3. 3
Removal ................................................................................................................................. 36
SolidWorks Static Studies .......................................................................................................... 42
Motion Analysis.......................................................................................................................... 45
Actuation Motion..................................................................................................................... 45
Weed Pulling Motion............................................................................................................... 45
Risk Assessment........................................................................................................................ 45
Product Assembly ...................................................................................................................... 47
Workspace Analysis................................................................................................................... 52
Cost Analysis ............................................................................................................................. 53
Product Cost........................................................................................................................... 53
Tolerancing and Closure............................................................................................................ 58
Column & Base Chuck Tolerance Loop.................................................................................. 58
Stationary Tooth Fitted into the Chuck Base .......................................................................... 62
Dowel Press-fitted into the Stationary Tooth .......................................................................... 64
Conclusion ................................................................................................................................. 66
References................................................................................................................................. 68
4. 4
Product Performance Specifications
Introduction
The FISKARS UpRoot®
weed and root remover is a product designed to deliver
accessible, convenient, and low ergonomic-impact weed and root remover to the average
consumer. Typical methods for removing weeds and unwanted roots generally include manually
removing them by hand, using chemical treatments on area in question, or using large-scale
mechanical solutions like a mower. However, for typical residential use, the UpRoot®
provides
consumers with a convenient, durable, and light weight weed removal solution. The product
specifications need to reflect the design intent of the product: for use with typical weeds and
roots found in residential areas, generally found in sizes ranging from less than 6 inches tall to
40 inches or taller.
Dimensional & Material Specifications
Specification Value Purpose
Handle Material Aluminum
Weight reduction, perceived consumer quality, and
increased yield strength over commercial Nylons.
Handle Length 750 mm
Needs to accommodate various human heights,
provides increased workspace ergonomics and
leverage.
Handle Max Diameter 34 mm
Needs to accommodate various human hand sizes,
increased workspace ergonomics.
Blade Material Stainless Steel
Provides good corrosion resistance to outside
environment.
Blade Length 115 mm
Provides reasonable insertion distance to remove
weed and root systems of various depths.
Ejector Material
Polyamide 30%
GF Nylon
Provides low reactivity, high-strength polymer for
relatively low-stress function.
In order to quantify a specification for the required pull-out force the UpRoot®
should be
able to withstand, data was gathered for 50 samples measuring the pull-out force required for
typical weeds found in a residential neighborhood. Data was collected in South-west Florida
which contains high sand and shell concentrations per unit soil. Results located in other parts of
the state will generate different statistical results based on soil and plant conditions.
5. 5
The distribution found for pull-out force is shown in the figure below:
Figure 1: Pull-out force distribution for typical weeds found in residential yard.
The mean for the above data set is 15.23 lbf with a standard deviation of 10.29 lbf. To
determine an appropriate pull-out force specification for the UpRoot®
, a six-sigma methodology
was used. Six-sigma methodology is a process typically used in the manufacturing of
assemblies to reduce the number of goods produced with manufacturing defects. However, this
methodology can be used to determine a product specification that ensures that a product will
not fail during operation approximately 99.99966% of the time.
In order to complete this analysis, the distribution must first be assumed to be Gaussian.
Looking at the above data, the distribution is not completely normal but is close enough for the
analysis to provide a reasonable approximation for a product specification. Thus, the maximum
expected loading condition can be estimated using the following equations:
Consequently, a reasonable performance specification for the UpRoot®
is determined to
be the following: to remove a weed or root system with a maximum pull-out force of 77 lbf
without loss of intended function.
6. 6
Product Functional Description
Introduction
The UpRoot®
is intended to facilitate weed and root removal. The process in which the
user can effectively exercise the UpRoot’s function can be divided into four distinctive steps:
pre-positioning, insertion, contraction, and removal. Although the first step in the process is
optional, it is highly recommended to ensure successful removal of the weed and root by the
fourth step.
When pre-positioning the UpRoot®
, or system, the user selects the weed of interest and
then centers it in between all four of the open teeth of the system while the system is either
suspended in the air or in light contact with the ground. After a desired position has been
attained, the user will hold the handle with one or two hands, and step downward with one foot
on the portion of the lever closest to the column. As these operations are performed, the system
will be plunged, or inserted, into the ground and through the soil. Once the system is firmly
submerged in the soil, the user will pull on the handle. Since the handle, column, and fixed
blade share the same degree of rotational mobility, the fixed blade will initiate contraction, or
squeezing, of the weed’s root and the surrounding soil. At this point, the lever is no longer in
contact with the user’s foot, but it is in contact with the top of the ground through its bottom
surface. The final step in the process requires the user to exert additional force to completely
remove the weed and its root. This force further compresses the root and soil and changes the
lever’s contact surface with the ground, such that its flat bottom surface is lifted off the ground at
an angle equal to the angle generated from additional force after contraction. The force flow
throughout insertion, contraction, and removal will be further elaborated in the theoretical
analysis section and will be presented visually through free body diagrams.
Product Patent Description
Introduction
The FISKARS UpRoot®
Weed and Weed remover is a design concluded from an evolution
of weed remover designs. Patents over the years show that some designs for weed removing
tools were outdated by having components that strained the user from completing the process
of easily removing weeds. Some of the positive attributes of the weed remover design are:
Handle allows for use in standing position.
Lever creates a larger torque for the easy removal of tougher weeds.
No hand actuator lever that will require the user to apply force from hands and fingers.
Ejector mechanism keeps the blades clean after each use.
Four blades; Three blades are design as cams to a pivot blade that allows for maximal
grip.
Blade design is simple and efficient from a manufacturing standpoint.
7. 7
Some of the negative attributes of the design are:
Handle grip can be designed to be more user friendly; T-shape design.
Position of the ejector requires the user to bend down or lift the weed remover higher
than necessary.
The weed remover does not have a basket design that allows the user to collect the
removed weeds.
The weed remover is not automated.
The positive and negative attributes of the weed remover can be accredited to the following
parts: The handle, lever, ejector, and blades. Neglecting the fact that a patent exists, each of
these features in the weed remover are patentable.
The handle measures about 750 mm in length. This length allows the user to be able to pick
up the weeds without needing to bend down. The design is beneficial with older people and
people with back injuries. Overall, the design makes the use of the weed puller convenient. A
picture of the handle is show below.
Figure 2: Length of handle allows for use in standing position
The design was created from previous designs that required the user to bend down to root
the weeds. Patent 5,529,130 claims an apparatus that is able to pick up the weed at the root
without leaving a hole in the ground after use. However, as seen in the picture below, the
apparatus contains a small handle that is inefficient for fast use.
8. 8
Figure 3: Patent 5,529,130 has a small handle attached to a shovel blade.
The handle grip, although not a big restraint, can be designed to be more user friendly. A
design could be made that would allow the user to use either one or two hands, if needed.
