Method for generating print timing signals, printing apparatus, and program for generating print timing signals

Abstract

This invention provides a printing device that can reduce the misalignment of ink droplets during acceleration and deceleration printing compared to conventional methods. [Solution] The length of each unit period (the period from the rising edge of the encoder pulse to the next rising edge) is measured by counting the number of internal clocks (S100). A reference signal is generated based on the length of the first unit period (the previous unit period) (S210). A print timing signal is generated based on the reference signal and a multiplication setting value that represents the relationship between the frequency of the print timing signal and the frequency of the reference signal (S220). The amount of misalignment is calculated based on the length of the first unit period and the length of the second unit period (the unit period two units prior) (S310), and the cumulative amount of misalignment is calculated by accumulating the amounts of misalignment (S320). If the cumulative amount of misalignment falls outside the allowable range of misalignment, the multiplication setting value is adjusted (S330).

Description

Technical Field

[0003]

[0001] The present invention relates to a printing apparatus that performs printing by discharging ink from a print head, and more particularly to a method for generating a printing timing signal that defines the timing for discharging ink from the print head of the printing apparatus.

Background Art

[0002] An inkjet printing apparatus that performs printing by discharging ink onto a printing medium by heat or pressure is widely known. In an inkjet printing apparatus that performs high-speed printing, typically, a long strip of printing paper (continuous paper) called roll paper is adopted as the printing medium. The long strip of printing paper is conveyed by a conveyance mechanism including conveyance rollers and the like, and printing is performed by discharging ink from a print head onto the conveyed printing paper.

[0003] When printing on a long strip of printing paper, the transport speed of the printing paper (the distance the printing paper is transported per unit time by the transport mechanism) gradually increases from a stopped state. In other words, the transport speed accelerates at the start of printing. Once the transport speed reaches a predetermined speed, printing is performed while maintaining a constant transport speed. After that, at the end of printing, the transport speed gradually decreases from the predetermined speed until the device stops. In other words, the transport speed decelerates at the end of printing. Furthermore, some inkjet printers offer multiple settable transport speeds (printing speeds). Generally, in such inkjet printers, printing is performed with the transport speed set to the highest of the multiple available speeds. However, during the period when printing is being performed with the transport speed set to the highest speed, it may be necessary to decelerate the transport speed for various reasons. For example, in an inkjet printer that offers "high speed" and "low speed" as settable transport speeds, if it becomes necessary to decelerate the transport speed during the period when printing is being performed with the transport speed set to high speed, the transport speed will be changed from high speed to low speed. Then, printing is performed while the transport speed is maintained at a low speed. After that, once the situation requiring printing at a low transport speed is resolved, the transport speed is changed from low to high speed, and printing is performed while the transport speed is maintained at high speed.

[0004] As described above, the transport speed of an inkjet printer is accelerated or decelerated during operation. Furthermore, some inkjet printers can perform printing not only during periods when the transport speed is constant, but also during periods when the transport speed is changing (i.e., during periods of acceleration or deceleration). Printing performed during periods of changing transport speed is called "acceleration / deceleration printing."

[0005] In general, in inkjet printers, a pulse signal is supplied to the head drive circuit that drives the print head to define the timing of ink ejection from the print head, so that ink is ejected from the print head onto the paper at the appropriate timing. In this specification, this pulse signal is referred to as the "print timing signal." The print timing signal is generated based on an encoder signal output from an encoder attached to the rotating shaft of the transport roller that constitutes the transport mechanism. As a result, when the transport speed is high, the print timing signal is generated so that ink is ejected from the print head at relatively short time intervals, and when the transport speed is low, the print timing signal is generated so that ink is ejected from the print head at relatively long time intervals.

[0006] Here, with reference to Figure 48, an example of a conventional method for generating the print timing signal PT will be described. In this example, the encoder signal consists of two phase signals (A-phase signal ENC_A and B-phase signal ENC_B), and the duty cycle of these two phase signals is 1 / 2. The print timing signal PT is a pulse signal, and the head drive circuit drives the print head so that ink is ejected from the print head at the rising edge of the pulse signal. The print timing signal PT is generated according to the period length of the encoder signal. For example, the print timing signal PT in period TA1 is generated based on the length of period A1 (the period from the rising edge of the A-phase signal ENC_A to the next rising edge), and the print timing signal PT in period TB4 is generated based on the length of period B4 (the period from the falling edge of the B-phase signal ENC_B to the next falling edge). Thus, with respect to Figure 48, if X is an arbitrary string, the print timing signal PT in period TX is generated based on the length of period X. The length of each period X can be determined by counting the number of internal clocks that occur during that period X.

[0007] Based on the print timing signal PT generated as described above, the head drive circuit drives the print head, causing ink to be ejected from the print head according to the paper transport speed. As a result, a good printed image is formed on the paper regardless of the transport speed during printing. However, when the acceleration / deceleration printing described above is performed, the transport speed when the print timing signal PT is generated differs from the transport speed when the ink is actually ejected from the print head. Therefore, the ink ejected from the print head lands on the paper at a position shifted from the desired landing position. This disruption in the ink's landing position prevents the acquisition of a good printed image.

[0008] Japanese Patent Publication No. 2007-118425 discloses an invention for a timing pulse generator that can output an appropriate printing timing signal (referred to as a "jet timing signal" in Japanese Patent Publication No. 2007-118425) even while the printing paper is accelerating or decelerating. According to this invention, the current encoder period is predicted by subtracting the difference between the encoder period two cycles ago and the previous encoder period from the previous encoder period (i.e., the predicted period is determined). Then, a preliminary timing signal is output by counting the pulses of the delay signal generated by applying a frequency division process to the predicted period, and a printing timing signal is generated based on this preliminary timing signal. [Prior art documents] [Patent Documents]

[0009] [Patent Document 1] Japanese Patent Publication No. 2007-118425 [Overview of the project] [Problems that the invention aims to solve]

[0010] However, according to the invention disclosed in Japanese Patent Publication No. 2007-118425, it is assumed that the transport speed changes at a constant rate when acceleration or deceleration printing is performed. Therefore, if the change in transport speed when acceleration or deceleration printing is performed is not constant (i.e., if there is a change in acceleration or deceleration), it is not possible to generate a printing timing signal so that ink is ejected from the print head at the appropriate timing. Consequently, misalignment of the ink's landing position occurs, and a good printed image cannot be obtained.

[0011] Therefore, the present invention aims to realize a printing apparatus that can reduce the misalignment of ink placement when acceleration and deceleration printing is performed compared to conventional methods. [Means for solving the problem]

[0012] The first invention relates to a printing apparatus comprising a print head for ejecting ink onto a printing medium, a moving mechanism for relatively moving the positional relationship between the print head and the printing medium, an encoder that outputs pulses at a period corresponding to the moving speed which is the speed at which the moving mechanism relatively moves the positional relationship, and an internal clock generation circuit that generates an internal clock at a constant period, wherein a printing timing signal generation method is used to generate a printing timing signal that defines the timing for ejecting ink from the print head, An encoder period length measurement step, which measures the length of each unit period by counting the number of internal clocks, with the unit period being the period from the rising edge of a pulse output from the encoder to the next rising edge, or the period from the falling edge of a pulse output from the encoder to the next falling edge; A reference signal generation step that generates a reference signal corresponding to a signal obtained by multiplying the frequency of the printing timing signal based on the length of the first unit period, which is the previous unit period, A printing timing signal generation step that generates the printing timing signal based on a multiplication setting value, which is a setting value of a multiplication number representing the relationship between the frequency of the printing timing signal and the frequency of the reference signal, and the reference signal. A positional displacement calculation step that calculates the amount of positional displacement caused by the difference between the moving speed in the second unit period and the moving speed in the first unit period, based on the length of the second unit period, which is two unit periods prior, and the length of the first unit period, A cumulative positional displacement calculation step, which calculates the cumulative positional displacement by accumulating the aforementioned positional displacement amounts, An adjustment step in which the multiplication setting value is adjusted based on the result of comparing the cumulative positional displacement with a predetermined threshold; Includes, The printing timing signal generation step is characterized in that the printing timing signal is generated when the number of times the reference signal has been generated after the previous printing timing signal has been generated becomes equal to the multiplication setting value.

[0013] The second invention is, in the first invention, In the step of calculating the amount of positional displacement, the product of the value obtained by subtracting the movement speed in the first unit period from the movement speed in the second unit period and the length of the first unit period, or the product of the value obtained by subtracting the movement speed in the second unit period from the movement speed in the first unit period and the length of the first unit period, is calculated as the amount of positional displacement.

[0014] The third invention is, in the second invention, The predetermined threshold includes a first threshold that is a negative value and a second threshold that is a positive value. In the position displacement calculation step, if the product of the value obtained by subtracting the movement speed in the first unit period from the movement speed in the second unit period and the length of the first unit period is calculated as the position displacement amount, then in the adjustment step, if the cumulative position displacement amount becomes smaller than the first threshold, 1 is subtracted from the multiplication setting value, and if the cumulative position displacement amount becomes larger than the second threshold, 1 is added to the multiplication setting value. In the position displacement calculation step, if the product of the value obtained by subtracting the movement speed in the second unit period from the movement speed in the first unit period and the length of the first unit period is calculated as the position displacement amount, the adjustment step is characterized in that, when the cumulative position displacement amount becomes smaller than the first threshold, 1 is added to the multiplication setting value, and when the cumulative position displacement amount becomes larger than the second threshold, 1 is subtracted from the multiplication setting value.

[0015] The fourth invention is, in the second invention, The predetermined threshold includes a first threshold that is a negative value and a second threshold that is a positive value. In the position displacement calculation step, if the product of the value obtained by subtracting the movement speed in the first unit period from the movement speed in the second unit period and the length of the first unit period is calculated as the position displacement, then, with K being a natural number, in the adjustment step, if the cumulative position displacement becomes less than K times the first threshold, K is subtracted from the multiplication setting value, and if the cumulative position displacement becomes greater than K times the second threshold, K is added to the multiplication setting value. In the position displacement calculation step, if the product of the value obtained by subtracting the movement speed in the second unit period from the movement speed in the first unit period and the length of the first unit period is calculated as the position displacement, then, with K being a natural number, in the adjustment step, if the cumulative position displacement becomes less than K times the first threshold, K is added to the multiplication setting value, and if the cumulative position displacement becomes greater than K times the second threshold, K is subtracted from the multiplication setting value.

[0016] The fifth invention relates to the third or fourth invention, The absolute value of the first threshold and the second threshold are equal.

[0017] The sixth invention is, in the first invention, In the positional deviation amount calculation step, the absolute value of the difference between the moving speed in the second unit period and the moving speed in the first unit period is multiplied by the length of the first unit period, and the result is calculated as the positional deviation amount.

[0018] A seventh invention is the invention according to the sixth invention, where the positional deviation amount, the cumulative positional deviation amount, and the predetermined threshold value are positive values, in the adjustment step, when the cumulative positional deviation amount becomes greater than the predetermined threshold value while the length of the first unit period is shorter than the length of the second unit period, 1 is subtracted from the multiplication setting value, and when the cumulative positional deviation amount becomes greater than the predetermined threshold value while the length of the first unit period is longer than the length of the second unit period, 1 is added to the multiplication setting value.

[0019] An eighth invention is the invention according to the sixth invention, where the positional deviation amount, the cumulative positional deviation amount, and the predetermined threshold value are positive values, in the adjustment step, when K is a natural number and the cumulative positional deviation amount becomes greater than K times the predetermined threshold value while the length of the first unit period is shorter than the length of the second unit period, K is subtracted from the multiplication setting value, and when the cumulative positional deviation amount becomes greater than K times the predetermined threshold value while the length of the first unit period is longer than the length of the second unit period, K is added to the multiplication setting value.

[0020] A ninth invention is the invention according to any one of the first to fourth, sixth to eighth inventions, where the absolute value of the predetermined threshold value is equal to a value obtained by dividing the interval between dots formed on the printing medium by the ink ejected from the print head by the multiplication setting value before being adjusted in the adjustment step.

[0021] A tenth invention is the invention according to any one of the first to fourth, sixth to eighth inventions, The multiplication setting value is changed from a predetermined reference value to an adjustment value in the adjustment step, and then when the print timing signal is generated in the print timing signal generation step, the multiplication setting value is changed from the adjustment value to the reference value.

[0022] The eleventh invention relates to any of the first to fourth or sixth to eighth inventions, If P is the number of times the reference signal should be generated in each unit period, the reference signal generation step is characterized in that, each time the internal clock is generated by the internal clock generation circuit, P is added to the first counter value, and when the first counter value becomes equal to or greater than the length of the first unit period, the length of the first unit period is subtracted from the first counter value and the reference signal is generated.

