Gentle handling of strawberries using a suction device

This study investigated the feasibility of gentle handling strawberries using a suction device. This picking-up method, in which the fruit itself is moved towards the suction device by a suctioning airflow, is proposed to prevent damage to the pericarp. The picking-up equipment comprises a Cartesian coordinate manipulator, suction device, machine vision system, belt conveyor, and control unit. The suction device has a tapered tube with an inner diameter of 25 mm, and generates a suction airflow of approximately 45 l min−1. The machine vision system assesses the orientation of the fruit, and the suction device approaches the fruit along the line of fruit orientation. An investigation of the effective space for suctioning revealed that the smaller the fruit, the larger the effective space. Its height was about equal to or slightly greater than half the fruit diameter; however, the permissible distance in the transverse direction was small. Because the inclination of the suctioned fruit varied considerably, our proposed picking-up method was not always able to hold the fruit in a constant posture. In the approach position (80° from the vertical), the suction device required a suction force more than double that required in the vertical position. In picking-up performance tests, success rates for four cultivars were more than 95% without dropping the fruit at an approach height of 16 mm; however, the rate decreased to 71.9% for the long-tapered ‘Deco rouge’ at a height of 19 mm. The time required to pick and transfer a fruit was 8.9 s.