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(12) EUROPEAN PATENT APPLICATION

(43) Date of publication: 01.02.2012 Bulletin 2012/05

(21) Application number: 11175651.6

(22) Date of filing: 27.07.2011

(51) Int Cl.:G06F 9/48 (2006.01) G05B 19/04 (2006.01)

(84) Designated Contracting States: AL AT BE BG CH CY CZ DE DK EE ES FI FR GB GR HR HU IE IS IT LI LT LU LV MC MK MT NL NO PL PT RO RS SE SI SK SM TRDesignated Extension States: BA ME

(30) Priority: 27.07.2010 JP 2010168218

(71) Applicant: Yokogawa Electric CorporationTokyo 180-8750 (JP)

(72) Inventor: Yagura, MasakiTokyo, 180-8750 (JP)

(74) Representative: Henkel, Breuer & PartnerPatentanwälte Maximiliansplatz 2180333 München (DE)

(54) Sequence controller

(57) A sequence controller includes a periodic exe-cution type sequence control module configured to exe-cute each regular processing function block in a prede-termined control period, an irregular processing functionblock storage configured to hold an irregular processingfunction block generated by a user, and a time-sharingexecution type sequence control module configured to

execute the irregular processing function block calledfrom the irregular processing function block storage infree time of the control period. The periodic executiontype sequence control module is configured to call theirregular processing function block from the irregularprocessing function block storage and to execute the ir-regular processing function block in the control period.

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Description

TECHNICAL FIELD

[0001] The present disclosure relates to a sequencecontroller having a periodic execution type sequencecontrol module which executes a regular processing fac-tion block in a predetermined control period, an irregularfunction block storage which holds an irregular functionblock generated by a user, and a time-sharing executiontype sequence control module which executes the irreg-ular function block called from the irregular function blockstorage in free time of the control period.

RELATED ART

[0002] Fig. 7 is a functional block diagram showing anexample of configuration of a process control systemhaving a sequence controller according to the related art.A control station 10 which formes a distributed controlsystem is equipped with a control application 20 and asequence controller 30.[0003] The control station 10 communicates with ahigher-level device 50 forming a distributed control sys-tem through a control bus 40, communicates with fielddevices 71, 72, ... 7N through a field bus 60 and controlsthese devices.[0004] An engineering station 80 which communicateswith the control station 10 and the higher-level device 50is connected on the control bus 40 so that a builder 81generates an operation/monitoring application operatingon the higher-level device 50, a control application 20operating on the control station 10 and a sequence func-tion block operating on the sequence controller 30 andthe higher-level device 50 and the control station 10download these applications.[0005] The sequence controller 30 has a timer controlmodule 31, an event control module 32, a periodic exe-cution type sequence control module 33, a time-sharingexecution type sequence control module 34, and an ir-regular processing function block storage 35. The se-quence controller 30 executes registered function blocksin accordance with execution order or processing priorityprescribed on a table.[0006] The event control module 32 requests the pe-riodic execution type sequence control module 33 andthe time-sharing execution type sequence control mod-ule 34 to execute predetermined sequence control basedon the sequence execution order or processing priorityat event timing notified by the timer control module 31.[0007] The periodic execution type sequence controlmodule 33 executes a regular processing function blockin a predetermined control period. Although the regularprocessing function block has a processing functionwhich is so fixed that a given regular process can beexecuted at a high speed, the regular processing functionblock does not support user’s customization.[0008] The time-sharing execution type sequence con-

