Door latch
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==Product Use== | ==Product Use== | ||
| + | For the type of doorknob that the group is assessing, there are two components to the product: (1) the door latch and (2) the lock. The purpose of the door latch is to keep the door in the closed position. It is designed to be closed easily one way by simply pushing on the door. Moreover, the doorknob is designed to be opened in one way only. The lock is designed to prevent the knob from turning. It should be noted that the lock does not stop the latch itself from moving. This allows the user to lock the door before closing it. The lock gives the user a level of privacy and security, for example, while using the bathroom. | ||
| + | |||
| + | ===Lock=== | ||
| + | In order to prevent the doorknob from turning, the user can rotate the locking mechanism at any point. This does not stop the door latch from moving, so the door can be closed after locking the door. Once closed, the locking mechanism prevents the doorknob from turning; this locks the door to let outsiders know that access to the room is prohibited. | ||
| + | |||
| + | ===Latch=== | ||
| + | Rotating the doorknob turns a mechanism that converts rotational motion to a translational motion, which is connected to the door latch. The door latch makes contact with a metal plate to guide the door latch into place, as well as improve durability after extended operation. Springs are attached to the doorknob as well as the door latch to facilitate the knob reset. | ||
==Bill of Materials== | ==Bill of Materials== | ||
Revision as of 19:16, 4 February 2012
Contents |
Executive Summary
Major Stakeholders
Major stakeholders for the doorknob include customers, manufacturers, distributors, and retailers. Their requirements are listed below.
Customers
- Cheap to purchase
- Reliable
- Reasonably secure/offers some sense of privacy
- Simple to operate
- Ergonomic
- Aesthetically pleasing
- Easy to assemble and install
- Easy to unlock from outside in case of emergency
Manufacturers
- Use limited number of parts
- Use limited types of parts
- Use few manufacturing and assembling processes
- Limit the number of parts for the consumer
Distributors
- Lightweight to reduce energy consumption during transport
- Packaging must be optimized to maximize number of products per load
- Product must be strong enough to survive the delivery
Retailers
- Packaging must be optimized for easy display
- Products must be readily available
Customers clearly have the most requirements for the doorknob, simply because they are in contact with the product for the longest time. However, we should not undermine the importance of the requirements of the other major stakeholders of this product.
Product Use
For the type of doorknob that the group is assessing, there are two components to the product: (1) the door latch and (2) the lock. The purpose of the door latch is to keep the door in the closed position. It is designed to be closed easily one way by simply pushing on the door. Moreover, the doorknob is designed to be opened in one way only. The lock is designed to prevent the knob from turning. It should be noted that the lock does not stop the latch itself from moving. This allows the user to lock the door before closing it. The lock gives the user a level of privacy and security, for example, while using the bathroom.
Lock
In order to prevent the doorknob from turning, the user can rotate the locking mechanism at any point. This does not stop the door latch from moving, so the door can be closed after locking the door. Once closed, the locking mechanism prevents the doorknob from turning; this locks the door to let outsiders know that access to the room is prohibited.
Latch
Rotating the doorknob turns a mechanism that converts rotational motion to a translational motion, which is connected to the door latch. The door latch makes contact with a metal plate to guide the door latch into place, as well as improve durability after extended operation. Springs are attached to the doorknob as well as the door latch to facilitate the knob reset.
Bill of Materials
| Part Name | QTY | Mass (g) | Function | Manufacturing Process | Material | Image |
|---|---|---|---|---|---|---|
| Door Holder Front | 1 | 13 | Secures Door-Latch to Door | Stamping | Steel (Coated) |  |
| Door Holder Front | 1 | 13 | Secures Door-Latch to Door | Stamping | Steel (Coated) | |
Design for Manufacturing and Assembly (DFMA)
Performing a Design for Manufacturing and Assembly (DFMA) analysis on our doorknob allows us to assess whether or not designs of the product could be changed in such a way that the cost, ease, or quality of manufacturing and assembly can be improved. In order to analyze the product, we had to dissect the doorknob, so we could at least consider the manufacturing process that went into producing the doorknob.
The main goal of the dissection and the analysis was to identify areas of the product where we believe the designer made good decisions, or where we believe improvements could be made. Did the designer:
- design the simplest solution?
