An approach to object-level stiffness regulation of hand-arm systems subject to under-actuation constraints
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An approach to object-level stiffness regulation of hand-arm systems subject to under-actuation constraints Virginia Ruiz Garate1
· Arash Ajoudani1
Received: 2 July 2019 / Accepted: 12 August 2020 © The Author(s) 2020
Abstract When using a tool with a robotic hand-arm system, the stiffness at the grasped object plays a key role in the interaction with the environment, allowing the successful execution of the task. However, the rapidly increasing use of under-actuated hands in robotic systems due to their robustness and simplicity of control, pose limitations to the achievable object-level stiffness. Indeed, due to the serial coupling of the hand and the arm, the resulting object-level stiffness is determined by the most compliant of both elements. To address this problem, we propose a novel controller that takes into account the limited achievable geometry of the object stiffness ellipsoid given by a hand with under-actuation constraints, and exploits the contribution of the robotic arm in reshaping the final stiffness towards the desired profile. The under-actuation is illustrated by a coordinated stiffening of the hand fingers. The proposed method is experimentally validated by a hand-arm system performing a peg-in-hole task. Keywords Grasping · Dexterous manipulation · Compliance control · Impedance control
1 Introduction Collaborative robotics is a rapidly emerging technology, as an increasing number of industries are seeking for flexible automation systems to become competitive (Ajoudani et al. 2018). These robotic systems are envisaged to work together with their human co-workers in order to perform a wide range of tasks in a productive and flexible way, which usually involve manipulation and interaction. They must therefore contain: a robotic end-effector able to perform the manipulation (e.g.: robotic hands, grippers, suction cups) and a robotic arm driving such end-effector along the task workspace (e.g., see Fig. 1). When dealing with human-like manipulation scenarios, robotic hands are usually preferred due to their increased manipulability and dexterity. Several studies have investigated the potential of such hand-arm systems, mainly focusing on the control of the position, orientation, and force This work is supported in part by the EU H2020 Project “SOPHIA” (No. 871237).
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Virginia Ruiz Garate [email protected] Human-Robot Interfaces and Physical Interaction Research Line, Istituto Italiano di Tecnologia (IIT), Via Morego 30, 16163 Genoa, Italy
at the object or arm end-effector level (Bae et al. 2006; Nagai and Yoshikawa 1995). Still, when tackling the collaborative scenarios, safe and controlled interactions become crucial requirements of the system. To this end, impedance control frameworks have been proposed with considerable advantages when dealing with unstructured environments and in human-robot interaction scenarios (Albu-Schaffer et al. 2003). Nevertheless, impedance controllers for hand-arm systems have been scarcely studied. In Wimbock et al. (2007), an object-level custom-built
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