NL2032816B1 - Label for use in a positioning system, positioning system, livestock management system and method - Google Patents

Abstract

The invention relates to a label for a positioning system, provided with a transmitting and receiving unit comprising coil antennas. Each of the coil antennas is located in the tag such that a longitudinal axis through the coil antenna, in use, extends parallel to an earth's surface. A first and a second coil antenna thereof are oriented differently. For transmitting a positioning signal, the transmitting and receiving unit comprises an excitation circuit for generating a first alternating magnetic field with the first coil antenna and a second alternating magnetic field with the second coil antenna. The transmitting and receiving unit is further provided with a read circuit that is adapted to determine a voltage potential of an alternating voltage in both the first coil antenna and the second coil antenna, for receiving an incoming positioning signal.

Description

P131524NL00

Title: Label for use in a positioning system, positioning system, livestock management system and working method

Field of the invention

The present invention relates to a label for use in a positioning system, wherein the label is provided with a transmitting and receiving unit for sending and receiving positioning signals, the transmitting and receiving unit comprising a plurality of coil antennas. The invention further relates to a positioning system, a livestock management system, and a method for determining a position of at least one first label of a plurality of labels.

Background

A label as described above is known per se for use in livestock farming, for example for managing herds of animals. The position of an individual animal, such as a cow in a herd of cows in a stable, can be determined when the distance between the animals and the distance to a small number of beacons is known. If the animal carries a device that can measure the distance to neighboring animals, the animal's position in the herd can ultimately be determined. In practice, this measuring instrument and the measuring method used must be able to withstand the conditions in a stable, which means that not all measuring methods are usable. In addition, the measuring instrument must regularly perform measurements, preferably in the order of a few seconds, and must therefore use energy sparingly due to battery power.

Furthermore, in a livestock management system, the distance to a significant number of other cows must be measured for a large number of cows at a rapid pace.

Measuring distance can be done in different ways. A contactless system is necessary to measure the distance between two cows.

Well-known methods are measuring with light (lidar), with sound (sonar) or with microwaves (radar). These measuring methods are not or less suitable for measuring the distance between two cows. The propagation of the measuring signal through the body of a cow in particular makes these systems unsuitable for use. To a greater or lesser extent, the accuracy for the different technologies is also limited by the transmission and reception range, the degree of sensitivity to reflection of transmission signals, as well as signal attenuation due to walls and other objects in the interior of a stable.

Summary of the Invention

It is an aim of the present invention to provide a label as described above with which a position, for example relative to other labels, can be determined with sufficient accuracy and which is suitable in an indoor space such as a stable and between other animals.

To this end, the invention provides, in accordance with a first aspect thereof, a label for use in a positioning system that is provided with a transmitting and receiving unit for sending and receiving positioning signals. The transmitting and receiving unit comprises a plurality of coil antennas. Each coil antenna is located in the tag such that a longitudinal axis through the coil antenna, in use, extends parallel to an earth's surface. The plurality of coil antennas includes at least one first coil antenna and at least one second coil antenna. The at least one first coil antenna and the at least one second coil antenna are oriented differently. The transmitting and receiving unit is furthermore provided with an excitation circuit for transmitting an outgoing positioning signal. The excitation circuit is designed to energize the transmitting and receiving unit with an electric signal, for generating a first alternating magnetic field with the first coil antenna and a second alternating magnetic field with the second coil antenna. The transmitting and receiving unit is further provided with a read circuit that is adapted to determine a voltage potential of both an alternating voltage in the first coil antenna and an alternating voltage in the second coil antenna. The readout circuit is in this manner designed to receive an incoming positioning signal.

The invention is based on the insight that measuring with magnetic fields can usually take place unhindered by environmental factors. The use of magnetic fields for the present application therefore provides a high position resolution and a sufficiently large distance range to make the measurements. Magnetic fields can also propagate effortlessly through a large body such as that of a cow, and are therefore much less sensitive to signal reflections, for example.

In order to be able to use magnetic fields for accurate distance measurements, such a label must be designed in such a way that the measurement is disturbed as little as possible by fields resulting from the interaction of the environment with the generated alternating magnetic fields. The main source of interference in the environment is the earth: for example, the subsurface reacts with eddy currents generated in it when changing magnetic fields have a field direction that is transverse to the subsurface/earth. The label according to the invention is designed to produce a horizontal alternating magnetic field with the aid of two coils (coil antennas).

An alternating field is not influenced by existing static magnetic fields. Furthermore, due to the horizontal direction of the generated fields, the measurement is insensitive to the presence of the soil/subsoil. .

In addition, a large distance range can be achieved using an alternating magnetic field.

The label according to the invention further uses horizontally oriented magnetic fields. This means that the magnets are generated by coil antennas whose longitudinal axis through the windings of the coil extends parallel to the earth's surface (in use). Theoretically, vertically oriented magnetic fields can also be used (fields where the north-south axis of the magnetic field is located perpendicular to the Earth's surface). The advantage of a vertically directed magnetic field is that such a field propagates symmetrically around the coil and therefore provides the same field strength for the same distance for every angle in the horizontal plane. The same signal is measured everywhere on an imaginary circle around the label, so that this is theoretically a suitable measure of the distance to this animal. However, from a practical point of view, this version is less suitable, because the earth forms a magnetic short circuit for changing magnetic fields.

The proximity of the earth's surface disrupts the generated alternating field, as a result of which the value of the measured field strength can deviate from the theoretically expected value even at a distance of more than two meters, causing a measurement error. The field to be measured will quickly become weaker at a distance and change direction, which limits the measuring distance. Because every surface has a varying composition, this cannot be corrected in advance. For this reason, this measuring method only provides a reliable measurement at a great height above the earth's surface, or near the earth's surface only over short measuring distances of up to approximately 3 meters, so that the methodology is not suitable for the present application in a stable.

