US Patent 7513570 Control mechanism for a chair

A tilt control mechanism for an office chair includes a spring assembly therein which controls the tilt tension on the back assembly. The tilt control mechanism includes a control plate mounted to the control shaft on which the uprights are mounted, wherein the control plate rotates in combination with the uprights. This control plate is located within the control body and cooperates with a front stop assembly and a back stop assembly to vary the limits of forward and rearward tilting of the seat and back assemblies. Also, the tilt control mechanism includes a pneumatic actuator assembly having fixed and rotatable cam blocks. The rotatable cam block rotates relative to the fixed block such that the rotatable cam block is driven downwardly to depress the control valve of the pneumatic cylinder and thereby vary the height of the seat assembly.