Made of piezoelectric ceramics and other non-magnetic materials, the Squiggle motor from New Scale Technologies is based on a unique design concept that uses a threaded nut and screw to create precise linear movement in a very small space.

According to David Henderson, president of Victor, New York, U.S.-based New Scale, the motor consists of four piezoelectric actuators bonded longitudinally on a metal tube with 90-degree equal spacing. "The inside of the metal tube is threaded to form a nut, and a mating screw is inserted," he explains. "Two-phase ultrasonic electric drive signals are applied to opposite pairs of plates, and the electrical signals produce expansion on one plate and contraction on the opposing plate. The plates work together in pairs to bend the housing to create an orbital motion."

As the bending occurs at ultrasonic frequencies, the tube/nut vibrates at its resonance frequency and moves in an orbital-or what Henderson calls a “hula hoop"-fashion. "The nut engages the mating screw, and the orbital motion, at the thread contact point, causes the screw to turn and translate [in and out],” he says.

"The linear speed is proportional to the amplitude of vibration," Henderson continues. "At resonance, the amplitude of the vibration is only a few micrometers, but vibrations cycle add together to create continuous bi-directional screw movement. The screw threads ensure high precision, with stiffness and stability."

In addition, the phase shift of the drive signals determines the direction in which the screw rotates. Reversing the phase shift makes the tube orbit in the opposite direction and, thus, reverses the screw shaft movement.

Currently, the motors are available in models as small as 3 mm in diameter. Henderson admits that making electromagnetic motors this small isn’t that difficult a design feat, but making them efficient is. "Efficiency of electromagnetic motors drops rapidly at sizes below about 6 mm in diameter because more and more of the electrical drive power is converted to heat rather than to mechanical motion," he explains. “Smaller motors must also operate at higher rpm to generate enough mechanical power to do practical work. The gear ratio reduction involved can be significant. The corresponding gear train tends to be complex, which further reduces efficiency and degrades precision."

The Squiggle motor, however, is said to eliminate the need for gear reduction because it drives loads directly with the screw via thread friction. In addition, when the power to the motor is off, the screw stays in its last stopping point. Therefore, the motor can move in small bursts and hold its position indefinitely, making it ideal for battery-powered applications.

Other applications for the patented motors include consumer electronic devices and medical appliances. In fact, the company recently developed a reference motor design for a mobile phone camera that features auto focus and optical zoom. Henderson says the motor enables high-quality imaging in a small package, with very little battery power.