转动副临界角分析及其在四连杆机构中的应用

滑动配合条件下，转动副（R副）通过接触面间的相对滑动提供一个转动自由度。由于接触面间的摩擦和间隙共同作用，R副会在一个小的摆角范围内发生自锁，这一摆角将在机构平衡时带来连杆长度误差和连杆偏角误差。本文指出了R副中临界角的存在，讨论了使得R副实现自锁的临界角范围，在考虑接触变形和不考虑接触变形2种条件下对临界角进行了计算，并以一平面四连杆机构作为应用算例，综合对比了铰链间隙、接触变形和摩擦因素对所在连杆机构输出精度的影响。算例结果表明，在一般的精度计算中铰链间隙及连杆弹性变形起主要影响作用，铰链本身的接触变形量可忽略。

Critical angle of revolute pin joint and its application in a four-bar mechanism

Revolute pin joint (revolute pair) possesses one degree of freedom, i.e. rotation movement, through relative sliding between contact pairs. Existence of friction and clearance in revolute joints has crucial effects on the overall precision of mechanism. Using the concept of critical angle, the marginal value in which revolute joints could keep in balance state is discussed in this study. Firstly, frictional angle and self-lock caused by friction and clearance in revolute pin joints are investigated, which contribute to not only length error but also angle error in mechanism with such joints. Then, critical angles are calculated with and without contact deformation respectively. Moreover, a four-bar mechanism with one revolute joint studied above is chosen as a case study to evaluate the impact of clearance of joint, contact deformation and friction on the overall precision. Analytical results indicate that the clearance in revolute joint and elastic deformation of mechanism play the most important roles in the system, and the contact deformation of joint could be neglected in the overall precision analysis.