Mechanisms: Rotational Motion to Nearly Linear/Linear Motion

For this assignment, we were asked to look at different methods of converting rotational motion to linear-ish motion. Exploring the Kinematic Models for Design from Cornell, I found quite a few fascinating mechanisms.

Slider-Crank Mechanism - Inversion

http://kmoddl.library.cornell.edu/model.php?m=20
https://www.youtube.com/watch?v=3zpDGtiJoaM

I was initially attracted to this mechanism because of the unprovided in-motion image and the description from Cornell's digital library stating that it was "one of the most useful mechanisms in modern history." I went to other sites to explore the mechanism and found many applications and a quick, informative video of its basic movement, which I thought was fascinating.

In this mechanism, there are four bodies (rods) connected by three cylindrical joints and a long, rectangular sliding joint. Two of the bodies are located the in front and two in the back. In the front, there is a joint connecting the shorter and longer bodies together, which I imagine would be the same for the two bodies in the back. Near the bottom, there is the a cylindrical joint connecting the bottom and front of the mechanism together, as well as the third one connecting the short bodies from front to back. The fascinating aspect of this mechanism is that it entirely flexible, and as the name implies, the rotation can be inverted if desired. Since the site where I found the image did not have a small clip showing how this mechanism moved, I assume the movements would be similar to the Youtube clip I searched. The cylindrical joint of both the back and the front where the short body and the long body meet would be fixed, as well as the long bodies to the cylindrical joint at the bottom. The sliding joint (the central piece of the mechanism) could have a thin, oval cut out at the bottom to allow the cylindrical joint to cross through to the back, as well as allow itself to move up and down as that cylindrical joint is fixed. As this sliding joint moves only in an up and down motion, restricted by the small oval cut out and the length of the connecting two bodies, the smaller of the rods (connected to the sliding joint with a joint that is loose enough to allow its rotation) is forced to move up and down as well, but in the image of a rotating radius with a permanent center, oscillating. Slightly protruded to the side and securely connected to the longer rod when at rest, the shorter rod allows the longer rod to be given the image of being shot upwards and downwards as it rotates, creating an different angles. The longer rod, however, consistently moves in the motion of a inverted pendulum, swinging side to side without losing energy, and is given this image of being shot upwards and down because it is the sliding joint that confuses the eye on the relative position of the longer rod. Both of these rods would be in fixed moving positions. This is the same for the back of the mechanism, and this way, they are both forever going in opposite directions. I imagine, like the mechanism example shown in the Youtube clip, the back and the front can set into motion in the opposite direction than it was originally, depending on where the protruding cylindrical joint (connecting smaller and larger rods) is placed at rest. 

According to the Cornell's Digital Library website, four different inversions of this kinematic chain are possible, depending on which body is fixed: the crank, the connecting link, the sliding link, and slot link. In the D-4 model shown above, it is the slot link that is fixed, meaning that the connecting rods (bodies) are fixed, producing an oscillatory motion. There are so many applications when deciding which component to fix, and depending on the decision, this slider-crank mechanism can be used in engines, pumps, and more, which I find lovely, complicated, and paradoxically simple.