Swedish-American inventor Henry Konrad Sandell designed this device, the Mills Violano Virtuoso. It’s like a mechanical player piano, but it plays a violin. He patented it in 1905 along with Henry S. Mills of the Mills Novelty Company, a firm that made a wide variety of coin operated machines. Later designs added a piano in order to make the music more enjoyable than a solo violin could manage. Here’s how the violin component functioned:
The strings are bowed by four small wheels made of discs of celluloid clamped together, applying just the right pressure to the strings. These are driven by a delicate variable speed controlled motor to vary the volume of sound produced.
via Neatorama
This mechanism seems to be more successful than 10CC’s Gizmo (1970s) for guitar strings.