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CONTROLLING AIRBLAST SPRAYER AIR FOR VARIABLE RATE
APPLICATION IN ORCHARDS
A THESIS PRESENTED TO THE GRADUATE SCHOOL
OF THE UNIVERSITY OF FLORIDA IN PARTIAL FULFILLMENT
OF THE REQUIREMENTS FOR THE DEGREE OF
MASTER OF SCIENCE
UNIVERSITY OF FLORIDA
2007 Naresh Pai
To Archana and Anant Pai
I would like to extend my thanks to the many individuals who have contributed to
make this project a success and my educational experience so enjoyable. I would like to
thank Dr. Masoud Salyani, my advisory committee chairman, for his faith in me, and for
his continued support and inspiration. His constant encouragement, timely critical
evaluation, and enthusiasm for my work have resulted in the successful completion of my
research. I am indebted to Mr. Roy Sweeb, Senior Engineering Technician, for his
insightful ideas, hands-on support, and training in the workshop and field, throughout the
I would also like to thank Dr. Thomas Burks and Dr. John Schueller for giving me
valuable knowledge through their courses and serving on my supervisory committee. I
want to acknowledge the Agricultural and Biological Engineering (ABE) department for
providing me the opportunity, and the Citrus Research and Education Centre (CREC) for
the assistantship and technical resources to conduct my research. I am also grateful to Dr.
Reza Ehsani, Mr. Troy Gainey, and the staff of the CREC maintenance department for
letting me use equipment needed for the project.
On a personal note, I would like to thank my parents and brother whose support
was of inestimable value. A final word of thanks goes out to all my friends who have
directly or indirectly contributed to the successful completion of my work.
TABLE OF CONTENTS
A C K N O W L E D G M E N T S ................................................................................................. iv
LIST OF TABLES ........... ..... ............. ........... .... ......... .............. .. vii
LIST OF FIGURES ............. ............. ........ ....... .......................... viii
A B ST R A C T .......... ..... ...................................................................................... x
1 IN TR OD U CTION ............................................... .. ......................... ..
1.1 Ju stification ............................................. ........ ...... .... ........ ... 1
1.2 T hesis O organization .......... .. ...... .......................................... .. .......... .. 2
2 B A C K G R O U N D ....................................................... 3
2.1 Pesticide U sage in Florida ................................................ ........................... 3
2.2 Pesticide Application Technology for Tree Crops .........................................4
2.2.1 Sprayers ........................................................................... ....... ........ ..... ........ 4
2.2.2 A ir-Carrier Sprayers ............................................................................. 4
188.8.131.52 Liquid delivery system ........................................... ............... 5
184.108.40.206 A ir delivery system ........................ ................ ................... 6
2.2.3 Testing Methodologies for Sprayer Air and Liquid Output.....................
2.3 Control Systems in Pesticide Application Technology ..........................................9
2.4 Objectives .................. ........ ..................... ........ .... .... ........ 12
3 M ATERIALS AND M ETHOD S ........................................ ......................... 13
3.1 A irblast Sprayer D description ........................................ .......................... 13
3 .2 L aser S en sor......................................................................................... 14
3.3 Prelim inary E xperim ents ................................................... ........ ............... 15
3.3.1 Airblast Spray Distribution Pattern .........................................................15
3.3.2 Restricted A ir-Input Test................................ ......................... ........ 16
3.3.3 D eflecting A ir at O utput...................................... .................. .... ........... 18
3.4 Automation of Deflector Plate Movement ..........................................................21
3.5 Real-time Collection of Tree Parameters Using Laser Sensor .............................27
3.6 Experiment 1: Air Penetration through Tree Canopy..................................29
3.7 Experiment 2: Effect of Deflector Plate on Spatial Distribution of Spray
D position ......................................................................................................32
4 RE SU LTS A N D D ISCU SSION ...................................................... .....................36
4.1 Evaluation of the Electromechanical Control System ..........................................36
4.2 Experiment I: Air Velocity Measurements...................................................38
4.3 Experim ent II: Spray D position ................................... .................................... 42
4.4 D discussion ...................................................................... .. ....... ...... 43
5 CON CLU SION S ..................................... .......... ......... ........... 48
A STEP MOTOR SIZING CALCULATION.....................................................49
B COM PONENT SPECIFICATION ................................... .............................. ...... 53
LIST OF REFEREN CES ............................................................ .................... 54
B IO G R A PH IC A L SK E TCH ..................................................................... ..................58
LIST OF TABLES
3.1 Characteristic of the horizontally deflected air due to various plate positions at
sp ray er o u tlet ................................................................... ................ 19
3.2 Input output relations of the control system ........................................ .................26
A.1 Specifications of the actuation mechanism ........... ........................................49
B.1 Ball screw and nut assembly specifications .................................. ............... 53
B.2 Step motor technical specifications.................... ...... .............. ...............53
B .3 Step m otor controller features ...................................................................... .. .... 53
LIST OF FIGURES
3.1 Schematic of the PowerBlast airblast sprayer......................................................14
3.2 Schematic view of spraying application....................... ....................... 15
3.3 Airblast sprayer with different air intake area............................... ............... 17
3.4 Effect of fan inlet diameter on the air output of airblast sprayer ............................18
3.5 Schematic view of the deflector plate motion ......................................................20
3.6 Effect of deflector plate location on air output......................................................20
3.7 Components of the control system .............. .. ..................................... 21
3.8 The step motor controller, m STEP-407 ....................................... ............... 23
3.9 Schematic of actuation mechanism for the deflector plate ....................................25
3.10 Relationship between indexing value to the controller board required for a range
of laser sensor density reading ........................................... .......................... 27
3.11 Tree canopies of different densities...................................... ........................ 30
3.12 Experimental setup for measuring air velocity............... ..... ...............31
3.13 Schematic view of spray application experiment and sampling layout ...................34
4.1 Relation between actual plate position and tree density........................................37
4.2 Mean air velocity due to different deflector plate location at 2.15 and 4.73 km/h. .40
4.3 Maximum air velocity due to different deflector plate location at 2.15 and 4.73
km /h ......... .................. .................................... ...........................4 1
4.4 Maximum air velocity at two ground speeds of the airblast sprayer. ...................42
4.5 Effect of two application volume rate on total deposition at two spatial sections...45
4.6 Low application rate: spatial distribution of deposition at different deflector
plate p o sition .........................................................................4 6
4.7 High application rate: spatial distribution of deposition at different deflector
p late p o sition s ...................................... ............................................. 4 7
A. 1 Block diagram used for stepper motor calculations .............................................49
Abstract of Thesis Presented to the Graduate School
of the University of Florida in Partial Fulfillment of the
Requirements for the Degree of Master of Science
CONTROLLING AIRBLAST SPRAYER AIR FOR VARIABLE RATE
APPLICATION IN ORCHARDS
Chair: Masoud Salyani
Major: Agricultural and Biological Engineering
Spray requirements vary considerably throughout the grove on account of
variability in citrus canopy size and foliage density. Configuring sprayers to suit this tree
variability is vital for efficient spraying. Currently, crops are sprayed uniformly
throughout the field based on experience. Uniform application of agrochemicals not only
wastes chemicals but also has environmental implications.
At present, airblast sprayers account for majority of sprayers for tree crop
application in Florida. While moving across the grove, these sprayers rely on a stream of
air supply generated by fan(s) to carry the material from the nozzles to the canopy. The
air volume generated in these sprayers range between 3.7 46.7 m3/s. A fully grown tree
has a different spray requirement as compared to a small or medium sized tree. It has also
been observed that a typical airblast sprayer may deposit 2-3 rows beyond the immediate
row for which it was intended. Since the tree size and density distribution on the field are
usually non-uniform, uniform spraying could result in substantial material losses as
ground fallout and drift.
