Field of the Invention The invention relates to beam-type load cells, and more particularly to beam- type load cells that are used as either wheel, axial, or on-board load weighers for trucks or other vehicles.

Background of the Invention

Beam-type load cells have been used in platform weighers for weighing loads carried by trucks and other vehicles for many years. Beam-type load cells have also been used on trucks or other vehicles as part of an on-board weighing system. In on-board applications, beam-type load cells are generally connected between a load carrying platform, such as the bed of the truck, and the vehicle frame. In most prior on-board beam-type load cells, the ends of the beam are rigidly attached to the vehicle frame and the center of the beam is attached to the load platform. Applying an increasing weight to the load platform results in an increasing load or bending force being placed on the load cell.

Strain gauges are mounted on the load cell and are connected to electrical monitoring equipment used to measure the resulting beam deflection or strain. These strain measurements are then used to calculate the force and thus, load placed on the load platform. In prior platform weighers, opposing beam-type load cells are generally attached between the ends of a load platform and a support frame. As with on-board weighing systems, beam-type load cells in platform weighers are generally configured so that the ends of the beam are attached to the support frame and the center of the beam is attached to the load platform.

Most prior platform weighers are large, heavy and cumbersome. Although some current platform weighers are sold as being "portable," they generally require a great deal of effort to disassemble, transport and set up at a new location. Difficulty in transporting current platform scales have prevented them from being readily utilized by police and other individuals to weigh trucks or other vehicles at random times and locations. Police and other state and federal transportation authorities have long desired an accurate portable weighing system that may be easily transported in the rear of a police car or other vehicle. Such a portable weighing system would allow a single individual to transport, set up and weigh vehicles at any desired location and time. Such a system would have significant advantages over the current system of dedicated weight stations located at preselected locations.

In addition to disadvantages caused by size and weight, past and current beam-type load cells are not as accurate as desired. As transportation regulations become more stringent, it is becoming increasingly important to improve the accuracy of both platform type and on-board type weighing systems. Recently, a great deal of effort has been directed towards improving the accuracy of the load cells.

One of the causes of inaccuracies in beam-type load cells is the introduction of undesirable loads in the load cell caused by the restraint conditions on the load cell. For example, rigidly mounting the ends of some load cells can introduce undesirable axial, torsional, or bending forces within the load beam during use. Some recent load cells have improved overall accuracy by moving to a "floating" load cell configuration, such as that disclosed by U.S. Patent Nos. 4,281,781 titled Vehicle Platform Scale, and 4,581,948 titled Load Cell Assembly for Use in a Vehicle Platform Scale (the "Reichow Patent"). In a floating beam-type load cell, such as that disclosed in Reichow, the beam is mounted so that at least one end of the beam is free to float axially and rotationally during loading. This axial and rotational freedom of movement helps prevent an axial or torsional load from being introduced into the beam during loading. In the Reichow patent, the load beam is supported on both ends by tapered rollers mounted within cylindrical slots in the ends of the load beam. At least one of the rollers and thus one end of the beam is free to float or move axially during loading. The cylindrical rollers are rotatably mounted in the load beam and thus also allow the ends of the beam to rotate slightly during beam bending. This additional freedom of movement helps prevent undesirable bending loads introduced by the end conditions from affecting measurement accuracy. Finally, the tapered rollers used in the Reichow patent allow the beam to rotate around its longitudinal axis during loading. This rotational

freedom of movement helps prevent the mounting conditions from inducing undesirable torsional loads within the load beam during loading. The use of floating- type load cells has helped increase measurement accuracy of current load cells. However, there still exists a need for improved load cells. For example, in the Reichow patent, the structure used to mount the load platform to the load beam limits the deflection of the load beam when a load is added to the load platform. Thus, the mounting of the load platform to the load beam introduces mounting conditions that can produce inaccuracies in the measurements obtained. The floating configuration used in Reichow also does not directly attach the load beam to the support frame. Thus, unless other mounting structures are used, the load platform and load beam may become detached from the support frame, possibly causing a dangerous condition. In addition, the use of rocker pins, such as those disclosed in the Reichow patent, does not result in a consistent load point between the rocker pin and the load beam. During use, the rocker pin can move transversely with respect to the load beam, thus moving the load point. The load point's movement can result in inconsistencies between consecutive measurements, thus creating inaccuracies.

