JP2018146452A - Tag reader - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a tag reader capable of identifying an object moving on a predetermined line without requiring a fixed tag. SOLUTION: A phase calculation unit (S10) for sequentially calculating the phase φr of a received wave, a phase difference calculation unit (S30) for calculating a phase difference Δφ, a phase difference Δφ, and a tag movement distance between two time points. Based on the above, it is provided with a tag angle calculation unit (S40) that calculates a tag angle θ, which is an angle between a straight line connecting an antenna of a tag reader and a wireless tag and a line on which the wireless tag moves. The phase difference Δφ is calculated by calculating at least one of the two time points for calculating the phase difference Δφ as different time points, calculating the first tag angle θ1 and the second tag angle θ2 from the two phase difference Δφ, and tag angle θ. The minimum distance Lmin between the antenna and the tag is calculated based on the distance between the position where is the first tag angle θ1 and the position where the tag angle θ is the second tag angle θ2, the first tag angle θ1, and the second tag angle θ2. A tag distance calculation unit (S50) for calculation is further provided. [Selection diagram] FIG. 7

Description

  The present invention relates to a tag reader, and more particularly to a technique for reading a wireless tag attached to an object moving on a line.

  Patent Document 1 discloses a technique for distinguishing whether a pallet has passed a conveyor or a vicinity of the conveyor. In the technique disclosed in Patent Document 1, in addition to installing a reader / writer in the vicinity of the conveyor, a fixed tag is arranged at a position facing the reader / writer across the conveyor. A tag (hereinafter referred to as a moving tag) is also attached to a pallet moving on the conveyor.

  When the moving tag is attached to a pallet that moves on the conveyor, there is a state in which the moving tag comes between the fixed tag and the reader / writer that are at positions facing each other across the conveyor. When the moving tag comes between the fixed tag and the reader / writer, communication between the fixed tag and the reader / writer is hindered. At this time, since the moving tag is closer to the reader / writer than the fixed tag, good communication with the reader / writer becomes possible.

  After that, when the pallet moves on the conveyor and the moving tag attached to the pallet does not exist between the fixed tag and the reader / writer, the fixed tag and the reader / writer can perform good communication. On the other hand, communication between the mobile tag and the reader / writer becomes impossible.

  If such a change can be observed, it can be determined that the moving tag is attached to an object moving on the conveyor.

  On the other hand, when the object to which the moving tag is attached passes near the conveyor, there is no time zone in which communication between the fixed tag and the reader / writer is hindered. Therefore, it is possible to distinguish whether the pallet to which the moving tag is attached has passed the conveyor or the vicinity of the conveyor.

JP 2012-98863 A

  The technique disclosed in Patent Document 1 requires a fixed tag. Therefore, there is a problem that a space for installing the fixed tag is necessary. For this reason, there has been a demand for a technique that can identify an object moving on a predetermined line such as a conveyor without a fixed tag.

  The present invention has been made based on this situation, and an object of the present invention is to provide a tag reader that can identify an object moving on a predetermined line without requiring a fixed tag.

  The above object is achieved by a combination of the features described in the independent claims, and the subclaims define further advantageous embodiments of the invention. Reference numerals in parentheses described in the claims indicate a correspondence relationship with specific means described in the embodiments described later as one aspect, and do not limit the technical scope of the present invention. .

To achieve the above object, the present invention provides:
A phase calculation unit (S10, S110) that sequentially transmits a radio wave to the radio tag and sequentially calculates a phase (φ _r ) of a received wave that is a radio wave transmitted from the radio tag as a response and received by the tag reader;
A phase difference calculation unit (S30) that calculates a phase difference (Δφ) that is a phase difference calculated by the phase calculation unit at two time points;
Based on the phase difference and the tag moving distance that is the distance that the wireless tag moves between the two time points, the straight line connecting the antenna (11) provided in the tag reader and the wireless tag, and the line (2 A tag angle calculation unit (S40) that calculates a tag angle (θ) that is an angle between
The phase difference calculation unit calculates two phase differences as at least one of two time points for calculating the phase difference as different time points,
The tag angle calculation unit calculates the first tag angle and the second tag angle as the tag angle using each of the two phase differences,
Based on the distance between the position where the tag angle becomes the first tag angle and the position where the tag angle becomes the second tag angle, the first tag angle, and the second tag angle, the line from the line where the wireless tag moves to the antenna A tag distance calculation unit (S50) that calculates the minimum distance between the antenna and the tag (Lmin), which is the minimum distance, is further provided.

  The present invention utilizes the fact that the phase of the received wave is determined by the propagation distance, does not depend on time, and the wireless tag moves on the line. The reason why the phase of the received wave is determined by the propagation distance will be described later.

  When a wireless tag moves on a line, if the direction from the wireless tag to the tag reader is between two short time points, the locus of the wireless tag moving between the two time points is the hypotenuse, and the tag angle is defined as one interior angle. A right triangle can be created. Note that the tag angle is an angle between a straight line connecting the antenna included in the tag reader and the wireless tag and a line along which the wireless tag moves.

  In the right triangle, the length of the adjacent side with respect to the tag angle is half of the difference in propagation distance. Since the phase of the received wave is determined by the propagation distance, half of the difference in propagation distance, that is, the length of the adjacent side can be determined from the phase difference of the received wave at two time points. The tag angle can be calculated from the length of the oblique side and the length of the adjacent side.

  Therefore, since one tag angle can be calculated from one phase difference, if two phase differences are calculated, the first tag angle and the second tag angle, which are tag angles at two positions moving on the line, are calculated. And can be calculated.