The invention therefore uses a horizontally oriented alternating magnetic field, and in particular a magnetic field rotating at a constant rotational speed that is generated with two horizontally oriented coil antennas placed at an angle to each other. Because the label uses these two alternating magnetic fields in the horizontal plane (the plane parallel to the Earth's surface), an elliptical or circular (depending on the frequency, direction and mutual phase of the magnetic fields) rotating or moving magnetic field is created. The magnetic field strength of this field can be determined with one or more further coil antennas of a receiving tag - which receiving coil antennas are also horizontally oriented with respect to the earth's surface. The distance to the transmitting label can be determined by determining the amplitude of the received magnetic field. The magnetic field strength decreases near the coil antennas with the cube of the distance, and at greater distances with the square of the distance (the transition from third to second power takes place at a relatively large distance (order of magnitude 200 meters) compared to with the measuring distance (a few meters to a few tens of meters)). The amplitude of the generated magnetic alternating field can be determined accurately. The label is thus able to determine the distance between two individual animals, regardless of the angle at which these two animals are positioned, by assuming the dependence of the decreases in the magnetic field with distance. In this way, the distance between animals can be determined in a stable with randomly placed cows.

In principle, the methodology can be applied with two horizontally oriented alternating magnetic fields as described above, some of the parameters of which are known or fixed. For example, according to some embodiments, the at least one first coil antenna and the at least one second coil antenna are oriented at an angle to each other. An arbitrary angle between the coil antennas in the horizontal plane, when the frequencies of both fields are not equal, provides a magnetic field that continuously changes direction and strength in the horizontal plane. However, for each direction, the sum of the two fields provided by the two coil antennas periodically adds up to a fixed maximum that depends on the distance. By receiving the signal for a sufficiently long time and measuring the field strength, this maximum can be determined and the distance is known.

There is also a similar relationship between the average magnetic field strength and the distance, as can be determined on the basis of statistics, so that it is not necessary to look for the maximum. Although this is a possible implementation of the invention, it is also not the most advantageous embodiment thereof because. This is due to the continuously changing result of the magnetic field. With the same frequency of the two fields, the result of such a measurement becomes more clear and therefore better, but the shape of the rotating magnetic field can be an elliptical orbit as a result of the arbitrary (but fixed and known) mutual angle between the two fields. . If both the angle and the phase between the two fields are known, the shape of this ellipse is fixed and the distance can be determined knowing the emitted amplitude. In a preferred embodiment, the at least one first coil antenna is oriented transversely with respect to the at least one second coil antenna. The mutually transversely oriented coil antennas allow the mutually perpendicular components of the field to be analyzed at the receiving end.

According to a further embodiment, the at least one first coil antenna and the at least one second coil antenna are located in each other's vicinity, preferably adjacent to each other. In these embodiments it is achieved that as a result of either reciprocal induction or capacitive coupling (or through a combination of both), energizing one coil antenna will also lead to the generation of a magnetic field with the other coil antenna. This occurs in particular efficiently with a sufficiently large coupling factor between the coils, for example with a coupling factor of 2.5% or more. As a result of this reciprocal inductive or capacitive coupling, the alternating magnetic fields will have a mutual phase difference of n/2 radians, and will provide a circularly rotating magnetic field in perpendicular orientation to each other. This makes the distance easy to determine in all directions. According to some embodiments, the energizing circuit is therefore adapted to energize the transmitting and receiving unit for generating the alternating magnetic field in the at least one first coil antenna. Naturally, this is only one of the possibilities, and the excitation circuit can also be designed to generate a field in both coils, or two excitation circuits can be present.

According to a further embodiment, the first and the second magnetic alternating fields are equal in frequency. As indicated earlier, the shape of the rotating magnetic field (circle or ellipse) is therefore fixed and is predictable when the phase is known (assuming a known amplitude). Furthermore, according to a further embodiment, the first and the second alternating magnetic fields have a mutual phase difference of a quarter of their wavelength (n/2 radians).

At the same frequency and with this phase difference, mutually perpendicular horizontal magnetic fields provide a circularly rotating alternating magnetic field, so that the field strength of the received magnetic field at the receiver becomes independent of the direction to the transmitting label. The distance 1s can then be determined directly from the amplitude of the signal.

Because the receiving tag also has two mutually perpendicular receiving antennas, determining the distance in this way becomes simple and accurate.

According to a further embodiment, the transmitting and receiving unit is provided with at least one first resonant circuit comprising the first coil antenna and at least one second resonant circuit comprising the second coil antenna, and wherein the excitation circuit is switchably connected to at least one of the first and the second coil antenna. second resonance circuit for energizing the transmitting and receiving unit for transmitting the outgoing positioning signal. In this embodiment the excitation circuit can be connected switchably and selectively to the resonance circuits of the first or second coil antenna so that one of the antennas can be energized to transmit an alternating magnetic field. The first and second coil antennas are preferably located sufficiently close to each other to be coupled by reciprocal induction, capacitive coupling, or both, as described above. However, this is not a requirement. Alternatively, it is also possible to selectively - and for example in a time-dependent manner using a controller - bring the excitation circuit into contact with both resonance circuits, for example if there is no or insufficient coupling between the coil antennas.

According to some of the above embodiments, the at least one first resonant circuit or second resonant circuit is a resonant circuit with a high quality value, such as a quality value of at least 100, preferably at least 200; such as a quality value of 300 or 400. In this way the resonator can vibrate independently for many tens of periods while only a small part of the energy in the resonator is lost. The two perpendicularly mounted coil antennas of the resonators are coupled together inductively, capacitively or by a combination of both.

