JP2007248336A - Position information acquisition system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To acquire correct position information with only few errors even in a position information acquisition system using GPS. <P>SOLUTION: The position information acquisition system includes an RFID tag 41 arranged at an entrance of a field and having identification information ID; a tag reader 42 for reading the identification information ID of the RFID tag 41; a mobile station unit 43 for detecting measured self-position information on the basis of radio waves from an artificial satellite ST; an external server 44 for relating reference position information of the RFID tag 41 with identification information and previously storing it; and a controller 40 mounted to a tractor 1. The tag reader 42 and the mobile station unit 43 are mounted to the tractor 1. The controller 40 acquires the reference position information from the external server when the tractor 1 is at the entrance of the field, computes correction information on the basis of measured position information at the time and the reference position information, and computes current self-position information of the tractor 1 on the basis of the correction information and the measured position information. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a position information acquisition system for acquiring position information of a work vehicle such as a traveling agricultural machine such as a tractor and a special work machine such as a crane truck.

  In recent years, in the field of agriculture, so-called commissioned farming, in which the management of a plurality of farm fields with different owners and locations is collectively entrusted to an individual or a corporation that owns a plurality of farm working machines, is increasing. For this reason, there is an increasing demand for traveling farm work machines (see, for example, Patent Documents 1 and 2) equipped with a navigation device capable of accurately recording work histories such as work dates and times and travel histories.

The navigation device for traveling agricultural machines uses a global positioning system (hereinafter referred to as GPS), for example, as in the case of automobiles. The positioning method is transmitted from an artificial satellite. There are a single positioning method using a radio wave (C / A code signal) as it is and a D-GPS method using a code phase.
JP-A-10-234204 JP 2001-251906 A

  By the way, a navigation device for a traveling farm work machine is required to have high positioning accuracy so that even if the operator changes, the progress of the work can be grasped from the past traveling history in the field.

  However, since the former single positioning method uses a commercial radio wave (C / A code signal) as it is, for example, an orbit error of an artificial satellite, a radio wave propagation delay due to the ionosphere and the atmosphere, and a multipath error ( Error due to reflected waves from buildings near the ground, the ground surface, etc.), and as a result, there is a positioning error of about 10 tens of meters, which is not suitable for the positioning method of the navigation device for traveling agricultural machines. there were.

  On the other hand, the latter D-GPS system is an application of a single positioning system, and measurement position information (pseudorange) measured by a ground GPS reference station whose position is clear and reference position information (between the reference station and the satellite). Is transmitted to the navigation device (mobile station) as ground information such as a medium wave beacon or FM broadcast, and the measurement position information of the navigation device is corrected based on the correction information. It is. For this reason, the positioning error of the D-GPS system is suppressed to about several tens of centimeters to several meters, and the D-GPS system has higher positioning accuracy than the single positioning system.

  However, in the D-GPS method, correction information from the reference station is transmitted by terrestrial waves such as medium wave beacons and FM broadcasts, so that positioning errors are difficult in places where terrestrial waves are difficult to reach, such as farm fields in mountainous areas. There was a problem that became larger.

  The present invention has been made in view of the current situation as described above, and it is a technical problem to provide a position information acquisition system capable of acquiring accurate position information while using GPS. It is.

  In order to achieve this technical problem, a position information acquisition system according to claim 1 is an information medium arranged at a predetermined location and having individual identification information, and for reading the identification information of the information medium. A reading means, a GPS positioning means for detecting its own measurement position information by radio waves from an artificial satellite, and a pre-stored memory that stores reference position information for specifying the location of the information medium in correspondence with the identification information Means, and information processing means connected to the GPS positioning means and the storage means by radio or wire. The reading means and the GPS positioning means are mounted on a work vehicle, and the information processing Means for storing the reference position information with respect to the identification information read by the reading means when the work vehicle is positioned at the location of the information medium; Obtaining and calculating correction information from the measurement position information detected by the GPS positioning means and the reference position information at this time, and based on the correction information and the measurement position information detected by the GPS positioning means Then, control is performed so as to calculate current self-position information of the work vehicle.

