We investigated the ability of two fingers to discriminate stiffness with stochastic resonance. It is known that the haptic perception at the fingertip improves when vibrotactile noise propagates to the fingertip, which is a phenomenon called the stochastic resonance. The improvement in the haptic sensation of a fingertip depends on the intensity of the noise propagating to the fingertip. An improvement in the haptic sensation of multiple fingertips does not require multiple noise sources, such as vibrators, to be attached to multiple fingertips; i.e., even a single vibrator can propagate noise to multiple fingers. In this study, we focus on stiffness discrimination as a task using multiple fingers, in which the thumb and index finger are used to touch an object and perceive its stiffness. Subsequently, we demonstrate that the stiffness perception is improved by propagating sufficiently intense noise to the thumb and index finger using only a single vibrator. The findings indicate the possibility of improving the haptic sensation at multiple fingertips using one vibrator.

The morphology and controller design of robots is often a labor-intensive task performed by experienced and intuitive engineers. Automatic robot design using machine learning is attracting increasing attention in the hope that it will reduce the design workload and result in better-performing robots. Most robots are created by joining several rigid parts and then mounting actuators and their controllers. Many studies limit the possible types of rigid parts to a finite set to reduce the computational burden. However, this not only limits the search space, but also prohibits the use of powerful optimization techniques. To find a robot closer to the global optimal design, a method that explores a richer set of robots is desirable. In this article, we propose a novel method to efficiently search for various robot designs. The method combines three different optimization methods with different characteristics. We apply proximal policy optimization (PPO) or soft actor-critic (SAC) as the controller, the REINFORCE algorithm to determine the lengths and other numerical parameters of the rigid parts, and a newly proposed method to determine the number and layout of the rigid parts and joints. Experiments with physical simulations confirm that when this method is used to handle two types of tasks-walking and manipulation-it performs better than simple combinations of existing methods. The source code and videos of our experiments are available online (https://github.com/r-koike/eagent).

A robot must exhibit softness so as not to accidentally damage its environment. However, stiffness is also necessary, so that the robot can transmit forces and perform tasks. In soft robotics, it is desirable to be able to switch between two states, namely a flexible state for adapt ion to the environment and a rigid state for the transmission of forces. String jamming mechanisms, which comprise many units connected in a bead-like pattern, have received attention for their ability to switch between flexible and rigid states. In this study, we propose a new design of the string jamming mechanism that enhances the maximum stiffness in the rigid state while maintaining a high fitting performance for the environment in the flexible state. We evaluate the fitting of the mechanism to the environment in a qualitative geometric discussion and compare the performance of the mechanism with that of existing string jamming mechanisms. The results of experiments measuring the maximum stiffness show the usefulness of the proposed mechanism from a quantitative point of view.

This article studies the min-consensus control of continuous-time real-valued multiagent systems, with sampled information, quantized communication, and switching topologies. Due to the limited bandwidth of the digital communication network, only finite-bit binary symbolic sequence can be exchanged among the agents. In order to realize the min-consensus control with quantized communication and limited bandwidth, a novel finite-level biased quantizer and a nonstrict decreasing scaling function are designed, and correspondingly a set of switching encoders and decoders are constructed. By means of the proposed encoders and decoders, the according sampled-data min-consensus control inputs are carefully constructed, and the memory variables are introduced into the control inputs and are monotonically decreasing no matter how the communication topology is switched. The proposed encoding-decoding-based control scheme can achieve accurate min-consensus with limited bandwidth, as long as the communication graphs are jointly strongly connected. The numerical simulations show the effectiveness of the proposed control scheme.

In the recently growing field of virtual reality, the virtual grasping sensation remains in its infancy, and the discrepancy between real and virtual grasping has become a problem. This article develops a new haptic glove that presents the sensation of different types of grasping (e.g., power/precision/intermediate grasping) a compliant object. To this end, we develop an exoskeleton that fixes the movements of fingers to present a braking force and a flexible pad that reproduces a wide range of stiffness. By applying the “string jamming mechanism,” our exoskeleton has functions that existing devices do not. In that, it constrains the motion of finger extension/flexion and adduction/abduction with only one actuator and presents the braking force to all surfaces of the finger. In addition, we propose a lightweight and compact variable-stiffness pad that reproduces an extensive stiffness range based on the layer jamming technique. We conducted experiments to evaluate the mechanical performance of the prototype integrating the exoskeleton and the variable-stiffness pad and demonstrated the usefulness of the proposed glove.

The snake robot, which mimics the mechanism of real snakes, is expected to be used in various environments. This article addresses the challenge of snake robots autonomously adapting to and moving inside and outside pipes having complex shapes using a helical rolling motion. We consider that an irregular helical form can be defined as a combination of three components, namely the axis, cross-sectional shape, and pitch angle, and that it is easier to consider deformations that have compliance only in a specific direction. Our proposed method deforms the cross-sectional shape of the snake robot locally so that it adopts the shape of the pipe accurately. Experiments were conducted using our developed snake robot to verify the effectiveness of the proposed method, and it was demonstrated that the proposed method can be used for a snake robot moving inside and outside of straight pipes and outdoor tree, including those having noncircular and varying cross sections.

This article studies the appointed-time attitude tracking control of the spacecraft on the special orthogonal group, with the attitude forbidden zone, the parameter uncertainties, and the external disturbances. A novel projection function is proposed, such that the normalized boresight vector of the sensitive instrument is mapped to a reduced dimensional vector in the Euclidean space. If the reduced dimensional vector is uniformly bounded, the constraint on the attitude forbidden zone will be satisfied at all the time. By virtue of the designed reduced dimensional vector and the associated auxiliary vectors, a set of vector-based error functions, the appointed-time performance constraints, and the according switching law is carefully constructed. The proposed vector-based adaptive control scheme ensures that the spacecraft attitude can satisfy the attitude constraint and appointed-time control performance simultaneously, in the presence of parameter uncertainties and external disturbances. Simulation results show the effectiveness of the designed control scheme.

