Angle Drift Research Articles

Divergent Component of Motion Planning and Adaptive Repetitive Control for Wearable Walking Exoskeletons.

Wearable walking exoskeletons show great potentials in helping patients with neuro musculoskeletal stroke. Key to the successful applications is the design of effective walking trajectories that enable smooth walking for exoskeletons. This work proposes a walking planning method based on the divergent component of motion to obtain a stable joint angle trajectory. Since periodic and nonperiodic disturbances are ubiquitous in the repeating walking motion of an exoskeleton system, a major challenge in the walking control of wearable exoskeleton is the joint angle drift problem, that is, the joint angle motion trajectories are not necessarily periodic due to the presence of disturbance. To address this challenge, this work develops an adaptive repetitive control strategy to guarantee that the motion trajectories of joint angle are repetitive. In particular, by treating the disturbance as system uncertainties, an adaptive controller is designed to compensate for the uncertainties based on an integral-type Lyapunov function. A fully saturated learning approach is then developed to achieve asymptotic tracking of repetitive walking trajectories. Extensive experiments are carried out to demonstrate the effectiveness of the tracking performance.

Online Thevenin’s Equivalent Using Local PMU Measurements

This paper presents a method for determining Thevenin’s Equivalent (TE) for a node in a power system using local PMU measurements at that node. Three consecutive voltage and current measurements are used to determine the TE. The proposed method recognizes and considers the phase angle drift caused by the slip frequency between the PMU sampling frequency and the power system frequency. The accuracy of the proposed method has been verified through application to the IEEE 30 bus test system as well as to a real system data measured at the terminals of a wind farm. The proposed method is going to be used to determine an online TE, which will be used to monitor the system capability to accommodate the wind power by updating a capability chart of the system at the node where the wind farm is connected.

Noninvasive Targeting System with Three-Dimensionally Printed Customized Device in Stereotactic Brain Biopsy

ObjectThree-dimensional (3D)-printed models are currently used in the medical field. This study aimed to evaluate the feasibility and safety of a 3D-printed guide plate for use in brain biopsy. MethodsTwelve patients with intracranial lesions were retrospectively reviewed to determine clinical outcomes and technical procedural operability. These patients underwent brain biopsy assisted with the 3D-printed guide plate. Post-operative computed tomography (CT) was performed to assess the accuracy and associated complications of this guide plate. ResultsAll patients received definite diagnoses assisted by this guide plate. The deviations of the entry and target points were 3.93 ± 0.96 mm and 2.59 ± 0.11 mm, respectively. The angle drift of the puncture path was 5.12 ± 0.14°, and the deviation of the puncture depth was 2.35 ± 1.13 mm. The operation time ranged from 38.5 min with local anesthesia to 76.2 min with general anesthesia. No patients experienced complications. ConclusionsThe 3D-printed guide plate was non-invasive and had acceptable accuracy and the flexibility of frameless systems. The economic and operative benefits of this device supported its status as a powerful tool for brain biopsy in medical facilities in economically disadvantaged areas or institutions without navigation systems.

Neural Dynamic Fault-Tolerant Scheme for Collaborative Motion Planning of Dual-Redundant Robot Manipulators.

To avoid the task failure caused by joint breakdown during the collaborative motion planning of dual-redundant robot manipulators, a neural dynamic fault-tolerant (NDFT) scheme is proposed and applied. To do so, a joint fault-tolerant strategy is first designed, and it is formulated as a time-varying equality constraint. Second, combining the robot position and orientation control, joint limit constraint, joint fault-tolerant equality constraint, and considering the repetitive motion optimization criterion, a fault-tolerant framework for the dual-redundant robot manipulators based on quadratic programming (QP) is constructed. Then, a varying-parameter recurrent neural network (VP-RNN) is designed to solve the QP issue. The fault-tolerant framework and the VP-RNN constitute NDFT scheme. With the NDFT scheme, the impact of faulty joints on the whole system can be remedied by healthy joints, thereby the end-effectors of the robot can complete the given end-effector task. Finally, computer simulations and physical experiments are implemented to verify the availability, physical realizability, and accuracy of the proposed NDFT scheme in the collaborative execution of end-effector tasks. Comparative experimental results with conventional repetitive motion planning schemes based on neural networks show higher accuracy and smaller joint angle drift.

