JP2006076223A - Inkjet recorder, and method and program for controlling its head temperature - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To effectively suppress the generation of density difference between recorded images before and after a temporary stop of recording, even if it is the smallest amount, by a comparatively simple head temperature control, in an inkjet recorder which carries out recording with a plurality of recording heads. <P>SOLUTION: Temperatures Ta1 to Ta12 of twelve recording heads are detected during recording. An average value Tave of head temperatures Tb1 to Tb12 just before a temporary stop is found when a suction recovery operation carried out by temporarily stopping recording is started (S101 to 104). Each head temperature is compared with a target temperature (the average value Tave + a predetermined temperature T°C) when the suction recovery operation is finished, and a head with a temperature lower than the target temperature is heated up to the target temperature (S105 to 107). Then, it is heated so as to keep the target temperature only for an additional time N (S108 to S111), and recording is resumed (S112). Thus, the generation of the density difference is effectively suppressed by making each head temperature substantially the same as the average value Tave when the recording is resumed. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an inkjet recording apparatus that performs recording by discharging ink from a plurality of recording heads onto a recording medium, a head temperature control method that controls the temperature of the recording head, and a head temperature control program thereof.

  As a recording device in a printer, a copier, a facsimile, or the like, or as a recording device used as a device for outputting information processed by a composite electronic device or workstation including a computer or a word processor, paper with a relatively simple configuration, 2. Description of the Related Art Inkjet recording apparatuses that can perform recording on various recording media such as cloth, plastic sheets, and OHP sheets have become widespread. The ink jet method is basically a non-contact recording method, and any kind of recording medium can be used. Therefore, in addition to the recording media normally used as described above, cloth, leather, non-woven fabric, metal, etc. are used as recording media. A recording apparatus to be used has also been proposed. In an ink jet recording apparatus, a so-called serial method in which an image is recorded while a recording head is scanned in a direction (main scanning direction) intersecting with a conveyance direction (sub-scanning direction) of a recording medium is mainstream. With the configuration, it is possible to record an image with relatively excellent reproducibility and uniformity. Among the ink jet methods, in particular, a so-called bubble jet (trade name) method in which bubbles are generated in ink using the thermal energy generated by the electrothermal conversion element and ink is ejected by the pressure of the bubbles is relatively In recent years, it has been widely used because it has various advantages such as the ability to arrange the discharge ports at high density and the low noise generated by the recording operation.

  By the way, in the ink jet recording apparatus, there is a case where the recording operation is temporarily stopped during the recording operation as necessary. For example, when outputting information processed by a computer, there may be a delay in information input to the ink jet recording apparatus due to the processing capability of the computer, and the ink jet recording apparatus may temporarily stop the recording operation. In addition, there are many ink jet recording apparatuses provided with a temporary stop function so that the temporary stop can be performed at the convenience of the user. Further, in an ink jet recording apparatus, an ink discharge recovery operation such as wiping, preliminary discharge, or suction recovery for maintaining a good ink discharge state of the recording head (hereinafter also simply referred to as “recovery operation” or “discharge recovery operation”). ), The recording operation may be temporarily stopped.

  For example, ink mist is generated when ink is ejected from the recording head, or splash occurs due to impact when the ejected ink lands on the recording medium, and these inks array the ink ejection ports of the recording head. In some cases, a discharge failure may occur, for example, by adhering to the discharged discharge port surface and closing the discharge port. On the other hand, wiping for wiping and removing ink adhering to the periphery of the ejection port is performed by moving the recording head while a blade made of an elastic material such as rubber is in contact with the ejection port surface.

  Also, during recording, ink is selectively ejected from a plurality of ejection ports of the recording head according to the recording data, but there is an ejection port that does not eject ink for a certain period of time. The state of being exposed to the ink continues to increase the viscosity, which may cause a discharge failure such as a decrease in the amount and speed of the discharged ink and a deflection in the discharge direction. On the other hand, in order to remove these thickened inks, preliminary ejection, which is ink ejection irrelevant to recording, is performed at a predetermined position of the apparatus.

  Also, due to continuous ink discharge or long-term non-use of the device, bubbles are mixed in or generated in the liquid path of the recording head or in the common liquid chamber, and the bubbles supply or discharge ink into the liquid path. It may hinder operation and cause ejection failure. In order to prevent such discharge failure, a cap made of a material such as rubber is brought into contact with the surface of the discharge port, and the ink near the discharge port is sucked out by negative pressure through the cap. Suction recovery is performed.

  These recovery operations are performed between one scan and the next scan before image formation (recording), after image formation is completed, or in the middle of image formation for one page. As a result, it is possible to always maintain the ink ejection state of the recording head appropriately, prevent deterioration in image quality, and perform good quality recording. In particular, when recording a relatively large area continuously, such as banner printing, it is important to perform a recovery operation during each scan during the recording of one page.

  By the way, the temperature of the ink in the recording head during the recording operation (which is the same as the temperature inside the recording head, hereinafter, simply referred to as “head temperature” or “recording head temperature”) starts recording by the energy applied for ejection. Generally, it is higher than immediately after. In this case, if the above-described temporary stop is performed between scans during the printing operation for one page, the head temperature decreases during this stop, and as a result, the discharge amount decreases, and the density starts from the middle of one page. An image with changed may be recorded.

