INSTITUTION: DEDAN KIMATHI UNIVERSITY OF TECHNOLOGY

COURSE: BSc. MECHANICAL ENGINEERING

GROUP MEMBERS:

1. MACHARIA ZACHARY KAMURI E023-01-0805/2013

2. VINCENT MUTHOKA E023-01-0790/2013
3. KUSENYA N. GABRIEL E023-01-0784/2013
4. MUNYIVA M. ANDREW E023-01-0791/2013
5. GEORGE MWAZI E023-1003/2012
6. MWIRIGI JOHN E023-01-0790/2013
7. KOOME RODNEY E023-01-0790/2013
8. KETER GEORGE E023-0979/2012

UNIT CODE: EMG 2506

UNIT NAME: REVERSE ENGINEERING

TASK: PROJECT REPORT

TITLE: REVERSE ENGINEERING OF A DOOR KNOB ASSEMBLY.

LECTURER: Prof. J.N. KIREITA

SUBMISSION DATE: 13/09/2017

 1. Summary
From this study a door knob has two main functions: that is turning the knob retracts a

latch that unhinges a door from its closed position, and activating the lock prevents the knob from

turning. Activating the lock does not disable the door latch. In other words, the user can lock the

door before closing it. Dissection showed that there were many small components that each had a

single function, suggesting that the doorknob may be overly complicated for its intended

function. As an example, the door hinge itself had a complicated spring mechanism simply to

retract the hinge and restore it to the original position.

A Design for Manufacture and Assembly (DFMA), were performed to learn more about

the doorknob. Results of the DFMA showed that some parts could be consolidated to come from

the same stock material under one manufacturing process (like stamping or casting). The

dissection showed that the two doorknobs that come with the product are not identical, which is

not ideal for manufacturing.

The study showed that with a Risk Priority Number (RPN) of 105, the user could break

the lock on the doorknob, causing the knob to be disabled. As a result, the user could lock himself

in the room.

The analysis further showed the packaging could be improved to maximize the number of

products that could be delivered in one trip. It also showed that material reduction could be

possible, but further studies like a Finite Element Analysis (FEA) may be necessary. Running the

Environmental Input Output Life Cycle Assessment (EIO-LCA) showed that most of the

environmental impact came from steel mills and power generation and supply, likely from

processing the metal and running the plant. Now with some understanding of the product, we can
begin to perform market research to find out what other users think of the doorknob in its current

state.

2. Background
The earliest known lock and key device was discovered in the ruins of Nineveh, the

capital of ancient Assyria. Locks such as this were later developed into the Egyptian wooden pin

lock, which consisted of a bolt, door fixture, and key. When the key was inserted, pins within the

fixture were lifted out of drilled holes within the bolt, allowing it to move. When the key was

removed, the pins fell part-way into the bolt, preventing movement.

With the onset of the Industrial Revolution in the late 18th century and the concomitant

development of precision engineering and component standardization, locks and keys were

manufactured with increasing complexity and sophistication.

The lever tumbler lock, which uses a set of levers to prevent the bolt from moving in the

lock, was perfected by Robert Barron in 1778. His double acting lever lock required the lever to

be lifted to a certain height by having a slot cut in the lever, so lifting the lever too far was as bad

as not lifting the lever far enough. This type of lock is still currently used today.

Doorknobs are ubiquitous to households. Most doors have doorknobs to allow people to

either open or close them as a way to offer a level of security and privacy. In an effort to

brainstorm improvements to doorknobs, a common household doorknob was reverse engineered.

3. PROJECT GOALS
1. To understand how the device works.

2. To understand how the various components, work together.

3. To understand how each component works.

4. To determine the forces transmitted through the pins and the mechanical advantage of the

device.

5. To understand how the device was manufactured and materials used.

4. TEST AND ANALYSIS PROCEDURE FOR DOOR KNOB

1. Investigation, Prediction, and Hypothesis

 Gather and organize customer needs

 Perform economic feasibility of redesign

 State process description or activity diagram

 Hypothesize refined functional decomposition

 Hypothesize product features

 List assumed working physical principles

2. Concrete Experience: Function & Form

 Plan and execute product disassembly

 Create BOM, exploded view, and parameter list

 Execute and document Subtract/Operate Procedure

 Experiment with product components

 Develop Force Flow Diagrams

  Create refined function structure of actual product

 Create morphological matrix

 Identify function sharing and compatibility

 Transform to engineering specs. & metrics (QFD)

3. Design Models

 Identify actual physical principles

 Create balance relationships

 Create engineering models and metric ranges — Example models: cost,

heat transfer, stress, strength, life-cycle (DFE), assembly, etc.

