Abstract:
A cement mixer truck and a weight measuring system is provided, comprising a mixing chamber, at least one rear roller bearing assembly, and a front mounting assembly. The rear roller bearing assembly includes a roller bearing and a first weight measurement device. The first measurement device can be configured to generate a first set of electrical signals corresponding to a load generated by the mixing chamber at the roller bearing. The front mounting assembly includes an engagement device and a second weight measurement device coupled to the engagement device. The second weight measurement device can be configured to generate a second set of electrical signals corresponding to a load generated by the mixing chamber at the engagement device. Means for electrically coupling the first and second weight measuring devices can calculate the weight of the chamber or the contents therein, or both.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention is directed toward a cement mixer truck, and more particularly toward a system and method for measuring the weight of the contents of a cement mixer truck. 
   2. Description of the Related Art 
     FIG. 1  is a schematic of a cement mixer truck  100  according to known art. The cement mixer truck  100  has a mixing chamber  110  (also referred to as a tub) that carries a load of cement or possibly other types of material with fluid-like qualities. Typically, a front mount  120  and a rear mount  130  rotatably support the mixing chamber  110  and its load. The front mount  120  may include rollers, gears, bearings and other structural units and/or drive mechanisms to support a portion of the weight of the mixing chamber  110  and load, and drive rotation of the mixing chamber  110 . Additionally, the rear mount  130  may include rollers, gears, bearings and other structural and/or rotatable devices to support a remainder of the weight of the mixing chamber  110  and load and facilitate rotation of the mixing chamber  110 . 
   The cement mixer truck  100  includes one weight measurement device (not shown). Typically, the front mount  120  includes the weight measurement device (i.e., scale). Although the weight measurement device can be calibrated to give a fairly accurate weight measurement when the mixing chamber  110  carries a predefined volume of material of a predefined density, the weight measurement becomes inaccurate as load material is either removed from or added to the mixing chamber  110 . In fact, if for example the weight measurement device is calibrated to give a fairly accurate weight measurement when the mixing chamber  110  carries a full load, the weight measurement becomes increasingly more inaccurate as more and more load material is removed from the mixing chamber  110 . In addition, if the mixing chamber  110  carries a load material of a density different from the predefined density used to calibrate the weight measurement device, the weight measurements generated by the weight measurement device will be inaccurate for at least one or more ranges of load volume of the mixing chamber  110 . The errors will depend upon the extent that the density of the load material differs from the predefined load material density used to calibrate the weight measurement device. 
   The weight measurement inaccuracies exist because the cement mixer truck  100  has only one weight measurement device (typically installed as a part of the front mount  120 ) for making a force measurement, although the mixing chamber  110  has two or more positions of support (i.e., front and rear mounts  120  and  130 ) over which the weight is distributed. A weight measurement system having only one weight measurement device to measure the weight of the mixing chamber  110  and load supported at two or more positions yields an accurate weight measurement only if a position for the center of mass of the mixing chamber  110  and load is known. However, although the center of mass of the mixing chamber  110  and load may be known for a predefined load, the center of mass shifts as load material is either removed from or added to the predefined load. Thus, since the center of mass is unknown, the weight measurement device of the known art cannot produce an accurate weight measurement. In order for the known art to produce an accurate weight measurement, the center of mass must be determined, which requires knowledge of the weight of the load, which is unknown. 
     FIG. 2  is a schematic of the mixing chamber  110  of  FIG. 1  being acted upon by external forces. As illustrated, forces F 1  and F 2  applied by the front mount  120  and the rear mount  130 , respectively, support the mixing chamber  110 . However, since only one weight measurement device (not shown) is installed as part of the front mount  120 , only F 1  will be measured. F 2  is not measured, and thus remains an unknown quantity. A reference coordinate system  202  is shown having an origin O. The front mount  120  is located at distance x 1  from the origin O, and the rear mount  130  is located a distance x 2  from the origin O. When the mixing chamber  110  contains a full load, the mixing chamber  110  and load is known to have a mass M, and the center of mass of the mixing chamber  110  and load is known to be located a distance x cm  from the origin O. A gravitational force M·g acts upon the mixing chamber  110  and load at the center of mass x cm . Since the mixing chamber  110  and load are static (i.e. at rest), the sum of all translational and rotational forces acting on the mixing chamber  110  and load must be zero. Equation (1) expresses that the net translational force acting on the mixing chamber  110  and load is zero, and equation (2) expresses that the net torque acting on the mixing chamber  110  and load with respect to the origin O is zero.
