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(YDOXDWLQJD)OH[LEOH$UFKLWHFWXUHIRU 'LVWULEXWHG&RQWURO P. Bellini*, M. Buonopane*, M. Montanelli#, P. Nesi* 'HSDUWPHQWRI6\VWHPVDQG,QIRUPDWLFV8QLYHUVLW\RI)ORUHQFH,WDO\ 7HO)D[QHVL#LQJILLQJXQLILLWQHVL#GVLXQLILLW Æ6('6SHFLDO(OHFWURQLF'HVLJQHPDLOFEUXQL#VHGQHWFRP 3URMHFWZZZVLWHKWWSZZZGVLXQLILLWaKSFQZZZPXSDDFZZZSDJKWPO $EVWUDFW PDFURSRLQWV. The operation of a CNC can be summarized $ORQJ SURGXFWLRQ SLSHOLQHV LQ PDQXIDFWRU\ LQGXVWULHV as follows: VHYHUDO HODERUDWLRQ SKDVHV LQ ZKLFK WKH PRYHPHQW RI • Interpretation of ISO programs and interpolation. LQWHUSRODWHGD[HVDUHSUHVHQW7KHVHDFWLYLWLHVKDYHWREH Specific versions of ISO programs can be used for V\QFKURQL]HG ZLWK VHYHUDO RWKHU VLPSOHU DFWLYLWLHV DORQJ describing both the operation made by the machine WKH SLSHOLQH &RPSXWHUL]HG QXPHULFDO FRQWUROV IRU VXFK and by its I/O ports in terms of logic equations; V\VWHPVKDYHWREHIOH[LEOHDQGVWURQJO\H[SDQGDEOHDQG • Execution of low-level commands for axes of the UHXVDEOH VLQFH SLSHOLQHV DUH IUHTXHQWO\ UHFRQILJXUHG WR machines and for the other auxiliary services by UHDOL]H GLIIHUHQWO\ DUUDQJHG SLSHOLQHV ZLWK GLIIHUHQW means of several digital and analog ports (sensors); WHFKQLFDO UHTXLUHPHQWV ,Q WKLV SDSHU WKH DVVHVVPHQW RI The CNC is capable of (i) detecting errors/faults that VXFK D IOH[LEOH DUFKLWHFWXUH LV SUHVHQWHG RQ WKH EDVLV RI may occur on the machine, and (ii) monitoring its ZKLFK WKH EXLOGLQJ RI IOH[LEOH GLVWULEXWHG FRQWUROV IRU production. Errors are corrected by a special set of SLSHOLQHVLVSRVVLEOH7KHDUFKLWHFWXUHKDVEHHQGHILQHGLQ instructions and/or are reported towards the other WKH (635,7 +3&1 +LJK 3HUIRUPDQFH &RPSXWHU microprocessor-based systems that are monitoring the 1HWZRUNLQJ SURMHFW 083$$& 0XOWL 3URFHVVRU automated area. $UFKLWHFWXUH IRU $XWRPDWLF &RQWURO 083$$& CNCs are used as the elementary component for DUFKLWHFWXUHDQGSURWRW\SHKDVEHHQDVVHVVHGLQRUGHUWR building complex production pipelines. These can be LGHQWLI\WKHPRVWLPSRUWDQWSHUIRUPDQFHLQGH[HV organized in three hierarchical levels. .H\ZRUGV numerical control, distributed control, The first is usually defined as FMM (Flexible performance evaluation, systems assessment, CNC, PCI, Manufacturing Module) -- i.e., the production islands. communication, CANBUS, fieldbus. FMMs are constituted by a single machine tool with auxiliary robots for charging and discharging pieces and ,QWURGXFWLRQ tools. When the required performance is low, the FMM Presently, most of the automatic machines (for milling, control may consist of a single microprocessor-based cutting, measuring, soldering, electron erosion, moving system that coordinates the machines and the auxiliary pieces, robots, tapes, etc.) used in pipelines of production tools and services (e.g., 3 interpolated axes for the are controlled by microprocessor-based systems. These machine plus 2-3 axes for each robot). When the provided are usually called CNCs (Computerized Numerical performance is high, the FMM has to be managed by a Controls) and provide a certain number of interpolated multiprocessor system. This solution highly increases the axes and digital sensors/actuators [1]. The CNCs are complexity of the system for both hardware and software typical real-time systems [7], [8], with all their classical aspects. In these cases, the production process of each problems. FMM is managed by a central control station. All the In general, a CNC system receives the instructions FMMs of the production pipeline have their own describing the elaboration to be performed in terms of an controllers that talk with a centralized system of control ISO 1037 program. The ISO programs are generated by and co-ordination by means of a local communication CAD/CAM stations. The ISO program is composed of network. elementary instructions that include instructions to specify The second level is the FMS (Flexible Manufacturing the PDFURSRLQWV for interpolation (plus eventually some System). It is made by several FMMs connected by a technical information). The CNC system, by means of an communication channel to a central station that manages interpolator, calculates the PLFURSRLQWV that are useful to the various production cells and the production flow. generate the profile required between the given Among the most important CNC producers, SIEMENS proposed a network based on IEEE 802.3. Other firms such as OMRON, ABB, Blue Chip have their own XVHG IRU FRQWUROOLQJ PRUH D[HV LQ VORZHU SLSHOLQHV RI communication networks for connecting only PLC SURGXFWLRQ VLQFH WKH\ DUH LQIOH[LEOH VROXWLRQV EDVHG RQ (Programmable Logic Controller) modules. Intelligent ORZ SHUIRUPDQFH &1&V FDQQRW EH FRPSRVHG IRU Instrumentation Inc. uses an Ethernet network to connect FRQWUROOLQJ KLJK SHUIRUPDQFH PDFKLQHV LQ KLJK its own ILHOG EXV modules such as Profibus, Bitbus