High-speed profile measurement for industrial applications.
In many cases, lasers are the ideal non-contact technique for distance measurement, as the high resolutions inherent in the physical properties of laser light give this method some advantages. Simple triangulation for distance measurement, as well as two-dimensional profile acquisition on the measurement surfaces is possible.
Laser triangulation is similar in principle to the method that is used for land surveying using a theodolite. A laser projects a spot of light, which is monitored by a camera, onto the surface to be measured. If the distance between the sensor and the surface changes, the angle at which the camera records the light spot also changes. The change of distance can be determined accurately using trigonometric calculations with resolution in the sub-micrometer range.
Extension to two or three dimensions
If, instead of a single spot of light, a line, of an infinite number of points is used, the method can be extended to cover two dimensions. And if the sensor is traversed over an object, an exact three-dimensional profile of the surface can be obtained. The scanControl 2800/2810 laser profile sensors from Micro-Epsilon employ this measurement technique to solve 3-dimensional measurement tasks. The system consists of a compact sensor with an integrated FireWire interface for control from a PC, which gives high data rates and preserves bandwidth.
To record the image, a CMOS matrix is used with an electronic shutter. The shutter facilitates the simultaneous reading of all the pixels in a complete image. The measurement therefore occurs synchronously along the laser line, eliminating distortion due to moving targets. In addition, the shutter can be controlled in real-time via an external trigger input located on the controller, allowing a number of measurement systems to be synchronised. The shutter enables the measurement system to work virtually independent of the speed and acceleration of the target. This is crucial in ensuring fast throughput times, particularly when the process speed varies.
Measuring profiles at high speed
The scanControl 2810 system was specially developed for the measurement of glue beads (seams) or grooves (gaps or channels) by evaluating the measured profiles. Using the digital and analogue outputs control signals can be produced, for example, proportional to the gap width or other typical measurement parameters. The system is easily configured using the set up and configuration software included.
If measurement tasks are more demanding the system can also be operated using a PC. Micro-Epsilon offers a special industrial PC for DIN rail mounting, which apart from parameterisation, can also be used for visual displays and storage. In this way complete measurement sequences can be logged and archived. Different parameter settings can also be saved, so that the system can be switched quickly between different measurement tasks.
Application for fitting windscreens
Windscreens are normally glued in place. The precise application of adhesive, usually carried out by robots, is of critical importance and it is not sufficient to check just whether adhesive has been applied. The height and width of the adhesive bead and its position relative to the border strip must also be checked to ensure they lie within specified tolerance bands. The robot that applies the adhesive carries out the inspection in a second movement using scanControl technology. The system assesses the position of the adhesive beading relative to the border, determines the width and height, and provides deviations from tolerance via digital outputs.
Flexible system
Applications for this measurement method are numerous anywhere surface profiles need to be measured precisely and at high speed. Typically, these range from quality assurance in tyre production to the inspection of welded seams.
For more information contact Associated Technology, +27 (0)11 802 3320, at@evanet.co.za, www.evanet.co.za
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