METHOD AND APPARATUS FOR POSITIONING CONSTRUCTION MACHINERY

Abstract: A construction machine (such as a piling rig) is correctly positioned on a work site by (a) providing the machine with a mast (5) having a nominally vertical axis passing through the centre of operation of the machine at ground level; (b) providing a satellite navigation system receiver (preferably a high-precision GPS P-code receiver) and locating its antenna (11) on the said axis at the top of the mast; (c) providing means (12) for determining the displacement of the mast from its nominal vertical position; (d) obtaining output readings from the said navigation system receiver when the displacement is less than a predetermined limit (which may be reduced as the target position is approached); and (e) positioning the machine manually or automatically in response to those output readings. If output readings are obtained when the displacement is outside the chosen limit, they are distinguished from usable positioning readings, for example by dimming or changing the colour of the display.

Description: Method and Apparatus for Positioning Construction Machinery This invention relates to a method of positioning construction machinery on the site of civil engineering or construction works (including offshore construction works) , and more especially (though not exclusively) positioning rigs for the installation or formation of piles or other foundation works. It includes apparatus for operation of the method and piling rigs and other construction machinery in which such apparatus is installed. In current practice, such machinery is positioned for operation by sighting with standard surveying instruments with reference to pegs or other markers laid out cn the site before work commences. This established technique is well able to provide the required positioning accuracy, but it is liable to require skilled surveyors on site for only occasional activity, expensive delays are liable to arise when markers are accidentally knocked over or displaced (not a rare event on sites where heavy construcion machinery is moving about) and even more expensive mistakes may arise if the markers are misinterpreted - for instance some surveyors will locate markers on the centre-line of a row of piles while others prefer to align them with a face of the piles - or if accidental displacement goes unnoticed. In the meantime, navigational sytems based on the use of satellites and in particular the Navstar Global Positioning System or GPS have been developed to the point at which their precision can achieve about ±5mm, except for short periods when the position of the system satellites is unfavourable. However, it is difficult and not always practicable to operate a GPS system with its antenna at ground level on a construction site, where the presence of large metallic bodies (such as the construction machinery itself and in some cases the metal frames of adjoining buildings) may attenuate the satellite signals to the point at which they cannot be detected, or worse may deflect them and give systematic errors in the GPS measurement. Deep foundation construction equipment (such as pile rigs and diaphragm wall rigs) and other like machines are normally tall enough for reliable readings to be taken with a GPS antenna at the top of the machine, but this only substitutes the problem of relating the position of the antenna to that of the working part of the machine at ground level, which may vary by up to a metre or so for instance as the machine follows the imperfect contour of the site surface, deflects in the wind, and/or vibrates. In accordance with the present invention, a method of positioning a construction machine on a work site comprises (a) providing the said machine with a mast having a nominally vertical axis passing through a point (herein considered the centre of operation of the machine) at ground level which it is desired to bring to predetermined locations; (b) providing a satellite navigation system receiver having an antenna located on the said axis at the top of the mast; (c) providing means for determining the displacement of the mast from its nominal vertical position; (d) obtaining output readings from the said navigation system receiver when the said displacement is less than a predetermined limit and distinguishing these said output readings from any other output readings that may be obtained when the said displacement is not less than the said predetermined limit; and (e) positioning the machine in response to these said output readings. In most cases the nominally vertical mast will be an intrinsic part of the machine, though a minor extension may be needed for positioning the antenna accurately on the axis. The navigation system is preferably one of the high-precision GPS receivers, such as those marketed or under development by Trimble Navigation Inc having its principal place of business at 645 Mary Avenue, Sunnyvale CA 94068, USA and a subsidiary Trimble Navigation (Europe) Ltd at Osborn Way, Hook, Hampshire (herein together called Trimble) . More especially, we recommend receivers which operate using the LI and L2 P-code and carrier when available and using LI CA code and cross-correlation of the encrypted Y-code when the LI and L2 signals are scrambled. At present we prefer to use receivers of Trimble's "4000" series with automatic initialisation on th fly, and most especially model 4000SSE. WO93/05588 is thought to describe some features of such receivers. The receiver may be provided with any appropriate conventional interpretation software, and in particular preferably with software for generating an output representing displacement from a target position entered manually or from a CAD file representing the design of the works to be executed. It may be desirable, if the movements of the mast are appreciable within the normal sampling period of the receiver (usually 1 or 2 seconds) to modify the software to sample at variable intervals when the mast is found to be sufficiently close to vertical. Various kinds of tiltmeter (also called an inclinometer