JPH08281937A - Drive circuit of ink jet head - Google Patents

Abstract

PURPOSE: To execute a time-sharing driving by preventing an overshoot of a piezoelectric element in a driving circuit wherein the ink jet head is driven in a time-sharing fashion by utilizing a piezoelectric operation of the piezoelectric element. CONSTITUTION: The title device comprises (n) piezoelectric element groups 1 each having (m) piezoelectric elements, (m) switching circuits S for grounding each is connected to one of the electrodes of the corresponding piezoelectric element of each group and activated in accordance with a driving signal and a pair of diodes D1, D2 which are provided to each of the piezoelectric elements 1 and connected to the other electrode of the piezoelectric element. It further comprises a charge scanning voltage generating section 12 that generates a charge scanning voltage having an inclination for charging the piezoelectric element 1, a discharge scanning voltage generating section 13 that generates a discharge scanning voltage having an inclination for discharging the piezoelectric element 1, a first application selecting means AS1 that connects the charge scanning voltage generating section 12 to the diode D1 in accordance with a selection signal and a second application selecting means AS2 that connects discharge scanning voltage generating section 13 to the other diode D2 in accordance with a selection signal.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a drive circuit for time-divisionally driving an ink jet head utilizing the electrostrictive operation of a piezoelectric element.

An ink jet printer is a device for ejecting ink from a head to perform recording. In this inkjet printer, there is provided an inkjet printer that utilizes the electrostrictive operation of a piezoelectric element.

In this ink jet head, a piezoelectric element provided in each nozzle is driven. This piezoelectric element is distorted by its driving. The ink chamber is deformed by the distortion of the piezoelectric element, and ink is ejected from the ink chamber.

In such an ink jet head, 1
Since many nozzles are provided in one head, it is necessary to selectively drive many piezoelectric elements. Therefore, a useful drive circuit for the piezoelectric element is required.

[0005]

2. Description of the Related Art FIG. 5 is a block diagram of a prior art.

The piezoelectric elements 93 are provided in m groups of n groups each. In the figure, three piezoelectric elements 93 are provided for three groups. Corresponding to each group of this piezoelectric element, n high-voltage side switching elements 92a to 92c
Is provided.

One electrode of each of the piezoelectric elements 93 of each group is commonly connected. Then, the high-voltage side switching elements 92a to 92 are respectively connected to the commonly connected portions.
c is connected. Also, serial print signal (drive signal)
Are converted into parallel print signals by the shift register 90 and latched by the latch circuit 91. The outputs of the latch circuits 91 are the high voltage side switching elements 92, respectively.
Drive a to 92c.

On the other hand, a resistor 9 is connected in parallel to each piezoelectric element 93.
4r is provided. Further, a diode 95d is connected in series to the other electrode of each piezoelectric element 93. The other electrode of the piezoelectric element 93 at the corresponding position of each group is connected to the time division switch 9 via the diode 95d.
6-1 to 96-3 are connected. Time division switch 96-
1 to 96-3 are driven by time division signals.

This operation will be described. According to the print signal,
The high voltage side switching elements 92a to 92c are selectively operated. At this time, the time divisional switches 96-1 to 96-3
Are turned on / off sequentially at a predetermined timing by a time division signal.
Turned off. Therefore, the high voltage side switching elements 92a to
In the group in which 92c is ON, and the time division switch 96
The piezoelectric element 93 in which -1 to 96-3 are on is selected. So-called time division driving is performed.

That is, the high voltage side switching elements 92a to 9a
The piezoelectric element 93 in which both 2c and the time divisional switches 96-1 to 96-3 are turned on is charged. After that, only the switching elements 92a / 92c on the high voltage side are turned off.
As a result, the electric charge stored in the piezoelectric element 93 is transferred to the resistor 9
4r, the diode 95d, and the time divisional switch 96 are discharged.

[0011]

FIG. 6 is a diagram for explaining the problems of the prior art.

First, as shown in FIG. 6, since there is no element that limits the current immediately after the start of charging, the drive voltage is pulsed. Therefore, the charging time is shortened and the piezoelectric element is charged rapidly. Therefore, the overshoot of the displacement of the piezoelectric element becomes large, and the time for the vibration to settle becomes long.
Therefore, there is a problem that satellite particles are generated and print quality is deteriorated.

