In the incoming goods department at Würth's VZ West distribution center in Künzelsau-Gaisbach, which opened in May 2013, 30 people work in two shifts every day, moving around 3,000 boxes. They stack the 500 g to 5 kg cuboid cartons full of screws, nuts, washers or steel components from pallets into small load carriers (SLC). This means that the total load of an employee over the shift is several tons. The monotony of the work is just as stressful for the employee. Until now, consistent rotation after four hours was considered the best way to counteract the ergonomics and monotony of manual handling. However, Würth wants to increase the level of automation in logistics in order to relieve the strain on employees, cover further growth and counteract the increasing shortage of skilled workers.

Lightweight gripper, smart eyes

J. Schmalz set itself the task of intelligently automating the existing manual handling process. Their 'SBPG' BinPicking gripper is suitable for handling cartons of different weights. This gripper is long enough to plunge into the boxes and light enough not to reduce the payload of smaller robots too much. This means that a space-saving cobot from Universal Robots can guide the gripper, while the 'Vision Eco-System for Schmalz VE4S' takes over the vision. By using standard components from the Robotics and Vision division, Schmalz has provided Würth with an economical solution for less than EUR 100,000, which can be implemented quickly without a great deal of engineering effort thanks to the plug-and-play systems.

Two details were particularly challenging: firstly, picking from the pallet and placing the packages tightly into the boxes despite the high variance, and secondly, recognizing a layer pad with an unknown print. To make matters worse, the design of the layer pads can be similar to that of the boxes. The only approach that worked reliably was therefore the use of artificial intelligence. Schmalz implemented the defined setting pattern with workpiece-specific programming: the process started with a limited range of parts that utilizes the first cell to 100% capacity. Subsequently, the picking performance of the subsequent cells must be optimized and the range of parts increased in order to be able to store additional items automatically.

Other challenges, which arose due to the tight space conditions at the site and the additional task of picking the empty containers from a crate conveyor, were relatively easy to meet: A laser scanner eliminates the need for a safety fence, making for a lean cell. As soon as a person approaches, the collaborative robot reduces its speed and continues to work safely with reduced forces.

One system, three grippers

To complete the various gripping tasks, the cobot can independently swap the suction cups of the BinPicking gripper SBPG and - thanks to the quick-change module - the entire gripper. For this purpose, one load receptor is always on the robot arm while the other is waiting in the gripper station. If, for example, a crate needs to be moved, the cobot fetches the 'PXT' gripper designed for this purpose, which is immediately ready for use thanks to the standardized connection and communication. Three suction cups are available to the SBPG so that the robot can safely handle any size of box. The required vacuum is provided by a pneumatic vacuum generator. Employees enter the current job via the user interface of software implemented by Schmalz. The software communicates with the camera, the cobot and the safety laser scanner and adapts the robot controller and the camera to the task after the input. Würth also controls the entire order management of the robot cell via the software. This includes features such as the target container check, in which the camera checks whether the KLT provided is really empty, the recognition and removal of the intermediate layers from the source box and the collision check. The software calculates the waypoints that the robot approaches and uses the digital twin to check whether there are any collisions. If this is the case, it avoids the obstacles and defines new waypoints.

The author: Matthias Frey is Business Development Robotics at J. Schmalz in Glatten.

© J. Schmalz

The collaborative robot has been in operation at the VZ West distribution center since the end of December 2021. In their day-to-day work with the cobot, employees use the pallet truck to move a Euro pallet with boxes to the designated area. The boxes are between 100 and 250 mm long, 90 to 100 mm high and 90 mm wide. The robot picks up the KLT target container itself from a conveyor belt. The robot cell fills as many KLT containers until the Euro pallet is emptied. As they are pushed onto the conveyor system, the containers are scanned and recorded in the SAP system.