Ink jet recording apparatus

The present invention relates to an ink jet recording apparatus used for recording information in the form of visual images and symbolic characters by means of ejecting ink droplets onto a recording medium such as paper sheets and so on.

JP-59 14 967 (A) describes a liquid detector for a recording head of a recording apparatus comprising ejection outlets for ejecting ink droplets, ink liquid passages and converting elements disposed therein. The condition of the liquid in the liquid passages is checked via the changes in the current supplied to the conversion elements.

An ink jet recording apparatus has several advantages. For instance, the level of noises generated by recording operations could be kept as low as their existence could be neglected and common paper sheets can be used without processing their own material and/or coating specific synthetic materials on their surfaces. There exist various kinds of ink jet ejecting methods used in the ink jet recording apparatus and in recent years, some pieces of apparatus based on these methods have been put into practical uses.

Among these kinds of ink jet ejecting methods, one ink jet ejecting method, for instance, as described in Japanese Patent Application Laying-Open No. 51837/1979 has a different feature from that of other kinds of ink jet ejecting methods in that kinetic energy for ejecting ink droplet is obtained by means of transferring thermal energy into ink. In this ink jet ejecting method, a rapid voluminous change occurs in ink in accordance with a state transition of the ink caused by the thermal energy so that an ink droplet is ejected from an ejection outlet formed at the front of a recording head to form a flying ink droplet. The flying droplet reaches the surface of the recording medium and thus information recording can be established.

A recording head using in the above descried ink ejecting methods, in general, has the ink ejection outlet for ejecting ink droplet and an ink liquid passage which runs to the ink ejection outlet and which includes a heat process portion for transferring the thermal energy to ink so as to eject ink droplet from the ink ejection outlet. The heat process portion of the ink liquid passage has an electro-thermal converting element for generating the thermal energy. The electro-thermal converting element has a resistance layer for heating and at least one pair of electrodes connected to the resistance layer. The resistance layer generates heat between said two electrodes by means of applying a voltage between said two electrodes. In this kind of a recording head, in general, forces applied into the ink of the ink liquid passage which are induced by capillary action, pressure drops or the like, are balanced so that a meniscus is formed in the ink liquid passage at the neighbor of the ink ejection outlet. Every time used for ejecting ink droplet is ink in the ink liquid passage, by means of the above mentioned balanced forces applied into ink, ink is supplied continuously into the ink liquid passage and a meniscus is formed again in the ink liquid passage at the neighbor of the ink ejection outlet.

In the recording head with its structure described above, a few disadvantages exist.

The first disadvantages can be stated as follows. In order to make an ink ejection action stable, the pressure of ink contained in the ink liquid passage and other portions of the recording head should be kept in an appropriate value. In order to do so, various kinds of arrangements related to the recording head have been proposed. For example, the recording head and an ink tank for preserving ink which is connected to the recording head through a tube or the like are arranged in such a manner that their relative positions there between in a vertical direction are appropriately determined so that the pressure in the ink liquid passage may be kept in an appropriate value. However, in case that a shock is given to the recording head during transport of the recording apparatus or in case that a pressure fluctuation occurs in the inside of a cap while an ink eject ion-outlet-disposed surface of the recording head is capped with the cap for preventing the evaporation of ink, the meniscus is moving downward from the neighbor of the ink ejection outlet to the inside of the ink liquid passage due to a force generated by the shock and the pressure fluctuation applied to the ink. This phenomena is designated a loss of ink feed. In the loss of ink feed, the ink droplet can not be ejected regularly. Furthermore, in case of trying to continue to transfer thermal energy generated by the electro-thermal converting element into an empty portion of the ink liquid passage where ink is lost, the electro-thermal converting element may be even damaged due to heat concentration there into.

The second disadvantages relates to an increase of viscosity of ink. That is, in case that a viscosity of ink in the ink liquid passage is getting higher due to the evaporation of solvent components of ink through the ink ejection outlet of the recording head and so on, an ink eject ion failure such as a decrease of the amount of the ejected ink droplet or non-election of ink occurs. Although an increase of viscosity of ink could be avoided to a certain extent by way of the capping as described earlier, such a way may not cope with this problem especially in case of trying ink ejection after a long period of time during which the ink ejection has not been performed.

The third disadvantages directs to bubble generated in the ink. Small-sized bubbles in the ink generated by heat unused for ejecting ink droplet and bubbles mixed into ink from outside of the recording head through an ink supply passage member such as a tube may grow up to bigger-sized bubbles in a long period of time. In case that the bigger-sized bubbles exist in the ink liquid passage, there may occur the ink ejection failure such as a deflection of ejected ink droplet and the decrease of the amount of ejected ink droplet.

For dissolving or preventing the first, second and third disadvantages described above, in some ink jet recording apparatuses, ejection recovery operations of the recording head or the like are performed. As for the ejection recovery operation, one approach is a suction method where ink in the ink liquid passage and other portions of the recording head is sucked to be discharged from the ink ejection outlet using a sucker pump and the other approach is a idle ejection method where the ink ejection is performed, independent of scheduled services of ink jet recording operations. A pressurizing method, similar to the suction method, is another approach where ink contained in the recording head is pressurized by pressure in the side of an ink supply passage to be discharged outside from the ink ejection outlet.

