Liquid discharging recording head

Abstract: A printer head for an ink jet printer includes at least two independent heating means (102-1, 102-2) arranged to heat the head at different rates. Sensing means (TH) determines the head temperature, and control means (Fig 3A) is arranged to drive the heating means (102-1 or 102-2) selectively via transistors Tr₁, Tr₂. Thereby the printer head can be heated rapidly when it is first switched on and waiting time before ink discharge can begin is reduced.

Description: The present invention relates generally to a liquid discharging or ejecting recording head of the type in which a heat energy is applied to a recording liquid so that the recording liquid is converted into liquid droplets which in turn are discharged or ejected from the recording head in order to record data and more particularly to a liquid discharging or ejecting head in which a temperature of such a head is compensated. Liquid discharging or ejecting recording methods such as a so-called ink jet recording method have recently been attracting an increasing interest because noise produced at the time of recording is almost negligible ; a high speed recording is possible ; and the liquid discharging or ejecting recording is made on plain paper without requiring any special fixing process. Of these methods, the liquid discharging recording method disclosed in Japanese Patent Application Laying-open No. 54-51837 and German Patent Application Laying-open (DOLS) No. 2843064 has a feature different from the other methods especially in that a thermal energy is applied to recording liquid so as to obtain an energy for jetting liquid droplets. More particularly, according to this method, when recording liquid is actuated by a thermal energy, the recording liquid changes its state, involving rapid expansion of a volume of the recording liquid. As a result of this change of state, the recording liquid is ejected from an orifice as an liquid discharging opening positioned at the end of the recording head by a force based upon the change of the state to form a frying droplet. The frying droplet lands on a recording medium such as recording paper, so that recording is made on the paper "frying" here will be understood to include boiling" Especially the liquid discharging recording method of the type disclosed in DOLS No. 2843064 is remarkably advantageously applied to a so-called drop-on demand recording method. Furthermore, according to this method, a recording head with a high degree of multi orifices in the form of full line can be easily constructed. Thus, the liquid recording head has a feature in that high quality image with a high degree of resolution can be obtained at a high speed. A recording head used in a recording apparatus constructed according to the above-mentioned method includes, in general, a liquid discharging portion having a plurality of orifices each of which ejects recording liquid to form a frying droplet and a plurality of recording liquid passages which partially have a thermal energy application portion for applying a thermal energy for discharging a droplet to the recording liquid ; and means for generating the thermal energy. So far, a liquid discharging recording head is constructed in the manner described above. Such a head, however, has various problems to be solved as will be described below. Firstly, some problems are caused by temperature characteristics of the liquid discharging recording head. Concerning a relation of a size of a recording dot formed by a recording liquid droplet landed on recording paper, i.e., a dot diameter with a temperature of the recording head, the dot diameter is closely dependent upon a temperature of the recording head. The reason is that in accordance with variations in temperature of the recording head, an initial bubble forming force required for forming a recording liquid droplet varies over a wide range. Especially when the temperature is low, the initial bubble forming force applied to the recording liquid is squall, so that a frying recording liquid droplet cannot be formed in a stable manner. As a result, it is impossible to obtain a high quality dot image. In order to overcome this problem, so far an external heating type heater such as a positive characteristic thermistor is used to heat the entire recording head from the exterior of the head. According to this method, however, the whole recording head is heated so that there are problems that the power consumption is higher and that a response speed of temperature rise is also slow. Furthermore, a liquid discharging head which utilizes thermal energy involves self-heating in principle and the recording liquid flows over a substrate so that the substrate is cooled. As a result, a temperature distribution of the head is complicated. As a consequence, in the case of a liquid discharging recording head of the type having a plurality of nozzles (a multi-orifice liquid discharging recording head), it is imperative to uniform the temperature distribution and to improve the characteristics of the recording head at a low temperature in order to obtain a high quality image. With the above in view, it has been proposed to arrange integrally heating means