| """Measure rotation and rebound against a STEP-derived rocker stop lug.""" |
|
|
| import argparse |
| import hashlib |
| import json |
| import math |
| import subprocess |
| import sys |
| from pathlib import Path |
|
|
|
|
| ROOT = Path(__file__).resolve().parent |
|
|
|
|
| def measure(step: Path, setup: dict) -> dict: |
| import cadquery as cq |
| from OCP.BRepGProp import BRepGProp |
| from OCP.GProp import GProp_GProps |
|
|
| shape = cq.importers.importStep(str(step)).val() |
| if shape.ShapeType() != "Solid" or not shape.isValid() or len(shape.Solids()) != 1: |
| raise ValueError(f"Expected one valid solid: {step}") |
| props = GProp_GProps() |
| BRepGProp.VolumeProperties_s(shape.wrapped, props) |
| if props.Mass() <= 0: |
| raise ValueError("Rocker volume must be positive") |
| density = setup["material_density_kg_m3"] |
| inertia = props.MatrixOfInertia() |
| bounds = shape.BoundingBox() |
| base = cq.Workplane("XY").box(120, 20, 20).translate((50, 0, 0)).val() |
| lug_region = cq.Solid.makeBox(20, 25, 20, cq.Vector(70, 10, -10)) |
| pocket_region = cq.Solid.makeBox(30, 8, 20, cq.Vector(30, -4, -10)) |
| bore = cq.Solid.makeCylinder(5, 20, cq.Vector(0, 0, -10)) |
| return { |
| "step_sha256": hashlib.sha256(step.read_bytes()).hexdigest(), |
| "volume_mm3": props.Mass(), |
| "mass_kg": props.Mass() * density * 1e-9, |
| "center_of_mass_mm": list(props.CentreOfMass().Coord()), |
| "inertia_tensor_kg_m2": [ |
| [inertia.Value(i, j) * density * 1e-15 for j in (1, 2, 3)] |
| for i in (1, 2, 3) |
| ], |
| "bounds_mm": [bounds.xmin, bounds.xmax, bounds.ymin, bounds.ymax, |
| bounds.zmin, bounds.zmax], |
| "external_added_mm3": shape.cut(base).cut(lug_region).Volume(), |
| "base_removed_mm3": base.cut(shape).cut(pocket_region).cut(bore).Volume(), |
| "pivot_bore_intrusion_mm3": shape.intersect(bore).Volume(), |
| "collision_vertices_mm": [[v.X, v.Y, v.Z] for v in shape.Vertices()], |
| } |
|
|
|
|
| def dynamics(properties: dict, setup: dict) -> dict: |
| import pychrono as ch |
|
|
| center = [value / 1000 for value in properties["center_of_mass_mm"]] |
| mass = properties["mass_kg"] |
| inertia_tensor = properties["inertia_tensor_kg_m2"] |
| pivot_inertia = inertia_tensor[2][2] + mass * (center[0] ** 2 + center[1] ** 2) |
| speed = setup["angular_impulse_N_m_s"] / pivot_inertia |
| angle = 0.0 |
| pivot_to_center = ( |
| center[0] * math.cos(angle) - center[1] * math.sin(angle), |
| center[0] * math.sin(angle) + center[1] * math.cos(angle), |
| ) |
| system = ch.ChSystemSMC() |
| system.UseMaterialProperties(False) |
| system.SetCollisionSystemType(ch.ChCollisionSystem.Type_BULLET) |
| system.SetGravitationalAcceleration(ch.ChVector3d(0, 0, 0)) |
| material = ch.ChContactMaterialSMC() |
| material.SetFriction(setup["contact_friction"]) |
| material.SetKn(setup["contact_stiffness_N_m"]) |
| material.SetGn(setup["contact_damping_N_s_m"]) |
| ground = ch.ChBody() |
| ground.SetFixed(True) |
| system.Add(ground) |
| stop = ch.ChBodyEasyBox( |
| *setup["stop_size_m"], 1000, False, True, material) |
| stop.SetPos(ch.ChVector3d(*setup["stop_center_m"])) |
| stop.SetFixed(True) |
| system.Add(stop) |
| rocker = ch.ChBody() |
| rocker.SetMass(mass) |
| inertia = ch.ChMatrix33d() |
| inertia.SetMatr(inertia_tensor) |
| rocker.SetInertia(inertia) |
| rocker.SetRot(ch.QuatFromAngleAxis(angle, ch.VECT_Z)) |
| rocker.SetPos(ch.ChVector3d(*pivot_to_center, center[2])) |
| rocker.SetAngVelParent(ch.ChVector3d(0, 0, speed)) |
| rocker.SetLinVel(ch.ChVector3d(-speed * pivot_to_center[1], |
| speed * pivot_to_center[0], 0)) |
| points = ch.vector_ChVector3d() |
| for x, y, z in properties["collision_vertices_mm"]: |
| points.push_back(ch.ChVector3d(x / 1000 - center[0], |
| y / 1000 - center[1], |
| z / 1000 - center[2])) |
| rocker.AddCollisionShape(ch.ChCollisionShapeConvexHull(material, points)) |
| rocker.EnableCollision(True) |
| system.Add(rocker) |
| hinge = ch.ChLinkLockRevolute() |
| hinge.Initialize(rocker, ground, ch.ChFramed(ch.ChVector3d(0, 0, 0))) |
| system.Add(hinge) |
| dt = setup["time_step_s"] |
| steps = round(setup["duration_s"] / dt) |
| if dt <= 0 or steps <= 0 or abs(steps * dt - setup["duration_s"]) > 1e-12: |
| raise ValueError("Invalid simulation duration or time step") |
| contact_steps = 0 |
| peak_angle = 0.0 |
| peak_rebound_speed = 0.0 |
| peak_pivot_reaction = 0.0 |
| peak_stop_contact_force = 0.0 |
| for _ in range(steps): |
| system.DoStepDynamics(dt) |
