JP6264894B2 - LIQUID DISCHARGE DEVICE, HEAD UNIT, AND NOZZLE GOOD / FAILURE JUDGING METHOD FOR LIQUID DISCHARGE DEVICE - Google Patents

Description

The present invention relates to a liquid ejection device, a head unit, and a nozzle quality determination method for a liquid ejection device.

2. Related Art An ink jet printer that prints an image or a document by ejecting ink is known that uses a piezoelectric element (for example, a piezo element). The piezoelectric element is provided in the head unit corresponding to each of the plurality of nozzles, and is driven according to a drive signal to discharge a predetermined amount of ink (liquid) from the nozzles at a predetermined timing. Yes.
In such a configuration, when the viscosity of the ink in the ejection unit increases (thickening), ejection abnormality occurs, and the image quality of the printed image decreases. In addition, when bubbles are included in the ink in the ejection unit, ejection abnormality occurs, and similarly, the image quality of the printed image is degraded.

Therefore, in order to realize high-quality printing, a technique has been proposed in which residual vibration generated by driving a piezoelectric element is detected, and the ink ejection state in the ejection unit is inspected based on the detection result ( For example, see Patent Document 1).
The head unit is provided with a large number (for example, 400) of nozzles and piezoelectric elements. Providing means for detecting residual vibration on a one-to-one basis for each of the nozzles only complicates the configuration, and a configuration in which the means is shared by a large number of nozzles becomes practical (FIG. 1 of the above-mentioned patent document 1). 30).

JP 2013-028183 A

However, in the configuration in which the means for detecting residual vibration is shared for many nozzles,
The inspection is performed while switching the nozzles (piezoelectric elements) to be inspected one by one, but it has been pointed out that with such a configuration, the accuracy of determining the quality of the nozzles is lowered.
Accordingly, one of the objects of some aspects of the present invention is to provide a technique that improves the accuracy of determining the quality of a nozzle in a configuration in which a means for detecting residual vibration is shared by a plurality of nozzles.

In order to achieve one of the above objects, a liquid ejecting apparatus according to an aspect of the present invention includes a piezoelectric element that is displaced according to a voltage between one terminal and the other terminal held at a predetermined first voltage. A cavity that is filled with liquid and whose internal volume increases and decreases due to displacement of the piezoelectric element, a nozzle that communicates with the cavity and that can discharge the liquid as droplets by increasing and decreasing the internal volume of the cavity, and one end A plurality of sets including a switch in which the one end is connected to one terminal of the piezoelectric element and the other ends are commonly connected to each other in the inspection period. When the nozzle of this test is to be inspected, after applying the voltage of the test pattern to one terminal of the one piezoelectric element corresponding to the one nozzle, the switch corresponding to the one piezoelectric element is A potential difference between a control unit that causes a switch corresponding to a piezoelectric element other than the one piezoelectric element to be in a non-conductive state, and a common connection point between the other terminal of the piezoelectric element and the other end of the switch. And an output unit that outputs a corresponding voltage.

In this aspect, the piezoelectric element functions as an actuator that discharges droplets during a period other than the inspection period, and functions as a sensor that detects residual vibration generated by application of the test pattern during the inspection period. The output unit outputs a voltage corresponding to the residual vibration sensed by the piezoelectric element to be inspected. For this reason, the quality of the nozzle to be inspected can be determined by analyzing the voltage waveform output from the output unit. At this time, since the switch of the piezoelectric element to be non-inspected is brought into a non-conductive state, the influence of the piezoelectric element to be non-inspected is kept small.

In the one aspect, the control unit may be configured such that a voltage at the end of the test pattern is the first voltage. The switch is generally configured by a transistor. In the above configuration, when a switch (transistor) corresponding to one piezoelectric element to be inspected is turned on after the test pattern is applied, Since one end is the first voltage (not so high), the transistor constituting the switch can be downsized. That the transistor is miniaturized means that the capacitance between the source and the drain in a non-conduction state is small. For this reason, when the switch corresponding to the piezoelectric element to be inspected is in a non-conducting state, the parasitic capacitance is reduced, so that the influence of the non-inspecting object can be suppressed.

In the above configuration, the control unit applies a voltage of a driving pattern starting from a predetermined second voltage and ending with the second voltage to one terminal of the piezoelectric element in a printing period other than the inspection period, In the first period of the inspection period, a voltage applied to one terminal of the piezoelectric element is gradually changed from the second voltage to the first voltage, and in the second period after the first period, the piezoelectric element is changed. A switch corresponding to the one piezoelectric element in a third period after the second period is applied to one terminal of the element by applying a test pattern voltage starting from the first voltage and ending with the first voltage. Is turned on, switches corresponding to the piezoelectric elements other than the one piezoelectric element are turned off, and a voltage applied to one terminal of the piezoelectric element in the fourth period after the third period is set to The above 1 the voltage may be gradually changed to the second voltage. Thereby, the printing period (during droplet ejection) and the inspection period can be alternately repeated.

The said structure WHEREIN: The said control part may apply the 3rd voltage higher than the said 2nd voltage to one terminal of the piezoelectric element not examined by the end of the said 2nd period. When the switch is composed of transistors, the voltage held by the non-inspected piezoelectric element increases.
The terminal (drain terminal) of the transistor connected to one terminal of the piezoelectric element is also increased, and the capacitance between the source and drain of the transistor in a non-conducting state is reduced. For this reason, the influence by a non-inspection object can be suppressed further smaller.

Note that the present invention can be realized in various modes. For example, it can be realized in various modes, such as a nozzle quality determination method for a liquid ejection device or a single head unit.

It is a figure which shows the structure of the control unit and head unit of the printing apparatus which concern on embodiment. It is a figure which shows the structure of the discharge part in a head unit. It is a figure which shows the nozzle arrangement | sequence in a head unit. It is a figure which shows the operation | movement of the printing period of a printing apparatus, and the waveform of a drive signal. It is a figure which shows the structure of the selection control part in a head unit. It is a figure which shows an example of the decoding content of a decoder. It is a figure which shows the structure of a selection part. It is a figure which shows the drive signal Vin selected by the selection part. It is a figure which shows an example of a structure of the driver in a head unit. It is a figure which shows the operation | movement range of each level shifter in a driver. It is a figure which shows an example of the relationship between the input and output in a driver. It is a figure which shows an example of the relationship between the input and output in a level shifter. It is a figure for demonstrating the flow of the electric current in a driver. It is a figure for demonstrating the flow of the electric current in a driver. It is a figure for demonstrating the flow of the electric current in a driver. It is a figure for demonstrating the flow of the electric current in a driver. It is a figure which shows the loss of charging / discharging of the piezoelectric element in a printing apparatus. It is a figure which shows the loss of charging / discharging of the piezoelectric element in a comparative example (the 1). It is a figure which shows the drive signal etc. in the printing period and test | inspection period of a printing apparatus. It is a figure which shows the detection waveform of the 3rd period in a test | inspection period. It is a figure which shows the example of the analysis result of a detection waveform. It is a figure which shows the equivalent circuit around a piezoelectric element in the 3rd period of a printing apparatus. It is a figure which simplifies and shows an equivalent circuit. It is a figure which shows the equivalent circuit of a piezoelectric element periphery in a comparative example (the 2). It is a figure which simplifies and shows an equivalent circuit.

  Hereinafter, embodiments for carrying out the present invention will be described with reference to the drawings.

<Overall configuration of printing apparatus>
The printing apparatus according to this embodiment forms a group of ink dots on a print medium such as paper by ejecting ink according to image data supplied from a host computer, and thereby an image corresponding to the image data ( An ink jet printer that prints characters, figures, etc., that is, a liquid ejection device.

FIG. 1 is a diagram illustrating a schematic configuration of the printing apparatus 1.
As shown in this figure, the printing apparatus 1 includes a control unit 10 that executes arithmetic processing for printing an image based on image data supplied from a host computer, and a head unit 20 having a plurality of nozzles. It is a configuration that includes. The control unit 10 and the head unit 20 are electrically connected via a flexible cable 190. The head unit 20 is mounted on a carriage (not shown) that can move in a direction (main scanning direction) substantially perpendicular to the print medium feeding direction (sub-scanning direction).

