JP7253443B2 - tag reading system - Google Patents

Description

The present disclosure relates to technology for reading RF tags attached to articles conveyed along a predetermined conveying path.

2. Description of the Related Art There is known a tag reading system that reads information on an RF tag attached to each article using a reader/writer provided in a conveying route for conveying the article. RF is an abbreviation for Radio Frequency.

Patent Literature 1 discloses a technique of using a plurality of highly directional antennas and changing the directivity of the antennas in the vertical direction in order to improve the tag reading rate.

Japanese Unexamined Patent Application Publication No. 2006-20083

However, in the conventional technology described in Patent Document 1, since beam scanning is performed in the vertical direction, it is possible to read a wide range in the height direction, but the beam width in the transport direction is narrow, and the RF tag is within the beam. The reading rate could not be improved because the time to stay at was short.

In addition, it is conceivable to improve the reading rate by setting the beam width of the transmitting/receiving antennas so as to expand along the transport direction, thereby increasing the time that each RF tag stays within the beam of one antenna. However, in this case, there is a problem that the possibility of erroneously reading the surrounding tags that do not need to be read increases.

An object of the present disclosure is to provide a technique for improving reading performance of RF tags attached to articles moving along a transport path.

One aspect of the present disclosure is a tag reading system, which may include a position detection section, a directivity variable antenna, a tag reading section, and a control section. The position detection unit detects the position of the article within the work section set on the conveying route for conveying the article. The directivity variable antenna emits radio waves toward the work section. The tag reader reads information from the RF tag attached to the article via the variable directivity antenna. The controller changes the direction of the beam of the variable directivity antenna along the transport path according to the position of the article detected by the position detector. In addition, the controller changes the transmission/reception conditions of the tag reader so that the closer the direction of the beam is to the entrance/exit of the work section, the lower the erroneous reading rate of the tag reader.

According to such a configuration, since the direction of the beam of the variable directivity antenna is changed according to the position of the article within the work zone, the length of time that the RF tag attached to the article stays within the beam, that is, the RF tag more time available for reading. As a result, the reading rate of the RF tag by the tag reading section can be improved.

In addition, since the transmission/reception conditions of the tag reader are changed so that the tag reading error rate decreases as the beam direction is closer to the entrance/exit of the work zone, it is possible to prevent erroneous reading of information on RF tags existing outside the work zone. can be suppressed.

In one aspect of the present disclosure, the transmission/reception conditions may include at least transmission power supplied by the tag reader to the variable directivity antenna.
In this case, the closer the direction of the beam is to the entrance/exit of the work section, the smaller the transmission power, thereby suppressing the leakage of radio waves to the outside of the work section.

In one aspect of the present disclosure, the transmission/reception conditions may include at least a parameter that changes the reception sensitivity of the tag reader to the signal received from the variable directivity antenna. This parameter may include, for example, a reception threshold that is used to identify whether the received signal is valid or not by the reception level.
In this case, it is possible to prevent the radio waves from the RF tags located outside the working zone from being received with a readable intensity.

In one aspect of the present disclosure, the variable directivity antenna may be arranged laterally of the work zone.
In this case, for example, the leakage of radio waves to the outside of the work section can be suppressed more easily than when the variable directivity antenna is arranged above the work section. For example, when a radio wave absorbing material is used to suppress the leakage of radio waves, it is sufficient to provide a side wall and place the radio wave absorbing material against irradiation from the side. radio wave absorbers must be placed on the road surface of the conveying route. In this case, the road surface on which the radio wave absorbing material is arranged becomes inconvenient due to, for example, unevenness.

In one aspect of the present disclosure, the position detector may comprise two edge sensors and a central sensor. The end sensors perform detection at both ends of the work zone, which are entrances and exits of the work zone. The center sensor detects at the center of the work zone. When only one of the two end sensors reacts, the control unit activates the tag reading unit and directs the beam of the variable directivity antenna in the direction of the entrance/exit of the work zone where the sensor that reacted is located. . Then, when the center sensor reacts, the beam may be controlled to be directed to the center of the working zone regardless of the reaction of the two end sensors.

With such a configuration, a longer reading time can be ensured under transmission/reception conditions in which the reading rate of the RF tags by the tag reading section is high, so that the reading rate of the RF tags can be improved in the entire work section.

