JPH02162060A - Heat sensitive printer - Google Patents

Abstract

PURPOSE:To maintain energy to be introduced into an ink ribbon and a printing sheet constant and to prevent printing density from varying by detecting the temperature of a thermal head and the temperature in a housing, and controlling supply power to the thermal head on the basis of both the detection outputs. CONSTITUTION:Since both thermistors 42 and 43 have negative temperature coefficient characteristics, when the temperature of a thermal head is raised, a voltage of a connecting midpoint P is lowered, and the output voltage of an operational amplifier 44A is also lowered. Thus, the gain of a drive amplifier 41 is reduced, the amplitude of a PWM current supplied to the thermal head is reduced, and the temperature of the thermal head is lowered. When the temperature in a cabinet is raised, the voltage of a connecting mid point Q is raised, and the output voltage of the operational amplifier 44A is lowered. Thus, the gain of the drive amplifier 41 is reduced, the amplitude of the PWM current supplied to the thermal head is reduced. That is, the energy to be introduced into the thermal head is reduced to prevent printing density from varying.

Description

[Detailed description of the invention] [Industrial application field] This invention relates to a thermal printer.

[Summary of the invention]

The present invention detects the temperature of the thermal head and the temperature inside the housing in a thermal printer, and controls the power supplied to the thermal head based on the rain detection output.
The energy injected into the ink ribbon and photographic paper is kept constant to prevent changes in print density.

[Conventional technology]

Conventionally, in thermal printers, the temperature of the thermal head is detected by a sensor, and when the detected temperature is high.

Depending on the temperature, the temperature of the thermal head is kept within a specified range by electrical heating and air cooling before printing, and during printing,
A device is known in which the energy injected into the thermal head is controlled by changing the width of the energization time to prevent changes in printing density (for example, Japanese Patent Laid-Open No. 62-233268
(see publication).

[Problem to be solved by the invention]

However, in thermal printers, the energy injected into the thermal head during printing is diffused into the ink ribbon, photographic paper, and platen. There was a problem in that the energy applied to the paper fluctuated, resulting in changes in print density.

In view of this, an object of the present invention is to provide a thermal printer that maintains constant energy injected into the ink ribbon and photographic paper regardless of temperature changes within the thermal head and housing, thereby preventing changes in print density. There it is.

[Means to solve the problem]

The present invention provides a thermal printer that includes a first temperature detection element (42) that detects the temperature of a thermal head (17), and controls the power supplied to the thermal head based on the detection output of this temperature detection element. In, the housing (10)
A second temperature detection element (43) is provided to detect the temperature inside the thermal head, and the power supplied to the thermal head is controlled based on the detection output of the second temperature detection element and the detection output of the first temperature detection element. This is a thermal printer that can be controlled.

[Operation] According to the present invention, the energy injected into the ink ribbon and photographic paper is kept constant regardless of temperature changes within the thermal head and the housing, thereby preventing changes in print density.

〔Example〕

Hereinafter, an embodiment of a thermal printer according to the present invention will be described with reference to FIGS. 1 to 6.

First, the mechanical configuration of an embodiment of the present invention will be described with reference to FIG.

In FIG. 6, a plurality of A6 size (postcard size) photographic papers P, for example, are stored in a paper feed tray (11) in a cabinet (10). This photographic paper P is, for example, a synthetic paper whose surface is coated with polyester as a coloring layer.

The photographic paper P taken out from the tray (11) is fed by a paper feed mechanism (not shown), and then moved through the guides (12) and (13).
The rubber roller is wound around the platen (rubber roller) (16) by guides (14) and (15).

As shown in the figure, the platen (16) rotates in opposite directions during printing and when discharging paper.

(17) is a thermal head, and in this embodiment, a thin film type is used, and for example, 512
resistors are formed in-line. During printing, the thermal head (17) is supported by a support mechanism (not shown).
The photographic paper P wrapped around the platen (16) and the ink ribbon (18) are pressed appropriately. 1 pair of reels (
The ink ribbon (18) stretched between 19s) and 19t is coated with sublimable dyes in the three primary colors of yellow (Y), magenta (M) and cyan (C) in sequence, and the thermal head (17) The amount of sublimation of the dye changes depending on the energy applied. This sublimated dye is transferred to photographic paper P.

