Peduncle Gripping and Cutting Force for Strawberry Harvesting Robotic End-effector Design

Abstract

Robotic harvesting of strawberries has gained much interest in the recent past. Although there are many innovations, they haven't yet reached a level that is comparable to an expert human picker. The end effector unit plays a major role in defining the efficiency of such a robotic harvesting system. Even though there are reports on various end effectors for strawberry harvesting, but there they lack a picture of certain parameters that the researchers can rely upon to develop new end effectors. These parameters include the limit of gripping force that can be applied on the peduncle for effective gripping, the force required to cut the strawberry peduncle, etc. These estimations would be helpful in the design cycle of the end effectors that target to grip and cut the strawberry peduncle during the harvesting action. This paper studies the estimation and analysis of these parameters experimentally. It has been estimated that the peduncle gripping force can be limited to 10 N. This enables an end effector to grip a strawberry of mass up to 50 grams with a manipulation acceleration of 50 m/s$^2$ without squeezing the peduncle. The study on peduncle cutting force reveals that a force of 15 N is sufficient to cut a strawberry peduncle using a blade with a wedge angle of 16.6 degrees at a 30-degree orientation.

Figures (10)

• Figure 1: Strawberry harvesting end effectors: [a]. Parallel jaw mechanism for simultaneous attachment and detachmenthayashi2010evaluation, [b].Suction head for attachment and blade action for detachmentarima2004strawberry, [c]. Suction head and two jaw fingers for attachment and bending action of end effector for detachmentyamamoto2014development, [d].Suction cup for attachment and thermal based detachmentfeng2012new, [e]. Soft gripping for attachment and followed by rotation with pulling action for detachmentde2018development, [f]. Detachment without any attachmentxiong2018design
• Figure 2: Universal testing machine (UTM) for applying and recording the compression force on specimens used for our experimental study.
• Figure 3: Blade profile measured using Scanning Electron Microscope
• Figure 4: (a). 3d printed fixtures (b). Experimental setup of studying cutting forces and its variation with change in angle of cut
• Figure 5: Force profile recorded for the specimens while applying compression load by the extending UTM ram. The final squeezing force is not presented here as the peak force (F$_{C}$) before sudden drop is the point of interest