Showing papers in "Robotics and Computer-integrated Manufacturing in 1988"

Feature-based representational scheme of a solid modeler for providing dimensioning and tolerancing information

Abstract: Presently available CAD data models have no problem handling the basic shape design of an object as required but they are not properly manufacturing-oriented. It is not possible to represent the dimensioning and tolerancing information or other technological information (such as material data, the surface roughness and accuracy data, feature information, etc.). This paper discusses the requirements of a new CAD data model and proposes a feature-based representation scheme based on the hybrid CSG/B-Rep data structure. This hybrid structure exploits the advantages of both CSG and B-Rep models in representing tolerance information. A relational graph structure (face-based data model of B-Rep) of the object is maintained at each hierarchical level of object construction for associating tolerance and other attributes.

Modelling machining processes with a view to their optimization and to the adaptive control of metal cutting machine tools

Abstract: This paper describes an orthogonal machining theory which can be used to determine the stresses, temperatures etc involved in chip formation from a knowledge of the work material flow stress and thermal properties and cutting conditions It is shown how these can be used to predict machinability factors such as power consumption, built-up edge range, tool wear rates (tool life) and those cutting conditions which cause plastic deformation of the cutting edge An oblique machining theory which is more representative of practical machining processes than the orthogonal theory is then described, taking into account machining on more than one cutting edge as in bar turning Throughout the paper comparisons are made between predicted and experimental results

Integrating dimensioning and tolerancing in computer-aided process planning

Abstract: Process planning is today recognized as the “missing link” between computer-aided design and computer-aided manufacturing. Special attention is directed toward the analysis of dimensioning and tolerancing in manufacturing which ensures the quality of the product in manufacturing and takes into account economy of production by allowing the largest tolerances to be conferred on manufacturing processes in accordance with machine capabilities. The number of published studies on this subject is still very limited, although a few basic investigations have tried to find better theoretical formulations of tolerance analysis. The review of some basic contributions confirms the need of developing computerized tolerancing modules for geometric modelers. A first step in this direction has been achieved in the field of tolerance transfer. A computerized module which has been developed for the one-dimensional case is described. A further step in tolerance analysis should now be undertaken by introducing in the transfer model geometrical tolerances of position and form.

Generation of workpiece orientations for machining using a rule-based system

Abstract: This paper deals with the automatic generation of workpiece orientations on a machine for machining operations. A system capable of this has a wide spectrum of applications in many areas of manufacturing planning and is essential to the development of dynamic process planning systems. However, such a system requires the ability to reason about geometrical and spatial relationships, a topic of great difficulty for automatic reasoning. A study of the problem characteristics is made and its results are implemented in a rule-based system. This system, when given a workpiece along with operation instructions and machine specifications is capable of generating a good orientation for the workpiece. The functioning of the system is demonstrated by an example.

Managing the flow of intelligent parts

Abstract: Advances in computer technology have brought the feasibility of intelligent system components to fuitation. Within the manufacturing environment, the regulation of parts' value-adding operations from entry into the system to completion as a finished product now can be individualized to depend on part specific information. The new CADENCE system, introduced in this research, manages the physical parts' operations and the information flow within manufacturing. Integration of both the physical flow dependencies and the information flow is provided by a negotiation procedure. CADENCE goes beyond previously proposed task bidding structures by utilizing distributed decision making in managing the flow of individual intelligent parts.

Computer-aided analysis of reconfigurable fixtures and sheet metal parts for robotic drilling

Abstract: This paper presents an automated manufacturing system for drilling sheet metal parts. All stand-alone systems such as the robot, a set of reconfigurable fixtures and the CAD/CAM workstation have been integrated into a flexible manufacturing system. This system analyzes and evaluates a given fixturing layout and assembles the reconfigurable fixtures automatically using a robot manipulator. An optimum fixturing layout and assembly are achieved by examining the workpart from a stress-strain point of view. In addition, issues such as geometric constraints, yielding and buckling, database design, collision detection, fixturing sequential control and the automatic assembly of fixture elements are considered. The computational and analytical concepts for the reconfigurable fixturing and drilling system are also presented in this paper.