My work describes design modification of an existing airblast sprayer to test the
idea of variable rate spray application by adjusting the air output. My project involved the
design, implementation and testing of an electromechanical system to change the volume
of air going to the trees based on the tree density information from a laser sensor. This
process gives real time change in air output characteristics as the sprayer moves across a
row of trees. By using this system, the air volume can be changed from 1.9 to 7.6 m3/s in
less than 3 seconds. Air penetration was quantified by measuring air velocity which
revealed that different settings of this air regulatory system can produce significantly
different air characteristics across a dead and medium density tree. Overall, increase in
air volume gave higher spatial distribution of spray material but for high volume
application changing air volume can produce significant high deposits in near locations
when compared to far locations thus reducing off-target wastage.
Florida is the second largest producer of citrus in the world and accounts for more
than one-third of the world's grapefruit production. These trees are mostly sprayed with
air-carrier sprayers. These sprayers use high volume and velocity air streams, produced
by axial-, centrifugal-, or cross-flow fans, to transport the spray droplets to tree canopies.
The aim is to replace the air within the trees by a stream of air and agrochemical droplets.
Spray requirements of a fully grown mature tree is substantially different from
those of medium or small sized tree. In addition, it is very common to find dead trees and
resets in the field. Efficient spraying in agriculture involves optimum usage of the
available resources. The ideal spraying deposits the material on the intended target, based
on the type of tree and minimizes ground deposit and drift. In contrast, at full air capacity
the sprayers could deposit the material 2-3 rows beyond the row for which it was
intended. This results in considerable amount of wastage of agrochemicals which has
economical as well as environmental concerns.
Many researchers and companies have successfully shown the advantage of
customizing the liquid output from nozzles based on the characteristics of the trees.
However, there have been fewer attempts to modify the air that carries the spray droplets
to the trees. The overall objective of this project is to evaluate the idea of variable rate
spray application by changing the air volume that is used to transport these spray
1.2 Thesis Organization
My thesis is divided into five chapters. The second chapter, Background, deals with
relevant literature review and past work done in this area. The third chapter, Materials
and Methods, describes the progressive steps taken to develop a system to address the
problem described in section 1.1. Subsequently, it also describes the experiments
conducted to test this system. The fourth chapter, Results and Discussion, evaluates the
control system, and further, discusses the results that were obtained from the experiments
described in chapter three. The fifth chapter, Conclusions, gives an overall perspective of
this research project.
This chapter gives the background and lays a foundation for this project. It
starts with statistics of the agricultural pesticide usage in Florida to recognize the
significance of developing technology which can maximize application efficiency and
minimize wastage. Pesticide application technology is then discussed to give a
general overview of equipment used for tree crops. Focus has been placed on airblast
sprayers as the aim of this project was to optimize air output in such sprayers. Finally,
control systems in airblast sprayers used for variable rate application are discussed.
2.1 Pesticide Usage in Florida
Pesticides are agrochemicals that are intended for controlling pests. Pesticides
in the form of sprays are commonly used to control pests that affect citrus. In 1999,
Florida Agricultural Statistics Services reported that herbicides were used on 96.3%
of the 316,840 ha of citrus and avocado. Similarly, insecticides and fungicides were
applied on 91.3 and 81.9% of the acreage respectively in the same year. This shows
the widespread use of pesticides for tree crops. Though the intention is to spray the
material to the target, a considerable amount of pesticide is wasted. These wastages
arise primarily from three sources:
Drift to air
Runoff from leaves falling on the ground
It was reported that about 22% of the spray material is wasted to the ground
and, about 21% drifted to air with commonly used airblast sprayer at application rate
of 950 L/ha (Miller et al., 2003). This not only has economic disadvantages, but also
leads to ground and surface water pollution, air pollution, disturbance in the
neighboring ecosystem and may also present health concern to humans. Hence,
efforts are being made to optimize the amount of pesticide usage in agriculture.
2.2 Pesticide Application Technology for Tree Crops
Pesticide application technology refers to the equipment that are used to
dispense pesticides. Pesticide applicators for tree crops are characterized by their high
volume application to cover the dense foliage of trees. Pesticides are applied in solid
or liquid formulation with or without assistance of air. Pesticides in solid formulation
are applied either in granular or powdered form. These applicators are called granular
pesticide applicators or dusters, respectively. Pesticides that are used in liquid
formulation are applied using sprayers. Commonly, sprayers use assistance of air to
carry the spray droplets, and for better canopy penetration. These sprayers are
designated as air-carrier sprayers.
Sprayers use hydraulic systems to transport and spray pesticides to the target.
These hydraulic systems comprise a tank to store the liquid formulation, a pump to
develop the necessary pressure, manifolds to transport the pressurized liquid and
nozzles to convert the liquid into droplets and disseminate the pesticide. These
sprayers have a boom to support the nozzles at the outlet.
2.2.2 Air-Carrier Sprayers
Air-carrier sprayers account for 89% of spray machines for citrus production in
Florida (Stover et al., 2002a) and hence, are important equipment for pesticide
application. These sprayers are commonly used for spraying tree crops having large
foliage. They use a stream of air to transport spray droplets towards the tree and
penetrate the canopy. The air in and around the trees is thus replaced with a mixture
of air and pesticide droplets. This method of application is considered superior as it
increases the deposition (Reichard, 1977; Salyani, 1988). These sprayers are available
in different shapes, sizes, fan types, nozzles and are operated with different volume
rates and ground speeds.
The working of an air-carrier sprayer system can be broadly divided into two
modules. The first one comprises of the components that handle the delivery of liquid
and is referred to as the liquid delivery system. The second module relates to the
delivery of air and is called air delivery system.
220.127.116.11 Liquid delivery system
The task of liquid delivery system in an air-carrier sprayer is to store, pressurize
and produce droplets of the liquid pesticide formulation. This is achieved by a
hydraulic circuit which employs a pump to pressurize and force the liquid from the
tank to the nozzles. The nozzles aligned on the sprayer can be categorized to be in
three sections namely; top, middle and bottom, reflecting the section of the tree that
the spray material affects. These nozzles produce droplets of liquid pesticide which
are transported to the target due to the functioning of air delivery system.
The number of nozzles, nozzle size, nozzle pressure, and ground speed of
sprayer play an important role in the deposition efficiency of a sprayer. These have to
be adjusted to maximize the efficiency of spraying. For instance, it was suggested by
Salyani (2000a) that for better deposition at lower application rates, reducing the
number of nozzles and using smaller nozzles would be advantageous rather than
driving the sprayer at higher speed. On the other hand, for higher volume applications
it would be helpful to use more nozzles and higher speed rather than using large disc
and core sizes. Investigation on the effect of ground speed of airblast sprayer (50 m3/s
capacity) on spray deposition by Salyani and Whitney (1990) revealed that increasing
the speed does not necessarily reduce the deposition.
Canopy structure in a grove is diverse and hence, uniform spraying can result in
some spray losses. To optimize the usage of pesticide on tree crops according to
canopy makeup, the general trend among researchers and commercial sprayer
manufacturers has been to develop spray systems which match the spray output with
canopy structure. Many researchers have successfully shown the advantage of
spraying tree crops according to vegetation volume (Balsari and Tamagnone, 1998;
Balsari et al., 2003; Escola et al., 2003; Giles et al., 1987). Commercial systems like
Roper's Tree-SeeTM (Roper Grower Cooperative, Winter Garden, FL), Durand
Wayland's Sin.hlt prayTM (Durand-Wayland Inc., LaGrange, GA) and AgTech's
Tree-SenseTM (AgTech Inc., Manhattan, KS) have implemented the same by using
sensors that target specific zones on a tree. The nozzles are then activated by electric
solenoid valves so that only the zone detected by the sensors is sprayed.
18.104.22.168 Air delivery system
Air delivery system in air-carrier sprayers is responsible for producing high
volume and velocity airflow to transport liquid droplets from the nozzles to the trees.
The main components in the air delivery system include a fan, airflow straightener
and air deflectors. Various types of fans that have been used in airblast sprayers are
axial-, centrifugal- and tangential-flow fans. Axial flow fans are most popular for
their large volume and low pressure applications. Airblast sprayers are a type of air-
carrier sprayers that use such fans. The fans consist of a series of radial blades
attached to a rotating hub. This assembly of blades and hub is termed impeller or
rotor. Air drawn by the rotor is discharged by the tangential component of velocity.
