JP2004050492A - Inkjet head driving circuit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To enhance ink ejection performance by connecting an inkjet head driving circuit with power supplies individually thereby stabilizing the operational performance thereof, and to prevent abnormal heating by setting a fixed relation among the voltages of respective power supplies thereby preventing latch up. <P>SOLUTION: The N<SP>+</SP>top contact, the source of a PMOS and the source of an NMOS are connected with respective power supplies and the P<SP>+</SP>top contact is connected with a Vss power supply (GND). The power supplies connected with the N<SP>+</SP>top contact, the source of the PMOS and the source of the NMOS are a VH power supply, a VDH power supply, and a VDL power supply, respectively. A relation of VD>VDH>VDL>Vss is set among the voltage levels of respective power supplies. The VDH power supply has a variable voltage whereas the VH power supply, the VDL power supply and the Vss power supply (GND) are fixed at constant voltage levels. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an inkjet head of an inkjet printer that forms an image by ejecting ink onto a recording medium, and more particularly, to an inkjet head driving circuit provided in the inkjet head.
[0002]
[Prior art]
2. Description of the Related Art Conventionally, in an ink jet printer, a shear mode type in which ink is ejected by utilizing slip deformation of a piezoelectric body formed of PZT (lead zirconate titanate) or the like provided in a recording head (also referred to as an ink jet head). A configuration using a method is known.
[0003]
The configuration and function of a recording head used in a conventional shear mode type ink jet printer will be described.
[0004]
FIG. 7 is a plan view showing a state in which a part of a recording head provided in a conventional ink jet printer is viewed from a recording medium side. FIG. 8 is a longitudinal sectional view of a recording head provided in a conventional ink jet printer. In FIG. 7, the ink tank 700 is not shown for convenience.
[0005]
As shown in FIGS. 7 and 8, the recording head 100 includes a piezoelectric body 200, a top plate 300, a plurality of ink chambers 400, and an ink tank 700.
[0006]
The piezoelectric body 200 is formed in a comb shape, and is formed such that the ink chamber 400 is fitted into the gap between the comb teeth with the comb teeth as wall surfaces.
[0007]
The ink chamber 400 includes a drive electrode 500 and a discharge nozzle 600 formed on both side walls.
[0008]
The top plate 300 is for fitting the plurality of ink chambers 400 into the piezoelectric body 200, and includes a connection electrode 900 to the outside of the recording head 100.
[0009]
The ink is stored in the ink tank 700 and is discharged from the discharge nozzle 600 via a common ink path 800 connected to the plurality of ink chambers 400. The ejection operation will be described with reference to FIGS.
[0010]
FIG. 9 is a diagram showing an operation of a recording head provided in a conventional ink jet printer at the time of image formation. FIG. 10 is a timing chart showing the timing of applying a voltage to a recording head provided in a conventional inkjet printer.
[0011]
As shown in FIG. 9, three adjacent ink chambers 400 are distinguished as A channel, B channel, and C channel, respectively. In addition, the ink ejection operation described below is for the case where ink is ejected from the B channel ink chamber 400, but the same applies to ink ejection from the A channel, B channel, and C channel ink chambers 400. .
[0012]
As shown in FIG. 9A, in the normal state in which the ink is not ejected, no potential difference is applied to any of the drive electrodes 500 among the ink chambers 400 of the A channel, the B channel, and the C channel. In addition, the piezoelectric body 200 is polarized in a direction parallel to the surface of the drive electrode 500, that is, in a direction perpendicular to the drive electric field so as to generate a shear mode deformation.
[0013]
When ink is ejected from the B channel, an ejection pulse is applied to the B channel drive electrode 500 as shown in FIG. On the other hand, no ejection pulse is applied to the drive electrodes 500 of the A channel and the C channel.
[0014]
Then, an electric field is generated from the B-channel drive electrode 500 toward the A-channel and C-channel drive electrodes 500. According to the direction of the electric field, the piezoelectric body 200 formed between the A channel and the B channel and the piezoelectric body 200 formed between the B channel and the C channel are sheared. As a result, as shown in FIG. 9B, the volume of the ink chamber 400 of the B channel is expanded. Thereby, the ink is sucked into the B channel.
[0015]
Thereafter, as shown in FIG. 10, a common pulse is applied to the driving electrodes 500 of the A channel and the C channel. Then, an electric field is generated from the driving electrodes 500 of the A channel and the C channel toward the driving electrode 500 of the B channel. According to the direction of the electric field, the piezoelectric body 200 formed between the A channel and the B channel and the piezoelectric body 200 formed between the B channel and the C channel are sheared. As a result, as shown in FIG. 9C, the volume of the ink chamber 400 of the B channel is reduced. Thus, the ink is ejected from the ejection nozzle 600 of the B channel.