Prediction of the drift trend in piezoelectrically actuated MEMS mirror by 2D reliability modelling

One of the most prominent applications of piezoelectric materials is in microelectromechanical systems (MEMS). A current challenge in piezo-MEMS is the prediction of the reduction in efficiency of piezoelectric materials towards the end of their lifespan. In this research, we assess the reliability of piezoelectrically actuated micromirrors (piezo-mirrors) and estimate the parametric drift, such as the drift of the opening angle, during the specified lifetime. We accomplish this assessment and evaluation by considering the impacts of both temperature and driving voltage. In this study, the analytical relationship between micromirror performance, driving voltage, temperature, and operative time has been described and predicted by using a 2D reliability model based on a characteristic function that explains the PZT stability. The operative time acceleration associated with distinct test conditions has been considered by using a power law model for voltage dependency and an Arrhenius model to describe the relationship between the temperature and its acceleration effect on the drift of the piezo-mirror performance. Micromirrors were subjected to experimental tests, and the results were employed to validate the reliability model presented in this work. Therefore, the model parameters were fine-tuned using experimental data from High-Temperature Operative Life (HTOL) test, and the reliability model was validated by comparing the experimental data from HTOL test performed under different test conditions.

Evaluation of Error-State Kalman Filter Method for Estimating Human Lower-Limb Kinematics during Various Walking Gaits.

Inertial measurement units (IMUs) offer an attractive way to study human lower-limb kinematics without traditional laboratory constraints. We present an error-state Kalman filter method to estimate 3D joint angles, joint angle ranges of motion, stride length, and step width using data from an array of seven body-worn IMUs. Importantly, this paper contributes a novel joint axis measurement correction that reduces joint angle drift errors without assumptions of strict hinge-like joint behaviors of the hip and knee. We evaluate the method compared to two optical motion capture methods on twenty human subjects performing six different types of walking gait consisting of forward walking (at three speeds), backward walking, and lateral walking (left and right). For all gaits, RMS differences in joint angle estimates generally remain below 5 degrees for all three ankle joint angles and for flexion/extension and abduction/adduction of the hips and knees when compared to estimates from reflective markers on the IMUs. Additionally, mean RMS differences in estimated stride length and step width remain below 0.13 m for all gait types, except stride length during slow walking. This study confirms the method's potential for non-laboratory based gait analysis, motivating further evaluation with IMU-only measurements and pathological gaits.

Identification and Correction of Phase Error for Whole-Angle Micro-Shell Resonator Gyroscope

The phase error is inevitable in the whole-angle control system and has a great impact on the gyroscope’s performance. In this article, the identification and correction of phase errors are carried out to eliminate the effects of phase errors under the whole-angle mode. The sources of phase errors are analyzed at first from the phase delay of the whole-angle control system. Furthermore, the effects of phase errors are also investigated from the theoretical and experimental analyses. It demonstrates that the phase error would produce coupling effects between the pattern angle and quadrature control loops and produce additional angle drift (AAD) affecting the performance of the whole-angle gyroscope. Therefore, the identification method of phase errors is presented on the basis of the observation of the AAD and the correction of phase errors can also be carried out by the phase shift module. After the correction of phase errors, the performance of bias instability and scale-factor nonlinearity improves by five and nine times, respectively.

Precision roll angle measurement system based on autocollimation.

The traditional autocollimation method is widely used for small angle measurement due to its high precision and high resolution, but it cannot be used to measure the roll angle. To overcome this problem, a roll angle measurement method based on autocollimation is proposed in this paper. To achieve roll angle measurement, a transmission grating is selected to generate a pair of measurement beams, and a combined target is designed as the angle sensor. A roll angle with higher accuracy and resolution can be obtained by differential measurement, because the measurement error introduced by the beam angle drift of the light source can be effectively suppressed. A series of experiments is carried out to verify the performance of the proposed system. In the experiments, the resolution of the roll angle is better than 0.05 arcsec, and the accuracy of the system is 0.20 arcsec with a measurement range of 250 arcsec.