Some weed removers, like patents 8,613,326 and 6,257,346 claim a T-shape grip that allows a
“comfortable handling of the tool by the user.”
Figure 4: Weed removers with T-shape grips.
A lever located at the end of the handle of the FISKARS UpRoot®
Weed aids in rooting
the tougher weeds. The long design creates a larger torque that allows the user to safely pull
back transferring a larger force. The lever design is an improvement from previous lever designs
that were too small to be able to root the tougher weeds or that just acted as foot-stands. Patent
6,257,346 shows a similar design to the lever in the FISKARS weed remover. The patent,
however, claims a foot-stand that provides the user with more force to dig into the dirt. The
evolution of the FISKARS design is that it can act as both a foot-stand and a lever. The lever
9. 9
also another design advantage; by being placed at the end of the handle it eliminates the weed
remover from having to hand actuator levers. Older designs that used hand actuator levers
caused strain on the user hands and made it difficult to remove the weeds. Patents 5,476,298
and 5,154,465 show the design of these hand actuator levers that were used in previous weed
removers to close the blades and pick up the weeds.
Figure 5: Patent 6,257,346 shows a foot stand design to increase force when inserting the apparatus into the
dirt (top-left). Patents 5,476,298 and 5,154,465 have hand actuator device that creates strain in the hands of
users (top-right and bottom).
Another design that is considered a positive attribute to the FISKARS Weed Remover is
the ejector mechanism. The ejector mechanism keeps the blades clear of remaining weeds that
are left attached in the blades after each use. Patent 8,613,326 uses a similar ejector design
that acts as a sleeve to the handle. The ejector mechanism contains a flat surface at the bottom
with holes that fit into each blade. The mechanism, then, translates up and down the handle and
is limited with an upper and lower stopper. There are two different design considerations that
may be improved from the ejector mechanism. First, after each use the user needs to either
bend down or lift the weed remover to reach the ejector grip. Moving the mechanism more
towards the top of the handle can lessen this strain. Second, after each use the, the user needs
10. 10
a separate basket to put the weeds on. Or, to avoid this, the user might be inclined to just leave
the weeds in the ground. A basket attached to the ejector mechanism improves these design
considerations. Patent 5,386,681 shows an example of the basket design.
Figure 6: Ejector mechanism in weed remover similar to the design in the FISKARS tool (left). Basket design
in weed removing tool (right).
The blade design in the FISKARS weed remover is another positive attribute. From a user
perspective, the blades facilitate in the picking of the weeds by having moveable blades that
come together to a pivot blade. The design is an improvement from previous stationary blades
found in weed removers. The stationary blades made the user use more force when rooting out
a weed. These previous weed removers created large holes in the ground from jamming the tool
in to get the root of the weeds. Some examples of stationary blades are seen in patents
5,469,923, 5,469,923, and 5,360,071.
Figure 7: Stationary blade design in weed removers
11. 11
The blades hold another advantage from a manufacturing perspective. Unlike other
blades, these blades are simple to make, yet efficient when in use. More intricate weed
removers have helical shaped blades or blades in clusters. These design are more expensive to
make, and adds a complexity for the user to keep it well maintained. Some examples are seen
in patents 5,865,259 and 7,347,276.
Figure 8: Complex blade designs in weed removers
Based on other patents, there is one final design attribute that could be improved upon
with the FISKARS weed remover, automating it. This change will increase the cost of the weed
remover, but will also increase the efficiency. The design itself does not have to be incorporated
into the weed remover. Patent 9,049,812 shows an example of how automation can be included
in the design by having a handle that allows a power tool to be inserted.
Figure 9: Power tool adds efficiency to weed removal device
13. 13
Handle
The handle is composed of solid aluminum which has been rolled, welded, and finished.
It is then ionized and powder coated to provide a resistant black finish. The handle allows the
user to exert a large mechanical advantage on the weed due to the relatively long length of the
handle which acts as a lever. The aluminum handle also provides corrosion resistance for harsh
outdoor environments, where lower quality steels may rust.
Specification Value
Material Aluminum
Length 750 mm
Max Diameter 34.29 mm
Volume 103.6 cm3
Density 2.30 g • cm-3
Weight 238.7 g
Mfg. Process(es) Rolled, welded
14. 14
Cap
The cap is composed of polyamide nylon which is injection molded and left to cool and
stabilize. The injection resin is combined with orange pigment to modify the optical properties of
the polymer, making it appear orange. The cap provides the user with a comfortable grip to
apply the torque required to remove the weeds.
Specification Value
Material Polyamide Nylon
Length 99.57 mm
Max Diameter 35.66 mm
Volume 19.3 cm3
Density 0.803 g • cm-3
Weight 15.5 g
Mfg. Process(es) Injection molded
15. 15
Ejector
The ejector is composed of polyamide nylon which is injection molded and left to cool
and stabilize. The injection resin is combined with black pigment to modify the optical properties
of the polymer, making it appear black. The ejector provides the user with the ability to expel
weeds that may have become entangled in the teeth.
Specification Value
Material Polyamide Nylon
Max Length 416.48 mm
Max Width 94.49 mm
Volume 59.44 cm3
Density 1.36 g • cm-3
Weight 81.2 g
Mfg. Process(es) Injection molded
16. 16
Ejector Handle
The ejector handle is composed of polyamide nylon which is injection molded. The
injection resin is combined with orange pigment to modify the optical properties of the polymer,
making it appear orange. The ejector handle provides the user with a grip to translate the
ejector up and down and expel weeds that may have become entangled in the teeth.
Specification Value
Material Polyamide Nylon
Length 89.0 mm
Hole Diameter 12.83 mm
Volume 21.16 cm3
Density 0.916 g • cm-3
Weight 19.4 g
Mfg. Process(es) Injection molded
17. 17
Handle Insert
The handle insert is composed of polyamide nylon which is injection molded. The
injection resin is combined with black pigment to modify the optical properties of the polymer,
making it appear black. The handle insert improves assembly efficiency by not requiring the use
of any fasteners to attach the column to the cap.
Specification Value
Material Polyamide Nylon
Length 150.9 mm
Width 13.97 mm
Volume 59.44 cm3
Density 0.5535 g • cm-3
Weight 32.9 g
Mfg. Process(es) Injection molded
18. 18
Base Chuck
The base chuck is composed of polyamide nylon which is injection molded. The injection
resin is combined with orange pigment to modify the optical properties of the polymer, making it
appear orange. The handle insert improves assembly efficiency by not requiring the use of any
fasteners to attach the stationary tooth to the column.
Specification Value
Material Polyamide Nylon
Length 73.03 mm
Max Diameter 38.10 mm
Volume 26.38 cm3
Density 0.982 g • cm-3
Weight 25.9 g
Mfg. Process(es) Injection molded
19. 19
Foot Lever
The foot lever is composed of polyamide nylon which is injection molded. The injection
resin is combined with black pigment to modify the optical properties of the polymer, making it
appear black. The foot lever allows the user to insert the teeth into the ground with assistance
from the user’s feet. As a result, this part experiences very high stresses during normal
operating conditions.
