Traditional robots have rigid underlying structures that limit their ability to interact with their environment. For example, conventional robot manipulators have rigid links and can manipulate objects using only their specialised end effectors. These robots often encounter difficulties operating in unstructured and highly congested environments. A variety of animals and plants exhibit complex movement with soft structures devoid of rigid components. Muscular hydrostats e.g. octopus arms and elephant trunks are almost entirely composed of muscle and connective tissue and plant cells can change shape when pressurised by osmosis. Researchers have been inspired by biology to design and build soft robots. With a soft structure and redundant degrees of freedom, these robots can be used for delicate tasks in cluttered and/or unstructured environments. This paper discusses the novel capabilities of soft robots, describes examples from nature that provide biological inspiration, surveys the state of the art and outlines existing challenges in soft robot design, modelling, fabrication and control.

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Soft robotics: Biological inspiration, state of the art, and future research

Presents an overview of research in dexterous manipulation. We first define robotic dexterous manipulation in comparison to traditional robotics and human manipulation. Next, kinematics, contact types and forces are used to formulate the dexterous manipulation problem. Dexterous motion planning is described, which includes grasp planning and quality measures. We look at mid- and low-level control frameworks, and then compare manipulation versus exploration. Finally, we list accomplishments in the different areas of dexterous manipulation research, and highlight important areas for future work.

An overview of dexterous manipulation

How to design an anthropomorphic hand with a few actuators to replicate the grasping functions of the human hand is still a challenging problem. This paper aims to develop a general theory for designing the anthropomorphic hand and endowing the designed hand with natural grasping functions. A grasping experimental paradigm was set up for analyzing the grasping mechanism of the human hand in daily living. The movement relationship among joints in a digit, among digits in the human hand, and the postural synergic characteristic of the fingers were studied during the grasping. The design principle of the anthropomorphic mechanical digit that can reproduce the digit grasping movement of the human hand was developed. The design theory of the kinematic transmission mechanism that can be embedded into the palm of the anthropomorphic hand to reproduce the postural synergic characteristic of the fingers by using a limited number of actuators is proposed. The design method of the anthropomorphic hand for replicating human grasping functions was formulated. Grasping experiments are given to verify the effectiveness of the proposed design method of the anthropomorphic hand.

Design and Implementation of an Anthropomorphic Hand for Replicating Human Grasping Functions

We present a unified framework for grasp planning and in-hand grasp adaptation using visual, tactile, and proprioceptive feedback. The main objective of the proposed framework is to enable fingertip grasping by addressing problems of changed weight of the object, slippage, and external disturbances. For this purpose we introduce the Hierarchical Fingertip Space as a representation enabling optimization for both efficient grasp synthesis and online finger gaiting. Grasp synthesis is followed by a grasp adaptation step that consists of both grasp force adaptation through impedance control and regrasping/finger gaiting when the former is not sufficient. Experimental evaluation is conducted on an Allegro hand mounted on a Kuka LWR arm.

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Hierarchical Fingertip Space: A Unified Framework for Grasp Planning and In-Hand Grasp Adaptation

Computer‐aided fixture design (CAFD) techniques have been advanced so rapidly that computers can now generate fixture configurations automatically, for both modular fixtures and dedicated fixtures. Computer‐aided fixture design verification (CAFDV) is the techniques for verifying and improving existing fixture designs. It verifies the followings: geometric constraining ability, achieved tolerance, fixturing stability, and fixturing accessibility. Two models – one geometric and one kinematic – are created for the verification.

https://digital.wpi.edu/downloads/05741r744

Computer‐aided fixture design verification

Stability is one of the important properties that a robot hand grasp must possess to be able to perform tasks similar to those performed by human hands. This paper discusses the dynamic stability of a grasped object. To analyze the stability of grasps, the authors build the model of the dynamics of the grasped object in response to the small perturbances. Furthermore, they determine the conditions associated with the dynamic stability and discuss the effects of various factors on the grasp stability. A quantitative measure for evaluating grasps is then presented. Finally, the effectiveness of the proposed theory is verified via examples.

On the Dynamic Stability of Grasping

It is necessary to plan the contact configuration to guarantee a stable grasp. This article discusses the grasping stability of multifingered robot hands. The fingers are assumed to be point contacts with friction. A stability index for evaluating a grasp, which is proportional to the ellipsoidal volume in the grasping task space, is proposed. The invariance of the index is proved under an object linear coordinate transformation and under a change of the torque origin. The similar invariance of the index is also proved under a change of the dimensional unit. The optimal grasping of an object by a multifingered robot hand can be obtained using the stability index to plan the grasp configurations. The index is applicable to plan adaptable fixtures as well. A nonlinear programming method to plan configurations is addressed. Several examples are given using the index to evaluate a grasp, in which the obtained optimal grasping is consistent with what human beings expect. The sensibility of the optimal grasping is analyzed in these examples. © 1998 John Wiley & Sons, Inc.

Stability index and contact configuration planning for multifingered grasp

Form-closure is considered as a purely geometric property of a set of unilateral contact constraints such as those applied on a workpiece by a mechanical fixture. This paper provided qualitative analysis of form-closure fixturing. The necessary and sufficient condition for form-closure fixturing is derived. Some fundamental problems related to form-closure are solved such as minimum number of frictionless contact points and the way to arrange them to achieve form-closure. On the basis of qualitative analysis, the quantitative evaluation of form-closure is investigated. To assess quantitatively the form-closure fixturing, two quantitative indices, one to minimize the sum of all normal contact forces and the other to minimize the maximum normal contact force, are presented. Finally, the given example verifies the analysis method and evaluating indices.

Qualitative analysis and quantitative evaluation of fixturing

Grasp capability analysis of multifingered robot hands

Because friction is central to robotic grasp, developing an accurate and tractable model of contact compliance, particularly in the tangential direction, and predicting the passive force closure are crucial to robotic grasping and contact analysis. This paper analyzes the existence of the uncontrollable grasping forces (i.e., passive contact forces) in enveloping grasp or fixturing, and formulates a physical model of compliant enveloping grasp. First, we develop a locally elastic contact model to describe the nonlinear coupling between the contact force with friction and elastic deformation at the individual contact. Further, a set of “compatibility” equations is given so that the elastic deformations among all contacts in the grasping system result in a consistent set of displacements of the object. Then, combining the force equilibrium, the locally elastic contact model, and the “compatibility” conditions, we formulate the natural compliant model of the enveloping grasp system where the passive compliance in joints of fingers is considered, and investigate the stability of the compliant grasp system. The crux of judging passive force closure is to predict the passive contact forces in the grasping system, which is formulated into a nonlinear least square in this paper. Using the globally convergent Levenberg-Marquardt method, we predict contact forces and estimate the passive force closure in the enveloping grasps. Finally, a numerical example is given to verify the proposed compliant enveloping grasp model and the prediction method of passive force closure. © 2005 Wiley Periodicals, Inc.

Youlun Xiong

Papers

On the Dynamic Stability of Grasping

Stability index and contact configuration planning for multifingered grasp

Qualitative analysis and quantitative evaluation of fixturing

Grasp capability analysis of multifingered robot hands

Compliant grasping with passive forces