Path integral policy improvement (PI2) is known to be an efficient reinforcement learning algorithm, particularly, if the target system is a high-dimensional dynamical system. However, PI2, and its existing extensions, have adjustable parameters, on which the efficiency depends significantly. This article proposes an extension of PI2that adjusts all of the critical parameters automatically. Motion acquisition tasks for three different types of simulated legged robots were performed to test the efficacy of the proposed algorithm. The results show that the proposed method cannot only eliminate the burden on the user to set the parameters appropriately but also improve the optimization performance significantly. For one of the acquired motions, a real robot experiment was conducted to show the validity of the motion.

A snake robot performs diverse motions. To realize a wide range functions in a complex environment, it is necessary to transition between various motions suited to each environment. In this article, we propose a method of transitioning the motion of a snake robot across different environments to expand the application environment of the robot. We first find that the motion at the connection point between two motions must coincide with the tangential movement during motion transition across different environments. We then design a gait called the circular pedal wave. This circular pedal wave allows a hoop-passing motion in which the whole body moves as if it is passing through a virtual hoop fixed in space in sequence from its head through combination with a proposed shift part. The hoop-passing motion allows motion transition across different environments. We propose three application examples of this hoop-passing motion, namely passing through a hole in a wall, entering an underfloor, and attaching to a ladder. We report on experiments conducted to verify the effectiveness of the proposed method and to realize the described motions.

A method for designing the motion of a snake robot negotiating complicated pipe structures having a constant diameter is presented. For such robots moving inside pipes, there are various "obstacles" such as junctions, bends, shears, and blockages. To surmount these obstacles, we propose a method that enables the robot to adapt to multiple pipe structures of a constant diameter. We designed the target form of the snake robot of two helices connected with an arbitrary shape. This method is applicable to various obstacles by designing a part of the target form conforming to the obstacle. The robot negotiates obstacles under shift control by employing a rolling motion. We demonstrated the effectiveness of the proposed method in various experiments.

To learn motor skills using a finger in many haptic training systems, a user places his or her finger in a holder to communicate with a haptic interface. It is known that the force-detection capability at the fingertip is reduced when the user's finger is enclosed in a holder. The learning performance might therefore be impaired in training. Stochastic resonance is known to improve sensitivity at the fingertip. We thus propose a fingertip force learning method using stochastic resonance. We first examine the effect of stochastic resonance on the user haptic performance in a two-dimensional task when the fingertip is within the finger holder. The outcomes indicate that the user fingertip sensitivity increases even when the finger is placed within a holder. We next perform force learning tasks in one- and two-dimensional space. Our proposed method that combines haptic feedback and stochastic resonance is compared with the method in which only haptic feedback is provided to the user in force leaning tasks. Results obtained using the proposed method indicate that the performance outcome of the proposed method is higher than that of the comparison method. This study demonstrates the potential of the proposed method for motor learning tasks.

To date, many gait generation strategies have been designed for robots with leg configurations that model those of natural creatures. However, their leg configurations are limited to the 2 × N type, such as hexapod or myriapod; hence, simultaneously, the potential ability of legged robots is implicitly limited. We consider single-legged modular robots that can be arranged to form a cluster with arbitrary 2-D leg configurations. By choosing configurations appropriately, these robots have the potential to perform several types of tasks, as is the case for reconfigurable modular robots. However, to use appropriate configurations for a given task, a unified gait generation system for various configurations of a cluster is required. In this article, we propose an autonomous distributed control system for each single-legged modular robot to collectively achieve static walking of the cluster with various leg configurations on planar ground. Moreover, our system is an autonomous distributed system with scalability and fault tolerance, in which each module determines the moving pattern of its foot through local communication without global information, such as the entire leg configuration of the cluster. We verified that several types of clusters achieved static walking using our system not only in dynamic simulations, but also in real robot experiments.

In this paper, we address the stability analysis of swarm robots with heterogeneous abilities for velocity and acceleration. Each robot also has a unique sensing region with a limited angle of field of view. We previously proposed a decentralized navigation method for such swarm robots. With the method, connectivity maintenance is achieved while satisfying physical limitations which are unique to each robot. Here, we focus on the shape of the whole swarm and mathematically prove that the shape and orientations of all robots eventually converge to the equilibrium state. Furthermore, we show experimental results to confirm the convergence.

This paper presents a method that allows a snake robot to climb a ladder. We propose a ladder climbing method for a snake robot that has a smooth surface shape. We design a novel gait for the snake using a gait design method that configures the target form of the snake robot by connecting simple shapes. The climbing motion is executed via shift control and the corresponding motion required to catch the next step on the ladder. In addition, we developed a snake robot that has a smooth exterior body surface through construction of pectinate-shaped parts of the links. We demonstrated the effectiveness of both the proposed gait and the design of the snake robot experimentally.

This paper presents a method for designing the gait of a snake robot that moves in a complicated environment. We propose a method for expressing the target form of a snake robot by connecting curve segments whose curvature and torsion are already known. Because the characteristics of each combined shape are clear, we can design the target form intuitively and approximate a snake robot configuration to this form with low computational cost. In addition, we propose two novel gaits for the snake robot as a design example of the proposed method. The first gait is aimed at moving over a flange on a pipe, while the other is the crawler gait aimed at moving over rough terrain. We demonstrated the effectiveness of the two gaits on a pipe and rough terrain in experiments.

This paper addresses the adaptive synchronization problem of networked mechanical systems in task space with time-varying communication delays, where both kinematic and dynamic uncertainties are considered and the information flow in the networks is represented by a directed graph. Based on a novel coordination auxiliary system, we first extend existing feedback architecture to achieve synchronization of networked mechanical systems in task space with slow-varying delays. Given that abrupt turns arise for the delays sometimes, we then propose a delay-independent adaptive synchronization control scheme which removes the requirement of the slow-varying condition. Both of the two control schemes are established with time-domain approaches by using Lyapunov-Krasovskii functions. Simulation results are provided to demonstrate the effectiveness of the proposed control schemes.

