EP1417864B1 - Illuminated sign for traffic control and method for functional monitoring of such a sign - Google Patents

Abstract

An illuminated sign is for traffic control, in particular for road traffic, and includes light sources for generation of the sign and a monitoring device for functional monitoring of the light source. The light sources are embodied as light diodes and the monitoring device is embodied as a device for the limited current loading of the light diodes. The functional monitoring of said sign can be achieved with reasonable technical requirements in both the deactivated and activated state thereof.

Description

The invention relates to a traffic light for traffic control, in particular road traffic, according to the preamble of claim 1 and a method for monitoring the operation of such a sign according to the preamble of claim. 8

In general, to support a smooth traffic handling signs of various kinds and importance are used to control the traffic. This applies to the ship's journey, for aircraft, for example at airports, as well as for the entire rail traffic, but especially for road traffic. Due to the ever-increasing volume of traffic, more and more traffic and light signals are used for regulating inner-city traffic or for managing long-distance traffic. An increasing part of these signs is generated by light sources. Typical examples of this are the alternating light signals of traffic lights at road intersections or the variable message signs on so-called motorway cross sections. In the case of the aforementioned light signals, mainly incandescent lamps are used today as light sources. Incandescent lamps may fail due to short-circuiting or interruption, causing a character to be generated by them to be mutilated, insufficiently lit, or not displayed at all. In order to avoid misleading the traffic participants, an incorrectly displayed light signal must be switched off immediately to avoid an accident risk. In order to be able to check the availability of a safety-relevant sign, such as a red traffic light, a speed limit or a warning display, even when it is switched off, the monitoring must be active, even when the corresponding sign is not active, ie not lit.

Functional monitoring of the incandescent lamps producing a sign can take place via the passage of current through their filaments. The inertia of a filament allows that by brief energization of the filament for example, 1 ms, the functionality of the incandescent lamp can be tested without light leaking. As a reference for such a cold lamp test for automatic inspection of a car light system, the article "On-board multiplexing system checks car's lights automatically" from Electronics International, pages 68 and 70, called. Through a microprocessor commands are given there to activate the lamps, monitors the signals of the lamps and sensors and informed the driver of a malfunction by a display on the dashboard. A power transistor connects the lighting system to the car battery. In parallel, a high-impedance voltage divider is connected whose center potential serves as a criterion when checking a lamp state. In operation, the microprocessor checks the value of the center potential of the voltage divider every 10 ms. When the light is on, the potential is 12V when it is off, 0V. However, in the event of a short circuit in the lamp circuit, it is 0V in both cases. To get a positive indication of all possible fault and light modes, the test must be extended. to include the OFF mode with the light on and the ON mode with the light off. A switched on lamp is switched off by the system once per second for approx. 100 ms; if it is off, the system will periodically turn on every 40 s for 100 ms. The test starts when the engine is started and ends 100 seconds after stopping. This prolonged operation ensures that lamp failures are also detected during the cooling period of the filament.

Now, the incandescent lamp is increasingly replaced by the LED, hereinafter abbreviated by LED, displaced as a low-maintenance and high-availability light source for optical characters many advantages for the economic operation of Traffic lights offers. The problem is that LED-generated characters could previously only be monitored in the switched-on state. Thus, the LED technology for safety-relevant characters, which must be monitored for functionality even when switched off, could not be used. Due to the quasi-inertia-free conversion of electricity into light in LED light sources, a functional test analogous to the so-called cold lamp test was not possible without producing disturbing and thus unacceptable light flashes. In complete darkness, pulses of a length of approximately 0.3 μs as well as continuous currents of approximately 5 μA will be distractingly noticeable in a LED operation with nominal current, largely independent of the repetition rate. Signs with a function monitoring, which generate sufficiently short or weak current pulses and can safely monitor, could not be realized so far with reasonable effort.

European Patent Application EP 0 434 859 A1 discloses an arrangement for monitoring the operation of an incandescent lamp. With no visible effect of the incandescent lamp, the continuity of the circuit is checked with low energy when switched off. In order to distinguish in such a review a short circuit or shunt generated continuity of the circuit from the continuity of the circuit with working light bulb and exclude positive test results despite defective light bulb, the ratio of the resistance of the device in the off state of the light bulb to the resistance of the device determined in the on state of the incandescent lamp and compared with the valid for each to be monitored incandescent lamp ratio of the cold-hot resistance.

