SI9300226A - Process for automatic control of liquid-cristal light transparency modulator for velding goggles - Google Patents

Abstract

In accordance with the method of the invention to automatically control a liquid crystal light tansmission modulator of welding protective glasses, across an active liquid crystal cell, when welding starts, a high transient control voltage (UAC) of the fifth level (U5) of an alternating polarity and of a varying amplitude is applied, which in several milliseconds from its initial value exceeding the optical threshold voltage of the active cell for an order of magnitude, drops to the control voltage of the third level (U3). In several hundred microseconds the transmission of the protective glasses drops for 95 % of the transmission (Psb) in the open state. After the termination of a welding flash, on the active cell there is the control voltage (UAC) of the fourth level (U4) of an alternating polarity and a constant amplitude and is slightly below the optical threshold voltage of the active cell.

Description

Joseph Stefan Institute

Procedure for automatic control of liquid crystal modulator of light transmission of welding glasses

The subject of the invention is a process for the automatic control of a liquid crystal modulator of the light transmission of welding goggles.

According to the International Patent Classification, the invention is classified in class F 16P 1/06.

In view of the disadvantages of the known methods of automatic control of the liquid crystal modulator of the light transmittance of the welding glasses, the technical problem of the invention is, in particular, to propose a method of the type according to which short switching time will be achieved by the multi-level automatic control of the liquid crystal modulator of the light switch in such a short time that its switching time is reached. DIN 4647/7 for maximum shading rates. The process of automatic control of the light switch should also ensure that it switches on automatically when welding begins and that the automatic testing of the power battery results in the welding glasses darkening when the power battery is exhausted.

Procedures for the automatic control of a liquid crystal modulator of light transmittance exist in known welding goggles, essentially in an attempt to achieve the triggering of the light switch in response to the start of welding. The process further focuses on reducing the likelihood of the light switch being triggered due to the strong illumination of the workspace. Light switch is activated by infrared light sensor and visible light sensor (US 4,039,803) or infrared light sensor and ultraviolet light sensor (EP 0 027 518 Al) or by microphone or microphone pair (US 4,241,286) .

The known procedures for the automatic control of the liquid crystal modulator of the light transmission of welding goggles essentially exist in the following. The liquid crystal modulator of light transmission in the light switch of the welding glasses consists of a passive and active liquid crystal cell. At the end of welding, the control voltage of the first control level of changing polarity and constant amplitude exceeding the voltage of the optical threshold of the passive cell is at the passive liquid crystal cell for a period shorter than the cut-off time of the welding glasses. This results in the passive cell being in a state of higher permeability. Otherwise, at the passive cell during welding and at the standstill of the welding goggles after the end of welding, for a time longer than the cut-off time, the control voltage of the second control level is equal to 0. The passive cell is thus in a state of low light transmittance. On the active cell, however, the control voltage of the third control level of variable polarity and constant amplitude beyond the optical threshold voltage of the active cell is adjustable during welding.

The welding glasses themselves are equipped with either semi-mechanical light switches (DE 30 17 241 Al) or liquid crystal light switches (DE 33 32 083 Al, DT 25 53 976 Al, EP 0 349 665 Al, US 4,039,803, US 4,241,286, EP 0 027 518 Al, EP 0091 514 BI).

Although some liquid crystal transmitters (US 4,039,803 and EP 0 027 518 Al) comprise only one liquid crystal cell, they are preferably provided with one passive and one or more active liquid crystal cells (EP 0 091 514 BI and F 22 93 188). ). These second liquid crystal modulators of light transmittance can attenuate the incident light more than the former, but also provide a more appropriate angular distribution of the transmitted light.

The light switches in these welding goggles have autonomous battery power, some (EP 0 349 665 Al and EP 0 091 514 BI) to extend the life of the battery equipped with a solid state solar cell.

A disadvantage of the known control procedures for a liquid crystal modulator is mainly in the switching dynamics of liquid crystal modulators of light transmittance, which do not fully comply with safety regulations at the highest shielding degrees of shading (DIN 4647/7). For all liquid crystal modulators of light transmittance, the speed of their electro-optical response is strongly dependent on temperature. As the properties of the liquid crystals, especially the viscosity, vary greatly with temperature, none of the liquid crystal modulators above, which are controlled so far in the known manner, do not meet the safety requirements for the highest protection levels (degrees 12 and 13) at temperatures below + 5 ° C. shading.