  If the tag angle at two time points on the line and the distance from the position of the wireless tag at the first tag angle to the position of the wireless tag at the second tag angle (that is, the tag moving distance) are known, The movement distance is defined as one side, and the angles at both ends of the one side are determined. Therefore, a triangle with the tag moving distance as one side and the tag reader as one vertex is determined. Since the minimum antenna-tag distance is the height of this triangle, the minimum antenna-tag distance can be calculated.

  A wireless tag that moves along a predetermined line should have a minimum antenna-tag distance determined based on the moving line. Therefore, based on the minimum distance between the antenna and the tag, it is possible to identify a wireless tag that moves on a predetermined line and an object to which the wireless tag is attached. A fixed tag was not used to calculate the minimum antenna-tag distance. Therefore, an object moving on a predetermined line can be identified without requiring a fixed tag.

The invention according to claim 2
A storage unit (19) for storing the moving speed of the line in advance;
The tag angle calculation unit calculates the tag moving distance from the time difference between the two time points and the moving speed of the line stored in the storage unit,
The tag distance calculation unit calculates the distance between the position at which the tag angle is the first tag angle and the position at which the tag angle is the second tag angle, and the time when the tag angle is the first tag angle and the tag angle is the first It is calculated from the time difference from the time when the angle was two tag angles and the moving speed of the line stored in the storage unit.

  In the invention according to claim 2, the moving speed of the line is stored in the storage unit. That is, the moving speed of the line is known. When calculating the tag angle, a distance by which the wireless tag moves between two time points is required. Further, when calculating the minimum antenna-tag distance, the distance between the position where the tag angle becomes the first tag angle and the position where the tag angle becomes the second tag angle is necessary. In the invention which concerns on Claim 2, when calculating these distances, the moving speed of the line memorize | stored in the memory | storage part is used.

  Unlike the present invention, the speed at which the wireless tag moves can be calculated as described below.

The invention according to claim 3
A storage unit (19) storing an antenna-line distance (Lset) which is a minimum distance from the antenna to the line;
A second phase difference calculation unit (S140) that calculates a phase difference calculated by using the phase gradient code switching point as one time point based on the phase that is sequentially calculated by the phase calculation unit;
Based on the distance between the antenna and the line stored in the storage unit and the phase difference calculated by the second phase difference calculation unit, the code switching adjacent which is the other time point when the phase difference is calculated together with the phase gradient code switching point A second tag distance calculation unit (S150) that calculates an antenna-tag distance that is a distance from the antenna to the wireless tag at the time point;
Based on the antenna-tag distance calculated by the second tag distance calculation unit and the antenna-line distance stored in the storage unit, a second tag angle calculation unit that calculates the tag angle at the code switching adjacent time point ( S160)
Based on the tag angle calculated by the second tag angle calculation unit, the antenna-tag distance calculated by the second tag distance calculation unit, and the antenna-line distance stored in the storage unit, the code switching adjacent time point A moving distance calculating unit (S170) for calculating a moving distance from the position of the wireless tag to the position of the wireless tag at the switching point of the phase gradient code;
A speed calculation unit (S180) that calculates a movement speed (V _tag ) of the wireless tag based on the movement distance calculated by the movement distance calculation unit and the time difference between the code switching adjacent time point and the phase gradient code switching point; Prepared,
The tag angle calculation unit calculates the moving distance that the wireless tag moves between two time points from the time difference between the two time points and the moving speed of the wireless tag calculated by the speed calculation unit,
The tag distance calculation unit calculates the distance between the position at which the tag angle is the first tag angle and the position at which the tag angle is the second tag angle, the time when the tag angle is the first tag angle, and the tag angle is Calculated from the time difference from the time when it was the second tag angle and the moving speed of the wireless tag calculated by the speed calculator,
The tag reader
Whether or not the wireless tag is moving on a predetermined line based on a comparison between the antenna-tag minimum distance calculated by the tag distance calculation unit and the antenna-line distance stored in the storage unit A line determination unit (S60-S80) is provided.

  Since the phase of the received wave is determined by the propagation distance, the phase gradient code representing the increase / decrease in the phase difference between the case where the antenna-tag distance gradually decreases and the case where the antenna-tag distance gradually increases. The sign is reversed.

  The position of the wireless tag where the phase gradient code is inverted is the position where the antenna-tag distance becomes the minimum, that is, when the antenna-tag distance becomes the antenna-line distance. In the present invention, since the distance between the antenna and the line is stored, the distance between the antenna and the tag can be known at the time of phase switching.

  Further, before and after the phase gradient code switching point, the antenna-tag distance is determined by the antenna-line distance and the phase difference. Therefore, the second tag distance calculation unit calculates the antenna-tag distance at the code switching adjacent time point from the phase difference calculated at the phase gradient code switching point and the antenna-line distance stored in the storage unit. .

  It can be seen that the distance between the antenna and the tag at the time when the code change is adjacent, and the distance between the antenna and the tag at the change point of the phase gradient code is the distance between the antenna and the line. From these, it is possible to geometrically calculate the distance between the position of the wireless tag at the adjacent point of code switching and the position of the wireless tag at the switching point of the phase gradient code.

  Then, the speed between the position of the wireless tag at the adjacent point of code switching and the position of the wireless tag at the switching point of the phase gradient code and the time difference between the adjacent point of code switching and the switching point of the phase gradient code can be determined. The calculation unit can calculate the moving speed of the wireless tag.

  Since the moving speed of the wireless tag can be calculated in this way, the tag angle calculating unit calculates the distance that the wireless tag moves between two time points using the moving speed of the wireless tag calculated by the speed calculating unit. . The line distance calculation unit uses the moving speed of the wireless tag calculated by the speed calculation unit to move the distance between the position where the tag angle is the first tag angle and the position where the tag angle is the second tag angle. Is calculated.

