GOAL: to enable automated design of print-and-fold robots, given the desired kinematics
Print-and-fold promises a rapid and inexpensive method for manufacturing robots. However, progress on this front is complicated by a lack of understanding of what types of motions can actually be produced by folding. In mechanism design not restricted to folding, the joints and links that are used to produce motion are readily available and can straightforwardly be connected together, making methods for automated mechanism design and analysis possible. Our approach is to enable such mechanism design tools to be used with folded structures by providing: 1) a library of foldable joints and rigid bodies, and 2) composition algorithms that allow the fold patterns of these library components to be connected together automatically.
Our fold patterns for basic revolute and prismatic joints are parameterized to achieve user-specified sizes and ranges of motion. The joints can be composed with each other (see below) to achieve joints with higher degrees of freedom or with rigid bodies to produce foldable linkage mechanisms. They also provide natural placement of actuators. We have created a system that allows users to specify a type of joint and the desired joint limits and that automatically produces the corresponding fold pattern, and we have used this system to generate and fabricate multiple joints.
To enable on-demand customization of printable machines, we are currently working on automatic composition of their fold patterns. So far, we have considered edge-compositions, compositions involving two surfaces connected at one edge. Our algorithm produces a one-piece, non-self-intersecting unfolding of the composite surface by attaching the unfoldings of the two original surfaces using a bridge of linking material. The algorithm is provably correct and has been tested on multiple surfaces. Future work includes other types of compositions, such as merging of faces. We are also investigating heuristics to minimize the total amount of wasteful linking material added to an unfolding.
We have implemented our composition algorithm in our system. In addition to generating joints, users can also input custom patterns for folded structures as a vector file. Users specify the edges or faces on separate folded structures that they wish to connect, and the system will generate a single-sheet fold pattern for the complete structure. The system provides views of both the at fold pattern and its folded state in 3-D so that users can visually verify that the composition is correct.
Using this system, we have designed several novel foldable mechanisms and robots. Print-and-fold manufacturing provides a natural method for incorporating actuation, sensing, and computation into a robot, specifically by printing circuitry and mounting components directly onto the fold pattern before folding. Using this method, we have produced fully functional robots that emulate the kinematics of the equivalent linkages built using standard machining techniques.