Jorn Malzahn

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.

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.

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.

Editorial: Advances in Mechatronics and Biomechanics Towards Efficient Robot Actuation

Despite the development of a large number of mobile manipulation robots, very few platforms can demonstrate the required strength and mechanical sturdiness to accommodate the needs of real-world applications with high payload and moderate/harsh physical interaction demands, e.g. in disaster-response scenarios or heavy logistics/collaborative tasks. In this work we introduce the design of a wheeled-legged mobile manipulation platform capable of executing demanding manipulation tasks, and demonstrating significant physical resilience while possessing a body size (height/width) and weight compatible to that of human. The achieved performance is the result of a combining a number of design and implementation principles related to the actuation system, the integration of body structure and actuation, and the wheeled-legged mobility concept. These design principles are discussed, and the solutions adopted for various robot components are detailed. Finally, the robot performance is demonstrated in a set of experiments validating its power and strength capability when manipulating heavy payload and executing tasks involving high impact physical interactions.

In this paper, we present a novel global tracking control approach for elastic-joint robots that can be efficiently computed and is robust against model uncertainties and input disturbances. Elastic-joint robots provide enhanced safety and resiliency for interaction with the environment and humans. On the other hand, the joint elasticity complicates the motion-control problem especially when robust and precise trajectory tracking is required. Our proposed control approach allows us to merge the main benefits of the two well-known control schemes: inverse-dynamics (ID) control, which can be efficiently computed thanks to modern recursive algorithms, and passivity-based (PB) tracking control, which provides enhanced robustness to model uncertainty and external disturbances. As an extension of our previous work, we present a detailed robustness analysis of our combined ID/PB controller, a new variant of the original scheme that shows practically relevant implications, and finally, experimental results that verify the effectiveness of the approach.

Research on link-elasticities offers the perspective to devise lightweight robots with intrinsic safety benefits for physical human-robot interaction and fast motions with reduced energy consumption. Moreover, their force/torque sensing capabilities mimic the functionalities of animalistic whiskers, putting the robot in a position to react gently to its environment. While many works consider single elastic links or planar settings, the present work addresses the controllability problem for link-elastic robots with multiple vibration planes. The paper introduces the reader to the modal controllability and accessibility problem emerging in such systems, and proposes a novel geometric controllability index with reduced complexity. The proposed index is compared and analysed with respect to existing indexes from literature in preparation for adaptive vibration control schemes.

In this paper, an alternative novel method for calibrating a non-redundant six-axis force/torque sensor is presented. Calibration is conducted online, with the aid of a visual interactive interface, and is based on robust regression, allowing to discard outliers from the data and continuously monitor the sensor's calibration quality online while calibration data are being collected. The method is experimentally applied and validated in the calibration of the custom six-dimensional force/torque load-cells used in the feet of WALK-MAN humanoid.