Designing a device to offer an alternative way to operate door handles

We open doors innumerable times in a day, without even thinking about it, but do we realise the implications of this action? In the last two years, during the Covid-19 pandemic, much more focus has been rightfully put on germs and their spread.

 

Germs and bacteria are also dangerous in “normal” situations. These include hospitals, where HAI (Healthcare associated infections) are very common. Only in the US, 1.7 Million hospitalised patients get infected with an HAI, and a further 98 000 die1 . Infectious bacteria and germs are transmitted through healthcare workers, and through infected surfaces 2 . Furthermore, HAIs account for more than 30$ billion in eccess healthcare costs in the US.³

 

As Haque et al state, “healthcare workers’ contaminated hands are the vehicle most often impli- cated in the cross-transmission of pathogens”. Thus, a product that would significantly contain the spread of germs on doorknobs would also help reduce the amount of infected patients.

 

This problem doesn’t only apply to healthcare, but also other environments such as schools or offices. Through a survey I conducted in school, to which I received 58 responses, I had a confirmation of the tangibility of the problem from the students view.

Furthermore, inclusivity is an issue with door handles, as people with amputated or absent limbs are not able to operate them, and need ex- ternal help.

 

Existing solutions often require the user to carry a device, which is clunky and often not comfortable, as the user needs to take the device out of their pocket for use.

The aim of this IA is to create a product that allows users to open doors without touching the handle, and without using hands, which are carriers of infectious germs and bacteria.4 This would minimise the spread of dangerous microbes in schools, offices and hospitals.

 

The target audience is very wide, as the groups of people who need to operate doors in schools, offices or hospitals are various. The age of the target user group consists of people approxi- mately between 10 and 80 years of age, including people with disabilities. The handle should be designed taking into account the 5th percentile, or the smallest users, in order for them to reach the handle.

 

The product must be -

• Simple,easy to operate and intuitive, in order for the user to swiftly use it
• Compatible with most handles
• Resistant to repetitive use
• Suitable for a wide range of the targeted users
• Generally respect the criteria of usability (topic 7.2)⁵

The final product will be a real size 3D printed model and a CAD model, representative of the real product. The prototype will be tested in school, but given its success it could be used in other envirnoments where spread of germs is a concern too, such as hospitals and offices.

Based on user preference and adherence to the brief, the further developments of idea 4 and 6 (labelled respectively as 4 and 6) will be considered. They will be evaluated against the specifications in the brief to find areas for improvement and further iterations.

As from the table above, idea 4 will be brought forwards for iterations of concept modelling, in order to improve the design. Idea 4 exceeds idea 6 in many requirements, for example the aesthetics, where 4 is preferred for its simplicity, making it less impactful on the design of the handle. Also, 4’s semplicity is preferred for ease of manufacturing,installation and use.

The main prototyping method used will be 3D printing, due to its rapid prototyping and high accuracy characteristics. (Topic3)

Despite the fact that the print didn’t come out as expected, I still tested it. I put it on the door handle with some tape, and asked some classmates to try it. They all succeded in opening the door, some with difficulties, others with none. Some appeared confused on how the design should operate (spec 3.4). The observations made while testing will be illustrated in the following figures. They will be used to improve the existing prototype, and eventually produce another one.

The print failure made me understand that my original design had a weak point at the bend (Topic 3). This made me change the way the design is secured to the handles in order to remove a possible failure point.

This design was chosen as the one that best meets the requirements in terms of function, user feedback and aesthetics. It allows the user to open the handle efficiently using forearm and elbow and without eccessive difficulties. When compared to the previous iterations of the design, this final product is simpler and more aestetically pleasing, respecting the specifications given in Criterion A3. It does not have the ridges that the first CAD model had, because they proved to be not functional and unaesthetic. The function that these ridges aimed to achieve will be fulfilled by a soft and grippy material, which will be discussed in the next section. It is also far simpler when compared to my previous ideas, for example the foot operated ones. These would only increase the difficulty of using the handle and deliver a bad user experience, going against the specifications, especially the ones regarding ease of operation and intuitiveness, based on the work of Norman. In this case, as the product has to be tested in school, the handle clamp has been modeled to match the handles in school. However, the opener design can be taken as modular, and the clamp can be redesigned to match any handle, using the same, clamp- on philosophy. A material suitable to grip to the handle will be chosen in the following section. This final CAD model was the result of various iterations, which started from sketches, and a refinement of two ideas which were both modeled in CAD. Out of these two, one was chosen two be 3D printed and tested. After some modifications, for example some more support for the forearm and some improvements to the clamp, these iterations were brought together in the final version presented above. A grey color was chosen to match the existing color of the handles and doors, and initial feedback from students and staff seems positive, based on the CAD models of the product.

