Ink jet recording method and apparatus

Abstract: A plurality of thin image data are generated based on desired image data. A single region on a recording medium is scanned a plurality of number of times on the basis of the plurality of thin image data, thereby recording the thin images a plurality of number of times. The scan interval in this case is set to be an interval equal to or longer than a required minimum interval, which does not cause deterioration of image quality due to blurring. Furthermore, the interval is properly changed according to the print duty, environmental condition, or the like.

Description: The present invention relates to an ink jet recording method and apparatus for performing recording by ejecting ink droplets onto a recording medium and, more particularly, to an ink jet recording method and apparatus for performing a multi-pass print operation. In recent years, OA equipment such as computers, wordprocessors, copying machines have widely become popular, and a large number of recording methods for recording apparatuses for such OA equipment have been developed. An ink jet recording apparatus has excellent features such as an easy high-definition recording operation, a high-speed operation, low noise, and an inexpensive structure. The ink jet recording apparatus is prepared with various recording modes in addition to a simple one-scan recording mode for the purpose of solving the problem associated with fixing characteristics of an ink on a recording medium such as a paper sheet, an OHP film, or the like, and preventing density nonuniformity inherent to a recording head. Of these recording modes, a multi-pass print mode for performing recording by scanning a single recording head a plurality of number of times on a single region on a recording medium is popularly used in various purposes. For example, when a print operation is performed on a recording medium having no ink absorbency or a very low ink absorbency, or when a color recording operation is performed on a recording medium having a low ink absorbency using a plurality of recording heads having different ink colors, ink overflows on the recording medium, and causes stripe-like nonuniformity (called "beading") or blurring at the boundary between different colors or densities (called "boundary blurring"), thus considerably deteriorating image quality. In order to prevent "beading" or "boundary blurring" caused by the overflowed ink, a so-called thin multi-pass print mode is employed. In this mode, a single scan pattern is thinned in checkerboard patterns, and a plurality of thinning patterns are recorded a plurality of number of times, thereby finishing an image corresponding to all the recording data. In this thin multi-pass print mode, it is considered that the following two effects reduce ink overflowing, and prevent "beading" or "boundary blurring". (1) The ink amount printed in each pass is less than that in a one-pass print mode, and ink is absorbed into a recording medium within a short period of time. (2) The ink is dried during an interval between adjacent passes. Fig. 25 is a schematic diagram of an ink jet recording apparatus for executing a conventional thin multi-pass print mode. In Fig. 25, a recording head 1 has a plurality of ink ejection orifices, and a plurality of electrothermal converting elements as ejection energy generating elements arranged in correspondence with the ejection orifices. An ejection signal according to recording data is supplied to each electrothermal converting element, and a bubble generated by heat causes a change in state in an ink, thereby ejecting an ink droplet from the corresponding ejection orifice. The apparatus shown in Fig. 25 includes a carriage 2 for holding the recording head, a guide shaft 3, arranged to oppose a recording medium P which is intermittently moved in a sub-scan direction by a sub scan roller (not shown), for supporting the carriage 2, a carriage belt 4 for reciprocally moving the carriage 2 along the guide shaft 3 (to perform a main scan operation), and a main scan motor 5 for driving the carriage belt. The apparatus also includes a print mode changing means 6 for changing a print mode automatically or in response to a manual switch operation of a user, a thin-print signal forming means 7 for, when the print mode changing means 6 selects the thin multi-pass print mode, forming thin-print signals for executing the thin multi-pass print mode from an input image signal (to be referred to as a print signal hereinafter) S, and a head driving means 8 for driving the recording head 1 according to a signal from the thin-print signal forming means 7. A main scan motor drive signal forming means 9 forms a signal for driving the main scan motor. When the print mode changing means 6 selects the thin multi-pass print mode, the means 9 sequentially generates driving signals corresponding to the number of passes. A main scan motor driving means 10 controls the driving operation of the main scan motor 5 according to the signal from the motor drive signal forming means. In this ink jet recording apparatus, the thin multi-pass print mode is executed as follows. When the print mode changing means 6 selects the thin multi-pass print mode automatically or in response to a manual switch operation by a user, an input image signal shown in Fig. 26A is thinned according to a predetermined thinning pattern (Fig. 26B) by the thin-print signal forming means 7 to be divided into thin-print signals S1 and S2, as shown in Figs. 26C and 26D. Of these signals, the thin-print signal S1 is supplied to the head driving means 8 to drive the recording head 1, and ink droplets are ejected from the ejection orifices of the recording head 1. In synchronism with this head driving operation (in practice, a required minimum pass interval before the head driving operation), the main scan motor drive signal forming means 9 generates a main scan drive signal for the carriage, and the main scan motor 5 is driven according to a signal from the driving means. Thus, the carriage 2 is moved along the guide shaft 3 to perform the first-pass print operation. Upon completion of the print operation, the main scan motor 5 is driven in the reverse direction, and the carriage 2 is returned to the start position. The remaining thin-print signal S2 is then supplied to the head driving means 8 to drive the recording head 1, and the second-pass print operation is performed in the same manner as in the first pass. Thereafter, the apparatus prepares for the print operation of the next line. During this interval, since the sub scan roller (not shown) is controlled not to move the recording medium P, the thin two-pass print operation can be realized. The thin two-pass print operation has been described. However, the same applies to multi-pass print modes using three or more passes. Upon execution of the above-mentioned thin multi-pass print operation, in order to prevent ink from overflowing on the recording medium, the number of times of multi-pass print operations is set to prevent "blurring" when a print operation is performed on the recording medium at the possibly highest ink density in an environment with the lowest ink drying speed among possible use environmental conditions. In addition, in order to prevent a decrease in throughput, the interval between the first and second passes (to be referred to as a multi-pass interval hereinafter) is set so that the print operation is started as soon as data are prepared. For this reason, in order to output an image free from defects such as "beading", "boundary blurring", and the like, the number of times of passes is set to be very large, and this results in e.g. the promotion of a mechanical wear of sliding portions, an increase in dust attachment frequency of the recording head, and a complex electrical circuit for forming thinning data. Thus, an inexpensive ink jet recording apparatus which can output a high-quality image, and has high durability and reliability, cannot be constituted. The present invention has been