DESCRIPTION
Title of Invention:
WIRELESS COMMUNICATION APPARATUS, WIRELESS STATION
APPARATUS, INSTRUMENT CONTROL METHOD, AND INSTRUMENT
CONTROL PROGRAM
Technical Field
[0001] The present invention relates to a wireless communication apparatus, a
wireless station apparatus, an instrument control method, and an instrument control
program.
Background Art
[0002] In the technique disclosed in Non-Patent Literature 1, a battery-powered
operator control terminal apparatus performs wireless communication with a wireless
station apparatus wire-connected to a control instrument to control the control
instrument.
For example, if an emergency stop button is pressed at the operator control terminal apparatus, the operator control terminal apparatus transmits an emergency stop command to the wireless station apparatus through wireless communication, and the wireless station apparatus brings the control instrument to an emergency stop in accordance with the emergency stop command.
[0003] In the technique disclosed in Non-Patent Literature 2, an operator control terminal apparatus periodically transmits a neutral frame to a wireless station apparatus and, if a press on an emergency stop button is detected, stops neutral frame transmission. A control instrument takes, as a cue, expiration of a neutral frame monitoring cycle for monitoring of neutral frame reception to stop.

[0004] As techniques for bringing a control instrument to an emergency stop through wireless communication, the techniques disclosed in Patent Literatures 1 and 2 are available. Citation List Patent Literature
[0005] Patent Literature 1: JP 10-283022A Patent Literature 2: JP 03-028890U Non-Patent Literature
[0006] Non-Patent Literature 1: "SIMATIC HMI HMI device Mobile Panel 277F IWLAN V2, Mobile Panel 277F IWLAN (RFID Tag) Operating Instructions", 08/2008, A5E01003835-01,P. 11 Non-Patent Literature 2: IEC 62745 Summary of Invention Technical Problem
[0007] According to the technique disclosed in Non-Patent Literature 1, even if the emergency stop button is pressed, an emergency stop command may not arrive at the wireless station apparatus and may fail to stop the control instrument, as in the following cases a) to c):
a) The communication quality of a wireless channel deteriorates due to electromagnetic interference or the like, and an emergency stop command does not arrive at the wireless station apparatus.
b) The operator control terminal apparatus is unable to transmit an emergency stop command due to a low battery condition of the operator control terminal apparatus.
c) The operator control terminal apparatus is present outside a wireless range and is unable to transmit an emergency stop command.

[0008] According to the technique disclosed in Non-Patent Literature 2, the control instrument is stopped if the wireless station apparatus is unable to receive a neutral frame. The technique can solve the problem with the technique of Non-Patent Literature 1.
However, according to the technique disclosed in Non-Patent Literature 2, the operator control terminal apparatus needs to generate and transmit, at fixed time intervals, a neutral frame notifying the wireless station apparatus that stoppage of the control instrument is unnecessary while stoppage of the control instrument is unnecessary. That is, the technique disclosed in Non-Patent Literature 2 suffers the problem of constant consumption of computing resources for notification of the lack of the need for stoppage of the control instrument to the wireless station apparatus.
Even the techniques disclosed in Patent Literatures 1 and 2 are incapable of solving the problem.
[0009] The present invention mainly aims at solving the above-described problem. More specifically, the present invention has as its major object to notify a wireless station apparatus that stoppage of an instrument is unnecessary without consuming computing resources while stoppage of the instrument is unnecessary and reliably stop the instrument through the wireless station apparatus if the need for stoppage of the instrument arises. Solution to Problem
[0010] A wireless communication apparatus including a wireless interface to continue transmitting a periodic signal at fixed intervals if once settings for transmission of the periodic signal are made, the wireless communication apparatus according to the present invention includes:
a first control unit to make, in the wireless interface, settings for transmission

of a first periodic signal which is a periodic signal giving notification that stoppage of an instrument is unnecessary if stoppage of the instrument is unnecessary and cause the wireless interface to continue transmitting the first periodic signal at the fixed intervals to a wireless station apparatus capable of stopping the instrument, while stoppage of the instrument is unnecessary; and
a second control unit to perform either one of periodic signal switching control and periodic signal stop control if a need for stoppage of the instrument arises, the periodic signal switching control making, in the wireless interface, settings for transmission of a second periodic signal which is a periodic signal giving notification that stoppage of the instrument is necessary and causing the wireless interface to continue transmitting the second periodic signal to the wireless station apparatus at the fixed intervals instead of the first periodic signal, the periodic signal stop control causing the wireless interface to stop transmission of the first periodic signal. Advantageous Effects of Invention
[0011 ] According to the present invention, if stoppage of the instrument is unnecessary, settings for transmission of the first periodic signal are made in the wireless interface. With the settings, the first periodic signal is continuously transmitted from the wireless interface to the wireless station apparatus while stoppage of the instrument is unnecessary. For this reason, it is possible to notify the wireless station apparatus that stoppage of the instrument is unnecessary without consuming computing resources while stoppage of the instrument is unnecessary. If a need for stoppage of the instrument arises, the instrument can be reliably stopped through the wireless station apparatus by the control that switches to transmission of the second periodic signal or the control that stops transmission of the first periodic signal. Brief Description of Drawings

[0012] Fig. 1 is a diagram illustrating an example of a system configuration according to Embodiment 1.
Fig. 2 is a diagram illustrating an example of a configuration of an operator control terminal apparatus according to Embodiment 1.
Fig. 3 is a diagram illustrating an example of a configuration of a wireless station apparatus according to Embodiment 1.
Fig. 4 is a chart illustrating an operation sequence according to Embodiment 1.
Fig. 5 is a chart illustrating an operation sequence according to Embodiment 1.
Fig. 6 is a flowchart illustrating an example of operation of the operator control terminal apparatus according to Embodiment 1.
Fig. 7 is a flowchart illustrating an example of operation of the wireless station apparatus according to Embodiment 1.
Fig. 8 is a chart illustrating an operation sequence according to Embodiment 2.
Fig. 9 is a flowchart illustrating an example of operation of an operator control terminal apparatus according to Embodiment 2.
Fig. 10 is a flowchart illustrating an example of operation of a wireless station apparatus according to Embodiment 2.
Fig. 11 is a chart illustrating an operation sequence according to Embodiment 3.
Fig. 12 is a chart illustrating an operation sequence according to Embodiment 3.
Fig. 13 is a flowchart illustrating an example of operation of an operator control terminal apparatus according to Embodiment 3.
Fig. 14 is a flowchart illustrating an example of operation of a wireless station
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Fig. 15 is a chart illustrating an operation sequence according to Embodiment 4.
Fig. 16 is a chart illustrating an operation sequence according to Embodiment 4.
Fig. 17 is a flowchart illustrating an example of operation of an operator control terminal apparatus according to Embodiment 4.
Fig. 18 is a flowchart illustrating an example of operation of a wireless station apparatus according to Embodiment 4. Description of Embodiments
[0013] Embodiments of the present invention will be described below with reference to the drawings. Parts, to which same reference numerals are assigned, in the following description of the embodiments and the drawings denote same parts or corresponding parts. [0014] Embodiment 1.
*** Description of Configuration ***
Fig. 1 illustrates an example of a system configuration according to the present embodiment.
[0015] An operator control terminal apparatus 1 is a wireless communication apparatus. The operator control terminal apparatus 1 includes an emergency stop button 4 and a wireless interface 5. The emergency stop button 4 is pressed by an operator if emergency stoppage of a control instrument 3 is necessary.
The wireless interface 5 includes an antenna for transmitting an annunciation signal (beacon frame) 8 and an RF (Radio Frequency) circuit. Once settings for transmission of the annunciation signal (beacon frame) 8 are made in the wireless interface 5, the wireless interface 5 continues transmitting the annunciation signal

