Low-damage mechanised harvesting of shallots: from biomechanical interaction mechanisms to bionic and flexible design strategies.

With the rapid expansion of the shallot industrial scale, the high costs and low efficiency associated with traditional manual harvesting have emerged as core bottlenecks restricting the sustainable development of the industry. When deployed in shallot fields, existing general-purpose root-crop harvesting equipment encounters a typical engineering mechanics contradiction: the "high pull-out resistance of deep root systems" versus the "high vulnerability of tender pseudostems". Consequently, achieving efficient, intact, and non-destructive harvesting remains challenging. To address the technical difficulties of the low-damage mechanised harvesting of shallots, this review systematically summarises the research progression of core engineering strategies based on the microscopic "machine-soil-plant" interaction mechanism. First, the viscoelastic rheological characteristics of shallot pseudostems and the pull-out mechanical responses of root-soil complexes are analysed to establish the physical damage boundaries for mechanical operations. Secondly, the bionic drag reduction technologies for soil-engaging components are highlighted, evaluating the efficacy of macroscopic geometric bionics and microscopic non-smooth surface features in optimising cutting stress fields and severing interfacial adhesion networks. Furthermore, the evolution of compliant mechanisms in the non-destructive clamping and conveying of pseudostems is explored. This includes an in-depth analysis of adaptive clamping mechanisms, which are transitioning from passive rigid-flexible coupling towards morphological enveloping driven by soft actuators. Finally, addressing the current wear-resistance bottlenecks of bionic materials in complex adhesive environments and the dynamic adaptation limitations of rigid-flexible coupled systems, this paper proposes cutting-edge developmental trends. These encompass the integration of multi-body dynamics and discrete element method (MBD-DEM) coupled simulations, alongside machine vision-based intelligent closed-loop control. This review aims to provide rigorous theoretical support and system integration references for the research and development of a new generation of intelligent, low-damage shallot harvesting equipment.