[0023] The twelfth invention relates to any of the first to fourth or sixth to eighth inventions, In the print timing signal generation step, 1 is added to the second counter value each time the reference signal is generated in the reference signal generation step, and when the second counter value becomes equal to the multiplication setting value, the second counter value is set to 0 and the print timing signal is generated.

[0024] The 13th invention relates to any of the 1st to 4th or 6th to 8th inventions, Each time a pulse is output from the encoder, the positional displacement amount is calculated in the positional displacement amount calculation step, and further, the cumulative positional displacement amount is calculated in the cumulative positional displacement amount calculation step.

[0025] The fourteenth invention is a printing apparatus, A print head that ejects ink onto the printing medium, A moving mechanism for relatively changing the positional relationship between the print head and the printing medium, An encoder that outputs pulses at a period corresponding to the movement speed, which is the speed at which the movement mechanism moves the relative positional relationship, An internal clock generation circuit that generates an internal clock at a constant period, An encoder period length measuring circuit measures the length of each unit period by counting the number of internal clocks, with the unit period being the period from the rising edge of a pulse output from the encoder to the next rising edge, or the period from the falling edge of a pulse output from the encoder to the next falling edge. A print timing signal generation circuit generates a print timing signal that defines the timing for ejecting ink from the print head, A print timing signal correction circuit for correcting the timing at which the print timing signal is generated, Equipped with, The aforementioned printing timing signal generation circuit is: A reference signal generation counter generates a reference signal corresponding to a signal obtained by multiplying the frequency of the printing timing signal by the number of internal clocks, based on the length of the first unit period, which is the previous unit period. The print timing signal generation counter generates the print timing signal when the number of reference signals generated by the reference signal generation counter is counted, and the number of times the reference signal has been generated after the previous print timing signal has been generated becomes equal to the multiplication setting value, which is a setting value of the multiplication number that represents the relationship between the frequency of the print timing signal and the frequency of the reference signal. Includes, The aforementioned printing timing signal correction circuit is: A positional displacement update circuit calculates the amount of positional displacement resulting from the difference between the moving speed in the second unit period and the moving speed in the first unit period, based on the length of the second unit period which is two unit periods prior and the length of the first unit period, and calculates the cumulative positional displacement amount by accumulating the amount of positional displacement, An adjustment circuit adjusts the multiplication setting value referenced by the printing timing signal generation counter based on the result of comparing the cumulative positional deviation amount with a predetermined threshold. It is characterized by including.

[0026] The 15th invention is a printing timing signal generation program that generates a printing timing signal that defines the timing for ejecting ink from the print head in a printing apparatus comprising: a print head for ejecting ink onto a printing medium; a moving mechanism for relatively moving the positional relationship between the print head and the printing medium; an encoder that outputs pulses at a period corresponding to the moving speed, which is the speed at which the moving mechanism relatively moves the positional relationship; and an internal clock generation circuit that generates an internal clock at a constant period. The computer included in the aforementioned printing device An encoder period length measurement step, which measures the length of each unit period by counting the number of internal clocks, with the unit period being the period from the rising edge of a pulse output from the encoder to the next rising edge, or the period from the falling edge of a pulse output from the encoder to the next falling edge; A reference signal generation step that generates a reference signal corresponding to a signal obtained by multiplying the frequency of the printing timing signal based on the length of the first unit period, which is the previous unit period, A printing timing signal generation step that generates the printing timing signal based on a multiplication setting value, which is a setting value of a multiplication number representing the relationship between the frequency of the printing timing signal and the frequency of the reference signal, and the reference signal. A positional displacement calculation step that calculates the amount of positional displacement caused by the difference between the moving speed in the second unit period and the moving speed in the first unit period, based on the length of the second unit period, which is two unit periods prior, and the length of the first unit period, A cumulative positional displacement calculation step, which calculates the cumulative positional displacement by accumulating the aforementioned positional displacement amounts, An adjustment step in which the multiplication setting value is adjusted based on the result of comparing the cumulative positional displacement with a predetermined threshold; Make it run, The printing timing signal generation step is characterized in that the printing timing signal is generated when the number of times the reference signal has been generated after the previous printing timing signal has been generated becomes equal to the multiplication setting value. [Effects of the Invention]

[0027] According to the first invention described above, the amount of positional misalignment caused by the difference between the printing speed in the second unit period (the speed at which the moving mechanism moves the relative positional relationship between the print head and the printing medium) and the printing speed in the first unit period is calculated based on the length of the second unit period, which is two unit periods prior, and the length of the first unit period, which is one unit period prior, with the generation period of the pulse output from the encoder as the unit period. Furthermore, the cumulative amount of positional misalignment is calculated by accumulating these amounts of positional misalignment. Then, based on the result of comparing the cumulative amount of positional misalignment with a threshold value, the setting value of the multiplication factor (multiplication setting value) that represents the relationship between the frequency of the reference signal used to generate the print timing signal and the frequency of the print timing signal is adjusted. Incidentally, the print timing signal is generated when the number of times the reference signal has been generated after the previous print timing signal has been generated becomes equal to the multiplication setting value. Therefore, by appropriately setting the threshold value so that the multiplication setting value is suitably adjusted, it becomes possible to generate the print timing signal at a suitable timing so that the magnitude of positional misalignment is reduced. Based on the above, a printing device has been realized that can reduce the misalignment of ink placement when acceleration and deceleration printing is performed compared to conventional methods. Furthermore, because the misalignment of ink placement is reduced, the need for reprinting is decreased, and the wasteful consumption of printing media and ink is suppressed. In this way, it can contribute to achieving the SDGs (Sustainable Development Goals).

[0028] According to the second invention described above, since the amount of misalignment is calculated accurately, the cumulative amount of misalignment is also calculated accurately. As a result, the timing for generating the printing timing signal is adjusted with high precision.

[0029] According to the third invention described above, if the cumulative misalignment exceeds a threshold during acceleration of the printing speed, a printing timing signal is generated at an earlier timing than usual, and if the cumulative misalignment exceeds a threshold during deceleration of the printing speed, a printing timing signal is generated at a later timing than usual. This effectively reduces the misalignment of ink placement when acceleration and deceleration printing is performed.

[0030] According to the fourth invention described above, even when the printing speed is greatly accelerated or greatly decelerated, the misalignment of the ink's landing position is effectively reduced.

[0031] According to the fifth invention described above, the same effects as those of the third or fourth invention described above can be obtained.

[0032] According to the sixth invention described above, the amount of misalignment is accurately calculated, and therefore the cumulative amount of misalignment is also accurately calculated. As a result, the timing for generating the printing timing signal is precisely adjusted.

[0033] According to the seventh invention described above, if the cumulative misalignment exceeds a threshold during acceleration of the printing speed, a printing timing signal is generated at an earlier timing than usual, and if the cumulative misalignment exceeds a threshold during deceleration of the printing speed, a printing timing signal is generated at a later timing than usual. This effectively reduces the misalignment of ink placement when acceleration and deceleration printing is performed.

[0034] According to the eighth invention described above, even when the printing speed is greatly accelerated or greatly decelerated, the misalignment of the ink's landing position is effectively reduced.

[0035] According to the ninth invention described above, if the initial value (reference value) of the multiplication setting is M, it is possible to suppress the magnitude of the ink impact position deviation to a maximum of about 1 / M of the dot spacing.

[0036] According to the tenth invention described above, the same effects as those of the first invention described above can be obtained.

[0037] According to the 11th invention described above, the shorter the length of the preceding unit period, the shorter the time interval at which the reference signal is generated, and the longer the length of the preceding unit period, the longer the time interval at which the reference signal is generated. Since the reference signal is generated in accordance with acceleration and deceleration in this way, it becomes possible to generate the printing timing signal at a suitable timing according to the acceleration and deceleration.

[0038] According to the 12th invention described above, it is possible to generate a printing timing signal at a suitable timing with a relatively simple configuration.

[0039] According to the 13th invention described above, since the cumulative positional deviation is calculated at a high frequency, the error between the ideal printing timing and the actual printing timing is suppressed.

[0040] According to the 14th invention described above, the same effects as those of the first invention described above can be obtained.

[0041] According to the 15th invention described above, the same effects as those of the first invention described above can be obtained. [Brief explanation of the drawing]

[0042] [Figure 1] This is a schematic diagram showing one example configuration of an inkjet printing apparatus according to one embodiment of the present invention. [Figure 2] This is a plan view showing one example of the configuration of the recording unit in the above embodiment. [Figure 3] The above embodiment is a diagram illustrating the arrangement of nozzles in the print head. [Figure 4] This is a block diagram showing the hardware configuration of the print control device in the above embodiment. [Figure 5] The above embodiment is a timing chart for illustrating the calculation of the positional deviation amount in the case where a printing timing signal is generated based on a one-phase encoder signal. [Figure 6] The above embodiment is a timing chart for illustrating the calculation of the positional deviation amount in the case where a printing timing signal is generated based on a two-phase encoder signal. [Figure 7] The above embodiment is a timing chart for illustrating the reference signal. [Figure 8] This figure illustrates the distance corresponding to one cycle of the printing timing signal in the above embodiment. [Figure 9]The above embodiment is a timing chart for illustrating the generation of the printing timing signal. [Figure 10] This is a block diagram showing the functional configuration of the control unit within the print control device in the above embodiment. [Figure 11] This is a block diagram showing the detailed configuration of the printing timing signal generation circuit in the above embodiment. [Figure 12] This is a block diagram showing the detailed configuration of the printing timing signal correction circuit in the above embodiment. [Figure 13] This figure shows the relationship between the first threshold, the second threshold, and the allowable misalignment range in the above embodiment. [Figure 14] The above embodiment is a flowchart illustrating the general process involved in generating the printing timing signal. [Figure 15] The flowchart above shows the detailed procedure of the processing performed in the encoder period length measurement circuit in the above embodiment. [Figure 16] The flowchart above shows the detailed procedure of the processing performed by the printing timing signal generation circuit in the above embodiment. [Figure 17] In the above embodiment, the flowchart shows the detailed procedure of the processing performed by the printing timing signal correction circuit. [Figure 18] The above embodiment is a timing chart illustrating a specific example of generating a printing timing signal when the transport speed is maintained at a constant speed. [Figure 19] The above embodiment is a timing chart illustrating a specific example of generating a printing timing signal when the transport speed is maintained at a constant speed. [Figure 20] The above embodiment is a timing chart illustrating a specific example of generating a printing timing signal when the transport speed is maintained at a constant speed. [Figure 21]The above embodiment is a timing chart illustrating a specific example of generating a printing timing signal when the transport speed is maintained at a constant speed. [Figure 22] The above embodiment is a timing chart illustrating a specific example of generating a printing timing signal when the transport speed is maintained at a constant speed. [Figure 23] The above embodiment is a timing chart illustrating a specific example of generating a printing timing signal when the transport speed is accelerating. [Figure 24] The above embodiment is a timing chart illustrating a specific example of generating a printing timing signal when the transport speed is accelerating. [Figure 25] The above embodiment is a timing chart illustrating a specific example of generating a printing timing signal when the transport speed is accelerating. [Figure 26] The above embodiment is a timing chart illustrating a specific example of generating a printing timing signal when the transport speed is accelerating. [Figure 27] The above embodiment is a timing chart illustrating a specific example of generating a printing timing signal when the transport speed is accelerating. [Figure 28] The above embodiment is a timing chart illustrating a specific example of generating a printing timing signal when the transport speed is accelerating. [Figure 29] The above embodiment is a timing chart illustrating a specific example of generating a printing timing signal when the transport speed is accelerating. [Figure 30] The above embodiment is a timing chart illustrating a specific example of generating a printing timing signal when the transport speed is accelerating. [Figure 31] The above embodiment is a timing chart illustrating a specific example of generating a printing timing signal when the transport speed is accelerating. [Figure 32] The above embodiment is a timing chart illustrating a specific example of generating a printing timing signal when the transport speed is accelerating. [Figure 33] The above embodiment is a timing chart illustrating a specific example of generating a printing timing signal when the transport speed is accelerating. [Figure 34] The above embodiment is a timing chart illustrating a specific example of generating a printing timing signal when the transport speed is reduced. [Figure 35] The above embodiment is a timing chart illustrating a specific example of generating a printing timing signal when the transport speed is reduced. [Figure 36] The above embodiment is a timing chart illustrating a specific example of generating a printing timing signal when the transport speed is reduced. [Figure 37] The above embodiment is a timing chart illustrating a specific example of generating a printing timing signal when the transport speed is reduced. [Figure 38] The above embodiment is a timing chart illustrating a specific example of generating a printing timing signal when the transport speed is reduced. [Figure 39] The above embodiment is a timing chart illustrating a specific example of generating a printing timing signal when the transport speed is reduced. [Figure 40] The above embodiment is a timing chart illustrating a specific example of generating a printing timing signal when the transport speed is reduced. [Figure 41] The above embodiment is a timing chart illustrating a specific example of generating a printing timing signal when the transport speed is reduced. [Figure 42] The above embodiment is a timing chart illustrating a specific example of generating a printing timing signal when the transport speed is reduced. [Figure 43] The above embodiment is a timing chart illustrating a specific example of generating a printing timing signal when the transport speed is reduced. [Figure 44] The above embodiment is a timing chart illustrating a specific example of generating a printing timing signal when the transport speed is reduced. [Figure 45] The above embodiment is a timing chart illustrating a specific example of generating a printing timing signal when the transport speed is reduced. [Figure 46] The above embodiment is a timing chart illustrating a specific example of generating a printing timing signal when the transport speed is reduced. [Figure 47] This is a schematic diagram showing one example of the configuration of an inkjet printing apparatus in a third modified example of the above embodiment. [Figure 48] This timing chart illustrates an example of a conventional method for generating print timing signals. [Modes for carrying out the invention]

[0043] One embodiment of the present invention will be described below with reference to the attached drawings.

