مدل سازی برای برنامه ریزی عملیات: ارتباط بین نهادهای برنامه ریزی عملیات

In an integrated design framework, each actor of the design process must have his own view of the product to efficiently participate and co-design. The product model used by the process planner is presented here: it is in fact extracted from the global product model of the whole design system by filtering. The links of dependence among the different entities of the model – links of availability, accessibility and quality – are particularly emphasised in this text. Their efficiency has been tested in process planning and product designing.

In an integrated design framework, all the actors of the product life cycle must cooperate all along the design process in order to define the best design, in the sense it satisfies all their constraints. Each of them brings competence and skills of his domain: he works with his own culture, reasoning and rationales, and uses data, knowledge and tools in his own environment. An efficient work of each actor needs a specific structure of a product model split in different views [1] and [2]. A view is dedicated to the work of an actor, expert in one particular domain. In this paper, the machining process planner's point of view is particularly emphasised. A product model useable by the experts in machining and process planning is proposed. It permits them to elaborate reliable process plans. The model is implemented in the CasCade environment [3]. Present CAD-CAM systems are geometrical-modelling-based. But product models required by the actors of the product life cycle are specific domain-feature-based. Three tracks have been explored until now to build product models (MAR 96). Design by features permits to design the product directly by handling functional features generally pre-defined and parameterised. Those functional features are generally geometrical features like form-features specially built for a particular domain. The main disadvantage comes from the fact that the model cannot support simultaneously all the life cycle points of view. The product must be re-defined for each domain [4]. The feature recognition permits to classically design from geometrical CAD-CAM modellers. Then domain features must be extracted from the geometrical representation of the product by applying domain expert rules. The difficult formalisation of the expertise from a given point of view and the poorness of available information in the geometrical data base lead to an incomplete recognition [5]. Those two approaches are widely exploited and are not sufficient. The most promising approach is a product model including one model for the design solution and several models of domain applications like for example one for process planning [6]. The expert person of the domain must exploit the design features to obtain a product model based on his domain features and from which he can work efficiently. This specific model is dependent on the way it can be used by specialists, the process planner for example. The whole product model is a multiple view and multiple actor model; the product model for the process planning point of view is extracted from this global model by filtering information useful in this view. The specifications for the product model in a process planning point of view have been studied. It has been pointed out, on the one hand the machining feature concept, particularly to obtain the form and the intrinsic quality of the form, and on the other the role of the tolerances on the geometrical relations between features. The product model must explicitly support these relations and the machining features. Rough features (pieces of part remaining rough in the finished part) must be added to have a complete description of the part. Locating-clamping features are capable of being either the location or the clamp for the part while machining is also necessary. It is the set of these four concepts that defines a product model in a machining process planning point of view. The models developed for a specific view are of course dependent of the models of the other views. In particular, the models of the machining process planning and rough obtaining views are strongly coupled. The aim of this paper is to show how a product and its environment are modelled in order to be efficient in a process planning point of view. The fact that the entities used in product and process planning modelling are not independent is particularly emphasised. The product model for a process planning point of view, then the resources for machining are reminded in Section 2. The mapping between those entities and the different entities used in process planning are presented in Section 3. The core of the paper in Section 4 deals with the links of dependence between these entities. A coherency between the product definition and the behaviour of the product process plan is ensured by these links. In conclusion, the implementation of the model and its usage in a multi-view system of design is discussed.

5.1. Implementation and use in process planning The product model described above, from a process planning point of view, has been successfully implemented in the CasCade environment: data structure is perfectly suitable to do it. We had already developed tools for process planner in our lab and all of those now run based upon this product model. It is particularly the case of PROPEL, our system that determines a process plan for the part under study, and MIAP, our system that determines all the suitable fixturing solutions to machine the part. 5.2. Use in product designing The product model from a process planning point of view is also used in the computer-aided integrated design modeller that we are developing in our lab. It is a multiple views and multiple users system [1]. Of course, this model is implemented for a use from the process planning view by a process planner. The interest is in the fact that the mapping between features handled by the product designer, that we call skin and skeleton features, and the features handled by the process planner as described above, is easily made by the process planner in most of the cases [12] and [13]. It really permits a good exchange and a co-ordination between the two engineers.