  Such a decrease in the head temperature results in a relatively long heat dissipation time between the scans and a relatively long heat dissipation time. This is because more heat is dissipated than a certain amount. In particular, when the operation is temporarily stopped for the recovery operation, the decrease in the head temperature during the suspension is often more significant than the delay of the input data or the suspension by the user.

  Specifically, when wiping is performed as a recovery operation, a certain amount of time is required for the wiping operation, and during this time, discharge heat such as thermal energy is not supplied to the recording head, and only heat radiation is performed. For this reason, the head temperature when recording is resumed is often lower than before the temporary stop. Similarly, if preliminary ejection is performed in the middle of recording, ejection energy such as thermal energy for preliminary ejection is provided to the ink, but is smaller than the ejection energy provided to the ink during recording, and during preliminary ejection. Since the effect of heat dissipation is greater, the temperature may drop so that the change in recording density is noticeable. Similarly, in the case of the suction recovery operation, similarly, a large amount of heat is dissipated in the time for the operation, and as described above, the ink whose temperature has been raised is discharged exclusively without causing thermal energy or the like. At the same time, due to the supply of ink having a relatively low temperature, a relatively noticeable head temperature drop occurs.

  The temporary stop that causes the head temperature to decrease as described above is performed in the middle of recording. Especially, when the difference between the recording density lowered by this and the recording density so far occurs in the adjacent area in the recorded image, Even a large density difference is noticeable and the recording quality is lowered.

On the other hand, according to the following Patent Document 1, the applicant of the present invention is to apply pressure or suction to the discharge port surface within the discharge port in order to eliminate contamination caused by ink droplets attached to the discharge port surface of the recording head during recording. A technique was proposed in which the head temperature is recovered to the temperature immediately before the recovery operation after the recovery operation of overflowing ink and cleaning the ejection port surface. Specifically, for each of the plurality of recording heads, a temperature sensor and a heater are provided, the head temperature immediately before the recovery operation is detected for each recording head, and after the recovery operation, based on the detected head temperature. Each heater is driven to control each head temperature so that it becomes the head temperature just before the recovery operation.
JP-A-6-328723

  However, although the technique according to Patent Document 1 can improve the density difference between recorded images before and after the recovery operation (before and after the temporary stop), it is not sufficient, and a minute density difference may occur. That is, the head temperature immediately before the recovery operation is detected, the heater is driven after the recovery operation to control the head temperature immediately before the recovery operation, and then the recording head is moved to the recording area to resume recording. The head temperature slightly decreases due to heat dissipation, and a minute density difference may occur due to a small decrease in the discharge amount. This causes a problem because the density difference occurs in adjacent regions.

  Further, in the technique of Patent Document 1, each head temperature is controlled using each head temperature immediately before the recovery operation as a target temperature for each recording head. Therefore, the head temperature control becomes more complicated as the number of recording heads increases. End up. For example, in addition to the commonly used yellow (Y), magenta (M), cyan (C), and black (K) inks, these inks also have different color material concentrations such as dyes or special color inks. In a recording apparatus including a recording head, the above-described control is performed for each of the many recording heads, and the control becomes complicated.

  On the other hand, the temperature drop of the ink of each recording head appears as a decrease in the amount of each ejected ink, and hence a decrease in the formed dot size, but since the recorded image is formed by a set of ink dots, The density change corresponding to the temperature drop of the ink appears as an average. Therefore, even if complicated control is performed as in Patent Document 1, there may be a case where an effect corresponding to the control cannot be obtained.

  The present invention has been made in view of the above circumstances, and in an ink jet recording apparatus that performs recording with a plurality of recording heads, a relatively simple head temperature control allows recording images to be recorded before and after the pause of the recording operation. An object is to effectively suppress the occurrence of a density difference so that a minute density difference does not occur.

In order to solve the above problems, in the present invention,
Recording is performed by discharging ink from a plurality of recording heads to a recording medium, and when necessary, the recording operation is temporarily stopped during the recording operation by the recording head, and the recording operation is resumed from the paused state. In an inkjet recording apparatus capable of performing the operation, a head temperature control method for controlling the temperature of the recording head, and a head temperature control program,
When the temperature of the plurality of recording heads is detected during the recording operation and the recording operation is paused halfway, the plurality of recording heads detected immediately before the suspension before the recording operation is stopped and the recording operation is resumed. A temperature higher than the average value of the print heads by a predetermined temperature is set as a target temperature for head temperature control, and a print head having a temperature lower than the target temperature is heated among the plurality of print heads to control the temperature of the print head to the target temperature. It is characterized by.

Furthermore, in the present invention,
Before resuming the recording operation after the pause, the recording head whose temperature is lower than the target temperature among the plurality of recording heads is heated to control the temperature of the recording head to the target temperature. It is characterized by controlling so as to maintain the target temperature only.