 Alternatively, or concurrently, build prototype model

4. Design Analysis

 Calibrate Model

 Create engr. analysis, simulation, optimization, or spread sheet applications

 Create prototype model with design of experiments

5. Parametric redesign

 Optimize design parameters.

 Perform sensitivity analysis/ tolerance

 Build and test prototype

6. Adaptive redesign

 Recommended new subsystems

 Search new effects

 Analyze force flow for all component

 Build and test prototype

 7. Original design

 Choose alternative

 Build and test prototype

 Apply concept in new field

The door knob and its components were evaluated as below:

Functional Requirements/Constraints Test

Functional Requirements

Provide access to secure rooms

Provide security of privacy and valuables

Durable, attractive, and practical, all at a low cost

Constraints

Forces

Input angular force transforms to linear Model angular forces in a predictive iconic

displacement model

Weigh less than 1kg Analyze the mass properties of materials

Maximum required angular force on knob of no Size angular momentum for maximum angular

more than XXX N-m force

Locking Mechanism should be able to withstand a Use a constructed test contraption to model the

force of YYY N-m use of an external force

Kinematics

Linearity of spring mechanism Test the linearity of spring using (F = kX)

Durability of moving parts Perform such tests as fatigue, temperature,

corrosion, and scratch resistance

Safety

Ease of disabling the lock Analyze the force required to apply the

maximum torsion to enable/disable the lock

Protect places where forces are transmitted Analyze housing and plate material

No protrusions or sharp edges that will cut hand Verify the schematics have no protrusions or

unnecessary edges

Ergonomics

Knob is designed to fit the contour of human hand Compare engineering drawings to the contour of

a human hand
Able to acquire a sturdy grip of the doorknob Ensure the presence of minimal friction through

material analysis

Aesthetic

Handle designed according to preference in Perform a survey within a diverse group

demand

Finish will withstand a long period of regular use Conduct a controlled time analysis of finish

Cost

Cost less than Ksh ZZ at retail cost Review all design, manufacturing, and shipping

costs

5. Dissection Details
The door handle consists of three major components – the outside doorknob, the inside

doorknob, and the latch mechanism. The inside and outside doorknob are connected by two

through bolts, with a quarter shaft in the center. When assembled, the latch mechanism is held in

place by the inside knob frame, and has the quarter shaft running through it.
 Latch mechanism

Latch Tab (Metal) - Keep door closed (retracted to allow opening). Its manufactured by

Casting process. Made of steel material.

Spring Latch - Returns latch to closed position. Made of Steel material.

Spring Holder - Provides surface for latch springs to press against. Manufactured by

Injection Molding. Made of Plastic (black).

 Latch Frame Front - Contains spring holder, houses latch during retraction. Manufactured

through Casting and it is made of Steel material.

Latch Frame Back - Holds the inner components at an adjustable distance from the latch

frame front. Manufactured through casting process. Made of Steel material.

Latch Hook - Rotates and pulls the Latch (Metal) back. Manufactured by casting

process.

Inside door knob

Lock Switch - User turns to lock/unlock door. Manufactured through casting process. It is

Plastic in nature.
Knob Turning Sleeve - Guides and centers shafts during assembly.

Quarter Shaft - Rotates with Door Knob, causing the latch mechanism to turn.

Door Knob Spring - returns Knob to original position after turning.

Locking Teeth - When locked, the locking teeth prevents the door knob from turning.

Outside door knob

Long through bolts - Connects two door knobs together.

 Outside Knob - User Handle (outside). Small hole in middle for Emergency Key.

Outside Knob Frame - Structural Frame for the outside knob. Connects to Inside Knob

Frame. Manufactured through casting process.

6. RESULTS
Design Functionality

When the doorknob is rotated, the quarter shaft turns, forcing the back metal shifter to

retract. The retraction causes the latch hook to rotate backwards, which then pulls back the latch

tab. Two springs are located right behind the latch tab as the restoring force in the latch

mechanism.

The inside doorknob houses the locking mechanism. When the user turns the lock switch,

the locking shaft rotates, causing the locking teeth to extend outward and grab onto a lip. The
locking teeth then prevent either knob from turning. One important thing to note is that the lock

does not prevent motion within the latch mechanism. This allows the door to close, even when

the doorknob is set to lock position.

This specific doorknob has an adjustable-backset latch mechanism, which allows the user

to choose the distance from the edge of the door to the center of the doorknob, also known as the

backset. To change the backset from 60mm to 70mm, a pin can be adjusted to slide the back

frame further out, increasing the length of the latch mechanism.