This results in a swirling motion of the air, commonly known as slipstream rotation.
The efficiency of the fan decreases with swirling as the air encounters more
resistance. This swirl is removed by the stator or straightener placed downstream of
the rotor. The dynamic pressure developed here is converted to static pressure rise.
The air is then deflected towards the nozzles by a set of deflector surfaces (plates),
sometimes, by about 900 to target trees lateral to the sprayer.
It was manually observed that the spray can reach 2-3 rows beyond where it is
intended. This was partially due to the large amount of air that is uniformly used to
transport the spray to the target. Whitney et al. (1986) have reported that Power-Take-
Off (PTO) powered airblast sprayers can have airflow rate from 3.77 to 25.01 m3/s. It
has also been suggested that such high air volume is justified only for large and
densely foliated trees (Balsari et al., 2001; Salyani and Farooq, 2003). Additionally,
such high volume can lead to drift of spray material into the air. An experiment was
conducted by Salyani and Farooq (2004) to quantify and compare drift potential of
the commonly used airblast sprayers. Due to the radial discharge of the PowerBlast
sprayer (used in this project), it had highest above canopy drift compared to other
sprayers. However, it was seen that lower ground speeds (2.4 to 2.8 km/h) of the
sprayer produced higher spray deposition as compared to higher ground speeds (4.8
to 5.8 km/h) (Salyani et al., 2000). Salyani and Hoffmann (1996) reported that, in
general, the velocity of air reduced at increasing distance from the sprayer. Further, it
was also found that air velocity from a traveling sprayer had lesser magnitude
compared to a stationary sprayer. It should be noted that these tests can be affected by
wind speeds and direction.
Efforts to optimize the material transport from the nozzles of airblast sprayers
can be complemented by a system that can control the amount of air that transports
this spray material based on the morphological characteristics of trees. In this regard,
Balsari et al. (2003) attempted to change the air output by using an adjustable
diaphragm at the axial fan inlet, but no real experiments were reported. Also, this
method is not suitable because equal amount of air will be output from each side of
the sprayer. This defeats the purpose of providing variable air output for trees of
different physical characteristics on each side of the sprayer as it travels through the
grove. Landers and Gil (2006) tested an air deflector system which directed the air
horizontally into the canopy on both sides of the sprayer. It was reported that a 25%
improvement in deposition could be achieved using this system.
2.2.3 Testing Methodologies for Sprayer Air and Liquid Output
An important aspect of testing airblast sprayer efficiency is to choose
appropriate methodology to quantify the spray deposits and air characteristics. There
are several factors that can affect the results obtained from such experimental design
and hence are reported along with the other results of the experiment. Some of these
factors are: ground speed of sprayer; number of nozzles; nozzle type; nozzle pressure;
nozzle orientation; air velocity and volume; type and location of targets; and
environmental conditions like temperature, relative humidity, wind speed and
Spray applications have been quantified using several methods. Each of these
methods has certain advantages and disadvantages. Hence, it is important to have
some idea about each of them before selecting an appropriate method. Fluorescent
tracers and fluorometry have largely been used to quantify deposition and drift of
spray material. A problem associated with this method is that the commonly used
water soluble dyes are prone to degradation under solar radiation (Salyani, 1993). An
alternative could be to use metallic tracers such as copper which do not degrade under
sunlight. The deposits in this case are quantified using colorimetry. To catch the
tracer in spray, a variety of targets have been used. Though leaf samples are ideal for
simulating the actual target, artificial targets such as paper, mylar, etc. can provide
certain advantages in quantifying the spray deposition. Salyani and Whitney (1988)
conducted an experiment to compare the deposition on leaf samples with mylar
targets using fluorometry and colorimetry. They published a correlation of R2=0.90
using colorimetry, and R2=0.85 using fluorometry between leaf and mylar target
deposits. Salyani and Fox (1999) compared oil and water sensitive papers as targets.
They reported major challenges in handling these targets because of their sensitivity
to air temperature, humidity and operator error. Additionally, for high volume
applications it might be difficult to quantify the spray amount as the targets become
over-covered with droplets. A comparison was made between string and ribbon
samplers by Salyani et al. (2006) in field applications. Spray mixtures in this
experiment consisted of fluorescent tracer at different volume rates and ground
speeds. It was reported that string samplers had higher capture efficiencies compared
to ribbon samplers for all sample locations.
2.3 Control Systems in Pesticide Application Technology
A control system is an integration of several electrical/mechanical components
used to regulate a desired output. Control systems have been traditionally used to
automate processes in various areas of the industry. In precision agriculture, they
have been used to realize some of the goals of variable rate application technology.
Control systems can be broadly classified as closed loop and open loop systems. In
open loop systems the controller directly gives commands to an actuator without
receiving feedback about the actuator's previous state. This form of control can be
applied when the actuation required is not very accurate. Closed loop control systems
continuously monitor the commands sent based on the feedback from the actuator's
previous state and information regarding the present state. This form of control can
result in higher accuracy and faster response (Cugati et al., 2006, Gebhardt et al.,
1974). The main components of a closed loop control system are plant,
computer/controller and sensor. The plant includes a set of electromechanical
components which act upon electrical signals sent by the controller to perform its
function. Computer/controllers are electronic devices that control the actuator and
indirectly vary the application rate of the products being applied based on information
from several sources such as the application equipment itself or other sensors.
Controllers form the fundamental component of any variable rate application system
(Clark & McGuckin, 1996). These controllers are typically driven by a
microprocessor that works based on a set of rules or algorithm. A sensor is a
transducer that is used to measure a physical quantity such as temperature, pressure,
etc. and convert it into an electrical signal. Sensors can also measure a particular state
of the plant and give feedback signal to the computer/controller.
Traditionally, in sprayers, control systems have been used to automatically
control nozzle discharge rate in the liquid delivery system (Stover, 2002). The
traditional approach to handle this has been to regulate the pressure across the nozzle
(Giles et al., 1996). But this form of control can have significantly delayed response
time resulting in poor performance (Han et al., 2000). To counter this, pulse-width
modulation (PWM) has been used to control electrically actuated solenoid valves that
are connected to the nozzles (Giles & Comino, 1990, Han et al., 2000). Electrical
solenoid valves can give considerable shorter response time compared to
conventional pressure-based flow control system.
Variability in application system can be initiated by two approaches: map based
application and sensor based application. Sensor based application, used in this
project, has an advantage over map based application due to higher accuracy (Sawyer,
1994) and real time control (Zhang et al., 2002). Gebhardt et al. (1974) developed an
automatic sprayer control system that changed the output from the nozzle based on
the ground speed of the sprayer. A tachometer generator sensor provided dc voltage
to a gear motor which in turn controlled the metering valve in real time at the output
of the spray tank. Ghate & Perry (1994) developed a similar system where a radar
sensor was used to sense ground speed which varied pesticide application rate by
controlling a 12 V dc step motor. Tangwongkit et al. (2006) used a software based
machine vision system that sensed greenness level of weeds to spray herbicide
accordingly. The machine vision sensor was connected to a laptop which sent
commands to a PWM circuit which in turn controlled a dc electric motor. A laser
sensor has been developed that can give the height, volume and density of each scan
on a laptop in real time as it travels in the grove (Wei and Salyani, 2005). This sensor
reportedly gave better results at low speed (1.6 km/h) as compared to high speed (3.2
km/h) due to higher number of scans it made at the lower speed (Salyani and Wei,
This research project aims at developing a control system to regulate the
amount of air in airblast sprayers to complement some of the systems designed to
control liquid flow. Regulating the amount of air using control system in a sprayer
introduces a new scenario and provides different challenges. The airflow from the
sprayer is at high velocity and turbulent in nature. The high inertia of axial fan
restricts any possibility of reducing the speed in real time for smaller trees. Moreover,
the correct amount of air needed to spray a particular tree may not be known. This
necessitates the development of a control system that can be reprogrammed and is
adaptable to changing air volume based on different sensor inputs relating to tree
Specific objectives of this project are:
* To design and fabricate an electromechanical system by which the amount of
air going to the trees can be regulated.
