Safety light curtains are commonly used to protect machinery and personnel in manufacturing plants. It is a technology known for several decades, which is still being developed and improved, appreciated for its reliability, ease of installation and high level of security it provides. It is perfect wherever machine operators work in a hazardous area. In this article, we will present these optoelectronic devices in more detail.
What are security light curtains?
The safety light curtain is a motion or presence sensor. It is equipped with a transmitter and a receiver that create a light barrier. The transmitter emits infrared rays. This device creates a two-dimensional sphere of photoelectric light beams between the transmitter and the receiver, with the help of which it detects objects entering it.
The light curtain is connected to the safety logic and, together with it, forms the safety control system. After detecting a break in the light beam, it reacts predetermined, allowing safe human access to the elements that threaten the machines to remove them.
The advantage of this solution is the lack of a mechanical guard blocking access to the dangerous zone of the machine, thanks to which operators gain:
- Quick access in case of failure,
- Better performance,
- Ergonomic workstation (no need to physically operate the curtain).
Safety light living room curtains are compact, so they can be installed in places with difficult access. Their invisible barrier also does not significantly affect the pace and course of the production process, as is the case with mechanical fencing, and the protection of machines is ensured.
Machine safety regulations
The Machinery Directive 2006/42/EC states that every manufacturer should build safe machines, which applies to the control system. It must be error-proof and fault-tolerant, especially when performing safety functions whose malfunction could endanger human beings. Light curtains are part of the safety system.
The requirements for them are set out in the EN IEC 61496-1 standard harmonized with the Machinery Directive, which lists the types of these devices and their requirements. The second part of the EN IEC 61496-2 standard describes the basic requirements for safety light curtains, including primarily optical requirements.
Basic types of safety curtains
There are two basic types of safety curtains – 4 and 2. Type 4 curtains are required when there is a high risk of danger. They are characterized by automatic repetitive cross-checking for glitches and errors. They are used to protect the fingers, hands and body.
Type 2 curtains are used when there is a lower degree of risk. They perform safety tests on their circuits periodically, so if there is a failure in the interval between them, they will not detect it. They are used to protect the body and hands.
What are safety light curtains used for?
Light curtains are used for three types of protection:
Hazardous point – used when frequent access to the machine is necessary, e.g. to assembly stations or presses. For total ergonomics of work, they are mounted very close to the place of the potential hazard. Type 4 curtains are needed here because of the need to detect the minor parts of the body – fingers;
Access – used when occasional access to a hazardous area is needed, e.g. for machines with a long production cycle. The task of the curtain is to detect human entry, so a type 2 device that will notice the body is sufficient here. Their ranges reach 90 cm, allowing you to fence off large areas and secure access from several sides. The downside is that they will not detect people already inside, so you need to consider the risk of using them each time, mainly used to prevent the machine from starting when someone is in the danger zone. The light curtain used here must have a suitable resolution, i.e. approx. 70 mm. If it is the only device installed there to detect entering a dangerous area, then its length must result from the required safe distance. Laser safety scanners are the most commonly used here, which can create areas of various shapes.
What functions can a light curtain perform?
The primary function of the light curtain is to interrupt the light beam, thereby deactivating the output functions and stopping the associated hazardous movements. You can perform a machine reset after verifying that no dangerous incident has occurred. This safe stop-and-start process can disrupt productivity and production flow, so it is constantly being developed and refined as safety curtains gain new features.
This function is used in applications where a temporary suspension of protection is required. The curtain with this function lets objects pass through it without blocking the operation of the machine. To perform muting, at least two independent signals are needed, which most often come from the ones located at the protective device, detecting a passing object. Sensors.
This function is proper when, due to the so-called safe distance, the light curtain must be installed at a certain distance from a dangerous place. Thus, an area is created between it and the machine where an undetected person can be. Additional monitoring devices are often used to avoid the machine starting despite its presence. Usually, a curtain is installed horizontally.
To simplify the electrical installation, the safety devices can be cascaded – signals from one are fed to the next. A cascade usually consists of a maximum of three devices, with only one connected to the control cabinet.
Some applications require specific objects to protrude beyond the protective field, e.g. when a stand or table is used to hold a heavy item delivered to the machine. The masking function changes the sensing capability of the safety light curtain without interrupting the entire production process. Masking can be fixed or movable, which allows the object to assume variable positions.
Modern safety light curtains are perfectly adapted to the needs of the automated industry. They can perform many functions that ensure the safety and efficiency of production. Therefore, the protection of machines and personnel is at the highest level.