Given the hostile conditions of extraterrestrial environments, unmanned rovers play a critical role in the exploration of planets and moons. NASA's Mars and lunar exploration rovers have significantly contributed to our understanding of these extraterrestrial bodies. Planetary surfaces often present challenging landscapes with slopes, craters, and dunes. More importantly, the presence of regolith, fine particles that cover these surfaces, poses a significant challenge for rover mobility. The slipping of rovers on these loose surfaces can hinder their progress and even jeopardize their missions.
Various methods, primarily relying on visual data from cameras, have been explored to detect the traveling state or slip condition of rovers. However, these methods have limitations as they may struggle to differentiate between various terrain features such as distinguishing rocks from loose sand. A solution to this problem is for the rovers to obtain information about the traction on each wheel. This way, the rover could detect its traveling state faster and correct its posture to avoid slipping.
To realize this, Professor Kojiro Iizuka from the Department of Machinery and Control Systems of the College of Systems Engineering and Science at Shibaura Institute of Technology (SIT), Japan, and Dr. Kohei Inaba, also from SIT, have recently developed a novel system that allows a rover to detect its traveling state by the change in shape of its chassis. "Our inspiration came from how humans detect their own traveling state based on muscle tension while walking. We aimed to develop a similar system that recognizes the traveling state based on the chassis shape deformation," explains Prof. Iizuka. Their study was published in Volume 15, Issue 17 of the journal Remote Sensing on August 30, 2023.
The muscles in the human body have special muscle fibers called nuclear chain fibers and nuclear bag fibers which help in detecting the traveling state of the body. The nuclear chain fibers detect the displacement of the tension in the muscles and help in determining the static posture of the body. On the other hand, nuclear bag fibers detect how fast muscle fibers stretch and help in detecting the dynamic state of the body.
Drawing parallels with human muscles, the researchers classified the change in the shape of the chassis of the rover, which manifests as strain, into two categories: displacement of strain and vibrational change in strain. They studied the strain displacement data using nuclear chain fibers analysis and strain velocity as nuclear bag fibers analysis.
The nuclear chain fiber analysis revealed that the forces acting vertically and in the direction of the rover's motion changed with strain. Therefore, monitoring strain changes can enable the detection of force alterations, ultimately indicating the rover's traveling state. In addition, through nuclear bag analysis, the researchers found that the rate of strain change could effectively gauge the level of slippage and subsequent alterations in the rover's travel state. Using this data, the system can determine the rover's condition in real time, thus enabling the rover to make essential maneuvers to avert potential slipping incidents.
The study also emphasizes the system's capabilities to detect environmental obstacles, such as rocks and stones, highlighting its potential to enhance the safety and efficiency of rover operations.
Highlighting the importance of this study, Prof. Iizuka remarks: "During rover route planning, the experiences from this study should be considered to ensure that the rovers can travel safely. These findings represent the first step towards incorporating elements of biological functionality in sensing moving objects. We believe that our approach will also be effective for unmanned aerial vehicles and automatic driving in the future."
In conclusion, this innovative study marks a significant step towards improving the safety and effectiveness of rover missions, promising advancements in our exploration of other planets and celestial bodies.
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Reference
DOI: https://doi.org/10.3390/rs15174270
About Shibaura Institute of Technology (SIT), Japan
Shibaura Institute of Technology (SIT) is a private university with campuses in Tokyo and Saitama. Since the establishment of its predecessor, Tokyo Higher School of Industry and Commerce, in 1927, it has maintained "learning through practice" as its philosophy in the education of engineers. SIT was the only private science and engineering university selected for the Top Global University Project sponsored by the Ministry of Education, Culture, Sports, Science and Technology and will receive support from the ministry for 10 years starting from the 2014 academic year. Its motto, "Nurturing engineers who learn from society and contribute to society," reflects its mission of fostering scientists and engineers who can contribute to the sustainable growth of the world by exposing their over 8,000 students to culturally diverse environments, where they learn to cope, collaborate, and relate with fellow students from around the world.
Website: https://www.shibaura-it.ac.jp/en/
About Professor Kojiro Iizuka from SIT, Japan
Kojiro Iizuka is currently a Professor at the Department of Machinery and Control Systems at the College of Systems Engineering and Science of Technology at Shibaura Institute of Technology (SIT), Japan. He received an M.S. degree in Mechanical Systems Engineering from the Tokyo University of Agriculture and Technology, Japan, in 1999 and his Ph.D. degree in Space and Astronautical Science from the Graduate University for Advanced Studies, Japan, in 2006. His research at the Terra-Mechatronics Researches Laboratory at SIT focuses on soft-ground driving systems and robotics. He has published around 90 research papers, which have been cited over 150 times.
Funding Information
This work was supported by JSPS KAKENHI Grant Number JP21K03952.
