Grasping behavior of the human hand during tomato picking

To comprehensively investigate the grasping behavior of the human hand during tomato picking, a new 16-channel data acquisition e-glove was developed and subsequently worn to randomly pick 60 tomatoes in a greenhouse. A 2-channel surface electromyography was used to record the electrical activity of the flexor pollicis longus and flexor digitorum superficialis in real time. Each fruit-picking process was divided into fruit-stem separation, fruit moving and release stages based on two peak pressures applied by the thumb distal region. The total grasping pressure at the moment of fruit-stem separation primarily depended on the intersection angle between the first and second stems of a fruit. Conversely, at the moment of fruit release, the total grasping pressure primarily depended on the fruit size (p < 0.05). The duration of the tomato-picking process ranged from 2.28 to 4.54 s. The duration of the separation between the first and second stems of a fruit ranged from 0.26 to 1.56 s, and the duration of the fruit release ranged from 0.34 to 2.02 s. The entry and departure sequences of 16 hand regions varied during picking. The frequency analysis results showed that the thumb distal region always entered first to contact the fruit surface for fruit-stem separation, while the ring finger distal region always departed first from the fruit surface for fruit release. At the moment of fruit-stem separation, the number of contact regions between the hand and the fruit significantly increased with the fruit size (p < 0.05), which was slightly different from that at the moment of fruit release. The distal regions of the thumb, middle finger and index finger always made the greatest pressure contribution to the picking of each fruit. The fruit surface pressure applied by the thumb and the other four fingers were moderately related to the mean absolute values of the electrical activity level of the flexor pollicis longus and the flexor digitorum superficialis, respectively.