What is an electrical slip ring?

A slip ring is an electromechanical instrument/device that transmits the electrical signal and power from a fixed part of the machine (stationary side) to a rotating structure part.

For that, the slip ring can be used in a wide range of electromechanical systems that require unrestrained, rotation while transmitting power or signals at the same time. It can improve the mechanical work performance, and simplify system operation. Besides, it can eliminate the waste resulting from the environment’s affected cables and damage-prone wires dangling from movable joints.

Slip Ring has many different and alternative names such as transmission ring, electrical rotary interfaces, electrical rotating connectors, electrical rotating collectors, swivels, or electrical rotary joints.

these transmission rings or rotating connectors are commonly found in many motors systems, AC electrical generators systems, and in packaging machinery, … etc. In general, they can be used on any rotating system to transfer power, control circuits, or analog or digital signals.

As a conclusion, there are many different types and sizes available of slip rings either standard or customized depending on the user requirements, and the industry type, and this will lead us to the next question.

 

What are the types of slip rings?

Regarding the wide range of use for the slip rings, different contact technologies solutions have been developed under different configurations and materials to meet the user requirement. Now, there are 4 main types according to the contact technology, they are Carbon Brush Slip Ring (Conductive Block), Liquid Metal, Fiber Brush, and Wireless.

Under these technologies there is a wide range of slip rings products depending on the components and industries requirements, such as Pancake slip rings, Pneumatic slip rings, Miniature slip rings, capsule slip ring, Mercury slip rings, Wireless slip rings, USB slip rings, Waterproof slip rings, Ethernet Slip Rings, and Fiber Optic slip rings, as the following:

    1. Pancake Slip Rings

      The shape of this slip is flat, for that, this type is also known as Flat slip ring or Platter slip ring, in this type, the conductors will be placing on a flat disc, and the concentric rings will be locating on the center of a rotating shaft, for that, this arrangement has more weight and volume, and it has greater capacitance and greater brush wear.

      Pancake slip rings will reduce the axial length; therefore, this type is designed for space-critical applications.

    2. Pneumatic slip ring

      This type of slip ring is used to transmit pneumatic pressure or void from a static inlet to a rotating outlet. In the meanwhile, stabilizing and separating the liquid connection while rotating 360 degrees.
      Pneumatic slip rings mostly used in commercial and industrial plants equipment, off-shore drilling rigs, and geotechnical tools.

    3. Miniature Slip Rings

      This type of slip ring is designed in a small size to fit the small device’s usage which required transmitting signal and power from fixed to the mobile or rotating systems, especially the systems that require low controlling signals.
      The size of this type of slip rings makes them ideal to use for medical and electrical devices such as control panels, video transmitters, and sensors.

    4. Capsule Slip Rings

      This type of slip ring is used widely in applications where power and signal transmission are required, especially for transmitting video signals in CCTV applications or other stimulating transmissions.
      The capsule slip rings are a blend of concentrated scope and high function making them perfect to use where the space is critical. Besides that, this type uses gold-on gold connects to assure high performance, longer-lasting, low noise, and reduced interference during the transmission processes.

    5. Mercury contact Slip Rings

      This type of slip rings is using liquid mercury metal as the conducting media. During the rotating process, the liquid mercury will form a linkage connection between the fixed part and the rotating structure.
      This type of slip ring is characterized by providing a high stability connection, with low-slung resistance and less noise.
      But at the same time, the use of this type is restricted for some industries (especially the industries that affect directly human health due to Mercury safety concerns) such as food, cosmetics, and pharmaceutical industries.

    6. Wireless Slip Rings

      This type of slip ring will transmit the power and the data (signal) wirelessly by generating an electromagnetic field between the coils which are placed on the receiver part (the rotating structure) and the transmitter stationary (the fixed part).
      The wireless slip rings considered the best choice alternative for the traditional types because they do not have any carbon brushes or friction-based metal rings, for that, this type reduces the mechanical contact and the maintenance processes, therefore, it can be used in harsh and specific environments.
      But on the contrary of the traditional types, the amount of power that can be transmitted in wireless slip rings is limited compared to the traditional types which can transmit a more amount of power for the same volume, and this can be the disadvantage of this type of slip rings.