[0016]
When ink is not ejected from any of the channels, a common pulse is applied to the drive electrodes 500 of the A and C channels, and a non-ejection pulse identical to the common pulse is applied to the drive electrodes 500 of the B channel. As a result, the drive electrodes 500 of the A to C channels have the same potential, so that no electric field is generated between the drive electrodes 500. Accordingly, the piezoelectric body 200 does not deform due to the electric field, and does not expand or contract the volume of the ink chamber 400 in any channel, so that ink is not ejected.
[0017]
As described above, the operation of the recording head 100 at the time of image formation is to eject ink from any of the A to C channels while sequentially switching the ink ejection channels. That is, the recording head 100 forms an image by discharging ink by driving each of the adjacent channels A to C.
[0018]
The time AL for applying the ejection pulse and the time AL 'for applying the common pulse are determined by the following equation (1).
[0019]
AL (AL ') = length of ink chamber / sonic velocity in ink ... (1)
Therefore, if all three channels have the same length of ink chamber,
AL '= 2AL
It becomes. In the case of a general inkjet printer, AL is about 2 μs.
[0020]
The recording head 100 including the piezoelectric body 200 is a driving IC (driver IC) constituting a head driving circuit (also referred to as an ink jet head driving circuit) connected to an image processing unit or the like of a control unit provided in the ink jet printer. Is controlled by
[0021]
In the drive IC constituting the conventional head drive circuit, when the print head is driven to discharge ink during image formation as described above, the drive for driving the print head to obtain stable ink discharge performance is performed. The voltage was being adjusted. The reason is due to the viscosity resistance of the ink. When the temperature of the ink is low and the viscosity is high, a high driving voltage (energy applied to the ink) is required so as not to cause non-discharge and insufficient discharge speed. When the temperature is high and the viscosity is low, it is necessary to reduce the driving voltage in order to prevent the spray (ink scattering near the nozzle) caused by the excessive pressure applied to the ink.
[0022]
Further, in the conventional driving IC, the output voltage exceeds the voltage of the power supply line (hereinafter, referred to as overshoot) due to the capacitance of the piezoelectric body 200 and the stray capacitance of the wiring. A current may flow through the diode and the parasitic transistor, causing latch-up breakdown.
[0023]
Therefore, Japanese Patent Application Laid-Open No. 5-318735 discloses that a series resistor is connected between a voltage output section and a piezoelectric body 200 as shown in an equivalent circuit diagram of a head drive circuit in FIG. A structure for preventing the overshoot by limiting the rising speed and the falling speed of the IC is disclosed, and Japanese Patent Application Laid-Open No. 2000-174140 discloses a structure for preventing the latch-up by separating the power supply inside the IC. ing.
[0024]
On the other hand, even in a drive IC of a type in which the output of an adjacent voltage is capacitively coupled, the potential of the output unit that outputs a voltage to the piezoelectric body 200 changes due to a change in the state of the potential of the output unit adjacent to the output unit. The output potential change is induced transiently based on the electric charge stored in the piezoelectric body 200 that forms a capacitive coupling between them and the potential change between adjacent outputs. Therefore, there is a possibility that the voltage of the output unit that outputs the above voltage instantaneously becomes higher than the power supply voltage or becomes lower than the GND level, and the drive IC may latch up.
[0025]
Therefore, in some cases, a discharge path for discharging the current of the output section is formed inside the drive IC of the head drive circuit when the potential of the output section becomes equal to or higher than the power supply voltage.
[0026]
For example, in a push-pull type driving IC in which a capacitance is applied between adjacent outputs as shown in the equivalent circuit diagrams of FIGS. 12 and 13, the driving IC generates noise due to induction noise from the adjacent output. The current flows through the parasitic diodes 90 and 92 and the parasitic transistors 91 and 93.
[0027]
As shown in FIG. 14, when the output section A connected to the VH power supply has a high output (VH level) and the adjacent output sections B and B ′ transition from a low output to a high output as shown in FIG. If the discharge path is not formed, the voltage on the output section A side will be twice the voltage of the VH power supply due to the charges charged in the piezoelectric body (capacitance) 200 connected between the two output sections. Is formed, the discharge is discharged to the VH power supply via the driving IC, and finally both the output section A and the adjacent output sections B and B 'are at the High level, that is, there is no potential difference between the both output sections. As a state, latch-up is prevented.
[0028]
[Problems to be solved by the invention]
However, if the drive voltage of the print head is adjusted by the viscosity of the ink, the drive voltage for driving the drive IC is the same as the drive voltage for driving the drive IC. Therefore, when the drive voltage of the print head is changed, the drive voltage of the drive IC also changes. Therefore, when the drive voltage is reduced, the operation speed of the drive IC tends to decrease. That is, since the operation speed of the drive IC varies due to the change in the drive voltage, the variation also occurs in the ink discharge operation, which adversely affects the ink discharge performance.
