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The inconvenient loading and unloading of a long and heavy drill pipe gives rise to the difficulty in measuring the contour parameters of its threads at both ends. To solve this problem, in this paper we take the SCK230 drill pipe thread-repairing machine tool as a carrier to design and achieve a fast and on-machine measuring system based on a lase...
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Context 1
... on the laser triangulation principle, a laser displacement sensor is mainly composed of laser driver, laser diode, collimating lens, imaging lens, photoelectric coupling surface CCD, and signal processing circuit. The basic principle is shown in Figure 4, in which X is the displacement of the measured object plane, X' is the displacement of the light spot image on the CCD, α is the angle between the optical axis of imaging lens and the laser beam, β is the angle between the optical axis of imaging lens and the CCD plane, L is the object distance of imaging lens, and L' is the image distance of imaging lens. According to the theorem of similar triangles, it can be concluded ...
Context 2
... (1) is the theoretical formula of laser triangulation, from which we can see the laser triangulation principle that the image displacement X' presented to CCD via imaging lens reflects the actual displacement X of the measured object. In the actual measurement, to ensure the data acquisition accuracy of the sensor, the Scheimpflug condition must be met, i.e., the imaging lens and the CCD receiving plane intersect at the point C of the laser beam, and the Gauss' law must be satisfied. From Figure 4 and the principle formula, the displacement measured by a sensor takes the vertical incidence of laser beam to the measured object plane as a base; nevertheless, the actual surface topography of a workpiece is so complex that the incident beam is inevitably not coincident with the surface normal. The angle between the incident beam and the surface normal is called the inclination angle θ (positive if clockwise), and this phenomenon is called the measuring point inclination angle. The reason for inclination error is that as the measuring point inclination angle changes the distribution of laser scattering field, the light received by the imaging lens is changed accordingly, with the result that the light spot centroid imaged in the CCD is not coincident with that at the time of vertical incidence. However, the sensor still calculates the displacement, providing there is no measuring point, and eventually the error is caused. Therefore, an inclination error model is to be built to effectively improve the data acquisition accuracy of the laser displacement sensor. Under ideal conditions, the measured object plane is considered as a diffuse surface without absorption. According to the Beer-Lambert Law (as shown in Figure 5), the spatial distribution of light scattering field ...
Citations
... Thread profiles are traditionally measured via contact on a coordinate measuring machine (CMM) by scanning with a self-centering tip. However, attempts to measure threads directly on a CNC machine, as found in the literature, primarily use optical methods [36][37][38][39]. Ensuring repeatability and stability in automated measurements within a shop floor environment poses a challenge addressed in Metrology 4.0, as outlined in [40]. ...
One of the key aspects of the automation of machining processes is the elimination of manual measurements. This is crucial in the production of precision parts, where the absence of in-process control can lead to an increased number of non-compliant parts, resulting in financial losses for the company. In addition to economic considerations, environmental care is a fundamental requirement for manufacturing companies. While many efforts focus on finding environmentally friendly coolants or reducing machining time, researchers often overlook the impact of the measurement method on the balanced development of machining. The conditions inside CNC machines are quite demanding in terms of maintaining measurement stability. For this reason, this paper presents a comparative study of two types of machine inspection probes. The influence of the measurement axis and the effect of returning the probe to the magazine on the accuracy of the measurement were examined. This study revealed that the probe with a kinematic resistive design has a higher measurement uncertainty (2.7 µm) than a probe based on strain gauges (0.6 µm). This paper emphasizes the positive impact of the conducted activity on the sustainability of machining, highlighting benefits such as resource savings, energy savings, and positive effects on the health and safety of operators.
... Furthermore, circular-laser and point-laser [9] based methods suffer from low accuracy and poor measurement integrity due to laser misalignment deformation caused by the light form and complex thread profile. The challenges above can be efficiently solved using the vision measurement method with line-laser lighting along the longitudinal section of the internal thread [15]. Chun-Fu Lin et al. [16] proposed a real-time system for internal thread defect measurement based on monocular structured light. ...
