Telecentric three-dimensional sensor with a liquid mirror for large-object inspection.

We describe a device that applies the advantages of the space invariance of telecentric triangulation with the measurement of large objects (1 m(3)). Because the scan motion of the laser beam is decoupled from the physical transport of the sensor head, the fast scanning of large volumes becomes feasible. The device consists of a triangulation laser telemeter head that uses a large liquid primary mirror and an aspheric secondary mirror to realize the telecentric f-theta objective. We propose using liquid-mirror technology to make low-cost large objectives that have low f numbers, a diffraction-limited performance, and low scattering in the visible. This new optical system is useful for 3-D measurement. We discuss the optical configuration of the system and the performance of a laboratory prototype. The prototype has a standoff distance of 1.5 m, a telecentric scan as long as 1 m, a depth of view of 1 m, and a relative depth resolution of 0.5-1 mm.