Bokeon Kwak

Toward Fast and Efficient Mobility in Aquatic Environment: A Robot with Compliant Swimming Appendages Inspired by a Water Beetle

Water beetles are proficient drag-powered swimmers, with oar-like legs. Inspired by this mechanism, here we propose a miniature robot, with mobility provided by a pair of legs with swimming appendages. The robot has optimized linkage structure to maximize the stroke angle, which is actuated by a single DC motor with a series of gears and a spring. A simplified swimming appendage model is proposed to calculate the deflection due to the applied drag force, and is compared with simulated data using COMSOL Multiphysics. Also, the swimming appendages are optimized by considering their locations on the legs using two fitness functions, and six different configurations are selected. We investigate the performance of the robot with various types of appendage using a high-speed camera, and motion capture cameras. The robot with the proposed configuration exhibits fast and efficient movement compared with other robots. In addition, the locomotion of the robot is analyzed by considering its dynamics, and compared with that of a water boatman (Corixidae).

Design of a robot with biologically-inspired swimming hairs for fast and efficient mobility in aquatic environment

A water beetle is skillful at drag-powered swimming by using its oar-like legs. Inspired by this mechanism, a miniature robot, whose mobility is obtained by a pair of legs attached with swimming appendages, was studied in this work. The robot in this paper has optimally designed linkage structures to maximize the sweep angle, which is actuated by a single DC motor with series of gears and a spring. A simplified swimming appendage model was proposed to calculate deflection by drag force applied. Also, each of swimming appendage was optimized individually by considering the attached locations on the legs using the two fitness functions, and three different configurations were selected. In the experiments, the performance of the proposed robots was verified using a high-speed camera, and motion capture cameras. The robot with the proposed configuration showed the fastest movement comparing with other robots.

Design of hair-like appendages and their coordination inspired by water beetles for steady swimming on the water surface

Locomotion of water beetles have been widely studied in biology owing to their remarkable swimming skills. Here, we investigated the coordination between the two pairs of legs to achieve steady swimming with novel hair-like appendages. Some design considerations and a fabrication of the hair-like appendages, which can passively adjust their projected area to obtain net thrust, are proposed. As do water beetles in nature, the coordination between the two pairs of legs were considered to achieve steady swimming without jerky motion by varying the beating frequency and phase of the legs. To verify the functionality of the hair-like appendages and their coordinations, six different types of appendages were fabricated, and two robots (one with single pair and the other with two pairs of legs) were built. Locomotion of the robots were compared through experiments, and steady swimming was achievable by properly coordinating the two-pairs of legs without sacrificing the swmming speed.

Development of a quadruped robot with redundant DOFs for high-degree of functionality and adaptation

This paper presents a quadruped robot with redundant degrees of freedom (DOFs), which exploits its kinematic redundancy for various types of locomotion and manipulation. Unlike previously developed quadruped robots, the proposed robot can change its body posture and suitably adapt to different environments. For example, the robot can walk on a plain terrain, pass through a narrow gap, surmount an obstacle, perform a simple task by using one of its legs as a manipulator, etc. Inverse kinematics of each leg was solved by using a newly proposed method: Improved Jacobian Pseudoinverse (IJP) algorithm. Also, a static stability of the robot was dealt with using a combined Jacobian of a center of mass (COM) and centroid of a support polygon. Performance of the proposed robot was verified in both simulations and experiments.

Design and analysis of a rotational leg-type miniature robot with an actuated middle joint and a tail (RoMiRAMT)

In this paper, a rotational leg-type miniature robot with an actuated middle joint and tail, called RoMiRAMT, is proposed for stable locomotion and improved climbing ability. The robot has four independently actuated rotational legs, giving it advantages of both wheel-type and leg-type locomotion. The design parameters of the rotational legs were determined by 3D simulation within the properly selected candidates. It also has unique characteristics inspired by biological structures: a spine and a tail. An actuated middle joint allows the frontal body to be lifted or lowered, which was inspired by a spine, to climb higher obstacles. Additionally, a multi-functional two degrees of freedom (2-DOF) tail was added; the tail provides instant deceleration, and minimized the likelihood of flipping, while allowing the robot to climb higher obstacles. A microcontroller was embedded in the robot, along with a micro-camera and an inertia measurement unit (IMU) sensor. By controlling the robot using the yaw angle signal measured by the IMU sensor, straight movement was enhanced. The body size of the RoMiRAMT is 155 × 80 mm without the rotational legs, and the weight is 593 g including batteries. The maximum velocity of the robot was 2.58 m/s (16.65 body lengths per second) and the maximum height of an obstacle that the robot can climb was 95 mm, which all were verified by experiments.

Design of hair-like appendages and comparative analysis on their coordination toward steady and efficient swimming

The locomotion of water beetles has been widely studied in biology owing to their remarkable swimming skills. Inspired by the oar-like legs of water beetles, designing a robot that swims under the principle of drag-powered propulsion can lead to highly agile mobility. But its motion can easily be discontinuous and jerky due to backward motions (i.e. retraction) of the legs. Here we proposed novel hair-like appendages and consider their coordination to achieve steady and efficient swimming on the water surface. First of all, we propose several design schemes and fabrication methods of the hair-like appendages, which can passively adjust their projected area while obtaining enough thrust. The coordination between the two pairs of legs, as with water beetles in nature, were also investigated to achieve steady swimming without backward movement by varying the beating frequency and phase of the legs. To verify the functionality of the hair-like appendages and their coordinations, six different types of appendages were fabricated, and two robots (one with a single pair of legs and the other with two pairs of legs) were built. Locomotion of the robots was extensively compared through experiments, and it was found that steady swimming was achieved by properly coordinating the two pairs of legs without sacrificing their speed. Also, owing to the lower velocity fluctuation during swimming, it was shown that using two pairs of legs was more energy efficient than the robot with single pair of legs.