Method And Device Of Screw Pitch Error Detection Based On Machine Vision

As a kind of work-piece which can realize the functions of transmission,positioning and measurement,lead screw occupies an important position in the mechanical industry chain.Pitch as an important index to measure the quality and accuracy of the lead screw,the processing quality will directly affect or even determine the accuracy of the lead screw.Therefore,detection of the screw pitch error is particularly important.With the increasing maturity of machine vision technology,use of image processing technology to detect screw pitch error has the advantages of low cost,high accuracy,non-contact and so on,which lays the foundation for the realization of automatic detection.At present,the domestic visual device for detecting pitch error of lead screw can only detect the specific specification of lead screw,which has poor universality,and the complicated data processing algorithm can not be applied to industrial production.The establishment of a widely applicable,convenient and efficient detection device for screw pitch error is of great significance to the intelligent unattended detection.The device combined the advantages of optical system and image processing technology to collect and process screw images in real time,and displayed pitch values and the corresponding error curve in real time on the visualization platform based on Lab VIEW.The experimental results showed that the device can detect pitch errors of various specifications of lead screw.The main research contents are as follows:(1)According to the detection task and precision requirements of the detection system,the hardware equipment,detection method and construction scheme matching the design requirements of the device were discussed and selected.In order to optimize the mechanical structure,a dual-track synchronous structure was proposed to drive the industrial camera(dual telecentric lens)and parallel light source.Backlight illumination was used to design the comparison experiment of light path and build the universal light path platform to solve the problem of screw image projection distortion.(2)Expand the range of the target image by image mosaic technology to obtain the complete pitch.Considering the factors such as stitching accuracy,precision and efficiency,an automatic stitching algorithm for large surface lead screw with repeated characteristics was proposed.The coarse registration points were solved by the phase correlation algorithm,and the sub-pixel registration points were located by the single-step discrete Fourier transform of matrix multiplication in the 1.5×1.5(pixel)neighborhood of the coarse registration points.According to the mapping relationship of the registration points,the projection transformation model between the images to be stitched was constructed,and the new coordinate system of the stitched images was established to complete the image stitching.(3)In order to accurately locate the edge of the lead screw,a subpixel edge location method based on morphology and fitting technology was proposed by improving the traditional algorithm to solve the problem of "blurring" at the edge of the lead screw caused by the reflection of the lead screw material.Morphological edge extraction method was used to locate the whole pixel lead screw edge,and image segmentation technology was used to extract the target image,refine the edge to a single pixel,and fitting technology was used to subdivide the edge pixel to achieve the purpose of sub-pixel location.(4)Develop automatic detection software for screw pitch error based on Lab VIEW.Including the login interface ?,camera configuration sub-VI,based on the embedded VISA design module to write automatic control driving platform and camera acquisition frequency sub-VI,image processing sub-VI,and according to the lead screw pitch calculation equation using the MATLAB interface to establish the error curve equation.(5)To verify the feasibility of the designed detection device,7 samples including ball screw samples and trapezoidal lead screw samples were taken as verification,and the device was used to complete the field detection of the sample pitch error in Jining Bote Precision Industry Company.The results show that the repeatability error of single pitch is stable within 7 ?m,and the relative error range is 0.0001%?0.0418%compared with that of standard instrument JCS-040A.The reliability of the device is verified,and it has industrial practical value.