Phil Webb

A direct comparison of the machining performance of a variax 5 axis parallel kinetic machining centre with conventional 3 and 5 axis machine tools

The current trend within the Tool and Die manufacturing sector is to machine components directly from hardened material using high speed 5-axis machining. This has been driven by the increasing requirements for cost competitiveness and lead-time reduction. Significant research effort has been applied to the optimisation of the process with factors such as tooling and machining strategies being considerably improved. However, the underlying structures of the machine tools used have remained unchanged and still consist of a serial kinematic chain. One of the standard justifications for the development of machines designed around parallel kinematic chains is that they should exhibit inherently greater stiffness, have higher axis accelerations and be capable of generating significantly higher cutting forces than conventional serial machines. This suggests that they should be ideally suited to the direct manufacture of tools and dies from hardened material. The comparison of different machine tool types is a complex and difficult process, particularly when their structures are fundamentally different. This paper describes an approach used to compare the performance of three very different types of machines. The technique uses two parameters; surface finish and geometric accuracy to assess the relative performance of different machine tools when cutting hardened material. The method is used to compare a serial kinematic 5-axis machining centre, a serial kinematic 3-axis machining centre and a parallel kinematic 6-axis machining centre. The results of the comparison are presented in this paper wand show that all the machine tools performed to an equal standard for materials with a hardness of 54HRc but for very hard materials, 62HRc, the parallel kinematic machine out performed the serial machine tools.

A Hybrid Fuzzy Knowledge-Based Expert System and Genetic Algorithm for efficient selection and assignment of Material Handling Equipment

Material Handling (MH) is one of the key issues for every production site and has a great impact on manufacturing costs. The core concern in the design of a MH system is selecting the most suitable equipment for every MH operation and optimising them totally in order to attain an optimum solution. This paper presents a hybrid method for the selection and assignment of the most appropriate Material Handling Equipment (MHE). In the first phase, the system selects the most appropriate MHE types for every MH operation in a given application using a Fuzzy Knowledge-Based Expert System consisting of two sets of rules: Crisp Rules and Fuzzy Rules. In the second phase, a Genetic Algorithm (GA) searches throughout the feasible solution space, constituting of all possible combinations of the feasible equipment specified in the previous phase, in order to discover optimum solutions. The validity of the methodology developed in this paper is proved through the use of a real problem. Finally a comparison of the method with the other available publicised methods reveals the effectiveness of this hybrid approach.

Measurement assisted robotic assembly of fabricated aero‐engine components

Purpose – The purpose of this paper is to describe the measurement‐assisted assembly of aero‐engine fabricated components and evaluate its capability.Design/methodology/approach – The system described in this paper uses in‐process measurement sensors to determine the components exact location prior to the assembly operation. The core of the system is a set of algorithms capable of best fitting measurement data to find optimal assembly of components.Findings – The paper demonstrates that with a combination of non‐contact metrology systems and mathematical processing, standard industrial robot can be used to assemble fabricated components. Scanning parts after it has been picked up was very effective as it compensates for possible components deformation during previous manufacturing processes and robot handling errors.Originality/value – The paper introduces techniques for compensating the deformation that occurs in aero‐engine fabricated components and potential component handling errors. The developed sy...

Metrology-assisted robotic processing of aerospace applications

Modern aerospace structures tend to consist of large numbers of geometrically complex structural components which by their very nature tend to suffer from significant levels of physical distortion and are thus difficult to assemble. One solution to this problem is to use large complex jigs which physically control the shape of the parts. These jigs are usually loaded using either direct manual labour or manual labour assisted by cranes or lifting devices. The use of manual operations represents a significant health and safety risk and increased likelihood of damaging components during assembly. The application of automation in the processing of such structures has so far been confined to small product specific cells owing to difficulties in pre-defining and fixing the exact geometry and positioning of parts within the work volume. The use of specially designed jigs, fixtures and aids such as drilling templates can be adapted to support automation but are expensive, have long manufacturing lead times and cannot be economically modified for use on other aircraft types. The paper proposes a solution to the above problems using standard industrial robots and an advanced control and non-contact metrology systems. The developed methodology is generic and has been evaluated and demonstrated in a number of different applications. The application described in this paper is the assembly of regional jet fuselage panels. Results are presented along with an analysis of the accuracy and repeatability of the system and its elements.

