bluuebunny/crossref_metadata_2025_split huggingface dataset:
Hypersurfaces of special configurations of serial manipulators and related concepts. part I: Theory and development of the hypersurfaces of special configurations
Authors: Soylu Resit , Duffy Joseph 
Published: July 2007

AbstractThis article is the first of three companion papers which introduce some novel concepts useful in the kinetmatic design, analysis, motion planning, control, and performance evaluation of serial manipulators. Here an efficient methodology is developed to classify the special configurations of an N DOF manipulator. This classification yields hyper‐surfaces in the joint space on each of which the manipulator loses a certain number of its degrees of freedom. The efficiency of the methodology is based on a theorem proved in Appendix B and the utilization of the minimal reference frames. These frames are obtained and tabulated for all possible types of manipulators. Furthermore the adaptability of a manipulator to a common control algorithm is quantified via an index. The numerical values of these indices are listed for all types of manipulators.
Acceleration feedback for control of a flexible manipulator arm
Authors: Kotnik Paul T. , Yurkovich Stephen , Özgüner Ümit 
Published: July 2007

AbstractMany studies to date have dealt with control and modeling strategies for endpoint positioning of flexible manipulator arm systems, and some actual experiments have been documented in verification of developed methods. This article describes laboratory results for a single‐link flexible manipulator arm in which three separate control strategies are compared and contrasted. Namely, the control schemes compared are: compensation using classical root locus techniques with endpoint position feedback, a full state feedback, observer‐based design, and compensation using endpoint acceleration feedback. The last technique, designs using accelerometer feedback, has received very little attention to date, and results here indicate great promise for use in flexible manipulator control.
The design and control of a robot finger for tactile sensing
Authors: Leaver S. O. , McCarthy J. M. , Bobrow J. E. 
Published: July 2007

AbstractThis article describes the design and control of a lightweight robot finger intended for tactile sensing research. The finger is a three‐link planar chain with the joints actuated through cables by two motors. Kinematic coupling of the three joints provides two degrees of freedom for finger tip manipulation, and a curling action of the finger for enclosing an object. Hall effect sensors in each joint provide position feedback, and strain gage sensors on each cable provide tension information. To minimize weight and power consumption, a high speed low torque motor together with a 172:1 speed reducer is used as the actuator. A force control loop around the motor speed reducer system reduces the effect of the friction inherent in the speed reducer. Flat mounting plates are provided on each link for special purpose grasping surfaces and sensors.
A modifed optical flow approach for robotic tracking and acquisition
Authors: Luo Ren C. , Mullen Robert E. 
Published: July 2007

AbstractA robotic system that can visually track and intercept an arbitrary object which is traveling in 2‐D at an unknown velocity on a conveyor is to be presented. An eye‐in‐hand vision system developed by the Robotics and Intelligent Systems Laboratory at NCSU is used as an integral part of the entire tracking and acquisition system. The eye‐in‐hand system is employed to characterize the object trajectory in real time via a modified optical flow approach. A control strategy has been developed which utilizes the kinematic data that is extracted by the tracking algorithm to intercept the moving object. An overall system configuration and its basic principles are described. The demonstration of the experimental results is presented.
Effect of inexact inertial parameters on robot manipulator system performance
Authors: Li Chang‐Jin , Hemami A. , Sankar T. S. 
Published: July 2007

AbstractThe effect of a manipulator inertial parameter errors on the manipulator system performance are studied. First, the relationships between the tracking error of the manipulator joint variables and the manipulator inertial parameter errors are derived. Then, using these relationships, the maximum steady state position, velocity, and acceleration errors of the joint variables are determined. The derived relationships allow us to acquire a desired steady state performance for joint variations either by increasing the control gains in the feedback control loops and/or by reducing the manipulator inertial parameter errors. These two problems are, also, addressed in this paper. The computational results of the maximum steady state position, velocity, and acceleration errors of the joints for a PUMA 560 arm are included.
Parallel computation of manipulator inverse dynamics
Authors: Fijany Amir , Bejczy Antal K. 
Published: July 2007

AbstractIn this article, parallel computation of manipulator inverse dynamics is investigated. A hierarchical graph‐based mapping approach is devised to analyze the inherent parallelism in the Newton‐Euler formulation at several computational levels, and to derive the features of an abstract architecture for exploitation of parallelism. At each level, a parallel algorithm represents the application of a parallel model of computation that transforms the computation into a graph whose structure defines the features of an abstract architecture, i.e., number of processors, communication structure, etc. Data flow analysis is employed to derive the time lower bound in the computation as well as the sequencing of the abstract architecture. The features of the target architecture are defined by optimization of the abstract architecture to exploit maximum parallelism while minimizing various overheads and architectural complexity. An algorithmically specialized, highly parallel, MIMD‐SIMD architecture is designed and implemented that is capable of efficient exploitation of parallelism at several computational levels. The computation time of the Newton‐Euler formulation for a 6‐degree‐of‐freedom (dof) general manipulator is measured as 187 μs. The increase in computation time for each additional dof is 23 μs, which leads to a computation time of less than 500 μs, even for a 12‐dof redundant arm.
Feedback control of one‐link flexible manipulator with gear train
Authors: Gorinevsky D. M. , Lensky A. V. , Sabitov E. I. 
Published: July 2007

