Self-folding machines

1. A self-folding machine, comprising a laminate including:

a flexible layer with a first side and a second side;

a first rigid layer including at least one gap laminated to the first side of the flexible layer;

a second rigid layer including at least one gap laminated to the second side of the flexible layer, wherein the rigid layers are more rigid than the flexible layer;

a first contractible layer laminated to the first rigid layer and extending across at least one gap in the first rigid layer; and

a second contractible layer laminated to the second rigid layer and extending across at least one gap in the second rigid layer, wherein the first and second contractible layers retract to respectively create folds in the machine across gaps in the first and second rigid layers when activated,

wherein the contractible layers are shape-memory layers.

2. The self-folding machine of claim 1 , wherein the laminate further comprises electrically conductive pathways electrically coupled with the first shape-memory layer and with the second shape-memory layer.

3. The self-folding machine of claim 2 , further comprising a voltage source electrically coupled with the electrically conductive pathways.

4. The self-folding machine of claim 3 , further comprising at least one motor coupled with the voltage source and including a mechanical actuator.

5. The self-folding machine of claim 4 , wherein gaps in at least one of the rigid layers are configured to fold the laminate to position a portion of the laminate to be displaced by the mechanical actuator of the motor.

6. The self-folding machine of claim 5 , wherein the actuator is a crank arm.

7. The self-folding machine of claim 5 , wherein a plurality of legs in the laminate structure are configured to be displaced by the actuator to transport the machine across a surface.

8. The self-folding machine of claim 2 , wherein the electrically conductive pathways are contained in or on the flexible layer.

9. The self-folding machine of claim 2 , wherein at least one of the shape-memory layers includes a shape memory polymer.

10. The self-folding machine of claim 9 , wherein the shape memory polymer comprises pre-stretched polystyrene.

11. The self-folding machine of claim 10 , wherein the rigid layer comprises a composition selected from paper, fiber-reinforced epoxy, and a metal.

12. The self-folding machine of claim 2 , further comprising slits or additional gaps defined in each of the first and second rigid layers, wherein the first shape-memory layer does not extend over the slits or additional gaps in the first rigid layer, wherein the second shape-memory layer does not extend over the slits or gaps in the second rigid layer, wherein the slits or additional gaps in the first rigid layer are aligned with gaps in the second rigid layer on an opposite side of the flexible layer, and wherein the slits or additional gaps in the second rigid layer are aligned with gaps in the first rigid layer on an opposite side of the flexible layer.

13. A method for self-folding a machine that includes a flexible layer with a first side and a second side; a first rigid layer including at least one gap laminated to the first side of the flexible layer; a second rigid layer including at least one gap laminated to the second side of the flexible layer, wherein the rigid layers are more rigid than the flexible layer; a first contractible layer laminated to the first rigid layer and extending across at least one gap in the first rigid layer; and a second contractible layer laminated to the second rigid layer and extending across at least one gap in the second rigid layer, wherein the first and second contractible layers retract to respectively create folds in the machine across gaps in the first and second rigid layers when activated, wherein the contractible layers are shape-memory layers, the method comprising:

actuating the first and second contractible layers to contract and fold the machine into a transformed three-dimensional structure.

14. The method of claim 13 , wherein the machine further comprises an actuator, the method further comprising:

folding the laminated layers by retracting at least one of the first and second shape-memory layers to couple a portion of the machine with the actuator; and

displacing the coupled portion of the machine via actuation of the actuator.

15. The method of claim 13 , wherein the machine includes a voltage source and wherein the laminated layers include electrically conductive pathways, the method further comprising delivering a voltage from the voltage source through the electrically conductive pathways to the first and second shape-memory layers to fold the machine.