Specification Value
Material Polyamide Nylon
Length 311.43 mm
Height: 37.43 mm
Volume 171.49 cm3
Density 1.45 g • cm-3
Weight 248.3 g
Mfg. Process(es) Injection molded
20. 20
Dowel
The four steel dowels are extruded through a cylindrical die, die cut into appropriate
lengths, and the chamfered on either end to facilitate being press fit into the foot lever. The steel
dowels allow the three non-stationary teeth to rotate about the axis of the dowel, allowing them
to grab onto the weed being removed.
Specification Value
Material Steel
Length 15.56 mm
Max Diameter 6.05 mm
Volume 4.67 cm3
Density 7.80 g • cm-3
Weight 3.65 g
Mfg. Process(es) Extruded, die cut
21. 21
Stationary Tooth
The single stationary tooth is stamped from a plate of stainless steel using a press. The
edges are then deburred to reduce handling injuries. The stationary tooth is press fit into the
base chuck and does not rotate around a steel dowel like the other teeth. As a result, all other
rotations and movement within the device are relative to the stationary tooth.
Specification Value
Material Stainless Steel
Length 187.40 mm
Thickness 2.62 mm
Volume 9.45 cm3
Density 10.97 g • cm-3
Weight 103.7 g
Mfg. Process(es) Stamped
22. 22
Rotating Teeth
The three rotating teeth are stamped from a plate of stainless steel using a press. The
edges are then deburred to reduce handling injuries. The rotating teeth each have a protrusion
that engages with the stationary tooth. When a torque is applied to the column, all of the teeth
rotate inwards due to the fact that the stationary tooth cannot rotate.
Specification Value
Material Stainless Steel
Length 114.91 mm
Thickness 3.63 mm
Volume 6.11 cm3
Density 7.82 g • cm-3
Weight 47.83 g
Mfg. Process(es) Stamped
23. 23
User Interface
All references of the user interface of the weeder will be done using a human standard
shown below.
Figure 10: Anthropometric man and woman
These measurements will decide the angles needed to determine if the user interface of
the weeder allows for comfort of the user.
24. 24
Insertion
There are two main components that the user interacts with during insertion of the tool: the
cap, that the user grips to place the tool in the best position to root a weed, and the foot lever
used, in this case, as a foot-stand to add force as the tool is inserted into the ground. The
handle is the component that separates the cap and the lever. The handle is designed so that
the tool can be used in an upright position. According to anthropometric measurements, 95% of
US males are between 1640 mm and 1905 mm and females are between 1540 mm and 1790
mm. All measurements that will be used in this analysis will be based on the 95% of the
population.
The total height of the FISKARS weed remover from blade to cap is about 1000 mm. This
height is somewhere above elbow height. This allows the user to use the weed remover by
bending the elbow around 90°. The cap of the tool falls in the 15° comfort zone of an
anthropometric human.
Figure 11: Comfort range of human when using tools
This zone allows the user to easily have a grip on the tool for initial use. When in use, the
tool operates about 235 mm to 270 mm away from the body of a male user and 220 mm to 255
mm away from the body of a female user. This prevents straining of the neck of the user by
having to move it past 120° downwards. The visualization range will be within the optimal
viewing range.
25. 25
Figure 12: The majority of viewing range the user will be focused on while using the tool
The final component the user will have interaction with during insertion of the tool is the
foot-lever. The foot lever has a length of 311.43 mm and width of about 99 mm. The 95th
percentile of US males has a foot length between 275 mm to 320 mm and width of 90mm to 100
mm. Female foot length is between 240 mm to 275 mm and width is between 85 mm to 100
mm. The lever is designed to be able to fit comfortably any length and width of feet. The length
of the lever is longer to account for the end part that allows the user to pivot the tool to pull back
the weed. The foot lever has an additional design purpose, and that is to allow the user to put a
downward force to assist the weed remover into the ground without having to take it out of the
15° comfort range. The lever is also designed to keep the user within a comfortable range of 65°
to 90°. Treating this lever as a pedal allows the user to add a force between 80 N to 250 N
based on anthropometric human forces for men and 57.6 N to 180 N for women.
Figure 13: Interface of foot-lever.
26. 26
Contraction
Once the tool is inserted into the ground, the cap might fall out of the comfortable rage of
15° depending on the user. The foot-lever is now touching the ground. The next step is for the
user to pull back the weed. The interaction is between the user and the cap. The user contracts
the blades to pull the weeds and the elbow joint moves between 90° to 180° with respect to the
rest of the arm. The design is created so that wrist rotation is not necessary when pulling out the
tool. The shoulder rotation of the arm is at maximum 200° with respect to the arm. These angles
allow the user to comfortably grip the cap and pull back. The user can be inclined to step back
and use the knee as a pivot point to be able to create more force. This is cautioned against
because the tool might fail. Moreover, the tool acts like a lever. The tool is designed to sustain
the 10 N-200 N for men and 7.2 N to 144 N for women of anthropometric force a user will apply.
Figure 14: Shoulder and elbow range during contraction.
Extraction
The final user interface occurs at extraction. The user pulls the weed out of the ground,
and the tool is ready for use. If there are weeds stuck between the blades, the user will use the
ejector to clean out the blades. This is the only time in the whole process that the user’s non-
dominant hand will be used. The FISKARS tool will be raised past the comfort zone by the cap
all the way until the ejector is about 775 mm to 920 mm off the ground and falls comfortably in
that 90° to 180° elbow range. From this position, the ejector acts as a handle slide.
Anthropometric forces range between 10 N to 200 N. The correction factor for being a non-
dominant hand is 9 N to 180 N for men and 6.48 N to 129.6 N for women.
27. 27
Product Theoretical Analysis
Insertion
It is important to distinguish between insertion, contraction, and removal because the
manner in which forces are interacting amongst system components changes throughout the
three mentioned steps in the overall process of weed and root removal. To begin, insertion will
be examined mainly because pre-positioning forces are not considered analytically significant to
this report as they should not lead to failure of the system. In Fig. 15, the forces exerted by the
user to hold the handle, Fhold, and to step down on the lever, Ffoot, are visible. These forces
produce torques about point A, which is the location where all four blades come into contact. As
all four blades penetrate the ground and pass through the soil, each the blades collectively
encounter a normal force from the soil, Fsoil, and insertion friction, Fi-friction.
Summing the torques about point A:
The moments created by the forces exerted by the pins cancel and is demonstrated in the
following later analysis, allowing for Fhold to be resolved as:
By examining the fixed blade in the assembly, or blade 1, a more detailed understanding
of the forces that are at work can be obtained. Focusing on Fig. 16, the forces at the handle and
lever are represented as torques, Thold and Tfoot. In addition, a more accurate presentation of the
soil force and friction is provided. Since there are four blades, it is assumed that the total normal
force from the soil, Fsoil, is evenly distributed amongst all four blades. In regards to the friction,
only the faces with the larger areas are considered for each blade. This means that there are
eight faces total – two faces for each blade. Below, equations demonstrating static equilibrium
are also provided.