or clinometer) are available and can be used to determine displacements of the mast from the vertical. The requirements are for a response time of a fraction of a second or better and an accuracy of the order of 1 in 2500 or.40 seconds of arc (to support an accuracy of ±lOmm when the mast is 25m high) . At present we prefer tiltmeters based on self-levelling of fluids with appropriate viscosity to damp oscillations and more especially "electronic" tiltmeters in which movement of the self-levelling fluid affects the capacitance between plates of a capacitor, so that no solid moving parts are needed. Good results have geen obtained with the tiltmeters sold by Monitran Ltd of 33 Hazlemere Road, Penn, Buckinghamshire, GB under the designation AccuStar Electronic Clinometer. If the mast cannot be set stably vertical to the required tolerance and random movements of the mast do not provide an adequately short sampling period, means may be provided to introduce oscillatory movements (around one or two axes close to ground level) to ensure that the mast will be frequently vertical. There is no necessity to obtain any output readings from the navigation system receiver when the mast is not vertical within the chosen tolerance, but it is convenient to do so provided that such readings are distinguished (for example by displaying them at reduced intensity or in a different colour from output signals obtained when it is vertical within the chosen tolerance) and are not relied on for positioning the machinery for operation. The predetermined limit below which the displacement of the mast from vertical must be before output readings are used may be a constant predetermined angle. We prefer, however, that the limit is reduced as the machine approaches its target position. The limit might be a continually changing function; for instance it might be tan " (r/5h) , where r is the most recently indicated distance from target and h the height of the mast (or a step function approximating it more or less closely) , so that the error due to deviation of the mast from vertical would be limited to half an order of magnitude less than the current displacement of the machine from its target position. We find it more practical, however, that the limit changes in a small number of large steps and the display of the output changes correpondingly, so that positioning comprises a short sequence of adjustments of increasing precision. The number and size of the steps can be chosen to suit the conditions of a particular site, if desired. The machine may be positioned in response to the output signals by a human driver, or in suitable cases the output signals may be input into a computer control system to allow the machine to seek its instructed position automatically. Especially in the latter case, final adjustment may be made by moving the mast with respect to the base of the machinery, rather than by moving the base of the machinery along the ground. The invention will be further described, by way of example, with reference to the accompanying drawings in which: Figure 1 is a diagrammatic view of a piling rig equipped with apparatus in accordance with the invention, and Figures 2-7 show one way in which output measurements may be presented to a human driver as a succession of "screens" in a computer display in his cab. For purpose of illustration, the rig shown in Figure 1 is an auger piling rig for making one kind of cast-in-situ concrete foundation pile. The rig comprises a body 1 (including a driver's cab 2) rotatably mounted on a tracked base 3, which can be driven relatively precisely in a forward and rearward direction and can be steered, with rather less precision, by differentially driving its two tracks in the usual way. On the front of the body is mounted a mast 5 supporting an auger 6 with appropriate drive gear 7, the rotation axis 8 of which defines the nominally vertical axis of the mast; the intersection 9 of this axis with the ground determines the centre of operation of the machine, where the auger will enter the ground and the pile will be formed. The problem is to locate the point 9 on the ground with sufficient accuracy, notwithstanding that the surface on which the rig stands may not be horizontal to the required accuracy, the hydraulic mechanism 10 holding the mast upright may not be set at the optimum angle, the wind may cause the mast to deflect and/or oscillate significantly and in some cases (mostly when the mast is already out of vertical for one of the other reasons) the mast, may bend. In accordance with the invention, the rig is provided with a GPS receiver and the antenna 11 of that receiver is located at the top of the mast 5, while at least the output display (Figures 2-7) is in the cab 2. A pair of electronic tiltmeters 12 (say of AccuStar electronic clinometers) is also fitted to the mast 5 and provides signals representing the displacement of the axis 8 from a truly vertical position in mutually perpendiculat directions - preferably on the pitch and roll axes relative to the body of the machine. (At some stages of operation, this signal will also be displayed to the driver to assist adjusting the mast to a vertical position) . A vector signal (using this expression in a broad sense to include, for example, a pair of error signals with + or - signs) is preferable as giving an immediate indication of corrective action to be taken for vertical setting of the mast. In the particular system illustrated by Figures 2-7, the driver's display initially shows (Figure 2) a listing 13 of the piles to be installed, with their intended location co- ordinates (Eastings and Northings, for instance in accordance with the United Kingdom Ordnance Survey's National Grid) which has previously been downloaded, say from a floppy disk produced by the design office computer. Contract and status information 14 may also be displayed. The operator selects a pile to be installed first, say by highlighting it in the list and pressing a function key or an enter key, and the display changes to show (Figure 3) a site plan 15 with the intended