Measurement Of Angular Acceleration Research Articles

Hardware design of electrostatic levitation accelerometer control system

The electrostatic levitation accelerometer is a high-precision inertial instrument for measuring small displacement and acceleration, and it plays a very important role in global gravity field measurement, space gravitational wave detection, and other space missions as a key payload for satellites. It can realize the measurement of three-axis linear acceleration and three-axis angular acceleration. The open loop is unstable, and the control system needs to control six degrees of freedom at the same time so that the test mass can be stably suspended in the center position of the capacitive pole plate. For the demand of multi-channel simultaneous control of electrostatic levitation accelerometer, this paper designs an eight-channel digital control system hardware circuit with DSP as the core and FPGA as the co-processor, which can realize the data acquisition and feedback control of six degrees of freedom, writes the driver using hardware description language (Verilog), and simulates and analyzes the driver timing by the timing simulation software Modelsim. Finally, the hardware circuit was tested for the onboard drive. The results show that the system can work normally, the average sampling error of ADC is 0.00198 V, and the output error of DAC is 0.004 V, which is small enough to meet the system requirements.

Constructive Equivariant Observer Design for Inertial Navigation⋆

Inertial Navigation Systems (INS) are algorithms that fuse inertial measurements of angular velocity and specific acceleration with supplementary sensors including GNSS and magnetometers to estimate the position, velocity and attitude, or extended pose, of a vehicle. The industry-standard extended Kalman filter (EKF) does not come with strong stability or robustness guarantees and can be subject to catastrophic failure. This paper exploits a Lie group symmetry of the INS dynamics to propose the first nonlinear observer for INS with error dynamics that are almost-globally asymptotically and locally exponentially stable, independently of the chosen gains. The observer is aided only by a GNSS measurement of position. As expected, the convergence guarantee depends on persistence of excitation of the vehicle's specific acceleration in the inertial frame. Simulation results demonstrate the observer's performance and its ability to converge from extreme errors in the initial state estimates.

Angular Velocities and Linear Accelerations Derived from Inertial Measurement Units Can Be Used as Proxy Measures of Knee Variables Associated with ACL Injury

Given the high rates of both primary and secondary anterior cruciate ligament (ACL) injuries in multidirectional field sports, there is a need to develop easily accessible methods for practitioners to monitor ACL injury risk. Field-based methods to assess knee variables associated with ACL injury are of particular interest to practitioners for monitoring injury risk in applied sports settings. Knee variables or proxy measures derived from wearable inertial measurement units (IMUs) may thus provide a powerful tool for efficient injury risk management. Therefore, the aim of this study was to identify whether there were correlations between laboratory-derived knee variables (knee range of motion (RoM), change in knee moment, and knee stiffness) and metrics derived from IMUs (angular velocities and accelerations) placed on the tibia and thigh, across a range of movements performed in practitioner assessments used to monitor ACL injury risk. Ground reaction forces, three-dimensional kinematics, and triaxial IMU data were recorded from nineteen healthy male participants performing bilateral and unilateral drop jumps, and a 90° cutting task. Spearman's correlations were used to examine the correlations between knee variables and IMU-derived metrics. A significant strong positive correlation was observed between knee RoM and the area under the tibia angular velocity curve in all movements. Significant strong correlations were also observed in the unilateral drop jump between knee RoM, change in knee moment, and knee stiffness, and the area under the tibia acceleration curve (rs = 0.776, rs = -0.712, and rs = -0.765, respectively). A significant moderate correlation was observed between both knee RoM and knee stiffness, and the area under the thigh angular velocity curve (rs = 0.682 and rs = -0.641, respectively). The findings from this study suggest that it may be feasible to use IMU-derived angular velocities and acceleration measurements as proxy measures of knee variables in movements included in practitioner assessments used to monitor ACL injury risk.