In one aspect of the present disclosure, the control unit activates the tag reading unit when there is no change in the detection result of the position detecting unit continuously for a predetermined allowable time or longer while the tag reading unit is operating. You can stop it.

According to such a configuration, it is possible to prevent the tag reading unit from continuing to operate unnecessarily after the article has normally left the work section or when an error has occurred such as the article staying in the work section. can.

1 is a block diagram showing the overall configuration of a tag reading system; FIG. It is a perspective view which shows the structure of a gate part. 4 is a flowchart of reading processing executed by a reader/writer; 4 is a flowchart of reading processing executed by a reader/writer; FIG. 4 is an explanatory diagram showing how the direction of a beam of a variable directivity antenna changes according to the position of an article;

Embodiments of the present disclosure will be described below with reference to the drawings.
[1. composition]
A tag reading system 1 of the present embodiment is provided on a transport path for transporting an article, and is for reading identification information from an RF tag attached to the transported article. The articles may be transported by an operator using a trolley, or may be automatically transported by a transport device such as a belt conveyor. Here, a case will be described in which a plurality of articles to which RF tags are attached are collectively transported using a trolley.

As shown in FIG. 1, the tag reading system 1 includes a gate section 2, a reader/writer 3, and a display device 4. As shown in FIG.
As shown in FIG. 2, the gate portion 2 includes a first side wall portion 21 and a second side wall portion 22 which are arranged opposite to each other on the left and right sides of the conveying path along the conveying path to limit the area through which the articles pass. . A section sandwiched between the first side wall portion 21 and the second side wall portion 22 in the transport path is called a work section.

The first side wall portion 21 and the second side wall portion 22 are assembled to have a thick, flat box-shaped outer shape by using, for example, a plurality of rod-shaped pipes and pipe connectors that connect the pipes. It is configured using a frame body.

An antenna unit 5 and a sensor unit 6 are attached to the facing surface 21 a of the first side wall portion 21 , and a mirror unit 7 is attached to the facing surface 22 a of the second side wall portion 22 . The opposing surfaces 21a and 22a refer to surfaces of the first side wall portion 21 and the second side wall portion 22 that face each other. The antenna unit 5 corresponds to a variable directivity antenna, and the sensor unit 6 and mirror unit 7 correspond to a position detection section.

The antenna unit 5 is arranged near the center in the height direction of the first side wall portion 21 . The sensor unit 6 is arranged near the lower end of the first side wall portion 21 at a position higher than at least the wheel axle of the truck 8 . The mirror unit 7 is arranged on the second side wall portion 22 at a position facing the sensor unit 6 of the first side wall portion 21 .

Both the facing surface 21a of the first side wall portion 21 other than the portion where the antenna unit 5 and the sensor unit 6 are attached and the facing surface 22a of the second side wall portion 22 other than the portion where the mirror unit 7 is attached absorb radio waves. covered with wood.

The antenna unit 5 has a plurality of antenna elements arranged in a row, and by changing the feeding phase to each antenna element according to the control signal from the reader/writer 3, the direction of the radiated beam changes. A variable antenna is used. The beam of the antenna unit 5 has a wide spread in the height direction and a narrowed shape in the horizontal direction. The beam is attached to the first side wall portion 21 so that its orientation changes in the horizontal direction, that is, in the direction along the conveying path.

The directions of the beam that can be controlled by the control signal are three directions, ie, the front direction, the first end direction, and the second end direction. When the direction of the beam is the front direction, radio waves are radiated near the center along the transport direction in the work section. When the direction of the beam is the direction of the first end, radio waves are radiated toward one of the two ends serving as the entrance and exit of the working section. When the direction of the beam is the direction of the second end, radio waves are radiated toward the other of the two ends serving as the entrances and exits of the working section. In FIG. 2, the direction toward the front side of the gate portion 2 is defined as the first end direction, and the direction toward the back side of the gate portion 2 is defined as the second end direction.

Further, the transmission/reception conditions of the reader/writer 3 include at least the transmission power to be supplied to the antenna unit 5 and the reception threshold used when identifying whether or not the reception signal from the antenna unit 5 is valid by the reception level. One side is included, and there are two stages, a normal setting and a restrained setting. Based on the transmission power and reception threshold in the normal setting, in the suppression setting, the transmission power is lower than the normal setting and the reception threshold is higher than the normal setting. It should be noted that other parameters that change the reception sensitivity may be used instead of the reception threshold.

