Kazuo Tsuchiya

Adaptive gait pattern control of a quadruped locomotion robot

The authors have proposed a control system of a quadruped locomotion robot by using nonlinear oscillators. It is composed of a leg motion controller and a gait pattern controller. The leg motion controller drives the actuators of the legs by using local feedback control. The gait pattern controller involves nonlinear oscillators with mutual interactions. In the paper, capability of adaptation of the proposed control system to variance of the environment is verified through numerical simulations and hardware experiments. With the input signals from the touch sensors at the tips of the legs, the nonlinear oscillators tune the phase differences among them through mutual entertainments. As a result, a gait pattern corresponding to the states of the system or to the properties of the environment emerges. The robot changes its gait pattern adaptively to variance of the environment and establishes a stable locomotion while suppressing the energy consumption.

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.

Dynamics of a Spacecraft during Extension of Flexible Appendages

This paper deals with the attitude behavior of a spacecraft with a rotor during extension of flexible appendages. The analysis is based on the method of multiple scales. The equations of motion are formulated using a spacecraft modal coordinate scheme. The analytical expressions for the attitude behavior of the spacecraft are obtained. The extension of the appendages plays a significant role in the stability of the attitude motion of the spacecraft: In some cases, the attitude motion of the spacecraft will become unstable.

A stability-based mechanism for hysteresis in the walk-trot transition in quadruped locomotion.

Quadrupeds vary their gaits in accordance with their locomotion speed. Such gait transitions exhibit hysteresis. However, the underlying mechanism for this hysteresis remains largely unclear. It has been suggested that gaits correspond to attractors in their dynamics and that gait transitions are non-equilibrium phase transitions that are accompanied by a loss in stability. In the present study, we used a robotic platform to investigate the dynamic stability of gaits and to clarify the hysteresis mechanism in the walk–trot transition of quadrupeds. Specifically, we used a quadruped robot as the body mechanical model and an oscillator network for the nervous system model to emulate dynamic locomotion of a quadruped. Experiments using this robot revealed that dynamic interactions among the robot mechanical system, the oscillator network, and the environment generate walk and trot gaits depending on the locomotion speed. In addition, a walk–trot transition that exhibited hysteresis was observed when the locomotion speed was changed. We evaluated the gait changes of the robot by measuring the locomotion of dogs. Furthermore, we investigated the stability structure during the gait transition of the robot by constructing a potential function from the return map of the relative phase of the legs and clarified the physical characteristics inherent to the gait transition in terms of the dynamics.

Variant and invariant patterns embedded in human locomotion through whole body kinematic coordination.

Step length, cadence and joint flexion all increase in response to increases in gradient and walking speed. However, the tuning strategy leading to these changes has not been elucidated. One characteristic of joint variation that occurs during walking is the close relationship among the joints. This property reduces the number of degrees of freedom and seems to be a key issue in discussing the tuning strategy. This correlation has been analyzed for the lower limbs, but the relation between the trunk and lower body is generally ignored. Two questions about posture during walking are discussed in this paper: (1) whether there is a low-dimensional restriction that determines walking posture, which depends not just on the lower limbs but on the whole body, including the trunk and (2) whether some simple rules appear in different walking conditions. To investigate the correlation, singular value decomposition was applied to a measured walking pattern. This showed that the whole movement can be described by a closed loop on a two-dimensional plane in joint space. Furthermore, by investigating the effect of the walking condition on the decomposed patterns, the position and the tilt of the constraint plane was found to change significantly, while the loop pattern on the constraint plane was shown to be robust. This result indicates that humans select only certain kinematic characteristics for adapting to various walking conditions.

Functional Roles of Phase Resetting in the Gait Transition of a Biped Robot From Quadrupedal to Bipedal Locomotion

Although physiological studies have shown evidence of phase resetting during fictive locomotion, the functional roles of phase resetting in actual locomotion remain largely unclear. In this paper, we have constructed a control system for a biped robot based on physiological findings and investigated the functional roles of phase resetting in the gait transition from quadrupedal to bipedal locomotion by numerical simulations and experiments. So far, although many studies have investigated methods to achieve stable locomotor behaviors for various gait patterns of legged robots, their transitions have not been thoroughly examined. Especially, the gait transition from quadrupedal to bipedal requires drastic changes in the robot posture and the reduction of the number of supporting limbs, and therefore, the stability greatly changes during the transition. Thus, this transition poses a challenging task. We constructed a locomotion control system using an oscillator network model based on a two-layer hierarchical network model of a central pattern generator while incorporating the phase resetting mechanism and created robot motions for the gait transition based on the physiological concept of synergies. Our results, which demonstrate that phase resetting increases the robustness in gait transition, will contribute to the understanding of the phase resetting mechanism in biological systems and lead to a guiding principle to design control systems for legged robots.

