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This article addresses the leader‐follower formation control problem for a group of quadrotors using only relative bearing measurements. Most existing methods require full position or velocity information, which cis challenging to obtain in harsh environments. In contrast, the proposed control scheme is based on a hierarchical system that does not rely on relative position or velocity measurements. The bearing‐only control law is designed to stabilize the desired formation, and each quadrotor maintains predetermined bearings with its neighbors. The control design relies on a non‐singular extraction algorithm for separate design of translation and rotation control. The outer loop of the control scheme utilizes a filter‐like approach to overcome the lack of bearing rate measurements in the bearing‐only formation controller. Moreover, employing differentiators following the separation principle with properties of asymptotic high accuracy, a uniform differentiator is provided for each following quadrotor to overcome the absence of linear velocity and acceleration feedback in the inner‐loop controller. Ultimately, the efficacy of the proposed control strategy is validated through a combination of Lyapunov stability theory and extensive numerical simulations. [ABSTRACT FROM AUTHOR]

This study discusses the problem of reducing the influence of external destabilizing factors on microelectromechanical angular velocity transducers. It reveals that for measurements of small angular velocities of the order of a few to tens of microradians per second, micro optoelectromechanical transducers that contain optical readout units are preferable to use. The effect of linear acceleration on the characteristics of a frame micro optoelectromechanical angular velocity transducer with two optical readout channels is analyzed. We consider two methods of angular velocity measurement error compensation when the frame micro optoelectromechanical transducer is under the influence of linear acceleration. The two compensation methods implement amplification factor control and force feedback, respectively. The readout unit, based on the optical tunnel effect and used for precision measurement of the amplitude of oscillations of the sensing element, is experimentally investigated; a function of converting the amplitude of oscillations of the sensing element into voltage is obtained. The possibility of forming transducer output signals, which are proportional to angular velocity and linear acceleration, is presented. The dependences of changes in the amplification factor on the zero off set voltage, proportional to the acting linear acceleration, are presented for different ranges of angular velocities. A system, consisting of a low-pass filter (LPF), a proportionalintegral regulator, and an additional pair of comb-type electrostatic actuators, is proposed for compensating the force effect of a destabilizing linear acceleration. Additional actuators are arranged perpendicular to the actuators that excite the primary oscillations. The measurement error of angular velocity when using the two methods of compensation, respectively, has been estimated. The proposed technical solutions enable to increase the accuracy of angular velocity measurements by micro optoelectromechanical transducers used in navigation and orientation systems of unmanned aircrafts of various types. [ABSTRACT FROM AUTHOR]

The aim of this explorative study was to determine the key inertial measurement unit-based wheelchair mobility performance components during a wheelchair tennis match. A total of 64 wheelchair tennis matches were played by 15 wheelchair tennis players (6 women, 5 men, 4 juniors). All individual tennis wheelchairs were instrumented with inertial measurement units, two on the axes of the wheels and one on the frame. A total of 48 potentially relevant wheelchair tennis outcome variables were initially extracted from the sensor signals, based on previous wheelchair sports research and the input of wheelchair tennis experts (coaches, embedded scientists). A principal component analysis was used to reduce this set of variables to the most relevant outcomes for wheelchair tennis mobility. Results showed that wheelchair mobility performance in wheelchair tennis can be described by six components: rotations to racket side in (1) curves and (2) turns; (3) linear accelerations; (4) rotations to non-racket side in (4) turns and (5) curves; and finally, (6) linear velocities. One or two outcome variables per component were selected to allow an easier interpretation of results. These key outcome variables can be used to adequately describe the wheelchair mobility performance aspect of wheelchair tennis during a wheelchair tennis match and can be monitored during training. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

