Dimensional Inspection System Research Articles

Calibrating a profile measurement system for dimensional inspection in rail rolling mills

Modern, high-speed, railway transportation requires rails to conform strictly to requirements specified in various standards. One key requirement is the conformance of the dimensions of the rail cross section to those of the corresponding rail model, within tight tolerances. This paper deals with a system for dimensional quality inspection during the manufacture of railway rails. Optical triangulation is used to build a profile from laser lines projected on the rails from four different locations. Then, the profile is compared to that of the corresponding rail model. The differences between certain numerical values (the dimensions) for the profile and the model are compared to standard tolerances for each dimension in order to detect dimensional defects. As a prerequisite for this, the cameras used to capture the laser lines must be calibrated. Standard calibration plates are unsuitable for sheet-of-light calibration in a production environment, as determining the location of the laser emitters relative to the plates would be an issue. For this reason, a cylinder-based calibration target is used instead. Different calibration algorithms are discussed and compared to said standard calibration. The results of accuracy and repeatability tests in the production environment are also shown. The accuracy of the system is found to be appropriate for the purpose of quality inspection under the requirements of applicable rail standards.

Decision Support System for Dimensional Inspection of Extruded Rubber Profiles

Since small and medium enterprises (SME) generate the most of gross domestic product and employment opportunities in developed countries, further progress of the Industry 4.0 strongly relies on the development of dedicated solutions for SMEs-specific problems. Dimensional inspection of extruded rubber profiles represents one such an open issue in the automotive industry, which currently requires a manual measurement and comparison of profiles' cross section with the corresponding technical drawings. Starting from the requirements acquired from the industry practice, this study proposes a novel solution that automates all steps during the inspection process allowing an operator to make the final decision with respect to his observations. The proposed workflow includes the following steps: 1) image acquisition, 2) system calibration, 3) profile segmentation, 4) landmark registration and 5) augmentation of the referent technical drawing over the acquired image. The overall solution was developed by using a single camera and dedicated algorithms for profile detection and augmentation of the referent technical drawing. The extensive validation showed that the solution increased operators' productivity and reliability by a considerable margin (~6%), while it remains affordable, user-friendly and generic.

Development of Telecentric Objectives for Dimensional Inspection Systems

Features of designing objectives telecentric in the object space are discussed. The optical layout of three telecentric objectives developed for dimensional inspection systems using the shadow projection method is presented. A method for monitoring the quality of manufacture of such objectives having small distortion (less than 0.02 %) and small non-telecentricity (less than 0.01°) is described. Comparison of experimentally obtained optical characteristics of two objectives manufactured by us and one objective manufactured by the Thorlabs company (U.S.) is carried out.

3D Optical Measuring and Laser Technologies for Science and Industry

Modern industry and science take novel 3D optical measuring systems and laser technologies with high resolution. For solving their actual problems we have developed the family of the optical measuring systems and technologies. Peculiarities of 3D image formation under partially coherent illumination using constructive calculation method are given. The optical methods and system for 3D dimensional inspection of ceramic parts are presented. The performances of 3D super resolution optical low-coherent micro-/nanoprofilometer are given. Using atomic perfectly-smooth mirror as a reference object, the breakthrough in-depth measurement with 20 picometers was achieved. The newest results in the field of laser technologies for high-precision synthesis of microstructures by updated image generator using the semiconductor laser are presented. The measuring systems and the laser image generator have been tested by the customers and are used in different branches of industry and science.

Moving towards in-line metrology: evaluation of a Laser Radar system for in-line dimensional inspection for automotive assembly systems

