FR2681443A1 - Electrooptic device for protecting the eyes - Google Patents

Abstract

The present invention relates to a device for protecting the eyes from being dazzled, comprising two negative-liquid-crystal obturating screens (2, 3) placed in front of the eyes, a photosensitive sensor (1), comprising a processing circuit (8, 9, 11, 12, 14) which is electrically connected to the liquid-crystal screens (2, 3) and to the photosensitive sensor (1), possessing a means for forming a threshold and a means (8) for measuring an average value of the signal coming from the photosensitive sensor (1) and providing a high-amplitude signal for driving (controlling) the screens (2, 3) when the signal coming from the photosensitive sensor (1) is greater than the sum of the said threshold and the said average value. The invention applies principally to masks for welders.

Description

 The present invention relates to an eye protection device. I1 is particularly applicable to the production of welding masks.

 It is known to use electro-optical screens, in particular liquid crystal screens to obscure the field of vision of welders as soon as an electric arc is detected.

 To avoid damage to the welder's retina, the darkening time of the electro-optical screens must be less than 3 milliseconds.

 Certain welding masks known to date include two electro-optical screens, in particular liquid crystal screens, at least one of which is of the positive type, that is to say obscure cis at rest. Therefore, the operating temperature range is limited to that of the liquid crystals used and does not provide good protection for high and low temperatures.

 Other devices known to date use two negative liquid crystal displays. However, their operating temperature range is reduced. In fact, the signals emitted by the liquid crystal control circuit do not make it possible to compensate for the viscosity increase effect appearing at low temperatures.

 Furthermore, certain control circuits for liquid crystal displays currently known comprise several light levels giving triggering thresholds and are very complex.

 The object of the present invention is to present an eye protection mask having a very short response time whatever the temperature of use and having protection at high and low temperatures.

 Another object of the present invention is to provide electronic circuits for controlling particularly simplified liquid crystal screens and avoiding any risk of dazzling.

 The invention proposes the use of two electro-optical screens, in particular liquid crystal, of positive type, that is to say clear at rest.

 The invention proposes the use of a high control voltage compensating for the increase in viscosity linked to the decrease in temperature.

 The invention further provides the detection of variation in brightness and the use of a circuit comprising a single threshold so that a variation of incident light on the device of a value greater than this threshold causes complete obscuration. of the electro-optical screen (s).

 Finally, the invention proposes a pulse width modulation of the signals received by the electro-optical screens in such a way that the obfuscation response time is always equal to the excitation time of the electro-optical screens and greater than the relaxation time. of these screens.

 The device which is the subject of the present invention is therefore a device for protecting the eyes against glare comprising two shutter screens with negative liquid crystals placed in front of the eyes, a photosensitive sensor whose axis of orientation is parallel to that of the liquid crystal screens. , characterized in that it comprises a processing circuit electrically connected to the liquid crystal displays and to the photosensitive sensor, comprising a threshold and a means for measuring an average of the signal value coming from the photosensitive sensor and supplying a signal for controlling large amplitude screens when the signal from the photo-sensitive sensor is greater than the sum of said threshold and said average value.

 The description which follows, given with reference to the appended drawings for explanatory purposes and in no way limited, makes it possible to better understand the advantages, aims and characteristics of the invention.

 Figure 1 shows a first embodiment of the front photosensitive sensor device.

 FIG. 2 represents a second embodiment of the device with rear photo-sensitive sensor.

 FIG. 3 represents a block diagram of electronic circuit which can be incorporated into the devices represented in FIGS. 1 and 2.

 FIG. 4 represents an electronic circuit carrying out the functions of that shown opposite FIG. 3.

 FIG. 5 represents the intermediate signals corresponding to the signal processing carried out by the circuits presented with reference to FIGS. 3 and 4.

