JPS63178063A - Thermal recording apparatus - Google Patents

Abstract

PURPOSE:To prevent the generation of dew condensation, by controlling the supply of a current to a thermo-module on the basis of the output of a sensor for detecting the temp. of a substrate having the heat generating element of a thermal head arranged thereto and the output of a sensor for detecting the temp. in an apparatus so as to make the temp. in the apparatus approximate to that of the substrate. CONSTITUTION:The supply of a current to a thermo-module 32 is controlled by a control circuit 34 so that the temp. of a substrate becomes almost equal to that in an apparatus. When the driving of a recording apparatus is started and the heat generating element 30 of a thermal head 20 generates heat, a part of said heat is lost by recording and the remainder thereof heats the substrate 28. The output of a temp. sensor 36 detecting the temp. of the substrate is compared with that of a sensor 37 detecting the temp. in the apparatus and, when the rising in the temp. of the substrate 28 is shown, the supply of a current to the thermo-module 32 is started by the control circuit 34 and the substrate 28 is cooled to the temp. in the apparatus. The opposite side surface of the thermo-module 32 is heated to temp. higher than that in the apparatus, but the heat is radiated by fins 32 to cool said surface. Since said cooling effect can be continued at a high level until the temp. of the substrate 28 reaches that in the apparatus, the rising in the temp. of the substrate 28 generated by the driving of the heat generating element 30 is rapidly and certainly prevented.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a thermal recording device that is used in facsimiles, printers, etc. and records images using a thermal head, and particularly relates to a thermal recording device that is used in facsimiles, printers, etc. and records images using a thermal head. It relates to a recording device.

[Conventional technology]

BACKGROUND ART Recording an image using a thermal head and a heat-sensitive recording medium, which are formed by providing a large number of segmented current-carrying heat-generating resistive elements on a substrate, is already well known and widely put into practical use in facsimile machines, printers, and the like.

For example, FIG. 9 is a diagram schematically showing a cross-sectional structure of a thermal head 1 called a thin film type. A glass gelase layer 3 for forming a smooth surface is laminated on the surface of the substrate 20 made of alumina or the like, and an ii1 electric heating resistor layer 4 made of NiCr, Ta or the like is formed thereon. moreover,
On the surface of this resistor layer 40, a patterned conductor layer 5 made of AJ or the like is laminated to segment the resistor layer 4 and enable selective energization, and segmented heating elements are arranged in a row. , and on its surface, T
Wear resistance and oxidation prevention 1 consisting of a, ○, S i C, etc.
? i6 is formed.

Thermal recording media include thermal recording paper that develops color when heated;
Heat-melt transfer ink sheets are made by coating a mixture of wax and pigment on a thin polyester sheet, etc., and heat-sublimation transfer ink sheets are made by coating a thin polyester sheet with a heat-sublimation dye dispersed in a binder. It is well known and has been put into practical use. In the case of thermal recording paper, the recording paper itself develops color to form an image, but in the case of heat-melting transfer ink sheets and heat-sublimation transfer ink sheets, the color is created by overlapping the image receiving paper and applying a thermal head from the base sheet side. An image is formed by selectively melting or sublimating the material and transferring it onto image-receiving paper.

When forming an image using a thermal head, electric pulses are selectively applied to each unit of segmented heating elements to generate heat according to the image data recorded.
This heat acts on a thermosensitive recording medium, for example, melts ink on a heat-melting ink sheet and transfers the ink to image-receiving paper to form an image.

By the way, in a thermal recording device that records an image using a thermal head and a thermal recording medium as described above, the thermal head generates heat and images are recorded using the thermal energy, so this device is installed. This is affected by the ambient temperature, such as the temperature of the environment in which the recording is performed, or the heat generated from the thermal head during recording.

In other words, if this device is used in a cold region or other low-temperature location, the temperature of the thermal head and substrate will be low, so the heat generation temperature of the thermal head will not reach the specified temperature. In recording methods in which the density of the dot does not change, the image dot size becomes small, and in methods that use thermal recording paper or in which the dot size is approximately constant and the image density changes, such as thermal sublimation recording, the image density decreases. , the image becomes faint and faded. Furthermore, when recording, the temperature of the thermal head and the substrate rises due to heat accumulation in the thermal head, which causes the heat generation temperature of the thermal head to rise above the predetermined temperature, resulting in an unnecessarily large image dot size and an increase in image density. , causing image blurring and fogging.

