This work presents a novel method to keep stable contact and balance while stepping over partial footholds for biped humanoid robots with flat feet. We exploit plantar tactile feedback to detect the geometry of the terrain and reconstruct online the new supporting polygon after landing every step. Plantar tactile feedback detects early contacts to stop the swing foot motion. Then we compute the convex hull of the cluster of contact points detected by distributed normal force sensors over the foot soles. The centroid of the supporting polygon is then used for retargeting the reference ZMP and DCM positions. Finally, the supporting polygon is used to define constraints for ZMP balance feedback control. These methods were implemented in two biped humanoid robots running different walking controllers.

The CoM-ZMP model represents the dominant behaviour of bipedal locomotion with surface contact. However, once the centre of mass (CoM) position goes out of a predefined spatial plane, the horizontal dynamics of the model can couple with its vertical dynamics to be nonlinear. This study theoretically investigates the properties of the 3-dimensional zero moment point (ZMP), lying apart from the actual ground to resolve the coupling. The presented discussion includes the compatibility of the 3D ZMP with ZMPs used in preceding research, such as the linear inverted pendulum mode, the existence of a virtual repellent point considering the arbitrary vertical CoM motion, the parameter invariance of the CoM-ZMP model, and feasible regions of the ZMP.

This paper presents a method for biped gait generation along a predefined curve with fully stretched knees. First, we design a spatial gait pattern as a function of the traveled distance on the path without considering dynamics. Then, a consistent dynamic walking motion is obtained by optimization that minimizes the zero-moment point and the speed errors while considering the trade-off between kinematics and dynamics. This method generalizes the spatially quantized dynamics-based gait generation, which is our former method restricted to straight paths, to walk on arbitrary curves. The generated gaits are validated by dynamic simulation.

A controller design to suppress vertical vibration of a position controlled biped walking robot is presented. The system model of structural vibration is estimated from a measurement of frequency response. By using the model, an optimal feedback controller with full state observer is designed. With a consideration of leg support phase, the vibration controller is combined into our walking controller. The effectiveness of our controller is experimentally demonstrated.

This paper presents a method for generating a turning motion in a humanoid robot by allowing the feet of the robot to slip on the ground. As humans, we exploit the fact that our feet can slip on the ground, and allowing humanoid robots to realize this same motion is a worthwhile study. In this paper, we propose the hypothesis that a turning motion is caused by the effect of minimizing the power generated by floor friction. A model of rotation from this friction is then described based on our hypothesis. The proposed model suggests that only the trajectory and shape of the robot's feet determine the amount of rotation from a slip, and that the friction coefficient between the floor and the soles of the robot, as well as the velocity of the feet, do not affect the resultant angle. Verification is conducted through an experiment with a humanoid robot known as HRP-2. Next, to obtain the foot motion necessary to realize the desired rotational angle, the inverse problem is solved by confining the trajectory of the center of the foot to an arc shape. This solution is verified through an experiment with another humanoid robot, HRP-4C.

In this paper, we describe three singing information processing systems, VocaListener, VocaListener2, and VocaWatcher, that imitate singing expressions of the voice and face of a human singer. VocaListener can synthesize natural singing voices by analyzing and imitating the pitch and dynamics of the human singing. VocaListener2 imitates temporal timbre changes in addition to the pitch and dynamics. In synchronization with the synthesized singing voices, VocaWatcher can generate realistic facial motions of a humanoid robot, the HRP-4C, by analyzing and imitating facial motions of a human singing that are recorded by a single video camera. These systems that focus on “imitation” are not only promising for representing human-like naturalness, but also useful for providing intuitive control means.

We present the realization of quick turning motion of a humanoid robot on its toes via slipping between its feet and the floor. A rotation model is described on the basis of our hypothesis that turning via slip occurs as a result of minimizing the power caused by floor friction. Using the model, the trajectory of the center of the foot can be generated to realize the desired rotational angle. Toe joints are used to realize quicker turning motion, while avoiding excessive motor load due to frictional torque. Quick slip-turn motion with toe support is successfully demonstrated using a humanoid robot HRP-4C.

In this paper, we describe VocaWatcher, a novel robot motion generator that enables a humanoid robot to sing with realistic facial expressions and naturally synthesized singing voices. This robot singer is an important and attractive humanoid robot application for the entertainment scene; moreover, it promotes state-of-the-art integration of robot engineering, music processing, and image processing. To overcome the difficulties of generating natural facial expressions that are precisely synchronized with singing voices, VocaWatcher imitates a human singer by analyzing a video clip of a human singing, recorded by a single video camera. VocaWatcher can control mouth, eye, and neck motions by imitating the corresponding human movements, which are estimated without using any markers in the video. It can also synthesize singing voices by imitating the pitch and dynamics of the human singing in the same video.

Hardware improvement of cybernetic human HRP-4C for entertainment is presented in this paper. We coined the word ¿Cybernetic Human¿ to explain a humanoid robot with a realistic head and a realistic figure of a human being. HRP-4C stands for Humanoid Robotics Platform-4 (Cybernetic human). Its joints and dimensions conform to average values of young Japanese females and HRP-4C looks very human-like. We have made HRP-4C present in several events to search for a possibility of use in the entertainment industry. Based on feedback from our experience, we improved its hardware. The new hand, the new foot with active toe joint, and the new eye with camera are introduced.

This paper presents the development of humanoid robotics platform - 4 (or HRP-4 for short). The high-density implementation used for HRP-4C, the cybernetic human developed by AIST, is also applied to HRP-4. HRP-4 has a total of 34 degrees of freedom, including 7 degrees of freedom for each arm to facilitate object handling and has a slim, lightweight body with a height of 151 [cm] and weight 39 [kg]. The software platform OpenRTM-aist and a Linux kernel with the RT-Preempt patch are used in the HRP-4 software system. Design concepts and mechanisms are presented with its basic specification in this paper.

