JP2004122533A - Inkjet recording device and inkjet recording method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an inkjet recording device which can jet a thickened ink in a recording head at the time of a recording operation without executing a different recovery operation from the recording operation, and to provide an inkjet recording method. <P>SOLUTION: A time while a jetting opening of the recording head 1 is exposed is measured by a timer 9. A jetting energy of ink to be impressed to the recording head 1 at the time of the recording operation is changed by a drive signal control part 5 in accordance with the measured time. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an inkjet recording apparatus and an inkjet recording method for recording on a recording medium using a recording head capable of discharging ink from a discharge port.
[0002]
[Prior art]
In the ink jet recording apparatus, the discharge port of the ink jet recording head is always exposed to the atmosphere during recording. That is, the plurality of ejection ports of the recording head are always exposed to the atmosphere during recording so that ink can be ejected immediately according to image data. At times other than recording, the ejection ports are usually capped by cap means. Therefore, as the printing operation time becomes longer, with respect to the nozzles that are not used for printing (nozzles that do not eject ink), the moisture in the ink in the nozzles evaporates and the viscosity of the ink increases. As a result, when another image is to be recorded using a nozzle whose ink has increased in viscosity, the ejection of ink from the ejection port of the nozzle may be unstable.
[0003]
[Problems to be solved by the invention]
However, in the above-described conventional example, particularly when recording is performed in a low-temperature and low-humidity environment using ink that tends to thicken, it is necessary to perform a recovery operation at short intervals. The recovery operation is an operation for maintaining a good ink discharge state in the recording head by, for example, discharging the thickened ink in the nozzle. For example, if the allowable exposure time (exposure time that enables stable ink ejection when the ejection opening of the recording head is exposed to the atmosphere) is only 5 seconds under a certain temperature and humidity environment, When recording based on variable image data, it is necessary to perform a recovery operation every several recordings, depending on the size of the paper. Therefore, the recording speed may be extremely reduced. Further, with the frequent recovery operation, the number of times ink is ejected from the recording head increases, so that the life of the recording head may be shortened.
[0004]
SUMMARY OF THE INVENTION An object of the present invention is to provide an ink jet recording apparatus and an ink jet recording method capable of discharging a thickened ink in a recording head during a recording operation without executing a recovery operation different from a recording operation.
[0005]
An object of the present invention is to provide an ink jet recording apparatus and an ink jet recording method capable of discharging a thickened ink in a recording head.
[0006]
[Means for Solving the Problems]
The inkjet recording apparatus of the present invention uses a recording head capable of ejecting ink from a plurality of ejection ports, and in an inkjet recording apparatus that performs recording on a recording medium, a time period during which the ejection ports of the recording head are exposed. It is characterized by comprising a time measuring means for measuring, and a variable means for changing the ejection energy of the ink applied to the ejection port of the recording head at the time of the recording operation in accordance with the time measured by the time measuring means.
[0007]
An ink jet recording method according to the present invention is an ink jet recording method for performing recording on a recording medium using a recording head capable of discharging ink from a plurality of discharge ports, wherein in the time when the discharge ports of the recording head are exposed. Accordingly, the discharge energy of the ink applied to the print head during the printing operation is changed.
[0008]
BEST MODE FOR CARRYING OUT THE INVENTION
(1st Embodiment)
First, a basic configuration example of an ink jet recording apparatus to which the present invention can be applied will be described.
[0009]
The ink jet recording device controls the amount of ink discharged by controlling the pulse width of the recording head drive signal according to the temperature of the recording head or the environmental temperature, taking into account the temperature dependence of the ink discharged from the recording head. There is something to do. With such control, even if the temperature of the recording head or the environmental temperature changes, the amount of ink discharged is kept within a predetermined constant range, and stable image formation is performed.
