Martin Sipos

Analyses of Triaxial Accelerometer Calibration Algorithms

This paper proposes a calibration procedure in order to minimize the process time and cost. It relies on the suggestion of optimal positions, in which the calibration procedure takes place, and on position number optimization. Furthermore, this paper describes and compares three useful calibration algorithms applicable on triaxial accelerometer to determine its mathematical error model without a need to use an expensive and precise calibration means, which is commonly required. The sensor error model (SEM) of triaxial accelerometer consists of three scale-factor errors, three nonorthogonality angles, and three offsets. For purposes of calibration, two algorithms were tested-the Levenberg-Marquardt and the Thin-Shell algorithm. Both were then related to algorithm based on Matlab fminunc function to analyze their efficiency and results. The proposed calibration procedure and applied algorithms were experimentally verified on accelerometers available on market. We performed various analyses of proposed procedure and proved its capability to estimate the parameters of SEM without a need of precise calibration means, with minimum number of iteration, both saving time, workload, and costs.

Calibration of low-cost triaxial inertial sensors

Accelerometers (ACCs) and gyroscopes (gyros) are commonly known as inertial sensors and their orthogonal triads generally form an inertial measurement unit (IMU) used as a core means of a navigation system. Before the navigation system is to be used, it is necessary to perform its calibration. A typical process of the IMU calibration usually estimates scale-factors, orthogonality or misalignment errors, and offsets of both triads. These parameters compose the so-called sensor error model (SEM). The process of obtaining accurate information that describes the motion performed within the calibration generally requires a costly and specialized means [1], [2]. Therefore, much effort has been put into cost-effective calibration using an optical motion tracking system [3]-[6], or transferring the calibration into a state estimation problem [7]. In the ACC case, most of the current calibration methods utilize the fact that ACCs are affected by gravity when they are under static conditions. Therefore, we proceed with calibration performed under static conditions, which utilizes the knowledge of the gravity magnitude and ACC output measurements collected at predetermined orientations and performs ACC SEM estimation using nonlinear optimization [6], [8]-[10]. In the gyro case, calibration based on the Earths rate might be inapplicable, for instance due to the fact that Earths rate is under or around the resolution of the gyro, and thus other means to apply and measure angular rates need to be used. This situation commonly arises in the case of low-cost MEMS (Micro-Electro-Mechanical System) based gyros. Thus, expensive mechanical platforms are often inevitable [11]-[14].

Flight attitude track reconstruction using two AHRS units under laboratory conditions

The paper describes a performance analysis of two low-cost AHRS (Attitude and Heading Reference Systems), calibration procedures, and the verification of INS (Inertial Navigation System) mechanization algorithm using dedicated automatic measurement system based on a real-time flight simulation. The measurement system included the flight simulation software FlightGear (FG) that offered a wide range of aircraft dynamics and track simulation possibilities. The FG output data were converted into the form suitable for a servo-controlled Rotational-Tilt Platform (RoTiP) which provided corresponding motion for two AHRS units mounted on it and reference information from optical sensors. The output data of the AHRS units were collected, processed and evaluated to verify the units accuracy and reliability. The methodology and results based on the performance analyses are presented.

Inertial reference unit in a directional gyro mode of operation

This paper deals with a cost effective inertial reference unit design providing both MEMS based navigation unit calibration means and an attitude and heading measurement system in a directional gyro mode of operation. A main contribution of this paper is a novel design of such a universal system not primary relying on a magnetometer (MAG) or GPS aiding. Generally, without this aiding Attitude and Heading Reference Systems (AHRSs) are not directionally stable. Also, having precise reference in a calibration process is crucial and in most cases the solution is expensive. We thus replaced an expensive solution of both applications with the cost effective one suiting mentioned purposes using only one single axis fiber optic gyro supported by an inertial MEMS based aiding system. We also proposed a calibration procedure and blended solution to provide both stable and reliable navigation data with accuracy better than 5 deg/h specified by the TSO-C5e.

