JP2006021339A - Head cooling device and printer - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a cooling device which can change the cooling performance according to a temperature change of a thermal head. <P>SOLUTION: The cooling device 6 fitted at the thermal head 5 consists of a fixing member 31, a plurality of laminated type piezoelectric elements 32 and a heat sink 33. The laminated type piezoelectric element 32 has one end face in a lamination direction fixed to the fixing member 31, and the other end face fixed to the heat sink 33. A system controller controls a driving voltage applied to the plurality of laminated type piezoelectric elements 32 through a driving circuit, whereby the heat sink 33 shifts between a contact position where it comes in contact with an aluminum substrate 28 and a retreat position where it retreats from the contact position. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a head cooling device that is attached to a recording head that records an image by causing a heat generating element to generate heat, and a printer including the head cooling device.

  Using a thermal head provided with a heating element array in which a plurality of heating elements are arranged in the main scanning direction, and while the recording paper is conveyed in the sub-scanning direction while the heating element array is pressed against the thermal recording paper, There is known a thermal printer that records heat on a line by line basis. The heating element array is provided on one surface of the ceramic substrate, for example. Since the thermal head reaches a high temperature when the heat generating element array generates heat, a heat sink as a heat radiating member is generally attached to the other surface of the ceramic substrate.

  However, when a heat sink is attached, most of the heat generated by the heating element array is used to warm the heat sink at the initial stage of printer startup, etc., and the heat transmitted to the thermal recording paper out of the heat generated by the heating element array. The problem that the thermal efficiency which is the ratio of becomes low arises. If the thermal efficiency is low, the heating element array must generate extra heat, which is an obstacle to power saving of the printer.

  As a countermeasure, it is conceivable to reduce the heat sink performance by reducing the heat sink, and to increase the amount of heat directed to the thermal recording paper. However, if the heat dissipation performance of the heat sink is lowered, the temperature of the thermal head continues to rise as shown in FIG. 6 when printing is performed continuously. If the temperature of the thermal head continues to rise, the thermal head will eventually overheat and printing will have to be interrupted. The temperature rise of the thermal head is more remarkable during high-speed printing. Further, when the temperature of the thermal head is higher than the reference temperature, the thermally recorded image has no blurred contrast, and there is a problem that the image quality is deteriorated. For example, FIGS. 7A, 7 </ b> B, and 7 </ b> C are waveforms showing drive voltage applied to the heating element array, temperature change in the vicinity of the heating element array, and density change of the image, respectively. This is when the head temperature is higher than the reference temperature. As can be seen from FIG. 7, even if the drive voltage applied to the heating element array is stopped, the heat density does not escape near the heating element array, and the temperature drop is slow, so the print density cannot be controlled. An ideal waveform is indicated by a two-dot chain line.

  Against this background, a thermal head capable of changing the heat dissipation performance has been proposed (see, for example, Patent Document 1 below). In the thermal head described in Patent Document 1 below, a piezoelectric element is provided between the heat storage member (glaze layer) and the substrate, the thickness of the piezoelectric element is changed, and the volume of the gap is changed to change the heat dissipation performance. I have to. Thereby, when energizing the heat generating element, the heat dissipation performance is lowered to increase the thermal efficiency, and when the energization to the heat generating element is stopped, the heat dissipating performance is increased to quickly reduce the temperature.

Japanese Patent Laid-Open No. 9-123503

  However, in the technique described in Patent Document 1, since only the piezoelectric element and the spacer connect the heat storage member and the substrate, the heat dissipation performance is not sufficiently improved when the heating element is not energized. Therefore, the thermal head is likely to overheat. In addition, so-called thermal tailing is likely to occur, resulting in a problem that image quality is degraded. Furthermore, the structure of the thermal head is complicated, and it is necessary to precisely manufacture and accurately arrange each component, resulting in an increase in manufacturing cost.

