This study introduces an approach for developing highly stretchable and compressible porous materials for soft robotics applications using vat photopolymerization 3D-printing technology. The materials are developed by a stable photopolymerizable water-in-oil (W/O) emulsion, where water droplets function as pore templates, and a polyurethane diacrylate forms the surrounding stretchable matrix. The emulsion is created by mixing the dispersed aqueous phase with the continuous phase containing photoinitiators and emulsifiers, resulting in a stable emulsion suitable for 3D printing. Finally, after photopolymerization and subsequent removal of the internal water droplets, an open-cell structure is achieved, exhibiting a remarkable elongation-at-break of 450% and excellent reversible compressibility at 80%. These properties endow the material with both high compliance and strength, essential for actuator performance. Furthermore, this method allows the fabrication of high-resolution complex objects with customized porosity, incorporating both macro-pores by design and inherent micro-pores. The potential of these materials is demonstrated through the creation of novel actuators for soft robotics, showcasing unique actuation performance, shape adaptability, and high holding force. The high compliance of this material is particularly relevant for actuators as it enables efficient deformation under low energy inputs, enhancing the performance and energy efficiency of soft robotic systems.

This paper presents the design of a variable stiffness actuator (VSA) using a multi-pulley system with a linear spring. To generate compliance for the VSA, twelve outer and six inner pulleys are evenly arranged around a center and are serially connected to a spring through a cable. The spring gets extended when the inner pulleys rotate about the center. The output stiffness is determined as the derivative of the elastic force exerted on the cable with respect to the time, and it can be varied by adjusting the locations of the inner pulleys. This design employs a cam disk to move the pulleys simultaneously, resulting in a compact design. This paper provides the design concept, theoretical analysis, and numerical examples to demonstrate the proposed VSA and its performance. Through some examples, it is found that the VSA can provide a maximum torque of 30 N-cm with a maximum defection of 40 degrees. These results can present a wide application and high adaptability of the proposed design to various robotic systems and devices.

Multi-dimensional movements and miniaturization are required for robotic joints motion, multi-axis optical alignments and other multiple degree-of-freedom (DOF) actuation scenes. However, it is a challenge for piezoelectric motors to guarantee multi-DOF movements, miniaturization, high load capacity and high resolution simultaneously. Inspired by synergic movement of body and caudal fin of fish in nature and the construction idea of metamaterials, we proposed a two-DOF linear piezoelectric motor (4mm^Height×3mm^Length×3mm^Width) based on the artificial elongation 31_z and shear 35_x/y mode by using Pb(In_1/2Nb_1/2)O₃–Pb(Mg_1/3Nb_2/3)O₃–PbTiO₃ (PIMNT) relaxor ferroelectric single crystal as piezoelectric elements. The results demonstrate that the motor is capable of achieving bidirectional motion in both X and Y axes, with the PIMNT crystal-based motor reaching a velocity of up to 94.8 mm/s. Its mechanical loading capacity per unit volume reaches as high as 1.39 mN/mm³, which exceeds the load capacity of currently reported two-DOF motors by 10 times. Moreover, it exhibits an exceptional step resolution of 5 nm, outperforming existing two-DOF motors by 1-2 orders of magnitude in terms of precision and accuracy. Furthermore, by modulating the driving signals of this motor, it can traverse any trajectory within the XY plane. The proposed ultrasonic motor has potential for applications in micro-robots, nano-precision motion, automatic visual systems and haptic interfaces.

