EP0702334B1 - System for controlling an ink jet print head in a franking machine by vernier control - Google Patents

Description

The invention relates to a franking machine including an inkjet print head for printing a postal imprint on a postage item moved relative to the head in a direction of movement, this print head comprising a plurality of nozzles arranged in at least two rows extending transversely to the direction of movement, these two rows being spaced apart by a distance D in this direction and a control means being provided to control the chronological succession of ejections of ink droplets from the plurality of nozzles so as to delay the ejection of ink droplets from the nozzles one of the two rows relative to that of the nozzles of the other row of a delay R based on a given previously recorded representative of an estimate of the distance D.

Such a franking machine is known from document US-5083153. Inkjet printing brings very high flexibility for franking machines, especially when it comes to printing on items of postal imprints containing both variable characters, like the numeric symbols of a postage amount, and color layouts, like the advertising flames.

According to a simple and economical arrangement of the head the two rows of nozzles can be part respectively of two mutually different housings offset transversely and longitudinally to the direction scroll. Indeed, today there are small housings enclosing a row of inkjet nozzles, by example of housings comprising 64 or 128 nozzles, which are now widely available at very low prices for equip inkjet printers to be connected to microcomputers. These inkjet printing boxes have a resolution of approximately 200 nozzles per inch (1 inch = 25.4 mm) which is suitable for the impression of a postal imprint. The linear brand printed by a box comprising for example 128 nozzles extends over approximately 16mm. We therefore understand that two boxes with a row of 128 nozzles each allow to print a linear mark over a length of approximately 30mm which corresponds to the height of a postal imprint.

Information to be printed by such a machine postage on a mail fold or label intended to be affixed to such a fold, for example a linear mark perpendicular to the direction of displacement, is recorded in digital form in a memory and partially transmitted to an interface circuit which, under the control of the control means, nozzles of the most row are operated simultaneously upstream in the direction of travel. Then after delay R during which the fold or label is moved by distance D, another part of the information in the memory is transmitted to the interface circuit which puts in simultaneously running all the nozzles on the other arranged in such a way as to finish printing the brand linear. This type of operation can extend to a number of nozzle rows greater than two.

The delay R in question can be given by a circuit fixed frequency clock if you don't take into account variations in the displacement speed V of the fold or label under the print head or otherwise at frequency synchronized to a signal representative of the speed of displacement of the fold or label detected in real time by a suitable speed sensor, for example a sensor optical. We understand that the delay R varies depending on the D / V ratio and an imprecise estimate of the distance D causes the appearance of a point alignment fault constituting the linear mark printed on the fold or the label, which can be eliminated by adjusting the value of representative previously recorded data of distance D.

The object of the invention is to provide a solution simple to set this data.

In an inkjet printer according to JP-A-56/072964, a first row of nozzles is spaced from a second row of nozzles by a distance in the direction moving the print head. Despite this row spacing, we avoid delay the second row droplet ejection commands by order report for the first row, because the second row is spaced from the first row also relative to the surface to be printed. The distance of the second row in relation to the surface to be printed exceeds the distance from the first row in relation to the surface to be printed. Therefore, two droplets ink ejected at the same time by two nozzles spaced in the direction of the displacement can nevertheless arrive at the same transverse line on the article to to print.

The inkjet printer according to document US-A-5,038,153 calculates time limits for delay ejection commands for four rows of nozzles spaced one of the other in the direction of travel.

According to the invention, the control means is arranged to order a first chronological sequence ejecting ink droplets from the nozzles of one of rows so as to print a first scale graduated rectilinear divided into first equal intervals according to the direction of travel and to order, after the delay R beginning at the start of said first sequence, a second chronological sequence of ejections from ink droplets from the nozzles on the other row of such so as to print a second straight graduated scale divided into second equal intervals in the direction of displacement and smaller than the first intervals, this second scale constituting a vernier associated with the first scale in order to obtain an error value for the setting of the recorded data.

Thus, adjusting the recorded data does not require only one visual examination, this examination consisting in locating two graduations which are arranged in alignment one with the other, one being part of the first scale, the other part of the second scale.

