毕业论文英文文献及翻译--一种精确测量倾斜角度的光学传感器

1、毕业论文英文文献及翻译-一种精确测量倾斜角度的光学传感器 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 Angle MeasurementFan Hua, Ivan Reading and Fang ZhongPingSingapore Institute of Manufacturing TechnologyNanyang Avenue 71, Singapore 638075, Email: hfansimtech.a-ABSTR

2、ACTA 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

3、 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. T

4、hese changes are reflected in the way of fringe patterns 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. Th

5、e 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

6、 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 pr

7、opose a novel optical method and build up an optoelectronic sensor with laser, 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 l

8、ighting 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

9、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

10、 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 eva

11、luated. 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

12、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

13、 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

14、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 opt

15、ical system. The fringes are circular fringes with common center. When the oil box is inclined the glass surface has a tilt angle a against to the oil surface. （1）where n is the refraction index of glass.When the tilt angle is tiny, the above equation can be simplified as （2）We can obtain the follow

16、ing equation from and （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

17、 close .Assume that so that h is negligible relative to D. 4 From equation 4 n, D and h are fixed once the setup is assembled. Let , called system constant. This system parameter can be obtained through calibration process.Hence equation 4 can be written as （5）where r can be calculated with image pr

18、ocessing technique and hence do the tilt angle .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 em

19、its 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 differe

20、nce, 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 optical path difference,

21、 where 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.

22、 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。 （6）Where andrepresent the diffraction index of the two medias. The closer the two re

23、flection indexes the less light reflected. When equals to there is no reflection occurring at this surface.While building the sensor one of the most important requirements is to make sure that the centers of all optical components are positioned on the same line, e.g. the optical axis. Due to mechan

24、ical tolerance and the precise requirements of the sensor head, a fine tune on the alignment of the optical head is necessary to make sure the sensor can work well. The method begins with aligning the laser to enable the laser beam parallel to the base plate that all the optical components will be m

25、ounted on. Subsequently install the beam splitter. The direction of laser beam will be change by a right angle and incident to the liquid oil box. Adjust the beam splitter until the laser beam incident to the liquid oil box perpendicular. Install beam expander to convert the parallel beam into a sph

26、erical laser beam. Align the beam expander axis with the system optical axis. The reflected wave fronts coming from glass surface and oil surface will go through beam splitter and change its direction at right angle by mirror to enter camera. The alignment of camera makes ensure the laser beam to be

27、 imaged at the center of the imaging plane. That is, the imaging axis is normal to the imaging plane. Furthermore, the method needs to further align the liquid oil box with the three screws 10 mounted in the oil box to ensure tilt angle within the measurement range. A pattern with circular fringes w

28、ill appear. Adjust the screw 10 until the center of the fringe pattern positioned in the center of image sensor as illustrated in Figure 4A.Fig. 3 Schematic diagram of oil boxFigure 3 shows the details of liquid oil box. The first surface is formed by air-glass, called air-glass surface; the reflect

29、ion ratio is about 3% since the refraction index of air is 1 and the glass we used is around 1.4. The second surface is formed by glass-oil, called glass-oil surface. There is almost no reflection in this surface since we choose proper oil with the close refraction index with the glass. The third su

30、rface is constructed by the oil and air. So the reflection ratio is about the same as the first surface. The two reflected wave fronts by the first glass-air surface and the third oil-air surface will meet together and interference each other to form a pattern with circular interference fringes as i

31、llustrated in Figure 4. When the glass surface is parallel with oil surface the center will be positioned in the optical axis Fig. 4A . The position of center of the circular fringes will shift when the tilt angle varies Fig. 4B .Fig. 4A Interference fringe patterns center position, non tilted Fig.

32、4B Interference fringe patterns side position, tilted angle IV. CALIBRATIONIt is vital for calibration of the sensor to ensure an accurate and reliable measurement. A proper calibration makes sure that the center of the circular fringes is positioned in the center portion of the image sensor when th

33、e sensor is placed horizontally. The purposes of the calibration are not only obtaining system constant h of equation 6 but also correcting errors caused by optical aberration. The concept of calibration is to put our sensor and the benchmark sensor onto the same plate then change the tilt angles of

34、 the plate to record the readings of our sensor and the benchmark sensors. Figure 5 shows schematic diagram of our calibration workstation for the calibration of the sensor. The workstation consists of a flat plate supported at three points and two high accurate single axis tilt angle sensors with a

35、ccuracy as high as 1 arc second. The two sensors are positioned at a right angle, one is alongwith x-axis to monitor the change in x direction and the other is along with y-axis to monitor the change in y direction.Fig. 5 Schematic diagram of calibration platformThe plate is supported at three point

36、s with three screws. It is easy to change the tilt angle of the plate by adjusting the three screws. Our optical sensor head is placed in the center of the plate and aligned with x and y axis of the station. First, adjust the base plate until the readings of the sensor equal to 0 to let the workstat

37、ion plate is parallel to the sea level. Second, mount our optical sensor that needs to be calibrated onto the plate. Align the x and y axis with the benchmark senor. Third, adjust the level of liquid oil box with the three screws on the cover of the liquid oil box until the center circular fringes m

38、ove to the center of the image sensor. This adjust can make sure the proper measurement range. Forth, change different tilt angles by means of adjusting the different heights of screw. Record the readings of the benchmark sensor and calculate the tilt angles of two axes with our sensor. The readings

39、 should cover the whole measurement range. Calibration coefficient can be obtained with this calibration data. After input the calibration coefficient into software application program, the calibration process is over. Fig. 6 A shows the calibration line in X axis. Fig. 6 B shows the calibration lin

40、e in Y axis.Fig. 6A Measurement results of X axisFig. 6B Measurement results of Y axisV. CONLUSIONA novel optical sensor was invented. A prototype has been built up and evaluated. Accuracy of +-1 arc second within the measurement range of 700 arc seconds has been achieved. It can measure inclination

41、 angle or tilt angle of two axes simultaneously and precisely. This sensor is based on the principle of laser interference. It has the following main advantages compare with other inclinometers. 1 High accurate. It is optical interference principle based sensor. Any variation less than , .3 micron i

42、n optical path will cause the movement of interference fringe pattern. This tiny change is detected and converted to tilt angle. 2 Insensitive to magnetic environment. 3 Optoelectronic sensor, no mechanical moving parts. 4 Two axes angles measurement at the same time.REFERENCES1 Olson, Jack R., “Ele

43、ctrolytic tilt sensor and method for manufacturingsame”, US patent, US6802132B1, 20042 Urano, Mitsuhiro, “Capacitance type liquid sensor”, Patent EP1515117A1,20053 Zabler, Erich, “ Tilt sensor”, Patent EP0768513A2, 1997一种精确测量倾斜角度的光学传感器摘要本文主要介绍了一种新型光学传感器，它可以测量倾斜角或两轴倾斜角度。这种传感器是基于激光干涉原理，因此具有很高的精度。这些变化反映在条纹图案的中心位置的转移方式。不同的干涉条纹的中心位置倾斜角干涉条纹图案进行记录和处理，转化为两轴水平和垂直倾斜角度。精度可高达+/ - 1弧关键词：倾斜角度传感器，倾斜仪，激光干涉有几种类型的商业倾斜角度测量传感器。电解液体电容和钟摆是。在这里，我们提出了一种新的光学方法，