  According to the present invention, the above head temperature control causes the temperature of each recording head when the recording operation is resumed after being temporarily stopped to be substantially the same as the average value of the temperatures of each recording head immediately before the pause. Image recording can be performed with high quality by effectively suppressing the occurrence of density differences so that a minute density difference does not occur in the recorded image before and after the stop, and the target temperature for head temperature control is common to each recording head. Since there is only one, it is possible to obtain an excellent effect that the head temperature can be controlled easily and easily.

  Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings. Here, an embodiment of an ink jet recording apparatus capable of performing color recording by a bubble jet (trade name) system is shown.

  FIG. 1 is a top view showing hardware of a recording unit of an ink jet recording apparatus according to Embodiment 1 of the present invention. This apparatus records on a relatively large format recording sheet (recording medium).

  In FIG. 1, an apparatus main body 1 including a paper transport system unit of an ink jet recording apparatus is provided with a carriage 2, which carries and moves 12 recording heads 5. A scan is made. That is, the carriage 2 is guided and supported by the guide shaft 11 so as to be movable along the guide shaft 11, and reciprocates in the left-right direction in the figure by the driving force transmitted through the belt 13. Here, as the ink used, for example, in addition to cyan, magenta, yellow, and black, ink of a total of six colors including light cyan and light magenta for the purpose of reducing graininess is used. For the purpose of improving the speed, two recording heads are used for each color ink.

  30A, 30B, 30C, and 30D are recovery mechanisms for keeping the ink discharge state of each recording head 5 in good condition. Although not shown in detail, each of the recording heads 5 includes a cap and a pump as a driving source. The ink suction operation is performed, and each recording head 5 is protected by capping when each recording head 5 is not used. 31 is an ink receiving box for receiving ink ejected by the preliminary ejection operation of each recording head 5, and 32 is a wiping mechanism for performing a wiping operation on the ejection port surface of each recording head 5.

  In the above apparatus configuration, when recording data is received from the host apparatus, control is performed so that the carriage 2 moves in the main scanning direction along the guide shaft 11 in order to record on recording paper sent by a paper transport unit (not shown). Further, each recording head 5 is driven to eject ink, whereby main scanning is performed, and an image for one band is recorded on the recording paper. When one main scan is completed, the recording paper is transported by one band in the sub-scanning direction orthogonal to the guide shaft 11 by the paper transport unit.

  An encoder film 12 for detecting the movement position of the carriage 2 is disposed along the movement path of the carriage 2, and an encoder sensor (not shown) mounted on the carriage 2 detects the detected signal. The position of the carriage 2 can be known, and, for example, the movement of the carriage 2 to the home position facing the recovery mechanisms 30A to 30D is controlled.

  Each recording head 5 has 256 ejection openings arranged at a density of, for example, 600 dpi (dots / inch) in the sub-scanning direction, and the ink is locally distributed in the ink liquid path communicating with each ejection opening. There is provided an electrothermal converter for heating the film to cause film boiling and discharging the ink by the pressure. Each recording head 5 has a temperature sensor 50 (see FIG. 2) for detecting the head temperature, which is the temperature of the inside of the recording head or the ink, on the substrate on which the electrothermal transducer is provided. Is provided.

  FIG. 2 is a block diagram showing the configuration of the control system in the ink jet recording apparatus of this embodiment.

  In the figure, reference numeral 800 denotes a controller that is a main control unit that controls the entire recording apparatus, and includes a CPU 801 that includes, for example, a microcomputer that executes control described later in FIG. 6 and the like, a program and a table corresponding to the control procedure, It comprises a ROM 802 that stores heat pulse voltage values, pulse widths, and other fixed data, and a RAM 803 that is used as an area for developing recording data, a work area, and the like.

  Reference numeral 805 denotes a host device such as a personal computer which is a recording data supply source. The recording data, other commands, status signals, and the like from the host device 805 are received by the controller 800 via an interface (I / F) 804. Is done.

  Reference numeral 806 denotes a head driver that drives the electrothermal transducer (ejection heater) of the recording head 5 in accordance with recording data or the like during recording or preliminary ejection. Further, as described above, each recording head 5 includes the temperature sensor 50, and a detected value of the head temperature detected thereby is input to the controller 800, thereby controlling the head temperature, which will be described later with reference to FIG. Can do. Note that an environmental temperature sensor 811 for detecting the temperature of the environment in which the recording apparatus is used is also provided, and the detected value of the environmental temperature is also input to the controller 800.

  A main scanning motor 809 is a driving source for moving the carriage 2 in the main scanning direction, and a driver 807 is the driver. Reference numeral 810 denotes a sub-scanning motor which is a drive source for conveying (sub-scanning) recording paper, and 808 denotes a driver thereof.

  In the ink jet recording apparatus having the above hardware, control of the head temperature when the recording operation is temporarily stopped and the suction recovery operation is performed as the ink discharge recovery operation of the recording head will be described below.

  First, as a comparative example to the head temperature control of this embodiment, an example of the transition of the head temperature when the head temperature control is not performed after the recording operation is temporarily stopped and the suction recovery operation is performed is shown in FIG. . FIG. 3 shows how the head temperature changes as recording is performed on the recording paper, with the recording position on the recording paper on the horizontal axis and the head temperature on the vertical axis.

