Research on Variable Baseline Coherent Angle Measurement Based on Nutation Scanning

In order to meet the requirement of high precision and micro-angle measurement on orbit, a self-calibrated optical non-contact real-time monitoring device is designed. Within three meters, the micro-angle variable of target relative to measuring basis can be measured in real-time. The range of angle measurement is ±50′′, the angle measurement accuracy is less than 2′′. The equipment can realize high precision real-time monitoring the micro-angle deformation, which caused by high strength vibration and shock of rock launching, sun radiation and heat conduction on orbit and so on.

An optical lever by using a mode-locked laser for angle measurement

Accurate and reliable angle and rotational speed measurement is crucial in various industrial and scientific applications. This paper develops a cost-effective, real-time system for angle and rotational speed measurement Using magnetic sensors. The setup comprises a magnetic sensor arranged around a turntable with a DC motor-driven magnet. Sensor signals are amplified and converted to digital via the ADC of an STM controller, with a high-precision timer recording relevant signal intervals. Processed data are framed per the USART protocol for transmission to a host computer. At the software layer, callback functions identify frame headers/tails for data extraction, filter signals via a low-pass filter to reduce noise, and enable real-time angular position display. System accuracy is validated through mathematical fitting to model and calibrate the sensor output-physical angle relationship, ensuring high precision and reliability with a measurement error as low as 0.6 °.

Precise Cobb Angle Measurement System Based on Spinal Images Merging Function

In order to determine the reliability of the Cobb angle measurement as it is used in the clinical management of scoliosis, a methodological survey was carried out. In the measurement of a Cobb angle two phases can be distinguished: (a) the production of a spinal radiograph and (b) the measurement of the angle itself. In respect of the first phase, the variation in production of the radiographs was calculated on Cobb angle measurements made by one investigator on serial radiographs of patients who underwent spinal fusion for scoliosis and therefore had a fixed spinal curvature. For the second phase, the accuracy of Cobb angle measurement was investigated by comparing measurements on the same radiographs of 46 scoliosis patients obtained by three investigators, namely two orthopaedic surgeons and an orthopaedic fellow who was assigned to a school screening project. Results were expressed as a Spearman correlation coefficient and a standard deviation of the differences. The Spearman correlation coefficient was 0.98 for the repeated radiographs (production variation) and also 0.98 for the repeated measurements on one radiograph (interobserver measurement variation). The standard deviation of the differences in Cobb angle for the repeated radiographs amounted to 3.2 degrees and for the repeated measurements on one radiograph it was 2.0 degrees. Although there is a good reproducibility of the Cobb angle measurement between different investigators, the variation in production of a spinal radiograph is an important source of error. This should be taken into account when making decisions in scoliosis management.

We demonstrate a full range rotational angle sensor system using two chemical etching intrinsic Fabry–Perot interferometers (FPIs) fabricated by an electrical arc discharge technique. The use of magnetic scale, combined packaged FPI detectors, allows the exploration of position characteristic with direction discrimination. Numerical simulation is employed for optimizing the distance $(d)$ between the detector and the circle magnetic scale. Experiments and numerical simulation show the interference dip shifts of FPI have sinusoidal relation with the rotational angle, as d ranging from 1 to 2.5 mm. Measurements showed five times ( $d=1$ ) and four times ( $d=1.5$ ) of magnitude greater than FBG detectors, with the linearity of 0.993 and 0.999, respectively. The sinusoidal function variations are displayed by two detectors with a phase difference of 90 degrees, which help to discriminate rotational direction. Moreover, two detectors have a low temperature cross-sensitivity of 2.3 pm/C°. The important advantage of our rotational angle sensor is their angle measurement range without limitation.

In the system of distributed radar array system using phase interference angle measurement, the phase center coordinate error of arrays and the phase difference error have relatively large influence on the angle measurement. The phase center position is often inconsistent with physical center position. Thus it is necessary to compensate these errors precisely. Far field radiation sources are often used to calibrate radar in traditional calibration methods. However, it is usually hard to achieve far field radiation sources for distributed radar array with large space between units surveilling space targets. In this paper, a calibration method based on the precise ephemeris of refined orbit satellites without measuring with special instruments is proposed. The phase error caused by coordinate error can be whitened by the precise ephemeris of multiple arcs, and the coordinate and phase difference will be searched out by matching the minimum variance. This method can get the errors easily. The simulation results and actual data verify that angle measurement accuracy gets large improvement by the method.

