Electric Razor

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Latest revision as of 17:55, 7 February 2008

Bucknell Mechanical Design Home

Group Members

Jerec Ricci

Chris Slavin

Brian Walker

Electric Razor

Figure 1: Conair Electric Razor Before Disassembly

Figure 2: Conair Electric Razor Primary Housing

Function

This electric razor was manufactured by Conair. It is used for personal grooming, such as shaving or trimming of facial hair. It is able to provide a close shave or cut longer hair with included attachments.

How It Shaves

The motor is powered by two AA batteries and turns an offset shaft. The rotation of the offset shaft is translated into only horizontal motion by allowing the offset shaft to move freely within a vertical slit on the blade base mount. This in turn moves the moving blade against a stationary blade to cut hair.

User Requirements

-Shaver is able to cut hair

-Will not cut face

-Long battery life

-Fits into a human hand

-Can trim beards/sideburns

-Comfortable

Engineering Specifications

-Hairs cut per pass (%)

-Angle of blade (degrees)

-Motor Efficiency (%) or Battery life (time)

-Fits users grip (% of population)

-Adjustable length (mm)

-Vibration (amplitude)

-Users like it (%)

Parts

The table belows lists the components for the Conair Electric Razor:

**Table 1: Conair Electric Razor Component List**
Part #	Part Name	Category	Function	Material
1	Primary Housing	Structural Component	Provides a mount for all other parts, user holds this part	Plastic
2	Electric Motor	Input	Moves the blade	Metal
3	Battery Door	Structural Component	Covers and holds batteries in place	plastic
4	Upper Housing	Structural Component	Holds taper control switch and serves as a mount for cutting heads	Plastic
5	Blade Base Mount	Motion Conversion Element	Serves as a mount for both blades and converts the motion of the motor output shaft to the side to side motion of the blade	Plastic with metal springs
6	Stationary Blade	Structural Element	Guides hairs to be cut and serves as an anvil for the moving blade	Metal
7	Moving Blade	Output	Cuts the hairs that have been guided by the stationary blade	Metal
8	Snap Mount	Structural Element	The blade base mount or nosehair trimmer snaps into the tabs on this part	Metal
9	Screws	Structural	Holds device together	Metal

Computer Rendered Components

Electric Motor

Isometric View

Analysis of Rendered Components

Electric Motor

1. The decisions that had to be made in the design of this component include the size of the motor for it to fit within the primary housing, the weight of the motor to meet the goals of a low weight shaver, the power produced by the motor in order for it to be able to cut hair efficiently, and the amount of power needed to be supplied to the motor for it to run properly.

2. The critical features of this motor are the offset bar to generate only side to side motion of the razor blade and the links going to the motor that connect the offset bar. The critical dimensions of this motor are its overall size compared to the primary housing and the size of the offset bar to give the right amount of side to side motion for cutting hair.

3. The loading that will be placed on the motor will be cyclic loading as it completes every revolution. There will also be cyclic loading on the components connecting to the motor.

4. To evaluate the performance of the motor it could be hooked up to a power source and tested to see how long it would run. The shaft could also be hooked to different weights for different trials to determine how much work or power the motor is able to produce.

Moving Blade

1. The decisions that had to be made in the design of the moving blade were how it could be mounted to the blade base mount, how many teeth it should have. The blade snaps onto the blade base mount using 2 circular holes that fit over the two circular protrusions on the blade base mount. The number of teeth the moving blade can have is limited by the stationary blade. Since the moving blade had to be narrower than the stationary blade, it was limited to 20 teeth.

2. The teeth on the moving blade are what actually cut hair. They work similarly to scissors, shearing hairs off using the stationary blade as an anvil. The moving blade was also limited in width by the stationary blade. If the moving blade was wider than the stationary blade, it would move its teeth beyond the teeth of the stationary blade, but no hairs would be cut by the moving blade teeth alone.

3. There should only be minimal loading on this component since it will pressed against someone's face. The rapid side to side motion of the the moving blade may stress the plastic on the blade base mount where it snaps together.

4. The most important aspect of this part is that mounts securely on its mount. To test this aspect, the holes that snap into the blade base mount should be within a small tolerance. The moving blade moves back and forth rapidly, so it should have a low weight to reduce its inertia. The moving blade should also be balanced or it could become unstable during its motion.

