Movement No. 98 converts continuous rotary motion into an irregular oscillating motion using a crank-pin and a grooved vibrating arm. A circular disk rotates continuously, carrying a fixed crank-pin on its face. This pin rides inside an endless groove cut along the length of a vibrating arm. As the disk rotates, the crank-pin traces a circular path and slides within the groove, pushing and pulling the arm from side to side. Because the groove runs along the arm rather than being a fixed pivot, the relationship between the disk’s rotation and the arm’s swing is non-uniform — the arm swings faster when the crank-pin moves across the arm and slower when it moves along it — producing a characteristically irregular oscillating motion. This mechanism is useful where a non-uniform or variable-speed oscillation is desired from a steady rotary input.
98. Irregular vibrating motion is produced by the rotation of the circular disk, in which is fixed a crank-pin working in an endless groove cut in the vibrating arm.