EP0702335A1 - System for controlling an ink jet head in a franking machine by printing the images in a stepped manner - Google Patents

Abstract

The control system (3) controls a first chronological sequence of ejected ink-drops from a first set of feeds (B1-B5) to print a first set of lines (MB1-MB5) extending longitudinally in the direction of displacement following a series of ladder steps. The system then controls a second chronological sequence of ejected ink-drops from a partic. feed (B'128) to print a second series of lines (MB'128) to one side of the first series of lines. The print head (2) has a photo-detection unit (22) arranged behind the ink feeds (R1,R2) following the direction of displacement. The detector (22) is mounted to move perpendicular to the displacement to detect in sequence the two print lines and provides a signal (22S) representing a detection sequence of the lines. The control system (3) is connected to the detector (22) to identify a feed from the first set which is in alignment with the particular feed (B'128), when the signal (22S) is received, and then stops operation of some of the feeds (B1-B3;B1,B2, B'B128) of the two set of feeds during printing of the franking design.

Description

The invention relates to a franking machine comprising an ink jet printing head for printing a postal imprint on a franking article moved relative to the head in a direction of movement, this printing head comprising a plurality of nozzles arranged in two rows extending transversely to the direction of movement, these two rows being mutually offset transversely and longitudinally to the direction of movement and control means being provided for controlling the chronological succession of ink droplet ejections of the plurality of nozzles.

Such an inkjet printing head franking machine is known from document US-5083153. Inkjet printing gives postage machines great flexibility, particularly when it comes to printing postal items on mail items with both variable characters, such as digital symbols a postage amount, and color schemes, such as advertising flames.

According to a simple and economical arrangement of the print head, the two rows of nozzles can be part of two different housings mutually offset transversely and longitudinally to the direction of movement so that a row of nozzles has a substantially screwed end opposite one end of the other row of nozzles. Indeed, today there are small boxes containing a row of ink jet nozzles, for example boxes comprising 64 or 128 nozzles, which are now widely distributed at very low prices to equip jet printers. ink to be connected to microcomputers. These jet printing boxes have a resolution of about 200 nozzles per inch which is suitable for printing a postal imprint. A box comprising for example 128 nozzles makes it possible to print a linear mark which extends over approximately 16mm. It will therefore be understood that two boxes comprising a row of 128 nozzles each, mounted in the print head make it possible to print a linear mark over a length of approximately 30mm which corresponds to the height of a postal imprint.

The information to be printed by such a franking machine on a mail fold or a label intended to be affixed on such a fold, for example a linear mark perpendicular to the direction of movement, is recorded in digital form in a memory and partially transmitted to an interface circuit which, under the control of the control means, simultaneously operates the nozzles of the row most upstream in the direction of movement. Then after the delay R during which the fold or label is moved (e) by the distance D separating the two rows of nozzles in the direction of movement, another part of the information in the memory is transmitted to the interface circuit which puts in all the nozzles in the other row operate simultaneously so as to finish printing the linear mark. This type of operation can extend to a number of rows of nozzles greater than two.

The delay R in question can be given by a clock circuit at a fixed frequency if the variations in the speed of movement V of the fold or label under the print head are not taken into account or otherwise at frequency synchronized on a representative signal the speed of movement of the fold or label detected in real time by an appropriate speed sensor, for example an optical sensor.

According to this principle, to obtain such a linear mark having a satisfactory quality, it is necessary that these two housings be mounted in such a way that the ends opposite the rows of nozzles (each defined by a nozzle) are spaced from one another in the direction transverse to the direction of movement by a distance equal to about 0.127 mm; that is to say the distance between two consecutive nozzles of one or the other of the rows of nozzles. In this way it is possible to keep the same resolution over the entire length of the linear mark, that is to say to print, over the entire height of a postal imprint, longitudinal lines in the direction of movement which are spaced regularly between them.

In practice, it turns out that it is difficult to obtain such a precise arrangement of the rows of nozzles and it is easier to mount, with a certain tolerance, the two housings in such a way that first end nozzles d 'a row of nozzles are arranged opposite second end nozzles of the other row of nozzles and then prohibit the operation, at the time of printing a postal imprint, of some of these first few or second nozzles so as to avoid breaking the regularity of the spacing between the lines mentioned above.

The object of the invention is to provide a simple solution for selecting the nozzles whose operation must be prohibited at the time of printing a postal imprint on a mail item.