[0044] <1. Configuration of an inkjet printing device> Figure 1 is a schematic diagram showing one configuration example of an inkjet printing apparatus 10 according to one embodiment of the present invention. This inkjet printing apparatus 10 consists of a printing press body 200, a printing control device 100 that controls the operation of the printing press body 200, a paper feeding unit 310 that supplies printing paper (in this example, roll paper) 5 as a printing medium to the printing press body 200, and a paper winding unit 320 that winds the printed printing paper 5 into a roll. This inkjet printing apparatus 10 outputs a printed image onto the printing paper 5 based on print data, which is rasterized data sent via a network such as a LAN, without using a printing plate. The present invention can also be applied when a printing medium other than printing paper (for example, film) is used.

[0045] The printing press body 200 includes a first drive roller 21 for transporting the printing paper 5 into the press, a plurality of transport rollers 22 for transporting the printing paper 5 inside the printing press body 200, a recording unit 24 for recording a print image on the printing paper 5, a drying mechanism 25 for drying the printing paper 5 on which the print image has been recorded, an imaging device (e.g., a contact image sensor) 26 for capturing the print image recorded on the printing paper 5 by the recording unit 24, and a second drive roller 27 for outputting the printing paper 5 from inside the printing press body 200. An encoder 23 is attached to the rotation axis of one of the plurality of transport rollers 22. The transport roller 22 on which the encoder 23 is attached is located upstream of the recording unit 24 in the transport direction of the printing paper 5. The imaging data obtained by the imaging device 26 capturing the print image is sent to the printing control device 100, where the printing control device 100 uses the imaging data to perform a process, for example, to detect a defective nozzle.

[0046] The transport mechanism for transporting the printing paper 5 is comprised of the paper feeding unit 310, the first drive roller 21, a plurality of transport rollers 22, the second drive roller 27, and the paper winding unit 320. In this embodiment, the transport mechanism realizes a moving mechanism that relatively moves the positional relationship between the print head 241 and the printing paper 5, which will be described later. Furthermore, the transport speed (printing speed) at which the transport mechanism transports the printing paper 5 corresponds to the moving speed that relatively moves the positional relationship between the print head 241 and the printing paper 5.

[0047] Figure 2 is a plan view showing one example configuration of the recording unit 24. The recording unit 24 is composed of a K-color head unit 240K that ejects K-color (black) ink, a C-color head unit 240C that ejects C-color (cyan) ink, an M-color head unit 240M that ejects M-color (magenta) ink, and a Y-color head unit 240Y that ejects Y-color (yellow) ink. Each head unit 240 is composed of a plurality of print heads 241 arranged in a staggered pattern. Each print head 241 contains a number of nozzles (not shown in Figure 2) that eject ink. Each nozzle of the print head 241 in the K color head unit 240K ejects K color ink, each nozzle of the print head 241 in the C color head unit 240C ejects C color ink, each nozzle of the print head 241 in the M color head unit 240M ejects M color ink, and each nozzle of the print head 241 in the Y color head unit 240Y ejects Y color ink. The timing of ink ejection from each nozzle is controlled by a printing timing signal.

[0048] Figure 3 is a diagram illustrating the arrangement of nozzles 242 in a print head 241. Typically, a print head 241 contains multiple rows of nozzles, each consisting of multiple nozzles 242 arranged in the paper width direction. In the example shown in Figure 3, the print head 241 contains four rows of nozzles. The parts labeled 41 in Figure 3 schematically show the landing positions of the ink ejected from each nozzle 242 on the printing paper 5. Multiple nozzles 242 in the print head 241 are arranged such that the landing positions of the ink ejected from the nozzles 242 in the first row of nozzles, the second row of nozzles, the third row of nozzles, and the fourth row of nozzles are all different from each other. For example, the landing position of the ink ejected from each nozzle 242 in the first row of nozzles is between the landing position of the ink ejected from the nozzle 242 in the third row of nozzles and the landing position of the ink ejected from the nozzle 242 in the fourth row of nozzles. In the example shown in Figure 3, the landing position 42 of the ink ejected from the nozzle labeled 242(p) is between the landing position 43 of the ink ejected from the nozzle labeled 242(q) and the landing position 44 of the ink ejected from the nozzle labeled 242(r).

[0049] Note that the configurations shown in Figures 1 to 3 are examples, and the specific configurations of the inkjet printing device 10, recording unit 24, and print head 241 are not particularly limited.

[0050] <2. Hardware configuration of the print control device> Figure 4 is a block diagram showing the hardware configuration of the print control device 100. As shown in Figure 4, the print control device 100 includes a main unit 110, an auxiliary storage device 121, an optical disc drive 122, a display unit 123, a keyboard 124, and a mouse 125. The main unit 110 includes a CPU 111, a memory 112, a first disk interface unit 113, a second disk interface unit 114, a display control unit 115, an input interface unit 116, and a communication interface unit 117. The CPU 111, memory 112, first disk interface unit 113, second disk interface unit 114, display control unit 115, input interface unit 116, and communication interface unit 117 are connected to each other via a system bus. The auxiliary storage device 121 is connected to the first disk interface unit 113. The optical disc drive 122 is connected to the second disk interface unit 114. The display unit (display device) 123 is connected to the display control unit 115. The input interface unit 116 is connected to a keyboard 124 and a mouse 125. The communication interface unit 117 is connected to the printer body 200 via a communication cable. The communication interface unit 117 is also connected to LAN 4. The auxiliary storage device 121 is a magnetic disk drive or the like. An optical disk 19, such as a CD-ROM or DVD-ROM, is inserted into the optical disk drive 122. The display unit 123 is a liquid crystal display or the like. The display unit 123 is used to display information desired by the operator. The keyboard 124 and mouse 125 are used by the operator to input instructions to this print control device 100.

[0051] The auxiliary storage device 121 stores a print control program 13 (a program for controlling the execution of printing processes by the printing press 200). The CPU 111 reads the print control program 13 stored in the auxiliary storage device 121 into the memory 112 and executes it, thereby realizing various functions of the print control device 100. The memory 112 includes RAM (Random Access Memory) and ROM (Read Only Memory). The memory 112 functions as a work area for the CPU 111 to execute the print control program 13 stored in the auxiliary storage device 121. The print control program 13 is provided stored on the above-mentioned computer-readable recording medium (non-transient recording medium). That is, for example, the user purchases an optical disc 19 as the recording medium for the print control program 13, inserts it into the optical disc drive 122, reads the print control program 13 from the optical disc 19, and installs it into the auxiliary storage device 121.

[0052] In the example shown in Figure 4, the print control device 100 is equipped with only one CPU 111 as a processor, but this is not the only option. Configurations using multiple processors, such as a configuration using multiple CPUs, can also be adopted. In addition to the CPU 111, other processors such as an MPU (Micro Processing Unit), GPU (Graphics Processing Unit), and DSP (Digital Signal Processor) can also be used. Furthermore, a combination of multiple types of processors can be used. Moreover, a configuration including an FPGA (Field-Programmable Gate Array) or ASIC (Application Specific Integrated Circuit) can also be adopted.

[0053] <3. Method for generating print timing signals> The generation of the printing timing signal in this embodiment will be described below. In the following description, the transport speed in each period refers to the average transport speed in that period.

[0054] <3.1 Overview> As described above, with conventional methods, when acceleration / deceleration printing is performed, the transport speed at which the printing timing signal is generated differs from the transport speed at which ink is actually ejected from the print head 241. As a result, the ink ejected from the print head 241 lands on the printing paper 5 at a position shifted from the desired landing position. In other words, a positional shift occurs in the ink landing on the printing paper 5.

[0055] With regard to positional misalignment, we will focus on the case where the printing timing signal is generated based on a one-phase encoder signal ENC, referring to Figure 5. If the transport speed in period T0 is V0 and the transport speed in period T1 is V1, the amount of positional misalignment (distance of misalignment) Z(T1) that occurs in period T1 is calculated by the following equation (1). Z(T1)=(V0-V1)×T1 ···(1)

[0056] If we let D be the diameter of the transport roller 22 to which the encoder 23 is attached, and NP be the number of pulses output from the encoder 23 during the period of one rotation of the transport roller 22, then the transport speed V0 in period T0 can be calculated by the following equation (2) (similarly for the transport speed V1 in period T1). V0 = (D × π / NP) / T0 ... (2)

[0057] Next, referring to Figure 6, we will focus on the case where a printing timing signal is generated based on two-phase encoder signals (A-phase signal ENC_A and B-phase signal ENC_B). If the transport speed in period Ta0 is Va0 and the transport speed in period Ta1 is Va1, the positional displacement Z(Ta10) occurring in period Ta10 is calculated by the following equation (3). Also, if the transport speed in period Tb0 is Vb0 and the transport speed in period Tb1 is Vb1, the positional displacement Z(Tb10) occurring in period Tb10 is calculated by the following equation (4). Z(Ta10)=(Va0-Va1)×Ta10 (3) Z(Tb10)=(Vb0-Vb1)×Tb10 ···(4)

[0058] The absolute value of the cumulative amount of misalignment described above (hereinafter referred to as "cumulative misalignment") increases as the transport distance of the printing paper 5 increases. Therefore, in this embodiment, a printing timing signal is generated in such a way that the cumulative misalignment is prevented from falling outside a predetermined tolerance range.

[0059] Regarding the generation of the printing timing signal, the inkjet printing apparatus 10 according to this embodiment uses a signal obtained by multiplying the frequency of the printing timing signal. More specifically, the printing timing signal for a certain period is generated based on a signal obtained by multiplying the frequency of the printing timing signal for the period immediately preceding that period. Therefore, hereafter, the signal obtained by multiplying the frequency of the printing timing signal (pulse signal) will be referred to as the "reference signal".

[0060] For example, a reference signal obtained by multiplying the frequency of the print timing signal by 32 is used. In this example, under normal circumstances, the print timing signal PT is generated every 32 times the reference signal R is generated (in other words, every 32 pulses output as the reference signal R, one pulse output as the print timing signal PT is output) (see the waveform of the print timing signal PT in the part labeled 61 in Figure 7). In this embodiment, when acceleration / deceleration printing is performed, if the cumulative misalignment amount falls outside the allowable misalignment range, the timing of generating the print timing signal PT is corrected. Specifically, when the transport speed is accelerating and the cumulative misalignment amount falls outside the acceptable misalignment range, the print timing signal PT is generated at the timing of the 31st reference signal R generated since the previous print timing signal PT was generated (see the waveform of the print timing signal PT in the part labeled 62 in Figure 7). When the transport speed is decelerating and the cumulative misalignment amount falls outside the acceptable misalignment range, the print timing signal PT is generated at the timing of the 33rd reference signal R generated since the previous print timing signal PT was generated (see the waveform of the print timing signal PT in the part labeled 63 in Figure 7). However, even during periods when acceleration / deceleration printing is being performed, if the cumulative misalignment amount remains within the acceptable misalignment range, the print timing signal PT is generated at the timing of the 32nd reference signal R generated since the previous print timing signal PT was generated, as in normal operation (see the waveform of the print timing signal PT in the part labeled 61 in Figure 7).

