【作者】 汤莎亮；

【导师】 刘书桂；

【作者基本信息】 天津大学 ， 测试计量技术及仪器， 2009， 硕士

【摘要】 光笔式三坐标测量系统基于视觉测量技术,具有重量轻、便携性好、组建灵活、操作简单、精度适中、测量不受被测物体表面差异影响等优点,代表着坐标测量技术的一个重要发展方向,具有广阔的应用背景。本课题组于2000年开始这项研究,取得了一系列成果。由于现场测量往往需要对光笔测头进行标定,围绕光笔测头的标定及相关技术,本论文做了如下工作:1、介绍了当前便携式三维坐标测量技术特别是其中的手持探头式便携坐标测量技术;2、从PNP问题的解的角度说明了光笔设计的正确性;3、通过对图像中测量背景对光笔控制点识别和处理造成干扰的部分进行屏蔽,使得在复杂背景下提取光笔区域成为可能,提高了控制点边缘和中心的定位精度;4、创造性地提出采用两种模式进行控制点中心定位。一种是经Canny边缘检测获得控制点边缘后,对边缘进行最小二乘椭圆拟合,用椭圆中心近似控制点中心,适用于近距离测量;另一种是对控制点中心初步定位后用改进的高斯曲面拟合法获得亚像素级的曲面极值点,适用于较远距离的测量。并给出了两种模式的控制点中心定位重复性精度。5、建立了测头中心在光笔坐标系中的坐标值的估算模型。利用一个标准锥,即可实现光笔测头的现场标定。实验证明利用标定所得测头数据进行测量,亦可达到使用测头中心精密位置数据时的测量精度。6、光笔式便携三坐标测量系统的测量精度与Brown-Sharp精密三坐标测量机的精度比对实验证明了前者测量的正确性。1.5m距离测量和4m距离测量的误差都在可容许的范围内。分析了系统的误差来源,提出了两种系统改进方案,一种是利用透视投影变换的直线不变性修正控制点中心在像面上的坐标,另一种是利用可控恒流源对控制点亮度进行调整。更多还原

【Abstract】 The light pen portable coordinate measuring system based on photogrammetry technology possesses many advantages such as light and portable device, fast and flexible construction, simple operation, precision of proper level, not been affected by differences of surfaces been measured. So it is an important representation of one of the directions of the development of the coordinate measuring technology. It has wide prospective applications in many fields. Our team began the research of this system in 2000 and has acquired a lot since that time. In order to realize the probe tip calibration for the light pen portable coordinate measuring system to assist the field measurement, the following work was done.1. Various portable 3D coordinate measuring systems, especially the hand-hold probe 3D coordinate measuring system, are introduced.2. The validity of the design of the light pen is explained from the perspective of the PNP problem.3. Eradicating the districts which can disturb the recognition of the control points of the light pen to obtain the very image district of the light pen. This can lend help to the edge detection of the image of the control points, thus can make the edge detected more precise.4. Two modes employed for the location of the center of the control points are introduced. One is to first obtain the edge of the control points, then use the least square ellipse fitting method to get the center of the control points. The other is to first obtain the initial center of the control points, and then the improved Gauss surface fitting method is employed. The maximum of the Gauss surfaces are considered to be the centers of the control points. The former is proper for the measurement of nearer objects, whereas the latter is proper for the measurement of further objects. The repeatability error of the two modes is given.5. The mathematical model for the coordinates of the probe tip center under the light pen coordinate system has been built. Simply with a standard cone, the probe tip center can be calibrated. Experiment showed that the measuring precision of the light pen portable coordinate measuring system could reach to the same level as with the measured probe tip center data when with the calculated probe tip center data.6. The measuring precision of the light pen portable coordinate measuring system have been compared with the Brown-Sharp coordinate measuring machine. This comparison proved the correctness of the mathematical model of the light pen portable coordinate measuring system. Experiment showed that the measuring errors of the light pen portable coordinate measuring system in distances of 1.5m and 4m are both tolerable. The sources of the measuring error have been discussed. Two methods to further improve the system are presented. One is to enable self-rectification of the light pen using the principle of projective invariance of lines. The other is to make the luminance of the LEDs be controlled by adjustable current source.更多还原