Patent Application
20070290846
Preferred embodiments of the present invention will be detailed subsequently referring to the appended drawings, in which:
a is a schematic illustration of a connection between a first and a second association signal, in particular a medium voltage and a voltage swing measured at an antenna of a transceiver according to the present invention;
b is an exemplary illustration of a medium voltage measurement at a transceiver plotted against a distance from a transponder to a transceiver according to the present invention;
c shows a schematic course of a medium voltage at a transceiver plotted against a magnetic coupling factor of a transponder to a transceiver according to the present invention;
d is an exemplary illustration of a voltage swing measurement at a transceiver plotted against a distance from a transponder to a transceiver according to the present invention;
e shows a schematic course of a voltage swing at a transceiver plotted against a magnetic coupling factor of a transponder to a transceiver according to the present invention;
a is a schematic illustration of orthogonally disposed coils as antennas according to the present invention;
b is a schematic illustration of coils arranged at arbitrary angles as antennas according to the present invention;
c is a schematic illustration of antenna means including six orthogonally arranged coils as antennas according to the present invention;
d shows an antenna arrangement including two mutually orthogonal Helmholtz coil pairs and a diagonal coil according to the present invention;
a shows an antenna arrangement including four rectangularly arranged coils for producing a magnetic field orientation of 0° according to the present invention;
b shows an antenna arrangement including four rectangularly arranged coils for producing a magnetic field orientation of 90° according to the present invention;
c shows an antenna arrangement including four rectangularly arranged coils for producing a magnetic field orientation of 135° according to the present invention;
d shows an antenna arrangement including four rectangularly arranged coils for producing a magnetic field orientation of 45° according to the present invention;
With regard to the subsequent description, it should be noted that in the different embodiments same functional elements or functional elements having the same effect have the same reference numerals and thus the descriptions of these functional elements in the different embodiments illustrated below are interchangeable.
Subsequently, the term “signal” is used for both currents and voltages, except where indicated otherwise.
A data transfer from the transponder 110 to the transceiver 100 makes use of the features of a transforming coupling effect between the coil L1 of the antenna means 102 of the transceiver 100 and the coil L2 of the antenna means 112 of the transponder 110, wherein the coil of the antenna means 102 of the transceiver 100 can be considered as a primary coil and the coil of the antenna means 112 of the transponder 110 can be considered as, a secondary coil of a transformer formed of the antenna means 102 and the antenna means 112.
Due to the mutual inductivity M depending on a magnetic coupling of the coils L1, L2, an alteration of a current I2 through the secondary coil L2 on the side of the transponder 110 also causes an alteration of a current I1 or voltage U1 at the primary coil L1 on the side of the transceiver 100, corresponding to the principle of a transformer. The magnetic coupling of the coils in turn depends on the distance d between the coil L1 of the antenna means 102 of the transceiver 100 and the coil L2 of the antenna means 112 of the transponder 110. To simplify subsequent discussions, a distance between transceiver and transponder or antenna means thereof will be frequently mentioned subsequently, wherein this is to signify the antenna distance.
An alteration of the current in the secondary coil L2 on the side of the transponder 110 also causes an alteration of the current or voltage at the primary coil L1 on the side of the reader 100, like in a transformer. This voltage, change at the reader antenna 102 in its effect corresponds to an amplitude modulation, however usually with a very small modulation factor. By switching an additional load resistor in the transponder 110 on and off clocked with the data to be transferred, data can be sent to the reader 100. This process is referred to as load modulation. The distance d is preferably to be provided such that the transponder 110 is in the near field of the antenna of the transceiver 100 to allow communication between the transceiver 100 and the transponder 110 by inductive coupling.
According to the present invention, the connection between the magnetic coupling of the coils L1, L2 and their mutual distance d is utilized for the inventive procedure for determining the position of the transponder 110 by inductive coupling by producing a magnetic alternating field which may, for example, have a frequency of 125 kHz or 13.56 MHz or even another frequency suitable for RFID systems, by means of the transceiver 100 and the antenna, means 102 and determining an electrical quantity as an association signal in the transceiver 100 and/or the transponder 110, wherein the electrical quantity represents a measure of the inductive coupling between the antenna means 102 of transceiver 100 and the transponder 110, and wherein the distance d from the transponder 110 to the antenna means 102 may be associated to the inductive coupling. This electrical quantity or association signal exemplarily results from the response field strength or the read field strength of the transponder or the changes thereof, from a field strength measurement of the electrical alternating field at the transponder or from an evaluation of a load modulation caused by the transponder.
Subsequently, different specific aspects of the inventive procedure for determining the position, direction or motion of a transponder in a radio system (RFID system) by means of inductive coupling will be detail subsequently, wherein further specific embodiments and designs of the present invention will be described subsequently referring to
As the subsequent discussion will clarify, an electrical quantity as an association signal representing a measure of inductive coupling between the antenna means of the transceiver and the transponder in the present invention can be determined either on the side of the transceiver or on the side of the transponder. A distance from the transponder to the antenna means of the transceiver and thus from the transponder to the transceiver may be associated to the electrical quantity and thus also the inductive coupling between the antenna means of the transceiver and the antenna means of the transponder.
