JPH09187949A - Ink-jet head-driving apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an ink-jet head-driving apparatus of stable printing quality by detecting a load change of concurrently driving piezoelectric elements and automatically making an inclination of a driving trapezoidal wave constant. SOLUTION: A load change of a recording head is detected by a load change- detecting means 2. A correcting data value of a memory element of a load change-correcting means 4 is selected based on data of counted driving pulses, thereby adjusting a current amount-limiting element 7 constituting a constant current-generating circuit, part 6. Since a charging/discharging current value is constant even when the load is changed, a driving trapezoidal wave of a constant inclination is generated.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention uses a piezoelectric element to
The present invention relates to a head driving device of an inkjet recording device that performs recording by applying a trapezoidal voltage waveform to a piezoelectric element and performing suction and discharge of ink.

[0002]

2. Description of the Related Art In an ink jet head printer for recording by ejecting ink droplets from a nozzle hole by expanding and contracting a piezoelectric element, a trapezoidal voltage waveform is applied to control the piezoelectric element. However, when the load changes, the slope of this trapezoidal wave deviates from a predetermined value, and the weight and flight speed of the ejected ink droplets change, which causes a problem that the printing quality becomes unstable.

In view of this, in Japanese Unexamined Patent Publication No. 6-000959, the number of piezoelectric elements simultaneously driven is detected from the print signal given to the head to detect the load variation, and the reference voltage is changed according to the detected value to drive. The print quality is stabilized by changing the constant voltage output of the power supply unit and driving the piezoelectric element with a predetermined voltage.

[0004]

However, in order to increase the driving frequency of the piezoelectric element, the driving waveform is complicated as shown in FIG. 1 and it is more accurate to eject a stable amount of ink droplets. Drive waveforms are required. Particularly, securing a stable intermediate potential and driving waveform inclination are indispensable for securing print quality.

In the technique of Japanese Patent Laid-Open No. 6-000959, when the load changes depending on the number of nozzles driven simultaneously, the output voltage of the drive power supply unit is changed to correct the change in the drive voltage due to the load change. To generate a trapezoidal wave, it is necessary to drive the piezoelectric element with a constant current, and it is difficult to obtain a stable drive waveform slope and an intermediate potential to be applied to the piezoelectric element during standby by voltage correction.

The present invention considers such a problem, and an object thereof is to eliminate variations in charging / discharging current to a capacitive load and to apply a trapezoidal voltage having a predetermined inclination to a piezoelectric vibrator. It is to provide a drive device that can perform.

[0007]

A load fluctuation detecting means for detecting a load fluctuation of a recording head, a load fluctuation correcting means for outputting a correction value corresponding to the detected load fluctuation, and a constant for generating a trapezoidal wave. A current generation circuit, a current amount limiting element for controlling the constant current amount thereof, and a trapezoidal wave drive unit for driving the recording head are provided, and the load is controlled by controlling the current amount control element of the constant current circuit by the correction value. It is characterized in that a predetermined stable trapezoidal waveform is generated and driven regardless of fluctuation.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention are shown in FIGS. FIG. 2 shows a block diagram of the invention and FIG.
2A shows a specific circuit example of the load fluctuation detecting means 2 and the load fluctuation correcting means 4 in FIG. 2, and FIG. 4 shows a specific circuit example of the charging / discharging constant current generating portion 6 in FIG.

In FIG. 2, reference numeral 1 is a control circuit, reference numeral 2 is load fluctuation detecting means, reference numeral 3 is host I / F means, reference numeral 4 is load fluctuation correcting means, reference numeral 5 is a storage element, and reference numeral 6 is a constant current generating section. Reference numeral 7 is a current amount limiting element, reference numeral 8 is a circuit for selecting a piezoelectric element to be driven, reference numeral 9 is a piezoelectric element (PZT), and reference numeral 10 is a drive signal.

Reference numeral 301 in FIG. 3 indicates a serial data print signal, reference numeral 303 indicates a serial data transfer clock, and reference numeral 3
Reference numeral 04 is a counter capable of counting the number of drive nozzles, reference numeral 30
Reference numeral 2 is a count enable signal, reference numeral 5 is a storage element, reference numeral 306 is drive nozzle number data, reference numeral 307 is a storage element read control signal, reference numeral 308 is correction data, reference numeral 309.
Is a latch, reference numeral 310 is a data latch signal, reference numeral 311
Is current amount limiting element control data.

Next, the operation of FIG. 3A will be described with reference to the time chart of FIG. The serial data print signal 301 for driving the head is transferred from the control circuit 1 in synchronization with the serial data transfer signal 303, and the high level signal becomes a signal for driving the piezoelectric elements 9, .... Therefore, when the serial data transfer signal 303 is input, if the number of times the serial data print signal 301 is the high-level count enable signal 302 is counted, the number of piezoelectric elements to be driven is determined, and the change in the load capacitance is detected, and the counter is detected. The count output 306 of 304 is
It is stored in the storage element 5.