Geometric parameter measurement of tubing internal thread is critical for oil pipeline safety. In response to the shortcomings of existing methods for measuring internal thread geometric parameters, such as low efficiency, poor accuracy, and poor accessibility, this paper proposes a vision system for measuring internal thread geometric parameters based on double-mirrored structured light. Compared to previous methods, our system can completely reproduce the internal thread tooth profiles and allows multi-parameter measurement in one setup. To establish the correlation between the structural and imaging parameters of the vision system, three-dimensional (3D) optical path models (OPMs) for the vision system considering the mirror effect of the prism is proposed, which extends the scope of the optical path analysis and provides a theoretical foundation for designing the structural parameters of the vision system. Moreover, modeling and three-step calibration methods for the vision system are proposed to realize high-accuracy restoration from the two-dimensional (2D) virtual image to the actual 3D tooth profiles. Finally, a vision measurement system is developed, and experiments are carried out to verify the accuracy and measure the three geometric parameters (i.e., taper, pitch, and tooth height) of typical internal threads. Based on the validation results using the reference system, the vision measurement accuracy and efficiency are 6.7 and 120 times that of the traditional system, which verifies the measurement effectiveness and accuracy of the vision system proposed in this paper.
... For the measurement method with a circular laser [19,20], a camera and a laser need to be connected coaxially through a glass cover to implement the measurement so that the imaging optical path will be refracted twice, which reduces the measurement accuracy. Additionally, with the effect of the lighting form and complex thread profile, the measurement methods based on a circular laser and a point laser [21,22] have the problems of low accuracy and incompleteness for measuring the tooth profiles caused by laser misalignment distortion and measurement inaccessibility. The vision-based measurement system of line laser illumination along the longitudinal cross-section of the internal thread can solve the above problems [23,24]. ...
Oilfield pipes with out-of-tolerance internal thread can lead to failures, so the internal thread geometric parameters need to be measured. To tackle the problem of the low efficiency, poor accuracy, easy wear, and poor accessibility of existing methods, a single-lens multi-mirror laser stereo vision-based system for measuring geometric parameters of the internal thread is proposed, which allows the measurement of three parameters in one setup by completely reproducing the three-dimensional (3D) tooth profiles of the internal thread. In the system design, to overcome the incomplete representation of imaging parameters caused by insufficient consideration of dimensions and structural parameters of the existing models, an explicit 3D optical path model without a reflecting prism is first proposed. Then, considering the intervention of the reflecting prism, a calculation model for the suitable prism size and the final imaging parameters of the vision system is proposed, which ensures the measurement accessibility and accuracy by solving the problem that the existing system design only depends on experience without theoretical basis. Finally, based on the American Petroleum Institute standard, internal thread geometric parameters are obtained from the vision-reconstructed 3D tooth profiles. According to the optimized structural parameters, a vision system is built for measuring the internal thread geometric parameters of two types of oilfield pipes. Accuracy verification and typical internal thread measurement results show that the average measurement errors of the vision system proposed for the pitch, taper, and tooth height are 0.0051 mm, 0.6055 mm/m, and 0.0071 mm, respectively. Combined with the vision measurement time of 0.5 s for the three parameters, the above results comprehensively verify the high accuracy and high efficiency of the vision-based system.
... The LiDAR data can also contain other information such as the intensity of the rebounds, the point classification (if applicable), number of returns, time, and source of each point [1,15]. LiDAR scanners use a laser pulse to measure the distance from the sensor using the time for the laser pulse to return in the case of time-of-flight sensors (Figure 1a) [16] or using the triangulation angle on the optical sensor for triangulation-based scanners (Figure 1b) [17]. The LiDAR scanners then generate an [x, y, z] position relative to the sensor's locations based on the distance from the sensor and the degrees of rotation of the sensor, such as pitch, roll, and yaw [18]. ...
... Time of Flight LiDAR sensor calculation (a)[16] and triangulation-b tion (b)[17]. ...
... Time of Flight LiDAR sensor calculation (a)[16] and triangulation-based LiDAR calculation (b)[17]. ...
Point clouds are one of the most widely used data formats produced by depth sensors. There is a lot of research into feature extraction from unordered and irregular point cloud data. Deep learning in computer vision achieves great performance for data classification and segmentation of 3D data points as point clouds. Various research has been conducted on point clouds and remote sensing tasks using deep learning (DL) methods. However, there is a research gap in providing a road map of existing work, including limitations and challenges. This paper focuses on introducing the state-of-the-art DL models, categorized by the structure of the data they consume. The models’ performance is collected, and results are provided for benchmarking on the most used datasets. Additionally, we summarize the current benchmark 3D datasets publicly available for DL training and testing. In our comparative study, we can conclude that convolutional neural networks (CNNs) achieve the best performance in various remote-sensing applications while being light-weighted models, namely Dynamic Graph CNN (DGCNN) and ConvPoint.
