Patent Publication Number: US-7717521-B2

Title: Metal detector for an asphalt milling machine

Description:
BACKGROUND OF THE INVENTION 
   The current invention relates to milling machines for milling asphalt or concrete in roads, sidewalks, parking lots, or other paved surfaces. While milling and resurfacing a paved surface, the milling machines often encounter metal objects which are covered partially or completely by the paved surface such as manhole covers or railroad tracks. In such circumstances, if the metal object isn&#39;t detected beforehand, the object, milling tools on the milling machine, or both may be damaged. In order to avoid this, a metal detector may be used to detect the objects before milling the paved surfaces. It may also be advantageous to know the size and depth of the metal objects. Some inventions of the prior art disclose metal detectors in combination with a pavement resurfacing machine. 
   U.S. Pat. No. 7,077,601 to Lloyd, which is herein incorporated by reference for all that it contains, discloses a machine for providing hot-in-place recycling and repaving an existing asphalt-based pavement, in which the pavement is first heated. 
   U.S. Pat. No. 5,786,696 to Weaver et al., which is herein incorporated by reference for all that it contains, discloses a metal detector which utilizes digital signal processing and a microprocessor to process buffers of information which is received at a periodic rate. The metal detector is able to determine the depth of a target by comparing the quadrature phase components received from first and second receive antennas. The size of the target is determined by reference to a look-up table based on the depth factor and the signal amplitude determined for the target object. 
   BRIEF SUMMARY OF THE INVENTION 
   In one aspect of the invention, a milling machine for milling a paved surface has milling tools connected to an underside of a body of the machine. At least one ferrous metal detector is attached to a front end of the machine. Electronic equipment is disposed within the machine and is in communication with the metal detector, the equipment being adapted to interpret feedback from the detector. 
   A detection range of the metal detector may be controlled by a variable voltage source. The metal detector may be adapted to determine a depth of a metal object. The metal detector may be adapted to determine the size of a metal object. The metal detector may be adapted to detect metal objects up to 1 foot deep. The metal detector may be vertically adjustable. The metal detector may be attached to the front end such that during operation the detector is positioned from 1 to 8 inches above the paved surface. The milling tools may be adapted to be automatically laterally adjusted in a closed loop system by the electronic equipment in response to feedback from the detector. 
   The metal detector may comprise a magnetic shielding intermediate the metal detector and the body, such that the detector is magnetically shielded from the body. The magnetic shielding may be made of a material selected from the group consisting of ferrite, aluminum oxide, chromium, nickel, copper, iron, molybdenum, alloys thereof, and any combination thereof. The magnetic shielding may be attached to the underside of the body. The magnetic shielding may comprise a relative magnetic permeability of at least 100. The magnetic shielding may focus a magnetic field from the detector in a predetermined direction. The magnetic shielding may comprise an open housing with a cross-section comprising a partial rectangular geometry, a partial polygonal geometry, a partial circular geometry, a partial elliptical geometry, a planar geometry, a u-shaped geometry, or any combination thereof. The metal detector may also be magnetically shielded from the milling tools. At least a portion of the detector may be disposed within the housing. 
   The machine may comprise at least two metal detectors positioned such that a detection range of a first detector extends farther into the surface than a detection range of a second detector. The machine may comprise a plurality of ferrous metal detectors arranged in a plurality of arrays, each array positioned at a different distance above the paved surface. The machine may comprise a plurality of ferrous metal detectors positioned at different angles. 
   In another aspect of the invention, a method for metal detection during milling of a paved surface comprises the steps of providing a milling machine having milling tools connected to an underside of a body of the machine and at least one ferrous metal detector attached to a front end of the machine; providing electronic equipment disposed within the machine and in communication with the metal detector, the equipment being adapted to interpret feedback from the detector; and applying a variable voltage to the detector, allowing the detector to detect metal objects over various ranges of depths. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a perspective diagram of an embodiment of a milling machine. 
       FIG. 2  is a cross-sectional diagram of another embodiment of a milling machine. 
