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2 7KH8QLYHUVLW\RI0LFKLJDQ Where am I? Sensors and Methods for Mobile Robot Positioning by J. Borenstein, H. R. Everett, and L. Feng Contributing authors: S. W. Lee and R. H. Byrne Edited and compiled by J. Borenstein April 1996 Prepared by the University of Michigan For the Oak Ridge National Lab (ORNL) D&D Program and the United States Department of Energy's Robotics Technology Development Program Within the Environmental Restoration, Decontamination and Dismantlement Project 1) Dr. Johann Borenstein 2) Commander H. R. Everett 3) Dr. Liqiang Feng The University of Michigan Naval Command, Control, and The University of Michigan Department of Mechanical Ocean Surveillance Center Department of Mechanical Engineering and Applied Mechanics RDT&E Division 5303 Engineering and Applied Mechanics Mobile Robotics Laboratory 271 Catalina Boulevard Mobile Robotics Laboratory 1101 Beal Avenue San Diego, CA Beal Avenue Ann Arbor, MI Ph.: (619) Ann Arbor, MI Ph.: (313) Fax: (619) Ph.: (313) Fax: (313) Fax: (313) Please direct all inquiries to Johann Borenstein.
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4 Acknowledgments This research was sponsored by the Office of Technology Development, U.S. Department of Energy, under contract DE-FG02-86NE37969 with the University of Michigan Significant portions of the text were adapted from "Sensors for Mobile Robots: Theory and Application" by H. R. Everett, A K Peters, Ltd., Wellesley, MA, Publishers, Chapter 9 was contributed entirely by Sang W. Lee from the Artificial Intelligence Lab at the University of Michigan Significant portions of Chapter 3 were adapted from Global Positioning System Receiver Evaluation Results. by Raymond H. Byrne, originally published as Sandia Report SAND , Sandia National Laboratories, The authors wish to thank the Department of Energy (DOE), and especially Dr. Linton W. Yarbrough, DOE Program Manager, Dr. William R. Hamel, D&D Technical Coordinator, and Dr. Clyde Ward, Landfill Operations Technical Coordinator for their technical and financial support of the research, which forms the basis of this work. The authors further wish to thank Professors David K. Wehe and Yoram Koren at the University of Michigan for their support, and Mr. Harry Alter (DOE) who has befriended many of the graduate students and sired several of our robots. Thanks are also due to Todd Ashley Everett for making most of the line-art drawings. 4
5 Table of Contents Introduction...10 PART I SENSORS FOR MOBILE ROBOT POSITIONING Chapter 1 Sensors for Dead Reckoning Optical Encoders Incremental Optical Encoders Absolute Optical Encoders Doppler Sensors Micro-Trak Trak-Star Ultrasonic Speed Sensor Other Doppler-Effect Systems Typical Mobility Configurations Differential Drive Tricycle Drive Ackerman Steering Synchro Drive Omnidirectional Drive Multi-Degree-of-Freedom Vehicles MDOF Vehicle with Compliant Linkage Tracked Vehicles Chapter 2 Heading Sensors Mechanical Gyroscopes Space-Stable Gyroscopes Gyrocompasses Commercially Available Mechanical Gyroscopes Futaba Model Helicopter Gyro Gyration, Inc Piezoelectric Gyroscopes Optical Gyroscopes Active Ring Laser Gyros Passive Ring Resonator Gyros Open-Loop Interferometric Fiber Optic Gyros Closed-Loop Interferometric Fiber Optic Gyros Resonant Fiber Optic Gyros Commercially Available Optical Gyroscopes The Andrew Autogyro" Hitachi Cable Ltd. OFG Geomagnetic Sensors Mechanical Magnetic Compasses Fluxgate Compasses Zemco Fluxgate Compasses
6 Watson Gyrocompass KVH Fluxgate Compasses Hall-Effect Compasses Magnetoresistive Compasses Philips AMR Compass Magnetoelastic Compasses Chapter 3 Ground-Based RF-Beacons and GPS Ground-Based RF Systems Loran Kaman Sciences Radio Frequency Navigation Grid Precision Location Tracking and Telemetry System Motorola Mini-Ranger Falcon Harris Infogeometric System Overview of Global Positioning Systems (GPSs) Evaluation of Five GPS Receivers by Byrne [1993] Project Goals Test Methodology Parameters tested Test hardware Data post processing Test Results Static test results Dynamic test results Summary of test results Recommendations Summary of problems encountered with the tested GPS receivers Summary of critical integration issues...92 Chapter 4 Sensors for Map-Based Positioning Time-of-Flight Range Sensors Ultrasonic TOF Systems Massa Products Ultrasonic Ranging Module Subsystems Polaroid Ultrasonic Ranging Modules Laser-Based TOF Systems Schwartz Electro-Optics Laser Rangefinders RIEGL Laser Measurement Systems RVSI Long Optical Ranging and Detection System Phase-Shift Measurement Odetics Scanning Laser Imaging System ESP Optical Ranging System Acuity Research AccuRange TRC Light Direction and Ranging System Swiss Federal Institute of Technology's 3-D Imaging Scanner Improving Lidar Performance Frequency Modulation
7 4.3.1 Eaton VORAD Vehicle Detection and Driver Alert System Safety First Systems Vehicular Obstacle Detection and Warning System PART II SYSTEMS AND METHODS FOR MOBILE ROBOT POSITIONING Chapter 5 Odometry and Other Dead-Reckoning Methods Systematic and Non-Systematic Odometry Errors Measurement of Odometry Errors Measurement of Systematic Odometry Errors The Unidirectional Square-Path Test The Bidirectional Square-Path Experiment Measurement of Non-Systematic Errors Reduction of Odometry Errors Reduction of Systematic Odometry Errors Auxiliary Wheels and Basic Encoder Trailer The Basic Encoder Trailer Systematic Calibration Reducing Non-Systematic Odometry Errors Mutual Referencing Internal Position Error Correction Inertial Navigation Accelerometers Gyros Barshan and Durrant-Whyte [1993; 1994; 1995] Komoriya and Oyama [1994] Summary Chapter 6 Active Beacon Navigation Systems Discussion on Triangulation Methods Three-Point Triangulation Triangulation with More Than Three Landmarks Ultrasonic Transponder Trilateration IS Robotics 2-D Location System Tulane University 3-D Location System Optical Positioning Systems Cybermotion Docking Beacon Hilare NAMCO LASERNET U.S. Bureau of Mines' application of the LaserNet sensor Denning Branch International Robotics LaserNav Position Sensor TRC Beacon Navigation System Siman Sensors and Intelligent Machines Ltd., ROBOSENSE Imperial College Beacon Navigation System TM MTI Research CONAC Spatial Positioning Systems, inc.: Odyssey
