Drive circuit, inkjet head, and inkjet recording apparatus

Abstract

To widen the output voltage range of a voltage amplification part and to reduce heat generation.SOLUTION: The operational amplifier 101 of the drive circuit 100a amplifies the voltage of the signal Vin. The current amplification unit 180 amplifies the current of the voltage-amplified signal Vin and outputs the amplified current as a signal Vout for driving a load unit for ejecting ink. The bias unit 150 is connected to an output terminal of the operational amplifier 101 and an input terminal of the current amplification unit 180. The bias section 150 outputs the voltage-amplified signal Vin to the current amplification section 180, and outputs a bias voltage for operating the current amplification section 180. The constant current source 160a is connected to the high potential side of the bias unit 150 and outputs a constant current to the bias unit 150. The constant current source 170a is connected to the low potential side of the bias unit 150, and outputs a constant current from the bias unit 150.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] The present invention relates to a drive circuit, an inkjet head, and an inkjet recording apparatus. [Background technology]

[0002] Conventionally, there are known drive circuits that are installed in inkjet recording devices and drive actuators for discharging ink in inkjet heads. For example, a power amplifier circuit is known that includes a voltage amplifier, a bias unit, a constant current source, and a current amplifier (see Patent Document 1). The voltage amplifier is composed of discrete components, such as a resistor and a pair of bipolar transistors, and amplifies the voltage of an input voltage signal. The bias circuit is a circuit that ensures that the transistors in the current amplifier operate at appropriate current and voltage. The constant current circuit is a circuit that supplies a constant current from the positive potential side to the bias circuit.

[0003] A voltage amplifier unit made up of discrete components has a large number of components, a large mounting area, and there is a risk of output offset and temperature drift occurring if there are differences in the characteristics of paired transistors. For this reason, a drive waveform amplifier circuit is known that includes a voltage amplifier unit using an operational amplifier, a bias unit, a current amplifier unit, and two resistors (see Patent Document 2). The two resistors are connected between the high voltage source and the bias unit, and between the ground and the bias unit, respectively. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2002-210958 [Patent Document 2] International Publication No. 2017 / 212865 Summary of the Invention [Problem to be solved by the invention]

[0005] However, conventional drive waveform amplifier circuits require the op-amp to supply current to drive the bias circuit. The output stage of the op-amp's internal equivalent circuit is a pair of bipolar transistors. As the output load current (collector current) Ic increases, the base-emitter voltage Vbe of each transistor in the pair increases. For this reason, the op-amp has the characteristic that the voltage range it can output becomes narrower as the output load current increases.

[0006] If the output voltage range becomes narrow, it becomes impossible to apply the voltage required to the actuator for ejecting ink, and the desired ink ejection characteristics cannot be obtained from the nozzle. Furthermore, the drive circuit is no longer able to output 0 V as a reference voltage, and the voltage floats by several volts. This causes the actuator to constantly have voltage applied to it, causing it to deteriorate. To widen the output voltage range of the drive circuit, the power supply voltage (the difference between the high power supply voltage VCC and the low power supply voltage VEE) can be increased. However, increasing the power supply voltage increases the heat generated by the drive circuit (particularly the pair of transistors in the current amplifier section).

[0007] An object of the present invention is to widen the output voltage range of a voltage amplifier and reduce heat generation. [Means for solving the problem]

[0008] In order to solve the above problem, the driving circuit of the invention described in claim 1 comprises: a voltage amplifier that amplifies the voltage of an input signal; a current amplifier that amplifies the current of the voltage-amplified input signal and outputs it as a drive signal that drives a load unit for ejecting ink; a bias unit connected to an output terminal of the voltage amplifier unit and an input terminal of the current amplifier unit, for outputting the voltage-amplified input signal to the current amplifier unit and outputting a bias voltage for operating the current amplifier unit; a first constant current unit connected to a high potential side of the bias unit and outputting a constant current to the bias unit; and a second constant current unit connected to the low potential side of the bias unit and causing the bias unit to output a constant current.

[0009] The invention described in claim 2 is the drive circuit described in claim 1, The constant current of the first constant current unit is equal to the constant current of the second constant current unit.

[0010] The invention described in claim 3 is the drive circuit described in claim 1, the first constant current unit is a current mirror type constant current source or a constant current source having a diode, a resistor, and a transistor, The second constant current unit is a current mirror type constant current source or a constant current source having a diode, a resistor and a transistor.

[0011] The inkjet head of the invention described in claim 4 comprises: A drive circuit according to any one of claims 1 to 3; The load section.

[0012] The inkjet recording apparatus according to the invention of claim 5 comprises: The inkjet head according to claim 4 is provided.

[0013] The inkjet recording apparatus according to the invention of claim 6 comprises: A drive circuit according to any one of claims 1 to 3; and an inkjet head having the load portion. [Effects of the Invention]

[0014] According to the present invention, the output voltage range of the voltage amplifier can be widened and heat generation can be reduced. [Brief explanation of the drawings]

[0015] [Figure 1] 1 is a diagram showing a schematic configuration of an inkjet recording apparatus according to a first embodiment of the present invention. [Figure 2]FIG. 2 is a schematic diagram illustrating the configuration of a head unit. [Figure 3] FIG. 2 is a block diagram illustrating a functional configuration of the inkjet printing apparatus. [Figure 4] FIG. 2 is a circuit diagram showing a drive circuit according to the first embodiment. [Figure 5] FIG. 1 is a graph showing the collector current versus the base-emitter voltage in a transistor. [Figure 6] 10 is a timing chart showing a drive voltage signal in a drive circuit without a bias unit. [Figure 7] 10 is a timing chart showing signals and bias voltages of transistors in a drive circuit without a constant current source. [Figure 8] FIG. 10 is a circuit diagram showing a drive circuit according to a second embodiment. [Figure 9] FIG. 10 is a block diagram showing the functional configuration of an inkjet recording apparatus according to a third embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0016] Advantages and features provided by one or more embodiments of the present invention will be more fully understood from the following detailed description and the accompanying drawings. However, these drawings are for illustrative purposes only and are not intended to define the limits of the present invention. Hereinafter, embodiments of the present invention will be described with reference to the drawings. However, the scope of the present invention is not limited to the disclosed embodiments.