* To integrate the signal from a laser sensor with the air regulator system to
enable variable rate spraying in the field.
* Evaluate the functionality of the developed system through air velocity
measurements across citrus canopies with different foliage densities.
* Determine spatial distribution of the spray droplets at different air volume
MATERIALS AND METHODS
This chapter documents materials and methods that were used in the design and
implementation and testing of an electromechanical air control system for the airblast
3.1 Airblast Sprayer Description
The sprayer used for this project was PowerBlast airblast sprayer (Model No.
PB533ST, Rear's Manufacturing Company, Eugene, OR). A schematic of this airblast
sprayer is shown in Figure 3.1. It is PTO-driven and has a single axial flow fan. This fan
has 9 blades with a diameter of 0.84 m and pitch of 32. The sprayer uses the tractor
Power Take Off (PTO) power through a Constant Velocity (C.V.) joint and 3-point hitch
The PTO driveline transfers heavy torque loads from the tractor to the axial flow
fan, which is operated by an electrical clutch. The speed of the fan, at P.T.O speed of 540
rpm, is around 2160 rpm. The fan rotates in a counterclockwise direction looking from
the rear of the sprayer. It is followed by a 24 blade flow straightener unit. The air outlet
of the sprayer has an inverted U-shape slot of 144.0 x 12.7 cm on each side along its
periphery. There are 24 hydraulic nozzles on each side of the sprayer. For the fan
configuration mentioned above and for PTO speed of 540 rpm, air passes over the
nozzles at a maximum speed of about 188 km/h (PTO PowerBlast manual, Rear's
Manufacturing Company, Eugene, OR). Under standard settings of fan, the total volume
rate of air output is about 16m3/s (approximately 33,901 cfm).
S Laser Axial flow fan
TO 11 Air
3 point Hydraulic nozzle
Figure 3.1. Schematic of the PowerBlast airblast sprayer
3.2 Laser Sensor
The sensor used in this research project was developed by Wei and Salyani (2004;
2005) to measure tree height, canopy volume and foliage density. It uses an infrared laser
emitter with a wavelength of 780 nm. A line scanner consisting of a motor, with an
incremental encoder, rotates the mirror that deflects the outgoing beam of the laser
emitter by 90 and sweeps it through 3600 as it rotates. The returning beam from the
target is deflected off the mirror back to a photodiode in the sensor.
The laser sensor has two RS232 interface cables which perform different functions.
One cable is used to calibrate the laser sensor using the COM1 port on a laptop while the
second cable connects to a High Speed InterFace (HSIF) Card and gives pulse signals.
Distance measurements are made by analyzing these pulse signals. Since the laptop does
not have slots for additional cards, a PCI to Cardbus adapter is used to establish
communication between HSIF card and laptop using the PCMCIA port. The HSIF card
also controls the motor and records its position using an encoder through a parallel
(DB25) port. The laser sensor was mounted to the front side of the sprayer on a vertical
pole at about 2.4 m from the ground (Figure 3.1).
3.3 Preliminary Experiments
It was discussed in the earlier chapter that air usage in airblast sprayer was not
optimum. To support this claim, several tests were conducted. These experiments and
their conclusions have been detailed in the sections below to assert the progressive nature
of this research project.
3.3.1 Airblast Spray Distribution Pattern
An initial visual assessment of the spraying pattern of the airblast sprayer was
made. Blue and lilac Albuz APT cone nozzles (Ceramiques Techniques, Desmarquest,
France) were used on left and right side of the sprayer to observe the effect of high and
low volume rate spraying (Figure 3.2), respectively.
High volume rate nozzles .. -"' m- 11u 1-
Figure 3.2. Schematic view of spraying application. (Adopted from Salyani (2003))
The following visual observations were made while spraying with the above
1. Deposition on trees was very good on immediate row of trees. The spray
evaporated very fast with lilac nozzles because of the small size of droplets.
2. Spray from blue nozzles moved up to 2 rows beyond the immediate row while for
the lilac nozzles it moved only by 1 row.
3. For both nozzles, considerable amount of material fell on the ground and some
droplets were sucked into the fan
4. Many droplets sprayed from the upper section of the nozzles went up in air without
hitting any target which could cause drift.
3.3.2 Restricted Air-Input Test
A possible solution to some of observations above was to adjust the air output to
the nozzles. Since droplets use air as a medium to transport them to target, adjusting air
flow can reduce some of the errors in spraying. To test this idea, an experiment was
conducted to reduce the volume of air at input in steps and quantify the output at the air
outlet. Annulus shaped wooden boards (Figure 3.3) of increasing diameter were cut and
attached to sprayer so as to change the amount of air input to the fan. The cuts were
curved to reduce turbulence at the edges. The four holes in the concentric boards had an
intake area of 0.1, 0.21, 0.36 and 0.55 m2
A pitot tube manometer was used to measure air pressure across a virtual grid of 10
x 5 points on each side of the sprayer air outlet. The ten points were across the periphery
of the sprayer while five points along the width of the outlet. Measurements were made in
three replications while the sprayer was stationary. An extra set of reading was taken
without any obstruction. Figure 3.3 shows progressive pictures of the boards that were
used to take air measurements.
Figure 3.3. Airblast sprayer with different air intake area (a) 0.1 m2 (b) 0.21 m2 (c) 0.36
m2 and (d) 0.55 m2
It was concluded that restricting the amount of air at fan input provided a means of
regulating air at output (Figure 3.4). But, annulus shaped wooden boards was not a viable
option because it resulted in equal amount of air volume on each side of the sprayer. In
general, trees may be of different shapes and sizes on either side of the sprayer. Hence, in
order to achieve the goal of optimizing the air output, it was essential to regulate the
amount of air independently on both side of the sprayer.
S0.21 Right Side
1 Left Side
0 2 4 6 8 10
Air Flow (m3/s)
Figure 3.4. Effect of fan inlet diameter on the air output of airblast sprayer
3.3.3 Deflecting Air at Output
A deflector plate was fabricated (Figure 3.5) using sheet metal. It was placed in the
space between the fan and the air outlet. Its horizontal positions from the outermost (1) to
innermost (5) would adjust the amount of air output from minimum to maximum,
respectively. The shape of the deflector was made aerodynamic to reduce the amount of
energy loss in air deflection. The height of the plate had to be limited to allow sufficient
horizontal motion of the plate and also to achieve reasonable air variability at the curved
periphery of the sprayer.
A similar experiment as described in previous section was conducted, by fixing the
deflector plate at different horizontal locations and measuring the air output at outlet.
Five horizontal locations were chosen to model the air output at the periphery. Based on
preliminary experiments described in section 3.3.2, it was found that the average air
volume coming out at the sprayer outlet on each side was about 7.67 m3/s. When the
deflector plate was installed on the left side of sprayer, the air output on this side was
split in two parts. A portion of it was discharged vertically while the other portion was
deflected horizontally toward the trees. Table 3.1 shows the characteristics of the
deflected air at each plate position when measured at the outlet. Since this outlet is
curved, as the plate position changes horizontally from 1-5, the deflected air comes
through an increasing outlet area. To account for this increase in area, the vertical
(peripheral) grid points over which data was measured was increased. It can be seen that
air volume and velocity increased as the deflector plate changed its position from setting
1 to setting 5. The results from this experiment demonstrated that the deflector plate
could regulate the amount of air at output of the sprayer (Figure 3.6).
Table 3.1. Characteristic of the horizontally deflected air due to various plate positions at
Deflector plate position Mean air velocity Mean air volume Measurement grid points
(m/s) (m3/s) (vertical x horizontal)
1 17.48 1.91 9x5
2 27.43 4.13 11x5
3 34.84 5.81 13 x 5
4 38.15 7.02 15 x 5
5 44.15 7.63 17 x 5
Note: Readings were based upon experiments described in section 3.3.3 with 3
replications. Vertical points are along the periphery of the sprayer while horizontal points
are along the width of the air outlet.
