JP2008260153A - Inkjet recording device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an ink jet recording apparatus in which a temperature difference between a discharge nozzle and a non-discharge nozzle is suppressed and uneven density of an image is suppressed.
In an ink jet recording apparatus, the amount of heat absorbed when ink ejected from a heater passes through the nozzle is predicted, and based on this, a short pulse heating amount for a non-ejection nozzle during printing is determined.
[Selection] Figure 1

Description

  The present invention relates to an ink jet recording apparatus used in an image forming apparatus such as a printer, a FAX, and a copying machine. More specifically, the present invention relates to ejection that is applied to a heating unit of a non-ejection nozzle during printing on a recording medium. It relates to the control of the heating amount by no heating signal.

  The ink jet recording apparatus performs image recording such as printing by ejecting ink from a recording head and adhering it to a recording medium. The recording head can be easily made compact and can record high-definition images at high speed. In addition, the running cost is low, the non-impact method is low in noise, and it is easy to record a color image using multi-colored inks.

  Examples of energy generating means for generating energy for ejecting ink in an ink jet recording head include those using an electromechanical transducer such as a piezo element, or those that heat a liquid by an electrothermal transducer having a heating resistor. There is.

  Among them, a recording head of a method (so-called bubble jet (registered trademark) method) that discharges liquid by using thermal energy (using film boiling phenomenon) can arrange the liquid discharge ports at high density. High-resolution recording is possible.

  Thus, the demand for inkjet recording apparatuses is increasing in a wide range of industrial fields as excellent recording means.

  On the other hand, an image formed on a recording medium by an ink jet recording apparatus has a problem that the image density is likely to fluctuate according to a temperature change. This is because the ink composition is sensitive to temperature changes, and as a result, the ejection amount changes depending on the temperature conditions during image formation. That is, when the temperature rises, the viscosity of the ink is lowered and the discharge amount increases.

  In particular, in the case of an ink jet recording apparatus that uses a bubble jet (registered trademark) type recording head that generates heat by causing an electrothermal transducer to boil and discharge ink at that pressure, the temperature of the ink is rapidly increased. There is also a problem that the concentration fluctuation of the water is large.

  For example, when recording is started, the head temperature suddenly rises, and while the recording is continued, the conditions for ink ejection gradually change from immediately after the start of recording, resulting in image distortion. come. On the other hand, if recording is not performed for a while, the head temperature decreases again, the ink viscosity increases, and the discharge amount may decrease.

  As a method of stabilizing the ink ejection state against such temperature changes, the head temperature is increased by preheating the electrothermal transducer with a pulse width or voltage within a range where ink is not ejected. There is a method (for example, refer to Patent Document 1). By performing such heating before recording, the head temperature immediately before recording can be raised, the image density immediately after starting recording increases, and the difference from the temperature when recording continues is reduced. Therefore, unevenness in the formed image can be made difficult to occur.

  However, the number of nozzles of the head tends to increase as the speed and resolution of the ink jet recording apparatus increase. In recent years, if the head is simply heated before recording, frequent ejection is required. If there is a nozzle that was performed in a short time and a nozzle that was hardly ejected, the temperature difference between the nozzles caused a difference in the volume of ink droplets ejected from each nozzle, resulting in unevenness in the image There is.

As a method for controlling such a temperature difference, temperature stability is achieved by applying a signal having a pulse width (so-called short pulse) in a range in which ink is not ejected to heaters other than those involved in recording during printing. ing. (For example, see Patent Document 2)
Japanese Patent Publication No. 5-30627 JP 2001-239655 A

  However, the discharge nozzle to which the print pulse signal accompanying ink discharge is continuously applied and the non-discharge nozzle to which the short pulse signal to which ink is not discharged are continuously applied increase due to a change in the amount of heat carried out by the discharge ink. A difference occurs in the temperature curve, and the temperature difference between the discharge nozzle and the non-discharge nozzle may increase during printing. Hereinafter, this will be described in detail based on the temperature rise curve of FIG.

