A method for simultaneous laser profilometer and hand-eye calibration in relation to an industrial robot as well as its implementation is presented. In contrast to other methods, the new calibration ...procedure requires the measurement of only one reference geometry to calculate all the transformation parameters. The reference geometry is measured with a laser profilometer from 15 different poses. The intrinsic parameters of the profilometer, as well as the extrinsic (hand-eye) parameters, are then numerically optimized to achieve the minimum deviation between the reference and the measured geometry. The method was characterized with experiments that revealed a standard deviation of the displacements between the reference geometry after the calibration of less than 0.105 mm in the case of using the robot-arm actuator and 0.046 mm in case of using a 5-axis CNC milling machine. The entire procedure, including measurement and calculation, can be completely automated and lasts less than 10 min. This opens up possibilities for regular on-site recalibration of the entire system.
•Monitoring system for height and layer thickness in laser metal deposition.•Simple and flexible integration on generic deposition setups.•Coaxial implementation of the triangulation height ...measurement.•Self-regulating mechanism of the process growth•Non-destructive diagnosis of deposition defects.
Laser metal deposition (LMD) is an additive manufacturing technique, whose performances can be influenced by several factors and parameters. Monitoring their evolution allows for a better comprehension and control of the process, hence enhancing the deposition quality. In particular, the deposition height is an important variable that, if it does not match the process growth, can bring to defects and geometrical inaccuracies in the deposited structures. The current work presents a system based on optical triangulation for the height monitoring, implemented on a LMD setup composed of a fiber laser, a deposition head, and an anthropomorphic robot. Its coaxial and non-intrusive configuration allows for flexibility in the deposition strategy and direction. A measurement laser beam is launched through the powder nozzle and hits the melt pool. A coaxial camera acquires the probe spot, whose position is converted to relative height. The device has been demonstrated for monitoring the deposition of a stainless steel cylinder. The measurements allowed to reconstruct a spatial map of the height variation, highlighting a transient in the deposition growth which can be explained in terms of a self-regulating mechanism for the layer thickness.
While the field of 3D-printing (3DP; formally known as additive manufacturing) has increasingly matured, its use in large-scale applications, e.g., building and infrastructure construction, remains ...limited. Although layer-wise slurry deposition/extrusion (LSD/E) methods are amenable to scale-up and offer versatility in terms of the materials that can be printed (i.e., “inks” that can be used), there is a lack of quantitative metrics to assess the geometrical attributes of printed components vis-à-vis their 3D-CAD (computer-aided design) inputs. To address this limitation, we present an original method to assess the external geometrical attributes of 3D-printed components using laser triangulation-based 3D-scanning. Significantly, a printability index (0 ≤ Ip ≤ 1, unitless) is presented which compares the overall geometric fidelity of the printed specimen to its CAD input. By adjusting the rheology of a model silicate-based slurry, we examine the relationships between slurry rheology, shrinkage and printability. The printability index offers a quantitative basis for assessment and quality control of 3D-printed components, while helping to develop an improved understanding of how slurry behavior, and optimizations therein can maximize printability.
•Laser triangulation sensor (LTS) with improved measurement accuracy via integrating a diffraction grating was proved.•The LTS obtains the measured displacement from several diffraction light spots, ...which offers the advantage of averaging-error effect.•The validity and effectiveness of the developed LTS has been confirmed from both simulation and experimental results.
In this paper, a laser triangulation sensor (LTS) with improved measurement accuracy via integrating a diffraction grating was proved. Compared to conventional LTS that only has the information of one light spot, the diffraction grating generates several diffraction light spots on CMOS image sensor. This enables to obtain multiple results of the object displacement simultaneously during one sampling period. Thus, it is achievable to obtain a higher measurement accuracy by averaging operation, due to the averaging-error effect. The operating principle of the proposed method is explained in detail, and a prototype LTS is developed. Contrastive experiments are performed to evaluate the nonlinearity and repeatability of the developed LTS, which are generally combined to present the measurement accuracy of LTS. In the full-scale measurement range of 20 mm (F.S. = 20 mm), the results show that the measurement nonlinearity and repeatability of the developed LTS with diffraction grating are 0.113% of F.S. and 0.89 μm respectively, which are significantly improved compared to that without diffraction grating.
