Yasuhiro Sugimoto

Evaluating functional roles of phase resetting in generation of adaptive human bipedal walking with a physiologically based model of the spinal pattern generator

The central pattern generators (CPGs) in the spinal cord strongly contribute to locomotor behavior. To achieve adaptive locomotion, locomotor rhythm generated by the CPGs is suggested to be functionally modulated by phase resetting based on sensory afferent or perturbations. Although phase resetting has been investigated during fictive locomotion in cats, its functional roles in actual locomotion have not been clarified. Recently, simulation studies have been conducted to examine the roles of phase resetting during human bipedal walking, assuming that locomotion is generated based on prescribed kinematics and feedback control. However, such kinematically based modeling cannot be used to fully elucidate the mechanisms of adaptation. In this article we proposed a more physiologically based mathematical model of the neural system for locomotion and investigated the functional roles of phase resetting. We constructed a locomotor CPG model based on a two-layered hierarchical network model of the rhythm generator (RG) and pattern formation (PF) networks. The RG model produces rhythm information using phase oscillators and regulates it by phase resetting based on foot-contact information. The PF model creates feedforward command signals based on rhythm information, which consists of the combination of five rectangular pulses based on previous analyses of muscle synergy. Simulation results showed that our model establishes adaptive walking against perturbing forces and variations in the environment, with phase resetting playing important roles in increasing the robustness of responses, suggesting that this mechanism of regulation may contribute to the generation of adaptive human bipedal locomotion.

Forward dynamic simulation of bipedal walking in the Japanese macaque: Investigation of causal relationships among limb kinematics, speed, and energetics of bipedal locomotion in a nonhuman primate

Japanese macaques that have been trained for monkey performances exhibit a remarkable ability to walk bipedally. In this study, we dynamically reconstructed bipedal walking of the Japanese macaque to investigate causal relationships among limb kinematics, speed, and energetics, with a view to understanding the mechanisms underlying the evolution of human bipedalism. We constructed a two-dimensional macaque musculoskeletal model consisting of nine rigid links and eight principal muscles. To generate locomotion, we used a trajectory-tracking control law, the reference trajectories of which were obtained experimentally. Using this framework, we evaluated the effects of changes in cycle duration and gait kinematics on locomotor efficiency. The energetic cost of locomotion was estimated based on the calculation of mechanical energy generated by muscles. Our results demonstrated that the mass-specific metabolic cost of transport decreased as speed increased in bipedal walking of the Japanese macaque. Furthermore, the cost of transport in bipedal walking was reduced when vertical displacement of the hip joint was virtually modified in the simulation to be more humanlike. Human vertical fluctuations in the bodys center of mass actually contributed to energy savings via an inverted pendulum mechanism.

Experiment and analysis of quadrupedal quasi-passive dynamic walking robot “Duke”

Much attention has been paid to passive dynamic walking as an approach to investigate the walking of human beings and animals. As for quadrupedal passive dynamic walking, it is confirmed that walking resembles that of animals, and that the gait of the robot changes depending on the structure of robot or the environment. Based on these facts, it is conceivable that quadrupedal passive dynamic walking is related to walking of animals, and the walking principle is inherent in passive dynamic walking. In this research, we approach the walking principle through realization of a walking on the level ground by rational-energy input and investigation how gait changes depending on the input. In this paper, a quadrupedal quasi-passive dynamic walking robot named Duke has been developed by applying passive dynamic walking. This robot has only two rolling actuators, which simply provide with rocking motion and not drive the knee or hip joint directly. We conduct walking experiments by Duke with various inputs, and observe its gaits. As a result of walking experiments, it was verified that walking speed was related to the frequency and the phase difference of rocking motion. In addition, through analysis of a shape of soles, we revealed Duke has a nonholonomic constraint that is comparable to that of “two-wheeled robot” on its sole. As a result of analyses based on the nonlinear control theory, we conclude that the sole shape contributes to the transition of walking speed accompanying with change of a phase difference.

Static and dynamic properties of McKibben pneumatic actuator for self-stability of legged-robot motion

Abstract A McKibben-type pneumatic actuator is widely used for utilization of its self-stabilization characteristics with a simple actuator model and a simple control method. However, how its characteristics act on the stability of robot motion have not been sufficiently discussed. The purpose of the paper is to analyze how various characteristics of McKibben pneumatic actuator (MPA) influence the stability of movements generated by MPA. In this paper, at first, we introduced two static models of the MPA which were proposed in the previous research and verified the models through validation experiments. The models of MPA form as simply as possible for a stability analysis. Next, we showed that the tension of MPA monotonically decreased according to the contraction velocity through validation experiments. Finally, the model was applied to a same simple robot model with the previous study and the stability of motions generated by the actuators was analyzed based on control theory. From the stability analysis, it was verified that the stability of the constant posture was achieved by the relatively simple static MPA model, the verified tension–velocity dependency of actuator, and the interaction with the properties of the actuator and the mechanical structure of the robot. This result suggests that the properties of MPA, particularly the verified velocity-dependent property, can contribute to the self-stability of a robot generated by the actuators, and it is important to consider the interaction between the mechanical structure and the actuator.

