Motion analysis and parameter allocation of a two-stage apple-harvesting robot

Abstract

A two-stage apple-harvesting robot was analyzed to improve motion coordination and harvesting efficiency in dwarf and high-density orchards. Screw theory was used to formulate the forward and inverse kinematics and spatial Jacobians of the positioning and picking mechanisms, while the Lagrangian and Newton–Euler methods were used to establish their dynamic models. Three predefined joint motion-time allocation schemes were compared under the same cycle constraint, and the link-length-proportional scheme was selected for subsequent analysis and experiments because it produced comparatively smooth actuator-load responses. Numerical comparison with an ADAMS rigid-body model showed close agreement under matched assumptions. Payload analysis indicated that the translational joint was most affected by increased fruit load. Planar boundary-point tracking tests produced maximum errors of 1.7 and 1.9 mm in the Y and Z directions, respectively, while the maximum joint errors were 1.7° for revolute joints and 1.6 mm for the prismatic joint. Orchard experiments achieved 287 successful picks among 371 targets, corresponding to a pooled success rate of 77.36% (95% Wilson CI: 72.83%-81.32%), with a mean picking time of 6.94 s per fruit. These results demonstrate the feasibility of the proposed modeling and motion-parameter allocation framework under the tested orchard conditions.

Keywords

Apple harvesting robot / screw theory / motion characteristics / motion-parameter allocation / dynamics

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