  According to a second aspect of the present invention, in the positional information acquisition system according to the first aspect, the work vehicle is a traveling farm work machine, the information medium is an RFID tag, and is located at an entrance of a predetermined farm field. The storage means stores field identification information such as field name and area information together with the reference position information in association with the identification information, and the information processing means stores the traveling farm work. A history storage means for storing the self-position information of the machine as time-series history information is connected wirelessly or by wire, and the traveling farm work machine includes the current self-position information, the history information, and Display means capable of displaying the field identification information is provided.

  A position information acquisition system according to a third aspect of the present invention is an information medium that is arranged at a predetermined location and stores reference position information for specifying the location, and a reading means for reading the reference position information of the information medium. , GPS positioning means for detecting its own measurement position information by radio waves from an artificial satellite, and information processing means connected to the GPS positioning means by radio or wire, the reading means and the GPS The positioning means is mounted on a work vehicle, and the information processing means includes measurement position information detected by the GPS positioning means when the work vehicle is located at the location of the information medium, Correction information is calculated from the reference position information read by the reading means, and based on the correction information and the measurement position information detected by the GPS positioning means, Is that controls so as to calculate the current self-position information of the work vehicle.

  According to a fourth aspect of the present invention, in the position information acquisition system according to the third aspect, the work vehicle is a traveling farm work machine, and the information medium includes field identification information such as field name and area information together with the reference position information. Is an RFID tag stored in correspondence with the identification information, and is arranged at the entrance of a predetermined farm field, and the information processing means stores the self-position information of the traveling agricultural machine on time. History storage means for storing the history information of the series is connected wirelessly or by wire, and the traveling farm work machine displays the current self-position information, the history information, and the field identification information. The display means to obtain is provided.

  According to the configuration of claim 1, which is an independent item, the reference position information for the identification information read by the reading means when the work vehicle is located at the location of the information medium is obtained from the storage means. At this time, the GPS positioning means Correction information can be calculated from the measured position information detected in step 1 and the reference position information, and the current self-position information of the work vehicle can be calculated based on the correction information and the measured position information. For this reason, if the information medium is arranged at a place where measurement is desired, even if the ground wave from the GPS reference station is difficult to reach, such as a farm field in a mountainous area, the positioning error is different from that of the D-GPS system. It can be maintained at the same level. Therefore, there is an effect that accurate position information can be obtained regardless of the reception status of the terrestrial wave, even though the GPS is used.

  In addition, according to the configuration of claim 3, which is an independent item, since the information medium stores the reference position information for specifying the arrangement location, the GPS positioning means is used when the work vehicle is located at the arrangement location of the information medium. Correction information can be calculated from the detected measurement position information and the reference position information read by the reading means at this time. And the present self position information of the work vehicle can be calculated based on the correction information and the measured position information detected by the GPS positioning means.

  Therefore, as in the case of claim 1, although GPS is used, there is an effect that accurate position information can be obtained regardless of the reception situation of terrestrial waves.

  Further, when configured as claimed in claims 2 and 4, high positioning accuracy can be realized only by using an RFID tag as an information medium instead of the D-GPS type GPS reference station, the cost can be reduced, and it is extremely economical. There is an effect that it is.

  DESCRIPTION OF EMBODIMENTS Embodiments embodying the present invention will be described below with reference to the drawings (FIGS. 1 to 7).

  1 to 6 show a first embodiment in which the present invention is applied to a farm tractor. 1 is a side view of a tractor according to the first embodiment, FIG. 2 is a plan view of the tractor, FIG. 3 is a functional block diagram of a position information acquisition system, and FIG. 4 is a screen of the display means. FIG. 5 is a plan view showing the positional relationship among the field, the RFID tag, and the tractor, and FIG. 6 is a flowchart of position information acquisition control. In FIG. 2, the cabin of the tractor is not shown.

  As shown in FIGS. 1 and 2, the tractor 1, which is an example of a traveling farm work machine as a work vehicle, has a traveling machine body 2 similar to a pair of left and right front wheels 3 and 3 and a pair of left and right rear wheels 4 and 4. It is supported by. The tractor 1 is configured to travel forward and backward by driving the front wheels 3 and 3 and the rear wheels 4 and 4 with the engine 5 mounted on the front portion of the traveling machine body 2.

  The engine 5 is covered with a bonnet 6. In addition, a cabin 7 is installed on the upper surface of the traveling machine body 2, and a steering circle that moves the steering direction of the front wheel 3 left and right by steering the steering seat 8 inside the cabin 7. A handle 9 is provided. The control round handle 9 is provided at a control column 10 located in front of the control seat 8.