ABS (Acrylonitrile butadiene styrene) was also considered as an alternative material, as it is cheap and commonly printed too. However, it was opted out due to its lower capabilites in strength and general performance, and also because it is more difficult to print accurately and succesfully

 

Nylon was also taken into consideration, as it is a material that is now being introduced as a filament. However, it is a very flexible plastic, and it does not have a lot of strength. Furthermore, it has a low coefficient of friction, making it more suitable for applications like gears or bearings

Other possible manufacturing techniques are listed below, alongside the reason for not choosing them as the process to build the prototype.

A bill of materials will now be presented. The data has been retreived from the slicer software (Ultimaker Cura). The weight was then multiplied by the cost per kg of the material to obtain the total cost. The sources for the value for price per kg has been cited.

The cost for the material for the production of one prototype came out to be at around 1 euro, proving how 3D printing was the right manufacturing choice because of its cheapness.

- Testing strategy #1,2 (physical resistance test and aesthetics analysis) - The prototype was observed under application of forces and stresses that would be normal under typical use, and annotations of the relevant findings were made. The design was also analysed in its aesthetic characteristics, which will be commented in the table below. Annotations were made on the figure.

- Testing strategy #3 (user testing): Users were given the task to use the product, without giving them instructions on how to use it. Observations were made, which will be summarised in the table below, alongside with a summary of a questionnaire asked to 24 users after their interaction with the product.

 

- Testing strategy #4 (expert feedback) - An expert in architechture and product design (Nicoletta Reginato) was given the specifications, final renders and drawings for the product, and photos of the 3D printed and installed prototype. She gave some feedback on the design which will be included in the table below.

Based on the improvements that came out of analysing the 3D printed prototype when compared to the specifications, and the ones suggested by the expert, suggestions for improvements will be made. For example, the clamp roughness could be increased, in order to improve resistance to forces that would make the product rotate on the handle. Furthermore, the product’s footprint on the door and handle could be reduced by totally removing the vertical side facing the door surface (as highlighted in figure).

This is because the 3D printed wall can be substituted by the door itself, and the forearm, or the elbow, can push on the door. However, some further testing has to be done to evaluate this design choice, as it might potentially reduce the comfort of the product. This is because the user won’t have a single surface on which to push on, and the more surfaces offer more possibility for the user’s forearm or eblow to slip. A careful consideration should be made, whether the increased risk of worse user experience is balanced by the improvement in aesthetics. Another possible improvement should focus on the intuitiveness of the design, as it was another issue of the design that emerged from testing and evaluation. Reducing the overall footprint of the design and adding curves to better integrate the design to the handle and make the transition from the handle to the product seamless might be a possible solution. This is because the user would perceive the product on a psychological level in a different way. With the prototype, the user still sees the handle, and associates the usual motion with it (using hands). This is because, the prototype, as is quite obvious from the figure above, doesn’t blend in efficiently with the handle. Adding curves and putting the two objects together better might push the user to detach from the usual hand movement and move towards forearm or elbow use.

An exploration of injection moulding as a manufacturing technique, and PVC (Polyvinil Chloride) as material for the main body of the product will now be presented. This is because they are more commercialy suitable processes and materials to satisfy requirements. The surface will be coated by a layer of polyisoprene, a type of synthetic rubber. The two materials will then be joined through the use of an adhesive.

An analysis of the three most produced polymers worldwide (polyethylene, PE, polypropylene. PP and polyvinyl chloride, PVC) will be conducted, in order to justify the most appropriate. Other polymers were considered too, but only these three were reported for the sake of brevity. From the stress-strain curves, PVC shows the highest stress bearing capabilities and overall strength. It has a yield point at around 50MPa, entering the plastic region, while the other materials have it at a significantly lower value. Furthermore, it has other characteristics that suit this project that have been previously listed.

Methylene chloride glue was chosen as an adhesive bonder between the PVC and the polyisoprene. It works by partially melting the two plastics and then letting them set into each other, creating a durable and resistant bond. It was preferred over other types of glues because it bonds the two plastics themselves, as opposed to other adhesives such as epoxy. A plan for manufacture of the injection moulded PVC product coated with the extruded polyisoprene layer will now be presented.

A bill of materials for the injection moulded product will now be presented. The volumetric data has been retreived from the CAD software, and then then the volume has been multiplied by the density to obtain the weight, which has been multiplied by the cost per kg to obtain the total price for one unit. The sources for the values for density and price per kg have been cited.

The cost per unit came out to be €1.13, not considering shipping and the initial setup costs for the molds for the injection moulding of the PVC and the extrusion of the polyisoprene. This is a very low price, as intended by the specifications, and would be accessible by most schools, hospitals and offices. As the product is quite simple in its geometry, the resultant shape of the injection mold is too, and it can be manufactured for cheap too. With new manufacturing tech- niques, such as resin 3D printing, a simple mold can be produced for as little as $10025. Similar- ly, extrusion molds can be manufactured for cheaper prices. Even considering the cost of the molds, it still remains a quite affordable product, and given that many units can be produced from the same mould, the price would be paid off in the long run.

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