Inertial measurement unit modelling

Inerciální měřící jednotka (IMU) patří mezi základní senzorické vybavení současných mobilních robotů, kde se používá především pro odhadování ohamžité orientace robotu v prostoru. V této práci se komplexně zabývám simulací IMU v robotickém simulátoru Gazebo za účelem co nejvěrnějšího modelování odhadovaného úhlu natočení robotu, který je jedním z přímých výstupů IMU senzoru Bosch BNO055. Pro podporu vyhodnocení kvality IMU modelu vzhledem k reálným datům z BNO055 jsem navrhl a implementoval simulační prostřední v rámci Robotického Operačního Systému (ROS), které aproximuje zadanou trajektorii, uloží data ze simulovaného IMU a vygeneruje podklady pro vyhodnocení kvality IMU modelu vzhledem k reálným datům z BNO055. Na základě nejlepších dostupných IMU pluginů v Gazebu jsem implementoval dva URDF/SDF modely IMU sensoru, jejichž funkčnost byla následně ověřena řadou experimentů v simulátoru. Provedené simulace potvrdily funkčnost modelů a zároveň poukázaly na limity realističnosti současných pluginů v Gazebu a nastínily možnosti dalšího vývoje pro zvýšení věrnosti simulací IMU.The inertial measurement unit (IMU) sensors are massively used in mobile service robots to provide orientation estimation. This thesis is concerned with modeling and simulation of IMU sensor in the robotics simulator Gazebo. The main goal of this thesis is to simulate the heading angle output of a real IMU sensor Bosch BNO055 with high fidelity. To enable the IMU model evaluation I designed and implmented a custom IMU simulation framework as a ROS package. This framework approximates the given trajectory with the help of a Gazebo simulation of a robot model with attached IMU sensor model, captures the simulated IMU output and generates data for the comparison concerning provided dataset measured by real BNO055. I used the best currently available IMU plugins to implement two different URDF/SDF IMU models. The simulations demonstrated the functionality of implemented IMU models, but also revealed the fidelity limitations of current IMU plugins in Gazebo, and led to a discussion about possible future improvements

Applications of MEMS Gyroscope for Human Gait Analysis

After decades of development, quantitative instruments for human gait analysis have become an important tool for revealing underlying pathologies manifested by gait abnormalities. However, the gold standard instruments (e.g., optical motion capture systems) are commonly expensive and complex while needing expert operation and maintenance and thereby be limited to a small number of specialized gait laboratories. Therefore, in current clinical settings, gait analysis still mainly relies on visual observation and assessment. Due to recent developments in microelectromechanical systems (MEMS) technology, the cost and size of gyroscopes are decreasing, while the accuracy is being improved, which provides an effective way for qualifying gait features. This chapter aims to give a close examination of human gait patterns (normal and abnormal) using gyroscope-based wearable technology. Both healthy subjects and hemiparesis patients participated in the experiment, and experimental results show that foot-mounted gyroscopes could assess gait abnormalities in both temporal and spatial domains. Gait analysis systems constructed of wearable gyroscopes can be more easily used in both clinical and home environments than their gold standard counterparts, which have few requirements for operation, maintenance, and working environment, thereby suggesting a promising future for gait analysis

Localization Precise in Urban Area

Nowadays, stand-alone Global Navigation Satellite System (GNSS) positioning accuracy is not sufficient for a growing number of land users. Sub-meter or even centimeter accuracy is becoming more and more crucial in many applications. Especially for navigating rovers in the urban environment, final positioning accuracy can be worse as the dramatically lack and contaminations of GNSS measurements. To achieve a more accurate positioning, the GNSS carrier phase measurements appear mandatory. These measurements have a tracking error more precise by a factor of a hundred than the usual code pseudorange measurements. However, they are also less robust and include a so-called integer ambiguity that prevents them to be used directly for positioning. While carrier phase measurements are widely used in applications located in open environments, this thesis focuses on trying to use them in a much more challenging urban environment. To do so, Real Time-Kinematic (RTK) methodology is used, which is taking advantage on the spatially correlated property of most code and carrier phase measurements errors. Besides, the thesis also tries to take advantage of a dual GNSS constellation, GPS and GLONASS, to strengthen the position solution and the reliable use of carrier phase measurements. Finally, to make up the disadvantages of GNSS in urban areas, a low-cost MEMS is also integrated to the final solution. Regarding the use of carrier phase measurements, a modified version of Partial Integer Ambiguity Resolution (Partial-IAR) is proposed to convert as reliably as possible carrier phase measurements into absolute pseudoranges. Moreover, carrier phase Cycle Slip (CS) being quite frequent in urban areas, thus creating discontinuities of the measured carrier phases, a new detection and repair mechanism of CSs is proposed to continuously benefit from the high precision of carrier phases. Finally, tests based on real data collected around Toulouse are used to test the performance of the whole methodology