The control unit 10 includes a main control unit 120, a main power supply circuit 140, a DAC (Digital to A
nalog Converter) 161, 162.
Based on the image data acquired from the host computer, the main control unit 120 executes arithmetic processing for printing such as image development processing, color conversion processing, ink color separation processing, and halftone processing, and the head unit A plurality of types of signals for ejecting ink from the 20 nozzles are generated. The plural types of signals include digital control data dA and dB, and the selection control unit 2
Various signals supplied to 00, specifically, a clock signal Sck, a data signal Data, and control signals LAT and CH are included.
Each calculation process for printing executed by the main control unit 120 may be executed by the host computer. Since the content of the arithmetic processing for printing is a well-known matter in the technical field of printing apparatuses, description thereof is omitted.
The main control unit 120 includes an analysis unit 130. The analysis unit 130 executes a predetermined program and converts the data Dk output from the head unit 20 into, for example, FFT (Fast Fo
frequency analysis by urier Transform).

The printing apparatus 1 includes a carriage motor that moves a carriage on which the head unit 20 is mounted in the main scanning direction, a conveyance motor that conveys a print medium in the sub-scanning direction, and the control unit 10 includes However, since it is a well-known matter, the description thereof is omitted.

The main power supply circuit 140 supplies a power supply voltage to each part of the control unit 10 and the head unit 20, and particularly supplies Vp and G as power supply voltages to the head unit 20.
Note that G (ground) is a ground potential, and unless otherwise specified in this description, is a reference of zero voltage. In addition, the voltage Vp is on the higher side with respect to the ground G in the embodiment.
The DAC 161 converts the control data dA into an analog drive signal COM-A and supplies it to the head unit 20. Similarly, the DAC 162 converts the control data dB into an analog drive signal COM-B and supplies it to the head unit 20.

The head unit 20 includes a plurality of sets of a driver 30, a piezoelectric element (piezo element) 40, and a transistor 240 in addition to the selection control unit 200, the selection unit 230, the resistance element 290, the amplifier 292, and the ADC 294. The selection control unit 200 is divided into blocks 210 and 220. The transistor 240 is a MOSFET (Metal-Oxide-Semiconductor Fiel
d-Effect Transistor) and functions as a switch.

In the present embodiment, the operation period is divided into a printing period in which the piezoelectric element is driven for printing and an inspection period in which an inspection for determining the quality of the nozzle is performed. In the inspection period, the main control unit 120 instructs one nozzle to be inspected.

A block 210 controls selection of the selection unit 230 according to various signals supplied from the main control unit 120 during the printing period.
The selection unit 230 is provided corresponding to each of the plurality of sets of the driver 30 and the piezoelectric element 40, and selects (or does not select) the drive signals COM-A and COM-B according to the control by the block 210. A drive signal Vin is supplied to the input terminal of the driver 30.
Further, the block 210 causes the selection unit 230 corresponding to the nozzles to be inspected to select the drive signal COM-A during the inspection period, and the selection unit 230 corresponding to the nozzles not to be inspected. The drive signal COM-B is selected.

The block 220 of the selection control unit 200 individually outputs control signals to the gate terminals of the respective transistors (FETs) 240.
Specifically, the block 220 applies the transistor 240 to the gate terminal of the transistor 240 corresponding to the nozzle (piezoelectric element 40) instructed by the main control unit 120 over the third period of the inspection period. A signal for turning on (conductive state) is output, and a signal for turning off (non-conductive state) is output to the other transistors 240. The block 220 outputs a signal for turning off all the transistors 240 including the printing period except for the third period.
The inspection period is divided into four periods from the first period to the fourth period, although details will be described later.
In addition, the main control unit 120 and the selection control unit 200 (blocks 210 and 220) control the voltage supplied to the piezoelectric element 40 during the printing period and the inspection period, and regulate ON / OFF of the transistor 240 as a switch. The control unit 120 and the selection control unit 200 (blocks 210 and 220) can be collectively considered as one control unit.

The driver 30 generates a voltage Vout according to the drive signal Vin supplied from the selection unit 230.
The drive signal is output to drive the piezoelectric element 40. Details of the driver 30 will be described later.
The auxiliary power supply circuit 280 divides the power supply voltages Vp and G supplied from the main power supply circuit 140 into six and outputs them. In particular, the auxiliary power supply circuit 280, a power supply voltage (Vp-G) and 6 divided, common across each driver 30 as a voltage _V 5 in descending order as the intermediate _{voltage, V 4, V 3, V} 2, V 1 Output to.
Note that the voltages V _{6 to} V ₀ are V ₆ = V p, respectively, with respect to the voltage V p.
V ₅ = 5Vp / 6,
V ₄ = 4Vp / 6,
V ₃ = 3Vp / 6,
V ₂ = 2Vp / 6,
V ₁ = Vp / 6,
V ₀ = G (= 0),
There is a relationship.

One terminal of the piezoelectric element 40 is connected to the output terminal of the corresponding driver 30 and the drain terminal which is one end of the transistor 240. The source terminals which are the other ends of the transistors 240 are connected in common and are connected to one input terminal of the amplifier 292. The other terminal of the piezoelectric element 40 is commonly connected to the feed line maintained at a voltage V _BS which is the first voltage. Therefore, the voltage held in the piezoelectric element 40 is the voltage Vout and the voltage V
It becomes the difference with _BS .
The other terminal of the piezoelectric element 40 is connected to the other input terminal of the amplifier 292 together with the feeder line.
In the present embodiment, V ₁ = V _{BS for} convenience.
And

In the amplifier 292, a resistance element 290 is electrically interposed between one input end and the other input end. The resistance element 290 converts the current flowing from one of the two terminals to the other into a voltage, and the amplifier 292 amplifies the converted voltage with a predetermined gain and outputs it as a signal Vk.
An ADC (Analog to Digital Converter) 294 converts the signal Vk into digital data Dk, and supplies the data Dk to the analysis unit 130 via the flexible cable 190.
Therefore, the resistor element 290 and the amplifier 292 (ADC 294) are collectively considered as an output unit that outputs a voltage corresponding to a potential difference between one terminal of the piezoelectric element 40 and the common connection point of the source terminal of the transistor 240. Is possible.

The piezoelectric element 40 is provided corresponding to each of the plurality of nozzles in the head unit 20. Then, the piezoelectric element 40 has a voltage Vout and a voltage V of the drive signal by the driver 30.
_The ink is displaced in accordance with the difference from _BS to eject ink. Next, a configuration for ejecting ink by driving the piezoelectric element 40 will be briefly described.

FIG. 2 is a diagram illustrating a schematic configuration of the ejection unit 400 corresponding to one nozzle in the head unit 20.
As shown in the drawing, the ejection 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 diaphragm 421 is
In the figure, the piezoelectric element 40 provided on the upper surface deforms (bends and vibrates) and functions as a diaphragm that expands / reduces the internal volume of the cavity 431 filled with ink. The nozzle 451 is an opening provided in the nozzle plate 432 and communicating 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. . In particular,
The piezoelectric element 40 is configured to bend upward when the voltage Vout of the drive signal increases, and to bend downward when the voltage Vout decreases. In this configuration, if the ink is bent upward, the internal volume of the cavity 431 is expanded. Therefore, if ink is drawn from the reservoir 441, if the ink is bent downward, the internal volume of the cavity 431 is reduced. In some cases, ink is ejected from the nozzle 451.

The piezoelectric element 40 is not limited to a unimorph type but may be a bimorph type or a laminated type that can deform the piezoelectric element 40 and discharge a liquid such as ink. Also,
The piezoelectric element 40 is not limited to bending vibration, and may be configured to use longitudinal vibration.
The piezoelectric element 40 is provided corresponding to the cavity 431 and the nozzle 451 in the ejection unit 400, and the piezoelectric element 40 is a transistor 240 as a switch in FIG.
Is also provided correspondingly. Therefore, a set of the piezoelectric element 40, the cavity 431, the nozzle 451, and the transistor 240 is provided for each nozzle 451.

FIG. 3 is a diagram illustrating an example of the arrangement of the nozzles 451.
As shown in this figure, the nozzles 451 are arranged in two rows. In detail, nozzle 4
51, when viewed in one row, a plurality of nozzles 451 are arranged at a predetermined pitch along the sub-scanning direction, while two rows are shifted by half the pitch in the sub-scanning direction. Yes.
Note that the nozzle 451 performs C (cyan), M (magenta), and Y for color printing.
A pattern corresponding to each color such as (yellow) and K (black) is provided along the main scanning direction, for example, but in this description, for the sake of simplicity, the description will be made assuming that monochrome printing is performed.