  After the start of recording on the recording medium, the nozzle temperature rises even if the above-mentioned preheating before recording is performed, and accordingly, the amount of heat that the ejected ink absorbs from the nozzle and is taken out of the head also increases. Go. The width of the print pulse applied to the heater of the nozzle that ejects ink is usually fixed, and the input power to the heater of the ejection nozzle is constant, so if the amount of heat that the ejected ink takes out of the head increases, In addition, the amount of heat accumulated additionally decreases, and as the recording proceeds, the slope of the temperature rise curve of the discharge nozzle tends to become gentle (the time constant is short).

  On the other hand, since the width of the short pulse applied to the non-ejection nozzle is shorter than that of the printing pulse, the input power to the heater is smaller than that of the ejection nozzle, and the temperature rise tends to be lower than that of the ejection nozzle immediately after the start of recording. However, since there is no discharge even during printing, the amount of additional heat accumulated inside the head does not change much (the time constant is long), and the temperature reverses with the discharge nozzle, where the temperature rises decelerate as recording progresses. Even after that, the temperature difference increases until the end of recording.

  When the temperature difference between the ejection nozzle and the non-ejection nozzle increases, a difference occurs in the ink ejection amount due to the temperature difference between the nozzles when a print pulse signal is applied to the non-ejection nozzle.

  That is, even if a short pulse signal is applied to the non-ejection nozzles in order to suppress the density unevenness, there is a problem that the density unevenness of the image is generated as the printing is prolonged.

  Accordingly, an object of the present invention is to suppress an excessive temperature rise of a non-ejection nozzle that applies a short pulse signal in a range where ink is not ejected, and to minimize a temperature difference with the ejection nozzle. Another object of the present invention is to provide an ink jet recording apparatus that suppresses image density unevenness caused by the above.

The present invention has been conceived in order to achieve the above-described object, and the ink jet recording head of the present invention has at least one nozzle array in which nozzles for ejecting ink droplets are arranged in a line by the heat generated by the heating means. In an inkjet recording apparatus that performs recording by moving the recording head or a recording medium in a direction substantially perpendicular to the nozzle row direction.
First heating signal generating means accompanied by ejection of ink droplets for printing, second heating signal generating means not leading to ink droplet ejection, and heating of the nozzles for each raster based on print data Heating signal generation and application means for selecting whether to apply the first heating signal or the second heating signal to the means and applying the selected heating signal to the nozzle heating means. The generating means predicts the amount of heat absorbed by the ejected ink when the first heating signal is applied to the means for heating the nozzle, and the amount of heat absorbed when the ejected ink passes through the vicinity of the means for heating the nozzle. And determining the amount of heating by the second heating signal based on the endothermic amount predicted by the ejected ink endothermic amount predicting means.

  Further, the second heating signal generating means generates a heat amount obtained by subtracting the heat absorption amount predicted by the ejected ink heat absorption amount prediction means from the heat amount by the first heating signal, according to the second heating signal. It is characterized by the heating amount.

  Alternatively, the second heating signal generating means may include a heat amount obtained by subtracting the heat absorption amount predicted by the ejected ink heat absorption amount prediction means from the amount of heat generated by the first heating signal, and the maximum heating that does not lead to discharge. It is characterized in that the smaller one is the amount of heating by the second heating signal.

  The second heating signal is a rectangular pulse signal, and the amount of heating by the second heating signal is adjusted by changing the pulse width of the pulse signal.

  According to the present invention having the above-described configuration, the amount of heat absorbed when the ejected ink passes through the nozzle from the heater serving as the heating means is predicted, and based on this, the second heating signal is obtained. Since the amount of heating by the short pulse signal is determined, even if the temperature of the nozzle rises and the heat absorption amount of the ejected ink increases, the amount of heating by the short pulse signal can be reduced by that amount and the head can store excessive heat. As a result, it is possible to provide an ink jet recording apparatus in which the temperature difference between the ejection nozzles and the non-ejection nozzles is suppressed and the uneven density of the image is suppressed.

(First embodiment)
FIG. 1 is a block diagram showing a schematic configuration of a head driving unit in the ink jet recording apparatus according to the first embodiment of the present invention. The head driving unit in the ink jet recording apparatus of the present embodiment mainly includes a recording head 1, an image generation circuit 2, a head drive signal generation circuit 3, a print pulse generation circuit 4, a short pulse generation circuit 5, and a head controller. 6.

