Kenichi Narioka

3D limit cycle walking of musculoskeletal humanoid robot with flat feet

Most of traditional biped walkers based on passive dynamic walking have arc feet and locked ankle joints. In this paper, we propose the method to substitute the arc feet with flat feet. We hypothesize that the shape of the arc feet corresponds to a circular roll-over shape (ROS), which is a shape of a trajectory of center of pressure in the shank-fixed frame. Firstly, we show that ankle joints driven by flexible muscles antagonistically can generate a circular ROS by simple simulation and real robot experiments. Radius of the ROS can be controlled by tension of the muscles. Then, we demonstrate stable 3D limit cycle walking by a biped robot with flat feet using the proposed ROS controlling method. We also investigate its behavior and stability when extra load is added to the robot and verified that the stability of the robot is maintained by keeping the ROS. The results suggest that the ROS can be a stability measure for limit cycle walkers to realize adaptive walking.

Motor development of an pneumatic musculoskeletal infant robot

This paper aims to clarify the mechanism of an infants locomotive development from the viewpoint of cognitive developmental robotics. We built up an infant-sized musculoskeletal robot driven by McKibben pneumatic actuators, which enable the robot to interact with its environment without any problems of mechanical damage and excessive heat in long-term experiments. We applied a learning algorithm based on central pattern generators and optimization method as a way for the robot to acquire its crawling motion. As a result of a developmental experiment, an efficient forward motion was acquired with the proposed method. We discuss how its musculoskeltal body, spinal structure and tonus of the artificial muscles affect its development of crawling behavior.

Synergistic 3D limit cycle walking of an anthropomorphic biped robot

Human walking emerges from synergy of whole body dynamics: not only legs, but also a torso, arms, and a head are compliantly connected with each other by antagonistic muscles. Although change of activation of a muscle affects whole body motion, such synergy is supposed to play a great role for realizing stable walking. This paper investigates synergistic 3D limit cycle walking of an anthropomorphic biped robot whose joints are driven by artificial pneumatic muscles antagonistically. Since its walking emerges from the synergy, we cannot design the desired trajectory in a top-down manner, but can change an activation pattern of the muscles and figure out appropriate parameters for stable walking. We experimentally demonstrate that the biped walks stably with a simple limit cycle controller. This is the pioneering work for investigating synergistic stable walking of a whole body humanoid.

Pneupard: A biomimetic musculoskeletal approach for a feline-inspired quadruped robot

Feline locomotion combines great acrobatic proficiency, unparalleled balance and higher accelerations than other animals. Capable of accelerating from 0 to 100 km h-1 in three seconds, the cheetah (Acinonyx jubatus) is still a mystery which intrigues scientists. Aiming for a better understanding of the source of such higher speeds, we develop a biomimetic platform, where musculoskeletal parameters (range of motion and moment arms) from the biological system can be evaluated with air muscles within a lightweight robotic structure. We performed experiments validating the muscular structure during a treadmill walk, successfully reproducing animal locomotion while adopting an EMG based control method.

Humanlike ankle-foot complex for a biped robot

In this paper, we propose a design of a robotic ankle-foot complex based on the human functional-anatomic ankle-foot structure. The proposed foot consists of three links, two joints, and four plantar muscles, whose mechanical stiffness can be controlled by utilizing McKibben pneumatic actuators. With this structure, a deformable medial longitudinal arch in a human foot can be emulated. We developed a musculoskeletal biped robot to which the proposed feet are implemented and measured its walking motion, especially the deformation of the robot foot. It is found that the foot generates a truss mechanism and a windlass mechanism, which are important functions of a human foot for shock absorption and energy storage and reuse. We also conducted a walking experiment with various parameters of a plantar muscles tonus to see how the tonus affects to ground reaction forces (GRFs) and its walking behavior. It is found that the GRF had two peaks as well as human walking and the shape of the GRF curve changes according to the tonus of the plantar muscle. We analyzed the impulse of GRF, finding out that a truss mechanism and a windlass mechanism works effectively with appropriate tonus of the plantar aponeurosis.

Development of a minimalistic pneumatic quadruped robot for fast locomotion

In this paper, we describe the development of the quadruped robot “Ken” with the minimalistic and lightweight body design for achieving fast locomotion. We use McKibben pneumatic artificial muscles as actuators, providing high frequency and wide stride motion of limbs, also avoiding problems with overheating. We conducted a preliminary experiment, finding out that the robot can swing its limb over 7.5 Hz without amplitude reduction, nor heat problems. Moreover, the robot realized a several steps of bouncing gait by using simple CPG-based open loop controller, indicating that the robot can generate enough torque to kick the ground and limb contraction to avoid stumbling.

