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a) Five production lines supply up to 40 cartons per minute of different size and color.
b) The color area sensor Simatic MV220
c) Touch Panel Simatic TP170B in the control cabinetHochwald Nahrungsmittel-Werke GmbH, a leading manufacturer of condensed milk employs aneasy to handle and economic vision sensor from Siemens to guid the growing number of different cartons at the final packaging onto the proper path prior to the palletising.
With the high-quality products Bärenmarke, Glücksklee and different export articles, the HochwaldNahrungsmittel-Werke GmbH located in Polling, Germany, has already many years ago thrown the switch for worldwide success. Efficient switchpositioning is also demanded to reliably sort the cartons with condensed milk at the packaging depot depending on the destination country.
At the Weiding plant, approximately 180 employees process about200 million liters of milk into condensed milk, milk powder specialties and fresh products. A large percentage of the condensed milk is intended for export and filled on five production lines into cans of 80, 170, 340 and 410 grams. The cans are then packaged in single, double orquadruple layers into cartons and reach the central carton depot viaa common conveyor route. There, before the palletising, the cartons have to be sorted again by type onto five accumulation tracks, which requires a definitive identification of the individual packages.
At the beginning, this could still be accomplished error-free via two sequentially arranged light barrier by means of the different heights and/or lengths of the cartons. However, with the growing variety – lastly about 100 different variations in 18 sizes – it became more and more difficult to sort the cartons solely by their dimensions. “To nevertheless achieve a reliable allocation of the cartons onto the proper accumulation track – without having to intervene manually – we were looking for a system that was as cost-effective and simple to set up as possible, which in addition could detect the cartons passing through bytheir color,” explains Markus Werkstetter, electrical engineering manager at Hochwald in Polling.
Simple, compact and cost-effective
After comparing several alternatives, the decision was made for a vision sensor Simatic MV220 from Siemens Automation and Drives (A&D). This innovative color area sensor is the synthesis of powerful image processing technology with simple, compact sensor technology. It is constructed to the IP 65 degree of protection and thus suitable for the application in rough industrial environments.
All elements required for the simple check of colored distinguishing features are groupedin a compact enclosure measuring 113 x 35 x 90mm. First of all, a digital camera featuring a CMOS chip for the color analysis of images with a resolution of 640 x 480 pixels and a continuously adjustable lenswith a variable image field from 40 x 30 to 200 x 150mm at object distances from 50 to 250mm. Add to this a white light illumination, a laser-based alignment aid as well as a simple operator and display unit with buttons, display and LEDs. The also integrated digital inputs and outputs are implemented via M12 connectors, just like the power supply.The vision sensor can learn up to 16 different test models, save themand reliably detect them in automatic mode either at stationary or moving objects.
Color Detection without extensive Programming
Beforehand, the system has to be aligned manually, which is assisted by two laser dots projected into the image window. Supplied templates help in the menu-driven adjustment of the sensor to the prevailingenvironmental conditions. The learning of the test tasks is then reduced to the presentation of one or several OK objects. Once the sensor has learned all models, the test operation can immediately be started.
To detect a single carton color or a printed on logo, Hochwald employs the test type “Matching” at an average test density of 64 colors –possible also are 16 and 2048 colors. The color sample (model) to bedetected is specified by the central controller and transmitted to thedevice via its digital inputs.
“For our purposes, it is at thepresent entirely sufficient to detect a single color sample and to link the result with the subsequent geometry scan,” says Markus Werkstetter. The central controller, a Simatic S7 300 with 315 2 DP CPU, can unambiguously and error-free determine the shape and color of the carton from this information, and accordingly its destination. The connection to the Simatic controller is implemented via the digital inputs andoutputs of the vision sensor and distributed, on-site ET 200 I/O stations by means of Profibus. For the local operation and monitoring of the carton depot, a Touch Panel Simatic TP170B is used. In the future,it is planned to network the autonomous control systems of the fillingstations and the carton depot with each other to make the processes even more transparent.
Until then, Hochwald checks the cartons as they pass through, with the exact time of the photo taking beingtriggered by a digital input. Each of the five supplying production lines possesses a capacity of 5 to 12 cartons per minute. This resultsin a theoretical overall output of 1 carton per second. In practice, clever production planning makes sure that as few as possible uniform and same-color cartons are loaded and that a maximum of about 40 cartons per minute pass through the detection at the depot. The MV220 is designed to take up to 30 photos per second and – in this regard – will not reach its limits anytime soon.
The sensory switch positioning with the vision sensor from Siemens has proven itself at Hochwald: “The functionality of the MV220 is tailor-made for our requirements; the handling is easy and convenient. Furthermore, no special know-how whatsoever is needed to get the device up and running. In short, the price/performance ratio is right,” concludes Werkstetter.
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