such as a compensating heater for temperature compensation on a heater board as a substrate having thereon thermal energy generating means for discharging the recording liquid, for example, a discharging heater, thereby increasing a thermal transmission efficiency and accordingly decreasing electric power consumption and enhancing the response speed. When the discharging heater and the compensating heater are disposed on the heater board in closely spaced relationship in the manner described above, the thermal energy transmission efficiency is improved so that a temperature rise time required for a temperature compensation starting from low temperature is greatly different from a temperature rise time required for a temperature compensation starting from room temperature. In addition, a temperature rise time at a starting time that an electric power source is turned on to start using the recording head is different from a temperature rise time at a waiting time after a series of recording operations are terminated. In other words, a time period required for temperature compensation varies in response to an environmental temperature and an operation condition of the printer. It follows, therefore, that if heating operation is carried out, uniformly regardless of the starting time or the waiting time, for instance, the waiting time for the recording processing is excessively elongated due to the uniform heating operation, so that there is the possibility that the printing errors occur. In order to solve the above-mentioned problem, it can be proposed to provide a temperature sensor and means for varying an electrical energy to be applied to the compensating heater in response to a detection signal from the temperature sensor. This solution, however, involves a problem that the cost of the recording head is expensive. It can also be proposed to apply an over power to the compensating heater so that a waiting time can be reduced under any condition of the recording head. There arises, however, another problem from the standpoint of durability of the compensating heater and its energy consumption. EP-A-0353925 discloses an ink jet printer having the features set out in the preamble to claim 1. The problem of providing a heater for a recording head that reduces the waiting time before printing can begin, that provides accurate temperature control and that is inexpensive to manufacture is solved by an ink jet printer having the features of claim 1. Other preferred features of the invention are defined in the accompanying claims 2 to 11. 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. Fig. 1 is a plan view showing a heater board of a first embodiment of a liquid discharging recording head in accordance with the present invention ; Figs. 2A and 2B are perspective view and a longitudinal sectional view, respectively, showing the first embodiment of the liquid discharging recording head fabricated by using the heater board shown in Fig. 1 ; Figs. 3A and 3B are circuit diagrams showing two embodiments of a heater drive circuit adapted for use with the heater board shown in Fig. 1 ; Fig. 4 is an explanatory diagram used to explain the temperature compensation of the recording head ; Fig. 5 is a circuit diagram showing a further embodiment of a heater drive circuit ; Figs. 6 and 7 are plan views showing a second and a third embodiments of a heater board in accordance with the present invention ; Fig. 8 is a schematic perspective view showing an embodiment of a liquid discharging recording apparatus in accordance with the present invention ; Fig. 9 is a schematic diagram illustrating an embodiment of an apparatus in accordance with the present invention to which the ink discharging recording apparatus shown in Fig. 8 is equipped ; and Fig. 10 is a schematic diagram illustrating an embodiment of a portable printer in accordance with the present invention. Now the present invention will become more apparent from the following description of some preferred embodiments thereof taken in conjunction with the accompanying drawings. Fig. 8 is a schematic perspective view showing an embodiment of a liquid discharging or ejecting recording apparatus having a liquid discharging ejecting recording head which utilizes a thermal energy as an energy for discharging liquid in accordance with the present invention. Typically, the apparatus is applicable to an ink jet recording apparatus. In Fig. 8, reference numeral 1 denotes an embodiment of a liquid discharging recording apparatus in accordance with the present invention Reference numeral 2 denotes a liquid discharging recording head which is mounted on a carriage 3 which is carried along a sliding shaft 10 and scanned in the direction of the shaft 10 by a carriage drive motor or CR motor (not shown) and a carriage drive belt 11. Electrical signal from a main board 7 are supplied to the recording head 2 via a flexible printed circuit board (FPC). Recording liquid, for instance, ink is fed to the recording head 2 via an ink feeding tube 5 and an ink subtank 4 on the carriage 3 from an ink cartridge (not shown). On rare occasions, discharging failure of the recording head 2 occurs due to inclusion of air bubbles or adhesion of the recording