SE512488C2 - Method and system for remote detection of markers - Google Patents

Abstract

A method and a system is provided for remote detection of markers (10), each marker comprising at least two magnetic elements (13) arranged in a predetermined relationship providing an identity of the marker, by either exciting a respective magnetic element (13) to resonate mechanically or by exciting an electrical resonant circuit (14), to which the respective magnetic element (13) is coupled, to oscillate electrically. A resonant frequency (f?res?) of the respective magnetic element or of the electrical resonant circuit depends on an applied magnetic field (H), which is given a varying orientation. A corresponding variation in the resonant frequency (f?res?) is monitored, and an extreme value (f?min local?) of the variation is detected. A momentary orientation ( alpha ?min local?) of the magnetic field is determined in response to the detection of the extreme value, and an orientation of the respective element (13) is determined from this momentary field orientation.

Description

The material, called the delta-E effect, further depends on the resonant frequency of each element also on the magnetic field strength or the flow intensity along the main direction (longitudinal direction) of the element. This material property is used according to WO88 / 01427 to enable simultaneous detection of several identical markers. A coil device is arranged to generate a heterogeneous magnetic bias field, wherein two markers present simultaneously in the detection zone will be exposed to different magnetic field strengths and will therefore also have different resonant frequencies for the magnetic elements included in the markers.

WO93 / 14478 discloses a similar system, in which, however, the markers are provided with one or more electrical resonant circuits, each of which is inductively coupled to a respective magnetic sensor element. The relative permeability of the magnetic element pp is affected by the heterogeneous magnetic field, and due to the inductive coupling between the magnetic element and the resonant circuit, the resonant frequency of the resonant circuit is also affected by the heterogeneous magnetic field. The markers in WO93 / 14478 are excited and detected by electromagnetic or magnetic signals.

The magnetic elements of each marker are arranged to represent a certain amount of information, such as an identity for each marker, an article number, and so on. For markers, where the magnetic elements are arranged in angular relations with respect to each other, the information is represented by the respective angles between pairs of magnetic elements, and for markers, where the magnetic elements are arranged parallel to each other, with fixed distances between adjacent elements, the information of the distances. Additional information can be represented by using elements of different types, for example of different lengths or with different masses. A method of achieving magnetic sensor elements with different masses, and consequently different resonant frequencies, is known from WO95 / 29534.

A method for simultaneous detection of several markers is known from WO95 / 29467. The markers and the magnetic elements contained therein are exposed to a sequence of different magnetic field situations. The resonant frequencies of all elements present in the detection zone are detected for each magnetic field situation, and the component of the magnetic field vector along the longitudinal direction of each element is determined from the corresponding-detected resonant frequency. All possible combinations of angular relationships between pairs of elements in a marker are determined, and for such a combination the resulting magnetic field vectors are calculated from different pairs of the determined components for a given magnetic field situation by using the angular relationships for the given combination. Each combination is eliminated which does not exhibit identical resulting magnetic field vectors when calculating for different pairs of elements, and the procedure is repeated until only those combinations remain which correspond to actual element combinations of markers within the detection zone.

The method according to WO95 / 29467 is advantageous in that it is able to simultaneously process and identify several identical markers in the detection zone. However, if the total number of possible code values (number of different angular element arrangements) is large, the total number of calculations that must be performed becomes very large, and the identification process may need to continue for a considerable time, until all elements present in the detection zone have been correctly identified. . There is therefore a need for a faster detection method and a faster detection system, which are able to identify the markers faster.

N U 20 25 30 35 r-stf-za; Summary of the Invention An object of the present invention is to enable faster detection of markers for remote detection of objects. The object is achieved by a method and a system according to the appended independent claims. The object has essentially been achieved by the realization that a marker can be identified very quickly by exposing it to a rotating magnetic field, whose magnetic field vector rotates 360 °, while continuously monitoring a variation of the resonant frequencies arising from the respective magnetic elements in order to detect the moment the resonant frequency variation reaches an extreme value, such as a minimum value. The actual orientation of the magnetic field vector is registered at the moment when the extreme value is detected, and the orientation of the respective magnetic element is determined from the instantaneous magnetic field orientation.

In short, when the magnetic field vector is rotated 360 °, the field vector will become more and more aligned with a first element of the cursor and will later become parallel to this element, the extreme value being detected and the orientation determined for the first element. As the field vector is rotated further, it will become less and less aligned with the first magnetic element but instead become more and more aligned with a second magnetic element.

The orientation of the second magnetic element is determined when the magnetic field vector is aligned with the second element, and the procedure is repeated for the remaining elements of the cursor. Once the correct element orientations have been determined, according to a preferred embodiment, one can determine the type of each element during a second step, where a magnetic field of varying field strength is applied along each determined element orientation in order to detect a global minimum / maximum resonant frequency for each element and determine its type by comparing this resonant frequency with a set of pre-stored data. 5 15 20 25 30 512v188, 5 Other objects, features and advantages of the present invention will become apparent from the following detailed description, from the drawings, and from the subclaims. General Description of the Drawings The present invention will now be described in more detail with reference to the accompanying drawings, in which: Fig. 1 is an overview view of a remote detection system according to the present invention, Fig. 2 is a general illustration of the method according to the invention, , which illustrates the method according to the invention, Fig. 4 illustrates a second step of the method according to a preferred embodiment of the invention and Fig. 5 is a frequency diagram, which illustrates the second step in Fig. 4.

