Patent Application
20130220709
The present invention relates to weighing systems and, more particularly, to weighing apparatus, systems and methods for weighing vehicles in motion.
Weigh-in-motion (WIM) devices are designed to capture and record vehicle (typically truck) or axle weights and gross vehicle weights as they drive over a sensor. Gross vehicle and axle weight monitoring is useful in an array of applications including the design, monitoring, and research of pavements and bridges, as well as weight enforcement on roads and highways.
The ability to weigh vehicles in motion offers many advantages over static weighing. Processing rates increase because trucks can be weighed as they travel at highway speeds, resulting in a significantly greater number of counted vehicles in a shorter period of time, as compared to conventional, static weight stations. In addition, the minimization of static weighing will significantly decrease vehicle accumulation at highway lanes leading to weight stations, improving safety in addition to efficiency.
An additional advantage of WIM is that truck traffic is monitored without alerting truck drivers. Truck operators may go to considerable lengths to avoid a weigh station for various reasons. This avoidance reduces the amount of data available to regulatory authorities as to truck traffic and also places heavy trucks on roads not designed for such traffic.
A WIM system may typically include a base anchored in concrete beneath the surface of the roadway, a weighing platform preferably disposed in a substantially level fashion with respect to the surface of the roadway, and load cells, mounted between the platform and the base, adapted to provide a signal indicating the load applied by the wheel contacting the platform.
As the wheel of a vehicle contacts the weighing platform it applies forces in the horizontal direction in addition to the vertical direction. The horizontal deflection affects the accuracy of the load cell. A typical way to solve this problem is to limit relative movement in the horizontal direction by inserting a stiff arm or flexure between the platform and the base in order to resist horizontal forces while remaining weakly resistant to vertical forces. Such a system is disclosed in U.S. Pat. No. 4,957,178 to Mills et al., which is hereby incorporated in its entirety by reference for all purposes, as if fully set forth herein.
This solution, however, limits freedom in the vertical direction enough to be highly inaccurate relative to static scales. According to the National Bureau of Standards, wheel load scales are required to have an accuracy of ±1% when tested for certification and must be maintained thereafter at ±2%. To the best of the present inventor's knowledge, the best accuracy obtained with the most expensive, commonly used WIM devices may be around 6% of actual vehicle weights, with a probability of approximately 0.95.
The present inventor has recognized a need for improved methods, apparatus, and systems for weighing vehicles in motion, and the subject matter of the present disclosure and claims is aimed at fulfilling this need.
According to the teachings of the present invention there is provided a weigh-in-motion system for accurately determining a weight of a moving vehicle on a roadway by measurement of vertical forces compensated by horizontal forces applied by a wheel of the vehicle to a weighing platform, the system including: (a) a base adapted to be anchored to a roadbed of the roadway; (b) a weighing platform mounted on the base and adapted to receive the wheel of the moving vehicle along a longitudinal axis of the platform, the platform having a length of at least 0.5 meters along the axis; (c) at least one load cell disposed between the base and the platform, and adapted to provide vertical load signals indicating vertical loads applied by the wheel on the platform; (d) a longitudinal differentiation mechanism, mechanically associated with the platform and the base, the longitudinal differentiation mechanism including: (i) a mechanical resistance-measuring unit adapted to provide a resistance to a relative horizontal movement between the base and the platform, the movement generally along the longitudinal axis, to differentiate horizontal forces produced by the wheel acting on the platform, and (ii) a measuring unit, associated with the resistance-measuring mechanical unit, the measuring unit adapted to make a measurement of a parameter associated with the resistance to the relative horizontal movement, and to produce an output signal relating to the measurement, and (e) a processing unit configured to: (i) receive the vertical load signals from the at least one load cell, and the output signal from the measuring unit, and (ii) measure a weight of the wheel on the platform by effecting a compensation for error in the vertical load signals with the output signal from the measuring unit, to produce a corrected weight signal.
