Mini-game
Cavity inspection
How joint motion bends the extension
You control a UR10 arm carrying a passive soft extension: a flexible rod with two tendons. Pulling one tendon bends the rod toward it, as Animation 1 shows. Here the tendons have no motors; anchors on the robot links change their external spans as the joints move, which changes tendon tension (interactive companion of the paper).
The end effector (EE) is the robot tip that holds the extension. Fixing its position still permits redundant joint motions, like moving your elbow while keeping your hand still. The planar toy example shows how varying q₁–q₃ changes the rod shape while the EE position remains fixed. In the game, apply the same principle to aim a tip camera inside a closed housing and identify three damaged parts.
Animation 1 · Direct tendon pull
Planar toy example
Inspection workspace
Use the joint controls to aim the tip camera and report damaged parts.
Joint commandsprojected onto the null space of the EE position constraint
Hold the − and + buttons, or the keys Q/A, W/S, E/D, R/F, T/G and Y/H, to move the joints q₁ to q₆. Press Report or Space when a damaged part is inside the circle of the camera image. Drag the external view to rotate it. P pauses.
How it works
- The end effector stays at the holeEach joint command is projected onto the null space of the EE position constraint, so the joints move without displacing the end effector. A faded joint means that the projection retains less than 25 % of its command.
- The tendons bend the extensionTwo tendons connect anchors on the forearm and first wrist link to the base of the extension. Changing the arm posture changes the external tendon spans and tensions, which bend the extension.
- Tip lighting sets image brightnessThe optical axis and tip light are aligned, so near surfaces appear bright and distant surfaces dark. Coloured arrows indicate unreported damaged parts; an inward arrow means that the part lies inside the report circle.
Damage signatures in tip-camera images
- Disconnected connectorThe plug lies out of its socket and its pins are exposed.
Intact Damaged - Damaged cableThe insulation is torn: copper conductor and loose strands.
Intact Damaged - Cracked bracketThe upright is cracked and bent; a fragment lies next to it.
Intact Damaged - Burnt terminalSoot around one terminal and a charred conductor.
Intact Damaged
Intact examples of the same four part types are installed elsewhere in the housing. The simulation uses the paper's UR10, Cosserat-rod extension, two elastic tendons and controller; the external tendon spans determine the tensions that bend the extension. A joint command u produces q̇ = N_c u + J_c⁺ k_c e_c, where N_c = I − J_c⁺ J_c projects onto the null space of the EE position constraint. Motion stops at contact or at the span-domain limits identified by probing motions. From the initial configuration, a damped least-squares law and a quadratic program with control barrier functions for the walls, housing contents and span domain move the tip to one viewpoint per damaged part. A report is accepted when the part is within 13° of the optical axis, within 24 cm and in line of sight.
Related work
- “Actuation and Control of Passive Tendon-Driven Soft Extensions Through Rigid Manipulator Motion,” interactive companion with simulations and code. ignaciocuiral.com/passive_soft_extension_control