Secondly, the discharge time is determined by the electrostatic capacity of the piezoelectric element and the resistance value of the resistor 94r. To shorten the printing repetition frequency, it is necessary to shorten the discharge time. For this purpose, it is necessary to reduce the resistance value of the resistor 94r. However, when the resistance value is reduced, the current during charging flows through the resistor. Therefore, there is a problem that a power supply with a large current capacity is required.

An object of the present invention is to provide a drive circuit of an ink jet head for time-division driving by preventing overshoot of displacement of a piezoelectric element.

Another object of the present invention is to provide a drive circuit of an ink jet head for improving the drive frequency without passing a wasteful current.

[0016]

FIG. 1 is a diagram illustrating the principle of the present invention.

According to a first aspect of the present invention, in an ink jet head drive circuit for time-divisionally driving each piezoelectric element of an ink jet head utilizing the electrostrictive operation of the piezoelectric element, n groups of m piezoelectric elements are provided. Of the piezoelectric elements 1 and m switching circuits S for grounding which are connected to the other electrode of the corresponding piezoelectric elements 1 of each group and which are operated by a drive signal or a time-division selection signal; A pair of diodes D1 and D2 provided in each of the piezoelectric elements 1 and connected to one electrode of the piezoelectric element 1, and a charging scanning voltage generator that generates a charging scanning voltage having an inclination for charging the piezoelectric element 1. 12, a discharge scan voltage generator 13 for generating a discharge scan voltage having an inclination for discharging the piezoelectric element 1, and n units corresponding to each of the groups are provided. First application timing selecting means AS1 for connecting the charging scanning voltage generator 12 and the one diode D1 in response to a selection signal or a drive signal, and n pieces are provided corresponding to each group, and time division is provided. It is characterized by further comprising second application timing selection means AS2 for connecting the discharge scan voltage generator 13 and the other diode D2 in accordance with a selection signal or a drive signal.

According to a second aspect of the present invention, in the drive circuit for an ink jet head according to the first aspect, the cathode of the diode D1 on one side and the anode of the diode D2 on the other side are connected in series, and the connecting portion is provided with the above. Piezoelectric element 1
One of the electrodes is connected, the anode of the one diode D1 is connected to the first application timing selecting means AS1, and the cathode of the other diode D2 is connected to the second
Is connected to the application timing selection means AS2.

According to a third aspect of the present invention, in the ink jet head drive circuit according to the first or second aspect, the discharge scan voltage generating section 13 continues to generate the charge scan voltage of the charge scan voltage generating section 12. A discharge scan voltage having a slope different from that of the charge scan voltage is generated.

According to a fourth aspect of the present invention, in the ink jet head drive circuit according to the first, second or third aspect, the charge scan voltage generating section 12 has a fall time shorter than a fall time of the discharge scan voltage. It is characterized by generating a charging scanning voltage.

According to a fifth aspect of the present invention, in the ink jet head drive circuit according to the first, second or third aspect, the charge scanning voltage generating section 12 has a falling voltage lower than a voltage at the time of the discharge scanning voltage falling. Is generated.

[0022]

According to the first aspect of the present invention, firstly, the charging scanning voltage generator 12 for generating the charging scanning voltage having an inclination for charging the piezoelectric element 1 is provided. As a result, the piezoelectric element 1 is slowly charged, so that it is possible to prevent displacement overshoot of the piezoelectric element 1.

Further, there is provided a discharge scan voltage generator 13 for generating a discharge scan voltage having an inclination for discharging the piezoelectric element 1. As a result, the piezoelectric element 1 can be discharged along the discharge scanning voltage. Therefore, the repetition frequency can be improved without passing unnecessary current.

Further, even in this case, since the pair of diodes D1 and D2 are provided, charging and discharging can be performed separately.

According to a second aspect of the present invention, the cathode of the diode D1 on one side and the anode of the diode D2 on the other side are connected in series, and one electrode of the piezoelectric element 1 is connected to the connection point. Since the anode of one diode D1 is connected to the first application timing selection means AS1 and the cathode of the other diode D2 is connected to the second application timing selection means AS2, charging and discharging can be performed separately. it can.

According to the third aspect of the present invention, since the discharge scan voltage having the slope different from the slope of the charge scan voltage is generated subsequent to the generation of the charge scan voltage of the charge scan voltage generator 12, the charge voltage falls. It is possible to prevent discharge due to. As a result, the piezoelectric element can be discharged according to the discharge scan voltage.