This memory device has a count output 30 in advance.
The correction data table with 6 as an argument is stored,
The correction data 308 is read from the storage element 5 in synchronization with the print timing output from the control circuit 1. The correction data 308 is data having a bit width sufficient to control the current amount limiting element 7, and for example, the current amount limiting element 7
The data width is 8 bits so that the resistance value of can be adjusted in 256 steps.

The correction data 308 is latched by the data latch signal 310 from the control circuit 1, and the output thereof controls the current amount limiting element 7 to correct the constant current value.

Next, the operation of the current amount limiting element 7 will be described. FIG. 8 shows an example of the relationship between the equivalent resistance value of the current limiting element 7 and the correction data 308.
8 illustrates 8-bit data, that is, a case where 256 is controlled in 256 steps. The equivalent resistance value R of the current source limiting element 7 when the number of driven piezoelectric elements 9, ... Is 0 is used as a reference to change the resistance value shown in FIG. An example of the current amount limiting element 7 capable of such control is an electronic volume.

The correction data table stored in the storage element 5 can be read and written from the host via the host I / F means 3. As the storage element 5,
A rewritable memory element such as SRAM is suitable.

Next, the constant current generator 6 will be described with reference to FIGS. 4 and 5. Reference numerals 403, 404, 4 in FIG.
23 is a PNP transistor, reference numerals 402, 412, 4
Reference numerals 405 and 4 denote NPN transistors 13 and 422.
Reference numerals 06, 414, and 415 represent resistors, reference numeral 421 represents a capacitor, reference numerals 401 and 411 represent control signals, and reference numeral 10 represents a drive signal. When the control circuit 1 outputs the control signal 401, the NPN transistor 402 is turned on, and the PNP transistor 404 is also turned on accordingly.

The PNP transistor 404 charges the capacitor 421 with a constant current Ic until the voltage of the capacitor 421 reaches a voltage (VH-VBE403) obtained by subtracting the base-emitter voltage VBE403 of the PNP transistor 403 from the power supply voltage VH. . Then, the power supply voltage (VH
When -VBE403) is reached, Ic becomes zero. Next, the voltage of the control signal 401 is set to low, and the PNP transistor 4
After turning off 04, the control signal 411 is output. Then, the NPN transistor 413 turns on, and the capacitor 4
The charge of the capacitor 421 is discharged by the constant current Id until the voltage of 21 reaches the base-emitter voltage VBE412 of the NPN transistor 412.

By the above operation, the voltage waveform VP shown in FIG. 5 is generated in the capacitor 421. The rising time Tc of the voltage waveform VP is Rc for the resistance value of the resistor 405, C0 for the capacitance of the capacitor 421, and PNP type transistor 40.
If the base-emitter voltage of 3 is VBE403, it is obtained by the following equation. Ic = VBE403 ÷ Rc (1) Tc = C0 × (VH−VBE403) ÷ Ic (2) Similarly, the fall time Td of the voltage waveform VP is also the resistance value of the resistor 414, the capacitance of the capacitor 421 is C0. , And the base-emitter voltage of the NPN transistor 412 is VBE412, it is obtained by the following equation. Id = VBE412 ÷ Rd (3) Td = C0 × (VH−VBE412) ÷ Id (4) From the equations (1) and (2), the rising slope of VP is expressed by the following equation, where k is a constant. (VH-VBE403) / Tc = Ic / C0 = VBE403 / (C0.Rc) = k / Rc (5) Similarly, from the equations (3) and (4), the falling slope of VP is k'as a constant. Then, it is expressed by the following formula. (VH-VBE412) / Td = Id / C0 = VBE412 / (C0.Rd) = k '/ Rd (6) That is, the slope of the voltage waveform can be adjusted by the magnitude of Rc and Rd.

The NPN type transistor 422 and the PNP type transistor 423 are current amplifiers for compensating the current driving ability of the constant currents Ic and Id.
The maximum voltage Vmax and the minimum voltage Vmin of 1 are Vmax = VH-VBE403-VBE422 (7) Vmin = VH-VBE412-VBE423 (where VBE422 and VBE423 are the base-emitter voltages of the NPN transistor 422 and the PNP transistor 423, respectively). 8) Also, let Tr be the rise time of the drive signal 431 from Vmin to Vmax and Tf be the fall time from Vmax to Vmin. Tr = C0 × (Vmax−Vmin) ÷ Ic (9) Tf = C0 × (Vmax− Vmin) ÷ Id (10).

The drive signal 431 from this current amplifier is supplied to the piezoelectric elements 9, ... Of the capacitive load, and the current amplifier has a constant charge current Ich and a constant discharge current Ids expressed by the equations (11) and (12). Will flow. Ich = (Vmax−Vmin) × C ÷ Tr (11) Ids = (Vmax−Vmin) × C ÷ Tf (12) Note that C in the equations (11) and (12) is the drive piezoelectric element 9 ,. Full capacity.