8 6.4 Summary Chapter 7 Landmark Navigation Natural Landmarks Artificial Landmarks Global Vision Artificial Landmark Navigation Systems MDARS Lateral-Post Sensor Caterpillar Self Guided Vehicle Komatsu Ltd, Z-shaped landmark Line Navigation Thermal Navigational Marker Volatile Chemicals Navigational Marker Summary Chapter 8 Map-based Positioning Map Building Map-Building and Sensor Fusion Phenomenological vs. Geometric Representation, Engelson & McDermott [1992] Map Matching Schiele and Crowley [1994] Hinkel and Knieriemen [1988] The Angle Histogram Weiß, Wetzler, and Puttkamer More on the Angle Histogram Siemens' Roamer Bauer and Rencken: Path Planning for Feature-based Navigation Geometric and Topological Maps Geometric Maps for Navigation Cox [1991] Crowley [1989] Adams and von Flüe Topological Maps for Navigation Taylor [1991] Courtney and Jain [1994] Kortenkamp and Weymouth [1993] Summary
9 Chapter 9 Vision-Based Positioning Camera Model and Localization Landmark-Based Positioning Two-Dimensional Positioning Using a Single Camera Two-Dimensional Positioning Using Stereo Cameras Camera-Calibration Approaches Model-Based Approaches Three-Dimensional Geometric Model-Based Positioning Digital Elevation Map-Based Localization Feature-Based Visual Map Building Summary and Discussion Appendix A A Word on Kalman Filters Appendix B Unit Conversions and Abbreviations Appendix C Systems-at-a-Glance Tables References Subject Index Author Index Company Index Bookmark Index Video Index Full-length Papers Index
10 INTRODUCTION Leonard and Durrant-Whyte [1991] summarized the general problem of mobile robot navigation by three questions: Where am I?, Where am I going?, and How should I get there?. This report surveys the state-of-the-art in sensors, systems, methods, and technologies that aim at answering the first question, that is: robot positioning in its environment. Perhaps the most important result from surveying the vast body of literature on mobile robot positioning is that to date there is no truly elegant solution for the problem. The many partial solutions can roughly be categorized into two groups: relative and absolute position measurements. Because of the lack of a single, generally good method, developers of automated guided vehicles (AGVs) and mobile robots usually combine two methods, one from each category. The two categories can be further divided into the following subgroups. Relative Position Measurements a. Odometry This method uses encoders to measure wheel rotation and/or steering orientation. Odometry has the advantage that it is totally self-contained, and it is always capable of providing the vehicle with an estimate of its position. The disadvantage of odometry is that the position error grows without bound unless an independent reference is used periodically to reduce the error [Cox, 1991]. b. Inertial Navigation This method uses gyroscopes and sometimes accelerometers to measure rate of rotation and acceleration. Measurements are integrated once (or twice) to yield position. Inertial navigation systems also have the advantage that they are self-contained. On the downside, inertial sensor data drifts with time because of the need to integrate rate data to yield position; any small constant error increases without bound after integration. Inertial sensors are thus unsuitable for accurate positioning over an extended period of time. Another problem with inertial navigation is the high equipment cost. For example, highly accurate gyros, used in airplanes, are inhibitively expensive. Very recently fiber-optic gyros (also called laser gyros), which are said to be very accurate, have fallen dramatically in price and have become a very attractive solution for mobile robot navigation. Absolute Position Measurements c. Active Beacons This method computes the absolute position of the robot from measuring the direction of incidence of three or more actively transmitted beacons. The transmitters, usually using light or radio frequencies, must be located at known sites in the environment. d. Artificial Landmark Recognition In this method distinctive artificial landmarks are placed at known locations in the environment. The advantage of artificial landmarks is that they can be designed for optimal detectability even under adverse environmental conditions. As with active beacons, three or more landmarks must be in view to allow position estimation. Landmark positioning has the advantage that the position errors are bounded, but detection of external 10
11 landmarks and real-time position fixing may not always be possible. Unlike the usually pointshaped beacons, artificial landmarks may be defined as a set of features, e.g., a shape or an area. Additional information, for example distance, can be derived from measuring the geometric properties of the landmark, but this approach is computationally intensive and not very accurate. e. Natural Landmark Recognition Here the landmarks are distinctive features in the environment. There is no need for preparation of the environment, but the environment must be known in advance. The reliability of this method is not as high as with artificial landmarks. f. Model Matching In this method information acquired from the robot's onboard sensors is compared to a map or world model of the environment. If features from the sensor-based map and the world model map match, then the vehicle's absolute location can be estimated. Mapbased positioning often includes improving global maps based on the new sensory observations in a dynamic environment and integrating local maps into the global map to cover previously unexplored areas. The maps used in navigation include two major types: geometric maps and topological maps. Geometric maps represent the world in a global coordinate system, while topological maps represent the world as a network of nodes and arcs. This book presents and discusses the state-of-the-art in each of the above six categories. The material is organized in two parts: Part I deals with the sensors used in mobile robot positioning, and Part II discusses the methods and techniques that make use of these sensors. Mobile robot navigation is a very diverse area, and a useful comparison of different approaches is difficult because of the lack of commonly accepted test standards and procedures. The research platforms used differ greatly and so do the key assumptions used in different approaches. Further difficulty arises from the fact that different systems are at different stages in their development. For example, one system may be commercially available, while another system, perhaps with better performance, has been tested only under a limited set of laboratory conditions. For these reasons we generally refrain from comparing or even judging the performance of different systems or techniques. Furthermore, we have not tested most of the systems and techniques, so the results and specifications given in this book are merely quoted from the respective research papers or product spec-sheets. Because of the above challenges we have defined the purpose of this book to be a survey of the expanding field of mobile robot positioning. It took well over 1.5 man-years to gather and compile the material for this book; we hope this work will help the reader to gain greater understanding in much less time. 11
