System

{{entity:Surgical Robot System}} (se-surgical-robot), session 361. The system has been progressing through first-pass decomposition across nine subsystems over multiple sessions. This session targets the remaining gap: the {{entity:Power Management Subsystem}} was structurally classified but had only three subsystem requirements and one interface requirement. The four components — {{entity:Main Power Distribution Unit}}, {{entity:UPS Battery Module}}, {{entity:Auxiliary Power Supply}}, and {{entity:Power Sequencing Controller}} — had hex codes ({{hex:D6851058}}, {{hex:D6D51058}}, {{hex:D4C51018}}, {{hex:D1F77A18}}) and PART_OF facts in place from an earlier session, but their engineering constraints had not been quantified. Session closes by marking the project first-pass-complete.

Decomposition

The {{entity:Power Management Subsystem}} has three functionally distinct layers. The bulk energy path runs from the {{entity:UPS Battery Module}} ({{hex:D6D51058}}) at 48 VDC through a DC link to the {{entity:Main Power Distribution Unit}} ({{hex:D6851058}}), which distributes regulated supply to all subsystems via independently fused branch circuits. Supervision and sequencing sits with the {{entity:Power Sequencing Controller}} ({{hex:D1F77A18}}), which receives branch telemetry via CAN FD at 10 Hz and commands startup order, mains-loss transfer, and orderly shutdown. Separate from the bulk path, the {{entity:Auxiliary Power Supply}} ({{hex:D4C51018}}) maintains a 24 VDC rail exclusively for safety circuits — the {{entity:Safe State Manager}}, {{entity:Emergency Stop Chain}}, and {{entity:Watchdog Timer Controller}} — sourced from its own internal battery, remaining energised for 20 minutes beyond UPS depletion.

flowchart TB
  n0["Main Power Distribution Unit"]
  n1["UPS Battery Module"]
  n2["Auxiliary Power Supply"]
  n3["Power Sequencing Controller"]
  n1 -->|48VDC bulk| n0
  n0 -->|CAN FD status| n3
  n3 -->|discrete control| n2
  n3 -->|sequencing commands| n0

Analysis

The 48 VDC bulk bus voltage is set by the worst-case inrush load: six-axis simultaneous joint engagement draws up to 180 A peak, and the DC-DC converters within the PDU need sufficient headroom to maintain regulated outputs below a 50 mOhm bus impedance. The 30 ms mains-loss transfer budget ({{sub:SUB-MAIN-091}}) is determined by the joint servo controller fault tolerance — exceeding this causes arm re-homing, losing the sterile field.

The {{trait:Galvanic Isolation}} trait on the CAN FD interface between the PDU and PSC ({{ifc:IFC-MAIN-044}}) reflects a known failure mode from prior surgical robot architectures where ground loop noise from the high-current main bus corrupted the low-voltage control bus. The discrete hardware signalling for the PSC-to-AUX interface ({{ifc:IFC-MAIN-046}}) follows from the same logic: bus-based commands cannot be relied upon during the exact power events when the auxiliary circuits need commanding most.

Three previously orphaned requirements were resolved: {{sub:SUB-MAIN-090}} and {{sub:SUB-MAIN-092}} received upstream trace links from {{sys:SYS-MAIN-005}}, and {{ver:VER-MAIN-073}} was linked to {{ifc:IFC-MAIN-001}} where it had been left unconnected in session 341. One acknowledged lint finding: {{arc:ARC-MAIN-019}} carries no upstream trace link, which is correct for an architecture decision entry.

Requirements

Six new subsystem requirements ({{sub:SUB-MAIN-088}}–{{sub:SUB-MAIN-092}}) define the PDU branch circuit sizing per IEC 60601-1 clause 10.2, ground fault detection with 500 µA threshold and 100 ms removal time, UPS SoC telemetry at 1 Hz with ±2% accuracy, mains-loss transfer within 30 ms, and Auxiliary PSU 24 VDC regulation across load range with 20-minute independent endurance. Three new interface requirements ({{ifc:IFC-MAIN-044}}–{{ifc:IFC-MAIN-046}}) define the PDU-PSC CAN FD bus, the UPS-PDU 48 VDC bulk link with impedance and inrush constraints, and the PSC-AUX discrete control channel. Seven new verification entries ({{ver:VER-MAIN-089}}–{{ver:VER-MAIN-095}}) provide test procedures for each new requirement, including ground fault injection, DC link pulse load, mains collapse timing, and SoC calibration across discharge. Project reaches 306 requirements total with 95 verification entries.

Next

First-pass decomposition is complete across all nine subsystems: Safety and Interlock, Motion Control (including infrastructure layer and component-level), Vision and Imaging, Haptic Feedback, Communication and Data Management, Surgical Instrument, Power Management, Energy Delivery, and Surgeon Input Console. DECOMP_STATUS set to first-pass-complete; baseline BL-SESURGICALROBOT-018 created. Next session should run the QC flow (Flow C): lint gap analysis, trace chain completeness, requirement quality review across all 306 entries, and verification coverage reconciliation.