A Vertical Seismometer With Build-in Retroreflector for Absolute Gravimetry

2018 ◽  
Author(s):  
Meiying Guo ◽  
Kang Wu ◽  
Jiamin Yao ◽  
Jin Qian ◽  
Lijun Wang
Keyword(s):  
Transfer Function ◽  
Ground Vibration ◽  
Free Fall ◽  
Correction Method ◽  
Step Response ◽  
Broadband Seismometer ◽  
Loop Control ◽  
Modified Method ◽  
Absolute Gravimetry ◽  
Feedback Voltage

A free-fall absolute gravimeter uses a Mach-Zehnder interferometer to track the free-falling object. Theoretically, it needs an inertial reference point, which is a reference retroreflector keeping static in inertial frame for an accurate absolute gravimetry. Practically, the reference retroreflector is always disturbed by the ground vibration. Traditionally, a vibration correction method with a broadband seismometer is used to reduce the effect of the ground vibration. The transfer function between the reference retroreflector and the seismometer is hypothesized as a proportional element with time delay. The difference between the hypothesized and the real transfer function limits the effect of the vibration correction. On this basis, a modified method, replacing the sensitive element of a seismometer with the reference retroreflector, is proposed. The motion of the reference retroreflector is measured directly by differential parallel plate capacitance detection. A closed-loop control circuit produces feedback voltage to make the reference retroreflector track the ground vibration. The feedback voltage represents the reference retroreflector’s motion directly. Experiments show the capacitance detecting circuit detects the displacement of the reference retroreflector relative to the ground with a resolution of 0.6 nm at 500 Hz. The acceleration resolution of the homemade vertical seismometer is about 10 mGal. The sensitivity of the seismometer is 316 V/g. The damp ratio of the homemade seismometer is little, and the natural frequency of the homemade seismometer is 104 Hz by analyzing the step response of the system. The bandwidth of the system is around 175 Hz. In the future, the homemade seismometer will be applied in absolute gravimeters for hostile measurement.

Vibration Correction With Kalman Filtering Based Data Fusion for Absolute Gravimeters

2019 ◽  
Author(s):  
Yi Wen ◽  
Kang Wu ◽  
Zhenxing Li ◽  
Jiamin Yao ◽  
Meiying Guo ◽  
...  
Keyword(s):  
Standard Deviation ◽  
Kalman Filtering ◽  
Ground Vibration ◽  
Free Fall ◽  
Vibration Signal ◽  
Correction Method ◽  
Fusion Method ◽  
Absolute Gravimeter ◽  
Single Sensor ◽  
Better Than

Abstract Free-fall absolute gravimeters are important classical high precision absolute gravimeters in many branches of scientific research. But its performance is always troubled by the ground vibration. Vibration correction method is used to correct the result by detecting the ground vibration with sensors. A Kalman filter based fusion method is proposed to obtain more accurate ground vibration signal by fusing the outputs of the seismometer and the accelerometer. Experiment is conducted with the homemade T-1 absolute gravimeter, the standard deviation of the corrected results using seismometer data and fused data are 586.32 μGal (1 μGal = 10−8 m/s2) and 508.59 μGal respectively, much better than the uncorrected result’s 6548.96 μGal. The results prove the superiority of fused data over data measured from single sensor. It is believed that the application scene of the vibration correction will be broadened and the performance of the vibration correction will also be improved by using the proposed fusion method in the future.

Identifying the Optimal Controller Strategy for DC Motors

2017 ◽  
Vol 6 (4) ◽  
pp. 252
Author(s):  
M. R. Qader
Keyword(s):  
Transfer Function ◽  
Angular Rate ◽  
Linear Quadratic Regulator ◽  
System Stability ◽  
Step Response ◽  
Phase Lag ◽  
Linear Quadratic ◽  
Loop Control ◽  
Dc Motors ◽  
Tuning Methods

<p class="Default"><span>The aim of this study is to design a control strategy for the angular rate (speed) of a DC motor by varying the terminal voltage. This paper describes various designs for the control of direct current (DC) motors. We derive a transfer function for the system and connect it to a controller as feedback, taking the applied voltage as the system input and the angular velocity as the output. Different strategies combining proportional, integral, and derivative controllers along with phase lag compensators and lead integral compensators are investigated alongside the linear quadratic regulator. For each controller transfer function, the step response, root locus, and bode plot are analysed to ascertain the behaviour of the system, and the results are compared to identify the optimal strategy. It is found that the linear quadratic controller provides the best overall performance in terms of steady-state error, response time, and system stability. The purpose of the study that took place was to design the most appropriate controller for the steadiness of DC motors. Throughout this study, analytical means like tuning methods, loop control, and stability criteria were adopted. The reason for this was to suffice the preconditions and obligations. Furthermore, for the sake of verifying the legitimacy of the controller results, modelling by MATLAB and Simulink was practiced on every controller.</span></p>

scholarly journals Decoupled Multi-Loop Robust Control for a Walk-Assistance Robot Employing a Two-Wheeled Inverted Pendulum

