Telecentric three-dimensional sensor with a liquid mirror for large-objectinspection

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 tr ansport of the sensor head, the fast scanning of large volumes becomes feas ible. 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 technolog y to make low-cost large objectives that have low f numbers, a diffraction- limited performance, and low scattering in the visible. This new optical sy stem is useful for 3-D measurement. We discuss the optical configuration of the system and the performance of a laboratory prototype. The prototype ha s 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. (C) 1999 Optic al Society of America.