Hi everyone! Welcome to my 6th and final blog! In this blog, I will be documenting the entire design process of my group's prototyping of an automatic door handle steriliser. My group consists of Devin, Brice, Ji Hinn, and myself. We have been working on this project since Week 5, and we are proud to announce that it is now complete, now that it is Week 18.
The significance of our product
Door handles are a significant culprit in the spreading of viruses and bacteria. This is because everyone must touch them to open the door, and they rarely get cleaned since they do not look dirty to the naked eye. Also, most door handles are made of stainless steel, which is a perfect material for bacteria to cultivate on. Some examples of viruses that can spread are the coronavirus (COVID-19), norovirus, hand foot and mouth disease, and influenza.
To emphasise, ever since COVID-19 started, the need for sterilisation tools/equipment/media to minimise its spread has increased. One of the commonly touched areas that requires specific sterilisation equipment is door handles. Disinfecting and sterilising are types of decontamination, a process that makes something safe to touch. The purpose is to kill enough germs so the risk of infection, in this case COVID-19, is extremely low.
Hence, producing an automatic door handle steriliser will be a great and convenient way to curb this problem.
Hand sketches of our product... from Week 5 to Week 18!
The following hand sketches are all one-point perspective sketches, with the point being located at the top right.
Allocation of roles in the team
Chief Executive Officer (CEO): Devin Tan Wei Jie
Chief Financial Officer (CFO): Ang Yu Han
Chief Operating Officer (COO): Leong Rui Ren, Brice
Chief Security Officer (CSO): Chang Ji Hinn
Finalised Bill of Materials (BOM)
Since most of the materials that we needed were mostly readily available at W319 (such as the Arduino kit, 3D printing filaments, hot glue, cardboard), we barely had to purchase anything.
Finalised Gantt Chart
Gantt Chart file:
Part 1: Arduino programming / Coding (done by Ji Hinn)
Link to Ji Hinn's blog:
Ji Hinn's hero shots!:
Ji Hinn's completed code in text form:
#include "pitches.h" const int trigPin = 9; const int echoPin = 10; int LED = 13; // connect LED to PIN 13 (UV light) long duration; int distance; // notes in the melody: int melody[] = { NOTE_C4, NOTE_C4, NOTE_C4, NOTE_C4, NOTE_C4, NOTE_C4, NOTE_C4, NOTE_C4, NOTE_C4, NOTE_C4, NOTE_C4, NOTE_C4, NOTE_C4, NOTE_C4, NOTE_C4, NOTE_C4, NOTE_C4, NOTE_C4, NOTE_C4, NOTE_C4, NOTE_C4, NOTE_C4, NOTE_C4, NOTE_C4 }; // note durations: 4 = quarter note, int noteDurations[] = { 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4 }; void setup() { pinMode(trigPin, OUTPUT); pinMode(echoPin, INPUT); pinMode(LED, OUTPUT); Serial.begin(9600); // Starts the serial communication } void loop() { digitalWrite(LED, LOW); //turns off UV light digitalWrite(trigPin, LOW); delayMicroseconds(2); // Reads the echoPin, returns the sound wave travel time in microseconds // Sets the trigPin on HIGH state for 10 micro seconds digitalWrite(trigPin, HIGH); delayMicroseconds(10); digitalWrite(trigPin, LOW); duration = pulseIn(echoPin, HIGH); distance = duration*0.034/2; Serial.print("Distance: "); Serial.println(distance); // if distance greater than 30 cm (no one nearby) if (distance > 30) { digitalWrite(LED, LOW); //turns off UV light } else { while (distance < 30) { digitalWrite(trigPin, HIGH); delayMicroseconds(10); digitalWrite(trigPin, LOW); duration = pulseIn(echoPin, HIGH); distance = duration * 0.034 / 2; Serial.print("Distance: "); Serial.println(distance); } delay(5000); digitalWrite(LED, HIGH); // turns on UV light for (int thisNote = 0; thisNote < 8; thisNote++) { // to calculate the note duration, take one second divided by the note type. //e.g. quarter note = 2000 / 4, eighth note = 2000/8, etc. int noteDuration = 2000 / noteDurations[thisNote]; tone(8, melody[thisNote], noteDuration); // to distinguish the notes, set a minimum time between them. // the note's duration + 30% seems to work well: int pauseBetweenNotes = noteDuration * 1.30; delay(pauseBetweenNotes); } digitalWrite(LED, LOW); // turns off UV light // stop the tone playing: noTone(8); } } |
Part 2: Computer Aided Design (CAD) & 3D Printing (done by Brice)
Link to Brice's blog:
Brice's hero shot!:
Part 3: Laser Cutting (done by Devin)
Link to Devin's blog:
Devin's hero shot!:
Part 4: Prototyping & Device Assembly (done by Yu Han/me)
I took up the task of prototyping, trial and error and assembling the device for our product prototype. (My hero shots will be included within my documentation of this section...!)