liquid to the surface of the discharging orifice. With this inview, a suction recovery mechanism is disposed at a home position of the carriage 3. A recording medium such as paper is fed upward along the surface of a platen 9 by a paper feed motor or LF motor (not shown). While the recording medium is moved intermittently in a paper feed direction, i.e., in a subscanning direction, the recording head 2 is moved in a direction of the shaft 10, i.e., in a main scanning direction to perform recording on the recording medium. First, the first embodiment of a liquid discharging recording head in accordance with the present invention will be explained with reference to Fig. 1 which schematically illustrates the portion of a heater board adjacent to a heater in the recording head. In the first embodiment shown in Fig. 1, reference numeral 101 denotes a heater board or a chip, on which a plurality of liquid discharging or ejecting heaters 103 as thermal energy generating means for discharging or ejecting recording liquid, a common electrode 105 and a plurality of electrodes 106 are arranged. The electrodes 105 and 106 apply the recording signals to the discharging heaters 103. In accordance with image information to be recorded. The number of the electrodes 106 corresponds to the number of dots corresponding to a recording density of an image to be recorded. The common electrode 105 is commonly connected to all the thermal energy generating heaters 103. The electrodes 106 are selection electrodes for selectively energizing the thermal energy generating heaters 103 independently of each other. A plurality of heaters 102-1 and 102-2 for heating the recording liquid are disposed on the same heater board 101 in order to accomplish the temperature compensation of the recording head. The temperature compensation heaters 102-1 and 102-2 are so formed in size and shape that the heaters 102-1 and 102-2 have different resistance values R 1 and R 2 (R 1 < R 2 ). More specifically, the size and the shape of the heaters 102-1 and 102-2 are determined in such a way that when the same voltage is applied across the heaters 102-1 and 102-2, a thermal energy generated by the heater 102-1 is larger than that generated by the heater 102-2. Here, the heater 102-1 is connected to a common electrode 104-A and a selection electrode 104-C. The heater 102-2 is connected to the common electrode 104-A and a selection electrode 104-B. An electric power is supplied to the heaters 102-1 and 102-2 via the electrodes 104-A and 104-C and via the electrodes 104-A and 104-B, respectively. A temperature rise character of the head can be suitably determined by selecting selection electrodes 104-B and 104-C. In the first embodiment, the temperature compensation heaters 102-1 and 102-2 can be formed by the same material as heat generating layers of the liquid discharging heaters 103 (for instance, HfB 2 ). Alternatively, the heaters 102-1 and 102-2 can be also formed by any other suitable material forming the heater board such as aluminum, tantalum, titan or the like. Aluminum is used to fabricate the electrodes. Titanium is used as a material which is interposed between the heat generating resistance layer of the discharging heater 103 and the electrode in order to enhance the adhesion therebetween. Tantalum is disposed on the heat generating resistance layer in order to increase its anti-cavitation characteristic. When these materials are selected, the temperature compensation heaters 102-1 and 102-2 can be fabricated simultaneously with the recording liquid discharging heaters 103 by a suitable film formation process. In. Fig. 1, only the heater board 101 is illustrated for the sake of easy understanding of the construction of the recording head. Next referring to Figs. 2A and 2B, an embodiment of a liquid discharging recording head in accordance with the present invention which can be structured by using the heater board 101 of the type describe above. Now referring to Figs. 2A and 2B, a nozzle plate 203 and a top plate 207 are laminated on the heater board 101 to define recording liquid passages 206. One end of each of the liquid passages 206 defines a discharging orifice communicating with the atmosphere. The other end of the passage 206 is communicated with a recording liquid chamber 205 as an ink supply source. The liquid chamber 205 is communicated with a recording liquid storage tank (not shown) via an ink supply portion 208. In Fig. 2B, the recording liquid is supplied to the liquid chamber 205 through a supply pipe 210 from the recording liquid storage tank. The heaters 102-1 and 102-2 as shown in Fig. 1 are disposed on the opposite sides of the array of the recording liquid discharging heaters 103 on the heater board 101, although the heaters 102-1 and 102-2 are not shown in Figs. 2A and 2B. Figs. 3A and 3B show two embodiments of a circuit for selectively driving the liquid temperature compensation heaters 102-1 and 102-2. The circuit can be arranged in a suitable portion of an apparatus to which the liquid discharging recording head shown in Figs. 2A and 2B is applied. For example, the head can be provided on a circuit board or substrate mounting a main control unit of the apparatus. A thermistor