In-Run Navigation Grade Quartz MEMS-Based IMU

EMCORE has demonstrated high-end tactical grade and navigation grade performance of a compact inertial measurement unit (IMU) based on quartz MEMS inertial sensor technology, originally developed by Systron Donner Inertial. Experimental results for the gyroscope reveal angle random walk lower than 0.001 °/$\surd$hr, and bias instability of 0.005 °/hr; bias over a dynamic temperature environment (−55 °C to +90 °C) is <0.2 °/hr and scale factor error is < 50 ppm. Experimental results for the accelerometer have demonstrated a velocity random walk of 0.3 $\mu$g/$\surd$Hz, with bias instability of $0.1 \mu \mathrm{g}$; accelerometer bias and scale factor drift over a full temperature range (−55 °C to +90 °C) were 20 mg and 25 ppm, respectively. This performance was achieved within the form factor of the SDI500 IMU (19 cubic inches, coffee mug size).

Fiber optic gyro (FOG) and metallic resonator Coriolis vibratory gyro (CVG) main accuracy parameters are compared in this paper. Manufacturers of the analyzed gyros are from Russia (FOG) and Ukraine (CVG). Methodics to measure and to calculate scale factor temperature instability and nonlinearity as well as bias components such as quantum noise, random walk and drift using Allan variance analysis are described. Scale factors temperature instability and nonlinearity graphs of both gyros are given and compared. Bias components calculation at stable temperature are also given and compared. Two CVGs: KVG25, KVG43 and one FOG: VG951D take part in comparative analysis.

This letter presents design and control innovations of wearable robots that tackle two barriers to widespread adoption of powered exoskeletons: restriction of human movement and versatile control of wearable co-robot systems. First, the proposed high torque density actuation comprised of our customized high-torque density motors and low ratio transmission mechanism significantly reduces the mass of the robot and produces high backdrivability. Second, we derive a biomechanics model-based control that generates assistive torque profile for versatile control of both squat and stoop lifting assistance. The control algorithm detects lifting postures using compact inertial measurement unit (IMU) sensors to generate an assistive profile that is proportional to the human joint torque produced from our model. Experimental results demonstrate that the robot exhibits low mechanical impedance (1.5 Nm backdrive torque) when it is unpowered and 0.5 Nm backdrive torque with zero-torque tracking control. Root mean square (RMS) error of torque tracking is less than 0.29 Nm (1.21% error of 24 Nm peak torque). Compared with squatting without the exoskeleton, the controller reduces 87.5%, 80% and 75% of the three knee extensor muscles (average peak EMG of 3 healthy subjects) during squat with 50% of human joint torque assistance.

Inertial navigation provides a unique ability to know where one has been, where one is currently, and where one is going, given only a starting position. The laws of physics permit the sensing of dynamic motion without external information, making inertial systems impervious to jamming, masking, or spoofing. Measurements of six degrees of freedom are required - three linear accelerations, and three angular rates - to fully propagate the velocity, position, and orientation of the system. The first inertial sensors are traced to the early 19th century and specialized inertial guidance systems appeared in the 1940s, yet inertial navigation systems did not become commonplace until the 1960s. This is largely due to the fact that requirements for navigation accuracy inertial sensors - accelerometers and gyroscopes - are very challenging. In the past fifty years, significant evolutionary and revolutionary changes have taken place in the designs of inertial sensors and systems. These include the progression from fluid-filled to dry instruments and the transition from mechanically complex stabilized inertial platforms to computationally intensive strapdown systems. Gyroscopes have evolved from large mechanical devices to highly refined precision mechanical sensors. Optical rotation sensors such as the ring laser gyro and the fiber optic gyro have enabled new system designs and capabilities. Coriolis vibratory gyroscopes such as the hemispherical resonator gyro are capable of extreme accuracy and reliability; new opportunities for miniaturizing these types of sensors will lead to new classes of accuracy for inertial navigation systems. Advanced gyroscope technologies such as the nuclear magnetic resonance gyroscope which uses atomic spin to detect rotation have already been demonstrated to achieve navigation accuracy requirements. Cold atom technologies may also provide the opportunity for very high accuracy accelerometers and gyroscopes in the future. Inertial navigation technologies and applications of the past, present, and future are discussed.

