Akio Ishiguro

A Quadruped Robot Exhibiting Spontaneous Gait Transitions from Walking to Trotting to Galloping

The manner in which quadrupeds change their locomotive patterns—walking, trotting, and galloping—with changing speed is poorly understood. In this paper, we provide evidence for interlimb coordination during gait transitions using a quadruped robot for which coordination between the legs can be self-organized through a simple “central pattern generator” (CPG) model. We demonstrate spontaneous gait transitions between energy-efficient patterns by changing only the parameter related to speed. Interlimb coordination was achieved with the use of local load sensing only without any preprogrammed patterns. Our model exploits physical communication through the body, suggesting that knowledge of physical communication is required to understand the leg coordination mechanism in legged animals and to establish design principles for legged robots that can reproduce flexible and efficient locomotion.

Gait control in a soft robot by sensing interactions with the environment using self-deformation

All animals use mechanosensors to help them move in complex and changing environments. With few exceptions, these sensors are embedded in soft tissues that deform in normal use such that sensory feedback results from the interaction of an animal with its environment. Useful information about the environment is expected to be embedded in the mechanical responses of the tissues during movements. To explore how such sensory information can be used to control movements, we have developed a soft-bodied crawling robot inspired by a highly tractable animal model, the tobacco hornworm Manduca sexta. This robot uses deformations of its body to detect changes in friction force on a substrate. This information is used to provide local sensory feedback for coupled oscillators that control the robots locomotion. The validity of the control strategy is demonstrated with both simulation and a highly deformable three-dimensionally printed soft robot. The results show that very simple oscillators are able to generate propagating waves and crawling/inching locomotion through the interplay of deformation in different body parts in a fully decentralized manner. Additionally, we confirmed numerically and experimentally that the gait pattern can switch depending on the surface contact points. These results are expected to help in the design of adaptable, robust locomotion control systems for soft robots and also suggest testable hypotheses about how soft animals use sensory feedback.

Non-centralized and functionally localized nervous system of ophiuroids: evidence from topical anesthetic experiments

ABSTRACT Ophiuroids locomote along the seafloor by coordinated rhythmic movements of multi-segmented arms. The mechanisms by which such coordinated movements are achieved are a focus of interest from the standpoints of neurobiology and robotics, because ophiuroids appear to lack a central nervous system that could exert centralized control over five arms. To explore the underlying mechanism of arm coordination, we examined the effects of selective anesthesia to various parts of the body of ophiuroids on locomotion. We observed the following: (1) anesthesia of the circumoral nerve ring completely blocked the initiation of locomotion; however, initiation of single arm movement, such as occurs during the retrieval of food, was unaffected, indicating that the inability to initiate locomotion was not due to the spread of the anesthetic agent. (2) During locomotion, the midsegments of the arms periodically made contact with the floor to elevate the disc. In contrast, the distal segments of the arms were pointed aborally and did not make contact with the floor. (3) When the midsegments of all arms were anesthetized, arm movements were rendered completely uncoordinated. In contrast, even when only one arm was left intact, inter-arm coordination was preserved. (4) Locomotion was unaffected by anesthesia of the distal arms. (5) A radial nerve block to the proximal region of an arm abolished coordination among the segments of that arm, rendering it motionless. These findings indicate that the circumoral nerve ring and radial nerves play different roles in intra- and inter-arm coordination in ophiuroids. Summary: Functional localization exists in the nervous system of ophiuroids although there is no evidence of a morphological counterpart to the central nervous system of other species.

TEGOTAE-Based Control Scheme for Snake-Like Robots That Enables Scaffold-Based Locomotion

Snakes exhibit “scaffold-based locomotion” wherein they actively utilize terrain irregularities and move effectively by pushing their body against the scaffolds that they encounter. Implementing the underlying mechanism in snake-like robots will enable them to work well in unstructured real-world environments. In this study, we proposed a decentralized control scheme for snake-like robots based on TEGOTAE, a Japanese concept describing how well a perceived reaction matches an expectation, to reproduce scaffold-based locomotion. A preliminary experimental result showed that reaction forces from environment are evaluated based on TEGOTAE in real time and those beneficial for propulsion of the body are selectively exploited.

