development and testing of a portable palm tree pruning machine

Paper No. 03-216
DEVELOPMENT AND TESTING OF A PORTABLE PALM TREE
PRUNING MACHINE
K.M. Ismail
Dept. of Ag. Eng'g, King Saud University/Gassim Branch, Saudi Arabia
K.A. Al-Gaadi
Dept. of Ag. Eng'g, King Saud University/Gassim Branch, Saudi Arabia
Written for presentation at the
CSAE/SCGR 2003 Meeting
Montréal, Québec
July 6 - 9, 2003
Abstract
Palm trees are considered to be very popular in the Kingdom of Saudi Arabia where over
12 million productive trees are planted throughout the kingdom (Bakry, 2000). The production of
dates requires a set of field operations. Unfortunately, most of these operations are not yet
mechanized, thus, they are inefficiently conducted, costly, tedious and time consuming (Bakry,
2000). One of the important field operations is the tree pruning which is widely conducted
manually using a conventional hand-held saw. Therefore, an AC-operated portable machine was
developed to mechanize the pruning operation. The performance of the machine was tested.
Power, energy, and time of cutting were considered for evaluating the machine’s performance. It
was found that the relationships between moisture content of petioles (MC) and power, energy
and time required for cutting were all significant, where the determination factors were 0.86,
0.71, and 0.81, respectively. The results revealed that both energy and time required for cutting
were proportional to the MC. The mean value of energy required to cut 1 cm 2 of petiole cross
section area was 35 W.sec at 70% MC, while it was 12 W.sec at 10% MC. The average time of
cutting was 3.5 sec/cm 2 at 70% MC, while it was about 1 sec/cm 2 at 10% MC. However, the
power required for cutting was found to be inversely proportional to the MC. A power of 28
W/cm 2 was required at 10% MC, while only 10 W/cm 2 was required at 70% MC.
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DEVELOPMENT AND TESTING OF A PORTABLE
PALM TREE PRUNING MACHINE
K. M. Ismail 1 and K. A. Al -Gaadi 2
1 Prof., and 2 Assis. Prof. at Dept. of Agric. Eng., King Saud University-Gassim, Saudi Arabia.
ABSTRACT
Palm trees are considered to be very popular in the Kingdom of Saudi Arabia where over
12 million productive trees are planted throughout the kingdom (Bakry, 2000). The production of
dates requires a set of field operations. Unfortunately, most of these operations are not yet
mechanized, thus, they are inefficiently conducted, costly, tedious and time consuming (Bakry,
2000). One of the important field operations is the tree pruning which is widely conducted
manually using a conventional hand-held saw. Therefore, an AC-operated portable machine was
developed to mechanize the pruning operation. The performance of the machine was tested.
Power, energy, and time of cutting were considered for evaluating the machine’s performance. It
was found that the relationships between moisture content of petioles (MC) and power, energy
and time required for cutting were all significant, where the determination factors were 0.86,
0.71, and 0.81, respectively. The results revealed that both energy and time required for cutting
were proportional to the MC. The mean value of energy required to cut 1 cm 2 of petiole cross
section area was 35 W.sec at 70% MC, while it was 12 W.sec at 10% MC. The average time of
cutting was 3.5 sec/cm 2 at 70% MC, while it was about 1 sec/cm 2 at 10% MC. However, the
power required for cutting was found to be inversely proportional to the MC. A power of 28
W/cm 2 was required at 10% MC, while only 10 W/cm 2 was required at 70% MC.
Keywords: Palm tree, pruning, energy, power, time, performance, cutting.
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INTRODUCTION
Palm trees have an exceptional importance in the body of agriculture in the Kingdom of
Saudi Arabia. The importance comes from the fact that the trees are widely planted all over the
Kingdom for their yield of dates and for decoration purposes. Palm dates are considered to be the
main fruit in Saudi Arabia supplied by 12 million palm trees spread over an area of 106,460
hectares, where the total production reaches 648,000 tons/year (Bakry, 2000). On the other hand,
palm trees, due to their durability, are commonly utilized in main streets and public parks for
decoration.
Sial and Khalid (1983), along with Shabbana and Mohamed (1982) reported that most of
palm tree farms in Saudi Arabia did not follow a specific engineering regime, where palm trees
are randomly planted and often inter-cropped with forage and vegetable crops and, sometimes,
even permanently inter-cropped with other fruit trees. They added that irrigation channels in
these farms were not well organized causing difficulty in machine maneuvering around palm
trees. Sial and Khalid (1983) stated that the traditional practice of climbing up a date palm was
hazardous, time consuming and require skilled labor. Al-Kiady (2000) reported that the trained
and specialized labors were becoming rare and expensive causing a serious depression in dates
production. Ahmad et al. (1986) added that a new technology was not readily transferable unless
major changes in the functional machine design or agricultural practices took place. That was
attributed to the fact that there were major mismatches between agricultural field conditions and
mobilized machine specifications.
