scholarly journals Measurement Method for Nonlinearity in Heterodyne Laser Interferometers Based on Double-Channel Quadrature Demodulation

Sensors ◽  
2018 ◽  
Vol 18 (9) ◽  
pp. 2768 ◽  
Author(s):  
Haijin Fu ◽  
Ruidong Ji ◽  
Pengcheng Hu ◽  
Yue Wang ◽  
Guolong Wu ◽  
...  
Keyword(s):  
Measurement Method ◽  
Reference Signal ◽  
Doppler Frequency ◽  
Uniform Motion ◽  
Quadrature Demodulation ◽  
External Reference ◽  
Heterodyne Laser Interferometer ◽  
Laser Interferometers ◽  
Double Channel ◽  
Better Than

The phase quadrature measurement method is capable of measuring nonlinearity in heterodyne laser interferometers with picometer accuracy whereas it cannot be applied in the new kind of heterodyne interferometers with bidirectional Doppler frequency shift especially in the condition of non-uniform motion of the target. To solve this problem, a novel measurement method of nonlinearity is proposed in this paper. By employing double-channel quadrature demodulation and substituting the external reference signal with internal ones, this method is free from the type of heterodyne laser interferometer and the motion state of the target. For phase demodulation, the phase differential algorithm is utilized to improve the computing efficiency. Experimental verification is carried out and the results indicate that the proposed measurement method achieves accuracy better than 2 pm.

The Study of Four-Position North Seeking System under Vibration Environment

2014 ◽  
Vol 668-669 ◽  
pp. 990-993
Author(s):  
Ming Hui Zong ◽  
Deng Hua Li
Keyword(s):  
Fiber Optic ◽  
Reference Signal ◽  
Vibration Signal ◽  
Pi Controller ◽  
Angle Sensor ◽  
The North ◽  
External Reference ◽  
Tilt Sensor ◽  
The Relationship ◽  
Better Than

In order to develop north seeking system with strong anti-interference ability, the influence caused by the swaying base on the performance of north seeker was investigated. The influence of sinusoidal signal of gyros and tilt sensor's output was analyzed based on four-position north seeking system which was consisted of a single axis gyro and a tilt sensor. Fiber optic gyros and tilt sensor are interference by the same vibration signal, according to the relationship between the output signal of gyro and the angle sensor, a PI controller was designed to compensate the gyro's output error. This real time compensation can effectively improve the north seeking accuracy and speed without complicated calculation or external reference signal. The north seeking accuracy is better than 0.03o. Simulation and actual north seeking result proved that this method significantly improves the north seeking performance in vibrant environment.

Model and Measurement Method of Optical Nonlinearities Caused by the Heterodyne and Homodyne Interference Terms in the Heterodyne Interferometer

2014 ◽  
Vol 613 ◽  
pp. 58-63
Author(s):  
Hai Jin Fu ◽  
Jiu Bin Tan ◽  
Peng Cheng Hu ◽  
Zhi Gang Fan
Keyword(s):  
Measurement Method ◽  
Laser Interferometer ◽  
Optical Nonlinearity ◽  
Laser Source ◽  
Optical Nonlinearities ◽  
Laser Polarization ◽  
Heterodyne Interferometer ◽  
Optical Mixing ◽  
Ultra Precision ◽  
Heterodyne Laser Interferometer

The heterodyne laser interferometer is widely applied in ultra-precision displacement measurement, but its accuracy is seriously restricted by the optical nonlinearity which arises from the optical mixing in the reference and measurement arms. In an ideal heterodyne laser interferometer, the beam from the laser source consists of two orthogonally linear-polarized components with slightly different optical frequencies and the two components can be completely separated by the polarizing optics, one traverses in the reference arm, the other traverses in the measurement arm, both of them are in the form of a pure optical frequency. However, in a real heterodyne laser interferometer, due to the imperfect laser polarization, the optics defect and the misalignment, the two components of the laser beam cant be perfectly separated, therefore both of the reference arm and the measurement arm contain a portion of the two laser components, which leads to an optical mixing in the two arms of the heterodyne interferometer and causes the cyclic nonlinearity of several to tens of nanometers.

scholarly journals VI. On a new astronomical clock, and a pendulum governor for uniform motion

1869 ◽  
Vol 17 ◽  
pp. 468-470
Keyword(s):  
Uniform Motion ◽  
Geometrical Transformation ◽  
Astronomical Clock ◽  
The Dead ◽  
Better Than

It seems strange that the dead-beat escapement should still hold its place in the astronomical clock, when its geometrical transformation, the cylinder escapement of the same inventor, Graham, only survives in Geneva watches of the cheaper class. For better portable time-keepers, it has been altered (through the rack-and-pinion movement) into the detached lever, which has proved much more accurate. If it is possible to make astronomical clocks go better than at present by merely giving them a better escapement, it is quite certain that one on the same principle as the detached lever, or as the ship-chronometer escapement, would improve their time-keeping. But the inaccuracies hitherto tolerated in astronomical clocks may be due more to the faultiness of the mercury compensation pendulum, and of the mode in which it is hung, and of the instability of the supporting clock-case or framework, than to imperfection of the escapement and the greatness of the arc of vibration which it requires ; therefore it would be wrong to expect confidently much improvement in the time-keeping merely from improvement of the escapement. I have therefore endeavoured to improve both the compensation for change of temperature in the pendulum, and the mode of its support, in a clock which I have recently made with an escapement on a new principle, in which the simplicity of the dead-beat escapement of Graham is retained, while its great defect, the stopping of the whole train of wheels by pressure of a tooth upon a surface moving with the pendulum, is remedied.