Stationary Blade

1. One decision that had to be made with this component was the size of the two circular holes at the bottom which lock the blade in place via screws. The number of prongs at the top (27), their shape, and the cut out angle that cuts into them were all decisions as well. Finally the thickness, length, and width were all decided upon.

2. The individual prongs/blades have two purposes. The first is to elevate/separate individual hairs. The second is to act as one end of the wedge between the moving blade and itself to actually lop off the hairs. There are 27 such prongs, each 0.025 inches wide and 0.142 inches long. The entire stationary blade is 1.122 inches tall and 1.103 inches wide. The two screw holes are 0.184 inches in diameter. The angled tip is 0.258 inches long and descends the entire thickness of the blade, or 0.092 inches, which gives it a slope of -0.3565 from the pointy tip of the blade if the sideways slot is at the top.

3. Loading on this component will come from pressure from the user's face or fingers. Some of this loading will be transferred to the screws holding it in place and some will be transferred to the moving blade behind it. These loadings will in most cases be minor.

4. User tests in which only the stationary blade is variable can measure performance. By varying the design of the stationary blade only, its performance can be compared to other stationary blades, and its relative performance would thus be evaluated. Since stress on this component would most likely be minor, stress tests would not be necessary.

Electric Razor

Latest revision as of 17:55, 7 February 2008

Contents

Group Members

Electric Razor

Function

How It Shaves

User Requirements

Engineering Specifications

Parts

Computer Rendered Components

Electric Motor

Analysis of Rendered Components

Electric Motor

Moving Blade

Stationary Blade

Views

Personal tools

Navigation

Search

Toolbox

@@ Line 1: / Line 1: @@
 [http://gicl.cs.drexel.edu/wiki/Bucknell_Mechanical_Design Bucknell Mechanical Design Home]
 <br><br>
+== Group Members ==
-==='''Electric Razor'''===
+Jerec Ricci
-[[Image:IMG_0002.jpg|left|thumb|300px|Figure 1: Conair Electric Razor Before Disassembly]]
+Chris Slavin
-[[Image:DVNoCase.jpg|left|thumb|300px|Figure 2: HP Deskjet 600c Without The Case]]
-=== Function ===
+Brian Walker
-This electric razor was manufactured by Conair. It is used for person grooming, such as shaving or trimming of facial hair.
-== How It Shaves==
+=='''Electric Razor'''==
-We will add a summary here.
+[[Image:ShaverAndMount.jpg|left|thumb|300px|Figure 1: Conair Electric Razor Before Disassembly]]
+[[Image:FrontCasing.jpg|left|thumb|300px|Figure 2: Conair Electric Razor Primary Housing]]
-) This has nothing to do with a razor
-[[Image:DVRollers.jpg|left|thumb|300px|Figure 3: Rubber Rollers That Advance The Paper]][[Image:DVRollerMotor.jpg|left|thumb|300px|Figure 4: The Stepper Motor That Powers the Rollers]]
@@ Line 40: / Line 38: @@
+== Function ==
+This electric razor was manufactured by Conair. It is used for personal grooming, such as shaving or trimming of facial hair.  It is able to provide a close shave or cut longer hair with included attachments.
+== How It Shaves ==
+The motor is powered by two AA batteries and turns an offset shaft.  The rotation of the offset shaft is translated into only horizontal motion by allowing the offset shaft to move freely within a vertical slit on the blade base mount.  This in turn moves the moving blade against a stationary blade to cut hair.
+== User Requirements ==
+-Shaver is able to cut hair
+-Will not cut face
+-Long battery life
-) or this.
+-Fits into a human hand
-[[Image:DVDockingStation.jpg|left|thumb|300px|Figure 5: Docking Station For The Carriage]][[Image:DVWormGear.jpg|left|thumb|300px|Figure 6: Stepper Motor That Drives The Dock Using A Worm Gear]]
+-Can trim beards/sideburns
+-Comfortable
+== Engineering Specifications ==
+-Hairs cut per pass (%)
+-Angle of blade (degrees)
+-Motor Efficiency (%) or Battery life (time)
+-Fits users grip (% of population)
+-Adjustable length (mm)
+-Vibration (amplitude)
+-Users like it (%)
+== Parts ==
-) This either.
-[[Image:DVDriveBelt.jpg|left|thumb|300px|Figure 7: Belt Drive System]][[Image:DVBeltMotor.jpg|left|thumb|300px|Figure 8: Stepper Motor That Drives The Belt Using A Toothed Pulley]]
-) Nope.
-[[Image:DVContacts.jpg|left|thumb|300px|Figure 9: Cartridge To CPU Interface]]
-==Parts==
 The table belows lists the components for the Conair Electric Razor:
@@ Line 121: / Line 87: @@
 | align="center"|Provides a mount for all other parts, user holds this part
