JP2574794B2 - Image printer preheat circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a pre-heat circuit of an image printer that performs density control and hue correction in full-color printing of an image by controlling the temperature of a thermal head in a thermal transfer system. About.

[Conventional technology]

The conventional preheat circuit generates a preheat pulse having a fixed pulse period and a fixed pulse width before the start of printing to heat the thermal head, as described in, for example, Japanese Patent Application Laid-Open No. Sho 60-56572.

A temperature sensor was attached to the back of the thermal head to detect an increase in the temperature of the head and stop generating the preheat pulse.

Further, printing is performed even when the temperature of the thermal head is low.

[Problems to be solved by the invention]

In the prior art described above, the heating resistor of the thermal head is heated by the preheat pulse, and the thermal head is heated to a set temperature or higher during a period in which the heat is transmitted to the temperature sensor.

Alternatively, when a print command comes, printing starts even if the head temperature is low.

Also, due to the difference in ambient temperature near the thermal head,
The heat transfer time from the heating resistor to the temperature sensor changes.

Therefore, the temperature of the heating resistor at the start of printing cannot be accurately controlled due to the ambient temperature and the temperature difference between the heating resistor of the thermal head and the temperature sensor. In particular, in a full-color printer, not only the density but also the hue changes. There was a problem that would.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a preheating circuit of an image printer capable of accurately controlling the temperature of a heating resistor of a thermal head at the start of printing and accurately controlling the color density of each color.

[Means for solving the problem]

The above object is achieved by a temperature sensor attached to a thermal head, a temperature signal detecting means connected to the temperature sensor, a preheat pulse cycle variable means or a preheat pulse width variable means connected to the temperature signal detecting means. And a preheat pulse generation circuit connected to these preheat pulse cycle variable means or preheat pulse width variable means, and performs head temperature detection and preheat control at power-on and immediately before printing.

[Action]

The temperature sensor and the temperature signal detecting means detect the temperature of the thermal head, convert the temperature into a temperature sense signal, and send it to the preheat pulse cycle variable means and the preheat pulse width variable means.

The preheat pulse cycle variable means determines a preheat pulse cycle suitable for the color to be printed based on the temperature sense signal and the color discrimination signal, and the preheat pulse width variable means also uses a preheat pulse suitable for the color to be printed based on the temperature sense signal and the color discrimination signal. Determine the width.

By these variable means, the preheat pulse generating means generates a preheat pulse having a cycle and a pulse width determined by the sense temperature of the thermal head, the color to be printed, and the like.

This preheat pulse is sent to the heating element of the thermal head,
Heat the thermal head.

With the above operation, a preheat pulse suitable for the temperature of the thermal head can be obtained.

〔Example〕

 Hereinafter, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a block diagram showing an embodiment of an image printer according to the present invention.
Is an A / D converter, 3 is an image memory, 4 is a D / A converter, 6 is a color selection circuit, 7 is a line memory, 8 is a black data generation circuit,
9 is a data conversion circuit, 10 is a black data switch, 11 is an energizing pulse switch, 12 is a shift register, 13 is a heating element energizing switch, 14 is a thermal head, 15 is a temperature sensor,
16 is an energization pulse generation circuit, 17 is a preheat pulse generation circuit, 18 is an energization pulse data table, 19 is a temperature signal detection means, 20 is a preheat pulse cycle variable means, 21 is a preheat pulse width variable means, 22 is a print control means, 200 is a thermal head assembly.

In the figure, a video signal is transmitted to an analog signal processing circuit 1.
Is converted to an RGB image signal and sent to the A / D converter 2. Here, the image data is converted into an RGB digital image signal, sent to the image memory 3, and stored.

The data in the image memory 3 is read and sent to the D / A converter 4 and the color selection circuit 6.

It is converted to an analog RGB image signal by the D / A converter 4,
The signal is sent to the analog signal processing circuit 5.

Here, the encoding process is performed, and the image is sent to a monitor to monitor the image.

On the other hand, one color is selected from the RGB digital image data from the image memory 3 by the color selection circuit 6 and sent to the line memory 7 controlled by the print control means 22.

The line memory 7 stores data for one vertical line of an image. Next, the image data for one vertical line is sent to the data conversion circuit 9, converted into ON / OFF data of the thermal head, and sent to the shift register 12 via the black data switch 10.

When the 0th gradation ON / OFF data for one line has been transferred to the shift register 12, the print control means 22 controls the conduction pulse data table 18 to supply the conduction pulse width data suitable for the 0th gradation. The signal is sent to the pulse generation circuit 16.

