DE69117810T2 - Ink jet recording method and related ink jet recording apparatus - Google Patents

Abstract

An ink jet recording apparatus for an ink jet recording apparatus includes a plurality of electrothermal transducer element for producing thermal energies for formation of recording liquids; and driving device for supplying electric energy to the electrothermal transducer elements in accordance with data to be recorded and a control signal, wherein the plural electrothermal transducers are grouped into plural groups, and the groups are simultaneously driven by the driving device, wherein the electrothermal transducer elements in a group are supplied with electric power in a period between maximum expansion of a bubble in a previously driven group and expiration thereof. <IMAGE>

Description

FIELD OF THE INVENTION AND RELATED ART

The present invention relates to an ink jet recording apparatus that can be used with an information processing apparatus such as an output terminal, or an ink jet recording apparatus that serves as a printer formed as a unit with an information processing apparatus, and particularly to an ink jet recording apparatus that can be used with a personal computer, word processor, copying machine, facsimile machine or the like. More particularly, the present invention relates to an ink jet recording apparatus that uses an electrothermal transducer for generating heat energy that contributes to ejecting ink in accordance with image information.

An ink jet recording apparatus in which a liquid droplet is ejected by generating a bubble corresponding to an instantaneous state change of the liquid by the heat energy generated by an electrothermal transducer is disclosed in US-A-4,723,129. The US patent discloses a simultaneous control system in which a plurality of electrothermal transducers are simultaneously driven and a non-simultaneous control system in which the plurality of electrothermal transducers are sequentially driven with a phase difference to perform recording in an inclined manner. A similar disclosure has been made in JP-A-109 672/1980. The US patent also discloses what is called a time-sharing control system for a large number of electrothermal transducers.

However, in a recording device using thermal energy that is used in practice, the above The simultaneous control system described has been considered to be the most advantageous since it has the advantage of enabling high speed recording.

Therefore, in most proposals in connection with the inkjet recording system, a prerequisite is that the control signals are supplied to the electrothermal transducers in accordance with recording signals at the same time or simultaneously.

JP-A-109 672/1980 discloses a liquid jet recording method in which a phase difference is provided between ejections from adjacent orifices.

This arrangement has an advantage that the drive current is reduced, and therefore the voltage drop due to the terminal resistance is reduced. However, this method has a problem in that although the recovery of the meniscus after ink ejection is fast when a small number of orifices are driven, the recovery is significantly delayed when a large number of orifices are driven. For example, the meniscus recovery frequency is reduced from 9 kHz during a small number drive to 5 kHz when a large number of orifices are driven. Therefore, the lower frequency is set as the drive frequency of the device.

One of the significant problems is that the drive frequency of the entire device is limited by the meniscus recovery frequency when driving a large number of apertures because high-speed recording is generally desired in the field of printers.

The invention is based on the object of creating an ink jet recording method and apparatus in which the liquid droplet generation frequency is increased compared to the prior art.

Another object of the invention is to provide an ink jet recording method and apparatus in which, in addition to the increase in frequency, the accuracy of the positions of the ejected recording liquid droplets is improved.

It has been considered that the decrease in the refill frequency when a large number of transducers are driven occurs due to a thermal problem, i.e. the refill time becomes longer due to the increase in the meniscus retraction due to the increase in the amount of ejected ink due to the decrease in the viscosity of the ink due to the increase in the ink temperature near the motor.

However, from various investigations and observations it has been found that the frequency can be increased significantly by suitably selecting a time difference between switching on adjacent or nearby openings.

According to the invention there is provided an ink jet recording method for an ink jet recording apparatus having a plurality of electrothermal transducer elements for generating heat energy for ejecting ink and a control device for supplying electric energy to the electrothermal transducer elements in accordance with data to be recorded and a control signal, the electrothermal transducers being grouped into a plurality of groups and the elements of each group being controlled simultaneously by the control device, characterized by supplying electric current to the electrothermal transducer elements in a group during the interval between a maximum expansion of a bubble in a previously controlled group and its decay.

According to the invention, an ink jet recording device for an ink jet recording apparatus is provided with a plurality of electrothermal transducer elements for generating heat energy for ejecting recording liquid and a control device for supplying electrical energy to the electrothermal transducer elements in accordance with data to be recorded and a control signal, the electrothermal transducers being grouped into a plurality of groups and the elements of each group being controlled simultaneously by the control device, characterized in that the control device is constructed such that the electrothermal transducer elements in a group are supplied with electrical current in a period between a maximum expansion of a bubble in a previously controlled group and its decay

According to the present invention, the printing frequency is increased and the deviation of the ink shot positions is improved, thus improving the printing quality.