12 Part I Sensors for Mobile Robot Positioning CARMEL, the University of Michigan's first mobile robot, has been in service since Since then, CARMEL has served as a reliable testbed for countless sensor systems. In the extra shelf underneath the robot is an 8086 XT compatible single-board computer that runs U of M's ultrasonic sensor firing algorithm. Since this code was written in 1987, the computer has been booting up and running from floppy disk. The program was written in FORTH and was never altered; should anything ever go wrong with the floppy, it will take a computer historian to recover the code... 12
13 CHAPTER 1 SENSORS FOR DEAD RECKONING Dead reckoning (derived from deduced reckoning of sailing days) is a simple mathematical procedure for determining the present location of a vessel by advancing some previous position through known course and velocity information over a given length of time [Dunlap and Shufeldt, 1972]. The vast majority of land-based mobile robotic systems in use today rely on dead reckoning to form the very backbone of their navigation strategy, and like their nautical counterparts, periodically null out accumulated errors with recurring fixes from assorted navigation aids. The most simplistic implementation of dead reckoning is sometimes termed odometry; the term implies vehicle displacement along the path of travel is directly derived from some onboard odometer. A common means of odometry instrumentation involves optical encoders directly coupled to the motor armatures or wheel axles. Since most mobile robots rely on some variation of wheeled locomotion, a basic understanding of sensors that accurately quantify angular position and velocity is an important prerequisite to further discussions of odometry. There are a number of different types of rotational displacement and velocity sensors in use today: & Brush encoders. & Potentiometers. & Synchros. & Resolvers. & Optical encoders. & Magnetic encoders. & Inductive encoders. & Capacitive encoders. A multitude of issues must be considered in choosing the appropriate device for a particular application. Avolio [1993] points out that over 17 million variations on rotary encoders are offered by one company alone. For mobile robot applications incremental and absolute optical encoders are the most popular type. We will discuss those in the following sections. 1.1 Optical Encoders The first optical encoders were developed in the mid-1940s by the Baldwin Piano Company for use as tone wheels that allowed electric organs to mimic other musical instruments [Agent, 1991]. Today s corresponding devices basically embody a miniaturized version of the break-beam proximity sensor. A focused beam of light aimed at a matched photodetector is periodically interrupted by a coded opaque/transparent pattern on a rotating intermediate disk attached to the shaft of interest. The rotating disk may take the form of chrome on glass, etched metal, or photoplast such as Mylar [Henkel, 1987]. Relative to the more complex alternating-current resolvers, the straightforward encoding scheme and inherently digital output of the optical encoder results in a lowcost reliable package with good noise immunity.
14 14 Part I Sensors for Mobile Robot Positioning There are two basic types of optical encoders: incremental and absolute. The incremental version measures rotational velocity and can infer relative position, while absolute models directly measure angular position and infer velocity. If non volatile position information is not a consideration, incremental encoders generally are easier to interface and provide equivalent resolution at a much lower cost than absolute optical encoders Incremental Optical Encoders The simplest type of incremental encoder is a single-channel tachometer encoder, basically an instrumented mechanical light chopper that produces a certain number of sine- or square-wave pulses for each shaft revolution. Adding pulses increases the resolution (and subsequently the cost) of the unit. These relatively inexpensive devices are well suited as velocity feedback sensors in medium- to high-speed control systems, but run into noise and stability problems at extremely slow velocities due to quantization errors [Nickson, 1985]. The tradeoff here is resolution versus update rate: improved transient response requires a faster update rate, which for a given line count reduces the number of possible encoder pulses per sampling interval. A very simple, do-it-yourself encoder is described in [Jones and Flynn, 1993]. More sophisticated single-channel encoders are typically limited to 2540 lines for a 5-centimeter (2 in) diameter incremental encoder disk [Henkel, 1987]. In addition to low-speed instabilities, single-channel tachometer encoders are also incapable of detecting the direction of rotation and thus cannot be used as position sensors. Phase-quadrature incremental encoders overcome these problems by adding a second channel, displaced from the first, so the resulting pulse trains are 90 degrees out of phase as shown in Figure 1.1. This technique allows the decoding electronics to determine which channel is leading the other and hence ascertain the direction of rotation, with the added benefit of increased resolution. Holle [1990] provides an in-depth discussion of output options (single-ended TTL or differential drivers) and various design issues (i.e., resolution, bandwidth, phasing, filtering) for consideration when interfacing phasequadrature incremental encoders to digital control systems. The incremental nature of the phase-quadrature output signals dictates that any resolution of angular position can only be relative to some specific reference, as opposed to absolute. Establishing such a reference can be accomplished in a number of ways. For applications involving continuous 360-degree rotation, most encoders incorporate as a third channel a special index output that goes high once for each complete revolution of the shaft (see Figure 1.1 above). Intermediate shaft I State S 1 Ch A High Ch B Low A S2 High High S3 Low High B S4 Low Low Figure 1.1: The observed phase relationship between Channel A and B pulse trains can be used to determine the direction of rotation with a phase-quadrature encoder, while unique output states S 1 - S 4 allow for up to a four-fold increase in resolution. The single slot in the outer track generates one index pulse per disk rotation [Everett, 1995].
