JP5541207B2 - Wireless tag reader, monitoring system - Google Patents

Description

  The present invention relates to a wireless tag reader capable of estimating the direction (arrival azimuth) of a wireless tag and a monitoring system using the wireless tag reader.

  A wireless tag system that reads a wireless tag using radio waves is being used for various purposes, and a wireless tag reader that is a main element of this system is required to have high functionality so that it can be applied to a wide range of uses. As an example of high functionality, for example, it is possible not only to simply read a wireless tag, but also to specify in which direction the wireless tag can exist, and to use it for searching for a wireless tag holder, It is being considered to use it to determine whether a person is present in an appropriate direction.

  As a technique related to specifying the direction of the wireless tag, for example, a technique as disclosed in Patent Document 1 has been proposed. This Patent Document 1 discloses a radio wave arrival direction detection method using an array antenna that includes a plurality of antenna elements and can change directivity characteristics. In this radio wave arrival direction detection method, an omnidirectional angle of 360 degrees is disclosed. Is used to estimate the direction of arrival of radio waves by switching the beam into 12 parts. Specifically, a plurality of received power patterns obtained by beam switching are correlated with a signal power pattern for each direction prepared in advance, and the angle at which the correlation is maximum is estimated as the arrival direction.

JP 2004-257820 A

  By the way, as a configuration that further develops the RFID tag system that can estimate the direction of the RFID tag, the RFID tag reader is used in combination with a laser sensor that can measure the distance and direction of an object in the surveillance region. A monitoring system that determines whether or not a person who has entered carries a wireless tag and issues a warning when the person does not carry the wireless tag can be considered. When the intruder is monitored by the monitoring system, for example, the distance and direction of a person who has entered the monitoring area are detected by a laser sensor, the direction of the wireless tag is estimated by a wireless tag reader capable of estimating the direction, and the laser sensor When the direction of the intruder detected by the radio tag reader matches the direction of the wireless tag estimated by the wireless tag reader, it is determined that the intruder is carrying the wireless tag. On the other hand, if there is no response from the wireless tag, or if the response from the wireless tag does not match the direction detected by the laser sensor, it is determined that the intruder is not carrying the wireless tag and a warning is issued. This can be notified to the outside by issuing.

  When constructing such a monitoring system, the laser sensor can accurately measure the distance and direction of the intruder in the monitoring area, so the reliability of determining whether the intruder is carrying a wireless tag is: It depends on whether or not the wireless tag reader can accurately estimate the direction of the wireless tag. However, the conventional RFID tag reader capable of estimating the direction may not be able to estimate the RFID tag direction so accurately depending on the environment, and is difficult to apply to the monitoring system as described above or a system that similarly requires reliability. There was a case.

  For example, in the radio wave arrival direction detection method of Patent Document 1, a certain degree of accuracy can be obtained in an environment where there is no radio wave reflector or radio wave interferer (for example, a dark room experiment). However, when such a method is applied to an actual monitoring system where radio wave reflectors and radio wave interferers exist, elements other than the radio wave direction from the radio tag (radio wave interference from radio wave reflectors ) Will affect the measurement pattern (received power pattern), so the obtained measurement pattern (received power pattern) may not be a waveform that strongly reflects only the radio waves from the wireless tag, and there is a wireless tag. In some cases, the correlation with the reference power pattern (signal power pattern) in the direction in which the signal is generated becomes low. When such a phenomenon occurs, it becomes difficult to estimate the direction of the wireless tag with high accuracy. Therefore, improvement is particularly required in a system that requires reliability as described above.

  The present invention has been made to solve the above-described problems, and an object of the present invention is to provide a communication area where an object that affects reflection, interference, or the like with respect to radio waves transmitted to and received from a wireless tag is transmitted. A wireless tag reader capable of estimating the direction (arrival azimuth) of a wireless tag more accurately, and a monitoring system using the wireless tag reader can be easily reduced even in an environment existing in the environment. It is to provide.

The invention described in claim 1
A wireless tag reader that receives radio waves of a wireless tag and estimates the arrival direction thereof,
An array antenna configured to switch directivity to a plurality of setting angles;
Directivity switching means for sequentially switching the directivity of the array antenna to a plurality of set angles;
Reception intensity measuring means for measuring the power intensity received by the array antenna;
When the directivity switching means switches and scans the set angle of the array antenna for one period, it arrives based on the power intensity pattern that is the power intensity for each set angle for one period measured by the reception intensity measuring means. A direction estimating means for estimating a bearing;
With
The direction estimating means includes
Pattern storage means for storing a reference power pattern indicating a power intensity pattern as a reference when radio waves arrive from each arrival direction, for each arrival direction;
The weight setting value is set in association with each set angle, and the set angle weight of the obstacle that reflects the radio wave with respect to the array antenna is smaller than the weight of the other predetermined set angle and 0 A weight setting means for setting a larger value ;
With
An error for each set angle when the reference power pattern for each direction of arrival is compared with the measured power intensity pattern is obtained by reflecting the set value of the weight associated with each set angle, and the error The direction corresponding to the set angle that minimizes is estimated as the arrival direction of the wireless tag.

In the wireless tag reader according to claim 1, the reference power intensity pattern (the power intensity pattern assumed when the directivity is set at each set angle) when the radio wave arrives from each arrival direction is used as the reference power pattern. By preparing for each azimuth (that is, for each set angle), the pattern actually measured (measurement pattern obtained by measurement when the array antenna directivity is switched to each set angle) is the reference for each arrival azimuth. It can be grasped as an error how much it differs from the power pattern. In this method, among the reference power patterns provided for each arrival direction (that is, for each set angle), the set angle with respect to a pattern in which an error from the obtained measurement pattern is small is the direction of the wireless tag (arrival direction). Therefore, it is possible to more accurately detect the arrival direction of the wireless tag by specifying such a pattern. In particular, in this method, since the entire measurement pattern obtained can be used for evaluation in estimating the orientation of the wireless tag, the method of simply estimating the orientation using only the maximum power value (for each change of directivity) Compared with the direction of the RFID tag that gives the maximum power value, the direction of arrival (arrival direction) due to sudden noise data is less likely to occur, and the arrival direction of the RFID tag Can be estimated more accurately.
In addition, in the present invention, each power intensity (reception power measurement value) when the directivity is switched to each set angle is not uniformly used for error calculation, but the weight set for each set angle is reflected. Since the error can be calculated, for example, by setting a weight that suppresses the reflected radio wave from the obstacle, it is easy to eliminate the erroneous detection of the arrival direction due to the reflected radio wave.

The wireless tag reader according to claim 2 uses a value that correlates with an angle at which an obstacle that reflects radio waves with respect to the array antenna is present as a weighting setting value, and therefore accurately eliminates the influence of the obstacle and wirelessly The direction of the tag can be estimated.

The wireless tag reader according to claim 3 uses the distance to the array antenna of an obstacle that reflects radio waves with respect to the array antenna, or a value correlated with the material of the obstacle as a weighting setting value. The direction of the wireless tag can be accurately estimated by properly responding to the distance and material of the material and eliminating the influence.

The RFID tag reader according to claim 4 has a specific error value with respect to an error function in which the horizontal axis obtained by interpolating the error value of each set angle is an angle and the vertical axis is an error value, and parallel to the error function. A straight line is drawn, and the angle at the half position of the line segment connecting the intersection of the line and the error function is estimated as the direction (arrival azimuth) of the wireless tag that has the minimum error. In other words, the measurable angle at which directivity can be obtained with an array antenna is physically limited, but the direction (arrival azimuth) of the wireless tag can be estimated even between the measurable angle. Become.

In the wireless tag reader of claim 5 , the setting angle for measuring the power intensity (reception power measurement value) is every 360 degrees / N, but the direction (arrival direction) of the wireless tag is also an angle between 360 degrees / N. Can be estimated.

The wireless tag reader according to claim 6 is characterized in that, with respect to an error function in which the horizontal axis obtained by interpolating the error value of each set angle is the angle and the vertical axis is the error value, the error is included in the values adjacent to the peak value where the error is minimum The line segment connecting the smaller value of the error and the adjacent value on the opposite side of the larger error and the opposite one of the larger error is extended, and then the larger error The line segment connecting the value and the value adjacent to the one with the larger error is extended, and the intersection of both line segments is estimated as the direction of the wireless tag that has the minimum error. In other words, the measurable angle at which directivity can be obtained with an array antenna is physically limited, but the direction (arrival azimuth) of the wireless tag can be estimated even between the measurable angle. Become.

In the invention of claim 7 , in the case where the array antenna is disposed in a space partially surrounded by the installation object and opened outside the area of the installation object, the weight setting means performs the directivity. Of the set angles that can switch the directivity of the array antenna by the switching means, the weight of the set angle from the array antenna toward the installation object is the weight of the set angle toward the open space outside the area of the installation object. Is set too small.
In this configuration, when the wireless tag is detected in a space partially surrounded by the installation object, for example, when the owner of the wireless tag tries to approach the array antenna, the radio wave of the wireless tag is transmitted to the installation object. The error between the measured pattern and the reference power pattern in each direction is calculated after relatively reducing the weight of the reflected wave that is reflected by the sensor and increasing the weight of the direct radio wave from the wireless tag. can do. Therefore, it is difficult for an error between the reference power pattern corresponding to the reflected wave and the actually measured measurement pattern to be small, and the error from the reference power pattern corresponding to the tag direction (direct wave direction) is made smaller. The direction can be accurately estimated by making it stand out.

In the invention according to claim 8, when the array antenna is disposed near the adjacent wall in a space surrounded by a predetermined adjacent wall and an opposing wall facing the adjacent wall, the weight setting unit includes: Of the set angles at which the directivity of the array antenna can be switched by the directivity switching means, the set angle toward the adjacent wall from the array antenna or the weight of the set angle toward the facing wall is weighted to the adjacent wall and the facing It is set smaller than the weight of the set angle toward the open space where the wall is not arranged.
In this configuration, the weight of the reflected wave generated by the radio wave reflected by the adjacent wall or the opposite wall is made relatively small, and the weight of the direct radio wave from the radio tag is made relatively large and measured. An error between the measurement pattern and the reference power pattern in each direction can be calculated. Therefore, it is difficult for an error between the reference power pattern corresponding to the reflected wave and the actually measured measurement pattern to be small, and the error from the reference power pattern corresponding to the tag direction (direct wave direction) is made smaller. The direction can be accurately estimated by making it stand out.

According to a ninth aspect of the present invention, when the array antenna is disposed near the adjacent wall in a space surrounded by a predetermined adjacent wall and a shielding wall extending in a direction intersecting the adjacent wall, the weighting is performed. In the setting means, of the setting angles at which the directivity of the array antenna can be switched by the directivity switching means, the setting angle toward the adjacent wall from the array antenna or the weighting of the setting angle toward the shielding wall is It is set smaller than the weight of the set angle toward the open space configured on the side facing the shielding wall.
In this configuration, the weight of the reflected wave generated by the radio wave reflected from the adjacent wall or shielding wall is made relatively small, and the weight of the direct radio wave from the radio tag is made relatively large, and then measured. An error between the measurement pattern and the reference power pattern in each direction can be calculated. Therefore, it is difficult for an error between the reference power pattern corresponding to the reflected wave and the actually measured measurement pattern to be small, and the error from the reference power pattern corresponding to the tag direction (direct wave direction) is made smaller. The direction can be accurately estimated by making it stand out.

According to a tenth aspect of the present invention, the array antenna includes the adjacent antenna in a space surrounded by a predetermined adjacent wall, an opposing wall facing the adjacent wall, and a shielding wall extending in a direction intersecting the adjacent wall. Among the setting angles that can switch the directivity of the array antenna by the directivity switching means in the weighting setting means when placed near the wall, the weighting of the setting angle from the array antenna toward the shielding wall Is set smaller than the weighting of the setting angle toward the open space configured on the side facing the shielding wall, the setting angle toward the adjacent wall, and the setting angle toward the facing wall.
In this configuration, when the owner of the wireless tag tries to approach the array antenna side from the opposite side (open space side) of the shielding wall, the weight of the reflected wave generated by reflecting the radio wave of the wireless tag on the shielding wall is particularly reduced. The error between the actually measured measurement pattern and the reference power pattern in each direction can be calculated while reducing the size and increasing the weight of the direct radio wave from the wireless tag relatively. Therefore, when the radio tag holder tries to approach the array antenna side from the opposite side of the shielding wall, the error between the reference power pattern in the direction of the reflected wave (that is, the direction of the shielding wall) and the actually measured measurement pattern becomes small. It is difficult to cause such a situation that a large angle error occurs such that the shielding wall side completely different from the normal tag direction is estimated as the tag direction.