This paper presents preliminary results and analysis on generating turning motion of a humanoid robot by slipping the feet on the ground. Humans unconsciously exploit the fact that our feet slip on the ground; such slip motion is necessary for humanoids so as to realize sophisticated human-like motions. In order to generate the slip motion, we need to predict the amount of slip. We propose the hypothesis that the turning motion is caused by the effect of minimizing the power generated by floor friction. A model of rotation by friction force is described on the basis of our hypothesis. The case that a robot applies the same force on both feet is discussed; then, we extend the discussion to the case of different force distribution. The hypothesis is verified through experiments with a humanoid robot HRP-2.

A novel framework of biped walking stabilization control is introduced. The target robot is a 42 DOF humanoid robot HRP-4C which has a body dimensions close to the average Japanese female. We develop a body posture controller and foot force controllers on the joint position servo of the robot. By applying this posture/force control, we can regard the robot system as a simple linear inverted pendulum with ZMP delay. After a preliminary experiment to confirm the linear dynamics, we design a tracking controller for walking stabilization. It is evaluated in the experiments of HRP-4C walking and turning on a lab floor. The robot can also perform an outdoor walk on an uneven pavement.

This paper proposes a novel user interface for creating whole body motions of biped humanoid robots just by giving key poses. Although such an interface is popular for CG character animation, there have not been any practical systems that can appropriately handle the kinematic and dynamic conditions required for moving actual biped robots stably without falling down. In our interface, every time a key pose is created, modified or removed, the system immediately processes automatic trajectory adjustment of the feet and the waist so that the key poses and the interpolated motion can always meet the conditions. This enables a user to edit variety of motions in an intuitive and flexible way without paying attention to the conditions. We implemented the interface and confirmed that characteristic whole body motions of a realistic humanoid robot HRP-4C were easily created with it and the actual HRP-4C successfully performed them.

We propose a solution which combines haptic sensing with safe interaction, at low cost. Contact locations are made through a flexible sheet of tactile binary switch matrix. This sheet covers the surface of a rigid bumper module assembled to the robot's basic link through a distributed pressure sensing units. Combination of location and force provides the haptic sensing module. The haptic system is covered with a flexible outer material which role is to absorb contact impacts and to cast local surface profile on which the robot can take support. This overall system allows having a combined haptic sensing with safe and robust physical interaction with both the environment and the human using active compliance. We discuss the benefit of such a simple and modular concept and present how to design the cover material. A simple prototype is realized and experienced.

In this paper, we generate the biped gait of a humanoid robot that looks like a human's one. To generate the human like motion, we first capture walking motion of a human. Then, we analyze the captured data and obtain several information such as the relationship between the step length and waist height etc. We consider applying these informations to the real humanoid robot. Also, when the human walks, the sway of the waist is smaller than most of the humanoid robot's one. By compensating the angular momentum of the robot and by modifying the ZMP trajectory, we show that sway of the robot's waist can be smaller. We show the effectiveness of the proposed method through simulation and experimental results.

This paper proposes the kinodynamic gait planning for humanoid robots where both kinematics and dynamics of the system are considered. We can simultaneously plan both the foot-place and the whole-body motion taking the dynamical balance of the robot into consideration. As a dynamic constraint, we consider the differential equation of the robotpsilas CoG. To solve this constraint, we assume two walking pattern generators; the offline and the online ones. We randomly sample the configuration space to search for the path connecting the start and the goal configurations. When sampling the configuration space, three milestones are sequentially connected to the parent milestone. To show the effectiveness of the proposed methods, we show simulation and experimental results where the humanoid robot HRP-2 walks on several environments.

This paper presents a biped humanoid robot that is able to walk on a rough terrain while touching a handrail. The contact wrench sum (CWS for short) is used as the criterion to judge if the contact between the robot and the environment is strongly stable under the sufficient friction assumption, where the contact points are not coplanar and the normal vectors at the points are not identical. It is confirmed that the proposed pattern generator can make the robot walk as desired in dynamics simulations and experiments, and the motions can be improved by a hand position control and using waist joints.

This paper presents a motion pattern generator of humanoid robots that walks on a flat plane, steps and a rough terrain. It is guaranteed rigorously that the desired contact between a humanoid robot and terrain should be maintained by keeping the contact wrench sum between them inside the contact wrench cone under the sufficient friction assumption. A walking pattern is generated by solving the contact wrench equations and by applying the resolved momentum control.

We discuss a ZMP-based running pattern generation for a biped robot equipped with toe springs. Our biped robot HRP-2LT has twelve active DoFs for its legs and two passive DoFs for its toes. The trajectory of the center of mass is designed to realize the specified running motion and the foot trajectories are determined to get proper spring action at lift off phases. They are interpreted into joint angles by using the resolved momentum control. By the simulation and the preliminary experiment, it is shown that the toe springs are effectively used for running and hopping.

This paper proposes a method of a real-time gait planning for humanoid robots which can change stride immediately at every step. Based on an analytical solution of an inverted pendulum model, the trajectories of the COG (center of gravity) and the ZMP (zero-moment point) are parameterized by polynomials. Since their coefficients can be efficiently computed with given boundary conditions, this framework can provide a real-time walking pattern generator for humanoid robots. To handle the unexpected result caused by immediate changes of foot placement, we made single support periods as an additional trajectory parameter and the ZMP fluctuation was suppressed by mixing the opposite phase of the ZMP error. The effectiveness of our method is shown by experiments of the humanoid robot HRP-2.

