Paul Kochendorfer made violins, guitars, harp guitars and lutes in Stuttgart, Germany from the early 1900s onwards.  Kochendorfer built a harp guitar for Otto Paret in 1911 that could change multiple fret positions at the same time - like a harp's pedal mechanism. The design had levers and sliding plates inside the neck and was previously awarded a German Reich Patent on November 27, 1910 (#235785).

Source: Paul Kochendorfer guitar label - ebay

Source: The Contemporary Guitar. John Schneider. Rowman & Littlefield, 20 Aug 2015