As understood from the equations (11) and (12), when Ich and Ids are constant, the waveform of the drive signal is the slope of the waveform when the capacitance C increases (Vmax-Vmin).
/ Tr and (Vmax-Vmin) / Tf become small. Therefore, in order to correct this, Ich and Ids may be supplemented.

Assuming that the base current of the NPN transistor 422 is Ib422 and the collector current is Ic422, Ich during the charging operation is Ich = Ib422 + Ic422 (13), and from FIG. 6 showing the correlation between Ib422 and Ic422, Ich It is understood that the base current Ib422 of the NPN transistor 422 may be replenished in order to replenish the current. That is, the fluctuation of Ich can be corrected by adjusting the charging constant current Ic.

Similarly, when the base current of the PNP transistor 423 is Ib423 and the collector current is Ib422, Ids during the discharging operation is Ids = Ib423 + Ic423 (14), and from FIG. 7 showing the correlation between Ib423 and Ic423. , Ids can be supplemented by supplementing the base current Ib422 of the NPN transistor 423. That is, the fluctuation of Ids can be corrected by adjusting the discharge constant current Id.

Therefore, by varying the resistances 405 and 414, it is possible to correct the capacitance load variation and make the waveform slope constant. The resistors 405, 4
Reference numeral 14 corresponds to the current amount limiting element 7 in FIG. 2, and is controlled by the current amount limiting element control data 311.

[0025]

As described above, in the ink jet head driving apparatus of the present invention, the fluctuation of the load is constantly detected,
Since the charge current and the discharge current to the capacitor that generates the trapezoidal waveform are adjusted by the correction value, it is possible to generate a stable trapezoidal wave according to the load and obtain high print quality.

Further, by using the correction data table written in the storage element as the correction value, it is possible to easily rewrite from the host. As a result, when the characteristics of the head are different, the optimum trapezoidal wave can be applied to the ink head by rewriting the correction data table in accordance with the characteristics. Further, since the control method is performed by a digital value, the inclination adjustment of the trapezoidal wave from the host can be easily performed by software.

[Brief description of the drawings]

FIG. 1 is a diagram showing an example of a drive waveform for increasing a drive frequency.

FIG. 2 is a block diagram showing a configuration of the present invention.

FIG. 3 is a circuit diagram and a time chart showing an embodiment of the load fluctuation detecting means of the present invention.

FIG. 4 is a circuit diagram showing an embodiment of a constant current generator of the present invention.

5 is a time chart explaining the operation of the circuit diagram of FIG.

FIG. 6 is a characteristic diagram of a PNP transistor 422.

FIG. 7 is a characteristic diagram of an NPN transistor 423.

FIG. 8 is a diagram showing an equivalent resistance value of a current limiting element.

[Explanation of symbols]

 1 ... Control circuit 2 ... Load fluctuation detection means 3 ... Host I / F means 4 ... Load fluctuation correction means 5 ... Storage means 6 ... Constant current generation Path 7 ... Current amount limiting element 8 ... Piezoelectric element selection circuit 9 ... Piezoelectric element (PZT) 10 ... Drive signal 11 ... Trapezoidal wave drive unit

Claims (6)

[Claims] 1. An ink jet having a plurality of piezoelectric elements and having a recording head for performing recording by applying a trapezoidal wave voltage to the piezoelectric elements and expanding and contracting the piezoelectric elements to eject ink droplets from nozzle holes. In the recording apparatus, a load fluctuation detecting unit that detects a load fluctuation of the recording head, a load fluctuation correcting unit that outputs a correction value corresponding to the load fluctuation detected by the load fluctuation detecting unit, and a constant that generates a trapezoidal wave. A current generation circuit and a current amount limiting element for controlling the constant current amount thereof and a trapezoidal wave driving unit for driving the piezoelectric element are provided, and the load is controlled by controlling the current amount control element of the constant current circuit by the correction value. An ink jet head drive device, which generates and drives a predetermined stable trapezoidal waveform regardless of fluctuations. 2. The load fluctuation detecting means has a counter, and detects the number of piezoelectric elements driven by counting the number of print data pulses for simultaneously driving the piezoelectric elements to detect the load amount. The inkjet head drive device according to claim 1. 3. The correction means has a storage means, and stores the correction value written in a storage element having an address of the storage means corresponding to a load change (load amount) detected by the load change detection means. The inkjet head drive device according to claim 1, wherein the inkjet head drive device is referred to. 4. The ink jet head drive device according to claim 1, wherein said storage means is connected to a host interface (hereinafter referred to as host I / F) means and rewritable from the host. 5. The correction value written in the storage means is classified according to the rank of the head load capacity and rewritable by the host I / F means.
The inkjet head driving device described. 6. The ink jet head driving device according to claim 1, wherein the current amount control element is adjusted by digital data.