Electromagnetic Force on an Aluminum Honeycomb Sandwich Panel Moving in a Magnetic Field.

This paper reports a method for calculating the electromagnetic force acting on an aluminum honeycomb sandwich panel moving in a magnetic field. This research is motivated by the non-contact electromagnetic detumbling technology for space non-cooperative targets. Past modeling of the electromagnetic forces and torques generally assumes that the target is homogeneous. However, aluminum honeycomb sandwich panels are extensively used in spacecraft structures to reduce weight without sacrificing structural strength and stiffness, which are so inhomogeneous and complicated that it is difficult to obtain the induced electromagnetic force even by numerical methods. An equivalent conductivity tensor of an aluminum honeycomb sandwich panel is proposed, which allows the aluminum honeycomb sandwich panel to be treated as a homogeneous structure when calculating the induced electromagnetic forces. The advantage of the equivalent conductivity tensor in the calculation of induced electromagnetic forces is verified by finite element simulations. The proposed method makes it possible to evaluate the electromagnetic force of a large aluminum honeycomb sandwich structure moving in a magnetic field.

Design and Analysis of a 2-DOF Electromagnetic Actuator with an Improved Halbach Array for the Magnetic Suspension Platform.

For large bearing capacity and low current consumption of the magnetic suspension platform, a 2-DOF electromagnetic actuator with a new structure of halbach array is proposed to improve driving force coefficients. The structure and the working principle are introduced. An accurate sub domain model of the new structure is established to accurately and rapidly calculate the magnetic field distribution for obtaining the parameters and performance of the electromagnetic actuators. The analytical model results are verified by the finite element method. The force/torque model of the magnetic suspension platform is established based on the proposed 2-DOF electromagnetic actuator. Three position-sensitive detectors and six accelerometers are applied to perceive in real time the posture and vibration acceleration of the platform, respectively. Their hardware information is introduced and measurement models are established based on the layout. Finally, the electromagnetic characteristics of the proposed actuator are investigated and compared with the conventional counterpart by finite element analysis. The results show that the average magnetic field, 0.432 T, horizontal and vertical force coefficient, 92.3 N/A and 30.95 N/A, and torque in x and z direction, 3.61 N·m and 8.49 N·m, of the proposed actuator are larger than those of the conventional one.

A Novel 2-DOF Lorentz Force Actuator for the Modular Magnetic Suspension Platform.

The modular magnetic suspension platform depends on multi degree of freedom of Lorentz force actuators for large bearing capacity, high precision positioning and structure miniaturization. To achieve the integration of vertical driving force and horizontal driving force, a novel 2- (two degrees-of-freedom) DOF Lorentz force actuator is developed by designing the pose of the windings and permanent magnets (PMs). The structure and the working principle are introduced. The electromagnetic force mathematical model is established by the equivalent magnetic circuit method to analyze the coupling of magnetic flux. The distribution characteristics of magnetic flux density are analyzed by the finite-element method (FEM). It is found that the coupling of the magnetic flux and the large magnetic field gradient severely reduce the uniformity of the air-gap magnetic field. The electromagnetic force characteristic is investigated by FEM and measurement experiments. The difference between FEM and experiment results is within 10%. The reasons of driving force fluctuation are explained based on the distribution of air-gap magnetic field. The actuator performance are compared under the sliding mode control algorithm and PID control algorithm and the positioning accuracy is 20 µm and 15 µm respectively. Compared with the similar configuration, the motion range and force coefficient of the Lorentz force actuator in this paper are larger. It has a certain guiding significance on the structure design of the multi degree of freed Lorentz force actuator.

Measurement Model and Precision Analysis of Accelerometers for Maglev Vibration Isolation Platforms.

High precision measurement of acceleration levels is required to allow active control for vibration isolation platforms. It is necessary to propose an accelerometer configuration measurement model that yields such a high measuring precision. In this paper, an accelerometer configuration to improve measurement accuracy is proposed. The corresponding calculation formulas of the angular acceleration were derived through theoretical analysis. A method is presented to minimize angular acceleration noise based on analysis of the root mean square noise of the angular acceleration. Moreover, the influence of installation position errors and accelerometer orientation errors on the calculation precision of the angular acceleration is studied. Comparisons of the output differences between the proposed configuration and the previous planar triangle configuration under the same installation errors are conducted by simulation. The simulation results show that installation errors have a relatively small impact on the calculation accuracy of the proposed configuration. To further verify the high calculation precision of the proposed configuration, experiments are carried out for both the proposed configuration and the planar triangle configuration. On the basis of the results of simulations and experiments, it can be concluded that the proposed configuration has higher angular acceleration calculation precision and can be applied to different platforms.

Design and Optimization of UAV Aerial Recovery System Based on Cable-Driven Parallel Robot.