made in consideration of the above situation, and has as its main concern to provide an improved ink jet recording method and apparatus. It is another concern of the present invention to provide a low-cost ink jet recording method and apparatus, which can output a high-quality image, and achieves high durability and reliability. It is still another concern of the present invention to provide an ink jet recording method and apparatus, which can record a high-quality image without causing an unnecessary decrease in throughput. It is still another concern of the present invention to provide an ink jet recording method and apparatus, which records a plurality of thin images a plurality of number of times at an interval equal to or longer than a required minimum interval on a single region of a recording medium so as to obtain a desired image free from blurring. It is still another concern of the present invention to provide an ink jet recording method and apparatus, which records a plurality of thin images a plurality of number of times at a proper interval based on a predetermined condition on a single region of a recording medium so as to obtain a desired image free from blurring. EP-A-0348181 discloses an ink jet apparatus where the printing is carried out in a number of scans on the same line of the printing medium. The interval between the scans is chosen such that undesired mixing of ink does not occur. According to the invention there is provided an ink recording method as claimed in claim 1. Further according to the invention there is provided an ink jet recording apparatus as claimed in claim 8. In the accompanying drawings :- Fig. 1 is a schematic diagram of an ink jet recording apparatus according to the first embodiment of the present invention; Fig. 2 is a table showing the correspondence between the number of times of print passes and the required minimum pass interval in the first embodiment; Fig. 3 is a schematic diagram of an ink jet recording apparatus according to the second embodiment of the present invention; Fig. 4 is a table showing the correspondence between the number of times of print passes and the required minimum pass interval in the second embodiment; Fig. 5 is a schematic diagram of an ink jet recording apparatus according to the third embodiment of the present invention; Fig. 6 is a table showing the correspondence between the number of times of print passes and the required minimum pass interval in the third embodiment; Fig. 7 is a schematic diagram of an ink jet recording apparatus according to the fourth embodiment of the present invention; Figs. 8A and 8B are views for explaining a method of obtaining a print duty; Fig. 9 is a table showing the correspondence between the maximum print duty and the multi-pass print interval; Fig. 10 is a graph showing the relationship between the print duty and the pass interval necessary for preventing beading; Fig. 11 is a table showing the correspondence between the maximum print duty and the multi-pass interval; Fig. 12 is a schematic diagram of an ink jet recording apparatus according to the fifth embodiment of the present invention; Figs. 13A to 13E are views for explaining a method of obtaining a mixed color print duty; Fig. 14 is a graph showing the relationship between the print ink density and the required pass interval; Fig. 15 is a table showing the correspondence between the maximum print ink density and the pass interval; Fig. 16 is a schematic diagram of an ink jet recording apparatus according to the sixth embodiment of the present invention; Fig. 17 is a table showing the correspondence between the relative humidity and the multi-pass interval; Fig. 18 is a graph showing the relationship between the relative humidity and the required pass interval; Fig. 19 is a table showing the correspondence between the relative humidity and the multi-pass interval; Fig. 20 is a schematic diagram of an ink jet recording apparatus according to the seventh embodiment of the present invention; Fig. 21 is a graph showing the relationship between the relative humidity and the pass interval when the print ink density is used as a parameter; Fig. 22 is a schematic diagram of an ink jet recording apparatus according to the seventh embodiment of the present invention; Fig. 23 is a graph showing the relationship between the print duty of a post-printed color and the multi-pass interval; Fig. 24 is a table showing the correspondence between the maximum print duty and the multi-pass interval; Fig. 25 is a schematic diagram of an ink jet recording apparatus for performing a conventional multi-pass print operation; and Figs. 26A to 26D are views for explaining thinning patterns. The preferred embodiments of the present invention will be described in detail hereinafter with reference to the accompanying drawings. Note that the present invention is not limited to the embodiments to be described below, and includes various modifications within the range described in the scope of claims. [First Embodiment] Fig. 1 is a schematic diagram of an ink jet recording apparatus adopting the present invention. In Fig. 1, constituting members 1 to 7 are the same as those in Fig. 25. This apparatus includes a multi-pass interval control means 18 used in a multi-pass print mode, a head driving means 19, a main scan motor drive signal forming means 20, and a main scan motor driving means 21. A multi-pass print interval in the ink jet recording apparatus with this arrangement is controlled as follows. When a print mode changing means 6 selects the thin multi-pass print mode automatically or in response to a manual switch operation by a user, an input image signal is input to a thin-print data forming means 7, and is divided into thin-print signals S1 and S2 by the same method described in Figs. 26A to 26D. The thin-print signals S1 and S2 are sequentially supplied to the multi-pass interval control means 18. The multi-pass interval control means 18 supplies the thin-print signals S1 and S2 to the head driving means 19 at an interval longer than a required minimum pass interval, thereby driving a recording head 1. In synchronism with this operation, the main scan motor drive signal forming means 20 forms a main scan motor drive signal, and supplies it to the main scan motor driving means 21. As a result, a main scan motor 5 is driven to move a carriage 2, and a two-pass print operation of the first line is performed. As a method of controlling the multi-pass interval in the multi-pass interval control means 18, the following method may be proposed. The multi-pass interval control means has at least memories M1 and M2 for holding thin-print data, a multi-pass interval measurement timer T, a comparator H for comparing a required minimum pass interval Ts with the value of the multi-pass interval measurement timer T, and an output means for outputting print data in the memories to the head driving means 19. After thin-print data S1 in the memory M1 is output to the head driving means 19, the multi-pass interval measurement timer T starts a time count operation, and at the same time, the comparator H begins to compare the value of the timer T and the required minimum pass interval Ts. When the comparator H determines that the value of the multi-pass interval measurement timer T exceeds the required minimum pass interval Ts, thin-print data S2 in the memory M2 is output to the head driving means 19. In this manner, an interval equal to or longer than the required minimum pass interval can always be formed between the first and second passes. In our experiments, the bubble ink jet recording head of the printer BJ330 available from CANON INC. was used as a recording head, the black ink for the printer BJ330 was used as an ink, and a recording medium prepared by forming a 2-µ thick polyvinyl alcohol (PVA) coat on a polyethylene terephthalate (PET) film was used. The experiments were conducted in an environment at a temperature of 35°C and a relative humidity of 90%. As a result, the relationship between the number of times of