Most of low cost 3D scanning devices that are nowadays available on the market are sold without a user calibration procedure to correct measurement errors related to changes in environmental ...conditions. In addition, there is no specific international standard defining a procedure to check the performance of a 3D scanner along time. This paper aims at detailing a thorough methodology to calibrate a 3D scanner and assess its measurement uncertainty. The proposed procedure is based on the use of a reference ball plate and applied to a triangulation laser scanner. Experimental results show that the metrological performance of the instrument can be greatly improved by the application of the calibration procedure that corrects systematic errors and reduces the device's measurement uncertainty.
•Most of low cost 3D scanning devices are sold without a user calibration procedure.•No standard procedures exist for checking the performance of a 3D scanner along time.•A method to calibrate a 3D scanner and assess its measurement uncertainty is defined.•The procedure uses a reference ball plate and is applied to a laser scanner.•Experimental results show that metrological performances of the scanner are improved.
•An on-machine measuring method is proposed for inner dimension inspection.•The proposed method is based on incoherent information fusion (IIF).•A measuring head is developed based on IIF by using ...double synergetic lasers.•Proposed method needs no discrete angular component and simplifies measurement setup.•The final measuring accuracy has nothing to do with the performance of machine tools.
Rapid and automatic measurement of inner dimensions has taken its place in the field of precision measurement. On-machine measurement has the significant advantage of integration of processing and measurement, which can greatly improve processing efficiency and reduce costs. However, the measuring accuracy of existing on-machine measuring methods is easily affected by the intrinsic accuracy of machining or auxiliary equipment. As a consequence, these measuring methods cannot meet the demands of precision measurement. In this paper, an on-machine measuring approach based on incoherent information fusion is proposed to measure inner dimensions by using double synergetic lasers (DSLs). DSLs and the spindle of machine tools are taken as the measuring source and rotary power source respectively. Once the spindle rotates continuously, then a set of incoherent information pairs (IIPs) acquired by DSLs represent the whole feature of measured inner section. The IIPs can be correlated and utilized on the principle of the invariance of measured section. In practical measurement, neither specific measuring position as geometric center nor auxiliary equipment as angle encoder is necessary, and the final measuring accuracy is independent of the influence of machine tools. Inner diameter and roundness measurements are taken as examples to showcase the effectiveness of the proposed approach.
Complex surface plays a vital role in the aeronautical industries for its preferable mechanical properties. However, machining such complexity is challenging without post-process inspection. ...Compensation derived from measurement is essential to ensure final form accuracy. The process efficiency can be improved significantly with real-time on-machine measurement. The laser triangulation technology is an excellent fit for such applications, because of its micrometric accuracy with a large measuring range and non-contact nature. In this paper, the recent research progress of laser triangulation on-machine measurement (LTOMM) has been reviewed. The measuring technique, error compensation, path optimization, and application of LTOMM are reviewed. More specifically, the possible errors in laser triangulation are reviewed and comprehensively analyzed based on the recent research published. The measurement path planning and optimization strategies are surveyed. An application is presented to illustrate the effectiveness and efficiency of LTOMM in propeller or turbine blade fabrication. Finally, the challenges, development trends and perspectives of laser triangulation on-machine measurement are discussed.
A non-contact optical inspection method for detecting voids in translucent composites is presented. Structured laser light is used to illuminate the inspected part. As the light penetrates the ...matrix, it scatters and is reflected from internal structures, rendering them perceptible in close proximity of the laser illumination. A systematic image acquisition and scanning approach is employed along with image processing to reconstruct and visually represent the internal composition of the inspected part. Experiments involving translucent epoxy and polyester based composites demonstrate capability to detect voids with depths reaching up to 5 mm. The detection depth is predominantly influenced by the light transmittance properties of the matrix, as well as the density and quantity of fiber layers. The arrangement of the camera and laser on the same side of the inspected part facilitates the examination of parts with varying thicknesses. The presented method is intended for automated inspection in mass production by leveraging its non-contact characteristics and high operational velocity.
•Voids are visible in close proximity to structured light illumination.•Void detection up to a depth of 5 mm, influenced by resin transparency and fiber density.•Independence of variations in part thickness.•Enables high-speed automated inspection in mass production.
The paper presents the automated on-line system for wood logs 3D geometry scanning. The system consists of 6 laser triangulation scanners and is able to scan full wood logs which can have the ...diameter ranging from 250 mm to 500 mm and the length up to 4000 mm. The system was developed as a part of the BIOSTRATEG project aiming to optimize the cutting of logs in the process of wood planks manufacturing by intelligent positioning in sawmill operation. This paper illustrates the detailed description of scanner construction, full measurement process, system calibration and data processing schemes. The full 3D surface geometry of products and their applied portion of selected wood logs formed after cutting out the cant is also demonstrated.
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