Expert system for wire cutting EDM, based on pulse classification and thermal modeling

Abstract: Although wire EDM has become a fully competitive machining technique during the last decade, the process performance is limited by some typical restrictions: the risk of wire rupture and the bending of the wire. Wire rupture drastically reduces the overall efficiency of the EDM operation and wire deflection restricts the obtainable geometrical precision. In order to improve machining performance, a multidisciplinary expert system was developed. It mainly consists of two parts: an observation procedure and a decision procedure. The observation of the wire EDM process is carried out by means of a powerful electronic device, called the EDM pulse discriminating system, which is used to detect and classify the occurring electric pulse types times. This device delivers “on-line” a “chaos” of information of the process. In the decision phase, the incoming data are analyzed and patterns are detected by means of a computer, and eventually, the parameter settings of the EDM machine are changed in order to obtain more optimal working conditions. This decision procedure is partially based on the results of a mathematical thermal model of the wire, enabling one to predict the influence of some parameter changes. Further, a technological database is permanently accessible for the control strategy program. As a result, supervision of the machining process is completely automated. Machining speed can be increased without enhancing the risk of wire rupture, because in the case of an increased danger of rupture, appropriate action is taken by the control strategy. The paper gives some results on how the thermal model may predict some thermal overload of the wire. It also describes how frequently observed breakage at sharp corners of the wire path may be dealt with. It further illustrates the actions taken by the expert system when various types of disturbance occur. The consideration of practical experience with a thermal model yields an increased level of machine autonomy ensuring a performance level obtainable only with a skilled operator.

Drill wear sensing and failure prediction for untended machining

Abstract: Real-time control of drilling was carried out by measuring the thrust force and determining its gradient. Using a microcomputer-based feedback control system, experiments were carried out under different cutting conditions to test the effectiveness of the thrust force gradient in predicting failure. The system was able to predict failure due to excessive wear commonly encountered with 5 and 8 mm drills. With such drills, excessive weat at the outer corner led to an increase in the local temperature which in turn increased the wear. This led to very high temperatures (>600°C), causing local welding of the drill material to the peripheral surface of the hole being drilled. Furthermore, the high temperatures reduced the compressive yield strength of the drill material, causing sub-surface fracture to occur under the influence of the cutting loads. This cyclic phenomenon of “seizure” due to local welding and “release” due to shear fracture (i.e. “stick-slip”) caused sharp fluctuations in the thrust force under constant feed. This paper discusses the effectiveness of the control system described above in predicting failure due to the excessive wear common to large drills. This system is also contrasted with another based on vibration measurements which has been successfully used to predict failure due to fracture common with small drills. This paper also presents other experimental sensor schemes in the literature. Finally, this paper proposes a framework for an “intelligent” machining process control system driven by multiple sensors, which would facilitate untended machining.

A case-based system for process planning

Abstract: Process planning is the phase of manufacturing that is concerned with the selection, and sequencing of manufacturing operations necessary to transform an initial stock material into a finished part. It is a tedious operation that requires highly skilled and experienced personnel of which there is currently great shortage. To disseminate the costly expertise and to reduce process planning times, which tend to add high costs to small batch production, many automated computer systems have been introduced and applied. All these systems, though, require the supervision of an experienced human being and fail to capture the knowledge and reasoning behind process planning decisions. The causes of the lack of an efficient automatic system for process planning are the unique characteristics of the domain. In contrast to other areas where knowledge-based and expert systems have been applied, process planning demands the solution of several different planning problems before a final solution is achieved. Every change introduced to the previous world model creates a completely new world model with its own, new constraints and preconditions that nedd to be satisfied. This, in turn, affects the applicability of the knowledge to the new model. To provide solutions to the above problems we have designed a prototypical knowledge-based system that uses the high level, dynamic memory structures of MOPs (Memory Organization Packages), meta-MOPs and TOPs (Thematic Organization Packets) to rearrange its knowledge according to its experiences and to predict and avoid errors. To model the dynamic, sharable knowledge and the constantly changing world model a knowledge-representation language named TOLTEC has been designed and used in the system. Furthermore, we propose a novel planning method based on abstract plans and constraints that can solve planning problems in uncertain domains given incomplete information.

Grinding of non-circular contours on CNC cylindrical grinding machines

Abstract: Grinding of non-circular workpieces on CNC cylindrical grinding machines is a new technique which opens a wide field of new possibilities both in design and manufacturing. Considerable economic reserves can be utilized on parts which consist of a combination of circular and non-circular cross-sections. These parts can now be completely machined in one operation. The research project “CNC Non-Circular Grinding” which is performed at the Technical University of Graz, Austria is supported by several research foundations, the national government and the Austrian industry. A brief description of some aspects of this work is given in the paper.

Advanced Process Monitoring - A Major Step Towards Adaptive-Control

Abstract: Adaptive Control (AC) of machine tools requires many kinds of measured input data. The more information about the complex metal cutting process that can be obtained, the better the process can be ...