(beacon frame) 8 at fixed intervals after that.
Before the emergency stop button 4 is pressed, that is, if emergency stoppage of the control instrument 3 is unnecessary, the operator control terminal apparatus 1 makes, in the wireless interface 5, settings for transmission of the annunciation signal (beacon frame) 8 with an added steady-state notification 7 giving notification that emergency stoppage of the control instrument 3 is unnecessary, as illustrated in Fig. 4. As a result, the annunciation signal (beacon frame) 8 with the added steady-state notification 7 is continuously transmitted from the wireless interface 5 at the fixed intervals while emergency stoppage of the control instrument 3 is unnecessary. The annunciation signal (beacon frame) 8 with the added steady-state notification 7 will hereinafter be referred to as a first annunciation signal (beacon frame) 81.
On the other hand, if the emergency stop button 4 is pressed, and the need for emergency stoppage of the control instrument 3 arises, the operator control terminal apparatus 1 makes, in the wireless interface 5, settings for transmission of the annunciation signal (beacon frame) 8 with the steady-state notification 7 deleted. After that, the annunciation signal (beacon frame) 8 with the steady-state notification 7 deleted from the wireless interface 5 is continuously transmitted from the wireless interface 5 at the fixed intervals. The annunciation signal (beacon frame) 8 with the steady-state notification 7 deleted will hereinafter be referred to as a second annunciation signal (beacon frame) 82. Note that the first annunciation signal (beacon frame) 81 and the second annunciation signal (beacon frame) 82 are collectively referred to as the annunciation signals (beacon frames) 8 if distinction between the first annunciation signal (beacon frame) 81 and the second annunciation signal (beacon frame) 82 is unnecessary.
Operation to be performed by the operator control terminal apparatus 1

corresponds to an instrument control method.
[0016] A wireless station apparatus 2 is connected to the control instrument 3 and brings the control instrument 3 to an emergency stop. The wireless station apparatus 2 includes a wireless interface 6 and an instrument interface 9.
The wireless station apparatus 2 receives the annunciation signal (beacon frame) 8 transmitted from the operator control terminal apparatus 1 via the wireless interface 6 and determines whether the annunciation signal (beacon frame) 8 includes the steady-state notification 7. The wireless station apparatus 2 does bit bring the control instrument 3 to an emergency stop as long as the annunciation signal (beacon frame) 8 includes the steady-state notification 7. On the other hand, if the annunciation signal (beacon frame) 8 does not include the steady-state notification 7, the wireless station apparatus 2 brings the control instrument 3 to an emergency stop via the wireless interface 6.
The wireless interface 6 includes an antenna for receiving the annunciation signal (beacon frame) 8 and an RF circuit.
The instrument interface 9 is a circuit which serves as an interface with the control instrument 3.
Note that operation to be performed by the wireless station apparatus 2 also corresponds to the instrument control method.
[0017] Fig. 2 illustrates an example of an internal configuration of the operator control terminal apparatus 1.
The operator control terminal apparatus 1 has a hardware configuration with a processor 901, a storage device 902, a timer 903, a display 904, and a battery 905. The operator control terminal apparatus 1 is a computer.
The storage device 902 stores a program which implements functions of a stop

monitoring unit 10, a wireless communication unit 11, and a display unit 13. The processor 901 reads out the program that implements the stop monitoring unit 10, the wireless communication unit 11, and the display unit 13 from the storage device 902 and executes the program, thereby operating as the stop monitoring unit 10, the wireless communication unit 11, and the display unit 13. Of the program, a program which implements the functions of the stop monitoring unit 10 and the wireless communication unit 11 corresponds to an instrument control program.
The timer 903 measures a time period.
The display 904 displays display information for controlling the control instrument 3.
The battery 905 supplies power to the operator control terminal apparatus 1.
The processor 901 measures a transmission interval for the annunciation signal (beacon frame) 8 through software control. The processor 901 measures the transmission interval for the annunciation signal (beacon frame) 8 by performing constant multiplication of the time period measured by the timer 903. For example, if the transmission interval for the annunciation signal (beacon frame) 8 is 100 ms, and the time period which is to be measured by the timer 903 is 10 ms, the processor 901 measures the transmission interval for the annunciation signal (beacon frame) 8 by performing multiplication of the measurement time period for the timer 903 by a factor of 10 (counting up to 10).
Note that the operator control terminal apparatus 1 may include a dedicated hardware for measuring the transmission interval for the annunciation signal (beacon frame) 8.
[0018] The stop monitoring unit 10 watches for presence/absence of a press on the emergency stop button 4. That is, the stop monitoring unit 10 determines whether

emergency stoppage of the control instrument 3 is necessary.
[0019] The wireless communication unit 11 makes, in the wireless interface 5, settings for transmission of the first annunciation signal (beacon frame) 81 giving notification that stoppage of the control instrument 3 is unnecessary if the emergency stop button 4 is not pressed, that is, if emergency stoppage of the control instrument 3 is unnecessary. As a result, the first annunciation signal (beacon frame) 81 is continuously transmitted from the wireless interface 5 at the fixed intervals while emergency stoppage of the control instrument 3 is unnecessary. The first annunciation signal (beacon frame) 81 corresponds to a first periodic signal. The steady-state notification 7 corresponds to notification information.
If the emergency stop button 4 is pressed, that is, the need for emergency stoppage of the control instrument 3 arises, the wireless communication unit 11 makes, in the wireless interface 5, settings for transmission of the second annunciation signal (beacon frame) 82 giving notification that emergency stoppage of the control instrument 3 is necessary instead of the first annunciation signal (beacon frame) 81. As a result, the second annunciation signal (beacon frame) 82 is continuously transmitted from the wireless interface 5 at the fixed intervals. The second annunciation signal (beacon frame) 82 corresponds to a second periodic signal. Note that control which makes, in the wireless interface 5, settings for transmission of the second annunciation signal (beacon frame) 82 instead of the first annunciation signal (beacon frame) 81 and causes the wireless interface 5 to continue transmission of the second annunciation signal (beacon frame) 82 to the wireless station apparatus 2 is called periodic signal switching control.
The wireless communication unit 11 corresponds to a first control unit and a second control unit. Operation to be performed by the wireless communication unit 11

corresponds to a first control process and a second control process.
[0020] If the wireless communication unit 11 sets a frame format for the annunciation
signal (beacon frame) 8 in the wireless interface 5, the annunciation signal (beacon
frame) 8 in the frame format is transmitted from the wireless interface 5 at the fixed
intervals.
For example, if the wireless interface 5 supports a wireless LAN (Local Area Network), when the wireless communication unit 11 sets an access point and the frame format for the annunciation signal (beacon frame) 8 in the wireless interface 5, the wireless interface 5 periodically transmits the annunciation signal (beacon frame) 8 in the set frame format to the wireless station apparatus 2 via the access point.
That is, if emergency stoppage of the control instrument 3 is unnecessary, the wireless communication unit 11 sets a frame format for the first annunciation signal (beacon frame) 81 in the wireless interface 5. The setting allows the wireless interface 5 to continue periodically transmitting the second annunciation signal (beacon frame) 82 to the wireless station apparatus 2 while emergency stoppage of the control instrument 3 is unnecessary. For this reason, the processor 901 can notify the wireless station apparatus 2 that stoppage of the control instrument 3 is unnecessary without consuming computing resources while emergency stoppage of the control instrument 3 is unnecessary.
Meanwhile, if the emergency stop button 4 is pressed, the wireless communication unit 11 sets a frame format for the second annunciation signal (beacon frame) 82 in the wireless interface 5. The setting allows the wireless interface 5 to continue periodically transmitting the second annunciation signal (beacon frame) 82 to the wireless station apparatus 2.
Setting the frame format for the first annunciation signal (beacon frame) 81 in

the wireless interface 5 will hereinafter be referred to as making settings for transmission of the first annunciation signal (beacon frame) 81. Setting the frame format for transmission of the second annunciation signal (beacon frame) 82 in the wireless interface 5 will be referred to as making settings for transmission of the second annunciation signal (beacon frame) 82. For example, if the wireless interface 5 supports a wireless LAN, the wireless communication unit 11 makes settings for transmission of the first annunciation signal (beacon frame) 81 by extending an Information Element in an annunciation signal (beacon frame) disclosed in "8.4.2, Part 11, IEEE Std 802.11™-2012" (Reference Literature). The wireless communication unit 11 makes settings for transmission of the second annunciation signal (beacon frame) 82 by deleting the Information Element in question.
Reference Literature:
IEEE Std 802.11™-2012, Part 11: Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) Specifications, 8.4.2 Information elements, P. 474 [0021] The display unit 13 outputs display information to be used to control the control instrument 3 to the display 904.
[0022] Fig. 4 illustrates an example of an internal configuration of the wireless station apparatus 2.
The wireless station apparatus 2 has a hardware configuration with a processor 911, a storage device 912, a timer 913, and a counter 914. The wireless station apparatus 2 is a computer.
The storage device 912 stores a program which implements functions of a wireless communication unit 15 and a stop control unit 16. The processor 911 reads out the program that implements the wireless communication unit 15 and the stop control unit 16 from the storage device 912 and executes the program, thereby operating

as the wireless communication unit 15 and the stop control unit 16. The program that implements the functions of the wireless communication unit 15 and the stop control unit 16 also corresponds to the instrument control program.
The timer 913 measures a time period.
The counter 914 counts the number of failures to receive the first annunciation signal (beacon frame) 81.
The processor 911 measures a reception interval for the annunciation signal (beacon frame) 8 through software control. The processor 911 measures the reception interval for the annunciation signal (beacon frame) 8 by performing constant multiplication of the time period measured by the timer 913. For example, if the reception interval for the annunciation signal (beacon frame) 8 is 100 ms, and the time period, which is to be measured by the timer 913, is 10 ms, the processor 911 measures the reception interval for the annunciation signal (beacon frame) 8 by performing multiplication of the measurement time period for the timer 913 by a factor of 10 (counting up to 10).
Note that the wireless station apparatus 2 may include a dedicated hardware for measuring the reception interval for the annunciation signal (beacon frame) 8. [0023] The wireless communication unit 15 receives the first annunciation signal (beacon frame) 81 or the second annunciation signal (beacon frame) 82. The wireless communication unit 15 corresponds to a reception unit. Operation to be performed by the wireless communication unit 15 corresponds to a reception process. [0024] The stop control unit 16 brings the control instrument 3 to an emergency stop if the wireless communication unit 15 receives the second annunciation signal (beacon frame) 82. The stop control unit 16 also brings the control instrument 3 to an emergency stop if the wireless communication unit 15 does not receive the first