  In FIG. 2, an image generation circuit 2 performs rasterization based on original image data, document data, and the like, and outputs the result to the head drive signal generation circuit 3 as raster data as shown in FIG. The print pulse generation circuit 4 continuously generates a print pulse having a height Vh (V) and a width pw1 (second) in synchronization with the ejection clock as shown in FIG. 2 to generate a head drive signal. Output to circuit 3. The short pulse generation circuit 5 generates a short pulse for each raster so that the temperature difference between the discharge nozzle and the non-discharge nozzle is minimized based on the temperature data detected by the temperature sensor built in the head chip. The optimum width pw2 is obtained, continuously generated in synchronization with the ejection clock as shown in FIG. 2, and output to the head drive signal generation circuit 3. A more detailed method for obtaining pw2 will be described later.

  The head drive signal generation circuit 3 extracts a print pulse if the raster data is “1”, extracts a short pulse if the raster data is “0”, and connects them in synchronization with the ejection clock, and uses the nozzle address as a drive signal. Together with the signal, it is output to the head controller 6.

  The head controller 6 collects the nozzles of the recording head 1 in units of blocks based on the address signal, and applies a drive signal to the heaters of the nozzles of the blocks collectively for each block.

  The recording head 1 is shown as a full-line head in which a plurality of head chips are arranged in series, but may be a serial head in which one or a plurality of head chips are arranged in parallel. .

  FIG. 3 is a plan view and a cross-sectional view showing the structure around the head chip in the ink jet recording apparatus of this embodiment.

  The head chip 20 is bonded and fixed to the base plate 10 so that the ink supply port 21 is aligned with the ink supply path 11 formed in the base plate 10. The head chip 20 has two nozzle rows 22 and 23 formed on the surface opposite to the ink supply side. The nozzle rows 22 and 23 share the ink supply port 21 and are supplied with ink through the ink supply path 11. The nozzle row 22 is provided at a pitch of 600 dpi, and the nozzle row 23 is provided at the same pitch as the nozzle row 22 so as to complement the nozzles of the nozzle row 22, and printing of 1200 dpi can be performed in two rows. Yes.

  The ink supplied to the nozzle rows 22 and 23 generates bubbles due to a phase change by a print pulse signal applied to the heater of each nozzle, and ink droplets are pushed out from the ejection openings. At this time, the ink droplet takes heat from the heater inside the nozzle and takes it out of the head. The difference in the heat dissipation path from the nozzle to which a short pulse signal is applied to the heater is mainly the presence or absence of heat that the ejected ink brings out, and this is accurately estimated and reflected in the width of the short pulse to increase the non-ejection nozzle. The temperature curve can be made substantially equivalent to the temperature rise curve of the discharge nozzle.

  The heat taken by the ejected ink from the heater is obtained by integrating the heat flux between the heater and the ink over the entire heater surface and one ejection cycle, but it is difficult to detect the heat flux between the heater and the ink. It substitutes by estimating the heat balance of the ink in the nozzle, that is, the difference in heat quantity between the ink flowing out from the nozzle and the ink flowing into the nozzle. In this embodiment, the nozzle temperature (= temperature of the ejected ink) is estimated from the detection results of the four temperature sensors 31 adjacent to the nozzle row incorporated in the head chip 20, and the temperatures of the four locations adjacent to the ink supply port are estimated. The temperature of the ink flowing into the nozzle is estimated from the detection result of the sensor 32, and the difference ΔTnz is multiplied by the thermal capacity of the ejected ink (= ink droplet volume Ui × ink specific heat Ci). The heat Qiout to take.

Qiout = Ui · Ci · ΔTnz (Formula 1)
As a method of estimating the nozzle temperature and the inflow ink temperature from the detection results of the temperature sensors 31 and 32, for example, a method of estimating and modeling the temperature sensor to the temperature estimation unit as a distributed constant model is conceivable.

  By subtracting the heat Qiout taken by the ejected ink from the heater from the heating amount Qh of the printing pulse as the short pulse heating amount Qsp, the Qsp substantially coincides with the amount of heat accumulated in the head chip due to ink ejection. The temperature difference between the nozzle and the non-ejection nozzle can be minimized.