[0010]
As the driving pulse of the recording head during the recording operation, for example, two separated pulse signals (double pulses) can be used. FIG. 2 is a diagram showing the waveform of the double pulse. The pulse signal is applied as a driving pulse to an ink jet recording head of a type in which ink droplets are ejected from nozzles by the heat generated by a heater (electrothermal transducer). In this recording head, the ink in the nozzles is foamed by the heat generated by the heater, and ink droplets are ejected from the ejection ports by the foaming energy. In FIG. 2, P1 indicates a preheat pulse width, P2 indicates an off time, and P3 indicates a main heat pulse width. During the printing operation, pulses are applied to the heaters of the printing head in the order of P1, P2, and P3, and each printing head of each ink color is driven based on an output value from a Di sensor as a temperature detecting unit in the printing head. The pulse width of the pulse is determined to control the ink ejection amount. P1 is a preheat pulse, which mainly plays a role of raising the ink temperature in the nozzles of the print head. P3 is a main heat pulse, which plays a role of stably ejecting ink droplets. That is, a bubbling phenomenon occurs in the ink on the heater, and ink droplets are ejected from the ejection ports by the bubbling energy. The pulse width of P1 needs to be set so that the foaming (pre-foaming) phenomenon does not occur in the ink due to the preheat pulse P1. P2 is an off time, and the discharge amount is controlled according to the width. In accordance with the widths P1, P2, and P3 of such drive pulses, the ejection energy of the ink applied to the recording head changes.
[0011]
In order to keep the ink ejection amount constant even if the printhead temperature rises due to continuous printing or changes in the environment, a table in which the printhead temperature and the optimal drive pulse are associated with each other is required. Can be used. At the time of actual printing, the temperature detected by the Di sensor in the print head is read, an optimum drive pulse corresponding to the head temperature is selected from a table, and the print head is driven based on the drive pulse. Such driving is referred to as PWM driving (Pulse Width Modulation; PWM), and a table of such driving pulses is referred to as a PWM table. FIG. 3 is an example of a PWM table, in which drive pulses whose widths of P1, P2, and P3 are adjusted so as to correspond to the head temperature detected by the Di sensor are ranked (ranks 1 to 12). . The higher the head temperature, the higher the rank and the smaller the discharge energy of the drive pulse.
[0012]
By the PWM drive using such a drive pulse, the ink ejection amount can be controlled. As a result, a change in the ink ejection amount due to a rise in the temperature of the recording head and a change in the environment can be suppressed, and It is possible to stabilize the density of the recorded image. Since the ink can be discharged with a smaller energy as the temperature increases, the PWM table is set so that the discharge energy applied to the print head is reduced as the temperature increases.
[0013]
4A and 4B are explanatory diagrams of a drive pulse applied to a heater of a nozzle that discharges ink during printing.
[0014]
As a driving pulse, a single pulse as shown in FIG. 4B may be applied to a heater of a nozzle which ejects ink at the time of recording, in addition to a double pulse as shown in FIG. In the ink jet recording head, the heater in the nozzle generates heat by such a driving pulse, and the ink is ejected from the ejection port with the bubbling of the ink in the nozzle due to the heat generation. Therefore, during recording, heat is applied to the nozzles.
[0015]
FIG. 5 is a schematic explanatory diagram of a configuration example of the ink jet recording apparatus. The paper (recording medium) 3 is transported by the transport device 4 in the direction of arrow C from the upstream side (paper feed side A) to the downstream side (paper discharge side B). The transport device 4 has, for example, a transport belt 4c stretched between pulleys 4a and 4b, and transports the sheet 3 in the direction of arrow C together with the transport belt 4c. When the paper 3 passes under the recording head 1, an image is formed on the paper 3 by discharging ink from the discharge ports of the nozzles 2 of the recording head 1. The recording head 1 has a long length in which a plurality of nozzles having ejection ports for ejecting ink are arranged so as to extend over the entire area of the recording surface in the width direction of the sheet 3 (the direction of the front and back of the sheet in FIG. 5). This is a recording head, and a plurality of recording heads are provided at equal intervals according to the color of ink to be ejected. Accordingly, an image is formed on the paper 3 by ejecting ink from the recording head 1 while continuously transporting the paper 3 in the direction of arrow C. A recording apparatus of such a type is generally called a full line type printer.
[0016]
FIG. 6 is a schematic block configuration diagram around the inkjet recording head 1.