[0061] To implement the method described above, this embodiment sets a frequency multiplier that represents the relationship between the frequency of the printing timing signal PT and the frequency of the reference signal R. Hereinafter, this setting value of the frequency multiplier will be referred to as the "frequency multiplier setting value". In the example above, the initial value (reference value) of the frequency multiplier setting value is 32.

[0062] Incidentally, if the print resolution is 1200 dpi, the dot spacing (the distance between the centers of two adjacent dots 45) is 21.17 μm, as shown in Figure 8. In this case, the distance corresponding to one period of the print timing signal PT is 21.17 μm. Then, if the reference signal R is a signal obtained by multiplying the frequency of the print timing signal PT by 32, the distance corresponding to one period of the reference signal R is 0.661 μm. In this embodiment, the print timing signal PT is generated in such a way that the absolute value of the cumulative positional displacement is suppressed from becoming greater than the distance corresponding to one period of the reference signal R.

[0063] For the sake of explanation, in the following, we will assume that the reference signal R is obtained by multiplying the frequency of the print timing signal PT by 4 (i.e., the initial value of the multiplication setting is 4). In this example, when the transport speed is accelerating, if the cumulative misalignment is within the acceptable range, the print timing signal PT is generated at the timing of the 4th reference signal R generated since the previous print timing signal PT was generated. If the cumulative misalignment falls outside the acceptable range, the print timing signal PT is generated at the timing of the 3rd reference signal R generated since the previous print timing signal PT was generated (see Figure 9). Also, when the transport speed is decelerating, if the cumulative misalignment is within the acceptable range, the print timing signal PT is generated at the timing of the 4th reference signal R generated since the previous print timing signal PT was generated. If the cumulative misalignment falls outside the acceptable range, the print timing signal PT is generated at the timing of the 5th reference signal R generated since the previous print timing signal PT was generated.

[0064] <3.2 Functional Configuration> Figure 10 is a block diagram showing the functional configuration of the control unit 50 within the print control device 100. Note that Figure 10 only shows the components related to the control of the operation of the recording unit 24. The control unit 50 includes an internal clock generation circuit 510, an encoder period length measurement circuit 520, a print timing signal generation circuit 530, a print timing signal correction circuit 540, a data holding unit 550, a halftone processing unit 560, and a head drive circuit 570.

[0065] The internal clock generation circuit 510 generates an internal clock CLK at a constant period. Typically, the internal clock generation circuit 510 is included in the CPU 111 (see Figure 4). The encoder period length measurement circuit 520 measures the period length of the encoder signal ENC (hereinafter referred to as "encoder pulse") output from the encoder 23 by counting the number of internal clock CLKs that occur during the period from the rising edge of the encoder pulse to the next rising edge. Hereinafter, the period length of the encoder signal ENC will be referred to as the "encoder period length," and the code EL will be attached to the encoder period length. Also, below, the period from the rising edge of the encoder pulse to the next rising edge will be referred to as the "unit period." The length of each unit period is the encoder period length EL for that unit period. In other words, the encoder period length measurement circuit 520 measures the length of each unit period by counting the number of internal clock CLKs, using the period from the rising edge of the encoder pulse to the next rising edge as the unit period. Alternatively, the period from the falling edge of the encoder pulse to the next falling edge may be treated as the unit period.

[0066] The print timing signal generation circuit 530 generates a print timing signal PT based on the internal clock CLK and the encoder period length EL for each unit period. The print timing signal correction circuit 540 corrects the timing at which the print timing signal PT is generated by the print timing signal generation circuit 530. In this regard, the print timing signal correction circuit 540 calculates the amount of positional deviation based on the encoder period length EL for each unit period each time the encoder pulse rises. Then, the timing at which the print timing signal PT is generated is corrected based on the cumulative amount of positional deviation described above. The correction of the timing at which the print timing signal PT is generated is performed by changing the multiplication setting value described above. Therefore, the print timing signal correction circuit 540 provides the print timing signal generation circuit 530 with data MD instructing a change in the multiplication setting value (hereinafter referred to as "multiplication number change instruction data"). Consequently, the generation of the print timing signal PT by the print timing signal generation circuit 530 is performed taking into account the multiplication number change instruction data MD. A more detailed explanation of the print timing signal generation circuit 530 and the print timing signal correction circuit 540 will be provided later.

[0067] The data storage unit 550 temporarily stores the print data PD sent via the network. The halftone processing unit 560 applies halftone processing to the print data PD held in the data storage unit 550 to generate halftone image data HA, which includes information indicating the ink dot size corresponding to each pixel. For example, three sizes (L size, M size, S size) are available for the ink dot size. The specific method of halftone processing is not particularly limited, and known methods such as error diffusion or dithering can be used.

[0068] The head drive circuit 570 drives each print head 241 that constitutes the recording unit 24 based on the halftone image data HA and the print timing signal PT. As a result, ink of the appropriate size is ejected from each of the multiple nozzles 242 contained in each print head 241 at the appropriate timing, and a printed image corresponding to the print data PD is formed on the printing paper 5.

[0069] Figure 11 is a block diagram showing the detailed configuration of the print timing signal generation circuit 530. The print timing signal generation circuit 530 includes a memory 531, a reference signal generation counter 532, and a print timing signal generation counter 533. For the sake of explanation, the counter value of the reference signal generation counter 532 will be referred to as the "first counter value," and the counter value of the print timing signal generation counter 533 will be referred to as the "second counter value." The first counter value will be denoted with the code CNTa, and the second counter value will be denoted with the code CNTb. Furthermore, when each unit period is used as a reference, the unit period immediately preceding it will be referred to as the "first unit period," and the unit period two periods prior will be referred to as the "second unit period."

[0070] The printing timing signal generation circuit 530 is supplied with the encoder period length EL from the encoder period length measurement circuit 520 for each unit period (i.e., each time the encoder pulse rises). The memory 531 is capable of holding the encoder period length EL for one unit period. Therefore, the encoder period length EL data in the memory 531 is overwritten for each unit period. Consequently, for each unit period, the encoder period length EL for the first unit period is held in the memory 531. Hereafter, the encoder period length for the first unit period will be denoted with the code EL1, and the encoder period length for the second unit period will be denoted with the code EL2.

[0071] The reference signal generation counter 532 generates a reference signal R based on the encoder period length EL1 held in the memory 531. In this regard, if P is the number of times the reference signal R should be generated in each unit period, the first counter value CNTa increases by P each time the internal clock CLK occurs. For example, if the number of times the reference signal R should be generated in each unit period is 6, then 6 is added to the first counter value CNTa each time the internal clock CLK occurs. When the first counter value CNTa becomes equal to or greater than the encoder period length EL1, the encoder period length EL1 is subtracted from the first counter value CNTa, and the reference signal R is generated. As described above, the reference signal generation counter 532 generates the reference signal R based on the length of the first unit period by counting the number of internal clock CLKs.

[0072] The print timing signal generation counter 533 is supplied with the reference signal R generated by the reference signal generation counter 532 and the multiplication factor change instruction data MD described above. When the print timing signal PT is generated, the second counter value CNTb is set to 0, and thereafter, the second counter value CNTb increases by 1 each time the reference signal R is generated. Then, when the second counter value CNTb becomes equal to the multiplication setting value described above, the print timing signal generation counter 533 generates the print timing signal PT. In summary, the print timing signal generation counter 533 generates the print timing signal PT after generating the previous print timing signal PT by counting the number of reference signals R generated by the reference signal generation counter 532, and when the number of times the reference signal R has been generated (second counter value CNTb) becomes equal to the multiplication setting value. In this embodiment, the initial value of the multiplication setting value is 4. During the period when the cumulative misalignment amount is maintained within the acceptable misalignment range, the multiplication setting value is maintained at 4, and the print timing signal PT is generated when the second counter value CNTb reaches 4. When the transport speed is accelerating and the cumulative misalignment amount falls outside the acceptable misalignment range, the multiplication setting value becomes 3, and the print timing signal PT is generated when the second counter value CNTb reaches 3. When the transport speed is decelerating and the cumulative misalignment amount falls outside the acceptable misalignment range, the multiplication setting value becomes 5, and the print timing signal PT is generated when the second counter value CNTb reaches 5.

[0073] Figure 12 is a block diagram showing the detailed configuration of the print timing signal correction circuit 540. The print timing signal correction circuit 540 includes memory 541 and memory 542, a positional deviation amount update circuit 543, and an adjustment circuit 544.

[0074] Memory 541 and memory 542 are each capable of holding the encoder period length EL for one unit period. Specifically, for each unit period, memory 541 holds the encoder period length EL1 for the first unit period, and memory 542 holds the encoder period length EL2 for the second unit period. That is, the encoder period length EL1 for the first unit period held in memory 541 is then held in memory 542 as the encoder period length EL2 for the second unit period in the next unit period. Note that writing the encoder period length EL data to memory 541 and transferring the encoder period length EL data from memory 541 to memory 542 are performed at the rising edge timing of the encoder pulse.

[0075] When the rise time of the encoder pulse occurs, the position misalignment amount update circuit 543 calculates the position misalignment amount that occurred in the first unit period based on the encoder period length EL1 for the first unit period and the encoder period length EL2 for the second unit period. The position misalignment amount update circuit 543 then adds the calculated position misalignment amount to the previously accumulated position misalignment amount MA. The position misalignment that occurs in the first unit period is due to the difference between the transport speed in the second unit period and the transport speed in the first unit period. Therefore, the position misalignment amount update circuit 543 calculates the position misalignment amount caused by the difference between the transport speed in the second unit period and the transport speed in the first unit period based on the length of the second unit period and the length of the first unit period, and calculates the accumulated position misalignment amount MA by accumulating the position misalignment amounts.

[0076] The adjustment circuit 544 compares the cumulative misalignment amount MA with two pre-prepared thresholds (first threshold TH1, second threshold TH2) and provides multiplication change instruction data MD to the print timing signal generation counter 533 in the print timing signal generation circuit 530, instructing a change in the multiplication setting value. In this way, the adjustment circuit 544 adjusts the multiplication setting value referenced by the print timing signal generation counter 533. As can be seen from equations (1), (3), and (4) above, when the transport speed is accelerating, the misalignment amount and cumulative misalignment amount MA are negative values, and when the transport speed is decelerating, the misalignment amount and cumulative misalignment amount MA are positive values. Therefore, two thresholds (first threshold TH1, second threshold TH2) are provided as described above. Figure 13 shows the relationship between the first threshold TH1, the second threshold TH2, and the allowable misalignment range. As can be seen from Figure 13, the first threshold TH1 is the lower limit of the allowable misalignment range, and the second threshold TH2 is the upper limit of the allowable misalignment range. In this embodiment, when the cumulative misalignment amount MA becomes smaller than the first threshold TH1, multiplication factor change instruction data MD is sent from the adjustment circuit 544 to the print timing signal generation counter 533, instructing that 1 be subtracted from the multiplication factor setting value. When the cumulative misalignment amount MA becomes larger than the second threshold TH2, multiplication factor change instruction data MD is sent from the adjustment circuit 544 to the print timing signal generation counter 533, instructing that 1 be added to the multiplication factor setting value.

[0077] In this embodiment, the first threshold TH1 and the second threshold TH2 are determined such that the absolute value of the first threshold TH1 is equal to the second threshold TH2, and that half the size of the positional deviation tolerance range shown in Figure 13 is equal to the distance corresponding to one cycle of the reference signal R. Therefore, the absolute values ​​of the thresholds (first threshold TH1, second threshold TH2) are equal to the distance corresponding to one cycle of the reference signal R. Here, the distance corresponding to one cycle of the reference signal R is equal to the value obtained by dividing the distance corresponding to one cycle of the printing timing signal PT (i.e., the dot spacing (see Figure 8)) by the multiplication setting value before adjustment by the adjustment circuit 544. In other words, the absolute values ​​of the thresholds (first threshold TH1, second threshold TH2) in this embodiment are equal to the value obtained by dividing the dot spacing formed on the printing paper 5 by the print head 241 by the multiplication setting value before adjustment by the adjustment circuit 544. By setting a threshold in this way, if we assume the initial value (reference value) of the multiplication setting is M, it becomes possible to suppress the magnitude of the ink's impact position deviation to a maximum of about 1 / M of the dot spacing.