TH1 is disposed in a suitable portion of the recording head to sense a temperature of the head. As shown in Figs. 2A and 2B, the thermistor TH1 is positioned on the rear side of the heater board 101 and in the middle between the discharging heaters 103. Here, the thermistor TH1 is positioned under an area where the heaters 103 aligned. It is of course possible to dispose the thermistor TH1 on the front side of the heater board 101 on both sides of the area of the aligned heaters 103. In this case, the thermistor TH1 can be fabricated together will the heaters 102-1, 102-2 and 103 at the same step. A voltage V TH obtained form a voltage divider having the thermistor TH1 and the resistor R 1 is compared with a reference voltage V 1 by a comparator COM1. When V 1 is higher than V TH , one level signal such as a low level signal is derived from the comparator COM1. When V 1 is lower than V TH , the other level such as a high level signal is obtained from the comparator COM1. More specifically, when a temperature of the recording head is low, a resistance value of the thermistor TH1 is high, so that the voltage V TH is also high and consequently the high level signal is derived from the comparator COM1. The output signal derived from the comparator COM1 is applied as an ON/OFF signal to a transistor Tr1 through a resistor R 2 . The transistor Tr1 drives or turn on or off the heater 102-1 having a resistance HR 1 . The output signal from the comparator COM1 is also supplied to an inverter INV1 whose output signal is applied as an ON/OFF signal to a transistor Tr2 through a resistor R 3 . The transistor Tr2 drives or turns on or off the heater 102-2 having a resistance R 2 . The transistors Tr1 and Tr2 receive a supply voltage V H through the heater resistors HR 1 and HR 2 , respectively. At a low temperature, the voltage V TH is higher than the reference voltage V 1 , so that the heater 102-1 is energized. As a result, the temperature of the heater board 101 rises. Then, the voltage V TH across the thermistor TH1 becomes lower than the reference voltage V 1 , so that the heater is de-energized, while the heater 102-2 is energized. Thus, the power consumption is varied, so that the temperature of the heater board or substrate 101 rises gradually. In order to interrupt a current to be supplied to the heaters 102-1 and 102-2 when the temperature of the substrate 101 rises and exceeds a predetermined temperature, a heat sensitive switch SW is interposed between the heaters 102-1 and 102-2 on the one hand and the transistors Tr1 and Tr2 on the other hand, so that the temperature of the substrate 101 is controlled not to exceed a predetermined temperature. A conventional thermostat can be used as the switch SW, so that the voltage V H to be supplied to the heaters 102-1 and 102-2 is interrupted. With the above inview, the circuit shown in Fig. 3A can be modified as shown in Fig. 3B. More particularly, a second thermistor TH2 which may be the same as the thermistor TH1 and a comparator COM2 for comparing the voltage or temperature sensed by the thermistor TH2 with a predetermined temperature value are further provided. An AND gate AND1 outputs an AND output of the output from the comparator COM2 and the output from the COM1. An AND gate AND2 outputs an AND output of the output from the comparator COM2 and the output from an inverter INV2 to which the output from the comparator COM1 is applied. In response to the outputs form the AND gates AND1 and AND2, the transistors Tr1 and Tr2 are turned ON/OFF, respectively, to energize/de-energize the heaters 102-1 and 102-2. Next, referring to Fig. 4, the mode of the temperature rise of the substrate 101 will be described. When the temperature T 0 of the substrate 101 is low (V 1 < V TH ) at an instant t 0 , the heater resistor HR 1 is energized, so that the substrate 101 is heated to rise its temperature quickly. Thereafter, when the substrate temperature rises to a predetermined temperature T 1 ( V 2 = V TH ) at an instant t 2 , the heater resistor HR 1 is de-energized, while the heater resistor HR 2 is energized, so that the substrate temperature rises slowly. When the substrate temperature rises and exceeds the upper limit T 2 at an instant t 2 , the switch SW is actuated, so that the current supply to the heater resistor HR 2 is interrupted. As a consequence, after some overshoot, the substrate is cooled. When the substrate temperature falls below the upper limit T 2 at an instant t 3 , the switch SW is actuated again, so that the current flows into the heater resistor HR 2 . As a result, the heating of the substrate is initiated again to rise the substrate temperature to T 2 . Thereafter, the above described operations of the temperature rise and fall are repeated on both sides of the substrate temperature T2, so that the temperature of the recording liquid ejection head is maintained substantially at T2. In this way, the temperature of the recording head can be compensated. According to the present invention, therefore, even though the power consumption is high at a low temperature, there is obtained an advantage that the substrate temperature rises within a short period of time. Furthermore, since the compensating heater which