JP3533455B2 - Wireless remote I/O device - Google Patents

Description

Detailed Description of the Invention

[0001]

The present invention relates to a wireless remote I/O device in which a wireless master station cyclically communicates with a wireless slave station directly or via a wireless relay station to perform I/O refresh.

[0002]

2. Description of the Related Art For example, in manufacturing sites, with the demand for computerization, programmable controllers, CNCs,
The use of networks for robot controllers and the like is advancing. Such FA networks are required to be faster and have improved performance to improve production efficiency, as well as to have higher data transmission speeds and higher data transmission reliability.

[0003] In the case of wired communications, when expanding or changing a line or changing the layout at a manufacturing site, it is necessary to re-install communication cables, and when transmitting data to moving workers or moving objects, it is necessary to reconnect communication cables, and when transmitting data to equipment mounted on a turntable, it is necessary to provide special equipment such as a rotating transformer or slip ring. Since the cost and effort required for these cannot be ignored, wireless communications have attracted attention as they are easy and low-cost to handle changes in layout and mobile communication stations that move during work, and there is a growing desire for the introduction and spread of wireless communications in such fields as well.

However, in wireless data communication using radio waves, the communication environment is far worse than that of wired communication, and errors occur in the data or packets are lost along the communication path due to noise contamination, fading caused by radio wave reflection, blocking of radio waves due to the passage of obstacles, reduction in radio wave strength, etc., resulting in communication errors that occur on a daily basis.

[0005] In wireless data communications, therefore, the wireless receiving station generally sends back a reception notification to the wireless transmitting station, and if this reception notification does not reach the wireless transmitting station within a specified time or is a notification of erroneous reception, the packet that caused the communication error is immediately resent, or a method such as error control is used, or communication with a wireless slave station in an area where radio waves cannot reach is performed via a wireless relay station, thereby maintaining the reliability of the wireless communications.

[0006] In addition, in a conventional so-called cyclic communication in which a wireless master station and a wireless slave station communicate cyclically to perform I/O refresh, it was normal for the wireless master station to sequentially poll all of the participating wireless slave stations registered as communication targets within one cycle (slot) of the communication cycle to perform I/O refresh.

[0007]

However, if methods such as retransmission and error control are used to ensure the reliability of data wireless communication, the amount of data to be communicated increases accordingly, lengthening the communication time, and if wireless relay is used, the communication time is inevitably lengthened by the amount of relay.
The period of cyclic communication between the wireless master station and the wireless slave station of the device is becoming longer, making it difficult to realize the high-speed communication required for FA networks that perform high-speed control of equipment.

If all participating wireless slave stations are polled in sequence and I/O refreshed within one slot of a communication cycle, wireless slave stations that do not require high-speed I/O response, such as wireless slave stations for displaying on a display device, and wireless slave stations that require high-speed I/O response, such as wireless slave stations for controlling the operation of assembly work, will be subjected to the same I/O refresh processing within one communication cycle without distinction, which will result in a longer communication cycle time. This is another factor that hinders the high-speed communication required for FA networks.

SUMMARY OF THE PRESENT EMBODIMENT The present invention provides a wireless remote I/O device which solves the above-mentioned problems, has a short communication cycle, and is capable of realizing the high-speed communication required for FA networks while maintaining high reliability.

[0010]

In order to achieve the above object, the present invention provides a wireless remote I/O device in which a wireless master station cyclically communicates with a wireless slave station directly or via a wireless relay station to perform I/O refresh, the device comprising a refresh cycle setting table for setting a refresh cycle for each wireless slave station, and a table for setting weighting factors that affect the refresh processing time for each wireless slave station, the weighting factors being included in the items of the refresh cycle setting table.
The wireless master station is characterized in that it comprises a weight setting table including the number of successive stages , a scheduling table for allocating wireless slave stations for performing refresh processing in each slot of a communication cycle based on the refresh period of the refresh period setting table and the weight elements of the weight setting table, and the wireless master station cyclically communicates with the wireless slave stations to perform I/O refresh in accordance with the scheduling table.

According to this invention , the polling period for each wireless slave station is determined according to the frequency with which an I/O refresh is required, and the wireless slave stations which undergo an I/O refresh are distributed and assigned to each slot of the communication cycle based on the time required for the I/O refresh and the polling period, thereby shortening the communication cycle time by the amount of distribution.

