Technical session talks from ICRA 2012
TechTalks from event: Technical session talks from ICRA 2012
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Selectively Compliant Underactuated Hand for Mobile ManipulationThe demands of mobile manipulation are leading to a new class of multi-fingered hands with a premium on being lightweight and robust as well as being able to grasp and perform basic manipulations with a wide range of objects. A promising approach to addressing these goals is to use compliant, underactuated hands with selectively lockable degrees of freedom. This paper presents the design of one such hand that combines series-elastic actuation and electrostatic braking at the joints. A numerical analysis shows how the maximum pullout force varies as a function of kinematic parameters, spring forces at the joints and brake torques.
Precision Grasping and Manipulation of Small Objects from Flat Surfaces Using Underactuated FingersIn this paper we demonstrate an underactuated finger design and grasping method for precision grasping and manipulation of relatively small objects. Taking a cue from human manipulation, we introduce the flip-and-pinch task, in which the hand picks up thin objects from a table surface by flipping it into a stable configuration. Despite the fact that finger motions are not fully constrained by the hand actuators, we demonstrate that the hand and fingers can be configured with the table surface to produce a set of constraints that result in a repeatable quasi-static motion trajectory. This approach is shown to be robust for a variety of object sizes, even when utilizing identical open-loop kinematic playback. Experimental results suggest that the advantages of underactuated, adaptive robot hands can be carried over to dexterous, precision tasks as well.
Grasp and Manipulation Analysis for Synergistic Underactuated Hands under General Loading ConditionsIn dexterous grasping, the development of simple but practical hands with reduced number of actuators, designed to perform some manipulation tasks, is both attractive and challenging. To carefully synthesize inter- and intra-finger couplings a rigorous way to establish grasping and manipulation properties of an underactuated hand is of paramount importance. In this paper, we propose a general approach to characterize the structural properties of underactuated hands focusing on their kinematic and force analysis. A complete kinostatic characterization of a given grasp (pure squeeze, spurious squeeze, kinematic grasp displacements and so on) is introduced. The analysis is quasi-static but it is not limited to rigid-body motions, encompassing also essential elastic motions, statically indeterminate configurations, and pre-loaded initial conditions. The introduction of generalized compliance at contacts and in the actuation mechanism is included, as it is an essential feature of safe and dependable modern hands. Efficient algorithms to characterize the system behavior are presented and applied in two different numerical examples.
Towards a Design Optimization Method for Reducing the Mechanical Complexity of Underactuated Robotic HandsUnderactuated compliant robotic hands exploit passive mechanics and joint coupling to reduce the number of actuators required to achieve grasp robustness in unstructured environments. Reduced actuation requirements generally serve to decrease design cost and improve grasp planning efficiency, but overzealous simplification of an actuation topology, coupled with insufficient tuning of mechanical compliance and hand kinematics, can adversely affect grasp quality and adaptability. This paper presents a computational framework for reducing the mechanical complexity of robotic hand actuation topologies without significantly decreasing grasp robustness. Open-source grasp planning software and well-established grasp quality metrics are used to simulate a fully-actuated, 24 DOF anthropomorphic robotic hand grasping a set of daily living objects. DOFs are systematically demoted or removed from the hand actuation topology according to their contribution to grasp quality. The resulting actuation topology contained 22% fewer DOFs, 51% less aggregate joint motion, and required 82% less grasp planning time than the fully-actuated design, but decreased average grasp quality by only 11%.
Seashell Effect Pretouch Sensing for Robotic GraspingThis paper introduces "seashell effect pretouch sensing", and demonstrates application of this new sensing modality to robot grasp control, and also to robot grasp planning. "Pretouch" refers to sensing modalities that are intermediate in range between tactile sensing and vision. The novel pretouch technique presented in this paper is effective on materials that prior pretouch techniques fail on. Seashell effect pretouch is inspired by the phenomenon of "hearing the sea" when a seashell is held to the ear, a phenomenon which depends on shell position. To turn this effect into a sensor, a cavity and microphone were built into a robot finger. The sensor detects changes in the spectrum of ambient noise that occur when the finger approaches an object. Environmental noise is amplified most at the cavity's resonant frequency, which changes as the cavity approaches an object. After introducing the sensing modality and characterizing its performance, the paper describes experiments performed with prototype sensors integrated into the Willow Garage PR2's gripper. We explore two primary applications: (1) reactive grasp control and (2) pretouch-assisted grasp planning.
Position Control of Tendon-Driven Fingers with Position Controlled ActuatorsConventionally, tendon-driven manipulators implement some force-based controller using either tension feedback or dynamic models of the actuator. The force control allows the system to maintain proper tensions on the tendons. In some cases, whether it is due to the lack of tension feedback or actuator torque control, a purely position-based controller is needed. This work compares three position controllers for tendon-driven manipulators that implement a nested actuator position controller. A new controller is introduced that achieves the best overall performance with regards to speed, accuracy, and transient behavior. To compensate for the lack of tension control, the controller nominally maintains the internal tension on the tendons through a range-space constraint on the actuator positions. These control laws are validated experimentally on the Robonaut-2 humanoid hand.