  In FIG. 3, point A is the recording position where the suction recovery operation has been performed, and the head temperature before point A is supplied with thermal energy for relatively continuous ink ejection according to the recording data. Gradually higher immediately after starting. On the other hand, after the point A, the head temperature immediately after resuming printing is significantly lower than that immediately before the ejection recovery operation. This is because, during the suction recovery operation, heat energy is not supplied to the ink and heat is exclusively dissipated, and ink having a relatively low temperature flows into the ink liquid path of the recording head.

  Since there is a relation between the head temperature and the ink discharge amount that the discharge amount increases as the head temperature increases as shown in FIG. 4, the discharge amount decreases particularly at the point A. As a result, when the head temperature control is not performed after the suction recovery process is performed during recording, a relatively large density change occurs before and after the point A as shown in FIG. Since this density change occurs in an adjacent area in the recorded image, a very small density change (for example, about 0.02 in terms of OD difference) may be conspicuous and lower the recording quality. In addition, when the wiping operation other than the suction operation or the preliminary discharge operation is performed as the discharge recovery operation in the middle of the recording operation, not only the discharge recovery operation but also the temporary stop by the delay of the input data and the temporary stop by the user Even in the case where it is performed, a density change similar to the density change shown in FIG.

  On the other hand, in this embodiment, after the recording operation is temporarily stopped and the suction recovery operation is performed as the discharge recovery operation, the temperatures of the plurality of recording heads decreased by the suction recovery operation are temporarily set before restarting the recording operation. The target temperature is controlled to be higher by a predetermined temperature than the average value of the temperatures of the plurality of recording heads immediately before the stop, and further, the head temperature is controlled so as to maintain the target temperature for a predetermined time.

  This head temperature control is performed as follows according to the control procedure shown in the flowchart of FIG. A head temperature control program corresponding to this control procedure is stored in the ROM 802 and executed by the CPU 801. The same applies to the control procedure of FIG.

  The processing in FIG. 6 is started at the start of image formation (recording). First, the head temperature is set at a predetermined periodic timing, for example, at the time of waiting until one main scan of the print head is finished and the next scan is started. It is monitored and whether or not the suction recovery operation has been activated is checked (steps S101 and S102). That is, the head temperatures Ta1 to Ta12 of each of the twelve recording heads 5 are detected by the temperature sensor 50, the detected value data is stored in the RAM 803 of the controller 800 (S101), and then the suction operation is activated during the standby time. It is determined whether it has been done (S102). If the suction operation is not started, steps S101 and S102 are repeated, and the values of the head temperatures Ta1 to Ta12 detected for each scanning are sequentially overwritten on the values stored in the previous scanning and stored. .

  If it is determined in step S102 that the suction recovery operation has been started, the head temperatures Ta1 to Ta12 stored in the RAM 803 at that time are used for the recording heads 5 immediately before the suction recovery operation (immediately before the recording operation is temporarily stopped). The head temperatures Tb1 to Tb12 are determined and stored in the RAM 803 (S103). Then, the average value Tave of the determined head temperatures Tb1 to Tb12 is calculated and stored in the RAM 803 (S104). FIG. 7 shows an example of the determined head temperatures Tb1 to Tb12 of each recording head 5. In this example, the average value Tave is 43 ° C.

  Next, it is determined whether or not the suction recovery operation has been completed, and the completion is waited (S105). When the suction recovery operation is completed, head temperature control is performed with a target temperature that is a predetermined temperature T ° C. (for example, 3 ° C.) higher than the average temperature Tave. (S106, S107). That is, the current head temperature detected by the temperature sensor 50 for each recording head 5 is compared with the target temperature (Tave + T ° C.) (S106), and if it is lower than the target temperature, the process reaches the target temperature in FIG. The indicated pulse is supplied to the electrothermal transducer of each recording head 5 to heat the inside of the head (heating of the ink) (S107). This pulse gives thermal energy that does not lead to ink ejection to the ink in the recording head 5.

  When the head temperature reaches the target temperature (Tave + T ° C.) or is originally higher than the target temperature, measurement of the additional time N (for example, 5 seconds) of the head temperature control is started (S108), and the head temperature control is performed for the additional time N. (S109 to S111). That is, the head temperature detected for each recording head 5 is compared with the target temperature (Tave + T ° C.) until the elapse of the additional time N is determined (S111), and if the temperature is lower than the target temperature, the target is detected. The pulses shown in FIG. 8 are supplied to the electrothermal transducers of the recording heads 5 until the temperature is reached to heat the heads (ink heating) (S110). When the additional time N has elapsed (S111), image formation is resumed (S112).

  Note that the recording head 5 whose head temperature was originally higher than the target temperature (Tave + T ° C.) is not heated in step S107, but if it becomes lower than the target temperature due to heat dissipation during the additional time N, it is heated in step S110. Controlled to target temperature. Further, even during the additional time N, even if the temperature is higher than the target temperature, the target temperature is approached by the heat radiation during that time.

