Structured lighting for machine vision
Machine vision does not have to depend upon Gaussian-shaped beams from gas lasers or badly shaped beams from diode lasers. A diffractive element can transform a laser beam from a spot to a ring, array of spots, stack of lines, homogenised intensity region in one or two dimensions, or almost any intensity pattern. Diffractive optics opens up weight-saving solutions to complicated lens systems. The thickness of a plastic diffractive element can be even less than one millimetre.
Unlike lenses and mirrors, the function of diffractive elements is based on scattering and interference. Although modern diffractive optics was introduced in the 1970´s, commercial exploitation started in the 1990´s hand by hand with improved computing power of computers, and microelectronic fabrication and replication technologies. Heptagon Oy, founded in 1993, is one of the pioneers.
A diffractive element is a thin flat substrate. On other side of the component there is a fine groove structure. Typical depth of the grooves is about one micrometre. Diffractive elements are made by using well-established microelectronic fabrication technologies, which are suited to low-cost mass production. Diffractive elements work either in transmission or reflection mode. Substrate material can be almost any, such as glass, fused silica, semiconductor, plastic, or metal. Diffractive elements can be used with any wavelength, from infrared to ultraviolet.
Among various applications in laser machining etc., diffractive optics is also becoming better known in machine vision. Diffractive elements can homogenise the intensity of a line or distribute light to almost any desired intensity distribution (Fig. 1). They are also most ideal components for structuring light. A single spot can be transformed to a flattop region, a ring, stack of lines, a viewfinder pattern, or almost any pattern (Fig. 2). The distorted image of a regular array of equal-intensity spots projected on non-flat surface (Fig. 3) opens up new possibilities to 3-D machine vision.
Heptagon Oy has world-leading
expertise in designing custom-specified diffractive elements and optical
systems based on micro optics, fabricating prototypes, and mass-producing