PURPOSE: A spring assembly is provided to keep an operation of the spring assembly even though any spring is damaged. CONSTITUTION: The first slider(142) of a slider unit(140) straightly moves by the rotation of the first link(120). The second slider(146) moves straight in a direction in which the second slider gets closer to the first slider by rotation of the second link(130). One end of a spring(160) is combined with the first slider. The other end of the spring is combined with the second slider. The spring is expanded and contracted in a straight direction by movement of the first and second sliders.