consumes less energy is energized at a temperature in the vicinity of the compensation temperature, the temperature control can be carried out with a high accuracy and the power consumption can be minimized. According to the present invention, the temperature compensation can be carried out with the above described two advantages. Next referring to Fig. 5, another embodiment of a heater drive circuit will be described. This heater drive circuit can energize the heaters at a higher degree of accuracy. The heater drive circuit has three comparator COM1, COM2 and COM3, each having one input terminal connected to a common thermistor TH. Three reference voltages V 1 , V 2 and V 3 to be applied to the other input terminals of the comparators COM1, COM2 and COM3 are selected, respectively, with respect to the common thermistor voltage V TH in such a way that (1) when V TH is lower than V 1 both of the heaters HR 1 and HR 2 are simultaneously energized to obtain the maximum quantity of heat, (2) when V TH is between V 1 and V 2 , only the heater HR 1 is energized, (3) when V TH is between V 2 and V 3 , only the heater HR 2 is energized, and (4) when the voltage V TH is higher than V 3 , both the heaters HR 1 and HR 2 are de-energized. More specifically, the outputs from the comparators COM1 and COM2 are inverted and applied to an AND gate AND1. The output from the comparator COM2 and the inverted output from the comparator COM3 are applied to an AND gate AND2. The outputs from the comparators COM2 and COM3 are inverted and applied to an AND gate AND3. The outputs from the AND gates AND1 and AND2 are applied to an OR gate OR. In response to the output from the OR gate OR, the transistor Tr1 is controlled to be turned on or off. In a like manner, in response to the output from the AND gate AND3, the transistor Tr2 is turned on or off. According to the heater drive circuit shown in Fig. 5 can control the temperature more precisely than the heat drive circuits shown in Figs. 3A and 3B. Furthermore, while in the heater drive circuit shown in Fig. 3A, the switch SW interrupts the current supply, in the case of the heater drive circuit shown in Fig. 5, the upper limit of the temperature rise of the substrate 101 as shown in Fig. 3A can be controlled by the same circuit, if the reference voltage V 3 is selected to be equal to the temperature T 2 . Fig. 6 shows a heater board or substrate in a further embodiment of the present invention. In this embodiment, heat generating elements for discharging recording liquid droplets and a connection circuit for supplying electric energy to the heat generating elements are disposed in a portion 502 defined by broken lines on a heater board or substrate 501. Immediately below the portion 502, compensating heaters 506-1 and 506-2 with a common electrode 505 and selection electrodes 504 are disposed on either surface of the substrate 501. In this embodiment, the compensating heaters 506-1 and 506-2 disposed immediately below the portion 502 can directly heat the recording liquid or ink to be ejected, so that the temperature compensation attained by the present invention can be further enhanced. In the case of the first embodiment shown in Fig. 1, it is preferable to dispose the compensating heaters 102-1 and 102-2 on both sides of the array of the recording liquid discharging heaters 103 in symmetrical relationship with each other so that a uniform temperature distribution can be obtained. In contrast, in this embodiment, the heaters 506-1 and 506-2 are disposed in the center portion of the heater board 501, so that there is an advantage that uniform heating of the heater board can be attained without the above-described symmetrical relationship. Fig. 7 shows a heater board in a further embodiment of the present invention. In this embodiment, the recording liquid discharging elements and their associated electrode circuits are disposed in a portion defined by the broken lines on a heater board 601. Heaters 606-1, 606-2, 606-3 and 606-4 with electrodes 604 and 605 are disposed on both sides of the portion 602. The heaters 606-1, 606-2, 606-3 and 606-4 have resistance values R 1 , R 2 , R 3 and R 4 , respectively. Then, a heating energy to be applied to the heater board 601 can be controlled by selectively driving the selection electrodes 604 with respect to the common electrode 605. For instance, when R 1 = R 2 = R 3 = R 4 and when the heaters 606-1 through 606-4 are all energized, it is possible to control the thermal energy twice as high as the thermal energy obtained when only the heaters 606-2 and 606-3 or only the heaters 606-1 and 606-4 are energized. Furthermore, when R 1 = R 4 and R 2 = R 3 , it is possible to control the heating energy at three steps ; that is, all the heater 606-1 through 606-4 are energized ; only the heaters 606-2 and 606-3 are energized ; and only the heaters 606-1 and 606-4 are energized. When resistance values of the heaters 606-1 through 606-4 are varied in this way, it is possible to freely control a temperature of the susbtrate. While in this embodiment the compensating heaters are selectively driven in accordance with a sensed temperature, an amount of electric power to be supplied to the compensating heaters may alternatively be controlled in accordance with a sensed temperature. The present invention is particularly suitably useable in an ink jet recording head having thermal energy means for producing thermal energy as energy used for ink ejection such as a plurality of electrothermal transducers, a laser apparatus for generating a plurality of laser beams or the like and a recording apparatus using the head. The thermal energies cause variation of ink condition thereby eject ink. This is because, the high density of the picture element, and the high resolution of the recording are possible. 