   F   1   +F   2   =M·g   (1)   F   1   ·x   1   +F   2   ·x   2   =M·g·x   cm   (2) 
   Now assume that a portion of the load has been removed, and an operator wishes to discover the remaining weight M·g of the mixing chamber  110  and load. As illustrated, F′ 1  and F′ 2  are the new forces applied to the mixing chamber  110  by the front mount  120  and rear mount  130 , respectively, and the center of mass has shifted to x′ cm  measured with respect to the origin O. One replaces F 1 , F 2 , M and x cm  of equations (1) and (2) with F′ 1 , F′ 2 , M′ and x′ cm , and simultaneously solves equations (1) and (2) for M′ (eliminating the unknown force F′ 2 ), obtaining
 
 M′=[F′   1   /g ]·[( x   2   −x   1 )/( x   2   −x′   cm )]  (3)
 
   Equation (3) generates an accurate value for M′ as long as the center of mass location x′ cm  is known. However, x′ cm  is not known. The method as practiced by the known art substitutes x cm  for x′ cm  in equation (3) to obtain an estimate for M′. Thus, the mass M′ computed by equation (3) will be larger than the true mass of the mixing chamber  110  and new load. (The mass M′ computed by equation (3) may also be smaller than the true mass, depending upon the value of x′ cm ). By using only one force measurement taken at one support position of the mixing chamber  110  (when the mixing chamber  110  is supported at two or more support positions), an inaccurate value for the mass, and hence weight, of the mixing chamber  110  and load is generated. 
   What is needed is a system and method for accurately determining the mass and weight of a cement mixer at all load volumes. 
   BRIEF SUMMARY OF THE INVENTION 
   According to one embodiment, the present invention provides a cement mixer truck, comprising a mixing chamber, at least one rear roller bearing assembly, and a front mounting assembly. The rear roller bearing assembly includes a roller bearing, configured to rotatably support the mixing chamber, and a first weight measurement device coupled to the roller bearing. The first weight measurement device can be configured to generate a first set of electrical signals corresponding to a load borne by the roller bearing and generated by the mixing chamber. The front mounting assembly includes an engagement device, rotatably coupled to the mixing chamber, and a second weight measurement device coupled to the engagement device. The second weight measurement device can be configured to generate a second set of electrical signals corresponding to a load borne by the engagement device and generated by the mixing chamber. 
   In accordance with another embodiment, the present invention provides a weight measuring system having a chamber, an engagement device, a first and a second weight measuring device, and means for electrically coupling the first and second weight measuring devices. The chamber can have a first end and a second end, and be operable to receive, store, and deposit a load. The engagement device is adapted to rotatably receive the first end of the chamber. The first weight measuring device can be adapted to removably couple to the engagement device and is operable to measure the weight of the first end of the chamber. The second weight measuring device can be adapted to rotatably receive the second end of the chamber and is operable to measure the weight of the second end of the chamber. The means for electrically coupling the first weight measuring device to the second weight measuring device is operable to calculate the weight of the load. 
   In yet another embodiment of the present invention, a method is provided for measuring a weight of a load in a chamber of a vehicle, comprising measuring a weight of a first end and a weight of a second end of the chamber. The method further includes determining a distance from a fixed reference point to a center of mass of the load, by means of the weight of the first end, the weight of the second end, and an axial distance from the first end and the second end, respectively, to the fixed reference point. The method also includes calculating a weight of the load from a cumulative weight of the first end and the second end, and the distance from the fixed reference point to the center of mass of the load. 

   
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
       FIG. 1  is a schematic of a cement mixer truck, according to known art; 
       FIG. 2  is a schematic of the mixing chamber of the cement mixer truck of  FIG. 1 ; 
       FIG. 3  is a schematic of a side view of a cement mixer truck, according to an embodiment of the invention; 
       FIG. 4  is an isometric view of a rear portion of the cement mixer truck of  FIG. 3 , according to an embodiment of the invention; 
       FIG. 5  is an isometric view of a roller bearing assembly of the rear portion of  FIG. 4 , according to an embodiment of the invention; 
       FIG. 6  is an isometric view of a load cell pin of the roller bearing assembly of  FIG. 5 , according to an embodiment of the invention; 
       FIG. 7A  is an end view of the roller bearing of  FIG. 5 ; 
       FIG. 7B  is a cross-sectional view of the load cell pin of  FIG. 6 ; 
       FIG. 8  is an isometric view of the front portion of the cement mixer truck of  FIG. 3 , according to an embodiment of the invention; 
       FIG. 9  is an isometric view of a load cell plate of the front portion of  FIG. 8 , according to an embodiment of the invention; and 
       FIG. 10  is a block diagram illustrating a load cell pin and a load cell plate, each electrically coupled to a decoder and a display device; 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   In the following description, certain specific details are set forth in order to provide a thorough understanding of various disclosed embodiments. However, one skilled in the relevant art will recognize that embodiments may be practiced without one or more of these specific details, or with other methods, components, materials, etc. In other instances, well-known structures and components associated with devices including, but not limited to, decoders and display devices have not been shown or described in detail to avoid unnecessarily obscuring descriptions of the embodiments. 
