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DEVELOPMENT OF AN AUTOMATED COCONUT SCRAPING MACHINE
BGV Mendes, K Dikgale, LK Tartibu, TJ Kunene
Mechanical Engineering Technology Department, University of Johannesburg, Doornfontein
Campus, Johannesburg 2028, South Africa.
(Email: [email protected])
Abstract
Coconuts are very popular fruits worldwide. They have a variety of uses, health, and
nutritional benefits. The uses of coconuts range from cooking and nutrition, skin health,
cancer prevention, beauty products, charcoal with a coconut shell. The coconut scraping
machines that are commercialized aren’t fully automated and require human hands. Scraping
coconut is a laborious and time-consuming process. The manual process requires the
operator to both rotate and apply human effort to scrape the meat portion of the coconut. The
semi-automated process, on the other hand, requires the operator to hold the coconut half-
shell against a rotary blade that rotates usually using an electric motor. Both ways, the
operator is presented with dangerous forms of hazards. In this paper, an automated coconut
scraping machine has been developed to solve a well know challenge regarding grating
coconuts. The design proposed in this study will eliminate virtually all hazards related to
coconut scrapers. It is a fully automated machine that takes both risks and effort from the
operator. The system incorporates an adjustable blade that allows the movements according
to two axes. A clamping mechanism that moves in the third direction allows a three-
dimensional movement. The mounting of the coconut half shell in the clamp is set to take no
more than fifteen seconds. Upon mounting, at a push of a start button, the scraping of the
coconut is to be completely autonomous. Details of the designing and the development of the
working model constitute the main contributions of this paper.
Keywords: Coconut, Scraper, Automated, Design, Development
INTRODUCTION
Coconuts are very popular fruits worldwide. It has a variety of uses including health and
nutritional benefits. The uses of coconut range from:
Cooking and Nutrition
Skin health, cancer prevention
Beauty products
Charcoal with coconut shell
In small scale coconut processing, coconuts are cracked by the use of a hammer or knife.
The kernel is extracted using hand tools or mounted type coconut scrapers. Even for small
scale coconut processing, the use of manual tools is very tedious and effort is required
(Practical Action, 2008). Manually operated coconut scraper machines are portable and may
be used effectively in households. The clamping screw may be used to clamp the entire
mechanism in a table securely. As one rotates the manual handle, the rotation is transferred
to the scraping bit (Figure 1a). The dehusked coconut half-shell is pressed against the sharp
bit while in rotation (Figure 1b). This device requires a fair amount of effort to grate a
coconut. Attention is required by the person operating because if a slip occurs, may result in
serious injuries.
(a) (b)
Figure 1: (a) Typical manually operated coconut scraper machine and (b) Coconut sectioned
layout
Many of the semi-automated commercialized scrapers use the scraping part of manually
operated scraper and coupled to an electric motor. The scraping bit may have a different
design but all have the same performance and require the same effort to scrape. A typical
semi-automated coconut scraper is shown in Figure 2.
Figure 2: Semi-automated coconut scraper (Adapted from Mock, 1940)
The design of a compact design for coconut scrapers was proposed by Sajil Raj et al. (2016).
The design consists mainly of a clamp (locking mechanism), movers (for lateral and forward
feed), a coconut holder, a motor (rotates the coconut), a plate holder, and blades (for scraping
of coconut). The design and fabrication of a coconut breaker extractor grater machine were
described by James et al. (2016). The design consists mainly of a motor, a breaking tool, a
grating tool, a body, an angle plate, a hanging weight, two pulleys (motor and shaft),
bearings, and a spring. A review of a multipurpose grating machine was conducted by Bapat
et al. (2018). The machine consists mainly of a cylindrical drum, blade, v belts, motor, and
steel frame. Senthilkumar et al. (2018) proposed a multi-blades coconut scraping machine
with a single drive. The system consists of a frame, worm shafts, worm gears, blades, a
motor, and chain drives. There are several existing patents related to “coconut scraper
(grater)” (Thompson & Thompson Noel, 1984, Kannukkaden, 1993, Kumar, 2004, Zaldivar,
2016). All of these offerings are either manual or semi-automatic with peculiar features. A
more flexible device for scraping and extracting coconut meat from a half coconut with
minimal human intervention and convenience was proposed by Mattathil (2019). This device
incorporates variable-width, variable-movement-control, and variable-opening-entry
mechanisms.