[0017]
Reference numeral 1 denotes one of a plurality of recording heads, includes a plurality of nozzles provided with ejection ports for ejecting ink, and further includes a plurality of Di sensors 6 for one recording head 1 as a temperature sensor. Are provided at predetermined intervals. The recording head 1 generally includes a cap member for capping a plurality of nozzles, and is configured such that the cap member exposes the ejection openings of the plurality of nozzles during a printing operation. Reference numeral 7 denotes a temperature detection unit which detects temperature information of the Di sensor 6 and sends the detected information to the drive signal unit 5. The drive signal control unit 5 includes a processing unit CPU, a program memory ROM, and a data memory RAM, and receives image data from an external host computer and controls recording. The processing unit CPU reads the program stored in the program memory ROM and controls the entire recording device. The program memory ROM stores programs and tables (FIGS. 3 and 7) corresponding to the flow shown in FIGS. 1 and 10 described below. The data memory RAM stores image data and control parameters (timer value, temperature information, etc.) as necessary. Reference numeral 8 denotes a temperature / humidity sensor for detecting the temperature in the recording apparatus, from which information is read by the drive signal control unit 5. Reference numeral 9 denotes a timer, the measured time of which is read by the drive signal control unit 5.
[0018]
During a printing operation, a drive pulse is sent from the drive signal control unit 5 to the print head 1 to eject ink from nozzles used for printing, and ink is ejected from designated nozzles to form an image. At the time of recording, a temperature detected by a Di sensor 6 as a temperature detecting means mounted in the recording head 1 is read by a temperature detecting unit 7, and based on the detected temperature, an optimum drive pulse is determined by a PWM table as shown in FIG. And the drive pulse is sent from the drive signal controller 5 to the recording head 1 (PWM control). The Di sensor 6 in the recording head 1 is provided at an appropriate location so that the temperature near the nozzle in the recording head 1 can be detected. Recording and other temperature control are performed based on the temperature read from the Di sensor 6. As described above, 8 is a temperature and humidity sensor for detecting the temperature and humidity inside the printing apparatus, that is, the temperature and humidity around the print head 1, and 9 is a timer for measuring time. is there.
[0019]
When performing the recovery operation for keeping the ink ejection state of the recording head 1 good, a temperature and humidity table can be used.
[0020]
That is, a temperature / humidity table is created by associating the environment (temperature and humidity) of the printing apparatus with the time during which the discharge port of the print head is exposed to the atmosphere (hereinafter also referred to as “exposure time”). This temperature / humidity table shows the temperature and humidity inside the printing apparatus, and the exposure time during which stable ejection of ink is possible when the ejection port of the inkjet recording head is exposed to the atmosphere under the conditions of the temperature and humidity. (Hereinafter also referred to as “permissible exposure time”). FIG. 7 is an example of such a temperature and humidity table. Basically, when the humidity is low, the viscosity of the ink in the nozzles tends to increase, so that the permissible exposure time during which stable ink ejection is possible is shortened, and when the humidity is high, the permissible exposure time is prolonged.
[0021]
At the start of recording, the temperature and humidity inside the recording device are detected by the temperature and humidity sensor 8 inside the recording device, and the allowable exposure time according to the detected temperature and humidity is detected by using the temperature and humidity table as shown in FIG. T can be determined. In FIG. 7, the temperature is ° C., the humidity is%, and the exposure time T is seconds. The exposure time t (second) during which the discharge port of the ink jet recording head is exposed to the atmosphere is counted by a timer 9 installed in the printing apparatus. Basically, when the exposure time t reaches the allowable exposure time T (t = T), a recovery operation for ejecting the thickened ink in the nozzles by a job for the next printing operation is performed. Execute. However, if the job at this time performs a printing operation based on the same image data as the previous job, the same nozzle is used, and no recovery operation is required. The recovery operation is performed separately from the printing operation, and the thickened ink discharged from the discharge port of the nozzle is received in the cap of the cap unit or the like, and does not contribute to the printing of an image.
[0022]
When performing a printing operation based on image data different from the previous time, there is a risk of using a nozzle whose internal ink has increased in viscosity. The ink inside is refreshed, and the ink ejection is stabilized.
[0023]
Next, the recording operation will be described with reference to the flowchart shown in FIG. 1 which best illustrates the recording operation in the first embodiment of the present invention.
First, at the start of printing, the timer 9 (see FIG. 6) installed in the printing apparatus starts counting the exposure time t during which the discharge port of the print head 1 is exposed to the atmosphere (step S1). Then, the temperature inside the print head 1 is detected by the Di sensor 6 (see FIG. 6) in the print head 1 (step S2), and the driving corresponding to the temperature inside the print head 1 is performed based on the PWM table as shown in FIG. With the pulse, the recording head 1 is driven by PWM to perform recording (step S3).
