Apparatus and Method for Determining Terrestrial Position

Technical Field

This invention relates generally to an apparatus and method for determining position and more ■ particularly to an apparatus and method for determining the terrestrial position of a dynamic reference point.

Background of the Invention

Today's construction site is designed by an architect. The architect's designs are copied to blueprints and are transmitted to the contractor. The contractor will stake the area, i.e., survey the undeveloped area and place stakes at predetermined positions. The contractor, by comparing the architect's plans and the results of the survey, will determine the amount of dirt that needs to be removed or placed at each marker to meet the design plans.

After this process, earthmoving vehicles, e.g., bulldozers, scrapers, or excavators, are used to remove or fill the areas around the stakes . An unprocessed island is left remaining around the stake. After all the areas have been processed, the site is surveyed once again to confirm that the processed site meets the design specifications.

The above process requires large amounts of manual labor. The site has to be surveyed, staked, processed and surveyed once again. Furthermore, only a highly trained operator can efficiently operate the vehicle to obtain the desired degree of accuracy. Laser systems have been used in order to provide a reference to the operator in performing this process. Typically, the laser system emits a laser

beam which is swept over the site in a plane. The vehicle must be equipped with a suitable receiver. The system is able to give the operator an indication of the height of the vehicle and/or work implement with reference to the laser beam.

However, the laser systems are limited by the range of the laser, the sensitivity of the laser detector and environmental limitations, e.g., rain. Furthermore, the laser system gives an indication of the relative height of the detector. The height or position of the work implement is determined through the geometry of the work implement. The geometry of the work implement changes based on the type of work implement and the relative positions of the work implement's linkages. Also, the blade of the work implement will wear over its life, changing its geometry. All of these factors decrease the accuracy of the operation of the vehicle.

In addition, the site must be manually surveyed again after the site has been processed. In order to accomplish this using the laser system, the vehicle must be stopped at each point which must be surveyed, the work implement must be set on the ground surface, and a reading taken. All this has to be done while the laser is in range. This is highly inefficient.

The present invention is directed to overcoming one or more of the problems, as set forth above.

Disclosure of the Invention

In one aspect of the present invention, an apparatus for determining the position of a dynamic reference point located on the ground surface is provided. The apparatus determines the terrestrial

position of a terrestrial reference point located on the apparatus and the location of the dynamic reference point relative to a local reference point located on the apparatus. The terrestrial position of the dynamic reference point is determined as a function of the terrestrial position of the terrestrial reference point and the relative location of the dynamic reference point.

In another aspect of the present invention, a method for determining the terrestrial position of a dynamic reference point on a site plan utilizing an apparatus is provided. The method includes the steps of determining the terrestrial position (x _t ,y _t ,z _t ) of a terrestrial reference point located on the apparatus and determining the location (x _ra ,y _m ,z _m ) of the dynamic reference point relative to a local reference point located on the apparatus. The terrestrial position (X _t ,Y _t ,Z _t ) of the dynamic reference point is determined as a function of the position of the terrestrial reference point and the relative location of the local reference point.

Brief Description of the Drawings

Fig. 1 is a diagrammatical illustration of a work vehicle having a work implement with a blade, shown as a track type tractor (TTT) ;

Fig. 2 is a diagrammatical illustration of a front view of the TTT of Fig. 1;

Fig. 3 is a diagrammatical illustration of an apparatus according to an embodiment of the present invention;

Fig. 4 is a diagrammatical illustration of the TTT of Fig. 1 including the apparatus of Fig. 3, according to an embodiment of the present invention;

Fig. 5 is a line illustration of the apparatus of Fig. 3 shown illustrating a terrestrial reference point, a local reference point and a dynamic reference point; Fig. 6 is an illustration of a two- dimensional orientation sensor; and

Fig. 7 is a block diagram of the apparatus of Fig. 3.

Best Mode for Carrying Out the Invention

With reference to Figs. 1-7, the present invention is directed towards determining the terrestrial position of a dynamic reference point. In one embodiment, the present invention includes an apparatus 302 for determining the terrestrial position of a dynamic reference point on the ground surface. The apparatus 302 may be connected to a vehicle 102 or may be adapted to be hand carried. The apparatus 302 is adapted to be positioned over the dynamic reference point and to determine its terrestrial position. By determining the position of a series of dynamic reference points over a site, real-time surveillance of a site plan may be accomplished. Terrestrial position refers to position relative to the Earth, i.e. a coordinate system having an origin at the center of the Earth. As used herein, terrestrial may also refer to a local site coordinate system. Thus, the local site reference coordinate system is fixed and transformations between the Earth coordinate system and the local site reference coordinate system is easily accomplished.

Typically, positions will be referred to in Cartesian coordinates (X,Y,Z), however other reference systems may be used.

With reference to Fig. 1, an exemplary work vehicle 102 is shown as a track type tractor (TTT) . However, the present invention may be adapted to other types of earthmoving vehicles, e.g., scrapers, motor graders, hydraulic excavators. In order to perform real-time surveillance, the present invention may be used with an earthmoving vehicle, as described below, or a non-earthmoving vehicle, e.g., a pick-up truck.

