JP6825427B2 - Tag reader - Google Patents

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 through a conveyor or a vicinity of a conveyor. In the technique disclosed in Patent Document 1, in addition to installing a reader / writer near 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 that moves on a 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 located at opposite positions 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 located closer to the reader / writer than the fixed tag, good communication with the reader / writer is possible.

After that, when the pallet moves on the conveyor and the moving tag attached to the pallet disappears between the fixed tag and the reader / writer, the fixed tag and the reader / writer can communicate well. On the other hand, communication between the mobile tag and the reader / writer becomes impossible.

When 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 an 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 obstructed. Therefore, it is possible to distinguish whether the pallet to which the movement tag is attached has passed the conveyor or the vicinity of the conveyor.

Japanese Unexamined Patent Publication No. 2012-98863

The technique disclosed in Patent Document 1 requires a fixed tag. Therefore, there is a problem that a space for installing a fixed tag is required. For this reason, a technique capable of identifying an object moving on a predetermined line such as a conveyor without a fixed tag has been desired.

The present invention has been made based on this circumstance, and an object of the present invention is to provide a tag reader capable of identifying 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 sub-claims define further advantageous specific examples of the invention. The reference numerals in parentheses described in the claims indicate, as one embodiment, the correspondence with the specific means described in the embodiments described later, and do not limit the technical scope of the present invention. ..

The present invention for achieving the above object
Sends a radio wave to the radio tag, the phase calculation section which sequentially calculates the phase (phi _r) of the received wave is a radio wave sent tag reader receives from the wireless tag (S10, S110) as a response,
A phase difference calculation unit (S30) that calculates a phase difference (Δφ), which is a phase difference calculated by the phase calculation unit at two time points, and
Based on the phase difference and the tag movement distance, which is the distance that the wireless tag moves between the two time points, a straight line connecting the antenna (11) provided in the tag reader and the wireless tag and a line (2) in which the wireless tag moves. ) Is provided with a tag angle calculation unit (S40) for calculating the tag angle (θ).
The phase difference calculation unit calculates the two phase differences by setting at least one of the two time points for calculating the phase difference as a different time point.
The tag angle calculation unit calculates the first tag angle and the second tag angle as tag angles by using the two phase differences, respectively.
From the line where the wireless tag moves to the antenna based on 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, the first tag angle, and the second tag angle. A tag distance calculation unit (S50) for calculating 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 and does not depend on time, and that the radio 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 the wireless tag moves on the line, if the direction from the wireless tag to the tag reader is short between two time points, the trajectory of the wireless tag moving between the two time points is the hypotenuse, and the tag angle is one internal angle. You can create a right triangle. The tag angle is an angle between a straight line connecting the antenna of the tag reader and the wireless tag and a line on which the wireless tag moves.

In the above right triangle, the length of the adjacent side with respect to the tag angle is half 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. Then, the tag angle can be calculated from the length of the hypotenuse and the length of the adjacent side.

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

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

A radio tag that travels on a defined line should have a minimum antenna-tag distance that is determined based on the line that travels. Therefore, based on the minimum distance between the antenna and the tag, it is possible to identify the radio tag that moves on a predetermined line and the object to which the radio tag is attached. The fixed tag was not used to calculate the minimum distance between the antenna and the tag. Therefore, it is possible to identify an object moving on a predetermined line without the need for a fixed tag.

The invention according to claim 2 is
A storage unit (19) that stores the moving speed of the line in advance is provided.
The tag angle calculation unit calculates the tag movement distance from the time difference between the two time points and the movement speed of the line stored in the storage unit.
The tag distance calculation unit determines 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, and the time when the tag angle is the first tag angle and the tag angle are the second. It is calculated from the time difference from the time when the two-tag angle was set 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, the distance that the wireless tag moves between the two time points is required. Further, when calculating the minimum distance between the antenna and the tag, 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 required. In the invention according to claim 2, when calculating these distances, the moving speed of the line stored in the storage unit is used.