  The present invention has been made in consideration of the above-described problems, and by changing the cooling performance in accordance with the temperature change of the recording head, the head cooling device and the head cooling which can increase the thermal efficiency and enable high-speed continuous printing. An object is to provide a printer including the apparatus.

  The present invention relates to a head cooling device attached to a recording head that heats a heating element on a head substrate to record an image on a recording material, a main heat sink that dissipates heat from the head substrate, and the main heat sink. It is characterized by comprising a main heat sink moving mechanism for moving between a contact position for contact with the substrate and a retract position for retracting from the contact position and leaving a gap with the head substrate.

  The main heat sink moving mechanism has one surface bonded to the main heat sink and a relative position between the piezoelectric substrate whose thickness changes according to an electric signal and the head substrate, and is bonded to the other surface of the piezoelectric element. A holding member that holds the main heat sink, and a piezoelectric element control unit that applies an electric signal to the piezoelectric element to control the thickness so as to move the main heat sink to the contact position or the retracted position. Is preferred.

  The main heat sink moving mechanism moves the main heat sink to the retracted position when the temperature of the recording head is below a reference temperature, and contacts the main heat sink when the temperature of the recording head exceeds the reference temperature. It is preferable to move to a position. Further, the main heat sink moving mechanism is configured to change the movement of the main heat sink to the contact position or the retracted position at the time of recording for recording an image on the recording material by the heating element, and at the time of recording for recording an image next. It is preferable to carry out between.

  The piezoelectric element control unit uses a plurality of pulse signals generated continuously as the electric signal, and controls the thickness of the piezoelectric element by using the pulse signal, whereby the main heat sink is moved to the contact position and the retracted position. It is preferable to change the heat radiation efficiency by changing the time ratio between the contact position and the retracted position in unit time by changing the duty ratio of the pulse signal periodically. In this case, it is preferable that the piezoelectric element control unit changes the duty ratio of the pulse signal so that the time ratio of the contact time per unit time increases as the temperature of the recording head increases.

  It is preferable that the head substrate includes a sub heat sink that is fixed in position and has lower heat dissipation than the main heat sink.

  The recording material is preferably a thermal recording paper that develops color when heated, and the recording head is preferably a thermal head that thermally records an image by pressing the thermal recording paper and the heating element. Further, the recording material is a color thermosensitive recording paper having a plurality of color developing layers that develop different colors with different thermal energy, and the recording head presses the color thermosensitive recording paper and the heating element to each color. A thermal head that thermally records an image every time is also suitable.

  A printer according to the present invention includes the above-described head cooling device.

  The head cooling device and the printer according to the present invention include a main heat sink that dissipates heat of the head substrate of the recording head, a contact position where the main heat sink is brought into contact with the head substrate, and a retreat from the contact position between the head substrate and the head substrate. Since the main heat sink moving mechanism is provided for moving between the retraction position and the clearance position, the cooling performance can be changed according to the state of the recording head. Thereby, the thermal efficiency of the recording head can be increased and continuous printing can be performed. Further, by increasing the thermal efficiency of the recording head, it is possible to reduce the power consumption of the printer. Furthermore, since the head cooling device and the printer of the present invention have a simple structure, manufacturing costs can be suppressed.

  As shown in FIG. 1, the thermal printer 2 includes a paper feed roller 3, a transport roller 4, a thermal head 5, a head cooling device 6, a platen roller 7, a light fixing device 8, a system controller 9, a paper discharge roller 10, a cutter. 11 and a discharge port 12 are provided. The thermal printer 2 is loaded with a recording paper roll in which a long color thermal recording paper 13 (hereinafter, recording paper 13) is wound into a roll.

  The paper feed roller 3 abuts on the outer periphery of the recording paper roll and pulls out the recording paper 13 to the conveyance path. The transport roller 4 transports the recording paper 13 in the feeding direction by rotating forward, and transports the recording paper 13 in the returning direction by rotating backward. The paper feed roller 3 and the transport roller 4 are driven by a motor (not shown), and the motor is controlled by a system controller 9.

