Abstract:
A virtual profilograph is disclosed that can provide measurements indicative of the ride quality of a roadway as the road is being constructed. As a result, a more timely, less costly indication of the ride quality of a roadway is obtained as compared to prior methods. In a first embodiment a Global Navigation Satellite System antenna is attached to a vehicle. When the vehicle travels over a roadway, measurements of the position of the antenna are recorded at different times. A profile of the roadway is created by measuring the elevation of the antenna as a function of the distance traveled from a starting point. In another embodiment, tilt sensors are used to measure the slope of the roadway and the tilt of the vehicle so that a precise orientation of the vehicle and, hence, the contours of the roadway, can be determined.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates generally to machines for road paving operations and, more particularly, to assessing the quality of a paved road surface using Global Navigation Satellite Systems. 
     Methods of designing and paving/surfacing streets, highways and other such roadways, and the equipment used in such paving operations, are extremely well known. For example, in one such method, an asphalt mixture is spread on a properly graded and prepared surface and the mixture is then compacted using, for example, an asphalt compactor. The terms asphalt compactor, roller and roller machine are used interchangeably herein. One skilled in the art will recognize that there are many different types of paving/surfacing operations suitable for different circumstances. 
     One key assessment of finished roadways is the quality of ride that is experienced by a vehicle as it passes over the roadway. Profilographs, which are well-known in the art, are typically used after construction of a roadway is completed as one method of measuring ride quality. A profilograph is a measurement device that is passed over a roadway to detect the presence and severity of bumps and dips in order to generate a longitudinal profile of the roadway.  FIG. 1  shows a prior art profilograph  100  useful for this purpose. Referring to that figure, profilograph  100  has a frame  102  which is, for example, a lightweight aluminum frame. Exemplary profilograph  100  has a length L of 25 feet. Frame  102  is supported above roadway  109  by wheel assemblies  101  and is adapted to be towed behind a vehicle in direction  110 . Measurement wheel  108  is attached to arm  107  which, in turn, is attached to mounting box  104  mounted to frame  102  in a way that permits arm  107  and, hence, wheel  108 , to move vertically to follow the contour of road  109  as the wheel passes over the road. Measurement wheel and/or arm  107  is connected to recording device  103  via cable  106  and flexible shaft  105 . As wheel  108  moves up and down vertically, i.e. over bumps and into dips in a roadway as the profilograph is towed, cable  106  shortens and lengthens, respectively and flexible shaft  105  rotates in relationship to the rotation of wheel  108 . Recording device  103  records the variations in the length of cable  106  as a function of the rotation of wheel  108  and compares the vertical position of wheel  108  to the known, fixed position of wheel assemblies  101 . Since the number of rotations of wheel  108  are directly proportional to the distance traveled by the profilograph, recording device  103  can accurately record the relative position of wheel  108  with respect to the wheel assemblies  101  in order to determine any fast elevation changes within the length of the profilograph  100  that may function to degrade ride quality. These elevation changes experienced along roadway  109  can then be plotted as a function of the distance from a starting point of the profilograph in order to generate a longitudinal profile of that roadway. Recording device  103  may be an analog device with a physical pen connected to cable  106 . In such a case, the pen moves proportionately with the change in length of cable  106  and records the dips and bumps on a roll of paper that is scrolled relative to the pen at a speed proportional to the rotational velocity of wheel  108 . Alternatively, recording device  103  may be a digital computing device that records roadway profile information in digital memory. In either case, the result is a profile or graph of a roadway showing any fast elevation changes as a function of distance traveled which can effect the ride quality of a vehicle passing over that roadway. 
     Other variations on profilographs have also been used. For example, profilographs that are shorter in length have been developed that are useful at higher speeds than the profilograph of  FIG. 1 , which is limited to relatively slow speeds. Additionally, laser ranging devices have also been used in profilographs, herein referred to as laser profilographs. Laser profilographs typically consist of one or more laser devices attached to a vehicle. The laser is pointed at the roadway as the vehicle moves and one or more sensors measure, for example, the time the light energy emitted from the laser takes to travel from the laser device to the sensor, thus allowing a measurement of the distance from the laser to the ground. The longer the light energy takes to travel from the laser device, be reflected by the road and reach the sensor, the greater the distance above the ground the laser device/sensor are located. The speed of the vehicle is recorded while the distance measurements are taken and this information is transmitted to a computer, which records the information in order to create a profile of the roadway. 
