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What happens when a ragtag group of engineers unite to solve a mystery? We will never know, because this team of engineers was assembled to design and construct a supportive chair. The goal of the project is to construct a modular highchair that offers a comfortable sitting position, along with head and lumbar support, for a child with cerebral palsy.
The client requested a supportive chair for a 13-month-old child with cerebral palsy and a G-tube for feeding. The child’s motor skills mirror that of a 3-month-old and the client would like to give the child more opportunities to socialize with their siblings and stimulate balanced muscular development. The family suggested a reclined, comfortable chair with a high table or tray. After further interactions with the family, mobility became a concern due to the prospect of the child needing to ride comfortably in a vehicle. The supportive chair needed to be lightweight, modular, and support social interaction and balanced muscular growth.
Background of Child’s Dimensions:
. The child weighs 20-25 lbs, so we will need a booster seat that can grow with the child for at least 2 – 3 years
Deliverables:
. Must be able to support the baby’s head to allow her to develop the ability to support it on her own
. The chair must be on a set of wheels to allow ease of movement around the house
. Must be able to adjust and lock into different recline positions
. Highly padded chair to prevent discomfort
. The chair must be able to adjust between 1.5 ft and 3 ft to allow for more interaction between her older and younger part of her family
. Allow for a table to either be attached or rolled up to the chair to help with hand motor skills development
Optional:
. Car seat base for ease of transportation
. Phone / tablet stand attachment to stimulate the ability to control her head
The child we are designing this chair for has diagnoses of hypoxic ischemic encephalopathy / Cerebral Palsy and is on a G-tube. Their symptoms include developmental milestones such as difficulty holding their head up, postural abnormalities, and preference of using one side of their body versus the other.
This first preliminary concept was based around this Special Tomato chair. A detachable seat that can be put on a lower base with locking wheels or on a regular dinning table chair. The lower base would have a rolling activity table to accompany it. We appreciated the soft touch design of the seat, and the possibility to attach it to various chairs and strollers. However, the cost of this system and the lack of adequate lumbar and head support made this option not feasible.
This concept basically consists of metal framing and foam supports, built from the ground up. It primarily focuses on height adjustability and mobility. The family mentioned they had some stairs and carpet in their home, so we wanted to incorporate those challenges in our design. After seeing the dorms on our campus using luggage trolleys with stair climbing wheels, we thought this would be an innovative idea to put in our own chair design. The two back legs would have these stair wheels while the front two legs would have robust locking wheels. This potentially gives the family an easier method to travel and move the chair to where they need it to be. We decided that pin-locking mechanisms for height adjustability would be the most practical.
Our final concept features a car seat paired with a semi-permanent height adjustable base, and an activity table that can be attached to the car seat. Due to our lack of expertise in postural ergonomics, especially for children with special needs, we asked the family if they had a car seat model they were looking at. They provided us with one that seems like it would be a perfect addition to our design. It can recline in multiple positions, good head and lumbar supports and straps, the added ability to function as a car seat, all at a very reasonable price. For mount design, we explored various options such as quick release clips from camera tripods. For simplicity and ease of use, we landed on draw latches as they are simple to use and attach without modifying the car seat extensively. We found these to be the easiest method to quickly attach and remove the car seat.
Our design is based off concept 3, where the frame, supports, and accessories are built on a car seat. This design kept the same concept where the car seat would be mounted to a base to solve the ultimate challenge of allowing the child to be more independent and social with the family. From concept 3, the frame holding the car seat would have been a T-slotted framing to create a cart-like structure that the seat would mount to. The only factor that drew us away was the immense cost of both the material and the hardware. After removing height adjustability from our needs, we ultimately decided to move in the more traditional path of building with wood. The tri-wheels for stairs, height adjustable base, and mounting draw latches from concept 3 were not carried over to this design because it would have been too complicated, difficult to build, and too involved to adjust; the latches are being replaced with straps to allow for a more secure and stable connection between the car seat and base.
For the tray, this was the accessory that allowed the child to be more independent and interactive. To have a separate tray, the mounting would be done on the cup holders from the car seat. Even though the cup holders are not robust as a metal mounting bracket, they are not going to be supporting large loads.
The wooden frame is made with walnut as it is a hard wood and is typically used in furniture applications. The back two legs are angled outward at a slight 8-degree angle to balance for the selected car-seats ability to recline. The caster wheels are ball casters with brakes to avoid snagging on carpet while still providing ample maneuverability and a locking function.
The legs are connected to a base of 1” walnut with an square extrusion in the center to fit the base of the car seat so that it’s movement on the chair is minimal. Movement is further restricted with Velcro in the square extrusion and car seat base, and two drop through bolts in the front that secure the seat to the base.
The tray would be made from high density polyethylene as it is both food-safe and easily cleanable. It is attached to the car seat through both cup-holders.
Seating
For the seating this project features the Safety 1st All-in-One Convertible Car Seat. This car seat is at its greatest dimensions 27″ x 18″ x 24.25″. Important measurements on the car seat include the base ( 13.75″ x 14.25″ x 2.75″) and the cup holders (diameter of 3″). This car seat is only modified in ways that do not compromise its structural integrity. No punctures, removal of parts, or large weights added.
