JP4710226B2 - Inkjet printer - Google Patents

Description

  The present invention relates to an ink jet printer, and more particularly to an ink jet printer using a long print head with a fixed position.

  As an ink jet printer, one using a long print head is known. In this type of printer, the print head is a fixed head having a length corresponding to the entire width of the recording medium, and a document or the like is formed by ink jet on a recording medium that is conveyed in a direction perpendicular to the longitudinal direction. Is printed (for example, see Patent Document 1).

This type of inkjet printer prints all the width of the recording medium at once with a long print head, so it is much faster than the so-called shuttle type printer that prints while moving the movable print head along the recording medium. Can be printed.
Japanese Patent Laid-Open No. 2003-200233 (third page, FIG. 1-2)

  The printer as described above is suitable for a job for printing a relatively large amount of document or the like due to its high speed. When used for printing work, it is required to increase the printing speed in order to improve efficiency.

  In order to increase the printing speed, it is necessary to increase the conveyance speed of the recording medium and the accompanying increase in the driving frequency of the print head. However, when the driving frequency of the print head is increased, the amount of ink droplets ejected and the flight angle In addition, variations in the flying speed and the like become large, and along with the increase in the conveyance speed of the recording medium, the landing position error of the ink droplet increases and the print quality deteriorates. In addition, quality deterioration due to changes in ink physical properties due to temperature rise of the print head, and problems such as ink overflow and contamination due to improper fixing and drying of the ink on the recording medium are likely to occur.

  In order to be able to conveniently use an ink jet printer having such a property as a business printer, it is necessary to devise a technique for increasing the print productivity as much as possible while taking into account its characteristics. Therefore, an object of the present invention is to realize an ink jet printer that achieves a trade-off between print speed and print quality with high productivity.

  The present invention as means for solving the above problems is as follows.

(1) According to the first aspect of the present invention, there is provided a print head having a plurality of nozzles for discharging ink over a length corresponding to the size of the recording medium in a direction perpendicular to the transport direction, and recording under the print head. Based on a user instruction, a medium conveying unit that supplies a medium and conveys a recording medium under the print head, a head driving unit that causes the print head to discharge ink in synchronization with the conveyance of the recording medium, and A speed setting means for setting a print speed, and a speed at which the recording medium is conveyed under the print head corresponding to the print speed set by the speed setting means, and the print becomes unstable depending on the apparatus conditions and conveying speed is a speed except for the conveying speed from the completion of printing of one page a time interval between the print start of the next page Determining the combination of the transport speed and the time interval between the time interval the effective printing speed matches the printing speed of the user settings when the combined saw, the transport and supply of a recording medium in this combination to the medium conveying means And a control unit that causes the head driving unit to eject ink from the print head at a frequency proportional to the conveyance speed.

  (2) The ink jet printer according to claim 1, wherein the print speed set by the speed setting means is a combination of a transport speed and a time interval.

(3) The invention according to claim 3 is the ink jet printer according to claim 1, wherein the print speed set by the speed setting means is the number of prints per unit time.

(4) The invention of claim 4, wherein the speed of printing by said device condition becomes unstable, a speed corresponding to a frequency which can not be stably drive the print head, claims 1, characterized in that An inkjet printer according to claim 3 .

(5) invention of claim 5, wherein the rate of printing by said device condition becomes unstable, a speed that can not convey the recording medium stably, either of the claims 1 to 3, characterized in that an ink jet printer according to any.

( 6 ) The invention according to claim 6 is characterized in that the control means determines the maximum value and time of the conveyance speed based on at least one of the characteristic value of the document to be printed, the type of the recording medium, the environmental temperature and the print head temperature. with limiting the minimum value of the interval, an ink jet printer according to any one of claims 1 to 5 users to view or restrict the maximum value of the settable printing speed, it is characterized.

(7) The invention of claim 7 wherein is an ink ejection number requiring the characteristic values on a printed document, an ink jet printer according to claim 6, characterized in that.

