Papers by Keyword: Fringe Projection

Abstract: According to the current state of the art, wear conditions of forging dies are assessed visually in the dismantled state, as there is no measuring procedure available for inline wear measurement of hot forging dies. This paper introduces a handling concept for automated loading and in-situ tool inspection for a hot forging process. Based on an industrial robot and quickchange systems, the process integration of hightemperature grippers and an endoscopic 3D-measurement sensor for the in-situ inspection of hot forging dies is carried out. By adapting the measuring method of fringe projection to an endoscopic design, the measuring system can be navigated into the difficult-to-access geometry of the die and take high-precision 3D-measurements inside. The ambient air heated by the forming process creates an inhomogeneous refractive index field around the measuring system and the hot die, so that the straight beam path required for optical measuring systems cannot be ensured. This can lead to strong deviations in the reconstructed point clouds and the functional geometries derived from them. By means of a compressed air actuator, the measuring system can be protected from the hot tool and dirt as well as the effect of inhomogeneous refractive index can be reduced. With this approach the in-situ wear measurement at highly stressed regions using the example of the mandrel radius and the flash radius will be demonstrated. These functional elements are of particular relevance, as the thermalstress is high and large material flow takes place. For the wear measurement, the functional elements of the tool are examined in detail by fitting geometrical features into the reconstructed point clouds and determining the deviations from a reference geometry. In addition, the measurement data is validated with the aid of a commercially available state-of-the-art measurement system.

Abstract: The technology of sheet-bulk metal forming enables the production of complex workpieces with filigree surface structures in only a few forming steps. In order to provide a rapid and production-related workpiece inspection of not only large workpiece features, but also small features in an appropriate quality, a multi-sensor optical measurement system with different resolutions is required. Workpiece features of medium size can be measured by two types of fringe projection sensors. With a structured approach according to Six Sigma, which is based on the five phases design, measure, analyze, improve and control complex tasks are divided into smaller individual problems. In each phase the Six Sigma method recommends tools for solving the individual problems effectively. With the support of the Six Sigma guideline an exemplary sheet-bulk metal forming workpiece feature is used in order to qualify the two measuring systems for a production-related measurement. After defining the explicit goal for the investigations, a detailed analysis of the measurement process leads to a couple of relevant influences. These are input factors for the design of experiments. By a full factorial design, not only an influence of a factor itself, also the interactions between multiple factors can be detected. In the analyze-phase, these results are calculated by different statistical methods. To present the results in a comprehensible way several types of diagrams are used. The shown approach gives an example for a traceable and methodical way to qualify a measurement system for challenging measurement tasks.

Abstract: A three-dimensional surface measurement using fringe projection technique has received attention among the researches for the last few decades.However choosing the best method is the challenge because one needs to consider the cost, measurement speed, system complexity, measurement accuracy and data reliability to ensure the success of the measurement. This paper focused on the successful manipulation of non-collimated light source and three step phase shifting for height measurement of a lead frame.The measurement done based on pixel determination from the saw tooth image. In addition, the scaling factor technique has been employed for the measurement accuracy. The experimental results achieved a high precision of measurement with simple system and high speed capability.

Abstract: We present some new idea to implement shadow modeling which is an important process for simulation of fringe projection system: The dot product between normal vector of object’s surface and vector that connecting projector lens centre and point on object’s surface, and the dot product between normal vector of object’s surface and vector that connecting camera lens centre and point on object’s surface are used to model the shadow on object’s surface. Our algorithm do not need to implement the calculation of the silhouettes of the occluders. Simulation result validates that the accuracy of our shadow modeling algorithm is same as shadow volumes algorithm, but our algorithm runs faster than shadow volumes algorithm.

Abstract: The paper deals with utilization of active triangulation method for shape investigation of cutting inserts after wear. For measuring of cutting insert shape a method using the structured light (fringe projection) was used. As a measuring device the optical 3D scanner GOM ATOS II TripleScan SO was used. Cutting inserts with different shapes was measured. With the measurement method mentioned in the paper the accurate shape of the cutting insert can be captured. From the 3D model moreover it is possible to measure the geometrical properties as well as tool wear, plastical deformation, build-up-edge, corner damage and chipping of cutting insert.

Abstract: This article proposed a way to reduce the error in the measurement of object morphology that based on the phase measurement profilometry with Optical Fiber Projection Grating. Some simulation of the actual light intensity distribution need to do first to get the error that caused by the aperiodic fringes, express the errors by phase. After that, compensate for this error based on the actual measurement results. There is a larger improvement in the accuracy of the recovery after the process proposed in this article than before through the simulation. The experiment verifies the correctness of this method through the measurement of given standard parts.

Abstract: We present a new method to define the reliability of pixel and path of phase unwrapping. The reliability function is calculated based on modulation, second difference of wrapped phase, and second differnce of modulation, and then we present the concept of smoothness of path, the reliability of path is calculated based on reliability of pixel and smoothness of path. Experiment results validate the correctness of our proposed algorithm.

Abstract: The implementation of selected full-field optical methods for monitoring and measurements of displacements, strains and shape of structures in power plants are reported. Digital Image Correlation, Fringe Projection and integrated thermovision-DIC method have been utilized for monitoring and control of repair processes of selected elements during general overhauls in power plants, including control of welds annealing process in boiler drum and steam pipes and measurements of geometry changes of steam pipes in “hot” and “cold” states. The experience gathered during the measurement sessions in power plants has been used for enhancement and adaptation of typical architecture of measurement systems to demanding and difficult industrial environment conditions. The measurements had been carried out in different power plants located in Poland. The possible future application of full-field optical measurement methods as the alternative to standard techniques (ultrasound, X-ray, strain gauges) and their advantages and disadvantages are discussed.

Abstract: Optical measurement has been widely used in many fields of science and engineering, such as CAD/CAM, machine vision, quality inspection, reverse engineering, etc, due to its properties of non-contact and high speed. Fringe projection methods have caused much more attentions in full field measurement and insensitive to the change of the objects’ reflectivity. This paper reviews state-of-the art progresses in the 3D shape measuring methods using fringe projection techniques. A comparison of the existing methods is performed with their advantages and drawbacks also are pointed out.

Abstract: Sheet bulk metal forming is a new forming technology, currently developed by several companies and research institutes. It creates high demands on the inspection of parts and tools, especially in the field of in-situ abrasion detection of the forming tool and its impacts on the work piece. This manuscript introduces two optical testing methods for fulfilling these inspection tasks: On the one hand the endoscopic fringe projection as a flexible small scale optical measurement principal with high depth of focus and accuracy for the acquisition of filigree form elements for a continuous abrasion determination and one the other hand the multi-scaled fringe projection for a holistic one shot measurement of the work piece for an adapted, multiscale deviation analysis. The development and advantages of both systems for the sheet bulk metal forming process are shown as well as potentials of the combination of the both systems close to the proposed application next to the production line.