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

The invention according to claim 3 is
A storage unit (19) that stores the antenna-line distance (Lset), which is the minimum distance from the antenna to the line, and
A second phase difference calculation unit (S140) that calculates a phase difference calculated with the switching point of the phase gradient code as one time point based on the phase 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 phase difference is calculated together with the switching point of the phase gradient code. The second tag distance calculation unit (S150) that calculates the distance between the antenna and the tag, which is the distance from the antenna to the wireless tag at the time point, and
The second tag angle calculation unit (2) that calculates the tag angle at the time when the code is switched adjacent to each other based on the antenna-tag distance calculated by the second tag distance calculation unit and the antenna-line distance stored in the storage unit. S160) and
Sign switching adjacent time points 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 moving distance calculation unit (S170) that calculates the 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 in
A speed calculation unit (S180) that calculates the 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 time point adjacent to the code switching and the switching point of the phase gradient code. Prepare,
The tag angle calculation unit calculates the moving distance of the wireless tag between the 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 determines 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, when the tag angle is the first tag angle and when 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 calculation unit.
The tag reader is also
Whether or not the wireless tag is moving on a predetermined line based on the comparison between the minimum antenna-tag distance calculated by the tag distance calculation unit and the antenna-line distance stored in the storage unit. A line determination unit (S60-S80) for determining the above is provided.

Since the phase of the received wave is determined by the propagation distance, a phase gradient code indicating an increase or 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 positive and negative are reversed.

The position of the radio tag where the phase gradient code is inverted is the position where the antenna-tag distance is minimized, that is, when the antenna-tag distance is 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 switching point of the phase gradient code, 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 time when the code is switched adjacent from the phase difference calculated at the switching point of the phase gradient code 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 sign is switched is known, and the distance between the antenna and the tag at the switching 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 radio tag at the time when the sign is switched and the position of the radio tag at the switching point of the phase gradient code.

Then, by knowing the distance between the position of the radio tag at the time point adjacent to the code switching and the position of the radio tag at the switching point of the phase gradient code, and the time difference between the time point adjacent to the code switching and the switching point of the phase gradient code, the speed 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 the two time points using the moving speed of the wireless tag calculated by the speed calculating unit. .. In addition, the line distance calculation unit uses the movement 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, in the present invention, whether or not the wireless tag is moving on a predetermined line by utilizing the fact that the minimum distance between the antenna and the tag can be calculated and the distance between the antenna and the line is stored. To judge.

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

In the present invention, the 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 is
The wireless tag is provided with a stop determination unit (S38, S39) for determining that the radio tag is stopped when there is no change in the phase calculated sequentially by the phase calculation unit.

In the present invention, in addition to obtaining the minimum distance between the antenna and the tag, it is also possible to determine 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. It is a block diagram which shows the structure of a tag reader 10. It is a figure which conceptually shows the communication paths CP1 and CP2 at time t1 and t2. It is a figure which shows the geometrical shape which can be approximated when the tag movement distance Δd is short. It is a figure explaining the calculation method of the minimum distance Lmin between an antenna and a tag. It is a flowchart explaining the process which a calculation unit 18 executes. It is a flowchart which shows the detailed processing of S3 of FIG. It is a flowchart which shows the process which the arithmetic unit 18 executes in 2nd Embodiment. It is a flowchart which shows the process which the arithmetic unit 18 executes in 3rd Embodiment.

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

[System configuration]
FIG. 1 is a diagram illustrating a configuration and a usage mode of a wireless tag system 1 provided with a tag reader 10 according to an embodiment of the present invention. The wireless tag system 1 includes a tag reader 10 installed near a belt conveyor line (hereinafter, simply a line) 2 and a wireless tag 20 attached to a luggage 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 wireless tag, from the antenna 11 toward the line 2. The frequency of the transmitted wave may be any frequency permitted by law. In this embodiment, the UHF band frequency is used.