28. 28
Figure 15: Forces acting on system during insertion.
Fhold
Ffoot
y
+
x
+
+ Fi-frictionFso
il
A
29. 29
Figure 16: Forces and torques acting on blade 1 during insertion.
Summing the forces in the y-direction:
And assuming that
The static equilibrium equation is as follows,
Fp
1
Thold
Fi-friction
̅ ̅ ̅ ̅ ̅ ̅ ̅ ̅ ̅ ̅ ̅ ̅
8
y
+
x
+
Fsoil
̅ ̅ ̅ ̅ ̅ ̅ ̅
4
Tfoot
30. 30
Such that the insertion friction force, Fi-friction, is:
Which yields,
As a final check, the forces contributing to static equilibrium during insertion in the lever
are analyzed in Fig, 17 below.
Figure 17: Forces and torques acting on the lever during insertion.
Again, summing the moments and torques about point A,
The moments created by the forces being exerted by the pins on the lever cancel each other
and leave the following equation:
Thold
Ffoot
Fp
3
Fp
4
Fp
2
Fp
1
A
y+
x
+
31. 31
Contraction
This step in the process, portrayed in Fig. 18, is essential for all four teeth to converge
on the root and its surrounding soil. Based off of the SolidWorks model, the largest angle at
which the handle, column, and fixed blade can be rotated at is roughly five degrees, or ϕ,
without lifting the lever off of the ground. As can be seen in the close-up view of Fig. 19, blade 1
is in contact with blade 2 and rotates about pin 1. As the portion of blade 1 in contact with blade
2 reaches the same angle as the handle, only off an axis perpendicular to the y-axis, it then lifts
blade 2 to the same angle off of an axis parallel to the x-axis, which in turn, lifts both blade 3
and blade 4 to the same angle. Lastly, the torque, Tground, is produced by the force from the
ground pushing on the bottom lever.
To begin analysis, a conservative estimation of Fpull is made, such that it is assumed to
be double the magnitude of Fhold since the soil has already been displaced from insertion. This
estimation also translates into a torque, Tpull, which is twice that of Thold. To determine Fground, the
sum of the moments about point B on the non-visible root is performed:
Since point B is located equidistantly between the fractional Froot-side load applications:
The moment equation is reduced to,
Leading to,
32. 32
Figure 18: Forces and torques acting on the system during contraction.
y+
x+
ϕ
Fpul
l
Tground
4 4
B
Froot-side
̅ ̅ ̅ ̅ ̅ ̅ ̅ ̅ ̅ ̅ ̅ ̅ ̅
Froot-side
̅ ̅ ̅ ̅ ̅ ̅ ̅ ̅ ̅ ̅ ̅ ̅ ̅
33. 33
Figure 19: Detail view of blades and blade angles during contraction.
From here, analysis similar to that of the insertion process was performed for individual
components of the system during contraction to resolve the remaining unknown loads.
However, although there are three unknowns in Fig. 20 around blade 1 and three possible static
equilibrium equations, it is evident that the particular loading on the blade leads to a scenario
where the third equation yields zero instead of an additional equation that could have been used
for substitution into the other two static equilibrium equations. For this reason, the force exerted
by the weed was derived from the average pull-out force of weed removal experiments
conducted earlier.
ϕ
ϕ
ϕ
x+
y+
Tground
Tpul
l
Froot-
side
̅ ̅ ̅ ̅ ̅ ̅ ̅ ̅ ̅ ̅ ̅
̅ ̅
4
Froot-
side
̅ ̅ ̅ ̅ ̅ ̅ ̅ ̅ ̅ ̅ ̅
̅ ̅
4
ϕ
ϕ
34. 34
These experiments measured the mostly vertical force in the y-direction required to
remove the weed and root from the soil. For the purpose of estimation and analysis in
contraction, the pull-out force is treated as a uniform force, or pressure, surrounding the root in
the soil, such that it can be compared to the case of hydrostatic pressure derived from a sphere
submerged in water.
Summing the moments about pin 1 allows for the force from blade 2, Fb2, to be determined:
Figure 20: Forces and torques acting on blade 1 during contraction.
Fp
1
Fb
2
Tpull
y
+
x
+
Froot-side
̅ ̅ ̅ ̅ ̅ ̅ ̅ ̅ ̅ ̅ ̅ ̅ ̅
4
Tground
ϕ
ϕ
ϕ
35. 35
The force on pin 1, Fp1, can be resolved from summing the forces in the x-direction:
Observing Fig. 21 of blade 2 in contraction, the new forces of blades 3 and 4 are
introduced. Taking into consideration the off-axis symmetry of blades 3 and 4, it will be assumed
that the total force exerted by blades 3 and 4, F34, on blade 2 will be the sum F3 and F4 and that
F3 and F4 are equal in magnitude.
Figure 21: Forces acting on Blade 2 during contraction.
Fb
3
Fb4
Fp
2
y+
x
+
Fb
1
4
ϕ
ϕ
Froot-
side
̅ ̅ ̅ ̅ ̅ ̅ ̅ ̅ ̅ ̅ ̅
̅ ̅
ϕ
36. 36
Assuming:
It follows that F34 can be found by
Such that,
Removal
Removal is the last step in the weed and root removing process and is illustrated in Fig.
22. It results from additional force, Fremoval, applied at the same point of contact during
contraction and produces an increase in the angle, previously ϕ, between the system’s vertical
axis and the y-axis. Below, Fig. 23 illustrates removal and respective forces, torques, and
angular changes around blade 1. By taking into account the removal angle, γ, the equation for
finding Fb1 from contraction, can be adapted to removal as,
Where,
38. 38
Figure 23: Forces acting on blade 2 during weed removal.
Continuing to draw off of contraction and summing the forces in the x-direction,
To resolve F34 at the onset of removal, which like in contraction, is the sum of the equal forces of
F3 and F4, the total force from blades 3 and 4 can be determined using by using the following
proportion:
39. 39
Where Fp1-c and Fb34-c are the forces exerted by pin 1 and the sum of forces exerted by blades 3
and 4 during contraction respectively, while Fp1-c and Fb34-r are the forces exerted by pin 1 and
the sum of the forces exerted by blades 3 and 4 during removal.
Summing the forces in the y-direction,
And treating,
The static equilibrium equation is,
Froot-tip is resolved as,
Examining the lever in Fig. 24, the new Fground can be determined since the application of
the full removal force will lead to the lever being lifted off of the surface parallel to the x-axis and
originally in contact with the ground. This rotational motion in the clock-wise direction, about the
far right-end of the lever means that the lever, as well as the components in contact with the
lever, are experiencing loadings of different magnitudes as the contraction angle increases to
the removal angle and as the point of contact between the lever and ground gradually extends
farther from the location of the weed and root.
