JP2008126623A - Inkjet recorder with head temperature controlling means - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve a decrease in throughput due to repeated heating processing keeping on until a temperature difference generated between a head temperature and an ink temperature is removed because a recording head temperature detecting means is present on a head surface and no ink temperature detecting means of an ink liquid chamber near nozzle arrays of the recording head is present, and consequently the head temperature reaches a heating threshold temperature before the ink is fully heated, stopping head heating control to result in generation of the temperature difference in relation to a head temperature control method in an inkjet recorder which carries out recording utilizing a thermal energy. <P>SOLUTION: The inkjet recorder has a heating means which instantaneously produces a recordable state by executing a heating means taking an ink of a large heat capacity into account when a detected temperature T0 of the recording head is lower than the heating threshold temperature Th. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a head temperature control method in an ink jet recording apparatus that performs recording using thermal energy, and relates to head temperature control in consideration of ink heat capacity.

  2. Description of the Related Art Conventionally, in an inkjet recording apparatus or the like, it is known that various adverse effects occur due to changes in environmental temperature or the temperature of a head in which recording elements are integrated. This is because physical property values such as ink viscosity and surface tension change depending on the temperature. Further, in a so-called bubble jet (registered trademark) recording method in which bubbles are generated in ink by heat energy and ink is discharged by the generation of bubbles, the conditions for generating bubbles change due to temperature changes.

  When such a change in physical property value of ink and a change in bubble generation conditions occur, variations occur in the ink droplet ejection amount and landing accuracy in the recording head, resulting in density fluctuations, density unevenness, and color change. It will occur.

  Therefore, temperature control of the head is important in the ink jet recording apparatus. Conventional temperature control uses a heater for heating the print head (a heater dedicated to temperature control or a heater for both ink discharge and temperature control) and a temperature sensor that detects the temperature related to the print head. Some have a configuration in which a temperature detected by a sensor is fed back to a heating amount by a heater. In addition, there is an apparatus that enables open loop control that can adjust the heater to an arbitrary temperature set without performing feedback control as described above (see Patent Document 1) (see Patent Document 2).

  As such a heater control method for the recording head, a method for constantly adjusting the head temperature (by feedback control based on the detected temperature), a method for adjusting the head temperature at regular intervals (by feedback control based on the detected temperature). ), A method of adjusting the head temperature when the head temperature becomes higher than the ambient temperature (by feedback control based on the detected temperature), and a method of performing the pulse width modulation of the heat pulse.

  In the above conventional temperature control method, the head temperature and the reference temperature are compared in real time, and the head temperature is generally controlled by applying a non-recording pulse to the head based on the difference between the head temperature and the reference temperature. (See Patent Document 3), (see Patent Document 4).

  There is also a technique for preheating the recording head during paper feeding or during acceleration or deceleration of the recording head (see Patent Document 5).

  In addition, there is a technique that suppresses fluctuation in the ejection amount from the recording head due to the head temperature and reduces self-temperature rise by changing the waveform of the drive signal based on the head temperature (see Patent Document 1).

  Further, as an effective head heating method, there is a technique in which heating is performed by a discharge heating unit up to a first temperature and heating is performed by a sub-heating unit having a sub-heater up to a second temperature higher than the first temperature (Patent Document). 6).

  Further, there is a technique of heating a recording head at a timing corresponding to a transport operation of each transport unit when a plurality of transport units are provided (see Patent Document 7).

  Also, the higher the quality of an image to be recorded, the greater the adverse effects caused by changes in density and color due to head temperature. Therefore, depending on whether the type of recording object is a character or an image, the head In order to change the discharge amount, the temperature is controlled according to the type of recording (see Patent Document 8).

  However, in the above control, there is a problem that the throughput is greatly reduced by providing the heating time of the head.

Therefore, as a method for solving the control problem, in the head temperature control method, a heating step for heating the recording head, a temperature detection step for detecting the head temperature of the recording head, and the temperature of the recording head, Prior to the recording operation, a comparison step for comparing with a predetermined heating threshold temperature and setting of a heating mode in which the recording head can be heated when the temperature detected by the temperature detection means is lower than the heating threshold temperature. A heating mode setting step to be performed, and a control step for controlling the heating means according to whether or not a comparison result by the comparison means and a heating mode are set, wherein the control step is set by the heating mode. And when the detected temperature of the recording head is lower than the heating threshold temperature, the heating step causes the recording head to There are control method and performing heat (see Patent Document 9), (see Patent Document 10).
JP-A-5-31905 Japanese Patent Laid-Open No. 5-220964 Japanese Patent Laid-Open No. 5-124195 JP-A-7-195698 JP-A-11-34260 Japanese Patent Laid-Open No. 5-220965 Japanese Patent Laid-Open No. 5-96718 JP-A-5-031886 JP 2003-39641 A JP 2003-39642 A