trol module 34 executes an irregular function block calledfrom the irregular processing function block storage 35by using free time in the control period. The irregularprocessing function block can be customized freely bythe user through the builder 81, downloaded into the ir-regular processing function block storage 35, and calledand executed by the time-sharing execution type se-quence control module 34.[0009] The regular processing function block executedsurely in a predetermined control period controls a se-quence which performs processing determined periodi-cally whereas the irregular processing function block con-trols a sequence which is so low in temporal restrictionso that free time in the control period can be used andwhich needs to be customized freely.[0010] The irregular processing function block is here-inafter referred to as SEBOL (SEquence and Batch Ori-ented Language) function block. SEBOL is a program-ming language which has characteristic specialized inbatch control in addition to operation of a general pro-gramming language usually used.[0011] Fig. 8 is a functional block diagram for explain-ing operation of an execution link generating module ina sequence controller according to the related art. Anengineer writes an execution sequence of regularprocessing function blocks (PID, SIO, PVI01, PVI02) andSEBOL function blocks (SEBOL01, SEBOL02) on an ex-ecution sequence definition screen 91.[0012] The engineer can further select componentizedfunction blocks from a component palette (not shown) orthe like and pastes the selected componentized functionblocks on a control drawing screen 92 so that the selectedcomponentized function blocks are written in order of ex-ecution to thereby form a sequence.[0013] The engineer delivers the contents written onthe control drawing screen 92 to the execution link gen-erating module 93 so that the execution link generatingmodule 93 processes the contents to thereby generatea periodic execution link 94 and a time-sharing executionlink 95. In the periodic execution link 94, an executionsequence of the regular processing function blocks (PID,SIO, PVI0I, PVI02) to be processed by the periodic ex-ecution type sequence control module 33 is prescribed.In the time-sharing execution link 95, an execution se-quence of SEBOL function blocks (SEBOL01,SEBOL02) to be processed by the time-sharing execu-tion type sequence control module 34 is prescribed.[0014] Fig. 9 is a time chart for explaining a flow ofsequence processing executed by the sequence control-ler according to the related art. The periodic executiontype sequence control module 33 performs execution byusing at least one of a basic control period, a middlespeed control period and a high speed control period.The middle speed control period and the high speed con-trol period are rapider than the basic control period.[0015] In the sequence controller 30, a plurality of pro-gram units perform processing in accordance with theirprocessing priorities. The term "program units" used

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herein means programs to be executed in accordancewith the high speed control period T1, the middle speedcontrol period T2 and the basic control period T3 (e.g. 1second) respectively.[0016] In the high speed control period T1 shown in(A) of Fig. 9, regular processing function blocks A, B andC are executed periodically. In the middle speed controlperiod T2 shown in (B) of Fig. 9, regular processing func-tion blocks A’, B’ and C’ are executed periodically. In thebasic control period T3 shown in (C) of Fig. 9, regularprocessing function blocks a, b and c are executed pe-riodically.[0017] Each of program units of the high speed, middlespeed and basic control periods is composed of controldrawings (92 in Fig. 8). For example, a control drawing100 of the regular processing function block a to be ex-ecuted in the basic control period is composed of functionblocks 101 to 105.[0018] Function blocks of each control period executeperiodically determined processing respectively. Thecurrent processing is interrupted when processing timingof a function block having higher priority has come beforecompletion of the processing. The interrupted processingis restarted after execution of higher-priority processing.Interruption of processing is performed in one of bound-aries between function blocks (e.g. 101 to 105).[0019] (D) of Fig. 9 shows a free time process usingfree time produced between regular processing functionblocks executed in each of the high speed, middle speedand basic control periods. The free time process is exe-cuted with the lowest priority in program units at suchtiming that there are no regular processing functionblocks operating in the high speed, middle speed andbasic control periods.[0020] Each program unit of free time processing iscomposed of function blocks 200. Each function block iscomposed of SEBOL function blocks each having linesin the programming language.[0021] Each SEBOL function block is executed not byfunction block but by unit of SEBOL lines (e.g. 20 lines)forming the function block. After execution of one unit afSEBOL 20 lines, a next unit of SEBOL 20 lines of thefunction block is executed successively to thereby ad-vance processing.[0022] Such processing that a predetermined quantityof processing is to be executed at regular intervals (otherblocks than SEBOL function blocks) is executed in thehigh speed, middle speed and basic control periods,whereas processing low in temporal restriction (SEBOLfunction blocks) is executed in the free time processing.The free time processing can be interrupted in eachboundary between adjacent units of SEBOL 20 lines.

