Abstract:
A method and apparatus for use with a satellite positioning system wherein the receive elements satellite positioning system receive antennas are maintained in an orientation with respect to the positioning system satellites in a way such that the strongest signals can be received from the greatest number of satellites. According to one embodiment, a housing of a positioning antenna is mounted in a gimbaled fashion onto a vehicle, such as an excavator. Such a gimbaled antenna maintains a horizontal orientation relative to a predetermined axis and, as a result, remains in a position to receive signals from positioning system satellites even during instances of high angular deflection of the antenna support, such as may occur during earth-moving operations.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates generally to satellite positioning systems and, more particularly, to antennas used with satellite positioning systems. 
     Various methods for machine control using position information from satellite positioning systems, such as the Global Positioning System (GPS), are known. In such methods, one or more satellite positioning system antennas are typically disposed on a vehicle, such as an earth-moving machine. Then the position of the antennas is determined using well-known positioning techniques in order to determine and control the positioning of the vehicle or various components of the vehicle, such as the various components of an earthmoving machine that are used in earthmoving operations. For example,  FIG. 1  shows one such one such earthmoving machine, an excavator, which is well known in the art. As shown in  FIG. 1 , excavators such as excavator  100  typically have a main body  101  with a vehicle operator cab  102 . Attached to the main body  101  is arm  103 , commonly referred to as a “boom”. Boom  103  is, in turn, attached to a second arm  104 , commonly referred to as a “stick.” Stick  104  may be adapted to hold different attachments. Here, stick  104  is attached, illustratively, to a bucket  105  for use in excavation/digging. Bucket  105  typically has prongs  106  attached to the leading edge of the bucket  105  that are used to break through ground and other materials to be excavated. Body  101  is attached to a base which is supported by, illustratively, tracks  107  that allow the excavator to move over a variety of surfaces. One skilled in the art will recognize that other bases have also been designed to be fixed in a single location and, therefore, have no tracks. Alternatively, some bases have been designed with wheels (instead of tracks) which may be desirable in different applications. Regardless the type of base, body  101  is typically attached to the base in a way such that body  101  is capable of rotating 360 degrees while the base remains stationary. Thus, the boom, stick and bucket are movable for digging or other purposes to all points around the base within a certain radius. One skilled in the art will recognize the bucket  105  may be moved with a high degree of flexibility within that given radius. For example, boom  103  may be raised or lowered by lengthening or shortening hydraulic pistons  108 , respectively. Similarly, stick  104  may be rotated about pivot point  109  to raise or lower bucket  105  by shortening or lengthening hydraulic piston  110 , respectively. Finally, bucket  105  may be rotated about pivot point  111  into a cupped or an open position by either lengthening or shortening hydraulic piston  112 . 
     Excavators, such as excavator  101  in  FIG. 1 , are useful for many applications. For example, excavators may be used in the digging of trenches, holes and foundations; demolition; general grading and landscaping; heavy lifting (e.g., lifting and placing pipes); river dredging; etc. Initially, the operation of such excavators was performed by skilled operators in conjunction with a ground crew, for example a crew of workers equipped with surveying instruments to ensure, for example, the correct dimensions of an illustrative foundation in the ground. This mode of operation continues to be in widespread use today. However, this mode of operation is time consuming and labor intensive. 
     In order to decrease the time and cost associated with earthmoving operations, there have been various attempts at automating the operation of excavators and other earthmoving machines. For example, in one method disclosed in U.S. Pat. No. 6,782,644 to Fujishima et al., a satellite-based navigation system, such as the well-known Global Positioning System (GPS) or the Global Orbiting Navigation Satellite System (GLONASS), is used to control an excavator by remote control. Other similar systems have also been used to precisely monitor the movement of excavators during earthmoving operations. 
       FIG. 2  shows a prior art excavator using satellite positioning to increase excavation accuracy. Specifically, antennas  201  and  202  are mounted on body  101  of excavator  100 . Using well known positioning techniques, the location of each antenna may be ascertained with a predetermined level of accuracy. The highest accuracy may typically be achieved with differential or real time kinematic (RTK) satellite positioning which uses a base station to help reduce the errors associated with received signals from positioning satellites. Such differential/RTK methods for reducing these errors are well known. Using such methods, the position of antennas  201  and  202  may be determined with a high degree of horizontal accuracy (illustratively plus or minus 5 millimeters) and vertical accuracy (illustratively plus or minus 12-18 millimeters). 