The wireless tag 20 is a passive tag, operates by electric power generated by receiving the transmitted wave, and transmits a signal in response to the transmitted wave to the tag reader 10 by radio waves. The signal transmitted by the wireless tag 20 includes an ID that identifies the wireless tag 20.

The tag reader 10 receives the radio waves transmitted by 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 carried by other means of transportation such as a forklift may be read around the line 2.

The reading range of the tag reader 10 may be narrowed, but 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 narrowing of the reading range.

FIG. 2 is a top view of FIG. 1. As shown in FIG. 2, the line 2 is a straight line. In addition, 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 baggage 3 is moving to the right side of the figure with the passage of time.

[Structure 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 a calculation unit 18.

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

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

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

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

Calculation unit 18 based on the phase phi _r of the received wave, the radio tag 20 as to move over the line 2, and calculates the distance the distance from the antenna 11 to the wireless tag 20 is minimized. This distance will be hereinafter referred to as the minimum distance Lmin between the antenna and the tag.

The non-volatile memory 19 corresponds to the storage unit of the claim, and the minimum distance between the antenna 11 and the line 2 is stored in advance. The minimum distance between the antenna 11 and the line 2 is hereinafter referred to as the antenna-line distance Lset. The antenna-line distance Lset is the length of the perpendicular line drawn 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.

Further, the moving speed of the line 2 is also stored in the non-volatile memory 19. 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 moving speed V _tag of the wireless tag 20 is stored in the non-volatile memory 19.

[Relationship between the phase phi _r of the received wave propagation distance]
Calculation unit 18, the phase phi _r of the received wave is determined by the propagation distance, utilizing the fact that does not depend on time. Therefore, first, the phase phi _r of the received wave is described that determined by the propagation distance.

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

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

Of the phases represented by Equation 2, ωt is the time phase and βL is the 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 almost equal. In Equation 3, φ _t represents the phase of the transmitted wave, but in other equations 3, φ _t represents the phase φ _r of the received wave at time t.

[Explanation of tag angle calculation formula]
An equation for calculating the tag angle θ can be derived using the equation 3. Next, the derivation of the formula 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 to the right in the figure. The distance between the antenna 11 and the wireless tag 20 is defined as the 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. The antenna-tag distance L can be said to be half (or one-way) of the propagation distance of the received wave.

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

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

Equation 5 is obtained by multiplying both sides of Equation 4 by the phase constant β.

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

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

From 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 movement speed V _tag . That is, one tag angle θ can be calculated by measuring the phase φ at two time points.

[Calculation of the minimum distance Lmin between the antenna and the tag]
Further, since one tag angle θ can be calculated by measuring the phase φ at two time points, two tag angles θ can be obtained by measuring the phase φ at three time points. FIG. 6 is a diagram showing the geometrical relationship between the two tag angles θ1 and θ2 and the minimum distance Lmin between the antenna and the tag.

When the triangulation formula is applied to the two right triangles shown in FIG. 6, the formula 8 is obtained. Equation 8 shows that the minimum antenna-tag distance Lmin can be calculated from the two tag angles θ1 and θ2 and the tag movement distance Δd.

The tag movement distance Δd can be calculated from the movement speed V _tag of the wireless tag 20 and the time difference Δt at 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, if the tag angles θ1 and θ2 are measured at two time points, the minimum distance Lmin between the antenna and the tag can be obtained. Can be calculated.

[Processing of calculation unit 18]
The calculation unit 18 calculates the minimum distance Lmin between the antenna and the tag to identify whether the wireless tag 20 is moving on a predetermined line 2. Next, the process executed by the calculation unit 18 for identifying whether the wireless tag 20 is moving on the predetermined line 2 will be described with reference to the flowchart shown in FIG. 7.

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

Step (hereinafter, abbreviated step) In S10, to create a time series data of the phase phi _r of the received wave. The time-series data, the phase phi _r of the received wave is data associated with the time of receiving a reception wave. Already, in the case where time-series data of the phase phi _r of the received wave has been created, in S10, it updates the time-series data already created.

