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Model-based Automatic Generation of Sequence Control Programs
Abstract
This paper proposes a new model-based tech-nique to automatically generate sequence controlprograms for mechatronics machines from designinformation . This technique solves one of thebottlenecks in developing mechatronics machinesby reducing burdens of software development . Inthis technique, a sequence control program is gen-erated from a model of the design object rep-resented in a mechanical CAD by searching thephysical causalities described by Qualitative Pro-cess Theory and by providing geometric informa-tion . Based on this technique, we implementeda prototype system named the Sequence Con-trol Program (SCP) Generator which integratesa mechanical CAD and a software generation sys-tem. An example of control program generationfor a photocopier with the SCP Generator is de-scribed .
Introduction
Y. ShimomuraMita Industrial Co ., Ltd .
Tarnatsukuri 1-2-28, Chuo-ku, Osaka 540,Email: siinomuracgrnita.co .jp
Design of mechatronics machines involves both that ofhardware and software . It is well known that one ofthe bottle necks in developing mechatronics machinesis software development., even if the control is based onsimple sequence control . Thus, a system to automatethis process is required .Although many researchers have studied methods to
automatically generate control programs . most of themare based on transformation knowledge from formalspecifications to codes (e.g . (Fickas 1985)) . For in-stance, Nakayama (Nakayama 1990) has developed atechnique to automatically generate sequence controlprograms based on a model of object from the require-ments for the object represented in the conceptual levelof the designer . Graves (Graves 1992) also succeededin automatic programming through generation of ac-tions which should be activated based on functionalconnections among the components of a plant .These techniques have the following problems in
Cornrnoru :
206 QR-96
from Design InformationT. Sakao and Y. Umeda and T. TomiyamaGraduate School of Engineering, the University of Tokyo
Hongo 7-3-1, Bunkyo-ku, Tokyo 113, JapanEmail : {sakao, urneda, tomiyarna}(Qzzz.pe.u-tokyo .ac.jp
2 .
Japan
Specifications for the control and those for the rnech-anism are often developed independently and incon-sistently.The designer is not able to make good use of infor-mation about the mechanism in the software designstage .In other words, the scope of previous studies is lim-
ited to design of software and such techniques are notfully integrated with a mechanical CAD, thus callingfor concurrent engineering problems . That is why thesetechniques are not useful for supporting the whole pro-cess of the design of mechatronics machines effectively.
This paper proposes a new model-based techniqueto automatically generate sequence control programsfrom models of a design object in the '*Knowledge In-tensive Engineering Framework" (KIEF) (Tomiyarna1994) . Within KIEF, the conceptual design stageis supported by the "Function-Behavior-State (FBS)Modeler" (Umeda et al. 1990) dealing with a modelof a design object that preserves designer's intentionsin the form of functions and physical causalities basedon Qualitative Process Theory (QPT) (Forbus 1984) .This method integrating a mechanical CAD and a soft-ware generation system solves the problems describedabove . Moreover . this method is applicable to situ-ations in which sequence control programs must bedynamically changed : consider a truly flexible man-ufacturing system that must be flexibly controlledor a function redundant self-maintenance machinethat dynamically changes its behaviors to maintainits functions (Umeda, Tomiyanra, & Yoshikawa 1992 :Umeda et cal. 1994) .In chapter 2 . KIEF is is briefly illustrated and our
strategy for generating sequence control programs isdescribed . Chapter 3 describes the prototype systemnamed a Sequence Control Program (SCP) Generatorand its algorithm . Chapter 4 illustrates an example ofgeneration of a sequence control program for a photo-copier with the SCP Generator . It also demonstratesthat the SCP Generator can generate sequence con-trol programs for different operation conditions from a
normal one . This is useful for dynamic software gen-eration during operation . Chapter 5 and G describediscussions and conclusions respectively.