The energizing pulse generation circuit 16 generates 0 based on the energizing pulse data.
The energizing pulse of the gradation is controlled by the heating element energizing switch 13 via the energizing pulse changeover switch 11, and this switch is closed.

Thus, the 0th gradation printing is performed based on the ON / OFF data of the shift register 12.

Thereafter, as described above, the image data of one vertical line is read out from the line memory 7 for the number of N gradations, and the printing of one line is completed.

This is repeated for M lines, and the printing of one color is completed.

In a full-color printer, the above operation is repeated for three colors in order to generally express a full color using three colors of cyan, magenta, and yellow, and one print is completed.

Next, the operation at the time of preheating in FIG. 1 will be described with reference to FIGS.
This will be described with reference to the drawings.

FIG. 2 is a timing chart showing the operation of FIG. 1 and a graph showing a temperature change of the thermal head.

A preheat signal is input for a certain period from a system controller (not shown because it is not directly related to the present invention). The preheat signal switches the black data changeover switch 10 to the black data generation circuit 8 side, and the energizing pulse changeover switch 11
Is switched to the preheat pulse generation circuit 17 side.

The black data generating circuit 8 always generates data that makes the print result black, for example, “H” data, and transfers it to the shift register 12 via the black data changeover switch 10.

On the other hand, the temperature of the thermal head 14 is detected by the temperature sensor 15 and the temperature signal detecting means 19, and the temperature data is transferred to the preheat cycle variable means 20 and the preheat pulse width variable means 21 together with a color discrimination signal for switching each color.

The preheat pulse cycle variable means 20 selects a preheat pulse cycle suitable for the head temperature and the color to be printed,
Generate a preheat period signal.

The preheat pulse width varying means 21 generates the flheat pulse width data suitable for the head temperature and the color to be printed in a cycle of the preheat cycle signal, and transfers the data to the preheat pulse generating circuit 17.

The pre-heat pulse generation circuit 17 generates a pre-heat pulse based on the pre-heat cycle signal and the pre-heat pulse width data, and sends the pre-heat pulse to the heating element energizing switch 13.

When the heating element energizing switch 13 is closed by the preheat pulse, the thermal head is energized by the black data stored in the shift register 12 to increase the temperature of the thermal head as shown in FIG.

The operation at the time of preheating in FIG. 1 will be described in more detail with reference to FIG.

FIG. 2 shows each control signal at the time of preheating and the temperature rise of the heat-sensitive head heating element at that time.

First, a preheat cycle variable unit that receives a preheat signal
A preheat cycle signal is output from 20 and at the same time, preheat pulse width data is output from the preheat pulse width varying means 21 (FIG. 2a).

Next, the preheat pulse generating circuit 17 loads the preheat pulse width data and simultaneously generates a preheat pulse (FIG. 2B).

The preheat pulse generating circuit 17 starts counting, performs counting based on the preheat pulse width data, and stops generating the preheat pulse (FIG. 2c).

The temperature of the heating element rises during the preheat pulse “H” in FIGS. 2b to 2c.

Subsequently, a preheat cycle signal is output from the preheat cycle variable means 20, and the preheat pulse generation circuit 17 generates a preheat pulse (FIG. 2d).

At this time, the preheat pulse width varying means 21 generates preheat pulse width data so as to output a pulse shorter than the previous time by a temperature sense signal accompanying the rise in the temperature of the heating element, and the preheat pulse generation circuit 17 outputs a preheat pulse shorter than the previous time. Output pulse.

Hereinafter, the above operation is repeated in the same manner, and the temperature of the heating element falls to a constant value.

Here, the timing chart in which the preheat pulse width is varied is shown, but the same effect can be obtained even if the preheat period is varied, or if both the preheat period and the width of the preheat pulse are varied.

FIG. 3 shows the preheat pulse generation circuit 1 shown in FIG.
7, a specific circuit diagram of one embodiment of the preheat pulse period variable means 20 and the preheat pulse width variable means 21, wherein 30 is a decoder A, 31 is a decoder B, and 32 and 37 are RR
Latch, 33 and 39 are counters, 34 is differentiator, 35 and 36 are RO
M and 38 are decoders, 40 is an OR gate, and 100 is an AND gate. The components denoted by the same reference numerals as those in FIG. 1 have the same functions.

The operation of the circuit diagram in FIG. 3 will be described with reference to FIG.

FIG. 4 is a timing chart showing the operation of FIG.

The temperature sensing signal from the temperature signal detecting means 19 and the color discrimination signal from the system controller (not shown) are stored in ROM3.
5 and send to ROM36.

