Bratislav Svetozarevic

The Puller-Follower Control of Compliant and Noncompliant Antagonistic Tendon Drives in Robotic Systems

This paper proposes a new control strategy for noncompliant and compliant antagonistic tendon drives. It is applied to a succession of increasingly complex single-joint systems, starting with a linear and noncompliant system and ending with a revolute, nonlinearly tendon coupled and compliant system. The last configuration mimics the typical human joint structure, used as a model for certain joints of the anthropomimetic robot ECCEROBOT. The control strategy is based on a biologically inspired puller-follower concept, which distinguishes the roles of the agonist and antagonist motors. One actuator, the puller, is considered as being primarily responsible for the motion, while the follower prevents its tendon from becoming slack by maintaining its tendon force at some non-zero level. Certain movements require switching actuator roles; adaptive co-contraction is used to prevent tendons slackening, while maintaining energetic efficiency. The single-joint control strategy is then evaluated in a multi-joint system. Dealing with the gravitational and dynamic effects arising from the coupling in a multi-joint system, a robust control design has to be applied with on-line gravity compensation. Finally, an experiment corresponding to object grasping is presented to show the controllers robustness to external disturbances.

SoRo-Track: A two-axis soft robotic platform for solar tracking and building-integrated photovoltaic applications

We present SoRo-Track, a two-axis soft robotic actuator (SRA) for solar tracking and building-integrated photovoltaic applications. SRAs are gaining increasing popularity compared to traditional actuators, such as dc motors and hydraulic or pneumatic pistons, due to their inherent compliance, low morphological complexity, high power-to-weight ratio, resilience to external shocks and adverse environmental conditions, design flexibility, ease of fabrication, and low costs. We present the design, modelling and experimental characterisation of SoRo-Track. Finally, we demonstrate the suitability of SoRo-Track for solar tracking applications, which makes it a viable component for dynamic building facades.

Modeling and Control of a Compliantly Engineered Anthropomimetic Robot in Contact Tasks

This paper attempts to develop a dynamic model and design a controller for a fully anthropomorphic, compliantly driven robot. To imitate muscles, the robot’s joints are actuated by DC motors antagonistically coupled through tendons. To ensure safe interaction with humans in a human-centered environment, the robot exploits passive mechanical compliance, in the form of elastic springs in the tendons. To enable simulation, the paper first derives a mathematical model of the robot’s dynamics, starting from the “Flier” approach. The control of the antagonistic drives is based on a biologically inspired puller-and-follower concept where at any instant the puller is responsible for the joint motion while the follower keeps the inactive tendon from slackening. In designing the controller, it was first necessary to use the advanced theory of nonlinear control for dealing with individual joints, and then to apply the theory of robustness in order to extend control to the multi-jointed robot body.Copyright

Hybrid AC/DC building microgrid for solar PV and battery storage integration

Dc power systems can integrate dc renewable generation, storage, and building electrical loads easier and more efficiently than conventional ac based systems. A key challenge for the successful market adoption of these systems is the integration with existing electrical loads and power grids in buildings. Hybrid ac/dc microgrids combine advantages of both ac and dc systems and may facilitate the integration process of dc power technologies into existing ac systems. In this work, the performance of a hybrid building microgrid coupling on-site PV generation with ac and dc loads of a residential building is investigated in simulation. An experimental dc network prototype, coupling PV electricity generation to LED lighting in a building, has been built and tested. Theoretical and experimental results are used for the design of a hybrid microgrid, planned to be implemented together with the PV system of a residential research building.