Browsing by Author "McMaster, R."
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Item Open Access An adaptive control system for off-line programming in robotic gas metal arc welding.(Cranfield University, 1997-10) Carvalho, G. C.; McMaster, R.The aim of this work was to develop an integration concept for using off-line programming in robotic gas metal arc welding of thin sheet steel. Off line -welding parameter optimization and on-line monitoring and adaptive control of process stability and torch-to-workpiece relative distance were used to ensure weld consistency. The concept developed included four main aspects: a) the use of a CAD system to design the workpiece; b) the use of a welding off-line programming system to design the welds, generate the welding parameters and to extract geometrical information from the CAD models to generate a robot program; c) the use of a graphical simulation system to simulate the robot movements; and d) the use of monitoring and adaptive control for ensuring that the required weld quality is delivered. The CAD system was chosen to be the basis for the development of the welding off-line programming system. The generation of optimized welding parameters was based on empirical welding models and the robot program generation was based on on-line programming experience. A PC based monitoring and control system was developed to provide on-line position and process control. The position control was carried out by pre-weld adjusting the initial position of the workpiece using a wire touch sensor and on-line adjusting the torch-to-workpiece distance by moving the workpiece based on the information provided by a through-the-arc sensor. The process control was carried out by automatically trimming the welding voltage such that the most stable process could be obtained. The stability of the process was estimated by using previously established monitoring indices. It was assumed that the off-line welding parameter optimization would provide the deposition rate necessary to produce the required weld quality. Successful welding control trials were performed showing the effectiveness of the adaptive control strategy. An off-line programming system has been developed and the programs generated have been tested by simulation. This showed that simulated positioning errors, produced by deliberate wrong path data, were successfully compensated for by the control system developed in this work.Item Open Access Automated off-line programming for Rapid Prototyping using Gas Metal Arc Welding(Cranfield University, 1995-06) Ribeiro, A. F. M.; Norrish, J.; McMaster, R.Rapid Prototyping is a recent CAD/CAM based manufacturing technique which produces prototypes of components in a fraction of the time normally required. This technique normally involves drawing the part as a 3 Dimensional solid model using a CAD program and then 'printing' it in 3 Dimensions. The raw material can be a photopolymer or thermoplastic which solidifies when in contact with light. Other materials are available although producing the final parts a 100% metal is not very usual. Some disadvantages of these techniques are: a) 100% metal prototypes cannot normally be made directly. b) only prototypes can be produced instead of the final component. c) machine size limits the size of the final component. d) very thin layers are deposited. This makes the build up more time consuming and mostly suitable to small components. The main objective of this work was to overcome these disadvantages by creating a new Rapid Prototyping technique using Robot Fusion Welding. In the pre-production phase, it is important to make a prototype not only for visualisation but also to test and assess it in its real function. Therefore, prototyping in resin a component which is going to be made in metal has no use for assessing purposes. This technique, besides making the prototype in metal can also be used as a production technique to make the real usable final component. It even allows the use of different metals along its structure in the welding filler wire is changed. This makes it possible to have different structural characteristics in the same component a required. None of the slicing algorithms developed for other Rapid Prototyping processes were applicable to this new technique and therefore a new slicing concept (and routine) was created specifically. I addition, an interface for off-line programming and quality documentation was evolved. The technique developed has been tested by fabricating several 'test' components and both the dimensional accuracy and component integrity have been evaluated and proved to be successful.Item Open Access On the effectiveness and efficiency of discrete-event simulation for designing manufacturing systems(Cranfield University, 2000-06) Potter, J.; Greenough, Richard; McMaster, R.; Sweeney, M.; Stone, K.This thesis investigates the effectiveness (doing the right thing) and efficiency (doing the thing right) of computer-based discrete-event simulation for designing manufacturing systems. This investigation looked at the use of this technology in the manufacture of discrete components in aerospace, automotive and consumer electrical (white goods) industries and for material handling (warehousing). Continuous and quasi-continuous manufacture have not been investigated and hence, the conclusions of this thesis cannot be generalised to cover these areas. Working hypotheses were developed and tested which looked at how discrete-event simulation influences the understanding of, confidence in and credibility of a system's design. Testing these working hypotheses lead to conclusions about how discrete-event simulation affects the quality of decision making and the lead-time to develop, commission and ramp-up a manufacturing facility. The following five factors were identified as influencing the efficiency of delivery of discrete-event simulation: l. Management of the simulation study and its intended benefits. 2. Management of customers' expectations. 3. Use of geometric animation. 4. Validation and establishing credibility. 5. How simulation's effectiveness varies over the life of a manufacturing system development project. A qualitative research methodology was employed to test these working hypotheses and to explore these efficiency factors. Twenty-three research subjects, in twelve companies, were drawn from the following three groups: ° Modellers (who provide the modelling service). ° Team members (who are closely involved with supporting the execution of a simulation study). Senior decision makers (who are not closely involved with the execution of the study, but who review its findings). A good practice model was developed for the efficient acquisition and application of the technology. This model consists of the following six elements: 1. Establishing and maintaining a DES modelling capability in the organisation. 2. Knowing whether to use DES modelling for this manufacturing system and when. 3. Defining the study's objectives and their means of measurement. 4. Specify responsibilities for supporting the study and implementing its findings. 5. There is no improvement in the effectiveness of DES modelling in using 2D rather than 3D geometric animation. 6. 3D geometric animation can increase the efficiency of a study, if used appropriately. Conclusions were made about the effectiveness of discrete-event simulation, how the above mentioned factors influence its efficiency of delivery and how to implement the good practice model.Item Open Access Optimised robot calibration using a vision-based measurement system with a single camera(Cranfield University, 1999-03) Motta, J. M. S. T.; McMaster, R.Robot calibration plays an increasingly important role in robot production as well as in robot operation and integration within computer integrated manufacturing or assembly systems. The production, implementation and operation of robots are issues where robot calibration results can lead to significant accuracy improvement and/or cost- savings. The thesis describes techniques for modelling, optimising and performing robot calibration processes using a 3-D vision-based measurement system for off-line programming. The identification of the nonrlnal kinematic model is optimised using numerical methods to eliminate redundant geometric parameters in the model. Calibration based on the optimised model shows improvement in robot accuracy when compared to the non-optimised model. The basics of the measurement system consist of a single CCD camera mounted on the robot tool flange, image processing software, and algorithms specially developed to measure the end-effector pose relative to a world coordinate system. Geometric lens distortions are included in the analytical technique. The target consists of two identical clusters of calibration points printed on photographic paper, and mounted on the sides of a 90-degree angle plate. Experimental work was performed to assess the measurement system accuracy at different distances from the camera to the target. An average accuracy from O.2mm to O.4mm was obtained at distances between 6S0mm to 9S0mm. Tests were also performed on three different robots to assess the improvement in the overall robot accuracy. The robots tested were: PUMA-SOO, IRB-2400 and IRB-6400. The errors before calibration for the three robots were approximately in a range from Smm to lSmm if measured in a large volume. The best average accuracy obtained after the calibration of the three robots was O.3Smm, O.60mm and O.4Smm respectively. This study shows that many different variables are involved in the calibration process. The influence of these variables was studied both experimentally and by means of simulation.