Knowledge Intensive Engineering
ArchitectureFramework
Our group at the University of Tokyo has been con-ducting research on the development of KIEF . KIEF isan integrated computational framework for engineeringactivities in various product life cycle stages, includingdesign, production, operation, maintenance, and recy-cling (see Figure 1) . Using various modelers, simula-tors, and a very large-scaled knowledge base (VLKB)in a flexible manner allows an engineer to create moreadded-value .
Within KIEF, the designer conducts conceptual de-sign with the FBS Modeler to be described in Sec-tion . The FBS Modeler decomposes functional designspecifications into physical behaviors of mechanisms .The SCP Generator, whose algorithm is described inChapter 3, takes this qualitative behavioral informa-tion of the mechanisms of a design object and gen-erates qualitative control sequence . The QualitativeProcess Abduction System (QPAS) (Ishii, Tomiyarna,& Yoshikawa 1993) reasons about appropriate physi-cal phenomena which realize the required qualitativechanges of the parameters based on physical causali-ties managed by the Qualitative Reasoning (QR) Sys-tem (Kiriyama, Tomiyama, & Yoshikawa 1991) . TheSCP Generator further incorporates quantitative geo-metric information of the mechanisms and generates asequence control program . The 2-D bit map modeler isa tool for handling geometric information of the designobject and the Spatial Reasoning (SR) System (Mat-sumoto et al. 1993) reasons about kinematic propertiesof the mechanisms .
All of these systems are integrated in KIEF thatallows flexible use of knowledge about design objects(see Figure 1) and enable the following :1 . The system can generate sequence control programs
from the results of conceptual design .2 . This results in easy modifications of sequence control
programs, contributing to increasing productivity ofsoftware development .
The Function-Behavior-State ModelerThe FBS Modeler deals with functions, behaviors, andstates occurring on mechanism . Behaviors and statesare managed based on physical causalities that. are rep-resented and reasoned by the QR System, which imple-ments QPT. It is important that the FBS Modeler canrepresent and reason about the trichotomy of function,behavior, and state, because control is a means to ob-tain the desired function through physical behaviors ofthe mechanism . Figure 12 shows an example of screenhardcopy of the FBS Modeler .
In QPT, a physical world is modeled with three com-ponents ; i .e ., individuals, individual views, and pro-cesses . An individual represents an entity, such as agear and water . An individual view represents a wayof seeing an entity, such as seeing a gear as a rotatableentity. A process represents a physical phenomenon,such as rotation of a gear pair and boiling of water . Inthe QR System, individuals. individual views, and pro-cesses are represented in a uniform framework nameda view.
Table 1 shows the scheme of function prototypesused to model functions in the FBS Modeler . Decom-position describes feasible candidates for detailing thisfunction in the form of networks of subfunctions whichinclude representation of needed temporal transitionsamong subfunctions . F-B relationship describes be-haviors that can perform this function in the form ofnetworks of views in the QR System .
Table 1 : Definition of a Function Prototype
Item
j ContentsName
I verb + objectivesDecomposition
subfunetion networksF-B Relationships I a network of views
Figure 2 : Examples of the Kinematic Pairs
Managing Geometric InformationGeometric reasoning and kinematic reasoning symbol-ically represent and reason about mechanisms (e.g .(Faltings 1987 ; Joskowicz & Sacks 1991 ; Gupta &Struss 1995)) . KIEF deals with geometric informationabout mechanisms using a geometric modeler pluggedinto the Metamodel System (Kiriyama, Toiniyama, &Yoshikawa 1991) through the Pluggable Mechanism(Yoshioka et al . 1993) and the SR. System can rea-son about the spatial characteristics of the design ob-jects such as kinematic pairs . Figure 2 shows simpleexamples of the kinematic pairs . The Metamodel Sys-tem maintains consistency among different design ob-ject models (such as qualitative model and geomet-
Sakao 207
208 QR-96
Figure 1 : Knowledge Intensive Engineering Framework
FBS Model
Generation of Qualitative Sequence of Behaviors
Qualitative Sequence ofBehaviors
Generation of Qualitative Control Sequence
Qualitative Control Sequence
IQuantitative Control Sequence
Figure 3 : Algorithm of the Sequence Control Programs Generation
ric model) by symbolically representing relationshipsamong them . In this study, a 2-D bit trap modelerhandles geometric information about design objects .However, alternatively a solid modeling system can beused, if geometry of the design object has enough de-tails .The designer makes the correspondence between the
geometric information of the design object representedon the 2-D bit trap modeler and the symbolic informa-tion of the physical states on the FBS Modeler . and theMetamodel System manages these correspondences .This architecture allows the SCP Generator to access
to geometric information for generating quantitativecontrol sequences .
