Oscillating fan
From DDWiki
Contents |
Executive Summary
A full dissection and analysis of the current version of the oscillating fan has been performed. The customer needs and use, function, design for manufacture and assembly, possible failure modes, and design for environment have all been studied. A detailed list of components, their functions, materials, and likely manufacturing process have also been provided. A mechanical analysis of the gear train of the fan has also been completed.
Customers need the fan to provide air circulation as a means of cooling a space. The fan must be able to operate quietly with multiple speeds and oscillate to provide coverage for a wide area. Customers interact with the fans on a daily basis during hot seasons. The fan is simply operated by a button and two knobs. When not in use, the fan should store conveniently.
The fan functions by converting AC current to rotation using an induction motor. The motor turns a shaft which spins the fan blades as well as the gearing for oscillation motion. The voltage can be regulated with a knob, thus controlling the speed of the motor. The fan's angle can be adjusted using an additional knob. The oscillation of the fan functions by engaging a gear train with the fan's shaft. This gear train transfers the fan's rotational motion into an oscillatory motion. The dissection showed that most components were made of injection molded plastic parts. Various cast metals and screws were also used for parts exposed to higher stress.
After analyzing the fan's components and function, examples of DFMA were evident, such as unidirectionally interlocking parts. Opportunities to improve DFMA were also examined. It was determined that small design changes could eliminate parts and fasteners and speed the assembly process. Possible failure modes were also considered. These failure modes were given a numerical value to gauge their severity. All possible failure modes proved to be minor and action is most likely unnecessary. Our most urgent potential failure was dislocation of the oscillation button, which had an RPN of 60 out of 1000.
According to EIO-LCA data, the major contributers to detrimental environmental releases associated with the manufacture of the fans are the household fans and energy generation economic sectors. The energy use of a fan during its lifetime was also estimated and compared to the energy used in production of the fan. The lifetime energy use was shown to be significantly greater than the energy cost of production, at over 1 million kWh. The approximations were deemed acceptable because the sector represents the product well.
A mechanical analysis of the gear train was conducted. The gear's diameter and number of teeth were measured. Calculations determined that a complete horizontal oscillation at 1500 rpm takes approximately 9 seconds. It was also determined that the gear train multiplies the input torque 11.52 times.
Customer Needs
The customer’s primary need is to cool a room by circulating air. More air circulation provides greater air movement and cooling potential. The fan’s noise level is a concern of the customer; quiet operation, with little to no vibrations is preferred. The customer must also be able to adjust the fan’s rotational speed to best suit the surroundings. This allows for quieter, lower energy, operation when maximum air circulation is unnecessary. Another necessity is the ability to vary the direction of where air is being blown. This includes altering the vertical orientation as well as providing horizontal oscillation. The fan should also be safe for the user. This involves shielding the fan blades, while still allowing air to pass through. This shielding prevents objects and body parts from coming in contact with the blades. The consumer also needs the power cord to be long enough to plug the fan in when an outlet is not close. Fans are generally only used during warm times of the year. As a result they must be easy to move and store while not in use, usually in closests, attics or basements. Consumers buy fans instead of air conditioners because they are much cheaper and are easier to use in varying locations. Because of this, the consumer will may wish to move the fan to a range of sites. This means that the oscillating fan must be able to survive many hits and bumps during the move; this includes electronics breaking, gears misaligning, or shell denting.
Function
An oscillating fan cools an area using forced convection thus increasing heat transfer. This is accomplished by spinning three plastic blades which circulates air in the desired direction. The blades are spun by an AC brushless motor, which is powered from a standard 120V wall outlet. The motor’s rotational speed can be adjusted by the user using a circular knob, which acts as a potentiometer and changes the amount of power supplied to the motor. The user can change the vertical direction of the fan by manually adjusting the direction that the head is facing. Forces of friction caused between the fan head couplings and wire holder allow the fan to be altered, but hold it in place once adjusted. The fan is also capable of horizontal oscillation. The user starts this movement by pushing a button at the top of the fan casing. This engages a gear train which spins a small plastic linkage. This linkage is connected to an aluminum bar which is attached to the casing. This simple mechanism translates circular motion to oscillatory horizontal motion. The gear train is powered by the same motor and shaft that spin the blades, thus slowing the speed of the blades, but not requiring an additional motor.