The means 104 for generating the drive signal Sst for driving the antenna means 102 may exemplarily be formed such that the drive signal Sst may be varied or such that the means 104 provides a constant drive signal Sst for the antenna means 102. The drive signal Sst may, for example, be a current for feeding the antenna means 102.
In the present embodiment of the invention, the transceiver 100 is connected to the antenna means 102 via two lines 106 and 107, wherein the line 106 carries the drive signal Sst for driving the antenna means 102 and the line 107 carries a signal SRx resulting from the antenna means 102. A separation between transmitting and receiving paths here exemplarily takes place in the antenna means 102. This separation between transmitting and receiving paths may, according to the present invention, also take place in the transceiver 100, wherein in this case it would be sufficient to connect the transceiver 100 to the antenna means 102 via one line only.
The processing means 108 for determining the association signal as a measure of the inductive coupling between the transceiver 100 and a transponder calculates a distance from the transponder to the transceiver 100 from the association signal which may exemplarily correspond to a voltage SRx at the antenna means 102, an antenna feed current Sst or digital data transferred in a transfer protocol from a transponder to the transceiver 100. Exemplarily, a microcontroller could take over the function of the means 104 and/or 108.
Subsequently, an embodiment of the present invention will be described where the association signal is calculated on the side of the transceiver.
According to an aspect of the present invention, a response field strength or read field strength of a transponder 110 may be taken as an indicator for determining the distance from the transponder to the antenna means 102 of the transceiver 100. The response field strength or response minimum field strength is that field strength where the transponder still operates just properly, i.e. the field strength is sufficient for a voltage supply of the transponder. The read field strength or read minimum field strength is the minimum field strength required for a communication between the transponder and the transceiver 100. The read minimum field strength thus is usually greater than the response minimum field strength.
If, exemplarily, a current through the antenna means 102 of the transceiver 100 is altered by the means 104 step by step, or continually, the magnitude of the magnetic field generated by the antenna means or of the magnetic alternating field at a certain location relative to the antenna means 102 will change correspondingly.
According to an embodiment of the present invention, the current through the antenna means 102 may exemplarily be controlled by means of a resistance network, as is exemplarily shown in
As does the coil L1 of the antenna means 102 of the transceiver 100, a coil L2 of antenna means 112 of a transponder 110 includes several important features. One such feature is converting a magnetic alternating field having a certain field strength into a current and a voltage for supplying the transponder 110 with energy. According to the invention, the antenna feed current Sst and thus the magnitude of the magnetic alternating field produced may be passed from a low starting value up to a maximum value or vice versa. If a transponder 110 is within reach of the antenna means 102 of the transceiver 100, the transponder 110 will “respond” as soon as its required response minimum field strength or read minimum field strength is reached. Thus, a distance from the transponder 110 to the antenna means 102 can be associated to different antenna feed currents Sst of the transceiver 100.
If the antenna feed current Sst and thus the magnitude of the magnetic alternating field generated increases from a flow starting value, the response minimum field strength of the transponder will at first be reached starting from a first antenna feed current Sst, which the transceiver “notices” due to an abrupt change of the antenna feed current Sst or the voltage at the primary coil L1 on the side of the transceiver 100, due to the mutual inductivity from the magnetic coupling of coils L1 and L2 on the side of the transponder 110. If the antenna feed current Sst and thus, the magnitude of the magnetic alternating field generated is increased further, the read minimum field strength of the transponder 110 will be reached starting from a second antenna feed current Sst, which may be recognized by the fact that a proper data communication between the transponder 110 and the transceiver 100 is possible starting from this read minimum field strength.
The response minimum field strength may, for example, be taken as an indicator for determining the distance from the transponder 110 to the antenna means 102 when there is only a single transponder within reach of the antenna means 102. If, however, a plurality of transponders are within reach, preferably the read minimum field strength should be selected as an indicator for determining the distance from the transponder 110 to the antenna means 102, since here communication between the transceiver 100 and the transponder 110 and thus a specific selection of the transponder 110 by anti-collision methods for differentiating the individual transponders is possible.
The processing means 108 comprises an input 108a and an output 108b. A variable antenna feed current Sst (or an equivalent signal) is fed to the input 108a. Within the processing means 108, a distance d from the transponder to the transceiver is associated according to a rule d=f(Sst) to that antenna feed current Sst where the magnetic alternating field generated by the transceiver is sufficiently great in order to generate the exact response minimum field strength required by the transponder at the position of the transponder so that a communication between the transponder and the transceiver is possible. The distance d determined in this way is provided at the output 108b of the processing means 108 for further processing. The antenna current Sst thus represents an association signal representing a measure of the inductive coupling between the antenna means of the transceiver and the transponder, wherein the distance d from the transponder to the antenna means may be associated to the inductive coupling.
