Previous research in force control has focused on the choice of appropriate servo implementation without corresponding regard to the choice of mechanical hardware. This report analyzes the effect of mechanical properties such as contact compliance, actuator-to-joint compliance, torque ripple, and highly nonlinear dry friction in the transmission mechanisms of a manipulator. A set of requisites for high performance then guides the development of mechanical-design and servo strategies for improved performance. A single-degree-of-freedom transmission testbed was constructed that confirms the predicted effect of Coulomb friction on robustness; design and construction of a cable-driven, four-degree-of- freedom, "whole-arm" manipulator illustrates the recommended design strategies.

This paper presents the research and development of a 3-legged micro Parallel Kinematic Manipulator (PKM) for positioning in micro-machining and assembly operations. The structural characteristics associated with parallel manipulators are evaluated and the PKMs with translational and rotational movements are identified. Based on these identifications, a hybrid 3-UPU (Universal Joint-Prismatic Joint-Universal Joint) parallel manipulator is designed and fabricated. The principles of the operation and modeling of this micro PKM is largely similar to a normal size Stewart Platform (SP). A modular design methodology is introduced for the construction of this micro PKM. Calibration results of this hybrid 3-UPU PKM are discussed in this paper. / Singapore-MIT Alliance (SMA)

The thesis focuses on the development of an experimental set up for a recently developed failure recovery technique of spatial robot manipulators. Assuming a general configuration of the spatial robot arm, a task is specified. This task contains constraints on position, velocity and acceleration to be satisfied. These constraints are derived from contact and curvature specifications. The technique synthesizes the serial chain and tests if the task can be satisfied in case of a joint failure. An experimental set up was developed in order to validate the failure recovery technique. It includes a robot arm mounted on a movable platform. The arm and platform are controlled by NI sbRIO board and are programmed in LabVIEW. The experimental results of the failure recovery technique were obtained for the case of Elbow failure in robot manipulators. The thesis considers two applications of the synthesis of spherical five –degree-of-freedom serial chains: Power assist for human therapeutic movement and Synthesis of Parallel Mechanical Linkages. A spherical TS chain has been synthesized for these two applications using the Mathematica software.

This thesis presents two unique micro-motion parallel kinematic manipulators (PKM): a three degrees of freedom (3-DOF) micro-motion manipulator and a 3-DOF micro-motion manipulator with actuation redundancy. The 3-DOF micro-motion manipulator has three linear-motion driving units, and the 3-DOF micro-motion manipulator with redundancy has four of these units. For both designs, the linear motion driving units are identical, and both machines have a passive link in the center of the structure. The purpose of this passive link is to restrain the movement of the manipulator and to improve the stiffness of the structure. As a result, both structures support 3-DOF, including one translation on the Z-axis and two rotations around the X and Y axes. The manipulator with redundancy is designed to prevent singularity and to improve stiffness. In this thesis, the inverse kinematic, Jacobian matrix and stiffness analyses have been conducted, followed by the design optimization for structures. Finally, the FEA (Finite Element Analysis) and dynamic analysis have also been performed. There are many practical applications for micro-motion parallel manipulators. The typical applications include micro-machine assembly, biological cell operation, and microsurgery . / UOIT

This thesis presents the design, analysis, and numerical and experimental evaluation of nonlinear controllers for co-operation among several hydraulic robots operating in the presence of significant system uncertainties, non-linearities and friction. The designed controllers allow hydraulically driven manipulators to (i) co-operatively handle a rigid object (payload) following a given trajectory, (ii) share the payload and (iii) maintain an acceptable internal force on the object. A general description of the kinematic and dynamic relations for a hydraulically actuated multi-manipulator system is presented first. The entire mathematical model incorporates object dynamics, robot dynamics, hydraulic actuator functions and friction dynamics. For the purpose of simulations, a detailed numerical simulation program of such a system is also developed, in which two three-link planar robot manipulators resembling the Magnum hydraulic manipulators manufactured by ISE, interact with each other through manipulating a common object. The regulating control problem is studied next, in which the desired position of the object and the corresponding desired link displacement change step-wise. Initially, a controller is designed based on a backstepping technique, assuming that full knowledge of the dynamics and kinematics of the system is available. The assumption is then relaxed and the control system is analyzed. Based on the analysis, the controller is then modified to account for the uncertainty of the payload, robot dynamic parameters and hydraulic functions. Next, the regulating controller is extended to a tracking controller, which allows the object to follow a given trajectory and is robust against parameter uncertainties. Additionally, an observer is added to the controller to avoid the need of acceleration feedback. To investigate the effect of friction force, the above controllers are examined by introducing the most recent and complete LuGre friction model into the system dynamics. The tracking controller is then redesigned to compensate the effect of friction. Observers are designed to observe the immeasurable friction states. Based on the observed friction states and estimated friction parameters, an appropriate friction compensation scheme is designed which does not directly use velocity in order to avoid the need of acceleration feedback by the controller. Finally, the problem of “explosion of terms” coming from the backstepping method is solved by using the concept of dynamic surface control in which a low pass filter is integrated to avoid model differentiation. Simulations are carried out for analysis of the control system and verification of the developed controllers. Experimental examinations are performed on an available hydraulic system consisting of two single-axis hydraulic actuators. / February 2008

