Design of hand-operated piggyback jaw gripper type simplified picker for pear

Abstract: In order to solve the problem of low efficiency and high labor intensity of pear picking, a hand-operated piggyback jaw type simplified pear picker was designed in this paper. The characteristics of pears were analyzed by selecting 3 kinds of pears commonly found in the market: 'Xuehua' pear, 'Yali' pear, and 'Apple-pear', the pear maturity was divided into A, B and C grades according to the fruit diameter size and the growth period. Referring to the previous research results on the shear mechanical properties of citrus and litchi fruit handles, the shear force measurement bench was constructed. Shearing tests of the fruit stem were carried out on the 3 kinds of pears with different maturity according to the lever principle. In the test, 60 fruits of each grade of maturity of each pear were taken and the average value of the measurement results was obtained. The result showed that the shearing force of the stems of the 3 varieties was different, with the increase of the fruit maturity level, the shearing force of the pear stems increases first and then decreases, the maximum shearing force of the fruit stem was 5.4 N among the 3 varieties. The picking device was composed of driving operating parts, picking head parts, adjustable straps and carrying "Z" type collecting bag. The length and position of the strap picker could be adjusted by pulling up the handle of the strap and pressing down the handle after moving the clamp block to the appropriate position according to personal use. The driving operating unit was connected to the picking head through the hollow aluminum tube through the dragline.The other components on the picking head were connected by cylindrical pins. The pear picking process was divided into 3 steps: in the first step, the operator placed the picking head near the pear and puted the pear into the tray of the picking head, so that the pear was accurately positioned. In the second step, the operator pulled the operating handle to hold the fruit and cuted off the handle. In the last step, after the picking, the operator released the operating handle, the clamping claw and blade automatically return to the position under the action of the reset spring, and the fruit slides into the fruit basket through the "Z" type collecting sack. The movement simulation of the picking head was conducted based on the software Recurdyn. The simulation result showed that the average shear force was 13.5 N, it was greater than the maximum shear force of 5.4 N which was the required shear force of the pear stem. The main stressed parts were analyzed based on ANSYS Workbench 15.0 software. The results demonstrated that the maximum deformation of the picker was located at the installation place of the picking head, and the maximum deformation was 0.072 571 mm, which was less than the maximum allowable deformation of the picker 0.1 mm. The maximum stress position of the picker was at the joint of the 2 rods. The maximum stress of the group was 19.267 MPa, which was much smaller than the allowable stress of the material 110 MPa, the strength of the picking device met the requirements. In order to verify the rationality of the design, the field experiments were carried out in the summer of 2018 at Mushan pear orchards in Shaoyang, Hunan Province. The test results demonstrated that the hand-held picker was simple and comfortable to operate. The picking efficiency was 57.1% higher than that of manual picking. The average damage rate was 1.0%. The reason of fruit damage during the picking process was maily that the diameter of the pear was more than 100 mm, which leaded to the wrong touch of the blade. The hand-operated piggyback pear picker improved the picking efficiency and the operational safety of picking process.