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Automation Technologies 3/2015

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Automation Technologies 3/2015


MACHINE VISION 6D camera with adaptive perception technology 3D cameras are a better solution than 2D cameras. They do, however, get a bad press as they are often regarded as too complicated and are usually only designed for one specific use. A slightly different universal 3D camera is now opening up new possibilities. In the field of packaging and logistics majority of the inspection is carried out by 2D cameras. In order to make any small recesses and surface structures visible, special lighting is used. The 2D camera then takes the images consecutively with different angles of light or colors. The cost of the entire operation is therefore high and the process involves a lot more variables apart from the performance of the camera itself. This process can be highly simplified using a 3D approach. The arguments against the use of 3D camera is that the initial cost of the camera itself is high and a special version of camera is required for every specific application, with very limited number of system integrators who are 3D-literate. To counter this arguments, the camera manufacturer Matrix vision decided to design, develop and manufacture a 3D camera. Their objective was to be able to maximize the applications and functionality of a single 3D camera. After evaluating the existing 3D procedures, their aim was to be able to combine all the benefits of the existing procedures while eliminating their restrictions. Time of flight Time of Flight (TOF) systems emit light and measure the phase shift of the reflected light (Diagram 1). The distance from the object can be determined as a result of this shift. The measurement is taken very quickly and both moving and stationary objects can be equally well detected. However, the light that is emitted must compete against the ambient light, which means that it is not really possible to use it in an outdoor setting. Multiple reflections can give rise to pseudo-objects. Company name: Matrix Vision GmbH Headquarters: Oppenweiler, Germany Employees: 80 Products: industrial cameras, smart camera, frame grabber, image processing software, Lenses About

MACHINE VISION Laser triangulation method In the case of laser triangulation, a laser line is projected onto an object at a defined angle (Diagram 2). The scene is captured by a camera at a different angle. Every change in height results in a shift in the projected line in the image. A height profile can be captured along an individual line as a result of this. In order to record the image, the object is moved underneath the recording system, during which time the recording speed must be synchronized with the speed of movement of the object. The measurement resolution and the scan time are extremely high in this procedure. next page 01 Operating principles for the time of flight method Stripe light projection method Stripe light projection is similar to laser triangulation. However, with this method, several stripes are projected onto the scene at the same time using a projector (Diagram 3). Instead of moving the object, the stripes are moved with the projector until the striped pattern is repeated. This procedure therefore only requires 10 to 30 images instead of hundreds. The accuracy of measurement is extremely high and depends on the angle of projection and the distance between the projector and the camera, which should be kept constant. The downside here is that the system is therefore sensitive to fluctuations in temperature and mechanical strains. A second camera can be used to construct a stereo system. This eliminates the problem of having to hold a hot projector in a constant position. However, the other disadvantages of the procedure still remain. Structured light method Another procedure uses what is known as structured light, where a static light source projects an irregular structure onto the object (Diagram 4). The light source is placed at a defined distance from the camera. The measuring principle is comparable with the stereo procedure. It is possible to achieve an enhanced version of this procedure using two cameras, the benefit of which is that the light source does not need to be kept at a constant angle or distance. The scene is captured with a single image and depth information can be calculated. Nevertheless, the measurement resolution is lower than with stripe light projection, as the projected structure has to be depicted in more than one pixel. 02 Operating principles for the laser triangulation method Dilemma of the 3D procedure 03 Stripe light projection or the frings protection method All of the systems described are constructed for a pre-defined measurement range. The comparison shows that every procedure offers specific benefits for each individual application. This therefore makes the decision more difficult for the user. A universal system that combines all of the benefits and only has a few disadvantages would be a worthwhile objective in terms of development. AUTOMATION TECHNOLOGIES 3/2015


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