EP0167445B1 - Display device consisting of individual electrically controlled elements controlled by a diode matrix - Google Patents

Abstract

1. A display device particularly intended for places with little access, comprising individual display elements which are electrically controlled and fed selectively by means of a diode matrix network, characterized in that, each display element (1) is fed by two diodes (5, 5'), (6, 6') in series, for each direction of the control current and in that during maintenance operations the display elements (1) are fed at a voltage which is sufficiently low not to activate the individual display elements (1) and which is at least equal to several times the fall in forward voltage of a diode, in such a way that the increase in current resulting from the short-circuiting of a diode can be detected.

Description

The present invention relates to display devices which consist of unitary electrically controlled display elements which are selectively supplied via a matrix array of diodes; these unitary display elements are for example constituted by pads mounted to pivot between a display position and a rest position, their pivoting being controlled by a relay preferably with double effect; these display elements can also be constituted by light devices.

The invention applies more particularly to display panels or devices which are placed in places which are difficult to access or in places which can only be accessed for short and infrequent periods. This is the case in particular, display panels used on motorways and more particularly on motorways or busy urban roads for which interruption of traffic for maintenance reasons risks creating problems and must therefore be limited in duration and frequency.

• - dans le premier cas, la liaison électrique est interrompue par exemple par la coupure d'un fil de bobine ou lorsqu'une diode de commande reste à l'état bloqué; une telle panne n'affecte que l'élément d'affichage défectueux et le message affiché sur le panneau reste lisible.

The document CH-A 516204 describes a display device with unitary elements of the electromechanical type in which each relay controlling the tilting of a _Þ tip is controlled in both directions for putting the tablet in the display position and for its return to the rest position, by means of a matrix array of diodes comprising a diode connected to the relay for each direction of the control current. There are two types of faults that can affect each display element:

• - in the first case, the electrical connection is interrupted for example by cutting a coil wire or when a control diode remains in the blocked state; such a failure only affects the defective display element and the message displayed on the panel remains legible.

On the other hand, when one of the two control diodes of a display element short-circuits, this creates, due to the currents derived by this short-circuit diode, a disturbance on a good part of the panel. display whose message may become illegible.

The invention therefore relates to a display device of the type described above in which any failure concerning a display element does not cause disturbances for the rest of the display device and in particular in which the setting short circuit of a control diode does not create stray current in the other display elements.

The display device according to the invention is notably remarkable in that each display element is supplied for each direction of the control current, by two diodes in series and in that, during maintenance operations, the elements of display are supplied at a sufficiently low voltage so that the display elements are not activated and at least equal to a few times the direct voltage drop of a diode and the absorbed current is measured to detect the diodes in short circuit.

Thanks to the provision of a second control diode in series with the first, the failure of a short-circuiting diode does not cause stray current in the control circuits of the other display elements; such parasitic currents would only be created in the extremely improbable case where the two diodes in series of the same command would be simultaneously defective by short-circuiting.

Furthermore, according to the invention, the maintenance operations are carried out without activating the display devices, which makes it possible to avoid the display of an erroneous or illegible message on the panel during the maintenance operations.

Because when a diode is short-circuited, the voltage across its terminals is zero, the current absorbed under a voltage which is slightly greater than the sum of the direct voltage drops across the diodes in series, will undergo a positive variation when one of the two diodes is in short circuit and this variation will be significant enough in relative value to be easily detected during the measurement of the absorbed current.

According to another characteristic of the invention, the operation of detecting short-circuit diodes is carried out automatically during periods of non-operation of the display device and the result of this operation is recorded.

This makes it possible to reduce as much as possible the operations for repairing the display device since it will suffice to replace the display elements whose faulty operation has been recorded.

Advantageously, in the case where the display device is provided with a control microprocessor, the operation for detecting diodes in short circuit is controlled and controlled by this microprocessor.

In the case where the display device is part of a set of display devices controlled by a central station to which they are connected by a telecommunications network, the result of the operation for detecting diodes in short circuit is forwarded to said central station. As a result, the faulty display panels being known in advance, it will suffice to intervene on these faulty devices only, which will further reduce the duration of the necessary interventions.

• - la Fig. 1 représente un schéma électrique d'une partie d'un dispositif d'affichage de type connu.
• - la Fig.2 est un schéma analogue représentant un dispositif d'affichage conforme à la présente invention.

Other characteristics and advantages of the invention will emerge from the description which follows, given with reference to the drawings, in which:

• - Fig. 1 shows an electrical diagram of part of a display device of known type.
• - Fig.2 is a similar diagram showing a display device according to the present invention.

