Patent Description:
Some sensors are configured to measure external forces exerted on housings of the sensors that hold and protect the sensing element(s) from the external forces. For example, weigh-in-motion sensors of the type disclosed in <CIT>, <CIT>, <CIT> and <CIT> are typically installed in a roadway and extend at least partially across a width of the roadway to measure the dynamic ground forces of vehicles (e.g., automobiles and trucks) traveling along the roadway as the vehicles move over the sensors. The measurement data from the weigh-in-motion sensors is typically used to calculate axle weights of the vehicles, and such information can be used to determine if any vehicles are non- compliant with set regulations (e.g., overweight), for future infrastructure planning, and the like.

The weigh-in-motion sensors typically include an elongated housing that has top and bottom plates and a cylindrical tube disposed between the top and bottom plates. The weigh-in-motion sensors also have narrow transitions or necks that join the cylindrical tube to the top and bottom plates. A sensing element is held within the cylindrical tube in pre-load between upper and lower interior surfaces of the tube. Known weigh-in-motion sensors are vertically symmetric, such that the sensing element is located at a vertical midpoint of the housing between the top and bottom plates.

There is a trade-off in weigh-in-motion sensors between sensitivity (e.g., accuracy and precision of measuring the forces) and structural integrity of the sensor housing. For example, sensitivity may be increased by directing more of the external load to the sensing clement, but known sensors housings that direct sufficient load to the sensing element for increased sensitivity suffer from high combined stresses, which may reduce the operational lifetimes of the sensor housings. Known sensor housings experience high stresses at the narrow transition or neck region between the lop plate and the cylindrical tube. The structural integrity of the housing may be improved (and the operational lifetime increased) by increasing the stiffness in the housing, which directs a greater percentage of the external load through structural support paths in the housing instead of through the sensing element. But, reducing the load that is directed to the sensing element may undesirably reduce the measurement sensitivity.

The problem to be solved is to develop a load transfer mechanism that has sufficient structural integrity to reliably withstand external loads for a desired operational lifetime while providing desired measurement sensitivity.

According to the invention there is provided a load transfer mechanism as defined in the appended claim <NUM>. The load transfer mechanism comprises a beam elongated along a depth axis of the load transfer mechanism, the beam comprising a plate with a load-bearing surface, a tube portion including a base wall and a cover and defining a cavity between the base wall and the cover, the base wall laterally extending from a first edge to a second edge that is opposite the first edge, wherein the cover is joined to the base wall at or proximate to the first and second edges and a neck extending between and joining the plate to the cover of the tube portion; a neutral axis where the stress is zero; and a sensing package disposed within the cavity of the beam and under pre-load characterized that the sensing package engages an interior surface of the cover and an interior surface of the base wall thereby to exert a force on both the cover and the base wall, and the sensing package is configured to measure forces exerted on the load-bearing surface of the plate.

Embodiments of the present disclosure provide a load transfer mechanism that includes a sensing package and a beam that structurally protects and supports the sensing package. The sensing package is configured to measure forces exerted on the beam. As used herein, the term "sensing package" refers to one or more electrical elements that generate an electrical output signal responsive to a mechanical force application on the sensing package. The sensing package may include at least one piezo-electric element. One technical effect of the embodiments of the load transfer mechanism is the ability to absorb external forces with reduced internal stress within the beam relative to known sensor housings. Another technical effect of the embodiments described herein is that, in conjunction with the reduced internal stress in the beam, the beam is able to direct a greater percentage of the external load through the sensing assembly than known sensor housings, providing a greater measurement sensitivity. As a result, the sensing assembly according to the embodiments described herein may be able to provide increased measurement sensitivity and improved structural integrity of the beam relative to known sensors.

Although one or more embodiments of the load transfer mechanism are described herein for use in a weigh-in-motion application to measure forces exerted by moving vehicles on a roadway, it is recognized that the load transfer mechanism is not limited to weigh-in-motion applications. For example, the load transfer mechanism may be used in other applications to measure external forces exerted on the beam, such as industrial applications, lab testing applications, and the like.