15 Chapter 1: Sensors for Dead Reckoning 15 positions are then specified by the number of encoder up counts or down counts from this known index position. One disadvantage of this approach is that all relative position information is lost in the event of a power interruption. In the case of limited rotation, such as the back-and-forth motion of a pan or tilt axis, electrical limit switches and/or mechanical stops can be used to establish a home reference position. To improve repeatability this homing action is sometimes broken into two steps. The axis is rotated at reduced speed in the appropriate direction until the stop mechanism is encountered, whereupon rotation is reversed for a short predefined interval. The shaft is then rotated slowly back into the stop at a specified low velocity from this designated start point, thus eliminating any variations in inertial loading that could influence the final homing position. This two-step approach can usually be observed in the power-on initialization of stepper-motor positioners for dot-matrix printer heads. Alternatively, the absolute indexing function can be based on some external referencing action that is decoupled from the immediate servo-control loop. A good illustration of this situation involves an incremental encoder used to keep track of platform steering angle. For example, when the K2A Navmaster [CYBERMOTION] robot is first powered up, the absolute steering angle is unknown, and must be initialized through a referencing action with the docking beacon, a nearby wall, or some other identifiable set of landmarks of known orientation. The up/down count output from the decoder electronics is then used to modify the vehicle heading register in a relative fashion. A growing number of very inexpensive off-the-shelf components have contributed to making the phase-quadrature incremental encoder the rotational sensor of choice within the robotics research and development community. Several manufacturers now offer small DC gear-motors with incremental encoders already attached to the armature shafts. Within the U.S. automated guided vehicle (AGV) industry, however, resolvers are still generally preferred over optical encoders for their perceived superiority under harsh operating conditions, but the European AGV community seems to clearly favor the encoder [Manolis, 1993]. Interfacing an incremental encoder to a computer is not a trivial task. A simple state-based interface as implied in Figure 1.1 is inaccurate if the encoder changes direction at certain positions, and false pulses can result from the interpretation of the sequence of state changes [Pessen, 1989]. Pessen describes an accurate circuit that correctly interprets directional state changes. This circuit was originally developed and tested by Borenstein [1987]. A more versatile encoder interface is the HCTL 1100 motion controller chip made by Hewlett Packard [HP]. The HCTL chip performs not only accurate quadrature decoding of the incremental wheel encoder output, but it provides many important additional functions, including among others: & closed-loop position control, & closed-loop velocity control in P or PI fashion, & 24-bit position monitoring. At the University of Michigan's Mobile Robotics Lab, the HCTL 1100 has been tested and used in many different mobile robot control interfaces. The chip has proven to work reliably and accurately, and it is used on commercially available mobile robots, such as the TRC LabMate and HelpMate. The HCTL 1100 costs only $40 and it comes highly recommended.
16 16 Part I Sensors for Mobile Robot Positioning Absolute Optical Encoders Absolute encoders are typically used for slower rotational applications that require positional information when potential loss of reference from power interruption cannot be tolerated. Discrete detector elements in a photovoltaic array are individually aligned in break-beam fashion with concentric encoder tracks as shown in Figure 1.2, creating in effect a non-contact implementation of a commutating brush encoder. The assignment of a dedicated track for each bit of resolution results in larger size disks (relative to incremental designs), with a corresponding decrease in shock and vibration tolerance. A general rule of thumb is that each additional encoder track doubles the resolution but quadruples the cost [Agent, 1991]. Detector array LED source Beam expander Collimating lens Cylindrical lens Multi-track encoder disk Figure 1.2: A line source of light passing through a coded pattern of opaque and transparent segments on the rotating encoder disk results in a parallel output that uniquely specifies the absolute angular position of the shaft. (Adapted from [Agent, 1991].) Instead of the serial bit streams of incremental designs, absolute optical encoders provide a parallel word output with a unique code pattern for each quantized shaft position. The most common coding schemes are Gray code, natural binary, and binary-coded decimal [Avolio, 1993]. The Gray code (for inventor Frank Gray of Bell Labs) is characterized by the fact that only one bit changes at a time, a decided advantage in eliminating asynchronous ambiguities caused by electronic and mechanical component tolerances (see Figure 1.3a). Binary code, on the other hand, routinely involves multiple bit changes when incrementing or decrementing the count by one. For example, when going from position 255 to position 0 in Figure 1.3b, eight bits toggle from 1s to 0s. Since there is no guarantee all threshold detectors monitoring the detector elements tracking each bit will toggle at the same precise instant, considerable ambiguity can exist during state transition with a coding scheme of this form. Some type of handshake line signaling valid data available would be required if more than one bit were allowed to change between consecutive encoder positions. Absolute encoders are best suited for slow and/or infrequent rotations such as steering angle encoding, as opposed to measuring high-speed continuous (i.e., drive wheel) rotations as would be required for calculating displacement along the path of travel. Although not quite as robust as resolvers for high-temperature, high-shock applications, absolute encoders can operate at temperatures over 125(C, and medium-resolution (1000 counts per revolution) metal or Mylar disk designs can compete favorably with resolvers in terms of shock resistance [Manolis, 1993]. A potential disadvantage of absolute encoders is their parallel data output, which requires a more complex interface due to the large number of electrical leads. A 13-bit absolute encoder using
17 Chapter 1: Sensors for Dead Reckoning 17 complimentary output signals for noise immunity would require a 28-conductor cable (13 signal pairs plus power and ground), versus only six for a resolver or incremental encoder [Avolio, 1993]. a. b. Figure 1.3: Rotating an 8-bit absolute Gray code disk. a. Counterclockwise rotation by one position increment will cause only one bit to change. b. The same rotation of a binary-coded disk will cause all bits to change in the particular case (255 to 0) illustrated by the reference line at 12 o clock. [Everett, 1995]. 1.2 Doppler Sensors The rotational displacement sensors discussed above derive navigation parameters directly from wheel rotation, and are thus subject to problems arising from slippage, tread wear, and/or improper tire inflation. In certain applications, Doppler and inertial navigation techniques are sometimes employed to reduce the effects of such error sources. Doppler navigation systems are routinely employed in maritime and aeronautical applications to yield velocity measurements with respect to the earth itself, thus eliminating dead-reckoning errors introduced by unknown ocean or air currents. The principle of operation is based on the Doppler shift in frequency observed when radiated energy reflects off a surface that is moving with respect to the emitter. Maritime systems employ acoustical energy reflected from the ocean floor, while airborne systems sense microwave RF energy bounced off the surface of the earth. Both configurations typically involve an array of four transducers spaced 90 degrees apart in azimuth and inclined downward at a common angle with respect to the horizontal plane [Dunlap and Shufeldt, 1972]. Due to cost constraints and the reduced likelihood of transverse drift, most robotic implementations employ but a single forward-looking transducer to measure ground speed in the direction of travel. Similar configurations are sometimes used in the agricultural industry, where tire slippage in soft freshly plowed dirt can seriously interfere with the need to release seed or fertilizer at a rate commensurate with vehicle advance. The M113-based Ground Surveillance Vehicle [Harmon, 1986] employed an off-the-shelf unit of this type manufactured by John Deere to compensate for track slippage. The microwave radar sensor is aimed downward at a prescribed angle (typically 45() to sense ground movement as shown in Figure 1.4. Actual ground speed V A is derived from the measured velocity V D according to the following equation [Schultz, 1993]:
18 18 Part I Sensors for Mobile Robot Positioning V A V D cos cf D 2F 0 cos (1.1) where V A = actual ground velocity along path V D = measured Doppler velocity = angle of declination c = speed of light F D = observed Doppler shift frequency F = transmitted frequency. 0 Errors in detecting true ground speed arise due to side-lobe interference, vertical V A V Figure 1.4: A Doppler ground-speed sensor inclined at an angle as shown measures the velocity component V D of true ground speed V A. (Adapted from [Schultz, 1993].) velocity components introduced by vehicle reaction to road surface anomalies, and uncertainties in the actual angle of incidence due to the finite width of the beam. Byrne et al. [1992] point out another interesting scenario for potentially erroneous operation, involving a stationary vehicle parked over a stream of water. The Doppler ground-speed sensor in this case would misinterpret the relative motion between the stopped vehicle and the running water as vehicle travel Micro-Trak Trak-Star Ultrasonic Speed Sensor One commercially available speed sensor that is based on Doppler speed measurements is the Trak- Star Ultrasonic Speed Sensor [MICRO-TRAK]. This device, originally designed for agricultural applications, costs $420. The manufacturer claims that this is the most accurate Doppler speed sensor available. The technical specifications are listed in Table 1.1. D α Figure 1.5: The Trak-Star Ultrasonic Speed Sensor is based on the Doppler effect. This device is primarily targeted at the agricultural market. (Courtesy of Micro-Trak.)