 In FIG. 1 are shown a photosensitive sensor 1 electrically connected by a link 5 to an electronic circuit 4, and two electro-optical screens 2 and 3, electrically connected by the electric links 6 and 7, respectively, to the electronic processing circuit. signal 4.

 The photo-sensitive sensor 1 is placed optically parallel to the electro-optical screens 2 and 3 so that the light which it perceives corresponds to that which is incident on the electro-optical screens 2 and 3. The photo-sensitive sensor 1 is adapted to emit a signal representative of the light intensity that it receives. It can notably include a photo-diode, a phototransistor, or a photo-resistance. However, preferably and according to the invention, the photo-sensitive sensor 1 consists of one or more solar or photo-voltaic cells.

 The electro-optical screens 2 and 3 are preferably clear at rest, that is to say negative. They each have two crossed polarizers. In this way, if their operating temperature is exceeded, their state becomes isotropic and the crossed polarizers absorb all the incident light.

 The electronic signal processing circuit 4 is adapted to control the transparency of the electro-optical screens 2 and 3 as a function of the signal it receives from the photo-sensitive sensor 1, so that the light intensity passing through the electro-optical screens is limited to the glare tolerances of the human eye.

 A preferred example of an electronic signal processing circuit 4 is shown with reference to FIGS. 3 and 4.

 The respective positioning, that is to say in parallel, of the photo-sensitive sensor 1 and of the electro-optical screens 2 and 3 makes it possible to achieve an optical control in open loop of the light flux passing through the electro-optical screens 2 and 3.

In the case where screens 2 and 3 contain liquid crystals, the electrical signals emitted by the electronic circuit 4 and received by screens 2 and 3 have an amplitude, expressed in volts, which is calculated as follows, to obtain a very low minimum operating temperature or less than
O ec by keeping a response time of less than three milliseconds: a doubling of the oscillation voltage corresponding to a division by at least five of the response time, and the minimum operating temperature corresponding to a multiplication by a factor
F of the viscosity compared to that measured at 20 C, the amplitude of the signals should be 4 times the darkening voltage of the liquid crystals twice raised to the fifth root power of F.

 The processing circuit 4 includes a threshold and a means for measuring an average of the value of the signal from the photo-sensitive sensor 1 and provides a control signal for the screens 2 and 3 of high amplitude when the signal from the photo sensor -sensitive 1 is greater than the sum of said threshold and said average value.

 It is notable that the average value can consist of an average over a given period of time, of a weighted average, in particular with an exponential weighting factor, or more simply of the charging and discharging of a capacitor.

 The threshold can be adjustable.

 In FIG. 2 are shown a photosensitive sensor 1 electrically connected by a link 5 to an electronic signal processing circuit 4, and two electro-optical screens 2 and 3, electrically connected by the electric links 6 and 7, respectively, to the circuit signal processing electronics 4.

 The photo-sensitive sensor 1 is placed optically behind the electro-optical screens 2 and 3 in such a way that the light which it perceives corresponds to that which passes through the electro-optical screens 2 and 3. It preferably comprises a photo-diode or a phototransistor.

 All the components represented in FIG. 2 have the same functions as those described with reference to FIG. 1.

 The respective positioning, that is to say in series, of the photo-sensitive sensor 1 and of the electro-optical screens 2 and 3 makes it possible to achieve an optical closed-loop control of the light flux passing through the screens 2 and 3.

 In Figure 3 are shown a photosensitive sensor 1 consisting of solar cells, connected on the one hand to an integration circuit 8 and on the other hand to a control circuit 13 of the screens 2 and 3. The integration circuit 8 is connected on the one hand to a monostable branch circuit 11 and on the other hand to a threshold circuit 9, themselves connected in parallel to an amplifier circuit with controllable gain 12. A duty cycle modulation circuit 14 is connected in its inputs on the one hand to the amplifier circuit 12 and on the other hand to an oscillator 10 and, at its output, to the control circuit 13. Finally, the screens 2 and 3 are connected to the control circuit 13.