To begin solving for Fground, the sum of moments is taken about point A:
Recalling from the insertion analysis that,
40. 40
And realizing that although Fp4 is not show, both Fp3 and Fp4 do not contribute to the moments in
the x-y plane, such that the following static equilibrium equations are obtained once the full
removal angle, β, has been reached:
Figure 24: Forces and torques acting on lever during weed removal.
Fp
2
Fp
1
Fground
β
Tremoval
Fp
3
A
x
+
42. 42
SolidWorks Static Studies
To provide some discussion on critical points of the lever and blade 1, a static study was
first conducted on the lever for the removal process. This decision was based on the knowledge
that the PA Type 6 plastic lever has a lower yield stress than the stainless steel blades.
Recalling that contraction at 5 degrees of handle rotation produced a 102.30 N load per pin from
the table in the theoretical analysis, a roughly 112 N load was applied to each pin hole and a
fixture was added to the opposite end of the applied loads to exemplify the onset of removal for
an angle greater than five degrees but less than 35 degrees. Fig. 25 illustrates the regions of
high tensile stress in red. It is evident that at the highest tensile stresses of 83.4 MPa, the
stresses in the lever surpass the yield stress of 103.6 MPa of the lever’s material. Although
there is no failure in this loading scenario, the predicted region of failure would be at the lever-
end opposite to the loading, since there is a larger moment as the applied loads move farther
away from the fixed, or grounded end of the lever.
Figure 25: SolidWorks von Mises stress plot of the lever under removal loads.
43. 43
Because of what the theoretical analysis seems to imply in table given in the theoretical
analysis, in regards to how large the forces acting on the blades can be when compared to the
user input force, a roughly 4,249 N load was applied to the pin hole of blade 1 and a fixture was
added around the surfaces of the fixed blade that would be force-fitted into the column to
exemplify the onset of removal for an angle of 35 degrees. Fig. 26 illustrates the regions of high
tensile stress in red. It is evident that at the highest tensile stresses of 81.1 MPa, the stresses in
the blade do not surpass the yield stress of 282 MPa of the blade’s AISI 1035 stainless steel.
Even with this more drastic loading scenario, failure is not experienced by the blade, however,
the finite element analysis does predict failure at the region of load application if the applied load
was higher.
Figure 26: SolidWorks von Mises stress plot of the fixed blade under removal loads.
44. 44
Another critical point to consider is the base of the column, since it contributes to the
formation of a large torque and is made of 6061 T6 Aluminum. A torque of 182 N·m was applied
to the column as the base was fixed. Fig. 27 illustrates the regions of high tensile stress in red. It
is evident that at the highest tensile stresses of 199 MPa, the stresses in the blade do not
surpass the yield stress of 275 MPa of the column’s material. With this loading scenario, failure
is not experienced by the column, however, just like the lever, the analysis does predict failure
at the base, which is opposite to the load application at the handle, if the applied load was
higher.
Figure 27: SolidWorks von Mises stress plot of the column under removal loads.
45. 45
Motion Analysis
Actuation Motion
To demonstrate how the UpRoot®
actuates, the foot lever was held fixed in space while
the handle, dowels, stationary tooth, and rotating teeth were free to move. Solid-body contact
was then applied for all parts with the friction coefficient set to aluminum (dry). A force was then
applied to the handle near where the user’s hand would be placed in order to induce a torque
about the dowel holding the stationary tooth in place. As a result, the stationary tooth acts as a
lever with significant mechanical advantage to actuate the other rotating teeth, allowing the
grasping of a root or weed.
Weed Pulling Motion
To demonstrate how the UpRoot®
removes solid objects from soil, the stationary floor
was held fixed in space while the handle, dowels, stationary tooth, foot lever, and rotating teeth
were free to move. Solid-body contact was then applied for all parts with the friction coefficient
set to aluminum (dry). A force was then applied to the handle near where the user’s hand would
be placed in order to induce a torque about the dowel holding the stationary tooth in place. As a
result, the other teeth actuate in order to grasp the root (modeled as a rectangular aluminum
prism). Furthermore, friction pads were added to the initial position of the root to demonstrate
the initial friction force that needs to be overcome before the root or weed will completely
disengage from the soil.
Risk Assessment
This risk assessment will classify the sources of hazards as follows:
Mechanical Components:
moving mechanisms that may
cause trapping or cutting within
the system or surrounding area
Hazardous Landscapes
Failures in the mechanism
Accidents from component
placement
Human error
Handling and replacement of
weeder parts
Wrongful use of equipment,
either inadvertent or deliberate
46. 46
Table II: Risk Assessment
Description of Risk Risk Estimation
Risk
Reduction
Safeguard Selection
For intended use only. The tool
should not be used for other
activities as it may cause serious
injury. Users should make sure to
keep device out of the reach of
children.
S2: Serious Injury
E2: Frequent
Exposure
A2: Unlikely
avoidance
R1
Hazard elimination. Labels
should be placed in box, tool,
and manual advising user of
risk. A safety video should be
included.
FISKARS UpRoot®
and Weed
Remover contains sharp blades
that may cause serious injury if not
handled well during proper use.
S2: Serious Injury
E2: Frequent
Exposure
A1: Likely
avoidance
R2A
Prevention of access to the
hazard: Warning label will be
placed on the handle. The use
of the tool should be prohibited
without proper safety shoes
and long pants
Store in a safe, well-lit location.
Tool can cause trip and fall,
serious injury, or puncture
containers with hazardous
materials.
S2: Serious Injury
E1: Infrequent
Exposure
A1: Likely
avoidance
R2B
Prevention of access to the
hazard: Engineering controls
should be implements to
prevent the hazard, such as:
blade protection in packaging,
or an interlock mechanism.
Teardown and rebuilding of tool
should be handled carefully and
with the right tools. Pinch points
are found in: blade pins, ejector
mechanism, and grips.
S1: Slight Injury
E2: Frequent
Exposure
A1: Likely
avoidance
R3A
Procedure: Users should be
given a assembly manual with
the right procedures and tools
for assembling and tearing
down the tool.
Maintenance of tool is important.
Not cleaning the tool periodically
may cause jamming in different
mechanisms and hinder the
performance of the weeder.
S1: Slight Injury
E2: Frequent
Exposure
A1: Likely
avoidance
R3A
Procedure: A maintenance
section should be included in
the operator’s manual to give
clear advice to the user how to
safely clean the tool.
Check landscape before use.
Landscapes densely filled with
rocks may cause damage to the
tool. Weeder is for outdoor use
only.
S1: Slight Injury
E1: Infrequent
Exposure
A1: Likely
avoidance
R4
Awareness on the use of the
weeder should be included in
the user’s manual.
Excessive force should be
prevented when pulling out weeds.
