"""Push and retract a STEP-derived wedge under a guided spring follower.""" 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("Wedge volume must be positive") bounds = shape.BoundingBox() inertia = props.MatrixOfInertia() density = setup["material_density_kg_m3"] envelope = cq.Solid.makeBox(500, 100, 50, cq.Vector(-250, 0, -25)) mount = cq.Solid.makeBox(10, 10, 50, cq.Vector(-250, 0, -25)) 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(envelope).Volume(), "mount_missing_mm3": mount.cut(shape).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 ch.ChCollisionModel.SetDefaultSuggestedEnvelope(1e-5) ch.ChCollisionModel.SetDefaultSuggestedMargin(1e-5) system = ch.ChSystemNSC() system.SetCollisionSystemType(ch.ChCollisionSystem.Type_BULLET) system.SetGravitationalAcceleration(ch.ChVector3d(0, -setup["gravity_m_s2"], 0)) material = ch.ChContactMaterialNSC() material.SetFriction(setup["contact_friction"]) ground = ch.ChBody() ground.SetFixed(True) system.Add(ground) radius = setup["follower_radius_m"] follower_mass = setup["follower_mass_kg"] follower = ch.ChBodyEasySphere( radius, follower_mass / (4 * math.pi * radius ** 3 / 3), False, True, material) reference_height = setup["follower_reference_height_m"] follower.SetPos(ch.ChVector3d(0, reference_height, 0)) system.Add(follower) follower_guide = ch.ChLinkLockPrismatic() follower_guide.Initialize(follower, ground, ch.ChFramed( ch.ChVector3d(0, reference_height, 0), ch.QuatFromAngleAxis(-math.pi / 2, ch.VECT_X))) system.Add(follower_guide) spring = ch.ChForce() follower.AddForce(spring) spring.SetMode(ch.ChForce.FORCE) spring.SetDir(ch.ChVector3d(0, 1, 0)) center = [value / 1000 for value in properties["center_of_mass_mm"]] origin = setup["wedge_initial_cad_origin_m"] wedge = ch.ChBody() wedge.SetMass(properties["mass_kg"]) inertia = ch.ChMatrix33d() inertia.SetMatr(properties["inertia_tensor_kg_m2"]) wedge.SetInertia(inertia) wedge.SetPos(ch.ChVector3d(*(origin[i] + center[i] for i in range(3)))) 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])) wedge.AddCollisionShape(ch.ChCollisionShapeConvexHull(material, points)) wedge.EnableCollision(True) system.Add(wedge) wedge_guide = ch.ChLinkLockPrismatic() wedge_guide.Initialize(wedge, ground, ch.ChFramed( ch.ChVector3d(*origin), ch.QuatFromAngleAxis(math.pi / 2, ch.VECT_Y))) system.Add(wedge_guide) push = ch.ChForce() wedge.AddForce(push) push.SetMode(ch.ChForce.FORCE) push.SetDir(ch.ChVector3d(1, 0, 0)) dt = setup["time_step_s"] steps = round(setup["duration_s"] / dt) if dt <= 0 or abs(steps * dt - setup["duration_s"]) > 1e-12: raise ValueError("Invalid simulation duration or time step") peak_height = reference_height peak_wedge_x = origin[0] first_lift_s = None for i in range(steps): t = i * dt spring.SetMforce(follower_mass * setup["gravity_m_s2"] - setup["follower_spring_stiffness_N_m"] * (follower.GetPos().y - reference_height)) push.SetMforce(setup["push_force_N"] if t < setup["push_duration_s"] else -setup["reverse_force_N"]) system.DoStepDynamics(dt) height = follower.GetPos().y cad_x = wedge.GetPos().x - center[0] if not math.isfinite(height + cad_x): raise ValueError("Nonfinite wedge or follower trajectory") if t < setup["push_duration_s"]: peak_height = max(peak_height, height) peak_wedge_x = max(peak_wedge_x, cad_x) if height >= setup["target_follower_height_m"] and first_lift_s is None: first_lift_s = (i + 1) * dt return { "peak_push_follower_height_m": peak_height, "peak_push_wedge_cad_origin_x_m": peak_wedge_x, "first_target_lift_s": first_lift_s, "returned_follower_height_m": follower.GetPos().y, "retracted_wedge_cad_origin_x_m": wedge.GetPos().x - center[0], } 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_below_target": bs["first_target_lift_s"] is None, "target_lift_reached": gs["first_target_lift_s"] is not None, "lift_gain": gs["peak_push_follower_height_m"] - bs["peak_push_follower_height_m"] >= setup["minimum_lift_gain_m"], "wedge_retracted": gs["retracted_wedge_cad_origin_x_m"] <= setup["maximum_retracted_wedge_x_m"], "follower_returned": gs["returned_follower_height_m"] <= setup["maximum_returned_follower_height_m"], "mass_fixed": abs(ap["mass_kg"] / bp["mass_kg"] - 1) <= setup["maximum_relative_mass_change"], "envelope_fixed": all(abs(a - b) <= setup["maximum_envelope_change_mm"] for a, b in zip(ap["bounds_mm"], bp["bounds_mm"])), "outer_envelope_kept": ap["external_added_mm3"] <= setup["maximum_external_added_mm3"], "mounting_foot_intact": ap["mount_missing_mm3"] <= setup["maximum_mount_missing_mm3"], } 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 follower height: {bs['peak_push_follower_height_m']} -> " f"{gs['peak_push_follower_height_m']} m") print(f"Task passed: {after['comparison_to_before']['passed']}") if not after["comparison_to_before"]["passed"]: raise SystemExit(1) if __name__ == "__main__": main()