The monitoring system according to claim 11 adjusts the set value of the weight according to the distance and direction of the object detected by the laser sensor. For this reason, for example, even when a truck or the like is parked in the monitoring area of the wireless tag reader, this can be detected by a laser sensor to eliminate the influence of radio wave reflection by the truck, and the wireless tag reader can estimate the direction of the wireless tag Can respond automatically.

1 is a schematic diagram of a monitoring system according to a first embodiment of the present invention. It is a block diagram which shows the electric constitution of the wireless tag reader of 1st Embodiment. It is explanatory drawing which shows the structure of an array antenna. It is a block diagram which shows the electric constitution of the wireless tag of 1st Embodiment. It is explanatory drawing in the case of detecting the direction (arrival azimuth | direction) of an intruder's wireless tag when the wireless tag reader of 1st Embodiment is installed in the place without an electromagnetic wave reflector. FIG. 6A is a graph of the measured value of the received electric field strength when there is an intruder (wireless tag) in the direction of 30 degrees (arrival azimuth), and FIG. 6B is a graph showing the array antenna 10 described above. Is a graph showing antenna characteristic values measured by setting the directivity to azimuth angles (set angles) of −60 degrees, −30 degrees, 0 degrees, 30 degrees, and 60 degrees (α). 7 is a chart showing a result of calculating a correlation value (error) with the power correlation pattern shown in FIG. 6B with respect to the received electric field strength shown in FIG. It is a graph which shows a received electric field strength with a dotted line, and a correlation value (error) with a continuous line. It is explanatory drawing in case the wireless tag reader of 1st Embodiment is attached to the entrance of an actual house, and detects the direction (arrival azimuth | direction) of an intruder's wireless tag. When there is a house on the back side (240 to 330 degrees), the measured value of the received electric field strength when there is an intruder (wireless tag) in the direction of 30 degrees (arrival azimuth) is a correlation value ( It is a graph which shows the calculation result of (error) with a continuous line. It is a graph which shows the result of having weighted reception electric field strength and calculating the correlation value (error) with the power correlation pattern. It is a graph which shows the calculation result of the correlation value (error) which performed the measured value of received electric field strength with a dotted line, and gave the weighting with a continuous line. It is a flowchart which shows the process by the controller of a monitoring system. It is a flowchart which shows the direction estimation process of the wireless tag by a wireless tag reader. It is a flowchart which shows the subroutine of the correlation error calculation process in FIG. It is a flowchart which shows the process in a wireless tag. It is a graph which shows the method of calculating | requiring a peak from a correlation value in the 1st modification of 1st Embodiment. It is a graph which shows the method of calculating | requiring a peak from a correlation value in the 2nd modification of 1st Embodiment. It is explanatory drawing in case the wireless tag reader of 2nd Embodiment detects the direction (arrival azimuth | direction) of an intruder's wireless tag. It is a graph which shows the setting value for performing weighting in 2nd Embodiment. It is explanatory drawing in case the wireless tag reader of 3rd Embodiment detects the direction (arrival azimuth | direction) of an intruder's wireless tag. It is a flowchart which shows the process which the wireless tag reader which concerns on 3rd Embodiment detects the reflector in a monitoring area | region, and sets weighting automatically. It is a graph which shows the value of the weight set to the radio | wireless tag reader of 3rd Embodiment. It is a flowchart which shows the direction estimation process of the wireless tag by the wireless tag reader of 4th Embodiment. It is a flowchart which illustrates the flow of the direction search communication process in FIG. It is explanatory drawing explaining the communication flow performed between a wireless tag and a wireless tag reader in 4th Embodiment. (A) is explanatory drawing which illustrates notionally the response frame transmitted from a wireless tag to a wireless tag reader at the time of independent transmission. (B) is an explanatory diagram conceptually illustrating a command frame transmitted from the wireless tag reader to the wireless tag. (C) is a response frame transmitted from the wireless tag to the wireless tag reader in response to command transmission from the wireless tag. Explanatory drawing explaining notionally the result of having performed the statistical process (average value calculation process) for every setting angle based on the radio wave intensity (power intensity) obtained for every setting angle in the modification 1 of 4th Embodiment. It is. FIG. 29A is an explanatory diagram illustrating an example in which the wireless tag reader according to the fifth embodiment is provided in an environment surrounded by an adjacent wall and a shielding wall, and the wireless tag reader estimates the direction (arrival azimuth) of the wireless tag. is there. FIG. 29B is an explanatory diagram illustrating the direction of a direct radio wave transmitted from a wireless tag entering from the open space side and the direction of a reflected wave when the radio wave is reflected by a shielding wall. 30A is a graph showing an estimation result when the direction (arrival azimuth) is estimated by the maximum power method in the environment of FIG. 29, and FIG. 30B is a graph for each direction in the environment of FIG. FIG. 30C is a graph showing an estimation result when the direction (arrival azimuth) is estimated by the power correlation pattern method without setting the weighting (for each set angle), and FIG. It is a graph which shows the estimation result at the time of setting weighting (for every setting angle) and estimating a direction (coming direction) by the power correlation pattern method. FIG. 31 relates to the first modification of the fifth embodiment, and is an explanatory diagram for explaining an example in which the direction (arrival azimuth) of the wireless tag is estimated by a wireless tag reader provided in an environment different from FIG. . FIG. 32A is a graph showing an estimation result when the direction (arrival azimuth) is estimated by the power correlation pattern method without setting the weight for each direction (for each set angle) in the environment of FIG. FIG. 32B is a graph showing an estimation result when weighting is set for each direction (for each set angle) and the direction (arrival direction) is estimated by the power correlation pattern method in the environment of FIG. FIG. 33 relates to a second modification of the fifth embodiment, and is an explanatory diagram for explaining an example in which the direction (arrival azimuth) of the wireless tag is estimated by a wireless tag reader provided in an environment different from FIG. . FIG. 34A is a graph showing an estimation result when the direction (arrival azimuth) is estimated by the power correlation pattern method without setting the weight for each direction (for each set angle) in the environment of FIG. FIG. 34B is a graph showing estimation results when the direction (arrival azimuth) is estimated by the power correlation pattern method with weighting set for each direction (for each set angle) in the environment of FIG. FIG. 35 shows the weight, average error, and abnormal value appearance rate of the direction of the shielding wall (set angle) when the direction (arrival direction) is estimated by the same power correlation pattern method as in the first embodiment in the environment of FIG. It is a graph which shows the relationship. FIG. 36 shows the weight, average error, and abnormal value appearance rate of the direction of the shielding wall (set angle) when the direction (arrival direction) is estimated by the same power correlation pattern method as in the first embodiment in the environment of FIG. It is a graph which shows the relationship. FIG. 37 shows the weight of the shielding wall direction (set angle), the average error, and the abnormal value appearance rate when the direction (arrival direction) is estimated by the same power correlation pattern method as in the first embodiment in the environment of FIG. It is a graph which shows the relationship. FIG. 38 (A) shows weighting for each angle with respect to a matching error between a measurement pattern when a wireless tag existing in a certain direction (arrival direction) is detected and a reference pattern of a set angle corresponding to that direction. It is explanatory drawing explaining the case where it correct | amends, FIG.38 (B) is explanatory drawing explaining the result of the matching process in that case. FIG. 39A is a diagram for explaining a case where a measurement pattern when a wireless tag existing in a certain direction (arrival direction) is detected is corrected by weighting the power intensity at each set angle for each set angle. FIG. 39B is an explanatory diagram for explaining the result of the matching process in that case. FIG. 40 relates to another embodiment, and is an explanatory diagram for explaining an example in which a wireless tag reader is provided in an environment different from that in FIG. 29 and the direction (arrival azimuth) of the wireless tag is estimated by this wireless tag reader. .

[First embodiment]
FIG. 1 is a schematic diagram of a monitoring system according to the first embodiment of the present invention.
The monitoring system uses a wireless tag reader 100 that can estimate the direction (arrival azimuth) of a wireless tag and a laser sensor 200 that measures the distance and direction of an object in the monitoring area, so that a person who has entered the monitoring area is wireless. The controller 300 determines whether or not the tag 400 is carried, and issues a warning when the tag 400 is not carried. In the monitoring system, first, the laser sensor 200 detects the distance and direction of a person who has entered the monitoring area, and the wireless tag reader 100 determines whether or not the wireless tag is carried. Here, a warning is issued when the wireless tag is not carried. When the presence of the wireless tag is confirmed, the direction of the wireless tag is further estimated by the wireless tag reader 100. When the direction matches the direction detected by the laser sensor 200, the intruder carries the wireless tag. Judge that On the other hand, when there is a response from the wireless tag but does not coincide with the direction detected by the laser sensor 200, the response is from a wireless tag placed in another place where the intruder is not carrying the wireless tag. A warning is issued.

The above processing by the controller 300 in the monitoring system will be described in more detail with reference to the flowchart of FIG.
The laser sensor 200 monitors whether an intruder enters the monitoring area (S12). And when an intruder enters (S12: Yes), the direction and distance of an intruder are acquired by the laser sensor 200 (S14). As will be described later, the directivity of the antenna is switched (S16), and the wireless tag reader 100 creates a command frame for the wireless tag (S18) and transmits it to the wireless tag (S20). Then, it is determined whether a reply signal is received from the wireless tag (S22). If no reply is received from the wireless tag (S22: No), it is determined that the intruder is not carrying the wireless tag, and an alarm is issued with an alarm sound or the like (S26). On the other hand, if a reply from the wireless tag is received (S22: Yes), the direction of the intruder detected by the laser sensor 200 matches the direction of the wireless tag estimated by the wireless tag reader 100. It is determined whether or not (S24). If the directions do not match (S24: No), it is determined that the intruder is not carrying a wireless tag and there is a wireless tag unrelated to the intruder in any of the monitoring areas, and an alarm is issued. (S26). If the directions match (S24: Yes), it is determined that the intruder is an intruder authorized to carry the wireless tag, and the process ends without issuing an alarm.

  The electrical configuration of the wireless tag reader used in the monitoring system will be described with reference to FIG. The wireless tag reader 100 includes a control unit 20 including a memory 22 and a timer 24, a code unit 32 that generates a code, a modulation unit 34 that modulates a code, and a transmission unit 30 that amplifies the modulated signal. Prepare. Further, the wireless tag reader 100 includes a demodulation unit 44 that demodulates a received signal, a decoding unit 42 that decodes a code from the demodulated received signal, and a carrier sense unit 46 that sets communication when transmission / reception with the wireless tag is started. Unit 40, array antenna 10 to be described later, and directivity control unit 50 for controlling the directivity of the array antenna. The receiving unit 40 is configured to measure the received radio wave intensity of the signal from the wireless tag.

  The electrical configuration of the wireless tag that performs communication with the wireless tag reader will be described with reference to FIG. The wireless tag 400 includes a control unit 420 including a memory 422 and a timer 424, a code unit 432 that generates a code, a modulation unit 434 that modulates the code, and a transmission unit 430 that amplifies the modulated signal. Prepare. Further, the wireless tag 400 includes a demodulation unit 444 that demodulates a reception signal, a decoding unit 442 that decodes a code from the demodulated reception signal, and a carrier sense unit 446 that sets communication when transmission / reception with the wireless tag reader is started. Unit 440, antenna 410, and built-in power supply 460. That is, in the first embodiment, an active tag with a built-in power supply is used as the wireless tag.

Here, the configuration of the array antenna 10 of the RFID tag reader described above with reference to FIG. 2 and the directivity control unit 50 for controlling the directivity of the array antenna will be described in more detail with reference to FIG.
The array antenna 10 includes one excitation element 10-0 and six non-excitation elements 10-1 to 10-6, and the excitation element 10-0 and the non-excitation elements 10-1 to 10-6. Is formed on the ground conductor 16. The excitation element 10-0 is disposed so as to be surrounded by six non-excitation elements 10-1 to 10-6 provided on the circumference having a radius r. The six non-excitation elements 10-1 to 10-6 are arranged at equal intervals on the circumference. The lengths of the exciting element 10-0 and the non-exciting elements 10-1 to 10-6 are set to λ (use frequency) / 4, and the radius r is also set to λ / 4. The feeding point of the excitation element 10-0 is connected to the transmission unit 30 and the reception unit 40 of the wireless tag reader described above with reference to FIG.

  The excitation element 10-0 is electrically isolated from the ground conductor 16. On the other hand, the six non-exciting elements 10-1 to 10-6 are grounded at high frequency with respect to the ground conductor 15 via the variable reactance circuits 12-1 to 12-6. The variable reactance circuits 12-1 to 12-6 are configured by a circuit including a variable capacitance diode whose reactance value changes with application of a bias voltage.