In the present paper, a dynamic analysis is presented, comparing three snake-like robot gaits: lateral undulation, sidewinding locomotion, and sinus-lifting motion. To simplify calculations, sidewinding locomotion and sinus-lifting motion are considered planar movements. Vertical movements are assumed to be small but play a critical role in change where contacts are made. Thus, the normal forces acting on grounded links and the torques applied to pitch joints can be calculated by solving equilibrium equations. The tradeoff between locomotion speed and energy efficiency is studied for all three gaits, at eight different environmental settings distinguished by friction coefficients. Simulation results reveal that sinus-lifting motion and sidewinding locomotion are generally more energy-efficient gaits than is lateral undulation. More specifically, if the anisotropy in friction is large enough, sinus-lifting motion is the most energy-efficient gait; otherwise, sidewinding locomotion is more efficient. However, there are some critical speeds at which the most efficient gait changes, in some environmental settings.

In many engineering problems, including those related to robotics, optimization of the control policy for multiple conflicting criteria is required. However, this can be very challenging because of the existence of noise, which may be input dependent or heteroscedastic, and restrictions regarding the number of evaluations owing to the costliness of the experiments in terms of time and/or money. This paper presents a multiobjective optimization algorithm for expensive-to-evaluate noisy functions for robotics. We present a method for model selection between heteroscedastic and standard homoscedastic Gaussian process regression techniques to create suitable surrogate functions from noisy samples, and to find the point to be observed at the next step. This algorithm is compared against an existing multiobjective optimization algorithm, and then used to optimize the speed and head stability of the sidewinding gait of a snake robot.

The observation of quadruped animals has suggested that the body flexibility is important for the bounding gait. In particular, the body flexibility is assumed to be crucial for determining the ground reaction force (GRF). In this paper, we investigated the dynamic effect of the body flexibility on the GRF in quadruped bounding with simple physical models by focusing on the vertical motion. More specifically, we first showed that the body flexibility reduces the GRF using a simple two legged model in sagittal plane. Next, to clarify the GRF reduction mechanism, we further simplified the model, which has only one leg. This allowed us to analytically obtain periodic solutions. Based on the solutions, we investigated the mechanism that the body flexibility reduces the GRF during quadrupedal bounding.

This study proposes a method to control a prosthetic hand by EMG signals based on muscle synergies. The muscle synergy model suggests a framework to transform commands of the central nervous system to a set of complex muscular movements. Using this method, we have tried to realize the proportional control of multiple degrees of freedom (DOF). This study focuses on controlling four kinds of hand/wrist movements of the prosthesis: open, close, pronate, and supinate. The nonnegative matrix factorization (NMF) algorithm is used to map muscle activities into these four movements through the calculation of a muscle synergy matrix. An EMG feature selection process along with a control scheme has been added, which smooths the output thereby stabilizing the movements. Ten healthy subjects performed an online experiment comprised of two tests: 1) proportional control on single DOF, and 2) simultaneous control of multiple DOFs. The results indicate that fluid hand/wrist movements could be estimated from EMG. The average R2values achieved by all subjects for the single-DOF test and the multiple-DOF test are 0.97 and 0.93, respectively.

In many robotic problems, optimization of the policy for multiple conflicting criteria is required. However this is very challenging due to the existence of noise, which may be input dependent, or heteroscedastic, and the restriction in the number of evaluations, due to robotic experiments which are expensive in time and/or money. This paper presents a multiobjective optimization (MOO) algorithm for expensive-to-evaluate noisy functions for robotics. We present a method for model selection between heteroscedastic and standard homoscedastic Gaussian process regression techniques to create suitable surrogate functions from noisy samples and find the point to be observed at the next step. This algorithm is compared against an existing MOO algorithm which assumes homoscedastic noise, and is then used to optimize the speed and head stability of the sidewinding gait of a snake robot.

Teleoperation system using past image records (SPIR) is a system that provides the third-person view image to the operator for the robot operation. The image is visually generated by overlaying the CG model of the robot on the background image taken by the robot-mounted camera at a past time. In this paper, we proposed a new user interface based on SPIR for the teleoperation of a mobile manipulator. By using the proposed user interface, the operator can control the end effector's position and orientation intuitively while looking the end effector from the third-person viewpoint.

In this paper, we consider “sinus-lifting motion” of a living snake, in which a snake lifts up some parts of its body from the ground, and switches the lifted parts dynamically. It is not clear whether imitating the sinus-lifting motion is the best locomotion or not for a snake like robot. The aim of this paper is to propose an appropriate motion pattern to a snake like robot considering the optimality of the sinus-lifting motion. We introduce two physical parameters, constraint forces and energy efficiency, as cost functions to optimize and propose switching strategies for generating optimal motion patterns of a snake like robot.

In this paper, we propose a new method of controlling a group of mobile robots based on formation abstraction. The shape of a formation is represented by a deformable polygon, which is constructed by bending a rectangle, to go through narrow spaces without colliding with obstacles. If the trajectory of the front end point, as well as the width and the length of the formation, are given, the formation automatically reshapes itself to fit the area through which the front part of the group has already safely passed. Furthermore, the robots continuously try to optimize their positions to decrease the risk of collisions by integrating a decentralized locational optimization algorithm into the formation control. We show that the objective function, taking into account the distance between robots, does not decrease for fixed and nonconvex polygonal formation shapes if the zero-order hold control is applied for a sufficiently short sampling period. We also analyze the influence of the decentralized locational optimization algorithm on the objective function in the case of variable formations. The effectiveness of the proposed method is demonstrated in both simulations and real robot experiments.

In this paper, a dynamical analysis of sidewinding locomotion by a snake like robot is presented. Sidewinding locomotion is treated as a planar movement for simplicity, and the normal forces acting on the grounded links and the torques applied on pitch joints are calculated by solving equilibrium equations. Energy efficiency of sidewinding locomotion is compared with that of lateral undulation. Simulation results show that the sidewinding locomotion is, generally, energetically more efficient, and in the case where the viscous coefficient is small, there is a lower bound in the mean velocity of center of mass for sidewinding locomotion to be more efficient than lateral undulation.

