Description
Following is a sample of the information contained on this CD: FIELD OF THE INVENTION The invention relates to light based range sensors, usually laser based range sensors, that make high precision optical measurements of surfaces having varying profiles and varying degrees of reflectivity. More specifically, the invention relates to non-contact sensors that optically measure the distance from the sensor head to the surface under test. BACKGROUND OF THE INVENTION High-precision surface-profiling devices of the past have been primarily of the contact type. A spherical ruby stylus (of radius typically 1 mm) is used to probe he surface under test. In some systems, the deflection of the probe is measured by the closure of a mechanical microswitch; in other systems, the deflection is measured capacitively. Although such probes can be exceedingly accurate on suitable materials, the range of suitable materials is limited. Inaccurate readings or damage may occur if the sample is unsuitable. Examples of unsuitable samples include: soft, liquid, or sticky materials, very thin samples that would deform under stylus pressure, samples with concavities of radius smaller than the tip radius, or samples that are hazardous to touch. Additionally, in order to minimize probe and sample wear, the speed of measurement must be made low. As an alternative to the electro-mechanical controllers and ruby-tipped contact probes, several types of measurement systems have been developed using optical triangulation. U.S. Pat. No. 4,733,969 discloses a laser probe for determining distance from the probe to the test object by projecting laser light onto a target surface through a source lens. The light is reflected from the target surface through a receiving lens and directed onto a pair of detectors. Light falling on the first detector indicates that the sensor (or probe) is within range for making a measurement. Light falling equally on, or in a predetermined proportion