As can be seen from the discussion above, there exists a need in the industry for improved accuracy load beam-type load cells for use in both on-board and platform weighing applications. There also exists a need for a portable load weighing system for use in weighing vehicles, such as trucks, etc. The present invention is directed toward fulfilling those needs.

Summary of the Invention The present invention is a beam-type load cell wheel weigher or on-board load weigher. In one embodiment, the wheel weigher includes a frame and a load platform onto which one or more tires of a vehicle or other load may be placed. One or more double ended shear beam load cells are connected between the frame and the load platform. The central portion of the load cells are rigidly connected to the frame and the opposing ends of the load cells are connected to the load platform by two opposing pairs of attachment brackets. The attachment brackets attach the opposing ends to the load platform while preventing undesirable torsional, bending or axial loads from being introduced into the load cell.

In accordance with other features of the invention, the load cell is attached to the load platform through the use of cylindrical pins that are rotationally mounted in holes in the ends of the load cell. Each of the holes includes a beaded ridge that extends around the circumference of the hole. The cylindrical pins rest on the beaded

ridges and are free to rock back and forth on the ridges in order to prevent torsional loading of the load cell. At least one of the cylindrical pins is also free to move back and forth along the longitudinal axis of the load cell in order to prevent axial loading of the load cell. In accordance with still further aspects of the invention, the load beam includes one or more dog bone-shaped sections in which the central portion of the dog bone is thinner that the ends of the dog bone. The load beam also includes one or more I-beam cross-sections shear sections. Each shear section includes upper and lower caps joined by a centrally-located shear web. Strain gauges are mounted on the shear webs in order to measure shear strains produced in the shear webs when a load is placed on the load platform.

In another embodiment of the invention, the load cell is configured for use in an on-board load weighing system.

The wheel weigher of the present invention has a number of advantages over the prior art. The wheel weigher is lighter, smaller, and easier to transport than prior platform weighers. This allows the wheel weigher to be used by policemen, state or federal transportation employees, and others to obtain accurate weight measurements at remote locations. In addition, the configuration of the present invention also reduces inaccuracies caused by mounting constraints on the load cell. For example, the present invention prevents the mounting conditions from introducing undesirable torsional, bending, or axial loads within the load cell. Thus, the present invention prevents the mounting conditions from introducing inaccuracies in measurements made using a load cell according to the invention.

Brief Description of the Drawings The foregoing aspects and many of the attendant advantages of this invention will become more readily appreciated as the same becomes better understood by reference to the following detailed description, when taken in conjunction with the accompanying drawings, wherein:

FIGURE 1 is a perspective view of a load beam-type wheel weigher according to the present invention;

FIGURE 2 is a partially exploded view of the wheel weigher of FIGURE 1; FIGURE 3 is an enlarged, partially exploded view of one of the beam-type load cells in the wheel weigher of FIGURE 1;

FIGURE 4 is a side elevation view of one of the load brackets of the load cell of FIGURE 3;

FIGURE 5 is a side elevation view of another of the load brackets of the load cell FIGURE 3;

FIGURE 6 is a side elevation view of one side of the load cell FIGURE 3; FIGURE 7 is a top view of the load cell of FIGURE 3; FIGURE 8 is a side elevation view of the other side of the load cell of

FIGURE 3;

FIGURE 9 is a side elevation view of an on-board beam-type load cell according to the present invention;

FIGURE 10 is an end view of the load cell of FIGURE 9; FIGURE 11 is a side elevation view of the load cell of FIGURE 9;

FIGURE 12 is a top view of the load cell of FIGURE 9; FIGURE 13 is a cross section of the load cell of FIGURE 9 at the location illustrated in FIGURE 11;

FIGURE 14 is a cross section of the load cell of FIGURE 9 at the location illustrated in FIGURE 11; and

FIGURE 15 is a side elevation view of one of the load brackets.