Modeling GRACE-FO accelerometer data for the version 04 release

GRACE and GRACE-FO require the reduction of non-gravitational accelerations, through an onboard accelerometer, to accurately estimate variations in the Earth’s gravitational field. Accuracy in the accelerometer measurements is vital to this mass change recovery and significant errors will reduce the quality of the recovered science data. This paper describes our current characterization of error sources in the GRACE-FO accelerometers and the error mitigation strategies used in the generation of the JPL/CSR GRACE-FO Version 04 accelerometer data for public release. Our current error characterization model describes flicker noise on readings of one accelerometer plate pair on GRACE-D, impulse response limitations on both accelerometers, nonphysical once per revolution variations in the roll angular acceleration measurements on both accelerometers, significant correlated errors on all axes on GRACE-D, nominal thermal bias dependencies on both accelerometers, and expected nominal inter-measurement aliasing (cross-talk - expected as heritage from GRACE). Attitude reconstruction strategies incorporating star camera, inertial measurement unit, and magnetorquer measurements visibly improve angular acceleration recovery independent of the accelerometer. Error mitigation strategies for the linear acceleration measurements, associated with the calibrated accelerometer product provided in the version 04 release, dramatically improve estimates of the Earth’s gravity field. While many of the error characterizations described here are not necessary for constructing the accelerometer transplant from GRACE-C to GRACE-D, as is currently done in the Version 04 release, the error characterizations described here lay the groundwork for future use of calibrated/corrected GRACE-D accelerometer data.

Development of a Low-Power Instrumented Mouthpiece for Directly Measuring Head Acceleration in American Football.

Instrumented mouthpieces (IM) offer a means of measuring head impacts that occur in sport. Direct measurement of angular head kinematics is preferential for accuracy; however, existing IMs measure angular velocity and differentiate the measurement to calculate angular acceleration, which can limit bandwidth and consume more power. This study presents the development and validation of an IM that uses new, low-power accelerometers for direct measurement of linear and angular acceleration over a broad range of head impact conditions in American football. IM sensor accuracy for measuring six-degree-of-freedom head kinematics was assessed using two helmeted headforms instrumented with a custom-fit IM and reference sensor instrumentation. Head impacts were performed at 10 locations and 6 speeds representative of the on-field conditions associated with injurious and non-injurious impacts in American football. Sensor measurements from the IM were highly correlated with those from the reference instrumentation located at the maxilla and skull center of gravity. Based on pooled data across headform and impact location, R2 ≥ 0.94, mean absolute error (AE) ≤ 7%, and mean relative impact angle ≤ 11° for peak linear and angular acceleration and angular velocity while R2 ≥ 0.90 and mean AE ≤ 7% for kinematic-based injury metrics used in helmet tests.

Biaxial Angular Acceleration Sensor with Rotational-Symmetric Spiral Channels and MEMS Piezoresistive Cantilevers.

Angular acceleration sensors are attracting attention as sensors for monitoring rotational vibration. Many angular acceleration sensors have been developed; however, multiaxis measurement is still in a challenging stage. In this study, we propose a biaxial angular acceleration sensor with two uniaxial sensor units arranged orthogonally. The sensor units consist of two rotational-symmetric spiral channels and microelectromechanical system (MEMS) piezoresistive cantilevers. The cantilever is placed to interrupt the flow at the junctions of parallelly aligned spirals in each channel. When two cantilevers are used as the resistance of the bridge circuit in the two-gauge method, the rotational-symmetric spiral channels enhance the sensitivity in the target axis, while the nontarget axis sensitivities are canceled. The fabricated device responds with approximately constant sensitivity from 1 to 15 Hz, with a value of 3.86 × 10−5/(rad/s2), which is equal to the theoretical value. The nontarget axis sensitivity is approximately 1/400 of the target axis sensitivity. In addition, we demonstrate that each unit responds according to the tilt angle when the device is tilted along the two corresponding rotational axis planes. Thus, it is concluded that the developed device realizes biaxial angular acceleration measurement with low crosstalk.

Usefulness of Mobile Devices in the Diagnosis and Rehabilitation of Patients with Dizziness and Balance Disorders: A State of the Art Review.

ObjectiveThe gold standard for objective body posture examination is posturography. Body movements are detected through the use of force platforms that assess static and dynamic balance (conventional posturography). In recent years, new technologies like wearable sensors (mobile posturography) have been applied during complex dynamic activities to diagnose and rehabilitate balance disorders. They are used in healthy people, especially in the aging population, for detecting falls in the older adults, in the rehabilitation of different neurological, osteoarticular, and muscular system diseases, and in vestibular disorders. Mobile devices are portable, lightweight, and less expensive than conventional posturography. The vibrotactile system can consist of an accelerometer (linear acceleration measurement), gyroscopes (angular acceleration measurement), and magnetometers (heading measurement, relative to the Earth’s magnetic field). The sensors may be mounted to the trunk (most often in the lumbar region of the spine, and the pelvis), wrists, arms, sternum, feet, or shins. Some static and dynamic clinical tests have been performed with the use of wearable sensors. Smartphones are widely used as a mobile computing platform and to evaluate the results or monitor the patient during the movement and rehabilitation. There are various mobile applications for smartphone-based balance systems. Future research should focus on validating the sensitivity and reliability of mobile device measurements compared to conventional posturography.ConclusionSmartphone based mobile devices are limited to one sensor lumbar level posturography and offer basic clinical evaluation. Single or multi sensor mobile posturography is available from different manufacturers and offers single to multi-level measurements, providing more data and in some instances even performing sophisticated clinical balance tests.