  However, even in the above-described control, even if the recording head is heated and reaches the heating threshold temperature immediately after the start of printing standby, the ink temperature does not rise immediately, and a temperature difference occurs between the head temperature and the ink temperature. For this reason, since the heat treatment is repeatedly performed until the temperature difference is eliminated, it takes time to raise the head temperature immediately after the ink-jet recording apparatus is turned on, and the throughput is reduced. This is because the head temperature detection means is on the head surface and there is no temperature detection means for the ink inside the head, so that the head temperature reaches the heating threshold temperature and the head heating control stops before the ink is sufficiently heated. Is the cause. Originally, it is desirable to detect not only the head temperature but also the ink temperature, but providing a plurality of temperature detecting means causes an increase in cost.

  Therefore, the present invention has the following configuration in order to further improve the throughput. That is, in the ink jet recording apparatus, heating is performed in consideration of ink having a large heat capacity as a heating means for heating the recording head.

  In the present invention having the above configuration, for example, the head temperature T0 and the heating threshold temperature Th are compared immediately after the start of printing. When the comparison result is T0 ≦ Th, the recording head is heated. The heat capacity applied in this heating is a heat capacity that raises the ink amount in the ink liquid chamber near the nozzle array of the recording head from the head temperature T0 to the heating threshold temperature Th. Q = H * A * (Th−) where A [g] is the ink amount in the ink liquid chamber near the nozzle row of the recording head, H [J / g · K] is the specific heat of the ink, and Q [J] is the heat capacity. T0).

  Therefore, the time Sh [s] required to heat the recording head to the heating threshold temperature Th is Sh = (H * A * (Th−T0), where W is the average power applied to the recording head. ) / W.

  As described above, by adding a heat capacity in consideration of the ink amount and specific heat of the liquid chamber provided in the recording head immediately before the start of printing standby, a plurality of temperature detecting means for detecting the environmental temperature and the ink temperature, Even if no correction means or the like is provided, it is possible to heat the head with only the head temperature detection means and without excess or shortage in a short time.

  A conventional heating operation sequence in the ink jet recording apparatus will be described with reference to FIG.

  Currently, after the ink jet recording apparatus is powered on and the ink jet recording apparatus is initialized, the main heating operation sequence is executed every 10 ms when waiting for printing. At that time, the head temperature T0 detected by the head temperature sensor is read (S11), and the read head temperature T0 is compared with a preset reference temperature Th (= 25 ° C.) (S12). If the head temperature is higher than the preset reference temperature, the head heating control is stopped (S14), and the heating sequence ends. If the head temperature is lower than the reference temperature, head heating control is started (S13).

  FIG. 2 shows a change state of the head temperature and ink temperature immediately after the start of heating control (start of printing standby) executed by the control operation shown in FIG. When the head temperature is equal to or lower than the heating threshold temperature, the heating process is performed for a predetermined time so as to reach the heating threshold temperature. When the head temperature reaches the heating threshold temperature, the heating process is stopped. However, if the ink is not sufficiently heated immediately after the start of the heating control, the head temperature decreases immediately after heat is transferred from the head to the ink. Therefore, the heating process is repeated until the ink temperature reaches the heating threshold temperature. . This is because the conventional head heating control does not consider the ink capacity.

  Therefore, originally, it is desirable to detect not only the head temperature but also the ink temperature and the environmental temperature, and stop the heat treatment after the ink temperature reaches the heating threshold temperature. However, it is possible to provide a plurality of temperature detecting means. This will increase costs. In addition, when detecting the environmental temperature, in order to eliminate the influence of heat generated by the drive of the printing apparatus, the temperature detection means is kept away from the heat generation point in the printing apparatus, or the temperature detection means is installed on the same substrate. In such a case, it is necessary to estimate the ambient temperature while adding correction while taking into consideration the influence of heat generation, resulting in increased cost and complicated control.

  Therefore, in the present invention, the following control is performed. A heating operation sequence executed immediately after the start of printing standby in the ink jet recording apparatus will be described with reference to FIG.