An Adaptive Angle Error Compensator for IPMSMs With Periodic Loads in the Flux Weakening Region

When the load of a motor changes periodically with the mechanical angle, the speed also changes. There are obvious amplitude attenuation and phase shift in the high-frequency band of the phase-locked loop, resulting in the periodic angle error between the estimated angle and the real angle when the motor is in the high-speed flux weakening region. The periodic angle error easily leads to the deterioration of the flux weakening control performance, and causes greater speed and current fluctuations. In this article, an adaptive angle error compensator (AAEC) is proposed to reduce the angle error caused by the periodic load and improve the performance of the flux weakening control. In order to avoid the influence of the angle error direct-current drift in the speed dynamic process on the AAEC iteration, the switch mode AAEC (SMAAEC) is proposed to replace the AAEC. The experimental results show that in the flux weakening region, the SMAAEC can greatly reduce the fluctuations of the speed, angle error, and currents, and improve the steady-state performance of the controller.

Neural-Dynamics Optimization and Repetitive Learning Control for Robotic Leg Prostheses

Rapid development in robotics and bionics makes it possible for robotic leg prostheses to help amputees while imposing challenges on duplicating the motion characteristics of the amputees’ healthy leg. One critical problem in prosthetic control is joint angle drift problem, that is, a repetitive motion trajectory in task space cannot guarantee that the generated motion trajectories in joint space are also repetitive. In order to solve this problem, in this article, we propose neural-dynamics optimization for robotic leg prostheses to generate the repetitive joint trajectories in real time. Our proposed method duplicates the self-selected walking speed of the amputees’ healthy leg. The online motion generation is formulated as a constrained quadratic programming (QP) optimization problem whose objective function adopts the kinetic energy and joint displacement performance criterion. The varying parameter convergent differential neural network is developed as a real-time QP solver which can globally converge to the optimal solution of the constrained QP problem. Then, a repetitive learning controller is designed for robotic leg prostheses to reduce the tracking errors while following the repetitive motion. Through the physical experiments on the developed two-degree-of-freedom robotic leg prosthesis worn on an amputee, the neural-dynamics optimization is substantiated to be a remedy of online motion generation, and the effectiveness of repetitive learning control for reducing the prosthetic tacking errors is verified.

Investigation of Angle Drift Induced by Actuation Electrode Errors for Whole-Angle Micro-Shell Resonator Gyroscope

The symmetry of the actuation electrode is of great importance for the whole-angle gyroscope. In this paper, the angle drift induced by actuation electrode errors of micro-shell resonator gyroscope is investigated. The actuation electrode errors due to the assembly of the micro-shell resonator and substrate electrode would result in interference effects between the energy and pattern-angle control loops and produce the additional angle drift which has great influences on the performance. The additional angle drift is investigated from experimental and simulation analysis under various actuation gain and angle errors. Furthermore, the characterization and compensation methods of actuation electrode errors are also proposed to eliminate the interference effects of control loops and the additional angle drift. After compensation, the scale-factor nonlinearity and bias instability has been improved by 3 and 2 times to 5.79ppm and 0.064 °/h.

Usability evaluation algorithm of sea area landmark

The landmarks encountered by a flight vehicle in its scene matching navigation are insufficient and distributed unevenly, thus being unable to effectively assist in its inertial navigation system (INS). Therefore, this paper proposes a novel algorithm for sea area landmark usability evaluation based on the probability model. The algorithm defines three types of sea area landmarks and gives their matching method and strategy. The visible range of each sea area landmark is determined according to its relative relations between each position and all landmarks in flight area, flight altitude, flight speed, camera field of view angle and INS drift error. The matching probability of different types of landmarks at different flight altitudes is calculated. Then the observable probability of each landmark is reckoned to give the probability cloud of the sea area landmark usability. The simulation results verify the effectiveness of the algorithm. The sea area landmark usability evaluation results can provide bases for INS to effectively utilize landmarks to perform route planning and realize long-time flight and high-precision navigation.

Characterization and Compensation of Detection Electrode Errors for Whole-Angle Micro-Shell Resonator Gyroscope

As for the whole-angle gyroscope, the detection symmetry along two axes is of significant importance to improve the gyroscope’s performance. This paper presents the characterization and compensation of detection electrode error for the whole-angle micro-shell resonator gyroscope. The detection electrode errors including detection gain and angle errors mainly result from the assembly process of the micro-shell resonator and substrate electrode. The angle estimation errors, as a direct effect of detection electrode error, are investigated through experiments and theoretical analysis under different detection gain and angle errors. Besides, the consistency of experimental and simulation results proves that the sin and cos components of angle estimation error can be used to characterize detection gain and angle errors respectively. This angle estimation error not only has direct effects on the gyroscope’s angle output but also results in the position error of applied actuation forces. Under this circumstance, the energy control force is observed to interfere with the free precession of the vibration pattern and produces additional angle drift. To eliminate the effects of the detection electrode error, the compensation parameters are identified based on the component analysis of the angle estimation error. After compensation, the bias instability has decreased from 0.118°/h to 0.041°/h and the scale-factor nonlinearity has been also improved by 36 times from 86.57ppm to 2.4ppm. [2021-0176]

