Page 84 - Robot Builders Source Book - Gordon McComb

3.2 Electromagnetic Drive 73

where

and
F e = force developed by the moving armature,
F r = resisting force made up of friction with the spring deformation force.
The main idea underlying this approach is that, for every magnet, Equations (3.36),
(3.37), and (3.38) are equal. [The symbol idem indicates this fact.] It means that if we
know the behavior of at least one electromagnet, we can derive the behavior of another
one of the same design pattern if its parameters are known. Let us say we have a device
about which all the information is known; then for any other device under design we
can determine the time, speed, and force describing the movement of the armature
of the new device. Denoting the similarity coefficients by indexes s, we can write

Let us consider some examples.
a. An electromagnet is given and its parameters are known; for instance, operation
time ti = 0.01 sec and dimensions /j are given. We then wish to find the operation time
f 2 of a new design which will have proportionally enlarged dimensions. Say the coef-
ficients have the values

We can use the above-given dependencies to obtain

From Equations (3.39), it follows that m s = l sd\ = 8 and we then obtain

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