Phase phi _r of the received wave is calculated from Equation 9. This S10 corresponds to the phase calculation unit of the claim.

The derivation of Equation 9 will be described by 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. The product of the complex conjugates of Equations 10-1 and 10-2 gives Equation 10-3. The I signal component and Q signal component of the formula 10-3 are represented by the formulas 10-4 and 10-5, respectively. Dividing Equation 10-5 by Equation 10-4 gives Equation 10-6. Multiplying both sides of equation 10-6 by tan ^-1 gives equation 10-7. Further, in the tag reader 10, since the transmitted wave and the received wave are mixed by the mixers 152i and 152q to obtain the I signal and the Q signal, the equations 10-8 and 10-9 hold. Substituting Equations 10-8 and 10-9 into Equation 10-7 gives Equation 10-10, ie Equation 9.

The time series data of the phase φ _r of the received wave is created or updated by associating the phase φ _r of the received wave obtained by the calculation of Equation 9 with the time when the received wave is received. Then, the time-series data is stored in a RAM or the like included in the calculation unit 18.

In S20, it is determined whether or not the number of readings is 3 or more. The number of readings is the number of times included in the time series data. If the determination in S20 is NO, the process shown in FIG. 7 ends. If the determination in S20 is YES, the process proceeds to S30.

In S30, the phase difference Δφ _n is calculated. This S30 corresponds to the phase difference calculation unit of the claim. 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, the correct phase difference Δφ _n cannot be calculated by simply subtracting the phase φ _r of the received wave obtained at the previous time from the phase φ _{r of the} received wave obtained at the later time. Therefore, the process shown in FIG. 8 including the phase difference period correction process is performed to calculate the phase difference Δφ _n .

In FIG. 8, in S31, the number of readings is saved and n is initialized. In the following S32, it is determined whether or not | φ _{tn −} φ _tun-1 | << | π + φ _tun −φ _tun-1 | holds. 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 the determination in S32 is YES, the process proceeds to S33. In S33, φ _{nt −} φ _tun-1 is calculated as the phase difference Δφ _n . On the other hand, if the determination in S32 is NO, the process proceeds to S34. In S34, the phase difference Δφ _n is obtained by subtracting the phase φ _nt-1 at the previous time point nt-1 from the value obtained by adding π to the phase φ _tun at the later time point tun. The process of S32-S34 is the phase period correction process.

After executing S33 or S34, the process proceeds to S35. In S35, it is determined whether or not n is the number of readings. If this determination is NO, the process proceeds to S36. In S36, 1 is added to n. After that, it returns to S32. On the other hand, when the determination in S35 is YES, the phase difference calculation process shown in FIG. 8 is terminated, and the process returns to FIG. According to the judgment of S20, S30 is executed when the number of readings is 3 or more. Therefore, at least two phase differences Δφ _n can be calculated. When the process shown in FIG. 8 is repeatedly executed, the calculation of the phase difference Δφ _n may be omitted for the number of readings for which the phase difference Δφ _n has already been calculated.

The explanation is returned to FIG. In S40, the tag angle θ is calculated. This S40 corresponds to the tag angle calculation unit of the claim. The tag angle θ is calculated from the tag angle calculation formula shown in Equation 11. Equation 11 is an equation in which the numerator of Equation 6 is replaced with Δφ and the denominator is replaced with Equation 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. Further, the moving speed V _tag of the wireless tag 20 is stored in the non-volatile memory 19. Since S40 is executed when S20 becomes YES, two or more tag angles θ can be calculated.

In the following S50, the minimum antenna-tag distance Lmin is calculated from Equation 8 using a combination of two tag angles θ whose measurement time points are continuous from the two or more tag angles θ calculated in S40. The tag moving distance Δd assigned to the equation 8 is calculated from the moving speed V _tag of the wireless tag 20 stored in the non-volatile memory 19 and the time difference Δt at two time points. This S50 corresponds to the tag distance calculation unit of the claim. Of the tag angles θ calculated in S40, the tag angle θ assigned to θ1 in Equation 8 is the first tag angle θ1, and the tag angle θ assigned to θ2 in Equation 8 is the second tag angle θ2.