The correspondence between the position of these two graduations and the error value is easier to establish if the control means is arranged to control ejecting ink droplets from the plurality of nozzles in such a way as to print symbols next to one straight scales, each symbol corresponds to a particular error value.

Alternatively, optical sensors are arranged in downstream of the print head in the direction of displacement of a support on which are printed the scale graduations, these sensors providing signals representative of a chronology of detections of these graduations on the basis of which the data recorded representative of the distance D is set automatically.

The invention extends to a method for adjusting a such a franking machine according to which the first and second straight scales are advantageously printed on a label in case the machine postage includes a vending machine of labels.

An example of realization of the machine postage according to the invention is now described in more detail below with reference to the drawings.

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

Figures 2 to 6 show examples of printing rectilinear scales useful for adjusting the data recorded representative of distance D.

Figure 7 shows two rows of nozzles partially overlapping in the direction of travel.

The franking machine in Figure 1 includes a conveyor system that moves the mail item 1 to be franked under an ink jet print head 2 stationary in the direction of travel F.

The print head here comprises two housings such as 20 and 21, each box comprising a row of nozzles, each row including for example 128 spaced nozzles evenly from a distance of 1/200 inch, i.e. about 0.127 millimeter. Note that more than two boxes can be mounted in the print head, boxes possibly having rows of size nozzles different, for example a housing with 128 nozzles and a housing with 64 nozzles. In the case of example, the boxes 20 and 21 are identical.

The two boxes are mounted in the head so that their rows of nozzles extend transversely to direction F, the two housings being offset from each other transversely and longitudinally to direction F.

The nozzles are represented by crosses on the Figure 1. The arrangement of the two boxes 20 and 21 is such that the distance between the last nozzle B128 of the housing 20 (the highest one in figure 1) and the first nozzle B'1 of the housing 21 (the lowest one in Figure 1) is at least equal to the height H of a postal imprint 10 represented by the rectangle in broken lines on Article 1. We therefore understand that the dimension of each row of nozzles and the height of the postal imprint determine the number of boxes needed to printing the postal imprint.

If possible, these two housings 20,21 are mounted from such that the first nozzle B1 of the housing 20 (that of the lower case 20 in FIG. 1) is spaced from the last nozzle B'128 of the housing 21 (that of the housing 21 the higher on figure 1), according to the direction perpendicular to direction F, a distance equal to about 0.127 millimeter (i.e. the distance between two consecutive nozzles from either of the rows of nozzles).

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

The franking machine further includes 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 ink droplet ejections from nozzles in response to clock signal synchronized or not with the speed of displacement of the fold or the label under the head 2, so that it is possible to produce dots on the fold or label that join together with a slight overlap along straight lines parallel to the direction F.

To print a linear mark transverse to the direction F and which extends over almost the entire height H of imprint 10 (like the bar of the character P shown on the Figure 1), unit 3 delays the ejection command ink droplets from the nozzles of row R2 (the nozzles of the box 21 which is furthest downstream in the direction F) by compared to the ink droplet ejection command nozzles of row R1 (the nozzles of the housing 20 which is most upstream in direction F), with a delay R varying depending on the ratio d / V or d is the adjustable data previously recorded in memory and representative of the distance D.

Due to the tolerances accepted during assembly of the housings 20 and 21 in the print head, the distance D varies from one printhead to another. Besides, it is very difficult to measure, with all the precision distance D. Therefore, after mounting the boxes 20 and 21, we load into unit 3, a data d whose value is an estimate (usually imprecise) the distance D which must then be adjusted.

To adjust this data d so as to obtain a linear mark whose points (formed by the droplets ink) are aligned satisfactorily transverse to direction F, control unit 3 is arranged as follows.

From an instant t defined as the point of start of a step for adjusting this datum d, unit 3, in response to the input of a control signal for example, commands a first chronological sequence of ejections from ink droplets from the nozzles of the housing 20 so as to print on paper (such as envelope 1 or analog) moved under the print head 2 according to the direction F, a first series of linear graduations transverse to direction F and constituting a first rectilinear scale divided into first equal intervals. Furthermore, the unit 3 still commands, in response to this control signal, a second chronological sequence ejecting ink droplets from the nozzles of the housing 21, from time t + R, so as to print, on this support, a second series of linear graduations transverse to direction F and constituting a second rectilinear scale divided into second equal intervals but smaller than the first intervals.

