Apparatus Having a Pair of Magnetic Field Generating Cables for Measuring Position of an Underground Excavator

The present invention relates to a position measuring apparatus of an underground excavator and, more particularly, to a position measuring apparatus of an underground excavator such as a shield machine which excavates underground.

Conventional methods of location survey for driving a shield machine used in the shield tunneling method include: a method in which the inside of a tunnel is surveyed with a transit or the like; and a method in which an optical oscillating device for generating a coherent light such as a laser beam is provided inside a vertical shaft of a shield machine, and in which the device emits the light along the planned tunnel line, and then the light spot on a target provided in the shield machine is read, and thus displacement and deflection angle of the shield machine are measured. In still another method, the position of the machine relative to a reference position is obtained with combinations of a direction gyro and a pressure-type subsidence recorder, and of a clinometer and driving distance recorder (referring to length of a segment). Further, the inventor has proposed (in Japanese Patent Laid-Open No. 62-169012) a method in which a magnetic field generating cable is provided on the ground surface and a magnetic field detecting element is provided in an underground excavator, and in which a magnetic field generated from the cable is detected by the detecting element and thus displacement in the horizontal position of the underground excavator is measured.

However, in a case where the inside-tunnel survey method employing a transit or the like is used to survey a to-be-bored tunnel which is curved or bent, many station points are required, increasing the number of work stages. Thus, such a method is not practical. If the method employing a laser beam is used to survey a curved or bent tunnel, the laser beam may not reach a target in some cases. In such cases, an optical oscillating device has to be moved to an appropriate position. Further, if a planned tunnel line is curved or bent, because, in such a case, a light beam can not directly irradiate the planned line, the displacement and deflection angle of the shield machine are usually obtained by measuring distances and angles between the target, the oscillating device and the planned tunnel line and by calculating from such measurements the positions thereof relative to one another. Therefore, extra work stages are required for the transposition of an oscillating device, the measurement and the calculation, and thus excavating efficiency decreases. A method employing a gyro has a problem in that because accumulated error becomes large, it is not suitable for a long-distance excavation. Further, a method employing a magnetic field has a problem in that though it measures horizontal displacement, it cannot measure excavating distance (such as a distance of excavation from a vertical shaft).

It is an object of the present invention to solve the above-mentioned problems by providing a position measuring apparatus of an underground excavator which easily and accurately measures the position on a horizontal plane or the like of a shield machine or the like which is excavating underground.

The first aspect of the present invention provides a position measuring apparatus comprising: a transmitter including at least two cables which are provided under or on the ground and around which AC magnetic fields are generated by electricity from an AC power source; a receiver which receives the AC magnetic fields; and a computing unit which identifies signals from the receiver and which calculates the position of the underground excavator. The second aspect of the present invention provides a position measuring apparatus in which the planes of the two cables are substantially perpendicular to each a two other. The third aspect of the present invention provides a position measuring apparatus in which the receiver includes two magnetic field detecting elements which are substantially perpendicular to each other. The fourth aspect of the present invention provides a position measuring apparatus in which the receiver is supported by a receiver supporting device which rotates, according to signals from a direction detecting device, so as to maintain these elements at specified angles to the two cables. Further, the fifth aspect of the present invention provides a position measuring apparatus comprising a timing output circuit which controls the application of power to the two cables so that AC magnetic fields are generated alternately from the two cables.

In a position measuring apparatus constructed as described above, the magnetic fields generated by supplying AC currents to at least two cables provided on or under the ground are received by the two magnetic field detecting elements which intersect each other at a specified angle on the receiver supporting device which is controlled so as to face in a constant direction, and such magnetic field reception by these elements provides a level of voltage, by which the position on a horizontal plane of an underground excavator is easily and accurately detected.

A position measuring apparatus as described above may include two more cables and another receiver, so that it can measure depth. The depth may also be measured by a conventional pressure-type subsidence recorder or a combination of a clinometer and a driving distance recorder.

FIG. 1 is a schematic plan view of a position measuring apparatus of an underground excavator according to the present invention;

FIG. 2 is a block diagram of a position measuring apparatus according to the first embodiment of the present invention;

FIG. 3 is a block diagram of a position measuring apparatus according to the second embodiment of the present invention;

FIGS. 4 and 5 are schematic drawings illustrating the principle of horizontal position detection according to the present invention; and

FIGS. 6 and 7 are schematic drawings showing exemplary placing of cables.