The patent application FR 2 724 749 A1 relates to a lamp with LEDs of a signal generator for road traffic with means for its function monitoring. A controller between the light emitting diodes and the control unit allows the conventional Use of presence or absence of power to monitor the operation of the lamp. A current mirror allows the passage of a current proportional to that at the terminals of the group of light-emitting diodes forming the lamp during the intervals in which the light-emitting diodes are nonconductive. This ensures the continuity of supply of the lamp while the LEDs are nonconductive at the zero crossing of the AC supply. The current may be interrupted by a switch which is controlled by a circuit monitoring the current through the light emitting diodes. When the current drops to a level indicative of a failure of a certain number of light emitting diodes, the switch is opened or it may be actuated in response to an operating controller.

US Pat. No. 6,147,617 discloses an apparatus and a method for fault detection of outdoor displays. Such displays are constructed of light-emitting elements such as colored light emitting diodes and small phosphor display tubes in matrix form to output character-based information, still images, dynamic images and so on. The display includes an error detection circuit comprising a unit pixel having a plurality of light emitting diodes, a pixel driver, a voltage divider detector, and an operational amplifier. In the off state, a leakage current is converted by the light emitting diodes into a voltage, which is applied to the voltage divider. The output of the voltage divider is compared by an operational amplifier with a reference value. If the output of the voltage divider is smaller, a failure of the unit pixels is detected.

The invention is therefore based on the object to provide a light signal and a method for monitoring the function of a character of the type mentioned, so that at reasonable technical effort, the functionality of the Sign can be monitored both in the on and in the off state.

A subtask is achieved by a light signal of the type mentioned above with the features mentioned in the characterizing part of patent claim 1. By limiting the current that builds up after switching on the light source through the light-emitting diodes according to time duration or intensity, the light emission of the LED that enters immediately can be restricted in such a way that it is no longer perceptible to the viewer even in the dark. As a result, the road users disturbing light flashes are avoided. As a criterion for the functionality of the current increase is used by the LEDs.

In a preferred embodiment of the invention, the monitoring device of the light signal comprises switching means for switching off the switched on current upon reaching a predetermined threshold value for the current intensity. The limitation of the current flowing through the LEDs electric current is achieved here by specifying a maximum threshold value at which the building up LED current is turned off. In the circuit implementation of this current control parts of the existing current monitoring device from the light bulb technology can be used in an advantageous manner and thus the circuit complexity can be minimized.

In an advantageous embodiment of the invention, the switching means are designed as a digital logic circuit with a memory element. The realization of the LED current limitation can be done for example by using a D flip-flop as a memory element and by means of other standard components of semiconductor circuit technology.

In a preferred embodiment of the invention, the monitoring device is further designed to measure the voltage drop across the energized light-emitting diodes. Through this separate additional monitoring of the voltage, a failed LED can be detected despite LED current flow, such as a short circuit. This increases the reliability of the functional test of a light signal according to the invention.

In further advantageous embodiments, the light sources are arranged as a chain of light-emitting diodes connected in series or as a cluster of light-emitting diodes connected to one another. This is advantageously used in the design of light signals with linear symbols or planar structures.

Preferably, inventive light signals with function monitoring in traffic signs, especially in such with changing display option different characters, or in traffic lights, so the well-known traffic lights, used.

The other sub-task is solved by a method of the type mentioned above with the features mentioned in the characterizing part of claim 8. In which the current supply of the light-emitting diodes is first turned on, the current monitoring signal representing the current through the LEDs is generated, and the energization is switched off again when a predetermined threshold value for the current monitoring signal, the designed as light emitting diodes light source of the light signal are so limited energized in the function monitoring in that only a light emission which is no longer perceptible by the viewer takes place.

In a preferred embodiment of the method according to the invention, a voltage monitoring signal representing the voltage dropping across the energized light-emitting diodes is additionally generated. The voltage monitoring signal is used as an additional criterion in the assessment of the functionality of a light-emitting diode in order to exclude a short circuit in the case of a positive LED energization.