  The directivity control unit 50 includes a reactance value control device 52 and a reactance value table memory 54. The reactance value control device 52 applies a bias voltage to the variable reactance circuits 12-1 to 12-6 based on a voltage setting value preset in the reactance value table memory 54, so that the angle directivity corresponding to the array antenna 10 is set. A beam pattern is generated. In the present embodiment, the control unit 20 and the directivity control unit 50 correspond to an example of directivity switching means, and function to sequentially switch the directivity of the array antenna 10 to a plurality of set angles. The “set angle” indicates the direction of directivity determined in the array antenna 10, and indicates the angle with respect to a predetermined reference direction (0 ° direction) determined in the array antenna 10. In this specification, the direction of directivity switched by the array antenna 10 is also referred to as “set angle”, and the direction of the wireless tag 400 relative to the wireless tag reader 10 is also referred to as “arrival direction”.

  Here, the angular orientation of the array antenna 10 is adjusted by appropriately changing the capacitance values of the variable capacitance diodes described above by the reactance circuits 12-1 to 12-6. For example, by reducing the capacitance value of the variable capacitance diode of the variable reactance circuit 12-1, the variable reactance circuit 12-1 having a capacitor property becomes a shortening capacitor, and the electrical length of the non-excitation element 10-1 is the excitation element 10-. It becomes shorter than 0 and works as a director. On the other hand, by increasing the capacitance values of the variable capacitance diodes of the variable reactance circuits 12-2 to 12-6, the variable reactance circuits 12-2 to 12-6 have inductance, and the variable reactance circuits 12-2 to 12- 6 becomes an extension coil, and the electrical length of the non-excitation elements 10-2 to 10-6 is longer than that of the excitation element 10-0, and functions as a reflector. As a result, the reactance value control device 52 adjusts the angular orientation of the array antenna 10 to be in the direction of the excitation element 10-1 in the 0 degree direction.

  The wireless tag reader according to the first embodiment holds in advance antenna characteristic values measured by setting the directivity of the array antenna 10 to azimuth angles of −60 degrees, −30 degrees, 0 degrees, 30 degrees, and 60 degrees (α). ing. With this antenna characteristic value, when the directivity of the array antenna 10 is set to the azimuth angle θ, a correlation value (error) is obtained from the measured received power as in the following equation, and the wireless tag, that is, the arrival of the radio wave is obtained by the correlation Estimate the direction.

Correlation value (error) Γ (θ) = | Σ (P (α) −Y (θ−α)) |
[α = −60, −30, 0, 30, 60]
P (α) is the antenna characteristic value Y (θ) when the antenna directivity is set to the azimuth angle α, and the received power measured when the antenna directivity is set to the azimuth angle θ.

FIG. 5 is an explanatory diagram when the direction of the wireless tag of the intruder is detected when the wireless tag reader is installed in a place where there is no radio wave reflector.
The wireless tag reader according to the first embodiment equally divides 360 degrees into 12 azimuths, and directs the array antenna to 0 degrees, 30 degrees, 60 degrees, 90 degrees, 120 degrees, 150 degrees, 180 degrees, 210 degrees. The received power is measured by setting the angle to 240 degrees, 240 degrees, 270 degrees, 300 degrees, and 330 degrees (that is, the set angles can be set as these angles). In this example, the description will be continued assuming that there is an intruder in the direction of 30 degrees.

  FIG. 6A is a graph of the measured value of the received electric field strength when there is an intruder (wireless tag) in the direction of 30 degrees, with the received intensity on the vertical axis and the azimuth on the horizontal axis. . The received electric field strength of 30 degrees is maximized.

  FIG. 6B shows antenna characteristic values measured by setting the directivity of the array antenna 10 described above to azimuth angles of −60 degrees, −30 degrees, 0 degrees, 30 degrees, and 60 degrees (α), that is, power. A correlation pattern is shown. The reception intensity is plotted on the vertical axis, and the azimuth is plotted on the horizontal axis. At 0 degrees, 0 dBm, 30 degrees, and −30 degrees, −1.5 dBm, 60 degrees, and −60 degrees are −5 dBm.

  FIG. 7 is a chart showing the results calculated using the correlation values (errors) described above in the power correlation pattern shown in FIG. 6B with respect to the received electric field strength shown in FIG. FIG. 8 is a graph showing the measurement value of the received electric field strength shown in FIG. 6A by a dotted line and the calculation result of the correlation value (error) by a solid line. As shown in FIG. 7, at an angle of 30 degrees where an intruder (wireless tag) is present, the power measurement value is maximum at −40.0 [dBm], and the correlation value (error) is minimum at 0.6 [dB]. It has become. As can be seen from the graph of FIG. 8, when the wireless tag reader shown in FIG. 5 is installed in a place where there is no radio wave reflector, both the method for obtaining the maximum power and the method for obtaining the correlation value (error), An angle of 30 degrees can be estimated, but a sharper peak is obtained by obtaining a correlation value (error).

FIG. 9 is an explanatory diagram when a monitoring system (wireless tag reader) is attached to an actual house entrance and detects the direction of the wireless tag of the intruder.
Here, with respect to the RFID tag reader, a house existing at an angle of 240 to 330 degrees becomes a reflection obstacle, and the direction is accurately determined by either the method of obtaining the maximum power by reflecting the radio wave or the method of obtaining the correlation value (error). Can no longer be estimated.

  FIG. 10 shows the measured value of the received electric field strength with a dotted line when there is an intruder (wireless tag) in the direction of 30 degrees when a house exists on the back side (240 degrees to 330 degrees) shown in FIG. 5 is a graph showing the calculation result of the correlation value (error) with a solid line. The measurement value of the received electric field strength indicated by the dotted line shows that the received electric field strength is large even for the radio wave of the beam directed to the 330 degree direction in addition to the 30 degree direction. Here, due to noise and other environmental influences, the 330-degree direction (set angle 330 degrees) may be measured as a stronger power than the original 30-degree direction. In this case, in the direction estimation based on the received electric field strength, there is a difference of 330 degrees from the original direction (30 degrees) by 60 degrees.

  Even in the method based on the correlation value (error) indicated by the solid line, the 0 degree direction is estimated by being dragged to the peak in the 330 degree direction (setting angle 330 degrees), and an error is generated.

  For this reason, in order to cope with the case where there is a reflector that reflects the radio wave measured by the wireless tag reader, in the first embodiment, the direction of the “reflection obstacle” is set in the wireless tag reader, and the “reflection magnitude” is set. By using the “weighting” according to the above, the above-described correlation value (error) is obtained using the following equation, thereby reducing the influence of the reflection obstacle.

Correlation value (error) Γ (θ) = | Σ ((P (α) −Y (θ−α))) W (θ)) |
× 5 / (Σ (W (θ))
[α = −60, −30, 0, 30, 60]
P (α) is the antenna characteristic value when the antenna directivity is set to the azimuth angle α Y (θ) is the received power W (θ) measured when the antenna directivity is set to the azimuth angle θ Is weighted by reflective obstacles as seen from the antenna

  Here, W (θ) sets the condition where there is no reflecting obstacle as 1 and makes the direction where the reflecting obstacle exists (240 degrees to 330 degrees in this example) smaller than 1. If the reflection is large, the value is set to a small value. Here, 0.2 is set because the house is a highly reflective object. Here, 0.2 is set in the case of a wooden house, but 0.15 is set in the case of a building having a large reflection, for example. The result of calculating the correlation value (error) using the above formula after performing this weighting is shown in the chart of FIG. Further, in the graph in FIG. 12, the measured value of the received electric field strength is indicated by a dotted line, and the calculation result of the weighted correlation value (error) is indicated by a solid line.

  As shown in FIG. 11, 0.2 is set as the weighting in the direction with the reflection obstacle (240 to 330 degrees), and 1 is set as the weighting in the direction without the reflection obstacle. The weighting value is a magnification. The power measurement value is −40.2 [dBm], the weighting value is 1, and the correlation value (error) is 0.3 [dB], which is the minimum at an angle of 30 degrees where the wireless tag exists. As can be seen from the graph of FIG. 12, the correlation value (error) has a peak at an angle of 30 degrees, and the direction can be estimated correctly.

The direction estimation processing by the wireless tag reader will be described in more detail with reference to the flowcharts of FIGS.
First, the above-described received power pattern P (α) [α = −60, −30, 0, 30, 60] is set (S32), and the above-described direction-specific weighting W (θ) [θ = 0, 30, 60 ... 330] is set (S34). This is an initial setting, S32 is set at the manufacturing stage for the wireless tag reader, and S34 is set when the wireless tag reader which is a component device of the monitoring system is attached.

  The wireless tag reader 100 waits for reception of a signal from the wireless tag 400 while transmitting a command (S36). Here, when a signal is received from the wireless tag (S36: Yes), first, the estimated angle θ is set to 0 degree (S38). The directivity of the array antenna is switched to the estimated angle θ as described above with reference to FIG. 3 (S40). Then, a command is sent to the wireless tag, and data from the wireless tag is received (S42). When there is reception from the wireless tag (S44: Yes), the received radio wave intensity at the time of data reception is set as the received power Y (θ) measured when the antenna directivity described above is set to the azimuth angle θ. Is set (S46). On the other hand, when there is no reception from the wireless tag (S44: No), a preset minimum value is set as the reception power Y (θ) (S48). Then, the measurement angle θ is increased by 30 degrees (S50), and it is determined whether the measurement angle is 360 degrees or more, that is, whether the measurement of the received radio wave intensity at all angles from 0 degrees to 330 degrees is completed (S52), Until the measurement is completed (S52: No), the process returns to S40. When the measurement is completed (S52: Yes), a correlation error is calculated as described later (S100). Then, the minimum direction of the correlation value error is output to the controller 300 side as the RFID tag direction (S54), and the process is terminated.

The correlation error calculation process described above will be described with reference to FIG. 15 showing a subroutine of the process.
First, the estimated angle θ is set to 0 degree (S102), and the error function Γ (θ) is set to 0 degree (S104). First, the azimuth angle α for the antenna directivity corresponding to the characteristic value of the antenna is set to −60 degrees (S106). Then, a correlation value (error) Γ (θ) is obtained using the following equation (S108).
Γ (θ) = Γ (θ) + | Σ (P (α) −Y (θ−α)) × W (θ)) |

Next, the antenna directivity corresponding to the antenna characteristic value is added to the azimuth angle α by 30 degrees (S110). Here, the azimuth angle α is set to 30 degrees, and the azimuth angle α exceeds 60 degrees, that is, It is determined whether the calculation from −60 degrees to 60 degrees is completed (S112). Here, until the calculation to 60 degrees is completed (S112: No), the process returns to S108 and the calculation of the correlation value (error) Γ (θ) is continued. On the other hand, when the calculation up to 60 degrees is completed (S112: Yes), a correlation value (error) Γ (θ) is obtained using the following equation (S114).
Γ (θ) = Γ (θ) × 5 / (Σ (W (θ))

  Then, 30 degrees is added to the estimated angle θ (S116), and it is determined whether the estimated angle is over 330 degrees, that is, the estimation of all angles from 0 degrees to 330 degrees is completed (S118), and the estimation is completed. Until (S118: No), the process returns to S104. When the estimation is completed (S118: Yes), the process is terminated.

With reference to FIG. 16, the processing in the wireless tag will be described.
The wireless tag is an active type with a built-in power supply, sleeps for a set period (S82), and transmits data to the wireless tag reader after sleep (S84). If the wireless tag enters the communication area of the wireless tag reader and receives a command from the wireless tag reader (S86: Yes), a response signal is transmitted to the wireless tag reader (S88). When a command is further received from the wireless tag reader (S90: Yes), the process returns to S88 and a response signal is transmitted to the wireless tag reader. On the other hand, when the command from the wireless tag reader is not received (S90: No), the process is terminated.

  In the present embodiment, the control unit 20 and the memory 22 correspond to an example of “direction estimation means”. The memory 22 corresponds to an example of “pattern storage unit”. The control unit 20 and the memory 22 correspond to an example of “setting unit”.

