Dai Owaki

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 2-D Passive-Dynamic-Running Biped With Elastic Elements

This is the first study of a real physical kneed bipedal robot that exhibits passive-dynamic running (PDR), i.e., a bipedal gait with a flight phase in a device without an actuator. By carefully designing the properties of the elastic elements implemented into the hip joints and the stance legs in this device, we achieved a stable PDR consisting of 36 steps. The main contribution of this paper is the demonstration of PDR in the real world, which fully exploits the elastic mechanical properties.

A two-dimensional passive dynamic running biped with knees

This is the first study of a real physical kneed bipedal robot that exhibits passive dynamic running (PDR). Passive dynamic walking (PDW), which has its roots in the pioneering research of McGeer, intrinsically offers not only nonlinear phenomena such as the pull-in effect and period-doubling bifurcation, but also offers an extremely interesting phenomenon that facilitates the engineering of a highly efficient walking robot. In recent years, a wide variety of verification experiments in PDW were performed using actual devices. In contrast, however, very few studies addressed PDR. In the present study, we developed a two-dimensional real physical passive dynamic running biped with knees. The device stands 400 mm tall and weights 4.8 kg. By carefully designing the properties of the elastic elements implemented into the hip joints and the stance legs in the present device, we achieved stable passive dynamic running of 36 steps. The device runs at about 0.83 m/s down a 0.22 rad slope. To the best of our knowledge, this is a first report of such a performance. This result is expected to prove useful not only for designing human-like natural and efficient bipedal robots, but also for understanding the principles underlying bipedal locomotion.

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.

Listen to body's message: Quadruped robot that fully exploits physical interaction between legs

Versatile gait patterns that depend on the locomo- tion speed, environmental conditions, and animal species are observed in quadrupeds. Locomotor patterns are generated via the interlimb coordination, which is partially controlled by an intraspinal neural network called the “central pattern generator” (CPG). However, there is currently no clear understanding of the adaptive interlimb coordination mechanism. We hypothesize that the interlimb coordination should rely more on the “physical” interaction between leg movements through the body rather than the interlimb neural connection. To understand the coordination mechanism, we developed a simple-structured quadruped robot and proposed an unconventional CPG model that consists of four decoupled oscillators with only local force feedback in each leg. Experimental results show that our CPG model allows the robot to exhibit steady gait patterns, adaptability to changes in body properties, and adaptive gait transition between walking and trotting. Our robot mimics locomotor patterns of real quadrupeds following which it can capture the basic mechanism underlying the adaptive interlimb coordination.

Enhancing Stability of a Passive Dynamic Running Biped by Exploiting a Nonlinear Spring

Recently, it has been widely recognized that control and mechanical systems cannot be designed separately due to their tight interdependency. However, there still leaves much to be understood about how well-balanced coupling between control and mechanical systems can be achieved. Therefore, as an initial step toward this goal, this study intensively discusses the effect of the intrinsic dynamics of a robots body on the resulting behavior, in the hope that mechanical systems appropriately designed will allow us to significantly reduce the complexity of control algorithm required. More precisely, we focus on the property of leg elasticity of a passive dynamic running biped, and investigate how this influences the stability of running. As a result, we have found that a certain type of nonlinearity in the leg elasticity plays a crucial role to enhance the stability of passive dynamic running. To the best of our knowledge, this has never been explicitly considered so far

Understanding the common principle underlying passive dynamic walking and running

In this study, we discuss the common stabilization mechanism underlying passive dynamic walking (PDW) and passive dynamic running (PDR), focusing on the feedback structures in analytical Poincaré maps. To this end, we have derived linearized analytical Poincaré maps for PDW and PDR, and analyzed these stabilities on two models, namely models with elastic elements and with stiff legs. Through our theoretical analysis, we have found an “implicit two-delay feedback structure”, which can be seen as a certain type of two-delay input digital feedback control developed as an artificial control structure in the field of control theory, is an inherent stabilization mechanism in PDR appearing from the model with elastic elements, and two-period and four-period PDW appearing from with stiff legs. This mechanism is the key to adaptive function underlying phase transition phenomenon between PDW and PDR and period-doubling bifurcation phenomenon in PDW. To the best of our knowledge, this has not yet to be addressed and studied so far. Our results shed new light on the common underlying principle of passive dynamic locomotion, including biped PDW and PDR

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.

Hereditary sensory and autonomic neuropathy types 4 and 5: Review and proposal of a new rehabilitation method.

Although pain is unpleasant, it should serve as a reminder for individuals to avoid similar damaging incidents in the future. Hereditary sensory and autonomic neuropathy (HSAN) includes genetic disorders involving various sensory and autonomic dysfunctions. They are classified by the mode of inheritance, clinical features, and related genes. HSAN type 4 (HSAN-4) and type 5 (HSAN-5) are characterized by insensitivity to pain and thermal sensation. Further, HSAN-4 is accompanied by decreased sweating and intellectual disabilities. These characteristics of HSAN-4 and -5 result in many clinical features, such as pediatric, psychiatric, orthopedic, oral, dermatological, and ophthalmological problems. Orthopedic problems include destructive injuries such as multiple fractures and joint dislocation. Studies on gait have shown greater speed and higher heel contact angular velocity in HSAN-4 and -5 patients compared with controls. Studies on grasp-lift-holding tasks have shown higher grasp force and fluctuations in acceleration of the object. We believe that these findings represent outcomes of deficient motor learning. We propose a new rehabilitation method for patients with HSAN-4 and -5, with the aim of decreasing their destructive injuries.

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.