In an advantageous embodiment of the method according to the invention, the energization takes place in an inactive state or periodically in an inactive phase of the light emitting diode. Thus, the function monitoring can be performed both when the light is - even for a longer period of several months - not in operation, as well as during operation, in which the regular LED lighting is turned off periodically for a short phase, in which then the even shorter test current takes place.

FIG 1

eine Schaltung zur Stromregelung in einem erfindungsgemäßen Lichtzeichen, in

FIG 2

die Zeitabschnitte eines LED-Ansteuersignals und in

FIG 3

die Logikschaltung als Schaltmittel der Überwachungseinrichtung

schematisch dargestellt sind.An embodiment and further advantages of the invention will be explained in more detail below with reference to the drawings, in which

FIG. 1

a circuit for controlling the current in a light signal according to the invention, in

FIG. 2

the periods of an LED drive signal and in

FIG. 3

the logic circuit as switching means of the monitoring device

are shown schematically.

An inventive light signal, such as a variable message sign for the alternate display of different traffic signs is generated, for example, in a trained as a sign bridge on roadways outdoor facility. The outdoor unit has a power supply for powering the LED strings, using a standard 48 V DC industrial switching power supply with 100 W input power. It is connected via a CAN bus to a route station, which includes a modem as well as a control and a master module. For example, 32 LED chains, divided into four groups of eight each, can be controlled via a common control module. The control module contains a digital part and an analog part. The digital part has modules for initialization, module detection, read / write logic, a test register, normal and test mode enable logic, LED current setting, and current and voltage monitoring, while the 32 LED current regulators provide Form analog part. Up to 8 such control modules can be connected to a common control unit. Control is provided by a processor module that executes a stored program for driving and monitoring the LED strings.

In a variable traffic sign for use on federal motorways, there is a light-emitting diode chain, for example, 11 to 19 series connected LEDs LED. Each LED chain is driven according to FIG. 1 by a transistor Q3 connected as a current source. As a command variable for the current is the output voltage of a digital-to-analog converter DAC, which is applied via a transistor Q4 to the base of the transistor Q3. If a positive drive signal is present at the LED turn-on signal LE, after a circuit-related delay time of approximately 1 μs in the transistor Q3, a collector current which approximately corresponds to the quotient of the voltage of the converter DAC and the resistor R5 is established. This constant current flows minus a small current flowing through the resistors R2 and R3 cross-flow as a working current through the LED chain. The chain current, in turn, causes a voltage drop in a resistor R1 upstream of the LED chain which, when the collector-emitter threshold of a transistor Q1 is reached, triggers it and generates the current monitoring signal IO. Resistors R2 and R3 also drive a transistor Q2 when the voltage drop across the LED string reaches a value set by voltage dividing ratio R2 to R3, thus generating a voltage monitoring signal UO through transistor Q2. For signal conversion to TTL level serve resistors R6 and R7 or R8 and R9. The monitoring signals IO and UO are stored in the control module and reported back to the control unit and processed there. The current monitoring is done for all chains with a uniform, fixed threshold: The current sensor output shows "OFF" if the chain current is less than 4 mA and it shows "ON" if it is greater than 7 mA. Similarly, the voltage monitoring of all LED chains with a uniform, fixed threshold. In test mode, all LED strings are checked cyclically and current errors are found within 10 s. In normal and test mode, an LED string will fail if the default set point for the voltage is "ON" and the actual measured sensor current value is "OFF" at the same time. A current error will only switch off if a currently required character is no longer recognizable can. A character is no longer representable if the number of defective LED strings exceeds the supplied limit.

The LED drive signal with active light source is constructed periodically according to FIG 2 with a period T _period of, for example, 10.0 ms. A period begins at the starting point t ₀ and is subdivided into a lighting time T _light , that is to say the maximum LED energizing time of, for example, 9.0 ms, and a test time T _pause of, for example, 1.0 ms. The lighting time T _light is composed of the actual energizing time T _current , which is about 0.1 to 1.0 times the lighting time T _light for dimming depending on the ambient brightness. During the test time T _break , the maximum 0.3 μs long _test pulse T _test for monitoring the function of the LED chain takes place. It is ensured by the pulse length that the LED lighting has no disturbing a road user light emission result. Of course, the _test pulse T _test can not only take place in a periodic interruption of the lighting time T _light , but also in a longer-lasting inactive state of the light source, so that the availability of the light signal for a safety-relevant application can be checked at any time.