According to the invention, the control means is arranged to control a first chronological sequence of ejection of ink droplets from said few first nozzles so as to print a first series of first rectilinear patterns extending longitudinally to the direction of movement following a staircase arrangement on the basis of a first pattern per step, and for controlling a second chronological sequence of ejections of ink droplets from a particular nozzle of the second nozzles so as to print a second series of second rectilinear patterns extending longitudinally to the direction of movement and in such a way that the second patterns are substantially opposite respectively the first patterns with respect to a direction perpendicular to the direction of movement. By a visual examination of the first and second rectilinear patterns, it is identified visually or automatically which is the nozzle among the first nozzles which is in alignment with said particular nozzle in the direction of travel. Then, it is easy to identify the nozzles among the first or second nozzles whose operation must be prohibited when printing a postal imprint. This prohibition may be based on an appropriate modification of the parameters of the program governing the control means.

This identification is facilitated if the control means is arranged to control the ejection of ink droplets from the nozzles of the plurality of nozzles so as to print symbols opposite the first or second rectilinear patterns, these symbols making it possible to establish a direct correspondence between the first patterns and the row of the first or second nozzles in the rows of nozzles.

The invention extends to a method for adjusting such a franking machine according to which the first and second patterns are advantageously printed on a label in the case where the franking machine includes an automatic label dispenser.

An embodiment of the franking machine according to the invention is now described in more detail below with reference to the drawings.

Figure 1 is a block diagram of the printhead forming part of a franking machine according to the invention on which appears an arrangement of the nozzles of the printhead in two parallel rows.

Figure 2 shows the overlap of the two rows of nozzles.

Figures 3 to 6 show examples of printing first and second rectilinear patterns.

The franking machine in FIG. 1 comprises a conveyor system which moves the mail item 1 to be franked under a stationary ink jet print head 2 in the direction of movement F.

The print head here comprises two housings such as 20 and 21, each housing comprising a row of nozzles, each row including for example 128 nozzles regularly spaced apart by a distance of 1/200 inch, that is to say approximately 0.127 millimeter. Note that more than two boxes can be mounted in the print head, the boxes possibly having rows of nozzles of different sizes, for example a box with 128 nozzles and a box with 64 nozzles. In the example, the housings 20 and 21 are identical.

The two housings are mounted in the print head in such a way that their rows of nozzles extend transversely to the direction F, the two housings being additionally offset with respect to each other transversely and longitudinally to the direction F.

The nozzles are represented by crosses in FIG. 1. The arrangement of the two housings is such that the distance between the last nozzle B128 of the housing 20 (the one uppermost in FIG. 1) and the first nozzle B'1 of the box 21 (the lowest one in FIG. 1) is at least equal to the height H of a postal imprint 10 represented by the rectangle in broken lines on article 1. It is therefore understood that the dimension of each row of nozzles and the height of the postal imprint determine the number of boxes required for printing the postal imprint.

Due to the space provided by the boxes, the two rows of nozzles R1 and R2 are spaced from each other by a distance D in the direction F of about 1cm.

The franking machine further comprises a control unit 3, such as a microprocessor and a program stored in a memory not shown, which is connected to control the chronological succession of ejections of ink droplets from the nozzles, in response to a signal d clock synchronized or not with the speed of movement of the fold or the label under the print head 2, so that it is possible to produce dots on the fold or the label which join one to the other with a slight overlap along straight lines parallel to the direction F.

Furthermore, these two housings 20, 21 are mounted in such a way that a few end nozzles of the row of nozzles R1, for example five nozzles like B1 to B5 are arranged substantially opposite a few end nozzles. of the row of nozzles R2, for example five nozzles like B'128 to B'124, as shown in FIG. 2.

This arrangement of the two rows of mutually overlapping nozzles considerably facilitates the mounting of the housings 20 and 21 in the print head. However, it is necessary to prohibit the operation of some of these end nozzles to avoid printing defects.

To select the nozzles whose operation must be prohibited, the control unit 3 is arranged as follows.

From an instant t defined as the starting point of an adjustment step, the unit 3, in response to the input of a control signal for example, controls a first chronological sequence of droplet ejections ink from nozzles B1 to B5 of the row of nozzles R1 so as to print on a paper support (such as envelope 1 or the like) moved under the print head according to the direction F, a first series of first rectilinear patterns extending longitudinally to direction F in a staircase arrangement at the rate of a first pattern per step, each pattern being printed by the aid of only one of these nozzles . As will be understood, these nozzles are excited in sequence, one after the other, starting, for example, with the most extreme nozzle of the row of nozzles R1 such as the nozzle B1. The dimension of each first pattern is in practice about 5 mm and the first patterns are spaced apart by the same distance in the direction F.