Detailed Description of the Preferred Embodiment

FIGURE 1 illustrates a load beam-type wheel or axle weigher 10 according to the present invention. The wheel weigher 10 includes a load platform 12, support frame 14, electronics housing 16, control panel 18, display 20 and carrying handle 22.

During use, the wheel weigher 10 is turned on, off and programmed using the control panel 18. A truck, other vehicle, or other load is then driven or placed onto the load platform 12. The wheel (not shown) of a truck or other vehicle is positioned on the load platform 12 so that the load platform is positioned directly beneath the wheel, thus preventing contact between the wheel and the ground. After a vehicle or other weight is placed on the load platform 12, the total weight placed on the platform is displayed to the user on display 20.

A single wheel weigher 10 can be placed under a single wheel or set of wheels of a vehicle to obtain wheel weights. Alternatively, two wheel weighers 10 may be placed under opposing sets of wheels to obtain axial weights. In still other applications, a wheel weigher 10 can be placed under each wheel or sets of wheels to allow a vehicle gross weight to be determined.

Unlike prior platform-type load weighers, the wheel weigher 10 of the present invention is truly portable. The wheel weigher 10 is sized so that it may be easily picked up and transported by a single individual by grasping and lifting up on

handle 22. The wheel weigher 10 may then be placed in the trunk or other storage area of a car or other vehicle, and transported and used at any desired location.

The structure and operation of the wheel weigher 10 will now be described by reference to FIGURES 2-8. As best seen in FIGURE 2, the external structure of the wheel weigher 10 includes the load platform 12, support frame 14 and electronics housing 16. Internally, the wheel weigher 10 includes four load cells 24, four pairs each of load brackets 30 and 32, and a series of mounting bolts 26 and mounting pins 27. Each load cell 24 is a rectangular double ended shear beam type load cell that extends at least partially across the width of the support frame 14. The four load cells 24 extend parallel to each other and are spaced approximately equally over the length of the support frame 14. Each load cell is attached between the load platform 12 and the support frame 14 as described below.

The support frame 14 is formed of two elongate rails 36 (FIGURE 2) that are attached to the opposing sides of a bottom support sheet 38 and two elongate rails 40 that are attached to the opposing ends of the support sheet. The rails 36 have a rectangular cross section and extend over the length of the opposing sides of the support sheet 38. The rails 40 also have a rectangular cross section and extend over the length of the opposing ends of the support sheet 38. The ends of the rails 40 are joined to the ends of the rails 36. The rails 36 and 40 act as stiffeners to structurally reinforce the support sheet 38, thus helping to prevent unwanted bending or twisting during use.

In the preferred embodiment, the support sheet 38 includes a number of milled-out rectangular cavities 42 located along the periphery of its upper surface adjacent the rails 36. The cavities 42 are used to reduce the overall weight of the load weigher 10. The cavities 42 are sized and located to reduce weight without reducing structural integrity in a manner well known by those of ordinary skill in the art.

In the preferred embodiment, the support frame 14, load platform 12 and electronics housing 16 are formed of a cast or milled aluminum alloy. In alternate embodiments, the support frame 19, load platform 12 and electronics housing 16 can be formed of other suitable metals, plastics or other materials capable of withstanding the design loads and deflections.

The upper surface of the support sheet 38 directly beneath the load cells 24 is milled out or otherwise configured to form a mounting surface 43. The surface 43 contacts and supports a center portion 25 of the load cell 24 when the load cell is bolted to the support sheet 38. The upper surface of the support sheet 38 also includes two rectangular cavities 44 located at opposing ends of each mounting

surface 43, directly beneath opposing ends 28 (FIGURE 2) of each load cell 24. The cavities 44 are sized to allow for clearance between the opposing ends 28 of the load cell 24 and the upper surface of the support sheet 38. The cavities 44 are sized and recessed to a sufficient depth to prevent the opposing ends 28 from contacting the upper surface of the support sheet 38 when they deform downward when a load is placed on the load platform 12.

