Design Process:
Kinematic Analysis:
For Kinematic Analysis, we will split it into two parts. The first is the palm of the claw, which contains the slider crank mechanism that transfers motion from the motor to the finger. The second analysis will be from the prototype and explain the motion of the finger.
Analysis of the slider crank mechanism:
After we have analyzed the slider crank mechanism, we can look at the analysis of the double chebyshev slider system. This was already calculated in the prototype, but the work will be put here for ease of reference.
Kinematic Analysis of Finger Mechanism:
In conclusion: these two systems can be related to each other by understanding that lever D in the slider crank is link A in the finger mechanism. Thus angle 4 in the slider crank is angle 2 in the finger mechanism and omega 4 in the slider crank is omega 2 in the finger mechanism. The Mechanical Advantage is graphed below:
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Implementation:
Final Demonstration:
As can be seen, a major issue was the backwards bending of the finger digits. This was caused by the mechanism going beyond it prescribed angle and locking out. Additionally, due to the low mechanical advantage, the friction of the mechanism was a significant factor. This affected the opening motion more than the closing.
Conclusion and Future Works:
In the end we accomplished our primary goal of making a grasping mechanism capable of holding onto objects. However, the extra goal of giving the mechanism the form of a human hand proved to be too ambitious in the limited time available for the RMD final project.
We learned several important concepts whilst working that will be useful in our careers as engineers. The most impactful on this project specifically was the method of turning simple circular motion into a complex velocity profile through the manipulation of linkages. Without the double chebyshev system that made up the claws fingers, it would be impossible to make a swinging motion with just one motor input. Another important lesson learned was the need to conceptualize not just the shape of a mechanism, but also the forces and motion involved. The linkage system created greatly amplified velocity at the cost of torque, which needed to be accounted for in motor selection. This ended up being the fatal flaw of the mechanism. The mechanical advantage was so low that the friction of screws stalled out the mechanism.
The members of team fifteen would like to thank our TA Connor Hennig for his recommendation of chebyshev linkages for the finger mechanism. These proved vital in creating the velocity profile reminiscent of a human finger.