Abstract:
Weigh sensed lift truck forks in which each standard fork is modified to accept an assembly including load sensing cells, spacers and a fork cover. Each cover provides protection for load cells affixed through spacers between the fork and fork cover, standard fork tip functionality and a load bearing surface and structure that interfaces through the spacers with the load cells and fork subassembly to provide accurate load weight data. The design of the components and method of their assembly result in improved manufacturing efficiency and cost effectiveness, easier installation, improved load weighing functionality, improved structural robustness, easier servicing and improved safety.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     Application Numbers 294,781; 591,470; 453,996; 783,760; Ser. No. 08/964,765; 492,739; 369,867. 
    
    
     STATEMENT REGARDING FEDERALLY SPONSERED RESEARCH OR DEVELOPMENT 
     Not Applicable 
     REFERENCE TO A MICROFICHE APPENDIX 
     Not Applicable 
     BACKGROUND OF THE INVENTION 
     The present invention relates in general to electrical/electronic weighing systems and more particularly to strain gauge load cells used on forklift trucks. 
     It is known that, in addition to typical lifting and transporting functions performed with forklift trucks and the like, weighing functions can also be carried out with this type of equipment when fitted with a weight measuring system. Various such systems have received patents and are being used. However, specific problems can and do arise with prior art systems with regard to carrying out lifting and weighing operations, manufacturing costs, installation and servicing. 
     Some systems require structural modifications or additional attachments to the lift truck, adding cost and resulting in more difficult and time consuming installation as evident in U.S. Pat&#39;s to Weigh-Tronix, U.S. Pat. Nos. 4,421,186 and 6,002,090. 
     Some systems are limited in ease of performing weighing functions in that they must be activated into the lift mode before weighing functions can be performed as evident in U.S. Pat. to Zefira, U.S. Pat. No. 5,739,478. 
     Some systems employ technically and physically elaborate approaches to address excessive vertical forces, lateral forces and binding in the weighing system that can cause inaccurate weight readings and damage to the load cells as evident in U.S. Pat&#39;s to Weigh-Tronix, U.S. Pat. Nos. 4,421,186 and 6,002,090. 
     Some systems use only a portion of the lifting surface for weighing, limiting load placement options, and employ partial shrouds or covers that do not extend over the entire fork and subassembly surface and will be prone to allowing foreign substances such as dirt and water that could cause false readings from the weigh system as evident in U.S. Pat. to Russo, U.S. Pat. No. 4,420,053. 
     Some systems employ mechanically elaborate designs, likely to be prone to mechanical malfunction and high manufacturing cost, to address weight measurement accuracy problems resulting from eccentric loads as evident in U.S. Pat. to Baldwin, U.S. Pat. No. 4,368,876. 
     Some system designs are not based on standard lift truck fork configurations and are thicker or higher in cross section or have component details that protrude above the general height of the fork lifting surface making it more difficult or impossible to slide the forks under a standard pallet as evident in U.S. Pat&#39;s to Boubille, U.S. Pat. No. 4,899,840 and S&#39;More, Inc., U.S. Pat. No. 5,861,580. Further, systems not based on standard lift truck forks tend to require more custom manufactured components and complexity, usually resulting in higher manufacturing costs and requiring more highly skilled or knowledgeable service personnel respectively. 
     Some systems require additional weigh system attachment components such as a secondary carriage that can create a potentially unbalanced and unsafe condition because the position of the forks is moved forward relative to the lift truck resulting in incorrect load centers specified by the lift truck manufacturer as evident in U.S. Pat&#39;s to Weigh-Tronix, U.S. Pat. Nos. 4,421,186 and 6,002,090. 
     Some systems do not allow weighing functions to be performed with the lifting surface in the fully lowered position making it difficult or impossible to safely check load weight relative to the maximum lifting capacity of the lift truck before attempting to lift the load as evident in U.S. Pat. to Zefira, U.S. Pat. No. 5,739,478. 
     BRIEF SUMMARY OF THE INVENTION 
     A weighing apparatus, in particular weigh sensed lift truck forks for which the design is generally based on a standard lift truck fork. These forks are each modified to accept an assembly of load sensing cells and their wiring, spacers, fasteners, reinforcing ribs and cover. Each cover provides load cell protection, standard fork tip functionality, a load bearing surface and a structure that interfaces through spacers with the load cells to provide load weight readings to an operator. Each fork cover is affixed through spacers to the load cells which are in turn affixed through spacers to each fork. The tip section from each standard fork is cut off, modified and welded flush to the front end of each fork cover, providing functionality for normal lift truck operations. 
     As various approaches in prior art address certain problems but not others, it is a prime objective of this invention to more fully address the range of problems that relate to the application of this type of equipment, within the scope of this invention. 
     A feature of this invention is the use of standard lift truck forks that minimize custom manufactured components and reduce manufacturing costs. 
