Optical Measurement System Research Articles

Optical measurement instrument for detection of powdery mildew and grey mould in protected crops

This study presents an initiative aimed at developing a real-time optical measurement system for non-contact measurement of fungal spores in protected crops such as strawberries, tomatoes and cucumbers. The system is based on a customized microscope. It has been tested in the field under real conditions and image processing algorithms have been developed to identify fungal spores in high resolution microscope images.

Design and Control of a Novel 3-D Piezoelectric Scanning Coaxial Optical Microscope System

This paper presents a novel three-dimensional (3D) optical measurement system combining an optical microscope (OM) and a z-axis piezoelectric scanner. The proposed system includes an advanced controller for the piezoelectric scanner and an algorithm to process OM imaging data. The z-axis piezoelectric scanner uses a back-propagation neural network (BPNN) to control the upward movement of the sample in a step-wise manner. At the point where each step induces a small steady-state error, the OM captures an image in that position. Each 2D OM image undergoes denoising via connected-component labeling (CCL) before being converted into 3D data via image processing. The layered images are then stacked in a 3D arrangement to construct an accurate 3D image of the sample.

Virtual task-specific measurement uncertainty determination for laser scanning

The framework of the Geometrical Product Specification defines the nominal geometry of the components and the characteristic tolerances. Various ISO standards describe the nine defined geometrical properties per characteristic of a workpiece. To prove conformance to the task specific tolerances according ISO 14253–1, the uncertainty budget needs to be determined. This paper presents a digital twin of an optical measurement system as a holistic concept to perform the task specific uncertainty determination. Different measurement strategies are applied to illustrate their effect on the measurement uncertainty of geometrical properties. Not all geometrical properties are relevant for an optical measurement system. Therefore, the discussed properties as a function of the optical measurement strategy in this paper are: size, distance, form and orientation.

A Study of 2D Contour Measurement System at Tool Center Point of Machine Tools

This study proposes a 2D contour measurement system at the tool center point (TCP) that consists of a Blu-ray pickup head and position sensitive detector (PSD). The TCP displacement is equivalent to the relative position between the tool and workpiece. When the machine tools operate the machine part along the desired contour, the TCP displacement affects the machining geometric accuracy. To evaluate the TCP displacement, the contour errors are measured by the cross-grid encoder (KGM) in practice. However, it is difficult to install KGM as it is large and expensive. In this study, an optical measurement system (OMS) is constructed to measure the TCP displacement, named TCP-OMS. A Blu-ray pickup head was installed on the spindle as a tool, and a PSD was installed on the table as a workpiece. To enhance the measurement signal’s resolution and precision of TCP-OMS, the noise was reduced by an AC voltage stabilizer, a DC regulator, and a low-pass filter. The experimental results show that the resolution of displacement measurement was less than 1 μm, and the linearity regions of the X-orientation and Y-orientation were ±3 mm. The motion test on the circular paths were performed on an actual machine tool, and the repeatability tests of this measurement system were verified. The measurement data of circular paths were collected by TCP-OMS and KGM and the results were then compared. When the feed rate of the circular paths increased, the circular deviations were magnified, simultaneously. The axis reversal spikes were observed at the quadrants of a circular path. These measurement results of TCP-OMS matched with the measurement results of KGM. The TCP-OMS developed in this study is characterized by simple installation, compactness, and a low price. It is suitable for 2D contour measurement at the tool center point of machine tools.

METROLOGICAL CHARACTERIZATION OF OPTICAL 3D COORDINATE MEASUREMENT SYSTEMS – COMPARISON OF ALTERNATIVE HARDWARE DESIGNS AS PER ISO 10360

Abstract. This research focuses on the characterization of the metrology of Optical 3D Coordinate Measurement Systems (O3DCMS). The focus is set on the identification and execution of the procedure indicated by the currently active technical standards related to industrial O3DCMS, for their metrological assessment, objective comparison, and performance tracking. This work leads to the implementation of an ad hoc software for the execution of the standard tests by the ISO 10360-13 standard. The implemented software application is employed in a real-case scenario for evaluating the performances of an industrial 3D scanner based on structured light. The specific hardware components to be assessed are two light sources of the active stereoscopic vision system, named Digital Light Projectors (DLP). The case study applies the procedures and metrics indicated by the active standards to objectively compare two alternative hardware design of the system under test. This results in the identification of the most performing hardware configuration, allowing the selection of the best system design, basing on objective metrological parameters.

