Safe Development Environments for Radiation Tracing Robots

Introduction

After a nuclear disaster (e.g. Chernobyl, Fukushima) or in some military scenarios, it is too dangerous for people to enter a contaminated area. This is a suitable field to deploy robots for measurements, repair or clearance. Several fully autonomous or remote operated robots have been already built for this purpose. Before operation the robot must be developed, built and tested safely for critical missions. So it is desirable to perform these activities without handling dangerous radiation sources. A further advantage of simulated environments is a higher flexibility. This paper describes two ways of safe development. For the work a self-built, wheeled, multi-purpose robot “EtaBot” has been used. Radiation tracing and optional radiation-based navigation have been implemented in ROS.

One simple way has been dubbed “light follower”. The radiation sensor has been substituted by a photo diode as a light sensor. For the light sensor an interface circuit emulates the signals which in true operation would come from the radiation sensor. The robot can run a given path and just measure radiation on this path, but additionally an algorithm has been implemented to follow actively the radiation source. In this mode a directive radiation source could be represented e.g. by a simple torch light, a distributed scenario by diffuse lamps.

A second, more sophisticated approach is a complete digital simulation of the contaminated environment using a hardware-in-the-loop simulator (HiL). This implies two technical core questions, on the one hand the representation of the contaminated environment and the robot motion in the HiL, on the other side the interfacing between the robot and the HiL. Depending on the interface further functionality needs to be implemented in the simulator. In the particular case of this article, the robot has been reduced to its computation platform. The ROS computer receives radiation signals from the HiL, passes motion commands to an additional microcontroller board which would control steering and the motors. The robot is jacked with its wheels free from ground, the PWM signals are intercepted and fed into the HiL to simulate the robot motion, its location and posture in the contaminated environment. With a graphical map creator, scenarios can be defined and uploaded to the HiL. Radiation exploring robots and the presented approaches are good examples where deep interaction of mechanics and electronics (mechatronics) solves problems (Habib, 2007). A very similar application is exploration for chemicals where sensors may be more complicated, but exploration is easier, because in contrast to the stochastic nature, chemical sensing delivers continuous values (Ishida, 2012).