As a disadvantage of the process of controlling the liquid crystal modulator of light transmittance in known welding goggles, it is further felt that the welding goggles need to be switched on with a mechanical switch before welding and that the battery testing must also be triggered by a special mechanical switch. None of the procedures for controlling the liquid crystal modulator of light transmittance in the above-mentioned welding glasses completely solves the technical problem.

Said technical problem is solved by the method according to the invention for the automatic control of a liquid crystal modulator of light transmission of welding glasses, according to which there is a passive liquid crystal cell which, with an active liquid crystal cell, forms a liquid crystal modulator of light transmittance in the light switch of the welding glasses, after the end of welding. is shorter than the cut-off time, the control voltage of the first control level of varying polarity and constant amplitude exceeding the optical threshold voltage of the passive cell so that the passive cell is in a state of greater permeability, otherwise it is on the passive cell during welding and in the standby mode of the welding glasses. after the end of welding for a period longer than the cut-off time, a control voltage of the second control level equal to 0 so that the passive cell is in a state of lower permeability and the control voltage of the third control level of variable polarity is adjustable on the active cell during welding and constant amplitudes e, which exceeds the optical threshold voltage of the active cell, wherein the method of the invention is characterized in that the control voltage of the fourth control level of varying polarity and constant amplitude is at the active cell after the end of welding at a time shorter than the cut-off time, slightly under the voltage of the optical threshold of the active cell, and that a short-term control voltage of the fifth control level of varying polarity and variable is established at the active cell at the beginning of welding which, after an interval shorter than the cut-off time, follows the end of pre-welding an amplitude which, after a few milliseconds, falls from its initial value, which exceeds the optical cell threshold of the active cell by an order of magnitude, to the control voltage of the third control level.

Furthermore, the process according to the invention for the automatic control of a liquid crystal modulator of the transmittance of welding goggles is characterized in that after the first welding flash, the entire control circuit of the light switch is automatically switched on and that the control voltage of the second appears on the passive cell when the power switch of the light switch is depleted. a control level equal to 0 to bring the passive cell to a state of low light transmittance.

The process according to the invention for the automatic control of a liquid crystal modulator of light transmittance allows the light transmittance of welding goggles to be reduced by at least 95% within a few hundred microseconds or within a time <1 ms after a welding flash occurs. Therefore, the dynamics of the electro-optical response throughout the temperature range of the liquid crystal modulator of light transmittance are sufficient for welding safety regulations (DIN 4647/7) even for the shading rates 12 and 13. The liquid crystal modulator is preferably controlled so that the glasses darken when the voltage of the supply battery falls below the permitted value , thus ensuring passive safety in the event of a voltage source being worn out.

The invention will be described in further detail on the basis of an embodiment and an accompanying plan showing in FIG. 1 the circuit of the light switch in the welding glasses for carrying out the method of the invention; FIG. 2 the circuit of the active and passive liquid crystal controller in the light switch of FIG. 1, FIG. 3 is a diagram of the time course of the brightness of the workplace and the control voltage on the active and passive liquid crystal cells and the light transmittance of the welding glasses in which the process according to the invention is used.

The process according to the invention automatically controls a liquid crystal modulator of the light transmittance LAM in welding goggles (Fig. 1). The liquid crystal LAM modulator of light transmittance is an integral part of the light switch whose circuit is shown in FIG. 1, consisting of passive PC liquid crystal cells and one or more active AC liquid cells.

On a passive liquid crystal cell PC, a control voltage U _{pc of} varying polarity and constant amplitudes is established at the time τ _οη after the end of the welding flash of each welding, ie at the time intervals RI, when the light conditions in the room determine the brightness I of the working area (Fig. 3). , which is equal to the voltage of the first control level Ul. The voltage of the first control level Ul exceeds the optical threshold voltage of the passive PC cell. The passive PC cell is then in the state of maximum light transmittance. The control voltage U _{pc of} said level is also maintained on the passive liquid crystal cell during the RI time interval from the end of the last welding flash to the expiration time T (about 20 min.) When the entire light switch circuit is automatically switched off.

