Page 46 - Robot Builders Source Book - Gordon McComb

1.6 Relationship between Robot "Intelligence" and the Product 35

Let us denote:
T = the lifetime of the automatic equipment or its concept, i.e., the time the
machine or its concept is useful;
T = the lifetime of the product produced by the automatic equipment, or the time
the product keeps being sold on the market, or the market demand for the
product is maintained;
T! = the time needed to design the equipment (to work out its concept), to build
it, and to implement it in industry.

For rough estimates we can derive obvious conclusions:
1. For T < T, bang-bang-type robotics is justified because it is cheaper, can be
implemented faster and, what is most important, no flexibility is needed: even
if the potential for flexibility does exist, it will not be utilized because the product
keeps going on the market longer than the machine is able to produce.
2. For T > T, the use of flexible manufacturing systems is justified. The machine
lives longer than the specific product manufactured. Thus the same machine
would be able to produce something else. It is expensive but its flexibility facil-
itates return on the expenses.
3. For bang-bang robots, but not for flexible manufacturing systems, the condi-
tion T > 7\ must be met.

Thus, for example, for the production of paper clips, the design engineer must decide
what level of complexity of machine is required, and the answer will most likely be:

• An open loop,
• Pure mechanical control,
• Rigid layout equipment.
In this case, the designer must ensure that T > T (so that as many copies of the machine
as are needed can be made), and that T> 7\. If on the other hand, the product is any
kind of molding die, the answer would instead be:
• A computerized, closed-loop, automatically controlled milling machine, if pos-
sible with an automatic tool exchange, dimensional control, and feedbacks, etc.
In the latter case, the condition T < T is ensured due to flexibility of the equipment
and the possibility of fitting it easily and cheaply to any (or many) kinds of die. The
condition

T<T l

is ensured because the specific dies are needed for relatively short time periods while
the machine is built for practically indefinite time T interval.
Figure 1.35 presents a graphic interpretation of the inequalities used. The area
limited by bisectors I and II contains the cases for which bang-bang or point-to-point
robots can (and, in the author's opinion, should) be used. For the other cases, effec-
tive manufacturing requires higher-level robots, i.e., robots with programmable and
computerized systems.
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