The intial CAD for this project was borrowed from
Table 1: Link Lengths
Figure 1: Initial CAD Borrowed from Research Paper and Altered
Initially, we hoped to 3D print only the fingertip and palm base of the hand (Links 1 and 6), and use laser-cut wooden pieces as the rest of the links. However, upon assembly, we realized we failed to account for the disparity between the listed thickness of the wood and the actual thickness. We found that there was no sold thickness of wood that matched, and so we opted to switch to 3D printing so as to not have to manually change the thickness of each piece in CAD. Despite this failure, it was still a worthwhile incident because we were able to roughly assemble the pieces and see that the mechanism did indeed work.
Figure 2: Prototype No. 1 - Failed due to lack of link thickness tolerancing
This design looked impressive, but it had several problems. First, it had a limited range of motion. As the mechanism is mirrored on both sides for stability, there needs to be a long bolt that crosses through joint __ . This ended up interfering with the motion of the finger by blocking the four-bar from extending further once it hit the bolt. This resulted in a limited range of motion and a high flexion distance from the finger to the palm, which would mean we could only really hold large objects. Another problem we faced was the difficulty of assembly, which took at least an hour and a half because of all the small bolts and the lack of tolerancing on the 3D-printed holes. Finally, the hole sizes were not uniform which led to there being a bit of play.
Figure 3: Prototype No. 2 - Failed due to lack of ROM of end-effector
We decided that this design did not meet our needs, and went back to the drawing board. We decided to simplify the design to make manufacturing and assembly easier and also to remove the bolt at joint __ to increase uor range of motion. This process was quick since we simply followed the same 3D sketch as the original and made extrudes in the assembly to get a skeleton of fundamentally the same linkage.
This prototype had several benefits over the previous one. First, it was better toleranced and assembled more easily since we standardized all the bolt sizes to M3. Secondly, it had a greater range of motion due to the lack of a bolt going across the middle connecting Link 2 to Link 4, which was previously hitting the mechanism and stopping it. Finally, it was overall simpler to manufacture and assembly. Going forward, this is the basic design we will be using for our
Figure 4: Initial Design 2, simplified linkages
Figure 5: Prototype No. 3 - Updated prototype with simpler linkage design, higher ROM
The next steps for our project will be to figure out how we will incorporate multiple of these fingers into a hand.
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Table 2: Projected Bill of Materials for Final Project