If the antenna means of the transceiver includes only a single coil (1-dimensional case), only the distance d from a transponder to the antenna means can be determined via the antenna current Sst by the antenna means. If, for example, a direction of movement of the transponder is known or preset, the position of the transponder will be detectable.
If a position of the transponder in a multi-dimensional space is to be determined, the inventive method described may be extended to several antenna elements, which will be discussed in greater detail below referring to
Subsequently, another procedure for short-range localization according to another aspect of the present invention will be discussed referring to
According to this other aspect of the present invention, at least one of two evaluation signals generated in an input circuit or reception path of the antenna means of the transceiver by a load modulation of the transponder is determined for localizing a transponder at the transceiver. The evaluation signals determined at the transceiver thus are formed by a transforming coupling effect of the transponder to the transceiver depending on the distance from the transponder to the transceiver.
A receive signal SRx, such as, for example, a voltage, of the input circuit of the antenna means of the transceiver is at the input 108a of the processing means 108. The signal SRx can be divided into a first evaluation signal S= or a second evaluation signal S˜ (see
In addition,
The first evaluation signal S= may, for example, correspond to a so-called medium voltage. The medium voltage S= thus corresponds to a direct voltage portion which is superimposed on the receive signal SRx after demodulation and exemplarily not separated by a coupling capacitor in an inventive transceiver 100, but evaluated explicitly. As has already been discussed, the coil L1 of the reader antenna 102 and the coil L2 of the transponder antenna 112 are coupled to each other in a transforming manner. Thus, the coil L1 of the reader 100 represents the primary coil and the coil L2 of the transponder 110 represents the secondary coil of a transformer. If a transformer is loaded on the secondary side, a secondary current (at the transponder, 110) will cause an additional magnetic alternating field. According to the law by Lenz, the magnetic field change caused by the secondary current is opposite in direction to that caused by the primary current (at the transceiver 100). The effective magnetic field change, when loaded, in the primary coil L1 of the reader antenna 102 is smaller than in an unloaded case, i.e. if there is no transponder 110. Thus, the voltage induced at the primary coil L1 of the reader 100 is smaller. Since the medium voltage S=corresponds to that voltage resulting from rectifying the voltage SRx at the primary coil L1, the medium voltage S= is also becoming smaller with secondary-side loading by a transponder 110.
If an inductive coupling factor κ of the primary and secondary coils is decreased, i.e. the distance between the transponder 110 and the reader 100 is increased, the medium voltage S= will increase correspondingly, since the coupling of the transponder 110 to the transceiver 100 becomes smaller. If the coupling factor κ is zero, the transponder 110 will be outside the response region of the reader 100 and the result will be the maximum voltage quantity of the medium voltage S=. This connection is illustrated schematically in
b shows, in a semi-logarithmic illustration, a measured course of the medium voltage S= plotted against a logarithmically plotted distance d of the transponder 110 from the reader 100.
Correspondingly,
In the processing means 108 shown in
This procedure for short-range localization will also work without data being transferred from the transponder. However, it should be kept in mind that in a plurality of transponders in the magnetic alternating field of the reader 100 the medium-voltage S= measured at the reader 100 may be interpreted as a coupling of the plurality of transponders. By using suitable anti-collision methods, however, inductive coupling of more transponders than the transponder to be localized may be avoided by, for example, separating the antenna resonant circuits of the transponders not to be localized for a certain period, i.e. idling, to be able to specifically determine an inductive coupling and thus a distance of the transponder to be localized. Furthermore, a differentiation of the plurality of transponders by different resonant frequencies of the transponder antennas is, for example, conceivable.
In addition, an improvement may, for example, be achieved by a combination of the medium voltage S= and the second evaluation signal S˜.
The second evaluation signal S˜ may, for example, correspond to a so-called voltage swing. The determination of the voltage swing S˜ is another possibility of determining the position of a transponder 110, which in turn may, for example, be used for determining motion. The voltage swing S˜ results when a carrier signal of the transceiver 100 at the antenna resonant circuit of the transceiver 100 is loaded by the transponder 110 in the rhythm of the data and thus a kind of amplitude modulation of the carrier is caused. An inventive transceiver 100 may then evaluate the quantity of this voltage swing to obtain a distance d from this. In this inventive method for determining the position, the quantity of the voltage swing S˜ is measured in the processing means 108. The voltage swing S˜ is linked to the input circuit of the reader 100 via the load modulation of the transponder 110 and thus is also related to the distance d from the transponder 110 to the reader 100 by the inductive coupling factor κ. The dependence, however, is reversed compared to the medium voltage S=. The closer a transponder 110 to the reader 100, the stronger the effects of the load modulation, and thus the voltage swing S˜ increases.
d shows, in a semi-logarithmic illustration, a measured course of a voltage swing S˜ plotted against a logarithmically illustrated distance d of the transponder 110 from the reader 100. Correspondingly,
In the processing means 108 shown in
The distance d determined by the medium voltage and/or the voltage swing is provided at the output 108b of the processing means 108 for further processing.
