Abstract:
A safety control system includes a plurality of safety control stations connected to a control bus to communicate with each other and with a distributed control system including a plurality of control stations connected to the control bus, wherein each of the plurality of safety control stations has an interface through which each of the plurality of safety control stations is connected to the control bus for transmitting own data of each of the plurality of safety control stations to all other safety control stations by broadcasting at a fixed cycle via the control bus and for receiving by each safety control station transmitted data from all other safety control stations, and wherein the interface implements a safety layer used to generate and diagnose safety information.

Description:
This application claims priority to Japanese Patent Application No. 2007-188462, filed Jul. 19, 2007, in the Japanese Patent Office. The Japanese Patent Application No. 2007-188462 is incorporated by reference in its entirety. 
     TECHNICAL FIELD 
     The present disclosure relates to safety assurance of communication between safety control stations provided in a safety control system that is integrated with a distributed control system, and connected to a control bus that is used commonly in both systems. 
     RELATED ART 
     As to the safety control system integrated with the distributed control system, the technical disclosure is made in Patent Literature 1.  FIG. 8  is a functional block diagram showing an integrated environment of the distributed control system and the safety control system, which is disclosed in Patent Literature 1. 
     Both the distributed control system indicated by a chain-line area A and the safety control system indicated by a chain-line area B are connected to a common control bus  1 , and communicate with an operation monitoring station  2  that is also connected to this control bus  1  commonly to both systems. 
     In the distributed control system A, control stations  31 ,  32  communicate with the operation monitoring station  2  via the control bus  1 , and also communicate with respective equipments (not shown) of a plant  4  and control them. 
     In the safety control system B, safety control stations  51 ,  52  communicate with the operation monitoring station  2  via the control bus  1 , and also communicate with the equipments of the plant  4 . When the safety control stations  51 ,  52  receive a trip request from the plant  4 , they execute a stop operation of the plant  4 . 
     The safety control system B can carry out the safety communication, which has gotten the approval at a SIL3 level, on the same control bus  1  as the distributed control system A. Thus, this safety control system B can build up the integrated system in which control communication of the distributed control system in the related art is mixed together. 
     In this case, the communication between the safety control stations makes it possible for each safety control station to inform quickly other safety control stations of an abnormal event that each safety control station sensed. Thus, the safety control station can deal quickly with the abnormal event in the plant, and therefore such communication is effective in preventing the hazards and narrowing the damage area. 
     The “safety communication” in the safety control system signifies the communication system that is equipped with an engineering to check the fact that safety-related data has been transferred certainly to the destination of communication through the existing unsafe communication system without fail. 
     In the safety communication, a safety layer for separating a safety function from the unsafe outside world is provided to the portion of the application layer of communication. Thus, all hazardous events that will happen in the communication (corruption, omission, delay, etc. of the data) are checked. 
       FIG. 9  is a functional block diagram explaining an engineering of the safety communication between two safety control stations  51 ,  52 . The communication data in the BOOL type, integral number type, or real number type data format are converted into the unique data format called the binding variable, and then flow through the control bus  1 . 
     In this binding variable, a time stamp of the transmission time, a sequence number, and a CRC (Cyclic Redundancy Check) code for use in error check of all communication data are stored in addition to the data value. It is a producer side function block  51   a  that formulates these safety information, and a binding variable  51   b  after converted is sent out to the control bus  1 . 
     In contrast, when received this variable, a consumer side function block  52   a  on the safety control station  52  side checks all abnormal events in communication by using a received binding variable  52   b . When senses the abnormal event, the consumer side function block  52   a  outputs a fail-safe value designated previously as data, and outputs the abnormal event to the data status, and also issues a system alarm indicating occurrence of an error. 
     Both the producer side function block  51   a  and the consumer side function block  52   a  constitute a safety layer  60  that is used for the safety communication between two safety control stations  51 ,  52 . 
       FIG. 10  is a conceptual illustration of the safety communication when plural pieces of transmitted/received data are present. A transmitting device of the safety control station on the producer side compiles once a plurality of transmitting binding variables, and then sends out the compiled variable to the destination station. A receiving device of the safety control station on the destination side distributes the received variable into corresponding receiving binding variables. 
       FIG. 11  is a functional block diagram of applications of the safety communication, which are formulated by the user. A basic concept is the safety communication on a one-to-one basis through the intermediation of the binding variable. The user constructs the binding variable and input/output function blocks, and connects them to the application logic. 
     [Patent Literature 1] Japanese Patent Application Publication No. 2006-164143 
     In the safety communication between the safety control stations in the related art, the information for securing the safety communication is added to the data one by one, and the diagnosis of the received data is made by the safety layer provided to the consumer side function block. Therefore, the safety communication can be secured on the same control bus  1  through which communication data of the distributed control system also flows. 
     However, following problems existed in the safety communication between the safety control stations in the related art. 
     (1) The user has to formulate both applications of the binding variable and the function block. Therefore, the engineering is troublesome, and thus the engineering man-hours are increased. 