  Further, according to the present invention, it is possible to calculate the minimum distance between the antenna and the tag and use the fact that the distance between the antenna and the line is stored, to determine whether or not the wireless tag is moving on a predetermined line. Judging.

The invention according to claim 4
A storage unit (19) storing an antenna-line distance (Lset) which is a minimum distance from the antenna to the line;
Whether or not the wireless tag is moving on a predetermined line based on a comparison between the antenna-tag minimum distance calculated by the tag distance calculation unit and the antenna-line distance stored in the storage unit A line determination unit (S60-S80) is provided.

  According to the present invention, a line determination unit is added to the inventions according to claims 1 and 2 as in the case of claim 3.

The invention according to claim 5
When there is no change in the phase sequentially calculated by the phase calculation unit, the wireless tag includes a stop determination unit (S38, S39) that determines that the wireless tag is stopped.

  In the present invention, in addition to obtaining the minimum antenna-tag distance, it can also be determined whether or not the wireless tag is stopped.

It is a figure explaining the structure of the wireless tag system 1 of 1st Embodiment. It is the figure which looked at the wireless tag system 1 from the top. 2 is a block diagram showing a configuration of a tag reader 10. FIG. It is a figure which shows notionally communication path CP1 and CP2 in the time t1 and t2. It is a figure which shows the geometric shape which can be approximated when tag moving distance (DELTA) d is short. It is a figure explaining the calculation method of the minimum distance Lmin between antenna-tags. It is a flowchart explaining the process which the calculating part 18 performs. It is a flowchart which shows the detailed process of S3 of FIG. It is a flowchart which shows the process which the calculating part 18 performs in 2nd Embodiment. It is a flowchart which shows the process which the calculating part 18 performs in 3rd Embodiment.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

[System configuration]
FIG. 1 is a diagram for explaining the configuration and usage of a wireless tag system 1 including a tag reader 10 according to an embodiment of the present invention. The wireless tag system 1 includes a tag reader 10 installed in the vicinity of a belt conveyor line (hereinafter simply referred to as a line) 2 and a wireless tag 20 attached to a load 3 moving on the line 2.

  The tag reader 10 includes an antenna 11 and transmits a transmission wave, which is a radio wave for reading a radio tag, from the antenna 11 toward the line 2. The frequency of the transmission wave may be any frequency that is permitted by law. In the present embodiment, a frequency in the UHF band is used.

  The wireless tag 20 is a passive tag, operates with power generated by receiving a transmission wave, and transmits a signal responding to the transmission wave to the tag reader 10 by radio waves. The signal transmitted by the wireless tag 20 includes an ID for identifying the wireless tag 20.

  The tag reader 10 receives radio waves transmitted from the wireless tag 20. The radio wave transmitted by the wireless tag 20 and received by the tag reader 10 is hereinafter referred to as a received wave.

  When the tag reader 10 receives the received wave, it can be seen that the wireless tag 20 exists in the reading range of the tag reader 10. However, when the reading range of the tag reader 10 is wide, there is a possibility that the wireless tag 20 attached to the luggage 3 being conveyed by other moving means such as a forklift is read around the line 2.

  The reading range of the tag reader 10 may be narrowed. However, if the reading range is narrowed, the time available for reading is reduced, so that the reading accuracy is lowered. Therefore, the tag reader 10 of the present embodiment determines whether the wireless tag 20 is moving on the line 2 while suppressing the reading range from being narrowed.

  FIG. 2 is a top view of FIG. As shown in FIG. 2, line 2 is a straight line. Unlike FIG. 1, in FIG. 2, the wireless tag 20 is attached to the side surface of the luggage 3 on the tag reader 10 side. Further, FIG. 2 shows that the same luggage 3 has moved to the right side of the figure as time elapses.

[Configuration of Tag Reader 10]
FIG. 3 shows a configuration diagram of the tag reader 10. The tag reader 10 has a known configuration except for the function of the calculation unit 18. In addition to the antenna 11, the tag reader 10 includes a transmitter 12, a coupler 13, an antenna duplexer 14, an orthogonal demodulator 15, bandpass filters 16i and 16q, AD converters 17i and 17q, and an arithmetic unit 18.

  The transmitter 12 generates and outputs a transmission signal that is a signal representing a transmission wave to be transmitted toward the wireless tag 20. This signal is branched by the coupler 13 and directed to the antenna duplexer 14 and the quadrature demodulator 15. The antenna duplexer 14 outputs a signal from the transmitter 12 to the antenna 11, and outputs a received signal representing a received wave received by the antenna 11 to the quadrature demodulator 15. The antenna 11 radiates a transmission wave in the air and receives a radio wave from the wireless tag 20.

  The received wave received by the antenna 11 is input to the quadrature demodulator 15. The quadrature demodulator 15 includes a phase shifter 151 and two mixers 152i and 152q. A signal representing a transmission wave branched by the coupler 13 is input to the phase shifter 151. One mixer 152i receives a reception signal and a transmission signal. When the reception signal and the transmission signal are mixed by the mixer 152i, an I signal that is an in-phase component of the baseband signal is obtained. The other mixer 152q receives the received signal and the signal obtained by shifting the phase of the transmission signal by 90 degrees by the phase shifter 151. From the mixer 152q, a Q signal which is an orthogonal component of the baseband signal is obtained.