The principle of a horizontal position detection according to the present invention will be described with reference to FIGS. 4, 5.

FIG. 4 is a schematic plan view. In the figure, two cables 10 formed in rectangular loops are provided vertically underground. A cable 10a is located in a vertical X-Z plane which is parallel to the horizontal direction of excavation (X-axis). The other cable 10b is located in a vertical Y-Z plane which is perpendicular to the direction of excavating and substantially perpendicular to the plane of the loop of cable 10a. One side of the loop of cable 10a touches one side of the loop of cable 10b. A receiver 30 has two magnetic field detecting elements S.sub.1, S.sub.2 whose magnetic field detecting directions intersect perpendicularly and are angled at 45.degree. to vertical planes of the cables 10a, 10b.

FIG. 5 is a schematic perspective view of what is shown in FIG. 4. An AC power source 11a supplies the cable 10a with voltage e.sub.1, current i.sub.1 and frequency .omega..sub.1, and another AC power source 11b supplies the cable 10b with voltage e.sub.2, current i.sub.2 and frequency .omega..sub.2.

Under these conditions, parameters are determined as follows:

2W: distance between two vertical legs of the cable 10a, and distance between two vertical legs of the cable 10b

X: distance of the magnetic field detecting elements S.sub.1 and S.sub.2 from the plane of the loop of cable 10b

Y: distance of the magnetic field detecting elements S.sub.1 and S.sub.2 from the plane of the loop of cable 10a

dX: horizontal displacement of the magnetic field detecting elements S.sub.1 and S.sub.2 from the horizontal center of the loop of cable 10a

dY: horizontal displacement of the magnetic field detecting elements S.sub.1 and S.sub.2 from the horizontal center of the loop of cable 10b

.theta..sub.1 : angle between the magnetic field detecting element S.sub.1 and a line perpendicular to the plane of the loop of cable 10a

.theta..sub.2 : angle between the magnetic field detecting element S.sub.2 and a line perpendicular to the plane of the loop of cable 10a

V.sub.11 : voltage induced in the magnetic field detecting element S.sub.1 by the cable 10a

V.sub.21 : voltage induced in the magnetic field detecting element S.sub.2 by the cable 10a

V.sub.12 : voltage induced in the magnetic field detecting element S.sub.1 by the cable 10b

V.sub.22 : voltage induced in the magnetic field detecting element S.sub.2 by the cable 10b

The horizontal displacement of the receiver 30 from the X-axis center of the loop of cable 10a is obtained as:

The horizontal displacement of the receiver 30 from the Y-axis center of the loop of cable 10b is obtained as:

The horizontal distances of the receiver 30 of an underground excavator 20 from the cables 10a, 10b are expressed as:

Thus,

where

Although the cable 10a and the cable 10b have the same distance between their vertical legs (2W) and one side of the loop of cable 10a touches one side of the loop of cable 10b in the above example, the horizontal distance of each loop from the receiver 30 on the underground excavator can naturally be obtained if the between-leg distances of the two cables 10a, 10b are different from each other and the sides of the cable loops which are touched in the above example are separated or intersected.

FIG. 1 shows a plan view of a position measuring apparatus 25 of an underground excavator 20 according to the present invention constructed on the basis of the above described principle. FIG. 2 shows a detailed block diagram of the position measuring apparatus. The figures show: a vertical start shaft SH; a vertical end shaft EH; a transmitter 10 including two cables, one being a cable 10a provided with one of its vertical legs in the vertical start shaft SH and its other vertical leg in the vertical end shaft EH, and the other being a cable 10b provided with both of its vertical legs inside the vertical start shaft SH; an underground excavator 20; a receiver 30 carried by the underground excavator 20 and including two magnetic field detecting elements S.sub.1 and S.sub.2 whose magnetic detecting directions are perpendicular to each other; an analog-to-digital converter 35; and a receiver supporting device 40 which rotates according to signals from a direction detecting device 50 in order to position the receiver 30 at a certain angle to the two transmitting loops. The direction detecting device 50 detects the direction in which the underground excavator 20 is driven, and controls the rotation of the receiver supporting device 40. A computing unit 60 calculates the position of the underground excavator 20 based on signals which the device 60 receives. An indicator 70 indicates the position of the underground excavator 20 according to the calculations by the computing unit 60. A depth measuring device 100 employs a pressure-type subsidence recorder or the like, according to this embodiment, to measure depth (Z-axis). The loop of cable 10a and the loop of cable 10b of the transmitter 10 are perpendicular to each other and are supplied with power by AC power sources 11a and 11b respectively.

