JP2010131861A - Head substrate and inkjet recording head - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a head substrate that enables high-quality recording by suppressing a fluctuation in an ejection amount of ink even when a temperature distribution of the head substrate is deviated, and to provide an inkjet recording head with the use of the head substrate. <P>SOLUTION: This head substrate, constituted so that a constant current is applied to a heater and the ink is ejected by thermal energy generated by the heater, is equipped with a plurality of constant current sources for supplying constant currents. Each of the constant current sources includes an element, such as a diode, having a temperature dependence and a MOS transistor connected thereto. An output current to the heater is varied by means of the MOS transistor according to the temperature. The constant current sources are disposed in the vicinity of the respective heaters. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a head substrate and an ink jet recording head, and more particularly to a head substrate that ejects ink using thermal energy generated from a heater and an ink jet recording head using the head substrate.

  2. Description of the Related Art Conventionally, an ink jet recording apparatus (hereinafter referred to as a recording apparatus) that performs recording by discharging ink by heating and foaming the ink is known. In such an apparatus, in order to obtain good image quality, in order to suppress the occurrence of density fluctuations and density unevenness in recorded images as much as possible, the amount of ink discharged from the recording head is stabilized. Various controls have been performed.

  According to the main methods adopted for these controls, if the temperature of the ink is high, the viscosity of the ink becomes low and the ink is easily ejected, resulting in an increased ejection amount. Control the ink viscosity that affects etc.

  Specific methods relating to such control of the discharge amount and the like are disclosed in, for example, patent literature. According to this method, a plurality of pulses are applied to an electrothermal transducer (hereinafter referred to as a heater) for generating energy to form one dot (ink droplet). Actually, before applying a pulse (main pulse) for foaming ink, a pulse (pre-pulse) for adjusting the temperature of the ink in the vicinity of the heater is applied. As a result, the energy at the time of foaming of the ink becomes constant, and the volume of the ejected ink droplet is stabilized regardless of the ink temperature.

  In the above control, since it is necessary to apply a plurality of pulses to the heater in order to eject one ink droplet, the time including the pre-pulse necessary for one ink ejection is a single time. This is longer than when ink is ejected in pulses.

  The time for heating the heater is 1 to several microseconds even when the ink is ejected by applying a plurality of pulses. On the other hand, since the ink is actually foamed by heating of the heater and the ink is ejected, it takes several tens of microseconds for the bubbles to disappear and the next ink is ejected. Is sufficiently short with respect to the discharge period.

  However, the number of heaters that can be driven simultaneously is limited due to the limited current supply capability of the power supply of the recording apparatus main body in order to drive the recording head. For this reason, instead of driving all the heaters at the same time, a time-division drive is conventionally used in which a plurality of heaters are divided into a plurality of blocks and the blocks are driven at different times. During the drive cycle of one block by time division drive, the drive for the number of block divisions is performed for other blocks.

  As a result, although the pulse application time to the heater is shorter than the period required for ink ejection, in order to drive all the heaters, a time obtained by multiplying the time by the number of divided blocks is required. When the pulse width necessary for one ink discharge becomes longer, the time required to drive all the heaters becomes longer at the same time.

  In order to meet the recent demand for higher definition of recorded images, the number of heaters that can be driven simultaneously is limited and the number of heater blocks time-division is increasing in recording heads with a significantly increased number of heaters. In order to meet the demand for higher recording speed, it is particularly important to shorten the pulse application time required for discharging ink once.

  However, as described above, if ink is ejected once by applying a plurality of pulses to the heater in order to suppress variation in the ejection amount due to the temperature of the ink, it is necessary to drive all the heaters as a result. The time increases, which hinders the speeding up of recording.

In order to avoid such a problem, a method has been proposed in which, when a single pulse is applied to the heater, the voltage or current applied to the heater is changed to suppress variations in the ink ejection amount due to temperature. In this case, if the voltage applied to the heater is kept constant and only the pulse application time is changed, ink foaming becomes unstable, so the voltage or current applied to the heater is changed according to the pulse application time. That is, when the ink temperature is high, the applied voltage (current) to the heater is increased, and when the ink temperature is low, the applied voltage (current) to the heater is decreased to make the ink discharge amount constant. is there.
JP-A-5-169659

  Now, for a plurality of heaters arranged on a substrate, when the position of the driven heater is uniform on the substrate, the temperature distribution on the substrate is uniform. However, depending on the image to be actually recorded, a positional deviation of the driven heater on the substrate may occur. If a positional deviation of the driving heater occurs, the temperature distribution on the substrate will not be uniform.