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 electrothermal transducer disposed on liquid (ink) retaining sheet or ink passage, the driving signal being enough to provide such a quick temperature rise beyond a departure from nucleation boiling point, by which the thermal energy is provide by the electrothermal 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 instantaneously, 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 electrothermal 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 plurality electrothermal 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 mounted 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 electrothermal transducer or by a combination of the ejection electrothermal 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 electrothermal 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 hand copy. Fig. 9 schematically illustrates one embodiment of a utilizing apparatus in accordance with the present invention to which the ink jet recording apparatus shown in Fig. 8 is equipped as an output means for outputting processed information. In Fig. 9, 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. 8. The ink jet recording apparatus (IJRA) 11000 receives processed information from the utilizing apparatus 10000 and provides a print output as hand copy under the control of the utilizing apparatus 10000. Fig. 10 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. 10, 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. 8 is 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. Although specific embodiments of a record apparatus constructed in accordance with the present invention have been disclosed, it is not intended that the invention be restricted to either the specific configurations or the uses disclosed herein. Modifications may be made in a manner obvious to those skilled in the art. For example, although the embodiments are described with regard to a serial printer, the present invention can also be applied to line printers. Here, the serial printer is defined as a printer that has a moving member on which the record head is mounted, the moving member being moved to and from in the direction perpendicular to the transporting direction of the recording paper. Accordingly, it is intended that the invention be limited only by the scope of the appended claims. As described above, according to the present invention, a plurality of compensating heaters are disposed on a heater board and are selectively energized, so that an energy consumption varies according to the selected energization. As a result, the substrate can be heated efficiently and the temperature compensation can be ensured. As a result, the temperature can be raised quickly when the temperature of the recording head is low, so that a waiting time before the operation of the liquid discharging recording head can be shortened. A variation in temperature is small in the vicinity of the temperature compensation region, so that a temperature compensation is precisely controlled. Accordingly, a variation in tone of a recorded image due to overrun can be reduced to minimum. If the above-described controls are carried out by a single heater, it is required to have means for sequentially controlling a power of the single heater between the maximum power and the minimum power. In contrast, in accordance with the present invention, the two or more compensating heaters are fabricated together with the discharging heating elements in the same substrate, so that the temperature compensation is realized by a simple circuit. In general, when the temperature of the substrate of the recording head is considerably lower than the temperature compensation region, the printer is in an unused condition while the power source is turned on. Under the condition, the recording operation is not immediately started and the maximum power is applied to the compensating heaters. However, in the temperature compensation region, the power supplied from the power source is divided into the power applied to the discharging heating elements and the power applied to the compensating heaters. In this case, if the power to be applied to the compensating heaters is decreased, a capacity of the electric power source to be supplied to the entire printer can be decreased. As a result, a cost of the entire printer can be reduced. In summary, the present invention can provide a liquid discharging recording head whose power consumption is small and which can raise the temperature of the recording head even at a low temperature within a short period of time so as to obtain a high quality image.

