Every year, some 1.2 million porcelain plates for the domestic and catering sectors leave the factory of the long-established manufacturer Rosenthal, which is based in Selb, Germany and forms part of the world''s largest supplier of tableware, Waterford Wedgwood plc. An intelligent DVT camera represents one of the key components of an Iso press system that employs a revolutionary plate manufacturing procedure and is setting new standards in terms of speed and automation.
The saying "I like what I see" seems to ring true for this manufacturer of high-quality crockery: generously sized china plates and dishes, of the sort that are being increasingly used for innovative and creative food presentations, now number among the best-selling products in this sector.
"Some two years ago, in view of the booming sales of these products, we decided to invest in a completely new system that operates completely automatically and permits considerably higher manufacturing speeds," says engineer Joachim Reuer, production manager in Rosenthal''s Rothbuhl factory in Selb. Nowadays, the successfully installed system uses the Iso press procedure in which the clay, previously used in the form of a liquid slip as the raw material for the high-pressure molding procedure, has been replaced by a special press granulate. This granulate is injected into a mold where it is compacted under a pressure of approximately 300 bar to form the blank plate.
"The main advantage of this so-called Iso press procedure is the high manufacturing speed it offers," explains Reuer: "Whereas with slip as the starting material, using the conventional procedure, we were able to manufacture about 180 items per shift, the system now produces approximately 220 blank plates per hour from the molded granulate and is therefore some 10 times faster!" According to Reuer, this innovative procedure has further advantages, such as its high precision and the lower number of rejects: "While, in the past, we needed to manufacture 150 blanks to get 100 good products, this figure has now sunk to 130."
Intelligent and Fully Automatic
"As far as the further processing of the blank plates is concerned, the high manufacturing speed was one of the reasons that prompted us to employ image processing to assist in the subsequent process stage," adds engineer Andreas Rother, an electrical engineer working for Sama Maschinenbau GmbH in Weibenstadt, Germany, who designed the complete system and accompanied it through to the commissioning stage.
For production reasons, the edges of the blank plates have a mold edge that first has to be coarse ground and then finely cleaned with a sponge before the plate is transported to the kiln to be baked at a temperature of 900°C. To ensure the high quality of the end products, it is essential that the tolerances, which demand a precision on the order of tenths of millimeters, are not exceeded during the grinding and cleaning process.
"To automate these processes at the required level of precision using robots, we needed to introduce an intermediate station at which the robots could grip the plates in a precisely defined manner," continues Rother.
This is where, in the words of the Sama employee, image processing had a role to play: "On the one hand, mechanical centering mechanisms would not have permitted the necessary degree of precision and, on the other, they would have demanded excessively long setup times on any switchover to another of the 60 or so plate forms currently manufactured. Consequently, we considered an image processing system to be the best way of implementing a versatile, fast, high-precision positioning unit at low cost."
Robotic Data in a Few Milliseconds
"The blank plates are conveyed to the control station by means of a suction mechanism and deposited there," says Rother, as he describes the flow of materials. At the heart of this station lies a DVT Series 600 SmartImage sensor, which is mounted above a plate discharge area. This intelligent camera takes a picture of the area, illuminated by four spotlights, which is then processed directly in the camera by the integrated FrameWork software.
This DVT software possesses numerous useful image processing algorithms such as Blob analysis, object recognition, color image processing, and many other tools. The functions required in any given situation can be selected without difficulty, thus permitting the highly efficient parameterization of the entire system.
The results of the evaluation carried out by this application consist of the precise X and Y positions of the plate, together with its angle of rotation, and are available within a few milliseconds. The camera determines the position of the item and uses this to calculate the correction data for the robot.
While a second suction mechanism takes up the previously analyzed plate and deposits it on a stepping circular table, the camera is already communicating the precise correction data for the robot via an interface to a controller running a memory-resident program. This controller provides the three downstream Mitsubishi 6-axis robots with the correction data they require in order to grip the plates on the circular table. "Because the plates are always located in an identical position at the robot arm, thanks to the correction data, the robots can always execute the same program for the current plate type," explains Rother, as he describes the advantages of this procedure. "No further corrections have to be factored into the programmed grinding and cleaning movements."
Image Processing Is Crucial
The Sama engineer knows that the performance of the employed image processing system is decisive for the quality of the manufactured plates from his own painful experience: "At the start of this project, we knew very little about image processing and we initially chose another manufacturer''s intelligent camera to perform this task. However, during the implementation phase, it became clear that this image processing system had difficulty in recognizing the range of plate forms, despite week-long testing and all the manufacturer''s attempts to support the system."
Rother was finally able to solve the problem when he phoned DVT''s sales partner in Germany, Puchheim-based Stemmer Imaging GmbH: "Once we had given them a precise description of the application on the basis of a few pictures, they advised us to use the DVT camera. Using this camera, we were able to get the system operating successfully in just a few days!" Rother was particularly impressed by the fact that he could set up and test new plate forms at Stemmer Imaging via the Internet.
"Since we started, we have stored approximately 60 plate forms in the programmable controller, with the result that we can change between production runs extremely quickly," continues Rothar. "When new forms are introduced, we can partially derive the necessary robot trajectories from the CAD drawings of the plates. To teach the camera the new plate type, we simply need to present it with the general contour in order to switch over production." This means that it is possible to change to a new plate type, including retooling, within two hours.
Rosenthal''s positive experiences with the existing system have since encouraged the manufacturer to install a second Iso press manufacturing line. "The new system will have a similar structure to the initial version. As far as image processing is concerned, we will make use of the DVT 600''s successor, that is to say a DVT 500 camera," Rothar says enthusiastically as he speaks about Sama''s next job.
According to Rosenthal''s production manager Reuer, the completion of the second system will result in a further increase in the overall level of automation: "In the near future, the two stations will be linked to permit automatic throughput through to kiln stage." It is possible that by then a second image processing system will be operational to check the manufacturer''s stamp on the underside of the products.
Wide Range of Applications
These Rosenthal applications are simply an example of the tasks that can be accomplished using intelligent cameras. Further possibilities will continue to open up in almost every sector of the production industry.