JP6217734B2 - Liquid ejection device - Google Patents

Description

  The present invention relates to a technique for ejecting droplets.

  2. Description of the Related Art Conventionally, a printing apparatus that ejects ink droplets from each nozzle by driving a piezoelectric element corresponding to each nozzle of a print head has been proposed. For example, in Patent Document 1, a plurality of switches (transmission gates) corresponding to a plurality of piezoelectric elements are arranged on a one-to-one basis, and a common control signal is selected for each piezoelectric element by each switch and supplied to each piezoelectric element. A printing apparatus is disclosed.

JP 2013-006424 A

  In a configuration in which a common control signal is selectively supplied to each piezoelectric element as in Patent Document 1, a control signal having an appropriate waveform is supplied to each piezoelectric element even when a large number (for example, all) of the piezoelectric elements are driven simultaneously. Therefore, it is necessary to supply a control signal with a very large current to the print head. Therefore, there is a problem that it is necessary to sufficiently ensure the withstand voltage performance and current withstand performance of the circuit used for supplying the control signal, and it is difficult to reduce the circuit scale. In view of the above circumstances, an object of the present invention is to reduce necessary withstand voltage performance or current withstand performance.

  In order to solve the above-described problems, a liquid ejection apparatus according to the present invention includes a nozzle that ejects liquid, a pressure chamber that communicates with the nozzle, and charging and discharging that are provided for each pressure chamber in accordance with a drive signal. The first discharge unit and the second discharge unit each including a piezoelectric element that discharges droplets from the nozzles, and a plurality of voltages are selectively applied to the first discharge unit. A first connection path selection unit to supply, a second connection path selection unit that is installed corresponding to the second discharge unit and selectively supplies a plurality of voltages to the second discharge unit; and the first connection path A voltage generation unit that generates and supplies the plurality of voltages common to the selection unit and the second connection path selection unit. In the above configuration, the first connection path selection unit corresponding to the first discharge unit and the second connection path selection unit corresponding to the second discharge unit are installed, and the plurality of voltages supplied from the voltage generation unit are The first connection path selection unit selectively supplies the first discharge unit and the second connection path selection unit selectively supplies the second discharge unit. Therefore, the withstand voltage performance and the withstand current performance required for the circuit are reduced compared with a configuration in which a control signal common to a plurality of nozzles is individually selected by a switch for each nozzle and is supplied to the piezoelectric element (as a result) There is an advantage that the circuit scale is reduced).

  A liquid ejection apparatus according to a preferred aspect of the present invention is installed corresponding to a control signal supply unit that supplies a control signal and the first connection path selection unit, and the control signal for the first connection path selection unit A first switch that controls supply / cutoff; and a second switch that is installed corresponding to the second connection path selection unit and controls supply / cutoff of the control signal to the second connection path selection unit. The first connection path selection unit selectively supplies the plurality of voltages to the first discharge unit according to a control signal supplied from the first switch, and the second connection path selection unit The plurality of voltages are selectively supplied to the second ejection unit in accordance with a control signal supplied from the second switch. In the above configuration, each of the plurality of switches controls supply / cutoff of the common control signal, whereby a plurality of voltages are selectively supplied to the piezoelectric element in accordance with the control signal supplied to each connection path selection unit. The Therefore, there is an advantage that the apparatus configuration and control processing are simplified as compared with the configuration in which the control signal is individually generated for each ejection unit.

  A liquid ejection apparatus according to a preferred aspect of the present invention is provided corresponding to the first connection path selection unit, generates a control signal, and supplies the control signal to the first connection path selection unit. A second control signal supply unit that is installed in correspondence with the second connection path selection unit, generates a control signal, and supplies the control signal to the second connection path selection unit, and the first connection path selection unit includes: The plurality of voltages are selectively supplied to the first discharge unit according to a control signal supplied from the first control signal supply unit, and the second connection path selection unit is configured to supply the second control signal supply unit. The plurality of voltages are selectively supplied to the second ejection unit in accordance with a control signal supplied from. In the above aspect, since the control signal supply unit installed for each ejection unit individually generates the control signal, for example, the control signal is adjusted for each ejection unit so as to compensate for the difference in characteristics of each piezoelectric element. Is possible.

  In the liquid ejection device according to a preferred aspect of the present invention, the first signal path to which the first voltage is applied by the voltage generator, and the second voltage higher than the first voltage is applied by the voltage generator. A second signal path, wherein the first connection path selection unit performs the first signal path or the second signal path according to the voltage of the control signal and the holding voltage of the piezoelectric element. The discharge unit and the voltage generation unit are electrically connected, and the second connection path selection unit is configured to select the first signal path or the second signal according to the voltage of the control signal and the holding voltage of the piezoelectric element. The second ejection unit and the voltage generation unit are electrically connected by a signal path. In the above aspect, the charging or discharging of the piezoelectric element is performed by electrically connecting the piezoelectric element to the first signal path or the second signal path. Since not only the voltage but also the holding voltage of the piezoelectric element is taken into consideration, the piezoelectric element can be controlled with a fine voltage. In addition, since charging and discharging of the piezoelectric element proceed in a stepwise manner, energy efficiency can be increased as compared with a conventional configuration that is performed at once between power supply voltages. Moreover, since a large current is not switched unlike the class D amplification, the occurrence of EMI (Electro Magnetic Interference) can be suppressed.

  The liquid ejection apparatus according to a preferred aspect of the present invention detects whether the holding voltage of the piezoelectric element is less than the first voltage, or whether the voltage is greater than or equal to the first voltage and less than the second voltage. A detection unit is provided. In the above aspect, it is detected whether or not the holding voltage of the piezoelectric element is less than the first voltage, or whether or not it is greater than or equal to the first voltage and less than the second voltage. In addition, as a detection part, the part which detects whether the holding voltage of a piezoelectric element is less than 1st voltage, and the part which detects whether it is more than 1st voltage and less than 2nd voltage are divided separately. It may be good or integrated.

  In a preferred aspect of the present invention, each of the plurality of connection path selection units including the first connection path selection unit and the second connection path selection unit is less than the first voltage through the first signal path. The electric charge charged in the piezoelectric element is controlled according to the voltage of the control signal, and the electric charge discharged from the piezoelectric element through the first signal path when the voltage is not lower than the first voltage and lower than the second voltage, or The electric charge charged in the piezoelectric element via the second signal path is controlled according to the voltage of the control signal. According to the above aspect, the electric charge charged and discharged to the piezoelectric element is controlled according to the voltage of the control signal.

  In a preferred aspect of the present invention, each of the plurality of connection path selection units includes a first transistor, a second transistor, and a third transistor. When the voltage is less than the first voltage, the first transistor is controlled by the control. In accordance with a voltage obtained by shifting the voltage of the signal to the lower side by a predetermined value, the electric charge charged in the piezoelectric element through the first signal path is controlled, and at the first voltage or more and less than the second voltage, The second transistor controls the charge discharged from the piezoelectric element through the first signal path according to a voltage obtained by shifting the voltage of the control signal to the higher side by the predetermined value, and the third transistor Controls the charge charged in the piezoelectric element via the second signal path in accordance with the voltage obtained by shifting the voltage of the control signal to the lower side by the predetermined value. In the above embodiment, the predetermined value may be zero if the first transistor, the second transistor, and the third transistor are ideal. For example, in the case of a bipolar transistor, the predetermined value is a voltage corresponding to the bias voltage. For example, in the case of a MOSFET (Metal-Oxide-Semiconductor Field-Effect Transistor), a voltage corresponding to the threshold voltage is preferable.

  In a preferred aspect of the present invention, if the voltage is not less than the first voltage, the first transistor is turned off. If the voltage is not less than the first voltage and less than the second voltage, the second transistor and the third transistor are turned off. . In the above aspect, if the holding voltage of the piezoelectric element is not less than the first voltage, the first transistor is turned off, so that the piezoelectric element is electrically disconnected from the first signal path and is equal to or higher than the first voltage. If it is not less than the second voltage, the second transistor and the third transistor are turned off, so that the piezoelectric element is electrically disconnected from the second signal path.