This paper studies an optimal planning of falling motions of a human-sized humanoid robot to reduce the damage of the robot. We developed a human-sized robot HRP-2FX which has a simplified humanoid robot shape with seven d.o.f. and can emulate motions in the sagittal plane of a humanoid robot. An optimal control is applied to generate the falling motion of HRP-2FX to minimize a performance index, and the optimality has been verified by the experiments on HRP-2FX.

In this paper, we plan the collision free motion for walking pattern generation of a humanoid robot. Our motion planner can take into account several features of the walking pattern generator. We first run the walking pattern generator by considering the contact wrench applied to the robot and monitor the collision among the links and the environments. Then, we plan the collision free motion for the period of time causing the collision. In our motion planner, we can consider the constraint condition which are the functions of time. Also, for keeping balance of the robot, we plan the motion with keeping the horizontal position of the COG as well as the position/orientation of the feet/hand. The effectiveness of the proposed method is confirmed by simulation and experiment.

We propose a simulation system that achieves realistic and efficient simulations of humanoid robots. This paper focuses on a constraint-based contact force solver and virtual spring-damper joints from among the components of the system. The contact force solver can accurately simulate contacts between rigid bodies including articulated rigid bodies. LCP-like formulation of constraint conditions is solved by an iterative calculation method that extends the Gauss-Seidel method. This paper clarifies how to integrate existing methods to implement a robust and efficient solver. Virtual spring-damper joints are proposed to simulate a shock absorbing mechanism that many biped humanoid robots have in their feet to increase the stability of walking motion. The combination of the rigid contact model and the elastic virtual joints can improve the accuracy of the simulation. The simulation system was verified by experiments using humanoid robot HRP-2, and the results shows the validity of the system.

This paper introduces a framework for whole-body motion generation integrating operator's control and robot's autonomous functions during online control of humanoid robots. Humanoid robots are biped machines that usually possess multiple degrees of freedom (DOF). The complexity of their structure and the difficulty in maintaining postural stability make the whole-body control of humanoid robots fundamentally different from fixed-base manipulators. Getting hints from human conscious and subconscious motion generations, the authors propose a method of generating whole-body motions that integrates the operator's command input and the robot's autonomous functions. Instead of giving commands to all the joints all the time, the operator selects only the necessary points of the humanoid robot's body for manipulation. This paper first explains the concept of the system and the framework for integrating operator's command and autonomous functions in whole-body motion generation. Using the framework, autonomous functions were constructed for maintaining postural stability constraint while satisfying the desired trajectory of operation points, including the feet, while interacting with the environment. Finally, this paper reports on the implementation of the proposed method to teleoperate two 30-DOF humanoid robots, HRP-1S and HRP-2, by using only two 3-DOF joysticks. Experiments teleoperating the two robots are reported to verify the effectiveness of the proposed method.

This paper proposes a universal stability criterion of the foot contact of legged robots. The proposed method checks if the sum of the gravity and the inertia wrench applied to the COG of the robot, which is proposed to be the stability criterion, is inside the polyhedral convex cone of the contact wrench between the feet of a robot and its environment. The criterion can be used to determine the strong stability of the foot contact when a robot walks on an arbitrary terrain and/or when the hands of the robot are in contact with it under the sufficient friction assumption. The determination is equivalent to check if the ZMP is inside the support polygon of the feet when the robot walks on a horizontal plane with sufficient friction. The criterion can also be used to determine if the foot contact is sufficiently weakly stable when the friction follows a physical law. Therefore, the proposed criterion can be used to judge what the ZMP can, and it can be used in more universal cases

A biped walking pattern generator which allows an additional ZMP control (auxiliary ZMP) is presented. An auxiliary ZMP is realized by an inverse system added to a pattern generator based on the ZMP preview control. To compensate the effect of the auxiliary ZMP, we apply virtual time shifting of the reference ZMP. As an application of the proposed method, a walking control on uneven terrain is simulated. The simulated robot can walk successfully by changing its walking speed as the side effect of the auxiliary ZMP control

This paper presents a motion suspension system to suspend humanoid motion in case of emergency. Once humanoids start their motions in human daily environments, there is a possibility that humanoids will meet with several emergencies such as hurting humans and injuring themselves. Even so, humanoids should be controlled so that they avert such emergencies in real-time. To realize this demand, we propose a method of real-time judgment of emergency prediction by humanoids. We also propose a simple and effective method of real-time pattern generation to force humanoids to stop immediately by one step without falling. To verify the validity of the proposed method, we finally present experimental results using a humanoid robot HRP-2, which include experiments at 2.8 [km/h] walks

A motion planner of emergency stop must make an operating humanoid robot to a stationary state under the emergency signal. It plays an important role in prevention of falling over because humanoid robots fall over easily. Immediately after the emergency signal, it must generate the emergency stop motion in real-time. We modeled a humanoid robot as a simple dynamic system consists of ZMP (zero-moment point) and COG (center of gravity) as its states. The emergency stop motion is generated by a state feedback. We determined optimal feedback gains in terms of the initial conditions and the pole assignment. The proposed method realized a reliable emergency stop with low computational cost. Furthermore, it can easily predict the possibility of the successful emergency stop at any time. The validity of the proposed method is confirmed by an experiment using humanoid robot HRP-2

This paper addresses the role of toe joints in increasing the walking speed of biped robots. It is worthy that adding a toe joint will increase the step length thanks to the additional degree of freedom. But, the originality of this work is that longer steps are obtained thanks to an under-actuated phase and an appropriate ZMP trajectory. The simulations showed that adding passive toe joints allows smoother and 1.5 faster walking

In this paper, we analyze the balance of a humanoid robot during manipulation tasks. By defining the generalized zero-moment point (GZMP), we obtain the region of it for keeping the balance of the robot during manipulation. During manipulation, the convex hull of the supporting points forms the 3-D convex polyhedron. The region of the GZMP is obtained by considering the infinitesimal displacement and the moment about the edges of the convex hull. We show that we can determine whether or not the robot may keep balance for several styles of manipulation tasks, such as pushing and pulling an object. The effectiveness of our proposed method is demonstrated by simulation.

