Original Experimental Setup
The objective of our senior design project is to provide preliminary data in the application of the PFG sensor in monitoring the G-force experienced by pilots. To accomplish this objective we came up with the following experimental setup. As shown in figure 1, we used a plastic skull with a spring-connected jaw to serve as our model of a pilot’s jaw. The spring-connected jaw allows us to pseudo-accurately mimic the clenching action of the jaw when a force is applied to the base.
We mounted the plastic skull to a baseboard using a PVC pipe. The plastic skull contains a whole in the bottom that allows for the insertion of the PVC pipe. We then bolted the skull onto the pipe using U-Bolts in order to securely mount it. Using U-Bolt fasteners allow us some flexibility by providing us the opportunity to change the position of the skull if necessary.
Inside the jaw of the plastic skull we placed a mouth guard, which contains a piezo ceramic with two leads attached to it. We then attached these two leads to the differential inputs of the AIM Lab PFG sensors and the PFG sensor is connected to an oscilloscope. The oscilloscope allows us to view the waveform of the output pulse train as well as the digital output frequency.
In order to not damage the tables in the lab we used a wood baseboard to contain the location of our experiment. We took this piece of wood and drilled a hole the size of the diameter of the PVC pipe. We inserted the PVC pipe into the slab of wood and then used PVC cement to secure the PVC into the wood baseboard.
As shown in figure 2, we used clamps to fix wood baseboard in place on the lab countertop. In front of the plastic skull we placed a linear feedback controlled actuator in order to move the jaw up and down.
The full extent of how all the components in our experiment interact with each other is shown in the block diagram in figure 3 below. The DC power supply connects to the relay, which is then connected to the Arduino UNO. We are using the Arduino UNO to control the position of the linear feedback actuator. Specifically the Arduino controls which pins in the relay are high or low, by setting pin IN1 high with IN2 low the actuator moves upwards and by setting pin IN2 high with IN1 low the actuator moves downwards. The Arduino connects to a PC over USB 2.0, which allows us to drive actuator position using a script we created. Specifically, we have programmed the Arduino to move to a certain “closed jaw” position, and then after one second it comes back down to the rest position. In the script we can increase the value of the “closed jaw” position in order to increase the force exerted on the piezo. This Arduino script allows us to simulate the chomping of a jaw with a large degree of control, as we have the ability to move our actuator with a degree of precision up to six thousandths of an inch.
Mounted on top of the actuator we have a force indicator. It displays the force exerted on the skull to the connected display box. This force indicator allows us to keep consistent track of the force exerted on piezo sensor in our experimentation.
After impact the output of the piezo can be read using the sensor breakout board and then viewed on the connected oscilloscope. Using a PC we can interact with the sensor breakout board through the test station using the MATLAB interface. Using this interface we can also control the sensor through the next command to iterate over the output of each of the seven channels of the PFG sensor.
With this experimental setup we hope to collect preliminary data on how the applied input force affects the output of the PFG sensor.
After running a series of experiments with our original setup we saw a need for an alternative approach. Specifically over various forces we saw no change in the output of the PFG sensor. Taking a look at our original experimental setup we saw that by putting the PFG sensor in the molar of the mouth guard, as seen in figure 4, it was not being impacted by the actuator. A basic diagram of the motion we saw on impact using the original experimental setup can be seen in figure 5 below. As the actuator applies force at the bottom of the jaw the molar area of the jaw actually moves downwards.
Therefore we concluded that our original experimental setup had too many pieces complicating the impact to the piezo. So we decided to simplify our experimental setup by taking an alternative approach. As shown in figure 6 and 7, we removed the skull and replaced it with a slab of wood with the piezo glued to the bottom.