  A liquid crystal display device 31 as a display means is provided at the upper part of the steering column 10. The liquid crystal display device 31 includes a color dot matrix type liquid crystal panel 32 (screen) capable of displaying information such as characters, symbols, and images, and a case 33 for housing the liquid crystal display device 31 (see FIG. 4).

  A step 11 on which the operator gets on and off is provided on the outer side of the cabin 7, and a fuel tank 12 for supplying fuel to the engine 5 is provided on the inner side of the step 11 and below the bottom of the cabin 7. Yes.

  The traveling machine body 2 includes an engine frame 15 having a bumper 13 and a front axle case 14, and left and right machine body frames 16 that are detachably fixed to the rear portion of the engine frame 15 with bolts. A transmission case 17 having a traveling speed change mechanism (not shown) for appropriately changing the rotational power from the engine 5 and transmitting it to the front and rear four wheels 3, 3, 4, 4 is mounted on the rear part of the body frame 16. ing. The rear wheel 4 is attached via a rear axle case 18 mounted so as to protrude outward from the outer surface of the mission case 17.

  The mission case 17 also includes a PTO speed change mechanism (not shown) for transmitting a part of the rotational power from the engine 5 to a PTO shaft 23 described later. The PTO speed change mechanism is for adjusting the magnitude of the rotational power steplessly or stepwise (changes speed as appropriate) at the entrance to the rotary transmission system of the rotary tiller 24 arranged at the rear of the traveling machine body 2. is there.

  A hydraulic lifting mechanism 20 for lifting and lowering the rotary tiller 24 is detachably attached to the rear upper surface of the mission case 17. The rotary cultivator 24 is connected to the rear portion of the mission case 17 via a three-point link mechanism including a pair of left and right lower links 21 and a top link 22. The front end sides of the left and right lower links 21 are connected to the left and right side rear portions of the mission case 17 so as to be rotatable by pins. The front end side of the top link 22 is connected to the top link hitch 27 of the hydraulic lifting mechanism 20 with a pin. On the rear surface of the transmission case 17, a PTO shaft 23 for transmitting a PTO driving force to the rotary tiller 24 is provided so as to protrude rearward. The PTO shaft 23 is connected to a PTO input shaft 26 projecting forward from the rotary tiller 24 via an extendable transmission shaft 25 having universal joints at both ends.

  A pair of left and right lift arms 28 that are rotated by a single-acting lift control hydraulic cylinder (not shown) are attached to the hydraulic work machine lift mechanism 20. The lower link 21 and the lift arm 28 on the left side in the traveling direction of the traveling machine body 2 are connected via a lift rod 29. The lower link 21 and the lift arm 29 on the right side in the traveling direction of the traveling machine body 2 are connected via a double-acting tilt control hydraulic cylinder 30.

  Next, the configuration of the position information acquisition system according to the first embodiment will be described with reference to FIGS.

  This position information acquisition system includes an RFID (Radio Frequency IDenti-fication) tag 41 as an information medium, a tag reader 42 as a reading means for reading the identification information ID of the RFID tag 41, and a radio wave from the artificial satellite ST. The mobile station unit 43 as a GPS positioning means for detecting its own measurement position information with (C / A code signal) and the reference position information BL for specifying the location of the RFID tag 41 are used as identification information for the RFID tag 41. An external server 44 serving as storage means stored in advance corresponding to the ID, and a controller 40 serving as information processing means connected to the mobile station unit 43 and the external server 44 wirelessly or by wire are provided.

  The RFID tag 41 is for transmitting its own (individual) identification information ID to the tag reader 42 in a non-contact (wireless communication) manner. In the first embodiment, an entrance at a predetermined location, for example, each farm field G, is used. It is laid at a location A (see FIG. 5).

  The RFID tag 41 of the first embodiment is a passive unit including an antenna unit 46 that enables wireless communication with the outside, a modulation / demodulation circuit 47 that modulates and demodulates a signal, and a memory unit 48 that stores its own identification information ID. Of the type. That is, the RFID tag 41 of the first embodiment is of a type that operates using radio waves from the tag reader 42 as a power source, and does not spontaneously transmit identification information. The RFID tag 41 may be an active type that has a built-in battery and can spontaneously transmit identification information.