According to the fourth aspect of the present invention, since the charge scanning voltage having the fall time shorter than the fall time of the discharge scan voltage is generated, the discharge due to the fall of the charge voltage can be prevented. As a result, there is no loss in the discharge scan voltage, and it is possible to prevent a wasteful current from flowing.

According to the fifth aspect of the present invention, since the charging scan voltage having the falling voltage lower than the voltage at the falling of the discharge scanning voltage is generated, the discharge due to the falling of the charging voltage can be prevented. As a result, there is no loss in the discharge scan voltage, and it is possible to prevent a wasteful current from flowing.

[0029]

FIG. 2 is a block diagram of an embodiment of the present invention, FIG. 3 is a waveform diagram of each part thereof, and FIG. 4 is an operation explanatory diagram thereof.

As shown in FIG. 2, the piezoelectric element group 1 has m ×
It is composed of n piezoelectric elements 1-1 to nm. The piezoelectric element group 1 includes m piezoelectric elements 1-1 to 1-m,
2-1 to 2-m-n-1 to nm are divided into groups 1 to n.

That is, the first group is composed of m piezoelectric elements 1-1 to 1-m, and the second group is composed of m piezoelectric elements 2-1 to 2-m. . The last n-th group is the m piezoelectric elements n-1 to nm.
It is composed of

The piezoelectric elements at the same position in each group are commonly connected to one electrode of each piezoelectric element 1-1 to nm of each group. For example, the first piezoelectric element 1-1 of the first group is the first piezoelectric element 2-1 of the second group to the first piezoelectric element n of the nth group.
-1 is commonly connected.

Grounding transistors S-1 to S-m are connected to the common connection point, respectively. The shift register 10 converts serial print data (drive signal) into m-bit parallel data. m-bit latch circuit 1
1 holds the parallel data of the shift register 10 according to the latch signal. Then, each output of the latch circuit 11 drives the grounding transistors S-1 to S-m.

On the other hand, a first diode (charging diode) 111 is provided on the other electrode of each of the piezoelectric elements 1-1 to nm.
~ Nm1 cathode is connected. Similarly, anodes of second diodes (discharging diodes) 112 to nm2 are connected to the other electrodes of the respective piezoelectric elements 1-1 to nm.

First (for charging) analog switch AS1
1 to AS1n are provided for each group. The first analog switches AS11 to AS1n connect the charge scanning waveform generation circuit 12 to the anodes of the first diodes 111 to n11 when the selection signals (time division selection signals) 1 to n are on. On the other hand, when the selection signals 1 to n are off, the anodes of the first diodes 111 to n11 are grounded.

Second (for discharging) analog switch AS2
1 to AS2n are provided for each group. The second analog switches AS21 to AS2n connect the discharge scan waveform generating circuit 13 to the cathodes of the second diodes 112 to nm2 when the selection signals 1 to n are on. On the other hand, when the selection signals 1 to n are off, the voltage Vh is supplied to the cathodes of the second diodes 112 to nm2.

The charging scanning waveform generating circuit 12 is composed of a constant current circuit. The charge scanning waveform generation circuit 12 is
In response to the trigger 1 signal, as shown in FIGS. 3 and 4, a charging scan waveform is generated which rises to a voltage Vh with a predetermined slope and then falls to 0 V.

The discharge scanning waveform generating circuit 13 is composed of a constant current circuit. This discharge scan waveform generation circuit 13
In response to the trigger 2 signal generated subsequently to the trigger 1 signal, as shown in FIGS. 3 and 4, the voltage Vh falls from 0 volt with a predetermined slope, and then the voltage Vh
Generate a discharge scan waveform that rises to.

The operation of the circuit shown in FIG. 2 will be described with reference to FIGS. 3 and 4.

Bit map data, which is print data from the controller that controls the printer, is transferred serially. The print data sent from the controller
The shift register 10 is sequentially driven by the clock shown in FIG.
Take in.

All the print data corresponding to the number m of the nozzle selection transistors S-1 to S-m are all in the shift register 10.
The clock stops when it is taken into. After that, the latch signal is input to the latch circuit 11, and the data in the shift register 10 is captured by the subsequent latch circuit 11.

After this latch signal is input, the transmission of data and clock is restarted in preparation for printing at the next timing.

The latch circuit 11 drives each of the nozzle selection transistors S-1 to S-m. When data is to be printed, the output of the latch circuit 11 becomes high level. Therefore, the succeeding transistors S-1 to S-m are turned on to bring one electrode side of the piezoelectric element to the ground level.

