US Patent 7434880 Mobile joint suitable for a sitting device

The present invention relates to a mobile joint (1) with spring resistance, suitable for a sitting device, comprising a first and a second joint element (10, 20), which are pivotally connected by a shaft (3), to allow tilting of the sitting device caused by the displacement of the users weight, comprising a first and a second parallel plate spring (18, 19) with first and second ends, with an intermediate blocking element (11), wherein each plate spring (18, 19) in the first end are connected to the first joint element (10), and in the second end are glidingly abutting the second joint element (20), the first and second plate spring (18, 19) each having an axis of rotation that is displaced in relation to each other and the shaft (3).