The increasing interest towards intelligent systems has led to a demand for the development of zero-defect strategies, with a paradigm shift from off-line and dedicated to in-line metrology with integrated robotic systems. However, a major barrier preventing the systematic uptake of in-line metrology is the lack of evaluation of system capability in terms of accuracy, repeatability and measurement time, when compared to the well-established coordinate measuring machine (CMM). In this study, a robotic Laser Radar (LR) solution is assessed in the context of automotive dimensional inspection of Body-In-White (BIW) applications. The objective is both to understand the effect of robot re-positioning error on measurement accuracy and repeatability and to compare measurement results against a CMM. Eighty-one surface points, six edge points, twenty-five holes and sixteen slots were selected from an industry standard measurement plan. Whilst LR exhibits a lower measurement accuracy than twin-column CMM, its repeatability is well within the specification limits for body shell quality inspection. Therefore, as a real-time in-line metrology tool, it is a genuine prospect to exploit. This research makes a significant contribution toward in-line metrology for dimensional inspection, for automotive application, for rapid detection and for correction of assembly defects in real time, with subsequent reduction of scrap and number of repairs/re-works.

A three-dimensional inspection system for high temperature steel product surface sample height using stereo vision and blue encoded patterns

Vision-based surface inspection system is extremely important research hotspot in the field of steel surface defect inspection. However, most of the vision-based surface inspection systems focus on the two-dimensional image processing, three-dimensional height information acquisition is still a major challenge, especially for high temperature steel product. To achieve the surface sample height information of high temperature steel product sample, a three dimensional inspection system for static object is designed in this paper. In this system, physical filter and digital filter methods are combined to obtain the images of steel product. The stereo rectification and column encoded patterns are employed to achieve the surface sample height information. Furthermore, the graphics processing unit (GPU) is used to improve the computation speed. Seven steel product surface samples are picked to verify the effectiveness of the proposed method. The actual experimental results of the proposed method are very close to the true height, that is, the smallest error is less than 1mm and the average error is less than 2mm.

Errors in non-contact sensor measurements due to misalignment and scanning methodology

Non-contact sensors are becoming an increasingly popular tool for use in dimensional measurement, inspection and quality control. However, there exist a number of challenges associated with the use of these non-contact sensors in dimensional inspection systems. One important challenge is to understand the associated measurement errors and determine the objective accuracy of such an inspection system. This paper examines the effect of misalignment and scanning methodology on the measurement accuracy of a non-contact dimensional inspection system. It is important to understand this topic since the majority of optical sensor manufacturers do not supply information about the alignment between the optical line of sight and the mechanical interface of the sensor or measurement system. We prove the evidence of this measurement error through both experimental results and simulation. Finally, by using a constant standoff measurement method we succeeded to show that the majority of inherent misalignment error can be eliminated.

An improved 3D imaging system for dimensional quality inspection of rolled products in the metal industry

Measurement, inspection and quality control in industry have benefited from 3D techniques for imaging and visualization in recent years. The development of machine vision devices at decreased costs, as well as their miniaturization and integration in industrial processes, have accelerated the use of 3D imaging systems in industry. In this paper we describe how to improve the performance of a 3D imaging system for inline dimensional quality inspection of long, flat-rolled metal products manufactured in rolling mills we designed and developed in previous works. Two dimensional characteristics of rolled products are measured by the system: width and flatness. The system is based on active triangulation using a single-line pattern projected onto the surface of the product under inspection for range image acquisition. Taking the system calibration into account the range images are transformed into a calibrated point cloud representing the 3D surface reconstruction of the product. Two approaches to improve the line detection and extraction method used in the original system are discussed, one intended for high-speed processing with lower accuracy, and the other providing high accuracy while incurring higher computational time expenses. A mechanism to remove, or at least reduce, the effects of product movements while manufacturing, such as bouncing and flapping, is also proposed to improve the performance of the system.

Planar Contour Primitive Recognition of Thin Sheet Part Dimensional Inspection System

According to the two indices of inspection accuracy and inspection speed, a planar contour primitive recognition method of thin sheet part dimensional inspection system based on curvature and HOUGH transform is proposed. A contour point classification algorithm based on neighborhood values is developed, and a curvature threshold method is selected to filter the contour points, and a projection height method is selected to distinguish the property of the primitive and classify the contour points, and the straight line primitive and arc primitive segmentation and merging algorithms are constructed respectively by HOUGH transform. The inspection accuracy and inspection speed of the proposed method are compared and analyzed by contrast experiments between the proposed method and four dominant point detection methods such as Chung & Tsai method and so on. The dominant point detection ability of the proposed method is tested by a simulation planar contour which includes all kinds of dominant points. The experimental results indicate that the proposed method can recognize primitives exactly, the inspection speed is fast and the universality is good.