The Algorithm of the Sequence ControlProgram Generation
After conceptual design and parametric design are fin-ished, the SCP Generator generates a sequence controlprogram that satisfies the designers intentions repre-sented as a sequence of needed functions on the FBSmodel . Figure 3 shows the algorithm .
In Figure 3 . a 2-D bit map model represents the
Transfer Charger
TC
0rm
Figure 4 : The Input FBS Model
----
QR System
HeuristicsifD Knowledge Base
C Code Library
Remarks
QPAS
ierFunction Node
objectiveViewSuper-Sub Relation
.-----~. : Temporal Order----------- : F-B Relationship
structure of the design object with its quantitativedata and the Heuristics Knowledge Base contains theheuristics for controlling devices . A qualitative controlsequence means a sequence of states in temporal or-der, while a quantitative one is a sequence that includestime information . The quantitative control sequence isconverted to a C program using respective C functionsstored in the C Code Library. Although we used the Clanguage, our technique can generate programs in anyother language by modifying this library .
In this chapter, we describe the algorithm to gen-erate sequence control programs with the SCP Gener-ator using an example FBS model depicted in Figure4 . Sequence control is a way to control according tothe conditions and the sequence prepared in advance .Since this example satisfies those, the algorithm de-scribed here does not lose its generality. Note thatwe do not deal with quantitative control, nor feedbackcontrol here .
In the FBS model of Figure 4, oval nodes in theupper half denote functions and represent as a wholethe functional hierarchy while rectangular nodes in thelower half denote views and represent as a whole be-
Sakao 209
haviors and states of the design object .
Generation of Qualitative Sequence ofBehaviorsThe SCP Generator derives a sequence of behaviorsfrom an FBS model that represents views to satisfy atransition sequence of subfunctions in request .
In the example of Figure 4, the top function is trans-fer image that can be decomposed into expose drum,and derive image. The arrow from expose to deriveindicates their temporal order ; i .e ., first expose drumshould happen and next derive image. The exampleFBS model also shows their F-B Relationships (seeTable 1) . Namely, expose drum and derive image areperformed by activating Flash and Toner Transfer, re-spectively. From this, a qualitative sequence of behav-iors (see Table 2) is derived from the initial FBS modelas a temporal sequence of statel and state2.
