Spectracular measurement with confocal chromatic sensors

23-10-2019

The advancements in the industry 4.0 demand high-speed operations with very high precision results in measurements of different materials. Some of these operations make use of Optical measurement technology, which is increasingly evolving in the field of production, inspection and quality control. Optical sensors are designed based on non-contact technology which deliver accurate results that are independent of the target material and surface properties. Confocal chromatic sensors are one of the examples of optical sensors, which are suitable for inline quality control in factory operations.

The confocal chromatic measuring principle uses polychromatic light, the same light that is produced by a standard incandescent light bulb. The white light is dispersed as monochromatic light of individual spectral colors by controlled aberration while being focused through a multi-lens optical system. Each wavelength is assigned a specific distance of the target by factory calibration, while only the wavelength which is entirely focused on the target is used for measurement. The reflected light is then passed through a confocal aperture onto a spectrometer for processing the spectral changes further.

Let us look into some advantages of using confocal Chromatic Sensors in quality assurance.

Material or surface independent

Confocal chromatic sensors perform displacement measurement and are independent of the surface. This allows the sensors to reliably measure on various kinds of surfaces such as dark, diffuse or highly reflective, shiny, mirrored or transparent surfaces. The sensors can also be used to measure on transparent and translucent materials such as glass. Furthermore, it is equipped with capability that enable one-sided thickness measurement of multi-layered glass. Special software used with the sensor allows the controller to enable real-time compensation for the surface’s reflectivity at high resolution and high-speed. The controller is also synchronised with encoders and other motion control devices during the entire operation.

Prevents shadowing effects

Confocal sensor consists of emitter and receiver that are arranged in one axis. The sensor sends a laser beam vertically down and the beam is reflected back vertically up from the target which leaves no scope for forming a shadow during operation.

Safe for vacuum applications

Confocal sensors are passive sensors and do not contain any electrical components. Therefore, they do not emit any heat radiation during operations. This makes them suitable for measurement in clean room or vacuum environments as well as in an environment where temperature rise is crucial. The housing cylinder is basically made up of a cylindrical tube with a series of lenses. This configuration prevents the components inside the sensor from getting mechanically expanded. The results are also more stable, reliable and accurate.

High resolution and small spot size

Confocal sensors have a very small spot size of 7-25 microns. This offers stable measurement even when used to measure on shiny, reflective and transparent materials with nanometer resolution. The light spot of the sensor remains constant over the entire measuring range, which allows the sensor to measure even the finest details such as surface roughness and IC pins on PCBs.

Thickness Calibration

With changing thickness or distance between the target and the sensor, there may be fluctuations and faults in measurement. For tackling such situations, a confocal chromatic sensor is equipped with thickness calibration feature that allows the adaptation of refractive indices of different materials that are stored in the controller. By doing this, the fluctuations and faults in the measurement can be automatically compensated which provides highly accurate results.

Multi-layered thickness measurement

Several electronic devices, solar panels and flat screens consist of multiple layers of transparent materials. Measurement of exact thickness of each layer with the air-gap between any of these layers is a very critical process during manufacturing. Confocal chromatic sensors provide multi-peak measurement feature that enables it to instantly the thickness of each layer in these multi-layered objects. These sensors can evaluate up to five layers of transparent material.

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