By means of the above mentioned suction method, pressurizing method or idle ejection method, high viscosity ink and the bubble growing in ink can be eliminated and also, by these ejection recovery operations which generate a force acting on ink contained in the recording head, the meniscus is returned to its regular position in the ink liquid passage so that the loss of ink feed can be dissolved.

The ejection recovery operations described above or the like are done properly when an electric power source to the recording apparatus is put on or the recording operations of the recording apparatus begins. However, at the time when the ejection recovery operations or the like are done, it is not necessarily found that an abnormal state in the ink liquid passage and other portions of the recording head such as the loss of ink feed and the increase of viscosity of ink mentioned above occur. In case of doing such unnecessary ejection recovery operations or the like, ink is used wastefully as well as the recording efficiency goes down due to wasting time for doing such recovery operation.

With respect to overcoming the above mentioned drawbacks in applying the ejection recovery operations, for example, as found in Japanese Patent Application Laying-Open No. 98542/1986, disclosed is a structure for detecting temperature of the recording head and for knowing a presence of the abnormal state based on the detected temperature. In this prior art structure, it is possible to execute the ejecting recovery operation, only when the abnormal state is found in the ink liquid passage and so on. However, the detection of abnormality is not directed to individual parts of a plurality of the ink liquid passages. In case that the abnormal state exists in a relatively small number of the ink liquid passages among all of them, the temperature change which occurs in the overall recording head by above mentioned small abnormal state is hard to be detected, therefore, it is difficult that the abnormal state is detected.

With respect to overcoming the above mentioned problem in abnormality detection which should be dissolved, for example, a structure disclosed in Japanese Patent Application Laying-Open No. 14967/1984 can be taken to be one approach to the solution. In the disclosed structure, by means of supplying the electric energy into the electro-thermal converting element for generating thermal energy for ejecting ink droplet, this electric energy being not enough to make ink drops ejected, temperature change is caused. And the abnormal state in the ink liquid passage is examined by detecting fluctuation of the electric energy being supplied into the electro-thermal converting element which is adversely caused by the above mentioned temperature change. In this structure for detecting the abnormal state, the abnormal state in the individual ink liquid passage can be detected separately by sensing up the electric current through the individual electro-thermal converting element.

However, because the above additive electric energy supplied to the electro-thermal converting element for detecting the abnormal state is taken to be low enough so that the energy may not contribute to ink droplet ejection, it takes a relatively longer time to detect a significant change in the electric energy induced by the temperature change caused by the additive electric energy. So far, it takes a longer time to detect the abnormal state, and because a number of fine-sized bubbles are generated by heat generated in ink while the electric energy is supplied continuously into the electro-thermal converting element for a relatively long time, these fine-sized bubbles may exert a bad influence on the ink droplet ejection. In addition, because detection procedures of the abnormal state are made independently of the ejection recovery operations, an occurrence of time spent for the detection procedures brings a lowering of efficiency of the overall recording procedures. And furthermore, a specific structure is required to supply the additive electric energy as low as the ink droplet eject ion never occurs.

An object of the present invention is to provide an ink jet recording apparatus for enabling to execute an appropriate ejection recovery operations by means of examining a presence of the abnormal state in the ink liquid passage and other portion by supplying an electric energy into the electro-thermal converting element for electing ink droplet and by detecting a predetermined state of the electro-thermal converting element caused by the supply of the electric energy.

This object is achieved by an apparatus according to claim 1.

The invention is further developed by the features mentioned in the subclaims.

The above and other objects, effects, features and advantages of the present invention will become more apparent from the following description of embodiments thereof taken in conjunction with the accompanying drawings.

Embodiments of the invention will now be described, by way of example and with reference to the accompanying drawings in which like parts are designated with like numerals throughout, and in which: <ul id="ul0001" list-style="none" compact="compact"><li>Fig. 1 is a schematic perspective view showing an example of an ink jet recording apparatus to which the present invention is applicable;</li><li>Fig. 2 is a perspective view illustrating a great detail of an example of a recording head and an ejection recovery unit in an embodiment of the present invention;</li><li>Fig. 3 is a block diagram illustrating an example of a major part of a control system in the ink jet recording apparatus;</li><li>Fig. 4A is a circuit diagram illustrating an embodiment of a heat generation part driving circuit and a resistance measurement circuit, both circuits shown in Fig. 3;</li><li>Fig. 4B is a block diagram of a detail of a comparison circuit in Fig. 3;</li><li>Fig. 4C is a timing chart of signals shown in Figs. 4A and 4B;</li><li>Fig. 5 is a flow chart illustrating an example of procedures in the control system shown in Fig. 3;</li><li>Fig. 6 is a graph illustrating temperature change in the heat generation part when a driving signal is supplied into the heat generation part shown in Fig. 3;</li><li>Figs. 7A and 7B are graphs representing two examples of the relationship between the temperature of the heat generation part and the resistance of a electro-thermal converting element;</li><li>Figs. 8A and 8B are flow charts of procedures in other two embodiments of the present invention;</li><li>Figs. 9A and 10A are circuit diagrams illustrating other two embodiment of the heat generation part driving circuit and a resistance measurement circuit, both circuits shown in Fig. 3;</li><li>Figs. 9B and 10B are block diagrams of a detail of a comparison circuit in Fig. 3;</li><li>Figs. 9C and 10C are timing charts of signals shown in Figs. 9A, 9B and 10A, 10B;</li><li>Fig. 11 is a schematic diagram illustrating an embodiment of an apparatus in accordance with the present invention to which the ink jet recording apparatus shown Fig. 1 is equipped; and</li><li>Fig. 12 is a schematic drawing illustrating an embodiment of a portable printer in accordance with the present invention.</li></ul>

Fig. 1 shows an embodiment of an ink jet recording apparatus to which the present invention is applicable.

