Design, Fabrication and Evaluation of a Hand-Operated Semi-Automatic Chopping Machine for Leafy Vegetables and Medicinal Herbs

A hand-operated semi-automatic vegetable chopping machine was designed, fabricated and evaluated to introduce an efficient chopping machine to ease the preparation of leafy vegetables and herbal medicines. The main features and components of the chopping machine were integrated cutting and feeding mechanism, operating handle, cylindrical container, piston, collecting drawer and the frame. The machine was designed to operate manually reducing the operational & capital cost and to ease the use in rural areas, where there is no electrical supply. A performance test was done for this machine using four different leafy vegetables and medicinal herbs [ Mukunuwenna ( Alternanthera sessilis), Kankun ( Ipomoea aquatica), Gotu kola ( Centella asiatica ) and Kathuru murunga ( Sesbania grandiflora) ] in comparison with manual chopping using a general kitchen knife. Five unskilled males and females were involved in a performance test with three replicates. The three-factor factorial experimental design was used in the evaluation. The actual capacity and the efficiency of the chopping machine were 1.81 kg h -1 and 74%, respectively compared to 1.02 kg h -1 and 76% of the manual kitchen knife. The average width of a particle cut by machine and kitchen knife were 1.87 mm and 3.38 mm, respectively. According to the user-feedback, this machine is a safe, affordable and convenient device for processing vegetables and herbal medicines.


Introduction
Leafy Vegetables are categorized under protective foods, because they are highly beneficial for good health and disease prevention (Subhasree et al. 2009).
Globally, vegetables are processed in various ways in the day-to-day life (Darkwa and Darkwa 2013

Design concept
This design integrated two main mechanisms as feeding and cutting, which were operated manually. A vertically rotating circular metal plate was fixed with two sharp blades and rigidly fastened to a horizontal threaded iron axis. A split nut was connected to the threaded iron so that the nut moves horizontally when the thread iron spins.
This movement of split nut pushes the piston towards the cutter, together with leafy vegetables inside the container.
The threaded axis was connected to an operating handle at the other end so that when the handle is rotated both the cutter and the feeding mechanism begin to function (Fig.1). Leafy vegetables should be packed tightly in the cylindrical container, in order to push them and cut simultaneously with handle movement. As the screw pitch of the threaded bar was 2 mm and two blades were fitted on exact opposite sides of the rotating plate, the theoretical minimum particle size would be 1 mm. Drawer type collector was placed below the cutter to collect chopped leafy vegetables. The simple mechanism of this machine with a threaded bar and a split nut gives higher durability with low maintenance.

Design considerations
The machine was designed giving high concern for user-friendly operation in removal of the processed product. To minimize the operational cost and to facilitate easy operation in rural areas, where there is no electricity supply, the machine was designed to work on manual power. The locally available standard materials were used in the fabrication in order to ensure the easy production, repairing and maintenance at the village level. All parts of the machine getting in contact with food items were fabricated with food-grade materials to avoid any possible health issues.

Cylindrical container and the piston
The container was an open cylinder into which the piston moves from the rear end and pushes leafy vegetables in it towards the cutter fixed close to its front end. The capacity of the container was 500 cm 3 with the dimensions of 6 cm and 18 cm, respectively for diameter and length (Fig.3).

Cutter section
Two stainless steel sharp blades were fixed on the exact opposite sides of a stainless steel circular plate of which the diameter was 16 cm (Fig. 4).

Collecting drawer
The capacity of the drawer type collector placed under the cutter was 600 cm 3 that would not be too small to collect all cut vegetables from the container. The special shape of the collector could collect all cut vegetable particles without dropping out. After cutting, the collector can be taken out very easily and emptied into another collector.

Material selection and fabrication
Availability, suitability for the working conditions and servicing and the cost were the major factors considered when selecting materials (Khurmi and Gupta 2005

Results and Discussion
After a series of tests and modifications, the design and the fabrication of the chopping machine was successfully completed (Plate 1). The cost of production of the machine was 6000.00 LKR, which includes both material and labour costs. However, the cost may be reduced further in bulk production.

Parameter Value
Length of the machine 47 cm Width of the machine 25 cm Height of the machine 25 cm The capacity of the container 500 cm 3 The capacity of the collector 600 cm 3 Screw pitch of the threaded bar 2 mm

The average width of sliced particles
The average width of the cut vegetable pieces is given in Table. 2.
As per the design specifications, the width of a cut particle needs to be 1 mm.
However, in the operational condition, it was approximately about 2 mm for all leafy vegetables tested. This is due to the different textures of leaves and stems, which effect on the shearing action of the knife. The inconsistencies were due to dragging of leafy vegetables downward through the gap between the container and the cutter and may also be due to the sharpness of the blade.

With high proportion of stem pieces of
Ipomoea aquatica the average size of cut pieces obtained were wider than 2 mm.
The similar sizes of cut pieces were observed in the manual method (knife) too.

User's feedbacks on the chopping machine
Summary of the user feedback is given in Table 5. All parameters tested were above the satisfactory level. More than 90% of the users mentioned that the appearance of the machine is acceptable and more than 80% guaranteed the safety of the machine (Table  5). However, possibilities were identified for further improvements.

Conflicts of Interest: The authors
declare that there are no conflicts of interest regarding the publication of this paper.

Conclusions
The new machine showed satisfactory results with a capacity of