Furthermore, the unit 3 still controls, in response to this control signal but after a delay R corresponding substantially to the duration for moving the printing medium over the distance D, a second chronological sequence of ejections of droplets of ink from a particular nozzle of the few nozzles in row R2, preferably the most extreme nozzle of the row of nozzles R2 such as nozzle B'128, so as to print, on the continuous ribbon of labels, one second series of second rectilinear patterns extending longitudinally in the direction F and in such a way that these second patterns are substantially opposite respectively the first patterns with respect to a direction perpendicular to the direction F. It is also understood that each second pattern is printed by the same nozzle. The dimension of the second patterns is in practice also around 5mm and they are spaced apart by the same distance. It is understood that the dimensions of the first and second patterns can advantageously be adjusted to facilitate the visual examination which follows the printing.

The visual examination which follows the printing of the first and second patterns consists of identifying the one of the first patterns which best coincides with one of the second patterns.

It is therefore understood that the last of the first nozzles excited according to the principle described above must at least be positioned to the left of the nozzle B'128 in FIG. 2 to obtain a possibility of coincidence between a first and a second pattern.

From the identification of such a coincidence, it is easy to identify among the first nozzles, that which is in alignment with the particular nozzle of the second nozzles in the direction F. The adjustment then consists in prohibiting the start-up of one of these two nozzles as well as some of the first nozzles as indicated below. It is understood that the same adjustment can be made on the basis of the excitation of several second nozzles to print the first rectilinear patterns and the excitation of only one of the first nozzles to print the second patterns.

FIGS. 3 to 6 show examples of printing the first and second patterns, the first patterns being referenced by MB1 to MB5 and the second patterns by MB'128 while the printing medium is referenced 11.

Numerical symbols such as 1 to 5 generally available for printing a postage amount are also printed next to the first patterns (or second patterns).

By way of example, in FIG. 3, it is the first pattern opposite the symbol 3 (pattern MB3) which is right-eye with a second pattern MB'128. If by convention, this first particular pattern is that printed by the third nozzle of the row of nozzles R1 starting from the nozzle B1 (it is therefore the nozzle B3 in FIG. 2), it is easy to identify the nozzles whose operation must be prohibited when printing a postal imprint. In the case of example, it is necessary to prohibit the putting into operation of the nozzles B3, B2 and B1 which can be easily achieved by adapting the unit 3, in particular the parameters of the program which governs it. Equivalently, it is also possible to prohibit only the operation of nozzles B1, B2 and B'128.

According to another embodiment, an optoelectronic sensor 22 is provided in the print head (or outside of it) downstream of the two rows of nozzles R1 and R2 in the direction F. This photo detection sensor is mounted movable perpendicularly to said direction F as shown in FIG. 1 so that as the support 11 (on which the patterns MB1-MB5 and MB'128 are printed) moves in this direction F, the sensor 22 detects in sequence the patterns MB1-MB5 and MB'128 and provides a signal 22S representative of a sequence of detections of these patterns. As visible in FIG. 1, this signal 22S presents a succession of pairs of peaks. The peaks of a pair correspond to the detection of a first pattern (like MB1) followed by the detection of a second pattern (like the pattern MB'128 opposite the pattern MB1. The time space between the two peaks of a pair of peaks is proportional to the relative distance between the two patterns corresponding to these two peaks. As a result, the smaller this time space between two peaks of a pair of peaks in the 22S signal, the more the patterns which correspond to them are straightforward. The signal 22S is supplied, after digitization, to the unit 3 which establishes a correspondence between the pairs of peaks present in the signal 22S and the nozzles used for printing the first patterns like MB1 to MB5. By comparing the different time spaces (time space between two peaks of a pair of peaks) between them, unit 3 obtains the one that is the smallest and, by correspondence, identifies the nozzle of the row R1 which is the best aligned with the nozzle B'128 of the row e R2 Then, the unit 3 prohibits the operation of some of the nozzles of one or the other or both of the rows of nozzles R1 and R2 when printing a postal imprint as indicated above. The support 11 used for printing the patterns MB1-MB5, MB'128 is preferably a label or a plurality of labels which is or are automatically supplied by a label dispenser (not shown) fitted to the franking machine. It is the unit 3 which controls the label dispenser so that the adjustment operation is carried out without an operator having to intervene. In practice, the control of the label dispenser is synchronized with the control of the nozzles to print a single first pattern like MB1 and a single second pattern like MB'128 on a label. It is understood that the printing of the first and second patterns on a label provided automatically by the label dispenser is advantageous even in the case of a visual examination because it dispenses the operator from inserting an envelope or any other medium in the franking machine.