The control signal is a DC signal having a plurality of signal levels, and each signal level is associated with a combination of beam direction and transmission/reception conditions. Here, the control signal has three signal levels, since the first end direction and suppression setting, the second end direction and suppression setting, and the center direction and normal setting are used. Also, the control signal is transmitted between the antenna unit 5 and the reader/writer 3 using the same signal line as the signal line for transmitting the high-frequency signal to be transmitted and received. However, the high-frequency signal and the control signal may be separately transmitted using different signal lines.

The beam direction, horizontal beam width (i.e., half-value angle), transmission power and reception threshold under the transmission/reception conditions are the reading rate from the RF tag located outside the work zone for both of the following two cases: is set so that the misreading rate is equal to or less than a preset allowable value. That is, when the beam is directed to the front direction and the transmission/reception conditions are set to normal, and when the beam is directed to the first end direction or the second end direction and the transmission/reception conditions are set to be suppressed.

The sensor unit 6 has three sensors 61-63 arranged in a row. A centrally located sensor (hereinafter referred to as central sensor) 62 is arranged so as to be located in the center of the working zone. Two sensors (hereinafter referred to as end sensors) 61 and 63 located on both sides of the central sensor 62 are arranged in the outer section and boundary at the entrance/exit of the working section, respectively. The mirror unit 7 also includes two mirrors 71 and 73 arranged at positions facing the end sensors 61 and 63 .

The central sensor 62 uses a sensor that emits infrared rays, ultrasonic waves, visible light, or the like and detects an object based on the intensity of reflection. The edge sensors 61 and 63 irradiate visible light or infrared rays (hereinafter referred to as light rays), and detect an object depending on whether reflected light is received from the mirrors 71 and 73 of the mirror unit 7 arranged in front. A mirror reflective sensor is used.

In other words, the end sensors 61 and 63 accurately detect an article present in a position that blocks the reciprocating path of the light beam, that is, an article that has entered the work zone or an article that has exited the work zone. The central sensor 62 detects objects existing in a wider range centered on the front direction. However, the detection range of the central sensor 62 is set so as not to include the detection ranges of the end sensors 61 and 63 .

The display device 4 is for displaying processing results and the like by the reader/writer 3, and a liquid crystal display or the like is used.
The reader/writer 3 is composed of a microcomputer including a CPU, ROM, RAM and the like. The reader/writer 3 also has a plurality of IO ports, which are used for controlling the antenna unit 5, the sensor unit 6, and the display device 4, and communicating with external devices.

The reader/writer 3 executes at least tag reading processing and main processing. The tag reading process is the original process of the reader/writer for extracting the information of the RF tag from the signal received by the antenna unit 5, and is an existing process, so the description is omitted here. The main process executes control of the antenna unit 5 and control of starting and stopping the tag reading process according to the detection signal from the sensor unit 6 . Note that the tag reading process corresponds to the tag reading section, and the main process corresponds to the control section.

The RAM of the reader/writer 3 is provided with at least an area for storing passage histories indicating how the sensors 61 to 63 belonging to the sensor unit 6 reacted as a group of articles passes through the work section. This passage history is deleted each time one item group has passed through the work section.

[2. process]
Main processing executed by the reader/writer 3 will be described with reference to the flowcharts of FIGS. 3 and 4. FIG.

The main process starts when any one of the sensors 61 to 63 in the sensor unit 6 reacts. However, when the reader/writer 3 is activated, the antenna unit 5 is initialized to an OFF state in which transmission and reception are not executed, and the tag reading process is initialized to a halted state.

When the main process is started, in S110, the reader/writer 3 determines whether or not the sensor in the sensor unit 6 that has reacted is one of the edge sensors 61 and 63. FIG. If the determination in S110 is affirmative, the process proceeds to S120, and if the determination in S110 is negative, the process proceeds to S160. Hereinafter, of the edge sensors 61 and 63, the edge sensor determined to have responded in this step is referred to as the entrance sensor, and the other edge sensor is referred to as the exit sensor.

In S120, the reader/writer 3 determines whether or not the passage history is recorded. If the determination is affirmative, the process proceeds to S150, and if the determination is negative, the process proceeds to S130. That is, a positive determination in S120 means that another product group has already entered the work zone, and a negative determination in S120 means that a new product group has entered the work zone.