[0024]
Thereafter, it is determined whether or not the count time (exposure time) t of the timer 9 has reached a predetermined allowable exposure time A (step S4). The allowable exposure time A is stable even when the recording head 1 is exposed to the atmosphere under the worst environment where the recording apparatus is used (the environment where the ink in the nozzles of the recording head 1 is most likely to thicken). The time is set so that the discharged ink can be sufficiently discharged.
[0025]
If the exposure time t of the recording head 1 does not reach the allowable exposure time A, it is determined whether or not the recording has been completed (step S4A). If the recording is not completed, the process returns to step S2, and if the recording is completed, the recording operation is completed.
[0026]
On the other hand, when the exposure time t of the recording head 1 becomes the allowable exposure time A (t = A), the job for the next recording operation is recorded based on the same image data as the job for the current recording operation. It is determined whether or not to operate (step S5). If the next job performs a printing operation based on the same image data as the current job, the same nozzle will be used in the next job, and the ink in the nozzle used will be thickened. Since there is not, the process returns to step S2 to continue the recording operation. When the next job performs a printing operation based on different image data, the following sequence (hereinafter, also referred to as a “first sequence”) is executed (step S6).
[0027]
In the first sequence of step S6, in order to discharge ink from the first to several nozzles used for printing, a drive pulse higher in rank than the original from the PWM table as shown in FIG. A drive pulse having a large energy used when the temperature of the head 1 is low is selected, and the drive pulse is sent from the drive signal control unit 5 to the recording head 1 to record an image. That is, first, when the first ink droplet is ejected from the nozzle used for recording, a drive pulse that is n ranks higher than the original rank is selected from the PWM table and used. Thereafter, when the second ink droplet is ejected from the nozzle, a drive pulse on the (n-1) rank higher than the original rank is selected and used, and further, the third ink droplet is ejected from the nozzle. At the time of ejection, a drive pulse on the (n-2) rank higher than the original rank is selected and used. In the same manner, the drive pulse ranks are brought closer to the original rank one by one, and the drive pulse of the original rank is selected and used when the nth ink droplet is ejected. The first n ink droplets ejected from such a nozzle are used for recording an image similarly to the ink droplets ejected thereafter.
[0028]
FIG. 9 is an explanatory diagram of a recording example when such a one-shot sequence is executed. By discharging ink droplets from the nozzles of the recording head 1 while transporting the paper 3 in the paper feed direction indicated by arrow C, ink dots are formed on the paper 3 to record an image. When the first ink droplet is ejected from the nozzle by the emission sequence, a relatively dark dot is formed because a drive pulse that is n ranks higher (+ n) than the original rank is used. Then, when the second, third,..., Nth ink droplets are ejected, the ranks {+ (n−1)}, Δ + (n−2) in which the drive pulse gradually returns to the original rank. )｝, {+ (N−3))｝ (± 0), and the dot density gradually returns to the original density.
[0029]
The value of n is set to a value sufficient for ejecting the thickened ink from the nozzle. When using an ink having a low viscosity, the value of n is reduced, and when using an ink having a high viscosity such as a pigment ink, the value of n is increased. However, it is desirable to set the value of n to such a degree that the density change of the recorded image due to an increase in the rank of the driving pulse is not conspicuous. In addition, the reason why the number of ink droplets ejected by using a drive pulse of a higher rank than originally intended is assumed to be a case where the thickened ink cannot be completely ejected by the ejection of the first ink droplet. Because he did. The reason why the rank of the drive pulse is gradually returned to the original rank is to make the density difference on the recorded image less noticeable. If the first ink droplet is ejected based on a driving pulse of a rank higher than the original, and then the driving pulse for ejecting the second ink droplet is returned to the driving pulse of the original rank at a stretch. In such a case, the recording by the ink droplet ejected at the first shot becomes dark, and the density difference may be conspicuous.
[0030]
It is not always necessary to linearly change the rank of the drive pulse in the PWM table one by one every time an ink droplet is ejected from the nozzle one by one. For example, as shown in FIG. 8, the rank of the drive pulse may be changed in a curved line. At times other than such a one-shot ejection sequence, the temperature in the print head 1 is detected by the Di sensor 6 in the print head 1 (step S2), and a drive pulse having a rank corresponding to the detected temperature is output to the PWM table. And recording is performed based on the drive pulse (step S3).
