Page 244 - Robot Builders Source Book - Gordon McComb

232 Feeding and Orientation Devices

pulling or feeding the material. Obviously, other means to disconnect the roller are
available; for instance, a mechanism to lift slider 5.
Another sort of device for interrupted feeding of materials is also based on creat-
ing frictional forces; however, feeding is done by pure pulling and pushing of the mate-
rials. Let us consider the scheme in Figure 7.6. Here, lever 1 is pressed by force Q against
strip 3 by means of spring 2. Strip 3 is clamped between the lever and surface 4. Due
to this pressure, frictional forces F occur at points A and A' (we assume that the net
forces acting on the surfaces can be considered at these points). Quantitative relations
between the forces are derived from the following equilibrium equations written with
respect to lever 1:

Here n = frictional coefficient between the materials of the strip and of the lever at
point A. We assume that the same condition exists at point A'. The four Equations (7.1)
contain four unknown quantities: N, N 0, F, and F 0. By substituting Equation 4 into Equa-
tion 3 we obtain

By substituting Equation (7.2), into the first equation, we obtain

From Equations (2) and (4) it follows that

The derived results reveal a very important fact: when

TEAM LRN FIGURE 7.6 Frictional clamping device (lever type).