The TTT 102 includes an undercarriage 104 which provides movement, an operator station 106, and an engine 108. The TTT's work implement 110 includes a push arm 112 on each side of the vehicle 102 (only one is shown) . A bulldozer blade 114 is rotatably connected to the ends of the push arms 112. A pair of tilt cylinders 116 provide movement of the blade 114 relative to the push arms 112. At least one lift cylinder 118 provides movement of the blade 114 relative to the vehicle 102.

The blade's movement relative to the vehicle are termed as pitch and tilt. Pitch refers to the blade's front and back movement as shown in Fig. 1 and labeled as G. As shown in Fig. 2 and labeled as F, tilt refers to the blade's rotational movement. For exemplary purposes only, the TTT 102 may have a maximum tilt angle of 25° and a maximum pitch angle of 7.3° .

The TTT dimensions as labeled are: A: length with blade straight

B width C blade height

D maximum digging depth E ground clearance at full lift F maximum tilt, and G maximum pitch.

In another embodiment, the apparatus 302 is connected to a work vehicle 102 and is adapted to determine the position of the work vehicle's 102 work implement 110 as it performs a fill or cut operation or rests on the ground surface. With reference to

Fig. 4, the apparatus 302 is connected to the vehicle 102 on or near the work implement 110. The apparatus 302 is adapted to determine the terrestrial position of a dynamic reference point behind the work implement. The terrestrial position of the dynamic reference point is used as an indication of the work implement's position and/or topography of the site. Referring to Figs. 3 and 5, the apparatus 302 includes a support member 304. A means 306 determines the terrestrial position of a terrestrial reference point 502 and responsively produces a terrestrial position signal. The terrestrial reference point position determining means 306 is connected to the support member 304. In the preferred embodiment, the terrestrial position determining means 306 consists of a Global Positioning System (GPS) . A GPS 306 receives signals from a constellation of man-made satellites orbiting the earth and determines position relative to the Earth by means of triangulation. Typically, a constellation consists of 3-4 satellites. Preferably, the U.S. Government's NAVSTAR GPS satellites are used. One suitable GPS system is disclosed in U.S. Application Serial Number 07/628,560 filed December 3, 1990 and titled "Vehicle Position Determination System and Method. "

Returning to Fig. 3, the terrestrial position determining means 306 includes a GPS antenna 308 and a GPS receiver 310. A suitable GPS antenna 308 is available from Magnavox Corp. of Torrance Ca as

model number 723010. In the preferred embodiment, the antenna and pre-amp are mounted on the apparatus 302. The GPS receiver is mounted elsewhere on the vehicle. The GPS receiver 310 is adapted to determine the terrestrial position of the terrestrial reference point which is typically located on the apparatus 302 or at the receiver 310.

A means 312 determines the location of the dynamic reference point 506 relative to a local reference point 504 located on the apparatus 302 and responsively produces a local position signal. The means 312 is connected to the support member 304.

In the preferred embodiment, the dynamic reference point location determining means 312 includes an ultrasonic sensor 314. The ultrasonic sensor 314 emits an ultrasonic wave aimed at the dynamic reference point 506, receives a reflection of the emitted wave and responsively determines the distance between the ultrasonic sensor and the dynamic reference point 506. The local reference point 504 is located on the ultrasonic sensor 314 and is the point from which the sensor measures the distance. One suitable ultrasonic sensor 314 is available from Agtek of Livermore, CA as model no. 9140. In the preferred embodiment, the ultrasonic sensor 314 includes a reference wire 316 to compensate for temperature effects on the sensor's 314 accuracy. The ultrasonic sensor 314 is adapted to determine the distance to the ground and to calibrate its measurements based on the measured and known distances to the reference wire 316.

In the preferred embodiment, the dynamic reference point location determining means 312 includes means 318 for determining the orientation of the apparatus 302 with respect to the ground surface.

In the preferred embodiment, the orientation of the apparatus 302 is characterized in terms of pitch (β) and tilt ( ) . If the apparatus 302 is connected to the blade 114, as in Fig. 4, the pitch and tilt of the apparatus 302 coincides with the pitch and tilt of the blade 114 (see Figs. 1,2,4, and 5). The pitch and tile of the apparatus 302 is used to determine the location of an adjusted dynamic reference point 506'. The terrestrial position of the dynamic reference point is determined as a function of the measured tilt and pitch (see below) .

In the preferred embodiment, the orientation determining means 318 includes a two dimensional bubble sensor 320. With reference to Fig. 6, the two- dimensional sensor 320 includes a casing 602 filled with an electrically conductive fluid. A bubble or pocket of gas 606, e.g., air, is trapped within the casing 602. As the orientation of the apparatus 302 changes, the location of the bubble 606 moves within the casing. The electrical impedance across the sensor 320 varies with the location of the bubble 606 and is proportional to the respective angles. The sensor 320 measures the electrical impedance across the casing on two perpendicular axes, as shown and responsively determines the pitch and tilt angles. A suitable 2-axis bubble sensor is available from Spetron Glass and Electronics Inc of Hauppauge, NY as model no. SP5000. In alternate embodiment, two single axis sensors, model no. L-212t may be used. Additionally, the present invention may alternately use a pendulum type sensor.