An opposing rectangular cavity 46 is located to either side of each cavity 44. Each cavity 46 is sized to allow clearance between the pairs of mounting brackets 30 and 32 that are used to attach the load cells 24 to the load platform 12. The cavities 46 are sized and recessed to a sufficient extent to prevent the brackets 30 and 32 from contacting the support sheet 38 when a load is placed upon the load platform 12.

As seen in FIGURE 2, in the preferred embodiment, the electronics housing 16 is formed as a separate unit and is bolted to one end of the support frame 14. The electronics housing 16 includes opposing rectangular mounting tabs 48 that are sized to attach to corresponding rectangular mounting tabs 50 on one end of the rails 36. The mounting tabs 48 are joined to the mounting tabs 50 through the use of fasteners, such as bolts 47. The bolts 47 extend through holes in the mounting tabs 48 and are received within threaded holes in the mounting tabs 50. The electronics housing 16 houses the electronics (not shown) used to operate the control panel 18, display 20 and to calculate loads placed on the load platform 12 as discussed in more detail below. The electronics housing 16 also includes a cavity (not shown) that houses batteries 52 used to power the electronics within the housing. The batteries 52 are inserted into the cavity and are maintained there by a threaded cap 53 that is received within the cavity.

The center portion 25 of each load cell 24 is attached to the support frame 14 at one of the mounting surfaces 43. Each load cell 24 is fastened to the support frame 14 using four bolts. The bolts 26 extend through holes 29 in the center portion 25 of each load cell 24 and are received within corresponding threaded holes 31 in the support surface 43. As best seen in FIGURES 3, 6 and 7, the upper portion of each of the holes 29 includes a countersunk recess 33 having a larger diameter than the rest of the hole. The depth and diameter of each recess 33 is sized to accommodate the head 35 (FIGURE 3) of the corresponding bolt 26 so that the top of the head of each bolt is approximately flush with the upper surface of the load cell 24.

As illustrated in FIGURES 3 and 6-8, the sides of the opposing ends 28 of each load cell 24 are milled or cast to form an I-beam cross-sectional configuration having upper and lower caps 56 and 54 respectively, and a centrally located shear web 58. In addition, the upper and lower surfaces of the center portion 25 of each load cell 24 are milled or cast to form a reduced thickness area or dog bone configuration as best seen in FIGURES 3, 6 and 8.

The opposing ends 28 of the load cells 24 are attached to the load platform 12 using two pairs of load brackets 30 and 32. Each of the load brackets 30 and 32 is attached to the lower surface of the load platform 12 through the use of two bolts 34. The bolts 34 extend through countersunk holes 54 in the upper surface of the load platform 12, and are received within threaded holes 60 (FIGURE 3) in the brackets 30 and 32. The load brackets 30 and 32 are in turn attached to the load cells 24 through the use of mounting pins 27.

Each mounting pin 27 is cylindrical and extends through a hole 62 (FIGURES 6-8) in one of the webs 58. The opposing ends of each pin 27 are received within holes or slots 72 or 74 in the brackets 30 or 32, respectively, as described in more detail below.

Each of the holes 62 has a centrally-located beaded ridge 64 (FIGURE 7) that extends around the circumference of the hole. As illustrated in phantom in FIGURE 7, the cylindrical mounting pin 27 rests on the beaded ridge 64, thus allowing the pin to rock within the hole 62 about the longevity of the axis of the load cell 24 as illustrated by arrow 66. The beaded ridge 64 also allows the cylindrical pin 27 to rotate freely within the hole 62 about an axis perpendicular to the longitudinal axis of the load cell. This freedom of movement prevents undesirable bending or torsional loads from being introduced into the load cell when a load is placed upon the load platform 12.

In order to prevent undesirable axial loading of the load cell 24, at least one end 28 is allowed to move axially during loading. In order to allow for axial movement, the ends of the pins 27 are received by holes 72 and slots 74 in brackets 30 and 32, respectively. As best illustrated in FIGURE 5, the holes in the brackets 30 are cylindrical and extend partially through the width of each bracket.

