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Optical sensors
Optical sensors
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Tactile sensors
Tactile sensors
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Coordinate measuring machines with X-ray computed tomography
Coordinate measuring machines with X-ray computed tomography
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Sensors

Physical sensor principles for recording the measurement points

When selecting the sensors, the conditions at the measuring object, such as the size of the geometries to be measured, the accuracy requirements and the contact-sensitivity must be taken into account. The selection of the sensor or – for multi-sensor applications – the sensors must therefore always take the measuring task into account. Economic aspects such as measuring time and costs also play a role here.

Optical sensors
Optical sensors
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Tactile sensors
Tactile sensors
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Coordinate measuring machines with X-ray computed tomography
Coordinate measuring machines with X-ray computed tomography
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Switching and measuring

The mechanical, optical, electronic and software structures of sensors are very different. This leads to very different properties, the basic understanding of which is required for optimum use. The sensors can have their own measuring range (measuring sensors) or only recognise the out-of-limit value (switching sensors) (Fig. 3).

Switching and measuring
<p>Fig. 3: Comparison of switching (left) and measuring sensors (right): A deflection, S signal course, M measuring range</p>

1D, 2D and 3D

The direction of action of the sensors can be reduced to one or two coordinate axes (1D, 2D sensors) or include all three axes (3D sensors) (Fig. 4). The measured values of the respective non-measuring axes are given by the sensor position (e.g. position of the measuring axis of the Sphere centre for 1D scanning probes or position of the object plane for image processing).

1D, 2D and 3D
<p>Fig. 4: One-, two- and three-dimensional sensors: basic representation of the kinematics without measuring systems: a) spring parallelogram, b) recording cylinder</p>

Points, lines and flats

Sensors can measure individual points (point sensors), contours (line sensors) or surface areas (area sensors) (Fig. 5). The properties mentioned can occur in almost any combination (see Fig. 57 Sensors and machine axes).

Points, lines and flats
<p>Fig. 5: Measurement of points, lines or surfaces</p>

Contour detection by scanning

Scanning contours, e.g. for the measurement of form and position tolerances, is possible with scanning sensors (scanning probes, distance sensors) in conjunction with the machine axes using suitable control methods. A touch trigger probe also offers this function in principle, but requires very long measuring times. When scanning with image processing, several images are automatically joined together during contour tracking to form overall contours. The size of the contours to be scanned is not limited by the sensor, but by the measuring range of the coordinate measuring machine.

Optical, tactile and X-ray tomography

Another key differentiation criterion for sensors is the physical principle of transmission of the primary signal. The majority of sensors commonly used today can be categorised as optical or tactile (Fig. 6). With optical sensors, information about the position of a measurement point is transmitted from the object to the sensor by light. Tactile sensors obtain this information by contacting the measuring object with a stylus tip, usually a stylus tip. With X-ray tomography sensors, an object area is penetrated by X-rays and the three-dimensional geometry of the measuring object is reconstructed from the radiographic images. From this, the position of the measurement points is deduced.

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Sensors