  The tag reader 42 includes an antenna unit 49 that enables wireless communication with the outside, and a modulation / demodulation circuit 50 that performs signal modulation / demodulation processing. The tag reader 42 of the first embodiment is attached to the lower surface of the traveling machine body 2 in the tractor 1 (more specifically, the lower surface of the mission case 17), and between the RFID tag 41 laid at the entrance A of the farm field G. The wireless communication is performed via the respective antenna units 46 and 49. The tag reader 42 reads the identification information ID stored in the memory unit 48 of the RFID tag 41. The tag reader 42 is connected to the input interface of the controller 40 mounted on the traveling machine body 2.

  The mobile station unit 43 is mounted on the traveling machine body 2 and includes a GPS antenna 51 attached to the ceiling of the cabin 7 and a GPS receiver 52 to which the GPS antenna 51 is connected. The GPS receiver 52 obtains the current measurement position information ML (and thus the measurement position information of the tractor 1) at present from the radio wave (the current position information of the satellite) captured by the GPS antenna 51. In order to output the measurement position information ML to the controller 40, it is connected to the input interface of the controller 40.

  As described above, the external server 44 stores the reference position information BL for specifying the location of the RFID tag 41 in advance in association with the identification information ID of the RFID tag 41. The external server 44 of the first embodiment is installed outside the tractor 1 (for example, a commissioned agricultural management company) and is connected to the radio base station BS via the Internet network IN. On the other hand, a radio communication device 54 having a radio antenna 53 is connected to the input / output interface of the controller 40 on the tractor 1 side, and between the controller 40 within a range where radio waves from the radio base station BS reach, It is configured to perform bidirectional wireless communication.

  In the external server 44 of the first embodiment, the field position specifying information FI such as the field name and area information is stored together with the reference position information BL corresponding to the identification information ID of the RFID tag 41, and the controller 40 is externally connected. When the reference position information BL is acquired from the server 44, the field specifying information FI is also read together with the reference position information BL.

  The field identification information FI according to the first embodiment includes field name NA and area information MA having an appropriate shape such as a substantially rectangular shape in plan view corresponding to an area (working area) surrounding the four corners C1 to C4 of the field G. (See FIG. 4). By displaying these information NA and MA on the liquid crystal panel 32 of the liquid crystal display device 31 in combination with the current self-position information TL of the tractor 1 and history information RE described later, the operator can display past and current work progress statuses and the like. Visually and accurately grasp.

  Instead of the external server 44, a database in which the reference position information BL of the RFID tag 41 is stored in advance in association with the identification information ID of the RFID tag 41 may be mounted on the traveling machine body.

  The controller 40 uses the measured position information ML of the tractor 1 detected by the mobile station unit 43 and the reference position information BL that specifies the location of the RFID tag 41 to obtain the current self-position information TL of the tractor 1. It is for getting as accurately as possible.

  The controller 40 according to the first embodiment includes a CPU 55 that executes various arithmetic processes and controls, an EEPROM 56 as a nonvolatile memory that stores programs and data for position information acquisition control described later, and temporarily stores the programs and data. RAM 57, an input / output interface (not shown) for exchanging data (control information) by connecting to input / output devices (liquid crystal panel 32, GPS receiver 52, etc.).

  The EEPROM 56 of the first embodiment is configured to store the self-position information TL of the tractor 1 as time-series history information RE. That is, the EEPROM 56 corresponds to the history storage means described in the claims.

  Next, an example of position information acquisition control by the controller 40 will be described with reference to the flowchart shown in FIG.

  First, following the start of the position information acquisition control shown in FIG. 6, it is determined whether or not the identification information ID of the RFID tag 41 at the entrance A in the predetermined field G can be read by the tag reader 42 (step S1). ).

  The case where the identification information ID cannot be read by the tag reader 42 is a state where the tractor 1 is not located at the entrance A in the predetermined field G (the RFID tag 41 is not present below the tag reader 42). Therefore, when it is determined that the identification information ID cannot be read by the tag reader 42 (S1: NO), the process returns to step S1 again to wait as it is.