The pins 27 are received within the holes 72 to allow rotational movement of the pin with respect to the bracket 30, but to prevent up and down or side-to-side movement.

As seen in FIGURE 4, the slots 74 in the brackets 32 allow the corresponding pin 27 to move left and right within the brackets as illustrated by arrow 76. As the load cell 24 deforms during loading, the end 28 of the load cell secured within

brackets 32 may move axially. This axial freedom of movement prevents an undesirable axial loading of the load cell 24 when a load is placed on the load platform 12.

In the preferred embodiment, one side of the load cell 24 is milled to produce a recess 90 (FIGURES 7 and 8) extending over the length of the load cell. The recess 90 provides a protective area in which to mount the gauges 82 and 84. Once the gauges 80, 82 and 84 are mounted on the load cell, they are potted with a protective silicon or other resin system to prevent environmental conditions from damaging the gauges or electrical connections. In order to calculate the magnitude of a load placed on the load platform 12, a series of strain gauges 80, and temperature compensation gauges 82 and 84 (FIGURE 8) are mounted in a recess 90 milled into one side of the load cell 24. In the preferred embodiment, the gauges 80 are mounted on the webs 58 and are oriented at 45 degrees to measure the shear strain in the webs 58. The strain gauges 82 are mounted in the recess 90 perpendicular to the longitudinal axis of the load cell 24 and are used to compensate for errors due to temperature variations. The gauges 84 are mounted in the recess 90 along the longitudinal axis of the load cell and are used to compensate for spanwise temperature induced errors.

The use of strain gauges, such as gauges 80, 82, and 84 are commonly known in the industry and their placement and use can be readily determined by one of ordinary skill in the art. The gauges 80, 82 and 84 are connected via electrical cables 87 (FIGURE 2) to electrical monitoring equipment (not shown) located within the electronics housing 16. Appropriate monitoring equipment is widely known and used by those of ordinary skill in the art. As a load is placed on the load platform 12, the gauges 80, 82 and 84 are used to measure the strains produced within the load cell 24. These strains are then used to calculate the magnitude of load placed on the load platform 12 in a manner well known in the art. The resulting calculated load is displayed to the user on display 20.

The wheel weigher 10 has many advantages over prior platform weighers. The wheel weigher 10 is lighter, smaller, and easier to transport than prior platform weighers. Unlike prior platform weighers, the wheel weigher 10 may be transported and used by a policeman, state or federal transportation employee or others to accurately obtain truck or other vehicle weights. The wheel weigher 10 is light enough and small enough to be placed within the trunk of a car or other vehicle and transported to a desired location.

In order to obtain some of the advantages offered by the wheel weigher 10, it is important to maintain the weight and thickness of the wheel weigher as low as possible. In the present invention, several features are used to reduce overall weight and thickness. For example, in the preferred embodiment, each load cell 24 is a double-ended shear beam configured in a dog bone configuration. The dog bone configuration allows an accurate double-ended shear beam to be produced while minimizing overall thickness of the load beam. In addition, in the preferred embodiment, the heads 35 of the bolts 26 are recessed within the load cell 24, thus further reducing overall mounting height. The use of support surfaces 43 and cavities 44 and 46 formed into the support sheet 38 allows for clearance between the load cells 24 and support frame 14 without increasing overall thickness.

The wheel weigher 10 also incorporates several features which increase measurement accuracy. These features include the use of a double-ended shear beam load cell 24. The double ended shear beam load cells 24 are supported in the center and loaded on the ends 28. This configuration enables accurate shear measurements to be taken. The ends 28 of the load cell are also mounted to the load platform 12 in a configuration that prevents undesirable loads from being introduced into the load cell by the mounting conditions. For example, in the preferred embodiment, the combination of the beaded ridge 64 and cylindrical pin 27 prevent the introduction of undesirable bending or torsional loads into the load cell. The combination of the cylindrical pins 27 mounted in slots 74 allows axial movement, thus preventing the introduction of undesirable axial loads in the load cells 24.