Detailed Description of the Invention Fig. 1 illustrates a detection system according to an illustrative embodiment of the present invention.

The detection system comprises excitation means 15, detection means 16, both of which are operatively connected to a system control unit 17, and a magnetic field generating means 18.

A marker 10 is provided with four magnetic sensor elements 13. In the illustrated embodiment, these magnetic elements are of a magnetoelastic (magnetostrictive) type known per se and are formed, for example, as thin strips, bands or wires which are arranged in an angular arrangement. of an amorphous metal alloy with special magnetic properties. However, the invention is equally applicable to markers to which a respective magnetic element 13 is connected.

Markers of these two types are described in, for example, WO88 / 01427 which includes electrical resonant circuits, 4312 and 530 "(433 and WO93 / 14478, which are referred to above and incorporated herein by reference.

(FIG. 2) are of different types and have different resonant frequencies. The different types of individual magnetic elements 13a-d can be selected from elements of different lengths and / or elements with different masses, shapes, etc.

The excitation means is arranged to generate magnetic or electromagnetic excitation signals, which put the magnetic elements 13 in a state of magnetic resonance. The magnetic signals generated by the self-oscillating magnetic elements 13 are detected by the detecting means 16 and applied to the system control unit 17.

The magnetic field generating means 18 is further arranged to generate a varying magnetic field H, which will be described in more detail below. Due to the variations in the magnetic field strength H, the material properties of the magnetic elements 13 will cause a corresponding variation in the resonant frequency fæs for the respective elements 13.

The system control unit 17 is arranged to drive the magnetic field generating means 18, so that it generates a magnetic field with a rotating field vector. The field vector preferably rotates 360 °. The rotation of the magnetic field vector is illustrated in FIG. 2, for a respective magnetic element 13 is illustrated in FIG and the resulting variation in resonant frequency fms 3. When the magnetic field field vector H begins to rotate from 0 ° to 360 °, then with a first magnetic element 13a of the cursor 10. the field vector As the field vector H becomes more and more aligned with this magnetic element, the resonant frequency fms of the element will decrease in value (illustrated by an arrow I in FIG. 3), since the projection of the magnetic field vector H along the first the longitudinal direction of the magnetic element 13a becomes larger and larger. At a certain angle of rotation agmloæl, the projected field vector H will reach the maximum (ideally completely parallel to the first magnetic element l3a), the resonant frequency f} $ reaching a minimum value for IWÜ. A further rotation of the field vector H will make it less perfectly aligned with the first element 13a, whereby the resonant frequency f; æ begins to increase, as illustrated by an arrow II in FIG. 3. At the moment when the resonant frequency reaches its local minimum point fwnlæa, the instantaneous angular rotation is recorded at the field vector H. Since the local minimum resonant frequency will occur when the field vector H and the first magnetic element l3a are parallel to each other, the momentary orientation of the element l3a is obtained directly from the field vector H ie amin local - When the field vector H is rotated continuously, it will become less and less aligned with the first element 13a but more and more aligned with the second element 13b.

At a certain angular rotation, the field vector H will become parallel to the second magnetic element 13b, its orientation being determined similarly to the above. Then a corresponding determination is made of the orientation of the third and fourth magnetic elements 13c and 13d, respectively.

According to a preferred embodiment of the present invention, the marker 10 is provided with magnetic elements 13a-d of different types, i.e. which have resonant frequencies within different (but possibly overlapping) frequency bands. For such a marker, the type of each magnetic element 13a-d is determined in the following manner, as soon as the orientations have been determined as above for the respective elements 13a-d. For each element orientation determined as above, the system controller 17 controls the magnetic field generating member 18 so as to generate a magnetic field H of varying strength along the respective orientation, as illustrated in FIGS. 4 and 5. When the magnetic field strength is varied along the longitudinal direction of a respective magnetic element 13a-d , its resonant frequency will decrease and finally reach a 10 15 20 25 30 35 1s12 «4sa global minimum value fkmg fl at a magnetic field strength Hnm1 fl w fl. The global minimum resonant frequency is directly associated with a respective element type, and the relationship between a global minimum resonant frequency and a certain element type is represented by a set of reference data, which is previously stored in a storage unit operatively connected to the system controller 17. Once the global minimum resonant frequency fängumü has been determined, the controller 17 will compare this value with the pre-stored set of reference data and select the particular element type for which the corresponding frequency value or band coincides with the detected global minimum resonant data. the frequency. For some cursor types, it is possible to detect a global maximum for the resonant frequency instead of its global minimum.

Thanks to the present invention, markers representing a respective code value can be quickly and reliably detected among a very large number of possible code values. For a marker similar to that illustrated in the drawings and containing four different magnetic elements, each of which is selected from four different types and arranged in one of 15 possible angular positions, for example, the total number of different code values becomes equal to 327,600.