  The signal obtained by the mixer 152i is input to the arithmetic unit 18 via the bandpass filter 16i and the AD converter 17i, and the signal obtained by the mixer 152q is input to the arithmetic unit 18 via the bandpass filter 16q and the AD converter 17q. Is done. The band pass filters 16i and 16q selectively pass signal components having no time phase ωt. The time phase ωt will be described with Expression 2.

  The calculation unit 18 is a computer including a CPU, a ROM, a RAM, and the like. The CPU executes a program stored in a recording medium such as a ROM while using a temporary storage function of the RAM, so that FIG. The process shown in the flowchart below is executed. Executing the processing shown in FIG. 7 and the following means that a method corresponding to the program is executed. Note that some or all of the functional blocks included in the calculation unit 18 may be realized by using one or a plurality of ICs (in other words, as hardware). In addition, some or all of the functions of the calculation unit 18 may be realized by a combination of software execution by the CPU and hardware members.

The computing unit 18 calculates a distance that minimizes the distance from the antenna 11 to the wireless tag 20 on the basis of the phase φ _r of the received wave, assuming that the wireless tag 20 moves on the line 2. This distance is hereinafter referred to as an antenna-tag minimum distance Lmin.

  The nonvolatile memory 19 corresponds to a storage unit in claims, and a minimum distance between the antenna 11 and the line 2 is stored in advance. Hereinafter, the minimum distance between the antenna 11 and the line 2 is referred to as an antenna-line distance Lset. The antenna-line distance Lset is the length of a perpendicular line dropped from the antenna 11 to the line 2. The antenna-line distance Lset may be stored for one line 2 or may be stored for a plurality of lines 2.

The non-volatile memory 19 also stores the moving speed of the line 2. When the wireless tag 20 is attached to the luggage 3 moving on the line 2, the wireless tag 20 also moves at the moving speed of the line 2. That is, the movement speed V _tag of the wireless tag 20 is stored in the nonvolatile memory 19.

[Relationship between received wave phase φ _r and propagation distance]
The calculation unit 18 uses that the phase φ _{r of the} received wave is determined by the propagation distance and does not depend on time. First, it will be described that the phase φ _{r of the} received wave is determined by the propagation distance.

The wave function of electromagnetic waves is expressed by Equation 1.

From Equation 1, the phase φ of the electromagnetic wave is expressed by Equation 2.

Of the phases shown in Equation 2, ωt is a time phase and βL is a spatial phase. Phase phi _r of the received wave, the equation 3 is expressed only in the spatial phase .beta.L, time phase ωt it can be seen to be erased. This is because the reception time _tr and the transmission time t _t are substantially equal. In Equation 3, φ _t represents the transmitted wave phase, but except for Equation 3, φ _t represents the phase φ _r of the received wave at time t.

[Description of tag angle calculation formula]
An expression for calculating the tag angle θ can be derived using Expression 3. Next, derivation of an expression for calculating the tag angle θ will be described. FIG. 4 conceptually shows the communication path CP1 at time t1 and the communication path CP2 at time t2. The wireless tag 20 moves on the line 2 in the right direction in the figure. The distance between the antenna 11 and the wireless tag 20 is an antenna-tag distance L, the antenna-tag distance L at time t1 is L1, and the antenna-tag distance L at time t2 is L2. Note that the antenna-tag distance L can also be said to be half (or one way) of the propagation distance through which the received wave propagates.

  The distance that the wireless tag 20 has moved between time t1 and time t2 is defined as a tag moving distance Δd. When Δd is sufficiently smaller than L1 and L2, that is, when the time from time t1 to time t2 is short, as shown in FIG. 5, the communication path CP1 and the communication path CP2 can be regarded as parallel. When the communication path CP1 and the communication path CP2 can be regarded as parallel, the locus of the movement of the wireless tag 20 between the two time points t1 and t2 shown in FIG. 5 is the hypotenuse, and the tag angle θ is one inner angle. You can draw a right triangle. When the tag angle θ is determined, the remaining angles are also determined, so that a right triangle is determined as one.

From this right triangle, the relationship between the tag angle θ, the length of the hypotenuse Δd, and the length of the adjacent side (L1−L2) is expressed in Equation 4.

When both sides of Equation 4 are multiplied by the phase constant β, Equation 5 is obtained.

By transforming Equation 5, Equation 6 representing the tag angle θ is obtained.

The denominator on the right side of Equation 6 is expressed by Equation 7.

From the equations 6 and 7, the tag angle θ can be calculated from the time difference Δt between the two time points t1 and t2, the phases φ _t1 and φ _t2 at the two time points, and the tag moving speed V _tag . That is, if the phase φ is measured at two time points, one tag angle θ can be calculated.

[Calculation of antenna-tag minimum distance Lmin]
Further, if the phase φ is measured at two time points, one tag angle θ can be calculated. Therefore, if the phase φ is measured at three time points, two tag angles θ can be obtained. FIG. 6 is a diagram illustrating a geometric relationship between two tag angles θ1 and θ2 and the minimum antenna-tag distance Lmin.

  Applying the triangulation formula to the two right triangles shown in FIG. Expression 8 indicates that the minimum antenna-tag distance Lmin can be calculated from the two tag angles θ1 and θ2 and the tag moving distance Δd.

The tag moving distance Δd can be calculated from the moving speed V _tag of the wireless tag 20 and the time difference Δt between the two time points. Therefore, when the moving speed V _tag of the wireless tag 20 is known, that is, when the speed of the line 2 is known, the antenna-tag minimum distance Lmin can be obtained by measuring the tag angles θ1 and θ2 at two points in time. It can be calculated.

