the pallet. The operators should therefore check the engagement of the combined cover-plus-forks in the fork-pocket. If there is a problem, certain adjustments can be made, for example to the height of the forks above the ground. The fact that some adjustments can be made does not, however, solve the problem of the lack of vertical space for the cover. The lower the height profile of the add-on fork-cover, the more likely it is that the cover-plus-fork combination can be made to engage smoothly into the fork-pocket. 
         [0007]    Designers of add-on load-measuring systems are beset by the problem of fitting the cover, and its associated load-cells, into the constricted vertical space. Typically, in traditional add-on load-measuring covers, having loadcells, a portion of the loadcell had to be let into the fork itself—which, usually, is disadvantageous and contra-indicated. 
         [0008]    It is an aim of the new technology as described herein to provide a load-measuring cover, which fits over the fork of a lift-truck, in which the height is minimized, at which the upper-surface of the cover resides above the upper-surface of the fork. As a general preference, the top surface of the fork-cover preferably should not be higher than the top surface of the fork by an added height of more than eight millimetres. More preferably, the added height should be no more than five or six mm. 
       SOME FEATURES OF THE INVENTION 
       [0009]    In the new technology as described herein, as with traditional covers, the cover is configured as an inverted channel, with a roof and side-walls, which is sized to fit over the fork of the lift-truck. But the new cover is made of very thin sheet metal. Typically, where the conventional cover is of five or six mm sheet metal, the new cover is of 3.5 mm sheet metal. Combined with very thin load-cells, e.g of the design as shown in WO-2009/143613, the cover with the loadcells attached can simply rest on top of the fork, and no provision need be made for letting the loadcells, or a portion of the loadcells, into the material of the fork itself. 
         [0010]    The cover being of thin sheet metal, it might be feared that, when a heavy load is placed on top of the cover, the roof of the cover might sag, and that the roof might sag so much that the undersurface of the roof of the cover comes into touching contact with the oversurface of the fork. 
         [0011]    It is important, of course, for accurate load-measurement, that all of the load must pass through the loadcells—if a portion of the load were to become supported by contact between the cover and the fork, that part of the load would not be measured by the loadcells. 
         [0012]    It is recognized that, despite the use of thin sheet metal in the cover, the cover can be made stiff enough not to sag, by increasing the thickness of the side-walls of the channel section. Preferably, this can be done by folding the thin sheet metal in such manner as to form a double thickness side-wall. 
     
    
     
       DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
         [0013]    The new technology will now be further described with reference to the accompanying drawings, in which: 
           [0014]      FIG. 1  is a cross-sectional end elevation of a fork of a lift-truck, upon which has been placed a fork-cover, the fork-cover having loadcells attached. 
           [0015]      FIG. 2  is a close-up of a detail of  FIG. 1 , showing a loadcell. 
           [0016]      FIG. 3  is the same view as  FIG. 2 , showing an alternative loadcell. 
           [0017]      FIG. 4  is a side-view of a manual lift-truck, having the forks shown in  FIG. 1 . 
           [0018]      FIG. 5  is a plan-view of the lift-truck, in which the roof of the fork-cover on the left fork has been removed. 
           [0019]      FIG. 6  is a close-up of part of  FIG. 5 . 
           [0020]      FIG. 7  is a pictorial view of one of the covers, without load-cells. ( FIG. 7  includes a ghost view of the cross-sectional profile of the fork-cover.) 
           [0021]      FIG. 8  is the same view as  FIG. 7 , except that loadcells have been added to the cover. 
           [0022]      FIG. 9  is an exploded view, showing the cover with a through-hole, a loadcell, and a protective plug. 
       
    
    
       [0023]    The scope of the patent protection sought herein is defined by the accompanying claims. The apparatuses and procedures shown in the accompanying drawings and described herein are examples. 
         [0024]    In  FIG. 1  the fork-cover  21  is made of sheet material that is considerably thinner than the material of traditional fork-covers. Typically, fork-cover material has been sheet steel of about 5 mm or 6 mm thickness. In  FIG. 1 , the fork-cover material is sheet steel of about 3.0 or 3.5 mm thickness. 
