The Technology Of CENO Conductive Slip Ring
Conductive slip-ring technology is widely used in celestial navigation, optoelectronic tracking, photoelectric measurement, photoelectric search and automatic machinery.Now CENO combine with the problem of conductive slip ring on the contact resistance, insulation property and anti - interference. A conductive slip ring transfers signals from a stationary device to a rotating device.Its main technical indexes include contact resistance, insulation performance, anti-interference and other properties.
l Contact resistance of conductive slip ring
If the contact resistance of conductive slip ring is big, the contact temperature will rise when the current passing, even will cause fusion welding between brush and slip ring and contact pressure increasing at the same time, these issue will affect the information transmission.So the smaller the contact resistance, the better for slipring transmitting signal.Factors affecting the size of contact resistance are contact part of the material, contact surface contact form and contact pressure.
l The materials of Contact the selection
The conductive slip ring consists of two main parts are the slip ring and the brushed wire.Its main properties are high conductivity of materials, good thermal conductivity, high melting point, small resistance temperature coefficient （such as anti-oxidation, anti-vulcanization, anti-corrosive gas, etc). It has a certain hardness, good wear resistance etc,( such as good anti-fusion welding performance, arc corrosion and burn) .It is better to use brass as conductive slip ring after testing.The material of brush can be used with beryllium bronze (QBe2), with more economic price than the price of gold nickel wire . In addition, it also be made of brass , and coated with palladium on the surface, which get good conductivity and prevent corrosion.
l The contact form of brush and slip ring
The contact form of brushed wire and slip ring could divided into point contact type and contact type.Because the contact area is small for point contact slipring, the current could be passed is small too, after many testing, the maximum current can't exceed 8 amperes.If the conductive slip ring requires current of more than 10 amperes, the surface contact type should be considered.The surface contact type of conductive slip ring requires a large radial dimension, complex structure ,to make sure enough space to use it.
l Brush pressure on the slip ring
The pressure of the brushed wire directly affects the contact resistance, and the greater the contact resistance, the smaller the contact resistance.But the increase of pressure has certain limit, if exceed the limit will increase the friction torque, make contact part wear very big.It is important to determine the size of the pressure. For making brush contact the slipring well,without affecting the rotation of the slip ring.Experiments show that the pressure is suitable for 12 ~ l5 grams., the contact minimum resistance of conductive slip ring can be finished between 0.03 ~ 0.05 Ω.
l Insulation performance of conductive slip ring
Better insulation performance of conductive slip ring, the insulation resistance is more than 10 m Ω for gap between ring to ring, withstand voltage 1000 V avoid to breakdown.The conductive slip ring is composed of many rings, and it is better that the distance between the rings is at least 1.5 mm.This depends on the ability to process the related 1.5mm groove for making sure the insulation strength after the glue filling in.The radial dimension of the conductive slip ring is large, the glue is easy filling and the size is small then the process of filling is difficult.Now CENO could do the a minimum conductive slipring with an outer diameter of 12.7 mm.The insulation strength of the conductive slip ring depends mainly on the material of the insulating material and the process of the glue filling.With our experimental process of preparing materials and glue made from conductive insulation resistance between the slip inside of up to 1000 m Ω, after high and low temperature test, still can reach more than 1000 m Ω insulation resistance, withstand voltage 1000 V without breakdown.
l Anti - interference of conductive slip ring
Conductive slip rings could transmit dozens of different electrical signals, with high frequency alternating current, high voltage alternating current, alternating current with large current, weak dc small signal.As the distance between the conductive slip ring is very close, all kinds of signals interfere with each other in the transmission process, and all kinds of interference seriously affect the accuracy of information transmission.The interference generated during signal transmission has electrostatic induction coupling, magnetic induction coupling and electromagnetic induction coupling.
l Interference caused by electrostatic induction coupling
This kind of interference is caused from the capacitance between the conductors and the distribution capacitance between the ring and the ring.The generated electrostatic induction voltage is related to the frequency of the interference source and the size of the above two capacitors.When the interference source is high voltage and small current, mainly caused by electrical interference. We adopt the electric field shielding to reduce this kind of interference.The anti-interfere with shield can be used, the shield side could contact with the earth.
l Interference from magnetic induction coupling
Because the conductor of the conductive slip ring is very close, the ring and the ring are also close.When an AC passing, the mutual inductance creates a mutual voltage between the adjacent wires and rings, interfering voltage.When the interference source is low voltage and large current, magnetic interference should be shielded by magnetic field.The magnetic field shielding mainly inhibits the coupling interference of the magnetic field, and the shielding of the low-frequency magnetic field often adopts ferromagnetic materials with high permeability.The shielding of high frequency magnetic field can be used as a good conductor material with low resistivity, and it is also grounded on both ends of the shielding conductor.
l Interference of electromagnetic field interference/electric field with magnetic field
When the disturbance source voltage is more higher and the frequency is more higher, electromagnetic shielding is easy to be used, and the conductive material can be used for shield ,for the interference and magnetic interference can be shielded. The "undisturbed information transmission device" is made of the conductive material for shielding.We will adopt the ring with the signal creating by anti-interfere to shield.At the same time, we use the shielding ring to shield the small signal which fearing disturbance, will also use shielding wire for the output of the slipring wire, input lead of the brush holder also use the shielded wire, and all the shielded wire through the brush holder to connect respectively.In the form of installing shielding to reduce interference, the structure is more complicated, and the volume is large. In the case of space permitting, the shield ring should be installed in the top and bottom of the ring that mainly produces the interferon source.
l Current voltage mutations cause interference
The input signal is caused interfere by the current voltage mutation during the switching process of the input line.To reduce this kind of interference, the filter can be added near the switch to reduce the interference voltage to the lead of the slip ring.
l The current voltage fluctuation produces interference
When a large current or a large voltage transmitting, the current voltage has the fluctuation of plus or minus lO, forming a sudden wave in the wire, thus causing interference.The interference can be reduced by the turbo suppressor.The above measures can reduce the electromagnetic interference between the conductive slip ring.
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