Whatever you do, it will always be necessary to change the gripper from time to time to match the handling task, and this causes a stoppage of the production process and reduces the productivity. This is particularly true in cases where products have to be stacked in layers on a pallet and sheets of paper or cardboard have to be inserted between the layers to provide the necessary stability. In most cases, the products, the sheets of paper or cardboard and the wooden or plastic pallets have widely varying properties. Messrs. STEIFF Förder- und Automatisierungstechnik GmbH in Giengen, manufacturers and system integrators of material-flow and handling solutions for many different requirements, frequently encounter this problem. As manufacturers and system integrators, STEIFF make use of the high-performance components available in the market. Recently, STEIFF were faced with the problem of packing and palleting transformers and consulted the vacuum technology specialists J. Schmalz GmbH in D-72293 Glatten.

The handling task consisted several steps using an industrial robot. The first step is to fetch a wooden Euro pallet from a stack and position it in a pallet-loading station. Packages of 10 transformers each than have to be lifted from a conveyor belt and placed in layers on the pallet. As each layer is completed, a sheet of paper or cardboard has to be laid on top of it, followed by further packages of transformers. This is repeated until the pallet is full. The pallet is then removed and, at the same time, the industrial robot positions a new empty pallet in the station.

It is thus necessary to handle three different products: transformers containing metal laminations, sheets of paper or cardboard and wooden pallets. While the sheets of paper and cardboard and the wooden pallets can be handled easily with a single gripper, the large-area vacuum gripper FX from Schmalz, the heavy packages of transformers present quite a problem. Due to their weight, their dimensions and the small available suction areas, these cannot be gripped and handled safely with vacuum. But the application specialists at Schmalz had a bright idea and implemented this in close cooperation with STEIFF. The solution was to use the magnetic grippers of the type SGM from the Schmalz product range. These operate with a permanent magnet which can be activated and deactivated either with a pneumatic valve (pressure-pressure) or with a compact ejector (pressure-vacuum).

The combination of a large area vacuum gripper FX and a magnetic gripper SGM was integrated into a robot gripper system in such a manner that the "wrist" of the robot moves either the vacuum gripper or the magnetic gripper to the working position. The swivelling action and the activation and deactivation of the magnets in the magnetic gripper are powered by compressed air, which means that no electric power is needed. This makes the construction of the gripper and the interface to the industrial robot much easier.

With the exception of the basic robot and the swivelling mechanism, most of the combined gripper was constructed from standard components from the Schmalz vacuum technology catalogue, such as the large-area vacuum gripper FX-600/120-SV, three magnetic grippers of the SGM80 series and spring plungers FSTE 3/8". The modular large-area vacuum gripper handles both the pallets and the sheets of cardboard. The three magnetic grippers handle the transformer packages, whereby three spring plungers, each with a stroke of 95 mm, compensate for any unevenness or varying heights of the packages. This relatively simple gripper system is characterised by its combination of vacuum and magnetic grippers which can handle three different products. By using standard components, it was possible to implement the gripper quickly and cheaply.