The amount of force will create
high stress and cause damage to
the handle.
S1: Slight Injury
E1: Infrequent
Exposure
A1: Likely
avoidance
R4
Awareness on the mechanical
misuse of the tool should be
noted to users. Labels placed
in the handle as warnings
should be placed.
47. 47
Product Assembly
1. Insert ejector into lever.
Alpha: 360
Beta: 360
HC: 30
IC: 00
Total Time: 1.95 + 1.5 = 3.45 s
2. Press stationary tooth into stationary insert.
Alpha: 360
Beta: 180
HC: 20
IC: 34
Total Time: 1.8 + 6 = 7.8 s
48. 48
3. Insert stationary tooth assembly into column.
Alpha: 360
Beta: 180
HC: 20
IC: 31
Total Time: 1.8 + 5 = 6.8 s
4. Insert column assembly into lever assembly.
Alpha: 360
Beta: 360
HC: 30
IC: 00
Total Time: 1.95 + 1. 5 = 3.45 s
49. 49
5. Insert 3 remaining teeth.
Alpha: 360
Beta: 360
HC: 30
IC: 18
Total Time: 1.95 + 9 = 10.95 s
6. Insert 4 pins including a flip.
Alpha: 180
Beta: 0
HC: 00
IC: 35
Total Time: 1.13 + 7 = 3.63 s
4(3.63) + 9 = 23.52 s
51. 51
9. Insert handle grip into handle shaft.
Alpha: 360
Beta: 180
HC: 20
IC: 31
Total Time: 1.8 + 5 = 6.8 s
Total assembly time: 114.92 s.
52. 52
Workspace Analysis
A typical workspace is shown in Fig. 28 and would span from 4 feet across to 4 feet wide
with enough space for operator movement and tool reach. As a result, the workstations can be
assembled as shown below on alternating sides of the conveyor. The layout of the
manufacturing space includes area for packaging the product, loading the product on pallets,
and moving the palletized goods to the loading dock. Furthermore, there is office space for the
support team and storage for supplies and materials.
Figure 28: Workspace
53. 53
Cost Analysis
Product Cost
In order to know why and how the FISKARS UpRoot®
Weed Remover cost was chosen,
an in depth cost analysis was done. There are several factors that determine the total cost of
the weed remover. Each component has a cost depending on what type of material it is.
Workers are paid to assemble, inspect, and package the weed remover. A third party contractor
is hired to ship the weed removers. The manager and engineer are paid to keep the plant
running and in good condition. Finally, there are facility costs and numerous taxes and rates that
come with hiring workers and using a facility. The figure below displays the model that is used to
find the total cost of the weed remover according to all the key factors mentioned above.
Figure 29: Cost model used to calculate the total cost of the weed remover.
The first step in calculating the total cost is to find the cost of the direct labor (DL). DL is
the cost of the workers who are on the assembly line putting the weed remover together. DL is
calculated by adding the gross wage per hour, additional taxes, and employer provided fringe
together. The next factor to calculate is the cost of indirect labor (IDL). These workers do not
assemble the product, but may inspect or package the product. The last cost to consider for the
employees is the burdened labor (BL) cost. The salaried employees such as the marketing
manager, facilities manager, and engineer make up the burdened labor of the company. These
employees are not physically involved in production or shipping, but they are critical assets to
the company from a business and quality aspect. The DL and IDL employees are paid hourly
and the BL employees are salaried. Along with the labor pay, this company also provided an
annual health insurance premium of $4401 per year per employee. Additionally, the company
has to pay taxes and social security for each employee. The table below breaks down the cost
of the three labor types.
54. 54
Table III: Displays Breakdown of Labor Costs
Wages ($/month) 13440
Taxes ($/month) 1478
Social Sec. ($/month) 833.28
Total ($/month) 15751
Total ($/min/month) 1.563
Wages ($/month) 6048
Taxes ($/month) 665
Social Sec. ($/month) 375
Total ($/month) 7088
Total ($/min/month) 0.7032
Direct Labor (DL)
Indirect Labor (IDL)
Quality Engineer ($/month) 5833
Facilities Manager ($/month) 5000
Marketing Specialist ($/month) 4167
Total ($/month) 15000
Social Security ($/month) 930
Fringe ($/month) 1100.25
Taxes ($/month) 1650
Total Overall ($/month) 18680.25
Burdened Labor (BL)
The next stage of the cost analysis is to calculate the landed costs. Landed cost is the
price the company pays for all of the parts in the assembly based off of the material and how the
piece was made. The table below shows a breakdown of the weed remover into each part and
how much it costs for a complete order that would assemble 50,000 weed removers.
Table IV: Landed Cost Breakdown by Part
Part Qty. Defect Rate Material Price Part Weight Tooling Labor Part Price Price
(%) ($/kg) (kg) ($) ($/hr) ($/part) ($)
Column 50000 5 0.4213 0.2387 75000 8 0.100564 80028.22
Dowel 200000 5 0.6350 0.0037 9400 8 0.002350 9869.90
Ejector Handle 50000 5 0.6214 0.0194 25000 8 0.012055 25602.76
Ejector 50000 5 0.9752 0.0812 50000 8 0.079186 53959.31
Handle 50000 5 0.6214 0.0155 25000 8 0.009632 25481.59
Handle Insert 50000 5 0.9752 0.0267 25000 8 0.026038 26301.89
Lever 50000 5 0.9752 0.2483 50000 8 0.242142 62107.11
Rotating Teeth 150000 5 0.6350 0.0478 75000 8 0.030353 79552.95
Stationary Tooth 50000 5 0.6350 0.1037 25000 8 0.065850 28292.48
Stationary Insert 50000 5 0.6214 0.0259 25000 8 0.016094 25804.71
Total 50000 5 - 0.8109 - - - 417000.91
55. 55
When calculating the total cost of the weed remover, the facility expenses (FE) must be
taken into account. For the assembly process, a warehouse is used for production, packaging,
and shipping. The components that contribute to the utilities are 12 2-light white utility lights that
use 64W each, 4 standard garage fans each using 150W to keep the employees cool, a
conveyor belt motor to keep supplies moving that uses 360W, and six outlets that use 900W
each. The rate charged for electricity is $0.15/kWhr. The rent is calculated by multiplying the
area of the production floor by $20/ft2
/yr. For production, an area of 66 m2
is needed.
Additionally, the raw space required is 100 m2
resulting in a total required area of 166 m2
. At
$20/ft2
/yr., the annual rent payment is $35,736. The remaining costs pay for liabilities, security,
phone & internet, water & sewage, taxes, marketing materials, and general supplies for the
company. The table below displays a breakdown of the FE.
