A Lower Extremity Exoskeleton: Human-Machine Coupled Modeling, Robust Control Design, Simulation, and Overload-Carrying Experiment

A robust H∞ control method and switched control algorithm for hydraulic actuator presents in human-machine coordinated motion to solve the motion delay of lower extremity exoskeleton. After the characteristic parameters synthesis of human limb and exoskeleton linkage, the human-machine coupled motion model is constructed to estimate the appropriate hydraulic pressure, which is considered as a structural uncertainty in hydraulic model. Then the robust controller is designed to improve the robust stability and performance under the structural and parametric uncertainty disturbances. Simulation results show that, in walking mode, this robust controller can achieve a better dynamic response and aid-force efficiency than PID controller. Then, according to gait divisions of person’s limb motion, the switched control algorithm is designed to reduce the delay of exoskeleton tracking person. Finally, the experimental results show that the human-machine coordinated walk with bearing 60 kg load and squat action with no external load are realized effectively by this proposed method

Low-cost and facile implementation of microfluidic colour-changing devices using dry film photoresist-based moulds

In this work, different microfluidic colour-changing devices are implemented by using dry film photoresist-based moulds instead of standard photolithography moulds. EtertecHT-115T negative dry film photoresist is employed to realise the rapid fabrication of the moulds for colour-changing layers. The major factors that may affect the fidelity of the dry film moulds during fabrication are summarised and analysed, including the optimum exposure times and the appropriate developing times. Especially, the impacts of different concentrations of sodium carbonate (Na2CO3) solution on developing rate are investigated for 1–5 layers (50–250 μm thick) of EtertecHT-115T dry film photoresists by experiments. The created dry film moulds show the advantages of low cost, high manufacturing efficiency and requiring no professional training. Each application of the microfluidic colour-changing devices presents high transparency and good colour-changing effect. The microfluidic colour-changing layers based on dry film moulds can be used in different wearable devices of human, and also can be applied for realising surface camouflage and display functions of soft machines/robotics

A liquid progressive multifocal lens adjusted by the deformation of a non-uniform elastic membrane due to the variation of liquid pressure

Abstract Background In this paper, a liquid progressive multifocal lens with solid-liquid structure is demonstrated, which mainly consists of two elastic polydimethylsiloxane (PDMS) membranes, a solid substrate and liquid. Methods To realize the adjustment of the focuses progressively, the thickness of one of the membrane is designed non-uniform. By controlling the liquid pressure working on the membranes, the curvature of the membrane can be changed continuously and the power of the lens can be altered simultaneously. In this paper, the structure and a fabrication method of the lens is introduced, and a power distribution model is built for the calculation of the power distribution characteristics. Moreover, the deformation of the non-uniform elastic membrane of the lens under different pressures is analysed with finite element method (FEM). Results Finally, a prototype of the lens is developed and tested by applying a micro laser displacement sensor, and it is demonstrated that the progressive multifocal lens is feasible. Conclusion A novel liquid progressive multifocal lens with a non-uniform thickness elastic membrane is proposed. From the simulation and experimental investigation, it can be concluded that the proposed liquid lens can realize progressive multifocal through using non-uniform elastic membrane and the power can be adjusted by the pressure which is controlled by the liquid volume filled in the lens

Damping Force Modeling and Suppression of Self-Excited Vibration due to Magnetic Fluids Applied in the Torque Motor of a Hydraulic Servovalve

As a key component of hydraulic control systems, hydraulic servovalves influence their performance significantly. Unpredictable self-excited noise inside hydraulic servovalves may cause instability and even failure. Being functional, with higher saturation magnetization and increased viscosity when exposed to a magnetic field, magnetic fluids (MFs) have been widely used in dampers, sealing, and biomedical treatment. In this paper, magnetic fluids are applied in the torque motor of a hydraulic servovalve to exert damping and resistance for vibration and noise suppression. Construction of the torque motor armature with magnetic fluids is introduced and the forces due to magnetic fluids on the torque motor armature are studied. Based on a bi-viscosity-constituted relationship, a mathematical model of the damping force from magnetic fluids is built when magnetic fluids are filled in the working gaps of the torque motor. Measurements of the properties of an Fe3O4 composite magnetic fluid are carried out to calculate the parameters of this mathematical model and to investigate the influence of magnetic fluids on the vibration characteristics of the armature assembly. The simulated and tested harmonic responses of the armature with and without magnetic fluids show the good suppression effects of magnetic fluids on the self-excited noise inside the servovalve