Therefore, various proposals have been made in the past in order to prevent variations in image density due to temperature changes in the thermal head and substrate as described above.

Figure 10 shows one of these proposals:
This is disclosed in Japanese Patent No. 141650, and its structure and operation will be briefly explained. A platen roller 8 is provided opposite the thermal head 7, and a thermal recording paper 9 as a thermal recording medium is introduced between the thermal head 7 and the platen roller 8 so as to be pressed against the thermal head 7 by the platen roller 2. There is. The thermal head 7 includes a substrate 10 and heating elements 11 provided in segments on the substrate. Furthermore, this thermal head substrate 10 is provided with heating/cooling means 12.

Then, the recording paper 9 is pressed against the heating element 11 of the thermal head 7, and an image and a recording signal are applied to the heating element 11 from a drive circuit (not shown) to generate heat, thereby recording an image. When recording, the heating/cooling means 12 maintains the temperature of the thermal head 7 at a predetermined constant temperature, thereby obtaining a stable recorded image density.

(Problem to be solved by the invention) By the way, if the thermal head is maintained at a predetermined constant temperature as described above, dew condensation will occur on the cooled thermal head and its surrounding areas in a high temperature and humid environment, causing the thermal head to deteriorate. This may cause problems such as damage to the device or its drive circuit, the recording paper absorbing water and making it impossible to record properly, and a large amount of condensed water accumulating inside the device, causing various problems.

Therefore, this invention was made by focusing on the above-mentioned problems, and is a thermal recording device that effectively prevents temperature fluctuations caused by the heat accumulation phenomenon of the thermal head, and also prevents dew condensation from forming on the thermal head. The purpose is to provide

[Means and effects for solving the problems] In order to solve the above problems, the thermal recording device of the present invention conducts electricity on a surface of the substrate different from the surface of the substrate on which the heating element of the thermal head is arranged. A thermo module is installed that cools one side and heats the other side, and includes a temperature sensor that detects the temperature of the substrate, and a temperature sensor that detects the internal temperature of the thermal recording device, based on the outputs of these temperature sensors. The device is characterized in that it includes a control circuit that controls energization of the thermo module so that the temperature of the substrate approximates the temperature inside the device.

By controlling the power supply to the thermo module so that the temperature of the board approximates the temperature inside the recording device, the temperature of the board is maintained close to the temperature inside the recording device, so that the temperature of the board due to the heat generated by the heating element is reduced. Temperature fluctuations in the thermal head due to heat accumulation phenomena are prevented, and dew condensation due to the substrate being cooled excessively below the internal temperature of the recording apparatus is also prevented.

〔Example〕

Hereinafter, the present invention will be described in detail based on examples.

(First Embodiment) FIG. 1 is a diagram showing a first embodiment of a thermal recording apparatus according to the present invention.

A platen roller 21 is disposed in contact with the thermal head 20, and the thermal head 20 and the platen roller 21
In between, a thermal transfer ink sheet 22 and an image receiving paper 23 are introduced in a superimposed manner as thermal recording media. The ink sheet 22 is supplied from a supply roller 24, passes between a thermal head 20 and a platen roller 21, and is wound around a take-up roller 25. Receiving paper 2
The ink sheet 2 is fed from a paper feed section (not shown), and is transferred to the thermal head 20 by a platen roller 21.
2 and are conveyed in the direction of arrow A and discharged to a discharge section (not shown).

This thermal radar 20 is attached by an attachment member 26 to a support rod 27 provided in a frame of a housing (not shown) of the recording apparatus. and thermal head 2
A connector 29 is provided at the end of the substrate 28 and is connected to a drive circuit 31 that selectively applies current to the heating element 30 according to recorded image data. This drive circuit 31
It also controls sequences such as feeding of the thermal transfer ink sheet 22 and image receiving paper 23.

The thermal head 20 includes a substrate 28 and a number of segmented heating elements 30 provided on the substrate. A thermo module 32 that operates based on the Beltier effect is fixed to the substrate of the thermal head 20.
Further, a fin 33 is fixed to the surface of the thermo module 32 opposite to the surface to which the substrate is fixed. Here, the thermo module 32, which operates based on the Beltier effect, is a plate-shaped element with no moving parts and has solid heating and cooling capabilities. is heated and the other surface is cooled, and by reversing the direction of the current, the heating and cooling surfaces can be reversed. Such a thermo module 32 has a thin plate-like structure and can be easily miniaturized, and is extremely convenient for mounting on the thermal head substrate 4 and controlling the temperature.

