January 19, 2024 - As an avid sushi enjoyer, I have always been a big fan of chopsticks - so simple, yet so effective, essentially acting as an extension of one's fingers. However, the commonplace design has stayed the same for over 5,000 years. So, with some free time on my hands, I wanted to see if I could make chopsticks better - easier to operate, more precise, more visually exciting, and reusable - all while maintaining the key functional characteristics.
The largest existing issue with traditional chopsticks is the way in which force is applied by one's hand to "clamp" a sushi roll. Since your fingers are responsible for closing and opening, they are primarily in contact with the sticks parallel to the rotation axis. Thus, it is a friction force that opens and closes the chopstick. This means that one's fingers must produce both a force normal to the chopstick (to generate the frictional force), and a force to the clamp the chopsticks. As a result, the strength of one's hand is balancing between two forces, and in trying to achieve more torque, extends fingers along the chopstick. In order to keep food from touching these elongating fingers, chopsticks are made quite long, which only then reduces the torque applied on the sushi roll.
The Better Chopsticks solve these issues. Despite being having a motion ratio (the ratio of the displacement of end of the chopstick to that of the fingers) greater than traditional chopsticks - the Better's being 4.5, compared to the traditional's 2.75 - the Better Chopsticks are able to exert greater clamping force. When pinching a scale, the Better Chopsticks could produce a maximum clamping force of 230g , while the traditional chopsticks could only produce 121g (image below).
This significant improvement is all thanks to a compliant spring that is responsible only for opening the chopsticks. As a result, one's fingers are only responsible for applying a single normal force to clamp a sushi roll. This is much more efficient, and means that fingers can take up less real estate on the device, enabling shorter arms and thus, greater torque. Not only does this mean that the chopsticks could be made smaller, but the movement is also much more intuitive, akin to eating with your fingers.
A design challenge that arises with shorter arms is less range of motion. This was solved with the lever mechanism, whose design was driven by a few factors. One functional characteristic of traditional chopsticks that I wanted to remain the same was the angle between upper and lower arms at the fully clamped and fully opened position. Therefore, a secondary bend was implemented on the pivoting arm. Finding the pivot points of the pivoting arm was also a challenge as it had to meet a compromise of torque, size, and shape. In addition, the path that the pivot points controlled would help to determine the effective stiffness of the compliant spring: if the pivoting arm followed the natural bend path of the spring, the spring would "feel weaker.
In summary, designing the Better Chopsticks was a blast. It reminded me of car suspension design, as altering one pivot point or minor detail affects everything else, and finding the best setup is "merely" an optimized compromise. I went though many prototypes in CAD, and two physically 3D printed prototypes (V1 & V2) before the final design (V3). The Better Chopsticks are not only easy to use, but also easy to print as they are print-in-place, meaning that they are fully assembled and functional off the print bed. In the end, I really enjoyed adding some artistic flair with the design and seeing that the chopsticks actually performed in the real world.
If your feeling hungry for some sushi, I encourage you to print your own below!