       FIG. 2   a  is a perspective diagram of another embodiment of a milling machine. 
       FIG. 3  is an orthogonal diagram of an embodiment of a metal detector. 
       FIG. 4  is an orthogonal diagram of another embodiment of a metal detector. 
       FIG. 5  is an orthogonal diagram of another embodiment of a metal detector. 
       FIG. 6  is an orthogonal diagram of another embodiment of a metal detector. 
       FIG. 7  is an orthogonal diagram of another embodiment of a metal detector. 
       FIG. 8  is an orthogonal diagram of another embodiment of a metal detector. 
       FIG. 9  is an orthogonal diagram of another embodiment of a metal detector. 
       FIG. 10  is an orthogonal diagram of another embodiment of a metal detector. 
       FIG. 11  is a cross-sectional diagram of an embodiment of milling tools milling a paved surface. 
       FIG. 12  is a block diagram of an embodiment of electronic equipment in a milling machine. 
       FIG. 13  is a flowchart diagram of a method for metal detection during milling of a paved surface. 
   

   DETAILED DESCRIPTION OF THE INVENTION AND THE PREFERRED EMBODIMENT 
     FIG. 1  depicts a milling machine  100  which may be used to remove asphalt or concrete from a paved surface (see No.  200  in  FIG. 2 ). Milling tools  101  such as a milling drum are attached to an underside  102  of a body  103  of the milling machine  100 . A conveyer  104  is adapted to lift the millings off the surface. Typically the millings are loaded into a bed of a truck (not shown) where the millings may be hauled away. 
   The milling machine  100  also comprises at least one ferrous metal detector  105  attached to a front end  106  of the machine  100  adapted to detect ferrous metal objects, such as manhole covers, in the paved surface at a predetermined detection depth. The detector  105  may be attached at a distance far enough away from a body  103  of the machine  100  such that metal in the body  103  doesn&#39;t interfere with the metal detector  105 . The machine may comprise an extension  107  on the front end  106  of the machine  100  to which the metal detector  105  may be attached. The extension  107  may comprise wheels  108  and may be pivotally attached to the body  103 , which may allow the extension  107  to move along the paved surface such that the detector  105  may maintain a constant height above the paved surface. 
   Referring now to  FIG. 2 , the detection depth  201  of the metal detector  105  may be fixed based on a cutting depth  202  of the milling tools  101 . After the cutting depth  202  of the milling tools  101  is set, the detection depth  201  of the metal detector  105  may be set at or below the cutting depth  202 , such that the metal detector  105  may detect ferrous metal objects  203  which may interfere with the cutting of the milling tools  101 . The sensitivity of the metal detector  105  may also be adjustable such that only metal objects  203  large enough to affect the milling may be detected. The detector  105  may be positioned from 1 to 8 inches above the paved surface. In some embodiments, the metal detector  105  may be adapted to detect metal objects  203  up to 1 foot deep. In other embodiments, the metal detector  105  may be adapted to detect metal objects  203  up to 3 feet deep. The detector  105  may also be adapted to determine the size of the objects. 
   The detector  105  may emit a magnetic field  301  which extends into the surface  200 . As the detector  105  passes over a metal object  203 , the magnetic field  301  may induce a magnetic field in the object  203 , depending on the material of the metal object  203 . The detector  105  may then be able to detect the change in the magnetic field of the object  203 , which may indicate a first edge  210  of the object  203 . As the metal detector  105  continues to pass over the object  203 , the magnetic field of the object  203  may remain constant until the field  301  of the detector  105  reaches a second edge  215  of the object  203 , in which instance the magnetic field of the object  203  changes again and is sensed by the detector  105 . In such instances, the detector  105  may be able to determine the size of the object  203 . In embodiments where the object  203  comprises first and second edges  210 ,  215  proximate each other, the detector  105  may only briefly induce a magnetic field in the object  203 . 
