JPH0511038A - Communication method for moving body - Google Patents

Abstract

PURPOSE:To make it possible to perform data communication positively between a mobile station and a fixed station by specifying the fixed station whose frequency becomes the maximum strength of an electric field among the received field strengths from other fixed station when the received field strength becomes less than a judging reference value. CONSTITUTION:A fork lift 1B performs data communication with a radio apparatus 9B of a fixed station. The fork lift 1B is moved to the position of a fork lift 1D. When the radio waves of frequencies f1-f3 are transmitted from fixed stations 9A-9C at the same time for judging the positions, respectively, the lift 1B receives only the frequency f2. The received field strength is compared with a judging reference level. When the strength becomes less than the level, the lift 1B sequentially finds the received field strengths of the received frequencies f1 and f3 and specifies the frequency where the field strength becomes the maximum value, i.e., f3 at this time. The lift 1B transmits the frequency f3 as the position data. In a host computer 14, it is judged that the position of the lift 1B is the position close to the radio apparatus 9C. Thereafter, the communication is performed with the radio apparatus 9C.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a mobile body position determination method using a wireless LAN (local area network).

[0002]

2. Description of the Related Art In recent years, a wireless LAN has been used to exchange desired data by using radio waves.
It enables the movement of data terminals. Since the data terminal is mobile, the LA of that wireless system is used.
N is used in a physical distribution system, for example, a physical distribution system using a forklift as a moving body.

That is, a forklift is equipped with a wireless device and a data terminal device as a mobile station, and a plurality of wireless devices distributed at appropriate positions on the premises are used as a plurality of fixed stations, each fixed from a host computer in the office. Desired data for cargo handling work is transmitted to a station-side wireless device, and a radio wave carrying the desired data is transmitted from the wireless device to the mobile station. In addition, the radio wave that carries the data transmitted from the mobile station is received by the wireless device on the fixed station side, and the data is transmitted to the host computer in the office.

Radio waves transmitted from the radio equipment on the fixed station side are limited to weak radio waves by the provisions of the Radio Law. Therefore, in order to effectively exchange data between a fixed station and a mobile station in a wide range of the premises, the communicable ranges of the fixed station side wireless devices distributed in the premises are overlapped with each other. , Its communication range has been expanded.

Then, by utilizing the interval of exchanging desired data and the like for cargo handling work between the fixed station and the mobile station, first the position determination of different frequencies pre-allocated to the fixed station is performed. Radio waves are simultaneously transmitted from each fixed station, and the transmitted radio waves are sequentially received while the mobile station tunes to determine the received electric field strength for each frequency. Then, after the transmission from all the fixed stations is completed, the received electric field strengths corresponding to the respective frequencies determined by the mobile station are compared with each other to identify the frequency having the largest received electric field strength. next,
The mobile station transmits the specified frequency to the fixed station as position data of the forklift equipped with the mobile station. The fixed station transmits its position data to the host computer,
The host computer has determined the current position of the forklift based on the position data.

Therefore, the desired data for the cargo handling work is sent by determining the current position of the forklift by utilizing the interval between the exchange of the desired data for the cargo handling work between the fixed station and the mobile station. You can always know the position of the forklift at this point. Therefore, when sending the desired data for cargo handling work, the fixed station closest to the forklift was selected, and it was possible to transmit radio waves from that fixed station, and data could be sent reliably and in a short time. ..

Further, since radio waves of different frequencies are simultaneously transmitted from each fixed station in order to determine the position of each forklift, the radio waves of the same frequency including identification data for identifying each fixed station from each fixed station. The time required for position determination was shortened as compared with the case of sequentially transmitting.

[0008]

However, the mobile station receives different radio waves for position determination transmitted by each fixed station as described above, determines the received electric field strength for each frequency, and compares them with each other. In the method of specifying the frequency that becomes the position data by relative comparison, that is, selecting the largest received electric field strength by doing so, when the received electric field strengths of multiple frequencies are equal, the frequency as the position data of the forklift is determined. Cannot be specified. Therefore, the mobile station cannot specify the fixed station and cannot reliably transmit the position data.

The present invention has been made to solve the above problems, and an object of the present invention is to make the electric field strengths of radio waves transmitted from a plurality of fixed stations for position determination received by mobile stations equal to each other. Another object of the present invention is to provide a mobile communication method capable of surely exchanging data between a mobile unit and a fixed station.