In Fig. 1, a recording sheet 63, which is the recording medium made from paper or plastic thin film, is moved in the direction of an arrow A, being guided by sheet feed rollers 61 and 62, both pairs of rollers being placed at the upper and lower sides of the recording apparatus at a designated interval. Being parallel with and in front of the portion of the recording sheet 63 which is located between sheet feed rollers 61 and 62 in the vertical direction, a pair of guide shafts 64 is disposed and with the guide shafts 64, a carriage 110 is mounted so as to slide along the guide shafts 64 horizontally. And a recording head unit 101 is mounted on the carriage 110. With this structure, facing the ink ejection outlets of the recording head to the recording sheet 63, the recording head can move horizontally in the direction of an arrow P in the figure in front of the recording sheet 63.

At the front side of the recording head unit 101, the plurality of ink ejection outlet for ejecting ink droplets, which will be designated as ejection outlet in the description that follow, disposed. As the recording head 101 is moving horizontally in front of the recording sheet 63, the clearance between these ejection outlets and the recording sheet 63 is kept to be a designated value, for instance, about 0.8 mm. A side-to-side motion of the carriage 110 is established by a transmission mechanism including a wire 69 and pulleys winding the wire 69 and by a carriage driving motor 68. Owing to this mechanism, the recording head unit 101 can be moved and positioned at designated positions.

The carriage 110 and a control unit of the recording apparatus of the embodiment of the present invention are connected electrically with a flexible cable for supplying the electric power source and communicating electric signals.

In the above structure, when the recording operation is performed, simultaneously with a movement of the carriage 100 in the direction of rows on the recording sheet, as shown by the arrow P in Fig. 1, the electro-thermal converting elements, each element provided with each corresponding ejection outlet in the recording head unit 101, are driven selectively in accordance with recording data so that ink droplets ejected from the ejection outlets corresponding to driven electro-thermal converting elements reach the surface of the recording sheet 63 and finally ink dots are established as forming recording information on the recording sheet 63.

The recording head unit 101 is positioned at a home position HP which is set outside the recording region by the recording head unit 101 when the recording head is not operated or at a scheduled time in a recording operation. In the neighboring area of the home position HP, placed is an ejection recovery unit 70 which has a cap for covering up the surface or which the ejection outlets of the recording head are disposed, and a pump for sucking ink from the ejection outlets through the cap and so on. The ejection recovery operations including the idle ejection and the ink suction which relate to the embodiment of the present invention and which are described later with reference to Fig. 5 are carried out by means of the ejection recovery unit 70 when the recording head unit 101 is positioned at the home position HP. An ink tank 105 used for containing ink supplied into the recording head unit 101 is arranged in an appropriate position in the recording apparatus. A tube 106 used for supplying the ink in the ink tank 105 for the recording head unit 101 has flexibility so as to follow the movement of the recording head unit 101.

Fig. 2 shows a great detail of the ejection recovery unit 70 and the recording head unit 101 as shown in Fig. 1.

As for an ink supply path 2 for supplying ink into the recording head 101H, one end 2a of the ink supply path 2 is connected with the ink tank 105 through the tube 106 and the other end 2b of the ink supply path 2 is connected with a common chamber 3 in the recording head 101H. A plurality of ink liquid passages 4 connected with the common chamber 3 are disposed in the recording head 101H in Fig. 2 where only three of the ink liquid passages 4 are shown. An ejection outlet 5 port is formed as an open hole, from which ink droplets are ejected, at the opposite end side of each ink liquid passage to the common chamber 3. In a top plate 6, a concave portion is formed in order to establish the common chamber 3 and the ink liquid passages 4 and a substrate 6B is bonded onto the top plate 6A. In very region on the substrate 6B corresponding to each ink liquid passage 4, an electro-thermal converting element 7 is formed for generating thermal energy to be used to eject ink droplets.

Driving signal is supplied into the electro-thermal converting elements 7 through a wiring 8 which is connected with the control unit through the flexible cable 67 as shown in Fig. 1. The secondary board 9 forms a base member of the recording head unit 101 by supporting the substrate 6B and so on. A plate 10 is disposed in a vertical position to the direction in which ink droplets are ejected from the ejection outlets 5 at the end side of the recording head 101H. Sealing materials are filled in the bonded portions between the plate 100 and either the substrate 6B or the top plate 6A in order to prevent ink from penetrating into the bonded portions.

