4.  Cams mechanism

Fig. 4.5.6 Cam mechanism

Cam mechanism is one of the accurate and reliable methods of indexing. It is widely used in industry despite the fact that the cost is relatively high compared to alternative mechanisms. The cam can be designed to give a variety of velocity and dwell characteristics. The follower of the cams used in indexing mechanism has a unidirectional rotary motion rather than oscillating rotary motion which is usually the case of axial cams. The cam surface geometry is more complicated in a cross over indexing type of cam as shown in Figure 4.5.6.

5.  Applications of indexing mechanisms

Some of the applications of indexing mechanism are discussed below.

5.1  Motion picture projectors

Fig. 4.5.7 Motion picture projector with Geneva mechanism

Geneva drive mechanism is used in conventional-mechanical type movie projectors. Figure 4.5.7 shows the schematic of movie projector with Geneva mechanism. The film does not run continuously through the projector. It is requited that the film should advance frame by frame and stands still in front of the lens for fraction of a second. Modern film projectors use an electronically controlled indexing mechanism which allows the fast-forwarding of the film.

5.2  Automated work assembly transfer lines

Fig. 4.5.8 Automated assembly line

In assembly lines, the parts to be assembled have to be moved over the assembling machine tool (Fig. 4.5.8). This is done using indexing mechanism. The part on the table is indexed to be in line with the assembly unit. Once the assembly is done the table is indexed to get the next part in line with the assembly.