This paper presents the design of a lightweight robot arm intended for safe physical human-robot interaction. The robot arm design combines tendon actuation with elasticity in the tendons to achieve a significant reduction in mass and passive compliant behavior. The use of elastic tendons in all joints in order to gain maximum safety and performance properties, however, results in a significant increase of the model complexity with oscillatory behavior and kinematic coupling of the joint equilibrium positions. Therefore, special effort needs to be made to model the robot arm dynamics, which is an essential basis for model-based algorithms utilizing and fully exploiting the particular properties of the robot arm. This paper therefore derives the full dynamics model of the robot arm with focus on the nonlinear elastic tendon actuators, the kinematic tendon coupling, and modeling complexity reduction by reflecting all model parameters to the joint space. The resulting model is validated by comparing the identified simulation model with experimental data of an application-related pick-and-place trajectory and a trajectory with undamped oscillating motions of the robot arm.

This paper presents the design of the lightweight BioRob manipulator with spring-loaded tendon-driven actuation developed for safe physical human-robot interaction. The safety of the manipulator is analyzed by an analytical worst-case estimation of impact and clamping forces in the absence of collision detection. As intrinsic joint compliance can pose a threat by storing energy, a safety evaluation method is proposed taking the potential energy stored in the elastic actuation into account. The evaluation shows that the robot arm design constrains the worst case clamping forces to only 25 N, while being able to handle loads up to 2 kg, and inherits extremely low impact properties, such as an effective mass of less than 0.4 kg in non near-singular configurations, enabling safe operation even in case of high velocities. The results are validated in simulation and experiments.

Bio-inspired, musculoskeletal design of bipedal robots offers great potential towards more human-like robot performance but imposes major challenges on their design and control, as it is challenging to analyze the contribution of each active and passive series elastic tendon to the overall joint, leg and robot dynamics. In this paper, detailed mathematical models of the tendon-driven, series elastically actuated mono- and biarticular structures of the BioBiped1 robot are presented. These enable a systematic analysis of the design space and characteristic curves as well as to derive guidelines for the design of improved prototypes. The derived models are applied to investigate the effects of the active and passive, mono- and biarticular structures on different performance criteria of 1D hopping motions by means of a detailed multi-body system dynamics simulation.