     Determining the precise locations of antennas  201  and  202  allows accurate determination of the orientation of the body  101  of the excavator  100 . For example, if one antenna is positioned lower than the other it would indicate that the body is tilted. Additionally, since the position of each antenna on the body of the excavator is known, determining the position of antenna  201  relative to the position of antenna  202  will provide an accurate measurement of the heading of body  101  of the excavator. Thus, using two antennas allows both tilt and heading measurements of the body  101 . However, simply knowing the tilt and heading of the body  101  is not sufficient for high-precision excavation. Instead, the precise orientation of the bucket  105  and, more particularly, the precise position and orientation of the leading (or cutting) edge of the bucket must be known. 
     Prior attempts have relied on various methods for determining the position and orientation of the leading edge of the bucket to facilitate precise excavation. For example, in one such method, angle sensors have been placed on the boom, stick and bucket linkage. Such angle sensors are also referred to herein interchangeably as inclinometers. Thus, referring once again to  FIG. 2 , sensor  203  is placed on body  101 , sensor  204  is mounted to boom  103 , sensor  205  is mounted on stick  104 , and sensor  206  is placed on bucket  105 . These sensors are calibrated for a given position of the cutting edge and or prongs of the bucket  105 . Thus, any angular movement of the sensor (i.e., movement of the associated portion) can be measured. The dimensions of the boom, stick and bucket are known, and the length from the positioning system antennas can be measured. Accordingly, for any angular change detected by sensors  203 - 206  in  FIG. 2 , the location of the cutting edge of bucket  105  can be geometrically calculated and excavation operations can be accurately performed in less time using fewer people than prior manual methods. 
     In another technique, satellite positioning antennas are mounted to the stick of an excavator. Such technique is described in copending U.S. patent application Ser. No. 11/108,013, filed Apr. 15, 2005, and titled Method and Apparatus for Satellite Positioning of Earth-Moving Equipment, which is incorporated by reference herein in its entirety. According to that technique, satellite inclinometers antennas are used to determine the position and orientation of the stick and, then by using geometric calculations with, for example, one or more angle sensors on the bucket, the precise location of a portion of an attachment of the excavator/backhoe, such as the prongs of a bucket, can be determined. 
     SUMMARY OF THE INVENTION 
     The present inventor has recognized that, while placing satellite antennas on the stick of an excavator is extremely advantageous and lowers cost, placing the antennas in such a position will subject those antennas to a wide range of motion. As a result of this wide range of motion, the orientation of the antennas may be such that the signal strength received from the positioning satellites by one or more of the antennas may fall below a threshold necessary for use in positioning calculations. In extreme cases, the signal may be lost entirely. As a result, critical real-time positioning calculations that are required during earthmoving operations may not be possible. 
     Therefore, the present inventor has invented a method and apparatus that allows the satellite antennas to be maintained in an orientation with respect to the positioning system satellites in a way such that the strongest signals can be received from the greatest number of satellites. In particular, the present inventor has invented an apparatus whereby a housing of a positioning antenna is mounted in a gimbaled fashion onto a vehicle, such as the aforementioned excavator. Such a gimbaled antenna maintains a horizontal orientation relative to a predetermined axis and, as a result, remains in a position to receive signals from positioning system satellites even during instances of high angular deflection of the antenna support, such as may occur during earth-moving operations. 
     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. 
    
    
     
       DESCRIPTION OF THE DRAWING 
         FIG. 1  shows an illustrative prior art excavator; 
         FIG. 2  shows an illustrative prior art excavator adapted to use a satellite positioning system; 
         FIG. 3  shows another illustrative prior art excavator adapted to use a satellite positioning system; 
         FIG. 4  shows how the illustrative excavator of  FIG. 3  may result in satellites in a satellite positioning system being out of view of satellite positioning system receive antennas; 
         FIG. 5  shows a satellite positioning system antenna in accordance with an embodiment of the present invention; 
         FIG. 6  shows how the antenna of  FIG. 5  may be used in excavation operations in accordance with an embodiment of the present invention; and 
         FIG. 7  shows an illustrative block diagram of a satellite positioning receiving system suitable for use with an excavator in accordance with the principles of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 3  shows a boom, stick and bucket assembly of an illustrative excavator such as that described above. The boom and stick are also referred to herein as “load-bearing arms”. Specifically, referring to  FIG. 3 , boom  301  is connected to stick  302  which is, in turn, attached to bucket  303 , as discussed above. However, unlike the previously discussed excavators that utilized a satellite positioning system to assist in the control of the machine, the antennas  305  and  306  are mounted on support structure  307  which is attached to stick  302  at illustrative point  308 . One skilled in the art will recognize that antennas  305  and  306  may be positioned in many different configurations. For example, the antennas may each be mounted separately on the stick. Additionally, while the antennas are shown mounted longitudinally along the stick, one skilled in the art will recognize that other mounting configurations are possible. 