[Processing of Calculation Unit 18]
The calculation unit 18 calculates the minimum antenna-tag distance Lmin to identify whether the wireless tag 20 is moving on the predetermined line 2. Next, processing executed by the calculation unit 18 to identify whether the wireless tag 20 is moving on the predetermined line 2 will be described with reference to the flowchart shown in FIG.

  The computing unit 18 executes the processing shown in FIG. 7 every time a received wave is received or every time a received wave is received a certain number of times, for example. Judgment that the received wave has been received is made based on whether or not a received wave having a certain amplitude or more has been received based on the I signal input from the AD converter 17i and the Q signal input from the AD converter 17q. .

In step (hereinafter, step is omitted) S10, time-series data of the phase φ _r of the received wave is created. The time-series data, the phase phi _r of the received wave is data associated with the time of receiving a reception wave. If the time series data of the phase φ _r of the received wave has already been created, the created time series data is updated in S10.

The phase φ _{r of the} received wave is calculated from Equation 9. This S10 corresponds to a phase calculation unit in claims.

The derivation of Equation 9 will be described with a series of equations shown in Equation 10.

From Equation 1 described above, the wave function of the transmitted wave is represented by Equation 10-1, and the wave function of the received wave is represented by Equation 10-2. Taking the product of the complex conjugates of Equations 10-1 and 10-2, Equation 10-3 is obtained. The I signal component and the Q signal component of Expression 10-3 are expressed by Expression 10-4 and Expression 10-5, respectively. Dividing Equation 10-5 by Equation 10-4 gives Equation 10-6. When both sides of Expression 10-6 are multiplied by tan ⁻¹ , Expression 10-7 is obtained. Further, in the tag reader 10, since the I wave and the Q signal are obtained by mixing the transmission wave and the reception wave with the mixers 152i and 152q, Expressions 10-8 and 10-9 are established. When Expression 10-8 and Expression 10-9 are substituted into Expression 10-7, Expression 10-10, that is, Expression 9 is obtained.

In association with the phase phi _r of the received wave obtained by the calculation of the equation 9 in time it received a reception wave, creating or updating the time-series data of the phase phi _r of the received wave. Then, the time series data is stored in a RAM or the like provided in the calculation unit 18.

  In S20, it is determined whether the number of readings is 3 or more. The number of readings is the number of times included in the time series data. If judgment of S20 is NO, the process shown in FIG. 7 will be complete | finished. If judgment of S20 is YES, it will progress to S30.

In S30, a phase difference Δφ _n is calculated. This S30 corresponds to a phase difference calculation unit in the claims. As shown in Equation 9, the phase phi _r of the received wave from being represented by tan, phase phi _r of the received wave has a periodicity of 180 °. Therefore, when simply pulling the phase phi _r of the received wave obtained in the previous time from the phase phi _r of the received wave obtained by the time after, it can not be calculated proper phase difference [Delta] [phi _n. Therefore, the phase difference Δφ _n is calculated by performing the processing shown in FIG. 8 including the phase difference period correction processing.

In FIG. 8, in S31, the number of readings is stored and n is initialized. In subsequent S32, it is determined whether or not | φ _tn −φ _tn−1 | <| π + φ _tn −φ _tn−1 | This determination is to determine whether the phase phi has had time to be π until the phase phi _tn at time tn after the phase phi _tn-1 at the previous reading time tn-1.

If judgment of S32 is YES, it will progress to S33. In S33, [phi] _{tn- [} phi] _tn-1 is calculated as a phase difference [Delta] [phi] _n . On the other hand, if judgment of S32 is NO, it will progress to S34. In S34, the value obtained by adding π to the phase phi _tn time tn after, the phase difference [Delta] [phi _n minus the phase phi _tn-1 at the previous time tn-1. The process of S32-S34 is a phase period correction process.

After executing S33 or S34, the process proceeds to S35. In S35, it is determined whether n is the number of readings. If this judgment is NO, it will progress to S36. In S36, 1 is added to n. Thereafter, the process returns to S32. On the other hand, if the determination in S35 is YES, the phase difference calculation process shown in FIG. 8 is terminated and the process returns to FIG. If the number of readings is 3 or more based on the determination in S20, S30 is executed. Therefore, the phase difference [Delta] [phi _n may be calculated at least two. In the case where the processing shown in FIG. 8 is repeatedly executed, for already Reads already determined the phase difference [Delta] [phi _n, it may be omitted to calculate the phase difference [Delta] [phi _n.

Returning to FIG. In S40, the tag angle θ is calculated. This S40 corresponds to a tag angle calculation unit in the claims. The tag angle θ is calculated from the tag angle calculation formula shown in Formula 11. Expression 11 is an expression in which the numerator of Expression 6 is replaced with Δφ and the denominator is replaced with Expression 7. Δφ in Equation 11 is the phase difference Δφ calculated in S30, and the time difference Δt corresponding to the phase difference Δφ is substituted into Δt in Equation 11. The moving speed V _tag of the wireless tag 20 is stored in the nonvolatile memory 19. Since S40 is executed when S20 becomes YES, two or more tag angles θ can be calculated.

In the subsequent S50, the antenna-tag minimum distance Lmin is calculated from Equation 8 using a combination of two tag angles θ at which measurement time points are continuous from the two or more tag angles θ calculated in S40. The tag moving distance Δd to be substituted into Expression 8 is calculated from the moving speed V _tag of the wireless tag 20 stored in the nonvolatile memory 19 and the time difference Δt between the two time points. This S50 corresponds to a tag distance calculation unit in the claims. Of the tag angles θ calculated in S40, the tag angle θ that is substituted into θ1 of Equation 8 is the first tag angle θ1, and the tag angle θ that is substituted into θ2 of Equation 8 is the second tag angle θ2.