annunciation signal (beacon frame) 81 for a predetermined time period.
For example, if the communication quality of a wireless channel deteriorates due to electromagnetic interference or the like, and the first annunciation signal (beacon frame) 81 does not arrive at the wireless station apparatus 2, the stop control unit 16 brings the control instrument 3 to an emergency stop. Additionally, if the operator control terminal apparatus 1 is unable to transmit the first annunciation signal (beacon frame) 81 due to a low battery condition of the operator control terminal apparatus 1, the stop control unit 16 brings the control instrument 3 to an emergency stop. Moreover, if the operator control terminal apparatus 1 is present outside a wireless range and is unable to transmit the first annunciation signal (beacon frame) 81, the stop control unit 16 brings the control instrument 3 to an emergency stop.
Note that operation to be performed by the stop control unit 16 corresponds to a stop control process. [0025] *** Description of Operation ***
An operation sequence of the operator control terminal apparatus 1 and the wireless station apparatus 2 before the emergency stop button 4 is pressed and an operation sequence of the operator control terminal apparatus 1 and the wireless station apparatus 2 after the emergency stop button 4 is pressed will be described with reference to Fig. 4.
[0026] Before the emergency stop button 4 is pressed, in the operator control terminal apparatus 1, the wireless communication unit 11 makes settings for transmission of the first annunciation signal (beacon frame) 81 in the wireless interface 5. For this reason, the first annunciation signal (beacon frame) 81 including the steady-state notification 7 is transmitted from the wireless interface 5 to the wireless station apparatus 2 at the fixed transmission intervals.

In the wireless station apparatus 2, the wireless communication unit 15 activates at the reception intervals corresponding to the transmission interval in the operator control terminal apparatus 1. The wireless communication unit 15 then receives the first annunciation signal (beacon frame) 81 via the wireless interface 6. The wireless communication unit 15 then extracts the steady-state notification 7 from the first annunciation signal (beacon frame) 81. Since the wireless communication unit 15 has succeeded in extracting the steady-state notification 7 from the first annunciation signal (beacon frame) 81, the control instrument 3 is not brought to an emergency stop.
[0027] If the emergency stop button 4 is pressed, in the operator control terminal apparatus 1, the stop monitoring unit 10 senses that the emergency stop button 4 is pressed. The stop monitoring unit 10 then outputs, to the wireless communication unit 11, a steady-state notification deletion instruction 18 giving an instruction to make settings for transmission of the second annunciation signal (beacon frame) 82. The wireless communication unit 11 makes settings for transmission of the second annunciation signal (beacon frame) 82 in the wireless interface 5 in accordance with the steady-state notification deletion instruction 18 (steady-state notification deletion 19). As a result, the second annunciation signal (beacon frame) 82 without the steady-state notification 7 is transmitted from the wireless interface 5 to the wireless station apparatus 2.
In the wireless station apparatus 2, the wireless communication unit 15 receives the second annunciation signal (beacon frame) 82 via the wireless interface 6. In this case, the wireless communication unit 15 cannot extract the steady-state notification 7 from the second annunciation signal (beacon frame) 82. For this reason, the wireless communication unit 15 outputs a stop signal instruction 20 to the stop

control unit 16. The stop control unit 16 transmits a stop signal 21 to the control instrument 3 via the instrument interface 9 in accordance with the stop signal instruction 20 to bring the control instrument 3 to an emergency stop (emergency stoppage 22). [0028] An operation sequence of the wireless station apparatus 2 in a case where the first annunciation signal (beacon frame) 81 does not arrive at the wireless station apparatus 2 will be illustrated with reference to Fig. 5.
[0029] In the example in Fig. 5, although the wireless interface 5 of the operator control terminal apparatus 1 transmits the first annunciation signal (beacon frame) 81, the first annunciation signal (beacon frame) 81 does not arrive at the wireless station apparatus 2 due to deterioration of the communication quality of the wireless channel resulting from, for example, electromagnetic interference. The wireless communication unit 15 counts the number of failures to receive the first annunciation signal (beacon frame) 81 using the counter 914. If the wireless communication unit 15 fails to receive the first annunciation signal (beacon frame) 81 N (N > 2) consecutive times, the wireless communication unit 15 outputs the stop signal instruction 20 to the stop control unit 16. The stop control unit 16 transmits the stop signal 21 to the control instrument 3 via the instrument interface 9 in accordance with the stop signal instruction 20 to bring the control instrument 3 to an emergency stop (the emergency stoppage 22).
[0030] An example of operation of the wireless communication unit 11 in the operator control terminal apparatus 1 will next be described with reference to Fig. 6. [0031] The wireless communication unit 11 determines whether the steady-state notification deletion instruction 18 is output from the stop monitoring unit 10 (step S21).
If the steady-state notification deletion instruction 18 is not output (NO in step

S21), the wireless communication unit 11 makes, in the wireless interface 5, settings for transmission of the first annunciation signal (beacon frame) 81 with the added steady-state notification 7 (step S22). Note that if the settings for transmission of the first annunciation signal (beacon frame) 81 have already been made in the wireless interface 5, the wireless communication unit 11 skips step S22. [0032] On the other hand, if the steady-state notification deletion instruction 18 is output (YES in step S21), the wireless communication unit 11 makes, in the wireless interface 5, settings for transmission of the second annunciation signal (beacon frame) 82 with the steady-state notification 7 deleted (step S23).
[0033] As described above, the wireless communication unit 11 makes, in the wireless interface 5, settings for transmission of the first annunciation signal (beacon frame) 81 that is a periodic signal giving notification that emergency stoppage of the control instrument 3 is unnecessary if emergency stoppage of the control instrument 3 is unnecessary. This allows the wireless communication unit 11 to continue transmitting the first annunciation signal (beacon frame) 81 from the wireless interface 5 to the wireless station apparatus 2 at the fixed intervals while emergency stoppage of the control instrument 3 is unnecessary.
On the other hand, if the need for emergency stoppage of the control instrument 3 arises, the wireless communication unit 11 makes, in the wireless interface 5, settings for transmission of the second annunciation signal (beacon frame) 82 that is a periodic signal giving notification that emergency stoppage of the control instrument 3 is necessary. This allows the wireless communication unit 11 to cause the wireless interface 5 to continue transmitting the second annunciation signal (beacon frame) 82 to the wireless station apparatus 2 at the fixed intervals, instead of the first annunciation signal (beacon frame) 81. Note that control which switches the wireless interface 5

from the first annunciation signal (beacon frame) 81 to the second annunciation signal
(beacon frame) 82 is called the periodic signal switching control. In the present
embodiment, the wireless communication unit 11 performs the periodic signal switching
control if the need for emergency stoppage of the control instrument 3 arises.
[0034] An example of operation of the wireless communication unit 15 in the wireless
station apparatus 2 will next be described with reference to Fig. 7.
[0035] The wireless communication unit 15 activates at the reception intervals for the
annunciation signal (beacon frame) 8. More specifically, the reception interval is set
in the timer 913. When the timer 913 expires, the wireless communication unit 15 is
activated by the timer 913.
If the wireless communication unit 15 activates to receive the annunciation signal (beacon frame) 8 via the wireless interface 6 (YES in step S31), the wireless communication unit 15 determines whether the received annunciation signal (beacon frame) 8 includes the steady-state notification 7 (step S32). That is, the wireless communication unit 15 determines whether the received annunciation signal (beacon frame) 8 is the first annunciation signal (beacon frame) 81 or the second annunciation signal (beacon frame) 82.
[0036] If the received annunciation signal (beacon frame) 8 is the first annunciation signal (beacon frame) 81 (YES in step S32), the wireless communication unit 15 initializes the counter 914 (step S33).
[0037] On the other hand, if the received annunciation signal (beacon frame) 8 is the second annunciation signal (beacon frame) 82 (NO in step S32), the wireless communication unit 15 determines that the emergency stop button 4 is pressed and outputs the stop signal instruction 20 to the stop control unit 16 (step S34). [0038] If the annunciation signal (beacon frame) 8 is not received in step S31 (NO in

step S31), the wireless communication unit 15 determines whether the wireless
communication unit 15 has failed to receive the annunciation signal (beacon frame) 8 N
(N > 2) consecutive times (step S35).
[0039] If the wireless communication unit 15 has failed to receive the annunciation
signal (beacon frame) 8 N consecutive times (YES in step S35), the wireless
communication unit 15 determines that the annunciation signal (beacon frame) 8 from
the operator control terminal apparatus 1 has not arrived and outputs the stop signal
instruction 20 to the stop control unit 16 (step S36).
[0040] On the other hand, if the number of failures to receive the annunciation signal
(beacon frame) 8 is less than N (NO in step S35), the wireless communication unit 15
increments a value in the counter 914 by one (step S37).
[0041] * * * Description of Advantageous Effects of Embodiment * * *
According to the present embodiment, if emergency stoppage of the control instrument 3 is unnecessary, settings for transmission of the first annunciation signal (beacon frame) 81 are made in the wireless interface 5. With the settings, the first annunciation signal (beacon frame) 81 is continuously transmitted from the wireless interface 5 to the wireless station apparatus 2 while emergency stoppage of the control instrument 3 is unnecessary. It is thus possible to notify the wireless station apparatus 2 that emergency stoppage of the control instrument 3 is unnecessary without consuming computing resources of the processor 901 while emergency stoppage of the control instrument 3 is unnecessary.
According to the present embodiment, if the need to bring the control instrument 3 to an emergency stop arises, it is possible to reliably bring the control instrument 3 to an emergency stop through the wireless station apparatus 2 by the control that switches to transmission of the second annunciation signal (beacon frame)