  When it is determined that the identification information ID can be read by the tag reader 42 (S1: YES), since the tractor 1 is in the position of the entrance A in the predetermined field G, the identification information ID is passed through the tag reader 42. Read (step S2).

  Next, the controller 40 reads, from the external server 44, the reference position information BL corresponding to the read identification information ID and the field identification information FI configured with the field name NA and the area information MA (step S3).

  Next, in a state where the tractor 1 is located at the location of the entrance A, the mobile station unit 43 measures the measurement location information ML at that location (step S4), and then obtains this measurement location information ML from the GPS receiver 52. Read (step S5).

  Next, the difference between the reference position information BL (the distance between the RFID tag 41 and the artificial satellite ST) read in step S3 and the measurement position information ML (pseudo distance) read in step S5 is used as correction information AJ. Obtained (step S6).

  Next, the current self-position information TL of the tractor 1 is calculated based on the correction information AJ and the measurement position information ML read in step S5 (step S7). The self-position information TL, the field name NA, and the like are calculated. The farm field specifying information FI is displayed on the liquid crystal panel 32 of the liquid crystal display device 31 in a state visible to the operator (step S8).

  Next, after a small amount of time has elapsed (after movement), the mobile station unit 43 measures the measurement position information ML of the tractor 1 that has moved slightly from the location of the entrance A (step S9). Reading from the GPS receiver 52 (step S10).

  Next, the current self-position information TL of the tractor 1 is calculated based on the correction information AJ and the measurement position information ML read in step S10 (step S11). The self-position information TL and time-series history information are calculated. The RE and the field identification information FI are displayed on the liquid crystal panel 32 of the liquid crystal display device 31 (step S12). Accordingly, the history information RE corresponding to the movement trajectory EX of the tractor 1 is also displayed on the liquid crystal panel 32. Then, the process returns to step S9.

  According to the above control, the reference position information BL corresponding to the identification information ID read by the tag reader 42 when the tractor 1 is located at the place where the RFID tag 41 is placed (the place of the entrance A) is extracted from the external server 44. Next, the correction information AJ is calculated from the measurement position information ML of the tractor 1 detected by the mobile station unit 43 and the reference position information BL, and based on the correction information AJ and the measurement position information ML, the current position of the tractor 1 is calculated. Since the self-location information TL can be calculated, if the RFID tag 41 is laid at a place to be measured (such as the farm field G), the ground wave from the GPS reference station is difficult to reach, such as the farm field G in a mountainous area. However, the positioning error can be maintained at the same level as that of the D-GPS system. Therefore, according to the position information acquisition system of the first embodiment, although the GPS is used, there is an effect that accurate position information can be acquired regardless of the terrestrial reception status.

  Further, in the first embodiment, high positioning accuracy can be realized only by using an RFID tag instead of the D-GPS type GPS reference station, and the cost is low, which is extremely economical.

  Further, the operator can display the field identification information FI including the field name NA and the area information MA on the liquid crystal panel 32 of the liquid crystal display device 31 in combination with the current self-position information TL and history information RE of the tractor 1. It is possible to grasp the past and present work progress status visually and accurately. For this reason, it can contribute to the improvement of workability | operativity.

  Next, a second embodiment showing another example of the RFID tag will be described with reference to FIG. FIG. 12 is a functional block diagram of the position information acquisition system in the second embodiment.

  In the second embodiment, the RFID tag 41 ′ itself stores in advance the reference position information BL and the field specifying information FI for specifying the location of the RFID tag 41 ′ itself, and for this reason, the external server 44 (the wireless communication device 54 is also included). ) Is different from that of the first embodiment in that it is no longer necessary. Since the other configuration is basically the same as that of the first embodiment, the same reference numerals as those of the first embodiment are assigned and detailed description thereof is omitted.

  In the case of such a configuration, the reference position information BL read by the tag reader 42 ′ when the tractor 1 is located at the place where the RFID tag 41 is placed (the place of the entrance A), and the mobile station unit 43 at this time The correction information AJ is calculated from the measured position information ML of the tractor 1 detected in this way, and the current self-position information TL of the tractor 1 can be calculated based on the correction information AJ and the measured position information ML. As in the case of the embodiment, although GPS is used, there is an effect that accurate position information can be acquired regardless of the reception situation of the terrestrial wave.