... They were able to obtain information about the workpiece with a laser scanner, which uses the same optical path as the laser beam connected to the camera [6]. Figure 1. The working principle of the triangulation method [7] The triangulation method shown in Figure 1 is used to measure distance in the laser sensor, which can be used in gas metal arc welding processes. The main function of this method is to calculate the distance to the ground on the material on which the beam falls [7]. ...
... The working principle of the triangulation method [7] The triangulation method shown in Figure 1 is used to measure distance in the laser sensor, which can be used in gas metal arc welding processes. The main function of this method is to calculate the distance to the ground on the material on which the beam falls [7]. However, the common use of triangulation in gas metal arc welding is to find the geometry of the weld line. ...
In processes conducted with welding robots, distortions may occur as a result of thermal deformations, especially in materials with high thicknesses. These shape distortions can be detected with the sensor systems connected to the end effector, which is the last joint of the robot system. As a result of these deformations, the weld bead path may change, and the position information previously introduced to the welding torch may also be incorrect. In order to find a solution to this problem, bead tracking systems using laser-based sensor have been developed. Although laser sensor systems have many advantages, they also have some disadvantages. This study aimed to develop an innovative Guide system as an alternative to laser seam tracking. The design studies of the system were completed with the Solidworks program and modeled with the PID algorithm in the MATLAB Simulink program. In Simulink software, the main elements of the Guide system were angle sensors, and values in degrees were obtained from these sensors at certain time intervals. When it was determined that there was a difference between these values and the degree values defined as the reference, optimizations were applied to the system in order to minimize the error at these points. It has been tested in the RoboDK simulation environment that the lead system can detect this situation in cases where deformation may occur even if fixtures are used in the weld seam tracking. As a result of the simulation, it has been observed that the robot system can rearrange the joint angle information and the system can continue to follow the weld seam without any problems.
... Contactless examination commonly utilizes eddy currents, lasers, or cameras. In [1,2], the authors utilized laser sensors for non-contact inspection of threads. In [3,4], the authors conducted optical examination of screw threads utilizing cameras. ...
... Figure 7. Utilizing the buffer, the ID can move through a slightly misaligned TH. The movement order is 1 ...
This article addresses a Thread Hole (TH) examination system capable of automatically examining a TH. We introduce a contact-based examination system with simple hardware. Our examination system examines TH defects by observing the torque generated when tightening the Inspection Device (ID) through the TH. A buffer with springs is utilized to overcome instances where the TH is not accurately aligned with the axis of the ID. The examination system observes the TH size utilizing a camera, then automatically performs an examination utilizing the optimal torque threshold associated with the TH size; in this way, our examination system is able to examine a TH regardless of its size. In this paper, the performance of the proposed system utilizing the optimal torque threshold is verified through experiments.
... Their performance affects the connection effect of the structure. Compared with the current mainstream thread-measuring equipment, three-dimensional (3D) threadmeasuring machines can accurately measure the main parameters of the thread in 3D space [1][2][3][4][5]. As the main measuring system of 3D thread-measuring machines, the probe can greatly affect their accuracy. ...
Coupling error is an important factor that affects the measurement accuracy of the contact scanning probe of a three-dimensional thread-measuring machine. To address this issue, this paper proposes a coupling error model for contact scanning probes. First, the mechanical structure of the contact scanning probe was introduced, and the main source of its coupling error was analyzed. Second, material mechanics was used to conduct a geometry–force analysis on the guiding mechanism of the probe, thereby establishing a coupling error model. Finally, the experiments were carried out to verify the accuracy of the coupling error model. From the experimental verification, the movement of the measuring head by 10 μm increased the deviation of the probe displacement by 2 μm, indicating the probe deflection. Moreover, the calculated probe deflection angle was consistent with the theoretical value, validating the proposed coupling error model. This method provides an important theoretical basis for the decoupling of measuring probe, thereby improving the accuracy of the probe guiding mechanism.
... The inclined surface with a Lambertian scattering characteristic shifts the laser spot image centroid as derived in [27]. Fortunately, both these effects can be effectively compensated for even for large surface inclination angles, as in the case of thread profile measurement [28]. ...