If the measurement is performed only for one antenna, only a one-dimensional distance determination may be performed, like in the inventive procedure for a short-range position determination described before. For the case that, for example, a multi-dimensional detection is required and the transponders exemplarily are in different angular relations to the reading antenna or are moving, principles having several antennas will be discussed subsequently.
Subsequently, another inventive procedure for short-range position determination according to another embodiment of the present invention will be discussed referring to
According to this further aspect of the present invention, localization or short-range position determination of a transponder may be obtained by detecting and, for example, rectifying and smoothing a voltage induced by the magnetic field generated by the transceiver 100, in the transponder 110, at a resonant circuit of antenna means 112 of a transponder 110 so that a direct voltage value corresponding to the voltage induced is the result. This direct current value is, for example, converted to a corresponding digital value by an analog-to-digital converter and then integrated and transferred as data in a corresponding data transfer protocol between the transponder and the transceiver. The voltage induced by the magnetic field could be digitalized and processed in a transponder having correspondingly powerful signal processing, exemplarily even directly, i.e. without rectifying and smoothing. The transceiver may then preferably filter out the digital field strength data integrated in the transfer protocol from the actual useful data of the communication so that they are available for evaluation, exemplarily by means of a PC. The digital data transferred in this way here is preferably proportional to the field strength of the magnetic field at the transponder, which in turn is a measure of the distance from the transponder to the transceiver.
The means 250 for providing an association signal STrans,Tx may, for example, be formed such that a voltage induced by the magnetic field (magnetic alternating field) generated by a transceiver 100 in the means 250 is rectified and smoothed at a resonant circuit of the antenna means 112 of the transponder 110 so that there is a direct voltage value corresponding to the voltage induced. This direct voltage value is, for example, converted to a corresponding digital value by an analog-to-digital converter and then provided as data for a corresponding data transfer protocol for a communication between the transponder 110 and the transceiver 100 (not shown in
In the present embodiment of the invention, the transponder 110 is connected to the antenna means 112 via two lines 252 and 254, wherein the line 252 carries the association signal STrans,Tx and the line 254 carries a signal STrans,Rx resulting from the antenna means 112. Thus, a separation between the transmitting and receiving paths here exemplarily takes place in the antenna means 112. This separation between transmitting and receiving paths may, however, according to the present invention equally take place in the transponder 110, wherein then it would be sufficient to connect the transponder 110 to the antenna means 112 via only one line.
The antenna means 112 of the transponder 110 usually includes a parallel resonant circuit including a coil and a capacitor. Thus, the coil may, for example, be formed as a frame or ferrite rod antenna. The magnetic alternating field generated by a transducer induces a voltage in the transponder coil. Since the magnetic field strength generated by the transceiver 100 is a function of the distance of the transponder 110 from the transceiver 100, the distance of the transponder 110 from the transceiver 100 may be calculated back in the transponder 110 by measuring the induction voltage by means of the means for measuring value detection 304.
Using the transponder 110 illustrated in
The transceiver or reader 100 may be formed to filter out, after the transfer, the digital direct voltage values integrated in the data protocol as a measure of the field strength of the magnetic alternating field at the transponder 110 from the actual useful data so that they are available for evaluation, exemplarily in a PC. The digital data transferred in this way thus depends on the field strength of the magnetic alternating field at the transponder 110. If this data is, for example, compared to calibrating data of an initial field determined before, where the field strength is known at any point, the distance from the transponder 110 to the reader antenna 102 may also be determined here. Correction values or correction factors may also be considered here. A correction value exemplarily considers the influence of the magnetic alternating field by integrating a transponder and/or an object where the transponder is mounted in the magnetic alternating field (measuring field), which is how, for example, the field strength at the location of the transponder is changed. Correction values or correction factors may also be used for considering any influences to the magnetic alternating field. The direct voltage values determined in the transponder 110 thus represent an association signal representing a measure of the inductive coupling between the antenna means of the transceiver and the transponder, wherein a distance from the transponder to the antenna means may be associated to the inductive coupling.
Optionally, the voltage STrans,Rx induced by the magnetic alternating field at the antenna means 112 could also be digitalized directly without rectifying and transferred by means of load modulation from the transponder 110 to the transceiver 100. However, the result would be a considerably greater amount of data to be transferred from the transponder 110 to the transceiver 100 to result and to be handled.
