Introduction and Background - SF

The goal of this project was to create a 1-DoF mechanism that would draw some cool figures on paper. Mechanisms that draw some kind of geometric pattern have always been interesting to me, and after seeing the motions of the various mechanisms discussed in ME 350R, it seemed natural that I could combine some of these mechanisms with a pen and a piece of paper to create some interesting designs. I did some initial research into various drawing and plotting mechanisms on the Internet and came across many linkages of varying complexity, such as pantographs, cycloid drawing machines, and multi-axis CNC-based drawing machines. In the end, after going through several design iterations, I chose to create a modified version of the geared five-bar linkage found in our textbook.

Figure 1. A pantograph-based drawing machine. InventorArtist

Figure 2. A cycloid drawing machine. Joe Freedman

Figure 3. A 2-DoF drawing machine. Youtube

By itself, the geared five-bar linkage is a 1-DoF linkage that looks physically similar to the 2-DoF drawing machine shown in Fig. 3. However, whereas both input arms in the device in Fig. 3 are coupled to separate motors, thus enabling more complex 2D motion, the input arms in the geared five-bar linkage are coupled to each other via a set of gears, enabling a single motor to drive the entire mechanism (albeit within a set path determined by the linkage geometry). To create a more interesting pattern, I added a spinning platter to my final mechanism, to which the paper would be fixed when drawing. This way, the curves created by the pen writing on the spinning platter would be cycloidal in nature.

Figure 4. A geared five-bar linkage. Design of Machinery

For the design of the mechanism, the ability to customize the linkage to create different patterns and complexity of said patterns were my primary concerns. I also wanted the mechanism to be as simple as possible to build, so that troubleshooting errors later on would not be complicated. I would consider the project a success if the mechanism is able to create several different interesting curves, with an added bonus being that the curves it creates matches those predicted in a simulation of the mechanism.