A brittle star-like robot capable of immediately adapting to unexpected physical damage

A major challenge in robotic design is enabling robots to immediately adapt to unexpected physical damage. However, conventional robots require considerable time (more than several tens of seconds) for adaptation because the process entails high computational costs. To overcome this problem, we focus on a brittle star—a primitive creature with expendable body parts. Brittle stars, most of which have five flexible arms, occasionally lose some of them and promptly coordinate the remaining arms to escape from predators. We adopted a synthetic approach to elucidate the essential mechanism underlying this resilient locomotion. Specifically, based on behavioural experiments involving brittle stars whose arms were amputated in various ways, we inferred the decentralized control mechanism that self-coordinates the arm motions by constructing a simple mathematical model. We implemented this mechanism in a brittle star-like robot and demonstrated that it adapts to unexpected physical damage within a few seconds by automatically coordinating its undamaged arms similar to brittle stars. Through the above-mentioned process, we found that physical interaction between arms plays an essential role for the resilient inter-arm coordination of brittle stars. This finding will help develop resilient robots that can work in inhospitable environments. Further, it provides insights into the essential mechanism of resilient coordinated motions characteristic of animal locomotion.

Decentralized Control Scheme for Myriapod Locomotion That Exploits Local Force Feedback

Legged animals exhibit adaptive and resilient locomotion through their inter-limb coordination. Our long-term goal of this study is to develop a systematic design scheme for legged robots by elucidating the inter-limb coordination mechanism of various legged animals from a unified viewpoint. As a preliminary step towards this, we here focus on millipedes. We performed behavioral experiments on a terrain with gap, and found that legs do not tend to move without the ground contact. Based on this qualitative finding, we proposed a decentralized control scheme using local force feedback.

Understanding Interlimb Coordination Mechanism of Hexapod Locomotion via “TEGOTAE”-Based Control

Insects exhibit surprisingly adaptive and versatile locomotion despite their limited computational resources. Such locomotor patterns are generated via coordination between leg movements, i.e., an interlimb coordination mechanism. The clarification of this mechanism will lead us to elucidate the fundamental control principle of animal locomotion as well as to realize truly adaptive legged robots that could not be developed solely by conventional control theory. In this study, we tried to model the interlimb coordination mechanism underlying hexapod locomotion on the basis of a concept called “TEGOTAE,” a Japanese concept describing how well a perceived reaction matches an expectation. Preliminary experimental results show that our proposed TEGOTAE-based control scheme allows us to systematically design a decentralized interlimb coordination mechanism that can well-reproduce insects’ gait patterns.

Decentralized control mechanism underlying interlimb coordination of millipedes

Legged animals exhibit adaptive and resilient locomotion through interlimb coordination. The long-term goal of this study is to clarify the relationship between the number of legs and the inherent decentralized control mechanism for interlimb coordination. As a preliminary step, the study focuses on millipedes as they represent the species with the greatest number of legs among various animal species. A decentralized control mechanism involving local force feedback was proposed based on the qualitative findings of behavioural experiments in which responses to the removal of part of the terrain and leg amputation were observed. The proposed mechanism was implemented in a developed millipede-like robot to demonstrate that the robot can adapt to the removal of the part of the terrain and leg amputation in a manner similar to that in behavioural experiments.

Leg Stiffness Control Based on “TEGOTAE” for Quadruped Locomotion

Quadrupeds exhibit adaptive limb coordination to achieve versatile and efficient locomotion. In particular, the leg-trajectory changes in response to locomotion speed. The goal of this study is to reproduce this modulation of leg-trajectory and to understand the control mechanism underlying quadruped locomotion. We focus primarily on the modulation of stiffness of the leg because the trajectory is a result of the interaction between the leg and the environment during locomotion. In this study, we present a “TEGOTAE”-based control scheme to modulate the leg stiffness. TEGOTAE is a Japanese concept describing the extent to which a perceived reaction matches the expected reaction. By using the presented scheme, foot-trajectories were modified and the locomotion speed increased correspondingly.

Short-Term Effect of Prosthesis Transforming Sensory Modalities on Walking in Stroke Patients with Hemiparesis

Sensory impairments caused by neurological or physical disorders hamper kinesthesia, making rehabilitation difficult. In order to overcome this problem, we proposed and developed a novel biofeedback prosthesis called Auditory Foot for transforming sensory modalities, in which the sensor prosthesis transforms plantar sensations to auditory feedback signals. This study investigated the short-term effect of the auditory feedback prosthesis on walking in stroke patients with hemiparesis. To evaluate the effect, we compared four conditions of auditory feedback from plantar sensors at the heel and fifth metatarsal. We found significant differences in the maximum hip extension angle and ankle plantar flexor moment on the affected side during the stance phase, between conditions with and without auditory feedback signals. These results indicate that our sensory prosthesis could enhance walking performance in stroke patients with hemiparesis, resulting in effective short-term rehabilitation.