Kusnacht, Switzerland--Flexible mo-tion control is unthinkable without information about the position of each axis. While inductive resolvers offer cost, mounting, and durability benefits over incremental and absolute encoders, they also present drawbacks: specifically, complex circuitry and speed/acceleration limits. Based on a solid rotor, a new resolver overcomes these disadvantages.
Problem: Traditional brushless resolvers incorporate a wound rotor and stator. Windings on the rotor generate an ac magnetic field with a sinusoidal distribution. This field induces voltages in the two stator windings whose amplitudes depend on the rotational angle of the rotor. To provide sine and cosine signals, the two secondaries are wound in space quadrature (90 physical degrees apart) in the stator.
Transferring energy from the stator to the rotor requires a rotary coupling transformer. Because its primary winding is built into the stator, and the secondary winding mounts on the rotor, many turns of wire are needed to generate usable output signal amplitudes.
The large number of turns means that a traditional resolver is a relatively high-impedance device, limiting its use at high excitation frequencies or rotational speeds. Typical maximum speeds are 10,000 rpm or less.
Solution: Unlike traditional brushless resolvers, the RotasynTM resolver from Admotec Precision AG incorporates both primary and secondary coils in the stator, eliminating the rotary transformer. The primary coil is wound circumferentially between the two stator stacks: the two secondary windings are wound in the stator slots in space quadrature. Hence, the induced voltage amplitudes correspond to the sine and cosine of the rotor angles, as in a traditional resolver. Advantages include:
High speed. The standard Rotasyn is rated to 30,000 RPM.
Low impedance. Relatively few turns of wire produce powerful output signals.
Reduced ripple. The absence of rotor slots eliminates induced pulsations.
Available in standard sizes 15 and 21, the new resolver is well-suited for sinusoidal commutation of ac and brushless dc servomotors, as well as for flux vector control of ac induction motors.
Additional details, Europe...Contact Admotec Precision AG, Seestrasse 68, CH-8700 Kusnacht, Switzerland, Tel: +41 1 910-3432, Fax: +41 1 910-3980.
Additional details, U.S....Contact Admo-tec Inc., 256 Route 5 South, Norwich, VT 05055-9465, Tel: (802) 649-5800, Fax: (802) 649-3908.
Automotive control systems