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Our next idea was to develop a crossed four-bar linkage configuration that was found to mimic the curved motion of a human finger. A patent that highlighted this mechanism and the respective motion for a finger is linked here. We based our model off of this patent a finger mechanism patent described in the kinematics section and developed a curved pattern that is similar to a curved motion of a finger.
Figure 2: Finger Mechanism Patent Figure Figure 2: Crossed Four-Bar Mechanism
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When starting our prototype, we began creating the mechanism with cardboard to map out the movement with physical pieces. We measured the the link lengths to approximately the desired lengths that were defined in Motion Gen. The goal for this prototype is to observe and understand the motion of the mechanism using physical components. However, cardboard is very flimsy and susceptible to breaking down after rep. 
Figure 13: Cardboard prototype of the open 4-bar mechanism
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For this prototype, we tried recreating the same prototype with the desired link lengths using laser cut wood and rods. We found that the motion is not as smooth as we desired and future iterations will have rods and bearings.
Figure 24: Laser cur prototype of our open 4-bar mechanism.
Prototype 2.1: Laser cut and Manual Motion
This prototype is similar to the previous in that we laser cut linkages; however, we replaced the rods with M6 screws and mounted it to a board to produce smooth motion. In the gif below you can see that the position profile of the end-effector models the position profile we determined in our kinematic analysis.
Figure 35: Moving laser cut prototype of our open 4-bar mechanism.
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Figure 46: Acrylic automated prototype of our open 4-bar mechanism.
Prototype 3.1: End Effector
We also iterated through the potential end effectors that we could use to lift the tab of the can. We first thought of ______
End-Effector
Prototype #1
Figures 3 & 4:
Prototype #2
Figure 5:
Prototype #3
Figure 6: needed something that is able to fit the opening between the tab and the lip of the can. Additionally, the end effector needs to be thin enough to slide under the tab. From these parameters, we created an end effector that is able to cup under the tab and lift the entire tab up.
End Effector Prototype 1:
Prototype 1 uses a bracket with a screw to lift the tab. This was the first material we thought of trying as it is thin and sturdy on the links.
Figure 7: Initial design of the end effector
End Effector Prototype 2:
After testing prototype 1 for the end effector, we found that the bracket is not strong enough to withstand the force needed at the tab. We saw that the bracket started to warp and much of the force from the links is being transferred into the deflection of the bracket instead of onto the tab. We switched out our bracket system and machined a steel piece that is both thin enough to get under the tab and strong enough to pull the tab.
Figure 8: Laser cut linkages with custom end effector
End Effector Prototype 3:
The last prototype was to fix the new end effector to the acrylic links. Below is the final iteration of the end effector piece.
Figure 9: Final end effector with acrylic linkages
Prototype 4: Final Iteration
With the previous iteration, we found that the torque output from motor does not supply enough force to open the can. Additionally, we currently don't have linkage system at the correct height to reach the top of the can. We addressed the torque issue by created a 49:1 gear systems from the motor shaft to the rotating link to overcome the lack of torque output. Because of the size of the gears, we elevated the system using two acrylic sheets, which addressed the height problem we were also having[Insert Picture of the .
Figure 10: Final Iteration]