Safety light grids and curtains: optoelectronic protective device overwiew.
Safety light grids and curtains are widely used in modern technological equipment and are designed to control areas of space near moving parts of presses, stamps, conveyors and other process equipment. They detect the intersection of the controlled zone with external objects and form the corresponding signals for the control system of this equipment.
Due to these signals the control system locks the moving parts or prohibits operations until the interference in the work area is eliminated. Else you can use light curtains and in the technological process for registration the movement along a conveyor, for recording the cells' employment in an automatic warehouse, to determine the presence or absence of a part on the platform.
The light grid is an electronic device consisting of two units — the transmitter of optical radiation (emitter) and the receiver of optical radiation.
- the optical system of the safety light grid which forms the radiation pattern (beams);
- array of emitters (LED) creating infrared radiation of the optical range;
- multiplexer generating a sequence of electrical pulses on the emitters.
Radiation receiver includes:
- optical system of the safety light grid which forms the radiation pattern of the radiation receiver (beams);
- array of photodetectors perceiving optical radiation and converting it into electrical signals;
- amplifiers increasing input signals to the required value;
- microcontroller measuring the parameters of input signals, forming control signals for the transmitter and output signals of the light grid or light curtain;
- electronic switches providing switching of output currents equipped with incorrect switching protection, overcurrent and short circuit protection;
- LED indicators located on the front side of the receiver showing the status of the output keys and the status of each beam which makes possible determining the operability of the light grid and to ensure prompt tuning.
The work of the safety light grid is settled on the principle of bounding the location with parallel light rays forming a zone of sensitivity. Most often invisible infrared radiation is used so it does not cause inconvenience to the staff. The sensitivity zone is formed in the space between the emitter and the photocell.
Safety light curtains and grids have a functional reserve which is set as the ratio of the maximum working distance between the emitter and the receiver to the maximum width of the monitored zone. It makes it possible to compensate for the attenuation of the signal as a result of contamination of the optics and the presence of aerosol components in the surrounding space.
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