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Abstract
The objective of this paper is the design and development of an autonomous vehicle which would be able to harvest saffron
flowers unsupervised. This vehicle will be able to collect the flowers of the saffron unharmed. The time for the harvest isn’t more
than the time needed by a human to accomplish the same task. Moreover, this procedure must be more cost effective compared
to the same task accomplished by a human. We also take under consideration that the plant appears to be very sensitive to the
fluctuation of pH and can be chemically destroyed in the presence of oxidizing factors and in an ionized environment. It is also
very sensitive to the atmosphere’s humidity (due to its trichoid stamen) however it seems to be resistant to heat. Generally, the
vehicle will be able to accomplish all the operations without the need of human supervision
Introduction
Nowadays, the technology of mechanical harvesting is focused on harvesting plants of large crops (e.g. wheat,
corn) using special mowers of large size and cost. On the other hand, in spite of the great technological advances,
the harvesting of vegetables, fruits and other corps (e.g. saffron) depends primarily on human labour. This affects
mainly the cost of production, the product’s quality, as well as the safety of workers in crops that have been sprayed with pesticides (e.g. greenhouses). The main reasons for the shortage of automated solutions are the difficulty in
tracking the corps and the difficulty in simultaneously cutting and collecting the corps without damaging them.
Saffron (Crocus sativus L) is one of the most expensive edible flowers of the world. Iran, Spain, Italy and Greece
are producers of dried saffron. A farm of saffron needs daily and manually harvesting because every plant of
saffron produces only three flowers in different height and days. There are 2170 flowers in each Kg of harvested
fresh flower, and processing every 78 Kg of fresh flowers results in one kg of dried saffron-spice [1].
This final product is actually the stigma part of flower. The stigma, as the only economic part of flower has
eatable and medicinal applications. One stigma of saffron weighs about 2 mg, each flower has three stigmas and
150,000 flowers are required to produce 1 kg spice. Harvesting the flowers and separation of stigmas from the
flower is a most difficult operation. It is time consuming, laborious and makes saffron the expensive spice of the
world. Picking of 1000 flowers requires 45–55 min, and another 100–130 min is required for removing the stigmas
for drying. Thus, 370–470 h is required to produce 1 kg of dried saffron. The flowers are picked exactly when they
are fully bloomed and the saffron strand or stigma is at its reddest. The harvesting must begin shortly after dawn. If
left exposed to the sun, saffron quickly loses its colour and flavour and withers under the sun light. The task includes
picking the flowers and separating the stigmas from the petals and stamens (Fig. 1). Flowers are picked at the base
of the segments, and put into basket in thin layers to avoid excess pressure and deformation of flowers organs,
particularly of the stigmas [2].
Many researchers are engaged on the automatic harvesting of fruits or vegetables but there is always the need for
the introduction harvest methods for saffron. Automation of harvest and post-harvest of saffron flower increases
harvest efficiency and consequently reduce the final cost of the product. Dimitriadis and al designed a conceptual
machine which operates by separating the petals, the stigmas and stamens from the plant individually in the field
using a combination of pneumatic and mechanical processes [3], Bertetto described and discussed a robotized
system with the aim to harvest and separate the saffron flower spice [4], Ruggiu et al developed a prototype for
harvesting the saffron [5], Javari developed a suitable algorithm for recognition and locating saffron flower using
machine vision [6], Gracia et al presented a new machine for automated cutting of saffron flowers in order to obtain
their stigmas [7], Emadi et al designed a vertical wind tunnel for separation of stigma from the other parts of saffron
flower using its aerodynamic properties [1].
This paper explores the feasibility of mechanization of the harvest procedure. It focuses in the design and
development of an autonomous vehicle which will be able to collect saffron flowers unsupervised.
The main elements that consist the structure of the vehicle are described as well as their combined operation
(sensors, motors, collision avoidance), the sequence followed in order to ensure that the right flowers are harvested,
the sequence followed in order for the vehicle to avoid colliding with any obstacles during its course and the
operation of the robotic arm and the gripper, which must operate according to strict specifications, regarding the
harvesting, the transportation and the storage of the flowers.