Calibration of a multi-sensor inertial measurement unit with modified sensor frame

Calibration of the inertial measurement units (IMU) used in navigation systems are crucial for ensuring accuracy of a navigation solution. It is common to discuss what calibration means, techniques, and algorithms can be utilized and implemented. For cost-effective measurement units it is desirable to use calibration means and approaches which are not expensive yet capable of providing sufficient accuracy. This paper thus focuses on multi-sensor inertial measurement unit which utilizes a modified sensor frames. Unlike the common IMUs which consist of 3-axial accelerometer and gyroscope frames, the proposed concept of the multi-sensor unit consists of ten modified accelerometer frames supplemented by an unmodified gyro frame. The modified frames of accelerometers are optimized for differential analogue signal processing in order to increase signal-to-noise ratio and hence overall sensing precision. Since the proposed concept of the measurement unit includes higher number of sensing frames it is required to develop a novel “easy to do and implement” calibration method which is the contribution of this paper. The proposed calibration approach was experimentally verified and results confirmed its usability.

Validation of nonlinear integrated navigation solutions

Abstract There exist numerous navigation solutions already implemented into various navigation systems. Depending on the vehicle in which the navigation system is used, it can be distinguished in most cases among; navigation, tactical, and commercial grade categories of such systems. The core of these systems is formed by inertial sensors, i.e. accelerometers and angular rate sensors/gyros. Navigation and tactical grade systems commonly rely on fiber optic/ring laser gyros and servo/quartz accelerometers with high resolution, sensitivity, and stability. In the case of cost-effective navigation systems, for example piloted light and ultralight aircraft, usually use commercial grade sensors, where the situation differs. The sensor outputs are less stable and sensitive, and suffer from manufacturing limits leading to temperature dependency, bias instability, and misalignment which introduces non-negligible disturbances. These conditions commonly limit the applicability of the navigation solution since its stand-alone operation using free integration of accelerations and angular rates is not stable. This paper addresses a cost-effective solution with commercial grade inertial sensors, and studies the performance of different approaches to obtain navigation solution with robustness to GNSS outages. A main goal of this paper is thus comparison of a nonlinear observer and two extended Kalman filter solutions with respect to the accuracy of estimated quantities and their sensitivity to GNSS outages. The performance analyses are carried out on real flight data and evaluated during phases of the flight when the solutions are challenged by different environmental disturbances.

Validation and Experimental Testing of Observers for Robust GNSS-Aided Inertial Navigation

This chapter is the study of state estimators for robust navigation. Navigation of vehicles is a vast field with multiple decades of research. The main aim is to estimate position, linear velocity, and attitude (PVA) under all dynamics, motions, and conditions via data fusion. The state estimation problem will be considered from two different perspec‐ tives using the same kinematic model. First, the extended Kalman filter (EKF) will be reviewed, as an example of a stochastic approach; second, a recent nonlinear observer will be considered as a deterministic case. A comparative study of strapdown inertial navigation methods for estimating PVA of aerial vehicles fusing inertial sensors with global navigation satellite system (GNSS)-based positioning will be presented. The focus will be on the loosely coupled integration methods and performance analysis to compare these methods in terms of their stability, robustness to vibrations, and disturbances in measurements.

Introducing Students to Aerospace Board Information Systems Using an Embedded Graphics System Simulator

A graduate-level engineering course in airborne sensor and control systems taught at the Czech Technical University in Prague under the title Board Information Systems takes a novel systematic and comprehensive approach to teaching airborne digital avionics systems, together with system certification and life-cycle operations. The course brings together materials from various sources to cover practical aspects of avionics systems ranging from design, prototyping, testing, certification and production through to maintenance. It prepares students to deal with a wide range of the type of real-world problems that they will meet in their professional careers. This is a required course offered in the 10th semester as a part of the study programme in Airborne Information and Control Instrumentation (AICI) by the Department of Measurement. The course was redesigned with new lecture content, practical exercises and field trips. The course evaluation survey results from 2008 and 2009 show that recent students have considered the course a valuable part of their curriculum, and that it has made them feel more competent in the field of digital avionics systems. The course syllabus and other data are available online at http://www.pacespavel.net/PRS/.

Modified Biaxial Accelerometer Framework in G-sensing Mode

This paper deals with an acceleration measuring unit, which uses two biaxial accelerometers, and compares its performance with a typical triaxial framework. In cases of small aircrafts, UAVs, robots, or terrestrial vehicle navigation units utilizing sensors manufactured by a MEMS technology are preferred due to their cost-effectiveness. In order to suppress imperfections of the measuring system (noise, drift, nonlinearities, small sensitivity) a solution based on the difference configuration of accelerometers is proposed.