Study On A Jointed Mobile Robot With Angle-changeable Tracks

Tracked mobile robots are widely employed in disaster area rescue, aerospace exploration, military reconnaissance and anti-terrorism. Because of promising application and the technical challenge, tracked mobile robots become one of the research hotspots in robotics technology. In unstructured environment, some Innovational design and theoretical analysis method should be used to improve terrain trafficability, obstacle-surmounting stability, anti-vibration and impact of tracked mobile robots. So in this paper, innovational structure, the interaction of track-terrain, centre of gravity(CG) kinematics and dynamics modeling, obstacle-surmounting motion planning, stability analysis and obstacle avoidance technology of a joint double-tracked mobile robot are introduced.In the first place, the innovational structure of a joint double-tracked mobile robot with an angle-changeable two segments of the platform frame is presented. When the robot meets a large obstacle or stairs, the movement attitude is adjusted by rotating of the front segment to make the robot have the good terrain trafficability and obstacle-surmounting stability. In order to prevent the tracks from dropping off so as to keep the necessary tension in process of climbing up an obstacle, adaptive method is presented according to the relationship between track’s variable angle and the forces.The interaction models of track-terrain are built based on the track system and terramechanics. At first the track system of the robot is divided into three parts: the front road wheel, the rear road wheel and the middle track. In the different parts of the track system, the terrain state is in the different process of loading, unloading and reloading. Therefore, the models of the three parts are different. And the whole model of the track system is obtained by connecting the three models. The influence of the track parameters on the trafficability is analyzed according to the whole model, and the interaction of track parameters and various terrain is introduced.The centre of gravity(CG) kinematics model is built, which plays an important role in the process of traveling over obstacles and climbing up stairs. Using this model, the effect of CG position, obstacle-surmounting motion planning, the robot pitch angle and the front segment rotation angle on obstacle-surmounting capability is analyzed. The maximum height formula of the obstacle which can be climbed up is obtained, and the relationship between the robot pitch angle and the height of the obstacle is introduced.Moreover, the movement posture of the front segment is adjusted to the changing terrain. So the CG position of the robot paltform is changed which affecting the static stability of the robot. Static stability of three typical rough terrains are chosen to be analyzed, namely, the common rugged terrain, the slope terrain and the stairs. The dynamics model of the mobile robot paltform is built based on Newton-Euler theory, and the dynamic stability criterions of the robot platform contacting stair steps in one point,two point and three points are obtained in the process of climbing stairs.The obstacle avoidance system of the robot is bulit based on multi-sensor detection and information fusion technology to the complex terrain. According to kinematic model of the differential driving robot and working principle of ultrasonic sensor, infrared sensors and electronic compass, multi-sensor information fusion method based on extended kalman filter(EKF), and obstacle avoidance algorithm based on fuzzy neural network are introduced.Finally, several experiments are designed for the obstacle-surmounting stability, terrain trafficability, complex road adaptability and obstacle avoidance performance of the joint double-tracked mobile robot. The analysis results are validated by these test results.