Light grid
Barrier-free safety
Thanks to reaction times of maximum 6 ms and the absence of dead zones, today's safety light curtains move even closer to the danger zone. But what makes these devices so special?
Safety solutions based on light grids are always the first choice in production and logistics when continuous access and egress, accessibility or human-machine interaction are required for process or production reasons.
In accordance with the Machinery Directive 2006/42/EC, suitable safety measures must be taken for machines and systems to eliminate or reduce the risk to people to a responsible level. They must correspond to the determined risk level and the normative specifications. In 2015, the IEC/EN 61496 standard established a link for the first time between the type classes of electro-sensitive protective equipment (ESPE), the safety requirement level (Safety Integrity Level SIL according to IEC 62061) and the degree of reliability with which a control system must fulfill a safety function (Performance Level PL, according to ISO 13849). As a result, since May 2015, type 2 light curtains may only be used in applications up to performance level PL c or SIL 1 and SIL CL 1. Type 3 light barriers were not available on the market until then - users were forced to switch to type 4, which is intended for PL e requirements, in order to meet the safety requirements of PL d. In most cases, this was significantly oversized - with correspondingly higher costs.
External specifications, framework changes and the resulting consequences often trigger innovative processes. Even before the change to the standard came into force, the automation company Pilz decided to close this 'type gap' with a type 3 light curtain that is precisely tailored to it - the 'PSENopt II' type 3 safety light curtain, which completely eliminates dead zones and is specially designed for applications up to PL d in accordance with EN/IEC 61496-1.
Functionally flexible handling
Safety solutions that meet the required safety categories and do not restrict handling or productivity are a basic requirement for light curtains. In their basic function, light curtains therefore also secure a defined area against any intrusion. At their core, they are based on a simple transmitter-receiver principle consisting of individual, invisible infrared beams. If one or more of these beams are interrupted, the control system brings potentially dangerous movements to a safe stop.
For the 'PSENopt II' light curtains, Pilz offers a complete solution comprising light curtains plus safe, configurable small controller 'PNOZmulti 2'.
© MushroomThe special thing about light curtains, however, is their flexible functions: In addition to safety features such as finger, hand and body protection, additional functions such as muting, blanking and cascading can be implemented depending on the version. This allows light curtains to be adapted to the desired requirements.
Another requirement is shock resistance. It is essential to cover this functionally when it comes to harsh environments in which vibration or collisions are prevalent.
In 2015, the IEC/EN 61496 standard established a link between the type classes of electro-sensitive protective equipment, the Safety Integrity Level SIL and the Performance Level PL for the first time.
© MushroomIn addition, an extremely fast response time and absolute protection of the surrounding area must be ensured: With short response times of maximum 6 ms and an absolute absence of dead zones, Pilz light curtains, for example, also protect such danger zones. They are equipped with a shock resistance of 50 g. The body-resolving version bridges distances of up to 50 m and reliably secures access to robot cells, packaging machines or presses. The status of all photoelectric sensors in this series can be easily read via the LED diagnostics, even under these conditions.
However, the space conditions on site often require special solutions. It must be possible to install light curtains freely and flexibly in the spatial arrangement according to the implementation requirements without impairing their functionality. The solution here can be coding, so that even light grids installed close together do not interfere with each other. If several pairs of light grids are in use, they are coded differently: if a receiver unit receives the light from another transmitter unit, there are no consequences. Safety areas can be set up cost-effectively with the mirror columns accessory. If, for example, three sides of a robot application need to be safeguarded, one pair of light curtains in conjunction with two mirror columns is sufficient.
Advanced functions
Mirrors enable the light grid beams to be deflected in order to protect a larger protective field, for which additional light grids would otherwise be necessary.
© MushroomMuting, blanking or cascading are often an issue. This is because where infeeds and outfeeds regularly transport objects through the light grid, machine downtime as a result of the interruption of light beams is undesirable. Muting is used to allow defined exceptions in a protective field. If a model does not include these functions, muting can alternatively be implemented with retrofittable light grids, for example. With the Pilz light curtains, for example, the muting function integrated in the small controller can be implemented if the manufacturer's safe configurable small controller 'PNOZmulti 2' is added.
If a component or machine part permanently protrudes into a defined protective field due to the process or design, this part can be blanked out by software. The blanking function blocks this part of the protective field permanently (fixed blanking). If objects only temporarily protrude into a protective field, 'floating blanking' is used.
Cascading is a suitable solution for applications that require either high protective fields or protection from behind. The light grids arranged one above the other and connected in series reduce the amount of wiring required.
Intuitive software
The multifunctional 'PSENopt Advanced' light grids offer extended functions that cover muting, blanking and/or cascading.
© MushroomSoftware tools tailored to light curtains support installation, commissioning and handling. Pilz, for example, has special software for the 'PSENopt Advanced' light grid: the 'PSENopt Configurator' makes every single beam visible. From alignment to functions such as muting, blanking and cascading, the light barriers can be configured with just one tool. Fast and targeted diagnostics, the location and cause of an interruption can also be traced immediately. It is also possible to read out the fault memory with plain text messages. All these features of the tool reduce downtimes and increase the availability of a system. Users can also transfer the configuration once it has been created to other machines via the programming adapter.
Author:
Sezgin Yumuk is Product Manager Sensors at Pilz in Ostfildern.
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