Laser Triangulation Displacement Sensor Research Articles

Novel Information-Driven Smoothing Spline Linearization Method for High-Precision Displacement Sensors Based on Information Criterions.

A noise-resistant linearization model that reveals the true nonlinearity of the sensor is essential for retrieving accurate physical displacement from the signals captured by sensing electronics. In this paper, we propose a novel information-driven smoothing spline linearization method, which innovatively integrates one new and three standard information criterions into a smoothing spline for the high-precision displacement sensors' linearization. Using theoretical analysis and Monte Carlo simulation, the proposed linearization method is demonstrated to outperform traditional polynomial and spline linearization methods for high-precision displacement sensors with a low noise to range ratio in the 10-5 level. Validation experiments were carried out on two different types of displacement sensors to benchmark the performance of the proposed method compared to the polynomial models and the the non-smoothing cubic spline. The results show that the proposed method with the new modified Akaike Information Criterion stands out compared to the other linearization methods and can improve the residual nonlinearity by over 50% compared to the standard polynomial model. After being linearized via the proposed method, the residual nonlinearities reach as low as ±0.0311% F.S. (Full Scale of Range), for the 1.5 mm range chromatic confocal displacement sensor, and ±0.0047% F.S., for the 100 mm range laser triangulation displacement sensor.

A Laser Triangulation Displacement Sensor Based on a Cylindrical Annular Reflector

The ellipticity of the spot caused by laser jitter has a significant effect on the measurement accuracy of the traditional laser triangulation method. In order to overcome the influence of laser characteristics on measurement and improve the accuracy of displacement measurement, this paper proposes a measurement model for a laser displacement sensor based on a cylindrical annular reflector. A physical prototype is designed through parameter optimization using NSGA-II, and a two-step detection algorithm is proposed for the imaging ring of the prototype. The algorithm performs contour thinning after rough positioning of the imaging annular ring, and then performs precise detection. Through physical experiments, it is verified that the repeatability error of this method can reach below 0.02%, and the accuracy is significantly improved compared to traditional laser triangulation displacement sensors. Meanwhile, the measurement results of displacement show linearity. The optical path design of this sensor is simpler than the previously proposed rotational symmetrical laser triangulation displacement sensor, which has good application prospects.

High Precision and Large Dynamic Range Measurement of Laser Triangulation Displacement Sensor Using Diffraction Grating

The conventional laser triangulation displacement sensor (LTDS) is difficult to achieve large dynamic range and high precision measurement simultaneously, since LTDS is affected by factors such as limited detector size, nonlinear input and output variables, laser power fluctuation, speckle noise, electronic noise, etc. Given the above background, we proposed a modified LTDS using a diffraction grating to improve the dynamic range and precision simultaneously. Different from the conventional LTDS, the modified LTDS generates more than one spots on the image sensor, thereby the displacements with different ranges can be obtained from the multiple order diffraction spots. Ultimately, the dynamic range and measurement accuracy will be improved simultaneously by integrating these displacements. In this paper, the principle of the modified LTDS for large dynamic range and high precision measurement is described in detail, and we verified the validity and effectiveness of this idea through the experiment. Compared with the traditional LTDS, the experimental results show that the linearity of the modified LTDS is improved by a factor of 1.5685 and the dynamic range is improved 1.2986 times as well as maintaining the same linearity.

Research on laser spot location accuracy of low-power laser diode source applied to high precision laser measurement system

The results of laser spot location have an important influence on the accuracy of a laser measurement system. Laser diode (LD) sources have been widely used in recent years because of its low cost and easy integration. Based on the low-power LD source, a conventional laser spot location system was built to study the factors that affect the accuracy of location. We analyzed the influencing factors on laser spot location from two aspects of LD driven and charge coupled device (CCD) imaging, and experiments were conducted to further obtain quantitative analysis results and laws on different influencing factors, including the LD temperature, LD injection current, the size of imaging laser spot and its intensity fluctuation. The drifting RMS and the dithering range R were adapted to evaluate the drift and dither of the laser spot respectively, and the influence laws of location error were discussed. Finally, laser triangulation displacement sensor was taken as an optimization design example when considering the influencing factors studied in this paper. As a result, the RMS accuracy of the design example was 3.6 μm and its repeatability was 2.17 μm. The experimental results provided guidance for the optimization design of laser spot location measurement system.

Development of a small-size laser triangulation displacement sensor and temperature drift compensation method

In practical applications, some special working scenarios need to take into account both narrow space and extreme temperature, which puts more strict requirements on the size and temperature adaptability of the laser triangulation displacement sensor (LTDS). In this paper, a small-size LTDS was developed and the measurement error caused by temperature drift of the sensor was corrected. Firstly, based on direct projection laser triangulation imaging with a reflector unit, a mathematical model of the compact geometry optical structure was established; then, an optimization process of the optical parameters was formulated, and the sensor was assembled. Secondly, a temperature drift error database was built by an extreme temperature experiment, and a general regression neural network model was constructed for error compensation. In addition, root mean square error and execution time were used to evaluate and compare different regression methods. Finally, the experimental results showed that the repeatability accuracy of the proposed sensor was ±2.3 µm, and the temperature linearity was 0.001% F.S. °C−1.

