13 research outputs found

    Velocity constrained trajectory generation for a collinear Mecanum wheeled robot

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    While much research has been conducted into the generation of smooth trajectories for underactuated unstable aerial vehicles such as quadrotors, less attention has been paid to the application of the same techniques to ground based omnidirectional dynamically balancing robots. These systems have more control authority over their linear accelerations than aerial vehicles, meaning trajectory smoothness is less of a critical design parameter. However, when operating in indoor environments these systems must often adhere to relatively low velocity constraints, resulting in very conservative trajectories when enforced using existing trajectory optimisation methods. This paper makes two contributions; this gap is bridged by the extension of these existing methods to create a fast velocity constrained trajectory planner, with trajectory timing characteristics derived from the optimal minimum-time solution of a simplified acceleration and velocity constrained model. Next, a differentially flat model of an omnidirectional balancing robot utilizing a collinear Mecanum drive is derived, which is used to allow an experimental prototype of this configuration to smoothly follow these velocity constrained trajectories

    Dual-mode model predictive control of an omnidirectional wheeled inverted pendulum

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    This article describes the position and heading control of a novel form of omnidirectional wheeled inverted pendulum platform known as a Collinear Mecanum Drive. This concept uses four collinear Mecanum wheels to balance in a similar manner to a typical two-wheeled inverted pendulum, whilst also being able to simultaneously translate directly along its balance axis. Control is performed using a constrained time-optimal infinite horizon model predictive controller, with feasibility maintained across the full reference input set. Explored in this article is the derivation of the system dynamics model and controller, a systematic approach to selection of controller parameters and analysis of their effect on control performance and complexity, and an evaluation of the controller's efficacy in both simulation and on a real-world experimental prototype for simple and complex trajectories

    Collinear mecanum drive: modelling, analysis, partial feedback linearisation, and nonlinear control

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    The Collinear Mecanum Drive (CMD) is a novel robot locomotion system, capable of generating omnidirectional motion whilst simultaneously dynamically balancing, achieved using a collinear arrangement of three or more Mecanum wheels. The CMD has a significantly thinner ground footprint than existing omnidirectional locomotion methods, which does not need to be enlarged with increasing robot height as to avoid toppling during acceleration or external disturbance. This combination of omnidirectional manoeuvrability and a thin ground footprint allows for the creation of tall robots that are able to navigate through much narrower gaps between obstacles than existing omnidirectional locomotion methods. This allows for greater manoeuvrability in confined and cluttered environments, such as that encountered in the personal service and automated warehousing robotics sectors. This article derives the kinematics and dynamics models of the CMD, analyses controllability and accessibility, and determines the degree to which a CMD can be linearised by feedback. A partial feedback linearisation is then performed, and three practically useful nonlinear controllers are derived using a backstepping design approach, all with convergence and stability guarantees for the fully-coupled nonlinear model. These are demonstrated both in simulation and on a real-world CMD experimental prototype

    MIRRAX: A Reconfigurable Robot for Limited Access Environments

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    The development of mobile robot platforms for inspection has gained traction in recent years with the rapid advancement in hardware and software. However, conventional mobile robots are unable to address the challenge of operating in extreme environments where the robot is required to traverse narrow gaps in highly cluttered areas with restricted access. This paper presents MIRRAX, a robot that has been designed to meet these challenges with the capability of re-configuring itself to both access restricted environments through narrow ports and navigate through tightly spaced obstacles. Controllers for the robot are detailed, along with an analysis on the controllability of the robot given the use of Mecanum wheels in a variable configuration. Characterisation on the robot's performance identified suitable configurations for operating in narrow environments. The minimum lateral footprint width achievable for stable configuration (<2o<2^\text{o}~roll) was 0.19~m. Experimental validation of the robot's controllability shows good agreement with the theoretical analysis. A further series of experiments shows the feasibility of the robot in addressing the challenges above: the capability to reconfigure itself for restricted entry through ports as small as 150mm diameter, and navigating through cluttered environments. The paper also presents results from a deployment in a Magnox facility at the Sellafield nuclear site in the UK -- the first robot to ever do so, for remote inspection and mapping.Comment: 10 pages, Under review for IEEE Transactions on Robotic

    Bio-Inspired Robotics

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    Modern robotic technologies have enabled robots to operate in a variety of unstructured and dynamically-changing environments, in addition to traditional structured environments. Robots have, thus, become an important element in our everyday lives. One key approach to develop such intelligent and autonomous robots is to draw inspiration from biological systems. Biological structure, mechanisms, and underlying principles have the potential to provide new ideas to support the improvement of conventional robotic designs and control. Such biological principles usually originate from animal or even plant models, for robots, which can sense, think, walk, swim, crawl, jump or even fly. Thus, it is believed that these bio-inspired methods are becoming increasingly important in the face of complex applications. Bio-inspired robotics is leading to the study of innovative structures and computing with sensory–motor coordination and learning to achieve intelligence, flexibility, stability, and adaptation for emergent robotic applications, such as manipulation, learning, and control. This Special Issue invites original papers of innovative ideas and concepts, new discoveries and improvements, and novel applications and business models relevant to the selected topics of ``Bio-Inspired Robotics''. Bio-Inspired Robotics is a broad topic and an ongoing expanding field. This Special Issue collates 30 papers that address some of the important challenges and opportunities in this broad and expanding field

    Performance evaluation and development of a synchro-drive mobile robot

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    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
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