JPH1128845A - Printer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To minimize a shift of a dot which may occur when a linear encoder is contracted or expanded by virtue of variation of a temperature or a humidity. SOLUTION: In this printer, a plurality of encoder sensors 12 mounted on a carriage base by corresponding to a linear encoder 11 provided in the carriage moving direction. Arrangement of nozzles which are covered by each of the encoder sensors 12 is minimized in the carriage moving direction. As a result, it is possible to minimize the influence due to a quantity of contraction of expansion of the linear encoder.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a printing apparatus which performs printing by landing ink droplets on a printing paper at a predetermined dot pitch while moving a print head of an ink jet system or the like in a certain direction. .

[0002]

2. Description of the Related Art A conventional printing apparatus prints dots at a predetermined print dot interval (for example, about 0.08 mm) while moving a print head to the left and right, so that a position signal generated from a linear encoder and an encoder sensor is generated. In general, the ink ejection timing of each nozzle is determined based on

The types of the linear encoder and the encoder sensor include an optical type and a magnetic type, but the optical type will be described here.

[0004] A tape-shaped one called a linear encoder is fixed in parallel to the moving direction of the print head. In this linear encoder, an evenly-spaced pattern of a transparent portion and an opaque portion is printed at a pitch P corresponding to a print dot interval. An optical encoder sensor having a light emitting element in one direction of the linear encoder and a light receiving element on the opposite side is fixed to the print head. As the printhead moves, the encoder sensor generates a position signal at a pitch equal to the pitch P of the linear encoder pattern. By ejecting ink from each nozzle on the print head in synchronization with this position signal, dot printing can be performed at a predetermined pitch.

[0005]

In a conventional printing apparatus, a large number of nozzles are arranged on a print head, and are arranged over a large range L (for example, L = 100 mm) in the carriage moving direction. I have. With respect to the nozzles arranged in this manner, the print timing of all nozzles is determined based on the position signal obtained from one encoder sensor.

The case of FIG. 3 will be further described.

On the front surface of the print head 1, nozzles 5 are arranged at equal intervals (P × N) in the carriage movement direction. Here, the distance between the nozzles in row 1 and the nozzles in row 10 is Ln = 9 × P × N in the carriage movement direction. After firing the nozzles in row 1, consider that the printhead moves Ls to the left and fires the nozzles in row 10. If the encoder sensor counts exactly (9 × N) during the movement of Ls, the print head has moved by Ls = 9 × N × P, and the dot position according to the previously printed row 1 and the carriage position The dots by row 10 can be printed at the same position in the moving direction. However, when the material of the linear encoder is a resin such as a polyester film, the length of the linear encoder expands and contracts due to changes in the temperature and humidity of the atmosphere. Linear encoder expands / contracts and pitch P
Is longer by ΔP. In this case, the distance that the encoder sensor moves while counting (9 × N) signals is longer by (9 × ΔP × N) than before the expansion and contraction. This difference in travel distance results in dots printed by columns 1 and 10 not being aligned at the same position. In other words, there is a problem that an improper array of print dots is generated due to expansion and contraction of the linear encoder.

According to the present invention, even when a print head has a large nozzle arrangement in the moving direction, even if a linear encoder having relatively large thermal deformation is used, the influence of an improper array of print dots is minimized. It is an object to obtain a printing apparatus having good printing quality.

[0009]

According to the present invention, there is provided a print head having means for printing dots on printing paper by ejecting ink,
Carriage means for moving the print head section to the left and right, a linear encoder mounted in parallel with the carriage movement direction of the print head section, and a print head section fixed to the print head section at a position corresponding to the linear encoder; And a encoder that generates a position signal at a predetermined pitch together with a printing device,
A plurality of the encoder sensors are attached to the print head unit.

Here, when there are N nozzle rows on the print head section, it is preferable to provide as many encoder sensors as the number of nozzle rows.

With the above configuration, the arrangement of the nozzles shared by the linear sensors is minimized in the moving direction. As a result, it is possible to minimize the influence of an improper array of print dots due to a dimensional change such as thermal expansion of the linear encoder.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to the drawings.

In FIG. 1, reference numeral 1 denotes a print head, which performs printing by ejecting ink from nozzles 5 arranged on the front surface of the print head. This print head 1 is fixed to a carriage base 2. The carriage base 2 is held on two guide rails 3 so as to be slidable left and right. Further, a carriage motor 24 is fixed to the frame 21, and the drive pulley 2
3 is fixed. A driven pulley (not shown) is mounted on the other end of the frame. Drive pulley 23
A timing belt 22 is hung between the driven belt and the driven pulley. One location on the circumference of the timing belt 22 is fixed to the carriage base 2 by a belt clamp 25. Power is transmitted to the carriage base 2 via the timing belt 22 by the forward and reverse rotation of the carriage motor 24, and the print head 1 moves left and right in the axial direction of the guide rail 3.

The linear encoder 11 is arranged parallel to the guide rail 3 and fixed on a frame 21. An encoder sensor 12 is attached to the carriage base 2 so as to face the linear encoder 11. Two encoder sensors 12 are provided, and are set apart by a fixed distance in the carriage movement direction. here,
The left encoder sensor 12a is arranged in the left half from row 1 to row 5
To determine the drive timing of the nozzle 5 up to
The right encoder sensor 12b is located in the right half from row 6 to row 1
This determines the drive timing of the nozzle 5 up to 0.

FIG. 2 is a diagram schematically illustrating the relationship between the nozzle arrangement and the encoder.

The encoder sensors 12a are arranged in rows 1 to 5
Up to the nozzle 5. In this case, the largest amount of dot displacement due to expansion and contraction of the linear encoder 11 occurs between the rows 1 and 5. The shift amount at this time is represented by (4 × ΔP × N), which can be reduced to less than half of the case of one encoder sensor 12 of the conventional method, and the print quality can be improved.

Preferably, the number of encoder sensors is increased to the same number as the number of nozzle rows, that is, ten in this example, and only one row of nozzles 5 is controlled for one encoder sensor 12 to provide an encoder. Sensor 12
Since the distance from the nozzle to the position of the nozzle 5 can be set to 0, the linear encoder 11 is not affected by expansion and contraction. For this reason, it is possible to obtain better print quality.

[Brief description of the drawings]

FIG. 1 is a perspective view showing an example of the printing apparatus of the present invention.

FIG. 2 is a schematic diagram showing a relationship between a nozzle arrangement and an encoder in FIG. 1;

FIG. 3 is a schematic diagram showing a relationship between a conventional nozzle arrangement and an encoder.

[Explanation of symbols]

1 is a print head, 2 is a carriage base, 3 is a guide rail, 5 is a nozzle, 11 is a linear encoder, 12
Is an encoder sensor, 21 is a frame, 22 is a timing belt, 23 is a drive pulley, 24 is a carriage motor, and 25 is a belt clamp.

Claims (2)

[Claims] 1. A print head unit having means for printing dots on printing paper by ejecting ink, a carriage means for moving the print head unit to the left and right, A printing apparatus comprising: a mounted linear encoder; and an encoder sensor fixed to a print head unit at a position corresponding to the linear encoder and generating a position signal at a predetermined pitch as the print head moves. A printing device, which is attached to a print head. 2. The printing apparatus according to claim 1, wherein the same number of encoder sensors as the number of nozzle rows on the print head unit are provided.