Method and apparatus for recording with an ink jet recording head

Abstract: Disclosed is a recording apparatus for performing recording using an ink-jet recording head (1) for discharging an ink from an array of a plurality of orifices, including a drive unit for driving the recording head (1) on the basis of a recording signal to cause a first orifice of the plurality of orifices to discharge an ink at a first timing, and to cause a second orifice to discharge an ink at a second timing, and a moving unit for moving the recording head (1) and a recording medium (2) relative to each other by an amount corresponding to a distance between the first and second orifices during a time interval between the first and second timings by the drive unit. There is also disclosed a recording method.

Description: BACKGROUND OF THE INVENTION : Field of the Invention The present invention relates to a recording apparatus using an ink-jet recording head and a recording method and, more particularly, to an ink-jet system recording apparatus for landing a plurality of ink droplets on the same portion of a recording medium to form one dot, and expressing gradation depending on the number of ink droplets to land, and a recording method. Related Background Art When recording is performed by an ink-jet recording apparatus, as a conventional method of expressing gradation in, e.g., an image to be recorded, various methods are known. For example, a method of changing the area of a dot formed by ink droplets on a recording medium by changing the size of the ink droplets to be discharged by various means (area gradation method), a method of expressing gradation by changing the number of dots forming one pixel which is formed by a plurality of dots formed at different positions (a density pattern method, a dither method, and the like), a method of performing recording using inks having different densities (shading ink method), a method of landing a plurality of ink droplets on the same portion of a recording medium to form one dot, and changing the dot area (density) in accordance with the number of ink droplets to land, thereby expressing gradation (multi-droplet method), and the like are known. On the other hand, as a recording method capable of achieving high-speed, high-density recording, a method wherein bubbles are grown by utilizing heat energy generated by electricity-heat converters of a recording head, and an ink is discharged based on a change in pressure caused by a change in state of the ink has been recently receiving a lot of attention. Since the ink-jet method utilizing the heat energy cannot desirably change the size of ink droplets, the multi-droplet method described above is effective as a method of expressing gradation. Since the size of one pixel can be reduced as compared to the density pattern method or the dither method, high-resolution recording can be performed. Unlike the shading ink method, a plurality of inks for the same color need not be prepared. Thus, the ink-jet method also has advantages of the apparatus arrangement. However, in the conventional multi-droplet method, recording gradation cannot often be changed in correspondence with a change in the number of ink droplets to land, or dot diameters (densities) vary even if dots are formed by the same number of ink droplets. As a result, a gradation range of the entire image to be recorded is narrowed, resulting in poor sharpness. In the conventional multi-droplet method, in order to form one dot, i.e., one pixel in this case, a plurality of ink droplets discharged from the same orifice land to form the pixel. For this reason, landing intervals of the plurality of droplets cannot become shorter than those defined by the discharging frequency. As a result, the first ink droplet may soak in the recording medium, or a solvent as a constituting component of an ink is evaporated before the next ink droplet lands, and an ink cannot be sufficiently spread. As a result, even if a plurality of ink droplets land, the dot diameter undesirably becomes smaller than a desired size corresponding to the number of ink droplets to land. In this manner, the conventional multi-droplet method suffers from a problem of impaired gradation of an image caused by a relatively long landing interval. When the dot densities formed by ink droplets discharged from orifices vary depending on variations of discharging diameters or opening directions of the orifices, variations of densities among dots (density nonuniformity) become more conspicuous in the conventional multi-droplet method since one dot is formed by discharging a plurality of ink droplets from the same orifice. US-A-4631548 discloses a multi-color ink jet printer which has a plurality of ink reservoirs, for different primary colors, and prints multi-color images by applying matrix dots to the recording medium consisting of a single primary color or a mixture of primary colors. The diameter of the matrix dots formed on the recording medium is maintained constant either by adjusting the volume of ink in each droplet inversely with the number of droplets formed in a matrix dot, or preselecting a constant small volume for the droplets and forming each matrix dot of the same number of droplets, irrespective of whether the matrix dots are formed from a single primary color or a mixture of primary colors. EP-A-0259541 discloses a thermal ink jet printer which emits drops that merge together on the surface of a substrate within the wetting time of the substrate. The size of