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Tesi etd-05042011-004454

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Tipo di tesi
Tesi di dottorato di ricerca
Designing Innovative Electronic Systems to Face the Challenges of Feasibility and Performance in Sensing and Control Applications
Settore scientifico disciplinare
Corso di studi
tutor Prof. Roberto Saletti
tutor Prof. Roberto Roncella
Parole chiave
  • PC-based acquisition systems
  • Optical Time-Domain Reflectometry (OTDR)
  • optical fibre distributed temperature sensors
  • Formula SAE
  • FPGA/ADC platform
  • cyclic Simplex codes
  • automotive electronics
  • Raman effect
  • shift-by-wire
Data inizio appello
Riassunto analitico
This thesis reports the results obtained during a three year research program on electronic systems design. Two advanced applications in the field of sensing and control electronics are analysed and discussed, with a particular emphasis on the design solutions which allowed to improve the performance provided by the state-of-the-art and, at the same time, to implement new functionalities previously considered unfeasible.

The first application is focused on the design, implementation and test of a long--range optical fibre Distributed Temperature Sensor (DTS). A new architecture, aiming to address the main design issues related to the sensing range extension and to the measurement time reduction, is presented. A low-noise APD-based optoelectronic front-end allows to optimize the input signal-to-noise ratio (SNR) of the system. A high level of configurability is also obtained by allowing the user to control the gain and offset of the amplification chain, as well as to fine tune the APD bias voltage and operating temperature. This way, the optimum multiplication factor of the APD, which ensures the best available input SNR, can easily be selected. Signals are acquired through a flexible ADC/FPGA-based platform. Here, a set of decimation and interleaved sampling algorithms allows to efficiently exploit the available memory resources and reach long measurement ranges. Finally, a patented SNR enhancing technique based on laser pulse coding allows to efficiently apply, for the first time, Simplex codes to long-range DTS systems, and therefore to significantly reduce the measurement time.

A prototype, which is able to cover distances up to 87.4 km with a spatial resolution of just 1.3 m, has been implemented. Preliminary tests on a 20 km range, carried out without coding, show a performance comparable with the state-of-the-art. The benefits of the coding technique have been instead evaluated on a 10 km range. It has been proved that an outstanding measurement time reduction up to 95 % with respect to conventional long-range uncoded systems is achievable.

The second application is instead focused on the development of automotive embedded systems for Formula SAE vehicles. For the first time, linear Voice Coil Actuators (VCAs) have been used to implement a robotized shift-by-wire system, which has been applied to the gear and the clutch devices of the first student-build race car developed at the University of Pisa. A numerical model of the electromechanical system allows to properly size the actuators, so as to obtain a shifting performance better than any other known solution adopted for Formula SAE vehicles. A DSP-based Gear Control Unit (GCU), has been specifically designed to implement the upshift, downshift and car start procedures, and to direct drive the actuators. On-track tests show that the achieved upshift time is just 40 ms, i.e. less than half of the one provided by counterparts.

Moreover, a data logging system and a telemetry system have been also implemented. Both are based on a 16 MHz, 8 b microcontroller and communicate with other on-board units through the CAN bus. The first is able to record on a removable SD card the information related to the speed of wheels, the suspensions stroke and the steering angle, as well as the data coming from a 3-axial accelerometer, a gyroscope and a GPS. Using a 2 GB card, signals can be logged for 97 h with a 40 Hz sampling frequency, which is a very good result if compared with commercially available products. Acquired data are also sent over the CAN bus and made available to other units. On the other hand, the telemetry system is composed by two twin units, one on-board and one connected to a PC via USB. The on-board unit listens to CAN activity and forwards messages to the PC unit over a 2.4 GHz wireless encrypted link. A custom developed LabVIEW application allows for the real-time monitoring of the vehicle status and for a rapid fault detection. The radio link is bidirectional, so that the PC is also able to send CAN messages back to on-board units, such as the GCU, and configure their parameters remotely. These capabilities, along with a maximum outdoor range of 2 km, make the system very interesting with respect to other Formula SAE products available on the market.