Lu Zhang

Exploration tasks in deep and complex underwater environments require robots that combine miniaturization, precise control at low speeds, and the capacity for burst movements. However, achieving this integration remains challenging for existing robotic systems. To address this, we propose a piezoelectric pump-based driving system utilizing a single-piston, multioutput configuration capable of simultaneously powering synthetic jet thrusters and a burst propulsion device based on energy storage. This system is integrated into an underwater robot. Particle image velocimetry (PIV) experiments and numerical simulations are conducted to investigate the principles of both low-speed and burst-mode propulsion, identifying sinusoidal signals as among the optimal driving inputs. Force measurements and motion experiments are further used to establish a dual-mode control strategy. The robot achieves a maximum average speed of 3.27 cm/s with a minimum turning radius of 62 cm in low-speed mode, and up to 20.23 cm/s in burst mode with agile turning performance. This work offers design insights for underwater robots employing energy-storage-based burst propulsion.

Inkjet printing is an efficient noncontact on-demand printing technology. However, traditional piezoelectric inkjet printing uses pressure waves generated by cavity deformation to jet droplets, air entering the cavity will lead to the failure of inkjet printing. Conventional gravity or pressure ink supply method also has problems such as difficulty in ink supply or difficulty in controlling pressure. These are very unfriendly to variable angle printing, especially at elevation angles. Aiming at the above problems, in this work, we propose a nozzle-driven inkjet with the ability of variable angle printing based on piezoelectric microjet technology and capillary constant pressure ink supply. It does not depend on the deformation of the cavity to jet droplets, so it can avoid the problem of performance reduction due to the bubble entering the cavity and enhance the fluid-solid coupling strength of jetting. We carry out the multiphysics coupling analysis to reveal the ejection mechanism of the proposed microjet head. The method to control the ejecting performance is proposed. Experiments results show that the proposed microjet printing can achieve variable angle printing of 360° in the horizontal direction and ±30° in the vertical direction, and the minimum spreading diameter is 293.6 μ m when the nozzle diameter is 300 μ m.

Nowadays, the exploitation of marine resources is urgent, underwater plane as an important tool to explore the ocean have been paid more and more attention. However, it is difficult to meet the comprehensive requirements of high water pressure resistance, micro size, and low power consumption at the same time, which means that the existing vehicles are difficult to achieve long-term operation in the narrow and complex deep water environment. The piezoelectric jet drive can realize miniaturization, good antipressure ability, and simple control method, while the underactuated mode can reduce energy consumption and extend the endurance time. In this work, a piezoelectric jet microsize unit with high water pressure resistance is proposed based on piezoelectric drive, and a piezoelectric jet-driven underwater plane with low power consumption is designed. Its maximum stable straight-line velocity can reach 47.62 mm/s (0.397 BL/s). It can realize a variety of actions such as horizontal forward, floating forward, diving forward, and rotation, and its power consumption in horizontal motion is much lower than that of a fully actuated vehicle. This article will provide an important reference for the research of long-endurance vehicles that operate in deep diving and narrow area.

Due to the limited energy storage of micro underwater vehicles, it is urgent to adopt drag reduction methods to improve their mileage and maneuverability. In view of the drag reduction requirements of micro vehicles, a piezoelectric traveling wave drag reducer (PTWDR) is proposed in this article. The PTWDR can be embedded into the surface of micro vehicles, with the merits of small size, high drag reduction efficiency and low energy consumption. We analyzed the structural changes of turbulent flow field caused by the actuation of PTWDR, and revealed the turbulent drag reduction mechanism. The control parameters selecting method to achieve required drag reduction performance under different operating conditions are proposed. The good drag reduction effects in various regions of the vehicles can be achieved by reasonably arranging PTWDR. The friction drag and total drag experiments are conducted to verify the effectiveness of PTWDR in achieving drag reduction, and the maximum drag reduction rate can reach 58%. Finally, the energy saving efficiency of PTWDR are studied, and it is confirmed that PTWDR can achieve net energy savings. This study provides an important reference for on-demand active drag reduction and net energy saving of micro vehicles.