When printing is completed, the platen (16) rotates in the opposite direction, and the photographic paper P is discharged onto the tray (22) via between the guides (14) and (21).

Although not shown, heat sources such as a video signal processing section and a power supply circuit section are present in the cabinet (10).

Next, the electrical configuration of an embodiment of the present invention will be described with reference to FIGS. 1 and 2.

In FIG. 1, (31) is a frame memory,
Red (R), green (G), and blue (B) video signals are digitized and written. From this memory (31), video data for one line of the thermal head is read out in the order of, for example, B, G, and R, and is inverted by an inverter (32) and converted into video data of complementary colors Y, M, and C. and stored in the line memory (33).

(34) is a halftone control circuit, and line memory (34) is a halftone control circuit.
3), the pulse width of the output pulse current having a period of 25 m5, for example, is controlled according to the level value of the digital video signal supplied from 3). Also, the nonlinear sensitivity characteristics of the ink ribbon and the video camera are corrected.

This halftone control circuit (34) includes a frame memory (3
1) and digital circuits such as a line memory (33), a control signal from a control circuit (35) is supplied.

The output pulse current of the halftone control circuit (34) is supplied to the thermal head (17) via the drive amplifier (41). As described above, a temperature detection element (42) such as a thermistor is attached to the thermal head (17).

Furthermore, in this embodiment, the second temperature detection element (43) is appropriately arranged near the thermal head (17), for example by being attached to a support mechanism (not shown) of the platen (16). , the temperature inside the cabinet (10) is detected.

(44) is a gain control circuit, and rain detection element (42)
A gain control signal is generated based on the detection outputs of (43) and (43), and this control signal is supplied to the drive amplifier (41).

In this embodiment, as shown in FIG. 2, an operational amplifier (44A) is used as the gain control circuit (44).

That is, in the same figure, the thermistor for the thermal head (
42) and a resistor (45) are connected in series, the connection midpoint P is connected to the non-inverting input terminal of the operational amplifier (44A), and the other end of the thermistor (42) is grounded, and the resistor A reference voltage Vref is supplied to the other end of the device (45).

Also, a thermistor (43) for detecting the temperature inside the cabinet.
and a resistor (46) are connected in series, the connection midpoint Q is connected to the inverting input terminal of the operational amplifier (44A), the other end of the resistor (46) is grounded, and the thermistor (43 ) is supplied with a reference voltage Vref.

A resistor (44A) is connected to the inverting input terminal of the operational amplifier (44A).
7) and (48), the reference voltage V ref is appropriately divided and supplied, and via the resistor (49),
The output voltage of the operational amplifier (44A) is fed back. This output voltage is used as a gain control signal to drive the amplifier (
41).

The operation of the main parts of the embodiment shown in FIG. 2 is as follows.

Since both thermistors (42) and (43) have negative temperature characteristics, when the temperature of the thermal head increases, the voltage at the connection midpoint P decreases, and therefore the operational amplifier (44A)
The output voltage of will also decrease. Along with this, a drive amplifier (4
The gain of 1) is reduced and the P supplied to the thermal head is
The amplitude of the WM current will decrease, and the temperature of the thermal head will drop.

Further, when the temperature inside the cabinet increases, the voltage at the connection midpoint Q increases, and therefore the output voltage of the operational amplifier (44A) decreases. Along with this, the drive amplifier (41)
The gain of PWM is reduced and the PWM is supplied to the thermal head.
The amplitude of the current decreases. In other words, the injection energy of the thermal head is reduced, thereby preventing changes in printing density.

When the temperature inside the thermal head or the cabinet drops, contrary to the above, feedback control is performed to correct the temperature drop, and a change in print density is similarly prevented.

Next, another embodiment of the present invention will be described with reference to FIG.

FIG. 3 shows the configuration of the main parts of another embodiment of the present invention. In FIG. 3, the same reference numerals are given to the parts corresponding to the above-mentioned first director and FIG. 2.

In the embodiment of FIG. 3, as the gain control circuit (44), R
An OM (44M) and a DA converter (44c) are used.

