Xinbin Zhang

Bioinspired aquatic microrobot capable of walking on water surface like a water strider.

Walking on the water surface is a dream of humans, but it is exactly the way of life for some aquatic insects. In this study, a bionic aquatic microrobot capable of walking on the water surface like a water strider was reported. The novel water strider-like robot consisted of ten superhydrophobic supporting legs, two miniature dc motors, and two actuating legs. The microrobot could not only stand effortlessly but also walk and turn freely on the water surface, exhibiting an interesting motion characteristic. A numerical model describing the interface between the partially submerged leg and the air-water surface was established to fully understand the mechanism for the large supporting force of the leg. It was revealed that the radius and water contact angle of the legs significantly affect the supporting force. Because of its high speed, agility, low cost, and easy fabrication, this microrobot might have a potential application in water quality surveillance, water pollution monitoring, and so on.

Why superhydrophobicity is crucial for a water-jumping microrobot? Experimental and theoretical investigations.

This study reported for the first time a novel microrobot that could continuously jump on the water surface without sinking, imitating the excellent aquatic locomotive behaviors of a water strider. The robot consisted of three supporting legs and two actuating legs made from superhydrophobic nickel foam and a driving system that included a miniature direct-current motor and a reduction gear unit. In spite of weighing 11 g, the microrobot jumped 14 cm high and 35 cm long at each leap. In order to better understand the jumping mechanism on the water surface, the variation of forces exerted on the supporting legs was carefully analyzed and calculated based on numerical models and computational simulations. Results demonstrated that superhydrophobicity was crucial for increasing the upward force of the supporting legs and reducing the energy consumption in the process of jumping. Although bionic microrobots mimicking the horizontal skating motions of aquatic insects have been fabricated in the past years, few studies reported a miniature robot capable of continuously jumping on the water surface as agile as a real water strider. Therefore, the present finding not only offers a possibility for vividly imitating and better understanding the amazing water-jumping capability of aquatic insects but also extends the application of porous and superhydrophobic materials to advanced robotic systems.

Vertical force acting on partly submerged spindly cylinders

When an object is placed on a water surface, the air-water interface deforms and a meniscus arises due to surface tension effects, which in turn produces a lift force or drag force on the partly submerged object. This study aims to investigate the underlying mechanism of the vertical force acting on spindly cylinders in contact with a water surface. A simplified 2-D model is presented, and the profile of the curved air-water interface and the vertical force are computed using a numerical method. A parametric study is performed to determine the effects of the cylinder center distance, inclined angle, static contact angle, and radius on the vertical force. Several key conclusions are derived from the study: (1) Although the lift force increases with the cylinder center distance, cylinders with smaller center distances can penetrate deeper below the water surface before sinking, thereby obtaining a larger maximum lift force; (2) An increase in the inclined angle reduces the lift force, which can enable the lower cylinders fall more deeply before sinking; (3) While the effect of static contact angle is limited for angles greater than 90°, hydrophobicity allows cylinders to obtain a larger lift force and load capacity on water; (4) The lift force increases rapidly with cylinder radius, but an increase in radius also increases the overall size and weight of cylinders and decreases the proportion of the surface tension force. These findings may prove helpful in the design of supporting legs of biologically-inspired miniature aquatic devices, such as water strider robots.

A miniature surface tension-driven robot using spatially elliptical moving legs to mimic a water strider’s locomotion

The highly agile and efficient water-surface locomotion of the water strider has stimulated substantial interest in biomimetic research. In this paper, we propose a new miniature surface tension-driven robot inspired by the water strider. A key feature of this robot is that its actuating leg possesses an ellipse-like spatial trajectory similar to that of a water strider by using a cam-link mechanism. Simplified models are presented to discuss the leg-water interactions as well as critical conditions for a leg penetrating the water surface, and simulations are performed on the robots dynamic properties. The final fabricated robot weighs about 3.9 g, and can freely and stably walk on water at different gaits. The maximum forward and turning speeds of the robot are measured as 16 cm s(-1) and 23°/s, respectively. Furthermore, a similarity analysis with Bond number and Weber number demonstrates that the locomotion of this robot is quite analogous to that of a real water strider: the surface tension force dominates the lifting force and plays a major role in the propulsion force. This miniature surface tension-driven robot might have potential applications in many areas such as water quality monitoring and aquatic search and rescue.