The initial alignment of the inertial navigation system of unmanned offshore platforms is interfered with the swaying motion induced by wave action. Departing from the traditional alignment model based on gravitational apparent motion, this paper derives the models of gravitational apparent acceleration and velocity in order to overcome the theoretical insufficiency of directly employing accelerometers to approximate gravity. Parameter identification and reconstruction of gravitational apparent motion are performed by recursive least squares algorithm (RLS) to determine the attitude of the strapdown inertial navigation system (SINS). Concurrently, a comparison is made between the calculated and reconstructed gravitational apparent motion for the separation of the platform's linear acceleration or velocity. Simulation and mooring experiment indicate that the method studied in this paper demonstrates superior convergence and accuracy compared to traditional anti-rocking coarse alignment methods. In particular, the parameter identification alignment method based on gravitational apparent velocity is capable of achieving the extreme accuracy of the inertial measurement unit (IMU). The error in separated linear motion does not diverge over time, which meets engineering requirements. This method has important implications for application scenarios such as the initialization of inertial navigation systems on unmanned platforms. • The proposed method significantly improves the accuracy and convergence of attitude angles compared with the traditional method. • The method addresses the theoretical limitations for alignment and allows the separation of linear acceleration or velocity. [ABSTRACT FROM AUTHOR]

In this article, we discuss a sequential algorithm for the computation of a minimum-time speed profile over a given path, under velocity, acceleration, and jerk constraints. Such a problem arises in industrial contexts, such as automated warehouses, where LGVs need to perform assigned tasks as fast as possible in order to increase productivity. It can be reformulated as an optimization problem with a convex objective function, linear velocity and acceleration constraints, and nonconvex jerk constraints, which, thus, represent the main source of the difficulty. While existing nonlinear programming (NLP) solvers can be employed for the solution of this problem, it turns out that the performance and robustness of such solvers can be enhanced by the sequential line-search algorithm proposed in this article. At each iteration, a feasible direction, with respect to the current feasible solution, is computed, and a step along such direction is taken in order to compute the next iterate. The computation of the feasible direction is based on the solution of a linearized version of the problem, and the solution of the linearized problem, through an approach that strongly exploits its special structure, represents the main contribution of this work. The efficiency of the proposed approach with respect to existing NLP solvers is proven through different computational experiments. Note to Practitioners—This article was motivated by the needs of LGV manufacturers. In particular, it presents an algorithm for computing the minimum-time speed law for an LGV along a preassigned path, respecting assigned velocity, acceleration, and jerk constraints. The solution algorithm should be: 1) fast, since speed planning is made continuously throughout the workday, not only when an LGV receives a new task but also during the execution of the task itself, since conditions may change, e.g., if the LGV has to be halted for security reasons and 2) reliable, i.e., it should return solutions of high quality, because a better speed profile allows to save time and even small percentage improvements, say a 5% improvement, has a considerable impact on the productivity of the warehouse, and, thus, determines a significant economic gain. The algorithm that we propose meets these two requirements, and we believe that it can be a useful tool for LGV manufacturers and users. It is obvious that the proposed method also applies to the speed planning problem for vehicles other than LGVs, e.g., road vehicles. [ABSTRACT FROM AUTHOR]

Objective: To determine whether unilateral chronic ankle instability (CAI) affects the kinematics of the uninjured contralateral ankle. Methods: In this case‐control study, 15 adult patients with unilateral CAI and 15 healthy controls were studied. Both the unstable and uninjured ankles in patients with unilateral CAI (CAI group, n = 15) were compared with that of healthy individuals (control group, n = 15). Applying body photo‐reflective markers, the participant's motion during gait was measured. Biomechanical variables including overall ankle‐toe angle, linear velocity, linear acceleration, angular velocity, angular acceleration, range of motion (RoM) in dorsiplantar flexion, and inversion‐eversion at initial contact, loading response, mid‐stance, terminal stance, pre‐swing, and swing phase of the gait were measured. Results: In patients with CAI, the injured and uninjured ankles were significantly different regarding angle‐toe angle, inversion‐eversion RoM, dorsiplantar flexion in mid‐stance, inversion‐eversion at initial contact and terminal stance as well as the pre‐swing and swing phases (p < 0.01). The uninjured ankles of patients showed lower ankle‐toe velocity (p = 0.01) and acceleration (p = 0.01) compared to both the left and right ankles of the controls. In addition, the uninjured ankles of the patients showed decreased ankle dorsiflexion and increased inversion during initial contact, loading response, mid‐stance, terminal stance, pre‐swing, and swing compared to the control group (p < 0.017). Conclusion: The results suggest that unilateral CAI can affect gait biomechanics in the contralateral uninjured ankle. Left unaddressed, unilateral CAI may lead to increased morbidity to the contralateral uninjured side. When surgery is not preferred for the management of unilateral CAI, rehabilitation protocols should focus on both sides. [ABSTRACT FROM AUTHOR]

