Incremental printing of symbolic information – Ink jet – Controller
Reexamination Certificate
2000-04-05
2002-04-02
Barlow, John (Department: 2853)
Incremental printing of symbolic information
Ink jet
Controller
C347S010000, C347S011000
Reexamination Certificate
active
06364443
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a thermal printer and a recording method thereof, and more particularly relates to a thermal printer and a recording method thereof provided with an encoder that detects a linear scale marker when a carriage having a thermal head is moved to generate pulse signals intermittently and provided with a control unit that generates and supplies a head pulse corresponding to the pulse signal generated by the encoder to the heater elements of the thermal head.
2. Description of the Related Art
In the technical field of the thermal printer provided with a carriage having a thermal head on which a plurality of heater elements are arranged that controls heating of the thermal head to thereby print a record composed of an aggregate of dots on a recording paper, various modifications have been introduced so that recording is performed on a printing paper by the thermal head with a constant dot pitch regardless of fluctuation in the moving speed of the carriage.
In detail, the thermal printer is provided with the carriage on which a thermal head is mounted having a plurality of heater elements, and the carriage is supported slidably so as to be reciprocated along a platen. Near the platen, a long linear scale comprising markers and blanks having the same length are formed alternately and continuously along the platen. The liner scale is provided in parallel to the platen.
At the position that is facing the linear scale of the carriage, an encoder for detecting the marker of the linear scale when the carriage is moved is provided. The encoder is provided with a light emitting element for emitting a light onto the linear scale and a light receiving element for detecting the light reflected on the marker.
The marker is reflective in nature, and the encoder detects the marker by detecting the reflected light from the marker when the encoder moves to the position of the marker. The encoder generates the detection result of the marker as a pulse signal.
On the other hand, the blank is transparent in nature, and the encoder does not detect the blank. The encoder does not generate a pulse signal when the encoder moves to the position of the blank.
The thermal printer is provided with a memory for storing the encoder signal that is the pulse signal generated by the encoder.
Furthermore, the thermal printer is provided with a control unit for generating and supplying the head pulse that is synchronous with the pulse signal to the heater elements of the thermal head.
Otherwise, the thermal printer is provided with a control unit for generating and supplying the head pulse composed of ON head pulse that is synchronous with the output starting timing of the pulse signal and OFF head pulse that is synchronous with the output ending timing of the pulse signal to the heater elements of the thermal head.
In the case that the conventional thermal printer having the structure described herein above is used recording, when the thermal printer is fabricated or before recording, at first the carriage is moved from the left end to the right end of the platen and the encoder detects the marker of the linear scale. At that time, the encoder generates the pulse signal intermittently every time when the maker (refer to the upper diagram in
FIG. 12
) is detected. Pulse signals generated intermittently by the encoder are components of a series of encoder pulse signal as shown in the middle diagram in FIG.
12
.
The length of each marker of the linear scale shown in the upper diagram of
FIG. 12
is formed of a constant interval and is read in a short time if the moving speed of the carriage is fast. On the other hand, the length of the marker is read in a long time if the moving speed of the carriage is slow. As the result, the length of the marker is represented in the form of the difference in the length of the output pulse signal.
The pulse signal generated by the encoder is stored in the memory.
Next, when the thermal printer is used for recording, the control unit reads out the pulse signal data from the encoder.
As shown in the lower diagram of
FIG. 12
, the head pulse that is synchronized with the pulse signal read out by the control unit is supplied to the heater elements of the thermal head.
As the result, even though the moving speed of the carriage fluctuates as shown with a broken line in
FIG. 13
from a constant speed v (referred to as theoretical speed hereinafter) shown with a solid line in
FIG. 13
, the output timing of the head pulse is synchronized with the output timing of the pulse signal of the encoder.
As described herein above, even though the moving speed of the carriage fluctuates, the dot scattering or overlapping will not occur from the theoretical view point because each dot pitch P recorded by the thermal head can be equalized to the length of one marker of the linear scale. Using the method described herein above, a recorded image of good quality with reduced recording density non-uniformity (so-called jitter) caused in the recording direction is obtained.
However, in the conventional thermal printer, the applied voltage V and the current flow time W of the head pulse are the same for all head pulses. Furthermore, the moving speed of the carriage and the recorded density are in the negatively proportional relation as shown in
FIG. 14
, and the moving speed of the carriage and the recorded area are in the positively proportional relation as shown in FIG.
15
.
As the result, as shown in
FIG. 16
, the recorded area of one dot recorded at the recording position where the moving speed of the carriage is faster than the theoretical speed is larger than the recorded area of one dot (referred to as theoretical recorded area hereinafter) recorded at the recording position where the moving speed of the carriage is equal to the theoretical speed, and the recorded density of one dot recorded at the recording position where the moving speed of the carriage is faster than the theoretical speed is lower than the recorded density of one dot (referred to as theoretical recorded density hereinafter) recorded at the recording position where the moving speed of the carriage is equal to the theoretical speed. On the other hand, the recorded area of one dot recorded at the recording position where the moving speed of the carriage is slower than the theoretical speed is smaller than the theoretical recorded area, and the recorded density of one dot is higher than the theoretical recorded density.
The recorded area and the recorded density can not be equalized at all the recording positions and jitter can not be removed perfectly, and the recorded image of good quality can not be obtained disadvantageously.
An another conventional thermal printer, in which the head pulse that is synchronized with the output starting time and the output ending time of the pulse signal read out by the control unit is supplied to the heater elements of the thermal head with motion of the carriage along the platen, has been known.
In this case, for the purpose of convenience, the time point shown with A in the upper diagram of
FIG. 17
is assumed to be the output starting time of the pulse signal and the time point shown with B in the upper diagram of
FIG. 17
is assumed to be the output ending time of the pulse signal. The length of each marker of the linear scale shown in the middle diagram of
FIG. 17
is the relative length viewed from the encoder. In detail, because the encoder reads one marker in a shorter time at the position where the speed of the carriage is fast, the length of the marker is shorter. On the other hand, because the encoder reads one marker in a longer time at the position where the speed of the carriage is slow, the length of the marker is longer.
In the conventional thermal printer, due to various causes such as the accuracy of the linear scale, the accuracy of a light emitting diode light source of the encoder, and the positional accuracy of the encoder and the linear scale, the discrepancy between the output time T
ON
Hiratsuka Kazuhiko
Katano Keiji
Alps Electric Co. ,Ltd.
Barlow John
Brinks Hofer Gilson & Lione
Dudding Alfred
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