[0017] (First embodiment) A first embodiment of the present invention will be described with reference to Figures 1 to 7. First, the device configuration of this embodiment will be described with reference to Figures 1 to 4.

[0018] As shown in FIG. 1, the inkjet recording apparatus 1A includes a transport unit 2, a head unit 3, and other components. Also, in FIG. 1, three axes are defined: X, Y, and Z. This also applies to FIG. 2. The transport unit 2 includes two transport rollers 2a and 2b and a ring-shaped transport belt 2c. The transport rollers 2a and 2b rotate around a rotation axis extending in the X-axis direction. The transport belt 2c is supported on its inner side by the transport rollers 2a and 2b. The transport roller 2a rotates in response to the operation of a transport motor (not shown), causing the transport belt 2c to move around the transport rollers 2a and 2b. The transport unit 2 transports the recording medium 4 in the direction of movement of the transport belt 2c, with the recording medium 4 placed on the transport surface of the transport belt 2c. Therefore, the movement direction of the transport belt 2c is the transport direction of the recording medium 4. This transport direction is parallel to the Y-axis direction. Note that the configuration of the transport unit 2 is not limited to that shown in FIG. 1. For example, the transport unit 2 may be configured to have a rotating cylindrical transport drum. In the transport unit 2 configured in this manner, the rotation of the transport drum moves the recording medium 4 placed on the cylindrical surface of the transport drum.

[0019] The recording medium 4 is, for example, a sheet of paper cut to a certain size. The recording medium 4 is supplied onto the conveyor belt 2c by a paper feeder (not shown). An image is recorded on the recording medium 4 by ejecting ink from the head unit 3 onto the recording medium 4. Roll paper may also be used as the recording medium 4. The material of the recording medium 4 is not particularly limited as long as it is possible to fix the ink that has landed on the surface. For example, the recording medium 4 may be paper such as plain paper or coated paper, fabric, or sheet-like resin.

[0020] The head units 3 eject ink at appropriate timing based on image data onto the recording medium 4 transported by the transport unit 2. In this way, the head units 3 record an image on the recording medium 4. The inkjet recording apparatus 1A is equipped with four head units 3, one for each of the four colors of ink: yellow (Y), magenta (M), cyan (C), and black (K). The head units 3 are arranged so that the ink ejection direction is vertically downward (-Z direction).

[0021] Fig. 2 is a plan view of the head unit 3 as seen from the side facing the transport surface of the transport belt 2c. As shown in Fig. 2, the head unit 3 has a plate-shaped support portion 3a and multiple inkjet heads 10A. The multiple inkjet heads 10A are fixed to the support portion 3a in a state where they fit into through holes in the support portion 3a. The inkjet heads 10A are fixed to the support portion 3a in a state where their ink ejection surfaces are exposed from the through holes in the support portion 3a toward the transport belt 2c. The ink ejection surfaces of the inkjet heads 10A have openings for the nozzles 5.

[0022] The inkjet head 10A has a plurality of nozzles 5 that are arranged at equal intervals in the X-axis direction. In this embodiment, each inkjet head 10A has nozzle rows 51, 52, 53, and 54. Each of the nozzle rows 51 to 54 is made up of nozzles 5 that are arranged one-dimensionally at equal intervals in the X-axis direction. The nozzle rows 51 to 54 are arranged such that the positions of the nozzles 5 in the X-axis direction are shifted from each other so that they do not overlap. In this embodiment, each nozzle row has 256 nozzles 5. However, the number of nozzles 5 that make up a nozzle row is not limited to this. Furthermore, the number of nozzle rows that the inkjet head 10A has is not limited to four, and may be three or less or five or more.

[0023] The inkjet head 10A has an ejection mechanism for ejecting ink droplets from each nozzle 5. The ejection mechanism includes a channel (ink flow path) that communicates with the nozzle 5 and supplies ink to the nozzle 5, and an actuator 12 (FIG. 3) that acts as a load and applies pressure changes to the ink in the channel. The actuator 12 is a piezoelectric element, such as PZT (lead zirconate titanate). When a predetermined voltage is applied to the actuator 12 via electrode films provided on both sides of the actuator 12, the actuator 12 bends and deforms, applying a pressure change to the ink in the channel. The actuator 12 is a capacitive load that charges and discharges during its bending deformation. The actuator 12 may deform in a shear mode or a bend mode. When a predetermined drive voltage signal is applied to the actuator 12, ink droplets are ejected from the nozzle 5 in response to a series of pressure changes caused by the drive voltage signal. The driving voltage signal is composed of one or more trapezoidal pulse voltage signals having a predetermined voltage and duration.

[0024] In the head unit 3, the multiple inkjet heads 10A are arranged in a staggered pattern so that the arrangement range of the nozzles 5 in the X-axis direction is continuous. The arrangement range of the nozzles 5 included in the head unit 3 in the X-axis direction covers the width of the area of ​​the recording medium 4 in the X-axis direction on which an image can be recorded. The head unit 3 is used in a fixed position when forming an image. The head unit 3 forms an image by a single pass method by ejecting ink from the nozzles 5 to each position at a predetermined interval in the transport direction as the recording medium 4 is transported.

[0025] 3, the inkjet recording apparatus 1A includes a main body control unit 30, an inkjet head 10A, a head drive control unit 20A, a transport control unit 41, a communication unit 42, and an operation display unit 43. The various units of the inkjet recording apparatus 1A are connected via a bus 44 so as to be able to send and receive signals.

