Secure zone monitoring: with laser scanners or radar

Thus, the laser light constantly passes through the room to monitor areas. When the laser beam hits an object, it is reflected back. Based on the time between emitting the beam and receiving it again, one can begin to determine the exact distance and the scanner knows if the object is in the monitored zone or not. Three zones are sub-divided by default. This is done according to your application and security requirements.

- Protection field: a radius of about 8 m around the safety laser scanner. If someone is in this zone, the potential danger must be neutralized immediately by switching off the machine. This is therefore also called the shutdown zone.

- Warning area: a radius of about 20 m around the safety laser scanner. If this zone is entered while the machines are in operation, they will ver-tragen and an alarm will sound. 

- Measuring field: radius up to 50 m around the safety scanner. Here there is no danger, but the scanner can still serve to determine contours. This can be interesting, for example, in mobile applications.

The safety laser scanner works on the basis of diffuse reflection. In applications that use reflective materials (glass, mirrors, shiny metals ...) this laser light will not be reflected diffusely but in one direction. Then one runs the -risk of not detecting the object. A second important consideration is resolution. This tells something about minimum size of an object that can be safely detected. The greater the distance, the smaller the resolution will become. An additional element to this is the sample rate. One can play with that to increase the resolution, but then the response time will slow down. Third, there are a number of other elements that can interfere with safety laser scanners: smoke, vapor or dust, electromagnetic interference, intense light sources and other laser scanners in the same area. There are filters and techniques to counteract these environmental conditions and make the scanner less sensitive, but that will have its impact on response time and thus safety distances. 

For about a year, radar technology has also existed for safety applications. Whereas laser light works two-dimensionally, radar waves (frequency 24 GHz) have a conical range. But the principle is otherwise similar: Based on the reflection of radar waves, one can form an exact image of the distance to an object. The advantages of radar over laser scanners is that sound waves are not affected by reflective surfaces and are less sensitive to dust and vapor. In contrast, they have a harder time with plastic and wood. The biggest advantage of radar, however, is that they can be set to respond only to motion. This allows objects to be admitted into a secure area, but because of the micro-movements specific to the human body (think of the heartbeat), people will always be safely detected. The disadvantages are mainly in the precision (tolerance of +/- 30 cm) and a minimum required distance of 1.3 m. Since this is a relatively young technology, evolutions are still expected.

PILZ has a high-performance solution for both techniques. The PSENscan is a safe 2D laser scanner suitable for applications up to Pl d, Type 3 and Sil 2. It detects a safety zone of 3 or 5.5 m at a respective resolution of 40 or 70 mm. Furthermore, it is equipped with a display, so you can immediately see which zone it detects and where exactly the detection is coming from. A second asset is its changeable memory. That way the scanner can be easily replaced or different scanners can have the same configuration. Other features include muting, EDM and override. Up to four laser scanners can be linked via the master-slave principle. The LBK system in turn consists of a radar sensor with evaluation unit for applications up to Pl d and SIL 2. Up to six radar sensors can be connected to it via CANbus that can detect 15 m x 4 m far. Synchronization takes place in such a way that they will not interfere with each other. In this way, free, flexible setups are possible.

Wondering what could be the best possible solution for your application? Then contact PILZ's safety specialists to get a clear understanding.