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

In S60, it is determined whether the minimum antenna-tag distance Lmin calculated in S50 is substantially equal to the antenna-line distance Lset. This determination determines whether or not the error, which is the difference between the antenna-line distance Lset and the antenna-tag minimum distance Lmin, is equal to or less than the margin of error. The margin of error can be set as appropriate. For example, the margin of error is the width of line 2 plus half a wavelength. Alternatively, the length may be the width of the line 2 plus λ / 4. 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 the distances in which the integral multiple lengths of the wavelength λ are different. The reason why the wavelength is set to 1/2 of the wavelength instead of 1 times the wavelength λ is that since the received wave is a wave generated based on the transmitted wave, an error occurs in both the outward path and the return path. Furthermore, when 1/4 of the half, the phase phi _r of the received wave is shown by the tangent, that is, not the lambda period is one wavelength, also consider a lambda / 2 period is a half wavelength it can.

If the determination in S60 is YES, the process proceeds to S70, and the wireless tag 20 that has received the received wave is assumed to be the wireless tag 20 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 of the claim.

[Summary of the 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 to move on line 2.

When the wireless tag 20 moves on the line 2, if the direction from the wireless tag 20 to the tag reader 10 is between two short time points t1 and t2 that can be regarded as the same, the equation 11 is obtained from the geometric 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 can be obtained. If the two tag angles θ are obtained, the minimum antenna-tag distance Lmin can be calculated as shown in FIG.

In order to obtain the 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 minimum antenna-tag distance Lmin can be calculated from Equation 8 (S50).

Then, by determining whether or not the minimum antenna-tag distance Lmin and the antenna-line distance Lset stored in advance are substantially equal, whether or not the wireless tag 20 is moving on the set line 2. To judge.

In this way, since it is determined whether or not the wireless tag 20 and the luggage to which the wireless tag 20 is attached are moving on the line 2, a fixed tag is not required.

Moreover, by sequentially calculating the minimum distance Lmin between the antennas and the tags for the same wireless tag 20, it can be determined whether each wireless tag 20 is moving on the same line 2 or on a different line 2. That is, it is possible to distinguish between a plurality of lines 2 while eliminating the need for a fixed tag.

In the above-described embodiment, it is determined whether or not the wireless tag 20 is moving on the defined line 2 by comparing the minimum antenna-tag 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 the other plurality of wireless tags 20 or not moving on the line 2, the antenna-line distance Lset is stored. You don't have to keep it.

<Second Embodiment>
Next, the second embodiment will be described. In the following description of the second embodiment, the elements having the same number as the codes used so far are the same as the elements having the same code in the previous embodiments, unless otherwise specified. Further, when only a part of the configuration is described, the embodiment described above 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. 7. In the process shown in FIG. 9, S38 and S39 are added to the process shown in FIG. 7. S38 and S39 correspond to the suspension determination unit of the claim.

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 almost zero, it is determined that there is no phase change. If there is no phase change, the determination in S38 becomes NO and the process proceeds to S39.

If 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 ends.

In this second embodiment, in addition to being able to determine 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, the third embodiment will be described. In the first and second embodiments, the antenna-line distance Lset and the moving speed V _tag of the radio tag 20 were known. On the other hand, in the third embodiment, the antenna-line distance Lset is known, but the moving speed V _tag of the radio tag 20 is unknown. In the third embodiment, the moving speed V _tag of the wireless tag 20 is also calculated.

In the third embodiment, the calculation unit 18 executes the process shown in FIG. 10 in a state where the moving speed V _tag of the wireless tag 20 is unknown.

The process shown in FIG. 10 is executed under the same conditions as in FIG. In FIG. 10 S110 are the same as S10 in FIG. 7, to create a time series data of the phase phi _r of the received wave. This S110 is also a process as a phase calculation unit.