  When there are a plurality of combinations of two tag angles θ at which the measurement time points are continuous, the antenna-tag minimum distance Lmin is calculated for each combination, and the average value is set as the final antenna-tag minimum distance Lmin.

In S60, it is determined whether the antenna-tag minimum distance Lmin calculated in S50 is substantially equal to the antenna-line distance Lset. This determination is to determine whether or not an error, which is a difference between the antenna-line distance Lset and the antenna-tag minimum distance Lmin, is equal to or smaller than an allowable error. The allowable error can be set as appropriate. For example, the allowable error is a length obtained by adding a half wavelength to the width of the line 2. Alternatively, it may be a length obtained by adding λ / 4 to the width of the line 2. The reason why the length based on the wavelength λ is added to the width of the line 2 is that when the length is calculated from the phase, it cannot be distinguished from a distance having a different integral multiple of the wavelength λ. The reason why the wavelength is not half the wavelength λ but ½ of the wavelength is that the reception wave is a wave generated based on the transmission wave, and thus an error occurs in both the forward path and the return path. Furthermore, in the case of ¼ of the half, the phase φ _{r of the} received wave is indicated by a tangent, that is, not a λ period corresponding to one wavelength but a λ / 2 period corresponding to a half wavelength. it can.

  If the determination in S60 is YES, the process proceeds to S70, and it is assumed that the wireless tag 20 that has received the received wave is the wireless tag 20 that is moving on the set line 2. On the other hand, if the determination in S60 is NO, the process proceeds to S80, and it is assumed that the wireless tag 20 moves outside the set line 2. S60, S70, and S80 correspond to the line determination unit in the claims.

[Summary of First Embodiment]
As described above, in the first embodiment described above, as described with reference to Equation 3, the phase phi _r of the received wave antenna - determined by the inter-tag distance L, and does not depend on the time t, and the wireless tag 20 Use moving on line 2.

  When the wireless tag 20 moves on the line 2, if it is between two short time points t1 and t2 in which the direction from the wireless tag 20 to the tag reader 10 can be regarded as the same, from the geometrical relationship shown in FIG. The tag angle calculation formula shown is obtained.

  The tag angle calculation formula means that if one phase difference Δφ is obtained, one tag angle θ is obtained. If two tag angles θ are obtained, the antenna-tag minimum distance Lmin can be calculated as shown in FIG.

In order to obtain two tag angles θ, two phase differences Δφ are required. Therefore, in order to obtain a two phase difference [Delta] [phi, in the present embodiment, three or more times, to calculate the phase phi _r of received waves (S10, S20). When two or more tag angles θ are obtained, the antenna-tag minimum distance Lmin can be calculated from Equation 8 (S50).

  Whether or not the wireless tag 20 is moving on the set line 2 is determined by determining whether or not the antenna-tag minimum distance Lmin and the previously stored antenna-line distance Lset are substantially equal. Determine whether.

  In this way, since it is determined whether or not the wireless tag 20 and the package to which the wireless tag 20 is attached are moving on the line 2, no fixed tag is required.

  Moreover, by sequentially calculating the antenna-tag minimum distance Lmin for the same wireless tag 20, it can be seen whether each wireless tag 20 is moving on the same line 2 or a different line 2. That is, it is possible to read a plurality of lines 2 while eliminating the need for a fixed tag.

  In the above-described embodiment, it is determined whether the wireless tag 20 is moving on the predetermined line 2 by comparing the antenna-tag minimum distance Lmin with the antenna-line distance Lset. However, if it is determined whether the wireless tag 20 is moving on the same line 2 as other wireless tags 20 or not moving the line 2, the antenna-line distance Lset is stored. There is no need to keep it.

Second Embodiment
Next, a second embodiment will be described. In the following description of the second embodiment, elements having the same reference numerals as those used so far are the same as elements having the same reference numerals in the previous embodiments unless otherwise specified. Further, when only a part of the configuration is described, the above-described embodiment can be applied to the other parts of the configuration.

  In the second embodiment, the calculation unit 18 executes the process shown in FIG. 9 instead of FIG. In the process shown in FIG. 9, S38 and S39 are added to the process shown in FIG. S38 and S39 correspond to a stop determination unit in the claims.

  In the process shown in FIG. 9, after calculating the phase difference Δφ in S30, S38 is executed. In S38, it is determined whether or not there is a phase change. If the phase difference Δφ calculated in S30 is substantially zero, it is determined that there is no phase change. If there is no phase change, the determination in S38 is NO and the process proceeds to S39.

  When there is no phase change, it can be said that the wireless tag 20 has not moved. Therefore, in S39, the wireless tag 20 is processed as a stop tag. When S39 is executed, the process of FIG. 9 is terminated.

  In the second embodiment, in addition to determining whether or not the wireless tag 20 is moving on the set line 2, it is also possible to determine whether or not the wireless tag 20 is stopped.

<Third Embodiment>
Next, a third embodiment will be described. In the first and second embodiments, the antenna-line distance Lset and the moving speed V _tag of the wireless tag 20 are known. On the other hand, in the third embodiment, the antenna-line distance Lset is known, but the moving speed V _tag of the wireless tag 20 is unknown. In the third embodiment, the moving speed V _tag of the wireless tag 20 is also calculated.

In 3rd Embodiment, the calculating part 18 performs the process shown in FIG. 10 in the state where the moving speed _Vtag of the wireless tag 20 is unknown.

The process shown in FIG. 10 is executed under the same conditions as in FIG. 10, S110 is the same as S10 in FIG. 7, and creates time-series data of the phase φ _r of the received wave. This S110 is also processing as a phase calculation unit.

