Takeshi Kano

Simple robot suggests physical interlimb communication is essential for quadruped walking

Quadrupeds have versatile gait patterns, depending on the locomotion speed, environmental conditions and animal species. These locomotor patterns are generated via the coordination between limbs and are partly controlled by an intraspinal neural network called the central pattern generator (CPG). Although this forms the basis for current control paradigms of interlimb coordination, the mechanism responsible for interlimb coordination remains elusive. By using a minimalistic approach, we have developed a simple-structured quadruped robot, with the help of which we propose an unconventional CPG model that consists of four decoupled oscillators with only local force feedback in each leg. Our robot exhibits good adaptability to changes in weight distribution and walking speed simply by responding to local feedback, and it can mimic the walking patterns of actual quadrupeds. Our proposed CPG-based control method suggests that physical interaction between legs during movements is essential for interlimb coordination in quadruped walking.

A decentralized control scheme for an effective coordination of phasic and tonic control in a snake-like robot

Autonomous decentralized control has attracted considerable attention because it enables us to understand the adaptive and versatile locomotion of animals and facilitates the construction of truly intelligent artificial agents. Thus far, we have developed a snake-like robot (HAUBOT I) that is driven by a decentralized control scheme based on a discrepancy function, which incorporates phasic control. In this paper, we investigate a decentralized control scheme in which phasic and tonic control are well coordinated, as an extension of our previous study. To verify the validity of the proposed control scheme, we apply it to a snake-like robot (HAUBOT II) that can adjust both the phase relationship between its body segments and the stiffness at each joint. The results indicate that the proposed control scheme enables the robot to exhibit remarkable real-time adaptability over various frictional and inclined terrains. These findings can potentially enable us to gain a deeper insight into the autonomous decentralized control mechanism underlying the adaptive and resilient locomotion of animals.

A decentralized control scheme for orchestrating versatile arm movements in ophiuroid omnidirectional locomotion.

Autonomous decentralized control is a key concept for understanding the mechanism underlying the adaptive and versatile behaviour of animals. Although the design methodology of decentralized control based on a dynamical system approach that can impart adaptability by using coupled oscillators has been proposed in previous studies, it cannot reproduce the versatility of animal behaviours comprehensively. Therefore, our objective is to understand behavioural versatility from the perspective of well-coordinated rhythmic and non-rhythmic movements. To this end, we focus on ophiuroids as a simple good model of living organisms that exhibit spontaneous role assignment of rhythmic and non-rhythmic arm movements, and we model such arm movements by using an active rotator model that can describe both oscillatory and excitatory properties. Simulation results show that the spontaneous role assignment of arm movements is successfully realized by using the proposed model, and the simulated locomotion is qualitatively equivalent to the locomotion of real ophiuroids. This fact can potentially facilitate a better understanding of the control mechanism responsible for the orchestration of versatile arm movements in ophiuroid omnidirectional locomotion.

Local reflexive mechanisms essential for snakes' scaffold-based locomotion

Most robots are designed to work in predefined environments, and irregularities that exist in the environment interfere with their operation. For snakes, irregularities play the opposite role: snakes actively utilize terrain irregularities and move by effectively pushing their body against the scaffolds that they encounter. Autonomous decentralized control mechanisms could be the key to understanding this locomotion. We demonstrate through modelling and simulations that only two local reflexive mechanisms, which exploit sensory information about the stretching of muscles and the pressure on the body wall, are crucial for realizing locomotion. This finding will help develop robots that work in undefined environments and shed light on the understanding of the fundamental principles underlying adaptive locomotion in animals.

Decentralized control scheme for adaptive earthworm locomotion using continuum-model-based analysis

Crawling locomotion has been the focus of attention in the field of robotics because various applications of it are expected. However, the design methodologies for crawling robots, which can be applied in various environments, are not yet established. Therefore, we considered an earthworm as our model and employed an unconventional approach: we analyzed the motion of the earthworm with a continuum model and derived an optimal force distribution for its efficient propulsion, based on which we proposed an autonomous decentralized control scheme. The validity of the proposed control scheme was confirmed via simulations. Graphical Abstract

Obstacles are beneficial to me! Scaffold-based locomotion of a snake-like robot using decentralized control

Snakes are able to move effectively by using terrain irregularities as scaffolds against which they push their bodies. This locomotion is attractive from a robotic viewpoint because irregularities in the environment of conventional robots interfere with their operation. In a previous work, we proposed a decentralized control mechanism of the scaffold-based locomotion of snakes, which combined curvature derivative control with local pressure reflex. Here, we practically demonstrate how a snake-like robot utilizing the proposed control scheme moves effectively by pushing its body against pegs.

Decentralized control of scaffold-assisted serpentine locomotion that exploits body softness

Snakes actively utilize irregularities in terrains and attain propulsion force by pushing their bodies against scaffolds. The objective of this study is to understand the mechanism underlying such functionalities of snakes on the basis of a synthetic approach. We construct a model of a serpentine robot with viscoelastic properties, and we design an autonomous decentralized control scheme that employs local sensory feedback based on the muscle length and strain of the body, the latter of which is generated by the body softness. Simulation results show that the robot exhibits locomotion effectively by utilizing scaffolds such as high-friction areas and pegs, which is in fairly good agreement with biological findings.

A CPG-based decentralized control of a quadruped robot inspired by true slime mold

Despite its appeal, a systematic design of an autonomous decentralized control system is yet to be realized. To bridge this gap, we have so far employed a “back-to-basics” approach inspired by true slime mold, a primitive living creature whose behavior is purely controlled by coupled biochemical oscillators similar to central pattern generators (CPGs). Based on this natural phenomenon, we have successfully developed a design scheme for local sensory feedback control leading to system-wide adaptive behavior. This design scheme is based on a “discrepancy function” that extracts the discrepancies among the mechanical system (i:e:, body), control system (i:e:, brain-nervous system) and the environment. The aim of this study is to intensively investigate the validity of this design scheme by applying it to the control of a quadruped locomotion. Simulation results show that the quadruped robot exhibits remarkably adaptive behavior in response to environmental changes and changes in body properties. Our results shed a new light on design methodologies for CPG-based decentralized control of various types of 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.

A snake-like robot driven by a decentralized control that enables both phasic and tonic control

Autonomous decentralized control is a key concept in our understanding of the mechanism underlying locomotion of animals, wherein the phasic pattern of motion and the excitation pattern of muscle tonus are well reconciled. In our recent work, we proposed a decentralized control scheme in which phasic control and tonic control are well coordinated. In this study, we develop a real snake-like robot to validate our proposed control scheme. Experimental results show that the robot exhibits highly adaptive behavior in response to environmental changes. The results obtained are expected to shed new light on the design of autonomous decentralized control systems.