print passes and the required minimum pass interval, which relation is necessary for preventing beading, is as shown in the table of Fig. 2. Thus, when the required minimum pass interval Ts was set to be 3 sec, and a thin two-pass print operation was performed, beading was prevented in the thin two-pass print operation, and a high-quality image could be printed. Thus, the number of times of print passes could be decreased. Note that the required minimum pass interval Ts does not include a time t after the print operation of the first pass is started until the carriage 2 is returned to the home position, and the scan operation of the second pass is enabled. Therefore, an actual pass interval is a time longer than the time Ts obtained from Fig. 2 by the time t. [Second Embodiment] Another embodiment of the present invention will be described below. Fig. 3 shows an embodiment wherein the present invention is applied to an ink jet recording apparatus, which has a plurality of recording heads for ejecting inks of different colors, and performs color image recording. The apparatus shown in Fig. 3 includes recording heads 31K, 31C, 31M, and 31Y for respectively ejecting black, cyan, magenta, and yellow inks, a carriage 32 for holding these four recording heads, a thin-print data forming means 27 for forming thinning pattern signals (Figs. 26A to 26D) of the respective colors from color print signals S Y , S M , S C , and S K , and a multi-pass interval control means 28 for control to set a pass interval in a multi-pass print mode to be an interval equal to or longer than the required minimum interval, as will be described later. Multi-pass print interval control based on a print duty in the ink jet recording apparatus with the above arrangement is performed as follows. When a print mode changing means 6 selects the thin multi-pass print mode automatically or in response to a manual switch operation by a user, print signals are supplied to the thin-print data forming means 27. The thin-print data forming means 27 divides the print signals into thin-print signals S1 (for four colors) and thin-print signals S2 (for four colors) by the same method as in Figs. 26A to 26D, and supplies these thin-print signals to the multi-pass interval control means 28. The multi-pass interval control means 28 supplies the thin-print signals S1 and S2 at an interval longer than the required minimum pass interval like in the first embodiment, thereby driving the recording heads 31Y, 31M, 31C, and 31K. In synchronism with this operation, a main scan motor drive signal forming means 20 forms a main scan motor drive signal, and supplies it to a main scan motor driving means 21. As a result, a main scan motor 5 is driven to move the carriage 32, and a two-pass print operation of the first line is performed. In our experiments, the bubble ink jet recording head (360 dpi, driven at 5 kHz) of the printer BJ330 available from CANON INC. was used as a recording head, the black ink for the printer BJ330 and color inks prepared by mixing cyan, magenta, and yellow dyes in a clear ink (an ink excluding a dye) were used as inks, and a PPC paper sheet was used as a recording medium. The experiments were conducted in an environment at a temperature of 35°C and a relative humidity of 90%. The table of Fig. 4 shows the relationship between the number of times of print passes and the required minimum pass interval, which relationship is necessary for preventing "boundary blurring" at a boundary between different colors which occurs in a two-color mixing print operation at a duty of 100% in the conventional thin two-pass print mode. Thus, when the required minimum pass interval Ts was set to be 6 sec, and a thin two-pass print operation was performed, "boundary blurring" could be prevented in the thin two-pass print operation, and a high-quality image could be printed. As a result, the number of times of print passes could be greatly decreased. Furthermore, since a time necessary for forming thin-print data can be prolonged, thin-print data can be formed in a color sequential manner. Thus, electrical processing can be simplified, and a low-cost electrical circuit board can be provided as compared to a case wherein thin-print data are parallelly formed in units of colors. In this embodiment, an actual pass interval is also longer than a time obtained from Fig. 4 by the above-mentioned time t. [Third Embodiment] Fig. 5 shows an embodiment wherein the present invention is applied to a multi-pass print method forsequentially recording four colors. The same reference numerals in Fig. 5 denote the same parts as in Fig. 3. The apparatus of this embodiment further includes a multi-pass interval control means 38. Multi-pass print interval control in the ink jet recording apparatus with the above arrangement is performed as follows. When a print mode changing means 6 selects the thin multi-pass print mode automatically or in response to a manual switch operation by a user, print signals S Y , S M , S C , and S K supplied to the multi-pass interval control means 38 are sequentially transferred to a head driving means 29 color by color in each pass at an interval longer than the required minimum pass interval, thereby driving corresponding heads. In synchronism with this operation, a main scan motor drive signal forming means 20 forms a main scan motor drive signal, and supplies it to a main scan motor driving means 21. As a result, a main scan motor is driven to move a carriage 32, and a four-pass print operation of the first line is performed. In our experiments, the bubble ink jet recording head (360 dpi, driven at 5 kHz) of the printer BJ330 available from CANON INC. was used as a recording head, the black ink for the printer BJ330 and color inks prepared by mixing cyan, magenta, and yellow dyes in a clear ink (an ink excluding a dye) were used as inks, and a PPC paper sheet was used as a recording medium. The experiments were conducted in an environment at a temperature of 35°C and a relative humidity of 90%. The table of Fig. 6 shows the relationship between the number of times of print passes and the required minimum pass interval, which relationship is necessary for preventing "boundary blurring" at a boundary between different colors which occurs in a two-color mixing print operation at a duty of 100% in a conventional color-sequential four-pass print mode. Thus, when the required minimum pass interval Ts was set to be 6 sec, and a color-sequential four-pass print operation was performed, "boundary blurring" could be prevented in the thin two-pass print operation, and a high-quality image could be printed. As a result, the number of times of print passes could be greatly decreased. Furthermore, since thin-print data need not be formed, a circuit for forming thin-print data can be omitted, and cost can be greatly decreased. In the third embodiment, the pass interval is fixed in the color-sequential multi-pass print mode. However, when different multi-pass intervals are set in correspondence with different colors, "boundary blurring" can be more effectively prevented. For example, when the color-sequential four-pass print operation is performed in the order of cyan, magenta, yellow, and black, the print intervals of yellow and black are set to be longer than those of the remaining colors, thereby effectively preventing "boundary blurring". Furthermore, the multi-pass interval may also be controlled depending on a difference in types of recording media (a PPC paper sheet, an ink jet coat paper sheet, and the like), an environmental condition, and a difference in recording modes (a two-pass mode, a four-pass mode, and the like). In this manner, when the print interval in the multi-pass print mode is controlled to be set to be always longer than the required minimum interval, an inexpensive apparatus, which can output a high-quality image, and has high durability and reliability, can be realized. In the above embodiment, the multi-pass interval is constant. However, when a recording apparatus is used in an