Subsequent S120 is the same as S20 in FIG. 7, and determines whether or not the number of readings is 3 or more. If the judgment of S20 is NO, the process returns to S10, and if YES, the process proceeds to S130.

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

As already explained, the phase phi _r of the received wave antenna - determined by the inter-tag distance L. Therefore, the switching point of the phase gradient code means the time when the magnitude relationship of the antenna-tag distance L at two time points is reversed. The position where the magnitude relationship of the antenna-tag distance L, which moves back and forth in time, is reversed is when the wireless tag 20 is located in front of the antenna 11. That is, the switching point of the phase gradient code 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 switching point of the phase gradient code, 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 claim, the phase immediately before the determination that the switching point of the phase gradient code has occurred is set to φ _t2 , the phase calculated immediately before that is set to φ _t1 , and the phase difference (φ) is set. Calculate _t2- φ _t1 ). In this case, t1 is the time point adjacent to the sign switching of the claim.

Instead of these two time points, the phase φ calculated immediately after it is determined 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 sign switching of the claim. Immediately before or immediately after it is determined that the switching point of the phase gradient code has occurred, the tag angle can be regarded as 90 degrees.

After executing S140, the process proceeds to S150. In S150, the antenna-tag distance L1 at the time point t1 is calculated from the equation 12. S150 corresponds to the second tag distance calculation unit of the claim. In Equation 12, L2 is the distance between the antenna and the line. Further, it is assumed that the phase constant β is set in advance. FIG. 2 illustrates the tag angles θ1 and θ2 and the antenna-tag distances L1 and L2.

Equation 12 is obtained by formulating the equation of Equation 3 at two time points, time point t1 and time point t2, subtracting the left side and the right side of the two formulated equations, respectively, and then transforming the equation.

In S160, which corresponds to the second tag angle calculation unit, the tag angle θ1 is calculated by substituting the antenna line distance L2 and the antenna-tag distance L1 calculated in S150 into Equation 13. Equation 13 is a modified equation obtained by applying the law of sines to the right triangle shown in FIG.

In S170, which corresponds to the moving distance calculation unit of the claim, 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 movement distance Δd is calculated.

In S180, which corresponds to the speed calculation unit of the claim, 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 points t1 and the time point t2 into the equation 15.

After calculating the moving speed V _tag of the wireless tag 20 in this way, the process proceeds to S30 of FIG. 7 or FIG. At this point, 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 denominator of the equation 11 is multiplied by the movement speed V _tag calculated in S180 by the time difference Δt at two time points to calculate the tag movement distance Δd in which the wireless tag 20 has moved. Further, also in S50, as in S40, the tag movement distance Δd is calculated by multiplying the movement speed V _tag calculated in S180 by the time difference Δt at two time points.

[Summary of Third Embodiment]
The position of the radio tag 20 where the phase gradient code is inverted is the position where the antenna-tag distance L is minimized, that is, when the antenna-tag distance L becomes the antenna-line distance Lset. Since the antenna-line distance Lset is stored in the non-volatile 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 switching point of the phase gradient code, as shown in Equation 12, the antenna-tag distance L1 can be calculated from the antenna-tag distance L2 and the phase difference (φ _t1- φ _t2 ). , 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 switching point of the phase gradient code is found to be the antenna-line distance Lset, the equations 13 and 14 are used. , The tag movement distance Δd from the position of the radio tag 20 at the time point t1 to the position of the radio tag 20 at the switching point of the phase gradient code can be calculated (S160, S170).

Then, by knowing the tag movement distance Δd between the position of the radio tag 20 and the switching point of the phase gradient code at the time point t1 and the time difference (t2-t1), in S180, the movement of the radio tag 20 is performed from Equation 15. The velocity 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 judged.

Although the embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments, and the following modifications are also included in the technical scope of the present invention. Various changes can be made within the range that does not deviate.

