There has been recently proposed a wireless control system utilizing wireless communication, for example, in order to make up or support a process control system in an industrial automation. Since a conventional wireless control system is made up by a wired network, there arises a problem that sensors for measuring a temperature, flow rate and so forth can not be disposed at the optimum positions in a plant due to limitation of a communication distance, limitation of leading of the wiring around the sensors, thereby deteriorating control accuracy. Accordingly, the invention has been developed to solve such a problem.
There is the following prior art reference relating to the conventional wireless control system.
[Patent Document] WO2003/061175 (JP 2005-515695A)
FIG. 9 is a block diagram showing a configuration of an embodiment of a conventional wireless control system. In FIG. 9, a supervisory node 1 is mutually connected to gateway nodes 2 and 3 via a network NW100. The gateway node 2 is connected to a wireless node 4 via a wireless network circuit (hereinafter referred to as wireless circuit) CN101, to a wireless node 5 via a wireless circuit CN102 and to a wireless node 6 via a wireless circuit CN103.
The gateway node 3 is connected to the wireless node 4 via a wireless circuit CN104, to the wireless node 5 via a wireless circuit CN105 and to the wireless node 6 via a wireless circuit CN106.
The wireless node 4 is connected to the wireless node 5 via a wireless circuit CN107, to a wireless node 7 via a wireless circuit CN109 and to a wireless node 8 via a wireless circuit CN110.
The wireless node 5 is connected to the wireless node 7 via a wireless circuit CN111, to the wireless node 8 via a wireless circuit CN112, to a wireless node 9 via a wireless circuit CN113 and to the wireless node 6 via a wireless circuit CN108. The wireless node 6 is connected to the wireless node 8 via a wireless circuit CN114 and to the wireless node 9 via a wireless circuit CN115.
The wireless node 8 is connected to the wireless node 7 via a wireless circuit CN116 and to the wireless node 9 via a wireless circuit CN117. In such a manner, the wireless nodes 4 to 9 form a mesh-type multihop wireless network. In FIG. 9, there is shown an operation of data communication NR100 wherein the wireless node 7 transmits data to the supervisory node 1 via the gateway node 2.
In the wireless control system in FIG. 9, the supervisory node 1 collects and stores therein measurement data measured by the wireless nodes 4 to 9 and grasps the measurement data. The gateway nodes 2 and 3 have a communication function to implement communication mainly with each wireless node and the supervisory node 1. The wireless nodes 4 to 9 are installed on a plant, and form a wireless sensor network, whereby they have a sensor function to measure physical quantity such as a temperature and flow rate, and a wireless communication function to implement wireless transmission of these measurement data, and they transfer data received from other wireless nodes.
Meanwhile, it may be configured that the supervisory node 1 transfers collected measurement data to a controller, not shown, and the controller calculates control data for operating and controlling a control instrument such as a valve, regulating valve, and so forth, not shown, in order to converge the measurement data in a prescribed target value, and operates and controls the control instrument based on the control data.
FIG. 10 is a block diagram showing a configuration of an example of a wireless communication function of the wireless node 7 in FIG. 9. In FIG. 10, a wireless communication section 71 is connected to an arithmetic and control section 72, and the arithmetic and control section 72 is connected to a storage section 73. The wireless communication section 71 implements wireless communication mainly between itself and other wireless nodes and gateway nodes 2 and 3. The arithmetic and control section 72 controls operations of each section. There are stored in the storage section 73 a program for operating the wireless nodes, information of route leading from a self-node to the gateway nodes 2 and 3, (hereinafter referred to route information) and so forth. The wireless nodes 4 to 6, 8 and 9 have the same configurations as that of the wireless node 7.
Meanwhile, it is supposed here that the wireless nodes 4 to 9 grasp in advance route information for transferring data to the gateway nodes 2 and 3 by implementing address/name resolution, and searching a route or setting route information in advance on each wireless node. Further, it is supposed that the gateway nodes 2 and 3 grasp in advance route information leading to the supervisory node 1.
An operation of the conventional wireless control system is described with reference to a flow chart in FIG. 11. First, in step S101, when the arithmetic and control section 72 of the gateway node 7 reads and executes the program stored in the storage section 73, thereby controlling a sensor to measure physical quantity such as a flow rate, temperature and so forth, and stores therein measured data in the storage section 73. Meanwhile, the operation of the arithmetic and control section 72 of the wireless node 7 to read and execute the program stored in the storage section 73 to control each section is also applied to other wireless nodes, and hence the operations of those of other wireless nodes are omitted.