 | align="center"|Plastic
-| [[Image:DVTray.jpg |center|thumb|50px]]
+| [[Image:FrontCasing.jpg |center|thumb|50px]]
 |-
 ! 2
@@ Line 128: / Line 94: @@
 |align="center"|Moves the blade
 | align="center"|Metal
-| align="center"|[[Image:DVHousing.JPG|center|thumb|50px]]
+| align="center"|[[Image:ElectricMotor.jpg|center|thumb|50px]]
 |-
 ! 3
@@ Line 135: / Line 101: @@
 | align="center"|Covers and holds batteries in place
 | align="center"|plastic
-| [[Image:DVLargeStep.JPG |center|thumb|50px]]
+| [[Image:BatteryDoor.jpg |center|thumb|50px]]
 |-
 ! 4
@@ Line 142: / Line 108: @@
 | align="center"|Holds taper control switch and serves as a mount for cutting heads
 | align="center"|Plastic
-| [[Image:DVDockMotor.JPG |center|thumb|50px]]
+| [[Image:UpperHousing.jpg |center|thumb|50px]]
 |-
 ! 5
@@ Line 149: / Line 115: @@
 | align="center"|Serves as a mount for both blades and converts the motion of the motor output shaft to the side to side motion of the blade
 | align="center"|Plastic with metal springs
-| [[Image:DVRail.JPG |center|thumb|50px]]
+| [[Image:BladeBaseMount.jpg |center|thumb|50px]]
 |-
 ! 6
@@ Line 156: / Line 122: @@
 | align="center"|Guides hairs to be cut and serves as an anvil for the moving blade
 | align="center"|Metal
-| [[Image:DVGears.JPG|center|thumb|50px]]
+| [[Image:StationaryBlade.jpg |center|thumb|50px]]
 |-
 ! 7
@@ Line 163: / Line 129: @@
 | align="center"|Cuts the hairs that have been guided by the stationary blade
 | align="center"|Metal
-| [[Image:DVCPU.JPG |center|thumb|50px]]
+| [[Image:MovingBlade.jpg |center|thumb|50px]]
 |-
 ! 8
@@ Line 170: / Line 136: @@
 | align="center"|The blade base mount or nosehair trimmer snaps into the tabs on this part
 | align="center"|Metal
-| [[Image:DVEject.JPG  |center|thumb|50px]]
+| [[Image:SnapMount.jpg  |center|thumb|50px]]
 |-
 ! 9
@@ Line 177: / Line 143: @@
 | align="center"|Holds device together
 | align="center"|Metal
-| [[Image:DVHeadMotor.JPG |center|thumb|50px]]
+| [[Image:TheScrews.jpg |center|thumb|50px]]
 |-
 |}
-==Computer Rendered Components==
-===Drive Belt System===
-[[Image:DVIsoBelt.jpg|left|thumb|400px|Isometric View]]
-[[Image:DVTopBelt.jpg|left|thumb|400px|Top View]]
-[[Image:DVSideBelt.jpg|left|thumb|300px|Side View]]
-[[Image:DVdissec picture.jpg|left|thumb|500px|Annotated View]]
-===Paper Advancing Rollers===
-[[Image:DVAdvanceIso.jpg|left|thumb|500px|Isometric View]]
-[[Image:DVAdvanceFront.jpg|left|thumb|300px|Front View]]
-[[Image:DVAdvanceSide.jpg|left|thumb|500px|Side View]]
-==Cool Animated Videos==
-<embed src="http://www.youtube.com/v/8_iTSznToHU" type="application/x-shockwave-flash" width="425" height="350"></embed>
-Animated Printer Carriage
-[[media:DVDriveBelt.avi|Right-click here and select "Save Link As" to download the video (.avi)]]
-<embed src="http://www.youtube.com/v/iayt04lR08E" type="application/x-shockwave-flash" width="425" height="350"></embed>
-Animated Paper Feed Mechanism
-[[media:DVGear2.avi|Right-click here and select "Save Link As" to download the video (.avi)]]
-==Analysis==
-===Analysis Of The Belt System===
-'''Scope of Analysis'''
-The two engineering specifications that are quantified for the printer belt tensioning system, are the force on the belt required to accelerate the printer head to its maximum speed, and the force to stop the printer carriage and change direction. Both of these specifications pertain to the Dots Per Inch design parameter. The best design is to obtain the maximum DPI rating in the quickest printing time. To achieve this goal, the belt must be able to cope with the forces to accelerate the printer carriage.
-'''Key Properties'''
-*Printer Prints 4 pages a minute at 300 DPI
-*Mass of Carriage With Ink Cartridge = 0.14 kg
-*Moment of Inertia of Pulley = 0.5 (.002kg)(0.005^2m) = 2.5 x 10^8
-*The belt is a trapezoidal design, meaning each tooth has the shape of the trapezoid
-*The belt is made out of polyurethane which has good wear resistance and low friction
-'''Assumptions'''
-Friction force exerted by the slider on the carriage is always constant when moving, and should have been reduced to a minimum by the manufacturer. Lower friction would reduce the force the stepper motor has to supply to move the carriage. Since it is difficult to measure the exact amount of friction force, and it is relatively small compared to the acceleration forces, friction can be neglected.
-'''Finding The Speed'''
