Line Laser Sensor Measurement Principle
The MIRIUM Laser Profile Scanner uses the principle of laser triangulation to scan a 2D profile of a variety of surfaces. The laser beam is amplified by a set of specific lenses to form a static laser line, which is projected onto the surface of the object. High-quality optics project the diffusely reflected light from the laser line onto a highly sensitive sensor matrix. In addition to the distance information from the sensor to the object (Z-axis), the controller can use this image to calculate the position along the laser line (x-axis). The sensor ultimately outputs a set of two-dimensional coordinate values, with the origin of the coordinate system fixed relative to the sensor itself. By moving either the object or the sensor, a three-dimensional measurement can be made.
Using a laser diode to emit laser light, a spot can be formed on the surface of the object to be measured. A special lens set is used to diffuse the laser spot into a line. Traditional beam-splitting laser sensors use a cylindrical lens to refract the laser light. The biggest problem with this conventional method is the very weak edge illumination due to the Gaussian light intensity distribution along the laser line. The scanCONTROL type profile sensors supplied by MIRIUM Germany utilize a precision wedge lens, which eliminates the problem of weakened edge illumination along the laser line
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Reflected light When measuring, the highly sensitive sensor CMOS matrix receives the light reflected back from the object to be measured, creating a highly accurate contour image. Any change in contour will change the shape of the laser line projected onto the surface of the DUT, thus changing the image result on the sensor matrix. If the probe or the object under test is moved, a number of scan line contours can be obtained, which can be combined to produce a 3D image result. This image is also called a "point cloud" because the image is made up of thousands of individual measurement points.
Taking this added dimension of measurement into account makes contour scanner sensors more complex than other types of displacement sensors. Basically, it is not possible to simply determine whether a measured object can be measured by a contour scanner sensor. Successful measurements often depend on which measurement value is to be obtained and in what environment the measurement is to be performed. Therefore the feasibility of the measurement needs to be evaluated from the beginning for each object to be measured. For example, the success of a measurement depends on how much time is available for the measurement. The slower the object passes through the probe beam, the more time is available for measurement. Therefore, it cannot simply be assumed that just because a static measurement works, it necessarily means that a dynamic measurement will also work. The result of the measurement also depends on the reflective properties of the surface of the object to be measured. This means that the reflective or light-absorbing properties of the surface of the object to be measured will determine whether a valid signal can be measured. The material to be measured also affects the measurement results. For example, if the transparency of a translucent object is too high, the measurement signal may be completely distorted. A final factor that should be taken into account is the contour defects of the object, contours that may create shadows, and the surface effects of multiple reflections. All of these basic factors can significantly affect the quality of the measurement signal as well as the measurement
results.
Correct setup
Without the above mentioned influences, a continuous signal reflected from a clearly recognizable contour surface can still be a defective signal that is difficult to use. If this is to be avoided, each individual parameter of the profiler must be set correctly and appropriate to the object being measured. Using the correct filter and exposure time settings can often improve the defective signal, and the test can eventually be completed after repeated attempts. For example, when measuring a fast moving black rubber object, a short exposure time and the high light absorption of the object are more likely to result in a poor measurement. In contrast, if the black object is not moving or is moving slowly, a longer exposure time may be more helpful in obtaining complete profile information.