Coordinated Control of a Mobile Manipulator

In this technical report, we investigate modeling, control, and coordination of mobile manipulators. A mobile manipulator in this study consists of a robotic manipulator and a mobile platform, with the manipulator being mounted atop the mobile platform. A mobile manipulator combines the dextrous manipulation capability offered by fixed-base manipulators and the mobility offered by mobile platforms. While mobile manipulators offer a tremendous potential for flexible material handling and other tasks, at the same time they bring about a number of challenging issues rather than simply increasing the structural complexity. First, combining a manipulator and a platform creates redundancy. Second, a wheeled mobile platform is subject to nonholonomic constraints. Third, there exists dynamic interaction between the manipulator and the mobile platform. Fourth, manipulators and mobile platforms have different bandwidths. Mobile platforms typically have slower dynamic response than manipulators. The objective of the thesis is to develop control algorithms that effectively coordinate manipulation and mobility of mobile manipulators. We begin with deriving the motion equations of mobile manipulators. The derivation presented here makes use of the existing motion equations of manipulators and mobile platforms, and simply introduces the velocity and acceleration dependent terms that account for the dynamic interaction between manipulators and mobile platforms. Since nonholonomic constraints play a critical role in control of mobile manipulators, we then study the control properties of nonholonomic dynamic systems, including feedback linearization and internal dynamics. Based on the newly proposed concept of preferred operating region, we develop a set of coordination algorithms for mobile manipulators. While the manipulator performs manipulation tasks, the mobile platform is controlled to always bring the configuration of the manipulator into a preferred operating region. The control algorithms for two types of tasks - dragging motion and following motion - are discussed in detail. The effects of dynamic interaction are also investigated. To verify the efficacy of the coordination algorithms, we conduct numerical simulations with representative task trajectories. Additionally, the control algorithms for the dragging motion and following motion have been implemented on an experimental mobile manipulator. The results from the simulation and experiment are presented to support the proposed control algorithms

Control of an anthropomorphic manipulator involved in physical human-robot interaction

Dissertação de mestrado em Engenharia MecânicaThe objective of the dissertation is to flexibly control the end effector velocity of a redundant 7-DOF manipulator by using a differential kinematics approach, while ensuring the safety of the robotic arm from exceeding the physical limits of joints in terms of position, velocity and acceleration. The thesis also contributes with a real-time obstacle avoidance strategy for controlling anthropomorphic robotic arms in dynamic obstacle environments, taking account of sudden appearances or disappearances of mobile obstacles. A method for compensating force errors due to changes in the orientation of end effectors, independent from structures of force sensors, is developed to achieve high accuracy in force control applications. A novel method, the Virtual Elastic System, is proposed to control mobile manipulators for physical Human-Robot Interaction (pHRI) tasks in dynamic environments, which enables the combination of an Inverse Differential Kinematics for redundant robotic arms and a Dynamical Systems approach for nonholonomic mobile platforms. Experiments with a 7-DOF robotic arm, side-mounted on a nonholonomic mobile platform, are presented with the whole robot obstacle avoidance, proving the efficiency of the developed method in pHRI scenarios, more specifically, cooperative human-robot object transportation tasks in dynamic environments. Extensions of the method for other mobile manipulators with holonomic mobile platforms or higher degrees of freedom manipulators are also demonstrated through simulations

Enabling a Pepper Robot to provide Automated and Interactive Tours of a Robotics Laboratory

The Pepper robot has become a widely recognised face for the perceived potential of social robots to enter our homes and businesses. However, to date, commercial and research applications of the Pepper have been largely restricted to roles in which the robot is able to remain stationary. This restriction is the result of a number of technical limitations, including limited sensing capabilities, and have as a result, reduced the number of roles in which use of the robot can be explored. In this paper, we present our approach to solving these problems, with the intention of opening up new research applications for the robot. To demonstrate the applicability of our approach, we have framed this work within the context of providing interactive tours of an open-plan robotics laboratory.Comment: 8 pages, Submitted to IROS 2018 (2018 IEEE/RSJ International Conference on Intelligent Robots and Systems), see https://bitbucket.org/pepper_qut/ for access to the softwar

Mechanical design of a four wheel omni directional mobile robot

Mestrado em ESTG-IPBOmni directional mobile robots have been popularly employed in several applications, especially in soccer player robots considered in Robocup competitions. Actually, the popular optimized robots are using three wheels in the mechanical structure. This situation brings the idea of omnidirectional robot at manufacturing. To design the omnidirectional wheels mobile robot respecting the requirement specifications of the factory lite competition, it’s recommended to design and optimize the proposed solution using Solidworks tool. To design a mobile robot using four omni wheels, it’s important to implement suspension system for each wheel. The suspension system will help the programmer when implementing the PID parameters and test the robot. Such a robot can respond more quickly and it would be capable of more sophisticated behaviors such as to transport materials and placed on processing machine and outgoing warehouses. This thesis has tried to focus the description of four wheel omnidirectional mobile robot to be applied to the Factory Lite competition