(8) The invention according to claim 8, wherein the characteristic value is the maximum value of the amount of ink discharged per unit area required to print the document, it is an inkjet printer according to claim 6, wherein.

( 9 ) The invention according to claim 9 is characterized in that when the set speed is changed by the speed setting means during printing, the control means applies a new conveyance speed corresponding to the next page and subsequent pages. an ink jet printer according to any one of claims 1 to 8, characterized.

( 10 ) The invention according to claim 10 is characterized in that the control means monitors the temperature of the print head and issues a warning when a temperature change exceeds a predetermined limit. The inkjet printer according to any one of 9 .

( 11 ) The invention according to claim 11 is characterized in that the control means monitors the temperature of the print head and stops printing when the temperature exceeds a predetermined limit. The inkjet printer according to any one of 9 .

(12) invention of claim 12, wherein said head drive means, any of claims 1 to 11 in a drive signal having a waveform corresponding to the conveying speed to drive the print head, it is characterized by It is an inkjet printer as described in above.

(13) invention of claim 13 wherein, settable printing speed by the speed setting means is a number of prints per variable unit time with a single unit, according to claim 1 to claim 12, characterized in that An inkjet printer according to any one of the above.

  According to the present invention, it is possible to realize an inkjet printer that achieves a trade-off between print speed and print quality with high productivity as follows.

(1) In the first aspect of the present invention, the control means causes the recording medium conveyance speed under the print head corresponding to the print speed set by the speed setting means, and printing is not possible due to the apparatus conditions. and conveying speed is a speed other than the speed becomes stable, the effective printing speed when combined with the conveying speed from the completion of printing of one page a time interval between the print start of the next page is a user setting determining the combination of the transport speed and the time interval between the time interval matching the printing speed, along with causing the transport and supply of a recording medium in this combination to the medium conveying means, the print on a frequency proportional to the conveying speed Ink ejection by the head is performed by the head driving means.

  That is, printing at a printing speed set by the user is broken down to a combination of the conveyance speed of the recording medium and the time interval from the end of printing of one page to the start of printing of the next page. Therefore, it is possible to realize an ink jet printer that achieves a trade-off between print speed and print quality with high productivity.

  (2) In the invention described in claim 2, the printing speed set by the speed setting means is a combination of the conveyance speed and the time interval. For this reason, in addition to the above, the user can set an optimal combination of the conveyance speed and the time interval.

(3) In the invention described in claim 3, the print speed set by the speed setting means is the number of prints per unit time. For this reason, in addition to the above, the user can perform printing with an optimal combination of the conveyance speed and the time interval only by setting the number of prints per unit time.

( 4 ) In the invention described in claim 4 , the speed at which printing becomes unstable due to the apparatus conditions is the speed corresponding to the frequency at which the print head cannot be driven stably. For this reason, in addition to the above, it is possible to prevent deterioration in print quality due to unstable operation of the print head.

( 5 ) In the invention described in claim 5 , the speed at which printing becomes unstable depending on the apparatus conditions is set to a speed at which the recording medium cannot be stably conveyed. For this reason, in addition to the above, it is possible to prevent a decrease in print quality due to unstable conveyance.

( 6 ) In the invention according to claim 6 , the control means determines the maximum value of the conveyance speed and the time interval based on at least one of the characteristic value of the document to be printed, the type of the recording medium, the environmental temperature and the print head temperature. In addition to limiting the minimum value, the maximum print speed that can be set by the user is displayed or limited. For this reason, in addition to the above, it is possible to prevent print quality deterioration due to the influence of the load condition of the print head, the type of recording medium, the environmental temperature, the print head temperature, and the like.

( 7 ) In the invention according to claim 7 , the characteristic value is the number of ink ejections required for printing the document. For this reason, in addition to the above, it is possible to prevent damage to the print head, an ink non-ejection phenomenon that requires cleaning, and the like.

( 8 ) In the invention according to claim 8 , the characteristic value is the maximum value of the ink discharge amount per unit area required for printing the document. For this reason, in addition to the above, contamination due to ink overflow on the recording medium can be prevented.

