Design Methodology of Scheduling Strategies and Scenarios of Complex Flexible Systems

The step-by-step methodology of design of scheduling scenarios and strategies for different complex flexible systems will be described. This approach give the possibility to design the task oriented scheduling of system and reach two main aims: functionality and high efficiency of system. The concept is based on priority structures and queues of orders and activities. This concept is implemented and verified on three flexible systems: flexible manufacturing system, flexible assembly system and flexible transport system; as a part of CIM factory solution. INTRODUCTION Modern FMS are composed from standard hardware system components (machine tools, computer, AGV, robots, buffers, ASRS, storage, tools,...) and software. The system components alone cannot guarantee the functionality of FMS. The information integration is the first and also the most important problem to be solved during the design of FMS. The efficiency of FMS directly depend on the quality of ideas and intelligence which are implemented in the FMS during design. This is the unique medium which ties together all the operational functions and activities that are completed by different components of system inside of FMS system border, including hardware and software [1]. To realise the complex FMS with limited resources and a lot of bottlenecks it is necessary to design and implement intelligent tools for optimisation of FMS working scenarios and to solve the conflict situation and control such a system in an intelligent way. This concept has been developed during the last seven years by Katalinic [2], [3], [4], [5] and later expanded by Nanasi [6], who developed intelligent adviser module, the concept has been implemented in practice, it has been tested and has shown good results. This concept is most suitable for application over a wide range of flexible manufacturing systems with the following characteristics: Range of products: Open range: which will be permanently changed during the lifetime of the system. Size of the run: From a few to several hundred pieces. Yearly production: from a few to several thousand pieces. Machine tools: the number and type of machine tools of one FMS is unlimited. The set-up of the machine tools can be carried out at least partly manually. Coordinate measuring machine: In this system one or more machines can be incorporated. Measurement and quality control during the machining: During the machining of one run it is possible to carry out the measurement, also in way that ensure that all parts of one run will be well machined. Operators: For the normal operation of FMS, intensive work by operators is required. Typical duties of operators involve the following: set up of machine tools; ensuring and supporting the material flow (tools and pieces) in the system; correction of interruptions during production; operating the central FMS computer (FMS control host). Automatic transport system: the whole material flow (tools and pieces) must go through the automatic transport system. The automatic transport system includes one or more AGV‘s and ASRS. Pallets: The whole material flow (the tools and pieces) is organised with pallets. Material flow pieces: to carry out one operation on all the pieces from one run it is necessary to bring the pieces onto the part loading/unloading station to the core system of the FMS, and after machining to take it out in the same way. Tool flow: the tool flow can be organised on a cassette or pallet system. Limited production resources: The production resources are limited in type and number, and can vary from time to time. Auxiliary production resources: auxiliary production devices can be independent of the machine or machine specific. Buffers: The core system of FMS includes a number of buffers which can be used for temporary storage of tools and pieces. This concept is possible to apply to all FMS which are similar to or simpler than those described above. Those that are simpler will not require all the possible functions. BEHAVIOUR OF FMS Through the realisation of this concept, Fig. 1., it is possible to achieve the following behaviour of FMS: System autonomy: FMS achieves autonomy, which means that the disturbances that come from outside have a limited negative influence on the efficiency and function of the system. Working mode: FMS has two working modes: a) all machine tools are scheduled from a FMS control host computer b) the system is scheduled from the FMS control host computer but one or more machine tools are excluded. Shift specific mode: The system is so organised that it is possible to function in a situation of a varying number of shop floor operators during a shorter period of time, or even shifts. Management and optimisation of use of production resources: All production resources (tools, pallets, robot end effector, measurement sensors, etc.) which can cause a bottle-neck will be organised by the management resources. Diagnostic: the system has a very detailed and broad diagnostic which refers to the FMS orders, production resources and state of the system. Prognosis: the system has the possibility to develop alternative production scenarios, based on the actual state of the system, for a period of time in advance. The period of time can be chosen freely, Fig. 2. Internal reserves of the system: reserves will be accumulated in the system and these reserves will be used to reduce the negative influence of outer disturbances. Interface between FMS and environment: the information and material flow between FMS and their environment are organised in such a way that it is possible for each single transaction to be protocolled and later reconstructed. Reaction of FMS: FMS react flexibly and efficiently under normal, typical conditions as well as under conditions of disturbances. Optimisation of production process: in the optimisation of FMS work the system has the possibility of choosing the most suitable working scenario of the different production alternatives (FMS virtual scenarios), Fig. 2. Implementation of this concept in one specific case has to be done step by step. Typical steps are a logistical analysis of the system, a logistical synthesis of the system, analysis and synthesis of the interactions concerning the information, material and organisation between the