High-precision Turntable Research Articles

Experimental Study of Hot-Sphere Anemometer Response in Stratospheric Environment.

Accurate wind speed measurement in low-pressure conditions is crucial for the thermal performance validation and attitude control of stratospheric aircraft. As air density decreases, traditional wind speed measurement systems based on principles such as dynamic pressure, heat transfer, ultrasound, and particle velocimetry face significant challenges when applied in low-pressure environments, often failing to achieve the required measurement accuracy. This paper presents the development of a wind speed simulation system based on a rotation method designed to operate in low-pressure conditions, utilizing a space environment simulation chamber in conjunction with a high-precision turntable. The system was employed to conduct response tests on a constant heat flow thermal sphere anemometer within a stratospheric pressure range of 1 kPa to 30 kPa. The experimental results revealed that at extremely low Reynolds numbers, the probe signal exhibited increasing nonlinearity, significantly affecting the response curve at pressures below 15 kPa. While the sensitivity of the hot-sphere probe remained relatively stable at wind speeds above 5 m/s, it decreased nonlinearly as the pressure dropped when wind speeds fell below 5 m/s. Furthermore, this paper analyzes the impact of various interpolation methods on wind speed conversion errors, providing valuable data to support the future development and validation of stratospheric aircraft.

Multi-Body Dynamics Modeling and Simulation of Maglev Satellites

The Lorentz force magnetic levitation gim2bal stabilized platform (LFMP), as a new generation of high-precision turntable for maglev satellites, can meet the requirements of future spacecraft for ultra-high attitude pointing accuracy and stability. To solve the problem of three-module multi-body attitude control under maneuvering conditions, the platform subsystem is first dynamically modeled based on the second type of Lagrangian equation, and the payload subsystem is dynamically modeled based on the Newton–Euler method. Secondly, a multi-loop control system is designed, consisting of high-precision and fast attitude pointing control for the payload, position tracking control for the platform subsystem, and tracking control for the maglev module. The final simulation results verified the feasibility and effectiveness of the payload-centered control method. An evaluation of the stability with a specific model has been performed, and the attitude accuracy of the payload is within 0.00002° and the attitude stability is within 0.00005°/s.

Quantitative analysis and cancellation of rotating modulation noise in gravity gradient measurement

Rotating accelerometer gravity gradiometer (RAGG) is an important instrument for auxiliary navigation and mineral exploration. The turntable in RAGG modulates the gravity gradient signal to a high frequency to avoid the influence of low-frequency noise. In order to quantitatively analyze and cancel the rotating modulation noise in gravity gradient measurement, the theoretical RAGG output error model with rotating modulation noise is derived and experimentally verified on a high-precision air-bearing turntable. The experimental results indicate that the dominant rotating modulation noise is turntable vibration noise, which results from the supply pressure fluctuations revealed by further analysis. Based on the rotating modulation noise characteristics, a deep neural network (DNN) is trained to cancel the rotating modulation noise from the RAGG output. Positively, the root-mean-square error (RMSE) of the trained DNN output is 1.7 E in sample data. Furthermore, a gravity gradient calibration platform is established to validate the effectiveness of this method by generating a gravity gradient signal with the same frequency as the rotating modulation noise and amplitude of 100 E. After cancelling the noise by the trained DNN, the RMSE of RAGG output reduced from 94 E to 7.7 E, while the RMSE of the result processed by wavelet analysis remains at 87 E. These results demonstrate that the trained DNN successfully cancels 92% of the rotating modulation noise in actual RAGG measurement without affecting the gravity gradient signal.