[0010]

SUMMARY OF THE INVENTION In order to solve the above problems, the present invention is controlled by a centralized control unit and any one of a plurality of fixed stations arbitrarily distributed.
In a mobile communication method of exchanging desired data between two fixed stations and a mobile station mounted on a mobile unit by using radio waves, radio waves of different frequencies pre-allocated to each of the fixed stations are transmitted. Transmitting from each fixed station, the mobile station receives the radio wave from the fixed station that is exchanging desired data using radio waves, calculates the reception electric field strength corresponding to the frequency, and the reception electric field strength is When it becomes smaller than the predetermined judgment reference level, the received electric field strengths corresponding to each frequency from other fixed stations are compared with each other and the frequency with the largest received electric field strength is specified, and the specified frequency It is designed to exchange data with a fixed station that sends the.

[0011]

According to the above construction, the mobile station is capable of exchanging desired data with a fixed station if the received electric field strength of the radio wave transmitted by the fixed station is equal to or higher than the judgment reference level. Exchange data. Therefore, the fixed station can be specified even if the electric field strengths of the radio waves transmitted by the plurality of fixed stations are equal in the mobile station.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment in which the present invention is embodied in a wireless LAN in a physical distribution system using a forklift will be described below with reference to FIGS.

As shown in FIG. 1, a manned forklift 1 as a plurality of (four in this case) moving bodies on the premises.
A, 1B, 1C, 1D are operating. Each of the forklifts 1A to 1D is equipped with a wireless device 2, a data terminal machine 3 and a printer 4 which constitute a mobile station as shown in FIG. The wireless device 2 on the mobile station side is a device that modulates and demodulates a signal for transmitting and receiving a radio wave containing desired data for cargo handling work. This wireless device 2 is connected to a data terminal 3 via a coaxial cable 5,
Data is exchanged between the three. Data terminal 3
Has a keyboard 6 for data input by an operator and a display 7 for displaying data.
The data terminal 3 also has a control function for controlling the operation of the wireless device 2. Further, the data terminal 3 is connected to the printer 4 via the coaxial cable 8, and the data input to the data terminal 3 can be output and printed by the printer 4.

On the other hand, at a suitable place near the ceiling in the premises, a plurality of (three in this case) radio stations 9 constituting fixed stations are provided.
A, 9B and 9C are distributed and arranged. Here, each of the wireless devices 9A to 9C on the fixed station side transmits and receives a radio wave including desired data for cargo handling work, and also performs frequency modulation and demodulation of a signal for the transmission and reception. In addition, since the radio waves transmitted from each of the wireless devices 9A to 9C are limited to weak radio waves in accordance with the regulations of the Radio Law, it is possible to communicate between the fixed station and the mobile station over a wide area of the premises. In order to do so, the communicable ranges of the wireless devices 9A to 9C on the fixed station side are overlapped with each other and spread over the entire area of the premises.

The wireless devices 9A to 9C on the fixed station side are connected to a wireless controller 11 via a coaxial cable 10,
The wireless controller 11 is also connected via a coaxial cable 12 to a command host computer 14 arranged in the office 13. The wireless controller 11 and the host computer 14 constitute an overall control unit 15. The host computer 14 manages desired data for cargo handling work transmitted to the data terminals 3 of the forklifts 1A to 1D, and the wireless controller 11 transmits the data to the wireless devices 9A to 9A to the fixed stations.
9C to each of the forklifts 1A to 1D that are the mobile stations
Wireless device 9A to
Control the operation of C.

Next, the wireless system L configured as described above is used.
The operation of the AN will be described with reference to the flowcharts shown in FIGS. FIG. 3 is a flow chart for explaining the processing operation of the host computer 14 in the office 13.

In this embodiment, each forklift 1A to
The processing operation for determining the position of each of the forklifts 1A to 1D is performed using the interval during which the normal cargo handling data is exchanged between the 1D and the office 13. Then, once the normal process for exchanging cargo handling data ends,
Let us move to the routine work of this flowchart.

First, step (hereinafter referred to as S) 101
In order to inform each of the forklifts 1A to 1D that the position determination is started, the wireless device 9 on the side of each fixed station
A to 9C are activated all at once to transmit the command radio wave for starting the position determination.

Next, in S102, radio waves for position determination of frequencies different from each other, which are pre-allocated to the radio devices 9A to 9C on the fixed station side, are transmitted to the radio devices 9 respectively.
Call from A to 9C at the same time for a predetermined time.

Then, in step S103, the wireless devices on the fixed station side are informed in order to notify the forklifts 1A to 1D that the transmission of the radio waves for position determination from the wireless devices 9A to 9C on the fixed station side have been completed. 9A to 9C are activated all at once to transmit a notification radio wave of completion of transmission.