Physico-mechanical properties of Sapindus mukorossi seed

This work characterized physical and mechanical properties of Sapindus mukorossi seed to explore the mechanical behaviors of the seed during compression in a roll crusher. A new method that combines simulations and calculations with experimental data obtained using a three-dimensional optical measurement system for the measurement of the Poisson ratio and elasticity modulus of the hollow-sphere seed hull was proposed. The modulus of elasticity was derived from a mechanics formulation and verified in a computer simulation based on experimental data. Scanning electron microscopy and energy-dispersive spectrometry were conducted to reveal the mesostructure and components of the seed hull. The results revealed that the average densities of the S. mukorossi seed shell and kernel were respectively 1.49 and 1.07 × 103 kg/m3, the average Poisson’s ratio was 0.185, and Young’s modulus ranged from 1.3 to 0.3 GPa. These values had little dispersion, demonstrating both the consistency of the processing techniques and the stability of the material properties. The given properties of the S. mukorossi can be used as a theoretical basis for the optimized processing of this biomass material. The proposed method provides a new direction in the study of the mechanical properties of biomaterials.

Uncertainty-Based Autonomous Path Planning for Laser Line Scanners

This study proposes an algorithm to autonomously generate the scan path for a laser line scanner mounted on a coordinate measuring machine. The scan path is determined based on task-specific measurement uncertainty in order to prove conformance to specified tolerances. The novelty of the algorithm is the integration of measurement uncertainty. This development is made possible by recent developments for digital twins of optical measurement systems. Furthermore, the algorithm takes all the constraints of this optical measurement system into account. The proposed algorithm is validated on different objects with different surface characteristics. The validation is performed experimentally by a physical measurement system and virtually by an in-house developed digital twin. The validation proves that theoretical coverable areas are measured properly, and the method applied to the equipment used leads to adequate measurement paths that give measurements results with sufficient measurement uncertainty to prove conformance to specifications.

Adaptive Inertial Sensor-Based Step Length Estimation Model

Pedestrian dead reckoning (PDR) using inertial sensors has paved the way for developing several approaches to step length estimation. In particular, emerging step length estimation models are readily available to be utilized on smartphones, yet they are seldom formulated considering the kinematics of the human body during walking in combination with measured step lengths. We present a new step length estimation model based on the acceleration magnitude and step frequency inputs herein. Spatial positions of anatomical landmarks on the human body during walking, tracked by an optical measurement system, were utilized in the derivation process. We evaluated the performance of the proposed model using our publicly available dataset that includes measurements collected for two types of walking modes, i.e., walking on a treadmill and rectangular-shaped test polygon. The proposed model achieved an overall mean absolute error (MAE) of 5.64 cm on the treadmill and an overall mean walked distance error of 4.55% on the test polygon, outperforming all the models selected for the comparison. The proposed model was also least affected by walking speed and is unaffected by smartphone orientation. Due to its promising results and favorable characteristics, it could present an appealing alternative for step length estimation in PDR-based approaches.

Evaluating parametric uncertainty using non-linear regression in fringe projection

Optical coordinate measurement systems, such as fringe projection systems, offer fast, high-density measurements of arbitrary surface topographies. The versatility, speed and information density of fringe projection measurements make them attractive as in-situ measurement devices and autonomous inspection systems. However, the complex nature of the measurement process makes evaluating uncertainty from a fringe projection measurement complex – even in the hypothetical simple case where the accuracy of a measurement is limited only by the accuracy in the quantities that define a measurement from an indication; named system parameters here. In this paper, by validating a series of assumptions, a method to explore the uncertainty in the system parameters of a fringe projection system is given. The results of this investigation imply the common distortion model (the Brown-Conrady model) is not specific enough to the camera or projector of a fringe projection system to evaluate its uncertainty.

