JP3186873B2 - Ink jet recording device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention relates to an ink by a piezoelectric element
A recording head that ejects ink droplets by changing the volume of the flow path
The present invention relates to an ink jet recording apparatus provided with:

[0002]

2. Description of the Related Art FIG. 8 shows an example of the structure of an ink jet head of an ink jet printer using a piezoelectric element.
In the ink jet head shown in FIG. 8, the piezoelectric element 3 is expanded and contracted in the direction of arrow 6 by applying a pulse voltage, and the printing liquid 4 is discharged from the nozzle 1 to the outside by the pressure wave of the printing liquid 4 generated at this time. Recording is performed on a recording medium 5 arranged before the outlet opening of the nozzle 1. As a conventional technique of the driving method of the inkjet head, for example,
According to JP-A-59-136266,
A method using the circuit shown in FIG. 9 has been devised. The operation of the circuit of FIG. 9 will be described below.

[0003] An input terminal IN101 is connected to an inverter U101 having an open collector output.
The output of 1 is pulled up to + 5V by R101. The output of the inverter U101 is connected to the base of the transistor Q101 whose emitter is grounded through R102. The collector of the transistor Q101 is pulled up to a high power supply voltage through R103. Further, the collector of the transistor Q101 is connected to the bases of the transistors Q102 and Q103 in the output stage. The emitters of the transistors Q102 and Q103 in the output stage are connected to each other to form an output terminal OUT101. This output terminal OUT101 and the transistor Q
A feedback capacitor C101 is inserted between the base and the base 101. Further, a piezoelectric element P101, which is a load of the driving circuit, is connected to the output terminal OUT101.

FIG. 10 is a timing chart of input / output signals of this drive circuit. Input terminal IN101 of drive circuit
Input signal such as IN to the input signal IN
Is "H", the transistor Q101 is turned off and the drive voltage rises to + VH.
The drive voltage waveform rises linearly because a Miller integrating circuit is composed of the capacitor C101 and the resistor R102. Similarly, when the input signal IN is "L", the drive waveform linearly falls to 0 V, and a trapezoidal drive voltage waveform such as OUT is obtained.

[0005]

However, since the viscosity of the printing liquid to be discharged changes due to the change in the environmental temperature at which the printer is used, even when the ink jet head is driven with the same drive waveform, the environmental temperature is high. Since the viscosity of the printing liquid is reduced and the amount of the discharged printing liquid is increased, problems such as increased printing bleeding and time required for drying the printing liquid occur. In addition, when the environmental temperature is low, the viscosity of the printing liquid becomes high, and the amount of the printing liquid to be discharged is reduced, so that there is a problem that the printing density is lowered. This
In order to solve such a problem as described in
No. 4 and JP-A-55-27210.
Using a temperature detection resistor as the discharge resistor
To form a charge / discharge circuit as a capacitor.
The voltage applied to the piezoelectric element was adjusted according to the resistance value of
The pulse width and voltage value are changed by the temperature detection means.
The pulse signal is applied to the piezoelectric element,
Correction of the ink droplet ejection characteristics due to
You. However, in the former method, each piezoelectric element
Requires connection of temperature detection resistor, complicates circuit configuration
And in the latter case use trapezoidal signals
There is a problem that it cannot be simply applied to a recording device.
The present invention has been made in view of such a problem.
Its purpose is to increase the complexity of the circuit structure.
Generated by the charge and discharge circuit of the resistor and the capacitor.
Adjust the trapezoidal drive signal according to the temperature, and
To prevent fluctuations in ink droplet ejection characteristics due to temperature changes
To provide an improved ink jet recording apparatus.

[0006]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention provides a flow path communicating with a nozzle,
Bei a piezoelectric element to eject ink droplets by changing the volume
The ink jet head, the charging resistance and the first switch.
To the voltage source via the switching means, and also to the discharge resistor and the second
Capacitor connected to earth through the switching means of
Output the charging voltage and discharging voltage of the sensor to the piezoelectric element.
That the drive signal generating means, for generating a pulse signal having a pulse width corresponding to <br/> temperature information detected by the temperature detecting means Pas
Pulse generating means, wherein the pulse signal is supplied to a first switch.
Charging time applied to the switching means
Is controlled.

