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The automation at the beginning and end of a line depends on how the workpieces are fed and stored. If the delivery involves removing a single layer of goods from a pallet; contour or feature recognition is sufficient for enabling automated gripping and transfer. If the workpieces are in several layers, such as stacked blister packs or tablet packages, the robot requires a 2½D or 3D system. In the former case, the third dimension is extrapolated using contour distances or gray-scale values. For a real 3D process, the system measures using points in space.
The same is true of positioning. The more accurately the workpiece has to be placed, the more demanding the requirements put on the vision system. Placement on a conveyor belt is simple; positioning within a machine tool is challenging. The more flexibility required for loading and unloading a workpiece (into and out of the machine), the more complex the system. There are also rules of conduct, such as detecting and handling missing or incorrect parts, and collision models. Liebherr automation systems have a response for these various challenges.
New vision systems for bin picking
Liebherr works with a selection of three different variants chosen specific to the requirements. A red light laser is used in 3D vision systems that use a laser time-of-flight method. It offers a highly robust solution that is separate from ambient light conditions and the level of contamination. An alternative is to use a 3D vision system using a precise two-stage laser triangulation process with a blue light laser. This type of system is ideal for workpieces made of metal, organic and semi-transparent or reflective materials. The third option is the highly-flexible 3D stereo vision system with a triangulation process and supported by an additional projector unit. This option is perfect for short cycle times. The 3D stereo vision system can create complete and homogeneous depth maps of the scene using special projector technology.
As a result, it provides fast and high-resolution image recognition. This allows a robot with patented additional axes to empty transport containers up to one meter in depth with process precision. Optical detection occurs within five seconds, depending on the vision system and the associated evaluation. That enables short cycle times for the overall system. Thanks to the high resolution, the data cloud interface is smooth and virtually noiseless. These high-quality measured values are transmitted to the main software of the bin picking system. The software enables easy teaching of workpieces, grippers and their grip points.