Deflected air / '""
\ Plate positions
Figure 3.5. Schematic view of the deflector plate motion
y = 0.02x + 2.43
6 Std. Dev.
0 50 100 150 200 25C
Plate position from outermost location (mm)
Figure 3.6. Effect of deflector plate location on air output
3.4 Automation of Deflector Plate Movement
An electromechanical system was designed and implemented to automate the
horizontal movement of the deflector plate only on the left side of the sprayer to test this
idea. The control objective for this system was to have horizontal motion of the plate as a
function of the density reading obtained from the laser sensor for each tree. The
procedure for real-time tree parameter data collection using laser sensor is discussed in
section 3.5. The system designed (Figure 3.7) consists of an actuator, which converts
electromagnetic energy into mechanical energy; a controller, which is the heart of any
control system; and a mechanical linkage, which takes an input and produces a different
output by changing the motion, velocity or acceleration of the input.
Controller Step Motor
Figure 3.7. Components of the control system
Actuator: The actuator used in this electromechanical system was a step motor (AMH23-
258-3, Advanced Micro System, Inc., Nashua, NH). This type of motor provides precise
positioning of the deflector plate. Like conventional motors, a step motor also converts
electromagnetic energy into mechanical energy but the difference being that it is done in
steps. This essentially means that power to this motor can be sent in pulses which results
in precise motion of the shaft. The motor used here was a 1.80 or 200 steps per revolution
motor. This step motor received signal commands from a step motor controller (mStep-
407, Advanced Micro Systems, Inc. Nashua, NH) which is described below. Detailed
specifications of the motor are listed in Appendix-B. The step motor was connected to a
36 V power supply (three 12 V batteries in series). Motor sizing calculations have been
provided in Appendix-A.
Controller: The mSTEP-407 (Figure 3.8) is an on-board intelligent step motor
controller. The choice of this controller was based on two main reasons. The first reason
was the necessity for it to integrate easily with the existing system. The laser sensor
developed for sensing the tree parameters used a laptop to calibrate and collect data.
Since, the controller includes a serial link communication port, it was convenient and
cost-effective to accept commands from the laser sensor, process and send pulse signals
to the step motor. The second reason was to have a controller that not only improved the
accuracy but also made motion of the step motor smooth. This can be achieved by micro-
stepping which involves sending pulses that will rotate the motor in fractions of its steps.
The controller has the feature of one-tenth micro-stepping resulting in higher accuracy
and smoother rotary motion of motor. Specifications of the mSTEP-407 controller board
are provided in Appendix-B. The controller board needed an 8-15 V logic power supply
which was obtained from one of the three batteries used to power the motor.
Figure 3.8. The step motor controller, mSTEP-407 (Advanced Micro Systems, Inc)
Mechanical Linkage: Mechanical linkages are a fundamental part of machine design.
The function of the mechanical linkage designed here was to convert rotary motion of the
step motor to horizontal motion of deflector plate. Figure 3.9 shows a schematic of this
actuation mechanism. Due to the limited space availability in the existing sprayer and its
ability to handle high torques, a ball screw and a nut assembly (Part number:
HL5134M20452, Techno Inc., New Hyde Park, NY) were used. Also, ball screw is a
very efficient and cost effective choice to position moving parts accurately. The
specifications of the ball screw have been given in Appendix-B. A cross bar connected
the nut on the ball screw with two shafts (Figure 3.5) on deflector plate. Two guide
rollers (Part number: VW-1, Modern Linear Inc., Corte Madera, CA) on shafts, fixed at
12 and 69 cm measured from the bottom, bear the weight of the deflector plate by riding
along a track (Part number: T-4, Modern Linear Inc., Corte Madera, CA) fixed on to the
sprayer. The step motor was coupled with ball screw using a right angle drive (Part
number: A 2Z28MC1010, 1:1 precision right angle drive,) and a cross joint type flexible
coupling (Part number: S50MCTM25P08P10).
It is important to estimate the expected loads and apply sufficient safety factor to
select linkages. Based on air measurements, it was expected that highest horizontal load
on the plate was about 221 N. This is based on a maximum air reading of 2.73 kPa and an
area of 0.08 m2 on the rear of deflector plate. To account for overloads, a safety factor of
10-15% was considered and hence, a maximum load of 250 N was used to design other
components of this system. A typical procedure used in designing mechanical motion
systems is to have a weak component in the mechanical linkage. This is done so that, in
case of heavy overload, the system breaks at that link thus protecting the more expensive
parts. In order to transmit the motion in normal circumstances, a coupling that had torque
limit of 2 N-m was used in this system. In situations when the deflector plate can get
stuck the coupling, which costs lesser, would break and stop the transmission but protect
the other expensive components from damage. Teflon sheets were placed on the sprayer
wall to reduce the friction that resulted when the plate rides along the wall.
*-Pnng CUU llll- Air
Ball nut Ball crew drive ir
-- ----- Track ,r
Figure 3.9. Schematic of actuation mechanism for the deflector plate
Input Output Relations of the Control System. The electromechanical system
can be characterized by five mathematical (Table 3.2) functions which provide a relation
between the input and output at various points.
Table 3.2. Input output relations of the control system
Nm Input Output y
(x) (y) x
Density reading from the Indexing value to the 240000
laser sensor controller board 40
Indexing value to the Rotation of motor shaft 1
2 controller board (revolutions) 2000
Rotation of motor shaft Rotation of screw rod 1
3 (revolutions) (revolutions) 1
Rotation of screw rod Horizontal movement of 5
4 (revolutions) plate (mm) 1
Horizontal movement of Air output to the tree 2.43
S plate (mm) (m/s) 0.02 +
Figure 3.10 shows the relation between indexing commands that were given by the
controller after getting density signal from laser sensor. The range 0.6-0.8 % for tree
density was chosen, based on trial runs of laser sensor for a particular row, to obtain
higher resolution of plate movement. Density readings less than 0.6 were assigned plate
location 0 mm (horizontal location 1) while readings greater than 0.8 were given 200 mm
(horizontal location 5). A linear relation was chosen for the purpose of simplicity. The
step motor indexing commands are based on 200 steps (1.80) per revolution step motor
and one-tenth resolution of the controller board. Hence, an indexing command of 2000
would rotate the motor shaft by one revolution.
Once the tree density (x,) from the laser sensor is obtained (explained in section
3.4), the value of transfer function number one in the above table can be calculated. This
is multiplied by transfer function numbers two, three and four in table 3.2 to obtain the
horizontal movement of the plate (x, ). An estimate of the horizontal airflow from the
lower part of the output can be obtained from Figure 3.6. Again, a linear equation was
used to estimate this for simplicity purpose. Based on this model, we can relate the
change in density value obtained from the laser sensor to change in horizontal airflow
output from the sprayer.
S80 y = 400000x -240000
0.6 0.65 0.7 0.75 0.8 0.85
Tree Density from Laser Sensor (%)
Figure 3.10. Relationship between indexing value to the controller board required for a
range of laser sensor density reading
3.5 Real-time Collection of Tree Parameters Using Laser Sensor
Among the various ways to measure the characteristics of tree canopy, a laser
sensor is by far the most accurate. Salyani and Wei (2005) have shown the algorithm to
measure the height, volume and density of each scan based on mathematical approach.
The values of these three features which, henceforth, will be referred to as tree
parameters from each scan, along with their individual GPS location values were needed
for post-processing to get information about a tree. To eliminate the manual post-
processing, lasers sensor algorithm was enhanced to accurately collect tree parameter
data depending on tree spacing of that particular row. Tree parameter data collected over
a tree was later used to decide the amount of air necessary for that particular tree.