( 9 ) In the invention according to claim 9 , when the set speed is changed by the speed setting means during printing, the control means applies a new transport speed corresponding to the next page and subsequent pages. For this reason, in addition to the above, the print quality in the same page can be kept constant.

( 10 ) In the invention according to claim 10 , the control means monitors the temperature of the print head and issues a warning when the temperature change exceeds a predetermined limit. For this reason, in addition to the above, it is possible to warn of a drop in print quality due to a change in droplet amount or a change in flying speed due to a temperature rise.

( 11 ) In the invention described in claim 11 , the control means monitors the temperature of the print head and stops printing when the temperature exceeds a predetermined limit. For this reason, in addition to the above, it is possible to prevent damage to the head due to temperature rise and non-ejection phenomenon that requires cleaning.

( 12 ) In the invention described in claim 12 , the head driving means drives the print head with a drive signal having a waveform corresponding to the conveyance speed. For this reason, in addition to the above, the print head can be optimally driven regardless of changes in the driving frequency corresponding to the conveyance speed.

( 13 ) In the invention of the thirteenth aspect, the print speed that can be set by the speed setting means is the number of prints per unit time that is variable in units of one sheet. For this reason, in addition to the above, the trade-off between print speed and print quality can be continuously adjusted.

  The best mode for carrying out the invention will be described below in detail with reference to the drawings. Note that the present invention is not limited to the best mode for carrying out the invention. FIG. 1 shows a block diagram of an ink jet printer. This apparatus is an example of the best mode for carrying out the invention. An example of the best mode for carrying out the present invention relating to an ink jet printer is shown by the configuration of the present apparatus.

  As shown in the figure, this apparatus has a print head 2, and the print head 2 performs printing on a recording medium P by inkjet. Ink is supplied from an ink tank (not shown).

  The print head 2 is a long print head, and has a length (297 mm) corresponding to the long side when the size of the recording medium P is, for example, A4 size. The position of the print head 2 is fixed. The recording medium P is conveyed under the print head 2 in a direction perpendicular to the longitudinal direction of the print head 2, that is, in the short side direction of the recording medium P as indicated by an arrow. Note that the length of the print head 2 may be adjusted to the length of the short side of the recording medium P, and the recording medium P may be conveyed in the long side direction.

  The print head 2 has a large number of ink ejection nozzles on the surface facing the recording medium P, and performs printing by ejecting ink from these nozzles. For example, if printing is performed with a dot density of 600 dots / 25.4 mm, the print head 2 has 7016 nozzles in the length direction. With these nozzles, a total of 4961 dots are printed in the short side length (210 mm) as the recording medium P is conveyed.

  The print head 2 may be configured as a single head as shown in FIG. 2, or may be configured as a combination of a plurality of units as shown in FIG. In the case of supporting full-color printing, such a print head is provided corresponding to a plurality of primary colors such as YMCK, for example. Hereinafter, an example in which the print head 2 is single will be described, but the same applies to the case of a plurality of heads. The print head 2 is an example of a print head in the present invention.

  The print head 2 is driven by the head drive unit 4. The recording medium P is transported by the medium transport unit 6. The recording medium P is supplied to the base of the print head 2 by the medium transport unit 6. The head drive unit 4 is an example of a head drive unit in the present invention. The medium transport unit 6 is an example of a medium transport unit in the present invention.

  As the medium transport unit 6, for example, as shown in FIG. 4, a transport belt 61 is wound around a pair of pulleys 62 and 63. One of the pair of pulleys 62 and 63 is the main driving side and the other is the driven side, and rotates in the same direction to convey the recording medium P placed on the belt 61 in the direction of the arrow. The belt 61 has air permeability, for example, and can hold the recording medium P by suction by a suction means (not shown).

