System

Surgical Robot System, session 354. Prior sessions established decomposition for six subsystems: Motion Control, Energy Delivery, Power Management, Safety and Watchdog, Surgeon Input Console, and Surgical Instrument. This session focused on the {{entity:Haptic Feedback Subsystem}} — the highest safety-criticality of the two remaining undecomposed subsystems — and resolved orphaned trace links from the Surgeon Input Console session.

Decomposition

The {{entity:Haptic Feedback Subsystem}} decomposes into four components forming a serial force chain from patient contact to surgeon hand. The {{entity:Force Sensing Module}} ({{hex:D4C51008}}) sits in the sterile field at the instrument tip, measuring six-axis interaction forces. The {{entity:Force Signal Conditioner}} ({{hex:D4A51018}}) performs analog conditioning, digitisation at 1kHz, and galvanic isolation ≥4kVrms. The {{entity:Haptic Controller}} ({{hex:54FD7208}}) executes the 1kHz render loop, scaling and tremor-filtering before commanding the {{entity:Master Handle Actuator}} ({{hex:D7F51008}}), a seven-DOF backdrivable brushless DC assembly in the surgeon console.

The key architectural decision ({{arc:ARC-MAIN-014}}) is the placement of the isolation barrier: a conductive path between patient side and surgeon side would violate IEC 60601-1 patient leakage limits. The Force Signal Conditioner is therefore the single safety-critical boundary in the haptic chain. Fibre-optic links were considered and rejected on sterile-field power budget grounds; an integrated single-controller architecture was rejected because it collapses this boundary.

flowchart TB
  n0["Force Sensing Module"]
  n1["Force Signal Conditioner"]
  n2["Force Signal Conditioner"]
  n3["Master Handle Actuator"]
  n0 -->|strain gauge signals| n1
  n1 -->|SPI 16-bit force data| n2
  n2 -->|CAN FD torque setpoints| n3

Analysis

UHT classification highlights an important distinction in this chain. The {{entity:Force Sensing Module}} and {{entity:Master Handle Actuator}} are Physical Objects (bit 1 present); the {{entity:Haptic Controller}} is not — it is classified as firmware executing on a safety-rated CPU, giving it the {{trait:Processes Signals/Logic}}, {{trait:Rule-governed}}, and {{trait:Temporal}} traits absent from the hardware components. This ontological split correctly identifies where the SIL2 obligation sits: on the software executing the render loop, not on the motor hardware.

Trait-based similarity search found Magnetorquer System ({{hex:54F53208}}, 30 shared traits with Haptic Controller) as the closest cross-domain analog. Spacecraft magnetorquers generate precisely controlled multi-axis torques at high update rates against a varying external impedance — structurally identical to the haptic render problem. The magnetorquer desaturation challenge (managing angular momentum accumulation in reaction wheels) has a direct analog in haptic systems: energy accumulation at virtual walls during stiff tissue contact, which drives {{trait:State-Transforming}} instability. The Z-width passivity constraint in {{sub:SUB-MAIN-063}} addresses the same physics that magnetorquer momentum management addresses in spacecraft attitude control — both are energy-bounded stability problems.

Lint identified {{entity:haptic feedback subsystem}} ({{hex:55F57018}}) as Regulated without compliance requirements. {{sub:SUB-MAIN-065}} adds the IEC 60601-1 Type CF applied part requirement. Cybersecurity findings for closed-loop internal digital controllers (kinematics engine, trajectory generator, tool tip articulation controller, energy delivery controller) were acknowledged as ontologically correct for components with no external network interface — risk is addressed at the system boundary.

Requirements

Three new subsystem requirements added this session. {{sub:SUB-MAIN-062}} requires the {{entity:Haptic Controller}} to achieve IEC 62061 SIL2 with safe-state transition to zero-torque within 10ms, derived from the force measurement safety obligation in {{sys:SYS-MAIN-004}}. {{sub:SUB-MAIN-063}} constrains the render loop to remain stable across tissue stiffness 0.1–10 N/mm and all scaling ratios — the Magnetorquer analog reinforces this is a boundary-driven, not a worst-case, requirement. {{sub:SUB-MAIN-064}} limits Master Handle Actuator backdrive torque to ≤0.05 Nm in STANDBY/DISABLED state, derived from {{sys:SYS-MAIN-001}} motion scaling. {{sub:SUB-MAIN-065}} establishes IEC 60601-1 Type CF compliance for the subsystem. Verification entries {{ver:VER-MAIN-047}} and {{ver:VER-MAIN-048}} cover the SIL2 assessment and full-envelope stability sweep respectively.

Six orphaned requirements from prior sessions were linked: {{ifc:IFC-MAIN-037}}, {{sub:SUB-MAIN-056}}, {{sub:SUB-MAIN-057}}, {{sub:SUB-MAIN-060}}, {{sub:SUB-MAIN-061}}, and {{ver:VER-MAIN-046}}, all gaining trace links to their parent system requirements.

Next

Vision and Imaging System PART_OF facts are confirmed as already stored. That subsystem’s internal block diagram is empty and needs blocks added from the six named components. The 64 low-severity lint findings include several compliance requirements missing from regulated subsystems (motion control, power management, console computer) — these can be addressed in a QC pass. With Haptic Feedback now complete, first-pass decomposition requires only the Vision diagram to be populated before status can advance to first-pass-complete.