   When a metal object  203  is detected which may interfere with the milling tools  101 , the milling tools  101  may be raised such that the milling tools  101  pass over the metal object  203 , as indicated by the vertical arrow  204 , which may prevent damage to the metal object  203  and/or the milling tools  101 . Other components such as a moldboard  205  may be raised to prevent damage as well. The components may be manually controlled by a machine operator or it may be automatically controlled by electronic equipment in a closed-loop system. 
     FIG. 2   a  is another embodiment of the milling machine with the detector  105  positioned between the front tracks  250  and the milling tools  101 . In some embodiments, the detector may be positioned between the front tracks. Shielding, such as the shielding described in  FIGS. 3-8  may be used to shield the affects from the milling tools, tracks, and frame of the milling machine. In some embodiments, the shielding may include an aluminum mesh cloth. 
   The detector may also be raised and lowered to maintain a constant distance from the paved surface. Sensors which may include SONAR, lasers, or optics, may be used to determined the distance. The detector may be repositioned through a closed loop system or it may be repositioned manually. In some embodiments, the position of the detector may be controlled hydraulically or electrically. 
   The machine  100  may comprise a magnetic shielding  300  intermediate the metal detector  105  and the body  103 , such that the detector is magnetically shielded from the body  103 , as in the embodiments of  FIGS. 3 through 6 . The magnetic shielding may be attached to the extension  107 . The shielding  300  may be adapted to focus a magnetic field  301  from the detector  105  in a predetermined direction. The shielding  300  may also shield the detector  105  from the extension  107 , which may allow electronics to be disposed within the extension  107 . The extension  107  may also be made of a non magnetic material. The magnetic shielding  300  may comprise an open housing  302  with a cross-section comprising a partial circular geometry  303 , a partial polygonal geometry  400 , a planar geometry  500 , a partial rectangular geometry  600 , a partial elliptical geometry, a u-shaped geometry, or any combination thereof. At least a portion of the detector  105  may be disposed within the housing  302 . 
   The shielding  300  may be made of a material selected from the group consisting of ferrite, aluminum oxide, chromium, nickel, copper, iron, molybdenum, alloys thereof, and any combination thereof. The shielding may comprise a relative magnetic permeability of at least 100. In some embodiments the relative magnetic permeability may be 2,000 to 30,000. Preferably, the relative magnetic permeability is large enough that the shielding prevents substantially all of the magnetic field of the detectors from metal objects on the machine. 
   The machine  100  may comprise a plurality of detectors  601 ,  602  positioned at different distances above the paved surface  200 , as in the embodiment of  FIG. 6 . As each detector  601 ,  602  passes over the metal object  203 , the detectors  601 ,  602  may or may not detect the object  203 , depending on the detection range  603 ,  604  of each detector  601 ,  602  and its distance above the surface  200 . This may allow the detectors  601 ,  602  to determine a depth of the metal object  203 . A first detector  601  may have a detection range  603  which is unable to detect the object  203 , whereas a second detector  602  may have a range  604  which is able to detect the object  203 . From this information, a general depth of the object  203  may be extrapolated. The accuracy of the information may be increased with more detectors. The machine may also comprise a plurality of detectors positioned at a same distance above the paved surface, but calibrated such that each detector has a different detection range, which may allow the detectors to determine the depth of the object. The detectors may also detect the object at a first power level, and then at subsequent power levels of greater or lower magnitude to determine the depth at which the object may be buried. If the depth is greater than the depth of cut of the milling tools then a decision may be made to mill over the object since the milling tools won&#39;t engage the object. However, if the object is determined to be within the depth of cut a decision to stop milling, raise the milling tools, or automatically shut off the milling machine may also be made. These decisions may be made manually or electronically through a closed loop system. 
   The metal detector  105  may be attached to a translatable arm  700 , as in the embodiment of  FIG. 7 . The arm  700  may be vertically adjusted such that the detection range of the detector  105  reaches the desired detection depth This may also be advantageous for determining the depth of objects in the surface  200 . 
