Coupled DEM–MBD analysis and experimental investigation of a dragon fruit end-effector

To address the excessive stem damage observed during robotic harvesting, this study designed a rotary cutting end-effector for harvesting dragon fruit. The operating parameters were optimised using a coupled Discrete Element Method–Multi-Body Dynamics (DEM–MBD) simulation. Based on the stem’s intrinsic properties, simulation parameters were calibrated through free-fall, sliding, and rolling tests. A double-layer discrete element flexible model of dragon fruit stems was then established, and the optimal working parameters of the end-effector were determined through Box–Behnken experiments. The results showed that the average density, Poisson’s ratio, and elastic modulus of the succulent part were 968.96 kg·m -3 , 0.329, and 0.981 MPa, while those of the lignified stem were 994.84 kg·m -3 , 0.293, and 8.931 MPa. The restitution coefficients of succulent stem–SKD11 steel, succulent stem–succulent stem, lignified stem–SKD11 steel, lignified stem–lignified stem, and succulent stem–lignified stem were 0.237, 0.280, 0.461, 0.273, and 0.331, respectively. The corresponding static friction coefficients were 0.598, 0.777, 0.289, 0.662, and 0.711, and the dynamic friction coefficients were 0.417, 0.591, 0.175, 0.265, and 0.446. Based on adhesive parameter calibration experiments, the optimal operating parameters of the end-effector were determined. When the closing speed was 5 mm·s -1 , the rotation speed was 5 r·min -1 , and the stretching speed was 15 mm·s -1 , the average leaf rib length after cutting was 2.601 cm, and the peak cutting force was 4.984 N. The average relative error between experimental and simulated results was 9.73%, verifying that the calibrated DEM parameters are suitable for simulating dragon fruit harvesting end-effectors.