Pallet or container racking essentially consists of vertical uprights and horizontal beams. The supporting structures are exposed to thermal and static influences as well as dynamic stresses and impact loads, for example through the integration of shuttle systems. The resulting deformation of racking components under load, for example due to deflection or expansion, must be closely monitored. Permissible limit deviations, deformations and clearances, for example for industrial trucks or storage and retrieval machines (SRMs) that operate adjustable pallet racking with a single depth, were regulated at an early stage in the European standard DIN EN 15620 "Fixed steel pallet racking". It ensures that the functional requirements are met and that suitable interaction with the SRMs is ensured at the same time.

Deformation due to load impact
Class 200 includes racks in which the SRMs are automatically controlled and which have a fine positioning system at the storage locations of the load units. For fine positioning, influences that affect the tolerances of the steel structure in the warehouse must be considered. In addition to mechanical tolerances due to material and assembly-related variances such as uneven hall floors, wall and wind loads, elastic deformations depending on the load condition, these also include static and dynamic loads of the stacker crane due to different load conditions (empty travel, retrieval with load), forces due to acceleration and deceleration as well as thermal deformations and material expansion under the influence of temperature changes. If we initially only consider the deformation caused by different load conditions, it quickly becomes clear that the horizontal position changes as a result of the deflection of the transom.

As the horizontal position changes, so can the vertical position, as the uprights also deform as a result of dynamic, thermal or impact loads. It is therefore important that the functional requirements for the precise positioning of a SRM are met.

Disadvantages of positioning with binary sensors
Coarse and fine positioning is usually carried out for positioning the stacker crane in the X and Y directions. Barcode positioning systems, optical distance sensors with a long range or incremental encoders are used for coarse positioning, for example. Once the coarse position has been reached, the compartment fine positioning takes over the precise approach of the SRM to its end position. For this purpose, at least two optical diffuse reflection sensors are mounted on the load handling attachment of the SRM for each positioning direction - i.e. at least four sensors for the X and Y directions. Without object detection, the outputs of the scanners are OFF. If a sensor detects the edge of a upright or a latch, the output status changes - the sensor output shows ON. With the new signal status, firstly the direction of movement of the SRM can be recognized and secondly the desired target position in relation to the edge can be calculated. However, this proven solution with binary sensors has disadvantages: limited space, risk of incorrect switching, complex alignment of the binary sensors and lack of further status information. New possibilities and solutions resulting from digitalization in the context of Industry 4.0 for diagnostics and predictive maintenance cannot be supported either.

Camera and specific evaluation
A camera-based positioning system with an evaluation algorithm tailored to the specific application is ideal for future-oriented compartment fine positioning. Users appreciate solutions in which the camera and evaluation unit are integrated into a compact system. They enable simple commissioning and operation. With the IPS 200i/400i product family, Leuze electronic offers the smallest camera-based sensor for compartment fine positioning of stacker cranes. With an additional quality indicator, it helps to reduce stacker crane downtimes and thus meets the requirement for condition monitoring. Time-consuming installation, alignment and readjustment during operation are no longer necessary. The IPS 200i/400i uses a quality indicator to report changes to the sensor or shelf. This allows the user to detect possible malfunctions in the operating process at an early stage and carry out preventive maintenance in the sense of predictive maintenance. The quality indicator helps to detect soiling or an overhanging film at any position, for example. The system area at risk can be localized in good time and system downtime due to incorrect positioning can be avoided.

Fast commissioning and high reading performance
The IPS 200i has been developed for single-deep bins or pallet warehouses, the IPS 400i for double-deep pallet warehouses. The web-based, multilingual configuration tool with user-guided wizard shortens the commissioning time. The IPS 200i/400i can be configured via XML commands or commissioned using printed parameterization codes via the code generator tool. Feedback LEDs provide direct feedback and make it easy to align the sensor, as the position of the marker relative to the sensor is indicated by the four LEDs on the side.

The sensor, which is optimized for high depth of field and has a fixed focus position, is used for the optical fine positioning of a stacker crane in the X or Y direction after rough positioning has been completed. It can transmit the correction coordinates to the stacker crane for the exact approach of a shelf. For this purpose, the sensor detects circular holes (markers) or reflectors in the latch or upright and determines the position deviation of pallets or containers in the X and Y directions relative to the target position. The 66 x 43 x 44 millimeter small IPS 200i /400i in industrial design with protection class IP 65 is suitable for use in the normal temperature range as well as optionally with integrated heating for the deep-freeze range down to minus 30 degrees Celsius. Thanks to three-sided mounting, it can be flexibly attached to the stacker crane.