[0078] Incidentally, it is also possible to implement functions equivalent to the encoder period length measurement circuit 520, the print timing signal generation circuit 530, and the print timing signal correction circuit 540 in software. In this case, for example, the print timing signal generation program is included as a subprogram in the print control program 13 (see Figure 4). Then, the CPU 111 reads the print timing signal generation program into memory 112 and executes it, thereby realizing functions equivalent to the encoder period length measurement circuit 520, the print timing signal generation circuit 530, and the print timing signal correction circuit 540.

[0079] <3.3 Processing Procedure> The following describes the procedure for generating the print timing signal PT.

[0080] <3.3.1 Overall Procedure Overview> Figure 14 is a flowchart illustrating the general process involved in the generation of the print timing signal PT. As can be seen from Figure 14, the encoder period length measurement circuit 520, the print timing signal generation circuit 530, and the print timing signal correction circuit 540 perform processing in parallel. In the encoder period length measurement circuit 520, as described above, the encoder period length EL is measured (in other words, the length of a unit period is measured) (S100). In the print timing signal generation circuit 530, the process of generating a reference signal R is performed (step S210), and the process of generating the print timing signal PT from the reference signal R generated in step S210 is performed (step S220). In the print timing signal correction circuit 540, the process of calculating the positional deviation amount is performed (step S310), the cumulative positional deviation amount MA is calculated based on the positional deviation amount calculated in step S310 (step S320), and the multiplication setting value is adjusted based on the cumulative positional deviation amount MA calculated in step S320 (step S330).

[0081] In this embodiment, step S100 is used to perform the encoder period length measurement step, step S210 is used to perform the reference signal generation step, step S220 is used to perform the print timing signal generation step, step S310 is used to perform the positional misalignment amount calculation step, step S320 is used to perform the cumulative positional misalignment amount calculation step, and step S330 is used to perform the adjustment step.

[0082] <3.3.2 Detailed Procedure> The following describes the detailed procedures for the processes performed by the encoder period length measurement circuit 520, the print timing signal generation circuit 530, and the print timing signal correction circuit 540. Since these processes are repeated throughout the operation of the inkjet printer 10, the flowcharts shown in Figures 15 to 17 omit illustrations of the start and end of these processes.

[0083] <3.3.2.1 Procedure for processing performed in the encoder period length measurement circuit> Figure 15 is a flowchart detailing the steps of the process performed by the encoder period length measurement circuit 520. In step S101, the value of the counter that counts the number of internal clock CLKs (hereinafter referred to as the "clock counter value") CNT(CLK) is set to 0. Then, when the internal clock CLK is detected (step S102), it is determined whether or not there is a rising edge of the encoder pulse (step S103). If there is a rising edge of the encoder pulse, the process proceeds to step S110; if there is no rising edge of the encoder pulse, the process proceeds to step S104.

[0084] In step S104, 1 is added to the clock counter value CNT(CLK). Then, the process returns to step S102.

[0085] In step S110, the clock counter value CNT(CLK) is transferred from the encoder period length measurement circuit 520 to the print timing signal generation circuit 530 and the print timing signal correction circuit 540. The transfer of the clock counter value CNT(CLK) occurs each time the encoder pulse rises. Therefore, the clock counter value CNT(CLK) transferred from the encoder period length measurement circuit 520 to the print timing signal generation circuit 530 and the print timing signal correction circuit 540 represents the encoder period length EL. In other words, in step S110, the encoder period length EL is essentially transferred from the encoder period length measurement circuit 520 to the print timing signal generation circuit 530 and the print timing signal correction circuit 540. After the completion of step S110, the process returns to step S101, and the clock counter value CNT(CLK) is set to 0.

[0086] As described above, in step S100 (steps S101 to S104), the length of each unit period is measured by counting the number of internal clock CLKs, with the period from the rising edge of a pulse output from encoder 23 to the next rising edge being used as the unit period.

[0087] <3.3.2.2 Procedure for processing performed in the printing timing signal generation circuit> Figure 16 is a flowchart showing the detailed procedure of the processing performed by the print timing signal generation circuit 530. As can be seen from Figure 16, each time the internal clock CLK is detected (step S211), the processing from step S212 onwards is performed.

[0088] In step S212, 6 is added to the first counter value CNTa in response to the detection of the internal clock CLK in step S211. Then, it is determined whether the first counter value CNTa is greater than or equal to the value indicating the length of the first unit period (encoder period length EL1 for the first unit period) (step S213). As a result, if the first counter value CNTa is greater than or equal to the value indicating the length of the first unit period, the process proceeds to step S214; if the first counter value CNTa is less than the value indicating the length of the first unit period, the process returns to step S211.

[0089] In step S214, a value indicating the length of the first unit period (encoder period length EL1 for the first unit period) is subtracted from the first counter value CNTa. Then, a reference signal R is generated (step S215). After that, 1 is added to the second counter value CNTb (step S221). Then, it is determined whether the second counter value CNTb is equal to the multiplication setting value (step S222). As a result, if the second counter value CNTb is equal to the multiplication setting value, the process proceeds to step S223; if the second counter value CNTb is not equal to the multiplication setting value (if the second counter value CNTb is less than the multiplication setting value), the process returns to step S211.

[0090] In step S223, the print timing signal PT is generated. Then, the second counter value CNTb is set to 0 (step S224), and the process returns to step S211.

[0091] As described above, in step S210 (steps S211 to S215), a reference signal R is generated that corresponds to a signal obtained by multiplying the frequency of the print timing signal PT based on the length of the first unit period, which is the previous unit period. In step S220 (steps S221 to S224), after the previous print timing signal PT has been generated, the print timing signal PT is generated when the number of times the reference signal R has been generated equals the multiplication setting value. Furthermore, if P is the number of times the reference signal R should be generated in each unit period (in the above example, P=6), then in step S210 (steps S211 to S215), P is added to the first counter value CNTa each time the internal clock CLK is generated by the internal clock generation circuit 510. When the first counter value CNTa becomes equal to or greater than the value corresponding to the length of the first unit period, the value corresponding to the length of the first unit period is subtracted from the first counter value CNTa, and the reference signal R is generated. Furthermore, in step S220 (steps S221 to S224), each time the reference signal R is generated in step S210, 1 is added to the second counter value CNTb. When the second counter value CNTb becomes equal to the multiplication setting value, the second counter value CNTb is set to 0 and the print timing signal PT is generated.

[0092] <3.3.2.3 Procedure for processing performed by the print timing signal correction circuit> Figure 17 is a flowchart detailing the steps of the processing performed by the print timing signal correction circuit 540. As can be seen from Figure 17, each time the rising edge of the encoder pulse is detected (step S300), the processing from step S310 onward is performed.

[0093] In step S310, the amount of positional displacement that occurred during the first unit period is calculated based on the encoder period length EL1 for the first unit period and the encoder period length EL2 for the second unit period. In other words, in step S310, the amount of positional displacement that occurred during the first unit period is calculated based on the length of the second unit period and the length of the first unit period.

[0094] Next, the cumulative positional displacement amount MA is calculated by accumulating the positional displacement amounts (step S320). More specifically, in step S320, the cumulative positional displacement amount MA is updated by adding the positional displacement amount calculated in step S310 to the previous cumulative positional displacement amount MA.

[0095] Subsequently, it is determined whether the cumulative misalignment amount MA calculated in step S320 is less than the first threshold TH1 (step S331). If the cumulative misalignment amount MA is less than the first threshold TH1, the process proceeds to step S332; if the cumulative misalignment amount MA is greater than or equal to the first threshold TH1, the process proceeds to step S333. In this regard, if the cumulative misalignment amount MA falls outside the acceptable range of misalignment during a period when the transport speed (printing speed) is accelerating, the process proceeds from step S331 to step S332. In step S332, 1 is subtracted from the multiplication setting value.

[0096] In step S333, it is determined whether the cumulative misalignment amount MA calculated in step S320 is greater than the second threshold TH2. If the cumulative misalignment amount MA is greater than the second threshold TH2, the process proceeds to step S334; otherwise, the process returns to step S300. In this regard, if the cumulative misalignment amount MA falls outside the acceptable range of misalignment during a period when the transport speed (printing speed) is reduced, the process proceeds from step S333 to step S334. In step S334, 1 is added to the multiplication setting value.

[0097] After the multiplication setting value is changed in step S332 or step S334, the cumulative positional misalignment amount MA is corrected (step S335). Specifically, after the multiplication setting value is changed in step S332, the first threshold TH1 is subtracted from the cumulative positional misalignment amount MA, and after the multiplication setting value is changed in step S334, the second threshold TH2 is subtracted from the cumulative positional misalignment amount MA. Subsequently, after the print timing signal PT is generated by the print timing signal generation circuit 530, the multiplication setting value is changed back to the initial value (step S336). The multiplication setting value after being changed in step S332 or step S334 is called the "adjusted value," because, as described above, after the multiplication setting value is changed from a predetermined initial value (reference value) to the adjusted value and then the print timing signal PT is generated, the multiplication setting value is changed back from the adjusted value to the initial value (reference value). After that, the process returns to step S300.

[0098] <3.4 Supplement> Incidentally, since the displacement amount is calculated by equation (1) above, when the transport speed is accelerating, the displacement amount and the cumulative displacement amount MA will be negative values, and when the transport speed is decelerating, the displacement amount and the cumulative displacement amount MA will be positive values. For this reason, if the cumulative displacement amount MA falls below the first threshold TH1, 1 is subtracted from the multiplication setting value, and if the cumulative displacement amount MA is greater than the second threshold TH2, 1 is added to the multiplication setting value. However, instead of equation (1) above, the displacement amount Z(T1) occurring during period T1 (see Figure 5) may be calculated by the following equation (5). Z(T1)=(V1-V0)×T1 ···(5)

[0099] If a configuration is adopted in which the positional displacement is calculated using the above equation (5), the positional displacement and cumulative positional displacement MA will be positive values ​​when the transport speed is accelerating, and the positional displacement and cumulative positional displacement MA will be negative values ​​when the transport speed is decelerating. In this case, if the first threshold TH1 is set to a negative value and the second threshold TH2 is set to a positive value, if it is determined in step S331 of Figure 17 that the cumulative positional displacement MA is less than the first threshold TH1, then 1 is added to the multiplication setting value in step S332, and if it is determined in step S333 of Figure 17 that the cumulative positional displacement MA is greater than the second threshold TH2, then 1 is subtracted from the multiplication setting value in step S334.

[0100] <4. Specific Examples> The following describes a specific example of operation, referring to the timing chart. In Figures 18 to 46, V represents the transport speed, N(1) represents the encoder period length for the corresponding unit period, N(2) represents the value of a counter assuming that there is a counter whose value increases by 1.5 each time the internal clock CLK occurs, PT_I represents the ideal print timing signal, and VM represents the multiplication setting value. In the following example, an encoder pulse is output every 100 μm of paper 5 is transported, the internal clock CLK occurs every 1 μs, the dot spacing is 66.7 μm (in other words, ideally the print timing signal PT is generated every 66.7 μm of paper 5 is transported), and the initial value of the multiplication setting value VM is 4. Since an encoder pulse is output every 100 μm of paper 5 is transported and the dot spacing is 66.7 μm, the number of times the print timing signal PT should be generated in each unit period is 1.5, and the number of times the reference signal R should be generated in each unit period is 6. Furthermore, the initial value of the multiplication setting VM is 4, and the dot spacing is 66.7 μm (i.e., the distance corresponding to one cycle of the print timing signal PT is 66.7 μm), so the distance corresponding to one cycle of the reference signal R is 16.67 μm. As described above, the allowable misalignment range is set to the distance corresponding to one cycle of the reference signal R, so the allowable misalignment range is 16.67 μm. Therefore, the first threshold TH1 is -16.67 μm, and the second threshold TH2 is 16.67 μm. Thus, in this embodiment, the absolute value of the first threshold TH1 and the second threshold TH2 are equal.

[0101] <4.1 Example of operation at constant speed> Before describing examples of operation during acceleration and deceleration, we will first describe an example of operation at a constant speed as a comparative example (see Figures 18 to 22). In this example, the transport speed V is maintained at 2.5 m / s.

[0102] At time t110, the length of the unit period from time t100 to time t110 is obtained. Since the internal clock CLK occurs 40 times during the unit period from time t100 to time t110, the length of this unit period is 40 μs. Therefore, during the unit period from time t110 to time t120, when the first counter value CNTa becomes 40 or greater, a reference signal R is generated and 1 is added to the second counter value CNTb.

