Knee joint

Abstract

A knee joint that is capable of widening a moveable range, and that has good energy efficiency and is small and lightweight is described. Also described is a knee joint that is of an active type, but comparatively inexpensive. A drive section moves a driven member. An elastic member is arranged between the driven member and a linear motion member. The linear motion member elastically moves in at least one direction, in accordance with movement of the driven member, by way of the elastic member. A crank mechanism can realize bending and extension of the knee joint by converting linear motion of the linear motion member to rotational motion.

1 . A knee joint, comprising a motor, a linear motion member that reciprocates in a linear direction in accordance with rotation of a ball screw that is rotated by the motor, and a crank mechanism for changing a knee angle, wherein:
 the crank mechanism comprises a connecting rod that is rotatably connected to the linear motion member, an arm member that is attached to the connected rod so as to be capable of rotating and that swings in accordance with movement of the connecting rod, and a rotation shaft constituting a center of rotation when the arm member swings, and the crank mechanism converts linear motion of the linear motion member to rotational motion; and   a reduction ratio of the crank mechanism becomes a maximum value when the knee angle is about 80° to 90°, and is a lower reduction ratio than the maximum value when the knee angle is about 0° to 20°, and is set so that reduction ratio becomes lower as knee angle becomes smaller.   
     
     
         2 . The knee joint of  claim 1 , wherein a point of connection between the linear motion member and the connecting rod is arranged offset by a specified offset amount from a rotational center of the rotation shaft, and
 the specified offset amount is determined so that the reduction ratio becomes a maximum value when the knee angle is about 80° to 90°.   
     
     
         3 . The knee joint of  claim 1 , further comprising an upper connection section for connecting a socket and the knee joint, wherein:
 the crank mechanism is connected to the upper connection section, and is configured to cause rotational movement of the upper connection section in forward and backward directions.   
     
     
         4 . The knee joint of  claim 1 , wherein the linear motion member includes a linear motion rod that extends in a movement direction of the linear motion member, and
 the connecting rod is rotatably connected to an end part of the linear motion rod.   
     
     
         5 . The knee joint of  claim 1 , further comprising a frame, wherein a rotational shaft of the crank mechanism is supported by the frame. 
     
     
         6 . A prosthetic leg provided with the knee joint of  claim 1 .