  As described above, as the target temperature for the head temperature control, a temperature that is higher by the predetermined temperature T ° C than the average value Tave of the 12 recording heads 5 immediately before the suction recovery operation (immediately before the recording operation is temporarily stopped) is used. If the head temperature is lower than the target temperature among the heads 5, after the head temperature control is completed, each recording head 5 forms an image after the head temperature control is completed by adding temperature control to maintain the target temperature. Even if the head temperature decreases due to heat dissipation while moving to the region, it is possible to prevent the occurrence of minute density differences and color differences. This is shown in FIGS. 9 and 10. FIG.

  FIG. 9 shows changes in the head temperature (average value of all heads) in the same manner as in FIG. 3 when the above-described head temperature control of FIG. 6 is performed after the suction recovery operation is performed during recording. . As shown in the figure, the head temperature during recording before the point A of the recording position is the same as in the example shown in FIG. 3 and decreases at the point A, but immediately after the end of the suction recovery operation as described above. Since the head temperature is controlled by pulse heating before restarting image formation, the head temperature immediately after point A at which the recording head reaches the recording area and restarts image formation is the head temperature immediately before point A (just before the suction recovery operation). Is approximately equal.

  FIG. 10 shows a change in image formation density when the head temperature control of this embodiment is performed. As shown in this figure, the density change is almost before and after the point A of the recording position where the suction recovery operation is performed. Does not occur.

  The predetermined temperature T ° C. is preferably in the range of 1 ° C. to 5 ° C. When the temperature is lower than 1 ° C., the influence of heat radiation during the movement to the image forming area becomes relatively large, and a minute density reduction occurs. On the other hand, when the temperature is higher than 5 ° C., the influence of heat dissipation during the movement to the image forming area becomes too small, and conversely, the discharge amount increases, resulting in a density difference.

  The additional time N is preferably in the range of 5 seconds or more and 20 seconds or less. If it is shorter than 5 seconds, only a very small portion inside the recording head is controlled to the target temperature, so that the temperature drop during moving to the image forming area becomes large and a minute density difference may occur. On the other hand, if it is longer than 20 seconds, the temperature in the recording head is uniformly controlled to the target temperature, but the throughput is greatly reduced.

  Further, in this embodiment, the head temperature control is performed by setting a temperature that is a predetermined temperature T ° C. higher than the average head temperature Tave detected immediately before the suction recovery operation for each of the 12 recording heads 5 as a target temperature. Since the target temperatures of the recording heads 5 are the same, the parameters used for head temperature control can be reduced, and the control can be simplified and facilitated.

  Note that the head temperature of each recording head when the recording is resumed after the head temperature control is different from the head temperature immediately before the suction recovery operation in terms of individual recording heads, but 12 images are recorded. Therefore, the variation in dot size for each ink is averaged depending on the recorded image, and the heads of the individual recording heads as described above are represented. The difference in temperature has little effect on the density of the recorded image.

  As the ink discharge recovery operation, in addition to the above-described suction recovery operation, a wiping operation and a preliminary discharge operation are performed, as well as a temporary stop due to delay of input data, a temporary stop due to user's convenience, and other reasons. In the case of stopping, the same head temperature control can be performed, and as a result, as shown in FIG. 10, almost no change in image density can be eliminated before and after the pause. As described above, according to the present embodiment, the density change of the image before and after the temporary stop of the recording operation can be almost eliminated by simple and easy head temperature control.

  In the first embodiment described above, the average value Tave of the head temperature for obtaining the target temperature of the head temperature control is the average value of the head temperatures of all the recording heads 5. However, the following two problems occur depending on the recording data. There is a case.

  First, for example, when there is a recording head whose ink discharge frequency is extremely low (no discharge or low frequency) depending on the recording data, the temperature of the recording head does not increase so much. In this case, if the average value Tave of the head temperatures of all the recording heads is uniformly obtained and the above-described head temperature control is performed based on the average value Tave, the ink ejection frequency greatly affects the overall density of the recorded image. Recording heads with high recording density, that is, recording heads with high recording density and immediately before the pause of the recording operation, the head temperature is controlled to be extremely low after the pause, so the density change (decrease) ) Will become larger. On the other hand, for recording heads with extremely low ink discharge frequency, low recording density, and low head temperature, the temperature is controlled to be extremely high, but no ink is discharged or the discharge frequency remains low even after a pause. The influence on the overall density of the print image is small, and the change in print density due to the print head having a high discharge frequency is not offset. That is, when the average value Tave is set to be lower due to the temperature of the recording head having a remarkably low ink discharge frequency, there is a problem that the overall density of the recording image immediately before the temporary stop may not be reflected in the head temperature control. is there.

  Also, if the recording data shows that the ink discharge frequency of all the recording heads is remarkably low and the recording density is low, even if the above-described head temperature control is not performed, the recording density decreases slightly due to a decrease in the head temperature during the pause. In some cases, however, the density change of the recorded image before and after the temporary stop is so slight that it does not cause a problem. In such a case, it is useless to perform the head temperature control described above, and there is a problem that the throughput of the ink jet recording apparatus is lowered.

