Optimal design and experiment of 2-DoF five-bar mechanism for flower seedling transplanting

Abstract

The currently used large-scale flower seedling transplanting equipment is expensive and has poor adaptability, while the small-scale transplanting equipment has problems with seedling damage and low automation. In view of this situation, a 2-DoF five-bar transplanting mechanism for multiple-point picking to single-point planting was designed. In a motion cycle, the seedlings could be picked from the four holes of a seedling disc and then planted in the flowerpot at a given point through the motion control of actuators, where the coordination among the transplanting, flowerpot transporting, and seedling delivering in the developed system was simplified. For seedling picking, the end-effector inserted into the substrate near the root of the seedling stem for damage avoidance, the transplanting trajectory was designed based on the given trajectory-type waypoints that satisfies the requirements of flower seedling transplanting. Besides, the mathematical model was established, where the relationship of the motion between the parameters of the developed 2-DoF five-bar transplanting mechanism and the two actuators were optimized by the genetic algorithm. Finally, the corresponding control system was designed, the two actuators were driven by two servo motors, and the end-effector was controlled by an electromagnet in the transplanting arm to realize the seedling clamping and releasing motion. In addition, a dual servo motor synchronous linkage control method was established based on the DDA linear interpolation algorithm to reduce the deviation of the servo motors, the linkage control of the electromagnet and the motor was realized through a single-chip microprocessor to achieve the coordination of the actuators. The overall design was deployed in real transplanting working conditions for validation, where several 30-day broccoli seedlings were used as experimental objects. The seedling height was around 80–100 mm and the transplanting rate was 40 plants/min. Three sets of seedlings (384 seedlings in total) were transplanted with an average transplanting success rate of 91.81%.