Abstract:
A distance and temperature sensing unit is used on paving vehicles. The unit has a first set of range sensors of a first diameter and a second set of range sensors of a second diameter. The unit calculates a weighted average distance to a road surface based on ranges measured by the multiple sensors. The unit also has a temperature sensor on a temperature bar. The bar is affixed to the unit by a flexible connection preventing break-off when the bar encounters obstacles, like the road surface, while the paving vehicle is moving.

Description:
[0001]    This application claims the benefit of U.S. Provisional Application No. 60/925,506 filed Apr. 20, 2007 which is incorporated herein by reference. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    The present invention relates generally to range sensing and more particularly to ultrasonic range sensing and temperature sensing in road finishing applications. In construction using asphalt and concrete materials (e.g., road finishing, paving, etc.) various systems and methods for sensing the distance to a surface (e.g., a road) have been used. 
         [0003]    Contacting and non-contacting systems have been used. Contacting systems suffer in that they are prone to damage and breakage. Prior non-contacting systems are not accurate enough. These systems generally employ a range sensor, such as an ultrasonic sensor, to measure the distance from the construction vehicle or sensing unit to the road surface. In some systems more than one homogenous sensor is used to measure distances to the surface from the sensing unit. These measured distances are averaged to determine an approximate distance between the sensing mechanism and the surface. 
         [0004]    In some cases, these sensing units or construction vehicles include some apparatus for temperature sensing. An example of a commonly used temperature sensor is a U-shaped metal attachment to the sensing apparatus that extends toward the road surface. The attachment is used to measure the temperature at the road surface. 
         [0005]    The prior range sensing set-ups often provide inaccurate measurements and/or inconsistent sensing because the construction vehicle and/or the sensors and sensing unit may be too close or too far away from the road surface. That is, the sensors may not be in their optimal performance range. Accordingly, improved systems and methods for range sensing are needed. 
       BRIEF SUMMARY OF THE INVENTION 
       [0006]    The present invention generally provides methods and apparatus for range and temperature sensing. A range sensing apparatus for determining a distance from the range sensing apparatus to a surface has at least one ultrasonic range sensor having a first size (e.g., diameter) and at least one ultrasonic range sensor having a second size (e.g., diameter). The range sensing apparatus also has a controller configured to calculate a distance to the surface based at least in part on distances measured by the range sensors. In at least one embodiment, the controller calculates the calculated distance by weighting the measured distances based on a predetermined distance to the surface and calculating a weighted average of the first and second sets of measured distances. 
         [0007]    In one embodiment of the invention, a range sensing apparatus has a housing, a flexible connection attached to the housing, a bar attached to the flexible connection, and a temperature sensor attached to the bar. In this embodiment, the controller is configured to receive temperature information from the temperature sensor. 
         [0008]    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 
         [0009]      FIG. 1A  depicts a bottom-side perspective view of a sensing unit according to an embodiment of the present invention; 
           [0010]      FIG. 1B  depicts a bottom perspective view of a sensing unit according to an embodiment of the present invention; 
           [0011]      FIG. 2A  depicts a bottom perspective view of an alternative sensing unit according to an embodiment of the present invention; 
           [0012]      FIG. 2B  depicts a bottom perspective view of an alternative sensing unit according to an embodiment of the present invention; 
           [0013]      FIG. 3  depicts a side schematic view of a sensing unit according to an embodiment of the present invention; 
           [0014]      FIG. 4  is a high level block diagram of a controller according to an embodiment of the invention; 
           [0015]      FIG. 5  illustrates a method of ultrasonic sensing; 
           [0016]      FIG. 6  depicts a paving system according to an embodiment of the present invention; and. 
