Cranial Fixation Ring & Ergonomic Frame
Ti-6Al-4V halo with viscoelastic polymer pads, fiducial markers, and articulated support frame. Maintains <0.2 mm registration drift for procedure duration.
The fixation halo is a single-piece Ti-6Al-4V (ELI grade 23) ring with six contact stations spaced at 60° intervals. Each station carries a viscoelastic polyurethane cushion (Shore 30A, durometer-stable through autoclave) that compresses 2–3 mm under nominal clamping force. The system reaches kinematic seating against the cranial vault without exceeding 4.5 N/cm² of contact pressure, which is well below the published capillary occlusion threshold for scalp tissue.
Three retro-reflective fiducial spheres (Ø 9.5 mm, sub-100 µm sphericity) are embedded in the halo at known geometric offsets. These provide the camera+LiDAR module a rigid optical reference for registering the patient frame to the robot base frame. Registration RMS error after Procrustes alignment is held below 120 µm.
The ergonomic frame is a 3-segment articulated arm with locking ball joints (M6 collet) that anchors the halo to the procedure chair. After clinician-driven coarse positioning, all joints are torqued to 8.5 N·m — verified by an integrated strain-gauge sleeve — producing rated drift below 0.2 mm over a 4-hour procedure window.
| Parameter | Value | Unit | Tolerance / Note |
|---|---|---|---|
| Halo material | Ti-6Al-4V ELI (Grade 23) | ASTM F136 | |
| Halo mass | 380 | g | |
| Contact stations | 6 | 60° spacing | |
| Pad material | Polyurethane Shore 30A | ||
| Max contact pressure | 4.5 | N/cm² | |
| Fiducial diameter | 9.5 | mm | |
| Fiducial sphericity | <100 | µm | |
| Registration RMS error | <120 | µm | |
| Drift over 4 h | <0.20 | mm | |
| Frame torque | 8.5 | N·m | All articulating joints |
| Sterilization | Autoclave 134 °C / 18 min | Halo + frame |