  In recent years, in order to respond to higher definition of recording images and higher speed of recording, in a recording head in which the number of heaters is remarkably increased, the size of the substrate in the heater arrangement direction has also increased. Further, when a plurality of heater arrays are arranged in parallel on the same substrate for color recording, the size of the substrate that is orthogonal to the heater arrangement direction is also increased at the same time.

  As described above, in the case of a substrate having an increased size, there is a large positional deviation with respect to driving of the heater on the substrate, and it takes time to conduct heat on the substrate. For this reason, the temperature distribution on the substrate tends to be biased and the temperature difference is large. As a result, depending on the generated temperature distribution, a large temperature difference also occurs in the ink that contacts the substrate.

  In the case of a substrate having such a large temperature difference, if the same drive control is performed on a plurality of heaters on the substrate by detecting a part of the temperature on the substrate that has been conventionally performed or using an average temperature, the following is performed. Problem arises. In other words, if the heaters are driven under the same conditions for inks having different viscosities caused by the temperature distribution deviation on the substrate, a difference in ink discharge amount occurs, resulting in uneven density in the recorded image, and the image quality is reduced. to degrade.

  In addition, the following problems occur when the pulse application time and voltage to the heater are controlled as in the conventional example.

  In recent years, TaN or TaSiN has been used as a heater material because of its high resistance and relatively high heater durability. This material has a negative temperature coefficient of several hundred ppm / ° C. with respect to its resistance value.

When the ink is foamed by applying a pulse voltage to the heater, the temperature of the heater rises slowly until the ink is foamed. To do. For those having a negative temperature coefficient, such as TaN or TaSiN, the resistance value decreases as the temperature rises, and the resistance value rapidly decreases immediately after foaming. If the voltage applied to the heater is V and the resistance value of the heater is R, the calorific value (Q) per unit time is Q = V ² / R. Therefore, when the voltage is constant, the amount of heat generation is inversely proportional to the resistance.

  The temperature of the heater immediately after the ink bubbling rises abruptly due to the effect of heat insulation because the ink is not on the upper surface of the heater and the effect of increasing the heat generation amount due to the decrease in resistance value. In particular, when the temperature of the ink is increased, the pulse time applied to the heater is shortened, and the applied voltage is increased as in the conventional case, the temperature is increased to the temperature at which the ink foams in a short time. The temperature rise is large. In particular, the temperature rise in the heater immediately after foaming is large.

  Such an excessive temperature rise of the heater promotes the deterioration of the heater and causes a decrease in the durability of the heater.

  The present invention has been made in view of the above conventional example, and provides a head substrate capable of suppressing fluctuations in the ink discharge amount regardless of the temperature on the head substrate, and an ink jet recording head using the substrate. With the goal.

  In order to achieve the above object, the head substrate of the present invention has the following configuration.

  That is, a head substrate having a plurality of heaters and a plurality of switching elements for driving the plurality of heaters, controlling the plurality of switching elements to supply a constant current to the plurality of heaters for driving. A plurality of constant current sources, and each of the plurality of constant current sources includes a circuit that adjusts a value of a constant current supplied from the constant current source depending on a temperature of the head substrate. To do.

  According to another invention, an ink jet recording head using the head substrate having the above-described configuration is provided.

  Therefore, according to the present invention, the current value supplied to the heater can be adjusted according to the temperature on the head substrate on which the heater is disposed. In particular, for example, since the adjustment is performed by a circuit included in a constant current source arranged in the vicinity of the heater, the adjustment according to the local temperature is possible, and the temperature distribution of the head substrate is uneven. Can be adjusted more accurately. As a result, the amount of ink discharged can be stabilized, and high-quality recording can be achieved.

  In addition, when driving by applying a single pulse to the heater, a constant current is generated and supplied from a temperature-dependent reference voltage. It can be carried out. This can contribute to high-quality recording and high-speed recording regardless of temperature changes. Further, by performing constant current driving, it is possible to suppress an excessive rise in the heater temperature during recording, and the durability of the heater is also improved.

