查看更多>>摘要：Unilateral motor impairment can disrupt the coordination between the joints,impeding the patient's normal gait.To assist such patients to walk normally and naturally,an adaptive control algorithm based on inter-joint coordination was proposed in this work for lower-limb exoskeletons.The control strategy can generate the reference trajectory of the affected leg in real time based on a motion coordination model between the joints,and adopt an adaptive controller with virtual windows to track the reference trajectory.Long Short-Term Memory(LSTM)network was also adopted to establish the coordina-tion model between the joints of both lower limbs,which was optimized by preprocessing angle information and adding gait phase information.In the adaptive controller,the virtual windows were symmetrically distributed around the reference trajectory,and its width was adjusted according to the gait phase of the auxiliary leg.In addition,the impedance parameters of the controller were updated online to match the motion capacity of the affected leg based on the spatiotemporal sym-metry factors between the bilateral gaits.The LSTM coordination model demonstrated good accuracy and generality in the gait database of seven individuals,with an average root mean square error of 3.5° and 4.1° for the hip and knee joint angle estimation,respectively.To further evaluate the control algorithm,four healthy subjects walked wearing the exoskeleton while additional weights were added around the ankle joint to simulate an asymmetric gait.From the experimental results,it was shown that the algorithm improved the gait symmetry of the subjects to a normal level while exhibiting great adapt-ability to different subjects.
查看更多>>摘要：This study aims to develop a magnetorheological(MR)damper for semi-active knee prostheses to restore the walking ability of transfemoral amputees.The core dimensions of the MR damper were determined via theoretical magnetic field calcula-tions,and the theoretical relationship between current and joint torque was derived through electromagnetic simulation.Then,a physical prototype of the semi-active prosthetic knee equipped with the MR damper was manufactured.Based on the data obtained from angle sensor,pressure sensor(loadcell),and inertial measurement unit(IMU)on the prosthesis,a matching control algorithm is developed.The joint torque of the MR damper can be adaptively adjusted according to the walking speed of the amputee,allowing the amputee to realize a natural gait.The effectiveness of the control program was verified by the ADAMS and MATLAB co-simulation.The results of the test and simulation show that the MR damper can provide sufficient torque needed for normal human activities.
查看更多>>摘要：In the natural world,leaf-cutting ants cause vibrations through their mutual scraping of file-scraper organs.In this study,we designed a Biomimetic Ultrasonic Exciter(BUE)that imitates leaf-cutting ants.The operating characteristics of the BUE were studied through experimental testing and finite element simulations.The results showed that the BUE could generate stable ultrasonic vibrations,and that the excitation frequency only needed to be half the Output Frequency(OF).This frequency-doubling phenomenon was conducive to achieving BUE miniaturization.To further explore the phenomenon of frequency-doubling vibration output,this study designed scrapers of five different sizes,conducted excitation and first-order natural frequency measurement tests,and the corresponding finite element simulations.It was found that each scraper could operate in frequency-doubling mode,but the operating frequency and natural mode frequencies did not correspond with one another.To further explicate experimental and simulation results,a two-degrees-of-freedom vibration model was developed.It was evident that the contact relationship between the dentate disc and scraper introduced strong nonlinear factors into the system,accounting for the frequency-doubling phenomenon and the difference between the BUE's operating and mode frequencies.The BUE could be expected to facilitate the production of high-power micro-ultrasonic generators and has potential application value in the fields of mechanical processing,industrial production,and medical health.