 The solar cells constituting the photosensitive sensor 1 serve to supply electrical energy to the entire circuit shown in FIG. 3 but also constitute the photo-sensitive sensor shown in FIGS. 1 and 2.

 It should be noted that additional electrical supplies, of the battery or accumulator type recharged by the solar cells constituting the photosensitive sensor can supplement the electrical supply presented here.

 The integration circuit 8 outputs a corresponding signal, for positive variations of the input signal to an output proportional to this signal, that is to say not integrated, and for negative variations to relaxation with a constant of predetermined time.

This time constant is chosen as a function of the emission frequencies of the light intensities. For example, in the case of arc welding, the time constant is greater than 10 ms and preferably much greater than this duration.

 The monostable bypass circuit 11 outputs a signal which is a function of the derivative of the signal which reaches it.

This output takes two values, depending on whether the derivative is greater than a predetermined threshold or not. This circuit therefore has a fixed or adjustable threshold.

 The threshold circuit 9 gives a value, which is preferably adjustable, of the device operating threshold, outside of the times when said derivative is greater than said threshold. This threshold circuit 9 is mounted in parallel with the integrator circuit 8.

 As a function of the threshold of the threshold circuit 9 and of the signal leaving the monostable bypass circuit 11, the controllable gain amplifier 12 emits a modulation signal intended for the duty cycle modulation circuit 14. The latter circuit 14 modulates the signal alternating output from the oscillator 10 so that the outgoing signal has a duty cycle depending on the signal from the amplification circuit 12.

 Finally, the control circuit 13 amplifies and transmits the signal leaving the duty cycle modulation circuit 14 to screens 2 and 3.

 The circuit represented in block diagram in FIG. 3 has the property of detecting the strong variations of incident light on the solar cells constituting the photo-sensitive sensor 1 and of consequently controlling the complete obscuration of the screens 2 and 3, using as a command an alternating signal with a duty cycle equal to 1. These large variations correspond in fact to risks of dazzling of the welder, for example during the ignition arc, at the effective start of the weld arc or at the start of a higher intensity welding near the welder.

 On the other hand, the small variations in light intensity simply and slowly vary the transparency of the screens 2 and 3 so that the visibility of the welder is good and without the risk of glare. These slight variations show, at the output of the duty cycle modulation circuit 14, duty cycles between 0 and 1, so that the average control voltage of screens 2 and 3 is less than the darkening voltage.

 It should be noted that the circuit presented in FIG. 3 does not react to the frequencies of emission of the electric arcs.

 For a better understanding of this circuit, Figure 5 presents the signals entering and leaving some of its components.

 The processing circuit 4, composed of the circuits 8, 9, 11, 12 and 14, comprises a threshold and a means for measuring an average of the value of the signal coming from the photo-sensitive sensor 1 and provides a signal for controlling the screens. 2 and 3 of high amplitude when the signal from the photo-sensitive sensor 1 is greater than the sum of said threshold and said average value.

 It is notable that the average value can be made up of an average over a given period, of a weighted average, in particular with an exponential weighting factor, or more simply of the charging and discharging of a capacitor.

 FIG. 4 represents an exemplary embodiment of the circuit shown in block diagram in FIG. 3.

 Are shown in Figure 4, solar cells lA and 1B, an integration circuit 8, a monostable bypass circuit it comprising a transistor 15 and two resistors 35 and 36, a threshold circuit 9 comprising a potentiometer 37 mounted in a divider bridge, a gain-controllable amplifier circuit 12 comprising an operational amplifier 17 and a potentiometer 16, a duty cycle modulation circuit 14 comprising two transistors 18 and 19, and two monostable integrated circuits 20, the oscillator 10, the command 13 and screens 2 and 3.

 For the sake of clarity, the filters, for example low pass, and certain power supplies are not shown in FIG. 4. The oscillator 10 and the control circuit 13 are of known types.