Stability analysis of robot motions driven by McKibben pneumatic actuator

It is well known that a robot driven by a McKibben pneumatic actuator generates stable motion in spite of its simple control and simple actuator model. However, how the characteristics of the McKibben pneumatic actuator act on the stability of a robots motion has not been sufficiently discussed. In this paper, a physical model of the McKibben pneumatic actuator is derived and the stability of a robot which is driven by the McKibben pneumatic actuator is analyzed.

Tripedal walking robot with fixed coxa driven by periodic rocking

This paper is concerned with realization of a new kind of three-legged walking machine. The proposed robot has neither coxa joint nor knee joint, so the three legs are just rigidly fixed to each other. Instead of pursuing elaborated joint mechanism for the coxa, we equipped it with two actuators and a pair of weights, so that it can generate torque about the yaw and the pitch axes. Thus it only rocks as a reaction of the mass driving unit. We show that, by appropriate choices of oscillatory controls (i.e., amplitudes, frequencies and phases of the pitch and the yaw actuators), it is indeed possible to achieve rotation and forwarding locomotion of the tripedal robot. In particular, combination of the frequencies selects the rotation/forwarding, while combination of the phases affects the direction of forwarding. We also remark that the realized motion naturally reflects the symmetry of the body structure.

Dual structure of Mobiligence—Implicit Control and Explicit Control—

In this paper, we propose an idea which can solve the complexity of the overlapping situation observed in control system of living things. We introduce an another element between controlled object and control law. This newly introduced element is named as Implicit Control Law and decided by interaction of the controlled object, the control law and the field. Furthermore, the Implicit Control Law does not only solve the indivisibility problem but also produces a start point for understanding of realtime environmental adaptation function of living thing with tiny brain. That is, the Implicit Control Law is a core principle of Mobiligence.

Hierarchical Implicit Feedback Structure in Passive Dynamic Walking

The purpose of this paper is to analyze the stability of Passive Dynamic Walking (PDW) using a linearized analytical Poincare map. In particular, in this paper, we focus on a bifurcation phenomenon in PDW. Although the bifurcation of the walking period is one of the well-known features of PDW, it have not been studied sufficiently so far. Using techniques similar to our previous research, we derive an analytical Poincare map for 2-period walking and discuss the stability of PDW with this map. In addition, we point out that there is a similar interesting structure in this Poincare map.

Analysis of implicit control structure in object clustering phenomena

Living things exhibit adaptive and supple locomotion under the real world characterized by rapid changes, high uncertainty, and limited availability of information. But the systematic design of the behavior of living things like ants or bees (e.g. constructing very big and complicated nests) whose brains have very tiny memory abilities, has not been well established. In recent research, this design principle is considered to come from the interaction among the mechanical system (i.e. body), the control law (i.e. brain), and the environment (i.e. real world). To understand these principles with interaction, we propose on Implicit Control Law, which reflects the interaction among the body, the brain, and the environment. In this research, some simple robots named Swiss Robot, Aggregator Robot, Coronoc Robot, are focused. These robots show us interesting object clustering behaviors even if each robot is equipped with simple Explicit Control Law or no Explicit Control Law. From the systematic analyses of clustering behaviors, each Implicit Control Law is formulated. Though the Explicit Control Law and mechanical structures of each robot are exactly different, we can see common parts (principles) of Implicit Control Law. Furthermore, we demonstrate the correspondance between the Explicit Control Law and its clustering ability of each robot (e.g. number of clusters, clustering position).

Static and dynamic characteristics of McKibben pneumatic actuator for realization of stable robot motions

A robot driven by a McKibben pneumatic actuator generates stable motion despite its simple control and simple actuator model. However, how its characteristics act on the stability of robot motion have not been sufficiently discussed. In this paper, a model of the McKibben pneumatic actuator is derived in which the actuator characteristics are considered. In modeling the McKibben pneumatic actuator, we concentrated on its dynamic characteristics. We applied the actuator model to a simple robot model and analyzed the stability of the motions generated by the actuators. From the stability analysis results, we found that the stability of the constant posture is satisfied by the static and dynamic characteristics of the McKibben pneumatic actuator.