  In order to solve such a problem, in the head temperature control of the ink jet recording apparatus according to the second embodiment of the present invention, an appropriate threshold temperature Ts of the head temperature is set, and the average value Tave of the head temperatures is set for all the recording heads. The average value of the head temperatures of the recording heads whose head temperature is higher than the threshold temperature Ts is used, and head temperature control is avoided when the head temperatures of all the recording heads are lower than the threshold temperature Ts. The hardware configuration of the apparatus of the second embodiment is the same as that of the apparatus of the first embodiment.

  FIG. 11 is a flowchart illustrating a control procedure of head temperature control of the ink jet recording apparatus according to the second embodiment. Steps S201 to S203 and S206 to S213 are common to steps S101 to S103 and S105 to S112 of FIG.

  In the process of FIG. 11, after the image formation is started, first, as in the first embodiment, all twelve are detected at a predetermined periodic timing, for example, when waiting for one main scan to end and the next scan to start. The head temperatures Ta1 to Ta12 of the recording heads are detected, and it is checked whether or not the recording operation has been paused (whether or not the suction recovery operation has been started) (S201, S202). The head temperatures Ta1 to Ta12 detected immediately before are determined as the head temperatures Tb1 to Tb12 immediately before the temporary stop (S203).

  Next, each of the head temperatures Tb1 to Tb12 is compared with the threshold temperature Ts, and it is determined whether there is any higher than the threshold temperature Ts (S204). The threshold temperature Ts is set as shown in FIG. 15 according to, for example, the environmental temperature of the ink jet recording apparatus detected by the environmental temperature sensor 811 and the conveyance length (paper feed amount) of the recording medium per sub-scan. However, details of the setting method will be described later.

  If at least one of the head temperatures Tb1 to Tb12 is higher than the threshold temperature Ts in step S204, the head temperature for setting the target temperature of the head temperature control using the average value of only the head temperature higher than the threshold temperature Ts. The average value Tave is calculated and stored in the RAM 803 (S205). For example, FIG. 12 shows an example of the head temperatures Tb1 to Tb12. Here, when the threshold temperature Ts = 35 ° C., the head temperatures higher than this temperature Ts are Tb2, Tb5, Tb6, Tb7, Tb8, and Tb11. Their average value Tave is 48 ° C.

  On the other hand, if the head temperatures Tb1 to Tb12 are all lower than the threshold temperature Ts in step S204, the average value Tave of the head temperature is extremely higher than the head temperature during normal recording regardless of the actual head temperatures Tb1 to Tb12. A low temperature, for example, 15 ° C. is set (S214), and the above-described head temperature control additional time N is set to 0 (S215).

  After step S205 or after step S215, head temperature control is performed in steps S206 to S212 in exactly the same manner as steps S105 to S111 of the first embodiment.

  That is, the process waits for the end of the temporary stop of the recording operation (end of the suction recovery operation) (S206). When the recording operation is completed, the target temperature is higher by the predetermined temperature T ° C (for example, 3 ° C) than the average temperature Tave. The head temperature is controlled to be the temperature (S207, S208). That is, the head temperature of each recording head 5 is compared with the target temperature (Tave + T ° C.) (S207), and if it is lower than the target temperature, a short pulse that does not reach ink ejection is reached until the target temperature is reached. 5 is supplied to the electrothermal transducer 5 to heat the inside of the head (S208).

  When the head temperature reaches the target temperature (Tave + T ° C.) or higher than the target temperature from the beginning, the measurement of the additional time N (for example, 5 seconds) of the head temperature control is started (S209). Temperature control is additionally performed (S210 to S212), and then image formation is resumed (S213).

  As described above, when the head temperature Tb1 to Tb12 immediately before the temporary stop is higher than the threshold temperature Ts, the average value of only the higher one is set as the average value Tave for head temperature control. Then, by controlling the head temperature of all the recording heads based on this, the average value Tave of the head temperature is lowered due to the influence of the low head temperature of the recording head whose ink ejection frequency is remarkably low as described above, and is temporarily stopped. It is possible to prevent the entire density of the immediately preceding recorded image from being reflected in the head temperature control. That is, by performing head temperature control that eliminates the influence of the recording head having a remarkably low recording density and a low head temperature, the density difference before and after the temporary stop can be eliminated with high accuracy.

  If all of the head temperatures Tb1 to Tb12 are lower than the threshold temperature Ts, the average value Tave is set to a significantly lower temperature (for example, 15 ° C.), and the additional time N is set to 0 to temporarily stop the operation. After the end (S206), each head temperature is compared with the target temperature (Tave + T ° C) (S207), and additional head temperature control processing (S209 to 212) is immediately exited from the loop, and unnecessary temperature control is performed. Thus, image formation can be resumed immediately.

  That is, the fact that all of the head temperatures Tb1 to Tb12 are lower than the threshold temperature Ts indicates that the ink discharge frequency of all of the recording heads 5 is remarkably low (no discharge or low frequency). This is the case when the concentration is very low. For this reason, even if there is a drop in head temperature during the pause, it is assumed that the resulting density drop is not recognized in the recording results, so there is no need to control the head temperature after the pause. It doesn't matter.