Anomaly Detection of Tire Tiny Text: Mechanism and Method

Due to the variety of tire specifications and poor contrast, it is difficult for ordinary 2D vision-based methods to accurately and autonomously detect anomalies in the tire text embossed on the tire sidewalls. In this paper, a 3D vision-based autonomous scanning mechanism and method is proposed, including three core components: a three-degree-of-freedom (3-DoF) robotic arm, a high-precision turntable and a composite vision probe. Based on the designed vision probe, the mechanism can autonomously scan the tire sidewall through a series of optimal viewpoints to obtain high-quality tire images even in the absence of tire CAD models. To obtain the optimal viewpoints, an information-driven viewpoint planning method is proposed. Combined with the real-time viewpoint adjustment strategy, the viewpoint of the vision probe is dynamically fine-tuned, which can effectively balance the scanning precision and motion cost. In the text anomaly detection phase, a three-stage tire text anomaly detection method based on deep learning and statistics strategy is proposed, which can accurately detect and recognize tire text, identify sub-mold categories, and judge text anomalies. Experimental results show that the proposed mechanism and method perform well in terms of accuracy ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$&gt;$</tex-math> </inline-formula> 96%) and efficiency (time per lap for a tire is less than 9 s); it shows that the proposed mechanism and method have certain industrial application value and can be applied to tire quality inspection of on-line production. <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Note to Practitioners</i> —Tire text may be incorrectly embossed during tire manufacturing. Due to the wide variety of tire specifications, poor contrast, and thin text strokes, it is difficult to detect abnormal tire text. In this paper, a 3D vision-based mechanism and method is developed to address this issue. Using a specially designed composite vision probe and scanning method, the mechanism can observe tiny text information on tires of different specifications from multiple angles and directions. By using our tire text anomaly detection method based deep learning and statistics strategy, the mechanism can accurately and robustly detect the region and content of abnormal text. The mechanism is efficient (with a detection time of less than 9 s per lap for one tire) and accurate ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$&gt;$</tex-math> </inline-formula> 96%), indicating that it has great potential in the first inspection or quality inspection step of tire manufacturing in industrial scenarios.

An Angle Precision Evaluation Method of Rotary Laser Scanning Measurement Systems with a High-Precision Turntable

Rotary laser scanning measurement systems, such as the workshop measurement positioning system (wMPS), play critical roles in manufacturing industries. The wMPS realizes coordinate measurement through the intersection of multiple rotating fanned lasers. The measurement model of multi-laser plane intersection poses challenges in terms of accurately evaluating the system, making it difficult to establish a standardized evaluation method. The traditional evaluation method is based on horizontal and vertical angles derived from scanning angles, which are the direct observation of wMPS. However, the horizontal- and vertical-angle-based methods ignore the assembly errors of fanned laser devices and mechanical shafts. These errors introduce calculation errors and affect the accuracy of angle measurement evaluation. This work proposes a performance evaluation method for the scanning angle independent of the assembly errors above. The transmitter of the wMPS is installed on a high-precision turntable that provides the angle reference. The coordinates of enhanced reference points (ERP) distributed in the calibration space are measured by the laser tracker multilateration method. Then, the spatial relationship between the transmitter and the turntable is reconstructed based on the high-precision turntable and the good rotational repeatability of the transmitter. The simulation was carried out to validate the proposed method. We also studied the effect of fanned laser devices and shaft assembly errors on horizontal and vertical angles. Subsequently, the calibration results were validated by comparing the residuals with those derived from the space-resection method. Furthermore, the method was also validated by comparing the reference and scanning angles. The results show that the maximum angle measurement error was approximately 2.79″, while the average angle measurement error was approximately 1.26″. The uncertainty (k = 1) of the scanning angle was approximately 1.7″. Finally, the coordinate measurement test was carried out to verify the proposed method by laser tracker. The results show that the average re-scanning error was 2.17″.

Modeling and digital calibration for the mirror normal pointing error of the 2D scanning reflector.

The 2D scanning reflector (2DSR) has been widely used in various important opto-mechanical systems. The pointing error of the mirror normal of the 2DSR will greatly affect the optical axis pointing accuracy. In this work, a digital calibration method for the pointing error of the mirror normal of the 2DSR is researched and verified. At first, the error calibration method is proposed based on the datum, which consists of a high-precision two-axis turntable and the photoelectric autocollimator. All the error sources, including the assembly errors and the datum errors in the calibration are analyzed comprehensively. Then the pointing models of the mirror normal are derived from the 2DSR path and the datum path by using the quaternion mathematical method. Additionally, the pointing models are linearized by the Taylor series first-order approximation of the error parameter trigonometric function items. The solution model of the error parameters is further established by using the least square fitting method. In addition, the procedure of the datum establishment is introduced in detail to strictly control the datum error to be small enough, and the calibration experiment is carried out subsequently. At last, the errors of the 2DSR are calibrated and discussed. The results show that the pointing error of the mirror normal of the 2DSR decreases from 365.68 to 6.46 arc seconds after the error compensation. The consistency of the error parameters of the 2DSR calibrated by digital calibration and physical calibration verifies the effectiveness of the digital calibration method proposed in this paper.