         [0025]    The loadcell  23  of FIGS.  1 , 2  is let into a through-hole  25  formed in the roof  24  of the fork-cover  21 . In FIGS.  6 , 7 , 8 , there are there are three loadcells per cover (as also shown in FIG. 6 of the said WO-2009/143,613), being two toe-end loadcells  23 T, and one heel-end loadcell  23 H. The preference is to use four load-cells per cover, as shown in  FIG. 5 . 
         [0026]    It would be possible to use just two load-cells per cover—one at the heel and one at the toe—if precautions are taken to prevent the cover from tipping. Tipping can be prevented by linking the left and right covers together, e.g optionally by means of a cross-bar  26 . 
         [0027]    The loadcell  23  includes a metal flexure-piece  27 , from a lower plate  29  of which protrudes a stem  30 , having a domed end  32 . A flange  34  surrounds the lower plate  29 . A chunky ring  36  extends upwards from the lower-plate, and an outer cylindrical surface  38  of the ring engages directly with the through-hole  25  in fork-cover  21 . 
         [0028]    The sidewalls  40  of the fork-cover  21  are doubled over, or folded, as shown, to improve the strength and stiffness, and resistance to sagging, of the fork-cover  21 . The doubled-over fold creates an outer-side  40 / 1  and a folded-under portion  40 / 2  of the side-wall  40 . 
         [0029]    Towards the rear of the cover  21 , the left and right folded sidewalls of the cover  21  are provided with respective cover-pivot-holes  42 . The holes  42  are made through the double thickness of the sheet metal of the sidewalls. Each cover has respective cover-pivot-holes  42  in the left and right side-walls  40 , the holes being co-axial. The cover-pivot-holes are located near the heel-ends of the covers. 
         [0030]    The fork-covers  21  and the associated loadcells  23  may be sold as a service-kit, and may be assembled over and to the existing forks  41  of a lift-truck  43 . First, the two covers, with the respective loadcells  23  factory-installed thereon, are placed over the forks  41 . Spacers  45  are provided ( FIG. 6 ), to ensure that the left and right fork-covers  21  lie squarely and symmetrically and centrally over the left and right forks  41 . 
         [0031]    The spacers  45  may take the form of e.g elastomeric buttons or pads, which are adhered at intervals to the inside faces of the folded sidewalls  40 , whereby the folded sidewalls of the covers are evenly spaced and located with respect to the respective forks. No spacers are provided between the oversurface of the fork  41  and the undersurface of the roof  24  of the cover  21 : the cover rests with the dome-ends  32  of the loadcells  21  resting on the oversurface of the fork  41 . 
         [0032]    The installer then makes sure that the front wall  47  of the fork-cover  21  is hard up against the toe-end  49  of the fork  41 . Now, the fork-cover  21  is residing in its desired operational position, and in particular, the cover-pivot-holes  42  in the sidewalls  40  of the cover  21  are in their correct location relative to the sides of the fork  41 . 
         [0033]    Now, using the cover-pivot-holes  42  in the sidewalls  40  as a template, the installer marks the location of the centres of the cover-pivot-holes on the respective sides of the forks. That is to say, the installer marks one centre each on the four sides of the two forks. 
         [0034]    The fork-covers  21  are removed, and the installer drills fork-pivot-holes into the material of the forks  41 . 
         [0035]    The covers  21  are then replaced, and threaded pivot-pins  52  are inserted into the cover-pivot-holes  42  in the sidewalls  40  of the covers  21 . The pins  52  extend inwards, and engage the fork-pivot-holes that have just been drilled in the sides of the forks  41 . The pins  52  are tightened with respect to the threaded cover-pivot-holes in the covers, but the inwardly projecting ends of the pins  52  are loose inside the fork-pivot-holes in the fork. 
         [0036]    It will be understood that four pivot-pins are provided, i.e two pivot-pins per fork, as shown in  FIG. 1 . When the left and right covers are joined by means of the cross-bar  26 , only one pivot-pin per fork need be provided. 
         [0037]    The function of the pivot-pins  52  is to retain the covers  21  on the forks  41 , during transport operations of the lift-truck  43 , but yet to enable the covers to float freely with respect to the forks at the moment when a load measurement is being taken. It should be noted that the pins  52  support and retain the covers against all forces tending to move the covers relative to the fork, apart from forces applied directly to the front of the fork. These latter forces are by far the largest forces involved, and are often the subject of abusive impacts. These impacts are supported by the engagement of the sturdy front wall  47  of the cover  21  with the solid toe-end  49  of the fork. 
