Vladimir R. Milačić

Context sensitive recognition of abrupt changes in cutting process

This paper presents a new generic approach to real-time monitoring of abrupt changes in cutting process. Proposed method is based on hierarchical fuzzy clustering of patterns obtained from discrete wavelet transform (DWT) of acquired signals correlated with cutting force variation in time. Cutting process is naturally highly dynamical and normally consists of mixture of various dynamic phenomena related to the chip formation process and dynamical responses of machining system, workpiece and tool itself. These phenomena are characterized by different time duration. The class of phenomena related to abrupt changes during short time interval is of special importance since they correspond to the most dramatic changes in cutting process, such as various kinds of tool failure or workpiece damage or even breakage. Due to their short time duration, discovery and recognition of these phenomena is extremely difficult. To solve given problem we have chosen DWT, fuzzy clustering and finite state automata as a formal platform for its analysis. Beside its good time localization properties, DWT is, due to asymmetric and irregular shapes of wavelets, especially suitable for analysis of signals having sharp changes or even discontinuities. Given properties make DWT an efficient means for extraction of representative and reliable information contents, thus making good basis for extraction of discriminative and representative features (as DWT coefficients combinations) for classification that will follow. Robustness of specific pattern recognition and learning may be achieved only by taking into consideration wider context. Therefore, in tool condition pattern recognition we have considered the entire context of changes in cutting process state space that precedes and appears after the phenomenon which should be recognized. The cutting process behavior and its evolution in time are considered rather then momentary state which is represented as a point in adopted feature hyperspace of classification machine. Efficiency and practical applicability of developed method is evaluated by extensive experiments in laboratory conditions.

Conceptual Design Based on the Linguistic Approach and the Automata Theory

Summary The paper is continuation of the research and the development of the CAD system in the field of production engineering. The formalized engineering knowledge structure is given as a quintuple of the knowledge block. The linguistic approach and automata theory are introduced as the basis for knowledge organization or the conceptual design system. Through the analysis of complex systems and their decompositing to subsystems, partial languages and corresponding grammars are defined representing their structure and the basic elements of the knowledge base. The theory of automata opens posibilities for practical development of the system and software and/or hardware solutions. Practical results are presented through examples of developed languages and corresponding operations and automata for-machine tools and CMC control units.

A model-based vision system using a small computer

Abstract This approach is based on a fast and simple off-line formation of synthetic binary images of mechanical parts generated from basic solid modelling system. From so farmed synthetic binary images characteristic features are extracted in a similar way to that applied to binary images from a real scene. Recognition is then reduced to the on-line formation of binary images of real objects, extraction of their features and matching with those that have been learned for the purpose of recognition.

New Feeding System for High Speed Assembly of Small Parts

Abstract This paper presents the new general purpose automatic feeding system, developed for high speed assembly of small parts. The new design is a result of the consequently applied Axiomatic Design Theory. The feeding system is functionally uncoupled, leading to minimization of problems in system tuning, parts damage and noise emission. Moreover, the new design gives the possibility for simple introduction of additional functional modules such as: sensorized modules for non-geometrical orientation of parts, or active orientation modules for improving efficiency of the system. The proposed system is verified by the prototype developed for feeding screws on pneumatic screwdriving station.

Steering rules for AGV based on primitive function and elementary movement control

Abstract The complete structure of an AGV control system is described in the first part of this paper. The AGV control system is hierarchical and consists of five levels. The structure of one level does not depend on the structures of the other levels. This means that the control system depends on the design of the AGV at the lowest level only, at the actuator servo-control level and its coordination in realizing AGV primitive functions. The second part of the paper describes rules applicable to AGV steering. The structure of these rules depends on two groups of factors. The first group is dependent on information groups fed to the AGV processor by the position sensor. The second group of factors represents aims and conditions and AGV steering such as positioning accuracy, positioning time, allowed room for maneuver, the shape of the given trajectory, etc. The AGV steering rules contain sequences of primitive functions. These primitive functions are of such types as “turn left”, “straighten” (correct), “go straight on”, etc. Trajectory, as one of the basic factors, is defined at the level of controlling an elementary movement. The term “to control an elementary movement” means to select a transport road throughout the transport network and to code it using “elementary movement” such as “go straight” (relating to road section), “turn left” (relating to turning at a crossroad) etc. The results of the AGV steering simulation are presented in the third part of the paper. An exact kinematic AGV model used for stimulating control models is also presented.

