GB2301185A

GB2301185A - Positioning system

Info

Publication number: GB2301185A
Application number: GB9608479A
Authority: GB
Inventors: Melvin Gerrard England
Original assignee: Cementation Piling and Foundations Ltd
Current assignee: Cementation Skanska Ltd
Priority date: 1995-05-09
Filing date: 1996-04-25
Publication date: 1996-11-27
Anticipated expiration: 2016-04-25
Also published as: GB2301185B; GB9608479D0

Abstract

A positioning system comprising a vehicle or rig 2 located within a predetermined region defined by at least three reflective targets 1 disposed at known locations, the vehicle or rig 2 including: i) an optical transmitter/receiver 3 which, in use, generates a beam of light 5 which is rotated so as sequentially to intersect with the reflective targets 1 and thereby to be reflected back towards the optical transmitter/receiver 3; ii) computer means 12 adapted to calculate the position of the optical transmitter/receiver 3 relative to the at least three reflective targets 1 by analysing the angle between the start and the end of reflection as the beam of light intersects the reflective targets 1 and combining this data with the known position and width of the reflective targets 1; and iii) remote sensing means 8, 9, 10 to determine the position, relative to the optical transmitter/receiver 3, of a pile or process tip or the like 11 mounted on the vehicle or rig 2, thereby enabling the absolute position of the pile or process tip or the like (11) within the predetermined region to be determined.

Description

IMPROVED POSITIONING SYSTEM This invention relates to a system for determining the position of a target within a defined region, and in particular, but not exclusively, to the positioning of a piling or ground treatment apparatus within a construction site.

In the construction and civil engineering industry, it is generally necessary to "set out" the construction site. This involves establishing to the required degree of accuracy the positions of the components of the structure prior to the commencement of work. In piling and foundation work, this can be an onerous task, since it is generally necessary for a surveyor to set out the locations where the pile or ground treatment is to be installed by marking each location with a steel peg. Aside from the time consuming nature of this procedure, the use of steel pegs is unsatisfactory since they can be accidentally or deliberately moved, this movement being difficult to detect before committing the pile or treatment to the ground.Furthermore, in piling and ground treatment work, large amounts of spoil can be generated on the site which can lead to the obliteration of locations previously marked.

It is known to determine the position of a laser beacon, and hence a point directly below the laser beacon, within a predetermined area by measuring its position relative to at least three individually identifiable bar-code reflectors located at known positions around the area. While this allows a construction site to be set out quickly and accurately, the piling or ground treatment locations must still be marked with steel pegs or the like, and consequently the problems caused by obliteration or movement of the pegs are not solved. Furthermore, the use of individually identifiable bar-code reflectors severely limits the size of the area in which positioning is to be undertaken, since individual determination of the reflectors is not possible beyond a certain range.

According to a first aspect of the present invention, there is provided a method of determining the position of a pile or process tip or the like within a predetermined frame of reference, wherein the position of an optical transmitter/receiver relative to the known positions of at least three reflective targets is determined by transmitting light from the optical transmitter/receiver and analysing the light reflected to the optical transmitter/receiver by the reflective targets, and wherein the position of the pile or process tip or the like is determined relative to the optical transmitter/receiver by remote sensing means.

According to a second aspect of the present invention, there is provided a positioning system comprising a vehicle or rig located within a predetermined region defined by at least three reflective targets disposed at known locations, the vehicle or rig including: i) an optical transmitter/receiver which, in use, generates a beam of light which is rotated so as sequentially to intersect with the reflective targets and thereby to be reflected back towards the optical transmitter; ii) computer means adapted to calculate the position of the optical transmitter/receiver relative to the at least three reflective targets by analysing the angle between the start and the end of reflection as the beam of light intersects the reflective targets and combining this data with the known position and width of the reflective targets; and iii) remote sensing means to determine the position, relative to the optical transmitter/receiver, of a pile or process tip or the like mounted on the vehicle or rig, thereby enabling the absolute position of the pile or process tip within the predetermined region to be determined.

Through the provision of the remote sensing means, it is possible accurately to determine the position of the pile or process tip relative to the known positions of the three or more reflective targets. This has the advantage over the known system that setting out with steel pegs is no longer required, since the position of the pile or process tip s determinable at any preselected time. Furthermore, in comparison to satellite-based Global Positioning Systems in which the accuracy of point determination is only of the order of +lm, improvable to +25mm through the use of a local substation, certain embodiments of the present invention allow the position of the optical transmitter/receiver to be determined to within +5mum.

Since the position of the process or pile tip relative to the optical transmitter/receiver is in practice controllable to around +10mum to +20mm, the accuracy of determination of the position of the optical transmitter/receiver is important given that the industry-specified absolute installation tolerance is generally around +25mm.