According to another aspect of the present invention there is provided a method of accurately determining a weight of a moving vehicle on a roadway by measurement of vertical forces compensated by horizontal forces applied by a wheel of a vehicle to a weighing platform, the method including the steps of: (a) providing a system including: (i) a base anchored to a roadbed of the roadway; (ii) a weighing platform mounted on the base and adapted to receive the wheel of the moving vehicle along a longitudinal axis of the platform, the platform having a length of at least 0.5 meters along the axis; (iii) at least one load cell disposed between the base and the platform, and adapted to provide load signals indicating loads applied by the wheel on the platform; (iv) a longitudinal differentiation mechanism, mechanically associated with the platform and the base, the longitudinal differentiation mechanism including: (A) a mechanical unit adapted to provide a resistance to a relative horizontal movement between the base and the platform, the movement generally along the longitudinal axis, to differentiate horizontal forces produced by the wheel acting on the platform, and (B) a measuring unit, associated with the mechanical unit, the measuring unit adapted to make a measurement of a parameter associated with the resistance and to produce an output signal relating to the measurement, and (v) a processing unit configured to: (A) receive the vertical load signals from the at least one load cell, and the output signal from the measuring unit, and (B) measure a weight of the wheel on the platform by effecting a compensation for error in the vertical load signals with the output signal from the measuring unit, to produce a corrected weight signal; (b) moving at least one wheel of a vehicle along the longitudinal axis of the platform to provide the load signals and to produce the relative horizontal movement; (c) producing the output signal containing the measurement; and (d) compensating for the error in the vertical load signals with the output signal from the measuring unit to produce a corrected weight signal.
According to further features in the described preferred embodiments, the at least one load cell includes at least two load cells, at least three load cells, or at least four load cells.
According to still further features in the described preferred embodiments, the measurement of the parameter is a plurality of measurements over a period in which the wheel is disposed on the platform.
According to still further features in the described preferred embodiments, at least one of the measuring unit and the processing unit is further configured to exclude from the compensation for error in the vertical load signals, at least one of an initial data spike and a final data spike in the output signal.
According to still further features in the described preferred embodiments, at least one of the measuring unit and the processing unit is further configured to exclude from the compensation for error in the vertical load signals, both an initial data spike and a final data spike in the output signal.
According to still further features in the described preferred embodiments, the measurement of the parameter is a plurality of measurements over a particular time interval, and wherein at least one of the measuring unit and the processing unit is further configured to exclude, from the compensation for error in the vertical load signals, the output signal produced during at least one of an initial period and a final period of the interval, or during both an initial period and a final period of the interval.
According to still further features in the described preferred embodiments, the measurement of the parameter is a plurality of measurements over a particular time interval, and wherein the processing unit is further configured to define a measurement window based on at least one pre-determined rule, and to solely utilize the output signal produced during the measurement window, in effecting the compensation for error in the vertical load signals.
According to still further features in the described preferred embodiments, the system further includes a restoration mechanism, mechanically associated with the platform, the restoration mechanism adapted to repeatably restore the platform to a particular position.
According to still further features in the described preferred embodiments, the system further includes a restoration mechanism, mechanically associated with the platform, the restoration mechanism adapted to repeatably and reversibly restore the platform to a particular position, within 0.5 seconds, within 0.3 seconds, or within 0.15 seconds.
According to still further features in the described preferred embodiments, the mechanical unit includes a spring, disposed to extend and contract in a plane parallel with respect to a weighing surface of the weighing platform.
According to still further features in the described preferred embodiments, the mechanical unit includes a hydraulic arm disposed and adapted to provide the resistance to the relative horizontal movement.
According to still further features in the described preferred embodiments, the mechanical unit includes a pneumatic arm disposed and adapted to provide the resistance to the relative horizontal movement.
According to still further features in the described preferred embodiments, the mechanical unit includes a spring disposed and adapted to provide the resistance to the relative horizontal movement.