Product Use
First, the customer must place the head of the fan on the stand. Then, the user would plug the fan into a 120V wall socket1. Once plugged in, the user may turn the fan on by rotating the knob from the off setting2. The user may adjust the fan's speed to low, medium, or high, by rotating the knob to the desired setting. The user can set the fan to oscillate by pressing down on the rear switch3. This oscillation allows the fan to cool multiple locations4&5. The user can stop the fan from oscillating by simply pulling the rear switch up6. The consumer may also change the vertical direction of the fan by manually rotating the head of the fan about the stand
7. For storage, the consumer must turn the knob to the off setting, unplug the fan from the 120V wall socket, wrap the power cord around the head of the fan, disassemble the fan head and stand, and place the pieces in the storage unit.
| 1 | 2 | 3 | 4 | 5 | 6 | 7 |
|---|---|---|---|---|---|---|
|  |  |  |  |  | 
|
Components:
| Part # | Part name | QTY | Function | Materials | Manufacturing Process | Picture |
|---|---|---|---|---|---|---|
| 001 | Front Fan Cover | 1 |
| Painted Zinc | Merging of Extruded Parts | 
|
| 002 | Threaded Cap for Blades | 1 |
| Plastic | Injection Molding | 
|
| 003 | Blade Unit | 1 |
| Plastic | Injection Molding | 
|
| 004 | Set Screw | 1 |
| Steel | Extrusion | 
|
| 005 | Rear Plate Fastener | 1 |
| Plastic | Injection Molding | 
|
| 006 | Rear Fan Cover | 1 |
| Plastic | Molded | 
|
| 007 | Motor Front Cover | 1 |
| Magnesium | Cast | 
|
| 008 | Swivel Adjustment Knob | 1 |
| Plastic/Steel | Injection Molding/Extrusion | 
|
| 009 | Nut for Swivel Adjustment Knob | 1 |
| Steel | Stamped | 
|
| 010 | Fan Head Coupling | 1 |
| Plastic/Steel | Injection Molding/Extrusion | 
|
| 011 | Speed Selection Knob | 1 |
| Plastic | Injection Molding | 
|
| 012 | Switch | 1 |
| Plastic/Copper | Injection Molding/Stamped | 
|
| 013 | Motor Housing | 1 |
| Plastic | Injection Molding | 
|
| 014 | Capacitor | 1 |
| Plastic/Other | N/A | 
|
| 015 | Electrical Wire | 7 |
| Plastic/Copper | Drawn | 
|
| 016 | Oscillation Gear Casing | 1 |
| Magnesium | Cast | 
|
| 017 | Gear Casing Cap | 1 |
| Plastic | Injection Molding | 
|
| 018 | Oscillation Control Knob | 1 |
| Plastic | Injection Molding | 
|
| 019 | Transmission Gear | 1 |
| Plastic | Injection Molding | 
|
| 020 | Small Ball Bearing | 1 |
| Steel | Cast | 
|
| 021 | Small Spring | 1 |
| Steel | Extrusion |
|
| 022 | Gear 1 | 1 |
| Plastic | Molded | 
|
| 023 | Gear 2 | 1 |
| Plastic | Injection Molding | 
|
| 024 | Plastic Shaft and Oscillation Linkage | 1 |
| Plastic | Injection Molding | 
|
| 025 | Oscillation Linkage | 1 |
| Magnesium | Stamped and Bent | 
|
| 026 | Shaft | 1 |
| Stainless Steel | Extrusion | 
|
| 027 | Permanent Magnet | 1 |
| Ferric Material | Coiled Wire | 
|
| 028 | Rear Shaft Support and Bearing | 1 |
| Magnesium | Cast | 
|
| 029 | Front Shaft Support and Bearing | 1 |
| Magnesium | Cast | 
|
| 030 | AC Motor Block | 1 |
| Steel | Cast/Rolled | 
|
| 031 | AC Motor Coils | 1 |
| Copper | Drawn | 
|
| 032 | Wire Holder | 1 |
| Plastic | Injection Molding | 
|
| 033 | Power Cable | 1 |
| Plastic/Steel | Molded/Stampled | 
|
| 034 | Screws | 22 |
| Iron/Steel | Extrusion/Rolled | 
|
| 035 | Bolts | 1 |
| Iron/Steel | Extrustion/Rolled | 
|
| 036 | Washers | 4 |
| Iron | Stamped/Bent | 
|
| 037 | Nut | 1 |
| Iron | Cast | 
|
| 038 | Wire Coupling | 1 |
| Plastic | Injection Molding | 
|
Design for Manufacturing and Assembly
Before any improvement on this oscillating fan can be accomplished, an analysis of its design for ease of assembly and/or manufacturing must be completed. This analysis can best be done by determining which individual components of the product can be combined into single, assembly free components. It should also focus on which individual fasteners could be eliminated by employing alternative "snap fastening" techniques. A brief description of the current DFMA status will be followed by recommendations for improvement.