21 0 QR-96
Table 2 : Qualitative Sequence of Behavior
Generation of Qualitative ControlSequenceIn this stage, the QR System and QPAS reason outrequired parameterc changes from the qualitative se-quence of behaviors generated in the previous stage .The QR System performs envisioning to see whetheror not the input model has a possibility to arrive atthe required states under feasible conditions regardingparameters, entities, and relations .To do so, first, the designer specifies the initial state
and the final state by giving the values of the param-eters . The system creates a parameter transition mapfor activating views needed for the sequence of behav-iors and completes a consistent transition map basedon the procedure below . For this example, the designersets the values of the parameters included in the designobject of statel and state2 at the initial state and atthe final state as follows :
initial state : Surface = charged, Angle = x0,Position = y0, Velocityl = 0, Vellocity2 = 0. Lamp- off, Charger = off, Developer = off, Motorl =off, Motorl = off,
final state : Surface = nothing. Angle = x3 .Position = y2 ; Velocityl = 0. Velocityl = 0, Lamp= off. Charger = off, Developer = off. Motorl =off, Motorl = off,
where Surface, Angle., and Velocityl belong to Drum,and Position. and Velocityl to Output Paper. Also,Surface is a non-controllable, sensory state parame-ter, Lamp, Charger, Developer, Motorl, and Motorlare controllable state parameters, and Angle, Position,Velocityl, and, Velocityl are variable parameters. Con-trollable state parameters are associated with control-ling methods described in the Heuristics KnowledgeBase .1 . Based on the knowledge shown in Table 3 main-
tained by the QR System, a specification transitionmap (see Figure 5) is created by providing infor-mation about the initial state and the final state .Also, new states, statel and state2, at which Flashand Toner Transfer are supposed to occur, are recog-nized . Table 3 denotes if the conditions of a physicalphenomenon are satisfied, its influences occur on thedesign object . Note that at this stage, we only fo-cus on uncontrollable parameters in conditions andinfluences of phenomena (see Figure 5) . In Figures5, 6 and 8, ch, ex, d-v and no are abbreviations forcharged, exposed, developed and nothing.
initial
finalstates state statel
state2 stateToner
. . .Surface . .. . . . . .5'.h.Angle. . . .. . . . . . .
.ggsition . � . ... .YO.
Vely . .. .Y . . ._ ._ . ..q .r . ..Lamp. . . . ._Af
Ch .irgcr__ ___ .- off_DCVq_kOIte_r
o__ ._. . .If._ Motorl _ . _. . .off~Motor2~,
. .. . .. . . .. chex
dy .. . . . .. .. ...xl
f .-.. .... . .. . . . . . . . . . . . . .. . . .. . . . ... . . ..-.:
. . . .. . . . . .x
P .. .... . . . .. . . .. . . . ... . ... . . . . .... . . .. . ...y.
------------
Transfer
Figure 5 : Specified Transition Map
no.. . .. . . .. . . .1 n9. . ... . . ... . . ... . ... . . .
. . . .. . . .. . Q.. . vfl: . .vll _.olL_.
411`._
olf_-
2 . QPAS reasons out the physical phenomena that ac-tivate the changes of the uncontrollable parame-ters reasoned out in the first step, because uncon-trollable parameters should be controlled indirectlyby activating an appropriate physical phenomenon .In the example, QPAS reasons out that Develop,Drum Rotation, and Paper Moving should be acti-vated, between statel and state2, at the initial state,and at statel, respectively. by considering paramet-ric changes . The system also adds a state namedstate 3 between statel and state2 to get Develop thatchanges the value of parameter Surface from exposedto developed (see Figure 6) .
3 . The QR System completes the conditions of con-trollable parameters for all the physical phenomenareasoned out . In the example, the transition of thevalues of five actuators is generated to activate thosefive phenomena (see Figure 6) .
state statel state2required function expose drum derive imageviews Flash Toner Transfer
Halogen Lamp Transfer ChargerOriginal Paper Output PaperDrum DrumFacingl Facing2
phenomena
11 Flash,
hcy
states
occurringphenomena
Angle x0y Position _ .. .-f~..Veloci_,_t~l ~0_,VelociY2__ . .. . . .Lamp. . .... . . .. f.
.Char er
oPevelope_r ._ . _ .. ojj :Motorl
.. .Motor2 . . . . . . .
Supplying Geometric Information
Table 3 : Definition of Each Physical Phenomenon in the QR . System
Develop
Dru?nRotation PaperMoving
initial statel state3stateFlash ' Develop
-Drum Rotation--PaperMoving
I TonerTransfcr
After these steps, the consistent transition map thatrepresents a qualitative control sequence shown in Fig-ure 6 is generated .