[0012]

According to the present invention , the communication cycle time is
Even if the communication cycle process is performed by setting the communication cycle time to a constant value slightly larger than the maximum value of the calculated sum of the processing times of the wireless slave stations, the communication cycle time becomes relatively short.

[0014]

According to this invention , the time required for relaying is added to the I/O refresh processing time between the wireless slave station and the wireless master station which communicate via the wireless relay station.

[0016] The invention of claim 2 is characterized in that, in the invention of claim 1, multiple identical wireless slave stations are assigned to one slot of the scheduling table, and within the one slot, the wireless master station performs I/O refresh with the same wireless slave station multiple times.

[0017] The invention of claim 3 is characterized in that, in the invention of claim 2 , multiple I/O refreshes between the wireless master station and the same wireless slave station are performed with I/O refreshes between the wireless master station and other wireless slave stations in between.

According to the second or third aspect of the present invention , a wireless slave station which performs I/O refresh multiple times within one communication cycle performs I/O refresh as frequently as if the communication cycle were shortened to "1/multiple times".

[0019] In accordance with a fourth aspect of the present invention , in the first aspect, the wireless slave station monitors polling from the wireless master station based on the communication cycle time determined by the wireless master station from the results of the scheduling table.

According to the fourth aspect of the present invention , when polling is no longer performed according to the schedule, the wireless master station detects this.

[0021]

[Embodiment of the Invention] The embodiment of the present invention will be described below.
The description will be given with reference to the drawings.

First, FIG. 1 shows a wireless remote control I
1 illustrates an example of a wireless communication network using a ./O device.

In FIG. 1, a wireless master station M is connected to a remote I/O master 10 of a programmable controller via a remote I/O network 20. This wireless master station M communicates directly with wireless slave stations S1 and S2 that perform I/O refresh with the wireless master station M through a network NW.
1, and polls the wireless slave receiving stations S1 and S2 in the network NW1 in sequence.
This cycle communication is executed according to a scheduling table, which will be described later.
Generally, W1 is equipped with a large number of wireless slave stations capable of direct wireless communication. For simplicity of explanation,
Here, two wireless slave stations S1 and S2 are shown.

[0024] Also, the radio transmitting station M is connected to the network NW
In addition, there are multiple wireless slave stations such as wireless slave stations S3, S4, and S5 in areas where direct communication is somewhat difficult.
The wireless slave station S1 in the network NW1 communicates with the wireless slave station outside the network NW1 as a wireless relay station.
The wireless slave station S2 is connected to an assembly device (not shown) and does not require frequent I/O refresh.
, and frequent I/O refresh is required to obtain high-speed I/O responsiveness.

The wireless relay station S1 has a network NW2 like the wireless master station M.
The cycle communication is wirelessly relayed to the wireless slave station S3 in the
I/O refresh is performed for S3, S4, and S5. This I/O refresh is also performed according to the scheduling table. Although not shown in the figure, many wireless slave stations are also deployed in the network NW2. This I/O refresh is also performed according to the scheduling table. Wireless slave station S5 is mounted on a wireless guided vehicle AGV, and since this AGV travels around the factory, it is often difficult for radio waves to reach the AGV, making communication unstable. Therefore, I/O refresh is performed for wireless slave station S5 using methods such as retransmission control and error correction,
This means that the I/O refresh processing time is lengthened.

FIG. 2 is a block diagram showing the main configuration of the present invention. 1 is a refresh cycle setting table, 2 is a
Weight setting table, 3 is a scheduling means, 4 is
is a scheduling table.

The refresh cycle setting table 1 is as follows:
The refresh period is set for each of the wireless slave stations S1, S2, . . . S5. As shown in FIG. 3, the refresh period is set for each of the wireless slave stations WNID #1, #2, #3, #4, #5.
The refresh period for performing the I/O refresh can be written in. In the example of Fig. 3, the wireless slave station S1 (WNID: #1) is specified to perform the I/O refresh once every four communication cycles.

The weight setting table 2 is used to set "weighting factors" that affect the I/O refresh processing time for each of the wireless slave stations S1, S2, . . . S5.
In the example of the weight setting table shown in , the number of wireless relay stages and the I/O data length are used as "weighting factors". The number of relay stages "0" indicates direct communication without relay, and the wireless slave station S1 (WNID: #1) indicates that there is no relay and that the I/O data length is 120 bytes. This weight setting table 2 is compiled from information stored in the system, not manually entered.