           [0017]      FIG. 7  illustrates a method of paving according to an embodiment of the invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0018]    The present invention generally provides systems and methods for improved range sensing in a construction environment. More specifically, the present invention provides more accurate distance determination. This may be achieved using multiple sensors of multiple sizes in a single sensing unit, infrared temperature sensing, and/or a foldable temperature bar. 
         [0019]    In an embodiment of the invention, multiple sensors of varying sizes (e.g., diameters) on a sensing unit are used to determine an approximate distance from the sensing unit to a reference point (e.g., from a range sensor to a surface). The present invention employs sensors of different sizes and diameters in order to more accurately determine the distance between the sensing mechanism and the intended point or surface of measurement. In such an embodiment, these sensors are used to determine most accurately this distance through the means of ultrasonic emission and reception whereby each sensor has a unique weighting or influence on a determined distance. That is, a mathematical calculation may be performed which more heavily regards (e.g., weights, assigns a multiplier to, etc.) distances measured by one set of sensors. These sensors are configured in a single housing or component piece, so as to enable more accurate determination of the distance to be measured. 
         [0020]    In the same and/or alternative embodiments of the invention, various temperature sensing apparatus (e.g., temperature sensors) are included at (e.g., integrated into and/or coupled to) the sensing unit. These temperature sensors establish a reference for use in determining (e.g., calculating) a distance to the road surface. Ideally, air temperature between the temperature sensor and the surface should be known because uncompensated variations in air temperature may compromise the accuracy of the range measurements. The temperature sensor may help compensate (e.g., aid in accounting, calculating, and/or adjusting) for variations in air temperature. While an appropriate compensation factor may be more easily determined when the air temperature is relatively constant between the sensor and surface and is only disturbed by temporary air turbulence, the inventive system may account for more significant fluctuations in temperature and conditions. Additionally and/or alternatively, one or more temperature sensors are used to determine the temperature of the work surface to determine if appropriate working conditions exist. 
         [0021]      FIGS. 1A and 1B  depict an exemplary sensing unit  100  according to an embodiment of the present invention.  FIG. 1A  shows a bottom-side perspective view of the sensing unit  100  and  FIG. 1B  shows a bottom perspective view of the sensing unit  100 . The sensing unit  100  comprises a housing  102 , which encloses a controller  400  (not shown in  FIGS. 1A and 1B , but discussed below with respect to  FIG. 4 ) for controlling the various components and functions of the sensing unit  100 . 
         [0022]    Sensing unit  100  includes one or more outer sensors  104   a  and  104   b.  In the exemplary embodiment of  FIGS. 1A and 1B , the sensing unit  100  has two outer sensors  104   a  and  104   b  located on a bottom surface  106  of the sensing unit  100 . It may be understood that, in some embodiments, other numbers of outer sensors  104  may be used. Also located on the bottom surface  106  are one or more inner sensors  108   a  and  108   b.  Similar to outer sensors  104   a  and  104   b,  any number of inner sensors  108  may be used. Of course, subsequent sensors, rows of sensors, or arrangements of sensors may be used such as a set of inner-inner sensors (e.g., sensors arranged inboard of the inner sensors  108   a  and  108   b ) or arranging the sensors in a substantially circular pattern or sets of concentric circles, for example. Generally, outer sensors  104   a  and  104   b  are located outboard (e.g., closer to an end or edge of sensing unit  100 ) of inner sensors  108   a  and  108   b.  In alternative embodiments, inner sensors  108   a  and  108   b  may be located outboard of outer sensors  104   a  and  104   b  and/or adjacent outer sensors  104   a  and  104   b.  As will be discussed further below with respect to  FIG. 3 , outer sensors  104   a  and  104   b  and inner sensors  108   a  and  108   b  may be spaced apart a predetermined distance from each other and/or from a point on or section of sensing unit  100  and may be of varying diameters and/or sizes which may be correlated to each other. Though depicted as residing on/within bottom surface  106 , outer sensors  104   a  and  104   b  and inner sensors  108   a  and  108   b  may be located in any other appropriate location on the sensing unit  100  (e.g., on an end, on top, projecting from a surface, etc.). 