[0029]
Further, in the configuration disclosed in Japanese Patent Application Laid-Open No. 5-318735, unnecessary overshoot can be prevented beforehand, but there is a problem that the series resistor has heat. Further, since the rising speed and the falling speed of the voltage output (pulse) are reduced, there is a limit in reducing the pulse width. As a result, high-speed image forming operation may be hindered.
[0030]
In the publication disclosed in Japanese Patent Application Laid-Open No. 2000-174140, the power supply inside the IC is separated in order to prevent latch-up. However, in another configuration of the above publication, the two are electrically separated between two regions. The head drive circuit does not have the above-described separation region, and the configuration of the above publication cannot be easily applied to the head drive circuit.
[0031]
In a drive IC of the type in which adjacent outputs are capacitively coupled, a discharge path is formed in the drive IC to prevent latch-up, but latch-up is not completely prevented. A description will be given using an example of a push-pull type driving IC using a capacitance between adjacent outputs as described above. Even if a discharge path is formed inside the driving IC, the discharge delays from the level transition of the output units B and B ′ adjacent to the output unit A due to the inductance component and the resistance component of the wiring from the piezoelectric body 200 to the power supply. Occurs. During this delay period, a state in which some potential difference (the output portion A has a higher potential than the adjacent output portions B and B ') remains in the piezoelectric body 200, and the voltage value of the output portion A temporarily becomes VH + α. turn into.
[0032]
At this time, when α is larger than the diffusion potential of 0.6 to 0.7 V, a current flows through the parasitic diode 90 and the parasitic transistor 91 generated in the drive IC. For this reason, this current may be a trigger to cause a latch-up state, which may lead to destruction of the driving IC.
[0033]
Also, as shown in FIG. 16, when the output section A is at the low voltage output (GND level) and the output sections B and B 'transition from High output to Low output, the voltage value of the output section A is similarly GND-α. Will be.
[0034]
At this time, similarly, when α is larger than the diffusion potential of 0.6 to 0.7 V, a current flows through the parasitic diode 92 and the parasitic transistor 93 generated in the driving IC, and a latch-up state occurs. There is a risk of destruction.
[0035]
SUMMARY OF THE INVENTION It is an object of the present invention to separately connect a power supply to an ink jet head drive circuit, stabilize the operation performance of the ink jet head drive circuit, improve ink ejection performance, and ensure that the voltage of each power supply has a constant relationship. An object of the present invention is to provide an ink jet head drive circuit which can prevent latch-up and abnormal heat generation by setting.
[0036]
[Means for Solving the Problems]
The present invention has the following configuration in order to solve the above problems.
[0037]
(1) In an ink jet head drive circuit having an output unit for outputting a voltage and connecting a piezoelectric body constituting at least a part of a plurality of adjacent ink chambers to the output unit as a load,
An N-well region and an NMOS transistor are provided in different portions on the P-type semiconductor substrate, a PMOS transistor is provided on the N-well region,
A first power supply to a fourth power supply are sequentially connected to the N-well region, the P-type semiconductor substrate, the source of the PMOS transistor, and the source of the NMOS transistor;
Setting the voltage of each power supply so as to satisfy a relationship of first power supply> second power supply> third power supply> fourth power supply;
A connection line between the drain of the PMOS transistor and the drain of the NMOS transistor is used as the output section.
[0038]
In this configuration, an N-well region of an ink-jet head drive circuit for driving an ink-jet head including a piezoelectric body and a plurality of adjacent ink chambers connected as a load to an output section for outputting a voltage, a P-type semiconductor The voltage of each of the four power supplies separately connected to the substrate, the source of the PMOS transistor, and the source of the NMOS transistor is set in a relation of first power supply> second power supply> third power supply> fourth power supply. Therefore, even when the potential of the output portion of the voltage connected to the piezoelectric body is higher than the second power supply used to drive the ink jet head (piezoelectric body) or lower than the third power supply, the circuit in the ink jet head drive circuit is not required. Each power supply is set and connected so that the above-described voltage relationship is satisfied so that the parasitic diode and the parasitic transistor generated in the above-mentioned state are not turned on. Therefore, no current flows through the parasitic diode and the parasitic transistor, and latch-up is prevented.
[0039]
(2) fixing the voltages of the first power supply and the fourth power supply,
The voltage of the second power supply or the third power supply is variable.
[0040]
In this configuration, the voltages of the first power supply and the fourth power supply necessary for operating the inkjet head drive circuit itself are fixed, and the voltage of the second power supply or the third power supply for driving the inkjet head is variable. Therefore, the voltage required to drive the ink head jet is adjusted by the viscosity of the ink, so that the ink ejection performance does not decrease.
[0041]
In addition, since the voltage of the power supply for operating the inkjet head drive circuit is fixed and the power supply for driving the inkjet head and the power supply for operating the inkjet head drive circuit are separated, there is no variation in voltage, and Since the driving circuit is supplied to the driving circuit, the operation speed of the driving circuit is stabilized.