Several attempts have been previously made to mechanize, on a small scale, some
farming operations related to date palm trees. Brown (1982) stated that mechanization of dates
production was essential due to the scarcity and high cost of labor. He developed a hydraulic
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lifter to reach the palm tree top for easier harvesting. His lifter, as he reported, reduced the
required labor by 80 percent and related cost by 50 percent. Abdalla et al. (1986) developed a
simple and inexpensive walk-up elevator to suit date farming operations. The elevator consisted
of a single beam with two walking up feet pedals and a seat. The elevator was designed where a
worker can lift himself up by pedaling and then sits when reaching the crown zone to perform
required operations. Omar et al. (1986) modified two lifts to be utilized in palm tree crownrelated
operations, such as pollination, pruning and harvesting. One lift was one man operated
called ‘Ben-10’, while the other was an aerial lift platform called ‘Palmates’. Modifications were
necessary for the improvement of traction capability, working height and machine
maneuverability. The modified two lifts were found to perform satisfactorily under palm tree
field conditions. Ahmad (1994) developed a mechanical elevator that could easily move through
palm trees and safely put labors at the tree crown level to perform desired operations. The
elevator had to be equipped with a motor to improve its performance.
A non-scientific trial was made by Bahdal (2002) where he developed a saw for pruning
palm trees. No tests for this saw were reported. However, it seems that the saw is not powerful
enough to perform heavy-duty jobs.
The above literature shows the necessity of exerting more efforts to mechanize palm tree
farm operations. Thus, the objectives of this paper were to develop a new portable machine to
perform palm tree pruning operation and test its performance.
MACHINE DESCRIPTION
The developed portable pruning machine shown in Fig. 1 and 2 was designed so it could
be carried around by one person. Thus, the total weight and size of the machine were carefully
considered in its design, where the weight and length were maintained at 7 kg and 130 cm,
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Figure 1: The developed portable palm tree pruning machine
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48 61 24
54 52.5
Handle, 3.5D 12
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Saw, 18D, 60 teeth
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Rotating Shaft, 0.9D
2.5
Spring
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Motor
2.5 D
ELEVATION VIEW
Bearing
Holding Tip
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90
Diff. Gears
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105
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PLAN VIEW
Dimensions in centimeters
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Figure 2: Elevation and plan views of the developed pruning machine.
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respectively. The machine was composed of an AC-operated drill motor with a power of 1200
W at 2400 rpm which was readily available in the local market. The motor was utilized to
provide the mechanical energy from the electrical energy. Connected to the motor was a one
meter long rotating shaft with a diameter of 0.9 cm. The shaft was used to transfer the motor's
rotational motion at one end to a couple of differential gears, pinion connected to the shaft and
crown connected to a cutting saw, at the other end. The functions of the gears were to convert the
horizontal shaft motion into a vertical motion and reduce its rotational speed before it was
supplied to the saw. Reduction of the speed was performed to increase the cutting torque on the
saw and was obtained by employing a 10 teeth, 3 cm radius pinion gear engaged with a 16 teeth,
4 cm crown gear. Thereby, the speed of the shaft was reduced by a ratio of 1.6 resulting in a saw
rotational speed of 1500 rpm at no load. A circular saw of 60 teeth and 18 cm diameter was
employed as the cutting component driven by the gears. Mounting bearings and the cutting saw
axis were carried by a frame composed of two parallel protection bars. In order to reduce
machine vibration and increase its stability during cutting operation, a 9 cm long tip was mounted
on the frame to function as a side supporter. A spring inside a metal tube was utilized to place a
force sufficient to inject part of the tip into the petiole required to be cut. Thereby, big portion of
the machine’s weight would be carried by the tip and stability of the machine would be increased
because the machine would be held by the tree through the tip. For safety purposes, a plastic
wrap was used to cover the moving parts close to the operator.
MACHINE'S PERFORMANCE EVALUATION
The machine's performance evaluation was designed to reveal the behavior of the
machine in terms of its consumption of electrical power and time required to cut one unit of a
petiole's cross section area (cm 2 ) at a predetermined petiole's moisture content (MC.) The time
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and power measurements were utilized to compute the energy required for cutting. Power, time
and energy were determined to be the dependent variables and were functions of the petiole
sample MC. Four different MC levels with 20 replicates each were obtained by subjecting fresh
green samples of petioles to different periods of natural drying and then placing them in a drying
oven for complete drying. For each MC level, 20 cuts were performed to form 20 replicates of
one MC level. During cutting operations, petiole samples were safely fixed horizontally on a
special arrangement designed for this purpose. The arrangement carrying the sample was
connected to a spring that was utilized to ensure that the sample was steadily held against and
constantly fed to the cutting edge.
Determination of petiole moisture content (MC)
The determination of petiole moisture contents was conducted on the wet basis using the
standard methods reported by Rygg (1948) and Ismail (2003). Samples were weighed before
oven drying using an electrical scale (LIBROR EB-4000H; model:1410D) of 0.01g accuracy.