position of the selected pile (the target position) 16 and the position of the piling rig as indicated by the GPS system (the indicated position) 17: at this stage it does not matter if the mast is out of vertical and the indicated position of the rig consequently inaccurate. The operator drives the rig towards the target position, and will have no difficulty in coming within a few metres of it; if desired, the track of the rig across the site can be displayed as a "snail trail" on the display. When the distance between the target position and the indicated position is less than 10m (say) , the display changes scale (as seen in Figure 4) to facilitate the next step of adjusting the position to within 2m (say) by driving the rig backwards or forwards, steering if necessary, and rotating the rig around its own nominally vertical rotation axis to make sideways adjustments within the range that the dimensions of the rig allow. At this stage the display changes again, to the form shown in Figure 5 comprising a bullseye display 18 showing the target position 16 with concentric circles 19-22 around it, along with the indicated position 17, and a tilt display 23 displaying the outputs of the tiltmeters as left-right and forward-back tilt indications 24, 25 respectively on a "cross¬ hair" diagram; the scale of each of these parts of the display will change progressively as the target position is approached. At this stage, the outer circle of the bullseye display corresponds to 2m on the ground and the scale of the tilt display 23 is such that the central space 26 between the fixed rectangles corresponds to a tilt range of ±15' of arc. When the difference between the indicated position and the target position falls below lm, the scale of the bullseye display- changes so that the outer circle represents lm, for greater precision of positioning; on a colour display, it may also change colour to give a conspicuous indication of the change. When the difference between the indicated position and the target position falls below 0.5m for the first time, the scale of the display (and its colour, if desired) changes again so that the outer circle now represents 0.5m, and at the same time the software imposes an angular tolerance on the tilt equal to ±15'; usually this tolerance will not be met, in which case the bullseye display is dimmed (on a monochrome screen) or set to grey (on a colour screen) to indicate that the mast is not sufficiently vertical for the indicated position to be accurate, and the operator next adjusts the mast using the standard equipment of the rig until the two tilt indications are brought within the central space 26 of the crosshair display or (if the mast is swaying) are oscillating across it. In the latter case, the GPS output signal is suppressed except when the tilt is within this tolerance, and in any case the display brightens (on a monochrome screen) or becomes coloured to indicate that the bullseye display is now accurate enough to be useful. The driver adjusts position accordingly, pausing to re-adjust the mast if dimming (or loss of colour) indicates that it is necessary. When (with the mast vertical within the ±15' angular tolerance) the distance between the target position and the indicated position falls below 0.25m, the angular tolerance is reduced to 6' and the crosshair display changes scale so that the central space 26 now represents 6' of arc. Adjustment continues as before to this new accuracy, and when the difference between the target position and the indicated position falls below 0.1m, a similar and final change occurs so that the angular tolerance is 0'30" of arc and the scale of the crosshair display corresponds to it; the bullseye continues to dim or lose colour, as the case may be, if the mast is not vertical within the tolerance set for the time being and the operator continues to respond to this, when necessary, by adjusting the mast. (The example figures in this paragraph are appropriate for a good quality site; on an uneven site, angular tolerances may need to be set significantly sooner) . When, with the maximum scale and lowest tolerances, the distance between the target position and the indicated position remains below 10mm for a sufficient time to indicate that the rig is stationary (say 1-2 seconds, or 1024ms may be convenient to some software) , a READY message 27 (Figure 6) is displayed, which the operator acknowledges with a function key, and pile installation can begin. The display may change again (Figure 7) to display a PILING IN PROGRESS message 28 while the GPS system continues to record position (which may change slightly while the pile is being installed) . Appropriate instrumentation may be added to allow the depth achived to be displayed as well, if desired. Further operation of a function key signals completion of piling and results in the recording of the final position measurement (in addition to the position when installation started, and final depth if instrumented) , and returns the display to the form of Figure 2 (but with the completed pile deleted from the list 13) , ready for the selection of the next pile to be installed. In a modification of the procedure described, the software is adjusted so that the inclinometer measuring tilt in the fore-and-aft direction of the rig gives a "correct" signal whan the mast is in fact tilted backwards by 8°, the reading from the other inclinometer being unaltered. Combining this angle with the known dimensions of the rig, its orientation provided by an additional electronic heading or gyroscopic compass system and the relative level of the antenna obtained by the GPS system allows the software by using routine trigonometric calculations to display the position of the axis of the mast at ground level (or at some other datum level) , which is not now (in either case) the same as at the vertical height of the antenna. By orienting the rig in the required direction and otherwise proceeding as described above, this enables a pile to be installed in the required position and at a raking angle of 8° forward from the rig.