The objective of this study was to characterize head biomechanics of video-recorded falls involving young children in a licensed childcare setting. Children 12 to < 36 months of age were observed using video monitoring during daily activities in a childcare setting (in classrooms and outdoor playground) to capture fall events. Sensors (SIM G) incorporated into headbands worn by the children were used to obtain head accelerations and velocities during falls. The SIM G device was activated when linear acceleration was ≥ 12 g. 174 video-recorded falls activated the SIM G device; these falls involved 31 children (mean age = 21.6 months ± 5.6 SD). Fall heights ranged from 0.1 to 1.2 m. Across falls, max linear head acceleration was 50.2 g, max rotational head acceleration was 5388 rad/s2, max linear head velocity was 3.8 m/s and max rotational head velocity was 21.6 rad/s. Falls with head impact had significantly higher biomechanical measures. There was no correlation between head acceleration and fall height. No serious injuries resulted from falls—only 1 child had a minor injury. In conclusion, wearable sensors enabled characterization of head biomechanics during video-recorded falls involving young children in a childcare setting. Falls in this setting did not result in serious injury. [ABSTRACT FROM AUTHOR]

In this article, a constrained image-based visual servoing control method for the shipboard landing problem of unmanned helicopters is proposed. First, the pitch and roll motion of ship are predicted by an autoregressive (AR) model to determine an appropriate period for landing. Subsequently, a novel robust sliding mode controller without linear velocity measurements is developed on the basis of the perspective image feature in a virtual image plane. Meanwhile, a modified Chebyshev neural network (CNN) is proposed to estimate the uncertainties, including the linear acceleration of ship and translational perturbation, while an adaptive law is employed to compensate the influence of rotational disturbances. The whole controller only requires the measurements feedback of a vision sensor and an inertial measurement unit (IMU). Ulteriorly, to prevent the visual target on the ship from going beyond the field of view of camera, the constrained controller is developed by a control barrier function and a quadratic programming, where the unknown relative velocity is estimated by a velocity observer. Finally, simulations are implemented to substantiate the capability of the presented shipboard landing control method. [ABSTRACT FROM AUTHOR]

In this paper, a novel spatial support mechanism for planar deployable antennas is designed based on the motion principle of planar deployable antennas and the spatial mechanism theory. The composition principle of the novel mechanism and its geometric characteristics are analyzed, and its degrees of freedom are calculated based on the constraint topological diagram. Subsequently, kinematic analysis is conducted, and the angular velocity, linear velocity, and linear acceleration of each component in the mechanism are calculated. Then, numerical calculation and simulation are performed to verify the correctness of the theoretical analysis results. The performance analysis of the spatial support mechanism is completed. A prototype of the proposed support mechanism is developed and tested to validate the feasibility of the mechanism principle. The present work can provide reference for the design and engineering application of this type of mechanisms. • 1.Propose a novel support mechanism for planar deployable antennas. • 2.Analyze the DOFs, kinematics, dynamics based on the constraint topological diagram. • 3.Develop a prototype of the proposed support mechanism and validate the motion principle. [ABSTRACT FROM AUTHOR]

This paper deals with the development of an adaptive robust controller for an Unmanned Aircraft System with variable mass. The goal is to improve trajectory tracking and energy performance while the aircraft mass is gradually reducing due to payload release. To improve the trajectory tracking performance, we propose an algorithm that merges the concepts of least squares method and sliding mode observer for the estimation of the vehicle mass. The nonlinear observer estimates the linear velocities and accelerations, which are further used to obtain the vehicle mass. A robust adaptive pole placement controller based on the Attractive Ellipsoid Method uses this estimation to update the controllers gains due to the mass variation. To validate the effectiveness of the proposed algorithm for performing aerial transportation and deployment of payloads, we present a numerical example comparing the performance of the proposed method with respect to using Proportional Derivative controllers as well as Robust Controllers. [ABSTRACT FROM AUTHOR]