When it is not the data to be printed, the output of the latch circuit 11 becomes low level. Therefore, the subsequent transistors S-1 to S-m are turned off, and the one electrode side of the piezoelectric element is made floating.

When one electrode of the piezoelectric element is at the ground level, a potential difference according to the voltage applied to the electrode on the opposite side is applied to both ends of the piezoelectric element. Therefore, the piezoelectric element is deformed.

When one electrode of the piezoelectric element is floating, the voltage induced by the voltage applied to the electrode on the opposite side appears on the floating side. Therefore, no potential difference is generated at both ends of the piezoelectric element, and the piezoelectric element is not deformed.

At almost the same timing as this latch signal, the selection signal 1 which is the control signal (time division selection signal) of the analog switches AS11 and AS21 is set to the high level. As a result, the analog switches AS11, AS21
Are connected to the charge scanning waveform generating circuit 12 and the discharge scanning waveform generating circuit 13, respectively. As a result, the charge scan waveform and the discharge scan waveform are applied to the piezoelectric elements of group 1.

On the other hand, since the other selection signals 2 to n are at low level, the analog switches AS12 to AS1n are set to 0.
Each analog switch AS22-AS2n,
The voltage Vh is output.

The charge scan waveform generating circuit 12 generates a charge scan voltage by the trigger 1 signal following the latch signal.

Nozzle selection transistor S- of group 1
For the piezoelectric elements 1 to Sm turned on, the diode 1 is turned on during the period when the charging scanning voltage output from the analog switch AS11 rises from 0V (the period from t0 to t1 in FIG. 4).
The piezoelectric element is charged through 11 to 1 m1 to deform the piezoelectric element.

At this time, since the analog switch AS21 supplies the voltage Vh, it is possible to prevent the current from leaking through the diodes 112 to 1m2 on the other electrode side of the piezoelectric element.

At time t1 when the charging scanning voltage reaches the peak (voltage Vh), the discharging period starts. Therefore, a discharge scan voltage is generated from the discharge scan waveform generation circuit 13 according to the trigger 2 signal.

At this time, as shown in FIGS. 3 and 4, the fall time of the charge scan voltage (t1 to t3 in FIG. 4) is shorter than the fall time of the discharge scan voltage (t1 to t2 in FIG. 4). To do. This allows the diode 1 used when charging
11 to 1m1 are made inoperative to prevent discharge due to the fall of the charge scanning voltage waveform.

Along with this, diodes 112 to 1 m
2 and the electric charge accumulated in the piezoelectric element is discharged by the fall of the discharge scanning voltage given through the analog switch AS21. As a result, the deformation of the piezoelectric element is restored and the ink is ejected. The discharge scan voltage falls to 0V and then rises and returns to the voltage Vh within a predetermined time.

After that, the latch signal input is set to the high level, the selection 1 signal is set to the low level, and the selection 2 signal is set to the high level to drive the piezoelectric elements of group 2. This operation is sequentially performed up to group n, and printing at predetermined positions of all piezoelectric elements is completed. Then, the printing operation of group 1 is started again.

In this way, since the piezoelectric element is driven by the charging scan voltage having a predetermined inclination, overshoot of the piezoelectric element can be prevented and satellite particles can be prevented from being generated. Therefore, the print quality can be improved.

Further, since the discharge scanning voltage having a predetermined inclination is used for driving, the discharge is performed along the discharge scanning voltage. Therefore, the driving frequency can be increased. Since the charge scan voltage and the discharge scan voltage have a predetermined slope, time-divisional driving can be performed without causing unnecessary current flow.

Since the discharge scan voltage having a slope smaller than the slope of the charge scan voltage is generated subsequent to the generation of the charge scan voltage by the charge scan voltage generation circuit 12, the discharge due to the fall of the charge voltage can be prevented. Therefore, the piezoelectric element can be discharged according to the discharge scan voltage. As a result, it is possible to prevent useless current from flowing.

In other words, since the charging scan voltage having the fall time shorter than the fall time of the discharge scan voltage is generated, the discharge due to the fall of the charge voltage can be prevented. As a result, there is no loss in the discharge scan voltage, and it is possible to prevent a wasteful current from flowing.