Neck Cushion and Comfort
The cushion, made out of memory foam, is sturdy enough to be supportive of the child’s neck as well as comfortable.
Tray
The tray, which was custom designed for this project, is made of HDPE. HDPE, is a child safe, food safe, and sturdy material. The tray can be removed of attached using the two cup holders that are on the car seat. The tray’s geometry is such that the child can easily and comfortably reach the table. The tray also has a smooth and round trim around the top edge, which serves to encompass the play area in a way that is void of hazardous sharp or splintery edges.
Base Plate
The base plate of the chair is a board made of walnut that both supports the weight of the car seat and limits its movement. The base plate has a rectangular section of wood cut out of the center of it about a quarter of an inch of the total board that matches the dimensions of the base of the car seat. The seat is further secured to the chair by using an adjustable buckle strap to make it easier to add and remove the chair.
Frame
The skeleton of the frame is made of 8/4 dark walnut. We chose walnut because: it was gratefully provided by Dr. Canfield; it is both a hard wood and aesthetically pleasing; and it is typically used in furniture applications. The rear legs of the chair are angled outward at slight 8 degree angle to provide stability for when the seat reclines.
For the tray, we simulated a force of 20 lbf that was applied to the tray from the vertical direction. This represents the maximum amount of force that the child could possibly put onto this tray. With this force, we get a maximum displacement of .01723 mm at the very tip of the tray. However, given her disability, she will not be able to place this amount of force onto the tray.
Foam is measured using two standards: density and indentation load deflection (ILD). Density is not related to how firm the foam is but how durable it can be. ILD is measured using the 25% test: using a 4 in block of foam sample and measuring how much force it takes to compress it by 25% (1 in). For the neck cushion, we decided to use memory foam because of its high density and low ILD; making the cushion both long lasting and comfortable for the child.
Additionally, the car seat we are buying has very minimal cushioning in the seat and around the head, so we are planning to use high density foam with a higher ILD value that will both last long but also provide enough structure to make the chair comfortable to sit in.
Assuming a max distributed load of 150lbf, we performed a SolidWorks static analysis on the wooden frame. The resulting Von Mises stress value was significantly lower than the yield stress of pine which gives us a very high safety factor for the frame. Looking at the deflection as well, the maximum deflection of 0.02in (0.45mm) is at the center of the frame where the load is located. The ½” thick plywood base is definetly sturdy enough to support both the chair and the child, even as she grows older.
Wood Base:
A lot of the wood preparation fabrication was done graciously by Dr. Andy Pardue. But we were very involved in putting together all of the parts with mortise and tenon joints. The caster wheels are the stem type, so a hole was drilled in each leg and the sleeve was tapped in. After it was done drying, we were able to sand all the surfaces and prepare for 3 coats of polyurethane. The legs are attached to the base with 8 screws.
Tray:
The tray is HDPE plastic that was cut with a water jet. The cup holder attachments to the tray were secured with 3M Scotch-weld to make a permanent attachment. After curing, the sharp edges were put through a router to round them out.
Neck Rest:
The inner base of the neck rest was constructed by cutting out EVA foam with a hot-wire foam cutter. It was then layered into the basic shape held together by foam specific craft glue. It was then covered with a layer of memory foam and finally we used two long wool socks as the outer cover.
The car seat is secured to the base with both Velcro on the underside of the chair and we drilled two holes in the base through the wood to add two bolts with wingnuts for further stability.
As you can see the wooden base is plenty strong to support both the car seat and the child as it can hold a 150 lbs both stationary and while rolling.
The caster wheels roll smoothly but do not prevent sliding on hard wood floors when fully braked, so we recommended the family to use a small rug if they want to keep it stationary.
The tray can support up to 20 lbs before we start to see any deformation.
Wooden Base and Car seat
Foam Insertions
Instructions for Tray Use
How to Attach:
The circular extrusions on the bottom of the tray should be lined up with the holes of the cupholders on the car seat. Insert the extrusions, making sure they are flush with the bottom of the cupholders.
Do Not:
1) Use the tray if the car seat is not mounted to the wooden base 2) Place objects on the tray past the reclined setting of 3
3) Place an object weighing more than 15 pounds on the tray
4) Attempt to remove extrusions from bottom of tray
Instructions for Neck Cushion Use
Instructions for Washing:
Our team is very thankful for having the privilege to undertake the designing and building an adaptable chair for the kid. This project has helped our development in communication skills and planning on the project. There were minor modifications done to the car seat to allow the seat to comply with safety standards so they can still use it for its original purpose while also adding in additional cushioning for comfort and bolts to attach the seat to the base. The support base will allow the kid to be more involved with the family since it elevates the child to the height of the parents and elder siblings. The tray will continue to help the child develop fine motor skills and use of their hands, and the neck brace will support the child’s head as they develop the necessary neck strength to keep their head up. Overall, we believe the project was successful and will meet the needs of the child and family as the child continues to make progression with its coordination. We would like to thank Dr. Pardue and Dr. Canfield for their help with procuring and manufacturing the wood base with us.