  In a preferred aspect of the present invention, each of the plurality of connection path selection units charges the piezoelectric element with a voltage obtained by subtracting a voltage obtained by subtracting a voltage held by the piezoelectric element from a voltage of the control signal. Charge to be discharged or discharged from the piezoelectric element. According to the above aspect, the voltage held in the piezoelectric element can be made to follow the voltage of the input signal with high accuracy and in a short time by negative feedback control.

1 is a diagram illustrating a schematic configuration of a printing apparatus. It is explanatory drawing of a control signal. It is a figure which shows the principal part structure of the discharge part in a print head. FIG. 3 is a partial block diagram of a print head. It is a figure which shows an example of a structure of the driver in a print head. It is operation | movement explanatory drawing of a driver. It is operation | movement explanatory drawing of the level shifter in a driver. It is a figure for demonstrating the flow of the electric current (electric charge) in a driver. It is a figure for demonstrating the flow of the electric current (electric charge) in a driver. It is a figure for demonstrating the flow of the electric current (electric charge) in a driver. It is a figure for demonstrating the flow of the electric current (electric charge) in a driver. It is explanatory drawing of the loss at the time of charging / discharging of a driver. It is a figure which shows an example of a structure of an auxiliary power supply circuit. It is operation | movement explanatory drawing of an auxiliary power supply circuit. It is a figure which shows schematic structure of the printing apparatus in 2nd Embodiment. It is a figure which shows an example of a structure of the application example (the 1) of a driver. It is a figure which shows an example of a structure of the application example (the 2) of a driver.

<First Embodiment>
FIG. 1 is a block diagram of a printing apparatus 100A according to the first embodiment of the present invention. The printing apparatus 100A according to the first embodiment is a liquid ejection apparatus that prints an image on a recording material by ejecting ink droplets (hereinafter referred to as “ink droplets”) onto the recording material such as printing paper.

  As shown in FIG. 1, the printing apparatus 100 </ b> A includes a control unit 10, a print head 20, and an FFC (Flexible Flat Cable) 70. Under the control of the control unit 10, ink droplets are ejected from each of the plurality of nozzles of the print head 20 onto the recording material. The printing apparatus 100A of the first embodiment is a serial type in which the print head 20 is mounted on a carriage (not shown) that moves in a direction (main scanning direction) that intersects the conveyance direction (sub-scanning direction) of the recording material. Inkjet printer. The control unit 10 is installed on a control board (not shown) outside the carriage. The FFC 70 is a flexible wiring board that electrically connects the control unit 10 and the print head 20.

  The control unit 10 is an element that executes arithmetic processing and control processing for printing an image instructed by image data supplied from a host computer (not shown), and includes a print data generation unit 120 and a control signal supply unit 140. And a main power supply unit 180.

The main power supply unit 180 generates a power supply voltage _VH and a ground potential (ground) G. The ground G corresponds to a voltage reference value (voltage zero), and the power supply voltage V _H is a voltage on the higher side of the ground G. The power supply voltage V _H and the ground G are supplied to the print head 20 via the FFC 70.

  The print data generation unit 120 and the control signal supply unit 140 in FIG. 1 are realized by an arithmetic processing unit (CPU) that executes a program stored in a storage circuit such as a RAM or various logic circuits. Note that an element for controlling a conveyance mechanism for conveying a recording material and an element for controlling a moving mechanism for moving a carriage are also installed in the control unit 10, but the illustration is omitted in FIG.

  The print data generation unit 120 executes various arithmetic processes (for example, image development process, color conversion process, color separation process, halftone process, etc.) on the image data supplied from the host computer, thereby printing data DP Is generated. The print data DP designates the presence or absence of ink droplet ejection and the ink droplet ejection amount for each nozzle of the print head 20. The print data DP generated by the print data generation unit 120 is supplied to the print head 20 via the FFC 70.

  The control signal supply unit 140 generates a control signal COM (COMA, COMB) for ejecting ink droplets from each nozzle of the print head 20. The control signal supply unit 140 according to the first embodiment includes a first generation unit 141 that generates a control signal COMA and a second generation unit 142 that generates a control signal COMB. Each of the first generation unit 141 and the second generation unit 142 includes a waveform generation unit 144 that generates a digital control signal dCOM, and a D / A conversion that converts the control signal dCOM into analog control signals COM (COMA, COMB). Instrument 145. As illustrated in FIG. 2, each of the control signal COMA and the control signal COMB is a voltage signal in which a plurality of drive pulses are arranged in time series for each printing cycle (one cycle) Ta. The waveforms of the control signal COMA and the control signal COMB are different. A configuration in which only one control signal COM is supplied from the control unit 10 to the print head 20 or a configuration in which each of the control signal COMA and the control signal COMB is supplied as a differential signal from the control unit 10 to the print head 20 is also employed. Can be done.

  As shown in FIG. 1, the print head 20 includes a head control unit 220, a selection unit 230, an element driving unit 240, an auxiliary power supply unit 50, and a piezoelectric element group 260. The piezoelectric element group 260 includes a plurality of piezoelectric elements 40 corresponding to different nozzles. Each piezoelectric element 40 is a capacitive load installed in a cavity (ink chamber) to which ink is supplied via a flow path. As a result of the piezoelectric element 40 being deformed by charging and discharging due to the supply of voltage and the volume of the cavity changing, ink droplets are ejected from the nozzle corresponding to the piezoelectric element 40.

  FIG. 3 is a diagram illustrating a schematic configuration of the ejection unit 400 corresponding to one nozzle in the print head 20. As shown in FIG. 3, the discharge unit 400 includes the piezoelectric element 40, the vibration plate 421, a cavity (pressure chamber) 431, a reservoir 441, and a nozzle 451. Among these, the vibration plate 421 is deformed by the piezoelectric element 40 provided on the upper surface in the drawing to enlarge / reduce the internal volume of the cavity 431 filled with ink. The nozzle 451 is an opening that communicates with the cavity 431.

  The piezoelectric element 40 shown in this figure is generally called a unimorph (monomorph) type, and has a structure in which a piezoelectric body 401 is sandwiched between a pair of electrodes 411 and 412. In the piezoelectric body 401 having this structure, the central portion in the figure bends in the vertical direction with respect to both end portions together with the electrodes 411, 412 and the diaphragm 421 in accordance with the voltage applied between the electrodes 411, 412. . Here, if the ink is bent upward, the internal volume of the cavity 431 increases, so that the ink is drawn from the reservoir 441. If the ink is bent downward, the internal volume of the cavity 431 increases, so that the ink It is discharged from the nozzle 451. The piezoelectric element 40 is not limited to a unimorph type, and may be any type such as a bimorph type or a laminated type that can deform a piezoelectric element and eject a liquid such as ink.

  The element driving unit 240 is an element that drives each of the plurality of piezoelectric elements 40. As illustrated in FIG. 1, a plurality of elements (the same number as the piezoelectric elements 40) corresponding to different piezoelectric elements 40 in the piezoelectric element group 260 are provided. A driver 30 is included. That is, each driver 30 of the element driving unit 240 and each piezoelectric element 40 of the piezoelectric element group 260 correspond one-to-one, and the print head 20 includes a plurality of sets of the piezoelectric element 40 and the driver 30. One end of each piezoelectric element 40 is connected to the output end of the driver 30 corresponding to the piezoelectric element 40, and the other end of each piezoelectric element 40 is grounded to the ground G.

