Coordinate-free semantic assembly

This directory defines the LCD25 reducer as a reusable mechanical design rather than a list of STEP filenames and placement matrices.

Authority

lcd25-harmonic-reducer.assembly-designir.json is the editable assembly authority. It contains:

product parameters and expressions;
replaceable component archetypes;
semantic interfaces constructed from generated geometry;
mating and support relations;
rigid groups, joints and harmonic transmission behavior;
edit operations and interfaces that must remain stable.

It intentionally contains no XYZ position, rotation, transform matrix, source STEP path, or occurrence coordinate. A backend generates each component, discovers its declared interfaces and solves the constraint graph. Numeric placements are compiler output and may be cached separately, but never become design authority.

Generality

The contract is not specific to LCD25. Component identities describe functional roles such as fixed_tooth_member, combined_load_support, and external_output_interface. Each role selects a replaceable generation family. The same contract can express harmonic, planetary, cycloidal, belt, chain and screw transmissions by changing archetypes, relations and the transmission block.

Structural modification

variants/add-output-shaft.patch.json demonstrates a structural edit. It adds:

editable shaft diameter and length;
a generated stepped-shaft component;
coaxial, shoulder-mate, insert and torque-lock relations;
output rigid-group membership;
a new public shaft-end interface.

No coordinate is supplied. The assembly solver must position the shaft from its relations to the output flange.

Validation

Validate the base model:

python3 models/lcd25-reducer/semantic-assembly/validate_assembly_design.py \
  models/lcd25-reducer/semantic-assembly/lcd25-harmonic-reducer.assembly-designir.json \
  --schema designir-pipeline/contracts/assembly-designir-1.0.schema.json

Apply and validate the shaft variant:

python3 models/lcd25-reducer/semantic-assembly/validate_assembly_design.py \
  models/lcd25-reducer/semantic-assembly/lcd25-harmonic-reducer.assembly-designir.json \
  --schema designir-pipeline/contracts/assembly-designir-1.0.schema.json \
  --patch models/lcd25-reducer/semantic-assembly/variants/add-output-shaft.patch.json \
  --resolved-output models/lcd25-reducer/semantic-assembly/generated/lcd25-with-output-shaft.assembly-designir.json

Compiler boundary

The next compiler stage must:

generate or select geometry for each component archetype;
resolve every semantic interface against generated topology;
solve relations from a scrambled initial state;
emit STEP occurrence placements only as derived output;
compile joints and transmissions to URDF/MJCF;
reject underconstrained, overconstrained or interfering assemblies.

The current validator proves schema integrity, coordinate independence, reference integrity and graph connectivity. It does not yet solve B-Rep constraints or generate the final reducer STEP.

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