In the wireless tag reader of the first embodiment and the monitoring system using the wireless tag reader,
Array antenna 10 configured to be able to switch directivity to a plurality of set angles (directions), and directivity switching means (control unit 20 and directivity control unit 50 to sequentially switch the directivity of array antenna 10 to a plurality of set angles. ), Reception intensity measurement means (control unit 20) for measuring the power intensity received by the array antenna 10, and reception intensity measurement when the set angle of the array antenna 10 is switched and scanned for one period (for example, 360 °). Direction estimation means (control unit 20 and memory 22) for estimating an arrival direction based on a power intensity pattern that is a power intensity for each set angle for one period measured by the means is provided.
Further, the direction estimation means includes a pattern storage means (memory 22) for storing a reference power pattern indicating a power intensity pattern as a reference when radio waves arrive from each arrival direction for each arrival direction, and each set angle. Weighting setting means (memory 22) for setting the weighting setting values in association with each other, and the control unit 20 serving as the main element of the direction estimation means is provided with a reference power for each arrival direction (for each set angle). The error for each set angle when the pattern is compared with the measured power intensity pattern is calculated by reflecting the weight setting value associated with each set angle, and the error corresponds to the set angle that minimizes the error. The direction is estimated as the arrival direction of the wireless tag.

In this configuration, a reference power intensity pattern (a power intensity pattern assumed when the directivity is set at each setting angle) when a radio wave arrives from each arrival direction is used as a reference power pattern for each arrival direction (that is, By preparing for each set angle), an actually measured pattern (measurement pattern obtained by measurement when the directivity of the array antenna 10 is switched to each direction (each set angle)) It can be understood as an error how much it differs from the reference power pattern. In this method, among the reference power patterns provided for each arrival direction (that is, for each set angle), the set angle with respect to a pattern in which an error from the obtained measurement pattern is small is the direction of the wireless tag (arrival direction). Therefore, it is possible to more accurately detect the arrival direction of the wireless tag by specifying such a pattern. In particular, in this method, since the entire measurement pattern obtained can be used for evaluation in estimating the orientation of the wireless tag, the method of simply estimating the orientation using only the maximum power value (for each change of directivity) Compared with the direction of the RFID tag that gives the maximum power value, the direction of arrival (arrival direction) due to sudden noise data is less likely to occur, and the arrival direction of the RFID tag Can be estimated more accurately.
In addition, in the present invention, each power intensity (reception power measurement value) when the directivity is switched to each set angle is not uniformly used for error calculation, but the weight set for each set angle is reflected. Since the error can be calculated, for example, by setting a weight that suppresses the reflected radio wave from the obstacle, it is easy to eliminate the erroneous detection of the arrival direction due to the reflected radio wave.

  In the wireless tag reader according to the first embodiment, since a value correlated with an angle at which an obstacle that reflects radio waves with respect to the array antenna exists is set as a weighting setting value, the influence of the obstacle is accurately excluded. The direction of the wireless tag can be estimated.

[First Modification of First Embodiment]
A wireless tag reader according to a first modification of the first embodiment will be described with reference to the graph of FIG.
Using the RFID tag reader of the first embodiment and the RFID tag reader of the first modification of the first embodiment, the power intensity (reception power measurement value) is measured for each directivity every 30 degrees of the array antenna, and the measured power intensity The process from weighting (received power measurement value) to obtaining the correlation with the reference power pattern is the same. However, in the first embodiment, the resolution was only up to the directivity of every 30 degrees of the array antenna (0 degrees, 30 degrees to 330 degrees). On the other hand, in the first modification of the first embodiment, higher resolution is realized by interpolating the correlation values every 30 degrees.

  In the first modification of the first embodiment, in order to obtain the minimum value of the error, a specific error value is used for an error function in which the horizontal axis obtained by interpolating the error value in each direction is the angle and the vertical axis is the error value. Draw a line parallel to the horizontal axis for the error function. Here, the specific error value is separated from the peak with the smallest error of the error function (in this example, 0 degree) by two in the direction for each angle (30 degrees) to be measured (−60 degrees, +60 degrees). Of these, the value on the lower error side. In this example, the error is 14 dB on the 60 degree side, whereas at −60 degrees, the error exceeds the maximum value of 30 dB on the graph, so the low error side is 60 degrees. A line parallel to the horizontal axis is drawn from the 60 degree side (error 14 dB), and the angle at the half position of the line segment connecting the intersection of the line and the error function (15 degrees in this example) is the minimum error. Estimated as the direction of the wireless tag.

  In the first embodiment, in this example, the minimum error error peak (0 degrees in this example) is estimated as the direction of the wireless tag, whereas in the first modification of the first embodiment, 15 degrees. It can be estimated. That is, the measurable angle at which directivity can be obtained by the number of elements in the array antenna is physically limited. However, in the first modification of the first embodiment, the measurable angle between the measurable angles (360 degrees). Even during every / 12: between 0 degrees and 30 degrees in this example), the direction of the wireless tag can be estimated.

[Second modification of the first embodiment]
A wireless tag reader according to a second modification of the first embodiment will be described with reference to the graph of FIG.
Using the RFID tag reader of the first embodiment and the RFID tag reader of the second modification of the first embodiment, the power intensity (reception power measurement value) is measured for each directivity every 30 degrees of the array antenna, and the measured power intensity The process from weighting (received power measurement value) to obtaining the correlation with the reference power pattern is the same. However, in the first embodiment, the resolution was only up to the directivity of every 30 degrees of the array antenna (0 degrees, 30 degrees to 330 degrees). On the other hand, in the second modification example of the first embodiment, similarly to the first modification example, the correlation value every 30 degrees is interpolated to realize higher resolution.

  In the second modification of the first embodiment, in order to obtain the minimum value of the error, the error is minimized with respect to an error function in which the horizontal axis obtained by interpolating the error value in each direction is the angle and the vertical axis is the error value. Of the values adjacent to the peak value (0 degrees in this example) (-30 degrees and 30 degrees in this example), the value (5 dB) of the smaller error (30 degrees in this example) and the smaller error Next, the line segment connecting the value (14 dB) of the adjacent side (60 degrees in this example) on the opposite side with the larger error is extended. Next, the value (3 dB) of the one with the larger error (−30 degrees in this example) and the value (8 dB) adjacent to the one with the larger error (−30 degrees) (−60 degrees in this example) ) Are extended, and the intersection of both line segments (15 degrees in this example) is estimated as the direction of the wireless tag that has the minimum error.

  In the first embodiment, in this example, the minimum error error peak (0 degrees in this example) is estimated as the direction of the wireless tag, whereas in the second modification of the first embodiment, 15 degrees. It can be estimated. That is, in the array antenna, the measurable angle at which directivity can be obtained by the number of elements is physically limited, but in the second modification of the first embodiment, the measurable angle is between 360 degrees (360 degrees). Even between every / 12), the direction of the wireless tag can be estimated.

[Second Embodiment]
A wireless tag reader according to the second embodiment will be described with reference to FIGS.
FIG. 19 is an explanatory diagram when the wireless tag reader according to the second embodiment detects the direction of the wireless tag of the intruder.
The wireless tag reader of the first embodiment is attached to the front of a house, and only the house has a reflector. On the other hand, in the second embodiment, there is a block wall that reflects radio waves in the monitoring area of the wireless tag reader on the front side of the house. For this reason, in the second embodiment, as in the first embodiment, weighting is performed in the direction on the house side, and weighting in the direction on the block wall side is performed in the initial setting of the attachment.

  FIG. 20 is a chart showing set values for weighting in the second embodiment. As in the first embodiment, 0.2 is set as a weight in a direction (240 degrees to 330 degrees) where there is a house that is a radio wave reflector, and a direction (30 degrees to 30 degrees) that is a block wall that is a radio wave reflector. The weight is set to 0.4, 0.6, and 0.8 according to the reflection angle and distance, and 1 is assigned to the weight in the direction where there is no reflection obstacle (0 degree and 180 degrees). It is set. Here, the block wall, which is a radio wave reflector, has a relatively large radio wave reflection. For example, for an obstacle with a small radio wave reflection such as a hedge, for example, 0.5 to 0.9 A larger weighting value is set.

  In the second embodiment, the direction of the wireless tag can be estimated appropriately in accordance with the radio wave reflection environment where the wireless tag reader is installed.

[Third embodiment]
A monitoring system according to a third embodiment will be described with reference to FIGS.
In the first and second embodiments, when the wireless tag reader is installed, the operator manually sets the weighting value for eliminating the influence of the reflecting object. On the other hand, in the third embodiment, a reflecting object is detected and a weighting value is automatically set.

  FIG. 21 is an explanatory diagram when the wireless tag reader of the third embodiment detects the direction of the wireless tag of the intruder. In the third embodiment, when the truck is stopped in front of the house in the monitoring area, this is detected by the laser sensor 200 (see FIG. 1), and the controller 300 is configured to eliminate the influence of the radio wave reflection by the truck. Automatically sets a weighting value to the wireless tag reader 100. Here, the weighting value when the truck is not stopped is 0 as the weighting in the housing direction (240 degrees to 330 degrees) so as to correspond to the house as in the first embodiment described above with reference to FIG. .2 is the default setting.

  FIG. 22 is a flowchart illustrating a process in which the controller 300 according to the third embodiment detects a reflecting object in the monitoring area and automatically sets weighting for the wireless tag reader. The controller 300 (see FIG. 1) of the monitoring system uses the laser sensor 200 to monitor whether a reflection object is in the monitoring area together with the intruder. Here, the intruder and the reflective object such as a truck use the size (for example, detected over an angle of 30 degrees or more) and the possibility of movement (they are present in the same place for 10 minutes or more). Identify.

  If there is a reflector in the monitoring area (S302: Yes), the controller 300 acquires the direction and angle of the reflector from the laser sensor 200 (S304). Then, a weighting setting value is calculated based on the direction and angle of the reflector (S306). The calculated value is set in the wireless tag reader (S308). On the other hand, when the reflection object, for example, the truck moves out of the monitoring area and there is no reflection object in the monitoring area (S302: No), the wireless tag reader is set to release the weighting value for the reflection object (S310). ).

  FIG. 23 is a chart showing weight values set in the wireless tag reader of the third embodiment. Here, the weighting values (120 degrees: 0.8, 150 degrees: 0) calculated by the controller 300 in accordance with the direction (120 degrees and 150 degrees) and angle of the reflecting object (track) detected by the laser sensor 200. .6) is set.

  The monitoring system of the third embodiment adjusts the weighting setting value according to the distance and direction of the object detected by the laser sensor 200. For this reason, for example, even when a truck or the like is temporarily parked in the monitoring area of the wireless tag reader 100, this is detected by a laser sensor to eliminate the influence of radio wave reflection by the truck, and the wireless tag reader It can respond automatically so that the direction can be estimated. In the above-described example, the initial setting is manually performed so as to eliminate the influence of the house to which the wireless tag reader is attached. However, in the third embodiment, the initial setting may be automatically set. In the case of such automatic setting, the control unit 20 corresponds to “set value adjusting means”.

[Fourth embodiment]
A monitoring system according to the fourth embodiment will be described mainly with reference to FIGS.
FIG. 24 is a flowchart illustrating wireless tag direction estimation processing by the wireless tag reader according to the fourth embodiment. FIG. 25 is a flowchart illustrating the flow of the direction search communication process in FIG. FIG. 26 is an explanatory diagram illustrating a communication flow performed between the wireless tag and the wireless tag reader in the fourth embodiment. FIG. 27A is an explanatory diagram for conceptually explaining a response frame transmitted from the wireless tag to the wireless tag reader during independent transmission, and FIG. 27B is a command frame transmitted from the wireless tag reader to the wireless tag. (C) is a response frame transmitted from the wireless tag to the wireless tag reader in response to command transmission from the wireless tag.

  The monitoring system of the fourth embodiment is different from the first embodiment only in that the direction estimation process in FIG. 14 is changed to that in FIGS. 24 and 25 and the frequency of the radio wave from the wireless tag can be switched. Otherwise, the rest is the same as in the first embodiment. Therefore, hereinafter, only the direction estimation process will be described with emphasis, and the detailed description will be omitted as it is the same as the first embodiment except for the direction estimation process. For example, FIGS. 1 to 13, 15, and 16 can employ the same configuration and processing as in the first embodiment, and will be described with reference to these drawings as appropriate.

  In the first to third embodiments, the configuration in which the radio wave transmitted from the wireless tag is set to a predetermined frequency is exemplified, but in the fourth embodiment, the radio frequency from the wireless tag can be switched. The radio wave intensity can be measured for each frequency to be switched. Then, the direction of the wireless tag is estimated based on the radio field intensity measurement result for each frequency.

In the present embodiment, the direction estimation process is performed according to the flow shown in FIG.
In this direction estimation process, first, the received power pattern P (α) [α = −60, −30, 0, 30, 60] described above is set in the same manner as in S32 (FIG. 14) of the first embodiment ( S232) and the weight W (θ) [θ = 0, 30, 60... 330] for each direction described above are set in the same manner as in S34 (FIG. 14) (S234). This is an initial setting, and S32 is set, for example, in the manufacturing stage of the wireless tag reader, and S34 is set, for example, when a wireless tag reader that is a component device of the monitoring system is attached.

