Design and experiment of the strip-collected pre-positioning mechanism for safflower picking robots

Mechanical harvesting safflower has increased rapidly, with the continuous expansion of planting areas in recent years. However, the branch swing of safflower generally interferes with accurate visual recognition positioning and harvesting quality in selective harvesting of safflower. In this study, a strip-collected pre-positioning mechanism was proposed for a picking robots to adjust the morphology of safflower plants before visual recognition. The key factors were clarified on the swing of branches during harvesting, according to the growth characteristics of safflower, including the one branch has one safflower, the high growth center of the top of the fruit ball, the different opening time, and symmetrical distribution of spatial morphology of safflower plants. A safflower plants strip-collected mechanism also ran with the trunk position recognition to explore the plant shape for the pre-positioned state of strip-collected. The key working parts were designed to determine the structural parameters of safflower plants strip-collected and trunk position recognition mechanism. Specific works included: 1) A kind of safflower plant club mechanism was designed to meet the requirements of strip-collected operation, according to the four-bar kinematics. The key parameters were also optimized for the strip-collected clamping plate drive mechanism and strip-collected clamping plate. 2) The cam motion was utilized to determine the key parameters of trunk position recognition. The position relationship between the strip-collected operation and each working section of the cam was further analyzed to match the working stroke of strip-collected operation and the trunk position recognition. 3) A field test showed that the qualified rate of exposed length of anti swing branch was 80.53%, the fruit ratio of safflower fruit ball was 2.04%, the damage rate of plant was 0.47%, the damage rate of fruit ball was 1.04%, the width-to-width ratio was 16.64%, the dispersion of fruit ball was 83.76%, and the shading rate of fruit ball was 6.51%. Consequently, the strip-collected pre-positioning operation can effectively reduce the swing of the branches, where the whole safflower fruit balls are orderly distributed, and finally reduce the difficulty of identification and picking of the whole safflower. This finding can provide a sound theoretical basis for automatic safflower picking in modern mechanical harvesting.