For complete drying, the samples were placed for 48 hours in a vacuum oven (Sheldon
Manufacturing Inc., USA) at a temperature of 65 o C and a vacuum of 762 mm Hg. The samples
were again weighed and MC% was calculated using the following formula:
WW
MC, % = *100
(1)
W
T
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where:
W W = weight of removed water,
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W T =
total weight of sample before oven drying.
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Power measurement
A power measuring device (WSE, LVM210) shown in Fig. 3 was used to measure the
electrical power required by the machine to perform cutting of different petiole samples (different
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moisture contents). The device was specified to have a capacity of 4000 W with an accuracy of
±0.5%. A stop watch was used to determine the time, in seconds, consumed in cutting. Energy
was calculated by multiplying the power measurement by the time consumed in petiole cutting.
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Figure 3: The experimental setup used for testing the developed machine
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Calculation of petiole cross-section area
For each cut (each replicate) the cross section area resulting from cutting was depicted on
a paper to obtain the actual exact shape and boundaries of the cut area on a sample. A computer
program was designed to calculate the area of the depicted shapes utilizing MATHCAD software.
The program used scanned images of the depicted shapes and computed the number of pixels
contained by the shapes. Through a calibration known area in cm 2 , the program conducted a
comparison and calculated the area of the scanned irregular shapes.
RESULTS AND DISCUSSION
The results of the performance tests are shown on Fig. 4, 5, and 6. Fig. 4 shows that the
power required for cutting is inversely proportional to the petiole MC. The determination factor
(R 2 ) of this relationship was found to be 0.86 suggesting a linear relationship between the two
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Cutting Power, W/cm 2
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35
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10
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0
R 2 = 0.86
0 20 40 60 80
Moisture Content, %
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Figure 4: Effect of petiole moisture content on cutting power.
Mean cutting time, sec/cm 2
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4.5
4
3.5
3
2.5
2
1.5
1
0.5
0
R 2 = 0.81
0 20 40 60 80
Moisture Content, %
2
Figure 5: Effect of petiole moisture content on cutting time.
Mean Energy, W.sec/cm 2
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40
30
20
10
0
R 2 = 0.71
0 20 40 60 80
Moisture Content, %
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Figure 6: Effect of petiole moisture content on energy required for cutting.
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variables. The regression model is indicated in equation 2. As shown, the cutting power required
for fresh petioles (60-75% MC) is 12 W/cm 2 while it is 27 W/cm 2 at more dry petioles (about
17% MC).
P = 32.17 − 0.3145 MC, R
2 = 0.86
(2)
where: MC= petiole moisture content, %
P= power required to cut 1 cm 2 of petiole cross section area (W).
Fig. 5 shows that the required time of petiole cutting is proportional to the petiole MC.
The R 2 of this relationship was found to be 0.81 suggesting a linear relationship. The regression
model is indicated in equation 3. As shown in Fig. 5, the fresh cut petioles of 60 to 75% MC
required a cutting time of at least 3 sec/cm 2 while the dried cut petioles of 5 to 15% MC required
about 0.9 sec/cm 2 . Clearly, the fresh cut petioles required more time than the dried ones. This is
attributed to the fact that moisture makes petiole fibers stronger and more tied to each other.
Thus, the petiole becomes more resistant to cutting.
T = 0.4187 + 0.0432 MC, R
2 = 0.81
(3)
where: T= time required for cutting (sec/cm 2 ),
MC= petiole moisture content, %.
Figure 6 shows that the energy required for cutting is proportional to the petiole MC.
Obviously, increasing petiole moisture content increased the cutting energy due to increasing
cutting time. Again, the fresh petioles of 60 to 75% MC required a cutting energy of 30 to 35
W.sec/cm 2 , while the dried petioles of 5 to 15% MC required 12 to 15 W.sec/cm 2 . The R 2 value
of the relationship was 0.71 suggesting a linear relationship. The regression model is indicated in
equation 4.
E = 7.13 + 0.399 MC, R
2 = 0.71
(4)
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where: E= energy required for cutting, W.sec/cm 2 ,
MC= petiole moisture content, %.
SUMMARY AND CONCLUSIONS
A machine was developed in order to mechanize the pruning operation of palm trees
where it is thought that the manual conventional way of performing the operation is costly,
tedious and time consuming (Bakry, 2000). The performance tests of this machine showed that
the machine could be efficiently used for pruning palm trees. Results showed that the required
cutting power was 10 and 28 W/cm 2 for the fresh cut petioles of about 70% moisture content
(MC) and the dried cut petioles of about 10% MC, respectively. Time required for cutting was
3.5 sec/cm 2 for the fresh cut petioles of about 70% MC, while it was 0.9 sec/cm 2 for the dried cut
petioles of about 10% MC. In addition, the mean energy required for cutting petioles was 35
W.sec/cm 2 for the fresh cut petioles of 70% MC, while it was 12 W.sec/cm 2 for the dried cut
petioles of about 10% MC.
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ACKNOWLEDGMENT
The authors would like to express their thanks to Dr. Ahmad Al-Shooshan in the
department of Agric. Eng., College of Agriculture for his great and valuable help in designing the
computer program used to calculate the petioles cross section areas.
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REFERENCES
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