Muscle roles on directional change during hopping of a biomimetic feline hindlimb

Cats, from tiny domestic cats (Felix Catus) to big tigers (Panthera Tigris), are well known for their great acrobatic skills and hunting ability. Aiming to better understand how the feline family interacts with the environment, we adopt a biomimetic approach on a hopping feline hindlimb. Using air muscles to simulate the compliance of biological muscles, this robotic hindlimb has seven muscles and changes hopping direction. We individually evaluate and estimate muscles contribution to the jumping direction. Finally, we successfully control the hopping direction using a non-linear curve fitting from experimental results, hopefully contributing to the understanding of our biological counterpart.

Roll motion control by stretch reflex in a continuously jumping musculoskeletal biped robot

Humans spinal reflexes response rapidly to the change of states of muscles, therefore, they are supposed to play an important role for dynamic motion. In order to realize three dimensional stable jumping, rapid control system is indispensable. In this paper, we investigate contribution of the stretch reflex for stabilizing roll motion of continuous jumping by constructing a musculoskeletal biped robot. By conducting numerical simulation and robot experiments, we show that the stretch reflex in the Soleus muscle effectively stabilizes the roll motion of the robot. Through investigation, we confirmed that roll motion was partially stabilized by implementation of the stretch reflex in the soleus muscle. This study may lead to understanding the role of spinal reflexes in human jumping and to realization of robust jumping of bipedal robots.

Producing alternating gait on uncoupled feline hindlimbs: muscular unloading rule on a biomimetic robot

Studies on decerebrate walking cats have shown that phase transition is strongly related to muscular sensory signals at limbs. To further investigate the role of such signals terminating the stance phase, we developed a biomimetic feline platform. Adopting link lengths and moment arms from an Acinonyx jubatus, we built a pair of hindlimbs connected to a hindquarter and attached it to a sliding strut, simulating solid forelimbs. Artificial pneumatic muscles simulate biological muscles through a control method based on EMG signals from walking cats (Felis catus). Using the bio-inspired muscular unloading rule, where a decreasing ground reaction force triggers phase transition, stable walking on a treadmill was achieved. Finally, an alternating gait is possible using the unloading rule, withstanding disturbances and systematic muscular changes, not only contributing to our understanding on how cats may walk, but also helping develop better legged robots.

Roll-Over Shapes of Musculoskeletal Biped Walker

Abstract In this paper, we investigate how the roll-over characteristic of a passivity-based walking robot with flat feet is created and affected by its musculoskeletal structure, which is easily modeled by an agonistic and antagonistic pair of muscles. We hypothesize that the curvature radius and the center position of the roll-over shape (ROS), defined as the centers of pressures transformed into a shank coordinate, is strongly related to the stiffness and the equilibrium posture of the ankle joint, which are determined by the tonuses of the agonistic and the antagonistic muscles. We built a new musculoskeletal biped walking robot driven by pneumatic actuators and conducted exhaustive walking experiment with various ankle conditions. The hypothesis is verified experimentally by analyzing the ROSs of the walking robot. Zusammenfassung In this paper, we investigate how the roll-over characteristic of a passivity-based walking robot with flat feet is created and affected by its musculoskeletal structure, which is easily modeled by an agonistic and antagonistic pair of muscles. We hypothesize that the curvature radius and the center position of the roll-over shape (ROS), defined as the centers of pressures transformed into a shank coordinate, is strongly related to the stiffness and the equilibrium posture of the ankle joint, which are determined by the tonuses of the agonistic and the antagonistic muscles. We built a new musculoskeletal biped walking robot driven by pneumatic actuators and conducted exhaustive walking experiment with various ankle conditions. The hypothesis is verified experimentally by analyzing the ROSs of the walking robot. In diesem Paper studieren wir das Abrollverhalten passiver Laufroboter und zeigen, wie dieses von muskuloskelettalen Eigenschaften abhängt. Das zugrunde liegende muskuloskelettale Modell besteht lediglich aus einem agonistisch-antagonistisches Muskelpaar. Wir stellten dabei die Hypothese auf, dass der Krümmungsradius und das Rotationszentrum der Abrollform — welche wir als Druckzentrum im Unterschenkelkoordinatensystem definieren — besonders von Steifigkeit und Gleichgewichtszustand im Fussgelenk abhängt. Letzere werden wiederum vom Tonus des agonistischen und des antagonistischen Muskels bestimmt. Wir bauten einen neuartigen muskuloskelettalen Laufroboter mit pneumatischen Aktuatoren und führten aufwändige Laufexperimente unter verschiedenen Fussgelenkbedingungen durch. Anhand der Analyse der Abrollformen des Laufroboters konnte die Hypothese schliesslich bestätigt werden.