Backrest elevator device

A backrest elevator device comprising;

• a main plate, an adjustment panel, a driven block, a spring, and a cover plate,
• the main plate having a corrugated slot, and a plurality of serrations,
• the adjustment panel being movably mounted on the main plate and having a chamber and a guide groove communicating with the chamber,
• the driven block being inserted into the chamber of the adjustment panel and having a protruded block protruded outward from the chamber of the adjustment panel and extended into the corrugated slot of the main plate to engage one of the serrations of the main plate, the driven block being engageable with the guide groove of the adjustment panel,
• the spring being mounted in the chamber of the adjustment panel and urged between the adjustment panel and the driven block,
• the cover plate being mounted on the adjustment panel to cover the driven block in the chamber of the adjustment panel, wherein:
• the adjustment panel has a curved groove, and the driven block has a protruded lower end flange inserted into the curved groove of the adjustment panel;
• the adjustment panel has an oblong groove, and the driven block has an upper end post inserted into the oblong groove of the adjustment panel;
• and
• the main plate has two protruded bars, and the cover plate has two channels to receive the protruded bars of the main plate.