That is, in the figure, the reference voltage V ref is appropriately divided by the thermistor (42) and resistor (45) for the thermal head, and the voltage at the connection midpoint P is applied to the A-D converter (
42c) to the X address terminal of the ROM (44M), and the reference voltage Vref (connection midpoint Q voltage) is supplied to the y address terminal of the ROM (44M) via the AD converter (43c).

This ROM (44M) has mapped control data for various combinations of the temperature of the thermal head and the temperature inside the cabinet, and both A-D converters (42c)
According to the output data of (43c), required gain control data is read from the ROM (44M). This control data is converted into an analog control signal by the DA converter (44c), and as described above, feedback control is performed to correct temperature fluctuations inside the thermal head and cabinet, resulting in changes in print density. is prevented.

Next, still another embodiment of the present invention will be described with reference to FIGS. 4 and 5.

FIG. 4 shows the configuration of a main part of still another embodiment of the present invention. In FIG. 4, parts corresponding to those in FIGS. 1 to 3 described above are given the same reference numerals, and explanations of the negative parts are omitted.

In the embodiment shown in FIG. 4, similarly to the embodiment shown in FIG. 3, R
The required control data is read from OM (44M),
The amplitude of the PWM current supplied to the thermal head is feedback-controlled.

In the embodiment shown in FIG. 4, the detection output of the thermistor (43) for detecting the temperature inside the cabinet is transmitted to the A-D converter (43c).
R O included in the halftone control circuit (34) via
M (34m). This ROM (34m)
As shown in FIG. 5, the energization time control data whose curve varies depending on the temperature is stored, and this control data is read out to determine the PWM current output from the halftone control circuit (34). Pulse width is controlled.

The energization time control operation of the embodiment shown in FIG. 4 is as follows.

When temperature-controlling only the amplitude of the PWM current supplied to the thermal head, when the inside of the cabinet is low temperature, if the printing time at the - point is kept constant and the energy given is increased, the concentration of the low-energy part will decrease. The density of the high-energy areas becomes saturated before the photon is released, and the surface of the photographic paper is damaged by heat. Conversely, when the temperature inside the cabinet is high, if you try to bring out the concentration of the high energy part, the concentration of the low energy part will become too high.

On the other hand, when controlling the energization time based on the internal temperature of the cabinet and the injection energy, if you want to apply high energy at low temperatures and increase the head voltage, the dynamic range of the printing time will become smaller and the gradation will become smaller at room temperatures. The maximum printing time of the - point affects the total printing time, so if you try to shorten the total printing time, you will not be able to take a long printing time and will not be able to make sufficient corrections.

Therefore, in the embodiment shown in FIG. 4, by simultaneously feedback controlling the pulse width and amplitude of the PWM current supplied to the thermal head based on the detection output of the temperature inside the cabinet, the print density can be adjusted while maintaining a wide range of gradations. Changes can be sufficiently prevented.

〔Effect of the invention〕

As described in detail above, according to the present invention, the temperature of the thermal head and the temperature inside the housing are detected, and the power supplied to the thermal head is controlled based on the rain detection output. Also, a thermal printer is obtained which can keep the energy injected into photographic paper constant and prevent changes in print density.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the overall configuration of an embodiment of a thermal printer according to the present invention, FIG. 2 is a block diagram showing the configuration of essential parts of an embodiment of the present invention, and FIG. FIG. 4 is a block diagram showing the configuration of the main part of another embodiment of the present invention,
FIG. 5 is a characteristic curve diagram of the embodiment of FIG. 4, and FIG. 6 is a sectional view showing the mechanical configuration of one embodiment of the present invention. (10) is a cabinet, (17) is a thermal head,
(34) is a halftone control circuit, (41) is a drive amplifier, (
42). (43) is a temperature detection element (thermistor), (44),
(448). (44M) is a gain control circuit.

Claims (1)

[Scope of Claims] A thermal printer comprising a first temperature detection element for detecting the temperature of a thermal head, and controlling power supplied to the thermal head based on the detection output of the temperature detection element, comprising: A second temperature detection element is provided to detect the temperature within the thermal head, and power supply to the thermal head is controlled based on the detection output of the second temperature detection element and the detection output of the first temperature detection element. A thermal printer characterized by: