| """Test holding and release torque of a CAD-derived over-center clamp.""" |
|
|
| 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.BRepAdaptor import BRepAdaptor_Surface |
| 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("Lever volume must be positive") |
| holes = [] |
| for face in shape.Faces(): |
| if face.geomType() != "CYLINDER": |
| continue |
| cylinder = BRepAdaptor_Surface(face.wrapped).Cylinder() |
| axis = cylinder.Axis().Location() |
| holes.append((cylinder.Radius(), axis.X(), axis.Y())) |
| fixed = sorted([[x, y] for radius, x, y in holes |
| if abs(radius - 5) < 1e-5]) |
| spring_pins = [[x, y] for radius, x, y in holes |
| if abs(radius - 3) < 1e-5] |
| if len(fixed) != 2 or len(spring_pins) != 1: |
| raise ValueError("Expected two 5 mm fixed bores and one 3 mm spring pin bore") |
| bounds = shape.BoundingBox() |
| inertia = props.MatrixOfInertia() |
| density = setup["material_density_kg_m3"] |
| bores = [cq.Solid.makeCylinder(5, 10, cq.Vector(x, y, -5)) |
| for x, y in ((0, 0), (80, 0))] |
| anchor_x, anchor_y = setup["spring_anchor_m"] |
| pin_x, pin_y = (spring_pins[0][0] / 1000, |
| spring_pins[0][1] / 1000) |
| overcenter_angle = (math.atan2(anchor_y, anchor_x) - |
| math.atan2(pin_y, pin_x)) |
| margin = math.radians(setup["closed_angle_deg"]) - overcenter_angle |
| 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], |
| "fixed_pin_centers_mm": fixed, |
| "spring_pin_center_mm": spring_pins[0], |
| "overcenter_margin_rad": margin, |
| "fixed_bore_intrusion_mm3": sum(shape.intersect(bore).Volume() |
| for bore in bores), |
| } |
|
|
|
|
| def dynamics(properties: dict, setup: dict) -> dict: |
| import pychrono as ch |
|
|
| center = [value / 1000 for value in properties["center_of_mass_mm"]] |
| pin = [(properties["spring_pin_center_mm"][i] / 1000 - center[i]) |
| for i in (0, 1)] |
| closed = math.radians(setup["closed_angle_deg"]) |
| anchor_x, anchor_y = setup["spring_anchor_m"] |
| 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") |
| results = {} |
| for release, name in ((False, "hold"), (True, "release")): |
| system = ch.ChSystemNSC() |
| system.SetGravitationalAcceleration(ch.ChVector3d(0, 0, 0)) |
| ground = ch.ChBody() |
| ground.SetFixed(True) |
| system.Add(ground) |
| lever = ch.ChBody() |
| lever.SetMass(properties["mass_kg"]) |
| inertia = ch.ChMatrix33d() |
| inertia.SetMatr(properties["inertia_tensor_kg_m2"]) |
| lever.SetInertia(inertia) |
| lever.SetRot(ch.QuatFromAngleAxis(closed, ch.VECT_Z)) |
| lever.SetPos(ch.ChVector3d( |
| center[0] * math.cos(closed) - center[1] * math.sin(closed), |
| center[0] * math.sin(closed) + center[1] * math.cos(closed), center[2])) |
| system.Add(lever) |
| hinge = ch.ChLinkLockRevolute() |
| hinge.Initialize(lever, ground, ch.ChFramed(ch.ChVector3d(0, 0, 0))) |
| system.Add(hinge) |
| spring = ch.ChForce() |
| lever.AddForce(spring) |
| spring.SetMode(ch.ChForce.FORCE) |
| spring.SetMforce(setup["spring_force_N"]) |
| load = ch.ChForce() |
| lever.AddForce(load) |
| load.SetMode(ch.ChForce.TORQUE) |
| load.SetDir(ch.ChVector3d(0, 0, 1)) |
| stop = ch.ChForce() |
| lever.AddForce(stop) |
| stop.SetMode(ch.ChForce.TORQUE) |
| stop.SetDir(ch.ChVector3d(0, 0, 1)) |
| angle = closed |
| minimum_angle = closed |
| maximum_reaction = 0.0 |
| for i in range(steps): |
| pin_world = lever.TransformPointLocalToParent(ch.ChVector3d( |
| pin[0], pin[1], -center[2])) |
| dx, dy = pin_world.x - anchor_x, pin_world.y - anchor_y |
| distance = math.hypot(dx, dy) |
| if distance <= 1e-6: |
| raise ValueError("Spring pin coincides with fixed spring anchor") |
| spring.SetVpoint(pin_world) |
| spring.SetDir(ch.ChVector3d(dx / distance, dy / distance, 0)) |
| pulse = (setup["release_pulse_torque_N_m"] |
| if release and i * dt < setup["release_pulse_s"] else 0) |
| load.SetMforce(-setup["opening_load_torque_N_m"] - pulse) |
| stop.SetMforce(-setup["stop_stiffness_N_m_rad"] * |
| max(0, angle - closed) - |
| setup["stop_damping_N_m_s_rad"] * |
| lever.GetAngVelParent().z) |
| system.DoStepDynamics(dt) |
| angle += lever.GetAngVelParent().z * dt |
| minimum_angle = min(minimum_angle, angle) |
| reaction = hinge.GetReaction1().force |
| maximum_reaction = max(maximum_reaction, |
| math.hypot(reaction.x, reaction.y)) |
| if not math.isfinite(angle + maximum_reaction): |
| raise ValueError("Nonfinite clamp trajectory") |
| results[name] = {"minimum_angle_rad": minimum_angle, |
| "end_angle_rad": angle, |
| "maximum_pivot_reaction_N": maximum_reaction} |
| return results |
|
|
|
|
| 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_opens_under_load": bs["hold"]["minimum_angle_rad"] |
| <= setup["maximum_baseline_held_angle_rad"], |
| "closed_position_held": gs["hold"]["minimum_angle_rad"] |
| >= setup["minimum_held_angle_rad"], |
| "release_travel_kept": gs["release"]["end_angle_rad"] |
| <= setup["maximum_released_angle_rad"], |
| "overcenter_margin": ap["overcenter_margin_rad"] |
| >= setup["minimum_overcenter_margin_rad"], |
| "pivot_reaction_limited": max( |
| result["maximum_pivot_reaction_N"] for result in gs.values()) |
| <= setup["maximum_pivot_reaction_N"], |
| "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"])), |
| "fixed_pins_intact": all(math.hypot(a[0] - b[0], a[1] - b[1]) |
| <= setup["maximum_fixed_pin_shift_mm"] |
| for a, b in zip(ap["fixed_pin_centers_mm"], |
| bp["fixed_pin_centers_mm"])), |
| "fixed_bores_clear": ap["fixed_bore_intrusion_mm3"] |
| <= setup["maximum_fixed_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"Minimum hold angle: {bs['hold']['minimum_angle_rad']} -> " |
| f"{gs['hold']['minimum_angle_rad']} rad") |
| print(f"Gold release end angle: {gs['release']['end_angle_rad']} rad") |
| print(f"Task passed: {after['comparison_to_before']['passed']}") |
| if not after["comparison_to_before"]["passed"]: |
| raise SystemExit(1) |
|
|
|
|
| if __name__ == "__main__": |
| main() |
|
|
