Data processing: generic control systems or specific application – Generic control system – apparatus or process
Reexamination Certificate
1998-08-20
2001-06-05
Sheikh, Ayaz (Department: 2155)
Data processing: generic control systems or specific application
Generic control system, apparatus or process
C700S001000, C700S032000, C700S121000, C700S005000, C700S060000, C700S063000, C702S182000, C709S213000, C709S241000, C710S013000, C710S120000, C710S028000
Reexamination Certificate
active
06243610
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a network control system for both an asynchronous network type control system and a synchronous network type control system. In particular, the invention relates to a control system in which in a case where a controlled object process and a control apparatus are connected to each other via an asynchronous network, the control apparatus performs a control by calculating control variables for the controlled object process on a real-time basis.
2. Description of the Related Art
In conventional control systems, it is necessary to design means for calculating an optimum value of a control variable in accordance with dynamic characteristics of a controlled object process and implement it in a control apparatus in advance, and to execute a series of processes such as observation of a process variable, control calculations, and output of a value of a manipulated variable (in this specification, “manipulated variable” is as same meaning as “control variables”) on a real-time basis, that is, at constant intervals. Therefore, it is necessary to construct a special network system (synchronous network) in which real-time operation is taken into account.
On the other hand, to keep the communication line cost low, extra costs are needed for development and maintenance for that purpose. In particular, where a controlled object process and a manipulation station including a control apparatus need to be installed at respective places that are very distant from each other, it is necessary to use a dedicated line in which real-time operation is taken into consideration. This requires a high communication line cost.
If an asynchronous network that is low in communication line cost is used, because it is a public line, there occurs a transmission delay that varies depending on a network state; for example, a large transmission delay occurs during a congested time. As a result, a variable, useless time occurs in a one-circulation path of a process signal or a control signal starting from a controlled object, reaching a control apparatus, and returning to the controlled object. This causes a problem that the control performance and the stability are lowered.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a network control system which, even with an network in which real-time operation is not taken into account, can improve the control performance and the stability by precisely controlling a variable, useless time by performing precise time management that involves process variable detection time and control signal reception time on the controlled object side.
Another object of the invention is to provide a network control system which can reduce a communication line cost by enabling use of public lines, the Internet, etc. by precisely managing a variable, useless time.
To attain the above objects, according to a first aspect of the invention, there is provided a network control system comprising a control apparatus comprising process signal receiving device for receiving a process signal that is transmitted from a controlled object and includes process variable detection time; control variable calculating device for calculating a control variable for a process in the controlled object based on the received process signal; and control signal transmitting device for transmitting a control signal including the calculated control variable and the received process variable detection time to the controlled object via a network; and the controlled object comprising: control signal receiving device for receiving the control signal that is transmitted from the control apparatus; driving device for driving the process in the controlled object based on the control variable included in the control signal; detecting device for detecting a process variable of the process thus driven; time measuring device for measuring detection time of the process variable and reception time of the control signal; and process signal transmitting device for transmitting a process signal including the detected process variable and the measured process variable detection time to the control apparatus via the network, wherein the control signal receiving device further calculates a transmission delay that is a difference between the control signal reception time and the process variable detection time that is included in the control signal, corrects the control variable by processing it in accordance with the transmission delay, and outputs a corrected control variable to the driving device.
According to a second aspect of the invention, in the network type control system according to the first aspect, the control variable calculating device sets a plurality of assumed transmission delays and calculates optimum control variables for the respective assumed transmission delays, the control signal transmitting device transmits the calculated control variables en bloc as the control signal, and the control signal receiving device selects one of the control variables included in the control signal corresponding to an assumed transmission delay that is closest to an actual transmission delay, and outputs the selected control variable to the driving device as the corrected control variable.
According to a third aspect of the invention, in the network type control system according to the first aspect, the control variable calculating device calculates an optimum control variable response locus for a predetermined period from a present time, the control signal transmitting device transmits the optimum control variable response locus in such a manner that it is included in the control signal, and the control signal receiving device stores the optimum control variable response locus included in the received control signal, and sequentially outputs, to the driving device, values of the optimum control variable response locus as the corrected control variables in accordance with time that is measured by the time measuring device until reception of a next control signal.
According to a fourth aspect of the invention, in the network type control system according to the third aspect, the process signal transmitting device combines a preceding control variable and preceding control signal reception time with the process variable and the process variable reception time to generate the process signal, and the control variable calculating device comprises a model holding section for holding a model of the controlled object process and a network model in which a transmission delay is assumed; a data buffer for storing process variable history data of past process variables and process variable detection time points up to immediately before a present time and control variable history data of past control variables and control signal reception time points up to a preceding cycle; a prediction calculation section for calculating a future process variable prediction response from the present time based on the models held by the model holding device and the process variable and control variable history data stored in the data buffer; and a control variable optimization section for determining a future optimum control variable response locus from the present time so that the process variable prediction response calculated by the prediction calculation section becomes as close to a preset target response locus as possible, and calculates, every time a new process signal is received, an optimum control variable response locus for a predetermined period from a present time by repeatedly performing calculations relating to the process.
According to a fifth aspect of the invention, in the network type control system according to the fourth aspect, a plurality of controlled objects are connected to the single control apparatus bidirectionally like a star connection via individual network; the control apparatus comprises process signal receiving device for receiving process signals from the controlled objects, control variable calculating device for calc
Iino Yutaka
Mitsumoto Kenji
Takagi Yasuo
Backer Firmin
Kabushiki Kaisha Toshiba
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Sheikh Ayaz
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