     Another feature of this invention is that because standard forks are employed, modifications to the lift truck or additional attachment components are not required making installation easier. Further, the standard nature and simplicity of design allow servicing by regular technicians without highly specialized knowledge and the option of servicing onsite. 
     Another feature of this invention is that it provides protection to load cells against vertical and lateral overloading and accomplishes this through simple component spacing, fastener tensioning and with only a few basic components. 
     Another feature of this invention is that weighing functions can be performed with the forks in the fully lowered position and as a result, load weight can be safely checked relative to the maximum lifting capacity of the lift truck before attempting to lift the load thus avoiding potential injury to the operator and damage to the lift truck. 
     Another feature of this invention is that because additional attachment components such as a secondary carriage for mounting the forks are not required, the position of the forks is kept safely at the distance from the lift truck specified by the manufacturer, thus maintaining proper balance between the forks and the truck for lifting and weighing functions. 
     Another feature of this invention is that the low profile and uniform top surface of the forks allow easy access to standard pallets. 
     Another feature of this invention is that the load cells are electronically matched to give accurate weight data regardless of the positioning of a load on the forks. 
     Another feature of this invention is that the cover completely surrounding the top and sides of the fork and load cell subassembly, minimizing contamination by foreign substances and shielding the subassemblies from direct impact. 
    
    
     DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is an exploded view of the weigh sensed lift truck fork embodying this invention and showing all components in its design. 
     FIG. 2 a  is a top view of the fully assembled weigh sensed lift truck fork with cover attached. 
     FIG. 2 b  is a top view of the assembled weigh sensed lift truck fork without cover. 
     FIG. 3 is a sectional view of the weigh sensed lift truck fork showing the complete assembly. 
     FIG. 4 a  is an enlarged fragmentary view of a weigh sensed lift truck fork load cell subassembly at rest. 
     FIG. 4 b  is an enlarged fragmentary view of a weigh sensed lift truck fork load cell subassembly under load. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Illustrated in FIGS. 1-4 b  is a weigh sensed lift truck fork  10  embodying this invention in the exemplary configuration. FIG. 1 illustrates a weigh sensed lift truck fork  10  depicting all components and features of the invention assembly typically used in pairs. A load bearing cover  11  responsive to load weight, with welded reinforcing brackets  12  on the side walls of its rear heel, countersunk bolt holes  31  positioned along the center line of its length and a cover notch  26  at its front end is shown in FIGS. 1 and 2 a.  Cover tip  25 , fabricated from the removed and modified front tip of standard fork  14 , is welded into cover notch  26  flush with cover surface  27  as shown in FIGS. 1,  2   a  and  3 . Modification of the front tip removed from standard fork  14  for attachment at cover notch  26  to form cover tip  25  entails the removal of rear sections at each side of the front tip. This removal of the said sections leaves recessed faces along the rear vertical edges of cover tip  25  to match and fit the shape of cover notch  26  as shown in FIG.  1 . The remaining front end of fork  14  is further modified to interface with cover tip  25 . This is done by the removal of side sections leaving recessed faces  22  and  23  along the front vertical edges of fork  14  to which reinforcing ribs  24  are welded flush as shown in FIGS. 1,  2   b  and  3 . Reinforcing ribs  24  provide structural reinforcement to cover  11  and cover tip  25  where they extend past the remaining front end of fork  14  as shown in FIGS. 2 b  and  3 . The cover  11  is attached by countersunk flathead bolt fasteners  13  fitted through countersunk bolt holes  31  through spacers  19  positioned immediately underneath cover  11  and into the threaded hole in the flexing end of load cells  20 . The non-flexing end of load cells  20  is tightly attached by countersunk flathead bolt fasteners  18  fitted through spacers  21  positioned immediately below load cells  20  into threaded holes  32  positioned along the centerline of machined channel  29  centered in the top surface of fork  14 . To provide limited space for the downward bending action of the flexing end of load cells  20  when subjected to load weight, spacers  19  position the top surface of load cells  20  relative to the underside of cover  11  and spacers  21  position the bottom surface of load cells  20  relative to the bottom surface of channel  29 . 
     Invention assembly  10  can be mounted in the typical manner of lift truck forks in pairs onto a standard fork mounting carriage of a commercially available lift truck by means of upper bracket  15  and lower bracket  16  welded to the outside vertical back wall of fork  14 . This can be done without modification or additional components such as a secondary carriage facilitating ease of installation and servicing and proper positioning and balance between invention assembly  10  and a lift truck, thus improving safety during lifting, weighing and transport functions. Load cells  20  are electrically interconnected by wiring  17  that is routed through channel  29  to a commercial display in a lift truck through hole  30  in the upright portion of fork  14 . 