  Hereinafter, preferred embodiments of the present invention will be described more specifically and in detail with reference to the accompanying drawings. In addition, the same code | symbol is attached | subjected to already demonstrated part and duplication description is abbreviate | omitted.

  In this specification, “recording” (sometimes referred to as “printing”) is not limited to the case of forming significant information such as characters and graphics, but may be significant. Furthermore, it also represents a case where an image, a pattern, a pattern, or the like is widely formed on a recording medium or a medium is processed regardless of whether or not it is manifested so that a human can perceive it visually.

  “Recording medium” refers not only to paper used in general recording apparatuses but also widely to cloth, plastic film, metal plate, glass, ceramics, wood, leather, and the like that can accept ink. Shall.

  Further, “ink” (sometimes referred to as “liquid”) should be interpreted widely as in the definition of “recording (printing)”. Therefore, by being applied on the recording medium, it is used for formation of images, patterns, patterns, etc., processing of the recording medium, or ink processing (for example, solidification or insolubilization of the colorant in the ink applied to the recording medium). It shall represent a liquid that can be made.

  Furthermore, unless otherwise specified, the “recording element” collectively refers to an ejection port or a liquid path communicating with the ejection port and an element that generates energy used for ink ejection.

  The head substrate used below does not indicate a simple substrate made of a silicon semiconductor but indicates a configuration in which each element, wiring, and the like are provided.

  Further, the term “on the substrate” means not only the element substrate but also the surface of the element substrate and the inside of the element substrate near the surface. The term “built-in” as used in the present invention is not a word indicating that each separate element is simply arranged separately on the surface of the substrate. It shows that it is integrally formed and manufactured on top.

<Description of Inkjet Recording Apparatus (FIG. 1)>
FIG. 1 is an external perspective view showing an outline of the configuration of an ink jet recording apparatus 1 which is a typical embodiment of the present invention.

  As shown in FIG. 1, an ink jet recording apparatus (hereinafter referred to as a recording apparatus) has an ink jet recording head (hereinafter referred to as a recording head) 3 that performs recording by discharging ink in accordance with an ink jet system. Recording is performed by reciprocating in the direction. A recording medium P such as recording paper is fed through the paper feeding mechanism 5 and conveyed to a recording position, and recording is performed by discharging ink from the recording head 3 to the recording medium P at the recording position.

  In addition to mounting the recording head 3 on the carriage 2 of the recording apparatus 1, an ink cartridge 6 for storing ink to be supplied to the recording head 3 is mounted. The ink cartridge 6 is detachable from the carriage 2.

  The recording apparatus 1 shown in FIG. 1 is capable of color recording. For this reason, the carriage 2 contains four inks containing magenta (M), cyan (C), yellow (Y), and black (K) inks, respectively. An ink cartridge is installed. These four ink cartridges are detachable independently.

  The recording head 3 of this embodiment employs an ink jet system that ejects ink using thermal energy. For this reason, an electrothermal converter is provided. The electrothermal transducer is provided corresponding to each of the ejection ports, and ink is ejected from the corresponding ejection port by applying a pulse voltage to the corresponding electrothermal transducer in accordance with the recording signal.

<Control Configuration of Inkjet Recording Apparatus (FIG. 2)>
FIG. 2 is a block diagram showing a control configuration of the recording apparatus shown in FIG.

  As shown in FIG. 2, the controller 600 includes an MPU 601, a ROM 602, a special purpose integrated circuit (ASIC) 603, a RAM 604, a system bus 605, an A / D converter 606, and the like. Here, the ROM 602 stores a program corresponding to a control sequence to be described later, a required table, and other fixed data. The ASIC 603 generates control signals for controlling the carriage motor M1, the transport motor M2, and the recording head 3. The RAM 604 is used as a development area for image data, a work area for program execution, and the like. A system bus 605 connects the MPU 601, the ASIC 603, and the RAM 604 to each other to exchange data. The A / D converter 606 inputs analog signals from the sensor group described below, performs A / D conversion, and supplies a digital signal to the MPU 601.

