Multi-articulated link knee joint

A multi-articulated link knee joint, comprising:

• a knee section of a multi-articulated link mechanism;
• a cylinder that restrains or assists an action of the knee section;
• extension and contraction amount detecting unit that detects an extension and contraction amount of the cylinder;
• and
• angle acquiring unit that acquires a bending angle of the knee section by converting the extension and contraction amount that is detected by the extension and contraction amount detecting unit,
• wherein the extension and contraction amount detecting unit includes a magnet and a magnetic sensor that detects a position of the magnet,
• a piston rod of the cylinder is formed of a non-magnetic material, and has a space that accommodates the magnet, in an inside thereof,
• the magnet is accommodated in the space of the piston rod of the cylinder, and extends in an extending direction of the piston rod to be longer than a stroke of the cylinder corresponding to an action range of the knee section, and a magnetizing direction is the extending direction of the piston rod,
• a length of the magnet is a length in a range in which at least linearity of the extension and contraction amount detecting unit is recognized, in the stroke of the cylinder,
• the magnetic sensor is fixed to a cylinder tube of the cylinder, and detects a position of the magnet according to a magnitude of a magnetic field that is generated by the magnet, and
• the extension and contraction amount detecting unit detects a position of the piston rod with respect to the cylinder tube by the magnet and the magnetic sensor, as the extension and contraction amount.