In-line accuracy and spatial position analysis of rocket fins

Need

The fin must be measured in motion and without contact: a contact probe would load it, and the actuator encoder cannot see the backlash and flexing in between. A single camera cannot tell a change in angle from a displacement in depth, and a small angle error is only millimetres at the tip.

Solution approach

Two cameras view the fin face from different directions; the ring light around each lens turns the retro-reflective markers into bright points on any background. The position of the same marker in the two images is triangulated into a 3D coordinate; three markers give the fin plane, and the plane gives the angle and tip position. The section is indexed so that the fins are measured in turn.

Process steps

1. 01

   Index

   The test section rolls 90° on its rollers; the next fin reaches the measuring position.

2. 02

   Markers

   The ring lights come on; both cameras find the marker points on the fin and triangulate them.

3. 03

   Angle

   The fin rotates on command; the measured angle is compared with the commanded one.

4. 04

   Position

   The 3D position of the fin tip is evaluated against its nominal position.

5. 05

   Decide

   Angle and position deviation are compared with the tolerance.