  After S234, the wireless tag reader 100 waits for reception of a signal from the wireless tag 400 while transmitting a command (S236). Here, when a signal is received from the wireless tag (S236: Yes), a direction search communication process using the first frequency (channel B, hereinafter also referred to as ch-B) is performed (S238).

The direction search communication processing (S238, S242) at each frequency is performed according to the flow shown in FIG.
The operation of the wireless tag 400 will be described as a premise of the direction search communication processing. In this embodiment, the processing on the wireless tag 400 side is performed in the same flow (FIG. 16) as in the first embodiment. Then, it sleeps for the set period (S82), and after the sleep, the self-send data is transmitted to the wireless tag reader 100 (S84). This independent transmission data has a configuration as shown in FIG. 27A, for example, and includes data such as a header, a reader ID, a tag ID, a command length, a response code, tag data, and CRC. The reader ID is a unique ID of the wireless tag reader 100 to be communicated, and the tag ID is a unique ID of the wireless tag 400 that independently transmits the data. All of these IDs are stored in the wireless tag 400 in advance. In addition, such independent transmission from the wireless tag 400 is performed by radio waves having a default frequency (reference frequency set in the tag) set in the wireless tag.

  On the other hand, in the direction search communication processing of the wireless tag reader 100 shown in FIG. 25, first, as shown in FIG. 26, the direction of the array antenna 10 is set to all directions to transmit and receive radio waves. When voluntary transmission data as shown in FIG. 27A is received from 400, a command frame including instruction data indicating the response frequency and the number of responses is transmitted (S250).

  This command frame has a structure as shown in FIG. 27B, for example, and includes data such as a header, a reader ID, a tag ID, a command length, a command, a response frequency, the number of responses, and a CRC. The reader ID is a unique ID of the wireless tag reader 100 that transmits the command frame, and the tag ID is a unique ID of the wireless tag 400 that has transmitted the voluntarily transmitted data. The response frequency is specified every time the direction search communication process of FIG. 25 is performed. In the case of the process of S238, for example, the first frequency (channel B) is specified. The number of responses is a preset number corresponding to the number of direction switching of the array antenna 10, and in this embodiment, the array antenna 10 is switched to 12 directions, so the number of responses is designated as “12 times”. Is done. With this configuration, the wireless tag 400 can acquire the response frequency and the number of responses indicated by the command frame regardless of the direction around the array antenna 10.

  On the other hand, when the wireless tag 400 enters the communication area of the wireless tag reader 100 and repeats the processes of S82 to S86 (FIG. 16) and receives the command frame from the wireless tag reader 100 (S86: Yes). 26, after returning an ACK (acknowledgment) as shown in FIG. 26 (not shown in FIG. 16), a response signal (cH-B shown in FIG. 26, number of times 1) is transmitted to the wireless tag reader 100 (S88). At this time, since the wireless tag 400 receives an instruction of the response frequency and the number of responses by the command frame, each time the process of S88 is performed until the response of the specified number of responses is completed, It operates to respond to radio waves of the response frequency indicated by the frame. Specifically, every time a command of S256 (described later) is received from the wireless tag reader 100 (S90: Yes), the process returns to S88 and transmits a response signal of the designated response frequency to the wireless tag reader. On the other hand, when the command from the wireless tag reader 100 is not received, that is, when the response of the designated number of responses is completed (S90: No), the processing of FIG. Note that the process of FIG. 16 is repeated in a short time in the wireless tag 400, for example.

  Here, returning to FIG. 25, the description of the processing after S522 in the wireless tag reader 100 will be continued. The operation on the wireless tag reader 100 side (S252 to S266) after the wireless tag is instructed with the frequency in S250 and the wireless tag 400 can respond at the frequency is basically S38 of the first embodiment. To S52 (FIG. 14).

  After S250, first, the estimated angle θ is set to 0 degree (S252). Then, as described above with reference to FIG. 3, the directivity of the array antenna 10 is switched to the estimated angle θ (S254). Then, a command is sent to the wireless tag 400 and data from the wireless tag is received (S256). When there is reception from the wireless tag (S258: Yes), the received radio wave intensity at the time of data reception is set as the received power Y (θ) measured when the antenna directivity described above is set to the azimuth angle θ. Is set (S260). On the other hand, when there is no reception from the wireless tag (S258: No), a preset minimum value is set as the reception power Y (θ) (S262). Then, the measurement angle θ is increased by 30 degrees (S264), and it is determined whether the measurement angle is 360 degrees or more, that is, the measurement of the received radio wave intensity at all angles from 0 degrees to 330 degrees is completed (S266). Until the measurement is completed (S266: No), the process returns to S254. When the measurement is completed (S266: Yes), the direction search communication process at the frequency is terminated.

Here, returning to FIG. 24, the processing after S238 will be described. After S238, the correlation error is calculated based on the measurement result at S238 (S238). The correlation error calculation process in S238 is the same as that in FIG. 15. First, the estimated angle θ is set to 0 degree (S102), and the error function Γ (θ) is set to 0 degree (S104). First, the azimuth angle α for the antenna directivity corresponding to the characteristic value of the antenna is set to −60 degrees (S106). Then, a correlation value (error) Γ (θ) is obtained using the following equation (S108).
Γ (θ) = Γ (θ) + | Σ (P (α) −Y (θ−α)) × W (θ)) |

Next, the antenna directivity corresponding to the antenna characteristic value is added to the azimuth angle α by 30 degrees (S110). Here, the azimuth angle α is set to 30 degrees, and the azimuth angle α exceeds 60 degrees, that is, It is determined whether the calculation from −60 degrees to 60 degrees is completed (S112). Here, until the calculation to 60 degrees is completed (S112: No), the process returns to S108 and the calculation of the correlation value (error) Γ (θ) is continued. On the other hand, when the calculation up to 60 degrees is completed (S112: Yes), a correlation value (error) Γ (θ) is obtained using the following equation (S114).
Γ (θ) = Γ (θ) × 5 / (Σ (W (θ))

  Then, 30 degrees is added to the estimated angle θ (S116), and it is determined whether the estimated angle is over 330 degrees, that is, the estimation of all angles from 0 degrees to 330 degrees is completed (S118), and the estimation is completed. Until (S118: No), the process returns to S104. When the estimation is completed (S118: Yes), the process is terminated.

  When the process of S240 is completed, the minimum direction of the correlation value error obtained in S240 is stored in the memory as the minimum direction of the correlation value error of the first frequency (channel B).

  After S240, the same direction searching communication process as S238 is performed (S242). The direction search communication process of S242 is different from S238 only in that the response frequency included in the command frame transmitted in S250 is a second frequency (channel C) different from S238, and otherwise is the same as S238. . After S242, a correlation error is calculated based on the measurement result in S242 (S244). Note that the process of S244 is performed in the same manner as in S240.

  When the processing of S244 is completed, the minimum direction of the correlation value error obtained in S244 is stored in the memory as the minimum direction of the correlation value error of the second frequency (channel C). Then, all correlation value errors obtained at both frequencies are compared, and the direction with the lowest correlation value error is output as the direction of the wireless tag.

  In the present embodiment, the control unit 20 that executes the processes of FIGS. 24 and 25 corresponds to an example of “direction estimation unit”, and changes the directivity characteristics of the array antenna 10 for receiving a radio signal from the radio tag 400. The direction of the wireless tag 400 is estimated based on the received power received.

  Further, the control unit 20 and the directivity control unit 50 correspond to an example of “directivity switching means”, and the directivity of the array antenna 10 is sequentially switched in each direction around the array antenna 10 and a predetermined command for instructing the frequency. Specifically, the switching operation for sequentially switching the directivity is performed a plurality of times at different frequencies.

  A radio wave intensity measurement circuit (not shown) provided in the control unit 20 and the reception unit 40 corresponds to an example of “radio wave measurement means”, and receives a response radio wave returned from the wireless tag 400 at a frequency specified by a predetermined command. At the same time, it functions to measure the radio wave intensity of the response radio wave. Specifically, it functions to measure the radio wave intensity of the response radio wave in each direction for each switching operation with different frequencies.

  The control unit 20 corresponds to an example of a “direction detection unit”, and functions to detect the direction of the wireless tag 400 based on the radio field intensity measured by the radio field intensity measurement unit. It functions to detect the direction of the wireless tag 400 based on the radio wave intensity in each direction measured for each frequency by the measuring means.

  In the present embodiment, the memory 22 of the wireless tag reader 100 holds a reference power pattern and set values of weights for each direction of the array antenna 10. Then, the control unit 20 corresponding to the “direction detection means” interpolates the power intensity (reception power measurement value) in each direction obtained by setting the directivity of the array antenna 10 in each direction with the reference power pattern. Thus, the error in each direction is calculated together with the set value of the weight, and the direction that becomes the minimum value of the error is set as the direction of the wireless tag 400.

(Main effects of this embodiment)
The wireless tag reader according to the present embodiment also includes an array antenna 10 configured to be capable of switching directivity to a plurality of set angles, and directivity switching means (the control unit 20 and the control unit 20) to sequentially switch the directivity of the array antenna 10 to a plurality of set angles. A directivity control unit 50), a reception intensity measurement unit (control unit 20) that measures the power intensity received by the array antenna 10, and a directivity switching unit that sets the set angle of the array antenna 10 for one period (for example, 360 degrees). Direction estimation means (control unit 20) for estimating the arrival direction based on the power intensity pattern that is the power intensity for each set angle for one period measured by the reception intensity measurement means when the scanning is switched in the angle range). And a memory 22).
Furthermore, the control unit 20 functions as a “command transmission unit” that transmits a predetermined command that indicates a frequency. Further, the control unit 20 further transmits power of a response radio wave returned from the wireless tag at a frequency specified by the predetermined command. When the strength is measured by the received strength measuring means, it functions as a “direction detecting means” for detecting the arrival direction of the wireless tag based on the measured power strength.
Then, the control unit 20 and directivity control unit 50 corresponding to directivity switching means perform a switching operation for sequentially switching directivity a plurality of times at different frequencies, and the control unit 20 corresponding to reception intensity measurement means has different frequencies. The power intensity of the response radio wave is measured at each set angle for each switching operation. Then, the control unit 20 corresponding to the direction detection unit detects the arrival direction of the wireless tag based on the power intensity at each set angle measured for each frequency by the reception intensity measurement unit.

  When detecting the direction (arrival azimuth) of the wireless tag 400 while switching the directivity of the array antenna 10, in an environment where an obstacle that reflects radio waves exists, in addition to the radio waves directly received from the wireless tag 400, The influence of the reflected radio wave becomes a problem, and when such a plurality of paths (multipath) occur, the direction (arrival direction) of the wireless tag 400 may not be detected accurately. In the present embodiment, in response to such a problem, it is possible to easily generate a reception environment with less influence of multiple paths (multipath) by using a change in reception environment when radio waves of different frequencies are used. The direction of the wireless tag 400 can be detected with higher accuracy based on the radio wave intensity (power intensity) in each direction (each set angle) measured for each frequency.

Also in this embodiment, a pattern storage means (memory 22) that stores a reference power pattern indicating a power intensity pattern that is a reference when radio waves arrive from each arrival azimuth for each arrival azimuth, and each set angle. Weighting setting means (memory 22) for setting weighting setting values in association with each other is provided, and the control unit 20 functioning as direction estimation means has the reference power pattern for each arrival direction and the measured power intensity pattern. The error for each set angle when comparing with each other is obtained by reflecting the weight setting value associated with each set angle, and the direction corresponding to the set angle that minimizes the error is determined as the arrival direction of the wireless tag. It is estimated.
According to this configuration, the same effects as those of the first embodiment can be obtained. In particular, in order to obtain the correlation between the power intensity (received power measurement value) when the directivity of the array antenna 10 is set in each direction using the reference power pattern, and to estimate the direction having the minimum error as the direction of the wireless tag 400 The direction of the wireless tag 400 can be accurately estimated using the array antenna 10 whose directivity is not sharp. Here, a correlation (interpolation) is obtained with the reference power pattern with respect to the power intensity (reception power measurement value), and an error in each direction is set together with a weighting set value for adapting to the actual environment where the array antenna 10 is placed. Therefore, the direction of the wireless tag 400 can be accurately estimated even when an obstacle that reflects radio waves exists.

