Measuring device
This is a continuation of application Ser. No. 06/305,155, filed Sept. 24, 1981. 
    
    
     BACKGROUND OF THE INVENTION 
     This invention relates to measuring devices and more particularly a density measuring device which permits continuous operation as it traverses the surface of the material whose density is being measured. 
     In certain paving operations, such as, for example, when a layer of asphalt is applied to a pre-existing concrete roadway, the asphalt is commonly applied with a paver which lays the material at a preselected thickness. Typically, a roller is then employed for compacting the material. The actual density of the asphalt will be influenced by a number of factors, including the vibration frequency and amplitude of the compactor, ballast, the forward travel speed, the temperature of the material, the degree of overlap, the number of roller passes and roller travel speed, and the reaction surface to which the material is being applied. The thickness of the material being applied may also affect the efficiency of the compactor and therefor, influence density. 
     It is important to know the material density to prevent over-rolling. This occurs when the maximum density of the material has been attained and further compaction thereafter tends to loosen the material. Also, in the compaction of asphaltic concrete, it is important to know how close the compactor can approach the asphalt paver and how far behind it can traverse before chilling is encountered. If the compactor is too close to the paver, the hot material displaces and cannot be compacted. On the other hand, if the roller trails the compactor by too great a distance, the material will cool excessively at the far end of the traverse so that compaction in that area is also not possible. 
     It is, therefore, desirable to provide a method for rapidly and accurately determining the density of an applied layer while it was still hot so that corrections in the compacting operation can be made to eliminate the necessity for costly reworking. 
     SUMMARY OF THE INVENTION 
     It is an object of the invention to provide new and improved apparatus for measuring density. 
     A more specific object of the invention is to provide a density measuring apparatus which continuously measures the density of material as the apparatus traverses the material surface. 
     These and other objects and advantages of the invention will become more apparent from the detailed description thereof taken with the accompanying drawings. 
     In general terms, the invention comprises density measuring device having a hollow, rotatably mounted roller and a shielded radioactive source and a detector mounted within the roller and at a substantially fixed distance from the surface of the material whose density is being measured as the roller moves therealong. In the preferred embodiment the roller is universally mounted to permit the roller to conform to uneven surfaces. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 shows one example of a mobile device in which the density measuring apparatus of the invention may be mounted; 
     FIG. 2 is a side elevational view, partly in section, of the density measuring device according to the preferred embodiment of the invention; 
     FIG. 3 is a cross-sectional view taken along lines 3--3 of FIG. 2; 
     FIG. 4 is the top plan view of the density measuring device shown in FIG. 2; and 
     FIG. 5 is the side elevational view of the density measuring device shown in FIG. 2. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     FIG. 1 shows the measuring device 10 according to the preferred embodiment of the invention to be mounted on a manual transporter 12. In general terms, the measuring device includes a cylindrical roller 14 mounted for rotation on a shaft 16 which in turn is supported on a bracket assembly 18 carried adjacent the front end of the base 20 of transporter 12. A radiation source 21 and detectors 22 and 23 are supported within the roller 14 (see FIG. 5) as will be discussed more fully below. At the rear of the base 20 there are a pair of spaced apart wheels 24 and an upwardly extending frame 25&#39; which terminates in 25. A microprocessor, a counter and a control panel 26 are mounted adjacent the upper end of frame 25&#39; and are connected to the detectors 22 and 23 by conductors 27. It will be appreciated that the handle 25 and wheels 24 permit the assembly to be maneuvered and moved in any direction over the surface 82 of the material being measured. It will also be evident that by tipping the assembl back onto the wheels 24, the measuring device 10 may be transported independently of the roller 14. 