     BRIEF SUMMARY OF THE INVENTION 
     While prior profilographs were advantageous in many aspects, they were also limited in certain regards. For example, all prior profilographs required careful calibration prior to operation in order to obtain accurate results. Also, typically, such measurements only took place after a roadway was completed and usually were accomplished by a different crew of workers than the crew that paved the roadway, thus increasing the cost and time associated with completing the construction of a roadway. Additionally, maneuvering such a large mechanical device as a prior profilograph was difficult and unwieldy. 
     Therefore, the present inventor has recognized there is a need for a more efficient and timely method of measuring the ride quality of a roadway. Accordingly, the present invention is a graphical virtual profilograph that can provide measurements indicative of the ride quality of a roadway as the road is being constructed. As a result, a more timely, less costly indication of the ride quality of a roadway is obtained as compared to prior methods. In one embodiment, a profilograph in accordance with the principles of the present invention allows a road construction crew to alter road construction in real time to improve the ride quality of the road. 
     In a first embodiment one or more Global Navigation Satellite System antennae are attached to a vehicle. When the vehicle travels over a roadway, measurements of the position of the antenna are recorded at different times. A profile of the roadway is created by measuring the elevation of the antenna as a function of the distance traveled from a starting point. In another embodiment, tilt sensors are used to measure the slope of the roadway and the tilt of the vehicle so that a precise orientation of the vehicle and, hence, the contours of the roadway, can be determined. 
     These and other advantages of the invention will be apparent to those of ordinary skill in the art by reference to the following detailed description and the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows a prior art profilograph; 
         FIG. 2  shows a virtual profilograph system on an asphalt compactor in accordance with an embodiment of the present invention; 
         FIG. 3  shows a GPS control system useful in the virtual profilograph system of  FIG. 2 ; and 
         FIG. 4  shows an illustrative display of the virtual profilograph system in accordance with an embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 2  shows a construction machine  202  in accordance with an embodiment of the present invention. Specifically, that figure shows an asphalt compactor, once again also referred to herein interchangeably as a roller, adapted to compact the material used to construct a roadway. In one particular embodiment, the roller  202  has two cylindrical compacting rollers  214  for compacting the road surface as roller  202  moves across the roadway. The configuration of a roller such as roller  202  is well-known in the art and will not be described in further detail herein other than is necessary to understand the principles of the present invention. Roller  202  has, illustratively, a satellite antenna  208  connected to the roller body  212  that is used to receive signals from Global Navigation Satellite Systems (GNSS). GNSS are well known and used to solve a wide variety of positioning/time related tasks. Two well known such systems are the Global Positioning System (GPS) of the United States and the GLObal NAvigation Satellite System (GLONASS) of Russia. For ease of reference, this description will generally refer to the GPS system, but it is to be understood that the present description is equally applicable to GLONASS, combined GPS+GLONASS, or other GNSS systems. 
     One skilled in the art will recognize that the position of GPS antenna  208  can be located with a high degree of precision. The precision can be further enhanced using differential GPS, or DGPS, which is well known. Such DGPS methods allow the position of antenna  208  to be determined within, for example, 2 cm vertically, along the y-axis in  FIG. 2 , and within, also by way of example, 1 cm laterally, along the x and z axes in  FIG. 2 . This precision can be even further enhanced via the use of more recent techniques that provide even more accurate position measurements. For example, some more recent satellite positioning systems incorporate laser transmitters at a stationary location to transmit a signal that is received by a laser receiver on roller  202 . Based on the signal characteristics of the signal received by the receiver and the known location of the stationary transmitter, positional measurements of a satellite positioning system can be enhanced such that the position of antenna  208  can be determined within, for example, 5 millimeter accuracy vertically, along the y-axis in  FIG. 2 , and within, also by way of example, 1 centimeter laterally, along the x and z axes in  FIG. 2 . 
     Thus, as one skilled in the art will recognize, the configuration described above allows for the precise measurement of the Cartesian coordinate position of antenna  208  on roller  202  as well as the linear velocity of that antenna. The antenna is mounted rigidly in a stationary position on the body of roller  202 . Therefore, the position of any other component of roller  202  that is also mounted stationary with respect to the body of the roller  202  can be located as accurately as that of the antenna via simple geometric calculations. Particularly, knowing the position of antenna  208  permits the precise position of the cylindrical rollers  214  to be known which, when combined with different measurements over time, allows the heading and position of the roller  202  to be determined with corresponding accuracy. In addition to GPS antenna  208 , in another embodiment roller  202  also has tilt sensors  204 A and  204 B, more generally. Tilt sensor  204 A may be used, for example, to measure whether roller  202  is traveling horizontally in the X-Z plane or whether it is traveling uphill or downhill with respect to that plane. Tilt sensor  204 B, on the other hand, may be used to determine whether roller  202  is tilted about the longitudinal axis of the roller, i.e., whether the roller is rolling to one side or the other with respect to a horizontal X-Z plane. 