A Method for Improving the Precision of FOG Scaling Coefficient Calibration Based on the High Precision Turntable

Aiming at the problem that the calibration accuracy of FOG depends on the precision of turntable, the relationship between the rotation excitation mode calibration and system-level calibration of FOG and the precision of turntable is analyzed. Firstly, the error model of fog is given, and the optimal rotation path is designed based on the principle of rotation excitation mode calibration. The rotation excitation mode calibration and system-level calibration simulation are carried out respectively. The comparison results show that when the precision of the turntable is 1”, the scale coefficient error of the rotation excitation mode calibration is about 60% lower than that of the system calibration. Through further simulation, it is found that the scale coefficient error of the gyroscope calibrated with 10 turns of the turntable is about 50% lower than that of the gyroscope calibrated with 5 turns, and the scale coefficient error can be effectively reduced by increasing the number of turns of the turntable. Finally, the actual experiment is carried out, and it is proved that the calibration accuracy of the rotating excitation mode is higher than that of the system level when the precision of the turntable is higher, which has a certain practical significance for improving the precision of the inertial navigation beacon.

Optimal Path Planning Method for IMU System-Level Calibration Based on Improved Dijkstra’s Algorithm

The calibration path of system-level calibration directly affects the incentive effect of the error term and thus the calibration accuracy. Currently, the planning of system-level calibration paths is predominantly designed based on personal experience, resulting in insufficient incentive for error terms, low calibration accuracy, and long calibration times. Therefore, this study proposes a system-level calibration optimal path planning method based on an improved Dijkstra’s algorithm. First, the system-level calibration optimal path planning problem was modeled as a multi-fork regular root tree model, and the adaptability of Dijkstra’s algorithm was improved. Second, a 30-dimensional Kalman filter model was designed for system-level calibration. Then, simulation experiments were conducted, and the results demonstrated that the calibration accuracy of the error term reached 90% within 330 s. Finally, a Micro-Electro-Mechanical system (MEMS) inertial sensor, model PA-IMU488B, was used for experimental verification, and the results were compared with the discrete calibration results. The results indicate that the bias and scale factor errors of the MEMS inertial sensor reached the target accuracy within 5 min. The optimal path planning method for system-level calibration proposed in this study is not dependent on a high-precision turntable, is applicable to sensors of different accuracies, and decreases calibration time while ensuring calibration accuracy.

Design and Experiment for N = 3 Wineglass Mode Metal Cylindrical Resonator Gyroscope Closed-Loop System

This paper studies a kind of gyro structure of N = 3 Wineglass Mode Metal Cylindrical Resonator Gyroscope (WMMCRG). Compared with traditional Cylindrical Vibrating Gyroscope (CVG), the designed structure has higher scale factor and lower frequency split. This paper provides a more specific processing method and the parameters of resonator materials. A closed-loop controlling system with low error and low noise is designed for WMMCRG. The system is composed of three independent closed-loop systems: drive closed-loop, sensing closed-loop, and quadrature error correction closed-loop. Through the test of the high-precision turntable, under the premise of the same material and processing technology, the bias instability, bias stability, zero bias, Angular Random Walk (ARW), and frequency split of WMMCRG is 1.974°/h, 10.869°/h, 10.3323°/s, 16 (°)/√h, 0.02 Hz, respectively.

Three-Step Autonomous Calibration Method for Low-Cost MEMS Inertial/Magnetic Sensors

The inherent error of low-cost microelectromechanical system (MEMS) inertial/magnetic sensor directly affects the measurement accuracy of attitude and heading reference system (AHRS), and the error calibration of inertial/magnetic sensor can significantly improve its performance and measurement accuracy. Based on the above problem existing in the magnetometer, accelerometer, and rate gyro (MARG) sensors, this article proposes a new three-step auxiliary autonomous calibration method (TSAAC) based on the combination of MEMS inertial/magnetic sensors, and the effectiveness and feasibility of the proposed method are jointly verified through numerical simulation and physical verification. The experimental results show that the actual calibration effect of the TSAAC is close to the calibration effect assisted by the high-precision turntable, which can achieve the autonomous calibration of the inertial/magnetic sensor combination without any external equipment assistance.

