FR2708233A1 - Method and device for dot printing. - Google Patents

Abstract

The device is equipped with a print head (1) associated with displacement members to effect relative displacement of the print head and of a document to be printed in at least one direction of movement (10), the printhead comprising a series of printing members (13) spaced from each other in the direction of movement (10) by an effective spacing distance d greater than a reference spacing distance while the displacement is carried out according to a step corresponding to the distance of reference spacing so that one ensures an overlap between the successive printed bands.

Description

The present invention relates to a printing method and device

by points, which may apply

especially fax.

  Dots printing devices are known comprising a dots printing head, for example an ink jet printing head mounted on a carriage associated with drive members for moving the carriage relative to a document in two substantially perpendicular directions of movement. A head of this type has a series of print nozzles arranged in a line or a matrix. The print nozzles are spaced from each other and are arranged so that a displacement of the print head in a first direction prints a strip formed of elementary dots emitted by the nozzles of the head which are controlled for printing. In this regard, it is recalled that the resolution of an ink jet print head is defined by the number of dots printed per unit of length according to the direction considered. Successive bands of dots are produced sequentially by carrying out a relative displacement of the print head and

  of the document in a second direction, for example in low

  sant to advance the document in a direction perpendicular to the direction of movement of the carriage, the number of bands

  being determined to scan the desired format of the document.

  In principle, the document advance in the second direction is calculated so that the successive bands are joined, that is to say that the document advance is equal to the product of the distance between nozzles taken in the direction of advance, by the number of nozzles included in the head

printing in this direction.

  However, the different mechanical clearances resulting from the manufacturing tolerances of the carriage mounting parts mean that two adjacent printed strips are not always exactly joined, which results in the appearance of a so-called fictitious white line. between these bands, that is to say that this white line was not provided in the print order. This white line is all the more visible as the print density is higher, thus seriously affecting the quality of the printed image especially when it is a graphic image. To remove the fictitious white lines from a document, a slight overlap zone could be created between each printed strip, for example by printing the strips at a reference resolution, that is to say a resolution which would theoretically allow to attach the bands by a corresponding advance, and to ensure a relative displacement of the document and the print head according to a step less than that corresponding to the reference resolution. However, the number of bands produced being determined regardless of the advance of the document, advancing at a step lower than that corresponding to the reference resolution would have the effect of shifting all the successive bands in the same direction, according to an increasing amplitude , which would decrease the format of the

printed document.

  According to the invention, a printing process is proposed.

  which includes the steps of printing dots at a resolution lower than the reference resolution while maintaining a relative displacement of the

  document and print head at a corresponding pitch

  with reference resolution.

  Thus, the decrease in resolution which is associated with a corresponding magnification of the dimension of the elementary points causes a widening of each strip, which is regularly distributed over the whole document and thus ensures a slight overlap of the strips without offset from them. and without any noticeable change in format.

  According to the invention, a device is also provided.

  dot printing device equipped with a printhead associated with displacement members for effecting a relative displacement of the printhead and of a document to be printed in at least one direction of displacement, the printhead printing comprising a series of printing members spaced from one another in the direction of movement of an effective spacing distance greater than a reference spacing distance, these printing members being produced for printing dots having an effective dimension greater than a reference dimension, the displacement being carried out at a step corresponding to the

  reference spacing distance.

  Other characteristics and advantages of the invention

  tion will appear on reading the description which follows

  of a particular nonlimiting embodiment of the invention in relation to the attached figures among which: - Figure 1 is a schematic partial perspective view of a carriage printing device, - Figure 2 is an enlarged schematic representation of the face of the print head which faces the document to be printed, - Figure 3 is a comparative diagram between the result of printing a document obtained with conventional printing means and the print result of the same

  document obtained with the process and the device of the invention.

  Referring to Figure 1, the ink jet print head 1 is carried by a carriage 2 which moves in a first direction 4 which will be referred to below

  horizontal direction. The carriage 2 slides on a guide 3 arranged parallel to the horizontal direction. Moves it

  ment of the carriage 2 on the guide 3 is provided by drive members (5, 6). In the illustrated embodiment, these members comprise a belt 6 fixed to the carriage 2 and a motor 5 driving this belt.

  The document to be printed 8, for example a sheet of paper, rests on a support 7 and moves thanks to drive means 9, relative to the print head 1 in a second direction 10 which will be referred to as direction vertical. The drive means 9 comprise two rollers 11 between which the document is pinched. The roller under the document is equipped with a

drive motor 12.

