Ming-Guo Her

The dynamics and control of a haptic interface device

Haptic interface devices are machines that are controlled by the human arm contact forces. These devices are necessary elements of virtual reality machines. These devices may be programmed to give the human arm the sensation of forces associated with various arbitrary maneuvers. As examples, these devices can give the human the sensation that he/she is maneuvering a mass, or pushing onto a spring or a damper. In general, these devices may be programmed for any trajectory-dependent force. To illustrate and verify the analysis of these machines, a two-degree-of-freedom electrically-powered haptic interface device was designed and built at the Human Engineering Laboratory (HEL) of the University of California-Berkeley. >

Robust tracking observer-based adaptive fuzzy control design for uncertain nonlinear MIMO systems with time delayed states

This paper addresses the problem of designing robust observer-based adaptive fuzzy tracking control scheme for a class of MIMO nonlinear systems with plant uncertainties, time delayed uncertainties, and external disturbances. A fuzzy logic system (FLS) is utilized to approximate the unknown nonlinear functions and an adaptive fuzzy observer is introduced for state estimations. The proposed control law is based on indirect adaptive fuzzy control and uses two on-line estimations. This allows for the simultaneous inclusion of identifying gains of the delayed state uncertainties and training of the weights of the fuzzy system by introducing estimated error vectors. The advantage of employing an adaptive fuzzy system is the use of linear analytical results instead of estimating nonlinear system functions with online update laws. The adaptive fuzzy tracking control using Variable Structure (VS) control technique is derived based on Lyapunov criterion and the Riccati-inequality to resolve system uncertainties, time delayed uncertainties, and external disturbances. This is done in such a way that all states of the system are bounded and the H ∞ tracking performance is achieved. Finally, a two-connected inverted pendulums on carts system (Liu et al., 2011) [29] is used for simulation purposes and some comparisons are given to illustrate the validity and effectiveness of the proposed method.

A virtual exercise machine

The dynamics and design of multiple-degree-of-freedom robotic systems built as general purpose exercise machines for the human arm are discussed. These machines may be programmed to give the human arm the sensation of forces associated with various arbitrary maneuvers. As examples, these machines can give the human the sensation that he or she is maneuvering a mass or pushing onto a spring or a damper. In general, the machines may be programmed for any trajectory-dependent forces. To illustrate and verify the analysis of these machines, a two-degree-of-freedom electrically powered exercise machine was designed and built.<<ETX>>

Anti-sway tracking control of tower cranes with delayed uncertainty using a robust adaptive fuzzy control

Tower cranes are very complex mechanical systems and have been the subject of research investigations to reduce the swaying of the payload for several decades. Inherently, the dynamical model of the tower cranes is highly nonlinear and classified as underactuated. Also, the actuators are far from the payload which makes the system non-colocated. It is proposed here to use an H ∞ based adaptive fuzzy control technique to control the swaying motion of a tower crane. The advantage of employing an adaptive fuzzy system is the use of linear analytical results instead of estimating the dynamics of the tower crane with an online update law. The proposed robust control law for payload positioning is based on a variable structure (VS) adaptive fuzzy control scheme. The adaptive fuzzy control technique fuses a VS scheme and it is derived based on a Lyapunov criterion and the Riccati-inequality. The control design overcomes modeling inaccuracies, such as drag and friction losses, effect of time delays from backlash, as well as parameter uncertainties and compensate for the effect of the external disturbances on tracking error such that all the states of the system are uniformly ultimately bounded (UUB). Therefore, the H ∞ tracking performance can be achieved such that the payload swing is reduced to as small as possible when the payload is moved from point to point. Simulations show that the proposed control scheme is effective in reducing payload swing in the presence of uncertainties, time delays, and external disturbances.

A study of the electrical discharge machining of semi-conductor BaTiO3

Abstract This paper investigates the machining performance of BaTiO 3 using the electrical discharge machining (EDM) process. The Taguchi orthogonal array technique is used for experimental design. A surface roughness model of the EDM process of semi-conductor BaTiO 3 can be obtained by regression of the experimental data. A genetic algorithm is used to calculate the machining parameters of the optimum surface roughness. To obtain a better surface roughness, positive polarity machining should be chosen in the EDM process of BaTiO 3 , whilst the current cannot be selected at too great a value or the workpiece may be broken during the process.