     The roller 14 is shown more specifically in FIGS. 2 and 3 to comprise a hollow, cylindrical member 30 and a pair of relatively thick annular end members 32 which are suitably secured to the cylindrical member 30 and provide a stiffening thereto. There are also an annular end cap 33 secured to each member and each supports a by suitable bearing 34 which rotatably support the roller 14 on the shaft 16. The shaft 16, the cylindrical member 30, the members 32 and the end caps 33 are preferably fabricated of the lightweight metallic material, such as aluminum. The surface of member 30 may also be coated with a material such as teflon so as to minimize the tendency of asphalt and other materials to adhere to its surface. 
     As seen in FIGS. 2, 4 and 5, the bracket 18 includes a generally rectangular top plate 36 and a pair of depending triangular side plates 38. A set of quick release clamps 40 secures the shaft 16 to the lower end of side plates 38 and in general parallels them with the top plate 36. In particular, each clamp 40 includes a top, downwardly facing jaw member 42 affixed to the lower corner of its associated side plate 38 and engaging the upper portion of shaft 16 and an upwardly facing lower jaw member 44 which engages the lower portion of shaft 16. The members 42 and 44 are interconnected by a pair of screws 46 which extend through suitable aligned openings formed in the ends of each clamp member and secured by nuts 48. The clamps 40 permit the rapid release of the shaft 16 from the bracket 18 so that the roller 14 and its radioactive source can be safely stored when not in use. 
     The bracket 18 is mounted on the base 20 by means of a universal support assembly 50 which permits the roller 14 to pivot three dimensionally so that it may follow the contour of the surface being traversed. More particularly, the assembly 50 includes a frame 52 which is connected to the base 20 for pivotal movement about a first axis 54 and which supports the bracket 38 for pivotal movement about second and third axes 55 and 56 lying in planes perpendicular to each other and to the first axis. 
     The frame 50 comprises a pair of parallel spaced-apart plates 58 and 60 which are interconnected by side portions 62. A hollow, rectangular rod 64 is disposed between plates 58 and 60 has a pair of appertured members 65 affixed to one end and disposed between a pair of spaced-apart appertured bracket members 68 mounted at the front of the carriage base 20. A pin 70 extends through the appertures in the members 65 and the bracket 68 and defines the first pivot axis 54. A second pin 72 extends upwardly from rod 64 at a point adjacent its opposite end and is received in a slot 74 formed in plate 58. The pin 72 defines the second pivot axis 55. Finally, a third pin 74 which defines the third pivot axis 56 extends through brackets 76 affixed in spaced-apart relation and extending downwardly from the plate 60. The pin 74 also extends through appertures formed-in-hinge members 78 affixed to the upper surface of plate 36. 
     Those skilled in the art will appreciate that the frame 52 and roller 14 supported thereby can pivot about the first axis 54 of pin 68 while the frame and roller can swivel on pin 72 relative to rod 64 and that the roller 14 can pivot about axis 56 of pin 74 or relative to frame 52. In this manner, the roller 14 is free to follow the contour of the surface of the material being traversed. In addition, the pin 72 and slot 74 permits the frame 50 and roller 14 to be repositioned relative to the base 20 to facilitate forward or rearward rolling movement relative to surface 82. 