According to some further embodiments, the tag is provided with a single first coil antenna and a single second coil antenna. The use of more than two coil antennas is certainly possible, but a sufficiently efficient and optimally effective embodiment can be obtained by using two coil antennas.

Furthermore, according to some embodiments, the read circuit comprises one or more switching units for selectively establishing and breaking a connection between at least one of the first or the second coil antenna and a ground potential, for selectively discharging the at least one coil antenna when establishing the connection, and for selectively determining the voltage potential of the at least one coil antenna when the connection is broken. To receive a transmitted transmission signal from a transmitting label, it is desirable to remove the energy present in the coil antenna, for example by discharging any charge that may have built up therein. By selectively connecting the coil antennas to a ground potential for a short time, the receiving label can be de-energized. When the connection to the ground potential is broken, the structure of the signal will mainly be determined by the received transmission signal, and disruption by residual signals left behind can be prevented.

Even better than discharge via a ground potential, according to some embodiments the coil antenna can be briefly connected to a capacitor in a power supply circuit, so that the energy built up in the coil partly flows back to the power supply (i.e. to the accumulator or battery).

In further embodiments, the tag comprises a management unit for operating the switchable connection between the energizing circuit and the at least one of the first and second resonant circuits, for energizing the transmitting and receiving unit for transmitting the outgoing positioning signal. The management unit can operate the switchable connections in the label, thus switching the label into a transmit mode or receive mode. In reception mode, the distance can optionally also be determined using the management unit, or characteristic signal values can be determined by the management unit and stored in, for example, an optional working memory of a label. Additional wireless communication means can also be optionally available for exchanging measurement data with a data network. In this latter embodiment, the management unit can be designed to periodically switch the label into a transmitting mode and then into a listening or receiving mode.

In some of these embodiments, the management unit is further adapted to manage the switching units for selectively establishing and breaking the connection between the at least one coil antenna and the ground potential/capacitor (or other discharge solution). Furthermore, according to some embodiments, the management unit may be arranged to operate the switching units, to determine the voltage potential of the plurality of coil antennas after a predetermined minimum period of time from the establishment and termination of the connection between the at least one coil antenna and the earth potential. The magnetic alternating field can, for example, be a periodic alternating field and the predetermined minimum time period in such an embodiment can be between fifteen and twenty-five periods, and preferably twenty periods. After re-opening the connection to the ground potential/capacitor (or other discharge solution), and during the reception of a transmission signal from another label in the vicinity, it is desirable to wait a number of periods before measuring the voltage across the coil antennas . The coupling between transmitter and receiver is relatively small and the waiting time is desirable to allow the voltage to build up across both coil antennas at the receiver. The range of fifteen to twenty periods given above represents a nice compromise between bandwidth, coupling and collected energy for the largest possible detection distance.

According to some further embodiments, the management unit is adapted to receive a synchronization signal and, on the basis of the synchronization signal, to determine time slots for operating the excitation circuit and the readout circuit.

Such embodiments provide an important advantage, making it possible to synchronize the labels with each other in order to switch them into a desired operating mode (transmit or receive mode) depending on the time slots. In this way, for example, in a group of labels, for example five hundred labels in a herd of five hundred cows, the labels can be switched into a transmit mode in turn, so that each of the labels can be listened to in the remaining time slots by putting them in the receive mode. to take. It is also possible to briefly discharge the receiving labels (i.e. the labels that are switched to receiving mode for that time slot) via the aforementioned ground potential in order to make an accurate measurement in each time slot at the beginning of each time slot. The measurement can then be determined, as discussed above, for example a number of periods after reopening the connection to the earth potential, by measuring the voltage on both coil antennas of the receiving label.

According to some of these embodiments, the management unit is arranged for operating the excitation circuit in a predetermined first time slot for transmitting the outgoing positioning signal, and for operating the readout circuit in a predetermined second time slot for receiving an incoming positioning signal originating from a further label. In a herd of animals, each label can be assigned its own time slot for transmission, while other labels are listened to in the other time slots. When all labels have had their turn to generate a transmission signal, the process can start again, so that the labels are each periodically brought into transmission mode.

According to some other or further of these embodiments, the label is provided with a clock system for determining the time slots based on the synchronization signal, the clock system being provided with a first and a second clock unit,

wherein the first clock unit is arranged to provide a first clock signal with a first time resolution and wherein the second clock unit is arranged to provide a second clock signal with a second time resolution, wherein the first time resolution is smaller than the second time resolution, and wherein the management unit is arranged to switch on the second clock unit on the basis of the clock signal from the first clock unit and at a time depending on the synchronization signal. By using a low-resolution clock and a high-resolution clock in the above manner, whereby the high-resolution clock is switched on at a predetermined time depending on the low-resolution clock, an accurate and continuously adaptable mutual synchronization can be achieved. can be achieved without the high-resolution clock having to remain switched on continuously. Energy consumption can be efficiently limited in this way.

In some embodiments, the synchronization signal includes synchronization triggers which are received at a fixed time interval, and wherein the control unit is configured to enable the second clock unit based on the first clock signal at a fixed time period prior to receipt of a first synchronization trigger, wherein the second clock unit is switched off synchronously with the start or end of the first synchronization trigger, and wherein a clock value of the switched off second clock unit is used by the management unit for calibrating the first clock signal, to accurately predict a reception of a second synchronization trigger after the first sync trigger.

In the embodiments described above, for example, a synchronization signal is sent centrally at fixed periodic times, which can be received by all labels. The time span between two synchronization signals is therefore known to the labels.

