Our group is designing a safety/sensory bed for a child with autism.
The main problem we are trying to solve is that the parent is concerned about the child wandering or escaping the bed/house at night. Our solution is to make a bed that doesn’t allow for the child to leave at night, while still keeping him content. Some additional concerns we are working to address are that the child tends to hit his head on wall, he needs his stuffed animals and blankets close by and needs a cup inside his bed. To accommodate these needs, we are planning to add padding to the exposed sides of the bedframe, have space inside of the bed for stuffed animals and a cup, and make sure the frame is made of materials that are easy to clean when spilling happens.
Each group member filled out a CTQ table, and an average was taken to determine the lead design.
This analysis of the bed frame was simulated in ANSYS. The bed frame is 75″ by 38″, with the material properties being those of poplar wood. (MoE = 1.5e6 and Poisson’s = 0.33). There is a distributed load on the entire frame because we will have a sheet of plywood on top of the frame. The load is 1 psi, which corresponds to 2850 lbf on the frame. Under 1 psi, it will deform by 0.012 inches, which is more than enough of a safety factor since a 30 lb boy can’t output 2850 lbf.
For the part of the bed where you can get in and out, we will use nylon mesh. This analysis assumes the boy weighs 110 lbs to account for his growth. Using material properties for Nylon-6, a safety factor was calculated to be 13.9. A dynamic impact factor was calculated for the mesh and was 973.6 lbs. This tells us that the absolute max amount of force the child could output if he got a running start would be 973 lbs. This yielded a safety factor of 1.6, which is close to failure. We then tested the mesh with our body weights and found that it held us well.
This is a simulation of the McCorry Sanded plywood sheet that is used for the bed and the shelf. An MoE of 5e8 psi and a Poisson’s ratio of 0.05 was used. A pressure load of 1 psi was applied to the entire sheet. This load would correspond to 4608 lbf being applied to the entire sheet of plywood. Minuscule deformation and no failure were observed under the 1 psi load.
Fabrication began by slotting the 4 corner posts at the top and the selected height for the mattress to sit. 2x6s were then slotted into these posts and screwed in to create a sturdy frame. We also added another 2×6 and some 2x4s as braces for our slats. The slats were screwed into these braces with a spacing of 3 inches to create a sturdy platform for the mattress to sit on. At this point, we attached 3/4in plywood to the back and sides (which was later switched to mesh at the request of the family). We then measured and cut mesh for the top and front, which was attached using snap fasteners for ease of removal when necessary. A #10 zipper was also sewn into the front mesh to allow for entry and exit. After the bed was completed and tested, we sanded any rough edges or corners, disassembled it, and painted and prepped it for delivery. Upon delivery of the bed, we reassembled the frame, added mesh to the back and sides, added foam to the exposed corners, placed the mattress inside, and reattached the top and front mesh. We also added a small hook to hook the zipper to on the outer right-hand post.
In summary, this project gave us great experience with hands-on woodworking and taught us a lot about navigating the balance between quality, constructability, and other factors. Starting with the preliminary designs, we made three different designs to choose from. To choose the design, we had to collectively evaluate each one in terms of safety, durability, cost, maintainability, constructability, and storage. The factors that stood out the most in the design we chose were cost, constructability, and durability. Constructability was a very important one, because we needed to be able to conveniently take apart the bed frame to transport it and rebuild it at the house. After that, we had meetings to create a list of materials that wouldn’t be too expensive. When it came to fabrication, there were some tricky cuts we had to do. This included cutting notches in the 4×4 posts with a router and cutting a 4 foot by 8-foot piece of plywood on a table saw. We definitely spent the majority of our time for this project working in the shop. In the last few days of the project, our client realized that they didn’t want the frame to be enclosed in plywood as we had originally designed, but luckily this was a relatively simple change, as we could just replace the plywood sides with mesh by stapling the mesh into the wood frame. This did create a problem though, as the original design included ~4 inch gaps between the mattress and the sides for there to be space to glue foam onto the plywood walls. These gaps left the slats exposed on the sides of the mattress, which could be hazardous since the child could get their legs stuck in gaps between the slats. Fortunately, since we planned to have plywood on the sides that eneded up unused, we decided that we would use the leftover unused plywood to drill to the bottom of the slats so there wouldn’t be any gaps in between the slats. So overall, the project took some unexpected turns, but our design was versatile enough to be changed to the liking of the client.