The attached drawing shows:

Fig. 1 is a diagram showing a relationship between response frequency and a time difference between control pulses,

Fig. 2A and 2B show an example of a control timing curve according to an embodiment,

Fig. 3 is a block diagram of a control system used in a device according to an embodiment,

Fig. 4 shows a control time curve through the circuit according to Fig. 3,

Fig. 5 is a diagram illustrating advantageous effects of the liquid flow arrangement usable with the present invention,

Fig. 6A is a sectional view of a recording head according to another embodiment illustrating the subscriber or time-sharing control,

Fig. 6B is a sectional view showing a liquid passage communicating with a common liquid chamber;

Fig. 7 shows a control signal time curve according to another example and

Fig. 8 is a sectional view of a recording head usable with the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The embodiments are described below with reference to the drawing.

Fig. 8 is a perspective view of an ink jet recording head to which the present invention can be applied. Reference numeral 11 denotes a heating section (heating element) of an electrothermal transducer which generates heat energy contributing to the ejection of the recording liquid (ink) by generating a bubble when the electrothermal transducer is supplied with electric power. The heater 11 is formed on a substrate 11 by a method similar to the semiconductor manufacturing method. The recording head also has ejection openings (orifices) 13 through which the recording liquid is ejected, ink passages (nozzles) 14 communicating with the corresponding ejection openings 13, and an ink passage forming member 15 for forming the ejection openings and the ink passages 14.

The recording head further includes a head plate 16 and a common liquid chamber 17 which is commonly communicated with the ink passages 14 and serves to store the ink supplied from an ink supply source not shown.

Fig. 3 is a block diagram showing an example of a control system for the ink jet recording head having a structure as shown in Fig. 8. The control system comprises a recording head control circuit 21, a recording head power source 22, a timing generator circuit 23, a recording data dividing circuit 24, and a recording data control timing generator circuit 25. The timing generator circuit 23 is responsive to the data to be recorded and control signals C1 and C2 from the control timing generator circuit 25 to generate a pulse width setting signal ENB and selection signals SEL1, SEL2, SEL3, and SEL4 for selecting the latch positions of the inputted recording data, selecting the electrothermal transducer elements to be driven, and generating a latch signal LAT2. The recording data dividing circuit 24 extracts and reconstructs the recording data for one line for supply to a recording head controller IC26.

Fig. 4 shows the control timing according to this embodiment. The recording data SI1 for one line constituted by the same number of bits as the number of electrothermal transducers is again introduced into recording data SI2 corresponding to the electrothermal transducer elements simultaneously driven by the recording data dividing circuit and transferred to the recording head. Thereafter, the data is read in the latch circuit in the control device IC which is selected by the selection signals SEL1 to SEL4 in accordance with the input of the latch signal LAT2. Then, the electrothermal transducers selected by the input of the ENB signal are supplied with the electric power. The data transfer, the application of the selection signals and the application of the pulse width setting signal are repeated for a predetermined number of times to carry out the printing of one line.

Fig. 2 illustrates the order of nozzle control according to this embodiment. The ink jet recording head 41 ejects the recording droplet 42. The nozzles of the ink jet recording head are grouped into four groups. Therefore, as shown in the figure, the electrothermal transducers in each of the groups are driven in the order of No. 1, No. 2, No. 3 and No. 4 with a time difference Td.

Fig. 1 shows the relationship between the control pulse time difference Td of the electrothermal transducers in a group and average response frequencies of the nozzles (measured on the basis of all discharges). As can be seen from the figure, the response frequency is substantially maximum within a range between a maximum bubble expansion and its collapse and decay. Therefore, at the time of the maximum size of the bubble, the next electrothermal transducer is preferably supplied with the electric power, thereby improving the response frequency of the nozzles.

As can be seen from Fig. 1, the timing of the maximum expansion of the bubble and the timing of the collapse of the bubble are different if the drive pulse width is different (3 µs and 7 µs). Therefore, in consideration of the generation of the bubble, the meniscus oscillates inversely after the decay of the bubble in the sequential drive. The inversion affects an adjacent nozzle or nozzles. Therefore, if the next drive is started during the period in which the ink flow in the previously driven flow is in one direction, the response frequency is increased and the ejection is stabilized because the instability factor is significantly reduced.