However, this algorithm has some problems and lim-itations . First, there is no guarantee that qualitativecontrol sequences as solutions exist. nor they are opti-mal . When there are multiple solutions, the designerhas to choose one . Second, this algorithm cannot dealwith situations of inter-dependent phenomena . For in-stance, phenomenon Pi assumes parameter X be high.,and P2 assumes Y be loin . If PI has an influence thatY becomes low and PZ has that X becomes high . andif there is no other phenomena that involve X or Y,Pl and P2 are inter-dependent phenomena.
state2Toner
Trqnsfer
,,-_~xl , ,_ x
finalstate
no _
, no _x3_.
. . . . . . ._ .. . . ... . . .. . . . . ._
old. .. . .. . . . . .. . . . .. ...- . . . .. . .
il~.. .. . .. . . ... . . .s~
. .. . . . . . . . . .. . . .. . . ... . . . .. . . .. . . 3 ... . . .. . . . .. . . .
~ ... . . ... . . .. . . .¢°fl. . .. . ..-tom .
Figure 6 : Transition Map with Qualitative Control Se-quence
In this stage, a quantitative control sequence is gener-ated from the generated qualitative control sequence .This is performed by supplying time information be-tween states in the qualitative control sequence andsensory information needed for the control . These twotypes of information are created from geometric infor-mation obtainable through the Metamodel System .For the example . the designer specifies geometric in-
formation of the mechanism by the 2-D bit map modelshown in Figure 7 . The following describes the algo-rithm we developed to supply geometric information
Figure 7 : The Input Bit Map Model
to qualitative control sequences .1. Giving Correspondences between Geometric Objects
in the Bit Map Model and Entities in the PhysicalModel.The designer gives correspondences between geoinet.ric objects in the 2-D bit map model and entitiesin the physical model maintained by the QR Sys-tem . For the example, the designer makes corre-spondences between the round object shown in thebit map model and Drum. in the FBS model of Figure4, and the rectangular object and Output Paper.
2. Reasoning about Kinematic Pairs.Motion takes place at kinematic pairs . To clearlyrecognize kinematic causality for motion control, theSR System finds out kinematic pairs in the designobject from its 2-D bit map model and its physicalmodel maintained by the QR System . This can bedone by comparing the necessary spatial conditionsfor each kinematic pair in the kinematic pair database with the spatial conditions represented by thephysical model such as fixed. In the example, a ro-tational pair and a sliding one are found .
3 . Giving Correspondences between Parameters Asso-ciated with Kinematic Pairs and Parameters in thePhysical Model.The SR System also sets a parameter associated witheach kinematic pair . The designer gives its corre-spondence to a parameter of the physical model . Inthe example, the designer gives correspondences be-tween angle set for the rotational pair and parameter
Sakao 21 1
conditions of Angle=xl Anggle=x3 Angle=x2the parameters Position=y0 Position=ylin the views Surface=charged Surface=developed Surface=exposed
Lamp=on. Charger=on Developer=on Motorl=on Motorl=on
influences Velocityl=zr0 Velocityl=ur0
at = Velocityl alt = Velocity2Surface=exposed Surface=nothing Surface= dei,eloped
4 . Supplying Time Information .
Angle of Drum, and position set for the sliding pairand Position. of Output, Paper.
Since variable parameters change their values withrespect to time according to differential equationsof the parameters, time intervals can be calculatedby integrating the equations assuming that the vari-able parameters are controlled precisely . Namely, ifa and ,(3 are related by equation da/dt = 13 and /3is constant between two states, the length of timeAt between the two states is calculated by equationAt = Ace//3 . The QR System searches this rela-tionship and the length of time between two statesis calculated using the geometric quantitative datafront the bit map model .In case that plural variables change during one inter-val, another state has to be added between those twostates, because each transition time is not necessarilyequivalent . Here, the heuristics that those variablesshould simultaneously start changing is used .In Figure 8, time information is added to the qualita-tive control sequence . Each time period is calculatedas follows :
tl = (XI - x0)/v0,t2 = (x2 - xl)/v0,t3 = (x3 - x2)/v0,t4 = (yl - y0)/w0 - t2 - t3, andt5 = (y2 - yl)/w0 .