The thermo module 32 is connected to a control circuit 34. The control circuit 34 is connected to the power supply circuit 35 and controls the current applied to the thermo module 32.

The output from a temperature sensor 36 such as a thermistor or thermocouple that detects the temperature of the thermal head 20 provided inside the base +Ii and 28, and the output from a temperature sensor 37 that detects the ambient temperature inside the recording device are as described above. Control circuit 34
is connected so that it is input to the

It is desirable that the temperature sensor 36 of this board be provided as close to the heating element 30 as possible to meet the purpose of control.
On the other hand, the temperature sensor 37 that detects the temperature inside the device is not affected by the heat of the thermal head 20 or the fins 33, and can be installed in any thermally stable place, such as in the space inside the device or in the device. You can select the frame section or recording paper path. The control circuit 34 is configured to receive the outputs of the temperature sensor 36 and the temperature sensor 37 and control the supply of electricity to the thermo module so that the substrate temperature becomes approximately equal to the internal temperature of the recording apparatus.

The effect based on such a configuration will be explained.

The heating element 30 selectively generates heat in accordance with the image recording signal output from the drive circuit 31 in accordance with the image data recorded on the ink sheet 22 pressed against the thermal head 20 by the platen roller 21 and the image receiving paper 23. An image is recorded by

By the way, in this embodiment, the thermo module 32
Since the control circuit 34 controls the current supply so that the substrate temperature is approximately equal to the internal temperature of the apparatus, when the recording apparatus is stopped, the temperatures of both are approximately equal, so that j1 to the thermo module 32 is There will be no electricity. Then, the recording device starts to drive and the thermal head 2
When the heating element 30 of No. 0 generates heat, part of the heat is lost due to recording, and the rest heats the substrate 28. When the output of the temperature sensor 36 that detects the substrate temperature indicates an increase in the temperature of the substrate 28 compared to the output of the sensor 37 that detects the internal temperature of the device, the control circuit 34 starts energizing the thermo module 32, and the substrate 28 It is cooled down to the temperature inside the device. The surface on the opposite side of the thermo module 32 will be heated to a temperature higher than the internal temperature of the device, but the fins 33 will dissipate the heat.
cooled down. Heat dissipation by the fins 33 is effective because the temperature is higher than the internal temperature of the device. Therefore, while the recording apparatus is running, the remaining heat that is not lost during recording out of the heat generated by the heating element 30 is not stored in the substrate 28 but is carried to the fins 33 by the thermo module 32 and radiated. is effectively maintained at approximately the internal temperature of the device. In this case, the thermo module 32
Since the cooling effect of the board 28 is controlled only by the amount of current applied, unlike air cooling, where the cooling effect is significantly affected by the temperature difference between the air temperature and the object to be cooled, the board 28 is The cooling effect can be maintained at a high level until reaching the
A rise in temperature of the substrate 28 caused by driving the heating element 30 is quickly and reliably prevented.

Therefore, in this embodiment, the thermal head 20
Since the temperature of the substrate 14 is always maintained approximately equal to the internal temperature of the device, stable recording can be performed without fluctuations in recording image quality due to temperature rise, and there is no condensation on the thermal head. Although the temperature is controlled to be approximately equal to the internal temperature of the apparatus, there is no need to control the temperature of the thermal head when the printing apparatus is not driven, and when printing is required, printing can be started immediately.

By the way, the measurement of the temperature inside the device may show different values depending on the installation location of the temperature sensor, and the temperature control may be slightly affected by the time lag and hysteresis of the circuit system for controlling the temperature of the thermal head support substrate based on the measured value of the sensor. It is not possible to prevent fluctuations in temperature, but this is not very important from the standpoint of preventing condensation.For example, when the equipment is placed in a relatively high humidity environment such as 25°C and 85% relative humidity. The cooling temperature limit when the thermal head is cooled too much and dew condensation occurs is 22.5°C. Therefore, with respect to the above environmental temperature, it can be said that the permissible value of 2.5° C. is 2.5° C. without causing any problems when the thermal head is excessively cooled. Similarly, if the device is used in an environment of 30°C and relative humidity of 90%, the permissible value for temperature control is 1.7°C because dew condensation will occur on surfaces cooled to 28.3°C or lower. This accuracy is a value that can be sufficiently achieved by a normal temperature control circuit.