[First Modification of Fourth Embodiment]
In the fourth embodiment, in the direction search communication process of FIG. 25 performed for each frequency, the received radio wave intensity in each direction is specified once. For example, instead of the determination of S266 at 360 °, 720 ° (2 laps) or 1080 ° (3 laps), etc., and the received radio wave intensity in each direction may be measured a plurality of times. For example, the example of FIG. 28 shows an example of the detection result when the determination of S266 is 1800 ° (5 laps) instead of 360 °, and the measurement result of the received radio wave intensity in each direction is shown in each lap. Has been obtained.

  In this case, after the processing in S238 and S242, the radio wave intensity in each direction may be obtained by statistical processing prior to the correlation error calculation in S240 and S244. Specifically, the average value calculation process (statistical process) for calculating the average value for each direction is performed for the radio field intensity in each direction measured for each frequency, and the average value calculation result (statistics) obtained for each direction is calculated. The processing result) may be the power intensity (reception power measurement value) in each direction. For example, in the direction of the angle 0 °, the radio wave intensity Wa obtained in the first round, the radio wave intensity Wa2 obtained in the second round, the radio wave intensity Wa3 obtained in the third round,... What is necessary is just to obtain | require average value Waave about the obtained WaN, and let this be the electric power intensity | strength (reception power measured value) of an angle 0 degree direction. Alternatively, in the direction of an angle of 240 °, the radio wave intensity Wi1 obtained in the first round, the radio wave intensity Wi2 obtained in the second round, the radio wave intensity Wi3 obtained in the third round,. What is necessary is just to obtain | require average value Wiave about the obtained WiN, and make this into the electric power intensity | strength (reception power measured value) of an angle of 240 degrees.

In this case, the control unit 20 corresponds to an example of a “statistical processing unit”, and the radio wave intensity in each direction measured for each frequency by the radio wave intensity measurement unit is averaged for each direction, and the average obtained for each direction is obtained. It functions so as to make the conversion result the power intensity (reception power measurement value) in each direction. In addition, the control unit 20 corresponding to the direction detection unit functions to detect the direction (arrival direction) of the wireless tag 400 based on the power intensity (reception power measurement value) in each direction obtained by the statistical processing unit. .
According to the first modification of the fourth embodiment, statistical processing can be performed for each set angle to obtain power intensity (reception power measurement value) reflecting a plurality of data, resulting from a single data It becomes easy to use highly reliable power intensity with reduced adverse effects (noise, etc.).

  In the first modified example of the fourth embodiment, as a statistical process for each direction, a process for calculating an average value for each direction with respect to the radio wave intensity obtained for each direction is illustrated, and the average value is represented by the power intensity ( However, the present invention is not limited to such an example. For example, statistical processing may be performed in which the median or mode of the radio field intensity obtained for each direction is used as the power intensity in each direction, or other known statistical processing for determining a representative value of the set may be used. .

[Second Modification of Fourth Embodiment]
In the fourth embodiment, the correlation value error is calculated independently for each frequency based on the measurement result obtained when each frequency is set, and the direction of the set angle that minimizes the correlation value error is determined by the wireless tag. The direction (arrival direction) is used, but statistical processing is performed for each direction based on the measurement results for all frequencies, and the correlation value error is obtained using the statistical processing results for each direction as the received power measurement value for each direction. It may be. For example, average value calculation processing (statistical processing) for calculating the average value for each direction is performed for the radio field intensity measurement results in all directions at all frequencies, and the average value calculation result (statistical processing result) obtained for each direction May be used as the received power measurement value in each direction. In this case, the RFID tag direction may be determined in the same manner as in the first embodiment based on the obtained received power measurement value in each direction (see S100 and S54 in FIG. 14).

[Fifth Embodiment]
Next, a fifth embodiment will be described.
Note that the fifth embodiment is the same as the first embodiment except for the environment in which the wireless tag reader is arranged and the setting method of the weighting in the representative example and any modified examples, except for the first embodiment. Therefore, the same parts as those of the first embodiment are denoted by the same reference numerals as those of the first embodiment, and detailed description thereof is omitted. The same configuration as that of the first embodiment will be described with reference to FIGS. 1 to 18 as appropriate.
(Representative example)
FIG. 29A is an explanatory diagram illustrating an example in which the wireless tag reader according to the fifth embodiment is provided in an environment surrounded by an adjacent wall and a shielding wall, and the direction of the wireless tag is estimated by the wireless tag reader. FIG. 29B is an explanatory diagram illustrating the direction of a direct radio wave transmitted from a wireless tag entering from the open space side and the direction of a reflected wave when the radio wave is reflected by a shielding wall. FIG. 30A is a graph showing an estimation result when the direction is estimated by the maximum power method in the environment of FIG. 29, and FIG. 30B sets weighting for each direction in the environment of FIG. FIG. 30C is a graph showing an estimation result when the direction is estimated by the power correlation pattern method without using the power correlation pattern method, and FIG. It is a graph which shows the estimation result at the time of estimating.

  The wireless tag reader 100 according to the fifth embodiment also includes the array antenna 10 configured to be able to receive a wireless signal from the wireless tag 400 and configured to be able to switch the directivity to a plurality of directions (set angles). Similarly to the first embodiment, the control unit 20 and the directivity control unit 50 shown in FIG. 2 constitute a “directivity switching unit”, which makes it possible to perform an array in the same manner as in the first embodiment. The directivity of the antenna 10 is switched to a plurality of directions (set angles) around the array antenna 10. In the following description, as in the first embodiment, the configuration in which the directivity of the array antenna 10 is switched to 12 steps every 30 ° is exemplified, but the angle width is made smaller than this to increase the number of steps. Alternatively, the angle width may be increased to reduce the number of steps.

  Also in this embodiment, the “direction estimation means” is configured by the control unit 20, the memory 22, and the directivity control unit 50 shown in FIG. 2, and the directivity of the array antenna 10 is switched to each direction (set angle). The error between the measurement pattern obtained by each power intensity and the reference power pattern determined for each arrival direction (each set angle) is set for each direction (for each set angle). Each weighted set value is reflected and the direction in which the error is minimized is estimated as the direction of the wireless tag.

  Also in this embodiment, the memory 22 corresponds to an example of a pattern storage unit, and functions to store a reference power pattern determined corresponding to each direction in which the directivity of the array antenna 10 can be switched. The control unit 20 and the memory 22 correspond to an example of a weight setting unit, and function to set weight setting values for each direction (each set angle) of the array antenna 10.

Next, features of this embodiment will be described in detail.
As shown in FIG. 29A, in the RFID tag reader 100 according to the present embodiment, the array antenna 10 is arranged in the passage space AR so that the passage space AR partially surrounded by the installation object becomes a communication area. Has been. Specifically, the shielding wall is surrounded by a predetermined adjacent wall H made of an outer wall of a house and the shielding wall Ma extending in a direction intersecting the adjacent wall H (a direction orthogonal to FIG. 29A). The passage space AR is configured so that the side facing Ma is open, and the array antenna 10 is disposed at a position near the adjacent wall H in the passage space AR. In the wireless tag reader 100, the communication area from the array antenna 10 is set so that the position of the shielding wall Ma is included in the communication area (area where communication with the array antenna 10 is possible). The shielding wall Ma is an object that can reflect radio waves, and corresponds to, for example, a wall part or door part mainly made of a metal material, or a wall part mainly made of concrete or ceramic containing a reinforcing bar.

  In the above configuration, as shown in FIG. 29B, when the wireless tag 400 enters from the side facing the shielding wall Ma (open space side) (that is, the person who owns the wireless tag 400 is from the open space side). When entering, not only the direct radio wave from the wireless tag 400 (see reference numeral F1) but also the reflected wave (see reference numeral F2) reflected by the shielding wall Ma enters the array antenna 10. Become. Therefore, in this embodiment, weighting is set so as to suppress the influence of such a reflected wave so that the direction of the reflected wave is not estimated as the direction (arrival azimuth) of the wireless tag.

  In the array antenna 10, a predetermined reference direction is set as a reference set angle (angle 0 °), and an angle range where the shielding wall Ma is present is weighted based on this direction (reference set angle) by weighting other than the angle range. Is set too low. In FIG. 29, the direction orthogonal to the wall surface of the adjacent wall H and toward the adjacent wall H is set as a reference setting angle (angle 0 °), and the angle increases by 240 ° counterclockwise from the reference setting angle. The shielding wall Ma is arranged between the direction (set angle of 240 °) at the time when the angle is increased and the direction (set angle of 270 °) when the angle is increased by 270 ° from the reference direction (reference set angle). . The weighting of this angular range (240 ° to 270 °) is set lower than the weighting of the angular range (approximately 90 ° to less than 240 °) that is not surrounded by the installation object. Further, the weighting of the angle range (240 ° to 270 ° range) of the shielding wall Ma is more than the weighting of the angle range (range of 0 ° to approximately 90 ° or more than 270 °) surrounded by the adjacent wall H. It is set low. Then, after determining the weight for each angle in this way, the error (correlation value) is calculated by the same method as in the first embodiment, and the direction (arrival direction) of the wireless tag 400 is estimated. .

  For example, as a setting example of weighting in the configuration as shown in FIG. 29, the weight of the angle range (240 ° or more and 270 ° or less) of the shielding wall Ma is set to 0.5, and the other angle range (0 °). The weight in the range of less than 240 ° or in the range of more than 270 ° and less than 360 °) can be set to 1.0.

  30 (A) to 30 (C) show experimental results when the direction (arrival azimuth) is estimated by performing weighting in this way in comparison with the experimental results of other methods. In the environment of FIG. 29, the direction estimation result (direction estimated at each time) every short time when the direction (arrival azimuth) of the wireless tag 400 changes as shown by a solid line with the passage of time. Show. Among these, FIG. 30A shows a direction estimation result (experimental result) by a method (maximum power method) in which a direction (set angle) in which received power is maximized each time is estimated as a tag direction. FIG. 30B shows a direction estimation result (experimental result) in the case where the direction (arrival direction) is estimated by the same method as in the first embodiment with all weights being uniform (1.0) in the environment of FIG. FIG. 30C shows the above-described weighting (weighting in the range of 240 ° to 270 ° is set to 0.5 and other weights are set to 1.0). Above, the experimental result at the time of estimating a direction (arrival azimuth | direction) with the method similar to 1st Embodiment is shown.

  As is apparent from the comparison of the graph of FIG. 30C with FIGS. 30A and 30B, the above weighting is performed on the direction (set angle) of the shielding wall Ma to estimate each time. The number of times that the direction to match or approximate the actual direction of the wireless tag 40 (the actual position of the wireless tag indicated by the solid line) is significantly increased, and noise that estimates the direction of the reflected wave as the tag direction is significantly increased. Less. Therefore, not only when compared with the estimation result by the maximum power method, but also when the comparison is made with the estimation result estimated by the power correlation pattern method without weighting (see FIG. 30B), the reflected wave is erroneously detected. Can be difficult.

  Also in this embodiment, the control unit 20 and the memory 22 correspond to an example of a setting unit, and among the directions (each set angle) in which the directivity of the array antenna 10 can be switched by the “directivity switching unit”, The weighting in the direction from the array antenna 10 toward the shielding wall Ma is set smaller than the weighting in the direction toward the open space formed on the side facing the shielding wall Ma.

As a weighting setting method, for example, when the user inputs weighting data for each direction (each set angle) using an operation unit (not shown), the control unit 20 stores this data in the memory 22. A simple setting method may be used. Alternatively, a laser sensor 200 that scans a laser beam in the horizontal direction is disposed on a position close to the lower portion of the wireless tag reader 100 so as to be on substantially the same axis, and a range other than the adjacent wall H is formed by the laser sensor 200. You may make it obtain | require the direction of the shielding wall Ma with respect to a reference direction as a detection area. In this case, the wireless tag reader 100 is configured to acquire data on the direction (angle range) of the shielding wall Ma detected by the laser sensor 200, and the wireless tag reader 100 is configured to obtain the direction (angle) of the shielding wall Ma based on the acquired data. The weight may be automatically set and stored so that the weight of (range) is lower than the other directions.
At this time, since the wireless tag reader and the laser sensor are on substantially the same axis, the angle of the laser sensor and the angle of the wireless tag reader substantially coincide.

(Modification 1)
Next, a first modification in which a part of the configuration in FIG.
FIG. 31 is an explanatory diagram illustrating an example in which the direction of the wireless tag is estimated by a wireless tag reader provided in an environment different from that in FIG. FIG. 32A is a graph showing an estimation result when the direction is estimated by the power correlation pattern method without setting the weighting for each direction in the environment of FIG. 31, and FIG. 6 is a graph showing an estimation result when a direction is estimated by the same power correlation pattern method as that of the first embodiment after weighting is set for each direction in the environment of FIG.

