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+# Floating Spring Joint
+
+tag: *DRL* *VSJ* 
+
+---
+![FSJ1](../meta/pic/FSJ1.png)
+
+Fig1. FSJ外观
+
+![FSJ2](../meta/pic/FSJ2.png)
+
+Fig2. FSJ半剖图
+
+FSJ最大的亮点是一个关节带有两个自由度，一个自由度用于控制位置，另一个自由度用于控制刚度。但是，由于机械构造的原因，刚度与第二个自由度的电机轴输出为非线性关系，而且，两个自由度之间存在一定的耦合，这给控制和建模带来了难度。
+
+## 变刚度原理
+![FSJ3](../meta/pic/FSJ3.png)
+
+![FSJ4](../meta/pic/FSJ4.png)
+
+## 拓展
+[1] The DLR FSJ: Energy based design of a variable stiffness joint, S. Wolf, et al. ICRA 2011.
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