Granular Material-Based Soft Gripper for Precision Chocolate Handling

This paper presents the design, implementation, and experimental validation of a granular jamming-based soft gripper for precision manipulation of delicate food products. Addressing the critical challenge of automating the handling of thermosensitive objects (e.g., chocolate), this work develops a vacuum-actuated gripper filled with ground coffee that conforms adaptively to irregular geometries without inducing damage. The system comprises a spherical granular membrane (maximum capacity: 350 g), a KUKA KR10 robotic arm, and closed-loop control via pneumatic actuation. Experimental validation consisted of 100 pick-and-place trials at three distinct operational speeds (50%, 75%, 100%) using chocolate bonbons of five different geometries. Results revealed a speed-accuracy trade-off: at 50 % speed, the gripper achieved 99.56% ± 0.36% success with 10.41 s cycle time; at 75 % speed, performance degraded to 97.53% ±1.14% with 9.10 s cycle time; at maximum speed (100 %), success dropped to 91.10% ±1.73 % with 7.37 s cycle time. Positioning error remained minimal (0.66-1.17mm across all speeds). Critical analysis reveals that 75% operational speed provides optimal balance between throughput (386 chocolates/hour) and reliability greater than 97 %. Compared to conventional rigid grippers, this granular approach demonstrates superior adaptability to product geometry variation and reduced product damage. Integration of real-time visual feedback could enable near- 100 % performance at higher speeds through corrective trajectory adjustment.