  The thermal head 5 is provided on the downstream side in the feed direction of the transport roller 4. The thermal head 5 is displaced between a printing position where the thermal head 5 is pressed against the recording paper 13 on the platen roller 7 and a retreat position where the thermal head 5 is separated from the platen roller 7. The thermal head 5 is driven by a head driver (not shown) based on image data sent from the system controller 9. A head cooling device 6 is attached to the thermal head 5. Details of the thermal head 5 and the head cooling device 6 will be described later.

  The platen roller 7 is provided at a position facing the thermal head 5 across the conveyance path. The platen roller 7 is driven to rotate as the recording paper 13 is conveyed.

  As is well known, the recording paper 13 is formed by sequentially providing a cyan thermosensitive recording layer, a magenta thermosensitive recording layer, and a yellow thermosensitive recording layer on a support. Each heat-sensitive recording layer is designed to develop color when predetermined heat energy is applied. The yellow thermosensitive coloring layer develops color with the smallest thermal energy, and the cyan thermosensitive coloring layer develops color with the greatest thermal energy. The yellow thermosensitive coloring layer loses the coloring ability of the uncolored portion when irradiated with yellow fixing light, which is blue-violet light having a wavelength of about 420 nm. Similarly, when the magenta thermosensitive coloring layer is irradiated with magenta fixing light, which is near-ultraviolet light having a wavelength of about 365 nm, the coloring ability of the uncolored portion is lost.

  The optical fixing device 8 is provided on the downstream side of the thermal head 5 in the feeding direction. The optical fixing device 8 includes a yellow fixing lamp 19 that emits yellow fixing light, a magenta fixing lamp 20 that emits magenta fixing light, and a reflecting plate 21 that reflects light from these lamps 19 and 20. The optical fixing device 8 is driven by a light driver (not shown) based on a signal from the system controller 9.

  The cutter 11 is provided on the downstream side in the feed direction of the optical fixing device 8. The cutter 11 cuts the recording paper 13 into a predetermined size. The paper discharge roller 10 and the discharge port 12 are provided on the downstream side in the feed direction of the cutter 11. The paper discharge roller 10 conveys the cut recording paper 13 to the discharge port 12.

  Hereinafter, the thermal head 5 and the head cooling device 6 will be described. As shown in FIG. 2A, the thermal head 5 includes a printed circuit board 24, a ceramic substrate 25, a glaze layer 26, a heating element array 27, an aluminum substrate 28, and a temperature sensor 29 (see FIG. 1). The printed circuit board 24 is provided with a driver IC (not shown), whereby the energization of each heating element 27a is controlled. The ceramic substrate 25 is formed in a flat plate shape. The glaze layer 26 is formed on the ceramic substrate 25 and is made of glazed glass. A part of the glaze layer 26 is a partial glaze 26 a raised from the cylindrical ridge. The heat generating element array 27 is disposed near the top of the partial glaze 26a, and includes a plurality of heat generating elements 27a arranged in the main scanning direction. The main scanning direction is a direction orthogonal to the conveyance direction (sub-scanning direction) of the recording paper 13. The aluminum substrate 28 is provided on the surface of the ceramic substrate 25 opposite to the surface on which the heating element array 27 is provided. The aluminum substrate 28 is a flat plate elongated in the main scanning direction, and also has a function as a heat radiating member. The temperature sensor 29 (see FIG. 1) measures the temperature of the thermal head 5 and sends the measured value to the system controller 9.