| q = rocker.GetRot() |
| current_angle = 2 * math.atan2(q.e3, q.e0) |
| peak_angle = max(peak_angle, current_angle) |
| contact_force = rocker.GetContactForce().Length() |
| peak_stop_contact_force = max(peak_stop_contact_force, contact_force) |
| if contact_force > 1e-8: |
| contact_steps += 1 |
| if contact_steps: |
| peak_rebound_speed = max(peak_rebound_speed, |
| -rocker.GetAngVelParent().z) |
| reaction = hinge.GetReaction1().force |
| peak_pivot_reaction = max(peak_pivot_reaction, |
| math.hypot(reaction.x, reaction.y)) |
| if not all(math.isfinite(x) for x in |
| (peak_angle, peak_rebound_speed, peak_pivot_reaction, |
| peak_stop_contact_force)): |
| raise ValueError("Nonfinite rocker response") |
| return { |
| "peak_angle_rad": peak_angle, |
| "peak_rebound_speed_rad_s": peak_rebound_speed, |
| "peak_pivot_reaction_N": peak_pivot_reaction, |
| "peak_stop_contact_force_N": peak_stop_contact_force, |
| "contact_steps": contact_steps, |
| "initial_angular_speed_rad_s": speed, |
| "angular_impulse_N_m_s": pivot_inertia * speed, |
| "steps": steps, |
| } |
|
|
|
|
| def invoke(python: str, phase: str, payload: dict) -> dict: |
| run = subprocess.run( |
| [python, str(Path(__file__).resolve()), "--phase", phase], |
| input=json.dumps(payload), text=True, capture_output=True, check=False, |
| ) |
| if run.returncode: |
| raise RuntimeError(f"{phase} failed:\n{run.stderr[-1600:]}") |
| return json.loads(run.stdout) |
|
|
|
|
| def main() -> None: |
| parser = argparse.ArgumentParser() |
| parser.add_argument("--cad-python", default=sys.executable) |
| parser.add_argument("--physics-python", default=sys.executable) |
| parser.add_argument("--phase", choices=("measure", "dynamics")) |
| args = parser.parse_args() |
| if args.phase: |
| payload = json.load(sys.stdin) |
| result = (measure(Path(payload["step"]), payload["setup"]) |
| if args.phase == "measure" |
| else dynamics(payload["properties"], payload["setup"])) |
| print(json.dumps(result)) |
| return |
|
|
| setup = json.loads((ROOT / "setup.json").read_text()) |
| results = {} |
| for name in ("before", "after"): |
| properties = invoke(args.cad_python, "measure", { |
| "step": str(ROOT / f"{name}.step"), "setup": setup, |
| }) |
| results[name] = { |
| "step_properties": properties, |
| "simulation_result": invoke(args.physics_python, "dynamics", { |
| "properties": properties, "setup": setup, |
| }), |
| } |
| before = results["before"] |
| after = results["after"] |
| bp = before["step_properties"] |
| ap = after["step_properties"] |
| bs = before["simulation_result"] |
| gs = after["simulation_result"] |
| checks = { |
| "baseline_rotates": bs["peak_angle_rad"] >= |
| setup["minimum_baseline_peak_angle_rad"], |
| "baseline_rebounds": bs["peak_rebound_speed_rad_s"] >= |
| setup["minimum_baseline_rebound_speed_rad_s"], |
| "rotation_limited": gs["peak_angle_rad"] <= |
| setup["maximum_peak_angle_rad"], |
| "rebound_limited": gs["peak_rebound_speed_rad_s"] <= |
| setup["maximum_peak_rebound_speed_rad_s"], |
| "pivot_reaction_limited": gs["peak_pivot_reaction_N"] <= |
| setup["maximum_peak_pivot_reaction_N"], |
| "mass_fixed": abs(ap["mass_kg"] / bp["mass_kg"] - 1) |
| <= setup["maximum_relative_mass_change"], |
| "mount_envelope_fixed": all( |
| abs(ap["bounds_mm"][i] - bp["bounds_mm"][i]) <= |
| setup["maximum_mount_envelope_change_mm"] |
| for i in (0, 1, 2, 4, 5)) and |
| ap["bounds_mm"][3] <= setup["maximum_lug_height_mm"], |
| "edits_in_allowed_regions": ap["external_added_mm3"] |
| <= setup["maximum_external_added_mm3"] and |
| ap["base_removed_mm3"] <= setup["maximum_base_removed_mm3"], |
| "pivot_bore_clear": ap["pivot_bore_intrusion_mm3"] |
| <= setup["maximum_pivot_bore_intrusion_mm3"], |
| "stop_contact_observed": bs["contact_steps"] > 0 and |
| gs["contact_steps"] > 0, |
| } |
| after["comparison_to_before"] = { |
| "checks": checks, |
| "passed": all(checks.values()), |
| } |
| for name, result in results.items(): |
| (ROOT / f"{name}.results.json").write_text(json.dumps(result, indent=2) + "\n") |
| print(f"Peak angle: {bs['peak_angle_rad']} -> {gs['peak_angle_rad']} rad") |
| print(f"Peak rebound speed: {bs['peak_rebound_speed_rad_s']} -> " |
| f"{gs['peak_rebound_speed_rad_s']} rad/s") |
| print(f"Task passed: {after['comparison_to_before']['passed']}") |
| if not after["comparison_to_before"]["passed"]: |
| raise SystemExit(1) |
|
|
|
|
| if __name__ == "__main__": |
| main() |
|
|