     In the illustrative excavator of  FIG. 3 , in order to conduct excavation operations with a high degree of accuracy, it is necessary to know the position of bucket  303  with a high degree of accuracy and, more particularly, to know the position (e.g., the height/depth) of cutting teeth/prongs  304 . As discussed above, some prior methods required knowledge of the dimensions of several excavator portions as well as multiple angle sensors to determine the location of prongs  304 . More recently, however, as described above and disclosed in the 11/108,013 application, the precise determination of the position of the prongs  304  of bucket  303  can be determined by mounting the antennas directly on the stick, as shown in the illustrative embodiment of  FIG. 3 . 
     As one skilled in the art will recognize, antennas such as antennas  305  and  306  typically receive signals from a plurality of positioning system satellites such as those used in GPS or GLONASS systems. In many typical examples, the more satellites from which such antennas receive signals, the greater the potential accuracy of the calculated position of the antennas. However, the present inventors have recognized that, by mounting antennas, such as antennas  305  and  306  to the stick  302 , those antennas may be moved during earth moving operations to an orientation in which they cannot receive satellite signals from a satellite positioning system.  FIG. 4  shows such an orientation. Specifically, referring to that figure, excavator  401  which is, illustratively, conducting earth-moving operations, has stick  407  with antennas  402  attached to the stick. One skilled in the art will recognize that antennas such as illustrative antennas  402  typically are only capable of receiving a signal from certain directions. When a satellite is in certain positions relative to the antennas (i.e., below the field of view of the antenna), then the signal will not be of sufficient strength as received at a receiver connected to the antennas to permit reception of the signal. As shown in  FIG. 4 , antennas  402  are positioned in a way such that signals from satellites  404  are received with sufficient strength for positioning calculations while, on the other hand, satellites  406  are positioned relative to the antennas in a way such that the signals cannot be received with such sufficient strength to support positioning system calculations. As one skilled in the art will recognize, depending upon the relative positioning of satellites  404  and  406  with respect to the antennas  402 , the number and strength of signals received by antennas  402  may be insufficient to permit accurate positioning calculations. 
     Therefore, in accordance with an embodiment of the present invention, the present inventors have recognized that satellite positioning system antennas, such as antennas  402  in  FIG. 4 , can be attached to the stick or other component of an earth moving machine to allow a greater number of satellites remain in view of the antennas, even when the position of the equipment upon which the antennas are mounted changes. More particularly, in accordance with a particular illustrative embodiment, antennas such as antennas  402  can be can be attached in a way such that the antennas are permitted to change their three-dimensional orientation with respect to the stick of the earthmoving machine. In this way, when the stick of the earthmoving machine moves, the antennas can remain positioned so that, for example, signals from all of satellites  404  and  406  in  FIG. 4  are received with adequate strength to permit accurate positioning calculations. 
       FIG. 5  shows one illustrative embodiment of how an antenna housing, such as antenna housing  501  can be mounted to permit a change in orientation of the housing as the surface it is mounted on moves, as discussed above. Referring to that figure, antenna housing  501  is a housing containing, for example, a receiving antenna element of a positioning system antenna. Housing  501  is mounted in a gimbal structure consisting of support structure  503  and gimbal ring  502 . Support structure  503  is, for example, mounted to surface  504  which is, illustratively, a surface of the stick of an earthmoving machine, such as stick  407  of excavator  401  of  FIG. 4 . Antenna housing  501  is illustratively mounted to gimbal ring  502  in a way such that the housing  501  can rotate in directions  511  about axis  512 . Gimbal ring  502 , in turn, is mounted to support structure  503  in a way such that the gimbal ring can rotate in directions  510  about axis  513 . Accordingly, as one skilled in the art will recognize, when surface  504  moves in directions  508  and  509 , as well as in the y-direction in  FIG. 5 , gravitational force in direction  514  acting on the antenna housing will cause the gimbal ring  502  and antenna housing  501  to rotate about axes  512  and  513  in a way such that the antenna housing will remain substantially horizontal, i.e., parallel with the x-z plane. One skilled in the art will recognize that the antenna of  FIG. 5  is merely illustrative and that other variations are possible. For example, while the gimbaled antenna  501  of  FIG. 5  is capable of maintaining the antenna in a horizontal orientation with respect to multiple axes (i.e., the x and z axes in  FIG. 5 ), one skilled in the art will recognize that such a complex structure may not be necessary. More particularly, referring once again to  FIG. 3 , an antenna mounted to a stick of an excavator may experience a large range of motion in directions  309  and  310 . However, the antennas will not typically experience large ranges of motion in other directions (e.g., a direction perpendicular to directions  309  and  310 ). Therefore, one skilled in the art will recognize that it may be desirable to mount antenna  501  of  FIG. 5  to the stick in a way such that it is only capable of rotating to compensate for the movement in directions  309  and  310 . While such a structure will not be able to fully compensate for the full range of motion of the excavator, such an arrangement would be satisfactory in many implementations. 