[0026] The main body control unit 30 controls the overall operation of the inkjet recording apparatus 1 A. The main body control unit 30 includes a CPU (Central Processing Unit) 31, a RAM (Random Access Memory) 32, a storage unit 33, and the like.

[0027] The CPU 31 performs various calculation processes. The CPU 31 reads out a control program stored in the storage unit 33, loads it into the RAM 32, and executes various processes in cooperation with the loaded program. The CPU 31 performs various control processes related to image recording and its settings.

[0028] The RAM 32 provides a working memory space for the CPU 31 and stores temporary data. The storage unit 33 includes a non-volatile memory that stores control programs, setting data, etc. The storage unit 33 may also include a DRAM (Dynamic RAM) that temporarily stores settings related to print jobs acquired from the outside via the communication unit 42, image data to be recorded, etc.

[0029] The head drive control unit 20A outputs a drive voltage signal at an appropriate timing according to each pixel data of the image data to be recorded. The drive voltage signal is a voltage signal that drives the actuator 12 of the inkjet head 10A. The head drive control unit 20A includes a head control unit 21, a DAC (Digital to Analog Converter) 22, a drive circuit 100a, etc. The components of the head drive control unit 20A may be arranged together on a substrate, or may be distributed throughout the inkjet recording apparatus 1A.

[0030] The head control unit 21 controls the operation of the head drive control unit 20A depending on whether or not there is image data to be recorded and the content of the image data. The head control unit 21 includes a CPU 211, a storage unit 212, etc. The head control unit 21 may be provided in common with the main body control unit 30.

[0031] The storage unit 212 stores waveform pattern data 2121, which includes information on drive waveform patterns for ejecting ink from the nozzles 5 and vibrating the meniscus. The waveform pattern data 2121 stores drive waveform patterns as digital discrete value array data. The storage unit 212 uses a nonvolatile memory such as a ROM (Read Only Memory) or a rewritable and updatable flash memory.

[0032] The CPU 211 selects an appropriate waveform pattern and outputs the data based on the image data to be recorded that is stored in the storage unit 212 or the storage unit 33. The waveform pattern is selected so that a drive voltage signal of an appropriate waveform pattern is output by the head drive control unit 20A depending on whether or not ink is to be ejected from each nozzle 5. The CPU 211 outputs the waveform pattern data at an appropriate timing according to a clock signal (not shown).

[0033] The DAC 22 converts into an analog input voltage signal the drive waveform signal (waveform pattern data) output at a predetermined clock frequency from the head control unit 21. The DAC 22 outputs the obtained input voltage signal to the drive circuit 100a.

[0034] The drive circuit 100a converts the analog input voltage signal input from the DAC 22 into a drive voltage signal and outputs it to the inkjet head 10A. The configuration of the drive circuit 100a will be described in detail later.

[0035] The inkjet head 10A includes the above-described ejection mechanism including an ejection selection switching element 11 and an actuator 12. The ejection selection switching element 11 selects the actuator 12 to which the drive voltage signal supplied from the drive circuit 100a is applied at each ejection timing based on the image data to be recorded. In other words, the ejection selection switching element 11 selects the nozzle 5 that will eject ink. Specifically, the ejection selection switching element 11 switches the connection state of the circuit between the drive circuit 100a and each actuator 12 so that the drive voltage signal is selectively supplied to the actuator 12 corresponding to the nozzle 5 that will eject ink at each ejection timing. A small-amplitude voltage signal that vibrates the ink meniscus may be applied to the actuator 12 corresponding to the nozzle 5 that will not eject ink. The ink meniscus is the ink liquid surface in the nozzle 5. The ejection selection switching element 11 repeatedly selects the actuator 12 to be driven at each ejection timing. As a result, ink is ejected from the nozzle 5 to an ejection position according to the image data, forming an image.

[0036] The transport control unit 41 rotates the transport roller 2a by operating a motor that rotates the transport roller 2a. As a result, the transport control unit 41 moves the recording medium 4 at an appropriate timing and speed using the transport belt 2c. The transport control unit 41 may have the same configuration as the main body control unit 30.

[0037] The communication unit 42 transmits and receives data to and from external devices in accordance with a predetermined communication standard. The communication unit 42 includes, for example, a connection terminal related to the communication standard to be used, and hardware such as a network card for a driver related to the communication connection.

[0038] The operation display unit 43 displays status information and menus related to image recording in response to instructions from the main body control unit 30. The operation display unit 43 also accepts input operations from the user. The operation display unit 43 has a display panel such as an LCD (Liquid Crystal Display) or ELD (Electro-Luminescent Display), and a touch panel. The touch panel is integrally provided on the display panel. The operation display unit 43 outputs an operation detection signal to the main body control unit 30 according to the position where the user has performed a touch operation and the type of operation.

[0039] As shown in FIG. 4, the drive circuit 100a includes an operational amplifier 101, resistors 111, 112, and 115, a bias unit 150, constant current sources 160a and 170a, and a current amplifier 180. The constant current sources 160a and 170a function as a first constant current unit and a second constant current unit, respectively. The bias unit 150 includes resistors 118 and 119 and a transistor 135. The constant current source 160a includes resistors 113 and 114 and transistors 131 and 132. The constant current source 170a includes resistors 116 and 117 and transistors 133 and 134. The current amplifier 180 includes resistors 120, 121, 122, and 123 and transistors 136, 137, 138, and 139.