The ROM 35 sends to the counter 33 preheat pulse cycle data suitable for the temperature of the thermal head at that time and the color to be printed.

The preheat signal (FIG. 4a) whose waveform has been shaped by the differentiating circuit 34 is input to the counter 33 via the OR gate 40, and the preheat pulse cycle data from the ROM 35 is loaded into the counter 33 in synchronization with the input signal.

The counter 33 starts counting. First, the count value is decoded by the decoder 30, then the count value is decoded by the decoder 31, and each outputs a decode pulse.

The decode values of the decoders 30 and 31 are configured such that the decoder 30 always outputs the decode pulse earlier.

The decoder pulse from the decoder 30 is input to S (set) of the SR latch 32, and the decode pulse from the decoder 31 is R (reset) of the SR latch 32 and the AND gate 1
Input to 00, the output of AND gate 100 loads counter 33 through OR gate 40.

The SR latch 32 outputs a preheat pulse period signal from the positive-phase output Q in response to the set and reset signals (FIG. 4b), and sends it to the RR latch 37 and the counter 39 at the next stage.
The positive-phase output Q of the R latch 37 is set to the “H” level, that is, a conducting state.

On the other hand, the ROM 36 in the preheat pulse width varying means 21 similarly sends a temperature detection signal and preheat pulse width data suitable for the color to be printed to the counter 39.

The counter 39 receives the positive-phase output Q of the SR clutch 32, and loads preheat pulse width data from the ROM 36 in synchronization with the output Q (FIG. 4b).

The counter 39 starts counting and sends the count value to the decoder 38. The decoder 38 decodes the count value of the counter 39, and when the count value reaches a predetermined count number, outputs a decoded signal S
-Input to R of the R latch 37 to stop the preheat pulse (FIG. 4c).

As in the above operation, the counter 33 and the counter 39 are stored in the ROM 35,
Load preheat pulse cycle data and preheat pulse width data from 36.

At this time, since the temperature of the thermal head has risen slightly, the data from the ROMs 35 and 36 according to the rise in the head temperature is loaded into the counters 33 and 39 and gradually changes.

The above operation is repeated, and when the temperature of the heating element reaches a certain temperature, the AND gate 100 is closed to end the preheating.

The preheat pulse cycle data and the preheat pulse width data are obtained by experiments to obtain data for converging the heating element temperature to a constant temperature in a direction in which the preheat cycle becomes longer and the preheat pulse width becomes shorter due to a temperature rise.
The data is input in advance as a data table.

FIG. 5 is a specific circuit diagram showing one embodiment in which the preheat pulse variable means 20 of FIG. 3 is replaced with a preheat interval variable means 50 (here, the interval means the OFF period of the preheat pulse). 50 is a preheat interval variable means, 52 is a decoder, 53 is a counter, and 54 is a ROM. 5 that have the same reference numerals as those in FIG. 3 have the same functions.

FIG. 6 is a timing chart showing the operation of FIG.

 The operation will be described with reference to FIGS.

ROM3 is detected by the temperature sense signal from the temperature signal detection means 19.
6, 54 outputs preheat pulse width data and interval data suitable for the thermal head temperature and printing color.

The preheat signal whose waveform has been shaped by the differentiating circuit 34 is input to the counter 39 via the OR gate 40, and the preheat pulse width data from the ROM 36 is loaded in synchronization with the input signal, and the counter 39 starts counting.

At the same time, the output of the OR gate 40 is input to the S of the SR latch 37, and the Q output of the SR latch 37 is set to "H" level to turn on.

Thereafter, the counter 39 counts up, and outputs a decode pulse from the decoder 38 when the count reaches a predetermined count.

The decode pulse is input to R of the SR latch 37,
The Q output of the R latch 37 is set to "L", and the output of the preheat pulse is stopped.

At the same time, the decoding pulse from the decoder 38 is input to the counter 53 via the AND gate 100.

On the other hand, the counter 53 loads the preheat interval data from the ROM 54 by the decode pulse from the decoder 38 and starts counting.

The decoder 52 decodes the count value of the counter 53,
The decode pulse is sent to the counter 39 and the S of the SR latch via the OR gate 40.

The SR latch 37 outputs a preheat pulse again from the Q output in response to the decode pulse input to S.

At the same time, the counter 39 receives the decode pulse and
, And starts counting.

Hereinafter, a preheat pulse is output from the SR latch 37 by repeating the above operation.

When the temperature of the heating element reaches a certain temperature, the temperature signal detecting means 19 closes the AND gate 100 and ends the preheating operation.