the dot printed is controlled by the number of drops emitted by the thermal ink jet printer within the wetting time of the substrate. According to the invention there is provided a recording apparatus for recording pixels having graduated tonal densities by causing an ink jet recording head having an array of a plurality of orifices, linearly disposed along an array direction, to discharge a plurality of ink droplets thereby performing recording, comprising means for bringing about relative movement of the recording medium and the recording head in a direction parallel to said array direction, and control means for driving the recording head based on a recording signal, characterised in that said control means is adapted to drive each said orifice in a group of said orifices to discharge a droplet of said ink only at a first predetermined timing and through a first orifice and to cause said second orifice to discharge a droplet of said ink only at a second predetermined timing and so forth for each successive orifice of the group, said group being used for forming the pixel; and to control the time interval between the discharge of ink through said first orifice and the discharge of ink through said second orifice, said time interval being such that droplets discharged by said first orifice at said first timing and from said second orifice at said second timing and so forth for each successive orifice of the group are deposited in overlapping relation on the recording medium, and such that the following droplet arrives at the recording medium prior to the preceding droplet having soaked into the recording medium or having dried, whereby the droplets are combined on said recording medium, so that a recording of graduated tonal density can be obtained. Further according to the invention there is provided a method for recording graduated tonal densities by performing recording on a recording medium using an ink jet recording head which discharges ink from an array of a plurality of orifices, said orifices being linearly disposed along an array direction, characterised by causing a first said orifice of said recording head to discharge a droplet of ink onto a predetermined position of said recording medium; moving a second said orifice of said recording head into registry with the predetermined position of said recording medium; and causing said second orifice to discharge an ink droplet onto the predetermined position of said recording medium such that droplets discharged from said first and second orifices are deposited in overlapping relation on the recording medium, and such that the following droplet arrives at the recording medium prior to the preceding droplet having soaked into the recording medium or having dried, whereby the droplets are combined on said recording medium, so that a recording of graduated tonal density can be obtained. By means of the present invention the recording apparatus can provide a high-gradation and sharp image free from variations of densities among the formed pixels. In the accompanying drawings:- Fig. 1 is a schematic perspective view of an ink-jet recording apparatus according to an embodiment of the present invention; Fig. 2 is a block diagram showing a control arrangement of the ink-jet recording apparatus; Fig. 3 is a view showing the principle of recording control according to the first embodiment of the present invention; Fig. 4 is a timing chart of a recording head driving operation in the recording control; Fig. 5 is a chart showing a pixel forming process in the first embodiment; Fig. 6 is a timing chart according to the second embodiment of the present invention; and Fig. 7 is a chart showing a pixel forming process in the second embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS : The preferred embodiments of the present invention will be described in detail hereinafter with reference to the accompanying drawings. (First Embodiment) Fig. 1 is a schematic perspective view showing an ink-jet recording apparatus according to an embodiment of the present invention. In Fig. 1, a recording head 1 has 32 ink orifices at a density of 16 orifices/mm, i.e., a density of orifice intervals of 62.5 µm. Each orifice comprises an electricity-heat converter for generating discharging energy to a liquid channel communicating with it. The electricity-heat converter generates heat in accordance with an electrical pulse applied thereto, and causes film boiling in an ink. An ink is discharged from each orifice in correspondence with growth of bubbles caused by the film boiling. In this embodiment, a discharging frequency at each orifice, i.e., a drive frequency of the electricity-heat converter is 2 kHz (pulse interval = 500 µsec). A carriage 4 mounts the recording head 1, and is movably guided along two guide shafts 5A and 5B which are slidably engaged with a portion of the carriage 4. An ink supply tube 6 supplies an ink from an ink tank (not shown) to the recording head 1. A flexible cable 7 transmits a drive signal based on recording data and a control signal from a control unit (not shown) of the apparatus of this embodiment to a head drive circuit arranged in a portion of the recording head 1. The ink supply tube 6 and the flexible cable 7 are formed of flexible members so as to be able to follow movement of the carriage 4. The carriage 4 is connected to a portion of a belt (not shown), parallel to the guide shafts 5A and 5B, for moving the carriage 4. When the belt is driven by a carriage motor (not shown), the carriage 