#!/usr/bin/env python3 """Mechanical clearance checks for the current CBM G1 assembly. This is an interference/stack-up check, not a substitute for tolerance analysis on vendor-returned CAD, insertion-force testing, or enclosure FEA. """ from __future__ import annotations import argparse import math from dataclasses import dataclass from pathlib import Path from cadquery import importers ROOT = Path(__file__).resolve().parent BIOCOIN_STEP = ROOT / "vendor" / "Biocoin_v1.3.step" @dataclass(frozen=True) class Design: shell_od: float = 44.0 shell_wall: float = 1.5 shell_inner_top: float = 18.00 shell_top: float = 19.00 daughterboard_od: float = 38.0 daughterboard_bottom: float = 2.24 daughterboard_thickness: float = 0.80 daughter_component_height: float = 1.60 cartridge_connector_initial: float = 2.54 cartridge_connector_working: float = 2.24 cartridge_connector_stroke: float = 0.61 biocoin_connector_initial: float = 6.782 biocoin_connector_working: float = 6.08 biocoin_connector_stroke: float = 1.397 battery_x: float = -11.50 battery_y: float = 0.0 battery_diameter: float = 12.10 battery_height: float = 4.0 battery_bottom: float = 12.95 battery_rf_keepout: float = 2.0 lmp_radius: float = 15.80 lmp_radial_size: float = 3.90 daughter_edge_keepout: float = 1.0 cartridge_frame_od: float = 40.0 adhesive_od: float = 54.0 adhesive_bottom: float = -0.87 needle_tip: float = -1.65 connector_contacts: int = 12 connector_force_gf_each: float = 60.0 latch_safety_factor: float = 2.5 @property def shell_inner_radius(self) -> float: return self.shell_od / 2 - self.shell_wall @property def daughterboard_top(self) -> float: return self.daughterboard_bottom + self.daughterboard_thickness @property def board_bottom_plane(self) -> float: return self.daughterboard_top + self.biocoin_connector_working @property def battery_top(self) -> float: return self.battery_bottom + self.battery_height @dataclass class Check: name: str actual: float minimum: float unit: str = "mm" note: str = "" @property def passed(self) -> bool: return self.actual + 1e-9 >= self.minimum def circle_to_rect_clearance( cx: float, cy: float, radius: float, xmin: float, xmax: float, ymin: float, ymax: float, ) -> float: nearest_x = min(max(cx, xmin), xmax) nearest_y = min(max(cy, ymin), ymax) return math.hypot(cx - nearest_x, cy - nearest_y) - radius def analyze() -> tuple[Design, dict[str, float], list[Check]]: d = Design() model = importers.importStep(str(BIOCOIN_STEP)).val() bbox = model.BoundingBox() solids = model.Solids() pcb = max(solids, key=lambda solid: solid.Volume()) pcb_box = pcb.BoundingBox() raytac = min( solids, key=lambda solid: abs(solid.BoundingBox().xlen - 15.5) + abs(solid.BoundingBox().ylen - 10.5) + abs(solid.BoundingBox().zlen - 2.05), ) ray_box = raytac.BoundingBox() fpc = min( solids, key=lambda solid: abs(solid.BoundingBox().xlen - 3.6) + abs(solid.BoundingBox().ylen - 11.7) + abs(solid.BoundingBox().zlen - 1.9), ) fpc_box = fpc.BoundingBox() center_x = (bbox.xmin + bbox.xmax) / 2 center_y = (bbox.ymin + bbox.ymax) / 2 z_shift = d.board_bottom_plane - pcb_box.zmin board_model_bottom = bbox.zmin + z_shift board_model_top = bbox.zmax + z_shift daughter_components_top = d.daughterboard_top + d.daughter_component_height board_half_diagonal = math.hypot(bbox.xlen / 2, bbox.ylen / 2) battery_radius = d.battery_diameter / 2 battery_outer_radius = math.hypot(d.battery_x, d.battery_y) + battery_radius ray_clearance = circle_to_rect_clearance( d.battery_x, d.battery_y, battery_radius, ray_box.xmin - center_x, ray_box.xmax - center_x, ray_box.ymin - center_y, ray_box.ymax - center_y, ) lmp_outer_radius = d.lmp_radius + d.lmp_radial_size / 2 connector_force_n = ( d.connector_contacts * d.connector_force_gf_each * 0.00980665 ) checks = [ Check( "Biocoin populated XY envelope inside shell", d.shell_inner_radius - board_half_diagonal, 1.5, note="Conservative rectangular-envelope diagonal.", ), Check( "Daughterboard edge inside shell", d.shell_inner_radius - d.daughterboard_od / 2, 1.0, ), Check( "LMP7721 package edge on daughterboard", d.daughterboard_od / 2 - lmp_outer_radius, d.daughter_edge_keepout, ), Check( "Biocoin bottom component to daughterboard components", board_model_bottom - daughter_components_top, 0.5, note="Excludes the four intentional spring-header interfaces.", ), Check( "Battery to highest Biocoin component", d.battery_bottom - board_model_top, 0.8, ), Check( "Battery to shell inner top", d.shell_inner_top - d.battery_top, 0.8, ), Check( "Battery radial edge to shell", d.shell_inner_radius - battery_outer_radius, 2.0, ), Check( "Battery XY clearance from full Raytac module body", ray_clearance, d.battery_rf_keepout, note="Conservative: clears the entire module, not only