Archive for the ‘Projects’ Category
In the cushion testing lab we have several cyclic loaders to test new wheel chair cushion designs. The devices are basically up-and-down pistons which cycle a specified number of times. The machines are controlled through LabView on a PC. Well over the years the machines have evolved and things have been slowly added, usually in an ad hoc sense. Well the past week I’ve completely disassembled the thing and rebuilt it with only the necessary hardware. The piston is pneumatically controlled by several switches and regulators and the old setup had quite a few redundancies. After properly documenting how the old setup worked, I drew up plans for a more streamline setup. The reason for the split in the flow diagram is that the “down” pushing pressure has to be adjustable, sometimes set very low. The force on the cushion needs to be constant and we have some very light and some very heavy buttock models, so the “up” lifting pressure needs to lift a large amount of weight.
Here is my schematic for the setup. I’ll take some pictures as it nears completion this week.
The articulating thigh mechanism is pretty much finished. It certainly doesn’t look like a real thigh/buttock but that’s what the next phase is for. We will begin to set the parameters and make cuts into the actual thighs to form them to correct shape. I had to cut some weight out of the right thigh because I overcast it. Some quick tests were run with on the Zwick with a Tekscan Conformat pressure mat. Part of the next phase will require reading the in-board buttock pressure sensors with and without the thighs attached and look for variations.
I am also working on a prototype grab bar (those bars mounted to the walls in handicap accessible bathrooms). This is an attachment to existing bars that will fold out out of the way. The secondary bar needs to lock as soon as any normal force is applied to it. I’ve found these shaft couplings on McMaster-Carr and thought they would be ideal.
Yesterday, after receiving the parts, I was a little disappointed in my choice. The parts fit together only at specific intervals. If the teeth didn’t line up perfectly, the two parts wouldn’t interlock. Well today Jowers had the idea to bevel the edges and it seemed to work. I turned them down on the lathe. I honestly expected the teeth to look like crap afterward. I expected a lot of knocking as the teeth passed the cutting tool. However they turned out 100% professional looking. I needed the mental win after yesterday.
I also wound some springs to hold the interlocking pieces apart until a load is applied. I used a tool we have called the Universal Spring Tool. It worked pretty well. See the how-to video below.
I needed to enlarge the space in the foam of the AP cushion to accommodate the new housing. So to cut the foam, I used an electric kitchen knife. It worked perfectly. The foam didn’t tear or rip. It made very smooth cuts and the cushion now fits perfectly over the new housing.
This was a last minute addition to the wound measurement device before it goes to clinical trials this week. The built-in cam was total crap so I added this webcam and gave it some ability to be repositioned. It doesn’t look very pretty, for sure. I really had hoped that we’d have the camera nailed down before I built an entire device around it =(. If we continue with the third party web cam, I envision version 5 of the device will be a Wiimote + Wii nunchuck style device: the camera and lasers in one hand and the computer in the other.
I had to document the Thigh Model Articulation Mechanism. I haven’t spent an entire day sitting still in front of my computer in a long while. I’m getting antsy; time for the weekend.
Some times we have to come up with absolutely ridiculous solutions that border on silly. One such solution was getting around the problem of not having access to the CNC mill table at AWPL. We were trying to make the positive mold for the thigh model. So instead of having some MDF cut on the CNC mill, we laid up several (13 to be exact) sheets of MDF into a large rectangular prism. We then took that over to COA’s Design Lab and used the wood lathe to turn the rectangle down into a cylinder. This took almost three days of getting beat up on the wood lathe. Then in order to turn down the cylinder into a cone shape, we built this rig, shown below, to mount on the student mill. The rig is basically a box with two lazy susans at each end, holding the cylinder in place. The cylinder is then turned as the mill table is moved along the X axis.
Work at AWPL was faster than expected and the final model was better than expected, also shown below. The cylinder was ultimately unnecessary but it was certainly a bizarre attempt.
Hinges, with bearing waiting to be pressed. Also waiting on some fasteners from McMaster-Carr.