DESIGN AND DEVELOPMENT OF AN OMNIDIRECTIONAL MOBILE BASE FOR A SOCIAL ROBOT

Master'sMASTER OF ENGINEERIN

Design and implementation of haptic interactions

This thesis addresses current haptic display technology where the user interacts with a virtual environment by means of specialized interface devices. The user manipulates computer generated virtual objects and is able to feel the sense of touch through haptic feedback. The objective of this work is to design high performance haptic interactions by developing multi-purpose virtual tools and new control schemes to implement a PUMA 560 robotic manipulator as the haptic interface device. The interactions are modeled by coupling the motions of the virtual tool with those of the PUMA 560 robotic manipulator;The work presented in this dissertation uses both kinematic and dynamic based virtual manipulators as virtual simulators to address problems associated in both free and constrained motions. Both implementations are general enough to allow researchers with any six degree-of-freedom robot to apply the approaches and continue in this area of research. The results are expected to improve on the current haptic display technology by a new type of optimal position controller and better algorithms to handle both holonomic and nonholonomic constraints;Kane\u27s method is introduced to model dynamics of multibody systems. Multibody dynamics of a virtual simulator, a dumbbell, is developed and the advantages of the Kane\u27s method in handling the non-holonomic constraints are presented. The resulting model is used to develop an approach to dynamic simulation for use in interacting haptic display, including switching constraints. Experimental data is collected to show various contact configurations;A two-degree of freedom virtual manipulator is modeled to feel the surface of a taurus shape. An optimal position controller is designed to achieve kinematic coupling between the virtual manipulator and the haptic display device to impose motion constraints and the virtual interactions. Stability of the haptic interface is studied and proved using Lyapunov\u27s direct method. Experimental data in various positions of the robotic manipulator is obtained to justify theoretical results. A shift mechanism is then implemented on the taurus shape, thus the motions of the robotic manipulator is further constrained. The difficulties in handling the motion constraints are discussed and an alternative approach is presented

Path and Motion Planning for Autonomous Mobile 3D Printing

Autonomous robotic construction was envisioned as early as the ‘90s, and yet, con- struction sites today look much alike ones half a century ago. Meanwhile, highly automated and efficient fabrication methods like Additive Manufacturing, or 3D Printing, have seen great success in conventional production. However, existing efforts to transfer printing technology to construction applications mainly rely on manufacturing-like machines and fail to utilise the capabilities of modern robotics. This thesis considers using Mobile Manipulator robots to perform large-scale Additive Manufacturing tasks. Comprised of an articulated arm and a mobile base, Mobile Manipulators, are unique in their simultaneous mobility and agility, which enables printing-in-motion, or Mobile 3D Printing. This is a 3D printing modality, where a robot deposits material along larger-than-self trajectories while in motion. Despite profound potential advantages over existing static manufacturing-like large- scale printers, Mobile 3D printing is underexplored. Therefore, this thesis tack- les Mobile 3D printing-specific challenges and proposes path and motion planning methodologies that allow this printing modality to be realised. The work details the development of Task-Consistent Path Planning that solves the problem of find- ing a valid robot-base path needed to print larger-than-self trajectories. A motion planning and control strategy is then proposed, utilising the robot-base paths found to inform an optimisation-based whole-body motion controller. Several Mobile 3D Printing robot prototypes are built throughout this work, and the overall path and motion planning strategy proposed is holistically evaluated in a series of large-scale 3D printing experiments

Wheeled Mobile Robots: State of the Art Overview and Kinematic Comparison Among Three Omnidirectional Locomotion Strategies

In the last decades, mobile robotics has become a very interesting research topic in the feld of robotics, mainly because of population ageing and the recent pandemic emergency caused by Covid-19. Against this context, the paper presents an overview on wheeled mobile robot (WMR), which have a central role in nowadays scenario. In particular, the paper describes the most commonly adopted locomotion strategies, perception systems, control architectures and navigation approaches. After having analyzed the state of the art, this paper focuses on the kinematics of three omnidirectional platforms: a four mecanum wheels robot (4WD), a three omni wheel platform (3WD) and a two swerve-drive system (2SWD). Through a dimensionless approach, these three platforms are compared to understand how their mobility is afected by the wheel speed limitations that are present in every practical application. This original comparison has not been already presented by the literature and it can be used to improve our understanding of the kinematics of these mobile robots and to guide the selection of the most appropriate locomotion system according to the specifc application