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An investigation into the applicability of the bond-graph methodology, using the so-called Model Transformation Tools software, has been undertaken to model parallel robots. This software is a novel, non-commercial, program developed at the University of Glasgow, and in addition to the standard bond graph, it contains a powerful tool called the Hierarchical Bond Graph for dealing with very large-scale dynamical systems. It is the first time this tool has been applied for the modelling of parallel manipulators. A General Method for modelling parallel robots using the Hierarchical Bond-Graph concept has been developed. The method is based on related work on the modelling of closed chain robots using the Lagrange method. Introduction of a new design concept to be known as the Multi-cell Parallel Planar Manipulator. The methodology allows for an increase in the workspace of the manipulator by increasing the number of cells without affecting the number of DOF. It can also be shown to enhance the manoeuvrability of the system. Application of the multi-cell approach to a specific 2-DOF planar parallel manipulator and recognition of the need for a general model led to the development of a general dynamic model for the multi-cell manipulator using the Lagrange method. The reason for using the Lagrange formulation is that the necessary generalisation cannot be formalised using the Bond Graph technique due to the dependency of a bond graph on the specified structure of the system being modelled. Static balancing of the new general manipulator was addressed and a new method for balancing has been introduced. The method reduces the number of parameters to be adjusted to only one.

This thesis explores the different aspects of robotic manipulator modelling and covers both the dynamic and the kinematic issues for the purpose of improving the overall manipulator accuracy. It is shown that the modelling should not stop at producing the model, but rather the model should be validated. The thesis presents a description of the modelling process and examines the three most important formulations for dynamic modelling. A comparison of their performance and ease of use is made, both for manual and computer assisted implementation. Three commercial computer modelling packages are also described and compared with regard to their performance and ease of use for robotic manipulator modelling. It is shown that some software development is required to make the packages easy to use for manipulator specific modelling. As part of this work, one such development was a programme written as a back end to AUTOLEV. This combination provides a powerful tool for dynamic modelling and simulation of manipulators. A more integrated computer aided engineering approach is also discussed through modelling a large industrial manipulator using a geometric modelling package along with another dynamic modelling and simulation program. This approach is very efficient in providing useful information which is difficult to otherwise obtain from direct measurements. The thesis emphasises validation as part of the modelling process. A model does not have to be an exact mathematical description of the manipulator, inclusive of all characteristics, but rather a valid description for the intended use. It is shown that a manipulator model can be split into several joint models and validation performed on each using a parameter estimation technique. It is also shown that friction parameter tuning produces acceptable parameter values for a valid model of a Puma 560 manipulator.

Many applications exist for unmanned vehicles, factory maintenance, planetary exploration, in reactor inspection etc. Robotic systems will inhabit a world which will contain obstacles, these obstacles will threaten their pursuit of a successful goal. In all but the most simple and benign environment these obstacles will be in motion. The presence or location of an obstacle will not be known a priori. Therefore in order to build practical, useful robots a means of sensing the environment in order to determine traversable/non-traversable space needs to be developed. In addition, to prevent them from becoming lost, practical robots will be required to generate an estimate of where they are in the world in relation to known features, this capability is referred to as localisation. Clearly the primary sense for determining traversable spaces is sight. However current research into machine vision has produced systems that are either too slow, too specific (i.e. related to a particular problem domain rather than a general one) to too unreliable. These factors have lead to the development of an active sensor, the motion structured light sensor. This sensor solves the ill-posed problem and the problem of large data rates by illuminating the world with a laser sheet and determining 3D topography from the image of the intersection of this sheet and the world. The sensor has been developed to detect and track moving obstacles over time and has also been used as a means of vehicle localisation with respect to an a priori map. Although vision, and in particular structured light, is a useful source of topographic information, other sensors offer the ability to determine the presence of geometric features in a scene, such as ultrasonic sensors and laser rangefinders. Motivated by the desire to generate richer descriptions of world state from disparate information sources the research area of Multi Sensor Data Fusion (MSDF) is addressed. A mechanism for combining information based on the first and second order statistics available from the Kalman filter is presented. The MSDF system is applied i) in simulation to a second order plant and ii) to a laboratory based robot. This approach leads to greater accuracy of state estimation which leads to greater system robustness and robustness with respect to sensor failure / sensor error. This thesis therefore presents a method of generating more accurate estimates of state by using multiple sources of information. This enables systems to be built that are more robust, not only due to the fact that state estimates are more accurate but also due to the fact that these systems will possess mutliple redundancy through the use of multiple sensors. It is shown that the use of multiple sensors also enables the system to become more robust with respect to the poor chose of noise models required by the Kalman filter.