  The selection unit 230 includes a plurality of switches (the same number as the piezoelectric elements 40) corresponding to the different piezoelectric elements 40. Each switch 232 corresponds to each set of the driver 30 and the piezoelectric element 40 on a one-to-one basis. The control signal COMA and the control signal COMB generated by the control signal supply unit 140 are commonly supplied to the input ends of the switches 232 of the selection unit 230, and the output ends of the switches 232 are the drivers 30 corresponding to the switches 232. Connected to the input terminal. Each switch 232 selects either the control signal COMA or the control signal COMB and supplies it to the driver 30.

  The head control unit 220 in FIG. 1 controls each of the plurality of switches 232 of the selection unit 230 according to the print data DP supplied from the print data generation unit 120. Specifically, as shown in FIG. 2, the head controller 220 sends the control signal COMA to each switch 232 in each of a plurality of sections t obtained by dividing the printing cycle Ta of the control signal COMA and the control signal COMB on the time axis. And any one of the control signals COMB is selected. Therefore, the control signal Vin obtained by selectively extracting one of the control signal COMA and the control signal COMB for each section t is supplied from the switch 232 to the driver 30 at the subsequent stage.

The auxiliary power supply unit 50 in FIG. 1 is a voltage generation unit (boost circuit) that generates a plurality of voltages using the voltage V _H supplied from the main power supply unit 180 of the control unit 10. The auxiliary power supply unit 50 of the first embodiment divides and redistributes the voltage V _H by the charge pump circuit, so that the voltage V _H is 1/6 times the voltage V _H (V _H / 6) as shown in FIG. Generates 2/6 voltage (2V _H / 6), 3/6 voltage (3V _H / 6), 4/6 voltage (4V _H / 6) and 5/6 voltage (5V _H / 6) To do. The plurality of voltages generated by the auxiliary power supply unit 50 are commonly supplied to the plurality of drivers 30 of the element driving unit 240. That is, the plurality of drivers 30 share the auxiliary power supply unit 50. Each driver 30 is a circuit (connection path selection unit) that drives the piezoelectric element 40 according to a control signal Vin supplied from the selection unit 230 using a plurality of voltages supplied from the auxiliary power supply unit 50. Specifically, a voltage Vout that varies following the voltage of the control signal Vin is supplied from each driver 30 to the piezoelectric element 40. Since one end of the piezoelectric element 40 is grounded, the voltage Vout corresponds to the voltage held by the piezoelectric element 40.

<Driver>
FIG. 5 is a diagram illustrating an example of the configuration of the driver 30 that drives one piezoelectric element 40 in the first embodiment. As shown in FIG. 5, the driver 30 has seven types of voltages including zero voltage, specifically, zero voltage (ground G) in the descending order, V _H / 6, 2V _H / 6, 3V _H / 6, 4V _H / 6, 5V _H / 6, V _H is used to generate the voltage Vout. The voltage _V H / 6 supplied from the auxiliary power unit 50 via a power line 511 to the driver 30, similarly, the voltage _{2V H / 6,3V H / 6,4V H} / 6,5V H / 6 , the power supply wiring The power is supplied from the auxiliary power supply unit 50 to each driver 30 via 512, 513, 514, and 515. As shown in FIG. 5, the driver 30 includes an operational amplifier 32, unit circuits 34a to 34f, and comparators 38a to 38e, and drives the piezoelectric element 40 in accordance with the control signal Vin.

The control signal Vin output from the selection unit 230 is supplied to the input terminal (+) of the operational amplifier 32 that is the input terminal of the driver 30. The output signal of the operational amplifier 32 is supplied to each of the unit circuits 34a to 34f, negatively fed back to the input terminal (−) of the operational amplifier 32 through the resistor Rf, and further grounded to the ground G through the resistor Rin. For this reason, the operational amplifier 32 non-inverting amplifies the control signal Vin by (1 + Rf / Rin) times.
The voltage amplification factor of the operational amplifier 32 can be set by resistors Rf and Rin, but for convenience, Rf is set to zero and Rin is set to infinity for convenience. That is, in the following description, it is assumed that the voltage amplification factor of the operational amplifier 32 is set to “1” and the control signal Vin is supplied as it is to the unit circuits 34a to 34f. The voltage amplification factor may be other than “1”.

The unit circuits 34a to 34f are provided in order of increasing voltage corresponding to two adjacent voltages among the seven types of voltages. Specifically, the unit circuit 34a corresponds to the voltage zero and the voltage V _H / 6, the unit circuit 34b corresponds to the voltage V _H / 6 and the voltage 2V _H / 6, and the unit circuit 34c corresponds to the voltage 2V _H / 6 and the voltage. 3V _H / 6, the unit circuit 34d corresponds to the voltage 3V _H / 6 and the voltage 4V _H / 6, the unit circuit 34e corresponds to the voltage 4V _H / 6 and the voltage 5V _H / 6, and the unit circuit 34f It is provided corresponding to voltage 5 V _H / 6 and voltage V _H.

The unit circuits 34a to 34f have the same circuit configuration, and include one corresponding to any one of the level shifters 36a to 36f, a bipolar NPN transistor 341, and a PNP transistor 342.
When the unit circuits 34a to 34f are generally described without being specified, the reference numeral is simply “34”, and similarly, the level shifters 36a to 36f are generally described without being specified. In the following description, the code is simply “36”.

  The level shifter 36 takes one of an enable state and a disable state. Specifically, in the level shifter 36, the signal supplied to the negative control end with a circle is L level, and the signal supplied to the positive control end with no circle is H level. Is in the enabled state, otherwise it is in the disabled state.

Among the seven types of voltage as described later, the five kinds of voltages excluding the zero voltage and the voltage V _H, respectively of the comparator 38a~38e is one-to-one correspondence. Here, when attention is paid to a certain unit circuit 34, the negative control terminal of the level shifter 36 in the unit circuit 34 is associated with the higher voltage of the two voltages corresponding to the unit circuit 34. The output signal of the comparator is supplied, and the output signal of the comparator associated with the lower voltage of the two voltages corresponding to the unit circuit is supplied to the positive control terminal of the level shifter 36. However, the negative control terminal of the level shifter 36f in the unit circuit 34f is grounded to the ground G of zero voltage corresponding to the L level, while the positive control terminal of the level shifter 36a in the unit circuit 34a is connected to the voltage V corresponding to the H level. Connected to a power supply wiring 516 for supplying _H.

Further, in the enabled state, the level shifter 36 shifts the voltage of the input control signal Vin in the minus direction by a predetermined value and supplies it to the base terminal of the transistor 341, while the voltage of the control signal Vin in the positive direction has a predetermined value. And is supplied to the base terminal of the transistor 342. In the disabled state, the level shifter 36 supplies a voltage for turning off the transistor 341, for example, the voltage V _H to the base terminal of the transistor 341, and a voltage for turning off the transistor 342, for example, zero voltage, regardless of the control signal Vin. Is supplied to the base terminal of the transistor 342.
The predetermined value is a base-emitter voltage (bias voltage, approximately 0.6 volts) at which current starts to flow through the emitter terminal. For this reason, the predetermined value is determined according to the characteristics of the transistors 341 and 342, and is zero if the transistors 341 and 342 are ideal.

The collector terminal of the transistor 341 is connected to a power supply wiring that supplies a higher voltage among the corresponding two voltages, and the collector terminal of the transistor 342 is connected to a power supply wiring that supplies a lower voltage. For example, in the unit circuit 34a corresponding to the voltage zero and the voltage V _H / 6, the collector terminal of the transistor 341 is connected to the power supply wiring 511 that supplies the voltage V _H / 6, and the collector terminal of the transistor 342 is the ground G having the voltage zero. Grounded. Further, for example, in the unit circuit 34 b corresponding to the voltage V _H / 6 and the voltage 2 V _H / 6, the collector terminal of the transistor 341 is connected to the power supply wiring 512 that supplies the voltage 2 V _H / 6, and the collector terminal of the transistor 342 is the voltage. It is connected to a power supply wiring 511 that supplies V _H / 6. In the unit circuit 34f corresponding to the voltage 5V _H / 6 and the voltage V _H , the collector terminal of the transistor 341 is connected to the power supply wiring 516 that supplies the voltage V _H, and the collector terminal of the transistor 342 receives the voltage 5V _H / 6. It is connected to the power supply wiring 515 to be supplied.

