Ink jet recording head and recording apparatus using said recording head

Abstract: An ink jet recording apparatus comprises a plurality of ink discharge portions having discharge ports (4) for discharging ink, ink channels (5) communicating to said discharge ports (4), and electricity-heat converters (3) for applying the heat energy to the ink within said ink channels (5), means for dividing said plurality of electricity-heat converters into plural groups and supplying a signal generating said heat energy to electricity-heat converters (3) for each group, and conveying means for conveying a recording medium to be recorded with the ink discharged from said discharge ports (4), wherein the shapes of said ink discharge ports (4) are changed between groups.

Description: The present invention relates to an ink jet recording apparatus, and more particularly to an ink jet recording apparatus for recording onto a recording medium by discharging the ink through discharge ports onto the recording medium by use of the heat energy generated with the block driving of a plurality of electricity-heat converters. Among various recording methods currently known, the so-called ink jet recording method, which is a non-impact recording method that generates almost no noises during recording and permits the printing at high speed onto plain paper without requiring special fixing processing, has been appreciated as a quite effective recording method. The ink jet recording method is one in which the recording is performed by discharging fine droplets of recording liquid called as ink to apply them onto a recording medium such as a paper. The ink jet recording method is such a method that in recording, electricity-heat converters provided on ink channels (thereafter referred to as nozzles) communicating to fine discharge ports for discharging the ink are energized and heated, thereby heating the ink around heat generating portions (thereafter referred to as heaters) of the electricity-heat converters, and the ink is discharged through the discharge ports by use of the pressure caused by abrupt changes of volumes produced at the bubbling. One of the driving methods for the ink jet recording apparatus is a so-called division driving method in which heaters are divided into n groups each for plural bits of a driving signal, which are driven in sequence. The reason is that a current of 250mA is required to drive one heater normally. Therefore, for example, when 64 nozzles are concurrently driven, a current of 16A will be required, so that a large power supply is needed, or bold wirings are required to flow large current. On the contrary, for example, if energization is made each for 16 nozzles in four times, the current required concurrently will be largely reduced up to 4A. Moreover, if energization is made each for eight nozzles in eight times, it can be reduced to 2A. However, if recording with such a driving method, there is a problem for resolving that positions of liquid droplets impinging on a recording medium are different between groups, so that the quality of image may be degraded. The present inventor has found that such impact position shifts between groups are caused by the following two factors, as a result of having observed minutely this phenomenon of impact position shifts. The first factor is necessarily caused by the division driving method. That is, it is caused by differences between energization timing for groups, and the relative movement between recording medium and recording head. The second factor is due to the fact that when a plurality of nozzles are driven in division for discharging substantially at the same time within each group, and at fixed intervals between groups, the discharging speed for the first group being driven first is faster than those for the second group and the following groups which are sequentially driven. Next, a specific example of the first factor in recording with a recording head and a recording apparatus to which the above-described conventional division driving is applied will be described. When the head having 64 nozzles are driven at 360 DPI, 6.3 kHz, a pulse width of 3 µs, four division driving pause time of 0.5 µs (see Fig. 7), and a clearance between head and recording medium is 1.2 mm, the impact position shift owing to differences between energization timing for groups which is the first factor as above described is, Wt = (3(µs) + 0.5(µs)) x (4-1)1(1/6300) x 10 6 = 0.07 (see Fig. 8) That is, a shift of 0.07 dots occurs on recording medium. The impact position shift Ws owing to differences between discharging speeds for groups, which is the second factor as above described, is shown in Table 1 as given below from experiments of the present inventors. Group Average discharge speed (m/s) Reaching time to recording medium (µs) Shift from dot in first group (dots) 1 12 100 --- 2 9 133 0.23 3 8 150 0.36 4 8 150 0.38 (See Fig. 9) As above described, the impact position shift due to differences between energization timing for groups is small, such as 0.07 dots, and in almost inconspicuous area, but the impact position shift due to differences between discharging speeds for groups may correspond to a maximum of 0.38 dots, having bad effects on the quality of print. US-A-4 463 359 discloses an ink jet printing apparatus having ink emission heads in staggered block arrangement for improving alignment density and time-division