Development of Flight Control Law for Improvement of Uncommanded Lateral Motion of the Fighter Aircraft

The Abrupt Wing Stall (AWS) at moderate Angle-of-Attacks (AoA) and transonic flight conditions can result in uncommanded lateral motions such as heavy wing, wing drop and wing rock that degrade handling qualities, mission performance and safety of flight for the aircraft. This phenomenon caused by asymmetric wing flows makes it difficult to perform precision tracking or maneuvering in the transonic flight envelope. According to the previous research results, this substantial phenomenon has occurred in a large number of the fighter aircraft programs, typically at the early flight test development stage, and a lot of budgets and efforts are required through the development period of the aircraft. To compensate for this drawback, Free-To-Roll (FTR) wind tunnel test is adopted as a method to identify the uncommanded lateral motions of the aircraft and improve the flight characteristics at the configuration design stage. However, using only the existing control methods such as the feed-forward control methods as well as the configuration design can reduce limitedly the uncommanded lateral motion. Besides, the feedback control methods using optimal control, adaptive and neural network control which do not provide a deterministic solution are limited to obtain the airworthiness certification. This paper presents a new design approach in which uncommanded lateral motions of the aircraft can be reduced even more than the existing methods. That is the additional augmentation control method, using angular acceleration measurement, that improves the flight characteristics using a feedback control technique based on the Incremental Nonlinear Dynamic Inversion (INDI). To evaluate the performances of the proposed control method, we perform the frequency-domain linear analysis and time-domain numerical simulations based on the mathematical model of advanced trainer aircraft. The evaluation result reveals that the proposed control method reduces effectively uncommanded lateral motions and improves the handling qualities of the aircraft.

Effective control allocation using hierarchical multi-objective optimization for multi-phase flight

For different flight phases in an overall flight mission, different control and allocation preferences should be pursued considering lift, drag or maneuverability characteristics. The multi-objective flight control allocation problem for a multi-phase flight mission is studied. For an overall flight mission, different flight phases namely climbing, cruise, maneuver and gliding phases are defined. Firstly, a multi-objective control allocation problem considering drag, lift or control energy preference is constructed. Secondly, considering different control preferences at different flight phases, the analytic hierarchical process method is used to construct a comprehensive performance index from different objectives such as lift or drag preferences. The active set based dynamic programming optimization method is used to solve the real-time optimization problem. For the validation, the Innovative Control Effector (ICE) tailless aircraft nonlinear model and the angular acceleration measurements based adaptive Incremental Backstepping (IBKS) are used to construct the validation platform. Finally, an overall flight mission is simulated to demonstrate the efficiency of the proposed multi-phase and multi-objective flight control allocation method. The results show that the comprehensive performance index for different phases, which are determined from the Analytic Hierarchy Process (AHP) method, can suitably satisfy the preference requirements for different flight phases.

Angular accelerometer‐based inertial navigation system

Angular acceleration sensors technologies are evolving and emerging in various applications. In this paper, we propose an angular accelerometer-based inertial navigation system. One application of such systems can be highly maneuvering platforms where direct measurement of angular acceleration is desired. To that end, a review of modern angular acceleration sensor technologies and their possible applications is provided. Two angular acceleration-based inertial navigation system architectures are suggested, and their equations of motion are derived. Additionally, an analytical assessment for short time periods of pure inertial navigation is provided with a comparison to traditional and gyro-free inertial navigation architectures.