In a preferred embodiment, the reflective targets have substantially identical reflective characteristics. This has the advantage over the known system, which uses individually identifiable bar-coded reflectors, that a substantially greater range between the optical transmitter/receiver and the reflective targets can be achieved by virtue of the avoidance of the need to resolve the coding on each target. In certain embodiments, ranges over lOOm are achieved. It is possible to extend the range to beyond 500m by suitable adjustment of the optical transmitter/receiver intensity and sensitivity. In operation, the optical transmitter/receiver generates a beam of light which is rotated so as sequentially to intersect with the reflective targets. As the beam intersects with each reflective target, a portion of the beam is reflected back to the transmitter/receiver.In a preferred embodiment, the transmitter/receiver is arranged to detect the angle between the start and the end of the reflection as the light beam intersects a reflective target. This data, coupled with the known position and width of the reflective target, enables the distance of the transmitter/receiver from the target to be calculated. With data from at least three targets, the position of the transmitter/receiver may be accurately determined by known means. An electronic compass may advantageously be utilised in order to resolve possible directional ambiguities.

In embodiments in which the optical transmitter/receiver is mounted on a vehicle or rig, problems can arise due to the variation of the plane of rotation of the light beam as the vehicle or rig, and hence the transmitter/receiver, tilts as a result of traversing uneven ground conditions. It is possible to compensate to some degree for this tilting by incorporating a first-order correction in the position calculating algorithm. However, the system will fail if the tilt is so severe that the plane of rotation of the light beam no longer intersects with at least three reflective targets. In order to overcome this problem, advantageous embodiments of the present invention are provided with an anti-tilt platform on which the optical transmitter/receiver is mounted. The anti-tilt platform is preferably adapted to respond to signals from a tilt sensor mounted on the vehicle or rig, which sensor is arranged to provide signals to motor means adapted to displace the platform in such a way as to compensate for the tilt of the vehicle or rig. In general, piling rigs are not stable when tilted at angles beyond around 20 . It is advantageous for the anti-tilt platform to be able to compensate for any amount of tilt which may be encountered in general field conditions. In some embodiments, the tilt platform is arranged to compensate for tilts of up to 15 . In other embodiments, tilts of up to 200 may be accommodated.

Once the position of the axis of the optical transmitter/receiver has been determined, it is necessary to determine the position of the pile or process tip before it is committed to the ground. In embodiments where the process tool or pile is disposed in a substantially fixed manner relative to the optical transmitter/receiver, and given the offset between the transmitter/receiver and a known point on the process tool or pile, only the tilt of the process tool or pile and its level of elevation above the ground need be monitored in order to calculate the location of the pile or process tip.

However, in preferred embodiments, the process tool or pile is supported on a mast before insertion into the ground. The mast may be movable with respect to the vehicle or rig in order to allow fine positional control of the pile or process tip without moving the vehicle or rig. In such embodiments, it is necessary to provide displacement sensors arranged to detect any variation of the offset between the transmitter/receiver on the vehicle or rig and a given point on the mast in order to determine the location of the given point. Alternatively, where the mast is tall enough to intersect the plane of rotation of the light beam transmitted by the optical transmitter/receiver, the mast is advantageously provided with one or more reflectors so that the distance from the point of intersection of the light beam and the mast to the optical transmitter/receiver may be determined directly.If required, data from an electronic compass may be used to determine unambiguously the position of the point of intersection. Through the provision of a tilt sensor on the mast and/or the process tool or pile, the location of the pile or process tip may be determined by projecting towards this location from the known location of the given point on the mast or process tool or pile along the angle determined by the tilt sensor. The mast-mounted tilt sensor can also be arranged so as to enable the mast inclination to be varied as required. It is normally desirable for the mast to be vertical, although in other applications, such as the installation of raking piles, the mast may be tilted to a predetermined angle. A level sensor may be provided to determine the elevation of the pile or process tip above the ground.

In order to take into account any tilt of the vehicle or rig itself, data from the tilt sensor mounted on the vehicle or rig may be included in the positioning calculations.

In a particularly preferred embodiment, the vehicle or rig is provided with a display device attached to a position-calculating computer so that a driver may be guided, without the need for directions from an external observer, to the precise locations at which piling dr ground treatment is required. The computer may additionally be provided with a record of predetermined locations which can be displayed to the driver in the preferred order of installation.

Furthermore, the computer may record each completed treatment location so as to ensure that the vehicle does not track unnecessarily over any previously treated locations. This is particularly advantageous where, for example, a pile which has been cast in situ comprises wet concrete which could be damaged by passage of the vehicle or rig. In addition, the path of the vehicle or rig may be recorded and analysed in order to verify process efficiency.

The computer mounted on the vehicle or rig may advantageously be in communication with a host computer which can provide location data, such as site coordinates, directly from, say, a computer-aided design (CAD) package in order to reduce operator input errors. In certain embodiments, data may be transmitted in real time so as to enable the ground treatment or piling process to be carried out under full remote control, either with operator intervention or completely automatically.