-Since, the actual printer head speed I could not be found, a few assumptions had to be made with the available information. The printer has a 300 DPI rating, which means that it can print 90,000 dots per square inch. It can print 4 pages of text per minute. Assuming that it prints 8.5” x 11” pages with a 1” top and bottom margin, and 1.25” side margins, it leaves a total of 54 square inches of text. This equates to 4.86 x 10^6 dots per page. Multiply the dots per page by the pages per minute, and that results in 2.43 x 10^7 dots per minute. 2.43 x 10^7 dots per minute is the average printing rate for the printer. However, if we assume the format is 12 point, Times New Roman font, the total area per line of text is 1.95 in^2 (6.5” x .3”) 0.54 square inches per page multiplied by 4 pages per minute, divided by 1.95 square inches per pass, and taking the reciprocal, yields .009 minutes per line, which is 0.54 seconds per line. Every line is 6.5 inches long, which means that the printer head moves at 12 inches per second. Since information on the acceleration of the printer carriage could not be obtained, it was instead estimated. After careful observation of other inkjet printers, the carriages reach their top speed almost instantaneously, so it was estimated that it takes 0.2 seconds to reach maximum velocity, and 0.25 seconds to stop and change direction.
-'''Calculations'''
-*Acceleration of Carriage From Rest
-Acceleration of Carriage = max velocity/ time = (0.3048 m/s) / 0.2 s = 0.15 m/s2
-Mass of Carriage With Ink Cartridge = 0.14 kg
-F = ma = (0.14)(0.15) = 0.021 N
-Therefore, it takes .021 N to accelerate the carriage from rest to the max velocity
-*Stopping and Changing Direction
-Change in velocity = (0.3048+.03048) = 0.6096 m/s
-Change in Time = 0.25 s
-F = (Mass*Change in Velocity)/ Change in time = 0.34 N
-Therefore, the maximum force exerted on the belt due to the change in direction is 0.34 N.
-As seen in Figure 10 below, the maximum force to pull the carriage is related to the torque supplied by the motor pulley. Furthermore, the carriage is fixed to one side of the belt, so it translates directly with the belt. During the analysis, the entire carriage is treated as a point mass and represented as a block. Figure 11 shows the free body diagram of the motor pulley. It is evident that the torque from the pulley is directly related to the force on the belt during acceleration.
-[[Image:DVFBD1.jpg|left|thumb|400px|Figure 10: Free Body Diagram Of System]]
-[[Image:DVFBD2.jpg|left|thumb|200px|Figure 11: Free Body Diagram Of Motor Pulley]]
-The analysis through ''Adams'' produced results that were similar to the calculated values. The maximum force, as seen in Figure 12, reached 1 N which was very close to the calculated value of 0.34 N.
-[[Image:DVForceBelt.jpg|left|thumb|600px|Figure 12: Force of the Drive Belt During Acceleration]]
+== Computer Rendered Components ==
+=== Electric Motor ===
+[[Image:Shaver_Motor.jpg|left|thumb|400px|Isometric View]]
+[[Image:Moving_blade_isometric.JPG|left|thumb|400px|Isometric View ]]
+[[Image:MECH DESIGN LAB 1B 3D VIEW.jpg|left|thumb|400px|Isometric View]]
@@ Line 425: / Line 170: @@
-'''Improvements'''
-To increase the maximum force that the belt could handle, a few options are available. The cross-sectional area could be increased to decrease the stress on the belt. According the stress equation, stress = load / area , the stress can be reduced by increasing the cross sectional area to compensate for load force. The cross sectional area can be increased by making the belt wider or thicker. Making it wider would be more beneficial because it would provide a greater surface area for the toothed pulley to grip onto. The drawbacks for increasing the surface are the increase in stiffness and cost of manufacturing. Making the belt thicker would reduce its flexibility, making it harder for it to move around the pulley. It would require more torque form the input motor to compensate. Making the belt wider would force the pulleys to be wider, which drives up the cost of the system.
-Another method to increase the stress capacity of the belt would be to use a curvilinear design instead of the current trapezoidal design. The curvilinear design looks very similar to the gear sprocket of a bicycle. Instead of a trapezoid shape, the curvilinear design uses a half circle shape. Therefore, the teeth are deeper in the gear which makes it less probable for tooth jumping during high accelerations. Furthermore, there is less material at the edges of the gear, which lowers the moment of inertia, allowing the gear to accelerate faster. [1]
-[[Image:DVNewBelt.jpg|left|thumb|600px|Figure 13: Photoelastic Stress Pattern [1]]]
@@ Line 455: / Line 196: @@
