Robots--Control systems

Multi-agent control is a very promising area of robotics. In applications for which it is difficult or impossible for humans to intervene, the utilization of multi-agent, autonomous robot groups is indispensable. This thesis presents a novel approach to reactive multi-agent control that is practical and elegant in its simplicity. The basic idea upon which this approach is based is that a group of robots can cooperate to determine the shortest path through a previously unmapped environment by virtue of redundant sharing of simple data between multiple agents. The idea was implemented with two robots. In simulation, it was tested with over sixty agents. The results clearly show that the shortest path through various environments emerges as a result of redundant sharing of information between agents. In addition, this approach exhibits safeguarding techniques that reduce the risk to robot agents working in unknown and possibly hazardous environments. Further, the simplicity of this approach makes implementation very practical and easily expandable to reliably control a group comprised of many agents.

Vision systems have been widely used for parts inspection in electronics assembly lines. In order to improve the overall performance of a visual inspection system, it is important to employ an efficient object recognition algorithm. In this thesis work, a genetic algorithm based correlation algorithm is designed for the task of visual electronic parts inspection. The proposed procedure is composed of two stages. In the first stage, a genetic algorithm is devised to find a sufficient number of candidate image windows. For each candidate window, the correlation is performed between the sampled template and the image pattern inside the window. In the second stage, local searches are conducted in the neighborhood of these candidate windows. Among all the searched locations, the one that has a highest correlation value with the given template is selected as the best matched location. To apply the genetic algorithm technique, a number of important issues, such as selection of a fitness function, design of a coding scheme, and tuning of genetic parameters are addressed in the thesis. Experimental studies have confirmed that the proposed GA-based correlation method is much more effective in terms of accuracy and speed in locating the desired object, compared with the existing Monte-Carlo random search method.

A user friendly graphical interface was developed to control a Stewart platform which is a six degree-of-freedom in-parallel mechanism. The interface allows the user to define the platform motion relative to various coordinate systems: base, platform and joint. The velocity/position reference to the platform's controller can be provided by the following ways: preprogrammed data file, serial communication RS-232, 6 degrees of freedom joystick and soft teach pendant. The platform was designed to be used as "Space Emulator" and therefore a 6 degrees of freedom force/torque sensor was needed. Two different models of such sensors were designed and analyzed using finite element analysis techniques. Based on the results one particular model was selected, fabricated, instrumented with strain gages and calibrated in order to obtain its stiffness matrix. The effect of drifting of the sensor output due to self heating of the strain gages and the electronic components of the strain gage amplifiers was also studied.

A Stewart platform is a six degree of freedom robot manipulator with its six links arranged in a parallel configuration. A dynamic model for the plant of each link, which consists of an amplifier, an electrohydraulic servo valve, and a hydraulic actuator, is found from open-loop step and frequency responses. To determine a model for the complete closed loop system, integrators located in the link input and feedback paths were added to the plant's model. PID controllers were designed to increase the system's bandwidth. Once control of the individual links was achieved, control algorithms were developed to control the motion of Stewart platform. The algorithm would move the platform through its initialization sequence, then control platform velocity, as dictated by the user.

In recent years robots have become increasingly important in many areas. A robotic controller requires high speed and high reliability and its design must continue these two aspects. This thesis presents a design for a Transputer based fault tolerant robot controller. For concreteness, we have designed this controller for a specific robot, the SEDAB, a prototype developed by IBM Corp. This design attempts to satisfy the two requirements of speed and reliability. Speed is achieved by the use of a concurrent structure composed of Transputers. Reliability is provided by a self-testing mechanism and a multiprocessor system architecture. The Occam implementation of the robot processes is described. We have evaluated the reliability of this controller. The reliability study shows that there is a significant increase in the reliability of this controller due to the new architecture and proposed fault detection mechanism. While we have not been able to actually control this robot, we have shown that some scheduling heuristics can be effectively used to provide a higher level of performance.

The research envisaged and reported in this thesis refers to finding comprehensive algorithms to determine the handoff probabilities of new and handoff calls encountered in mobile communications. The traditional expressions for these probabilities that are reported in the literature, are deduced only on the basis of call arrival statistics applied to RF links between base station (BS) and the mobile unit (MU). However, such radio links inevitably suffer from fading. These channels are normally modeled by appropriate probability density functions (pdfs) of the faded signal envelope. Rayleigh, Rician and Nakagami-m distributions are popularly considered in depicting such fading channel characteristics. The traditional (queueing-theoretic) based estimation of handoff probabilities does not account for the hysteresis-specific handoff statistics in the relevant fading channels. This is in contrary to the reality, inasmuch as fading is an inherent part of RF channels in mobile communications. The present study offers a tractable method of combining queuing-theoretic (call arrival) statistics and the hysteresis-crossing statistics of a RSS metric so as to obtain proper expressions for new and handoff call handoff probabilities. The (upper and lower) bound specified spread of the handoff probabilities indicates that care should be exercised in resource allocation efforts with a margin. To the best of the knowledge of the author, this research exercise is new and has not been reported elsewhere in open literature.

When a control system for an Autonomous Underwater Vehicle (AUV) requires thrust, it is common to apply a simplified model to estimate the force generated. Even though this model takes into account several parameters, it will never recover the real value. Our challenge is to directly measure the force, in real time, from the tunnel thrusters used in the positioning control of the Mini AUV known as Morpheus. Therefore, a force sensor system has been designed, optimized, machined and tested, that supports the thruster assembly. The sensor implements strain gages to measure the deformation in a beam. To optimize the capabilities of the sensor, a finite elements analysis has been run. The sensor has been fabricated and tested to determine the static and dynamic characteristics. This thesis discusses the design implementation, optimization, fabrication and testing of the force sensor. The discussion begins with an overview of the problem, then explains the fabrication, optimization, testing and concludes with recommendation for future work.