Machines ◽  
2021 ◽  
Vol 9 (10) ◽  
pp. 205
Author(s):  
Fu-Cheng Wang ◽  
Yu-Hong Chen ◽  
Zih-Jia Wang ◽  
Chi-Hao Liu ◽  
Pei-Chun Lin ◽  
...  
Keyword(s):  
Robust Control ◽  
Transfer Function ◽  
Inverted Pendulum ◽  
Control Structure ◽  
Position Tracking ◽  
Loop Control ◽  
Wheeled Inverted Pendulum ◽  
Decoupled Control ◽  
Rotational Motions ◽  
Electrical Motors

This paper develops a decoupled multi-loop control for a two-wheeled inverted pendulum (TWIP) robot that can assist user’s with walking. The TWIP robot is equipped with two wheels driven by electrical motors. We derive the system’s transfer function and design a robust loop-shaping controller to balance the system. The simulation and experimental results show that the TWIP system can be balanced but might experience velocity drifts because its balancing point is affected by model variations and disturbances. Therefore, we propose a multi-loop control layout consisting of a velocity loop and a position loop for the TWIP robot. The velocity loop can adjust the balancing point in real-time and regulate the forward velocity, while the position loop can achieve position tracking. For walking assistance, we design a decoupled control structure that transfers the linear and rotational motions of the robot to the commands of two parallel motors. We implement the designed controllers for simulation and experiments and show that the TWIP system employing the proposed decoupled multi-loop control can provide satisfactory responses when assisting with walking.

Effect of gravity curvature on large-scale atomic gravimeters

2021 ◽  
Author(s):  
Dorothee Tell ◽  
Étienne Wodey ◽  
Christian Meiners ◽  
Klaus H. Zipfel ◽  
Manuel Schilling ◽  
...  
Keyword(s):  
Large Scale ◽  
Vibration Isolation ◽  
High Sensitivity ◽  
Free Fall ◽  
Theory Approach ◽  
Gravity Gradients ◽  
Lower Saxony ◽  
German Research Foundation ◽  
Absolute Gravimetry ◽  
Funding Program

&lt;p&gt;In terrestrial geodesy, absolute gravimetry is a tool to observe geophysical processes over extended timescales. This requires measurement devices of high sensitivity and stability. Atom interferometers connect the free fall motion of atomic ensembles to absolute frequency measurements and thus feature very high long-term stability. By extending their vertical baseline to several meters, we introduce Very Long Baseline Interferometry (VLBAI) as a gravity reference of higher-order accuracy.&lt;/p&gt;&lt;p&gt;By using state-of-the-art vibration isolation, sensor fusion and well controlled atomic sources and environments on a 10 m baseline, we aim for an intrinsic sensitivity &amp;#963;&lt;sub&gt;g&lt;/sub&gt; &amp;#8804; 5 nm/s&amp;#178; in a first scenario for our Hannover VLBAI facility. At this level, the effects of gravity gradients and curvature along the free fall region need to be taken into account. We present gravity measurements along the baseline, in agreement with simulations using an advanced model of the building and surroundings [1]. Using this knowledge, we perform a perturbation theory approach to calculate the resulting contribution to the atomic gravimeter uncertainty, as well as the effective instrumental height of the device depending on the interferometry scheme [2]. Based on these results, we will be able to compare gravity values with nearby absolute gravimeters and as a first step verify the performance of the VLBAI gravimeter at a level comparable to classical devices.&lt;/p&gt;&lt;p&gt;The Hannover VLBAI facility is a major research equipment funded by the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation). This work was supported by the DFG Collaborative Research Center 1464 &amp;#8220;TerraQ&amp;#8221; (Project A02) and is supported by the CRC 1227 &amp;#8220;DQ-mat&amp;#8221; (Project B07), Germany&amp;#8217;s Excellence Strategy EXC-2123 &amp;#8220;QuantumFrontiers&amp;#8221;, and the computing cluster of the Leibniz University Hannover under patronage of the Lower Saxony Ministry of Science and Culture (MWK) and the DFG. We acknowledge support from &amp;#8220;Nieders&amp;#228;chsisches Vorab&amp;#8221; through the &amp;#8220;Quantum- and Nano-Metrology (QUANOMET)&amp;#8221; initiative (Project QT3), and for initial funding of research in the DLR-SI institute, as well as funding from the German Federal Ministry of Education and Research (BMBF) through the funding program Photonics Research Germany.&lt;/p&gt;&lt;p&gt;[1] Schilling et al. &amp;#8220;Gravity field modelling for the Hannover 10 m atom interferometer&amp;#8221;. &amp;#160;Journal of Geodesy 94, 122 (2020)&lt;/p&gt;&lt;p&gt;[2] Ufrecht, Giese, &amp;#160;&amp;#8220;Perturbative operator approach to high-precision light-pulse atom interferometry&amp;#8221;. Physical Review A 101, 053615 (2020).&lt;/p&gt;