[0040] The operational amplifier 101 is a circuit element that functions as a differential amplifier circuit, which is a voltage amplifier. The positive power supply terminal of the operational amplifier 101 is connected to a high voltage source of a high power supply voltage VCC. The negative power supply terminal of the operational amplifier 101 is connected to a low voltage source of a low power supply voltage VEE (<reference voltage 0 [V]). The high power supply voltage VCC is greater than the low power supply voltage VEE. Note that the low power supply voltage VEE may be configured to be a positive power supply voltage lower than the high power supply voltage VCC or to be the reference voltage 0 [V]. The non-inverting input terminal of the operational amplifier 101 is connected to the output terminal of the DAC 22. The inverting input terminal of the operational amplifier 101 is connected to resistors 111 and 112. The resistors 111 and 112 are voltage-dividing resistors that divide the feedback signal of the signal Vout. One end of the resistor 112 is connected to the output terminal of the current amplifier 180. The other end of the resistor 112 is connected to the resistor 111 and the inverting input terminal of the operational amplifier 101. One end of the resistor 111 is connected to the resistor 112 and the inverting input terminal of the operational amplifier 101. The other end of the resistor 111 is connected to the ground.

[0041] That is, the operational amplifier 101 receives the signal Vin at its non-inverting input terminal and receives the feedback signal voltage-divided by resistors 111 and 112 at its inverting input terminal. The signal Vin is an input voltage signal input from the DAC 22. The signal Vout is a drive voltage signal output from the drive circuit 100a to the ejection selection switching element 11. The operational amplifier 101 amplifies the voltage difference between the signal Vin and the voltage-divided feedback signal, and outputs it as a signal Vop.

[0042] The bias unit 150 is a circuit that outputs a signal Vop to the current amplifier unit 180 and causes the transistors 136 to 139 of the current amplifier unit 180 to operate at an appropriate voltage. One end of the resistor 118 is connected to the constant current source 160a and the high-potential output terminal of the bias unit 150. The other end of the resistor 118 is connected to the resistor 119 and the transistor 135. One end of the resistor 119 is connected to the resistor 118 and the transistor 135. The other end of the resistor 119 is connected to the output terminal of the operational amplifier 101, the constant current source 170a, and the low-potential output terminal of the bias unit 150.

[0043] The transistor 135 is an NPN bipolar transistor. The base of the transistor 135 is connected to resistors 118 and 119. The collector of the transistor 135 is connected to the high-potential output terminal of the bias unit 150, the resistor 118, and a constant current source 160a. The emitter of the transistor 135 is connected to the low-potential output terminal of the bias unit 150, the resistor 119, and a constant current source 170a. The output terminal of the operational amplifier 101 may be connected to the resistor 118, the constant current source 160a, and the collector of the transistor 135.

[0044] The constant current source 160a is a current mirror type constant current source that supplies a constant current from the high potential side to the bias unit 150. One end of the resistor 113 is connected to a high voltage source. The other end of the resistor 113 is connected to a transistor 131. One end of the resistor 114 is connected to the high voltage source. The other end of the resistor 114 is connected to a transistor 132. The transistors 131 and 132 are each a PNP type bipolar transistor. The base of the transistor 131 is connected to the emitter and the base of the transistor 132. The emitter of the transistor 131 is connected to the resistor 113. The collector of the transistor 131 is connected to the base and is connected to the constant current source 170a (transistor 133) via the resistor 115. The base of the transistor 132 is connected to the base and collector of the transistor 131. The emitter of the transistor 132 is connected to the resistor 114. The collector of transistor 132 is connected to resistor 118 and the collector of transistor 135 .

[0045] The constant current source 170a is a current mirror type constant current source that outputs a constant current from the low potential side to the bias unit 150. One end of the resistor 116 is connected to the low voltage source. The other end of the resistor 116 is connected to the transistor 133. One end of the resistor 117 is connected to the low voltage source. The other end of the resistor 117 is connected to the transistor 134. The transistors 133 and 134 are each an NPN type bipolar transistor. The base of the transistor 133 is connected to the collector and the base of the transistor 134. The collector of the transistor 133 is connected to the base and is connected to the constant current source 160a (the collector of the transistor 131) via the resistor 115. The emitter of the transistor 133 is connected to the resistor 116. The base of the transistor 134 is connected to the base of the transistor 133. The collector of the transistor 134 is connected to the resistor 119 and the emitter of the transistor 135. The emitter of transistor 134 is connected to resistor 117 .

[0046] The current amplifier 180 is a circuit that amplifies the current of the signal Vop. The transistor 136 is an NPN bipolar transistor. The base of the transistor 136 serves as the high-potential input terminal of the current amplifier 180 and is connected to the high-potential output terminal (collector of the transistor 135) of the bias unit 150. The collector of the transistor 136 is connected to a high-voltage source. The emitter of the transistor 136 is connected to the transistor 138 and, via the resistors 120 and 121, to the transistor 137. Note that the current amplifier 180 may be configured without the resistors 120 and 121.

[0047] The transistor 137 is a PNP bipolar transistor. The transistors 136 and 137 form a transistor pair. The base of the transistor 137 serves as the low-potential input terminal of the current amplifier 180 and is connected to the low-potential output terminal (the emitter of the transistor 135) of the bias unit 150. The emitter of the transistor 137 is connected to the transistor 139 and, via the resistors 121 and 120, to the emitter of the transistor 136. The collector of the transistor 137 is connected to a low-voltage source.

[0048] Transistor 138 is an NPN bipolar transistor. The base of transistor 138 is connected to the emitter of transistor 136 and resistor 120. The collector of transistor 138 is connected to a high voltage source. The emitter of transistor 138 is connected to transistor 139 via resistors 122 and 123.

[0049] The transistor 139 is a PNP-type bipolar transistor. The transistors 138 and 139 form a transistor pair. The base of the transistor 139 is connected to the emitter of the transistor 137 and the resistor 121. The emitter of the transistor 139 is connected to the emitter of the transistor 138 via the resistors 123 and 122. The collector of the transistor 139 is connected to a low-voltage source. The resistors 122 and 123 are connected to the output terminal of the current amplifier 180.