         [0023]    Sensing unit  100  may also include one or more temperature sensing devices. In the embodiment depicted in FIGS. IA and  1 B, the temperature sensing device may be a temperature bar  110  protruding from the bottom surface  106 . The temperature bar  110  may be coupled (e.g., attached) to the sensing unit  100  via a flexible or otherwise moveable, rotatable, and/or detachable connection  112  at its proximal end and may include a temperature detector  114  at its distal end. As shown in  FIG. 1B , a portion on or near the distal end of temperature bar  110  may be securable to the housing  102  at one or more catches  116  when the temperature bar  110  and/or the temperature detector  114  is not in use, when the sensing unit  100  is being transported, etc. Temperature bar  110  may additionally or alternatively be secured to the housing  102  at other locations along its length using other catches or any other appropriate securing means. Other temperature sensing means such as temperature sensor  118  may also be included. 
         [0024]    Sensing unit  100  may be a stand-alone unit and/or may be included as part of a construction system (e.g., attached to a paving vehicle  602  of  FIG. 6 ). In some embodiments, the sensing unit  100  may be coupled to the paving vehicle  602  ( FIG. 6 ) such that it is capable of feeding back information such as temperature and/or range information. Such information may be recorded (e.g., with control circuitry of controller  400 ), displayed to one or more users, or otherwise catalogued so as to provide information in real-time and/or in a memory to one or more users. That is, the sensing unit  100  may record and/or send temperature and/or range information to a paving vehicle operator for use during construction operations. Similarly, one or more parts (e.g., components) of the sensing unit  100  may provide distance and/or temperature information to an automated system (e.g., in conjunction with a system such as paving system  600  of  FIG. 6 ). Additionally, sensing unit  100  may be removable, angleable, and/or otherwise positionable to provide the most accurate temperature and range information possible. 
         [0025]    Outer sensors  104   a  and  104   b  and inner sensors  108   a  and  108   b  may be ultrasonic sensors as are known. Other types of sensors may be used as appropriate such as highly collimated light beam (e.g., laser) sensors, optical sensors, interferometers, etc. Outer sensors  104   a  and  104   b  and inner sensors  108   a  and  108   b  may be controlled via control circuitry of the sensing unit  100  (e.g., controller  400 ), by an external source, or by any other appropriate method. Outer sensors  104   a  and  104   b  and inner sensors  108   a  and  108   b  may be configured to measure a respective distance from the sensor to a surface and/or object. That is, outer sensors  104   a  and  104   b  and inner sensors  108   a  and  108   b  are used to measure a distance from the sensing unit  100  to a surface. 
         [0026]    Temperature bar  110  may be a rod, shaped wire, substantially U-shaped bar, support means, etc. of any appropriate length secured to the sensing unit  100  via a flexible connection  112  or secured directly to the sensing unit  100 . Flexible connection  112  may be a spring, hinge, pivot, or other flexible apparatus to secure temperature bar  110  to the housing  102 , but also to allow temperature bar  110  to be moved. In some cases, temperature bar  110  may be moved manually (e.g., secured by a user to catch  116 ). In other cases, temperature bar  110  may be moved in response to an obstacle. That is, in the course of operation, the temperature bar  110  and/or temperature detector  114  may contact an obstacle (e.g., a road surface, rock, debris, etc.) and the flexible connection  112  may allow the temperature bar  110  to move (e.g., swing and/or bend) out of the way of the obstacle without breaking off as in prior rigid extended temperature sensors. In some embodiments, temperature bar  110  may itself be flexible such that it is capable of bending, flexing, and/or moving as when encountering an obstacle or acted upon (e.g., pushed) by an outside force. 
         [0027]    Temperature-detector  114  may be a temperature sensor. Similarly, temperature bar  110  may be a temperature sensor and/or may be adapted to transmit temperature information from the temperature detector  114  to a controller  400  of  FIG. 4  or other appropriate location as discussed above. In operation, the temperature detector  114  (or the temperature bar  110  if no temperature detector  114  is used) may measure a temperature near a surface and/or may measure one or more temperatures of air between the sensing unit  100  and a surface. 