Claims: An ink jet printer comprising a recording head including a substrate (101), an array of energy generating elements (103) for ejecting ink, said elements being disposed on the substrate (101)to form a row extending along a predetermined direction, a plurality of heaters (102-1, 102-2) disposed on the substrate (101) for adjusting the temperature of the substrate, sensing means (TH) for sensing the temperature of the substrate which is related to that of the ink in the recording head, and control means arranged to energise the heaters when the output from the sensing means (TH) indicates that the sensed temperature is below a predetermined value T 2 , the control means providing the heaters (102-1, 102-2) independently of one another with power characterised in that the control means is arranged so that when the output from the sensing means indicates that the sensed temperature is below another value T 1 less than T 2 it switches from energising one heater (102-2) of lower heat output to energising another heater (102-1) of higher heat output or it switches from energising one heater (102-1) to energising more than one heater (102-1 and 102-2) so that the substrate (101) is heated relatively rapidly when its temperature is less than T 1 and more gradually when its temperature is above T 1 . The printer of claim 1, wherein the heaters (102-1, 102-2) are disposed symmetrically on opposite sides of the array of energy generating elements. The printer of claim 1, wherein the heaters (506-1, 506-2) are disposed at a region (502) of said substrate in which the heat generating elements are disposed and are on either face of the substrate immediately below the heat generating elements. The printer of any preceding claim, wherein the size and shape of the heaters is such that when the same voltage is applied across them the heater (102-1) which is closer to the energy generating elements (103) generates more heat than the heater (102-2) which is further from the energy generating elements (103). The printer of claim 4, wherein the control means (COM 1 - COM 3, AND 1 - AND 3, OR) is arranged to provide power to both the closer heater (102-1) and the further heater (102-2) when the temperature of the recording head is below a first threshold, to provide power only to the closer heater (102-1) when the temperature of the recording head is above the first threshold but below a second higher threshold, and to provide power only to the further heater (102-2) when the temperature of the recording head is above the second threshold. The printer of any preceding claim, wherein the heaters (102-1 and 102-2) are spaced apart along a direction transverse to the predetermined direction along which the row of energy generating elements (103) extends. The printer of any preceding claim, wherein the energy generating elements (103) are electrothermal conversion elements for bringing about a change of state of the ink and thereby ejecting ink from an orifice (209). The printer of claim 7, wherein the heaters (102-1) and (102-2) are formed of the same material as the energy generating elements (103). The printer of claim 8, wherein the heaters (102-1) and (102-2) and the energy generating elements (103) are of hafnium boride (HfB 2 ). The printer of any preceding claim, wherein the temperature sensing means (TH) is a thermistor located on the substrate (101) underneath and in the middle of the array of energy generating elements (103). The printer of any claims 1 to 9, wherein the temperature sensing means (TH) is located at the front of the substrate and is a thermistor located at one side of the array of energy generating elements (103) or is thermistors located on both sides of the array of energy generating elements (103).

Inventors: IKEDA MASAMI, KARITA SEIICHIRO, IKEDA, MASAMI, KARITA, SEIICHIRO
Applicants: CANON KK, CANON KABUSHIKI KAISHA
Application year: 1991
Main classification: B41J2
IPC codes: B41J2