Author：Kaohsiung District Agricultural Research and Extension Station
I. Introduction
Figure 1. Manual removal of onion stems, leaves, and roots.Onion is an important cash vegetable in Taiwan, with a planting area of 1,399 hectares and an output of 75,768 tons in 2018. It is mainly cultivated in regions including Pingtung County, Yunlin County, Changhua County, and Kaohsiung County. Onion seedlings can be harvested about 4 months after field planting, which is time-consuming and labor-intensive in the cultivation management process as, from seedling raising and transplantation to harvesting, many operations including planting, pest and disease management, intertillage and weeding, fertilization, and harvesting and transportation need to be implemented. Pest and disease management, intertillage and weeding, and fertilization have been mechanized in onion cultivation management. However, planting, harvesting, and stem and leaf (or root hair) removal are still performed manually (FIG. 1).
In manual operation, planting and stem and leaf (or root hair) removal requires the most labor. In the early days, onion harvesting was assisted by military troops. In recent years, however, due to the reduction of military manpower (which leads to decreased military assistance in harvesting), shortage and aging of rural labor force, and rising wages, production costs have increased as market competitiveness decreased. Additionally, young adults are more and more unwilling to engage in farming, leading to a decrease in area planted with onions. To solve the above-mentioned problems, increase operational efficiency, and improve the working environment, the mechanization of onion stem and leaf (or root hair) removal is imperative.
II. Materials, Equipment and Methods
(I) Materials
Figure 2. The onion stem, leaf, and root removal machine.1. Stainless steel materials
The body of the onion stem, leaf, and root removal machiner is made of stainless steel (FIG. 2), with the surface of the steel plate being treated with electroplating technology. The steel plate is mainly for the installation of various transmission and control systems or leaf-cutting mechanism modules. The control unit is hidden inside the body. That is, the external body is resistant to washing to maintain the equipment and facilitate the normal operation of the equipment.
2. Electrical control elements
Various electrical control elements including circuit breakers, single-phase (or three-phase) motors and motor variable frequency drives, magnetic contactors, thermal relays, and other elements are used for the machine. The machine mainly uses two sets of inverters to control the speed of stem and leaf turning and conveyance as well as root turning and conveyance.
3. The onions are of the Golden No. 3 variety cultivated by the villagers from Fenggang Village in Pingtung County, and the samples are collected the day after harvest.
(II) Equipment
1. Construction of the machine body
The main structure of the machine is divided into two major units, namely the stem and leaf turning mechanism (including the conveying screw rod and leaf cutter) and the root hair turning mechanism (including the brush-made conveying screw rod and root cutter).
2. Mechanism elements
(1) Stem and leaf turning mechanism (FIG. 3)
To prevent damage to the onions due to high pressure and impact during feeding and conveyance, the conveying screw rod for stem and leaf turning is covered with soft rubber materials.
(2) Root hair turning mechanism (FIG. 4)
This mechanism consists of elements with soft brushes made into the shape of a screw. The main function of the mechanism is to press the onion root hairs downward with the screw-shaped plastic brushes and make the onion root hairs stand upright at the bottom.
Figure 5. The clamping mechanism and cutter.(3) Clamping mechanism and cutter (FIG. 5)
The clamping mechanism includes cylinders consisting of soft sponge. The main function of the mechanism is to clamp and fix the onions to be turned and conveyed by the screw rod to facilitate the removal of stems, leaves, and root hairs.
In addition, a cutter is a device with two jagged blade discs opposite to each other. The main function of the cutter is to assist in clamping and fixing as well as removing the stems, leaves, or root hairs.
(III) Methods
1. Implementing turning, clamping, and cutting tests with onions in different size and of different diameters (43mm to 118mm).
2. Testing turning, pushing and conveying, and clamping capabilities as well as the effectiveness of cutting at different rotational speeds of the conveying screw rod.
III. Results and Discussion
(I) Results
The machine is for performing an integrated operation of conveying, turning, clamping, and removing stems and leaves (or root hairs) with the mechanisms after manual feeding.
1. The process of removing onion stems, leaves, and roots mechanically is as follows:
2. Physical property tests of (onion) samples (Table 1): The average diameter is about 78mm (with a minimum of 43mm and a maximum of 118mm); the average height is about 83mm (with a minimum height of 69mm and a maximum height of 102mm); the average length of root hairs is about 85mm (with a minimum of 60mm and a maximum of 112mm); the average length of stems and leaves is 413mm (with a minimum of 381mm and a maximum of 456mm).
Table 1. Survey of Physical Property of Onions.3. Conditions after removal of stems, leaves, and root hairs
(1) Manual removal: Stems and leaves are left at 2cm to 3cm while root hairs are completely removed (FIG. 6).
(2) Mechanical removal: Stems and leaves are left at about 2cm to 6cm, and root hairs at about 1cm to 5 cm. The removal of root hairs is challenging. Root hairs crinkle after the onions are pulled out and dried, making them difficult to remove (FIG. 7).
(II) Discussion
1. Comparison between manual and mechanical operations:
Though onion stems, leaves, and root hairs are more neatly pruned in manual removal operation than in mechanical removal operation, manual removal is more laborious and has a risk of dangerous occupational injury due to long periods of work. In terms of the efficiency of manual operation, the removal for an onion is completed about every 3 to 5 seconds. On the other hand, the removal for an onion is completed about every 1.5 to 2 seconds in mechanical operation (single-line operation).
2. Mechanical pruning problems:
(1) When the diameter of the onion is less than 50mm, or if the onion has poor smoothness due to the outer film of the onion skin peeling off, the onion would be easily caught by the turning and conveying screw rod, which results in damage to the onion skin.
(2) Every onion is different in the diameter’s length and clamping positions, affecting the length of the cut stems, leaves, and roots. The longer the diameter of the onion, the longer the stems and leaves left after cutting. The shorter the diameter of the onion, the shorter the stems and leaves left after cutting.
(3) When the rotational speed of the turning and conveying screw rod is greater than that of the clamping mechanism, the screw rod causes a pushing phenomenon and results in ineffective clamping as well as uneven heights.
(4) The jagged cutters leave a jagged cross section on the cut onion stems and leaves, which is widely considered a disadvantage by farmers.
IV. Conclusion and Recommendations
An onion stem, leaf, and root removal machine is designed and manufactured based on the aforementioned mechanisms. After operational efficiency tests, the time required from feeding to the completion of stem, leaf, and root hair removal turned out to be about 1.5 to 2.0 seconds per onion. Though the mechanical operation of root hair removal is not satisfactory, farmers consider the completeness of root hair removal to be of little concern as onion root hairs fall off automatically once dried. As a result, since the machine removes stems and leaves completely and is more effective than manual operation, the goal of saving labor can be achieved. Furthermore, danger and injuries incurred due to carelessness during manual operation can be avoided. Hence, research on onion stem, leaf, and root removal machine provides substantial assistance and contribution to the operation of removing onion stems, leaves, and roots.
The machine developed in this R&D process is a single-row machine. Although its operating efficiency is 1-2 times that of manual operation, to further increase the efficiency, an increase in the number of rows in operation is recommended. In addition, regarding the problem of the turning and conveying screw rod damaging the onion skin when clamping, it is recommended to use a stainless steel material with good smoothness for the turning and conveying screw rod.