Central pattern generators (CPGs) play a crucial role for animal locomotion control. They can be entrained by sensory feedback to induce proper rhythmic patterns and even store the entrained patterns through connection weights. Inspired by this biological finding, we use four adaptive neural oscillators with synaptic plasticity as CPGs for locomotion control of our real snake-like robot with screw-drive mechanism. Each oscillator consists of only three neurons and uses adaptive mechanisms based on frequency adaptation and Hebbian-type learning rules. It autonomously generates proper periodic patterns for the robot locomotion and can be entrained by sensory feedback to memorize the patterns. The adaptive CPG system in conjunction with a simple control strategy enables the robot to perform self-tuning behavior which is robust against short-time perturbations. The generated behavior is also energy efficient. In addition, the robot can also cope with corners as well as move through a complex environment with obstacles.

In this paper, we investigated the dynamics of a hexapod robot model whose legs are driven by nonlinear oscillators with a phase modulation mechanism including phase resetting and inhibition. This mechanism changes the oscillation period of the oscillator depending solely on the timing of the foot's contact. This strategy is based on observation of animals. The performance of the controller is evaluated using a physical simulation environment. Our simulation results show that the robot produces some stable gaits depending on the locomotion speed due to the phase modulation mechanism, which are simillar to the gaits of insects.

Electrooculogram (EOG) signals are potential responses generated by eye movements, and event related potential (ERP) is a special electroencephalogram (EEG) pattern which evoked by external stimuli. Both EOG and ERP have been used separately for implementing human-machine interfaces which can assist disabled patients in performing daily tasks. In this paper, we present a novel EOG/ERP hybrid human-machine interface which integrates the traditional EOG and ERP interfaces together. Eye movements like the blink, wink, gaze, and frown are detected from EOG signals using double threshold algorithm. Multiple ERP components, i.e., N170, VPP and P300 are evoked by inverted face stimuli and classified by linear discriminant analysis (LDA). Based on this hybrid interface, we also design a control scheme for the humanoid robot NAO (Aldebaran robotics, Inc). On-line experiment results show that the proposed hybrid interface can effectively control the robot's basic movements and order it to make various behaviors. While normally operating the robot by hands takes 49.1 s to complete the experiment sessions, using the proposed EOG/ERP interface, the subject is able to finish the sessions in 54.1 s.

Stable locomotion indicates a stable limit cycle generated in the dynamic system. Although quadrupedal bound gait models have been investigated, there is no research which shows the generation of limit cycle and its dynamic properties. In the present study, we analyze a quadrupedal bound gait model which goes down slope and has back and front bodies with spring-damper joint between the bodies. We found the periodic bound gait which achieves a stable limit cycle and convergence property against perturbations.

This paper presents a shape transformation control method of a mobile robot with wheel-arms. The proposed method aims at transformation from a four-wheeled mode for high-speed mobility to an inverted pendulum mode, which has advantages of high viewing position and small turning radius. The transformation starts with lifting up the wheel-arms to raise the center of gravity of the whole robot including the main body and arms. From such initial states, the body is lifted up and controlled to the target angle by partial linearization, while returning the arms to the initial angle. Then, the robot position is controlled by manipulating the target body angle. Unlike existing methods, we take into account the effects of the body angular velocity and the tracking error of the body angle by constructing a model set, which is composed of a single nominal model and its polytopic uncertainty for the system matrices. In order to derive the model set, we assume that the target body angle is constrained to a prescribed range. Therefore, the target body angle is manipulated using a model predictive control method, such that the closed-loop system is asymptotically stabilized, while the given constraint is satisfied, for all systems in the model set. The effectiveness of the proposed method is demonstrated in both simulations and real robot experiments.

This paper presents a model predictive control (MPC) approach for multivehicle formation taking into account collision avoidance and velocity limitation with reduced computational burden. The first part of the paper constructs a formation control law using feedback linearization with MPC in order to reduce the optimal control problem to a mixed-integer quadratic programming problem for a group of unicycles. The second part constructs a new branch-and-bound (B& B) -based algorithm for collision-avoidance problems. Numerical examples and experiments show that the proposed method significantly reduces computation time.

In this paper, we consider “sinus-lifting motion” which is an effective motion of a snake for rapid movement. In this motion, a snake lifts up some parts of its body from the ground, and switches the lifted parts dynamically. This motion is analyzed based on a dynamic model of an n-link snake robot. We introduce the energy efficiency as a cost function to generate motion of a snake robot. We propose a control strategy for switching grounded parts of the snake robot so as to minimize the energy consumption. Simulation results show that the motion optimizing the energy efficiency of the snake robot differs depending on the velocity to be generated and the optimal motion is similar to the sinus-lifting motion.

When a legged-robot walks on an irregular terrain such as a damaged area, some footholds may collapse due to the external force caused by the walking robot, and consequently the robot will stumble and fall. We have earlier proposed a locomotion method in which the quadruped robot does not stumble and cause a large collapse of the surrounding area on a weak horizontal plane. In this paper, we extend this method to weak and irregular slopes. In the case of slopes, we should consider “slippage”. We propose a force distribution method for the leg-grope that also considers slippage. To demonstrate the effectiveness of proposed method, we will show an experimental result.

In this paper, we develop a new type of snake-like robot using screw-drive units that are connected by active joints. The screw-drive units enable the robot to generate propulsion on any side of the body in contact with environments. Another feature of this robot is the omnidirectional mobility by combinations of screws' angular velocities. We also derive a kinematic model and apply it to trajectory tracking control. Furthermore, we design a front-unit-following controller, which is suitable for manual operations. In this control system, operators are required to command only one unit in the front; then, commands for the rest of the units are automatically calculated to track the path of the preceding units. Asymptotic convergence of the tracking error of the front-unit-following controller is analyzed based on a Lyapunov approach for the case of constant curvature. The effectiveness of the control method is demonstrated by numerical examples and experiments.

This paper presents a shape transformation control method of a mobile robot with wheel-arms. The proposed method aims at transformation from a four-wheeled mode for high speed mobility to an inverted pendulum mode, which has advantages of high viewing position and small turning radius. The transformation starts with lifting up the wheel-arms to raise the center of gravity of the whole body. From such initial states, the body is lifted up and controlled to the target angle by partial linearization, while returning the arms to the initial angle. Then, the wheels are slowed down by properly changing the target pitch angle of the body. Stability analysis is carried out by taking into account the transient response of the body angle to the target value, which is neglected in existing work. The effectiveness of the proposed method is demonstrated by experiments.