Claims: CLAIMS : 1 A method of positioning a construction machine on a work site comprising (a) providing the said machine with a mast having a nominally vertical axis passing through a centre of operation of the machine at ground level; (b) providing a satellite navigation system receiver having an antenna located on the said axis at the top of the mast; (c) providing means for determining the displacement of the mast from its nominal vertical position; (d) obtaining output readings from the said navigation system when the said displacement is less than a predetermined limit and distinguishing these said output readings from any other output readings that may be obtained when the said displacement is not less than the said predetermined limit; and (e) positioning the machine in response to these said output readings. 2 A method as claimed in claim 1 in which the said receiver is a GPS receiver. 3 A method as claimed in claim 2 in which the GPS receiver is of the kind which operate using the LI and L2 P-code and carrier when available and using LI CA code and cross- correlation of the encrypted Y-code whaen the LI and L2 signals are scrambled. 4 A method as claimed in any one of claims 1-3 in which the said receiver is provided with software for the determination and display of distance from an entered target position. 5 A method as claimed in claim 4 in which the said limit is reduced as the machine approaches its target position. 6 A method as claimed in claim 5 in which the said limit is reduced in steps. 7 A method in accordance with any one of claims 4-6 in which the said distance from target position is supplied to control apparatus enabling the machine to seek its target position automatically. 8 A method as claimed in any one of claims 1-7 in which the said means for determining the displacement of the mast from its nominal vertical position is a tiltmeter based on self- levelling of a fluid with sufficient viscosity to damp oscillations. 9 A method as claimed in any one of claims 1-7 in which the said means for determining the displacement of the mast from its nominal vertical position is an electronic tiltmeter 10 A method as claimed in any one of claims 1-9 in which no output readings are obtained from the said navigation system receiver except when the mast is vertical within the required tolerance. 11 A method of positioning a piling rig substantially as described with reference to the drawing. 12 Apparatus for positioning a construction machine on a work site comprising (a) a mast on the machine having a nominally vertical axis passing through a centre of operation of the machine at ground level; (b) a satellite navigation system receiver having an antenna located on the said axis at the top of the mast; (c) means for determining the displacement of the mast from its nominal vertical position; (d) means for obtaining output readings from the said navigation system when the said displacement is less than a predetermined limit and distinguishing these said output readings from any other output readings that may be obtained when the said displacement is not less than the said predetermined limit; and (e) means for positioning the machine in response to these said output readings. 13 Apparatus as claimed in claim 12 in which the said receiver is a GPS receiver. 14 Apparatus as claimed in claim 13 in which the GPS receiver is of the kind which operate using the LI and L2 P- code and carrier when available and using LI CA code and cross- correlation of the encrypted Y-code when the LI and L2 signals are scrambled. 15 Apparatus as claimed in any one of claims 12-14 in which the said receiver is provided with software for the determination and display of distance from an entered target position. 16 Apparatus as claimed in any one of claims 12-15 in which the said limit limit is reduced as the machine approaches its target position. 17 Apparatus as claimed in claim 16 in which the said limit is reduced in steps. 18 Apparatus in accordance with any one of claims 15-17 in which the said distance from target position is supplied to control apparatus enabling the machine to seek its target position automatically. 19 Apparatus for positioning a piling rig substantially as described with reference to the drawing. 20 A constuction machine fitted with apparatus in accordance with any one of claims 12-19. 21 A construction machine in accordance with claim 20, being a piling rig. 22 A construction machine in accordance with claim 20, being a diaphragm wall rig. 23 A piling rig substantially as described with reference to and as shown in Figure 1. 24 A construction machine substantially as described with reference to Figures 2-7. 25 A piling rig substantialy as described with reference to Figures 1-7.

Inventors: WELTMAN AUSTIN, WELTMAN, AUSTIN
Applicants: BICC PLC, WELTMAN AUSTIN, BICC PUBLIC LIMITED COMPANY, WELTMAN, AUSTIN
Application year: 1995
Main classification: G01S5
IPC codes: G01S5