According to still further features in the described preferred embodiments, the measuring unit is adapted to measure a change in length associated with the relative horizontal movement.
According to still further features in the described preferred embodiments, the measuring unit includes an extensometer.
According to still further features in the described preferred embodiments, the extensometer includes a mechanical extensometer.
According to still further features in the described preferred embodiments, the mechanical extensometer includes an electrical transducer.
According to still further features in the described preferred embodiments, the electrical transducer includes a strain-gauge device.
According to still further features in the described preferred embodiments, the electrical transducer includes a linear variable differential transformer sensor.
According to still further features in the described preferred embodiments, the mechanical unit includes a spring adapted to provide the measurable resistance to the relative horizontal movement.
According to still further features in the described preferred embodiments, the load cell includes a mechanical strain gauge.
According to still further features in the described preferred embodiments, the system further includes the roadway and the roadbed.
According to still further features in the described preferred embodiments, a top weighing surface of the platform forms a part of a top surface of the roadway.
According to still further features in the described preferred embodiments, the platform is angularly positioned away from a normal position with respect to a longitudinal direction of the roadway.
According to still further features in the described preferred embodiments, the platform is angularly installed in the roadway whereby an angle of rotation α, with respect to the normal position, equals at least 5°, at least 6°, at least 7°, or at least 8°.
According to still further features in the described preferred embodiments, the angle of rotation α equals at most 25°, at most 20°, at most 18°, or at most 15° degrees.
According to still further features in the described preferred embodiments, a shape of the platform is a non-rectangular parallelogram.
According to still further features in the described preferred embodiments, the restoration mechanism includes a rocker.
According to still further features in the described preferred embodiments, the rocker has a conical body.
According to still further features in the described preferred embodiments, at least a portion of the secondary restoration mechanism is disposed around the rocker.
According to still further features in the described preferred embodiments, the secondary restoration mechanism includes a pre-stressed membrane disposed around the rocker.
According to still further features in the described preferred embodiments, the at least one load cell includes at most eight load cells, at most six load cells, or at most five load cells.
According to still further features in the described preferred embodiments, the at least one load cell is adapted to be calibrated by a static load. The static load may be a substantially solely vertical static load, having substantially no horizontal component.
According to still further features in the described preferred embodiments, the base is substantially parallel to a top or weighing surface of the weighing platform.
The invention is herein described, by way of example only, with reference to the accompanying drawings. With specific reference now to the drawings in detail, it is stressed that the particulars shown are by way of example and for purposes of illustrative discussion of the preferred embodiments of the present invention only, and are presented in the cause of providing what is believed to be the most useful and readily understood description of the principles and conceptual aspects of the invention. In this regard, no attempt is made to show structural details of the invention in more detail than is necessary for a fundamental understanding of the invention, the description taken with the drawings making apparent to those skilled in the art how the several forms of the invention may be embodied in practice. Throughout the drawings, like-referenced characters are used to designate like elements.
In the drawings:
a is a logical flow diagram according to one aspect of the method of the present invention;
b is a logical flow diagram according to another aspect of the inventive method;
a shows a horizontal displacement of the flexure of
b shows a vertical displacement of the flexure of
The principles and operation of the weigh-in-motion (WIM) system and method of the present invention may be better understood with reference to the drawings and the accompanying description.
Before explaining at least one embodiment of the invention in detail, it is to be understood that the invention is not limited in its application to the details of construction and the arrangement of the components set forth in the following description or illustrated in the drawings. The invention is capable of other embodiments or of being practiced or carried out in various ways. Also, it is to be understood that the phraseology and terminology employed herein is for the purpose of description and should not be regarded as limiting.
Referring now to the drawings,
Mechanical resistance unit (element or assembly) 152 may include a spring such as a cylindrical or spiral spring, a hydraulic arm a pneumatic arm, or other mechanical resistance unit adapted to measurably resist the relative horizontal movement between the base and the platform. As used herein in the specification and in the claims section that follows, the term “measurably resist”, “measurable resistance”, and the like is meant to refer to a resistance that is repeatable in a manner that enables meaningful measurement of the resistance, so as to enable analysis of the resistance.