19 deadre05.ds4,.wmf, 10/19/94 Chapter 1: Sensors for Dead Reckoning Other Doppler-Effect Systems A non-radar Doppler-effect device is the Monitor 1000, a distance and speed monitor for runners. This device was temporarily marketed by the sporting goods manufacturer [NIKE]. The Monitor 1000 was worn by the runner like a front-mounted fanny pack. The small and lightweight device used ultrasound as the carrier, and was said to have an accuracy of two to five percent, depending on the ground characteristics. The manufacturer of the Monitor 1000 is Applied Design Laboratories [ADL]. A microwave radar Doppler effect distance sensor has also been developed by ADL. This radar sensor is a prototype and is not commercially available. However, it differs from the Monitor 1000 only in its use of a radar sensor Table 1.1: Specifications for the Trak-Star Ultrasonic Speed Sensor. Parameter Value Units Speed range Speed resolution Accuracy Transmit frequency m/s mph cm/s in/s ±1.5%+0.04 mph 62.5 khz Temperature range -29 to to +120 Weight Power requirements head as opposed to the ultrasonic sensor head used by the Monitor The prototype radar sensor measures centimeters (6 4 2 in), weighs 250 grams (8.8 oz), and consumes 0.9 W. (C (F kg lb VDC A 1.3 Typical Mobility Configurations The accuracy of odometry measurements for dead reckoning is to a great extent a direct function of the kinematic design of a vehicle. Because of this close relation between kinematic design and positioning accuracy, one must consider the kinematic design closely before attempting to improve dead-reckoning accuracy. For this reason, we will briefly discuss some of the more popular vehicle designs in the following sections. In Part II of this report, we will discuss some recently developed methods for reducing odometry errors (or the feasibility of doing so) for some of these vehicle designs Differential Drive Figure 1.6 shows a typical differential drive mobile robot, the LabMate platform, manufactured by [TRC]. In this design incremental encoders are mounted onto the two drive motors to count the wheel revolutions. The robot can perform dead reckoning by using simple geometric equations to compute the momentary position of the vehicle relative to a known starting position. Figure 1.6: A typical differential-drive mobile robot (bottom view).
20 20 Part I Sensors for Mobile Robot Positioning For completeness, we rewrite the well-known equations for odometry below (also, see [Klarer, 1988; Crowley and Reignier, 1992]). Suppose that at sampling interval I the left and right wheel encoders show a pulse increment of N L and N R, respectively. Suppose further that c = %D /nc (1.2) m n e where c m = conversion factor that translates encoder pulses into linear wheel displacement D n = nominal wheel diameter (in mm) C e = encoder resolution (in pulses per revolution) n = gear ratio of the reduction gear between the motor (where the encoder is attached) and the drive wheel. We can compute the incremental travel distance for the left and right wheel, U L,i and U R,i, according to U = c N L/R, i m L/R, i (1.3) and the incremental linear displacement of the robot's centerpoint C, denoted U, according to i U = (U + U )/2. (1.4) i R L Next, we compute the robot's incremental change of orientation = (U - U )/b i R L (1.5) where b is the wheelbase of the vehicle, ideally measured as the distance between the two contact points between the wheels and the floor. The robot's new relative orientation can be computed from i = + i i-1 i (1.6) and the relative position of the centerpoint is x i = x i-1 + U i cosi y = y + U sin i i-1 i i (1.7a) (1.7b) where x i, y i = relative position of the robot's centerpoint c at instant i.
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Wind Energy Plants in South Korea
Location: South Korea
Operator: Hanshin Energy Co Ltd
Configuration: 11 X 3-MW MW V-90
Operation: 2009
WTG supplier: Vestas
EPC: Kepco
Quick facts: This $70mn plant was the first large-scale, private wind park on Jeju Island.
Photograph courtesy of Hanshin Energy Co Ltd
Location: South Korea
Operator: Eurus Energy Holdings
Configuration: 20 X 2 MW V-82
Operation: 2008
WTG supplier: Vestas
EPC: Posco E&C
Quick facts: This wind farm is near Taegisan mountain in Hwoengseong-gun and Bongpyeong-myeon in Pyeongchang-gun, Gangwon-do. This is the highest peak in Hoengseong-gun at 1,261m. Development started in Apr 2005 when Posco E&C signed a project MOU with the provincial government and Eurus Energy. Of 85bn won invested in the project, 42.5bn came from foreign investors. With an average 26% load factor, the project is expected to supply 98 GWh/yr to the grid and generate annual revenues of 9-11.3bn won. The turbines are installed in two groups, one in Hoengseonggun (9 units) and the second in Pyeongchang-gun (11units). The plant was opened on 26 Nov 2008.
Photograph courtesy of Posco E&C
Location: South Korea
Operator: Unison Co Ltd
Configuration: 15 X 1.65 MW V-82
Operation: 2005
WTG supplier: Vestas
EPC: Hyundai, owner
Quick facts: This was the first non-recourse project financing for an Asian wind project. Sponsors include Unison, Marubeni Corp, and Vestas. Korean Development Bank was financial advisor.