This paper studies the balance of a humanoid robot carrying a heavy object. Without knowing the mass and the position of the center of gravity of the object, the humanoid robot carries a heavy object stably by using the force sensor information attached at the wrists and the ankles. We first show how to generate the motion of a humamoid robot by taking the force sensor information into consideration. We also show the method for generating the gait pattern by taking the dynamics of the carried object. The effectiveness of the proposed method is shown by experiments.

This article explains a control system, which stabilizes running biped robot HRP-2LR. The robot uses prescribed running pattern calculated by resolved momentum control, and a running controller stabilizes the system against disturbances. The running controller consists of posture stabilization, inverted pendulum stabilization, contact torque control, impact absorbing control, foot vertical force control and torque distribution control. Applying the proposed controller, HRP-2LR could successfully run with average speed of 0.16(m/s) repeating flight phase of 0.06 (s) and support phase of 0.3 (s).

This paper proposes a method for a humanoid robot to generate 3D model of the environment using a stereo vision, find a movable space using it and plan feasible locomotion online. The model is generated by an accumulation of 3D grid maps which are made from the range data of the field of view obtained by a correlation based stereo vision. The locomotion is planned by an online whole body pattern generator which can modify robot’s waist height, an upper body posture and so on according to the size of the movable space.

This paper describes a generation method for spatially natural biped walking. By limiting the COG (Center of Gravity) motion space to a sculptured surface, the degree of freedom of the COG matches to the number of the ZMP (Zero Moment Point) equations. The COG motion can be uniquely generated along a specified surface satisfying the ZMP constraint with low calculation cost. Spatial and time parts are separable by representing motion surface of the COG as parametric variables. The motion surface defines the relative height of the COG from the landing foot position. Thus, the proposed method reflects geometric information directly to the motion planning without considering walk stability. In this paper, we show two actual examples, walking pattern including mostly stretched knee and going up stairs. The validity of the proposed method is confirmed by simulation. Walking with mostly stretched knee is also shown in experiment using HRP-2.

This paper presents a slip observer towards stabilizing biped walks on a low friction floor. Although biped humanoid robots are expected to easily adapt to environments designed for human, in fact they tend to tip over easily on real environments. For a practical use, it is one of important issues to stabilize a biped walking on an unexpected slippery floor with a low friction. In this paper, we propose the slip observer detecting skids that would occur at walking on unexpected slippery floor. We also propose a basic study of slip stabilizer towards reducing posture rolling caused by skids. Finally, we present experimental results using a humanoid robot HRP-2 to verify the validity of the proposed control scheme.

This paper presents an emergency stop algorithm of a walking humanoid robot. There are many cases which force a walking robot to stop quickly without falling. Since an emergency occurs at unpredictable timing and at any state of robot, the stopping motion must be generated in real-time. To overcome these problems, our emergency stop motion is divided into four phases according to the role of the zero-moment point (ZMP). In each phase, approximate analytical solutions of the center of gravity (COG) dynamics is used to generate the motion. During the single support phase, a landing time and position are determined by evaluating the average velocity of the swing leg and the horizontal position of the COG. During the double support phase, the travel distance of the COG and the ZMP are evaluated. The validity of the proposed method is confirmed by simulation and experiment using a humanoid robot HRP-2.

We previously reported the first human-sized humanoid robot that can fall down safely and stand up again. This paper examines the falling motion control by supplementary simulations and presents an improvement of the control by optimizing the control parameters. The UKEMI falling over control of a human-sized humanoid robot is simulated, the simulation results are compared with the experimental results of real humanoid robot.

This work proposes a new style of manipulation by a humanoid robot. Focusing on the task of pushing an object, the foot placement of it is planed in real-time according to the result of manipulation of an object. By controlling the arms using the impedance control, a humanoid robot can push an object stably regardless of the mass of an object. If an object is heavy, a humanoid robot pushes an object with walking slowly, and vice versa. Also, for planning the gait in real-time, we newly propose an analytical method where the newly calculated trajectory of the robot motion is smoothly connected to the current one. The effectiveness of the proposed method is confirmed by simulation and experiment.

Aiming for a humanoid robot of the next generation, we have been developing a biped which can jump and run. This paper introduces biped robot HRP-2LR and its hopping with both legs as our first attempt towards running. Using a dynamic model of HRP-2LR, hopping patterns are pre-calculated so that it follows the desired profiles of the total linear and angular momentum. For this purpose we used resolved momentum control. Adding small modifications to negotiate the difference between the model and the real hardware, we successfully realized a steady hopping motion of 0.06 [s] flight phase and 0.5 [s] support phase. A hopping with forward velocity of 15 [mm/s] was also realized. Finally, a running pattern of 0.06 [s] flight and 03 [s] support phase was tested. HRP-2LR could successfully run with average speed of 0.16 [m/s].

This work studies locomotion planning of humanoid robots to pass through narrow spaces. Humanoid robots can alter the style of the locomotion while wheeled robots can not. The proposed method generates a 3D local map from visual information and plans the appropriate locomotion based on the map from biped walking with the variable height and the width and from crawling.

A development of humanoid robot HRP-2 is presented in this paper. HRP-2 is a humanoid robotics platform, which we developed in phase two of HRP. HRP was a humanoid robotics project, which had run by the Ministry of Economy, Trade and Industry (METI) of Japan from 1998FY to 2002FY for five years. The ability of the biped locomotion of HRP-2 is improved so that HRP-2 can cope with uneven surface, can walk at two third level of human speed, and can walk on a narrow path. The ability of whole body motion of HRP-2 is also improved so that HRP-2 can get up by a humanoid robot's own self if HRP-2 tips over safely. In this paper, the appearance design, the mechanisms, the electrical systems, specifications, and features upgraded from its prototype are also introduced.