A reference numeral 12 in Fig. 2 designates a cap for forming the ejection recovery unit 70 as shown in Fig. 1 with which the face of the recording head 101H where the ejection outlets 5 are disposed can be covered. The cap 12 and a pump not shown in Fig. 2 are connected through a suction tube 13. So far, the cap 12 moves in the direction shown by an arrow in Fig. 2 by means of a moving means not shown in Fig. 2 which forms one part of the ejection recovery unit 70, and the cap 12 can cover up the face where the ejection outlets 5 are formed. By way of capping with the cap 12, evaporation of the solvent component of ink can be suppressed so that an increase of viscosity of ink can be prevented. In addition, by means of sucking ink by negative pressure in the cap 12 produced by the pump, the ejection outlets of the recording head 101H being covered with the cap 12, sticky ink and bubbles in ink which cause ink ejection failures can be removed, and further, fresh ink is refilled.

Fig. 3 shows a major part of a control system for the ink jet recording apparatus as shown in Fig. 1.

A control unit 50 supplies driving data and control signals to a heat generation part driving circuit 51 for driving electro-thermal converting elements, the heat generation part driving circuit 51 being formed in the recording head unit 101, so as to execute procedures described later with reference to Fig. 4. The control unit 50 may take a form of a micro computer including a CPU for executing the procedures mentioned above, a ROM for storing computer programs of the procedures and a RAM having a data expansion area and a work area used for the procedures and so on. And further, the control unit 50 controls mechanical actions of sheet feed rollers 61, 62 for feeding the recording sheet 63 and the carriage 110. The driving circuit 51 drives electro-thermal converting elements 7 according to the driving data supplied from the control unit 50. A resistance measurement circuit 53 measures the resistance value of the electro-thermal converting element 7, and a comparison circuit 56 compares the measured value obtained by the resistance measurement circuit 53 with a reference value designated by the control unit 50.

Fig. 4A is a circuit diagram illustrating one embodiment of circuit structures of the heat generation part driving circuit 51 and the resistance measurement circuit 53.

In Fig. 4A, a plurality of electro-thermal converting elements 7 disposed in the recording head 101H are designated as R₁, R₂ and so on, and transistors TR₁, TR₂ and so on forming the heat generation part driving circuit 51 are provided, each corresponding to each of electro-thermal converting elements R₁, R₂ and so on. The transistors TR₁, TR₂ and so on switch on and off corresponding electro-thermal converting elements R₁, R₂ and so on according to driving signals S₁, S₂ and so on. Transistors tr₁, tr₂ and so on form the resistance measurement circuit 53. In measuring the resistance value of electro-thermal converting elements R₁, R₂ and so on transistors tr₁, tr₂ and so on are switched on and off by switching signals P₁, P₂ and so on from the control unit 50 so that each of measurement signals A₁, A₂ and so on can be obtained in response to the each resistance value of electro-thermal converting elements R₁, R₂ and so on. Each of AND gates AN1, AN2 and so on gets each of the driving signals S₁, S₂ and so on at one input terminal, and gets each of the switching signals which are fed to the resistance measurement circuit 53 at the other input terminal. Owing to this configuration, it will be appreciated that an unfavorable situation in recording information can be avoided where transistors used for measuring resistance are operated by switching signals unnecessarily supplied in some reason while these switching signals are intended to drive transistors Tr₁, Tr₂ and so on for driving electro-thermal converting elements.

Now referring to Figs. 4B and 4C, there is given an explanation of generation scheme of signals shown in Fig. 4A.

In this embodiment of the present invention, the electro-thermal converting elements are alternately driven by two blocks; a block of R₁, R₃ and so on and a block of R₂, R₄ and so on. As shown in a timing chart in Fig. 4C, at first, the driving signals S₁, S₃ and so on corresponding to the first block are generated as a sequence of five pulses and supplied to corresponding transistors Tr₁, Tr₃ and so on. Next, electric pulses in response to this sequential pulses are applied to the electro-thermal converting elements R₁, R₃ and so on so that in an ordinary case, ink droplets are ejected out of each ejection outlets. At the time a designated time t₁ has passed after these driving signals S₁, S₃ and so on were supplied, switching signals P₁, P₃ and so on corresponding to the block of the electro-thermal converting elements R₁, R₃ and so on are supplied to corresponding transistors tr₁, tr₃ and so on. In this way, designated electric signals are applied to the electro-thermal converting elements R₁, R₃ and so on in response to the switching signals P₁, P₃ and so on so that the measurement signals A₁, A₃ and so on are generated, each measurement signal has its own voltage value corresponding to the resistance value of each electro-thermal converting elements R₁, R₃ and so on. Fig. 4C shows a case where the measurement signal A₃ detects an abnormal state of the ink liquid passage in which the electro-thermal converting element R₃ is formed. In other words, for instance, in case that the viscosity of ink increases, in case that bubbles are generated in ink or in case that a loss of ink occurs in the ink liquid passage, heat generated by the electro-thermal converting element R₃ is not diffused outside of the element R₃ but contributes directly to a temperature rise of the element R₃ itself and further. In the case where the electro-thermal converting element R₃ has a characteristic that its resistance increases with the increase in the temperature as shown in Fig. 7B, the temperature rise of the element R₃ itself makes the resistance value of the element R₃ greater. Owing to an increase of the resistance of the element R₃, the voltage value of the detected measurement signal A₃ gets smaller. The measurement signal A₃ to be supplied as a signal D₂ into the comparison circuit 563B gets smaller than the reference value, and hence, an output signal C₂ from the comparison circuit 563B turns into "0".