If the four elements are selected from a total of ten different types, each cursor can represent one of 13,628,160 different code values for the same number of different angular positions.

Within the scope of the present invention, it is possible to detect more than one marker at the same time, even if the elements are identically oriented on the markers. In order to simultaneously detect, for example, two markers, one of which is rotated a certain angle relative to the other, it is possible to distinguish the two markers by considering the sequence of absolute angular position values obtained for all elements of the two markers. Assuming that the respective first elements of the two markers have 0 ° i) 10 15 20 25 30 sw ras 9 orientation relative to a given reference orientation, while the second elements have 10 ° and the third elements have 25 ° ° orientation, the following exemplary sequence of absolute angular position values can be obtained during the rotation of the magnetic field: {0 °, 7 °, 10 °, 17 °, 25 °, 32 °, ...} From the above sequence it is concluded that each other value is offset 7 ° from the previous value. This indicates that one of the markers is offset 7 ° relative to the other, which enables the two markers to be distinguished from each other.

If, on the other hand, the two markers are completely parallel, they can still be identified individually by applying a field gradient of the rotating magnetic field. The rotating field vector thus does not have uniform strength but increasing amplitude, whereby the two markers will show different variations in resonant frequency, when they are exposed to the rotating magnetic field.

The invention has for exemplary but non-limiting reasons been described above with reference to an illustrative embodiment. One skilled in the art will readily appreciate that embodiments other than those shown herein are possible within the scope of the invention, as defined by the appended independent claims.

In a situation where the plane in which the marker elements are oriented is significantly different from the plane of rotation of the magnetic field, it may be appropriate, for example, to subject the cursor to a sequence of two or more different rotating magnetic fields, the planes of rotation of which are non-parallel (preferably: orthogonal), to ensure a reliable determination of the element orientations.

Claims (11)

W U 20 25 30 35 s12É1aa 10 PATENTKRAV A method for remote detection of markers (10), wherein each marker comprises at least two magnetic elements (13), which are arranged in a predetermined relationship, which gives the marker an identity, by either excising (13), so that it or electrically excite a respective magnetic element self-oscillating mechanically, nan circuit, to which the respective magnetic element (13) is coupled, so that the resonant circuit self-oscillates) of the respective magnetic element or of the electric (H), electrically, wherein a resonant frequency The phase of the resonant circuit depends on an applied magnetic field, characterized in that the magnetic field (H) is given a varying orientation, a corresponding variation in the resonant frequency (fæQ is monitored, an extreme value (f¿n1Wu) is detected in the variation, an instantaneous orientation as a result of the detection of said extreme value and an orientation is determined for each element (13) by said instantaneous field orientation. A method according to claim 1, wherein the instantaneous field orientation is substantially parallel to a longitudinal axis of the respective magnetic elements (13). Method according to claim 1 or 2, wherein the orientation of the respective element (13) is determined to be substantially parallel to the determined instantaneous field orientation. A method according to any one of the preceding claims, wherein said extreme value is a maximum or minimum value. A method according to any one of the preceding claims, further comprising the steps of, after determining the respective element orientation, determining a type for each element (13) by: generating a magnetic field (H) of varying field strength along a respective determined element orientation, detect a minimum or maximum value of the resonant frequency for each element (13), compare said detected minimum or maximum value of the resonant frequency with a pre-stored set of reference data, which connects a plurality of frequency values or frequency bands with respective element types, and select a certain such type from the pre-stored element types, for which the associated pre-stored frequency value or frequency band coincides with the detected minimum or maximum value of the resonant frequency. A method according to any one of the preceding claims, wherein the magnetic elements (13) comprise an amorphous metal alloy. A method according to any one of the preceding claims, wherein the magnetic elements (13) are formed as strips, strips or wires. A method according to any one of the preceding claims, wherein at least two of the magnetic elements (13) are arranged according to a mutual angular relationship with respect to a longitudinal direction of the elements (13). Method according to one of the preceding claims, wherein at least two of the magnetic elements (13) are arranged according to a certain distance ratio. A system for remotely detecting markers (10), each marker comprising at least two magnetic elements (13) arranged in a predetermined ratio, the system comprising excitation means (15, 17), detecting means (16, 17) and magnetic field generating means (18) and is arranged to detect a resonant frequency (fms), which is associated with respective magnetic elements and depends on a magnetic field (H), which is generated by the magnetic field generating means, characterized in that (18) is arranged to generate a rotating magnetic field (H), and that (16, 17) is arranged to detect the magnetic field generating means detecting means an extreme value (fn1Wn) of a variation in the resonant frequency (fms). ), which variation is caused by the rotating magnetic field (H), and to determine from an instantaneous orientation (dmnlæa) of the rotating magnetic field (H) an orientation of the respective magnetic elements (13). 11. ll. The system of claim 10, wherein the magnetic field generating means (18) is further arranged to generate a magnetic field of varying field strength to determine a respective type of respective magnetic elements (13).