Diamond Roll-Rings® are designed to roll. Slip-rings are designed to wear. The maintenance-free benefit of Diamond Roll-Rings® is derived from its design concept, a ring of spring copper rolling between two conductive races. Slip-rings must create wear debris to function properly thus requiring periodic maintenance.
Diamond Roll-Ring® Air Traffic Control units must operate without interruption to keep skies safe. To understand just how long a Diamond Roll-Ring® would last in service, a standard unit was operated at 200 rpm for well over two years and accumulated 240 million revolutions or the equivalent of thirty years in Air Traffic Control search radar service. After the test was concluded, the Diamond Roll-Ring® was evaluated and found to perform in specification. Diamond Antenna & Microwave has supplied over nineteen countries, including the US Military, with multiple-channel Air Traffic Control rotary joints with Diamond Roll-Rings® since 2001. To date, no Diamond Roll-Ring® has been returned for service.
Diamond Roll-Rings® are made from a spring copper alloy then plated for low electrical resistance and corrosion resistance. Diamond Roll-Ring® Engineers design the gap between the races such that the spring copper Diamond Roll-Ring® will never accumulate fatigue stresses which would lead to a fatigue failure. The plating system chosen for the races and the rings is designed for long life with virtually no wear.
Diamond Roll-Ring® units contain no wear items with the common exception of bearings and seals. The sixteen Diamond Roll-Ring® units aboard the International Space Station have been in continuous service since activation with several of them operating in excess of ten years, all without any maintenance. A standard Air Traffic Control Diamond Roll-Ring® unit underwent accelerated life testing for 240 million revolutions or the equivalent of 30 years of uninterrupted operation. In other words, each Diamond Roll-Ring® rolled 63,480 miles or 2.5 times around the earth before the test was concluded.
Diamond Roll-Rings® are designed to handle low noise signal circuits, 0 - 15 milliamps, to high current power circuits for wind turbines, over 200 amps per Roll-Ring®. ¾” diameter is the smallest Diamond Roll-Ring® currently designed into new units with the largest at 3” for wind turbine generator service.
Diamond Roll-Ring® Engineers start with a customer’s current requirements then calculate the necessary number of races to safely handle the current at operating condition. There is no upper limit to the ability of a Diamond Roll-Ring® system to handle current. As of May 2012, a 1,200 Amp 1,800 rpm unit is in operation in the R&D center. The next iteration will be capable of handling 2,400 Amps.
Diamond Roll-Rings® do not require relative motion to be able to pass current and can remain in one position indefinitely without degradation in performance. While most Diamond Roll-Ring® units are designed to handle full in-rush currents at 0 rpm, some, like wind turbine applications, can double their current carrying capability by passing full current only under rotation.
Very Low Torque
The original design intent for Diamond Roll-Rings® was to drastically reduce the torque required for slip-rings used in directional and attitudinal gyroscopes for aircraft. The first Diamond Roll-Ring® device ever produced reduced slip-ring torque in gyroscopes by 99%.
Diamond Roll-Rings® do not require friction to enable contact like slip-rings. The Diamond Roll-Ring® rolling interface is much like a steel railroad wheel on a railroad track, if given a push and a flat section of good track it will seemingly roll forever. The torque of the 2,400 amp Wind Collector Diamond Roll-Ring® unit comes only from the two bearings that maintain the spacing of the rotor and stator relative to each other. By netting out the effect the bearings, there is no practical measurable torque required to rotate the Diamond Roll-Rings® inside a 2,400 amp unit.
Diamond Roll-Rings® are made from spring copper and are under slight compression when installed in their races. Combining well designed rotor and stators frames with a good bearing system keeps the races in close relative position to one another during extreme shock and vibrations. This close relative race position combined with the properties of the spring copper means the Diamond Roll-Ring® is well captured and because of its very light weight is not strongly affected by high shock or vibration loads.
Slip-rings utilize a spring of one form or another to hold the brush contact against the rotor. Since the spring is constrained only by its spring constant a shock or vibratory load can cause the brush contact to momentarily leave the surface and potentially draw a damaging arc. Diamond Roll-Rings® do not have this issue by design.
Low Signal Noise
Units with two Diamond Roll-Rings® per channel, the standard configuration, routinely demonstrate noise in the +20 mΩ range. If an additional Diamond Roll-Ring® is added in parallel with the first two, noise can be reduced to the +10 mΩ range. Speed does have an impact on the noise measured and each application must be reviewed individually by Diamond Roll-Ring® Engineers to provide the best estimate of performance.
Data Transfer Rates
Diamond Roll-Rings® have been proven to successfully transfer data at 15 Mbit/sec for RS-485 signals while rotating at 1,200 rpm. Diamond Roll-Rings® are also capable of transferring a variety of other signal types including RS-422 and RS-232.
The diameter of the clear bore drives the data rate capability. As the diameter increases additional mitigating design techniques must be employed to maintain performance. Diamond Roll-Ring® Engineers are continually testing the upper data transfer capability of various design configurations as they are manufactured. Power Over Ethernet (PoE) is slated for Diamond Roll-Ring® testing during the summer of 2012.
Air Traffic Control Radar Diamond Roll-Ring® units are capable of operating at above 3,000 rpm. The ability of a Diamond Roll-Ring® device to operate at high speeds is a function of the clear bore allowed in the customer’s application. The smaller the clear bore the faster the Diamond Roll-Ring® unit can spin and maintain performance.
Diamond Roll-Ring® Engineers are continually evaluating their products to determine the upper operating limit of the design. Pictured below is one test fixture rotating an ATC Diamond Roll-Ring® unit at 2,400 rpm for an accelerated life test.
A customer requested Diamond Roll-Ring® Engineers to design a 6,000 rpm unit capable of conducting 1,000 Amps for greater than one year of continuous operation minimum. Slip-ring companies declined to bid on the application due to the speeds. An initial design was completed by Diamond-Roltran which successfully handled the speed required.
High Transfer Efficiency
Diamond Roll-Rings® roll in races that are gold plated. Diamond Roll-Rings® themselves are gold plated. This gold on gold interface provides for very low electrical resistance as well as a surface completely resistant to oxidation. 3” Diamond Roll-Rings® for wind turbine generator service measured at 2.65 mΩ in rotation which equates to a transfer efficiency of 99.735%. This calculates to a power loss in a wind turbine generator application of 954 Watts total. Comparable numbers for slip-rings are not published by their manufacturers.
All Diamond Roll-Ring® products are designed, manufactured and tested in Littleton, Massachusetts. The New England area of the United States contains a vast array of suppliers which enables Diamond-Roltran to source components locally, with rapid turnaround times for prototypes or large production runs at competitive economics.
This excellent supply base combined with a talented local labor force enables Diamond-Roltran to design and build custom Diamond Roll-Ring® units in as little as five and one half weeks after receipt of an order. Normal lead-time is 12-22 weeks depending on complexity or required design iterations. We welcome the opportunity to work with you to design and supply your Mission Critical Diamond Diamond Roll-Ring® device.