A practical procedure for conceptual design and testing of machine tool structure

Abstract This paper discusses the initial development of a machine tool and its structure (concept, calculation, design) and the verification of the prototype. The topics studied include two issues: static rigidity and dynamic stability. For static rigidity several experiments and modelling studies using the finite element method have been carried out in order to identify the model parameters. In this way differences between models of bolted joints, slideways and the cross-section of the structural elements have been determined. The model is formed by design documentation and later verified through experiments on the prototype of the machine. The approach is different in the case of dynamic stability. The model is not made on the basis of design documentation or static calculations, but by experiments performed on the prototype. This relates to an oriented transfer function; parameters are determined by fitting experimental transfer function curves. With this model, the stability is analyzed under different machining conditions. Specific features of this methodology are as follows: • • The finite element method is used for qualitative comparison of different machine tool structure concepts during the conceptual and design stages. Only after completion of the prototype may the parameters of the prototype model be adjusted for the purpose of obtaining quantitative indicators. • • Dynamics are analyzed by parameter identification of the oriented transfer function model. The dominant degree of freedom is naturally selected by experiment and not from hypotheses about the behavior of structures obtained from mathematical manipulations such as expansion of the model according to the finite element method. If necessary another machine tool structure may be modelled; in this way hypotheses are drawn about the stability of the reconstructed prototype. Such a procedure has been applied and verified on the machine tool structure of a horizontal machining center. Results for static rigidity and dynamic stability have been obtained from the model and experiments performed on the prototype. The following techniques have been used: • • finite element method for qualitative identification of static behavior, • • self-excitation of the machine, • • digital signal processing on the FFT basis, • • smoothing of curves and digital filtration, • • function fitting of the transfer function (modal analysis), • • coefficient calculus and oriented transfer function, • • stability assessment of the fitted model under different machining conditions, and • • modelling of the regenerative machining effect by cutting. Necessary tests have been done by instruments required for the use of the above techniques. Such a combined static-dynamic criteria procedure for structuring a machine tool enables efficient follow-up of all results and facilitates necessary future expansion, the utilization of universal equipment, the combination of modelling and experiments, and the synthesis of simple models of the examined machine with behavior identical to the machine. The well-known machining system dynamic stability theories are applied to such models.

Factory environment and CIM

Abstract This contribution on the topic of factory environment and CIM is divided into two parts. The first part deals with some fundamental aspects of intelligent manufacturing systems for the new generation factories. This subject is divided into three blocks: intelligent manufacturing systems, expert systems and intelligent CAE/CAD/CAM. Based on the input-output approach, some basic requirements for IMS definition are given. The second part deals with the problem of the factory environment and CIM, more specifically from historical aspects to the contemporary factory and some conceptual designs aspects of FMS. At the end, an example of structural pattern recognition of FMS is given.

A model-based vision system for industrial parts using a small computer

Abstract A model-based vision system has been successfully implemented in a small computer environment. This approach uses a basic solid modeling system to develop three-dimensional models of mechanical parts. From those models, two-dimensional projections are taken for every stable state of the object, with many orientations around the objects vertical axis for each stable state. These two-dimensional projections are treated as synthetic binary images, from which a variety of features may be measured and extracted. A similar procedure is used for a binary image of an object from a real scene, and features are also extracted for that image. A simple matching procedures uses the model-based feature sets to determine the real objects stable state position and orientation. This paper describes the system in detail and shows examples of its use.

Closed-Form Resolution Scheme of the Direct Kinematics of Parallel Link Systems Based on Redundant Sensory Information

Abstract In this paper, the direct kinematics transformation in parallel link systems, based on redundant sensing approach is addressed. The redundant sensory information is provided by additional position sensors, connected directly to the parallel structure in a parallel manner. Optimization of position and the number of redundant sensors is performed by a proposed Geometrical-Structure-Partitioning Method. The efficiency of the method is verified by two examples — type 3-3 and 6-3 spatial structures, where only one redundant sensor is identified as sufficient for unique closed-form solution of the direct kinematics problem.

Mathematical model of an industrial robot with articulated configuration and six degrees of freedom

Abstract This paper analyses the load influence on a d.c. drive motor servo system for all six degrees of freedom of industrial robots with an articulated configuration. Through the analyses, the analytical equations of total inertia and gravitation moments of an industrial robot servo system for external coordinate function were obtained. A mathematical model of an electro-mechanical industrial robot system was also developed.