To achieve a balanced walking for a humanoid, it is necessary to estimate the dynamic stability of the system. However, in a small size humanoid with restricted system resource, it is hard to satisfy the performance level desired by dynamics analysis. Therefore, in this paper, we propose the feasible methods to generate gait pattern and stabilize walking based on coupled oscillators which have a clear correlation between oscillator parameters and system dynamics without a real time ZMP calculation. The proposed method was tested on the open humanoid platform DARwIn-OP for the evaluation, and the result showed that a real time gait pattern generation and stabilization were realized.

In this paper, we discuss an optimal shape of the grounded part of a snake robot with passive wheels for jumping. First, we derive a relationship between constraint forces for the wheels and necessary friction forces, and propose a constraint force ellipse. Next, we introduce an evaluation index for the optimal shape of the grounded part (base part) of a snake robot using the constraint force ellipse. Finally, in order to demonstrate the validity of the optimal shape that minimizes the evolution index, simulations have been carried out.

Recently various autonomous mobile robots are developed for practical use. For coexistence with the robots and human in the real environment, the consideration of safety is very important. We should consider a region with a limitation of a maximum velocity of a mobile robot for the safety. In this paper, we propose path planning and trajectory generation methods for a mobile robot which moves in the environment with predetermined velocity constraints. In order to demonstrate the validity of the proposed methods, numerical simulations and experiments have been carried out.

In this paper, we consider “sinus-lifting motion” which is the effective motion of a snake for rapid movement consisting of lifting some parts of its body off the ground, and switching the lifted and grounded parts dynamically. This motion is analyzed based on control theory. We focus on the constraint force of passive wheels and switching of grounded parts of the snake robot to minimize the constraint force. Simulations show that the motion that minimizes the constraint force of the snake robot is similar to the sinus-lifting motion in appropriate amplitudes and periods of the body shape.

In the current research we consider the scenario of post disaster rescue operations using multiple robots inside damaged buildings where the damage is not very extreme. The objective the of the work is to develop systems to support efficient rescue missions involving creation and exchange of environment maps enriched with information important to rescue operations, among multiple robots and rescue workers. In current days many research institutes are developing robots with widely different types and capabilities to support rescue operations. In rescue missions involving multiple robots it is essential to have sharable map information for efficient search and navigation irrespective of the differences in the structures and capabilities of the participating robots. In this paper we address the above issue by proposing a map description which combines the geographical data as well as the information about robot behaviors called ¿behavioral trace map¿. We describe the algorithm for generation of such maps and we present experimental results using rescue robots developed in our laboratory.

In this paper, we consider the trajectory tracking control of a 3-dimensional (3D) snake robot by using redundancy. We discuss the motion control which accomplishes the trajectory tracking and other tasks, for example singular configuration avoidance, obstacle avoidance, etc., for the 3D snake robot. Features of the internal motion caused by the kinematic redundancy are considered and the dynamic model of the 3D snake robot is derived by introducing shape controllable points. By utilizing redundancy, we propose the controller which accomplishes the trajectory tracking as the main-task and several sub-tasks. Simulation results show the effectiveness of the proposed controller.

In this paper, we consider a issue that the reliable and the inexpensive communication method in swarm robotics. The ants forage for preys by using pheromone trails. They lay down the pheromone trails between preys and a nest. By detecting the trail pheromone, they can find the preys. Though they do not have excellent intelligence, they can communicate with each other and cooperate by adding information to the environment, like a pheromone. This communication method has a merit that an agent does not need to memorize the place of the preys. We consider to answer the issue that ldquoHow do the swarm robots communicate using pheromone trail?rdquo. We construct a swarm behavior simulator and develop swarm robots that communicate using the pheromone trail. We demonstrate the effectiveness of the communication using the pheromone trail by computer simulations and experiments using swarm robots. To realize this purpose, we design a swarm behavior algorithm, based on 4 perceptual signs (stimuli) and 3 effector signs (actions). In the simulations, an experimental field is discretized by computational grids, and evaporation and diffusion are phenomena of the pheromone modeled by discretized equations. The proposed algorithm is demonstrated by the simulation. Simulation result shows that proposed algorithms act effectively. Based on the simulation results, we set three robots, one nest and one prey in the flat experimental field. We observe three robotspsila behavior and the state of the environment for 20 minutes. The robots laid down the pheromone trail between the nest and the prey, and reinforced the pheromone trail many times. This fact means that swarm robots can realize the function of the chemical, indirect, plastic and local communication like ants by using the pheromone trail.

This paper presents a path-tracking control method for a snake-like robot using screw drive mechanism. The operators are required to command only one unit in the head, then commands for the rest of the units are automatically calculated to track the path of the preceding units. Although the velocity commands for exact path tracking can be calculated using past command signals due to the omni-directional property of the robot, a simpler control law without using past signals is adopted from the implementation viewpoint. Asymptotic tracking error is investigated based on a Lyapunov approach for the case of a constant curvature. Furthermore, the effectiveness of the proposed method is investigated by computer simulations and laboratory experiments.

In robot teleoperation a robot works as a physical agent at a remote site for a robot operator. There are mainly two tasks such as environment recognition using visual information and robot control according to the recognition in robot teleoperation using camera images. In this paper we propose a teleoperation method for a mobile robot through a virtual robot. In the proposed method we manage above two tasks in the same manner which are usually treated separately. This method is an intuitive robot teleoperation method where an operator do not need to concern about robot body orientations and can absorb difference of robot driving mechanisms. That is this method frees an operator from being bothered from controlling a robot and the operator can concentrate on where he/she intends to go. This method mainly consists of two technologies: an omni-directional image stabilization technology and automatic robot orientation control. The conducted experiments show effectiveness of the proposed method.

In this paper, we develop a prototype of a new snake-like robot using the screw drive mechanism, and design a control system design for trajectory tracking. First, we explain the outline of the snake-like robot using the screw drive units and joint units, as well as the principle of the screw drive mechanism. Next, in order to achieve the trajectory tracking of the robot, we derive a kinematic model. Finally, the validity of the derived model and the effectiveness of the proposed control system are demonstrated by simulations and experiments.