A Multilegged Modular Robot That Meanders: Investigation of Turning Maneuvers Using Its Inherent Dynamic Characteristics

This paper deals with the motion of a multilegged modular robot. The robot consists of a set of homogenous modules, each of which has a body and two legs and is connected to the others through a three-degree-of-freedom rotary joint. The leg joints are manipulated to follow periodic desired trajectories, and the joints between the modules act like a passive spring with a damper. This robot has characteristic dynamic properties. Specifically, a straight walk naturally turns into a meandering walk by changing the compliance of the joints between the modules without incorporation of any oscillatory inputs. We first show that this transition is excited due to a Hopf bifurcation, based on a numerical simulation and Floquet analysis. Following that, we examine whether the maneuverability and agility of the robot increase by utilizing the dynamic characteristics inherent in the robot. In particular, we conduct an experiment in which the robot pursues a target moving across the floor. We propose a simple controlle...

Motion control of a two-wheeled mobile robot

The design of the controller of a two-wheeled mobile robot is usually based on a kinematical model. The kinematical model is derived under the assumption that the wheels do not skid or float. However, in the real world, wheels may skid on the ground or float away from the ground due to the rotational motion of the body. This paper analyzes the effects of the skid and the float on the robot with a controller designed based on the kinematical model—by the use of the Lyapunov control method. Numerical simulations are carried out based on the dynamic model including the translational and rotational motion of the body, and then experiments are performed using a hardware model.

Generation of bipedal walking through interactions among the robot dynamics, the oscillator dynamics, and the environment: Stability characteristics of a five-link planar biped robot

We previously developed a locomotion control system for a biped robot using nonlinear oscillators and verified the performance of this system in order to establish adaptive walking through the interactions among the robot dynamics, the oscillator dynamics, and the environment. In order to clarify these mechanisms, we investigate the stability characteristics of walking using a five-link planar biped robot with a torso and knee joints that has an internal oscillator with a stable limit cycle to generate the joint motions. Herein we conduct numerical simulations and a stability analysis, where we analytically obtain approximate periodic solutions and examine local stability using a Poincaré map. These analyses reveal (1) stability characteristics due to locomotion speed, torso, and knee motion, (2) stability improvement due to the modulation of oscillator states based on phase resetting using foot-contact information, and (3)xa0the optimal parameter in the oscillator dynamics for adequately exploiting the interactions among the robot dynamics, the oscillator dynamics, and the environment in order to increase walking stability. The results of the present study demonstrate the advantage and usefulness of locomotion control using oscillators through mutual interactions.

Motion Control of a Nonholonomic System Based on the Lyapunov Control Method

AnewdesignmethodofafeedbackcontrollerfornonholonomicsystemsbasedonLyapunovcontrolispresented. In Lyapunov control, the control input is obtained by multiplying the gradient vector of the Lyapunov function by a tensor. The main contribution of our method is that this tensor is composed of two components, one of which is a negative deenite symmetric tensor and the other of which is an asymmetric one. As a result, the goal point in the state space of the controlled system becomes the only globally stable equilibrium point, and exponential convergence tothe goal point can beachieved. The proposed method isapplied toa two-wheeled mobile robot, and the effectiveness is conermed by numerical simulations. HEmotioncontrolofanonholonomicsystemhasbeenfocused on by many researchers. The motion control of a two-wheeled mobile robot is a typical terrestrial application, whereas typical ap- plications in space include the attitude control of a rigid spacecraft with two reaction wheels and the motion control of a planar space manipulator composed of three links. In nonholonomic systems, there exist constraints that are not integrable, for example, a no-slip condition for the wheels of the wheeled vehicle, the law of conser- vation of angular momentum for a space robot, and soon. Although this class of nonlinear systems are not controllable locally, they may be controlled globally by exploiting the constraints. They can not be controlled with the method of linear control theory, however, because they are not exactly linearizable. 1 Moreover, they can not be stabilized to an equilibrium point by any smooth state feedback control, even if they are controllable globally. 2 Therefore, it is dife cult to design a feedback controller that sta- bilizes a nonholonomic system to an equilibrium point, and the re- search on this problem has been extensive.The controllers thathave been proposed thus far are classie ed as time-varying controllers 3i6 and discontinuous time-invariant controllers. 7i9 Time-varying con- trollers were originated by Samson. 3 Pomet proposed a method of designing this type of controller by using a time-varying Lyapunov function. 4 Theircontrollersaresmoothtime-varyingcontrollers,but the ratesofconvergence arenot exponential.Sordalen and Egeland 5 and MCloskey and Murray 6 proposed nonsmooth time-varying controllers that provide exponential rates of convergence. On the other hand, discontinuous time-invariant feedback con- trollers have also been proposed, such as the class of controllers based on the idea of sliding mode control, proposed by Khennouf and Canudas de Wit. 7 They designed the controller by combining a linear feedback law and a discontinuous feedback law. The discon- tinuous feedback law stabilizes the invariant manifolds formed by the linear feedback law. 7 Lafferriere and Sontag proposed a method of designing a controller by using a piecewise smooth Lyapunov function. 10 Astole proposed a method of designing a controller by transforming an original system through a nonsmooth coordinate transformation and designing a smooth, time-invariant controller for the transformed system. 8;9 The controllers designed in Refs. 7 and 9 provide exponential rates of convergence.