4 can be moved. A cylindrical drum 3 extends to be parallel to the guide shafts 5A and 5B in its longitudinal direction, and is rotated by a drive means comprising, e.g., a motor 12, in a direction of an arrow in Fig. 1 at a tangential velocity of 625 mm/sec on the drum. A recording paper sheet 2 having, e.g., an A1 size, as a recording medium is mounted along the cylindrical side surface of the drum 3 to cover the entire surface. Thus, the recording head 1 can discharge an ink to a portion of the recording paper 2 facing the orifices upon movement of the carriage 4 to perform recording. A cap 13 and a blade 14 are arranged near the end portion of the drum 3. The cap 13 and the blade 14 can be inserted or removed in or from the moving path of the recording head 1 upon movement of the head 1. The blade 14 is engaged with an orifice surface of the recording head 1 to wipe it. Thus, dew drops attached to the orifice surface can be removed. The cap 14 covers and closes the orifice surface, and draws an ink in the orifices by a suction force of, e.g., a pump (not shown), thereby preventing an ink from being dried in a non-recording state. Fig. 2 is a block diagram showing a control arrangement of the ink-jet recording apparatus shown in Fig. 1. In Fig. 2, a control unit 100 is arranged in a predetermined portion of the apparatus of this embodiment in the form of a circuit board. The control unit 100 comprises a CPU 100A for executing processing of the entire apparatus, and control processing of operations, a RAM 100B used as a work area in control processing by the CPU 100A, and a ROM 100C for storing a processing sequence of the control processing. The CPU 100A controls rotation of a drum motor 11 for rotating the drum 3 and a carriage motor 10 respectively through a drum motor drive circuit 11A and a carriage motor drive circuit 10A. Drive operations of the electricity-heat converters of the recording head 1 are controlled on the basis of drive signals based on recording data, and control signals for controlling drive timings, and the like, which are transmitted from the control unit 100. The recording data is supplied from a host device 200 to the control unit 100. As the host device 200, a host computer, a scanner having a reading means, a facsimile receiver for receiving a transmitted facsimile signal, and the like are available. With the above arrangement, recording control to be described below is performed. Fig. 3 is a view for explaining the principle of recording control according to the embodiment of the present invention, Fig. 4 is a timing chart of a recording head drive operation in the recording control, and Fig. 5 is a view showing a pixel forming process in the recording control. Note that the timing chart of Fig. 4 mainly illustrates possible discharging intervals of each orifice, and discharging intervals among the orifices. In actual recording, discharging intervals of each orifice are determined in consideration of the rotational speed of the drum 3 and the positions of pixels to be formed with respect to the recording paper. As shown in Fig. 4, each orifice can discharge an ink at time intervals of 500 µsec in consideration of time required for refilling an ink. Among the orifices, an ink is discharged at time intervals of about 100 µsec in accordance with the rotational speed of the drum 3 and the distance between the adjacent orifices in this embodiment. As described above, since the tangential velocity of the drum 3 is 625 mm/sec, the drum and each orifice are moved relative to each other by 62.5 µm during an interval of 100 µsec. When an ink is discharged at the discharging intervals of 100 µsec, ink droplets discharged from a plurality of orifices land on the same portion of the recording paper. The discharging intervals can be variously set by changing the rotational speed of the drum 3 and the distance between the adjacent orifices. A formation process of one pixel will be explained below with reference to Figs. 3 to 5. At timing t₁, an ink droplet discharged from a first orifice lands on the recording paper 2 (a dot A in Figs. 3 and 5). The dot A is moved to a position of a dot B in Figs. 3 and 5 after an elapse of about 100 µsec (timing t₂), and an ink droplet discharged from a second orifice adjacent to the first orifice lands on the dot B. These operations are repeated to form one pixel. The number of ink droplets for forming one pixel is determined in accordance with the density of a pixel to be formed. For example, when recording is performed at a density half a maximum density of this embodiment (an ink is discharged from all the 32 orifices), a pixel is formed by ink droplets discharged from 16 orifices (timing t₁₆). At timing t₆ after an elapse of 500 µsec from the first discharging operation, the first orifice performs the second discharging operation, thus starting formation of the second pixel at the dot A in Fig. 5. For the second pixel, the 2nd, 3rd,..., 32nd orifices discharge an ink to have delay times of 100 µsec like in the first pixel, thereby forming a pixel by a plurality of ink droplets. The drum 3 is rotated once while sequentially repeating such pixel formation. In this embodiment, a discharging interval of one orifice is 500 µsec, and is five times a discharging timing interval of 100 µsec between adjacent orifices. In this case, since an interval between pixels formed by one orifice (e.g., dots A and F in Fig. 5) is five times an interval between the adjacent orifices, the density of a pixel formed during