  In FIG. 2, reference numeral 610 denotes a computer (or a reader for image reading, a digital camera, etc.) serving as a supply source of image data, and is collectively referred to as a host device. Image data, commands, status signals, and the like are transmitted and received between the host apparatus 610 and the recording apparatus 1 via an interface (I / F) 611. This image data is input in a raster format, for example.

  Reference numeral 620 denotes a switch group, which includes a power switch 621, a print switch 622, a recovery switch 623, and the like.

  Reference numeral 630 denotes a sensor group for detecting the apparatus state, and includes a position sensor 631, a temperature sensor 632, and the like.

  Further, 640 is a carriage motor driver that drives a carriage motor M1 for reciprocating scanning of the carriage 2 in the direction of arrow A, and 642 is a conveyance motor driver that drives a conveyance motor M2 for conveying the recording medium P.

  The ASIC 603 transfers data for driving a recording element (ejection heater) to the recording head while directly accessing the storage area of the RAM 604 during recording scanning by the recording head 3.

  The heater provided on the head substrate built in the recording head 3 is driven by a switching element such as a MOS transistor, and constant current driving is used for this driving.

In the constant current drive, the current is a constant current, and a constant current is always passed with respect to fluctuations in voltage and heater resistance. When a constant current is applied to the heater in pulses, the heat generation amount (Q) per unit time is Q = I ² × R, where I is the constant current value and R is the resistance value of the heater.

  If the resistance value of the heater material, such as TaN or TaSiN, has a negative temperature coefficient, the heater resistance value decreases due to the heat generated by the heater. If the heater is driven at a constant current value, heat generation per unit time The amount decreases. For this reason, when a pulse is applied with constant voltage drive, the temperature suddenly increased immediately after ink bubbling, whereas when a constant current value was applied, a rapid temperature increase at the heater occurred immediately after ink bubbling. Can be suppressed.

  When the pulse application time to the heater is constant, when the ink temperature rises by 1 ° C., the ink ejection amount changes from 0.5% to several percent. In order to suppress the fluctuation of the discharge amount, it is possible to change the pulse application voltage (current) to the heater with respect to the temperature rise.

  FIG. 3 is a diagram showing the relationship of the pulse current applied to the heater with respect to the temperature when the ink discharge amount is stabilized.

  Next, several embodiments of the recording apparatus having the above configuration and a head substrate that is used in the recording head and that is driven by constant current will be described.

  FIG. 4 is a diagram showing a circuit configuration of the head substrate according to the first embodiment of the present invention.

  This head substrate is roughly composed of a reference voltage circuit 105, a voltage / current conversion circuit 104, and a constant current source block 106. The head substrate of this embodiment is provided with (x × m) heaters, each of which is composed of m groups for accommodating x heaters.

  In FIG. 4, the reference voltage circuit 105 generates a voltage Vref serving as a reference for the voltage-current conversion circuit 104. The voltage / current conversion circuit 104 performs current conversion based on the reference voltage Vref to generate a reference current Iref.

  The reference current Iref and the constant current sources 103a to 103m constitute a current mirror circuit, and the constant current sources 103a to 103m output the constant currents Iha to Ihm based on the reference current Iref, respectively. The constant current sources 103a to 103m individually have means for varying the output currents Iha to Ihm according to the ambient temperature at which they are arranged.

  The constant current source block 106 includes heaters 101a1 to 101mx, switching elements 102a to 102mx, and constant current sources 103a to 103m. The constant current source block 106 is divided into m groups 106a, 106b,... 106m corresponding to the m groups.

  FIG. 5 is a diagram showing a relationship between the constant current source block and a control circuit for driving and controlling the constant current source block.

  In FIG. 5, the same components as those shown in FIG. 4 are denoted by the same reference numerals.

  The switching element (shown as a MOS transistor in FIG. 5) is controlled to short-circuit and open-circuit current between terminals by a control signal from the control circuit.

  As shown in FIGS. 4 to 5, heater resistors 101a1 to mx and switching elements (MOS transistors in FIG. 5) 102a1 to mx for driving control of each heater resistor are connected in series, and the switching element side in the group The terminal and the heater side terminal are commonly connected. On the other hand, the output terminals of the constant current sources 103a to 103m provided for the groups 106a to 106m are respectively connected to the common connection ends of the groups 103a to 103m in which the heater and the switching element are connected in series. The drive control of the current to the heater is performed by applying the output currents Iha to Ihm of the constant current sources 103a to 102m provided for each group to the desired heater by switching the switching elements in the group by a control signal. The

  Next, the operation of the heater drive circuit will be described.

