Shape memory alloy pre-loaded deployment hinge

1. A latching hinge comprising:

a first member;

a second member rotatably coupled to the first member about a hinge such that:

in a hinge-closed condition, a first interface surface of the first member is restrained substantially parallel and proximate to a second interface surface of the second member by a latch mechanism, and

in a hinge-open condition, the first interface surface is at a substantial angle to the second interface surface; and

a shape memory alloy (SMA) pre-load device, the SMA pre-load device configured to transition from a first phase to a second phase when heated to a transformation temperature, wherein, when the SMA pre-load device is transitioned from the first phase to the second phase while the latching hinge is in the hinge-closed condition, expansion of the SMA pre-load device loads the latch mechanism so as to press one or more first contact areas on the first interface surface into substantially gapless contact with one or more corresponding second contact areas on the second interface surface.

2. The latching hinge of claim 1 , wherein the SMA pre-load device is further configured such that expansion of the SMA pre-load device when the latching hinge is in the hinge-closed condition loads the latch mechanism primarily along an axis substantially perpendicular to a hinge axis of the hinge.

3. The latching hinge of claim 1 , wherein:

the SMA pre-load device has a first length in the first phase and expands to a second length in the second phase, and

the SMA pre-load device is positioned such that the expansion of the SMA pre-load device induces a pre-load in the latch mechanism without plastic deformation of the latch mechanism.

4. The latching hinge of claim 1 , wherein the SMA pre-load device uses a one-way SMA.

5. The latching hinge of claim 1 , wherein the SMA pre-load device includes a thick-wall tube of SMA and an electrical heating element configured to heat the SMA to the transformation temperature.

6. The latching hinge of claim 1 , wherein:

the first member includes a first pre-load application area substantially centered with respect to the one or more first contact areas;

the second member includes a second pre-load application area substantially centered with respect to the one or more second contact areas, wherein the first pre-load application area and the second pre-load application area are spaced apart by a first distance when the latching hinge is in the hinge-closed condition;

the latch mechanism includes:

a third pre-load application area,

a fourth pre-load application area, and

one or more latching members joining the third pre-load application area and the fourth pre-load application area, wherein, when the latching hinge is in the hinge-closed condition:

the third pre-load application area and the fourth pre-load application area are spaced apart by a second distance larger than the first distance when the SMA pre-load device is in the first phase;

the latch mechanism and SMA pre-load device are positioned such that the first pre-load application area, the second pre-load application area, the third pre-load application area, the fourth pre-load application area, and the SMA pre-load device are all substantially centered on a common pre-load axis, the first pre-load application area faces the third pre-load application area, and the second pre-load application area faces the fourth pre-load application area; and

the SMA pre-load device, when transitioned from the first phase to the second phase, increases in length along the common pre-load axis by an amount greater than any inter-component compliance in a direction parallel to the common pre-load axis and between the first pre-load application area and the third pre-load application area added to any inter-component compliance in the direction parallel to the common pre-load axis and between the second pre-load application area and the fourth pre-load application area.

7. The latching hinge of claim 6 , wherein:

the first pre-load application area faces away from the first interface surface,

the second pre-load application area faces away from the second interface surface,

the third pre-load application area and the fourth pre-load application area face each other, and

the latch mechanism is configured to allow the third pre-load application area to swing clear of the first pre-load application area while the latching hinge is transitioned between the hinge-open condition and the hinge-closed condition.

8. The latching hinge of claim 7 , wherein:

the latch mechanism has a latching member and the latching member, the third pre-load application area, and the fourth pre-load application area form a C-shape with the third pre-load application area and the fourth pre-load application area located along horizontal portions of the C and the one or more latching members provided by a vertical portion of the C, and

the latch mechanism is rotatably connected with the second member.

9. The latching hinge of claim 8 , further comprising a flexible beam spring, wherein:

the latch mechanism is connected at an end near the fourth pre-load application area to the flexible beam spring,

the flexible beam spring connected to the second member, and

the flexible beam spring is configured to allow the latch mechanism to rotate into an unlatched position when the flexible beam spring is in an elastically unstable state and to cause the latch mechanism member to rotate into a latched position when the flexible beam spring relaxes into an elastically stable state.

