US Patent 11751691 Seat connecting device with adjustable backrest

Embodiments provide a seat connecting device with an adjustable backrest, belonging to the technical field of swivel chairs. In the embodiments, the seat connecting device includes a seat back tightness control assembly including a control handle, a universal joint, a transmission rod, a first bevel gear, a second bevel gear, a lifting part, a mounting seat of the lifting part, and a tightness adjust rod.