[0050] The overall operation of the drive circuit 100a will be briefly summarized below. First, the input voltage signal output from the DAC 22 is input to the operational amplifier 101 as the signal Vin. The operational amplifier 101 amplifies the difference between the signal Vin and the divided voltage signal of the signal Vout, and outputs the result as the signal Vop to the bias unit 150. The bias unit 150 receives a constant current from constant current sources 160a and 170a. The bias unit 150 outputs the signal Vop to the current amplifier 180. The bias unit 150 also outputs a bias voltage to the current amplifier 180 that appropriately adjusts the base-emitter voltage Vbe to operate the transistors 136 to 139 of the current amplifier 180. The current amplifier 180 amplifies the current of the signal Vop and outputs it to the ejection selection switching element 11 as the signal Vout (drive voltage signal).

[0051] The current amplifier 180 has a two-stage configuration, consisting of a stage made up of transistors 136 and 137 and a stage made up of transistors 138 and 139. Each stage amplifies the current of the input signal. Because the current amplifier 180 has a two-stage configuration, it can achieve a higher current amplification degree than a current amplifier with a single stage configuration. However, the current amplifier 180 is not limited to the circuit configuration shown in FIG. 4. For example, the current amplifier 180 may have one or three or more stages. Furthermore, the current amplifier 180 may be configured to use unipolar transistors such as FETs (Field Effect Transistors) instead of bipolar transistors.

[0052] Next, the function of each part of the drive circuit 100a will be described with reference to Figs. 5 to 7. Fig. 5 is a diagram showing the collector current Ic versus the base-emitter voltage Vbe in a transistor. Fig. 6 is a timing chart showing a drive voltage signal in the drive circuit 100a that does not have the bias unit 150. Fig. 7 is a timing chart showing the signal Vop and the bias voltage (Vc-Ve) of the transistor 135 in the drive circuit 100a that does not have the constant current sources 160a and 170a.

[0053] First, the function of the bias unit 150 in the drive circuit 100a will be described. The transistors used in the drive circuit 100a have a collector current Ic [mA] characteristic versus base-emitter voltage Vbe (hereinafter referred to as voltage Vbe) [V], as shown in FIG. 5, for example. The characteristic curves in FIG. 5 are for temperatures Tc=25 and 100°C. The collector current Ic is the current flowing between the collector and emitter of a transistor. If the temperature Tc=25°C, the transistors 136 to 139 used in the current amplifier 180 will not operate (collector current Ic>0) ​​unless a voltage Vbe of approximately 0.6 V is applied.

[0054] If Vbe of transistors 136 to 139 is 0.6 [V], the collector voltage Vc minus the emitter voltage Ve of transistor 135 (hereinafter referred to as bias voltage (Vc-Ve)) is 2.4 [V]. The bias voltage (Vc-Ve) of transistor 135 can be adjusted by the resistance values ​​of resistors 118 and 119. First, the voltage Vbe of transistor 135 is set to 0.6 [V]. Here, the resistance values ​​of resistors 118 and 119 are R118 and R119, respectively. The voltage applied to resistor 119 is 0.6 [V].

[0055] The current I1 flowing through resistors 118 and 119 in order is I1 = 0.6 [V] / (R119). The voltage across resistor 118 is I1 × (R118). The bias voltage of transistor 135 is (Vc - Ve) = 0.6 [V] + I1 × (R118). In this way, the resistance values ​​R118 and R119 are set so that the bias voltage (Vc - Ve) of transistor 135 is, for example, 2.4 [V].

[0056] Let us now consider a drive circuit 100a that does not include the bias unit 150 and the constant current sources 160a and 170a. In other words, the output terminal of the operational amplifier 101 is directly connected to the bases of the transistors 136 and 137 of the current amplifier 180. As shown in FIG. 6, the operational amplifier 101 outputs the drive waveform of the signal Vop, indicated by the solid line. The current amplifier 180, which does not include the bias unit 150, outputs the signal Vout, indicated by the dashed-dotted line, in response to the drive waveform of the signal Vop. At the beginning of the rising and falling edges of the drive waveform of the signal Vop, the voltage Vbe becomes less than 0.6 V, creating regions in which the transistor 135 does not operate. The regions in which the transistor 135 does not operate are the region from time t1 to time t2 and the region from time t3 to time t4. During the falling edge of the signal Vout after time t2, the low-side transistors 137 and 139 operate. During the rising edge of the signal Vout after time t4, the high-side transistors 136 and 138 are activated. As a result, the drive waveform of the signal Vout is distorted at the point where it switches to the active region, resulting in a deterioration in the waveform quality of the drive waveform of the signal Vout.

[0057] In the driving circuit 100a of this embodiment, the bias voltage (Vc-Ve) of the bias unit 150 keeps the transistors 136-139 of the current amplifier unit 180 always in their operating range. This eliminates distortion in the driving waveform of the signal Vout. For example, when the voltage of the signal Vout is 20 V, the voltage Vbe of the transistors 136-139 is 0.6 V, and the bias voltage (Vc-Ve) of the transistor 135 is 2.4 V. The voltage at the high-potential output terminal of the bias unit 150 is 21.2 V, and the voltage at the low-potential output terminal is 18.8 V.

[0058] Next, the function of the constant current sources 160a and 170a will be explained. Consider a driver circuit 100a in which a resistor is provided instead of the constant current source 160a, and the constant current source 170a is not provided. The resistor supplies current to the bias unit 150. Specifically, one end of the resistor is connected to a high-voltage source, and the other end is connected to the resistor 118 and the emitter of the transistor 135. The resistor is not a constant current source. Therefore, fluctuations in the signal Vop from the operational amplifier 101 also cause fluctuations in the bias voltage (Vc-Ve) of the transistor 135 in the bias unit 150. For example, consider the signal Vop, which starts rising at time t11 and finishes falling at time t12, as shown in FIG. 7. In response to the signal Vop, the bias voltage (Vc-Ve) of the transistor 135 fluctuates from time t11 to time t12. If the bias voltage (Vc-Ve) becomes larger than necessary, a through current I2 flows through the transistors 138 and 139 of the current amplifier 180, causing the transistors 138 and 139 to generate unnecessary heat.