one revolution of the drum is 1/5 times an orifice density. In this manner, since the pixel density becomes relatively small, the drum must be rotated several times in one-line recording to increase the pixel density, thereby forming new pixels between adjacent already formed pixels (e.g., between adjacent ones of dots A to F in Fig. 5). In this embodiment, the drum is rotated five times during one-line recording so as to perform recording at a pixel density of 16 pixels/mm. After one-line recording is performed in this manner, the carriage 4 is moved to move the recording head 1 to the next line, and the same recording operation is performed. Upon repetition of these operations, an image can be formed. As can be apparent from the above description, according to this embodiment, in each orifice group (e.g., first to sixth orifices) for forming a pixel, a dot is formed on a recording medium by an ink discharged from the first orifice of the array, and thereafter, the recording medium is transferred. When the dot reaches a position facing the second orifice of the array, an ink is discharged from the second orifice, and a dot is formed at the same position as the former dot. In this manner, in each orifice group, one pixel is formed by the plurality of orifices. According to this embodiment, in order to form one pixel, landing intervals of the plurality of ink droplets can be shortened as compared to a conventional apparatus without being influenced by a response frequency (discharging minimum period). Therefore, a first ink droplet can be prevented from soaking in a recording medium, or an ink aqueous component can be prevented from being evaporated between adjacent landing timings. As a result, a pixel having a density according to the number of landing ink droplets can be obtained, and a high-gradation, sharp image can be obtained. Furthermore, since one pixel is formed by ink droplets from different orifices, even if ink droplets discharged from the orifices suffer from variations, the variations can be averaged in pixel formation. Therefore, a density variation (density nonuniformity) of a pixel to be formed can be reduced. (Second Embodiment) The second embodiment of the present invention will be described below. In the second embodiment of the present invention, substantially the same recording operation as in the first embodiment is performed, except that a recording head which has 256 orifices at the same orifice density (16 orifices/mm) as that in the first embodiment is employed, a rotational speed of a drum is set to be 2,000 mm/sec, and a head drive timing is as shown in Fig. 6. Fig. 7 shows a pixel formation process at that time. In this embodiment, recording paper 2 on the drum is moved by 1 mm, i.e., 16 orifice pitches for 500 µsec. Therefore, when discharging operations are performed according to the timing chart shown in Fig. 6, for example, a first pixel (dot A₁ in Fig. 7) is formed by ink droplets discharged from 1st, 17th, 33rd, 49th,..., 241st orifices. An nth pixel is formed by ink droplets discharged from (k+16m)th 16 pixels (m = 0 to 15) where k is the remainder obtained by dividing n by 16. By changing the number of ink droplets to be discharged in accordance with an image signal, 17-value gradation recording can be performed. According to this embodiment, since one pixel is formed by ink droplets from different orifices like in the first embodiment, even if ink droplets discharged from the orifices suffer from variations, the variations can be averaged in pixel formation. Therefore, a density variation (density nonuniformity) of a pixel to be formed can be reduced, and gradation can be improved. In the first and second embodiments, recording is performed while winding the recording paper around the drum. Even in a conventional serial type printer, an orifice array of a recording head can be mounted to be parallel to the scanning direction, thus obtaining the same effects as in the above embodiments. (Comparative Example) The same recording head (orifice interval = 63.5 µm) and the same ink-jet recording apparatus as those in the first embodiment were used, a rotational speed of a drum with recording paper was set to be 125 mm/sec, and recording was performed by discharging ink droplets from a single orifice at 500-µsec intervals like in the conventional apparatus to form one pixel. Note that the recording paper was moved by 63.5 µm equal to the orifice port interval during a 500-µsec interval. When image recording was performed in this manner, an image in which a high-density portion had a relatively low density and slightly low gradation as compared to the first and second embodiments was obtained. Note that as an ink used in the present invention, both water- and oil-based inks can be used. However, the water-based ink is preferable in terms of odor and safety. As a recording medium used in the present invention, any media normally used in ink-jet recording, such as coated paper on a surface of which an ink receiving layer is formed, normal paper such as high-quality paper, letter paper, copy paper, and the like, a transparency film, and the like can be used. A recording medium such as coated paper on a surface of which an ink receiving layer is formed, a transparency film, or the like is preferably used to obtain a high-quality image. Note that the present invention can provide a remarkable effect in a recording head and a recording apparatus which particularly employ a system wherein heat energy is given to an ink by a means