Results from a GRACE/GRACE-FO attitude reconstruction Kalman filter

This paper outlines JPL’s V03 GRACE attitude processing strategy, characterizes the accelerometer angular measurement error profile, analyzes impact upon GRACE time-varying gravity field products as part of a complete mission reprocessing campaign, and presents implications for linear acceleration measurements. A Kalman filter-based strategy fuses star camera and angular acceleration measurements to reconstruct spacecraft attitude with reduced high-frequency noise and fewer gaps and corrects a pair of processing errors. Running data from tailored accelerometer characterization maneuvers in 2017, K-band calibration maneuvers in 2003, and nominal mission operations through our Kalman filter, estimated aliasing factors from linear to angular acceleration account for multiple forms of observed noise. During most of the mission, V03 produced very limited gains in our gravity field products, but during early and late mission high error regimes the reduction in high-frequency attitude noise substantially damped systematic gravity solution effects (latitudinal bands) and noise (stripes).

Integrated guidance and control design for the hypersonic interceptor based on adaptive incremental backstepping technique

This paper deals with the development of Integrated Guidance and Control (IGC) law for a class of hypersonic interceptors which are equipped with the infrared seeker. Since in practice the line-of-sight (LOS) angular rates are difficult to measure for this class of hypersonic interceptor, an unknown state observer based on high order sliding mode technique is firstly proposed to estimate the unknown state and disturbance precisely with the partial measurable state. Then, an adaptive Incremental Backstepping (IBS) scheme that relies on estimates of the LOS angular rates, angular acceleration measurements of the current control deflections is proposed to achieve robust tracking of a maneuvering target. The stability analysis of the closed-loop system is also conducted. At last, a series of simulation results are presented to show the great potential of the proposed IGC method in interception accuracy, even if the LOS angle rates are unmeasurable. It is shown that the proposed scheme is not only more robust to uncertainties in the hypersonic interceptor dynamics compared to conventional IGC, but also has better trajectory characteristic with less control effort. The hit-to-kill interception is achieved in the simulation results.

Enhanced Attitude Control of Unmanned Aerial Vehicles Based on Virtual Angular Accelerometer

The small unmanned aerial vehicles are susceptible to wind disturbances due to the turbulent environment at their low operational altitude. Compared to conventional IMU output, the phase-advanced information provided by angular acceleration measurement is more beneficial for flight stability. This paper presents a general and systematic approach to enhance the attitude stability of small fixed-wing unmanned aerial vehicles. The methodology begins by designing a virtual angular accelerometer (VAA), which is based on 4 MEMS IMUs measurement fusion. Then, the angular acceleration is exploited to estimate and compensate disturbances. Finally, an enhanced attitude control scheme is developed to improve attitude tracking performance, where linear or nonlinear control approaches can be adopted. A VAA-based backstepping controller (BS) is designed and its stability is analyzed via Lyapunov function. Three simulation cases are carried out to verify the performance of tracking accuracy, robustness, and disturbance rejection. PID and backstepping methods are applied to the scheme. As a comparison, a widely used nonlinear disturbance observer (NDO)-based robust controller (RC) is studied. The simulation results show the excellent performance of the sensor-based VAA to observe the fast time-varying disturbance, where the NDO causes the time delay and phase lag. The tracking accuracy of the enhanced controllers (PID+VAA, BS+VAA, and RC+VAA), compared to the basic controllers, are improved by 14.3%-93.7% and the closed-loop control systems gain notable robustness.

A Dynamic Parameter Identification Method for Flexible Joints Based on Adaptive Control

This paper investigates the dynamic parameter identification for flexible joints without additional sensors. The estimation accuracy of traditional methods based on the original dynamic model is limited by measurement of angular acceleration. Recently, approaches using integral operations are raised to solve this problem. However, the integral operations easily result in error accumulation and deteriorate the parameter estimation accuracy. This study proposes a new dynamic parameter identification method for flexible joints. By constructing an alternative system function and estimating its outputs through nonmodel-based adaptive control, we avoid the measurement of angular acceleration and integral operations. On this basis, dynamic parameters of flexible joints are estimated using the recursive least squares (RLS) method. The experimental results indicate that the proposed method possesses better estimation accuracy than the general RLS- and integral-based methods. It is also validated that the proposed method can provide accurate estimation even under a relatively low-resolution system. Applications to model-based motion control and physical human-robot interaction are also verified.