environment with a high drying speed of an ink, or when the print operation with a low ink density is to be performed, the multi-pass interval may be shortened to further improve the throughput. This embodiment will be described below. [Fourth Embodiment] Fig. 7 is a schematic diagram of an ink jet recording apparatus of this embodiment. In Fig. 7, constituting members 1 to 6 are the same as those shown in Fig. 25. The apparatus shown in Fig. 7 includes a print duty detecting means 117 for detecting a maximum print duty in one line of a print signal S, a multi-pass interval control signal forming means 118 for determining a multi-pass print interval according to a signal from the print duty detecting means 117, and forming a multi-pass interval control signal, a thin-print signal forming means 119, a head driving means 120, a main scan motor drive signal forming means 121, and a main scan motor driving means 122. Multi-pass print interval control based on a print duty in the ink jet recording apparatus with the above arrangement is performed as follows. When a print mode changing means 6 selects the thin multi-pass print mode automatically or in response to a manual switch operation by a user, an input image signal is supplied to the print duty detecting means 117 to detect the maximum value of print duties in one line. The detected maximum value is supplied as a signal to the multi-pass interval control signal forming means 118. A method of detecting the maximum value of print duties in this embodiment is as follows. As shown in Fig. 8A, a pixel range B (indicated by hatching in Fig. 8A) including the specific number N of pixels (in this embodiment, N = 9) is assumed, and the number n of print pixels (n = 1 in the range B in Fig. 8A) in the range is checked to calculate n/N. Thus, n/N is determined as a print duty D at a central pixel C. The print duty determined in this manner is obtained for all the pixels in a print region, and the maximum value of the obtained print duties is determined as a maximum value of print duties in one line. Fig. 8B shows print duties of pixels in a print pattern shown in Fig. 8A, which are obtained by the above-mentioned method. In this case, the maximum value of the print duties is that of a pixel surrounded by a bold line in Fig. 8B, i.e., D = 9/9 (= 100%). The multi-pass interval control signal forming means 118 determines a multi-pass interval according to a signal indicating the maximum print duty input from the print duty detecting means 117, and forms a multi-pass interval control signal. This signal is sent to the thin-print signal forming means 119. The multi-pass interval is determined on the basis of, e.g., a table in Fig. 9 showing the correspondence between the maximum print duty and the multi-pass print interval (an arbitrary unit in Fig. 9). The multi-pass interval control signal for controlling a transfer interval of thin-print data is formed so that the print operations can be performed at the determined multi-pass interval, and is supplied to the thin-print signal forming means 119. The thin-print signal forming means 119 divides an input print signal into thin-print signals S1 and S2 by the same method as in Figs. 26A to 26D, and sequentially supplies the thin-print signals to the head driving means 120 at a corresponding time interval according to the multi-pass interval control signal, thereby driving a recording head 1. In synchronism with this operation, the main scan motor drive signal forming means 121 forms a main scan motor drive signal, and supplies it to the main scan motor driving means 122. As a result, a main scan motor 5 is driven to move a carriage 2, and a two-pass print operation of the first line is performed. In our experiments, the bubble ink jet recording head (360 dpi, driven at 5 kHz) of the printer BJ330 available from CANON INC. was used as a recording head, the black ink for the printer BJ330 was used as an ink, and a recording medium prepared by forming a 2-µ thick polyvinyl alcohol (PVA) coat on a polyethylene terephthalate (PET) film was used. The experiments were conducted in an environment at a temperature of 35°C and a relative humidity of 90%. When an image was printed in the conventional thin two-pass print mode, the above-mentioned "beading" could not be prevented unless the interval between the first and second passes was set to be 3 sec or more. When the conventional thin-print pass method is used, if the pass interval in the two-pass print mode is set to be 3 sec, the print time is prolonged by about 200 sec per A4-size recording medium as compared to a one-pass print mode independently of the print duty. However, according to our experiments, a pass interval necessary for preventing "beading" in the two-pass print mode tends to be shortened as the print duty becomes lower, as shown in the graph of Fig. 10. Thus, a table showing the correspondence between the maximum print duty and the pass interval was created, as shown in Fig. 11, and the multi-pass interval control described in the above embodiment was performed. At this time, as a print image, when an image at a duty of 100% was printed on the upper half of an A4-size recording medium, and an image at a duty of 30% was printed on the lower half of the recording medium, the print time could be shortened by about 100 sec as compared to the conventional thin multi-pass print method, and an image free from image quality deterioration such as "beading" could be obtained, thus providing remarkable effects. Note that the required minimum pass interval in Fig. 10 does not include a time t after the print operation of the first pass is started until the carriage 2 is returned to the home position, and the scan operation of the second pass is enabled. Therefore, an actual pass interval is a time longer than the time obtained from Fig. 11 by the time t. [Fifth Embodiment] Still another embodiment of the present invention will be described below. Fig. 12 shows an embodiment wherein the present invention is applied to an ink jet recording apparatus which has a plurality of recording heads for ejecting different color inks to perform color image recording. The apparatus shown in Fig. 12 includes recording heads 131K, 131C, 131M, and 131Y for respectively ejecting black, cyan, magenta, and yellow inks, a carriage 132 for holding these four recording heads, and a mixed color print ink density detecting means 137. Note that constituting members 3 to 6 and 118 to 122 are the same as those in Fig. 7. Multi-pass print interval control based on a print duty in the ink jet recording apparatus with the above arrangement is performed as follows. When a print mode changing means 6 selects the thin multi-pass print mode automatically or in response to a manual switch operation by a user, an input image signal is supplied to the mixed color print ink density detecting means 137 to predict a maximum value of print ink densities in one line. The predicted maximum value is supplied as a signal to a multi-pass interval control signal forming means 118. A method of predicting the maximum value of print ink densities of a mixed color portion of a color image in this embodiment is as follows. The print duty per pixel of each color is obtained by the method described in the fourth embodiment with reference to Figs. 8A and 8B. The print duties per pixel at the same pixel position of the respective colors are added to obtained a mixed color print duty at that pixel position. This mixed color print duty is determined as a mixed color print ink density of each pixel, and the maximum value of the mixed color print ink densities is then obtained. Figs. 13A to 13E show an example. In Figs. 13A to 13E, as for a pixel of interest (a pixel surrounded by a bold line), the K print duty is 6/9, the C print duty is 4/9, the M print duty is 0/9, and the Y print duty is 5/9. Thus, the mixed color print duty to be obtained (i.e., the print ink density) is 6/9 + 4/9 + 0/9 + 5/9 = 15/9. The multi-pass interval control signal forming means 118 determines a multi-pass