  FIG. 13 shows the temperature change when the temperatures Tb1 to Tb12 of the recording heads 5 just before the temporary stop are all lower than the threshold temperature Ts, that is, when the temperature control is not performed. A change in head temperature occurs slightly before and after point A of the recording position where the temporary stop is performed. However, since the change is minute and the head temperature is very low, the change in the ink discharge amount is also minute. Even in the recording after the temporary stop, the density change is very slight as shown in FIG. The change in density occurring before and after point A is so small that it cannot be recognized as a change in density and color for humans.

  Therefore, when almost no change in density is likely to occur due to a temporary stop as a whole of a plurality of recording heads, the throughput of the inkjet recording apparatus can be reduced by avoiding unnecessary head temperature control and immediately restarting the recording operation. Can be improved.

  If all the head temperatures Tb1 to Tb12 are lower than the threshold temperature Ts in step S204, the head temperature control may be avoided by performing other processes instead of performing the processes in steps S214 and S215. For example, in this case, a flag indicating that the head temperatures Tb1 to Tb12 are all lower than the threshold temperature Ts is set in the RAM 803 or the like, and when the pause is finished in step S206, it is confirmed whether or not the flag is set. If standing, the process jumps to step S213 to avoid the head temperature control, and if not standing, the head temperature control in steps S207 to S212 may be performed.

  Next, details of a method for setting the threshold temperature Ts used for the head temperature control described above will be described.

  FIG. 15 shows the contents of a table in which the threshold temperature Ts is set according to the environmental temperature of the ink jet recording apparatus and the recording medium transport length (paper feed amount) per sub-scan. The data of this table is stored in the ROM 802, and when the CPU 801 performs head temperature control, the environmental temperature detected by the environmental temperature sensor 811 and the transport length per sub-scan set at that time are set. The corresponding threshold temperature Ts data is obtained from the table and the threshold temperature Ts is set. In FIG. 15, N indicates the number of ink discharge ports arranged in the sub-scanning direction in each recording head 5, and the paper feed amount is N (or N / 2 or N / 4) × discharge port pitch. It is shown that.

  As shown in FIG. 15, the threshold temperature Ts is set higher as the transport length per sub-scan is longer. This is because the longer the transport length per sub-scan, the wider the band (row) printed in one main scan, the more ink is ejected from the print head 5, This is because the thermal energy supplied to the ink continuously increases and the head temperature also increases. This is shown in FIG. That is, in the formation of images having the same density, the longer the transport length per sub-scan, the higher the head temperature at the same recording position, and the ejection recovery operation is performed at the same recording position. The longer the hit conveyance length, the higher the head temperature immediately before the discharge recovery operation. In other words, the density of the recorded image is very low, and the head temperature immediately before the temporary stop, which does not cause a problem even if the head temperature control is not performed, becomes higher as the transport length per sub-scanning is longer. . Accordingly, by increasing the threshold temperature Ts as the transport length per sub-scan increases, unnecessary head temperature control is avoided, and unnecessary recording head temperature control is performed. Increase can be prevented.

  Further, as shown in FIG. 15, the threshold temperature Ts is increased as the environmental temperature is higher. This is because, when the environmental temperature is high, the head temperature rises during recording. This is shown in FIG. That is, in the formation of images having the same density, the higher the environmental temperature, the higher the head temperature immediately before the temporary stop. Accordingly, by increasing the threshold temperature Ts as the environmental temperature increases, unnecessary head temperature control can be avoided as in the case of the paper feed amount, and an increase in recording time can be prevented.

  The ink jet recording apparatuses of Examples 1 and 2 described above are apparatuses that perform color recording. However, if the apparatus performs ink jet recording with a plurality of recording heads, gradation recording with the same color and different densities is possible. The same effect can be obtained by applying the present invention to an apparatus that performs both color recording and gradation recording. Further, according to the present invention, if the apparatus performs ink jet recording with a plurality of recording heads, a configuration using a replaceable ink jet cartridge in which the recording head and the ink tank are integrated, or the recording head and the ink tank are separated from each other. The present invention can be similarly applied to any arrangement of the recording head and the ink tank, such as a configuration in which the ink is connected by an ink supply tube or the like, and the same effect can be obtained.

  In addition, the present invention provides an excellent effect in an ink jet recording apparatus using a recording head that discharges ink using thermal energy, among other ink jet recording methods. Of course, the present invention can also be applied to an apparatus.