   Another method for determining the depth of metal objects may be triangulation. The machine may comprise a plurality of detectors  801 ,  802  positioned at different angles, as in the embodiment of  FIG. 8 . A first detector  801  may be positioned on the extension  107  at a first known angle  803  with respect to the surface  200 , while a second detector  802  may be positioned at a second known angle  804  with respect to the surface  200 . The extension  107  may also comprise more detectors positioned at other angles for better accuracy. A plurality of detectors  801 ,  802  may also make it easier to determine the size of the object  203  and/or its shape. 
   The machine may comprise a plurality of detectors  105  arranged in an array  900 , as in the embodiment of  FIG. 9 . The array  900  of detectors  105  may be laterally translatable. This may allow the detectors  105  to detect metal objects over a wide pathway, such as on a road. The machine may also comprise a plurality of arrays  900  of detectors  105 , as in the embodiment of  FIG. 10 . The arrays  900  may be staggered such that no lateral gaps are present in the cumulative detection range of all the detectors. 
   The present invention may be used in a milling machine comprising a plurality of rotary bits  1100  as milling tools  101 , as in the embodiment of  FIG. 11 . The milling tools may be adapted to be automatically laterally adjusted in a closed-loop system. The detectors  105  may be in electrical communication with electronic equipment in the closed-loop system, such that feedback from the detectors may be used to automatically control the lateral positions of the milling tools. As the detectors pass over a metal object such as a manhole cover  1101 , the feedback from the detectors may be interpreted by a processor and stored in memory. Sensors may be positioned on the machine to determine how far the machine travels such that the electronic equipment may be able to determine when a detected metal object reaches the milling tools. The electronic equipment may comprise a controller in electrical communication with the milling tools adapted to control the lateral movement of the milling tools such that the tools may mill around the metal object. The controller may also control the rotation of the tools. The detector may be attached to the front end of the milling machine and proximate the milling tools. The metal detector may be magnetically shielded from the milling tools in addition to being shielded from the body of the machine. The shielding may be attached to the underside of the body. 
   Referring now to  FIG. 12 , the electronic equipment  1215  may comprise a controller  1200 ; a processor  1201 ; sensors  1202 , including motion sensors  1203  or torque sensors  1204 ; indicators  1205 , including lights  1206  or speakers  1207 ; memory  1208 ; wireless communication circuitry  1209 ; filters  1210 ; switches  1211 ; or power supplies  1212 , including constant or variable voltage/current sources  1213 ,  1214 . 
   The controller  1200  may control the way the electronic equipment  1215  interacts with mechanical devices such as the milling tools  101  or other elements on the machine. Processors  1201  may be used to process the information and feedback from the detectors  105  or sensors  1202  such as motion sensors  1203  on the machine or torque sensors  1203  on the milling tools for use in a closed-loop system or for use by an operator. The equipment  1215  may comprise memory  1208  for storing the information for use as the machine traverses the paved surface. The information may also later be used for statistical or analytical purposes, or when repaving the surface. When a metal object is detected, indicators  1205  may alert an operator with both lights  1206  and speakers  1207 . The electronic equipment  1215  may comprise wireless communication circuitry  1209  such that information gathered by the detectors  105  or sensors  1202  may be transmitted to a remote location. The equipment  1215  may comprise power supplies  1212  such as voltage or current sources  1213 ,  1214 , which may either be constant or variable for powering the detectors  105  or sensors  1202 . The equipment  1215  may also comprise filters  1210 , switches  1211 , or other electronic devices for performing such functions as determining the type of ferrous metal of the object. 
     FIG. 13  discloses a method  1300  for metal detection during milling of a paved surface, comprising the steps of providing  1305  a milling machine having milling tools connected to an underside of a body of the machine and at least one ferrous metal detector attached to a front end of the machine; providing  1310  electronic equipment disposed within the machine and in communication with the metal detector, the equipment being adapted to interpret feedback from the detector; and applying  1315  a variable voltage to the detector, allowing the detector to detect metal objects over various ranges of depths. 
   Whereas the present invention has been described in particular relation to the drawings attached hereto, it should be understood that other and further modifications apart from those shown or suggested herein, may be made within the scope and spirit of the present invention.