FIG. 7 is a diagram in which the preheat pulse cycle varying means 20 in FIG. 3 is replaced by a preheat cycle generation circuit 70, in which 60 is a counter, 61 is a decoder, and 70 is a preheat cycle generation circuit. 7 have the same functions as those shown in FIG.

 Hereinafter, the operation of FIG. 7 will be described.

First, the preheat signal is waveform-shaped by the differentiating circuit 34, and the OR
The signal is sent to the S input of the SR latch 37 via the gate 60 and the counter 60 via the AND gate 100, and to the counter 39.

The counter 60 receives the differentiated preheat signal,
The counter is started, and the count value is sent to the decoder 61. The decoder 61 decodes the count value of the counter 60 and sends the decoded signal to the counter 60 via the OR gate 40.

The counter 60 is reset by the decode signal and operates as a cyclic counter that starts counting again. By repeating this, a cycle of the preheat pulse is generated.

On the other hand, the counter 39 loads data suitable for the temperature of the thermal head and the color to be printed by the output of the OR gate 40, starts counting, and sends the count value to the decoder 38.

Decoder 38 sends the decode signal to the R input of SR latch 37.

The SR latch 37 receives the decode signal from the decoder 61 and the decode signal from the decoder 38, repeats the inversion, and generates a preheat pulse at the Q output.

Note that the cycle of the decode signal from the decoder 61 is longer than or equal to the cycle of the decode signal from the decoder 38.

FIG. 8 shares the ROM 36 in the preheat pulse width varying means 21 in FIGS. 3, 5 and 7 with the print pulse width ROM used during printing by the image printer, and switches the address by the preheat signal. 70 is a preheat / printing energizing pulse generating means, 71 is a preheat / printing interval variable means, 72 is a preheat / printing pulse width variable means, 73 is a ROM, and 74 is a gradation counter. In FIG. 8, components denoted by the same reference numerals as those in FIGS. 3, 5, and 7 have the same functions.

 Hereinafter, the operation of FIG. 8 will be described.

First, the preheat signal is waveform-shaped by the differentiating circuit 34, and the OR
It is sent to the S input of the SR latch 37 via the counter 39 via the gate 40 and the AND gate 100.

The SR latch 37 inverts the latch by the S input and generates a preheat pulse.

On the other hand, the ROM 73 is supplied with the count value of the gradation counter 74, the temperature sense signal from the temperature signal detecting means 19, the color discrimination signal, and the preheat signal.

In the ROM 73, comma data for determining the print density at the time of printing and preheat pulse width data for determining the preheat pulse width at the time of preheating are stored, and their addresses are converted by a preheat signal and a color discrimination signal.

The ROM 73 receives the color discrimination signal, the preheat signal and the temperature sense signal, and selectively generates preheat pulse width data.
Send to counter 39.

The counter 39 loads the preheat pulse width data based on the differentiated preheat signal, starts counting,
The count value is sent to the decoder 38.

The decoder 38 decodes the count value from the counter 39 with a certain value, and outputs the decoded signal to the R-R latch 37.
Input and send to counter 60.

The SR latch 37 inverts the latch by the R input, and stops the preheat pulse.

The counter 60 receives the decode signal from the decoder 38, starts counting, and sends the count value to the decoder 61.

The decoder 61 decodes the count value and sends the decoded signal to the S input of the SR latch 37 and the counter 39 via the OR gate 40 and the AND gate 100.

The SR latch 37 inverts the latch and generates a preheat pulse, the counter 39 loads the preheat pulse width data, and starts counting again.

Hereinafter, the above operation is repeated to generate a preheat pulse.

According to this embodiment, the RO for preheat pulse width data
It is possible to generate a preheat pulse suitable for the thermal head temperature with a simple circuit that uses both the M and the print pulse width ROM.

FIG. 9 is a diagram for generating a pulse width suitable for the temperature sensing signals of the two temperature sensors based on the temperature sensing signals of the two temperature sensors installed on the thermal head and in the atmosphere near the thermal head. Is a ROM, 81 is a preheat pulse width varying means, 82 is a temperature signal detecting means, and 83 is a temperature sensor. In FIG. 9, the components denoted by the same reference numerals as those in FIGS. 1 and 7 have the same functions.

 Hereinafter, the operation of FIG. 9 will be described.

First, the waveform of the preheat signal is shaped by the partial circuit 34, and the OR
The signal is sent to the S input of the latch 37 and the counters 60 and 39 via the gate 40.

The SR latch 37 inverts the latch according to the S input, generates a preheat pulse, and sends it to the thermal head 14.