82.
[0042] According to the technique of Non-Patent Literature 2, there is a problem in that the control instrument 3 needs a function of terminating a neutral frame, which increases resources needed for the control instrument 3. According to the present embodiment, the wireless station apparatus 2 terminates the annunciation signal (beacon frame) 8, and the control instrument 3 need not be changed.
Even after transmission of the second annunciation signal (beacon frame) 82 brings the control instrument 3 to an emergency stop, the operator control terminal apparatus 1 and the wireless station apparatus 2 are connected by a wireless link. The operator control terminal apparatus 1 is thus capable of monitoring the status of the control instrument 3 in an emergency stopped state via the wireless station apparatus 2. [0043] Embodiment 2.
In the present embodiment, if an emergency stop button 4 is pressed, an operator control terminal apparatus 1 purposely stops transmission of an annunciation signal (beacon frame) 8.
Note that the annunciation signals (beacon frames) 8 are not divided into a first annunciation signal (beacon frame) 81 and a second annunciation signal (beacon frame) 82, unlike Embodiment 1. That is, in the present embodiment, only the annunciation signal (beacon frame) 8 without a steady-state notification 7 is transmitted from the operator control terminal apparatus 1 to a wireless station apparatus 2.
In the present embodiment, the annunciation signal (beacon frame) 8 is transmitted from a wireless interface 5 to the wireless station apparatus 2 while emergency stoppage of a control instrument 3 is unnecessary. The wireless station apparatus 2 determines that emergency stoppage of the control instrument 3 is unnecessary while the wireless station apparatus 2 receives the annunciation signal

(beacon frame) 8. That is, in the present embodiment, the annunciation signal (beacon frame) 8 corresponds to a first periodic signal.
If the need for emergency stoppage of the control instrument 3 arises, and the emergency stop button 4 is pressed, the operator control terminal apparatus 1 stops transmission of the annunciation signal (beacon frame) 8 from the wireless interface 5. The wireless station apparatus 2 no longer receives the annunciation signal (beacon frame) 8, determines that emergency stoppage of the control instrument 3 is necessary, and brings the control instrument 3 to an emergency stop. [0044] *** Description of Configuration ***
A system configuration according to the present embodiment is as illustrated in Fig. 1.
An example of a configuration of the operator control terminal apparatus 1 according to the present embodiment is as illustrated in Fig. 2. Note that, in the present embodiment, a wireless communication unit 11 stops transmission of the annunciation signal (beacon frame) 8 from the wireless interface 5 when the emergency stop button 4 is pressed. Components other than the wireless communication unit 11 perform same operations as in Embodiment 1.
An example of a configuration of the wireless station apparatus 2 according to the present embodiment is as illustrated in Fig. 3. Components of the wireless station apparatus 2 perform same operations as in Embodiment 1. [0045] *** Description of Operation ***
An operation sequence of the operator control terminal apparatus 1 and the wireless station apparatus 2 before the emergency stop button 4 is pressed and an operation sequence of the operator control terminal apparatus 1 and the wireless station apparatus 2 after the emergency stop button 4 is pressed will be described with

reference to Fig. 8.
[0046] Before the emergency stop button 4 is pressed, in the operator control terminal apparatus 1, the wireless communication unit 11 makes settings for transmission of the annunciation signal (beacon frame) 8 in advance in the wireless interface 5. For this reason, the annunciation signal (beacon frame) 8 is transmitted from the wireless interface 5 to the wireless station apparatus 2 at fixed transmission intervals.
In the wireless station apparatus 2, a wireless communication unit 15 activates at reception intervals corresponding to the transmission interval in the operator control terminal apparatus 1. The wireless communication unit 15 then receives the annunciation signal (beacon frame) 8 via a wireless interface 6. Since the wireless communication unit 15 has succeeded in receiving the annunciation signal (beacon frame) 8, the control instrument 3 is not brought to an emergency stop. [0047] If the emergency stop button 4 is pressed, in the operator control terminal apparatus 1, a stop monitoring unit 10 senses that the emergency stop button 4 is pressed. The stop monitoring unit 10 then outputs, to the wireless communication unit 11, an annunciation signal (beacon frame) stop instruction 40 giving an instruction to stop transmission of the annunciation signal (beacon frame) 8. The wireless communication unit 11 stops transmission of the annunciation signal (beacon frame) 8 from the wireless interface 5 in accordance with the annunciation signal (beacon frame) stop instruction 40 (annunciation signal (beacon frame) stoppage 41). As a result, transmission of the annunciation signal (beacon frame) 8 from the wireless interface 5 is stopped.
In the wireless station apparatus 2, since transmission of the annunciation signal (beacon frame) 8 has stopped in the operator control terminal apparatus 1, the wireless communication unit 15 does not receive the annunciation signal (beacon frame)

8. The wireless communication unit 15 counts the number of failures to receive the annunciation signal (beacon frame) 8 using a counter 914. If the wireless communication unit 15 has failed to receive the annunciation signal (beacon frame) 8 N (N > 2) consecutive times, the wireless communication unit 15 outputs a stop signal instruction 20 to a stop control unit 16. The stop control unit 16 transmits a stop signal 21 to the control instrument 3 via an instrument interface 9 in accordance with the stop signal instruction 20 to bring the control instrument 3 to an emergency stop (emergency stoppage 22).
[0048] An example of operation of the wireless communication unit 11 in the operator control terminal apparatus 1 will next be described with reference to Fig. 9. [0049] The wireless communication unit 11 determines whether the annunciation signal (beacon frame) stop instruction 40 is output from the stop monitoring unit 10 (step S41). If the annunciation signal (beacon frame) stop instruction 40 is not output (NO in step S41), the wireless communication unit 11 make settings for transmission of the annunciation signal (beacon frame) 8 in the wireless interface 5 (step S42). Note that if the settings for transmission of the annunciation signal (beacon frame) 8 have already been made in the wireless interface 5, the wireless communication unit 11 skips step S42.
[0050] On the other hand, if the annunciation signal (beacon frame) stop instruction 40 is output (YES in step S41), the wireless communication unit 11 instructs the wireless interface 5 to stop transmission of the annunciation signal (beacon frame) 8 (step S43). This stops transmission of the annunciation signal (beacon frame) 8 from the wireless interface 5.
[0051] As described above, the wireless communication unit 11 makes, in the wireless interface 5, settings for transmission of the annunciation signal (beacon frame) 8 that is

a periodic signal giving notification that emergency stoppage 01 the control instrument 3 is unnecessary if emergency stoppage of the control instrument 3 is unnecessary. This allows the wireless communication unit 11 to continue transmitting the annunciation signal (beacon frame) 8 from the wireless interface 5 to the wireless station apparatus 2 at the fixed intervals while emergency stoppage of the control instrument 3 is unnecessary.
On the other hand, if the need for emergency stoppage of the control instrument 3 arises, the wireless communication unit 11 instructs the wireless interface 5 to stop transmission of the annunciation signal (beacon frame) 8. This allows the wireless communication unit 11 to stop transmission of the annunciation signal (beacon frame) 8 from the wireless interface 5. Note that control which stops transmission of the annunciation signal (beacon frame) 8 from the wireless interface 5 is called periodic signal stop control. In the present embodiment, the wireless communication unit 11 performs the periodic signal stop control if the need for emergency stoppage of the control instrument 3 arises.
[0052] An example of operation of the wireless communication unit 15 in the wireless station apparatus 2 will next be described with reference to Fig. 10. [0053] In the present embodiment as well, the wireless communication unit 15 activates at the reception intervals for the annunciation signal (beacon frame) 8. More specifically, the reception interval is set in a timer 913. When the timer 913 expires, the wireless communication unit 15 is activated by the timer 913.
If the wireless communication unit 15 receives the annunciation signal (beacon frame) 8 via the wireless interface 6 (YES in step S51), the wireless communication unit 15 initializes the counter 914 (step S52). [0054] On the other hand, if the wireless communication unit 15 does not receive the

