This paper presents a procedure and the results of an optimal design of the kinematic structure of a manipulator to be used for autonomous cucumber harvesting in greenhouses. The design objective included the time needed to perform a collision-free motion from an initial position to the target position as well as a dexterity measure to allow for motion corrections in the neighborhood of the fruits. The optimisation problem was solved using the DIRECT algorithm implemented in the Tomlab package. A four link PPRR type manipulator was found to be most suitable. For cucumber harvesting four degrees-of-freedom, i.e. three translations and one rotation around the vertical axis, are sufficient. The PPRR manipulator described in this paper meets this requirement. Although computationally expensive, the methodology used in this research was found to be powerful and offered an objective way to evaluate and optimise the kinematic structure of a robot to be used for cucumber harvesting.
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