Technical session talks from ICRA 2012
TechTalks from event: Technical session talks from ICRA 2012
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A General Mechanical Model for Tendon-Driven Continuum ManipulatorsRecently, continuum manipulators have drawn a lot of interest and effort from the robotic community, nevertheless control and modeling of such manipulators are still a challenging task especially because they require a continuum approach. In this paper, a general mechanical model with a geometrically exact approach for tendon-driven continuum manipulators is presented. This model can be applied to a wide range of manipulators thanks to the generality of the parameters which can be set. The approach proposed could as well be a powerful tool for developing the control strategy. The model is also capable of properly simulating the couple tendon drive, because it takes into account the torsion of the robot arm rather than neglecting it, as it is common practice in other existing models.
A Two Dimensional Inverse Kinetics Model of a Cable Driven Manipulator Inspired by the Octopus ArmControl of soft robots remains nowadays a big challenge, as it does in the larger category of continuum robots. In this paper a direct and inverse kinetics models are described for a non-constant curvature structure. A major effort has been put recently in modelling and controlling constant curvature structures, such as cylindrical shaped manipulators. Manipulators with non-constant curvature, on the other hand, have been treated with a piecewise constant curvature approximation. In this work a non-constant curvature manipulator with a conical shape is built, taking inspiration from the anatomy of the octopus arm. The choice of a conical shape manipulator made of soft material is justified by its enhanced capability in grasping objects of different sizes. A different approach from the piecewise constant curvature approximation is employed for direct and inverse kinematics model. A continuum geometrically exact approach for direct kinetics model and a Jacobian method for inverse case are proposed. They are validated experimentally with a prototype soft robot arm moving in water. Results show a desired tip position in the task-space can be achieved automatically with a satisfactory degree of accuracy.
Characterizing the Stiffness of a Multi-Segment Flexible Arm During MotionA number of robotic studies have recently turned to biological inspiration in designing control schemes for flexible robots. Examples of such robots include continuous manipulators inspired by the octopus arm. However, the control strategies used by an octopus in moving its arms are still not fully understood. Starting from a dynamic model of an octopus arm and a given set of muscle activations, we develop a simulation technique to characterize the stiffness throughout a motion and at multiple points along the arm. By applying this technique to reaching and bending motions, we gain a number of insights that can help a control engineer design a biologically inspired impedance control scheme for a flexible robot arm. The framework developed is a general one that can be applied to any motion for any dynamic model. We also propose a theoretical analysis to efficiently estimate the stiffness analytically given a set of muscle activations. This analysis can be used to quickly evaluate the stiffness for new static configurations and dynamic movements.
Robotic Underwater Propulsion Inspired by the Octopus Multi-Arm SwimmingThe multi-arm morphology of octopus-inspired robotic systems may allow their aquatic propulsion, in addition to providing manipulation functionalities, and enable the development of flexible robotic tools for underwater applications. In the present paper, we consider the multi-arm swimming behavior of the octopus, which is different than their, more usual, jetting behavior, and is often used to achieve higher propulsive speeds, e.g., for chasing prey. A dynamic model of a robot with a pair of articulated arms is employed to study the generation of this mode of propulsion. The model includes fluid drag contributions, which we support by detailed Computational Fluid Dynamic analysis. To capture the basic characteristics of octopus multi-arm swimming, a sculling mode is proposed, involving arm oscillations with an asymmetric speed profile. Parametric simulations were used to identify the arm oscillation characteristics that optimize propulsion for sculling, as well as for undulatory arm motions. Tests with a robotic prototype in a water tank provide preliminary validation of our analysis.
Developing Sensorized Arm Skin for an Octopus Inspired Robotsoft skin artefacts made of knitted nylon reinforced silicon rubber were fabricated mimicking octopus skin. A combination of ecoflex 0030 and 0010 were used as matrix of the composite to obtain the right stiffness for the skin artefacts. Material properties were characterised using static uniaxial tension and scissors cutting tests. Two types of tactile sensors were developed to detect normal contact; one used quantum tunnelling composite materials and the second was fabricated from silicone rubber and a conductive textile. Sensitivities of the sensors were tested by applying different modes of loading and the soft sensors were incorporated into the skin prototype. Passive suckers were developed and tested against squid suckers. An integrated skin prototype with embedded deformable sensors and attached suckers developed for the arm of an octopus inspired robot is also presented.
Artificial Adhesion Mechanisms Inspired by Octopus SuckersWe present the design and development of novel suction cups inspired by the octopus suckers. Octopuses use suckers for remarkable tasks and they are capable to obtain a good reversible wet adhesion on different substrates. We investigated the suckers morphology that allow octopus to attach them to different wet surfaces to obtain the benchmarks for new suction cups showing similar performances. The investigation was performed by using non-invasive techniques (i.e. ultrasonography and magnetic resonance imaging). We acquired images of contiguous sections of octopus suckers, which were used to make a 3D reconstruction aimed to obtain a CAD model perfectly equivalent to the octopus sucker in terms of sizes and anatomical proportion. The 3D information was used to develop the first passive prototypes of the artificial suction cups made in silicone. Then, in accordance with Kier and Smithâ€™s octopus adhesion model, we put in tension the water volume in the interior chamber of the artificial suction cup to obtain suction. The characterization of the passive sucker was addressed by measuring both the differential pressure between external and internal water volume of suction cup (~ 105) and the pull-off force applied to detach the substrates from the suction cup (~ 8N).