Another preferable condition is considered below. Even in the preferable range described above, the response frequency decreases if the time difference Td becomes longer. Moreover, the positions of the shots of the recording liquid droplets deviate slightly, and therefore the print quality is slightly deteriorated. The investigations using a recording head with 64 nozzles capable of printing at 360 dots/inch or dpi, in which the nozzles are arranged in four groups of 16 nozzles each and printing is carried out at 6.5 kHz with a pulse width of 3 µs, have shown that a part of the shot positions deviate slightly if the time difference Td exceeds 20 µs. If the time difference Td exceeds 25 µs, the deviation is conspicuous.

Therefore, another preferred condition is that the time difference is not more than 20 µs. The upper limit is the maximum bubble expansion point in the previous control.

Further detailed studies of the ejected liquids have shown that in the course of a column-shaped ejection of the liquid through the ejection opening, the liquid inevitably wets the area around the ejection opening due to bubble generation. However, the wetness is less than in a conventional method or apparatus. The wetness is relatively small after 4 µs has elapsed from the maximum expansion of the bubble, and particularly, it is smaller after 10 µs has elapsed thereafter. On the other hand, it is relatively large before 4 µs has elapsed from the maximum expansion of the bubble. It is assumed that if the heater is energized before about 4 µs has elapsed from the maximum bubble expansion by the previously energized heater, the wetting remains around the previously energized ejection port, and the wetting slightly affects the ejection direction of the next ejection. This has been observed for a portion of the ejection ports.

From the above, it is clear that in order to obtain the high frequency even when a large number of nozzles are switched on, the power supply must be switched on in a period from the maximum expansion and the collapse or decay of the bubble created by the previous injection. In addition, injection is preferably started after 4 µs have elapsed from the maximum expansion, or preferably after 10 µs have elapsed thereafter.

Instead of the control system according to Fig. 4, the electrothermal transducers are supplied with control pulses in the order of 1, 3, 2 and 4, or according to Fig. 7 they can be controlled in the order of 1, 2, 4 and 3. In these cases, the response frequency can be improved by starting the application of supply pulses in the period between the maximum bubble expansion and the collapse of the bubble.

As described above, the plurality of electrothermal transducer elements are grouped into n groups in each of which the electrothermal transducers are driven simultaneously, and the groups are driven sequentially with a time difference. The electrothermal transducers in a certain group are driven simultaneously in a period from the maximum expansion of the bubbles in the previously driven group to the collapse or decay of their bubbles.

Due to this feature, the following beneficial effects are achieved:

(1) The frequency at which the recording liquid droplets can be ejected when the nozzles are simultaneously driven so that the recording speed can be increased.

(2) The possible adverse influence on the shot position accuracy due to the significant wetting of the ejection openings of the adjacent nozzles can be prevented, so that the printing quality is improved.

The further preferred conditions are described with reference to Figs. 5 to 7.

Referring to Figs. 6A, 6B and 7, the main part of the embodiment will be described. The ink jet recording head 42 ejects the ink droplet along a path 42. In the figure, the nozzles of the ink jet recording head are grouped into four groups. In Fig. 7, the electrothermal transducers for the flows are sequentially driven by the control pulses with the time difference Td in the order of No. 1, No. 3, No. 2 and No. 4. The reference numerals in parentheses in Fig. 7 indicate the order of driving each of the groups of electrothermal transducer elements. In this embodiment, the first electrothermal transducer is driven and then the second electrothermal transducer is driven (time difference Td between adjacent pulses). With the same timing, the fourth electrothermal transducer is driven and the third electrothermal transducer is driven. Therefore, adjacent electrothermal transducers are not driven simultaneously within the groups and between adjacent groups.

Fig. 6B is a sectional view of an ink flow of an ink jet recording head, showing the planar heater 11 in which the discharge opening is smaller than the liquid flow in cross-sectional area. According to the figure, the area of the heater is, for example, 3790.5 µm² (133 x 28.5 µm). A distance La from a downstream end of the heater to the opening with respect to the direction of discharge flow of the ink is 120 µm. The recording head is of a type in which the direction of discharge of the ink is substantially parallel to the heating surface. However, when they are not parallel, according to the invention, the distance La is defined as the minimum distance between the discharge opening 13 and the heater 11. As can be seen, the definition applies to both types. It has been found that a distance from an upstream end of the heating element to an upstream end of the ink flow (supply port 13A) Lb with respect to the direction of flow of the ejection ink the frequency of recording droplet formation and therefore the printing speed is significantly influenced.