During the welding flashes, this is in FIG. 3 at the time intervals Wl, W, and at the standstill of the welding goggles, that is, at the RI interval after the end of the cut-off time T since the end of the last welding flash, the control voltage U _{pc of the} second control level U2 equal to the passive liquid crystal cell PC 0. The passive liquid crystal PC cell is therefore in the state of minimum light transmittance.

On the active liquid crystal cell AC, the polarity adjustable voltage U _{AC of the} third control level U3 is changing at the time intervals Wl, W at which welding flashes occur. Its amplitude is constant and exceeds the optical threshold voltage of the active liquid crystal AC cell.

At the active liquid crystal cell AC, a control voltage U _{AC of the} fourth control level U4 of varying polarity is restored at time τ _οη , which is of the order of 10 ms, at each time the welding flash stops, ie at RI time intervals. Its amplitude is slightly below the voltage of the optical threshold of the active liquid crystal AC cell. However, such a control voltage U _AC is also present on the active liquid crystal AC cell during the RI time interval, but only until the switch-off time T has elapsed.

At the very beginning of welding, which follows the end of the last flash of pre-welding earlier than after the cut-off time T, that is, at the beginning of the time interval W, a short-term control voltage U _{AC of the} fifth control level U5 of variable polarity and variable amplitude is established on the active liquid crystal cell AC. The amplitude of the control voltage rapidly increases to an initial value that exceeds the optical threshold threshold of the active liquid crystal AC cell by an order of magnitude and drops to the amplitude of the third control level U3 after a few milliseconds.

According to the method according to the invention, as soon as the first welding flash occurs at the beginning of the first welding time interval W1 after a long interval (time interval RI ') after pre-welding, the entire control circuit of the light switch is automatically switched on. At the very beginning of the first welding time interval W1, therefore, the control voltage U _AC on the active liquid crystal AC cell does not reach an initial value that exceeds the optical threshold voltage of the active liquid crystal AC cell by an order of magnitude but slightly exceeds the amplitude of the third control U3 level (Fig. 3 ).

According to the process of the invention, the control voltage U _pc on the passive liquid crystal cell PC drops to zero each time the light switch power supply battery is consumed, and thus the passive liquid crystal cell PC enters the state of minimum light transmittance.

Since at the very beginning of the first welding interval W1 the control voltage U _AC does not reach the high voltage of the fifth control level U5, the light transmittance P of the welding glasses from the light transmittance P _off in the time interval RI 'decreases at the beginning of the welding interval W1 during r _x , which is of the order of 10 ms, by 95% to the value of P _w . In the RI intervals or in the RI interval until the switch-off time T has elapsed, the welding goggles are on standby and their light transmittance P _sb is higher, by about 50 times, than the light transmittance P _ofp, so the working area is clearly visible through the welding goggles already at lighting conditions in the workspace. The high voltage of the fifth control level U5, which is established at the beginning of the time intervals W on the active liquid crystal AC cell, allows the light transmittance P of the welding glasses to be reduced by 95% in a very short time t of several hundred microseconds, or <1 ms at -10 ° C. In fact, the light transmittance of P welding goggles drops even slightly below the value of P _w for a few milliseconds immediately after the onset of the welding flash.

The light switch for carrying out the process according to the invention for the automatic control of a liquid crystal modulator of light transmittance in welding glasses consists of a control circuit and a liquid crystal modulator of LAM of light transmittance (Fig. 1).

The standard static light transmittance is achieved by means of a LAM light transmittance liquid crystal modulator consisting of one passive PC liquid PC and one or more active AC LCD cells.

The passive liquid crystal cell PC attenuates light most when the electric voltage U _pc on it is zero. The electro-optical response of a passive liquid crystal PC cell, that is, the rate of decrease in light transmittance, to instantaneous changes in the amplitude of the control voltage U _pc does not depend on the voltage U _pc . A passive liquid crystal PC cell should be thin and equipped with a low viscosity liquid crystal because its speed of light transmittance is inversely proportional to the thickness of the liquid crystal layer and its viscosity. The voltage of U _pc is at RI time intervals, when the light transmittance of the passive liquid crystal PC cell should be as high as possible, preferably above the cell's optical threshold.

