Low-complexity Input Research Articles

Bending and twisting with a pinch: Shape morphing of creased sheets

In this letter, we introduce a unique behavior seen in creased sheets where localized changes in the folding (i.e., a pinch) result in global bending and twisting deformations. Using isometric deformation theory, we identify the connections between pinching, crease curvature, and crease torsion that begin to explain the shape-morphing behavior. Given the limitations of isometric deformations, we expand our understanding of the behavior using a mechanics-based bar and hinge model of creased sheets, where the sheet is allowed to stretch. With this tool, we found that the increase in crease curvature and torsion due to pinching are proportional to the curvature of the crease before folding and that curved creases facilitate the bending and twisting. Additionally, we explored the bending and twisting of sheets with more than one crease. We found that sheets with an even number of creases generate more intense twisting than those with an odd number of creases and experience twisting even when the creases are straight. The number of creases had little effect on the pinch-induced bending of the origami. The stiffness of the sheets had little effect on the amount of bending and twisting, but greater spacing between the creases resulted in more bending with little effect on the twisting. Based on these results, we created a framework to design crease patterns to have desirable bending and twisting that can be coupled or not, and demonstrated this programmability with simulations and by pinching physical prototypes. Our findings enable shape morphing of creased sheets with a low-complexity input and a versatile output.

A QPR-Based Low-Complexity Input Current Control Strategy for the Indirect Matrix Converters With Unity Grid Power Factor

Unity grid power factor (GPF) is essential for the indirect matrix converter (IMC) applications to satisfy the grid-friendly requirement. The existing unity GPF control strategies usually consist of high-complexity structures, resulting in difficult parameter adjustments and high-speed processor requirements. In this paper, a low-complexity input current control (LCICC) strategy is proposed for the IMC operating at the unity GPF. Unlike the conventional strategies designed in the $d$ -$q$ synchronous coordinate frame, the proposed LCICC strategy is set up in the $\alpha $ -$\beta $ stationary coordinate frame. Then, the quasi-proportional resonant (QPR) controllers are utilized for a novel input current control manner, which is implemented to regulate the input currents based on the reconstructed grid voltage and current vectors. By this design, the proposed strategy can help to reduce the control complexity, with the advantages of the conventional closed-loop control strategies reserved. The steady-state and dynamic-state performance of the proposed strategy is validated by the experiments on a downscaled prototype. Besides, comparative experimental research with respect to an existing typical strategy indicates that the computational burden can be reduced 14.9% by the proposed strategy.

Identification of Time-Delay Systems: a State-Space Realization Approach

A state-space realization approach is presented for the identification of time-delay dynamic systems. It is proposed an experiment with low complexity input signals such as the double pulse. The proposed identification method is a generalization of the Ho-Kalman-Kung technique for pulsed input signals. Due to its state-space formulation, it is essentially suitable to both SISO and MIMO systems.