[0031]
As described above, the thickened ink in the nozzles caused by the exposure of the print head 1 does not need to be removed by a recovery operation different from the printing operation, and can be ejected at the time of printing. As a result, for example, printing can be performed without lowering the throughput even when ink having a low viscosity is used and when printing is performed in an environment in which the ink tends to thicken, such as a low-temperature and low-humidity environment.
[0032]
(Second embodiment)
FIG. 10 is a flowchart for explaining a recording operation according to the second embodiment of the present invention.
[0033]
At the start of recording, first, the temperature and humidity inside the apparatus are detected by the temperature / humidity sensor 8 (see FIG. 6) inside the apparatus of the recording apparatus (step S8), and as described above, the temperature and humidity table shown in FIG. Then, an allowable exposure time T corresponding to the temperature and the humidity is determined (step S9). Then, the exposure time t of the recording head 1 is counted by the timer 9 (see FIG. 6) installed in the machine (step S10). Then, the temperature in the recording head 1 is detected by the Di sensor 6 (see FIG. 6) in the recording head 1 (step S11), and the rank corresponding to the temperature in the recording head 1 is determined based on the PWM table as shown in FIG. The recording head 1 is driven by PWM with the driving pulse of (1) to perform recording (step S12).
[0034]
Then, it is determined whether or not the exposure time t of the recording head 1 has reached the allowable exposure time T (step S13). When the exposure time t of the recording head 1 does not reach the allowable exposure time T, it is determined whether or not the recording has been completed (step S13A). If the recording is not completed, the process returns to step S11, and if the recording is completed, the recording operation is completed.
[0035]
On the other hand, when the exposure time t of the recording head 1 becomes the allowable exposure time T (t = T), the job for the next recording operation is recorded based on the same image data as the job for the current recording operation. It is determined whether or not to operate (step S14). If the next job performs a printing operation based on the same image data as the current job, the same nozzle will be used in the next job, and the ink in the nozzle used will be thickened. Since there is no recording operation, the process returns to step S11 to continue the recording operation. When the next job performs a recording operation based on different image data, the same emission sequence as in the above-described embodiment is executed (step S15).
[0036]
As described above, the thickened ink in the nozzles caused by the exposure of the print head 1 does not need to be removed by a recovery operation different from the printing operation, and can be ejected at the time of printing. As a result, for example, printing can be performed without lowering the throughput even when ink having a low viscosity is used and when printing is performed in an environment in which the ink tends to thicken, such as a low-temperature and low-humidity environment.
[0037]
Further, in the present embodiment, by using the temperature and humidity table as shown in FIG. 7, the allowable exposure time of the recording head 1 can be extended according to the environment. Therefore, as compared with the first embodiment described above, the execution frequency of the first recovery sequence can be reduced, the energy applied to the recording head 1 can be reduced, and the life of the recording head 1 can be extended.
[0038]
(Third embodiment)
In the above-described embodiment, the nozzles for which the first recovery sequence is executed may be only non-printing nozzles (nozzles that do not eject ink) that are not used for printing. Since the ink in the nozzles used for recording does not increase in viscosity, such nozzles can perform sufficiently stable ink ejection by the driving pulse of the original rank. As described above, in the case where only the non-printing nozzles are the execution target nozzles of the one-shot recovery sequence, the energy applied to the recording head 1 is reduced as compared with the case where the execution target nozzles are all the nozzles. Thus, the life of the recording head 1 can be extended.
[0039]
(Other embodiments)
The present invention can be applied not only to a full-line type recording apparatus as shown in FIG. 5, but also to a serial scan type recording apparatus in which a recording head moves in the main scanning direction.
[0040]
Further, the method of ejecting ink in the recording head is not limited to the above-described ejection method using a heater, and may be, for example, a method of ejecting ink using a piezo element or the like.
[0041]
【The invention's effect】
As described above, the present invention changes the ejection energy of the ink applied to the recording head during the recording operation in accordance with the time during which the ejection port of the recording head is exposed, so that the exposure of the ejection port of the recording head can be reduced. As a result, the thickened ink can be ejected during the printing operation, and it is not necessary to remove the ink by a recovery operation different from the printing operation. As a result, recording can be performed without lowering the throughput.