Furthermore, errors in measuring the temperature inside the device caused by improper installation of the temperature sensor are usually based on a local temperature rise due to heat generation within the device, so it is rather likely that the thermal head's control set temperature will be slightly higher. Although it may shift, there is no risk of it being set low and causing condensation.

The easiest way to calculate the temperature at which condensation starts for a given environmental temperature and humidity is to use an psychrometric diagram, and the required temperature is calculated based on the highest humidity environment in which the device will be used. Control accuracy can be determined.

Note that the control circuit 34 may be configured to control a temperature slightly higher than the internal temperature of the device (for example, +2° C.) so that the substrate temperature does not rise above that temperature. In this case, the substrate temperature will fluctuate between the temperature inside the device and the +α temperature, so it is desirable that the +α is 5°C or less, but there will be no condensation on the thermal head and the control energy will be reduced. It has advantages.

(Second Embodiment) FIG. 2 is a diagram showing a second embodiment of the thermal recording apparatus according to the present invention, and is a view of the thermal head viewed from the thermomodule mounting surface side. The same parts as those described in the first embodiment are given the same reference numerals, and details will be omitted.

In this embodiment, the thermo module 3 in the first embodiment
Temperature sensors 36a to 36f are installed in the substrate 28 corresponding to these thermo modules 328 to 32f, and the outputs from these temperature sensors are are input to control circuits 343 to 34f provided correspondingly.

Outputs from a temperature sensor 37 that detects the internal temperature of the device are input to these control circuits 34a to 34f, respectively. Further, control outputs from these control circuits 343 to 34f are inputted to corresponding thermo modules 323 to 32f through connectors 38 provided on the board 28.

Control circuits 34a to 34f receive outputs from corresponding temperature sensors 36a to 36f and temperature sensor 37, respectively, and control energization to corresponding thermo modules 32a to 32f so that the corresponding substrate temperature becomes approximately equal to the internal temperature of the device. It is something. Note that the fins 33 are fixed across these thermo modules 32a to 32f.

The operation of this embodiment will be explained.

Since the substrate temperature is approximately equal to the internal temperature of the apparatus at the start point when the drive circuit 31 drives the heating element and the thermal recording medium transport mechanism (not shown), the control circuits 348 to 34
The thermo module is not energized from f. As the drive progresses, the temperature of the substrate 28 will rise unevenly due to the heating elements that are selectively heated in accordance with the image recording signal. Therefore, each temperature sensor 36a
The outputs of ~36f will be different. However, the corresponding control circuits 34a to 34f independently control the energization of the corresponding thermo modules 328 to 32f based on the outputs from the temperature sensors 36a to 36f, and
Since the temperature of the corresponding portion of the thermal head is maintained substantially equal to the internal temperature of the apparatus, stable image recording without unevenness is performed also in the width direction of the thermal head.

Note that the control circuit of this second embodiment includes each temperature sensor 36a.
Control circuits 34 independently provided corresponding to ~36f
8 to 34f, however, if time sharing is used to switch the energization, each of the thermo modules 328 to 32f may be controlled to be energized by a single control circuit.

According to the second embodiment, uneven image recording in the width direction of the thermal head, which cannot be prevented in the first embodiment, can be prevented, and dew condensation can be prevented more stably.

(Third Embodiment) FIG. 3 is a diagram showing a third embodiment of the present invention, in which the same parts as in the first embodiment are given the same reference numerals, and details are omitted. This embodiment is partially added to the configuration of the first embodiment, and a recording signal correction circuit 39 is included in the drive circuit 31.
is provided so that the output of a temperature sensor 37 that detects the temperature inside the apparatus is inputted to this recording signal correction circuit 39. This recording signal correction circuit 39 corrects the image recording signal output from the drive circuit 31 according to the internal temperature of the apparatus, so that as the internal temperature of the apparatus increases, the intensity of the image recording signal becomes smaller. The correction is made so that the intensity of the image recording signal increases as the intensity decreases.