[Prior Technical Document]

[Patent Document]

[0023] [Patent Document 1] JP-A-08-076836

[Non-Patent Document]

[0024] [Non-Patent Document 1] CENTUM VP Refer-ence SEBOL Edition, Document No. IM 33M01A30-40,Yokogawa Electric Corporation[0025] The degree of freedom in user’s writing and set-ting each SEBOL function block is so high that theprocessing time of the SEBOL function block varies wide-ly. For this reason, the related art is provided on the as-sumption that the SEBOL function block is executed ina free time processing and when the whole of the SEBOLfunction block cannot be processed completely in the freetime processing, the remaining processing is carried overto a free time processing of the next basic period. Thishas been regarded as a merit.[0026] On the other hand, processing load in the highspeed, middle speed and basic control periods is soheavy that there is a possibility that processing may bedisabled for a long time when there is no free time existed.There is a problem that execution cannot be warrantedwhen periodically determined processing is desired to beperformed in the SEBOL function block.

SUMMARY

[0027] Exemplary embodiments of the present inven-tion provide a sequence controller which makes it possi-ble to operate SEBOL function blocks in a control periodin which a periodic execution type sequence control mod-ule executes regular processing function blocks.[0028] A sequence controller according to an exem-plary embodiment of the invention, comprises:

a periodic execution type sequence control moduleconfigured to execute each regular processing func-tion block in a predetermined control period;an imegular processing function block storage con-figured to hold an irregular processing function blockgenerated by a user; anda time-sharing execution type sequence controlmodule configured to execute the irregular process-ing function block called from the irregular process-ing function block storage in free time of the controlperiod,wherein the periodic execution type sequence con-trol module is configured to call the irregular process-ing function block from the irregular processing func-tion block storage and to execute the irregularprocessing function block in the control period.

[0029] The periodic execution type sequence controlmodule may be configured to perform execution in atleast one of a basic control period, a middle speed controlperiod and a high speed control period, the middle speedcontrol period and the high speed control period beingrapider than the basic control period.[0030] The irregular processing function block may beexecuted in accordance with each program unit having

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a predetermined number of lines, andswitching from the irregular processing function blockcalled and executed by the periodic execution type se-quence control module in the control period to the regularprocessing function block may be executed after com-pletion of processing of the last line of the program unit.[0031] The irregular processing function block calledand executed by the periodic execution type sequencecontrol module in the control period may be formed sothat repeated processing of the irregular processing func-tion block is limited to one loop in the basic control period.[0032] The irregular processing function block calledand executed by the periodic execution type sequencecontrol module in the control period may be formed sothat processing of the irregular processing function blockis interrupted in the basic control period when processingof jumping to a forward designated address is performed.[0033] According to the embodiment of the invention,the following effects can be expected. (1) Periodic exe-cution type SEBOL used when periodically determinedprocessing is to be performed on SEBOL function blockscan be provided as a new execution form in addition tothe existing time-sharing execution type SEBOL usedwhen temporal restriction is so low that there are a lot ofprocessing contents in SEBOL function blocks.[0034] A user can select one from the two executionforms of time-sharing execution type SEBOL and peri-odic execution type SEBOL in accordance with require-ments of process control, so that the general purpose ofSEBOL function blocks can be enhanced.

