FR2471864A1 - Thermal print head allowing immediate reading - has series connected heating resistances at edge of substrate and obviates need for common conductor - Google Patents

Abstract

The print head which allows the print out to be viewed immediately it is written comprises heating resistances at the edge of an isolating substrate. The thin film resistances are chemically constructed on a substrate from nickle-chrome alloy or tantalum nitride. The supply and return conductors for each resistance are perpendicular to the edge of the print head, allowing the resistances to be placed right at the edge of the substrate. An electronic circuit supplies the required conductors to give the print line required to build up the characters to be printed. The resistances can be adjusted globally by thermal oxidising. In a thin film embodiment, the substrate can have a thickness of 0.5 mm and can be made of glass.

Description

 The present invention relates to an immediate-reading thermal printing head, comprising, deposited on an insulating substrate, a plurality of heating resistors arranged in line and current conductors to said resistors.

 The present invention also relates to a method for the construction of said head.

 Usually, the heating resistors consist of a deposit of resistive material on an insulating substrate, deposited by conventional thin-film or thick-film techniques, said resistors being protected by an electrically insulating and thermally conductive layer which is resistant to friction of the paper.

Usually, current is supplied by means of a conductor for each of the resistors and the current return by a common conductor which can be led to conduct the current of a large number of resistors at a time. this fact, this return conductor must have a large width to not introduce parasitic resistance. In other cases, a multiplexing is used and said return conductor is then divided into several narrower conductors, but whose overall size is, in total, at least as important
Frequently, the information to be printed arrives in groups and a long time may elapse between the arrival of each group. If the user needs to be informed of the content of a group without waiting for the arrival of the group next, it will be necessary that the printing is visible as it occurs, which is impossible in known printers, because the width of the substrate occupied by the, or the return conductors hides the paper on a height generally greater than that of a line of characters. Also, if you want to keep the layout, especially when it comes to drawings and not text, it is impossible to advance the paper to read what has just been printed.

 One solution is to pass the common conductor on the wafer of the substrate and then connect it from below the substrate, a provision known from French Patent No. 2,222,845. However, this solution raises important technological problems because it makes it difficult to performing either a thick film screen printing or a thin film photolithography in different planes (the faces and the edge of the substrate) and also the fragility of the conductor on the edges between the edge and the face of the substrate.

 The present invention aims to overcome the above disadvantages. It is based on the emptied to modify the connection of the resistances so as to remove the common conductor, and therefore be able to place said resistors at the edge of the substrate. Indeed, according to the invention, a thermal printing head, comprising, deposited on an insulating substrate, a plurality of in-line heating resistors and current supply conductors to said resistors is particularly remarkable in that the resistors are connected together in series and in that each conductor feeds two adjacent resistors, this organization for arranging the resistors at the edge of the substrate.

 This organization, in fact, allows the common return conductor to be removed, since each of the conductors can play, according to its connection, the role of supply or the role of return of current, which makes it possible to dispose the resistances at the edge of the substrate and-thus to be able to see the text or the figures and curves as and when they are printed. This is achieved without manufacturing technology difficulties particularly due to the provision of resistors at the edge of the substrate.

The invention also relates to a method for manufacturing said printing head, in particular that, starting from a substrate having at least one determined excess dimension and placing on said substrate resistors having a dimension at least equal to the dimension As well as the corresponding conductors, the edge of the substrate along which the resistors are at the edge and also the edge of said resistors are defined by a reduction in said determined dimension of said substrate.
In an alternative embodiment, the method according to the invention is still remarkable in that a substrate of multiple dimension of the final dimension is prepared, a plurality of configurations of conductors and resistors, configurations intended for each to form a head, and which are positioned two by two, contiguous by their resistances and in that the heads are then separated by cutting the substrate by defining at the same time by said cutout the edge of the resistors which thus becomes at the edge of said substrate
This method offers the advantage that the resistors are strictly edge because their edge has been defined at the same time as that of the substrate.

 The following description, with reference to the accompanying drawings describing non-limiting examples will make it clear how the invention can be achieved.

FIG. 1 represents a perspective view of a head arranged according to the invention
Figure 2 shows a section along II-I I of the head shown in Figure 1.

 FIG. 3 represents the electrical diagram of the head according to FIG. 1, in a particular state of excitation given by way of example.

 Figure 4 shows an embodiment of the head before final cutting of the substrate.

