A method is described for the synchronization of nonlinear discrete-time dynamics. The methodology consists of constructing observer–receiver dynamics that exploit at each time instant the drive signal and buffered past values of the drive signal. In this way, the method can be viewed as a dynamic reconstruction mechanism, in contrast to existing static inversion methods from the theory of dynamical systems. The method is illustrated on a few simulation examples consisting of coupled chaotic logistic equations. Also, a discrete-time message reconstruction scheme is simulated using the extended observer mechanism.

This paper presents a novel joint torque-based impedance controller for antagonistically driven flexible joints actuated by pneumatic cylinders and compares it with the current state of the art. The work targets on transferring soft-robotics control concepts from classical motor-gear-torque sensor setups to pneumatic systems, with the goal of achieving similar performance levels in comparison to this well established technology. A detailed flexible joint model is derived that incorporates the pneumatic and mechanical dynamics of the proposed antagonistic design. This model is used for analyzing model-based control approaches, which in turn are based on reduced order dynamics. The tendon-based joint level impedance controller enables the simultaneous adjustment of closed-loop stiffness and damping. The proposed scheme shows good simulation results for both, position tracking and compliance performance, respectively. Experimentally, an angular position tracking of 7 Hz could be achieved. Also, stable rigid contacts could be established at considerable impact speed.

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Abstract-For creating robots that are capable of human like performance in terms of speed, energetic properties and robustness, intrinsic compliance is a promising design element. In this paper we investigate the principle effects of elastic energy storage and release for basketball dribbling in terms of open-loop cycle stability. We base the analysis, which is performed for the 1-degree-of-freedom (DoF) case, on error propagation, peak power performance during hand contact and robustness with respect to varying hand stiffness. As the ball can only be controlled during contact, an intrinsically elastic hand extends the contact time and improves the energetic characteristics of the process. To back up our basic insights, we extend the 1-DoF controller to 6-DoFs and show how passive compliance can be exploited for a 6-DoF cyclic ball dribbling task with a 7-DoF articulated Cartesian impedance controlled robot. As a human is able to dribble blindly, we decided to focus on the case of contact force sensing only, i.e. no visual information is used in our approach. We show via simulation and experiment that it is possible to achieve a stable dynamic cycle based on the 1 DoF analysis for the primary vertical axis together with control strategies for the secondary translations and rotations of the task. The scheme allows also the continuous tracking of a desired dribbling height and horizontal position. The approach is also used to hypothesize about human dribbling and is validated with captured data.

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