With reference to Fig. 7, the apparatus 302 includes a controlling means 700. Preferably, the controlling means 700 includes a microprocessor. In

the preferred embodiment, a notebook computer is used.

The controlling means 700 includes a means 702 for receiving the terrestrial position signal and the local position signal, responsively determining the terrestrial position of the dynamic reference point 506 and producing a dynamic reference point terrestrial position signal.

In the preferred embodiment, the terrestrial position of the dynamic reference point is determined by the equations: x _t γ _t z. m- α sm β) ^1/2 , where

X _t , Y _t , Z _t define the terrestrial position of the dynamic reference point in Cartesian coordinates; x _t , y _t , z _t define the terrestrial position of the terrestrial reference point in Cartesian coordinates; h _s is the measured distance between the local reference point and the dynamic reference point; h _g is the known distance between the terrestrial reference point and the local reference point; and β is the measured pitch angle; and o. is the measured tilt angle.

A means 704 produces a desired reference point position signal. In the preferred embodiment, the desired reference point position signal producing means 704 includes storage memory, e.g., random access memory (RAM) , erasable programmable read only memory (EPROM) , a fixed disk drive, a hard disk drive or other suitable type of storage device. The storage

device retains the site plan including a series of points on the site plane and their respective desired terrestrial heights or positions. The desired reference point position signal corresponds to the desired height or position of the current dynamic reference point according to the site plan.

A means 706 receives the desired reference point position signal and the dynamic reference point terrestrial position signal, compares the received signals, and responsively producing a difference signal. The difference signal corresponds to the amount of material that has to be removed or filled in order to meet the site plan specifications.

A storing means 708 receives signals and stores the signals in a storage medium. The storing means 708 may include any of the types of memory listed above. The storing means 708 may be adapted to download stored data to an external computer either directly or through other means, e.g., a satellite network. In one embodiment, the storing means 708 receives and stores the difference signal. In another embodiment, the storing means 708 receives and stores the dynamic reference point terrestrial position signal. A means 710 receives signal and displays the information to the operator. In one embodiment, the display means 710 receives the dynamic reference point terrestrial position signal and responsively displays dynamic reference point terrestrial position signal. In another embodiment, the display means 710 receives the difference signal and responsively displays the difference signal. The display means 710 may display the -received information in a number of different formats, e.g., a number, a graphic illustration showing the information relative to the site plane,

and/or a graphic showing the difference. Other types of displays and/or formats are possible and the present invention is not limited to any such type of display. In an alternate embodiment, the information may be relayed over a radio link to a remote location for display and/or storage.

Industrial Applicability With reference to the drawings and in operation the present invention or apparatus 302 is adapted to determine the terrestrial position of a dynamic reference point. As discussed above, the dynamic reference point is preferably a point on the ground surface and may be used to accomplish real-time surveying of a site or may be used to determine the position of a work vehicle's implement. The terrestrial position of the dynamic reference point 506 is determined utilizing the apparatus 302 discussed above and the method described below.

First, the terrestrial position (x _t ,y _t ,z _t ) of a terrestrial reference point 502 is produced. Preferably this is accomplished utilizing a global position system (GPS) . The GPS system includes a GPS receiver 310 which receives electromagnetic signals from orbiting satellites and determines the position of a point on the receiver 310 (terrestrial reference point 502) with respect to the Earth. "Terrestrial" refers to a reference coordinate system. In one embodiment, the terrestrial reference coordinate system is centered at the Earth. The GPS receiver 310 determines positions relative to this coordinate system. In another embodiment, the reference coordinate system is fixed at the particular site. A

simple transformation converts between the two coordinate systems.

Second, the location (x _ra ,y _ra ,z _m ) of the dynamic reference point (506) relative to a local reference point (504) located on the apparatus (302) is determined and a local position signal is responsively produced. In the preferred embodiment, this step entails using an ultrasonic sensor 314 for determining the distance (h _s ) between a local reference point 504 located on the apparatus 302 and the dynamic reference point and an orientation sensor 320 for determining the tilt and pitch of the apparatus 302. The local position signal is preferably indicative of the determined distance, h _s . The terrestrial position (X _t ,Y _t ,Z _t ) of the dynamic reference point is determined as a function of the terrestrial position of the terrestrial reference point, the distance between the local reference point and the dynamic reference point and the orientation of the apparatus 302 (see discussion above) .

The terrestrial position of the dynamic reference point maybe used as an indicator of tool position or may be used as an indicator of the topography of the work site. In one embodiment, the apparatus 302 is mounted on a vehicle, e.g., a pickup or a bulldozer. The topography of the work site may be obtained by driving over the work site. If done with the bulldozer, this is accomplished with the blade in a raised position.

Other aspects, objects, and features of the present invention can be obtained from a study of the drawings, the disclosure, and the appended claims.