FIG. 2 is a top view illustrating a mechanical configuration of a recording unit of an inkjet recording apparatus according to Examples 1 and 2 of the present invention. 2 is a block diagram illustrating a configuration of a control system of the ink jet recording apparatus. FIG. FIG. 6 is a diagram illustrating a relationship between a recording position and a head temperature when a recording operation is temporarily stopped and head temperature control is not performed. FIG. 6 is a diagram illustrating a relationship between a head temperature and an ink discharge amount. FIG. 6 is a diagram showing a density change of a recorded image when a recording operation is temporarily stopped and head temperature control is not performed. FIG. 6 is a flowchart illustrating a control procedure of head temperature control according to the first embodiment. FIG. 3 is a table showing an example of the temperature of each recording head immediately before a temporary stop in the head temperature control of the first embodiment. It is a signal waveform diagram showing a short recording head drive pulse used for heating the recording head in the head temperature control. FIG. 6 is a diagram showing a change in head temperature when head temperature control is performed after performing a suction recovery operation in Example 1. FIG. 6 is a diagram illustrating changes in recorded image density when head temperature control is performed according to the first exemplary embodiment. FIG. 10 is a flowchart illustrating a control procedure of head temperature control according to the second embodiment. 6 is a table showing an example of the temperature of each recording head immediately before a temporary stop in Example 2. FIG. FIG. 10 is a diagram illustrating a temperature change when the temperatures of the recording heads immediately before the temporary stop are all lower than the threshold temperature in the head temperature control of the second embodiment. It is a diagram which shows the density | concentration change of the recording image according to the temperature change of FIG. FIG. 10 is a table showing the contents of a data table for setting a threshold temperature used for head temperature control according to the second embodiment in accordance with an environmental temperature and a paper feed amount. It is a diagram showing a change in each head temperature when the conveyance length per sub-scanning is different. It is a diagram which shows the change of each head temperature when environmental temperature differs.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Inkjet recording device main body 2 Carriage 5 Recording head 11 Guide shaft 12 Encoder film 13 Belt 30A, 30B, 30C, 30D Recovery mechanism 31 Ink receiving box 32 Wiping mechanism 50 Temperature sensor 800 Controller 801 CPU
802 ROM
803 RAM
804 Interface 805 Host device 806 Head driver 807, 808 Motor driver 809 Main scanning motor 810 Sub scanning motor 811 Environmental temperature sensor

Claims (12)

Recording is performed by discharging ink from a plurality of recording heads to a recording medium, and when necessary, the recording operation is temporarily stopped during the recording operation by the recording head, and the recording operation is resumed from the paused state. A head temperature control method for controlling the temperature of a recording head of an ink jet recording apparatus capable of performing the operation,
Detecting the temperature of the plurality of recording heads during a recording operation;
When the recording operation is paused halfway, before the recording operation is stopped and the recording operation is resumed, a temperature higher than the average value of the temperatures of the plurality of recording heads detected immediately before the pause is set by the head temperature control. As the target temperature, a temperature control step of heating a recording head having a temperature lower than the target temperature among the plurality of recording heads to control the temperature of the recording head to the target temperature;
A method for controlling a head temperature of an ink jet recording apparatus, comprising:   In the temperature control step, before resuming the recording operation after the suspension, the recording head having a temperature lower than the target temperature among the plurality of recording heads is heated to control the temperature of the recording head to the target temperature. 2. The head temperature control method for an ink jet recording apparatus according to claim 1, further comprising a control for maintaining the target temperature for a predetermined additional time.   2. The head temperature control method for an ink jet recording apparatus according to claim 1, wherein the predetermined temperature is a temperature within a range of 1 [deg.] C. or more and 5 [deg.] C. or less.   The head temperature control method for an ink jet recording apparatus according to claim 2, wherein the additional time is a time within a range of 5 seconds or more and 20 seconds or less.   2. The average value of the temperatures of a plurality of recording heads detected immediately before the temporary stop is an average value of the temperatures of recording heads having a temperature higher than a predetermined threshold temperature among all the recording heads. 2. A method for controlling the head temperature of the ink jet recording apparatus described in 1.   6. The head temperature control method for an ink jet recording apparatus according to claim 5, wherein the head temperature control is avoided when all the temperatures of the plurality of recording heads detected immediately before the temporary stop are lower than the threshold temperature.   7. The head temperature control method for an ink jet recording apparatus according to claim 5, wherein the threshold temperature is set to a different value according to an environmental temperature of the ink jet recording apparatus. The ink jet recording apparatus performs recording on a recording medium by repeating recording scanning for recording while scanning the recording head in the main scanning direction and sub scanning for conveying the recording medium in the sub scanning direction.
The inkjet recording according to any one of claims 5 to 7, wherein the threshold temperature is set to a different value according to a conveyance length of the recording medium per sub-scan of the inkjet recording apparatus. Device head temperature control method.   9. The head temperature control method for an ink jet recording apparatus according to claim 1, wherein the temporary stop is a temporary stop for performing an ink discharge recovery operation of the recording head.   A head temperature control program for an ink jet recording apparatus, comprising: a control procedure for performing head temperature control by the head temperature control method for an ink jet recording apparatus according to any one of claims 1 to 9. Recording is performed by ejecting ink from a plurality of recording heads onto a recording medium, and when necessary, the recording operation is temporarily stopped during the recording operation by the recording head, and the recording operation is resumed from the paused state. In an inkjet recording apparatus capable of operating
Temperature detecting means for detecting temperatures of the plurality of recording heads;
Heating means for heating the plurality of recording heads;
10. The head temperature control of an ink jet recording apparatus according to claim 1, wherein when the recording operation is paused halfway, the heating unit is driven according to a detection result of the temperature detection unit. An ink jet recording apparatus comprising: a head temperature control means for controlling the temperature of the recording head by the method.   Each of the plurality of recording heads is provided with an electrothermal converter that generates heat for ejecting ink, and the head temperature control unit performs head temperature control using the electrothermal converter as the heating unit. The inkjet recording apparatus according to claim 11.

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