By the way, in the ejection unit 400, there is a case where an ejection abnormality occurs in which an ink droplet is not ejected normally from the nozzle 451 even though the ink ejection operation is executed. Specifically, this ejection abnormality is caused by the fact that dots are not formed on the print medium, the amount of ink droplets is too small, or the flight direction (ballistic trajectory) of the ink droplets is misaligned. This is a phenomenon that it is not properly formed on the print medium.
In addition, as a cause of occurrence of the ejection abnormality, there are bubbles mixed in the cavity 431, ink viscosity increase (thickening) near the nozzle 451, and the like.

  Here, for convenience, the waveforms of the drive signals COM-A and COM-B will be described.

FIG. 4 is a diagram illustrating waveforms of the drive signals COM-A and COM-B.
As shown in the figure, the drive signal COM-A has a trapezoidal waveform Adp arranged in a period T1 from the rise of the control signal LAT to the rise of the control signal CH in the printing cycle Ta.
1 and a trapezoidal waveform Adp2 arranged in a period T2 from the rise of the control signal CH to the rise of the next control signal LAT in the printing cycle Ta.
In the present embodiment, the trapezoidal waveforms Adp1 and Adp2 are substantially the same waveforms.
If each is supplied to the driver 30 and the piezoelectric element 40 is driven based on the waveform, a predetermined amount, specifically, a medium amount of ink is supplied from the nozzle 451 corresponding to the piezoelectric element 40. Each is a waveform to be discharged.

The drive signal COM-B has a waveform in which the trapezoidal waveform Bdp1 arranged in the period T1 and the trapezoidal waveform Bdp2 arranged in the period T2 are continuous. In this embodiment, trapezoidal waveform B
dp1 and Bdp2 have different waveforms. Among these, the trapezoidal waveform Bdp1 is a waveform for preventing the viscosity of the ink from increasing by causing the ink near the opening of the nozzle 451 to vibrate. For this reason, even if the trapezoidal waveform Bdp1 is supplied to the driver 30 and the piezoelectric element 40 is driven based on the waveform, ink droplets are not ejected from the nozzle 451 corresponding to the piezoelectric element 40. The trapezoidal waveform Bdp2 is a trapezoidal waveform Adp1 (Adp2).
It has a different waveform. If the trapezoidal waveform Bdp2 is supplied to the driver 30 and the piezoelectric element 40 is driven based on the waveform, the ink smaller than the predetermined amount is ejected from the nozzle 451 corresponding to the piezoelectric element 40. It is a waveform.
Note that the voltage at the start timing and the voltage at the end timing of the trapezoidal waveforms Adp1, Adp2, Bdp1, and Bdp2 are all the same as Vc that is the second voltage. That is,
The trapezoidal waveforms Adp1, Adp2, Bdp1, and Bdp2 are drive patterns that start at the voltage Vc and end at the voltage Vc, respectively.

FIG. 5 is a diagram illustrating a configuration of a block 210 that controls selection of the selection unit 230 in the selection control unit 200 in FIG.
As shown in this figure, the block 210 includes a clock signal Sck, a data signal Data.
, Control signals LAT and CH are supplied from the control unit 10. In the block 210, a set of a shift register (S / R) 212, a latch circuit 214, and a decoder 216 is provided corresponding to each of the piezoelectric elements 40 (nozzles 451).

The data signal Data defines the amount of ink ejected from one nozzle when forming one dot of an image. In the present embodiment, in order to express four gradations of non-recording, small dots, medium dots, and large dots, the data signal Data is composed of two bits, an upper bit (MSB) and a lower bit (LSB).
The data signal Data is sent to the head unit 20 for each nozzle in synchronization with the clock signal Sck.
Is supplied serially from the main control unit 120 in accordance with the main scanning. The shift register 212 is a configuration for temporarily holding the serially supplied data signal Data for 2 bits corresponding to the nozzle.
Specifically, the shift registers 212 having the number of stages corresponding to the piezoelectric elements 40 (nozzles) are connected in cascade, and the serially supplied data signal Data is sequentially transferred to the subsequent stage according to the clock signal Sck. ing.
When the number of piezoelectric elements 40 is m (m is a plurality), in order to distinguish the shift register 210, the first, second,..., M stages in order from the upstream side to which the data signal Data is supplied. It is written.

The latch circuit 214 latches the data signal Data held in the shift register 212 at the rising edge of the control signal LAT.
The decoder 216 receives the 2-bit data signal D latched by the latch circuit 214.
Ata is decoded, and selection signals Sa and Sb are output for each of the periods T1 and T2 defined by the control signal LAT and the control signal CH, thereby defining the selection by the selection unit 230.

FIG. 6 is a diagram showing the decoding contents in the decoder 216.
In this figure, the latched 2-bit print data Data (MSB, LS
B). For example, the decoder 216 receives the latched print data Data (0).
1) means that the logic levels of the selection signals Sa and Sb are outputted as H and L levels in the period T1, respectively, and are outputted as L and H levels in the period T2, respectively.
Note that the logic levels of the selection signals Sa and Sb are the clock signal Sck and the print data D.
The level is shifted to a high amplitude logic by a level shifter (not shown) rather than the logic levels of ata, control signal LAT and control signal CH.

FIG. 7 shows a selection unit 230 corresponding to one piezoelectric element 40 (nozzle 451) in FIG.
FIG.
As shown in this figure, the selection unit 230 includes inverters (NOT circuits) 232a, 2
32b and transfer gates 234a and 234b.
The selection signal Sa from the decoder 216 is supplied to the positive control terminal of the transfer gate 234a, while being logically inverted by the inverter 232a and supplied to the negative control terminal of the transfer gate 234a. Similarly, the selection signal Sb is transferred from the transfer gate 2.
While being supplied to the positive control terminal of 34b, the logic is inverted by the inverter 232b,
It is supplied to the negative control terminal of the transfer gate 234b.
The drive signal COM-A is supplied to the input terminal of the transfer gate 234a, and the drive signal COM-B is supplied to the input terminal of the transfer gate 234b. The output terminals of the transfer gates 234a and 234b are commonly connected to serve as an input terminal to the driver 30.
When the selection signal Sa is at the H level, the transfer gate 234a conducts (turns on) between the input end and the output end, and when the selection signal Sa is at the L level, the transfer gate 234a does not conduct between the input end and the output end. (Off). Similarly, the selection signal Sb is applied to the transfer gate 234b.
In response to this, the input end and the output end are turned on and off.

Next, operations of the block 210 and the selection unit 230 in the selection control unit 200 will be described with reference to FIG.

The data signal Data is serially supplied from the main control unit 120 for each nozzle in synchronization with the clock signal Sck, and sequentially transferred in the shift register 212 corresponding to the nozzle.
When the supply of the clock signal Sck is stopped, each shift register 212 has
The data signal Data corresponding to the nozzle is held. The data signal Data is
They are supplied in the order corresponding to the last m stages,..., 2 stages, and 1 stage nozzles in the shift register 222.
Here, when the control signal LAT rises, each of the latch circuits 214 simultaneously latches the data signal Data held in the shift register 212. In FIG. 4, L1, L
2,..., Lm indicate the data signal Data obtained by latching the data signal Data by the latch circuit 214 corresponding to the first, second,.

In accordance with the ink amount defined by the latched data signal Data, the decoder 216
In each of the periods T1 and T2, the logic levels of the selection signals Sa and Sa are output as shown in FIG.
That is, first, the decoder 216 has the data signal Data (1, 1),
When prescribing ejection of a large dot ink amount, the selection signals Sa and Sb are set to H in the period T1.
, L level, and H and L level also in the period T2. Second, the decoder 216 sets the selection signals Sa and Sb to the H and L levels in the period T1 when the data signal Data is (0, 1) and regulates the ejection of the medium dot ink amount. L, H at T2
Level. Third, the decoder 216 sets the selection signals Sa and Sb to L and L levels in the period T1 when the data signal Data is (1, 0) and defines the ejection of the small dot ink amount. At T2, L and H levels are set. Fourth, the decoder 216 selects the selection signals Sa and S when the data signal Data is (0, 0) and defines non-recording.
b is set to L and H levels in the period T1, and is set to L and L levels in the period T2.