  The head cooling device 6 includes a fixing member 31, a plurality of stacked piezoelectric elements 32, a heat sink 33, and a piezoelectric element driving circuit 34 (see FIG. 1). The fixing member 31 is fixed to a housing (not shown) of the thermal printer 2. A fixing screw 35 is fixed to the fixing member 31, and the tip of the fixing screw 35 is fixed to the aluminum substrate 28 of the thermal head 5. The fixing member 31 is formed in a flat plate shape and is spaced apart from the aluminum substrate 28 so as to face the aluminum substrate 28. As is well known, the laminated piezoelectric element 32 has a structure in which piezoelectric ceramic layers and internal electrode layers are alternately laminated, and the internal electrode layers are connected to a pair of external electrodes so that each internal electrode layer becomes a counter electrode. The length changes in the stacking direction by application. The stacked piezoelectric element 32 has one end surface in the stacking direction fixed to the surface 31 a of the fixing member 31 on the thermal head 5 side. A plurality of stacked piezoelectric elements 32 are arranged in parallel at predetermined intervals on the surface 31a. The other end surface of the multilayer piezoelectric element 32 in the stacking direction is fixed to a heat sink 33 described later. The piezoelectric element drive circuit 34 (see FIG. 1) applies a drive voltage to the plurality of stacked piezoelectric elements 32 based on an instruction from the system controller 9 (see FIG. 1).

  The heat sink 33 has a substantially U-shaped cross section, and has a flat surface portion 33a elongated in the main scanning direction, and bent portions 33b and 33c extending obliquely from both ends of the flat surface portion 33a. The flat surface portion 33 a of the heat sink 33 is formed to have substantially the same area as the area of the aluminum substrate 28, and is disposed between the aluminum substrate 28 and the fixing member 31 so as to be parallel to the aluminum substrate 28 and the fixing member 31. . The other end surface of the multilayer piezoelectric element 32 is fixed to the surface of the flat portion 33a on the fixing member 31 side. A through hole 36 is formed in the flat portion 33 a, and a fixing screw 35 is passed through the through hole 36. As a result, the heat sink 33 is guided to move the aluminum substrate 28 in the normal direction. The heat sink 33 is displaced in the normal direction of the aluminum substrate 28 in accordance with the change in length of the multilayer piezoelectric element 32 in the stacking direction, whereby the distance between the heat sink 33 and the aluminum substrate 28 changes.

  The system controller 9 (see FIG. 1) compares the measured temperature measured by the temperature sensor 29 with a preset reference temperature. This reference temperature is determined according to the printing environment, the printing color, and the like. When the measured temperature is equal to or lower than the reference temperature, the system controller 9 reduces the length of the multilayer piezoelectric element 32 via the piezoelectric element drive circuit 34 (see FIG. 1), while the measured temperature is the reference temperature. Is exceeded, the length of the multilayer piezoelectric element 32 is controlled via the piezoelectric element driving circuit 34 so that the length of the multilayer piezoelectric element 32 is increased. As a result, when the temperature of the thermal head 5 is low, the heat sink 33 is positioned at a retracted position where the flat portion 33a is separated from the aluminum substrate 28 and leaves a gap between the aluminum substrate 28 as shown in FIG. When the temperature of the thermal head 5 is high, the flat surface portion 33a is located at a contact position where it contacts the aluminum substrate 28 as shown in FIG. If the heat sink 33 is in the retracted position, the heat dissipation efficiency decreases, and if the heat sink 33 is in the contact position, the heat dissipation efficiency increases.

  The head cooling device 6 of the present example can change the heat radiation efficiency in accordance with the temperature change of the thermal head 5, thereby increasing the thermal efficiency of the thermal head 5 to save power and preventing the thermal head 5 from being heated. To enable continuous printing.

  In addition, the image quality can be kept good during continuous printing. For example, FIGS. 3A, 3 </ b> B, and 3 </ b> C are waveforms showing a driving voltage applied to the heating element 27 a, a temperature change in the vicinity of the heating element array 27, and a change in image density, respectively. In this example, the heat sink 33 of the head cooling device 6 is in the contact position. An ideal waveform is indicated by a two-dot chain line. From FIG. 3, when the driving voltage applied to the heating element 27a is stopped, the heat in the vicinity of the heating element array 27 escapes to the heat sink 33 through the ceramic substrate 25 and the aluminum substrate 28. It can be seen that the decrease in color quickly approaches an ideal waveform, and the print density can be controlled.

