M.G. Mehrabi

Reconfigurable manufacturing systems: Key to future manufacturing

Presented in this article is a review of manufacturing techniques and introduction of reconfigurable manufacturing systems; a new paradigm in manufacturing which is designed for rapid adjustment of production capacity and functionality, in response to new market conditions. A definition of reconfigurable manufacturing systems is outlined and an overview of available manufacturing techniques, their key drivers and enablers, and their impacts, achievements and limitations is presented. A historical review of manufacturing from the point-of-view of the major developments in the market, technology and sciences issues affecting manufacturing is provided. The new requirements for manufacturing are discussed and characteristics of reconfigurable manufacturing systems and their key role in future manufacturing are explained. The paper is concluded with a brief review of specific technologies and research issues related to RMSs.

Trends and perspectives in flexible and reconfigurable manufacturing systems

To better understand future needs in manufacturing and their enabling technologies, a survey of experts in manufacturing has been conducted. The survey instrument (i.e., questionnaire) tries to assess the experience to date with the use of flexible manufacturing systems (FMS) and to examine the potential roles and enabling technologies for reconfigurable manufacturing systems (RMS). The results show that two-thirds of respondents stated that FMSs are not living up to their full potential, and well over half reported purchasing FMS with excess capacity (which was eventually used) and excess features (which in many cases were not eventually used). They identified a variety of problems associated with FMS, including training, reconfigurability, reliability and maintenance, software and communications, and initial cost. However, despite these issues, nearly 75% of respondent expressed their desire to purchase additional, or expand existing FMSs. The experts agreed that RMS (which can provide exactly the capacity and functionality needed, exactly when needed) is a desirable next step in the evolution of production systems. The key enabling technologies for RMS were identified as modular machines, open-architecture controls, high-speed machining, and methods, training and education for the operation of manufacturing systems.

Reconfigurable manufacturing systems and their enabling technologies

A reconfigurable manufacturing system (RMS) is designed for rapid adjustment of production capacity and functionality in response to new market conditions and new process technology. It has several distinct characteristics including modularity, integrability, customisation, convertibility and diagnosability. There are a number of key interrelated technologies that should be developed and implemented to achieve these characteristics. This paper examines and identifies these technologies. After a brief description of the RMSs and their goals, aspects of reconfiguration (reconfigurable system, software, controller, machine, and process) are explained; this provides one with a better understanding of the enabling technologies of RMSs. Some of the issues related to the technology requirements of RMSs at the system and machine design levels, and ramp -up time reduction are then explained. The paper concludes with descriptions of some of the future research directions for RMSs.

Hidden Markov Model-based Tool Wear Monitoring in Turning

This paper presents a new modeling framework for tool wear monitoring in machining processes using hidden Markov models (HMMs). Feature vectors are extracted from vibration signals measured during turning. A codebook is designed and used for vector quantization to convert the feature vectors into a symbol sequence for the hidden Markov model. A series of experiments are conducted to evaluate the effectiveness of the approach for different lengths of training data and observation sequence. Experimental results show that successful tool state detection rates as high as 97% can be achieved by using this approach.

Parallel Structures and Their Applications in Reconfigurable Machining Systems

Reconfigurable Machine Tools (RMTs), assembled from machine modules such as spindles, slides and worktables are designed to be easily reconfigured to accommodate new machining requirements. Their goal is to provide exactly the capacity and functionality, exactly when needed. In this paper, we present a novel parallely-actuated work-support module as a part of an RMT to meet the machining requirements of specific features on a family of automotive cylinder heads. A prototype of the proposed module is designed/built and experimental results regarding its performance are presented.

A new control strategy for tracking in mobile robots and AGVs

The tracking problem of a wheeled mobile robot or an automated guided vehicle is considered. For the vehicles with a steering wheel, a control strategy is proposed to determine the steering angle at each instant based on measured errors, i.e. the offset from the path and the deviation in orientation. The results of computer simulation of the dynamics of the system and comparisons with other proposed control policies are presented. It is shown that by implementing the new policy significant improvement in tracking capability can be achieved.<<ETX>>

Analysis of steering control in vehicles with two independent left and right traction wheels

Based on the kinematic studies of motion for a vehicle equipped with a pair of motorized wheels which, by having appropriate velocities, can provide traction forces as well as steering action, a steering control strategy is derived. The angular velocities for the right and left wheels are considered, the two control inputs which cause a system to follow a desired trajectory. Assuming these inputs to be linear functions of the two errors associated with path tracking problem (position and orientation errors), through an appropriate Lyapunov function, a control policy is determined. The path tracking behaviour of a mobile robot using such a control law is demonstrated by computer simulation.<<ETX>>

Mapping theory: a new approach to design of multi-sensor monitoring of reconfigurable machining systems (RMS)

Abstract Effective monitoring of a manufacturing process is essential for ensuring product quality. Single-sensor systems have often proven not to be very effective due to the relatively large number of parameters and the complexity of machining processes. Multi-sensor systems have therefore been investigated in recent years to improve the reliability of tool failure monitoring. This paper outlines a fundamental theory (“Mapping Theory”) that will form a framework for selecting an appropriate monitoring system for any given machining system. In particular, such a theory should facilitate development of monitoring systems for reconfigurable machining. Presented are the concepts of Fault, Sensor, Signal Processing, and Computing Spaces, and their generic characteristics. Study of their fundamental properties reveals that there are certain levels of uncertainty involved in describing them. This has led to the adoption of fuzzy systems theory as a fundamental tool for development of the “Mapping Theory.” This article reports on recent progress made in this regard and outlines some of the preliminary results obtained. It is shown that, based on the characteristics of the faults and the type of machining operations, it is possible to rank the sensors based on their characteristics and to come up with an appropriate multi-sensor monitoring system. Examples are provided to show the effectiveness of the approach.

A Method for Sensor Selection in Reconfigurable Process Monitoring

Sensor selection is important for process monitoring. Each time a machining system is reconfigured, the corresponding monitoring system needs to be re-designed for effective detection of the faults of interest. To accomplish this, a sensor selection methodology is proposed in this paper. Fuzzy theory is utilized for the multi-criteria decision-making process. Evaluation criteria are selected based on a thorough study of fault characteristics. Under subjective criteria, the ratings of different sensors are evaluated using linguistic terms, which are converted to trapezoidal fuzzy numbers. Under objective criteria, the fuzzy performance of each sensor is obtained directly from its specifications. The suitable sensor or sensors can be selected by aggregating and ranking the fuzzy numbers. Sensor selection in the turning process is used to illustrate the proposed methodology.

Control of a wheeled mobile robot with double steering

The motion of a vehicle with automated guidance (an AGV or a wheeled mobile robot) equipped with two steerable traction wheels in the front and rear is studied. Compared with a conventional form of these vehicles, there is some degree of redundancy in their system of path tracking. If this redundancy is utilized appropriately, there are certain advantages over the conventional vehicles in terms of their performance in path tracking. A scheme for steering control of this class of vehicle is proposed. Simulation results demonstrate the good performance of a vehicle controlled according to the proposed scheme.<<ETX>>