Sensorless control strategies were first suggested well over a decade ago with the aim of reducing the size, weight and unit cost of electrically actuated servo systems. The resulting algorithms have been successfully applied to the induction and synchronous motor families in applications where control of armature speeds above approximately one hundred revolutions per minute is desired. However, sensorless position control remains problematic. This thesis provides an in depth investigation into sensorless motor control strategies for high precision motion control applications. Specifically, methods of achieving control of position and very low speed thresholds are investigated. The developed grey box identification techniques are shown to perform better than their traditional white or black box counterparts. Further, fuzzy model based sliding mode control is implemented and results demonstrate its improved robustness to certain classes of disturbance. Attempts to reject uncertainty within the developed models using the sliding mode are discussed. Novel controllers, which enhance the performance of the sliding mode are presented. Finally, algorithms that achieve control without a primary feedback sensor are successfully demonstrated. Sensorless position control is achieved with resolutions equivalent to those of existing stepper motor technology. The successful control of armature speeds below sixty revolutions per minute is achieved and problems typically associated with motor starting are circumvented.

Pneumatic actuators are low-cost, safe, clean, and exhibit a high power to weight ratio. In this thesis a novel servo pneumatic system based on miniature cylinders is presented. The first cylinder investigated has a 9.5 mm bore size. Four low-cost 2-way proportional valves are incorporated to provide greater design flexibility than the traditional single 4-way servo valve solution. A nonlinear system model is developed and validated using open-loop experiments. The use of bipolynomial functions to model the valve flow rates is shown to provide a more accurate solution than the commonly used nozzle flow equations. Two multiple-input single-output nonlinear position controllers are designed using the inverse dynamics and backstepping method respectively. In addition to position control, the control designs allow a second control objective to be implemented. In the inverse dynamics controller, the chamber pressures are controlled in inner loops and the position is controlled in an outer loop. In the backstepping controller, the stability analysis includes the effects of friction modeling error and valve modeling error. In experiments with a 1.5 kg moving mass, the inverse dynamics controller produced SSE within ±0.08mm and the backstepping controller ±0.05mm. The two control laws produced maximum tracking errors of ±0.5 mm and ±0.3mm for a 1 Hz sine wave trajectory respectively. The tracking errors are shown to be 85% less than those produced by a linear controller. Experiments demonstrate that the two controllers are robust to the system operating in horizontal and vertical orientations. They are also robust to an increase of payload but not to a decrease of payload. This problem can be overcome by tuning the controller parameters for the smallest payload. The two controllers are further tested with miniature cylinders with different bore diameters and stroke lengths. The smallest cylinder tested has a 4 mm bore diameter. / Thesis / Master of Applied Science (MASc)

Tese de mestrado. Automação, Instrumentação e Controlo. Faculdade de Engenharia. Universidade do Porto. 2009

This thesis presents a skillful robotic wrist system using a visual servo control technique to demonstrate dexterity of the mechanical wrist from the viewpoint of the table tennis. A ball and plate system is chosen as the first stage of this long-term project. A two degrees-of-freedom robotic wrist with an acrylic plate attached as the end effector is developed. A visual feedback control system is implemented with a web cam and a personal computer to acquire the ball's position. In order to implement decision making for changing orientation of the plate, a Linear Quadratic Regulator (LQR) is designed. As a result, the ball can be balanced at specific positions. Experimental results exhibit preliminary and promising achievement. Based on this progress, further improvement and deeper exploration can be carried on in the future.

In this thesis, an image-based uncalibrated visual servo is proposed for image tracking tasks in highly disturbed environment, such as a remotely operated vehicle performing observing or investigation objects under the influence of undersea current. For the conditions that the target model and the camera parameters are unknown, the control framework applies the scale invariant feature transform (SIFT) to extract image features. Furthermore, a robust adaptive control law is implemented to overcome the effect caused by camera calibration parameters. Then by using three different types of camera¡¦s motion: pan, tilt, and zoom to maintain the target always at the central position on the image plane.

The study and application of machine vision in early years mostly focus on a single camera. However, the trend of research on multiple cameras has been developed recently. Due to highly complicated correlation among multiple images, the arrangement of multiple cameras was restricted to the encirclement layout for acquiring more than one views of a target object. Furthermore, it has been well known that the special architecture of insect compound eyes contributes outstanding capability for precise and efficient observation of moving objects. If this technique can be transferred to the domain of engineering applications, significant improvement on visual tracking of moving objects will be greatly expected. This thesis builds a visual servo system with trinocular cameras by mimicking the configuration of compound eye of insects for tracking an object moving in 2D space. The arrangement of the trinocular cameras is divergent, and this system can function properly without the information of distance between the object and the cameras.

Optical flow, caused by relative motion of the object and the viewer, is the distribution of apparent velocities of brightness pattern in an image. The advantage of the optical-flow-based visual servo method is that feature of the object does not need to be defined or known in advance. This research plans to build an image servo technique to deal with the problem of 3D relative motion of the viewer and the environment. The images are treated as input and output signals of the control system and are fed back to extract the relative velocity information between contiguous image patterns. Then the video camera will automatically follow the motion to maintain the target image unchanged.

No description available.

A Read-While-Write (RWW) operation for tape and/or potentially disk applications is needed in the following three cases: 1. High reliability; 2. Data servo systems; 3. Buried servo systems. All these applications mean that the read (servo) head and write head are operative simultaneously. Consequently, RWW operation will require work to suppress the so-called crossfeed field radiation from the write head. Traditionally, write-read crossfeed has been reduced in conventional magnetic recording heads by a variety of screening methods, but the effectness of these methods is very limited. On the other hand, the early theoretical investigations of the crossfeed problem concentrating on the flux line pattern in front of a head structure based on a simplified model, may not be comprehensive. Today a growing number of magnetic recording equipment manufacturers employ thin-film technology to fabricate heads and thereby the size of the modern head is much smaller than in the past. The increasing use of thin-film metallic magnetic materials for heads, along with the appearance of other new technologies, such as the MR reproductive mode and keepered media, has stimulated the need for an increased understanding of the crossfeed problem by advanced analysis methods and a satisfactory practical solution to achieve the RWW operation. The work described in this thesis to suppress the crossfeed field involves both a novel reproductive mode of a Dual Magnetoresistive (DMR) head, which was originally designed to gain a large reproduce sensitivity at high linear recording densities exceeding 100 kFCI, playing the key role in suppressing the crossfeed (the corresponding signal-noise ratio is over 38 dB), and several other compensation schemes, giving further suppression. Advanced analytical and numerical methods of estimating crossfeed in single and multi track thin-film/MR heads under both DC and AC excitations can often help a head designer understand how the crossfeed field spreads and therefore how to suppress the crossfeed field from the standpoint of an overall head configuration. This work also assesses the scale of the crossfeed problem by making measurements on current and improved heads, thereby adapting the main contributors to crossfeed. The relevance of this work to the computer industry is clear for achieving simultaneous operation of the read head and write head, especially in a thin-film head assembly. This is because computer data rates must increase to meet the demands of storing more and more information in less time as computer graphics packages become more sophisticated.

No description available.