The establishment of an intuitive and effective whole body operation method is essential for the utilization of humanoid robots in real world tasks. Here we introduce a method for humanoid robot foot teleoperation, as a part of our whole body teleoperation system using only a simple joystick device. This paper explains a framework for real-time foot operation which incorporates the operator's foot command and robot's autonomy in maintaining balance. We describe the algorithm of an autonomous function which shifts the position of the robot's center of mass interactively based on the operator's command and the current feet condition of the robot. We report on successful experimental results of teleoperating a real humanoid robot HRP-2 using the proposed method.

This paper studies a falling motion control of a human-size humanoid robot when it falls forward. Safe knee landing of the robot is realized as a first step to minimize the damage of the falling over. The landing follows the detection of the falling, the decrease of the knee height after the detection, and the brake of landing speed. It is confirmed that the proposed method can soften the landing impact significantly by the proposed method.

This paper shows some preliminary results on the dynamical balance of a humanoid robot grasping an environment. By grasping an environment, it becomes easier for the robot to keep balance. By using the linear programming, a necessary condition for keeping balance of the robot is formulated taking the grasping force into consideration. We show that the occasion exists where the stronger the hand of a humanoid robot grasps the handrail, the larger the region of ZMP for keeping balance becomes. We further show an experimental result of a humanoid robot climbing up a big gap increasing the stability by grasping a handrail.

Biped walking on a low friction floor is analyzed in this paper. For a given walking pattern, we can calculate a necessary friction coefficient which allows the robot to perform the expected motion. To reduce the maximum necessary friction coefficient, a pattern generation based on preview control theory is explained. We also describe a calculation of slip concerned ZMP, which provides a good prediction of falling caused by slips. Finally, we test a walk of 135 [km/h] on low friction environment using a humanoid robot HRP-2. The robot could successfully walk over the slippery area whose friction coefficient is 0.14.

Aiming for a humanoid robot of the next generation, we have been developing a biped which can jump and run. This paper introduces a method of running pattern generation and running experiment of biped robot HRP-2LR. Based on the physical parameters of HRP-2LR, running patterns are pre-calculated so that it follows the desired profiles of the total linear and angular momentum. For this purpose we used resolved momentum control. The vertical momentum is calculated considering the compliant elements in order to realize accurate flight duration. The horizontal momentum is calculated to satisfy the ZMP patterns given in advance. Using our pattern, HRP-2LR could successfully run with average speed of 0.16[m/s] with repeat flight phase 0.06 [s] and support phase 0.3 [s].

This paper discusses the pushing manipulation of an object by a humanoid robot. For such a pushing task, we show that there are two kinds of ZMPs, i.e., the conventional "Zero Moment Point (ZMP)" considering all sources of the force/moment acting in the foot supporting area, and the "Generalized Zero Moment Point (GZMP)" which is an generalization of ZMP for a humanoid robot whose hands do not contact with an object. We first obtain the stable region of the GZMP on the floor. Moreover, since the difference between these two ZMPs corresponds to the magnitude of contact force applied by the hands, we propose the pushing manipulation by a humanoid robot by modifying the desired ZMP trajectory for a humanoid. The effectiveness of the proposed method is confirmed by simulation results.

We have developed a software platform, called OpenHRP, for humanoid robotics which consists of a dynamic simulator and motion control library for humanoid robots. This paper attempts to answer a frequently asked question "do the dynamic simulations and the experiments of biped walking of humanoid robots correspond?". Using OpenHRP and humanoid robots HRP-1S and HRP-2P, the comparisons between the simulations and experiments are shown at various aspects.

We introduce a new method of a biped walking pattern generation by using a preview control of the zero-moment point (ZMP). First, the dynamics of a biped robot is modeled as a running cart on a table which gives a convenient representation to treat ZMP. After reviewing conventional methods of ZMP based pattern generation, we formalize the problem as the design of a ZMP tracking servo controller. It is shown that we can realize such controller by adopting the preview control theory that uses the future reference. It is also shown that a preview controller can be used to compensate the ZMP error caused by the difference between a simple model and the precise multibody model. The effectiveness of the proposed method is demonstrated by a simulation of walking on spiral stairs.

This paper presents a humanoid robot that has the same size as a human and that can lie down to the floor and get up from the floor with the robot face upward and downward. We believe that the robot is the first life-size humanoid robot with the capability. The motions are realized by the combination of novel hardware and software. The features of the hardware are a human-like proportion and joints with wide movable ranges including two waist joints. The software segments the motion into the sequence of the contact states between the robot and the floor and assigns an appropriate controller to each transition between the consecutive states. The experimental results are presented.

This paper describes a possibility of a running humanoid robot based on the physical properties of an existing humanoid robot HRP-2L. To generate running motion, we develop a general method to control the total linear/angular momentum of a multi-link system. By this method, we can generate a reliable running pattern. Conducting simulations which take into account physical restrictions, we show that our humanoid robot can run at least at 0.5 m/s.

This paper proposes a new method for the teleoperation of humanoid robots which integrates human operator's intention with robot's autonomy. Getting hints from human conscious and subconscious motion generations, we propose a method which generates whole body motions of a humanoid robot satisfying operator's desired movement of specific points on which the operator focuses as well as the robot's balance. The proposed method is based on a whole body momentum control. We also introduce a function of automatic adjustments of the position of the center of mass and torso orientation in order to expand the reachable area of a humanoid robot. The effectiveness of the method is confirmed by using humanoid robot simulator OpenHRP with physical parameters of real humanoid robot HRP-1S.