         [0028]    Temperature sensor  118  may be an infrared sensor capable of measuring a temperature at and/or near to a surface and transmitting the temperature information to the sensing unit  100  and/or another appropriate location. Similar to temperature detector  114  and temperature bar  110 , temperature sensor  118  may also be capable of measuring one or more temperatures of air between the sensing unit  100  and a surface. In some embodiments, the temperature sensor  118  may be capable of triggering an alarm condition when a detected temperature is outside of a predetermined temperature range. That is, temperature sensor  118  (or similarly temperature bar  110  and/or temperature detector  114 ) may be configured to transmit temperature information to controller  400 . The temperature information may be used to indicate (e.g., by controller  400 ) an alert condition (e.g., surface too hot, a temperature difference between the sensing unit  100  and the work surface, etc.). Temperature sensor  118  may also be any other appropriate type of sensor. 
         [0029]    In some embodiments, temperatures determined using temperature bar  110  and/or temperature detector  114  (e.g., a temperature of air between sensing unit  100  and a surface) and temperatures determined using temperature sensor  118  (e.g., a temperature at or near to the surface) may be used in combination to estimate a curve of air temperatures between the sensing unit  100  and the surface. For example, sensing unit  100  and/or controller  400  of  FIG. 4  may utilize one or more temperatures determined using temperature bar  110 , temperature detector  114 , and/or temperature sensor  118  to approximate a distribution of the actual air temperatures between the sensing unit  100  and the surface. 
         [0030]      FIGS. 2A and 2B  depict an alternative exemplary sensing unit  200  according to an embodiment of the present invention.  FIG. 2A  shows a bottom perspective view of the sensing unit  200  with an extended temperature bar  210  and FIG.  2 B shows a bottom perspective view of the sensing unit  200  with a folded temperature bar  210 . The sensing unit  200  may be similar to sensing unit  100  of  FIGS. 1A and 1B  and accordingly comprises similar components. For simplicity of presentation, only those components of sensing unit  200  that differ from sensing unit  100  are discussed in further detail. Substantially similar components of sensing unit  200  are referred to hereinafter and in  FIGS. 2A and 2B  by the same reference numerals. 
         [0031]    In the embodiment depicted in  FIGS. 2A and 2B , sensing unit  200  includes a temperature bar  210  protruding from the bottom surface  106 . The temperature bar  210  may be coupled (e.g., attached) to the sensing unit  200  via a flexible or otherwise moveable, rotatable, and/or detachable connection  212  and may include a temperature detector  214 . As shown in  FIG. 2B , a portion of temperature bar  210  may be securable to the housing  102  at one or more catches  216  when the temperature bar  210  and/or the temperature detector  214  is not in use, when the sensing unit  200  is being transported, etc. Temperature bar  210  may additionally or alternatively be secured to the housing  102  at other locations along its length using other catches or any other appropriate securing means. 
         [0032]    In the exemplary embodiment of  FIGS. 2A and 2B , temperature bar  210  may be a rod, shaped wire, or substantially U-shaped bar of any appropriate length secured to the sensing unit  200  via flexible connection  212 . In some embodiments, temperature bar  210  may be a  3  mm steel wire shaped into an approximately U-shaped configuration and including a crossbar  218  near the “open” end of the U-shaped wire. Temperature bar  210  may be secured to the housing  102  at the crossbar  218  such that a portion of the length of temperature bar  210  is free to pivot away from the housing  102  as shown in  FIG. 2B . Of course, other configurations and materials may be used. For example, a temperature detector  214  may be secured between multiple temperature bars  210  moveably secured to sensing unit  200 .  FIGS. 1A ,  1 B,  2 A, and  2 B depict exemplary configurations of temperature bars, but any appropriate temperature sensing mechanism and/or means may be used in their stead. 
