Our project is tailored to help a 2 year old who is growing very quickly. The child is about the size of a 4 year old, and still has developmental needs at her current age. Our goal is to help with one of those needs while she is at the dining table. We were tasked with designing a specialized highchair that will help with her development needs no matter where the family would go. This chair will help the child, keeping her comfortable while she grows up, and help the family with providing care for her.
The chair needs to assist the child for at least three to five years during her development as a growing child. The chair must be a safe and inviting for the child, as well as practical for the family. It must be easy to use, clean, and move. Making it portable so the family could take it to public places like restaurants was also requested. All these things are important, as it will help the family use the chair while the child still needs it.
While the chair needs its practical components, there are also some stimulus things we must focus on retaining for the child, as we are building an environment to help her feel comfortable while she eats. One of the simpler, yet equally important requests was a cupholder. We must focus on designing a seat and backing that are both sturdy and ergonomic for maximum support during use.
For portability, we are still assessing ways we could make the chair fold into a smaller shape. With our time, we are looking for a practical working solution. Our current ideal goal is to make sure that the chair operates smoothly, but the structural integrity of the chair is our first priority.
For our research, we referenced the current highchair the family was using to see what the child may desire in a chair. This gave us a rough idea of what the child would enjoy in her highchair. We also referenced other folding chairs, to see how we could design a mechanism to help the chair fold for portability.
Images in order:
1. The current chair the family is using.
2. Some current market designs look similar to this.
3. Folding chair we looked at for mechanism inspiration.
4. Foam seat inspiration.
For our first Concept Design, we brainstormed on the idea of the chair having adjustable height, arm width, and adjustable tray position. This would allow for the chair to be adjusted to any height, as well as give the seat any size that would be needed. The height latching mechanism for chair designs 1 and 2 are the same. (click image to see full image)
Concept Design 2 builds off of Concept Design 1. The sides are eliminated in favor of only having the chair backing. This simplifies our design in favor of making the seat more comfortable to sit in. The tray is attached to one arm and has a leg divider that can be removed as needed. The tray could be slid towards or away from the chair backing, as well as left or right on the bar it sits on. Since adjustable height was not needed, we opted to remove it in favor of a portable design. A sliding mechanism was designed so the chair could be folded into a compact form, ideal for sitting in the back of a car. The gif animation provided is how we imagine the sliding mechanism would function. (click images to see full images and gif animation)
Concept Design 3 takes our second concept design and simplifies the design a lot more. Getting rid of weight and making it easier to adjust. The chair has a simpler mechanism to support it, simply being two legs that are free to move as needed. The tray will have a selection of slide positions to choose from. The frame holding the seat and latching mechanism will be made of aluminum, while the frame of the highchair will be made of a strong wood like poplar. The wood will be sanded and stained accordingly.
Our selected design will be concept design number 3. This design is the most simple and reliable. This will ensure longevity for the family as the child grows. It is also the most compact design we have discussed thus far. None of the designs were particularly more difficult to clean than the others. This removed it as a component we needed to worry about for our final design. This design will also be the most cost effective for the support it can provide. With our limited time frame, this design is the best choice. Not only can we make it functional, but smooth and user friendly. This is a huge priority for the family, and the cushioned seat and specially designed tray should help make the child feel at home.
The chair will be made of a strong wood (like poplar or oak). This will provide something that is not only strong, but lightweight for transportation. The seat frame will be made from aluminum, allowing us to make it small and able to withstand the weight it may face reliably. There will be plastic/rubber feet at the bottom of the chair. These will probably be 3D printed with a plastic like TPU. These will prevent the chair legs from scuffing whatever floor it may be on, as well as adding extra grip so the chair doesn’t slide.
The legs will be made to stand in a triangle formation, giving us a strong truss-like support to hold the weight of the user. The aluminum was chosen to withstand any stresses that the user will put on the seat. This also will allow for a smooth slide when mounting the seat in the highchair frame.
A weather resistant fabric was chosen to make the seat comfortable and easy to clean. The wood will also be sanded and stained, to ensure that it is nice to the touch and stain resistant. All of this should allow for the chair to be stain resistant for any possible spills that could happen. The tray will also be made of a food safe plastic.