Design, Optimization, and Compensation of a High-Precision Single-Excitation Absolute Capacitance Angular Encoder up to ±4$^{\prime\prime}$

This paper presents a single-excitation absolute capacitive rotary encoder that is small in size, lightweight, robust, and highly precise. The encoder consists of two plates: a rotor and a stator. The rotor consists of a planar coupling ring, a petal-form sensitive electrode, and a rough sensitive electrode, whereas the stator consists of a planar excitation ring and eight groups of collection electrodes. First, the two sensitive electrodes together with the eight sets of collection electrodes encode the angular position into amplitude-modulated signals, which are read out by a single-excitation electronic system. High-precision absolute position information is obtained by using the combination of 36 petal-form sensitive electrodes and a rough sensitive electrode. Then, a linear programming method is used to optimize the critical dimensions of the encoder within a limited area to achieve a miniaturized design. Finally, a harmonic frequency compensation method is used to reduce repeatable and periodical measurement errors, which are caused by manufacturing, circuit, and installation errors. A prototype is fabricated and tested on a high-precision testing turntable. The measurement results show that the resolution is 0.00015° and the accuracy over the full absolute range is 0.0022°, indicating that the encoder has considerable potential for use in high-precision applications.

In-Field Calibration Method for DTG IMU Including g-Sensitivity Biases

Navigation performance can be significantly enhanced by the inertial measurement unit (IMU) calibration. Aiming at the dynamically tuned gyro IMU, a novel in-field calibration method is proposed in this paper. Taking gravity and earth’s rotation rate as a reference, all accelerometer errors, the constant biases, and the g-sensitivity biases of gyro can be calibrated using the unscented Kalman filter based on the norm-observed method. The scale factor errors and installation errors of gyro can be estimated though the Kalman filter with velocity errors as observation. In order to guarantee that all error parameters are observable, a 26-position and its optimized 12-position rotation schemes are designed. The proposed method can achieve correct calibration without a high-precision turntable. Besides, it can improve the ability of analysis and the deviation of interference sources when some error parameters are calibrated unreasonable. The simulations and in-field calibration experiments are conducted to verify the effectiveness of the proposed method. The simulations demonstrate that the calibration accuracy of two schemes is almost equivalent. Compared with the system-level calibration, the calibration results of two schemes are within a reasonable range. The semi-physical simulations indicate that finding out and separating interference sources can be achieved easily with the proposed method. Thus, the proposed method has great application values in in-field calibration.

A Full-Parameter Self-Calibration Method Based on Inertial Frame Filtering for Triaxis RINS Under Swaying Base

The navigation performance of the rotational inertial navigation system (RINS) could be greatly improved by self-calibration of error parameters. The traditional instrument-level calibration depends on high-precision turntable. System-level calibration takes zero velocity as a reference to estimate error parameters. However, zero velocity is invalid in the situation of swaying base and the calibration accuracy will be decreased with the traditional method. Aiming at the swaying base environment, the filtering method for tri-axis RINS in an inertial frame is proposed in this paper. Taking the velocity errors in the inertial frame as the reference, full-parameter calibration on swaying base can be achieved. Simulation verifies the feasibility of the proposed method. Experimental results demonstrate the stability of the proposed method is better than the traditional calibration method, and it satisfies the application requirements. Thus, the proposed method has great application values under swaying base.

基于EPNP算法的单目视觉测量系统研究

The method of pose measurement using computer vision is widely used in modern control, navigation, tracking and other fields. A monocular visual pose measurement method was studied and designd based on P4P rectangular distribution of planar target and EPNP algorithm in this paper. Firstly, a single camera was used to obtain the plane target image. After the image processing, the pixel coordinates of the four feature points were obtained, and the EPNP algorithm was used to perform the attitude calculation. Secondly, the simulation analysis of pose error measurement provides theoretical guidance and basis for improving attitude measurement accuracy. Finally, a coordinate system registration method combined with a high-precision two-dimensional turntable was proposed. The method was used to verify the accuracy of the three-direction attitude angles. The experimental results show that the rotation angle around the x and y axes is[-6, 6], the pose measurement error is less than 0.1 to meet the measurement application requirements.

Plant Phenotyping: An Active Vision Cell for Three-Dimensional Plant Shoot Reconstruction.

Three-dimensional (3D) computer-generated models of plants are urgently needed to support both phenotyping and simulation-based studies such as photosynthesis modeling. However, the construction of accurate 3D plant models is challenging, as plants are complex objects with an intricate leaf structure, often consisting of thin and highly reflective surfaces that vary in shape and size, forming dense, complex, crowded scenes. We address these issues within an image-based method by taking an active vision approach, one that investigates the scene to intelligently capture images, to image acquisition. Rather than use the same camera positions for all plants, our technique is to acquire the images needed to reconstruct the target plant, tuning camera placement to match the plant's individual structure. Our method also combines volumetric- and surface-based reconstruction methods and determines the necessary images based on the analysis of voxel clusters. We describe a fully automatic plant modeling/phenotyping cell (or module) comprising a six-axis robot and a high-precision turntable. By using a standard color camera, we overcome the difficulties associated with laser-based plant reconstruction methods. The 3D models produced are compared with those obtained from fixed cameras and evaluated by comparison with data obtained by x-ray microcomputed tomography across different plant structures. Our results show that our method is successful in improving the accuracy and quality of data obtained from a variety of plant types.