A second embodiment of the invention intended for use in on-board weighing systems is illustrated in FIGURES 9-15. In the second embodiment, the load cell 100 is mounted between a support frame 102, such as the frame of a truck, and a load platform 104, such as the bed of a truck. The configuration and operation of the load cell 100 is similar to that described with respect to the load cells 24 of the first embodiment. Features of the second embodiment not described below function similar to the load cells 24 of the first embodiment and may be understood by reference to the discussion of the first embodiment.

As best seen in FIGURES 9 and 11, the load cell 100 is a beam that includes a rectangular central portion 106. The central portion 106 is bolted to the upper surface of the support frame 102 through the use of fasteners, such as two bolts 108. The bolts 108 extend through holes 110 in the central portion 106, through a support ledge 112 (FIGURES 9 and 10) on the support frame 102 and are maintained in position by a locking washer 113 and a nut 114.

Opposing rectangular ends 116 of the load cell 106 are attached between U-shaped brackets 118 and 120 that extend downward from the lower surface of the load platform 104. The ends 116 are attached to the brackets 118 and 120 through the use of cylindrical pins 122 (FIGURES 9 and 10) that extend through holes 130 in the ends 116 and through holes 124 or slots 126 in brackets 118 and 120 respectively, as described in more detail below.

In a manner similar to that described above with respect to the first embodiment, each of the holes 130 include a beaded ridge 132 (FIGURES 12 and 13). The beaded ridge 132 is centrally located within the hole 130 and extends around its circumference. As described in detail above with respect to the first embodiment, the pins 122 are free to rock on the beaded ridge 132 as illustrated by arrow 134 (FIGURE 12). The pins 122 are also free to rotate within the holes 130 on the ridges 132. The pin 122 extending through the slots 126 in the right brackets 120 (FIGURE 15) may also move left or right axially, as illustrated by arrow 140. This mounting configuration prevents undesirable axial, torsional or bending loads from being introduced into the load cell 100 during loading.

In a manner similar to that described with respect to the first embodiment, the load cell 100 is a double-ended shear beam-type load cell. In order to form the opposing shear beams, the portions of the load cell 100 located between the rectangular center portion 106 and the rectangular ends 116 are milled to form an I-beam or sheer section 150, as best seen in FIGURE 13. The top and bottom of each I-beam or shear section 150 is milled, cast or otherwise formed into a dog bone configuration as illustrated in FIGURES 9 and 11. The I-beam cross section is formed by milling rectangular recesses or cavities 152 into the sides of the shear sections 150. The cavities form the shear sections 150 into upper and lower caps 160 and 162 that are joined by a centrally located shear web 164 (FIGURE 14). In alternate embodiments, the cavities 152 could be cylindrical, oval or other shapes.

As described above with respect to the first embodiment, strain gauges (not shown) oriented at 45 degrees are mounted on the shear webs 164. The strain gauges are used to measure the shear strains produced in the webs 164 when a load is placed on the load platform 104. The measured shear strains are then used to calculate the magnitude of the load placed on the load platform 104. Additional temperature compensation gauges may be mounted on the sides of the load cell 110 to account for temperature-induced inaccuracies. The load cell 100 has a number of advantages over prior art load cells. For example, the use of cylindrical pins 122 combined with beaded ridges 132 allows the

ends 116 to rotate freely around the pins. The pins 122 may also rock on the beaded ridges 132. This configuration prevents the mounting conditions between the load platform 104, support frame 102 and load cell 106 from introducing undesirable torsional or bending loads within the load cell. As the load platform 104 and load cell 100 bend or otherwise deform, the right load bracket 120 (as illustrated in FIGURE 9) may also move left and right, within the slots 126, with respect to the load cell 100. This axial freedom of movement prevents undesirable axial loads from being introduced into the load cell. By eliminating the introduction of undesirable forces into the load cell, the present invention increases the accuracy of measurements taken using the load cell.

While the preferred embodiment of the invention has been illustrated and described, it will be appreciated that various changes can be made therein without departing from the spirit and scope of the invention.