FIG. 8 shows a control signal Vi selected according to the data signal Data and supplied to the driver 30.
It is a figure which shows the voltage waveform of n.
When the data signal Data is (1, 1), since the selection signals Sa and Sb are at the H and L levels in the period T1, the transfer gate 234a is turned on and the transfer gate 234b is turned off. Therefore, the trapezoidal waveform Ad of the drive signal COM-A in the period T1
p1 is selected. Since the selection signals Sa and Sb are at the H and L levels even during the period T2,
The selection unit 230 selects the trapezoidal waveform Adp2 of the drive signal COM-A.
As described above, the trapezoidal waveform Adp1 is selected in the period T1, and the trapezoidal waveform Adp2 is selected in the period T2, and is supplied to the driver 30 as the drive signal Vin. Driver 3
0 outputs the voltage Vout so as to follow the voltage of the drive signal Vin, as will be described later, and drives the piezoelectric element 40 corresponding to the nozzle. For this reason, the trapezoidal waveform Adp is used as the drive signal Vin.
When 1, Adp2 is selected and supplied to the driver 30, a medium amount of ink is ejected in two from the nozzle corresponding to the piezoelectric element 40 driven by the driver 30. Accordingly, the respective inks land on the print medium and coalesce, and as a result, large dots as defined by the data signal Data are formed.

When the data signal Data is (0, 1), the selection signals Sa and Sb are at the H and L levels in the period T1, so that the transfer gate 234a is turned on and the transfer gate 234b is turned off. Therefore, the trapezoidal waveform Ad of the drive signal COM-A in the period T1
p1 is selected. Next, since the selection signals Sa and Sb are at the L and H levels in the period T2, the trapezoidal waveform Bdp2 of the drive signal COM-B is selected.
Therefore, medium and small amounts of ink are ejected from the nozzle in two steps. Accordingly, the respective inks land and merge on the print medium, and as a result, medium dots as defined by the data signal Data are formed.

When the data signal Data is (1, 0), the selection signals Sa and Sb are both at the L level in the period T1, so that the transfer gates 234a and 234b are turned off. For this reason, neither trapezoidal waveform Adp1 nor Bdp1 is selected in the period T1.
When both the transfer gates 234a and 234b are turned off, the driver 3
The path to the input terminal of 0 is in a high impedance state that is not electrically connected to any part. However, since the voltage Vc immediately before turning off is held by the capacitive component parasitic on the path, the voltage of the drive signal Vin does not become indefinite.
Next, since the selection signals Sa and Sb are at the L and H levels in the period T2, the drive signal CO
The MB trapezoidal waveform Bdp2 is selected. For this reason, since a small amount of ink is ejected from the nozzle only in the period T2, small dots as defined by the data signal Data are formed on the print medium.

When the data signal Data is (0, 0), the selection signals Sa and Sb are at the L and H levels in the period T1, so that the transfer gate 234a is turned off and the transfer gate 234b is turned on. For this reason, the trapezoidal waveform Bd of the drive signal COM-B in the period T1
p1 is selected. Next, since the selection signals Sa and Sb are both at the L level in the period T2, neither of the trapezoidal waveforms Adp2 and Bdp2 is selected.
For this reason, the ink in the vicinity of the nozzle opening only slightly vibrates in the period T1, and the ink is not ejected. As a result, no dot is formed, that is, the data signal Dat.
No record as specified in a.

As described above, the selection unit 230 performs the driving signal COM according to the control by the block 210.
-A or COM-B is selected (or not selected), and the driver 30 is used as the drive signal Vin.
And the driver 30 drives the piezoelectric element 40 in accordance with the drive signal Vin.
For this reason, during the printing period, the piezoelectric element 40 of each nozzle receives the corresponding data signal Data.
The ink is driven according to the amount of ink specified in (1).
Note that the drive signals COM-A and COM-B illustrated in FIG. 4 are merely examples. Actually, various combinations of waveforms prepared in advance are used according to the moving speed of the head unit and the properties of the print medium.
In addition, here, an example in which the piezoelectric element 40 bends upward as the voltage increases will be described.
When the voltage supplied to the electrodes 411 and 412 is reversed, the piezoelectric element 40 bends downward as the voltage increases. For this reason, in the configuration in which the piezoelectric element 40 bends downward as the voltage increases, the drive signals COM-A and COM-B illustrated in the figure have waveforms that are inverted with respect to the voltage Vc.

The piezoelectric element 40 is provided corresponding to each of a plurality of noises in the head unit 20 and is driven by a driver 30 that is a counterpart of the pair. That is, the piezoelectric element 40 is configured to be driven by a drive signal (voltage Vout) output from the driver 30.

FIG. 9 is a diagram illustrating an example of the configuration of the driver 30 that drives one piezoelectric element 40.
As shown in this figure, the driver 30 includes an operational amplifier 32 and unit circuits 34a to 3-3.
4f and comparators 38a to 38e, and the piezoelectric element 4 according to the drive signal Vin
It is the structure which drives 0. Further, voltages V _{0 to} V ₆ are supplied to the driver 30 via wirings 510 to 516, respectively.

The drive signal Vin selected by the selector 230 is supplied to the input terminal (+) of the operational amplifier 32 which 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. Therefore, the operational amplifier 32 converts the drive signal Vin to (1 + Rf /
Rin) times non-inverting amplification.
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 voltage of the drive 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 34 a to 34 f have seven types of voltages V _{6 to} V supplied from the auxiliary power circuit 280.
₀ is provided in order of increasing voltage corresponding to two voltages adjacent to each other. In detail
The unit circuit 34a corresponds to the voltage _{V 0} and the voltage _{V 1,}
The unit circuit 34b corresponds to the voltage _{V 1} and the voltage _{V 2,}
Unit circuit 34c corresponds to the voltage _{V 2} and the voltage _{V 3,}
Unit circuit 34d corresponds to the voltage _{V 3} and the voltage _{V 4,}
Unit circuit 34e corresponds to the voltage _{V 4} and the voltage _{V 5,}
Unit circuit 34f is provided corresponding to the voltage _{V 5} and the voltage _{V 6.}

The unit circuits 34a to 34f have the same circuit configuration, and level shifters 36a to 36
one corresponding to any one of f and bipolar NPN (P-type) transistor 3
41 and a PNP-type (N-type) 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 also generally described without being specified. In some cases, the code is simply described as “36”.
In addition, as for the transistors 341 and 342, the selection unit 2 is more preferably a MOSFET.
Although it is easy to integrate with the 30 constituent elements and the switch 240, in this description, the bipolar type is described for convenience.

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.

As will be described later, among the seven types of voltages, the five intermediate voltages V _{1 to} V ₅ are each associated one-to-one with the comparators 38a to 38e.
Here, when paying attention to a certain unit circuit 34, the negative control end to which the circle mark is attached among the control ends of the level shifter 36 in the unit circuit 34 corresponds to the unit circuit 34.
Among the two voltages, the output signal of the comparator associated with the higher voltage is supplied,
Of the level shifter 36, the positive control terminal not marked with a circle is supplied with the output signal of the comparator associated with the lower voltage of the two voltages corresponding to the unit circuit. Is done.
However, the negative control terminal of the level shifter 36f in the unit circuit 34f is connected to the wiring 510 that supplies the voltage V ₀ (L level), while the level shifter 3 in the unit circuit 34a.
The positive control terminal 6a is connected to a wiring 516 that supplies a voltage V ₆ (H level).

In the enabled state, the level shifter 36 shifts the voltage of the drive signal Vin in the minus direction by a predetermined value and supplies it to the base terminal of the transistor 341, and shifts the voltage of the drive signal Vin in the plus direction by a predetermined value. To the base terminal of the transistor 342. Level shifter 36 is in the disable state, the drive signal regardless of Vin, the voltage for turning off the transistor 341, for example, a voltage V ₆ the transistor 3
Supplies to the 41 base terminal of the supply voltage for turning off the transistor 342, for example, the voltage V ₀ to the base terminal of the transistor 342.
The predetermined value is, for example, a base-emitter voltage (bias voltage, about 0.6 volts) at which current starts to flow through the emitter terminal. That is, the predetermined value here is a property determined according to the characteristics of the transistors 341 and 342, and is zero if the transistors 341 and 342 are ideal.

