Welding mask with automatic LCD shutter. Scheme, description

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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING
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Welding mask with automatic LCD shutter. Encyclopedia of radio electronics and electrical engineering

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Encyclopedia of radio electronics and electrical engineering / Power Supplies

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It is known that when carrying out welding work, the welder must protect the eyes and skin of the face with a special mask.

Danger to the eyes are ultraviolet and infrared radiation. If the eyes are not protected by a light filter that weakens the light flux, then due to the inertia of the visual system, the retina has time to receive a large share of the radiation (to catch a "bunny"). The now widely used fiber mask contains a set of replaceable light filters. The principle of its operation is simple: with the mask folded back, the welder performs preparatory work, then ignites the electric arc and only after that lowers the mask. This is where visual damage can occur.

The idea to use a dynamic shutter in a welder's mask arose several decades ago. The first dynamic shutters were mechanical, like a camera, their reliability and efficiency was low. More than 20 years ago, automatic shutters based on high-speed LCD modulators, sometimes called "chameleons", appeared. The automatic shutter allows you to free both hands of the welder and concentrate on the quality of the weld. Its use provides ultra-reliable eye protection and less welder fatigue.

Now masks with an automatic LCD shutter are produced by a number of companies in France, Japan, Germany, Sweden and Switzerland. The main manufacturers of these masks in Europe are the Swedish company ESAB and the Swiss company OPTREL. The LCD shutter cassette is a separate module and is attached to the front of the mask, forming a single helmet structure.

Welding mask with automatic LCD shutter

The device of the optical module or dynamic filter is shown in Fig.1. He contains:

a protective filter made of polycarbonate 1,2 mm thick, protecting the outer optical surfaces from mechanical environmental influences, harmful gas fumes in the welding zone, melted drops of the material being welded, sand and dust;
composite UV and IR light filter;
two or three successive high-speed LCD cells (Fig. 2), providing, on the one hand, a quick transition from a transparent to an opaque state, and, on the other hand, the necessary transmittance in the visible part of the spectrum for the selected welding mode;
protective filter made of polycarbonate 1,2 mm thick.

Welding mask with automatic LCD shutter

The LC cell (Fig. 2) contains polarizing films with a high absorption coefficient in the UV range and solves the problem of UV filtering. If an absorbing type IR filter is used in the IR range of the electric arc radiation, then the filter itself and the entire LCD shutter will become very hot. Therefore, LC reflective filters based on composite interference film coatings are used in the design, which consist of alternating thin metal (silver) and oxide films (SiO2 or In2O3). As a substrate, special glass of the C3C21 brand is used.

The LCD cells are controlled by an electronic module that contains:

two photosensors (one each on the left and right sides of the LCD shutter cassette) and a signal amplifier from them;
control circuit for two LCD modulators;
a microcontroller that provides selection of the shutter operation mode (transmittance in the closed state), pairing with photo sensors, indication on the LCD display of the welding mode selected by the welder and formation of a diagram for the control circuit of LCD modulators;
solar batteries from 9 or more sections of solar cells based on amorphous silicon, providing voltage from 4,5 to 8 V and current in operating mode up to 2-3 mA;
back-up source on a 3 V lithium battery, a high-capacity low-leakage capacitor, or on a solar-powered battery;
functional keypad (3-4 buttons), as a rule, membrane type;
encoder or variable resistor to control the optical density (protection level).

Figure 3 shows the automatic LCD shutter control circuit. The degree of complexity of the control scheme is determined by the class and cost of the welder's mask. Simple inexpensive models with low LCD shutter speeds (10-20ms) usually do not have a microcontroller, LCD display or function keyboard. Power is supplied from a "Krona" type battery with manual activation.

Welding mask with automatic LCD shutter

Expensive models ($400-500) provide a wide range of protection levels, automatic activation when a welder approaches, selection of welding and protection modes using a functional keyboard and display.

Author: A. Samarin

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