<FIG> is a perspective view of a measurement system <NUM> that includes multiple sensor assemblies <NUM> in accordance with an embodiment. Each of the sensor assemblies <NUM> includes a respective beam <NUM> and at least one sensing package <NUM>. The sensing packages <NUM> are held within the respective beams <NUM>. The two sensor assemblies <NUM> in the illustrated embodiment are disposed side-by-side, but may be spaced apart from each other in an alternative embodiment. The measurement system <NUM> is oriented with respect to a lateral axis <NUM>, a vertical axis <NUM>, and a longitudinal or depth axis <NUM>. The axes <NUM>-<NUM> are mutually perpendicular. Although the vertical axis <NUM> appears to extend in a vertical direction parallel to gravity in <FIG>, it is understood that the axes <NUM>-<NUM> are not required to have any particular orientation with respect to gravity.

The beams <NUM> of the sensor assemblies <NUM> are elongated along the depth axis <NUM>. Each of the beams <NUM> extends vertically from a load-bearing surface <NUM> to a mounting surface <NUM>. The mounting surfaces <NUM> are disposed on a foundation structure <NUM>. The beams <NUM> define cavities <NUM> that are vertically spaced apart from the load-bearing surfaces <NUM> and the mounting surfaces <NUM>. The sensing packages <NUM> are disposed within the cavities <NUM>.

In the illustrated embodiment, the measurement system <NUM> is a weigh-in-motion sensor system. <FIG> shows a portion of a wheel <NUM> of a vehicle traveling on the load-bearing surfaces <NUM> of the sensor assemblies <NUM>. The load-bearing surfaces <NUM> of the adjacent sensor assemblies <NUM> are generally flush with a road surface <NUM>. For example, the sensor assemblies <NUM> may be embedded within a road material <NUM>, such as concrete, gravel, asphalt, or the like, that defines the road surface <NUM>. The vehicle may be an automobile, truck, a motorcycle, a recreational vehicle, or another type of vehicle. The vehicle moves generally laterally such that the wheel <NUM> moves over the adjacent sensor assemblies <NUM>, and exerts a mechanical force on the load-bearing surface <NUM> of each of the beams <NUM>. The mechanical force exerted by the wheel <NUM> on the load-bearing surface <NUM> is transmitted through the internal structure of the beam <NUM>, and at least a portion of the force is exerted on the sensing package <NUM> within the cavity <NUM>. In an embodiment, the force exerted on the sensing package <NUM> causes the sensing package <NUM> to generate an electrical output signal proportional to the amount of force. The electrical output signal is conveyed along one or more electrical wires <NUM> to a remote processor (not shown), which is configured to convert the electrical output signal to a measurement parameter, such as a weight of the vehicle at the axle including the wheel <NUM>.

Although the two sensor assemblies <NUM> are side-by-side in the illustrated embodiment, the measurement system <NUM> may have various different numbers and arrangements of sensor assemblies <NUM> in alternative embodiments. For example, two or more sensor assemblies <NUM> may be arranged end-to-end along the depth axis <NUM> across at least one lane of the road. In another example, two or more sensor assemblies <NUM> may be spaced apart laterally from each other such that the road material <NUM> is disposed between and separates the two sensor assemblies <NUM>.

Although in the illustrated embodiment the wheel <NUM> directly engages the load-bearing surfaces <NUM>, in an alternative embodiment the load-bearing surfaces <NUM> may be separated from the wheel <NUM> via one or more intervening layers. The one or more intervening layers may include a layer of pavement, concrete, gravel, adhesive binders, or the like. The beams <NUM> optionally may be at least partially embedded within a filler material, such as concrete, dirt, gravel, adhesive binders, or the like, to secure the positioning of the beams <NUM>.

<FIG> is a cross-sectional view of one of the sensor assemblies <NUM> of the measurement system <NUM> according to an embodiment. The beam <NUM> includes a plate <NUM>, a neck <NUM>, and a tube portion <NUM>. The plate <NUM> defines the load-bearing surface <NUM>. The tube portion <NUM> defines the cavity <NUM> that holds the sensing package <NUM>. The neck <NUM> extends between the plate <NUM> and the tube portion <NUM> and joins the plate <NUM> to the tube portion <NUM>.