Qsp = Qh−Qiout (Formula 2)
The short pulse width pw2 at this time is calculated from the print pulse width pw1 as shown in the following equation.

pw2 = pw1 (1-Qiout / Qh) (Formula 3)
However, the short pulse width pw2 is finally calculated as follows so that the maximum short pulse width pw2max that does not lead to ejection is not exceeded.

pw2 = MIN ((pw2max, pw1 (1-Qiout / Qh)) (Formula 4)
The short pulse width pw2 is obtained for each raster from (Expression 1) and (Expression 4), and is output to the head drive signal generation circuit 3 as a short pulse signal by the short pulse generation circuit 5.

  Examples of the short pulse width obtained as described above are shown in FIGS.

  FIG. 4 shows typical nozzles when printing of all solids (print pulse signals are continuously applied to all nozzles) is started from a reference temperature on five recording sheets by the ink jet recording apparatus of this embodiment. FIG. 6 is a diagram showing the temperature profile of the ink and the ink inflow temperature to the nozzle. The supplied ink temperature is a reference temperature, and printing on one sheet of recording paper is composed of, for example, 9600 rasters.

  In the figure, the discharge nozzle temperature rises rapidly in each printing section, whereas the ink has a large heat capacity and low thermal conductivity, so it is difficult to raise the temperature, and low-temperature ink is refilled one after another. The temperature gradually increases and the temperature change in the printing section is small.

  If this temperature profile is estimated from the detection results of the temperature sensors 31, 3231, 32, a difference ΔTnz between the discharge nozzle temperature and the ink temperature flowing into the nozzle is obtained for each raster from the graph. FIG. 5 is a graph showing the short pulse width pw2 for each raster in each printing section from the obtained ΔTnz and (Expression 1) and (Expression 3), together with the positions of pw1 and pw2max.

  In the figure, it can be seen that the short pulse width pw2 is limited to pw2max immediately after the start of printing in each printing section, but then suddenly decreases as the discharge nozzle rises in temperature.

  As described above, with the configuration shown in this embodiment, it is possible to suppress an excessive temperature rise of the non-ejection nozzle due to the application of a short pulse signal in a range where ink is not ejected, and to minimize the temperature difference from the ejection nozzle. The density unevenness of the image due to the temperature difference between the nozzles can be suppressed.

(Second embodiment)
As shown in FIG. 5 showing an example of the change in the short pulse width in the ink jet recording apparatus of the first embodiment, in continuous printing, the decrease curve of the short pulse width is almost the same in each printing section as the number of printed sheets advances. It becomes. If the temperature is adjusted by preheating the nozzles and the reference temperature is raised to a temperature in a thermal equilibrium state, the short pulse width decrease curve in each printing section settles into a certain shape earlier. Therefore, in the second embodiment of the present invention, instead of estimating the heat taken by the ejected ink from the heater for each raster for each page and determining the short pulse width, it is determined in advance for each raster in the printing section.

  FIG. 6 is a block diagram illustrating a schematic configuration of a head driving unit in the ink jet recording apparatus of the present embodiment. In this embodiment, unlike the first embodiment, the detection result by the temperature sensor is not fed back to obtain the short pulse width. Accordingly, the temperature data detected by the temperature sensor from the recording head 1 to the short pulse generation circuit 5 is not output. Since the other configuration conforms to the first embodiment, the description is omitted.

  FIG. 7 is a graph showing the width of the short pulse generated by the short pulse generating circuit 5 in the printing section. Based on this short pulse width curve, the same short pulse is applied to each non-ejection nozzle heater.

  As shown in FIG. 8, the printing section may be divided into, for example, three small sections, and the same short pulse width may be applied to the heaters of the non-ejection nozzles in each raster of each small section.

  As described above, the configuration of the head drive unit can be simplified by using the configuration shown in the present embodiment, and the temperature difference between the discharge nozzle and the non-discharge nozzle is minimized with a simple configuration. It is possible to suppress the density unevenness of the image due to the temperature difference between the nozzles.