Using the first low-resolution clock signal, the high-resolution clock unit in each label can be switched on in time prior to receipt of the synchronization signal, so that the high-resolution clock unit is active at the moment of receipt of the synchronization signal. For example, the time span — which can be used as a reference value — can be counted down with the low-resolution clock signal, and at a fixed time prior to the expected reception the second clock unit can be switched on. The first clock unit can now be tuned with the high-resolution clock signal from the second clock unit. For example, related to the above-mentioned time period, such as at a fixed moment after the switch-on moment of the second clock, a counter can be started based on the high-resolution clock signal that counts the number of elapsed cycles in the high-resolution time signal until the start or end of the synchronization trigger — this moment is a centrally determined fixed moment that can be synchronized very accurately. The counted number of cycles is then used to speed up or slow down the clock signal of the first clock unit to match and fine-tune it with respect to the synchronization signal. The number of cycles counted can, for example, be stored as a value for some time in a buffer or other memory, and serve as a reference value upon receipt of a next synchronization signal. If more cycles are counted, the low-resolution clock signal runs a little too fast, so that the second clock is switched on a little too early by 1 s, and the speed can be accelerated. Conversely, if fewer cycles are counted, the low-resolution clock signal runs a little too slowly, so that the second clock is switched on a little too late, and a delay can occur.

In some of these embodiments, the management unit is further adapted to selectively switch on at least one of the read circuit or the excitation circuit on the basis of the second clock signal. For example, the management unit can simultaneously activate the readout circuit (receiver circuit) and also start the counter mentioned above.

In some embodiments of the present invention, the management unit is adapted to operate the read circuit for receiving an incoming positioning signal from a further label, and for producing positioning data based on the voltage potentials of the alternating voltages of the first and second coil antennas. belonging to the further label. In these embodiments, the positioning data relative to the transmitting label are determined with the reading circuit and the management unit on the basis of the determined voltage across the coil antennas of the label.

This positioning data includes, for example, the distance to the transmitting label.

In some embodiments of the present invention, the label is adapted to wirelessly transmit a data signal comprising positioning data of the label and/or positioning data of one or more further labels to at least one of: a receiver of the positioning system, and the one or more further labels.

In this way, the positioning data can be exchanged, so that the mutual positions of all labels can be determined together with positioning data from other labels. The positioning data can be processed centrally in this way, for example, by sending it to a receiver of a central livestock management system. It is also possible for the positioning data to be processed (in whole or in part) decentrally in the labels themselves, for example because each label determines the distances to a number of immediately adjacent (or possibly even all) labels.

According to a second aspect, the invention further provides a positioning system for determining positions of a plurality of labels according to one of the embodiments discussed above, wherein the system is provided with at least one receiver for receiving data signals comprising positioning data of one or more of the plurality labels, further comprising a synchronization unit configured to transmit a synchronization signal to the plurality of labels.

According to a third aspect, the invention provides a livestock management system provided with a positioning system as described above, wherein each of the labels is adapted to be worn by an animal.

Furthermore, according to a fourth aspect thereof, the invention provides a method for determining a position of at least one first label of a plurality of labels as described above, in a positioning system as described above, wherein each of the plurality of labels is provided with a transmitting and receiving unit comprising a plurality of coil antennas, each of the coil antennas being located in the tag such that a longitudinal axis through the coil antenna, in use, extends parallel to an earth's surface, the plurality of coil antennas of each tag having at least one first coil antenna and comprises at least one second coil antenna, and wherein the at least one first coil antenna and the at least one second coil antenna are oriented differently from each other; the method comprising the steps of: transmitting, with the first label, a positioning signal by means of energizing the transmitting and receiving unit for generating a first alternating magnetic field with the first coil antenna and a second alternating magnetic field with the second coil antenna of the first tag; and determining, with a read circuit of a second label of the plurality of labels, a voltage potential of both an alternating voltage in the first coil antenna of the second label and an alternating voltage in the second coil antenna of the second label, for receiving an incoming positioning signal .

According to some embodiments, the at least one first coil antenna and the at least one second coil antenna are oriented at an angle to each other. In a special embodiment hereof, the at least one first coil antenna is oriented transversely (in particular, for example perpendicularly) to the at least one second coil antenna. Furthermore, in some embodiments the first and second alternating magnetic fields may be equal in frequency, and the first and second alternating magnetic fields may have a mutual phase difference of a quarter of their wavelength. In such a case, a circular rotating magnetic field is created as a result of the coil antennas, so that the decrease in the measurable amplitude upon reception only depends on the distance. In particular, the amplitude decreases near the coil antennas with the third power of the distance, and at greater distances with the second power of the distance.

Brief description of the figures

The invention will be discussed below on the basis of specific embodiments thereof that are not intended to be limiting, with reference to the attached figures, in which:

Figure 1 schematically shows the field of a label provided with a coil antenna oriented in the vertical direction (z-direction);

Figure 2 schematically shows the field of a label according to an embodiment of the invention;

Figure 3 schematically shows the construction of a rotating magnetic field using a label according to an embodiment;

Figure 4 schematically shows a potential profile in a coil antenna with which an alternating magnetic field is received, as produced with a label according to an embodiment;

Figure 5 schematically shows a transmitting circuit of a label according to an embodiment;

Figure 6 schematically shows a transmit-receive circuit of a label according to an embodiment that receives a signal from another label according to an embodiment;

Figure 7 schematically shows a synchronization process as implemented in a label according to an embodiment;

Figure 8 schematically shows a livestock management system based on labels according to an embodiment of the invention;

Figure 9 schematically shows a label according to an embodiment of the invention.

