Zhenguo Sun

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...

Under-actuated passive adaptive grasp humanoid robot hand with control of grasping force

Conventional dexterous hands have too many DOFs, their driver systems are too big to be installed in a humanoid robot arm, and their controls are tool complex. This paper develops an under-actuated passive adaptive grasp humanoid robot hand named TH-1 hand with control of grasping force. With humanoid appearance and size, TH-1 hand is light, fewer DOFs, and can be easily controlled. Its motors and driver circuit boards are embedded in itself. These features make it fit to be installed in a humanoid robot arm. In addition, for stably grasping operation, a mechanical finger with control of grasping force is designed and applied in TH-1 hands index. To get more DOFs with fewer drivers, a novel under-actuated passive adaptive grasp mechanical finger is design and applied in TH-1 hands thumb.

Passive adaptive grasp multi-fingered humanoid robot hand with high under-actuated function

This paper proposed a design idea of a novel under-actuated finger mechanism, and designed the finger mechanism. The finger has no actuator in itself, is only driven by the other finger joints and object grasped. The finger is similar to a human finger and can be easily arranged in series to realize a finger with super under-actuation and high integration. It can be mounted in humanoid robot hand to make the hand obtain more DOFs with less actuators, and good grasping function of shape adaptation, decrease the requirement of control system. This paper analyzed the relationship between the grasping force of the finger and its design parameters, proposed the design principle of structure optimization of the finger. Based on the finger, a multi-fingered humanoid robot hand: TH-2 Hand has been designed. TH-2 Hand has many excellent features: high personification, super under-actuation and be very compact, easy to real-time control, small volume, light in weight, strong grasping function, etc.

A Robot for Welding Repair of Hydraulic Turbine Blade

This paper proposed a scheme of using rail-free multifunctional robot in onsite repair of hydraulic turbine blade for large-scale axial-flow and Francis runners. The robot processes such functions as profile detection and measurement, air-gouging cleaning, grinding, welding and so on. The robots main body is composed of an all-position rail-free mobile platform and a multiple degree-of-freedom (DOF) manipulator. The mobile platform, on which the manipulator equipped with all kinds of exchangeable operating tools is mounted, adheres to the surface of the hydraulic turbine blade to be repaired. The operator can control the robot to carry out repairing work automatically through man-machine conversation interface of a monitoring system. Simulation of the process of welding repair using the robot was conducted. And prototypes of key components of the robot system were developed. Preliminary experimental results proved the feasibility of scheme of the repairing robot.

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.

LISA Hand: Indirect self-adaptive robotic hand for robust grasping and simplicity

Humanoid robotic hand is one of most impressive research focus in robotics. There are two important requirements in robotic hands: on the one hand, a hand has a good humanoid appearance and sizes and can grasp almost all of common objects, on the other hand, the same hand is very simple in structure, very easy in control and very low in cost. Most of present dexterous robotic hands could not balance above two aspects. In searching for simple architecture and effective grasp at once, a novel under-actuated robotic hand is designed and manufactured and could achieve the above requirements perfectly, which is called Linkage Indirectly Self-Adaptive Under-actuated Hand, LISA Hand. The key of the LISA Hand is special and simple structure of its fingers. The indirectly under-actuated LISA finger can utilize the inverse forces from objects grasped to realize action of the next joint without any motor. Each of LISA fingers is composed of multiple-class block-linkage-slot transmission mechanisms, multiple springs and only one motor with a reducer. The LISA Hand has 5 fingers, 14 joint DOFs and only 5 motors. All fingers in the LISA Hand are similar. The thumb has two joints, and each of the other four fingers has three joints. Self-adaptation for good grasping performance is designed as the main function of the LISA finger. The grasping principle, process and force analysis of LISA Hands are given. Force analysis shows that the LISA Hand is valid and could be regarded as an end-effecter of humanoid robots.

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

A novel visual image sensor for CO2 short circuiting arc welding and its application in weld reinforcement detection

In this paper, a novel visual image sensor was designed to detect the weld pool images during CO2 short circuiting arc welding. Based on a charge coupled device (CCD) camera, the new sensor was smaller than the previous one. As a result, larger operation space is achieved for the welding torch which is attached to it. Moreover, the mismatching problem between the fixed shooting schedule of the CCD camera and the random short circuiting metal transfer during welding was successfully resolved. By eliminating the influences from welding arc and spatter, clear and complete welding pool images were acquired from different angles around the welding torch. Based on these images, the shape parameters of the welding pool were defined and the relationship between these parameters and weld reinforcement was analysed. In addition, the multiple linear regression (MLR) model and the artificial neutral network (ANN) model were proposed and trained, respectively, to detect weld reinforcement from weld pool images. Results of both the MLR model and the ANN model show that weld reinforcement can successfully be detected.

PASA finger: A novel parallel and self-adaptive underactuated finger with pinching and enveloping grasp

The traditional dexterous robot hand has always many grasping modes but it is difficult to control due to a lot of actuators and grasping tasks for different objects. A self-adaptive underactuated robot hand uses few motors to drive several joints, but is lack of the ability to pinch objects. In order to combine the abilities of dexterous hand and self-adaptive hand, this paper presents a novel design of a parallel and self-adaptive underactuated robot finger with pinching and enveloping grasp, called PASA finger. Due to its special structure, it can realize the pinching grasp or enveloping grasp, according to the different positions, shapes and sizes of the target object, which is a self-adaptive process. Analysis results show that an application force on the distal phalange keeps the parallel mechanism unchanged, while an application force on the proximal phalange destroys the parallel mechanism and leads the distal phalange move towards the target object, which is another self-adaptive process. The PASA hand is suitable for both industry and home application.

Attitude and gyro bias estimation by the rotation of an inertial measurement unit

In navigation applications, the presence of an unknown bias in the measurement of rate gyros is a key performance-limiting factor. In order to estimate the gyro bias and improve the accuracy of attitude measurement, we proposed a new method which uses the rotation of an inertial measurement unit, which is independent from rigid body motion. By actively changing the orientation of the inertial measurement unit (IMU), the proposed method generates sufficient relations between the gyro bias and tilt angle (roll and pitch) error via ridge body dynamics, and the gyro bias, including the bias that causes the heading error, can be estimated and compensated. The rotation inertial measurement unit method makes the gravity vector measured from the IMU continuously change in a body-fixed frame. By theoretically analyzing the mathematic model, the convergence of the attitude and gyro bias to the true values is proven. The proposed method provides a good attitude estimation using only measurements from an IMU, when other sensors such as magnetometers and GPS are unreliable. The performance of the proposed method is illustrated under realistic robotic motions and the results demonstrate an improvement in the accuracy of the attitude estimation.