MOTIVATIONS
The objective of this paper is to describe the development of an automated coconut scraping
machine. Coconut fruits come in different shapes and sizes. For the design to be automated, it
would have to reduce significantly all operator input during operation. Besides, the new
design needs to accommodate various sizes and shapes of the coconut fruits (Table 1). The
new scraping machine has to be designed in such a way that it can be self-adjusting based on
the size and shape of the coconut. In conventional coconut scrapers, the sharp bit turns at
high revolutions/s. The operator holds the dehusked coconut shell and presses the inside of
the shell, containing the meat, against the rotating sharp bit. This process is time-consuming
and poses a couple of safety hazards as well. Designing a mechanism that can mimic the
operator during scraping coconuts is therefore necessary. To the authors’ knowledge, there
are no studies that describe the development of a fully automated scraping machine. The
coconut scraping machines that are commercialized aren’t fully automated and require human
hands.
Table 1: Coconut particulars (Adapted from Sabale and Kolhe, 2016)
Particulars Dry Coconut
Shape Ovoid
Length, mm 210-270
Diameter, mm 160-206
Weight, kg 0.62-1.25
Shell Diameter, mm 80-120
Husk Thickness – at pedicel end, mm 62
Husk Thickness – at apex end, mm 34
Husk Thickness – 1/4th distance from pedicel end,
mm 32
Husk Thickness – 1/2th distance from pedicel end,
mm 24
Husk Thickness – 3/4th distance from pedicel end,
mm 28
Grating coconuts is time-consuming and laborious. For several decades, coconuts have been
scraped in the same manner. In this paper, we propose a concept that could make the coconut
scraping process fully automated. It is expected that the design proposed in this paper will
reduce significantly coconut scraping and most importantly mitigate risks linked to scraping.
METHODOLOGY
The approach leading to the coconut scraping machine’s concept described in this paper can
be summarised as a five-step process: - problem definition and research objective; - literature
review; - development of the scraper mechanism; - development of the clamp mechanism; -
description of the electrical and control systems; - detailed design. The problem and objective
have been defined in the first two sections of the paper as a preliminary step of the design
process. A literature review was conducted to understand coconut particulars. Existing
concepts of coconut machines have been analysed to identify features that could be
incorporated in the proposed model. The scraper mechanism was developed to make
provision of movement in at least two axes. The selection of material was done based on the
existing design and the coconut kernel requirement. The clamp mechanism was developed to
maintain the coconut in place adequately and ensure that the time taken to mount the coconut
is relatively shorter. The brief overview of the control electrical and control circuits were
based on the working of the main sub-systems of the model proposed in this paper.
DESCRIPTION OF THE DESIGN
Specifications and requirements
This following summarises the specifications and requirements considered for the designing
of the scraper machine:
The machine must be portable. The size has been estimated to be 1.045 m x 0.46 m x
0.143 m;
The system must be fully automated;
The effort required to grate the coconuts must be reduced significantly;
There must be little to no contacts with moving parts;
The machine must be highly autonomous after the half shell coconut is mounted to the
clamp;
The machine must be capable of running at relatively high speed;
The machine must be robust.
Development of scraper mechanism
a. Scraping blade mechanism
Figure 3 provides the details of the coconut scraping blade mechanism. The stepper motor
activates the linear movement of the pusher sleeve. The pusher sleeve, in turn, adjusts the
angle of the scraping blade to accommodate the shape of the coconut to be scraped.
Underneath we have a DC Motor providing rotation to the blade through the pulley belt.
Figure 3: Scraping blade mechanism
b. Scissor mechanism
The scissor mechanism allows for the adjustment of the blades at the end. The bearings are
press-fitted into the pulley housing. The Nylon bushing decreases the friction and allows the
rotation of the scissor mechanism independently from the stepper motor. The majority of the
mechanism is machined from 316ss stainless steel. The pivot joints are kept firmly by the
use of steel pins and circlips as a retainer. Details of the scissor mechanism are shown in
Figure 4.
Figure 4: Scissor mechanism of the scraper blade
c. Bushings
The scraper mechanism has several moving parts. Hence, a method of reducing friction
between moving parts is essential. There are two types of bushing used in the proposed
design. The nylon bushings were chosen to take advantage of the self-lubricating properties
of nylon. Nylon to steel has a coefficient of friction of 0.4 (Engineering toolbox, online). The
nylon bushings (white coloured parts) in the scraper mechanism allow the scraper blades to
rotate about the driven pulley without rotating the stepper motor at the back (Figure 5). It
provides a separation between the sleeves and the scissor mechanism. The sleeve provides
linear movement to allow the scraper blades to adjust the distance between them. At the
bottom of the frame, a retainer was installed to prevent the sleeve from rotating. The pivot
bushing in Figure 6 is important in the sense that it separates metal to metal contact. A quiet
rotation will be the result of including nylon bushings in critical moving parts. The brass
bushing is used in the design to centralize the lead screw at the free end. Brass is a material
very commonly used as a bushing due to its malleability. Brass is softer than stainless steel.
