Mechanical motion added to 3D-printed creations

The methods are said to apply to two specific types of characters – planar mechanical characters that are similar to shadow puppets, and linkage-based characters formed by networks of rigid links and hinged joints. In either case, the researchers have developed tools that lead the user in designing mechanisms that will achieve a desired cyclical motion.

The same team of researchers, including scientists from Disney Research Zurich, ETH Zurich and Columbia University, developed both methods and will present them this week at ACM SIGGRAPH 2014, the International Conference on Computer Graphics and Interactive Techniques held in Canada.

’Despite the fact that the linkages are made from very basic components, they can create complex and often surprising motions’

‘The machinery for fabricating personalised mechanical toys, artefacts and even robots is becoming widely available, thanks to 3D printing,’ said Bernhard Thomaszewski, a Disney Research Zurich associate research scientist. ‘But without the assistance of specialized software, designing such animated characters is a virtually impossible task for casual users.’

In July 2014 the team presented ChaCra, their interactive system for designing planar mechanical characters. These are inspired by shadow puppets, which are rigidly articulated and whose motion is controlled through a number of rods. In these characters, however, the rods aren’t controlled by a puppeteer behind a screen, but are animated by a single actuator.

Users can sketch the body parts and pose them as desired; ChaCra then automatically computes the mechanical structure required to move the character to achieve those poses.

Stelian Coros, a Disney Research Zurich research scientist, said in a statement that the team was able to make the design process manageable by building each structure from three simple mechanisms: connectors that define relative motion between two components, trimmers that limit motion to a desired range, and propagators that transmit actuation from it source to the extremities. Each of these building blocks consists of two interconnected bars for which it is easy to set parameters.

At ACM SIGGRAPH 2014, the team will present a design system for linkage-based characters and kinetic sculptures, in which networks of rigid members and simple joints animate the structure and become part of the work of art.

‘Despite the fact that the linkages are made from very basic components, they can create complex and often surprising motions,’ Coros said.

The team’s process is said to begin with a design for a mechanical structure in which the motion of every joint is controlled by a motor – a design that is impractically complex and expensive, but which enables the designer to freely configure the desired motion. The design tool enables the user to then successively replace the joint motors with new rigid links that mechanically couple the motions of different parts of the assembly.

Such an approach would be tedious and frustrating if done manually, but proved to be enjoyable with the design tool, Thomaszewski said. The tool not only makes this easier, but also enables the user to explore a number of possible configurations of linkages that can better approximate the desired motion while avoiding pitfalls that could cause the mechanism to grind to a halt.