Claims (6)

1.) A franking machine comprising an ink jet printing head (2) for printing a postal imprint (10) on an article to be franked (1) moved relative to it in a direction of movement (F), this printhead comprising a plurality of nozzles (B1-B5, B128; B'1, B'124-B'128) arranged in at least two rows (R1, R2) extending transversely to the direction of movement, these two rows being mutually offset transversely and longitudinally to the direction of movement so that a few first nozzles (B1-B5) at the end of a row of nozzles (R1) are disposed opposite one another of a few second nozzles (B'124-B'128) at the end of the other row of nozzles (R2) and a control means (3) being provided for controlling the chronological succession of ejections of ink droplets from the plurality of nozzles, characterized in that the control means is further arranged for comma nder a first chronological sequence of ejection of ink droplets from said first few nozzles so as to print a first series of first rectilinear patterns (MB1-MB5) extending longitudinally to the direction of movement in a step arrangement staircase at the rate of a first pattern per step, and to control a second chronological sequence of ejections of ink droplets from a particular nozzle (B'128) of the second nozzles so as to print a second series of second patterns rectilinear (MB'128) extending longitudinally to the direction of movement and in such a way that the second patterns are substantially opposite respectively the first patterns with respect to a direction perpendicular to the direction of movement, and in this that said print head has furthermore, photodetection means (22) arranged downstream of the rows of nozzles (R1, R2) in said direction of movement, this photodetection means being mounted movable perpendicular to said direction to detect said first and second patterns in sequence and operating to provide a signal (22S) representative of a sequence of detections of said patterns, the control means (3) being connected to the photo detection means (22) to identify which is the nozzle among the first nozzles which is in alignment with said particular nozzle (B'128) on the basis of said signal (22S) supplied by the photo detection means and, on the basis of this identification, prohibit the putting into operation of certain (B1-B3; B1, B2, B ' 128) of said first or second nozzles when printing a postal imprint. 2.) The machine according to claim 1, wherein the control means (3) is arranged to control the ejection of ink droplets from the nozzles of the plurality of nozzles so as to print symbols opposite the first or second rectilinear patterns. 3.) The machine according to claim 1, wherein the two rows of nozzles (R1, R2) are respectively part of two housings (20,21) mutually offset transversely and longitudinally to the direction of movement. 4.) A method for setting up a franking machine comprising an ink jet printing head (2) for printing a postal imprint (10) on a franking article (1) displaced relative to it according to a direction of movement, this printhead comprising a plurality of nozzles (B1-B5, B128, B'1, B'124-B'128) arranged in at least two rows (R1, R2) extending transversely to the direction of movement, these two rows being mutually offset transversely and longitudinally to the direction of movement so that a few first nozzles (B1-B5) at the end of a row of nozzles (R1) are arranged opposite a few second nozzles (B'124-B '128) at the end of the other row of nozzles (R2) and a control means (3) being provided for controlling the chronological succession of ejections of ink droplets from the plurality of nozzles, this method comprising the following steps : a) controlling, via the control means (3), a first chronological sequence of ejection of ink droplets from said few first nozzles (B1-B5) so as to print a first series of first rectilinear patterns ( MB1-MB5) extending longitudinally to the direction of travel in a staircase arrangement on the basis of a first pattern per step; b) controlling, via the control means (3), a second chronological sequence of ejections of ink droplets from a particular nozzle (B'128) from the second nozzles so as to print a second series of second rectilinear patterns (MB'128) extending longitudinally to the direction of movement and in such a way that the second patterns are substantially opposite respectively the first patterns with respect to a direction perpendicular to the direction of movement; c) identify, by photodetection means (22) disposed downstream of the rows of nozzles (R1, R2) in said direction of movement, which is the nozzle among the first nozzles which is in alignment with said particular nozzle (B'128 ) following the direction of travel; d) prohibit, by adapting the control means, the putting into operation of certain (B1-B3; B1, B2, B'128) of said first nozzles or second nozzles when printing a postal imprint. 5.) The method according to claim 4, further comprising a step of controlling, by via the control means (3), ejecting ink droplets from the nozzles of the plurality of nozzles so as to print symbols opposite the first or second rectilinear patterns. 6.) The method according to one of claims 4 or 5, wherein the first and second patterns are printed on a label (11) from an automatic label dispenser fitted to the franking machine.

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