This means that the charge scanning voltage having a falling voltage lower than the voltage at the time of the discharge scanning voltage falling is generated. Therefore, it is possible to prevent discharge due to the fall of the charging voltage. As a result, there is no loss in the discharge scan voltage, and it is possible to prevent a wasteful current from flowing.

In addition to the above embodiment, the present invention can be modified as follows.

The transistors S-1 to S-m are driven by the print data (driving signal), but the transistors are driven by the time division selection signal and the analog switch is driven by the driving signal (printing signal). You may.

The print data is serially transferred,
You may transfer in parallel.

The present invention has been described above with reference to the embodiments.
Various modifications are possible within the scope of the invention, and these modifications are not excluded from the scope of the invention.

[0065]

As described above, according to the present invention,
The following effects are obtained.

A charging scanning voltage generator 12 for generating a charging scanning voltage having an inclination for charging the piezoelectric element 1 is provided. As a result, the piezoelectric element 1 is slowly charged, so that it is possible to prevent displacement overshoot of the piezoelectric element 1.

A discharge scan voltage generator 13 for generating a discharge scan voltage having an inclination for discharging the piezoelectric element 1 is provided. As a result, the piezoelectric element 1 can be discharged along the discharge scanning voltage. Therefore, the repetition frequency can be improved without passing unnecessary current.

Further, even in this case, since the pair of diodes D1 and D2 are provided, charging and discharging can be performed separately.

[Brief description of drawings]

FIG. 1 is a principle diagram of the present invention.

FIG. 2 is a configuration diagram of an embodiment of the present invention.

FIG. 3 is a waveform diagram of each part of FIG.

FIG. 4 is an operation explanatory diagram of FIG. 2;

FIG. 5 is a configuration diagram of a conventional technique.

FIG. 6 is a diagram illustrating a problem of the conventional technique.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Piezoelectric element group 12 Charge scanning voltage generating circuit 13 Discharge scanning voltage generating circuit AS1 and AS2 switches D1 and D2 Diodes S Grounding switch

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Satoshi Senba, Satoshi Senba, 1015 Kamiodanaka, Nakahara-ku, Kawasaki-shi, Kanagawa, Fujitsu Limited (72) Inventor Tomohisa Mikami, 1015, Kamedota, Nakahara-ku, Kawasaki, Kanagawa, Fujitsu Limited

Claims (5)

[Claims] 1. A drive circuit of an inkjet head for time-divisionally driving each piezoelectric element of an inkjet head using electrostrictive operation of the piezoelectric element, wherein a piezoelectric element group in which n groups of m piezoelectric elements are provided, M grounding switching circuits that are connected to the other electrodes of the corresponding piezoelectric elements of each of the groups and that operate by a drive signal or a time-division selection signal; A pair of diodes connected to one of the electrodes, a charge scan voltage generator that generates a charge scan voltage having a slope for charging the piezoelectric element, and a discharge having a slope for discharging the piezoelectric element. A discharge scan voltage generator that generates a scan voltage, and n discharge scan voltage generators are provided for each group, and the charge scan voltage generator is generated according to a time division selection signal or a drive signal. First application timing selection means for connecting the raw section and the one diode, and n discharge timing voltage generation sections provided corresponding to each group, according to a time division selection signal or a drive signal. A driving circuit for an ink jet head, comprising: a second application timing selecting unit that connects to the other diode. 2. The drive circuit for an inkjet head according to claim 1, wherein a cathode of the one diode and an anode of the other diode are connected in series, and one electrode of the piezoelectric element is connected to the connection point. The drive circuit of the inkjet head, wherein the anode of the one diode is connected to the first application timing selecting means and the cathode of the other diode is connected to the second application timing selecting means. 3. The drive circuit for an inkjet head according to claim 1, wherein the discharge scan voltage generator has a slope different from that of the charge scan voltage subsequent to generation of the charge scan voltage by the charge scan voltage generator. A drive circuit for an inkjet head, which generates a discharge scan voltage having an inclination. 4. The drive circuit for an inkjet head according to claim 1, 2, or 3, wherein the charge scan voltage generator generates a charge scan voltage having a fall time shorter than a fall time of the discharge scan voltage. A drive circuit for an inkjet head, characterized by: 5. The inkjet head drive circuit according to claim 1, wherein the charge scan voltage generator generates a charge scan voltage having a falling voltage lower than a voltage at the time of the discharge scan voltage falling. A drive circuit for an inkjet head, characterized in that