Gimbaled satellite positioning system antenna

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.

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. 1shows one such one such earthmoving machine, an excavator, which is well known in the art. As shown inFIG. 1, excavators such as excavator100typically have a main body101with a vehicle operator cab102. Attached to the main body101is arm103, commonly referred to as a “boom”. Boom103is, in turn, attached to a second arm104, commonly referred to as a “stick.” Stick104may be adapted to hold different attachments. Here, stick104is attached, illustratively, to a bucket105for use in excavation/digging. Bucket105typically has prongs106attached to the leading edge of the bucket105that are used to break through ground and other materials to be excavated. Body101is attached to a base which is supported by, illustratively, tracks107that 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, body101is typically attached to the base in a way such that body101is 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 bucket105may be moved with a high degree of flexibility within that given radius. For example, boom103may be raised or lowered by lengthening or shortening hydraulic pistons108, respectively. Similarly, stick104may be rotated about pivot point109to raise or lower bucket105by shortening or lengthening hydraulic piston110, respectively. Finally, bucket105may be rotated about pivot point111into a cupped or an open position by either lengthening or shortening hydraulic piston112.

Excavators, such as excavator101inFIG. 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. 2shows a prior art excavator using satellite positioning to increase excavation accuracy. Specifically, antennas201and202are mounted on body101of excavator100. 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 antennas201and202may 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 antennas201and202allows accurate determination of the orientation of the body101of the excavator100. 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 antenna201relative to the position of antenna202will provide an accurate measurement of the heading of body101of the excavator. Thus, using two antennas allows both tilt and heading measurements of the body101. However, simply knowing the tilt and heading of the body101is not sufficient for high-precision excavation. Instead, the precise orientation of the bucket105and, 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 toFIG. 2, sensor203is placed on body101, sensor204is mounted to boom103, sensor205is mounted on stick104, and sensor206is placed on bucket105. These sensors are calibrated for a given position of the cutting edge and or prongs of the bucket105. 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 sensors203-206inFIG. 2, the location of the cutting edge of bucket105can 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.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 3shows 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 toFIG. 3, boom301is connected to stick302which is, in turn, attached to bucket303, as discussed above. However, unlike the previously discussed excavators that utilized a satellite positioning system to assist in the control of the machine, the antennas305and306are mounted on support structure307which is attached to stick302at illustrative point308. One skilled in the art will recognize that antennas305and306may 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 ofFIG. 3, in order to conduct excavation operations with a high degree of accuracy, it is necessary to know the position of bucket303with a high degree of accuracy and, more particularly, to know the position (e.g., the height/depth) of cutting teeth/prongs304. 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 prongs304. More recently, however, as described above and disclosed in the 11/108,013 application, the precise determination of the position of the prongs304of bucket303can be determined by mounting the antennas directly on the stick, as shown in the illustrative embodiment ofFIG. 3.

As one skilled in the art will recognize, antennas such as antennas305and306typically 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 antennas305and306to the stick302, 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. 4shows such an orientation. Specifically, referring to that figure, excavator401which is, illustratively, conducting earth-moving operations, has stick407with antennas402attached to the stick. One skilled in the art will recognize that antennas such as illustrative antennas402typically 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 inFIG. 4, antennas402are positioned in a way such that signals from satellites404are received with sufficient strength for positioning calculations while, on the other hand, satellites406are 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 satellites404and406with respect to the antennas402, the number and strength of signals received by antennas402may 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 antennas402inFIG. 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 antennas402can 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 satellites404and406inFIG. 4are received with adequate strength to permit accurate positioning calculations.