BRIEF DESCRIPTION OF THE DRAWINGS

[0035]

Fig. 1 is a functional block diagram showing an ex-ample of a process control system having a se-quence controller according to an embodiment of theinvention.Fig. 2 is a functional block diagram for explainingoperation of an execution link generating module inthe sequence controller according to the embodi-ment of the invention.Fig. 3 is a time chart for explaining a flow of sequenceprocessing executed by the sequence controller ac-cording to the embodiment of the invention.Fig. 4 is a functional block diagram showing generalconfiguration of a buffer provided in the time-sharingexecution type SEBOL.Fig. 5 is a functional block diagram for explainingbuffer contention between the time-sharing execu-tion type SEBOL and the periodic execution type SE-BOL.Fig. 6 is a functional block diagram showing bufferconfigurations of time-sharing execution type SE-BOL and periodic execution type SEBOL withoutbuffer contention.Fig. 7 is a functional block diagram showing an ex-

ample of configuration of a process control systemhaving a sequence controller according to the relatedart.Fig. 8 is a functional block diagram for explainingoperation of an execution link generating module ina sequence controller according to the related art.Fig. 9 is a time chart for explaining a flow of sequenceprocessing executed by the sequence controller ac-cording to the related art.

DETAILED DESCRIPTION

[0036] The invention will be described below in detailwith reference to the drawings. Fig. 1 is a functional blockdiagram showing an example of a process control systemhaving a sequence controller according to an embodi-ment of the invention. The same parts as those in thebackground-art configuration described with referenceto Fig. 7 are referred to by the same numerals and de-scription thereof will be omitted.[0037] In Fig. 1, a characteristic portion of the inventionadded to the configuration according to the related artshown in Fig. 7 is configuration in which a periodic exe-cution type sequence control module 300 can access anirregular processing function block storage 35 to call anSEBOL function block stored in the irregular processingfunction block storage 35 and execute the SEBOL func-tion block.[0038] Fig. 2 is a functional block diagram for explain-ing operation of an execution link generating module inthe sequence controller according to the embodiment ofthe invention. The difference of the operation of the ex-ecution link generating module from operation accordingto the related art shown in Fig. 8 will be described. Anengineer writes order of execution of regular processingfunction blocks (PID, SIO, PV101, PV102) and SEBOLfunction blocks (SWEBOL(P), SEBOL(T)) on an execu-tion sequence definition screen 91’.[0039] Here, the SEBOL function block SEBOL(P) isan SEBOL function block which will be called from theirregular processing function block storage 35 and exe-cuted by the periodic execution type sequence controlmodule 300. The SEBOL function block SEBOL(T) is anSEBOL function block which will be called from the irreg-ular processing function block storage 35 and executedby a time-sharing execution type sequence control mod-ule 34 in the same manner as in the related art.[0040] Componentized function blocks are selectedfrom a component palette (not shown) or the like andpasted on a control drawing screen 92’ so that the com-ponentized function blocks can be written in order of ex-ecution to thereby configure a sequence.[0041] The engineer delivers the contents written onthe control drawing screen 92’ to an execution link gen-erating module93’ so that the execution link generatingmodule 93’ processes the contents to thereby generatea periodic execution link 94’ and a time-sharing executionlink 95’. In the periodic execution link 94’, order of exe-

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cution of function blocks (pied, SEBOL(P), SIO, PVI01,PVI02) as a mixture of regular processing function blocksand an SEBOL function block to be processed by theperiodic execution type sequence control module 300 isprescribed. In the time-sharing execution link 95’, orderof execution of an SEBOL function block (SEBOL(T)) tobe processed by the time-sharing execution type se-quence control module 34 is prescribed.[0042] With respect to an SEBOL function block whichwill be called from the irregular processing function blockstorage 35 and executed by the periodic execution typesequence control module 300, a user registers the SE-BOL function block identified/written as SEBOL(P) on theexecution sequence definition screen 91’ and the controldrawing screen 92’, so that the execution link generatingmodule 93’ registers the SEBOL function block in theperiodic execution link 94’.[0043] Because the periodic execution type sequencecontrol module 300 cannot execute any SEBOL functionblock directly, the periodic execution type sequence con-trol module 300 calls the SEBOL function block from theirregular processing function block storage 35 and exe-cutes the SEBOL function block when the SEBOL func-tion block appears in the execution link of the high speed,middle speed and basic control periods.[0044] Fig. 3 is a time chart for explaining a flow ofsequence processing executed by the sequence control-ler according to the embodiment of the invention. A con-trol drawing 100 of a regular processing function block ato be executed in the basic control period T3 is composedof function blocks 101 to 105 in the same manner as inthe background-art configuration shown in Fig. 9. Thedifference of Fig. 3 from the related art lies in that thefunction block 102 is an SEBOL function block SEBOL(P).[0045] Although the SEBOL function block substantial-ly has the same operation in the case where the SEBOLfunction block is processed by the periodic execution typesequence control module 300 and in the case where theSEBOL function block is processed by the time-sharingexecution type sequence control module 34, processingof the SEBOL function block is different in the followingpoint.[0046] Processing of the SEBOL function block (SE-BOL(P)) operating in each of the high speed, middlespeed and basic control periods is not interrupted ac-cording to units of SEBOL 20 lines but continued to thelast. However, when there appears an instruction state-ment which means interruption because of processingtiming of a higher-priority control period, access to anexternal device and the programming language, theprocessing of the SEBOL function block (SEBOL(P)) isinterrupted.[0047] Interruption is performed in a boundary be-tween adjacent units of SEBOL 20 lines. With respect tointerruption due to the higher-priority control period, theprocessing of the interrupted SEBOL function block isrestarted in the same period after completion of execution