For modern information, measuring, and optoelectronic systems based on micro- and nanomechanical sensors of angular velocity and linear acceleration, it is important to ensure their stable functioning in the presence of external factors. The paper presents the results of a study of the effect of a random vibration on the characteristics of micromechanical accelerometers (MMAs) obtained using the LDS V455 vibration bench. The dependence of the spectral density of vibration acceleration on the frequency of one of the samples, intended for acceleration measurements in the range up to ±1.2 g, has a noticeable shift from its predetermined profile. To establish the reasons for this discrepancy, the design of the MMAs' sensitive element (SE) under the effect of a random vibration is studied. Calculations and simulations are performed in the ANSYS program. The deformations of the MMAs' SE along the sensitivity axis Z and the capacitance changes due to the acceleration and random vibration along the X, Y, and Z axes, taking into account the crystallographic orientation of the SE's material (silicon) are determined. The effect of the crystallographic orientation of silicon used to manufacture the MMAs' SE on the deformation (deflection) of the rotor is considered. The presented results of the theoretical and experimental studies, as well as computer modeling, coincide, which allows us to improve the design of the MMAs' SE. [ABSTRACT FROM AUTHOR]

Goal. Investigation of the main kinematic parameters of a shredding machine with two moving tanks connected by a translational kinematic pair and performing complex spatial motion to be able to further predict the technological result at the design stage of such equipment and the corresponding technological operations of machining parts. Method. Using the SolidWorks-2016 Motion computer-aided design system, 3D modeling was carried out, followed by kinematic analysis, of a machine for processing parts with two movable capacities, which are interconnected by a translational kinematic pair and perform complex spatial motion. The essence of kinematic analysis was to determine the linear velocities and accelerations of points that coincide with the ends of the working tanks of the machine. Results. Based on 3D modeling and kinematic analysis in the SolsdWorks-2016 Motion computeraided design system, some kinematic parameters of the machine are determined, in particular, the law of the change in the angular velocity of the driven shaft of the machine is obtained in the form of graphical dependencies, the change in the translational speed and translational acceleration of four points, which are conventionally located in the center, is studied the ends of each of the working capacities. Scientific novelty. The relationship between some kinematic parameters of the developed machine design with two moving capacities that perform complex spatial motion is established. Practical importance. It was found that the kinematic parameters of the two tanks of the machine differ from each other, as a result of which, during the execution of the corresponding technological operations, the intensity of movement of the working array in the two capacities will differ from each other. In addition, the ends of each of the working capacities move with almost the same kinematic parameters, which will facilitate the movement of the working array between the opposite ends of both tanks in opposite directions with the same intensity. The results obtained make it possible to determine the most rational functional purpose of the machine under study. [ABSTRACT FROM AUTHOR]

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This paper deals with the problem of full state estimation for vehicles navigating in a three dimensional space. We assume that the vehicle is equipped with an Inertial Measurement Unit (IMU) providing body-frame measurements of the angular velocity, the specific force, and the Earth's magnetic field. Moreover, we consider available sensors that provide partial or full information about the position of the vehicle. Examples of such sensors are those which provide full position measurements (e.g., GPS), range measurements (e.g., Ultra-Wide Band (UWB) sensors), inertial-frame bearing measurements (e.g., motion capture cameras), or altitude measurements (altimeter). We propose a generic semi-globally exponentially stable nonlinear observer that estimates the position, linear velocity, linear acceleration, and attitude of the vehicle, as well as the gyro bias. We also provide a detailed observability analysis for different types of measurements. Simulation and experimental results are provided to demonstrate the effectiveness of the proposed estimation scheme. [ABSTRACT FROM AUTHOR]