Current DFMA
- Plastic Components
- The transmission gear, gear one, and the gearbox housing cover are all separate pieces fastened using an obscure spring and ball system
- Gear two and the plastic shaft and oscillation linkage are molded with corresponding fittings for aligned engagement during assembly
- The motor housing is designed to accommodate the oscillation knob, speed selector, and electronics switch all in a single molding
- The swivel adjustment knob contains a plastic molding and extruded part likely glued together
- Fan blade attachment parts are designed to snap together in a specific orientation
- Fasteners
- Many screws to fasten multiple parts together
- Most screws are needed based on the design of the parts
- Some screws are hard to access when disassembling
- Metal Components
- Front and back fan gratings connect using interlocking fittings
- Gearbox housing and cover are designed to interlock in one direction only
- Front and rear motor casings are designed to fit the motor block, support the shaft, hold bearings, and connect using four screws
- Rod to connect motor casing to wire holder is a different material riveted in place
- Name plate on front grating is connected using three screws
Recommended Improvements
- Plastic Components
- The transmission gear, gear one, and the gearbox housing cover could all be made with a single molding
- The swivel adjustment knob can be either a single plastic or single metal part as opposed to two joined parts
- Two of the blade attachment parts could be made into a single molding
- Swivel adjustment system could be improved to utilize fewer parts of all one material
- Fasteners
- Screws could be standardized for a single type of Phillips driver
- Metal Components
- Rod to connect motor casing to wire holder could be made from a single casting
- Name plate on front grating could be fastened using snaps instead of screws
Failure Mode Effects Analysis
| Item and Function | Failure Mode | Effects of Failure | S | Causes of Failure | O | Design Controls | D | RPN | Recommended Action | Responsibility and Deadline | Actions Taken | S | O | D | RPN |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Motor/Shaft | Inhibited Rotation | Inefficient Operation | 5 | Debris (e.g. dust) in Fan | 4 | Run Under Extreme Dust and Debris Conditions | 2 | 40 | Filter, Accessibility for Cleaning, Better Protection of Rotating Parts | Motor Housing | - | 5 | 3 | 2 | 30 |
| Swivel Mount | Nut Stripping, Plastic Fracture | Cannot Adjust Vertical Directoin Fan Cannot Effectively Circulate Air | 8 | Overtightening, Material Failure | 3 | Overtightened Screw, Force applied on Swivel Area | 1 | 24 | Use Torque Limited Fastening, Using Stronger Plastic | Swivel | - | 8 | 2 | 1 | 16 |
| Oscillation Button | Dislocation of Button | Cannot Toggle Oscillation | 6 | Stripped Gear, Button Disengaged | 5 | Stronger Gears, Improved Connection | 2 | 60 | Fatigue Testing | Gears and Button | - | 6 | 3 | 2 | 36 |
| Blade Cover | Inhibited Rotation, Blade Fracture | Complete Inoperable | 8 | Penetration of Cover | 4 | Penetrate Repeatedly | 1 | 32 | Warning Label, Redesign Cover | User | - | 8 | 3 | 1 | 24 |
| Shaft | Non-concentric Rotation | Vibration and Noise | 5 | Broken Bearing, Unbalanced Weight, Shaft Non-Uniformity | 2 | Quality Control | 3 | 30 | Vibration Testing | Assembly | - | 5 | 1 | 3 | 15 |
| Electronics | Short Circuit | Completely Inoperable | 8 | Exposure to Water | 3 | Water Exposure Testing | 2 | 48 | Waterproof Housing of Electronics | Housing | - | 8 | 1 | 2 | 16 |
The results of this table tell us that none of these failure modes demand immediate attention. The highest RPN is 60 out of a potential 1000. This is relatively low priority, and is probably not worth taking action to fix. RPN values are extremely low because all failures are easily detectable by the consumer and in most cases are due to consumer negligence rather than design or manufacturing failures. The proposed actions do significantly lower the occurrence of these failures.
