Nowadays, 3D geometric dimensional measurements of step height are performed on many types of samples using different instruments, such as AFM, optical microscopy, et.al. For step height measurements generally, the traceability of the z-axis is very importance. In this paper, displacement metrology in the vertical direction or z-axis is first determined, thus having a known and specific relationship between the physical edge on the sample and the location of the detected edge in the image. By consider of the location of the step, a step height is calculated by requirement of fitting to upper and lower surfaces. An algorithm is introduced to fit the upper and lower terraces. Then, we locate the edge and determine the step height by the data extrapolation of those fits. In order to reduce the uncertainty budget for step height measurements, 50nm, 100nm, 200nm, 500nm and 1000nm step height are respectively tested, and dominant sources are also discussed.
Laser interference system has been extensively applied in high-precision geometric metrology benefit from the advantages of high accuracy, high resolution and stability in linear displacement measurement. In this paper, we present a novel and compact mechanical structure to realize the conversion between angular and linear displacement, so that the slight angular displacement can be enlarged and obtained by using the characteristics of high-precision linear displacement measurement of laser interference system. A series of experiments are carried out on this device, the conversion ratio of angular and linear displacement we achieved is 5.76 arcsec/ μm, which is determined by the transmission ratio of the worm gear pair and the pitch of the ball screw. By comparing the measured angular values with 23 reference values distributed on the whole circumference, the maximum original error of angular displacement measurement in this system without correction or compensation is ± 25 arcsec and the resolution is 0.6 arcsec.
The characteristics of turbidity in the watershed of Chongqing City’s water supply system in interconnected reservoir basins between JiaLingJiang River and Chang Jiang River are investigated and analyzed by dynamic light scattering method (DLS). Three months of continuous turbidity measurements in seven sampling sites along the JiaLingJiang River were respectively performed from March to May in 2018. The experiment results demonstrated that the particles with highly similar light-scattering features are the main contribution to turbidity in the JiaLingJiang River. The analysis of turbidity time series showed that the particle populations from water sources impacts in downstream waters and the influence of urban wastewater pollution and wet weather pollutant was not obvious in those months. On the other hand, the relative errors of turbidity measurement results were always less than 3% with national turbidity standard.
A CMM with multiple probing systems have the power to deliver tremendous benefits to most notably manufacturing, and have the advantage of high automation, high integration and high precision. These probing system combinations must be tested to check their compliance with the specifications and to trace back the measurement results. In this paper, we present a novel multi-ring artifact and appropriate test procedures for probing system combinations similar to the well-known test procedures described in the ISO standard 10360-9. The characteristic of multi-rings artifact is keeping topology geometric relationships among 2D rings. Then, a series of representative experiments were carried out on a commercial combined probing system equipped with an imaging probe and a line laser scanner, and results have proved such multi-ring artifact as a fast way for performance test.
This article presents a novel multi-layer artifact for systematic error correction of a gap measuring system, consisting a 3D laser scanner and motorized linear stages. This artifact representation of five-layers gap shape with continuous free-form surface was designed, which include diverse form dimensions. Then, in order to improve the measurement accuracy of the range dimension of the gaps, a one-step calibration procedure based on an experimental process has been developed. The influence of the three parameters on width error, depth error and flush error, defining the relative position and the orientation between the scanner and the range gaps, is respectively considered. The results obtained in accuracy and repeatability tests performed on this multi-layer artifact primitives attest to the viability of this correction method for gap measuring system.
In industrial manufacturing processes, the dimensional inspection of the gaps on the free-form shape parts is critical and challenging, and is directly associated with subsequent assembly and terminal product quality. In this paper, a fast measuring method for automated gap inspection based on laser scanning technologies is presented. The proposed measuring method consists of three steps: firstly, the relative position is determined according to the geometric feature of measuring gap, which considers constraints existing in a laser scanning operation. Secondly, in order to acquire a complete gap profile, a fast and effective scanning path is designed. Finally, the range dimension of the gaps on the free-form shape parts including width, depth and flush, correspondingly, is described in a virtual environment. In the future, an appliance machine based on the proposed method will be developed for the on-line dimensional inspection of gaps on the automobile or aerospace production line.
Non-contact measurement techniques using laser scanning have the power to deliver tremendous benefits to most notably manufacturing, and have the advantage of high speed and high detail output. However, a major obstacle to their widespread adoption in more complex on-line producing environments is their geometric constraints and low accuracy compared to the contact-based counterparts. The work presented in this paper introduces a performance evaluation test of laser line scanning for in-process inspection of 3D geometries. Some straightforward test methods that use a designed artifact are proposed. First, one work aims to experimentally investigate the location accuracy of knee point or corner point of edge features using a commercial laser stripe scanner, which is common in mechanical parts. Another work experimentally investigates the formation of outliers that may be usually promoted by reflective surfaces around surrounding area of corner point, and these outliers are characterized with large measurement errors, which significantly deteriorate the quality of the scanned point cloud data. Scanning path planning and outlier filter design are respectively discussed.