A device for variable adjustment of the timing of gas exchange valves of an internal combustion engine, which has a hydraulic phase shifting device, a camshaft and a pressurizing medium distributor. Specifically, the second harmonic generating device of a laser beam source includes a laser beam source, an optical resonator into which the said laser beam is injected, and KTP crystals provided in the said optical resonator. The robot is guided progressively to the correct behaviour through the use, normally the repeated use, of a secondary reinforcer.