Tao Yao

Flexible tactile sensors have important application value in the field of artificial intelligence and internet of things. At present, it is a great challenge for tactile sensors to maintain high sensitivity and stability in a large pressure range. This article proposes a flexible capacitive tactile sensor with high sensitivity and large measuring range, which has a sandwich structure. The purpose of this paper is to determine the relationship between the thickness, surface microstructure, sensitivity, and sensing range of poly(vinylidene fluoride) (PVDF) films. The sensor uses conductive sponge with a microstructure surface and an ultra-thin PVDF film as the electrode and dielectric layer, respectively, and provides a comprehensive study in terms of sensor design, theoretical calculation, computer simulation and applications. The minimum detection limit of the sensor are tested by sound vibration, needle blowing, and human physiological signals. It has been shown that the thicker the PVDF film, the lower the sensitivity and the wider the sensing range. The proposed sensor can accurately identify physiological signals such as respiration, pulse and swallowing, and can perceive the softness, hardness and weight of the object as well as identifying the grasping posture. Moreover, the sensor has the characteristics of short response time, good recoverability and stability.

The recycling of petroleum‐based polymers such as polypropylene (PP) and polyethylene (PE) is an effective means of reducing environmental pollution. However, the incompatible PP and PE blended waste is difficult to separate accurately, which reduces the quality of the recycled material. In this paper, the trifunctional acrylate monomer (trimethylolpropane triacrylate), peroxide (2,5‐dimethyl‐92,5‐di[tert‐butylperoxy] hexane) and free radical activity modifier (zinc dimethyldithiocarbamate) were applied to in situ generate the copolymer of isotactic polypropylene and high‐density polyethylene (iPP‐co‐HDPE) with a long‐chain co‐branched structure via a melt blending method. The co‐crystallization of the branched copolymer chain segments with the chemical identical homopolymers vastly improved the compatibility of iPP and HDPE components. This in situ co‐branching compatibility strategy resulted in a significant improvement in the mechanical properties of PE and PP mixed wastes. The temperature gradient extraction method was used to separate the co‐branching modified iPP/HDPE blends. The results confirm that the separated iPP‐co‐HDPE components have a highly co‐branched structure. The significant improvement in compatibility resulted in a large increase in elongation at break and impact strength of the iPP/HDPE blends, which provides an economic and effective method for the recycling of mixed PE and PP wastes.

Human motion monitoring is an important field of study in various fields such as medical care, physical condition monitoring, and motion correction. The main objective of the present study is to design a low-cost, lightweight and flexible, long-lasting multifunctional human motion sensor based on the bionic caterpillar structure. Through the caterpillar-like structure design, the main sensing unit has three measurement modes, including non-contact approach, contact pressing, and angle bending. Moreover, the side sensing unit is used to identify the working mode of the main sensing unit. The performed analyses show that the pressing sensitivity can reach 393.06 mV/N, and the minimum resolution is 0.1 N. The key characteristics of the various modes are determined using the output voltage and fitting analysis of the variable distance, pressing, and bending experiments. The sensors are fixed on feet, wrists, and elbows to complete the violation monitoring and action correction of the three-step layup. The obtained results demonstrate that the designed sensor can record joint bending, foot pressing, and other movements in real-time.

Aiming at the capture and conversion of multidirection wave energy, a multifreedom direct-drive wave-energy converter (WEC) based on a parallel mechanism is studied. The dynamic model of WEC was conducted based on force analysis and hydrodynamic theory, and the inverse kinematic solutions of each branch chain of the mechanism were obtained following the space vector method. Furthermore, the kinetics response of the linear generator branch chain was obtained. Moreover, the influence on the capture efficiency of the device’s geometric structure scale was investigated under different sea conditions. To evaluate the performance of the WEC, a linear generator model was simulated and analyzed by COMSOL Multiphysics. A laboratory prototype was manufactured. The test results indicated that the multifreedom device can achieve better power conversion performance than traditional single degree of freedom (DOF) devices. This study provides ideas for the design and development of large multi-DOF wave-energy-conversion devices.