   Reference throughout this specification to “one embodiment” or “an embodiment” means that a particular feature, structure or characteristic described in connection with the embodiment is included in at least one embodiment. Thus, the appearances of the phrases “in one embodiment” or “in an embodiment” in various places throughout this specification are not necessarily all referring to the same embodiment. Furthermore, the particular features, structures, or characteristics may be combined in any suitable manner in one or more embodiments. 
   Reference throughout this specification to “weight measuring device”, “load cell”, “load cell pin”, “load cell plate”, or “scale” is not intended in a limiting sense, but is rather intended to refer to any device operable to measure a mass or a weight of an object or to measure a magnitude of an applied force. 
   Reference throughout this specification to “truck”, “cement mixer truck”, or “vehicle” is not intended in a limiting sense, but is rather intended to refer to any vehicle, mechanism, or support device or platform operable to carry a load or to support other structure or enclosure, which can carry a load. 
   Reference throughout this specification to “mixing chamber” or “chamber” is not intended in a limiting sense, but is rather intended to refer to any structure that is operable to receive, store, and/or deposit or dispense a load. 
     FIG. 3  is a schematic side view of a cement mixer truck  300  in accordance with an embodiment of the invention. The cement mixer truck  300  includes a frame  302  that is removably coupled to a cab  304 . The cement mixer truck  300  includes a platform  306  and a wheel assembly  308  mounted to the frame  302 . The wheel assembly  308  includes axles, bearings, wheels, tires, brakes, and all other supporting structures that are known by one of skill in the art. Additionally, the cement mixer truck  300  includes a forward portion  310  having a forward mounting assembly  312  and a rear portion  314  having a rear mounting assembly  316  for rotatably mounting a mixing chamber  318 . 
     FIG. 4  is an isometric view of the rear portion  314  of the cement mixer truck  300  of  FIG. 3 . As illustrated, the rear mounting assembly  316  includes two roller bearing assemblies  402  and a rear pedestal  404 . The roller bearing assemblies  402  are removably connected to the rear pedestal  404 . The rear pedestal  404  is rigidly mounted to the platform  306  ( FIG. 3 ) and/or the frame  302  ( FIG. 3 ). The roller bearing assemblies  402  support a portion of the weight of the mixing chamber  318  and mixing chamber load (not shown), and facilitate rotation of the mixing chamber  318 . 
     FIG. 5  is an isometric view of the roller bearing assembly  402  of  FIG. 4 , according to an embodiment of the present invention. The roller bearing assembly  402  includes a roller bearing  502 , a load cell pin  504  and a pin holder  506 . The pin holder  506  includes upper mounting brackets  508  having collars  509 , and a lower mounting plate  510 . As appreciated by one of skill in the art, the pin holder  506  may be cast as a unitary body, or alternatively, the upper mounting brackets  508  may be welded to the lower mounting plate  510 . The lower mounting plate  510  includes a set of openings (not shown) that align with a set of openings (not shown) in the rear pedestal  404  ( FIG. 4 ) for removably connecting the lower mounting plate  510  to the rear pedestal  404 . In one embodiment, mounting bolts  512  are positioned through the set of aligned openings in the lower mounting plate  510  and the rear pedestal  404 . The mounting bolts  512  receive mounting nuts  514  to removably secure the lower mounting plate  510  to the rear pedestal  404 . The scope of the invention covers other means known to one of skill in the art for connecting the pin holder  506  to the rear pedestal  404 , including other types of fasteners or weld joints, for example. 
