RoboCut Turns Robot Arms Into a Flexible Hot-Wire Subtractive Fabrication System for Complex Shapes

Proven in prototype using a dual-arm Yumi robot, RoboCut can slice polystyrene into complex shapes thanks to a unified, global algorithm.

The prototype RoboCut proved capable of carving complex shapes. (📷: Dünser et al)

Scientists at ETH Zürich has come up with an algorithm designed to turn two robot arms working in concert into a highly-accurate automated hot-wire cutter capable of carving even complex shapes: RoboCut.

Controlling a robot arm is one problem; controlling two that work together is considerably more challenging; and when the tool they're using flexes and bends, the challenge is still harder. When it comes to hot-wire cutting of materials under computer control, the difficulties multiply — but RoboCut may have them solved.

"Hot-wire cutting is a subtractive fabrication technique used to carve foam and similar materials. Conventional machines rely on straight wires and are thus limited to creating piecewise ruled surfaces," the researchers explain in their paper. "In this work, we propose a method that exploits a dual-arm robot setup to actively control the shape of a flexible, heated rod as it cuts through the material."

"While this setting offers great freedom of shape, using it effectively requires concurrent reasoning about three tightly coupled sub-problems: 1) modeling the way in which the shape of the rod and the surface it sweeps are governed by the robot's motions; 2) approximating a target shape through a sequence of surfaces swept by the equilibrium shape of an elastic rod; and 3) generating collision-free motion trajectories that lead the robot to create desired sweeps with the deformable tool."

The solution to all three problems: A computational framework designed specifically for computer-controlled dual-arm flexible hot-wire cutting which attacks all three problems at the same time, and which has been proven in both simulation and physically in a prototype system based on the ABB Yumi dual-arm robot platform which is capable of carving complex shapes including hearts and rabbits.

"The complex optimisation calculations are what make RoboCut special," explains ETH Zürich's Simon Dünser, who came up with the system. "These are needed to find the most efficient tool paths possible while melting the desired shape from the polystyrene block as precisely as possible."

Dünser further claims the same technique can be applied to other cutting and milling systems, including electrical discharge machining and the creation of building blocks for mortar-free construction — a concept the team intends to prove in partnership with EPF Lausanne.

The team's work has been published under open-access terms in the journal ACM Transactions on Graphics.

Gareth Halfacree
Freelance journalist, technical author, hacker, tinkerer, erstwhile sysadmin. For hire: freelance@halfacree.co.uk.
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