In order to get the start and end of each tree, latitude-longitude information from
GPS input signal was used to continuously calculate distance traveled by laser sensor
from its starting position. This distance was constantly compared with tree spacing data,
until tree spacing length was reached, to decide the start time and stop time for collecting
data for a particular tree. This is the default method for data collection.
Sometimes under dense canopy cover GPS signal might be unreliable. In order to
ensure validity of the GPS signal, a check was included in the laser program. To ensure
that the tree parameter data is accurate regardless of unreliable GPS signal, the user is
prompted to input expected nominal travel speed initially. Then the time required to
travel each tree is calculated. An in-built software timer counts in steps equal to the
nominal time required to travel successive trees, signaling that the laser sensor has
reached the end of tree. If GPS signal is unreliable, the system switches to this method of
data collection, thus, ensuring continuity. The program is restored back to its default
method as soon as the GPS signal is valid.
Another feature added to the program was collection of data when resolution of
GPS is not fine enough. At times, it is possible that distance calculated might not be equal
to the exact tree spacing distance. For example, for a 4.6 m tree spacing the travel
distance calculated have readings of 3.7, 4.0, 4.3 and 4.9 m thus skipping the 4.6 m
reading at which the program should have completed collection for that particular tree
spacing. This situation was handled by providing a range of 0.3 m to ensure that correct
data was collected for each tree spacing. A parallel time-based check was also
implemented if the resolution degraded to more than 0.3 m. This can be understood more
clearly with an example. If for a 4.6 m tree spacing row, the GPS did not log distances
between 4.3 and 4.9 m, then a time based check would complete the collection of data for
the tree using GPS speed information and tree spacing data. The procedure used is the
same as the one described above for the case when GPS signal is unreliable.
At the end of each tree spacing an average of the density readings is calculated.
This average density is used to obtain a corresponding motor indexing command. A serial
port communication feature was added to the laser program to send this motor indexing
command to the step motor with accurate amount of turns to move the deflector plate.
With these improvements to the laser program, the electromechanical system and
laser sensor were integrated with negligible delay between detecting the density of tree
and the deflector plate movement.
3.6 Experiment 1: Air Penetration through Tree Canopy
The objective of this experiment was to test the effectiveness of the plate locations
on air penetration through tree canopies with different densities. The velocity of air
passing through trees with four different densities at five horizontal locations of the
deflector plate was measured. The trees were visually selected based on observation in
increasing order of densities and are termed as dead canopy (D), low density (L), medium
density (M) and high density (H) trees (Figure 3.11).
Figure 3.11. Tree canopies of different densities. (a) Dead canopy (b) Low density (c)
Medium density (d) High density
Mean and maximum air velocity measurements were made with a hot film
anemometer (FlowMaster, Type 54N60, Dantec Measurement Technology, Denmark) at
a distance of 4.8 m from the center of the sprayer and at a height of 1 m from the ground
(Figure 3.12). The mean and max air velocities were taken over a period of 10 s while the
sprayer traveled across a 4.6 m tree. Measurements were taken while the sprayer was
drawn by a tractor at PTO speed of 540 rpm and at ground speeds of 2.15 and 4.73 km/h
heading in the east direction on a row that was aligned in the east-west direction.
Measurements were made in four replications.
S 1.8m 3.0 m
Figure 3.12. Experimental setup for measuring air velocity. Note: Anemometer was held
perpendicular to the holder and going in to the page.
Weather data was obtained at a height of 2 m from the ground from FAWN
(Florida Automated Weather Network) for interval of the test. Ambient air temperature,
relative humidity, wind speed and direction during the experiment were 9.9-21.7C, 46-
92%, 1.34-4.02 m/s and 44-118o (0 represents north and 900 represents east),
Data Analysis. The experiment was conducted as a Randomized Complete Block
Design (RCBD). Mean and maximum air velocities were analyzed using analysis of
variance. Interaction between factors was analyzed by considering this design as a three
factor split-split plot experiment and data was analyzed using MIXED procedure in SAS
(Freund et al., 1986). The three factors considered were sprayer ground speed, deflector
plate setting and tree density. Two sprayer ground speeds (2.15 and 4.73 km/h) divided
each of the four blocks replicationss) into 8 whole plots. Each plot was further divided in
five split plots by randomly assigning five deflector plate settings. Each split plot was
divided into four split-split plots, and four tree densities (dead, low, medium and high
density) were randomly assigned. A grand total of 160 measurements were available for
analysis. Means were separated using LSMEANS with PDIFF option at 5% level of
3.7 Experiment 2: Effect of Deflector Plate on Spatial Distribution of Spray
The objective of this experiment was to determine the effect of sprayer air volume
rate on spatial distribution of spray droplets. Spray deposition was quantified by having
paper targets (Fisherbrand filter paper, Fisher Scientific, Pittsburgh, PA) at nine spatial
locations perpendicular to the direction of the travel of the sprayer. The sprayer was
operated with six open nozzles on the left side since they were directly affected by the
change in air volume due to the horizontal position of the deflector plate. Two types of
nozzles: lilac and blue Albuz APT cone nozzles (Ceramiques Techniques, Desmarquest,
France) were used to see the effect of low and high volume application, respectively. The
measured discharge rates of the six nozzles, at about 1000 kPa pressure, were 2.9 and
21.4 L/min respectively. These volumes corresponded to application rates of 215 and
1585 L/ha based on row spacing of 6 m and ground speed of 2.7 km/h. Five locations of
deflector plate, labeled 1, 2, 3, 4 and 5 corresponded to an air volume rate 1.9, 4.1, 5.8,
7.0 and 7.6 m3/s, respectively, of air deflected towards the targets at PTO speed of 540
rpm. The test structure made from PVC piping consisted of nine horizontal locations
labeled A to I at distances of 2.4, 3, 3.9, 4.8, 6.0, 7.2, 8.4, 9.6 m from the point of
discharge and at a height of 1.5 m from the ground (Figure 3.13). The travel direction
was towards west on a row that was oriented in the east-west direction.
Spray solutions contained Pyranine-1OG fluorescent dye (Keystone Aniline, Inc.,
Chicago, IL) as deposition tracer at a constant rate of 566 mg/L (ppm).Water sensitive
paper (Spraying Systems Co., Wheaton, IL) targets were also placed on each location to
visually compare it with results from paper targets. These targets were held by target
holders to keep them steady and perpendicular to spray direction during each sprayer
pass. The exposed area on the paper targets was 42.77 cm2. After each sprayer pass,
targets were immediately placed in sealable plastic bags, and stored in an enclosed
container for further laboratory analysis. Experiments were made in four replications. In
the laboratory, spray (dye) deposits on each target were quantified by fluorometry
(Salyani, 2000b). The deposits were normalized for differences in the application volume
Ambient air temperatures and relative humidity were monitored at a height of 1.8
m, using a temperature/RH indicator (Model 870H, General Eastern, Watertown, MA).
Wind speed was measured using a vane anemometer (Model HH-30, Omega
Engineering, Stamford, CT) at the same height. A white ribbon tied to a pole was used to
visually note the wind direction. The ranges of temperature, relative humidity and wind
speed during the experiment were 4.2 26.0C, 24.3 52.2% and 0.2 2.5 m/s,
respectively. The wind direction was primarily from the north and north-east direction
and did not seem to have any significant effect on spraying as magnitude of winds were
low during the entire experiment.
I H G F
Figure 3.13. Schematic view of spray application experiment and sampling layout
Data Analysis. The experiment was conducted as a Randomized Complete Block Design
(RCBD). Mean tracer depositions at near (ABC), far (DEFGHI) and at each target location,
were analyzed using analysis of variance. Analysis was done by considering this
experiment as a three factor split-split plot experiment and using MIXED procedure in
SAS (Freund et al., 1986). The three factors considered were nozzle type, deflector plate
setting and target distances. Two nozzle types (lilac and blue, with application rates of
215 and 1585 L/ha, respectively) divided each of the four blocks replicationss) into 8
whole plots. Each plot was further divided in five split plots by randomly assigning five
deflector plate settings. Each split plot was divided into two split-split plots by
considering two target locations (near and far). Means were separated using LSMEANS
with PDIFF option at 5% level of significance.
