Dynamics identification of a damped multi elastic link robot arm under gravity

Malzahn J, Reinhart F, Bertram T. Dynamics identification of a damped multi elastic link robot arm under gravity. In: 2014 IEEE International Conference on Robotics and Automation (ICRA). Institute of Electrical & Electronics Engineers (IEEE); 2014

Blending of Series-Parallel Compliant Actuation With Field Weakening Control for Explosive Motion Generation

In this work, we investigate and validate two methods that can extend the explosive motion capabilities of series elastic actuated robots during standing jumps. First, field weakening control is exploited on multiple joints of a monoped to boost their peak velocities. However, field weakening operation reduces actuation torque capacity at those velocities, due to consuming current reserves. To address this torque reduction, we leverage energy-efficient parallel elastic actuators, in biarticulated knee-ankle and monoarticulated knee configuration. The proposed concept therefore combines the torque and inter-joint power transfer benefits of parallel and biarticulated articulation with the velocity increase permitted by field weakening to amplify the explosive power output in a monoped robot prototype. A substantial performance increase of up to 54% in jump height is achieved after experimentally tuning the motion for each configuration. This validates the efficacy of the approach for improving the explosive capabilities of series elastic actuated robots

On the efficient control of series-parallel compliant articulated robots

Torque distribution in redundant robots that combine the potential of asymmetric series-parallel actuated branches and multi-articulation pose a non-trivial challenge. To address the problem, this work proposes a novel optimization based controller that can accommodate various quadratic criteria to perform the torque distribution among dissimilar series and parallel actuators in order to maximize the motion efficiency. Three candidate criteria are composed and their performances are compared during periodic squat motions with a 3 degree of freedom series-parallel compliant articulated leg prototype. It is first shown that by minimizing a criterion that takes into account the actuator hardware specifications such as torque constant and transmission ratio, the gravity-driven phases can be lengthened. Thereby, this particular criterion results in slightly better performance than when adopting a strategy that maximizes the torque allocation to the higher efficiency actuators. Furthermore, valuable insights such as that the efficacy of maximum utilization of the highly-efficient parallel actuation branches decreases progressively at high frequencies were observed

Toward a Plug-and-Work Reconfigurable Cobot

The ongoing trend from mass-produced to mass-customized products with batch sizes as small as a single unit has highlighted the need for highly adaptable robotic systems with lower downtime for maintenance. To address these demands, this article proposes the development of a novel reconfigurable collaborative robot (cobot), which has the potential to open up many new scenarios within the rapidly emerging flexible manufacturing environments. As the technological contribution, we present a complete hard- and software architecture for a quickly reconfigurable EtherCAT-based robot. This novel approach allows to automatically reconstruct the topology of different robot structures, composed of a set of body modules, each of which represents an EtherCAT slave. As the theoretical contribution, we propose a method to obtain in an automatic way the kinematic and dynamic model of the robot and store it in universal robot description format (URDF) as soon as the physical robot is assembled or reconfigured. The method also automatically reshapes a generic optimization-based controller to be instantly used after reconfiguration. While this article focuses on reconfigurable manipulators, the proposed concept can support arbitrary serial kinematic tree-like configurations. We demonstrate the contributions with examples of the following: how the topology of the robot is reconstructed and the URDF model is generated, and a Cartesian task application for a cobot built with the basic modules, demonstrating the quick reconfigurabilty of the system from a 4-degrees-of-freedom (DOF) robot to a 5-DOF robot, in order to satisfy new workspace requirements

An Overview on Principles for Energy Efficient Robot Locomotion.

Despite enhancements in the development of robotic systems, the energy economy of today's robots lags far behind that of biological systems. This is in particular critical for untethered legged robot locomotion. To elucidate the current stage of energy efficiency in legged robotic systems, this paper provides an overview on recent advancements in development of such platforms. The covered different perspectives include actuation, leg structure, control and locomotion principles. We review various robotic actuators exploiting compliance in series and in parallel with the drive-train to permit energy recycling during locomotion. We discuss the importance of limb segmentation under efficiency aspects and with respect to design, dynamics analysis and control of legged robots. This paper also reviews a number of control approaches allowing for energy efficient locomotion of robots by exploiting the natural dynamics of the system, and by utilizing optimal control approaches targeting locomotion expenditure. To this end, a set of locomotion principles elaborating on models for energetics, dynamics, and of the systems is studied