We all know that ER is more than just a terrific television series about dramatic events in the emergency room. Yes, ER has its own special meaning to design engineers, often with the same panic-filled connotation, depending on just how far you have passed your project deadline. You know what I’m talking about here — fastER, cheapER, bettER, and all of their relatives. Oh, did I forget to mention yestERday? Relax, grab a hot cup of coffee, and read up on a few new methods to approach two of today’s most sought after design sisters — smallER and lightER. From shape memory alloys used in motors to ordinary pipe that morphs into a lightweight precision drive shaft, these recent innovations are sure to spark your creative enERgy.

A little muscle

The CDC-100 digital machine vision camera from Cognex merges high performance digital camera technology with low cost CMOS image sensing. Shown here on a Kawasaki robot.

Billed by market analysts as the first major change in electric motor technology in more than 170 years, the NanoMuscle actuator (motor + interface) is making waves throughout the motion industry. As one of the company’s key investors — Jacob Tal of Galil Motion Control — says, “The jury is still out, but this technology has earthshaking potential.” Unlike conventional motors that use electromagnetism as their source of motion, these motors — from NanoMuscle Inc., Antioch, Calif. — use shape memory alloys (SMA) to produce movement. The best news? They’re typically one-tenth to one-twentieth the size and weight — and a fraction of the cost — of traditional small motors and solenoids. For example, a NanoMuscle actuator weighing just 1.1 gm offers a load rating of 70 gm. The company also makes custom designs that offer longer stroke and higher force ratings than its standard actuators.

President and CEO Rod MacGregor says, “Right now, we’re doing what’s called market-driven R&D. If a customer comes to us and wants an actuator for a specific application, we’ll build it — within certain limits of course.”

Since these actuators do not require additional components — such as gearboxes and complex mechanical systems — to translate rotary to linear motion, they can be manufactured for a fraction of the cost of a comparably sized electromagnetic motor. Then there’s the noise issue. Electromagnetic motors produce electrical noise during operation and their gearboxes produce acoustic noise. NanoMuscle actuators produce neither.

Then and now

Commissioned by the U.S. Navy, SMA technology was developed by Raychem Corp. during the 1950s for military applications. However, Raychem’s use of SMA in motors never really took shape because of the unpredictable nature of the material. NanoMuscle believes it has found the most effective way to harness the power of SMA without sacrificing the durability and consistency of the wire structure. The SMA in a NanoMuscle actuator is made of nickel-titanium wire stretched out across a set of supports. An electrical current causes the wire (through heating) to snap back to its original shape, creating a force strong enough to lift 140 gm.

Silicon nitride balls from Thomson Precision Ball Co. weigh 40% less than steel.

The macro-scale motion of a NanoMuscle actuator is produced by a large number of elements, each just a few nanometers across. These elements are assembled into thin wires around 50 μm in diameter. Several of these wires are then combined to produce a macro-scale linear motor with a stroke measured in mm. At the bottom of the hierarchy, each tiny element is actually a single crystal of NiTi specially treated to exhibit the shape memory effect. A microprocessor precisely regulates current to the SMA wire, controlling the speed of contraction. The actuator contracts when activated and requires a return force, such as a spring, to bring it back to its initial configuration. Life cycle is stated as more than 1,000,000 repetitions.

“Right now, we’re working on several new developments. Some involve NanoMuscles with higher forces — bigger, more powerful motors for use in automobile applications,” says MacGregor. “Another direction we’re going is making the units more self-contained, for example, a complete miniature system that could be used for mirror positioning in the photonics industry.”

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