[0103] At time t110, the first counter value CNTa is 0, the multiplication setting value VM is 4, and the second counter value CNTb is 0. Subsequently, 6 is added to the first counter value CNTa each time the internal clock CLK occurs. As a result, at time t111, the first counter value CNTa becomes 42. That is, at time t111, the first counter value CNTa is 40 or greater. This generates the reference signal R, and the second counter value CNTb becomes 1. At time t111, since the second counter value CNTb is less than the multiplication setting value VM, the print timing signal PT is not generated. Also, 40 is subtracted from the first counter value CNTa, so the first counter value CNTa becomes 2.

[0104] Similarly to time t111, the reference signal R is generated at times t112 and t113. At both time t112 and t113, the second counter value CNTb is smaller than the multiplication setting value VM, so the print timing signal PT is not generated.

[0105] Subsequently, at time t114, a reference signal R is generated, and the second counter value CNTb becomes 4. At this time, since the multiplication setting value VM is 4, the second counter value CNTb becomes equal to the multiplication setting value VM. As a result, the print timing signal PT is generated at time t114. Then, at time t115, the second counter value CNTb is set to 0.

[0106] At time t120, the length of the unit period from time t110 to time t120 is obtained. Since the internal clock CLK occurs 40 times during the unit period from time t110 to time t120, the length of this unit period is 40 μs. Therefore, in the unit period from time t120 to time t130, similar to the unit period from time t110 to time t120, when the first counter value CNTa becomes 40 or greater, a reference signal R is generated and 1 is added to the second counter value CNTb.

[0107] By the way, since the length of the unit period from time t100 to time t110 is equal to the length of the unit period from time t110 to time t120, there is no positional shift in the unit period from time t110 to time t120.

[0108] From time t120 onward, at times t121 and t130, the fourth reference signal R is generated after the previous print timing signal PT was generated. That is, at times t121 and t130, the second counter value CNTb becomes equal to the multiplication setting value VM, and the print timing signal PT is generated. Note that, similar to the unit period from time t110 to time t120, no positional shift occurs in the unit period from time t120 to time t130.

[0109] As described above, when the transport speed is maintained at a constant speed, the print timing signal PT is always generated every four times the reference signal R is generated. Furthermore, no positional misalignment occurs, and as shown in Figures 19 to 22, the actual print timing signal PT is generated at the timing when the ideal print timing signal PT_I should be generated.

[0110] <4.2 Examples of operation during acceleration> Referring to Figures 23 to 33, a specific example of generating the printing timing signal PT when the transport speed is accelerating will be explained. Here, we will focus on an example where the transport speed gradually accelerates from 2.5 m / s to 3.85 m / s.

[0111] At time t210, the length of the unit period from time t200 to time t210 is obtained. Since the internal clock CLK occurs 40 times during the unit period from time t200 to time t210, the length of this unit period is 40 μs. Therefore, during the unit period from time t210 to time t220, when the first counter value CNTa becomes 40 or greater, a reference signal R is generated and 1 is added to the second counter value CNTb.

[0112] At time t210, the first counter value CNTa is 0, the multiplication setting value VM is 4, and the second counter value CNTb is 0. Subsequently, 6 is added to the first counter value CNTa each time the internal clock CLK occurs. As a result, at time t211, the first counter value CNTa becomes 42. That is, at time t211, the first counter value CNTa is 40 or greater. This generates the reference signal R, and the second counter value CNTb becomes 1. At time t211, since the second counter value CNTb is less than the multiplication setting value VM, the print timing signal PT is not generated. Also, 40 is subtracted from the first counter value CNTa, so the first counter value CNTa becomes 2.

[0113] Similarly to time t211, the reference signal R is generated at times t212 and t213. At both time t212 and t213, the second counter value CNTb is smaller than the multiplication setting value VM, so the print timing signal PT is not generated.

[0114] Subsequently, at time t214, a reference signal R is generated, and the second counter value CNTb becomes 4. At this time, since the multiplication setting value VM is 4, the second counter value CNTb becomes equal to the multiplication setting value VM. As a result, the print timing signal PT is generated at time t214. Then, at time t215, the second counter value CNTb is set to 0.

[0115] At time t220, the length of the unit period from time t210 to time t220 is obtained. Since the internal clock CLK occurs 38 times during the unit period from time t210 to time t220, the length of this unit period is 38 μs. An encoder pulse is output every time the printing paper 5 is transported by 100 μm, so the transport speed V during the unit period from time t210 to time t220 is 2.63 m / s. Since the length of the unit period from time t210 to time t220 is 38 μs, during the unit period from time t220 to time t230, when the first counter value CNTa becomes 38 or greater, a reference signal R is generated and 1 is added to the second counter value CNTb.

[0116] The length of the unit period from time t200 to time t210 is 40 μs, while the length of the unit period from time t210 to time t220 is 38 μs. Therefore, a positional displacement occurs during the unit period from time t210 to time t220. Using equation (1) above, the amount of positional displacement that occurred during the unit period from time t210 to time t220 is calculated to be -5 μm.

[0117] At time t220, the cumulative displacement MA is -5 μm. Therefore, the cumulative displacement MA is greater than the first threshold TH1 (the cumulative displacement MA is within the acceptable displacement range). Thus, the multiplication setting VM is maintained at 4.

[0118] During the unit period from time t220 to time t230, the second counter value CNTb becomes 4 when the reference signal R is generated at time t221. Therefore, at time t221, the second counter value CNTb becomes equal to the multiplication setting value VM, and the print timing signal PT is generated.

[0119] At time t230, the length of the unit period from time t220 to time t230 is obtained. Since the internal clock CLK occurs 36 times during the unit period from time t220 to time t230, the length of this unit period is 36 μs. From this, the transport speed V during the unit period from time t220 to time t230 is calculated to be 2.78 m / s. Also, at time t230, the amount of positional displacement that occurred during the unit period from time t220 to time t230 is calculated. Using equation (1) above, the amount of positional displacement that occurred during the unit period from time t220 to time t230 is calculated to be -5.26 μm.

[0120] The displacement amount that occurred during the unit period from time t210 to time t220 was -5 μm, and the displacement amount that occurred during the unit period from time t220 to time t230 was -5.26 μm. Therefore, the cumulative displacement amount MA at time t230 is -10.26 μm. Consequently, the cumulative displacement amount MA is greater than the first threshold TH1. Therefore, the multiplication setting VM is maintained at 4.

[0121] During the unit period from time t230 to time t240, the second counter value CNTb becomes 4 when the reference signal R is generated at time t231 and time t232. Therefore, the print timing signal PT is generated at time t231 and time t232.

[0122] At time t240, the positional displacement amount that occurred during the unit period from time t230 to time t240 is calculated to be -5.56 μm. The cumulative positional displacement amount MA is -15.82 μm, which is greater than the first threshold TH1. Therefore, the multiplication setting value VM is still maintained at 4. Subsequently, at time t241, when the reference signal R is generated, the print timing signal PT is generated.

[0123] At time t250, the displacement amount that occurred during the unit period from time t240 to time t250 is calculated to be -5.88 μm. As a result, the cumulative displacement amount MA at time t250 is -21.70 μm. Since the first threshold TH1 is -16.67 μm, at time t250, the cumulative displacement amount MA becomes smaller than the first threshold TH1 (the cumulative displacement amount MA falls outside the acceptable displacement range). Consequently, 1 is subtracted from the multiplication setting value VM, and the multiplication setting value VM becomes 3. Furthermore, by subtracting the first threshold TH1 from the cumulative displacement amount MA, the cumulative displacement amount MA is calculated to be -5.03 μm.

[0124] Subsequently, at time t251, the reference signal R is generated and 1 is added to the second counter value CNTb. As a result, the second counter value CNTb becomes 3. As mentioned above, the multiplication setting value VM is 3 at time t250. Therefore, the printing timing signal PT is generated when the second counter value CNTb becomes 3 at time t251. After the printing timing signal PT is generated in this way, at time t252, the multiplication setting value VM is changed from 3 to its initial value of 4, and the second counter value CNTb is set to 0. Then, at time t253, the printing timing signal PT is generated when the reference signal R is generated.

[0125] At time t260, the positional displacement amount that occurred during the unit period from time t250 to time t260 is calculated to be -6.25 μm. The cumulative positional displacement amount MA is -11.28 μm, which is greater than the first threshold TH1. Therefore, the multiplication setting value VM is maintained at 4. Subsequently, at time t261, when the reference signal R is generated, the print timing signal PT is generated.

[0126] At time t270, the positional displacement amount that occurred during the unit period from time t260 to time t270 is calculated to be -6.67 μm. As a result, the cumulative positional displacement amount MA at time t270 is -17.95 μm. Since the first threshold TH1 is -16.67 μm, at time t270 the cumulative positional displacement amount MA becomes smaller than the first threshold TH1 (the cumulative positional displacement amount MA falls outside the allowable positional displacement range). As a result, 1 is subtracted from the multiplication setting value VM, and the multiplication setting value VM becomes 3. Furthermore, by subtracting the first threshold TH1 from the cumulative positional displacement amount MA, the cumulative positional displacement amount MA is calculated to be -1.28 μm. Also at time t270, a reference signal R is generated and 1 is added to the second counter value CNTb. As a result, the second counter value CNTb becomes 3. As mentioned above, the multiplication setting value VM is set to 3, so the print timing signal PT is generated at time t270. Then, at time t271, the multiplication setting value VM is changed from 3 to its initial value of 4, and the second counter value CNTb is set to 0.

[0127] <4.3 Examples of operation during deceleration> Referring to Figures 34 to 46, a specific example of generating the printing timing signal PT when the transport speed is decreasing will be explained. Here, we will focus on an example where the transport speed gradually decreases from 2.5 m / s to 2.0 m / s.

[0128] At time t310, the length of the unit period from time t300 to time t310 is obtained. Since the internal clock CLK occurs 40 times during the unit period from time t300 to time t310, the length of this unit period is 40 μs. Therefore, during the unit period from time t310 to time t320, when the first counter value CNTa becomes 40 or greater, a reference signal R is generated and 1 is added to the second counter value CNTb.

[0129] At time t310, the first counter value CNTa is 0, the multiplication setting value VM is 4, and the second counter value CNTb is 0. Subsequently, 6 is added to the first counter value CNTa each time the internal clock CLK occurs. As a result, at time t311, the first counter value CNTa becomes 42. That is, at time t311, the first counter value CNTa is 40 or greater. This generates the reference signal R, and the second counter value CNTb becomes 1. At time t311, the second counter value CNTb is less than the multiplication setting value VM, so the print timing signal PT is not generated. Also, 40 is subtracted from the first counter value CNTa, and the first counter value CNTa becomes 2.

[0130] Similarly to time t311, the reference signal R is generated at times t312 and t313. At both time t312 and t313, the second counter value CNTb is smaller than the multiplication setting value VM, so the print timing signal PT is not generated.

[0131] Subsequently, at time t314, a reference signal R is generated, and the second counter value CNTb becomes 4. At this time, since the multiplication setting value VM is 4, the second counter value CNTb becomes equal to the multiplication setting value VM. As a result, the print timing signal PT is generated at time t314. Then, at time t315, the second counter value CNTb is set to 0.

[0132] At time t320, the length of the unit period from time t310 to time t320 is obtained. Since the internal clock CLK occurs 42 times during the unit period from time t310 to time t320, the length of this unit period is 42 μs. An encoder pulse is output every time the printing paper 5 is transported by 100 μm, so the transport speed V during the unit period from time t310 to time t320 is 2.38 m / s. Since the length of the unit period from time t310 to time t320 is 42 μs, during the unit period from time t320 to time t330, when the first counter value CNTa becomes 42 or greater, a reference signal R is generated and 1 is added to the second counter value CNTb.

[0133] The length of the unit period from time t300 to time t310 is 40 μs, while the length of the unit period from time t310 to time t320 is 42 μs. Therefore, a positional displacement occurs during the unit period from time t310 to time t320. Using equation (1) above, the amount of positional displacement that occurred during the unit period from time t310 to time t320 is calculated to be 5 μm.

[0134] At time t320, the cumulative displacement MA is 5 μm. Therefore, the cumulative displacement MA is smaller than the second threshold TH2 (the cumulative displacement MA is within the acceptable displacement range). Hence, the multiplication setting VM is maintained at 4.

[0135] During the unit period from time t320 to time t330, the second counter value CNTb becomes 4 when the reference signal R is generated at time t321 and time t322. Therefore, at time t321 and time t322, the second counter value CNTb becomes equal to the multiplication setting value VM, and the print timing signal PT is generated.

