A slip - ring is an electrochemical device that allows the transmission of signals and power from a stationary to a rotating structure such as space satellites, radar antenna, sensor gimbals, and electro - optics. They are used in those electromechanical systems which mostly involve rotation while carrying out the transmission of power. It helps to make the operation more simplified, and we can see the mechanical performance getting increased. The slip rings are also known as the commutator and electrical slip ring. It is known by many other names such as electrical rotary joint, rotating electrical connector, and electrical swivels.
The electrical slip ring can allow an infinite number of rotations of the connected object, whereas a slack cable only allows a few rotations before it gets bound up and restricts the rotation process.
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A slip ring consists of stationary graphite, or you can say a metal contact (brush) which is getting rubbed on the outside diameter of the rotating metal ring. The connection between the stationary brush and metal ring is generated when the metal ring turns, and electric current or signal is conducted through the stationary brush to the metal ring. If more than one electrical circuit is required, then it is necessary to stack an additional ring or brushes along the rotating axis. In this mechanism, either the brush or the ring is stationary whereas the other components are rotating in the axis. This simply has been used for years now as a rudimentary method to pass current from a stationary component to a rotating component.
Electrical slip rings are built-in in various types and sizes.
Mercury - Wetted Slip Rings
Mercury - wetted slip rings are known for their low resistance ability and for generating a stable connection all the time. They use a different principle in which the sliding brush contact is replaced with a pool of liquid metal molecularly bonded to the contacts. During the rotating mechanism, the liquid metal holds the connection between the stationary contact and the rotating contact. However, the use of a toxic substance like mercury raises the safety concerns of the process.
This type of slip ring is not used in operations like food manufacturing, processing pharmaceutical equipment, or any other process where contamination can cause serious troubles. If the mercury gets leaked, it can cause unrecoverable problems and could be extremely serious. Another disadvantage of this device is temperature as mercury solidifies at -40 degrees celsius.
Pancake Slip Rings
A pancake slip ring had the conductors arranged as concentric rings on a flat disc, and it is centered on the rotating shaft. This configuration provides greater weight and volume for the same circuits. They also provide greater capacitance and crosstalk, greater brush wear, and collect debris more rapidly from its vertical axis. A reduced axial length is provided by pancake slip rings for the number of circuits, which is why it is appropriate for use in some applications.
Wireless Slip Rings
Since the time slip rings were invented, they rely on the friction-based metal and carbon brush contact methods for the transmission of power or signal. However, the wireless slip rings don't rely on either the friction-based metal or the carbon brush contact method. This makes them a lot different from the above two types. In a wireless slip ring, the coils placed in the rotating receiver and the stationary transmitter create a magnetic field through which the power and signal get transmitted. These slip rings are considered as an upgrade for the traditional slip rings.
Wireless slip rings are the best for harsh operating environments and require very little maintenance because of the absence of mechanical rotating parts in it. One of the disadvantages of using these slip rings is that the amount of power or signal that can be transmitted is limited whereas the traditional slip rings can transfer a huge volume of power or signal without any difficulties.
A slip ring is used in many places such as industrial automation applications and some equipment like tower and jib cranes, in cables and hose winders where a portion can spin freely with the base remaining fixed. Devices such as gyroscopes, electrical generators, synchros, and various alternators are using slip rings in their operations or functions. They are also used in wind turbines, machines for semiconductor processing, aerospace, defense, marine, packaging industry, and synchronous electric motors.