Dong Du

Super under‐actuated multi‐fingered mechanical hand with modular self‐adaptive gear‐rack mechanism

Purpose – The purpose of this paper is to present recent work designing a mechanical robotic hand for self‐adaptive grasping, human‐like appearance, which can be used in a humanoid robot. Conventional robotic devices are relatively complex, large, cumbersome and difficult to be installed in a humanoid robot arm. Under‐actuated robot hands use less motors to drive more rotating joints, thus to simplify the mechanical structure, decrease the volume and weight and finally lower the difficulty of control and the cost.Design/methodology/approach – A novel under‐actuated finger mechanism is designed, which is based on a gear‐rack mechanism, spring constraint and an active sleeve middle phalanx. The principle analyses of its self‐adaptive grasp and end power grasping are given. A new multi‐fingered hand named as TH‐3R Hand is designed based on the finger.Findings – The design finger mechanism can be used in a robotic hand to make the hand obtain more degrees of freedom (DOF) with fewer actuators, and good graspi...

A Dexterous and Self-adaptive Humanoid Robot Hand: Gesture-Changeable Under-Actuated Hand

A novel concept called gesture-changeable under-actuated (GCUA) function is proposed to improve the dexterities of traditional under-actuated hands and reduce the control difficulties of dexterous hands. Based on the GCUA function, a new humanoid robot hand, GCUA Hand is designed and manufactured. The GCUA Hand can grasp different objects self-adaptively and change its initial gesture dexterously before contacting objects. The hand has 5 fingers and 15 DOFs, each finger is based on screw-nut transmission, flexible drawstring constraint and belt-pulley under-actuated mechanism to realize GCUA function. The analyses on grasping static forces and grasping stabilities are put forward. The analyses and Experimental results show that the GCUA function is very nice and valid. The hands with the GCUA function can meet the requirements of grasping and operating with lower control and cost, which is the middle road between traditional under-actuated hands and dexterous hands.

TWO-DOF COUPLED AND SELF-ADAPTIVE (COSA) FINGER: A NOVEL UNDER-ACTUATED MECHANISM

A large amount of effort has been devoted to design better under-actuated robot hands. The most widely adopted approaches include rigid coupled hands and self-adaptive hands. The objective of this research is to design a robot finger which combines advantages of both ways and overcomes their disadvantages. The concept of coupling and self-adaptation (COSA) was introduced. A linkage-based two-DOF (degree of freedom) COSA robot finger was designed, optimized and studied in this paper. The theoretical analysis and the experiments on the finger show that it is able to execute human-like motion and adaptive grasps in multiple patterns. The research exposes a promising novel under-actuated mechanism for hands design with wide applications.

Seam Tracking of Articulated Robot for Laser Welding Based on Visual Feedback Control

Laser welding has a quite high demand on trajectory accuracy of articulated robot. To improve dynamic trajectory accuracy of articulated robots for laser welding, a novel 3D seam tracking method is proposed based on stereo visual feedback control. The method constructs a visual feedback control system with two convergent cameras mounted at the end of industrial robot. A tool coordinate system is constructed to transfer the end-link displacement of robot to that of the tool. A proposed GPI transform method, binocular vision technologies and a modified algorithm of line-line matching are utilized to calculate the positions of laser focus and weld seam, which makes the dynamic trajectory error between laser focus and weld seam can be calculated. The robot is finally commanded to move and decrease the trajectory error as soon as possible based on robot kinematics. Experimental results show that the method can effectively improve the trajectory accuracy of industrial robot for laser welding

Linkage under-actuated humanoid robotic hand with control of grasping force

The single-motor multiple DOFs under-actuated finger is the focus of robot research. The grasping force of traditional under-actuated hands based on linkages is hard to control. The traditional hands also have many differences from human hands in appearance. Aiming to solve these problems, this paper has presented a novel under-actuated hand based on linkages, which also comprises of slider mechanisms and springs. Its finger has a changeable force output controlled by a motor with humanoid appearance. It also can adapt to the shape of objects. This article analyzed the force properties of the finger. According to this, a 2-DOF finger and a 3-DOF finger were designed. Finally, they are included in the hand named TH-3L, which comprises of five fingers and six motors with 15 DOFs.

