Luffing mechanism is a key component of the construction machinery. This paper proposes a two degree of freedom (2-DOF) luffing mechanism, which has one more pair of driving cylinders than the single DOF luffing mechanism, to improve the performance of the machinery. To establish the dynamic model of the 2-DOF luffing mechanism, firstly, we develop a hierarchical method to deduce the Jacobian matrix and Hessian matrix for obtaining the kinematics equations. Subsequently, we divide the luffing mechanism into six bodies considering actuators, and deduce the kinetic equations of each body by the Newton-Euler method. Based on the dynamic model, we simulate the luffing process. Finally, a prototype is built on a pile driver to validate the model. Simulations and experiments show that the dynamic model can reflect the dynamic properties of the proposed luffing mechanism. And the control strategy that the front cylinders retract first shows better mechanical behavior than the other two control strategies. This research provides a reference for the design and application of 2-DOF luffing mechanism on construction machinery. The modeling approach can also be applied to similar mechanism with serial closed kinematic chains, which allows to calculate the dynamic parameters easily and exactly.

变幅机构是工程机械的关键部件。本文提出了一种两自由度（2-DOF）变幅机构，与单个DOF变幅机构相比，它具有多一对驱动缸，以提高机械性能。为了建立二自由度变幅机构的动力学模型，首先，我们开发了一种层次方法来推导雅可比矩阵和黑森矩阵，以获得运动学方程。随后，我们将变幅机构分为六个带有致动器的物体，并通过牛顿-欧拉方法推导每个物体的动力学方程。基于动态模型，我们模拟了变幅过程。最后，在打桩机上构建原型以验证模型。仿真和实验表明，该动力学模型可以反映所提出的变幅机构的动力学特性。并且前汽缸首先缩回的控制策略显示出比其他两种控制策略更好的机械性能。该研究为工程机械二维自由度变幅机构的设计和应用提供了参考。该建模方法还可以应用于具有串行闭合运动链的类似机构，从而可以轻松，准确地计算动态参数。