drive circuitry. An object of the present invention is to resolve such conventional technical problems, and to provide an ink jet recording head and a recording apparatus using the head, in which impact position shifts are eliminated. According to the invention there is provided an ink jet recording head driven by issuing a division driving signal comprising a plurality of ink discharge portions having discharge ports for discharging ink, ink channels communicating with said discharge ports, electricity-heat converters for applying heat energy to ink within said ink channels; and plural groups of electricity-heat converters adapted to receive signals to cause said electricity-heat converters to generate said heat energy, characterised in that said ink discharge portions related to one group of electricity-heat converters have the same shape and said ink discharge portions related to a different group of electricity-heat converters have a different shape, each group of electricity-heat converters being adapted to be simultaneously driven. In the accompanying drawings:- Figs. 1A to 6 show examples of an ink jet recording head, for use with an ink jet recording apparatus, of the present invention. Fig. 1A is a typical external perspective view. Fig. 1B is a typical view showing a cross-section taken along the line A-A of Fig. 1A. Fig. 2A is a typical external perspective view. Fig. 2B is a typical view showing a cross-section taken along the line A-A of Fig. 2A. Fig. 3 is a typical external perspective view. Figs. 4 to 6 are typical views showing cross-sections, respectively. Fig. 7 is a view for explaining the time division driving method. Fig. 8 is a view for explaining impact point shift due to differences between energization timings for groups. Fig. 9 is a view for explaining impact point shift due to differences between discharging speeds for groups. Fig. 10 is a perspective view showing schematically the external constitution of an ink jet recording apparatus in which the division driving is performed with a recording head of the present invention mounted. In the following, an example of the present invention will be described in detail with reference to the drawings. In Figs. 1A to 6, 7 is a recording head, 1 is a substrate, 2 are ink channels (nozzles), 5 is a common,liquid chamber for each nozzle, 6 is a partition wall, 8 is a ceiling plate, and 3 are electricity-heat converters (heat generating elements) for generating the heat energy to be used in discharging the ink through discharge ports 4. An ink discharge portion in the present invention includes discharge ports, and ink channels and electricity-heat converters. If the voltage is applied, the heat generating element 3 is rapidly heated, so that the ink in the vicinity of the heat generating element is instantaneously vaporized and bubbles are grown. By this growth of bubbles, the pressure within the nozzle is increased, so that the balance between the meniscus of the ink and the external pressure is broken at the face of discharge port 4, and the ink is discharged through the discharge port. At this time, there is already no current flowing through the heat generating element, a heat generating portion of the heat generating element is cooled by the heat transfer with the substrate 1 and the ink, and the temperature on its surface is decreasing. Then, along with the shrinkage of air the bubbles, the ink will flow backward from the face of the discharge port to the inside of nozzle, and further with new supply of ink, the ink will make contact on the surface of the heat generating portion of the heat generating element while the air bubbles shrink. As the external pressure is placed at a higher level than that of the nozzle internal pressure on the face of the discharge port, the meniscus is large enough to enter the inside of the nozzle. With the capillary action, air bubbles are extinguished by the ink resupplied. With consecutive repetition of such a mechanism, the ink is discharged, in which the heat generating elements for each group are driven in division from the first group sequentially. Since the discharging speed of ink is affected by the pressure vibration or temperature propagating between adjacent nozzles, and further subjected to fluidal interference of ink from a liquid chamber to nozzles, the discharging speed is changed in the sequence of bubblings with the division driving. Owing to such causes, the discharging speed from the nozzles in the first group becomes faster. Next, an example as shown in Figs. 1A and 1B will be described. Using a conventional recording head in which a total of 64 nozzles are divided into four groups each of 16 nozzles, each one of common lines is commonly used with four nozzles from the first to fourth groups, and the time division driving (see Fig. 1) is used in four divisions with a driving pulse input for four nozzles being shifted by the amount of pulse width (3 µs) + division driving pause time (0.5 µs), when recording liquid droplets are discharged from all nozzles, it has been found that the discharging speeds are different between groups, as previously described. That is, its average speed is 12 m/s for the first group, 9 m/s for the second group, and 8 m/s for the third and fourth groups, as shown in Table 1. As a result, the difference between speeds for the first group which is fastest and for the third group which is slowest