Keyboard device and key structure thereof

A keyboard device comprising plural key structures, wherein each key structure comprises:

• a plate assembly comprising a membrane switch;
• a keycap assembly located over the plate assembly;
• an elastic element arranged between the plate assembly and the keycap assembly;
• a scissors-type connecting member arranged between the plate assembly and the keycap assembly, wherein the keycap assembly is movable upwardly or downwardly relative to the plate assembly through the connecting member, and the connecting member comprises a triggering part;
• and
• a signal generator installed on the plate assembly and aligned with the triggering part of the connecting member, wherein the signal generator comprises an infrared emitter and an infrared receiver, which are aligned with each other, wherein the infrared emitter emits an infrared ray to the infrared receiver, and a region between the infrared emitter and the infrared receiver is defined as a sensing region, wherein the triggering part of the connecting member comprises a light-shielding structure, wherein while the keycap assembly is moved downwardly relative to the plate assembly through the connecting member, the light-shielding structure of the connecting member is correspondingly moved to the sensing region, so that the signal generator is triggered to generate the first signal,
• wherein while the keycap assembly is moved toward the plate assembly through the connecting member, the triggering part of the connecting member is moved downwardly to trigger the signal generator to generate a first signal, wherein after the signal generator is triggered, the keycap assembly is continuously moved downwardly and the elastic element is moved downwardly to trigger the membrane switch to generate a second signal, wherein the first signal and the second signal are different types of signals.