Xinhan Huang

Adaptive Task-Space Tracking Control of Robots Without Task-Space- and Joint-Space-Velocity Measurements

The task-space tracking control of robots without the exact knowledge of kinematics and dynamics has been studied before with the assumption that the joint velocities are available for controller designs. However, the velocity measurements can be contaminated by noises, thereby resulting in poor system performance, or even leading to instability problems. Therefore, in this paper, we propose a new tracking controller for robots in the task space without the use of both task-space and joint-space-velocity measurements, under the condition that both the robot kinematics and dynamics are unknown. To overcome these incapacities without the velocity measurements, we introduce the well-known sliding-observer-design techniques to estimate the joint velocities for the purpose of our controller design. Our main concern, i.e., the stability analysis of our controller design incorporated with the siding observer, is presented with the help of Lyapunov-analysis methodology and the sliding-patch concept. Simulation results are presented to show the performance of our controller-observer designs.

Development of A Robotic Microassembly System with Multi-Manipulator Cooperation

Due to scaling effects robotic assembly of micron-sized parts is quite different from the macro one. Poorly understood mechanisms of micromanipulation and unpredictable effects of microphysics present a great challenge to perform complex 3D microassembly operation with high precision. This paper introduces an experimental microassembly system with multi-manipulator cooperation. The workcell consists of two 4 DOF master micromanipulators and one 3 DOF slave micromanipulator. Two kinds of micro end effectors, vacuum gripper and piezoelectric-bimorphs tweezer, are developed to handle micro parts under stereo microscopic vision monitoring. A semi-autonomous microassembly strategy is investigated with human-robot task plan interaction and sensor-based control approaches. The prevalent operation by microassembly workcell is introduced and the accomplished experiment demonstrates the system executes micro parts assembly reliably and availably

Fuzzy Adaptive Kalman Filtering based Estimation of Image Jacobian for Uncalibrated Visual Servoing

An image Jacobian estimate method for uncalibrated visual servoing is proposed in this paper. With less or no prior knowledge to robotic parameters and filtering statistics, the method employs a Kalman filter to provide an optimal estimate of the Jacobian elements and fuzzy logic controllers to adjust the Kalman noise covariance matrices Q and R adaptively. The adaptations are performed based on a matching technique of the filter residual mean value and covariance error. It greatly improves the Jacobian estimate adaptability to unknown dynamic imaging applications. A microscopic image Jacobian model has been developed for the 4 degree-of-freedom micromanipulator in our microassembly system. Its Jacobian estimate results demonstrate a good performance of the proposed method

Three-Layered Control Architecture for Microassembly with Human-Robot Task Plan Interaction

Assembly manipulation in the micro world presents challenges not found in the macro domain. A three-layered control architecture for microassembly with human-robot task plan interaction is proposed in this paper. The architecture combines the abilities of human decision making and task planning with visual servo strategies to ensure the reliability and automaticity of micromanipulation. It has three control levels: the behaviour layer interacts with the real physical world to control actuators and sensors. The task layer specifies assembly goals by human task planning. As the middle level, the strategy layer yields visual servo schemes from abstract assembly goals and expands them into low-level behaviour commands. TaskML, the task markup language, is designed based on XML for human task planning. Task plan tree (TPT) data specifies microassembly tasks underlying TaskML. Microassembly task planner (MTP) software has been developed to support TaskML editing and task plan tree building

Improved Stability Results for Visual Tracking of Robotic Manipulators Based on the Depth-Independent Interaction Matrix

As we know, the dynamic visual-tracking control, which is based on the depth-independent interaction matrix, has been proposed to cope with the general 3-D motion of robot manipulators. To deal with the unknown camera parameters, an adaptive law has been designed. It is noted, however, that the designed adaptive law uses a vector signal defined by the true depths of feature points, which are unavailable when the camera parameters are unknown. Nevertheless, such an adaptive law can still be implemented by replacing the exact depths with the estimated depths, since the estimated depths can be readily calculated by using the estimated values of the camera parameters. In this case, however, we cannot definitely say whether or not the robot system can be guaranteed to achieve asymptotical stability or even stable behavior. To overcome this problem, in this paper, we redefine the mentioned vector signal using the estimated depths and show that the design based on the new vector signal can make the robot system asymptotically stable. Additionally, the existing tracking control design based on the concept of depth-independent interaction matrix is initial-state dependent. Thus, in this paper, we also modify the existing design to obtain an initial-state-independent result. To show the performance of the proposed designs, simulation results based on a two-link planar manipulator are presented. In addition, preliminary experimental results using an industrial manipulator are also given.

