Design and Control of Compliant Actuation Topologies for Energy-Efficient Articulated Robots

Considerable advances have been made in the field of robotic actuation in recent years. At the heart of this has been increased use of compliance. Arguably the most common approach is that of Series-Elastic Actuation (SEA), and SEAs have evolved to become the core component of many articulated robots. Another approach is integration of compliance in parallel to the main actuation, referred to as Parallel- Elastic Actuation (PEA). A wide variety of such systems has been proposed. While both approaches have demonstrated significant potential benefits, a number of key challenges remain with regards to the design and control of such actuators. This thesis addresses some of the challenges that exist in design and control of compliant actuation systems. First, it investigates the design, dynamics, and control of SEAs as the core components of next-generation robots. We consider the influence of selected physical stiffness on torque controllability and backdrivability, and propose an optimality criterion for impedance rendering. Furthermore, we consider disturbance observers for robust torque control. Simulation studies and experimental data validate the analyses. Secondly, this work investigates augmentation of articulated robots with adjustable parallel compliance and multi-articulated actuation for increased energy efficiency. Particularly, design optimisation of parallel compliance topologies with adjustable pretension is proposed, including multi-articulated arrangements. Novel control strategies are developed for such systems. To validate the proposed concepts, novel hardware is designed, simulation studies are performed, and experimental data of two platforms are provided, that show the benefits over state-of-the-art SEA-only based actuatio

Modeling and Control of Adjustable Articulated Parallel Compliant Actuation Arrangements in Articulated Robots

Considerable advances in robotic actuation technology have been made in recent years. Particularly the use of compliance has increased, both as series elastic elements as well as in parallel to the main actuation drives. This work focuses on the model formulation and control of compliant actuation structures including multiple branches and multi-articulation, and significantly contributes by proposing an elegant modular formulation that describes the energy exchange between the compliant elements and articulated multi-body robot dynamics using the concept of power flows, and a single matrix that describes the entire actuation topology. Using this formulation, a novel gradient descent based control law is derived for torque control of compliant actuation structures with adjustable pretension, with proven convexity for arbitrary actuation topologies. Extensions towards handling unidirectionality of elastic elements and joint motion compensation are also presented. A simulation study is performed on a 3-DoF leg model, where series-elastic main drives are augmented by parallel elastic tendons with adjustable pretension. Two actuation topologies are considered, one of which includes a biarticulated tendon. The data demonstrate the effectiveness of the proposed modelling and control methods. Furthermore, it is shown the biarticulated topology provides significant benefits over the monoarticulated arrangement

3D-printable low-reduction cycloidal gearing for robotics

The recent trend towards low reduction gearing in robotic actuation has revitalised the need for high-performance gearing concepts. In this work we propose compact low-reduction cycloidal gearing, that is 3D-printable and combined with off-the-shelf components. This approach presents an enormous potential for high performance-to-cost implementations. After discussing parameter selection and design considerations, we present a prototype that is combined with a low-cost brushless motor to demonstrate its potential. Extensive experimental results demonstrate high performance, including >40Nm torque, low friction and play, and high impact robustness. The results show that the proposed approach can yield viable gearbox designs

Bipedal Walking Gait with Variable Stiffness Knees

Abstract-The Segmented Spring-Loaded Inverted Pendulum model is analysed, and it is shown that it exhibits walking gait. We propose a control architecture that exploits control of the knee stiffness to provide robustness of the system with respect to changes in gait. This controller is extended for a realistic bipedal robot model that uses variable stiffness actuators to control the knee stiffness. The variable knee stiffness is then used to stabilise the system into a walking gait and to inject energy losses generated by friction and foot impacts

Bipedal walking gait with variable stiffness knees

The Segmented Spring-Loaded Inverted Pendulum model is analysed, and it is shown that it exhibits walking gait. We propose a control architecture that exploits control of the knee stiffness to provide robustness of the system with respect to changes in gait. This controller is extended for a realistic bipedal robot model that uses variable stiffness actuators to control the knee stiffness. The variable knee stiffness is then used to stabilise the system into a walking gait and to inject energy losses generated by friction and foot impacts

Low-cost vision-based 6-DOF MAV localization using IR beacons

The autonomous operation of Micro Aerial Vehicles (MAVs) is a challenging area of research that has received much research interest in recent years. Particularly, accurate localisation of MAVs is an issue, most important during tasks that require high accuracy, such as indoor flight and landing. Many existing solutions are either not accurate, heavy or expensive. We present a low-cost vision-based solution to the localisation problem of MAVs. An on-board infrared tracking sensor with built-in vision processing is used to detect infrared markers and a point-based pose estimation algorithm is implemented to obtain 6 DOF localisation at high rates. The system performance is compared against Inertial Measurement Unit (IMU) and external stereo vision measurements as ground truth. We show that the system produces accurate 6 DOF estimates at low cost and weight in a computationally inexpensive way, and are immediately usable in control implementations. Thus our solution provides a feasible localization solution for MAVs

The Compliant Joint Toolbox for MATLAB: An Introduction with Examples

This article presents the Complianhis Compliant Joint Toolbox for the modeling, simu lation, and controller development of compliant robot actuators. The object-oriented toolbox is written in MATLAB/Simulink. In a few lines of code, it can batch-generate ready-to-use joint actuator model classes from multiple parameter sets, in corporating a variety of nonlinear dynamics effects