T. I. Tsay

A controller design framework for telerobotic systems

A framework for designing a telerobotic system controller is presented. This controller is designed so the dynamic behaviors of the master robot and the slave robot are functions of each other. These functions, which the designer chooses based upon the application, are described, and a control architecture is proposed to achieve these functions. To guarantee that the specified functions and proposed architecture govern the system behavior, H/sub infinity / control theory and model reduction techniques are used. Several experiments were conducted to verify the theoretical derivations. This control method is unique, because it does not require any transfer of either position or velocity information between the master robot and the slave robot; it only requires the transfer of forces. Although this property leads to a wider communication bandwidth between the master and slave robots, the entire system may still suffer from a positional error buildup between the master robot and slave robot. >

Stability criteria for robot compliant maneuvers

A nonlinear approach for the stability analysis of robot manipulators in constrained maneuvers is presented. Stability of the environment and the manipulator taken as a whole has been investigated, and a bound for stable manipulation has been derived. The authors show that for stability of the robot, there must be some initial compliancy either in the robot or in the environment. The general stability condition has been extended to the particular case where the environment is very rigid in comparison with the robot stiffness. The stability analysis has been investigated using unstructured models for the dynamic behaviour of the robot manipulator and the environment. This unified approach of modeling robot dynamics is expressed in terms of sensitivity functions as opposed to the Lagrangian behavior of all the elements of a robot manipulator (i.e., actuators, sensors, and the structural compliance of the links) in addition to the rigid body dynamics.<<ETX>>

Robust nonlinear control of robot manipulators

A new nonlinear manipulator control scheme is proposed in this paper which is robust against modeling errors and unknown disturbances. It is based on the principle of sliding mode control (SMC) but with the application of fuzzy logic control (FLC). The control method provides a simple way to achieve asymptotic stability of the system. In addition, the method can not only overcome the chattering problem caused by sliding mode control, but also determine the rules and parameters for fuzzy logic control. Experimental results are presented to verify the theoretical derivations.<<ETX>>

A design framework for telerobotics using the H ∞ approach

This paper presents a design framework for a controller of a telerobotic system. The controller is designed so the dynamic behaviors of the master robot and the slave robot are function of each other. This paper first describes these functions, which the designer sets based upon the application, and then proposes a control architecture to achieve these functions. To guarantee that the specified functions and proposed architecture govern the system behavior, H∞ control theory and model reduction technique are used. Several experiments were conducted to verify the theoretical derivations.

Pose control of mobile manipulators with an uncalibrated eye-in-hand vision system

Mobile manipulators, which consist of a mobile base and a robot manipulator equipped with a vision system, are appropriate for transferring small quantities of a range of different materials in production lines. Position and orientation errors of the mobile base relative to the station are inevitably caused by the non-horizontality of the ground and positioning errors of the mobile base. Hence, this study utilises an uncalibrated eye-in-hand vision system to provide visual information for controlling the manipulator mounted on the mobile base, to pick up a workpiece located on the station. A vision-guided control strategy is proposed. It is based on selected image features and an image-based look-and-move control structure. The control law employed in the control structure is based mainly on the off-line estimate of the transformation from feature space to Cartesian space using the least squares estimation algorithm. Finally, the positioning performance of the eye-in-hand manipulator is experimentally evaluated by controlling the end-effector of the manipulator to approach and grasp the workpiece in various locations on a station.

Control and Stability Analysis of Cooperating Robots

The work presented here is the description of the control strategy of two cooperating robots. A two-finger hand is an example of such a system. The control method allows for position control of the contact point by one of the robots while the other robot controls the contact force. The stability analysis of two robot manipulators has been investigated using unstructured models for dynamic behavior of robot manipulators. For the stability of two robots, there must be some initial compliancy in either robot. The initial compliancy in the robots can be obtained by a non-zero sensitivity function for the tracking controller or a passive compliant element such as an RCC.

Development of a mobile robot for visually guided handling of material

Mobile robots frequently replace humans in handling and transporting wafer carriers in semiconductor production lines. A mobile robot is constructed in this paper. The developed mobile robot is primarily composed of a mobile base, a robot manipulator, and a vision system. Since the guidance control system of the mobile base inevitably causes positioning errors of the mobile base, this study employs the eye-in-hand vision system to provide visual information for controlling the manipulator of the mobile robot to grasp accurately stationary material during pick-and-place operations between a predefined station and the mobile robot. This work further proposes a position-based look-and-move task encoding control strategy for eye-in-hand vision architecture, that maintains all target features in the cameras field of view throughout the visual guiding. Moreover, the manipulator can quickly approach the material and precisely position the end-effector in the desired pose. Numerous techniques are required for implementing such a task, including image enhancement, edge detection, corner and centroid detection, camera model calibration method, robotic hand/eye calibration method, using a camera with controlled zoom and focus, and task encoding scheme. Finally, the theoretical results for the proposed control strategy are experimentally verified on the constructed mobile robot. Specific experimental demonstrations include grasping the target object with different locations on the station and grasping the target object tilted by different angles to the station.