    7. USB Slip Rings

      This is a specialized type of slip ring, which used to transmit a USB signal from the fixed part to the rotating part when it is moving at 360° continuously without twisting the USB cable with each other. The USB slip rings are used in many USB devices and equipment.

    8. Waterproof Slip Rings

      This is a specialized type of slip ring, which is used in the presence of moisture, corrosion environment, and in underwater systems.
      Depending on the operational environment, this type of slip rings can be classified into various classes such as IP65, IP67, IP68, and more, where:

        • IP stands for Ingress Protection
        • The first digit indicates the degree that the connector is protected against contact with moving parts, as well as the degree to which equipment is protected against solid foreign bodies intruding into an enclosure.
        • The second digit indicates the degree of protection of the equipment inside the enclosure against the harmful entry of various forms of moisture.

    9. Ethernet Slip Rings

      This is a specialized type of slip ring, which is used with some specific products with the purpose to transmit ethernet protocol besides the power in the rotary systems.
      Return loss, Insertion loss, and Crosstalk are the important three factors that must be taken into consideration while choosing this type of slip ring for communication. However, the Ethernet slip rings designed to meet the requirement of matching impedance, reducing losses, and controlling crosstalk.

    10. Fiber Optic Slip Rings

      It can be called Fiber Optic Joint, or Fiber Electric Rotary Joint. it classified as a special type of slip ring because it is designed to pass signals across the rotating interfaces when a large amount of data required to be transmitted.
      The Fiber-optic slip rings keep and maintain the essential benefits of fiber from end to end. And they are mainly used to transmit two-way and four-way fiber optic connectors, for that, the design should be carefully crafted as the fiber’s diameter is small moreover single-mode fiber’s diameter is just 9nm. Therefore, the design should maintain precision which makes it challenging to process the structure of the product.
      This type of slip ring is used in the application like; sensor signal management, HD video transmission system, radar, and video monitoring system, medical equipment, microwave communication, etc.

What are the contact technologies of the slip rings?

There are Four contact technologies of the slip rings, all of them share the same performance principle which is transmitting power and signal from the fixed part to the rotating structure, but they are different in the component types. The following table will clarify the performance factors efficiency for each technology type.

Factor Type Power Signal Speed Circuit Density Lifetime Custom Costs
Carbon Brush High Low Medium Low Low High High
Liquid Metal Medium Low Medium Medium Low Low Medium
Fiber Brush Medium High Medium High Medium High Medium
Wireless Low Medium High Low High Low Low
    1. Carbon Brush Slip Ring / Conductive Block

      Carbon brush slip rings (also called Conductive block slip rings, or Classic slip rings) are the simplest type of configuration. This type is using widely in applications that do not require high technology, especially for transmitting power and simple type of signals.
      The main parts of this type are the brushes and the rings. The first part is the brushes, they are usually spring-loaded to obtain and secure contact with the rings in case of shock and vibration. The brush’s contact point consists of a block shape made of carbon (classic graphite) for power transmission. The second part is the rings, the rings are usually will be made by a mixture alloy of precious metal to allow the signal transmission.
      The advantages and disadvantage.

      Advantages Disadvantages
      Low cost High dynamic resistance variation
      High circuit power density Sparking may occur in the presence of dust
      Easily customized for mechanical assemblies since the brushes and rings are available separately The contact circuits are similar in size to the power circuits
      Not recommended to use for complex signal transmission such as encoders, fieldbus applications, … etc.
      High corrosion rate especially in the brush’s contact part
      Continuous preventive maintenance to prevent conductive dust collecting in the slip ring

    2. Liquid metal

      Nowadays, this type of contact technology is the most commonly used due to the high performance in a small package. In this type of contact technology, a conductive liquid metal is used to transmit the power and the signal between the fixed and rotating components.
      The main liquid metal used in this technology of slip rings is the Mercury (Hg), and sometimes Gallium (Ga) alloy can be used.
      This type of slip ring can be used in a few industries and markets due to RoHS regulations related to the use of heavy metals.

