Light Curtains

Light Curtains

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Safety light curtains are electro-sensitive protective equipment (ESPE) used in machinery safety. Whenever they detect the presence of a person within a monitored area, usually close to the machine danger points, the light curtains emit a stop signal that instantly halt any mechanical movement.

Their technology is based on an operating principle involving the interruption of infrared beams, whose emission and reception are regulated by an integrated controller. There are light curtains with different detection resolutions, based on the number and position of the beams: resolution of 14 mm, for example, corresponds to the detection of a finger, while 30 mm one to the detection of a hand; up to light grids with two, three or four beams, which can detect the whole body.

Light curtains consist of an emitter and a receiver. The maximum distance between these components equals the maximum length of the monitored area, while its height equals the active part of the light curtain, where the receivers are physically installed. Retro-reflective light curtains are an exception: in this case emitters and receivers are both located on the barrier active part. When the passive part is activated, it sends the beams back to the active one, making use of a suitably oriented system of mirrors.

In addition to the main detection function, some light curtains models include other operative features such as the manual resetof the outputs following a shutdown, the monitoring of external devices connected to the barrier outputs (EDM), and the diagnostic functions to facilitate proper alignment between emitter and

Datalogic light curtains are designed with operating principles, redundant architectures, and internal diagnostics accordingly to rigorous international standards relating to safety components, and they are   certified for automatic machines related applications with a third-party approval. Depending on the model, they guarantee up to performance level “E”, the highest standard for machinery safety.


Most common applications of safety light curtains


  • Access control
    The most common application refers to the installation of physical guards, either fixed or mobile, to protect people once the dangerous points of the machinery have been identified. However, machinery such as presses and bending machines that require frequent interaction for manufacturing, it is necessary to leave some gate open. At these gates, light curtain provides immaterial protection, which causes the machine to stop whenever it detects a person crossing over. SG BASE barriers are designed to operate in scenarios like the aforementioned, by selecting the proper resolution.

  • Perimeter control 
    When machinery cannot be fenced with physical protections, light curtains can be adequately positioned around it to form a perimeter, after which they will be able to detect people approaching and shut down the machine. In such cases, human protection safety light grids (SG BODY COMPACT, SG BODY BIG) are often employed due to their longer operating distance (up to 60m). To reduce installation costs, the beams can be arranged as to be diverted with horizontally deflecting mirrors.

  • Presence control
    In addition to detecting a person crossing a gate or perimeter, when the light curtain is horizontally positioned it can also detect a person standing close to the danger zone. In this case its outputs can prevent the machine from restarting until the area is cleared. Some barriers (SG4 EXTENDED, SLIM) can be interconnected in series, allowing the combination of a vertical access control with a horizontal presence control, all in a single system.

  • Access control with muting
    Sometimes open gates are because material needs to frequently transit either when entering or exiting the machinery. In such a case, to prevent the barriers from shutting down the machinery, they are temporarily muted by a sequence of signals emitted from sensors (muting sensors) that detect the material approaching. The signals sequence and the sensor positioning are designed in such a way that a person crossing cannot activate the muting, thus maintaining safety level. The SG MUTINGSG4 EXTENDED barriers have this feature integrated and can as well be connected to accessories with pre-installed muting sensors, ready to be linked to the barrier.

  • Access control with blanking
    While muting is a temporary, automatic suspension of the safety function, some installations require to permanently disable some of the light curtain beams, whether they are at fixed positions (fixed blanking) corresponding to the location of objects that causes their permanent interruption or at variable positions, although limited in number, for example when wires or sheets cross the barrier monitored area. SG4 EXTENDED models allow the programming of these blanking zones.


Most common benefits of light curtains


Light curtains are necessary to secure machinery in places where physical protection devices cannot be employed. The following is a list of the main benefits:


  • High level of safety 
    Thanks to their operative features and high self-diagnostic coverage, light curtains achieve the highest level of safety among the standards for automatic machines.

  • Robustness and quality
    The manufacturer who wants to minimize machine maintenance can benefit from the quality of Datalogic products.

  • Ease
    Datalogic light curtains can count on three levels of customization: by wire for barriers with basic functions, by DIP-Switches for barriers with the most common features such as muting, and by graphical user interface for programmable barriers, in which the setting of specific configurations and the use of blanking are permitted. In all these cases the use is simple and immediate.

  • Flexibility 
    This variety of integrated functions, including different types of muting (one-way or two-way, total or partial) and blanking (fixed or mobile, with or without surveillance), makes Datalogic barriers adaptable to the most demanding requirements in machine design.

  • Specificity
    Among Datalogic light curtain series, some have been developed to best address distinct applications and needs: SG4-H is a barrier with a stainless steel body, glass window, IP69K protection and Hygienic design suitable for the aseptic environments of the pharmaceutical industry; SLIM is a barrier with an extremely small section and many height settings, available for installation even in tight, limited spaces; SG4 FIELDBUS is a barrier with integrated openSAFETY protocol, ready to be connected to safety PLC.

  • Scalability
    A wide choice of series and models allows customers to always find the barrier that best meets their needs, thereby optimizing the performance/cost ratio of the safety system.