Before CNC (computer numerical control) came along, automated machines utilized mechanisms like cams and tapers to act as guides. Those are physical components with precise contours meant to guide the tool, like an artist tracing lines with a pantograph. Such mechanisms are uncommon today, as CNC is far more versatile and much easier to implement. But Mr Innovative turned to those traditional techniques to build this cam-following plotter that can draw many shapes.
A “cam” is a rotating or pivoting component in a mechanism, which has an irregular profile to control the actuation of something. Internal combustion engines, for example, often contain rotating cams that to open and close the valves at the proper times. In this case, the plotter’s cam controls the movement of the pen in the X axis. Wider portions of the cam push the pen further right, while narrower portions of the cam allow the pen to move left. A rubber band pulls the pen arm cam follower tight against a cam. The paper moves at a constant rate in the Y axis, and its speed combined with the shape of the cam determine the resulting plot shape.
This machine will look familiar to those of you who have seen a Mr Innovative project in the past. It uses an Arduino Nano board paired with Mr Innovative’s own driver board design to control the two motors. One stepper motor controls the rotation of the cam and a second stepper motor controls the paper feed. The user can set the number of cam rotations using a Nextion touchscreen LCD panel. Mr Innovative 3D-printed the mechanical parts and mounted them to a small sheet of wood, with a standard linear rail and bearing restricting the movement of the pen arm to the X axis. It can’t draw any shape, but this machine is quite versatile and can produce quite a few interesting plots.