Abstract:
A scale for weighing a vehicle which includes a removable platform supported by a plurality of load cells, the removable platform having a plurality of centering fixtures with each centering fixture having a cavity in its bottom section with a perimeter. The scale further including a plurality of centering projections having an outer surface which the perimeter of the cavity of the plurality of centering fixtures is guided upon lowering the removable platform onto the plurality of load cells.

Description:
FIELD OF THE INVENTION 
     The present invention relates generally to truck scales. More particularly, the present invention relates to an improved truck scale having a platform that can be easily removed and repositioned without the need to be realigned or recalibrated. 
     BACKGROUND OF THE INVENTION 
     A basic truck scale configuration uses four load cells and a single platform, which is generally 25′ long×12′ wide. However, the platform size and number of load cells used can vary widely depending on the application. For example, two or more basic scales can be set end to end or side by side to build a longer or wider scale, a section of foundation could be built between the two scales, or a spacer platform could be hung between two scales. Furthermore, truck scales can be installed in a variety of different ways such as above ground, inside a deep pit, inside a shallow pit, or in some combination such as a three-sided pit. 
     Designing a scale for the weighing of heavy vehicles, such as cargo carrying trucks, presents a number of unique problems. For example, a conventional truck scale is normally an outdoor installation which is exposed not only to the elements, but also to chemicals, such as road salts, oil, transmission fluid, brake fluid, antifreeze, diesel, gasoline, and so on. Some scales are even subject to more extreme elements such as garbage, coal, and aggregate. For instance, scales used in garbage dumps are often subject to over filled trucks, which spill their contents onto the platform of the scale. The spilled garbage then finds its way into the pit below the platform along with other fluids leaked from the truck. This necessitates not only the scale being robust in order to withstand these elements, but also the removal of the platform for cleaning and/or servicing. 
     Another unique scale design problem is that once a scale is installed it must be calibrated in order to provide accurate readings. A calibrated scale must precisely maintain its configuration as established at the time of calibration in order to provide accurate and repeatable measurements. This calibration can be lost if even one of the load cells is shifted out of position by more than a minute amount. This generally means that a scale must be realigned and recalibrated each time the platform is removed, which is a time consuming and costly activity. 
     In order to avoid the need for realignment and recalibration, the platform must be placed precisely where it was at the time it was initially calibrated. 
     What is desired, therefore, is a truck scale with a removable platform that does not require to be realigned and recalibrated each time the platform is removed. 
     SUMMARY OF THE INVENTION 
     Accordingly, it is an object of the present invention to provide a truck scale with a removable platform that includes an alignment mechanism, which eliminates the need to realign and recalibrate the scale after returning the platform into position. 
     Another object of the present invention is to provide a truck scale having the above characteristics and which has a simplified design, so as not to be overly expensive to produce or prone to failure. 
     A further object of the present invention is to provide a truck scale having the above characteristics and that is simple to operate. 
     These and other objects of the invention are achieved by providing a removable platform, a plurality of centering fixtures on said removable platform, each said centering fixture having a bottom section with a cavity having a perimeter; a plurality of load cells to support said removable platform; a plurality of centering projections having an outer surface, said plurality of centering projections being removable; wherein the perimeter of the cavity of said plurality of centering fixtures is guided over the outer surface of said plurality of centering projections; and wherein upon lowering said removable platform onto said plurality of load cells, said centering projections are removed. 
     In some embodiments, the centering projections have a top section which is one of domed, conical, frusto conical, triangular, and rounded. 
     In some embodiments, the cavity of said plurality of centering fixtures has an opening which is one of chamfered, flared, angled, and rounded. 
     In some embodiments, the outer perimeter of at least one of said plurality of centering projections is larger than the outer perimeter of the rest of said plurality of centering projections. 
     Other objects of the present invention are achieved by providing a removable platform, a plurality of centering fixtures on said removable platform, each said centering fixture having a bottom section with a cavity having a perimeter, a plurality of load cells to support said removable platform, a plurality of centering projections having an outer surface, and wherein the perimeter of the cavity of said plurality of centering fixtures is guided over the outer surface of said plurality of centering projections upon lowering said removable platform onto said plurality of load cells. 
     In further embodiments, other objects of the present invention are achieved by providing a removable platform, said removable platform having a raised and a lowered position; a plurality of load cells to support said removable platform in the lowered position; a plurality of centering projections, said centering projections being removable when said removable platform is in the lowered position; a plurality of centering fixtures on said removable platform; and wherein upon moving said removable platform from the raised position to the lowered position, said plurality of centering projections are inserted into said plurality of centering fixtures, guiding the removable platform onto said plurality of load cells. 