         [0033]    Flexible connection  212  may be a spring, hinge, pivot, or other flexible and/or moveable apparatus to secure temperature bar  210  to the housing  102 , but also to allow temperature bar  210  to be moved. In at least one embodiment, flexible connection  212  may include multiple components to secure the temperature bar  210 . For example, a clasp, pin, bar, or other means for securing may be used to hold the crossbar  218  of  FIGS. 2A and 2B  to the bottom surface  106 , but allow rotational movement of the crossbar  218 ; this allows the temperature bar  210  and temperature detector  214  to be capable of pivoting, but holding the temperature bar fast to sensing unit  200 . In some cases, temperature bar  210  may be moved manually (e.g., secured by a user to catch  216 ). In other cases, temperature bar  210  may be moved in response to an obstacle. That is, in the course of operation, the temperature bar  210  and/or temperature detector  214  may contact an obstacle (e.g., a road surface, rock, debris, etc.) and the flexible connection  212  may allow the temperature bar  210  to move (e.g., swing and/or bend) out of the way of the obstacle without breaking off as in prior rigid extended temperature sensors. In some embodiments, temperature bar  210  may itself be flexible such that it is capable of bending, flexing, and/or moving as when encountering an obstacle or acted upon (e.g., pushed) by an outside force. 
         [0034]    Temperature detector  214  may be a temperature sensor. Similarly, temperature bar  210  may be a temperature sensor and/or may be adapted to transmit temperature information from the temperature detector  214  to a controller  400  of  FIG. 4  or other appropriate location as discussed above. In operation, the temperature detector  214  (or the temperature bar  210  if no temperature detector  214  is used) may measure a temperature near a surface and/or may measure one or more temperatures of air between the sensing unit  200  and a surface. 
         [0035]      FIG. 3  depicts a side schematic layout of the sensing unit  100  according to an embodiment of the present invention. Various diameters and frequencies of sensors may be used in operation of the sensing unit  100 .  FIG. 3  is presented as an illustrative embodiment to show the interaction of multiple sensors and is not meant to limit the invention to a single set of outer sensors  104   a  and  104   b  of a specific diameter or a single set of inner sensors  108   a  and  108   b  of a specific diameter. 
         [0036]    In the exemplary embodiment of  FIG. 3 , outer sensors  104   a  and  104   b  may have a diameter A and a frequency f A . In one embodiment, the diameter A may be substantially  25  mm and the frequency f A  may be approximately 120 kHz. Similarly, inner sensors  108   a  and  108   b  may have a diameter B and a frequency f B . In one embodiment, the diameter B may be substantially 16 mm and the frequency f B  may be approximately 200 kHz. Each of sensors  104   a  and  104   b  and  108   a  and  108   b  may be separated by a center-to-center distance (e.g., approximately C). In practice, larger diameter sensors generate a wider radiation cone while smaller diameter sensors generate a narrower radiation cone. The distance C between sensors is preferably such that at the minimum advantageous reading distance L (discussed below) all radiation cones very slightly overlap. Though depicted here as pairs of sensors having equal diameters and frequencies, it may be understood that each sensor may have its own unique diameter and/or frequency. As discussed generally above, temperature bar  110  may be a length L, extending from the bottom surface  106 . 
         [0037]    In some embodiments, a controller  400  may be included and may be or may include any components or devices which are typically used by, or used in connection with, a computer or computer system. Such a controller may be control circuitry as described with respect to  FIGS. 1A and 1B , reside at another location in the sensing unit  100 , and/or be associated with (e.g., be in communication with and/or coupled to) the paving vehicle  602  discussed below with respect to  FIG. 6 . 
         [0038]      FIG. 4  is a schematic drawing of a controller  400  according to an embodiment of the invention. Controller  400  contains a processor  402  which controls the overall operation of the controller  400  by executing computer program instructions which define such operation. The computer program instructions may be stored in a storage device  404  (e.g., magnetic disk, database, etc.) and loaded into memory  406  when execution of the computer program instructions is desired. Thus, applications for performing the herein-described method steps, such as weighting measured distances (step  508  of method  500 ) and determining calculated distance (step  510  of method  500 ), are defined by the computer program instructions stored in the memory  406  and/or storage  404  and controlled by the processor  402  executing the computer program instructions. The controller  400  may also include one or more network interfaces  408  for