[0136] At time t330, the length of the unit period from time t320 to time t330 is obtained. Since the internal clock CLK occurs 44 times during the unit period from time t320 to time t330, the length of this unit period is 44 μs. From this, the transport speed V during the unit period from time t320 to time t330 is calculated to be 2.27 m / s. Also, at time t330, the amount of positional displacement that occurred during the unit period from time t320 to time t330 is calculated. Using equation (1) above, the amount of positional displacement that occurred during the unit period from time t320 to time t330 is calculated to be 4.76 μm.

[0137] The displacement amount that occurred during the unit period from time t310 to time t320 was 5 μm, and the displacement amount that occurred during the unit period from time t320 to time t330 was 4.76 μm. Therefore, the cumulative displacement amount MA at time t330 is 9.76 μm. Consequently, the cumulative displacement amount MA is smaller than the second threshold TH2. Therefore, the multiplication setting VM is maintained at 4.

[0138] During the unit period from time t330 to time t340, the second counter value CNTb becomes 4 when the reference signal R is generated at time t331. Therefore, the print timing signal PT is generated at time t331.

[0139] At time t340, the positional displacement amount that occurred during the unit period from time t330 to time t340 is calculated to be 4.55 μm. The cumulative positional displacement amount MA is 14.31 μm, which is smaller than the second threshold TH2. Therefore, the multiplication setting value VM is still maintained at 4. Subsequently, the print timing signal PT is generated when the reference signal R is generated at time t341 and time t342.

[0140] At time t350, the displacement amount that occurred during the unit period from time t340 to time t350 is calculated to be 4.35 μm. As a result, the cumulative displacement amount MA at time t350 is 18.66 μm. Since the second threshold TH2 is 16.67 μm, at time t350, the cumulative displacement amount MA becomes greater than the second threshold TH2 (the cumulative displacement amount MA falls outside the acceptable displacement range). Consequently, 1 is added to the multiplication setting value VM, making the multiplication setting value VM 5. Furthermore, by subtracting the second threshold TH2 from the cumulative displacement amount MA, the cumulative displacement amount MA is calculated to be 1.99 μm.

[0141] When the reference signal R is generated at time t351, the second counter value CNTb becomes 2; when the reference signal R is generated at time t352, the second counter value CNTb becomes 3; and when the reference signal R is generated at time t353, the second counter value CNTb becomes 4. Since the multiplication setting value VM is 5 at time t350, the print timing signal PT is not generated even though the second counter value CNTb becomes 4 at time t353.

[0142] Subsequently, at time t354, the reference signal R is generated and 1 is added to the second counter value CNTb. As a result, the second counter value CNTb becomes 5. As mentioned above, the multiplication setting value VM is 5 at time t350. Therefore, at time t354, the second counter value CNTb becomes 5, generating the print timing signal PT. After the print timing signal PT is generated in this way, at time t355, the multiplication setting value VM is changed from 5 to its initial value of 4, and the second counter value CNTb is set to 0.

[0143] At time t360, the positional displacement amount that occurred during the unit period from time t350 to time t360 is calculated to be 4.17 μm. The cumulative positional displacement amount MA is 6.16 μm, which is smaller than the second threshold TH2. Therefore, the multiplication setting value VM is maintained at 4. Subsequently, the print timing signal PT is generated when the reference signal R is generated at time t361 and time t362.

[0144] <5. Effects> According to this embodiment, the amount of misalignment caused by the difference between the transport speed in the second unit period and the transport speed in the first unit period is calculated based on the length of the second unit period (two previous unit periods) and the length of the first unit period (one previous unit period), with the period from the rising edge of the encoder pulse to the next rising edge as the unit period. Furthermore, the cumulative misalignment amount MA is calculated by accumulating these misalignment amounts. When the cumulative misalignment amount MA falls outside the allowable misalignment range, the setting value of the multiplication factor (multiplication setting value) that represents the relationship between the frequency of the reference signal R used to generate the print timing signal PT and the frequency of the print timing signal PT is adjusted, and the print timing signal PT is generated so that the magnitude of the misalignment is reduced. Thus, according to this embodiment, an inkjet printing apparatus 10 is realized that can reduce the misalignment of ink placement when acceleration and deceleration printing is performed compared to conventional methods. Furthermore, because the misalignment of ink placement is reduced, the need for reprinting is reduced, and the wasteful consumption of printing paper 5 and ink is suppressed. In this way, it can contribute to achieving the SDGs (Sustainable Development Goals).

[0145] <6. Variation> Modifications of the above embodiment will be described below.

[0146] <6.1 First variation> In the above embodiment, when the cumulative misalignment amount MA falls outside the allowable misalignment range, 1 is subtracted from the multiplier setting value when the transport speed is accelerating, and 1 is added to the multiplier setting value when the transport speed is decelerating. That is, when the cumulative misalignment amount MA falls outside the allowable misalignment range when the transport speed is accelerating, the print timing signal PT is generated at a timing earlier than normal by a period equivalent to one cycle of the reference signal R, and when the cumulative misalignment amount MA falls outside the allowable misalignment range when the transport speed is decelerating, the print timing signal PT is generated at a timing later than normal by a period equivalent to one cycle of the reference signal R. However, depending on the acceleration or deceleration of the transport speed, it is preferable to make the timing of generating the print timing signal PT significantly different from normal. Therefore, in this modified example, the multiplier setting value is adjusted as follows.

[0147] In this modified example, the adjustment circuit 544 (see Figure 12) within the print timing signal correction circuit 540 provides the print timing signal generation counter 533 with multiplication factor change instruction data MD, where K is a natural number, indicating that when the cumulative positional deviation amount MA becomes less than K times the first threshold TH1, K should be subtracted from the multiplication factor setting value. When the cumulative positional deviation amount MA becomes greater than K times the second threshold TH2, the adjustment circuit 544 (see Figure 12) provides the print timing signal generation counter 533 with multiplication factor change instruction data MD, indicating that K should be added to the multiplication factor setting value.

[0148] Furthermore, if it is determined in step S331 of Figure 17 that the cumulative displacement amount MA is less than the first threshold TH1, the multiplication setting value is subtracted in step S332 as follows (in this case, the cumulative displacement amount MA and the first threshold TH1 are negative values). If the cumulative displacement amount MA is 2 times or more the first threshold TH1 and less than the first threshold TH1, 1 is subtracted from the multiplication setting value. If the cumulative displacement amount MA is 3 times or more the first threshold TH1 and less than 2 times the first threshold TH1, 2 is subtracted from the multiplication setting value. If the cumulative displacement amount MA is 4 times or more the first threshold TH1 and less than 3 times the first threshold TH1, 3 is subtracted from the multiplication setting value. In this way, with K being a natural number, when the cumulative displacement amount MA becomes less than K times the first threshold TH1, K is subtracted from the multiplication setting value.

[0149] Furthermore, if it is determined in step S333 of Figure 17 that the cumulative displacement amount MA is greater than the second threshold TH2, the multiplication setting value is increased in step S334 as follows (in this case, the cumulative displacement amount MA and the second threshold TH2 are positive values): If the cumulative displacement amount MA is greater than the second threshold TH2 and less than or equal to twice the second threshold TH2, 1 is added to the multiplication setting value; if the cumulative displacement amount MA is greater than twice the second threshold TH2 and less than or equal to three times the second threshold TH2, 2 is added to the multiplication setting value; and if the cumulative displacement amount MA is greater than three times the second threshold TH2 and less than or equal to four times the second threshold TH2, 3 is added to the multiplication setting value. In this way, with K being a natural number, when the cumulative displacement amount MA becomes greater than K times the second threshold TH2, K is added to the multiplication setting value.

[0150] Furthermore, if the displacement is calculated using equation (5) above instead of equation (1), the multiplication setting value is adjusted as follows, with the first threshold TH1 set to a negative value and the second threshold TH2 set to a positive value: Let K be a natural number. When the cumulative displacement MA becomes less than K times the first threshold TH1, K is added to the multiplication setting value, and when the cumulative displacement MA becomes greater than K times the second threshold TH2, K is subtracted from the multiplication setting value.

[0151] According to this modified example, the multiplication setting value is added or subtracted according to the acceleration or deceleration of the transport speed. Therefore, even when the transport speed accelerates or decelerates significantly, the deviation of the ink's landing position is effectively reduced.

[0152] <6.2 Second variation> In the above embodiment, the amount of misalignment was calculated using equation (1) or equation (5) above. In that case, a negative value appears as the value of the amount of misalignment. In contrast, in this modified example, in order to prevent the amount of misalignment from being a negative value, with respect to the example shown in Figure 5, if the transport speed in period T0 is V0 and the transport speed in period T1 is V1, then the amount of misalignment (distance of misalignment) Z(T1) occurring in period T1 is calculated using the following equation (6). Z(T1)=|V0-V1|×T1 ···(6)

[0153] As can be seen from equation (6) above, in this modified example, the displacement is calculated as the product of the absolute value of the difference between the transport speed in the second unit period and the transport speed in the first unit period and the length of the first unit period. According to equation (6) above, the displacement cannot be a negative value, and therefore the cumulative displacement cannot be a negative value either. In other words, if a displacement occurs, both the displacement and the cumulative displacement will be positive values. For this reason, in this modified example, only one threshold is set for comparison with the cumulative displacement. That threshold is also a positive value.

[0154] Incidentally, when the cumulative positional displacement MA exceeds the threshold, if the transport speed is accelerating, it is necessary to subtract 1 from the multiplier setting value, and if the transport speed is decelerating, it is necessary to add 1 to the multiplier setting value. Therefore, a determination is made as to whether the transport speed is accelerating or decelerating based on the relationship between the length of the first unit period (encoder period length EL1 for the first unit period) and the length of the second unit period (encoder period length EL2 for the second unit period). Specifically, if the length of the first unit period is shorter than the length of the second unit period, it is determined that the transport speed is accelerating, and if the length of the first unit period is longer than the length of the second unit period, it is determined that the transport speed is decelerating.

[0155] Therefore, in this modified example, if the cumulative positional displacement amount MA exceeds the threshold when the length of the first unit period is shorter than the length of the second unit period, 1 is subtracted from the multiplication setting value. If the cumulative positional displacement amount MA exceeds the threshold when the length of the first unit period is longer than the length of the second unit period, 1 is added to the multiplication setting value.

[0156] Furthermore, this modified example and the first modified example described above may be combined to adjust the multiplication setting value as follows: Let K be a natural number. When the length of the first unit period is shorter than the length of the second unit period, if the cumulative positional displacement amount MA becomes greater than K times the threshold, K is subtracted from the multiplication setting value. When the length of the first unit period is longer than the length of the second unit period, if the cumulative positional displacement amount MA becomes greater than K times the threshold, K is added to the multiplication setting value.

[0157] <6.3 Third variation> In the above embodiment, an inkjet printing device 10 capable of single-sided printing was used. However, the present invention is not limited to this. The present invention can also be applied when an inkjet printing device 10 capable of double-sided printing is used, as in this modified example.

[0158] Figure 47 is a schematic diagram showing one example of the configuration of the inkjet printing apparatus 10 in this modified example. The inkjet printing apparatus 10 in this modified example consists of a paper feeding unit 310, a front-side printing machine 10a, a reversal unit 330 for reversing the front and back sides of the printing paper 5, a back-side printing machine 10b, and a paper winding unit 320. The front-side printing machine 10a consists of a printing machine body 200a for front-side printing and a first printing control device 100a for controlling the operation of the printing machine body 200a. The back-side printing machine 10b consists of a printing machine body 200b for back-side printing and a second printing control device 100b for controlling the operation of the printing machine body 200b. The internal configuration of the printing machine bodies 200a and 200b is the same as the internal configuration of the printing machine body 200 in the above embodiment. Note that the components of the front-side printing machine 10a are denoted by "a" at the end of their reference numerals, and the components of the back-side printing machine 10b are denoted by "b" at the end of their reference numerals.

[0159] In the configuration described above, in the front-side printing press 10a, a printing timing signal PT that defines the timing for ejecting ink from each print head 241 constituting the recording unit 24a is generated by the first printing control device 100a based on the encoder signal output from the encoder 23a, and in the back-side printing press 10b, a printing timing signal PT that defines the timing for ejecting ink from each print head 241 constituting the recording unit 24b is generated by the second printing control device 100b based on the encoder signal output from the encoder 23b. In this regard, the generation of the printing timing signal PT in the first printing control device 100a and the second printing control device 100b is performed in the same manner as in the above embodiment.

[0160] According to this modified example, when acceleration and deceleration printing is performed with an inkjet printer 10 capable of double-sided printing, it becomes possible to reduce the misalignment of ink placement on both the front and back surfaces of the printing paper 5 compared to conventional methods.