   As illustrated, the load cell pin  504  is mounted through the collars  509  of the upper brackets  508  of the pin holder  506 . In one embodiment, the diameter of the collar  509 A is adjustable via a clamping assembly (not shown) to allow the collar diameter to be reduced once the load cell pin  504  is inserted through the collars  509 , thus fixedly, but removably securing the load cell pin  504  to the upper brackets  508  of the pin holder  506 . In the embodiment as illustrated, the load cell pin  504  includes a key slot  511  that aligns with a key (not shown) permanently connected to an inside edge (not shown) of the collar  509 B. An important aspect of an embodiment of the present invention illustrated herein is that the load cell pin  504  is removably mounted to the pin holder  506 , thus facilitating conversion of conventional roller bearing assemblies by replacing a conventional roller bearing pin of the known art with the load cell pin  504  of the present invention. Additionally, if a load cell pin is faulty, it may be easily removed and replaced by a new load cell pin  504 . 
   However, the scope of the present invention covers mounting the load cell pin  504  either removably or permanently to the upper brackets  508  by any means known to one of skill in the art. For example, in another embodiment of the present invention, the load cell pin  504  may be fixedly mounted to the collars  509  of the upper brackets  508  by weld joints. 
   As illustrated, the roller bearing  502  includes an aperture extending along a longitudinal axis of symmetry through which the load cell pin  504  is inserted. Roller bearing sleeves  516  are fixedly connected to walls of the aperture located proximate lateral sides  517  of the roller bearing  502 . The roller bearing sleeves  516  facilitate rotation of the roller bearing  502  about a central axis  518  of the load cell pin  504 . Each roller bearing  502  is in contact with the mixing chamber  318  ( FIG. 4 ) to facilitate rotation of the mixing chamber  318 . The location of the roller bearing sleeves  516  along the central axis  518  will be discussed further below in conjunction with  FIG. 6 . 
   Each load cell pin  504  supports a portion of the weight of the mixing chamber  318  and load. The portion of weight supported by each load cell pin  504  depends upon the mass of the mixing chamber  318 , the mass of the load contained in the mixing chamber  318 , and the location of the center of mass of the mixing chamber  318  and load. The load cell pins  504  include sets of strain gages (not shown) that produce analog electrical signals based upon shear forces applied to the strain gages. The shear forces are generated by the weight of the mixing chamber and load, which is transferred to the strain gages via the roller bearing  502  and roller bearing sleeves  516 . The strain gages are disclosed in U.S. Pat. No. 6,118,083, which is incorporated herein by reference. In one embodiment of the present invention, the load cell pin/strain gage assembly may be configured similar to the trunnion/strain gage assembly as disclosed in U.S. Pat. No. 6,118,083. 
     FIG. 6  is an isometric view of the load cell pin  504  of  FIG. 5 , according to an embodiment of the present invention. The load cell pin  504  includes a collar portion  602  and an axle portion  604 . In the embodiment as illustrated, the diameter of the collar portion  602  is larger than the diameter of the axle portion  604 . In one embodiment, when the load cell pin  504  is mounted to the pin holder  506  ( FIG. 5 ), the collar  509 A ( FIG. 5 ) encloses the collar portion  602 , fixedly securing the collar portion  602 . The axle portion  604  includes the central axis  518  and the key slot  511 . The key slot  511  engages a key (not shown) mounted to an inside surface of the collar  509 B ( FIG. 5 ). In the embodiment as illustrated, the axle portion  604  includes two apertures  606  that can extend completely through the load cell pin  504 , thereby allowing stress (caused by the weight of the mixing chamber  318  and its load) to be concentrated on inner aperture walls  706 , illustrated in  FIG. 7B . As illustrated further below in conjunction with  FIG. 7B , the inner aperture walls  706  are located proximate to the longitudinal axis of the load pin cell. 
   As discussed further below in conjunction with  FIG. 7B , and more fully in U.S. Pat. No. 6,118,083, at least one strain gage  701  is located on at least one wall  706  of at least one inner aperture  704 , preferably along major axes of stress. Referring back to  FIG. 5 , when the load cell pin  504 , roller bearing  502  and pin holder  506  are assembled, the bearing sleeves  516  are positioned circumferentially around the two apertures  606  ( FIG. 6 ) of the load cell pin  504 . The bearing sleeves  516  are positioned such as to allow the stress caused by the weight of the mixing chamber  318  ( FIG. 3 ) and load to be transferred to a region of the central axis  518  proximate to the apertures  606 , thus allowing the stress to be concentrated on the inner aperture walls and the strain gages  701 . 