10. The latching hinge of claim 6 , further comprising an eccentric, wherein the eccentric is positioned, when the latching hinge is in the hinge-closed condition, in a location intersecting the common pre-load axis and selected from the group consisting of a location between the first pre-load application area and the third pre-load application area and a location between the second pre-load application area and the fourth pre-load application area.

11. The latching hinge of claim 6 , wherein, when the latching hinge is in the hinge-closed condition, the SMA pre-load device is positioned in a location selected from the group consisting of a location between the first pre-load application area and the third pre-load application area and a location between the second pre-load application area and the fourth pre-load application area.

12. The latching hinge of claim 6 , wherein:

the one or more first contact areas include at least three substantially symmetric first pairs of opposing, slanted surfaces,

each of the substantially symmetric first pairs of opposing, slanted surfaces has a first axis of symmetry,

the first axes of symmetry for the at least three substantially symmetric first pairs of opposing, slanted surfaces intersect at a first substantially common location,

the one or more second contact areas include at least three substantially symmetric second pairs of opposing, slanted surfaces,

each of the substantially symmetric second pairs of opposing, slanted surfaces has a second axis of symmetry, and

the second axes of symmetry for the at least three substantially symmetric second pairs of opposing, slanted surfaces intersect at a second substantially common location.

13. The latching hinge of claim 12 , wherein at least two of the first axes of symmetry are orthogonal to one another.

14. The latching hinge of claim 12 , wherein:

the one or more first contact areas include at least four substantially symmetric first pairs of opposing, slanted surfaces,

the fourth substantially symmetric first pair of opposing, slanted surfaces also has a first axis of symmetry,

the first axes of symmetry for the at least four substantially symmetric first pairs of opposing, slanted surfaces intersect at the fourth substantially symmetric first pair of opposing, slanted surfaces,

the one or more second contact areas include at least four substantially symmetric second pairs of opposing, slanted surfaces,

the fourth substantially symmetric second pair of opposing, slanted surfaces also has a second axis of symmetry, and

the second axes of symmetry for the at least four substantially symmetric second pairs of opposing, slanted surfaces intersect at the fourth substantially symmetric second pair of opposing, slanted surfaces.

15. The latching hinge of claim 1 , further comprising a torsion spring drive mechanism substantially centered on a pivot axis of the hinge, the torsion spring drive mechanism configured to urge the first member and the second member to rotate about the pivot axis such that the first interface surface and the second interface surface come into contact.

16. The latching hinge of claim 1 , wherein the one or more latching members include a driven link and a drive link arranged to form a linkage, wherein:

the drive link is configured to pivot about a first linkage axis that is fixed with respect to the first member,

the driven link is configured to pivot about a second linkage axis that is substantially fixed with respect to the second member,

the driven link and the drive link are rotatably connected to one another about a third linkage axis, and

the linkage is configured such that rotation of the drive link about the first linkage axis when the locking hinge is in the hinge-open condition causes the drive link to:

rotate into the first member,

draw the driven link into the first member, and

draw the first member and the second member towards each other such that the locking hinge transitions from the hinge-open condition to the hinge-closed condition.

17. The latching hinge of claim 16 , wherein the linkage is configured so that a portion of the driven link contacts an end of the drive link near the first linkage axis when the latching hinge is in the closed hinge condition and the SMA pre-load device is in the second phase.

18. The latching hinge of claim 16 , wherein the linkage is configured so that when the latching hinge is transitioned from the hinge-open condition to the hinge-closed condition, the third linkage axis passes through and past bottom dead center with respect to an axis passing through the first linkage axis and the second linkage axis.

19. The latching hinge of claim 1 , wherein the latch mechanism is configured to restrain the first member and the second member from rotating relative to each other after the first interface surface and the second interface surface come into contact by applying a motion constraint along an axis substantially centered on the first interface surface and the second interface surface.

20. A spacecraft comprising:

a main body;

a boom; and

the latching hinge of claim 1 , the boom coupled to the main body by the latching hinge and the spacecraft configured to transition from a stowed state to a deployed state by releasing the boom from the stowed state, rotating the boom so as to close the latching hinge, engaging the latching mechanism, and pre-loading the latching mechanism by transitioning the SMA pre-load device from the first phase to the second phase.