29 research outputs found
Parameter identification and model based control of direct drive robots
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Precision engineering center. 1988 Annual report, Volume VI
To reverse the downward trend in the balance of trade, American companies must concentrate on increasing research into new products, boosting productivity, and improving manufacturing processes. The Precision Engineering Center at North Carolina State University is a multidisciplinary research and graduate education program dedicated to providing the new technology necessary to respond to this challenge. One extremely demanding manufacturing area is the fabrication and assembly of optical systems. These systems are at the heart of such consumer products as cameras, lenses, copy machines, laser bar-code scanners, VCRs, and compact audio discs - products that the Japanese and other East Asian countries are building dominance. A second critical area is the fabrication of VLSI and ULSI circuits. The tolerances required to produce the next generation of components for such systems have created the need for new approaches - approaches that could either make or break America`s competitive position. This report contains individual reports on research projects grouped into three broad areas: measurement and actuation; real-time control; precision fabrication. Separate abstracts for these articles have been indexed into the energy database
CHANNEL CODING TECHNIQUES FOR A MULTIPLE TRACK DIGITAL MAGNETIC RECORDING SYSTEM
In magnetic recording greater area) bit packing densities are achieved through increasing
track density by reducing space between and width of the recording tracks, and/or
reducing the wavelength of the recorded information. This leads to the requirement of
higher precision tape transport mechanisms and dedicated coding circuitry.
A TMS320 10 digital signal processor is applied to a standard low-cost, low precision,
multiple-track, compact cassette tape recording system. Advanced signal processing and
coding techniques are employed to maximise recording density and to compensate for
the mechanical deficiencies of this system. Parallel software encoding/decoding
algorithms have been developed for several Run-Length Limited modulation codes. The
results for a peak detection system show that Bi-Phase L code can be reliably employed
up to a data rate of 5kbits/second/track. Development of a second system employing a
TMS32025 and sampling detection permitted the utilisation of adaptive equalisation to
slim the readback pulse. Application of conventional read equalisation techniques, that
oppose inter-symbol interference, resulted in a 30% increase in performance.
Further investigation shows that greater linear recording densities can be achieved by
employing Partial Response signalling and Maximum Likelihood Detection. Partial
response signalling schemes use controlled inter-symbol interference to increase
recording density at the expense of a multi-level read back waveform which results in an
increased noise penalty. Maximum Likelihood Sequence detection employs soft
decisions on the readback waveform to recover this loss. The associated modulation
coding techniques required for optimised operation of such a system are discussed.
Two-dimensional run-length-limited (d, ky) modulation codes provide a further means of
increasing storage capacity in multi-track recording systems. For example the code rate
of a single track run length-limited code with constraints (1, 3), such as Miller code, can
be increased by over 25% when using a 4-track two-dimensional code with the same d
constraint and with the k constraint satisfied across a number of parallel channels. The k
constraint along an individual track, kx, can be increased without loss of clock
synchronisation since the clocking information derived by frequent signal transitions
can be sub-divided across a number of, y, parallel tracks in terms of a ky constraint. This
permits more code words to be generated for a given (d, k) constraint in two dimensions
than is possible in one dimension. This coding technique is furthered by development of
a reverse enumeration scheme based on the trellis description of the (d, ky) constraints.
The application of a two-dimensional code to a high linear density system employing
extended class IV partial response signalling and maximum likelihood detection is
proposed. Finally, additional coding constraints to improve spectral response and error
performance are discussed.Hewlett Packard, Computer Peripherals Division (Bristol
NASA Tech Briefs, April 1990
Topics: New Product Ideas; NASA TU Services; Electronic Components and Circuits; Electronic Systems; Physical Sciences; Materials; Computer Programs; Mechanics; Machinery; Fabrication Technology; Mathematics and Information Sciences
A multi-mode sonar transmitter
This project was initiated to evaluate appropriate microprocessor and
digital logic techniques that could increase the flexibility and effectiveness of
a sonar transmitter. The study led to a multi-channel signal synthesis concept
designed to exploit 'phased array' steering techniques. Two versions of the
equipment have now been built and evaluated. Mk.I is a relatively low power
15 channel system with 2 kilowatts total electrical power using a 40 kHz
15 λ x 1 line array. This system proved the practicability of the basic concept
and its success led to the 16 kilowatt Mk2 high power version which
drives a 16λ x 16 λ wideband transducer array.
The study included:
The design and construction of a multi-channel signal generator.
The writing of control and signal synthesis software.
The design, evaluation and commissioning of suitable linear power
amplifiers .
Investigations into suitable transducers and phased array design, leading
to the manufacture of suitable matched wide band multi-channel 'staved'
transducer arrays.
Finally, a series of trials were made in a variety of open water conditions
to evaluate the systems performance and investigate the multiple modes
of operation that have been developed.
The system has successfully demonstrated that transmitter beam steering
is both practical and flexible. The techniques implemented permit sector
interrogation by 'within-pulse' type sweeps, by 'Ripple-fire' and by transmitting
steered 'Pings' sequentially on prededermined bearings. Each mode allows
considerable flexibility in the generated waveform shape and frequency.
The 'Multi-Mode' capability of this approach was conceived primarily
as a research tool but many of the modes can be isolated and exploited in
dedicated applications
Study report recommendations for the next generation Range Safety System (RSS) Integrated Receiver/Decoder (IRD)
The Integrated Receiver/Decoder (IRD) currently used on the Space Shuttle was designed in the 1980 and prior time frame. Over the past 12 years, several parts have become obsolete or difficult to obtain. As directed by the Marshall Space Flight Center, a primary objective is to investigate updating the IRD design using the latest technology subsystems. To take advantage of experience with the current designs, an analysis of failures and a review of discrepancy reports, material review board actions, scrap, etc. are given. A recommended new design designated as the Advanced Receiver/Decoder (ARD) is presented. This design uses the latest technology components to simplify circuits, improve performance, reduce size and cost, and improve reliability. A self-test command is recommended that can improve and simplify operational procedures. Here, the new design is contrasted with the old. Possible simplification of the total Range Safety System is discussed, as is a single-step crypto technique that can improve and simplify operational procedures
NASA Tech Briefs, January 1990
Topics include: Electronic Components and Circuits. Electronic Systems, Physical Sciences, Materials, Computer Programs, Mechanics, Machinery, Fabrication Technology, Mathematics and Information Sciences, and Life Science