Protecting people and machines from hazardous processes in production and logistics is a top priority for Dr. Weigert, alongside our responsibility for hygiene and the environment," says Dirk Böttger, Deputy Plant Manager at Dr. Weigert, the Hamburg-based developer and manufacturer of cleaning agents and disinfectants. For example, in fast, automated processes such as in the area of the film winder and roller door. The company's partners include Industrieautomation Dirk Hähner as a service provider for programming and service work and Leuze electronic, manufacturer of the safety-related protective devices for safeguarding the inflow and outflow of material in the area of the film winder and roller shutter.

Safety requirements

Material flow: After a robot has stacked filled cleaning agents on a Euro pallet, they are transported on to secondary packaging.

© Leuze electronic

Dr. Weigert mixes cleaning agents and disinfectants for cleaning and disinfection in laboratory and medical technology, in the canteen kitchen sector and in the pharmaceutical, cosmetics and food industries using only recipes developed in-house. After the mixing process, the chemical products are filled into plastic canisters of different volumes and shapes and then stacked on pallets by robots. Automated guided vehicles transport the products stacked on Euro pallets to the area where the 'Tosa 126 E' film wrapper wraps the goods.

The complete material flow process - from the infeed to the film winder, through its outfeed to passing through the roller door on the way to the warehouse - is controlled by a safe system solution concept from Leuze electronic.

Securing the roller shutter

When the Tosa film winder was commissioned, the roller shutter door at the outlet of the material flow towards the warehouse was replaced with a new one at the same time. The previous door was not protected by any safety technology. However, innovations in the Machinery Directive now make safety monitoring mandatory. "Securing the roller shutter door was not easy, as muting with sensors was hardly feasible for space reasons - and we would not have been awarded the contract without a coherent, holistic safety concept," says Dirk Hähner, Managing Director of the company in question. One specific safety requirement was that material transport would in future be carried out safely into and out of the danger zone, which was secured against unauthorized access. Due to the space restrictions in the area of the roller shutter, a space-saving safety solution was sought that would detect the approach of the wrapped Euro pallet on the conveyor belt, temporarily bypass the protective field and thus ensure uninterrupted passage of the transported goods. However, it was important that the protective field is only bridged when the transported goods approach, but that access by persons is prevented. Previously, additional sensors were essential for detecting the transported goods - and therefore also for distinguishing between people.

Smart Process Gating

Dirk Hähner relies on 'Smart Process Gating' (SPG), a sensorless muting process from Leuze electronic. This muting method does not require additional muting sensors when safeguarding hazardous areas that need to be secured against unauthorized access. It is based on type 4 safety light curtains from the 'MLC' series and is integrated into the MLC 530 SPG variant. The basic principle of the SPG method uses two control signals: the first signal (Control Signal, CS) is provided by the system control, the second signal (Protective Field Interruption, PFI) is generated by the safety light curtain itself when the protective field is interrupted.

As Smart Process Gating does not require any space for muting sensors in front of and behind the light curtain, space-saving solutions are possible.

© Leuze electronic

In order to bridge the protective field of the safety light curtain for the passage of the transported goods, the first switching signal is sent from the process control to the safety light curtain shortly before the goods enter the protective field. The time must be set so that the transported goods are closer than 200 mm in front of the protective field. This is necessary to prevent people from slipping through. The SPG procedure therefore requires knowledge of the position of the transported goods so that the necessary PLC control signals are present at the safety light curtain in the correct time window. The safety light curtain generates the second signal when it enters the protective field. This starts the bridging of the protective field. The bridging ends after a fixed time once the transported goods have left the protective field again.

The integration of an SPG application into a system must be viewed as a safety-related system solution that is created by the interaction of the safety light curtain, system control and, if necessary, mechanical elements. For this, the system manufacturer needs experience in safety design, as he programs the gating sequence in the PLC, for example, and creates the safety system solution himself. An important requirement is that the system controller knows the current position of the transported goods. The PLC must know when the transported goods reach or leave the protective field in order to send the necessary control signals to the safety light curtain at the right time. The achievable performance level of the solution is determined by the system controller used: performance level d is achieved with a standard controller, while performance level e is achieved with a safety controller.

Thanks to the Smart Process Gating application, the pallets at Dr. Weigert are transported in a fail-safe manner - even interrupted pallets with a gap between the load.

Author:
Martina Schili is responsible for Corporate Communications and Public Relations at Leuze electronic in Owen.