Page 56 - Robot Builders Source Book - Gordon McComb

2.2 How Does One Find the Concept of an Automatic Manufacturing Process? 45

1. To shift the part from one operational position to the next;
2. To avoid interference between one operation and the next.

Obviously, these time intervals dictate the productivity of the machine. [The reader
is again referred to Formulas (1.1-1.7), which deal with these concepts and with the
time components influencing system productivity.]

2.2 How Does One Find the Concept of an
Automatic Manufacturing Process?

There are several approaches to this problem. The first approach is to try to copy
the manual process, that is, to imitate the manipulations of the human hands and arms
by mechanical means. Weaving is a good illustration; another example is the forging
hammer. As the blacksmith manipulated his hammer, so the first mechanical hammers
(driven by horse or waterwheel) made practically the same monotonous up and down
motions. Direct copying is, in general, less successful than roundabout solutions. For
example, the forge hammer can be fastened to the piston rod of a hydraulic cylinder
to effect reciprocating vertical (or, if needed, horizontal) motion. Combination of steam
power with hydraulics permits us to achieve a force of the order of thousands of tons.
By contrast, a relatively small force can be developed in pneumatic or electromagnetic
hammers for fine smithery. The explanation lies in the fact that human hands work in
concert with other senses such as touch, sight, and feel. In addition, the number of
degrees of freedom possessed by the human hand develops a flexibility that has never
been achieved by any mechanism. Thus the only way to succeed is to modify the con-
ception of the manual process. Sewing is another well-known example; instead of the
single thread and the needle with a hole at the tail used in manual sewing, two threads
and a needle with a hole at the tip are used in mechanical and automatic sewing.
Consider, for instance, the problem of producing aneroid barometers by a solder-
ing technique (Example 3). The manual process begins by cleaning the membrane's
flange surface by soldering flux. This is usually done with a wad moistened with the
flux. The next step is to tin-plate the flanges of the membranes, which is done with the
usual soldering iron. The membrane is held in one hand while the other hand manip-
ulates the wad or soldering iron. Both hands can gauge pressure and relative move-
ments, while the eyes control all procedures; none of this is true in a mechanized
process, and so the approach must be altered. Figure 2.10 shows a possible layout for
a four-stage tin-plating process for beryllium-bronze membranes: In the first position
a membrane is taken from a magazine 1 containing 500-800 membranes (remember,
the thickness of a membrane is about 0.2 mm) by means of a vacuum suction cup 2.
The four suction cups are in permanent rotation. In the second position the mem-
brane is pressed against rollers 3 which free rotate, the lower part of the rollers being
immersed in the flux liquid. Thus, the flange of the membrane gets cleaned. The third
position is the soldering one. A soldering iron 4 made of copper rotates in a pool of
melted tin covered by a special flux which protects the tin from oxidation. The sol-
dering iron is electrically heated from the inside and thus the flange is tin-plated by
rotation of both iron and membrane. The fourth and last position is meant for extrac-
tion of the tin-plated membrane, which falls freely when the vacuum is disconnected
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