Effects of the wedge prism angle on the accuracy of angle measurement using the transmitted phase shifting differential interference contrast (DIC) technique were studied in this paper. The optical model was constructed and serious of simulations were conducted to fulfill this study. Various prism angles were tested in the simulations. As expected, results indicated that the reconstructed wedge angle measured by the DIC system was incorrect because the light propagation became irregular. Regardless of the profile reconstruction result, the original optical path differences of light were highly correlated to the prism angle. Therefore, modification is needed to calculate the wedge angle accurately when the DIC approach is adopted. It is also found that the magnification of the objective lens (correspond to the numerical aperture and the working distance) have significant effects on the measurement. These results suggest that modification is needed to calculate the wedge angle accurately when the DIC approach is adopted. This study might provide some valuable information for adopting the DIC technique when it comes to complex geometry measurement in the future.

The photoelectric rotary and angle encoder is a digital angle measuring device, which is integrated with optics, mechanics and electrics. Because of its simple structure, high resolution, and high accuracy, it has been widely used in precision measurement of angle, digital control and digital display system. With the needs of fast tracking and accurate orientation on the horizon and air targets, putting forward higher requirements on accuracy of angle measurement and resolution of photoelectric rotary and angle encoder. Influences of manufacturing, electronics segmentation, optical and mechanical structure and eccentric shaft to photoelectric encoder precision and reducing methods are introduced. Focusing on the eccentricity error, building up an error correction model to improve the resolution of angle encoder and the model was verified by test.

Vector field measurement is demonstrated with an all-optical scalar atomic magnetometer using intrinsic parameters related to its scalar operation. The Bell-Bloom type atomic magnetometer measures the Larmor precession of cesium atoms through on-resonant absorption of a probe beam. While the AC component of the probe signal is used for the field magnitude measurement, the probe DC signal contains information about the polar angle, defined as the angle between the magnetic field and the probe beam. Additional polar angle information is obtained from the light-shift-induced magnetic field caused by the frequency modulation of the probe beam. With a measurement time of 100 ms, better than 0.02° sensitivity has been achieved using a commercial miniaturized sensor at the optimal sensor orientation. The angle measurement accuracy is checked against an optical encoder over the entire polar angle range of 0°–180°. Better than 1° error is recorded over most set polar angles. Azimuthal angle measurement is also exhibited with two orthogonally oriented sensors.

In order to balance a rotor, the standard rotor balancing methods involve measurement of vibration amplitude and vibration phase angle. But accurate phase angle measurement is generally difficult because vibration phase is sensitive to speed variations and it is difficult to maintain a constant speed in operating condition. Also, phase angle measurement requires very high end instrumentation for accurate phase angle measurement. Number of trial runs during balancing process also plays an important criterion in deciding the effectiveness of that method. A Method is considered to be more effective if it balances a rotor in less number of trial runs. This paper presents a novel rotor balancing method called amplitude subtraction method in which vibration amplitudes are measured only. Performance of this method is analysed by a comparative study with phase angle based rotor balancing method (trim balancing method). Trim balancing and amplitude subtraction method are compared on the basis of its accuracy and number of trial runs during balancing process. The results of experimentation demonstrate successful implementation of proposed method.

Spin is a kind of complicated, dangerous and abnormal flight status when airplane stalls in the air. Spin and recovery research is usually done in vertical wind tunnel test. This method has the advantages of low-cost, short cycle and so on. For the measurement of spin attitude angles, a set of stereo vision measurement system using two CCD cameras and other equipments is built. By the research of coordinate system transformation and digital image processing algorithms, 3D parameters of man-made markers of the model surface are obtained, and the measurement of spin attitude angles is realized. The test results show that the technology has the features of non-contact, high recognition rate and flexibility, the measurement accuracy of attitude angles reaches 0.1 °.

Skin movement errors in measurement of sagittal lumbar and hip angles in young and elderly subjects

The accuracy of side-slip angle and yaw rate measurements is important in vehicle motion control. However, vehicle side-slip angle measurement is difficult. In general, side-slip angle can be estimated by observer. In this paper, we propose a vehicle state estimation method based on Moving Horizon Estimation (MHE) using acceleration sensor and gyro sensor. Measurement data of inertial sensor has large noise, since S/N ratio is small, especially if estimation object is a light weight vehicle. Moreover, outlier of yaw rate measurement value is caused by road surface disturbance. MHE is used for vehicle state estimation that can suppress the measurement noise on inertial sensors. In this paper, we show the efficacy of the proposed method through the simulation.

A novel hollow cylindrical cube-corner reflector (HCCCR) for the autocollimator (AC) is proposed. The angle measuring range of AC will be effectively increased by using the parallel propagation characteristics of the reflected light and the incident light in local area of this reflector. And the yaw and pitch angles of HCCCR will be measured through the morphological changes of the reflected beam. The experimental results show that the measuring range of the autocollimation angle measurement method is extended from ±30' to ±30°, and the dynamic measurement distance is 0.2∼5m, the measurement accuracy of pitch angle and yaw angle is better than 69" and 51", respectively.