[0161] <7. Other> The present invention is not limited to the above embodiments (including modifications), and can be implemented with various modifications without departing from the spirit of the invention. For example, in the above embodiments (including modifications), an inkjet printing apparatus 10 that performs color printing was used. However, the present invention is not limited thereto, and an inkjet printing apparatus that performs monochrome printing may also be used. Also, in the above embodiments (including modifications), an inkjet printing apparatus 10 that uses water-based ink was used. However, the present invention is not limited thereto, and an inkjet printing apparatus that uses UV ink (ultraviolet-curing ink), such as an inkjet printing apparatus for label printing, may also be used. In this case, inside the printing press body 200 (see Figure 1), instead of a drying mechanism 25, an ultraviolet irradiation mechanism is provided to cure the UV ink on the printing paper 5 by ultraviolet irradiation.

[0162] Furthermore, in the above embodiment (including modifications), printing on the printing paper 5 is performed by ejecting ink from a fixed print head 241 while moving the printing paper 5. In other words, a one-pass inkjet printing device 10 is employed. However, the present invention can also be applied when a shuttle-type inkjet printing device is employed. In a shuttle-type inkjet printing device, after the print head moves from one end to the other end of the printing medium such as the printing paper 5 while ejecting ink (i.e., after moving in the main scanning direction), the print head moves a predetermined distance in the sub-scanning direction (a direction perpendicular to the main scanning direction). After that, the print head moves from the other end to the one end of the printing medium while ejecting ink. Then, the print head moves again a predetermined distance in the sub-scanning direction. [Explanation of Symbols]

[0163] 10…Inkjet printing equipment 22... Conveyor rollers 23… Encoder 24…Records Department 100…Printing control device 200... Printing machine body 241...Print head 242… Nozzle 510...Internal clock generation circuit 520… Encoder period length measurement circuit 530...Print timing signal generation circuit 532...Reference signal generation counter 533...Print timing signal generation counter 540...Print timing signal correction circuit 543... Position shift amount update circuit 544…adjustment circuit 570... Head drive circuit CLK...Internal clock ENC… Encoder signal MD...Data for changing the multiplier PT...Print timing signal R…Reference signal TH1…First threshold TH2…Second threshold

Claims

1. A printing apparatus comprising a print head for ejecting ink onto a printing medium, a moving mechanism for relatively moving the relative positions of the print head and the printing medium, an encoder that outputs pulses at a period corresponding to the moving speed which is the speed at which the moving mechanism relatively moves the relative positions, and an internal clock generation circuit that generates an internal clock at a constant period, wherein a printing timing signal generation method is generated for generating a printing timing signal that defines the timing of ejecting ink from the print head, An encoder period length measurement step, which measures the length of each unit period by counting the number of internal clocks, with the unit period being the period from the rising edge of a pulse output from the encoder to the next rising edge, or the period from the falling edge of a pulse output from the encoder to the next falling edge; A reference signal generation step that generates a reference signal corresponding to a signal obtained by multiplying the frequency of the printing timing signal based on the length of the first unit period, which is the previous unit period, A printing timing signal generation step that generates the printing timing signal based on a multiplication setting value, which is a setting value of a multiplication number representing the relationship between the frequency of the printing timing signal and the frequency of the reference signal, and the reference signal. A positional displacement calculation step that calculates the amount of positional displacement caused by the difference between the moving speed in the second unit period and the moving speed in the first unit period, based on the length of the second unit period, which is two unit periods prior, and the length of the first unit period, A cumulative positional displacement calculation step, which calculates the cumulative positional displacement by accumulating the aforementioned positional displacement amounts, An adjustment step in which the multiplication setting value is adjusted based on the result of comparing the cumulative positional displacement with a predetermined threshold; Includes, A method for generating a printing timing signal, characterized in that, in the printing timing signal generation step, the printing timing signal is generated when the number of times the reference signal has been generated after the previous printing timing signal has been generated becomes equal to the multiplication setting value.

2. The printing timing signal generation method according to claim 1, characterized in that in the step of calculating the amount of positional deviation, the product of the value obtained by subtracting the movement speed in the first unit period from the movement speed in the second unit period and the length of the first unit period, or the product of the value obtained by subtracting the movement speed in the second unit period from the movement speed in the first unit period and the length of the first unit period, is calculated as the amount of positional deviation.

3. The predetermined threshold includes a first threshold that is a negative value and a second threshold that is a positive value. In the position displacement calculation step, if the product of the value obtained by subtracting the movement speed in the first unit period from the movement speed in the second unit period and the length of the first unit period is calculated as the position displacement amount, then in the adjustment step, if the cumulative position displacement amount becomes smaller than the first threshold, 1 is subtracted from the multiplication setting value, and if the cumulative position displacement amount becomes larger than the second threshold, 1 is added to the multiplication setting value. In the positional displacement amount calculation step, if the product of a value obtained by subtracting the movement speed in the second unit period from the movement speed in the first unit period and the length of the first unit period is calculated as the positional displacement amount, the adjustment step is characterized in that, when the cumulative positional displacement amount becomes smaller than the first threshold, 1 is added to the multiplication setting value, and when the cumulative positional displacement amount becomes larger than the second threshold, 1 is subtracted from the multiplication setting value, as described in claim 2.

4. The predetermined threshold includes a first threshold that is a negative value and a second threshold that is a positive value. In the position displacement calculation step, if the product of the value obtained by subtracting the movement speed in the first unit period from the movement speed in the second unit period and the length of the first unit period is calculated as the position displacement, then, with K being a natural number, in the adjustment step, if the cumulative position displacement becomes less than K times the first threshold, K is subtracted from the multiplication setting value, and if the cumulative position displacement becomes greater than K times the second threshold, K is added to the multiplication setting value. In the step of calculating the amount of positional displacement, if the product of a value obtained by subtracting the movement speed in the second unit period from the movement speed in the first unit period and the length of the first unit period is calculated as the amount of positional displacement, with K being a natural number, in the adjustment step, if the cumulative amount of positional displacement becomes less than K times the first threshold, K is added to the multiplication setting value, and if the cumulative amount of positional displacement becomes greater than K times the second threshold, K is subtracted from the multiplication setting value, characterized in that, the printing timing signal generation method according to claim 2.

5. The printing timing signal generation method according to claim 3 or 4, characterized in that the absolute value of the first threshold and the second threshold are equal.

6. The method for generating a printing timing signal according to claim 1, characterized in that in the step of calculating the amount of positional deviation, the product of the absolute value of the difference between the moving speed in the second unit period and the moving speed in the first unit period and the length of the first unit period is calculated as the amount of positional deviation.

7. The aforementioned displacement amount, the cumulative displacement amount, and the predetermined threshold are positive values. The printing timing signal generation method according to claim 6, characterized in that, in the adjustment step, if the cumulative positional deviation amount is greater than the predetermined threshold when the length of the first unit period is shorter than the length of the second unit period, 1 is subtracted from the multiplication setting value, and if the cumulative positional deviation amount is greater than the predetermined threshold when the length of the first unit period is longer than the length of the second unit period, 1 is added to the multiplication setting value.

8. The aforementioned displacement amount, the cumulative displacement amount, and the predetermined threshold are positive values. The printing timing signal generation method according to claim 6, characterized in that, in the adjustment step, K is a natural number, if the length of the first unit period is shorter than the length of the second unit period and the cumulative positional deviation amount is greater than K times the predetermined threshold, K is subtracted from the multiplication setting value, and if the length of the first unit period is longer than the length of the second unit period and the cumulative positional deviation amount is greater than K times the predetermined threshold, K is added to the multiplication setting value.

9. The method for generating a printing timing signal according to any one of claims 1 to 4, 6 to 8, characterized in that the absolute value of the predetermined threshold is equal to the value obtained by dividing the spacing between dots formed on the printing medium by the multiplication setting value before adjustment in the adjustment step.

10. A method for generating a printing timing signal according to any one of claims 1 to 4, 6 to 8, characterized in that when the multiplication setting value is changed from a predetermined reference value to an adjustment value in the adjustment step, and then the printing timing signal is generated in the printing timing signal generation step, the multiplication setting value is changed from the adjustment value to the reference value.

11. A method for generating a printing timing signal according to any one of claims 1 to 4, 6 to 8, characterized in that, if P is the number of times the reference signal should be generated in each unit period, in the reference signal generation step, P is added to the first counter value each time the internal clock is generated by the internal clock generation circuit, and when the first counter value becomes equal to or greater than a value corresponding to the length of the first unit period, a value corresponding to the length of the first unit period is subtracted from the first counter value and the reference signal is generated.

12. A method for generating a printing timing signal according to any one of claims 1 to 4, 6 to 8, characterized in that in the printing timing signal generation step, 1 is added to the second counter value each time the reference signal is generated in the reference signal generation step, and when the second counter value becomes equal to the multiplication setting value, the second counter value is set to 0 and the printing timing signal is generated.

13. A method for generating a printing timing signal according to any one of claims 1 to 4, 6 to 8, characterized in that each time a pulse is output from the encoder, the amount of positional deviation is calculated in the positional deviation amount calculation step, and further, the cumulative amount of positional deviation is calculated in the cumulative positional deviation amount calculation step.

14. A print head that ejects ink onto the printing medium, A moving mechanism for relatively changing the positional relationship between the print head and the printing medium, An encoder that outputs pulses at a period corresponding to the movement speed, which is the speed at which the movement mechanism moves the relative positional relationship, An internal clock generation circuit that generates an internal clock at a constant period, An encoder period length measuring circuit measures the length of each unit period by counting the number of internal clocks, with the unit period being the period from the rising edge of a pulse output from the encoder to the next rising edge, or the period from the falling edge of a pulse output from the encoder to the next falling edge. A print timing signal generation circuit generates a print timing signal that defines the timing for ejecting ink from the print head, A print timing signal correction circuit for correcting the timing at which the print timing signal is generated, Equipped with, The aforementioned printing timing signal generation circuit is: A reference signal generation counter generates a reference signal corresponding to a signal obtained by multiplying the frequency of the printing timing signal by the number of internal clocks, based on the length of the first unit period, which is the previous unit period. The print timing signal generation counter generates the print timing signal when the number of reference signals generated by the reference signal generation counter is counted, and the number of times the reference signal has been generated after the previous print timing signal has been generated becomes equal to the multiplication setting value, which is a setting value of the multiplication number that represents the relationship between the frequency of the print timing signal and the frequency of the reference signal. Includes, The aforementioned printing timing signal correction circuit is: A positional displacement update circuit calculates the amount of positional displacement resulting from the difference between the moving speed in the second unit period and the moving speed in the first unit period, based on the length of the second unit period which is two unit periods prior and the length of the first unit period, and calculates the cumulative positional displacement amount by accumulating the amount of positional displacement, An adjustment circuit adjusts the multiplication setting value referenced by the printing timing signal generation counter based on the result of comparing the cumulative positional deviation amount with a predetermined threshold. A printing apparatus characterized by including

15. A printing apparatus comprising a print head for ejecting ink onto a printing medium, a moving mechanism for relatively moving the relative positions of the print head and the printing medium, an encoder that outputs pulses at a period corresponding to the moving speed which is the speed at which the moving mechanism relatively moves the relative positions, and an internal clock generation circuit that generates an internal clock at a constant period, wherein a printing timing signal generation program generates a printing timing signal that defines the timing for ejecting ink from the print head, The computer included in the aforementioned printing device An encoder period length measurement step, which measures the length of each unit period by counting the number of internal clocks, with the unit period being the period from the rising edge of a pulse output from the encoder to the next rising edge, or the period from the falling edge of a pulse output from the encoder to the next falling edge; A reference signal generation step that generates a reference signal corresponding to a signal obtained by multiplying the frequency of the printing timing signal based on the length of the first unit period, which is the previous unit period, A printing timing signal generation step that generates the printing timing signal based on a multiplication setting value, which is a setting value of a multiplication number representing the relationship between the frequency of the printing timing signal and the frequency of the reference signal, and the reference signal. A positional displacement calculation step that calculates the amount of positional displacement caused by the difference between the moving speed in the second unit period and the moving speed in the first unit period, based on the length of the second unit period, which is two unit periods prior, and the length of the first unit period, A cumulative positional displacement calculation step, which calculates the cumulative positional displacement by accumulating the aforementioned positional displacement amounts, An adjustment step in which the multiplication setting value is adjusted based on the result of comparing the cumulative positional displacement with a predetermined threshold; Make it run, A print timing signal generation program characterized in that, in the print timing signal generation step, the print timing signal is generated when the number of times the reference signal has been generated after the previous print timing signal has been generated becomes equal to the multiplication setting value.

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