Of the two corresponding voltages, the higher voltage is supplied to the collector terminal of the transistor 341, and the lower voltage is supplied to the collector terminal of the transistor 342.
For example, in the unit circuit 34 a corresponding to the voltage V ₀ and the voltage V ₁ , the transistor 34
1 the collector terminal is connected to a wiring 511 for supplying a voltage _{V 1,} the collector terminal of the transistor 342 is connected to a wiring 510 for supplying the voltage _{V 0.} Further, for example, in the unit circuit 34b corresponds to the voltage _{V 1} and the voltage _{V 2,} is connected to the wiring 512 for supplying the collector terminal voltage _{V 2} of the transistor 341, the voltage _{V 1} is the collector terminal of the transistor 342
Is connected to the wiring 511 for supplying the power. In the unit circuit 34f correspond to the voltage _{V 5} and the voltage _{V 6,} is connected to the wiring 516 for supplying the collector terminal voltage _{V 6} of the transistor 341, the wiring 515 for supplying the collector terminal voltage _{V 5} of the transistor 342 Connected.

On the other hand, in the unit circuits 34 a to 34 f, the emitter terminals of the transistors 341 and 342 are commonly connected to one terminal of the piezoelectric element 40.

Comparator 38a~38e are the five kinds of voltages V ₁ ~V _6, correspond one-to-one, respectively, by comparing the level of the voltage respectively supplied to two input terminals, a signal indicating the comparison result Is output. Here, of the two input ends of the comparators 38a to 38e, one end is supplied with a voltage corresponding to itself, and the other end is connected to one terminal of the piezoelectric element 40 together with the emitter terminals of the transistors 341 and 342. Commonly connected. For example, voltage V ₁
In the corresponding comparator 38a to one of the two inputs, at one end, is supplied with voltages V ₁ corresponding to itself, also for example in the comparator 38b corresponds to the voltage V _2, out of the two input terminals, one end , the voltage V ₂ corresponding to itself is supplied.

Each of the comparators 38a to 38e is at the H level (voltage V ₆ ) 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 L when the voltage Vout is less than the voltage at one end.
A signal having a level (voltage V ₀ ) is output.
Specifically, for example, the comparator 38a is a voltage Vout to the H level as long as voltages V ₁ or more, and outputs the L level signal is less than voltages V _1. Further, for example, the comparator 38b is set to the H level if the voltage Vout voltage _{V 2} or more, is less than the voltage _{V 2} L
A level signal is output.

When attention is paid to one voltage among 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, As described above, the voltage is supplied to the positive input terminal of the level shifter 36 of the unit circuit whose voltage is the lower voltage.
For example, the output signal of the comparator 38a which corresponds to the voltages V ₁ is a negative input terminal and, low voltage the voltage V ₁ of the level shifter 36a of the unit circuit 34a associated with the voltages V ₁ as high-side voltage Are respectively supplied to the positive input terminal of the level shifter 36b of the unit circuit 34b. Further, for example, the comparator 38b corresponding to the voltage _{V 2}
The output signal, the level shifter of the negative input and the unit circuit 34c associated with the voltage V ₂ as low voltage level shifter 36b of the voltage V ₂ to the high-potential voltage as the associated unit circuit 34b 36c is supplied to the positive input terminal.

Next, the operation of the driver 30 will be described.
First, the level shifters 36a to 36 with respect to the voltage Vout at one end of the piezoelectric element 40.
Consider what state f will be in.

FIG. 10 is a diagram illustrating a voltage range in which the level shifters 36a to 36f are enabled with respect to the voltage Vout.
First, in a first state voltage Vout is lower than the voltage _{V 1,} the comparator 38a~38f
All output signals are at 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 second state the voltage Vout is lower than voltages V ₁ or more voltage V _2, only the output signal of the comparator 38b becomes the H level, the output signal of the other comparator has an L level. Therefore, in the second state, only the level shifter 36b is enabled, and the other level shifters 36a, 36c to 36f are disabled.

The subsequent, the voltage Vout, in the third state is less than the voltage V ₂ equal to or higher than the voltage V _3, only the level shifter 36c is enabled state, the fourth state lower than the voltage V ₃ equal to or higher than the voltage V _4,
Only the level shifter 36d is enabled state, in the fifth state of less than the voltage V ₄ or the voltage V _5, only the level shifter 36e is enabled state, in the sixth state above voltages V _5, the level shifter 36f only is enabled It becomes a state.

When the level shifter 36a is enabled in the first state, the level shifter 36a supplies a voltage signal obtained by level shifting the drive 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 drive 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 drive signal Vin is higher than the voltage Vout (the connection point 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, the voltage Vout gradually rises and approaches the voltage of the drive signal Vin, and when the voltage Vout eventually matches the voltage of the drive signal Vin, the transistor 34 at that time.
The current flowing in 1 becomes zero.

On the other hand, when the voltage of the drive 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 drive signal Vin and eventually the voltage Vout matches the voltage of the drive 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 are
Control is performed so that the voltage Vout matches the drive signal Vin.

In the first state, in the unit circuit 34b~34f other than the unit circuit 34a, the level shifter 36 becomes disabled state, the voltage _{V 6} is supplied to the base terminal of the transistor 341, the base terminal of the transistor 342 Is supplied with voltage V ₀ . Therefore, in the first state, in the unit circuits 34b to 34f, the transistors 341 and 342 are provided.
Is turned off, and is not involved in the control of the voltage Vout.

Moreover, although the case where it is the 1st state is demonstrated here, it becomes the same operation | movement also about a 2nd state-a 6th state. Specifically, according to the voltage Vout held by the piezoelectric element 40,
Any one of the unit circuits 34a to 34f is enabled, and the transistors 341 and 342 of the enabled unit circuit 34 are controlled so that the voltage Vout matches the drive signal Vin. For this reason, when the driver 30 is viewed as a whole, the voltage Vout follows the voltage of the drive signal Vin.

Thus, as shown in (a) of FIG. 11, changes from the driving signal Vin, for example, the voltage V ₀ when rises to the voltage V _6, the voltage V ₀ to the voltage V ₆ the voltage Vout to follow the driving signal Vin To do. Further, as shown in the figure (b), the driving signal Vin when lowered from the voltage V _6, the voltage Vout also changes from the voltage V ₆ to follow the driving signal Vin.

FIG. 12 is a diagram for explaining the operation of the level shifter.
When the drive signal Vin rises from the voltage V ₀ to the voltage V ₆ , the voltage Vout is also the drive signal Vi.
Follows n and rises. In the course of this increase, the voltage Vout when the first state is less than the voltage V _1, the level shifter 36a is enabled. For this reason, as shown in FIG. 5A, the voltage (denoted as “P type”) supplied to the base terminal of the transistor 341 by the level shifter 36a shifts the drive signal Vin in the minus direction by a predetermined value. The voltage (indicated as N-type) supplied to the base terminal of the transistor 342 is a voltage obtained by shifting the drive 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 is V _{6 and the} voltage supplied to the base terminal of the transistor 342 is V _0. .

In addition, (b) of the figure shows the voltage waveform which the level shifter 36b outputs, and (c) of the figure
) Shows a voltage waveform output from the level shifter 36f. Level shifter 36b is enabled state when the voltage Vout of the second state is less than voltages _{V 1} or more voltage _{V 2,} the level shifter 36f, when the voltage Vout of the sixth state of less than the voltage _{V 5} or more voltage _{V 6} If you take note of the fact that it will be enabled, no special explanation will be required.
Further, the level shifter 3 in the process of increasing the voltage (or voltage Vout) of the drive signal Vin
A description of the operations of 6c to 36e and a description of the operations of the level shifters 36a to 36f in the process of decreasing the voltage (or voltage Vout) of the drive signal Vin are also omitted.

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

13, when the first state (the state of the voltage Vout lower than the voltage V _1), is a diagram illustrating the operation of when the piezoelectric element 40 is charged.
In the first state, the level shifter 36a is enabled, and the other level shifters 3
Since 6b to 36f are disabled, it is only necessary to focus on the unit circuit 34a.
When the voltage of the drive 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. On the other hand, the transistor 342 of the unit circuit 34a is off.

At the time of charging in the first state, the current is changed from the wiring 511 → as shown by the arrow in the figure.
The current flows through the path of the transistor 341 (from the unit circuit 34a) to the piezoelectric element 40, and the piezoelectric element 40 is charged. This charging increases the voltage Vout. Eventually, when the voltage Vout approaches and coincides with the voltage of the drive signal Vin, the transistor 341 of the unit circuit 34a is turned off, and charging to the piezoelectric element 40 is stopped.
On the other hand, if the drive signal Vin rises to voltages V ₁ or more, the voltage Vout also becomes voltages V ₁ or more so as to follow the driving signal Vin, a second state (voltage Vout voltages V ₁ or the voltage from the first state to migrate to V ₂ less than the state).

