Soft pneumatic grippers for reducing fruit damage during strawberry harvesting

Abstract

Strawberry is a delicate fruit that has substantial economic value. Strawberries can be easily damaged during harvesting due to their soft nature. Therefore, strawberry harvesting requires skilled labourers who can gently yet effectively handle this soft fruit. There is a skilled labour shortage for strawberry harvesting, so automating this process would benefit strawberry farmers. Here we present a novel soft gripper design to minimize strawberry damage during harvesting. The proposed gripper comprises two doughnut-shaped single chamber pneumatic actu- ators inspired by biological Sphincters. The proposed balloon-type actuator is fabricated from thermoplastic polyurethane (TPU) coated fabric by thermal sealing. The blocked force performance of this balloon-type actuator and the holding force of the doughnut-shaped gripper is experimentally evaluated. The balloon-type actuator can apply 19.3 N at 40 kPa when displaced by 20 mm. The developed soft gripper can apply a holding force of 14.8 N at 40 kPa. Preliminary field testing was conducted to validate the applicability of the proposed soft gripper for strawberry harvesting. The field test showed 100% success in harvesting with 85 % success without any damage (n = 7). This shows the potential of the proposed soft gripper in reducing fruit damage during strawberry harvesting.