Modeling and Parameter Identification of the Vibration Characteristics of Armature Assembly in a Torque Motor of Hydraulic Servo Valves under Electromagnetic Excitations

The resonance of the armature assembly is the main problem leading to the fatigue of the spring pipe in a torque motor of hydraulic servo valves, which can cause the failure of servo valves. To predict the vibration characteristics of the armature assembly, this paper focuses on the mathematical modeling of the vibration characteristics of armature assembly in a hydraulic servo valve and the identification of parameters in the models. To build models more accurately, the effect of the magnetic spring is taken into account. Vibration modal analysis is performed to obtain the mode shapes and natural frequencies, which are necessary to implement the identification of damping ratios in the mathematical models. Based on the mathematical models for the vibration characteristics, the harmonic responses of the armature assembly are analyzed using the finite element method and measured under electromagnetic excitations. The simulation results agree well with the experimental studies

A liquid progressive multifocal lens adjusted by the deformation of a non-uniform elastic membrane due to the variation of liquid pressure

Background: In this paper, a liquid progressive multifocal lens with solid-liquid structure is demonstrated, which mainly consists of two elastic polydimethylsiloxane (PDMS) membranes, a solid substrate and liquid. Methods: To realize the adjustment of the focuses progressively, the thickness of one of the membrane is designed non-uniform. By controlling the liquid pressure working on the membranes, the curvature of the membrane can be changed continuously and the power of the lens can be altered simultaneously. In this paper, the structure and a fabrication method of the lens is introduced, and a power distribution model is built for the calculation of the power distribution characteristics. Moreover, the deformation of the non-uniform elastic membrane of the lens under different pressures is analysed with finite element method (FEM). Results: Finally, a prototype of the lens is developed and tested by applying a micro laser displacement sensor, and it is demonstrated that the progressive multifocal lens is feasible. Conclusion: A novel liquid progressive multifocal lens with a non-uniform thickness elastic membrane is proposed. From the simulation and experimental investigation, it can be concluded that the proposed liquid lens can realize progressive multifocal through using non-uniform elastic membrane and the power can be adjusted by the pressure which is controlled by the liquid volume filled in the lens

Flow and heat transfer analysis of the microfluidic thermal camouflage film based on bionic structure

With the rapid advancement of infrared (IR) detection techniques, the importance of thermal camouflage technology has become increasingly prominent. Inspired by spider webs and honeycombs, microfluidic thermal camouflage films based on two bionic structures are proposed to IR cloak targets by circulating microfluidics in the film. The film displays an adaptive thermal camouflage effect by automatically adjusting the microfluid temperature. Microcavity and microchannel are used as the main internal structure of camouflage film. To compare the thermal camouflage performance of two corresponding bionic structures, heat transfer and fluid flow mechanisms are analyzed. The structure and working principle of the film are introduced, and the testing system is developed to explore the flow and heat transfer characteristics of the bionic spider web micro-channel film and honeycomb cell film. The comparison reveals that the honeycomb cell film's temperature distribution uniformity and heat transfer performance are better than the spider web micro-channel film's, which is suitable for thermal camouflage. Considering the influence of the liquid low-velocity stagnation zone on the camouflage performance, rounded corners of the honeycomb cell are designed to improve the fluid flow properties, and the relationship between the corner radius and the heat transfer characteristics is further investigated. Finally, the honeycomb cell film's parameters are optimized by orthogonal tests, and the optimal solution enhances the thermal camouflage performance. The results show that the film has a good stealth effect, which is expected to motivate the further application of bionic structures in the military field

Analysis of pressure oscillation and structural parameters on the performance of deflector jet servo valve

The performance of deflector jet servo-valve is highly affected by the flow field characteristics in the pilot stage of the deflector jet servo-valve. This research used the large eddy simulation method to study the pressure pulsation characteristics of the front stage flow field of DJSV, which has a high significance for the reasonable design of DJSV and the suppression of self-excited oscillation. The geometric model of the three-dimensional flow field of the jet pilot stage of the servo valve deflection plate was established. LES method was used to analyze the influence of the geometric parameters of the jet outlet, amplifier and receiving port on the flow field distribution characteristics of the pre-stage. The results show that pressure oscillation is highly affected by the inlet pressure. Structure optimization is a good solution for decreasing pressure oscillation in deflector jet servo valve