       FIG. 6  shows one illustrative embodiment of how the gimbaled antenna structure of  FIG. 5  can be used with the excavator of  FIG. 3 . Referring to  FIG. 6 , as described above in association with  FIG. 3 , antennas  601  and  602  are once again mounted on stick  613  which is, in turn, attached to boom  612 . However, in the embodiment of  FIG. 6 , instead of the antennas being mounted in a fixed position, which causes the aforementioned potential loss of signal from positioning satellites, antennas  601  and  602  are mounted using the illustrative gimbal structure as described above in association with  FIG. 5 . Thus, for example, when stick  613  moves in direction  605 , the antenna housings of antennas  601  and  602  remain oriented in horizontal positions  603  and  604  with respect to surface  611 . Similarly, when the stick is moved in direction  606 , the antenna housings will once again remain oriented in horizontal positions  603  and  604 . Thus, illustratively, during both types of operations (i.e., when stick  613  is moved in direction  605  or in direction  606 ), both signals  609  and  610  from satellites  607  and  608 , respectively, will continue to be received by antennas  601  and  602 . 
       FIG. 7  is a block diagram showing one illustrative embodiment of a satellite positioning system that may be used with the gimbaled positioning system antennas, as described above. Specifically, as discussed above, a plurality of satellite positioning system antennas, such as GPS positioning antennas  701  and  702 , are positioned on the stick of an excavator, such as stick  104  in  FIG. 1 . Each of these antennas is connected to a corresponding receiver  703  and  704  which determine the precise position of each antenna  701  and  702 . The position of each antenna may be more accurately obtained in the illustrative implementation of  FIG. 7  by incorporating a correction signal obtained from a base station transmitter. As discussed above, the use of such a correction signal is typically referred to as “differential” positioning or as “real time kinematic” correction of positioning. The correction signal transmitted by the base station is received by a radio receiver  706  via antenna  705  and is used in the calculations of the positioning receivers  703  and  704  to obtain more accurate positions of antennas  701  and  702 . Inclinometers/angle sensors  707  and  708  are used, as described illustratively above, to measure both the scoop of the bucket as well as the slope of the body of the excavator. These calculations are made and used in illustrative graphics computer  709  that is, for example, used by the excavator operator in controlling the excavation operations. Graphics computer  709  may be any suitable computer adapted to compute and/or display the position of the prongs and/or the bucket. Computer  709  may have, illustratively, a processor  710  (or multiple processors) which controls the overall operation of the computer  709 . Such operation is defined by computer program instructions stored in a memory  711  and executed by processor  710 . The memory  711  may be any type of computer readable medium, including without limitation electronic, magnetic, or optical media. Further, while one memory unit  711  is shown in  FIG. 7 , it is to be understood that memory unit  711  could comprise multiple memory units, with such memory units comprising any type of memory. Computer  709  also comprises interface  712  which provides for the transmission of antenna positional data associated with antennas  701  and  702  from GPS receivers  703  and  704  to computer  709 . Computer  709  also illustratively comprises interface  715  adapted to receive slope and/or inclination data associated with the earthmoving machine/excavator or a component thereof. Although shown separately in  FIG. 7 , one skilled in the art will recognize that interface  712  may be the same interface as interface  715 . Additionally, computer  709  also illustratively comprises one or more input/output devices, represented in  FIG. 7  as I/O  713 , for allowing interaction, for example, with an excavator operator or technician. Finally, computer  709  also illustratively comprises a storage medium, such as a computer hard disk drive  714  for storing, for example, data and computer programs adapted for use in accordance with the principles of the present invention as described hereinabove. One skilled in the art will recognize that computer  709  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. 
     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. For example, while the above described embodiments involve an excavator, one skilled in the art will recognize that the principles described therein are equally applicable to other machines such as, for example, a backhoe. Typically backhoes differ from excavators in that the booms of backhoes are mounted in a way such that the boom can rotate about a pivot point relative to the body of the machines. Thus, while the body of the machine stays in one position, the boom rotates to move the bucket or other tool. The body and boom of excavators, on the other hand, are typically connected in a fixed manner such that the body and boom always have the same heading. In order to change the direction of the bucket, it is necessary to rotate the entire body of the excavator about a base. One skilled in the art will fully appreciate how the above described aspects of the embodiments of the present invention may be modified for use with such backhoes and other vehicles, such as dozers.