Reliable detection with the MLG-2 light grid

6. March 2015

Reliable measurements no matter how diverse or colorful the products

Mixed pallet handling is required in the retail sector to increase efficiency in sales locations. Logistics service providers are responding to this need with compatible automation solutions. Due to shining, transparent or dark packaging material, there are major optical challenges to be faced from one end of the logistics process to the other. It was in this context that Dematic worked in close collaboration with SICK to develop a specialist solution for reliable volume measurement.



The pallets used to supply goods to retailers today are loaded with all manner of goods in every color of the rainbow. In the warehouse, the pallets are loaded in exactly the same order in which they will subsequently be unloaded in the supermarket, layer after layer, and the goods stacked on the shelves. This speeds up processes and can save retailers’ storage space. And for smaller shops and kiosks, this is simply the only way to supply goods. So that this can work, the entire logistics process, from goods being placed into storage through loading and shipping of pallets, must run smoothly – in spite of the major challenges faced in the detection of “colorful mixed” goods.   The logistics experts at Dematic design and develop high-performance systems to automate and customize as many stages of this process as possible: from identifying the best possible storage location, using software to calculate the pallet loading sequence through the provision of the required items in the correct order, the picking of items for the pallet, and the wrapping of the pallet in film for high transportability. The software used to calculate the loading sequence also simultaneously optimizes the loading density of the pallet and makes it possible for pallets to be stacked one on top of the other, so that transport costs are reduced.

Volume measurement for optimum storage space

Vital to identify the best place in storage as well as for the optimum loading of mixes pallets is the provision of basic data such as the dimension of goods, the volume, weight and packaging properties. Finding a reliable way to obtain this data was a major challenge for Dematic. The “mixture” of the goods on the pallet is reflected in the varying sensory challenges posed by the objects to be detected. Each and every one has to be detected and measured safely and without errors: products inside black or dark blue packages, shiny film, or transparent film packages.

Successful tests with the MLG-2

It was this very challenge that the design engineers from Dematic and SICK came together to take on. The volume of the various goods loaded onto and transported along a belt had to be detected and determined. Initial tests were carried out with the VML Pro volume measurement system, which uses the MLG-2 measuring automation light grid.



The high measurement accuracy, reliable detection of transparent objects, and rapid response time were a perfect match for Dematic’s requirements. The LED sender/receiver technology in the light grid is not specifically linked to the physical features of the object to be detected. The MLG-2 can be relied upon to detect transparent bottles, black or dark blue packages, or even goods wrapped in film. Therefore, the light grid was the solution of choice for Dematic’s project.       The customer has set up a loop with two light grid sender units and two light grid GA_Cover_PI_VML_Pro_madness_140507receiver units positioned vertically and horizontally in relation to the belt. The volume of the goods is determined as they pass through this “light beam curtain”, providing the perfect solution for the application. Adapting the beam evaluation produced an even more stable application solution for non-aligned or unusually shaped products which has proved its worth in subsequent tests. The data captured is processed on a connected industrial PC and sent to the control system via the MSC800 controller, whose interface protocol has been adapted by Dematic to the company’s existing structures. Finally, the volume measurement system was installed in the new application at Dematic and underwent exhaustive tests.

Clever protection against dirt

As the project developed, the requirement for special protection against contamination quickly became clear. Although the light grid located underneath the conveying equipment is not affected by dust, if a package splits and sticky lemonade, for example, spills over it and dirt takes hold as a result, seamless operation may be at risk. Enclosing the light grid inside a perspex tube mitigates this risk. A continuous supply of compressed air is fed through this tube to prevent dirt taking hold.

Successful use in the retail sector

Work to adapt the MLG-2 light grid to meet requirements for reliable detection and volume measurement at Dematic has been completed successfully and the system is now in operation in a distribution center operated by a large retail chain. This is yet another example of SICK’s specialists working in close collaboration with their customers to provide effective solutions for application-specific requirements. Moreover, it also evidences the sensors’ flexibility and adaptability. The VML Pro solution is now also available as a complete system for volume measurement with light grids for other logistics applications.



  • The VML Pro track and trace system (a light-grid-based volume measurement system) is your object measurement solution for challenging logistics applications. Based on LED light grid technology, the VML Pro enables accurate determination of the smallest enveloping cuboid of objects, irrespective of their surface properties. It can thus be relied upon to measure transparent objects and objects wrapped in film in logistics applications.
  • The modular structure, in combination with the MSC800 system controller, ensures full compatibility with existing intralogistics solutions from SICK. At the same time, a high degree of flexibility is assured, which enables individual adaptation to specific application requirements. Amongst other things, the focus lies on the expansion through auto-identification and weighing systems.
  • The result is a reliable solution for challenging dimensioning tasks.




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