FIG. 14 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 3
Since 6a and 36c to 36f are disabled, it is only necessary to focus on the unit circuit 34b.
When the drive 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. On the other hand, the unit circuit 34b
The transistor 342 is off.

At the time of charging in the second state, the current is shown in FIG.
The charge flows in the path of the transistor 341 (of the unit circuit 34 b) → the piezoelectric element 40 and charges the piezoelectric element 40. That is, when the piezoelectric element 40 is charged in the second state, one terminal of the piezoelectric element 40 is electrically connected to the auxiliary power supply circuit 280 via the wiring 512.
As described above, when the voltage Vout is increased and the state is shifted from the first state to the second state, the current supply source is switched from the wiring 511 to the wiring 512.

Eventually, when the voltage Vout approaches and coincides with the drive signal Vin, the transistor 341 of the unit circuit 34b is turned off, and charging to the piezoelectric element 40 is stopped.
On the other hand, if the drive signal Vin rises to the voltage V ₂ or more, so to follow the voltage Vout also driving signal Vin, the voltage V ₂ or more becomes a result, the third state (voltage Vout voltage V ₂ or from the second state shifts to state) less than the voltage _{V 3.}
The charging operation from the third state to the sixth state is almost the same, and although not particularly shown, the current (charge) supply source is sequentially switched to the wirings 513, 514, 515, and 516.

FIG. 15 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 drive 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. On the other hand, the transistor 34 of the unit circuit 34b.
1 is off.

At the time of discharging in the second state, the current is shown in FIG.
The electric current is discharged from the piezoelectric element 40 through a route of 0 → transistor 342 (of the unit circuit 34b) → wiring 511. 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 terminal of the piezoelectric element 40 is connected to the auxiliary power circuit 280. Electrical connection is established via the wiring 511. The 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 the auxiliary power supply circuit 280.

Eventually, when the voltage Vout approaches and coincides with the drive 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, if the drive signal Vin falls below the voltage V _1, the voltage Vout to follow the driving signal Vin, so less than the voltage V _1, the transition from the second state to the first state.

FIG. 16 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 drive 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 the time of discharging in the first state, the current is shown in FIG.
The electric current is discharged from the piezoelectric element 40 through the route of 0 → transistor 342 → of the unit circuit 34a → wiring 510.

Here, the unit circuits 34a and 34b are taken as an example and described separately during charging and discharging. However, the unit circuits 34c to 34f have transistors 341 and 3 for controlling current.
Except for the point 42 is different, the operation is almost the same.
Further, in the discharge path and the charge path in each state, the path from one terminal of the piezoelectric element 40 to the connection point between the emitter terminals of the transistors 341 and 342 is common.
As described above, in this embodiment, the voltage Vou of the drive signal so as to follow the voltage of the drive signal Vin.
t is controlled.

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.

Here, it is assumed that the piezoelectric element 40 is charged / discharged without voltage division when the drive signal Vin changes in the range from the voltage Vp to the voltage G (Comparative Example 1). In Comparative Example No. 1, the loss during charging corresponds to the sum of the areas of the region a hatched in FIG. 18, and the loss during discharge corresponds to the area of the region b hatched in FIG. To do.

On the other hand, the piezoelectric element 40 is charged and discharged in stages using a voltage obtained by dividing the power supply voltage (Vp, G) into six. For this reason, the loss at the time of charge and the loss at the time of discharge can be suppressed low. Specifically, the loss at the time of charging in this embodiment corresponds to the sum of the areas of the areas a hatched in FIG. 17, and the loss at the time of discharge is the area of the areas b of the hatched areas in FIG. Since it corresponds to the sum, the loss during charging / discharging can be kept low compared to Comparative Example 1.

In the printing period, the block 210 performs driving signals COM-A, C according to the data signal Data.
The OM-B is combined and supplied to the driver 30 as the drive signal Vin, and the driver 30 supplies the piezoelectric element 40 with a drive signal having a voltage Vout that follows the voltage of the drive signal Vin. For this reason, in the printing period, the piezoelectric element 40 ejects ink droplets of the ink amount specified by the data signal Data to the printing medium.

On the other hand, in the inspection period, the following operation is performed.
That is, as described above, the block 210 causes the selection unit 230 corresponding to the nozzle 451 (piezoelectric element 40) to be inspected to select the drive signal COM-A, and the other selection units 230 While the drive signal COM-B is selected, the block 220 is connected to the gate terminal of the transistor 240 corresponding to the nozzle (piezoelectric element 40) to be inspected.
Over the third period of the inspection period, a signal for turning on the transistor 240 is output, and a signal for turning off the other transistor 240 is output.

FIG. 19 is a diagram illustrating waveforms of the drive signals COM-A and COM-B in the inspection period.
As shown in this figure, and as described above, the inspection period is divided into four periods. Specifically, the inspection period includes, in order of time, the first period Ts1, the second period Ts2, and the third period T.
It is divided into s3 and a fourth period Ts4. And before and after this inspection period, the drive pattern in the printing period described above is obtained.

The drive signal COM-A has the following waveform as shown in FIG.
That is, for the drive signal COM-A,
In the first period Ts1, the voltage Vc gradually decreases to the voltage V _BS (= V ₁ ),
In the second period Ts2, a trapezoidal waveform Tsp is obtained,
Constant at the voltage _{V BS} in the third period Ts3,
Gradually rises to the voltage Vc from the voltage _{V BS} in the fourth period Ts4,
It has a waveform.

Here, trapezoidal waveform Tsp is the test pattern to be applied to the piezoelectric element 40 of nozzles subject to testing, rises from the voltage V _BS for example voltage Va, and once a constant in the voltage Va after, and it has a waveform returns to the voltage V _BS.
When the trapezoidal waveform Tsp of the drive signal COM-A is supplied to the piezoelectric element 40 of the nozzle to be inspected in the second period Ts2 of the inspection period, the piezoelectric element 40 moves upward as the voltage increases. After pulling the ink into the reservoir 441, it returns to its original state as the voltage drops, but in the interior of the nozzle (cavity 431), the vibration of the viscous ink does not immediately stop, but remains while being attenuated. become. Such vibration may be referred to as residual vibration.

On the other hand, the drive signal COM-B has the following waveform as shown in FIG.
That is, for the drive signal COM-B,
Gradually increases from the voltage Vc to _{V 6,} for example the third voltage in the first period Ts1,
It becomes constant at the voltage _{V 6} at a second time period Ts2 and the third period Ts3,
Gradually decreases to the voltage Vc from the voltage _{V 6} in the fourth period Ts4,
It has a waveform.

As described above, the driver 30 adjusts the voltage Vou so as to follow the voltage change of the control voltage Vin.
t is controlled, but the voltage Vout (control voltage Vin) is V ₆ , V ₅ , V ₄ , V ₃ , V ₂ , V _1.
, V ₀ , the voltage between the base and the emitter in the transistor 341 or 342 becomes the bias voltage, so that a current hardly flows between the emitter and the collector. For this reason, the drive signal C is applied to the piezoelectric element 40 of the nozzle to be inspected.
OM-A is, in a case that has been supplied is selected by the selection unit 230 to the driver 30, when it becomes temporally constant voltage V _BS in the third period Ts3, one terminal of the piezoelectric element 40 is This is equivalent to a state where it is electrically disconnected from the driver 30.
Similarly, the drive signal COM-B is transmitted to the piezoelectric element 40 of the nozzle that is not the inspection target, and the selection unit 2.
A case that has been supplied is selected to the driver 30 by 30, when it becomes temporally constant voltage V ₆ in the third period Ts3, one terminal of the piezoelectric element 40, the driver 30 when viewed electrically Equivalent to the state of being disconnected from.
On the other hand, the other terminal of each piezoelectric element 40 is held by the voltage-V _BS.