     (2) Since the data are transmitted/received individually, the communication and the CPU performance are expended. Therefore, it is impossible for many stations to share the data, and thus the communication performance is restricted. 
     (3) Since the data is diagnosed piece by piece, the alarms of the same number as the data are informed when the producer side safety control station is stopped. Therefore, a flood of alarms is caused. 
     SUMMARY 
     Exemplary embodiments of the present invention provide a safety control system that enables a large number of control stations to share information by a simple engineering without expenditure of the communication and the CPU performance. 
     Exemplary embodiments of the present invention is constructed as follows. 
     (1) A safety control system, includes a plurality of safety control stations connected to a control bus to communicate with other; and a link transmission communicating means having a function of transmitting own data to other safety control station at a fixed cycle via the control bus every safety control station and also receiving transmitted data from other safety control station. 
     (2) In the safety control system set forth in (1), the safety control station adds safety information to the data that is to be transmitted to the control bus at a fixed cycle. 
     (3) In the safety control system set forth in (1) or (2), the safety control station has a safety layer, which is used to generate and diagnose the safety information, in an interface to the control bus. 
     (4) In the safety control system set forth in (2) or (3), the safety information contains a CRC code. 
     (5) In the safety control system set forth in any one of (1) to (4), the safety control station communicates with a distributed control system via the control bus. 
     According to the present invention, advantages described as follows can be expected. 
     (1) The safety communication data can be transmitted by using the link transmission communicating means utilizing the control bus. Therefore, a large number of stations can share simply the information at a high speed. Also, the consumer side safety control station can receive freely the data at any timing. Therefore, the user can add the application simply. 
     (2) The safety communication data is transferred while using the predetermined data area of the link transmission. Therefore, only the function block used to access the data in this area and the database for storing the layout definition are needed. As a result, the engineering is made easy. 
     (3) The consumer side safety control station conduct a diagnosis on the assembly of the received data. Therefore, the load of the CPU becomes small. Also, even though the producer side control station is stopped, merely the alarm corresponding to the concerned station may be output. Therefore, a flood of alarms is not caused. 
     Other features and advantages may be apparent from the following detailed description, the accompanying drawings and the claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a functional block diagram showing an embodiment of a safety control system to which the present invention is applied. 
         FIG. 2  is a data configurative view showing a data area of a safety communication and communication contents, which are provided to each safety control station. 
         FIG. 3  is a functional block diagram explaining an engineering of the safety communication between safety control stations, to which the present invention is applied. 
         FIG. 4  is a functional block diagram explaining applications and a user-defined database to handle link transmission data. 
         FIGS. 5A and 5B  are flowcharts showing procedures of a transmitting process and a receiving process of the safety communication in the safety control system, to which the present invention is applied. 
         FIG. 6  is a functional block diagram explaining data sharing between the control stations of the distributed control system and the safety control station. 
         FIGS. 7A and 7B  are data configurative views showing a difference between control station data and safety control station data, which the safety control station receives. 
         FIG. 8  is a functional block diagram showing an integrated environment of the distributed control system and the safety control system. 
         FIG. 9  is a functional block diagram explaining an engineering of the safety communication between the safety control stations. 
         FIG. 10  is a conceptual illustration of the safety communication when plural pieces of transmitted/received data are present. 
         FIG. 11  is a functional block diagram of applications of the safety communication, which the user formulates. 
     
    
    
     DETAILED DESCRIPTION 
     The present invention will be explained in detail with reference to the drawings hereinafter.  FIG. 1  is a functional block diagram showing an embodiment of a safety control system to which the present invention is applied. The same reference symbols are affixed to the same elements as those of the conventional system explained by reference to  FIG. 8 , and their explanation will be omitted herein. 
     The present invention provides the safety control system that enables the safety control stations to share the data in the safety communication more simply, by utilizing the link transmission communicating means that is installed to share the data among the safety control stations in the distributed control system. 
     In  FIG. 1 , safety control stations  501  (tag name SCS 0101 ),  502  (tag name SCS 0102 ), . . . ,  50   n  (tag name SCS 010   n ), to which the present invention is applied, are connected to a control bus  100 , into which the link transmission communicating means is installed, via interfaces  601 ,  602 , . . . ,  60   n . The safety layer for use in the safety communication is formed in these interfaces. 
     The functional configuration of each safety control station will be illustrated hereunder, while using the safety control station  502  as a typical example. The safety control station  502  transmits its own transmitted data to be communicated with other safety control station from the user&#39;s application to the control bus  100  at a fixed cycle via the interface  602  (indicated with an arrow S). 
     At the same time, the safety control station  502  can receive the transmitted data of other safety station from the control bus  100  (indicated with an arrow R), and then the user&#39;s application can acquire the data via the interface  602 . 
     Also, remaining safety control stations have the same function. The link transmission communicating means holds the transmitted data until the data of each safety control station is updated by the fixed-cycle transmission. 
