Nikos G. Tsagarakis

Improving Safety of Human-Robot Interaction Through Energy Regulation Control and Passive Compliant Design

Modern production processes continuously require enhancement in production time and the quality of the products. The use of robots in this field of application has formed an increasingly important aspect of the drive for efficiency. These robots typically work in restricted areas to prevent any harmful interaction with humans and are designed for repeatability, speed and precision. However, new opportunities are arising in homes and offices that mean that robots will not be confined to these relatively restricted factory environments and this sets new demands in terms of safety and ability to interact with the environment. These new requirements make industrial heavy and stiff manipulators controlled with high gain PID controllers not suited to cooperate and work closely with humans. In order to cope with this, impedance control (Hogan, 1985; Ikeura and Inooka, 1995; Zollo, Siciliano et al., 2002; Zollo, Siciliano et al., 2003) for decreasing the replicated output impedance of the system to safe values and safety-oriented control strategies (Heinzmann and Zelinsky, 1999; Bicchi and Tonietti, 2004; Kulic and Croft, 2004) to react safely when a Human-Robot Interaction is detected have been introduced. The mentioned control algorithms work well for slow interaction transients and within specific frequency bands, however when the frequencies are above the closed loop bandwidth of the robot, these strategies are ineffective in reacting safely making the resulting system to be dangerous. When a sudden and fast impact occurs, the output impedance of the robot is dominated by the link and the rotor reflected inertia. This latter term is usually high due to the high reduction ratio of the gear making the overall robot output impedance large and dangerous meaning that the system’s safety is once again compromised. An alternative to this “active” approach is the incorporation of intrinsically safe structures particularly focusing on the actuation systems design. Several actuator prototypes have been developed embedding either passive compliant elements in the structure (Pratt and Williamson, 1995; Sugar, 2002; Yoon, Kang et al., 2003; Hurst, Chestnutt et al., 2004; Zinn, Khatib et al., 2004; Hollander, Sugar et al., 2005; Tonietti, Schiavi et al., 2005; Schiavi, Grioli et al., 2008; Tsagarakis, Laffranchi et al., 2009; Catalano, Grioli et al., 2010; Jafari, Tsagarakis et al., 2010; Tsagarakis, Laffranchi et al., 2010) or, more recently, clutches/damping devices (Lauzier and Gosselin, 2011; Shafer and Kermani, 2011) to decouple the link (i.e. the part usually interacting with the human) from the rotor during interaction with either the environment

XBotCore: A Real-Time Cross-Robot Software Platform

In this work we introduce XBotCore (Cross-Bot-Core), a light-weight, Real-Time (RT) software platform for EtherCAT-based robots. XBotCore is open-source and is designed to be both an RT robot control framework and a software middleware. It satisfies hard RT requirements, while ensuring 1 kHz control loop even in complex Multi-Degree-Of-Freedom systems. It provides a simple and easy-to-use middleware Application Programming Interface (API), for both RT and non-RT control frameworks. This API is completely flexible with respect to the framework a user wants to utilize. Moreover it is possible to reuse the code written using XBotCore API with different robots (cross-robot feature). In this paper, the XBotCore design and architecture will be described and experimental results on the humanoid robot WALK-MAN [17], developed at the Istituto Italiano di Tecnologia (IIT), will be presented.

Hybrid gait pattern generator capable of rapid and dynamically consistent pattern regeneration

We propose a two-stage gait pattern generation scheme for the full-scale humanoid robots, that considers the dynamics of the system throughout the process. The fist stage is responsible for generating the preliminary motion reference, such as step position, timing and trajectory of Center of Mass (CoM), while the second stage serves as dynamics filter which employs a multi-body model and based on Zero Moment Point (ZMP) reference trajectory generates CoM reference trajectory which defines a locomotion stable when executed on the full-scale multi-degree-of-freedom humanoid robot. The approach thanks to introducing a dynamic model at the stage of feet placement planning provides the ZMP reference, which is ensured to be feasible for the robot. Thanks to the fact it enables instantaneous regeneration of motion. The paper contains description of two approaches used in the first and second stage, as well as experimental results proving the effectiveness of the method. The fast calculation time and the use of the systems dynamic state as initial conditions for pattern generation makes it a good candidate for the real-time gait pattern generator.

Compliant Leg Mechanism of Coman

The incorporation of passive compliance in robotic systems has the potential to improve their performance during interactions and impacts, enhance their energy storage and efficiency, and facilitate greater general safety for the robots, humans, and environment. This chapter introduces the design and mechatronics of the leg mechanisms developed for COmpliant huMANoid COMAN. The COMAN leg is powered by passive compliance drives based on a series elastic actuation principle (SEA). Within the chapter, the design and implementation of the COMAN leg is discussed including the details of the SEA drive, the realization of the different leg joints, and the tuning of the joint distributed passive elasticity. The joint stiffness is a critical parameter in the compliant leg design as it defines the overall intrinsic adaptability of the leg, and strongly affects the control of its actuation system. The chapter presents a systematic method to optimally tune the joint elasticity of the multi-dof SEA leg based on resonance analysis and energy storage maximization criteria. The method is applied to the selection of the passive elasticity of COMAN legs. The chapter concludes with a discussion on future research directions and challenges in compliant actuation and robot design.