A piezoelectric bimorph micro-gripper with micro-force sensing

A new piezoelectric bimorph micro-gripper with micro-force sensing is presented in the paper. The micro-gripper is based on the dual cantilevers structure and is driven by two piezoelectric bimorphs. Sticking two strain gauges on both sides of the base of the piezoelectric bimorph to sense free end transmutation of the bimorph, we can get displacement-voltage relationship and force-strain relationship respectively. As a result the gripper has the ability to detect micro-force when it is gripping micro-parts. The experiment results show that the gripper works reliably and safely. It is satisfied with the tasks of micro assembly.

An adaptive method for Chinese license plate location

In the vehicle license plate recognition system, the accuracy of location directly decides the effect of latter recognition part. Since the Chinese license plates have complex colors and characters, former methods only can locate certain bounding rectangle of the plate but not the minimum one. Therefore interferences like plate frame and vehicle light may be included in the rectangle, and lead to difficulty in character recognition. This paper proposes a localization method using wavelet analysis and IHLS (improved HLS) color decomposition and Hough line detection. First, a wavelet multi-resolution analysis is implemented to locate the bounding rectangle. Then foreground (text) and plate background are separated by IHLS color decomposition. Through determining the overlap region between foreground and background, a minimum bounding rectangle is extracted from the image. Finally, an optional Hough transform can be used to revise the edge. Because in IHLS space, saturation is completely independent of brightness in theory, this method is much better than former ones under complex background, non-uniform illumination conditions and inclined license plate conditions. The experimental results tested on a large number of data confirm that.

Modeling and robust stability criterion of uncertain networked control systems with time-varying delays

In this paper, the problem of delay-dependent stability for a class of networked control systems (NCSs) with uncertainties and time-varying delays is investigated. A continuous time model for a class of multi-input and multi-output (MIMO) NCSs with many independent sensors and actuators is proposed. Based on descriptor system approach combined with linear matrix inequality (LMI) techniques, a novel delay-dependent robust stability criterion in terms of LMI is obtained. Compared to some existing results, the proposed method can give a much less conservative maximum allowable delay bound (MADB) and the result is more effective. Numerical example is illustrated the effectiveness of the proposed criterion and is an improvement over previous ones.

A Novel Adaptive Feedforward Compensation Algorithm for Hard Disk Drive

This paper applies a novel adaptive feedforward compensation (AFC) algorithm for runout cancellation on voice coil motor (VCM) actuator servo system. The parametric update laws of this adaptive algorithm can be precisely deduced. The AFC controller can attenuate selectively the intended harmonic runout without amplifying other harmonics. The testing results in time domain and frequency domain show that this scheme is effective in dealing with runout

A novel hybrid method for mobile robot path planning in unknown dynamic environment based on hybrid DSm model grid map

This study presents a novel hybrid approach for mobile robot aiming to efficiently plan smooth paths in an unknown dynamic environment. The single robot is treated as a multi-agent system, and the corresponding architecture combined with cooperative control is constructed. Then, a new method of information fusion, i.e. Dezert–Smarandache Theory (DSmT) is introduced to build the map of the unknown dynamic environment. Considering the characteristics of sonar sensors, the grid map method is adopted and a sonar sensor mathematical model is constructed based on DSmT. Meanwhile, a few general basic belief assignment functions are constructed to deal with the uncertain, imprecise and sometimes even highly conflicting information obtained by the sonar. Safety guard district search method and an optimising approach for searched paths are proposed. Also, the parameters of internal proportional-integral-derivative controller in the goto agent are adjusted through practical experiments to smooth the path. Finally, two experiments are carried out with mobile robot: one uses the hybrid method, while the other the artificial potential field. The experimental results testify the validity of hybrid DSm model for fusing imprecise information, and also reveal the validity and superiority of the hybrid method for path planning in unknown dynamic environment.