FIG. 4 shows an example of correcting the image recording signal by the recording signal correction circuit 39. The image recording signal applied to each heating element 30 of the thermal head 20 is usually a pulse signal of several pulses, and one pixel is formed on the thermal recording medium. Assuming that the image recording signal W corresponding to one pixel before correction has a voltage V, a pulse width t, and a number of repetitions n, an example of correction of the image recording signal is (1) in FIG.
), (2), and (3), (1) Example of changing the voltage V of the pulse X, x', t2) Example of changing the pulse width t y, y' (3) Number of pulses n Example 2 of increasing or decreasing
．． 2' and combinations thereof. For the image recording signals x, y, and z shown on the left side of each side, the intensity of the image recording signal is greatly corrected according to the amount of temperature drop to prevent the image density from decreasing when the temperature inside the device becomes low. In this example, X is an example where the voltage V' is set to v'>v, y is an example where the pulse width t' is set to t'>t, and 2 is the number of pulses n'.
This is an example in which n'>n. In addition, the image recording signals X', y', and 2' shown on the right side of each side are This is an example in which the intensity is corrected to a small value. This is an example. In order to perform such a correction in the recording signal correction circuit 39, the pulse voltage is corrected by controlling the power supply voltage according to the output of the internal temperature detection from the temperature sensor 37 using a variable voltage power supply, so that the pulse width t is corrected. Correction is 0N in the pulse generation circuit
-The time difference between the signals specifying OFF is controlled by the output from the temperature sensor 37, and the pulse number n is corrected by controlling the pulse number determining circuit for one pixel by the output from the temperature sensor 37. .

Therefore, in this embodiment, as in the first embodiment, the temperature of the substrate 28 of the thermal head 20 is controlled to be approximately equal to the internal temperature of the apparatus, and the recording signal correction circuit 39, which is not provided in the first embodiment, adjusts the internal temperature of the apparatus. Since the intensity of the image recording signal is corrected in accordance with the fluctuation, the recorded image density is stabilized with extremely high accuracy.

In this embodiment, a temperature sensor 37 for detecting the device temperature is used.
The output of the heating element 31 is manually inputted to the recording signal correction circuit 39, but if the output of the temperature sensor 36 that detects the substrate temperature is inputted to the recording signal correction circuit 39 to correct the image recording signal, the heating element 31 Since the image recording signal is corrected based on the substrate temperature, which is directly affected by the temperature of the substrate, more accurate correction is possible.

Regardless of whether the image recording signal is corrected using the temperature sensor 37 or the temperature sensor 36, both sensors 36, 37
Since the substrate temperature is controlled by the control circuit 34 to be approximately equal to the internal temperature of the device based on the output of Therefore, the mutual effects work together in a systematic manner, which is extremely effective for stabilizing image density.

(Fourth Embodiment) FIGS. 5 to 7 are diagrams illustrating a fourth embodiment of the present invention.

In this embodiment, the control circuit 34 in the first embodiment shown in FIG. 2 is changed, and as shown in FIG. '
The thermo module 32 is energized so as to be maintained at 1ll', and when the temperature inside the device is higher than the specified temperature T'C, the energization of the thermo module 32 is controlled so that the substrate temperature is approximately equal to the temperature inside the device. It uses a control circuit. Therefore, when the temperature inside the device is above T'C, the substrate temperature is controlled to be approximately equal to the temperature inside the device due to cooling by the thermo module against heat accumulation in the board during operation, and when the temperature inside the device is below T'C, the substrate temperature is controlled to be approximately equal to the temperature inside the device. is controlled to T'C by heating by a thermo module,
The substrate temperature is maintained at T''C by reducing the heating amount of the thermo module in accordance with the amount of heating of the substrate due to the drive of the device, that is, the heat generated by the heating element, or by cooling the substrate by switching the current direction of the thermo module. That will happen.

