By merging several sensors into a multisensor, costs are reduced and operation is simplified. The Chromatic Focus Zoom offers high flexibility and accuracy for non-contact measurements without sensor offset in all three spatial directions.

After integrating the Werth Laser Probe (WLP) into the patented Werth Zoom and the Werth Multisensor System, Werth Messtechnik has developed yet another multisensor. For the patented Chromatic Focus Zoom (CFZ), a chromatic distance sensor was combined with a tele-centric zoom lens. The zoom enables quality overviews at low magnification and fast measurements “in the image” together with high precision measurements at high magnification. The CFZ has a zoom that allows the field of view to be changed from approximately 10 mm × 8 mm to a nearly 20 times smaller field of view, while simultaneously increasing the resolution to measure even the finest details. Transmitted light, as well as bright-field and dark-field incident light, enable high-contrast illumination of different types of workpieces. With tele-centric lenses, an aperture in the beam path ensures that the image size remains nearly constant within the tele-centric range. This feature allows measurement deviations to become negligible if small defocusing goes unnoticed.

Chromatic distance sensors project white light onto the workpiece surface with the aid of a special lens. The distance between the sensor and the workpiece is determined by different focal planes for the different wavelengths of the white light. This sensor principle offers high accuracy in combination with a high degree of independence from the workpiece surface. Even relatively strongly inclined, reflective, and transparent surfaces can be measured reliably. The large measuring range also enables high measuring speeds by utilizing fast scanning without sensor tracking.

Combination of Two High-Performance Sensors

With the different sensor principles, this multisensor has a high degree of flexibility. The image processing sensor is the best sensor for measurements in the plane perpendicular to the optical axis. With the Chromatic Focus Point (CFP) sensor, distance measurements are carried out along the optical axis. The combination of a high performance image processing sensor and a high performance distance sensor, enables non-contact measurements with high accuracy and fast measuring speeds in all three spatial directions.

The patented multisensor Chromatic Focus Zoom (CFZ): Camera (a) and imaging optics (b) of the image processing sensor (simplified, illumination not shown) are combined with the imaging optics of the Chromatic Focus Point distance sensor (c) via a beam splitter. The measuring head is connected to an evaluation unit (d) via a long optical fiber. It is also connected to the broadband white light source (f) and the spectrometer (g) via a fiber coupler (e). The spectra (h) represents the distance of the object (position 1, 2, and 3) to the measuring head.

High-precision lateral measurements scanned with the image processing sensor (left) and contours on the surface scanned using the chromatic distance sensor (blue – middle). These measurements are used for the 3D nominal-actual comparison (right).

Since positioning is no longer necessary when switching sensors, a quick change from the image processing sensor to the distance sensor is possible. In addition, the sensor offset in all three spatial directions is negligible. Therefore, the entire measuring volume of the coordinate measuring machine is available for combined measurements with both sensors. The compact arrangement of the sensor system minimizes measurement deviations caused by temperature-related changes in sensor offset. As a result, a combined multisensor measurement is more accurate, even under production conditions, than a standard conventional multisensor measuring machine that uses multiple single sensors in different positions. The CFZ is easy to operate; with the help of image processing, the measuring spot of the CFP can be visualized on the workpiece. The risk of collision is also reduced since the measuring range is not limited by the second sensor, which is conventionally mounted at a distance. In addition, the overall costs are lower because only one sensor has to be purchased instead of two. Also, the required multisensor measuring range can be achieved with a smaller device, saving valuable installation space.

Wide Range of Applications

The Chromatic Focus Zoom enables both the automatic acquisition of the entire workpiece with Raster Scanning HD, and the imaging of the workpiece surfaces in a 3D measuring point cloud for tasks like flatness measurements. The sensor is particularly suitable for measurements on glass displays. Markings on the displays can be measured with the image processing sensor and freeform surfaces can be measured with the CFP. Many other measurement tasks in medical technology, automotive engineering, and other industries can be improved with this sensor. With the patented HD raster scanning, the image processing sensor takes an image of the entire workpiece. Then, the distance and contour measurements are carried out with the CFP.

Product page with demonstration video