Detailed description

Figure 8 schematically shows a livestock management system 2 based on labels 4 according to an embodiment of the present invention. In system 1, among other things, the positions of cows 3 are monitored. Furthermore, the labels 4 can be designed to integrate a number of other functions for the purpose of livestock management, such as monitoring the health status of the animals 3, operating farm functions such as: an automatic feeder, a separation fence, a milking machine, a scale, etc. . The system monitors a multitude of animals, including cows 3-1, 3-2 and 3-3. Each animal is provided with a label 4, for animals 3-1 to 3-3 these are 4-1, 4-2 and 4-3 respectively. With each of the labels 4 an alternating magnetic field can be generated, as will be further described below. Furthermore, the labels 4-1 to 4-3 can be arranged to send data to station 8, which is connected to livestock management server 12 via network 9. The data can be the distance data of each of the labels 4-1 to 4. -3 to any other of labels 4-1 through 4-3. The livestock management server 12 can process this data and determine the relative positions of all labels 4 relative to each other. In an alternative embodiment it is possible that the labels 4 themselves have a processor and memory and are able to determine their relative positions 4-1 to 4-3 relative to each other. Naturally, partial processing of the data can also take place with the labels 4, with the server 12 carrying out the remaining analysis and data processing.

In accordance with the present invention, system 2 uses magnetic fields to determine the mutual distances of labels 4-1 to 4-3. For this purpose, labels 4 have coil antennas 10 and 11 with which a horizontal alternating magnetic field can be generated. The labels 4-1 to 4-3 are therefore able to determine the distance between the individual cows 3-1 to 3-3, regardless of the mutual orientation and position of the animals. A good measuring system 2 can be built up by measuring using varying magnetic fields. Static magnetic fields are less applicable for various reasons, 0.4. as a result of the earth's magnetic field.

High-frequency signals cannot propagate sufficiently in large watery objects and are therefore less suitable. However, alternating magnetic fields with a frequency smaller than 5 megahertz (MHz), preferably smaller than approximately 2 MHz, are very suitable for this purpose. The wavelengths associated with these frequencies are typically (much) longer than the measuring distance to be bridged of a few to a maximum of a few tens of meters.

Figure 1 schematically shows a cow 3 provided with a label 4 containing a vertically oriented coil antenna. The coil antenna provides a vertically directed magnetic field B, directed in the direction of the longitudinal axis 5, the vertical direction being referred to in the figure as the z-direction. The field lines 7 extend on all sides from pole to pole as indicated in figure 1, and partly run through the subsoil under the animal 3. Most of the field lines are therefore partly located in the subsoil on which the animal 3 is standing. However, Earth 1 is able to generate a new alternating field in response to the alternating field. This field disrupts the desired field line pattern, as a result of which the value of the measured field strength can deviate annoyingly from the theoretically expected value even at a distance of more than two meters, thus introducing a measurement error. The field to be measured will quickly become weaker at a distance and change direction, which limits the measuring distance. Because each substrate 1 varies in composition, this cannot be corrected in advance.

Figure 2 shows an embodiment according to the invention, which is provided with two horizontally oriented coils 10 and 11. A random cow (not shown) is located in the center of the image in Figure 2, at the location where coil antennas 10 and 11 are schematically displayed. This cow is provided with a label 4 according to an embodiment of the invention. Such a label is shown schematically in figure 9. The label 4 is provided with a transmitting and receiving unit 50 for sending and receiving positioning signals. The transmitting and receiving unit 50 comprises a transmitting circuit 40 and a reading circuit or receiving circuit 60, both of which are connected to coil antennas 10 and 11. The coil antennas 10 and 11 can be regarded as external parts of the transmitting and receiving unit 50, or as separately coupled components; this is not relevant to the operation of the invention. The label 4 further comprises a power supply 41, for example an accumulator, battery, photovoltaic cell, or another type of power supply. The power supply 1s is connected to an excitation circuit that forms part of the transmitter circuit 40. A processor 57 serves as a management unit for operating the functions of the label 4, and is further designed to analyze the received signals from the receiver circuit 60. Furthermore, the label 4 is optionally provided with a communication unit 59 with which the label 4 can, for example, communicate with a central server 12 via station 8 (see figure 8) or with other labels 4. The communication unit 59 is shown with its own antenna. However, if desired, this can also be connected to the coil antennas 10 and 11. Optionally, but preferably, the label is further provided with a plurality of sensors 48 with which various parameters, such as animal parameters or environmental values, can be determined for the livestock management system.

In figure 2, the transmitting label 4 generates a rotating magnetic field in order to determine its position relative to other labels worn by other animals 3-1 to 3-3. The rotating magnetic field is produced with the aid of a first alternating magnetic field 15 and a second alternating magnetic field 16. The first alternating magnetic field 15 is produced with coil antenna 10. The second alternating magnetic field 16 is produced with coil antenna 11. The manner in which, according to an embodiment, the magnetic rotating field is built up with the aid of the alternating magnetic fields 15 and 16, is shown in Figure 3 and will be discussed further below. To understand Figure 2, it is sufficient to know that the two fields result in a magnetic rotating field (the direction of the field rotates around its axis in time). The three cows 3-1, 3-2 and 3-3 on the dotted line all have the same distance from the transmitting label 4 in the center. The magnetic field produced by the transmitting label 4 couples inductively with the coil antennas

X and Y direction in the labels of cows 3-1 to 3-3. This received field can be measured as alternating voltage on the coils of the receiving labels. In this way the receiving labels are able to determine the distance to the transmitting label 4. This does not depend on the orientation of each animal 3 relative to fields 15 and 16.

Figure 3 shows the principle of building a rotating magnetic field using two orthogonal, or transversely oriented, alternating magnetic fields 15 and 16. The course over time t of field 15 (Bi) in the Y direction is shown in the horizontal graph 20 above the figure.

The development over time t of field 16 (By) in the X direction is shown in the vertical graph 21 next to the figure. The time t=0 is shown in each of the figures. The time t=t1 (t1:>0) is shown in graph 20 as point 23, and in graph 21 this time is shown as point 24. The alternating magnetic fields 15 and 16 have the same waveform, frequency and amplitude, but a mutual phase difference ¢ of a quarter wavelength: so the phase difference is g=+n/2 in radians. At time t=0, the field strength of field 15 (Bi) is maximum and positive, and the field strength of field 16 (Bg) is zero.