Design and analysis of underactuated humanoid robotic hand based on slip block-cam mechanism

Compared with traditional dexterous humanoid robotic hands, underactuated robotic hands have the advantages of selfadaptive grasp and easy real-time control. In this paper, the development of a novel underactuated robotic hand is presented. This hand has five fingers and through using underactuation, the selfadaptability of each finger is achieved. This underactuated humanoid robotic hand can accomplish complicated selfadaptive grasp without high demand for real-time control system. In the first place, the design of a two degree-of-freedom underactuated finger is given. Then the parameters affecting the rotary angle and grasp force of the underactuated finger are analyzed and optimized. Finally, taking one finger as a module, the entire humanoid robotic hand is designed. This robotic hand is similar to human hand on appearance and size. It has many good merits such as good selfadaptability, compactness, easy real-time control, small volume and light weight.

Development of the CA Robot Finger with a Novel Coupled and Active Grasping Mode

This paper proposes a novel coupled and active (CA) grasping mode for robot finger. While coupled grasping mode enables the phalanges of the finger to rotate in an anthropomorphic way, the active grasping mode enables the finger to adapt to the object’s shape automatically. Combination of these grasping modes can greatly reduce the controlling complexity and enlarge the application of coupled hands. The CA finger is developed based on the pulley-belt mechanism. It is composed of a finger base and two mobile phalanges. The control process of the finger is also introduced in this paper. Grasping capabilities is validated by experiments. Theoretical and experimental results show that the CA grasping mode is effective.

An indirect style linkage under-actuated humanoid robot hand

Based on the analysis of the development of recent robotic hands, proposes the design of a new under-actuated humanoid hand, the object seized drives the first segment slip inside under the forces applied by the other active joints or fingers, thus the first segment presses the active link to rotate and consequently make the second segment rotate through the passive link. This paper also evaluates the characteristics of kinesiology and dynamics. This hand fits to be mounted in a humanoid robot because of its high personification, satisfied self-adaptation, super under-actuation, compactness with easy real-time control, small volume, lightweight, strong grasping function.

The indirect style under-actuated robotic finger with tendon-slider mechanisms

This paper proposed a novel concept of indirect under-actuation with tendon-slider mechanism. A mechanical finger with the mechanism was designed and integrated into a humanoid robotic hand-TH-2T Hand. The tendon-slider under-actuated finger proves simple but works well. In the design of the finger, the reaction force against a slider in the base segment produced by the grasped object was adopted to make the next segment bend, which relies on a special tendon-slider mechanism. Further, all the five fingers on the TH-2T Hand applies the indirect under-actuated mechanism. Compared with those full-active fingers, the finger and hand designed in this paper have strong self-adaptation to the grasped object; compared with those direct under-actuations, the designed mechanism effectively simplifies the structure, decreases the volume and costs of manufacturing.

Circular Sub-window Multi-Step GPI Method in Seam Tracking of Welding Robot Based on 3D Vision

Laser welding requires quite high trajectory accuracy of articulated welding robot. To increase this dynamic trajectory accuracy, a novel 3D seam tracking method is proposed based on stereo visual feedback control, in which a key task is to detect the seam from the vision image. To improve the precision and efficiency of the GPI seam-detecting method, this paper proposed a new method, the multi-step gray projecting integral (MSGPI) method with a circular sub-window. This method applies a circular division in image as the sub-window for detection and the means of GPI values, based on while surpassing the Standard GPI method. It adopts a link table to store edge points gained by Sobel filtering previously to reduce the amount of computation. A threshold method is employed to effectively eliminate noises caused by scratching and rust. The searching range of the lines angle in GPI process is divided into coarse searching and fine searching, which not only ensures detection accuracy but also greatly reduces the amount of computation. The experimental results show that the MSGPI method can achieve rapid and accurate detection for weld seam even if the seam is quite narrow, and can thus greatly improve the trajectory accuracy of industrial robot for laser welding, and the system using this method could meet the demand of high accuracy trajectory tracking.