Haptic Direct-Drive Robot Control Scheme in Virtual Reality

This paper explores the use of a 2-D (Direct-Drive Arm) manipulator for mechanism design applications based on virtual reality (VR). This article reviews the system include a user interface, a simulator, and a robot control scheme. The user interface is a combination of a virtual clay environment and human arm dynamics via robot effector handler. The model of the VR system is built based on a haptic interface device behavior that enables the operator to feel the actual force feedback from the virtual environment just as s/he would from the real environment. A primary stabilizing controller is used to develop a haptic interface device where realistic simulations of the dynamic interaction forces between a human operator and the simulated virtual object/mechanism are required. The stability and performance of the system are studied and analyzed based on the Nyquist stability criterion. Experiments on cutting virtual clay are used to validate the theoretical developments. It was shown that the experimental and theoretical results are in good agreement and that the designed controller is robust to constrained/unconstrained environment.

Delayed Output Feedback Control for Nonlinear Systems With Two-Layer Interval Fuzzy Observers

In this paper, the design problem of a delayed output feedback control scheme using two-layer interval fuzzy observers for a class of nonlinear systems with state and output delays is investigated. The Takagi-Sugeno-type fuzzy linear model with an online update law is used to approximate the nonlinear system. Based on the fuzzy model, a two-layer interval fuzzy observer is used to reconstruct the system states according to equal interval output time delay slices. Subsequently, a delayed output feedback adaptive fuzzy controller is developed to overcome the nonlinearities, time delays, and external disturbances such that H∞ tracking performance is achieved. The linguistic information is developed by setting the membership functions of the fuzzy logic system and the adaptation parameters to estimate the model uncertainties directly using linear analytical results instead of estimating nonlinear system functions. The tracking error dynamics are designed to enable our adaptive controller to avoid the filtering of the basis vectors whose dimension is much larger than that of the state vector of the controlled system. This is achieved by not imposing the strictly positive real condition. Based on the Lyapunov stability criterion and linear matrix inequalities, some sufficient conditions are derived so that all the states of the system are uniformly ultimately bounded. Therefore, the effect of the external disturbances on the tracking error can be attenuated to any prescribed level, and H∞ tracking control is achieved. Building on our previous work in this area, the proposed control scheme is extended to handle a class of uncertain nonlinear systems with state and output delays and external disturbances. This is achieved through the use of a robust variable structure scheme and H∞ control techniques. Finally, a numerical example of a two-link robot manipulator is studied to illustrate the effectiveness of the proposed control scheme.

Design of an interactive pipeline inspection VR system

Pipeline inspection is a costly and necessary task for oil producing companies. Moreover, it requires very specialized equipment and specific knowhow to analyze the results of the inspection. In this article, we present a novel interactive pipeline inspection system that could be used to educate students and engineers about the process. A motion simulator is built and used in conjunction with a virtual reality (VR) environment that will allow the operator feel as if s/he is inside the pipe and recognize the various types of defects that might be encountered. A haptic interface device is used in the setup which will alert the operator about the presence of a defect. The control scheme for the simulator uses the change in velocity and acceleration that the operator imposes on the joystick, the environmental changes imposed on the motion simulator, and the haptic feedback to the operator to maneuver the simulator in the real environment. The stability of the closed‐loop system is analyzed based on the Nyquist stability criteria.

Design and control of a haptic interactive motion simulator for virtual entertainment systems

In this paper, an interactive virtual reality motion simulator is designed and analyzed. The main components of the system include a bilateral control interface, networking, a virtual environment, and a motion simulator. The virtual reality entertainment system uses a virtual environment that enables the operator to feel the actual feedback through a haptic interface as well as the distorted motion from the virtual environment just as s/he would in the real environment. The control scheme for the simulator uses the change in velocity and acceleration that the operator imposes on the joystick, the environmental changes imposed on the motion simulator, and the haptic feedback to the operator to maneuver the simulator in the real environment. The stability of the closed-loop system is analyzed based on the Nyquist stability criteria. It is shown that the proposed design for the simulator system works well and the theoretical findings are validated experimentally.

Application of neural networks augmenting Taguchi's orthogonal arrays for simulating kinematics problems of robotics

This research focuses on integrating back propagation with the concepts of Taguchis orthogonal arrays to map both robot forward kinematics and robot inverse kinematics. Traditionally, end users were required to have some experience with robot kinematics training programs in order to analyse the kinematics and train the robots. When the type of robot changes, end users must again analyse the robot kinematics and solve extensive mathematical equations in order to control the new robot. An alternative approach for developing robot manipulator models is to use the concepts of neural networks to approximate robot kinematics to overcome the drawbacks of the existing methods. Moreover, an additional benefit is derived from the use of Taguchis orthogonal arrays. This study shows that using orthogonal arrays for data collection can reduce the amount of data required to map robot kinematics, although some accuracy is lost with solving the inverse kinematics problems. The simulations used to verify the model developed have been conducted on the Jumbo Drilling robot.