When performing retransmission processing, error control, etc. in the event of a communication error in order to increase the reliability of communication, this network setting information also becomes a "weighting factor," so it is advisable to add it to the items in the weight setting table 2 above.

"Weighting Factor" of Weighting Setting Table 2 in FIG.
In the case of a single wireless relay, the relay process takes about 10 ms.
The I/O refresh processing time is calculated based on these values and is shown in Figure 5.
The wireless master station M and the wireless slave station S1 are connected via I/O.
It shows that 12 ms is required for the I/O refresh of the wireless master station M and the wireless slave station S2, and 2 ms is required for the I/O refresh of the wireless master station M and the wireless slave station S2.
is shown for the purpose of explanation, and it is not necessary to create a table like that of FIG.

The scheduling means 3 generates a scheduling table 4 from the refresh cycles in the refresh cycle setting table 1 and the weighting factors (number of relay stages and I/O data length) in the weighting setting table 2. An example of the scheduling table 4 is shown in FIG. 6. In FIG. 6, "1" to "12" in "refresh slot"
means communication cycles 1 to 12, and the wireless slave station S1 (#1) cyclically performs I/O refresh processing in slots 1, 5, and 9, i.e., the first, fifth, and ninth communication cycles.
2 (#2) performs I/O refresh processing cyclically in the communication cycle of all slots 1, 2, ... 12.
In this way, the I/O refresh is performed at different periods and phases for each wireless slave station.
These 12 slots are executed repeatedly.

[0032] The "communication cycle time" in the bottom row of the scheduling table 4 in Figure 6 is the sum of the calculated processing times (see Figure 5) of the wireless slave stations marked with circles in each slot. For example, in slot 1, it shows that it takes 43 ms to execute I/O refresh processing for the three wireless slave stations S1, S2, and S4.
Incidentally, this "communication cycle time" does not necessarily have to be stored in the scheduling table 4, but may be saved in another area or discarded after the scheduling and the actual communication cycle time (the communication cycle time actually in operation) are set.

The scheduling table 4 prepared as described above is used for cyclic communication in accordance with the flow of communication processing shown in Fig. 7. In Fig. 7, in step 701, at system startup, the scheduling table 4 is loaded into an area for cyclic communication processing.
Next, the maximum value of the calculated communication cycle time obtained from this scheduling table 4 (in the example of FIG. 6, "71 m
The fixed actual communication cycle time is set to, for example, 100 ms, with some margin in the "time period"("s"), and the process proceeds to step 702, where the actual communication cycle time and the period of each wireless slave station (the period at which the I/O refresh process is performed) are set to each of the wireless slave stations S1, S2, S3, S4, S5, S6, S7, S8, S9, S10, S11, S12, S13, S14, S15, S16, S17, S18, S19, S20, S21, S22, S23, S24, S25, S26, S27, S28, S29, S30, S31, S32, S33, S34, S35, S36, S37, S38, S39, S40, S41, S42, S43, S44, S45, S
The next step 703 is to notify I
In the routine for the /O refresh process, a communication cycle is repeatedly executed, with the set actual communication cycle time being one period. During the progress of the communication cycle, the wireless slave stations S1, S2, S3, S4, and S5 monitor, for example, the wireless slave station S2 for polling from the wireless master station M and the wireless slave station S3 for polling from the wireless relay station S1 based on the notified period and the actual communication cycle time. If no polling is received within a predetermined time,
It is judged as an "abnormality" and abnormality processing is started.

The process of generating the scheduling table 4 in Fig. 6 will be described with reference to the flow chart in Fig. 8. First, in step 801, the scheduling table 4 is generated from the refresh cycle setting table 1 in Fig. 3.
The minimum common multiple of the refresh periods is the number of slots T, and T
= 12.

Next, in step 802, it is checked whether or not the scheduling of all wireless slave stations S1, S2, S3, S4, and S5 has been completed and allocation (circles in FIG. 6) has been completed. If allocation has been completed (yes), the scheduling ends. If allocation has not been completed (no), the process moves to step 803, and periodic allocation of the next wireless slave station begins. First, in step 803, the wireless slave station i with the smallest WNID among the wireless slave stations whose allocation has not been completed is selected as the allocation target. Next, in step 804, the refresh period Ti ("4" in the case of #1) is obtained from refresh period setting table 1 in FIG. 3, and
In the next step 805, the weight (processing time) of the processing of the wireless slave station i ("12 ms" in the case of #1) shown in FIG. 5 is calculated from the weight setting table 2 in FIG.

