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Abstract: The purpose of this research is to design, fabricate, test, and evaluate the prototype
of a semi-automatic young coconut fruit cutting machine. The design concept is that fruit cutting is
accomplished by pneumatic press on a young coconut sitting on a sharp knife in a vertical plane. The
machine consists of 5 main parts: 1) machine frame, 2) cutting base, 3) knife set, 4) pneumatic system,
and 5) tanks receiving coconut juice and cut fruits. The machine parts contacting edible parts of the fruit
are made of food-grade stainless steel. In operation, a young coconut is placed on the cutting base and
the pneumatic control is switched on. The coconut is automatically moved to the pressing unit and cut
in half by a knife set. The coconut juice flows down to the tank while the cut fruits are separated and
moved into the other tank. The machine is found to operate safely without damage to the fruits. The
machine capacity is 480 fruits/hr with the total operating cost of about 2.63 USD/1000 fruits.
Keywords: young coconut, coconut cutting machine
Introduction
In Thailand, the Nam-Hom coconut, which is commonly known as the young coconut, is popular
for its nice scent, sweet juice and high nutritional value. The young coconut can be consumed fresh or
processed into canned products such as coconut juice and coconut jelly. The total export volume of
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young coconuts in 2006 was 33,334 tons and valued at 11.2 million USD [1]. The young fruit sold to
the fresh market is usually trimmed to its outer husk so that the coconut looks attractive and can easily
be opened. To ready the fruit for consumption, the husk and shell of the fruit must be cut open.
Traditionally, a big knife is used to manually chop the husk and shell and create a hole of approximately
60 mm diameter at the top of the fruit. However, this method is hazardous and requires a skilled
operator [2].
In an earlier attempt to open the coconut, Sapsomboon [3] invented a coconut opener for retail
sale. This device was made of a circular zinc strip with the bottom side made like a saw while the other
side was covered with a plastic dome. When the opener was covered on the top of the trimmed young
coconut, it was manually pressed and the plastic dome was turned around by hand, then the husk and
shell were cut by the saw strip of the opener. This opener was good for coconut retailing. The average
time for opening was 41.4 sec/fruit [4].
Jarimopas and Kuson [2] later designed and constructed a young coconut fruit opening machine.
The operating system was like a lathe machine which consisted of a fruit holder, a height control
mechanism, a knife and its feed controller, and a power transmission system. During operation, the
small stainless steel knife slowly penetrated through the husk and shell of the turning fruit in a direction
perpendicular to its surface, thus resulting in a circular opening at the top of the fruit. The speed of
opening each fruit was 30 seconds on the average.
However, in the industrial process of coconut juice canning for export in Pratumtanee province,
fresh coconuts are required to be cut in half without outer husk trimming. Figure 1 shows a manual
cutting machine for young coconuts consisting of a table with cutting base and a sharp knife which is
mounted to a cantilever bar and a spring. When the operator places a young coconut on the cutting
base and presses the cantilever bar, the coconut is cut in half by the sharp knife and the coconut juice
pours down into the bowl which is beneath the cutting base. This method is considered very awkward,
takes longer time and requires a strong operator for pressing the cantilever bar. Besides, the capacity of
production is 2000-3000 fruits per day. The objective of this research, therefore, is to design and
develop a semi-automatic cutting machine for the canned coconut juice industry. The specific objectives
include: (1) the design and development of the semi-automatic cutting machine for young coconuts at a
rate of 300 fruits/hour without outer husk trimming, and (2) testing and evaluation of the efficiency of
the cutting machine.
Materials and Methods
Design and operation
Design parameters for a cutting machine consist of the size of young fresh coconut and the
maximum compressive force used for cutting the coconut in half by a sharp knife. For the first
parameter, 20 uniform and intact samples of mature coconut were randomly selected, weighed and
measured by a size-measuring apparatus (Figure 2). The results of a 3-dimensional size of the fruit was
19.22±0.88 mm, 15.91±0.58 mm and 15.2±0.47 mm, with an average weight of 2.04 ±0.15 kg. For the
second parameter, a sharp knife was mounted on a steel frame and placed at the bench of the universal
testing machine (Testometric model M500-10kN) for measurement of the cutting force. The samples
were divided into 4 groups, each group containing 5 fruits for testing at 4 different cutting speeds (10,
15, 20 and 25 cm/min). The fruit was placed between the knife edge and the cross head of the universal
testing machine which was attached to a 10 kN load cell (Figure 3). The highest cutting force at each
loading speed was recorded. Results showed that the higher the speed of cutting, the lower was the
compressive force. However, the maximum force of 2535 N at 25 cm/min of loading speed was selected
for the design of the machine. Variation of the cutting force happened due to the shell strength, which
depended further on the fruit maturity.
The design concept of the machine was that the fruit cutting has to be accomplished by
pneumatic pressing on a young coconut sitting on a sharp knife in a vertical plane. So it was necessary
to calculate the diameter of the vertical pneumatic cylinder. The values used in calculation consisted of
the pressure for pneumatic system (7 bars), the compressive force (2535 N) and the safety factor (3
times). The net cutting force was therefore, 2535 x 3=7605 N.
Meanwhile, the compressive force F of the pneumatic cylinder was calculated by the following
formula [5]:
F = 10 (A x P) (1)
and D =
4A
(2)
where A = cylinder area, cm2
P = air pressure, bar
D = diameter of pneumatic cylinder, cm
The calculated diameter was 11.8 cm and the size available in the market was 12.5 cm.
Therefore, the diameter of vertical pneumatic cylinder was 12.5 cm and the length of cylinder was 25.0
cm. Another set of two horizontal pneumatic cylinders which were used for the lateral movement of the
cutting base had a diameter of 1.6 cm and length of 28 cm. These cylinders were placed side by side of
the cutting base.
The prototype was designed and fabricated (Figure 4) to comprise : 1) machine frame, 2) cutting
base, 3) knife set, 4) pneumatic system, and 5) tanks for coconut juice and cut fruits. The machine parts
which were in contact with the edible parts of the fruit were made of food-grade stainless steel. The
operation procedure was as follows: first, the young fruit was placed on the cutting base, then the
operator switched on the control to automatically move the base to be under the pressing unit. The base
automatically stopped as sensed by a limit switch and the centre of the fruit was aligned with that of the
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cutting knife. The other limit switch simultaneously triggered the downward movement of the pressing
unit to press the young coconut fruit to be cut in half by the cutting knife. The coconut juice was
allowed to flow down to the middle tank while the cut fruits were separated into another tank beside.