  As shown in FIG. 31, also in the RFID tag reader 100 according to the first modification, the array antenna 10 is arranged in the passage space AR so that the passage space AR partially surrounded by the installation object becomes a communication area. . Specifically, it is surrounded by a predetermined adjacent wall H composed of an outer wall of a house and the like and a shielding wall Ma extending in a direction intersecting the adjacent wall H (a direction orthogonal to FIG. 31), and is opposed to the shielding wall Ma. The passage space AR is configured so that the side to be opened is open, and the array antenna 10 is disposed at a position near the adjacent wall H in the passage space AR. Also in this wireless tag reader 100, the communication area from the array antenna 10 is set so that the position of the shielding wall Ma is included in the communication area (area where communication with the array antenna 10 is possible). The shielding wall Ma used in the configuration of FIG. 31 is the same as that of FIG. 29 in terms of material, and only the length is different from the example of FIG.

  In the example of FIG. 31 as well, the direction perpendicular to the wall surface of the adjacent wall H and toward the adjacent wall H is set as the reference setting angle (angle 0 °), and counterclockwise from this reference setting angle (reference direction). The shielding wall Ma is arranged between the direction when the angle is increased by 220 ° (set angle of 220 °) and the direction when the angle is increased by 270 ° from the reference direction (set angle of 270 °). ing. In the wireless tag reader 100 of FIG. 31, the weighting of this angular range (220 ° to 270 °) is more than the weighting of the angular range (approximately 90 ° to less than 220 °) that is not surrounded by the installation. It is set low. Further, the weighting of the angle range (the range of 220 ° to 270 °) of the shielding wall Ma is greater than the weighting of the angle range (the range of 0 ° to approximately 90 ° or a range exceeding 270 °) surrounded by the adjacent wall H. It is set low. Then, after determining the weight for each angle in this way, the error (correlation value) is calculated by the same method as in the first embodiment, and the direction (arrival direction) of the wireless tag 400 is estimated. .

  In the configuration as shown in FIG. 31, for example, the weight of the angle range (the range of 220 ° or more and 270 ° or less) of the shielding wall Ma is set to 0.5, and the other angle range (0 ° or more and 220 °). Less than a range of less than or less than 360 ° and less than 360 °).

  32 (A) and 32 (B) show the experimental results when the direction is estimated by performing weighting in this way in comparison with the experimental results of other methods. The direction estimation result (direction estimated at each time) for each short time when the direction (arrival azimuth) of the wireless tag 400 changes as shown by a solid line as time passes is shown. Among these, FIG. 32A shows the direction estimation result (experimental result) when the direction is estimated by the same method as in the first embodiment with all the weights being uniform (1.0) in the environment of FIG. In FIG. 32B, the above weighting (weighting in the range of 220 ° or more and 270 ° or less is set to 0.5 and the other weights are set to 1.0) is performed. The experimental result at the time of estimating a direction with the method similar to 1 embodiment is shown.

  As apparent from the comparison of the graph of FIG. 32B with FIG. 32A, the above weighting is performed on the direction of the shielding wall Ma in the environment of FIG. The number of times that the direction matches or approximates the actual direction of the wireless tag 40 (the actual position of the wireless tag indicated by the solid line) is remarkably increased, and there is significantly less noise that estimates the direction of the reflected wave as the tag direction. Become. Accordingly, it is possible to make it difficult to erroneously detect a reflected wave even when compared with an estimation result (see FIG. 31A) estimated by the power correlation pattern method without weighting.

(Modification 2)
Next, a second modified example in which a part of the configuration of FIGS. 29 and 31 is changed will be described.
FIG. 33 is an explanatory diagram illustrating an example in which the direction of the wireless tag is estimated using a wireless tag reader provided in an environment different from that in FIGS. 29 and 31. FIG. 34A is a graph showing an estimation result when the direction is estimated by the power correlation pattern method without setting the weighting for each direction in the environment of FIG. 33, and FIG. 32B is the graph of FIG. 6 is a graph showing an estimation result when a direction is estimated by the same power correlation pattern method as that of the first embodiment after weighting is set for each direction in the environment of FIG.

  As shown in FIG. 33, also in the wireless tag reader 100 according to the modification example 2, the array antenna 10 is arranged in the passage space AR so that the passage space AR partially surrounded by the installation object becomes a communication area. . Specifically, it is surrounded by a predetermined adjacent wall H composed of an outer wall of a house and the like and a shielding wall Ma extending in a direction intersecting with the adjacent wall H (a direction orthogonal to FIG. 33) and is opposed to the shielding wall Ma. The passage space AR is configured so that the side to be opened is open, and the array antenna 10 is disposed at a position near the adjacent wall H in the passage space AR. Also in this wireless tag reader 100, the communication area from the array antenna 10 is set so that the position of the shielding wall Ma is included in the communication area (area where communication with the array antenna 10 is possible). Note that the shielding wall Ma used in the configuration of FIG. 33 is the same as that of FIG. 29 in terms of material, and only the length is different from the example of FIG.

  In the example of FIG. 33 as well, the direction perpendicular to the wall surface of the adjacent wall H and toward the adjacent wall H side is set as the reference setting angle (angle 0 °), and counterclockwise from this reference setting angle (reference direction). The shielding wall Ma is disposed between the direction when the angle is increased by 200 ° (the set angle of 200 °) and the direction when the angle is increased by 270 ° from the reference direction (the set angle of 270 °). ing. In the wireless tag reader 100 of FIG. 31, the weighting of this angle range (200 ° to 270 ° range) is more than the weighting of the angle range (approximately 90 ° to less than 220 °) not surrounded by the installation object. It is set low. Further, the weighting of the angle range (the range of 220 ° to 270 °) of the shielding wall Ma is greater than the weighting of the angle range (the range of 0 ° to approximately 90 ° or a range exceeding 270 °) surrounded by the adjacent wall H. It is set low. Then, after determining the weight for each angle in this way, the error (correlation value) is calculated by the same method as in the first embodiment, and the direction (arrival direction) of the wireless tag 400 is estimated. .

  33, for example, the weight of the angle range (range of 200 ° to 270 °) of the shielding wall Ma is set to 0.5, and the other angle range (0 ° to 220 °). Less than a range of less than or less than 360 ° and less than 360 °).

  34 (A) and 34 (B) show experimental results when the direction (arrival direction) is estimated by weighting in this way in comparison with the experimental results of other methods. In 33 environments, the direction estimation result (direction estimated at each time) for every short time (every time) when the direction of the wireless tag 400 changes as shown by a solid line in accordance with the passage of time is shown. Among these, FIG. 34A shows the direction estimation result (experimental result) when the direction is estimated by the same method as in the first embodiment with all the weights being uniform (1.0) in the environment of FIG. In FIG. 34B, the above weighting (weighting in the range of 200 ° or more and 270 ° or less is set to 0.5 and the other weights are set to 1.0) is performed. The experimental result at the time of estimating a direction with the method similar to 1 embodiment is shown.

  As is apparent from the comparison of the graph of FIG. 34B with FIG. 34A, the above-described weighting is performed on the direction of the shielding wall Ma in the environment of FIG. The number of times that the direction matches or approximates the actual direction of the wireless tag 40 (the actual position of the wireless tag indicated by the solid line) is remarkably increased, and there is significantly less noise that estimates the direction of the reflected wave as the tag direction. Become. Therefore, it is possible to make it difficult to erroneously detect a reflected wave even when compared with an estimation result (see FIG. 34A) estimated by the power correlation pattern method without weighting.

(Experimental result when weighting is changed)
FIG. 35 is a graph showing the relationship between the weight of the direction of the shielding wall, the average error, and the abnormal value appearance rate when the direction is estimated by the power correlation pattern method similar to the first embodiment in the environment of FIG. . FIG. 36 is a graph showing the relationship between the weight of the direction of the shielding wall, the average error, and the abnormal value appearance rate when the direction is estimated by the same power correlation pattern method as in the first embodiment in the environment of FIG. . FIG. 37 is a graph showing the relationship between the weight of the shielding wall direction, the average error, and the abnormal value appearance rate when the direction is estimated by the same power correlation pattern method as in the first embodiment in the environment of FIG. .

  FIG. 35 is a result of calculating the average error and the abnormal value appearance rate for the experimental results obtained by each weighting based on the experimental results when the weighting in the direction of the shielding wall is various values in the environment of FIG. Is shown. In this example, the weighting is changed by 0.1 from 0 to 1.0, and the average error and the abnormal value in each experiment result when the experiment result similar to FIG. It shows the appearance rate.

  The “average error” is the value obtained by averaging the errors obtained over the entire period (all times) by calculating the error between the estimated direction and the actual position for each time the data was collected. is there. For example, when the weight is 0.5, the estimated direction and the actual direction (actual of the wireless tag) at each time (each time for estimating the direction (arrival direction)) based on the experimental result as shown in FIG. The average value of these errors obtained in all periods (all times) is defined as “average error when weighting is 0.5”. In the experimental result of FIG. 30C, the direction (arrival azimuth) estimated at the Mth time is Fm, and the direction (arrival azimuth) estimated at the Nth time is Fn. The error between the estimated direction (Fm) at the Mth time and the actual position is denoted by Am, and the error between the estimated direction (Fn) at the Nth time and the actual position is denoted by An. The “average error” is a value obtained by adding all the values such as Am and An and dividing by the total number of times.

  In addition, the “abnormal value appearance rate” is the time when the error is 90 ° or more when the error between the estimated direction and the actual position is obtained every time the data is collected. This indicates the rate of appearance in (all times). For example, when the weight is 0.5, the estimated direction and the actual direction (actual position of the wireless tag) are determined at each time (each time for estimating the direction) based on the experimental result as shown in FIG. And the number of times that the error is 90 ° or more is obtained, and the ratio of the number of times (the number of times that the error is 90 ° or more) to the period (total number of times) is “weighting 0.5. The abnormal value appearance rate ”. In FIG. 30C, for example, the M-th error Am exceeds 90 °, and the number of times that the estimated direction has such a result is counted, and the abnormal value appearance rate is obtained by dividing by the total number of times. it can.

  When the experiment is performed by setting the weighting of the direction of the shielding wall Ma to each value in the environment of FIG. 29, the weighting of the direction of the shielding wall Ma is set to the weight of the other direction (1.0) as shown in FIG. It has been found that both the average error and the abnormal value appearance rate can be reduced when the value is lower than that. In particular, it has been found that when the weight in the direction of the shielding wall Ma is set to 0% to 80% of the weight (1.0) in the other direction, the average error and the abnormal value appearance rate are significantly reduced.

  Also, in FIG. 36, based on the experimental results when the weighting in the direction of the shielding wall Ma is various values in the environment of FIG. The calculated result is shown. Also in this example, the average error and the abnormal value appearance rate in each experimental result when the weighting is changed by 0.1 from 0 to 1.0 and the same experimental result as in FIG. Is shown. Note that the method of obtaining the average error and the abnormal value appearance rate at the time of each weighting is the same as in FIG. 35. For example, when the weighting is 0.5, based on the experimental results as shown in FIG. The error between the estimated direction and the actual direction (actual position of the wireless tag) is obtained each time (each time for estimating the direction), and the average value of these errors obtained over the entire period (all times) is weighted. Average error at 0.5 ”. When the weight is 0.5, the estimated direction and the actual direction (actual position of the wireless tag) are determined at each time (each time for estimating the direction) based on the experimental result as shown in FIG. The ratio of “the number of times when the error is 90 ° or more” in the entire period (the total number of times) is obtained as “the abnormal value appearance rate when weighting is 0.5”.

  As is apparent from the experimental results of FIG. 36, even in the configuration as shown in FIG. 31, when the weight in the direction of the shielding wall Ma is made lower than the weight in the other direction (1.0), the average error and abnormal value appearance rate. It has been found that both can be reduced. In particular, it has been found that when the weight in the direction of the shielding wall Ma is set to 0% to 80% of the weight (1.0) in the other direction, the average error and the abnormal value appearance rate are significantly reduced.

  Also, in FIG. 37, based on the experimental results when the weighting in the direction of the shielding wall Ma is various values in the environment of FIG. 33, the average error and the abnormal value appearance rate for the experimental results obtained by each weighting are shown. The calculated result is shown. Also in this example, the average error and the abnormal value appearance rate in each experimental result when the weighting is changed by 0.1 from 0 to 1.0 and the same experimental result as in FIG. Is shown. Note that the method of obtaining the average error and the abnormal value appearance rate at the time of each weighting is the same as in FIG. 35. For example, when the weighting is 0.5, based on the experimental results as shown in FIG. The error between the estimated direction and the actual direction (actual position of the wireless tag) is obtained each time (each time for estimating the direction), and the average value of these errors obtained over the entire period (all times) is weighted. Average error at 0.5 ”. When the weight is 0.5, the estimated direction and the actual direction (actual position of the wireless tag) are determined every time (each time for estimating the direction) based on the experimental result as shown in FIG. The ratio of “the number of times when the error is 90 ° or more” in the entire period (the total number of times) is obtained as “the abnormal value appearance rate when weighting is 0.5”.