scholarly journals Improving Angular Accuracy of a Scanning Mirror Based on Error Modeling and Correction

Sensors ◽  
2019 ◽  
Vol 19 (2) ◽  
pp. 367 ◽  
Author(s):  
Yue Fan ◽  
Wenli Ma ◽  
Ping Jiang ◽  
Jinlong Huang ◽  
Kewei Chen ◽  
...  
Keyword(s):  
Eddy Current ◽  
Correction Method ◽  
Calculation Model ◽  
Error Model ◽  
Error Modeling ◽  
Angular Error ◽  
Displacement Sensor ◽  
Physical Parameters ◽  
Loop Control ◽  
Scanning Mirror

Scanning mirrors appear to be key components in optoelectronic systems for line-of-sight (LOS) stabilization. For improving the angular accuracy of a scanning mirror based on the eddy current displacement sensor measurement, an angular error-correction method is proposed and demonstrated. A mathematic angular error model with physical parameters was developed, and the cross-validation method was employed to determine the reasonable order of the Maclaurin series used in the error model, which increased the exactitude and robustness of the correction method. The error parameters were identified by accurately fitting the calibrated angular errors with the error model, which showed excellent error prediction performance. Based on the angular calculation model corrected by the error model, the closed-loop control system was established to obtain accurate deflection angles. Experimental results show that within the deflection angle of ±1.5 deg, the angular accuracy was improved from 0.28 deg to less than 1.1 arcsec, and the standard deviation for six measurements was less than 1.2 arcsec, which indicates that the angle correction method was effective in improving the linearity of the eddy current sensors and reducing the influence of manufacturing and installation errors.

Dynamic System Identification Using a Step Input

2005 ◽  
Vol 24 (2) ◽  
pp. 125-134
Author(s):  
Manabu Kosaka ◽  
Hiroshi Uda ◽  
Eiichi Bamba ◽  
Hiroshi Shibata
Keyword(s):  
Steady State ◽  
System Identification ◽  
Transfer Function ◽  
Step Response ◽  
Output Data ◽  
Mass System ◽  
Input And Output ◽  
Rational Transfer ◽  
Line Identification ◽  
The Moment

In this paper, we propose a deterministic off-line identification method performed by using input and output data with a constant steady state output response such as a step response that causes noise or vibration from a mechanical system at the moment when it is applied but they are attenuated asymptotically. The method can directly acquire any order of reduced model without knowing the real order of a plant, in such a way that the intermediate parameters are uniquely determined so as to be orthogonal with respect to 0 ∼ N-tuple integral values of output error and irrelevant to the unmodelled dynamics. From the intermediate parameters, the coefficients of a rational transfer function are calculated. In consequence, the method can be executed for any plant without knowing or estimating its order at the beginning. The effectiveness of the method is illustrated by numerical simulations and also by applying it to a 2-mass system.

Study on the Method of Modified Random Decrement for Transfer Function

2003 ◽  
Author(s):  
Zhenzhong Zhang ◽  
Shijian Zhu
Keyword(s):  
Transfer Function ◽  
Steady State Response ◽  
Vibration System ◽  
State Response ◽  
Modified Method ◽  
Conventional Process ◽  
Random Decrement ◽  
Initial Excitation ◽  
Function Calculation ◽  
Random Decrement Method

This paper presents a modified random decrement method to obtain the steady-state response of vibration system. The expressions are deduced. Two numerical simulations and verification are given. The efficiencies of the modified method and the conventional process are compared. It is shown that the method is more efficient than the conventional process to diminish the influence of the initial excitation on the transfer function calculation of the vibration system.

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