Safety light curtains usually detect people and initiate safety measures if necessary, while automation light grids detect objects and control the corresponding subsequent processes. With its broad technology portfolio, Sick succeeds in ensuring both effectiveness and safety by integrating measuring and safety functions in a single product. These solutions optimize automated logistics processes and guarantee maximum machine safety.

If we look at the technological principles from the historical development, light grids or light curtains consist of an arrangement of several individual optoelectronic sensors and an evaluation unit. The sensor system contains a transmitter and receiver unit. When the light beams emitted by the transmitter reach the receiver unit, it receives the beam until it is interrupted or influenced by an object. In this way, several light beams generate a two-dimensional detection field, which is referred to as a protective field in safety terms and enables the contactless detection of objects. In technical circles, the terms "light grid" or "light curtain" have historically been established for this type of sensor and are used synonymously.

Light curtains for both safety and automation

Sick distinguishes between "safety light curtains" and "automation light curtains" depending on the function of the technology in the product portfolio. The term "light curtain" is used as a superordinate category in this text. The individual beams of such a light curtain are arranged at certain distances, which define the minimum detectable object and the "MDO" (minimum detectable object) or "resolution" parameter. The beams are evaluated cyclically to ensure reliable and interference-free detection. Depending on the cycle time and the number of individual beams, this results in a response time, which is an important safety-related parameter and is also crucial for the automation of downstream processes.

For greater productivity in the material flow, the deTec4 safety light curtain, for example, has integrated pattern recognition of objects with rectangular contours and reliably distinguishes between material and people. The function analyzes individual beam data - as is typically the case with automation light curtains - and allows the results to be used for the purposes of machine safety. Unnecessary downtimes are thus avoided and maximum safety is guaranteed while productivity remains the same.

Smart Box Detection, which requires neither external signals nor additional sensors to distinguish people from material, offers further advantages. The protective field remains active above a passing object and therefore offers additional protection against intrusion. This enables a cost-efficient and flexible machine design that significantly optimizes the space required for the safety function.

Automation light grids detect and measure challenging objects

Maintaining exactly the same distances between products during transportation and handling is crucial for the availability of conveyor technology and in production machines. Light curtains detect the front and rear edges of passing objects. The SLG-2 automation light curtains from Sick are equipped with innovative multiple cross-beam technology. This increases the resolution in the detection field and precisely detects even particularly small, very flat or irregularly shaped objects such as polybags.

Another productive function is the transparent mode of the MLG-2 measuring automation light grids, with which even transparent objects are reliably detected and measured in height and width. This improves the productivity of downstream processes and increases availability, as faulty objects are detected and ejected by means of measurement and protrusion control.

As both the light curtain applications for automation and those for safety at Sick have the simple but high-performance IO-Link interface, all the data obtained can be used to control downstream processes. For example, the beam data transmitted via IO-Link can also be used for height measurement or quality inspection of the products passing through. The Detec4 safety light curtain achieves this with a resolution of 14 or 30 millimetres, while an automation light curtain is even more precise with resolutions of up to 2.5 millimetres.

In the packaging sector, where reliable differentiation between people and materials is just as important as the detection of unsealed packages, the Detec4 safety light curtain performs both tasks. This is because, in addition to its actual safety function in the horizontal direction of movement, it also detects open flaps as height jumps in the package via IO-Link. No safety function is required in the vertical direction; the open tabs can be detected here with an SLG-2 automation light grid via IO-Link.

Easier integration and commissioning

The standardized IO-Link communication interface results in a number of additional benefits that offer increased productivity: shared infrastructure, the standardized Sopas Engineering Tool operating software and reduced integration effort. The commissioning process is also much simpler thanks to the standardized housing and connection design and the use of identical accessories such as brackets or cables. For maximum system availability, diagnostic data is provided in accordance with a standardized smart sensor concept, making maintenance and fault diagnosis more effective.

As automation and safety tasks in machines and systems are located close to each other, or even in the same process step, Sick has used its many years of experience in both areas to combine the solution portfolio. In this way, both tasks can be solved cost-effectively, sometimes even using just one product. This combination of the best of both product worlds makes it possible to save time and costs in the material flow, increase the system throughput and thus increase the efficiency and productivity of the conveying processes.

This article appeared in issue 10/23