After that, in S104, after waiting for the reception of the radio wave from the mobile station radio device 2 mounted on each of the forklifts 1A to 1D, when the radio wave is received, S105 is received.
Then, in step S105, radio waves including position data from the wireless device 2 on the side of each mobile station are sequentially received and input. Here, the position data is data for instructing a fixed station side wireless device which is currently used by each of the forklifts 1A to 1D to exchange data with the host computer 14.

Next, in S106, the input current position data is sequentially stored in the internal memory, and in S107, it is determined whether or not the storage of the current position data of all the forklifts 1A to 1D is completed. If the storage has not been completed, the process returns to S105. Further, when the storage is finished, the subsequent processing is once finished.

On the other hand, FIGS. 4 and 5 show the forklifts 1A-
It is a flow chart explaining processing operation of data terminal 3 of 1D. In this embodiment, the wireless device 9A on the nearest fixed station side is provided between the usual exchanges of cargo handling data.
When a command radio wave for starting the position determination sent from any of 9C to 9C is received, the flow shifts to the routine work of this flowchart.

That is, in S201, after waiting for the reception of the command radio wave for starting the position determination from the radio equipment 9A to 9C on the fixed station side, when the radio wave is received, the process proceeds to S202.

In S202, it is judged whether or not the position data which is the result of the previous position determination is stored in the internal memory of the data terminal device 3, and if it is stored, S2 is stored.
10, the process proceeds to S203 if not stored. Since the position data is not stored in the initial state, S20
Move to 3.

In S203, radio waves of different frequencies simultaneously transmitted from the radio devices 9A to 9C on the fixed station side are sequentially received while being tuned. That is, radio waves of different frequencies are sequentially received while scanning.

Next, in S204, the received electric field strength corresponding to each frequency of each received radio wave is calculated, and S
At 205, the received electric field strength corresponding to each frequency is stored in the internal memory, and the process proceeds to S206.

In S206, it is determined whether or not the transmission end notification radio wave has been received from any of the fixed station side radio devices 9A to 9C which transmitted the position determination start command radio wave received in S201. If the notification radio wave has not been received, the processing of S203 to 206 is repeated. If the notification radio wave is received, S207
Move to.

Then, in S207, the received electric field strengths corresponding to the wireless devices 9A to 9C on the fixed station side stored in the internal memory are compared, and the frequency having the largest received electric field strength, that is, the fixed station is specified.

Subsequently, in S208, the specified frequency is used as the position data of the forklift, and a radio wave including the position data is transmitted from the wireless device 2 on the mobile station side, and the process proceeds to S209.

In step S209, the specified frequency which is the position data is stored in the internal memory of the data terminal device 3. Then, the process returns to S201 and waits for reception of the command radio wave for position determination again.

Therefore, from this point on, the desired data for the cargo handling work between the host computer 14 and the forklift is exchanged using the radio equipment on the fixed station side corresponding to this position data.

Next, when the command radio wave for the position determination is received again, the position data as the result of the previous position determination is stored in the internal memory in S202.
Move to 10.

In S210, among the radio waves of different frequencies transmitted simultaneously from the radio devices 9A to 9C on the fixed station side, the radio waves from the radio device on the fixed station side corresponding to the position data are tuned and received. ..

Then, in S211, the received electric field strength of the received radio wave is calculated, and then in S212, the received electric field strength is stored in the internal memory. Succeedingly, in S213, it is compared whether or not the received electric field intensity stored in the internal memory in S212 is equal to or higher than a predetermined determination reference level. Here, the determination reference level is the level of the received electric field strength at which the desired data for the cargo handling operation cannot be exchanged when the received electric field strength of the mobile station becomes smaller than that. If the received electric field strength stored in the internal memory is smaller than the determination reference level, the process proceeds to S203 to execute the same process as above to select a new wireless device on the fixed station side. If so, the process proceeds to S214.

In S214, it is determined whether or not the radio waves 9A to 9C on the fixed station side have been transmitted to notify the end of transmission. When the notification radio wave is received, the process proceeds to S215.

In step S215, the same frequency as the frequency identified in the previous position determination is used as the position data of the forklift, and a radio wave including the same position data is transmitted from the wireless device 2 on the mobile station side. Then, the process returns to S201 and waits for reception of the command radio wave for position determination again.

Next, the position determination of the forklift 1B in FIG. 1 will be described as an example. First, when radio waves of different frequencies f1, f2, and f3 are simultaneously transmitted from the radio devices 9A to 9C on the fixed station side for the first position determination, the data terminal device 3 of the forklift 1B.
Then, the received electric field strengths of the radio waves sequentially received while being tuned by the wireless device 2 are calculated, and the frequency having the largest received electric field strength is specified.