While in contact, the brass will deform to make up for the tolerance inaccuracies of
fabrication and machining.
Figure 5: View of scraper mechanical bushings
Figure 6: Pivot bushings and rotation section view
d. Pulley system
The pulley system was designed in the simplest way possible (Figure 7). The system consists
of two pulleys: the driver and the driven pulleys. The driver pulley is mounted directly to the
DC motor, while the driven pulley system performs three functions: transmission of power,
bearing housing, and mounting features for the scissor plates in the pivot section. The
bearing is press-fit onto the driven pulley and the frame. The bearing may be taken as the
main rotation section of the mechanism.
Figure 7: Illustration of the pulley system
e. Rotation to linear motion conversion
The motor shaft and lead screw are coupled via a brass coupler, the free end of the lead screw
is centralized and supported by using a brass bushing as shown in Figures 7 and 8. The
motor rotation causes a linear movement of the sleeve which is treaded to the same
specifications as the lead screw. The movement of the sleeve is transferred to the scissor
mechanism via the Nylon bushings.
Figure 8: Section view of rotation to linear conversion
f. Scraper frames
The frames are constructed from aluminium 6068-T6, which is advantageous for its weight to
strength ratio. The frame shown in Figure 9 will be used to mount the stepper motor. The
front part allows for the press-fitting of the bearing and the assembly of the scissor
mechanism of the scraper blade. The frame shown in Figure 8 will be fastened to the coupler
frame using six M8 screws and nuts. This structure acts as a supporting frame for the DC
motor. The DC motor in turn is coupled to a driver pulley as shown in Figure 5. The
manufacturing process to adopt for the fabrication of the parts shown in Figure 9 & 10 may
be sheet metal bending. The features on the plate may be done by CNC, Plasma cutting, or
Water Jet cutting.
Figure 9: Stepper motor and coupler Frame
Figure 10: DC motor frame
Development of the clamp mechanism
a. Coconut clamping mechanism
The coconut clamp was designed to clamp various sizes or shapes of half shell dehusked
coconut. The design consists of three clamp arms spaced 120 degrees apart. A clamp
tightening rod is part of the design to secure the coconut in place and restrain any movement
during scraping. A second stepper motor is used to move the clamp linearly using a lead
screw coupled to the stepper motor. With the scraping blade mechanism and clamp
mechanism aligned, scraping can be regulated through a suitable control system. Details of
the clamping mechanism are shown in Figure 11.
Figure 11: Coconut clamping mechanism
b. Clamp arms and tightening rod
The clamp arms are part of the clamping mechanism, three clamp arms are separated by 120o.
At one end, a pivot hole feature is machined. At the other end, a 90o coconut shell edge
retainer feature. A leaf spring is used to maintain the arms at an initial position at all times.
This spring is attached to the arms. When inserting a half shell of a coconut, the spring will
deflect allowing the coconut to enter past the 90o coconut shell edge retainer feature. The
spring-loaded end piece is assembled with the intent of facing the back and perpendicular to
the cut section of the half shell coconut (Figure 12). As the coconut half-shell is inside the
clamp, the spring-loaded end piece will deflect and will serve the function of a stopper, such
that the coconut isn’t pushed in too far. The threaded rod that is assembled to the end piece is
tightened via the knob. The result is a secured coconut ready for the scraping process. The
three-sided plate is assembled to the sleeve that serves multiple functions. The sleeve is
designed such that it provides the pivot support required by the clamp arms. It provides a
mounting face for the arm springs and the three-sided plate. The three-sided plate has the
guide rod bushings and stepper motor sleeve mounting features. All components are
mounted to a frame made from aluminium 6063-T6 (Figure 13).
Figure 12: Spring loaded piece
Figure 13: Coconut clamp
c. A brief overview of the electrical and control systems
When the motor is running at no-load current, the current needed by the motor is only to
overcome internal friction. The torque load may be assumed to be zero. This zero torque may
only be achieved when the scraper mechanism is running without a coconut. The relationship
between torque and current tells us that the torque produced by a motor is proportional to the
current. As the scraper blades contact the meat of the coconut, the torque load increases as
the coconut will react to the force being applied to it. The current range while the blades are
in contact with the meat portion of the coconut is to be programmed on the control circuit as
the scraping current. The resistance of the shell is much higher than the meat. Therefore, the
torque produced by the motor when in contact with the hard coconut shell will be higher.
This hardshell torque must be considered during programming. The control circuit will avoid
the hard shell by decreasing the angle of the scissor mechanism. It will increase the angle
when it is rotating in free air and the torque is nearly zero. Figure 14 provides the circuit
layout that could be used to control the rotation of both Clamp Stepper Motors. This circuit
will receive signals from the current sensor and adjust the rotation of the motors accordingly.