-Figure 13 shows the photoelastic stress pattern of both designs, and it is evident that the curvilinear shape distributes stress more evenly. This is due to the larger tooth cross section. Since the curvilinear shape handles stress better than the trapezoidal shape, a narrower curvilinear belt could be used in place of a wider trapezoidal belt, thus, saving material and cost. [1] The trade off may be in increased cost to manufacture, since curvilinear belts are not as common as trapezoidal belts.
-A final option to consider is to change the material of the belt. Using a more durable and stress resilient material such as steel or composites, may work better. However, it is most likely that these materials are more difficult to manufacture, which increases the cost
-==References==
-[http://www.sdp-si.com/D260/PDF/part1.pdf#page=45 (1) SDP/SI : The World Of Timing Belts]
-===Analysis Of The Paper Feeder===
-'''Part 1'''
-The engineering specification chosen to analyze for this dissection was the force that was exerted on the two interlocking gears that managed the motion of the paper feed mechanism.  This force was then translated into a stress and then examined to see if the gears would deform under the load.  Both the geometry of the paper feeder and the size and type of motor contributed significantly to the loading of this problem.  The larger the moment of inertia of the paper rollers and the center rod, the more resistance there is to the motion of the entire system, resulting in a larger gear force.  The motor that was used in this model was a stepper motor.  This was most likely chosen for its usefulness for moving the paper at a given increment.  However, the stop and go nature of this motor increased the gear force by creating sudden starts and stops of the system rotation.
-'''Part 2'''
-Analysis will have to be performed on the operating conditions of the printer.  The coefficient of the rubber wheels on the paper will have to be found along with all of the geometric parameters of the system.  For example, the radii of the wheels, their thickness, and their density will all have to be found in order perform the analysis in ADAMS.  All geometric parameters, moments of inertia and yield strengths will be have to be found to perform the analysis.  Finally, the force that is necessary to slide the paper (adding to the resistance of the motion) will also need to be found.  This will be found by using the coefficient of friction mentioned earlier.
-Simplifications in the model can be made in this analysis.  Since we are only concerned with what is going on at the gears, the yield stresses will be unnecessary for the rod and the wheels.  Also, the wheels (which are composed of both rubber and plastic) can be considered to be entirely rubber since the density of rubber is greater than that of plastic.  If the calculations indicate that stresses are such that they are close to the yield stress, than this simplification will have to be done away with in order to get a more accurate value for the gear force.
-'''Part 3'''
-'''Engineering Specification for Paper Feeder'''
-Gear Force (and Stress)
-*The force that is exerted on the two gears at their intersection (and the stress that results from this force).
-*Target Value:  Force < 1e5 N (from the 40 MPa Tensile Strength of Plastic)
-*Direction of Improvement:  Down (smaller gear force)
-*Related user requirement:  Paper feeds smoothly
-Design decisions/parameters affected
-*Geometry of System
-*Size and Type of Motor
-Key geometric, inertia, and material properties
-*Length, radius, density of rod (stainless steel)
-*Thickness, radius, density of Wheels (rubber)
-*Thickness, radius, density of Gears (steel and plastic)
-*Moment of inertia for all components
-'''Analysis'''
-Brittle Fracture Analysis: Maximum Normal Stress Theory
-[[Image:DVEquations.jpg|left|300px]]
@@ Line 530: / Line 243: @@
-'''Results'''
-[[Image:DVForceAdvance.jpg|left|thumb|500px|Gear Force]]
+== Analysis of Rendered Components ==
+===Electric Motor===
+. The decisions that had to be made in the design of this component include the size of the motor for it to fit within the primary housing, the weight of the motor to meet the goals of a low weight shaver, the power produced by the motor in order for it to be able to cut hair efficiently, and the amount of power needed to be supplied to the motor for it to run properly.
+. The critical features of this motor are the offset bar to generate only side to side motion of the razor blade and the links going to the motor that connect the offset bar.  The critical dimensions of this motor are its overall size compared to the primary housing and the size of the offset bar to give the right amount of side to side motion for cutting hair.
