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.