New trends in machine tool monitoring and diagnostics

Abstract: The line of evolution of manufacturing systems indicates rapidly increasing complexity at every system level, which necessitates enhanced requirements for the monitoring and diagnostic sybsystems applied in these manufacturing complexes. This means they must correspond—in performance, complexity and intelligence—to the entire material and data-processing system. This paper summarizes the fundamental requirements for a new family of monitoring and diagnostic equipment and describes two multipurpose, flexible machine tool monitoring systems, which can be regarded as first attempts in this direction. Special emphasis is placed on the generation of reference data for such complex monitoring equipment. Process modelling and teaching approaches are discussed. Pattern recognition methods during learning and decision-making are suggested. Among the most important research and development trends, the use of AI techniques in monitoring and diagnostics is also investigated.

Intelligent manufacture of laser cutting, punching and bending parts

Abstract: It is possible to carry out the flexible manufacture of small parts using existing machine tools. Various computer programs and expert systems are required for this purpose. Continuous further development of the installation is possible with expert systems. The most important software component is a CAD system suitable for the input of sheet parts and which is externally accessible, along with expert systems, for the determination of developed projections and bending sequences and also for the generation of laser and punching plans for the sheet blanks. The system described here, for the flexible manufacture of small parts, was designed for best possible compatibility with different machines and adaptibility to new information.

Development and classification of expert systems for chemical process fault diagnosis

Abstract: Fault diagnosis of process plants has been addressed by a variety of techniques, including quantitative and qualitative model-based methods and expert systems approaches The strengths and weaknesses of model-based and experience-based methods are discussed, and it is concluded that both types of reasoning are useful in fault diagnosis Strategies for development of expert systems that merge model-based information with heuristic and experiential knowledge are examined

Programming robot systems with knowledge

Abstract: In this paper we describe the framework of an object-oriented knowledge base to facilitate automatic robot programming. In this framework, we take the object data model as the basis for knowledge representation, and utilize the knowledge in transforming high-level task descriptions to robot programs. In contrast to most current approaches, which are heuristic in nature, we show that robot assembly problems can be regarded as a subclass of the general planning problem and can be synthesized in a non-ad hoc way.

Computation and conceptual design

Abstract: Design is the transformation between a functional and a structural description of a device. Conceptual design is the initial stage of this transformation. We hypothesize that most new design are derived from knowledge of existing designs. We identify a special case of this process and call it novel combination . By describing an implemented program which designs novel mechanical fasteners, we explain how knowledge of existing devices can be represented and used. We highlight the issues arising from this implementation and propose four areas of future research. This work is important for establishing a fundamental understanding of conceptual design, leading to enhanced design teaching and better design tools.

An attempt to implement expert system techniques in CAPP

Abstract: This paper presents the development of a generative computer-aided process planning system that covers part of macro level planning activities. The system's task is to generate all appropriate machining operation sequences and select the most promising ones, according to a given set of criteria, while the final choice is to be made by the user. The system acts as a classical “production” system that interprets expert rules on input workpiece data according to the knowledge and data in the engineering knowledge base. By using the technological knowledge in rule form the system largely constrains the solution space and produces a reasonably small set of meaningful alternatives. The advantage of the expert system approach also lies in the program's flexibility which enables easy adjustment of the system according to specific shop-floor environments.

A connectionist model for material handling

Abstract: Connectionist models have traditionally been motivated by the desire to imitate human intelligence by copying biological information processing mechanisms. We can also apply them to tasks that are not usually associated with human cognition, by taking advantage of promising mappings between their features (such as distribution, local computation, constraint propagation and computation by relaxation) and certain problem domains. This paper reports the design and implementation of CASCADE, a system for performing the material handling function in a discrete parts manufacturing environment. CASCADE draws heavily on connectionist models, and has been implemented in an experimental machining cell (Parunak e al., Fractal actors for distributed manufacturing control. Proceedings of the 2nd IEEE Conference on AI Applications, 1985, Parunak et al., An architecture for heuristic factory control. Proceedings of the 1986 American Control Conference, 1986). We discuss • • the problem domain of material handling; • • the connectionist framework that we are using; • • the structure of CASCADE in terms of the connectionist model; and • • some computational implications of the model that we exhibit.