In the next step 806, the processing slot for wireless slave station i is assigned from among the 12 slots. If the slot with the number equal to or less than the refresh period Ti of wireless slave station i is not assigned first in the slot sequence, the period Ti cannot be maintained. Also, since it is desired to shorten the communication cycle time by making the calculated processing time of each slot as small as possible, wireless slave station i is assigned to slot X, which is within the range equal to or less than the refresh period Ti and has the shortest calculated slot processing time (the sum of the calculated processing times of each wireless slave station already assigned to this slot).
Assign the I/O refresh of (circle in Figure 6) (#
If it is 1, then "X=1").

In step 806, the wireless slave station i
When the first allocation of I/O refresh is completed, in the next step 807, it is checked whether or not another allocation is possible. If "the previously allocated X" + "refresh period Ti" is equal to or less than the number of slots T (yes), further allocation is possible, so the process moves to the allocation process in step 808. If it exceeds the number of slots T (n
o), the process returns to step 802 to start allocation of the next wireless slave station.

In step 808, the next I/O refresh of the wireless slave station i is allocated to the (X+Ti)th slot (in the case of #1, "5"). Next, the process proceeds to step 809, where Ti is added to X to check whether it can be allocated to a further slot (in the case of #1,
The result of the addition is "X=5"), and the process returns to step 807.
The loop of steps 807 to 809 is repeated until Ti≦T (in the case of #1, "X=9" is further assigned).

In the scheduling table 4 (see FIG. 6) obtained in this way, the calculated communication cycle time is the maximum value of "71 ms" for slots 2 and 8. This "71 ms" is reduced to about 60% of the calculated communication cycle time of "113 ms" in the conventional case where I/O refresh is performed for all wireless slave stations in every communication cycle, and the communication cycle time can be shortened accordingly, making it possible to construct a FA network with high response. Furthermore, if the maximum value of the calculated communication cycle time is small, the actual communication cycle time can be set with a sufficient margin, and the margin can be used for data retransmission and recovery processing, which is particularly convenient for wireless communication where these processes are highly necessary.

In the above embodiment, each wireless slave station is scheduled to perform a maximum of one I/O refresh per slot, but if there is a wireless slave station that requires an I/O refresh very frequently, this wireless slave station can be scheduled to perform an I/O refresh multiple times per slot (one communication cycle). Figures 9 and 10 show examples of the refresh period setting table 1 and the scheduling table 4 in this case. The weight setting table 2 used is that shown in Figure 4.

In the refresh cycle setting table 1 of FIG. 9, when multiple I/O refreshes are assigned to one slot, for example, "-" is added before the number of times in the refresh cycle item to distinguish it from a normal cycle and specify multiple I/O refreshes per slot (2 times in the example of FIG. 9). A detailed explanation of the flow of the process for generating the scheduling table 4 shown in FIG. 10 in this case will be omitted, but the table can be generated in accordance with the process flow of FIG. 8. In the case of the wireless slave station S2 (#2), the cycle in step 804 in FIG. 8 is Ti=-2, and in step 806
10, two slots #2 are allocated to each slot. In allocating the slots, if the wireless slave station S2 performs I/O refresh continuously in a communication cycle, the wireless master station M or the wireless slave station S2 may not be able to prepare data in time, resulting in an empty I/O refresh. Therefore, it is desirable to allocate the I/O refresh of other wireless slave stations as much as possible during that time.
In the example of the scheduling table 4 in FIG. 10, the first I/O refresh #2 of the wireless slave station S2 is in the second column, and the second I/O refresh #2 of the wireless slave station S2 is in the fifth column.
In the second row, other wireless slave stations S3, S
The I/O refresh rates are arranged from top to bottom, with I/O refresh rates #3 and #4 sandwiched between them, and the I/O refresh rates are arranged from top to bottom, with #1, #2, #4, and #2 in slot 1, and #2, #3, #2, and #5 in slot 2.
O refresh is set to occur.

[0042] As in this embodiment, if I/O refresh is performed multiple times for the same wireless slave station within one communication cycle, responses and data exchange between the wireless slave station and the wireless master station will be frequent, and the number of IN refreshes will increase, so that changes in the IN data will be transmitted quickly to the I/O remote master station 10, thereby achieving high-speed response. In addition, even if a communication error occurs, recovery will be made quickly.

