International Journal of Humanoid Robotics

This paper contains an adjustment of the stiffness and control algorithm of an ankle joint to maintain the posture of a humanoid biped walking robot using an IMU (Inertial measurement Unit) in single support phase. One of the difficulties in maintaining the balance of a robot in single support phase involves the sole of the robot, which is easy to separate from the ground. This phenomenon is caused by an external disturbance or when the sole lands on uneven terrain. A method of adjusting the compliance in the ankle joint is introduced to reduce the tendency of this type of occurrence. In order to maintain the posture of a robot with a compliant ankle joint, a posture controller composed of a body balancing controller and a vibration reduction controller is adopted. A walking experiment is implemented using a compliant ankle joint and the posture controller. The proposed method is shown to enable rapid walking as well as walking on uneven terrain.

We propose a self collision avoidance system for humanoid robots designed for interacting with the real world. It protects not only the humanoid robots' hardware but also expands its working range while keeping smooth motions. It runs in real-time in order to handle unpredictable reactive tasks such as reaching to moving targets tracked by vision during dynamic motions like e.g. biped walking.

The collision avoidance is composed of two important elements. The first element is reactive self collision avoidance which controls critical segments in only one direction — as opposed to other methods which use 3D position control. The virtual force for the collision avoidance is applied to this direction and therefore the system has more redundant degrees of freedom which can be used for other criteria. The other second element is a dynamic task prioritization scheme which blends the priority between target reaching and collision avoidance motions in a simple way. The priority between the two controllers is changed depending on current risk.

We test the algorithm on our humanoid robot ASIMO and works while the robot is standing and walking. Reaching motions from the front to the side of the body without the arm colliding with the body are possible. Even if the target is inside the body, the arm stops at the closest point to the target outside the body. The collision avoidance is working as one module of a hierarchical reactive system and realizes reactive motions. The proposed scheme can be used for other applications: We also apply it to realizing a body schema and occlusion avoidance.

A bipedal walking mechanism with knees is designed and built to study the passive dynamic gait. The effects of changing the ramp angle and the mass distributions of the thighs and the shanks on the gait patterns and walking robustness are studied. It is shown that the changes in the ramp angle and the mass distribution have significant effects on the step lengths and the robustness (the successful rate of launching and the step-count) of the passive gait. More specifically, as the ramp angle increases or the mass center of the entire walker is raised, the step length increases, which dictates the walking speed. However, our experiments show that the changes in the ramp angle and the mass distribution have slight effects on the step period. The optimal ramp angle and mass distribution of the passive walker are also identified, of which the passive walker has the highest successful rate of launching and the step-count. Our experimental results are compared with previous work based on simulations. This research can provide important information for validating/adjusting mathematical models of passive dynamic walking. The work also enables us to gain a better understanding of the mechanics of walking.

A bipedal robot will fall if it encounters large disturbances. If this fall is detected in advance, an emergency action can be taken to minimize damage or even to prevent the fall. Recently we introduced a new method for the detection of upcoming falls, called the Multi-way Principal Component Analysis (MPCA) detection method, and we showed that it is successful in detecting the fall of the simplest walking model. The aim of this paper is to study the performance of the MPCA detection method on bipedal prototypes. We implemented the detection method on one of our prototypes called 'Meta' and conducted a parameter study for two parameters: sampling time and number of planes used for modeling the nominal behavior. The performance of the detection method was quantified with the average detection time and the amount of false positives. The results of this study show that the MPCA detection method is only able to detect the fall of the prototype after the last stance leg transition before the fall. The detection time is improved for an increase in number of planes or a decrease of the sampling time, but it will never detect a fall before the last heel strike. Thus, the method is useful for triggering bracing actions, but not for preventive foot placement.