This paper investigates a method through which human-size humanoid robot can fall over backwards safely. Squatting-extending motion of legs reduce impact of falling and shock-absorbing parts of the robot keep the force at a permissible range. The robot could stand up itself again after falling.

This paper newly considers the ZMP (zero moment point) of a humanoid robot under arm/leg coordination. By considering the infinitesimal displacement and the moment acting on the convex hull of the supporting points, we show that our method for determining the region of ZMP can be applicable to several cases of the arm/leg coordination tasks. We first express two kinds of ZMPs for such coordination tasks, i.e., the conventional ZMP, and the "generalized zero moment point (GZMP)" which is a generalization of the ZMP to the arm/leg coordination tasks. By projecting the edges of the convex hull of the supporting points onto the floor, we show that the position and the region of the GZMP for keeping the dynamical balance can be uniquely obtained. The effectiveness of the proposed method is shown by simulation results.

We introduce a method to generate whole body motion of a humanoid robot such that the resulted total linear/angular momenta become specified values. First, we derive a linear equation, which gives to total momentum of a robot from its physical parameters, the base link speed and the joint speeds. Constraints between the legs and the environment are also considered. The whole body motion is calculated from a given momentum reference by using a pseudo-inverse of the inertia matrix. As examples, we generated the kicking and walking motions and tested on the actual humanoid robot HRP-2. This method, the resolved momentum control, gives us a unified framework to generate various maneuvers of humanoid robots.

This paper presents a whole body teleoperation system for a humanoid robot integrating operator's intention and the robot's autonomy. Instead of giving command to all the joints of the body, we have been proposing a switching command based teleoperation system of which the operator selects only the necessary points of the robot's body to manipulate depending on the required tasks. We have also proposed a whole body motion generation method, which satisfies both, and the desired movement of specific points of the robot's body and the robot's balance constraint. This paper first explains the concept of the proposed teleoperation system and the autonomous functions for maintaining balance and expanding the reachable area of a humanoid robot. Then the paper reports on the experimental results using the proposed methods to teleoperate a real humanoid robot HRP-1S to perform balanced whole body motions satisfying operator's input command.

For real-time walking control of a biped robot, we analyze the dynamics of a three-dimensional inverted pendulum whose motions are constrained onto an arbitrarily defined plane. This analysis leads us a simple linear dynamics, the Three-Dimensional Linear Inverted Pendulum Mode (3D-LIPM). Geometric nature of trajectories under the 3D-LIPM is discussed, and an algorithm for walking pattern generation is presented. Experimental results of real-time walking control of a 12-DOF biped robot HRP-2L using an input device such as a game pad are also shown.

A method of running pattern generation for a humanoid robot using the dynamics of a simple inverted pendulum is proposed. The dynamic simulation using a model of an actual humanoid robot shows that the robot can run by applying a generated pattern with slight modifications. The simulation is used to evaluate the required performance of the actuators for an actual running robot.

This paper introduces an open architecture humanoid robotics platform (OpenHRP) on which various building blocks of humanoid robotics can be investigated. OpenHRP is a virtual humanoid robot platform with a compatible humanoid robot, and consists of a simulator of humanoid robots and motion control library for them which can also be applied to a compatible humanoid robot as it is. OpenHRP is expected to initiate the exploration of humanoid robotics on an open architecture software and hardware, due to the unification of the controllers and the examined consistency between the simulator and a real humanoid robot.

This paper presents an advanced leg module developed for HRP-2. HRP-2 is a new humanoid robotics platform,. which we have been developing in phase two of HRP. HRP is a humanoid robotics project, which has been launched by Ministry of Economy, Trade and Industry (METI) of Japan from 1998FY to 2002FY for five years. The ability of the biped locomotion of HRP-2 is improved so that HRP-2 can cope with rough terrain in the open air and can prevent the possible damages to a humanoid robot's own self in the event of tipping over. In this paper the mechanisms and specifications of leg module, electrical system, simulation results utilized for deciding specifications, and experimental results are also introduced.

This paper investigates a method to minimize damage to a humanoid robot when it falls over to the ground. The strategy involves controlling the attitude of the robot while it is falling over so that it lands on the ground at one of shock-absorbing parts of the robot. A simulation study has confirmed that the proposed algorithm can make the robot land at specified shock-absorbing parts.

This paper presents an advanced leg module developed for HRP-2, a new humanoid robotics platform, which has been developed in phase two of the Humanoid Robotics Project (HRP), a five year program sponsored by the Ministry of Economy, Trade and Industry of Japan (METI) from 1998FY to 2002FY. The biped locomotion ability of HRP-1, the humanoid robotics platform developed in phase I is to be improved so that HRP-2 can cope with rough terrain and can prevent possible damage to the robot body caused by tipping over. In this paper, the mechanisms and specifications of the leg module, the electrical system, the simulation results utilized for deciding specifications, and some experimental results are presented.

This paper presents a prototype humanoid robotics platform developed for HRP-2. HRP-2 is a new humanoid robotics platform, which we have been developing in phase two of HRP HRP is a humanoid robotics project, which has been launched by Ministry of Economy, Trade and Industry (METI) of Japan from 1998FY to 2002FY for five years. The ability of the biped locomotion of HRP-2 is improved so that HRP-2 can cope with rough terrain in the open air and can prevent the possible damages to a humanoid robot's own self in the event of tipping over. The ability of whole body motion of HRP-2 is also improved so that HRP-2 can get up by a humanoid robot's own self even tough HRP-2 tips over. In this paper, the mechanisms and specifications of developed prototype humanoid robotics platform, and its electrical system are introduced.