To assess and evaluate the performance of robots and machine tools dynamically, it
is desirable to have a precision measuring device that performs dynamic measurement
of end-effector positions of such robots and machine tools. Among possible
measurement techniques, Laser Tracking Systems (LTSs) exlnbit the capability of high
accuracy, large workspace, high sampling rate, and automatic target-tracking,. and thus
are well-suited for robot calibration both kinematically and dynamically.
In this dissertation, the design and implementation of a control system for a homemade
laser tracking measurement systems is addressed and calibration of a robot using
the laser tracking system is demonstrated Design and development of a control system for a LTS is a challenging task. It
involves a deep understanding of laser interferometry,. controls, mechanics and optics,.
both in theoretical perspective and in implementation aspect. One of the most important
requirements for a successful design and implementation of a control system for the
LTS is proper installation and alignment of the laser and optical system,. or laser
transducer system. The precision of measurement using the LTS depends highly on the
accuracy of the laser transducer system, as well as the accuracy of the installation and
alignment of the optical system. Hence, in reference to the experimental alignment
method presented in this dissertation, major error sources affecting the system
measurement accuracy are identified and analyzed. A manual compensation method is
developed to eliminate the effects of these error sources effectively in the measurement
system. Considerations on proper design and installation of laser and optical
components are indicated in this dissertation.
As a part of the conventional control system design, a dynamic system model of the
LTS is required. In this study, a detailed derivation and analysis of the dynamic model
of the motor gimbal system using Lagrange-Euler equations of motion is developed for
both ideal and complete gimbal systems. Based on this system model,. a conventional
controller is designed.
Fuzzy Logic Controllers (FLC) are designed in order to suppress noise or
disturbances that exist in the motor driver subsystem. By using the relevant control
strategies. noise and disturbances present in the electrical control channels are shown to
reduce significantly. To improve the system performance further, a spectrum analysis of the error sources and disturbances existing in the system is conducted. Major noise
sources are effectively suppressed by using a two-stage fuzzy logic control strategy. A
comparison study on the performances of different control strategies is given in this
dissertation, in reference to the following: An ideal system model, a system with a long
time delay, a system with various noise sources and a system model with uncertainties.
Both simulation and experimental results are furnished to illustrate the advantages of
the FLC in respect of its transient response, steady-state response, and tracking
performance. Furthermore, noise reduction in the laser tracking system is demonstrated.
Another important issue concerning a successful application of the LTS in the
calibration of a robot is the estimation of system accuracy. Hence, a detailed analysis of
system accuracy of the LTS is presented in this worL This analysis is also verified by
experimental methods by means of tracking a Coordinate Measuring Machine available
in the FAU Robotics Center. Using the developed LTS, a PUMA robot in the FAU
Robotics Center is calibrated. The results obtained are confirmative with the data
available in the literature.
In summary, the proposed methodology towards the design and implementation of a
control system for LTSs has been shown to be successful by performing experimental
tracking and calibration studies at the FAU Robotics Center.

Laser tracking coordinate measuring machines have the potential of continuously measuring three dimensional target coordinates in a large workspace with a fast sampling rate and high accuracy. Proper calibration of a laser tracking measurement system is essential prior to use of such a device for metrology. In the absence of a more accurate instrument for system calibration, one has to rely on self-calibration strategies. In this dissertation, a kinematic model that describes not only the motion but also geometric variations of a multiple-beam laser tracking system was developed. The proposed model has the following features: (1) Target positions can be computed from both distance and angular measurements. (2) Through error analysis it was proven that even rough angular measurement may improve the overall system calibration results. A self-calibration method was proposed to calibrate intelligent machines with planar constraints. The method is also applied to the self-calibration of the laser tracking system and a standard PUMA 560 robot. Various calibration strategies utilizing planar constraints were explored to deal with different system setups. For each calibration strategy, issues about the error parameter estimation of the system were investigated to find out under which conditions these parameters can be uniquely estimated. These conditions revealed the applicability of the planar constraints to the system self-calibration. The observability conditions can serve as a guideline for the experimental setup when planar constraint is utilized in the machine calibration including the calibration of the laser tracking systems. Intensive simulation studies were conducted to check validity of the theoretical results. Realistic noise values were injected to the system models to statistically assess the behavior of the self-calibration system under real-world conditions. Various practical calibration issues were also explored in the simulations and therefore to pave ways for experimental investigation. The calibration strategies were also applied experimentally to calibrate a laser tracking system constructed at the Robotics Center in Florida Atlantic University.

Self-calibration is a desirable feature for an intelligent machine such as a robot that must function outside of controlled laboratory conditions. This is because it is inevitable that variations in the kinematic model arise from imperfections in the manufacturing process and changes of environment conditions. Self-calibration has the potential of (a) removing the dependence on external pose sensing, (b) producing high accuracy measurement data over the entire workspace of the system with an extremely fast measurement rate, (c) being automated and completely non invasive, (d) facilitating on-line accuracy compensation, and (e) being cost effective. This dissertation concentrates on the study of self-calibrating parallel-link mechanisms. A framework of self-calibration of a parallel-link mechanism is created, which is based on kinematic analysis and the construction of measurement residuals utilizing the information provided by redundant sensors embedded in the system. Forward and inverse kinematic measurement residuals of the mechanisms are proposed. To avoid the estimation of redundant kinematic parameters of the mechanism, the concept of relative residuals is introduced. Guidelines for placement of sensors for self-calibration are presented. An approach to determining the number of independent kinematic parameters of the mechanism is introduced. Extensive simulation and experimental studies conducted on a parallel-link mechanism, the Stewart platform built in the Robotics Center at Florida Atlantic University, confirm the effectiveness of the proposed approach.