  On the other hand, the emitter terminals of the transistors 341 and 342 in the unit circuits 34 a to 34 f are commonly connected to one end of the piezoelectric element 40. For this reason, as described above, the common connection point of the emitter terminals of the transistors 341 and 342 is connected to one end of the piezoelectric element 40 as the output end of the driver 30.

Comparator 38a~38e, said 7 of the type of voltage, 5 kinds of voltages _V H _/ 6,2V excluding the zero voltage and the voltage _{V H H / 6,3V H / 6,4V} H / 6,5V H / 6, _VH , and compares the levels of the voltages supplied to the two input terminals, and outputs a signal indicating the comparison result. Here, of the two input ends of the comparators 38a to 38e, one end is connected to a power supply wiring that supplies a voltage corresponding to itself, and the other end is connected to the emitter terminals of the transistors 341 and 342 and the piezoelectric element 40. Commonly connected to one end. For example the comparator 38a corresponding to the voltage _V H / 6, of the two input terminals, one end is connected to the voltage _V H / 6 corresponding to itself to the power source line 511 supplies, also for example, a voltage _2V H / One of the two input terminals of the comparator 38b corresponding to 6 is connected to a power supply wiring 512 that supplies a voltage 2V _H / 6 corresponding to itself.

Each of the comparators 38a to 38e outputs a signal that is at the H level if the voltage Vout at the other end at the input end is equal to or higher than the voltage at one end, and is at the L level if the voltage Vout is less than the voltage at one end.
Specifically, for example, the comparator 38a is a voltage Vout to the H level if the voltage V _{H /} 6 or more, and outputs an L level signal is less than the voltage V _{H /} 6. Further, for example, the comparator 38b, the voltage Vout is set to the H level if the voltage _2V H / 6 or more, and outputs an L level signal is less than the voltage _2V H / 6.

When attention is paid to one of the five types of voltages, the output signal of the comparator corresponding to the noticed voltage is the negative input terminal of the level shifter 36 of the unit circuit having the voltage as the higher voltage, and the voltage. Is supplied to the positive input terminal of the level shifter 36 of the unit circuit having a low-side voltage as a low-side voltage.
For example, the output signal of the comparator 38a corresponding to the voltage V _H / 6 includes the negative input terminal of the level shifter 36a of the unit circuit 34a associated with the voltage V _H / 6 as a higher voltage, and the voltage V _H / 6 is supplied to the positive input terminal of the level shifter 36b of the unit circuit 34b associated with the low-order side voltage. Further, for example, the output signal of the comparator 38b corresponding to the voltage 2V _H / 6 includes the negative input terminal of the level shifter 36b of the unit circuit 34b associated with the voltage 2V _H / 6 as the higher voltage, and the voltage 2V. _H / 6 is supplied to the positive input terminal of the level shifter 36c of the unit circuit 34c associated with the lower voltage.

Next, the operation of the driver 30 will be described.
First, the state of the comparators 38a to 38e and the level shifter 36 with respect to the voltage Vout held by the piezoelectric element 40 will be described.

In a state where the voltage Vout is equal to or higher than zero and lower than the voltage _VH / 6 (first state), all output signals of the comparators 38a to 38e are at the L level. Therefore, in the first state, only the level shifter 36a is enabled, and the other level shifters 36b to 36f are disabled.
In the state the voltage Vout is less than the voltage _V H / 6 Exceeded a voltage _2V H / 6 (second state), the output signal of the comparator 38a becomes H level, the output signal of the other comparator 38b~38e L level. Therefore, in the second state, only the level shifter 36b is enabled, and the other level shifters 36a and 36c to 36f are disabled.
In a state where the voltage Vout is equal to or higher than the voltage 2V _H / 6 and lower than the voltage 3V _H / 6 (third state), the output signals of the comparators 38a and 38b become the H level, and the outputs of the other comparators 38c to 38e. The signal becomes L level. Therefore, in the third state, only the level shifter 36c is enabled, and the other level shifters 36a, 36b, 36d to 36f are disabled.
In a state where the voltage Vout is equal to or higher than the voltage 3V _H / 6 and lower than the voltage 4V _H / 6 (fourth state), the output signals of the comparators 38a, 38b, and 38c become the H level, and the other comparators 38d and 38e. Output signal becomes L level. Therefore, in the fourth state, only the level shifter 36d is enabled, and the other level shifters 36a to 36c, 36e, and 36f are disabled.
In a state where the voltage Vout is equal to or higher than the voltage 4V _H / 6 and lower than the voltage 5V _H / 6 (fifth state), the output signals of the comparators 38a to 38d are at the H level, and the output signals of the other comparators 38e are L level. Therefore, in the fifth state, only the level shifter 36e is enabled, and the other level shifters 36a to 36d and 36f are disabled.
In the state the voltage Vout is less than the voltage _{V H} A at the voltage _5V H / 6 or more (Sixth state), all the output signals of the comparator 38a~38e includes becomes H level. Therefore, in the sixth state, only the level shifter 36f is enabled, and the other level shifters 36a to 36d are disabled.

In this way, only the level shifter 36a is enabled in the first state, and thereafter, similarly, only the level shifter 36b in the second state, only the level shifter 36c in the third state, and only the level shifter 36d in the fourth state. However, only the level shifter 36e is enabled in the fifth state, and only the level shifter 36f is enabled in the sixth state.
Note that the voltage from the first state to the sixth state is defined by the voltage Vout, but this can be rephrased as the state of charges held (accumulated) in the piezoelectric element 40.

  When the level shifter 36a is enabled in the first state, the level shifter 36a supplies a voltage signal obtained by level shifting the control signal Vin by a predetermined value in the minus direction to the base terminal of the transistor 341 in the unit circuit 34a. A voltage signal obtained by level shifting the control signal Vin by a predetermined value in the plus direction is supplied to the base terminal of the transistor 342 in the unit circuit 34a.

  Here, when the voltage of the control signal Vin is higher than the voltage Vout (connection voltage between the emitter terminals), the difference (the voltage between the base and the emitter, strictly speaking, the voltage between the base and the emitter is reduced by a predetermined value. Current corresponding to the voltage) flows from the collector terminal of the transistor 341 to the emitter terminal. For this reason, when the voltage Vout gradually increases and approaches the voltage of the control signal Vin, and eventually the voltage Vout matches the voltage of the control signal Vin, the current flowing through the transistor 341 at that time becomes zero.

On the other hand, when the voltage of the control signal Vin is lower than the voltage Vout, a current corresponding to the difference flows from the emitter terminal of the transistor 342 to the collector terminal. For this reason, when the voltage Vout gradually decreases and approaches the voltage of the control signal Vin and eventually the voltage Vout matches the voltage of the control signal Vin, the current flowing through the transistor 342 becomes zero at that time.
Therefore, in the first state, the transistors 341 and 342 of the unit circuit 34a execute control to make the voltage Vout coincide with the control signal Vin.

In the first state, in the unit circuits 34b to 34f other than the unit circuit 34a, the level shifter 36 is disabled, so that the voltage _VH is supplied to the base terminal of the transistor 341 and the base terminal of the transistor 342 is supplied to the base terminal. Is supplied with zero voltage. Therefore, in the first state, in the unit circuits 34b to 34f, the transistors 341 and 342 are turned off, so that they are not involved in the control of the voltage Vout.

  In addition, although the case where it is a 1st state is demonstrated here, it becomes the same operation | movement also about a 2nd state-a 6th state. More specifically, one of the unit circuits 34a to 34f is activated according to the voltage Vout held by the piezoelectric element 40, and the transistors 341 and 342 of the activated unit circuit use the voltage Vout as the control signal Vin. Control to match. For this reason, when the driver 30 is viewed as a whole, the voltage Vout follows the voltage of the control signal Vin.

