When the need for slip rings arises, the following must be considered:
NUMBER OF CIRCUITS
The total number of circuits of the slip ring must be identified. Slip rings are usually made up by groups of circuits which could be identified under power or high current circuits and signal circuits. Signal circuits could be subdivided under i.e. video circuits, gyro circuits, various communication bus interface circuits, etc. Identification of the groups are required in order to minimise problems associated with cross coupling of electrical noise.
CURRENT
The continuous operating current is the maximum current that will pass through the slip ring for 100% of the time without causing any damage.
The peak operating current is the maximum current that will pass through the slip ring for a short period of time, without causing any damage.
Current value’s are required in order to determine the size of the conductors inside the slip ring assembly and also to determine the ability to dissipate heat. Circuits can be doubled up for higher current ratings.
VOLTAGE
The maximum operating voltage is required in order to determine the spacing between conductive parts inside the slip ring assembly and the slip ring housing.
CONTACT RESISTANCE
Contact resistance or noise, is a varying resistance value to be added to the circuit resistance of the slip ring assembly. Contact resistance is caused by imperfections in the slip ring assembly caused by surface roughness of the rings, varying brush pressure on the slip ring, high rotational speed, etc.
CIRCUIT RESISTANCE
Circuit resistance is the total resistance of a single slip ring circuit, including the resistance of the wiring to the brushes and the rings and the resistance of the brush and the ring.
ROTATIONAL SPEED
High rotational speed causes unacceptable high levels of contact resistance and wear. The preferred maximum tangential velocity for gold alloy wire brushes sliding in hard gold plated V-grooves, should not exceed 0,5 m/s. For higher speeds the contact resistance value will rise. The increasing contact resistance is reduced with the implementation of multiple wire brushes or higher brush contact force.
STARTING TORQUE
For certain applications, i.e. stabilised positioner systems require the least possible break away torque from the slip ring assembly. This is achieved by utilising the smallest possible ring diameter or lowest possible brush pressure.
CAPSULE OR HOUSED RING ASSEMBLY
The term, capsule or housed slip ring assembly refers to a self contained slip ring assembly, including mechanical components such as shaft, housing, bearings, etc. It must be stated whether extensive sealing is required or not.
UNHOUSED SLIP RING ASSEMBLY
The term unhoused refers to slip ring and brush parts, provided as separate loose components. The customer accepts the responsibility to mechanically integrate the slip ring assembly according to the information supplied by M-TEK.
ELECTRICAL INTERFACE
The electrical interface defines the electrical termination’s including connector type, if required, wire lengths and markings. Wire types such as twisted pairs, screened pairs, coaxial cables with specified resistance’s, etc., can be specified, but implementation thereof will be considered on a case by case basis, depending on space constraints of the specific slip ring design.
INTERFACE AND MOUNTING
Dimensions on drawings, i.e. outside and inside diameters, lengths, mounting distances, etc. are specified in millimeters.
In the case where loose components are supplied, the slip rings should be mounted with radial and axial play of less than one tenth of a millimeter. The slip ring eccentricity should be less than one tenth of a millimeter. The brush assembly should be mounted parallel to the slip ring centre line within one tenth of a millimeter.
ENVIRONMENTAL SPECIFICATIONS
For reliable long term operation, slip ring assemblies require clean, uncontaminated and dry environments. Standard slip ring assemblies are qualified to work under extreme temperatures of -20 ° C to +55 ° C. Lower and higher temperatures are possible. In order to reduce the detrimental effects of mechanical vibration and shock, it is important to minimise relative movement between the slip ring and the brush assembly by utilising stiff bearing arrangements.
For reliable long term operation, slip ring assemblies require clean and dry environments, which can be provided with use of seals, heaters, etc.
PERCULIAR CUSTOMER REQUIREMENTS
M-TEK slip rings are regularly fitted with additional functionality which include: coaxial rotary joints, wave guides, pneumatic or hydraulic channels, angular sensors, cam driven limit switches, water drain pipes, anti-freeze heaters, etc.
»SLIP RING SELECTION
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