Light curtain

PMMA (or Plexiglas, also known as acrylates or acrylics) is made from the monomer methyl methacrylate (MMA), and are known for their excellent optical clarity, colour stability, and good weatherability characteristics. They are mostly used for glazing, lighting, curtain-wall panels as a sealant, and for decorative features. PMMA can contain some of its monomer, MMA, which can also be evolved from thermal degradation of PMMA. MMA is toxic. 

Detailed information is provided on safety procedures and safety devices for machine operations, including guards, doors, emergency stops, light curtains, safety bars, and hydraulic and compressed air safety. 

Infra-red light curtains at the stripper loading station and stacking conveyor discharge points shut down the operation of the machine triggered by an operator. Pull-switches and emergency stop pushbuttons located at strategic points perform the same task manually. 

Safety components such as light curtains, sensor mats, and two-hand controls are regulated by Machinery Directive 89/392/EEC which requires a manufacturer s declaration of conformity but no CE marking. EU type-approval marks are also highly recommended for safety components. 

Minilight curtains use either visible or infrared light. Visible-light curtains are apt to be affected by drops of oil being blown through the curtain. The curtain reacts to oil droplets the same as it does to parts It sends a (false) signal to the... 

To get a larger sensing area, several diffuse reflective sensors can be stacked and connected to one input on the control to make a diffu.se light curtain (see Fig. 18). 

HSG 180 Application of electro-sensitive protective equipment using light curtains and light beam devices to machinery (1999)... 

Light curtain (protects access to hazardous zone from front during dangerous part of cycle)... 

Guillotine with access to blades guarded by light curtain... 

Dangerous machine safeguarded by fixed fencing and light curtain across access aperture... 

Fig. 13.17 Electrical meat stimulator with entry and exit apertures safeguarded using floor-scanning light curtains.

Type 2 devices can be manufactured with a single output signal switching device but must have a periodic test to reveal any failures to danger. Such failures must be detected immediately, or as a result of the periodic test occurring after the failure occurs, or at the next actuation of the light curtain. 

The standard defines a series of optional extras. For example, there is an option for a stopping performance monitor, which allows for monitoring of the time taken for the machine to reach standstill after the beam has been interrupted. As another example, there is an option for external device monitoring which allows, for example, auxiliary contacts on contactors to be fed back to a light curtain controller and for the controller to enter a lock out condition if there were to be a detected disparity between the desired and actual condition of the contactor. The standard also specifies the optical requirements for the devices, including their immunity to optical interference, reflections and so on. 

C is an additional distance in millimetres, based on intrusion towards the danger zone prior to actuation of the light curtain, which will typically be linked to the detection capability of the device. 

Safety sensors sensing devices of mechanical and non-mechanical presence that send signal to interrupt or prevent the onset of dangerous functions, as light curtains, optoelectronic motion detectors, laser multi-beam, optical barriers, area monitors, or scanners, stops, carpets and position sensors ... 

Similarly there are established products in the automation sector using safety certified bus communications for safety devices such as emergency stops and light curtains with safety PLCs being added where needed. 

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