[0042]
(3) A diode is connected in a forward direction from the first power supply line to the second power supply line or from the third power supply line to the fourth power supply line.
[0043]
In this configuration, a diode is connected in a forward direction from the first power supply line to the second power supply line or from the third power supply line to the fourth power supply line. Therefore, since the diode is connected in the forward direction, a voltage drop due to the diode occurs, and the voltage value of the first power supply and the second power supply is such that the first power supply> the second power supply, and the third power supply and the fourth power supply Since the third power supply> the fourth power supply, the relationship between the voltages of the respective power supplies is maintained even when the voltage of some power supplies is not supplied. No current flows through the parasitic diode and the parasitic transistor, and latch-up is prevented.
[0044]
(4) connecting a diode in a forward direction from the output unit to a second power supply line or a third power supply line to the output unit;
The voltage value due to the voltage drop in the forward connection of the diode is equal to or less than the voltage difference between the voltage values of the first power supply and the second power supply in the case of connection from the output unit to the second power supply line. In the case of connection to the output unit, the voltage difference between the third power supply and the fourth power supply is not more than the difference voltage.
[0045]
In this configuration, a diode is connected in a forward direction from the output unit that outputs a voltage to the piezoelectric body to the second power supply line or from the third power supply line to the output unit. In addition, when the voltage value due to the forward voltage drop of the diode when the output unit and the second power supply line are connected is equal to or less than the voltage difference between the voltage values of the first power supply and the second power supply, the third power supply line and the output unit Are connected such that the voltage value due to the forward voltage drop of the diode when the voltage is connected is equal to or less than the voltage difference between the voltage values of the third power supply and the fourth power supply.
[0046]
Therefore, since the output section and the second power supply line or the third power supply line are connected by a diode having a constant forward voltage drop, when the voltage of the output section becomes equal to or higher than the second power supply voltage, A current flows from the output unit to the second power supply line via the diode. Further, when the voltage of the output section becomes equal to or lower than the third power supply voltage, a current flows from the third power supply line to the output section via the diode. Therefore, no current flows through the parasitic diode and the parasitic transistor included in the inkjet head drive circuit, and latch-up is prevented.
[0047]
BEST MODE FOR CARRYING OUT THE INVENTION
1 and 2 are a side view and a perspective view, respectively, showing a schematic configuration of an ink jet printer to which a head drive circuit according to an embodiment of the present invention is applied.
[0048]
As shown in FIGS. 1 and 2, a paper feed unit 2 is arranged from the rear (right side in FIG. 1) to the upper part of the ink jet printer 1 which is the main body device of the present invention. 1, a separation unit 3, a conveyance unit 4, an image forming unit (printing unit) 5, and a discharge unit 6 are arranged in this order. Further, the inkjet printer 1 is of a shear mode type in which a piezoelectric body, which will be described later, forming a wall surface of the ink chamber is deformed to discharge ink stored in the ink chamber.
[0049]
The paper supply unit 2 includes a paper supply tray 7 and a pickup roller (not shown), and supplies a sheet P to the image forming unit 5 when performing image formation. The sheet feeding unit 2 has a function of storing the sheet P when image formation is not performed.
[0050]
The separating unit 3 includes a sheet feeding roller 8 and a separating device 9 and separates the sheets P supplied from the sheet feeding unit 2 to the image forming unit 5 one by one. In the separation device 9, the friction between the sheet P and the pad portion of the separation device, which is the contact portion with the sheet P, is set to be larger than the friction between the sheets P. The paper feed roller 8 is set so that the friction between the paper feed roller 8 and the sheet P is larger than the friction between the pad portion and the paper P and the friction between the papers P. Thus, even if two vertically stacked sheets P are sent to the separation unit 3, these sheets P are separated by the feed roller 8 and only the upper sheet P is sent to the conveyance unit 4. Can be.
[0051]
The transport unit 4 includes a guide plate 10 and a roller pair (transport mechanism) 11, and transports the sheets P supplied one by one from the separation unit 3 to the image forming unit 5. The roller pair 11 conveys the sheet P so that the ink ejected from the recording head 12 is blown to an appropriate position on the sheet P when the sheet P is sent between a recording head (ink-jet head) 12 and a platen 13 described later. To adjust.
[0052]
The image forming unit 5 includes a recording head 12, a platen 13, a carriage (ink-jet head carriage) 14, and a guide shaft 15, and discharges ink onto a sheet P supplied from the roller pair 11 of the transport unit 4 to form an image. Do. The guide shaft 15 guides the carriage 14 on which the recording head 12 is mounted in the direction of arrow D2, which is the main scanning direction. The platen 13 supports the sheet P during image formation.
[0053]
The discharge unit 6 includes a discharge roller 16, a discharge tray 17, and an ink drying unit (not shown), and discharges the sheet P on which image formation has been completed from the inside of the inkjet printer 1 to the outside.