Measuring unit 154 may include an extensometer. An extensometer is an instrument for measuring changes in length that are caused by application of force. Various types of extensometers are known. Changes in length may be measured directly by some types of devices, such as clip-on extensometers, or indirectly by non-contact or video extensometers.
Mechanical or contact-type extensometers may use electrical transducers such as linear variable differential transformer (LVDT) sensors or strain-gauge devices (and sometimes combinations of the two) to generate an electrical signal proportional to change in length or strain. An extensometer system may also incorporate electronics for amplification of small signals.
WIM system 100 also includes a processing unit or processor 180, such as a central processing unit (CPU). Processor 180 may be configured to receive the load signals from the at least one load cell and the output signal from the measuring unit, and to produce a weight indication based on the load signals and the output signal from the measuring unit.
WIM system 100 is preferably equipped with a restoration mechanism such as restoration mechanism 140, which serves to restore a position of weighing platform 120 with respect to base 110, in preparation for another wheel rolling on to weighing platform 120. In WIM system 100, load cell 130 is a column-type load cell, and restoration mechanism 140 includes cupped surfaces on the top and on the bottom of load cell 130.
One aspect of the method of the present invention will now be described, with reference to the logical flow diagram provided in
WIM system 100 may also measure a parameter (step 3) associated with these horizontal forces, and produce an output signal based on, or related to, this measured parameter (step 4).
In step 5, a processing unit such as processor 180 processes the vertical load signals along with the output signal from step 4 to produce a WIM weight indication. A restoration mechanism such as restoration mechanism 140, which serves to restore a position of weighing platform 120 with respect to base 110, may be activated (step 6) in preparation for another wheel rolling on to weighing platform 120.
Another aspect of the method of the present invention will now be described, with reference to the logical flow diagram provided in
WIM system 100 includes a longitudinal differentiation mechanism, such as longitudinal differentiation mechanism 150 described hereinabove. A mechanical unit (element or assembly) thereof, such as mechanical unit 152, provides a measurable resistance to the relative horizontal movement between base 110 and platform 120, generally along longitudinal axis X of platform 120, to longitudinally differentiate horizontal forces produced by wheel 50 acting on platform 120 (step 3).
A measuring unit (element or assembly), associated with mechanical unit 152, such as measuring unit 154, makes a measurement of a parameter associated with this measurable resistance and produces an output signal relating to this measurement (steps 4, 5).
In step 6, a processing unit such as processor 180 processes the vertical load signals along with the output signal from step 4 to produce a WIM weight indication. A restoration mechanism such as restoration mechanism 140, which serves to restore a position of weighing platform 120 with respect to base 110, may be activated (step 7) in preparation for another wheel rolling on to weighing platform 120.
One of ordinary skill in the art may readily appreciate that there are various ways of calibrating, correlating or transforming the output signal (e.g., that of step 5 in
Thus, in practice, a truck wheel or axle engaging the weighing platform will produce a dynamic vertical weight along with measured horizontal forces or a measured opposition to the horizontal movement between the weighing platform and weighing base. The measure horizontal term may be converted to a vertical weight correction term, which may be added to correct or improve the value of the dynamic vertical weight, whereby the corrected vertical weight may closely approach or more closely approach the actual stationary weight of the truck wheel or axle.
As used herein in the specification and in the claims section that follows, the term “extensometer” refers to an instrument for measuring a longitudinal displacement or extension caused by an application of force.
Mechanical resistance unit (element or assembly) 152 may include a spring or other resistance units that, at least ideally, approach the behavior delineated by Hooke's law. In the ideal case, the extension produced is directly proportional to the load:
F=−k·x
wherein:
F is the restoring force exerted by the material, and
k is the spring constant (in units of force per unit length).