initial
finalstates state states state3 state4 state2 stateFlash Develop
Toner-Drum Rotat;on-------o "
TransferPaper Movir, e
. . . Surfacg . . .. . . . .. .(. . . . . .. . .
ch ex .
ex;de .. . . . . .. . . .I. . . . . . . . .. dv, n~ . . ... . . .. . . 1no .Angle. . . . ... . . .? . . . . . ..
... .. .>z1 i--3px3
x..
x.~ ... . . ..
0.. . . .. . . . . . . . . . . . . ... . . .. . . ... . . .. . . . .. . . . .. . . . . .. . .Pasition . . . .. . . .Yb . . . . ... . . ...YO. . . .. . . . . .. . . .. . . e. . . . .. . . . . . . . . . . . . ... . .. .+a. . . .. . . ... . . . .. . . .Y~ ..
vo 1 o
o. .. . . .... . . .. . . ,. . . . .. . . . .. . . . .. . . . . . . . . .
. . . .. . . . .. . . ... .
... . . ... . . . .. . .
. . . . . ..velggt 2 . .. . . . .. . . .
wo
'"
wo. . ._Lam_P_ . . .. . . ..4f. . ._ ...__ ...on . . .._______. .o._____. . . ..._ . . _._.._ ._ ... . ._.
__.. . . ..._ . .. . . P17. ..Char -_ .. .__ ._. . . .. .. ;_..----------- . ------ __ .._an.
Pf. .Develgper ._
i9Ll. ..Motors o on_._ t
occurringphenomena
. . Motor2 ,- . . off
Figure 8 : Modified Transition Map Including Time In-formation
5 . Supplying Sensory Information .Some variable parameters are difficult to controlprecisely only based on time information . In or-der to control those parameters. sensory informationshould be added . It is determined by the way of con-trol represented on the physical model and the kindof a kinematic pair whether the control of a param-eter with a kinematic pair is achieved precisely ornot . As to kinematic pairs for which precise controlis difficult, the condition of such a variable parame-
21 2 QR-96
ter is exchanged to that of a sensor value if there isa respective sensor s .In the example, sensory information is added to con-trol parameter Position, by exchanging the condi-tions of Position = yl and Position = y2 to Sen-sorl = on and Sensor2 = on, respectively, where wemake the following assumption :A super-class phenomenon of PaperMoving is toslide an object by friction, and therefore, parame-ter Position on the sliding pair is difficult to con-trol precisely. On the other hand, a super-class phe-nomenon of DrumRotation is to rotate an object bygear transmission, and therefore, parameter Angleon the rotational pair is controlled precisely.Then, the quantitative control sequence is gener-ated . It is in the form of the "if-then" rule tempo-rally ordered . Here, "charged (Surface)" means thatthe value of Sur face is charged. "make(Lamp,on)"means to set the actuator value Lamp to "on." The"if" part specifies conditions for activating the rules .The '`then" part designates the "after t [ms]" timinginformation and actions the rule has to fire . Somerules can specify waiting conditions in the "SensorXvoll --+ volt, action" format, which means that ac-
tion should be taken waiting for SensorX becomingvolt from volt .From the example above, the following quantitativecontrol sequence is generated .1 . if charged (Surface) & off(Lalnp) & off(Charger)& off(Developer) & off(Motorl) & off(Motor2)then after 0 [ins], nlake(Motorl,on)
2 . if charged(Surface) & off(Lanlp) & off(Cllarger)& off(Developer) & orl(Motorl) & off(Motor2)then after tl [ms], make(Lainp,on) .nlake(Motor2,on)
3 . ifexposed(Surface) & off(Lamp) & off(Cllarger)& off(Developer) & on(Motorl) & on(Motor2)then after t2 [nls], make(Developer,on)
4 . if developed(Surface) & off(Lanlp)& off(Cllarger) & off(Developer) & on(Motorl)& oll(Motor2)then after t3 [ms], make(Motorl,off)
5 . if developed(Surface) & off(Lanlp)& off(Charger) & off(Developer) & on(Motorl)& on(Motor2)then after Sensorl : off -+ on,snake(Cllarger,on )
6 . if nothing(Surface) & off(Lamp) & off(Charger)& off(Developer) & off(Motorl) & oil(Motor2)then after Sen.sor2: off --+ on,nlake(Motor2,off )
'This information is included in the Heuristics Knowl-edge Base .
