Biological Stiffness Measurement

The aim of the project is to design and develop a handheld device that can accurately measure the stiffness of a biological tissue, specifically a brain in a medical environment.

Background
Currently doctors have just been using their fingers to attempt to get an estimation on brain stiffness for use as a symptom of a disease. Doctors can use magnetic resonance elastography (MRE) to obtain stiffness, but there really isn't a device in place to in a matter of moments determine biological tissues stiffness. Brain stiffness has been investigated increasingly as an indicator of neurological diseases, including Alzheimer's disease.

Deliverables

 * Concept sketches/CAD models of the device with sensors in place
 * Final machined device
 * Matlab and Arduino programs used to obtain raw data from sensors and send it to computation in order to establish a best fit modulus of elasticity

Final Design


The final design (shown above) accommodates all the rib sizes and will help workers to safely and effectively accomplish all the required assembly operations on the ribs. More importantly it also accommodates the workers by taking in to consideration all the ergonomic factors. One key component that has been left out, is a way of holding the actual ribs. This was done so because at the time Boeing had not figured out which rib areas could be utilized. To compensate for that, our rib holding frame will be made from Bosch tubing. This will allow for compatibility with whatever holding design/mechanism they decide to use. Overall the final workstation has a few key components that allow our design to comply with the specifications set by Boeing and the group. These key components are definitely worth mentioning.

Bosch Tubing Frame


The Bosch tubing frame is key to attaching and holding the ribs. By having the vertical bosch frames attached to sliders (which then attach to a horizontal bosch piece), they can be moved out, at which point the rib can be brought through, and then moved back in to hug the rib. The locking mechanisms (red handles) can then be locked into place preventing the rib and bosch tubing from moving. This design allows for a quick and easy process of loading and unloading ribs.

Hoop/Rollers


Rotation is key to our design. It is of the utmost importance that we be able to rotate the hoop component and in turn the rib. The rotation is what allows us to be able to meet all the ergonomic requirements, thereby making it easier and faster to complete all the assembly operations necessary, on the rib. To achieve this, the outer edge of the hoop component comes into contact with 12 rollers (placed all around the hex-frame) allowing it to rotate smoothly as well as offsetting the weight and balance making the hoop component concentric. To prevent the hoop component from sliding out of place to either side, 12 vertical cam followers are placed around the outside of the hex-frames and come into contact with the side faces of the hoop. This system together enables for the hoop to rotate smoothly while staying vertical and concentric inside the hex-frames.

Locking Mechanism


With regard to ergonomics, we need to be able to lock the hoop at certain angles that allow for the worker to be in the strike zone of the rib area they intend to work on. We determined six necessary rotational positions that would allow the assembler to work comfortably on the rib faces. To achieve this, we intend to drill radial holes at the intended angle locations on the hoop. We then developed the locking mechanism. Basically the pin is compressed against the outside diameter of the hoop, and when the hoop is rotated the pin will push itself into the holes. This effectively locks the hoop in that rotational position. The worker can then safely work on the rib without having to worry about movement. Overall the stop mechanism provides two functions, an ability to meet all the strike zone requirements and acting as a rotational safety lock.

Hoop Design
The hoop is the most critical part of our design. It sustains the frame which will hold the ribs in place. It is the component that allows for rotation, thereby meeting the ergonomic and manufacturing standards necessary to work on the ribs in an effective manner. In a sense we have built the frame and all other components from the hoop out. While Boeing will have the capabilities to create such a product in a solid state, we have had to rely on a company that has bent metal bars into the proper shape. However, these bars are off somewhat and must also be welded at the ends. If the hoops are not identical and concentric to one and other, then our design will not function as intended. To fix this we will be using a fixture plate to trim and align them on a rotary table (as can be seen). This will then enable us to satisfy the design requirements.



Manufacturing Process


With regards to manufacturing the prototype, there was quite a bit of work done. We milled and machined a lot of the parts using the mill and lathe. Some of the parts such as the hex frame, required us to make jigs/fixtures that would allow us to machine them. The support frame, hex frame, and hoop required welding. We also 3D printed quite a few parts such as the bosch tubing sliders. All in all, there was a ton of machining, welding, and 3D printed which then led to the assembly process at which time we had to make adjustments and then painted the parts. In the end everything came together perfectly.