On the other hand, the temperature sense signals from the temperature sensor 15 in the thermal head and the temperature sensor 83 in the atmosphere near the thermal head are sent to the ROM 80 via the temperature signal detecting means 19 and 82, respectively.

In the ROM 80, preheat pulse width data suitable for the temperature of the thermal head 14, the difference between the thermal head temperature and the ambient temperature, and more suitable for the color to be printed are input.

The ROM 80 sends the preheat pulse width data to the counter 39.

At the start of preheating, the counter 39 loads preheat pulse width data from the ROM 80 based on the differentiated preheat signal from the differentiating circuit 34.

The count 39 starts counting and sends the count value to the decoder 38.

The decoder 38 decodes the count value and sends a decoded signal to R of the SR latch 37.

The SR latch 37 inverts the latch by the R input, and stops the preheat pulse.

On the other hand, the counter 60 starts counting simultaneously with the generation of the preheat pulse, and sends the count value to the decoder 61.

The decoder 61 decodes the counter value and sends the decoded signal to the counter 60, the SR latch 37 and the counter 39 via the OR gate 40.

Hereinafter, the above operation is repeated to generate a preheat pulse.

According to this embodiment, since the temperature rise curve of the thermal head can be predicted before the start of preheating by the two temperature sensors, it is not necessary to narrow the preheat pulse width by the temperature rise as in the above-described embodiment, and it is possible to reduce the time. This has the effect that the thermal head can be set to the set temperature.

〔The invention's effect〕

As described above, according to the present invention, a preheat pulse suitable for the temperature of the thermal head is sent to the heating element of the thermal head, and by applying power, the temperature of the thermal head immediately before the printing of each color is accurately adjusted to the vicinity of the color development. Since the temperature can be increased, a printed image with accurate density and hue can be obtained under any temperature environment, and a pre-heat circuit for an image printer with little deterioration in image quality is provided except for the above-mentioned disadvantages of the prior art. be able to.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an embodiment of an image printer according to the present invention, FIG. 2 is a timing chart showing the operation of FIG. 1, and a graph showing a temperature change of a thermal head, and FIG. FIG. 4 is a timing chart showing the operation of FIG. 3, and FIG. 5 is a timing chart showing the operation of the pre-heat pulse generation circuit 17, pre-heat pulse cycle varying means 20, and pre-heat pulse width varying means 21. FIG. 6 is a specific circuit diagram showing an embodiment in which the preheat pulse period variable means 20 is replaced with a preheat interval variable means 50. FIG. 6 is a timing chart showing the operation of FIG. 5, and FIGS. The figure is a circuit and a block diagram showing another embodiment. 15,83 temperature sensor, 17 preheat pulse generation circuit, 19,82 temperature signal detection means, 20 preheat pulse cycle variable means, 21,81 preheat pulse width variable means, 50 preheat Interval variable means.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Toshihiko Goto 292 Yoshida-cho, Totsuka-ku, Yokohama-shi Inside the Home Appliances Research Laboratory, Hitachi, Ltd. (72) Inventor Yasuyuki Kobori 292 Yoshida-cho, Totsuka-ku, Yokohama-Hitachi Home Appliances, Ltd. In the laboratory (56) References JP-A-60-90781 (JP, A) JP-A-60-67178 (JP, A) JP-A-59-96976 (JP, A) Jpn. ) Actually open 55-179846 (JP, U)

Claims (3)

(57) [Claims] An image storage means for temporarily storing an image signal;
A data conversion unit that is connected to the image storage unit and converts an image signal into data suitable for controlling the thermal head; and a thermal head that is connected to the data conversion unit and converts the data into thermal energy. In an image printer that prints a color image in a superimposed manner, a preheat pulse generating unit that outputs a control signal for heating a heating element of the thermal head before printing each color, and a preheat pulse width output from the preheat pulse generation circuit is variable. A preheat pulse width varying unit that generates a preheat pulse signal to be supplied to the heating element of the thermal head from a preheating pulse width variable signal output from the preheating pulse width varying unit, thereby generating a temperature of the heating element of the thermal head. And a preheat pulse generation circuit for controlling
A preheating circuit for an image printer, wherein a heating element of the thermal head is preheated before each color printing. 2. A preheating circuit for an image printer according to claim 1, wherein said preheating pulse generating means has a variable pulse period. 3. The preheat circuit of an image printer according to claim 1, wherein said preheat pulse generating means includes a preheat pulse generating means for detecting a position on said thermal head and a vicinity of said thermal head.
An image, comprising: a preheat pulse width changing means for changing a preheat pulse to be applied to a heating element of the thermal head before printing each color in accordance with detection signals from the two temperature sensors. Preheating circuit for printer.