By the way, the piezoelectric element 40 functions as an actuator that is displaced according to the voltage when a voltage is applied from the outside. However, when a displacement is applied from the outside, the piezoelectric element 40 outputs a voltage according to the displacement. It functions as a sensor.
In the third period Ts3 immediately after the trapezoidal waveform Tsp is applied to the piezoelectric element 40 of the nozzle to be inspected, residual vibration is generated inside the nozzle. In the third period Ts3, one terminal of the piezoelectric element 40 is disconnected from the driver 30, since the other terminal is held at a voltage V _BS, the voltage Vout of the one terminal is in FIG. 19 (b) As shown, the voltage waveform corresponds to the residual vibration inside the nozzle.
The voltage corresponding to the residual vibration is amplified by the amplifier 292 and output as the signal Vk. The waveform of the signal Vk is, for example, as shown in FIG. The signal Vk is converted into data Dk by the ADC 294 and supplied to the analysis unit 130.
Here, the waveform of the residual vibration is classified as follows according to the state of the nozzle.

FIG. 20 is an enlarged view of the voltage waveform corresponding to the residual vibration, and is classified into the following four types according to the state of the nozzle 451. In addition, the horizontal axis of this figure shows the elapsed time when the start point of the third period Ts3 is zero, and the vertical axis shows the voltage of the signal Vk.
In this figure, (a) is a waveform when the nozzle 451 is normal. (B)
This is a waveform when the ink is in a thickened state. Since the viscosity is high, the amplitude of the residual vibration is smaller than (a). (C) is a waveform in a state in which a bubble is mixed in the nozzle 451 and thus a dot dropout occurs, that is, a phenomenon that an ink droplet is not ejected even when an ink droplet is ejected. (D) is a waveform in a state in which dots are not formed normally due to misalignment of the flying direction of ink droplets due to the inclusion of bubbles and failure to land properly.
Incidentally, one terminal of the piezoelectric element 40, since the voltage V _BS when the residual vibration is converged, the waveform of the signal Vk that corresponds to the residual vibration, strictly speaking, should converge to zero voltage. However, in FIG. 20, each waveform is offset by about 4.6 volts for convenience.

FIG. 21 shows the waveforms of (a), (b), (c) and (d) in FIG.
It is a figure which shows the result (spectrum) processed by FT. In this figure, the horizontal axis represents frequency (logarithmic display), and the vertical axis represents frequency level (intensity). The starting point of FFT is
In FIG. 20, in the waveform after 12 μs, it is a point that crosses the offset voltage. For this reason, the points of zero phase are aligned in each waveform.

As shown in FIG. 21, the peak of the frequency in (a) in the normal state protrudes as compared with (b), (c), and (d) in the abnormal state.
Therefore, the analysis unit 130 processes the data Dk by FFT, and determines whether the nozzle to be inspected is normal depending on whether or not the resulting spectrum passes through the region Wa set in advance in FIG. It is possible to determine whether or not it is good. Region W
a may be set and changed individually according to, for example, the production lot, the specification of the piezoelectric element 40, and the like.

FIG. 22 is a diagram illustrating an equivalent circuit of the head unit in the third period Ts3.
In this figure, a set of a driver 30, a transistor 240 and a piezoelectric element 40 corresponding to each nozzle is shown in a state of being arranged in the vertical direction. Among these, the leftmost set of columns in the figure shows a state in which the transistor 240 is turned on and the other set is other than the subject of inspection and the transistor 240 is turned off.
In the figure, a with a circle represents the off impedance of the transistor 240 in the off state, and the off resistance Roff and the off capacitance Coff between the source and drain terminals.
Shown in parallel connection. The symbol “b” indicates the off-impedance parasitic in each driver 30. As described above, when it becomes temporally constant voltage V _BS or the voltage V ₆ in the third period Ts3, one terminal of the piezoelectric element 40, the driver 30
In this example, since the off-impedance parasitic in the driver 30 is considered, it is shown in the figure. A circle c1 represents an impedance parasitic on the path from the output terminal of the driver 30 to the drain terminal of the transistor 240, and a circle c2 represents a path from the source terminal of the transistor 240 to one terminal of the resistance element 290. It represents the parasitic impedance. The circled d is
The impedance of the piezoelectric element 40 is indicated by a parallel connection of a capacitance component C and a resistance component R.

FIG. 23 is a simplified representation of the equivalent circuit shown in FIG. 22 with respect to the piezoelectric element 40 to be inspected.
In this figure, A with a circle represents the sum of a with a circle in FIG. Similarly,
B with a circle represents the sum of b with a circle, C1 with a circle represents the sum of c1 with a circle, and D with a circle represents the sum of d with a circle. Since the path from the source terminal of the transistor 240 to the one terminal of the resistor element 290 is fixed at the voltage V _BS, for the sum of the impedance which corresponds to the c2 of ○ mark, it is necessary to consider the equivalent circuit in FIG. 23 There is no.

Further, in FIG. 23, of each impedance, an influential capacitive component is represented by its size (thickness). More specifically, the largest capacitive component is D marked with a circle indicating the capacitive component of the piezoelectric element 40, and then the marked with a circle of impedance parasitic on the path from the output terminal of the driver 30 to the drain terminal of the transistor 240. C1. A and B with a circle are smaller than D and C1 with a circle.

As shown in the figure, one terminal of the piezoelectric element 40 of the nozzle that is the object of inspection is a parallel connection of a capacity of A that is not subject to inspection and a capacity of B, C1, and D that is marked with ○. However, it becomes the structure electrically connected in series with the part to which the electric potential was fixed.
The other terminal of the piezoelectric element 40, since it is fixed at the voltage V _BS, key on either one of the terminals is a voltage that reflects the how correctly residual vibration, that is, to increase the determination accuracy of the nozzle quality It becomes.

Here, before describing the superiority of the configuration for detecting the residual vibration of the piezoelectric element 40 in this embodiment, a comparative example (part 2) for detecting the residual vibration will be described.

FIG. 24 is a diagram illustrating an equivalent circuit of the comparative example (part 2).
As shown in this figure, in the comparative example (2), to one terminal of the piezoelectric element 40, the voltage V _BS from the driver 31 is applied by turning on the transistor 241. The transistor 241 is provided corresponding to each of the piezoelectric elements 40, and is the same as the transistor 240 of the embodiment in that the one to be inspected is turned on and the others are turned off. The driver 31 is assumed to be an amplifier that outputs the drive signal COM-A, not the driver 30 of the embodiment.

The other terminals of the plurality of piezoelectric elements 40 are commonly connected to one input terminal of the amplifier 292. Note that a voltage V _BS is applied to the other input terminal of the amplifier 292, and both ends of a resistance element 290 in which the amplifier 292 is electrically interposed between one input terminal and the other input terminal. The point that the voltage generated in is amplified with a predetermined gain and output as the signal Vk is the same as in the embodiment.
In this figure, c2 marked with a circle is the amplifier 292 from the other terminal of the piezoelectric element 40.
This is different from FIG. 22 in that it represents the parasitic impedance in the path to one of the input terminals, but is the same in nature.

FIG. 25 is a simplified representation of the piezoelectric element 40 that is the object of inspection in the comparative example (part 2). In this figure, C2 with a circle represents the total sum of c2 with a circle in FIG.

In Comparative Example (Part 2), one terminal of the piezoelectric element 40 is kept at the voltage _{V BS} by the driver 31. Accordingly, or if noise is superimposed on the power supply line supplied with a voltage V _BS, when the voltage V _BS or varied, as long as the common mode rejection ratio of the amplifier 292 is not ideally zero, the output of the amplifier 292 The signal Vk is affected by the noise or the like.

Further, the following capacitance is added in parallel to the other terminal of the piezoelectric element 40 of the nozzle to be inspected between the fixed potential. That is, first, D marked with ◯, and ○
The component in which the parallel connection of C1 and A of the mark is connected in series, and secondly, the C2 of the circle is the piezoelectric element 40
Are added in parallel between one terminal and a fixed potential. As described above, D marked with a circle is relatively large, and C2 marked with a circle is also medium, so that a capacity that cannot be ignored is added to one terminal of the piezoelectric element 40. For this reason, in the comparative example (No. 2), when residual vibration is generated in the nozzle to be inspected, the output by the piezoelectric element 40 (
A part of the charge) diffuses toward the capacitive component added to the other terminal.

Thus, in Comparative Example (Part 2), the signal Vk is one capacitive component and added to the terminal of the piezoelectric element 40, such as by variation of the voltage V _BS, it does not correctly reflect the residual vibration, the nozzle acceptability There is a problem that the determination accuracy decreases.