RESULTS AND DISCUSSION
This chapter begins with an evaluation of the designed control system, followed by
a discussion of the results from the experiments described in the previous chapter.
4.1 Evaluation of the Electromechanical Control System
The electromechanical system designed in the previous chapter successfully
performed its function of adjusting the output of air from the sprayer. This system was
evaluated under the following topics:
Performance: The control system was able to automate the plate movement
satisfactorily. Figure 4.1 shows the data from one of the runs made in a row of 51 trees.
On the right Y-axis are the density values (shown as dots on graph) of 51 trees obtained
from laser sensor. The range of densities obtained for this trial run was 0.65 to 0.86%.
The left Y-axis shows actual plate positions (shown as bars on graph), ranging from 0 to
200 mm that were prescribed based on the corresponding density values. Density
readings above 0.80% were assigned plate position 5 which corresponds to 200 mm. It
can be observed from the graph that the change in density reading data corresponds
closely to change in plate movements. Further implications of the change in plate
movement on the air volume and spray deposition will be discussed in detail in sections
4.2 and 4.3. The response time of the plate to move between extreme ends, that is, when
moving from high density to low density tree, was seen to be less than 3 seconds.
0 Plate position
0 Tree density 0.85
1 5 10 15 20 25 30 35 40 45 50
Figure 4.1. Relation between actual plate position and tree density
User-friendliness: The control program prompts the user to enter the tree spacing
distance and a nominal speed initially. After this no operator intervention is required
while spraying. A software switch is provided within the Graphical User Interface (GUI)
of the program to stop the process, should the operator choose to do so. Also the program
makes a log of each tree parameter data, plate movement and time information. These can
be used in further analysis. A hardware switch (Figure 3.8) was also installed which made
it easy to start or stop the controller manually.
Integration: The control system that was implemented for this project was easily
integrated with the existing sprayer. In cases where a control system is to be implemented
to test a particular idea, it is important to design with reversibility in mind. In other
words, if the automation of a particular system does not prove a certain idea it should be
fairly easy to revert to the original system. The airblast sprayer at plate setting 5 gives
almost the same air output as the sprayer would in normal circumstances. This allows the
sprayer to be used with the current method, but also enables testing with different air
4.2 Experiment I: Air Velocity Measurements
The aim of this experiment was to quantify the effect of deflector plate position on
mean and maximum air velocity measurements through trees of different densities at two
different ground speeds.
Figure 4.2 shows the mean air velocities recorded over a 10 s interval while the
sprayer passed trees of varying densities with five plate settings and two speeds. It must
be noted that the dead tree chosen for this test had a dense tree preceding it. The foliage
of this dense tree was extending into the dead tree spacing. While taking measurement it
was likely that mean velocity averaged over this tree spacing would result in lower
values. Nonetheless, it can give a fair idea of dynamics of the plate in modifying the
mean air output. Figure 4.3 shows the maximum air velocity profile for trees with varying
density due to change in deflector plate setting. In general as the density of the tree
increased, mean and maximum air velocity across them decreased. However, for a
particular tree, as the deflector plate position changed from 1 to 5 the mean and
maximum velocities increased. For example it was found that, for the dead tree at 2.15
km/h, there was significant increase in maximum air velocity between plate setting pairs
1-2, 1-3, 1-4 and 1-5. It may be concluded that, when the sprayer encounters a dead tree it
may be beneficial to have plate setting 1. At 4.73 km/h, there was significant increase in
air velocity between the pairs 1-5, 2-5 and 3-5 for medium tree. For the dead tree, mean
air velocities at plate settings 1, 2 and 3 were significantly lesser compared to plate
settings 4 and 5. It may be concluded that by using lower plate setting at 4.73 km/h,
significantly lesser air velocities can be obtained while spraying. Change in air velocity
also leads to change in volume as can be seen from Table 3.1. It was published that there
was little or no relation between air velocity and spray deposition on leaf samples
(Salyani and Hoffmann, 1996) while, results from Balsari et al. (2001) showed that
reducing the air volume lead to a better spray deposition. Nonetheless, an
electromechanical system like this can help in efficiently testing spray deposition with
different air volume and velocity.
Figure 4.4 shows the maximum air velocity averaged over all plate settings for each
type of tree to see the effect of ground speed. Overall for both the speeds, maximum air
velocity decreased as the density of the tree increased. Lower ground speed resulted in
greater maximum air velocity which agrees with results from Salyani and Hoffmann
(1996). There was also interaction effect between the sprayer ground speed and deflector
plate setting. Higher deflector plate setting resulted in increased reduction in maximum
air velocity from lower to higher ground speeds. But this interaction was inconsistent
with the high density tree as it resulted in almost same air velocities at both speeds. This
could be attributed to the dense foliage of the tree which substantially blocked the air
from coming onto the hot-wire anemometer, leading to the inconsistent result. It may also
be noted that some high volume of air may be necessary to move the heavy foliage and
transport the spray droplets for high density trees (Salyani and Farooq, 2003).
1 2 3 4 5 1 2 3 4 5
Plate position Plate position
Mean air velocity due to different deflector plate location at 2.15 and 4.73 km/h. Lowercase bold, lowercase italics and
uppercase letters show mean separation between plate settings at 2.15, 4.73 km/h and combined ground speeds,
B B T I- mI
I I 1
b h ab a
b ab b a ab
_6 E02 2.15 km/hr
SMedium Densitv I Hih Density Tree
El 4.73 km/hr
-B AB r Mean separation
2. A A A A A
1 2 34 5 1 2 3.. 4 5
Plate position Plate position
Figure 4.3. Maximum air velocity due to different deflector plate location at 2.15 and 4.73 km/h. Lowercase bold, lowercase italics
and uppercase letters show mean separation between plate settings at 2.15, 4.73 km/h and combined ground speeds,
A0 2.15 km/-
/ -E 0 4.73 km/-
"- 6 Mean separation letter
2I T I
a b a br
dead low medium high
Figure 4.4. Maximum air velocity at two ground speeds of the airblast sprayer. Note:
Averaged over five plate settings. Lowercase bold, lowercase italics and
uppercase letters show mean separation between different tree densities at
2.15, 4.73 km/h and combined ground speeds, respectively
4.3 Experiment II: Spray Deposition
The aim of this experiment was to quantify the effect of changing air volume and
application volume rate on the spatial distribution of spray droplets.
Plate setting 1 resulted in lower total deposition recovery from targets compared to
other plate settings due to its low air velocity profile. The air volume output decreases by
about 75% from plate setting 5 to 1. Hence, most of the spray droplets dropped to the
ground even before reaching the first target. In general, mean deposition decreased as the
target distance from the sprayer increased (Figure 4.6 and 4.7). Total depositions were
calculated as near (A-C) for the first three locations and far (D-I) for the last six
locations. These also signified spray material going to the tree and away from the tree,
respectively. Figure 4.5 shows the deposition at these two spatial sections for two
application volume rates due to different deflector plate settings. In all replications, the
deposition was higher in the near location than the far locations except for plate setting 1.
Plate setting l's air distribution was such that some of the output from the top most
nozzle (Figure 3.17) was exposed to high volume air that was vertically directed from
behind the deflector plate. This contributed to the excess deposition at far sections.
However, at plate settings 2-5 the trend reversed and there were more depositions at near
locations. Thus, depending on the spray requirement, particular plate setting can be
chosen to obtain variable deposition to the tree.
P-values of 0.09 at low application rate and 0.0001 at high application rate were
obtained between far and near location, respectively. It can be inferred that effect of
change in air volume on spray deposition is significant for high volume application
compared to low volume application. There was interaction effect between plate setting 2
and application rate which produced lower deposition at far location during high
application rate compared to other plate settings. Also, there were some interaction
effects between application volume rate and target location. For a particular plate setting,
it is natural to expect more deposition at near location compared to far location. However,
plate settings 3 and 4 resulted in lesser difference between near and far locations at high
application rate compared to other plate settings.