     The link transmission data is the broadcast communication that informs respective safety control stations of the 32-byte data, for example, in a 100 mm sec period every safety control station. Each safety control station receives the data necessary for the process in the logic from other safety control stations, and transmits its own calculated data. 
     The producer side safety control station has no awareness of which safety control station is receiving its own transmitted data. This broadcast communication is the passive type communication in which the safety control station that needs the concerned data receives the data at its own starting timing. 
       FIG. 2  is a data configurative view showing the data area that each safety control station has for the safety communication and communication contents. Respective tag names are common to those in  FIG. 1 . Each safety control station has the data areas in the same number as the related control stations, and can write the data only in its own area as the transmission buffer. 
     Each data area has a size of 32 byte. In this embodiment, in order to handle the safety communication by utilizing the link transmission communicating means, a former half 16 byte is used as the data area and a latter half 16 byte is used as the safety information. The safety information adds a sequence number, a time stamp representing a transmitted time, and a CRC code to the 16-byte data. 
       FIG. 3  is a functional block diagram explaining an engineering of the safety communication between safety control stations  501  and  502 , to which the present invention is applied. A feature portion of the present invention is a safety layer  700  that is added newly to the interfaces  601  and  602  for the control bus  100 . 
     In the producer side safety control station  501 , the function of the safety layer  700  adds the safety information to the transmitted data of an output function block  801  that is used to transmit the result of the application logic as the safety communication data. Then, the function of the safety layer  700  transmits the resultant data as the link transmission data onto the control bus  100 . 
     In the consumer side safety control station  502 , the function of the safety layer  700  diagnoses the safety information that is received from the safety control station  501  via the control bus  100  and is added to the link transmission data. Then, the function of the safety layer  700  sends out the system alarm when the abnormal event is sensed. After the abnormality diagnosis, the link transmission data is transferred to the application logic via an input function block  802 . 
       FIG. 4  is a functional block diagram explaining applications and a user-defined database to handle the link transmission data.  FIG. 4  shows the safety control station  502  (tag name SCS 0102 ) as a typical example. 
     The safety control station has a simple configuration that only an input function block  802   a  and an output function block  802   b  are arranged on the application logic. A transmission definition and a reception definition both held in a database  802   c  indicate how the actual input/output function blocks and the transmission/reception data are coupled mutually respectively. 
     The user can lay out freely the transmission definition and the reception definition of this database and set them. The input/output function blocks  802   a ,  802   b  can know which data its own block should access, by referring to the definition of this database. 
     In this manner, the input/output function blocks and the link transmission communicating means make a promise of data positions in advance, and handle the transmitted/received data of the safety communication as an assembly of 16-byte data. As a result, the safety information can be assembled into one piece. 
       FIGS. 5A and 5B  are flowcharts showing procedures of the transmitting process and the receiving process of the safety communication in the safety control system, to which the present invention is applied.  FIG. 5A  shows a flowchart of the transmitting process, and  FIG. 5B  shows a flowchart of the receiving process. 
     In the transmitting process in  FIG. 5A , in step S 1  and step S 2 , the output function block completes the writing of all data in the designated positions. Then, in step S 3 , the safety information for the safe communication is added. Then, in step S 4 , the data is transmitted to the link transmission communication. 
     In the receiving process in  FIG. 5B , in step S 1 , the data is acquired from the link transmission communication. Then, in step S 2 , a diagnosis of the safety information is made. If the diagnosis result is OK in step S 3 , the data is copied as the assembly as it is in step S 4 , and the input function block picks up the necessary data. In contrast, if the diagnosis is not passed in step S 3 , the error process is executed in step S 5 . 
     Essentially, in the control station (FCS) of the distributed control system, the link transmission communicating means is used for the data communication between the FCSs as the global switch. Also, in the safety control system (SCS), even if it can be recognized by using this link transmission communicating means that the communication destination is either the FCS or the SCS, this link transmission communicating means can be used to share the data between the FCS and the SCS. 
       FIG. 6  is a functional block diagram explaining the data sharing between control stations of the distributed control system and the safety control station.  FIG. 6  shows such a conceptual illustration that the safety control system FCS 0103  receives the link transmission data of the control station FCS 0101  of the distributed control system, and inputs the data into the logic via the input function block. 
       FIGS. 7A and 7B  are data configurative views showing a difference between the control station data and the safety control station data, which the safety control station receives.  FIG. 7A  shows a data configuration of the safety control station (SCS), and  FIG. 7B  shows a data configuration of the control station (FCS). 
     The FCS data gives the data in the 32-byte fully, while the SCS data gives the data in the first half 16-byte only. The FCS can refer to the 16 byte of the transmitted data from the SCS as the global switch. 
     While the invention has been described with respect to a limited number of embodiments, those skilled in the art, having benefit of this disclosure, will appreciate that other embodiments can be devised which do not depart from the scope of the invention as disclosed herein. Accordingly, the scope of the invention should be limited only by the attached claims.