2. Mounting requirements that define how the Roll-Ring® will be connected to the rest of the system. Details such as flanges and bolt-hole patterns are usually defined here. It is important not to rigidly mount both the rotor and stator ends of any rotary joint since any misalignment will overload the bearings and result in damage.

3. Wiring and connector requirements that specify how the electrical connections are made. Many high performance applications have specific wiring requirements that need to be considered early in the design process. The connector requirements are especially important. Should integral connectors or flying leads be provided? What orientation and location is required (axial / radial)?

If flying leads are required, what are the cable lengths? What are the labeling requirements?

Defining Electrical Requirements -Power
and Low Data Rate Control Signals

A detailed understanding of the application and the duty cycle is required in order to avoid over-specifying these performance parameters. Proper specification of currents and voltages enables Diamond engineers to provide cost effective solutions in the minimum mechanical envelope.

The bottom line is that everyone pays for performance. Take for example:

• A 10 circuit Roll-Ring® with:
• 3 - 20 A high power circuits
• 3 - 5 A low power circuits
• 4 - 0.5 A data or signal circuits

Specifying all 10 circuits at 20 A in order to have 100% interchangeability will result in a larger, heavier, more expensive design. Additionally if 20 A is a surge current value and 10 A is the continuous current specification; this would also result in a larger, more expensive design.

It is helpful to identify if there is a critical requirement for the circuit resistance or the resistance variation. For example, circuit resistance can often be tuned by selecting the wire or flexure size based on resistance instead of current handling capability.

If you have any questions about the proper specification of the current and voltage circuits contact a Diamond engineer. Diamond’s engineers will work with you to properly document your application and identify your requirements.

Defining High Data Rate Circuits

• Insertion loss
• Impedance of the assembly
• Impedance of the cables
• Differential time delay
• Crosstalk between circuits
• Frequency response of the cables and connectors

Frequency response (or bandwidth) is the primary factor to consider. Errors reduce performance and are introduced into digital data streams when a digital signal is distorted in either amplitude or phase. This distortion results in data or timing errors within the digital system. Digital signals are composed of multiple harmonics as multiple analog signals are combined to define digital square wave pulses. Therefore the bandwidth requirement of the Roll-Ring® is typically several times the data rate, e.g. a 10 MHz data rate may require a 50 - 70 MHz frequency capability in order to maintain optimum pulse shape.

Frequency defines wavelength which in turn defines the size of transmission components. Therefore high data rate products generally require smaller diameter Roll-Ring®s. Design of high frequency components is a complex task. Diamond understands these complexities well and leverages its 50 year history of designing high frequency microwave rotary joints in the design of high data rate Roll-Ring®s.

Given that there are some wavelength defined performance constraints that must be considered it is not sufficient to simply specify “10 Mbit Ethernet” for high data rate channels. It is critical that the entire system be understood and specified since it usually requires a compromise between performance, size, weight, number of channels, the external environment and cost.

The following parameters should be specified to enable Diamond engineers to evaluate different designs:

• Data bus used to transmit data, i.e. 10 Base T or 100Base T Ethernet, Firewire
• Cable and connector types used
• Maximum cable length between transmitter and receiver
• Maximum data rate
• Maximum error rate that can be tolerated

For the most advanced and challenging applications Diamond integrates fiber optic rotary joints (FORJs) into our Roll-Ring® designs. Diamond works with its FORJ partner to provide single and multi channel FORJs. The FORJ is used on the very high data rate channels or on circuits requiring very low crosstalk. In these applications the Roll-Ring® would be used to transmit power and more traditional, low data rate control signals. Diamond and its FORJ partner can also provide the hardware to perform the EO/OE (electrical to optical) conversion.

Defining the Mechanical Requirements

1. Operating speed (rpm) is an important design parameter because it helps drive bearing selection which in turn drives costs.

2. Duty cycle of the application – This is an essential parameter to understand when selecting components such as bearings and seals.

Duty cycle questions to consider include:

• Will the unit rotate at a single continuous speed? Will it do so 24 hrs per day / 7 days per week / 365 days a year?
• Will the unit rotate thru several different speed & duration profiles? If so how often do they repeat? Is there a period of static operation? Is direction of rotation constant?

3. Design life or target MTBR / MTBF (Mean Time to Repair / Mean Time between Failures). It is necessary to understand the design life and how it is measured. Used in combination with duty cycle it allows Diamond engineers to make cost effective design trade offs.

Defining the Environmental Requirements

Questions to consider and ranges to define include:

• Will the unit be operating in an extreme temperature regime?
• Will the unit be exposed to radiation?
• Will the unit be exposed to the elements (rain, snow, high humidity, dust, …)?
• Will the unit be exposed to shock or vibration? What type (road, drop, gun fire…)?

Defining RoHS / WEEE Requirements

Beyond the Sale - Program Requirements

That is why Diamond engages with the entire organization. In order to meet ever increasing quality standards such as Six-Sigma many organizations have defined stringent acceptance testing and product qualification processes. Other organizations are not as formally structured or industry standards are not clear. These customers often rely on Diamond’s expertise and guidance in these areas.

Questions to consider include:

• Is there a formal process to approve a purchase specification? Is one or more design review required (for a custom design)?
• Is a first article report required on the base technology or each design?
• Is a vendor audit required? If so how often?
• Is there a defined Acceptance Test Plan (ATP)?
• Is there a defined, stage gated Product Qualification process? If so is there a clear predefined Qualification test requirement?
• If MIL specifications are referenced - is MIL test certification required?
• Are there regulatory hurdles (such as licenses, CE Mark or UL approval) that must be addressed?

Diamond’s engineers will work to clearly identify all of the programmatic requirements and to provide the highest level of customer service possible.

For assistance specifying your Roll-Ring® requirements please contact us at engineering@diamond-roltraon.com.