毕业论文英文文献及翻译

毕业设计说明书英文文献及中文翻译学生姓名：学号：学院：信息与通信工程学院专业：通信工程指导教师：2011年 6 月Novel Optical Sensor for Precise Tilt AngleMeasurementFan Hua, Ivan Reading and Fang ZhongPingSingapore Institute of Manufacturing TechnologyNanyang Avenue 71, Singapore 638075, Email: hfan@.sgABSTRACTA novel optical sensor, which can measure inclination angle or tilt angle of two axes simultaneously and precisely, is introduced. This sensor is based on the principle of laser interference so it has very high accuracy. A prototype sensor is designed, built and evaluated to demonstrate the novel concept. It is an optoelectronic sensor. There are no moving parts in the sensor. A fluid horizontal that is absolutely perpendicular to the true vertical provides the reference plane. The angle between the sensor and the absolute horizon changes with the inclination of the object being measured. These changes are reflected in the way of fringe pattern’s centre position shift. Different interference patterns centre locations are generated when tilt angle varied. The interference fringe pattern are recorded and processed to translate into the tilt angles of two axes, horizontal and vertical. The accuracy can reach as high as +/- 1 arc second with the measurement range of 700 arc seconds when 1024 by1024 pixels image sensor is utilized.Key words: tilt angle sensor, inclinometers, laser interferenceI. INTRODUCTIONThere are several kinds of commercial sensor for tilt angle measurement, which are available in the market. Some known as tilt angle sensor, some are known as inclinometers. They base on different working principles. Electrolytic liquid [1], capacitance [2] and pendulum [3] are the three main working principles that most tilt angle sensor or inclinometer usually base on. Here we propose a novel optical method and build up an optoelectronic sensor withlaser, optical components and image sensor. It can do precise tilt angle measurement simultaneously. There is no mechanical movement part. The working principle is based on optical interferometry. Coherent laser is used as the lighting source. It will go through a liquid oil box, which is built by a glass container filled with liquid oil. A fluid horizontal that is absolutely perpendicular to the true vertical provides the reference plane. When laser beam pass through the oil box two beams are reflected back by surface of the liquid and container glass. Interference fringes are formed with these two beams. The fringe patterns will shift in corresponding to the changes of the tilt angles. The fringe patterns is captured and processed to give the tilt angle information. Optical working principle makes it insensitive to magnetic field. The sensor can measure two axes inclination angle simultaneously. A fluid horizontal make sure the reference plane is an absolute horizontal plane. High sensitive optical interference measurement principle assures the high accuracy.A prototype of the method has been built up and evaluated. Experimental results show the tilt angle changes relative to sea level can be detected at the accuracy of +-1 arc second within the measurement range of 700 arc seconds.II. PRINCIPLEFigure 1 illustrates the schematic diagram of working principle. Point O is the focal point of beam expanding lens. Point O can be considered as a point light source. It emits spherical wave-front. Liquid oil surface will always maintain horizontally due to the gravity force of the earth. The oil surface is used as the reference plane. The container is made of glass. Its bottom surface will incline together with the target object when the sensor is placed on the target. The light from oil surface and glass surface will interference to form circular fringes pattern (see Fig. 4). The incline angle can be measured with the centre position changes of circular fringes. P is the mirror image of O against to glass-air surface and Q is the mirror image of O against to oil-air surface. The oil-air surface represents the horizontal plane. When the glass surface positioned parallel with oil surface the P and Q are in the same line perpendicular with oil surface. This line is also the optical axis of the optical system. The fringes are circular fringes with common center. When the oil box is inclined the glass surface has a tilt angle aagainst to the oil surface.αθsin sin n = （1）where n is the refraction index of glass.When the tilt angle is tiny, the above equation can be simplified asαθn ≈ （2）We can obtain the following equation from OPS ∆and OQS ∆nhD r D r n 222+-=α （3） where r is the center position of circular fringes. D is the distance of the receiving screen to the glass surface of oil box. h is the thickness of glass and oil. n is the refraction index of glass and oil ( here we assume the glass and oil have same index since they are very close).Assume that h nD >>so that h is negligible relative to D.222222Dn rh h nD r nD r ≈+-=α (4) From equation (4) n, D and h are fixed once the setup is assembled. Let 222D n h =η, called system constant. This system parameter can be obtained through calibration process. Hence equation (4) can be written asnr =α （5）where r can be calculated with image processing technique and hence do the tilt angle α.Fig. 1 Schematic diagram of measurement principleIII. DESCRIPTION OF SENSORFigure 2 shows the detail layout of the optical head of the sensor. It includes laser 1, beam expander 2, beam splitter 3, mirror 4 and liquid oil box 5. A point light source emits spherical wave-front. This beam goes through the oil box. It is reflected by the glass surface and oil surface respectively. These two wave-fronts meet together again after they pass different optical paths. If the coherent length of the point light source is longer than the optical path difference, these two beams will interfere and form circular fringes. When one surface tilts the center of the circular fringes will shift accordingly. When the optical path changes, the fringes will be generated or absorbed accordingly. One fringe change occurs in corresponding to 2λoptical path difference, where λ is the wavelength of the light source.Fig. 2 Layout of optical sensor headAs illustrated in Figure 2, the laser 1 emits a laser beam. This laser beam is expanded by a beam expander 2 to form a spherical wave-front beam. Subsequently this beam goes through the liquid oil box 5 perpendicularly. The reflections occur in the surfaces formed by medias layers with different refraction indexes. The reflection ratio is determined by the formula when incident direction is perpendicularly to the reflection plane 。