[0059] In the drive circuit 100a of this embodiment, the bias unit 150 is operated by constant current sources 160a and 170a, so that the bias voltage (Vc-Ve) of the transistor 135 does not fluctuate. As a result, waveform distortion and unnecessary through current I2 are eliminated, and heat generation in the transistors 138 and 139 is also reduced.

[0060] Next, the function of resistors 122 and 123 of the current amplifier 180 will be explained. Let us consider a driver circuit 100a that does not have resistors 122 and 123. First, we will explain the initial state of operation of the driver circuit 100a that does not have resistors 122 and 123 (initial first operation). Assume that the temperature of transistors 138 and 139 is 25°C. The collector current Ic-voltage Vbe characteristics of transistors 138 and 139 are represented by the characteristic curve shown in Figure 5 for Tc = 25°C. The bias voltage (Vc-Ve) of transistor 135 is set to 2.4V. The voltage Vbe of transistors 138 and 139 (and transistors 136 and 137) is 0.6V. The operating point at the initial stage of first operation is indicated by the solid arrow in Figure 5. Almost no through current I2 (collector current Ic) flows through transistors 138 and 139.

[0061] The operating state (referred to as the first operation) of the driver circuit 100a without resistors 122 and 123 will now be described. When the driver circuit 100a without resistors 122 and 123 starts operating due to the input of an input voltage signal, the temperature of the transistors 138 and 139 rises. Assume that the temperature of the transistors 138 and 139 reaches, for example, 100°C. The transistors 138 and 139 then have a characteristic curve for temperature Tc=100°C, as shown in FIG. 5. The voltage Vbe of the transistors 138 and 139 is 0.6V. Therefore, the collector current Ic (through current I2) of the transistors 138 and 139 is approximately 200mA, as shown in FIG. 5. When the through current I2 flows, the transistors 138 and 139 further heat up. As the transistors 138 and 139 heat up, the through current I2 further flows. In this way, the flow of the through current I2 and the generation of heat by the transistors 138 and 139 are repeated, and the transistors 138 and 139 eventually self-destruct (thermal runaway).

[0062] The initial stage of operation (initial stage of second operation) of the drive circuit 100a of this embodiment is similar to the initial stage of the first operation of the drive circuit 100a without the resistors 122 and 123. The operating state of the drive circuit 100a of this embodiment (hereinafter referred to as the second operation) will be described. Assume that the drive circuit 100a with the resistors 122 and 123 starts operating, and the temperature of the transistors 138 and 139 rises to, for example, 100°C. According to the characteristic curve for temperature Tc = 100°C in Figure 5, a collector current Ic (through current I2) flows through the transistors 138 and 139. The flow of the through current I2 causes a voltage drop (for example, 0.2 V) across the resistors 122 and 123. Due to the 0.2 V voltage drop across the resistors 122 and 123, the voltage Vbe across the transistors 138 and 139 becomes 0.4 V. In this way, the voltage applied to the transistors 138 and 139 is reduced due to the through current I2 and the voltage drop across the resistors 122 and 123. The operating points of the transistors 138 and 139 are indicated by the dashed arrows in the second operation in Figure 5. This makes it possible to suppress the through current I2 and to prevent thermal runaway of the transistors 138 and 139.

[0063] Regarding the method for determining the bias voltage (Vc-Ve), if the bias voltage (Vc-Ve) is set too high, a through current I2 will flow, causing thermal runaway. On the other hand, if the bias voltage (Vc-Ve) is set too low, the drive waveform of the signal Vout will be distorted, resulting in poor waveform quality. For this reason, the bias voltage (Vc-Ve) is set to a value that allows acceptable waveform quality without causing thermal runaway, and is generally set to about 1.2 to 2.4 [V]. In this embodiment, the bias voltage (Vc-Ve) is set to 2.4 [V].

[0064] Next, the function of constant current sources 160a and 170a will be explained. As shown in Figure 4, current I3 is a current that flows in order through resistor 113, the emitter and collector of transistor 131, resistor 115, the collector and emitter of transistor 131, and resistor 116. Current I4 is a current that flows in order through resistor 114, the emitter and collector of transistor 132. Current I5 is a current that flows in order through the collector and emitter of transistor 134 and resistor 117.

[0065] First, the resistance values ​​of resistors 113, 114, 116, and 117 are R113, R114, R116, and R117, respectively. Current mirror constant current source 160a generates current I4, which is an output current equal to current I3, which is a reference current. Current I3 is calculated using the following equation (1): I3=(VCC-VEE-Vbe1-Vbe2) / (R113+R115+R116) …(1) Here, the voltage Vbe1 is the voltage Vbe of the transistor 131. The voltage Vbe2 is the voltage Vbe of the transistor 132.

[0066] Here, the voltage applied to resistor 113 is V113. V113=I3×R113. The current I4 on the high potential side is calculated by the following equation (2). I4={(Vbe1+V113)-Vbe1)} / R114 =V113 / R114 =(I3×R113) / R114 …(2) Here, if R113=R114, then I3=I4.

[0067] Current mirror type constant current source 170a generates current I5, which is an output current equal to current I3, which is a reference current. Here, the voltage applied to resistor 116 is voltage V116. V116 = I3 × R116. Current I5 on the low potential side is calculated using the following equation (3). I5={(Vbe2+V116)-Vbe2)} / R117 =V116 / R117 =(I3×R116) / R117 …(2) Here, if R116=R117, then I3=I5.

