According to Treotham Automation, the photoelectric safety barriers are electro-sensitive components using one or more light beams, emitted by an emitter and received by a receiver, to create an intangible area under control.
Safety category defines the self-control and safety principles contained in the device; it must be chosen as a function of the risk level characterising the machine.
When the chosen safety device is a photoelectric barrier, the latter shall belong to TYPE 2 or 4 as laid down in Standard EN 61496-2.
The resolution of a photoelectric barrier is the minimum size of the objects that, upon going through the controlled area, will obscure the controlled zone and hence stop the hazardous movement of the machine.
Consider, P = Pitch, D = Lens Diameter, and R = Resolution = P+D.
For single beam barriers, the resolution R is the same as the diameter of the lens. R = D
For multibeam barriers, the resolution R is the same as the sum of the lens diameter + the distance between two adjacent lenses. R = P+D
The protected height is the height controlled by the barrier. If it is positioned horizontally this value shows the depth of the protected zone.
The range is the maximum working distance that may exist between the emitter and the receiver. When deflector mirrors are used, it is necessary to take into account the attenuation factor introduced by each of them, which varies between 10% and 25%.
The general formula for the determination of the minimum safety distance is:
S is the minimum safety distance between the protection and hazardous point, expressed in mm,
K is the speed of approach of the body or parts of the body expressed in mm/sec,
T is the total stopping time of the machine, consisting of: t1-reaction time of the protective device in seconds and t2- the reaction time of the machine is seconds, until it stops the hazardous action; and
C, which is an additional distance, which is based on the possibility of the body or part there of being introduced into the hazardous area before the activation of the protective device, expressed in mm.
The response time is the time it takes for the barrier to transmit the alarm signal from the time the protected zone is interrupted.
Following are the advantages of the photoelectric barriers:
- Effective protection in the event of fatigue or distraction of the operator
- Increase in the productive capacity of the machine, as the barrier does not require the manual handling of physical guards or waiting for them to open
- Faster machine loading/unloading operations
- Reduced times of approach to the working areas
- Elimination of the risk of tampering, since any irregular intervention on the barrier stops the machine
- Simple and quick installation with greater flexibility of adjustment on the machine, even in the case of subsequent repositioning
- Possibility to build up large sized protections either linear or along a perimeter, on several sides, at greatly reduced costs
- Facilitated and fast maintenance of the machine, as there is no need to remove physical guards, such as grids and gates
- Improved appearance and ergonomic effectiveness of the machine
For the photoelectric safety protections to be effective, it is necessary to verify that:
- It must be possible to electrically interface into the control unit of the machine.
- It must be possible to stop at once the hazardous movements of the machine. In particular, it is important to know the machine stopping time so as to place the barrier at the correct distance.
- The time taken to reach the hazardous point must be greater than the time necessary to stop the hazardous movement.
- The machine must not create secondary dangers due to the projection or fall from above of materials. It this danger exists, provide additional protections of a mechanical nature.
- The minimum size of the object to the detected must be equal to or greater than the chosen barrier resolution.
Following are the criteria of selection of a photoelectric barrier:
- Definition of the zone to be protected.
- Definition of types of item to be detected: fingers or hands, approaching body of a person, presence of a person in a hazardous area.
- Definition of the safety distance between the barrier and the hazardous point.
- Definition of the safety class to be adopted.
Treotham Automation were previously known as Treotham .