In S130, the reader/writer 3 orients the directivity of the antenna toward the entrance sensor, sets the transmission/reception condition to a suppression setting, and starts the tag reading process to start reading the RF tag.

In subsequent S140, the reader/writer 3 stores the entrance sensor as the passage history, and advances the process to S160.
In S150, the reader/writer 3 checks the passage history, executes error determination, and advances the process to S310. In this error determination, it is determined whether or not the group of articles to which the entrance sensor has reacted is an unauthorized entry. Specifically, if an edge sensor and a center sensor that are different from the edge sensor that reacted this time are already stored in the passage history, it is not an error because the detection is due to the movement of the sensor currently being read. is determined. If only the edge sensor that reacted this time is already stored in the passage history, it is determined that the error is due to the illegal entry of a new group of articles despite the fact that reading is currently being performed. If only the edge sensor that is different from the edge sensor that reacted this time is already stored in the passage history, an error due to the fact that the group of articles being read has slipped through the central sensor 62 for some reason, or the central sensor 62 has failed. determined to be an error due to

In S160, the reader/writer 3 determines whether or not the central sensor 62 has reacted in the sensor unit 6. If the determination is affirmative, the process proceeds to S180; Transition. If an affirmative determination is made in S110, a positive determination is made if the article group has reached the detection area of the central sensor 62, and a negative determination is made if the article group has not reached the detection area according to the movement status of the article group in the work zone. be.

In S170, the reader/writer 3 determines whether or not a preset allowable time has elapsed since the entrance sensor reacted. is returned to S160.

In S180, the reader/writer 3 determines whether or not there is a passage history of the entrance sensor. If the determination is affirmative, the process proceeds to S200, and if the determination is negative, the process proceeds to S190. In other words, a positive determination in S180 means that the group of articles has moved from the entrance sensor to the detection range of the center sensor 62, and a negative determination in S180 means that the end sensors 61 and 63 do not react and It means that the central sensor 62 has reacted.

In S190, the reader/writer 3 checks the passage history to execute error determination, and advances the process to S310. Specifically, the following determinations are made in the error determination. If the process proceeds to this step due to an affirmative determination in S170, only the entrance sensor is recorded in the passage history. In this case, it is determined that the group of articles that have entered the work zone are staying in front of the detection range of the central sensor 62, or that the central sensor 62 is out of order. If the process proceeds to this step due to a negative determination in S180, the group of articles slipped through the edge sensors 61 and 63 for some reason, or the edge sensors 61 and 63 are out of order. is determined.

In S200, the reader/writer 3 switches the directivity of the antenna to the central direction and switches the transmission/reception conditions to the normal setting while continuing to read the RF tag by the tag reading process.

In subsequent S210, the reader/writer 3 adds the central sensor 62 to the passage history.
In subsequent S220, the reader/writer 3 determines whether or not the exit sensor has reacted in the sensor unit 6. If the determination is affirmative, the process proceeds to S250; Transition.

In S230, the reader/writer 3 determines whether or not a preset allowable time has passed since the central sensor 62 reacted. The process returns to S220. The allowable time used in this step may have the same length as the allowable time used in S170, or may have a different length.

In S240, the reader/writer 3 confirms the passage history, executes error determination, and advances the process to S310. Specifically, the following determinations are made in the error determination. That is, in this case, since the entrance sensor and the central sensor 62 are recorded in the passage history, the group of articles that have entered the work zone stay within the detection range of the central sensor 62 or in front of the detection range of the exit sensor. Alternatively, it is determined that the exit sensor has failed.

In S250, the reader/writer 3 determines whether or not the central sensor 62 is reacting. If the determination is affirmative, the reader/writer 3 repeats this step to wait, and if the determination is negative, the process proceeds to S260. It should be noted that the affirmative determination in S250 means that the center sensor 62 is also responding although the exit sensor is responding, and that a long group of articles is passing through the work section along the conveying path. means Also, a negative determination in S250 means that the group of articles that entered the work zone reached the detection range of the exit sensor without any abnormality being detected.

In S260, the reader/writer 3 switches the directivity of the antenna to the direction of the exit sensor and switches the transmission/reception condition to the suppression setting while continuing to read the RF tag by the tag reading process.

