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论文.doc

毕业设计说明书英文文献及中文翻译Novel Optical Sensor for Precise Tilt Angle MeasurementFan Hua, Ivan Reading and Fang ZhongPingSingapore Institute of Manufacturing TechnologyNanyang Avenue 71, Singapore 638075, Email: .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 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. 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 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 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 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 following 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 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 processing 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 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 optical path difference, 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. 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 reflection 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 mechanical 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 mounted 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 spherical 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 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 will 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 reflection 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 surface 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 illustrated 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. 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 the 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 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 accuracy 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 points 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 workstation 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 move 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 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 line 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 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 , e.g.0.3 micron in 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., “Electrolytic 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，它可以同时准确地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。设计制作了一个传感器的模型来论证这个新的方法，这是一个光电传感器,传感器中没有移动的部分。由正交于铅垂面的流动水平面提供参考面。传感器和绝对水平面之间的角度随着被测量的物体倾斜而改变，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随倾斜角的变化而改变。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。当使用1024*1024像素的传感器时，测量范围为700弧秒，其精度可高达+/ - 1弧秒。关键词：倾斜角度传感器，倾斜仪，激光干涉I 介绍市场上目前有几种类型的商业倾斜角度测量传感器。有些是角度传感器，有些是倾斜仪，它们的工作原理不同。电解液体、电容和钟摆是现在大多数倾斜角度传感器和倾斜仪的三个主要工作原理。在这里，我们提出了一种新的光学方法，建立了一个用激光、光学元件和图像传感器的光电传感器，它可以同时做精确的倾斜角度测量，不需要进行机械的移动，其工作原理是基于光学干涉，相干激光作为光源。光线通过一个装满液态油的玻璃油盒。由正交于铅垂面的流动水平面提供参考面。