  Below, the effect | action by the said structure is demonstrated. When the thermal printer 2 is turned on and a print instruction is given, the heat sink 33 moves to the retracted position. In this state, the recording paper 13 is conveyed in the feeding direction, and the yellow image is thermally recorded and optically fixed. When the yellow image thermal recording and light fixing are finished, the recording paper 13 is conveyed in the returning direction, and then the magenta image thermal recording and light fixing and the cyan image thermal recording are performed in the same procedure, and a full color image is obtained. It becomes. During thermal recording of each color image, since the heat sink 33 is located at the retracted position, a state where the thermal efficiency is high is maintained. During the above operation, the temperature of the thermal head 5 gradually increases. The full color image recorded on the recording paper 13 is cut by the cutter 11 and discharged. One series of printing is completed by these series of operations.

  If the measured temperature of the temperature sensor 29 attached to the thermal head 5 is equal to or lower than the reference temperature, thermal recording is performed with the heat sink 33 in the retracted position as described above. However, when a plurality of prints are continuously performed, the temperature of the thermal head 5 increases, and the measurement temperature eventually exceeds the reference temperature. When the measured temperature exceeds the reference temperature, the heat sink 33 moves to the contact position and cools the thermal head 5. Thereby, heating of the thermal head 5 is prevented, and continuous printing can be continuously performed. After a while after the end of continuous printing, the measured temperature becomes lower than the reference temperature, so the heat sink 33 moves to the retracted position. Thereby, the thermal head 5 is kept at an appropriate temperature.

  In the above embodiment, the heat sink is moved between the retracted position and the contact position at an arbitrary timing based on the comparison result between the measured temperature and the reference temperature. However, the following may be used. That is, as shown in the flowchart of FIG. 4, the measured temperature and the reference temperature are compared between the end of a predetermined print and the start of the next print, and the heat sink is moved based on the comparison result. I will do it. As a result, the heat sink does not move during thermal recording of an image by the thermal head, so that vibrations accompanying the movement of the heat sink are not transmitted to the thermal head. Instead of printing between prints, the heat sink may be moved after thermal recording of an image of a predetermined color is finished and before thermal recording of an image of the next color is started.

  In the above embodiment, the heat sink is arbitrarily moved based on the comparison result between the measured temperature and the reference temperature. Therefore, the heat sink is moved between the retracted position and the contact position regardless of whether the image is recorded or not. Although moved, it may be as follows. In other words, the heat sink is always positioned at the retracted position during image recording by the thermal head, and the heat sink is arbitrarily moved only during non-recording. Thereby, it is possible to always have a high thermal efficiency during image recording.

  In the above embodiment, the heat sink is moved between the retracted position and the contact position based on the comparison result between the measured temperature and the reference temperature. However, the following may be used. That is, the heat sink is periodically displaced at high speed between the contact position and the retracted position while changing the time ratio between the contact position and the retracted position within the unit time. At this time, the multilayer piezoelectric element is given a pulse signal from the piezoelectric element control unit at a duty ratio changed based on the measured temperature. At this time, the higher the measurement temperature, the larger the time ratio of the contact time per unit time to improve the heat dissipation performance. As a result, the temperature of the thermal head can be finely adjusted, and the control performance of temperature control can be improved.

  In the above embodiment, the heat sink is displaced between the contact position and the retracted position, but the distance between the heat sink and the thermal head is arbitrarily set based on the difference between the measured temperature from the temperature sensor and the reference temperature. It may be changed.