 The solar cells 1A and 1B constitute the photo-sensitive sensor 1 presented with reference to FIGS. 1, 2 and 3.

The solar cells 113 supply a signal which is processed by the electronic circuit presented opposite FIG. 3. The solar cells 1A serve to supply a high voltage to the control circuit 13 of the liquid crystal screens 2 and 3.

 The integration circuit 8 is composed of a diode and an inductor placed in series. The monostable bypass circuit corresponds to a known arrangement of a PNP 15 type transistor, three resistors and a capacitor. This circuit presents at output two values as a function of derivative of the incoming signal. If this derivative is positive and greater than a threshold determined by the ratio of the resistance values electrically connected to the base, the output is saturated and presents a signal of given value. In all other cases, the output signal takes a second given value.

 The threshold circuit 9 consists of a potentiometer mounted in a voltage divider bridge. It makes it possible to adjust the offset, with respect to the zero voltage, of the signal leaving the transistor 15. The amplification circuit with controllable gain 12 consists of an amplifier assembly of an operational amplifier comprises in loop a potentiometer 16 and of which the positive input is connected to the output of the integration circuit 8 and of the threshold circuit 9.

 The monostable bypass circuit ll comprises a triggering threshold consisting of the ratio of resistors 35 and 36 multiplied by the bias voltage of transistor 15.

 Finally, the duty cycle modulation circuit 14 is made up of two PNP type transistors receiving the signals leaving the amplifier circuit 12 and controlling the inputs of the monostable integrated circuits 20, the respective outputs of which are connected to the control circuit 13.

 As an example of a monostable integrated circuit 20, mention may be made of the integrated circuits referenced 4538.

 The circuit shown in FIG. 4 only represents an exemplary embodiment of the device which is the subject of the invention.

Any other circuit performing the same functions remains in accordance with the spirit of the invention.

 According to this circuit, the variation of the duty cycle is done without changing the alternation frequency of the signal leaving the duty cycle modulation circuit 14.

 According to a first variant, the variation of the duty cycle is done by varying the transmission frequency of a rectangular signal of fixed duration.

 FIG. 5 represents the successive transformations and treatments of the signals leaving the photosensitive sensor t and constituting at the output the signals transmitted to the screens 2 and 3. On the absente is time and on the ordinate the amplitude of the signals.

 These signals present the functions of the components and circuits described with reference to FIG. 3.

 The first signal corresponds to the outgoing signal from the photo-sensitive sensor 1. It represents pulses of very small widths 21, 22 and 23 corresponding to the electric arcs of an arc weld. The pulses 21 is isolated. The pulses 22 are brought together over time but over a short period. The implusions 23 are brought together over time and over a long period of time.

 For example, the pulse 21 corresponds to an isolated accidental arc, the pulses 22 correspond to starting arcs and the pulses 23 correspond to an effective weld.

 The second signal corresponds to the output of the integration circuit 8. This circuit has a time constant much greater than the duration separating two pulses 22 or two pulses 23. This signal has, for each pulse 21, 22 or 23 saturation, that is to say a maximum amplitude, then, between these pulses 21, 22 and 23, decreases in amplitudes 25 and 26 corresponding to the time constant of the integration circuit 8. The decreases in amplitudes 25 separate two arcs distant in time and the decreases in amplitudes 26 separate two pulses 22 or 23 close together.

 The third signal corresponds to the output of the branch circuit 11. It represents the derivative of the second signal. This derivative has high positive peaks 27, low positive peaks 29 and negative values 28. The peaks correspond to pulses 21, 22 and 23.

The high peaks 27 correspond to the first pulses of each of the sets of pulses 21, 22 and 23. The low positive peaks correspond to the other pulses.

 The threshold level is represented by a thin horizontal line. This level is greater than zero and corresponds to the ratio of resistors 35 and 36 multiplied by the threshold voltage of transistor 15.