Wireless motion and miniature size are two essential features for deep-sea robots applying in the practical confined area, which are incompatible due to the existence of onboard power supply and anti-pressure devices. Here, inspired by the energy-saving hitchhiking behavior of marine remora, we propose a piezoelectric-jetting father–son robot with size of Φ 14 3 13 cm ³ . The untethered father robot provides power for the adsorbed 5-cm-length son robot, and the micro agile son can detach to freely move in the small space that is inapplicable for father. The structural shapes of lateral jetting unit are optimized by numerical simulation and the corresponding flow field characteristics are elaborated to assist the optimization analysis. Then, the pressure-resilience electronics circuits are designed, and it can normally output high-frequency square wave of 210 V _p-p and excite the father–son robot to implement the wireless 3-DoF motions under 20 MPa environment. Finally, two robots cooperate to detect a cornering channel with width of close to father diameter, and the son recombines the father and together return voyage after the son achieves the multiple high-difficulty movements in such a narrow channel. This work can supply solution of developing the underwater robot in complex deep-sea occasions.

Moving rapidly and agilely in high-pressure environment is a challenge for existing miniature underwater robots, which limits deeply the ocean exploitation. Here, we present a spherical underwater robot with diameter of 7 cm, and it has merits of miniature structure without bulky and antihydropressure devices, 3-DOFs agile motion, and good adaptability for 25 MPa environment simultaneously. Four designed piezoelectric double-jet actuators are embedded directly in the spherical shell without transmission mechanism, which enables the robot with relatively fast motion speed by compared with the published robots. Six motion modes are implemented by the cooperation of actuators, including rising, hovering, and sinking motions in the vertical direction and straight driving, turning, and in-situ turning motions in the horizontal plane. A robot prototype was fabricated, and its performance was tested. Experimental results indicated that the rising, straight driving, and in-situ turning speed reached up to 95.2 mm/s (1.36 BL/s), 99.6 mm/s (1.42 BL/s), and 5 rad/s, respectively. Besides, the robot could also rapidly turn at 1.3 rad/s with the turning radius of 22.1 mm. The speed deviation within 10% under different water pressures was obtained. The obstacle avoidance was successfully fulfilled by controlling the robot to pass through the narrow gap with width of only 1.5 body length of robot. There excellent characteristics demonstrate agile mobility and give the robot ability to move in the confined area of deep sea.

The driving performance and endurance mileage of microunderwater vehicle can be improved by reducing the wall friction drag. The existing underwater drag reducers can achieve good drag reduction performance, but they are not suitable for microunderwater vehicle due to the large structure size and the high energy consumption. An active drag reducer, which is driven by piezoelectric actuator and can be embedded into the outer wall of microunderwater vehicle hardly changing the streamline structure and structural strength of the wall, is proposed. The active drag reduction on demand and effective energy saving can be realized by combining with the motion monitoring system of the underwater vehicle. The drag reduction mechanism of the proposed drag reducer driven by piezoelectric actuator is discussed. The influences of single parameter and comprehensive effect of parameters on the characteristics of the near-wall turbulent boundary layer are obtained, and the control methods of drag reduction performance for meeting different requirements are proposed. The simulation and experimental results show that the proposed microdrag reducer can effectively reduce the frictional and total drag, and can achieve positive energy saving. The drag reduction rate of 37.82% can be achieved with the excitation amplitude of 150 V and the operating frequency of 1500 Hz. This article can provide an important reference for the research of active drag reduction of microunderwater vehicle.

The improvement of sailing speed and endurance of microunderwater vehicle can be achieved by reducing the wall friction drag. We proposed a piezoelectric drag reducer (PDR), which can be embedded into the wall of the underwater vehicle without affecting the original streamline. We discussed the drag reduction characteristics of the PDR with different arrangement angles based on the simulation analyses, and a maximum friction drag reduction rate of 45.3% can be achieved when the arrangement angle between the direction of PDR and the incoming flow is 60°. The influences of key parameters on the turbulence characteristics are obtained with a view to select control parameters for meeting different drag reduction requirements. In order to verify the simulation results, we carried out experimental tests, the experimental data have been analyzed using turbulence statistical method. The relative errors of friction drag reduction results between simulation and experiment are less than 12%, which proved the effectiveness of the proposed arrangement and control parameter selection methods. Then, the feasibility of achieving high-efficiency active drag reduction of microunderwater vehicle, based on the proposed PDR, is verified to be effective according to the test results of total drag experiments.