Research on Dimensional Inspection System of Thin Sheet Part Based on Machine Vision

Key technologies of dimensional inspection system of thin sheet part based on machine vision are investigated, and an entire machine vision inspection system is developed. A cad information-based line scanning step adaptive optimization method used for image grabbing of inspected part is proposed. A rectangle lens subpixel edge detection method based on cubic spline interpolation used for edge detection is advanced. A planar contour primitive recognition method based on curvature and HOUGH transform used for image recognition is raised. The inspection accuracy of the inspection system can reach to 1μm, and the inspection time can satisfy the requirements of on-line real-time inspection, so the inspection system is feasible.

Automatic High-Speed Optoelectronic System for Dimensional Inspection of Distant Articles in Industry and Transport

Advanced automated optoelectronic system for contact wire wear inspection on the go using a structured light method is presented. The algorithm of the video stream analysis and approaches to its implementation using high-performance electronic equipment are given. The automated system described has allowed measuring wear parameters with 10 mm interval at the inspection wagon velocity of 60 km per hour. The root-mean-square error for the measurements of the remaining height and contact plot constitutes 0.15 and 1.5 mm2 correspondently that allows one to make a considered decision about changing a worn section of a contact wire network. The system also can be utilized to inspect public transportation network and to measure the geometric parameters of cables and tubes being fabricated with rolling technique.

Develop a Non-contact Automated Dimensional Inspection System for Automotive Manufacturing Industry

Develop a Non-contact Automated Dimensional Inspection System for Automotive Manufacturing Industry

Air gauges as a part of the dimensional inspection systems

Air gauges for dimensional measurement are known for decades. They have been applied in many technological processes, especially in the systems of in-process control. The air gauges are connected with pneumatic measuring devices able to generate control signals. Nowadays, however, it is not enough to just indicate dimensional bounds of tolerance. The Quality Management Systems require recorded and processed data achieved during the measurement. Investigations led to the development of air gauges integrated with piezoresistive pressure transducers. In those systems the results of measurement are achieved in digital form, they are processed and recorded. Additionally, dynamical properties of integrated air gauges appear much better. Multipoint linearization of the air gauge appears to be advantageous, though some companies offer the adjustment using one setting master only.

Dynamic Error Characterization for Non-Contact Dimensional Inspection Systems

High-precision non-contact dimensional inspection systems typically utilize high-precision motion stages to manipulate the sensor. Such motion stages are susceptible to position errors, which need to be characterized. While geometric and thermal errors can be characterized and compensated, compensation of dynamic errors is a challenging task. This paper presents a method for dynamic error characterization that is significantly different from dynamic error characterization on contact-based systems. A mathematical model to translate the vibrations on the sensor to the measurement errors on the part is presented. Through experiments on a four-axis system, a relationship between sensor motion speed, sampling frequency, and measurement accuracy is derived. The results of the experiments are used to describe the selection of optimal operating parameters for best accuracy and least uncertainty.

Develop a Non-contact Automated Dimensional Inspection System for Automotive Manufacturing Industry

Recently, a variety of 3D sensors have been developed for rapid freeform surface measurement. However, an automated dimensional inspection system is required by automotive industry to bring this state-of-the-art technology into applications. This paper introduces a robot-integrated area sensing system that is developed to meet this industrial requirement. The dimensional inspection system includes a sensor planner, an error map generator, and a sensor affixed to a robot. The sensor planner is adapted to automatically generate robot path based on the CAD model of a workpiece. The path data is indicative for moving the sensor in relation to the surface of the workpiece. Based on the measured point clouds, the sensor planner is able to further modify the path data for the area sensor to improve the measurement performance. The error map generator is adapted to calculate the deviation of 3D shapes between measurement point clouds and the CAD information. Keywords: Automated dimensional measurement, robot sensor planning, quality control