AbstractThis article reports experimental results in control of a one‐link flexible manipulator. A d.c. drive with gear train rotates the link with a tip‐mass in the horizontal plane. A “stiff” hardware servo‐system tracks the commanded drive velocity. We describe the experimental setup and develop a dynamic model for the one‐mode flexible vibration control. We design and experimentally test controllers for active damping of the vibrations and stabilization of the link‐tip position. Results for continuous control implemented with an analog computer and a sampled‐data, digital‐computer control are reported. A high control performance is achieved despite the gear‐train friction influence. In addition, sampled‐data digital controllers for tracking control of the link reference motion are designed and tested.
NASA laboratory telerobotic manipulator control system architecture
Authors: Rowe J. C. , Butler P. L. , Glassell R. L. , Herndon J. N. 
Published: July 2007

AbstractIn support of the National Aeronautics and Space Administration (NASA) goals to increase the utilization of dexterous robotic systems in space, the Oak Ridge National Laboratory (ORNL) has developed the Laboratory Telerobotic Manipulator (LTM) system. It is a dexterous, dual‐arm, force‐reflecting teleoperator system with robotic features for NASA ground‐based research. This article describes the overall control system architecture, including both hardware and software. The control system is a distributed, modular, and hierarchical design with flexible expansion capabilities for future enhancements of both hardware and software.
Intermodulation in multiple fixed beam distributed amplifier phased array antenna systems
Authors: Johannsen K. G. , Hintze J. 
Published: July 2007

AbstractIn the recent development of phased array/distributed amplifier systems for application to mobile satellite or thin route communication systems, the intermodulation (IM) generated by the element amplifiers is spatially dispersed in such a way that some of the IM radiated energy falls outside the intended beam area. In addition, some of the IM falling inside the beam area has frequencies different from the carriers intended for that area.It is known that for fixed beam systems with frequency reuse, an average IM noise reduction of several dB can be realized. In the specific case under investigation, of four beams, nine frequencies and 12 carriers (1‐33 frequency reuse factor), an IM improvement of about 2‐0 dB is realized. The improvement in carrier‐to‐IM‐noise ratio can be applied to increase system capacity, or for given capacity it can be used to reduce RF power amplifier back‐off, which can be translated into a reduction of spacecraft prime power requirement.The considerable advantage gained from the multiple beam distributed amplifier approach makes it worthwhile to explore the workings of such a system and other benefits it may offer. One of the benefits is a common RF power pool for all carriers and beams, and the other is the spatial dispersion of intermodulation (IM). A satellite multiple beam pattern and the spatial dispersion of IM products are shown in Figure 1.
Carrier recovery and inter‐burst interference in a symbol‐synchronous tdma system
Authors: Harris R. A. , Yarwood M. 
Published: July 2007

AbstractESA is studying future communications satellite systems involving switching and processing on board the satellite. One concept uses a symbol‐synchronous MF‐TDMA system with very short data bursts. This paper investigates QPSK carrier phase estimation for coherent demodulation in such a system. The Viterbi and Viterbi algorithm is used to produce one phase estimate separately for each data burst. The algorithm and its properties are reviewed and computer simulation results are presented to show its performance. It offers excellent performance under the conditions planned for the MF‐TDMA system and is robust against distortions and interference.One potential problem in such a system, with no interburst guard‐time and possible level differences between adjacent bursts, is interburst interference. It is found that clear‐weather level differences of several dB can be tolerated easily. Atmospheric attenuation of the wanted burst may result in major level differences between adjacent bursts, but the interburst interference itself does not increase with respect to the thermal noise environment and so does not contribute any new problems. Any requirement for power control, for instance, will be determined by considerations of noise rather than interference.The burst timing accuracy in such a system is set by normal intersymbol interference considerations, rather than by the interburst interference or the needs of the phase estimator.
Error probability of m‐ary fsk with a limiter‐discriminator detector in satellite mobile channels
Authors: Korn I. 
Published: July 2007