     FIG. 7A  is an end view of the roller bearing assembly  402  of  FIG. 5 .  FIG. 7B  is a cross-sectional view of the roller bearing assembly of  FIG. 7A . As illustrated, the apertures  606  include an outer aperture portion  702  and an inner aperture portion  704 . The inner aperture portion  704  has a diameter that is smaller than a diameter of the outer aperture portion  702 , although the scope of the invention covers all combinations of inner and outer aperture portion diameters, including the aperture  606  having a constant diameter (i.e., diameters of the inner and outer aperture portions  704  and  702  being the same). As disclosed in U.S. Pat. No. 6,118,083, particularly  FIGS. 4–7 ,  12  and  14 , one or more strain gages  701  are mounted on aperture walls  706  of the inner aperture portion  704 . In one embodiment of the invention, two strain gages are mounted on the aperture walls  706  of each inner aperture portion  704 . 
     FIG. 8  is an isometric view of the front portion  310  of the cement mixer truck  300  of  FIG. 3 . As illustrated, the forward mounting assembly  312  includes a mixing chamber engagement device (i.e., a gear assembly)  802  and a front pedestal  804 . The engagement device  802  rotatably engages the mixing chamber  318 . The forward mounting assembly  312  further includes a load cell plate  806  removably fastened between the engagement device  802  and the pedestal  804 . 
     FIG. 9  is an isometric view of the load cell plate  806  included in the mounting assembly  312  ( FIG. 8 ). In the illustrated embodiment of  FIG. 9 , the load cell plate  806  includes a plurality of strain gages  808 , for example eight strain gages, with two strain gages positioned proximate to each corner of the load cell plate. In operation, a strain difference between each pair of strain gages  808  in all corners can be measured to calculate the load, which may be proportional to the strain difference. An electrical coupling device  810  can transmit this data to a receiver, controller, or decoder, or other data processing or display device. The load cell plate  806  may include a plurality of optional apertures  812  positioned proximate to the strain gages  808  to concentrate the strain toward the strain gages  808 . This feature may minimize errors that may arise due to the torsion loads on the load cell plate  806 . The illustrated load cell plate  806  is removably fastened to the engagement device  802  ( FIG. 8 ) using fastening means, for example, bolts and nuts. 
   It will be understood that various embodiments may or may not incorporate one or more of the aforementioned components, or may incorporate a load cell plate  806  of a different shape. For example, the load cell plate  806  may use other coupling means, such as welding, for coupling to the engagement device  802  and/or to the pedestal  804 . Additionally, or alternatively, the load cell plate  806  may preclude apertures  812 . The shape of the load cell plate  806  may also be different. For example, a load cell pin may be incorporated, similar to the load cell pin  504  ( FIG. 5 ) for the rear mounting assembly  316  ( FIG. 3 ). An individual of ordinary skill in the art, having reviewed this disclosure, will appreciate these and other variations that can be made to the front portion  310  without deviating from the spirit of the invention. 
   As disclosed in U.S. Pat. No. 6,118,083, the analog electrical signals generated by each set of strain gages in the load cell pins  504  are transmitted to a decoder  1002 , illustrated in  FIG. 10 . The decoder  1002  produces a digital weight signal and transmits the digital weight signal to a display unit  1004  located in the cab  304  ( FIG. 3 ). The display unit  1004  combines this digital weight signal with a digital weight signal received from the decoder  1002 , corresponding to a digital weight signal received from the load cell plate  806 , installed as part of the forward mounting assembly  312  ( FIG. 3 ). The display unit  1004  displays either the weight of the load contained in the mixing chamber  318 , the weight of the load and mixing chamber  318 , or the weight of the cement mixer truck  300  ( FIG. 3 ). In a further embodiment of the invention, the decoder is an LC100S decoder and the display unit is an LM100P onboard digital display meter as produced by CREATIVE MICROSYSTEMS of Renton, Wash. 
   The system and method for weight measurement according the present invention has been shown to improve the accuracy of calculating the weight of a vehicle, a chamber thereon, or a load within the chamber, or a total weight of all three or of any combination thereof, to within approximately 0.5% of the actual weight, whereas, existing methods can only reach an accuracy of within approximately 10% of the actual weight. 
   All of the above U.S. patents, U.S. patent application publications, U.S. patent applications, foreign patents, foreign patent applications and non-patent publications referred to in this specification and/or listed in the Application Data Sheet, are incorporated herein by reference, in their entirety. 
   From the foregoing it will be appreciated that, although specific embodiments of the invention have been described herein for purposes of illustration, various modifications may be made without deviating from the spirit and scope of the invention. Accordingly, the invention is not limited except as by the appended claims.