Lower pairs are desirable from a design standpoint since the load at the joint and the resultant wear is spread over the contact surface. Thus, geometric changes or failure due to high contact stresses and excessive wear may be prevented. In actual practice, we may utilize a ball ot roller bearing as a revolute pair to reduce friction. In so doing, the advantages of contact over a large surface are sacrificed.
由于在接点处的负载与合力磨损覆盖在接触表面，从设计角度出发低副是合乎需要的。因此，由于高接触面应力和过度磨损而成几何级数增减的变化和故障可以预防（避免）。我们可以利用球形物或滚柱轴承外翻低副以减少磨擦。
Kinematic Chain
A kinematic chain is an assembly of links and joints. In s closed kinematic chain, each link is connected to two or more other links.
Mechanism is a kinematic chain in which one link is considered fixed for the purpose of analysis, but motion is possible in other links. As noted above, the link designated as the fixed link need not actually be stationary relative to the surface of the earth. A kinematic chain is usually identified as a mechanism if its primary purpose is the modification or transmission of motion.
运动链系
运动链系是一种连接和对接的装配。在一个封闭的运动链系中，每一个链环都是连接在两个或两个以上的链环上。
Machine
A mechanism designed for the purpose of transmitting forces or torques is usually called a machine.
机器
为传送矢量或转矩为目的而设计的机械装置通常称为机器。
Engine
A machine that involves conversion of energy to produce mechanical power is commonly called an engine. Thus, the crankshaft, connecting rod, piston, and cylinder of an automotive engine would be an engine by the above definitions, while other drive train components such as the transmisson, differential, and universal joint would be considered machines. Machines and engines may have the same configuration as other mechanisms that do not convert energy and are not intended to transmit significant levels of force or torque. Thus, for the purpose of kinematic analysis, the above distinctions between mechanism, machine, and engine may be of only academic importance.
发动机
一台包括能量转换生成机械动力的机器一般称作发动机。因此，汽车发动机的机轴、连杆、活塞和气缸依据上述定义将会成为.一台发电机，而其他的诸如传送、差速器和万向接头之类的动力传动系统会被认为是机器。机器和发动机如同其他不转化能量并且不确定为传送力或者转矩显著水平的机械装置一样可以具有同样的构造。因此，因机动分析起见，在机械装置、机器和发动机之间的上述差别可以是唯一的理论价值的差别。
Linkage
Since we may wish to examine kinematic chains without regard to their ultimate use , it is convenient to identify any assemblage of rigid bodies connected by kinematic pairs as a linkage. Thus, both mechanisms and machines may be considered linkages. In some references, however, the term linkage is restricted to kinematic chains made up of lower pairs.
连杆机构
既然我们会期望在不考虑它们最终用途的情况下检查运动链系，识别由作为连杆机构的运动副连接任何刚体的装配是适当的。因此，机械装置和机器二者都可以被视作连杆机构。然而在一些参考书中，连杆机构的提法限于由低副装配的运动链系。
Planar Motion
If all points in a system move in paralled planes, then that system undergoes planar motion.
平面运动
如果系统中所有的点都在平面运动，那么该系统就进行平面运动。
Planar Linkage
All the links in a planar linkage have planar motion. If we examine the linkage made up of the crank, connecting rod, and piston in a piston engine, we see that it is a planar linkage. Most of the mechanisms in common use may be treated as planar linkages.
平面连杆机构
在平面连杆机构中所有的链环都有平面运动。如果我们在活塞发动机内检查这种曲柄、连杆和活塞装配的连杆机构，我们就会看到那是一种平面连杆机构。大多数通用的机械装置都可以以平面连杆机构对待。
Spatial Linkages
The more general linkages in which motion cannot be described as taking palce in parallel planes are called spatial or three-dimensional linkages.
空间连杆机构
更多的内部不能描述为进行平面运动的连杆机构被称为空间连杆机构或者三维连杆机构。
Inversion
The absolute motion of a linkage depends on which of the links is fixed, that is, which link is selected as the frame. If two linkages have the same configuration but different fixed link, then each is an inversion of the other. Relative motion will be the same in both linkage.
反演
一个连杆机构的绝对运动依靠链环被固定的连杆机构，就是说，选择哪一种链环作为该机构的机架。如果两种连杆机构都有同样的构造但是却有不同的固定链环，那么一种就是另一种的反演。相对运动在两种连杆机构中会是相同的。