Photograph courtesy of Vestas
Data: industcards, Platts UDI World Electric Power Plants Data BaseUpdated 12-Nov-2014

subset: commoncrawl


text:
This website is all about adventures in verse and prose. These are my adventures, of course. I assume your adventures
are on your website.
Fifteen years ago,
I began the process of becoming a novelist. Writing one novel, cover to cover and head to toe twelve times over, has taught me a few things.
But only a few.
For me, being a writer is a lifelong apprenticeship. Hopefully, aided by organic food, strenuous exercise, and stem-cell therapy, I will have a hundred more years to hone my craft. Or to finish that sweater I started in 1995. It's a toss up.


text:
By Simon Herrmann
At the beginning of the year stock markets across the world plummeted and investors feared that 2016 would be a horrendous year. However despite 'Brexit' and Trump's election, equities have rebounded strongly and U.S. stocks are now trading near all-time highs. The ASX looks set to finish the year moderately in the black supported by rising commodity prices and a late rebound in banking shares.
Looking at five household names – Commonwealth Bank, BHP Billiton, Telstra, Wesfarmers and CSL Limited – the average 2016 return excluding dividends is approximately +3.1% (as of 16 December 2016). However this is largely due to the 40% return from BHP as most of the other major blue-chip stocks have underperformed. It is recommended to have exposure to these companies as the additional income is attractive.
But at Wise-owl we believe it makes sense to have additional exposure to high quality growth companies in the small-mid cap space. Middle market companies form the backbone of the Australian economy while small-caps often present investors with 'blue-sky' opportunities.
Here are three of our top growth picks for 2017 which are designed to complement your existing blue-chip portfolio
Talisman Mining (TLM) - $37m Market Cap
Talisman Mining is an Australian minerals company with operations in WA. The company has a 30% interest in the Springfield Joint Venture (JV) and also holds the Sinclair nickel project , which was acquired in 2014.
Talisman's board, management and share registry are very attractive with numerous members who have previously been involved in the $3 billion sale of the Jubilee Mine to Xstrata (now owned by Glencore). Technical studies at the Monty deposit have potential to drive near term interest towards the stock, whilst the Sinclair Project underpins a longer term value play.
However keep in mind that Talisman Mining is a speculative opportunity which needs to be carefully considered. There is no guarantee existing resources at Monty can be economically mined, or extended through additional exploration. Talisman is reliant on external capital and there is no guarantee it will be able to deliver its share of development capex at the Springfield JV.
Regardless the overall package makes a good investment case for Talisman which offers speculative exposure to the copper and nickel mining industries. With exploration and feasibility activities progressing concurrently, we believe the risk to reward ratio is very attractive.
Clearview Wealth (CVW) - $870m Market Cap
ClearView Wealth is an Australian financial services company focused on life insurance and wealth management. The Life Insurance division accounts for approximately 85 per cent of earnings, while Wealth Management makes up less than 10 per cent.
Clearview Wealth is a growth and income play. Management has increased the dividend for the past two consecutive years and the company has increased operating revenue for the past five financial years at an average annual growth rate of 16 per cent. Management may reward shareholders with higher distributions if growth targets are met. In addition, merger and acquisition activity provides further upside as seen in October when Sony Life Insurance acquired a 14.9% stake in the company.
Cooper Energy (COE) - $237m Market Cap
Cooper Energy is an Australian oil and gas exploration and production company with oil assets in the Cooper Basin and gas resources in the Gippsland and Otway Basin.
With the final investment decision for the 100% owned Sole Gas project due in the March 2017 quarter, procurement of project finance is the major catalyst. The project would increase Cooper's production 4-fold to approximately 1 million barrels in FY17.
An investment in Cooper should however be regarded as speculative. Risks include reliance on external capital, procurement of project financing and reliance on volatile commodity prices.
Cooper Energy is positioned to address a tightening gas supply landscape in East Australia and the upcoming offtake agreement for the Sola Gas Project could transform the company and present a near-term driver.
Final Word
Always keep in mind that diversification is key when it comes to investing. It is important that you don't put all your eggs in one basket regardless if you're looking at individual stocks, sectors or even markets.
Click here for a 21 day free trial to Wise-owl.
By Simon Herrmann


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Congratulations to this week's Coldwell Banker McMahan Champions of Character award recipient, soccer's Caitlin Williams. The Tiger sophomore was selected because of her leadership in her team's initiative to sponsor a Haitian girls' soccer team through the Haiti Health Foundation. The team captain's willingness to help others is a perfect example of the tenant of servant leadership in the NAIA Champions of Character Program.


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Battle of Britain Hurricane Pilot signed card
- Sold for: Start Free Trial or Sign In to see what it's worth.
- Item Category: Books, Paper & Magazines
- Source: eBay UK
- Sold Date: Oct 15, 2014
- Channel: Auction House Sell similar item on eBay
Postcard size Battle of Britain Museum Hurricane cardsigned by Battle of Britain Pilot Squadron Wing Commander R.W. 'Bob' Foster Bob flew Hawker Hurricanes with No 605 Squadron during the Battle of Britain
Card has been signed in pen


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For God to condemn you just to die for you is ridiculous and immoral.
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Christianity has the strangest and completely impossible beliefs. God condemns no one, people condemn themselves.
God Loves ALL
If we condemn ourselves then we can also forgive ourselves. Right?
All we need do is recognize that we cannot help but do evil and that that is the way God planned it.
It was God's plan from the beginning to have Adam and Eve eat the forbidden fruit. This can be demonstrated by the fact that the bible says that Jesus "was crucified from the foundations of the Earth," that is to say, God planned to crucify Jesus as atonement for sin before he even created human beings or God damned sin.
If God had not intended humans to sin from the beginning, why did he build into the Creation this "solution" for sin? Why create a solution for a problem you do not anticipate?
God knew that the moment he said "don't eat from that tree," the die was cast. The eating was inevitable. Eve was merely following the plan.
This then begs the question.
What kind of God would plan and execute the murder of his own son when there was absolutely no need to?
Only an insane God. That's who.
The cornerstone of Christianity is human sacrifice, thus showing it's immorality.
One of Christianity's highest form of immorality is what they have done to women.
