Patent ID: 8313534

Claim:
An artificial knee joint, comprising: a four-bar linkage; an extension bar having a first end pivotally connected to the four-bar linkage; and a restoring device, connected to a bottom of the four-bar linkage and comprising a transmission rod having a first end pivotally connected to and retractably moving a second end of the extension bar, wherein the four-bar linkage comprises a first connecting bar, a second connecting bar, a third connecting bar, and a fourth connecting bar, wherein a first end of a first connecting bar and a second end of a second connecting bar are pivotally connected together by a first pivot axle, a first end of a second connecting bar and a second end of a third connecting bar are pivotally connected together by a second pivot axle, a first end of a third connecting bar and a second end of a fourth connecting bar are pivotally connected together by a third pivot axle, a first end of a fourth connecting bar and a second end of a first connecting bar are pivotally connected together by a fourth pivot axle, a first straight line joins the first pivot axle and the second pivot axle, a second straight line joins the second pivot axle and the third pivot axle, a third straight line joins the third pivot axle and the fourth pivot axle, and a fourth straight line joins the fourth pivot axle and the first pivot axle, the first end of the extension bar is pivotally connected to the fourth pivot axle, by means of the actions of gravity and the restoring device on the extension bar and further on the fourth pivot axle, the four-bar linkage is expanded to a limited state or a locked state, at this moment an included angle θ 1 defined between the first straight line and the second straight line is between 21°-23°, an included angle θ 2 defined between the second straight line and the third straight line is between 159°-161°, an included angle θ 3 defined between the third straight line and the fourth straight line is between 97°-99°, and an included angle θ 4 defined between the fourth straight line and the first straight line is between 78°-80°.