     Other objects of the invention and its particular features and advantages will become more apparent from consideration of the following drawings and accompanying detailed description. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a partial cutaway isometric view of the scale in accordance with an exemplary embodiment of the present invention. 
         FIG. 2  is and exploded isometric view of the scale shown in  FIG. 1 . 
         FIG. 3  is an isometric view of the alignment mechanism in  FIG. 1 . 
         FIG. 4  is an isometric exploded view of the alignment mechanism in  FIG. 1 . 
         FIG. 5  is a cross-sectional view of the alignment mechanism in  FIG. 1 . 
         FIG. 6  is a side view of the alignment mechanism in  FIG. 1  with the platform removed. 
         FIG. 7 . is a side view of the alignment mechanism in  FIG. 1  with the platform being positioned. 
         FIG. 8  is a magnified view of the alignment mechanism in  FIG. 7 . 
         FIG. 9  is a side view of the alignment mechanism in  FIG. 1  with the platform in position. 
         FIG. 10  is a side view of the alignment mechanism in  FIG. 1  with the platform in position and the centering projection being removed. 
         FIG. 11  is a side view of another embodiment of the alignment mechanism. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIGS. 1 and 2  show a truck scale  10  with alignment mechanisms  20  according to the preferred embodiment of the present invention. The alignment mechanisms  20  are comprised of a plurality of centering projections  21  with corresponding centering fixtures  22 , which are used to precisely guide the platform  40  back to its original position at the time the scale  10  was calibrated. The platform  40  also has support brackets  41  resting on top of load cells  50  for supporting the platform  40  above a foundation  60 . In the preferred embodiment a centering projection  21  is placed next to each load cell  50 . 
     It is beneficial to have access to both the load cells  50  and alignment mechanisms  20 . Access can be through the top of the platform  40  via an access panel  42  or from the side of the platform  40  (not shown). If access is from the side, and the scale  10  is mounted in a pit, then access pockets must be made into the sides of the pit near where the load cells  50  are located (typically at the four corners). The alignment mechanisms  20  can either be attached under scale&#39;s platform  40  (internally) as shown or to the side of the platform  40  (externally), but should be accessible by some means such as those described above. 
     In the preferred embodiment, each load cell  50  and its corresponding centering projection  21  are fixed to a common base plate  70  on the foundation  50 . The advantage of having each load cell  50  and centering projection  21  paired with a common base plate  70  is it allows for easy installation since the fixed relationships are essential for the platform  40  to be precisely relocated. 
       FIGS. 3-5  show several views of the preferred embodiment of the alignment mechanism  20 . The alignment mechanism  20  includes a centering projection  21  with a frusto conical top  23 , and a centering fixture  22  with a circular hole therethrough. The frusto conical top  23  of the centering projection  21  forces alignment with the hole in the centering fixture  22  as the platform  40  is lowered. When fully aligned, the center of the circular hole in the centering fixture  22  is substantially coincident with the longitudinal axis of the centering projection  21 , such that the pair provides for precise relocation. The clearance between the centering projection  21  and the centering fixture  22  is determined by the level of precise placement required. Typically this clearance is 1/64 th  of an inch or less however, larger clearances can be used depending on the application and precision needed. 
     Another aspect of the alignment mechanism  20  is the angle of top  23  of the centering projection  21  and the angle of the tapered portion  33  hole  24  of the centering fixture  22 . In the preferred embodiment shown, both portions are angled at approximately 45 degrees to allow for easy alignment. However, it is possible to only angle either the centering projection  21  or the centering fixture  22 , as shown in  FIG. 11 . Furthermore, although both the centering projections  21  and centering fixtures  22  have been shown as having a round cross-section and the centering fixture  22  has only been shown to have a frusto conical shape, other shapes and cross sections can be used. For instance, the centering projections  21  need not be blunt but may also be pointed and any regular polygon with a suitably shaped projection  21  may be used, an example of which would be a square cross section with a pyramid projection. Also, it can be advantageous to have one or more centering projections  21  to be a different size or shape so as to prevent the platform  40  from being placed back in a different orientation. 
     Still another aspect of the preferred embodiment is that the centering projections  21  are removable once the platform  40  is positioned on the load cells  50 . The removal of the centering projections  21  prevents the centering fixtures  22  from interfering with the scales performance when the clearance between the centering projections  21  and the centering fixtures  22  is tight. The removable centering projection  21  contains a hole  25  in its bottom that slides down over a dowel pin  26 . In addition, as can be seen in  FIGS. 4 and 5 , the centering fixtures  22  are attached with bolts  27  to a bracket  28  fixed to the platform  40 . This configuration allows the centering fixtures  22  to be easily replaced if one is damaged. The bracket  28  that the centering fixture  22  is attached also contains a through hole  29 , which allows the removable centering projection  21  to be pulled off the dowel pin  26 . However, it is also possible to have the centering fixture  22  made in one piece with the bracket or the platform  40  itself. 