[0068] The components of the constant current sources 160a and 170a are selected so that I4 = I5 (= I3). As a result, the current I4 from the constant current source 160a flows entirely to the constant current source 170a as current I5, and no current flows to the operational amplifier 101. This prevents the operational amplifier 101 from increasing its output load current and widens its output voltage range. A wider output voltage range allows the necessary voltage to be applied to the actuator 12, achieving the desired ink ejection characteristics in the nozzle. Furthermore, the reference voltage 0 [V] is included in the output voltage range, preventing deterioration of the actuator 12. Furthermore, since the difference between the high power supply voltage VCC and the low power supply voltage VEE does not need to be widened, heat generation in the drive circuit 100a (particularly transistors 138 and 139) can be reduced. The bias section drive current I0 is comprised of current I4, the collector current of transistor 135, and current I5.

[0069] As described above, according to this embodiment, the drive circuit 100a includes an operational amplifier 101, a current amplifier 180, a bias unit 150, and constant current sources 160a and 170a. The operational amplifier 101 amplifies the voltage of the signal Vin. The current amplifier 180 amplifies the current of the voltage-amplified signal Vin and outputs it as a signal Vout that drives the actuator 12 to eject ink. The bias unit 150 is connected to the output terminal of the operational amplifier 101 and the input terminal of the current amplifier 180. The bias unit 150 outputs a signal Vop, which is the voltage-amplified signal Vin, to the current amplifier 180. At the same time, the bias unit 150 outputs a bias voltage (Vc-Ve) that operates the current amplifier 180 to the current amplifier 180. The constant current source 160a is connected to the high-potential side of the bias unit 150 and outputs a constant current to the bias unit 150. The constant current source 170a is connected to the low potential side of the bias unit 150, and causes the bias unit 150 to output a constant current.

[0070] Therefore, the bias unit 150 is driven by a constant current flowing between the constant current sources 160a and 170a, so no current flows through the operational amplifier 101, widening the output voltage range. As a result, the output voltage range of the operational amplifier 101 is widened, so the necessary voltage can be applied to the actuator 12, and the desired ink ejection characteristics can be obtained from the nozzle. Furthermore, deterioration of the actuator 12 can be prevented, and heat generation from the drive circuit 100a can be reduced.

[0071] The constant current (current I4) of constant current source 160a is equal to the constant current (current I5) of constant current source 170a. Therefore, constant current is exchanged between constant current sources 160a and 170a, which makes it possible to further widen the output voltage range of operational amplifier 101, further prevent deterioration of actuator 12, and further reduce heat generation in drive circuit 100a.

[0072] The constant current source 160a is a current mirror type constant current source. The constant current source 170a is a current mirror type constant current source. Therefore, the constant current sources 160a and 170a can be easily configured.

[0073] The inkjet recording apparatus 1A includes a drive circuit 100a and an inkjet head 10A having an actuator 12. This makes it possible to widen the output voltage range of the operational amplifier 101, reduce heat generation in the drive circuit 100a, and simplify the configuration of the inkjet head 10A.

[0074] (Second embodiment) A second embodiment of the present invention will be described with reference to Fig. 8. Fig. 8 is a circuit diagram showing a drive circuit 100b.

[0075] The device configuration of this embodiment is the same as that of the inkjet recording apparatus 1A of the first embodiment, except that the drive circuit 100a is replaced with a drive circuit 100b. Therefore, the following mainly describes the parts that are different from the inkjet recording apparatus 1A of the first embodiment, and the same parts are denoted by the same reference numerals and their description will be omitted.

[0076] 8, the drive circuit 100b includes an operational amplifier 101, resistors 111, 112, and 115, a bias unit 150, constant current sources 160b and 170b, and a current amplifier unit 180. The constant current source 160b includes diodes 191 and 192, a resistor 124, and a transistor 140. The constant current source 170b includes diodes 193 and 194, a resistor 125, and a transistor 141.

[0077] The constant current source 160b is a constant current source that includes a diode, a resistor, and a transistor and supplies a constant current from the high potential side to the bias unit 150. The anode of the diode 191 is connected to the high voltage source. The cathode of the diode 191 is connected to the diode 192. The anode of the diode 192 is connected to the cathode of the diode 191. The cathode of the diode 192 is connected to the resistor 115 and the transistor 140. One end of the resistor 124 is connected to the high voltage source. The other end of the resistor 124 is connected to the transistor 140. The transistor 140 is a PNP-type bipolar transistor. The base of the transistor 140 is connected to the cathode of the diode 192 and the resistor 115. The emitter of the transistor 140 is connected to the resistor 124. The collector of the transistor 140 is connected to the resistor 118, the collector of the transistor 135, and the base of the transistor 136.

[0078] The constant current source 170b is a constant current source that includes a diode, a resistor, and a transistor and outputs a constant current from the low potential side to the bias unit 150. The anode of the diode 193 is connected to the resistor 115 and the transistor 141. The cathode of the diode 193 is connected to the diode 194. The anode of the diode 194 is connected to the cathode of the diode 193. The cathode of the diode 194 is connected to the low voltage source. The transistor 141 is an NPN bipolar transistor. The base of the transistor 141 is connected to the resistor 115 and the anode of the diode 193. The collector of the transistor 141 is connected to the output terminal of the operational amplifier 101, the resistor 119, the emitter of the transistor 135, and the base of the transistor 137. The emitter of the transistor 141 is connected to the resistor 125. One end of the resistor 125 is connected to the emitter of the transistor 141. The other end of the resistor 125 is connected to a low voltage source.

[0079] Next, the functions of constant current sources 160b and 170b will be explained. As shown in Fig. 8, current I6 is a current that flows sequentially through resistor 124, the emitter, and the collector of transistor 140. Current I7 is a current that flows sequentially through the collector and emitter of transistor 141, and resistor 125.