Real-Time Measurement Method of Doppler Based on GPS Carrier Signals

2012 ◽  
Vol 226-228 ◽  
pp. 2050-2055 ◽  
Author(s):  
Shao Feng Dong ◽  
Bao Qiang Du ◽  
Wei Zhou
Keyword(s):  
Frequency Shift ◽  
Real Time ◽  
Measurement Method ◽  
Dynamic Range ◽  
Time Synchronization ◽  
Influencing Factor ◽  
Doppler Frequency ◽  
Time Measurement ◽  
Time Frequency ◽  
Real Time Measurement

According to Doppler effect of satellite on the time synchronization technology between satellite and the ground station, a real-time measurement method of Doppler is proposed based on GPS carrier signals. Using Doppler observations from GPS receiver, the method can real-timely measure Doppler frequency shift of GPS including dynamic Doppler and media Doppler whose error can be timely modified in the receiver end. Simulation results show that the frequency shift caused by dynamic Doppler, a main influencing factor in the course of transmission of time-frequency signal by GPS satellite, is between plus or minus several thousands Hz. Comparing to traditional measurement method of Doppler, the method makes it possible to fast track phase of signal in large dynamic range in synchronous technology.

Calibrator for 2D Grid Plate Using Imaging Coordinate Measuring Machine with Laser Interferometers

2015 ◽  
Vol 9 (5) ◽  
pp. 541-545 ◽  
Author(s):  
Mariko Kajima ◽  
◽  
Tsukasa Watanabe ◽  
Makoto Abe ◽  
Toshiyuki Takatsuji
Keyword(s):  
Measurement Method ◽  
Laser Interferometer ◽  
Coordinate Measuring Machine ◽  
Calibration Procedure ◽  
Expanded Uncertainty ◽  
Geometrical Error ◽  
Grid Plate ◽  
Measuring Machine ◽  
Laser Interferometers

A calibrator for 2D grid plates have been developed. The calibrator was based on a commercial imaging coordinate measuring machine (imaging CMM). A laser interferometer for the calibration of the x-coordinate and two laser interferometers for the calibration of the y-coordinate were attached to the imaging CMM. By applying multistep measurement method for the calibration procedure, the geometrical error in the calibrator was reduced. The calibration of a precision 2D grid plate was demonstrated, and the expanded uncertainty was estimated to be 0.2 μm (k =2).

scholarly journals Direction of Arrival Estimation Accuracy Enhancement via Using Displacement Invariance Technique

2015 ◽  
Vol 2015 ◽  
pp. 1-10
Author(s):  
Youssef Fayad ◽  
Caiyun Wang ◽  
Qunsheng Cao ◽  
Alaa El-Din Sayed Hafez
Keyword(s):  
Performance Enhancement ◽  
Doppler Frequency ◽  
Direction Of Arrival ◽  
Estimation Accuracy ◽  
Direction Of Arrival Estimation ◽  
Target Movement ◽  
Nonlinearity Effect ◽  
Esprit Algorithm ◽  
Cramer Rao Bound ◽  
Better Than

A new algorithm for improving Direction of Arrival Estimation (DOAE) accuracy has been carried out. Two contributions are introduced. First, Doppler frequency shift that resulted from the target movement is estimated using the displacement invariance technique (DIT). Second, the effect of Doppler frequency is modeled and incorporated into ESPRIT algorithm in order to increase the estimation accuracy. It is worth mentioning that the subspace approach has been employed into ESPRIT and DIT methods to reduce the computational complexity and the model’s nonlinearity effect. The DOAE accuracy has been verified by closed-form Cramér-Rao bound (CRB). The simulation results of the proposed algorithm are better than those of the previous estimation techniques leading to the estimator performance enhancement.

scholarly journals Design controler of the quasi-time optimization approach for stabilizing and trajectory tracking of inverted pendulum

2018 ◽  
Vol 226 ◽  
pp. 02007 ◽  
Author(s):  
Nguyen Xuan Chiem ◽  
Hai Nguyen Phan
Keyword(s):  
Inverted Pendulum ◽  
External Disturbance ◽  
Reference Signal ◽  
Lyapunov Stability Theory ◽  
Vertical Position ◽  
Control Law ◽  
Optimization Approach ◽  
Time Control ◽  
Time Optimization ◽  
Better Than

This article describes the method of stabilizing and tracking the trajectory of the inverted pendulum with the quasi-time optimization approach. The controller proposed in this paper is not only to stabilize the inverted pendulum in a vertical position but also to cause the inverted pendulum to follow a predetermined reference signal even when there is an interference effect. The focus of this project is the design of a quasi-time control law based on the quasi-time optimization approach and Lyapunov stability theory. The simulation and experimental results suggest that the proposed controller controls the inverted pendulum balance and cart position stability which are better than the LQR method even when there is an external disturbance effect.

Measurement of Impulse Grounding Resistance

2012 ◽  
Vol 546-547 ◽  
pp. 289-294
Author(s):  
Hua Jing Shen
Keyword(s):  
Measurement System ◽  
Measurement Method ◽  
Frequency Measurement ◽  
Grounding Resistance ◽  
Result Show ◽  
Better Than ◽  
Software Scheme

A kind of measurement method of impulse grounding resistance is proposed. The measurement method of impulse grounding resistance is also analyzed and discussed theoretically. The hardware and software scheme of measurement system is given. The method of simulation of thunder current and transformation calculation is better than the method of work-frequency measurement by the analysis and comparison. By using the method, the thundering course can not only be simulated , but also the impulse grounding resistance can be calculated directly in the scene. In the end, a simulation result is given. Simulation result show that the method proposed in the paper is effective and feasible.

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