[0054]
When performing image formation, a request for image formation and image data are output to the inkjet printer 1 from an external device such as a computer (not shown). The ink jet printer 1 receiving the above request and the image data carries out the sheet P on the paper feed tray 7 by the pickup roller. The conveyed sheet P is conveyed to the conveyance unit 4 through the separation unit 3 by the paper feed roller 8. In the transport unit 4, the sheet P is transported between the recording head 12 and the platen 13 by the roller pair 11.
[0055]
Next, in the image forming unit 5, ink is sprayed on the sheet P on the platen 13 from a discharge nozzle provided in the recording head 12 based on the image data. At this time, the sheet P temporarily stops on the platen 13, and the carriage 14 is guided by the guide shaft 15, and sprays ink from the recording head 12 onto the sheet P while scanning in the direction of arrow D <b> 2. Is formed, and then the sheet P is moved by a certain width in the direction of arrow D1, which is the sub-scanning direction orthogonal to the main scanning direction. An image is formed on the entire surface of the sheet P by continuously performing the above-described processing according to the image data.
[0056]
The sheet P on which the image formation is completed is discharged from the discharge tray 17 to the outside of the inkjet printer 1 by the discharge roller 16 via the ink drying unit, and the sheet P is provided to the user as an image formed product.
[0057]
FIG. 3 is a block diagram showing a configuration of a control unit of an ink jet printer to which the head drive circuit according to the embodiment of the present invention is applied.
[0058]
As shown in FIG. 3, the control unit 20 provided in the inkjet printer 1 includes an interface unit 21, a memory 22, an image processing unit 23, and a drive system control unit 24.
[0059]
The interface unit 21 is a circuit that exchanges signals with an external device or the like, the image processing unit 23, and the drive system control unit 24. Image data sent from an external device or the like is sent to the image processing unit 23 via the interface unit 21.
[0060]
The image processing unit 23 performs image processing based on image data sent from an external device or the like via the interface unit 21. Further, the image processing section 23 is connected to a head drive circuit (inkjet head drive circuit) 30 for controlling the drive of the recording head 12.
[0061]
Note that the head drive circuit 30 corresponds to the inkjet drive circuit of the present invention. Details of the head drive circuit will be described later.
The memory 22 temporarily stores the image data sent to the image processing unit 23. The drive system control unit 24 controls driving of the carriage 13 and conveyance of the sheet P. Further, the drive system control unit 24 is connected to a carriage drive circuit 31 that controls the drive of the carriage motor 40 and a paper transport drive circuit 32 that controls the drive of the paper transport motor 41.
[0062]
4 and 5 are an equivalent circuit diagram of the head drive circuit according to the embodiment of the present invention and a diagram in which a part of the equivalent circuit diagram is enlarged.
[0063]
As shown in FIGS. 4 and 5, the head drive circuit 30 is a circuit including a push-pull transistor using the piezoelectric body 50 provided in the recording head 12 as a load. That is, the circuit has a logic section (pre-driver section) and a final stage. FIG. 4 shows the structure of the last stage in detail.
[0064]
In addition, in order to prevent the final stage of the PMOS and the NMOS from being turned on at the same time and a through current from flowing, the driving is performed by a general method of providing a time difference (a period of simultaneous OFF) between the operations of the PMOS and the NMOS when the output state is switched. Is going.
[0065]
The head drive circuit 30 of the present invention is configured by an IC (hereinafter, referred to as a drive IC 60). In the driving IC 60, a PMOS is provided on an N-well region provided on a P-type semiconductor substrate. Further, an NMOS is provided on the P-type semiconductor substrate. Also, in order to make electrical contact easy, N well region has N ⁺ P for top contact, P-type semiconductor substrate ⁺ Top contact is provided. Further, an output unit A, which is a voltage output unit connecting the drain of the PMOS and the drain of the NMOS, is connected to a piezoelectric body 50 formed of PZT or the like corresponding to one ink chamber, and applies a voltage.
[0066]
With the above-described circuit configuration, the driving IC 60 has a PNP-type bipolar transistor (hereinafter, referred to as a first parasitic transistor) and a P-type semiconductor having an N-well as a base, a PMOS source or drain as an emitter, and a P-type semiconductor substrate as a collector. As a result, an NPN bipolar transistor (hereinafter, referred to as a second parasitic transistor) having a substrate as a base, an NMOS source or drain as an emitter, and an N well as a collector is obtained. Further, a diode (hereinafter, referred to as a first parasitic diode) is provided between the source or drain of the PMOS and the N-well region, and a diode (hereinafter, referred to as a first parasitic diode) is provided between the source or the drain of the NMOS and the P-type semiconductor substrate. As a result).
[0067]
Further, a plurality of circuits having the above configuration are provided in the drive IC 60 so as to correspond to the piezoelectric bodies 50 constituting the wall surfaces of the respective ink chambers provided in the recording head 12, and a voltage output unit is connected to the piezoelectric bodies 50 in the same manner as in the above configuration. I do. By changing the voltage of each output unit, a potential difference is applied to the piezoelectric body 50 to generate an electric field, and the piezoelectric body 50 is sheared to change the volume of the ink chamber to eject ink.
