Developing a control system for a mobile robot for use in hostile and hazardous environments
25 January 2018
Founded in 1969, Lappeenranta University of Technology (LUT) in Finland is a pioneering institution that brings together the fields of science and business. The LUT international community includes approximately 6,000 students and experts engaged in scientific research and academic education.
Lappeenranta University of Technology (LUT) in Finland
The Intelligent Machines group at LUT carries out research on mechatronic machine design, especially using virtual technologies and simulators, and demanding industrial robotics.
The group has developed a special mobile robot that can sense, navigate, and monitor its surroundings and conduct repairs and assembly tasks in inhospitable areas and dangerous environments where humans cannot operate.
This article, adapted from a piece by National Instruments, provides an overview of the control system solutions adopted by the group in the design and development of the robot, named TIERA.
Engineering solutions to international challenges
In 2011, an earthquake off the Pacific coast of Japan triggered a powerful tsunami that caused a major disaster at the Fukushima nuclear power plant. The tsunami disabled the emergency power to the reactor cooling systems, which led to three nuclear meltdowns, chemical explosions, and the release of radioactive material.
To prevent further catastrophe, 50 volunteer technicians ventured into the exclusion zone surrounding the power plant to stabilise the reactors. These brave individuals, known as the ‘Fukushima 50’, had to perform simple repair work, including closing valves, in one of the most hazardous environments on Earth. The exposure to extreme radiation could have had serious ramifications for their long-term health.
The Intelligent Machines group felt inspired by the Fukushima 50, but, while admiring their bravery, felt that modern mechatronic systems could remove the need for humans having to perform menial repair work in such hazardous environments. This became the inspiration for the design and development of a mobile assembly robot.
Graphical Overview of TIERA's systems
TIERA is a versatile, mobile robot that can conduct repair and assembly operations in hazardous areas. The functionality and composition of the robot are defined by the tasks it is expected to perform and the harsh environments it will work in. Environmental factors in the design includes radiation, corrosion, toxicity, explosion, biohazard, high voltage, and extreme temperatures.
High mobility was another key design feature to enable effective travel across hazardous environments. This contrasts with most industrial robots, which are usually stationary and consist of a jointed arm attached to a fixed surface. A major consideration was how to make it possible for an expert operator to remotely control the robot from a safe location, and the design of sensory, communication (WiFi and 4G), virtual reality, and haptic feedback systems required for intuitive teleoperation was key to achieving this.
Additional key features of TIERA include:
• Fanless embedded computer controlling most of the robot’s hardware
• Robotic manipulators and tools to perform various repair tasks
• Vision system allowing operator to receive video feedback from robot’s cameras
• Sensors to gain information about the surrounding environment
Strengthening the Initial Control System
In the beginning of the project, the control system of the whole robot was a Linux-based distribution of the Robot Operating System (ROS), running on an Advantech industrial computer. Project engineers quickly learned that the industrial controller alone was not enough to satisfy the needs of the project, and decided to use CompactRIO as the main control system based on NI Linux Real-Time in communication with ROS. This new control architecture provided a powerful system which increased robot controllability to very high accuracy with very low latency.
The team eliminated the need for separate subsystems by connecting to sensors, displays, cameras, motors, databases directly to the CompactRIO controller. The LabVIEW graphical environment was used to define how the CompactRIO handled all this data, and LabVIEW was also used to program the embedded and FPGA processors within the CompactRIO. The team used built-in LabVIEW functions to intuitively manage timing and memory, and simplified the development of signal processing, analysis, control, and mathematical routines.
A complete list of TIERA’s motion, sensory, and control systems
Built-in drivers and APIs to move data between components enabled the team to focus on robot development. Furthermore, the extensible LabVIEW architecture ensures that the system can be easily customised and reconfigured through software—even after deployment.
The main feature of TIERA’s central control system is integration of NI Linux Real-Time and CompactRIO with the flexibility and features of ROS, which generated many novel features for the robot.
Digital communication plays a vital role in any advanced robot. It can include communication between an operator and a robot, between a robot’s control devices and its peripheral hardware, between different programmatic nodes being executed by a robot’s processor, and much more.
A local net allows the transmission of control messages for movement of robot sections, which are published into ROS topics by the main station. Then an onboard computer subscribes to topics and reads messages. From the computer installed on the robot, a signal spreads to each device according to instructions. Signals from a remote control reach the main station, and then they are processed in ROS and sent to the Advantech by WiFi.
The CompactRIO controller can be integrated into the whole robotic system using the LabVIEW library to publish information into ROS topics in the same local net. Tufts University developed this library, which is freely available on the LabVIEW Tools Network.
The ROS and LabVIEW collaboration enabled the use of different types of devices and controllers connected to the one network.
The Future of TIERA
The team is making rapid progress with the TIERA robot. All of its systems are fully operational, and the first full system tests are in progress with further upgrades being planned.
Schematic of CompactRIO in connection with sensors, actuators, and ROS system
The versatility and modularity of the TIERA and its CompactRIO controller means that it is not limited to assembly and repair in hazardous environments. The robot can quickly be repurposed for multiple industries and other spheres of human activity, including:
• Hospitals: drug delivery, transportation of food and medicine
• Cleaning: automatic cleaning of large areas, such as supermarkets, airports, industrial sites
• Warehouses, Distribution, and Logistics: efficient relocation of materials from stocking shelves to order fulfillment zones
• Industry: assembly, materials delivery
• Military and Security: diffusion of explosives, providing vision and monitoring in dangerous areas
• Mining: exploration of the mines, operation in hazardous areas
• Shipyards: performing welding and cutting
• Research: volcanic research, Antarctica and Arctic research
TIERA team co-leader Prof. Hamid Roozbahani told Hazardex that the team aimed to continue testing up to the end of March 2018, and to apply for IECEx or similar certification to use the robot in potentially explosive atmospheres soon after.
TIERA is already capable of performing to a certain level in difficult environments. During design, development and parts selection the team aimed to satisfy quite a long list of standards. For instance all the electronics used in the robot have IP67 and mechanical parts have IP42051, Roozbahani said.
His colleague Prof. Heikki Handroos said the technology was likely to see early use in nuclear reactor remote maintenance systems research. The group is participating in the EUROFUSION DEMO project and is collaborating closely with China’s Institute of Plasma Physics (ASIPP), he said.