Diamond-Roltran, LLC 59 Porter Road, Littleton, Massachusetts 01460, USA Ph: 978-486-0039, Fax: 978-486-0069 Roll-Ring Technology
Table of Contents Table of Contents... i List of Figures... i List of Tables... i Background of Roll-Ring technology... 1 Diamond - Roll-Ring Test Equipment... 5 Roll-Ring Achievements to Date... 6 Related Work... 8 List of Figures Figure 1: Functional components of the rolling electrical interface... 1 Figure 2: Mechanical compression of the flexure as a function of annulus variation... 2 Figure 3: Constriction Resistance as a Function of Contact Force... 3 Figure 4: Caged Coupler prototype demonstration unit utilizing the alternating-cage geometry. 3 Figure 5: Life test data for alternating cage coupler -mean resistance and 6σ noise... 4 Figure 6: Data Logger VI... 5 Figure 7: Data Viewer VI... 5 Figure 8: Roll-Ring Life Test Stand... 5 Figure 9: Modeled flexure fatigue data for vs. theoretical & experimental data... 8 Figure 10: Roll-Ring Design Study Cross Section...10 Figure 11: Demonstration unit with coupler in place for power transfer...10 List of Tables Table 1: Speed ramp performance data for initial alternating-caged coupler prototype... 4 Table 2: Roll-Ring Test Equipment utilized at Diamond s facility... 6 Table 3: Key Parameters that have been achieved by Previous Roll-Rings... 7 October 2008 i
Background of Roll-Ring technology Roll-Rings are an alternative to traditional slip rings. Roll-Rings capture a rolling flexure, shaped like a wedding band, between a rotor and a stator. As the rotor rotates the flexure orbits around the stator, similar to a planetary gear, maintaining constant contact. Contrary to the sliding contact employed by slip rings, Roll-Rings are based on this rolling interface extending the functional life of the unit. Conversely, slip rings produce wear debris, which builds up over time and results in degraded electrical performance. As a result slip rings are unable to provide the high reliability needed in critical applications such as space, airborne and ground based antennas, where access can be difficult and downtime for maintenance cannot be tolerated. Figure 1: Functional components of the rolling electrical interface Typically each circuit of the rolling interface consists of concentric inner and outer rings and a flexing rolling contact (flexure). The electrical wiring is attached to the concentric rings. Either of the inner or outer ring assemblies can rotate. The rings can be stacked for multiple circuits and each ring can have multiple grooves, which provides higher current handling capability and lower circuit resistance. Insulating barriers separate the circuits. The insulating barriers are designed according to MIL-E-917, which defines the over-surface creepage and thru-air clearance requirements between circuits. The heart of the Roll-Ring is the interface between the rolling contact and the inner and outer rings. This contact, which is called a flexure, is sandwiched between the inner and outer rings, but unlike slip ring brushes, the flexure rolls rather than sliding on the rotating surface. By rolling, the flexure has an extremely long, maintenance-free life, and the electrical parameters are consistent throughout the Roll-Ring life. The flexure is a gold plated, spring-like conductive October 2008 page 1
metal, which provides excellent corrosion resistance and maintains contact between the inner and outer rings. The spring effect allows for manufacturing tolerances when fabricating the inner and outer rings illustrated in Figure 2. Figure 2: Mechanical compression of the flexure as a function of annulus variation There are four points of contact for each flexure, which provides redundancy or higher current capacity. The contact is compressed within the groove to ensure compliant contact with the inner and outer rings, which can accommodate considerable misalignment without losing preload. For example, a.44-inch diameter contact when axially misaligned by.050 inch will exhibit.003-inch loss in compression, which represents a negligible amount of total compression. The radial spacing between the rings determines the maximum stress in the contact. For fatigue considerations, this stress is kept below the allowable stress level for the flexure material at 1 billion (10 9 ) cycles. In addition to reduced maintenance, Roll-Rings provide low electrical resistance and low variation in electrical resistance due to rotation as in comparison to brush-based slip rings. Figure 3 illustrates that the constriction resistance of the flexure at the point of contact is below 1 milliohm. Roll-Rings employ a proprietary, wear-resistant gold-on-gold interface and operate with a minimized contact force, allowing Diamond to maximize both the performance and life of a unit simultaneously. October 2008 page 2
Figure 3: Constriction Resistance as a Function of Contact Force * Diamond s most recent development in the Roll-Ring technology has been the introduction of the coupler which is designed to replace the flexure on high power applications. Originally developed for power transfer for the Navy s propeller de-icing systems, the coupler is capable of handling much higher currents due to the larger cross-sectional area of the solid coupler halves. Because these coupler halves are non-flexible, they cannot generate their own preload as is the case on flexure-based Roll-Rings. As a result, a conventional compression spring is used in compression to create the required contact force between the couplers and rotor/stator conductors. Because of the rigid contact member Diamond has been able to incorporate an axle system allowing for multiple coupler components to be installed on a single groove. By doing this, not only is the current capacity of the unit increased, but the axial length required is reduced. Figure 4: Caged Coupler prototype demonstration unit utilizing the alternating-cage geometry * Slade, Paul, Electrical Contacts- Principles and Applications, 1999. October 2008 page 3