The aim of the research is to analyze the possibility of the development and realization of a common laser triangulation sensor arrangement-based probe for the measurement of slots and bore sides with the help of a mirror attachment. The analysis shows the feasibility and limits of the solution with respect to the maximum measurement depth and surface distance measurement working range. We propose two possible solutions: one for maximizing the ratio of the measurement depth to the measured bore size and the second for maximizing the total depth, intended for the measurement of slots and large bore sizes. We analyzed measurement error sources. We found that the errors related to the reflection mirror misalignment can be fully compensated. We proved the validity of the proposed solution with the realization of a commercial laser triangulation sensor-based probe and demonstrated a slot side and a bore side surface distance scanning measurement. The probe working range was assessed with regard to the obscuration effect of optical beams.
... Moreover, the stronger the denoising capacity, the more serious the elimination of real data will be, thus causing data distortion after the reconstruction and influencing the final measurement accuracy. In the aspect of fitting, the least square method has been extensively used for piecewise fitting by virtue of its high fitting efficiency and simple operation [30]. Nevertheless, in view of the fact that the continuity and differentiability of the function cannot be satisfied at piecewise points, the data fitting precision is poor, thus affecting the final measurement accuracy. ...
Great length, large weight and other factors may cause difficulty in measuring the profile accuracy of the double-headed screw rotor. To solve this problem, an on-machine measuring system based on a laser-displacement sensor (LDS) was designed and implemented in this paper by taking an LXK100 four-axis whirlwind milling machine as the carrier. To improve the measurement accuracy of the system, the generalized variable-structural-element morphological method, polynomial interpolation algorithm and ellipse fitting method were first combined to realize the rapid subpixel centroid extraction from a noise-containing spot image, thus improving the data acquisition accuracy of the LDS, and then the hybrid method was experimentally verified. Next, a wavelet threshold function with high-order differentiability and adaptive wavelet coefficient contractility was constructed based on the hyperbolic tangent function, so as to inhibit the disturbance from random errors and preserve real profile information, and this method was simulated and verified. Subsequently, a smoothing algorithm for point cloud data was proposed based on the Lagrange multiplier method to avoid the defect of the piecewise curve-fitting method, that is, function continuity and differentiability could not be satisfied at piecewise points. Finally, the profile accuracy was calculated in real time according to the data reconstruction result and the machining quality was judged. The measurement experiment of the double-headed screw rotor indicates that the proposed on-machine measuring system can complete the profile accuracy measurement for a screw pitch within 39.7 s with measurement accuracy reaching ±8 μm, and the measurement uncertainties of the major axis, minor axis and screw pitch are 0.72 μm, 0.69 μm and 1.24 μm, respectively. Therefore, the measurement accuracy and efficiency are both remarkably improved.
... Because of the vacuum environment and strong metal vapor in the electron beam freeform fabrication process, the optical device will be quickly contaminated. This makes many existing 3D reconstruction techniques difficult to use in this environment, such as the structured laser technology which is widely used in 3D reconstruction of parts [6][7][8][9][10][11]. Dong et al. [12,13] realized the online measurement of helical rotor pitch by using structural laser technology. Sun et al. [14] achieved surface measurements on aero-engine blades based on laser triangulation. ...
In the process of electron beam freeform fabrication (EBF3), due to the continuous change of thermal conditions and variability in wire feeding in the deposition process, geometric deviations are generated in the deposition of each layer. In order to prevent the layer-by-layer accumulation of the deviation, it is necessary to perform online geometry measurement for each deposition layer, based on which the error compensation can be done for the previous deposition layer in the next deposition layer. However, the traditional three-dimensional reconstruction method that employs structured laser cannot meet the requirements of long-term stable operation in the manufacturing process of EBF3. Therefore, this paper proposes a method to measure the deposit surfaces based on the position information of electron beam speckle, in which an electron beam is used to bombard the surface of the deposit to generate the speckle. Based on the structured information of the electron beam in the vacuum chamber, the three-dimensional reconstruction of the surface of the deposited parts is realized without need of additional structured laser sensor. In order to improve the detection accuracy, the detection error is theoretically analyzed and compensated. The absolute error after compensation is smaller than 0.1 mm, and the precision can reach 0.1%, which satisfies the requirements of 3D reconstruction of the deposited parts. An online measurement system is built for the surface of deposited parts in the process of electron beam freeform fabrication, which realizes the online 3D reconstruction of the surface of the deposited layer. In addition, in order to improve the detection stability of the whole system, the image processing algorithm suitable for this scene is designed. The reliability and speed of the algorithm are improved by ROI extraction, threshold segmentation, and expansion corrosion. In addition, the speckle size information can also reflect the thermal conditions of the surface of the deposited parts. Hence, it can be used for online detection of defects such as infusion and voids.
