Realization of three-dimensional walking of a cheetah-modeled bio-inspired quadruped robot

Adaptability of quadruped animals is not solely reached by brain control, but by the interaction between its body, environment, and control. Especially, morphology of the body is supposed to contribute largely to the adaptability. We have tried to understand quadrupedal locomotion by building a bio-inspired quadruped robot named ”Pneupard”, which has a feline-like muscular-skeletal structure. In our previous study, we successfully realized alternative gait of hindlimbs by reflex control based on the sole touch information, which is called an unloading rule, and that of forelimbs as well. In this paper, we finally connect forelimbs and hindlimbs by a rigid spine, and conduct 3D walking experiments only with the simple unloading rule. Through several preliminary experiments, we realize that the touch information on the sole is the most critical for stable 3D walking.This work was partially supported by Grant-in-Aid for Scientific Research on 23220004, 25540117 of Japan.This is the accepted manuscript. The final version is available at http://dx.doi.org/10.1109/ROBIO.2014.7090426

Stable reflex-based walking of forelimbs of a bio-inspired quadruped robot-modeled cheetah

In contrast to the high movement adaptability of quadruped animals in many environmental conditions, it is hard for conventional quadruped robots to operate in complex environment conditions. We investigate the adaptability of animals’ musculo-skeletal systems, by building a bio-inspired quadruped robot named ”Pneupard” which duplicates a feline musculo-skeletal system. In this study, we built Pneupard’s forelimb which has 14 active muscles, 4 passive muscles and 8 degrees of freedom (DOF). We propose sole reflex-based control and verify its effectiveness by conducting walking experiments, in which the robot performed stable walking with a two-dimensional restriction.This work was partially supported by a Grant-in-Aid for Scientific Research(23220004) from the Japanese Ministry of Education, Culture, Sports, Science and Technology.This is the accepted manuscript. The final version is available at http://dx.doi.org/10.1109/ROBIO.2013.673973

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.The authors acknouledge the Japanese Research Grant KAKENHI Kiban 23220004 and 25540117.This is the author accepted manuscript. The final version is available from Taylor & Francis via http://dx.doi.org/10.1080/01691864.2013.87049

Exploring muscular contribution during stepping of biomimetic feline hindlimbs

Although robotic locomotion have greatly advanced over the past years, the abyss that separates such locomotion from even the simplest animal locomotions prompt us to approach robotic locomotion taking cues from animals. The animal musculoskeletal structure, often ignored by roboticists due to its high redundancy and complexity, might hold the secret for self-stable locomotion observed in bipeds and quadrupeds. Aiming to better understand how muscles contribute to selfstable locomotion we take the feline structure as a model on a biomimetic approach. Using 6 air muscles per hindlimb to mimic real muscles, this robot walks stably on a treadmill while supported by a slider, simulating forelimbs. We individually evaluate muscle contribution to walking stability, performing a comparison between mono and biarticular synergistic muscles at the ankle and concluding that a higher compliance on the biarticular muscle improved walking stability. A better understanding of such complex phenomena may help on the development of better legged robots in the future, truly taking advantage of concepts developed by nature over the years.This work was partially supported by KAKENHI Kiban(S) 23220004.This is the accepted manuscript. The final version is available at http://ieeexplore.ieee.org/xpls/abs_all.jsp?arnumber=6739573&tag=1

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.This work was partially supported by KAKENHI Kiban(S) 23220004.This is the accepted manuscript. The final version is available at http://dx.doi.org/10.1109/IROS.2013.6696540

N=2 Supersymmetric Sigma Models and D-branes

We study D-branes of N=2 supersymmetric sigma models. Supersymmetric nonlinear sigma models with 2-dimensional target space have D0,D1,D2-branes, which are realized as A-,B-type supersymmetric boundary conditions on the worldsheet. When we embed the models in the string theory, the Kahler potential is restricted and leads to a 2-dim black hole metric with a dilaton background. The D-branes in this model are susy cycles and consistent with the analysis of conjugacy classes. The generalized metrics with U(n) isometry is proposed and dynamics on them are realized by linear sigma models. We investigate D-branes of the linear sigma models and compare the results with those in the nonlinear sigma models.Comment: 23 pages, 5 figure

Quadrupedal locomotion based on a muscular activation pattern with stretch-reflex

Cyclical locomotion, such as walking, hopping and running, is known to be generated at the spinal cord, guiding human and animal strides over different gaits. Over the last years, many researchers concentrated their study on the origin of such signals, replicating them by either controlling joint angles or torques. In this work, we use a quadruped pneumatic robot to reproduce stable walking on a treadmill through a muscular activation pattern. Unlike previous studies, neither angles or torques are taken into consideration. Similarly to biological morphology, with variating moment arms, muscles contract rhythmically and their inherent compliance adapts to the floor. Proportional feedback upon touching the floor (stretch-reflex) is also tested, and its effects are explained. In the future, this methodology can be used to produce adaptive gait and improve current robotic by exploring interaction between control and soft bodies.This work was aided by KAKENHI Kiban(S) 23220004 and 25540117.This is the accepted manuscript. The final version is available at http://dx.doi.org/10.1109/ROBIO.2014.7090425

Quantum and Classical Aspects of Deformed c=1c=1 Strings.

The quantum and classical aspects of a deformed $c=1$ matrix model proposed by Jevicki and Yoneya are studied. String equations are formulated in the framework of Toda lattice hierarchy. The Whittaker functions now play the role of generalized Airy functions in $c<1$ strings. This matrix model has two distinct parameters. Identification of the string coupling constant is thereby not unique, and leads to several different perturbative interpretations of this model as a string theory. Two such possible interpretations are examined. In both cases, the classical limit of the string equations, which turns out to give a formal solution of Polchinski's scattering equations, shows that the classical scattering amplitudes of massless tachyons are insensitive to deformations of the parameters in the matrix model.Comment: 52 pages, Latex

G/G Models and W_N strings

We derive the BRST cohomology of the G/G topological model for the case of A^{(1)}_{N-1} . It is shown that at level k={p/q}-N the latter describes the (p,q) W_N minimal model coupled to $W_N$ gravity (plus some extra ``topological sectors").Comment: 17 page