Results to date on the latest iteration of high-power coupler are favorable. Early generations of the coupler-based Roll-Ring have been improved upon to not only allow for exceptional performance at lower speeds, but with the incorporation of the alternating cage coupler; speedindependent performance over any required range of speed. As a result Diamond has been able to meet power handling specifications not obtainable with a flexure-based unit, without exceeding the dynamic noise requirement for individual channels. Speed Ramp Performance Data RPM Resistance (mω) 6σ Noise (mω) 7 48.6 6.0 25 48.3 4.9 50 47.4 4.0 100 47.2 3.9 250 46.9 4.0 513 47.3 4.8 Table 1: Speed ramp performance data for initial alternating-caged coupler prototype The introduction of the conventional spring allows for larger variations in the annulus with minimal reduction in contact force and subsequent performance. Furthermore, by de-coupling the electrical and mechanical properties of the transfer component as in the case of the coupler, the electrical performance and functional life of the unit can be tuned by simple modifications to the spring force. Current coupler units have been life tested in excess of 12 million revolutions at 100% speed, exceeding the 420 hour operating life for a comparable slip ring by a factor of 2x. Figure 5: Life test data for alternating cage coupler -mean resistance and 6σ noise October 2008 page 4
Diamond - Roll-Ring Test Equipment Diamond has developed advanced LabVIEW Virtual Instrument (VI) Roll-Ring test programs. Diamond uses these LabVIEW VI s to perform automated acceptance tests in which the LabVIEW VI s can control all aspects of the test from current / voltage profiles to motor speed profiles and capture all test data electronically. Additionally Diamond has developed a standalone data viewer application which allows Diamond to share the electronic test data with team members and customers without purchasing a LabVIEW license. This will enable team members and customers to view the test data and perform independent analysis on the electronic data. Diamond has multiple generic and specialized Roll-Ring test fixtures for both our Roll-Ring and Roll-Block products. Diamond has 2 single position test stations and 3 three (3) position Roll- Ring test stands. One (1) test stand is used for production testing and two (2) are used for life testing. In addition to specialized Roll-Ring test fixtures Diamond has a full suite of electronic test equipment including Network Analyzers. The LabVIEW VI s developed for Roll-Ring testing are designed to be very intuitive to operate with a standard MS Windows look and feel to the interface. All Roll-Ring technicians have been trained on how to make proper connections and operate the LabVIEW test programs. All of Diamond s technicians are trained and experienced users of the Network Analyzers which are used for testing the RF rotary joint products as well as high data rate Roll-Ring engineering tests. Figure 6: Data Logger VI Figure 7: Data Viewer VI Figure 8: Roll-Ring Life Test Stand October 2008 page 5
Parameter Method Comment S/W based data capture Electrical Performance NIPCI-6259 DAQ LabVIEW R8.5 Oscilloscopes Strip Chart Continuous data capture Computer based analysis techniques Multiple data capture paths Azimuth optical encoders US Digital E6S Integrated with LabVIEW Slip Ring Drum / Platter Mechanical Run Out Power Supplies Digital Run Out Gage Lambda 120 A Powermate BPA-10f-V Integrated with LabVIEW, Solid Works & COSMOS Motion Control & measurement integrated with LabVIEW Table 2: Roll-Ring Test Equipment utilized at Diamond s facility Roll-Ring Achievements to Date Although the coupler-based technology is a new development, Roll-Rings have a 27-year history. Sperry Flight Systems initially developed the flexure-based rolling interface in 1975. During the 1980 s and 1990 s Honeywell further developed the rolling interface and supplied Roll-Rings for the International Space Station. Since that time, Roll-Rings have been used in many applications, such as the Trident Missile System Sensor, X-Ray tubes, Semiconductor Ion Implanters, flight simulators, pharmaceutical process systems, radar systems, inertial gyro test tables, semiconductor fabrication equipment, and helicopter test stands to name a few. Roll-Rings allow AC and DC electrical power to pass through a rotating electrical interface without degradation and avoid creating wear particles or debris. In previous applications, Roll- Rings handled voltages as high as 3 kv and currents as high as 200 amps at rotational speeds of up to 10,000 rpm. Table 3 shows some of the key parameters that have been achieved to date. October 2008 page 6
Item Parameter Comments Life 1 billion revolutions Test was stopped without failure Number of Circuits 1 to 120 Steady State Current Transfer 200 amps Surge Current Transfer 5000 amps 420 times steady state. This can be tailored to each application Voltage Electrical Isolation Data Rate 3000 VAC - 70 db 1553 and Ethernet, >30Mbps Dynamic Resistance Typically 1 to 20 mω This can be tailored to each application Rotational Speed Envelope ID Envelope OD Envelope Axial Length.001 to 10,000 rpm No ID to 6.5 inches.38 to 16 inches.5 to 44 inches Operating Temperature -60 to 250 C Mechanical Shock Vibration: sine Vibration: random 300 g s peak over 11 ms 5 g s peak 14.4 g (rms) Ambient Pressure 1 X 10 8 Torr Space application Table 3: Key Parameters that have been achieved by Previous Roll-Rings Roll-Rings offer excellent growth potential as well as improved performance in comparison