The receiver 30 includes: two magnetic field detecting elements S.sub.1 and S.sub.2 ; each element having a respective pair of filters f.sub.1 and f.sub.2 connected thereto; and two pairs of receiving amplifiers Am.sub.1 and Am.sub.2, with each amplifier being connected to a respective one of the filters f.sub.1, f.sub.2. The receiver 30 is connected through the AD converter 35 to the computing unit 60. The receiver supporting device 40 is rotated by a pulse motor 42 which is controlled by a motor controller 41 according to the signals from the direction detecting device 50, in order to maintain the positions of the magnetic field detecting elements S.sub.1, S.sub.2 or the like at constant angles. The magnetic field detecting elements S.sub.1, S.sub.2 are placed on a table (not shown).

Operation of the position measuring apparatus constructed as described above will be described. The AC power source 11a supplies the cable 10a with an AC current at a frequency .omega..sub.1. The AC power source 11b supplies the cable 10b with an AC current at a frequency .omega..sub.2. The AC currents thus generate magnetic fields around the cables 10a and 10b. The magnetic fields are detected by the magnetic field detecting elements S.sub.1 and S.sub.2. The filters f.sub.1 and f.sub.2 determine from which cable the magnetic field inducing the voltage in each of the magnetic field detecting elements originated. The signals from the filters f.sub.1 and f.sub.2 are amplified by the respective receiving amplifiers Am.sub.1 and Am.sub.2. Then, the amplified signals are converted into digital values by the AD converter 35. The computing unit 60 performs the calculation described above based on these signals, and obtains X and Y-coordinates of the position of the receiver 30 of the underground excavator 20. The computing unit 60 also controls the receiver supporting device 40, according to the signals from the direction detecting device 50, so that the two magnetic fields detecting elements S.sub.1 and S.sub.2 will be at constant angles.

FIG. 3 is a block diagram of a position measuring apparatus 250 of an underground excavator 20 according to the second embodiment of the present invention. The parts equivalent to those of the first embodiment are denoted by the same numerals as in the first embodiment, and the description thereof will not be repeated.

Two cables 110a and 110b of a transmitter 110 are positioned with their loops substantially perpendicular to each other, and are alternately, according to signals from a timing output circuit 200, supplied with the same current (voltage e.sub.c, current i.sub.c, frequency .omega..sub.c) from AC power sources 111a and 111b. A receiver 130 includes two magnetic field detecting elements, such as coils, S.sub.1 and S.sub.2 ; two filters f.sub.1, each being connected to a respective one of these elements S.sub.1 and S.sub.2 ; two receiving amplifiers Am.sub.1 connected to a respective filter f.sub.1. The receiver 130 is connected through an AD converter 35 to a computing unit 60.

The operation of such a construction will be described. The AC power sources 111a and 111b supply current having a frequency .omega..sub.1 to the cables 110a and 110b alternately according to the signals from the timing output circuit 200. AC magnetic fields are thus alternately generated in concentric configurations about cables 110a and 110b. The magnetics fields are detected by the magnetic field detecting elements S.sub.1 and S.sub.2. The detection signals are shaped by the filters f.sub.1. Because the signals from the timing output circuit 200 are inputted to the computing unit 60, it can be determined from which cable the detected magnetic field originated.

FIG. 6 illustrates an application of the present invention, wherein a horizontal shaft H is provided between a vertical start shaft SH and a vertical cable shaft V and a cable 10 is provided in these vertical shafts. FIG. 7 illustrates another application, wherein a cable 10a is provided underground between a vertical start shaft SH and a vertical end shaft EH and a cable 10b is provided on the ground surface EP therebetween.

A vertical shaft may be bored not only from the ground surface but from an underground portion of a building. In the case where vertical shafts are provided but no horizontal shafts, a cable may be grounded at a lower portion of a vertical shaft, providing similar effects to those in the above embodiments.

A position measuring apparatus according to the present invention advantageously detects automatically, continuously and instantaneously the horizontal position of an excavator, such as a shield machine, excavating underground.

Since the present invention can be realized by simply providing the necessary cables, a position measuring apparatus according to the present invention can be suitably used for boring a tunnel which is sharply curved or continuously curved with its depth varying greatly.