The speed at which drone technology is developing has led to an infinite stream of ideas for enhancing drone effectiveness. Drone combat performance may be greatly enhanced by lowering the resistance to air. Vortex motion and turbulence are managed by the winglet. Winglets may now be used on drones to increase flying range and cost-effectiveness due to their extensive use in both military and commercial aircraft. This article focuses on the effects of various winglets on increasing lift and decreasing resistance of small consumer drones since different winglets have varying effects on drone flying performance. Specifically, the wingtip fencing, the double forked scimitar winglets, and the fusion winglet are considered to be the three exemplary winglets that serve as the specialized study objects.A thorough introduction is given to the designs for structures and aerodynamic properties. A brief explanation of the role that winglets play in enhancing aircraft effectiveness, conserving energy, and protecting the environment is provided. This article might serve as a guide for drone design. By precisely controlling circulation at the wing edge, the winglet's design and placement may lessen turbulence and the development of vortices, which lowers aerodynamic opposition and increases lift efficacy. Drone applications are going to increasingly rely on the winglet's design and optimization as well as upcoming technological developments. According to wind tunnel testing, the whole vehicle's generated drag can be decreased by 25% to 30%. The drone’s increased flying efficiency and effectiveness include lower energy consumption, longer flight times, higher carrying capacities, enhanced agility, and stability thanks to their refined design and the addition of winglets. The use of winglets has accelerated the advancement of drone technology and opened up new avenues for creativity and technological advances in applications for drones down the road. The fusion winglet has a straightforward design, which typically results in cost savings. Fusion winglets are often added to tiny drones to increase performance and decrease design complexity at short ranges.In terms of minimizing drag, the double-fork scimitar winglet performs better than the winglet of fusion type. However, because of production costs, this sort of wingspan may be employed on massive, very resistant drones with wide wing spans without adding to the weight of the fuselage. With an abundance of design freedom, the wingtip barrier may be easily modified to suit changing situations. However, because of the challenging design, wingtip fences tend to raise design and manufacturing costs, so using them in drone design is not advised. The addition of winglets to drones increases the aircraft's range, stability, and energy efficiency.Therefore, it is a useful measure for airliners to enhance the quality of their products.

Active Disturbance Rejection Control (ADRC) is widely applied in automatic machines, like electric motors, proved effective in performance enhancement. However, there is little report in its application in Electro-Hydrostatic Actuators (EHAs), where hydrostatics and power electronics coupled heavily. This paper gives both theoretical and experimental study on ADRC application in an EHA for the thrust vector control of a launcher. The mathematical model and state space model of the system were established and the system disturbances were estimated and compensated. The performances were compared to the counterpart using traditional proportional-integral-differential (PID) algorithm. It shows that ADRC is more effective than PID in rejecting system disturbances and model uncertainties，significantly reducing tracking errors and improving EHA dynamics.

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During a vibrational transport of a rigid body on a vibratory conveyor having electromagnetic vibratory actuator, a rigid body exerts by equal, but opposite force to a surface’s reaction force. This paper covers research on a reactive force that the body exerts on the EVA during its relative motion. The reactive force is a vector sum of the surface's normal contact force and tangential force of friction, modeled with the Coulomb friction model. For a general case of vibratory transport, the friction force is defined and given as a piecewise function. Additionally, differential equations for the rigid body’s relative motion are defined and solved to find potential moments in time when the body starts and stops with relative motion. During the period of the relative motion, a dynamic friction force is used. Conditions for a special case of a no-hopping motion are defined and presented graphically. For a given vibratory conveyor and vibratory regime a graph for reactive force that acts as a load on the EVA is shown. Computer simulation using Solidworks® is performed and its results are compared to the previously obtained mechanical model.

This paper examined how rotary force feedback in knobs can enhance control over musical techniques, focusing on both performance and user experience. To support our study, we developed the Bend-aid system, a web-based sequencer with pre-designed haptic modes for pitch modulation, integrated with TorqueTuner, a rotary haptic device that controls pitch through programmable haptic effects. Then, twenty musically trained participants evaluated three haptic modes (No-force feedback (No-FF), Spring, and Detent) by performing a vibrato mimicry task, rating their experience on a Likert scale, and providing qualitative feedback in post-experiment interviews. The study assessed objective performance metrics (Pitch Error and Pitch Deviation) and subjective user experience ratings (Comfort, Ease of Control, and Helpfulness) of each haptic mode. User experience results showed that participants found force feedback helpful. Performance results showed that the Detent mode significantly improved pitch accuracy and vibrato stability compared to No-FF, while the Spring mode did not show a similar improvement. Post-experiment interviews showed preferences for Spring and Detent modes varied and people provide suggestions for future knob designs. These findings suggest that force feedback may enhance both control and the experience of control in rotary knobs, with potential applications for more nuanced control in DMIs.

