With the safe radar system 'LBK', Leuze has added a sensor system to its portfolio that implements a new functional principle in safety technology. The radar technology used is known, for example, from locating aircraft or ships. The manufacturer of the 3D system is Inxpect S.p.A., a company based in Italy.

The system operates in a frequency range of 24 GHz. This means that the electromagnetic waves are much shorter than sound waves. Unlike light, radar waves can penetrate non-metallic objects. The way it works is simple: the sensors with their integrated antennas emit electromagnetic waves that are reflected by objects. The sensors receive these reflections and then evaluate them. The radar system's electromagnetic waves are completely harmless to personnel.

New applications can be solved

If the properties of electromagnetic waves in the radar frequency range are used in sensors, applications that could previously only be solved unreliably with optical sensors can also be solved. For example, non-metallic objects such as dust, welding sparks or chips are penetrated without affecting the sensor. This makes the system particularly suitable for applications in harsh environments, for example when processing wood or plastic. In these areas, a large number of particles are traditionally produced, which then float in the air. However, the 'LBK' remains unaffected by this in its task of detecting and protecting a person. Even if radar waves penetrate these particles, they still reflect a small proportion of the waves. As the amount of radar waves reflected by a person differs significantly from that of wood chips or moisture, the radar system can recognize whether the reflection is a person or non-metallic particles. If a person is detected, the system switches off safely. The LBK sensor emits its radar waves into a three-dimensional space so that not only its surface but also its volume is monitored. This means that people entering or staying in a hazardous area are detected regardless of whether they are standing, kneeling or lying down.

Recognize human movements

The safe radar system 'LBK' enables 3D area monitoring in harsh environments and reliably distinguishes between static and dynamic objects.

© Leuze

However, the 3D radar system not only operates in a new wavelength range for safety technology. It also uses FMCW, a new operating principle in safety technology. FMCW stands for Frequency Modulated Continuous Wave.
The transmission frequency changes within a defined bandwidth. Starting at a basic frequency, it increases continuously up to a maximum frequency and then returns to the basic frequency. If a person reflects this signal, it reaches the receiver with a time delay. Subtracting the received signal from the transmitted signal results in a difference frequency. If the distance between the sensor and the person remains the same, the difference frequency also retains its value. However, if the person moves, the time offset between the transmitted and received signal changes - and with it the difference frequency. The faster the person moves, the more the difference frequency changes. In this way, the sensor can determine the speed of the person.

Precise determination of movements

This method - also known as radar Doppler - can be used to determine movements very precisely. The sensor therefore not only detects a moving person, but also one who is standing still. Because even if a person is standing still, they are never completely still, but always in motion, for example due to their pulse and heartbeat. The radar sensor uses this to reliably distinguish a person in a danger zone from a static object such as a pallet or a material container. The slight movements of a person are enough to generate a safe shutdown signal for the machine. This means that the system only interrupts the operating process if someone is actually in the danger zone. For example, completely static, motionless material containers can be left in the protected area without interrupting the process. In this way, the LBK system avoids unnecessary downtimes and thus increases the availability and efficiency of the system. On the other hand, the machine does not start up again until all persons have left the danger zone.

Simple installation

Rolf Brunner is Senior Safety Expert at Leuze electronic in Owen.

© Leuze

In addition to use in harsh environments, the safe radar system is primarily used to protect against unintentional restarting and to monitor areas that cannot be seen. Users can adapt it to their individual requirements. The system consists of a controller to which a maximum of six radar sensors can be connected. The positioning of the sensors, the adjustable range and the selectable opening angle allow the monitored area to be flexibly adapted to the danger zone. This means that areas on steps or plinths can also be reliably monitored. Users can set system parameters using the easy-to-use configuration software. Project planning and commissioning can be carried out by certified safety experts from Leuze on request.