HYBRID POSITION/FORCE MANIPULATION OF MULTIFINGERED HAND

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Coordinated control and autonomous grasp with multifingered robot hands

Presents major achievements in researches on coordinated control with multifingered robot hands by first briefing the present status of researches on multifingered robot hands, then discussing the coordinated control with multifingered robot hands, and finally exploring the way of achieving autonomous grasp, and thoughts on future researches.

Static Stability Analysis of a Single Planar Object Grasped by a.Multifingered Hand

In this study, the static stability of the grasp of a single planar object is analyzed using the potential energy method. In previous papers, we considered cases in which individual fingers were replaced by a multidimensional translational spring model, in which each finger is constructed with prismatic joints. Human hands and the most developed mechanical hands are constructed with revolute joints. In this paper, the effects of fingertip rotation and a revolute joint spring model are investigated. A grasp stiffness matrix is analytically derived by considering not only frictional rolling contact but also frictionless sliding contact. The difl＇erence between the frictional stiffness matrix and the frictionless one is analytically obtained. The effect of local curvature at contact points is analytically derived. The grasp displacement directions affected by the change in curvature and the contact condition are also obtained. The derived stiffness matrix of the revolute joint model is compared with that of the prismatic joint model, and then the stiffness relation is clarified. The gravity effect of the object is also considered. The effectiveness of our method is demonstrated through numerical examples. The stability is evaluated by the eigenvalues of the grasp stiffness matrix, and the grasp displacement direction is obtained by the corresponding eigenvectors. The effect of joint angle is also discussed.

ESTIMATION OF OBJECT GRAVITY AND WRENCH EXERTED ON OBJECT USING MULTIFINGERED HAND WITH FORCE/TORQUE SENSORS

From the point of view of real application of multifingered hand, the problem of estimating the gravity of a grasped object and the wrench exerted on the object by the external environment, using multifingered hand equipped with force/torque sensors, is addressed. At first the problem is modeled mathematically by the concept of wrench, then gravitational effect of fingertips is taken into accounted to eliminate the biasing effect in real implementation. On experimental system HKUST HAND, some experiments are carried out to implement and verify the proposed approach. This is an introduction to real application of multifingered hand, such as assembly of parts.

Linearizing the soft finger contact constraint with application to dynamic force distribution in multifingered grasping

Currently, most efficient algorithms for force-closure analysis and dynamic force distribution utilize linear programming, but friction models are nonlinear. Substituting polyhedral cones for circular cones of Coulomb friction realizes the linearization of the frictional point contact constraint. So far, however, there is no approach to soft finger contact. This paper present such an approach. Then the foregoing algorithms can be extended to grasping with soft finger contact. Herein an optimal force distribution algorithm for soft multifingered grasps is developed with an illustrative example.

Task Oriented Optimal Grasp Planning by Three Fingered Robot Hands

This paper presents a way for research on grasp planning of three fingered robot hands. According to the assortment of human hand grasping, two typical grasping poses for three finger grasps are summarized. The task requirements, the geometrical and physical features of the object and the information from the environment are synthesized. Grasp pose is deduced by task analysis, and the graspable plane is sought and determined. The process of grasp planning is finally carried out by determining three grasp points on the feasible grasp plane.

Continuous adaptive gaits manipulation for three-fingered robotic hands via bioinspired fingertip contact events

The remarkable skill of changing its grasp status and relocating its fingers to perform continuous in-hand manipulation is essential for a multifingered anthropomorphic hand.A commonly utilized method of manipulation involves a series of basic movements executed by a high-level controller.However,it remains unclear how these primitives evolve into sophisticated finger gaits during manipulation.Here,we propose an adaptive finger gait-based manipulation method that offers real-time regulation by dynamically changing the primitive interval to ensure the force/moment balance of the object.Successful manipulation relies on contact events that act as triggers for real-time online replanning of multifinger manipulation.We identify four basic motion primitives of finger gaits and create a heuristic finger gait that enables the continuous object rotation of a round cup.Our experimental results verify the effectiveness of the proposed method.Despite the constant breaking and reengaging of contact between the fingers and the object during manipulation,the robotic hand can reliably manipulate the object without failure.Even when the object is subjected to interfering forces,the proposed method demonstrates robustness in managing interference.This work has great potential for application to the dexterous operation of anthropomorphic multifingered hands.

Anthropomorphism Indexes of the Kinematic Chain for Artificial Hands

Anthropomorphic hands have received increasing research interest in the fields of robotics and prosthetics.But it is not yet clear how to evaluate their anthropomorphism.Similarity in the kinematic chain is essential to achieve both functionality and cosmesis.A few previous works have addressed the definition of anthropomorphism indexes,although they have some limitations in its definition.In this study,three different anthropomorphism indexes have been defined to compare the kinematic chain of artificial hands with that of the human hand.These indexes are based on the comparison of:(I)the parameters of the kinematic chain(dimensions,type of joints,orientations and ranges of motion),(2)the reachable workspace,and(3)common grasping postures.Five artificial hands with different degrees of anthropomorphism have been compared using the three Anthropomorphism Indexes of the Kinematic Chain(AIKC).The results show a high correlation between the first and third AIKC for the hands compared.The second AIKC presents much lower values than the other two,although they are higher for hands that combine abduction/adduction and flexion/extension movements in the kinematic chain of each finger.These indexes can be useful during the initial stage of designing artificial hands or evaluating their anthropomorphism.

Grasp evaluation and contact points planning for polyhedral objects using a ray-shooting algorithm

Grasp evaluation and planning are two fundamental issues in robotic grasping and dexterous manipulation. Most traditional methods for grasp quality evaluation suffer from non-uniformity of the wrench space and a dependence on the scale and choice of the reference frame. To overcome these weaknesses, we present a grasp evaluation method based on disturbance force rejection under the assumption that the normal component of each individual contact force is less than one. The evaluation criterion is solved using an enhanced ray-shooting algorithm in which the geometry of the grasp wrench space is read by the support mapping. This evaluation procedure is very fast due to the efficiency of the ray-shooting algorithm without linearization of the friction cones. Based on a necessary condition for grasp quality improvement, a heuristic searching algorithm for polyhedral object regrasp is also proposed. It starts from an initial force-closure unit grasp configuration and iteratively improves the grasp quality to find the locally optimum contact points. The efficiency and effectiveness of the proposed algorithms are illustrated by a number of numerical examples.

Mechanical design,modeling,and identification for a novel antagonistic variable stiffness dexterous finger

This study traces the development of dexterous hand research and proposes a novel antagonistic variable stiffness dexterous finger mechanism to improve the safety of dexterous hand in unpredictable environments,such as unstructured or man-made operational errors through comprehensive consideration of cost,accuracy,manufacturing,and application.Based on the concept of mechanical passive compliance,which is widely implemented in robots for interactions,a finger is dedicated to improving mechanical robustness.The finger mechanism not only achieves passive compliance against physical impacts,but also implements the variable stiffness actuator principle in a compact finger without adding supererogatory actuators.It achieves finger stiffness adjustability according to the biologically inspired stiffness variation principle of discarding some mobilities to adjust stiffness.The mechanical design of the finger and its stiffness adjusting methods are elaborated.The stiffness characteristics of the finger joint and the actuation unit are analyzed.Experimental results of the finger joint stiffness identification and finger impact tests under different finger stiffness presets are provided to verify the validity of the model.Fingers have been experimentally proven to be robust against physical impacts.Moreover,the experimental part verifies that fingers have good power,grasping,and manipulation performance.