The maximum LED lighting time required for the purpose of avoiding visible flashes of light is achieved by supplementing the current regulator circuit - as described in FIG. 1 - with a logic circuit according to FIG. The LED switch-on signal LE is controlled via the output OR_out of an OR gate OR, eg of the type 74HC32. In regular LED current supply, the input OR_in1 is 1 and thus the output OR_out is also 1. In test mode, the LED input OR_in1 is equal to 0 and the test input is equal to 1. This is located at one input XOR_in2 of an EXOR gate XOR, eg Type 74HC86, on. At the other input XOR_in1, first the state 0 is present, so that the output XOR_out assumes the value 1 due to the different input states. The exit XOR_out is connected to the second input OR_in2 of the OR gate OR, which thus also assumes the value 1. Consequently, OR_out equals 1, which turns on the LED test power. The input XOR_in1 is connected to the output FF_Q_out of a clock-state-controlled D flip-flop FF, for example of the type 74HC74, to whose D input FF_Reset the signal of the test input is applied, ie the value 1. The flip-flop FF responds first to the initial state when the clock variable assumes the value 1 at the C input FF_Clock. This is the case when the current monitoring IO supplies the value 1, that is, the LED current intensity has exceeded the predetermined threshold value. Now the Q output FF_Q_out of the flip-flop FF will assume the value 1, corresponding to Q the value 0. On the one hand, this changes the input state at XOR_in1 from 0 to 1, which leads to an output state XOR_out of 0; This switches off the LED current supply via the OR gate. On the other hand, it is signaled via FF_Q_out equal to 1 that the LED chain is in order.

Claims (10)

1. Illuminated sign for traffic control, in particular for road traffic, having light sources for production of the sign and having a monitoring device for functional monitoring of the light sources, wherein the light sources are in the form of light-emitting diodes (LED), and the monitoring device is designed to produce a limited current flow through the light-emitting diodes (LED), characterized in that the monitoring device comprises switching means for switching off the current flow, once it has been switched on, when the current level reaches a predetermined threshold value, with the current flow time being restricted such that the light emission from the light-emitting diodes (LED) is not perceptible by a viewer.
2. Illuminated sign according to Claim 1, characterized in that the switching means are in the form of a digital logic circuit with a memory element (FF).
3. Illuminated sign according to Claim 1 or 2, characterized in that the monitoring device is furthermore designed to measure the voltage which is dropped across the light-emitting diodes (LED) through which a current is being passed.
4. Illuminated sign according to one of Claims 1 to 3, characterized in that the light sources are arranged as a chain of series-connected light-emitting diodes (LED).
5. Illuminated sign according to one of Claims 1 to 3, characterized in that the light sources are arranged as a cluster of light-emitting diodes (LED) which are connected to one another.
6. Traffic sign, in particular for alternately displaying different signs, having an illuminated sign according to one of Claims 1 to 5.
7. Light signalling system, in particular a traffic light, having an illuminated sign according to one of Claims 1 to 5.
8. Method for functional monitoring of an illuminated sign for traffic control, in particular for road traffic, having light sources in the form of light-emitting diodes (LED) in order to produce the sign, characterized in that the current flow through the light-emitting diodes (LED) is switched on, in that a current monitoring signal which represents the current level through the light-emitting diodes (LED) is generated, and in that the current flow is switched off when the current monitoring signal reaches a predetermined threshold value, with the current flow time being restricted such that the light emission from the light-emitting diodes (LED) is not perceptible by a viewer.
9. Method according to Claim 8, characterized in that a voltage monitoring signal which represents the voltage that is dropped across the light-emitting diodes through which a current is flowing is also generated.
10. Method according to Claim 8 or 9, characterized in that the current flows when the light-emitting diodes are in an inactive state, or periodically in an inactive phase.

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