Three-fingered Robot Hand Research Articles

Evaluation of 3D grasps with physical interpretations using object wrench space

SUMMARYIn this paper we propose an intuitive and practical grasp quality measure for grasping 3D objects with a multi-fingered robot hand. The proposed measure takes into account the object geometries through the concept of object wrench space. Physically, the positive measure value has a meaning of the minimum single disturbance that grasp cannot resist, while the negative measure value implies the minimum necessary helping force that restores a non-force-closure grasp into a force-closure one. We show that the measure value is invariant between similar grasps and also between different torque origins. We verify the validity of the proposed measure via simulations by using computer models of a three-fingered robot hand and polygonal objects.

An Algorithm for Force-Closure Grasping of Three-Fingered Hand

On the assumption of FCWF model, the conditions of three-fingered robot hand force-closure grasping are equivalent to grasp matrix be full rank and exist rigorous internal forces. Based on the analysis to the geometrical characteristics of contact points, the existence condition of the frictional sectors is established. By means of studying the relative location relationships between the frictional sector borderlines and their intersections, the existence condition of the concurrent polygon of three internal forces is presented. Taking the equilibrium relation of internal forces into consideration, a general algorithm using vector calculation for force-closure grasping is established. An example is given to illustrate the validity of the algorithm.

Force Sensorless Impedance Control of Dual-Arm Manipulator-Hand System

In this paper, we describe the manipulation of nuts and flexible objects for assembly work by incorporating force sensorless impedance control in a robot. This robot is a dual-arm manipulator, and each of its end effectors is a three-fingered robot hand. Generally, a force sensor is used for recognition of external force on the fingertips. However, such sensors are very expensive and easily damaged by inappropriate contact with the object. This motivated us to estimate the external force without using a force sensor. In this study, the external force on the robot fingertip was estimated using a disturbance observer. Then, estimated results were compared with measurement results of the force sensor to validate the former. Impedance control was designed for a three-fingered robot hand by using this estimated external force. By application of the designed impedance control to the robot hand, the robot was successfully able to grasp nuts ranging in size from 2 mm to 12 mm through an algorithm formulated in the study. In this algorithm, we incorporated a method called following control to retain the contact of the finger with the worktable while performing the grasping task. Thus, the nut grasping task could be performed at a higher success rate, despite some errors in the robot position and vision data. Furthermore, a boiled egg considered as a flexible object was successfully grasped through force sensorless impedance control. An impedance controller for the boiled egg was designed using identified model parameters of the egg, and its effectiveness was validated experimentally.

Research on Velocity Directional Manipulability of Dexterous Robot Hand

On the basis of manipulability ellipsoid of manipulator, the velocity directional manipulability of three-fingered dexterous robot hand is defined. Under the condition of given position and orientation, taking the velocity directional manipulability as objective function, the optimal velocity transmission direction is presented in this paper. The given example shows the velocity transmission performance of three-fingered dexterous robot hand on a specific position and orientation.

Analysis and design for changing finger posture in a robotic hand

Abstract In this paper, design considerations are proposed for improving grasping capabilities of a low-cost easy-operation three-finger robotic hand. Through a suitable additional mechanism design, a special planetary gear mechanism has been designed to adjust the position and orientation of two fingers during hand’s operation. This novel solution significantly improves the flexibility of a robotic hand in terms of sizes and shapes of objects which can be grasped. Furthermore, both pinching and enveloping grasp configurations can be achieved similarly to human hands. Simulations are performed in Adams environment whose results show effectiveness of the proposed mechanism design both in terms of kinematic and dynamic performance.

Interactive teaching of task-oriented robot grasps

This paper focuses on the problem of grasp stability and grasp quality analysis. An elegant way to evaluate the stability of a grasp is to model its wrench space. However, classical grasp quality measures suffer from several disadvantages, the main drawback being that they are not task related. Indeed, constructive approaches for approximating the wrench space including also task information have been rarely considered. This work presents an effective method for task-oriented grasp quality evaluation based on a novel grasp quality measure. We address the general case of multifingered grasps with point contacts with friction. The proposed approach is based on the concept of programming by demonstration and interactive teaching, wherein an expert user provides in a teaching phase a set of exemplar grasps appropriate for the task. Following this phase, a representation of task-related grasps is built. During task planning and execution, a grasp could be either submitted interactively for evaluation by a non-expert user or synthesized by an automatic planning system. Grasp quality is then assessed based on the proposed measure, which takes into account grasp stability along with its suitability for the task. To enable real-time evaluation of grasps, a fast algorithm for computing an approximation of the quality measure is also proposed. Finally, a local grasp optimization technique is described which can amend uncertainties arising in supplied grasps by non-expert users or assist in planning more valuable grasps in the neighborhood of candidate ones. The paper reports experiments performed in virtual reality with both an anthropomorphic virtual hand and a three-fingered robot hand. These experiments suggest the effectiveness and task relevance of the proposed grasp quality measure.