Combination of wheels and legs has the potential to realize efficient locomotion on a flat surface and also negotiation of artificial irregularity such as stairs or steps. We have been studying on biped leg-wheeled system to realize flexible locomotion in our daily, life environment. This paper describes the design concept of the self- contained biped leg-wheeled system and its locomotion concept. The system has three locomotive modes - 4-wheeled locomotive mode, 2-wheeled locomotive mode, stair negotiation mode. In the first mode, it can travel quickly and steer like a car with its four wheels contacting the ground In the second mode, it can travel and steer like a wheeled inverted pendulum with two wheels contacting the ground In the stair negotiation mode, it can negotiate the stairs with front and rear wheels continuously in contact with the horizontal and vertical surfaces of stairs. In this mode torque control of both wheels while maintaining the posture of the system is the key to successful negotiation. The control scheme and method for stair negotiation, which can be applied generally to a leg-wheeled system, are introduced The effectiveness of the system is demonstrated by a successful experiment of the lift-up motion of the wheel using a biped leg-wheeled system developed in the authors' previous research.

A teleoperation system for whole body motions of a humanoid robot using a simple joystick master device is developed. Humanoid robots are physically similar to humans and usually possess a large number of degrees of freedom. By using hints from the shifting of the focus of attention for body motions between the joints of the human body during task executions, we propose a switching command based teleoperation system in which the operator selects only the necessary point of the humanoid robot's body for manipulation. In this paper, we present the implementation of this switching command based teleoperation system and experimental results using this system to teleoperate the humanoid robot HRP-1S developed in the Humanoid Robotics Project of the Ministry of Economy, Trade and Industry of Japan.

Meltran V, a new biped robot with telescopic legs, is introduced. For 3D walking control of the robot we analyze the dynamics of a three-dimensional inverted pendulum in which motion is constrained to move along an arbitrarily defined plane. From this analysis we obtain simple linear dynamics, the three-dimensional linear inverted pendulum mode (3D-LIPM). Using a real-time control method based on 3D-LIPM, the Meltran V robot successfully demonstrated 3D dynamic walking without the use of any prepared trajectories.

A balance control method for a humanoid robot is presented. It consists of a contact torque controller which is designed to have a good backdrivability and a feedback control of the total angular momentum and the center of gravity of a robot. A simulation result of a balance control using a 26 DOF humanoid robot model is shown.

For 3D walking control of a biped robot we analyze the dynamics of a 3D inverted pendulum in which motion is constrained to move along an arbitrarily defined plane. This analysis yields a simple linear dynamics, the 3D linear inverted pendulum mode (3D-LIPM). Geometric nature of trajectories under the 3D-LIPM and a method for walking pattern generation are discussed. A simulation result of a walking control using a 12-DOF biped robot model is also shown.

This paper presents a virtual humanoid robot platform (V-HRP for short) on which we can develop the identical controller for a virtual humanoid robot and its real counterpart. The unification of the controllers for the virtual and real robot has been realized by introducing software adapters for two robots respectively and employing ART-Linux on which real-time processing is available at the user level. Thanks to the unification, the controllers can share softwares with the dynamics simulator of V-HRP, including the parameter parser, kinematics and dynamics computations and the collision detector. This feature can make the development of the controllers more efficient and the developed controllers more reliable.

Biped robots have better mobility than conventional wheeled robots, but they tend to tip over easily. To be able to walk stably in various environments, such as on rough terrain, up and down slopes, or in regions containing obstacles, it is necessary for the robot to adapt to the ground conditions with a foot motion, and maintain its stability with a torso motion. When the ground conditions and stability constraint are satisfied, it is desirable to select a walking pattern that requires small torque and velocity of the joint actuators. We first formulate the constraints of the foot motion parameters. By varying the values of the constraint parameters, we can produce different types of foot motion to adapt to ground conditions. We then propose a method for formulating the problem of the smooth hip motion with the largest stability margin using only two parameters, and derive the hip trajectory by iterative computation. Finally, the correlation between the actuator specifications and the walking patterns is described through simulation studies, and the effectiveness of the proposed methods is confirmed by simulation examples and experimental results.

Since a biped robot tends to tip over easily, stable and reliable biped walking is a very important achievement. In this paper, we propose a balance control method based on an off-line planned walking pattern with real-time modification. First, a method of generating a highly stable, smooth walking pattern is presented. Then, a method of real-time modification consisting of body posture control, actual zero moment point control and landing time control based sensor information is proposed. By combining the proposed off-line walking pattern with real-time modification, the biped robot can walk smoothly and adapt to unknown environments. The effectiveness of the proposed method is confirmed by dynamic simulator such as walking on unexpected irregular rough terrain, soft ground and in environments in the presence of disturbances.

Biped robots have better mobility than conventional wheeled robots, but they tip over easily. In order to walk stably in various environments such as rough terrain, up and down slopes, or regions containing obstacles, it is desirable to adapt to such ground conditions with a suitable foot motion, and maintain the stability of the robot by a smooth hip motion. We propose a method to plan a walking pattern consisting of a foot trajectory and a hip trajectory. First, we formulate the constraints of a foot trajectory, and generate the foot trajectory by 3rd order spline interpolation. By setting the values of constraint parameters, it is easy to produce different types of foot motion. Then, we formulate a hip trajectory using a 3rd order periodic spline function, and derive the hip trajectory with high stability. Finally, the effectiveness of the proposed method is illustrated by simulation examples.

Since most conventional robots cannot easily be adapted to environments designed for humans, a human-size biped robot is expected to be able to play an important role in assisting human activities. The selection of suitable joint actuators is an important point when developing a human-size biped robot. In order to select suitable actuators and effectively utilize the selected actuators, it is necessary to clarify the relationship between walking patterns and the specifications of each joint actuator, and this is the issue tackled in the paper. First, a method of generating a high stability, smooth walking pattern is presented, and it is shown how various walking patterns can be produced by setting a series of defined walking parameters. Then, the dynamics of the robot, including the reaction force between the feet and the ground, are formulated. Finally, by simulation studies, the correlation found between actuator specifications and walking patterns is described, and the effectiveness of the proposed method is suggested.

