Abstract:
Existing date harvesting machines are vehicles equipped with a long arm to lift a man
on a platform to harvest the fruits. The arm and the vehicle are heavy (4 to 8 tonnes),
expensive (from £16 000) and are not sufficiently manoeuvrable in constricted date
groves. Most dates in the main producing countries, including Iran, are therefore
harvested manually. The manual method is unsafe, slow, expensive (£0.63 per tree)
and the fruit quality is often damaged.
A light, weight 4 wheel drive, remotely controlled tree climbing machine is, therefore,
a potential solution to the problems of harvesting and servicing (such as pollinating
and pruning). A prototype of such a device was designed, developed and evaluated
under laboratory conditions. To determine the operating characteristics and feasibility
the machine was designed to climb the tree using pneumatic tyres as traction wheels.
The machine can be transformed to ground drive and move between trees under its
own power. This approach reduces the machine weight, cost and size because the
tree trunk is used as a support for the machine to climb to the fruits. It is operated
and controlled from the ground which improves the operator safety.
A vertical traction theory for this type of machine has been developed based on the
tree size and surface characteristics and machine size and weight which can be used to
design date harvesting and climbing machines with different capacities. The test
results showed that the experimental machine could achieve a tractive efficiency of
90% and that the optimum wheel slippage was between 10 - 15%. The machine
consumes a maximum of 1.4 kW power which is only 3% of the power requirement
of existing systems. The machine weight is 150 kg which is 2- 4% of the existing
systems' weight. It is capable of climbing the tree at a maximum speed of 0.27 m/s
although the optimum speed is 0.17 m/s for best control. The prototype can carry a
payload of 100 kg of dates and, considering a field efficiency of 75%, it can
potentially harvest a tree in 22 minutes which is 18 % faster than the manual system in Iran and 6% faster than one of the mechanised systems used in Saudi Arabia. The
harvester can work on tree diameter ranges from 300 to 850 mm and can pass over
the tree leaf bases of 41 mm high. The machine should not damage the tree because
the tree resists the machine stresses with a minimum safety factor of 7.
An economic analysis showed that it can be manufactured in Iran at 20 % of the cost
of existing systems. The machine cost per tree is equal to the hand harvesting method
(£O. 63 per tree) for Iranian farmers if it harvests 978 trees per year.