Investigation of temperature sensitivity of a MEMS gravimeter based on geometric anti-spring.

This paper describes a technique for temperature sensitivity or thermal sag measurements of a geometric anti-spring based microelectromechanical system (MEMS) gravimeter (Wee-g). The Wee-g MEMS gravimeter is currently fabricated on a (100) silicon wafer using standard micro-nano fabrication techniques. The thermal behavior of silicon indicates that the Young's modulus of silicon decreases with increase in temperature (∼64 ppm/K). This leads to a softening of the silicon material, resulting in the proof mass displacing (or sagging) under the influence of increasing temperature. It results in a change in the measured gravity, which is expressed as temperature sensitivity in terms of change in gravity per degree temperature. The temperature sensitivity for the silicon based MEMS gravimeter is found to be 60.14-64.87, 61.76, and 62.76 µGal/mK for experimental, finite element analysis (FEA) simulation, and analytical calculations, respectively. It suggests that the gravimeter's temperature sensitivity is dependent on the material properties used to fabricate the MEMS devices. In this paper, the experimental measurements of thermal sag are presented along with analytical calculations and simulations of the effect using FEA. The bespoke optical measurement system to quantify the thermal sag is also described. The results presented are an essential step toward the development of temperature insensitive MEMS gravimeters.

Six-degree-of-freedom geometrical errors measurement system with compensation of laser beam drifts and installation errors for linear stage

In this paper, an optical measurement system is proposed to measure the six-degree-of-freedom (6DOF) geometrical errors of a linear stage, and the errors are analyzed by the interferometric method and the geometrical optics method. Among them, the interferometric method is mainly used for the position error analysis. This method can solve the problem that geometrical optics is limited by the size of the sensor in our previous system, and improve the measurement accuracy of the position error. The geometrical optics method is used for the error analysis of the remaining 5DOF geometrical errors to simplify the data acquisition time and calculation amount. In addition, this paper also proposes a methodology to compensate for laser beam drifts and installation errors of optical components. We use two sensors to measure the 4DOF laser beam drifts and add them into the proposed mathematical model to solve these errors. We also use sensitivity analysis to analyze the influence of each installation error of optical components and find out the installation errors that need to be considered. Then we bring them into the mathematical model and solved them with least square methods. Finally, we verify the feasibility of the proposed measurement system through repeated experiments and comparisons with a commercial interferometer and an electronic level.

An automatic measurement system for the wall thickness of corrugated plate based on laser triangulation method

Wall thickness is an important parameter used in the characterization of the surface quality of chevron corrugated plates. However, current measurement techniques such as contact mechanical or destructive modes are timing-consuming and are limited by the complex morphology of the measured object. In this study, an optical measurement system is established for experimental evaluation of the wall thickness. Its optical design and working characteristic are described based on the triangulation principle. By performing normal vector estimation, and combining with the search results about the best possible reconstructed mesh surface, the wall thickness at each measurement point can be evaluated. A series of comparison experiments with the maximum deviation 0.043 mm show that our proposed method can provide effective and automatic technical support for dimensional detection of complex components.

Design of a measurement system for measuring geometric errors of a workpiece table during two-axis synchronous motion

With the increasing customer demand for high-precision workpieces, the accuracy performance of CNC machine tools has become an increasingly important hot topic for almost all machine tool manufacturers. For fine surface finish workpieces, the performance of multi-axis synchronous motion has a significant impact on lathe processing. Accordingly, it is necessary to calibrate and identify the geometric errors of the workpiece table during multiple-axis synchronous motion. Therefore, this study proposes a novel noncontact optical measurement system for measuring the geometric errors of the workpiece table while the two axes are moving simultaneously. In addition, the horizontal CNC lathe machine iTC-2000LM, produced by Tongtai machine & tool Co., Ltd., was taken as the research vehicle. The proposed measurement system comprises an optics module composed of several reflectors, lenses, and cubic beam splitters; a sensing module composed of multiple two-dimensional position-sensitive detectors (PSDs); and a laser. Based on the principle of geometric optics theory and the optical triangulation method, complete mathematical models that describe the geometric errors of the workpiece table during two-axis synchronous motion were established using the skew-ray tracing method. Additionally, the essential features of the proposed measurement system were verified using the optical design software Zemax. Finally, a laboratory prototype system was constructed to experimentally verify the proposed measurement system. As mentioned above, the main contribution of this study is to design a novel and highly efficient measurement system with established measurement mathematical models and experimental verifications.