In this case, the highest received electric field strength is the frequency f2 transmitted from the nearest wireless device 9B.
And the data terminal 3 of the forklift 1B uses the identified frequency f2 as position data for the wireless device 2
Call from. And the frequency f which is the position data
2 is stored in the internal memory.

Therefore, the host computer 14 determines that the current position of the forklift 1B is close to the wireless device 9B on the fixed station side based on the frequency f2 which is the position data of the radio wave transmitted from the forklift 1B. ..

Then, desired data for cargo handling work is exchanged between the forklift 1B and the radio equipment 9B on the fixed station side. Next, for the second position determination,
It is assumed that the forklift 1B is moving to the position of the forklift 1C according to the arrow when radio waves of different frequencies f1, f2, and f3 are simultaneously transmitted from the radio devices 9A to 9C on the fixed station side.

Then, the data terminal unit 3 of the forklift 1B compares the received electric field strength of the radio wave of the frequency f2, which is the position data specified in the first position judgment, with the predetermined judgment reference level.

In this case, the electric field strength of the radio wave from the fixed station side wireless device 9C (frequency f3) is larger than that of the fixed station side wireless device 9B (frequency f2), but the fixed station side wireless device 9B. Since the received electric field strength of the radio wave of (frequency f2) is equal to or higher than the determination reference level, the data terminal machine 3 of the forklift 1B transmits the frequency f2 as position data from the wireless device 2. That is, the same position data as at the time of the first position determination is transmitted. Also, when the received electric field strengths of radio waves of the fixed station side wireless device 9B (frequency f2) and the fixed station side wireless device 9C (frequency f3) become equal,
Since the received electric field strength of the radio wave of the frequency f2 is equal to or higher than the determination reference level, the position data of the forklift 1B has the frequency f2.

Therefore, in the host computer 14, based on the frequency f2 which is the position data of the radio wave transmitted from the forklift 1B, the current position of the forklift 1B is set to the fixed station side as in the first position determination. It is determined that the position is close to the wireless device 9B.

Then, desired data for cargo handling work is exchanged between the forklift 1B and the radio equipment 9B on the fixed station side. Further, for the third position determination, when radio waves of different frequencies f1, f2, f3 are simultaneously transmitted from the radio devices 9A to 9C on the fixed station side, the forklift 1B moves to the position of the forklift 1D. Suppose that

Then, the data terminal unit 3 of the forklift 1B receives only the radio wave of the frequency f2 which is the position data specified in the first position judgment, and the received electric field strength is calculated to be a predetermined judgment reference level. Compare.

In this case, when the received electric field strength of the radio wave of the radio equipment 9B (frequency f2) on the fixed station side falls below the judgment reference level, the data terminal 3 of the forklift 1B receives the radio equipment 2 successively on the fixed station side. Radio devices 9A-9
The received electric field strength of the radio wave of C is calculated, and the frequency having the largest received electric field strength, that is, the fixed station is specified.

In this case, the highest received electric field strength is the frequency f3 transmitted from the nearest wireless device 9C.
, The data terminal 3 of the forklift 1B transmits the specified frequency f3 from the wireless device 2 as position data. Then, the frequency f3 which is the position data is stored in the internal memory.

Therefore, the host computer 14 determines, based on the position data (= frequency f3) transmitted from the forklift 1B, that the current position of the forklift 1B is close to the wireless device 9C on the fixed station side.

Then, desired data for cargo handling work is exchanged between the forklift 1B and the radio equipment 9C on the fixed station side. As described above, in the present embodiment, in the position determination for determining the fixed station and the mobile station that exchange desired data for the cargo handling work, the mobile station transmits the desired data before the position determination. If the received electric field strength of the radio wave of the fixed station with which the mobile station has exchanged is equal to or higher than a predetermined determination reference level, the frequency of the radio wave is used as the position data of the mobile station.

That is, in the mobile station, the radio waves for position determination transmitted by each fixed station are not always compared with each other. Therefore, in the mobile station of the radio wave for position determination transmitted by each fixed station. Even if the received electric field strength becomes equal,
The position data can be specified.

Further, it is not necessary to perform the operation of sequentially receiving the radio waves emitted by each fixed station while the mobile station tunes each time the position determination is made, calculating the received electric field strength for each frequency, and making a comparison. Therefore, the time required for the operation can be shortened.