Aerial recovery and redeployment can effectively increase the operating radius and the endurance of unmanned aerial vehicles (UAVs). However, the challenge lies in the effect of the aerodynamic force on the recovery system, and the existing road-based and sea-based UAV recovery methods are no longer applicable. Inspired by the predatory behavior of net-casting spiders, this study introduces a cable-driven parallel robot (CDPR) for UAV aerial recovery, which utilizes an end-effector camera to detect the UAV's flight trajectory, and the CDPR dynamically adjusts its spatial position to intercept and recover the UAV. This paper establishes a comprehensive cable model, simultaneously considering the elasticity, mass, and aerodynamic force, and the static equilibrium equation for the CDPR is derived. The effects of the aerodynamic force and cable tension on the spatial configuration of the cable are analyzed. Numerical computations yield the CDPR's end-effector position error and cable-driven power consumption at discrete spatial points, and the results show that the position error decreases but the power consumption increases with the increase in the cable tension lower limit (CTLL). To improve the comprehensive performance of the recovery system, a multi-objective optimization method is proposed, considering the error distribution, power consumption distribution, and safety distance. The optimized CTLL and interception space position coordinates are determined through simulation, and comparative analysis with the initial condition indicates an 83% reduction in error, a 62.3% decrease in power consumption, and a 1.2 m increase in safety distance. This paper proposes a new design for a UAV aerial recovery system, and the analysis lays the groundwork for future research.

Transient wave propagation in the ring stiffened laminated composite cylindrical shells using the method of reverberation ray matrix.

The method of reverberation ray matrix is extended to investigate the transient wave propagation and early short time transient responses of the ring stiffened laminated composite cylindrical shells subjected to impact loads. The ring stiffened laminated cylindrical shells are modeled as the continuous coupling systems between the vibration of the un-stiffened laminated cylindrical shell and the motion of the curved beams. The dynamic models of the laminated cylindrical shell and curved beams in the Laplace phase space are established on the basis of the first order shear deformation theory. The reverberation ray matrix can be determined by the boundary and continuous conditions of the ring stiffened laminated cylindrical shell. Using the fast Fourier transform algorithm, the dynamic responses of the ring stiffened laminated cylindrical shells can be computed. Through the numerical simulations, it can be seen that the early short time transient accelerations of the ring stiffened laminated cylindrical shells under impact loads are very large, while the early short time transient shear strains and displacements are very small. Furthermore, the influences of the ring stiffener number and impact load types on the early short time transient responses of the ring stiffened laminated cylindrical shells are also investigated.

Origami-inspired Bionic Soft Robot Stomach with Self-Powered Sensing.

The stomach is a vital organ in the human digestive system, and its digestive condition is critical to human health. The physical movement of the stomach during digestion is controlled by the circular and oblique muscles. Existing stomach simulators are unable to realistically reproduce the physical movement of the stomach. Due to the complexity of gastric motility, it is challenging to simulate and sense gastric motility. This paper proposes for the first time a bionic soft robotic stomach (BSRS) with an integrated drive and sensing structure inspired by origami and self-powered sensing technology. This soft stomach (SS) can realistically simulate and sense the movements of various parts of the human stomach in real-time. The contraction force and contraction rate of the BSRS are investigated with different viscosity contents, and the experimental values are similar to the physiological range (maximum contraction force is 3.2 N, and maximum contraction rate is 0.8). This paper provides an experimental basis for the study of gastric digestive medicine and food science by simulating the peristaltic motion of the BSRS according to the human stomach and by combining the triboelectric nanogenerator (TENG) sensing technology to monitor the motion of the BSRS in real-time. This article is protected by copyright. All rights reserved.

A shape memory alloy actuated release device using non-self-locking thread.

This paper proposes a novel non-explosive and resettable release device driven by shape memory alloy (SMA), which can replace the commonly used pyrotechnic device. In the scheme, a flywheel nut with bidirectional thread is connected with two screws through the non-self-locking thread, and the target adapters are fixed with the two screws and then locked into a hole by the flywheel nut. When unlocking, the offset SMA actuator releases the flywheel nut by triggering the pulley assembly and multi-level levers. Under the pulling force of the pre-tightening load of the screws, the flywheel nut rotates at high speed to unlock the screws, thus releasing the target adapters. After separation, the device can be quickly reset with the reset tool without replacing any parts. The prototype of the release device is fabricated and tested; according to the performance test results, the device can bear the maximum bi-directional preload of 10 kN and the average unlocking force is 9.73 N. The unlocking time decreases with the increase in driving voltage, and the average unlocking response time is 342 ms under 9 V voltage. Furthermore, the actuator can function well with a lifetime of more than 50 cycles. It is concluded that this scheme has potential advantages to replace the traditional non-reusable explosive driving device.

Resistance Characteristics of SMA Actuator Based on the Variable Speed Phase Transformation Constitutive Model.

The shape memory alloy (SMA)-based actuators have been increasingly used in different domains, such as automotive, aerospace, robotic and biomedical applications, for their unique properties. However, the precision control of such SMA-based actuators is still a problem. Most traditional control methods use the force/displacement signals of the actuator as feedback signals, which may increase the volume and weight of the entire system due to the additional force/displacement sensors. The resistance of the SMA, as an inherent property of the actuator, is a dependent variable which varies in accordance with its macroscopic strain or stress. It can be obtained by the voltage and the current imposed on the SMA with no additional measuring devices. Therefore, using the resistance of the SMA as feedback in the closed-loop control is quite promising for lightweight SMA-driven systems. This paper investigates the resistance characteristics of the SMA actuator in its actuation process. Three factors, i.e., the resistivity, the length, and the cross-sectional area, which affect the change of resistance were analyzed. The mechanical and electrical parameters of SMA were obtained using experiments. Numerical simulations were performed by using the resistance characteristic model. The simulation results reveal the change rules of the resistance corresponding to the strain of SMA and demonstrate the possibility of using the resistance for feedback control of SMA.