Optimized Filter Design for Non-Differential GPS/IMU Integrated Navigation

The endeavours in improving the performance of a conventional non-differential GPS/MEMS IMU tightly-coupled navigation system through filter design, involving nonlinear filtering methods, inertial sensors' stochastic error modelling and the carrier phase implementation, are described and introduced in this thesis. The main work is summarised as follows. Firstly, the performance evaluation of a recently developed nonlinear filtering method, the Cubature Kalman filter (CKF), is analysed based on the Taylor expansion. The theoretical analysis indicates that the nonlinear filtering method CKF shows its benefits only when implemented in a nonlinear system. Accordingly, a nonlinear attitude expression with direction cosine matrix (DCM) is introduced to tightly-coupled navigation system in order to describe the misalignment between the true and the estimated navigation frames. The simulation and experiment results show that the CKF performs better than the extended Kalman filter (EKF) in the unobservable, large misalignment and GPS outage cases when attitude errors accumulate quickly, rendering the psi-angle expression invalid and subsequently showing certain nonlinearity. Secondly, the use of shaping filter theory to model the inertial sensors' stochastic errors in a navigation Kalman filter is also introduced. The coefficients of the inertial sensors' noises are determined from the Allan variance plot. The shaping filter transfer function is deduced from the power spectral density (PSD) of the noises for both stationary and non-stationary processes. All the coloured noises are modelled together in the navigation Kalman filter according to equivalence theory. The coasting performance shows that the shaping filter based modelling method has a similar and even smaller maximum position drift than the conventional 1st-order Markovian process modelling method during GPS outages, thus indicating its effectiveness. Thirdly, according to the methods of dealing with carrier phase ambiguities, tightly-coupled navigation systems with time differenced carrier phase (TDCP) and total carrier phase (TCP) as Kalman filter measurements are deduced. The simulation and experiment results show that the TDCP can improve the velocity estimation accuracy and smooth trajectories, but position accuracy can only achieve the single point positioning (SPP) level if the TDCP is augmented with the pseudo-range, while the TCP based method's position accuracy can reach the sub-meter level. In order to further improve the position accuracy of the TDCP based method, a particle filter (PF) with modified TDCP observation is implemented in the TDCP/IMU tightly-coupled navigation system. The modified TDCP is defined as the carrier phase difference between the reference and observation epochs. The absolute position accuracy is determined by the reference position accuracy. If the reference position is taken from DGPS, the absolute position accuracy can reach the sub-meter level. For TCP/IMU tightly-coupled navigation systems, because the implementation of TCP in the navigation Kalman filter introduces additional states to the state vector, a hybrid CKF+EKF filtering method with the CKF estimating nonlinear states and the EKF estimating linear states, is proposed to maintain the CKF's benefits while reducing the computational load. The navigation results indicate the effectiveness of the method. After applying the improvements, the performance of a non-differential GPS/MEMS IMU tightly-coupled navigation system can be greatly improved

Theoretical framework for In-Car Navigation based on Integrated GPS/IMU Technologies

In this report the problem of vehicular navigation based on the integration of the global positioning system and an inertial navigation system is tackled. After analysing some fundamental technical issues about reference systems, vehicle modelling and sensors, a novel solution, combining extended Kalman filtering with particle filltering, is developed. This solution allows to embed highly non-linear constraints originating from digital maps in the position estimation process and is expected to be implementable on commercial hardware platforms equipped with low cost inertial sensorsJRC.G.6-Digital Citizen Securit

High-frequency tri-axial resonant gyroscopes

This dissertation reports on the design and implementation of a high-frequency, tri-axial capacitive resonant gyroscopes integrated on a single chip. The components that construct tri-axial rotation sensing consist of a yaw, a pitch and a roll device. The yaw-rate gyroscope has a wide bandwidth and a large full-scale range, and operates at a mode-matched condition with DC polarization voltage of 10V without frequency tuning requirement. The large bandwidth of 3kHz and expected full-scale range over 30,000˚/sec make the device exhibit fast rate response for rapid motion sensing application. For the pitch-and-roll rate sensing, an in-plane drive-mode and two orthogonal out-of-plane sense-modes are employed. The rotation-rate sensing from lateral axes is performed by mode-matching the in-plane drive-mode with out-of-plane sense-modes to detect Coriolis-force induced deflection of the resonant mass. To compensate process variations and thickness deviations in the employed silicon-on-insulator (SOI) substrates, large electrostatic frequency tunings of both the drive and sense modes are realized. A revised high aspect ratio combined polysilicon and silicon (HARPSS) process is developed to resolve the Coriolis response that exists toward out-of-plane direction while drive-mode exists on in-plane, and tune individual frequencies with minimal interference to unintended modes. To conclude and overcome the performance limitation, design optimization of high-frequency tri-axial gyroscopes is suggested. Q-factor enhancement through reduction of thermoelastic damping (TED) and optimizations of physical dimensions are suggested for the yaw disk gyroscope. For the pitch-and-roll gyroscope, scaling property of physical dimension and its subsequent performance enhancement are analyzed.Ph.D