The plant appears to be very sensitive to the fluctuation of pH and can be chemically destroyed in the presence of
oxidizing factors and in an ionized environment. It is also very sensitive to the atmosphere’s humidity (e.g. fog, frost
net and wind currents due to its trichoid stamen) however it seems to be resistant to heat. Therefore, it is essential
that the harvesting vehicle and gripper must handle the flowers very gently. Due to the plant’s sensitivity, the
harvest procedure should be completed within a time period of one day, or two at the maximum, from the moment
that the flower blooms (so that its flavour and fragrance could be sealed off), the vehicle is designed to complete this
procedure within the time period of one day. In addition, as the harvest of the saffron must take place early in the
morning or late in the afternoon, when the concentration of the plant’s oil is higher, the vehicle has four working
hours in the morning and four working hours in the afternoon.
. Description and Operation of the Vehicle
The following assumptions are made, concerning the surface of the field on which the vehicle is collecting the
saffron (Fig. 2):
x The movement of the vehicle must follow specific restricted paths within the plant lines, and collect the
flowers from them.
x The plants are ordered in rows, and the distance between them is approximately 60 cm.
x The flowers are situated at a distance of 10 – 30cm (depending on the farmer).
The maximum surface that this particular vehicle can serve is up to 1,200 squared meters (i.e. 60m x 20m). The
surface of the field is considered to be not smooth with a mean height fluctuation d= ±5cm. The height of the plants
is from 5 to 10cm.
The vehicle should start from one side of the field and after collecting all the flowers it terminates at the other
side of the field. The vehicle should drive across a row and collect its flowers. Marks can be positioned along the
rows in order for the vehicle to be properly oriented but also to define the start and the end of the process.
The vehicle should be also able to store the products from the half the field (four hour period) in a special
designed container, on its undercarriage, making sure that all the special conditions of light, humidity, pressure and
the other factors have being considered. The vehicle should also have the ability to check the flower in order to
determine whether it is appropriate to be harvested otherwise it would proceed to the next flower. Moreover, the
vehicle should be able to move along the roughness of the surface ±5cm but also it should have the ability to
overcome various physical obstacles e.g. stones during its movement, without affecting the harvest procedure.
2.1. General description of the Vehicle
The vehicle must accomplish the following operations:
x Begin its operation with voice message.
x Follow a specified route determined by coloured marks which are detected by a colour sensor.
x Detect the next flower using distance sensors.
x Evaluate the quality of the flower with the use of colour sensors.
x Harvest the flower with a use of the gripper.
x Complete its operation when detecting the end of the field.
The vehicle consists of the following equipments (all the necessary calculations have been made for the selection of
devices-components listed in parenthesis):
x 2 colour sensors (IFM Electronics 05-C500)
x Distance sensor (Sharp 2D120X)
x Voice sensor (BOB-099.24)
x Gripper
x Worm gear, worm wheel system
x Movement motor (Transmotec 750 series)
x Gearbox (Tamiya 4-Speed Crank-Axle Gearbox)
x Servomotors for the movement of
the robotic arm – gripper system (Hightec HS-485HB Deluxe Servo)
x Servomotor controller (Phidget AdvancedServo 4)
x Wheels
x Motherboard to control the operations (GRoboduino)
x Electrical Supply-Battery (BQY 11,1V LiPo 3S 5200 mAh)
2.2. Operation of the Robotic Vehicle
The operation of the vehicle begins when the voice sensor detects a voice signal “BEGIN”. The vehicle is guided
by coloured marks situated along the plant rows of the field.
A colour sensor is situated on the front centre of the vehicle. It is situated there because of its low accuracy. This
sensor is responsible to maintain the vehicle on its route along the red mark.
The distance sensor, the colour sensor and the gripper are placed at the right side of the vehicle on a system of
worm gear-butterfly system (an axis with internal thread). The sensors are fixed on the axis shell and the gripper is
moving mechanically and automatically along this axis (robotic arm).
The distance sensor calculates the distance of the next flower by sending active signals and reading the reflected
signal. It is situated near the ground, at the bottom-end of the axis, in order to detect the smallest flowers taking into
account that the height of the plant is between 5cm and 10cm and the fluctuation of the field is r5cm.
When the colour sensor, which is situated exactly above the open gripper (and the flower), determines that the
flower is suitable for harvesting the gripper closes and moves upwards 1 cm, cutting the flower with a motion
similar to that of the human hand. Then the axis rotates 90o
and the gripper turns towards the inner side of the
vehicle and drops gently the flower in the properly developed container. The container is at the back of the vehicle
and has dimensions 30x10x10cm and capacity 3 litres.
If the flower is considered to be inappropriate for harvesting, the axis along with the gripper rotates 90o
and the
vehicle moves on without hurting the plant. This process is repeated until the vehicle reaches the end of the field.