Thus, as shown in (a) of FIG. 6, when the control signal Vin to increase, for example, from voltage zero to the voltage V _H, is changed from zero voltage to the voltage V _H to follow the voltage Vout to the control signals Vin. Further, as shown in FIG. 5B, when the control signal Vin decreases from the voltage _VH to the voltage zero, the voltage Vout also changes from the voltage _VH to the voltage zero following the control signal Vin.

FIG. 7 is a diagram for explaining the operation of the level shifter.
When the voltage of the control signal Vin rises varies from zero voltage to the voltage V _H, the voltage Vout rises to follow the control signal Vin. In the rising process, the level shifter 36a is enabled when the voltage Vout is in the first state in which the voltage is zero or more and less than the voltage _VH / 6. Therefore, as shown in FIG. 5A, the voltage (indicated as “P type”) supplied to the base terminal of the transistor 341 by the level shifter 36a shifts the control signal Vin in the minus direction by a predetermined value. The voltage supplied to the base terminal of the transistor 342 (denoted as “N-type”) is a voltage obtained by shifting the control signal Vin in the plus direction by a predetermined value. On the other hand, since the level shifter 36a is disabled in a state other than the first state, the voltage supplied to the base terminal of the transistor 341 becomes V _H and the voltage supplied to the base terminal of the transistor 342 becomes zero. .

In addition, (b) of the same figure shows the voltage waveform which the level shifter 36b outputs, (c) of the same figure shows the voltage waveform which the level shifter 36f outputs. Level shifter 36b is enabled state when the second state the voltage Vout is less than the voltage _2V H / 6 or more voltage _2V H / 6, the level shifter 36f, a voltage Vout voltage _5V H / 6 or more voltage _{V H} If it is noted that the enable state is entered in the sixth state which is less than the above, no special explanation will be required.
Also, the operation of the level shifters 36c to 36e in the process of increasing the voltage (or voltage Vout) of the control signal Vin, and the operation of the level shifters 36a to 36f in the process of decreasing the voltage (or voltage Vout) of the control signal Vin. The description is also omitted.

  Next, the flow of current (charge) in the unit circuits 34a to 34f will be described separately for charging and discharging, taking the unit circuits 34a and 34b as an example.

FIG. 8 is a diagram illustrating an operation when the piezoelectric element 40 is charged in the first state (the state where the voltage Vout is equal to or higher than zero and lower than the voltage V _H / 6).
In the first state, the level shifter 36a is enabled and the other level shifters 36b to 36f are disabled, so that only the unit circuit 34a needs to be noted.
When the voltage of the control signal Vin is higher than the voltage Vout in the first state, the transistor 341 of the unit circuit 34a passes a current corresponding to the voltage between the base and the emitter. Therefore, the transistor 341 of the unit circuit 34a functions as the first transistor. At this time, the transistor 342 of the unit circuit 34a is off.

  At this time, the current flows along the path of the power supply wiring 511 → the transistor 341 (in the unit circuit 34 a) → the piezoelectric element 40 as indicated by the arrow in the drawing, and the electric charge is charged in the piezoelectric element 40. This charging increases the voltage Vout.

When the voltage Vout matches the voltage of the control signal Vin, the transistor 341 of the unit circuit 34a is turned off, so that charging of the piezoelectric element 40 is stopped.
On the other hand, when the control signal Vin rises to the voltage V _H / 6 or higher, the voltage Vout also follows the control signal Vin. Therefore, the voltage V _H / 6 or higher is reached and the second state (the voltage Vout is changed from the first state). The voltage V _H / 6 or higher and less than 2 V _H / 6).

FIG. 9 is a diagram illustrating an operation when the piezoelectric element 40 is charged in the second state.
In the second state, the level shifter 36b is enabled and the other level shifters 36a, 36c to 36f are disabled, so that only the unit circuit 34b needs to be noted.
When the control signal Vin is higher than the voltage Vout in the second state, the transistor 341 of the unit circuit 34b passes a current corresponding to the voltage between the base and the emitter. Therefore, the transistor 341 of the unit circuit 34b functions as the third transistor. At this time, the transistor 342 of the unit circuit 34b is off.

At this time, as shown by the arrows in the figure, the current flows through the path of the power supply wiring 512 → the transistor 341 (of the unit circuit 34b) → the piezoelectric element 40, and the piezoelectric element 40 is charged. That is, when the piezoelectric element 40 is charged in the second state, one end of the piezoelectric element 40 is electrically connected to the auxiliary power supply unit 50 via the power supply wiring 512.
As described above, when the voltage Vout is increased and the first state is shifted to the second state, the current supply source is switched from the power supply line 511 to the power supply line 512.

When the voltage Vout matches the control signal Vin, the transistor 341 of the unit circuit 34b is turned off, so that charging of the piezoelectric element 40 is stopped.
On the other hand, when the control signal Vin rises to the voltage 2V _H / 6 or higher, the voltage Vout also follows the control signal Vin. As a result, the voltage 2V _H / 6 or higher results in the second state to the third state (the voltage Vout becomes The voltage shifts to 2V _H / 6 or more and less than 3V _H / 6.
Note that the charging operation from the third state to the sixth state is not particularly illustrated, but the current supply source is gradually switched to the power supply wirings 513, 514, 515, and 516.

FIG. 10 is a diagram illustrating an operation when the piezoelectric element 40 is discharged in the second state.
In the second state, the level shifter 36b is enabled. In this state, when the control signal Vin is lower than the voltage Vout, the transistor 342 of the unit circuit 34b passes a current corresponding to the voltage between the base and the emitter. Therefore, the transistor 341 of the unit circuit 34b functions as a second transistor. At this time, the transistor 341 of the unit circuit 34b is off.

At this time, as indicated by the arrows in the figure, the current flows through the path of the piezoelectric element 40 → the transistor 342 (of the unit circuit 34 b) → the power supply wiring 511, and the electric charge is discharged from the piezoelectric element 40. That is, when the electric charge is charged in the piezoelectric element 40 in the first state and when the electric charge is discharged from the piezoelectric element 40 in the second state, one end of the piezoelectric element 40 is connected to the power supply line 50 with respect to the auxiliary power supply unit 50. 511 is electrically connected. Further, the power supply wiring 511 supplies current (charge) when charging in the first state, and collects current (charge) when discharging in the second state.
The collected charges are redistributed and reused by an auxiliary power supply unit 50 described later.

When the voltage Vout matches the control signal Vin, the transistor 342 of the unit circuit 34b is turned off, so that the discharge of the piezoelectric element 40 is stopped.
On the other hand, when the control signal Vin falls below the voltage V _H / 6, the voltage Vout also follows the control signal Vin, and thus becomes less than the voltage V _H / 6 and shifts from the second state to the first state.

FIG. 11 is a diagram illustrating an operation when the piezoelectric element 40 is discharged in the first state.
In the first state, the level shifter 36a is enabled. In this state, when the control signal Vin is lower than the voltage Vout, the transistor 342 of the unit circuit 34a passes a current corresponding to the voltage between the base and the emitter.
At this time, the transistor 341 of the unit circuit 34a is off.
At this time, the current flows along the path of the piezoelectric element 40 → the transistor 342 (in the unit circuit 34 a) → the ground G as indicated by the arrow in the figure, and the electric charge is discharged from the piezoelectric element 40.