11 is a flowchart showing another example of the process for generating the scheduling table 4. The flowchart in FIG. 11 shows a process for generating the I/O of the wireless slave station so as to minimize the maximum value of the calculated communication cycle time for each slot in the scheduling table 4 (see FIG. 6 and FIG. 10).
This is an example of allocating refresh.
In step 111, similarly to step 801 in FIG.
The number of slots T in the scheduling table 4 is calculated.

Next, the process proceeds to step 112, where all the wireless slave stations set in the refresh cycle setting table 1 are provisionally assigned with their refresh cycles, starting from the left in the slot column. For example, slots 1, 5, and 9 are assigned to #1 in Fig. 2, slots 1, 3, 5, 7, 9, and 11 are assigned to #3 and #4, and slots 1 and 7 are assigned to #5.

Next, the process proceeds to step 113, where the maximum value of the sum of the calculated times (see FIG. 5) of the wireless slave stations assigned to each slot is found. If the flow goes directly to step 113 from step 112, the maximum value of the sum appears in slot 1, and in the above example, the value is "113".

In the next step 114, the maximum sums are compared between the allocation combinations, and the combination with the smallest maximum sum is retained. In the first flow, there is nothing to compare it with, so the combination with the maximum sum "113" is saved. In the case of the flow via step 116, which will be described later, the combination with the smallest maximum sum among the maximum sums obtained so far remains as the comparison target, so this is compared and the combination with the smaller maximum sum is retained.

In the next step 115, a check is made to see if the "combination shifting operation" described later has been completed and all combination operations have been completed. The first time, of course, it is not completed (no), so the process proceeds to step 116. Here, new combinations are made by sequentially shifting the allocations tentatively made in step 112. In the above example, for example, #
The allocation of the wireless slave station 115 is shifted to slots 2 and 8, while the allocation of the other wireless slave stations is left unchanged. As a result, the maximum value of the sum in step 113 appears in slots 1, 5, and 9, and its value is "78".
In the same manner, the allocation of #5 is shifted in sequence, and the allocations of the other wireless slave stations are also shifted in sequence, so that the refresh cycle of each wireless slave station is maintained while T×n
When all the combinations (number of wireless slave stations) are compared in sequence, a step 115 is reached in which "exhaustive selection completed" (yes
s), and the last remaining combination is adopted in the scheduling table 4. According to this flow, the maximum value of the calculated communication cycle time for each slot is minimized, and the actual communication cycle time can be shortened to the shortest. The shorter the actual communication cycle time, the faster the response of the FA system becomes.
Production efficiency will also improve.

[0048]

As described above, according to the present invention, a refresh cycle setting table for setting a refresh cycle for each wireless slave station and a table for setting a weighting factor that affects an I/O refresh processing time for each wireless slave station are provided.
and a scheduling table which allocates wireless slave stations which perform I/O refresh processing in each slot of a communication cycle based on the refresh period of the refresh period setting table and the weighting factor of the weight setting table. According to the scheduling table, the wireless master station cyclically communicates with the wireless slave stations to perform I/O refresh. Therefore, the polling period of each wireless slave station is determined according to the frequency at which I/O refresh is required, and the wireless slave stations which perform I/O refresh are distributed and allocated to each slot of the communication cycle based on the time required for the I/O refresh and the polling period. This shortens the communication cycle time, and even when a highly reliable wireless communication method such as retransmission processing, error control, wireless relay, etc. is adopted, the wireless communication speed is increased, and the responsiveness of the wireless remote I/O device is improved.

[0049] According to this invention , the scheduling table is allocated so that the maximum value of the sum of the calculated processing times of the wireless slave stations allocated to each slot in the scheduling table is as small as possible. Therefore, even if the communication cycle time is set to a constant value slightly larger than the maximum value of the sum of the calculated processing times and simple fixed-period communication cycle processing is performed, the communication cycle time can be made relatively short, and high-speed wireless communication can be easily achieved, making it highly practical.

According to this invention , since the items in the weight setting table include the number of wireless relay stages, the time required for relaying is added to the I/O refresh processing time,
The I/O refresh processing time using wireless relay is
This is reflected in the schedule of the wireless I/O refresh, and the communication cycle time of the wireless remote I/O device equipped with the wireless relay station can be set more accurately.