In subsequent S270, the reader/writer 3 adds an exit sensor to the passage history.
In subsequent S280, the reader/writer 3 detects the passage direction of the article group from the contents of the passage history.

In subsequent S290, the reader/writer 3 determines whether or not the exit sensor is responding. A positive determination in S290 means that part of the article group remains in the work section, that is, the passage of the article group through the work section has not been completed. It means that the passage of the working section by the group has been completed.

In S300, the reader/writer 3 turns off the transmission/reception by the antenna unit 5, and stops the tag reading process to finish reading the RF tag. Furthermore, the reader/writer 3 displays the reading result of the RF tag, and advances the process to S320. The reading result of the tag reading process includes the number of tags read and the passing direction of the group of articles. The passing direction can be used as information for identifying, for example, shipment or arrival.

In S310, the reader/writer 3 assumes that some kind of error has been detected, turns off transmission/reception by the antenna unit 5, and terminates the reading of the RF tag by stopping the tag reading process. Furthermore, the reader/writer 3 causes the display device 4 to display the type of the detected error, etc., and advances the process to S320.

In S320, the reader/writer 3 outputs the processing result to the external device.
In subsequent S330, the reader/writer 3 deletes the passage history and terminates the process.
[3. motion]
In the tag reading system 1, as shown in FIG. 5(a), when the trolley 8 carrying the group of articles to which the RF tags are attached enters the gate section 2 (that is, the work zone) from the end sensor 61 side, Edge sensor 61 reacts. In this case, the edge sensor 61 is the entrance sensor, and the edge sensor 63 is the exit sensor. Then, the direction of the beam B of the antenna unit 5 is set to face the entrance of the work section where the end sensor 61 is arranged, the transmission/reception condition is set to the suppression setting, and the reading of the RF tag by the reader/writer 3 is performed. is started.

When the truck 8 advances through the work section and reaches the detection range of the central sensor 62, as shown in FIG. The transmission/reception conditions switch to normal settings.

Even if the cart 8 further advances through the work section and reaches the position where the end sensor 63, which is the exit sensor here, reacts, while the center sensor 62 is reacting, the direction of the beam B and the transmission/reception conditions Settings are retained.

When the cart 8 further advances through the work zone and reaches a position outside the detection range of the central sensor 62, as shown in FIG. However, as the end sensor 63 is switched to the direction facing the entrance/exit of the work zone, the transmission/reception condition is switched to the suppression setting.

After that, when the truck 8 leaves the work zone and reaches a position outside the detection range of the end sensor 63, the transmission and reception by the antenna unit 5 is turned off, and the reading of the RF tag by the reader/writer 3 is also stopped.

[4. effect]
The embodiment described above has the following effects.
(a) The tag reading system 1 detects the position of the carriage 8 and the group of articles mounted on the carriage 8 within the work zone, and follows the direction of the beam according to the detection results that change according to the movement of the carriage 8. For this reason, the time during which the RF tag attached to each article belonging to the article group stays within the beam of the antenna unit 5, that is, the time that can be used for reading the RF tag becomes longer. can be improved.

(b) In the tag reading system 1, when the direction of the beam is in the direction of the entrance/exit of the work zone, the transmission/reception conditions are set to be suppressed, thereby reducing the rate of misreading of the RF tag by the reader/writer 3. Therefore, it is possible to suppress erroneous reading of information of RF tags existing outside the work zone.

(c) In the tag reading system 1, since the detection results of the sensors 61 to 63 belonging to the sensor unit 6 are stored as a passage history, not only can the passage direction of the group of articles in the work section be detected from this passage history, but also errors can be detected. The type of error can be determined when it occurs.

[5. Other embodiments]
An embodiment of the present disclosure has been described above, but the present disclosure is not limited to the above-described embodiment, and can take various forms without departing from the gist of the present disclosure.

(a) In the above embodiment, the sensor unit 6 uses the three sensors 61 to 63 to detect the position of the group of articles, and according to the detection results, the antenna unit 5 controls the direction of the beam in three directions. but not limited to these. The sensor unit 6 may have two or four or more sensors. Moreover, the directions of the beams controlled by the antenna unit 5 may be two directions or four directions or more.