An Improved Fast Self-Calibration Method for Hybrid Inertial Navigation System under Stationary Condition

The navigation accuracy of the inertial navigation system (INS) can be greatly improved when the inertial measurement unit (IMU) is effectively calibrated and compensated, such as gyro drifts and accelerometer biases. To reduce the requirement for turntable precision in the classical calibration method, a continuous dynamic self-calibration method based on a three-axis rotating frame for the hybrid inertial navigation system is presented. First, by selecting a suitable IMU frame, the error models of accelerometers and gyros are established. Then, by taking the navigation errors during rolling as the observations, the overall twenty-one error parameters of hybrid inertial navigation system (HINS) are identified based on the calculation of the intermediate parameter. The actual experiment verifies that the method can identify all error parameters of HINS and this method has equivalent accuracy to the classical calibration on a high-precision turntable. In addition, this method is rapid, simple and feasible.

Calibration error analysis of inertially stabilized platforms using quaternions and octonions in rotation decomposition

In the calibration process of the inertially stabilized platforms with a high-precision turntable and an autocollimator, significant calibration errors can result from the axis misalignments between the inertially stabilized platforms and the turntable. Based on the relationship between spatial rotations and quaternions or octonions, this article proposes a representation using octonions to realize the decomposition of the rotation axis in two perpendicular axes and subsequently derives the calibration error model. The test results demonstrated that the error is significantly improved after compensation. The azimuth variance is reduced from 0.1379(°)2 to 0.0492(°)2, which offers a more accurate set of data for further compensation based on the error model of the platform itself.

Calibration of laser inertial navigator with dual-axis rotation

The calibration of inertial measurement units (IMU) is required to determine the coefficients in the input/output models of inertial sensors. High accuracy turntables and information on the north direction and the local level are usually required in traditional calibration methods. But for a laser inertial navigator with dual-axis rotation, in which the IMU is usually compactly designed, it is usually not convenient to remove the IMU from the navigator to high precision turntable for calibration. To improve the affordability, a simple calibration method is proposed using the dual-axis rotation function of the navigator itself. The method relaxes the orthogonality requirement of the rotation axes and eliminates the need of north information. Rough knowledge of the local plumb-line direction is enough to determine the signs of accelerometer calibration parameters. No re-installation of the IMU is required during the calibration and thus it makes automatic calibration easy to implement. Simulations show that the proposed method is feasible. The proposed method is also tested on an experimental laser inertial navigator with dual-axis rotation, and the navigation results show that the calibration accuracy meets the requirements of high performance inertial navigations.

Optimal artificial fish swarm algorithm for the field calibration on marine navigation

With the rapid development of the optic gyrocompass in aerospace and marine navigation systems, as well as the characteristics of the long-running navigation system which are utilized in this study has created unique developments in the field of marine navigation. It is necessary to re-calibrate the inertial measurement unit (IMU) parameters for maintaining the accuracy and reliability of the system. However, the conventional system re-calibration method needs to disassemble the system and move back to the indoor laboratory with high precision turntable, which is costly and has a heavy workload. This study proposes a novel calibration method by using the optimal artificial fish swarm algorithm (AFSA) on a vehicle aided by a computer. The algorithmic principle is described in detail, and the results obtained from both the simulation and the navigation experiments show the proposed calibration method can meet the calibration accuracy and reliability requirements of the marine gyrocompass.

The Research of High-Precision Turntable’s Countertop Tilting Dynamic Testing Technology

The dynamic tilting of high-precision turntable has a very significant impact on the parameters of measurement and processing during the operation.In order to achieve long-term stability and control the turntable’s dynamic tilting angle at the second level, only improving the mechanical precision of the turntable is not realistic, and it may greatly enhance the cost of the turntable. A precision turntable dynamic tilting test method based on laser and CCD technology is put forward in this paper. The system uses laser as the light source, and uses CCD image sensor to receive the reflected signal of the turntable. According to the amount movement of the laser spot on the CCD target surface and the corresponding geometric relationships, we can measure the inclination error of the turntable. During debugging analysis and practical application, it proves that the system can achieve differentiate accuracy at the second level and meet the needs of online measurement.