 The fourth signal corresponds to the duty cycle of the control signal of screens 2 and 3. Each time the third signal exceeds the threshold, the fourth signal has a duty cycle of 1 maintained for a predetermined duration 30. Outside these durations, the fourth signal has a corresponding and increasing duty cycle as a function of the average of the light intensity measured on the first signal. If the measured light intensity is zero, the duty cycle is zero as shown during the time intervals 31. If the measured light intensity is not zero, the duty cycle 32 is not zero but very low, so that the screens 2 and 3 receive a control signal whose average value corresponds to a partial darkening.

 The fifth signal corresponds to the transparency of screens 2 and 3. This transparency varies as a function of the duty cycle shown opposite the fourth signal.

When the duty cycle is equal to 1, the transparency decreases very quickly and reaches a value close to zero. During the time intervals 30, the transparency of the screens 2 and 3 increases by relaxation, that is to say slowly, compared to the excitation times corresponding to the durations 30. Finally, during the time interval 32, the transparency increases and reaches an intermediate value allowing a good vision of the electric arc.

Claims (9)

1 / Device for protecting the eyes against glare comprising two shutter screens (2,3) with negative liquid crystals placed in front of the eyes, a photosensitive sensor (1) whose axis of orientation is parallel to that of the screens (2, 3) liquid crystal, characterized in that it comprises a processing circuit (4) electrically connected to the liquid crystal screens (2,3) and to the photosensitive sensor (1), comprising a means for forming a threshold ( 35,36,15) and a means (8) for measuring an average of the signal value coming from the photo-sensitive sensor (1) and supplying a signal for controlling the screens (2,3) of high amplitude when the signal from the photo-sensitive sensor (1) is greater than the sum of said threshold and said average value. 2 / Device according to claim 1 characterized in that when the signal from the photo-sensitive sensor (1) is less than the sum of the threshold and the average value, the control signal sent to the screens (2,3) by the processing circuit (4) has an average value (33) which is a function of the average value (26) of the signal from the photo-sensitive sensor (1). 3 / Device according to one of claims 1 or 2 characterized in that the amplitude of the high amplitude signal is greater than 4 times the darkening voltage of the liquid crystals twice raised to the tenth root power of F, F being the viscosity multiplication factor between the temperature of 20 C and the lowest operating temperature desired. 4 / Device according to any one of the preceding claims, characterized in that the processing circuit (4) provides a signal of constant amplitude, the duty cycle of which varies as a function of the signal emitted by the photosensitive sensor (1). 5 / Device according to claim 4 characterized in that the function connecting the signal emitted by the photosensitive sensor (1) and the duty cycle of the signal emitted by the processing circuit (4) and received by the liquid crystal screens (2, 3), apart from the signals of high average amplitude (30) is a linear function and in that it comprises a means of adjustment (37) of the value at the origin. 6 / Device according to one of claims 4 or 5 characterized in that the function connecting the signal emitted by the photosensitive sensor (1) and the duty cycle of the signal emitted by the processing circuit (4) and received by the screens to liquid crystal (2,3) apart from the high amplitude signals (30) is a linear function and in that it comprises a means for adjusting (16) the slope. 7 / Device according to any one of claims 4 to 6 characterized in that the signal emitted by the processing circuit (4) and received by the liquid crystal screens (2,3) comprises square slots emitted at constant frequency including duration is an increasing function of the signal emitted by the photosensitive sensor (1). 8 / Device according to any one of claims 4 to 6 characterized in that the signal emitted by the processing circuit (4) and received by the liquid crystal screens (2,3) comprises square slots whose frequency of appearance is an increasing function of the signal emitted by the photosensitive sensor (1). 9 / Device according to any one of the preceding claims, characterized in that the photosensitive sensor (1) is a series of solar cells (lA, lB) which also supplies the supply voltage of the treatment circuit (4) and screens (2,3).