After the ink ejection and the resistance measurement procedures with respect to the first block of electro-thermal converting elements R₁, R₃ and so on were terminated, then the ink ejection and the resistance measurement procedures are carried out with respect to the second block of electro-thermal converting elements R₂, R₄ and so on in the same manner. So far, the first and second blocks of electro-thermal converting elements are driven alternatively. In this case, as shown in Fig. 4B, using data selectors 561A, 561B and so on, signals used in the comparison circuits are alternated to be A₁ with A₂, A₃ with A₄ and so on according to switching signals P₁, P₂ and so on. Owing to this circuit configuration, a structure of the comparison circuits 563 and the control unit 50 following to the data selectors 561 can be made simpler. The control unit 50 reads output signals from the comparison circuits 563A, 563B and so on in response to switching signals P₁, P₂ and so on, and uses its own procedures.

Incidentally, the circuit configuration and the timing chart as shown in Figs. 4A and 4C, respectively, are provided to be supplied with the switching signals (measuring signals) Pk after continuous fine pulses of the driving signal Sk are supplied. Instead of the above arrangement, a circuit configuration and a timing chart may be provided to be supplied with the measuring signals Pk while the driving signals Sk are being supplied. In this case, as the detecting of the abnormal state faster, can be carried out the number of the driving signals for detecting the abnormal state can be reduced so that a possibility of damaging the electro-thermal converting element can be further reduced.

Furthermore, the number of the driving signals, which is fine in the embodiment described with reference to Figs. 4A to 4C, is set within a certain extent which is determined by considering thermal influence on other ink liquid passages, and a magnitude of the electric energy of the driving signal or the like. In other words, the measurement of the resistance value can be carried out without influences exerted by other ink liquid passages by the number of the driving signals within the certain extent being supplied to the electro-thermal converting element.

As described above, it will be appreciated that a state of each ink liquid passage can be detected by means of measurement signals of resistance of its corresponding electro-thermal converting element to each ink liquid passage. That is, in case that there exists any abnormal state in the ink liquid passage such as the increase of viscosity of ink, the existence of bubbles generated in ink or a loss of ink, the output signal from the comparison circuit turns into "0".

Driving signals S₁, S₂ and so on are, as described above, also used to be driving signals for ejecting ink droplets in recording operation and in case that there exists no abnormal state in the ink liquid passages, ink droplets are ejected from the ejection outlets in response to supplied driving signals S₁, S₂ and so on. Therefore, the procedure for detecting the abnormal state of the ink liquid passages can be done in a part of a procedure for the ejection recovery operations capability as described later in Fig. 5. In this case, the ink ejection by means of driving signals S₁, S₂ and so on is a so-called idle ejection and by the idle ejection, ink which has high viscosity and/or contains bubbles can be removed from the ink liquid passages. In addition, if the meniscus of ink is displaced downward from the ejection outlet to a little extent, the meniscus can be moved into a proper position by the idle ejection of ink. So far, in this embodiment of the present invention, only the serious abnormal state in the ink liquid passages which cannot be recovered by the above mentioned idle ejection is detected and the suction procedure can be performed in accordance with the abnormal state detection, it will be appreciated that unnecessary suction procedure can be eliminated.

However, from a point of view with respect to time spent in procedures and capacity of an electric power supply source, the method for driving the electro-thermal converting element which is used for the recording operation is more preferable where the elements are driven alternatively by blocks to be applied equally to driving the electro-thermal converting elements for the idle ejection of ink and to measuring resistance of the elements. In a specific example of this method for driving electro-thermal converting elements, as well known in prior art systems, for instance, there exist 128 ejection outlets and their corresponding 128 electro-thermal converting elements, and 16 blocks, each containing 8 electro-thermal converting elements, are selected alternatively to be driven at one time. According to this circuit configuration, in driving the elements both for recording operation and for procedures related directly to the embodiment of the present invention, driving procedures of each block of electro-thermal converting elements can share circuits for driving the elements such as the driving signal generation circuit, the comparison circuit and the control unit and so on. Furthermore, in case that the recording head has relatively many electro-thermal converting elements, the time for detecting the abnormality can be reduced by that the electro-thermal converting elements are driven and the resistance of the elements are measured alternatively by blocks.

Fig. 5 shows procedures to which the present invention is applied and which can be invoked at any time such as before the recording operation begins, after recording a designated amount of information, after recording for a designated time, when recording operation is interrupted and so on.

At the first step of the procedures in Fig. 5, in step S1, the recording head unit 101 moves to the home position HP, and the ejection outlets 5 and their neighboring area are covered with the cap 12 and insulated from atmospheric air.

Next, in step S3, selected are a plurality of ejection outlets of the designated block in accordance with driving signals Sk as described in Figs. 4A, 4B and 4C. In step S5, to corresponding heat generation part driving circuit 51, the designated number of sequential pulse signals Sk is supplied so that the idle ejection of ink are carried out as a part of the ejection recovery operation. As a result, thermal energy is given to ink at the electro-thermal converting elements Rk.

In step S5, if there exist no abnormal state in the corresponding ink liquid passages, in ink to which the thermal energy was given, a state change and a rapid voluminous change occur, and thereby, ink droplet is ejected respectively by means of this rapid voluminous change of ink.