for generating the heat energy (electricity-heat converter, laser, or the like) to discharge an ink among ink-jet recording systems. According to this system, high-density, high-quality recording can be attained. As to its representative constitution and principle, for example, one practiced by use of the basic principle disclosed in, for example, U.S. Patents 4,723,129 and 4,740,796 is prepared. This system is applicable to either 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 an electricity-heat converters arranged corresponding to the sheets or liquid channels holding liquid (ink), heat energy is generated at the electricity-heat converters to effect film boiling at the heat acting surface of the recording head, and consequently the bubbles within the liquid (ink) can be formed corresponding one by one to the driving signals. By discharging the liquid (ink) through an opening for discharging 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 accomplish more preferably discharging of the liquid (ink) particularly excellent in response characteristic. As the driving signals of such pulse shape, those as disclosed in U.S. Patents 4,463,359 and 4,345,262 are suitable. Further excellent recording can be performed by employment of the conditions disclosed in U.S. Patent 4,313,124 of the invention concerning the temperature elevation rate of the above-mentioned heat acting surface. As the constitution of the recording head, in addition to the combination of discharging orifice, liquid channel, electricity-heat converter (linear liquid channel or right angle liquid channel) as disclosed in the above-mentioned respective specifications, the constitution by use of U.S. Patents 4,558,333, 4,459,600 disclosing the constitution having the heat acting portion arranged in the flexed region is also included in the present invention. In addition, the present invention can be also effectively made the constitution as disclosed in Japanese Patent Laid-Open Application No. 59-123670 which discloses the constitution using a slit common to a plurality of electricity-heat converters as the discharging portion of the electricity-heat converter or Japanese Patent Laid-Open Application No. 59-138461 which discloses the constitution having the opening for absorbing pressure wave of heat energy correspondent to the discharging portion. In addition, the present invention is effective for a recording head of the freely exchangeable chip type which enables electrical connection to the main device or supply of ink from the main device by being mounted on the main device, or for the case by use of a recording head of the cartridge type provided integrally on the recording head itself. Also, addition of a restoration means for the recording head, a preliminary auxiliary means, etc. provided as the constitution of the recording device of the present invention is preferable, because the effect of the present invention can be further stabilized. Specific examples of these may include, for the recording head, capping means, cleaning means, pressurization or aspiration means, electricity-heat converters or another heating element or preliminary heating means according to a combination of these, and it is also effective for performing stable recording to perform preliminary mode which performs discharging separate from recording. Further, as the recording mode of the recording device, the present invention is extremely effective for not only the recording mode only of a primary color such as black etc., but also a device equipped with at least one of plural different colors or full color by color mixing, whether the recording head may be either integrally constituted or combined in plural number. Moreover, in the embodiments of the present invention described above, a liquid ink is used. For example, an ink which is solidified at room temperature or lower, and is softened or liquidized at the room temperature, or an ink which is liquidized upon application of a use recording signal may be employed since an ink-jet recording system normally performs temperature adjustment of an ink itself within a range of 30°C to 70°C to temperature-control an ink viscosity to fall within a stable discharging range. In addition, a temperature rise caused by heat energy may be positively utilized as energy for changing a state of an ink from a solid state to a liquid state so as to prevent solidification of an ink, or an ink which is solidified in a leaving state for the purpose of preventing evaporation of an ink may be used. In any case, the present invention is applicable to a case using an ink which can only be liquified by heat energy, such as an ink which is liquified upon application of heat energy according to a recording signal to discharge a liquid ink, or an ink which begins to be solidified when it reaches a recording medium. In these cases, an ink may face electricity-heat converters while being held in a liquid or solid state in a porous sheet recess portion or through holes, as disclosed in Japanese Patent Laid-Open Application No. 54-56847 or 60-71260. In the present invention, the above-mentioned film boiling method is most effectively executed for the above-mentioned inks. In addition, the ink-jet recording apparatus of the present invention may be one used as an image output terminal of an information processing equipment such as a computer, a copying machine as a combination with a reader, or the like, a facsimile apparatus having a transmission/reception function, and the like.

