Babyproof door knob lock
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Revision as of 23:12, 23 September 2007
Contents |
Executive Summary
Babyproof door knob locks are a common method in many households to restrain children within a certain area. This information page analyzes both the babyproof lock in addition to type of door knob to which it is attached. By fully understanding the consumer needs in addition to the exact function and manufacturing methods of the system under study our team hopes to innovate and improve upon products already available for purchase. By not only analyzing the babyproofing cover but also studying the complex mechanism of the doorknob itself, this study is provided extra depth.
A doorknob's primary purpose is to allow selective entry and exit between connected rooms. This simple of objective has evolved a complex mechanism with many points for possible failure. Locking and unlocking, the doorknob-to-door interface, and even the impact of rotation must be accommodated by the doorknob within a reasonable failure tolerance. Via product dissection, a deeper understanding of each item of the assembly is gained. FMEA allowed possible failure areas to be outlined and ranked while DFMA structured possible improvements in a systematic fashion.
A babyproof door knob lock's initial simplicity is complicated by its defined interaction with the doorknob mentioned previously. Deconstruction and analysis must always take into consideration what effect each component has upon a doorknob. Varying standards in size, quality and complexity of doorknobs themselves complicate the manufacture of the door knob locks. By combining the information from both of these products, a comprehensive improvement plan can be produced that minimizes parts and cost while maximizing effectiveness.
Customer Needs
A customer with a toddler needs to safeguard their home while the child is in a stage where they want to explore their surroundings and abilities but are unaware of hidden dangers. To deter a child from opening or closing a door but still make it as accessible to normal adult traffic as possible, a special mechanism is needed, potentially on the doorknob. Customers need to also take into consideration the type of door knob (knob, lever, etc.), it's size, shape, and whether or not the knob has a lock that they also want to easily access in other situations.
Product Use
An uncovered, unlocked doorknob is simply turned to open or close a door. To deter a small child from doing so, there are two different types of covers we're exploring. The first is specifically for round doorknobs. It covers the knob loosely so that it spins freely unless tabs are pressed on its side that creates friction between the cover and knob, causing the knob to turn when the cover is turned. The second is for levers. There is a lever cover and a "lock". This lock is a latch that is attached to the door above the knob with a tab that fits into a notch in the cover. The tab prevents the cover from moving unless the tab is lifted.
System Function
(include pictures)
Bill of Materials (Doorknob)
| # | Name | Origin | Weight (oz) | Material | Manufacturing Process | Function | photo |
|---|---|---|---|---|---|---|---|
| 1 | circular wedge | latch | 0.2 | Aluminum | stamped | access a wedge to keep latch assembled in place inside door | 
|
| 2 | pop rivot | latch | <0.1 | brass | molded | holds latch case | 
|
| 3 | turning shaft | outer doorknob | 0.7 | steel | molded | functions key lock | 
|
| 4 | screws x2 | outer doorknob | 0.1 | brass plated | cold heading, thread wooling | locks inner and outer doorknobs in place | 
|
| 5 | latch plate | latch | 0.5 | brass | stamped | attaches to door jam (on door side) | 
|
| 6 | strike plate | latch | 0.7 | brass | stamped and bent | attaches to door jam, allows latch to fit in hole | 
|
| 7 | spring | inner doorknob | <0.1 | harden steel, nickel based alloy | wound, prehardened or hardened during fabrication | guides the lock by creating resistance in a locking shaft and keeping it aligned in a locking or unlocking position | 
|
| 8 | lock shaft | inner doorknob | 0.1 | plastic and brass | two molded parts, press fitted | turns shaft into lock/unlock positions | 
|
| 9 | ring | inner doorknob | 0.1 | aluminum | stamped | serves as a buffer between knob spring and spring housing | 
|
| 10 | inner doorknob torsional spring | inner doorknob | <0.1 | steel | molded and wrapped | creates resistance when turning doorknob, prevents free spinning | 
|
| 11 | spring housing | inner doorknob | 0.2 | brass | stamped and bent | houses and secures torsional spring | 
|
| 12 | outer plate locking mechanism | latch | 0.5 | brass | stamped | attaches to door, similar to strike plate | 
|
| 13 | inner plate locking mechanism | latch | 0.2 | brass | stamped | wedges between #12 and the door | 
|
| 14 | latch | latch | 0.6 | steel | molded | latches door to door jam | 
|
| 15 | lock attachment | latch | <0.1 | steel | molded | attaches to latch, does not slide when locked | 
|
| 16 | face for outer doorknob | outer doorknob | 0.1 | brass | stamped | aesthetically pleasing | 
|
| 17 | hook | latch | <0.1 | brass | stamped | hooks to latch or lock attachment | 
|
| 18 | large hooks x2 | latch | 0.1 | steel | stamped | pulls back latch | 
|
| 19 | hook mechanism plate | latch | <0.1 | plastic | molded/injection molding | hooks #18 to latch | 
|
| 20 | small hook from lock | latch | <0.1 | brass | molded | (unknown use) | 
|
| 21 | pin | latch | <0.1 | brass | stamped and bent | adjusts locking mechanism between two different lengths | 