However, in case that the loss of ink in the ink liquid passages takes place or there exist the increase of viscosity of ink or the generation of small-sized bubbles in ink, then thermal energy given to the electro-thermal converting element Rk is not used to eject ink droplet but stored as heat at the electro-thermal converting element itself and its neighboring heat generation part. As a result, as shown in Fig. 6, temperature of the heat generation part increases more rapidly and saturation temperature is higher than the case, for example, where ink is filled at the heat generation part. In this case, as shown in Fig. 7A or Fig. 7B, in proportion to a temperature increase of the heat generation part, the electric resistance value of the electro-thermal converting element decreases or increases. Depend on the property of materials used for forming an electro-thermal converting element, electro-thermal converting elements are categorized into two types with respect to their characteristics to temperature change. In this specification, described in a case where used is an electro-thermal converting element with its material having the characteristic as shown in Fig. 7B. The invention may be embodied in other kind of materials used for electro-thermal converting elements with its characteristics shown in Fig. 7A without departing from the invention's spirit or essential concept.

Next, in step S7, as described in Figs. 4A through 4C, by means of switching signals Pk, the operation mode of the circuit is turned from driving mode to resistance measurement mode and then, the resistance of an electro-thermal converting elements Rk are measured with measuring signals Ak to estimate a change in resistance value of an electro-thermal converting elements Rk according to measured signals Ak.

And further, in step S9, the measured signal Ak is compared with a designated reference value with which there exist no abnormal state found in the ink liquid passage, and determined is whether the abnormal state occurs in the ink liquid passage or not according to the comparison result output Ck. If there exists some abnormal state in step S15. The ejection recovery operations are done by sucking ink for eliminating such an abnormal state. In a detail description, by means of operating the suction pump mounted in the ink jet recording apparatus and making pressure down in the cap 12 ink is discharged from the ejection outlets so that fresh ink can be supplied into all the ink liquid passages in the recording head easily. In addition, in case that elimination of an abnormal state cannot be attained even after three times of the ejection recovery operations, this situation is reported by alarm signals (step S13).

Because a set of steps, S3, S5, S7, S9, S13 and S15, is served in a repetitive manner to test every ejection outlets, where its repetition is controlled by step S11, and the abnormal state of each ink liquid passage can be detected independently, ink is refilled by the suction operation only when the ejection outlet with their corresponding ink liquid passage is detected to be abnormal. In this way, the ink jet recording apparatus can be formed not to waste unnecessary ink for the ejection recovery operations but to attain an efficient and stable operation of the apparatus.

Having described above the preferred embodiment of the present invention, the following will be appreciated. <ul id="ul0002" list-style="none" compact="compact"><li>(1) By means of sucking ink only when necessary and reducing the amount of ink wasted unnecessarily, the consumption of ink can be reduced,</li><li>(2) By means of repeating automatically the ejection recovery operations until the abnormal states of all the ink liquid passages, if any, are restored and making an operator free from repetitive works for observing recorded ink dots and operating ejection recovery operations with above mentioned apparatus, time spent for recovery operations can be reduced.</li><li>(3) By means of measuring resistance of the electro-thermal converting elements, a breaking down of wire and a short circuit in a heat generation part can be detected.</li></ul>

Fig. 8A shows procedures relating to another embodiment of the present invention.

In this example, emphasized is a feature of an electro-thermal converting element in which the resistance of the element is deviated after electric energy for ejecting ink droplets is applied, and more specifically, its deviation value depends on a presence of the abnormal state in the ink liquid passage. Based upon this feature, in step S2 in Fig. 8A which is inserted between steps S1 and S3 in Fig. 5, is judged whether measurement of an initial resistance of the electro-thermal converting element, i.e., the resistance before application of electric energy for ink droplets ejection, has been done or not. In case that the measurement of the resistance of all the electro-thermal converting elements has not been yet completed, all the resistance of all the electro-thermal converting elements are measured before applying electric energy for ink droplets ejection in steps S21, S23 and S25. And after the measurement of the initial resistance of all the electro-thermal converting elements is completed, the resistance after applying of electric energy for ink droplets ejection is measured in steps S3, S5 and S7. And further, in step S9, a presence of the abnormal state of respective electro-thermal converting elements is detected according to the deviated value in the resistance of the element.

The embodiment shown in Fig. 8A also brings the same effect as the embodiment shown in Fig. 5 does. In addition, in the embodiment shown in Fig. 8A, as a presence of the abnormal state of electro-thermal converting elements can be detected according to the resistance change corrected with the temperature change in the surrounding parts around the elements, there is an advantage in that the detection of abnormal states is little influenced by the temperature change in the surrounding parts around the elements.

Fig. 8B shows procedures in further embodiment of the present invention.

Procedures shown in Fig. 5 can be invoked at any time in the recording operation with the recording head, for example, when the recording operation of a set of information is interrupted, i.e., at starting a new line in a serial-type printer. This embodiment relates to the case where these procedures for the ejection recovery operations at the ejection outlets at the time of starting a new line.

In this embodiment, after ejecting ink droplets by driving electro-thermal converting elements for recording a single unit of information on a designated line in step S31, the next control signal is examined to be whether for staring a new line or not in step S33. If the next control signal is for starting a new line, procedures for detecting the abnormal state in the ink liquid passages are executed in steps S3, S5, S7, S9, S11, S13 and S15 before starting recording information in the next line. Then, the procedures described above have been done until the recording ends (step S35).

