3D safety systems: the key factors when scrutinising danger zones
3D safety systems are regarded as a good option for reliably monitoring danger zones. They present a safe alternative, even in harsh environments where sparks, dirt and dust occur, for example. They are therefore also a solution for applications where previously optical sensors were unable to provide a reliable answer.
“For over 50 years, Leuze, as a high-tech company and pioneer in the field of optical sensors, has repeatedly set new technological milestones and standards on the market,” states the company. “Particularly in the area of safety technology, Leuze's optical safety components, services and solutions can be used for a wide variety of different applications.”
With the LBK safety radar system, Leuze has now added a new sensor system to its product range. “This system implements an operating principle new to safety technology. As a result, it is also able to provide a solution for applications that previously could not be solved reliably using optical sensors. The LBK safeguards danger zones close to machinery and systems using radar technology.”
Detection of objects using radar waves
The LBK system operates in a frequency range of 24 GHz. This means that the electromagnetic waves are much shorter than sound or light waves. Unlike light, the radar waves can penetrate non-metallic objects. The compact sensors with their integrated antennas emit electromagnetic waves. These waves are reflected off objects. The sensors receive these reflections and then evaluate them. The electromagnetic waves of the LBK radar system are completely harmless to personnel.
New applications solved using LBK
Utilising the properties of the radar frequency electromagnetic waves in sensors provides a solution for applications where optical sensors have so far proven unreliable. Even non-metallic objects, such as dust, welding sparks or chips, are penetrated without the sensor being influenced.
As a result, the LBK system is particularly suitable for applications in harsh environments. For example, in wood or plastic processing. Such applications typically produce a large quantity of particles that are then suspended in the air. However, these particles do not prevent the LBK from performing its task of reliably detecting and protecting persons.
Even if radar waves penetrate the particles, the latter still reflect a small proportion of the waves. As the quantity of radar waves reflected by a person is significantly different to that reflected by wood chips or moisture, the LBK can detect whether the reflection comes from a person or from non-metallic particles. In other words, particles in the air are not detected, whereas a person is.
The LBK therefore switches off reliably when a person is located in the danger zone. The LBK sensor emits its radar waves in three dimensional space, so that not only the surface area, but also the volume of this space, is monitored. This allows the LBK to detect persons who enter a hazardous area or who are located in this area, regardless of whether they are standing, kneeling or lying. LBK reliably differentiates between static and dynamic objects.
Detecting human movements
The LBK 3D radar system not only operates in a wavelength range new to safety technology. It also uses FMCW, an operating principle, which is also new to safety technology. FMCW stands for Frequency Modulated Continuous Wave. Here, the transmission frequency changes within a defined bandwidth. Starting at a fundamental frequency, it increases continuously up to a maximum frequency and then returns to the fundamental frequency again. If a person reflects this signal, it reaches the receiver with a time delay.
Subtraction of the reception signal from the transmission signal produces a difference frequency. If the distance between the LBK sensor and the person remains constant, the difference frequency also retains its value. However, if the person moves, the time delay between the transmitted and received signal changes, and therefore also the difference frequency. The faster the person moves, the greater the change in difference frequency will be. In this way, the LBK sensor is able to determine the speed at which the person is moving.
This method is also referred to as 'radar Doppler'. It allows movements to be determined with a very high degree of accuracy. The LBK sensor therefore detects not only a moving person, but also a person who is currently standing still, even if the movement is extremely slight. Even if a person is standing still, they are never absolutely motionless – there is always some movement, such as from their pulse or heartbeat etc.
The LBK sensor utilises this to reliably distinguish a person in a danger zone from a static object – eg, a pallet or material container. The slight movements of a person are sufficient to generate a reliable switch-off signal for the machine. As a result, the LBK system interrupts the operating process only if somebody is actually located inside the danger zone. For example, completely static, motionless material containers can be left inside the protected area without them leading to interruption of the operating process.
In this way, the LBK system prevents unnecessary downtimes, and thereby increases the availability and cost effectiveness of the system. On the other hand, it ensures that the machine only starts to run again when all persons have left the danger zone and therefore contributes to reliable personnel protection.
Flexible in use
In addition to use in harsh environments, the LBK safety radar system is used primarily for preventing unwanted restarts and for monitoring hidden areas. Users can adapt it to their individual requirements. The system consists of a controller to which up to six radar sensors can be connected. The positioning of the sensors, the adjustable operating range and the selectable opening angle allow flexible adaptation of the monitored area to the danger zone.
This also enables areas on steps or pedestals to be monitored reliably. The user can define the system parameters using the easy to operate configuration software. Certified safety experts from Leuze are available to assist with configuration and commissioning, if required, adds the company.