Module Assembly

skrobot.assembly.module_assembly composes robots out of reusable URDF modules: parse each part once into a RobotModule (its links become connection ports, each a full SE(3) frame), place instances in a RobotAssembly, connect ports, and build a combined URDF or a live RobotModel.

from skrobot.assembly import RobotAssembly, RobotModule

arm = RobotModule.from_urdf('arm', 'arm_module.urdf')
gripper = RobotModule.from_urdf('gripper', 'gripper_module.urdf')

assembly = RobotAssembly('my_robot')
assembly.add_module_instance('arm1', arm)
assembly.add_module_instance('hand', gripper)
# mate=True seats the child port onto the parent port
# (keyed connector: origins coincide, Z opposed, X aligned)
assembly.connect('arm1', 'flange', 'hand', 'base_link', mate=True)
assembly.set_root('arm1', 'base_link')
urdf_path = assembly.build()
robot = assembly.build_robot_model()

Connections are fixed joints by default; pass joint_type='revolute' (or 'continuous' / 'prismatic') to turn the connected port pair itself into an articulation, so linkages can be assembled from bare links with no module-internal joints.

Closed loops

A URDF is a tree, so a closed linkage (four-bar, parallel mechanism) declares its cut edge with connect(..., loop=True): the two ports must coincide at the zero pose and their common Z axis is the passive hinge. build() writes a loop_closures.yaml sidecar (the runtime-IK relay contract) next to the output URDF, injects exact <mimic> tags when the loop is a parallelogram four-bar (verified numerically before writing), and keeps the config on assembly.loop_closures. A general loop is closed in-process with LoopClosureSolver:

from skrobot.kinematics import LoopClosureSolver

robot = assembly.build_robot_model()
solver = LoopClosureSolver(robot, assembly.loop_closures)
robot.crank_joint.joint_angle(0.4)
solver.solve()  # dependent joints updated so the loop closes

See examples/module_assembly_four_bar.py for a complete closed-loop assembly built from bare links.

Classes

`skrobot.assembly.Port`	Represents a connection port on a robot module.
`skrobot.assembly.RobotModule`	Represents an individual URDF part (module) in the robot catalog.
`skrobot.assembly.Connection`	Represents a connection between two module ports.
`skrobot.assembly.RobotAssembly`	Manages the assembly state of multiple robot modules.
`skrobot.kinematics.LoopClosureSolver`	Solve a robot's declared loop closures in place.