 Figure 5 shows a circuit diagram coding signals to be applied to the resistors of the head.

 FIG. 6 represents an exemplary preferred embodiment of a coding circuit in which the necessary voltages are generated sequentially for the resistors arranged according to the invention.

 According to FIG. 1, a plurality of resistors 11 arranged in line at its edge which coincide with the wafer 31 of the insulating substrate 41.

 The current supply or return conductors 21 each supply two resistors 11. For example, the conductor 21n + 1 feeds the two resistors lin and lln + 1.

 The conductors 21 are themselves powered by elements not shown in the figure such as: a miniaturized special connector, or a ply of flexible conductors soldered to said conductors 21.

 Resistors 11 may be made of nickel-chromium alloy, or tantalum nitride, or some other material used for so-called thin-film hybrid circuits. They can be adjusted globally, inter alia by a physicochemical means such as thermal oxidation. They can also be made by screen printing of resistive pastes, followed by cooking, operations as are practiced for so-called thick-layer hybrid circuits.

 According to FIG. 4, starting from a substrate 41 having at least one determined excess dimension, and placing on this substrate resistors 11 having a dimension 51 at least equal to the desired dimension, as well as the afferent conductors 21, it is possible to define the edge of the substrate along which the resistors are edged and also the edge of said resistors by a reduction of said excess determined size of said substrate, removing what protrudes outside the lines 61 and 62.

 A plurality of configurations of conductors and resistors may be prepared on a multi-dimensional substrate of the final dimension, configurations intended for each of them to form a head and which are positioned two by two together by their resistances, for example , according to FIG. 4, the four configurations 81, 84 and 82, 83, and the heads are then separated by cutting the substrate, along the axes 91 and 92, defining at the same time that said cut-out the edge of the resistances which becomes on the edge of said substrate.This can be obtained by matching the thickness of a saw blade to the dimensions of the pattern made on the substrate, so that, by passing this blade along the axis 91, the edges of the substrates and resistances are are brought on the lines 61 and 63, thus giving their correct dimensions to the resistors.

The passage of a saw blade along the axis 92 will separate the substrates from each other in the other direction. The dimensions can be chosen so as to place the edges 62 and 64 of the substrates in the middle of the feed conductors, so that by juxtaposing two substrates an iterative configuration of resistors and conductors is obtained.

 FIG. 2, which represents a section along II-II of FIG. 1, shows, in the case of a thin-layer embodiment, the substrate 41 which may have a thickness of 0.5 mm and which may be made of glass (of which the low thermal conduction here is an advantage), a conductor 21n + 1 which feeds the resistors 11n and 11n + 1 and which also delimits said resistors 11n and 11n + 1 in a continuous layer 12 passing under the conductors 21.This layer 12 can it is advantageous to use nickel-chromium with a thickness of 0.0150 micrometers, photo-etched, and the conductors 21, also photogravated, may be made of nickel having a thickness of 0.1 microns, covered with gold to a thickness of some micrometers.

 The size of the resistors may advantageously be 0.2 × 0.3 mm and the width of the conductors be 0.2 mm.

 Figure 3 shows the electrical diagram corresponding to a bar of eight resistors. With the thicknesses and dimensions given above, each resistor will be about 200 Ohms and will have to be fed under about 10 volts for about ten milliseconds to print a point.

Suppose we want to heat the resistors 11a, 11c, lld, llf. If the supply voltage is called V, one of its terminals V + must be connected to the conductors 21b, 21c, 21e, 21f and the other terminal V- to the conductors 21a, 21d, 21g, 21h, 21i. Thus, only the resistors pila, ilc, ild and 11f will have a voltage across their terminals.

Figure 5 shows a combination of "OR-EXCLUDED" doors
SIF "to obtain the result shown in Figure 3 from a coding provided for the case where a driver resistance is supplied.The structure of the assembly is quite repetitive, except for the conductors 21a and 21b. doors "EXCLUSIVE-OR" L1 to L7 has one of its inputs connected to the output of the previous door and the other connected to the corresponding input conductor (31b to 31h) .There is the following table of truth

<tb> Driver <SEP> Output <SEP> element <SEP> Output <SEP> from
<tb> (31b <SEP> to <SEP> 31h) <SEP> L <SEP> previous <SEP> the <SEP> L element
<tb><SEP> O <SEP> O <SEP> O <SEP>
<tb><SEP> o <SEP> 1 <SEP> 1
<tb><SEP> 1 <SEP> O <SEP> 1
<tb><SEP> 1 <SEP> 1 <SEP> 0
<Tb>
A resistor (11a to 11h) is powered if it sees different states at both ends, and it is the case if the input connection corresponding to it (31a to 31h) is in the logic state 1, this which is the goal.