Claims: A recording apparatus for recording pixels having graduated tonal densities by causing an ink jet recording head having an array of a plurality of orifices, linearly disposed along an array direction, to discharge a plurality of ink droplets thereby performing recording, comprising means (11, 11A; 10, 10A) for bringing about relative movement of the recording medium and the recording head in a direction parallel to said array direction, and control means (100) for driving the recording head (1) based on a recording signal, characterised in that said control means is adapted to drive each said orifice in a group of said orifices to discharge a droplet of said ink only at a first predetermined timing and through a first orifice and to cause said second orifice to discharge a droplet of said ink only at a second predetermined timing and so forth for each successive orifice of the group, said group being used for forming the pixel; and to control the time interval between the discharge of ink through said first orifice and the discharge of ink through said second orifice, said time interval being such that droplets discharged by said first orifice at said first timing and from said second orifice at said second timing and so forth for each successive orifice of the group are deposited in overlapping relation on the recording medium, and such that the following droplet arrives at the recording medium prior to the preceding droplet having soaked into the recording medium or having dried, whereby the droplets are combined on said recording medium, so that a recording of graduated tonal density can be obtained. An apparatus as claimed in claim 1, characterised in that said group of orifices used for forming the pixel have a first orifice and a second orifice, and said drive means drives said recording head to cause said first orifice to discharge an ink at a first timing and to cause said second orifice to discharge an ink at a second timing. An apparatus as claimed in claim 1, characterised in that said group of orifices used for forming the pixel are adjacent ones, and said drive means drives said recording head to sequentially cause said adjacent orifices to discharge an ink. An apparatus as claimed in any one of claims 1, 2 or 3, characterised in that said moving means performs relative movement by rotating a rotary member (2) around which said recording medium is wound. An apparatus as claimed in any one of claims 1-3, characterised in that said moving means performs relative movement by scanning a carriage on which said recording head is mounted. An apparatus as claimed in any one of claims 1-3, characterised in that said drive means drives an orifice adjacent the first orifice as the second orifice. An apparatus as claimed in any one of claims 1-3, characterised in that said drive means drives an orifice separated from the first orifice by a predetermined number of orifices as the second orifice. An apparatus as claimed in any previous claim, characterised in that said ink droplets are of at least two colours. An apparatus as claimed in any previous claim, including a recording head, characterised in that said recording head comprising energy generation means, arranged in correspondence with said orifices, for applying heat energy to an ink to cause a change in state, and causing said orifices to discharge the ink on the basis of the change in state, thereby forming flying liquid droplets. An apparatus as claimed in claim 9, characterised in that the change in state is growth of bubbles caused by film boiling. An apparatus as claimed in any previous claim, further comprising supply means for supplying the recording signal to said drive means for driving said recording head. An apparatus as claimed in claim 11, characterised in that said supply means is a host computer. An apparatus as claimed in claim 11, characterised in that said supply means is a scanner having reading means. An apparatus as claimed in claim 11, characterised in that said supply means is a facsimile receiver. An apparatus as claimed in claim 1, characterised in that said drive means drives adjacent orifices as the group of orifices. An apparatus as claimed in claim 1, characterised in that said drive means sets the number of orifices to be driven of the group of orifices in accordance with density data of the recording signal corresponding to the pixel to be formed. An apparatus as claimed in claim 1, characterised in that the density of said array is equal to the density of a plurality of pixels formed on said recording medium. A recording method for recording graduated tonal densities by performing recording on a recording medium using an ink jet recording head which discharges ink from an array of a plurality of orifices, said orifices being linearly disposed along an array direction, characterised by causing a first said orifice of said recording head to discharge a droplet of ink onto a predetermined position of said recording medium; moving a second said orifice of said recording head into registry with the predetermined position of said recording medium; and causing said second orifice to discharge an ink droplet onto the predetermined position of said recording medium such that droplets discharged from said first and second orifices are deposited in overlapping relation on the recording medium, and such that the following droplet arrives at the recording medium prior to the preceding droplet having soaked into the recording medium or having dried, whereby the droplets are combined on said recording medium, so that a recording of graduated tonal density can be obtained. A method as claimed in claim 18, characterised in that the relative movement is performed in an array direction of said plurality of orifices of said recording head. A method as claimed in claim 18, characterised in that the relative movement is performed by rotating a rotary member around which said recording medium is wound. A method as claimed in claim 18, characterised in that the relative movement is performed by scanning a carriage on which said recording head is mounted. A method as claimed in claim 18, characterised in that the first orifice is adjacent to the second orifice. A method as claimed in claim 18, characterised in that the first and second orifices are separated by a predetermined number of orifices. A method as claimed in claim 18, characterised in that heat energy is applied to the ink by energy generation means to cause a change in state, whereby said orifices discharge the ink on the basis of the change in state, thereby forming flying liquid droplets. A method as claimed in claim 24, characterised in that the change in state is growth of bubbles caused by film boiling.

Inventors: OKAZAKI TAKESHI C O CANON KABU, SHIOYA MAKOTO C O CANON KABUSH, OKAZAKI,TAKESHI, C/O CANON KABUSHIKI KAISHA, SHIOYA, MAKOTO, C/O CANON KABUSHIKI KAISHA
Applicants: CANON KK, CANON KABUSHIKI KAISHA
Application year: 1991
Main classification: B41J2
IPC codes: B41J2