Micro Capacitive Sensor

The goal of this project is to develop a printed circuit board (PCB) that utilizes capacitive sensors and an off-the-shelf capacitive to-digital-converter (CDC) to detect and monitor micro entities. The monitoring process is an autonomous process that displays a plot of real-time capacitance values.

Background
The counting and classifying of particles on the micrometer scale is expensive if automated and difficult if done using non-automated methods. An inexpensive automated counting and classification method for small particles needs to be created to lower the cost and increase the ease of use for this process.

Deliverables

 * PCB designed with CDC chips and multiple capacitive sensor designs
 * An easy to use graphing method that accurately displays capacitance vs time on a PC from the CDC chip
 * A capacitive sensor design, or multiple designs, that successfully detects micro-particles

Assembly Operations/Schematic




Boeing is currently in the process of constructing a new airplane, the 777X. With a new design come new challenges. One in particular is the manufacturing and handling of the parts. The ribs in particular cannot be handled in the same way they have been with regards to preparing them for installation. Boeing has given us the task of constructing a tool/workstation that will make the assembly of components on the rib easy and efficient.

Ergonomics
Because the main purpose of this project is to facilitate easy handling and manipulation of large objects, ergonomics are a primary concern and focus. These considerations primarily center around the minor assembly that is to be performed on the wing component held by our tool. First and foremost we need to keep all assembly operations centered within the ergonomic strike or power zone. This region is identified by the vertical extent between the hip and top of the shoulder and approximately one to one and a half forearm lengths horizontally from the hip to shoulder line. The ideal vertical location is abeam to and one forearm length away from the elbow. This allows the technician or mechanic to support their tool or part with the least about of physical strain, using their body weight as the main force.

To quantify this area, anthropometric data tables were used to construct a diagram that shows how to calculate a universal strike zone for any rib size. The diagram uses the 95th percentile shoulder height for males and the 5th percentile elbow height for females to create the absolute bounds for our strike zone range. This means an ideal fit for 90 percent of possible user statures. The result of this analysis showed that the vertical movement that our machine must accommodate to fit this range would be close to the full vertical extent of the largest given rib. The overlap between male and female strike zones may ultimately be removed from this distance. Based on these findings we may have to reevaluate our strike zone goal since our calculations require almost 5 feet of vertical adjustability. Designs that use a variety of rib positioning to accommodate this full range may be a better alternative.



Repetitive injury from tool use is an issue that we will plan to address using a variety of tool counter balance or support devices. Finally safety considerations related to the placement of emergency stop buttons and protection of pinch or catch points related to any mechanical function of our eventual final design will need to be carefully considered.

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.