The robot-guided depalletising systems from Polyplan require less than ten seconds cycle time per small load carrier (slc) when stacking these standardised reusable containers from a pallet. In addition to a wide variety of small load carriers on a pallet, the turnkey, integrable systems also master a wide range of challenges. These include reliable gripping even with position tolerances and position errors, recognising damaged crates, position detection and reading barcode labels or pre-sorting mixed slc during stacking.
The plant manufacturer Polyplan from Straßlach near Munich, which is part of the Pepperl+Fuchs Group, has realised around 20 such systems worldwide - still mainly in the automotive industry. However, not least due to the shortage of skilled workers, interest in the company's automated small load carrier depalletising systems is also growing in the intralogistics of industrial companies or distribution and distribution centres. Here too, multi-layer pallets loaded with small load carriers will no longer be unloaded manually in incoming goods or in goods distribution, but rather robotically guided. The depalletising systems from Polyplan can be designed very individually in terms of robotics, gripper technology, sensor technology, control technology, programming, conveyor connection and operation technology and information technology integration according to customer specifications. Some functions, such as differentiating between different types of small load carriers, are supported by machine learning - a feature that will also help to master new challenges in automated depalletising in a process- and future-proof manner.
Automated depalletising with maximum degrees of freedom
In practice, the flexibility and efficiency of systems for the automated depalletising of pallets depends significantly on the extent to which the large number of possible degrees of freedom can be taken into account and controlled in terms of process technology. Everyday practice presents a variety of challenges:
- pallets can be stacked in up to eight layers or a height of 1.4 metres,
- the pallet can be strapped to secure the load,
- there may be a pallet lid on the top layer of slc,
- there may be different types of slc on each layer,
- the stacking scheme may differ from layer to layer,
- the pallet or the load layer may have alignment or position errors,
- interfering contours and foreign objects, e.g. lost cargo, must be expected,
- slc may be damaged, gripping holes on the crates may be covered.
Polyplan's robot-guided depalletising systems master these challenges reliably and cost-effectively.
Application-orientated engineering of robotics and gripping technology
The design of a system is initially based on the customer's specifications. For example, the depalletising stations can currently be equipped with robots from KUKA, ABB or FANUC, depending on preference. Polyplan has the corresponding technology packages for the respective robot controllers for the operation technology integration of these makes into the system plc via PROFISAFE. The selection and design of the robot is based on the planned or actual spatial conditions on site and the expected load capacity. With a maximum slc weight of 25 kg and a gripper mass of around 95 kg, Polyplan provides robots with a payload of 150 kg to 210 kg, including a "safety reserve".
In order to be able to pick up the various types of small load carriers flexibly and safely, Polyplan equips the depalletising robot with a special multifunctional gripper with servomotor-driven pick-up mechanism, which moves automatically depending on the type of crate and orientation and adapts to the position of the gripping holes of the respective small load carrier. Two robot-controlled servomotors drive the linear travel units of the gripper, while the linear feed of the gripper axes takes place via spindle drives. The travelling and gripping movements are monitored by inductive initiators, which detect the correct gripping of the slc just as reliably as overgripping of a slc, a collision or the end stop of the spindle drives. The sensor signals are collected in the PROFINET IO box on the multifunction gripper and transmitted to the plc via a switch.
In addition to safe gripping, the robot's functionality can be further enhanced by optional modules, for example for handling EPP containers or cardboard boxes, for removing pallet strapping or for removing pallet lids.
3D sensor technology enables slc detection without loss of cycle time
The main objectives when using depalletising robots for destacking small load carriers include optimised personnel deployment and increased throughput. The latter is directly related to the reduction of cycle times. Polyplan achieves this in its systems with a measuring 3D vision solution. This reliably determines the stacking pattern of the top pallet level, identifies the crate types present and detects their orientation. These measured values are then converted into path coordinates for the robot's visual guidance.
Many automation solutions (still) use image processing cameras or sensors that are mounted directly on the gripper and display the individual captured pixels as grey values. In addition to problems with the detection of slc, which often have a different appearance due to dirt, colour deviations, gloss effects or lighting fluctuations, for example, and can therefore impair the availability and quality of grey-scale processing, this approach has a negative impact on the cycle time of the system. This is because the gripper has to approach the next crate to be picked up in order to determine its type. Even if this only takes a few seconds, valuable cycle time is lost with up to 80 slc per pallet.
In contrast, Polyplan uses a distance-measuring 3D vision solution from VMT Vision Machine Technic Bildverarbeitungssysteme GmbH - also a Pepperl+Fuchs Group company - in its slc depalletising systems. However, Polyplan has not integrated the measuring system into the multifunctional gripper, but installed it in a static position above the depalletising station. This enables it to determine an updated 3D image of the stacking scheme of the top pallet layer after each gripping operation, as well as the contour, height and position values for each small load carrier. In addition, position errors are recognised, which can be compensated for up to ± 20° around all rotation axes. The robot cycle - and therefore the speed of depalletising - is not affected by multiple approaches of the gripper and its sensors for measuring purposes - on the contrary: with a cycle time of less than ten seconds per slc, the robot-guided depalletising systems from Polyplan are among the fastest systems of their kind on the market. And this is achieved with maximum process reliability, as the individual pixels are not displayed as grey values, but as precise 3D distance and position values that are independent of the optical appearance of the surface and possible lighting fluctuations or extraneous light influences. This high-performance geometry and position measurement provides reliable path and gripping data for precise, collision-free guidance of the robot and positioning of the multifunctional gripper.
Feasibility test and pre-commissioning possible in our own vision and robotics laboratory
Polyplan has now implemented around twenty robot-guided slc depalletising systems worldwide - and has found that hardly any two systems are the same. For this reason, individual tasks can be comprehensively tested for feasibility in the in-house and specially equipped vision and robotics laboratory and boundary conditions can be taken into account when designing a depalletising system. The movements and gripping processes of robots can be simulated and optimised at an early stage. This makes applications controllable in terms of sensors, kinematics and handling technology. In addition, customer solutions can be set up and validated 1:1 before commissioning - which simplifies and speeds up acceptance on site.
Polyplan's robot-guided depalletising systems offer a high degree of process reliability, efficiency and cost-effectiveness from the project phase through to productive operation - especially as they can also be seamlessly integrated into existing automated production lines and material flow routes as well as their operation technology and information techgnology systems.
Pressekontakt
Polyplan-GmbH Polyurethan-Maschinen
Head of Sales, Aftersales and Marketing
Mr Jan Jacobi
Mitterstrassweg 23
D-82064 Strasslach
Phone: +49 (0)8170 - 9305 - 48
Fax: +49 (0)8170 - 9305 - 55
Email: jan.jacobi[at]polyplangmbh.de
Internet: www.polyplangmbh.de