Xiaoli Wang

Accurate pressure sensing and early slip detection are essential for safe, non-destructive grasping in flexible grippers. However, existing tactile sensors often struggle to simultaneously achieve a wide linear pressure range and high sensitivity, while slip detection commonly relies on multi-electrode or array designs that increase structural complexity and signal crosstalk. Here, a textured triboelectric-piezoelectric tactile sensor based on P(VDF-TrFE), termed T-PTS, is proposed. By replacing the conventional spacer-supported flat interface with a pyramid micro-textured interface, the sensor enhances responsiveness to subtle grasping-force fluctuations induced by slip and enables integrated pressure and slip sensing. To guide texture design, an electrostatic force solution under triboelectric-piezoelectric coupling was derived by considering texture-induced stress redistribution and charge inhomogeneity, and was further incorporated into adhesive contact and electrical models for the pyramid-textured P(VDF-TrFE)/Cu interface. Numerical analysis clarified the effects of texture parameters on contact area and open-circuit voltage, leading to texture optimization. Grasping experiments with a flexible gripper integrated with the optimized T-PTS showed that, compared with a conventional spacer-supported flat sensor, the linear pressure sensing range was extended from 0-6 N to 0-10 N and the sensitivity was increased from ~0.33 to 1.04 V/N. In addition, slip was identified within 0.034 s, much earlier than with the flat sensor (0.643 s). These results demonstrate the strong potential of T-PTS for intelligent tactile perception in flexible grippers.

Accurate pressure sensing and early slip detection are essential for safe, non-destructive grasping in flexible grippers. However, existing tactile sensors often struggle to simultaneously achieve a wide linear pressure range and high sensitivity, while slip detection commonly relies on multi-electrode or array designs that increase structural complexity and signal crosstalk. Here, a textured triboelectric-piezoelectric tactile sensor based on P(VDF-TrFE), termed T-PTS, is proposed. By replacing the conventional spacer-supported flat interface with a pyramid micro-textured interface, the sensor enhances responsiveness to subtle grasping-force fluctuations induced by slip and enables integrated pressure and slip sensing. To guide texture design, an electrostatic force solution under triboelectric-piezoelectric coupling was derived by considering texture-induced stress redistribution and charge inhomogeneity, and was further incorporated into adhesive contact and electrical models for the pyramid-textured P(VDF-TrFE)/Cu interface. Numerical analysis clarified the effects of texture parameters on contact area and open-circuit voltage, leading to texture optimization. Grasping experiments with a flexible gripper integrated with the optimized T-PTS showed that, compared with a conventional spacer-supported flat sensor, the linear pressure sensing range was extended from 0-6 N to 0-10 N and the sensitivity was increased from ~0.33 to 1.04 V/N. In addition, slip was identified within 0.034 s, much earlier than with the flat sensor (0.643 s). These results demonstrate the strong potential of T-PTS for intelligent tactile perception in flexible grippers.

The method of introducing lubricant at the friction interface of sliding triboelectric nanogenerators (TENGs) can reduce material wear and charge density attenuation caused by dry friction. However, the triboelectric mechanism of metal-polymer under oil lubrication remains ambiguous, leading to a lack of guidance for the design of high-performance oil-lubricated TENGs. In this paper, squalane, castor oil, and CD-15W-40 are introduced into the polyimide (PI)-copper (Cu) friction interface of a sliding TENG, and the effects of lubricant species on open-circuit voltage, coefficient of friction, and mass loss are investigated. The results show that the conductivity and electron affinity of the lubricant are key factors affecting the electrical output. Compared to the dry condition, the castor oil and CD-15W-40 reduced the electrical output of the sliding-mode TENG due to the charge carrier shielding effect formed at the friction interface caused by their high conductivity. In contrast, squalane has both extremely low conductivity and a higher electron affinity than polyimide, which enhances interfacial charge transfer through oil-solid contact electrification, thereby increasing the electrical output. Compared to the sliding-mode TENGs with castor oil and CD-15W-40, the sliding-mode TENG with squalane has a lower friction coefficient and mass loss, as well as higher output and stability, showing that squalane is more suitable for the TENG. This work can provide guidance for the design of a sliding TENG under lubrication.

Aerostatic conical bearings with micro-orifices (ACBMOs) can simultaneously withstand both radial and axial external loads and have high power density. Nevertheless, due to the larger surface-to-volume ratio and length-to-diameter ratio of micro-orifices, the gas flow through micro-orifices is more susceptible to frictional loss. Since frictional loss in micro-orifices has been ignored in the literature, an aerostatic conical bearing lubrication model with frictional loss in micro-orifices and a transient model of their nonlinear dynamics are established. The effects of the micro-orifice length-to-diameter ratio and relative roughness on lubrication performance, nonlinear behaviors, and ACBMO–rotor system stability are investigated, followed by experimental validation. The results indicate that the gas mass flow rate of the micro-orifices, gas film pressure, and load capacity in the ACBMOs decrease with the increase in micro-orifice relative roughness and length-to-diameter ratio, which cannot be observed in the conventional model without frictional loss. Meanwhile, both the onset speed of instability and the failure speed decrease when frictional loss occurs in micro-orifices are considered.

To reveal the effect of coating properties on the mixed lubrication evolution during the start–stop process of gas foil bearing (GFB), a transient gas mixed lubrication-wear model for coating surface is established. In the developed model, a method of the extended equivalent modulus by the film thickness ratio is proposed, which can extend the classic Greenwood and Tripp contact model for homogeneous materials to the coating contact involving layered materials. Moreover, a gas foil bearing start–stop experiment is conducted to verify the predicted results of the developed model. The effects of coating materials and standard deviation of coating surface on the start–stop performance of GFB are investigated. Within the scope of this article, the results show that during start-up, the gas film pressure first increases and then decreases with the increase in time, the minimum film thickness increases, while the asperity contact decreases. The opposite evolution is observed during shut-down. Compared with uncoated GFB, the friction torque and lift-off speed of GFB with polyimide (PI) and polytetrafluoroethylene (PTFE) are reduced, with PI reducing friction torque by 24.27% and PTFE by 49.03%. The minimum lift-off speed with PTFE is the smallest. The lift-off speed, friction torque, and wear volume increase with the increase in the standard deviation of coating surface. The friction torque and lift-off speed decrease as the start–stop cycle increases until both reach stability. This paper can provide theoretical guidance for the design of the top foil coating surface of GFB.

The contact electrification of ferroelectric polymer can be more complicated due to its ordered permanent molecular dipoles and dipole–dipole interactions. Herein, the polyvinylidene fluoride (PVDF)‐Cu is taken as an example to investigate the mechanism of ferroelectric polymer‐metal contact electrification via first‐principles calculations. It is revealed that different from non‐ferroelectric polymers, when ferroelectric polymers are in contact with metals, the charge transfer occurs not only at the interface but also inside the polymer due to the existence of polar phases. Specifically, the polar phases in the crystallization region can effectively enhance the charge transfer between the ferroelectric polymer and metal because the polar molecules in PVDF possess the stronger electrostatic potential, more delocalized lowest unoccupied molecular orbital, and additional dipole–dipole interactions compared with nonpolar molecules. In addition, the coupling mechanism of piezoelectricity and triboelectricity in ferroelectric polymer‐metal contact electrification under compression is also investigated. It is demonstrated that the deformation increases the degree of noncoincidence between positive and negative charge centers in polar phases and causes charge transfer between the polar molecular chains of PVDF, thus producing the extra charge transfer between the ferroelectric polymer and metal. This study provides a theoretical basis for the material design of triboelectric nanogenerators based on ferroelectric polymers.