Integrated Sensor Orientation on Micro Aerial Vehicles

Mapping with Micro Aerial Vehicles (MAVs whose weight does not exceed 5 kg) is gaining importance in applications, such as corridor mapping, road and pipeline inspections, or mapping of large areas with homogeneous surface structure, e.g. forest or agricultural fields. When cm-level accuracy is required, the classical approach of sensor orientation does not deliver satisfactory results unless a large number of ground control points (GCPs) is regularly distributed in the mapped area. This may not be a feasible method either due to the associated costs or terrain inaccessibility. This thesis addresses such issues by presenting a development of MAV platforms with navigation and imaging sensors that are able to perform integrated sensor orientation (ISO). This method combines image measurements with GNSS or GNSS/IMU (Global Navigation Satellite System/Inertial Measurement Unit) observations. This innovative approach allows mapping with cm-level accuracy without the support of GCPs, even in geometrically challenging scenarios, such as corridors. The presented solution also helps in situations where automatic image observations cannot be generated, e.g. over water, sand, or other surfaces with low variations of texture. The application of ISO to MAV photogrammetry is a novel solution and its implementation brings new engineering and research challenges due to a limited payload capacity and quality of employed sensors on-board. These challenges are addressed using traditional as well as novel methods of treating observations within the developed processing software. The capability of the constructed MAV platforms and processing tools is tested in real mapping scenarios. It is empirically confirmed that accurate aerial control combined with a state-of-the-art calibration and processing can deliver cm-level ground accuracy, even in the most demanding projects. This thesis also presents an innovative way of mission planning in challenging environments. Indeed, a thorough pre-flight analysis is important not only for obtaining satisfactory mapping quality, but photogrammetric missions must be carried out in compliance with state regulations

Micropropulsion Trade Study and Investigation for Attitude Control of Nanosatellites

Since their inception two decades ago, CubeSats have become dominant in the small satellite market, enabling new mission architectures, technology development, and education opportunities. However, the limited mass, power, and volume inherent in this small platform, constrains the on board subsystems and thus the capabilities compared to larger satellites. Attitude control is essential to maximizing the potential of CubeSats and other nanosatellites, though traditional momentum control systems such as reaction wheels are not feasible on the smallest CubeSats. Micropropulsion is an intriguing alternative to traditional methods, and many miniaturization efforts have been made for chemical and electrical propulsion systems. One such micro-propulsion unit is Film Evaporation Microelectromechanical System Tunable Array (FEMTA). FEMTA manipulates the temperature dependence of liquid water capillary action to produce controllable and precise thrust in the 10 to 100 microNewton range. FEMTA has been demonstrated in both thrust tests and in single axis rotation tests. This work describes the further characterization of FEMTA technology through these tests and compares it to other micropropulsion technologies in a trade study for micropropulsion as attitude control devices on various sizes of CubeSats

Pilot Assisted Inertial Navigation System Aiding Using Bearings-Only Measurements Taken Over Time

The objective of this work is to develop an alternative INS aiding source other than the GPS, while preserving the autonomy of the integrated navigation system. It is proposed to develop a modernized method of aerial navigation using driftmeter measurements from an E/O system for ground feature tracking, and an independent altitude sensor in conjunction with the INS. The pilot will track a ground feature with the E/O system, while the aircraft is on autopilot holding constant airspeed, altitude, and heading during an INS aiding session. The ground feature measurements from the E/O system and the INS output form measurements provided to a linear KF running on the navigation computer to accomplish the INS aiding action. Aiding the INS will be periodically repeated as operationally permissible under pilot discretion. Little to no modeling error will be present when implementing the linear Kalman filter, indicating the strength of the INS aiding action will be exclusively determined by the prevailing degree of observability

Development of a software in the loop simulation approach for risk mitigation in unmanned aerial system development

A common method to reduce risk during the development of new designs is simulation and estimation. The extent to which these simulation and estimation techniques can be relied upon for small Unmanned Aerial Systems (sUAS) is unknown. Combining the autopilot together with a simulator for Software in the Loop (SITL) allows designers to tune and observe autopilot behavior before the design is finished. This thesis extends the tools provided through SITL to present methodology that can both provide early insight to the handling qualities of the aircraft and validation of the simulator.ArduPilot and X-Plane 11 are used as the autopilot and simulator. New features were developed to extend the functionality of ArduPilot. Additional software was developed to assist in both identification of aircraft modes and validation of simulation. With mixed results from validation of X-Plane, the need to perform flight testing of real aircraft is still more desirable for precision tuning of sUAS for more desirable handling qualities. What can be gained from SITL is risk mitigation from unconventional additions to sUAS and detailed analysis of failsafe behavior of the autopilot