is 4 m/s, and the impact position has a shift Ws of 0.38 dots at maximum as shown in Fig. 9. Thus, in this example, the distances between discharge port 4 and heat generating element 3 was set to be 120 µm for the first group (as conventionally), 107 µm for the second group, 103 µm for the third group, and 100 µm for the fourth group, as shown in Figs. 1A and 1B, in view of differences between discharging speeds. In this case, the average discharging speeds for group were 12 m/s for the first group, 12.4 m/s for the second group, 12.9 m/s for the third group, and 13.4 m/s for the fourth group, respectively, when recording liquid droplets were discharged from the whole nozzles, whereby the difference between maximum speed for groups could be reduced to 1.4 m/s, and the impact position shift on recording medium was not found in practice. An example as shown in Figs. 2A and 2B, with a constitution in which the areas of discharge ports 4 are made smaller from the first group sequentially (or larger from the fourth group sequentially), can compensate for differences between discharging speeds for groups in the same way as for the example shown in Figs. 1A and 1B, and thus eliminate the impact position shift on the recording medium. It should be noted that in this example, the discharging speed is increased by reducing the area of the discharge port, which can be determined by taking into consideration the differences between discharging speeds of groups. In the example as shown in Figs. 2A and 2B, the areas of the discharge ports are adjusted in a direction of discharge port array, whereas in an example as shown in Fig. 3, the areas of the discharge ports are adjusted by changing the lengths in a direction perpendicular to the substrate 1 between groups. Also, this example, with a constitution that the central heights of the nozzles are lowered sequentially from the first group (or raised sequentially from the fourth group), can compensate for differences between discharging speeds of groups and eliminate the impact position shift on the recording medium in the same way as for the example as shown in Figs. 1A and 1B. An example as shown in Fig. 4, with a constitution that the areas of the heat generating elements 3 are increased sequentially from the first group sequentially, can compensate for differences between discharge speeds of groups and eliminate the impact position shift on the recording medium, in the same way as for,the example as shown in Figs. 1A and 1B. It is also feasible by decreasing the resistances of the heat generating elements 3 sequentially from the first group with varied ratios between areas or lengths. An example as shown in Fig. 5, with a constitution that the widths of nozzles 2 are decreased sequentially from the first group, can compensate for differences between discharging speeds of groups and eliminate the impact position shift on the recording medium, in the same way as for the example as shown in Figs. 1A and 1B. An example as shown in Fig. 6, with a constitution that the lengths of the nozzles 2 are increased sequentially from the first group, can compensate for differences between discharging speeds of groups and eliminate the impact position shift on recording medium, in the same way as for the example as shown in Figs. 1A and 1B. It will be recognized that each example of compensation of the discharging speed of ink can be fulfilled singly or in combination with other methods. Fig. 10 is a perspective view showing schematically the external constitution of an ink jet recording apparatus in which the division driving is performed with a recording head of the present invention mounted. In Fig. 10, 1 is an ink jet recording head (thereafter referred to as a recording head) for recording a desired image by discharging the ink based on a predetermined recording signal, and 2 is a carriage which moves for scanning in a direction of recording line (main scan direction), while mounting the recording head 1 thereon. The carriage 2 is slidably supported by guide shafts 3, 4 and reciprocates in a main scan direction by engagement with a timing belt 8. The timing belt 8 in engagement with pulleys 6, 7 is driven via a pulley 7 by a carriage motor 5. A recording paper 9 is guided by a paper platen 10 and conveyed by conveying means such as a paper feed roller, not shown, pressed by a pinch roller. This conveyance is performed by a paper feed motor 16 as a driving source. As the recording paper 9 being conveyed is tensioned by a paper exhausting roller 13 and a spur 14 and pressed against a heater 11 by a paper presser plate 12 formed of an elastic member, it is conveyed in close contact with the heater 11. The recording paper 9 on which the ink jetted by the head 1 is deposited is warmed by the heater 11, and deposited ink is fixed on the recording paper with it solvent evaporated. It should be noted that the fixing on heating with the heater 11 is not necessary, but may be provided on a recording apparatus as appropriate in accordance with the characteristics of ink. 15 is a unit referred to as a recovery system for maintaining the discharge characteristics in normal condition by removing foreign matters adhering to the discharge ports (not shown) of the recording head 1 or thickened ink. 18a is a cap constituting a part of the recovery unit 15, for preventing the occurrence of cloggings by capping the discharge ports of ink jet recording head 1. In the inside of the cap 18a is disposed an ink absorber 18. On a recording area side of the recovery unit 15 is provided a cleaning blade 17 for cleaning foreign matters or ink droplets adhering to the face of discharge ports by coming into contact with the face on which the discharge ports of recording head 1 are formed. The present invention brings about excellent effects particularly in a recording head, recording device of ink jet system utilizing heat energy among the ink jet recording systems. 