Research On Measurement Accuracy Of Light-pen Three-coordinate Measurement System Based On Monocular Vision

In today's measurement environment with variable measurement sites and diversified measurement locations,traditional measurement instruments can no longer meet the needs of today's measurement era.The light-pen three-coordinate measurement system is an online measurement device based on machine vision technology that uses the feature points on the light-pen body as the direct monitoring target.It is characterized by a large measurement range and portability,which can meet the field measurement requirements of many changes and can measure the smaller and better hidden position.such as complex workpiece surfaces,workpiece inner cavity surfaces,deep holes,etc.At present,the foreign light-pen three-coordinate measurement technology is very mature and has been put into market production,but the domestic is still in the research stage,and accuracy of measurement is not as high as that of foreign mature products.In order to study the measurement accuracy of the light-pen three-coordinate measurement system,this paper established a set of light-pen three-coordinate measurement system and designed an object image matching algorithm for the feature point distribution of the light pen.Through 5 light pens with the same number and distribution of feature points,and different dispersion,the relationship between the dispersion of feature points and measurement accuracy was studied.The main work of the thesis is as follows:(1)This paper builds a light-pen three-coordinate measurement system,including a computer,a CCD camera and a light-pen body.The system is based on a CCD camera,and the infrared light-emitting diode on the light-pen body is used as the direct detection target.When measuring,a filter with a wavelength corresponding to the infrared lightemitting diode is placed in front of the lens to filter out visible light.The CCD camera shoots the light-pen to obtain high-quality images,and the captured images are transmitted to the computer,and the three-dimensional coordinates of the light-pen probe are solved through related algorithms.(2)The existing literature shows that when the number of feature points exceeds 8,the improvement rate of measurement accuracy will decrease,and the more the number of feature points,the more complicated the calculation;when the feature point distribution is linear or rectangular,the measurement accuracy will be relatively higher.Based on the above research,this paper proposes a new type of light-pen feature point distribution,the number of feature points is 8,of which 6 feature points are coplanar,the distribution is linear and rectangular,and the other 2 feature points are higher than the other 6 feature points in the z-axis direction,which are used to improve the measurement accuracy in the direction of the camera's optical axis.The influence of the dispersion of characteristic points on the measurement accuracy is analyzed,and based on the new type of characteristic point distribution,five light-pens with different dispersions are designed to study the influence of the dispersion of characteristic points on the measurement accuracy.(3)Based on the new feature point distribution,this paper proposes an object image matching algorithm for feature points.The feature points are numbered,and then the oneto-one correspondence of the object image numbers can be completed quickly and accurately,which effectively guarantees the accuracy of the image coordinates of the feature points and provides accurate input variables for subsequent calculations.(4)The stability of the measurement system is verified by repeating experiments with different distances and different orientations on the built-up light-pen threecoordinate measurement system.The single-point repeatability experiment results show that the measurement system can guarantee the subsequent measurement and comparison experiment measurement results effectiveness.Five light-pens with different characteristic point dispersions are used to measure the width of the same standard cone in the same environment and within the same time period.By comparing the measurement results of 5 light-pens,the influence of characteristic point dispersion on the measurement accuracy of the measurement system is studied.Experimental results show that the dispersion of the characteristic points of the light-pen has an impact on the measurement accuracy,and it is found that when the dispersion of the characteristic points does not exceed a certain range,increasing the dispersion of the characteristic points helps to improve the measurement accuracy.Single-point repeatability experiments and measurement experiments show that the stability and measurement accuracy of the lightpen three-coordinate measurement system built in this paper can be applied to general measurement occasions.