Page 318 - Robot Builder's Bonanza

Chapter 25

Robot Movement with

Shape Memory Alloy

metal with a memory? You bet. As early as 1938, scientists observed that certain metal
A alloys, once bent into odd shapes, returned to their original form when heated. This
property was considered little more than a laboratory curiosity, but research into metals with
memory took off in 1961, when William Beuhler and his team of researchers at the U.S.
Naval Ordnance Laboratory developed a titanium- nickel alloy that repeatedly displayed the
memory effect. Beuhler and his cohorts developed the first commercially viable shape mem-
ory alloy, or SMA. They called the stuff Nitinol, a fancy- sounding name derived from Nickel
Titanium Naval Ordnance Laboratory.

Shape Memory Alloy Comes to Robotics

In 1985, a Japanese company, Toki Corp., unveiled a type of shape memory alloy specially
designed to be activated by electrical current and made this material available in small quanti-
ties to business and hobbyists. The availability of short and inexpensive lengths of shape
memory alloy for experimental use greatly enhanced the spread of interest in the material.
Toki’s shape memory alloy, trade- named BioMetal, offered all of the versatility of the
original Nitinol, with the added benefit of near instant electrical actuation.
BioMetal and materials similar to it— Muscle Wire from Mondo- Tronics or Flexinol from
Dynalloy— have many uses in robotics, including novel locomotive actuation. From here on
out we’ll refer to this family of materials generically as shape memory alloy, or simply SMA.

Basics of Shape Memory Alloy

SMA is basically a strand of metal wire made with nickel and titanium. You know that titanium
is a kind of “super- space- age” metal, about as strong as steel, yet some 50 percent lighter in
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