The tube portion <NUM> includes a base wall <NUM> and a cover <NUM>. The cavity <NUM> is defined between the base wall <NUM> and the cover <NUM>. The base wall <NUM> defines the mounting surface <NUM>. The cover <NUM> is located between the neck <NUM> and the base wall <NUM> and is joined to the neck <NUM>. The base wall <NUM> laterally extends (e.g., along the lateral axis <NUM>) between a first edge <NUM> of the base wall <NUM> and a second edge <NUM> of the base wall <NUM> (which is opposite the first edge <NUM>). The cover <NUM> is joined to the base wall <NUM> at or proximate to the first and second edges <NUM>, <NUM>. In the illustrated embodiment, the cover <NUM> is joined to the base wall <NUM> at the first and second edges <NUM>, <NUM>. But, in an alternative embodiment, the cover <NUM> may be joined proximate to, but not at, the edges <NUM>, <NUM>, such as within designated threshold distance from each of the edges <NUM>, <NUM>. For example, the designated threshold distance may be <NUM>% or <NUM>% of the lateral width of the base wall <NUM>. From the edges <NUM>, <NUM> of the base wall <NUM>, the cover <NUM> extends vertically upward (e.g., towards the plate <NUM>) and laterally.

In the illustrated embodiment, the cavity <NUM> has an oblong cross-sectional shape that is elongated along the lateral axis <NUM>. Although not shown in the illustrated cross-sectional view, the cavity <NUM> may extend along the depth axis <NUM> (shown in <FIG>) with the beam <NUM>.

The neck <NUM> tapers from a wide end <NUM> at the plate <NUM> to a narrow end <NUM> at the cover <NUM>. The wide end <NUM> has a greater lateral width or thickness than the narrow end <NUM>. The neck <NUM> is configured to transmit forces exerted on the load-bearing surface <NUM> of the plate <NUM> to the sensing package <NUM> via the cover <NUM> of the tube portion <NUM>. For example, the neck <NUM> defines a determinate load path, which is a single path that transmits the load from the plate <NUM> to the cover <NUM>. The neck <NUM> may also limit or reduce stress concentrations internally within the beam <NUM> (e.g., relative to the housings of known sensor assemblies). Optionally, the plate <NUM> may have a greater lateral width than the wide end <NUM> of the neck <NUM>.

In an embodiment, the beam <NUM> has a unitary, one-piece, monolithic structure. The neck <NUM> is integrally connected to the plate <NUM> and the tube portion <NUM>, and the cover <NUM> of the tube portion <NUM> is integrally connected to the base wall <NUM>. For example, the beam <NUM> may extend continuously, without seams, from the plate <NUM> to the base wall <NUM>. The beam <NUM> in an embodiment may be formed via an extrusion process. The beam <NUM> may be composed of a metal material, such as aluminum, steel, and/or another metal.

The sensing package <NUM> within the cavity <NUM> is disposed under pre-load between the cover <NUM> and the base wall <NUM>. For example, the sensing package <NUM> engages an interior surface <NUM> of the cover <NUM> and an interior surface <NUM> of the base wall <NUM>. The cavity <NUM> is defined between the interior surfaces <NUM>, <NUM>. The sensing package <NUM> is under pre-load such that the sensing package <NUM> exerts a force on both the cover <NUM> and the base wall <NUM>.

The sensing package <NUM> may include multiple layers. In the illustrated embodiment, the sensing package <NUM> includes a first electrode <NUM>, a second electrode <NUM>, and a piezoelectric element <NUM> stacked between the two electrodes <NUM>, <NUM>. The first electrode <NUM> is disposed between the cover <NUM> and the piezoelectric element <NUM>. The second electrode <NUM> is disposed between the piezoelectric element <NUM> and the base wall <NUM>. The piezoelectric element <NUM> may be a crystal of quartz, tourmaline, lead zirconate titanate (PZT), or the like. Although the piezoelectric element <NUM> is described as singular, the piezoelectric element <NUM> may represent a plurality of piezoelectric elements within the sensing package <NUM>. In the illustrated embodiment, the sensing package <NUM> also includes a guide plate <NUM> between the first and second electrodes <NUM>, <NUM>. The guide plate <NUM> at least partially circumferentially surrounds the piezoelectric element <NUM> to control the position and alignment of the one or more piezoelectric elements. The first and second electrodes <NUM>, <NUM> may include respective metal plates or sheets. The sensing package <NUM> optionally includes a substrate <NUM> vertically disposed between the second electrode <NUM> and the base wall <NUM>. The substrate <NUM> may include a dielectric material, such as one or more plastics, and/or a conductive material, such as one or more metals. The sensing package <NUM> may have different components in alternative embodiments.