AbstractWe derive formulae for the error probability of M‐ary frequency shift keying with a limiter‐discriminator detector in a satellite mobile channel, which includes as special cases the land mobile (Rayleigh) channel and the Gaussian channel. The received signal in this channel is composed of a specular signal, a diffuse signal and white Gaussian noise; hence the composite signal is fading with a Rician envelope. The error probability depends on the signal‐to‐noise ratio, the power ratio of the specular and diffuse components, the frequency deviation, the Doppler frequency, the maximum Doppler frequency, the time delay between diffuse and specular components, the autocorrelation of the diffuse component and the transfer function of the receive filter. Numerical results are presented as functions of the various parameters. Effects of the receive filter on the signal dependent components are neglected.
Global corporate communications with integrated services digital networks
Authors: Chan Conway , Eng Jim M. 
Published: July 2007

AbstractThis paper presents proposals and justification for standards governing the implementation of integrated service digital networks (ISDN). Using several programming protocols in a layered architecture provides continuing service during system evolution. The authors use a corporate communications environment for examples as the most probable initial implementation of the networks described. Some ISDN sites are operating, although not yet on a global scale, and present the building blocks for more advanced services in the near future. The authors present arguments supporting a concerted effort be started now to establish global standards for ISDN, so that design and development can comply in the most time‐effective manner.
Pereormance analysis of slotted ALOHA for land mobile satellite networks
Authors: Tan Harry H. , Hung Santiago V. 
Published: July 2007

AbstractThe ALOHA protocol has been proposed for accessing reservation channels in demand‐assigned channel access protocols for land mobile satellite communications networks. This paper provides a rigorous performance analysis of both the slotted ALOHA protocol and two‐packet replication ALOHA protocol taking into account the effects of the fading multipath communications environment. Throughput, delay and stability of these two protocols are determined using a Gilbert channel error model with memory. Comparison of slotted ALOHA and two‐packet replication ALOHA shows that a smaller average delay can be achieved by replication. Moreover average throughput is improved in some cases. However replication reduces stability.
A rural messaging network using spread ALOHA access with VSAT satellite terminals
Authors: Goel M. K. , Chandra Vinod 
Published: July 2007

AbstractThis paper underlines the characteristics of a proposed mesh network for messaging applications in C‐band using spread ALOHA protocol. A simulation program has been developed for studying the behaviour of large networks employing ALOHA access or its variants. It is a simulation for a large population network consisting of thin traffic small messaging terminals (SMTs), and models an infinite user population which employs fixed length data packets. The program is general and allows for the study of either the mesh or the star connected networks. Certain variations of the classical ALOHA schemes, such as slotted ALOHA (with user selectable slot length) and spread ALOHA, have been studied for network operation. In the case of spread ALOHA access, the program can be run with Barker, pseudorandom, Ping Fai Li or any other spreading sequence. The results of the simulation have confirmed the utility of spread ALOHA as an access protocol for MESCOMNET. It has identified an operating point on the throughput‐traffic curve at which spread advantage is available for power reduction of SMTs.
Land mobile satellite communication channel model for simultaneous transmission from A land mobile terminal via two separate satellites
Authors: Robet P. P. , Evans B. G. , Ekman A. 
Published: July 2007

AbstractThere are certain data services that could use transmit‐only land‐mobile satellite communication terminals. Such terminals would not be able to receive acknowledged messages and transmit them onward. Thus it is of interest to study alternative means of improving the system reliability. In this paper we propose the use of transmission to two satellites separated in azimuth and elevation in order to improve the reliability of throughput.We have investigated the improvements by building upon the model proposed by Lutz for land mobile satellite communications via one satellite, and extended this using measurements of the shadowing coefficient in different areas (suburban, countryside and city) to two separated satellites. The measured data is used to produce an empirical model of the equivalent shadowing coefficient variations with the separation angle variation between two satellites.The results show good agreement with the shadowing coefficients produced by the Lutz model for a single satellite. The degree of improvement produced by using two separated satellites in the different environments, in terms of bit rate and probability of the received power is given.
Transmission of group 3 facsimile over inmarsat maritime digital satellite mobile channels
Authors: Dimolitsas Spiros , Rieser Jack , Davis Earl , Ragland Rod , Feldman Howard 
Published: July 2007

AbstractThe importance of facsimile communication over public telephone networks is evidenced by the rapid growth in the number of Group 3 facsimile end‐user terminals. In this paper the main characteristics of a real‐time bit‐rate reducing approach are described whereby facsimile signals are demodulated and their associated protocols converted by a facsimile interface unit (FIU) to a format suitable for transmission over Inmarsat‐B maritime digital satellite channels. The FIU concept was developed to allow ‘off‐the‐shelf’ facsimile terminals to be interconnected via the PSTN through Inmarsat's satellite networks and to permit the provision of enhanced user services by converting Group 3 facsimile protocols to broadcast operation. In addition, the FIU concept is designed to compensate for the longer access and transport link delays encountered in mobile satellite systems, and to permit facsimile call recovery procedures to be successfully concatenated with satellite channel error detection mechanisms.
Burst error characterization of FEC coded digital channels
Authors: Kennedy D. J. , Nakhla M. B. 
Published: July 2007

