Research On Motion Stability Of An Articulated Vehicle In Unstructured Terrain

For years, professors in vehicle and robotics field focus on the research and design of the locomotion concepts running in unstructured terrain. In this paper, we present an innovative passive frame for rough terrain supported by the National High-Technology Research and Development Program ("863" Program) of China. The innovative locomotion has the 2 DOF articulated frame, four-wheel drive and articulated steering. With reshaping its articulated assembly, the frame could adapt the terrain automatically and achieve the excellent unstructured-terrain mobility eventually.The articulated frame (AF) has been separated into two parts, front body and back body, which are joined by a 2 DOF hinge assembly. Two bodies could rotate along x and z directions separately. The innovation structure reduces the torsional stiffness and torsional angle of entire frame.The AF shows the well following performance, Which also causes the complicated motion of these two bodies, when it runs in terrain. The mass ceters of all the bodies have the complex traces. In this paper, the written mainline performs by dynamic model, theory analysis, comparison test and simulative application.It is important to establish an accurate mathematics model to describe the motion characteristic of AF. When AF is running in the terrain, the moving and rolling movement of the front body or the back body creat a complicated mutibody system. The motion state is determined by the variation of elements including displacement, velocity, acceleration and angular velocity. The model has been establish based on three-dimensional space. The analytical model has been developed with yaw angle, pitch angle, roll angle of back body and relative pitch angle, roll angle of front body investigated.Do research on the movement details of two bodies to observe the articulated steering process. The transfer function, steering angle input and yaw rate out, has been deduced by the foundation model. The foundation model has been vetified by the similar trends of curves, which obtained from experiment and simulation.The obvious characteristic of terrain is unstructured obstacle. All the tires do not appear on the same plane, when AF moves in terrain. It is necessary to establish an inverse kinematics using the transformation relation of each body coordinates. The model would be developed assuming fixed the frame and moved terrain. We can get the AF motion characteristic with the tire coordinates input. The simulation results indicate that:The increase of the vehicle velocity or the obstacle amplitude, causes the intensity of palstance, so are the energy of movement and rotation. The AF performs much more unstable characteristic.The excellent moving ability of AF in unstructured terrain determined by the structure of 2 DOF assembly. If one of the bodies loses its stability, this body could rotate continuously until it knocks on the block of the hinge assembly. After that, all the bodies would be in move-together state till they lose the entire stability. The tip-over stability of the entire frame is determined by the state of the stable one before they move together.We define the correlative stability for AF, to demonstrate the influence that the stability of single body and the hinge state between the bodies work on the entire frame stability..The degree of correlative stability is proposed to describe the correlative stability.The simulation results base on the former model indicate the influence of the roll angle, yaw angle between two bodies, and the vehicle velocity. The analyses conclude that:If the slope angle of front body forms the same direction as the back body, AF keeps stable. The steering movement helps in increasing the degree of correlative stability. If the slope angles of two bodies form the opposite direction, AF performs unstable characteristic. The steering movement destroys the degree of correlative stability.The main innovations as followed: 1. The articulated frame with active steering control and passive follow terrain abilities has been proposed.2. The model has been established based on three-dimensional space. The analytical model has been developed with yaw angle, pitch angle, roll angle, longitudinal direction, lateral direction, vertical direction, and the sideslip angle of tire investigated.3. We define the correlative stability for AF. The research on the static correlative stability and the dynamic correlative stability emphasize the process, which demonstrates one of the bodies loses its stability, this body could rotate continuously until it knocks on the block of the hinge assembly and then all the bodies would be in move-together state till they lose the entire stability.