The center of Figure 3 shows the resulting magnetic field B at times t=0 and t=t1. At time t=0, the field B is fully oriented in the direction of B, as shown by vector 27. At time t=t; the field strength of B» is now greater than the instantaneous field strength Bi. The instantaneous magnitude of the two fields 15 and 16, vectors B; and B», 1s shown in the upper left corner. The resulting magnetic field B at time t=t is shown in Figure 3 by vector 28. As can be seen from both graphs 20 and 21, and the resulting magnetic field B, magnetic field B has rotated clockwise, as shown by rotation 29. At the expiration of a complete wave, field B will have returned to the starting position represented by vector 27. The tip of vector 28 of the resulting magnetic field B thus traces a circle as shown in figure 3.

On the receiving side it makes no difference how the receiving coils 10 and 11 of the receiving label are oriented.

With an accurate phase difference of g=+n/2, the vector 28 of the rotating field describes a perfect circle. The distance can then be determined accurately even with the signal from one receiving coil, by determining the amplitude of the received alternating voltage signal in the coil: after all, this is the same for every orientation. With an arbitrary phase difference of g#+n/2, the resulting field vector of the field B will not describe a circle, but a line if the fields 15 and 16 are in phase (p=0 or ¢=n) or an ellipse at any different phase difference. In that case, the signal from one coil 10 or 11 is not sufficient to determine the distance accurately, but this can be done by determining the amplitudes of the signals from both coils 10 and 11. Incidentally, in the preferred embodiment, when the coils 10 and 11 of the transmitting label 4 are in each other's vicinity and one of these coils is energized, a stable equilibrium will automatically arise, with both coils 10 and 11 having a phase difference of p=+ n/2 will transmit. In that case, the magnetic rotating field is created automatically.

Figure 4 shows the reception signal 33 as received on one of the coils 10 or 11 of the receiving label. The originally transmitted signal 32 is also shown. The amplitude Vnax of the received signal 33 is shown with double arrow 36 and level line 37. The amplitude Vo of the originally transmitted signal 32 is shown with double arrow 35 and level line 30. The ratio between the amplitude Vma of the received signal 33 and the amplitude Vo of the transmitted signal 32 is indicative of the distance between the transmitting label 4 and the receiving label.

The above example embodiment, depicted in Figures 3 and 4, provides only one possible embodiment or class of embodiments.

In a variant of this embodiment, only one coil antenna 10 of the coil antennas 10 and 11 of the transmitting tag 4 is energized, and the energy flows from the energized coil antenna 10 to the other coil antenna 11 through coupling between the coils 10 and 11. the coil 11 will therefore be built up to the maximum value in the periods following energization. This happens — depending on the coupling factor — in a number of periods, for example 20 periods.

Accordingly, there will then be a variation between the amplitudes of the first magnetic field 15 and the second magnetic field 16. For example, the first magnetic field 15 starts with a maximum amplitude that decreases over the subsequent periods (for example in a time period equal to 20 periods); and the second magnetic field 16 starts with an amplitude that is zero and which is built up over the subsequent periods to the maximum (equal to 20 periods in the same time period). By averaging, integrating or cumulating the amplitudes measured during reception over this time period (20 periods) in each direction, the same value is ultimately obtained for each direction, from which the amplitude of the received signal and thus the distance can be determined. In Figures 3 and 4 such a progression, which occurs, among other things, when only one of the coils 10 or 11 is energized, is not shown.

Figure 5 shows a transmitting circuit 40 of a transmitting and receiving unit 50 in a label 4. The transmitting circuit 40 comprises a first and a second coil antenna 10 and 11. The first coil antenna 10 is connected to a resonant circuit 47 comprising a coil connected in parallel with the coil 10. capacitance Cy and resistance Ry. By means of switch Si, which can preferably be operated by means of a controller such as processor 57 (see figure 9), the first resonant circuit 47 can be brought into conductive connection with an excitation circuit consisting of the battery 41 and the capacity 42. The second coil antenna 11 is connected to a resonant circuit 49 comprising a capacitance Cx and resistance Rx connected in parallel with the coil 11. By means of switch Sg, which can preferably also be operated by means of the controller such as processor 57 (see figure 9), the second resonant circuit 49 can be brought into conductive connection with the excitation circuit consisting of the battery 41 and the capacity 42. In fact, one of the two switches S; or Ss may also be permanently open, or one of the two resonant circuits 47 or 49 may not even be connected to the excitation circuit at all. The development of the field in the unexcited coil 10 or 11 is caused by reciprocal induction when the coils 10 and 11 are in close proximity to each other. The values of the resonant circuits 47 and 49 (capacitors Cy and Cy, resistances Ry and Ry, and coil properties L and Ly) will allow the signal to resonate between the circuits with little loss.

The idea of the circuit in figure 5 is that the coil Ly is charged via Si to a current with a predetermined maximum value. After opening S; the Ly will then vibrate spontaneously with the help of C,. A small part of the energy is lost in Ry, but most of it is transferred to the equivalent resonator around Ly and C via coupling 52. The switch Sz is only closed after about 20 periods when the current in Ly has increased to a maximum value . The remainder then flows back to the power supply via Sz (via buffer C 42).

Figure 6 shows the interaction between two labels 4. The upper part of Figure 6 shows the transmitter circuit 40 of Figure 5. The lower part of Figure 6 shows a complete transmitter and receiver circuit, including a readout circuit 60 and a controller 57. The receiving coils 10 and 11 are inductively coupled remotely to each of the transmitting coils 10 and 11 of the transmitting tag. In the receive mode, switches 44 and 45 between coils 10 and 11 and the exciter circuit will remain open.

