In context
Spherical robots have been studied for less than 30 years, offering unique rolling locomotion with a single ground contact point, enabling high maneuverability and potential applications in inspection, rescue, and surveillance. However, most designs use a rigid shell of fixed diameter, limiting their ability to traverse uneven terrain or pass through narrow gaps. This work addresses that limitation by introducing a variable-diameter spherical shell.
What was reported
Researchers at Dalian University of Technology designed a variable-diameter spherical robot with a shell composed of 20 hexagonal and 12 pentagonal cells, connected by custom joints, and covered with curved surface elements to ensure smooth rolling. A differential centering mechanism keeps internal components at the shell's center, allowing the diameter to be controlled between 220 mm and 329 mm via PID control.
The robot's motion is decomposed into linear and steering components. Lagrangian dynamics model the linear motion, with closed-loop control of the forward motor's angular velocity to track a Gaussian-based target speed profile. Steering is analyzed using the Newton-Euler method, with closed-loop control of the center-of-mass lateral bias, enabling uniform circular motion with a radius of about 1 meter.
When the robot falls, the shell's diameter change and the centering motors' resistance torque absorb impact, protecting internal electronics. The prototype uses FOC controllers, an MPU6050 IMU, and magnetic encoders for precise control. The maximum surface roughness due to diameter variation is only 3.82%, minimizing vertical displacement during rolling.
“The change in diameter of the spherical shell and the resistance torque of the motors in the centering mechanism are used to reduce the impact and protect the internal structure of the robot.”
Why it mattered
This design enhances the adaptability of spherical robots, allowing them to navigate varied environments by adjusting their diameter. The integration of variable geometry with robust control strategies could expand the practical use of spherical robots in industrial inspection, search-and-rescue, and other confined-space applications, where fixed-size robots face limitations.
Source: 《机器人》期刊 (robot.sia.cn) · Published 2024-09-15 · “一种变直径球形机器人结构设计与控制”