This second scale constitutes a vernier associated with the first scale and by simple visual examination of the coincidence between a graduation that is part of the first scale and a graduation part of the second scale it's easy to determine a value error which corresponds to the difference between the data recorded representative of the distance estimate D and the exact value of this distance D. According to the difference between the intervals of the two scales, this error can be obtained with the desired precision.

Figures 2 to 6 show examples of printing scales, the first scale being referenced by 110 and the second by 111 while the print medium is referenced 11. Numerical symbols like 1 to 9, generally available for printing an amount are also printed next to the graduations of the first scale. The first graduations printed by the print head, are those located to the left of Figures 2 to 6. It is understood that if the first graduation of the scale 110 is right-eye with the first graduation of scale 111, data d is an exact estimate of distance D (as shown in Figure 4). Otherwise, the error value determined by visual inspection, is subtract or add, as the case may be, to the data d saved.

Unit 3 can be arranged to accept data representative of the size of the intervals A and B for the two scales on the basis of which it can adapt the length of the scales to a desired length print media, for example to facilitate examination visual scales.

In the example case, the distance between two points consecutive printed on a longitudinal line at the direction F corresponds to a print pitch set to 1/200 inch, or about 0.127mm. Furthermore, the dimension of boxes 20 and 21 generally allows them to be mounted offset longitudinally to direction F so that the distance D is approximately 100 printing steps, that is to say about 1.27mm. If by order, A is set at 50 steps (i.e. about 6.35mm) and B is set at 49 steps (i.e. 6.223mm), just 50 graduations on both scales 110 and 111 to get an error value having an accuracy of 2/100 steps.

To make it even easier to spot a coincidence between two graduations of scales 110 and 111, the housings 20 and 21 are mounted in such a way that the row of nozzles R1 partially overlaps the row of nozzles R2 according to the direction F as shown in figure 7 (i.e. the two rows of nozzles R1 and R2 have a printing area common which is located in the middle of height H). It it follows that the graduations of the two scales 110 and 111 are partially overlap as shown in Figures 2 to 5. However, in this case, when printing a postal imprint, it is necessary to prohibit the operation of some of the nozzles of one or the other of the two rows to avoid printing defects. Through example, with reference to figure 7, unit 3 should prohibit the operation of nozzles B1 to B3.

According to another embodiment, two sensors optoelectronics 22 and 23 are provided in the head (or out of it) downstream of the two rows R1 and R2 in direction F. These photo sensors detection 22 and 23 are mounted in such a way that the sensor 22 detects the graduations of the scale 110 and the sensor 23 detects the graduations of the scale 111. Each sensor provides a signal that is representative of a chronology of detections of graduations of a scale. In Figure 1, signals 22S and 23S each have two peaks which correspond to the detection of two successive graduations of a ladder. Since the interval between two graduations of scale 110 is greater than the interval between two graduations of scale 111, it follows that the interval of time between two peaks of the 22S signal is greater than the time interval between two peaks of signal 23S. These signals are supplied, after digitization, to unit 3 which counts the number of peaks present in 22S signals and 23S since the start of the adjustment phase, compare in time the occurrence of the peaks in the 22S signal with the occurrence of the peaks in the signal 23S so as to find a particular peak in the 22S signal which is in phase with a particular peak in the 23S signal and which, based on the serial number of these particular peaks (according to the established accounting), determines the error value relating to data d and finally automatically adjusts this last. The support 11 used for printing the scales 110 and 111 is preferably a label which is supplied by an automatic label dispenser (not shown) equipping the franking machine and which is moved under the print head. It is unit 3 which orders the label dispenser in response to pressing a key on the machine keyboard postage for example so the operation of setting of data d is done without an operator having to intervene. It is understood that the printing of the scales on a label is advantageous even in the case of an examination visual scales because it exempts the operator from inserting an envelope or other support in the machine postage.

