TESASCAN uses high resolution linear CCD arrays for the measurement of round parts. Each array sensor is sub-divided into thousands of light sensitive pixels. The sensor can be electronically interrogated at pixel level to detect changes in light pattern at sub-micron resolution. The sensors act effectively like "light sensitive rulers", which measure the Workpiece image.
The workpiece is illuminated with parallel white light and its image is projected onto the linear CCD sensors. These are orientated radially about each side of the workpiece center line. They provide information from the image that allows exact determination of the workpiece diameter.
2D Measurement
To obtain dimensions along the workpiece axis, the table supporting the workpiece is traversed axially. The location of the table and hence the workpiece is registered by an electronic scale. This, combined with the optical measurement, provides the second dimension to the system. A unique feature of the TESASCAN system is the orientation of the linear sensors to the workpiece image. The sensors are not perpendicular to the center line as this would provide no data directly from the edges of the image. In the TESASCAN system the sensors are inclined to the perpendicular. This ensures that real data is collected from vertical edges.
Even when complex grooves are scanned, real data will be obtained from all the individual elements such as edges, angles, diameters and radii. The second dimension is realised from true data rather than from an estimate based on the change in diameter.
Dynamic Measurement
A mechanism for rotating a workpiece round its center line is a standard feature of the TESASCAN system. Functions are available to rotate the workpiece whilst scanning the periphery to measure such features as concentricity and ovality.
More complex features such as straightness are easily measured by combining rotation with axial movement. In a similar way any surface of the workpiece can be scanned dynamically to define the axis of the part for true 3D alignment and for reference purposes.
Thread Measurment
External threads are an important feature of round parts and the measurement of them is a highly labor intensive operation. The true profile of any thread form can only be obtained by viewing parallel to the thread helix angle. Most TESASCAN machines offer the option of a mechanism for tilting the thread through the helix angle to give correct alignment to the optics. This guarantees high accuracy measurement of many different types of thread form.