AbstractThis paper reports on laboratory measurements to determine the characteristics of error bursts encountered on INTELSAT IDR and IBS links for data rates between 64 and 44,736 kb/s. In addition to burst length distributions, several other burst statistics are presented: number of errors per burst, average BER within bursts, and the distribution of error‐free block lengths. These results are intended for use in system design and evaluation of video/speech/data codec performance which are employed on such links.
Improving concatenated coding communications by employing signal editing techniques
Authors: Ng W. H. , Ungar J. L. 
Published: July 2007

AbstractSignal editing (SE) is a technique used to locate and erase unreliable data before error correction decoding. Consider a concatenated coding (CC) communication system in which the inner code employs convolutional encoding with Viterbi decoding (CEVD) and the outer code could employ either a convolutional or a Reed‐Solomon code. In this study, we show that useful information can be derived from the inner Viterbi decoding process to perform two special operations: (i) to locate and erase unreliable decoded data and (ii) to estimate the input channel noise level. As a result, the number of errors input to the outer decoder is reduced and the overall CC system performance is improved.
Standardization of VSAT communication systems in the CCIR
Authors: Ito Yasuhiko , Amadesi Paolo 
Published: July 2007

AbstractThis paper presents an overview of the CCIR Recommendations on VSAT systems. The first part presents the activities of the CCIR Task Group 4/2 which was created in 1990 and issued five Recommendations for VSAT earth‐stations. These Recommendations specify the RF characteristics of the VSAT earth‐stations and their maintenance functions. The TG 4/2 finished its task in 1991. The second part of this paper presents the activities of the CCIR Task Group 4/3 which was created in 1991 for the preparation of Recommendations on the connection of VSAT networks with the public switched networks. The activities of the TG 4/3 are still going on, and the Draft Recommendations will be formalized in two more meetings. The subjects of dicussion and the expected outcomes will be briefly presented.
The development of VSAT performance standards in the United States of America
Authors: Mitchell Michael W. , Hedinger Robert A. 
Published: July 2007

AbstractDuring the 1980s, when satellite communication systems and applications experienced significant growth, the Federal Communications Commission (FCC) in the U.S. recognized that special regulations were required for the licensing and operation of VSAT systems in order to maintain efficient use of the radio spectrum and geostationary orbit (GSO) and to expedite the authorization of VSAT networks featuring large numbers of earth‐stations. The FSS allocated frequency bands, which are used extensively by domestic satellite communication systems in the U.S. and throughout Region 2, are in the 4–6 GHz and 12–14 GHz bands. In order to satisfy the heavy demand in the U.S. for fixed satellite services in these bands, the FCC devised an orbit plan of two degrees spacing between satellites in the relevant portion of the GSO. In a co‐coverage environment, the two most important technical factors for controlling interference between neighbouring satellite systems are (1) earth‐station antenna discrimination and (2) cross‐polarization. Since VSAT systems, by definition, use very small aperture terminals with relatively low levels of antenna discrimination, it was necessary to establish limits for transmit power flux densities and the minimum size of antennas. These limits, based on compatible operation at two‐degree satellite orbit separations, evolved into VSAT standards for the U.S. domestic satellite industry. To expedite the licensing of large numbers of VSAT terminals, conforming systems were given ‘blanket authorizations’ for all VSATs in a network. This paper traces the history of the development of VSAT standards in the U.S. and discusses the technical considerations which were used in these developments. A brief review of receive‐only (RO) terminals is also provided.
VSAT networks in the intelsat system
Authors: Albuquerque J. , Buchsbaum L. , Meulman C. , Rieger F. , Zhu X. 
Published: July 2007

AbstractThis paper describes how VSAT networks currently operate in the INTELSAT system. Four classes of VSAT networks (data transaction; circuit‐switched; data distribution; microterminals) are identified, and it is verified that all of them can operate with INTELSAT satellites. Most VSAT networks in operation on INTELSAT today operate in fractional transponder leases. Fractional transponder capacity estimates are presented for a wide range of scenarios and different INTELSAT satellite series. These estimates clearly show increasing bandwidth utilization efficiencies for newer generations of INTELSAT satellites. Provided that VSAT and hub sizes are appropriately selected, efficiencies are already significant with existing satellites.Two possible ways of increasing the utilization of satellite resources are examined in the paper: demand assignment multiple access (DAMA) and multiple channel‐per‐carrier (MCPC) techniques. The impact of using DAMA in circuit‐switched VSAT networks is quantified.