Self-folding is a promising technique for assembling robots from flat sheets. However, existing implementations do not include reliable methods for sensing the folding angle, making feedback control impossible. In this paper, we present novel angle sensors for foldable robots and machines. They are inkjet printed and fully integrated into robots' laminate. This additional sensor layer tracks the angle motion of robot hinges, to better guide robot assembling by folding and to perform more complicated tasks that requires feedback control, making folded robots more capable in real world applications. We introduce the fabrication process, property assessments, and demonstrate sensor performance by measuring folding angles of a cube and controlling folds on a gripper.