| """Measure lift dwell and filtered follower acceleration for a STEP cam.""" |
|
|
| 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("Cam volume must be positive") |
| bounds = shape.BoundingBox() |
| inertia = props.MatrixOfInertia() |
| density = setup["material_density_kg_m3"] |
| outer = cq.Solid.makeCylinder(120, 20, cq.Vector(0, 0, -10)) |
| bore = cq.Solid.makeCylinder(10, 20, cq.Vector(0, 0, -10)) |
| base_rim = (cq.Solid.makeCylinder(100, 20, cq.Vector(0, 0, -10)) |
| .cut(cq.Solid.makeCylinder(90, 20, cq.Vector(0, 0, -10)))) |
| hub = (cq.Solid.makeCylinder(20, 20, cq.Vector(0, 0, -10)) |
| .cut(bore)) |
| lobe_vertices = [[v.X, v.Y, v.Z] for v in shape.Vertices() |
| if v.Y >= 65 and abs(v.X) <= 85] |
| if len(lobe_vertices) < 6 or max(v[1] for v in lobe_vertices) < 110: |
| raise ValueError("Cam needs a STEP-resolved lift lobe") |
| 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(outer).Volume(), |
| "base_rim_missing_mm3": base_rim.cut(shape).Volume(), |
| "hub_missing_mm3": hub.cut(shape).Volume(), |
| "bore_intrusion_mm3": shape.intersect(bore).Volume(), |
| "lobe_collision_vertices_mm": lobe_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, 0, 0)) |
| material = ch.ChContactMaterialNSC() |
| material.SetFriction(setup["contact_friction"]) |
| ground = ch.ChBody() |
| ground.SetFixed(True) |
| system.Add(ground) |
| center = [value / 1000 for value in properties["center_of_mass_mm"]] |
| angle = setup["initial_cam_angle_rad"] |
| cam = ch.ChBody() |
| cam.SetMass(properties["mass_kg"]) |
| inertia = ch.ChMatrix33d() |
| inertia.SetMatr(properties["inertia_tensor_kg_m2"]) |
| cam.SetInertia(inertia) |
| cam.SetRot(ch.QuatFromAngleAxis(angle, ch.VECT_Z)) |
| cam.SetPos(ch.ChVector3d( |
| center[0] * math.cos(angle) - center[1] * math.sin(angle), |
| center[0] * math.sin(angle) + center[1] * math.cos(angle), center[2])) |
| base_points = ch.vector_ChVector3d() |
| for i in range(64): |
| theta = 2 * math.pi * i / 64 |
| for z in (-0.01, 0.01): |
| base_points.push_back(ch.ChVector3d( |
| 0.1 * math.cos(theta) - center[0], |
| 0.1 * math.sin(theta) - center[1], z - center[2])) |
| lobe_points = ch.vector_ChVector3d() |
| for x, y, z in properties["lobe_collision_vertices_mm"]: |
| lobe_points.push_back(ch.ChVector3d( |
| x / 1000 - center[0], y / 1000 - center[1], z / 1000 - center[2])) |
| cam.AddCollisionShape(ch.ChCollisionShapeConvexHull(material, base_points)) |
| cam.AddCollisionShape(ch.ChCollisionShapeConvexHull(material, lobe_points)) |
| cam.EnableCollision(True) |
| system.Add(cam) |
| hinge = ch.ChLinkLockRevolute() |
| hinge.Initialize(cam, ground, ch.ChFramed(ch.ChVector3d(0, 0, 0))) |
| system.Add(hinge) |
|
|
| reference_y = setup["follower_reference_y_m"] |
| follower = ch.ChBodyEasySphere(setup["follower_radius_m"], |
| setup["follower_density_kg_m3"], |
| False, True, material) |
| follower.SetPos(ch.ChVector3d(0, reference_y, 0)) |
| system.Add(follower) |
| guide = ch.ChLinkLockPrismatic() |
| guide.Initialize(follower, ground, ch.ChFramed( |
| ch.ChVector3d(0, reference_y, 0), |
| ch.QuatFromAngleAxis(-math.pi / 2, ch.VECT_X))) |