  Immediately after the start of printing standby, the head temperature T0 detected by the head temperature sensor is read (S21), and the read head temperature T0 is compared with a preset heating target temperature Th (= 25 ° C.) (S22). When the head temperature is higher than a preset reference temperature, the heating sequence ends. If the comparison result is T0 ≦ Th, the heat capacity is added to the recording head (S23). The heat capacity applied at this time is a heat capacity for raising the ink amount in the ink liquid chamber near the nozzle array of the recording head from the head temperature T0 to the head heating threshold temperature Th. The ink amount in the ink liquid chamber near the nozzle row of the recording head is determined by the structure of the head. The ink amount in the ink liquid chamber in the vicinity of the nozzle row of the recording head (S31 in FIG. 5) is A [g], and the specific heat of the ink is calculated. If H [J / g · K] and the heat capacity is Q [J], then Q = H * A * (Th−T0). Therefore, the time Sh [s] (S24) required for heating the recording head to the predetermined heating threshold temperature Th is Sh = (H, where the average power of the recording head is W [J / s]. * A * (Th-T0)) / W.

  FIG. 4 shows a change state of the head temperature and ink temperature immediately after the start of heating control (start of printing standby) executed by the control operation shown in FIG. When the head temperature is equal to or lower than the heating threshold temperature, heating is performed by adding a heat capacity considering the ink amount and specific heat so that the head instantaneously reaches the heating threshold temperature. At that time, the head temperature once rises above the heating threshold temperature, but the ink temperature instantaneously reaches the heating threshold temperature, and then the entire head temperature becomes the heating threshold temperature.

  Hereinafter, a heating control operation by the ink jet recording apparatus according to the present embodiment will be described.

First, the average power W applied to the recording head is as follows. The driving voltage of the recording head is 17.2 V, the discharge heater resistance (1 nozzle) of the recording head is 100Ω, and the number of nozzles of the recording head is 640 nozzles.
W = (17.2) ² /100*640=1893.3 [W].

The heat capacity Q applied to the recording head is such that the head temperature T0 detected by the head temperature sensor immediately after the start of printing standby is 15 [° C.], the heating threshold temperature Th is 25 [° C.], and the ink liquid near the nozzle row of the recording head. When the ink amount in the chamber is 0.13 [g] and the specific heat of the ink is 4.2 [J / g · K],
Q = (25-15) * 4.2 * 0.13 = 5.46 [J].

Accordingly, the time Sh [s] required to heat the recording head to the heating threshold temperature Th is 0.6 [μs] for the non-recording pulse time of the recording head and 55.5 [μs] for the driving cycle. Then,
Sh = (5.46 / 1893.3) * (55.5 * 10 ⁻⁶ /0.6*10 ⁻⁶ ) = 266.74 [ms].

It is a flowchart which shows the control operation in the conventional inkjet recording device. FIG. 2 is a diagram showing a state of temperature change of the recording head by the control operation shown in FIG. 3 is a flowchart showing a control operation in the ink jet recording apparatus according to the present invention. FIG. 6 is a diagram showing a temperature change of a recording head in the present invention. FIG. 3 is a schematic cross-sectional view for explaining an ink liquid chamber in the vicinity of a nozzle row of a recording head in the present invention.

Explanation of symbols

T0 Head temperature [° C]
Th Heating threshold temperature [° C]
A Mass of ink in the ink liquid chamber near the nozzle row [g]
H Specific heat of ink in the ink chamber near the nozzle row [J / g · K]
Q Energy corresponding to the heat capacity to raise the head temperature T0 to the heating threshold temperature Th [J]
W Average power of the recording head [J / s]
Sh Time [s] required to heat the recording head to a predetermined heating threshold temperature Th

Claims (3)

An ink jet recording apparatus that performs recording by ejecting ink from a nozzle provided in a recording head onto a recording medium includes the following means.
Heating means for heating the recording head without ejecting ink; temperature detecting means for detecting the head temperature of the recording head; comparing means for comparing the temperature of the recording head with a predetermined heating threshold temperature Th; and the temperature detecting means When the detected temperature T0 of the recording head is lower than the heating threshold temperature Th, the energy Q corresponding to the difference (Th−T0) between the heating threshold temperature Th and the detected temperature T0 of the recording head is set before the recording operation. And means for supplying the recording head with heating means.
An ink jet recording apparatus comprising the above means. 2. The energy Q according to claim 1, wherein the amount of ink in the ink liquid chamber near the nozzle row of the recording head is A [g] and the specific heat of the ink is H [J / g · K].
Q = A * H * (Th−T0)
An ink jet recording apparatus characterized by the above. 3. The heating time Sh [s] by the heating means is Sh = (A * H * (Th−T0)) / W, where the average power of the recording head is W [J / s].
An ink jet recording apparatus comprising: a heating time control means for controlling to become.

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