communicating with other devices via a network (e.g., a Controller Area Network (CAN)). These devices may be other sensing units  100 ,  200 , other controllers  400 , or any other relevant device. The controller  400  also includes input/output devices  410  (e.g., display, keyboard, mouse, speakers, buttons, etc.) that enable user interaction with the controller  400 . Controller  400  and/or processor  402  may include one or more central processing units, read only memory (ROM) devices and/or random access memory (RAM) devices. One skilled in the art will recognize that an implementation of an actual controller could contain other components as well, and that the controller of  FIG. 4  is a high level representation of some of the components of such a controller for illustrative purposes. 
         [0039]    According to some embodiments of the present invention, instructions of a program (e.g., controller software) may be read into memory  406 , such as from a ROM device to a RAM device or from a LAN adapter to a RAM device. Execution of sequences of the instructions in the program may cause the controller  400  to perform one or more of the method steps described herein, such as those described below with respect to methods  500  and  700 . In alternative embodiments, hard-wired circuitry or integrated circuits may be used in place of, or in combination with, software instructions for implementation of the processes of the present invention. Thus, embodiments of the present invention are not limited to any specific combination of hardware, firmware, and/or software. The memory  406  may store the software for the controller  400 , which may be adapted to execute the software program and thereby operate in accordance with the present invention and particularly in accordance with the methods described in detail below. However, it would be understood by one of ordinary skill in the art that the invention as described herein could be implemented in many different ways using a wide range of programming techniques as well as general purpose hardware sub-systems or dedicated controllers. 
         [0040]    Such programs may be stored in a compressed, uncompiled and/or encrypted format. The programs furthermore may include program elements that may be generally useful, such as an operating system, a database management system and device drivers for allowing the controller to interface with computer peripheral devices, and other equipment/components. Appropriate general purpose program elements are known to those skilled in the art, and need not be described in detail herein. 
         [0041]    In operation, sensing units  100 ,  200  may be used to determine a distance from the sensing unit  100 ,  200  to a surface S.  FIG. 5  illustrates the method steps of a method  500  of ultrasonic sensing using the sensing unit  100 ,  200  and will be described in conjunction with  FIG. 3 . The method begins at step  502 . 
         [0042]    In step  504 , distances to a surface are measured using sensors. For example, outer sensors  104   a  and  104   b  and inner sensors  108   a  and  108   b  each measure a respective distance D 1 , D 2 , D 3 , and D 4  to a surface S as shown in  FIG. 3 . Specifically, sensor  104   a  measures distance D 1 , sensor  108   a  measures distance D 2 , sensor  108   b  measures distance D 3 , and sensor  104   b  measures distance D 4 . 
         [0043]    In step  506 , temperatures are measured. In some embodiments, a temperature may be measured by, for example, temperature bar  110 , temperature detector  114 , and/or temperature sensor  118 . In such embodiments, the temperature may be a temperature in the vicinity of a work surface. Additionally and/or alternatively, temperatures may be measured in more than one location (e.g., at the work surface, midway between the work surface and sensing unit  100 , and at sensing unit  100 , etc.). In this way, temperature variations may be measured. 
         [0044]    In step  508 , the measured distances (e.g., D 1 -D 4 ) are weighted. As is known, measurement devices (e.g., sensors) may be more or less accurate under certain conditions. In the context of the present invention, range sensors of a smaller diameter may be more accurate when close to a surface than range sensors of a larger diameter. Similarly, the larger diameter range sensors may be more accurate than the smaller diameter range sensors at a greater distance to the surface. Accordingly, it may be preferable to give more account to the sensors that are more likely to be more accurate at a certain distance. In this way, the input of multiple sensors may be used in determining the distance from the sensors to the surface while taking into account the likelihood that the inputs (e.g., measured distances) are accurate. 