 It has been assumed, for the sake of clarity, that the logic circuits could deliver adequate electrical power to directly feed the resistors.

 FIG. 6 shows the overall diagram of a code generation assembly, based on the use of a microprocessor, and which can supply a print head according to the invsnw tion, said head comprising in this example, sixty resistors divided into twelve groups of five, and so allows the printing of lines of twelve characters, each of them being defined by a matrix 5 x 7 points. The first five points of the twelve characters are printed together on one line (60 points), then the next five times twelve, and so on.

 The device shown in Figure 6 is a known device, of which only paragraphs 5 and 6 below describe a particular use specific to the invention.

Operation is according to the following sequence
1- The logical unit (61) reads the characters presented a. the input 60 by means of the input module 62 to which it is connected by the bundles of data and address conductors 65 and 66 ("bus" in English) according to a known process.

 2 Said logic unit (61) fetches in the memory (63) the coding of the 5 X 7-point matrix (35 points) corresponding to the presented character and sends it in a sequence of thirty-five bits in the RAM (64).

 3- The unit (61) thus proceeds, sequentially for a whole line of twelve characters.

 4- The unit (61) then reads, in memory (64), five points every thirty-five points so as to take only the first line of each of the matrices 5 × 7 and thus constitute a sequence of sixty points to be printed.

 5- As the unit (61) reads this sequence a. of points, it replaces it with another sequence ss using its logical choice possibilities. It will proceed iteratively in the following way o if the point n of the sequence R is different from the point n + 1 of a, then the point n + 1 of ss will be 1, otherwise it will be 0. To begin, it will take the point number 1 of ss identical to point number 1 of a.

 6- The unit (61) replaces in the memory (64) the elements of the series a by those of the series ss because it no longer needs the previous elements of the series.

 7- The unit (61) fills the memories of the output elements (71) to (78) either progressively or in block at the end of the previous treatment.

 8- When the sixty positions are filled in the elements (71 to 78), the unit (61) gives a signal to the output element (79) which generates the permission to read tenable ") on the driver (80) controlling unrepresented "latch" doors which will retain the data for the time necessary to heat the resistors.

 During this time, the unit (61) can begin to read in (64) the next line, and process it as described above.

 In the case of printing curves or drawings and not characters, at a given moment a sequence of bits placed in a memory and representing the line of points to be printed is available. It suffices to apply to this sequence of bits the processing described above in paragraphs 5 and 6, to replace said sequence with a new one suitable for feeding the connections of a print head according to the invention (for example connections 21 in Figure 3).

 If we call V + and V- the two terminals of the supply, we will connect the first conductor (21a, Fig. 3) always to V-, then the following ones to V + or V- according to the logical states of the outputs doors (71 to 78, Fig. 6) are respectively 1 or 0.

Claims (3)

 - Claims  An immediate-reading thermal printing head, comprising, deposited on an insulating substrate (41), a plurality of heating resistors (11) arranged in line and current supply conductors (211-) to said resistors, characterized in that the resistors (11) are connected together in series, and in that each conductor (21) feeds two adjacent resistors, this arrangement making it possible to arrange the resistors at the selvedge (31) of the substrate (41).  2. A method for the construction of a printing head according to claim 1, characterized in that, starting from a substrate (42 having at least one determined excess dimension and placing on this substrate resistors. having a dimension (51) at least equal to the desired dimension, as well as the conductors (21) which are afferent thereto, defining the edge of the substrate along which the resistors are at the edge and also the edge of said resistors by a reduction said determined dimension of said substrate.  3. A process according to claim 2, characterized in that a plurality of configurations (89 to 84) of conductors and resistors are prepared on a multi-size substrate (41) of the final dimension; configurations for each of them to form a head, and which are positioned two by two joined by their resistors (81,84 and 82,83) and in that the heads are then separated by cutting the substrate, defining in same time by said cutting the edge of the resistors (11) which becomes large said substrate.