The work described in this thesis is concerned with the performance of the mechanical system of a mobile robot that is capable of omnidirectional motion. The main attribute of such mobile robots is that their direction of motion is independent of chassis orientation. This attribute endows them with exceptional manoeuvrability, but it is also found to pose substantial problems by changing the level of accuracy and stability of the robot as its direction of travel changes. The main objective of the research is to conduct a detailed evaluation of the performance of a mobile robot which is capable of omnidirectional movement achieved by means of a synchronized all-wheel steering and all-wheel drive (Synchro-drive) technique. The objective is met by comparing the synchro-drive method with other configurations used for mobile robots, by comparing different designs of the synchro-drive method and by analyzing synchro-drive mechanical behaviour in response to drive and steering inputs. A kinematic model of the synchro-drive arrangement is formulated and this is used to analyze different designs and to assess the limits of the control variables beyond which a Synchro-Drive Mobile Robot (SDMR) operation will become unstable. A new version of the synchro-drive arrangement was developed and was used to perform extensive practical testing in order to determine factors affecting positional accuracy and the trajectory actually executed by the mobile robot. The analysis of the boundaries of the control space revealed the limits on acceleration which may be allowed by the robot's control system for it to remain stable. It also showed that the acceleration limits depend on the angle between the wheel heading and the chassis orientation, which is defined as the robot's posture. Practical experimentation identified the major influences on robot accuracy and also related the form, magnitude and direction of these errors to the robot's posture. The experiments revealed that the errors were due partly to aspects of the design itself and partly due to inevitable errors in the complete mechanical system. A continuous position error correction method is proposed which uses experimental data as the basis for correction. Correction quantities vary with posture, and the method uses a modification to the steering rate to minimize trajectory error. Overall the study reveals the factors which must be considered to enable the potential of the synchro-drive mobile robot to be fully realized.

For adaptive motion control of an autonomous vehicle, operating in a generally structured environment, position and velocity feedback are required to ascertain the vehicle location relative to a reference. Whilst the literature offers techniques for guiding vehicles along external references, autonomous vehicles should be able to navigate between despatch locations without the need to rely on external guidance systems. Considerations of the vehicle stability and manoeuvrability favour a vehicle design with four independently steered wheels. A new motion control methodology has been proposed which utilises the geometric relationship of the angular displacements and the rotations of the wheels to estimate the longitudinal and lateral motions of the vehicle. The motion controller consists of three building blocks: the motion control system comprising the position tracking and the motion command generation; the electronic system comprising a data acquisition system and proprietary power electronics; the mechanical system which includes an undercarriage enabling permanent contact of the wheels with the floor. The components have been designed not only to perform optimally in their specific functions but also to ensure full compatibility within the integrated system. For reliable deduction of the wheel rotations with a high degree of accuracy a dedicated data acquisition interface has been developed, which enables data to be captured in parallel from four optical encoders mounted directly on the wheel axles. Parallel sampling of the angular wheel position and parallel actuation of all steering motors improves the accuracy of the system state and gives a higher degree of certainty. Considering only circular motion of the vehicle, a method for calculating the steering angles and wheel speeds based on the complex notation is presented. By cumulating the displacement vectors of the vehicle motion and the location of the centre of rotation between consecutive samples of the controller, the path of the vehicle is estimated. The difference between the nominal and the deduced centre of rotation is determined to minimise deviations from the reference trajectory and to allow the controller to adapt to changes in the road/tyre interface characteristics. The individual mechanical and electronic components have been assembled and tested. Additionally, the performance of the electronic interface has been evaluated on a purpose built test-bed. For the experimental validation of the methodology, a simple method of mapping the centre of curvature with a pen mounted at the nominal centre of rotation has been proposed. Experiments have been conducted with both the steering angles fixed to their theoretical values for the nominal centre of rotation and with the proportional steering controller enabled. The results from the latter method have shown a significantly reduced deviation from the nominal centre of rotation. The data captured of the angular wheel positions and steering angle settings has been analysed off-line. Good agreement is obtained between the deduced and the actual centres of rotation for the measurements averaged over 1.5 seconds. A number of different centres of rotation have been investigated and the required steering angles to compensate for the deviation have been plotted to form a control surface for the motion controller. The deviation between the estimated and the actual centre of curvature was less than 1.6% and adequate results could be obtained with the proportional steering controller.

No description available.

No description available.

No description available.