Gareth Milton

An application study of online reference governor to boost pressure control for automotive diesel engines

In this paper, we consider an application of an online reference governor (RG) to boost pressure control of automotive diesel engines. In order to treat the system nonlinearity, the plant is expressed as a piecewise affine model through system idenfication for each fixed operating condition of engine speed and fuelling. The plant model is utilized for the future prediction in the online RG. Then, an online iterative RG algorithm based on the gradient descent method is applied to generate the optimal modified reference so that the constraint on the maximal turbocharger rotation speed is satisfied. We show the effectiveness of the present method through an experiment with a production vehicle.

Reference Management for Aftertreatment Temperature Control of Automotive Diesel Engines

Abstract This paper describes aftertreatment temperature control of automotive diesel engines based on reference governor (RG). The RG algorithm computes a modified reference of catalyst temperature so that the predicted output of the closed-loop system on a finite prediction horizon does not exceed the constraint of its maximal temperature. We apply a bisectional search algorithm to the RG where the search region is extended in order to take account of model uncertainties. We show the effectiveness of the present method through an experiment with a production vehicle.

The effect of optical fiber endface surface roughness on light coupling

This paper presents a quantitative measurement of the effect of surface roughness of optical fiber end-faces on light coupling efficiency. Fibers tested included cleaved fibers and fibers with ground endfaces of varying degrees of surface roughness. The endfaces were ground on a specially built nano-grinding machine. The assessment was based on the Gaussian distribution of the intensity of light collected from both the cleaved and the ground endfaces of the fibers. Measurements of the total amount of light at the output end were also made. Results showed that light-coupling efficiency has improved dramatically with the improvement of surface finish. Surface roughness measurements were carried out using atomic force microscopy (AFM)

Mechanical fabrication of precision microlenses on optical fiber endfaces

This paper presents a purely mechanical means of producing highly concentric spherical lenses at the endfaces of optical fibers. The production process has two stages. First conical lenses are produced in a grinding process that ensures excellent concentricity. Then the conical lenses are transformed to spherical lenses using a novel process called loose abrasive blasting. The cone grinding is carried out on a micro-grinding machine that has a sophisticated control system that enables the production of precision conical lenses. The blasting is carried out on a diamond blasting machine. Plots showing automatic centering performance of the micro-grinding machine and scanning electron microscopy photographs of the conical and spherical lenses are presented.

Nanogrinding of microprofiles and microlenses on optical fibers endfaces for use in optical-fiber sensors

This paper presents nanogrinding as an alternative technique for the fabrication of optical fiber micro profiles. Grinding of these lenses is carried out on a nanogrinding machine (NGM) specially built for this purpose. Cleaved single mode optical fibers with core diameter of 9 &mgr;m and outside diameter of 125 &mgr;m were used. Optical fiber endfaces with a multitude of micro profiles were successfully made. This includes conical lenses, tapered lenses, D-shaped endfaces, and fibers with oblique endfaces. The results are presented in the form of optical microscopy and scanning electron microscopy images of the produced lenses.

Vision based ultra-precision centering of optical fibers for microlens fabrication

An optical fiber is mounted on a precision spindle, that can be indexed as well as speed controlled, in readiness for precision microlens grinding. A cluster of piezoelectric actuators, mounted on the spindle itself, carry out the crucial task of centering the fiber. Together with the indexing carried out using the spindle drive motor, the piezoelectric actuators allow position and angle adjustments in two perpendicular plains to achieve complete centering. An imaging system, using sub-pixel localization methods and a high magnification lens, simultaneously senses the eccentricity and angular misalignment of the optical fiber. A closed loop multi-axis centering controller has been implemented to achieve eccentricities and angular misalignments within 500 nm and 0.02/spl deg/, respectively.