Engaging with the Latching End Effector (LEE) involves several stages:
- Initial manual alignment using a camera on the LEE and a target on the object’s grapple.
- Capture using a 3-wire wire snare
- Final alignment by drawing the grapple into the LEE using traction on the snare.
- Coupling. Details depend on the variant of Grapple Fixture and LEE (Flight releasable FLGF or Latchable LGF)
The basic capture and alignment can be illustrated by the simplest variant, the FRGF and the associated CANADARM 1 LEE:
The LEE is manipulated under video control to place the pin inside the space formed by the three snare wires. Motorized carriers move the snares to close around the pin shaft. The snares are then moved axially by a screw mechanism within the LEE housing, exerting traction on the pin knob and drawing the LEE and grapple together. The shoulders of the cam arms engage with the cam cutouts, correcting any residual misalignment. Secure coupling of LEE and Grapple is dependent on maintaining tension on the 3 snare wires by the tensioning screw.
Later variants added power and electrical connections, as well as locking couplers. As well, a gear-like curvilinear coupling ring reduces backlash.
The newer design is backwards compatible and capable of handling more massive objects. The curvilinear coupling is passive, in that it is engaged by the same action which engages the cam arm shoulders in the cam cutouts. The four couplers are engaged by motor. At that point, tension is released on the snare system. Secure coupling is not reliant on the snare wires, but on the multiply redundant locking couplers.
Detailed description: https://ntrs.nasa.gov/citations/19950020841