     Lifting and transport functions of this invention illustrated in FIGS. 1-4 b  can be performed in the same manner as with typical standard forks used on commercially available lift trucks while also maintaining load weighing functionality because the design of this invention is based on a standard lift truck fork. However, arrangements of forks with load weighing functionality using a full unmodified fork with a full cover completely enclosing the top and side surfaces of the fork right to its tip become vertically too high with overlapping components, especially at the tip, to allow easy access under a typical standard pallet or a load with limited access space. In such arrangements, the cover has to extend past the fork tip, vertically and horizontally tapering towards the front end to achieve the slender profile of the fork tip itself. As the cover construction would not have the body mass to provide the required structural integrity of the fork tip, standard fork functionality would not be achieved. The frontal section of such arrangements would either be too vertically thick for easy access under standard pallets and limited spaces or structurally too weak for adequate load support, especially when engaged in the common practice of maneuvering a load position with the cover tips. Therefore this invention integrates the modified front tip removed from standard fork  14  with cover  11  and utilizes reinforcing ribs  24  to address these problems while still maintaining load weighing capability of the invention. The recessed faces  22  and  23  along the front vertical edges of fork  14  provide the attachment positions for reinforcing ribs  24 . These ribs reinforce structural integrity at and past the remaining front end of the fork  14  and compensate for the removal of the fork&#39;s front tip to be utilized as cover tip  25 . Integration of a standard lift truck fork tip with cover  11  provides a standard fork tip profile and functionality to cover  11 . 
     The low profile of the load bearing surface of invention assembly  10  and the uniform cover surface  27  as illustrated in FIG. 3 enhances easy and unobstructed access of the load bearing surface under a typical standard pallet or load with limited access space. 
     Load weight readouts are sent to a commercial display mounted appropriately in a lift truck. When weight is place on cover  11 , cover  11  depresses, bending the flexing end of load cells  20  spaced above the bottom surface of channel  29  as shown in FIGS. 4 a  and  4   b  downward regardless of fork height to send a weight signal through wiring  17  to said display. The non-critical fork height position for weight measurement allows a load to be weighed with forks in the fully lowered position, facilitating safe load weight measurement relative to the weight lifting capacity of the lift truck before the forks are raised. Vertical overload protection of load cells  20  from excessive load weight is achieved because the flexing end of the load cells vertically positioned above channel  29  by spacers  21  will bottom out on the bottom surface of channel  29  before load weight exceeds their functional limit. When this happens, load cells  20  will not flex further and will move with fork  14  as a whole. Lateral overload protection of load cells  20  from excessive lateral forces is achieved firstly by not fully tightening countersunk flathead bolt fasteners  13  as shown in FIGS. 4 a  and  4   b.  Secondly, the said lateral overload protection is achieved by the spacing provided between any adjacent faces of cover  11 , countersunk flathead bolt fasteners  13 , spacers  19 , load cells  20 , fork  14 , cover tip  25  and reinforcing ribs  24  as shown in FIGS. 3,  4   a,  and  4   b.  This spacing allows lateral movement between cover  11  with integral cover tip  25  and load cells  20 , fork  14  and reinforcing ribs  24 . Further, each countersunk flathead bolt fastener  13  has an unthreaded shoulder as shown in FIGS. 4 a  and  4   b  that flexes within the space around it when invention assembly  10  is subjected to significant lateral force. Lateral overloading from the front of invention assembly  10  is prevented when the rear vertical surface of cover tip  25  bottoms out against the front vertical surface of fork  14  before the force applied to the front of cover tip  25  exceeds the functional limits of load cells  20 . Lateral overloading from the side of invention assembly  10  is prevented when the rear side vertical surface of cover tip  25  bottoms out against the inside vertical surfaces of reinforcing ribs  24  where they extend past the remaining front end of fork  14  before the force applied to either side of cover  11  exceeds the functional limit of load cells  20 . 
     Binding between said components of invention assembly  10  that could affect the accuracy of load weight signals sent to an attached load weight display is prevented by the said spacing between these components and by not fully tightening countersunk flathead bolt fasteners  13 . 
     Further loosening of the countersunk flathead bolt fasteners  13  is prevented by tension pins  28 . A tension pin is driven into a hole drilled into the head of each countersunk flathead bolt fastener  13  and then through an aligned hole in cover  11  to create a locking configuration as shown in FIGS. 4 a  and  4   b.  Full top and side coverage of fork  14  is provided by cover  11  that completely encloses the top and side surfaces of the fork. This enhances protection of load cells  20  from the impact of excessive forces, reduces contamination by foreign substances that could further cause binding between the invention assembly components and maximizes the functional load weighing surface of cover  11 . Further, the extensive coverage provided by cover  11  over fork  14  in conjunction with load cells  20  that are electronically matched to address variations in weight readings because of irregularly configured loads, make load positioning on cover surface  27  non-critical for accurate weight measurement.