Table V: All Expenses of the Facility
Wd. remover per WS (wd. remover/month/WS) 5099
Workstations (WS) 10
Facility Area (m2
) 166
Rent ($/month) 2978
Electricity
Lights (kWhr) 129
Fans (kWhr) 100.8
Outlets (kWhr) 907.2
Conv. Motor (kWhr) 60.48
Total (kWhr) 1197.48
Total ($/month) 179.62
Phone/Internet ($/month) 80
Water & Sewer ($/month) 150
Licenses ($/month) 100
Security ($/month) 15
Insurance ($/month) 5435
Marketing Materials ($/month) 100
Supplies ($/month) 1000
Property Tax ($/month) 375
Total ($/month) 10412.62
Facility Expenses (FE)
Once the weed removers are packaged and ready for departure, a third party
transportation vendor is hired to move the supplies to five distribution centers in the
southeastern U.S. The distribution centers are located in Charleston, SC, Atlanta, GA,
Jacksonville, FL, Miami, FL, and Mobile, AL. The average distance traveled is 290 miles and the
$/mile rate for the vendor was $3.58, based off of the current market prices of fuel, contracts,
and location. The table below shows the shipping costs.
56. 56
Table VI: Breakdown of Shipping Cost per Weed Remover
Truck
Contract ($/mile) 1.83
Spot ($/mile) 1.51
Fuel ($/mile) 0.24
Total ($/mile) 3.58
Average Trip (mile) 290
Freight Storage (m3
) 7.25
Box Volume (m3
) 0.0305
1
3770
Shipping Cost ($/wd. Remover) 0.275
Weed remover per load
Shipping
Weed remover per box
After all aspects are accounted for, the total cost to assemble and ship the weed
remover can be calculated. To find the overall cost for the weed remover at each WS, the use
rate (UR) was calculated by adding the DL, IDL, and BL together and dividing by the sum of the
number of WS. This number is added to the DL ($/min) and converted to an hourly rate to
produce the fully burdened labor rate (FBLR). The FBLR is a combination of all expenses
needed to operate. To find the total cost of one weed remover, the landed cost, assembly cost,
and the shipping cost are added together to give the final cost. The overhead rate was
calculated as 230%. This indicates that there is $2.30 of overhead costs to every $1 of DL. The
table below shows the breakdown of the cost of one weed remover.
Table VII: Overall Cost Analysis of Weed Remover
Use Rate (UR) ($/min) 0.36
Direct Labor (DL) ($/min) 0.16
Assembling Time (min) 1.92
Assembling Cost ($/wd. remover) 0.99
Landed Cost ($/wd. remover) 8.34
Shipping Cost ($/wd. remover) 0.275
Total Cost ($/wd. remover) 9.60
Production (wd. remover/month) 52628
Annual Production (wd. puller/yr) 631535
Overhead (%) 230
FBLR ($/hr) 30.91
Weed Remover Costs
Assuming every laborer fulfilled their quota of 5268 weed removers, 52,628 weed
removers would be assembled and packaged each month. This would overshoot the company
quota by 2628, leaving room for defects or workers not keeping up with production. The annual
57. 57
production would make an extra 31,536 weed removers if all laborers met quota. The goal of the
company is sell enough weed removers to cover all costs at a monthly rate. The table below
displays the company budget and the minimum amount that must be made to keep the
company from going into debt.
Table VIII: Monthly Budget Based Off of All Costs
DL ($/month) 15751.28
IDL ($/month) 7088.00
BL ($/month) 18680.25
FE ($/month) 10412.62
Landed Cost ($/month) 417000.91
Total ($/month) 468933.06
Monthly Budget
The total cost to assemble and ship one weed remover is $9.60. At that cost, in order to
meet the total monthly budget, 48,887 weed removers must be sold. Having a maximum
monthly production of 52,628 weed removers indicates a potential margin of profit. If the
projected 50,000 weed removers are sold, the company will profit $11,067. If all 52,628 weed
removers are sold, the company will have $36,296 left over each month. The MSRP is $29.97,
indicating that the company purchasing the weed remover would have a substantial markup of
212%. For a potential to make a higher profit, the assembly company would sell the weed
removers to a distributor for $13.00, or a 35% markup. This would allow the company to
potentially profit $215,257 a month, or $2.5 million annually. The distributor would still be able to
obtain for themselves a markup of 130%, assuming they are sold at an MSRP of $29.97. At
$13.00, the assembly company would only need to sell 36,070 to become profitable for the
month and allow for a much larger safety margin. Most or all distributors would be attracted to
the product due to such a large potential for profit, resulting in obtaining or exceeding the
monthly quota consistently for the company.
Additionally, the weed remover could be manufactured in China and then shipped over
to the United States. In the past, the cost to manufacture in China was much cheaper due to
wages. In 2015, the cost of manufacturing has increased in China due to wages, primarily.
Along with higher wages, the cost of shipping also adds to the price of the weed remover. The
United States has lower energy prices to produce since natural gas in collected in U.S. has
driven down oil prices. Ultimately, the determination factor will depend upon where the product
is being shipped. If the product was to be shipped in the U.S., the price will be much lower if the
made product is made in the U.S., rather than in China. Finally, deciding on whether to
manufacture in the U.S. or China also depends on the quantity of production. Shipping rates
from China are about the same no matter what the quantity. Therefore, if millions of the
products were needed, then it would be more potentially profitable to manufacture in China. On
the other hand, lower quantities can be made in the U.S. without labor costs cutting out profits.
58. 58
Tolerancing and Closure
Column & Base Chuck Tolerance Loop
Figure 30: Full section view of the stationary insert press-fitted inside the column.
Figure 31: Close-up of press-fit between stationary insert and column showing the horizontal vector
relationship.
C O
I
59. 59
Since the stationary insert (base chuck), I, is supposed to be press-fitted into the column
(handle), C, the overlap, O, should be positive. For calculation purposes, the minimum gap
should be zero. This is essential because the stationary insert is what holds the stationary tooth,
and if the stationary tooth isn’t completely mobile, all the forces acting on the tooth/gripper
system will be out of balance and cause the mechanism to fail. Because the column is rolled,
the relative tolerance used is 0.004 in/in. The stationary insert is injection molded, so the relative
tolerance is assumed to be 0.008 in/in.
Summing up the vectors in Fig. 31 leads us to the following equations:
The tolerances for both parts:
The minimum overlap should be greater than or equal to zero to ensure an interference fit:
The maximum overlap should be greater than zero and greater than the minimum gap:
Because the minimum overlap of 0.0018 in is greater than zero, there will always be an
interference fit between the column and the stationary insert using the above mentioned
nominal values.
60. 60
Figure 32: Close-up of press-fit between stationary insert and column showing the vertical vector
relationship.
Since the stationary insert, I, is supposed to be press-fitted into the column, C, the
overlap, G, should be positive. For calculation purposes, the minimum gap should be zero. This
is essential because the stationary insert is what holds the stationary tooth. The change in
vector direction has no impact on the value for the relative tolerances.
