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Robot cell equipped with Cognex vision keeps knives sharp

SIR Italy knife sharpening with vision enabled robotic arm

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SIR, an Italian machine builder specialized in robotics, has created a special cell for knife grinding and surface finishing using powerful PatMax® tools from Cognex

SIR is an Italian machine builder located in Modena. They have recently conceived and produced a cell that is dedicated to metalworking. The objective is to re-work worn out knives, which after being grinded and used have lost their original shape.

The peculiarity of this application is that it allows the refurbishing of different types of knives, whose blade shape is unknown, to their original conditions. In order to carry out a correct grinding, it is not possible to do a rough estimate of the degree of the knife’s usage and to assume a calculated path starting from the original one. Knives are usually grinded manually and the theoretic shape does not correspond with the real one. For this reason the use of a vision system has become necessary in order to estimate in real time the right profile of each knife.

The cell working process consists in the robot’s taking the knife and positioning it under the vision system in order to get the shape. Then both sides of the blade are grinded separately. Subsequently the knife is scoured in order to make the blade edge smoother and homogenous. At the end, the cold trimming operation eliminates any tailings due to the grinding from the blade. When this is over the knife is placed in a basket that is similar to the one from which it was taken.

The vision system cycle consists of a first recognition of the type of knife handle, as not all handles are the same even for the same kind of knives. Afterwards the blade is scanned in order to calculate all the necessary points to reconstruct the original shape. After getting the profile, the execution of the first analysis of the blade serves to discriminate all the anomalous points and verify the presence on the same blade of too many deep niches in order to continue with the normal working cycle.

Once the first analyses are finished, the profile is standardized in order to bring the knife back to its original shape. Once the standardized profile is obtained, the execution of the second analysis cycle allows verification of the degree of blade use in order to correct the working parameters such as speeds and incidence angles. Next step is to decide what point to start the work from in order to avoid ruining the knife handles, in case of very damaged blades.  Even the finishing points are decided from time to time, after having taken into consideration the angles and the shape of the knife tip.

The robot is made up of a Cognex VPM-8501 image acquisition card with VisionPro® using PatMax software tools. An analogical resolution standard camera is connected to the card and the front or back system. Lighting can be driven alternatively depending on the analysis type to be carried out. The communication with the robot is via Internet and thanks to the transmission of files, quotes and angles in which are described all the processes of grinding, scouring, cold trimming that he have to be carried out as well as the beginning and the end of the working process. The software leverages simple screenshots for the regulation of the research parameters.

This unique application is having great success as it allows the system to acquire an outstanding decision skill level, which is demanding, considering that the production is random and that no knife will be like another.

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