Hopping motion is a prerequisite for running motion, and thus, there have been various approaches for running and/or hopping motion. However, no methods provide an optimal hopping motion for general humanoid robots although the hopping motions have been implemented successfully. Various considerations exist for the optimal hopping of the humanoid robot, and this complicated problem can be formulated as an optimization problem. In this paper, an evolutionary optimization problem for optimal hopping motion of the humanoid robot is formulated to achieve efficient hopping with maximum flight time as well as stable hopping. The validity of the proposed method is verified through a simulation and an experiment with an actual humanoid robot platform.

This paper introduces an anthropomorphic robot hand that has variable grasping stiffness to unknown objects without damage. The robot hand has four fingers, 13 DoFs (Degrees of Freedom) with three SEA (Series Elastic Actuator) modules in the index, middle, and ring finger. The performance for broader grasping stiffness using variable impedance control based on the parameter update block and the procedure of grasping capability evaluations of the robot hand are explained. The robot finger modules are constructed with a thumb, index, middle, and ring finger to complete the anthropomorphic type robot hand. The robot finger module has three DoFs and functions as one actuator based on an under-actuated mechanism. Additionally, external force measurement is possible in the fingertip force sensor and SEA (Series Elastic Actuator) module. For the variable impedance control implementation, a parameter update block is added to adjust the desired impedance parameter. To implement the parameter update block, we define and evaluate the correlation equation between the fingertip force, shore hardness, and damping ratio.

This paper proposes a general stability control method that uses the concept of zero-moment-point (ZMP) and a turning algorithm with a light detection and ranging (LiDAR) sensor for a bipedal alpine skiing robot. There is no elaborate simulator for skiing robots since the snow has complicated characteristics, such as compression and melting. However, real experiments are laborious because of the many varied skiing conditions. The proposed skiing simulator could be used, so that a humanoid robot can track its desired turning radius by modeled forces that are similar to real ones in the snow. Subsequently, the robot will be able to pass through gates with LiDAR sensors. By using ZMP control, the robot can avoid falling down while tracking its desired path. The performance of the proposed stabilization method and autonomous turning algorithm are verified by a dynamics simulation software, Webots, and the simulation results are obtained while using the small humanoid robot platform DARwIn-OP.

Model‐based control algorithms commonly use joint acceleration as a desired trajectory. As the velocity trajectory in the task space is converted into joint velocity by multiplying using a Jacobian matrix, to derive the acceleration in joint space, Jacobian differentiation is required. Although the numerical method for Jacobian differentiation gives sufficiently accurate approximations, it incurs a high computation cost because this method involves computing the forward kinematics twice and Jacobian derivation for every element of the Jacobian matrix. Consequently, this causes difficulties for real‐time control. To resolve this, an analytical differentiation method is proposed. Through recursive computation, differentiation is performed without any approximation, in an acceptably small computational time. Performance of the proposed method was verified by comparison with numerical derivation using a computer simulation.

A coaxial cable drive mechanism is proposed to implement a high reduction gear ratio. The cable drive mechanism has great advantages such as lightweight, zero backlashes and high degrees of freedom in terms of mechanical design. However, it is restrictively utilised in robotic applications because it is difficult to implement a high reduction gear ratio of more than 10:1 due to the complexity of adjusting tension components, which causes the mechanical structure to be rather bulky and heavy to be mounted. To overcome this, in the present author's previous work a multi‐level reduction mechanism, by adopting a seamless winding method which links the previous output axis to the next input axis, was developed. The performance of the previous work, by adopting a coaxial mechanism to drive the multi‐level reduction system is improved. Significantly, the proposed mechanism reduces the overall size due to efficient integration of mechanical parts. On the basis of the proposed mechanism, a three‐dimensional computer‐aided design is provided and the prototype is manufactured, where the usability of the prototype is verified by experimental results.