A Feedback Design to a CAD-Guided Area Sensor Planning System for Automated 3D Shape Inspection

A feedback-based area sensor planning system is introduced in this paper. This system is developed for automated 3D shape inspection. A CAD-guided area sensor planning system had been developed previously. However, physical properties of a part surface are usually difficult be modeled for an area sensor. Shadows, reflections, and image quality are three problems related to surface measurement quality, which cannot be predicted from a CAD model. Feedback from a measured 3D point cloud can be used for dealing with those problems by adding more viewpoints in iterations. In feedback mode, the inspection system generates viewpoints according to point clouds measured in each step. The loop stops when the obtained point clouds satisfy the measurement quality requirements. In this paper, a general framework of such area sensor planning system is introduced. The developed feedback system has been implemented for a robot-aided dimensional inspection system.

3D optical measuring technologies for dimensional inspection

The results of the R & D activity of TDI SIE SB RAS in the field of the 3D optical measuring technologies and systems for noncontact 3D optical dimensional inspection applied to atomic and railway industry safety problems are presented. This activity includes investigations of diffraction phenomena on some 3D objects, using the original constructive calculation method, development of hole inspection method on the base of diffractive optical elements. Ensuring the safety of nuclear reactors and running trains as well as their high exploitation reliability takes a noncontact inspection of geometrical parameters of their components. For this tasks we have developed methods and produced the technical vision measuring systems LMM, CONTROL, PROFILE, and technologies for non-contact 3D dimensional inspection of grid spacers and fuel elements for the nuclear reactor VVER-1000 and VVER-440, as well as automatic laser diagnostic system COMPLEX for noncontact inspection of geometrical parameters of running freight car wheel pairs. The performances of these systems and the results of the industrial testing at atomic and railway companies are presented.

Synthesis of the measurement system on the machine tool

The design methodology of a 2½-dimensional measurement and inspection system realized on a machine tool using a touch trigger probe and measuring G codes is studied in this paper. The reliability of measuring results, the agility of measurement, and user friendliness are synthesized in the design process. Algorithms for calibration and compensation of measuring errors are proposed to ensure the measuring accuracy by using a laser interferometer and ring gauges. Classification of probing feedrates and a collision-check algorithm can reduce measuring time and implement stylus-fracture-free measurements. To improve the previous onmachine measurement processes, all functions required for measurement and inspection processes are constructed as measuring G codes with similar forms of machining G codes. The interactive measuring program generating tool, which can automatically generate measuring G codes, is developed and potted in a ROM of a CNC, and can be called to perform an operation by the CNC without interfacing with personal computers. The validity and effectiveness of the developed system are verified on a horizontal machining centre with a Fanuc 15MA.

Metric Exploitation of still Video Imagery

The development of still video CCD cameras with digital image storage has made feasible the concept of offline, single sensor vision metrology. This paper reports on practical evaluations of such a system for dimensional inspection of aircraft tooling and for structural monitoring for large scale engineering. A further application of still video technology for low altitude aerial mapping is also reported. In each case a Kodak DCS200 camera has been employed for the photography in order to take advantage of the relatively high sensor resolution and adequate on‐board image storage capacity. Aspects of the measurement operations, which yielded object space accuracies to 1:80 000 in the industrial measurement projects, are discussed and the results analysed.

Design and Analysis of a Laser Oriented, Automatic Dimensional Inspection System for High-Speed Process Control

Recent advances in the technology of high-speed manufacturing systems have introduced the need for a new approach in the design of process control systems. Computerized process control systems require automatic quality inspection stations which are capable of converting measures of product attributes into electronic information. In this study, a noncontact, electro-optic inspection system was developed which automatically measures product outer dimension at high speeds. Two approaches were taken in the system design. One approach required a photodetector as an analog measuring device, and the other utilized a photodiode matrix as a digital measuring device. The performance capability of each system was in the order of 100% detection of outer dimensions that were 0.01 in. out of specification to 97% for 0.001 in. variations. Both design approaches resulted in fast, accurate, and inexpensive inspection systems which could easily be adapted to most production environments.