  The recording medium P is fed from the delivery-side stacker 65 by the paper feed roller 64 and supplied onto the belt 61. The printed recording medium P is discharged to the stacker 66 on the receiving side. When the recording medium P is a continuous medium such as roll paper, for example, as shown in FIG. 5, the recording medium P is unwound from the paper feed roll 65 ′ and taken up on the take-up roll 66 ′ after printing. It is done.

  The driving of the print head 2 by the head driving unit 4 and the conveyance of the recording medium P by the medium conveying unit 6 are performed under the control of the control unit 8. The transport synchronization signal detected by the encoder 10 is input to the control unit 8. For example, a rotary encoder or a linear encoder is used as the encoder 10. The carrier synchronization signal is multiplied by a PLL or the like as necessary. The control unit 8 controls the head driving unit 4 based on the conveyance synchronization signal, and causes ink ejection synchronized with the conveyance. The control unit 8 is an example of a control unit in the present invention. By such ink ejection control, the drive frequency of the print head 2 becomes proportional to the conveyance speed of the recording medium P. Hereinafter, the drive frequency of the print head 2 is also referred to as an ejection frequency.

  Further, the head temperature and the environmental temperature detected by the temperature sensors 12 and 14 are input to the controller 8. The control unit 8 also uses these temperature detection signals for print control.

  A display unit 16 and an operation unit 18 are connected to the control unit 8. These are the user interfaces. The user grasps the state of the apparatus based on the information displayed on the display unit 16 and inputs an appropriate command through the operation unit 18 to cause the apparatus to perform a desired print job. The print speed is also set through the operation unit 18. The operation unit 18 is an example of speed setting means in the present invention.

  The control unit 8 includes a document data memory 20 and a control data memory 22. The document data memory 20 stores document data to be printed. The document data is read by the control unit 8 and the contents are printed on the recording medium P as a hard copy. The control data memory 22 stores data related to print control. The control unit 8 performs print control using this control data.

  The print control by the control unit 8 will be described. The purpose of print control is to increase productivity as much as possible within the range of print quality acceptable by the user. Since the productivity is proportional to the printing speed, it is sufficient to increase the printing speed in order to increase the productivity. However, an increase in the printing speed is accompanied by a decrease in print quality, so a trade-off is necessary. The trade-off is determined by the user, but it is desirable that the print speed set by the user can be adjusted steplessly in order to enable a delicate trade-off.

  On the other hand, there may be a speed zone where printing becomes unstable depending on the conditions of the ink jet printer, that is, the mechanical or electrical conditions of the recording medium conveyance system or print head. It is not appropriate to reflect on the speed.

  Therefore, in order to cope with such circumstances, the control unit 8 performs control of the conveyance speed and the print interval, control to avoid an unstable speed band, control of the timing of changing the conveyance speed, and control based on the temperature of the print head. Do. Hereinafter, these will be sequentially described.

(1) Control of transport speed and print interval and control to avoid unstable speed band The document print speed is primarily determined by the transport speed of the recording medium. The time interval from the end of printing to the start of printing the next page is also related to the printing speed. Therefore, by controlling each of them, the effective print speed can be matched with the print speed set by the user. Hereinafter, the conveyance speed of the recording medium is also simply referred to as conveyance speed, and the time interval from the end of printing one page to the start of printing the next page is also simply referred to as time interval or print interval.

  The print speed is set through the operation unit 18. The operation unit 18 can set the printing speed steplessly. The user sets an arbitrary print speed through the operation unit 18. The print speed is set as the number of prints per unit time, for example, the number of print pages per minute.

  The control unit 8 obtains a combination of the conveyance speed and the time interval for achieving the printing speed based on the set printing speed. At that time, the conveyance speed is obtained by excluding a speed band in which printing becomes unstable depending on apparatus conditions. Then, the time interval is determined so that the effective print speed under such a conveyance speed matches the print speed set by the user.