In an embodiment, the electrically conductive material (e.g., metal sheets) of the electrodes <NUM>, <NUM> of the sensing package <NUM> is mechanically separate from and electrically isolated from the beam <NUM>. For example, an electrically insulating layer <NUM> is disposed between the cover <NUM> and the metal sheet of the first electrode <NUM>. The insulating layer <NUM> may include a dielectric material, such as one or more plastics. The insulating layer <NUM> may be a discrete component from the first electrode <NUM>, or alternatively may represent a portion of the first electrode <NUM>. The second electrode <NUM> is separated from the beam <NUM> by the substrate <NUM>. Optionally, the substrate <NUM> may be composed of a dielectric material such that the substrate <NUM> is an electrically insulating layer that electrically isolates the second electrode <NUM> from the base wall <NUM> of the beam <NUM>. Alternatively, or additionally, the second electrode <NUM> may include a discrete electrically insulating layer (not shown) disposed between the conductive metal sheet of the second electrode <NUM> and the substrate <NUM> (which may or may not be electrically conductive), such that the electrically insulating layer provide electrical isolation of the second electrode <NUM> from the beam <NUM>. Since the sensing package <NUM> is electrically isolated from the beam <NUM>, the beam <NUM> may not be used as a ground return path through direct ohmic contact between the electrodes <NUM>, <NUM> and the beam <NUM>, which may beneficially reduce electrical interference and noise within the load transfer mechanism <NUM>.

The base wall <NUM> defines an aperture <NUM> that extends through the base wall <NUM> from the mounting surface <NUM> to the interior surface <NUM>, such that the aperture <NUM> is open to the cavity <NUM>. The aperture <NUM> receives a fastener <NUM> therethrough to secure the sensing package <NUM> in the cavity <NUM>. In the illustrated embodiment, the fastener <NUM> is a threaded set screw, and the aperture <NUM> has respective threads that are complementary to the set screw <NUM>. In an alternative embodiment, the fastener may be a bolt, a type of screw other than a set screw, or the like. The fastener <NUM> is installed from below the mounting surface <NUM> of the beam <NUM>. The fastener <NUM> is received into a mounting opening <NUM> of the substrate <NUM> of the sensing package <NUM>. The fastener <NUM> engages the substrate <NUM> to secure the positioning of the sensing package <NUM> relative to the beam <NUM>. In an alternative embodiment in which the sensing package <NUM> lacks the substrate <NUM>, the fastener <NUM> may engage a bottom side of the second electrode <NUM>.

In an embodiment, the depth that the fastener <NUM> extends into the base wall <NUM> and/or the cavity <NUM> may be adjusted in order to set an amount of pre-load on the sensing package <NUM>. In the illustrated embodiment, the depth of the set screw <NUM> is adjusted by imparting a torque on the set screw <NUM>. For example, increasing the depth that the fastener <NUM> extends into the cavity <NUM> may increase the amount of pre-load exerted on the sensing package <NUM>, and reducing the depth that the fastener <NUM> extends into the cavity <NUM> may decrease the amount of pre-load exerted on the sensing package <NUM>. By adjusting the positions of the fasteners <NUM> that engage multiple sensing packages <NUM> along a depth of a single load transfer mechanism <NUM> or multiple sensor assemblies <NUM>, an operator can individually tune each of the sensing packages <NUM> to a designated pre-load, thereby reducing or eliminating pre-load discrepancies caused by component irregularities and imperfections. Individually tuning the pre-load on each of the sensing packages <NUM>, via the fasteners <NUM> extending through the base wall <NUM>, may improve the uniformity of output as a function of applied load across the entire depth of the load transfer mechanism <NUM>.