2 This kind of hierarchy is described in VLKB (see Figure1) .
Generation of C CodesFinally, the quantitative control sequence is translatedinto a C program . Each rule in the quantitative controlsequence is converted to a sentence in C by translat-ing conditions and actions into respective C functionsstored in the, C code library . The generated C pro-gram which consists of translated functions above anda main function executing thein sequentially is com-piled to an executable program . Figure 9 shows partof the generated C codes corresponding to the fourthrule and the fifth in the quantitative control sequenceabove .
if(count[4)[11&&countertimepassed(4))
makeoff(C4) ;setcounterinactive(4) ;
1 ;
if(count[5)[11&&sensorchanged(5))
makeon(C2) ;sensorinactive(5) ;
1 ;
Figure 9 : Part of the Generated C Codes
ApplicationsWe implemented the SCP Generator and developedan experimental photocopier controlled by a personalcomputer with generated sequence control programs(see Figure 10) . Figure 11 depicts the structure of thephotocopier .
Sequence Control Program DesignIn this section . an example of sequence control pro-gram design on the SCP Generator is described . Fig-ure 12 and Figure 13 show the FBS model and thebit map model of the photocopier, respectively. Fromthese models, the SCP Generator generates a sequencecontrol program .An output image in A4 size by the generated pro-
gram is Figure 14 (b), while one with the embeddedprogram in ROM of the photocopier is (a) . Althoughthe SCP Generator succeeded in automatic generationof a sequence control program . Figure 14 shows thetop positions of the outputs (a) and (b) are slightlydifferent .The SCP Generator considers slipping of paper and
the lag time between the start of control of an actu-ator and its actual start, which are not included inthe object model, by including sensory information .However, it still needs minor adjustments to incorpo-rate empirical know-hows in controlling real actuators .which are considered in the embedded program. This isthe major reason for the difference of the top positionsin Figure 14 (a) and (b) . The embedded program also
has some routines to handle errors, such as paper jani-ining . which cannot. be reasoned out from the physicalknowledge discussed in this paper .
Figure 10 : Overview of the Experimental Photocopier
O')Halogen
~C]utchLampMain Charger
Original Pier
Developing Unit
uu A 0 RollerPosition ensor
Separation Charger Transfer Charger
Figure 11 : Structure of the Photocopier
MainCharge Lr Expose
MainCha
Drum
Halogenlamp
ClutchF
ransferCharge
ferCharger
eCharge
rateCharger
CopyMachineTahle I ~ paper
Sakao
Table
Figure 12 : The FBS Model of the Experimental Pho-tocopier
213
214 QR-96
NIkD-
N !1!Cj cl -/iJ4, 3< .
J
\ o J
tom:R3V0 n 92:.