[0007]

[Function] A table for applying a voltage to a piezoelectric element according to a change in environmental temperature
The voltage of the shape of the signal is appropriately set, the discharge amount of printing fluid
Prevents changes due to temperature.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail below based on illustrated embodiments. FIG. 1 is a block diagram showing an embodiment of the present invention. The control unit 11 includes a CPU 12, a ROM 13 for storing programs and data, and a RAM 14 as a working memory of the CPU 12.
The temperature information from the temperature detection unit 16 composed of the A / D converter 19 and the thermistor 20 is input through the controller, and a control signal for obtaining an appropriate pulse voltage amplitude in accordance with the input temperature information is pulsed. The configuration is such that the pulse voltage output to the voltage generator 17 and generated by the pulse voltage generator 17 is applied to the piezoelectric element of the inkjet head 18.

FIG. 2 is a circuit diagram of the pulse voltage generator of FIG. 1, and FIG. 3 is a timing chart of input / output signals used in the first embodiment of the present invention.

In FIG. 2, IN1 and IN2 are input terminals for input signals, Q6 is a level shift transistor, transistors Q8 and Q9, and a resistor R1 are constant current circuits for charging waveforms.
Transistors Q4, Q5, resistor R2 are constant current circuits for discharging waveforms, C1 is a capacitor for forming driving waveforms, OUT1
Is a drive waveform output terminal, and P1 is a piezoelectric element as a load.

The operation of this circuit will be described below.
When a signal such as Pc is input to the input terminal IN1 and Pd is input to the input terminal IN2, first, when the Pc signal becomes "H", the transistor Q6 is turned on. At this time, the transistor Q8 is turned on, and the capacitor C1 connected to the collector of the transistor Q8 is charged. The collector current of the transistor Q8 flows through the resistor R1 connected to the emitter of the transistor Q8,
The potential difference between both ends of 1 becomes the potential between the base and the emitter of the transistor Q9. When the transistor Q9 is on, the potential between the base and the emitter is substantially constant, so that the resistance R
The current for charging the capacitor C1 via the constant 1 becomes a constant current. Since the capacitor C1 is charged with a constant current, the waveform of the potential difference between both ends of the capacitor C1 rises linearly from 0 [V] as shown by Po1 in FIG. The rising time constant τc [V / sec], which is the slope of the waveform, is equal to the resistance R1
Resistance value r1 [Ω] and the capacitance value c1 of the capacitor C1
[F] and the base-emitter voltage V of the transistor Q9
From BE9 [V], τc = VBE9） (r1 × c1), which is adjusted by changing the resistance value r1 of the resistor R1 or the capacitance value c1 of the capacitor C1. If the state of the Pc signal remains “H” as it is, the potential difference between both ends of the capacitor C1 rises to the power supply voltage VM. However, the Pc signal becomes “tc” after tc [sec] after the Pc signal becomes “H”.
When it becomes "L", the transistor Q6 is turned off,
Since the transistor Q8 is turned off, the capacitor C
The potential difference V1 [V] between both ends of 1 rises up to V1 = τc × tc, and the potential difference is held by the electric charge accumulated in the capacitor C1. Further, when the Pd signal becomes “H” after th [sec], the transistor Q4 is turned on, and the electric charge accumulated in the capacitor C1 is transferred to the resistor R.
Discharge via 2. Since the potential difference between both ends of the resistor R2 becomes the potential between the base and the emitter of the transistor Q5, the capacitor C1 is discharged with a constant current as in the case of the rise, and the waveform of the potential difference between both ends of the capacitor C1 falls linearly. Falling time constant τ which is the slope of the waveform
d [V / sec] is obtained from the resistance value r2 [Ω] of the resistor R2, the capacitance value c1 [F] of the capacitor C1, and the base-emitter voltage VBE5 [V] of the transistor Q5, as follows: τd = VBE5 ÷ (r2 × c1) ) Is adjusted by changing the resistance value r2 of the resistor R2 or the capacitance value c1 of the capacitor C1. By making the time td [sec] from the time when the Pd signal becomes “H” to the time when the Pc signal becomes “L” sufficiently longer than td = V1 ÷ τd, the potential difference between both ends of the capacitor C1 becomes 0 [V]. Fall down linearly. In this way, a pulse voltage having an arbitrary voltage amplitude, a rise time, a time during which a constant voltage is maintained, and a fall time is transferred to the capacitor C.
1 occurs at both ends.