Thus, for systems in which the extension produced is well correlated (using Hooke's law or any other correlation) with the load—in this case, horizontal forces—accurate measurement of the extension of mechanical resistance unit 152 may, in turn, enable accurate computation of the load.
Referring now to
In one embodiment, WIM system 800 may be adapted to simultaneously receive both wheels (or all wheels) of a single vehicle axle. In another embodiment, the weighing system may include two or more separate parallel weighing platforms 320 installed in roadway 60, each adapted to receive a single wheel 50 (or in the case of double wheels—a double wheel on a single side) of a vehicle axle.
I believe that it is highly preferable for the weighing platforms to be of sufficient length so as to fully support motor vehicle wheel 50. This is in sharp contrast to various strips or cables of the prior art, which receive—at most—a fraction of the weight exerted by wheel 50, the remainder of the weight being supported by the roadway itself.
Thus, the weighing platform of the present information (such as platforms 120, 320 described hereinabove) may typically have a length of at least 0.50 meters, at least 0.60 meters, at least 0.70 meters, at least 0.80 meters, or at least 0.90 meters.
It may be advantageous for the weighing platform of the present information to enable solely a single wheel or wheels from a single axis to be disposed on the platform at any particular time. Thus, the weighing platform of the present information (such as platforms 120, 320 described hereinabove) may typically have a length of at most 2.50 meters, at most 2.30 meters, at most 2.20 meters, at most 2.00 meters, at most 1.90 meters, at most 1.70 meters, at most 1.50 meters, at most 1.30 meters, at most 1.10 meters, at most 1.00 meter, or at most 0.90 meters.
The schematic, exemplary embodiment of a weighing module 200, provided in
Weighing module 200 may further include an overload protector 500, adapted to protect weighing module 200 against excess horizontal forces, a restoration mechanism including rocker mechanism 400 for each load cell 230, and a flexure 300 connecting between top element 210 and bottom element 220. Flexure 300 may serve as part of the restoration mechanism.
The horizontal measurement obtained by measuring unit 240 may be used to correct the vertical load cell measurement obtained by load cells 230. Processor 250 may process the received signals, correct for horizontal displacement, and determine the weight of wheel 50 on weighing platform 120.
a shows a horizontal displacement of flexure 300.
Referring again to the schematic exemplary embodiment in
I have discovered that in imparting the desired horizontal flexibility to the WIM system of the present invention, severe problems may occur in restoring the initial horizontal position of weighing platform (such as weighing platforms 120, 320 described hereinabove), which may yield inaccurate and non-repeatable results. In order to correct this problem, a restoration mechanism including rocker mechanism 400 may be advantageously disposed between load cell 230 and bottom element 220.
Referring now to
Because of horizontal flexibility inherent in the WIM system of the present invention, I have further found that various conventional sphere or rocker mechanisms may not restore the position of the elements fast enough, especially when measuring loads from multiple axes of trucks traveling at high speeds. Moreover, conventional sphere or rocker mechanisms may compromise the accuracy of measurement as horizontal forces on the sphere or rocker may be translated into vertical forces applied against top element 210.
Referring again to the schematic exemplary embodiment in
I have further found that under high-speed conditions, wheels rolling onto weighing platform may produce sudden horizontal forces, thereby increasing the noise component of both the horizontal and vertical displacement measurements. This noise component causes inaccurate load calculations of the partial vehicle load on the wheel. One solution is to lengthen weighing platform, but this significantly raises the cost of the system, both in parts and installation. Moreover, the natural frequency is lowered, thereby increasing oscillation and reducing weighing precision. Also, the length of the platform may be limited to a length allowing the wheel or wheels of a single axle to be disposed on the platform at any given time.
My inventive solution to this problem is shown in the top, schematic view provided in
As discussed hereinabove, existing WIM axle-weighing systems may be characterized by low accuracy (+/−15-20%) compounded by a finite (non-unity) probability (typically 80%-95%) of achieving that accuracy. I have found that the amplitude/intensity of horizontal forces is a strong indication of the accuracy of the associated weight measurement. When the amplitude/intensity of horizontal forces is low, the accuracy of the associated weight measurement is high, and vice versa.