  When the print speed is increased, the quality may be reduced depending on the cause, for example, "the quality deteriorates due to the change in the physical properties of the ink due to the temperature rise of the print head", the transport speed (and the ejection frequency proportional to it) Some improvements can be achieved by lowering the print speed by reducing the print speed by at least one of lowering or increasing the print interval, and reducing the number of print pages per unit time. Variation in the appropriate amount of ink liquid, flying angle, flying speed, etc., and the increase in the landing position error of the ink droplets combined with the increase in the transport speed of the recording medium, the deterioration of graininess and the occurrence of banding However, even if the print interval is increased, it cannot be improved. Without lowering the discharge frequency) is proportional to Bisore some of which can not be improved.

  In view of this point, in order to reduce the number of printed pages per unit time in order to avoid a decrease in print quality, it is necessary to lower the conveyance speed (and the discharge frequency proportional to it) while keeping the print interval at the minimum value. Sometimes it takes priority.

  However, there are unstable speed regions and discharge frequency regions in the transport speed and the discharge frequency depending on the characteristics of the transport device and the print head. Note that the unstable conveyance speed means that, for example, vibration at the resonance frequency of the conveyance system becomes large, the recording medium vibrates, the landing is disturbed, and the print quality is deteriorated. Also, the unstable ejection frequency means that, for example, due to the interaction between the acoustic vibration generated in the ink in the head and the drive, it becomes impossible to eject ink or the amount of ejected liquid becomes unstable, and the print quality becomes unstable. Deterioration occurs.

  Therefore, if the transport speed (and the discharge frequency proportional to it) is in an unstable speed range (or discharge frequency range) with the print interval at the minimum value, the transport speed (and the discharge frequency proportional to it) will be reduced. The minimum value in the range higher than the stable region is fixed, and the print interval is increased.

  The method of lowering the print speed starting from the maximum print speed will be described. First, the print speed is lowered by lowering the transport speed (and the ejection frequency proportional thereto) while keeping the print interval at the minimum value.

  If the transport speed (and the discharge frequency proportional to it) is lowered and the transport speed or the discharge frequency proportional to it enters the unstable area, fix it to the lowest value in the range higher than the unstable area and print. Increase the interval.

  If the printing speed is further reduced and the printing speed becomes lower than the printing speed that is lower than the unstable area (and the ejection frequency proportional to it) even at the minimum printing interval, the printing interval is minimized and maintained again. The printing speed is lowered by lowering the transport speed (and the ejection frequency proportional to it).

An example of determination of such conveyance speed and time interval is shown below. Assume that the apparatus conditions of this apparatus are given as follows, for example. This apparatus condition is stored in the control data memory 22 in advance.
-Page length: 210mm (A4 short side, long side is 297mm)
-Number of dots in the page length direction: 4961 (600 dots / 25.4 mm)
・ Maximum conveyance speed: 1000 mm / second ・ Minimum time interval: 0.1 second ・ Maximum print head drive frequency: 23.6 kHz
-Driving frequency range where printing becomes unstable: 19.2 kHz-20.9 kHz
(813mm / sec-880mm / sec in terms of conveyance speed)
・ Conveying speed range where printing becomes unstable: 780 mm / sec.−850 mm / sec. ・ Maximum printing speed: 194 pages / min. Conveyance speed and time interval determined by the control unit 8 under such apparatus conditions. The combination is shown in FIG. As shown in the figure, with respect to a user-set print speed of 194 pages / minute, the transport speed and time interval are determined to be 1000 mm / second and 0.1 second, respectively. This achieves the highest print speed. For a printing speed of 178 → 194 pages / minute, the transport speed and time interval are determined as 885 → 1000 mm / second and 0.1 second, respectively. That is, the transport speed can be changed in response to a change in the print speed setting value while keeping the time interval at the minimum value.

  For the printing speed 161 → 178 pages / minute, the transport speed and time interval are determined as 885 mm / second and 0.1 → 0.135 second, respectively. That is, an effective print speed is achieved by changing the time interval while keeping the transport speed constant regardless of the change in the print speed set value. The constant conveyance speed is out of the upper limit of the speed range in which printing becomes unstable. That is, both the upper limit of the conveyance speed corresponding to the drive frequency range in which printing becomes unstable and the upper limit of the conveyance speed range in which printing becomes unstable are deviated.