The transistors Q1, Q2, Q3, and Q7 form a current buffer, output a waveform similar to the voltage waveform generated at both ends of the capacitor C1 to the output terminal OUT1, and output a piezoelectric signal of a load connected to OUT1. It supplies the current necessary to drive the device. At this time, the voltage amplitude V2 of the voltage waveform Po2 output to the output terminal OUT1
[V] is the voltage amplitude V of the voltage waveform across the capacitor C1.
1 to bases of transistors Q1, Q2, Q3, Q7
V2 is reduced by the voltage between the emitters, and V2 becomes V2 = V1- (| VBE1 | + | VBE3 | +) from V1 and the voltages VBE1, VBE2, VBE3, and VBE7 between the base and the emitter of the transistors Q1, Q2, Q3, and Q7. | VBE2 | + |
VBE7 |). In this embodiment, the current buffer is constituted by two-stage amplification by Darlington connection of the transistors Q1 and Q3 and the transistors Q2 and Q7. However, depending on the current required to drive the piezoelectric element of the load, one stage or one stage is used. It is also possible to use three or more stages of transistors, and it is clear that a similar effect can be obtained in such a case. In this case, the voltage amplitude of the voltage waveform output to the output terminal OUT1 is smaller than the potential difference V1 across the capacitor C1 by the voltage between the base and the emitter of the transistor constituting the current buffer.

In the ink jet head having the pulse voltage generating section for performing the above-described operation, the rising time constant τc and the falling time constant τd of the pulse voltage are appropriately set in advance, and the appropriate pulse voltage of each ink jet head is set. The rising time tc of the input signal Pc is set to tc = (V2 + | VBE1 | + | VBE3 | + | VBE2 | +
By setting | VBE7 |) ÷ τc as a standard, the voltage amplitude of an arbitrary pulse voltage can be set.

FIG. 4 is a flowchart showing the operation of the block diagram of FIG. First, according to procedure a, the temperature detector 1
The temperature T [° C.] detected from step 6 is obtained. Next, the rise time tc of the input signal Pc for obtaining the appropriate voltage amplitude V2 of the pulse voltage at the temperature T is obtained from the temperature T obtained in the procedure a in the procedure a. The method of calculating tc is based on the method of obtaining the voltage amplitude V2 of the appropriate pulse voltage with respect to Tn [° C] from each temperature T1 [° C] experimentally obtained in advance.
c is changed from tc1 [sec] to tcn [sec] and stored in the ROM 13 of the control unit 11 in a format as shown in FIG. 5. If the detected temperature T is lower than T2, tc becomes tc1 and T becomes tc1. T
When the temperature is 2 or more and less than T3, tc is set to tc2, and when the temperature T is more than T3 and less than T4, tc is set to tc3, and the temperature T is set to Tn.
In the above case, tc is set to tcn so that tc
Ask for. Further, in the procedure C, the interface 15
By inputting the control signals Pc and Pd corrected based on the environmental temperature to the pulse voltage generating unit 17 via the, the pulse voltage generating unit 17 described above in the procedure d. A waveform having the voltage amplitude V2 is output and applied to the piezoelectric element of the inkjet head 18.

Next, a second embodiment of the present invention will be described. In the first embodiment described above, in the control unit using the CPU, the control signals Pc and P
Although d has been generated, this can also be realized by a pulse generation circuit as shown in FIG. FIG. 7 is a timing chart of input / output signals of the pulse generation circuit of FIG.
In FIG. 6, U201, U202, and U203 are monostable multivibrators, R201, R202, and R203 are time constant adjusting resistors, C201, C202, and C203 are time constant adjusting capacitors, and Rth is a temperature detection and time constant correction thermistor. . Monostable multivibrator U201, U2
02 and U203, U201 generates a pulse that determines tc at the fall of the print timing signal, U202 generates a pulse that determines th at the fall of this pulse, and U203 generates a pulse that determines td at the fall of this pulse. Occurs. Q output of U201 is output terminal OU
T201, the control signal P to the pulse voltage generator
c, and the Q output of U203 is output terminal OUT202.
And outputs a control signal Pd to the pulse voltage generator. The time of the pulses output from U201, U202, and U203 is determined by the resistance value r of the externally connected resistor and the capacitance value c of the capacitor. The time tw [sec] of the output pulse is obtained by tw = 0.33 × r × c in the case of 74LS123, for example. According to the above equation, for the resistor R202 connected outside of the U202, the capacitor C202, the resistor R203 connected outside of the U203, and the capacitor C203, the resistance value of the resistor and the capacitance value of the capacitor are set in accordance with the desired th time and td time. . The resistor connected to the outside of U201 is configured by connecting the resistor R201 and the thermistor Rth in series. Thermistor Rth
The characteristic of the resistance value is small when the temperature is high,
When the temperature is low, select one with a large resistance value. As a result, when the temperature is high, the voltage amplitude V2 of the pulse voltage is reduced by shortening tc, and the discharge amount of the printing liquid is reduced. When the temperature is low, the voltage amount V2 is increased by increasing tc, and the discharge amount of the printing liquid is increased. Therefore, a change in the amount of the printing liquid ejected due to a change in the environmental temperature can be corrected.

