GR1009521B - Geomagnetic scanner and utilisation method thereof - Google Patents

Abstract

Novelty: a geophysical arrangement and a respective utilisation method for the magnetic imaging-scanning of a ground surface are disclosed. Technical features: full automation of the scanning process via a differential magnetometer moving on two axis and being adapted on a system of stretched-out strings. Purpose: speedy detailed and accurate geomagnetic imaging. Embodiments: the main application of the invention is the drawing of consultative magnetic maps useful for the evaluation of excavation positions, the drawing of archeological excavation works and even the determination of the underground structure on the basis of the magnetic properties of the underground materials.

Description

DESCRIPTION

Geomagnetic scanner and method of use

The geomagnetic scanner and the related method of use refers to a geophysical device and the corresponding methodology, which captures in detail the vertical gradient of the intensity of the magnetic field on a terrestrial scanning surface. The arrangement is developed in the shape of a horizontal "H" of stretched ropes (figure 1), where the parallel lines represent the fixed sections, while the transverse line of the "H" can be displaced parallel to its original position. The scanning is achieved by a moving differential magnetometer, the head (1), which moves along the transverse line, and which, combined with the translational movement of the line, can be found in all the positions of the surface that define the ends of the deployment ( motion in two axes).

Arrangements with similar geometry for movement in two vertical axes have been repeatedly used both in small devices such as scanners and printers, and in giant cranes for lifting and transporting loads. In contrast to the above cases where the used shafts are rigid, in the present invention the rigid shafts are replaced by stretched ropes. The use of ropes offers the advantage of easy transport and the possibility of developing very long shafts.

Corresponding geomagnetic impressions are still made today with portable devices (hand-held differential magnetometers). In these impressions, the operator moves along the lines of an imaginary canvas recording the field values for each desired point with the help of a built-in recorder. In this way the process becomes laborious and time-consuming and it is practically difficult to take successive measurements at a distance of less than one meter. OL locations of the measurements on the imaginary canvas are determined by approximation in the judgment of the operator, and errors also arise from the orientation of the portable magnetometer as well as the effect of the operator on the field.

Advantages of the present invention are that it offers a greater density of measurement network, recording with greater detail and precision the local magnetic field, with less effort and greater speed.

The geomagnetic scanner according to the present invention consists of ropes, equipment for supporting, tying and adjusting the tension of the ropes (uprights, stakes, rings, tensioners) and three electromechanical devices: two nodes (2) and one head (1). To facilitate the understanding of the structure of the device, TABLE 1 (p. 10) is listed, which presents the complete list of the individual parts of the geomagnetic scanner.

Figure 1 shows the layout of the geomagnetic scanner in full deployment, in plan view. The shape of the "H" can be seen.

As shown in figure 2, a key feature of the device is a "bridge", formed by the nodes (2), the transverse rope (8) that joins them, the head (1) suspended from it, and the rope-strap (9). The bridge rests on the parallel ropes (6) with the C-type wheels (16) of the hubs (2). The knots moving synchronously on the parallel ropes carry the entire "bridge" in parallel successive positions.

Polyester ropes with external mesh, of three different cross-sections, 8, 4 and 3mm, are used. Specifically, for the two parallel ropes (6) and the struts (7), a rope with a cross-section of 8mm is used, for the transverse rope (8), a rope with a cross-section of 4mm, and for the rope-strap (9) a rope with a cross-section of 3mm is used.

The whole device rests on four uprights (12) where the ends of the two parallel ropes (6) are tied, as shown in figure 1.

Fig. 3 is an enlargement of a part of Fig. 1, and gives a plan view of the method of attachment for each of the uprights (12). Each upright (12) has holes every 25cm to place the upright ring (5) to which the parallel rope (6) will be attached, in the hole that best serves the verticality of the system. A second upright link (5) (opposite orientation placement) is also installed, having two struts (7) attached with a tensioner at the other end, to be anchored to stakes (13) driven into the ground. Each of the parallel ropes (6), as well as all struts (7) carry tensioners (3), in order to adjust the desired tension in the ropes and to ensure the vertical orientation of the uprights (12) and the static balance of the system. In figure 3, the parallel rope (6) is suspended on the stanchion eye (5) using a climbing eye (11). The rope brake (10) is inserted between the rope and the climbing ring, which allows the passage of the passing rope only once.

The nodes (2) mediate the points of contact of the two parallel ropes with the transverse rope (8), which is attached to the loops of the nodes (23), and have the possibility of synchronized movement on the two parallel ropes.

In figure 4, the node (2) and all the parts that make it up are shown.