Although action isn't necessary, these failure modes show areas of the fan that can be improved or redesigned. For example, failure due to water exposure has a low RPN, but the consumer may appreciate waterproofing as an additional feature.
Design for Environment
Environmental Impact Approximations
The environmental impact of a single oscillating fan may seem negligible. This seemingly innocent arbiter of consumer comfort provides "cool" circulated air in times of heat, but could one's fan actually be adding to the problem of global warming? The environmental impact of oscillating fans will now be analyzed.
As a baseline for all calculations and data, all analysis will be done per million dollars of economic activity. According to NAICS data from 1997, the economic sector responsible for the manufacture of oscillating fans is 335211 Electric Housewares and Household Fan Manufacturing. Data about this and other sectors associated with it are compiled in the Economic Input-Output Life Cycle Assessment (EIO-LCA) database. This utility allows one to locate data and calculate various aspects of economic and environmental activity related to any economic sector. For sector 335211, the sector responsible for most economic activity is itself. This means that most of the money put into the production of fans (and more) is used by the fan producing industry. The other major sectors associated with the economic aspects of production are wholesale trade, management of companies and enterprises, Plastics plumbing fixtures and all other plastics products, and All other forging and stamping (each accountable for fractional amounts of the total capital of the sector).
A major environmental concern related to manufacturing any product is the amount of greenhouse gases and other air pollutants released into the atmosphere. According the the EIO-LCA database, the leading contributer of conventional air pollutants (SO2, NOx, CO, etc.) related to fan manufacture is power generation, producing over half of all pollutants (power used to create components, etc.). The next closest is the Electric Housewares and Household Fan Manufacturing sector. These two individually contribute the most relative to all other sectors, and it is the remaining 490 associated sectors that produce about 1/5 of the gases released. Totals for emissions are given as about 2 metric tons of SO2, over 7 metric tons of CO, and 1.6 metric tons of NOx compounds, among others. Results for greenhouse gases (specifically CO2, CH4, CFC's, and N2O) are similar. Power generation produces roughly 1/3 of all CO2 release associated with the fan manufacture. Other large producers are truck transportation, steel mills, and of course, the fan manufacturing sector itself. About 600 metric tons of CO2 are released for every million dollars of fans produced.
The largest single producer of toxic wastes related with the fan sector is itself, contributing about 1/5 of the several tons of toxic waste released per million dollars of product. Many of these releases are associated with the many plastic components used in fans. Not surprisingly, the plastics sector takes second place in this category. About half of all toxins released are related to most of the smaller sectors involved in production.
