Trafficability Research And Design For A Six Articulated Wheel-legged Forestry Machinery Chassis

At present,the chassis of forestry equipment has some limitations when traffic across the difficult surface such as shrubs,obstacles,sinkholes,steep slopes and high mountain corners.The research and development of the chassis with high trafficability and stability is helpful to solve the problems.In this paper,the structure of a six articulated wheel-legged forestry chassis is proposed.The chassis has the advantage of a larger adjustment rangement,so that the chassis can pass through obstacles more smoothly.The main research work and innovations are as follows:1.The structure of the articulated wheel-legged chassis is proposed based on the combination between the characteristics of the forestry machinery chassis and the articulated mobile robots.The structure is a seriel-parallel hybrid mechanism with the articulated steering form from the forestry machinery chassis.The combination of the four-bar pendulum arm and the “doorlike” pendulum arm is used as a series arm in a chassis for the first time.The parameters of the pendulum arm and the installation position and stroke of the hydraulic cylinder were optimized based on the genetic algorithm.The finite element method was used for checking the pendulum arm.A test prototype was developed in the proportion of one tenth as the designed chassis for verification.2.Analysis of chassis' s profile trafficability: G-K algorithm was used to calculate the degree of freedom(DOF)of chassis and the kinematic model of chassis was established based on the screw theory to get the coordinates of wheel's center points.According to the kinematics model,the side slope leveling capacity of the chassis is 28.7°and longitudinal slope leveling capacity is 22°.The minimum passing radius is 3088 mm.The flexible wheel center coordinates of the test prototype chassis were modified based on the finite segment method.The correctness of the chassis kinematics was verified through the comparison of the test prototype data.Finally,the advantages and disadvantages of various forestry chassis were compared and summarized.3.Dynamic characteristics analysis of the chassis obstacle surmounting: Based on certain assumptions,the dynamics model of the chassis was established by the Lagrange equation.The dynamic model of the four-bar mechanism was simplified through the least square method to replace the complex nonlinear relationship.The model was verified by simulation.The vertical wheel force and the chassis tilt angle were influenced by the swing arm's extension.A slope passing strategy was proposed based on the former analysis.The simulation and test results showed that the strategy of passing slope can reduce the tilt angle of the prototype and the passing time at the same time.4.Dynamic characteristics analysis of chassis obstacle avoidance: The steering radius of the chassis is the main factor affecting the obstacle avoidance ability.Based on certain assumptions,Lagrange equation is also applied to the the chassis' s obstacle avoidance dynamic model.Combined with the simulation of ADAMS,the steering radius of the chassis with different pose and position were analyzed under the condition of maximum turning angle.The minimum steering radius,which was 724.9mm,was obtained when the inner pendulum arms extend and the outer ones contract.According to the design requirements,the process of trees avoidance in fixed scene is simulated.