To reduce the risk of radiation leakages similar to the incident at the Fukushima Daiichi Nuclear Power Station, robots have been employed to remove fuel debris from reactors. To perform this process safely, it is important to monitor the interior of a reactor. A camera and neutron sensors are attached to the end of a robotic arm to monitor the interior of the reactor. The basic design requirement for the monitoring system is that the arm must be highly extendable and rigid. To achieve this, a novel compact long-reach manipulator with a joint structure built using a low-melting-point alloy (LMPA) is proposed. The LMPA enables switching between the free and locked states of the rotational joints of the manipulator. Herein, we first explain the design of the proposed joint structure and verify whether it has adequate mechanical strength. The required maximum torque to be sustained by the structure was calculated using the cantilever model, and the actual breaking torque was measured by the tensile test. Experimental results confirmed that the joint could withstand approximately 1.86 times the required torque. Finally, the effectiveness of induction heating, which is used to switch between the free and locked states of the joints, was evaluated experimentally. The LMPA arm was installed in the coil of the induction heating module, and the time required to melt LMPA was measured. The experimental results confirmed that the induction heating can change the state of the LMPA joint, and the time required for the melting is approximately 30.3 s. Therefore, the findings of this study show that the proposed system is capable of averting nuclear disasters through the prevention of radiation leakages at nuclear plants.

The ongoing development of the Inverted PENdulum Type Assistant Robot (I-PENTAR) is being undertaken by the authors. The I-PENTAR has many tasks like lifting objects with unknown mass, pushing and pulling a carts and many more. During execution of these tasks unknown disturbances enter the system and cause dynamic responses and errors. Most notably, the wheels of the robot move with excessively transients. To alleviate this problem, a strain gauge based sensor is attached to the existing structure of the robot to gain information regarding the disturbances. This allows minimal change to the system design while improving robustness to disturbances. In this paper the development of the sensor, the corresponding model and a method of updating the existing purely estimation based control is presented together with tests.

Applying differential drive robots to cooperative systems introduces difficulties regarding the maneuverability of the cooperative system. These difficulties are caused by the sliding constraint of the plain wheels typically used by differential drive robots and mainly affects the turning capability of the cooperative system. This can be a problem when a cooperative system traverses narrow spaces or manipulates large objects. Conversely, differential drive robots are simple to design and control for single robot tasks. To enable differential drive robots to participate in multi-robot cooperative systems, a novel wheel capable of switching between plain and omni-wheel modes is proposed. By selecting the appropriate mode, differential drive robots would be able to work in both single and multi-robot tasks seamlessly without adding complex control to the single robot case or degrading the maneuverability of the cooperative system. As an initial step, the kinematic modeling and the prototype of the wheel is presented together with tests using two differential drive robots implemented with the proposed wheel.

This paper discusses the development of a control method intended for an Inverted PENdulum Type Assistant Robot (I-PENTAR) that can be applied to an array of tasks and motions using a single controller. This idea of “a single controller for different tasks” differs from most controllers in its class because it does not intend to estimate certain parameters and change gain values like in adaptive control, nor does it perform switching of the control gains based on a certain condition. Instead it estimates changes in the parameters and external forces as disturbances. At the heart of the control is the Extended State Observer that performs this estimation and compensation. Discussion regarding the application of the controller to the wheeled inverted pendulum as well as tests that represent the planned tasks of the system is presented.

In this paper the subtasks of lifting, pushing, and pulling of an Inverted PENdulum Type Assistant Robot (IPENTAR) are described. These three motions comprise the initial work for the larger task of transporting of a load. During execution of these tasks, the forces that are applied on the robot are seen as disturbances and cause errors in the system. If these errors are not compensated the system may become unable to perform the task. One way of compensating for these errors is to implement an observer that can estimate the applied disturbance and then use the estimated value as feedback. Most observers rely heavily on the system model parameters which can have inaccuracies or are difficult to obtain. And so an observer that requires little system information known as the Extended State Observer is applied to the system. Disturbance tests and the control for the pushing, pulling, and lifting are discussed and results are presented.

In this paper, we describe a novel low backlash reducer using precessing crown gears. we call this mechanism Crown Reducer. The features of this reducer are low backlash, high reduction ratio, advantage in miniaturizing. These features greatly contribute to design various small mechanisms such as a finger joint of a robot hand. The crown gear pair is meshing in face to face, one acts as a rotor and the other as a stator. The rotor gear has N teeth and the hub is connected to the output shaft. The spokes of rotor gear are elastically deformed according to gears rolling. The stator gear fixed on a housing has N - 1 teeth (or N + 1). The meshing of crown gear pair with several shapes of rack tooth are simulated, and proper parameters of rack to improve high rigidity of teeth are calculated. Finally, backlash and minimum input torque to rotate are evaluated using a prototype reducer.