  For a printing speed of 161 pages / minute, the transport speed and time interval are determined to be 770 mm / second and 0.1 second, respectively. At this time, the conveyance speed is out of the lower limit of the speed range in which printing becomes unstable. That is, both the lower limit of the conveyance speed corresponding to the drive frequency range in which the printing becomes unstable and the lower limit of the conveyance speed range in which the printing becomes unstable.

  For a print speed of 0 → 161 pages / minute, the transport speed and time interval are determined as 0 → 770 mm / second and 0.1 second, respectively. That is, the conveyance speed can be changed in response to a change in the print speed setting value while keeping the time interval at the minimum value. This transport speed is out of the lower limit of the speed range in which printing becomes unstable. That is, both the lower limit of the conveyance speed corresponding to the drive frequency range in which the printing becomes unstable and the lower limit of the conveyance speed range in which the printing becomes unstable.

  The control unit 8 causes the medium transport unit 6 to transport the recording medium P according to the combination of the transport speed and the time interval thus obtained, and causes the head driving unit 4 to perform ink ejection in synchronization therewith. Accordingly, it is possible to perform printing at an effective speed that matches the user setting while avoiding a conveyance speed at which printing becomes unstable.

  Under the control of the control unit 8, the head drive unit 4 drives the print head 2 with a drive signal having a waveform corresponding to the drive frequency. For the waveform of the drive signal, the optimum drive waveform at that drive frequency is determined in advance by changing the voltage, changing the pulse width, changing the slope of the rising and falling edges of the pulse, etc. according to the frequency, When the conveyance speed is changed, a driving frequency synchronized with the predicted driving frequency is predicted, and driving is performed with an optimum driving waveform corresponding to the predicted driving frequency. As a result, stable ink ejection can be performed over the entire range of the conveyance speed, and the print quality becomes constant regardless of the conveyance speed.

  The print speed set by the user may be set as a combination of the conveyance speed and the time interval. Thus, fine print speed setting can be performed. At this time, it is convenient to display a conveyance speed range in which printing becomes unstable on the display unit 16 in advance, and to allow user settings to be avoided. Alternatively, a settable range may be displayed as a guideline, or an unstable conveyance speed range may not be set.

  If there is a margin at the end of the page, the document data is analyzed to detect the margin at the end of the page, and this portion is controlled so as to increase the printing speed by conveying it at a speed higher than the conveying speed at the time of printing. You can also.

(2) Control of timing for changing conveyance speed The user may change the setting of the printing speed during printing as necessary. In response to such a change in setting, the control unit 8 obtains a new combination of the conveyance speed and the time interval. The new combination is applied to the conveyance at a selected timing. That is, the change of the conveyance speed by a new combination is performed after printing of one page is completed. For this reason, conveyance with a new combination is performed for the next page and thereafter. By doing so, it is possible to prevent the conveyance speed from changing during the printing of the page and causing a step in the print image quality. However, although there may be a change in image quality between pages, it is not noticeable because it is not a change within the same page.

(3) Control based on print head temperature Since the print head 2 ejects ink using a piezo element or an electrothermal conversion element, power consumption in the piezo element or electrothermal conversion element, power consumption due to electric resistance of the wiring pattern The temperature rises due to heat generation due to consumption, power consumption in the head and the driving IC provided in the vicinity of the head, and the like.

  Since the heat generation per unit time of the head increases as the driving frequency increases for the same document data, the temperature rise increases as the printing speed increases. If the printing speed is the same, the temperature rise increases as the number of ink ejections per page increases, and a partial temperature rise occurs where the amount of ink ejection per unit area is large. Since temperature rise is a balance between heat generation and heat dissipation, it is also affected by environmental temperature.

  When the temperature of the print head 2 rises, the ink temperature in the head rises and the physical properties of the ink change, and when the ink physical properties change, for example, the appropriate amount of ink to be ejected and the flying speed change to change the color and density of the print. . Many high-speed printers print the same document or a large number of documents that are almost the same but differ only by a small part. In this case, it is not preferable that the color and density change between prints.