When the receiving label is switched into the receiving mode, switches 52 and 53, after being closed briefly to discharge the resonant circuits of coils 10 and 11 from spurious signals, will be opened by controller 57. The received signal on each of the coils 10 and 11 is then amplified by amplifiers 55 and 56, and the value of the amplitudes is determined by controller 57. When the original field strength (amplitude Vo of the transmission signal) is known, the distance can be determined. This amplitude Vo can either be fixed to a fixed known value, or can for example be communicated in some other way between the labels 4 or between each label 4 and the central server 12. Various implementations are possible at this point.

In order for the labels 4 within a group of labels to efficiently monitor each other's positions, it makes sense to use a synchronization system. This can be done, for example, by sending a synchronization signal via station 8 (figure 8) with which the operation of all labels 4 can be synchronized. Figure 7 shows such a synchronization system. Herein, a synchronizer 65 provides a periodic synchronization pulse 66, shown in time in the figure as pulses 66-1, 66-2 and 66-3. The label 4 has a clock circuit 70. This can, for example, form part of the controller 57, but a separate clock circuit 70 can also be provided. The clock circuit 70 comprises a first low-resolution clock 71 and a second high-resolution clock 72. low resolution clock 71 consumes relatively little energy due to the lower time resolution. However, the clock signal 75 of the low resolution clock may contain inaccuracies, so that the clocks of different labels may diverge. Because the synchronization pulses 66 are sent with a fixed period, the time at which a next pulse is received is known. The clock signal 75 of the low resolution clock 71 can be accurately corrected for this by using the high resolution clock 72. The clock circuit 70 switches the high resolution clock 72 on some time before the new synchronization signal 66-1 is received at the time indicated by 79- 1. The high resolution clock 72 builds up its signal 76, and at some point 80-1 the clock circuit 70 turns on its receiver 73 to receive the synchronization pulse 66-1, simultaneously starting a counter on the high resolution clock signal 76. counter continues to count until a universally determined moment that is the same for all labels, such as the end 81-1 (or precisely the beginning) of the received synchronization pulse 66-1.

By comparing the value of the counter with the previous value of the counter (at the previous synchronization pulse 66), the clock signal 75 of the low resolution clock 71 can be corrected by, for example, accelerating or slowing it down. For example, with the aid of the counter value at pulse 66-1, the clock signal 75 at the next synchronization pulse 66-2 can be corrected by comparing these counter values at pulses 66-1 and 66-2.

In the above manner it can be achieved that the labels 4 can operate on the basis of assigned time slots, where, for example, one label 4 always transmits while the other labels listen. The resonant circuits can also be operated on the basis of the clock signal 75 in such a way that energy from the transmission coils 10 and 11 can be recovered in buffer capacitor 42 (figures 5 and 6), by

JO switches 44 and 45 to operate.

The specific embodiments of the invention described above are intended to illustrate the principle of the invention.

It is believed that the embodiment and operation of the invention will be apparent from the foregoing description and the accompanying illustrations.

The invention is not limited to any embodiment described or shown herein. For the sake of clarity and conciseness of the description, features have been described here as part of the same or separate embodiments, it will be clear to the skilled person that the scope of protection of the invention also includes embodiments that include combinations of all or some of the features described. . Within the expert's ability, changes are possible that are considered to be within the scope of protection. Also included within the scope of the present invention are all kinematic reversals. Expressions such as “consisting of,” when used in this specification or the accompanying claims, are not to be construed as an exhaustive list, but rather in an inclusive sense of “consisting at least of.” Indications such as "a" or "one" should not be construed as limiting to a single copy only, but have the meaning of "at least a single copy" and do not exclude multiples.

Expressions such as: “means for…” should be read as: “component designed for…” or “element constructed to…” and should be understood to include all equivalents for the described constructions.

The use of expressions such as: critical, "advantageous", "preferred", "desirable", etc., is not intended to limit the invention.

Furthermore, properties that are not specifically or expressly described or required in the construction according to the invention, but which are within the reach of the skilled person, can also be included without deviating from the scope of protection as determined by the following claims.

Claims (25)

