Establishment and verification on static equivalent model of end load posture of continuum picking manipulator

Abstract: Harvesting machinery has been the focus of agricultural equipment in recent years, especially the picking manipulator. Traditionally, the picking manipulator consists of series multi-link structure, which owns good motive performance during assignment of fruit harvesting. However, the multi-link picking manipulator is difficult to cross through the complicated agriculture environment. Thus, this paper proposes a novel continuum picking manipulator for the agricultural harvesting. The continuum picking manipulator is a novel agricultural operation robot with full flexibility and self-adaptability, which provides a good ability to complete various tasks in the complicated agriculture environment. The main structure of the continuum picking manipulator consists of 4 fiber-glass rods, several guide shelves and rubber tubes. The fiber-glass rods cross the hole of the guide shelves and rubber tubes that form slide joint, and the guide shelves are distributed among the continuum picking manipulator uniformly through the separation of the rubber tubes. The movement of the continuum picking manipulator is fulfilled by 4 servo driven modules which are composed of ball screw slipway and servo motors. The space motion and the flexibility feature are due to the combination of bending motion of the fiber-glass rods, which are achieved through controlling 4 driven modules harmoniously. Although the flexible features of the continuum picking manipulator bring the considerable dexterousness in the process of fruit harvesting, the loading posture of the continuum picking manipulator has deformed, which affects motion performance of the continuum picking manipulator due to the flexibility feature. Thus, this paper presents an innovative method to solve the problem of load posture deformation at the free end of the continuum picking manipulator. Firstly, the kinematics is obtained and the workspace is analyzed. Secondly, the continuum pick manipulator is simplified by static analysis. Finally, the theoretical model of the loading posture is set up according to the theory of large deflection and the principle of unit force. The posture function of continuum picking manipulator and the free-end coordinates can be calculated based on the presented theoretical model, and the input variables are bending angle, rotation angle, length and the load. Further, the theoretical model is verified through the systematic multi-parameter experiments by using the distortionless camera with 50 mm focal length, and the load posture error between theoretical and experimental values is no more than 7.8%. Finally, the influences of different posture parameters and the load on the model errors of the continuum picking manipulator are discussed. The error increases with the load, due to the gravity effect and the structure of the continuum picking manipulator. The maximum free end position error is 7.8% and the minimum error is 3.8%. The presented theoretical model is featured with less calculation to fit on-line real-time control of the manipulator. Furthermore, this model can extend to multi-section continuum picking manipulator with consideration of each lower section is a payload of its upper sections.