Caging mechanism for a single- or multi-axis positioning mechanism

1. A positioning mechanism comprising:

a first rotational joint with a first base and a first rotatable part rotationally coupled with the first base via a first rotational bearing mechanism, the first rotatable part configured to rotate about a first rotational axis with respect to the first base; and

a first caging mechanism configured to transition from a clamped configuration to an unclamped configuration, wherein:

the first caging mechanism is separate from the first rotational bearing mechanism of the first rotational joint,

the first caging mechanism, in the clamped configuration, contacts the first base and contacts the first rotatable part with sufficient radial clamping force to prevent the first rotatable part from rotating with respect to the first base,

the first caging mechanism is configured, in the unclamped configuration, to avoid contact with the first rotatable part, and

the positioning mechanism is configured to transition between the clamped configuration and the unclamped configuration while keeping the first base and the first rotatable part at a constant offset from one another along the first rotational axis.

2. The positioning mechanism of claim 1 , further comprising:

a first tensioning mechanism that is configured to maintain the first caging mechanism in the clamped configuration; and

a release device, the release device configured to releasably maintain the first tensioning mechanism in a first tensioned state to hold the first caging mechanism in the clamped configuration, wherein:

the first caging mechanism transitions to the unclamped configuration when the first tensioning mechanism is released from the first tensioned state,

the first rotatable part includes a substantially radially-symmetric first bearing surface, and

the first caging mechanism includes a plurality of first segments arrayed about the first bearing surface such that each first segment has a first interior surface that is offset from the first bearing surface by a first distance when the first caging mechanism is in the unclamped configuration and the first interior surface of each first segment contacts the first bearing surface when the first caging mechanism is in the clamped configuration.

3. The positioning mechanism of claim 2 , further comprising:

a second rotational joint with a second base and a second rotatable part rotationally coupled with the second base via a second rotational bearing mechanism, the second rotatable part configured to rotate about a second rotational axis with respect to the second base, wherein the first rotational axis is parallel to a reference axis that is orthogonal to the second rotational axis; and

a second caging mechanism configured to transition from a clamped configuration to an unclamped configuration, wherein:

the second caging mechanism is separate from the second rotational bearing mechanism of the second rotational joint,

the second base is fixed with respect to the first rotatable part,

the second caging mechanism, in the clamped configuration, contacts the second base and contacts the second rotatable part with sufficient radial clamping force to prevent the second rotatable part from rotating with respect to the second base,

the second caging mechanism, in the unclamped configuration, does not contact the second rotatable part with sufficient clamping force to prevent the second rotatable part from rotating with respect to the second base, and

the positioning mechanism is further configured to transition between the clamped configuration and the unclamped configuration while keeping the second base and the second rotatable part at a constant offset from one another along the second rotational axis.

4. The positioning mechanism of claim 3 , wherein the positioning mechanism is a dual-axis positioning mechanism for use on spacecraft deployable appendage assemblies.

5. The positioning mechanism of claim 3 , further comprising:

a second tensioning mechanism that is configured to maintain the second caging mechanism in the clamped configuration, wherein:

the release device is further configured to releasably maintain the second tensioning mechanism in a second tensioned state,

the second caging mechanism transitions to the unclamped configuration when the second tensioning mechanism is released from the second tensioned state,

the second rotatable part includes a substantially radially-symmetric second bearing surface, and

the second caging mechanism includes a plurality of second segments arrayed about the second bearing surface such that each second segment has a second interior surface that is offset from the second bearing surface by a second distance when the second caging mechanism is in the unclamped configuration.

6. The positioning mechanism of claim 5 , wherein the release device is configured to release both the first tensioning mechanism and the second tensioning mechanism responsive to a common signal.

7. The positioning mechanism of claim 2 , wherein the first caging mechanism comprises a thin-wall tube with a radial array of slits in one end, wherein the first segments are located between each pair of adjacent slits.

8. The positioning mechanism of claim 7 , wherein the thin-wall tube is fixed with respect to the first base.

9. The positioning mechanism of claim 2 , wherein:

each of the first interior surfaces has a first cross-sectional profile in a first reference plane coincident with the first rotational axis and intersecting the first interior surface,

the first bearing surface has a second cross-sectional profile in the first reference plane,

the first cross-sectional profile includes a portion that is raised or recessed with respect to a neighboring portion or portions of the first cross-sectional profile,

the second cross-sectional profile includes a portion that is recessed or raised with respect to a neighboring portion or portions of the second cross-sectional profile, and

the recessed or raised portion, respectively, of the first cross-sectional profile engages with the raised or recessed portion, respectively, of the second cross-sectional profile when the first caging mechanism is in the clamped configuration.