[0080] First, let Vf be the voltage due to the voltage drop across each of diodes 191 to 194. Let Vbe be Vbe3 and Vbe4 for transistors 140 and 141, respectively. Let R124 and R125 be the resistance values ​​of resistors 124 and 125, respectively. Current I6 is calculated using the following equation (3). I6=(2×Vf-Vbe3) / R124 …(3) The current I7 is calculated by the following equation (4). I7=(2×Vf-Vbe4) / R125 …(4)

[0081] The components of the constant current sources 160b and 170b are selected so that I6 = I7. As a result, the current I6 from the constant current source 160b flows entirely to the constant current source 170b as the current I7, and no current flows to the operational amplifier 101. This prevents the output load current of the operational amplifier 101 from increasing, and the output voltage range is also widened. The wide output voltage range allows the necessary voltage to be applied to the actuator 12, thereby achieving the desired ink ejection characteristics in the nozzles. This also prevents deterioration of the actuator 12 and reduces heat generation in the drive circuit 100b (particularly the transistors 138 and 139). The constant current sources 160b and 170b have the same characteristics and cost as the constant current sources 160a and 170a of the first embodiment.

[0082] As described above, according to this embodiment, the constant current source 160a is a constant current source having diodes 191 and 192, a resistor 124, and a transistor 140. The constant current source 170a is a constant current source having diodes 193 and 194, a resistor 125, and a transistor 141. Therefore, the same effects as those of the drive circuit 100a of the first embodiment can be achieved, and the constant current sources 160b and 170b can be easily configured.

[0083] (Third embodiment) A third embodiment of the present invention will be described with reference to Fig. 9. Fig. 9 is a block diagram showing the functional configuration of an inkjet recording apparatus 1B.

[0084] As shown in FIG. 9, the configuration of the apparatus of this embodiment is an inkjet recording apparatus 1B. Inkjet recording apparatus 1B has a configuration in which inkjet head 10A in inkjet recording apparatus 1A of the first embodiment is replaced with inkjet head 10B. Furthermore, inkjet recording apparatus 1B has a configuration in which head drive control unit 20A is replaced with head drive control unit 20B. Therefore, the following mainly describes the parts that are different from inkjet recording apparatus 1A of the first embodiment, and the same parts are denoted by the same reference numerals and their description will be omitted.

[0085] The head drive control unit 20B has a head control unit 21. The inkjet head 10B has a DAC 22, a drive circuit 100a, an ejection selection switching element 11, and an actuator 12. Since the head drive control unit 20B does not have the DAC 22 or drive circuit 100a, the configuration is simplified. Note that the head drive control unit 20B may have the DAC 22 and part of the drive circuit 100a, and the inkjet head 10B may have the remaining part of the drive circuit 100a. Part of the drive circuit 100a is an operational amplifier 101, etc.

[0086] As described above, according to this embodiment, the inkjet recording apparatus 1B includes an inkjet head 10B having a drive circuit 100a and an actuator 12. This makes it possible to widen the output voltage range of the operational amplifier 101, reduce heat generation in the drive circuit 100a, and simplify the configuration of the head drive control unit 20B.

[0087] The above-described embodiment is merely an example of the drive circuit, inkjet head, and inkjet recording apparatus according to the present invention, and is not intended to limit the scope of the present invention.

[0088] A configuration may be adopted in which at least two of the configurations of the first to third embodiments are combined. For example, in the drive circuit 100a, the constant current sources 160a and 170a may be replaced with constant current sources 160a and 170b, or constant current sources 160b and 170a. These configurations will achieve the same characteristics and effects as the drive circuit 100a (constant current sources 160a and 170a). Furthermore, the constant current sources used in the drive circuits 100a and 100b are not limited to current mirror types or diode types (constant current sources 160b and 170a), and other types of constant current sources may be used.

[0089] Although embodiments of the present invention have been described and illustrated in detail, the disclosed embodiments are made for purposes of illustration and example only, and not limitation, and the scope of the present invention should be construed by the terms of the appended claims. [Explanation of symbols]

[0090] 1A, 1B Inkjet recording device 2a, 2b Conveyor rollers 2c Conveyor belt 3 Head Unit 3a Support part 4. Recording media 5 nozzles 51, 52, 53, 54 nozzle rows 30 Main unit control section 31 CPU 32 RAM 33 Storage section 10A, 10B inkjet head 11 Discharge selection switching element 12 Actuators 20A, 20B Head drive control section 21 Head control unit 211 CPU 212 Storage section 22 DAC 100a, 100b drive circuit 101 Operational Amplifier 111,112,113,114,115,116,117,118,119,120,121,122,123,124,125 Resistance 150 Bias section 160a,170a,160b,170b Constant current source 180 Current Amplifier 131,132,133,134,135,136,137,138,139,140,141 Transistors 191,192,193,194 Diodes 41 Transport control unit 42 Communications Department 43 Operation display section 44 Bus

Claims

1. a voltage amplifier that amplifies the voltage of an input signal; a current amplifier that amplifies the current of the voltage-amplified input signal and outputs it as a drive signal that drives a load unit for ejecting ink; a bias unit connected to an output terminal of the voltage amplifier unit and an input terminal of the current amplifier unit, for outputting the voltage-amplified input signal to the current amplifier unit and outputting a bias voltage for operating the current amplifier unit; a first constant current unit connected to a high potential side of the bias unit and outputting a constant current to the bias unit; a second constant current unit connected to the low potential side of the bias unit and causing the bias unit to output a constant current;

2. 2. The drive circuit according to claim 1, wherein the constant current of the first constant current unit is equal to the constant current of the second constant current unit.

3. the first constant current unit is a current mirror type constant current source or a constant current source having a diode, a resistor, and a transistor, 2. The drive circuit according to claim 1, wherein the second constant current unit is a current mirror type constant current source or a constant current source having a diode, a resistor, and a transistor.

4. A drive circuit according to any one of claims 1 to 3; an inkjet head comprising the load portion.

5. An inkjet recording apparatus comprising the inkjet head according to claim 4.

6. A drive circuit according to any one of claims 1 to 3; an inkjet head having the load portion;

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