Optical design of rotationally symmetric triangulation sensors with low-cost detectors based on reflective optics

Abstract

Classical triangulation sensors exhibit a orientation depend signal if the scattering properties of the work-piece are not symmetrical like at curved surface locations. This problem is avoided by rotational symmetric triangulation sensors. Due to this attractive property in a lot of applications such a sensor was introduced very recently on the market. This sensor is based on refractive optics and a special PSD detector, both custom made resulting in high costs. Additionally, the existing optical design approach does not offer an optical layout to start with, thus a good amount of trial and error is required and non-optimal solutions are probable. Therefore, there is great interest for a clear optical design strategy that results in layouts that are suitable also to use low cost commercial available detectors, such as CCD or CMOS image detectors. In this paper such a design procedure is presented for optical designs that use reflecting optical surfaces. Several solutions are depicted and discussed. The designs are not only attractive from the optical point of view and from detector considerations, but also from opto-mechanical design issues. For example designs with only one opto-mechanical part are possible. The resulting optical designs consist of aspherical surfaces which are obtained directly by using only some new relations of first order optics for off-axis objects. The designs are validated by exact ray tracing. These ray tracing results show already very good performance. Nevertheless, it was possible to further optimize the optical designs very efficiently using ray tracing software, thus yielding improved optical properties.

Rotationally Symmetric Triangulation Sensor with Integrated Vision System

“…But due to this optical design concept the ring is not in focus on the detector. The new sensor presented here avoids all these disadvantages (Ott 2003).…”

“…In rotationally symmetric triangulation the illumination axis is oriented orthogonally to the image plane; see Figure 1 and Ott (2003). In Ott (2005) the fundamental equations and the generalized Scheimpflug condition for tilted optical surfaces are presented.…”

“…The ring-formed optic of the sensor is based on a classic optical imaging system and consists of several spherical lenses with a hole in the center. This design is used to obtain a high degree of specific spherical aberration (Ott 2003). The spherical aberration is trimmed in such a way that a circular shaped light pattern with maximum sharpness is displayed on the image plane.…”

“…The integration of all radial sections yields a ring on the detector. The diameter of the ring is proportional to the distance to the measurement object in order to use a small low-cost standard 2D detector like a CCD or CMOS (Ott 2003).…”

A Novel Double Triangulation 3D Camera Design

“…Some novel structures were presented as solutions for surface inclination and blocking in measurement. [3] [4] [5]. Some algorithms for calculate centre of laser strip were given and their performance were compared [6] [7] [8].…”