or SHUIRUPDQFHSURGXFWLRQSLSHOLQHV6\VWHPVLQFOXGLQJERWK CANBUS (Control Area Network BUS). These ORZ DQG KLJK SHUIRUPDQFH &1&V FDQQRW EH EXLOW DW connections are master-slave. The master manages the UHDVRQDEOH FRVWV VLQFH WKH UHVWUXFWXULQJ RI D SLSHOLQH RI communications, thus a typical centralized non-distributed SURGXFWLRQ IUHTXHQWO\ SURYRNH WKH LQFOXVLRQ RI QHZ controller is obtained. PDFKLQHV ZLWK GLIIHUHQW &1&V WKDW FDQQRW EH HDVLO\ At the third level, the Factory General Supervisor LQWHJUDWHGHDFKRWKHUV (FGS) is present. Frequently, the role of FGS is covered Moreover, these systems present several variables that by a couple of specialized machines one for managing the influence their performance on the basis of the administrative part and the other for controlling the configuration chosen. This approach can be inverted to production process. look for a configuration that have the required Please note that, the strong integration among layers of performance at the lowest price. Thus, the evaluation of control and the different machine tools is frequently these critical systems has to be carefully performed. A claimed by CNC producers. In effect, it is an illusion, detailed evaluation and model allows identifying the since it is possible only by using modules with correct configurations and the final performance. homogeneous performance. Most of the production In this paper, MUPAAC (Multi Processor Architecture pipelines are specifically set up for a given production, for Automatic Control) architecture is presented together and then they are destroyed when the production is with its assessment. MUPAAC HPCN ESPRIT IV project concluded, in favor of a new pipeline. has been developed in order to solve most of the above discussed problems [2], [3]. HPCN technology has been &RQWH[W employed in defining the parallel and distributed Presently the complexity of FMSs is growing since a architecture MUPAAC. A solution has been found by higher number of robots and services are needed and these studying and implementing a set of more flexible cannot be confined in FMMs. Some of these services components that can be reused in a variety of need many axes for their control. This local complexity of combinations for covering from low to high performance. control cannot be managed by using decentralized The evaluation reported has been performed for validating numerical controllers since the remote connection by the results obtained by the project, which has been means of serial or specific channels is not fast enough for successfully concluded in February 1999. MUPAAC is coordinating axes. For these reasons, some builders are suitable for implementing CIM (Computer Integrated improving the capabilities of their CNCs by increasing the Manufacturing) solutions. The discussion of CIM policies power of the microprocessor. is not on the focus of this paper. The general diffuse problems of the above mentioned The MUPAAC solution is a three layer architecture. A solutions is the lack of flexibility (see also OSACA and FGS controls the whole production pipeline by means of a NETCIM EC projects). At the first level, the number of set of industrial computers connected via local area controlled axes and their performance can change network. Each industrial computer can control one or radically from a machine to another. The solution to more machines by means of a set of specific DSP-based provide a controller per axis is too expensive and boards. These specific boards and the industrial inflexible to be acceptable. At the second level, the computers control all digital inputs/outputs, sensors and controller of FMM can be in some cases even unuseful actuators of the pipeline of production via CANBUS. It and under-exploited. While, the communication between allows the construction of a variety of configurations. the FMM controller and the other CNCs has to be The partners of MUPAAC project have been: SED provided by means of high performance communication Inc.; University of Florence with the Departments of channels and not only by Field Busses, which have a Systems and Informatics and that of Electronic limited bandwidth. Engineering; VALIANI Inc. (as end-user and validator); More recently, few builders of CNCs in USA are and CESVIT (High-Tech Agency) as TETRApc-TTN beginning to study multiprocessor-based systems (parallel HPCN (Technology Transfer Node) partner. The architectures) for implementing flexible CNCs and FMSs. prototype produced has been tested and validated by This flexibility also reduces the complexity and the VALIANI in the specific field of builders for cutting cost/price of complex numerical controls and increases the machines for producing passpartout (e.g., ZUND, Swiss; modularity of the system. Gunnar, Swiss).

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