         [0045]    In some embodiments, the distances are weighted based on the distance from the sensors (e.g., sensors  104   a,    104   b,    108   a,  and  108   b ) to the surface S. This may be an approximate predetermined distance that may be input by a user, may be known at controller  300 , and/or may be approximated based on the measured distances. That is, sensors  104   a,    104   b,    108   a,  and  108   b  may each measure a distance to the surface S and the approximate predetermined distance may be determined using these initial measurements. 
         [0046]    In the same or alternative embodiments, when the surface S is greater than a distance L (e.g., the closest the sensing unit  100  can be to the surface S without impacting temperature bar  110  and/or temperature detector  114 ) and less than a maximum advantageous sensing distance of the inner sensors  108   a  and  108   b,  the distances measured by the inner sensors  108   a  and  108   b  (e.g., distances D 3  and D 4 ) are weighted by a factor of X (e.g., X(D 3 ) and X(D 4 ), X(D 3 +D 4 ), etc.). In an alternative embodiment, each measured distance has its own weighting factor (e.g., X 1 (D 3 ), X 2 (D 4 ), etc.). 
         [0047]    In practical application, the minimum sensing distance may be limited by the function of the chosen sensor and not the length L of the temperature bar  110 . That is, the minimum sensing distance may be limited by the abilities of the sensors and the related electronics. 
         [0048]    In the example described herein, inner sensors  108   a  and  108   b  have a diameter B of 16 mm and a frequency f B  of 200 kHz and a minimum sensing distance (e.g., the minimum distance at which an acceptably stable reading may be achieved) of approximately 20 cm and a maximum advantageous sensing distance of approximately 40 cm. When the surface S is further away than the maximum advantageous sensing distance of the inner sensors  108   a  and  108   b  (e.g., approximately 40 cm), the distances measured by the outer sensors  104   a  and  104   b  (e.g., distances D 1  and D 2 ) are weighted by a factor of Y (e.g. Y(D 1 ) and Y(D 2 ), Y(D 1 +D 2 ), etc.). In an alternative embodiment, each measured distance has its own weighting factor (e.g., Y 1 (D 1 ), Y 2 (D 2 ), etc.). Of course, other inner sensors,  108   a  and  108   b  and/or outer sensors  104   a  and  104   b  with different respective diameters A and B and/or frequencies f A  and f B  may be used. In such cases, different minimum sensing distances and maximum advantageous sensing distance may be used. 
         [0049]    In an exemplary embodiment, when sensing unit  100  is relatively far from the surface (e.g., greater than approximately 50 cm), the distances measured by the outer sensors  104   a  and  104   b  (e.g., distances D 1  and D 2 ) are each weighted by a factor of 50% and the distances measured by the inner sensors  108   a  and  108   b  (e.g., distances D 3  and D 4 ) are each weighted by a factor of 0%. Similarly, when the sensing unit  100  is relatively close to the surface (e.g., less than approximately 25 cm), the distances measured by the inner sensors  108   a  and  108   b  (e.g., distances D 3  and D 4 ) are each weighted by a factor of 50% and the distances measured by the outer sensors  104   a  and  104   b  (e.g., distances D 1  and D 2 ) are each weighted by a factor of 0%. When the sensing unit  100  is positioned at intermediate distances (e.g., between approximately 25 cm and approximately 50 cm), the relative weights for each sensor varies linearly with the distance from the surface. Of course, other variation gradients and/or weights may be used for various distances from the surface. 
         [0050]    Measured distances D 1 -D 4  may be weighted based at least in part on a measured temperature. That is, an additional weighting factor may applied to one or more of the measured distances to account for variations in temperature between the sensing unit  100  in the region of the sensors  104   a,    104   b,    108   a,  and  108   b  and the surface S. Since each sensor may be affected differently by variations in temperature, each sensor may have its own weighting factor. Similarly, equal weighting factors may applied to similar sensors (e.g., the same weighting factor for sensors  104   a  and  104   b  and a different weighting factor for sensors  108   a  and  108   b,  etc.). 
         [0051]    In step  510 , a calculated distance is determined. In some embodiments, a weighted average distance is calculated. The weighted measured distances may be averaged to determine an approximate calculated distance (ACD). Thus, in the above example: 
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                                     2 
                                   