annunciation signal (beacon frame) 8 (NO in step S51), the wireless communication unit 15 determines whether the wireless communication unit 15 has failed to receive the annunciation signal (beacon frame) 8 N (N > 2) consecutive times (step S53). [0055] If the wireless communication unit 15 has failed to receive the annunciation signal (beacon frame) 8 N consecutive times (YES in step S53), the wireless communication unit 15 determines that the annunciation signal (beacon frame) 8 from the operator control terminal apparatus 1 has not arrived and outputs the stop signal instruction 20 to the stop control unit 16 (step S54).
[0056] On the other hand, if the number of failures to receive the annunciation signal (beacon frame) 8 is less than N (NO in step S53), the wireless communication unit 15 increments a value in the counter 914 by one (step S55). [0057] *** Description of Advantageous Effects of Embodiment ***
According to the present embodiment, if emergency stoppage of the control instrument 3 is unnecessary, settings for transmission of the annunciation signal (beacon frame) 8 are made in the wireless interface 5. With the settings, the annunciation signal (beacon frame) 8 is continuously transmitted from the wireless interface 5 to the wireless station apparatus 2 while emergency stoppage of the control instrument 3 is unnecessary. It is thus possible to notify the wireless station apparatus 2 that emergency stoppage of the control instrument 3 is unnecessary without consuming computing resources of a processor 901 while emergency stoppage of the control instrument 3 is unnecessary.
According to the present embodiment, if the need to bring the control instrument 3 to an emergency stop arises, it is possible to reliably bring the control instrument 3 to an emergency stop through the wireless station apparatus 2 by the control that stops transmission of the annunciation signal (beacon frame) 8.

[0058] Embodiment3.
In the present embodiment, when an emergency stop button 4 is pressed, an operator control terminal apparatus 1 transmits a stop instruction frame which is a stop instruction signal to a wireless station apparatus 2 before stopping transmission of an annunciation signal (beacon frame) 8. If the stop instruction frame fails to arrive at the wireless station apparatus 2, the operator control terminal apparatus 1 stops transmission of the annunciation signal (beacon frame) 8, like Embodiment 2.
The present embodiment is obtained by adding a procedure for transmission of a stop instruction frame to the procedure according to Embodiment 2.
In the present embodiment, the annunciation signals (beacon frames) 8 are not divided into a first annunciation signal (beacon frame) 81 and a second annunciation signal (beacon frame) 82, like Embodiment 2. [0059] *** Description of Configuration ***
A system configuration according to the present embodiment is as illustrated in Fig. 1.
An example of a configuration of the operator control terminal apparatus 1 according to the present embodiment is as illustrated in Fig. 2. Note that, in the present embodiment, a stop monitoring unit 10 instructs a wireless communication unit 11 to transmit a stop instruction frame when the emergency stop button 4 is pressed. The wireless communication unit 11 transmits the stop instruction frame to the wireless station apparatus 2. If the stop instruction frame fails to arrive at the wireless station apparatus 2, the wireless communication unit 11 stops transmission of the annunciation signal (beacon frame) 8 from a wireless interface 5. Components other than the stop monitoring unit 10 and the wireless communication unit 11 perform same operations as in Embodiment 2.

An example of a configuration of the wireless station apparatus 2 according to the present embodiment is as illustrated in Fig. 3. Note that, in the present embodiment, a wireless communication unit 15 transmits an acknowledgment of receipt to the operator control terminal apparatus 1 upon receipt of a stop instruction frame. The wireless communication unit 15 also instructs a stop control unit 16 to bring a control instrument 3 to an emergency stop, in response to the receipt of the stop instruction frame. Components other than the wireless communication unit 15 perform same operations as in Embodiment 2. [0060] * * * Description of Operation * * *
An operation sequence of the operator control terminal apparatus 1 and the wireless station apparatus 2 before the emergency stop button 4 is pressed and an operation sequence of the operator control terminal apparatus 1 and the wireless station apparatus 2 after the emergency stop button 4 is pressed will be described with reference to Fig. 11.
[0061] Before the emergency stop button 4 is pressed, in the operator control terminal apparatus 1, the wireless communication unit 11 makes settings for transmission of the annunciation signal (beacon frame) 8 in advance in the wireless interface 5. For this reason, the annunciation signal (beacon frame) 8 is transmitted from the wireless interface 5 to the wireless station apparatus 2 at fixed transmission intervals.
In the wireless station apparatus 2, the wireless communication unit 15 activates at reception intervals corresponding to the transmission interval in the operator control terminal apparatus 1. The wireless communication unit 15 then receives the annunciation signal (beacon frame) 8 via a wireless interface 6. Since the wireless communication unit 15 has succeeded in receiving the annunciation signal (beacon frame) 8, the control instrument 3 is not brought to an emergency stop.

[0062] If the emergency stop button 4 is pressed, in the operator control terminal apparatus 1, the stop monitoring unit 10 senses that the emergency stop button 4 is pressed. The stop monitoring unit 10 then outputs, to the wireless communication unit 11, a stop instruction frame transmission instruction 52 giving an instruction to transmit a stop instruction frame 53. The wireless communication unit 11 transmits the stop instruction frame 53 from the wireless interface 5 in accordance with the stop instruction frame transmission instruction 52.
In the wireless station apparatus 2, the wireless communication unit 15 receives the stop instruction frame 53. Since the wireless communication unit 15 has succeeded in receiving the stop instruction frame 53, the wireless communication unit
15 outputs a stop signal instruction 20 to the stop control unit 16. The stop control unit
16 transmits a stop signal 21 to the control instrument 3 via an instrument interface 9 in accordance with the stop signal instruction 20 to bring the control instrument 3 to an emergency stop (emergency stoppage 22).
[0063] An operation sequence of the operator control terminal apparatus 1 and the wireless station apparatus 2 in a case where the stop instruction frame 53 does not arrive at the wireless station apparatus 2 will be illustrated with reference to Fig. 12. [0064] In the operator control terminal apparatus 1, the wireless communication unit 11 determines whether transmission of the stop instruction frame 53 has been completed, that is, the stop instruction frame 53 has arrived at the wireless station apparatus 2 ("HAS TRANSMISSION OF STOP INSTRUCTION FRAME BEEN COMPLETED?" 54). More specifically, if the wireless communication unit 11 receives an acknowledgment of receipt of the stop instruction frame 53 from the wireless station apparatus 2, the wireless communication unit 11 determines that the stop instruction frame 53 has arrived at the wireless station apparatus 2. On the other hand, if the

wireless communication unit 11 does not receive an acknowledgment of receipt of the stop instruction frame 53 from the wireless station apparatus 2, the wireless communication unit 11 determines that the stop instruction frame 53 has not arrived at the wireless station apparatus 2. If the stop instruction frame 53 has not arrived at the wireless station apparatus 2, the wireless communication unit 11 stops transmission of the annunciation signal (beacon frame) 8 from the wireless interface 5 (annunciation signal (beacon frame) stoppage 41). As a result, transmission of the annunciation signal (beacon frame) 8 from the wireless interface 5 is stopped.
In the wireless station apparatus 2, since transmission of the annunciation signal (beacon frame) 8 is stopped in the operator control terminal apparatus 1, the wireless communication unit 15 does not receive the annunciation signal (beacon frame) 8. The wireless communication unit 15 counts the number of failures to receive the annunciation signal (beacon frame) 8 using a counter 914. If the wireless communication unit 15 has failed to receive the annunciation signal (beacon frame) 8 N (N > 2) consecutive times, the wireless communication unit 15 outputs the stop signal instruction 20 to the stop control unit 16. The stop control unit 16 transmits the stop signal 21 to the control instrument 3 via the instrument interface 9 in accordance with the stop signal instruction 20 to bring the control instrument 3 to an emergency stop (the emergency stoppage 22).
[0065] An example of operation of the wireless communication unit 11 in the operator control terminal apparatus 1 will next be described with reference to Fig. 13. [0066] The wireless communication unit 11 determines whether the stop instruction frame transmission instruction 52 is output from the stop monitoring unit 10 (step S61). If the stop instruction frame transmission instruction 52 is not output (NO in step S61), the wireless communication unit 11 makes settings for transmission of the annunciation

signal (beacon frame) 8 in the wireless interface 5 (step S62). Note that if the settings for transmission of the annunciation signal (beacon frame) 8 have already been made in the wireless interface 5, the wireless communication unit 11 skips step S62. [0067] On the other hand, if the stop instruction frame transmission instruction 52 is output (YES in step S61), the wireless communication unit 11 determines whether the wireless communication unit 11 has already transmitted the stop instruction frame 53 to the wireless station apparatus 2 (step S63).
If the wireless communication unit 11 has not yet transmitted the stop instruction frame 53 to the wireless station apparatus 2 (NO in step S63), the wireless communication unit 11 generates the stop instruction frame 53 and transmits the stop instruction frame 53 to the wireless station apparatus 2 via the wireless interface 5 (step S64).
On the other hand, if the wireless communication unit 11 has already transmitted the stop instruction frame 53 to the wireless station apparatus 2 (YES in step S63), the wireless communication unit 11 determines whether the stop instruction frame 53 has arrived at the wireless station apparatus 2 (step S65).
If the stop instruction frame 53 has not arrived at the wireless station apparatus 2 (NO in step S65), the wireless communication unit 11 instructs the wireless interface 5 to stop transmission of the annunciation signal (beacon frame) 8 (step S66). This stops transmission of the annunciation signal (beacon frame) 8 from the wireless interface 5.
[0068] As described above, the wireless communication unit 11 makes, in the wireless interface 5, settings for transmission of the annunciation signal (beacon frame) 8 that is a periodic signal giving notification that emergency stoppage of the control instrument 3 is unnecessary if emergency stoppage of the control instrument 3 is unnecessary. This

