Sensors that measure the distance to an object have many application areas in the manufacturing industry and in quality control. The requirements for the measurement system differ substantially depending on the respective application. The distance to be measured, the speed, the accuracy required and the type and surface of the object are just a few of the numerous factors that determine the choice of sensor. Sensors based on an optical measurement principle have the advantage of being neither subject to effects of electromagnetic interference fields, nor to the effects of wear. In addition, optical measurement principles enable very high resolution, accuracy and repeatability using a true non-contact technology. The unique optical confocalDT measurement system from Micro-Epsilon is based on the optical measuring principle, which specifically takes advantage of the so-called chromatic aberration of light. This refers to the Different refraction of light in relation to its wavelengths. It measures distances by means of wavelength (spectrometry). MEASUREMENT PRINCIPLE The confocal-chromatic sensor system uses a white LED of which the light is transported from the controller to the sensor via an optical fiber. Polychromatic (white) light is focused onto the target surface by a multi-lens optical pen. These lenses are arranged so that the white light is dispersed into a monochromatic light by controlled chromatic aberration. This implements that light with different wavelength or color is also focused differently. The focus for blue light is closer to the sensor than the one for red light. Back in the controller, the light reflected by the surface passes through the fiber optics again and is projected onto a precision spectrometer. Inside the controller, the specific wavelength of the reflecting light is determined which represents the distance to the measurement object. TECHNOLOGY ADVANTAGES Due to the factory calibration, a certain distance to the measurement object is assigned to each light wavelength or color. The surface properties do not influence the measurement accuracy. This unique measuring principle enables high precision distance and displacement measurement for diffuse and reflecting surfaces even on mirror and liquid. The measurement spot is not larger than few microns and stays constant even with changing measurement distances. During a scan, extremely high lateral resolution in all directions can be achieved providing microscopic topography results. Using a high-powered light source and a high-speed spectrometer, measurement rates up to 70,000 Hz can be reached. The system is inherently immune to EMI and even suitable for EX-proof environments. MULTI-PEAK THICKNESS MEASUREMENT Safety glass, solar cells, flat screens and smartphone displays are made up of several material layers. Measuring the exact thickness of individual layers in production is a physically complex process – a challenge for measurement technology. For quality inspection and process control of manufactured transparent multi-layer materials, Micro-Epsilon offers its confocal-chromatic sensors with multi-peak feature. The confocal-chromatic measuring principle allows one-sided thickness measurement of these layers to micrometer accuracies. The confocalDT series of sensors measures up to 5 layers by evaluating 6 measurement values on the boundary areas. To accurately determine the thickness of each layer, the controller retrieves the refractive index For each layer from the material database. Each refractive index is corrected depending on the wavelength: three refractive values are used for thickness calibration (beginning, end, middle of the layer). MEASUREMENT IN HOLES AND RECESSES The beam path of the sensor is compact and concentric. This enables the system, for example, to measure inside drilled holes, which other optical methods, such as the triangulation technique, find difficult or even impossible due to shadow formations. For measurements of this nature, the confocal miniature IFS2402 sensors, which have a sensor diameter of only 4 mm, are particularly suitable.
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