to a traditional slip ring. Data rates have been demonstrated in excess of 30 Mbps and with enough development speeds of 100 Mbps are thought to be attainable in the right application. In terms of power transfer, Roll-Rings have successfully passed currents up to 200 Amps per groove utilizing Diamond s coupler technology with upside power handling of over 1000 Amps per channel currently available by using parallel grooves. Diamond is in the process of establishing life test data is for the newer coupler technology. For the flexure based technology, extensive fatigue data has been compiled and current unit designs operate such that maintenance schedules are driven by bearing and seal requirements. By optimizing the preload on the flexures controlling the variation of the annulus in which they operate, it is possible to keep the alternating stress on the flexures below the endurance limit of the base material, such that fatigue failures are no longer the limiting factor. Diamond has design models that allow critical design parameters with tolerances to be entered with output values automatically calculated and plotted against existing theoretical and experimental data (Figure 9) factoring in the specific duty cycle of a given application, resulting in highly robust designs. October 2008 page 7
Figure 9: Modeled flexure fatigue data for vs. theoretical & experimental data Related Work Diamond has supplied a number of projects and programs with both flexure-based and couplerbased technology. In particular Diamond has conducted / is conducting a number of Slip Ring replacement projects for various platforms, including: 2008 Roll-Ring coupler development for Boeing Helicopter rotor This development for Boeing and the U.S. Army represents Phase III SBIR funding in utilizing the offset coupler design developed under an SBIR for the V-22 helicopter. Boeing will use Roll-Rings for power transfer to replace slip rings in this rotor blade thermal de-icing application. 2008 Roll-Ring coupler development for American Superconductor This commercial coupler development utilizes Roll-Rings to energize the magnet on a megawatt turbine used in wind power generation. Roll-Rings are being used in lieu of slip rings to provide maintenance-free transfer in this traditional brush motor application, October 2008 page 8
bringing the advantages of smaller size and cheaper design to realization without the traditional limitations of a slipping brush interface. 2008 Roll-Ring flexure production for Air Traffic Control radar Diamond has manufactured and delivered over 34 units this year for multichannel rotary joints used in air traffic control antenna pedestals. These assemblies allow users to avoid field maintenance of slip ring brush blocks, scheduling factory service when the bearings and seals of the assembly are due for replacement. 2008 Roll-Ring flexure development for U.S. Navy AN/SPS-48 shipboard Radar This development for the ISEA and ITT Gilfillan implements an additional source of supply for this high powered rotary joint and also upgrades the assembly to use Roll- Rings in place of traditional slip rings. Roll-Rings will allow for factory maintenance of the entire assembly at scheduled intervals, thereby precluding the need for field service and unscheduled maintenance which represents a threat to mission readiness. 2006 - Phase I SBIR Topic N05-106 entitled Innovative and Affordable Materials / Concepts for Improving Rotorcraft Slip Ring Reliability. This program was the precursor to the current Phase II program Diamond has been awarded and is presently working on. In this program Diamond presented a design study illustrating that Roll-Ring technology could meet the space claim, though cable routing would be a challenge. Most significantly this program demonstrated superior power handling capability and signal quality of Diamond s Roll-Ring and coupler technology. The Phase I demonstration unit exceeded requirements, transferring 200 Amps with < 1 mω of signal variation over rotation during capability demonstration testing and 100 Amps with < 1 mω of signal variation over rotation during an extended 8 hour extend duration test. October 2008 page 9
Figure 10: Roll-Ring Design Study Cross Section Figure 11: Demonstration unit with coupler in place for power transfer 2006 Joint Development Agreement with Ideal Aerosmith This commercial program is underway to upgrade aerospace rate tables to use Roll- Rings. Slip rings have been a limitation in these applications due to the dual requirements of high speed and low noise; transferring analog signals requires high fidelity low noise signal transfer across these rotating junctions. These Roll-Rings are currently in beta evaluation with Honeywell. 2006 - Phase II SBIR Topic N68335-05-0097 entitled Improved Propeller De-Icing Systems This program, also for NAVAIR, applies Diamond s Roll-Ring and Roll-Block technologies to improve the propeller de-ice slip ring of the E-2C Hawkeye aircraft. Diamond has developed an improved Roll-Block design, based on a compliant, conductive metal tire called a Flex-Wheel. Diamond has demonstrated the quality of the Flex-Wheel suspension system and its power handling capability (40 Amps per wheel) over a range of shaft speed in excess of 1500 rpm. The Phase II program investigated system level architectural and mounting issues, and demonstrated the robustness and durability of the Flex-Wheel hardware. 2001 Roll-Ring developed for Boeing / Helicopter rotor The development for Boeing involved a 36-channel, high-speed, Roll-Ring. This Roll- Ring successfully transferred high current, and data at 30 Mbps per the specified October 2008 page 10
requirements at 400 RPM, performing at peak speeds up to 800 RPM as reported by Boeing in FFTN-2004-002. October 2008 page 11