An active liquid crystal AC cell attenuates light when the U _AC voltage on it is non-zero. The electro-optical response of an active liquid crystal AC cell to the instantaneous changes in the amplitude of the control _AC voltage U _AC , that is, the rate of decrease or increase in the light transmittance of the active liquid crystal AC cell, is proportional to the magnitude of the voltage U _AC . A very fast decrease in the light transmittance at the beginning of the time intervals W is achieved by the control voltage U _{AC of the} fifth control level U5. A faster response to this control level is achieved by already having a voltage U _AC at the U3 level in the RI time interval, which is slightly below the optical threshold of the active liquid crystal AC cell.

The light switch consists of a sensor-power circuit 1, an input amplifier 2, a logic control circuit 3, a battery tester 4, a voltage regulator 5, a selector switch 6, a controller 7, 8 of an active or passive liquid crystal cell to which the LAM light modulator is connected , C meter and O oscillator.

In the sensor-power circuit 1, the emitter terminal of the PT1 phototransistor is connected, on the one hand, to the input Ion of the voltage converter VC1 and via the resistor Rl to the BI power supply and to one of the power terminals of the voltage converter VC1 and, on the other, to the non-inverting input of the amplifier A2 in the input amplifier 2. The sliding terminal of P2 potentiometer, whose permanent terminals are connected to the supply voltage of the circuit or ground, is connected to the inverting input of amplifier A2, the output of which is connected to the interconnected inputs of NAND gate G31 in the logic control circuit 3. Output of NAND gate G31 is connected to the output 3c of the logic control circuit 3 and to the interconnected inputs of the N32 port G32 whose output is coupled to the output 3a of the circuit 3 and to the capacitor C3, the second terminal of which is connected to the output 3b of the circuit 3 and via a resistor R3 to ground. The output 3a of the logic control circuit 3 is connected to the reset input Cr of the meter C whose output Co is connected to the cut-off input loff of the voltage converter VC1 via an NAND port G33 with mutually coupled inputs.

The power connections of the circuits in the light switch are connected to the low-voltage output 11 of the VC1 voltage converter.

The output 3b of the logic control circuit 3 is connected to the base of the switch transistor T62 in the selector switch 6 via the resistor R6 and via the switch transistor T61, whose emitter is connected to the high voltage output lh of the voltage converter VC1 and the collector via the output terminal 6a of the selector switch 6 to the power terminal 7a of controller 7 of active liquid crystal AC cell.

The output of the logic control circuit 3b 3 is simultaneously connected to the reset input Or of the oscillator O, whose clock output Ocl is connected to the clock input Cel counter C and to the clock input 7b, 8b of the controller 7, 8 of the active or passive liquid crystal cell AC, PC.

The output of the logic control circuit 3c 3 is connected to the inverter input of the operational amplifier A5 in the voltage regulator 5 via the adjustable resistor R51 and diode D5, whose non-inverting input is connected to the reference voltage of the Zener diode ZD, which is connected to the supply voltage via the resistor R generates at the low-voltage output 11 of the voltage converter VC1. The inverting input of the operational amplifier A5 is connected via a temperature-dependent (NTC) resistor 53 to the amplifier output, which is connected via diode D6 to the output 6a of the selector switch 6. The output 6a is connected to the capacitor terminal C6, the other terminal of which is connected to ground.

The output of the logic control circuit 3c 3 is connected via a resistor R43 to a non-inverting input of an operational amplifier A4, which is connected to a positive feedback loop by a resistor R44, whose inverting input is connected to a Zener diode ZD terminal and whose output is connected to a control terminal 8c of controller 8 passive liquid crystal PC cells.

The low voltage output 11 of the voltage converter VC1 is connected to ground in the circuit of the battery tester 4 via the series resistors R41, R42 and the common resistor terminal R41, R42 is connected to the non-inverting input of the operational amplifier A4.