[0068]
Also, N ⁺ A power supply is connected to the top contact, the source of the PMOS, and the source of the NMOS, respectively. ⁺ GND (also referred to as Vss power supply) is connected to the top contact. N ⁺ Each power supply connected to the top contact, the source of the PMOS, and the source of the NMOS is a VH power supply, a VDH power supply, and a VDL power supply. Further, the relationship between the voltage values of the respective power supplies is as follows.
VH>VDH>VDL> Vss
Set so that
[0069]
Further, the voltage of the VDH power supply is variable, and the VH power supply, the VDL power supply, and the Vss power supply (GND) are fixed at a constant voltage.
[0070]
Note that the VH power supply, the VDH power supply, the VDL power supply, and the Vss power supply correspond to the first power supply, the second power supply, the third power supply, and the fourth power supply of the present invention, respectively.
[0071]
As described above, in the push-pull type driving IC 60 which is the head driving circuit 30 of the present invention and the load is the piezoelectric body 50 which is the capacitance between the adjacent voltage output units, the power supply is separately supplied to the circuit. With this arrangement, it is possible to prevent a parasitic diode and a parasitic transistor in the drive IC 60 from being turned on due to induction noise between adjacent output units, to prevent latch-up of the head drive circuit 30, and to generate abnormal heat. Can be prevented.
[0072]
For example, when the VH power supply is 30 V, the VDH power supply is 27 V, the VDL power supply is 5 V, and the Vss power supply (GND) is 0 V, the output unit A is High (27 V = the PMOS is in the ON state) and is adjacent to the output unit A. When the output section changes from Low (5 V) to High (27 V), the potential of the output section A exceeds 27 V due to the charge stored in the piezoelectric body (capacitor) 50 of the load. The current moves (discharges) to the VDH power supply, but the state of the adjacent output unit changes (the voltage changes from 5 V to 27 V) due to the inductance component and the resistance component of the wiring and the like from the piezoelectric body 50 to the VDH power supply. ), The voltage becomes (27 + α) V and a voltage is applied to the emitter of the first parasitic resistor connected to the drain of the PMOS. The PMOS of the base has been applied voltage 30V of the VH power. In other words, if the base voltage 30V is larger than the emitter voltage (27 + α) V, α ≦ 3V, the first parasitic transistor is not turned on, so that the current can be prevented from flowing through the collector.
[0073]
In other words, the potential of the VH power supply and the potential of the VDH power supply are
VH−VDH ≧ α
By setting, latch-up can be avoided.
[0074]
As another example, when the VH power supply is 30 V, the VDH power supply is 27 V, the VDL power supply is 5 V, and the Vss power supply (GND) is 0 V, the output unit A is low (5 V = NMOS is in ON state) and When the output section adjacent to A changes from High (27 V) to Low (5 V), the potential of the output section A becomes (5-α) V and the drain of the NMOS, that is, the emitter of the NPN-type second parasitic transistor. Applied to. The base of the second parasitic transistor is connected to 0 V of the Vss power supply. However, if the base voltage is smaller than the emitter voltage, that is, if α ≦ 5 V, the second parasitic transistor is not turned on. In addition, current can be prevented from flowing through the collector.
[0075]
That is, considering the magnitude of α, the potentials of the VDL power supply and the Vss power supply are changed.
VDL voltage−Vss voltage ≧ α
By setting, latch-up can be avoided.
[0076]
Further, as a characteristic of the capacitor, for example, when one side A of a certain capacitor is at a potential of 15 V and is in an electrically open state, when the opposite side B is changed from 0 to 15 V, a potential of 15 V from the beginning is obtained. One side A of the existing capacitor becomes 30V. This is called a charge pump, and is caused by the characteristic that the capacitor tries to maintain the initial potential difference (15 V in this case). However, there is actually no OPEN state in terms of electrical connection, and one side A of the capacitor is in a state where a 15 V power supply is connected while having some impedance, and the potential change on the opposite side B rises to some extent. Since it takes time, although there is a delay, there is a transfer of electric charge from one side A to the 15V power supply, and it does not reach the charge pump. However, although the charge is not completely pumped, the voltage rises due to a delay in the transfer of the charge to the 15V power supply, which causes inductive noise. As a result, a current may flow through a parasitic transistor or the like on the circuit, leading to latch-up.
[0077]
Further, when the drive IC 60 is mounted on the carriage 14, an overshoot may be caused due to an increase in stray inductance due to wiring connected to the carriage 14. Further, since the recording head 12 itself is a piezoelectric material, electric noise may be generated due to operation vibration of the carriage 14 itself or mechanical vibration such as capping. The above-mentioned overshoot and electric noise from the piezoelectric body are easily caused.