  Subsequent S120 is the same as S20 in FIG. 7, and it is determined whether the number of readings is three or more. If judgment of S20 is NO, it will return to S10, and if it is YES, it will progress to S130.

In S130, it is determined whether or not a phase gradient code switching point has occurred. The phase gradient code means a sign of a value obtained by subtracting the phase φ _tn−1 one point before from the latest phase φ _tn sequentially calculated in S110.

As already described, the phase φ _{r of the} received wave is determined by the antenna-tag distance L. Therefore, the switching point of the phase gradient code means a time point at which the magnitude relationship between the antenna-tag distances L at the two time points is reversed. The position where the magnitude relationship of the antenna-tag distance L that fluctuates in time is reversed is when the wireless tag 20 is located in front of the antenna 11. That is, the phase gradient code switching point indicates a position where the tag angle θ is 90 degrees.

  If the determination in S130 is YES, that is, if it is determined that there is a phase gradient code switching point, the process proceeds to S140, and if the determination in S130 is NO, the process returns to S110.

In S140 corresponding to the second phase difference calculation unit of the claims, the phase immediately before it is determined that the phase gradient code switching point has occurred is defined as φ _t2 , the phase φ _t1 calculated immediately before is determined, and the phase difference (φ _t2 −φ _t1 ) is calculated. In this case, t1 is a sign switching adjacent time point in the claims.

  Instead of these two time points, the phase φ calculated immediately after determining that the phase gradient code switching point has occurred and the phase φ calculated next may be used. In this case, the later time point is the time point adjacent to the code change in the claims. The tag angle can be regarded as 90 degrees immediately before or immediately after determining that the phase gradient code switching point has occurred.

After executing S140, the process proceeds to S150. In S150, the antenna-tag distance L1 at time t1 is calculated from Equation 12. S150 corresponds to a second tag distance calculation unit in the claims. In Equation 12, L2 is an antenna-line distance. It is assumed that the phase constant β is set in advance. FIG. 2 shows the tag angles θ1 and θ2 and the antenna-tag distances L1 and L2 here.

  Formula 12 is obtained by formulating Formula 3 at two points in time t1 and t2, subtracting the left side and the right side of the two formulas, and then modifying the formula.

In S160 corresponding to the second tag angle calculation unit, the tag angle θ1 is calculated by substituting the distance L2 between the antenna lines and the antenna-tag distance L1 calculated in S150 into Expression 13. Note that Expression 13 is an expression obtained by modifying the expression obtained by applying the sine theorem in the right triangle shown in FIG.

In S170 corresponding to the movement distance calculation unit of the claims, the tag angle θ1 calculated in S160, the antenna-tag distance L1 calculated in S150, and the antenna line distance L2 are substituted into Equation 14, The tag moving distance Δd is calculated.

In S180 corresponding to the speed calculation unit in the claims, the moving speed V _tag of the wireless tag 20 is calculated by substituting the tag moving distance Δd calculated in S170 and the time difference between the time point t1 and the time point t2 into Expression 15.

After calculating the moving speed V _tag of the wireless tag 20 in this way, the process proceeds to S30 in FIG. 7 or FIG. At this time, in addition to being able to calculate the moving speed V _tag of the wireless tag 20, it is also determined that the number of readings is 3 or more, so S10 and S20 are omitted and the process proceeds to S30. .

In S40 executed in the second embodiment, the tag moving distance Δd in which the wireless tag 20 has moved is calculated by multiplying the denominator of Equation 11 by the time difference Δt between two time points and the moving speed V _tag calculated in S180. Also in S50, similarly to S40, the tag moving distance Δd is calculated by multiplying the moving speed V _tag calculated in S180 by the time difference Δt between two time points.

[Summary of Third Embodiment]
The position of the wireless tag 20 where the phase gradient code inversion occurs is the position where the antenna-tag distance L becomes the minimum, that is, when the antenna-tag distance L becomes the antenna-line distance Lset. Since the antenna-line distance Lset is stored in the nonvolatile memory 19, it can be determined that the antenna-tag distance L is the antenna-line distance Lset at the time of phase switching.

Further, before and after the phase gradient code switching point, the antenna-tag distance L1 can be calculated from the antenna-tag distance L2 and the phase difference (φ _t1 -φ _t2 ) as shown in Equation 12, so in S150 The antenna-tag distance L1 is calculated.

  When the antenna-tag distance L1 at the time point t1 is known and the antenna-tag distance L2 at the phase gradient code switching point is found to be the antenna-line distance Lset, the equations 13 and 14 are used. The tag moving distance Δd from the position of the wireless tag 20 at the time point t1 to the position of the wireless tag 20 at the switching point of the phase gradient code can be calculated (S160, S170).

Then, by knowing the tag moving distance Δd between the position of the wireless tag 20 at the time point t1 and the switching point of the phase gradient code and the time difference (t2−t1), in S180, the movement of the wireless tag 20 is calculated from Expression 15. The speed V _tag can be calculated.

Since the moving speed V _tag of the wireless tag 20 can be calculated in this way, even if the moving speed V _tag of the wireless _tag is unknown, whether or not the wireless tag 20 is moving on the defined line 2 as in the first embodiment. Can be determined.

  As mentioned above, although embodiment of this invention was described, this invention is not limited to the above-mentioned embodiment, The following modification is also contained in the technical scope of this invention, Furthermore, the summary other than the following is also included. Various modifications can be made without departing from the scope.

<Modification 1>
In any of the embodiments described above, the tag angle θ can be calculated sequentially. When the tag angle is 90 degrees, it can be determined that the wireless tag 20 has passed the front of the tag reader 10. Therefore, the passage determination may be performed based on the tag angle θ.