Here, the unit circuits 34a and 34b have been described by way of example as being charged and discharged, but the unit circuits 34c to 34f are substantially the same except that the transistors 341 and 342 for controlling currents are different. It becomes operation.
That is,
The power supply wiring 512 supplies current (charge) at the time of charging in the second state, and collects current (charge) at the time of discharging in the third state.
The power supply wiring 513 supplies current (charge) at the time of charging in the third state, and collects current (charge) at the time of discharging in the fourth state.
The power supply wiring 514 supplies current (charge) at the time of charging in the fourth state, and collects current (charge) at the time of discharging in the fifth state.
The power supply wiring 515 supplies current (charge) at the time of charging in the fifth state, and collects current (charge) at the time of discharging in the sixth state.
The power supply wiring 516 supplies a current (charge) at the time of charging in the sixth state,
The collected charges are redistributed and reused by the auxiliary power supply unit 50.
In the discharge path and the charge path in each state, the path from one end of the piezoelectric element 40 to the connection point between the emitter terminals of the transistors 341 and 342 is shared.

In general, when the capacity of a capacitive load such as the piezoelectric element 40 is C and the voltage amplitude is E, the energy P stored in the capacitive load is
P = (C · E ² ) / 2
It is represented by
The piezoelectric element 40 works by being deformed by the energy P, but the work amount for ejecting ink is 1% or less with respect to the energy P. Therefore, the piezoelectric element 40 can be regarded as a simple capacitance. When the capacitor C is charged with a constant power source, energy equivalent to (C · E ² ) / 2 is consumed by the charging circuit. When discharging, the same energy is consumed by the discharge circuit.

<Advantages of driver>
In the first embodiment, when charging the piezoelectric element 40 from the voltage zero to the voltage V _H ,
From voltage zero to voltage V _H / 6,
From voltage V _H / 6 to voltage 2 V _H / 6,
From voltage 2V _H / 6 to voltage 3V _H / 6,
From voltage 3V _H / 6 to voltage 4V _H / 6,
From voltage 4V _H / 6 to voltage 5V _H / 6,
From voltage 5V _H / 6 to voltage V _H ,
It is charged through 6 stages. For this reason, in the first embodiment, the loss during charging is equivalent to the area of the hatched region in FIG. In particular, the loss in charging the piezoelectric element 40 in the first embodiment, as compared with the linear amplification for charging once from zero voltage to the voltage V _H, requires only 6/36 (= 16.7%).
On the other hand, in the first embodiment, since it is stepwise even at the time of discharge, the loss at the time of discharge is represented by the voltage corresponding to the area of the hatched area in FIG. Compared with the linear system that discharges at a stroke from V _H to zero voltage, 6/36 (= 16.7%) is sufficient.
However, in the first embodiment, out of the charge counted as the loss at the time of discharge, except for the case of discharging from the voltage V _H / 6 to the voltage zero, it is recovered by the auxiliary power supply unit 50 described later and redistributed and reused. Thus, further reduction in power consumption can be achieved.

  In the configuration of Patent Document 1 (hereinafter referred to as “proportional”) in which a single control signal common to a plurality of piezoelectric elements is individually selected by a switch for each nozzle and directly supplied to the piezoelectric elements (hereinafter referred to as “proportional”), Even when the control signals are simultaneously supplied to the piezoelectric elements, it is necessary to ensure a sufficient amount of current on the path of the control signals in order to supply the control signals having an appropriate waveform to each piezoelectric element. Therefore, the wiring for transmitting the control signal and each switch for selecting the control signal are required to have sufficient withstand voltage performance and current resistance performance, and there is a problem that it is difficult to reduce the circuit scale. In the first embodiment, the driver 30 installed for each piezoelectric element 40 generates the voltage Vout from the control signal Vin by the above-described configuration and operation and supplies it to the piezoelectric element 40. Therefore, the control signal COM (COMA, COMB) The amount of current on the path is greatly reduced compared to the proportionality. Therefore, the withstand voltage performance and the withstand current performance required for the wiring of the FFC 70 that transmits the control signal COM and each switch 232 of the selection unit 230 are reduced as compared with the proportionality. That is, according to the first embodiment, it is possible to reduce the circuit scale. In addition, since each switch 232 of the selection unit 230 does not consume power, there is an advantage that heat generation of the selection unit 230 can be avoided.

By the way, in class D amplification, energy efficiency is higher than linear amplification. The reason is that the active element in the output stage operates in a saturated state and consumes almost no power, and a loss such as linear amplification at the time of charging by exchanging magnetic energy by the inductor L constituting the low-pass filter and energy by the capacitor C. This is because no current is generated, and current is regenerated to the power supply by current switching during discharge.
However, in actual class D amplification, the resistance of the active element in the output stage is not zero even in a saturated state, the magnetic field leaks, loss occurs due to the resistance component of the inductor L, and the inductor L may be saturated during modulation. , Etc.
In class D amplification, there are problems that the waveform quality is further poor and EMI countermeasures are required. The waveform quality can be improved by adding a dummy capacity or a filter, but this increases the power consumption and costs. EMI is due to the fundamental problem of class D amplification switching. That is, when the switching is performed, not only does the current flowing at the time of on-state increase from several times to about several tens of times compared to the linear amplification, but the amount of the magnetic field radiated increases accordingly. For measures against EMI, it is necessary to add a filter or the like, resulting in high costs.

In the driver 30 of the printing apparatus 100A according to the first embodiment, the transistors 341 and 342 corresponding to the output stage do not perform switching as in the class D amplification, and since the inductor L is not used, the waveform quality is high. There is no problem that it is bad or EMI countermeasures are necessary.
In the first embodiment, since the voltage Vout follows the control signal Vin, the piezoelectric element 40 can be controlled with a fine voltage. That is, the start voltage and end voltage of the voltage Vout applied to the piezoelectric element 40 is independent of the voltage _{V H / 6,2V H / 6,3V H} / 6,4V H / 6 and _5V H / 6 used in the driver It is.

<Auxiliary power supply>
FIG. 13 is a diagram illustrating an example of the configuration of the auxiliary power supply unit 50.
As shown in this figure, the auxiliary power supply unit 50 includes switches Sw1d, Sw1u, Sw2d, Sw2u, Sw3d, Sw3u, Sw4d, Sw4u, Sw5d, Sw5u, and capacitive elements C12, C23, C34, C45, C56, C1, The configuration includes C2, C3, C4, C5, and C6.
Among these, all the switches are single pole double throw, and the common terminal is connected to one of the terminals a and b according to the control signal A / B. For example, the control signal A / B is a pulse signal having a duty ratio of about 50%, and its frequency is set to, for example, about 20 times the frequency of the control signal COM. Such a control signal A / B may be generated by an internal oscillator (not shown) in the auxiliary power supply unit 50 or may be supplied from the control unit 10 via the FFC 70.
On the other hand, the capacitive elements C12, C23, C34, C45, and C56 are for charge transfer, and the capacitive elements C1, C2, C3, C4, and C5 are for backup. Note that the capacitor C6 is for the supply of the power supply voltage _{V H.}
The switch is actually configured by combining transistors in a semiconductor integrated circuit, and the capacitor is externally mounted on the semiconductor integrated circuit. The semiconductor integrated circuit preferably has a configuration in which the plurality of drivers 30 are also formed.

Now, the power supply line 516 for supplying a voltage _{V H} in the auxiliary power supply unit 50 is connected to the terminal a of the one end and the switch Sw5u capacitive element C6. The common terminal of the switch Sw5u is connected to one end of the capacitive element C56, and the other end of the capacitive element C56 is connected to the common terminal of the switch Sw5d. The terminal a of the switch Sw5d is connected to one end of the capacitive element C5 and the terminal a of the switch Sw4u. The common terminal of the switch Sw4u is connected to one end of the capacitive element C45, and the other end of the capacitive element C45 is connected to the common terminal of the switch Sw4d. The terminal a of the switch Sw4d is connected to one end of the capacitive element C4 and the terminal a of the switch Sw3u. The common terminal of the switch Sw3u is connected to one end of the capacitive element C34, and the other end of the capacitive element C34 is connected to the common terminal of the switch Sw3d. The terminal a of the switch Sw3d is connected to one end of the capacitive element C3 and the terminal a of the switch Sw2u. The common terminal of the switch Sw2u is connected to one end of the capacitive element C23, and the other end of the capacitive element C23 is connected to the common terminal of the switch Sw2d. The terminal a of the switch Sw2d is connected to one end of the capacitive element C2 and the terminal a of the switch Sw1u. The common terminal of the switch Sw1u is connected to one end of the capacitive element C12, and the other end of the capacitive element C12 is connected to the common terminal of the switch Sw1d. A terminal a of the switch Sw1d is connected to one end of the capacitive element C1.