A water-walking robot mimicking the jumping abilities of water striders

The highly efficient and agile water-surface locomotion of water striders has attracted substantial research attention. Compared with imitating the horizontal rowing motion, imitating the jumping capability of water striders is much more challenging because the strong interaction in the jumping process easily causes the robot to sink. This study focuses on designing a miniature robot capable of continuously jumping on the water surface. A spring-based actuating mechanism is proposed to produce a large jumping force. The center of gravity of the robot is carefully designed to allow the robot to jump on the surface continuously and smoothly. The influences of several critical factors, including the area of the supporting legs, the spring stiffness, the jumping angle, etc on jumping ability are analyzed by means of dynamic simulation and experiments. The jumping performance under different jumping angles is tested. The fabricated robot weighs approximately 10.2 g and can continuously jump on water with a maximum leap height and length of 120 and 410 mm, respectively. This study helps researchers understand the jumping mechanism of water striders and provides a reference for developing water-jumping robots that can perform various aquatic tasks in the future.

A water walking robot inspired by water strider

Recent studies on water striders have revealed the mechanism of their floating and walking on water. By fast swinging their middle legs backward and striking the water, water striders get the driving force to move forward. This paper introduces a new water walking robot mimicking the rowing locomotion of water strider. The robot weighs 10 g and utilizes superhydrophobic nickel foam sheets as supporting legs and a spring-based actuating mechanism. Motion and force analysis for the supporting legs and the spring-based actuating mechanism were made and corresponding mechanics analysis models were built, based on which the simulation analysis of the robot was carried out. The robot can move over a distance of 30 cm per stroke with an average speed of 30 cm/s. This robot not only can help us better understand the mechanism of water strider rowing on water, but also can be developed for many applications in water quality monitoring, aquatic exploration, search and rescue on water, etc. in the future.

A miniature surface tension-driven robot mimicking the water-surface locomotion of water strider

Aiming at mimicking water striders water-surface locomotion, this study proposes a new miniature surface tension-driven robot. A key feature of this robot is that its actuating legs possess ellipse-like spatial trajectories like water strider by using a cam-link mechanism, and never pierces water surface when rowing. A set of simple models and equations are proposed to analyze the interaction forces between leg and water as well as the critical condition for a leg penetrating a water surface. The final fabricated robot weights about 3.9 g with a load capacity of 5.6 g. By controlling the motions of actuating legs, the robot can freely and stably walk on water with different gaits. The maximum forward and turning speeds of the robot are measured as 16 cm/s and 23 °/s, respectively. Moreover, a similarity analysis with Bond Number and Weber Number reveals that the locomotion of this robot is quite analogous to that of a water strider: surface tension force dominates the lifting force and plays a major role in the propulsion.

A continuous jumping robot on water mimicking water striders

Aiming at mimicking the jumping locomotion of water striders, a new continuous jumping robot on water is proposed. Compared with the horizontal rowing motion, the jumping capability of water striders is challengeable to imitate, since the impact force on water is easy to cause the sinking of the robot. In this paper, a jumping mechanism based on springs is designed to produce a large thrust for the robot to jump. The shape of supporting legs and center of gravity of the robot are carefully designed so that the robot can jump on the surface continuously and smoothly. Influences of several critical factors, including the area of supporting legs, spring stiffness and jumping angle, on jump performance are analyzed by means of dynamic simulation and experiments. The fabricated robot weighs about 10.2 g and can continuously jump on water with the maximum leap height and length of 120 mm and 410 mm, respectively.

Design and Test of a New Spiral Driven Pure Torsional Soft Actuator

Owing to the twist degree of freedom (DOF), soft torsional motion can increase flexibility and quickly achieve positional and attitude adjustment in complex and narrow spaces. Compared with bending actuator, there is much less research on soft torsional actuators. Current soft torsional actuators often accompany with other motion couplings, so it is difficult to provide pure twist. Based on the princi-ple of spiral chambers with pneumatic driving, a new type of torsional actuator module is designed in this paper. Combined with finite element simulation, the ge-ometric parameters of the module are optimized and then fabrication is carried out by two stages. In order to control the module, a kinematic model, which is the relationship between the air pressure and the twist angle, is established by means of experimental calibration. Finally, a test platform is set up, which is used for measuring the static characteristics of the designed module. The maximum ob-tainable torsion angle and torque are obtained separately through the experiments on torsion angle test and torsion torque test.

Water-Surface Stability Analysis of a Miniature Surface Tension-Driven Water Strider Robot

When water strider robots row on water, the periodically stroking water surface of the actuating legs will unavoidably bring vibrations and instabilities that might cause the robots to sink into water. In this work, a stability analysis model for water strider robots rowing on water was proposed and a mass-spring-damper-like model was defined to describe the robot-water interactions. We applied this model to evaluate the water-surface stability of a miniature surface tension-driven water strider robot by detaily discussing the effects of the actuating legs’ rowing with different rowing frequencies on the vibration, pitching and swinging motions. The theoretical results indicates the robot possesses a good water-surface stability. The stability analysis model presented in this study can help with the design of water strider robots in future.