Design for Manufacturing and Assembly (DFMA) analysis

Performing a Design for Manufacturing and Assembly (DFMA) analysis on our doorknob

allows us to determine 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

processes 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:

 1. design the simplest solution?

2. make good cost-saving decisions?

3. design for easy manufacturing?

4. 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 We found there to be a lot of small parts inside the doorknob, especially

Count: considering its function (open, close, lock, unlock).

Dissection revealed that the inner and outer doorknobs were in fact not the
Standardize
same part. Instead, it appears that different molds were used to create them.
Components:
In general, we are looking to make the product as symmetric as possible.

It appears that most of the components are either stamped or cast. Thanks

Communize to this small number of types of manufacturing, training can be minimized,

Product Line: and employees become more flexible in terms of position on the production

line.
 Again, small differences in the design of the two doorknobs require
Standardize
different molds to produce each doorknob. We believe improvements can
Design Features:
be made to use one mold for both doorknobs.

Many of the parts inside the doorknob only serve one unique function.

Multifunctional Moreover, each part is unique, requiring multiple manufacturing processes.

Parts: Design changes should be considered to replace some of the parts with one

part that performs multiple functions.

Dissecting the product revealed that the two primarily materials used in

production were mostly steel and some plastic. While switching to one
Ease of
material should be considered, some choices were made with a functional
Fabrication:
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

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 is not clear enough with markings or

Mistake-Proof: 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.

There were only two sets of fasteners in this doorknob: one set to attach the
Minimize
outer doorknob to its reinforced frame, and another set for the customer to
Fasteners:
install the door latch holder to the door or the door frame.

Redesign of Doorknob

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.

Throughout the years, the doorknob has been revised many times. Through the reverse

engineering project, the group found more changes that could be made to make the doorknob

even better. The changes that were considered dealt with changing the material of the slant and

changing the design of the emergency unlocking mechanism.

As the project was in progress, we realized that some parts of the slant were made out of metal,
and other parts out of plastic. Therefore, in order to make the doorknob better, the group

proposed to make the whole slant out of plastic. The reasons we came to this conclusion are that

our doorknob is an indoor use doorknob, which really does not need to be able to support forces

used in a forced entry situation. Another reason why the group thought that the plastic slant was

better was because the use of plastic would reduce the amount of noise made when closing a

door. Everyone has experienced a situation where someone wants to shut a door quietly, but no

matter how hard a person tries, the door always manages to make a loud noise. Through

experimentation, we found that the doorknob makes most of the noise. The last reason why we

thought the doorknob should be made out of plastic is to reduce manufacturing cost. There is no

need for the slant to be made out of metal for an indoor doorknob. In fact, it would be better to

have the whole slant made out of plastic since it would reduce noise. Therefore, through the

discussion of these points the group thought it would be better to have the whole slant assembly

to be made out of plastic.

When we disassembled the doorknob, the group realized that the emergency unlocking

mechanism was simply too hard to unlock. The doorknob was designed so that in case of an

emergency, the users of the doorknob would be able to unlock the door by sticking a slim piece

of metal into the door and twisting it until the door unlocks. The problem with this design is that

the metal piece can easily be lost or thrown away, which would make the emergency unlocking

mechanism worthless. Therefore, through discussion, the group concluded that the doorknob

should have a wider hole so that almost any piece can be placed through the whole to unlock the

door. This would allow the users of the doorknob to use almost any available item to unlock the

door in case of an emergency. Through this redesign the unlocking mechanism would be more

useful and time efficient during an emergency.

 7. CONCLUSION
A door knob assembly is created to facilitate the means of securing an entrance. The door handle
consists of three major components – the outside doorknob, the inside doorknob, and the latch mechanism.
Design for Manufacturing and Assembly (DFMA) analysis on our doorknob allowed us to
determine 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. Several redesign models were
developed that involved, Making the correct orientation, changing the material of the slant and
changing the design of the emergency unlocking mechanism.

8. REFERENCES
Ertas, A., & Jones, J. C. (1996). The engineering design process. Chichester: Wiley.

Dieter, G. E., & Schmidt, L. C. (2013). Engineering design. New York: McGraw-Hill.

Haik, Y., Sivaloganathan, S., & Shahin, T. M. M. (2018). Engineering design process.

Shetty, D. (2016). Product design for engineers.

Ullman, D. G. (2016). The Mechanical Design Process. Boston: McGraw-Hill Higher Education.

Whitney, D. E. (2004). Mechanical assemblies: Their design, manufacture, and role in product

development. New York: Oxford University Press.