[Brief description of the drawings]
FIG. 1 is a flowchart illustrating a recording operation according to a first embodiment of the present invention.
FIG. 2 is an explanatory diagram of a double pulse as an example of a driving pulse of the inkjet recording head.
FIG. 3 is an explanatory diagram of an example of a PWM table.
FIG. 4A is an explanatory diagram of a double pulse as an example of a driving pulse of the inkjet recording head, and FIG. 4B is an explanatory diagram of a single as another example of a driving pulse of the inkjet recording head.
FIG. 5 is a schematic configuration diagram of a full-line type ink jet recording apparatus.
FIG. 6 is a block diagram of a recording head peripheral portion in the recording apparatus of FIG. 5;
FIG. 7 is an explanatory diagram of an example of a temperature and humidity table.
FIG. 8 is an explanatory diagram of another modified example of the drive pulse in the first embodiment of the present invention.
FIG. 9 is an explanatory diagram of a dot formation example according to the first embodiment of the present invention.
FIG. 10 is a flowchart illustrating a recording operation according to the second embodiment of the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Ink jet recording head 2 Nozzle 3 Paper (medium for recording)
4 transport means 5 drive signal control unit (variable means)
6 Di sensor 7 Temperature detector 8 Temperature / humidity sensor (detection means)
9 Timer (measuring means)
A Transport upstream side B Transport downstream side C Transport direction

Claims (14)

In an ink jet recording apparatus that performs recording on a recording medium by using a recording head capable of discharging ink from a plurality of discharge ports,
Time measuring means for measuring the time during which the ejection openings of the recording head are exposed,
An ink jet recording apparatus comprising: a variable unit that changes an ejection energy of ink applied to an ejection port of the recording head during a recording operation according to a time measured by the time measurement unit. 2. The ink jet recording apparatus according to claim 1, wherein the recording head changes a discharge amount of the ink according to the discharge energy. The inkjet recording apparatus according to claim 1, wherein the time measuring unit includes a recording operation time as the time to be measured. The variable means temporarily increases the ejection energy to such an extent that the thickened ink in the recording head is ejected when the time measured by the time measuring means exceeds a predetermined time. 4. The inkjet recording apparatus according to any one of 1 to 3. The variable means does not change the ejection energy when the same image is repeatedly recorded on a predetermined unit of the recording medium, and when a different image is recorded on the predetermined unit of the recording medium. 5. The ink jet recording apparatus according to claim 1, wherein the ejection energy is changed. The ink jet recording apparatus according to claim 1, wherein the variable unit changes the ejection energy for all of the plurality of ejection ports in the recording head at the same time. 6. The printing apparatus according to claim 1, wherein the changing unit changes the ejection energy of the plurality of ejection ports of the recording head that have not ejected ink for a predetermined time or more. The inkjet recording apparatus according to any one of the preceding claims. Temperature detection means for detecting the temperature of the recording head,
Control means for controlling a drive signal of the recording head so as to maintain a constant amount of ink discharged from the discharge port in accordance with a temperature detected by the temperature detecting means,
8. The ink-jet apparatus according to claim 1, wherein the variable unit changes the driving signal so as to temporarily change the ejection energy according to a time measured by the time measuring unit. 9. Recording device. A detecting unit that detects at least one of a temperature and a humidity around the recording head,
9. The ink jet recording apparatus according to claim 1, wherein the variable unit changes the ejection energy according to a detection result by the detection unit and a measurement time by the time measurement unit. 9. The inkjet recording apparatus according to claim 1, further comprising a unit configured to relatively move the recording head and the recording medium. The inkjet recording apparatus according to claim 1, wherein the recording head includes an electrothermal transducer that generates heat energy according to the ejection energy. In an inkjet recording method for performing recording on a recording medium using a recording head capable of discharging ink from a plurality of discharge ports,
An ink jet recording method, comprising: changing an ejection energy of ink applied to the recording head during a recording operation according to a time during which the ejection port of the recording head is exposed. 2. The ink jet recording apparatus according to claim 1, further comprising cap means for capping the discharge port of the recording head. 14. The ink jet recording apparatus according to claim 13, wherein the time measuring means includes a time during which the cap means exposes the discharge port as a time to be measured.

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