Spur Gear Profile Measurement Based On Structured Light System

Based on light and electricity physical phenomena, structured light vision technologyobtain and process the image of the structured light on the measured object to reconstruct thethree-dimensional geometry. It can be mainly used for the measurements of complex surfaceor freedom three-dimensional surface. The structured light vision technology is used inmechanical industry, which has the outstanding advantages of non-contact, high speed, highdegree of automation. Thus, more and more people pay attention to the use of structuredlight vision technology in the machinery industry.Gear is an important part of the transmission. The application of spur gear is particularlywidespread. With the increasingly high quality requirements of the gear, measuring gear isalso stricter. The development of measurement precision has an influence on theimprovement of manufacturing technology. As a result, the research of more advanced gearmeasuring technology has a very important role on the overall improvement of the gearmanufacturing technology.When there is a large gear profile error, the work profile is not the correct tooth profile.The trajectory of the engagement point theoretically no longer meets the basic laws of gear,resulting the occurrence of the change of instantaneous transmission ratio. It will have animpact on the stability of gear transmission job. Therefore, the measurement of the geartooth error is particularly important in measuring the parameters of the gear. This paperestablishes structured light vision measurement system with CCD camera, optical lenses,semiconductor lasers and computers. Based on the geometric characteristics of the spur gear,a measurement method of gear profile error based on structured light vision technology ispresented.Firstly, this paper analyzes the model of structure light vision, which is divided into twoparts: For the imaging model of the CCD camera, based on the assumption of pinhole imaging principle, a non-linear relationship of the coordinate transformation is established.Using the classic two-step calibration method, the parameters in the model is calculated; Forthe parameter model of structured light plane, based on the analysis of the traditionalcalibration method, an improved calibration method based on global parameter is proposed.The parameters variables of the system are optimized. The calibration accuracy of thestructure light system is effectively improved. At last, the experiments of calibratingstructured light system showed that the best calibration results can be got by6images ofcoplanar target and the stripe width of5pixel.Secondly, according to the geometric characteristics of the measured spur gear, a toothprofile measurement model is established. As the structured light measurement plane is notperpendicular to the rotation axis of the measured gear, a pseudo structured light plane basedon the rotation axis is established. The target point which is reconstructed by the structuredlight vision imaging system will project onto the pseudo structured light plane. Ten, aninvolute is formed on the direction of the rotation axis. To simplify the calculation of profileerror, this paper establishes a local coordinate system on the pseudo structured light plane,the three-dimensional coordinates of the measured points are transformed to thetwo-dimensional coordinate plane. In this two-dimensional coordinate system, according tocoordinate method, the radius of the base circle and profile errors is calculated.To improve resolution of structure light vision system, obtaining a sub-pixel position ofthe light center from the image is essential. This paper analyses several of sub-pixeldetection method of the light center. Based on the classical detection method proposed bySteger, the optimal choose of each parameter is discussed. For the lack of traditionalevaluation methods, this paper presents an accuracy evaluation method based on the blocksize, taking actual measurement error as criterion of accuracy evaluation, which conforms torequirements of actual measurement.Finally, the experiments verify the accuracy of the proposed measurement method basedon structured light vision. Experiments were divided into two parts: measurements of thebase circle and measurement of profile error. Experimental results show that the installationlocation of the structured light vision measurement system platform, the number of gear teeth and the angle between the plane of structured light and the cross-section plane of gearhave no significant effect on the measurement accuracy. The greater the gear modulus is, thehigher the accuracy of the measurement method is.The work and research in this article has certain significance for applying structuredlight vision measurement technology in engineering.