FIGS. 6A and 6B show an example of a control circuit that controls the energization of the thermo module by switching the operation mode of the thermal head based on T'C. In FIG. 6(A), 40 is a DC power supply, Dl to D4 are diode type switching elements, and 39 is a control signal circuit. The control signal circuit 39 compares the output of the temperature sensor 37 for the internal temperature of the device with the set output value of T'C, and when the internal temperature of the device exceeds T'C, the output of the temperature sensor 36 for the substrate temperature is The thermo module 32 enters an operation mode in which energization is controlled so that the temperature is approximately equal to that of the internal temperature of the device, and the output of the temperature sensor 37 becomes T.
When the internal temperature of the device is below T'C compared to the set output value of °C, the operation mode is set to control the energization of the thermo module 32 so that the output of the substrate temperature sensor 36 becomes equal to the set output value of T'C. . In other words, in the operating mode when the internal temperature of the device is higher than T°C, the control signal circuit 39
6. When the detected temperatures of 37 are equal, switching element D1
~ When D4 is turned OFF and the temperature detected by the temperature sensor 36 becomes higher than the temperature detected by the temperature sensor 37, for example, the switching elements D2 and D are turned ON to flow a current in the direction of the arrow, and the thermo module 32 cools the board. do. In the operation mode when the temperature inside the device is below T'C, the control signal circuit 39 detects that the temperature detected by the temperature sensor 36 is T'C.
When the temperature is lower than , the switching elements R, D are turned on, and a current in the opposite direction to the arrow is passed through the thermo module 28 to heat the board, and the temperature detected by the temperature sensor 36 becomes T'C.
When the temperature is exceeded, the switching elements Dt and D3 are turned on to reverse the direction of current flow to the thermo module 32 and cool the board. FIG. 6(B) shows another example of a circuit for reversing the direction of energization to the thermo module 32, which in this case is composed of an AC current B41 and diode-type switching elements D5 and D6. When either Ds or D6 is turned ON in response to an output from the control i11 signal circuit similar to 39, the direction of current supply to the thermo module 32 is reversed, and the heating and cooling effects are reversed.

According to this embodiment, when the temperature inside the device is T'C or higher, the first
It has the same effect as the embodiment, and when the temperature inside the device becomes lower than T'C, the substrate temperature is maintained at T'C, so the substrate temperature decreases and the recorded image density decreases significantly. This prevents this from happening. This is due to a problem in Embodiment 1.2 where the substrate temperature drops below the practical range as the internal temperature of the device decreases, significantly reducing the recorded image density, and in Embodiment 3, the recorded image density decreases due to the decrease in substrate temperature. This also overcomes problems such as electric circuit limitations and shortened lifespans of heating elements in increasing the amount of energy by correcting the intensity of the image recording signal in order to prevent a decrease in density. Therefore, the designated temperature T'C is set according to the conditions of the printing apparatus and the permissible range of variation in density of the printed image.

Incidentally, in this embodiment, the operation mode of the control signal circuit is switched by comparing the internal temperature of the device measured by the temperature sensor 37 and the specified temperature T'C, but by comparing the substrate temperature measured by the temperature sensor 36 and the specified temperature T'C, the operation mode of the control signal circuit is switched. It is also possible to switch the operating mode.

Alternatively, a heater for heating the substrate may be provided separately, and the thermo module may be used only for cooling the substrate. Note that when the substrate 28 is heated by the thermo module 32, the surface on the opposite side of the thermo module and the fins 33 may be cooled and condensation may occur or frost may adhere, so that condensed water does not drip toward the thermal pad. A means for storing and discharging condensed water may be provided. However, Fig. 7 (A), (B
), a heater 42 is provided on the opposite surface of the thermo module opposite to the substrate fixing surface, and when the thermo module 32 heats the substrate 28, the heater 42 is installed at the same time.
It is more desirable to prevent dew condensation and frost from forming on the cooling surface side of the thermo module by energizing the thermo module. Figure 7 (A
) shows an example in which a heater 42 is attached to the fin 33. Further, FIG. 7(B) shows an example of a control circuit that energizes the heater 42 in conjunction with the energization of the thermo module 32. This circuit has a configuration in which a heater 42 consisting of a current-carrying heating resistor and a diode 43 are connected in series, and this is connected in parallel with the thermo module 32 in the circuit shown in FIG. 6(A). With this configuration, the current passes through the diode 43 and the heater 42 is energized only when the thermo module 32 is energized in the direction of the arrow to heat the substrate. Furthermore, the seventh
Although the heater 42 is inserted into the fin 33 in FIG. 3A, the arrangement of the heater can be changed in various ways, such as by arranging a plate-shaped heater between the thermo module 32 and the fin 33.

(Fifth Embodiment) In the fourth embodiment, the substrate is heated when the temperature is lower than the specified temperature T'C to prevent a decrease in the recorded image density. Since it has been left unattended, it remains a factor that causes fluctuations in recorded image density. In order to overcome this problem, a fifth embodiment is described in which an internal heating means is provided, and when the internal temperature of the apparatus is lower than T'C, it is energized to maintain the internal temperature of the apparatus at T'C. It is shown in Figure 8. In the figure, the same parts as those explained in the first embodiment are denoted by the same reference numerals, and details are omitted.