interval according to a signal indicating the maximum print duty input from the mixed color print ink density detection means 137, and forms a multi-pass interval control signal. This signal is supplied to a thin-print signal forming means 119. The thin-print signal forming means 119 divides print signals into thin-print signals S1 (for four colors) and thin-print signals S2 (for four colors) by the same method as in Figs. 26A to 26D, and sequentially supplies these thin-print signals to a head driving means 120 at a corresponding time interval according to the multi-pass interval control signal, thereby driving the recording heads 131K, 131C, 131M, and 131Y. In synchronism with this operation, a main scan motor drive signal forming means 121 forms a main scan motor drive signal, and supplies it to a main scan motor driving means 122. As a result, a main scan motor 5 is driven to move the carriage 132, and a two-pass print operation of the first line is performed. In our experiments, the bubble ink jet recording head (360 dpi, driven at 5 kHz) of the printer BJ330 available from CANON INC. was used as a recording head, the black ink for the printer BJ330 and color inks prepared by mixing cyan, magenta, and yellow dyes in a clear ink (an ink excluding a dye) were used as inks, and a PPC paper sheet was used as a recording medium. The experiments were conducted in an environment at a temperature of 35°C and a relative humidity of 90%. In a two-color mixing print operation at a duty of 100% in the conventional thin two-pass print mode, "boundary blurring" at a boundary between different colors occurred, and image quality was considerably deteriorated. Thus, a satisfactory image could not be obtained unless the interval between the first and second passes was set to be 6 sec or more. When the conventional thin-print pass method is used, if the pass interval in the two-pass print mode is set to be 6 sec, the print time is prolonged by about 400 sec per A4-size recording medium as compared to a one-pass print mode independently of the print ink density. However, according to our experiments, a pass interval necessary for preventing "boundary blurring" in the two-pass print operation tends to be abruptly shortened as the maximum print ink density becomes lower, as shown in the graph of Fig. 14. Thus, the multi-pass interval control described in the above embodiment was performed according to a table showing the correspondence between the maximum ink density and the pass interval, as shown in Fig. 15. At this time, as a print image, when a block pattern in which different two-color mixed blocks at a duty of 100% were aligned was printed on the upper half of an A4-size recording medium, and a two-color mixed image at a print duty of 30% was printed on the lower half of the recording medium, the print time could be shortened by about 200 sec as compared to the conventional thin multi-pass print method, and an image free from image quality deterioration such as "boundary blurring" could be obtained, thus providing remarkable effects. In this embodiment, an actual pass interval is also longer by the time t than the time obtained from Fig. 15. [Sixth Embodiment] Fig. 16 shows the sixth embodiment of the present invention. The same reference numerals in Fig. 16 denote the same constituting members as in Fig. 12. The apparatus shown in Fig. 16 includes a relative humidity detector (e.g., a semiconductor humidity sensor) 147 arranged on a carriage 132, a relative humidity detecting means 148 for detecting a relative humidity near a recording unit upon reception of a signal from the relative humidity detector 147, a multi-pass interval control signal forming means 149 for determining a multi-pass print interval according to a signal from the relative humidity detecting means 148, and forming a multi-pass interval control signal, a thin-print signal forming means 150, a head driving means 151, a main scan motor drive signal forming means 152, and a main scan motor driving means 153. Multi-pass print interval control based on a print duty in the ink jet recording apparatus with the above arrangement is performed as follows. When a print mode changing means selects the thin multi-pass print mode automatically or in response to a manual switch operation by a user, the relative humidity detecting means 148 drives the relative humidity detector 147 to detect a relative humidity near the relative humidity detector 147, and supplies it as a signal to the multi-pass interval control signal forming means 149. The multi-pass interval control signal forming means 149 determines a multi-pass interval according to the input relative humidity signal, and forms a multi-pass interval control signal. The multi-pass interval control signal is supplied to the thin-print signal forming means 150. The multi-pass interval is determined on the basis of, e.g., a table in Fig. 17 showing the correspondence between the relative humidity and the multi-pass print interval (an arbitrary unit in Fig. 17). The multi-pass interval control signal for controlling the transfer interval of thin-print data is formed, so that the print operations can be performed at the determined multi-pass interval, and is supplied to the thin-print signal forming means 150. The thin-print signal forming means 150 divides print signals into thin-print signals S1 (for four colors) and thin-print signals S2 (for four colors) by the same method as in Figs. 26A to 26D, and sequentially supplies these thin-print signals to the head driving means 151 at a corresponding time interval according to the multi-pass interval control signal, thereby driving heads. In synchronism with this operation, the main scan motor drive signal forming means 152 forms a main scan motor drive signal, and supplies it to the main scan motor driving means 153. As a result, a main scan motor 5 is driven to move the carriage 132, and a two-pass print operation of the first line is performed. In our experiments, the bubble ink jet recording head (360 dpi, driven at 5 kHz) of the printer BJ330 available from CANON INC. was used as a recording head, the black ink for the printer BJ330 and color inks prepared by mixing cyan, magenta, and yellow dyes in a clear ink (an ink excluding a dye) were used as inks, and a PPC paper sheet was used as a recording medium. The experiments were conducted in an environment at a temperature of 35°C and a relative humidity of 90%. In a two-color mixing print operation at a duty of 100% in the conventional thin two-pass print mode, "boundary blurring" at a boundary between different colors occurred, and image quality was considerably deteriorated. Thus, a satisfactory image could not be obtained unless the interval between the first and second passes was set to be 6 sec or more. When the conventional thin-print pass method is used, if the pass interval in the two-pass print mode is set to be 6 sec, the print time is prolonged by about 400 sec per A4-size recording medium as compared to a one-pass print mode independently of the print ink density. However, according to our experiments, a pass interval necessary for preventing "boundary blurring" in the two-pass print operation tends to be shortened as the relative humidity near the print unit becomes lower in an environment at 35°C, as shown in the graph of Fig. 18. Thus, a table showing the correspondence between the relative humidity and the pass interval was created, as shown in Fig. 19, and the multi-pass interval control described in the above embodiment was performed. At this time, as a print image, when a block pattern in which different two-color mixed blocks at a duty of 100% were aligned was printed on the entire surface of an A4-size recording medium in an environment at a relative humidity of 50%, the print time could be shortened by about 200 sec as compared to the conventional thin multi-pass print method, and an image free from image quality deterioration such as "boundary blurring" could be obtained, thus providing remarkable effects. In this embodiment, an actual