Summing up the vectors in Fig. 32 leads us to the following equations:
The tolerances for both parts:
G
I
C
61. 61
The minimum overlap should be greater than or equal to zero to ensure an interference fit:
The maximum overlap should be than zero and greater than the minimum gap:
Because the minimum overlap of 0.0004 in is greater than zero, there will always be an
interference fit between the column and the stationary insert using the above mentioned
nominal values.
62. 62
Stationary Tooth Fitted into the Chuck Base
Figure 33: Cross-section of the stationary tooth fitted inside the stationary insert.
Since the stationary tooth, T, is supposed to be press-fitted into the stationary insert, I,
the gap, G, should be negative. For calculation purposes, the maximum gap should be zero.
This is essential because the stationary tooth must remain immobile in order for the other three
teeth to perform together. The relative tolerance for the stationary insert remains 0.008 in/in;
however the stationary tooth was punched from stainless steel, and therefore has a relative
tolerance of 0.008 in/in. The fact that the relative tolerances are the same is merely a
coincidence.
Summing up the vectors in Fig. 33 leads us to the following equations:
The tolerances for both parts:
I
GT
63. 63
The maximum gap should be less than or equal to zero to ensure an interference fit:
The minimum gap should be less than zero and less than the maximum gap:
Because the maximum gap of 0.0164 in is greater than zero, there won’t always be an
interference fit between the column and the stationary insert using the above mentioned
nominal values. However in the case of this particular item, the dimensions result in a zero gap.
64. 64
Dowel Press-fitted into the Stationary Tooth
Figure 34: Assembly that shows the dowel that is supposed to be press-fitted into the stationary tooth.
Figure 35 – Close-up of the dowel inside the tooth.
D G
T
65. 65
Since the dowel, D, is supposed to be press-fitted into the stationary tooth, T, the gap,
G, should be negative. For calculation purposes, the maximum gap should be zero. This is
essential because the dowel holds all the parts together. The relative tolerance for the tooth
remains at a value of 0.008 in/in. Because the dowel was cold extruded, its relative tolerance is
0.004 in/in.
Summing up the vectors in Fig. 35 leads us to the following equations:
The tolerances for both parts:
The maximum gap should be less than or equal to zero to ensure an interference fit:
The minimum gap should be less than zero and less than the maximum gap:
Because the maximum gap of -0.0009 in is less than zero, there will always be an interference
fit between the tooth and the dowel using the above mentioned nominal values.
66. 66
Conclusion
After conducting an in-depth theoretical analysis on the system, it becomes apparent
that insertion, contraction, and removal are steps in the weed and root removal process that
merit their own individual analysis. In reality, the downward force during penetration will be
highly variable on soil density and soil inconsistencies such as rocks and other organic debris.
This means that insertion loads have a wide range of magnitudes. Soil and weed-root
composition inherently affect the loads seen in contraction and removal of the weed and root
itself as well. What is of particular interest is how significant the angle at which the handle
rotates about its pivot point is. Equations in the theoretical analysis demonstrate that the
magnitude of forces can be greatly influenced by angle changes after the sum of moments has
been taken. For example, an increase from 5 to 35 degrees can easily produce a load that is
85% larger than a load produced from an angle change of 5 degrees alone. This can be
demonstrated by performing the percent increase between sin (5°) and sin (35°).
In regards to the static studies, it appears that the material selection and loading
scenario plays a large role as to whether the system undergoes failure. For the particular
loadings applied via SolidWorks, failure was not observed, but specific regions where failure
could occur were made evident. Ultimately, it would appear that failure in the system would
likely occur in the lever because of its lower yield stress in comparison to the column and
blades/teeth, in addition to the high stresses that would form at the opposite end of load
application. Taking this into consideration, caution should be taken when trying to remove
excessively large and/or dense weeds to avoid failure of the system and injury to the user.
The FISKARS UpRoot®
Weed and Weed Remover was designed through an evolution
of previous weed remover creations. Previous patents show that the Fiskar’s weed remover has
been able to adapt many of the positive attributes that had already been created. Some of the
positive attributes of the weed remover are: being able to use it standing up, foot-lever that
creates torque, no hand actuator to strain the user hands, an ejector mechanism, and a blade
design that is simple to use and manufacture. There are some negative aspects of the weed
remover. These aspects are not necessarily considered negative in the way that is a trade-off.
For example, a better handle grip, a basket mechanism, and an actuator will dramatically
improve the device but will increase the cost. The ejector mechanism can also be put higher,
but that would throw off the user interface that it is already designed for the weed remover.
The FISKARS weed remover, as with any other appliance, has certain risks associated
with it. Most of these are small scale risks, but there is a high priority risk that can cause major
damage. If the tool is not used in any way by the way that it is designed to be used, the user can
cause serious injury to himself or anyone surrounding him. Other risks include: minor cause,
equipment damage, and slip accidents. Safeguards are created in place to take care of these
risks. Labels imprinted into the handle of the weed remover advise the user to handle the tool
certain ways. These labels also enforce the use of protective gear when using the tool. Advice is
also given in the user’s manual to prevent serious bodily harm.
67. 67
The user interface of the weed remover is focused on four main components. During
insertion, the user interacts with the cap, the handle, and the foot lever. The cap acts as a
middle component to transfer the movement of the user to the handle. The handle is long
enough to make the weed remover be placed in a comfort zone based on anthropometric data.
The foot lever helps the user insert the weed remover into the ground. It is shaped so that it fits
comfortable the 95th percentile of the population, as the rest of the tool is designed to be as
well. During contraction, the user interacts with the cap to pull the handle to take out the weed.
The rotation of the elbow and the shoulder is within comfort range of anthropometric data.
Finally, after extraction, the user interacts with the ejector mechanism. The user places his off-
hand in the mechanism while using the dominant hand to place the mechanism in the comfort
range. The mechanism is a sleeve around the shaft that has a small frictional resistant and it is
easy for the user.
The expected assembly time per widget is about 115 seconds. The layout of the
manufacturing space includes ten workspaces, area for packaging the product, loading the
product on pallets, and moving the palletized goods to the loading dock. A typical workspace
would span from 4 feet across to 4 feet wide with enough space for operator movement and tool
reach. Furthermore, there is office space for the support team and storage for supplies and
materials. The warehouse layout proposed uses 540 sqft.
The cost analysis revealed that the majority of the cost to produce one weed remover
comes from high landed costs. The material is cheap, but the cost to make the individual part
drives up the price. The assembly cost is much lower, due to minimal facility expenses and a
high amount of assembled weed removers each month. Lastly, the shipping cost of only $0.275
per weed remover is due to being able to ship large quantities of weed removers in each
shipping load and a low average of miles traveled per trip. Since the weed remover is only
shipped to the southeast, it is not necessary to manufacture in China due to lower number of
products compared to an average shipment that has millions of the product and high fixed
shipping costs.
Overall, the design seems to be effective in most, if not all regards, and achieves its
purpose in facilitating weed and root removal with minimal effort and strain to the user during
operation.
68. 68
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