FOUR-BAR LATCH ASSEMBLY
The present disclosure is directed to a four-bar assembly for use in various circumstances such as docking, coupling, or capture operations. The four-bar assembly may include an upper link, a middle link, and a lower link connected to form a four-bar linkage. The middle link may serve as an active latching element for engaging a latch feature on a mating structure. A cam or slider may control the potential range of motion of the lower link, allowing the middle link to move between a retracted and an engaged position to effect capture, and a second range of motion to then allow the middle link to move between an engaged and released position to effect release. In some embodiments, the four-bar assembly includes contingency mechanisms such as hold-down and release devices (HDRMs), a contingency lever, or dual-surface cams configured to selectively disable or isolate motion of the latching components during overload or fault conditions.
1 . A four-bar assembly comprising:
an upper link;
a middle link operably connected to the upper link, the middle link to engage a mating structure;
a lower link operably connected to the middle link; and
a cam to drive the lower link through a first range of motion and a second range of motion,
wherein the first range of motion of the lower link drives the middle link between a retracted position and an engaged position relative to the mating structure, and
wherein the second range of motion of the lower link drives the middle link between an engaged position and a released position relative to the mating structure.
2 . The four-bar assembly of claim 1 , wherein the middle link comprises a roller disposed at a distal end of the middle link, the roller to roll along the mating structure and to reduce friction during engagement and release.
3 . The four-bar assembly of claim 1 , wherein the cam comprises a first cam surface and a second cam surface, the lower link to transition from the second cam surface to the first cam surface in response to a contingency load.
4 . The four-bar assembly of claim 1 , further comprising a contingency mechanism to selectively deactivate the middle link in response to at least one of a detected fault, overload, or release command.
5 . The four-bar assembly of claim 4 , wherein the contingency mechanism comprises a hold-down and release mechanism (HDRM) operably coupled to at least one of the upper link, the cam, or a contingency link.
6 . The four-bar assembly of claim 4 , wherein the contingency mechanism comprises a slider movable within a cavity, the slider to cause the lower link to move within the first range of motion, and to free, when the slider is displaced, the lower link to the second range of motion.
7 . The four-bar assembly of claim 4 , wherein the contingency mechanism comprises a contingency lever coupled between the upper link and a contingency link, the contingency lever being positioned within a slot such that breakage of the contingency link allows the contingency lever and upper link to move freely.
8 . The four-bar assembly of claim 4 , wherein the contingency mechanism comprises a split slider comprising two halves held together by a frangible fastener or HDRM, the lower link including a wedge to separate the two halves upon activation.
9 . The four-bar assembly of claim 1 , wherein the cam is in direct mechanical contact with the lower link.
10 . A method comprising:
actuating a cam to drive a lower link, in a four-bar assembly, through a first range of motion;
driving, by the lower link, a middle link from a retracted position to an engaged position;
engaging the middle link with a mating structure; and
releasing the middle link from the mating structure by actuating the cam to drive the middle link through a second range of motion.
11 . The method of claim 10 , further comprising rolling a roller disposed at a distal end of the middle link.
12 . The method of claim 10 , further comprising, in response to a contingency event, activating a hold-down and release mechanism (HDRM) to decouple at least one link of the four-bar assembly.
13 . The method of claim 12 , wherein activating the HDRM causes an upper link to translate within a slot.
14 . The method of claim 12 , wherein activating the HDRM causes a cam link to disengage from the cam and the lower link to move in a third range of motion.
15 . The method of claim 10 , further comprising sliding a slider along a cavity to disengage a lower link hook, and permitting the lower link to rotate.
16 . A four-bar docking assembly, comprising:
an upper link;
a middle link to latch onto a mating structure;
a lower link; and
a slider to drive the lower link through a first range of motion and a second range of motion,
wherein the first range of motion of the lower link drives the middle link between a retracted position and an engaged position relative to the mating structure, and
wherein the second range of motion of the lower link drives the middle link between an engaged position and a released position relative to the mating structure.
17 . The four-bar docking assembly of claim 16 , further comprising a contingency element to disable the middle link under one or more contingency conditions, wherein the contingency element comprises a dual-surface cam comprising a first cam surface and a second cam surface to produce two or more ranges of motion for the lower link.
18 . The four-bar docking assembly of claim 16 , wherein the lower link comprises a spring to bias the lower link clockwise against the slider.
19 . The four-bar docking assembly of claim 17 , wherein the contingency element comprises a contingency lever and frangible connector, the contingency lever to move freely within a slot upon breakage of the frangible connector.
20 . The four-bar docking assembly of claim 17 , wherein the contingency element comprises a split slider restrained by a hold-down and release mechanism (HDRM), the split slider to separate upon activation and allow free movement of the lower link.