Patent ID: 8690249

Claim:
A chair having an adjustable backrest for spinal protection having a seat plate part with a plurality of supporting legs capable of sitting a user thereon, a cushion part with a lumbar support (a), a thoracic support (b), and a cervical support (c) formed on back surface of the seat plate part and that supports and protects a spine including lumbar, thoracic, and cervical vertebras of a user at the back thereof, and a backrest for fixing and supporting the cushion part thereto comprising: a backrest height adjusting means for coupling the backrest to the seat plate part and adjusting the height of the backrest; a lumbar supporting plate formed between the cushion part and the backrest and that supports flexibly the lumbar vertebra, the position of the lumbar supporting plate being changed according to sitting heights of the users; a rack and pinion means connected and fixed to a fixing bracket, which is formed at an end portion of the backrest height adjusting means and that allows the backrest and lumbar supporting plate to slide vertically so as to control adjustably the height thereof; and a backrest fixing guide bracket formed at a lower end portion of the backrest so as to slidably attach the backrest fixing guide bracket to the backrest height adjusting means and that inserts the backrest height adjusting means therein so as to slide vertically the backrest height adjusting means, wherein the rack and pinion means comprises a big pinion and a small pinion formed in contiguity with each other so as to be rotated to a fixing axis of the fixing bracket, the backrest comprises a backrest rack interlocked with the big pinion so as to linearly and vertically move the backrest, the lumbar supporting plate comprises a plate rack formed at an inside thereof and interlocked with the small pinion so as to linearly and vertically move the lumbar supporting plate, and the backrest comprises a slot groove for vertically sliding and guiding the fixing axis.