In addition, since each fixed station simultaneously transmits radio waves for position determination of different frequencies, each fixed station sequentially emits radio waves for position determination including identification data for identifying each fixed station. The time required for position determination can be shortened as compared with the case where the position determination is performed.

In addition, since the processing for knowing the current position of each forklift is carried out while the desired data for the cargo handling work is exchanged, the time when the desired data for the cargo handling work is sent. You can always know the position of each forklift.

Further, since the host computer 14 can grasp the current positions of the forklifts 1A to 1D, the cargo handling work can be efficiently managed. The present invention is not limited to the above embodiment, but may be carried out as in the following (1) to (5). (1) The criterion level may be set to any value as long as the following conditions are satisfied. When the received electric field strength of the mobile station becomes smaller than that, it becomes impossible to exchange desired data for cargo handling work. The level at which the electric field strengths of two or more radio waves of the position determination radio waves transmitted from each fixed station are smaller than the level at which they become equal at any point on the premises. (2) In the above-described embodiment, three wireless devices 9A to 9C are provided on the fixed station side, and four forklifts 1A to 1D are provided as moving bodies, and the wireless device 2 and the data terminal device 3 on the mobile station side are provided respectively. However, the number of wireless devices and forklifts on the fixed station side may be other than the above. That is, the scale of the physical distribution system using the wireless LAN can be appropriately expanded or reduced. And, especially when the scale of the logistics system is expanded, the effect of determining the position of each forklift is further demonstrated, and
The effect of shortening the time required for position determination is also increased. (3) In the above-described embodiment, in the data terminal 3 of each forklift 1A to 1D, the wireless devices 9A to 9A on the side of each fixed station are provided.
Although the wireless devices 9A to 9C having the received field strength corresponding to C are specified, the data of the received field strengths corresponding to the wireless devices 9A to 9C on the fixed station side are transferred from the wireless device 2 on the mobile station side to the fixed station side. The wireless devices 9A to 9C may be temporarily sent to the wireless devices 9A to 9C, and then the host computer 14 may specify the wireless devices 9A to 9C having the highest received electric field strength.

Regarding the comparison between the judgment reference level and the received electric field strength at the mobile station of the radio wave transmitted by each of the fixed station side wireless devices 9A to 9C, the mobile station side wireless device 2 to the fixed station side wireless device is compared. It is also possible to once send the data for comparison to 9A to 9C and then specify the wireless devices 9A to 9C by the host computer 14. (4) In the above embodiment, the wireless LAN is embodied in the physical distribution system, but the physical distribution system may be embodied in the case of simply exchanging data between a fixed station and a mobile station. (5) In the above embodiment, the manned type forklift 1A to
Although it is embodied as a physical distribution system using 1D, it may be embodied as a physical distribution system using an automatically operated unmanned forklift or an automated guided vehicle.

[0057]

As described above in detail, according to the present invention, even if the electric field strengths of the radio waves transmitted from a plurality of fixed stations for position determination are equal to each other in the mobile station, the mobile body and the fixed station are not affected. There is an excellent effect that data can be reliably exchanged between them.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram showing a wireless LAN according to an embodiment of the present invention.

FIG. 2 is a diagram showing a configuration of a mobile station mounted on each forklift.

FIG. 3 is a flowchart illustrating a processing operation of a host computer.

FIG. 4 is a flowchart illustrating a processing operation of the data terminal.

FIG. 5 is a flowchart illustrating a processing operation of the data terminal.

[Explanation of symbols]

1A to 1D ... Forklift as a moving body, 2 ... Radio equipment constituting mobile station, 3 ... Data terminal equipment constituting mobile station, 9A-9C ... Radio equipment constituting fixed station, 11 ...
Wireless controller constituting the integrated control unit, 14 ... Host computer constituting the integrated control unit, 15 ... Integrated control unit

Claims (1)

Claim: What is claimed is: 1. A mobile station mounted on a mobile body and an arbitrary fixed station among a plurality of fixed stations which are controlled by a centralized control unit. In a mobile communication method for exchanging desired data between and using radio waves, radio waves of different frequencies pre-allocated to each of the fixed stations are transmitted from each of the fixed stations, and in the mobile station, When the radio wave is received from a fixed station that exchanges desired data using radio waves, the received electric field strength corresponding to the frequency is calculated, and when the received electric field strength becomes smaller than a predetermined judgment reference level. , Compare the received electric field strengths corresponding to each frequency from other fixed stations with each other, identify the frequency with the largest received electric field strength, and send the data between the fixed station transmitting the specified frequency. Mobile communication method adapted to the Ritori.