Vision system at the cutting edge

Edited by the Engineeringtalk editorial team Aug 29, 2005

An Italian machine builder specialising 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, Italy.

The company has recently conceived and produced a cell that is dedicated to metalworking.

The objective is to rework worn out knives, which after being ground and used have lost their original shape.

The novelty 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 ground manually and the theoretic shape does not correspond with the real one.

For this reason the vision system is needed to estimate in real time the correct profile of each knife.

When the cell is in operation, the robot takes the knife and positions it under the vision system in order to determine the shape.

Then both sides of the blade are ground 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 standardised in order to bring the knife back to its original shape.

Once the standardised 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.

The next step is to decide at which point to start the work in order to avoid ruining the knife's handle, 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 incorporates a Cognex VPM-8501 image acquisition card with VisionPro using PatMax, Blob and Caliper 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.