Control of Grasp and Manipulation by Soft Fingers with 3-Dimensional Deformation

In this paper, we consider control of grasp and manipulation of an object in a 3-dimensional space by a 3- fingered hand robot with soft finger tips. We firstly propose a 3-dimensional deformation model of a hemispherical soft finger tip and verify its relevance by experimental data. Second, we consider the contact kinematics and derive the dynamical equations of the fingers and the object where the 3-dimensional deformation is considered. For the system, we thirdly propose a method to regulate the object and the internal force with the information of the hand, the object and the deformation. A simulation result is presented to show the effectiveness of the control method. rolling contact in a two-dimensional space. They considered vertical deformation to the flat part of the soft finger and de- formation parallel to the surface of the contacted object. These studies proposed reasonable deformation models and control methods for grasp and manipulation, which take into account the properties of the deformation. However, since their de- formation models and control methods are considered in re- stricted two-dimensional space, their methods can not be ap- plied to manipulation in a 3-dimensional space. Yokokohji et al. (10) considered the grasp and manipulation of an object in 3-dimensional space by a three-fingered robot hand with hemi- spherical soft fingers and proposed a controller with friction compensation of the torsion moments about contact normals. However, the deformation of the soft finger is not considered because the contact is assumed to be point. In this paper, we firstly derive a three-dimensional deforma- tion model of a hemispherical soft finger, which is composed of three translational forces and one torsion moment about the contact normal. The all four force components generated by a soft finger (11) is included in this model. The relevancy of the deformation model is verified by experiment data. With this model, we consider control of grasp and manipulation of an object in 3-dimensional space by a 3-fingered hand robot, each of which has three degrees of freedom. Second, we consider the contact kinematics with the finger deformation and derive the dynamical equations of the fingers and the grasped object with deformation effects. For the system, we thirdly propose a method to regulate the object and the internal force with the information of the hand, the object and the deformations. A simulation is presented to show the effectiveness of the control method.

1A2-D08 力覚センサレスインピーダンス制御による柔らかい把持の実現

Our research group study about the autonomous dual-arm assembly robot. The first of goal as assembly work is tightening up nut to bolt. We propose force sensorless impedance control of the three-fingered robot hand and it is proposed to produce soft grasping. Force control is one of the important aspects in industrial and nursing robots for accurate and safe operations. Generally, force sensor is often used for this purpose despite of its expensive cost. This has lead us to use the current sensor instead, where the current between motor and motor driver is measured and used to estimate the external force applied to the finger. Finally, we describe the following control with force sensorless impedance control. In this paper, the proposed method has successfully grasped the M3 sized nut.

Algorithm for Internal Force Concurrent Polygon Existence of Three-fingered Robot Hand

The internal forces play an important role in the stable grasping of three-fingered robot hand. Under the condition of fixed-point contact models with friction between the fingertips and the object surface, it is necessary for the three internal forces to lie in relative frictional sectors of contact points and intersect at a point within concurrent polygon. As a result, the research on optimized algorithm for internal force should be made on the basis of concurrent polygon existence. Based on the analysis of the geometrical characteristics of contact positions on the object surface, the existence condition of the frictional sectors is established. The angle between inner normal vector and relative inner normal vector of each contact point should be smaller than friction cone angle. By means of studying the relative location relationships between the frictional sector borderlines and their intersections, the existence condition of the concurrent polygon for the three internal forces is presented. All intersections of any two frictional sectors are not less than one lying in absolute inner of the third frictional sector or not less than three lying on the borderlines of the third frictional sector. At last, a general algorithm for judging the existence of concurrent polygon is founded, by which the self-balancing internal forces can be determined and used to regulate the fingertip manipulating forces. An example is given to illustrate the validity of the algorithm.

1A1-G08 双腕組立作業ロボットのマスタ・スレーブ制御(作業をするロボット)

In this paper, we propose Master-slave control of Dual-Arm Robot. The purpose of the study is developing a autonomous dual-arm assembler robot. The first of goal as assembly work is tightening up nut to bolt. In order to do the work, we work out a design of the end effector. The end effector is a robot hand having three fingers. The control system of the three-fingered robot hand is designed LQI control (linear quadratic integral control system). In addition, we operate Dual-Arm Robot which we use a master-slave system for. By using the master-slave system, we are able to operate Dual-Arm Robot even if we do not create complicated trajectory program. It is presented the master-slave system is effective for operability and following capability. The control system of the Dual-Arm Robot is designed PID control.

