Background
Most paper towel holders on the market have one center rod and then one static rod used to apply pressure to the outside of the roll so that the user can tear off a sheet with one hand. However, as the roll decreases in size, the static rod begins to apply less pressure. Soon, no pressure is applied to the roll, making it difficult to tear off a single sheet of paper towel with one hand. The client (OXO) had a paper towel holder that used an arm to apply pressure to the outside of the roll regardless of its diameter. However, the client wanted Bally Design to come up with a design that used a mechanism invisible to the user. During my internship with Bally Design, I brainstormed with industrial designers, performed analysis on the different braking mechanisms, assisted in developing the design of the paper towel holder, constructed functional prototypes, and evaluated the product's performance.
Existing Product
Concept Generation
When developing initial concepts, we wanted the paper towel holder to be noise-free. We also wanted to ensure the optimal amount of resistance was applied to tear off a single piece of paper. The latter task proved difficult, as the amount of torque applied to the center part of the holder varies depending on the number of paper towels left on the roll. Due to this variable, there was the risk that if the resistance was just right for a full roll of paper towels, the resistance would be too great when nearing the end of the roll. Determining the correct resistance was a task I completed through analysis and testing.
With these goals in mind, I collaborated with a team of industrial designers to brainstorm different methods of slowing a paper towel from spinning when a user pulled a paper towel from the roll. We developed various concepts, including a friction braking system and an eddy current brake. After comparing ideas, we decided to evaluate the friction braking system with further analysis and prototyping. The friction braking system would use pads with springs to apply pressure so that the frictional force applied to the cardboard would increase.
Sizing & Analysis
Using the concept of the friction braking system, multiple prototypes were constructed that varied the force supplied by a spring. We tested the prototypes with paper towel rolls and then selected the one that gave the best performance. Using this prototype, we were able to understand how much the spring was compressed and thus deduce the amount of force that was applied to the cardboard on the inside of the roll. Using information online, I estimated the kinematic coefficient of friction between the brake pads and cardboard and was able to quantify the frictional force applied to the inside of the roll.
Prototyping & Testing
After determining the correct amount of force to apply to the cardboard on the inside of the roll, additional prototypes were constructed that altered the number of pads and their geometry. To thoroughly test the devices, I used rolls of paper towels from various brands. During testing, it was found that the inside diameter of the cardboard rolls varied with each brand. This resulted in a varied force being applied to the inside of the roll, depending on the brand. Therefore, we decided that the braking system should be internalized. The shaft of the paper towel holder would be used to ensure the cardboard did not move and rotate with the shaft, and a braking mechanism would be placed inside the base of the paper towel holder.
Outcomes
A new design was created based on the results of my testing. The braking mechanism was placed into the base of the paper towel holder. This product was later delivered to the client and brought into production.
Reflection
The paper towel holder that we created accomplished the goals that we set out to achieve. However, not all users utilize an upright paper towel holder. Instead, some users have paper towel holders mounted on the wall. In addition to the paper towel holder we created, I would have liked to have created a product with the same idea in mind but for use on a wall. It is more difficult to tear a single sheet of paper from a holder mounted on the wall, and to my knowledge, no consumer-level products are on the market to solve this problem. It would have been an intriguing challenge to design a product to fill this hole in the market.