Robotics and remote technology | Fukushima
Exploring inside3 September 2012
Quince robots have been a valuable tool in the quest to examine the stricken Fukushima Daiichi nuclear power plant, conducting radiation surveys and taking videos and photos inside reactor buildings that are too dangerous for humans to enter.
Co-developed by three Japanese institutions, Quince robots have conducted a number of survey missions at the Fukushima Daiichi nuclear power plant since being first deployed at the site in June 2011.
Quince was developed by Chiba Institute of Technology, Tohoku University and the International Rescue System Institute to support rescue crews by conducting surveys at the scenes of chemical, biological, radiological, nuclear or explosive disasters. In particular, the robot was expected to be useful in enclosed spaces.
The battery-powered robot, which weights around 26 kg, is able to navigate rough terrain and climb stairs with wide caterpillar tracks on its body and four independently-adjustable swivelling ‘legs’, which are also mounted with tracks. Quince is typically equipped with front, rear and overhead cameras, as well as a microphone, speaker and position sensing detector (PSD). It can also be fitted with extras such as a pan, tilt and zoom (PTZ) camera, a manipulator with six degrees of freedom, infrared or carbon dioxide sensors and a 3D laser mapping tool.
As originally designed, Quince is waterproof and dustproof and able to survive a two-metre drop. However, some modifications were needed to improve its hardware and communications reliability and to add new sensors (primarily a dosimeter) before the robot could be deployed at the Fukushima site.
Three versions of the Quince robot have been used at Fukushima. The first, Quince 1, pictured below, has been stranded on the third floor of the unit 2 reactor building after its communications cable snagged while conducting a survey in October 2011.
The two robots currently used at Fukushima are slightly different. Both are equipped with the following common sensors: a dosimeter, thermometer, hygrometer, stills camera, fully automatic cable-winding device and radio. The difference is that the robot used at unit 2 had a built-in dust sampler, while the version used at unit 3 had a 3D scanner.
As shown in the main figure, a conventional digital dosimeter is mounted on the robot at a height of 1.2 m (around the height of the main internal organs). The dosimeter is read using a nearby camera.
To secure reliable communication, Quince uses a combination wireless/wired network; reactor-building missions require a wired connection because the robot cannot receive wireless signals inside. To enable tangle-free motion of the communications cable, an automatic cable rewind function was added.
Hardware reliability was a key factor due to both the radiation environment (which would preclude maintenance) and the possibility of robot control by novice operators, who might damage the robot.
Modifications to the original Quince design for Fukushima included replacing the PTZ camera, which had movable parts, with a camera without any mechanical motion. The radiation-hardness of the robot was also checked by gamma-ray irradiation testing of electrical components prior to deployment. The reliability of the power supply system was also improved.
Finally, the operability of Quince was improved by implementing a new tele-operation system composed of two PCs, two game pads and operation software. The software was simplified, for instance by adding an extra button that could acquire all the sensor data simultaneously.
The operational screen includes video feeds from seven cameras: front and rear high-mount, and ground-level views, right side view, cable winder, and dosimeter read-out. It also displays digital indications including pitch and ‘leg’ positions, roll, air temperature and humidity, direction of travel and cable pay-out.
Various organisations were involved in the development of Quince for use at Fukushima in partnership with the robot’s co-developers. These included: The University of Tokyo, the Japan Atomic Energy Research Institute, Hamaoka Nuclear Power Station, the Robotics Task Force (ROBOTAD), chaired by Professor Hajime Asama from the University of Tokyo, and of course utility TEPCO.
Quince robots have conducted investigations at units 1, 2 and 3 of the Fukushima Daiichi nuclear power station. Missions have included dust sampling in unit 2 (June 2011), a building condition surveys at unit 3 (August 2011), unit 1 traversing in-core probe room (July 2012), as well as detailed radiation surveys and photographic missions at all three units. Video of the missions have been published on the internet (www.youtube.com/neimagazine).
This article was originally published in the August 2012 issue of Nuclear Engineering International
Manufacturer: Mobile Robot Laboratory Co., Ltd.