Furthermore, it is optionally also conceivable that the digital data corresponding to the direct voltage value not to be integrated in a data transfer protocol between the transponder 110 and the transceiver 100 but exemplarily transferred directly in an uncoded or coded manner by means of load modulation from the transponder 110 to the transceiver 100, as is indicated in
Data processing for determining the position of the transponder could also take place in the transponder itself, given corresponding performance, wherein in this case the location determined by the transponder could, for example, be transferred from the transponder to the transceiver.
The voltage STrans,Rx induced at a transponder coil 112 is a measure of the field strength of the magnetic alternating field at the location of the transponder 110. The field strength of the magnetic alternating field in turn may be associated to the distance from the transponder 110 to the transceiver. As can be seen from
The first signal branch A comprises an optional impedance converter 412a and a low-pass filter 414 connected thereto or only the low-pass filter 414. The second signal path B comprises an optional impedance converter 412b, a low-pass filter 416, a downstream amplifier 418 and a circuit 420 connected to the amplifier for generating a direct voltage (so-called medium voltage). The third signal path C comprises an optional impedance converter 412c, a low-pass filter 422, followed by a circuit for suppressing a direct voltage 424 and an amplifier 426.
In order to transmit data, a transmit signal path D to the antenna 102 exemplarily includes an adjustable phase shifter 428, a modulator 430 and a controllable amplifier 432.
The first signal branch A with the optional impedance converter 412a and the low-pass filter 414 connected thereto exemplarily serves to evaluate data of a transponder, wherein the data in the transponder 110 may contain direct voltage values determined as an association signal representing a measure of the inductive coupling between the antenna means 102 of the transceiver and the transponder 110, wherein a distance from the transponder 110 to the antenna means 102 may be associated to the inductive coupling. Equally, data of a transponder 110 may also be evaluated via this first signal path A, responding as soon as its required response minimum field strength or read minimum field strength has been reached. As is described above, the response minimum field strength or read minimum field strength of the transponder 110 serves as an indicator for determining the distance to the antenna 102 of the reader.
The second signal path B with the optional impedance converter 412b, the low-pass filter 416, the downstream amplifier 418 and the circuit 420 for generating a direct voltage connected to the amplifier 418 exemplarily serves for evaluating the medium voltage S= described before as an association signal representing a measure of the inductive coupling between the antenna means 102 of the transceiver 100 and the transponder 110, wherein a distance from the transponder 110 to the antenna means 102 may be associated 110 to the inductive coupling.
The third signal path C comprises the optional impedance converter 412c, the low-pass filter 422, followed by the circuit for suppressing a direct voltage 424 and the amplifier 426. Exemplarily it serves for evaluating the voltage swing S˜ described before as an association signal representing a measure of the inductive coupling between the antenna means 102 of the transceiver 100 and the transponder 110, wherein a distance from the transponder 110 to the antenna means 102 may be associated to the inductive coupling.
The transmit signal path D includes the adjustable phase shifter 428 by which a phase of a high-frequency carrier signal may be varied. The phase shifter 428 is connected to the modulator 430 to modulate the data to be transmitted onto the high-frequency carrier. Finally, a controllable amplifier 432 is connected between the antenna resonant circuit 400, 402 and the modulator 430 to be able to vary, for example, a current as a drive signal Sst for the antenna 102.
The circuit arrangement illustrated in
So far, the description of the inventive methods and devices for determining the position of inductively coupled transponders have generally discussed antenna means 102 on the side of the transceiver 100. In a simplest case, the antenna means 102 only includes one single antenna. Only a one-dimensional positional determination or distance determination from the antenna may be performed with a single reader antenna, as has been described before, i.e. only a distance from the transponder to the reader antenna can be determined. If, for example, a direction of movement of the transponder is known, a position in a multi-dimensional space may nevertheless be determined. If the direction of movement is not known or if the transponder does not move, at least two antennas will be necessary to perform a positional determination in the 2-dimensional space. At least three antennas are correspondingly required to determine a position of the transponder in the 3-dimensional space, in case the direction of movement of the transponder is not preset or known.
Possible realizations and designs of antennas or antenna patterns which may inventively be employed for short-range localization of inductively coupled transponders to realize the antenna means 102 will be discussed subsequently referring to
Thus, the transponder comprises an orientation in the 3-dimensional space defined by angles θ and φ, θ indicating the angle to the x-z plane and φ indicating the angle to the x-y plane.
Fundamentally, the position of an object in a space may be described using three space coordinates (x, y, z). If a statement is additionally to be made about the orientation of the object, generally three solid angles should additionally be known. In the case of an RFID transponder, the number of solid angles to be determined is reduced to two when it is assumed that the rotation of the transponder around its own axis does not provide a contribution due to the rotational symmetry. Due to a directional characteristic of a transponder antenna, a description of % the position of the transponder without knowing the solid angles θ and φ is not possible.
