tailieunhanh - Mechanism Design - Enumeration of Kinematic Structures According to Function P3

Structural Representations of Mechanisms The kinematic structure of a mechanism contains the essential information about which link is connected to which other link by what type of joint. The kinematic structure of a mechanism can be represented in several different ways. Some methods of representation are fairly straightforward, whereas others may be rather abstract and do not necessarily have a one-to-one correspondence. In this chapter various methods of representation of the kinematic structure of a mechanism or kinematic chain are described. For convenience, the following assumptions are made for all methods of representation. . | Chapter 3 Structural Representations of Mechanisms Introduction The kinematic structure of a mechanism contains the essential information about which link is connected to which other link by what type of joint. The kinematic structure of a mechanism can be represented in several different ways. Some methods of representation are fairly straightforward whereas others may be rather abstract and do not necessarily have a one-to-one correspondence. In this chapter various methods of representation of the kinematic structure of a mechanism or kinematic chain are described. For convenience the following assumptions are made for all methods of representation. 1. For simplicity all parallel redundant paths in a mechanism will be illustrated by a single path. Parallel paths are usually employed for increasing load capacity and achieving better dynamic balance of a mechanism. For example Figure depicts the components of a basic planetary gear train whose schematic diagram is shown in Figure . Although the gear train has four planets the structural representation is sketched with only one as illustrated in Figure . Similarly when a link is supported by several coaxial bearings only one will be shown. 2. All joints are assumed to be binary. A multiple joint will be substituted by a set of equivalent binary joints. In this regard a ternary joint will be replaced by two coaxial binary joints a quaternary joint will be replaced by three coaxial binary joints and so on. 3. Two mechanical components rigidly connected for the ease of manufacturing or assembling will be considered and shown as one link. For example two gears keyed together on a common shaft to form a compound gear set will be treated as one link. 2001 by CRC Press LLC FIGURE A basic planetary gear train. Functional Schematic Representation Functional schematic representation refers to the most familiar cross-sectional drawing of a mechanism. Shafts gears and other mechanical elements are drawn