Efficient weed control in orchards demands autonomous solutions due to labor shortages and rising operational costs. This study developed an autonomous orchard weeding robot featuring a detachable variable-width mechanism. The mechanism integrates contactbased obstacle detection to dynamically adapt to orchard environments with varying row spacings. The mechanism was designed to automatically adjust its weeding width and height, significantly enhancing coverage by reducing missed and redundant weeding areas. Field experiments conducted at two orchard sites demonstrated that, particularly in narrower working paths of 3.0 m and 4.0 m width, total weeding coverage markedly improved from approximately 87–92% (fixed-width operation) to over 99% (variable-width operation). Additionally, although the variable-width mechanism required an extra 22.7% power consumption (300W), its improved operational efficiency effectively reduced overall energy use per unit area. These results confirm that the proposed weeding system can significantly enhance both operational and energy efficiency, particularly in orchards with narrow interrow spacing and frequent obstacles.