FEATURE THERMAL IMAGING & VISION SYSTEMS VISION SYSTEMS AND QUALITY CONTROL
Roptec has teamed up with Stemmer Imaging to provide a customer in the paper industry with an effective vision system that ensures each paper roll is perfectly packed
they reach the printing machines. According to Rossbruch, the particular
challenge is the fact that very large objects need to be evenly illuminated: “Besides that, the packaging line shouldn’t have to slow down or stop to carry out the evaluation. Stopping the line was only permitted in the case of an error detection.” The enormous weight of the paper rolls required a robust steel construction to protect the mounting of the imaging system and the camera housing from damage caused by “derailed” rolls.
H
igh requirements for speed and accuracy make machine vision an
ideal solution for quality control in the print and paper industries. The German company Roptec proves that this technology goes far beyond the mere production process. Their machine vision system is used for optical quality control in the handling of paper rolls. With up to 2,000m of paper web passing modern systems each minute, the paper industry has to deal with extremely high production speeds. Paper rolls weighing up to 5,000kg with widths of up to 5m and diameters of 1.5m are wrapped in order to prevent them from damage, and are then transported for further processing. On arrival they are unwrapped, placed in printing machines and are eventually changed at full production speed by an automatic paper roll changer. Even the smallest defects on these rolls can cause the tearing of the paper during paper roll changes, resulting in production stops or printing errors. Another source of error lies in the
packaging of the paper rolls: their end faces and sides are wrapped in thin paper for shipment to protect them against damage during transportation and further handling and to ensure consistent quality in the subsequent printing process. Damage to this packaging can lead to expensive malfunctions in the automatic crane systems which are used to handle
18 APRIL 2018 | INSTRUMENTATION
Roptec machine vision systems inspect up to 5,000kg heavy paper rolls for transportation and handling damages and read the labels on the rolls before they reach the printing machines. Credit: Roptec
the paper rolls during storage and retrieval due to their great weight. The necessary consequence is manual intervention, which involves additional risks and hazards - they can damage or even knock over other rolls, which must be avoided at all costs due to the danger to employees and for economic reasons.
Example of error detection: Incorrect labelling. Credit: Roptec
Example of error detection: Ruptured wrapping. Credit: Roptec
OBJECT SIZE AS A CHALLENGE Frank Rossbruch and his company have specialised in this industry segment and developed the RCx Roptec Control System which uses machine vision to detect faulty wrapped paper rolls. Roptec managing director Rossbruch explains: “The task was to check the packaging of the paper rolls’ end faces for possible defects and to automatically sort out the poorly packed ones and repack them. Apart from that, labels should be checked on the end faces of the rolls for presence, wrinkle-free application and positioning. The labels for the identification of the rolls are applied in moist condition. In some cases, labels might slip, wrinkle or even fall off when applied by the robot arm. If one of these errors occurs, the system stops immediately and allows the operator to apply a new label.” Roptec machine vision systems inspect up to 5,000kg heavy paper rolls for transportation and handling damages and read the labels on the rolls before
FINAL INSPECTION ACCORDING TO SCHEDULE According to Rossbruch, it was unusual that his customer was completely unaware of how many defective rolls were fed into production every day. He assumed a certain number, which was solely based on random observations. With the help of Roptec, this question can now be answered precisely. Rossbruch describes the further course of the project: “First, we built a prototype of the system and used the identical hardware regarding camera, lens and illumination as in the final version. During a test run of three days, all paper rolls were initially recorded from one end face and evaluated manually. This enabled us to identify specific defects. Based on these data and images, we were able to work out the perfect machine vision solution.” Rossbruch is particularly proud that the system could be implemented as planned after a detailed specification in accordance with Part 2 of VDI/VDE 2632 and additional discussions with the client. It passed the final inspection without any open issues well before the due date.
EXPERT PARTNER FOR MACHINE VISION Stemmer Imaging, Roptec’s machine vision partner, contributed to the smooth running of the entire project. Rossbruch praises the excellent support: “As a first step, we attended basic machine vision training at the European Imaging Academy. Following this, we arranged an individual training session tailored to our specific questions on the system, which saved us a great deal of time and facilitated the successful implementation. For example, Stemmer Imaging simulated
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