pass interval is also longer by the time t than the time obtained from the table shown in Fig. 19. [Seventh Embodiment] Fig. 20 shows the seventh embodiment of the present invention. The same reference numerals in Fig. 20 denote the same constituting members as those in Figs. 12 and 16. In Fig. 20, a multi-pass interval control signal forming means 154 determines a multi-pass print interval on the basis of signals from a humidity detecting means 148 and a mixed color print ink density detecting means 137, and forms a multi-pass interval control signal. The multi-pass interval control signal is supplied to a thin-print signal forming means 150, and a multi-pass print operation is performed in the same manner as in the sixth embodiment. The relationship between the relative humidity and the multi-pass interval when the print ink density is used as a parameter has characteristics, as shown in Fig. 21. More specifically, as the print ink density becomes higher, the multi-pass interval must be prolonged. Also, as the humidity becomes higher while the print ink density is kept constant, the multi-pass interval must be prolonged. Thus, a table showing the correspondence among the maximum ink density, the relative humidity, and the pass interval can be created on the basis of the characteristics like in the above embodiment so as to control the multi-pass interval. [Eighth Embodiment] Fig. 22 shows an embodiment wherein the present invention is applied to a multi-pass print method for performing recording in a four-color sequential manner. The same reference numerals in Fig. 22 denote the same constituting members as those in Fig. 12. The apparatus shown in Fig. 22 includes a print duty detecting means 167, a multi-pass interval control means 168, and a multi-pass interval control signal forming means 169. Multi-pass print interval control in the ink jet recording apparatus with this arrangement is performed as follows. When a print mode changing means 6 selects the thin multi-pass print mode automatically or in response to a manual switch operation by a user, an input image signal is supplied to the print duty detecting means 167, and the maximum print duty in one line of each color is detected by the same method as in the fourth embodiment. The detected maximum print duty is supplied as a signal to the multi-pass interval control signal forming means 169. The multi-pass interval control signal forming means 169 determines a multi-pass interval according to the input maximum print duties of the respective colors, and forms a multi-pass interval control signal. The multi-pass interval control signal is supplied to the multi-pass interval control means 168. As a means for determining the multi-pass interval on the basis of the maximum print duties of the respective colors, a table showing the correspondence between the maximum print duty and the multi-pass interval is created on the basis of the maximum print duty of a color to be printed like in the above embodiment, and the multi-pass interval is determined on the basis of this table. Print signals S Y , S M , S C , and S K supplied to the multi-pass interval control means 168 are sequentially transferred to a head driving means 120 color by color in each pass at the multi-pass interval determined by the multi-pass interval control signal, thereby driving recording heads 131Y, 131M, 131C, and 131K. In synchronism with this operation, a main scan motor drive signal forming means 121 forms a main scan motor drive signal, and supplies it to a main scan motor driving means 122. Thus, a main scan motor 5 is driven to move a carriage 132, and a four-pass print operation of the first line is performed. In our experiments, the bubble ink jet recording head (360 dpi, driven at 5 kHz) of the printer BJ330 available from CANON INC. was used as a recording head, the black ink for the printer BJ330 and color inks prepared by mixing cyan, magenta, and yellow dyes in a clear ink (an ink excluding a dye) were used as inks, and a PPC paper sheet was used as a recording medium. A color-sequential four-pass print operation was performed in the order of cyan, magenta, yellow, and black in an environment at a temperature of 35°C and a relative humidity of 90%. In a two-color mixing print operation at a duty of 100%, "boundary blurring" occurred at a boundary between different colors, and image quality was considerably deteriorated. Thus, a satisfactory image could not be obtained unless the interval between adjacent passes was set to be 6 sec or more. When the conventional thin-print pass method is used, if the pass interval in the two-pass print mode is set to be 6 sec, the print time is prolonged by about 1,200 sec per A4-size recording medium as compared to a one-pass print mode independently of the print duty. However, according to our experiments, a pass interval necessary for preventing "boundary blurring" upon execution of the color-sequential multi-pass print operation tends to be shortened as the maximum print duty of a post-printed color becomes lower when an image at a duty of 100% is previously printed. Thus, a table showing the correspondence between the maximum print duty and the multi-pass interval was created, as shown in Fig. 24, and the multi-pass interval control described above was performed. At this time, as a print image, when a block pattern in which different two-color mixed blocks at a duty of 100% were aligned was printed on the upper half of an A4-size recording medium, and a two-color mixed image at a print duty of 30% was printed on the lower half of the recording medium, the print time could be shortened by about 800 sec as compared to the conventional thin multi-pass print method, and an image free from image quality deterioration such as "boundary blurring" could be obtained, thus providing remarkable effects. Furthermore, the ink density of the mixed color portion need not be detected, and thin-print data need not be formed. Therefore, electrical circuits for these operations can be omitted, and cost can be greatly reduced. [Other Embodiments] In the above embodiments, upon execution of color image recording, it is more effective if different multi-pass control operations are performed depending on a difference in unit colors or mixed colors. For example, when "boundary blurring" is conspicuous like at a boundary between yellow and black, the pass interval between these colors may be set to be longer than those for the remaining colors, or the print duties of the respective colors to be added when the print ink density is obtained may be multiplied with different weighting coefficients. For example, in the eighth embodiment, in the color-sequential multi-pass print operation, the pass interval is fixed independently of colors. When different multi-pass intervals are set depending on a color difference, "boundary blurring" can be more effectively prevented. In our experiments, when the color-sequential four-pass print operation was performed in the order of cyan, magenta, yellow, and black, the print interval between yellow and black was set to be longer than that for the remaining colors so as to effectively prevent "boundary blurring". In the above embodiments, as an example of the thin multi-pass print method, the method of thinning print data of each unit color into checkerboard or inverted checkerboard patterns, and performing a multi-pass print operation using these patterns has been described. However, a thinning method of print data is not limited to this. In the above embodiments, the print duty detecting means and the print ink density predicting means are arranged at the input side of the thin-print data forming means. However, these means may be arranged at the output side of the thin-print data forming means. Alternatively, the above-mentioned means may be arranged at both the input and output sides of the thin-print data forming means to detect a print duty and to predict a print ink density, thereby finely controlling multi-pass intervals according to these signals. Thus, further