     One skilled in the art will recognize that, instead of tilt sensors  204 A and  204 B, multiple GPS antennas can be placed on the body of roller  202  to accomplish the same function. For example, if a second antenna is placed on the roller body, but is offset in both the z and x directions with respect to antenna  208 , both the tilt and slope orientation of roller  202  can be determined by comparing the relative three-dimensional positions of the two antennas. One skilled in the art will be able to devise various equally advantageous placements and configurations of GNSS antennas in order to determine the positions and orientations of roller  202  and cylindrical rollers  214  as described above. Thus, the precise position, velocity, heading and orientation (e.g., slope and tilt) of roller  202  and its various components, such as rollers  214 , can be determined. Therefore, by taking multiple measurements over time as the roller moves across a surface, a precise profile of the roadway can be determined. 
     One skilled in the art will also recognize that the antenna  208  of  FIG. 2  may be connected to a GNSS control system, such as GPS receiver  210  in  FIG. 2 , which may be implemented on a programmable computer adapted to perform the steps of a computer program to calculate and display the position of the roller  202  and/or the cylindrical rollers  214  on illustrative terminal  206  in  FIG. 2 . Referring to  FIG. 3 , such a control system  210  may be implemented on any suitable computer adapted to receive, store and transmit data such as data associated with the aforementioned antenna location(s). Specifically, illustrative control system  210  may have, for example, a processor  302  (or multiple processors) which controls the overall operation of the control system  210 . Such operation is defined by computer program instructions stored in a memory  303  and executed by processor  302 . The memory  303  may be any type of computer readable medium, including without limitation electronic, magnetic, or optical media. Further, while one memory unit  303  is shown in  FIG. 3 , it is to be understood that memory unit  303  could comprise multiple memory units, with such memory units comprising any type of memory. Control system  210  also comprises illustrative modem  301  and network interface  304 . Control system  210  also illustratively comprises a storage medium, such as a computer hard disk drive  305  for storing, for example, data and computer programs adapted for use in accordance with the principles of the present invention as described hereinabove. Finally, control system  210  also illustratively comprises one or more input/output devices, represented in  FIGS. 2 and 3  as terminal  206 , for allowing interaction with, for example, a technician or machine operator. Terminal  206  illustratively has display  307  and input device (here, a keyboard)  308 . One skilled in the art will recognize that control system  210  and terminal  206  may be located directly on roller  202  or, for example, may be located remote from roller  202 . One skilled in the art will also recognize that control system  210  is merely illustrative in nature and that various hardware and software components may be adapted for equally advantageous use in a computer in accordance with the principles of the present invention. 
       FIG. 4  shows an illustrative graph  400  created by the control system and displayed on a paper graph or, alternatively, on a display, such as display  307  of terminal  206  in  FIG. 3 . Referring to  FIG. 4 , graph  400  has vertical axis  402  representing the elevation of the GNSS antenna  208  of  FIG. 2  with respect to an initial starting elevation  404 . Illustratively, the elevation represented by axis  402  is displayed in centimeters. Graph  400  also has horizontal axis  403  representing the distance traveled from a starting point on a roadway, illustratively shown as starting point  405  in graph  400 . The distance represented by axis  403  is, for example, displayed in feet. One skilled in the art will recognize that many different resolutions using different units of measurement for axes  402  and  403  may be used with equally advantageous results depending on road conditions (i.e., the relative roughness or smoothness of the road). One skilled in the art will also recognize that the distances represented by axes  402  and  403  may be expressed in any suitable units or, alternatively, may be a relative unit-less elevation. As roller  202  of  FIG. 2  moves across the roadway, vertical and horizontal position measurements taken by the GNSS control system of  FIG. 3  and as described above are plotted on graph  400  as a function of the distance traveled by the roller. Alternatively, the raw positional data represented by these vertical and horizontal position measurements may be averaged, for example over various distances, or otherwise mathematically smoothed to simulate the way a mechanical profilograph measures fast elevation changes of wheel  108  in  FIG. 1  with respect to wheel assemblies  101 , as discussed above. In either case, plot  401  represents the surface of the roadway across which the roller moves and, thus, may be used to assess the ride quality of vehicles traveling across the surface of the roadway. 
     The foregoing Detailed Description is to be understood as being in every respect illustrative and exemplary, but not restrictive, and the scope of the invention disclosed herein is not to be determined from the Detailed Description, but rather from the claims as interpreted according to the full breadth permitted by the patent laws. It is to be understood that the embodiments shown and described herein are only illustrative of the principles of the present invention and that various modifications may be implemented by those skilled in the art without departing from the scope and spirit of the invention.