<Modification example 1>
In any of the above-described embodiments, the tag angle θ can be calculated sequentially. When the tag angle reaches 90 degrees, it can be determined that the wireless tag 20 has passed in 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 in front of the tag reader 10, the distance L between the antenna and the tag becomes the minimum. Therefore, the passage may be determined by determining whether or not the distance between the antenna and the tag has been minimized.

1: Wireless tag system 2: Line 3: Luggage 10: Tag reader 11: Antenna 12: Transmitter 15: Orthogonal demodulator 18: Arithmetic unit 19: Non-volatile memory 20: Wireless 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 Movement 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: Phase difference β: Phase constant βL: Spatial phase θ: Tag angle φ: Phase ωt: Time phase

Claims (5)

A tag reader (10) that communicates 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) for calculating a phase difference (Δφ), which is a phase difference calculated by the phase calculation unit at two time points,
Based on the phase difference and the tag movement distance, which is the distance that the radio tag moves between the two time points, a straight line connecting the antenna (11) included in the tag reader and the radio tag, and the radio tag The tag angle calculation unit (S40) for calculating the tag angle (θ), which is the angle between the moving line (2) and the line (2), is provided.
The phase difference calculation unit calculates the two phase differences with at least one of the two time points for calculating the phase difference as a different time point.
The tag angle calculation unit calculates the first tag angle and the second tag angle as the tag angles by using the two phase differences, respectively.
The wireless tag is based on 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, the first tag angle, and the second tag angle. A tag reader further including a tag distance calculation unit (S50) for calculating the minimum distance (Lmin) between an antenna and a tag, which is the minimum distance from the moving line to the antenna. In claim 1,
A storage unit (19) that stores the moving speed of the line in advance is provided.
The tag angle calculation unit calculates the tag movement distance from the time difference between the two time points and the movement speed of the line stored in the storage unit.
The tag distance calculation unit determines 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, and the tag angle is the first tag angle. A tag reader calculated from the time difference between the time point and the time point when the tag angle is the second tag angle and the moving speed of the line stored in the storage unit. In claim 1,
A storage unit (19) that stores the antenna-line distance (Lset), which is the minimum distance from the antenna to the line, and
A second phase difference calculation unit (S140) that calculates the phase difference calculated with the switching point of the phase gradient code as one time point based on the phase sequentially calculated by the phase calculation unit.
The other that calculates the phase difference together with the switching point of the phase gradient code 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. A second tag distance calculation unit (S150) that calculates the distance between the antenna and the tag, which is the distance from the antenna to the wireless tag at the time point adjacent to the code switching.
The tag angle at the time point adjacent to the sign switching is calculated based on the antenna-tag distance calculated by the second tag distance calculation unit and the antenna-line distance stored in the storage unit. 2 tag angle calculation unit (S160) and
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 moving distance calculation unit (S170) for calculating the moving distance from the position of the wireless tag at the time point adjacent to the sign switching to the position of the wireless tag at the switching point of the phase gradient code,
A speed calculation unit that calculates the movement speed (V _tag ) of the radio tag based on the movement distance calculated by the movement distance calculation unit and the time difference between the time point adjacent to the code switching and the switching point of the phase gradient code. With (S180)
The tag angle calculation unit calculates the moving distance of the wireless tag between the 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 determines 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, and the tag angle is the first tag angle. Calculated from the time difference between the time point and the time point when the tag angle was the second tag angle, and the moving speed of the wireless tag calculated by the speed calculation unit.
The tag reader further
The wireless tag moves a predetermined line based on a comparison between the minimum antenna-tag 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 the antenna is used. In claim 1 or 2,
A storage unit (19) that stores the antenna-line distance (Lset), which is the minimum distance from the antenna to the line, and
The wireless tag moves a predetermined line based on a comparison between the minimum antenna-tag 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 the antenna is used. In any one of claims 1 to 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 calculated sequentially by the phase calculation unit.

Images