A human foot with high degrees of freedom (DOF) that has multi-DOF toe joints and a two-DOF ankle provides multiple benefits, such as increased stride length and walking speed, impact mitigation, and enhanced balancing. However, creating such mechanisms for legged robots has been challenging due to increased complexity, heavy weight, and vulnerability to impact. In this paper, a novel leg and toe mechanism inspired by human biomechanics, featuring a one-DOF knee joint, two-DOF ankle joint, and one-DOF toe joint, is developed. All actuators are located at the proximal part of the thigh frame to minimize the distal mass. High payload timing belts and unique linkage mechanisms are utilized in the transmission to achieve high backdrivability and high joint stiffness. Actuation torques are intentionally coupled inspired by human anatomy, enduring the high propulsive force to the ground for dynamic movements, such as jumping. The implemented leg and toe mechanisms weigh 8.16 kg, and the height from the ground to the hip center is 786 mm. The proposed mechanism has been proven to be effective through force test and distance jump experiments.

This paper presents a three-degrees-of-freedom (DOF) gravity compensation mechanism for the waists of cooperative robots whose centers of mass change according to the arm poses. It comprises 2-DOF and 1-DOF gravity compensation mechanisms in series, and is capable of natural and agile motions such as bobbing and weaving. The 2-DOF mechanism for the upper part of the waist acts as a universal joint. To compensate for the gravity of this 2-DOF motion, a simple and robust link mechanism with one compressive spring is proposed. Moreover, for the complete gravity compensation regardless of the arm poses, a three-dimensional (3D) parallel link structure that maintains the upper body parallel to the ground is introduced. The 1-DOF gravity compensation mechanism, which provides the motions of the hip and thigh, also has a parallelogram structure to maintain the waist parallel to the ground. The implemented 3-DOF waist mechanism can compensate for up to 23 kg and its own weight. It has an adjusting mechanism that can easily calibrate the amount of compensation in case the weight of the upper body changes. The large workspace enables the upper body to move in any direction in a 3D space without singularity. Therefore, the robot with this waist can touch the ground to pick up objects on the ground as well as reach an object at a height of 2145 mm.

In this paper, a dual-arm robot system for high-speed manipulations, which is named LIMS2-AMBIDEX and is developed to compete in the IROS2018 Robotic Challenge, is presented. It has two seven-degrees-of-freedom (DO$F$) lightweight arms, a three-DOF head, and a one-DOF gripper to manipulate foldable objects. Because all the heavy actuators are placed at the shoulder, it has remarkably low mass beyond the shoulder (2.63 kg), which guarantees an inherent safety at high speeds. Utilizing tension-amplification mechanisms, the high stiffness and strength are achieved, and thus it has the control performance comparable to conventional industrial manipulators. A unique three-DOF wrist mechanism, whose motions directly represent the quaternion values of the joint orientation, can manipulate objects without singular points in the entire range of motion. In order to utilize the object's inertia during rapid manipulation, the gripper was specially designed: it has a one-DOF finger to grasp the upper rib of the foldable fan and two supporting forks to grasp the bottom rib stably. For real-time performance and increased scalability, a software framework was developed based on Robot Operating System (ROS). The real-time capability is achieved by using the real-time development framework Xenomai and the high-speed communication protocol EtherCAT. As most of the algorithms are implemented in the distributed nodes using ROS, it is convenient to expand, improve, and replace the algorithms. Consequentially, the entire motion of the Fan Robotic Challenge Phase I Modality B required 1.05 s, which is substantially faster than a similar manipulation by most humans.