US Patent 9925822 Pen track

A pen track has an outer shell, a transmitting group, a rotating group, and a linking group. The transmitting group is mounted in the outer shell and has a portion rotatably abutting a drawing surface. The rotating group is mounted in the outer shell and has a modeling block. The modeling block is mounted in the outer shell, is rotated with the transmitting group, and has an outer surface and a modeling segment annularly formed on the outer surface of the modeling block and having multiple curved surfaces connecting each other. The linking group is mounted in the outer shell and has a pushing protrusion pressed against the modeling segment of the modeling block to move the linking group reciprocally relative to the outer shell along the curved surfaces of the modeling segment.