      Advantages Disadvantages
      Low cost Restricted according to RoHS regulations
      High current density circuits Complicated configuration with more than 10 circuits
      High electrical current density

    3. Fiber brush

      This type of technology is most widely used due to the flexibility in use which offers the opportunity of use in a wide range of applications that require high power transmission to high-frequency signal transmission.
      This type of slip ring can contain a mono-fiber brush used in small capsule slip rings or multi-fiber brushes to provide the best performance and high quality of connectivity. In addition to that, the corrosion factor and dust will be reduced (comparing with the carbon brush slip rings type) due to the low friction between the contact components.
      Multi-fiber brushes composed of a bundle of thin metal filaments that provides high quality of contact performance, besides low corrosion due to their flexibility. Depending on the industry and user requirements, different types of contact materials and substrates in this type of slip rings can be used to optimize the slip rings performance, for example, alloys of steel and other common metals are used for power transmission, while a tempered gold alloy (gold does not oxidize for that the quality of the contact will not degrade over time) can be used for signal transmission.

      Advantages Disadvantages
      No sparking / dust Higher cost comparing with carbon brush type
      Excellent volume-current ratio Can be corrupt/wear in minimum rate over time
      Low dynamic resistance variation
      No restrictions due to RoHS regulations
      Complex configurations up to hundreds of circuits
      High frequency electric signal transmission (up to 10 GHz)

    4. Wireless

      Wireless slip rings are the new type of contact technology that works without any contact. They work on electromagnetic induction (the principle of capacitive or inductive coupling) for power and signal transmission from the stator to the rotor by exciting the coils at high frequency without contact between the rotating and static components, where the stator is attached with an inbuilt transmitter while the rotor has a receiver to carry out the slip ring function.
      The absence of any physical contact means lacks of corrosion or absence of friction, and this also can affect directly the efficiency of the slip rings by obtaining more output. But at the same time, the efficiency can decrease due to the distance between the coupled components. In fact, this type of technology is not yet widespread, but because of the absence of contact between the components, this will lead to a zero noise, which makes this type of technology perfect to be used in sensitive environments and in niche applications characterized by high rotational speed and poor access for maintenance.

What are slip rings used for?

Slip rings are electromechanical instruments used to transmit the electrical power and signals from a fixed part to a rotating structure, which will result to simplify operations and improve mechanical performance. All types of slip rings have different and unique features depending on the user requirement and the industry type and used with applications or systems where there is unrestrained, intermittent, or continuous rotation and power/data needs to be transmitted, such as construction, agriculture, aerospace, packaging, food, cosmetics, and pharmaceuticals.
In conclusion, including the slip ring within industry application can provide many benefits such as:

Cost-effective

Reliable
High quality performance Long life
IP protection rate

Well suited to extreme environment

Some of commonly using for slip rings in the different applications:

  • Video systems
  • Moving head projectors
  • Capping machines
  • Automatic machines
  • Control systems
  • Machine tools
  • Wind turbines
  • Medical systems
  • Pharmaceutical production lines
  • Packaging
  • Bottle labelling machines
  • Robots
  • CCTV Systems

How to choose the suitable type of slip rings?

  • It is important to specify the correct user requirements when it comes to choosing the suitable type. There are many factors that must be taken into consideration that can determine the type of chosen slip rings, such as:
  • User requirement specifications: for example, what will be transmitted, how many volts, how many amperes, what kind of signal, operation speed, contact material, wire length, housing material, torque, operating temperature, … etc.
  • Installation environment does the slip rings must be resistant against specific environmental factors such as temperature, water, dust, humidity, … etc.
  • Dimension, where will be the slip rings installed, what is the installation space dimension.
  • Industry/safety regulations, protection levels, are there any restrictions to use a specific component of the slip ring.

For that, it is important to understand the characteristics, the parameters and the effect of the functions of the slip rings when it is needed to choose the correct type because the wrong choice of the slip rings may not be installed correctly and even it may lead to major damage in the main machine or effecting on the human safety.
you can ask our professionals info@slip-ring.com) to help you when choosing the suitable type of slip rings.

Conclusions about slip rings

Slip rings are used in a wide range of applications that require transmitting power and signals from a stationary part to a rotating structure. The slip rings types and specifications are founded to fit with the specific applications, machinery, and operating environments, such as weather conditions and waterproofing while other types are thick and insulated to withstand harsh environments.
For that, it is important to identify the specifications of the needed slip ring before using it. Review all mechanical and electrical specifications, including the material used, current and circuits, size, and dimensions. In addition to that, choosing the right supplier and a reputable brand can be one of the most important factors to ensure the quality of performance.

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