查看更多>>摘要：At present,the existing piezoelectric stick-slip actuators have an inherent back-slip problem,which greatly limits the devel-opment and application of stick-slip actuators.In order to inhibit the regression phenomenon,a new bionic lemongrass stickslip actuator was prepared by using polymer PDMS to replicate natural biological surface.The surface microstructure of the grass was copied by PDMS,and the PDMS film was prepared.The rigid and flexible bionic friction pair was further prepared,and the flexible anisotropic PDMS stick slip actuator was developed.It was found that the anisotropic friction characteristics of the surface microstructure of the grass inhibited the anti-sliding motion,and the elastic potential energy of the PDMS film improved the output characteristics of the driver.By adjusting the input voltage to control the contact between the drive foot and the rotor,the rigid and flexible hybrid drive can be realized and the backsliding phenomenon can be suppressed.The actuator is compact,lightweight and can achieve high speed and high resolution output without preloading force,which has important application value in the field of fast and accurate positioning with load limitation.
查看更多>>摘要：Flexible attachment actuators are popular in a wide range of applications,owing to their flexibility and highly reliable attachment.However,their reversible adhesion performance depends on the actual effective contact area and peel angle during operation.Therefore,a good actuator must ensure a uniform and reliable pre-pressure load on an adhesive surface,to increase the effective contact area of the attached surface,thereby maximizing adhesion.This study was inspired by fusion bionics for designing a hierarchical attachment structure with vacuum-adsorption and dry-adhesion mechanisms.The designed structure used the normal force under the negative pressure of a suction cup as a stable source of a pre-pres-sure load.By optimizing the rigid and flexible structural layers of the attachment structure,a load was applied uniformly to the adhesion area;thus,reliable attachment was achieved by self-preloading.The structure achieved detachment by exploiting the large deformation of a pneumatic structure under a positive pressure.The hierarchical attachment structure achieved up to 85％of the optimal performance of the adhesive surface.Owing to its self-preloading and reliable attach-ment characteristics,the designed structure can be used as an attachment unit in various complex scenarios,such as small,lightweight climbing platforms and the transport of objects in long,narrow pipelines.
查看更多>>摘要：When a human lands from a high drop,there is a high risk of serious injury to the lower limbs.On the other hand,cats can withstand jumps and falls from heights without being fatally wounded,largely due to their impact-resistant paw pads.The aim of the present study was to investigate the biomechanism of impact resistance in cat paw pads,propose an optimal hierarchical Voronoi structure inspired by the paw pads,and apply the structure to bionic cushioning shoes to reduce the impact force of landing for humans.The microstructure of cat paw pads was observed via tissue section staining,and a simulation model was reconstructed based on CT to verify and optimize the structural cushioning capacity.The distribu-tion pattern,wall thickness of compartments,thickness ratio of epidermis and dermis,and number of compartments in the model were changed and simulated to achieve an optimal composed structure.A bionic sole was 3D-printed,and its performance was evaluated via compression test and a jumping-landing experiment.The results show that cat paw pads are a spherical cap structure,divided from the outside to the inside into the epidermis,dermis,and compartments,each with different cushioning capacities.A finite element simulation of different cushioning structures was conducted in a cylinder with a diameter of 20 mm and a height of 10 mm,featuring a three-layer structure.The optimal configuration of the three layers should have a uniform distribution with 0.3-0.5 mm wall thickness,a 1:1-2 thickness ratio of epidermis and dermis,and 100-150 compartments.A bionic sole with an optimized structure can reduce the peak impact force and delay the peak arrival time.Its energy absorption rate is about 4 times that of standard sole.When jumping 80,100,and 120 cm,the normalized ground reaction force is also reduced by 8.7％,12.6％and 15.1％compared with standard shoes.This study provides theoretical and technical support for effective protection against human lower limb landing injuries.
