What the slip ring has to handle
- Very large bore (patient aperture) with the slip ring wrapped around it
- Several kilowatts of power transferred through contacting rings to the X-ray generator and rotating electronics
- Non-contacting high-speed data link (optical or RF/capacitive) for detector data, typically 1-20+ Gbps aggregate
- Bidirectional control channel between stationary and rotating gantry electronics
- High surface speed at the ring circumference: gantry speeds of 120-280 rpm on a large diameter
- Low wear debris, low audible noise and long maintenance-free life
- Tight control of EMI from the data link and power rings, plus patient-safety insulation and leakage requirements
Typical figures
| Speed | Gantry rotation 120-280 rpm; slip rings run at 200+ rpm on a 1 m ring |
|---|---|
| Bore | Inside diameter up to 1270 mm (50 in) |
| Data | Non-contacting data channels 1-20+ Gbps; single optical or RF channels typically 1.25-5 Gbps, spatially multiplexed optical links above 10 Gbps |
| Power | Several kilowatts through contacting power rings |
Example figures from the published sources listed below. Your requirement may differ; an engineer will confirm against your duty cycle.
Recommended slip ring types
Standards to consider
- IEC 60601-1 - general safety and essential performance of medical electrical equipment (insulation, leakage current, protection)
- IEC 60601-1-2 - EMC requirements for medical electrical equipment, relevant to the gantry data link and power rings
- IEC 60601-2-44 - particular requirements for X-ray equipment for computed tomography
The complete system
A slip ring rarely works alone. For cT scanners & medical imaging it is usually specified together with:
- large-diameter gantry bearing
- direct-drive or belt-drive gantry motor
- servo drive
- high-resolution encoder
- contactless data link
- brake
Specifying these together avoids mismatched connectors, cable routes and feedback interfaces, and gives you one point of contact for the whole axis.
Common problems to design out
- Data link errors or EMI affecting image reconstruction
- Brush wear debris contaminating rings and causing arcing or noise
- Audible noise and vibration at high gantry speed
- Contact resistance rise on power rings leading to heating
Series used in this application
Frequently asked questions
Why do CT scanners use contactless data transmission?
Detector data from a modern scanner typically exceeds 1 Gbps in aggregate, which sliding contacts cannot carry reliably. Optical or RF near-field links move the image data across the rotating gap while brushes are kept for power.
How fast does a CT gantry slip ring rotate?
Gantries commonly turn the tube and detector at roughly 120 to 280 rpm. Because the ring is around a metre across, the contact surface speed is very high, which drives brush material choice.
Optical or RF data ring - which is better for CT?
Optical links avoid high-frequency electrical signals on the large ring and can be fully isolated from the structure, which helps EMC. RF near-field links are usually slightly cheaper in electronics. Both typically run 1.25-5 Gbps per channel and can be multiplexed for more.
Sources
- https://www.moog.com/markets/medical-oem/ct-scan-slip-rings.html
- https://www.moog.com/news/blog/Industrial/key-slip-ring-technology-behind-medical-ct-systems.html
- https://www.moog.com/news/blog/Industrial/image-data-transfer-across-a-slip-ring-in-ct-machines.html
- https://www.moog.com/content/dam/moog/literature/MCG/fiberbrush.pdf