Incremental printing of symbolic information – Ink jet – Controller
Reexamination Certificate
1997-01-15
2001-04-17
Barlow, John (Department: 2853)
Incremental printing of symbolic information
Ink jet
Controller
C347S037000, C347S040000, C400S279000, C400S283000
Reexamination Certificate
active
06217143
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a printing method and printing apparatus in which a print head is scanned in a direction transverse to the feeding direction of a printing medium to achieve printing of an image line by line.
2. Description of the Related Art
Heretofore, printing apparatuses using various image formation means have been practically used, and among these, an ink-jet type is relatively inexpensive, compact in structure, low in noise, and being used in a variety of applications from personal to office use.
As a method of image formation in a printing apparatus, a serial scan system has been generally known. In the serial scan system, while the print head is being reciprocally scanned, the printing medium is fed in a direction perpendicular to the scanning direction of the print head, intermittently in an amount equal to the printing width of one scan, to sequentially form the image line by line.
The serial scan system is also widely applied in the area of ink-jet type recording apparatus.
Heretofore, the ink-jet type printing apparatus has been disadvantageous in that the image formation speed is slower as compared with an electrophotographic type. However, recently, with improved integration ink ejection ports of the print head, some of print heads having 512 ink ejection ports arranged in a recording density of 400 dpi (dot per inch) have been practically applied, which achieves an image formation speed comparable to the electrophotographic system.
However, when an image is formed by serial scanning, it is necessary that the printing medium is fed exactly in a predetermined amount in order to obtain an image of good quality. To realize such feeding, a feeding unit of the printing medium is normally composed of a roller pair disposed at the upstream side or downstream side with respect to the feeding direction in the vicinity of the print portion of the printing medium, a drive source to drive the roller pair, drive transmission means for transmitting the driving force from the drive source to the roller pair, and the like. As the drive source, a pulse motor which can easily control the feeding amount of the printing medium is generally used, and as the drive transmission means, a pulley and rubber belt or the like is generally used.
However, if the feeding amount of the printing medium becomes in is shortened even slightly, image overlapping (black stripes) will occur, or if the feeding amount is excessive, image discontinuity (white stripes) will occur. Such error in the feeding amount becomes visually notable when occurring even in an amount of about a half picture element (about 30 &mgr;m) for a 400 DPI image, which considerably degrades the image quality. Causes of the error include machining precision of the feeding roller and driver pulley for feeding the printing medium, stopping precision of the drive source, and machining precision of the teeth of belt or pulley; in particular, error due to an eccentricity of the feeding roller and drive pulley on the feeding roller shaft is important.
To reduce the effect of the eccentricity, it is best that the circumferential length of the feeding roller is made equal to the printing width of one scan. That is, for a print head of 400 dpi, 512 ink ejection ports, since the printing width of one scan is 32.512 ink ejection ports, effect of eccentricity between the feeding roller and the drive pulley which is linked to the shaft thereof can be almost eliminated when a roller is used as the feeding roller which satisfies the requirement that its diameter of 10.349 mm corresponds to the circumferential length. In this case, when a reduction ratio between the feeding roller and the drive pulley on the same shaft is set to an integer, vibration of the drive pulley due to the motor and feeding errors generated from the stopping precision of the motor itself can be almost eliminated, and a practically sufficient feeding precision can be realized where the printing medium is fed in an amount equal to the printing width of one scan of the print head.
However, if the printing medium feeding amount is set always to a constant value, depending on the size of the printing medium, a large blank may occur at the rear end of the image, the blank amount may differ with different sizes of the printing medium. Then, in a printing apparatus which can handle different sizes of the printing medium, one of a plurality of printing movments to one printing medium is printed in a smaller printing width than usual to adjust the length of the blank.
Feeding during the one printing movement is referred to as a fractional feeding, the length of which can be calculated as a remainder of the integer portion of {(L−a−b)/X}, herein X is a printing width by a normal one scan of the print head, L is a total length of the printing medium in the feeding direction, a is a front blank, and b is a rear end blank. For example, when printing is made on a printing medium of A4 size which is fed along a longitudinal direction thereof, that is, 297 mm in total length, by an apparatus with a print head of 400 dpi, 512 ink ejection ports, that is, a normal printing width X by one scan of 32.512 mm, a front blank a of 2 mm, and a rear end blank b of 10 mm, the number of printing movements is 9, of which one movement may be made in a fractional printing (hereinafter referred to as fractional recording) with a printing width of 24.904 mm which is smaller than usual.
With the above fractional recording, image blank on the printing medium can always be made to a constant size irrespective of the size of the printing medium, but if the fractional recording is made at the top print line (hereinafter referred to as top line) at the downstream side with respect to the feeding direction or an intermediate print line (hereinafter referred to as intermediate line), it becomes necessary to feed the printing medium by a distance equal to the width of the fractional recording. Feeding of the printing medium according to the position where the fractional recording is made will be described with reference to the accompanying drawings.
(A) When fractional recording is made in the top line using the ink ejection ports at the downstream side of the print head
In
FIG. 16A
, a printing medium P fed from the right side in the direction of arrow C stops at the position where the leading end thereof advances by 2 mm blank from the print area (hatched area in FIG.
16
A). A print head
51
makes fractional recording using 392 ink ejection ports at the downstream side with respect to the feeding direction of the printing medium P corresponding to the 24.904 mm fraction. After completion of the fractional recording, the printing medium P is fed in the direction of arrow C in
FIG. 16B
by the fraction equal to the present printing width. Thereafter, printing using all ink ejection ports of the print head
51
and feeding of the printing medium P by the distance of the entire ink ejection ports width are repeated to achieve printing. The numeral
52
indicates a feeding roller.
(B) When fractional recording is made in the intermediate line using the ink ejection ports at the downstream side of the print head
Until fractional recording is made, printing of the entire ink ejection ports width and feeding of the printing medium P of the entire ink ejection ports width are repeated. During fractional recording, first, after making fractional recording using the ink ejection ports for the fraction at the downstream side of the print head, the printing medium P is fed in an amount equal to the fractional recording amount. Thereafter, printing using all the ink ejection ports and feeding of the printing medium P of the entire ink ejection ports width are repeated.
(C) When fractional recording is made in an intermediate line using the ink ejection ports at the upstream side of the print head
As shown in
FIG. 17A
, after completion of printing of a line immediately before the fractional recording is made, as shown in
FIG.
Munakata Atsushi
Takada Hideaki
Barlow John
Canon Kabushiki Kaisha
Fitzpatrick ,Cella, Harper & Scinto
Hallacher Craig A.
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