This paper presents three basic bipedal walking gait adjustment modes: step-frequency, step-length and biped lower extremities' pattern adjustments. All the adjustment modes are based on a simple Fourier Series formulation named the Truncated Fourier Series (TFS) model which is newly proposed as a walking pattern generator. Making use of these three gait adjustment modes, bipedal walking can be modified in real-time according to the environment changes. In this paper, the developed gait adjustment modes have been studied by dynamic simulations. The results obtained show that stable walking on uneven terrains as well as human-like walking behaviors can be achieved.

This paper proposes an efficient walking pattern mapping algorithm from motion capture data onto biped humanoid robots. Currently, the technology known as human motion capture is widely utilized to generate various humanlike motions in many applications, including robotics. An important thing is that several difficulties are associated with motion capture data. These include a data offset issue, noise, and drift problems due to measurement errors caused by imperfect camera calibration, and marker position. If a biped robot uses motion capture data without suitable post-processes, the walking motion of the robot will differ from an actual walking motion, and the Zero Moment Point (ZMP) will be asymmetrical and noisy, leading to unstable walking. A further difficulty exists in the walking pattern mapping process due to the different joint numbers, link sizes, and weights between a human and a robot. Although walking pattern mapping is suitable after addressing the above difficulties, a slip problem between the feet and the ground can continue to cause problems. To solve these difficulties efficiently, a Fourier fitting method is proposed in this research. Improvements of walking pattern and the ZMP trajectory are confirmed using the proposed method. Furthermore, a geometric mapping method is introduced to generate walking patterns for various biped robots while maintaining a degree of similarity to humans. By applying a no-slip constraint to the feet and modifying the joint angles through inverse kinematics, the slip problem is also solved. The effectiveness of the proposed algorithm is verified through computer simulations of two different biped robots that have different sizes, weights, walking cycles, and step lengths.

In this paper, problems for an anthropomorphic robot arm are approached for an application in a humanoid robot with the specific features of cost oriented design and user-friendly operation. One DOF solution is proposed by using a suitable combination of gearing systems, clutches, and linkages. Models and dynamic simulations are used both for designing the system and checking the operation feasibility.

In this paper we are concerned with the problem of sensory motor coordination of a robotic finger in order to evoke rolling maneuvers in a force-positioning task on a flat rigid surface. We use two different approaches to modeling the reaction of the soft fingertip with the contacted surface. Firstly, we assume that the environment imposes a purely kinematic rolling constraint on the end-effector motion in the tangent direction of the contacted surface. This implies no energy transfer or dissipation between the fingertip and the environment due to frictional forces. On the other hand, we assume that it is feasible for the fingertip to slip in which case pure rolling motion could be disturbed. The two different models are subsequently used to show by simulation that control laws, which have been designed on a rolling constraint dynamic model for frictional forces, fail to perform rolling in various environments. An extra control input that uses a reference rolling trajectory that is state dependent is proposed, which, if superimposed on a conventional force-position control law, can achieve rolling even on a surface with low friction characteristics. The proposed feedback signal does not utilize the modeling information in the control formulation, and thus permits easy implementation. Finally, the total controller is shown to achieve asymptotic convergence to the desired force-positioning task by simultaneously evoking pure rolling motion for the fingertip.

The article presents the facts about the pioneering research results of Professor Nikolai Bernstein in the area of man's voluntary movements. Relevant data are given concerning the priority of introducing the notion of feedback in the process of active voluntary human movements, twelve years before the known Wiener's publication. Bernstein demonstrated how the problems of general physiology can be explored in terms of the structural analysis of movements. He dealt with the most important aspects of the vital activity of higher organisms, and how this has been accorded the place in physiology and, when it developed, promised to be of the greatest value in cybernetics and in the exact mathematical formulation of a physiological theory of motor behavior. In his research, Bernstein modeled the function of the central nervous system and offered the cyberneticists a system for the development of analogs for experimental model-making that was not only incomparably richer than examples of internal stabilizing processes (blood-pressure, temperature and sugar-level regulating systems, for example), and also more complex than the systems of dynamic regulation that have already been studied in some depth, such as the mechanisms of ocular accommodation, or of the pupillary reaction.