CONCLUSIONS 1. Label for use in a positioning system, wherein the label is provided with a transmitting and receiving unit for sending and receiving positioning signals, the transmitting and receiving unit comprising a plurality of coil antennas, each of the coil antennas being located in the label in such a way that a longitudinal axis through the coil antenna extends, in use, parallel to an earth's surface; wherein the plurality of coil antennas comprises at least one first coil antenna and at least one second coil antenna, wherein the at least one first coil antenna and the at least one second coil antenna are oriented differently from each other; and wherein the transmitting and receiving unit, for transmitting an outgoing positioning signal, is further provided with an energizing circuit for energizing the transmitting and receiving unit with an electrical signal, for generating a first alternating magnetic field with the first coil antenna and a second alternating magnetic field with the second coil antenna; wherein the transmitting and receiving unit is further provided with a read circuit which is adapted to determine a voltage potential of both an alternating voltage in the first coil antenna and an alternating voltage in the second coil antenna, for receiving an incoming positioning signal. The label of claim 1, wherein at least one of: the at least one first coil antenna and the at least one second coil antenna are oriented at an angle to each other; or wherein the at least one first coil antenna is oriented transversely to the at least one second coil antenna. 3. Label according to claim 1 or 2, wherein the at least one first coil antenna and the at least one second coil antenna are located in each other's vicinity, preferably adjacent to each other. Description: coupling factor for example 2.5% 4. Label according to claim 3, wherein the energizing circuit is designed to energize the transmitting and receiving unit for generating the alternating magnetic field in the at least one first coil antenna. 5. Label according to any one of the preceding claims, wherein the first and the second magnetic alternating fields are equal in frequency. 6. Label according to claim 5, wherein the first and the second magnetic alternating fields have a mutual phase difference of a quarter of their wavelength. 7. Label according to any one of the preceding claims, wherein the transmitting and receiving unit is provided with at least one first resonant circuit comprising the first coil antenna, and at least one second resonant circuit comprising the second coil antenna, and wherein the excitation circuit is switchably connected to at least one of the first and the second resonance circuit for energizing the transmitting and receiving unit for transmitting the forward positioning signal. 8. Label according to claim 7, wherein the at least one first resonance circuit or second resonance circuit is a resonance circuit with a high quality value, such as a quality value of at least 100, preferably at least 200, such as 300 or 400. 9. Label according to any one of the preceding claims, wherein the label is provided with a single first coil antenna and a single second coil antenna. 10. Label as claimed in any of the foregoing claims, wherein the readout circuit comprises one or more switching units for selectively establishing and breaking a connection between at least one of the first or the second coil antenna and a ground potential, for selectively discharging the ten at least one coil antenna when establishing the connection, and for selectively determining the voltage potential of the at least one coil antenna after breaking the connection. 11. Label as claimed in any of the claims 4-7, further comprising a management unit for operating the switchable connection between the energizing circuit and the at least one of the first and the second resonant circuit, for energizing the transmitting and receiving unit for transmitting of the outgoing positioning signal. 12. Label according to claims 10 and 11, wherein the management unit is further designed to manage the switching units for selectively establishing and breaking the connection between the at least one coil antenna and the ground potential. 13. Label according to claim 12, wherein the management unit is adapted to operate the switching units, for determining the voltage potential of the plurality of coil antennas after a predetermined minimum period of time from the establishment and termination of the connection between the at least one coil antenna and the ground potential. 14. Label according to any one of the preceding claims, wherein the management unit is designed to receive a synchronization signal and to determine time slots for operating the excitation circuit and the read circuit on the basis of the synchronization signal. 15. Label according to claim 14, wherein the management unit is designed for operating the excitation circuit in a predetermined first time slot for transmitting the outgoing positioning signal, and for operating the readout circuit in a predetermined second time slot for receiving an incoming signal. positioning signal coming from a further label. 16. Label as claimed in any of the claims 14 or 15, wherein the label is provided with a clock system for determining the time slots on the basis of the synchronization signal, wherein the clock system is provided with a first and a second clock unit, wherein the first clock unit is arranged to provide a first clock signal with a first time resolution and wherein the second clock unit is arranged to provide a second clock signal with a second time resolution, wherein the first time resolution is less 1 s than the second time resolution, and wherein the management unit is adapted to provide the second clock unit in to be switched on the basis of the clock signal of the first clock unit and at a time depending on the synchronization signal. 17. Label according to claim 16, wherein the synchronization signal comprises synchronization triggers which are received at a fixed time interval, and wherein the management unit is arranged to switch on the second clock unit on the basis of the first clock signal at a fixed period of time prior to the reception of a first synchronization trigger, wherein the second clock unit is switched off synchronously with the start or end of the first synchronization trigger, and wherein a clock value of the switched off second clock unit is used by the management unit for calibrating the first clock signal, for accurately predicting a reception of a second synchronization trigger after the first synchronization trigger. 18. Label as claimed in any of the claims 16 or 17, wherein the management unit is further designed to selectively switch on at least one of the read circuit or the excitation circuit on the basis of the second clock signal. 19. Label according to any one of the preceding claims, wherein the management unit is designed to operate the readout circuit for receiving an incoming positioning signal from a further label, and for determining the alternating voltages of the first and second coil antenna on the basis of the voltage potentials. producing positioning data associated with the further label. 20. Label according to any one of the preceding claims, wherein the label is designed to wirelessly send a data signal comprising positioning data of the label and/or positioning data of one or more further labels to at least one of: a receiver of the positioning system, and the one or more further labels. 21. Positioning system for determining positions of a plurality of labels according to any one of the preceding claims, wherein the system is provided with at least one receiver for receiving data signals comprising positioning data of one or more of the plurality of labels, further comprising a synchronization unit arranged to transmit a synchronization signal to the plurality of labels. 22. Livestock management system provided with a positioning system according to claim 21, wherein each of the labels is designed to be worn by an animal. 23. Method for determining a position of at least one first label of a plurality of labels according to any one of claims 1-20 in a positioning system according to claim 21 or 22, wherein each of the plurality of labels is provided with a transmitting and receiving unit comprising a plurality of coil antennas, each of the coil antennas being located in the tag such that a longitudinal axis through the coil antenna extends, in use, parallel to an earth's surface, the plurality of coil antennas of each tag having at least one first coil antenna and at least one second coil antenna, and wherein the at least one first coil antenna and the at least one second coil antenna are oriented differently; the method comprising the steps of: transmitting, with the first label, a positioning signal by means of energizing the transmitting and receiving unit for generating a first alternating magnetic field with the first coil antenna and a second alternating magnetic field with the second coil antenna of the first tag; and determining, with a read circuit of a second label of the plurality of labels, a voltage potential of both an alternating voltage in the first coil antenna of the second label and an alternating voltage in the second coil antenna of the second label, for receiving an incoming positioning signal . The method of claim 23, wherein at least one of: the at least one first coil antenna and the at least one second coil antenna are oriented at an angle to each other; or wherein the at least one first coil antenna is oriented transversely to the at least one second coil antenna. 25. Method according to claim 24, wherein at least one of: the first and the second magnetic alternating field are equal in frequency; and the first and the second magnetic alternating fields have a mutual phase difference of one quarter of their wavelength.