Before any 3D printing or laser cutting was conducted, I took charge of producing a cardboard prototype and the device assembly (with the except of the Arduino programming assembly). By doing so, we can make sure that our 3D printed or laser cut item will be of the proper specifications and can work well. This can save time, and also materials used. This is because should our 3D print fail due to incorrect specifications, we would have wasted a lot of time to wait for the print to complete. Cardboard prototyping also helps us to visualise how the actual printed prototype will look like.
However, in our case, cardboard is not only used as a prerequisite to 3D printing, but also used as the final product. We had used it to wrap our 3D printed pieces, create our cylinder lid, and secure our mechanism that activates the prototype when the user has opened the door.
I had made a total of 5 cardboard cylindrical prototypes (including the successful one) in this product prototyping journey to check for the size feasibility. I will then showcase the final cardboard prototype that made it through.
Cardboard prototype
My cardboard prototype had the following specifications:
Outer diameter | Height | Thickness |
100 mm | 125 mm | 3 mm |
To allow the cardboard piece to be bent into a cylindrical shape, I scored the cut rectangle piece that accommodates to the required inner diameter and height in intervals of 10 mm. Since the cardboard already has a thickness of 3 mm, I did not have to cater to the thickness requirement of 3 mm.
I then used hot glue to glue the ends of the rectangular piece and the circular base of the cylinder together.
Afterwards, I placed the larger components of the prototype (such as the Arduino board and breadboard) inside the cardboard cylinder to check if the size is feasible.
My team and I compared the cardboard prototype to an actual door knob to visualise the design in real life.
Wrapping the 3D printed piece with cardboard
Since the 3D printed piece had very poor structural integrity, my team and I decided to wrap it in cardboard. I used hot glue to secure the cardboard to the 3D print.
Since we had added an extra 60 mm of cylindrical structure above the original one, I made another cardboard wrapping to match the prototype design.
The updated specifications of the prototype are as follows:
Outer diameter | Height | Thickness |
106 mm | 185 mm | 6 mm |
Making the prototype's removable cover out of cardboard
A cap was required to cover the prototype. I chose to design a cap that can close the cylinder by pushing it in, and open the cylinder by pulling it out. To create a cap, I first created 2 cylinders of different sizes out of cardboard before gluing them together to form a cap. The smaller cylinder has a diameter of 94 mm and height of 15 mm. The larger cylinder has a diameter of 106 mm and height of 18 mm. In total, the entire cap has a height of 33 mm. Hot glue was added to 4 locations that are evenly spaced apart on the bottom smaller cylinder and hardened. This provides more grip for the cap, as cardboard will experience wear and tear rather quickly, which can cause the cap to loosen. Providing more grip on the cap will solve the issue.
The updated specifications of the prototype are as follows:
Outer diameter | Height | Thickness |
106 mm | 203 mm | 6 mm |
Securing the mechanism using cardboard
The mechanism to allow the ultrasonic motion sensor to detect when the user has opened the door is made out of acrylic, and needs a mounting method to attach it to the door. I created a cardboard backing for it so that the screw can be drilled through the cardboard to attach the mechanism to the cardboard and create a pivot point for the mechanism. To ensure that the mechanism has a bottom backing so that it does not droop too much and possibly cause a quicker wear and tear of the hole in the cardboard where the screw is drilled, I designed a bottom shelf using cardboard to hold the mechanism in place and to support it.
Final product prototype
Internals of the prototype
The prototype in use!
Group hero shot of the finished prototype!!!
Problems and Solutions
Throughout our prototyping journey, we have experienced several hiccups that required us to change our design. There were so many changes, small and big, that I cannot explain it all using just short paragraphs. Hence, let me bring you through the entire prototyping process, including documentations of our failures... The hand sketches of our product from Week 5 to Week 18 will be able to illustrate our problems and how we solved it.
Week 5
In week 5, we started on the Part 1 of our CA2 report and our initial design idea for our prototype. We initially designed a cylindrical design, with the following features:
One end of the product will be able to stick to the door
UV light will be placed at the same level of the door handle
A waring light and buzzer will exist as a rim around the top of the product
Week 9
In week 9, we completed the Part 1 of our CA2 report, leading to a more in-depth research regarding our design and decided on the types of components that we will use to facilitate the sterilisation of the door handle. The completion of TRIZ especially helped to refine our prototype. The following features were implemented:
The warning light and buzzer will remain situated at the rim of the cylinder top.