(b) In the above embodiment, the sensor unit 6 and the mirror unit 7 are arranged near the lower ends of the first side wall portion 21 and the second side wall portion 22. Any position can be used as long as the position of the group can be detected. Also, the first side wall portion 21 and the second side wall portion 22 may have a structure in which the positions and orientations of the sensor unit 6 and the mirror unit 7 can be arbitrarily changed. Further, depending on the type of sensor used, the sensor unit 6 may be arranged on the ceiling wall portion covering the upper portion of the first side wall portion 21 and the second side wall portion 22, or on the floor portion covering the lower portion thereof.

(c) In the above embodiment, the sensor unit 6 uses different sensors for the end sensors 61 and 63 and the center sensor 62, but the same type of sensor may be used for all. Also, the type of sensor to be used is not particularly limited.

(d) In the above embodiment, the end sensors 61 and 63 are arranged to detect a group of articles entering the work zone and a group of articles leaving the work zone. , and a group of items that have just left the work zone.

(e) In the above embodiment, after the exit sensor responds, the reading of the RF tag ends when the response disappears. You can finish reading.

(f) In the above embodiment, the antenna unit 5 is arranged so as to irradiate the beam from the side of the transport path, but the ceiling wall is provided at the upper end of the first side wall 21 and the second side wall 22, You may arrange|position so that it may irradiate toward the downward direction from a ceiling wall part. In this case, the floor surface may be covered with a radio wave absorber in order to suppress reflection from the floor surface of the transport path. Also, the first side wall portion 21 and the second side wall portion 22 may have a structure that allows the position and orientation of the antenna unit 5 to be changed arbitrarily. In this case, the antenna unit 5 may be arranged, for example, so as to emit light obliquely downward from near the upper end of the first side wall portion 21 .

(g) In the above embodiment, only one antenna unit 5 is provided in the gate section 2, but a plurality of antenna units 5 may be provided at different heights. In this case, the reader/writer 3 may individually process the signals from the plurality of antenna units 5 by time division.

(h) When a plurality of items with RF tags attached are stored in one storage box, and the storage box is also attached with a tag or barcode, a A reader may be provided to read information from the attached tag or barcode. In this case, until one storage box passes through the gate section 2, control or the like can be implemented to prevent other storage boxes from entering the gate section 2. FIG.

DESCRIPTION OF SYMBOLS 1... Tag reading system 2... Gate part 3... Reader writer 4... Display device 5... Antenna unit 6... Sensor unit 7... Mirror unit 8... Carriage 21... First side wall part 22... Second 2 side wall portions, 21a, 22a, facing surfaces, 61, 63, end sensors, 62, central sensors, 71, 73, mirrors.

Claims (6)

a position detection unit configured to detect the position of the article within a work section set on a conveying route for conveying the article;
a variable directivity antenna configured to emit radio waves toward the work section;
a tag reader configured to read information from an RF tag attached to the article via the variable directivity antenna;
According to the position of the article detected by the position detection unit, the direction of the beam of the variable directivity antenna is changed along the conveying route, and the closer the direction of the beam is to the entrance/exit of the work zone, a control unit configured to change transmission/reception conditions of the tag reading unit so as to reduce an erroneous reading rate of the tag reading unit;
tag reading system. The tag reading system according to claim 1,
The transmission/reception conditions include at least transmission power supplied by the tag reading unit to the variable directivity antenna,
tag reading system. The tag reading system according to claim 1 or claim 2,
The transmission/reception conditions include at least a parameter that changes the reception sensitivity of the tag reader to a signal received from the variable directivity antenna,
tag reading system. The tag reading system according to any one of claims 1 to 3,
The variable directivity antenna is arranged on the side of the work section,
tag reading system. The tag reading system according to any one of claims 1 to 4,
The position detection unit includes two end sensors that perform detection at both ends of the work section serving as entrances and exits of the work section, and a center sensor that performs detection at the center of the work section,
When only one of the two end sensors responds, the control unit activates the tag reading unit and directs the directivity in the direction of the entrance/exit of the work zone where the sensor that responded is located. A tag reading system that directs the beam of a variable antenna and, if the center sensor responds, controls the beam to be directed to the center of the work zone regardless of responses at the two end sensors. The tag reading system according to any one of claims 1 to 5,
The control unit stops the tag reading unit when there is no change in the detection result of the position detecting unit for a time that is set in advance by the position detecting unit or longer during operation of the tag reading unit. tag reading system.

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