In this embodiment, a heater 4B made of a planar heating element such as a silicon rubber heater is provided in the recording device of the first embodiment covered with a cover 49, 50, 51, and a temperature sensor 37 is provided.
The present invention is characterized in that when the internal temperature of the apparatus detected by is lower than T'C, the heater 48 is energized and controlled by the heater control circuit 52 to maintain the internal temperature of the apparatus at T'C. Note that 44 is an image receiving paper supply roller, and 45 and 46 are pressure rollers that hold the image receiving paper 23 in contact with the platen roller 21.

The temperature inside the device reaches the specified temperature T according to the output of the temperature sensor 37.
When it is detected that the temperature has dropped below 'C, the heater control circuit 5
2, the heater 48 is energized and the temperature inside the device reaches approximately T'C.
controlled so that it is maintained at On the other hand, since the temperature of the substrate 28 is controlled by the control circuit 34 shown in FIG. 1 to be approximately equal to the temperature inside the device, the temperature of the substrate 28 is controlled as follows in this embodiment. That is, the temperature inside the device is T'C.
When the temperature is lower, the heater 48 is energized and the temperature inside the device is T'
The temperature of the substrate is maintained at T''C, and the temperature of the substrate rises as the temperature inside the device increases and is maintained at T''C.

Also, when the temperature inside the device is higher than T''C, the heater control circuit 5
2, the heater 48 is not energized, so the substrate temperature is controlled and maintained by the control circuit 34 to be approximately equal to the internal temperature of the device.

The technical concept of this embodiment is that when the temperature inside the recording device is below T'C, the temperature inside the recording device is controlled to be T'C, and the substrate temperature is controlled to be approximately equal to the temperature inside the device. When the temperature inside the device exceeds T''C, the substrate temperature is controlled to be approximately equal to the temperature inside the device.

As a result, the recording members including the thermal head in the apparatus are maintained at approximately the same temperature, so that the recorded image becomes extremely stable and no dew condensation occurs on the thermal head.

As a modification of this embodiment, an in-device heater 48 and a heater control circuit 52 are provided in the device and control mechanism of the fourth embodiment, and the device internal temperature and substrate temperature are controlled separately based on the specified temperature T'C. You can also.

〔Effect of the invention〕

In this invention, since the thermo module is energized so that the temperature of the substrate of the thermal head and the temperature inside the device are approximated, the heat accumulation phenomenon of the substrate due to the drive of the heating element, that is, the temperature rise of the thermal head, is prevented, and thermal recording is possible. In addition to stabilizing the recorded image on the medium, it is possible to prevent the substrate from being excessively cooled by the thermo module and causing dew condensation.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram for explaining a first embodiment of this invention, FIG. 2 is a schematic diagram for explaining a second embodiment of this invention, and FIG. 3 is a schematic diagram for explaining a third embodiment of this invention. A schematic diagram for explanation, FIG. 4 is a diagram showing an example of correction of the image recording signal in the third embodiment, FIG. 5 is a graph showing the control mode of the fourth embodiment of the present invention, and FIG. ) and (B) are circuit diagrams showing an example of the control circuit of this fourth embodiment, and FIG. 7 (A
) is a schematic diagram showing an example of a heater for heating a thermo module arranged in the device of the fourth embodiment, FIG. 7(B) is a circuit diagram showing an example of a circuit for driving the heater in FIG. 7(A), FIG. 8 is a schematic diagram for explaining a fifth embodiment of the present invention, FIG. 9 is a cross-sectional view showing an example of the configuration of a thermal head, and FIG. 10 is a schematic diagram for explaining a conventional thermal recording S3 device. It is a diagram.

Claims (1)

[Scope of Claims] A thermal recording device that records an image using a thermal head having a large number of segmented current-carrying heating elements on one surface of a substrate and a thermal recording medium, comprising: a thermal recording medium provided on the other surface of the substrate; A thermo module that cools one side and heats the other side when electricity is applied, a temperature sensor that detects the temperature of the board, a temperature sensor that detects the internal temperature of the thermal recording device, and based on the outputs of these temperature sensors. 1. A thermal recording device comprising: a control circuit that controls energization of a thermo module so that the temperature of a substrate approximates the temperature inside the device.