One end of the capacitive element C5 is connected to the power supply wiring 515. Similarly, one ends of the capacitive elements C4, C3, C2, and C1 are connected to power supply wirings 514, 513, 512, and 511, respectively.
Each terminal b of the switches Sw5u, Sw4u, Sw3u, Sw2u, and Sw1u is connected to one end of the capacitive element C1 together with the terminal a of the switch Sw1d. The other ends of the capacitive elements C6, C5, C4, C3, C2, and C1 and the terminals b of the switches Sw5d, Sw4d, Sw3d, Sw2d, and Sw1d are commonly grounded to the ground G.

FIG. 14 is a diagram illustrating a connection state of switches in the auxiliary power supply unit 50.
Each switch takes two states, a state where the common terminal is connected to the terminal a (state A) and a state where the common terminal is connected to the terminal b (state B) by the control signal A / B. (A) of the same figure shows the connection of the state A in the auxiliary power supply 50, and (b) shows the connection of the state B in an equivalent circuit.
In the state A, the capacitive elements C56, C45, C34, C23, C12, and C1 are connected in series between the voltage _VH and the ground G. In the state B, since one ends of the capacitive elements C56, C45, C34, C23, C12, and C1 are connected to each other, these capacitive elements are connected in parallel to equalize the holding voltage.

Therefore, when the states A and B are alternately repeated, the voltage V _H / 6 that is equalized in the state B is multiplied by 1 to 5 by the series connection of the state A and held in the capacitive elements C1 to C5, respectively. In addition, the holding voltage at this time is supplied to the driver 30 via the power supply wirings 511 to 515.

Here, when the piezoelectric element 40 is charged by the driver 30, one of the capacitive elements C1 to C5 whose holding voltage is reduced appears. The capacitive element whose holding voltage is reduced is replenished with electric charge from the power source by the series connection of the state A and is equalized by redistribution by the parallel connection of the state B. balanced so as to maintain the voltage _{V H / 6,2V H / 6,3V H} / 6,4V H / 6,5V H / 6.
On the other hand, when the piezoelectric element 40 is discharged by the driver 30, one of the capacitive elements C <b> 1 to C <b> 5 whose holding voltage rises appears, but electric charges are discharged by the series connection of the state A, and the reconnection by the parallel connection of the state B is performed. since the equalized in the allocation, when viewed across the auxiliary power supply unit 50, to balance so as to maintain the voltage _{V H / 6,2V H / 6,3V H} / 6,4V H / 6,5V H / 6. Note that when the discharged electric charge is absorbed by the capacitive elements C56, C45, C34, C23, C12, and C1, the remaining electric charge is absorbed by the capacitive element C6, that is, regenerated to the power supply system. . For this reason, if there is a load other than the piezoelectric element 40, it is used to drive the load. If there is no other load, it is absorbed by other capacitive elements including the capacitive element C6, so that the power supply voltage _VH rises, that is, a ripple occurs. This can be avoided practically by increasing the capacity. As understood from the above description, the auxiliary power supply unit 50 (capacitance elements C1, C2, C3, C4, and C5) functions as an element (charge supply source) that supplies charges to each driver 30 (each piezoelectric element 40). To do.

In the auxiliary power supply unit 50, when the piezoelectric element 40 is discharged by the driver 30, the holding voltage of any of the capacitive elements C1 to C6 corresponding to the power supply wiring used for the discharge temporarily rises. By repeating A and B, the voltage V _H / 6 is balanced so as to maintain a multiplied voltage of 1 to 6 times. Similarly, when the piezoelectric element 40 is charged, the holding voltage of any of the capacitive elements C1 to C6 corresponding to the power supply wiring used for the charging is temporarily reduced. Balance so as to maintain a multiplied voltage of 1 to 6 times V _H / 6.
As can be seen from the voltage waveform of the control signal COM in FIG. 4, the voltage increase for drawing ink and the voltage decrease for discharging ink are a set, and the set is repeated in the printing operation. For this reason, in the auxiliary power supply unit 50, the electric charge recovered by the discharge of the piezoelectric element 40 is used for the subsequent charging.
Therefore, in the first embodiment, when the entire printing apparatus 100A is viewed, the power consumed by the collection and reuse of the electric charges discharged from the piezoelectric element 40 and the stepwise charging / discharging in the driver 30 is reduced. It can be kept low.

In the auxiliary power supply unit 50, when the common terminal of each switch is switched from one to the other of the terminals a and b, if there is a characteristic variation in a plurality of (10 in FIG. 13) switches, the switches are simultaneously switched. It is possible that a non-existent state occurs and both ends of the capacitive element are short-circuited. For example, when the terminal a is connected to the common terminal by the switches Sw1u, Sw1d, and Sw2d at the time of switching, if a state occurs in which the terminal b is connected to the common terminal by the switch Sw2u, both ends of the series connection of the capacitive elements C12 and C23 They are short-circuited.
For this reason, at the time of switching the switch, a configuration in which the occurrence of the short circuit is suppressed through a neutral state in which the switch is not connected to either of the terminals a and b is preferable.

Second Embodiment
FIG. 15 is a block diagram of a printing apparatus 100B according to the second embodiment. As illustrated in FIG. 15, the printing apparatus 100B according to the second embodiment replaces the print data generation unit 120 and the control signal supply unit 140 in the control unit 10 of the printing apparatus 100A according to the first embodiment with a control unit 160. In this configuration, the head control unit 220 and the selection unit 230 of the print head 20 are replaced with a signal generation unit 280. In addition, about the element which an effect | action and function are the same as that of 1st Embodiment in each form illustrated below, the reference | standard referred by description of 1st Embodiment is diverted, and each detailed description is abbreviate | omitted suitably.

  The signal generation unit 280 in FIG. 15 is an element that supplies the control signal Vin to each driver 30 of the element driving unit 240, and a plurality (the same number as the piezoelectric elements 40) of control signal supply units 282 corresponding to different piezoelectric elements 40. It comprises. That is, each control signal supply unit 282 corresponds to each set of the driver 30 and the piezoelectric element 40 on a one-to-one basis. Each control signal supply unit 282 of the second embodiment is an element that generates the control signal Vin and supplies the control signal Vin to the driver 30 at the subsequent stage, and includes a waveform generation unit 284 and a D / A converter 286. The waveform generation unit 284 generates a digital control signal dCOM as with the waveform generation unit 144 of the first embodiment. Similar to the D / A converter 145 of the first embodiment, the D / A converter 286 converts the control signal dCOM generated by the waveform generation unit 284 into an analog control signal Vin and supplies it to the driver 30. That is, in the first embodiment, the common control signal COM is distributed to the plurality of drivers 30 by the selection unit 230 over the plurality of piezoelectric elements 40, whereas in the second embodiment, each control signal supply unit 282 is distributed. Thus, the control signal Vin is generated independently for each piezoelectric element 40 and supplied to each driver 30.