  As is apparent from the experimental results of FIG. 37, even in the configuration of FIG. 33, when the weight in the direction of the shielding wall Ma is made lower than the weight in the other direction (1.0), the average error and the abnormal value appear. It has been found that both rates can be reduced. In particular, it has been found that when the weight in the direction of the shielding wall Ma is set to 0% to 80% of the weight (1.0) in the other direction, the average error and the abnormal value appearance rate are significantly reduced.

(About correction method by weighting)
FIG. 38 shows an actual measurement pattern in the case where the wireless tag exists in the direction of 135 ° in the environment as shown in FIG. 29A, a reference pattern prepared for 135 °, and these measurement pattern and reference pattern. The result of having calculated | required the error for every angle at the time of contrasting with is shown. The error shown in FIG. 38 is not weighted for each angle. In the present embodiment, when weighting is performed so that the weight of the angle at which the shielding wall Ma exists is lower than the weight of the other angles, the corresponding error is obtained for each error obtained for each angle as described above. A method can be used in which weighting is multiplied and the sum of the multiplication results (multiplication values) obtained for each angle is used as the final matching error (correlation value). In this way, as indicated by the arrow in FIG. 38A, the error in the angle range in which the weight is set low can be further reduced. Therefore, compared with the case where no weighting correction is performed, a matching error (correlation value) when the measurement pattern is compared with an appropriate reference pattern (that is, a reference pattern in a direction close to the direction of the actual wireless tag) is extremely small. It can be made smaller and it becomes easier to grasp the actual angle. The graph of FIG. 38B shows the effect when the matching error (correlation value) is obtained by such a method, and when the measurement pattern as shown in FIG. 38A is obtained. The experiment results when the matching error (correlation value) is obtained by the above-described method in comparison with the reference patterns prepared for each angle are shown. In this graph, Pc represents the case where the weight of the range of the shielding wall Ma is 0.5, Pd represents the case where the weight of the range of the shielding wall Ma is 0, and Pe represents the case where no weight is applied. The matching error when Pc when the weight is 0.5 and Pd when the weight is 0 is compared with the reference pattern corresponding to the actual angle (135 °) has the smallest error. The angle change of the matching error near the angle is steep. The sharp change in angle indicates that it is difficult to make an erroneous determination in the wrong direction, and it is easy to obtain the actual direction.

  Note that FIG. 39 is a comparison with the above method. FIG. 39A shows an actual measurement pattern in the case where the wireless tag exists in the direction of 135 ° in the environment as shown in FIG. 29A, with respect to the measurement value at each angle (power intensity for each angle). The case of multiplying the corresponding angle weights is shown. For example, when the range of the shielding wall Ma is 240 ° to 270 ° and only the weight of this range is lower than the other ranges, correction is made so as to reduce the measurement value of this range. In FIG. 39B, with respect to the measurement pattern obtained as shown in FIG. 39A, when the correction amount of the range of the shielding wall Ma is −3 dB (that is, in the measurement pattern, the range of 240 ° to 270 °). Pf is a case where a matching error is calculated after correcting the measured value by -3 dB), Pg is a case where the correction amount of the range of the shielding wall Ma is -6 dB, and Ph is a case where the above correction is not performed. ing. Even in this case, the actual position (135 °) can be detected by increasing the correction amount to some extent. However, since the angle change of the matching error near the actual angle (135 °) is steeper in the method of FIG. 38B, the actual direction is detected by using the method described in FIG. It becomes easy to do.

(Main effects of this embodiment)
In this configuration, when the wireless tag 400 is detected in the passage space AR surrounded by the adjacent wall H and the shielding wall Ma, in particular, the owner of the wireless tag 400 is opposite to the shielding wall Ma (open space side). When approaching the array antenna 10 side from the antenna, the weight of the reflected wave generated by the reflection of the radio wave of the radio tag 400 by the shielding wall is made relatively small, and the weight of the direct radio wave from the radio tag 400 is made relatively The error between the actually measured measurement pattern and the reference power pattern in each direction can be calculated. Therefore, when the holder of the wireless tag 400 tries to approach the array antenna side from the opposite side of the shielding wall Ma, the reference power pattern corresponding to the direction of the reflected wave (that is, the direction of the shielding wall Ma) and the actually measured measurement pattern In such a case, it is difficult to cause a situation in which the error is reduced, and a large angle error such as estimating the shielding wall side completely different from the normal tag direction as the tag direction is less likely to occur.

(Other embodiments)
In 5th Embodiment, although the adjacent wall H and the shielding wall Ma were provided as an installation object, and the weight of the direction of at least the shielding wall Ma was set lower than the other directions, it showed only the direction of the shielding wall Ma. Alternatively, the error calculation and the direction estimation similar to those in the first and fifth embodiments may be performed after setting the weight of the direction of the adjacent wall H to be low.

  In the fifth embodiment, an example in which the adjacent wall H and the shielding wall Ma are provided as the installation object has been described. However, as illustrated in FIG. 40, there is a wall portion (opposing wall Mb) that faces the adjacent wall Ma. A wireless tag reader may be used in such an environment. FIG. 40 shows an example in which an adjacent wall H, a shielding wall Ma, and an opposing wall Mb (a wall portion facing the adjacent wall H) are provided so as to surround the passage space AR. When used in such an environment, not only the weighting of the direction of the shielding wall Ma (in FIG. 40, the set angle of 240 ° to 270 °), but also the direction of the opposing wall Mb (160 ° to 180 ° in FIG. 40). The weighting of the setting angle) is set lower than the weighting of the direction other than these installations (that is, the direction other than the direction of the shielding wall Ma and the adjacent wall Mb), and the same error calculation as in the first and fifth embodiments is performed. Direction estimation may be performed. As a result, not only the reflected light in the direction of the shielding wall Ma but also the reflected light in the direction of the opposing wall Mb is difficult to be erroneously detected. In this case, the weight of the direction of the shielding wall Ma (in FIG. 40, the set angle of 240 ° to 270 °) is lower than the weight of the direction of the adjacent wall (set angle) and the direction of the opposite wall (set angle). It is desirable to set.

DESCRIPTION OF SYMBOLS 10 Array antenna 10-0 Excitation element 10-1 to 10-6 Non-excitation element 12-1 to 12-6 Variable reactance circuit 20 Control part (Direction estimation means, directivity switching means, reception intensity measurement means, weight setting means, Command transmission means, set value adjustment means)
22 Memory (Direction estimation means, pattern storage means, weight setting means)
50 Directivity control unit (directivity switching means)
52 Reactance Value Control Device 100 Wireless Tag Reader 200 Laser Sensor 300 Controller 400 Wireless Tag H1 Adjacent Wall (Installation)
Ma Shielding wall (installed object)
AR passage space

Claims (11)

A wireless tag reader that receives radio waves of a wireless tag and estimates the arrival direction thereof,
An array antenna configured to switch directivity to a plurality of setting angles;
Directivity switching means for sequentially switching the directivity of the array antenna to a plurality of set angles;
Reception intensity measuring means for measuring the power intensity received by the array antenna;
When the directivity switching means switches and scans the set angle of the array antenna for one period, it arrives based on the power intensity pattern that is the power intensity for each set angle for one period measured by the reception intensity measuring means. A direction estimating means for estimating a bearing;
With
The direction estimating means includes
Pattern storage means for storing a reference power pattern indicating a power intensity pattern as a reference when radio waves arrive from each arrival direction, for each arrival direction;
The weight setting value is set in association with each set angle, and the set angle weight of the obstacle that reflects the radio wave with respect to the array antenna is smaller than the weight of the other predetermined set angle and 0 A weight setting means for setting a larger value ;
With
An error for each set angle when the reference power pattern for each direction of arrival is compared with the measured power intensity pattern is obtained by reflecting the set value of the weight associated with each set angle, and the error A wireless tag reader characterized by estimating an azimuth corresponding to a set angle at which is minimum as an arrival azimuth of the wireless tag. The array antenna includes one excitation element, a plurality of non-excitation elements provided at a predetermined interval from the excitation element, and variable reactance elements respectively connected to the plurality of non-excitation elements, By changing the reactance value of the element, the directivity setting angle can be switched every 360 degrees / N (where N is a natural number).
The weighting setting value set by the weighting setting means is set every 360 degrees / N degrees, and is a value that correlates with the angle at which an obstacle that reflects radio waves with respect to the array antenna exists. The wireless tag reader according to claim 1, wherein: The weighting setting value set by the weighting setting means is set to 1 for the predetermined setting angle, and the setting angle of the obstacle that reflects the radio wave to the array antenna is set to transmit the radio wave to the array antenna. 3. The radio according to claim 2 , wherein the distance to the array antenna of the obstacle to be reflected or a value correlated with at least one of the materials of the obstacle is set to be larger than 0 and smaller than 1. 5. Tag reader. In order to obtain the minimum value of the error, the direction estimation means uses a specific error value for the error function with the horizontal axis interpolating the error value of each set angle as the angle and the vertical axis as the error value, and the error A line parallel to the horizontal axis is drawn with respect to the function, and the angle at the half position of the line segment connecting the intersection of the line and the error function is estimated as the arrival direction of the wireless tag that is the minimum value of the error. The wireless tag reader according to any one of claims 1 to 3 . The set angle for measuring the power intensity is every 360 degrees / N,
The specific error value is a value on a lower error side among two values separated by a setting angle of 360 degrees / N from a minimum error peak of the error function. Item 5. The wireless tag reader according to Item 4 . In order to obtain the minimum value of the error, the direction estimating means calculates a peak value that minimizes the error with respect to an error function in which the horizontal axis obtained by interpolating the error value of each set angle is the angle and the vertical axis is the error value. Extend the line connecting the value with the smaller error and the value with the smaller error next to the adjacent value on the opposite side of the larger error. The line segment connecting the value with the larger error and the adjacent value to the person with the larger error is extended, and the intersection of both line segments is the arrival direction of the wireless tag that is the minimum value of the error wireless tag reader according to any one of claims 1-3, characterized in that the presumed. When the array antenna is partially surrounded by an installation object and disposed in a space that is open outside the area of the installation object,
In the weight setting means, among the setting angles at which the directivity of the array antenna can be switched by the directivity switching means, the weight of the setting angle from the array antenna toward the installation is outside the area of the installation. wireless tag reader according to any one of claims 1-6, characterized in that it is set smaller than the weight of the set angle towards the open space. When the array antenna is disposed closer to the adjacent wall in a space surrounded by a predetermined adjacent wall and an opposing wall facing the adjacent wall,
In the weight setting means, among the setting angles at which the directivity of the array antenna can be switched by the directivity switching means, the setting angle toward the adjacent wall from the array antenna or the setting angle toward the opposite wall is weighted. , said adjacent wall and the wireless tag reader according to any one of claims 1-7, characterized in that said opposing wall is smaller than the weight of the set angle towards the open space that is not disposed. When the array antenna is disposed close to the adjacent wall in a space surrounded by a predetermined adjacent wall and a shielding wall extending in a direction intersecting the adjacent wall,
In the weight setting means, among the setting angles at which the directivity of the array antenna can be switched by the directivity switching means, the setting angle from the array antenna toward the adjacent wall or the setting angle toward the shielding wall is weighted. , wireless tag reader according to any one of claims 1-7, characterized in that it is set smaller than the weight of the set angle towards the open space formed on the side opposite to the shield wall. When the array antenna is disposed near the adjacent wall in a space surrounded by a predetermined adjacent wall, an opposing wall facing the adjacent wall, and a shielding wall extending in a direction intersecting the adjacent wall In addition,
In the weighting setting means, the setting angle weighting from the array antenna toward the shielding wall among the setting angles capable of switching the directivity of the array antenna by the directivity switching means is a side facing the shielding wall. set angle towards the configured open space, the setting angle toward the adjacent wall, and any one of claims 1-7, characterized in that the is smaller than the weighting of the set angle towards the opposing wall The wireless tag reader according to Item. A monitoring system using the wireless tag reader according to any one of claims 1 to 10 ,
A laser sensor for measuring the distance and direction of an object in the monitoring area;
A monitoring system comprising weighted set value adjusting means for adjusting the weighted set value according to the distance and direction of an object detected by a laser sensor.

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