Normal‐ and Reversed‐Boomerang Stripes on Electron Pitch Angle Distributions: Solar Wind Dynamic Pressure Effect

AbstractIn the inner magnetosphere dominated by the dipole magnetic field, energetic electrons of 90° pitch angle drift faster than those of other pitch angles. Electron flux oscillations initiated by injections or drift resonances will be observed earlier at a 90° pitch angle, that is, 90°‐leading boomerang‐shaped stripes on pitch angle distributions(PADs) are expected. In this work, reversed‐boomerang stripes (90° observed last) are first reported from the observations of RBSP‐A at L‐shell ∼5.9 on 11 March 2016. The corresponding solar wind dynamic pressure is over 10 nPa, which suggests that strong compression on the magnetosphere changes the magnetic field and drift frequencies of energetic electrons. Test particles running in an image‐dipole magnetic field (off‐equatorial minima exists at dayside large L‐shell) reproduce the abnormal (90° slower) drift velocities at L‐shell >5.8 but are normal at L‐shell <4.5 dominated by a dipole field. Normal boomerang stripes on PADs are indeed observed by RBSP‐B at L‐shell ∼4.0, indicating the solar wind dynamic pressure effect.

Effect of Radar Incident Angle on Full-Wave Inversion for the Retrieval of Medium Surface Permittivity for Drone-Borne Applications

Drone-borne ground-penetrating radar (GPR) has proven to be efficient and promising for high-resolution topsoil moisture mapping at the field scale. However, in practice, the radar incident angle may change as a function of the terrain slope and unstable flying conditions. In this respect, we analyzed the effect of radar incident angle on full-wave inversion for soil permittivity characterization. Specifically, using the frequency-domain radar equation, antenna characteristic functions with different incident angles were determined for a horn antenna as an example. Then, numerical analyses and field measurements were performed to quantify the errors on the retrieved permittivity resulting from incident angle drifts. In agreement with the radar equation concept, we observed that the angle- and frequency-dependent global transmission functions of the antenna correspond well to its radiation pattern. Numerical and field results show that errors in the permittivity estimation can be very significant as a function of the antenna radiation pattern and the incident angle. Nevertheless, if the incident angle is known and the characteristic antenna functions are determined as a function of the incident angle, full-wave modeling and inversion remain accurate, provided that the signal-to-noise ratio remains sufficient.

0.79\u2009ppm scale-factor nonlinearity whole-angle microshell gyroscope realized by real-time calibration of capacitive displacement detection

Whole-angle gyroscopes have broad prospects for development with inherent advantages of excellent scale factor, wide bandwidth and measurement range, which are restrictions on rate gyroscopes. Previous studies on the whole-angle mode are based mostly on the linear model of Lynch, and the essential nonlinearity of capacitive displacement detection is always neglected, which has significant negative effects on the performance. In this paper, a novel real-time calibration method of capacitive displacement detection is proposed to eliminate these nonlinear effects. This novel method innovatively takes advantage of the relationship between the first and third harmonic components of detective signals for calibration. Based on this method, the real-time calibration of capacitive displacement detection is achieved and solves the problems of traditional methods, which are usually related to the vibration amplitude, environmental variations and other factors. Furthermore, this novel calibration method is embedded into a whole-angle control system to restore the linear capacitive response in real time and then combined with a microshell resonator for the first time to exploit the enormous potential of an ultrahigh Q factor and symmetric structure. The effectiveness is proven because the angle drift is reduced significantly to improve the scale-factor nonlinearity by 14 times to 0.79 ppm with 0.0673°/h bias instability and a 0.001°/s rate threshold, which is the best reported performance of the MEMS whole-angle gyroscope thus far. More importantly, this novel calibration method can be applied for all kinds of resonators with the requirement of a linear capacitive response even under a large resonant amplitude.