  FIG. 6 is a timing chart regarding the voltage applied to the x heaters and the supplied current, focusing on the x heaters accommodated in the group 106a.

  The waveforms of VG1 to VGx in FIG. 6 indicate control signals for controlling on (short circuit) or off (open) corresponding to the switching elements 102a1 to 102ax, respectively. In the following description, it is assumed that the level of the control signal VGi (i = 1 to x) is turned on when “H” and turned off when “L”. Here, the description will be made assuming that all the heaters of the group 106a are driven.

  As shown in FIG. 6, the levels of the control signals VGi are all “L” during the period up to time t = t1, the output of the constant current source 103a and the heater are open, and no current flows through the heater. . Next, in the period from time t = t1 to t2, the control signal VG1 becomes “H”, the switching element 102a1 is short-circuited, and the output current Iha of the constant current source is applied to the heater 101a1. Furthermore, the level of the control signal VG1 becomes “L” from time t = t2, and the current to the heater 101a1 is cut off. During a period from time t = t1 to t2, a current is applied to the heater 101a1, the ink on the upper surface of the heater is heated and foamed, and ink is ejected from the nozzles, thereby recording dots on the recording medium.

  Subsequently, the level of the control signal VG2 becomes “H”, the switching element 102a2 is short-circuited, and the output current Iha of the constant current source 103a is applied to the heater. Similarly, the levels of the control signals VG3 to VGx are sequentially set to “H”, so that the output current Iha of the constant current source 103a is sequentially applied to the heaters 101a1 to 101ax through the switching elements 102a1 to 102ax. In this way, all the heaters accommodated in the group 106a are driven.

  The case where all the heaters of the group 106a are driven has been described above, but only the heater for forming a desired dot is actually driven. Accordingly, when recording a desired dot, only the control signal VGi for supplying a current to the corresponding heater becomes “H”.

  The above operation is simultaneously performed for the heaters accommodated in the groups 106b to 106m, and as a result, any of the (x × m) heaters can be driven.

  Next, current-dependent temperature control will be described.

  In this embodiment, applied currents (heater currents) Iha to Ihm to the heater are changed with respect to the ink temperature according to the temperature characteristics shown in FIG. Thereby, the fluctuation | variation of the discharge amount of the ink by a temperature change can be stabilized.

  An example of a specific circuit configuration for performing such control is shown in FIG.

  As described above, the reference current circuit 104 and the constant current sources 103a to 103m constitute a current mirror circuit, and generate heater currents Iha to Ihm based on the reference current Iref.

  As shown in FIG. 5, the reference current circuit 104 and the current mirror circuit of the constant current sources 103a to 103m are connected in common to the gates of the MOS transistors, and a diode is connected between each source and the ground power supply. Yes.

  FIG. 7 is an enlarged view of one of the constant current sources, and shows the voltage applied to each part.

  FIG. 8 is a diagram showing the temperature dependence of the voltage and current of one constant current source.

  The voltage Vg shown in FIG. 7 is generated from the sum of the gate-source voltage Vgs of the MOS transistor in the reference current circuit 104 and the forward voltage Vf of the diode based on the reference current Iref of the reference current circuit 104.

  Here, the circuit operation of one constant current source will be described assuming that the generated voltage Vg is constant.

  The forward voltage of the diode decreases at about 2 mV / ° C. when the current flowing with temperature rise is constant. Therefore, the forward voltage Vf also decreases with respect to temperature as shown in FIG. On the other hand, as shown in FIG. 8, since the voltage Vg is constant, the voltage Vgs between the gate and the source of the MOS transistor increases as the temperature rises. Since the voltage Vgs between the gate and the source of the MOS transistor determines the heater current Ih, the heater current Ih increases as Vgs increases due to the temperature rise.

  The amount of decrease in the forward voltage Vf due to the temperature is about 2 mV / ° C. with a constant current. However, since the current increases as the Vgs voltage increases, the amount of change in the forward voltage Vf is It will be less than about 2 mV / ° C.