Thus, by measuring horizontal forces (and processing them), the quality of an associated weight measurement may be indicated, without effecting a compensation for error in the vertical load signals. By way of example, based on a particular measurement of horizontal forces, the inventive method may determine that a particular weight measurement is within 7% of the true (static) value, with a certainty approaching 100% (as opposed to the 80%-95% achieved in various prior-art technologies). Alternatively or additionally, the inventive method may be used to determine, with the same 80%-95% certainty achieved by prior-art technologies, that a particular weight measurement is within only 2% of the true value.
Theoretically, a horizontal behavior measuring system could be retrofitted to various existing, prior-art WIM systems, in order to improve the certainty of the weight measurements, and/or to identify particular weight measurements having a particularly high or pre-determined accuracy.
It is important to emphasize that even within the plateau region of the plot, the vertical force signal F is not constant. Moreover, the average value may be appreciably different from the static (real) weight exerted by the wheel.
With reference now to the plot of the horizontal force signal H as a function of time, the scale of the Y-axis has been magnified in order to better view the details of the plot. This plot reveals a (positive) spike during the initial time period in which the wheel rolls on to the weighing platform, and an additional, negative spike during the final or end period in which the wheel rolls off to the weighing platform.
Techniques for identifying such spikes are readily available to those of ordinary skill in the art of signal processing. Such techniques may include identifying peaks having a slope above a pre-determined value; identifying peaks having a slope above a pre-determined value and a magnitude, with respect to the magnitude thereafter (for an initial spike) or therebefore (for an end spike). A measurement window may be identified in the time period between the initial and end spikes.
In one embodiment of the present invention, the processor processes the vertical load signal along with the horizontal force signal to produce a WIM weight indication. The WIM weight indication may be an average weight indication, e.g., taken over a period of time in which the load on the vertical load cells has substantially plateaued.
Determining the plateau width and absolute load will be readily apparent to one of ordinary skill in the art of signal processing.
In another embodiment of the present invention, the processor processes the horizontal force signal and may identify at least one time period containing a spike (or other disturbance-related phenomenon). The processor is further adapted to exclude the disturbed time period(s) from a sampling time window W, which is illustratively shown in
As used herein in the specification and in the claims section that follows, the term “mechanical resistance-measuring unit” is meant to include a mechanical resistance-measuring element or a mechanical resistance-measuring assembly.
As used herein in the specification and in the claims section that follows, the term “horizontal movement” and the like is meant to refer to a movement that is horizontal with respect to the weighing surface of the weighing platform.
As used herein in the specification and in the claims section that follows, the term “adapted to be calibrated by a static load” and the like, with respect to a load cell, is meant to exclude piezoelectric elements and other elements that require dynamic calibration, or which calibrate poorly under static load conditions.
Although the invention has been described in conjunction with specific embodiments thereof, it is evident that many alternatives, modifications and variations will be apparent to those skilled in the art. Accordingly, it is intended to embrace all such alternatives, modifications and variations that fall within the spirit and broad scope of the appended claims. All publications, patents and patent applications mentioned in this specification, including U.S. Pat. No. 4,957,178, are herein incorporated in their entirety by reference into the specification, to the same extent as if each individual publication, patent or patent application was specifically and individually indicated to be incorporated herein by reference.
This application is a Continuation in Part (CIP) of PCT Application No. PCT/IB2011/001657, filed Jul. 17, 2011, which draws priority from U.S. Provisional Patent Application Ser. No. 61/365,323, filed Jul. 17, 2010, both of which are hereby incorporated by reference for all purposes as if fully set forth herein.
| Number | Date | Country | |
|---|---|---|---|
| Parent | PCT/IB2011/001657 | Jan 2012 | US |
| Child | 13741409 | US |
