Three-dimensional measurement of small inner surface profiles using feature-based 3-D panoramic registration

Automatic Thread Defect Examination System

This article addresses a Thread Hole (TH) examination system capable of automatically examining a TH. We introduce a contact-based examination system with simple hardware. Our examination system examines TH defects by observing the torque generated when tightening the Inspection Device (ID) through the TH. A buffer with springs is utilized to overcome instances where the TH is not accurately aligned with the axis of the ID. The examination system observes the TH size utilizing a camera, then automatically performs an examination utilizing the optimal torque threshold associated with the TH size; in this way, our examination system is able to examine a TH regardless of its size. In this paper, the performance of the proposed system utilizing the optimal torque threshold is verified through experiments.

A New Image Grating Sensor for Linear Displacement Measurement and Its Error Analysis

To improve the accuracy of the current vision-based linear displacement measurement in a large range, a new type of linear displacement sensing system, namely, image grating, is proposed in this paper. The proposed system included a patterned glass plate attached to the moving object and an ultra-low distortion lens for high-accuracy image matching. A DFT local up-sampling phase correlation method was adopted to obtain the sub-pixel translation of the patterns onto the target plate. Multiple sets of stripe patterns with different designs were located on the glass plate to expand the measurement range, based on the principle of phase correlation. In order to improve the measurement accuracy, the main errors of the image grating system were analyzed, and the nonlinear error compensation was completed based on the dynamic calibration of the pixel equivalent. The measurement results, after the error compensation, showed that the total error of the proposed system was less than 2.5 μm in the range of 60 mm, and the repeatability was within 0.16 μm, as quantified by standard deviation.

Algorithm for real-time defect detection of micro pipe inner surface

Quantitative analysis and identification of unknown shaped defects have always been difficult and challenging in the quality control of micro pipes. A series of algorithms for defect detection and feature recognition is presented in this study. A lightweight convolution neural network (LCNN) is introduced to realize defect discrimination. A shallow segmentation network is employed to cooperate with LCNN to obtain pixel-wise crack detection, and a feature recognition algorithm for quantitative measurement is presented. The experimental results show that the proposed algorithms can achieve defect detection with an accuracy of 98.5%, segmentation with mean intersection over union of 0.834, and latency of only 0.2 s. It can be used for online feature recognition and defect detection of the inner surface of a hole.

Panoramic reconstruction of quasi-cylindrical objects with digital holography and a conical mirror

In this work, we present a panoramic digital holographic system for the first time capable of obtaining 3D information of a quasi-cylindrical object by using a conical mirror. The proposed panoramic digital holographic system is able to scan the entire surface of the object to determine the amplitude and phase simultaneously. This paper demonstrates the feasibility of analyzing quasi-cylindrical objects in a short time (0.5 s) with a single camera and a minimum number of optical components. In addition, it can be applied to determine not only topographic measurement of the cylindrical surface but also measurements of radial deformations. Experimental results are presented at different magnifications, thus illustrating its capabilities and versatility.

Adjustable panoramic inspection system for submillimeter fasteners

Fasteners are critical and indispensable locking components in mechanical assembly. Submillimeter fasteners are massively and widely used in electronic devices. This study proposed an adjustable panoramic inspection system for M2 to M0.8 submillimeter fasteners. The system mainly consists of a panoramic imaging module, a back-light module, and an image grabbing and computing module. The panoramic imaging module would form four equal optical path lengths to keep the same imaging amplification between the different directions of the field of view. The back-light module was designed to provide uniform illumination and enhance the contrast of the pitch edge between the fasteners and the background. The image grabbing and computing module with a high-speed camera was designed to be adjustable for different sizes of submillimeter fasteners. The realized system can offer the function of four images in one shot to make a panoramic scene, independent illumination for recognizing, inspect screws from M0.8 to M2.0 screws, and short time consumption of image processing, such as 3.284 ms for M0.8 screws and 2.384 ms for M2.0 screws, to achieve examination of 6000 pieces in 1 min.

Three-dimensional measurement of an inner surface profile using a supercontinuum beam

We demonstrate an inner surface profile measurement that has a smooth spatial distribution. A supercontinuum beam suppresses the speckle contrast to 22% and the standard deviation of the point cloud to 40%, compared to equivalent values obtained by use of a conventional green He-Ne laser at a wavelength of 543.5 nm. A compact probe for the inner surface profile measurements using the supercontinuum beam measures the depth removed by wear of a small hole in an automobile component. The radial spatial resolution was evaluated to be 2 μm, which was of the same order as the wavelength of the supercontinuum beam. The supercontinuum beam enables fivefold improvement of the radial spatial resolution compared to the monochromatic wavelength beam because of a reduction in speckle effects.