An infrared sensor module and infrared motion sensor will both be used to detect any motion by the user, so that the UV light will not be active when the user is nearby. This is because UV light is harmful to us.
3M tape on a circular piece will be secured to the door, so that the product can be removed or returned to the door at any time required.
The product will be rechargable. This will be facilitated through the addition of a USB-C female charging port.
A UV light bulb will be used to generate the UV light
Week 15
In week 15, we started improvising on the Part 1 of our CA2 report and started on deciding the specific specifications for our product. We also received feedback from our lecturer, Mr Chua. We then utilised his feedback and the takeaways from our discussions to make certain changes to our product. The following changes were made:
The diameter and height of the cylinder was decided to be 70 mm and 125 mm respectively.
The LED warning light was abolished.
The warning buzzer will be a separate component inside the cylinder, instead of on the rim at the cylinder top.
Instead of using a female USB-C charging port, we received feedback to use a portable power bank instead, and we decided to implement this feedback.
Week 16
In week 16, we decided to make certain changes to our product due to certain realisations and more feedback received from Mr Chua. We changed certain components and the overall working principle of the product. The following describe the changes:
Firstly, we recalled that a gear, lever, or any mechanism is required to be present in our product, but we had none of that. After a quick discussion, we decided to abolish the infrared sensor module and infrared motion sensor as the component used to detect motion. As a replacement, we decided to use a light dependent resistor (LDR) instead. We designed a mechanism that will cover the LDR when the door handle is opened, blocking light to the LDR and resulting this action to cause the UV light to turn off.
However, for this mechanism to work, the product can only be used on doors that have a door handle, instead of a door knob or such. This is because when the door handle is opened, it will press down on one side of the mechanism, lifting the other side up, and resulting in the LDR being blocked. This mechanism include two pieces of acrylic stuck together through the use of 3 springs fixed on both pieces of acrylic on the side that the door handle will press on. The other side of the mechanism includes a single spring that is only fixed to the bottom piece of acrylic, allowing that side to lift up when the other side is pressed.
Also, since we were not allowed to use actual UV light for our product prototype as it is dangerous and because we are still in the prototyping period, we used a LED light bulb as a replacement and illustrated it on the sketch.
Lastly, we were advised by Mr Chua to use the in-built piezo buzzer on the Arduino board instead of a separate buzzer. The warning light was also abolished as we decided that just the warning buzzer would be enough. We then implemented this.
Week 17
In week 17, we decided to abolish the LDR and use an ultrasonic motion sensor instead to detect the presence of the user. This is because using the LDR will lead to inconsistent results, as the lighting at different locations will be different. Using an ultrasonic motion sensor would be better and will conceive more consistent results. The working principle remains the same as week 16 (when the LDR is planned for use). Since Ji Hinn had also completed and finalised the code that week, we drafted up a more specific explanation as to how the product will work. To explain, the prototype is to be placed 300 mm away from the door handle. The edge (with the 3 fixed springs) of mechanism will be placed right under the door handle. When the door is opened by the user, the door handle will press onto the edge of the mechanism and lift up the other side of the mechanism, causing the ultrasonic motion sensor to detect motion within an estimated 150 to 200 mm. After receiving an input caused by the ultrasonic motion
sensor detecting motion, the UV light bulb (replaced by a LED light bulb) will light up and the in-built piezo buzzer will sound 5 seconds after the door was opened, and disinfect the door handle.
Week 18
In Week 18, several changes were made on different days.