Estimation of pedestrian crowds' properties using commercial tablets and smartphones

ABSTRACTIn this study, an alternative method to estimate velocity and density in pedestrian crowds is presented. The proposed approach uses angular velocity and acceleration measurements obtained from inertial sensors to judge amount of body motion and therefore estimate walking velocity. Taking into consideration practical aspects, commercial devices (generic tablets and smartphones) are used to measure inertial quantities showing application potentials but also limitations in regard to accuracy. Several experiments have been performed in increasingly realistic scenarios to assess the suitability of the method for public pedestrian spaces. Results show that estimation for speed and density is very accurate when position and orientation of the devices are known. Estimations are still reliable in more heterogeneous situations employing different devices, with accuracy increasing with the number of pedestrians being surveyed. The proposed approach may help getting a general picture of pedestrian crowds' condition over large areas with greater employment flexibility.

Calibrating Away Inaccuracies in Ultra Wideband Range Measurements: A Maximum Likelihood Approach

A calibration framework for an ultra-wideband localization system employing inertial measurement units is presented. No external motion capture system or other sensors are required for the calibration procedure. Given a covariance function for the error in the range measurements, a range measurement model based on a Gaussian process is obtained by maximizing the joint likelihood of angular rate, acceleration, and range measurements. The framework is experimentally evaluated, and it is shown how the resulting measurement model, integrated in a standard Kalman filter, can be used for real-time localization on a platform with limited computational resources. The calibration significantly improves the localization accuracy for randomly generated trajectories and different localization system setups.

Fiber Bragg grating-based measurement of random-rotation parameters.

A preloaded rotational sensor featuring a spring packaged within the magnetic head has been proposed and experimentally demonstrated. The aforementioned fiber Bragg grating-based system can convert the strain information into rotation angles without rotation angle limitations in terms of the proposed angle transfer mathematical model. The random-angular displacements were well fitted by the model with the maximum deviation of 0.5°. The linearity of the calculated rotational velocity reaches up to 0.998 in the range of 0 to 2021.4 rpm. This sensor can also be applied in the angular acceleration measurement.

Hybrid Observer Combining Measurements of Different Fidelities

Abstract: A signal-based hybrid observer combining measurements of different fidelities is proposed for position and velocity estimation of marine vessels. The concept assumes that noisy position measurements are available only sporadically at a non-constant sampling rate. Predictions of position between the samples are provided by integrating acceleration measurements, which are available at a high rate (approximated to be continuous sampling). Estimates with smaller variance are computed by averaging multiple observer copies of the position. This work is a continuation of the observer proposed in Brodtkorb et al. (2015). The main contributions of this paper is extending the observer to the more realistic scenario where linear velocity and angular acceleration measurements are not available. A simulation study showed that the observer performed well in closed loop with a controller conducting dynamic positioning operations of a marine vessel.

Response of an Impact Test Apparatus for Fall Protective Headgear Testing Using a Hybrid-III Head/Neck Assembly.

A test method based upon a Hybrid-III head and neck assembly that includes measurement of both linear and angular acceleration is investigated for potential use in impact testing of protective headgear. The test apparatus is based upon a twin wire drop test system modified with the head/neck assembly and associated flyarm components. This study represents a preliminary assessment of the test apparatus for use in the development of protective headgear designed to prevent injury due to falls. By including angular acceleration in the test protocol it becomes possible to assess and intentionally reduce this component of acceleration. Comparisons of standard and reduced durometer necks, various anvils, front, rear, and side drop orientations, and response data on performance of the apparatus are provided. Injury measures summarized for an unprotected drop include maximum linear and angular acceleration, head injury criteria (HIC), rotational injury criteria (RIC), and power rotational head injury criteria (PRHIC). Coefficient of variation for multiple drops ranged from 0.4 to 6.7% for linear acceleration. Angular acceleration recorded in a side drop orientation resulted in highest coefficient of variation of 16.3%. The drop test apparatus results in a reasonably repeatable test method that has potential to be used in studies of headgear designed to reduce head impact injury.

Unidirectional fiber optic sensor for angular acceleration measurement

A concept of a fiber optic sensor consisting of a light source, a fiber coil, and a two-beam interferometer measuring angular acceleration is described. The principle differs essentially from common fiber optic gyroscopes (FOGs) still exploiting the Sagnac effect but sending light of the monochromatic source only unidirectionally into the fiber coil. A change in the optical path length in the fiber coil due to the Sagnac effect maintains proportionality to angular acceleration and could be detected by means of a subsequent two-beam interferometer. The sensitivity of this approach is in contrast to common FOGs determined not only by the total surface area enclosed by the fiber turns but also by the characteristics of the particular interferometer used.