remarkable effects can be provided. In the above embodiments, the multi-pass interval control is performed using one parameter. However, it is more effective that the multi-pass interval is finely controlled using some of a (unit color) print duty signal, a (mixed color) print ink density signal, and a relative humidity signal. Furthermore, the above embodiments may be combined with multi-pass interval control based on a difference in types of recording media (a PPC paper sheet, an ink jet coat sheet, and the like) and a difference in recording modes (a two-pass mode, a four-pass mode, and the like). In the fourth embodiment, control is made using the maximum print duty. Alternatively, control may be made by detecting an average value in one line. In the sixth embodiment, a means for detecting not only the relative humidity but also the temperature may be used, and the multi-pass interval may be finely controlled based on both the relative humidity and the temperature near a recording unit, thus providing further remarkable effects. In this manner, a recording interval used when a desired image is obtained by recording thin images a plurality of number of times on a single region of a recording medium is properly controlled according to a predetermined condition such as the print duty, environmental condition, and the like. Therefore, a high-quality image free from blurring can be obtained without decreasing the throughput. [Others] The present invention brings about excellent effects particularly in a recording head and a recording device of a system, which comprises means (e.g., an electrothermal converting element, laser light, and the like) for generating heat energy as energy utilized upon execution of ink ejection, and causes a change in state of an ink by the heat energy, among the ink jet recording systems. According to this system, a high-density and high-definition recording operation can be attained. As to its representative construction and principle, for example, one practiced by use of the basic principle disclosed in, for instance, U.S. Patent Nos. 4,723,129 and 4,740,796 is preferred. The above system is applicable to either one of the so-called on-demand type and the continuous type. Particularly, the case of the on-demand type is effective because, by applying at least one driving signal which gives rapid temperature elevation exceeding nucleus boiling corresponding to the recording information on electrothermal converting elements arranged in a range corresponding to the sheet or liquid channels holding liquid (ink), heat energy is generated by the electrothermal converting elements to effect film boiling on the heat acting surface of the recording head, and consequently the bubbles within the liquid (ink) can be formed in correspondence to the driving signals one by one. By ejecting the liquid (ink) through an ejection port by growth and shrinkage of the bubble, at least one droplet is formed. By making the driving signals into pulse shapes, growth and shrinkage of the bubble can be effected instantly and adequately to more preferably accomplish ejection of the liquid (ink) particularly excellent in response characteristics. As the driving signals of such pulse shapes, the signals as disclosed in U.S. Patent Nos. 4,463,359 and 4,345,262 are suitable. Further excellent recording can be performed by using the conditions described in U.S. Patent No. 4,313,124 of the invention concerning the temperature elevation rate of the above-mentioned heat acting surface. As a construction of the recording head, in addition to the combined construction of an ejection orifice, a liquid channel, and an electrothermal converting element (linear liquid channel or right angle liquid channel) as disclosed in the above specifications, the construction by use of U.S. Patent Nos. 4,558,333 and 4,459,600 disclosing the construction having the heat acting portion arranged in the flexed region is also included in the invention. The present invention can be also effectively constructed as disclosed in Japanese Laid-Open Patent Application No. 59-123670 which discloses the construction using a slit common to a plurality of electrothermal converting elements as an ejection portion of the electrothermal converting element or Japanese Laid-Open Patent Application No. 59-138461 which discloses the construction having the opening for absorbing a pressure wave of heat energy in correspondence with the ejection portion. More specifically, according to the present invention, recording can be reliably performed with high efficiency regardless of constructions of recording heads. Furthermore, the present invention can be effectively applied to a full-line type recording head having a length corresponding to the maximum with of a recording medium, which can be used in recording of a recording apparatus. Such a recording head may have an arrangement which satisfies the length by combining a plurality of recording heads, or an arrangement as a single recording head which is formed integrally. In addition, of the above serial type recording heads, the present invention is effective for a recording head fixed to an apparatus main body, a recording head of the freely exchangeable chip type which enables electrical connection to the apparatus main body or supply of ink from the apparatus main body by being mounted onto the apparatus main body, or for the case by use of a recording head of the cartridge type, which has an ink tank provided integratedly on the recording head itself. It is also preferable to add a restoration means for the recording head, preliminary auxiliary means, and the like provided as a construction of the recording apparatus of the invention because the effect of the present invention can be further stabilized. Specific examples of them may include, for the recording head, capping means, cleaning means, pressurization or aspiration means, and electrothermal converting elements or another heating element or preliminary heating means according to a combination of them. It is also effective for stable recording to realize the preliminary ejection mode which executes ejection separately from recording. Moreover, in the embodiments of the present invention, an ink is described as a liquid. Alternatively, the present invention may employ an ink which is solidified at room temperature or less, and is softened or liquefied at room temperature, or an ink, which is liquefied upon application of a use recording signal since it is a general practice to perform temperature control of the ink itself within a range between 30°C and 70°C in an ink jet system so that the ink viscosity can fall within a stable ejection range. In addition, a temperature rise caused by heat energy may be prevented by positively utilizing the temperature rise as energy for a change in state from a solid state to a liquid state of the ink, or an ink which is solidified in a non-use state for the purpose of preventing evaporation of the ink may be used. In any case, the present invention can be applied to a case wherein an ink, which can be liquefied by heat energy such as an ink which is liquefied upon application of heat energy according to a recording signal, and is ejected in a liquid state, an ink which begins to be solidified when it reaches a recording medium, or the like may be used. In this case, an ink may be held in a liquid or solid state in recess portions or through holes of a porous sheet, as described in Japanese Laid-Open Patent Application No. 54-56847 or 60-71260, and the porous sheet may be arranged to oppose electrothermal converting elements. In the present invention, the above-mentioned film boiling system is most effective for the above-mentioned inks. In addition, the ink jet recording apparatus of the present invention may be used as an image output terminal of an information processing equipment such as a computer, or a copying machine as a combination of the recording apparatus, a reader, and the like, or a facsimile apparatus having a transmission/reception function.