Incidentally, the idle ejection in step S5 which is also a part of the abnormality detection procedures to be carried out before the recording of the new line starts, is carried out not at the inside of the cap as described with respect to the embodiments, but at the ink absorber or the like (not shown in Fig. 1) which is disposed between the cap and the region for recording by the recording head. Instead of this arrangement, one more ink absorber may be disposed at another side of the region for recording. This arrangement is especially effective for an ink jet recording apparatus wherein the ink ejection for recording information is carried out in accordance with reciprocating movements of the recording head.

Furthermore, the idle ejection in step S5 may be carried out at the cap not capping the recording head. Furthermore, in step S12, the preparation procedure for the recording operation is performed before the recording operation in step S31.

In this embodiment, it will be appreciated that an unfavorable situation can be avoided where driving signals for recording information are applied to electro-thermal converting elements in recording the set of information while the appropriate ejection recovery operations can not be taken and ink droplets can not be ejected from the ejection outlets where the abnormal state occurs.

Furthermore, in this embodiment, the abnormality detection procedure is carried out when the recording operation is interrupted so that a reliable recording operation can be carried out without increasing the time for the recording operation and without the ejection failure. Further, the abnormality detection procedure of this embodiment can be carried out by using a common method for driving the electro-thermal converting elements.

The present invention is not limited to the above embodiments, and its modifications and alternatives can be practiced. For example, with respect to an apparatus for ejection recovery operations by refilling fresh ink into the ink liquid passages, there may be an apparatus where sticky or bubble-containing ink is sucked from a designated number of ejection outlets in stead of being sucked from all the ejection outlets. In this apparatus, the consumption of ink can be further reduced. And in stead of using suction operation by the cap covering the ejection outlets, the present invention may be embodied by using pressurizing operation of ink in the ink supply passage. And furthermore, only by using the idle ejection of ink from ejection outlets if the number of the pulses signals for ink droplets ejection could be taken to be an appropriate number, the ejection recovery operation can be accomplished thereby, and as a result, it will be appreciated that only the ink liquid passages having the abnormal state can be restored.

Figs. 9A, 9B and 9C show another embodiment of circuit described earlier in Figs. 4A through 4C. In this embodiment, the switching signal Pk and the AND gate ANk in the embodiment shown by Figs. 4A through 4C are used commonly in each block of electro-thermal converting elements. That is, in driving electro-thermal converting elements for measuring the resistance of the elements, a single switching signal can be used for switching each single block. Owing to this circuit configuration, for example, in case of driving electro-thermal converting elements by two blocks, only two switching signals can be used. Figs. 9A though 9C show the same case that shown in Figs. 4A through 4C where electro-thermal converting elements are driven as shown in the time chart and there exists the abnormal state in the ink liquid passage corresponding to the electro-thermal converting element R₃.

Figs. 10A through 10C show further embodiment of circuit described earlier in Figs. 4A through 4C. In this embodiment, the resistor r for detecting measurement signals and the output terminal of measurement signals in the embodiment of shown by Figs. 4A through 4C are used commonly in each block of electro-thermal converting elements. Assuming here that electro-thermal converting elements are grouped into two blocks, as the electro-thermal converting elements R₁ and R₂, or R₃ and R₄ so on are not grouped in an identical block with respect to their driving, they are not driven concurrently for measuring their resistance. Using this characteristics of driving operation of the blocked electro-thermal converting elements, the single resistor r for detecting measurement signals and the single output terminal of measurement signals can be used for measuring the resistance of each single block of electro-thermal converting elements, and hence, the circuit structure can be simplified. And furthermore, the data selector can be eliminated.

The typical structure and the operational principle are preferably the one disclosed in U.S. Patent Nos. 4,723,129 and 4,740,796. The principle is applicable to a so-called on-demand type recording system and a continuous type recording system particularly however, it is suitable for the on-demand type because the principle is such that at least one driving signal is applied to an electro-thermal transducer disposed on liquid (ink) retaining sheet or liquid passage, the driving signal being enough to provide such a quick temperature rise beyond a departure from nucleate boiling point, by which the thermal energy is provide by the electro-thermal transducer to produce film boiling on the heating portion of the recording head, whereby a bubble can be formed in the liquid (ink) corresponding to each of the driving signals. By the development and collapse of the bubble, the liquid (ink) is ejected through an ejection outlet to produce at least one droplet. The driving signal is preferably in the form of a pulse, because the development and collapse of the bubble can be effected instanteously, and therefore, the liquid (ink) is ejected with quick response. The driving signal in the form of the pulse is preferably such as disclosed in U.S Patent Nos. 4,463,359 and 4,345,262. In addition, the temperature increasing rate of the heating surface is preferably such as disclosed in U.S. Patent No. 4,313,124.

The structure of the recording head may be as shown in U.S Patent Nos. 4,558,333 and 4,459,600 wherein the heating portion is disposed at a bent portion in addition to the structure of the combination of the ejection outlet, liquid passage and the electro-thermal transducer as disclosed in the above-mentioned patents. In addition, the present invention is applicable to the structure disclosed in Japanese Patent Application Laying-Open No. 123670/1984 wherein a common slit is used as the ejection outlet for a plurality of electro-thermal transducers, and to the structure disclosed in Japanese Patent Application Laying-Open No. 138461/1984 wherein an opening for absorbing pressure wave of the thermal energy is formed corresponding to the ejecting portion. This is because, the present invention is effective to perform the recording operation with certainty and at high efficiency irrespective of the type of the recording head.