In this paper, we propose a novel wafer-level approach for fabrication and 3-D integration of MEMS devices in miniature multi-axis assemblies of inertial, acoustic, and optical sensors. The approach is based on simultaneous fabrication of all sensors on the same substrate connected by flexible electrical interconnects, mechanical hinges and latches. A multi-axis sensor system is then obtained by folding the fabricated structures into 3-D cubes, pyramids, or other rigid shapes, and subsequently micro-welded. In the current work, we demonstrate feasibility of the folded cube approach for creation of miniature MEMS IMU with &amp;lt;1 cm3 volume. Design of the IMU consists of a folded cube or pyramid backbone structure with micromachined accelerometers and gyroscopes on its sidewalls. Silicon-on-insulator (SOI) wafers are used as a substrate for fabrication of both the inertial sensors and the folded backbone structure. Fabrication of the sensors consists of lithography, deep reactive ion etching (DRIE), and HF acid release of the inertial proof masses. Flexible polymer hinges connecting faces of the folded structures are defined on the same substrate and incorporate electrical interconnects. To provide rigidity to the assembled 3-D structure, interlocking silicon latches are fabricated along the edges of each sidewall, which are silicon-to-silicon welded after assembly. The approach allows for creating miniature multi-axis sensor systems without compromising performance of individual sensors. Gyroscopes integrated in the current folded cube IMU have experimentally demonstrated 3-dB bandwidth of 250 Hz and angle random walk (ARW) below 0.1 (deg/s)/rt-Hz in atmospheric pressure. Measured uncompensated temperature coefficients of gyroscope bias and scale factor were 313 (deg/h)/degC and 351ppm/degC, respectively. Accelerometers on the cube have been characterized, yielding a noise floor of 570μG/√Hz. Sensitivity of the accelerometers is measured at 40mV/G with a bandwidth of 100 Hz.

In order to improve the angular rate sensitivity in Coriolis Vibratory Gyroscopes (CVG), an electrostatic frequency tuning mechanism is often used to reduce the split in the resonant frequency of gyroscopes. In this paper, the effect of the amplitude-frequency coupling, as a ramification of the electrostatic frequency tuning, on gyroscope operation in the open-loop angular rate mode is studied. We demonstrate that the amplitude-frequency coupling results in instability in the resonant frequency along the drive axis which degrades the noise performance of a CVG. We present a model that describes the non-linear dynamics of a gyroscope along the drive axis, including the amplitude-frequency coupling terms beyond the Duffing and quintic nonlinearity. Analytical equations were derived to estimate the correlation between frequency noise and amplitude noise. The non-linear electrostatic spring stiffness and the frequency noise in a Dual Foucault Pendulum (DFP) gyroscope were characterized and a good agreement with the predictive analytical model was observed. Our study suggests that as the required tuning voltage for mode-matching is increased, the frequency stability in the gyroscope degrades and the quadrature noise limits the noise performance of the gyroscope. In the case of the DFP gyroscope, we demonstrated that a reduction of the drive amplitude, which reduces the amplitude-frequency coupling, resulted in a 3 times improvement in the Angle Random Walk (ARW) and Bias Instability (BI).

This paper proposes a calibration and compensation method of an inertial measurement unit (IMU) composed of two dynamically tuned gyros (DTGs) and three quartz accelerometers. Considering the DTG IMU for the position and orientation system (POS) used in the air remote sensing, it is found that the gyro scale factor has a hyperbolic relationship with the input angular rate and a linear relationship with the temperature shown from the experiments. Based on this, the equations of the gyro scale factor, the input angular velocity and the temperature are established by applying the least-square fit. Next, a hybrid multiposition calibration method of the IMU is given to estimate the error model parameters and compensate system errors. At last, a laboratory rate test and a car-mounted experiment are carried out to assess the efficiency of the proposed method. It is demonstrated from the experiment results that the attitude accuracy of the DTG POS can be improved with the calibration based on the compensation of scale factor errors.

The toolbox to study the Universe grew on 14 September 2015 when the LIGO–Virgo collaboration heard a signal from two colliding black holes between 30 and 250 Hz. Since then, many more gravitational waves have been detected as detectors continue to increase sensitivity. However, the current and future interferometric detectors will never be able to detect gravitational waves below a few Hz due to oceanic activity on Earth. An interferometric space mission, the laser interferometer space antenna, will operate between 1 mHz and 0.1 Hz, leaving a gap in the decihertz band. To detect gravitational-wave signals also between 0.1 and 1 Hz, the Lunar Gravitational-wave Antenna will use an array of seismic stations. The seismic array will be deployed in a permanently shadowed crater on the lunar south pole, which provides stable ambient temperatures below 40 K. A cryogenic superconducting inertial sensor is under development that aims for fm/√Hz sensitivity or better down to several hundred mHz, and thermal noise limited below that value. Given the 106 m size of the Moon, strain sensitivities below 10−20 1/√Hz can be achieved. The additional cooling is proposed depending on the used superconductor technology. The inertial sensors in the seismic stations aim to make a differential measurement between the elastic response of the Moon and the inertial sensor proof-mass motion induced by gravitational waves. Here, we describe the current state of research toward the inertial sensor, its applications, and additional auxiliary technologies in the payload of the lunar gravitational-wave detection mission.