They have denied them equality and subjugated them to men.
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Christians are always trying to absolve God of moral culpability in the fall by whipping out their favorite "free will!", or " it's all man's fault".
That is "God gave us free will and it was our free willed choices that caused our fall. Hence God is not blameworthy."
But this simply avoids God's culpability as the author of Human Nature. Free will is only the ability to choose. It is not an explanation why anyone would want to choose "A" or "B" (bad or good action). An explanation for why Eve would even have the nature of "being vulnerable to being easily swayed by a serpent" and "desiring to eat a forbidden fruit" must lie in the nature God gave Eve in the first place. Hence God is culpable for deliberately making humans with a nature-inclined-to-fall, and "free will" means nothing as a response to this problem.
If all sin by nature then, the sin nature is dominant. If not, we would have at least some who would not sin.
Having said the above for the God that I do not believe in, I am a Gnostic Christian naturalist, let me tell you that evil is all human generated. Evil is our responsibility.
Much has been written to explain what I see as a natural part of evolution.
First, let us eliminate what some see as evil. Natural disasters. These are unthinking occurrences and are neither good nor evil. There is no intent to do evil even as victims are created.
Evil then is only human to human.
As evolving creatures, all we ever do, and ever can do, is compete or cooperate.
Cooperation we would see as good as there are no victims created. Competition would be seen as evil as it creates a victim. We all are either cooperating, doing good, or competing, doing evil at all times.
Without us doing some of both, we would likely go extinct.
This, to me, explains why there is evil in the world quite well.
Be you a believer in nature, evolution or God, we should all see that what Christians see as something to blame, evil, we should see that what we have, competition, deserves a huge thanks for being available to us.
There is no conflict between nature and God on this issue. This is how things are and should be. We all must do what some will think is evil as we compete and create losers to this competition.
Theistic evolution.
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Title: Rowden, Tina
URL: http://www.tinarowden.com
Description: Wedding, lifestyle and feature film photographer who brings a unique, editorial style to her work. Based in Atlanta, USA.
Date Submitted: 09/15/12
Listed / Last Time Edited: 10/02/12
Main Category: > Wedding Photography > Wedding Photographers in USA
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Number of visitors we sent to this photo site: 82 time(s).


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- Brookdale09.Feb 2016
- Employee
Support from Management
The upper management is the problem here! You can't go to them for help, or conflict resolution. They take the side of the managers they put in charge. The manager in charge of my dept. wouldn't listen to the staff's input, though we knew the residents and she was brand new. It says a lot about a place when 4 people from the same dept, quit within six months!
Communication between departments is not good. Nobody is on the same page.


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Albert and Emily Hollins and their son Henry are on holiday at Cockleton-on-Sea. His parents are happy enough, but Henry is bored - until one particularly wet and windy day, when he steps into Samual Swain's inflatable shop, just as a great adventure is about to start.
"synopsis" may belong to another edition of this title.
£ 6
From United Kingdom to U.S.A.
Book Description 1986-05-29., 1986. Book Condition: New. Young Lions. New edition. Paperback. Book: GOOD. 128pp. . Bookseller Inventory # NF-1748377
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Book Description Young Lions, 1986. Paperback. Book Condition: New. book. Bookseller Inventory # 0006724361
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We quite often go away on overnight or 3 to 4 day trip. Our dogs are very much attached at the hip. One a PomChi - 5lb and the other a Bichon Poodle -28lb. We need to be assured they have a secure fenced in yard and a space they can sleep together. They are both very well groomed, up to date with all flea treatments and vaccines and are both well behaved.
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The Maroochydore State Electorate has always been a collection of distinct towns and communities in the centre of the Sunshine Coast. From the 2009 State Election, it included Coolum Beach, joining Point Arkwright, Yaroomba, Mt Coolum, Marcoola, Mudjimba, Pacific Paradise, Twin Waters, Alexandra Headland, and Mooloolaba as well as Maroochydore.
The northern boundary is the Coolum Beach sports complex. The western boundary is the Sunshine Motorway. The southern boundary is the Mooloolah River in Mooloolaba. The suburbs and towns west of the Sunshine Motorway such as Kuluin, Kunda Park, Forest Glen, Buderim North, and Diddillibah, are now in the seat of Buderim which was created in 2009 due to the growth on the Sunshine Coast.
The State seat of Maroochydore was created from the seats of Nicklin and Cooroora in 1992, with the main population centre based on the town of Maroochydore. However the Maroochydore electorate covers much more than this town – stretching from Coolum Beach to Mooloolaba with the Sunshine Motorway as the western boundary. It is located in the centre of the Sunshine Coast, along the Maroochy River. The Sunshine Coast's Glass House Mountains were first sighted by Captain James Cook in 1770, with the Maroochy River explored by Andrew Petrie in 1842. He named the area "Maroochydore" derived from "murukutchi-dha" in the language of the Aboriginal people who accompanied Petrie on his exploration. Meaning, place of red beaks, or place of the black swan, "Maroochydore" is still an area of natural beauty and wildlife even though it is facing the infrastructure and growth challenges currently experienced by the whole south-east corner. Located about one hour's drive north of Brisbane on the Sunshine Coast, the area is a popular tourist destination with some of Australia's best beaches and a vibrant hospitality sector. European history and Aboriginal legend link the towns of the Maroochy with the beautiful Maroochy River ever at the heart, surrounded by the rugged rocky edifices of Mt Coolum and Mt Ninderry and the smaller Mudjimba Island (Old Woman Island) just north of the river mouth. In the Aboriginal myth of the area, Ninderry and Coolum were warriors who fought over the beautiful young woman, named Maroochy. Ninderry knocked off Coolum's head and it rolled into the sea to become Mudjimba Island. The Creator, known to the local Undanbi tribe as Birral, punished Ninderry by turning his body into a huge stone. Maroochy fled to the mountains where her tears became the Maroochy River. When European settlers came to the area in the 1800s, the Maroochy River was the lifeline along which local commerce transpired. The town of Maroochydore, originally served as a port for the region's large inland timber industry. Later the cane industry was the major regional agricultural produce until the Nambour mill's closure in 2003. Today the local industries are dominated by the tourism service sector as well as building, fishing and other agricultural industries. There is a strong push to widen the economic base with a focus on innovative industry and education and training.
