What does machine safety mean?
In short, machine safety is the elimination and / or management of risks that can be caused by a machine. The measures that can be taken herein can relate to before, during and after use. The risks in question are not only in the form of bodily injury but also, for example, in the prevention of sparks coming from a machine.
In essence, light curtains are more aimed at preventing physical injury to workers who are in the (direct) environment of a machine. A machine cannot stop working if it does not 'know' that a person is nearby. The light curtains come into their own in this.
How is this safety determined? There are safety standards that provide handles. Below are a number of relevant standards for safety light curtains:
- EN 61496-1: Machine safety - Non-contact electrical protection devices
- EN 13849: Safety of machinery - Safety related parts of control systems
- EN 61508: Functional safety of electrical / electronic / programmable electronic systems related to safety
What does machine safety mean?
Safety light curtains are safety components that make it possible to prevent or limit injuries to personnel and damage to machines. Light frames can be found in the market under various names, including light curtains and safety screens.
A safety light curtain always consists of a transmitter and a receiver. These are rectangular elongated profiles that are placed opposite each other. The profile that acts as a transmitter contains diodes built in parallel and emitting light to the receiver. This creates a so-called light screen between the transmitter and receiver. In this receiver there are photo diodes that receive and process the emitted light.
Een voorbeeld van een lichtscherm dat gebruikt wordt in toepassingen voor machineveiligheid is de body protection type 4 van Micro Detectors. Wat dit type inhoudt wordt nader toegelicht.
Categories and types of safety light curtains
Light curtains for promoting machine safety can be further divided into different types, types and categories. These concepts seem to describe the same thing, but the distinction is very significant when it comes to light curtains. In the explanation below it will become clear why.
Types of safety light curtains
Safety light curtains can be roughly divided into two types: POC and PAC. POC stands for Point of Operation Control and relates to small-scale applications where hands, fingers and arms must be able to operate a machine in a safe manner. These are therefore applications in which machines are in the immediate vicinity of the hands, fingers and arms of the workers. When detecting, for example, a finger in a dangerous location in or around the machine at the wrong time, the detection causes the machinery to be shut down to prevent injury.
As for PAC, or Perimeter Access Control, workers are not in direct contact with the machines, but are in the vicinity of these machines. These create a fence around the machinery to prevent people from getting too close. However, if a person (or object) enters the danger area beyond the light curtains, switch them and ensure that the machines come to a standstill.
Categories do not have direct involvement to the safety light strips. The categories that are named here are related to machinery and thus the application in which these operate. The earlier mentioned (safety)type from the safety light curtain has to correpsond with this. This means that an application with Category 4 machinery requires a Type 4 lightcurtain for machine safety. However, the recommandation, design and approval of an application for machine safety needs to be carried out by an (intern) safety expert, who is authorized to do this.
Safety screens typing
The classification of safety light curtains based on types refers to their degree of safety. For example, a type 4 light curtain is suitable for applications with higher safety requirements. Type 2 light curtains have, in comparison, not only a lower safety standard but also fewer features. The differences are explained in the table below:
|Type 2||Type 4|
|1. Detection||Periodic test cycles with breaks in between, so that not everything is immediately detected||Immediate detection and shutdown|
|2. Field of view||Optical angle of ± 5°Wider opening angle which increases the chance of mis-detection||Optical angle of ± 2.5°Smaller angle of view|
|3. Price||Cheaper, partly due to the lower safety standard.||More expensive due to more features and higher safety standard.|
|4. Available variants||Only used in body protection and hand protection. Not accurate enough for finger protection.||Available for body, hand and finger protection due to the higher resolution.|
|5. Operating modes||Often used as a secondary protection to supplement current safety components.||Used almost exclusively as a primary safety component.|
Which functionalities and applications do safety light curtains have?
Light strips are safety components that make it possible to prevent or limit injuries to personnel and damage to machines. Light frames can be found in the market under various names, including light curtains and safety screens.
A light frame always consists of a transmitter and a receiver. These are rectangular elongated profiles that are placed opposite each other. The profile that acts as a transmitter contains diodes built in parallel and emitting light to the receiver. This creates a so-called light screen between the transmitter and receiver. In this receiver there are photo diodes that receive and process the emitted light.
An example of a light curtain that is used in applications for machine safety is the body protection type 4 from Telemecanique.
Muting is a functionality at which a part of the diodes in a safety light strip are turned off temporarily to prevent that these switch unnessarily and thus stop the machinery. Think of a conveyor belt where the strips need to swith on people, not on products. Often a detection on a product, which needs no switching, is done by a secundary and supporting sensor. When this sensor switches, the safety light strip knows that it needs to ignore the detection temporarily.
Blanking is in operation the same as muting, however in blanking a part of the light curtain is permanently turned off. With this function, no secundary sensor has te be installed which tells the safety light strips when to ignore the detection and when not. Think in this case of applications where identical products are transported on a conveyor belt and thus can be ignored permantly. There are two possibilities here: fixed and floating blanking. Fixed means that the muted zone is certain and with floating this muted zone can change during the operation of the machine.
A cascade works with a setup of senders and receivers which are placed horizontally (or vertically, depending on the application) in series. This results in a long barrier of rays of light which allow to make a bigger detection field.