We see in Figure 1 the diagram of part of the electrical circuit of a display device with electromechanical display elements such as articulated pads (not shown) which can take two positions, one of display in which they are visible on the display panel and the another rest in which they are erased and invisible on the display panel. The movement of these display pads is controlled in both directions, namely towards the display position and towards the rest position by means of a winding (1) supplied by a matrix array of diodes so as to allow the passage of a current in one or the other direction.

This network comprises vertical “column” conductors (2) to each of which are connected one of the terminals of the coils (1) of the same column and horizontal “line” conductors (3 and 4); the horizontal conductors (3) are each connected to the second terminal of the coils (1) of the same line by means of a first control diode (5), each of the diodes (5) being connected by the same electrode (for example the anode in the example shown) to the coil (1).

Similarly, each of the conductors (4) is connected to the second terminal of the coils (1) of the same line by means of a diode (6) connected in the opposite direction, that is to say with its cathode connected to the coil (1).

It can be seen that the control of a display element constituted by a chip towards its rest position or its operating position is obtained by applying an appropriate voltage between the conductor (2) of the column of the element in question, and the conductor (3) and the conductor (4) of the line of the element considered.

We see that when a diode (5) short-circuits this leads to the creation of derivative currents, in particular through the conductors (3, 4) and consequently, a malfunction of part of the device display whose displayed message can become incomprehensible.

According to the invention, as can be seen in Figure (2) which is a diagram similar to that of Figure (1) of a device according to the invention, a second diode is introduced in series with each diode two diodes in series having the same direction of direct conduction.

Thus each activation of the display element, that is to say, each movement of the display pad in the example shown, is controlled by means of two diodes in series, namely the diodes (5 ) and (5 ') for one of the movements and the diodes (6) and (6') for the reverse movement.

Due to the low value of the direct voltage drop of a diode relative to the supply voltage of the coils, the introduction of a second diode in series has a negligible influence on the operation of the display device. Thus for a supply voltage of 30 V, intended to supply a control current of 3 A, the reduction in the control current is only about 2%. On the other hand, when, in order to detect the short-circuit diodes, a voltage is supplied which is sufficiently low so that the display elements are not activated but which is at least equal to several times the direct voltage drop of a diode, the increase in current created by the short-circuiting of a diode is sufficiently large. * n relative value to be easily measured and detected. So for example if in the example indicated above, the voltage 30 V is replaced by a voltage of 5 V, that is to say a voltage equal to approximately 7 times the direct voltage drop of a diode, the increase in current resulting from the short-circuiting of a diode and consequently from the suppression of the direct voltage drop of this diode, is of the order of 20%, which can easily be detected.

Advantageously, the operation for detecting diodes in short circuit is carried out while the device or display panel is not in operation; this operation can be carried out automatically by means of a control device successively testing all the display devices, the result of these tests being recorded so that when the display device can be accessed there is no 'Only replace the defective display elements.

In the case where the display device is controlled by a microprocessor integrated in said display device, this operation of detecting diodes in short circuit can be controlled by this microprocessor.

It is also possible that a certain number of display devices are part of a set controlled by a central station to which they are connected by a telecommunication system, this is for example the case of all the display panels motorway or expressway. In this case, it is advantageous for the result of the short-circuit diode detection operations to be transmitted to the central station so that the display devices comprising defective elements are known in advance, thereby avoiding work on display devices that do not contain defective elements; this notably further reduces the duration of maintenance operations.

Claims (4)

1. A display device particularly intended for places with little access, comprising individual display elements which are electrically controlled and fed selectively by means of a diode matrix network, characterized in that, each display element (1) is fed by two diodes (5, 5' ), (6,6') in series, for each direction of the control current and in that during maintenance operations the display elements (1) are fed at a voltage which is sufficiently low not to activate the individual display elements (1) and which is at least equal to several times the fall in forward voltage of a diode, in such a way that the increase in current resulting from the short-circuiting of a diode can be detected.

2. A device according to claim 1, characterized in that the detection operation for short-circuited diodes is carried out automatically during the periods when the display device is not in use and in that the result of this operation is recorded.

3. Display device according to claim 2, characterized in that, if it is provided with a controlling microprocessor, the detection operation for short-circuited diodes is controlled and monitored by the said microprocessor.

4. A device according to one of the claims 2 or 3, characterized in that, if the display device forms part of a group of display devices controlled by a central station to which they are connected by a telecommunications network, the result is transmitted to the said central station.

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