|
| 22 | black plastic | inner doorknob | <0.1 | plastic | molded | (unknown use) | 
|
| 23 | locking mechanism housing | latch | 0.6 | brass | molded and hole punched | houses small pieces in latch | 
|
| 24 | short pin | latch | <0.1 | brass | molded | slides back and forth when size is adjusted | 
|
| 25 | plastic hooks | latch | <0.1 | plastic | molded | slides back and forth when size is adjusted, may pull back when hook is tilted to latch | 
|
| 26 | latch housing | latch | 0.6 | brass | molded and hole punched | houses mechanism controlling hooks for latch | 
|
| 27 | sliding plate | latch | 0.2 | brass | molded and hole punched | slides back and forth, may align holes to those in the door or second housing piece | 
|
| 28 | two lock springs | latch | <0.1 | steel/nickel alloy | wound | impacts latch mechanism | 
|
| 29 | inner doorknob ring | inner doorknob | <0.1 | aluminum | stamped and molded | locks doorknob into rose, locks doorknob's cylindrical connector | 
|
| 30 | inner doorknob back plate | inner doorknob | 0.4 | brass | stamped and bent | attaches doorknob to door, acts as faceplate | 
|
| 31 | inner doorknob rose | inner doorknob | 1.3 | brass | stamped and bent | connects door to doorknob, attaches and connects inner and outer doorknobs | 
|
| 32 | inner doorknob | inner doorknob | 1.7 | brass | molded/pressed/clamped | it is gripped by the user to engage latch from inside the door | 
|
| 33 | spring housing | outer doorknob | 0.4 | brass | stamped and bent | houses spring mechanism on the outer doorknob | 
|
| 34 | bottom spring plate | outer doorknob | <0.1 | steel | stamped | spring pushes against it to create torque | 
|
| 35 | top spring plate | outer doorknob | <0.1 | steel | stamped | spring pushes against it to create torque | 
|
| 36 | outer knob torsional spring | outer doorknob | <0.1 | steel | molded/wrapped | creates resistance when turning doorknob to prevent free spinning of the knob | 
|
| 37 | outer doorknob back plate | outer doorknob | 0.4 | brass | stamped and bent | attaches doorknob to door, acts as a faceplate | 
|
| 38 | outer doorknob rose | outer doorknob | 3.0 | steel | molded and tapped | houses screws and connects inner doorknob to outer doorknob | 
|
| 39 | outer doorknob ring | outer doorknob | <0.1 | aluminum | stamped and molded | secures doorknob connector into rose | 
|
| 40 | cylindrical connector | inner doorknob | 0.8 | steel | molded | connects doorknob to rose and secured with ring | 
|
| 41 | spindle | outer doorknob | 1.0 | brass plated steel | molded | semi-cylinder that wraps around the turning shaft | 
|
| 42 | outer doorknob | outer doorknob | 1.6 | brass | molded/pressed/clamped | is gripped by user to engage latch from outside the door | 
|
| 43 | cone-shaped connector | outer doorknob | 1.5 | steel | molded | secures outer doorknob to rose and houses locking mechanism, spindle, and locking shaft | 
|
| 44 | lock mechanism | outer doorknob | 2.4 | steel/aluminum/other | stamped/sealed/molded/assorted | mechanism engages lock | 
|
DFMA
FMEA (doorknob)
Who Are the Stake Holders?
- Homeowners, families
- Anyone who wishes to enter or exit a door
- Anyone who wants to secure a door
What it Does and How it is Used
Secures a door
- Allows selective entry or exit
- Steps:
1. Walk to a door
2. Lift hand
3. Grasp doorknob firmly
4. Twist the knob away from door jam
5. Push or pull the door open/close
Potential Failures
- If latch disconnects or mis-aligns, door does not open
- Loosening of the knob
- Material fatigue
- Rusting and sticking
- Loss of spring constant
How Failure Affects Consumers
- Doorknob becomes difficult or impossible to operate
- Doors may or may not be opened
- Repair or replacement
How Dangerous the Failures Would Be
- Cannot leave room during an emergency
- No longer reserving privacy
- Small parts may be swallowed by children
How Likely/Often Failure Would Occur
- 5~60 years
FMEA (doorknob protector)
i think we should combine the FMEA's (doorknob and doorknob protector) into a chart...
don't edit anything under the FMEA's yet, i'll get back to it tomorrow~
Quantitative Mechanical Analysis
DFE
The analysis for this section is broken down into DFE for the doorknob and DFE for the doorknob protector. The first analysis consists of just the doorknob. The following tables show the data obtained using the 1997 purchaser price model in the EIOLCA for $1 million worth of “Metal household furniture manufacturing”
Figure 1 EIOLCA data for toxic gas emissions
Figure 2 EIOLCA data for greenhouse gas emissions
Figure 3 EIOLCA data for conventional air pollution
Figure 4 EIOLCA data for energy consumption
The accuracy of these approximations is fairly rough as doorknobs do not necessarily take part in all sectors that contribute to certain areas, ie paper mills & copper smelting. However, this data gives a rough idea of sectors that have the largest effect on environmental areas.
| Production | Transportation | Use | End of Life |
|---|---|---|---|
| cell 1,1 | cell 1,2 | blank | blank |
| cell 2,1 | cell 2,2 | blank | blank |
Bill of Materials (doorknob protector)
| # | Name | Origin | Weight | Material | Manufacturing Technique | Function |
|---|---|---|---|---|---|---|
| 45 | blank | blank | -- | blank | blank | blank |
| 46 | blank | blank | -- | blank | blank | blank |
| 47 | blank | blank | -- | blank | blank | blank |
| 48 | blank | blank | -- | blank | blank | blank |
| 49 | blank | blank | -- | blank | blank | blank |
| 50 | blank | blank | -- | blank | blank | blank |
24-441 Engineering Design Course, Fall 2007, Carnegie Mellon University