Single-Channel Control for Hemispherical Resonator Gyro Based on Time Division Multiplexing and Demultiplexing

With the feature of high precision, strong reliability, and long life, hemispherical resonator gyro (HRG) has a broader prospect in the field of inertial navigation. However, the electrical gain (EG) and electrical phase (EP) between the two control channels in whole angle mode operation are usually unbalanced, which inevitably lead to drift error in the output angle of gyro. In this paper, the analysis of angle drift error in circumferential range from 0 degree to 90 degree caused by EG unbalance and EP unbalance is conducted theoretically and verified by experiments. To deal with the problem of electrical unbalance, a single-channel control strategy based on time division multiplexing and demultiplexing is proposed. Compared with the traditional dual-channel control, the single-channel control can fundamentally eliminate the angle drift error caused by both EG unbalance and EP unbalance and suppress the peak-to-peak value of angle drift error by 5x. What’s more, the proposed single-channel control strategy can also achieve reducing the cost, size, weight, and power (CSWaP) of gyro control system, which is beneficial to HRG miniaturization.

MECHANICAL BEHAVIOR RESEARCH OF A NEW TYPE OF DOUBLE-SKIN STEEL-CONCRETE COMPOSITE SHEAR WALL

A new type of double-skin steel-concrete composite shear wall with vertical seams between shear wall and boundary elements were proposed, and the wall plates are connected using bolts and plate connectors. Quasi-static tests on four specimens were carried out to study the seismic behavior of the composite shear wall. The results of tests were compared with the same types of composite shear walls without vertical seams, in which the upper and lower steel faceplates were weld together. The test results showed that the new type of double-skin steel-concrete shear wall had good seismic performance. The average values of the yield drift angle and ultimate drift angle of the four specimens were 1/169 and 1/37, respectively. The seams weakened the bearing capacity of the test specimen, but improved the ductility and the performance of energy consumption. The failure mode of specimens was bending failure at the bottom of the wall, indicating that the stress between walls could be effectively transmitted through bolts and plate connectors. A finite element model was developed using ABAQUS to analyze the performance of this type of double-skin composite shear wall. The force mechanism of bolt group in the plate connectors, the effects of vertical seams on the failure mode of boundary columns, and other factors including strength of material, shear-span ratio and axial compression ratio which may affect the performance of the composite shear wall, were also analyzed based on the FEM model.

Adaptive compensation of damping asymmetry in whole-angle hemispherical resonator gyroscope

Damping asymmetry is one of the most important factors that determines the performance of the hemispherical resonator gyroscope. In this paper, the error mechanism of damping asymmetry in the Whole Angle (WA) mode is investigated, and an adaptive compensation method is proposed to eliminate the angle drift induced by the damping asymmetry. This adaptive compensation approach adopts the recursive least-squares method to identify the damping asymmetry, and the optimal parameters can be calculated through simulation. Furthermore, a self-precession method is applied to make this compensation method available for more occasions. This compensation method is able to automatically complete the compensation process without any angular input or a priori information on damping distribution. According to the experimental results, the angle-dependent bias has been reduced from 0.0316 s−1 to 0.0051 s−1 by this method. The presented method is widely applicable for gyroscopes working in the WA mode, which may be useful for further research on inertial sensors with high accuracy.

Algorithm design and experimental verification of a heading measurement system based on polarized light/inertial combination

In recent years, polarized light navigation has been widely used for the application of the autonomous heading measurement of small unmanned combat platforms to satellite navigation rejection. However, current techniques of polarized light navigation yield low accuracy when measuring the heading angle in dynamic environments, and the use of a single source of navigation has some shortcomings as well. In the environment of satellite navigation rejection, a method to measure the heading angle using angle compensation based on three-dimensional image geometric correction is proposed in this paper. A model of polarized light/inertial combination based on the Cubature Kalman Filter (CKF) is established using this, and was verified by outdoor experiments that employed the polarized light/inertial combination heading measurement system. The results showed that the overall stability of the heading angle as calculated by the data fusion algorithm of polarized light and the inertial system based on the CKF followed the trend of the polarized light, which adequately suppressed the angle drift caused by data of the inertial system. Following the application of the CKF filtering algorithm, the root mean square error of the heading angle was 1.0719°, which improved the accuracy of calculating the heading angle of the polarized light/inertial integrated system in non-horizontal road environments.