The results presented in this research demonstrate that the modified sprayer could
customize the deposition by changing air output. Further testing can be done on the spray
deposition across a row of trees of variable densities while the plate moves in real time to
see the effect of deflector plate location on penetration of spray inside a canopy.
The distance between the laser sensor and the sprayer air outlet was 2.7 m (Figure
3.1). For a 3 m tree spacing, by the time the laser has obtained the tree data the air outlet
has already sprayed 10% of the tree spacing with different air volume. This can result in
inaccurate spraying for a portion of the tree. This can be improved by having the laser
sensor at a distance at least equal to the tree spacing of the block to be sprayed.
A 3-second travel time was achieved for plate travel between extreme ends. For a 3
m tree spacing and travel speed 1.61 km/h, it would take about 6 seconds to travel the
tree spacing. For the worst case, wherein, the sprayer has to move across a high density
tree to a dead tree, the travel time of the plate will result in 50% of the tree being in
transition period from full to least air volume. This 3 second travel time can be reduced
by using a superior motor or higher power, thus improving the design.
Effect of two application volume rate on total deposition at two spatial
sections. Lowercase bold, lowercase italics and uppercase letters show mean
separation between plate settings at near (A-C), far (D-I) and combined (A-I)
1 2 3 4 5
0 .0 ,. ,
1.0 A Target location
B Plate 5
0.5 C D
G H T
2 4 6 8 10 12
Distance from sprayer nozzles (m)
Figure 4.6. Low application rate: spatial distribution of deposition (see Figure 3.13) at
different deflector plate position
Std. dev. Pate 1
0.0 ,- -
0 .0-. i.. .. i .,
1.0 Target location
B C Plate 5
C -H T
2 4 6 8 10 12
Distance from sprayer nozzles (m)
Figure 4.7. High application rate: spatial distribution of deposition (see Figure 3.13) at
different deflector plate positions
One of the objectives of my project was to be able to spray a particular row based
on the morphological characteristics of the tree. The electromechanical system developed
modifies the air characteristic and thus gives variable spray deposition. The density
values from the laser sensor were used as an input to achieve this variability. Evaluation
of my system shows that different settings of the deflector plate results in changing air
velocity through the canopy of different densities. A 61% reduction in air velocity was
obtained at the outlet of sprayer from outermost to innermost deflector plate position.
Further, spatial distribution of the spray droplets at different output volume was
determined. A change of plate setting from outermost to innermost yields about 37%
reduction in deposition at far location at high application rate. This results in some
reduction of off-target spraying. Since the volume of air coming out of sprayer depends
upon commands sent by the computer, it can be customized based on the requirement.
This is important as the idea of changing air volume in sprayer for variable rate
application is relatively new and hence may need fine tuning. A complementary system
that shuts off sections of nozzles based on tree height information from sensor will
further improve this system.
STEP MOTOR SIZING CALCULATION
The step motor used in this research project was selected based on calculations that
have been described below (Oriental Motor General Catalog, 2004) (Figure A-1).
Variables used in the equations are listed in Table A-1.
Programmable Step motor PB
Figure A. 1. Block diagram used for stepper motor calculations (Adopted from Oriental
Motor General Catalog, 2004)
Table A.1. Specifications of the actuation mechanism
Total mass of the plate m = 2
Ball screw efficiency 7 = (
Internal frictional coefficient of ball nut /o = C
Ball screw shaft diameter DB = 1
Total length of travel LB =2
Material of ball screw Steel
Density of steel p = 7
Pitch of the ball screw PB = 5
Step size of motor s = 1
Maximum load F =
Motor rotor inertia Jo = 3
.9 kg (6.5 lb)
6 mm (0.63 inch)
00 mm (7.87 inch)
'.8 g/cm3 (4.64 oz/in3)
mm (0.2 inch)
43.9 g-cm2 (1.88 oz-in2)
Inertia of the ball screw (JB) is given by,
J = -pL BD = x 4.64 x 7.87 x 0.634 = 0.56 oz-in2
Inertia of the plate (Jp) is given by,
Jp= = 6.51b x 16 x 0 ev 0.11 oz-in
Total Inertia (Jr)
JT = J, + Jp = 0.56 + 0.11 = 0.67 oz-in2 = 122.5 g-cm2
The motor rotor inertia (JM) should not be very small compared to total inertia (Jr)
< 30 (Clarence, 2005)
where JM = Motor inertia
J > 4.1 g-cm2
Number of operating pulses (A) required for the entire travel length of the deflector plate
is given by,
Travellength (LB) 360" 7.87 3600
A = x = x = 7870 pulses
Ball screw pitch (PB) Step angle (8,) 0.2 1.80
This implies, 7870 pulses are required to move the deflector plate between extreme
positions. Based on several design iterations on the type of motor available, its size and
cost, it was decided to select a motor using a 3 s time interval (t) required to complete the
entire travel length (LB) The pulse frequency (f) is determined based on this positioning
Number of Operating Pulses (A) 7870
f = 2623 Hz
Positioning Period (t) 3
Thus, the operating speed (N) of the step motor required to achieve this motion is given
N= fx x60 =2623 x x 60 = 787 rpm
Load Torque (TL):
The load torque is the maximum torque encountered by the motor while moving the
deflector plate. The deflector plate faces maximum air resistance when moving from
outermost position towards the innermost position. Based on the air measurements made
at sprayer outlet, it was found that the maximum load (F) on the plate was about 250 N.
The load torque is a summation of this load, F and the pilot load, Fp, due to friction of
ball nut bearings. A rule of thumb is to consider this pilot load to be approximately a third
of the load F. Hence, F = = 83.3 N.
FPB PoFpPB 250(5) 0.3(83.3)(5)
TL P + + =0.24 N-m
2ir7 2r 2((0.9) 2i
Acceleration torque (Ta)
Acceleration torque is the torque required by the motor to initially step up to the required
operating speed of 787 rpm. This is calculated based on the rotor inertia (Jo), total inertia
(Jr) and the pulse frequency (/). An acceleration time (tl) equal to 25% of positioning
time, t = 3 s is allowed to step up to the required operating speed.
SJo +Jr 7XTO f 1.88+0.67 ;(1.8) 7870 N-
Tx- x-- x- =2.17 oz-in. = 0.015 N-m
g 180 t, 386 180 0.75
Required Torque (T):
The total torque required by the step motor will be summation of the load torque (TL) and
the acceleration torque (Ta) considering a safety factor of 2.
T= (TL + Ta) x Safety factor = (0.24 + 0.015) x 2 = 0.5 N-m
Based on this requirement, availability and cost, the step motor with model number
AMH23-258-3 (Advanced Micro Systems, Inc., Nashua, NH) which had a torque
capacity of 1.82 N-m was chosen for the project. Further specifications of this motor have
been provided in Appendix-B.
Table B.1. Ball screw and nut assembly specifications
Material Cf 53, induction hardened to HRC 62 + 2.
Pitch accuracy 0.1 mm/300 mm
Diameter 16 mm
Pitch 5 mm
Features Ball screw designed for greater than 90% efficiency in
converting rotary to linear motion. Ball nut is designed
to prevent backlash
Table B.2. Step motor technical specification
No. Of leads
Table B.3. Step motor controller features
Model No. mStep-407
Current 7 A
Voltage 24 V (dc) to 80 V (dc)
Communication RS232/Serial Port
Memory 2 kb non-volatile
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Naresh Pai was born in 1981, in Mumbai in Maharashtra, India, to Archana and
Anant Pai. He received his Bachelor of Engineering degree in mechanical engineering
from the Manipal Institute of Technology, India, in June 2003. He then enrolled in
the Graduate School of the University of Florida. He expects to receive a Master of
Science degree in agricultural engineering and a concurrent Master of Science
in mechanical engineering degree in May 2007. After completing his Master of Science
degrees, he plans to work in the field of controls and automation using the technical skills
he acquired during his studies.