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A rotary (rotatory) transformer is a specialized
A rotary (rotatory) transformer is a specialized transformer
In electrical engineering, a transformer is a passive component that transfers electrical energy from one electrical circuit to another circuit, or multiple Electrical network, circuits. A varying current in any coil of the transformer produces ...
used to couple electrical signals between two parts that rotate in relation to each other. They may be either cylindrical or 'pancake' shaped.
Slip ring
A slip ring is an electromechanical device that allows the transmission of Electric power, power and electrical Signal, signals from a stationary to a rotating structure. A slip ring can be used in any Electromechanics, electromechanical system ...
s can be used for the same purpose, but are subject to friction
Friction is the force resisting the relative motion of solid surfaces, fluid layers, and material elements sliding against each other. Types of friction include dry, fluid, lubricated, skin, and internal -- an incomplete list. The study of t ...
, wear
Wear is the damaging, gradual removal or deformation of material at solid surfaces. Causes of wear can be mechanical (e.g., erosion) or chemical (e.g., corrosion). The study of wear and related processes is referred to as tribology.
Wear in ...
, intermittent contact, and limitations on the rotational speed that can be accommodated without damage. Wear can be eliminated by using a pool of liquid mercury or liquid metal alloy instead of a solid ring contact, but the toxicity
Toxicity is the degree to which a chemical substance or a particular mixture of substances can damage an organism. Toxicity can refer to the effect on a whole organism, such as an animal, bacteria, bacterium, or plant, as well as the effect o ...
and slow corrosion of mercury are problematic, and very high rotational speeds are again difficult to achieve. A rotary transformer has none of these limitations.
Rotary transformers are constructed by winding the primary and secondary windings into separate halves of a ''cup core''; these concentric halves face each other, with each half mounted to one of the rotating parts. Magnetic flux
In physics, specifically electromagnetism, the magnetic flux through a surface is the surface integral of the normal component of the magnetic field B over that surface. It is usually denoted or . The SI unit of magnetic flux is the we ...
provides the coupling from one half of the cup core to the other across an air gap, providing the mutual inductance that couples energy from the transformer's primary to its secondary.
In brushless synchros, typical rotary transformers (in pairs) provide longer life than slip rings. These rotary transformers have a cylindrical, rather than a disc-shaped, air gap between windings. The rotor winding is a spool-shaped ferromagnetic core, with the winding placed like thread on a spool. The flanges are the pole pieces. The stator winding is a ferromagnetic cylinder with the winding inside, and end poles that are discs with holes, like washers
Washer most commonly refers to:
*Washer (hardware), a thin usually disc-shaped plate with a hole in the middle typically used with a bolt or nut
*Washing machine, for cleaning clothes
Washer may also refer to:
*Dishwasher, a machine for cleani ...
.
Uses
Rotary transformers are most commonly used invideocassette recorder
A videocassette recorder (VCR) or video recorder is an electromechanical device that records analog audio and analog video from broadcast television or other AV sources and can play back the recording after rewinding. The use of a VCR to reco ...
s, as well as other tape drives that use rotary heads to implement helical scan
Helical scan is a method of recording high-frequency signals on magnetic tape, used in open-reel video tape recorders, video cassette recorders, digital audio tape recorders, and some computer tape drives.
With this technique, magnetic tape he ...
, such as those used for tape backup. Signals must be coupled from the electronics of the VCR or other tape drive to the fast-moving tape head
''Tape Head'' is the seventh studio album by American rock band King's X, released in 1998 via Metal Blade Records.
A music video was made for the song "Fade". "World" is a reworked song from the band's ''Sneak Preview'' demos. The controv ...
s carried on the rotating head drum; a rotary transformer is ideal for this purpose. Most VCR designs require more than one signal to be coupled to the head drum. In this case, the cup core has more than one concentric winding, isolated by individual raised portions of the core. The transformer for the head drum shown to the right couples six individual channels.
Another use is to transmit the signals from rotary torque sensors installed on electric motors, to allow electronic control of motor speed and torque using feedback
Feedback occurs when outputs of a system are routed back as inputs as part of a chain of cause and effect that forms a circuit or loop. The system can then be said to ''feed back'' into itself. The notion of cause-and-effect has to be handle ...
.
Because they are transformers, rotary transformers can only pass AC, not DC, power and signals. The supporting electronics, including the tape heads or torque sensors, must be designed to accommodate this.
See also
* Metadyne *Rotary converter
A rotary converter is a type of electrical machine which acts as a mechanical rectifier, Power inverter, inverter or frequency converter.
Rotary converters were used to convert alternating current (AC) to direct current (DC), or DC to AC power, ...
* Variable-frequency transformer
References
{{Electric transformers Electric transformers