Fiber Optic Gyroscope Nonlinear Error Compensation Based On Curve Fitting

Strapdown inertial navigation system(SINS) is a complex system consisted of multiple inertial measurement devices and measurement units. Gyroscope plays s a important role in a variety of measuring devices. In the modern time, SINS uses Fiber Optic Gyroscope(FOG). It has more advantages than the traditional gyroscope such as smaller size, higher accuracy, no moving parts, high dynamic measurement range and strong anti-shock and anti-interference ability. Not only in the navigation system, but also in the space flight and aviation, precision instrumentation, national defense industry, weapons manufacturing industrial and other areas,it has a wide application.FOG scale factor determines its output accuracy. However, scale factor of FOG does not reflect its linearity characteristic absolutely, in the actual test of FOG performance. Scale factor error will increase significantly in some angular velocity range, caused by nonlinearity.As the result,it has an adverse impact on the accuracy of navigation. According to these problems above mentioned,this article make several aspect researches as followed:First of all, the article introduces the basic principle of FOG and the structure of two types of FOG. At the same time, it elaborates the method of signal detection and phase modulation. A modulation method for all-digital closed-loop FOG is also introduced in detail.Secondly,the mathematical model of FOG is determined according to the relationship between input, output and error of FOG. The article also introduces procedures and the calculation process of FOG scale factor and its nonlinearity in detail. Then,it also introduces the basic principle and structure of FOG-SINS. According to the SINS error equation, the relationship between the scale factor error and moving angular rate is established. And the influence of scale factor error on the SINS output accuracy is deduced with this relationship.Simulation verifies the conclusion above mentioned by using matlab software.Then, this article analyzes relevant factors of scale factor error, and a adaptive segmentation fitting method is proposed. Before using this method, the order of fitting polynomial is required to determine. Data of FOG angular velocity test experiment are piecewise fitting, and segmented scale factors are obtained. Experiment of sea trials sway will verify result applied segmented scale factor. The result shows that navigation accuracy using segmented scale factor is superior to the traditional situation. And this method is easy to implement in engineering practice,is also a simple and efficient way to improve the stability of the scale factor.Finally,this article introduces basic concepts of programmable logic devices briefly, and design a system circuit board combined with one of the programmable logic device FPGA.This design choices EP4CE6 chip of Cyclone IV series made by Altera company. FPGA chip within a series of software modules designed to achieve several. A series of software modules are designed in FPGA chip to achieve input, output and segment processing. Logic modules are tested and verified with using logic analytical tool.