An improved kinematic model for calibration of serial robots having closed-chain mechanisms

Many industrial robots employ closed-loop actuating elements such as the parallelogram mechanism for increased stiffness. Modeling these manipulators for the purpose of calibration presents a challenge due to complex nonlinear couplings between parameters of the chains. The modeling method presented in this paper involves the integration of the open-and closed-loop elements whose errors can be resolved as linear functions of their parameters. As a result, the model is similar to that of a serial-link robot, which makes it possible to use existing well-defined calibration techniques in the area. Simulation and experimental studies on an industrial robot for verifying the correctness and effectiveness of the proposed model are also described.

A sub goal seeking approach for reactive navigation in complex unknown environments

Reactive-based approaches are widely used in autonomous navigation. However, in complex unknown environments, pure reactive-based navigation still poses a few challenges since it can be easily trapped by a local minimum and may produce some extra manoeuvres. This paper presents the design of a reactive-based approach for navigation in complex and unknown environments called sub goal seeking, in which depth point maps of the environment are analysed to extract free spaces around the robot. These spaces are then evaluated the one that is most likely to lead to the final goal is chosen as a sub goal. The robot then drives towards these sub goals, instead of the final goal until it is visible. By analysing the environmental structure, dead-ends within robot sensory range are able to be detected thus reducing the chance of being trapped and also reducing unnecessary manoeuvres. This paper also evaluates the performance of the sub goal seeking approach using three criteria, goal achievable ability, safety and maneuvering through extensive simulation and real mobile robot experiments.

Development of a hybrid crisp-fuzzy logic algorithm optimised by genetic algorithms for path-planning of an autonomous mobile robot

This paper deals with the problem of autonomous mobile robot navigating in unknown environments. The approach developed is reactive in a behaviour-based framework aimed at multiple obstacle avoidance. We use a novel hybrid logic integrating fuzzy and crisp to enable the robot with a human like decision-making ability and avoid failure when world set-ups mismatch with the fuzzy system designer expectancies. Finally, a genetic algorithm is used as means of optimised search within the space of the fuzzy parameters of the hybrid system.

The integration of contactless static pose recognition and dynamic hand motion tracking control system for industrial human and robot collaboration

Purpose – The purpose of this paper is to describe the integration of a gesture control system for industrial collaborative robot. Human and robot collaborative systems can be a viable manufacturing solution, but efficient control and communication are required for operations to be carried out effectively and safely. Design/methodology/approach – The integrated system consists of facial recognition, static pose recognition and dynamic hand motion tracking. Each sub-system has been tested in isolation before integration and demonstration of a sample task. Findings – It is demonstrated that the combination of multiple gesture control methods can increase its potential applications for industrial robots. Originality/value – The novelty of the system is the combination of a dual gesture controls method which allows operators to command an industrial robot by posing hand gestures as well as control the robot motion by moving one of their hands in front of the sensor. A facial verification system is integrated ...

A reactive reconfigurable tool for aerospace structures

Purpose – The purpose of this paper is to describe the development, testing and scientific evaluation of a novel, load‐cell‐controlled reactive reconfigurable tooling (RRT) solution. This RRT not only addresses the underlying inherent problems with traditional reconfigurable tools but also potentially expands their use into the area of condition monitoring.Design/methodology/approach – The paper covers the design intent and methodology. The construction and evaluation of both a simple prototype and a fully functional tool are described.Findings – The tool was successfully demonstrated using friction stir welding (FSW) of fuselage panels as a demanding application and the full functionality of the tool was demonstrated. The condition and process monitoring system was also demonstrated and shown to be able to distinguish both between different types of weld and tool failure conditions.Research limitations/implications – Having successfully designed and tested the novel RRT system under the extreme condition...

Justification for the selection of manufacturing technologies: a fuzzy-decision-tree-based approach

In this paper, a developed model for the justification of alternative manufacturing technologies is presented. The approach, based on fuzzy decision trees, provides a methodology capable of identifying patterns within a technology case repository to support the evaluation of manufacturing systems. Experts are highly influential individuals in the decision process; they provide support and guidance when selecting investments. The experience-oriented task is founded on previous cases or an experts’ experience, and therefore difficult to express in a rational form. The concept is based on a number of characteristics of the case-based reasoning, rule induction and expert system theory. Structured around the fuzzy-decision-tree data-mining technique, the framework provides the ability of using regulated case information to act as structured experience for assisting in the decision process. Fuzzy induction extracts formal rules from a set of experience data, and the expert system philosophy computes the experience base of human expertise for problem-solving. A test case indicates the stability of the classification algorithm and verifies the applicability within the domain.