Inverse Kinematics Analysis and COG Trajectory Planning Algorithms for Stable Walking of a Quadruped Robot with Redundant DOFs

This paper presents a new Center of Gravity （COG） trajectory planning algorithm for a quadruped robot with redundant Degrees of Freedom （DOFs）. Each leg has 7 DOFs, which allow the robot to exploit its kinematic redundancy for various locomotion and manipu- lation tasks. Also, the robot can suitably adapt to different environment （e.g., passing through a narrow gap） by simply changing the body posture. However, the robot has significant COG movement during the leg swinging phase due to the heavy leg weights; the weight of all the four legs takes up 80% of the robot＇s total weight. To achieve stable walking in the presence of undesired COG movements, a new COG trajectory planning algorithm was proposed by using a combined Jacobian of COG and centroid of a support polygon including a foot contact constraint. Additionally, the inverse kinematics of each leg was solved by modified improved Jacobian pseudoinverse （mIJP） algorithm. The mIJP algorithm could generate desired trajectories for the joints even when the robot＇s leg is in a singular posture. Owing to these proposed methods, the robot was able to perform various modes of locomotion both in simulations and experiments with improved stability.

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 Multiphysies. 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 and Analysis of a Rotational Leg-type Miniature Robot with an Actuated Middle Joint and a Tail （RoMiRAMT-II）

In this paper, a rotational leg-type miniature robot with a bioinspired actuated middle joint and a tail 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 seven candidates that selected by a newly proposed metric. It also has unique characteristics inspired by biological structures： a middle joint and a tail. An actuated middle joint allows the frontal body to be lifted or lowered, which was inspired by a flexible body joint of animals, to climb higher obstacles. Effectiveness of the middle joint was analytically verified by the geometric analysis of the robot. Additionally, a multi-functional one Degree Of Freedom （1-DOF） tail was added; the tail prevented the body being easily flipped, while allowed the robot to climb higher obstacles. A bristle-inspired micro structure was attached to the tail to enhance straightness of locomotion. Body size of the robot was 158 mm × 80 mm × 85 mm and weighed 581 g including a 7.4 V Li-Polymer battery. The average velocity of the robot was 2.74 m·s ^-1 （17.67 body lengths per second） and the maximum height of an obstacle that the robot could climb was 106 mm （2.5 times of leg length）, which all were verified by experiments.