查看更多>>摘要：The enhancement of adhesive perception is crucial to maintaining a stable and comfortable grip of the skin-touch products.To study the tactile perception of adhesive surfaces,subjective evaluation,skin friction and vibrations,and neurophysi-ological response of the brain activity were investigated systematically.Silicone materials,which are commonly used for bionic materials and skin-touch products,were chosen for the tactile stimulus.The results showed that with the increasing of surface adhesion,the dominant friction transferred from a combination of adhesive friction and deformation friction to adhesive friction.The friction coefficient and vibration amplitude had strong correlations with the perceived adhesion of surfaces.The parietal lobe and occipital lobe were involved in adhesive perceptions,and the area and intensity of brain acti-vation increased with the increasing surface adhesion.Surfaces with larger adhesion tended to excite a high P300 amplitude and short latency,indicating that the judgment was faster and that more attentional resources were involved in adhesive perception.Furthermore,the electroencephalograph signals of the adhesive perception were simulated by the neural mass model.It demonstrated that the excitability and intensity of brain activity,and the connectivity strength between two neural masses increased with the increasing surface adhesion.This study is meaningful to understand the role of surface adhesion in tactile friction and the cognitive mechanism in adhesive perception to improve the tactile experience of adhesive materials.
查看更多>>摘要：Surface electromyography(sEMG)-based gesture recognition is a key technology in the field of human-computer interaction.However,existing gesture recognition methods face challenges in effectively integrating discriminative temporal feature representations from sEMG signals.In this paper,we propose a deep learning framework named TFN-FICFM comprises a Temporal Fusion Network(TFN)and Fuzzy Integral-Based Classifier Fusion method(FICFM)to improve the accuracy and robustness of gesture recognition.Firstly,we design a TFN module,which utilizes an attention-based recurrent multi-scale convolutional module to acquire multi-level temporal feature representations and achieves deep fusion of temporal features through a feature pyramid module.Secondly,the deep-fused temporal features are utilized to generate multiple sets of gesture category prediction confidences through a feedback loop.Finally,we employ FICFM to perform fuzzy fusion on prediction confidences,resulting in the ultimate decision.This study conducts extensive comparisons and ablation studies using the publicly available datasets Ninapro DB2 and DB5.Results demonstrate that the TFN-FICFM model outperforms state-of-the-art methods in classification performance.This research can serve as a benchmark for sEMG-based gesture recognition and related deep learning modeling.
查看更多>>摘要：This study investigates the friction and deformation behavior of the skin in contact with a rigid massage ball and its influ-encing factors.Pressing and stretching experiments were conducted using a collaborative robot experimental platform.The experiments encompassed a loading normal force range of 2 N to 18 N and a sliding speed range of 10 mm/s to 20 mm/s.The friction response curve exhibits two different stages:static stick state and dynamic stick-slip stage,both of which have been mathematically modeled.By analyzing the experimental data,we analyzed the effects of elastic modulus,sliding speed and normal loading force on skin tangential friction and tensile deformation.The results indicate that as the normal load increases,both friction and deformation exhibit an increase.Conversely,they decrease with an increase in elastic modulus.Notably,while deformation diminishes with higher sliding speed,friction force remains relatively unaffected by velocity.This observation can be attributed to the strain rate sensitivity resulting from the viscoelastic characteristics of the skin under substantial deformation.This study advances the understanding of friction and deformation behavior during skin friction,offering valuable insights to enhance the operational comfort of massage robots.
查看更多>>摘要：Almost all living organisms exhibit autonomic oscillatory activities,which are primarily generated by the rhythmic activi-ties of their neural systems.Several nonlinear oscillator models have been proposed to elucidate these neural behaviors and subsequently applied to the domain of robot control.However,the oscillation patterns generated by these models are often unpredictable and need to be obtained through parameter search.This study introduces a mathematical model that can be used to analyze multiple neurons connected through fast inhibitory synapses.The characteristic of this oscillator is that its stationary point is stable,but the location of the stationary point changes with the system state.Only through reasonable topology and threshold parameter selection can the oscillation be sustained.This study analyzed the conditions for stable oscillation in two-neuron networks and three-neuron networks,and obtained the basic rules of the phase relationship of the oscillator network established by this model.In addition,this study also introduces synchronization mechanisms into the model to enable it to be synchronized with the sensing pulse.Finally,this study used these theories to establish a robot single leg joint angle generation system.The experimental results showed that the simulated robot could achieve synchronization with human motion,and had better control effects compared to traditional oscillators.
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