Light section sensors: reliable detection of medicine packages

Light section sensors operate according to the so-called light-section method, a commonly used method for optical shape recognition. With this method, a line projector projects a wide light beam onto the measurement object at a known angle. In the case of the line profile sensors (LPS) from Leuze electronic, a laser that produces a narrow and bright light on the measurement object is used. The thereby produced light plane cuts the object along the profile line, which is why such sensors are often referred to as profile section sensors.

From the perspective of a position-sensitive detector (camera), the path of this profile is bent to a greater or lesser extent as a function of the object height. With knowledge of the geometry of light beam and camera, exact 3D coordinates of the test sample can be determined according to the triangulation principle. Due to its accuracy and robustness, this process has proven itself in many areas of application. A big advantage of this type of object detection over camera-based image processing systems is the exceptionally economical price/performance ratio as well as the overall very compact and easy-to-integrate sensor system.

The LPS light section sensors from Leuze electronic combine the laser as light source and the camera in one housing. Measuring just 160 × 74 × 56mm, they are the most compact sensors of their type on the market and can also be used when space is very tight.

Compact design is, however, just one of the advantages of these sensors, which is why Maximilian Pfau, software developer at Gollmann Kommissioniersysteme GmbH, chose the LPS 36 from Leuze electronic. The company from Halle (Saale) is among the leading manufacturers of picking machines for pharmacies. With this patented, automated, roll-fronted system, the "wandering gap' storage principle - proven over decades - achieves a very high storage density and, compared to conventional storage methods with classic drawer systems, reduces space by up to two-thirds.

Depending on the design, the compact and flexible picking systems in a pharmacy hold several thousand packages in every meter of housing length. In such a system, each package lies ready in its own storage space for direct and fast access. Even in the basic version, these systems allow for the storage and immediate availability of 100 packages in less than 8 minutes as well as the retrieval of 350 packages per hour.

Direct dispensing of stored packages

The stored packages can be dispensed directly at the machine or at any location in the room by means of an optional conveyor system. The benefits of this system include an increase in retail space and in time savings in inventory management. The acceptance of goods, returns, inventory, goods issue and assortment maintenance can be handled much more effectively, allowing resources to be used for other value-creating activities in the pharmacy and making more time available to consult with customers.

The light section sensors from Leuze electronic are used in fully automated warehousing modules, which can optionally be adapted to the picking machines. With these modules, the picking machines are loaded fully automatically within seconds. Goods deliveries are simply emptied unsorted into a container and separated on a conveying belt. An LPS 36 light section sensor then detects the contour, position and volume of the individual medicine packages as they pass through.

Pfau explains: "We originally wanted to use image recognition systems here; due to the widely varying patterns and colours of the medicine cartons, however, this did not function reliably." In spite of the considerable effort taken to create stable lighting conditions through the use of additional lights, not all packages were fully detected depending on pattern and colour differences.

Pfau confirms: "With the height information provided by the light section sensors, reliable detection of all packages was ensured right from the start." In this regard, Pfau greatly values the fact that no additional lighting is needed for the LPS 36. The sensors function exclusively with their own laser light.

Using the 3D coordinates ascertained for the medicine cartons, the handling system in the warehousing module can correctly and gently receive the packages and deposit them in the transfer bin of the picking machines.Pfau adds: "At the same time, the volume information is used for space-saving storage in the picking machines."

For data transfer, he uses the Ethernet interface of the LPS 36, eliminating the need for a serial connection or laying of a USB cable. Pfau says: "Even aside from this, the Leuze electronic sensors ideally complement our application. With a line length of 600 millimetres and a measurement range of up to 800 millimetres, we detect the entire range of package sizes, from the smallest eye ointment to the largest dressing package." The detection of this variety of products over the required range is considered a big plus.

For further information about light section sensors from Leuze electronic please visit www.leuze.co.uk.