     As seen in FIGS. 2 and 3, the source 21 and the detectors 22 and 23 are mounted on shaft 16 by means of a support assembly 80 such that the source and detectors will remain a relatively fixed distance above the surface 82 of the material being measured as the roller 14 is rolled therealong. More specifically, the assembly 80 includes a pair of elongated support members 84 and 86 which are generally L-shaped in vertical section and are respectively defined by short legs 87 and 88 and long legs 89 and 90. The member 84 is affixed to shaft 60 with its short leg 86 engaging the upper-most portion of shaft 16 and leg 89 extending downwardly along one side and in engagement therewith. In addition, member 86 is mounted with its short leg 88 engaging the leg 87 and its long leg 90 extending downwardly along the opposite sides of shaft 16. A plurality of screws 92 affix the members 84 and 86 to the shaft 60 so that the legs 89 and 90 extend vertically downwardly in a generally parallel, spaced relation. Disposed in the gap between the lower ends of legs 89 and 90 is an elongate, generally rectangular in section, shield 94 which is formed of any suitable material such as lead. The shield 94 is suitably secured in this position in any suitable manner, such as by screws 95. The source 21 is disposed in a first cavity 96 formed in shield 94. An opening 98 in the lower end of cavity 96 exposes the surface 82 immediately below the source 22 to the radiation emitting from source 21 while the shield 94 prevents radiation upwardly and to the sides. The first detector 23 is similarly disposed in a recess 100 in shield 92 and there is a similar opening 102 in the lower end of the shield which permits reflected or scattered radiation from the source 22 to impact the detector 22. Detector 23 on the other hand is positioned on the leg 90 exteriorly shield 92 and adjacent to the source 22. Electrical conductors 104 and 106 are connected to conductors 22 and 23 respectively and extend therefrom to the interior of shaft 16 from which they emerge at one end for connection to the counter, microprocessor and control panel 26. 
     It will be appreciated that as the roller 20 is rolled across the surface of the material being measured, the source 21 in the detectors 22 and 23 will remain in a relatively fixed distance above the surface 82 of the material. It will also be appreciated that because the assembly rests on rollers 20 and 24, the source and detector will remain in a perpendicular orientation relative to the surface 82 as the cart 12 is moved. 
     Those skilled in the art will appreciate that when a layer of asphalt, for example, is being applied to a base layer of another material, such as concrete, it is common to employ a device such as a paver, which is preset to apply material at predetermined thickness. To achieve the desired density, the asphaltic material must be compacted by making a number of passes over the asphalt layer with a heavy roller, for example. However, because of variables, such as temperature, ballasts, the surface to which the material is being applied, the frequency of vibration of the compactor and the number of roller passes, actual density of the material may vary. The deviation of any of these variables from optimums can substantially affect rolling times. The density measuring apparatus shown in accordance with a preferred embodiment of the invention can be used in conjunction with the roller to measure the material density as the roller is traversing its surface so that rapid adjustments can be made to insure compliance with specifications. In addition, adjustments in the variable factors can be made so as to minimize rolling times. Further, the device according to the invention permits the source 21 to be located relatively close to the surface 82 for safety and economy. 
     More specifically, the thickness of the top layer of asphalt material is first determined from the specifications, and that information is provided to the microprocessor 26. The microprocessor will also be provided with an instrument constant which is determined when the device is manufactured and which will depend upon the nature and strength of the source 21, the geometry of the apparatus and the sensitivity of the detectors 22 and 23 and will vary slightly from instrument to instrument. 
     Before the layer of material whose density is to be measured is applied, the density measuring device will be employed to provide an average density measurement for the sub-layer. This information will also be provided to the microprocessor for determination of density in a well-known manner. After the material laying apparatus has applied the surface layer and the same has been partially compacted by a roller, the manual transporter 12 will be passed over the surface and continuous reading of density will appear on the instrument panel 26 whereby the operator can immediately determine what further compacting or adjustments, if any, is required. Density is measured by the air-backscatter and will be calculated by the microprocessor in accordance with the method disclosed in U.S. patent application No. 227,913 filed Jan. 23, 1981 and assigned to the assignee of the present invention. In addition, moisture may be measured in the conventional manner by the detectr 23. For example, the method employed by the Seaman Nuclear Series 100 Density/Moisture Meter may be employed. 
     While only single embodiment of the invention has been illustrated and described, it is not intended to be limited thereby. For example, instead of mounting the roller 16 on a manual transporter, the same could be mounted directly on a roller compacter and with the microprocessor, counter and instrument panel mounted in position for easy observation by the operator. In this manner, the operator of the roller could make direct readings and adjust his rolling passes accordingly. Also, instead of employing a radioactive source other well known types of radiation sources, such as, X-ray tubes, microwave generators, electric-magnetic devices and the like, may be employed.