JPS62214965A - Ink jet printer - Google Patents

Abstract

PURPOSE:To make a nozzle displacement caused by the warp of a pole screw smaller than the warp of the pole screw and thereby prevent deterioration of printing quality by shortening a distance from a reference guide member to a nozzle as compared to a distance between the reference guide member and the pole screw. CONSTITUTION:A reference guide member 8 is arranged in parallel with the rotational shaft of a drum 3 and contacts a pole bearing 11 without vibration. An auxiliary guide member 9 is approx. 0.4mm clear from the pole bearing 11 fixed on a head base 7, and arranged in parallel with a pole screw 10. Nozzles 6 are radially arranged on the head base 7. It is so constituted that a distance gammaA between a reference guide member 8 to the nozzle may by approx. 1/2 of a distance gammaB between the reference guide member 8 and the pole screw 10. Therefore, if any displacement generated in the pole screw fitting part of a printing head 20, even the maximum nozzle displacement approx. 25mum or a value equivalent to almost 1/6 of the usual displacement value. Consequently a displacement value in the deflection height of ink droplets is reduced to approx. 3mum, thus significantly improving a printing quality.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to an inkjet printer in which sub-scanning of a print head is guided by a guide member and driven by a ball screw.

[Background of the invention]

Problems that must be solved by conventional inkjet printers will be explained with reference to FIGS. 3 and 4. The main scanning is performed by controlling the rotation of a drum 3 rotatably supported by the side plates 1 and 2 with a drum motor 5, and the sub-scanning is performed by controlling the rotation of a drum 3 which is rotatably supported by the side plates 1 and 2, and is fixed to the side plates 1 and 2 and provided approximately parallel to the drum 3. The print head 20t guided by the reference guide member 8 and the auxiliary guide member 9 is reciprocated by a ball screw 10 driven by a head motor 29. The print head 20 is equipped with a plurality of nozzles 6 and the like. A nozzle 6 is mounted on the head base 7 that fixes the ball bearing 11, and pressurized ink is supplied to the nozzle 6 from an ink supply system (not shown) via an ink tube 23t, and ink M14t is ejected.
Ink Ml 4t necessary for printing is selectively charged and deflected by the control electrode 21, skips over the gutter 22f, and reaches the paper 4 wound on the drum 3 to perform printing. Printing is performed by rotating the drum 3 counterclockwise in the drawing at a constant speed, rotating the ball screw 10t at a constant speed, and moving the print head 20 to the right in the drawing at a constant speed. Several rows of steel balls are incorporated into the reference guide member 8 and the ball bearing 11 in an endless manner, so that the print head 20 can slide smoothly even if the fit with the reference guide member 8 is a press fit. . On the other hand, a gap of approximately 3.4 full is provided between the auxiliary guide member 9 and the helad base 7 to prevent deviations in parallelism between the reference guide member 8 and the auxiliary guide member 9 due to processing accuracy and assembly accuracy of each part. The print head 20 is designed to absorb the amount of water and allow the print head 20 to slide smoothly from side to side. Furthermore, the ball screw 10
The ball screw 1 is engaged with the ball screw 1 through the rigid ball with almost no clearance in both the axial and radial directions.
0 is incorporated so that it is as parallel to the reference guide member 8 as possible. Also, since the paper 4e of A3 size is wound horizontally around the drum 3, the distance between the side plates 1 and 2 reaches approximately 500 yen.

Such conventional examples have the following drawbacks. Even if the ball screw 10 is of the highest quality, it will have a warp of several tens of microns when the total length reaches about 50011 irises.
0 rotates, the print head 20 moves toward the reference guide member 8.
The 10 parts of the ball screw will be displaced by several tens of microns around . The distance between the center of the reference guide member 8 and the center of the ball screw 10 is γ81, the center of the reference guide member 8 and the nozzle 6.
The distance from the tip of the nozzle 6 to the tip is krA, and the displacement of the print head 20 in the direction of arrow B at the fitting part with the ball screw lO based on the warp of the ball screw lO is δB1 Similarly, the displacement of the nozzle 6 at the tip of the nozzle 6 in the direction of arrow B is JA. For example, JA can be expressed as follows. δA=(rA/l)xδB1
δB is caused by warping of the ball screw 10 and reaches a maximum of about 50μ, and γA/γB is about 3, so in this conventional structure, the maximum value of JA is amplified to about 150μ.
Therefore, the distance from the nozzle 6 to the paper 41 changes by about 150 μ for each rotation of the ball screw. Strictly speaking, the problem is that the distance from when the ink droplet 14 reaches the control voltage @21 until it reaches the paper 4 varies by about 150 μ.

In other words, the amount of deflection of the ink droplets 14 varies by the amount of change, and a pattern of coarse and dense stripes occurs in the direction of deflection, particularly in the print head traveling direction, at a pitch corresponding to one rotation of the ball screw IO, degrading the print quality. let The set distance from the control electrode 21 to the paper 4 is approximately 15 mm, so 1
50μ corresponds to about 1% of 15m, and when the total deflection amount is 2as, it appears as a change in the deflection amount of 20μ.