  By appropriately selecting the size of the MOS transistor, the amount of change in the heater current Ih with respect to the temperature can be matched with the characteristics shown in FIG.

  FIG. 9 is a diagram showing a layout of each element mounted on the head substrate according to this embodiment.

  In FIG. 9, the same reference numerals are used for the same components as those described in FIGS.

  The layout shown in FIG. 9 is such that the components are arranged symmetrically with respect to the ink supply port 100 in the vertical direction of the head substrate.

  According to this layout configuration, the constant current sources 103a to 103m that supply current to the heaters are arranged in the vicinity of the heaters 101a1 to 101mx, respectively.

As described above, in the head substrate according to this embodiment, the heater and the constant current source for supplying current to the heater are arranged relatively equally. Therefore, according to the embodiment described above, the temperature distribution on the head substrate is biased. Even if it occurs, the constant current source can supply a current value corresponding to the temperature in the vicinity of the heater to be driven. This realizes stable ink ejection independent of temperature changes.

  FIG. 10 is a diagram showing a circuit configuration of the head substrate according to the second embodiment of the present invention.

  In FIG. 10, the same components as those of the head substrate shown in the first embodiment are denoted by the same reference numerals, and the description thereof is omitted.

  A characteristic configuration of this head substrate is a reference current circuit 107 provided between n constant current source blocks 106-1 to 106-n having the same configuration as that of the voltage / current conversion circuit 104. Each of the constant current source blocks 106-1 to 106-n has substantially the same configuration as the constant current source block 106 described in the first embodiment, but each of the constant current source blocks has different reference currents IR1, IR2,. Is supplied.

  FIG. 11 is a diagram showing a layout of the head substrate shown in FIG.

  Also in FIG. 11, the same reference numerals are assigned to the same components as those of the head substrate and the layout shown in the first embodiment, and the description thereof is omitted. This layout is different from the first embodiment in that three ink supply ports are provided, and the components are arranged symmetrically in the vertical direction of the head substrate with respect to each ink supply port.

  In this embodiment, the reference current circuit 107 generates a plurality of reference currents IR1 to IRn based on the reference current Iref generated by the voltage-current conversion circuit 104. Actually, as shown in FIG. 10, the voltage-current conversion circuit 104 and the reference current circuit 107 constitute a current mirror circuit, which generates n reference currents IR1 to IRn proportional to the reference current Iref. This is supplied to n constant current source blocks 106-1 to 106-n.

  Each of the n constant current source blocks outputs the constant currents Iha to m from the current sources 103a to 103m in each constant current source block using the reference currents IR1 to IRn.

  Therefore, according to the embodiment described above, even in the head substrate having n constant current source blocks, the applied currents Iha to Ihm to the heater change with respect to the ink temperature according to the characteristics shown in FIG. Can be made. Thereby, the fluctuation | variation of the discharge amount of the ink by a temperature change can be stabilized.

  Here, a case where ink is ejected by applying a single pulse to the heater of the head substrate will be described.

  FIG. 12 is a diagram in which the relationship between the ink ejection amount and the pulse application time when a single pulse is applied to the heater at a constant temperature is obtained experimentally.

  According to FIG. 12, the ink ejection amount decreases as the pulse application time is shortened.

  When the pulse application time is constant, the ink ejection amount increases as the temperature of the ink rises. Accordingly, it is possible to suppress fluctuations in the ink discharge amount due to changes in ink temperature using the characteristics shown in FIG.

  Regarding ink temperature change, in order to stably eject ink using the characteristics of the pulse application time, it is necessary to adjust the input energy (electric power) to the heater in accordance with the pulse application time. In this embodiment, the heater current is changed in accordance with the pulse application time. The relationship between the temperature and the heater current is as described with reference to FIG.

  FIG. 13 is a diagram showing the relationship between the pulse application time to the heater and the temperature.

  According to FIG. 13, in order to make the ink ejection amount constant even when the temperature rises, the pulse application time to the heater is shortened. On the other hand, as shown in FIG. 12, when the pulse application time is shortened, the ink discharge amount is decreased. Therefore, in this embodiment, the shortage of energy required for ink foaming caused by shortening the pulse application time is compensated by increasing the pulse current value.