A product modeling system for constructing intelligent CAD and CAM systems

Abstract: It is essential for the achievement of intelligent manufacturing systems to properly encode manufacturing knowledge in computer systems. We propose a product modeling system that is a framework for representing and utilizing models of both design objects and design tasks. The key concept in the framework is that of constraint. Several prototypical CAD/CAM applications constructed on the framework are shown.

SAPT―Knowledge-based capp system

Abstract: The system for automatic programming technology (SAPT system) is a part of the designer-expert system. The new developments in artificial intelligence are promising for design and use knowledge-based expert systems. For a manufacturing process planning knowledge base, the method of knowledge representation and reasoning strategy are given. GT and TT concepts are discussed in detail from a KB approach. Production rules are given for knowledge sources, tasks and meta-knowledge. For two real life, examples, a LISP-program has been written and executed. The results obtained are encouraging and further research is in progress.

Explanation of random vibrations in cutting on grounds of deterministic chaos

Abstract: This article presents a model of orthogonal cutting on an elastic system. The dynamics of the system is described by the differential equations in which the forces are expressed by empirical nonlinear relations. The oscillations of the system determined by numerical solutions of nonlinear differential equations exhibit chaotic characters in certain domains of typical parameters and thus represent a new example of deterministic chaos. This indicates that, besides the irregular properties of cut material, nonlinear dynamics must also be taken into account in order to explain the random character of vibrations observed in cutting systems.

Model-based low-level control in flexible manufacturing systems

Abstract: Low-level (supervisory) control of flexible manufacturing systems (FMS) assures conflict-free operation and enforces production requirements such as priorities. It forms a crucial link between medium and higher-level decision making, on the one hand, and the various machine-controllers and servomechanisms on the other. In the absence of a suitable control methodology, ad hoc development is the current practice and compromised results at high cost are far too common. Here we described a model-based framework for a new, systematic approach to supervisory control.

PERCE's GRIPES: A robot grasp planner

Abstract: PERCE's GRIPES (Purdue Engineering Research Center's Grip Evaluation System) is an offline robot grasp planner for three-fingered grippers. The planner is based on a generate and test paradigm. Candidate triples of faces (or grasp configurations) are generated using heuristics. The precise coordinates of grip points are selected for each configuration by numerical solution of optimization problems. The constraints imposed by stability considerations are built into the optimization formulations. The accessibility of each candidate grasp is checked based on swept volume computation. Other criteria are used to rank the feasible grasps. This paper describes the modular design and the implementation of PERCE's GRIPES.

A connectionist net approach to autonomous machine learning of effective process control strategies

Abstract: The feasibility of connectionist nets of the Rumelhart semi-linear feedforward type for learning and exercising intelligent process and system control is investigated. Of particular interest is the ability of such nets to discover the basis for decision and control. Of great interest also is an unexpected finding that such a net automatically builds up a great deal of redundacy within itself, so that it has a certain holographic quality; its performance degrades gradually with internal damage.

Design of the database for CAD based on group technology

Abstract: An important part of integrated CAD/CAPP/CAM is represented by the database in which all the information and data relevant for the design, planning and manufacturing of a component are available to the designer. The database must thus include relevant data about the geometrical primitives, materials, surfaces, tolerances, etc. This paper reports on the design of a database to be used in CAD/CAPP/CAM with particular reference to GT principles. The data required in the CAD process are strongly structured, so that their computer representation actually yields a structural model of the component. The elements which form the component model are parameterized shape primitives generating the matrix of the primitives for forming rotational and non-rotational components. The organization of their data and the communication between the designer and the database are discussed in detail. In this context a solution is proposed which enables the designer not only to draft a component by means of a computer, but, at the same time, to classify the component into a part family using a pattern recognition method for computer-aided GT classification.

A knowledge-based system for information management in an automated and integrated manufacturing system

Abstract: In recent years there has been considerable interest in flexible automation of manufacturing processes in an effort to improve the productivity of manufacturing industry. Central to an integrated, flexible and intelligent manufacturing system is the information management function. The sharing of data is the basis of flexible and intelligent decision-making, the means of integrating the system components, the mode of synchronizing their processes and the method of maintaining the consistency of their states. It appears that the data management and manipulation function in manufacturing systems is increasingly becoming a bottleneck for further performance improvement of manufacturing systems. New information management systems need to be developed that meet the needs of modern manufacturing systems in terms of efficiency, flexibility, reliability and intelligence. A new model for an integrated manufacturing information system is presented. A double structure of two parallel but independent system is proposed for manufacturing control and manufacturing information management. The objective is to improve service efficiency. representational adequacy, consistency of information and reliability in the information system.