  Further, when the wireless tag 20 passes through the front of the tag reader 10, the antenna-tag distance L is minimized. Therefore, the passage determination may be performed by determining whether or not the antenna-tag distance is minimized.

1: Radio tag system 2: Line 3: Baggage 10: Tag reader 11: Antenna 12: Transmitter 15: Quadrature demodulator 18: Arithmetic unit 19: Non-volatile memory 20: Radio tag 151: Phase shifter 152i: Mixer 152q: Mixer S10, S110 phase calculation unit, S140 second phase difference calculation unit, S150 second tag distance calculation unit, S160 second tag angle calculation unit, S170 travel distance calculation unit, S180 speed calculation unit, S30 phase difference calculation unit, S38, S39 Stop determination unit, S40 Tag angle calculation unit, S50 Tag distance calculation unit CP1: Communication path CP2: Communication path L: Distance between tags Lmin: Minimum distance between antenna and tag Lset: Distance between lines Vtag: Movement speed Δd: Tag movement Distance Δt: Time difference Δφ: Retardation beta: phase constant .beta.L: spatial phase theta: Tags angle phi: Phase .omega.t: Time Phase

Claims (5)

A tag reader (10) communicating with a wireless tag (20),
Wherein wirelessly transmitting the electric wave to the tag, the phase calculation unit for sequentially calculating the phase (phi _r) of the received wave is being transmitted radio wave received by the tag reader from said RFID tag as a response (S10, S110) When,
A phase difference calculation unit (S30) that calculates a phase difference (Δφ) that is a phase difference calculated by the phase calculation unit at two time points;
Based on the phase difference and a tag moving distance that is a distance that the wireless tag moves between the two time points, a straight line connecting the antenna (11) included in the tag reader and the wireless tag, and the wireless tag A tag angle calculation unit (S40) that calculates a tag angle (θ) that is an angle between the line (2) and
The phase difference calculation unit calculates two phase differences as at least one of the two time points for calculating the phase difference as different time points,
The tag angle calculation unit calculates a first tag angle and a second tag angle as the tag angle using each of the two phase differences,
Based on the distance between the position at which the tag angle is the first tag angle and the position at which the tag angle is the second tag angle, the first tag angle, and the second tag angle, A tag reader, further comprising a tag distance calculation unit (S50) that calculates an antenna-tag minimum distance (Lmin) that is a minimum distance from the moving line to the antenna. In claim 1,
A storage unit (19) for storing the moving speed of the line in advance;
The tag angle calculation unit calculates the tag moving distance from a time difference between the two time points and a moving speed of the line stored in the storage unit,
The tag distance calculation unit calculates a distance between a position where the tag angle is the first tag angle and a position where the tag angle is the second tag angle, and the tag angle is the first tag angle. A tag reader that calculates from a time difference between the time when the tag angle is the second tag angle and a moving speed of the line stored in the storage unit. In claim 1,
A storage unit (19) storing an antenna-line distance (Lset) which is a minimum distance from the antenna to the line;
A second phase difference calculation unit (S140) that calculates the phase difference calculated by using the phase gradient code switching point as one time point based on the phase that is sequentially calculated by the phase calculation unit;
Based on the antenna-line distance stored in the storage unit and the phase difference calculated by the second phase difference calculation unit, the other phase difference is calculated together with the phase gradient code switching point. A second tag distance calculation unit (S150) that calculates an antenna-tag distance, which is a distance from the antenna to the wireless tag, at a code switching adjacent time point that is a time point;
Based on the antenna-tag distance calculated by the second tag distance calculation unit and the antenna-line distance stored in the storage unit, the tag angle at the time point adjacent to the code change is calculated. A two-tag angle calculation unit (S160);
Based on the tag angle calculated by the second tag angle calculation unit, the antenna-tag distance calculated by the second tag distance calculation unit, and the antenna-line distance stored in the storage unit. A moving distance calculation unit (S170) for calculating a moving distance from the position of the wireless tag at the time point adjacent to the code switching to the position of the wireless tag at the switching point of the phase gradient code;
A speed calculating unit that calculates a moving speed (V _tag ) of the wireless tag based on the moving distance calculated by the moving distance calculating unit and a time difference between the code switching adjacent time point and the phase gradient code switching point. (S180)
The tag angle calculation unit calculates a moving distance that the wireless tag moves between the two time points from a time difference between the two time points and a moving speed of the wireless tag calculated by the speed calculation unit,
The tag distance calculation unit calculates a distance between a position where the tag angle is the first tag angle and a position where the tag angle is the second tag angle, and the tag angle is the first tag angle. And the time difference between the time point when the tag angle is the second tag angle and the moving speed of the wireless tag calculated by the speed calculation unit,
The tag reader further includes
The wireless tag moves on a predetermined line based on a comparison between the antenna-tag minimum distance calculated by the tag distance calculation unit and the antenna-line distance stored in the storage unit. A tag reader provided with a line determination unit (S60-S80) for determining whether or not. In claim 1 or 2,
A storage unit (19) storing an antenna-line distance (Lset) which is a minimum distance from the antenna to the line;
The wireless tag moves on a predetermined line based on a comparison between the antenna-tag minimum distance calculated by the tag distance calculation unit and the antenna-line distance stored in the storage unit. A tag reader provided with a line determination unit (S60-S80) for determining whether or not. In any one of Claims 1-4,
A tag reader including a stop determination unit (S38, S39) that determines that the wireless tag is stopped when there is no change in the phase that is sequentially calculated by the phase calculation unit.

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