[0078]
Also in the above case, when the drain voltage becomes equal to or higher than VH or equal to or lower than Vss, the parasitic diode and the parasitic transistor of the driving IC 60 are turned on. However, even if the magnitude of the electrical noise α acts on the VDL (Low side) or VDH (High side) of the drive reference voltage, and a voltage in the range of VDL−α to VDH + α is applied to the drain, , Vss ≦ VDL−α and VH ≧ VDH + α, the above-described overshoot and latch-up due to electrical noise can be reliably prevented.
[0079]
Further, the variable drive voltage (execution value VDH-VDL) of the inkjet head 12 and the fixed drive voltage (execution value VH) of the drive IC 60 are different from each other because the power supply is different. Regardless of the change, the drive voltage of the drive IC 60 can be kept constant, so that the operation speed of the drive IC 60 can be kept constant and high-speed image formation is possible.
[0080]
FIG. 6 is an equivalent circuit diagram of the head drive circuit according to the embodiment of the present invention.
[0081]
As shown in FIG. 6, it is preferable that the driving IC 60 be supplied with a VH power supply and a VDH power supply, and a VDL power supply and a Vss power supply from a common power supply. That is, the diode 70 is connected from the VH power line to the VDH power line so as to have a forward bias, and the diode 71 is also connected from the VDL power line to the Vss power line so as to have a forward bias.
[0082]
With this configuration, it is possible to prevent the power supply sequence from being reversed, which occurs when the VH power supply and the VDH power supply are used as separate power supplies.
[0083]
The above-mentioned reverse rotation means that, for example, when the power supply of the drive IC 60 is turned on, the VDH power supply rises earlier than the VH power supply, or when the drive IC 60 is turned off, the VH power supply is compared with the VDH power supply. If the voltage falls first, there is a situation where the relationship of VH> VDH is reversed.
[0084]
Since the power supply is shared, the voltage of the VH power supply is lowered to obtain the voltage of the VDH power supply. Therefore, the voltage of each power supply can maintain the relationship of VH> VDH. Similarly, the relationship of VDL> Vss can be maintained.
[0085]
With the above configuration, the relationship of VH> VDH and VDL> Vss can be reliably maintained, so that the latch-up of the inkjet jet drive circuit 13 can be more reliably prevented, and abnormal heat generation can be prevented.
[0086]
As shown in FIG. 6, the drive IC may connect diodes 72 and 73 (surge killer diodes) in the forward direction from the output section at the last stage to the VDH power supply line and from the VDL power supply line to the output section at the last stage. preferable.
[0087]
The above connection is configured so as to satisfy the relationship of (VH−VDH)> VFh and (VDL−Vss)> VFL.
[0088]
VFh is a forward voltage drop of a diode connected between the output section of the final stage and the VDH power supply line, and VFL is a voltage drop of the diode connected between the output section of the final stage and the VDL power supply line. It is a forward voltage drop.
[0089]
With the above configuration, the current can be discharged through the line connecting the diode before the current flows through the parasitic diode or the parasitic transistor, and the latch-up of the head drive circuit 30 can be more reliably prevented, and abnormal heat generation can be prevented.
[0090]
【The invention's effect】
As described above, according to the present invention, the following effects can be obtained.
[0091]
(1) An N-well region, a P-type semiconductor substrate, and a PMOS of an ink-jet head driving circuit that drives an ink-jet head including a piezoelectric body and a plurality of adjacent ink chambers connected as a load to an output unit that outputs a voltage. The voltage of each of the four power supplies separately connected to the source of the transistor and the source of the NMOS transistor is set in a relation of first power supply> second power supply> third power supply> fourth power supply, thereby connecting to the piezoelectric body. Even when the potential of the voltage output section is higher than the second power supply used for driving the ink jet head (piezoelectric body) or lower than the third power supply, a parasitic diode or a parasitic transistor generated in the ink jet head driving circuit is generated. The ON state can be prevented. Therefore, current can be prevented from flowing through the parasitic diode and the parasitic transistor, and latch-up can be prevented, so that abnormal heating of the inkjet head drive circuit can be prevented.
[0092]
(2) By fixing the voltages of the first power supply and the fourth power supply necessary for operating the ink jet head driving circuit itself and changing the voltage of the second power supply or the third power supply for driving the ink jet head, The voltage required to drive the head jet can be adjusted by the viscosity of the ink, and the voltage of the power supply for operating the inkjet head drive circuit is fixed, and the power supply for driving the inkjet head and the power supply for operating the inkjet head drive circuit Is separated, the variation in the voltage of the power supply for operating the drive circuit can be suppressed, and a constant voltage can be supplied to the drive circuit. Therefore, the operation speed of the drive circuit can be stabilized, Influence on the ink ejection operation can be eliminated, and the ink ejection performance can be improved. In addition, even at the time of high-speed image formation, the ink ejection performance can be maintained.