  When the temperature of the print head 2 rises beyond the allowable range, the change in the physical properties of the ink becomes large and ejection becomes unstable, and the nozzle surface of the print head 2 becomes dirty with broken droplets, or bubbles are mixed in the head. As a result, ink cannot be ejected. In such a case, unless ink is forcibly sucked from the nozzles or head cleaning is performed such that the nozzle surface is wiped with a blade, stable ejection cannot be performed again.

  Therefore, the control unit 8 monitors the head temperature and the environmental temperature detected by the temperature sensors 12 and 14 and performs control to prevent a problem that the print quality is deteriorated or the head cleaning is required. In addition to the absolute value of the head temperature, the speed of change is monitored.

  The change in temperature is how many degrees C the temperature changes in a unit time, for example, 1 second. When the temperature change exceeds a predetermined limit, the appropriate amount of ink liquid and the flying speed change, and the print color and Since it is predicted that the density will change, the display unit 16 warns the user of this fact, and lowers the print speed setting in the case of a positive temperature change (or print speed setting in the case of a negative temperature change). Recommended). At this time, a plurality of predetermined limits may be provided and a strong recommendation or warning may be given step by step.

  If the user lowers the print speed setting based on the recommendation or warning, a change in print quality can be prevented. If the change in print quality is allowed, the user may continue printing with the original settings regardless of the warning.

  Further, when the temperature change exceeds a predetermined limit, the print speed setting may be automatically lowered for a positive temperature change and increased for a negative temperature change. . As a result, it is possible to prevent a change in print quality due to carelessness of the user.

  When the controller 8 determines from the head temperature and the head temperature change that the head temperature may exceed a predetermined limit, the controller 8 automatically reduces the print speed. At this time, the user may be notified of this through the display unit 16.

  Further, when the absolute value of the head temperature exceeds a predetermined limit and there is a possibility that stable ejection cannot be performed again unless a return operation such as head cleaning is performed, the control unit 8 automatically stops printing. In this way, it is possible to avoid a change in print quality change due to a rise in head temperature and a serious failure of the head.

  An increase in head temperature can be predicted from the contents of the document. That is, a document including many full-color pages can be predicted to have a large temperature rise because the total number of ink ejections for printing the document is large. On the other hand, since the total number of ink ejections is small for a document with only a large margin, it can be predicted that the temperature rise is small. That is, the total number of ink ejections can be used as a document characteristic value for temperature rise prediction.

  Further, even if the total number of ink ejections is not necessarily large, it can be predicted that a document having several places where ink ejection is concentrated is greatly increased in head temperature. It can also be predicted that fixing and drying defects are likely to occur. Such a portion can be predicted from the maximum value of the ink discharge amount per unit area. That is, the ink discharge amount per unit area can be used as a document characteristic value for temperature rise prediction or print quality prediction.

  Therefore, the control unit 8 analyzes the document data to be printed stored in the document data memory 20 and determines the increase in head temperature or the print quality when printing is performed at the standard print speed from the characteristic value of the document. Predict. Then, when the predicted temperature exceeds a predetermined limit, the maximum value of the print speed capable of keeping the head temperature or the print quality within the allowable range even under such a characteristic value is obtained. The maximum value of the printing speed is obtained as a combination of the maximum value of the conveyance speed and the minimum value of the time interval. Such a maximum value of the print speed is displayed on the display unit 16.

  As a result, the user can know in advance the upper limit of the print speed that can be set. Therefore, the print speed can be set within the range. Alternatively, setting of a print speed exceeding the upper limit may be prohibited. As a result, it is possible to perform printing without quality deterioration due to an increase in head temperature.

  It should be noted that the current value of the head temperature and the ambient temperature before the start of printing may also be used for the head temperature prediction to increase the certainty of the prediction. Also, since the ink fixing / drying speed varies depending on whether the recording medium is plain paper, high-quality paper, coated paper, etc., the printing speed based on the head temperature prediction or print quality prediction is also used for information on the recording medium type. It is preferably used for restriction.