To search victims in the narrow space at the disaster site, we have developed the snake-like rescue robot called "KOHGA". The robot is constructed by connecting multiple crawler vehicles serially by active joints. KOHGA has a problem that obstacles are caught to the joints and then the robot is stuck. To solve this problem, we developed an unit assembled robot "KOHGA2". It can be rearranged. The robot can swing crawler-arms and avoid the stuck. In this paper, we report the construction of the hardware and the control system of KOHGA2, the basic mobility performance, and the stuck avoidance strategy.

Our research perspective is to develop mechanisms for gathering information efficiently in disaster sites. Ideally this requires mechanisms with capabilities of flexible, on-site, adaptation of the overall shape and of the locomotion strategy to unknown and unstable environments. We have been developing three-legged modular robots which can be interconnected to cooperatively achieve multiple locomotion modes and collaboratively perform tasks that cannot be done by a single module. In this paper, we report the development of experimental modular robots and experimentations with their cooperative activities which evolve out of their various inter-connectivity options.

In this paper we consider modeling and control of a redundant snake robot with wheeled link mechanism based on kinematic model. We derive a kinematic model of a snake robot with introducing links without wheels and shape controllable points in the snake robot's body in order to make the system redundancy controllable. By using redundancy, it becomes possible to accomplish the main objective of controlling the position and the attitude of the snake robot head and the shape of the snake robot, and the sub-objective of the singular configuration avoidance. Simulations and experimental results show the validity of the control law and how snake robots move at the neighborhood of the singular configuration.

This paper presents a new branch-and-bound (B&B) method to reduce the computational burden of online optimization in multi-vehicle formation control with collision avoidance that is formulated by model predictive control. One of the possible reasons for extremely heavy computation time of the standard B&B algorithm is that so many subproblems are generated since integer constraints are rarely satisfied in “relaxed” problems. The purpose of the proposed method is to decrease subproblems based on a new branching rule taking into account the inherent properties of collision avoidance problems. Numerical examples and experiments show that the proposed method drastically reduces computation time of online optimization for multi-vehicle formation control.

Extended Kalman filter (EKF) has been a popular choice to solve simultaneous localization and mapping (SLAM) problems for mobile robots or vehicles. However, the performance of the EKF depends on the correct a priori knowledge of process and sensor/measurement noise covariance matrices (Q and R, respectively). Imprecise knowledge of these statistics can cause significant degradation in performance. The present paper proposes the development of a new neurofuzzy based adaptive Kalman filtering algorithm for simultaneous localization and mapping of mobile robots or vehicles, which attempts to estimate the elements of the R matrix of the EKF algorithm, at each sampling instant when a ldquomeasurement updaterdquo step is carried out. The neuro-fuzzy based supervision for the EKF algorithm is carried out with the aim of reducing the mismatch between the theoretical and the actual covariance of the innovation sequences. The free parameters of the neuro-fuzzy system are learned offline, by employing particle swarm optimization in the training phase, which configures the training problem as a high-dimensional stochastic optimization problem. By employing a mobile robot to localize and simultaneously acquire the map of the environment, under several benchmark environment situations with varying landmarks and under several conditions of wrong knowledge of sensor statistics, the performance of the proposed scheme has been evaluated. It has been successfully demonstrated that in each case, the neuro-fuzzy assistance is able to improve highly unpredictable, degrading performance of the EKF and can provide robust and accurate solutions.

In this paper, we derive a dynamic model and a control law for cooperative task of two snake robots which have wheeled links and demonstrate the validity of proposed controller by simulation and experiment. First, we derive a dynamic model of single snake robot with redundancy by introducing the shape controllable points. Next, we extend it to the model for the cooperative task of two redundant snake robots and propose a control law to accomplish this task. Finally, in order to demonstrate the validity of the derived model and effectiveness of the proposed control law, simulation and experiment are carried out

Common wheeled robots face many difficulties when traveling in complex environments, especially its incapability to climb over obstacles higher than its wheel radius. Many alterations were made to these robots to allow them to travel in rough terrains or conquer high obstacles, nevertheless, most designs are complex in nature and lost several original wheeled robot advantages by gaining others. In this paper, we propose a novel wheeled type robot with variable structure functionality. It is designed with simple structure consisting of three main robot parts, the main body, the left and right wheel-arm units. The robot could achieve five locomotion modes that allows the robot to travel in various environments and climb over high obstacles. Moreover, the fast-speed advantage in flat floor condition that common wheeled robot originally hold is still remained. The confirmation of the effectiveness of the robot's maneuverability is shown by several experimental results

In this paper, we derive a dynamic model and a control law for cooperative task of three snake robots which have wheeled links and demonstrate the validity of proposed controller by simulation. First, we derive a dynamic model of single snake robot with redundancy by introducing the shape controllable points. Next, we extend it to the model for the cooperative task of three redundant snake robots and propose a control law to accomplish this task. Finally, in order to demonstrate the validity of the derived model and effectiveness of the proposed control law, simulation is carried out

In this paper, we derive a dynamic model and a trajectory tracking control law for snake robots, which have passive wheels and active joints, based on the dynamic model. For a trajectory tracking control of snake robots, it is one of the important problem to avoid the singular configuration like a straight line. Using input-ouput linearization for the head position of snake robots based on dynamic model, we can control the head position by PD feedback, but the robot will converge to the singular configuration. In order to solve this problem, we propose a control law that controls shape controllable points for avoiding the singular configuration. Using the proposed control law, the robot can accomplish trajectory tracking of the head position without converging to the singular configuration. Simulation results show the effectiveness of the proposed control law.

In this paper we report the development of a new rescue robot platform. The robot is constructed by connecting multiple crawler vehicles serially, resulting a long and thin structure so that it can enter narrow space. The units are connected by 2-DOF active joints and 3-DOF passive joints, so that the robot can have both the capability to climb over obstacles as well as adaptation to irregular surfaces. Basic steering and experiments for the robot are also shown.