This paper describes motion control and planning for the standing and sitting motions of an inverted pendulum-type assist robot, I-PENTAR. Whole-body motion based on redundant control that takes positional control of a composite center of gravity(CCoG) and a wrist roller as goal tasks is adopted. Using the motion control, motion planning of the robot can be described intuitively and in a simple manner. Compliance motion of a manipulator by force control of a wrist roller is adopted to move the position of CCoG and to maintain the robotpsilas stability when the wrist roller contacts with the ground, which is an important factor in successfully achieving a sitting motion. Based on this motion control, standing and sitting motion planning is also proposed, which considers the stability and the operational time efficiency of the process. The proposed control method and motion planning were tested experimentally with I-PENTAR, and it was confirmed that standing and sitting motions were achieved stably in a short time period.

We have developed a positioning system that uses a phased array sensor to measure the distance and direction of multiple landmarks relative to the position of a mobile robot so that the robot can self-localize. The positioning system can control the strength and the width of the beam from the phased array sensor and observe the multiple landmarks at the same time. By using the distance and direction of plural landmarks, our positioning system is able to use various self-localizing methods. A main part of our work has been incorporating our various techniques for making a robot positioning error smaller into a system in which the most suitable self-localizing method is selected on the basis of sensitivity, which is defined as the ratio between localizing and sensor errors. We propose using a set of indices to evaluate the accuracy of self-localizing methods. The indices are derived from the sensitivity. We used these indices to compare the accuracy of three methods for the self-localizing of a mobile robot using landmarks, and we demonstrated a rational way to minimize a localizing error.

This paper describes the mobile control and the standing and sitting motions of an Inverted PENdulum Type Assistant Robot-(I-PENTAR) aiming at the coexistence of safety and work capability. I-PENTAR consists of a body with a high powered waist joint, arms designed for safety, and a wheeled inverted pendulum mobile platform. It is modeled as a three-dimensional robot with controls for inclination angle, linear position, and steering angle, and is controlled by state feedback control based on the LQR method. The motion planning of standing and sitting-important motions for an inverted pendulum type robot in practical use-is proposed. It was experimentally confirmed that I-PENTAR could realize a series of fundamental motions required in practical use, which are standing, running, turning, and sitting stably.

Recently, developers have created a number of manipulators designed to provide physical services to human beings. Collisions between those manipulators and humans or other objects in the environment generate massive impacts, causing injury or limiting execution speed. These collisions are unavoidable, however; therefore it is essential that the force of such impacts be reduced, thus improving safety and task performance. One of the most effective methods to reduce impact force is to decelerate by braking immediately before the collision. In this paper, we propose dynamic acceleration polytope braking (DAPB), a method which is optimal braking to decelerate impact velocity quickly and without varying the direction of motion in redundant manipulators. DAPB uses a dynamic acceleration polytope to represent the acceleration ability, while considering manipulator dynamics to determine braking torque. By adopting DAPB, the velocity at impact can be decelerated faster than by zero-braking, which decelerates all joint velocities to zero; as a result, impact force can be greatly reduced. Moreover, since the path of the impact point does not stray from the initial impact direction, additional dangerous situations could be avoided. Several simulations and experiments are executed to confirm the braking performance of DAPB

Robots working in human environment for personal service should have both safety and dexterity function. Since these two functions have characteristics that influence each other on an implementation process, it is necessary to treat them together in a system. In this paper, we propose a safety serve manipulator system (SSM) which has the potential to realize both the safety and dexterity simultaneously, and discuss on the effectiveness of slip motion that is one of the safety functions of the SSM in reduction of contact force. The SSM slip motion is realized by torque limiters located on the base. We confirm the effectiveness of the torque limiters in reduction of harmful force at various limit torque and improve the reduction efficiency by controlling the limit torque. These are confirmed through simulations and experiments.

In this paper, we propose a basic control method for the leg-wheel robot moving on unexplored rough terrains. When moving on a rough terrain, the compliance values and the trajectories of legs are set up according to the environment without using external sensors. And the step axis mechanism that we have developed, realizes the stable rolling movement of the robot. The proposed method is evaluated by a walking experiment in an outdoor natural terrain.