Acoustic Roughness Measurement of Railway Tracks: Implementation of a Chord-Based Optical Measurement System on a Train

A large part of the noise emissions from rail traffic originates from rolling noise. This is significantly determined by the surface roughness of the wheel and the rail. To quantitatively assess the noise generation from the wheel–rail contact, it is necessary to measure the surface roughness of the rail network. Direct measurements via trolley devices are usually associated with the need for a free track and limitation in velocity. Indirect measurements of rail roughness, such as measuring axle-box accelerations, enable operation during regular passage but only estimate the acoustic roughness. In this study, the potential of an optical and consequently contact-free measurement method using laser triangulation sensors to measure rail roughness from the train is investigated. The approach can combine the advantage of operation during regular passage with the characteristics of a direct measurement, enabling large-scale monitoring of the rail network. A measurement run with a train was carried out on a meter-gauge track at speeds up to 80 km h−1 The results of the optical measurement approach were compared with a tactile reference measurement on the track. The results show good agreement of the new measurement setup for dry rail surface conditions at 50 km h−1, with a mean deviation of 1.48 dB.

Locking the Taylor Spatial Frame – The effect of three additional longitudinal rods on osteotomy site movements.

BackgroundIn clinical practice, even when the fixator is locked, a noticeable laxity of the construct can be observed. This study was designed to measure the stiffness of the fixator and to analyze the movements of the osteotomy site. Furthermore, the effect of three additional longitudinal rods on the locking of the construct was analyzed. MethodsFive synthetic tibia/fixator models (Model A) were tested under rotational torque (40 Nm) and axial compression (700 N). Three additional rigid rods were subsequently mounted, and the tests were repeated (Model B). The movements of the fixator as well as the osteotomy site were registered by a digital optical measurement system. Load- deformation curves, and so stiffness of the models, were calculated and compared. FindingsUnder rotational and axial loadings, Model A was found to be less rigid than Model B (p = 0.034; p = 0.194). Notably, Model A showed a region of laxity around neutral rotational (ΔF = 5 Nm) and axial (ΔF = 16.64 N) loading before a linear deformation trend was measured. Concomitantly, greater osteotomy site movement was measured for Model A than for Model B under full loading (p = 0.05) and within the region of increased laxity (p = 0.042). InterpretationThe fixator showed an element of laxity around neutral axial and rotational loading, which transferred to the bone and led to a notable amount of osteotomy gap movement. Mounting three additional rods increased the stiffness of the construct and therefore reduced the movement of the osteotomy site.

Bubble size distribution and electrode coverage at porous nickel electrodes in a novel 3-electrode flow-through cell

A novel 3-electrode cell type is introduced to run parametrical studies of H2 evolution in an alkaline electrolyte on porous electrodes. Electrochemical methods combined with a high-speed optical measurement system are applied simultaneously to characterize the electrodes and the bubble dynamics in terms of bubble size distribution and coverage of the working electrode. Three different cathodes made of expanded nickel are investigated at applied current densities of |j| = 10–200 mA cm−2 without forced flow and at a flow rate of 5 ml min−1. The applied current density is found to significantly influence both the size of detached bubbles and the surface coverage of the working electrode. The forced flow through the cathodes is found to strongly reduce the bubble size up to current densities of about 100 mA cm−2, whereas the initial transient until the cathode surface is completely covered by bubbles is only marginally affected by the flow-through.