In FIG. 2 shows the controller 7, 8 of the active or passive liquid crystal cells AC, PC. Driver 7 with transistors T71, T72 and resistors R71, R72, and transistors T73, T74 also allows a high control voltage U _{AC of} varying polarization to be supplied at the electrode of an active liquid crystal AC cell. The control voltage U _{pc of} varying polarization is produced by controller 8, which consists of the exclusive NOR port G81, ..., G84.

The PT1 Photo Transistor detects a welding flash and turns on the VC1 voltage converter, switching on the entire light switch circuit. Each time a welding flash occurs, a pulse is reset at output 3b of the logic-control circuit 3, which resets oscillator O. The pulse at output 3b of the logic-control circuit 3 further opens transistor T62 for a duration to produce high voltage at the output 6a of selector switch 6. . This high voltage at W intervals, when the power is on from previous welding flashes, reaches the control level U5. During the welding process, the voltage at output 3c of the logic control circuit 3, via the adjustable resistor R51 and the amplifier A5, determines the voltage at the output 6a of the selector switch 6. This voltage determines the control voltage U _AC on the active liquid crystal AC cell and after a period of several milliseconds , the control level U5 corresponds to the control level U3. At the same time, output 3c via resistor R43 and amplifier A4 determines the control level at terminal 8c of controller 8 such that the amplitude of the control voltage U _pc drops to zero.

When the welding flash goes off, the voltage at the output 3c of the logic control circuit 3 via the amplifier A4 enables the control voltage U _pc on the passive liquid crystal cell to reach a value corresponding to the voltage of the first voltage level Ul. At the same time, the voltage at the output 3c via the amplifier A5 determines the control voltage U _{AC of the} fourth voltage level U4 on the active liquid crystal AC cell. The voltage level U4 is determined by the ratio of resistors R53 and R52, therefore, it follows the temperature dependence of the optical threshold of the active liquid crystal AC cell, since the NTC resistor R53 is temperature dependent. For the duration of the welding flash, the voltage at the output 3a of the logic control circuit 3 is continuously reset by the counter C, which, after the switch-off time T, switches off the entire circuit of the light switch after the NAND port G33 and the loff terminal of the voltage converter.

Claims (3)

1. A process for the automatic control of a liquid crystal modulator of light transmission of welding goggles according to which, on a passive liquid crystal cell PC, which, with an active liquid crystal cell AC, forms a liquid crystal modulator of light transmittance in a light switch of welding goggles, after the end of welding, for a period shorter than switch-off time T, control voltage U _{pc of the} first control level Ul of varying polarity and constant amplitude beyond the optical threshold voltage of the passive PC cell, so that the passive PC cell is in a state of higher light transmittance, otherwise it is on the passive PC cell during hatching and in at the standstill of the welding goggles after the end of welding for a time longer than the cut-off time T, a control voltage U _{pc of the} second control level U2 equal to 0 that the passive PC cell is in a state of low light transmittance and is on the active cell AC between rolling control adjustable voltage U _{AC of the} third control level U3 of varying polarity i n a fixed amplitude exceeding the optical threshold voltage of an active AC cell, characterized in that the control voltage (U _AC ) of the fourth control level is at the active cell (AC) after the end of welding for a time shorter than the cut-off time (T). (U4) of varying polarity and constant amplitude slightly below the voltage of the active cell optical threshold (AC) to be at the active cell (AC) at the start of welding following the end of pre-welding at an interval shorter than the cut-off time ( T), establishes a short-term control voltage (U _AC ) of the fifth control level (U5) of variable polarity and with a variable amplitude that, after a few milliseconds, drops from its initial value, exceeding the optical threshold voltage of the active cell (AC) by an order of magnitude, at control voltage (U _AC ) of the third control level (U3). Method according to claim 1, characterized in that, after the first welding flash, the entire control circuit of the light switch is automatically switched on. Method according to claim 2, characterized in that a control voltage (U _pc ) of the second control level (U2) equal to 0 that the passive cell occurs on the passive cell (PC) when the power switch of the light switch is consumed (PC) enters a state of low light transmittance.