The distance Lb is the minimum distance between the feed opening 13A and the heating element 11.

The distance Lb will be described with reference to Fig. 5. Fig. 5 is a diagram showing a relationship between a meniscus recovery frequency fr (filling frequency) and the distance Lb when all the nozzles are switched on or driven simultaneously. The solid curve in this diagram represents the frequency fr when the heating elements according to Fig. 6 are driven sequentially or one after the other in the order of their arrangement with a pause period Td of 13 µs in the subscriber or time-sharing drive. The dashed curve in the diagram represents the frequency fr when the time difference Td is 0, i.e. the heating elements are not driven in the subscriber or time-sharing drive.

From this figure it can be seen that the frequency fr increases with a decrease in the distance Lb, and in particular that the frequency fr increases abruptly in the range Lb ≤ 110 µm. Furthermore, the frequency fr can be increased significantly by using the time difference Td = 13 µs compared to the simultaneous or concurrent control. This is due to the interference between the nozzles. The rate of increase by using the subscriber control is larger if the distance Lb is shorter, i.e. the influence of the interference is stronger.

In the curve A, a point Al represents 6.3 kHz at 70 µm, A2 5 kHz at 90 µm and A3 4.35 kHz at 110 µm. The tendency is similar in the case of the control order shown in Figs. 7A and 2.

From the above, it can be seen that in the ink jet recording head controlled in the subscriber mode for the adjacent nozzles, the frequency fr increases and that the Frequency increases significantly by satisfying the condition Lb &le; 110 µm, so that the recording speed is significantly improved.

In addition, the distance Lb is preferably not greater than 70 µm, since then the frequency is greater than the frequency in the case of simultaneous control. In this case, the distance La is preferably 120 µm.

The distance La is described below. It has been found that there is an optimal distance La. If the distance La is significantly smaller than 130 µm, the following problems arise:

(1) When the meniscus retreats after ejection of the recording liquid, the bubble which is about to collapse contacts the meniscus with the result that air is introduced into the nozzle, resulting in failure of the liquid ejection, and this occurs in a period of time of 25 to 35 µs from the application of the ejection pulse.

(2) When the size of the bubble reaches its maximum, the leading edge of the bubble passes through the orifice with the result of the introduction of external gases into the nozzle, leading to ejection failure, and this occurs in a time period of 5 to 15 µs from the application of the energy of the ejection pulse.

The phenomena described above occur in the range of La < 90 JLM, therefore the distance La is preferably not less than 110 µm.

If the distance La is significantly larger than 130 µm, the following problems arise:

(1) The impedance to the flow of the recording liquid in the ejection direction from the center of the heater is increased, resulting in a reduced ejection speed of the recording liquid, which leads to a deterioration in the accuracy of the position of the liquid shot on the recording medium and therefore to the deterioration of the quality of the recorded image, and

(2) the above-mentioned increase in impedance leads to a reduced amount of ejected recording liquid, resulting in a lower image density of the print on the recording medium and therefore the deterioration of the image quality.

The phenomena occur in the range of La > 130 µm, which is why the distance La is preferably not more than 130 µm.

Regarding the relationship between the distances La and Lb, the distance La is preferably larger than the distance Lb, since then the amounts of liquid ejected are uniform.

In addition, all of the above-described conditions La > Lb, 90 ≤ La ≤ 130 (µm) and Lb " 110 (µm) are preferably met, since then all of the above-described advantageous effects are achieved.

The advantageous effects of the present invention are achieved even if the sequentially driven electrothermal transducers are not adjacent but are arranged close to each other (nozzles 1 and 3, 2 and 4 in Figs. 7A and 7C, nozzles 2 and 4 in Figs. 8A and 8C). The advantageous effects are particularly remarkable when the distance between the centers of the heating sections of the simultaneously driven electrothermal transducers is not more than 100 µm, and especially when it is not more than 80 µm.

The advantage of the present invention increases with an increase in the number of groups of liquid flows and therefore electrothermal transducers. In particular, when the number of groups is not less than 48, the difference between the simultaneous driving and the driving of the present invention is remarkable. In addition, the present invention is particularly advantageous when the ejection openings are arranged in high density. From the perspective of stabilizing the ejection performance, the heating surface of the heating element is preferably not more than 4190 µm² and not less than 3390 µm².

