Safety is important to a robot that is used in a way that can impact on the wellbeing of people. However, understanding and managing the safety information of a robot is not a trivial task. The quantity of this information is large, and it is usually stored in text-based formats. These factors mean that maintaining safety information when it changes is error prone, and understanding it requires manually searching through lengthy reports. In this paper, we demonstrate that a robot's safety information can be stored in a model-based format. We use the SafeML modelling language to model the results of a safety analysis performed on a semi-autonomous wheelchair. We then illustrate and discuss the benefits of storing and managing safety information using a model, both to maintainability of the information and to understanding the safety of the robot.

In order to maintain balance, the motors of an inverted pendulum-style, two-wheeled self-balancing vehicle need to continuously control its wheels. The vehicle is at risk of falling over if any of its motors does not function properly. Some research in this regard has been devoted to gaining redundancy by using more motors geared to a common shaft, but such technique is not effective for a seizing failure. In this paper, we propose a differential redundant mechanism to prevent a seizing failure in such vehicles. This mechanism unifies plural motors using a differential mechanism, and allows redundant motors to operate at different speeds. Therefore, the vehicle can maintain balance even if a motor fails. Furthermore, our mechanism can form a redundant system of two outputs using only three motors. We also propose a controller for this redundant mechanism that does not require changing the control mode when seizing failures occur.

Development of a system is complex, requiring a well-structured process to manage the range of tasks involved and their work products. There are many models and processes available for structured development, including the well-known Waterfall and Agile models. Recent standards for safety-critical system development utilise the V-model, such as the process given in the ISO 26262 standard for functional safety of road vehicles. However, the process clashes with the commonly-expressed desire for greater reuse of development artifacts in robotics. We have experimented with applying a process, the Object-Oriented Systems Engineering Method, to the design of a robotic wheelchair. This paper describes our application of the process to a safety-critical robot, as well as our use of SysML for managing design information and ZipC for code generation and verification. We discuss our experiences, both good and bad, in order to inform other robot developers of what to consider when choosing a process and tools.

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 motion planner of getting up motion using Mahalanobis distance. It is an indispensable function for humanoid robots to get up by itself and some humanoid robots are able to get up by themselves, but the motion can start only from the states specified a prior. The robots have to get up from an arbitrary lying state which may result after an unexpected falling. The proposed method (l) determines the degree of similarity between the current falling state and predefined falling states using Mahalanobis distance, (2) generates a collision-free motion to the most similar state, and (3) plans a sequence of motions using a state transition graph.

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.

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 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 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.

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.

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.

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 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.

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.

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.

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 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.