SLIP RING ASSEMBLIES
The main function of a slip ring assembly is to transfer electrical power and electrical signals from a stationary to a rotating platforms. M-TEK specialises in the design and production of compact, instrumentation slip ring assemblies designed for AC and DC current, digital data, control signals and video signals.

M-TEK’s slip ring technology is based on gold-on-gold contacts which are implemented by
utilising closely spaced gold alloy wire brushes, sliding into closely spaced hard gold-plated V-grooved rings, which provide low electrical noise levels and also provide exceptional compactness. For high power applications, sliding carbon brushes on copper alloy rings, are utilised. A wide variety of slip ring assemblies are produced, for applications including periscopes, sighting systems, arial observation platforms, optronic and radar positioners, winch reels, cranes, robotics, industrial applications. The slip rings may comply with or include the following:

  • Power, discrete signals, digital signals, (Ethernet, RS422, etc), video
  • Low noise, gold-on-gold technology, < 20 mOhm, used for instrumentation slip ring assemblies
  • Current capability up to 450 A peak used in rotary base junctions
  • Applications available for land, sea and air
  • Slip ring assemblies can be integrated with Fibre Optical Rotary Joints, Coaxial Rotary Joints, Wave Guides, Angular Sensors, Air Channels, Heaters, etc.
  • Designed and qualified for harsh environmental and EMC conditions

SLIP RINGS TECHNICAL REQUIREMENTS
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 can be identified as power or high current circuits and low current signal circuits. Signal circuits can be subdivided under i.e. video circuits, gyro circuits, various communication bus interface circuits, discrete signals, 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 over heating. The peak operating current is the maximum current that will pass through the slip ring for a short period of time, without causing over heating. 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 the variation in resistance produced by the sliding contacts. Contact resistance is caused by imperfections in the slip ring assembly such as 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.

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.

Slip Ring Format

  • Capsule or Housed Slip 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.

Mechanical 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 Specification
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.

Peculiar Customer Requirements
M-TEK slip rings are regularly fitted with additional functionality which include: ethernet module, 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
In order to establish a slip ring requirement, the user should attempt to address as many as possible of the parameters mentioned above.

Housed and Capsuled Slip Ring Assemblies
The slip ring assembly is usually supplied as a self contained mechanical assembly, including bearings, seals, mechanical mounting surfaces and also connectors if required. Slip rings can be supplied with hollow shafts. Angular sensors can be included into the assembly.

  • Current, continuous, on single circuit up to 2.6 A
  • Voltage up to 100 VDC
  • Insulation resistance >200 Megaohm at 500 VDC
  • Contact resistance <20 milliohm
  • Typical speed 60 rpm
  • Hollow shaft inside diameter 7 to 30 mm
  • Slip ring length. The number of circuits and bearing arrangement will determine the final length of the slip ring
  • Number of circuits up to 140

Hollow Modular Slip Rings
The slip ring assembly is usually supplied as separate ring and brush assemblies, and will be an integral part of the user’s mechanical design.

  • Current, continuous, on single circuit Up to 5 A
  • Voltage Up to 440 VAC
  • Insulation resistance >200 Megaohm at 1000 VDC
  • Contact resistance <20 milliohm
  • Maximum recommended surface speed 0.5 m/s
  • Inside diameter up to 220 mm
  • Outside diameter up to 250 mm
  • Slip ring length. The number of circuits will determine the final length of the slip ring
  • Number of circuits up to 80

Rotary Base Junctions
Rotary Base Junctions or RBJ’s, are assemblies which include besides low and very high current circuits, also varied functionality such as pneumatic or hydraulic junctions, wave guides, resolvers, connectors, etc.

  • Current, continuous, on single circuit up to 450 A
  • Current, peak, on single circuit up to 600A for 30 seconds
  • Voltage up to 440 VAC
  • Insulation resistance >200 Megaohm at 1000 VDC
  • Speed up to 60 rpm
  • Hollow shaft inside diameter Up to 100 mm
  • Outside size typical 400 by 400 mm by 400mm

Industrial Slip Ring Assemblies
Industrial slip rings are usually enclosed assemblies fitted with carbon brushes and copper alloy rings, and are frequently used for factory automation. It is common to fit pneumatic junctions to the assemblies.

  • Current, continuous, on single circuit up to 20A
  • Current, peak, on single circuit up to 30A for 30 seconds
  • Voltage up to 440 VAC
  • Insulation resistance >200 Megaohm at 100 VDC
  • Contact resistance <20 milliohm
  • Speed up to 200 rpm
  • Hollow shaft inside diameter up to 100 mm
  • Outside diameter up to 300 mm
  • Length up to 300 mm