These environmental considerations have just taken the production of fans within this sector into account. The environmental impact of the use of the fans will now be considered. For this analysis, some estimations will be used. Taking an average price for a common household oscillating fan such as the one analyzed as $50.00, the total number of fans per million dollars is 20000. The average power consumed during normal use is about 40W. During peak fan use season (Summer, about 90 days)the average fan user likely uses the product for 3 hours a day. A typical fan probably lasts about 5 years. 40W * 3h * 90days * 20000fans * 5years = 1.08 million kWh of power consumed by fans. According to EIO-LCA data, the total amount of energy consumed in producing this amount of fans is about 0.5 million kWh. Therefore the amount of energy consumed by the use of the fans heavily outweighs the energy used in producing them. Assuming $0.10 per kWh of electricity used, this results in $108,000.00 worth of economic activity for the power generation sector. Running this amount of activity through the LCA database yields the pollutants and CO2 emissions from the use of the fans. 5.85 metric tons of SO2 and 2.77 metric tons of NOx result from this use, as well as over a thousand metric tons of CO2.
This analysis shows that the pollutants released as a result of the use of the fans outweighs those released due to production. The power generation sector was the economic sector most responsible for the majority of the greenhouse and pollutant releases.
Accuracy of Approximations
The data from the EIO-LCA database should be a fairly accurate representation of the actual environmental impact of oscillating fans. The economic sector chosen represents these types of fans very well, so the data should reflect fan production. The calculations on the energy cost of a fan's lifetime is a conservative estimate, assuming a relatively low amount of use per day.
Mechanical Analysis
Components Analyzed
| Part # | Part Name | # of teeth | Diameter | Picture |
|---|---|---|---|---|
| 026 | Shaft | 14 - Worm Gear | 7/8" |
|
| 019 | Transmission Gear | 50 | 1" |
|
| 022 | Gear 1 | 13 | 5/16" |
|
| 023 | Gear 2 | 58 | 9/8" |
|
| 024 | Plastic Shaft and Oscillation Linkage | - | 11/16" lever arm |
|
| 025 | Oscillation Linkage | - | 3" center to center |
|
Rotational speed analysis
The fan's oscillation speed can be examined by comparing the number of teeth on each gear of the compound gear train. For two interacting gears, a single tooth pass will advance the mating gear by one tooth. Thus if a gear with 100 teeth is mates with a gear with 50, a single rotation of the 100 tooth gear will rotate the 50 tooth gear 2 times. All gears have matching pitch and the final output speed is directly related to the input speed. A gear ratio is determined for each two gear interaction. This ratio compares the input and output rpm using the number of teeth.
Assumed Fan RPM: 1500 rpm (High Speed)
The shaft is a worm gear. A single rotation of the worm gear advances the mating gear a single tooth. This leads to a 1/50 gear ratio.
Shaft -> Transmission Gear 
Rotation speed is constant for the Transmission Gear and Gear 1 because they are on the same shaft, thus spinning at the same speed. The gear ratio of Gear 1 and Gear 2 is 13/58. This is calculated by comparing the number of teeth on the two gear, which have matching pitch.
Gear 1 -> Gear 2 (plastic part) 
6.72rpm translates to one rotation every 8.93 seconds. This means that a full oscillation of the fan is completed in about 9 seconds. By changing the gearing the time can be increased or decreased to better suit the consumer's needs. Currently there is no way for the user to modify the oscillation time except by changing the speed of the fan.
Using the same analysis method for 1000 rpm (Low Speed) an oscillation time of of 13.39 seconds is calculated. The rotational speed is decreased 223 times the fan blade rotation.
Torque Analysis
As the rotation speed is decreased torque is amplified by the geartrain. The torque can be analyzed using the same method as speed, but the gear ratios will be inverted.
Assumed Input Torque: Ti
Shaft -> Transmission Gear 
The torque of the Transmission Gear and Gear 1 are equal because they are on the same shaft. Gear 1 and Gear 2 have the same pitch so they can be analyzed by comparing number of teeth.
Gear 1 -> Gear 2 (plastic part) 
This analysis shows that torque is multiplied 223 from the motors input through the shaft. This agrees with a power analysis, because input torque * input speed must equal output torque * output speed. A major increase in torque allows the fan to oscillate without significantly decreasing the rotation speed of a the fan. If the geartrain did not step down as far as it did, fan cooling may be compromised when oscillation begins.