  Figure 2 is an enlarged schematic representation of the face of the print head which faces the document to be printed. The head 1 has a line of nozzles 13 inclined at an angle A relative to the vertical direction to obtain the desired resolutions in the horizontal and vertical directions. The distance of deviation-15 ment taken in the vertical direction is the inverse of the resolution taken in this direction. At this resolution

  corresponds to a dimension of the nozzles to achieve a print-

  zion of elementary points joined when nozzles

  adjacent are simultaneously ordered for printing.

  A reference resolution, for example equal to 7.7 point per millimeter in the vertical direction 10, corresponds to a reference spacing distance, ie 0.1299 millimeter in the example mentioned. For a print head with 64 nozzles, the reference feed

  corresponding document will have a reference pitch of 8.31 mm.

  According to the invention, while controlling the motor 12 sequentially to obtain a document advance equal to the reference pitch, the vertical resolution of the print head is modified so that it is less than the reference resolution, for example 7.65 points per millimeter, which corresponds to an effective distance of separation d in the vertical direction greater than the reference distance of separation, that is 0.1307 mm in

the example cited.

  So while in convention-

  nels the width of a strip is 8.31 mm, we obtain here a strip width of 8.36 mm, which allows to absorb a

0.05 mm clearance between two strips.

  In FIG. 3, the result of the printing of four successive bands of theoretically contiguous dots is partially illustrated, the left part of the figure illustrating the result obtained with a conventional inkjet printhead, and the part right illustrating the

  result obtained according to the invention. In both cases the im-

  pressure is assumed to be carried out by means of a head

  inkjet printers with three print nozzles

  if we. On the left-hand side of FIG. 3, the successive bands bear the reference 14 and the references

  14.1, 14.2, 14.3, and 14.4. The basic points

  They are numbered 15 and have been hatched with different inclinations depending on the band to which they belong. The elementary dots 15 are printed by a print head at the reference resolution and the advance of the document to pass from one strip to the other is carried out at a step corresponding to this reference resolution. However, due to the mechanical games of the carriage, the successive printed bands 14 are not always perfectly joined, this results for example in the appearance of a fictitious white line 16 between the bands

14.2 and 14.3.

  On the right-hand side of FIG. 3, the result of the printing of the four successive bands of the document has likewise been illustrated, this time obtained by the

  process and device of the invention, the successive bands

  They bear the general reference number 18 and the specific references 18.1, 18.2, 18.3 and 18.4. The elementary points bear the reference numeral 17. The elementary points 17 are printed with a print head at a resolution lower than the reference resolution and have

  an effective dimension greater than the reference dimension

  Reference points 15. The relative displacement step of the document and the head remains that corresponding to the reference resolution. This is shown in the figure by the coincidence of the center line of the bands 14 and 18 illustrated.

  in the figure by a solid line.

  Due to the lower resolution than the reference resolution and the corresponding increase in the size of the elementary dots, the printed bands 18 are wider than the bands 14, which results in a slight overlap 19 between the bands 18.1 and 18.2 d on the one hand, and the bands 18.3 and 18.4 on the other hand, and the disappearance of the fictitious line 16 between the bands 18.2 and 18.3 without general offset of the bands. This widening of the bands is reflected

  by a very slight overflow of the end bands. The agran-

  resulting format is however totally

  imperceptible due to its extremely small amplitude.

  Of course, the invention is not limited to the embodiment described and it is possible to make variant embodiments without departing from the scope of the invention such as

defined by the claims.

  In particular, although the print head has been described with a single line of nozzles, it may include a series of nozzles arranged in a matrix. It is even possible to provide a print head comprising a number of nozzles sufficient to carry out a whole strip of elementary dots at once, the relative displacement of the print head

  and the document being made in one direction.

  Although the invention has been described in relation to a resolution taken in the vertical direction, it can also be implemented in the horizontal direction. Although the invention has been described in relation to an ink jet printing head, it can be implemented for any dot printing device,

  including a thermal print head.

Claims (2)

  1. Method for printing a document (8) by means of a dot print head (1) comprising a series of printing members (13), this method comprising the steps of sequentially printing of points and a   relative movement of the document (8) and the print head   sion (1) according to a step corresponding to a reference resolution, characterized in that the printing of dots is carried out at a resolution lower than the resolution of reference.   2. Point printing device equipped with a printing head (1) associated with displacement members   (9) to effect a relative movement of the print head   pressure and a document to be printed (8) according to at least one   direction of travel (10), the print head   as a series of printing members (13) spaced from each other by an effective spacing distance in the direction of movement (10), for printing dots having an effective dimension, the displacement being effected in a step corresponding to a reference spacing distance associated with a reference dimension of the points, characterized in that the effective spacing distance and the effective dimension of the points are respectively greater than the reference spacing distance and the dimension of reference.