  The relationship between the document characteristic value, the type of recording medium, the head temperature, the environmental temperature, and the print speed upper limit value is obtained in advance through experiments and simulations, and is stored in the control data memory 22 as a control data table. The control unit 8 obtains the print speed upper limit value by referring to the control data table.

It is a block diagram of an inkjet printer. It is a schematic diagram of a print head. It is a schematic diagram of a print head. It is a schematic diagram of a medium conveyance part. It is a schematic diagram of a medium conveyance part. It is a figure which shows an example of a response | compatibility with printing speed, conveyance speed, and a time interval.

Explanation of symbols

P Recording medium 2 Print head 4 Head drive unit 6 Medium transport unit 8 Control unit 10 Encoder 12, 14 Temperature sensor 16 Display unit 18 Operation unit 20 Document data memory 22 Control data memory 61 Belt 62, 63 Pulley 64 Feed roller 65, 66 Stacker

Claims (13)

A print head having a plurality of nozzles for discharging ink over a length corresponding to the dimension of the recording medium in a direction perpendicular to the transport direction;
Medium conveying means for supplying a recording medium to the print head and conveying the recording medium under the print head;
Head driving means for causing the print head to discharge ink in synchronization with conveyance of the recording medium;
Speed setting means for setting a print speed based on a user instruction;
A transport speed corresponding to the print speed set by the speed setting means, a transport speed of the recording medium under the print head, excluding a speed at which printing becomes unstable depending on apparatus conditions ; and The time interval from the end of printing one page to the start of printing the next page, and the transport speed and time interval when the effective print speed when combined with the transport speed matches the user-set print speed. And a control unit that causes the medium transport unit to transport and supply the recording medium in this combination, and causes the head driving unit to eject ink by the print head at a frequency proportional to the transport speed. When,
An inkjet printer characterized by comprising: The printing speed set by the speed setting means is a combination of a conveyance speed and a time interval.
The ink jet printer according to claim 1.   2. An ink jet printer according to claim 1, wherein the print speed set by said speed setting means is the number of prints per unit time. The speed at which printing becomes unstable due to the apparatus conditions is a speed corresponding to a frequency at which the print head cannot be stably driven .
The ink jet printer according to claim 1, wherein the ink jet printer is provided. The speed at which printing by the device condition becomes unstable, a velocity that can not be stably conveying a recording medium,
The ink jet printer according to claim 1 , wherein the ink jet printer is provided. The control means limits the maximum value of the conveyance speed and the minimum value of the time interval based on at least one of the characteristic value of the document to be printed, the type of recording medium, the environmental temperature, and the print head temperature. Display or limit the maximum print speed that can be set,
An ink jet printer according to any one of claims 1 to 5, wherein The characteristic value is the number of ink ejections required for printing a document.
The ink jet printer according to 請 Motomeko 6 you wherein a. The inkjet printer according to claim 6 , wherein the characteristic value is a maximum value of an ink discharge amount per unit area required for printing a document. When the set speed is changed by the speed setting means during printing, the control means applies a new conveyance speed corresponding to the next page and subsequent pages.
The ink jet printer according to claim 1 , wherein the ink jet printer is provided. The control means monitors the temperature of the print head and issues a warning when a temperature change exceeds a predetermined limit;
The ink jet printer according to claim 1, wherein the ink jet printer is provided. It said control means, print Ru was stopped when the temperature of the monitored temperature of the print head exceeds a predetermined limit,
The ink jet printer according to any one of claims 1 to 9, characterized in that. The head driving means drives the print head with a drive signal having a waveform corresponding to the conveyance speed;
The ink jet printer according to any one of claims 1 to 11, characterized in that. The print speed that can be set by the speed setting means is the number of prints per unit time that is variable in units of one sheet.
The ink jet printer according to claim 1, wherein the ink jet printer is provided.

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