当激光束穿过油箱有两束光线反射回来，一束是液体的表面产生的，另一束是容器玻璃产生的，干涉条纹就是由这两条光线形成的，条纹图案将随着倾斜角度的变化产生相应的变化，条纹图案采集和处理后将反映倾斜角度信息，光学工作原理使它不受磁场的影响。该传感器可以同时测量两轴倾角。流动的水平面确保了参考面是一个绝对的水平面。高灵敏度光学干涉测量原理，保证了较高的精度。II 原理图1说明了工作原理示意图，O点是光线扩大镜头的焦点，O点可以看作是点光源，它发出球面波。由于地球重力的影响，液体油面始终保持水平，因此用油面作为参考平面。该容器是玻璃材料的。当传感器被放在目标表面时，其底部表面将连同目标对象一起倾斜。图1 测量原理工作示意图从油面和玻璃表面射出的光将干涉形成圆形图案（见图4）。倾斜角度可以通过圆形图案中心位置的改变测量得出。P是点O在玻璃和空间之间形成的镜像，点Q则是点O在油和空气之间形成的镜像，油空气平面代表了水平面。当使玻璃面平行油面，点P和点Q在垂直于油面的同一条线上，这条线也是光学系统的轴线。边缘与共同中心圆形边缘。当油箱倾斜玻璃表面有一对以油面的倾斜角，这是同心圆图案。当油盒倾斜时，玻璃面相对于油面有个倾斜角。 （1）其中n是玻璃的折射率。当倾斜角度很小，上面的方程可以简化为 （2）我们可以从和得到以下方程：（3）其中是圆条纹中心的位置，D是接收屏幕到油箱玻璃表面的距离，H是玻璃和油的厚度，n是玻璃和油折射率（因为玻璃和油的折射率非常接近，这里假设它们相等）。假设折射率nD远远大于h，因此相对于来说h可以忽略不计。 (4)从方程（4）可知，一旦装置安装好后，n,d,h是固定的。令,为系统常量，系统参数可以通过校验过程获得。 因此方程(4)可以写成 （5）其中可以通过图像处理技术计算出,由此可以得出值。III. 传感器的描述图2显示了传感器的光学头部详细布局。它包括激光1，扩束2，光束分离器3，平面镜4和液体油盒5。一个点光源发出球面波，这束光线穿过油箱。这束光线分别被玻璃表面和油的表面反射，两束不同路线的光将再次相遇再次相聚。如果点光源相干长度大于长的光程差，这两束光线将产生干涉形成环形条纹。当一个表面发生倾斜，圆形条纹中心将相应地转变。当光学路径变化，条纹将相应的出现或者被吸收。条纹变化发生在一个相对应的光程差，其中为光源的波长。图2 光学传感器布局如图2所示，激光发射激光束1。激光束通过扩束2被扩大，形成一个球形波前束，随后这束光线垂直穿过液态油盒5，在几种不同折射率的媒介表面形成反射。当入射方向垂直于反射面时，反射率是由下面公式决定的。（6）其中，和代表了两个媒介的衍射指数。两个反射率越近，将会有更少的光被反射。当等于时，这个表面不存在反射。然而构建这个传感器的最终要的一个要求是所有光学器件的中心放在同一条线上，例如：光轴。由于机械公差和传感器头部的明确要求，对光学器件进行校准微调是必要的，以确保传感器能够正常工作。该方法首先对准激光，使激光束平行于所有的光学组件安装在基板，然后安装光束分离器，激光束的方向随一个直角和入射到油盒的光线改变。调整光束分离器直到入射光线垂直入射到液体油盒，对准光轴与系统扩束轴。从玻璃表面和油表面的反射光波将被平面镜以直角改变方向射入相机，使相机对准确保激光束在成像平面的中心成像。也就是说，成像轴垂直于成像平面。而且，该方法需要用三个10号螺丝进一步配合三个油箱安装，以确保倾斜角度在测量范围内，这样一个圆形条纹图案将出现。调整10号螺丝直到条纹图案中心放在图像传感器中心，如图4A所示 图3 油盒原理图图3显示了液态油盒的原理图。第一个表面是由空气和玻璃形成的，称为空气-玻璃表面，其反射率约为3，因为空气的折射率是1，我们使用的玻璃折射率约为1.4。第二面是玻璃和油形成的，称为玻璃-油面，这个表面几乎没有反射，因为我们选择的油的折射率和玻璃的相近。第三个表面是油和空气形成的，因此这个反射率大约等于第一个表面的。第一个玻璃-空气表面和第三个油-空气表面反射的波相遇后互相干涉，形成一个如图4所示的圆形的干涉图案。当玻璃表面与油面平行，该中心将被定位在（图4A）光轴。当倾斜角度变化时，圆形条纹中心的位置也将变化（图4B）。图4A 干涉条纹图案（中心，无倾斜角） 图4B 干涉条纹图案（边缘，有倾斜角）IV. 校准对于传感器来说，为确保一个精确和可信的测量，校准是很重要的。当传感器水平放置时，一个好的校准可确保圆形图案的中心放在图像传感器的中心部分。该校准的目的不仅是获取方程（6）中系统的常数h，而且可以纠正光学像差引起的误差。校准的概念是把我们的传感器和基准传感器放在同一个板上，然后改变板的倾斜角度，记录传感器和基准传感器的读数。图5显示了为传感器校准的校准工作台装置图，工作台由一个三点支撑的平板和两个精度高达1狐秒的单轴角度传感器组成。这两个传感器形成了一个直角，一个沿着X轴监控X轴光线方向的改变，另一个沿着Y轴监控Y轴光线方向的改变，这个板是由三个螺丝支撑的。通过调整三个螺丝很容易改变板的倾斜角度。图5 校准平台原理图我们的光学传感头是安置在板中心，并与工作台的X和Y轴对齐。首先，调整底座，直到传感器的读数等于0，然后使工作台平行于海平面。第二，安装需要在板上校准的光学传感器，将X轴和Y轴与基准传感器对齐。第三，通过油盒外面的三个螺丝调整液态油盒面圆形图案的中心移到图像传感器的中心，这种调整可以确保合适的测量范围。第四，通过调整螺丝的不同高度改变倾斜角度。记录基准传感器的读数并用传感器计算两个轴的倾斜角度，该读数应覆盖整个测量范围，标定系数可以从此校准数据获得。然后将校准系数输入到应用软件程序中，则校准过程结束。图6A显示了在X轴刻度线，图6B显示了在Y轴的刻度线。图6A X轴测量结果图6B Y轴测量结果V. 总结本文主要发明了一种新型光学传感器，建立了模型并进行了评估，测量范围为700弧秒，精度为+ -1弧秒，它可以同时准确地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。与其他倾角仪比较它具有以下几个主要优点。（1）精度高。它是基于传感器的光学干涉原理。任何小于的变化，0.3微米的光路改变都会引起干涉条纹图案的变化，检测到微小的变化并转换为倾斜角。（2）对电磁环境不敏感。（3）光电传感器，无机械运动部分。（4）同一时间进行两轴角度测量。袁节膅薂羄肅蒃薁蚃芀荿薀螆肃芅蕿袈芈膁蚈羀肁蒀蚇蚀袄莆蚇螂肀莂蚆羅袂芈蚅蚄膈膄蚄螇羁蒂蚃衿膆莈蚂羁罿芄螁蚁膄膀螁螃羇葿螀袅膃蒅蝿肈羆莁螈螇芁芇莄袀肄膃莄羂艿蒂莃蚂肂莈蒂螄芈芄蒁袆肀膀蒀罿袃薈葿螈聿蒄葿袁羁莀蒈羃膇芆蒇蚃羀膂蒆螅膅蒁薅袇羈莇薄罿膄芃薃虿羆艿薃袁节膅薂羄肅蒃薁蚃芀荿薀螆肃芅蕿袈芈膁蚈羀肁蒀蚇蚀袄莆蚇螂肀莂蚆羅袂芈蚅蚄膈膄蚄螇羁蒂蚃衿膆莈蚂羁罿芄螁蚁膄膀螁螃羇葿螀袅膃