Research on novel shape memory alloy multi-fingered humanoid hand

Two new type actuators named planar bending embedded shape memory alloy actuator (ESMAA) and spacial bending ESMAA were presented. Using shape memory effect of SMA wires and elasticity of room temperature vulcanization silicone rubber, the ESMAAs could output force and bend displacement steadily. Furthermore, a novel three-fingered humanoid robot hand consisting of six ESMAAs was developed first. The structural parameters of the actuators, such as rod's radius, wire's radius, wire's recoverable curvature, and offset distance were optimized by combining analytical model with experimental results. On the basis of bionics, the lengths of hand's knuckles were determined through statistical research on the configuration of human beings' hands. The locations of fingers were carefully chosen through a volume optimal index. It is shown in the experiments that maximum angle between ends' tangents of each finger are 68.5°, 79°, and 79°, respectively. The tip of each finger could reach its final position approximately at the same time and by controlling the bending of each finger, the hand could accomplish fine manipulation like that of a human being.

Design and control of a shape memory alloy based dexterous robot hand

Modern externally powered upper-body prostheses are conventionally actuated by electricservomotors. Although these motors achieve reasonable kinematic performance, theyare voluminous and heavy. Deterring factors such as these lead to a substantialproportion of upper extremity amputees avoiding the use of their prostheses.Therefore, it is apparent that there exists a need for functional prosthetic devicesthat are compact and lightweight. The realization of such a device requires analternative actuation technology, and biological inspiration suggests that tendon basedsystems are advantageous. Shape memory alloys are a type of smart materialthat exhibit an actuation mechanism resembling the biological equivalent. Assuch, shape memory alloy enabled devices promise to be of major importancein the future of dexterous robotics, and of prosthetics in particular. This paperinvestigates the design, instrumentation, and control issues surrounding the practicalapplication of shape memory alloys as artificial muscles in a three-fingered robothand.

Virtual circle mapping for master–slave hand systems

The classical mapping methods were developed based on anthropomorphic robot hands. Normally, they are not applicable or cannot provide satisfactory performance if the robot hand is non-anthropomorphic. This paper presents a virtual circle mapping method dealing with the three-fingered non-anthropomorphic robot hand. The basic idea is to express the operator's motion by a virtual circle determined by the three fingertips. Four sets of parameters are used to describe the circle: circle radius, central angles, circle center and circle orientation. By transforming the four sets of parameters from the human frame to the robot frame, the information of relative positions between the fingertips is delivered. The robot fingertip positions are then computed according to the transformed parameters. The concept is introduced and implemented on a specific three-fingered non-anthropomorphic robot hand. The simulation results and the experiments have shown that the proposed method is able to obtain better workspace matching and, thus, the operator can tele-control the robot hand more intuitively.

Vision-based three-finger grasp synthesis constrained by hand geometry

This paper addresses the problem of designing a practical system able to grasp real objects with a three-fingered robot hand. A general approach for synthesizing two- and three-finger grasps on planar unknown objects is presented. Visual perception is used to reduce the uncertainty and to obtain relevant information about the objects. We focus on non-modeled planar extruded objects, which can represent many real-world objects. In addition, particular mechanical constraints of the robot hand are considered. First, a vision processing module that extracts from object images the relevant information for the grasp synthesis is developed. This is completed with a set of algorithms for synthesizing two- and three-finger grasps taking into account force-closure and contact stability conditions, with a low computational effort. Finally, a procedure for constraining these results to the kinematics of the particular hand, is also developed. In addition, a set of heuristic metrics for assessing the quality of the computed grasps is described. All these components are integrated in a complete system. Experimental results using the Barrett hand are shown and discussed.

On Quality Functions for Grasp Synthesis, Fixture Planning, and Coordinated Manipulation

Planning a proper set of contact points on a given object/workpiece so as to satisfy a certain optimality criterion is a common problem in grasp synthesis for multifingered robotic hands and in fixture planning for manufacturing automation. In this paper, we formulate the grasp planning problem as optimization problems with respect to three grasp quality functions. The physical significance and properties of each quality function are explained, and computation of the corresponding gradient flows is provided. One noticeable property of some of these quality functions is that the optimal solutions are also force-closure grasps if they do exist for the given object. Furthermore, when specialized to two-fingered or three-fingered grasps on a spherical object, the optimal solutions become the familiar antipodal grasp, or the symmetric grasp, respectively. Thus, by following the gradient flows with arbitrary initial conditions, the optimal grasp synthesis problem is solved for objects with smooth geometries manipulated by hands with any number of fingers. Also, note that our solutions do not involve linearization of the friction cones. We discuss two simplified versions of these problems when real-time solutions are needed, e.g. coordinated manipulation of a robotic hand with contact points servoing. We give simulation and experimental results illustrating validity of the proposed approach for optimal grasp planning. Note to Practitioners: This paper presents three new quality functions for comparing and planning grasps and fixtures. These measures improve on the traditional measure of force closure. We propose a method for computing the optimal solutions of these functions, and a method for reducing their computation time through reasonable simplification/approximation. Preliminary experiments with a three-fingered robotic hand demonstrate that the proposed functions can be used to optimize the grasp quality during manipulation/manufacturing, and keep the optimal grasp configuration once it is reached. However, we only obtain the local optimal solutions for the functions without simplification except for some special cases. We also assume that the object/workpiece is ideally rigid in all three functions. In future research, we will improve these limitations through a compliance model.