Claims (8)

1. A postage meter including an ink jet print head (2) for printing a postage imprint (10) on an article to be franked (1) which is displaced relative to the print head in a displacement direction (F), said print head including a plurality of nozzles (B1-B3, B128, B'1, B'128) disposed in at least two rows (R1, R2) extending transversely to the displacement direction, said two rows being spaced apart from each other in said direction by a distance D, and control means (3) being provided to control the timed succession of ink droplet ejection from the plurality of nozzles in such a manner as to retard the ejection of ink droplets from the nozzles of one of the two rows (R1) relative to ejection from the nozzles of the other row (R2) by a delay R based on previously recorded data (d) representative of an estimate of the distance D, the postage meter being characterized in that the control means is also organized to control a first timed sequence of ejections of ink droplets from the nozzles of one of the two rows (R1) in such a manner as to print a first graduated rectilinear scale (110) subdivided into first equal divisions in the displacement direction, and after the delay (R) starting from the beginning of said first sequence, to control a second timed sequence of ink droplet ejections from the nozzles of the other row (R2) in such a manner as to print a second graduated rectilinear scale (111) subdivided into second equal divisions in the displacement direction that are smaller than the first divisions, said second scale constituting a vernier associated with the first scale for the purpose of obtaining an error value for adjusting the recorded data.
2. A postage meter according to claim 1, in which the control means (3) is organized to control ink droplet ejection from the plurality of nozzles in such a manner as to print symbols in association with the graduations of one of the rectilinear scales (110, 111).
3. A postage meter according to claim 1, in which the two rows (R1, R2) of nozzles form parts respectively of two packages (20, 21) that are mutually offset transversely and longitudinally relative to the displacement direction.
4. A postage meter according to claim 3, in which the two packages are mounted in such a manner that the two rows (R1, R2) of nozzles have a print zone in common.
5. A postage meter according to claim 1, further including photodetection means (22, 23) disposed downstream from the rows (R1, R2) of nozzles in said displacement direction to detect said graduations of the first and second scales (110, 111), said graduations being detected chronologically, said photodetection means providing a first signal (22S) representative of the times at which graduations of the first scale (110) are detected, and a second signal (23S) representative of the times at which graduations of the second scale (111) are detected, the control means (3) being connected to said photodetection means so as to adjust said recorded data on the basis of the first and second signals.
6. A method of adjusting a postage meter including an ink jet print head (2) for printing a postage imprint (10) on an article to be franked (1) which is displaced relative to the print head in a displacement direction (F), said print head including a plurality of nozzles (B1-B3, B128, B'1, B'128) disposed in at least two rows (R1, R2) extending transversely to the displacement direction, said two rows being spaced apart from each other in said direction by a distance D, and control means (3) being provided to control the timed succession of ink droplet ejection from the plurality of nozzles in such a manner as to retard the ejection of ink droplets from the nozzles of one of the two rows (R2) relative to ejection from the nozzles of the other row (R1) by a delay R based on previously recorded data (d) representative of an estimate of the distance D, said method comprising the following steps:

   a) using the control means to control a first timed sequence of ink droplet ejections from the nozzles of one of the two rows (R1) in such a manner as to print a first graduated rectilinear scale (110) subdivided into first equal divisions in the displacement direction;

   b) using the control means, after the delay R starting from the beginning of said first sequence, to control a second timed sequence of ink droplet ejections from the nozzles of the other row (R2) in such a manner as to print a second graduated rectilinear scale (111) subdivided into second equal divisions in the displacement direction and smaller than the first divisions, said second scale constituting a vernier associated with the first scale;

   c) visually inspecting the first and second scales to identify which graduation of the first scale coincides with a graduation of the second scale in order to obtain an error value relating to the recorded data; and

   d) modifying the recorded data on the basis of the error value.
7. A method according to claim 6, further including a step consisting in using said control means (3) to control ink droplet ejection from the plurality of nozzles in such a manner as to print symbols in association with the graduations of one of the rectilinear scales (110, 111).
8. A method according to claim 6 or 7, in which the first and second rectilinear scales (110, 111) are printed on a label (11) coming from a label dispenser fitted to the postage meter.

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