Abstract
The optimization-based alignment (OBA) methods, which are implemented by the optimal attitude estimation using vector observations—also called double-vectors—have proven to be effective at solving the in-flight alignment (IFA) problem. However, the traditional OBA methods are not applicable for the low-cost strap-down inertial navigation system (SINS) since the error of double-vectors will be accumulated over time due to the substantial drift of micro-electronic- mechanical system (MEMS) gyroscope. Moreover, the existing optimal estimation method is subject to a large computation burden, which results in a low alignment speed. To address these issues, in this article we propose a new fast IFA method based on modified double-vectors construction and the gradient descent method. To be specific, the modified construction method is implemented by reducing the integration interval and identifying the gyroscope bias during the construction procedure, which improves the accuracy of double-vectors and IFA; the gradient descent scheme is adopted to estimate the optimal attitude of alignment without complex matrix operation, which results in the improvement of alignment speed. The effect of different sizes of mini-batch on the performance of the gradient descent method is also discussed. Extensive simulations and vehicle experiments demonstrate that the proposed method has better accuracy and faster alignment speed than the related traditional methods for the low-cost SINS/global positioning system (GPS) integrated navigation system
Highlights
The strap-down inertial navigation system (SINS) has been widely used in the determination of attitude, velocity and position of an object based on the dead-reckoning by making use of the measurements provided by the inertial measurement unit (IMU) [1,2,3]
To reduce the long-time navigation error mainly caused by the bias of accelerometers and gyroscopes, the SINS is often integrated with the global positioning system (GPS), which constructs the SINS/GPS integrated navigation system [4,5,6,7,8]
The SINS is composed of three gyroscopes of which bias is 1◦ /h (1σ) and three accelerometers of which bias is 1 mg (1σ), the position and velocity accuracy of GPS is 2 m (1σ) and 0.2 m/s (1σ) respectively
Summary
The strap-down inertial navigation system (SINS) has been widely used in the determination of attitude, velocity and position of an object based on the dead-reckoning by making use of the measurements provided by the inertial measurement unit (IMU) [1,2,3]. The heart of guaranteeing the performance of SINS is to accomplish the initial alignment and obtain an accurate initial condition [9,10]. In the SINS/GPS integrated navigation system, the initial velocity and position can usually be obtained directly from GPS. Sensors 2020, 20, 512 initial alignment is to determine the initial attitude between the body frame and reference navigation frame [11]. Many attitude determination methods have been proposed for the initial attitude alignment, for example, analytic alignment method, transfer alignment method [12,13,14,15,16]
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