A mobile robot can identify its own position relative to landmarks, the locations of which are known in advance. The main contribution of this research is that it gives various ways of making the self-localizing error smaller by referring to a sensitivity which is defined as the ratio of the localizing error to sensor error. In this paper, the authors propose a set of indices to evaluate the accuracy of the self-localizing methods, and the indices are derived from the sensitivity. And then, the accuracy of self-localizing a mobile robot with landmarks based on the indices is compared, and a rational way to minimize the localizing error is proposed. Finally, we discuss a method to reduce the computational cost of selecting the best self-localizing method.

This paper addresses the function distribution and behavior design problem for a multirobot system which incorporates a behavior-based dynamic cooperation strategy for object handling. The proposed multiple robot system is composed of a managing robot and homogeneous behavior-based robots. The cooperation strategy in this system is realized in two steps: designing the distributed robot's cooperative behavioral attributes according to the robot's abilities, and organizing these behavioral attributes so that team cooperation is realized. For indicating an incremental style of local behavior construction, an advanced design of cooperative behavior for coping with unknown disturbance is addressed. Additionally, two extended cooperation strategies designed for a path tracking task are described. These three strategies are based on the same concept on performing manipulation in coordination. Therefore, by considering the function distribution among the managing robot and worker robots, and considering behavior design of each worker robot, the proposed system is able to achieve the object handling task with different performances according to the task requirement, such as with or without path tracking and with or without contact with the environment. Experimental results demonstrate the applicability of the proposed system.

Road-following by mobile robots under varying outdoor illumination demands special care to be taken on development of an algorithm, which should be flexible to color changes in sunny or shadow parts. The ill-structured weak-paved or dirt roads such as forest or mountain roads have no significant geometrical shape and are not planar. This paper describes a selective color-based road extraction method, in which appropriate color parameters are selected by one sample color of the road. We also report on experiments with mission of a small 4-wheel mobile robot equipped with a color camera sensor through a real natural field.

A real-time obstacle avoidance algorithm is presented for autonomous mobile robots equipped with a CCD as its only sensing modality. The approach uses segmentation technique to segregate ground from other fixtures. It uses a simple computation for the threshold value. The processing speed of the algorithm is fast enough that it can avoid some active obstacles. The algorithm was tested in various lighting conditions in an indoor environment and is remarkably robust. Results of the different thresholding techniques are also presented in conjunction with our computation of the threshold value.

Describes a multi-robot system which incorporates a behavior-based dynamic cooperation strategy for object transportation with various requirements on task performance. This cooperation strategy is realized in two steps: designing the distributed robot's cooperative behavioral attributes according to its abilities and task dynamics, and organizing these behavioral attributes so that the team cooperation is realized. Through the behavior design, this strategy allows the dynamic cooperation control to be distributed equally to each robot. Constraint-based behavior is designed to cope with the requirements of task performance. In organizing robots' abilities, the concept of form closure is introduced as the basic strategy and additional closure rules are introduced to realize various constrained motions.

We have constructed a leg-wheel mobile robot called ChariotII that has mechanically separated wheels and legs which allows it to utilize the advantages of the two mechanisms. A new motion control approach, the leg-wheel passive hybrid crawl gait (LWPCG) motion control approach, for moving ChariotII is discussed under the environment of unexplored rough terrain in this paper. To enable the robot to negotiate a extensive range of unexplored terrain, an automatic control function which shifts the profile of the desired foot trajectory (automatic profile shift, or APS) has also been implemented. The proposed motion control approach is extremely simple computationally, does not require knowledge of the robot's dynamic model or environmental parameters, and does not necessitate late the use of external sensors. The effectiveness of this method is confirmed through simulations and experiments.

In this paper, the mechanism, the kinematics, the control, and the experimental results of a newly designed nonholonomic omni-directional vehicle "ODV9" are discussed. ODV9 has four wheel modules, with each wheel module incorporating a motor, brake, and a wheel. Compared with other ODVs, the advantages of ODV9 are not limited to the simplicity of its mechanism. Benefiting from using a normal type wheel equipped with a tire, ODV9 is capable of moving in various environments. The proposed controller for ODV9 is designed using digital optimal control theory. The experimental results show that ODV9 can be practically utilized for various mobile platforms.

A robot manipulator with passive joints has the following features: a light weight manipulator can be fabricated by implementing simple hinge; and the manipulator is fault-tolerant to actuator failure by using frictional torque at the passive joint.. A motion control of a two-link robot manipulator actuated only at the second joint is presented in this paper. The first integral of the system is derived and the motion is described as a variation of the integral constant. Also, the dynamically enforced motion and free motion are analyzed based on the first integral approach proposed in this paper. An effective motion control algorithm is established using the dynamic characteristics positively. Finally a simple numerical example is given.