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Did Australian Aborigines reach America first?
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Did Australian Aborigines reach America first?Tags: None
InterestingAncestral Health Info
I design websites and blogs for a living. If you would like a blog or website designed by someone who understands Primal, see my web page.
Primal Blueprint Explorer My blog for people who are not into the Grok thing. Since starting the blog, I have moved close to being Archevore instead of Primal. But Mark's Daily Apple is still the best source of information about living an ancestral lifestyle.
They need to do some serious genetic testing, but I would not be surprised. I think our ancestors, including the aborigines of Australia and Polynesia, were incredibly adroit sailors. The Polynesians traveled in canoes as far as 3000 miles to people the islands of the Pacifc. This is certainly not a skill they picked up overnight.Start weight: 250 - 06/2009
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I've seen a TV programme where a wall painting in a South America cave seemed to be showing a battle between two different groups of people, one painted darker than the other.
It's been suggested that the people in Tierra del Fuegia may have been the last remnants of such a population.
Google: fuegians australia
There was a fascinating study done by a woman in New Zealand to figure out where the native Maori population came from. It was originally believed that they were polynesian. The Mitochondrial DNA tests showed though that they are a combination of native Taiwanese and New Guinean. This fited perfectly with their folklore that said that families had travelled in 40 canoes and picked up guides along the way and married them!
There were remains of Australian aborigines found in Brazil. Apparently they lived there for some time. The walls of the cave in the area had many paintings -- old paintings-- showing battles between black skinned people and red skinned people. The remains had indications of "war damage" inflicted by the new invaders into the region.
About ten years ago remains found in one of the North American Gulf states were determined to be the oldest remains found in the North America. They were Caucasian remains. When the face was reconstructed with clay, etc, by the forensic people, it looked like a bust of Sir Patrick Stewart. ( I think that is the name of the actor who played Captain Picard in the Star Trek series.)
Further study was squashed very rapidly by a legal proceeding initiated by numerous Native American tribes and the remains were buried in some undisclosed but sacred site for Native Americans. I guess they didn't want to loose their claim to being first.
I could care less what my number is. Incidentally, This is not an anti-Indian post. I have Taino forbears ---Taino were the people who 'discovered' Columbus. That event in history led to the Taino dodging extinction by Cherokee, Seminole, and Carib. Nothing hateful here either, just reflecting on history.Tayatha om bekandze
Bekandze maha bekandze
Randza samu gate soha
Originally posted by periquin View PostAbout ten years ago remains found in one of the North American Gulf states were determined to be the oldest remains found in the North America. They were Caucasian remains.
George Catlin in Letters and Notes noted that the Mandan sometimes had blue eyes and had hair of several different colours, including grey (as a normal colour not as a result of aging):
... so forcibly have I been struck with the peculiar ease and elegance of these people, together with the diversity of complexions, the various colours of their hair and eyes; the singularity of their language, and their peculiar and unaccountable customs, that I am fully convinced that they have sprung from some other origin than that of the other North American tribes ...
and amongst the women particularly, there are many whose skins are almost white, with the most pleasing symmetry and proportion of features; with hazel, with grey, and with blue eyes ...
The diversity in the colour of hair is also equally as great as that in the complexion; for in a numerous group of these people (and more particularly amongst the females, who never take pains to change its natural colour, as the men often do), there may be seen every shade and colour of hair that can be seen in our own country, with the exception of red or auburn, which is not to be found.
And there is yet one more strange can probably be seen nowhere else accounted for, other than it is a freak or order of Nature, for which she has not seen fit to assign a reason. There are very many, of both sexes, and of every age, from infancy to manhood and old age, with hair of a bright silvery grey; and in some instances almost perfectly white.
There was some rather off-the-wall speculation that the Mandan were descended from some lost mediaeval Welsh sailors. I believe that DNA work has now been done on the descendants of survivors* - most of the Mandan got wiped out by smallpox and then fell prey to stronger neighbours - and there's actually nothing Welsh about them. Possibly it's just human diversity rather than some particular origin.
I think I misremembered this. I just googled it, and all I could find was that some Welsh organization wanted to do DNA sampling, but the reaction of a Mandan when asked about it was that "nobody was sticking needles in him".
I think the whole idea is pretty crazy. In the 18th century a Welsh-speaking explorer, John Evans, trekked out there, on the basis that people had been saying the Mandan language contained some Welsh words, and after visiting said he was able to say definitively that the language was nothing like Welsh.Last edited by Lewis; 10-07-2010, 11:01 PM. Reason: Add additional information
Lewis: Thanks for the post. You filled in some of the facts about things that I half remembered.
I also heard stories about a Welsh origin of Native Americans. Both Mandan and Modoc were included as possibles in the papers that I read. Part of the theory was that the name 'Modoc' was derived from the family name of the Welsh forbears--Murdoch.
Interesting tale, but I am not getting that excited about it. The story also said that one of the Murdoch brothers left and continued on to South America near the Patagonia Mountains. There is a Welsh community there that still looks like a Welsh village of years ago. Who knows?Tayatha om bekandze
Bekandze maha bekandze
Randza samu gate soha
Originally posted by periquin View PostThere is a Welsh community there [in Patagonia] that still looks like a Welsh village of years ago.
It's just an area where a lot of Welsh people went. I'm not sure why. it could be that particular skills they had were in demand in Patagonia. There was a lot of mining expertise in South Wales, for example.
Bruce Chatwin mentions the Welsh in Patagonia in his book In Patagonia:
I can't remember what drew them there, but he tells the story in that book.


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|Please note: This article is about the courtier. For other uses of the term, please see Himiko (disambiguation).
Yasuki Himiko was a courtier of the Crab Clan.
Colonies Edit
Himiko was appointed in the Second City, living in the Merchant District, in a small house attended by few servants and a single bodyguard. She became a permanent fixture of the Ivory Court where she had many allies and very few enemies. [1]
Appearance Edit
Himiko was a small, and very thin courtier with soft voice, who always wore beautiful kimono even in the thick heat of the Colonial summer, maintaining an impeccable appearance and acting with great politeness and respect toward other samurai. Her mix of charm, skill, and genuine interest in satisfying her contacts' demands made her very successful. [1]
See also Edit
|This Crab Clan related article is a stub. That means that it has been started, but is incomplete. You can help by adding to the information here.