As an experimental platform for modular legged robots, generic limb modules are developed which are used to implement 3-limb robot units. Benefits of 3-limb modularity are discussed in the context of multi-legged robot assembly. A CPG network based locomotion gait generation approach for generic multi-leg formations is considered.

Robots are useful for search and detection missions for trapped victims after disasters due to their abilities enter places where human rescuers cannot go without risking their own lives. We have experienced and found much knowledge about rescue robots while participating in the RoboCup Rescue Competitions. In this paper we introduce examples of "effective multiple robot cooperative activities" and "a study of the number of robots and operators in a multiple robot team" from our experiences in these competitions.

Reinforcement learning is very effective for robot learning. It is because it does not need prior knowledge and has higher capability of reactive and adaptive behaviors. In our previous works, we proposed new reinforce learning algorithm: "Q-learning with dynamic structuring of exploration space based on genetic algorithm (QDSEGA)". It is designed for complicated systems with large action-state space like a robot with many redundant degrees of freedom. However the application of QDSEGA is restricted to static systems. A snake-like robot has many redundant degrees of freedom and the dynamics of the system are very important to complete the locomotion task. So application of usual reinforcement learning is very difficult. In this paper, we extend layered structure of QDSEGA so that it becomes possible to apply it to real robots that have complexities and dynamics. We apply it to acquisition of locomotion pattern of the snake-like robot and demonstrate the effectiveness and the validity of QDSEGA with the extended layered structure by simulation and experiment.

In this paper, we derive a kinematic model and a control law for 3D snake robots which have wheeled link mechanism. We define the redundancy controllable system and find that introduction of links without wheels makes the system redundancy controllable. Using redundancy, it becomes possible to accomplish both main objective of controlling the position and the posture of the snake robot head, and sub-objective of the singular configuration avoidance. Computer simulations demonstrate the effectiveness of the proposed control law.

Reinforcement learning has recently been receiving much attention as a learning method for not only toy problems but also complicated systems such as robot systems. It does not need priori knowledge and has higher capability of reactive and adaptive behaviors. However, increasing of action-state space makes it difficult to accomplish the learning process. In most of the previous works, the application of the learning is restricted to simple tasks with a small action-state space. Considering this point, we present a new reinforcement learning algorithm: Q-learning with dynamic structuring of exploration space based on genetic algorithm. The algorithm is applicable to systems with high dimensional action and interior state spaces, for example, a robot with many redundant degrees of freedom. To demonstrate the effectiveness of the proposed algorithm simulations of locomotion patterns for a 12-leged robot were carried out. As the result, an effective behavior was obtained by using our proposed algorithm.

We present a type of locomotion mode, path planning of shape transition, and design and implementation of a 3-dimensional hyper-redundant snake-like robot. First we explain the multiple locomotion modes, for example ring mode, inching mode, bridge mode, and so on. We propose a new type of locomotion "twisting mode" and analyze the principle of the locomotion based on statics. Next, the motion planning using genetic algorithm for transition of locomotion modes is explained and simulation results for the GA research is shown. Finally, we explain the designed prototype system and experimental results are shown.

In this paper, we propose a force and attitude control law of an asteroid sample return robot to obtain an enough constraint force for taking samples from the surface of the asteroid during contact. In a phenomenon of the impact between the robot and the asteroid, there is a complementary relation between the robot acceleration and the constraint force on the contact point. To pay attention to the complementarity, we derive a condition to constrain the robot on the surface of the asteroid based on complementarity system (CS). We design a control law which achieves the desired force and attitude with keeping the contact, and verify the effectiveness of the proposed control law by experiments.

Underactuated systems are those processing fewer actuators than degrees of freedom, but generally they are difficult to control. In this paper we realize the crawling motion by an underactuated robot. By changing the location of the fixed point of the robot to the environment, the constraint of the system is changed. Local accessibility of the system with changing the constraints as a nonholonomic system is shown. The control law based on partial feedback linearization is proposed and the stability of the closed-loop system is studied. We discuss the trajectory planning of the robot based on geometric relation. Experiments were carried out to demonstrate the effectiveness of the proposed controller.

We propose an attitude control law of a space robot with initial angular momentum. We consider a class of the 3-state and 2-input affine nonholonomic systems with a drift term as general system representation for a planar two-link space robot with initial angular momentum. We propose the coordinate and input transformation algorithm which converts an affine system with a drift term into the time-state control form, and propose a controller design method using exact linearization. An asteroid sample-return robot with nonzero initial angular momentum is considered as an example. By using the transformation algorithm. We obtain the time-state control form for the robot. The attitude controller of the robot is designed on the basis of the time-state control form, and simulation and experiment have been carried out.

Cooperative control of two flexible arms is discussed. Dynamics of the cooperative flexible arms are described as a distributed parameter system subject to geometric constraint. The control purpose is to accomplish the desired grasping force for a common rigid object and the vibration absorption of the flexible arms. An output PDS feedback control synthesis is developed for cooperative two one-link flexible arms. The synthesis is carried out in the infinite-dimensional setting, mathematical features of which give rise to a stabilizing control algorithm. Due to simplicity of the implementation, the algorithm becomes extremely attractive under limitations on the computer power in the space. The effectiveness of the control strategy proposed is supported by experimental tests.

We consider a class of the 3-state and 2-input affine nonholonomic systems with a drift term. First, we propose an expanded chained form which is expressed as the simulation of the drift term and the chained form, and the controller design method based on it. Next, we propose the coordinate and input transformation algorithm which converts an affine system with a drift term into the time-state control form, and propose the controller design method using the exact linearization. Finally, an asteroid sample-return robot with non-zero initial angular momentum is considered as an example. By using the transformation algorithm, we obtain the time-state control form for the robot. The attitude controller of the robot is designed on the basis of the time-state control form, and simulation has been carried out.

