Printing with sensor-based positioning of printing paper

Details Printing with sensor-based positioning of printing paper Printing with sensor-based positioning of printing paper

2001-09-25

2003-03-04

Pham, Hai (Department: 2853)

Incremental printing of symbolic information

Ink jet

Controller

C347S016000, C347S014000

Reexamination Certificate

active

06527360

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a technique for recording dots on the surface of a recording medium with the aid of a dot-recording head, and more particularly to a technique for printing images while accurately positioning the printing paper.
2. Description of the Related Art
Inkjet printers have recently become popular as computer output devices.
FIG. 27
is a side view depicting the periphery of a print head for a conventional inkjet printer. Printing paper P is fed in the direction of arrow A by the upstream paper feed rollers
25
p
and
25
q
disposed upstream of a platen
26
o
and by the downstream paper peed rollers
25
r
and
25
s
disposed downstream of the platen
26
o
, and is stopped at specific positions. The printing paper P is supported on the platen
26
o
while facing the head
28
o
. Numerous ink droplets Ip are ejected from the print head in the direction of a specific position on the platen
26
o
while the printing paper is advanced in small increments in the direction of arrow A. The ink droplets Ip are deposited on the printing paper P on the platen
26
o
, and images are recorded on the printing paper.
In such printers, images cannot be formed at the intended positions on the printing paper when the printing paper shifts away from the intended position, which is shown by a broken line in FIG.
27
. In addition, the image initially designed to be formed near the edges of the printing paper sometimes ends up extending beyond the printing paper. In such cases, the ink droplets end up missing the initially targeted edge portions of the printing paper, deposit on the platen, and soil the printing paper transported over the platen in the next step, as shown in FIG.
27
.
It is an object of the present invention to overcome the above-described shortcomings of the prior art and to provide a technique for printing images while accurately positioning the printing paper.
SUMMARY OF THE INVENTION
The present invention envisages adopting the following structure in order to at least partially overcome the above-described shortcomings. This dot-recording device records ink dots on a surface of a print medium with the aid of a dot-recording head provided with a plurality of dot-forming elements for ejecting ink droplets. This dot-recording device comprises: a main scanning unit configured to move the dot recording head relative to the print medium to perform main scanning; a head drive unit configured to drive at least some of the plurality of dot-forming elements to form dots during the main scanning; a sub-scanning unit configured to move the print medium to perform sub-scanning in a sub-scanning direction; a sensor for detecting presence of the print medium at a specific detection point; and a controller configured to control the dot-recording device. The sensor is disposed at a point outside paths of the ink droplets ejected by the plurality of dot-forming elements during the main scanning. Adopting such an embodiment allows the print medium to be accurately positioned, dots to be recorded, and images to be formed on the print medium by detecting the presence of the print medium with the sensor.
The dot-recording device should preferably print images in the following manner. A sub-scan feed is started from a state in which the print medium is absent from the detection point, the sub-scanning being a scanning operation for driving the print medium across the main scanning direction. The sub-scan feed of the print medium is stopped at a specific position of sub-scanning associated with a position where the sensor detects the presence of the print medium. Main scanning is started and ink droplets are ejected from the dot-forming elements after the print medium reaches the specific position of sub-scanning. Printing images in this manner allows the print medium to be positioned by a method in which the arrival of the leading edge of the print medium to a specific detection point is used as reference.
It is preferable that the sensor comprises: a light emitter configured to emit light to the detection point; and a light receiver configured to receive the light reflected by the print medium. With this arrangement, the print medium can be detected by a noncontact technique, and dots can be recorded unimpeded on the print medium.
It is preferable that the sensor is configured to be moved together with the dot-recording head during the main scanning. Adopting such an embodiment removes any interference between the sensor and the dot-recording head during the main scanning.
It is preferable that the sensor is provided proximate to a dot-forming element position along the sub-scanning direction. The dot-forming element is located at a downstream and in the sub-scanning direction among the dot-forming elements used for printing. Adopting such an embodiment allows the presence of a print medium to be detected and the print medium to be positioned in the vicinity of dot-forming elements for printing images along the front edge of the print medium. The; print medium can therefore be accurately positioned relative to the dot-forming elements for printing images along the leading edge of the print medium.
The printing device preferably further comprises a platen configured to support the print medium that is extending in the main scanning direction and is disposed opposite the dot-forming elements at least along part of a main scan path. The platen has a downstream slot extending in the main scanning direction. The downstream slot is disposed at a position opposite a dot-forming element that is located at a downstream end in the sub-scanning direction. The detection point is located inside the downstream slot and within a sub-scanning range containing the plurality of dot-forming elements. Adopting such an embodiment makes it possible to determine that the leading edge of a print medium has reached the opening of the downstream slot, and to allow the dot-forming elements to start recording dots near the leading edge of the print medium.
According to this embodiment, the platen is provided with a lateral slot connected to the downstream slot and is disposed at least in the area in which ink droplets are deposited from the plurality of dot-forming elements in the sub-scanning direction. In addition, the following structure should preferably be adopted. The platen further has a lateral slot. The lateral slot is connected to the downstream slot and extending in a sub-scanning range in which ink droplets are ejected from the plurality of dot-forming elements. The dot-recording device further comprises a guide configured to guide the print medium to be at a specific position in the main scanning direction during the sub-scanning, the specific position being where the print medium is in a main scanning range in which the dot-recording head is moved and where one of side edges of the print medium is above the lateral slot. The detection point is in the area of connection of the lateral slot and the downstream slot. Adopting such an embodiment makes it possible to start recording dots on the print medium upon determining that the leading edge of the print medium is disposed at the opening of the downstream slot and that the side edges are disposed above the openings of the lateral slots.
It is preferable that the lateral slot comprises first and second lateral slots. The first and second lateral slots are configured such that the side edges of the print medium are above the first and second lateral slot when the print medium is set at the specific position. With such an embodiment, one of the side edges of the print medium is disposed above the opening of the second lateral slot when it is determined that the leading edge of the print medium is disposed at the opening of the downstream slot and the other side edge is disposed above the openings of the first lateral slot. The recording of dots on the print medium can be started when the existence of such an arrangement is confirmed.
It is preferable that the sensor is positioned ups

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