76 research outputs found
Applications of the orthogonal property of binary chain codes
Imperial Users onl
Speckle pattern interferometry : vibration measurement based on a novel CMOS camera
A digital speckle pattern interferometer based on a novel custom complementary metaloxide-
semiconductor (CMOS) array detector is described. The temporal evolution of the
dynamic deformation of a test object is measured using inter-frame phase stepping. The
flexibility of the CMOS detector is used to identify regions of interest with full-field time
averaged measurements and then to interrogate those regions with time-resolved
measurements sampled at up to 7 kHz.
The maximum surface velocity that can be measured and the number of measurement
points are limited by the frame rate and the data transfer rate of the detector. The custom
sensor used in this work is a modulated light camera (MLC), whose pixel design is still
based on the standard four transistor active pixel sensor (APS), but each pixel has four
large independently shuttered capacitors that drastically boost the well capacity from that
of the diode alone. Each capacitor represents a channel which has its own shutter switch
and can either be operated independently or in tandem with others. The particular APS of
this camera enables a novel approach in how the data are acquired and then processed.
In this Thesis we demonstrate how, at a given frame rate and at a given number of
measurement points, the data transfer rate of our system is increased if compared to the
data transfer rate of a system using a standard approach. Moreover, under some
assumptions, the gain in system bandwidth doesn’t entail any reduction in the maximum
surface velocity that can be reliably measured with inter-frame phase stepping
High performance DSP-based servo drive control for a limited-angle torque motor
This thesis describes the analysis, design and implementation of a high performance
DSP-based servo drive for a limited-angle torque motor used in thermal imaging
applications. A limited-angle torque motor is an electromagnetic actuator based on the Laws' relay principle, and in the present application the rotation required was from - 10° to + 10° in 16 ms, with a flyback period of 4 ms. To ensure good quality picture
reproduction, an exceptionally high linearity of ±0.02 ° was necessary throughout the forward sweep. In addition, the drive voltage to the exciting winding of the motor should be less than the +35 V ceiling of the drive amplifier. A research survey shows that little literature was available, probably due to the commercial sensitivity of many of the applications for torque motors. A detailed mathematical model of the motor drive, including high-order linear dynamics and the significant nonlinear characteristics, was developed to provide an insight into the overall system behaviour. The proposed control scheme uses a multicompensator, multi-loop linear controller, to reshape substantially the motor response characteristic, with a non-linear adaptive gain-scheduled controller to compensate effectively for the nonlinear variations of the motor parameters. The scheme demonstrates that a demanding nonlinear control system may be conveniently analysed and synthesised using frequency-domain methods, and that the design techniques may be reliably applied to similar electro-mechanical systems required to track a repetitive waveform. A prototype drive system was designed, constructed and tested during the course of the research. The drive system comprises a DSP-based digital controller, a linear power amplifier and the feedback signal conditioning circuit necessary for the closed-loop control. A switch-mode amplifier was also built, evaluated and compared with the linear amplifier. It was shown that the overall performance of the linear amplifier
was superior to that of the switch-mode amplifier for the present application. The control software was developed using the structured programming method, with the
continuous controller converted to digital form using the bilinear transform. The 6-
operator was used rather than the z-operator, since it is more advantageous for high
speed sampling systems. The gain-scheduled control was implemented by developing
a schedule table, which is controlled by the DSP program to update continuously the
controller parameters in synchronism with the periodic scanning of the motor.
The experimental results show excellent agreement with the simulated results, with
linearity of ±0.05 ° achieved throughout the forward sweep. Although this did not
quite meet the very demanding specifications due to the limitations of the
experimental drive system, it clearly demonstrates the effectiveness of the proposed control scheme. The discrepancies between simulated and experimental results are analyzed and discussed, the control design method is reviewed, and detailed suggestions are presented for further work which may improve the drive performance
Numerical Modeling of Microstrip Discontinuities and Related Structures
Coordinated Science Laboratory was formerly known as Control Systems LaboratoryJoint Services Electronics Program / N00014-90-J-127
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