for the higher-priority control period.[0048] Although processing of the SEBOL functionblock according to the related art is interrupted regardlessof the contents written in the programming languagewhen there is no time left in the basic control period, thereis a possibility that the periodic execution type SEBOLto be executed by the periodic execution type sequencecontrol module 300 may have an infinite loop generatedaccording to the contents written in the programming lan-guage to thereby make the processing endless becausethe periodic execution type SEBOL has such a specifi-cation that processing is continued to the last even if thereis no time left in the basic control period.[0049] Statement processing which may be conceivedas a factor of generation of an infinite loop in the periodicexecution type SEBOL is processing (while, repeat, for)of repeating under a specific condition and processing(goto) of jumping to a designated address.[0050] As for these statement processes, the periodicexecution type SEBOL therefore has such a specificationthat processing (while, repeat, for) of repeating is limitedto one loop in the basic control period and that processing(goto) of jumping to a designated address is formed sothat processing for the basic period is interrupted whenjumping to a forward address is performed. Consequent-ly, an infinite loop can be avoided in the periodic execu-tion type SEBOL.[0051] Fig. 4 is a functional block diagram showinggeneral configuration of a buffer provided in the time-sharing execution type SEBOL. An SEBOL function block400 which is generated in a free time processing accord-ing to the related art for accessing an external device isstopped until a response to the request is received. Whilethe SEBOL function block 400 is waiting for a responsefrom the device, the buffer 500 is used for holding theaccess request so that this processing is reserved andprocessing of another SEBOL function block is executed.[0052] The buffer has such a specification that the buff-er is released when there is a response to the request.Because the number of buffers is finite, the buffer over-flows when the buffer takes a long time for receiving theresponse or when the request to the external device isissued more frequently than the buffer size. The over-flowing request is stored in a queue 600. When the bufferfull state is improved in accordance with the responsefrom the external device, a process of transferring theoverflowing request from the queue 600 to the buffer 500is performed.[0053] Fig. 5 is a functional block diagram for explain-ing buffer contention between the time-sharing executiontype SEBOL and the periodic execution type SEBOL.This is an issue in the invention in the case where theperiodic execution type SEBOL operating in each of thehigh sped, middle speed and basic control periods is add-ed.[0054] Although there is no problem in the time-sharingexecution type SEBOL 400 in which the buffer 500 andthe queue 600 are managed in accordance with a single