<FIG> is a cross-sectional view of the beam <NUM> the load transfer mechanism <NUM> shown in <FIG>. The sensing package <NUM> and fastener <NUM> are omitted for clarity in <FIG>. The beam <NUM> extends a height <NUM> from the load-bearing surface <NUM> of the plate <NUM> to the mounting surface <NUM> of the base wall <NUM>. The cavity <NUM> extends a height <NUM> from the interior surface <NUM> of the cover <NUM> to the interior surface <NUM> of the base wall <NUM>. In the illustrated embodiment, a midpoint <NUM> of the height <NUM> of the beam <NUM> (e.g., half way between the load-bearing surface <NUM> and the mounting surface <NUM>) is spaced apart vertically from a midpoint <NUM> of the height <NUM> of the cavity <NUM>. Specifically, the midpoint <NUM> of the beam <NUM> is disposed above the midpoint <NUM> of the cavity <NUM>, such that the midpoint <NUM> is located vertically between the midpoint <NUM> and the load-bearing surface <NUM> of the plate <NUM>. Since the cavity <NUM> is not vertically centered with the beam <NUM>, the sensing package <NUM> (shown in <FIG>) within the cavity <NUM> is also not vertically centered relative to the beam <NUM>.

The neck <NUM> extends a height <NUM> from the plate <NUM> to the cover <NUM>. The height <NUM> of the neck <NUM> is at least <NUM>% of the height <NUM> of the beam <NUM>. For example, if the beam <NUM> is <NUM> tall, then the neck <NUM> is at least <NUM> tall, and optionally at least <NUM> tall. The neck <NUM> combined with the plate <NUM> have a combined height <NUM> from the load-bearing surface <NUM> to the cover <NUM>. In the illustrated embodiment, the combined height <NUM> may be at least <NUM>% of the height <NUM> of the beam <NUM>.

The plate <NUM> extends a lateral width <NUM> from a first edge <NUM> to an opposite, second edge <NUM> thereof. The wide end <NUM> of the neck <NUM> that is joined to the plate <NUM> has a width <NUM> that is at least half (e.g., <NUM>%) of the width <NUM> of the plate <NUM>. Thus, the neck <NUM> has a relatively thick width at the wide end <NUM> and gradually tapers to the narrow end <NUM>. The thick, tapered neck <NUM> may be able to dissipate stress over a larger area than the transition or neck regions of known sensor assemblies, resulting in a reduced peak stress within the neck <NUM>.

The base wall <NUM> has a vertical thickness <NUM> from the mounting surface <NUM> to the interior surface <NUM> of the base wall <NUM>. The cover <NUM> has a thickness <NUM> from the interior surface <NUM> to an exterior surface <NUM> of the cover <NUM>. The exterior surface <NUM> is joined to the neck <NUM>. In the illustrated embodiment, the thickness <NUM> of the base wall <NUM> is greater than the thickness <NUM> of the cover <NUM>. For example, the thick base wall <NUM> provides a support base for the beam <NUM>. The cover <NUM> may be relatively thin to provide structural support while allowing load transfer from the neck <NUM> to the sensing package <NUM> (<FIG>) within the cavity <NUM>.

In the illustrated embodiment, the cover <NUM> of the beam <NUM> includes two upright members <NUM> and a ceiling member <NUM> extending between and connecting the two upright members <NUM>. The upright members <NUM> are joined to the base wall <NUM> at, or proximate to, the first and second edges <NUM>, <NUM> thereof. For example, the upright members <NUM> include a first upright member 330a joined to the base wall <NUM> at the first edge <NUM> and a second upright member 330b joined to the base wall <NUM> at the second edge <NUM>. The upright members <NUM> extend generally vertical, parallel to the vertical axis <NUM>. For example, axes or planes of the upright members <NUM> may be within <NUM> degrees, <NUM> degrees, or <NUM> degrees of the vertical axis <NUM>. The ceiling member <NUM> is connected (e.g., joined) to respective upper ends <NUM> of the upright members <NUM>, spaced apart from the base wall <NUM>. As used herein, relative or spatial terms such as "upper," "lower," "top," "bottom," "front," and "rear" are only used to distinguish the referenced elements and do not necessarily require particular positions or orientations relative to gravity and/or the surrounding environment of the beam <NUM> or load transfer mechanism <NUM> (<FIG>).

