One safety solution instead of multiple light barriers with muting sensors: On multiple-track transport systems, this type of access guarding offers a significantly more efficient, more compact and often more economical alternative.
Transfer stations and material locks as risk factor
Automated processes must be safe: People present in production and logistic areas must not be endangered at any point in time. At the same time, safety solutions should enable operation that is as smooth and interruption-free as possible and result in only minimal service costs.
The Sensor People from Leuze develop efficient safety solutions for use in automated environments that satisfy these requirements. Safety solutions from Leuze show their strengths in, among other places, transfer stations and material locks: One example is the safety system for multiple-track transport systems that operates with laser scanners.
Access guarding must satisfy multiple requirements
The system is ideal for multiple-track transport systems such as are used in many production or logistics areas. From a technical perspective, a multiple-track transport system consists of multiple roller conveyors that are positioned next to one another. A cross conveyor feeds pallets to the roller conveyors. These pallets are transported to the transfer position on the individual tracks by means of gravity. There, an employee removes the pallets using a lift truck or forklift truck.
The requirement is that the danger zone around the cross conveyor be secured to prevent people from accessing the danger zone. For the area guarding, the protective device should only release the track on which the pallet is being output. Other basic requirements: The entire pallet transfer process must run interruption free. The installation work should be kept to a minimum and the system should be easily retrofittable.
Classic approach: Light barriers and muting sensors
To satisfy these requirements, conventional safety concepts operate with light barriers and muting sensors. A separate light barrier that safeguards the respective roller conveyor is needed for each individual roller conveyor. The muting sensors are used to allow the pallets to enter or exit. They immediately switch off a dangerous movement if a person enters the protected area – the sensors are able to distinguish here between the material on the pallet and a person. Two sensors are necessary per track if, for example, time-controlled cross muting is used.
If sequential muting is used, up to four muting sensors are connected in sequence per track. The advantage of these safety light barriers with integrated muting is that they can easily be integrated in the system control via two OSSD outputs. Moreover, there are pre-mounted muting sensor sets that further streamline installation.
High costs due to large numbers of sensors
With multiple-track systems in particular, however, this conventional type of access guarding also has disadvantages: The many individual components mean high costs for installation and service. The muting sensors also need space before and after the light barrier. If a muting sensor is accidentally moved or turns away, the muting process is no longer triggered and the sensor must be readjusted by a technician. In
addition, according to EN 62046, the distance between light barrier and transport material must not be greater than 200 millimeters in applications of protective equipment for the presence detection of persons because a person could otherwise enter the danger zone alongside the transport material. As a consequence, a safety light barrier with muting function is to be provided for each track.
Innovative and compact safety solution
As an alternative, Leuze offers an innovative multiple-track safeguard based on laser scanner technology that can be implemented much more compactly. The operating principle: Two safety laser scanners are installed above the roller conveyor. They create a vertical protective field over all tracks. If the transverse side-tracking skate passes a pallet, this is signalled to the control of the safety solution and a window the size of the transport material is opened at a corresponding point in the protective field. As soon as the pallet has passed, the protective fields of the safety laser scanner return to their starting position and the window closes again.
If necessary, a window can also be released for two adjacent tracks to allow two pallets (double pallet) to pass through simultaneously. Moreover, it is also possible to store windows of different sizes in the control. To do this, one only needs the information about which package passes which location. The solution is based on the innovative Smart Process Gating from Leuze – the process prevents the access of people without the use of additional muting sensors.
Just one system for ten tracks
Especially with larger systems with many roller conveyors, this saves costs – instead of multiple light barriers and muting sensors, a system with two safety laser scanners is used. Other components are a system control and the safety program. A system covers up to ten tracks and nine meters of width, thereby enabling a space-saving system design. Another advantage is the high protection against interference, since the two scanners are not located where people move, but rather above them. Fewer components also mean a manageable amount of service work: Annual inspections are required only for the two scanners and not for the many individual muting light barriers for each track. The protective fields produced by the laser scanners are scalable. As a result, the safety solution can easily be adapted to the given number of tracks.
High protection against bypassing
Such a system scores above all with optimum safety: Even during the ejection process, it constantly monitors the entire access area. Only one window of normatively permitted size is opened – thereby preventing a person from entering next to the package. Performance level d in accordance with EN ISO 13849-1 and safety level SIL 2 in accordance with IEC 61508 are achieved. Another advantage is the high level of protection against bypassing because the necessary control signal of the higher-level control makes tampering nearly impossible.
Less work and easily retrofittable
The safety solutions are pre-developed and individually tailored to the respective layout of the system. This saves time and money and guarantees optimum safety – from a legal vantage point as well. Practical for the system operating company: If necessary, the safety experts from Leuze can perform all steps for a smooth implementation, from the initial target/actual analysis to the hardware selection including accessories, to the configuration, commissioning support and acceptance of the system. Retrofitting is also easily possible because the safety solution is integrated in the safety circuit of the system control via a two-channel safety output.