In step S102, the arithmetic and control section 72 of the wireless 7 selects the wireless node or gateway node serving as a relay point for transferring the measurement data to the supervisory node 1 based on route information stored in advance in the storage section 73, and transmits the measurement data of physical quantity such as the flow rate, temperature, and so forth to the selected wireless node or gateway node. For example, the arithmetic and control section 72 of the wireless 7 selects the wireless node 4 as a relay point based on the route information stored in advance in the storage section 73, and transmits the measurement data to the selected wireless node 4 via the wireless circuit CN109.
In step S103, the wireless node 4 selects the wireless node or gateway node serving as a relay point for transferring the measurement data to the supervisory node 1 based on route information stored in advance in a storage section, not shown, and transmits measurement data received from the wireless node 7 to the selected wireless node or gateway node. For example, the wireless node polarization film 4 selects the gateway node 2 and transmits the measurement data acquired from the wireless node 7 to the gateway node 2.
In step S104, the gateway node 2 transmits measurement data received from the wireless node 4 to the supervisory node 1 via the network NW100. That is, the wireless node 7 transmits the measurement data to the supervisory node 1 via the wireless node 4 and gateway node 2 as shown in the data communication NR100 in FIG. 9.
The supervisory node 1 stores therein data transferred from the gateway node 2, and grasps measurement data measured by the wireless node 7. Since the supervisory node 1 collects and stores therein measurement data likewise from the other wireless nodes, it can grasp an operation condition of the plant. Further, it may be configured that the supervisory node 1 transfers measurement data collected from any wireless node to a controller, not shown, and the controller converges the measurement data in a target value in which a measurement value is previously set, thereby controlling prescribed control instruments such as a valve, heater and so forth, not shown so that the plant can be operated optimally.
As a result, the supervisory node 1 can grasp the operation condition of the plant by collecting and storing the measurement data from each wireless node, thereby supporting the optimum operation of the plant.
Meanwhile, when structuring such a wireless control system, it is necessary that each wireless node grasps the number of the gateway nodes, installing positions of gateway nodes and network information such as an IP address, and so forth.
Consequently, it is carried out that network information is acquired via a wireless network by setting network information in advance on each wireless node or utilizing address/name resolution mechanism.
Further, since the gateway node collects data from many wireless nodes, a communication load on the gateway node increases, so that the performance of the system is liable to decrease. Accordingly, it is carried out that the communication load on the gateway node is dispersed by installing a plurality of gateway nodes so as to decrease the communication load on the gateway node.
Still further, it is carried out that a gateway node for urgency dedicated for alarm data having high level of urgency is installed, and the wireless node selects a route via the gateway node for urgency based on a name inherent in the gateway node for urgency, and identification information such as ID and so forth, thereby transmitting alarm data to the selected route.
However, according to a method of setting in advance network information on each wireless node, when the change or extension of configuration of the system such as newly installation of a gateway node or wireless node or the change of address is carried out, network information set on each wireless node has to be changed, causing a problem in terms of extension and flexibility of the system.
Further, according to a method of acquiring network information via a wireless network utilizing an address/name resolution mechanism, each wireless node acquires address information of the gateway node from a wireless node having a directory service function for the address/name resolution mechanism via the wireless circuit, resulting in the increase of traffic of the wireless network, causing a problem that the performance of the entire system decreases.
Still further, even in a method of dispersing a communication load by installing a plurality of gateway nodes, there is a likelihood that the communication load on the gateway node is biased depending on the installing position of the wireless node or gateway node, causing a problem that the load on the gateway node 22 can not be controlled.
More still further, in the case of installing a gateway node for urgency, every time the configuration of the system is changed owing to the change of the name or ID of the gateway node, and so forth, newly installation and removal of the gateway node, the wireless node has to acquire identification information of the gateway node which has been changed or newly installed, resulting in the increase of traffic in the same manner as the case of utilizing the forgoing address/name resolution mechanism, so that the performance of the entire system decreases.
Depending on the installing position of the wireless node, radio disturbance will occur if there exists an obstacle, so that wireless communication is liable to get into an unstable state and the communication load on the gateway node is biased, causing a problem that the performance of the entire system decreases.