This type of inkjet printer has a printing dot diameter of approximately 1
00μ is common, and the lead of the ball screw 10 is hard, for example, 100μ.) When the same pattern is printed on white paper with a print density of 1-contact, the density or density, that is, the light and shade that occurs regularly every time, is clear to humans. It is recognized as a pattern. Note that the displacement of the nozzle 6 is 5A.
The value differs depending on each of the four nozzles 6 for the four colors, but in any case, if each nozzle 6 is regularly displaced, it is inevitable that regular changes will occur in printing.
There are inkjet printers equipped with non-deflecting nozzles such as on-demand nozzles, but these also have the same disadvantage of reducing print quality because the flight time of the ink droplets varies due to JA variation. .

[Purpose of the invention]

The object of the present invention is to eliminate the above-mentioned drawbacks of the prior art and to improve the performance of this type of inkjet printer.

[Summary of the invention]

If there are two points A and B with the same rotation center 0, the line segment OA
= r A s line segment 0B = l, and if the displacement of point B is f and aB, then the displacement of point A is δA = (rA/, ra)xa
B, and when δB is constant, in order to reduce aAt-, it is necessary to at least reduce TA or increase rB. Point A is the tip of the nozzle mounted on the print head, and point B is the point on the print head that engages with the ball screw and undergoes displacement. The layout has been devised.

[Embodiments of the invention]

An embodiment of the present invention will be described with reference to FIGS. 1 and 2. The reference guide member 8 is disposed above the drum 3 in parallel with the rotation axis of the drum 3, and has a gap of several microns or less from the ball bearing 11 fixed to the head base 7, or is press-fitted so that there is no play. On the other hand, the auxiliary guide member 9 is arranged below the drum 3 at a position where it almost straddles the drum 3 by the reference guide member 8. The distance between the auxiliary guide member 9 and the ball bearing 11 fixed to the helad base 7 is about 0.
4. They are in contact with each other with a gap between them, and the ball screw lO
It is arranged below the drum 3 in parallel with the drum 3. Nozzle 6
There are 4 drums for 4 colors.
They are arranged radially opposite to the upper middle part of the circumference, and two of them are arranged with the reference guide member 8 in between.

In this embodiment, since the distance γA from the reference guide member 8 to the farthest nozzle 6 is approximately 10 of the distance fljrB from the reference guide member 8 to the ball screw 10, Even if the displacement of the ball screw engaging portion of the print head 20 due to the unavoidable warping occurs by 50 μ as in the conventional case, the displacement of the nozzle 6 is at most about 25 μ, which is approximately % of the conventional value. Therefore, the displacement of the deflection height of the ink droplets 14 can be reduced from the conventional 20β to about 3μ, and the printing quality can be greatly improved.

In general, this type of inkjet printer includes a guide member 9, a ball screw 10. In addition to the nozzle 6, a paper feeder 30, a paper discharge member 31, etc. are arranged, so it is necessary to effectively utilize the entire circumference of the drum 3. When considering increasing the distance between the reference guide member 8 and the ball screw 10, the arrangement with the drum 3 sandwiched therebetween becomes one ideal arrangement. Generally, the nozzle 6 is placed on the upper side of the drum 3 for handling ink, but in this case, in order to minimize the distance between the nozzle 6 and the reference guide member 8, considering the above conditions and the reference guide member 8. It is also ideal to arrange the member 8t above the drum 3.

Furthermore, since the two nozzles 6 were arranged on both sides of the reference guide member 8, the four nozzles A/6 could be grouped together near the reference guide member 8.

In the example, two nozzles 6 were arranged with a certain break guide member 8 in between, but the same result could be obtained even if two nozzles 6 were arranged on each side with a reference guide member 8 in between. It can be effective.

〔Effect of the invention〕

According to the present invention, since the distance from the reference guide member to the nozzle is made shorter than the distance from the reference guide member to the ball screw, the displacement of the nozzle due to warpage of the ball screw can be made smaller than the warp of the ball screw. I can do it.

As a result, there is an effect that deterioration in print quality can be prevented.

[Brief explanation of drawings]

FIG. 1 is a front view showing an embodiment of an inkjet printer of the present invention, FIG. 2 is a sectional view taken along the line t- in FIG. 1, FIG. 3 is a front view of an example of a conventional inkjet printer, and FIG. It is a sectional view taken along the line ■-■ in FIG. 3. In the figure, 3 is a drum, 4 is paper, 6 is a nozzle, 8 is a reference guide member, 9 is an auxiliary guide member, 10 is a ball screw, and 20 is a print head.

Claims (1)

[Scope of Claims] 1. A drum that rotates around which paper to be printed is wound, at least two guide members extending along the width direction of the drum, and a ball screw extending substantially parallel to the guide members; An inkjet printer comprising at least one nozzle and a print head driven by the ball screw to reciprocate along a guide member, wherein one and the other of the guide members are respectively attached to the print head with play. A reference guide member and an auxiliary guide member are in contact with each other with no play and are arranged so as to substantially straddle the drum, and the distance from the reference guide member to the ball screw is
An inkjet printer characterized in that the distance from the reference guide member to the nozzle is greater than the distance from the reference guide member to the nozzle. 2. A plurality of the nozzles are provided so that at least two nozzles are positioned across the reference guide member, and these nozzles are arranged radially on the print head so as to face approximately the upper half of the circumference of the drum. The inkjet printer according to claim 1, wherein an inkjet printer is attached. 3. The inkjet printer according to claim 1, wherein the reference guide member, the ball screw, and the auxiliary guide member are arranged above and below the drum, respectively.