Claims: An ink jet recording method of recording an image by ejecting ink droplets from a recording device comprising a plurality of ejection elements to a recording medium, said method comprising the steps of: recording in a first recording step a thinned image onto a predetermined area of the recording medium by driving the recording device on a basis of an image signal thinned according to a first thinning pattern; and recording in a second recording step a thinned image onto the predetermined area of the recording medium by driving the recording device on a basis of an image signal thinned according to a second thinning pattern which is the complement of the first thinning pattern, characterised by determining whether a predetermined time period has elapsed since said first recording step was effected, the predetermined time period being variable in accordance with a predetermined condition, wherein recording in the second recording step is executed after in said determining step it is determined that the predetermined time has elapsed to enable appropriate drying and/or absorbtion to take place thereby obviating deterioration of image quality. A method as claimed in claim 1, characterised in that the predetermined time period is varied in accordance with a print duty of the image data to be recorded by the recording device. A method as claimed in claim 2, using a recording device comprising a plurality of recording heads for ejecting mutually different color inks, characterised in that in said determining step, recording intervals are determined on a basis of print duties of respective color image data given with a predetermined amount for the plurality of recording heads. A method as claimed in claim 1, characterised in that an environmental condition near the recording device is detected, and the predetermined time period is varied in accordance with the detected environmental condition. A method as claimed iii claim 4, characterised in that at least one of a temperature and a relative humidity near the recording device is detected as the environmental condition. A method as claimed in claim 1, 2 or 3, characterised in that the thinned images are recorded by moving the recording device relative to the recording medium a plurality of number of times. A method as claimed in any of claims 1 to 6, characterised in that the recording device ejects the ink by causing a change in state in the ink by heat energy. An ink jet recording apparatus comprising: recording means (1) for ejecting ink droplets onto a recording medium (P), said recording means comprising a plurality of ejection elements; data generation means (7) for generating first image data thinned according to a first thinning pattern and second image data thinned according to a second thinning pattern which is the complement of the first thinning pattern; and control means (18) for controlling said recording means to sequentially perform on a predetermined area of the recording medium a first image recording based on the first image data generated from said data generation means and a second image recording based on the second image data, characterised by setting means (18) for setting a time interval between the first image recording and the second image recording, said time interval being variable in accordance with a predetermined condition to enable appropriate drying and/or absorbtion to take place. An apparatus as claimed in claim 8, characterised in that said setting means comprises detection means (117) for detecting a print duty of image data for the predetermined area, and the time interval is variably set in accordance with the print duty detected by said detection means. An apparatus as claimed in claim 9, characterised in that the setting means is adapted so that when the print duty detected by said detection means exceeds a predetermined value, said setting means sets the time interval to be a first time interval, and when the print duty is less than the predetermined value, said setting means sets the time interval to be a second time interval which is shorter than the first time interval. An apparatus as claimed in claim 9, characterised in that said plurality of recording heads for ejecting ink droplets in mutually different colors to a recording medium are provided, each of said recording means comprising a plurality of ejection elements, and said detection means detects print duties of the sets of image data for the respective colors corresponding to the respective color images to be recorded on the predetermined area of the recording medium. An apparatus as claimed in claim 8, characterised in that said setting means comprises detection means (147) for detecting an environmental condition near a recording position of said recording means, and changes the time interval in accordance with a detection signal from said detection means. An apparatus as claimed in claim 12, characterised in that said detection means detects at least one of temperature and relative humidity near the recording position. An apparatus as claimed in any one of claims 8 to 13, characterised by moving means (2) for moving said recording means (1) relative to the recording medium, wherein a thinned image according to the first image data and a thinned image according to the second image data are recorded on the recording medium by effecting relative movement with said moving means. An apparatus as claimed in claim 14, characterised in that said setting means (18) sets the time interval between the relative movements of said moving means (2). An apparatus as claimed in any one of claims 8 to 15, characterised in that said recording means ejects the ink by causing a change in state in the ink by heat energy.

Inventors: AKIYAMA YUJI, ARAI ATSUSHI, HIRABAYASHI HIROMITSU, MATSUBARA MIYUKI, NAGOSHI SHIGEYASU, SUGIMOTO HITOSHI, AKIYAMA, YUJI, ARAI, ATSUSHI, HIRABAYASHI, HIROMITSU, MATSUBARA, MIYUKI, NAGOSHI, SHIGEYASU, SUGIMOTO, HITOSHI, AKIYAMA, YUJI, C/O CANON KABUSHIKI KAISHA, ARAI, ATSUSHI, C/O CANON KABUSHIKI KAISHA, HIRABAYASHI, HIROMITSU, C/O CANON KABUSHIKI KAISHA, MATSUBARA, MIYUKI, C/O CANON KABUSHIKI KAISHA, NAGOSHI, SHIGEYASU, C/O CANON KABUSHIKI KAISHA, SUGIMOTO, HITOSHI, C/O CANON KABUSHIKI KAISHA
Applicants: CANON KK, CANON KABUSHIKI KAISHA
Application year: 1992
Main classification: B41J2
IPC codes: G06K15, B41J2