Noncontact 3D measurement method on hole-structure precision inspection

In order to implement 3D point cloud scanning of small hole structure, which could not be contacted or damaged, we propose a noncontact 3D measuring method. The system contains a laser triangulation displacement sensor, a Michelson interferometer system and a coordinate measuring machine, with the advantages of non-invasive scanning, fast measurement speed and high precision. Focusing on reconstructing 3D point cloud data, random sample consensus is used to separate surface data and hole data respectively from the raw dataset. Least square optimization determines the function of the cylinder, as well as hole diameter and inclined angle between the hole and the surface. In the experiment scanning a round hole, the estimated result has diameter error and angle error within 30 µm and 0.2°, respectively. Results manifest the effectiveness and feasibility of this system and express practicality in manufacturing industry.

A Fast Laser Adjustment-Based Laser Triangulation Displacement Sensor for Dynamic Measurement of a Dispensing Robot

Height measurement and location by a laser sensor is a key technology to ensure accurate and stable operation of a dispensing robot. In addition, alternation of dynamic and static working modes of a robot, as well as variation of surface and height of a workpiece put forward strict requirements for both repeatability and respond speed of the location system. On the basis of the principle of laser triangulation, a displacement sensor applied to a dispensing robot was developed, and a fast laser adjustment algorithm was proposed according to the characteristics of static and dynamic actual laser imaging waveforms on different objects. First, the relationship between the centroid position of static waveform and peak intensity for different measured objects was fitted by least square method, and the intersection point of each curve was solved to confirm the ideal peak intensity, and therefore reduce the interference of different measured objects. Secondly, according to the dynamic centroid difference threshold of two adjacent imaging waveforms, the static and dynamic working modes of the sensor were distinguished, and the peak intensity was adjusted to different intervals by linear iteration. Finally, a Z direction reciprocating test, color adaptability test, and step response test were carried out on the dispensing robot platform; the experiments showed that the repeatability accuracy of the sensor was 2.7 um and the dynamic step response delay was 0.5 ms.

Optimizing laser triangulation displacement sensor of 3D positioning and posture using COA Based BPNN

PurposeThe purpose of this paper is to propose cuckoo optimization algorithm (COA)-based back propagation neural network (BPNN) to reduce the effect of the nonlinearities presented in laser triangulation displacement sensors. The 3D positioning and posture sensor allows access to the third dimension through depth measurement; the performance of the sensor varies according to the level of nonlinearities presented in the system, which leads to inaccuracies in measurement.Design/methodology/approachWhile applying optimization approach, the mathematical model and the relationship between the key parameters in the laser triangulation ranging and the indexes of the measuring system were analyzed.FindingsBased on the performance of the parametric optimization method, the measurement repeatability reached 0.5 µm with an STD value within 0.17 µm, an expanded uncertainty of measurement was within 5 µm, the angle error variation of the object’s rotational plane was within 0.031 degrees and nonlinearity was recorded within 0.006 per cent in a full scale. The proposed approach reduced the effect of the nonlinearity presented in the sensor. Thus, the accuracy and speed of the sensor were greatly increased. The specifications of the optimized sensor meet the requirements for high-accuracy devices and allow wide range of industrial application.Originality/valueIn this paper, COA-based BPNN is proposed for laser triangulation displacement sensor optimization, on the basis of the mathematical model, clarifying the working space and working angle on the measurement system.

Flying spot laser triangulation scanner using lateral synchronization for surface profile precision measurement.

High-speed surface profile measurement with high precision is crucial for target inspection and quality control. In this study, a laser scanner based on a single point laser triangulation displacement sensor and a high-speed rotating polygon mirror is proposed. The autosynchronized scanning scheme is introduced to alleviate the trade-off between the field of view and the range precision, which is the inherent deficiency of the conventional triangulation. The lateral synchronized flying spot technology has excellent characteristics, such as programmable and larger field of view, high immunity to ambient light or secondary reflections, high optical signal-to-noise ratio, and minimum shadow effect. Owing to automatic point-to-point laser power control, high accuracy and superior data quality are possible when measuring objects featuring varying surface characteristics even in demanding applications. The proposed laser triangulation scanner is validated using a laboratory-built prototype and practical considerations for design and implementation of the system are described, including speckle noise reduction method and real-time signal processing. A method for rapid and accurate calibration of the laser triangulation scanner using lookup tables is also devised, and the system calibration accuracy is generally smaller than ±0.025 mm. Experimental results are presented and show a broad application prospect for fast surface profile precision measurement.

