Thesis (M.Phil.)--Hong Kong University of Science and Technology, 2006. / Includes bibliographical references (leaves 67-68). Also available in electronic version.

M.Ing. / Shaft encoders, are devices generally used in speed and position control applications for sensing position of rotational and linearly moving objects. Most conventional shaft encoders operate on the principle of reading encoded information off a disk, which is fitted to the shaft or using resolver units. Problems are often experienced in fitting high-resolution encoder disks or resolvers to small motors or moving objects. The resolution of an encoder system, using an encoded disk, is a function of the maximum number of slots that are cut in the disk. If the disk itself has to be very small, physical constraints limit the accuracy of the encoder. However, any machined surface will have characteristic marks on it and it is believed that these marks can be used to obtain a unique analogue signature for the shaft. This analogue signature can then be used to gain further knowledge about the rotational speed and possibly the position of the shaft. This project was an investigation into the possibility of gaining accurate, absolute positional information for a rotating shaft. An optical source- and detector system is used in the process of observing the irregularities on the shaft surface. This signal data is gathered and processed using a technique, which compensates for variation in shaft speed during the period in which data is sampled. The entire algorithm, which calculates the absolute position of the shaft from the data gathered, was implemented on a digital signal processor board. Results were evaluated and the maximum non-linearity of the test system was found to vary between 1.8% and 3.7% of full-scale deflection. The resolution of the sensor was between 1.5 and 2.5 degrees with hysteresis between 1% and 1.5% of full scale deflection. The test system allows for rotation in any direction. Possible problems that might be encountered with this type of encoder system are pointed out in this report. Future developments and possible improvements are also discussed.

General purpose operating systems have been designed to provide fast, loss-free disk service to all applications. However, multimedia applications are capable of tolerating some data loss, but are very sensitive to variation in disk service timing. Present research efforts to handle multimedia applications assume pessimistic disk behaviour when deciding to admit new multimedia connections so as not to violate the real-time application constraints. However, since multimedia applications are ``soft' real-time applications that can tolerate some loss, we propose an optimistic scheme for admission control which uses average case values for disk access. Typically, disk scheduling mechanisms for multimedia applications reduce disk access times by only trying to minimize movement to subsequent blocks after sequencing based on Earliest Deadline First. We propose to implement a disk scheduling algorithm that uses knowledge of the media stored and permissible loss and jitter for each client, in addition to the physical parameters used by the other scheduling algorithms. We will evaluate our approach by implementing our admission control policy and disk scheduling algorithm in Linux and measuring the quality of various multimedia streams. If successful, the contributions of this thesis are the development of new admission control and flexible disk scheduling algorithm for improved multimedia quality of service.