10. The positioning mechanism of claim 2 , wherein the first distance is at least 0.001″ to 0.010″.

11. The positioning mechanism of claim 7 , wherein the first caging mechanism further includes a radial array of cutouts, each cutout located within one of the first segments.

12. The positioning mechanism of claim 7 , wherein the thin-wall tube has a wall thickness at the first segments that is between about 0.005″ and 0.100″.

13. The positioning mechanism of claim 2 , wherein the first tensioning mechanism comprises a first tensioning strap that is wrapped around the first segments and positioned such that the first segments are drawn into contact with the first bearing surface when the first tensioning strap is tightened.

14. The positioning mechanism of claim 2 , wherein:

the first caging mechanism comprises a thin-wall tube with a radial array of substantially triangular first cutouts in one end, and

the first segments are located between each pair of adjacent triangular first cutouts.

15. The positioning mechanism of claim 14 , wherein:

the first bearing surface includes a radial array of raised segments offset from the first bearing surface in a radial direction by an amount less than the first distance, and

in the clamped configuration, the first segments are each located between pairs of the raised segments.

16. The positioning mechanism of claim 14 , wherein:

the first caging mechanism further includes a radial array of substantially triangular second cutouts,

the triangular second cutouts are oriented approximately 180° with respect to the first triangular cutouts, and

each first triangular cutout is located within a first segment.

17. The positioning mechanism of claim 2 , wherein:

the first segments are discrete components that, when radially arrayed, form a substantially tubular structure that surrounds the first bearing surface, and

the first interior surfaces have a radius of curvature that corresponds with a radius of curvature of the first bearing surface.

18. The positioning mechanism of claim 17 , further comprising a substantially radially-symmetric first base bearing surface located on the first base, wherein the first caging mechanism contacts both the first bearing surface and the first base bearing surface when in the clamped configuration.

19. The positioning mechanism of claim 2 , wherein:

the release device is configured to transition between an open state and a closed state,

the release device draws the first tensioning mechanism into the first tensioned state when transitioned to the closed state, and

the release device releases the first tensioning mechanism from the first tensioned state when transitioned to the open state.

20. The positioning mechanism of claim 19 , wherein the release device includes an actuator to transition the release device back and forth between the open state and the closed state.

21. The positioning mechanism of claim 5 , wherein the first tensioning mechanism and the second tensioning mechanism are provided in part by a common cable that is wrapped around both the first segments of the first caging mechanism and the second segments of the second caging mechanism.

22. The positioning mechanism of claim 21 , wherein the first tensioning mechanism and the second tensioning mechanism are provided in further part by:

a common cable guide;

a first cable anchor point; and

a second cable anchor point, wherein:

the common cable guide includes a contact surface configured to contact a portion of the common cable spanning between the first caging mechanism and the second caging mechanism,

a first end of the common cable is connected to the first cable anchor point,

a second end of the common cable is connected to the second cable anchor point, and

the release device is configured to change the distance between the contact surface and at least one of the first cable anchor point and the second cable anchor point.

23. The positioning mechanism of claim 5 , wherein:

the first tensioning mechanism includes a) a first tensioning strap that is wrapped around the first segments and positioned such that the first segments are drawn into contact with the first bearing surface when the first tensioning strap is tightened and b) first tabs that extend away from the first tensioning strap in a substantially radial direction,

the second tensioning mechanism includes a) a second tensioning strap that is wrapped around the second segments and positioned such that the second segments are drawn into contact with the second bearing surface when the second tensioning strap is tightened and b) second tabs that extend away from the second tensioning strap in a substantially radial direction,

the first tabs and the second tabs are aligned with one another when the first caging mechanism and the second caging mechanism are both in the clamped configuration,

the release device includes at least two bridging links that span between the first tabs and the second tabs,

the first tabs and the second tabs are interposed between the at least two bridging links, and

the release device is configured to draw the first tensioning mechanism into the first tensioned state and the second tensioning mechanism into the second tensioned state by drawing the at least two bridging links together.

24. The positioning mechanism of claim 23 , wherein:

the release device further includes a spring mechanism configured to cause the at least two bridging links to rotate clear of the area where the first tabs travel when the first tensioning mechanism is rotated about the first rotational axis.