Papers by Author: Yi Hua Fan

Abstract: An optical mechanism composed of a movable part and a fixed part for the increment high-resolution optical displacement encoders is proposed in this paper. The parallel light emitted from the movable part passes through a double-concave lens and a specially designed optical grating; it is then projected onto a phototransistor array receiver to indicate the displacement of the movable part. The relationship equation of the lens is developed to design an optical mechanism which can enlarge the displacement so that it becomes observable. Based upon the simulation results, a specially designed optical grating is designed to compensate for the deviations on the detecting surface and to derive the increment movement of the light source. The simulation results indicated that the optical mechanism with 50 times magnification could make the 10 nm movement intervals of a light source be about 500 nm movement intervals in the detecting surface. Furthermore, an experimental system with a 200 nm resolution is established to verify the possibility of the proposed structure.

Abstract: This paper proposes a novel nano-scale micro-machining machine based on the pantograph mechanism. It is designed to satisfy the need for achieving high accuracy and process efficiency in the manufacture of increasingly small industrial products. The target platform is mounted on a pantograph and small x-y sliders, and is driven by a traditional X-Y platform with common precision. The theoretical and simulation results indicate that the proposed method is feasible for development of a micro-machining machine capable of achieving nano-level precision. In addition, test results indicate that the micro-machining machine can position the target platform with a resolution of 500nm

Abstract: This paper presents a new switching control scheme for an active magnetic bearing (AMB) system using self-tuning fuzzy proportional-integral-derivative (PID) control. The research process consists of three stages. First, four types of self-tuning fuzzy PID-type controllers (FPIDCs) consisting of two most commonly used fuzzy inference systems: Mamdani and Takagi-Sugeno types, and two efficient parameter adaptive methods: function tuner and relative rate observer, are used to control a highly nonlinear AMB system, respectively. Hence, there are two kinds of FPIDCs can be obtained by comparing experimental results of these tests: one has the fastest transient response and the other has the minimum steady-state error. Next, the switching-type self-tuning FPIDC is proposed by combining the two kinds of FPIDCs. Namely, the AMB system is dominated by the scheme with the fastest transient response when the rotor is at rest and by the one with the best steady-state performance when the rotor is in rotation. Finally, experimental results demonstrate that the proposed switching-type self-tuning FPIDC performs better overall performance than the other self-tuning FPIDCs, particularly when controlling an AMB system.

Abstract: A passive magnetic thrust bearing for a small vertical wind generator system is considered in this paper. The passive magnetic bearing is designed to reduce the axial load of the rotor system. The load capacity of the passive magnetic bearing is analyzed by finite element analysis software. From the simulation results, a suitable solution for the passive magnets of the test wind generator system is verified to be 225.6N with about a 2mm air gap. The experiment results show that a wind generator system with the additional passive magnetic bearing can start at a lower wind speed and transfers more power to the generator. The proposed hybrid bearing system can increase efficiency by 20%~50%, as compared with a traditional system supported by roller bearings at the same wind speed.

Abstract: A novel optical displacement encoder was proposed in this paper. An optical mechanism was designed by the equations of thick lens to change and modify the paths of light, and then to get a more visible position change in the optical detector to improve the measurement accuracy. The simulation results indicated that the optical mechanism with 5 mm stroke, which the lens radii of curvature of the incident and the exit surface on the lens were -0.625 cm and 1.25 cm, respectively, and the magnification was 50 times in imaging distance of 38 cm, could make the 1 nm movement intervals of light source to be about 50 nm movement intervals in the detecting surface. Thus we can combine the optical mechanism and a photo-detector array with 50 nm resolution and 25 cm total detecting length to form the optical displacement encoder with 1 nm measuring accuracy.

Abstract: The paper proposes a novel time based brightness compensation circuit for LED back light modules. The brightness of LED decays while running under constant current driven condition. We have designed a suitable controller to compensate the driving currents to maintain the brightness. The compensation data were calculated from the relative luminous efficiency – time curve provided by the LED manufacturer and were stored in the microprocessor. -The embedded system used the running time of the LED in the back light module as an independent variable for tuning the driving current. The experiment results showed that the brightness of different operating times’ LED arrays can be held almost the same as the new ones.

Abstract: Using TracePro® Monte-Carlo ray-tracing simulations, this paper investigates the improved light extraction efficiency (LEE) obtained by patterning the surface and/or substrate of GaN LEDs with unique three-dimensional micro-cavity patterns. The simulations commence by considering the case of a sapphire-based GaN LED. The effects on the LEE of the micro-cavity dimensions, the absorption coefficient of the active layer, the point source location, and the chip dimensions are systematically examined. Subsequently, the LEE performance of the sapphire-based GaN LED is compared with that of a thin-GaN LED for various surface texturing strategies. In general, the results show that patterning either the surface or the substrate of the LED structure provides an effective improvement in the LEE of both the sapphire-based GaN LED and the thin- GaN LED. For both LED structures, the maximum LEE enhancement is obtained by patterning both the upper surface of the LED and the substrate surface. However, the simulation results indicate that the improvement obtained in the LEE is the result primarily of pattering the upper surface of the LED.