The latch housing is expected to experience significant loading, so it must be designed to withstand that force. We chose aluminum alloy 6061 for its excellent strength-to-weight ratio and durability. In our analysis, the sides and bottom surfaces that are connected to the chair leg were defined as fixed supports, while a 250 lb (1112 N) load was applied to the surface attached to the seat. The resulting maximum stress was 17.52 MPa, which is well below the yield strength of 6061 aluminum (310 MPa). The maximum displacement at the farthest point was only 0.00234 mm, an extremely small value. Overall, the latch housing is more than capable of safely supporting a 250 lb (1112 N) person applying their full weight directly on it.
The fabrication process was straightforward, but quite intricate. The team had to learn a lot about how to manufacture certain parts to get them made. There were three major materials we had to work with. The materials being wood, metal, and plastic.
Woodworking was done for the majority of the frame. This gave us a solid material that wasn’t too heavy for the chair, as well as a nice finish when the main parts of the chair were fabricated. All of the wood was cut to specification, then sanded to look nice and feel better to the touch. The seat backing and bottom were glued together. The seat was reinforced with a thin sheet of metal to give it extra strength. Finally, the wood was stained to protect the wood and give it a nice look.
Metal was used for areas where we needed more strength and stress resistance. Most of our mechanisms on the chair were designed using aluminum. This is what we also used to support the tray and its locking mechanism. The metal parts were much harder to make, due to the need of precise measurements.
The plastic parts, except the tray, were all 3D printed. Since the lock for the tray would not be bearing a lot of load, we decided to 3D print it using PETG. While the seat bolt covers and feet covers were 3D printed with TPU. The main part of the tray was cut from a sheet of polypropylene using a waterjet and CNC mill. Polypropylene is a commonly used food safe plastic for cutting boards.
Once all of our parts were made, assembly was fairly simple. Some of our holes were a little too small initially, but widening them ever so slightly made all the parts fit seamlessly together.
Photos of fabrication:
1-6: chair legs
7-9: seat and backing glue-up
10-13: staining and initial assembly
14-17: Finished links and checking work (feat. John and Skye)
18-20: Tray bracket frame and lock
21-26: Fabrication of seat latches (feat. Gavin)
27: Tray cutout sitting in CNC machine
28-29: Modified wood bracket for tray
(photos can be right clicked to open viewing options)
Testing of the chair constituted of three main tests.
These are five tests we had to answer while making the chair.
As for test 1, we were shocked at how much weight the chair could hold. We had intended for it to hold a 200lb person with relative ease. However, this chair could probably hold 400lbs with ease. We have only tested it up to 250lbs as of the last time this website was updated.
Test 2, the chair folded just as we had hoped. Our aluminum links did the job perfectly.
Test 3, our chair slid in and held very well. The slots for the seat latches were too tight, and were expanded slightly using a dremel. This allowed the seat to move in and out smoothly. Once we sanded and used the dremel on the latch slots, the latches would hold the seat right in place.
Test 4, while the tray slid in to the supports we made in practice, it did not work when we made the final product. Due to errors that appeared during manufacturing, the tray would not slide in with our original bracket design. We had to create a wooden bracket that would support the tray, while allowing it to slide loosely. This fixed any issues we had with supporting the tray. The tray is really easy to remove from it’s own aluminum frame, allowing for easy cleaning.
Test 5, one request for the chair we had was for it to be fairly portable. While we had intended on this working in the beginning, we ended up choosing red oak for our wood choice. This ended up making the chair too heavy, so we needed to modify the chair so it could be moved easily. A handle and set of casters were added to make it easy to transport.
This chair was a wonderful and very intense project! The team had fun and was very excited to hear the final product. Throughout the project, multiple different things needed to be researched. For making the seat, that was learning how to properly glue wood together for a strong bond. For the metal and tray, that was learning how to cut and drill it properly. Many adaptations had to be made for our original design. There was a lot of learning how tolerances could affect how parts fit together. How machines could or couldn’t cut or modify certain parts. All of this was researched to make a strong and stellar looking final product. Our team enjoyed working on our first big design project and hope that the family can make great use of the chair!