On the other hand, in this embodiment, as shown in FIG. 23, one terminal of the piezoelectric element 40 of the nozzle to be inspected is disconnected from the driver 30 in the third period Ts3. , or if noise is superimposed on the power supply line supplied with a voltage V _BS,
Even or the voltage V _BS changes, the signal Vk is the output of the amplifier 292 is less sensitive to the noise.
Further, as shown in the figure, one of the terminals of the piezoelectric element 40 of the nozzle to be inspected, although the parallel capacity of B, C1, and D, especially the capacity of D, is not negligible. Are connected via a series connection with a relatively small capacity of A marked with ◯, so that the added capacity component is smaller than that of the comparative example (part 2).
Therefore, in this embodiment, compared with the comparative example (part 2), the signal Vk reflects the residual vibration more correctly, so that the determination accuracy of nozzle quality can be improved.

In the present embodiment, when the transistor 240 corresponding to the nozzle to be inspected is turned on after applying the trapezoidal waveform Tsp that is the test pattern in the second period Ts2, the drain terminal of the transistor is not so high. Since the voltage is V _BS (= V ₁ ),
The transistor 240 can be downsized. That the transistor 240 is downsized means, in other words, that the capacitance between the source and the drain in the off state is small.

Furthermore, in the present embodiment, in the inspection period, the drive signal COM-B is selected and supplied as the drive signal Vin to the driver 30 corresponding to the piezoelectric element 40 corresponding to the nozzle other than the inspection target.
Drive signal COM-B is the voltage _{V 6} at the end of the second period Ts2. Therefore, in the third period Ts3, one terminal of the piezoelectric element 40 corresponding to the nozzle of the non-inspected, that is, the drain terminal of the transistor 240 corresponding to the piezoelectric element 40 is held at a relatively high voltage V ₆ In this state, the transistor 240 is turned off. MOSFET
The capacitance between the source and drain when the transistor is off in
The one where the voltage between drains is high is small compared with the case where it is low.

Even if the capacitance between the source and drain in one transistor 240 is very small,
In this embodiment, since there are a plurality of m nozzles, there is a possibility that the capacity cannot be ignored in a configuration in which m nozzles are arranged in parallel.
However, in this embodiment, the transistor 2 corresponding to the nozzle other than the inspection target.
In 40, the transistor 240 is miniaturized and further turned off with a high drain voltage, so that the off-capacitance of the transistor 240 is reduced.
In particular, in the present embodiment, the equivalent circuit of A in FIG. 23 is between the one terminal of the piezoelectric element 40 of the nozzle to be inspected and the parallel connection of B, C1, and D in the circle. Since the insertion is inserted, the off-capacitance of the transistor 240 corresponding to the nozzle other than the inspection target becomes small, so that the capacitance component parasitic on the piezoelectric element 40 becomes so small that it can be ignored. Can be further improved.
Here, although the driving signal COM-B at the end of the second period Ts2 and voltage V _6, this object is achieved, since the transistor 240 is to reduce the capacitance between the source and drain when off, What is necessary is just to be more than the voltage Vc.

<Modification>
The present invention is not limited to the above-described embodiments, and various modifications as described below are possible, for example. Note that one or more arbitrarily selected aspects of the modifications described below can be appropriately combined.

<FFT etc.>
In the embodiment, the time information is lost because the analysis unit 130 processed the data Dk by fast Fourier transform (FFT). However, for example, processing such as wavelet transform may be performed so as to leave the time information.

<Number of unit circuit stages, etc.>
In the embodiment, the six stages of the unit circuits 34a to 34f are provided in order of decreasing voltage so as to correspond to two voltages adjacent to each other among the six kinds of voltages. However, in the present invention, the unit circuit 34 is provided. As shown in the application example (part 2), the number of is not limited to this, and may be two or more. As the number of unit circuits 34 increases, the loss during charging / discharging decreases,
The configuration is complicated.
Further, the transistors 341 and 342 in the unit circuit 34 are not limited to the bipolar type, and may be MOSFETs as described above.

DESCRIPTION OF SYMBOLS 1 ... Printing apparatus (liquid discharge apparatus) 10 ... Control unit 20 ... Head unit, 30 ...
Driver, 34a-34f ... Unit circuit, 36a-36f ... Level shifter, 38a-3
8f ... Comparator 40 ... Piezoelectric element 50 ... Auxiliary power supply circuit 130 ... Analysis unit 200
... selection control unit, 210, 220 ... block, 240 ... transistor (switch), 29
2 ... Amplifier, 341, 342 ... Transistor, 400 ... Discharge part, 431 ... Cavity,
451 ... Nozzle, 510-516 ... Wiring.

Claims (5)

A piezoelectric element that is displaced according to the voltage between one terminal and the other terminal held at a predetermined first voltage;
A cavity that is filled with liquid and whose internal volume increases or decreases due to displacement of the piezoelectric element;
A nozzle that communicates with the cavity and can discharge the liquid as droplets by increasing or decreasing the internal volume of the cavity; and
A switch that is in a conductive or non-conductive state between one end and the other end, the one end is connected to one terminal of the piezoelectric element, and the other ends are connected in common;
Multiple sets including
When one nozzle is to be inspected during the inspection period, after applying a test pattern voltage to one terminal of one piezoelectric element corresponding to the one nozzle, the switch corresponding to the one piezoelectric element is in a conductive state. And a control unit that turns off a switch corresponding to a piezoelectric element other than the one piezoelectric element, and
An output unit that outputs a voltage according to a potential difference between the other terminal of the piezoelectric element and a common connection point between the other ends of the switch;
Equipped with,
The controller is
A liquid ejecting apparatus , wherein the voltage at the end of the test pattern is the first voltage . The controller is
In the printing period other than the inspection period,
A voltage of a driving pattern starting from a predetermined second voltage and ending with the second voltage is applied to one terminal of the piezoelectric element,
In the first period of the inspection period,
The voltage applied to one terminal of the piezoelectric element is gradually changed from the second voltage to the first voltage,
In a second period after the first period,
A voltage of a test pattern starting from the first voltage and ending with the first voltage is applied to one terminal of the piezoelectric element,
In a third period after the second period,
The switch corresponding to the one piezoelectric element is made conductive, and the switch corresponding to the piezoelectric element other than the one piezoelectric element is made non-conductive,
In a fourth period after the third period,
Gradually changing the voltage applied to one terminal of the piezoelectric element from the first voltage to the second voltage;
The liquid ejection apparatus according to claim 1 , wherein The controller is
By the end of the second period, a third voltage higher than the second voltage is applied to one terminal of the non-inspected piezoelectric element,
The liquid discharge apparatus according to claim 2 , wherein A piezoelectric element that is displaced according to the voltage between one terminal and the other terminal held at a predetermined first voltage;
A cavity that is filled with liquid and whose internal volume increases or decreases due to displacement of the piezoelectric element;
A nozzle that communicates with the cavity and can discharge the liquid as droplets by increasing or decreasing the internal volume of the cavity; and
A switch that is in a conductive or non-conductive state between one end and the other end, the one end is connected to one terminal of the piezoelectric element, and the other ends are connected in common;
Have multiple sets, including
When one nozzle is to be inspected during the inspection period, the switch corresponding to the one piezoelectric element is turned on after the voltage of the test pattern is applied to one terminal of the one piezoelectric element corresponding to the one nozzle. A switch corresponding to a piezoelectric element other than the one piezoelectric element is made non-conductive,
Output a voltage according to the potential difference between the other terminal of the piezoelectric element and the common connection point between the other ends of the switch ,
The head unit according to claim 1, wherein the voltage at the end of the test pattern is the first voltage . A piezoelectric element that is displaced according to the voltage between one terminal and the other terminal held at a predetermined first voltage;
A cavity that is filled with liquid and whose internal volume increases or decreases due to displacement of the piezoelectric element;
A nozzle that communicates with the cavity and can discharge the liquid as droplets by increasing or decreasing the internal volume of the cavity; and
A switch that is in a conductive or non-conductive state between one end and the other end, the one end is connected to one terminal of the piezoelectric element, and the other ends are connected in common;
Have multiple sets, including
When one nozzle is to be inspected during the inspection period, after applying a test pattern voltage to one terminal of one piezoelectric element corresponding to the one nozzle, the switch corresponding to the one piezoelectric element is in a conductive state. The switch corresponding to the piezoelectric element other than the one piezoelectric element is made non-conductive,
Determining the quality of the one nozzle based on the voltage according to the potential difference between the other terminal of the piezoelectric element and the common connection point between the other ends of the switch ;
A method for determining whether or not a nozzle of a liquid ejection apparatus is good, wherein the voltage at the end of the test pattern is the first voltage .

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