The movement of the node, on the parallel rope (6), is done with the help of the M2 stepper motor (20) with the E type gear (18) attached, suitable for 8mm rope. The toothed wheel of type E (18), forces the parallel rope passing through the wheels of type C to deviate slightly from its straight course, while at the same time it is pressed against it (action-reaction), so as to exclude sliding between them and displacement of the node (2) is achieved by rotating the toothed wheel E (18). The amount of deflection determines the tension of the rope on the sprocket, it can be adjusted by varying the distance of the wheels C from the frame of the hub (21), which is achieved by loosening the nuts of the arm (24), and moving it to an elongated guide .

The two nodes have mirror image symmetry and during operation of the device they have the node frame (21) in a horizontal position due to the tension of the transverse cord (8), which is adjusted using a tensioner.

The individual components that make up each node are fitted to the node frame (21). These are: stepper motors M1 (19) and M2 (20), with D-type (17) and E-type (18) gears attached respectively, two C-wheels (16), fitted to the frame with brackets (24), the knot ring (23) for tying the cross rope (8), rechargeable knot battery (24), lithium ion capacity 12000mAh, and the electronic circuit of the knot located under the protective cover (22). The electronic circuit of the node is built on a challenging soldered board of electronic components (32) (breadboard), and is based on the ATmega328 processor, includes the SRX882 (433MHz) receiver, while the stepper motors are controlled with the TB6612FNG integrated circuit.

Figure 6 shows the diagram of the electronic circuit of the node, where the way of connecting the components is shown.

TABLE 2 (page 11) outlines the abbreviations used in the Figure 6 diagram, along with additional component information.

Figure 5 shows the head, which during operation of the device is suspended from the transverse rope (8) by two wheels of type A (14), resting on the frame of the head (27), while two smaller wheels of type B (15) , located on the other side of the transverse rope (8) are used to normalize the movement and exclude its deflection from the rope. Also attached to the head frame (27) are the pre-wired electronics board (32) with the head electronics attached, the head battery (29) (1800mAh Li-ion rechargeable battery), and the tubular frame (30) carrying the axial magnetic sensors (31), the ones are in protective cases made of materials of minimal magnetic effect. Their adaptation to the tubular frame is done in a way that allows their alignment and the change of the distance between them.

The electronic circuit of the head is also based on the same ATmega328 processor and also includes an STX882 transmitter, a magnetic recording unit and a buzzer, while the conversion of the analog signals of the magnetic sensors (31) is done with the 24-bit analog signal converter ADS1256.

Figure 7 shows the diagram of the electronic circuit of the head (1), where the connection method of the electronic components is shown. Table 3 (p 12) describes the abbreviations used along with additional information about the components.

The movement of the head (1) along the transverse rope (8) is made with the help of the belt-rope (9), closed route, driven by the pair of stepper motors M1 (19), carrying D-type toothed wheels ( 17), and located one at each node. The ends of the shoe-strap (9) are attached to the attachment points of the head (28) located at antidiametrical points of the head frame (27).

OL stepper motors M1 (19), move simultaneously with a balanced direction of rotation and are responsible for the translational movement of the head along the transverse rope (8). The stepper motors M2 (20) move simultaneously in the opposite direction so that the "bridge" moves parallel to its initial position, along the parallel ropes (6).

The coordinated movements of the two pairs of motors lead the head to perform a scan, moving in consecutive parallel paths, in opposite directions, across the surface defined by the edges of the deployment. During this movement, synchronized measurements of the magnetic field strength values (vertical component) are taken by the two magnetic sensors (31) (differential magnetometer), simultaneously recording the corresponding position coordinates. The data is recorded on a magnetic storage medium (microSD memory card).

TABLE 4 on page 13 gives information regarding the mechanical characteristics of the used wheels located on the head and hubs.

The typical application of the present invention aims at uncovering underground structures or constructions in the context of the archaeological research project, in order to evaluate the excavation site and plan the excavation works. For the above needs, magnetic maps (tapes) are drawn up with the data collected during the scanning process. The region of interest should be divided into rectangular scan boxes of appropriate size.

The use of the geomagnetic scanner is carried out according to the following method:

The process begins by defining the scan box selected, in the search field. The four points defining the rectangular scan frame are determined by surveying methods in the field, and are the points where the uprights (12) will be placed. The two points should not have a height difference of more than one meter, and also within the frame there should be no trees or other obstacles at a height greater than that determined by the final placement of the ropes. For the case of scanning an approximately horizontal area, the maximum permitted height of the obstacles is slightly greater than one meter, for any other case it will be smaller, and the suitability of the area should be assessed empirically, since it depends each time on the morphological specificity of the of land area to be scanned.