[0016]

As described above, according to the present invention ,
A trapezoidal drive applied to the piezoelectric element in response to changes in environmental temperature
The voltage of the motion signal is appropriately set, the discharge amount of printing fluid temperature
This can prevent the change.

[Brief description of the drawings]

FIG. 1 is a block diagram of an embodiment of the present invention.

FIG. 2 is a circuit diagram of a pulse voltage generator according to the embodiment of the present invention.

FIG. 3 is a timing chart of input / output signals according to the embodiment of the present invention.

FIG. 4 is a flowchart of an embodiment of the present invention.

FIG. 5 is a conceptual diagram of a storage state of data of an environmental temperature and a rise time of a pulse voltage.

FIG. 6 is a circuit diagram of a pulse generation circuit according to a second embodiment of the present invention.

FIG. 7 is a timing chart of input / output signals of a pulse generator circuit according to a second embodiment of the present invention.

FIG. 8 is a cross-sectional view showing the structure of the inkjet head.

FIG. 9 is a circuit diagram of an embodiment of the prior art.

FIG. 10 is a timing chart of input / output signals according to an embodiment of the prior art.

[Explanation of symbols]

REFERENCE SIGNS LIST 11 inkjet head control unit 12 CPU 13 ROM 14 RAM 15 interface 16 temperature detection unit 17 pulse voltage generation unit 18 inkjet head 19 A / D converter 20 thermistor IN1 input signal input terminal of pulse voltage generation unit IN2 pulse voltage generation unit Q6 Transistor for level shift of pulse voltage generator Q8 Transistor for constant current of charge waveform of pulse voltage generator Q9 Transistor for constant current of charge waveform of pulse voltage generator R1 Pulse voltage generator A constant current resistor having a charge waveform of Q4 A transistor having a constant current of a discharge waveform of a pulse voltage generator Q5 A transistor having a constant current of a discharge waveform of a pulse voltage generator R2 A constant current transistor having a discharge waveform of a pulse voltage generator Resistance C1 Drive voltage of pulse voltage generator Forming capacitor OUT1 Output terminal of drive waveform of pulse voltage generator P1 Piezoelectric element of load of pulse voltage generator IN201 Input terminal of input signal of pulse generator U201 Monostable multivibrator of pulse generator U202 Unit of pulse generator Stable multivibrator U203 Monostable multivibrator for pulse generation circuit R201 Resistance for time constant adjustment of pulse generation circuit R202 Resistance for time constant adjustment of pulse generation circuit R203 Resistance for time constant adjustment of pulse generation circuit C201 Time constant adjustment for pulse generation circuit C202 Capacitor for adjusting the time constant of the pulse generating circuit C203 Capacitor for adjusting the time constant of the pulse generating circuit Rth Thermistor for detecting the temperature of the pulse generating circuit OUT201 Output terminal of the output signal of the pulse generating circuit OUT202 Output terminals of the output signal of the pulse generating circuit

──────────────────────────────────────────────────続 き Continuing on the front page (72) Munehide Kanaya 3-3-5 Yamato, Suwa City, Nagano Prefecture Seiko Epson Corporation (72) Inventor Shuichi Yamaguchi 3-5-5, Yamato Suwa City, Nagano Prefecture Seiko -Epson Corporation (72) Inventor Takakazu Fukano 3-5-5 Yamato, Suwa City, Nagano Prefecture Seiko-Epson Corporation (56) References JP-A-3-272854 (JP, A) JP-A-55-27210 ( JP, A) JP-A-59-42965 (JP, A) JP-A-3-16956 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) B41J 2/045 B41J 2/055

Claims (1)

(57) [Claims] 1. A and the flow path communicating with the nozzles, said each flow path
A piezoelectric element that ejects ink droplets by changing the volume.
The ink jet head, the charging resistance and the first switch.
To the voltage source via the switching means, and also to the discharge resistor and the second
Capacitor connected to earth through the switching means of
Output the charging voltage and discharging voltage of the sensor to the piezoelectric element.
A driving signal generating means for generating a pulse signal having a pulse width corresponding to the temperature information detected by the temperature detecting means.
Pulse generating means, wherein the pulse signal is supplied to a first switch.
Charging time applied to the switching means
Is controlled by an inkjet recording apparatus.