Abstract
Endowing tele-manipulation frameworks with the capability to accommodate a variety of robotic hands is key to achieving high performances through permitting to flexibly interchange the end-effector according to the task considered. This requires the development of control policies that not only cope with asymmetric master–slave systems but also whose high-level components are designed in a unified space in abstraction from the devices specifics. To address this dual challenge, a novel synergy port is developed that resolves the kinematic, sensing, and actuation asymmetries of the considered system through generating motion and force feedback references in the hardware-independent hand postural synergy space. It builds upon the concept of the Cartesian-based synergy matrix, which is introduced as a tool mapping the fingertips Cartesian space to the directions oriented along the grasp principal components. To assess the effectiveness of the proposed approach, the synergy port has been integrated into the control system of a highly asymmetric tele-manipulation framework, in which the 3-finger hand exoskeleton HEXOTRAC is used as a master device to control the SoftHand, a robotic hand whose transmission system relies on a single motor to drive all joints along a soft synergistic path. The platform is further enriched with the vision-based motion capture system Optitrack to monitor the 6D trajectory of the user’s wrist, which is used to control the robotic arm on which the SoftHand is mounted. Experiments have been conducted with the humanoid robot COMAN and the KUKA LWR robotic manipulator. Results indicate that this bilateral interface is highly intuitive and allows users with no prior experience to reach, grasp, and transport a variety of objects exhibiting very different shapes and impedances. In addition, the hardware and control solutions proved capable of accommodating users with different hand kinematics. Finally, the proposed control framework offers a universal, flexible, and intuitive interface allowing for the performance of effective tele-manipulations.
Highlights
Performing a task using a teleoperated robot avatar makes possible to safely handle hazardous material as well as to take advantage of the machines’ superior sensing and actuation capabilities, enabling the execution of tasks that require high precision and large wrenches
A promising approach to tackle this difficulty lies in the development of unified frameworks promoting the synthesis of hardware-independent algorithms that can be indifferently used to control a variety of end-effectors. This can be achieved through adopting a two-layer architecture, where the low-level layer is used to encapsulate the kinematics, sensing, and actuation specifics of the device, while the high-level layer focuses on the resolution of the manipulation problem
The term synergy has been employed to conceptualize coordination at various levels including kinematics, i.e., joints motion coordination (Santello et al, 1998), kinetics, i.e., digit force coordination (Zatsiorsky et al, 2000), neuromuscular, i.e., multi-muscle activation patterns (Bizzi et al, 2008), or neurosensorial, as the perceptual counterpart of the motor synergies (Bicchi et al, 2011), we will use here the definition proposed in Turvey (2007), according to which a synergy is “a collection of relatively independent DOFs that behave as a single functional unit.”
Summary
Performing a task using a teleoperated robot avatar makes possible to safely handle hazardous material as well as to take advantage of the machines’ superior sensing and actuation capabilities, enabling the execution of tasks that require high precision and large wrenches. Preoperative automated task supervision features can be implemented to improve safety with, for instance, the introduction of motion constraints and safeguards to contain the risks stemming from accidental commands or external disturbances. Teleoperation enables to project the skills of an operator into a remote environment but it permits to extend and enhance the human’s manipulation capabilities with higher power, higher motion precision, and with greater safety. This powerful tool allows merging the strengths of men and machines so as to achieve enhanced performances. To take advantage of the potential benefits offered by tele-manipulation, a number of considerations need to be addressed both at the hardware and software levels
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