Figure 13 : The Bit Map Model of the ExperimentalPhotocopier
Figure 14 : Outputs
(a) The Original Program
(b) The Program Generatedwith the SCP Generator
Dynamic Generation and Modification ofSequence Control ProgramsThe technique proposed in this paper is also appli-cable to dynamic generation and modification of se-quence control programs during operation, if comput-ing speed is fast enough . This is useful for . e .g . . flexi-ble manufacturing systems of which control programsmust be dynamically generated or modified in tomor-row's responsive manufacturing environment . It is alsouseful for a function redundant self-maintenance ma-chine (Umeda, Tomiyama, & Yoshikawa 1992 : Umedaet al. 1994) that reconfigures its behaviors to main-tain its functions even when a critical fault occurs .Since this reconfiguration is performed by rearrangingcontrol software, its dynamic generation and modifica-tion is extremely critical . This section demonstratesan example of dynamic generation of sequence controlprograms for function redundant self-maintenance ma-chines .To conduct function redundant design during the
conceptual design stage, we developed a tool called an
FR Designer (Unieda, Tomiyama, & Yoshikawa 1992 ;Umeda et al . 1994) . This system allows the designerto find out alternative behaviors that can still maintaina target function even when some parts are malfunc-tioning or losing their function, by using other partsin a slightly different way from the original . The SCPGenerator can automatically generate sequence controlprograms from an FBS inodel that represents such sit-uations .
Figure 15 (a) shows an output image with the orig-inal program before the maintenance (i.e . . faulty im-age) and one with the generated program (b) . We canpoint out the following :
2 .
3 .
The SCP Generator succeeded in functional inainte-nance based on function redundancy by dynamicallygenerating a sequence control prograin .The lower half of (b) is basically faulty, not becauseof self-maintenance, but because the radius of thedrum is too sinall to print out a full A4 image ina function redundant mode that requires the drumto rotate twice . It is peculiar to this experimentalphotocopier .It took more time to take one copy in (b) than in(a), because the drum has to be rotated twice in (b) .
(a) Faulty
(b) The Program GeneratedDynamically
Figure 15 : Outputs in Faulty States
DiscussionsIt. i s possible to automatically generate sequence con-trol programs froin design information . The programgeneration method with the SCP Generator signifiesthat integrating various kinds of design knowledge cancreate more added-value such as automatic softwaregeneration . This method . therefore, advocates knowl-edge intensioe software design.This technique allows dynainic generation and mod-
ification of sequence control programs, so that the ina-chine can adjust itself to environmental changes, faults,and changes of the user's requirements . This is also
applicable to frequent changes of sequence control pro-grams for manufacturing systems of. particularly, smallvolume or even one-off production . because the SCPGenerator is applicable not only to a photocopier butalso to mechatronics machines in general by replacingthe knowledge base . We call such machines soft, ma-chines in that they can flexibly reconfigure and self-organize themselves (Tomiyama et, al. 1995).The FBS Modeler represents a function in the form
of "verb -f objectives ." Therefore, other designers areable to easily understand and modify an FBS Model .which results in easy modifications of sequence controlprograms .As described before, the control methods are limited
to on-off control . Namely, neither methods to controlquantity directly nor feedback control can be handledby the algorithm proposed in this paper . The con-trols either change the values of discontinuous stateparameters or make the differential values of continu-ous variable parameters plus or minus . That physicalknowledge on control is managed by the QR System .
ConclusionsThis paper presented a method for a model-based au-tomatic generation of sequence control programs fromdesign information including causalities of physicalphenomena and geometric information of mechanisms .The SCP Generator, which implements this technique,succeeded in automatically generating a sequence con-trol program . This results from integration of a CADfor functional design (the FBS Modeler), a syntheticreasoning system (QPAS), a geometric modeling sys-tem, a spatial reasoning system . and a sequence controlsoftware generation system on an integrated frame-work (KIEF) with the Metamodel mechanism . Thismethod is applicable to sequence control software de-sign of mechatronics machines in general . By allowingdynamic generation and modification of sequence con-trol programs, these machines can become more flexi-bly reconfigurable, self-organizable, and robust, adapt-ing themselves to environment changes, faults, andchanges of the user's requirements .
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