In previous descriptions of the inventive procedures for short-range localization of inductively coupled transponders, the considerations with regard to a communication range between the reader and the transponder were made under the prerequisite that the transponder antenna and the antenna of the reader be preferably aligned to each other such that the maximum possible inductive coupling between the antennas is ensured. This ideal case for inductive coupling, however, will only apply if both antenna coils or coil opening areas are arranged in parallel to each other, i.e. the middle axes of the coils are basically identical or coincide. The coil middle axis forms a normal to the coil opening areas which the magnetic alternating field flows through.
If, however, the coils or coil opening areas of the transponder and transceiver are perpendicular to each other, the inductive coupling will vanish and a communication between the transceiver and the transponder is not longer possible. In a general case, there is, on the one hand, an angle greater than 0° between the coil middle axes of the transponder and the transceiver, on the other hand, the coils are not on the same axis but are shifter with regard to each other. Due to the inhomogeneity of the coil field, the results are different angular constellations for minimum and maximum inductive coupling.
The dependence of the inductive coupling factor on the transponder orientation should preferably be considered when orienting the reader antennas when being applied for determining a position. For the case that the transponder orientation is constant, the inductive coupling factor can be adjusted corresponding to the field orientation of the read field. In the two-dimensional case with the two solid angles θ and φ, with an unknown transponder orientation, two unknown coordinates are added to the also unknown coordinates of the transponder.
Referring to
One at least approximately orthogonal arrangement of reader antennas may preferably be provided for determining the coordinates of a transponder in the Cartesian coordinate system, as is illustrated in
a shows two top views of antenna means 102 having two at least approximately mutually orthogonal coils 550a, 500b, the middle axes 502a and 502b of which are perpendicular. That means the two coil opening areas are arranged in an angle in a range of 90°. In addition,
Preferred values for angles between two coil opening areas of antenna means are, exemplarily, in a range of 90°±15°.
In the at least approximately orthogonal arrangement of the two reader antennas 500a and 500b illustrated in
By the dependence described before of the inductive coupling factor on the transponder orientation to the antennas of a transceiver, the result could be arrangements where a positional determination of the transponder is not possible. This is, for example, the case when the transponder coil 510 is parallel to an antenna coil 500a, and thus orthogonal to the second antenna coil 500b of the transceiver (see right part of
To solve this problem, one or several additional antennas can be mounted in an angle of, for example, 45° to the existing orthogonal antenna system of the transceiver (diagonal antenna). This can ensure that a sufficient number of antennas are available for determining the distance and, thus, position of the transponder, independently of angle and position.
b shows a top view of antenna means 102 having two coils 500a and 500b, the coil opening areas of which are arranged in an angle α in a range of 60°. In addition,
Preferred values for angles between two coil opening areas of antenna means exemplarily are in a range of 60°+15°.
The resulting triangle also ensures a positional determination, even with unfavorable transponder arrangements. According to this possible design in
When the at least approximately orthogonal arrangement of the antennas of the transceiver illustrated in
c schematically shows antenna means 102 having six antenna coils 500a-f, each forming a side of an (imaginary) cube. Apart from a temporal sequential antenna drive of the individual antennas 500a-f to determine a position of a transponder within the space surrounded by the coils 500a-f, Helmholtz coil pairs may, for example, be formed by opposite coils (e.g. 500c and 500d). Furthermore, all antennas 500a-f could be driven simultaneously by drive signals having certain phase relations to one another and thus, among other things, realize the procedures for determining an orientation and for excluding ambiguities when determining the position described below.
In addition to the three or six antennas 500a-f, the antenna means 102 may additionally exemplarily be supplemented by an additional diagonal antenna, wherein constellations of this kind will be discussed in greater detail below.
In a simple three-dimensional temporally sequential driving of the antennas 500a-f by control means, the three antennas not required could, for example, also be used for difference or control measurements (plausibility checks).
For the antenna arrangements described referring to
Adding the transponder angle, i.e. the positioning of the coil middle axis of the transponder, cannot simply be realized by means of further antennas. Due to the strong directional characteristic of the transponder coil, the resulting problems for determining the angle of the coil middle axis must additionally be considered. An inventive approach is using special antenna constellations, such as, for example, Helmholtz coils, for estimating the transponder angle.
d shows a top view of exemplary antenna means 102 having five antenna coils 500a-e, of which four antenna coils 500a-d are arranged in the shape of a rectangle or square. An antenna coil 500e forms a diagonal coil running diagonally in the square formed by the antenna coils 500a-d.