Abstract 15277: High-Throughput Optical Oxygen Measurements for Human IPSC-Cardiomyocytes and Ventricular Fibroblasts in 96-Well Plates

For metabolically active cells like cardiomyocytes, a balanced state of oxygen supply and demand is crucial for basic cell function. Human-induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) are a valuable experimental model due of their scalability and relevance to human physiology. Oxygen consumption and availability have not been characterized in high-throughput format (HT), used in pre-clinical studies. Here, we quantified pericellular oxygen in syncytia of hiPSC-CM and human cardiac fibroblasts, grown in glass-bottom 96-well plates ( Fig 1A-C ). We deployed Ruthenium-based oxygen sensors and a ratiometric optical oxygen measurement system ( Fig 1B ) to track pericellular oxygen over time across all wells. Measured ratios were calibrated to % oxygen using two-point calibration with 5% Na 2 SO 3 and upon saturation with ambient air. Solution height and cell density were varied (4 solution heights, 3 cell densities) to understand their role in oxygen diffusion and oxygen consumption rate (OCR) by the cells. Michaelis-Menten kinetics and the Thiele modulus were used to computationally simulate oxygen availability in matching conditions. Without active perfusion or mass transport, for all tested conditions in the hiPSC-CMs, oxygen was depleted to <5% within approximately an hour. The drop of oxygen occurred in two phases - a zero-order decrease phase, followed by Michaelis-Menten kinetic phase ( Fig 1D ). Increase in culture medium volume/ height was found to be a powerful determinate of oxygen availability in simulations and in experiments ( Fig 1E n = 5 per group). Higher cell density correlated with steeper slope in the first phase of decline in oxygen availability, n = 4 per group. Cardiac fibroblasts followed a similar pattern (n = 4 per group) with noticeably slower OCR. Overall, our results indicate that pericellular oxygen in HT glass-bottom plates may reach hypoxic levels quickly; solutions for active mass transport need to be considered.

A High‐Speed Camera‐Based Measurement System for the High‐Pressure Entrained‐Flow Gasification

AbstractA continuously operated optical measurement system for observation and characterization of the flame structure in an entrained‐flow gasifier operated at 40 bar and 1200 °C is presented. The experimental setup, the image processing system, and the derived parameters for flame characterization are introduced. First results from gasification experiments concerning flame lift‐off distance, flame angle, and flame dynamics are demonstrated.

A high-throughput fully automatic biosensing platform for efficient COVID-19 detection

We propose a label-free biosensor based on a porous silicon resonant microcavity and localized surface plasmon resonance. The biosensor detects SARS-CoV-2 antigen based on engineered trimeric angiotensin converting enzyme-2 binding protein, which is conserved across different variants. Robotic arms run the detection process including sample loading, incubation, sensor surface rinsing, and optical measurements using a portable spectrometer. Both the biosensor and the optical measurement system are readily scalable to accommodate testing a wide range of sample numbers. The limit of detection is 100 TCID50/ml. The detection time is 5 min, and the throughput of one single robotic site is up to 384 specimens in 30 min. The measurement interface requires little training, has standard operation, and therefore is suitable for widespread use in rapid and onsite COVID-19 screening or surveillance.

Raster angle impact on FDM-based additive manufactured fluidic oscillator

The interior surface of a fluidic oscillator produced by FDM (Fused Deposition Modeling)-based additive manufacturing is associated with a directional pattern corresponding to the 3D printing raster angle. The present research explores the impact of raster angle α = 0 , 45, and 90° from three commercial 3D printers versus a CNC machined oscillator. The surface is characterized using an optical 3D measurement system. The performance of the emanated jet is assessed using hot-wire anemometry downstream of the outlet nozzle, and the required supply pressure is measured at the actuator inlet. Printer P 1 with an actuator average roughness S ̄ a = 8 . 3 μm and printer P 2 with S ̄ a = 29 . 9 μm inherit clear raster patterns while actuators printed by printer P 3 , more economical compared to printer P 1 , do not exhibit an evident pattern related to raster angle with S ̄ a = 17 . 7 μm. Regardless of the type of printer and associated surface texture, oscillators with 0° raster angle provoke higher jet spreading accompanied by a lower required supply pressure compared to the milled sample. Strikingly, the performance for P 3 0 and P 3 90 is noticeably superior to the other printed oscillators and surpasses the milled actuator in terms of jet switching quality. Power-law fit is depicted to estimate the jet spreading versus surface roughness for each raster angle.