The army combined arms weapon system (TACAWS) is currently being developed as a technology demonstration program at the US Army Missile Command (MICOM) located at Redstone Arsenal, AL. The thrust behind the development of TACAWS is to provide the 21st century Army a multi-purpose, multi-target, and multi-platform weapon system that can be easily deployed to any location in the world. The TACAWS land navigation system (LNS) incorporates data from 3 ring laser gyros, 3 quartz accelerometers, a precision lightweight GPS receiver (PLGR) and an odometer into the position and attitude solutions. The LNS is being installed on a modified M2 Bradley vehicle, for the purpose of navigation, targeting, data link attitude control, and missile initialization. Missile initialization includes the transfer of the LNS's north alignment accuracy to the missile's inertial measurement unit. The LNS test results reported include alignment accuracy (static and moving) and drift, inertial sensor error estimation, alignment transfer accuracy, and navigation accuracy with and without GPS data.

This paper exploits the idea of integrating the outputs of several optical flow sensors (OFSs) and a micro-electro-mechanical systems (MEMS) inertial measurement unit (IMU). Several optical flow sensors are fixed on an unmanned aerial vehicle (UAV). Their locations and orientations are different so as to detect the optical flow from different directions. By fusing the optical flow information and inertial navigation system (INS) measurements using an extended Kalman filter (EKF), the INS errors can be estimated and compensated. The integration of optical flow sensors and MEMS-based IMU provides a small size, low cost and self-contained scheme for UAVs navigation at low height above the ground in GPS denied environments. The preliminary simulation results presented in this article illustrate the effectiveness of the proposed integrated navigation scheme.

Comparison of IMU Measurements of Curling Stone Dynamics with a Numerical Model

In this paper, the MEMS-based IMU (Inertial Measurement Unit) was used in a fusion navigation system comprising a MEMS-based IMU and a GPS device with the map database. The attitude angle of a vehicle at a specific location is detected by the MEMS-based IMU and compared with the identifying information from the map database for judging whether the vehicle is on a correct route or not. The fusion navigation system generates a navigation route in accordance with the start and destination and determines whether the attitude angle is conformed to the identifying information from the map database with respect to the specific location on the navigation route. If the attitude angle is not conformed to the identifying information, the navigation route for the vehicle could be modified immediately. This method could help the GPS device to determine whether the vehicle is traveling on the viaduct bridge or on the surface road and whether a driver of the vehicle had taken a route other than the navigation route at the first instant, and thus modifying the navigation route according to the comparison for guiding the driving on a correct route to the destination specified in the navigation information.

Prior experiments have confirmed that specific terrain-based localization algorithms, designed to work in GPS-free or degraded-GPS environments, achieve vehicle tracking with tactical-grade inertial sensors. However, the vehicle tracking performance of these algorithms using low-cost inertial sensors with inferior specifications has not been verified. The included work identifies, through simulations, the effect of inertial sensor characteristics on vehicle tracking accuracy when using a specific terrain-based tracking algorithm based on Unscented Kalman Filters. Results indicate that vehicle tracking is achievable even when low-cost inertial sensors with inferior specifications are used. However, the precision of vehicle tracking decreases approximately linearly as bias instability and angle random walk coefficients increase. The results also indicate that as sensor cost increases, the variance in vehicle tracking error asymptotically tends to zero. Put simply, as desired precision increases, increasingly larger and quantifiable investment is required to attain an improvement in vehicle tracking precision.

The paper deals with consideration of the possibility to improve the Coriolis vibratory gyroscopes with the goal to simplify information processing, increase reliability, and compensate bias. Improvement of the Coriolis vibratory gyroscope includes introducing of the phase detector and additional excitation unit. The possibility to use the improved Coriolis vibratory gyroscope in the stabilization system is shown by means of simulation technique.

This paper presents a navigation grade micro-electromechanical system (MEMS) inertial measurement unit (IMU) that was successfully applied for the first time in the Lobster-Eye X-ray Satellite in July 2020. A six-axis MEMS gyroscope redundant configuration is adopted in the unit to improve the performance through mutual calibration of a set of two-axis gyroscopes in the same direction. In the paper, a satisfactory precision of the gyroscope is achieved by customized and self-calibration gyroscopes whose parameters are adjusted at the expense of bandwidth and dynamics. According to the in-orbit measured data, the MEMS IMU provides an outstanding precision of better than 0.02 °/h (1σ) with excellent bias instability of 0.006 °/h and angle random walk (ARW) of around 0.003 °/h1/2. It is the highest precision MEMS IMU for commercial aerospace use ever publicly reported in the world to date.