[0093]
(3) By connecting a diode in the forward direction from the first power supply line to the second power supply line or from the third power supply line to the fourth power supply line, a voltage drop due to the diode occurs. The voltage value of the second power supply is the first power supply> the second power supply, and the voltage value of the third power supply and the fourth power supply is the third power supply> the fourth power supply. Therefore, the voltage of some power supplies is not supplied. Even in such a case, the relationship between the voltages of the respective power supplies can be maintained. As a result, current can be prevented from flowing through the parasitic diode and the parasitic transistor included in the inkjet head drive circuit, and latch-up can be prevented. Therefore, abnormal heating of the inkjet head drive circuit can be prevented.
[0094]
(4) A diode is connected in the forward direction from the piezoelectric body voltage output section to the second power supply line or from the third power supply line to the piezoelectric body voltage output section. Further, the voltage value due to the forward voltage drop of the diode when the output unit and the second power supply line are connected is equal to or less than the voltage difference between the voltage values of the first power supply and the second power supply. By connecting so that the voltage value due to the forward voltage drop of the diode at the time of connection becomes equal to or less than the voltage difference between the voltage values of the third power supply and the fourth power supply, the voltage of the output unit becomes higher than the second power supply voltage. In this case, a current flows from the output unit to the second power supply line via the diode. Further, when the voltage of the output section becomes equal to or lower than the third power supply voltage, a current flows from the third power supply line to the output section via the diode. Therefore, it is possible to prevent a current from flowing through a parasitic diode or a parasitic transistor included in the inkjet head drive circuit, prevent latch-up, and prevent abnormal heating of the inkjet head drive circuit.
[Brief description of the drawings]
FIG. 1 is a side view showing a schematic configuration of an ink jet printer to which a head drive circuit according to an embodiment of the present invention is applied.
FIG. 2 is a perspective view showing a schematic configuration of an ink jet printer to which the head drive circuit is applied.
FIG. 3 is a block diagram illustrating a configuration of a control unit of the ink jet printer to which the head drive circuit is applied.
FIG. 4 is an equivalent circuit diagram of the head drive circuit.
FIG. 5 is an enlarged view of a part of an equivalent circuit diagram of the head drive circuit.
FIG. 6 is an equivalent circuit diagram of the head drive circuit.
FIG. 7 is a diagram illustrating a state in which a part of a recording head included in a conventional inkjet printer is viewed from a recording medium side.
FIG. 8 is a view showing a longitudinal sectional view of a recording head provided in a conventional ink jet printer.
FIG. 9 is a diagram illustrating an operation of a recording head provided in a conventional ink jet printer when forming an image.
FIG. 10 is a timing chart showing the timing of applying a voltage to a recording head provided in a conventional inkjet printer.
FIG. 11 is an equivalent circuit diagram of a head drive circuit provided in a conventional recording head.
FIG. 12 is an equivalent circuit diagram of a head drive circuit provided in a conventional recording head.
FIG. 13 is an enlarged view of a part of an equivalent circuit diagram of a head drive circuit provided in a conventional recording head.
FIG. 14 is a diagram illustrating a change in potential of an output unit that connects a piezoelectric body provided in a conventional recording head.
And FIG. 15 is a diagram showing a change in potential of an output unit for connecting a piezoelectric body provided in a conventional recording head.
[Explanation of symbols]
1- Inkjet printer
12-recording head
30-head drive circuit
50-piezoelectric
60-Drive IC

Claims (4)

An inkjet head drive circuit having an output unit for outputting a voltage, and a piezoelectric body constituting at least a part of a plurality of adjacent ink chambers connected to the output unit as a load,
An N-well region and an NMOS transistor are provided in different portions on the P-type semiconductor substrate, a PMOS transistor is provided on the N-well region,
A first power supply to a fourth power supply are sequentially connected to the N-well region, the P-type semiconductor substrate, the source of the PMOS transistor, and the source of the NMOS transistor;
Setting the voltage of each power supply so as to satisfy a relationship of first power supply> second power supply> third power supply> fourth power supply;
An ink jet head driving circuit, wherein a connection line between a drain of a PMOS transistor and a drain of an NMOS transistor is used as the output section. Fixing the voltages of the first power supply and the fourth power supply,
2. The ink jet head drive circuit according to claim 1, wherein the voltage of the second power supply or the third power supply is variable. 3. The ink jet head driving circuit according to claim 1, wherein a diode is connected in a forward direction from the first power supply line to the second power supply line or from the third power supply line to the fourth power supply line. Connecting a diode in a forward direction from the output unit to a second power supply line or a third power supply line to the output unit;
The voltage value due to the voltage drop in the forward connection of the diode is equal to or less than the difference voltage value between the first power supply and the second power supply in the case of connection from the output unit to the second power supply line, and 4. The ink jet head drive circuit according to claim 1, wherein the connection to the output unit is equal to or less than a voltage difference between the third power supply and the fourth power supply.

Images