Measurement of Cutting Edge Width of a Rotary Cutting Tool by Using a Laser Displacement Sensor

This paper introduces the widthmeasurement of a cutting tool edge by utilizing a laser triangulation displacement sensor. By using the reflected light intensity of the laser displacement sensor, micrometric edge width which is smaller than the diameter of the laser beam spot can be measured. With regard to the quantitative evaluation of the laser spot diameter, a calibration method of the laser spot diameter is achieved by using the pin-gauges. The diameter of the laser spot is obtained by using the pin-gauges, and the relationship between the reflected light intensity and the diameter of the pin-gauges are investigated. The width of the cutting tool edge is measured by the calibrated laser spot diameter, and then the reproducibility is evaluated.

Validation of Noninvasive MOEMS-Assisted Measurement System Based on CCD Sensor for Radial Pulse Analysis

Examination of wrist radial pulse is a noninvasive diagnostic method, which occupies a very important position in Traditional Chinese Medicine. It is based on manual palpation and therefore relies largely on the practitioner′s subjective technical skills and judgment. Consequently, it lacks reliability and consistency, which limits practical applications in clinical medicine. Thus, quantifiable characterization of the wrist pulse diagnosis method is a prerequisite for its further development and widespread use. This paper reports application of a noninvasive CCD sensor-based hybrid measurement system for radial pulse signal analysis. First, artery wall deformations caused by the blood flow are calibrated with a laser triangulation displacement sensor, following by the measurement of the deformations with projection moiré method. Different input pressures and fluids of various viscosities are used in the assembled artificial blood flow system in order to test the performance of laser triangulation technique with detection sensitivity enhancement through microfabricated retroreflective optical element placed on a synthetic vascular graft. Subsequently, the applicability of double-exposure whole-field projection moiré technique for registration of blood flow pulses is considered: a computational model and representative example are provided, followed by in vitro experiment performed on a vascular graft with artificial skin atop, which validates the suitability of the technique for characterization of skin surface deformations caused by the radial pulsation.

NON-INVASIE MICRO-OPTO-ELECTRO-MECHANICAL SYSTEM ADAPTATION TO RADIAL BLOOD FLOW PULSE AND VELOCITY ANALYSIS

Radial pulse examination is one of the most important diagnostic methods in traditional Chinese medicine. It has been used in establishing diseases and in guiding medicine selection for thousands of years. Blood flow fluctuation types present in radial artery contains rich and critical information which can reflect the state of various problems with health. Having precisely mastered the art of blood flow pulse practitioners can exactly determine what kind of health problems (i.e. problems with: gallbladder, kidneys, stomach, lungs, heart, high level of cholesterol and more) the patient has. Being non-invasive diagnostic technique this type of examination depends on the practitioner’s subjective analysis and may be unreliable and inconsistent. In this paper, we present novel computerized non-invasive micro-opto-electro-mechanical radial pulse signal analysis techniques strongly correlating with the valuable knowledge of traditional Chinese medicine. First, the fluctuations of blood flow are registered by laser triangulation displacement sensor. Then, using computer based techniques the signal is filtered from possible noise. Possible prototype model of final object is presented. Experiment results show that the proposed system works accurately and could be especially effective and helpful in ambulance medicine because of its portability and manufacturing price. DOI: http://dx.doi.org/10.5755/j01.mech.18.4.2343

Technology platform for hybrid integration of MOEMS on reconfigurable silicon micro-optical table

This work presents a novel approach to the development of MOEMS devices by robotic micro-assembly of individual microoptical components onto reconfigurable free-space micro-optical table (RFS-MOT). Various micro-optical elements (e.g. microlenses, micromirrors) are integrated within a generic structure of silicon holders. The holders are manipulated by 3D microassembly station with active microgripper, then aligned with nanometer precision within the guiding rails of silicon baseplate, and finally fixed by release of integrated mechanical snap connector. The fabrication of RFS-MOT components involves bulk micromachining of standard silicon wafer (baseplate) or SOI wafer (holders). The design and technology of RFS-MOT is presented. The successful micro-assembly of holders is demonstrated as an experimental validation of the proposed approach. The new method for measuring of position of assembled holder, based on laser triangulation displacement sensor, is described.

Simultaneous measurement of the shape and thickness of a dragonfly wing

A new method has been developed to measure the thickness and shape of a dragonfly wing simultaneously. The innovation in the method, which we call the TSM (thickness and shape measurement) method, is the combination of a heterodyne interferometer and a laser triangulation displacement sensor into one optical system. We confirmed the accuracy of the method by measuring the displacement of a glass plate and the thickness variation generated by a tilted glass plate. The method was then applied to a tilted glass plate and a dragonfly wing. The TSM system has a relative accuracy of 1% in the shape measurement and 1.8% in the thickness variation measurement. The results indicated that the method is very effective in biomechanics studies, such as evaluating the flight performance of dragonflies. In such evaluations, it is essential to measure with high accuracy the variations in both shape and thickness of the wing simultaneously.