Robert Ducheron was an artisan frame builder based at 123 Avenue Parmentier in Paris. If, in the middle of the 20th century, you were French and wanted an exquisitely built frame, with every conceivable braze-on, his was one of a small number of shops that you would consider.

In the late 1940s he patented a derailleur design, and appears to have progressed far enough with it for a very finished example to have been pictured in Le Cycle magazine. I do not know if it was produced in any volume.