its antenna.", ), Check( "Cartridge connector compression", d.cartridge_connector_initial - d.cartridge_connector_working, 0.30, note=f"Full available stroke {d.cartridge_connector_stroke:.2f} mm.", ), Check( "Biocoin header compression", d.biocoin_connector_initial - d.biocoin_connector_working, 0.69, note=f"Full available stroke {d.biocoin_connector_stroke:.3f} mm.", ), Check( "Needle protrusion beyond adhesive skin plane", d.adhesive_bottom - d.needle_tip, 0.70, ), Check( "Latch retention design load", connector_force_n * d.latch_safety_factor, 17.5, unit="N", note=f"Connector preload ≈ {connector_force_n:.2f} N.", ), ] measured = { "biocoin_x": bbox.xlen, "biocoin_y": bbox.ylen, "biocoin_z": bbox.zlen, "pcb_thickness": pcb_box.zlen, "biocoin_bottom_component_depth": pcb_box.zmin - bbox.zmin, "biocoin_top_component_height": bbox.zmax - pcb_box.zmax, "fpc_x": fpc_box.xlen, "fpc_y": fpc_box.ylen, "fpc_z": fpc_box.zlen, "board_model_bottom": board_model_bottom, "board_model_top": board_model_top, "raytac_x": ray_box.xlen, "raytac_y": ray_box.ylen, "raytac_z": ray_box.zlen, "connector_force_n": connector_force_n, } return d, measured, checks def markdown(d: Design, measured: dict[str, float], checks: list[Check]) -> str: rows = [] for check in checks: rows.append( f"| {'PASS' if check.passed else 'FAIL'} | {check.name} | " f"{check.actual:.2f} {check.unit} | ≥ {check.minimum:.2f} " f"{check.unit} | {check.note} |" ) status = "PASS" if all(check.passed for check in checks) else "FAIL" return f"""# CBM G1 — Mechanical Fit Report Generated by `cad/validate_mechanical_stack.py` from the actual upstream `Biocoin_v1.3.step`. Overall geometric stack status: **{status}** ## Measured upstream geometry - populated Biocoin envelope: **{measured['biocoin_x']:.3f} × {measured['biocoin_y']:.3f} × {measured['biocoin_z']:.3f} mm** - PCB thickness in STEP: **{measured['pcb_thickness']:.3f} mm** - deepest bottom-side component below PCB: **{measured['biocoin_bottom_component_depth']:.3f} mm** - highest top-side component above PCB: **{measured['biocoin_top_component_height']:.3f} mm** - Molex FPC body envelope: **{measured['fpc_x']:.3f} × {measured['fpc_y']:.3f} × {measured['fpc_z']:.3f} mm** - Raytac module envelope: **{measured['raytac_x']:.3f} × {measured['raytac_y']:.3f} × {measured['raytac_z']:.3f} mm** ## Frozen axial stack | Plane | Z (mm) | | --- | ---: | | cartridge hard-gold pad plane | 0.00 | | interface daughterboard bottom | {d.daughterboard_bottom:.2f} | | interface daughterboard top | {d.daughterboard_top:.2f} | | Biocoin PCB bottom pad plane | {d.board_bottom_plane:.2f} | | populated Biocoin lowest point | {measured['board_model_bottom']:.2f} | | populated Biocoin highest point | {measured['board_model_top']:.2f} | | CP1240 battery bottom | {d.battery_bottom:.2f} | | CP1240 battery top | {d.battery_top:.2f} | | shell inner ceiling | {d.shell_inner_top:.2f} | | shell exterior top | {d.shell_top:.2f} | ## Clearance checks | Result | Check | Actual | Requirement | Note | | --- | --- | ---: | ---: | --- | {chr(10).join(rows)} ## Assembly hardware now represented - four upstream-exact Biocoin docking headers: `855-22-010-10-001101` ×2 and `855-22-008-10-001101` ×2; - one 12-position ultra-low-profile cartridge connector: `817-22-012-30-001101`, modeled at 2.24 mm working height; - one 38 mm full daughterboard carrying six LMP7721 buffers, ADS124S08, connector footprints, guarded routing, and the cartridge connector; - an offset, tabbed VARTA CP1240 in a shell-supported cradle, with a JST ACHR-02V-S / SACH-003G-P0.2 harness to the Biocoin battery header; - four board-edge capture clips derived from the upstream Biocoin fixture; - three cartridge snap hooks and a hard compression stop sized for at least **{measured['connector_force_n'] * d.latch_safety_factor:.1f} N** retention; - a die-cut contact gasket and a separate enclosure seam gasket. ## What this report does not prove - molded snap-hook fatigue or release force (requires FEA and cycle testing); - gasket compression set and sweat-ingress performance; - actual antenna efficiency in the final enclosure (requires VNA/OTA testing); - connector coplanarity after real assembly; - microneedle insertion, fracture, coating, and biological performance; - vendor tolerances until production drawings and return CAD are received. """ def main() -> None: parser = argparse.ArgumentParser() parser.add_argument("--write-report", type=Path) args = parser.parse_args() design, measured, checks = analyze() report = markdown(design, measured, checks) print(report) if args.write_report: args.write_report.write_text(report) if not all(check.passed for check in checks): raise SystemExit(1) if __name__ == "__main__": main()