The apparatus which can operate continuously for a very long period in a stabilized manner will be described below. If the distance Lb is very small, the vibration of the meniscus resulting from the recovery of the meniscus increases toward the opening after the ejection of the recording liquid, whereby the opening is wetted with the liquid in some cases after a long recording operation. If this occurs, the straightness of the recording liquid is deteriorated by the wetting with the result that the accuracy of the positions of the shot deposition on the recording material is slightly deteriorated. In order to stabilize the ejection of the recording liquid by avoiding the above, it has been found that Lb ≥ 40 µm is preferable. Moreover, it is preferable that the structure of the flow is the same as that shown in Fig. 1 from the inlet port to the heating element.

In the nozzle having a flow resistance element upstream of the heater element for reducing the ink flow area for the purpose of flowing the ink upstream, the printing quality is guaranteed over a region with a smaller distance Lb compared with the nozzle shown in Fig. 1B by the increase in impedance by the flow resistance element. In particular, if Lb > 30 µm, good printing is ensured for a long period of time at a high printing speed.

The control pulse of the control signal according to this embodiment preferably has the form described in US-A-4 463 359 and US-A-4 345 262. In addition, the conditions concerning the temperature increase of the heating surface disclosed in US-A-4 313 124 are preferably used.

The advantageous effects of the present invention are significant when the present invention is applied to a full-line recording head. The full-line recording head may be of a type of plural recording heads covering the entire length of the maximum recording line as a whole and of a type in which one recording head covers the entire line.

The present invention can be applied to the recording head with a replaceable circuit in which, when the circuit or chip is inserted, it is electrically connected to the apparatus and can be supplied with the recording liquid from the main apparatus, or to a cartridge type recording head with an ink supply source.

The present invention can be particularly advantageously used in an ink jet recording apparatus or head in which the print data for the plurality of electrothermal transducer elements is divided and transmitted for each plurality of bits and the adjacent electrothermal transducers are sequentially driven with a time difference.

As described above, the usable recording frequency can be increased, and therefore the recording speed can be increased.

Claims (11)

1. Ink jet recording method for an ink jet recording apparatus having a plurality of electrothermal transducer elements for generating heat energy for ejecting ink and a control device for supplying electrical energy to the electrothermal transducer elements in accordance with data to be recorded and a control signal, the electrothermal transducers being grouped into a plurality of groups and the elements of each group being controlled simultaneously by the control device, characterized by supplying electrical current to the electrothermal transducer elements in a group during the interval between a maximum expansion of a bubble (42) in a previously controlled group and its decay. 2. Method according to claim 1, characterized in that the feeding of a later fed element occurs before the end of the collapse of the bubble generated by an earlier fed element. 3. Inkjet recording device with a plurality of electrothermal transducer elements (7) for generating thermal energy for ejecting recording liquid and a control device (4, 5, 22, 23, 24, 25) for supplying electrical energy to the electrothermal transducer elements (7, 11) in accordance with data to be recorded and a control signal, wherein the electrothermal transducers are grouped into a plurality of groups and the elements of each group are controlled simultaneously by the control device, characterized in that the control device is constructed in such a way that the electrothermal converter elements (7, 11) in a group are supplied with electrical current in a period between a maximum expansion of a bubble in a previously controlled group and its decay. 4. Device according to claim 3, characterized in that the control device is constructed in such a way that the feeding of a later element occurs before the collapse of the bubble generated by an earlier element. 5. Device according to claim 3 or 4, characterized in that a time difference between the electrical supply for one group and that for a next group is less than 25 microseconds. 6. Device according to claim 3 or 4, characterized in that a time difference between the electrical supply for one group and that for a next group is 20 microseconds or less. 7. Device according to claim 3, characterized in that the electrical current is supplied approximately four microseconds after the maximum expansion. 8. Device according to claim 3, characterized in that the electrical current is supplied approximately ten microseconds after the maximum expansion. 9. Device according to one of claims 3 to 8, characterized in that the electrothermal converters (11) are each housed within nozzles (13). 10. Method according to claim 1 or 2, characterized in that the transducer elements are grouped in such a way that no adjacent pair of transducer elements is controlled simultaneously. 11. Device according to one of claims 3 to 9, characterized in that the transducer elements are grouped in such a way that no adjacent pair of transducer elements is controlled simultaneously.