Resolver (electrical)

A resolver is a type of rotary electrical transformer used for measuring degrees of rotation. It is considered an analog device, and has digital counterparts such as the digital resolver, rotary (or pulse) encoder. A rotating coil induces voltage in two stationary coils, and by comparing the phase of the signal in the two secondaries, the angle can be accurately determined. These systems were commonly used in mechanical control systems, for instance, counting the number of revolutions of a screw jack to move an aircraft's flaps to a specific extension.

A resolver is a type of rotary electrical transformer used for measuring degrees of rotation. It is considered an analog device, and has digital counterparts such as the digital resolver, rotary (or pulse) encoder. A rotating coil induces voltage in two stationary coils, and by comparing the phase of the signal in the two secondaries, the angle can be accurately determined. These systems were commonly used in mechanical control systems, for instance, counting the number of revolutions of a screw jack to move an aircraft's flaps to a specific extension. ==Description== The most common type of resolver is the brushless transmitter resolver (other types are described at the end). On the outside, this type of resolver may look like a small electrical motor having a stator and rotor. On the inside, the configuration of the wire windings makes it different. The stator portion of the resolver houses three windings: an exciter winding and two two-phase windings, usually labeled "x" and "y". The exciter winding is located on the top and is mounted such that it can rotate around the horizontal axis to produce a rotary transformer. The two two-phase windings are on the bottom, wound on a lamination and mounted at 90 degrees from each other. The rotor houses a coil, which is the secondary winding of the rotating transformer, and a separate primary winding in a lamination, exciting the two two-phase windings on the stator. The primary winding of the transformer, fixed to the stator, is excited by a sinusoidal electric current, which by electromagnetic induction induces current in the rotor. As these windings are arranged on the axis of the resolver, the same current is induced no matter what its position. This current then flows through the other winding on the rotor, in turn inducing current in its secondary windings, the two-phase windings back on the stator. The two two-phase windings produce a sine and cosine feedback current. The relative magnitudes of the two-phase voltages are measured and used to determine the angle of the rotor relative to the stator. Upon one full revolution, the feedback signals repeat their waveforms. This device may also appear in non-brushless type, i.e., only consisting in two lamination stacks, rotor and stator. Resolvers can perform very accurate analog conversion from polar to rectangular coordinates. Shaft angle is the polar angle, and excitation voltage is the magnitude. The outputs are the [x] and [y] components. Resolvers with four-lead rotors can rotate [x] and [y] coordinates, with the shaft position giving the desired rotation angle. Resolvers with four output leads are general sine/cosine computational devices. When used with electronic driver amplifiers and feedback windings tightly coupled to the input windings, their accuracy is enhanced, and they can be cascaded ("resolver chains") to compute functions with several terms, perhaps of several angles, such as gun (position) orders corrected for ship's roll and pitch. For the position evaluation, resolver-to-digital converters are commonly used. They convert the sine and cosine signal to a binary signal (10 to 16 bits wide) that can more easily be used by the controller. ==External links== AMCI Resolver Tutorial What is a resolver?

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