  When the heat sink in the above embodiment is a main heat sink, a sub heat sink having lower heat dissipation than the main heat sink may be provided in the thermal head. As shown in FIG. 5, the sub heat sink 40 is fixed to the aluminum substrate 28 of the thermal head 5. Thereby, overheating of the thermal head 5 can be prevented, and the temperature of the thermal head 5 can be further stabilized.

  In the above embodiment, a thermal head used in a thermal printer is taken as an example of a recording head to which a head cooling device is attached. For example, a thermal head used in a thermal transfer printer, a thermal nozzle head used in an inkjet printer, or the like. It may be. Furthermore, the head cooling device of this example may be used in place of a heat sink fixed to a device whose energy efficiency deteriorates at low temperatures.

It is a schematic block diagram of a thermal printer. It is sectional drawing of a thermal head and a head cooling device. It is a graph which shows the temperature change of a thermal head. It is a flowchart which shows operation | movement of the heat sink at the time of printing. It is sectional drawing of the thermal head and head cooling device in another embodiment. It is a graph which shows the temperature change of the conventional thermal head. It is a graph which shows the temperature change of the heat generating element array vicinity in the past.

Explanation of symbols

DESCRIPTION OF SYMBOLS 5 Thermal head 6 Head cooling device 9 System controller 13 Recording paper 27 Heat generating element array 31 Fixing member 32 Multilayer piezoelectric element 33 Heat sink 34 Piezoelectric element drive circuit

Claims (10)

In a head cooling device attached to a recording head that heats a heating element on a head substrate and records an image on a recording material,
A main heat sink that dissipates the heat of the head substrate, a contact position where the main heat sink is brought into contact with the head substrate, and a retreat position where the head substrate is retreated and a gap is formed between the head substrate and the head substrate. A head cooling device comprising a main heat sink moving mechanism for moving.   The main heat sink moving mechanism has one surface bonded to the main heat sink and a relative position between the piezoelectric substrate whose thickness changes according to an electric signal and the head substrate, and is bonded to the other surface of the piezoelectric element. A holding member that holds the main heat sink, and a piezoelectric element control unit that applies an electric signal to the piezoelectric element to control the thickness so as to move the main heat sink to the contact position or the retracted position. The head cooling device according to claim 1.   The main heat sink moving mechanism moves the main heat sink to the retracted position when the temperature of the recording head is below a reference temperature, and contacts the main heat sink when the temperature of the recording head exceeds the reference temperature. The head cooling device according to claim 1, wherein the head cooling device is moved to a position.   The main heat sink moving mechanism moves the main heat sink to the contact position or the retracted position between a recording time when an image is recorded on the recording material by the heating element and a recording time when the image is recorded next. 4. The head cooling device according to claim 1, wherein the head cooling device is performed as described above.   The piezoelectric element control unit uses a plurality of pulse signals generated continuously as the electric signal, and controls the thickness of the piezoelectric element by using the pulse signal, whereby the main heat sink is moved to the contact position and the retracted position. And changing the duty ratio of the pulse signal to change the time ratio between the contact position and the retracted position in unit time to change the heat radiation efficiency. The head cooling device according to claim 2.   The said piezoelectric element control part changes the duty ratio of the said pulse signal so that the time ratio of the said contact time in unit time becomes large, so that the temperature of the said recording head is high. Head cooling device.   The head cooling device according to claim 1, wherein the head substrate includes a sub heat sink whose position is fixed and whose heat dissipation is lower than that of the main heat sink.   2. The recording material according to claim 1, wherein the recording material is a thermal recording paper that develops color when heated, and the recording head is a thermal head that presses the thermal recording paper and the heating element to thermally record an image. Or a head cooling device according to any one of 7 to 7;   The recording material is a color thermal recording paper having a plurality of color-developing layers that are colored in different colors by different thermal energy, and the recording head presses the color thermal recording paper and the heating element for each color. 8. The head cooling apparatus according to claim 1, wherein the head cooling apparatus is a thermal head for thermally recording an image.   A printer comprising the head cooling device according to claim 1.

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