- make good cost-saving decisions?
- design for easy manufacturing?
- design for easy assembly?
The doorknob is somewhat unique in that some assembly by the customer is required, so design for assembly should take the customer's point of view in consideration in addition to the assembly plant's point of view.
The table below lists guidelines that we followed as well as our findings in this analysis.
| Design for Manufacturing Guidelines | |
|---|---|
| Minimize Part Count: Eliminate fasteners, part consolidation | We found there to be a lot of small parts inside the doorknob, especially considering its function (open, close, lock, unlock). |
| Standardize Components: Take advantage of economies of scale & known component properties | Dissection revealed that the inner and outer doorknobs were in fact not the same part. Instead, it appears that different molds were used to create them. In general, we are looking to make the product as symmetric as possible. |
| Commonize Product Line: Economies of scale and minimum training and equipment | It appears that most of the components are either stamped or cast. Thanks to this small number of types of manufacturing, training can be minimized, and employees become more flexible in terms of position on the production line. |
| Standardize Design Features: Common dimensions for fewer tools and setups | Again, small differences in the design of the two doorknobs require different molds to produce each doorknob. We believe improvements can be made to use one mold for both doorknobs. |
| Multifunctional Parts: | Many of the parts inside the doorknob only serve one unique function. Moreover, each part is unique, requiring multiple manufacturing processes. Design changes should be considered to replace some of the parts with one part that performs multiple functions. |
| Ease of Fabrication: Choose materials easy to work with | Dissecting the product revealed that the two primarily materials used in production were mostly steel and some plastic. While switching to one material should be considered, some choices were made with a functional purpose. For example, a low-friction plastic piece on the door latch was meant to facilitate the door latch sliding on surfaces. |
| Design for Assembly Guidelines | |
| Mistake-Proof: unambiguous, unique assembly orientation | Some components of the doorknob, like the latch frame, are not symmetric, which makes insertion difficult during assembly. Moreover, because the asymmetry of the components are not clear enough with markings or indentations, a customer could have trouble or confusion during installation.
We also had difficulty connecting the two doorknobs to each other because they were not symmetric, and there was no clear indication for how we should connect them. We believe other customers who are installing a doorknob could run into the same problem. |
| Minimize Fasteners: snap fits and part consolidation | There were only two sets of fasteners in this doorknob: one set to attach the outer doorknob to its reinforced frame, and another set for the customer to install the door latch holder to the door or the door frame. |
In general, we believe there are too many parts inside the doorknob, many of which have only one function. This aspect of the product results in a complicated assembly, which leads to lower productivity. Design changes should be considered to consolidate multiple functions into one part. The end goal is to create the simplest design for the doorknob; focusing on consolidating multiple functions in one part can reduce the number of parts inside the doorknob, standardize components, and make manufacturing more cost-effective.
Secondly, we believe that the customer could face problems while installing the doorknob, because it is difficult to orient the knobs before connecting the two through the door. Making the correct orientation more obvious would reduce or eliminate this problem.
Failure Mode and Effects Analysis (FMEA)
Performing a failure mode and effects analysis (FMEA) allows us to determine potential areas of concern, particularly ways in which our product can fail. The FMEA also allows us to prioritize each failure mode. After determining the severity (S), the probability of occurrence (O), and detectiblity of failure (D), on a scale of 1-10, the three values are multiplied, which yields a risk priority number (RPN). This number is then used to order the failure modes in terms of importance. The table below shows the results of our FMEA analysis on our doorknob.
| Item and Function | Failure Mode | Effects of Failure | S | Causes of Failure | O | Design Controls | D | RPN | Recommended Actions |
|---|---|---|---|---|---|---|---|---|---|
| Locking mechanism | Shaft fails | User cannot lock or unlock | 7 | User turns locking lever too hard | 3 | None | 5 | 105 | |
| Doorknob | Doorknob fails | Door cannot be opened | 8 | User turns doorknob to hard | 1 | None | 5 | 40 | |
| Door latch | Latch spring fails | Door inoperable - fails to stay closed | 7 | Age/wear | 1 | None | 5 | 35 |
