Design and experiment of screw drive granary robot running on the loose grain surface

Abstract: Most postharvest operations on bulk grain surface in the granary management are mainly done manually in current China, such as flatting the grain surface, spraying, turning over grain. In grain-processing industries, it is inevitable to bring high cost, time-consuming, labor-intensive, and dust working environment in the postharvest management. At present, the highly mechanized production requires a new computer-assisted support system for high quality preservation of stored grain. However, the current machinery working on the grain surface easily slips, or overturn, even losing some traction, due mainly to the surface of bulk grain is loose ground, particularly on the discrete corn. It is highly urgent to develop new automatic machinery with a strong driving ability on the loose grain surface, thereby providing a mobile platform for the work on the bulk grain surface. In this study, a novel Screw-Drive Granary Robot (SDGR) was designed to flexibly travel on the bulk grain surface in a granary, where the walking mechanism consisted of two screw-drive wheels with opposite rotation directions. The driving mechanism and control system was presented, according to the interaction relationship between the spiral and the grain surface. The walking robot with the control system can move forward, backward, rotate, and steer differentially on the surface of discrete corn. A running test was conducted under different driving directions and speeds using the prototype on the surface of bulk corn. The results showed that this kind of screw-drive robot has an excellent driving performance on the loose grain surface, where the process of driving in the straight line was very smooth in the field experiment. When the rotational speeds of helical driving wheels were 0.33, 1.06, 1.72, and 1.92 r/s, the straight-line speeds of the robot were 0.07,0.22,0.34, and 0.37 m/s, respectively, while, the rotational driving speeds of the robot were 0.10, 0.24, 0.39, and 0.53 r/s, respectively. Furthermore, the straight-line speed and rotational driving speed were directly proportional to the driving rotation speed of screw-drive wheels in the robot. The scale coefficients of linear fitting were approximately 0.197 and 0.251 for the straight-line speed and rotational driving speed, while, the coefficients were 0.999 5 and 0.993 3, respectively, indicating a highly significant linear correlation with the driving rotation speed of screw-drive wheels. The fitting curve showed that the slip rate increased gradually, whereas, the sinking depth gradually decreased, as the driving rotation speed increased, when the screw-drive robot running in a straight line within the test range of rotational speed. Specifically, the sinkage increased significantly, as the driving speed of the robot decreased in a straight line. In addition, the maximum sinkage was 70 mm, about 63.64% of the diameter of the drum in the robot, while the slip rates were very small, indicating the better mobility of the robot on the loose grain surface. This finding can provide a sound reference for the structural design and control system of the screw-drive granary robot traveling on loose grain surface in mechanized production.