This work simulates the process of nanosecond pulse laser cleaning of acrylic paint on 7075 aluminum alloy surfaces by establishing a finite element, three-dimensional, numerical, transient model. The resulting temperature field and ablation depth for the laser-cleaned paint layer are analyzed by changing the energy density and scanning speed of the Gaussian heat source, which are also verified experimentally. The results show that the scanning speed affects the cleaning efficiency as the overlap rate; a slower scanning speed gives a lower cleaning rate. An acceptable cleaning efficiency is obtained when the spot overlap rate is 50%. The maximum temperature of the paint and the substrate surface increases linearly with laser energy density. When the energy density reaches 24 J/cm2, the paint material in the irradiated laser area of the alloy surface is completely removed, and the ablation depth of the aluminum alloy base is 48.2 μm. Aluminum alloy cleaning experiments at a laser energy density of 24 J/cm2 and a scanning speed of 2000 mm/s can obtain a metal surface that meets the standards of painting processes. This article provides theoretical simulations of laser cleaning for paint removal and has theoretical guidance for cleaning operations.

Gesture recognition is one of the most important functions of human-computer interaction (HCI). In this regard, a self-powered finger ring hand motion sensor was proposed in the present study. To this end, a single sensing unit consisting of a Polydimethylsiloxane (PDMS) film, a polyethylene oxide (PEO) film and a spacer was constructed. Then the finger bending and stress were monitored through numerous sensing units. In order to increase the contact area, ordinary textile stripes were used on the PDMS film surface. Then finite element simulations were carried out to evaluate the performance of the proposed sensor under different conditions. The obtained results show that the sensor has promising charge transfer features. Moreover, it was found that the sensitivity of the sensing unit in the range of 0–7 N is 94.48 mV/N. Then the ring finger hand motion sensor was set on a single finger to simulate a mouse and distinguish click, double-click and click time. Accordingly, it was demonstrated that numbers, letters and phrases in the ASL sign language can be accurately identified even in similar cases with small differences.

Considering the irregularity of wave motion, a wave energy converter (WEC) based on 6-UCU parallel mechanism has been investigated. A buoy connected to moving platform is used to harvest wave energy. Each chain is equipped with the linear generator of the same structure, which can convert the absorbed wave energy into electrical energy. Based on the inverse kinematics analysis of parallel mechanism, the position of the parallel mechanism is solved by using the space closed-loop vector method; the relative motion of stator and translator is obtained. Through electromagnetic numerical simulations, the influences of linear generator parameters such as magnetization mode, air gap, and yoke shape on electromagnetic performance were evaluated. Numerical results show axial magnetization and Halbach magnet array can increase magnetic flux intensity more than radial mode. Furthermore, the rule of electromagnetic resistance is discussed with the change of the speed amplitude and the angle frequency. For a case, dynamic differential equation of the whole system is established. The conversion rate of wave energy is derived.

Rotation detection is widely applied in industries. The current commonly used rotation detection system adopts a split structure, which requires stringent installation requirements and is difficult to miniaturize. This paper proposes a single-piece self-powered non-contact sensor with an interdigital sensitive layer to detect the rotation of objects. The electric field generated between a polyurethane (PU) film and a polytetrafluoroethylene (PTFE) film is utilized for perceiving the rotation. The surface of the PU film is subjected to wet etching with sulfuric acid to increase the surface area and charge density. Through finite element analysis and experimental testing, the effects of the areas of the sensitive films as well as the horizontal and vertical distances between them on the output voltage are analyzed. Tests are performed on adjustable-speed motors, human arms, and robotic arms. The results show that the sensor can detect the speed, the transient process of rotation, and the swing angle. The proposed rotation sensor has broad application prospects in the fields of mechanical automation, robotics, and Internet of Things (IoT).