121 筋電信号による動作識別とロボット制御(GS-2.15 人間・機械協調系)

The number of amputees is increasing by industrial or traffic accidents, although safety control and accident prevention are made much of. Since amputees use prosthesis, the needs of prosthesis are increasing year after year. This work represents a research on multi-functionalization of myoelectric upper limb prosthesis. Pattern recognition motions of hands from Electromyogram (EMG) signals were attempted. The target function of each operation is given and EMG signals measured on the skin surface are separated the signal corresponding to each operation using linear multiple regression model. Using this technique, three motions (a grip, a knob, an opening of a hand) were recognized. The validity of the proposed signal separation by the proposed technique is verified by the experiment using three-fingered robot hand. In this experiment, EMG was measured, the model was created, and the robot hand was operated on-line. The result showed that high precision of recognition with this method.

Kinematic feasibility analysis of 3-D multifingered grasps

Planning of a dextrous manipulation task for a multifingered hand requires the feasibility of all the grasps involved throughout the manipulation process. In this paper, we address the problem of determining whether a desired grasp of a polyhedral object is kinematically feasible. In our study, we define a grasp in terms of a system of contact pairs between the topological features of the hand and the object, and formulate the grasp feasibility analysis as a set of equality and inequality constraints in the variables of the hand and object configurations. The feasibility of a grasp then becomes equivalent to the simultaneous satisfaction of all the constraints. This allows us to cast the feasibility analysis conveniently as a constrained nonlinear optimization problem and solve it numerically with commercially available software. The effectiveness of our approach is illustrated with an example of grasping a cuboid using a three-fingered robotic hand.

Development of anthropomorphic robot hand SKK robot hand I

In this paper, a three-fingered anthropomorphic robot hand, called SKK Robot Hand I, is presented. By employing a two-DOF joint mechanism, called Double Active Universal Joint (abbreviated as DAUJ from now on) as its metacarpal joint, the hand makes it possible to mimic humanlike motions. We begin with addressing the motivation of the design and mention how the anthropomorphic feature of a human is realized in the design of SKK Hand I. Also, the mechanism of the hand is explained in detail, and advantages in its modular design are discussed. The proposed hand is developed for use as a testbed for dextrous manipulation. It is expected to resolve the increasing demand for robotic applications in unstructured environments. We describe its hardware construction as well as the controller structure including the preliminary results of experiments.

Stable grasp planning by evolutionary programming

This paper deals with the problem of synthesis of stable grasp by multifingered hands. First, a mathematical description of the problem is formulated. The grasp to be synthesized should satisfy equilibrium conditions and unilateral frictional constraints. In addition, it should be stable against disturbances applied to the object. Two types of stability conditions, contact stability and Lyapunov stability, are taken into consideration. Contact points, contact forces and joint stiffnesses are considered as the problem variables. The objective function maximizes admissible linear and rotational disturbances applied to the object, Since the dimension and the complexity of the resulting constrained optimization problem is high enough, the evolutionary programming (EP) approach is explored. Two EP techniques, a conventional one and a specially designed robust technique with a genetic drift, are discussed. The feasibility of these techniques is verified for the synthesis of stable grasp by a three-fingered robotic hand.

On dynamic control of finger sliding and object motion in manipulation with multifingered hands

Dynamic control of a three-fingered robot hand manipulating an object in 3D space, while allowing one of the three fingers to slide in order to change its grasp location on the object surface, is formulated. The static and dynamic friction between the sliding finger and the object surface are explicitly considered and their effects regarding the behavior of the finger and object are discussed. Motion equations of the whole system are derived and a dynamic control law for realizing the desired object motion, as well as the desired finger sliding and the desired grasping force, is proposed. The realizability of the given trajectories under the constraints of maximal static friction and dynamic friction at the grasp points, and of joint driving torque, are also discussed. A simulation example to demonstrate the use of the proposed control law is given. The results of this work will have useful application to a multifingered robot hand in performing certain tasks involving the re-grasping and re-orientation of an object without interrupting the grasp.