                                 
                                 ) 
                               
                             
                             + 
                             
                               ( 
                               
                                 
                                   D 
                                   3 
                                 
                                 + 
                                 
                                   D 
                                   4 
                                 
                               
                               ) 
                             
                           
                           4 
                         
                         , 
                       
                     
                     
                       
                         
                           if 
                            
                           
                               
                           
                            
                           estimated 
                            
                           
                               
                           
                            
                           A 
                            
                           
                               
                           
                            
                           C 
                            
                           
                               
                           
                            
                           D 
                         
                         &gt; 
                         
                           40 
                            
                           
                               
                           
                            
                           cm 
                         
                       
                     
                   
                 
                 . 
               
             
           
         
       
     
         [0052]    It is understood that the weighting factors X and Y may be the same, may be of any value (e.g., 0, 0.5, 1, 2, etc.), and/or may be predetermined and/or continually re-determined. If more or less sensors are used, different and/or additional weighting factors may be used. Similarly, a weighting factor based on the one or more measured temperatures may also be used in the calculation of the distance to the surface. 
         [0053]    Following step  510 , the method  500  may return control to step  504 . That is, a new distance may be measured by one or more sensors to be used in calculation of a weighted average distance (e.g., ACD). This method may be repeated continually in real-time to provide a constant updated of the distance to the surface for use in construction operations. 
         [0054]    In step  512 , the method  500  ends. 
         [0055]      FIG. 6  depicts a top schematic view of a paving system  600  for distance and/or temperature sensing according to an embodiment of the present invention. The system  600  comprises a paving vehicle  602 . Paving vehicle  602  may be a construction vehicle for use in road paving and/or construction or may be any other type of movable and/or stationary platform. Coupled to paving vehicle  602  may be one or more sensing units  100  as described above.  FIG. 6  also shows a first lane of road  604 , a second lane of road  606 , and the joint  608  between them. In operation, the paving vehicle  602  may be used in ultrasonic distance sensing, temperature measurement, and/or related construction tasks such as road paving. 
         [0056]    For illustrative purposes,  FIG. 7  illustrates the method steps of a method  700  of paving. The method begins at step  702 . 
         [0057]    In step  704 , the paving vehicle  602  paves a first section of road (e.g., first lane  604 ). In some embodiments, the paving vehicle  602  paves a lane of road at a time. When laying asphalt (e.g., paving) on a first lane  604 , the joint  608  of asphalt exposed to a future second lane  606  (e.g., the section to be asphalted) may cool. This may prevent the second lane  606  from properly bonding with the first lane  604 . 
         [0058]    In step  706 , a temperature of a road surface is measured. In some embodiments, the temperature bar  110 , temperature detector  114 , and/or temperature sensor  118  will measure the temperature of the asphalt on the first lane  604 . Any of these or other sensors may be used to measure such a temperature as appropriate. 
         [0059]    In step  708 , the suitability of the measured temperature for paving operation is determined. If the road surface is an unsuitable temperature, an alarm condition is triggered in step  710 . In step  712  corrective action is taken. In at least one embodiment, the alarm condition may comprise an indication to heat the joint  608  (e.g., the corrective action of step  712 ) using an appropriate method or may be transmitted to a user by controller  400  (e.g. via input/output device  410 ). After corrective action is taken, the method passes to step  706  to re-measure the surface temperature and/or to step  714 . If the road surface temperature is measured as a suitable temperature, the method passes control to step  714 . 
         [0060]    In step  714 , a second section of road (e.g., second lane  606 ) is paved by the paving vehicle  602 . The method ends at step  716 . 
         [0061]    The foregoing description discloses only particular embodiments of the invention; modifications of the above disclosed methods and apparatus which fall within the scope of the invention will be readily apparent to those of ordinary skill in the art. For instance, it will be understood that, though discussed primarily as a stand-alone unit with one set of inside sensors and one set of outside sensors, any number and/or type of sensors in any suitable arrangement may be used with a corresponding weighting and/or calculating algorithm. Similarly, other components may perform the functions of methods  500  and  700  even when not explicitly discussed. 
         [0062]    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. Those skilled in the art could implement various other feature combinations without departing from the scope and spirit of the invention.