| system.Add(guide) |
| spring = ch.ChForce() |
| follower.AddForce(spring) |
| spring.SetMode(ch.ChForce.FORCE) |
| spring.SetDir(ch.ChVector3d(0, 1, 0)) |
| drive = ch.ChForce() |
| cam.AddForce(drive) |
| drive.SetMode(ch.ChForce.TORQUE) |
| drive.SetDir(ch.ChVector3d(0, 0, 1)) |
|
|
| 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") |
| heights = [] |
| speeds = [] |
| for _ in range(steps): |
| spring.SetMforce(-setup["follower_preload_N"] - |
| setup["follower_spring_stiffness_N_m"] * |
| (follower.GetPos().y - reference_y)) |
| error = setup["target_rotation_speed_rad_s"] - cam.GetAngVelParent().z |
| command = setup["speed_controller_gain_N_m_s_rad"] * error |
| limit = setup["maximum_motor_torque_N_m"] |
| drive.SetMforce(max(-limit, min(limit, command))) |
| system.DoStepDynamics(dt) |
| heights.append(follower.GetPos().y) |
| speeds.append(cam.GetAngVelParent().z) |
| if not all(math.isfinite(value) for value in heights + speeds): |
| raise ValueError("Nonfinite cam trajectory") |
| width = max(1, round(setup["acceleration_smoothing_s"] / dt)) |
| smooth = [] |
| for i in range(steps): |
| lo = max(0, i - width // 2) |
| hi = min(steps, i + width // 2 + 1) |
| smooth.append(sum(heights[lo:hi]) / (hi - lo)) |
| span_s = width * dt |
| peak_acceleration = max(abs((smooth[i + width] - 2 * smooth[i] |
| + smooth[i - width]) / span_s ** 2) |
| for i in range(width, steps - width)) |
| return { |
| "peak_follower_height_m": max(heights), |
| "high_dwell_s": sum(value >= setup["high_follower_y_m"] |
| for value in heights) * dt, |
| "filtered_peak_follower_acceleration_m_s2": peak_acceleration, |
| "mean_rotation_speed_rad_s": sum(speeds) / len(speeds), |
| "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_has_short_dwell": bs["high_dwell_s"] |
| < setup["minimum_high_dwell_s"], |
| "useful_high_dwell": gs["high_dwell_s"] |
| >= setup["minimum_high_dwell_s"], |
| "peak_acceleration_reduced": gs["filtered_peak_follower_acceleration_m_s2"] |
| <= bs["filtered_peak_follower_acceleration_m_s2"] * |
| (1 - setup["required_relative_acceleration_reduction"]), |
| "rotation_speed_held": min(bs["mean_rotation_speed_rad_s"], |
| gs["mean_rotation_speed_rad_s"]) |
| >= setup["minimum_mean_rotation_speed_rad_s"], |
| "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_radius_limited": ap["external_added_mm3"] |
| <= setup["maximum_external_added_mm3"], |
| "base_rim_intact": ap["base_rim_missing_mm3"] |
| <= setup["maximum_base_rim_missing_mm3"], |
| "hub_interface_intact": ap["hub_missing_mm3"] |
| <= setup["maximum_hub_missing_mm3"], |
| "shaft_bore_clear": ap["bore_intrusion_mm3"] |
| <= setup["maximum_bore_intrusion_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"High dwell: {bs['high_dwell_s']} -> {gs['high_dwell_s']} s") |
| print(f"Filtered peak acceleration: " |
| f"{bs['filtered_peak_follower_acceleration_m_s2']} -> " |
| f"{gs['filtered_peak_follower_acceleration_m_s2']} m/s^2") |
| print(f"Task passed: {after['comparison_to_before']['passed']}") |
| if not after["comparison_to_before"]["passed"]: |
| raise SystemExit(1) |
|
|
|
|
| if __name__ == "__main__": |
| main() |
|
|