For a better understanding of the invention, and to show how it may be carried into effect, reference will now be made, by way of example, to the accompanying drawing.

A construction site is provided with at least three reflective targets (1) which are strategically positioned at predetermined known locations. A casting vehicle (2) is provided with an optical transmitter/receiver (3) mounted on an anti-tilt mechanism (4). In order to determine the location of the transmitter/receiver (3) relative to the targets (1), a light beam (5) is generated by the transmitter/receiver (3) and rotated so that it intersects sequentially with the targets (1) and is reflected back to the transmitter/receiver (3). Since the reflective portions of, the targets (1) have identical known widths, the distance to each target (1) can be determined by measuring the angle through which the light beam (5) rotates while still being reflected by the target (1). An electronic compass (not shown) is used to remove any ambiguity as to the direction of any particular target (1).The anti-tilt mechanism (4) includes a tilt sensor (not shown) which determines the tilt of the vehicle (2), thereby enabling the anti-tilt mechanism (4) to adjust the attitude of the transmitter/receiver (3) so as to compensate for the tilt accordingly. This helps to keep the plane of rotation of the light beam (5) within the level defined by the height of the targets (1). A movable mast (6) carrying a pile (7) is provided on the front of the vehicle (2). The mast (6) is provided with reflective targets (8) which allow the distance of the mast (6) from the optical transmitter/receiver to be determined, and this distance, combined with data from the electronic compass, is used to determine the precise location of the point of intersect ion between the light beam (5) and the mast (6). The mast (6) is also provided with a tilt sensor (9) which, in combination with a level sensor (10), provides positional data sufficient to determine the location of the pile tip (11) relative to the targets (1), and hence the position of the pile tip (11) within the construction site is accurately specified.

The vehicle (2) carries an on-board computer (12) which displays positional information to the driver of the vehicle so as to allow accurate positioning without the need for directions from external observers. The on-board computer (12) may be programmed by way of a data cartridge (13) which is pre-loaded with positional data from a CAD computer system (14).

Claims

CLAIMS:

1. A method of determining the position of a pile or process tip or the like within a predetermined frame of reference, wherein the position of an optical transmitter/receiver relative to the known positions of at least three reflective targets is determined by transmitting light from the optical transmitter/receiver and analysing the light reflected to the optical transmitter/receiver by the reflective targets, and wherein the position of the pile or process tip or the like is determined relative to the optical transmitter/receiver by remote sensing means.

2. A method according to claim 1, wherein the reflective targets have substantially identical reflective characteristics.

3. A method according to claims 1 or 2, wherein the optical transmitter/receiver transmits a light beam which is rotated so as sequentially to intersect with the reflective targets.

4. A method according to claim 3, wherein the optical transmitter/receiver detects the angle between the start and the end of the reflection as the rotating light beam intersects a reflective target.

5. A method according to claims 3 or 4, wherein the orientation of the plane of rotation of the light beam is adjusted by means of an anti-tilt platform associated with the optical transmitter/receiver so as to ensure that the plane of rotation intersects at least three of the reflective targets.

6. A method according to claim 5, wherein the anti-tilt platform is controlled by motor means responsive to signals generated by a tilt sensor.

7. A method according to any of claims 3 to 6, wherein the pile or process tip depends from a mast provided on a vehicle or rig.

8. A method according to claim 7, wherein the mast intersects the plane of rotation of the light beam and wherein the position of the mast relative to the optical transmitter/receiver is determined by analysing the light reflected from one or more reflective targets provided on the mast.

9. A method according to any preceding claim, wherein an electronic compass is used to provide additional directional data.

10. A method according to any preceding claim, wherein the position of the pile or process tip within the frame of reference and relative to one or more predetermined points is monitored and/or controlled by computer means.

11. A method according to claim 10, wherein the computer means is adapted to display a representation of the location of the pile or process tip within the frame of reference and relative to one or more predetermined points.

12. A positioning system comprising a vehicle or rig located within a predetermined region defined by at least three reflective targets disposed at known locations, the vehicle or rig including: i) an optical transmitter/receiver which, in use, generates a beam of light which is rotated so as sequentially to intersect with the reflective targets and thereby to be reflected back towards the optical transmitter; ii) computer means adapted to calculate the position of the optical transmitter/receiver relative to the at least three reflective targets by analysing the angle between the start and the end of reflection as the beam of light intersects the reflective targets and combining this data with the known position and width of the reflective targets; and iii) remote sensing means to determine the position, relative to the optical transmitter/receiver, of a pile or process tip or the like mounted on the vehicle or rig, thereby enabling the absolute position of the pile or process tip within the predetermined region to be determined.

13. A method of determining the position of a pile or process tip substantially as hereinbefore described with reference to or as shown in the accompanying drawing.

14. A positioning system substantially as hereinbefore described with reference to or as shown in the accompanying drawing.