  As described above, when the ink temperature rises, the pulse application time is shortened and the heater current is increased according to the characteristics shown in FIG. In this case, the temperature rise in the heater immediately after the ink foaming is different from the case of pulse application in the constant voltage drive, and in the constant current drive, the amount of heat generated by the heater per unit time is suppressed after foaming compared to before foaming. For this reason, the rapid temperature rise of the heater after foaming can be suppressed.

  FIG. 14 is a diagram showing a circuit configuration of the head substrate according to the third embodiment of the present invention.

  In FIG. 14, the same components as those of the head substrate shown in the first embodiment are denoted by the same reference numerals, and the description thereof is omitted.

  In the control according to this embodiment, in the head substrate shown in FIG. 14, the heater currents Iha to Ihm are changed with respect to the ink temperature in accordance with the characteristics shown in FIG. 3, and the current values are supplied for the time obtained from the relationship shown in FIG. . By doing so, it is possible to stabilize fluctuations in the ink ejection amount due to temperature changes.

  In the head substrate shown in FIG. 14, since the heater currents Iha to Ihm are obtained from the reference voltage Vref, the temperature dependence of the current shown in FIG. 3 is applied to the heater currents Iha to Ihm using the temperature characteristics of this voltage. Can be given. Specifically, the voltage characteristics of the reference voltage circuit 105 are given temperature characteristics.

  The reference voltage Vref output from the reference voltage circuit 105 is a voltage between the base and emitter of a diode-connected transistor obtained by multiplying a voltage difference (ΔVf) between the base and emitter of the two transistors 105a and 105b by a resistance ratio. It is determined by adding (Vf). The differential voltage ΔVf has a positive temperature characteristic with respect to the temperature rise, and the voltage Vf has a negative temperature characteristic. On the other hand, since the reference voltage Vref is obtained by adding both voltages using the resistance ratios R1, R2, and R3, Vref can have an arbitrary temperature characteristic by appropriately selecting this resistance ratio.

  Even if the reference voltage Vref is constant with respect to the temperature, the voltage-current conversion circuit 104 can give the currents Iha to Ihm temperature characteristics. For example, in the case of the circuit configuration shown in FIG. 14, since the reference voltage Vref is converted into current by the resistor R4, by using a resistor R4 having a desired temperature characteristic, the temperature characteristics are applied to the currents Iha to Ihm. It can be given.

  Therefore, according to the embodiment described above, even when ink is ejected by applying a single pulse to the heater, the pulse application time and heater current depending on the temperature change of the ink can be controlled. As a result, high-speed recording can be realized, and an excessive temperature rise to the heater can be suppressed, so that there is an advantage that the durability of the heater is also improved.

  The configuration of the head substrate shown in the third embodiment can be applied to a configuration having a plurality of constant current source blocks as described in the second embodiment.

  FIG. 15 is a diagram showing a circuit configuration of the head substrate according to the fourth embodiment of the present invention.

  In FIG. 15, the same reference numerals are assigned to the same components as those of the head substrate shown in the first to third embodiments, and the description thereof is omitted. The head substrate is provided with a reference current circuit 107 between n constant current source blocks 106-1 to 106-n having the same configuration as the voltage-current conversion circuit 104. Each of the constant current source blocks 106-1 to 106-n has substantially the same configuration as the constant current source block 106 described in the first embodiment, but each of the constant current source blocks has different reference currents IR1, IR2,. Is supplied.

  Also in this configuration, the temperature characteristics as shown in FIG. 3 can be obtained in the constant currents Iha to Ihm by providing the reference voltage Vref, the reference currents Iref, and IR1 to IRn with desired temperature characteristics as in the third embodiment. it can.

  The reference voltage circuit 105 can give the reference voltage Vref an arbitrary temperature characteristic by appropriately selecting the resistance ratio as in the third embodiment. The reference current circuit 107 is composed of a MOS transistor current mirror circuit having a plurality of output currents. Thereby, a plurality of reference currents IR1, IR2,... IRn proportional to the reference voltage Vref output from the reference voltage circuit 105 and the reference current Iref obtained by the current conversion circuit 104 are output.

  Therefore, according to the embodiment described above, even in the configuration in which the head substrate includes n constant current source blocks, the pulse application time and the heater current depending on the temperature change of the ink can be controlled as in the third embodiment. Can be done.