Apart from a temporally sequential antenna drive of the individual antennas 500a-e for determining a position of a transponder within the planes surrounded by the coils 500a-e, a transponder angle can also be determined using the antenna arrangement shown in
In the inventive method where a response minimum field strength of the transponder 110 is used as an indicator for determining the distance from the transponder 110 to the antenna means 102 of the transceiver 100, less energy is available for the transponder 110 when turning since the induction voltage decreases due to the smaller magnetic flow through the coil-opening area of the transponder coil. The field strength it requires for responding thus is no longer reached starting from a certain threshold or a certain angle. This change may be measured using the control of the antenna current by the Helmholtz coil of the antenna means 102. The transponder angle may thus be estimated up to a rotation of about 45°. Starting at 45°, reception is no longer possible since the transponder is rotated too much from the field orientation of the Helmholtz coil including the coils 500a,c or 500b,d. If, however, a second Helmholtz coil including 500b,d or 500a,c which is rotated by at least about 90° relative to the first Helmholtz coil including 500a,c or 500b,d is employed, the missing angle range can also be covered. Inventively, a rectangular system having two Helmholtz arrangements can be realized to ensure an optimum utilization of the antenna ranges in this way.
In the inventive method where an analog voltage induced by the magnetic field generated by the transceiver 100 is exemplarily rectified and smoothed at an input circuit of antenna means 112 of the transponder 110, so that the result is a direct voltage portion corresponding to the voltage induced, reduced field strengths are measured in the transponder 110 and transferred to the reader 100 due to the rotation of the transponder 110. Thus, a directional determination is possible with a temporally sequential evaluation of two Helmholtz arrangements, arranged in at least, approximately 90° angles, of the antenna means 102 of the transceiver 100.
A defined maximum range for a communication between the transceiver 100 and the transponder 110 is obtained with the antennas 500a-e employed, as is illustrated in
Case 1 will arise if there is no transponder in the field of the antennas 500a-e or no functioning transponder. Case 2 essentially does not provide useful information due to the mirror symmetry of the diagonal antenna 500e, even if a previous transponder position is available. This measuring value determined before, however, may be used in cases 3 and 5. Assuming that the other parameters remain constant, the measuring value given by the association signal is considered in the positional change. Inevitably, imprecision results since slight changes of the quantities assumed to be constant may add up to form considerable errors. The desirable cases are cases 4, 6, 7 and 8 since here at least two antenna signals are available so that a two-dimensional position can be calculated. The angular position of the transponder 110 is estimated by means of the results of the Helmholtz coils 500a,c or 500b,d and the diagonal antenna 500e. Since a rotation of the transponder 110 by 180° does not influence the measuring result, the angle estimation should preferably only take place in the from 0° to 180°. In the range from 0° to 90°, the transponder 110 is in the receiving range of the diagonal antenna 500e, at angles greater than 90° this is no longer the case. A first estimation can take place in this manner. Only a precise specification of the angle by up to ±5° can be performed by means of the two Helmholtz coils 500a,c or 500b,d.
Compared to the possibility described before of sequentially driving antennas or antenna pairs, it is possible by using several antennas which are, for example, arranged rectangularly to selectively influence the orientation of the field line within the space spanned by the antennas. One might do without diagonal antennas here.
This connection is schematically illustrated in
a-d each show a top view of antenna means 102 having four antenna coils 500a-d arranged in the shape of a rectangle or square.
In
In
In
In
If the direction of the field lines is altered according to a certain pattern, the orientation of the transponders may be determined by evaluating the transponder reactions, i.e. the inductive coupling of the transponder.
In the case of the method for measuring the response minimum field strength or the read minimum field strength of a transponder, a first phase pattern is at first generated by means of the drive signals of the antennas 500a-d (e.g. 0°) and thus the response of the transponder 110 is measured by varying the drive signals (e.g. current) for the antenna means 102 of the reader 100. Subsequently, the measurements are repeated for other phase patterns. The orientation of the transponder 110 may be determined by evaluating the different response minimum field strengths to the different phase patterns.
In the case of the method for measuring the field strength in the transponder 110, the following is obtained by changing the orientation of the magnetic field by varying the phase positions of the antenna currents fed in the different antennas 500a-e. The voltage induced by the overall field generated in the transponder resonant circuit is measured and transferred to the reader 100 to be evaluated in the manner described before. Subsequently, another phase relation of the antenna currents fed is established and the voltage induced in the transponder resonant circuit is also measured and transferred. If at sufficient number of constellations of orientations of field lines are produced in this manner, the orientation of the transponder 110 in the space spanned by the antennas 500a-d may also be determined here by evaluating the data measured.
In the case of the method for measuring the medium voltage or voltage swing, a first phase pattern of the antenna currents fed may also at first be generated and thus the medium voltage or voltage swing at the reader 100 be evaluated. If the orientation of the field lines of the magnetic alternating field generated by the different phase relations of the antenna currents and the orientation of the transponder coil medium axis are perpendicular, the voltage swing at the reader 100 will become maximal or the medium voltage minimal. If the transponder coil medium axis and the field lines generated are parallel, the voltage swing will become minimal and the medium voltage maximal. Values in between result for different phase relations.
If the direction or orientation of the transponder has been determined by one of the procedures described before, the corresponding phase relation of the antenna feed currents may, for example, also be utilized to always supply the transponder with certain predetermined or maximally possible field strengths. Maximum field strengths will be possible if the measuring field penetrates the transponder coil approximately perpendicularly, i.e. in an angle in a range of 90°±30°. The transponder itself thus may of course have any orientation in space.
