| Grain storage is an important link to ensure grain,to prevent grain mildew and moisture condensation caused by grain quality decline.It is necessary to monitor the CO2concentration,temperature and humidity and other information in the granary.Replacing manual operation with granary detection robot s can significantly reduce the manpower cost of grain situation information collection.At present,because of the large size,easy to overturn,movement limitation and other problems,the existing granary robot only works on the grain surface,and it is diffic ult to complete the information collection in the depth of the grain pile.Therefore,this paper proposes and designs a drill-in spiral robot（spiral robot for short）for the collection of grain situation information in the depth of grain pile.it has good movement space when walking and turning inside the grain pile,which can solve the problem of difficult detection inside the grain.The main research of this paper is as follows:（1）According to the operating environment characteristics and design requirements of the granary,the screw was selected as the driving mechanism of the drill-in spiral robot for granary.A spiral transport mechanism was arranged in the middle position of the robot to transmit grain to reduce movement resistance.The overall structure,driving structure and screw transport mechanism of the robot were designed.The steering performance of the robot was analyzed and the motion control strategy of the robot was given.（2）The trajectory of the screw in the space coordinate system was described and the kinematics model of the robot in the grain pile was established.The kinematic model of grain particles in spiral transport mechanism was established.The normal stress and shear stress of screw at different depths were analyzed.Combined with Janssen’s theory of grain storage pressure and Janosi’s shear-displacement equation,a shear stress model was established.Then the dynamic model of screw was derived from shear stress model.It provides theoretical basis for robot control system design.（3）DEM-MBD co-simulation was used to simulate the walking process of the robot.The effects of screw helix angle,blade height,rotation speed and operating depth on the robot’s motion performance were studied by single factor expe rimental design method.Orthogonal test was carried out on the main influencing factors.The best walking performance was determined when the screw helix angle was 35°,the screw blade height was 8mm and the screw speed was 5r/s.The steering simulation experiment was carried out to verify the influence of different speed difference on steering.（4）The experimental device was designed and built.A single screw was placed in a grain pile,and the speed of the screw and the height of the grain pile were selected as influencing factors.Different speed and pressure combinations were used for full factor experiments.The axial force and resistance torque of screw were measured by torque sensor and pressure sensor.The propulsive characteristic curve of screw was obtained.The measured experimental data were analyzed and compared with the theoretical values.The average relative error of the axial force model is 14%and that of the resistance torque model is 24%. |