This paper introduces the RoboCup-Rescue Simulation Project, a contribution to the disaster mitigation, search and rescue problem. A comprehensive urban disaster simulator is constructed on distributed computers. Heterogeneous intelligent agents such as fire fighters, victims and volunteers conduct search and rescue activities in this virtual disaster world. A real world interface integrates various sensor systems and controllers of infrastructures in the real cities with the virtual world. Real-time simulation is synchronized with actual disasters, computing complex relationship between various damage factors and agent behaviors. A mission-critical man-machine interface provides portability and robustness of disaster mitigation centers, and augmented-reality interfaces for rescue parties in real disasters. It also provides a virtual reality training function for the public. This diverse spectrum of RoboCup-Rescue contributes to the creation of the safer social system.

Underactuated systems are those processing fewer actuators than degrees of freedom. Decrease of the number of actuators is a merit from the point of view of size and weight of the system. But generally it is difficult to control the underactuated system. In this paper we realize crawling motion by an underactuated robot. Control law based on partial feedback linearization is proposed and stability of the closed-loop system is discussed on the basis of zero dynamics. To demonstrate the effectiveness of the proposed controller experiments have been carried out.

The RoboCup Rescue project aims to simulate large urban disasters and rescue agents' activities. The simulator must support both simulation of heterogeneous agents such as fire fighters, victims' behaviors and interface to disaster's environments in the real world. The RoboCup Rescue simulator is a comprehensive urban disaster simulator into which a new disasters simulator or rescue agents can be easily plugged. In the paper, the simulator's specification based on the Hanshin-Awaji Earthquake and the simulator's architecture are described.

Modeling and robust control of force and vibrations of a flexible arm with an asymmetric rigid tip body are discussed. By using Hamilton's principle and Lagrange multiplier method, dynamic equations of the constrained flexible arm are derived. We analyze the stability of the compliance control and the direct force feedback as the force control of the flexible arm. We construct robust controllers of an optimal controller with low-pass property and an H/sub /spl infin// controller. Simulations have been carried out.

In this paper, an experimental study on robust control of bending and torsional vibrations and contact force of a one-link flexible arm is discussed. The flexible arm carries a symmetric rigid tip body, of which the mass center lies on the center axis of the arm. We derive dynamic equations of the joint angle, the vibrations of the flexible link, and the contact force. On the basis of a finite-dimensional modal model of a distributed-parameter system, robust controllers are constructed. Some experimental results are shown.

In this paper, robust control of bending and torsional vibrations and contact force of a one-link flexible arm is discussed. The flexible arm carries a rigid tip body, of which the mass center lies on the center axis of the arm. We derive dynamic equations of the joint angle, the vibrations of the flexible link, and the contact force by using Hamilton's principle. On the basis of a finite-dimensional modal model of a distributed-parameter system, an optimal controller with low-pass property and a robust H/sub /spl infin// controller are constructed. A set of simulations has been carried out.

In this paper, an exact dynamic model and a control architecture are developed for the closed chain motion of two two-link flexible manipulators holding a common rigid object in a horizontal workspace. On the basis of some assumptions we derive the quasistatic equations and design the cooperative controller of two flexible manipulators. A set of experiments for the cooperative control of two flexible manipulators using a force sensor has been carried out.

In this paper, a dynamic model and robust controllers are developed for two one-link flexible arms holding a rigid object in a horizontal workspace. On the basis of the exact model we derive a finite dimensional modal model. To compensate the spillover instability an optimal controller with low-pass property and a robust H/sub /spl infin// controller are constructed. A set of simulations has been carried out.

In this paper, robust force control of a flexible arm is considered. We derive the dynamic equations of the joint angle and vibration of the flexible arm and its contact force. On the basis of a finite-dimensional model of distributed-parameter systems, an LQ controller, an optimal controller with low-pass property and a robust N/sub /spl infin// controller are constructed. A set of simulations has been carried out and responses for three controllers are compared.>

In this paper, task understanding and optimal strategies for handling flexible beams by using N-link manipulators are discussed. We consider the planning of the input torque and the trajectory of the manipulator as not to excite the vibration of the flexible beam. First, the equations of the motion of a general type of N-link manipulators with a flexible beam are derived. On the basis of the dynamic equations, the optimal input torque, which accomplishes the desired end-position of the manipulator and the diminution of the vibration of the flexible beam, is calculated by employing an iterative numerical algorithm. As the equation of the vibration of the flexible beam implies that the acceleration of the end-point of the manipulator excites the vibration, we consider an optimal trajectory planning so as to minimize the end-point acceleration of the manipulator. The validity of the optimal input torque and the optimal trajectory are demonstrated by computer simulations and experiments for an air-driven robot arm, respectively.>

A method is proposed whereby both contact force exerted by a flexible manipulator and position of end-effector while in contact with a surface are controlled. The authors derive dynamic equations of joint angles, vibrations of flexible links, and contact force by means of Hamilton's principle. On the basis of some assumptions the authors derive the quasi-static equations and design the hybrid position/force controller of the flexible manipulator. A set of experiments for the hybrid control of the flexible manipulator using a force sensor has been carried out. Several experimental results are shown.>

A simple model that considers the flexibility of constrained manipulators by introducing a set of equivalent springs is proposed. On the basis of the model, the authors derive a controller, which compensates the vibrations of the contact force. For measuring the vibrations and the contact force, accelerometers and a force sensor are used. Output signals of the sensors are fed back to the driving motors for controlling the position of the end-effector and the contact force. Experimental results are shown.

A method is proposed whereby both the contact force exerted by a flexible manipulator and the position of the end effector while in contact with a surface are controlled. Exact dynamic equations for joint angles, vibration of the flexible link, and constraint force are derived by means of Hamilton's principle. A controller for the hybrid position/force control of the flexible manipulator is designed on the basis of the obtained model. A set of experiments for the hybrid control of the flexible manipulator using a force sensor has been carried out. Several experimental results are shown.>

A method is proposed whereby both the contact force exerted by a flexible manipulator and the position of the end-effector while in contact with a surface are controlled. The authors first derive the exact dynamic equations of joint angles, vibration of the flexible links, and contact force by means of the Hamilton's principle. Then, a controller for the hybrid position/force control of the flexible manipulator is designed on the basis of the model obtained. A set of experiments for the hybrid control of the flexible manipulator using a force sensor has been carried out. Several experimental results are shown.>