For the cases 4 and 6 of the table shown above, there is only one signal of either a horizontal antenna or a vertical antenna, and additionally the signal of the diagonal antenna. Due to the structure of the antenna arrangement illustrated in
Like
In the methods for utilizing several pieces of temporally sequential antenna information described before, ambiguities of transponder locations can be excluded in addition to determining the orientation. If, for example, several locations were determined for a transponder due to field or symmetry features, ambiguity may be reduced or ruled but completely in the following manner referring to
Since it is possible by means of the methods described above to determine an orientation of the transponder 110 and thus the transponder orientation for another procedure is known, regions having different field instances may be generated by varying the phase relations of the drive signals for the antennas 500a-e of the antenna means 102 of a transceiver 100, i.e. at first a first field constellation is generated and possible locations of the transponder 110 are determined. Usually, ambiguities will result here. If subsequently the measurement is repeated with a field exemplarily oriented to the left, for example by driving the coils 500a,d, a considerably higher field strength will be available for the transponder position (x1,y1) than for the transponder position (x2,y1), i.e. if the transponder 110 is not in the position (x1,y1), no reaction of the transponder 110 will result despite sufficient energy supply. The transponder 110 thus is in the position (x2,y1) from where it cannot respond because it does not receive sufficient energy for responding. For reasons of safety, this measurement may also be reversed, i.e. exemplarily by driving the coils 500a,b, and thus the result checked. This advantage, too, of the procedure described above is inventively applicable to all methods referring to
If a movement of a transponder within the space spanned by the antennas is to be determined, this may generally take place by repeatedly determining the position according to a procedure described above. If, for example, the direction or orientation of the transponder has been determined by one of the procedures described before, the corresponding phase relations of the antenna feed currents may, based on the orientation determined, for example, be used for supplying the transponder with certain predetermined or maximally possible field strengths of the measuring field and thus be able to improve traceability of the measuring results. Subsequently, a movement of the transponder within the space spanned by the antennas can be determined by repeatedly determining the position according to one of the procedures described before. A current direction of movement of the transponder can be deduced from a combination of two successive positional measurements.
Finally, further optional transceivers according to other embodiments of the present invention of an RFID system for determining the position of a transponder by inductive coupling are to be described referring to
For determining the position, orientation and movement, one or several antennas of the antennas 500a-f are required depending on the number of coordinates to be determined. The distance and the orientation of a transponder from the antennas 500a-f can be determined by means of these antennas. The inventively modified write/read unit 100 thus may include one or several transmitting and receiving paths. Via the antenna selection module 620 controlled by the control module 610, either individual antennas of the antenna means 102 one after the other (sequentially) or several or all antennas 500a-f simultaneously with different phase relations can be driven by antenna feed currents via the transmit paths. In order to determine an orientation of a transponder within the space surrounded by the antennas 500a-f, Helmholtz coil pairs may be formed and driven correspondingly for example by opposite coils (e.g. 500c and 500d). One or several receive paths are available also for evaluating the signals.
The RFID write/read apparatus 10 (exemplarily a conventional reader) provides an antenna current which may be varied via the microcontroller 210 and the controllable amplifier 730 of the control means 710. Additionally, the microcontroller 210 is formed to select the antennas 740 and 750 by the controllable switch 720. By means of the method described above and the PC 630, a distance to a transponder (not shown) may be determined for each of the two antennas 740 and 750 and thus finally a position of the transponder in the two-dimensional space can be calculated, as has already been described above referring to
Transponders in a predetermined volume, for example in the order of magnitude of one or several cubic meters (m3) may be localized by the inventive methods, and devices described. Fields of application are, for example, identifying and localizing animals, such as, for example, localizing animals in the ground or localizing and identifying objects in non-accessible or difficult-to-access regions, such as, for example, chemical reaction regions. The usage of passive transponders allows the smallest setups of transponders.
In particular, it is pointed out that, depending on the circumstances, the inventive scheme may also be implemented in software. The implementation may be on a digital storage medium, in particular on a disc or a CD having control signals which may be read out electronically, which can cooperate with a programmable computer system and/or microcontroller such that the corresponding method will be executed. In general, the invention thus also is in a computer program product having a program code stored on a machine-readable carrier for performing the inventive method when the computer program product runs on a computer and/or microcontroller. Put differently, the invention may also be realized as a computer program having a program code for performing the method when the computer program runs on a computer and/or microcontroller.
| Number | Date | Country | Kind |
|---|---|---|---|
| 102006026495.9 | Jun 2006 | DE | national |
This application claims priority to German Patent Application No. 102006026495.9, filed Jun. 07, 2006, all of which is herein incorporated in its entirety by this reference thereto.
