We have developed biped robots with a passive dynamic walking mechanism. This study proposes a compass model with a wobbling mass connected to the upper body and oscillating in the horizontal direction to clarify the influence of the horizontal dynamics of the upper body on bipedal walking. The limit cycles of the model were numerically searched, and their stability and energy efficiency was investigated. Several qualitatively different limit cycles were obtained depending mainly on the spring constant that supports the wobbling mass. Specific types of solutions decreased the stability while reducing the risk of accidental falling and improving the energy efficiency. The obtained results were attributed to the wobbling mass moving in the opposite direction to the upper body, thereby preventing large changes in acceleration and deceleration while walking. The relationship between the locomotion of the proposed model and the actual biped robot and human gaits was investigated.

Our research team has been developing biped robots based on the nature of passive dynamics. We aim to both investigate the effect of wobbling mass and apply the findings to biped robots to achieve high-performance running. We used an elastically supported wobbling mass in the trunk of biped robots because humans utilize their elastic organs in the upper body and arms to improve running performance. To investigate the characteristics and mechanisms of passive dynamics of the wobbling mass focusing on the vertical ground reaction force, we used a simple model equipped with an elastically supported wobbling mass and analytically derived periodic solutions. The normal mode analysis of the obtained solutions explained the mechanism under which periodic solutions are achieved, and analytic solutions showed similar vertical locomotion to human running and suggested the mechanism under which high-performance locomotion is achieved from the viewpoint of the ground reaction force and energy efficiency. Based on these solutions, we conducted experiments using a prototype and a biped robot equipped with wobbling mass. Experimental results showed similar characteristics in the vertical movement to the simple model and human running. These findings will help improve our understanding of biped running and contribute to producing human-like running of biped robots.

To date, many gait generation strategies have been designed for robots with leg configurations that model those of natural creatures. However, their leg configurations are limited to the 2 × N type, such as hexapod or myriapod; hence, simultaneously, the potential ability of legged robots is implicitly limited. We consider single-legged modular robots that can be arranged to form a cluster with arbitrary 2-D leg configurations. By choosing configurations appropriately, these robots have the potential to perform several types of tasks, as is the case for reconfigurable modular robots. However, to use appropriate configurations for a given task, a unified gait generation system for various configurations of a cluster is required. In this article, we propose an autonomous distributed control system for each single-legged modular robot to collectively achieve static walking of the cluster with various leg configurations on planar ground. Moreover, our system is an autonomous distributed system with scalability and fault tolerance, in which each module determines the moving pattern of its foot through local communication without global information, such as the entire leg configuration of the cluster. We verified that several types of clusters achieved static walking using our system not only in dynamic simulations, but also in real robot experiments.

The observation of quadruped animals has suggested that the body flexibility is important for the bounding gait. In particular, the body flexibility is assumed to be crucial for determining the ground reaction force (GRF). In this paper, we investigated the dynamic effect of the body flexibility on the GRF in quadruped bounding with simple physical models by focusing on the vertical motion. More specifically, we first showed that the body flexibility reduces the GRF using a simple two legged model in sagittal plane. Next, to clarify the GRF reduction mechanism, we further simplified the model, which has only one leg. This allowed us to analytically obtain periodic solutions. Based on the solutions, we investigated the mechanism that the body flexibility reduces the GRF during quadrupedal bounding.