[0051] According to the invention of claim 2 , in the invention of claim 1, a plurality of identical wireless slave stations are assigned to one slot of the scheduling table, and within the one slot, the wireless master station performs I/O refresh with the same wireless slave station a plurality of times. Therefore, a wireless slave station which performs I/O refresh a plurality of times within one communication cycle is I/O refreshed frequently, as if the communication cycle had been shortened to one or more times the actual communication cycle, resulting in the effect of significantly shortening the communication cycle by that amount.

According to the third aspect of the present invention , a plurality of I/O refresh operations between the wireless master station and the same wireless slave station are performed, and the I/O refresh operations between the wireless master station and another wireless slave station are performed.
Since the I/O refresh is performed with a refresh in between, there is a slight time interval between I/O refreshes of the same wireless slave station.
"Empty I/O" which is likely to occur when refresh is performed continuously
This avoids "refreshing" and allows for effective I/O refreshes to be performed frequently.

According to the fourth aspect of the present invention , in the first aspect of the present invention, the wireless slave station monitors polling from the wireless master station based on the communication cycle time determined by the wireless master station from the results of the scheduling table. Therefore, when the polling from the wireless master station is no longer according to schedule, the wireless master station detects this and stops the normal I/O refresh.
It is possible to switch to abnormal processing.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating an example of a wireless communication network using a wireless remote I/O device of the present invention.

FIG. 2 is a block diagram showing a scheduling process in the wireless remote I/O device of the present invention.

FIG. 3 is an explanatory diagram showing an embodiment of a refresh cycle setting table in the wireless remote I/O device of the present invention.

FIG. 4 is an explanatory diagram showing an embodiment of a weight setting table in the wireless remote I/O device of the present invention.

5 is an explanatory diagram showing processing time calculation values based on the weight setting table of FIG. 4;

6 is an explanatory diagram showing a scheduling table obtained from the refresh cycle setting table of FIG. 3 and the weight setting table of FIG.

FIG. 7 is a flowchart showing a communication processing flow in the wireless remote I/O device of the present invention.

FIG. 8 is a flowchart showing a flow of an embodiment of scheduling in the wireless remote I/O device of the present invention.

FIG. 9 is an explanatory diagram showing another embodiment of a refresh cycle setting table in the wireless remote I/O device of the present invention.

10 is an explanatory diagram showing a scheduling table obtained from the refresh cycle setting table of FIG. 9 and the weight setting table of FIG.

FIG. 11 is a flowchart showing the flow of scheduling in a wireless remote I/O device according to another embodiment of the present invention.

[Explanation of symbols]

1 Refresh period setting table 2 Weight setting table 3 Scheduling means 4 Scheduling table M Wireless master station NW1, NW2 Network S1 Wireless relay station (wireless slave station) S2, S3, S4, S5 Wireless slave stations

───────────────────────────────────────────────────────── Continued from the front page (56) References JP 2-79536 (JP, A) JP 3-187644 (JP, A) JP 5-260572 (JP, A) JP 7-115423 (JP, A) (58) Field of investigation (Int.Cl. ⁷ , DB name) H04L 12/28

Claims (4)

(57) [Claims] [Claim 1] In a wireless remote I/O device in which a wireless master station performs I/O refresh by cyclically communicating with a wireless slave station directly or via a wireless relay station, the device comprises a refresh cycle setting table for setting a refresh cycle for each wireless slave station, and a table for setting weighting factors that affect the refresh processing time for each wireless slave station , the weighting factors being ineffective in the items.
a scheduling table for allocating a wireless slave station to perform a refresh process in each slot of a communication cycle based on a refresh period of the refresh period setting table and a weighting factor of the weight setting table, wherein a wireless master station cyclically communicates with the wireless slave stations to perform I/O refresh in accordance with the scheduling table. [Claim 2] A wireless remote I/O device as described in claim 1, characterized in that multiple identical wireless slave stations are assigned to one slot of the scheduling table, and within the one slot, a wireless master station performs I/O refresh with the same wireless slave station multiple times. [Claim 3] The wireless remote I/O device as described in claim 2, characterized in that multiple I/O refreshes between the wireless master station and the same wireless slave station are performed with I/O refreshes between the wireless master station and other wireless slave stations in between. 4. The wireless remote I/O device according to claim 1 , wherein the wireless slave station monitors polling from the wireless master station based on a communication cycle time determined by the wireless master station from the results of the scheduling table.