1 is a block diagram illustrating a schematic configuration of a head driving unit in an ink jet recording apparatus according to a first embodiment. Timing chart of various signals synchronized with the ejection cycle of the first embodiment The top view and sectional drawing showing the structure around the head chip in the ink jet recording apparatus of the first embodiment The figure which showed the temperature profile of a typical nozzle, and the ink inflow temperature to a nozzle when printing of all the solids was started from the reference temperature continuously with five recording paper with the inkjet recording device of 1st Example. FIG. 5 is a graph obtained by calculating the short pulse width for each raster in each printing section in the first embodiment. The block diagram showing the schematic structure of the head drive part in the inkjet recording device of 2nd Example. The graph which made the short pulse width in 2nd Example a graph in a printing area. The figure which plotted another example of the short pulse width in 2nd Example in the printing area A graph showing the temperature rise curves of the discharge nozzle and non-discharge nozzle of the conventional example

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Recording head 2 Image generation circuit 3 Head drive signal generation circuit 4 Print pulse generation circuit 5 Short pulse generation circuit 6 Head controller 10 Base plate 11 Ink supply path 20 Head chip 21 Ink supply port 22, 23 Nozzle row 24, 25 Heater 31, 32 Temperature sensor

Claims (7)

A recording head having at least one nozzle row in which nozzles for ejecting ink droplets by heat generated by the heating means are arranged in a row, and the recording head or the recording medium is moved in a direction substantially perpendicular to the nozzle row direction; In an inkjet recording apparatus that performs recording,
First heating signal generating means accompanied by ejection of ink droplets for printing, second heating signal generating means not leading to ink droplet ejection, and heating of the nozzles for each raster based on print data Heating signal generation and application means for selecting whether to apply the first heating signal or the second heating signal to the means and applying the selected heating signal to the nozzle heating means. The generating means predicts the amount of heat absorbed by the ejected ink when the first heating signal is applied to the means for heating the nozzle, and the amount of heat absorbed when the ejected ink passes through the vicinity of the means for heating the nozzle. An ink jet recording apparatus, wherein the heating amount by the second heating signal is determined based on the endothermic amount predicted by the ejected ink endothermic amount prediction means.   The second heating signal generating means generates a heat amount obtained by subtracting the heat absorption amount predicted by the ejected ink heat absorption amount prediction means from the heat amount obtained by the first heating signal, and the heating amount by the second heating signal. The inkjet recording apparatus according to claim 1, wherein:   The second heating signal generating means includes a heat amount obtained by subtracting an endothermic amount predicted by the ejected ink endothermic amount predicting means from a heating amount by the first heating signal, and a maximum heating amount that does not lead to ejection. 2. The ink jet recording apparatus according to claim 1, wherein the smaller one is set as a heating amount by the second heating signal.   The said 2nd heating signal is a rectangular-shaped pulse signal, The heating amount by the said 2nd heating signal is adjusted by changing the pulse width of the said pulse signal, It is characterized by the above-mentioned. Inkjet recording apparatus.   The ejected ink heat absorption amount predicting means predicts an outflow heat amount taken out from the nozzle by application of the first heating signal to the heating means of the nozzle and an inflow heat amount brought in by the ink flowing into the nozzle. 4. The ink jet recording apparatus according to claim 1, wherein a heat amount obtained by subtracting the inflow heat amount from the outflow heat amount is set as a heat absorption amount of the ejected ink.   The discharge ink heat absorption amount prediction means prepares for each raster the heat amount directly absorbed by the discharge ink from the nozzle heating means as heat absorption amount data, and discharges each raster with reference to the previous heat absorption amount data. 4. The ink jet recording apparatus according to claim 1, wherein the ink heat absorption amount is a predicted value.   The discharge ink heat absorption amount prediction means predicts or detects the nozzle temperature and the ink temperature flowing into the nozzle, obtains the outflow heat amount from the nozzle temperature, the discharge ink capacity, and the specific heat of the ink, and calculates the ink flowing into the nozzle. 6. The ink jet recording apparatus according to claim 5, wherein the inflow heat amount is obtained from a temperature, a discharge ink capacity, and a specific heat of the ink.

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