The ceiling member <NUM> laterally extends between the two upright members <NUM>. The ceiling member <NUM> may be arched or curved in an upward direction away from the base wall <NUM>. The ceiling member <NUM> defines the exterior surface <NUM> of the cover <NUM> that is joined to the neck <NUM>. The neck <NUM> may be joined to the exterior surface <NUM> at a lateral center of the ceiling member <NUM>, which is a midpoint between the two upright members <NUM>. The ceiling member <NUM> defines the interior surface <NUM> that engages the sensing package <NUM>. The cavity <NUM> is defined laterally between the two upright members <NUM> and vertically between the interior surface <NUM> of the base wall <NUM> and the interior surface <NUM> of the ceiling <NUM>. In the illustrated embodiment, the cavity <NUM> has an oblong cross-sectional shape such that a width <NUM> of the cavity <NUM> is greater than the height <NUM> of the cavity <NUM>. Thus, the cavity <NUM> does not have a circular cross-sectional shape in the illustrated embodiment.

Referring now to <FIG>, the load transfer mechanism <NUM> according to the embodiments described herein has a beam <NUM> that is asymmetrical along the height <NUM> of the beam <NUM>, such that a top half of the beam <NUM> (e.g., including the plate <NUM>) does not mirror a lower half of the beam <NUM> (e.g., including the base wall <NUM>). The designed shape of the beam <NUM> may lower the neutral axis of the beam <NUM> below the geometric midpoint <NUM> of the beam <NUM>. The neutral axis represents the axis through the beam <NUM> where the stress is zero, without compression or tension. The neutral axis may align with the cavity <NUM>, such that the sensing package <NUM> is located at or proximate to the neutral axis. Locating the sensing package <NUM> at the neutral axis may eliminate (or at least reduce) shear stress influence on the sensing package <NUM> (relative to spacing the sensing package <NUM> apart from the neutral axis).

Claim 1:
A load transfer mechanism (<NUM>) comprising:
a beam (<NUM>) elongated along a depth axis (<NUM>) of the load transfer mechanism, the beam (<NUM>) comprising:
a plate (<NUM>) comprising a first edge (<NUM>), a second edge (<NUM>) and a load-bearing surface (<NUM>) extending there between, the plate having a lateral width (<NUM>) between said first and second edges;
a tube portion (<NUM>) including a base wall (<NUM>) and a cover (<NUM>) and defining a cavity (<NUM>) between the base wall (<NUM>) and the cover (<NUM>), the base wall (<NUM>) laterally extending from a first edge (<NUM>) to a second edge (<NUM>) that is opposite the first edge (<NUM>), wherein the cover (<NUM>) is joined to the base wall (<NUM>) at or proximate to the first and second edges (<NUM>, <NUM>) and the beam (<NUM>) extends a height (<NUM>) from the load-bearing surface (<NUM>) of the plate (<NUM>) to a mounting surface (<NUM>) of the base wall (<NUM>) and the cavity (<NUM>) extends a height (<NUM>) from an interior surface (<NUM>) of the cover (<NUM>) to an interior surface (<NUM>) of the base wall (<NUM>); and
a neck (<NUM>) extending between and joining the plate (<NUM>) to the cover (<NUM>) of the tube portion (<NUM>), the neck having a height (<NUM>) between said plate (<NUM>) and said cover (<NUM>) and tapering from a wide end (<NUM>) at the plate (<NUM>) to a narrow end (<NUM>) at the cover (<NUM>), the wide end of the neck having a width (<NUM>);
a sensing package (<NUM>) disposed within the cavity (<NUM>) of the beam (<NUM>) and under pre-load in engagement with the cover (<NUM>) and the base wall (<NUM>), the sensing package (<NUM>) configured to measure forces exerted on the load-bearing surface (<NUM>) of the plate (<NUM>); and
characterized in that:
the height (<NUM>) of the neck (<NUM>) is at least <NUM>% of the height (<NUM>) of the beam (<NUM>) and the width (<NUM>) of the neck (<NUM>) at the wide end (<NUM>) is at least half (<NUM>%) of the width (<NUM>) of the plate (<NUM>).