At each of the above points, a wooden stake (13) is nailed to the ground with a hole for attaching the nose of the post, in the upper part. The stakes (13) of the uprights (12) remain in the field even after scanning, as characteristic points of position identification and georeferencing of the resulting magnetography. Two stakes are also placed per post (figure 3), at predetermined points, which serve to support it with struts. The stake rings (4) are screwed into the holes of these stakes.

After anchoring the tensioners of the struts to the pile rings (4) of the support piles, and placing the nose of the upright in the hole of the corresponding pile, the upright (1) is placed in a vertical direction and is awaiting the attachment of the parallel rope (6 ).

The attachment of each parallel rope is done with the hook of the tensioner at one end, and with an attached climbing ring (11) at the other, to the corresponding upright rings (5) that are placed in the positions that ensure the verticality of the system. The rope brake (10) is inserted between the rope and the climbing ring, which allows the rope to pass through only once (figure 3). The horizontal ropes should be tensioned as much as possible by the use of a polysplitter or other technique, and then the verticality of the stanchions should be adjusted by the strut tensioners.

Next is the placement of the knots (2) and the transverse rope (8). Each hub is suspended from each of the parallel ropes (6) so that it passes between the C-type wheels (16) and the E-type sprocket (18). To facilitate the passage of the taut rope, the C-type wheels (16) can be moved by loosening the arm nuts (24), increasing the passage space of the rope, and then repositioned in the original position. OL hanging knots (2) are initially oriented vertically due to their weight, but are forced into a horizontal orientation by placing the cross rope (8), which has a tensioner with a hook at one end and a climbing eye (11) at the other, to be attached to the knot rings (23).

The transverse rope tensioner serves to apply the desired tension to the rope.

Next is the placement of the head (1) and the rope-strap (9). The head is suspended on the cross rope (8) so that it passes between the pair of wheels A (14) and the pair of wheels B (15). To facilitate the passage of the rope between the wheels, its tension can be temporarily reduced by the corresponding tensioner.

The head (1) is oriented vertically by its weight, suspended by the pair of type A wheels (14), which can roll passively on the transverse rope (8), while the pair of smaller wheels B (15), serves to normalize of the movement of the head, and preventing it from being deflected by the cross rope (8).

Finally, the strap-rope (9) is placed, the ends of which are tied to the two tie-down points (28) located diametrically opposite the head frame (27). The rope-belt (9) "embraces" the D-type sprockets (17) of the two hubs, so that the transfer movement of the head is achieved with the simultaneous and balanced rotation of the D-type sprockets (17) (figure 2).

Tensions are transferred between the knots from both the transverse rope (8) and the strap-rope (9), with the result that when one of the two is stretched, the other is relaxed. These stresses can be appropriately distributed by using the transverse rope tensioner.

The process is completed with the final check and the scan is performed. After the installation of all the components and the arrival of a few minutes of time, the weights of the objects affect the elasticity of the rope, resulting in variations in the tensions of the ropes and deviations from the original vertical directions of the uprights (12). Thus, all settings should be rechecked and the necessary corrections made using the tensioners (3).

At start up both the head (1) and the "bridge" should be in the programmed start position at the ends of the scan frame. Then the three electromechanical devices, head (1) and nodes (2), should be put into operation by the respective switches and finally the start of the scan is done by the start switch (33), located on the head (figure 2 ).

At a random time during the scanning operation, the representation of Figure 1 can be considered.

The scanning process is fully automated and does not require operator intervention at any stage. When the scan is complete, the device stops automatically, and the operator can remove the memory card to use the recordings.

The data can be plotted on grade equipotential lines or field strength equipotential lines in the form of geomagnetic maps, or used for any other processing with the help of suitable computer software.

Claims (3)

1. a. Geomagnetic; scanner consisting of a head (1), two electromechanical hubs (2), polyester ropes and equipment for supporting, tying and adjusting the tension of the ropes, and scans a terrestrial frame, by the combined movement of the head in two perpendicular axes, b. A geomagnetic scanner in which the head (1) and electromagnetic nodes (2) are attached to a horizontal arrangement of "H" shaped taut ropes. 2. Geomagnetic scanner, according to claim 1, where the head (1) can move in two vertical axes of the horizontal plane, with the help of the electromechanical nodes (2). 3. A method of using the geomagnetic scanner according to claims 1 and 2, and comprising deploying the device in the survey field, performing the scanning operation, and extracting the recorded values and data obtained during its operation.