  In the above embodiment, the liquid droplets ejected from the recording head applied to the recording apparatus are described as ink, and the liquid stored in the ink tank is described as ink. Is not limited to ink.

  In addition, the above embodiment includes means (for example, an electrothermal converter) that generates thermal energy as energy used for performing ink ejection, particularly in the ink jet recording system. For this reason, it is possible to achieve higher recording density and higher definition by using a system in which the thermal energy causes a change in the state of the ink.

  In addition, the ink jet recording apparatus according to the present invention may be used as an image output apparatus for information processing equipment such as a computer, a copying apparatus combined with a reader, or a facsimile apparatus having a transmission / reception function. It may be one taken.

1 is an external perspective view showing an outline of a configuration of an inkjet recording apparatus 1 that is a typical embodiment of the present invention. FIG. 2 is a block diagram illustrating a control configuration of the recording apparatus illustrated in FIG. 1. It is a figure which shows the relationship of the pulse current applied to a heater with respect to the temperature when the discharge amount of ink is stabilized. It is a figure which shows the circuit structure of the head substrate according to Example 1 of this invention. It is a figure which shows the relationship between a constant current source block and the control circuit which controls this. It is a timing chart about the voltage applied to x heaters, and the current supplied paying attention to x heaters accommodated in group 106a. It is a figure which expands one of the constant current sources and shows the voltage applied to each part. It is a figure which shows the temperature dependence of the voltage and electric current of one constant current source. FIG. 6 is a diagram showing a layout of each element mounted on the head substrate according to the first embodiment. It is a figure which shows the circuit structure of the head substrate according to Example 2 of this invention. It is a figure which shows the layout of the head board | substrate shown in FIG. FIG. 5 is a diagram obtained by experimentally determining the relationship between the amount of ink ejected by applying a single pulse to a heater and the pulse application time under a constant temperature. It is a figure which shows the relationship between the pulse application time to a heater, and temperature. It is a figure which shows the circuit structure of the head substrate according to Example 3 of this invention. It is a figure which shows the circuit structure of the head substrate according to Example 4 of this invention.

Explanation of symbols

3 Recording Head 100 Ink Supply Ports 101a1 to 101mx Heaters 102a1 to 102mx Switching Elements 103a to 103m Constant Current Source 104 Voltage Current Conversion Circuit 105 Reference Voltage Circuit 106 Constant Current Source Block 107 Reference Current Circuit 108 Control Circuit

Claims (9)

A head substrate having a plurality of heaters and a plurality of switching elements for driving the plurality of heaters,
A plurality of constant current sources for controlling the plurality of switching elements to drive the plurality of heaters by supplying a constant current;
Each of the plurality of constant current sources includes a circuit that adjusts a value of a constant current supplied from the constant current source depending on a temperature of the head substrate. Each of the plurality of constant current sources includes a MOS transistor,
The circuit includes a temperature dependent diode;
The head substrate according to claim 1, wherein the diode is connected to a source of the MOS transistor.   3. The head substrate according to claim 1, wherein the MOS transistor included in each of the plurality of constant current sources has a characteristic that an output current value increases as the temperature rises. 4.   4. The head substrate according to claim 1, wherein the plurality of constant current sources are disposed in the vicinity of the plurality of heaters and the plurality of switching elements. 5.   The head substrate according to any one of claims 1 to 4, wherein a constant current of a single pulse is supplied to drive the plurality of heaters. A voltage-current conversion circuit that generates a reference current that is a reference of a constant current supplied from each of the plurality of constant current sources;
A reference voltage circuit that generates a reference voltage serving as a reference for generating the reference current;
The head substrate according to claim 5, wherein the reference voltage has temperature dependency.   The head substrate according to claim 6, wherein the reference voltage has a characteristic of increasing with an increase in temperature. A plurality of constant current source blocks having the plurality of heaters, the plurality of switching elements, and the plurality of constant current sources;
Furthermore, a reference current circuit that generates a plurality of different reference currents based on a reference current output from the voltage-current conversion circuit is provided between the plurality of constant current source blocks and the voltage-current conversion circuit,
8. The head substrate according to claim 6, wherein different reference currents are supplied from the reference current circuit to each of the plurality of constant current source blocks.   An ink jet recording head using the head substrate according to claim 1.

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