     Each centering projection  21  also has a horizontal bore  30  that serves as a finger grip for use when removing the centering projection  21 . The bore  30  also vents air so that the centering projection  21  can slide down over the dowel pin  26  easily. One could also thread a strong wire through the bore  30  for more leverage if the centering projection  21  were to get jammed on the dowel pin  26 . Further embodiments of the centering projection  21  can utilize other ways to help grip the centering projection  21  such as indentations or a channel along the perimeter of the centering projection  21 . 
     Since space is usually limited around the load cell  50 , the dowel pin  26  can also be removable in order to facilitate installation and maintenance. One way to make the dowel pin  26  removable is shown in  FIG. 5 . As can be seen, the dowel pin  26  is sitting in a base block  31  that is fixed to the base plate  70 . The hole  34  in the base block  31  is such that the dowel fits securely in the base block  31 . To further clear space, it is also possible to make the base block  31  holding the dowel detachable from the base plate  70 . This can be helpful if the load cell  50  needed servicing when the platform  40  is in place or removed. If the base block  31  were removed when the platform  40  was in place, the base block  31  would need to be slid underneath the centering fixture  22  and the dowel pin  26  dropped into place through the hole in the centering fixture  22 . The clearance between the hole in the removable centering projection  21  and dowel pin  26  is a slip fit. Ideally the slip fit is tight enough to maintain the precision of the location, but also loose enough to allow for the centering projection  21  to be easily removed. 
     The base block  31  shown in  FIG. 5  consists of a square base with a round boss  32  on top. This shape provides a step which helps prevent debris from building up where the centering fixture  22  rests during operation of the scale  10 . Such buildup could negatively affect performance of the scale  10  or prevent the centering projection  21  from sitting properly. Although the base block  31  has been shown with a square base and a round boss  32  other shapes are also suitable. Furthermore, the base block  31  and the round boss  32  can either be separate pieces connected together or be formed in one piece. 
     The removable centering projection  21 , dowel pin  26  and centering fixture  22  are ideally made of hard, corrosion resistant material such as 17-4PH stainless steel. Such a material is good at preventing wear and rust, which would negatively affect the alignment capability; therefore a grade of hardened stainless steel or other durable and corrosion resistant material are ideal in order to ensure long life and good performance. 
       FIGS. 6-10  show an alignment mechanism  20  near one of the load cells  50  in various states of operation while the platform  40  is being lowered into place. In the preferred embodiment each load cell  50  has its own corresponding centering projection  21 .  FIGS. 6-10  are representative of what happens at each load cell  50  located in the corners of the scale  10  shown in  FIG. 1 . 
       FIG. 6  shows the platform  40  in a raised position ready to be lowered back into place with the removable centering projection  21  in position. It should be noted that while lowering the platform  40  into place care should be taken to ensure that the platform  40  is maintained reasonably level and that the centering projection  21  can be seen through the centering fixture  22 . The centering projection  21  does not need to be perfectly centered in the hole, just visible, since the frusto conical top  23  of the centering projection  21  will guide the platform  40  into position. 
       FIG. 7  shows the centering fixture  22  in contact with the centering projection&#39;s  21  frusto conical top  23 . In this position, as the platform  40  is lowered the centering fixture  22  is slid down over the centering fixture  22  aligning the platform  40  into position on top of the load cell  50 .  FIG. 8  shows a close-up view of the alignment taking place. 
       FIG. 9  shows the platform  40  firmly in place on top of the load cell  50  and the centering projection  21  still in place.  FIG. 10  shows the centering projection  21  being removed, returning the scale  10  to service. 
     It should be noted that although the preferred embodiment has been shown with four alignment mechanisms  20 , it is theoretically possible to achieve alignment with as few as two such mechanisms  20  positioned on a common diagonal. However, it is preferred to have at least one alignment mechanism  20  for each load cell  50 . Furthermore, the removal of the centering projection  21  is only necessary when the clearance between it and the centering fixture  22  is tight for precision alignment. If a precise alignment of the platform  40  is not necessary and the clearance allows, the scale  10  could be operated with fixed centering projections  21 . 
     Although the invention has been described with reference to a particular arrangement of parts, features and the like, these are not intended to exhaust all possible arrangements or features, and indeed many other modifications and variations will be ascertainable to those of skill in the art.