We are studying a wheeled robot with the ability of going up and down stairs. We previously developed a wheeled robot called a 'variable structure type four-wheeled robot' capable of using over a single step, but it cannot negotiate the stair whose tread is short compared with the wheelbase of the robot. In this paper, we propose a 'biped type leg-wheeled robot' which has ability to pass over stairs with short treads. We also propose a trajectory planning method which uses a nominal static walking trajectory as a reference for the dynamic control of the robot and investigate a trajectory control method using computer simulation. We finally confirm the effectiveness of our proposed method with a successful experiment of going up stairs by this robot.

We develop a wheeled robot, called a 'variable structure type four-wheeled robot' which, with a simple structure, has the ability to pass over a step. We have realized its dynamics for passing over a step of known height. In this paper, we consider the control of dynamic passing over steps of known heights. We propose the method for planning a dynamic trajectory by evaluating the robot's stability against falling down in landing. We also confirm the possibility of detecting the height of the step using an existing rotary encoder without adding any external sensors. As the result, we have successfully realized an experiment of this robot going up steps whose height is unknown within only four seconds.

In this paper, realtime control of dynamic biped locomotion using sensor information is investigated. The authors used an ultrasonic range sensor mounted on the robot to measure the distance from the robot to the ground surface. During the walking control, the sensor data is converted into a simple representation of the ground profile in realtime. The authors also developed a control architecture based on the linear inverted pendulum mode which they proposed previously for dynamic walking control. Combining the sensory system and the control system enabled the authors' biped robot, Meltran II, to walk over ground of unknown profile successfully.

Cooperative transportation of an object by two or more mobile robots requires each robot to exert an appropriate force to support and move the object, to move along the object, and to maintain its attitude. A mechanically unstable robot, such as a wheeled inverted pendulum, needs to control the force and follow the object as standing stably against the force in an integrated manner. We call this a cooperative behavior. To realize this behavior of a wheeled inverted pendulum, we built control systems to estimate the external force and maintain standing and to exert a specified force. We applied them to a wheeled inverted pendulum. Experiments were conducted of cooperative transportation between a human and the robot. In the future, we aim to realize cooperative transportation by two wheeled inverted pendulums using the control systems.

An experimental study of a biped robot is presented. A new scheme, named the "linear inverted pendulum mode" is utilized for controlling biped walking on rugged terrain. We developed a 6 d.o.f. biped robot "Meltran II" which has light weight legs and moves in a two dimensional vertical plane. To check the effects not well discussed in the theory, we carried out two experiments, the support phase experiment and the support exchange experiment. The support phase experiment was carried out to check the actual dynamics of biped walking when using the proposed control. It was shown that the dynamics of the robot can be regarded as linear even though the mass of the legs, which was neglected in the theory, exists, The support exchange experiment was performed to check leg support exchange. We found that a smooth leg support exchange is achieved by making the foot contact with a certain vertical speed and holding two leg support for a certain short period. Based on these results, a whole biped control system was implemented. In our experiment the robot walked over a box of 3.5 cm height at a speed of 20 cm/s.

We have developed a robot called a ' structure type four-wheeled robot' which, with a simple structure, has ability to pass over a step. This robot has only one degree of freedom to change the body's structure and can run on four wheels (4-wheeled mode) or on two wheels like a wheeled inverted pendulum (2-wheeled mode). For the realization of stepping up and down, there are three difficult problems to be solved: stable control in 2-wheeled state, transfer from 4- to 2-wheeled mode (swing-up), and transfer from 2- to 4-wheeled mode (landing). The control method we have developed for a wheeled inverted pendulum is used to control the 2-wheeled state using the signal of a rate gyroscope. In this paper, we mainly discuss control methods for transfers from 4- to 2-wheeled mode and from 2- to 4-wheeled mode. Especially in the transfer from 4- to 2-wheeled state, we make effective use of the driving torque of the motor which change the body's structure. In the transfer from 2- to 4-wheeled state, we have investigated a control method for soft landing to minimize the touch-down impact of the robot which is nonholonomic system. By combining our control methods, we have realized an experiment of passing over a step successfully.

To reduce the complex walking dynamics of a biped, a particular class of trajectories of an ideal biped model where the center of gravity of the body moves horizontally and the horizontal motion of the center of gravity can be expressed by a simple linear differential equation is introduced. The authors coin the phrase 'potential energy conserving orbit' to describe this class of trajectories. Based on these properties, control laws were formulated for walk initiation, walk continuation, and walk termination. The walking motion is controlled by support leg exchange. Robust realization of the walking control is also considered. An experimental walking machine was designed as a nearly ideal biped model. To make the legs lighter, four DC motors were mounted in the body, and the legs are parallel link structures. The results of the experiment describe five steps of dynamic walking including walk initiation.>

A novel control method for biped locomotion on rugged terrain is introduced, assuming an ideal robot model which has massless legs. By applying constraint control to the robot body so that it moves on a particular straight line and rotates at a constant angular velocity, the dynamics of the center of mass of the body becomes completely linear. Such motion of the ideal model is called the linear inverted pendulum mode, and it is used to develop the control scheme of the biped walking on rugged terrain. Under the control method in the linear inverted pendulum mode, walking on a particular rugged ground is shown to be equivalent to walking on a level ground. It is also shown that the additional use of the ankle torque makes the proposed control scheme robust and applicable to a real biped robot with mass legs. Simulation results are presented.>