The present invention is effectively applicable to a so-called full-line type recording head having a length corresponding to the maximum recording width. Such a recording head may comprise a single recording head and a plurality recording head combined to cover the entire width.

In addition, the present invention is applicable to a serial type recording head wherein the recording head is fixed on the main assembly, to a replaceable chip type recording head which is connected electrically with the main apparatus and can be supplied with the ink by being amounted in the main assembly, or to a cartridge type recording head having an integral ink container.

The provision of the recovery means and the auxiliary means for the preliminary operation are preferable, because they can further stabilize the effect of the present invention. As for such means, there are capping means for the recording head, cleaning means therefor, pressing or sucking means, preliminary heating means by the ejection electro-thermal transducer or by a combination of the ejection electro-thermal transducer and additional heating element and means for preliminary ejection not for the recording operation, which can stabilize the recording operation.

As regards the kinds and the number of the recording heads mounted, a single head corresponding to a single color ink may be equipped, or a plurality of heads corresponding respectively to a plurality of ink materials having different recording color or density may be equipped. The present invention is effectively applicable to an apparatus having at least one of a monochromatic mode solely with main color such as black and a multi-color mode with different color ink materials or a full-color mode by color mixture. The multi-color or full-color mode may be realized by a single recording head unit having a plurality of heads formed integrally or by a combination of a plurality of recording heads.

Furthermore, in the foregoing embodiment, the ink has been liquid. It may, however, be an ink material solidified at the room temperature or below and liquefied at the room temperature. Since in the ink jet recording system, the ink is controlled within the temperature not less than 30°C and not more than 70°C to stabilize the viscosity of the ink to provide the stabilized ejection, in usual recording apparatus of this type, the ink is such that it is liquid within the temperature range when the recording signal is applied. In addition, the temperature rise due to the thermal energy is positively prevented by consuming it for the state change of the ink from the solid state to the liquid state, or the ink material is solidified when it is left is used to prevent the evaporation of the ink. In either of the cases, the application of the recording signal producing thermal energy, the ink may be liquefied, and the liquefied ink may be ejected. The ink may start to be solidified at the time when it reaches the recording material. The present invention is applicable to such an ink material as is liquefied by the application of the thermal energy. Such an ink material may be retained as a liquid or solid material on through holes or recesses formed in a porous sheet as disclosed in Japanese Patent Application Laying-open No. 56847/1979 and Japanese Patent Application Laying-Open No. 71260/1985. The sheet is faced to the electro-thermal transducers. The most effective one for the ink materials described above is the film boiling system.

The ink jet recording apparatus may be used as an output means of various types of information processing apparatus such as a work station, personal or host computer, a word processor, a copying apparatus combined with an image reader, a facsimile machine having functions for transmitting and receiving information, or an optical disc apparatus for recording and/or reproducing information into and/or from an optical disc. These apparatus requires means for outputting processed information in the form of hard copy.

Fig. 11 schematically illustrates one embodiment of a utilizing apparatus in accordance with the present invention to which the ink jet recording system shown in Fig. 1 is equipped as an output means for outputting processed information.

In Fig. 11, reference numeral 10000 schematically denotes a utilizing apparatus which can be a work station, a personal or host computer, a word processor, a copying machine, a facsimile machine or an optical disc apparatus. Reference numeral 11000 denotes the ink jet recording apparatus (IJRA) shown in Fig. 1. The ink jet recording apparatus (IJRA) 11000 receives processed information form the utilizing apparatus 10000 and provides a print output as hard copy under the control of the utilizing apparatus 10000.

Fig. 12 schematically illustrates another embodiment of a portable printer in accordance with the present invention to which a utilizing apparatus such as a work station, a personal or host computer, a word processor, a copying machine, a facsimile machine or an optical disc apparatus can be coupled.

In Fig. 12, reference numeral 10001 schematically denotes such a utilizing apparatus. Reference numeral 12000 schematically denotes a portable printer having the ink jet recording apparatus (IJRA) 11000 shown in Fig. 1 in incorporated thereinto and interface circuits 13000 and 14000 receiving information processed by the utilizing apparatus 11001 and various controlling data for controlling the ink jet recording apparatus 11000, including hand shake and interruption control from the utilizing apparatus 11001. Such control per se is realized by conventional printer control technology.

An ink jet recording apparatus records information by ejecting ink droplets onto a recording medium (63). The ink jet recording apparatus has a recording head (101H); driving circuits (51), measuring circuit (53), and a judging unit (50). The recording head (101H) has ejection outlets (5) and ink liquid passages (4), connecting to the ejection outlets (5) respectively, an electro-thermal converting element (7) being disposed in each of the ink liquid passages (4), for generating thermal energy for ejecting the ink droplets. The driving circuits (51) drive the electro-thermal converting element (7) to generate the thermal energy enough to eject the ink droplet. The measuring circuit (53) individually measures a resistance value of the electro-thermal converting element (7) when the driving circuits (51) drive the electro-thermal converting element (7). The judging unit (50) judges presence of an abnormal state in the ink liquid passage (4) according to the resistance value.