No description available.

Modern motion controllers of robot manipulators require knowledge of the system's dynamics in order to intelligently predict the torque command. The main objective for this thesis is to apply various motion controllers on a parallel direct drive robot in simulations and verify if one can take advantage of the model knowledge to improve performance of controllers. The controllers used in this thesis varied from simple PD control with position and velocity reference only applied independently at each joint to more advanced PD control with full dynamic feedforward term and computed torque control, which incorporate full dynamic knowledge of the manipulator. In the first part, a thorough study of deriving dynamic equation using Lagrange formulation has been presented as well as the actual derivation of dynamic equations for MINGUS2000. Next, in order to prepare proper sets of inputs for the simulations, detailed discussions of end effector trajectory path planning and inverse kinematics determination have been presented. Finally, background theories of various controllers used in this thesis have been presented and their simulation results on the closed-chain direct drive robot have been compared for verification purposes.

Piezoelectric effect was discovered in the 19th century, but the applications of piezoelectric effect were realized until the 20th century. In this paper, piezoelectric actuators, which are made based on piezoelectric effect, are employed to establish a three-degree-of-freedom micro-manipulator. The mechanism of this micro-manipulator is designed as a parallel-type mechanism. The kinematics of the micro-manipulator is also analyzed. In addition, a remote control framework is implemented with a control system and this achievement can be a demonstration for future feasibility of application of this micro-manipulator to robotic systems.

Commercially available wheelchair-mounted robotic arms (WMRAs) are becoming more prevalent internationally but have yet to be largely developed and approved by the Food and Drug Administration in the United States. The purpose of this study was to experimentally evaluate commercially available WMRAs in a controlled test environment. The goal was to quantitatively compare each device through a standardized testing protocol. The study produced theoretical manipulability measurements as well as efficacy ratings of each device based on Denavit-Hartenberg kinematic parameters and physical testing, respectively. Both the manipulator and control devices of WMRA systems were evaluated. The iARM WMRA system was presented to be more effective than the JACO WMRA system based on kinematic analysis. Despite this, the JACO system was shown to be more effective than the iARM system in three of four experimental tasks. Effective design features were brought to light with these results. The study and its procedures may serve as a source of quantitative and qualitative data for the commercially available WMRAs.

The effort in this work has been to innovatively use range information from a laser sensor mounted on the end effector of a remote robotic arm in a telerobotic system to assist the user in carrying out remote tasks in unstructured environments. Assistance is provided in the form of Traded Supervisory Control where the human is involved in high level activities such as decision making and the machine generates task plans and executes tasks autonomously using laser data and machine intelligence. In this way human planning and high level decision making capabilities are combined with machine computational and precision task execution capabilities in an optimal way. Laser range data has been used in a novel way to generate trajectories and virtual constraints that assist the user either by executing trajectories autonomously or by guiding the user in teleoperation along specific virtual constraints. The ability of the laser to generate path plans and execute them autonomously, and generate 3D geometry information is another novel feature of the project. This has been achieved without using sophisticated sensory suite and extensive computer processing. The user simply points to certain locations in the unstructured environment by teleoperating the remote arm using the master arm and presses certain keys on the keyboard. The machine using laser data and its intelligence generates the appropriate trajectories, virtual geometric surfaces and path plans which assist the user in executing the task. Time and accuracy results in executing a remote manipulation tasks on a real-time telerobotic system with master and slave arms, with and without laser based assistance have been generated and compared to validate the hypothesis that laser based assistance improves task performance and reduces the cognitive load on the user. To improve dexterity of the arm and to enable smooth and stable control of the arm, singularity avoidance techniques have been implemented and results in simulation have been presented. Accuracy results to validate the motion control algorithms of the robot by comparing trajectories in simulation and on the robot have been generated.