+. The loading that will be placed on the motor will be cyclic loading as it completes every revolution.  There will also be cyclic loading on the components connecting to the motor.
+. To evaluate the performance of the motor it could be hooked up to a power source and tested to see how long it would run.  The shaft could also be hooked to different weights for different trials to determine how much work or power the motor is able to produce.
+===Moving Blade===
+. The decisions that had to be made in the design of the moving blade were how it could be mounted to the blade base mount, how many teeth it should have. The blade snaps onto the blade base mount using 2 circular holes that fit over the two circular protrusions on the blade base mount. The number of teeth the moving blade can have is limited by the stationary blade. Since the moving blade had to be narrower than the stationary blade, it was limited to 20 teeth.
+. The teeth on the moving blade are what actually cut hair. They work similarly to scissors, shearing hairs off using the stationary blade as an anvil. The moving blade was also limited in width by the stationary blade. If the moving blade was wider than the stationary blade, it would move its teeth beyond the teeth of the stationary blade, but no hairs would be cut by the moving blade teeth alone.
+. There should only be minimal loading on this component since it will pressed against someone's face. The rapid side to side motion of the the moving blade may stress the plastic on the blade base mount where it snaps together.
+. The most important aspect of this part is that mounts securely on its mount. To test this aspect, the holes that snap into the blade base mount should be within a small tolerance. The moving blade moves back and forth rapidly, so it should have a low weight to reduce its inertia. The moving blade should also be balanced or it could become unstable during its motion.
+===Stationary Blade===
+. One decision that had to be made with this component was the size of the two circular holes at the bottom which lock the blade in place via screws.  The number of prongs at the top (27), their shape, and the cut out angle that cuts into them were all decisions as well.  Finally the thickness, length, and width were all decided upon.
+. The individual prongs/blades have two purposes.  The first is to elevate/separate individual hairs.  The second is to act as one end of the wedge between the moving blade and itself to actually lop off the hairs.  There are 27 such prongs, each 0.025 inches wide and 0.142 inches long.  The entire stationary blade is 1.122 inches tall and 1.103 inches wide.  The two screw holes are 0.184 inches in diameter.  The angled tip is 0.258 inches long and descends the entire thickness of the blade, or 0.092 inches, which gives it a slope of -0.3565 from the pointy tip of the blade if the sideways slot is at the top.
-From this graph, the maximum gear force was found to be about 0.3 N.  This value is much less than the force at which the plastic gear would deform (1e5 N), verifying that the design is a safe for operation.  This also verifies that this design meets the user requirement that the gear set up would not fail due to deformation.
+. Loading on this component will come from pressure from the user's face or fingers.  Some of this loading will be transferred to the screws holding it in place and some will be transferred to the moving blade behind it.  These loadings will in most cases be minor.
-'''Improvements'''
-From this analysis, it is clear that the smaller plastic gear is more robust than is necessary.  The amount of force that is applied to the gear is no where near a force that would cause any significant deformation.  However, it is important to remember that this analysis is only of one aspect of the forces that are applied to this gear.  It is possible that cyclic loading forces the gear to be as large as it is.  Also, it is possible that this gear size is either easily manufactured or readily available.  Therefore, it would be less expensive to use this gear rather than manufacture a gear that is of a different size.
+. User tests in which only the stationary blade is variable can measure performance.  By varying the design of the stationary blade only, its performance can be compared to other stationary blades, and its relative performance would thus be evaluated.  Since stress on this component would most likely be minor, stress tests would not be necessary.