Firstly, I had completed a cardboard prototype for our design. It had a diameter of 70 mm and a height of 125 mm. However, after including the components (Arduino board, breadboard, power bank, wires) into the cardboard prototype, we realised that the prototype was way too small. As a result, we scaled the cylinder up to have a diameter of 100 mm and height of 125 mm instead. After concluding the new specifications of the product, we proceeded to 3D print it next. However, there were certain unknown issues regarding the print. Despite creating an entirely new CAD of the design and converting it into a file type that is suitable for the 3d printer (Creality Ender 6), the specifications remained as the initial one (with a diameter of 70 mm and length of 125 mm). Also, the 3D printer was faulty in some way, and our 3D print turned out absolutely sloppy and unsuited for use. We then stopped the print halfway through. The following images describe the problems faced:
Next, since majority of the 3D printers at W319 were faulty or occupied and we were unable to book any other 3D printers at other locations, we were only able to start the print with the updated specifications 3 days later. However, the print turned out to be rather sloppy again, with printing filaments poking out everywhere on the inside of the cylinder. The structural integrity was also rather poor, and could break at any exerted force. There were also black plastic marks around the inside of the cylinder. We guessed that the nozzle of the Creality Ender 3 3D printer must have melted onto the print, and also blocked the nozzle, blocking the melted printing filament from coming out to an extent, resulting in our 3D printed prototype to be very messy and thin. Regretfully, it was not possible for us to restart the print again anytime soon as there were many people trying to get their print done as well. (And there were at least 3 faulty printers!) As a way to curb this problem, we decided to cover the outside of the 3D printed cylinder with cardboard to improve the structural integrity. The following images describe the problem and the solution used:
Afterwards, due to time constraint and the lack of 3D printers available as well, we constructed a cap out of cardboard. This cap is consists of 2 cardboard cylinders of different diameters stuck together. The total height of the cap is 33 mm, with the bottom smaller part being 15 mm in height and the top larger part being 18 mm in height. Although the cap was a perfect fit, we noted that it may get loose over time as the cardboard may tear due to the friction caused by opening and closing the cap. Hence, to make sure that the cap will stay tight, we added hot glue and let it cool down on 4 points that are equally spaced apart on the cap. This will add more grip as the hardened glue has a certain rubbery texture to it. It worked!
To our shock, we realised that the length of the cylinder was too short. This is because the wire connected to the Arduino board and the portable power bank was protruding out, and also because our cap will require an extra head space of 15 mm to work. Hence, to solve this problem, we decided to extend the cylinder by 60 mm by 3D printing a baseless cylinder with a height of 60 mm. Luckily, there was a 3D printer available at that point of time. Although 3D printing the entire prototype would be a better solution, we had no time, as the print will require 8 hours to complete. It was 1pm at that point of time, and the lab would close at 5pm. Hence, we proceeded to print the baseless cylinder instead. To match with the original design, we also added the cardboard layer around the new print, despite how the new print had a strong structural integrity and was really neat and pretty... The updated specifications of the prototype includes a diameter of 106 mm, length of 203 mm, and thickness of 6 mm.
We then added the cap on. With that, the casing of our prototype was complete! The following images show the updated hand sketch and the completed prototype casing.
Afterwards, we started testing our prototype on doors with door handles. We then noticed how hard it was to get one side of the acrylic to lift up when the other side is pressed down by the door handle, partly because the door handle is not pressing down on the center of the acrylic (that has a fixed spring installed). This made our prototype very inconsistent, as the amount of times that the acrylic will lift up correctly was rare. To fix this problem, we decided to abolish the springs and the bottom piece of acrylic, leaving only the top piece and the center pivot that fixes the acrylic to the door. The image on the left hand side below shows the initial mechanism design with the springs, and the image on the right hand side shows the updated mechanism design without the springs. The image on the second row shows the updated hand sketch.
Finally, our prototype is complete! We then fixed it to a door and started testing it out. Well, thankfully, it worked and we are satisfied with the outcome!!!
Project design files
All the files required for our prototype (CAD file for 3D printing, CAD file for laser cutting, Arduino program file, etc.) are in the google drive link below:
Learning reflection
Wow, this product prototyping process was a tedious one. The prototyping process ranged over 13 weeks, and it was always at the back of our minds during our learning semesters. We are all really glad that it is finally over.
I recall stressing over my exams and submissions, and still having to go to W319 to work on our prototype. It was truly a hectic period of time. However, now that I look back on it, I am glad that all of us put in that much effort for our prototype. This project will truly be a core memory of my experience in this diploma. The prototyping of our automatic door handle steriliser was a really fun and enriching process. We managed to apply all the different product prototyping skills that we have learnt at our own will, meaning that we could decide where we wanted to implement our skills at for different purposes in the prototype. These skills include hand sketching using 1/2 point perspectives, cardboard prototyping and different cardboard joinery types, CAD, 3D printing, laser cutting, Arduino programming, and such. By doing so, my group members and I have refined our prototyping skills. We have learnt a lot, especially through the mistakes that we have made along the way. These refined skills will surely serve us well in our upcoming Final Year Capstone Project.
Also, my group members and I noticed how short on time we were. We had only completed the prototype on the Friday of the week before the prototype presentation (which is held on Monday). One thing that we have realised was that we should have planned out our time better and referred to the Gantt Chart frequently. There were several tasks that we have started rather late, and this could have been avoided if we had split the work between us more efficiently. Nevertheless, every mistake is something learnt. We will make sure to take note of this in our upcoming projects.
With that, I would like to announce that this blog entry is finally over... This is the longest blog entry I have ever written, is it not? Well, I had fun documenting everything that I have learnt and done for the past few blog entries, and thank you for sticking to the end. Until we meet again! :-)
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