         [0038]    The loadcell unit  56  of  FIG. 3  is inverted relative to that shown in  FIG. 2 .  FIG. 3  shows some further measures which can be taken by a designer seeking to reduce the headroom required by the installation, to a minimum. 
         [0039]    In  FIG. 2 , the strain-gauges  54  in the loadcell faced upwards, and therefore they had to be protected. That protection is provided by a metal disc or plug  58  inserted into the formed hole  25  in the roof  24  of the cover  21 . In  FIG. 3 , the strain-gauges  54  in the loadcell  56  are cemented to the underside of the flexure-piece of the loadcell  56 , and therefore face downwards, and no plug is required. 
         [0040]    Also, in  FIG. 3 , the connecting wires  60  from the strain-gauges are shown passing out from the loadcell  56  though a cut-out or relief  61  in the flange  34  of the loadcell  56 . Thus the thickness of the wires is accommodated within the thickness of the flange  34 , rather than being added to it, as was the case in  FIG. 2 . 
         [0041]    As shown in  FIG. 8 , the connecting wires  60  should traverse, from the loadcells, laterally out to the sides of the fork-cover, and from there, along the sides of the cover, to a bridge circuit which is located in the body of the lift-truck  43 . 
         [0042]    The wires  60  should not be located between the undersurface of the cover and the oversurface of the fork except in the immediate vicinity of the loadcells, as shown in  FIG. 8 . If the roof of the cover were to deflect by sagging, under a load, and if the wires were to be present underneath the sag of the roof, that would shorten the amount of sag that could be accommodated. If the roof were to sag to the extent that the wires became pinched between the roof and the fork, a portion of the load would then be supported on the wires—which would negate the accuracy of the load measurement, and also might damage the wires. 
         [0043]    Preferably, the folded side-walls are configured in such manner as to leave a recess  63  that extends lengthwise along the cover, and the wires from the load-cells are led out along this recess. Thus, the wires cannot be pinched between the cover and the fork, and also the wires are tucked away and well-protected generally. 
         [0044]    The thin sheet metal from which the cover  21  is formed should be less than four millimetres, and preferably, should be 3 mm or 3.5 mm. When the sidewalls of the cover are formed by bending and folding, as shown, the thickness of the sidewalls is double that of the roof. The preference is that the sidewalls should be six mm or more in thickness. 
         [0045]    It is important that the vertical height of the loadcell should be minimized—or rather, that the distance the loadcell protrudes below the undersurface of the cover should be minimized. The thickness of the flange can be as thin as 0.6 mm, but the preference is that the flange should be less than 1.5 mm. The domed-end  32  of the stem  30  of the loadcell preferably should protrude no more than three mm from the undersurface of the cover. 
         [0046]    It will be understood that, using the technology described herein, even though the cover and the loadcells simply rest on the fork without any need for cavities or holes to be cut in the forks, still the oversurface of the cover can be as little as 5 mm or 6 mm above the oversurface of the forks. At this, it can be expected that the forks, with the covers in place, will encounter little difficulty entering the fork-pockets of standard pallets. 
         [0047]    The numerals used in the accompanying drawings can be summarized as:
     21  fork-cover     23  loadcell     23 T loadcell at toe-end of fork     23 H loadcell at heel end     24  roof of cover     25  through-hole in roof     26  crossbar linking left and right covers     27  flexure-piece of loadcell     29  lower-plate of flexure-piece     30  stem of loadcell     32  domed end of stem     34  flange of loadcell     36  chunky ring of loadcell     38  outer cylindrical surface of ring     40  sidewall of fork cover     41  fork     42  cover-pivot-hole     43  lift-truck     45  positioning spacers     47  front wall of fork-cover     49  toe-end of fork  41       50  fork-pivot-hole     52  threaded pivot-pin     54  strain-gauge     56  loadcell of  FIG. 3       58  plug or disc     60  connecting wires from loadcell     61  relief or cut-out in flange     63  recess for wires, within sidewall