Thin sensor gets the skinny on angles

Sept. 1, 2007
For countless industrial products that have evolved over time, smaller, better, and less expensive is the name of the game. After designing and manufacturing

For countless industrial products that have evolved over time, smaller, better, and less expensive is the name of the game. After designing and manufacturing resolvers for more than four decades, Tamagawa Seiki Co. has followed the same diminutive path of downsizing dimensions and cost, with enormous results in reliability.

Original mil spec designs of the 1960s involved resolvers with brushes that had two windings on the rotor and stator, with a total of 48 integrated parts. During the 70s and 80s, the resolvers went brushless, then morphed into smaller, more highly integrated versions. In the 90s, Tamagawa introduced an even more compact design, consisting of four windings (on the rotor, stator, and rotary transformer) and 20 parts. The latest step in this “downward” path — a variable reluctance type resolver — employs windings only on the stator, further reducing the parts count to just five.

In all, VR resolvers consist of stator laminations, a stator winding, rotor laminations, an optional protective cover, and slot insulators. The design concept features no contacting parts, as the stator is fixed and the rotor (a silicon steel lamination stack) is keyed to the motor shaft. The design is also inherently robust, able to withstand high levels of vibration, wide temperature fluctuations, and solvent and oil-mist atmospheres.

VITAL STATS

On display: Singlsyn absolute angle sensor

Key features: Ultra-thin construction of this built-in resolver minimizes mounting dimensions. Using a laminated steel rotor rather than a wound rotor makes for a more reliable solution.

What it means to you: Need less room to mount a feedback device (axial length can be held to 15 mm despite ODs more than 125 mm) that's more rugged and less expensive than conventional alternatives.

What else: Measure angles consistently in temperatures from -55° to 155° C and in harsh environments — tolerating vibration to 20 g, shock to 100 g, and humidity to 90% RH.

Innovator: Tamagawa Seiki Co. Ltd.

For more info: advantechinternational.com or (800) 322-6150

Angle wrangler

The contour of the rotor forms a specially curved airgap between the rotor and stator, achieving a sinusoidal relationship, corresponding to the angle of the rotor shaft. One excitation winding and two output windings (on the stator) detect changes in the airgap, producing phased output voltages proportional to the sine and cosine angles of the rotor. The analog signals are converted to digital equivalent angles using conventional resolver-to-digital (R/D) converters. So far, three rotor shapes have been used — elliptical (2X), triangular (3X), and cross (4X) — achieving different levels of precision.

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