allows the wireless communication unit 11 to continue transmitting the annunciation signal (beacon frame) 8 from the wireless interface 5 to the wireless station apparatus 2 at the fixed intervals while emergency stoppage of the control instrument 3 is unnecessary.
On the other hand, if the need for emergency stoppage of the control instrument 3 arises, the wireless communication unit 11 transmits the stop instruction frame 53 to the wireless station apparatus 2. If the stop instruction frame 53 has not arrived at the wireless station apparatus 2, and therefore the control instrument 3 has not been brought to an emergency stop, the wireless communication unit 11 instructs the wireless interface 5 to stop transmission of the annunciation signal (beacon frame) 8. This allows the wireless communication unit 11 to stop transmission of the annunciation signal (beacon frame) 8 from the wireless interface 5.
[0069] An example of operation of the wireless communication unit 15 in the wireless station apparatus 2 will next be described with reference to Fig. 14. [0070] In the present embodiment as well, the wireless communication unit 15 is activated at reception intervals for the annunciation signal (beacon frame) 8. More specifically, the reception interval is set in a timer 913. When the timer 913 expires, the wireless communication unit 15 is activated by the timer 913.
If the wireless communication unit 15 receives the stop instruction frame 53 via the wireless interface 6 (YES in step S71), the wireless communication unit 15 transmits an acknowledgment of receipt of the stop instruction frame 53 to the operator control terminal apparatus 1 (step S72). The wireless communication unit 15 also outputs the stop signal instruction 20 to the stop control unit 16 (step S73). [0071] On the other hand, if the wireless communication unit 15 does not receive the stop instruction frame 53 (NO in step S71) and receives the annunciation signal (beacon

frame) 8 (YES in step S74), the wireless communication unit 15 initializes the counter
914 (step S75).
[0072] On the other hand, if the wireless communication unit 15 does not receive the
annunciation signal (beacon frame) 8 (NO in step S74), the wireless communication
unit 15 determines whether the wireless communication unit 15 has failed to receive the
annunciation signal (beacon frame) 8 N (N > 2) consecutive times (step S76).
[0073] If the wireless communication unit 15 has failed to receive the annunciation
signal (beacon frame) 8 N consecutive times (YES in step S76), the wireless
communication unit 15 determines that the annunciation signal (beacon frame) 8 from
the operator control terminal apparatus 1 has not arrived and outputs the stop signal
instruction 20 to the stop control unit 16 (step S77).
[0074] On the other hand, if the number of failures to receive the annunciation signal
(beacon frame) 8 is less than N (NO in step S76), the wireless communication unit 11
increments a value in the counter 914 by one (step S78).
[0075] * * * Description of Advantageous Effects of Embodiment * * *
According to the present embodiment, if emergency stoppage of the control instrument 3 is unnecessary, settings for transmission of the annunciation signal (beacon frame) 8 are made in the wireless interface 5. With the settings, the annunciation signal (beacon frame) 8 is continuously transmitted from the wireless interface 5 to the wireless station apparatus 2 while emergency stoppage of the control instrument 3 is unnecessary. It is thus possible to notify the wireless station apparatus 2 that emergency stoppage of the control instrument 3 is unnecessary without consuming computing resources of a processor 901 while emergency stoppage of the control instrument 3 is unnecessary.
According to the present embodiment, if the need to bring the control

instrument 3 to an emergency stop arises, the stop instruction frame 53 is transmitted to bring the control instrument 3 to an emergency stop. If the stop instruction frame 53 has not yet arrived at the wireless station apparatus 2, it is possible to reliably bring the control instrument 3 to an emergency stop through the wireless station apparatus 2 by control which stops transmission of the annunciation signal (beacon frame) 8. [0076] Embodiment 4.
In the present embodiment, a first annunciation signal (beacon frame) 81 and a second annunciation signal (beacon frame) 82 are used, like Embodiment 1.
In the present embodiment, when an emergency stop button 4 is pressed, an operator control terminal apparatus 1 transmits a stop instruction frame which is a stop instruction signal to a wireless station apparatus 2 before transmitting the second annunciation signal (beacon frame) 82 instead of the first annunciation signal (beacon frame) 81. If the stop instruction frame fails to arrive at the wireless station apparatus 2, the operator control terminal apparatus 1 starts transmission of the annunciation signal (beacon frame) 82, like Embodiment 1.
The present embodiment is obtained by adding a procedure for transmission of a stop instruction frame to the procedure according to Embodiment 1. [0077] *** Description of Configuration ***
A system configuration according to the present embodiment is as illustrated in Fig. 1.
An example of a configuration of the operator control terminal apparatus 1 according to the present embodiment is as illustrated in Fig. 2. Note that, in the present embodiment, a stop monitoring unit 10 instructs a wireless communication unit 11 to transmit a stop instruction frame when the emergency stop button 4 is pressed. The wireless communication unit 11 transmits the stop instruction frame to the wireless

station apparatus 2. If the stop instruction frame fails to arrive at the wireless station apparatus 2, the wireless communication unit 11 makes settings for transmission of the second annunciation signal (beacon frame) 82 in a wireless interface 5. Components other than the stop monitoring unit 10 and the wireless communication unit 11 perform same operations as in Embodiment 1.
An example of a configuration of the wireless station apparatus 2 according to the present embodiment is as illustrated in Fig. 3. Note that, in the present embodiment, a wireless communication unit 15 transmits an acknowledgment of receipt to the operator control terminal apparatus 1 upon receipt of a stop instruction frame. The wireless communication unit 15 also instructs a stop control unit 16 to bring a control instrument 3 to an emergency stop, in response to the receipt of the stop instruction frame. Components other than the wireless communication unit 15 perform same operations as in Embodiment 1. [0078] *** Description of Operation ***
An operation sequence of the operator control terminal apparatus 1 and the wireless station apparatus 2 before the emergency stop button 4 is pressed and an operation sequence of the operator control terminal apparatus 1 and the wireless station apparatus 2 after the emergency stop button 4 is pressed will be described with reference to Fig. 15.
[0079] Before the emergency stop button 4 is pressed, in the operator control terminal apparatus 1, the wireless communication unit 11 makes settings for transmission of the first annunciation signal (beacon frame) 81 in the wireless interface 5. For this reason, the first annunciation signal (beacon frame) 81 is transmitted from the wireless interface 5 to the wireless station apparatus 2 at fixed transmission intervals.
In the wireless station apparatus 2, the wireless communication unit 15

activates at reception intervals corresponding to the transmission interval in the operator control terminal apparatus 1. The wireless communication unit 15 then receives the first annunciation signal (beacon frame) 81 via a wireless interface 6. The wireless communication unit 15 then extracts a steady-state notification 7 from the first annunciation signal (beacon frame) 81. Since the wireless communication unit 15 has succeeded in extracting the steady-state notification 7 from the first annunciation signal (beacon frame) 81, the control instrument 3 is not brought to an emergency stop. [0080] If the emergency stop button 4 is pressed, in the operator control terminal apparatus 1, the stop monitoring unit 10 senses that the emergency stop button 4 is pressed. The stop monitoring unit 10 then outputs, to the wireless communication unit 11, a stop instruction frame transmission instruction 52 giving an instruction to transmit a stop instruction frame 53. The wireless communication unit 11 transmits the stop instruction frame 53 from the wireless interface 5 in accordance with the stop instruction frame transmission instruction 52.
In the wireless station apparatus 2, the wireless communication unit 15 receives the stop instruction frame 53. Since the wireless communication unit 15 has succeeded in receiving the stop instruction frame 53, the wireless communication unit
15 outputs a stop signal instruction 20 to the stop control unit 16. The stop control unit
16 transmits a stop signal 21 to the control instrument 3 via an instrument interface 9 in accordance with the stop signal instruction 20 to bring the control instrument 3 to an emergency stop (emergency stoppage 22).
[0081] An operation sequence of the operator control terminal apparatus 1 and the wireless station apparatus 2 in a case where the stop instruction frame 53 does not arrive at the wireless station apparatus 2 will be illustrated with reference to Fig. 16. [0082] In the operator control terminal apparatus 1, the wireless communication unit