  The control unit 160 of the control unit 10 sequentially instructs the control signal Vin to be generated by each control signal supply unit 282 to each of the plurality of control signal supply units 282 according to the image data (print data DP). Specifically, the control unit 160 controls the control signal Vin for each control signal supply unit 282 for each printing cycle Ta so that each piezoelectric element 40 ejects ink droplets of an ejection amount corresponding to the image data from the nozzles. Instruct. Since each control signal supply unit 282 individually generates a control signal Vin in accordance with an instruction from the control unit 160, the control signal Vin generated by each control signal supply unit 282 has a waveform or position (phase) on the time axis. It can be different. That is, the ejection amount of ink droplets by the piezoelectric element 40 (the diameter of dots formed on the recording material by ink droplets) and the ejection timing (landing position of the ink droplets on the recording material) are individually adjusted for each piezoelectric element 40. The

  Also in the second embodiment, since the driver 30 installed for each piezoelectric element 40 generates the voltage Vout from the control signal Vin and supplies the voltage Vout to the piezoelectric element 40, similarly to the first embodiment, each wiring and each circuit There is an advantage that required withstand voltage performance and withstand current performance can be reduced as compared with the proportionality. In the second embodiment, each control signal supply unit 282 generates a control signal Vin individually for each piezoelectric element 40. Therefore, for example, by adjusting the waveform and position of the control signal Vin for each piezoelectric element 40 in accordance with the characteristics of each ejection unit 400 (for example, the conversion efficiency of the piezoelectric element 40), the influence of the difference in the characteristics of each piezoelectric element 40 is affected. There is an advantage that it can be reduced.

<Application and modification>
The present invention is not limited to the above-described embodiments, and various applications and modifications as described below are possible, for example. Note that one or a plurality of arbitrarily selected aspects of application / deformation described below can be appropriately combined.

<Negative feedback control>
FIG. 16 is a diagram illustrating an example of the configuration of the driver 30 according to the application example (part 1) of the embodiment. As shown in this figure, in this application example, the voltage Vout at one end of the piezoelectric element 40 is negatively fed back to the input end (−) of the operational amplifier 32. In this configuration, when the voltage of the control signal Vin is different from the voltage Vout, the transistors 341 and 342 are controlled in a direction to eliminate the difference. For this reason, even when the response characteristics of the level shifters 36a to 36f and the transistors 341 and 342 are poor, the voltage Vout can be made to follow the control signal Vin relatively quickly and with high accuracy.
The negative feedback amount is preferably configured to be appropriately set according to the characteristics of the level shifters 36a to 36f and the transistors 341 and 342. For example, in the example of the figure, the operational amplifier 32 is configured to output a voltage obtained by subtracting the voltage Vout from the voltage of the control signal Vin. The subtracted voltage is multiplied by an appropriate coefficient and supplied to the level shifters 36a to 36f. It is good also as composition to do.

FIG. 17 is a diagram illustrating an example of the configuration of the driver 30 according to another application example (part 2) of the embodiment. In the driver 30 described with reference to FIG. 5, the transistors 341 and 342 of the unit circuits 34 a to 34 f are bipolar types. However, in the application example (part 2) illustrated in FIG. 17, each of the transistors 341 and 342 is P, N-channel MOSFETs (Metal-Oxide-Semiconductor Field-Effect Transistors) 351 and 352 are used.
When the MOSFETs 351 and 352 are used, a backflow preventing diode may be provided between each drain terminal and one end of the piezoelectric element 40. When the MOSFETs 351 and 352 are used, if the level shifters 36a to 36f are in the enabled state, the voltage of the control signal Vin is shifted in a minus direction by a predetermined value to correspond to the threshold voltage, and the P-channel MOSFET 351 is used. The voltage of the control signal Vin is shifted in the plus direction by an amount corresponding to the threshold voltage and supplied to the gate terminal of the N-channel MOSFET 352.
Further, when the MOSFETs 351 and 352 are used, a configuration in which the voltage Vout is negatively fed back as shown in FIG. 16 may be applied.

<Drive target>
In the above-described embodiment, the piezoelectric element 40 has been described as an example of the driver 30 to be driven. The present invention is not limited to the piezoelectric element 40 as a driving target, and can be applied to all loads having capacitive components such as an ultrasonic motor, a touch panel, a flat speaker, a liquid crystal display, and the like.

<Number of unit circuit stages>
In the embodiment, the six stages of unit circuits 34a to 34f are provided in order of increasing voltage so as to correspond to two voltages adjacent to each other among the seven types of voltages. The number of stages is not limited to this, but may be two or more. Further, the voltages do not necessarily have to be equally spaced.

<Comparator>
In the embodiment, for example, if the determination result of the comparator 38a is false (output signal is L level), it is detected that the state is the first state, and the determination result of the comparator 38a is true (output signal is H level). In addition, if the determination result of the comparator 38b is false, the second state is detected. That is, the configuration for detecting the first state and the second state is not a separate body, but is a configuration that partially overlaps, and the configuration in which the comparators 38a to 38e detect the first state to the sixth state. Met. The configuration is not limited to this, and each state may be detected individually.

<Disabled level shifter>
In the embodiment, the level shifters 36a to 36f in the disabled state supply a voltage zero to the base (gate) terminal of the transistor 341 (351) and supply the voltage _VH to the base (gate) terminal of the transistor 342 (352). However, the present invention is not limited to this as long as the transistors 341 and 342 can be turned off. For example, when the level shifters 36a to 36f are in a disabled state, the level shifters 36a to 36f supply an off signal obtained by shifting the voltage of the control signal Vin in the positive direction to the base (gate) terminal of the transistor 341 (351), and the control signal Vin Alternatively, an off signal obtained by shifting the voltage in the negative direction may be supplied to the base (gate) terminal of the transistor 342 (351).
According to this configuration, since the transistors 341 (351) and 342 (352) have low withstand voltage, the transistor size when formed on the semiconductor substrate can be reduced.

DESCRIPTION OF SYMBOLS 100 ... Printing apparatus (liquid discharge apparatus) 10 ... Control unit 120 ... Print data generation part 140 ... Control signal supply part 180 ... Main power supply part 20 ... Print head 30 ... Driver (connection) (Path selection unit), 32 ... operational amplifier, 34a to 34f ... unit circuit, 36a to 36f ... level shifter, 38a to 38f ... comparator, 40 ... piezoelectric element, 50 ... auxiliary power supply unit (voltage generation unit), 341, 342 ... Transistors 220... Head control unit 230... Selection unit 240 240 element drive unit 400.

Claims (3)

1st discharge including the nozzle which discharges a liquid, the pressure chamber connected to the said nozzle, and the piezoelectric element which is provided for every said pressure chamber and discharges a droplet from the said nozzle by charge and discharge according to a drive signal And a second discharge part,
A plurality of voltages that are installed corresponding to the first discharge unit and selectively include a first voltage, a second voltage that is higher than the first voltage, or a third voltage that is higher than the second voltage. A first connection path selection unit that supplies the first ejection unit;
A second connection path selection unit that is installed corresponding to the second ejection unit and selectively supplies a plurality of voltages including the first voltage, the second voltage, or the third voltage to the second ejection unit. When,
A voltage generator that generates and supplies the plurality of voltages to the first connection path selector and the second connection path selector;
Comprising
Each of the first connection route selection unit and the second connection route selection unit is
A first transistor connected to a first signal path to which the first voltage is applied; and a second transistor connected to a second signal path to which the second voltage is applied. A first transistor pair in which a voltage at a connection portion between the other end of the second transistor and the other end of the second transistor is supplied to the discharge portion;
A third transistor connected to the second signal path; and a fourth transistor connected to a third signal path to which the third voltage is applied. The other end of the third transistor and the fourth transistor A second transistor pair in which the voltage at the connection with the other end of the transistor is supplied to the discharge section;
Each including a liquid ejection device. The voltage generator is
The second voltage is generated using a charge discharged from the piezoelectric element through the first signal path.
The liquid ejection apparatus according to claim 1. Prior Symbol first connection path selection section,
According to the holding voltage of the piezoelectric element, the first discharge unit and the voltage generation unit are electrically connected by the first signal path or the second signal path,
The second connection path selection unit is
3. The liquid ejection apparatus according to claim 1, wherein the second ejection unit and the voltage generation unit are electrically connected by the first signal path or the second signal path in accordance with a holding voltage of the piezoelectric element.