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 preferred. 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 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 wihtin the liquid (ink) can be formed corresponding one by one to the driving signals. By discharging the liquid (ink) though 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 described 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 constitutions 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. Patent 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 Application Laid-Open 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 application Laid-Open No. 59-138461 which discloses the constitution having the opening for absorbing pressure wave of heat energy correspondent to the discharging portion. Further, as the recording head of the full line type having a length corresponding to the maximum width of recording medium which can be recorded by the recording device, either the constitution which satisfies its length by combination of a plurality of recording heads as disclosed in the above-mentioned specifications or the constitution as one recording head integrally formed may be used, and the present invention can exhibit the effects as described above further effectively. 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 elements 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 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 numbers. Further, the form of ink jet recording apparatus according to the invention, in addition to what is used as image output terminal of a data processing apparatus such as computers, may be those of a copying apparatus combined with readers or facsimile apparatus having transmitting and receiving functions.

Claims: An ink jet recording head comprising a plurality of ink discharge portions having discharge ports (4) for discharging ink, ink channels (2) communicating with said discharge ports (4), electricity-heat converters (3) for applying heat energy to ink within said ink channels on receipt of driving signals; said portions being divided into plural groups of which the electricity-heat converters are adapted to receive driving signals sequentially between groups, each group of electricity-heat converters being adapted to be simultaneously driven; characterised in that said ink discharge portions of one group have the same shape and said ink discharge portions of a different group of electricity-heat converters have a shape different to that of said one group, whereby compensation for differences in the discharging speeds of respective groups of portions can be achieved to eliminate the impact position shift of ink droplets from different groups of portions. An ink jet recording head as claimed in claim 1, characterised in that the shape of said ink discharge portion is such that the distance between said discharge port and said electricity-heat converter is shorter in the group for which said signal is supplied later. An ink jet recording head as claimed in claim 1, characterised in that the shape of said ink discharge portion is such that the area of said discharge port is smaller in the group for which said signal is supplied later. An ink jet recording head as claimed in claim 1, characterised in that the shape of said ink discharge portion is such that the central height of said discharge port is lower in the group for which said signal is supplied later. An ink jet recording head as claimed in claim 1, characterised in that the shape of said ink discharge portion is such that the area of electricity-heat converter is smaller in the group for which said signal is supplied later. An ink jet recording head as claimed in claim 1, characterised in that the shape of said ink discharge portion is such that the resistance of said electricity-heat converter is smaller in the group for which said signal is supplied later. An ink jet recording head as claimed in claim 1, characterised in that the shape of said ink discharge portion is such that the width of said ink channel is smaller in the group for which said signal is supplied later. An ink jet recording head as claimed in claim 1, characterised in that the shape of said ink discharge portion is such that the length of said ink channel is longer in the group for which said signal is supplied later. An ink jet recording apparatus comprising an ink jet head as claimed in any one of claims 1-8 and conveying means (2-8) for conveying a recording medium to be recorded with the ink discharged from said discharge ports. An ink jet recording apparatus as claimed in claim 9, further comprising means for supplying driving signals to said ink jet recording head.

Inventors: MISUMI YOSHINORI, MISUMI, YOSHINORI, Misumi, Yoshinori, c/o Canon Kabushiki Kaisha
Applicants: CANON KK, CANON KABUSHIKI KAISHA
Application year: 1991
Main classification: B41J2
IPC codes: B41J2