11 determines whether transmission of the stop instruction frame 53 has been completed, that is, the stop instruction frame 53 has arrived at the wireless station apparatus 2 ("HAS TRANSMISSION OF STOP INSTRUCTION FRAME BEEN COMPLETED?" 54). More specifically, if the wireless communication unit 11 receives an acknowledgment of receipt of the stop instruction frame 53 from the wireless station apparatus 2, the wireless communication unit 11 determines that the stop instruction frame 53 has arrived at the wireless station apparatus 2. On the other hand, if the wireless communication unit 11 does not receive an acknowledgment of receipt of the stop instruction frame 53 from the wireless station apparatus 2, the wireless communication unit 11 determines that the stop instruction frame 53 has not arrived at the wireless station apparatus 2. If the stop instruction frame 53 has not arrived at the wireless station apparatus 2, the wireless communication unit 11 makes settings for transmission of the second annunciation signal (beacon frame) 82 in the wireless interface 5 (steady-state notification deletion 19). As a result, the second annunciation signal (beacon frame) 82 without the steady-state notification 7 is transmitted from the wireless interface 5 to the wireless station apparatus 2.
In the wireless station apparatus 2, the wireless communication unit 15 receives the second annunciation signal (beacon frame) 82 via the wireless interface 6. In this case, the wireless communication unit 15 cannot extract the steady-state notification 7 from the second annunciation signal (beacon frame) 82. For this reason, the wireless communication unit 15 outputs the stop signal instruction 20 to the stop control unit 16. The stop control unit 16 transmits the stop signal 21 to the control instrument 3 via the instrument interface 9 in accordance with the stop signal instruction 20 to bring the control instrument 3 to an emergency stop (the emergency stoppage 22). [0083] An example of operation of the wireless communication unit 11 in the operator

control terminal apparatus 1 will next be described with reference to Fig. 17. [0084] The wireless communication unit 11 determines whether the stop instruction frame transmission instruction 52 is output from the stop monitoring unit 10 (step S81). If the stop instruction frame transmission instruction 52 is not output (NO in step S81), the wireless communication unit 11 makes settings for transmission of the first annunciation signal (beacon frame) 81 in the wireless interface 5 (step S82). Note that if the settings for transmission of the first annunciation signal (beacon frame) 81 have already been made in the wireless interface 5, the wireless communication unit 11 skips step S82.
[0085] On the other hand, if the stop instruction frame transmission instruction 52 is output (YES in step S81), the wireless communication unit 11 determines whether the wireless communication unit 11 has already transmitted the stop instruction frame 53 to the wireless station apparatus 2 (step S83).
If the wireless communication unit 11 has not yet transmitted the stop instruction frame 53 to the wireless station apparatus 2 (NO in step S83), the wireless communication unit 11 generates the stop instruction frame 53 and transmits the stop instruction frame 53 to the wireless station apparatus 2 via the wireless interface 5 (step S84).
On the other hand, if the wireless communication unit 11 has already transmitted the stop instruction frame 53 to the wireless station apparatus 2 (YES in step S83), the wireless communication unit 11 determines whether the stop instruction frame 53 has arrived at the wireless station apparatus 2 (step S85).
If the stop instruction frame 53 has not arrived at the wireless station apparatus 2 (NO in step S85), the wireless communication unit 11 makes settings for transmission of the second annunciation signal (beacon frame) 82 in the wireless interface 5 (step

S86). This switches an annunciation signal (beacon frame) 8 transmitted from the wireless interface 5 from the first annunciation signal (beacon frame) 81 to the second annunciation signal (beacon frame) 82.
[0086] As described above, the wireless communication unit 11 makes, in the wireless interface 5, settings for transmission of the first annunciation signal (beacon frame) 81 that is a periodic signal giving notification that emergency stoppage of the control instrument 3 is unnecessary if emergency stoppage of the control instrument 3 is unnecessary. This allows the wireless communication unit 11 to continue transmitting the first annunciation signal (beacon frame) 81 from the wireless interface 5 to the wireless station apparatus 2 at the fixed intervals while emergency stoppage of the control instrument 3 is unnecessary.
On the other hand, if the need for emergency stoppage of the control instrument 3 arises, the wireless communication unit 11 transmits the stop instruction frame 53 to the wireless station apparatus 2. If the stop instruction frame 53 has not arrived at the wireless station apparatus 2, and therefore the control instrument 3 has not been brought to an emergency stop, the wireless communication unit 11 makes settings for transmission of the second annunciation signal (beacon frame) 82 in the wireless interface 5. This switches the annunciation signal (beacon frame) 8 transmitted from the wireless interface 5 from the first annunciation signal (beacon frame) 81 to the second annunciation signal (beacon frame) 82.
[0087] An example of operation of the wireless communication unit 15 in the wireless station apparatus 2 will next be described with reference to Fig. 18. [0088] In the present embodiment as well, the wireless communication unit 15 is activated at the reception intervals for the annunciation signal (beacon frame) 8. More specifically, the reception interval is set in a timer 913. When the timer 913 expires,

the wireless communication unit 15 is activated by the timer 913.
If the wireless communication unit 15 receives the stop instruction frame 53 via the wireless interface 6 (YES in step S91), the wireless communication unit 15 transmits an acknowledgment of receipt of the stop instruction frame 53 to the operator control terminal apparatus 1 (step S92). The wireless communication unit 15 also outputs the stop signal instruction 20 to the stop control unit 16 (step S93). [0089] On the other hand, if the wireless communication unit 15 does not receive the stop instruction frame 53 (NO in step S91) and receives the annunciation signal (beacon frame) 8 (YES in step S94), the wireless communication unit 15 determines whether the received annunciation signal (beacon frame) 8 is the first annunciation signal (beacon frame) 81 or the second annunciation signal (beacon frame) 82 (step S95). [0090] If the received annunciation signal (beacon frame) 8 is the first annunciation signal (beacon frame) 81 (YES in step S95), the wireless communication unit 15 initializes a counter 914 (step S96).
On the other hand, if the received annunciation signal (beacon frame) 8 is the second annunciation signal (beacon frame) 82 (NO in step S95), the wireless communication unit 15 outputs the stop signal instruction 20 to the stop control unit 16 (step S93).
[0091] If the wireless communication unit 15 does not receive the annunciation signal (beacon frame) 8 (NO in step S94), the wireless communication unit 15 determines whether the wireless communication unit 15 has failed to receive the annunciation signal (beacon frame) 8 N (N > 2) consecutive times (step S97). [0092] If the wireless communication unit 15 has failed to receive the annunciation signal (beacon frame) 8 N consecutive times (YES in step S97), the wireless communication unit 15 determines that the annunciation signal (beacon frame) 8 from

the operator control terminal apparatus 1 has not arrived and outputs the stop signal
instruction 20 to the stop control unit 16 (step S98).
[0093] On the other hand, if the number of failures to receive the annunciation signal
(beacon frame) 8 is less than N (NO in step S97), the wireless communication unit 11
increments a value in the counter 914 by one (step S99).
[0094] *** Description of Advantageous Effects of Embodiment ***
According to the present embodiment, if emergency stoppage of the control instrument 3 is unnecessary, settings for transmission of the first annunciation signal (beacon frame) 81 are made in the wireless interface 5. With the settings, the first annunciation signal (beacon frame) 81 is continuously transmitted from the wireless interface 5 to the wireless station apparatus 2 while emergency stoppage of the control instrument 3 is unnecessary. It is thus possible to notify the wireless station apparatus 2 that emergency stoppage of the control instrument 3 is unnecessary without consuming computing resources of a processor 901 while emergency stoppage of the control instrument 3 is unnecessary.
According to the present embodiment, if the need to bring the control instrument 3 to an emergency stop arises, the stop instruction frame 53 is transmitted to bring the control instrument 3 to an emergency stop. If the stop instruction frame 53 has not yet arrived at the wireless station apparatus 2, it is possible to reliably bring the control instrument 3 to an emergency stop through the wireless station apparatus 2 by control which switches to transmission of the second annunciation signal (beacon frame) 82.
[0095] The embodiments of the present invention have been described above. Two or more of the embodiments may be combined and carried out.
Alternatively, one of the embodiments may be partially carried out.

