3. Mechanism Design

Our basic design goal was to make a mechanism that can make a translation motion along the x-axis, and this x-axis as explained earlier in the actual mechanism helps to locate the location where the device is needed. The other motion was the lift motion i.e the y-axis motion, we want the device to be able to move up and down, and this is necessary because of the height of the gas compartment, or the charging port of the car. It was necessary that we keep this restrictions in mind as part of our design to ensure universality in our final prototype. We finally decide to go with the mechanism that can be seen in Figure 3.1. This device exemplified the motions that we required as mentioned earlier.                                                              

Figure 3.1

For the x-axis we were looking for linear motion mechanism, but most of them are not suitable for our mechanism since they are either not stable enough for heavy load or have undesirable range of movement. Finally we borrowed the idea from the mechanism of level-luffing crane (Figure 3.2), which mechanism is used for moving cargo horizontally, because in this way energy will not be wasted.

Figure 3.2 [2]

Through length optimization, we obtained the desired link length and made the x-axis movement mechanism, as shown in Figure 3.3. 

Figure 3.3

Since the charger is supposed to be parallel to the ground all the time, two pairs of parallelogram mechanisms are applied in order to provide a platform for the charger. The added mechanism is in white in Figure 3.4.

Figure 3.4

For the y axis motion we considered a lift mechanism that can be coupled with the level-luffing crane mechanism to move up and down. For this part we used an 8-bar mechanism (Figure 3.5) that can generate linear motion using rotation input. Through simulation, we found that for a certain range of movement, the platform has linear motion.                                           

Figure 3.5 [3]

Controlling both the x position and y position of the charger requires two motors to control, but the use of one motor in this class is highly desirable, and we also realized that this class is a mechanism design class and not a controls class. We coupled the two movement together by calculating the linear range of both x-axis and y-axis mechanism and connecting them via a common joint to ensure that one motor was going to be able to drive these two components. One good thing about this design is that although we use one motor for this prototype, we can always use the same mechanism but add another motor to build a fully functional product that is capable of moving freely on the x-y plane to find the port.