Hazardous industrial conditions?
Vector type CCD detectors are valuable tools in many optical measurement applications where their high resolution, speed and the large number of picture elements can be exploited. The linear scanning of objects is not always possible: CCD Photonics Ltd (Espoo, Finland) has applied area sensors for determining the orientation of curved magnet parts on a conveyor belt and for controlling the X-ray beam position in the alignment of a diffraction goniometer. Classifying magnet orientations The NEO magnets manufactured by Neorem Magnets Oy (Ulvila, Finland) proceed from fine Nd-Fe-B powder through a complex process of high-pressure pressing and high-temperature sintering to be ground into their final forms. The design of shape giving moulds is done in order to save expensive raw material lost in machining; arc shaped magnets used in electric motors are a typical example. A collection of such parts is shown in Fig. 1. The dimensional range of arcs varies from less than 10 mm to more than fivefold. The variation of curvature radius is even higher.
Fig. 1. The projection of a semiconductor laser line illustrates the bowing of NEO magnets for electric motors. The motor magnets are produced in high volumes at Neorem Magnets Oy. This means that the parts cannot be machined using manual tools before final inspection and coating. Instead, they are picked continuously from a vibratory feeder onto a conveyor belt, where they appear to be in mixed positions: the bow may point up- or downwards and the rotation axis of the cylindrical arc may be aligned along or across the conveyor belt movement. This means that we have the total of four distinct positions of a part entering the gap between grinding stones. Only one orientation is valid: a magnet entering in a wrong position will necessarily jam the grinding unit, in the worst case the unit will be damaged. The orientation of entering parts is distinguished by means of an area type CCD camera with an accompanying microprocessor unit provided by CCD Photonics Ltd. The optical device is shown as a black box in the middle of Fig. 2.
Fig. 2. High speed grinding facility at Neorem Magnets Oy. The parts are oriented automatically according to optical information at the input stage of grinding stones. The optical unit consists of a red semiconductor line laser which makes the magnet orientation visible to the CCD camera. The orientation cases of Fig. 1 are evident; the red laser line projected onto a part is pointing either down or up, if the rotation axis of magnets coincides with the belt movement and if, at the same time, the laser line is aligned across the said movement. The orientations, where the rotation axis is parallel with the laser line, are more complex. The latter cases are processed using the height data obtained from the red line during the passage of a part through the observation gate. The height is determined using a normal triangulation principle. A fast ”pick and turn” manipulator is used for reorientation of badly positioned parts. Dr. Mauri Veistinen (mauri.veistinen@neorem.fi) expresses his satisfaction with the optical control gate: ”The system adapts well to many sizes of magnets and it can handle even cases, where the other side of a part is not curved, but flat. It is also important that our personnel is able to concentrate on the total quality control of the process instead of fingering at the small parts on the belt.” The optical inspection
methods of quality related issues, i.e. the occurrence of shape distortion,
edge chipping and internal cracks, based on a NEOVISION camera were described
in Machine Vision News 1999.
Increasing the safety of X-ray work The detection of X-ray diffraction from a metal structure has been used for measuring the residual stress of a material since 1980’s. The Stresstech Group (Jyväskylä, Finland) has introduced the next generation measurement technology exploiting a light-sensitive CCD- type transducer for detection of higher-energy X-ray photons. The operation principle is illustrated in Fig. 3.
Fig. 3. The collimator part of a stress-measuring device is shown in vertical position at left and in tilted position at right. Diffracted X-rays are registered using two opposite CCD sensors at curved rails. X-rays are scattered from the surface into a cone having two maximum intensity angles. The relative positions of the intensity peaks at opposite detectors indicate the value of the residual stress. In order to obtain a stress reading, at least two measurements have to be done; the first one in a vertical and the second one in a tilted position of the X-ray beam. The goniometer unit needs to be aligned properly in order to get valid results. This is especially important, if the surface to be measured is not flat. Typical examples of this case are e.g. a gear root and cylindrical parts with a small radius. The goniometer is typically aligned with the help of a fluoroscopic screen which makes the X-rays visible as is shown in Fig. 3. This procedure used to be done manually; the reference lines observed in a vertical position were drawn on the fluoroscopic screen using a pencil and the bright spot was then monitored by the naked eye during the tilting and rotating of the mechanism. The major disadvantages of this method have been poor accuracy, poor documentation and, most of all, the increased risk of a radiation exposure. These problems have been solved by the introduction of a CCD camera designed by CCD Photonics Ltd. The processor camera reads the fluorescent image of the X-ray spot on the screen. The movements of the spot can be recorded into a data file together with mechanical adjustment data. Says Mr. Lasse Suominen (lasse.suominen@stresstech.fi): ”We aim at high reliability and repeatability in the use of our instruments. Our customers, such as DaimlerChrysler, Ford, Renault, Toyota, Volvo, Aerospatiale, Boeing and General Electric, have high quality standards and we certainly live up to their expectations.”
Fig. 4. The X-ray diffraction laws are obeyed even in the harsh conditions of Finnish winter. The measurement of residual stress is carried out using an XSTRESS instrument from Stresstech Oy. Spin-off company CCD Photonics Ltd is a spin-off
company from Technical Research Centre of Finland (VTT), founded in 1990
by Dr. Kimmo Simomaa, one of the founding members of the Vision Club of
Finland. The company welcomes any challenging development tasks where modern
machine vision methods should be taken into use in old or new designs.
Contact Dr. Kimmo Simomaa
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