Alternatively, two or more of the embodiments may be partially combined and carried out.
Note that the present invention is not limited to the embodiments and that the embodiments can be variously changed, as needed. [0096] *** Description of Hardware Configuration ***
Finally, a supplemental explanation of the hardware configurations of the operator control terminal apparatus 1 and the wireless station apparatus 2 will be given.
The processors 901 and 911 are ICs (Integrated Circuits) which perform processing.
The processors 901 and 911 are each a CPU (Central Processing Unit), a DSP (Digital Signal Processor), or the like.
The storage devices 902 and 912 are each a RAM (Random Access Memory), a ROM (Read Only Memory), a flash memory, an HDD (Hard Disk Drive), or the like. [0097] The storage devices 902 and 912 also each store an OS (Operating System).
At least a part of the OS is then executed by the processor 901 or 911.
The processor 901 executes a program which implements functions of the stop monitoring unit 10, the wireless communication unit 11, and the display unit 13 while executing at least a part of the OS.
The processor 911 executes a program which implements functions of the wireless communication unit 15 and the stop control unit 16 while executing at least a part of the OS.
The processors 901 and 911 each execute the OS, thereby performing task management, memory management, file management, communication control, and the like.
The operator control terminal apparatus 1 may include a plurality of processors

which replace the processor 901. The wireless station apparatus 2 may include a plurality of processors which replace the processor 911.
Information, data, signal values, and variable values indicating results of processing by the stop monitoring unit 10, the wireless communication unit 11, and the display unit 13 are stored in at least any of the storage device 902 and a register and a cache memory inside the processor 901.
Similarly, information, data, signal values, and variable values indicating results of processing by the wireless communication unit 15 and the stop control unit 16 are stored in at least any of the storage device 912 and a register and a cache memory inside the processor 911.
The program that implements the functions of the stop monitoring unit 10, the wireless communication unit 11, and the display unit 13 may be stored in a portable storage medium, such as a magnetic disk, a flexible disk, an optical disc, a compact disc, a Blu-ray (a registered trademark) disc, or a DVD.
Similarly, the program that implements the functions of the wireless communication unit 15 and the stop control unit 16 may be stored in a portable storage medium, such as a magnetic disk, a flexible disk, an optical disc, a compact disc, a Blu-ray (a registered trademark) disc, or a DVD.
[0098] The "unit" in each of the stop monitoring unit 10, the wireless communication unit 11, the display unit 13, the wireless communication unit 15, and the stop control unit 16 may be replaced with the "circuit", the "step", the "procedure", or the "process".
The operator control terminal apparatus 1 and the wireless station apparatus 2 may each be implemented as an electronic circuit, such as a logic IC (Integrated Circuit), a GA (Gate Array), an ASIC (Application Specific Integrated Circuit), or an FPGA (Field-Programmable Gate Array).

Note that the processors and the above-described electronic circuits are also collectively referred to as processing circuitry. Reference Signs List
[0099] 1: operator control terminal apparatus; 2: wireless station apparatus; 3: control instrument; 4: emergency stop button; 5: wireless interface; 6: wireless interface; 7: steady-state notification; 8: annunciation signal (beacon frame); 9: instrument interface; 10: stop monitoring unit; 11: wireless communication unit; 13: display unit; 15: wireless communication unit; 16: stop control unit; 18: steady-state notification deletion instruction; 20: stop signal instruction; 21: stop signal; 22: emergency stoppage; 40: annunciation signal (beacon frame) stop instruction; 41: annunciation signal (beacon frame) stoppage; 52: stop instruction frame transmission instruction; 53: stop instruction frame; 81: first annunciation signal (beacon frame); 82: second annunciation signal (beacon frame); 901: processor; 902: storage device; 903: timer; 904: display; 905: battery; 911: processor; 912: storage device; 913: timer; 914: counter.

We Claim:
[Claim 1] A wireless communication apparatus including a wireless interface to
continue transmitting a periodic signal at fixed intervals if once settings for transmission of the periodic signal are made, the wireless communication apparatus comprising:
a first control unit to make, in the wireless interface, settings for transmission of a first periodic signal which is a periodic signal giving notification that stoppage of an instrument is unnecessary if stoppage of the instrument is unnecessary and cause the wireless interface to continue transmitting the first periodic signal at the fixed intervals to a wireless station apparatus capable of stopping the instrument, while stoppage of the instrument is unnecessary; and
a second control unit to perform either one of periodic signal switching control
and periodic signal stop control if a need for stoppage of the instrument arises, the
periodic signal switching control making, in the wireless interface, settings for
transmission of a second periodic signal which is a periodic signal giving notification
that stoppage of the instrument is necessary and causing the wireless interface to
continue transmitting the second periodic signal to the wireless station apparatus at the
fixed intervals instead of the first periodic signal, the periodic signal stop control
causing the wireless interface to stop transmission of the first periodic signal.
[Claim 2] The wireless communication apparatus according to claim 1, wherein
the second control unit transmits a stop instruction signal giving an instruction
to stop the instrument from the wireless interface to the wireless station apparatus if the
need for stoppage of the instrument arises and performs either one of the periodic signal
switching control and the periodic signal stop control if the wireless station apparatus
fails to receive the stop instruction signal.
[Claim 3] The wireless communication apparatus according to claim 1, wherein

the first control unit makes, in the wireless interface, the settings for transmission of the first periodic signal that is a periodic signal including notification information giving notification that stoppage of the instrument is unnecessary, if stoppage of the instrument is unnecessary, and
the second control unit makes, in the wireless interface, the settings for
transmission of the second periodic signal that is a period signal without the notification
information, when performing the periodic signal switching control.
[Claim 4] A wireless station apparatus capable of stopping an instrument, the
wireless station apparatus comprising:
a reception unit to receive either one of a first periodic signal giving notification that stoppage of the instrument is unnecessary and a second periodic signal giving notification that stoppage of the instrument is necessary which are transmitted from a wireless communication apparatus which determines whether or not stoppage of the instrument is necessary; and
a stop control unit to stop the instrument in either one of a case where the
reception unit receives the second periodic signal and a case where the reception unit
does not receive the first periodic signal for a predetermined time period.
[Claim 5] The wireless station apparatus according to claim 4, wherein
the reception unit may receive a stop instruction signal giving an instruction to stop the instrument, which is transmitted from the wireless communication apparatus, and
the stop control unit stops the instrument even in either one of a case where the second periodic signal is not received by the reception unit and a case where a time period for which the reception unit does not receive the first periodic signal is less than the predetermined time period, if reception of the stop instruction signal by the

reception unit is detected.
[Claim 6] The wireless station apparatus according to claim 4, wherein
the reception unit receives, as the first periodic signal, a periodic signal
including notification information giving notification that stoppage of the instrument is
unnecessary and receives, as the second periodic signal, a periodic signal without the
notification information.
[Claim 7] An instrument control method comprising:
by a wireless communication apparatus including a wireless interface to continue transmitting a periodic signal at fixed intervals if once settings for transmission of the periodic signal are made, making, in the wireless interface, settings for transmission of a first periodic signal which is a periodic signal giving notification that stoppage of an instrument is unnecessary if stoppage of the instrument is unnecessary and causing the wireless interface to continue transmitting the first periodic signal at the fixed intervals to a wireless station apparatus capable of stopping the instrument, while stoppage of the instrument is unnecessary; and
by the wireless communication apparatus, performing either one of periodic
signal switching control and periodic signal stop control if a need for stoppage of the
instrument arises, the periodic signal switching control making, in the wireless interface,
settings for transmission of a second periodic signal which is a periodic signal giving
notification that stoppage of the instrument is necessary and causing the wireless
interface to continue transmitting the second periodic signal to the wireless station
apparatus at the fixed intervals instead of the first periodic signal, the periodic signal
stop control causing the wireless interface to stop transmission of the first periodic
signal.
[Claim 8] An instrument control method comprising:

by a wireless station apparatus capable of stopping an instrument, stopping the
instrument in either one of a case where non-reception of a first periodic signal for a
predetermined time period is detected and a case where reception of a second periodic
signal is detected, the first periodic signal giving notification that stoppage of the
instrument is unnecessary and being transmitted from a wireless communication
apparatus which determines whether or not stoppage of the instrument is necessary, the
second periodic signal giving notification that stoppage of the instrument is necessary
and being transmitted from the wireless communication apparatus.
[Claim 9] An instrument control program that causes a wireless communication
apparatus including a wireless interface to continue transmitting a periodic signal at fixed intervals if once settings for transmission of the periodic signal are made, to execute:
a first control process of making, in the wireless interface, settings for transmission of a first periodic signal which is a periodic signal giving notification that stoppage of an instrument is unnecessary if stoppage of the instrument is unnecessary and causing the wireless interface to continue transmitting the first periodic signal at the fixed intervals to a wireless station apparatus capable of stopping the instrument, while stoppage of the instrument is unnecessary; and
a second control process of performing either one of periodic signal switching control and periodic signal stop control if a need for stoppage of the instrument arises, the periodic signal switching control making, in the wireless interface, settings for transmission of a second periodic signal which is a periodic signal giving notification that stoppage of the instrument is necessary and causing the wireless interface to continue transmitting the second periodic signal to the wireless station apparatus at the fixed intervals instead of the first periodic signal, the periodic signal stop control

causing the wireless interface to stop transmission of the first periodic signal.
[Claim 10] An instrument control program that causes a wireless station
apparatus capable of stopping an instrument, to execute:
a reception process of receiving either one of a first periodic signal giving notification that stoppage of the instrument is unnecessary and a second periodic signal giving notification that stoppage of the instrument is necessary which are transmitted from a wireless communication apparatus which determines whether or not stoppage of the instrument is necessary; and
a stop control process of stopping the instrument in either one of a case where reception of the second periodic signal by the reception process is detected and a case where non-reception of the first periodic signal by the reception process for a predetermined time period is detected.