  Note that the memory unit 48 'of the RFID tag 41' can be read / written, and the tag reader 42 'has not only a reader function (read function from the memory unit 48') but also a writer function (to the memory unit 48 '). If the writing function is provided, the time-series history information RE can be stored in the memory unit 48 ′ of the RFID tag 41 ′ after the work is completed. Therefore, it is preferable that information regarding work can be stored for each field G.

  The present invention is not limited to the above-described embodiment, and can be embodied in various forms. For example, the information medium of the present invention is not limited to an RFID tag, and a contact type such as a barcode can also be applied.

  Further, the location of the information medium is not limited to one location at the entrance A. For example, if an information medium is installed in each of the corners C1 to C4 of the farm field G, the reference position information is based on the information on the approach position when the work vehicle enters from any corner C1 to C4. BL and thus self-position information TL of the work vehicle can be obtained. Of course, since the field G has various shapes, the region information MA can have various shapes along the boundary, and an appropriate number of information media can be arranged along the boundary.

  In addition, the configuration of each unit is not limited to the illustrated embodiment, and various modifications can be made without departing from the spirit of the present invention.

It is a side view of the tractor in a 1st embodiment. It is a top view of a tractor. It is a functional block diagram of the position information acquisition system in a 1st embodiment. It is explanatory drawing of the state which displayed on the screen of a display means the present self position information of a tractor, log | history information, and field specific information. It is a top view which shows the positional relationship of an agricultural field, an RFID tag, and a tractor. It is a flowchart of position information acquisition control. It is a functional block diagram of the positional information acquisition system in 2nd Embodiment.

Explanation of symbols

BL Reference position information FI Field identification information ID Identification information MA Area information ML Measurement position information NA Field name information TL Self-position information 1 Tractor 2 Traveling machine body 31 Liquid crystal display device 32 Liquid crystal panel 40 Controller 41 RFID tag 42 Tag reader 43 Mobile station unit 44 External server

Claims (4)

An information medium arranged at a predetermined location and having individual identification information, a reading means for reading the identification information of the information medium, and a GPS for detecting own measurement position information by radio waves from an artificial satellite Positioning means, storage means for preliminarily storing reference position information for specifying the location of the information medium corresponding to the identification information, and information processing connected to the GPS positioning means and the storage means wirelessly or by wire Means and
The reading means and the GPS positioning means are mounted on a work vehicle,
The information processing means acquires, from the storage means, the reference position information for the identification information read by the reading means when the work vehicle is located at an arrangement location of the information medium,
At this time, correction information is calculated from the measurement position information detected by the GPS positioning means and the reference position information,
Based on this correction information and the measured position information detected by the GPS positioning means, control to calculate the current self-position information of the work vehicle,
Location information acquisition system. The work vehicle is a traveling farm work machine,
The information medium is an RFID tag, and is disposed at the entrance of a predetermined farm field.
The storage means stores field identification information such as field name and area information along with the reference position information in association with the identification information.
The information processing means is connected to a history storage means for storing the self-location information of the traveling farm work machine as time-series history information, wirelessly or wiredly,
The traveling farm work machine includes display means capable of displaying the current self-location information, the history information, and the farm field specifying information.
The position information acquisition system according to claim 1. An information medium arranged at a predetermined location and storing reference position information for identifying the place, reading means for reading the reference position information of the information medium, and own measurement position information by radio waves from an artificial satellite GPS positioning means for detecting, and information processing means connected to the GPS positioning means wirelessly or by wire,
The reading means and the GPS positioning means are mounted on a work vehicle,
The information processing means includes the measurement position information detected by the GPS positioning means when the work vehicle is located at the location where the information medium is disposed, and the reference position information read by the reading means at this time. Calculate correction information,
Based on this correction information and the measured position information detected by the GPS positioning means, control to calculate the current self-position information of the work vehicle,
Location information acquisition system. The work vehicle is a traveling farm work machine,
The information medium is an RFID tag that stores field identification information such as field name and area information together with the reference position information in association with the identification information, and is arranged at the entrance of a predetermined field. ,
The information processing means is connected to a history storage means for storing the self-location information of the traveling farm work machine as time-series history information, wirelessly or wiredly,
The traveling farm work machine includes display means capable of displaying the current self-location information, the history information, and the farm field specifying information.
The position information acquisition system according to claim 3.

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