Figure 14: Basic circuit layout of the main components
Detailed design
a. Scraper mechanism and clamp mechanism
Both the clamp and scraper mechanisms are mounted to an injection moulded bottom base
and aligned. As seen in Figures 15 and 16, the stepper motors and DC motor are electrically
connected to the control circuit containing the current sensor. The control system design was
outside the scope of this paper. Hence, a detailed description of the control circuit has not
been discussed in this paper. As shown in Figure 15, rubber feet are assembled to the
injection moulded bottom base, providing fiction that eliminates any unwanted movement
due to the vibrations of the machine. It acts as a vibration absorber.
Figure 15: Aligned clamp and scraper mechanisms
Figure 16: Top view of aligned scraper and clamp mechanisms
b. Overall design
The concept developed in this paper incorporates a scraping blade mechanism that can be
self-adjusting based on the size of the coconut while in rotation. The spreading of the
scraping blade is regulated by an electric stepper motor. A DC motor coupled to a pulley
system facilitates the rotation of the blade. The coconut half-shell is then mounted to the
coconut clamp. A coconut clamp tightening rod is used to clamp and tighten the coconut
shell. The clamp mechanism is also fitted with a stepper motor to create a linear movement to
the clamped coconut. Through a suitable control system, both stepper motors may be
controlled such that scraping may take place efficiently. By controlling the current flowing
through the DC motor (and subsequently the torque), it is possible to maintain a constant
torque which linked to the steps of both stepper motors. This contact torque is the torque
required to overcome friction when the blade is in contact with the coconut meat. An
overview of the autonomous coconut scraping machine is shown in Figure 17(a) & (b). The
working of each mechanism is described in the following sections.
(a)
(b)
Figure 17: Coconut scraper concept
SCRAPING PROCESS
Knowing that the coconut meat has a certain resistance (or rather friction coefficient to
overcome to scrape), the hard shell also has a coefficient of friction different from the
coconut meat. The control system can be programmed to assess and detect the differences.
The resistance will cause an increase or decrease in torque, which will ultimately cause a
change in the current flowing through the DC motor. By knowing the range of resistance
caused by the coconut meat, the blade can be restricted to scrape only the coconut meat. The
following summarizes the scraping process:
Step 1. The rotating blade cuts through the first section of the coconut meat, this is
made possible by activating the clamp stepper motor moving the clamp forward for
contact (Figure 18).
Figure 18: Step 1 of the scraping process
Step 2. Figure 19 shows the spreading of the scraping blades. This is done by
activating both stepper motors, the stepper motor in the clamp mechanism, and the
stepper motor in the blade mechanism.
Figure 19: Step 2 of the scraping process
Step 3. The same process happens. All the processes are made possible by controlling
the friction levels in the circuitry that controls all the mechanism (Figure 20).
Figure 20: Step 3 of the scraping process
CONCLUSION AND RECOMMENDATIONS
Coconuts are considered fruits with a variety of uses. The eatable meat part of the coconut is
one of the softest parts of the coconut, yet it may require some work to be removed from the
coconut. Several approaches are proposed to remove the meat portion of the coconut with
less effort. The approaches can be classified as manual, semi-automatic, and automatic
corresponding respectively to the manual scraper, semi-automatic scraper, and automated
scrapers. This paper's objective was to design an automated scraper that will reduce time,
effort, and be more efficient when compared to the manual and semi-automatic scrapers. The
design incorporates two stepper motors, a DC motor, a scraping blade mechanism, a
clamping mechanism, a scissor mechanism, scraper frames, bushings, pulley systems, clamp
arms, tightening rod and the control circuit. A detailed description of the components, the
modules, and the mechanism used to develop the automated system is provided. The coconut
clamp was designed to clamp various sizes or shapes of half shell dehusked coconut. The
concept developed in this paper incorporates a scraping blade mechanism that can be self-
adjusting based on the size of the coconut while in rotation. The spreading of the scraping
blade is regulated by an electric stepper motor. A DC motor coupled to a pulley system
facilitates the rotation of the blade. The coconut half-shell is then mounted to the coconut
clamp. A coconut clamp tightening rod is used to clamp and tighten the coconut shell. The
clamp mechanism is also fitted with a stepper motor to create a linear movement to the
clamped coconut. Through a suitable control system, both stepper motors may be controlled
such that scraping may take place efficiently. Future work will provide clarity about the
materials used, the size of all components/modules, and the control circuit suitable for this
system.
ACKNOWLEDGMENTS
This Conference paper was partly supported financially by the National Research Foundation
of South Africa with Grant number: 127395.
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