Microelectromechanical systems (MEMS) have recently allowed to attain unprecedented results in different fields of applications, due to their versatile functionalities. In light of the continuous trend towards miniaturization, MEMS reliability is becoming more and more a critical concern, especially in dynamic environments characterized by shocks and repeated loadings. The interplay between the said external excitations and possible microfabrication defects, can detrimentally affect the long-term performance of inertial MEMS. In this research activity, focusing on the Silicon-on-Insulator (SOI) technology the reliability issues are studied as mainly driven by mechanical actions, in cases leading to a fatigue-induced delamination of polysilicon films from the substrate. By exploiting a piezoelectric actuation to induce vibrations characterized by kHz frequencies, the geometry of the movable parts of a testing device is optimized to maximize the stress leading to delamination. Results are presented for a statically-indeterminate structure, designed in order to cause a delamination of epitaxial polysilicon from silicon dioxide under cyclic loadings.

This work explores the application of reinforcement learning (RL) for advanced control of linear actuators in a simulated environment. We present the development of an RL agent using Python libraries to control the position of a linear actuator modelled with a specific dynamic system. The agent interacts with the simulated environment, receiving rewards based on its performance in achieving desired positions. Through continuous learning and exploration, the agent refines its control strategy, surpassing traditional methods in terms of improved accuracy and tuning effort. This approach offers a data-driven solution for complex control problems, particularly beneficial for actuators with non-linearities or uncertainties.

This paper presents the design, fabrication and characterization of a thermo-magnetic film generator for efficient conversion of low-grade thermal energy into mechanical energy and an additional piezoelectric layer to convert the mechanical into electrical energy. Harnessing the abundant waste heat available at low temperatures holds immense potential to power off-grid electronics, such as IoT systems and wearable medical devices. In previous work, we introduced a new class of thermo-magnetic film-based generators (TMGs) for conversion of low-grade thermal energy consisting of movable cantilevers oscillating in resonant self-actuation mode, which boosts power output up to 50 µW/cm² while relative efficiencies can reach up to 5% even at temperature difference below 10 K [1]. Based on the concept of resonant self-actuation, we explore the option of converting the mechanical energy of oscillation into electrical energy using an additional piezoelectric layer. Compared to inductive energy conversion, this approach enables an increased voltage output, which can be rectified and stored by standard electronic components.

As shown in Figure 1 (a), the initial part of the cantilever is designed as a three-layer system consisting of brass, epoxy and a piezoelectric layer. The piezoelectric layer is fabricated from 100 µm thick bulk PZT and thinned down to 30 µm by mechanical grinding. The cantilever onset is rigidly clamped to a substrate. Two films made from the magnetic shape-memory-alloy Ni-Mn-Ga of 10 µm thickness are stacked and bonded, then attached to the end part of the cantilever and positioned beneath a magnet, which also serves as a heat source. A finite element model and an analytic model based on Bernoulli’s theory are used to design the piezoelectric layer and optimize its power density.

In ferromagnetic state below the Curie temperature (T_C), the Ni-Mn-Ga film is attracted by the magnet. While in solid-solid contact with the heated magnet, it heats above T_C and becomes paramagnetic. Therefore, the magnetic attraction force strongly decreases allowing the elastic forces of the cantilever to reset the initial deflection. As the film cools down below T_C, it transforms back to its ferromagnetic state and the cycle begins anew.

In this work, we demonstrate resonant self-actuation of the hybrid piezoelectric thermo-magnetic film generator by fine-tuning the oscillation frequency of the cantilever to achieve a sufficient temperature change during solid-solid contact with the heated magnet. Due to the epoxy and PZT layers, the thermal behavior of the system is altered, changing the conditions needed for resonant self-actuation. These changes are compensated by reducing the length of the piezoelectric layer and increasing the surface of the brass layer for enhanced convection. Characterization of a cantilever reveals peak output values of 1.5 V and 17 µA at a stroke of 1 mm and a frequency of 100 Hz. With a compact footprint of 0.2 cm², this results in a peak power density of 38 µW/cm². As shown in Figure 1 (b), the peak power output of a demonstrator device is 0.9 µW.

These preliminary performance results underline the potential of the concept of resonance self-actuation. In particular, the achieved electrical output facilitates the development of a power management system for energy use.

Figure 1: (a) Schematic of the multilayer piezoelectric thermo-magnetic film generator. (b) Power output of the generator device operating in resonant self-actuation mode.

References
[1] Joseph, J., Ohtsuka, M., Miki, H., & Kohl, M. (2020). Upscaling of Thermomagnetic Generators Based on Heusler Alloy Films. Joule, 4(12), 2718-2732. Elsevier. https://doi.org/10.1016/j.joule.2020.10.019