FIG. 5shows one illustrative embodiment of how an antenna housing, such as antenna housing501can 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 housing501is a housing containing, for example, a receiving antenna element of a positioning system antenna. Housing501is mounted in a gimbal structure consisting of support structure503and gimbal ring502. Support structure503is, for example, mounted to surface504which is, illustratively, a surface of the stick of an earthmoving machine, such as stick407of excavator401ofFIG. 4. Antenna housing501is illustratively mounted to gimbal ring502in a way such that the housing501can rotate in directions511about axis512. Gimbal ring502, in turn, is mounted to support structure503in a way such that the gimbal ring can rotate in directions510about axis513. Accordingly, as one skilled in the art will recognize, when surface504moves in directions508and509, as well as in the y-direction inFIG. 5, gravitational force in direction514acting on the antenna housing will cause the gimbal ring502and antenna housing501to rotate about axes512and513in 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 ofFIG. 5is merely illustrative and that other variations are possible. For example, while the gimbaled antenna501ofFIG. 5is capable of maintaining the antenna in a horizontal orientation with respect to multiple axes (i.e., the x and z axes inFIG. 5), one skilled in the art will recognize that such a complex structure may not be necessary. More particularly, referring once again toFIG. 3, an antenna mounted to a stick of an excavator may experience a large range of motion in directions309and310. However, the antennas will not typically experience large ranges of motion in other directions (e.g., a direction perpendicular to directions309and310). Therefore, one skilled in the art will recognize that it may be desirable to mount antenna501ofFIG. 5to the stick in a way such that it is only capable of rotating to compensate for the movement in directions309and310. 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. 6shows one illustrative embodiment of how the gimbaled antenna structure ofFIG. 5can be used with the excavator ofFIG. 3. Referring toFIG. 6, as described above in association withFIG. 3, antennas601and602are once again mounted on stick613which is, in turn, attached to boom612. However, in the embodiment ofFIG. 6, instead of the antennas being mounted in a fixed position, which causes the aforementioned potential loss of signal from positioning satellites, antennas601and602are mounted using the illustrative gimbal structure as described above in association withFIG. 5. Thus, for example, when stick613moves in direction605, the antenna housings of antennas601and602remain oriented in horizontal positions603and604with respect to surface611. Similarly, when the stick is moved in direction606, the antenna housings will once again remain oriented in horizontal positions603and604. Thus, illustratively, during both types of operations (i.e., when stick613is moved in direction605or in direction606), both signals609and610from satellites607and608, respectively, will continue to be received by antennas601and602.

FIG. 7is 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 antennas701and702, are positioned on the stick of an excavator, such as stick104inFIG. 1. Each of these antennas is connected to a corresponding receiver703and704which determine the precise position of each antenna701and702. The position of each antenna may be more accurately obtained in the illustrative implementation ofFIG. 7by 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 receiver706via antenna705and is used in the calculations of the positioning receivers703and704to obtain more accurate positions of antennas701and702. Inclinometers/angle sensors707and708are 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 computer709that is, for example, used by the excavator operator in controlling the excavation operations. Graphics computer709may be any suitable computer adapted to compute and/or display the position of the prongs and/or the bucket. Computer709may have, illustratively, a processor710(or multiple processors) which controls the overall operation of the computer709. Such operation is defined by computer program instructions stored in a memory711and executed by processor710. The memory711may be any type of computer readable medium, including without limitation electronic, magnetic, or optical media. Further, while one memory unit711is shown inFIG. 7, it is to be understood that memory unit711could comprise multiple memory units, with such memory units comprising any type of memory. Computer709also comprises interface712which provides for the transmission of antenna positional data associated with antennas701and702from GPS receivers703and704to computer709. Computer709also illustratively comprises interface715adapted to receive slope and/or inclination data associated with the earthmoving machine/excavator or a component thereof. Although shown separately inFIG. 7, one skilled in the art will recognize that interface712may be the same interface as interface715. Additionally, computer709also illustratively comprises one or more input/output devices, represented inFIG. 7as I/O713, for allowing interaction, for example, with an excavator operator or technician. Finally, computer709also illustratively comprises a storage medium, such as a computer hard disk drive714for 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 computer709is 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.