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program as shown in Fig. 4, processing earlier in process-ing timing, for example, periodic execution type SEBOL700 occupies the whole of the buffer 500 when one bufferis managed in accordance with two programs of the pe-riodic execution type SEBOL 700 and the time-sharingexecution type SEBOL 400.[0055] As a result, there is a possibility that processingof the time-sharing execution type SEBOL 400 may notbe performed at all. Accordingly, there is a possibility thatan extreme difference in processing performance will begenerated between the periodic execution type SEBOL700 and the time-sharing execution type SEBOL 400.[0056] Fig. 6 is a functional block diagram showingbuffer configurations of time-sharing execution type SE-BOL and periodic execution type SEBOL without buffercontention. Fig. 6 is the same in basic configuration andoperation as in the related art but is characterized in thata buffer 800 and a queue 900 exclusive to the periodicexecution type SEBOL 700 are provided independentlyin addition to the buffer 500 and the queue 600 exclusiveto the time-sharing execution type SEBOL 400.[0057] The time-sharing execution type SEBOL 400transmits/receives a request using the buffer 500 and thequeue 600 for time-sharing execution type SEBOL. Theperiodic execution type SEBOL 700 transmits/receivesa request using the buffer 800 and the queue 900 forperiodic execution type SEBOL.[0058] Because the time-sharing execution type SE-BOL and the periodic execution type SEBOL have ex-clusive buffers and queues respectively as describedabove, requests from one side of the time-sharing exe-cution type SEBOL and the periodic execution type SE-BOL can be prevented from occupying all the buffers.Accordingly, it is possible to solve the problem that adifference in processing efficiency is generated betweenthe time-sharing execution type SEBOL and the periodicexecution type SEBOL.[0059] While certain embodiments have been de-scribed, these embodiments have been presented byway of example only, and are not intended to limit thescope of the invention. Indeed, the novel system de-scribed herein may be embodied in a variety of otherforms; furthermore, various omissions, substitutions andchanges in the form of the system, described herein maybe made without departing from the sprit of the invention.The accompanying claims and their equivalents are in-tended to cover such forms or modifications as would fallwithin the scope and sprit of the invention.

Claims

1. A sequence controller comprising:

a periodic execution type sequence controlmodule configured to execute each regularprocessing function block in a predeterminedcontrol period;

an irregular processing function block storageconfigured to hold an irregular processing func-tion block generated by a user; anda time-sharing execution type sequence controlmodule configured to execute the irregularprocessing function block called from the irreg-ular processing function block storage in freetime of the control period,wherein the periodic execution type sequencecontrol module is configured to call the irregularprocessing function block from the irregularprocessing function block storage and to exe-cute the irregular processing function block inthe control period.

2. The sequence controller according to Claim 1,whereinthe periodic execution type sequence control moduleis configured to perform execution in at least one ofa basic control period, a middle speed control periodand a high speed control period, the middle speedcontrol period and the high speed control period be-ing rapider than the basic control period.

3. The sequence controller according to Claim 1 or 2,whereinthe irregular processing function block is executedin accordance with each program unit having a pre-determined number of lines, andswitching from the irregular processing functionblock called and executed by the periodic executiontype sequence control module in the control periodto the regular processing function block is executedafter completion of processing of the last line of theprogram unit.

4. The sequence controller according to any one ofClaims 1 to 3, whereinthe irregular processing function block called and ex-ecuted by the periodic execution type sequence con-trol module in the control period is formed so thatrepeated processing of the irregular processingfunction block is limited to one loop in the basic con-trol period.

5. The sequence controller according to any one ofClaims 1 to 4, whereinthe irregular processing function block called and ex-ecuted by the periodic execution type sequence con-trol module in the control period is formed so thatprocessing of the irregular processing function blockis interrupted in the basic control period whenprocessing of jumping to a forward designated ad-dress is performed.

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REFERENCES CITED IN THE DESCRIPTION

This list of references cited by the applicant is for the reader’s convenience only. It does not form part of the Europeanpatent document. Even though great care has been taken in compiling the references, errors or omissions cannot beexcluded and the EPO disclaims all liability in this regard.

Patent documents cited in the description

• JP 8076836 A [0023]

Non-patent literature cited in the description

• CENTUM VP Reference SEBOL Edition. YokogawaElectric Corporation [0024]