JPH06959A - Ink jet recorder - Google Patents

Abstract

PURPOSE:To prevent printing quality from deteriorating by a method wherein an influence of stray capacity of a driving circuit is reduced in a multinozzle on demand type ink jet recording head. CONSTITUTION:A detection part detects the number of piezoelectric elements which are driven simultaneously from a printing signal given a head driving part according to a printing command. A CPU 101 detects a detected result of the detection part via an I/O part 108. When alteration of driving voltage is required, transistors Tr2, Tr3, Tr4 of a standard voltage setting part of the driving power source part are slectively turned on to change standard voltage. Output voltage of the driving power source part is varied, and driving of a piezoelectric element is carried out by specific driving voltage.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to controlling an ink jet recording apparatus.

[0002]

2. Description of the Related Art FIG. 2 shows an example of an ink jet recording head for recording by ejecting ink droplets from a nozzle by applying a driving pulse to a piezoelectric element provided on a wall surface of a part of an ink pressurizing chamber. 13 is an ink tank, 10 is an ink pressurizing chamber communicating with the ink tank, 4 is a piezoelectric element, 12 is a vibrating plate, 1
1 is a nozzle. FIG. 3 shows a drive circuit for the inkjet recording head. 4A to 4C are a drive timing chart and a drive voltage waveform of the inkjet recording head.

The principle of operation of the ink jet recording head will be described with reference to FIGS. 2, 3 and 4. Before time t1 in FIG. 4, the transistors 5, 6, and 7 are in the off state, and the piezoelectric element 4 is charged to the voltage VH. This is done through the charging resistance element 2 by turning on the transistor 6 as an initial operation when the power of the recording apparatus is turned on. In the standby state of this voltage VH, the piezoelectric element 4 shown in FIG. 5 is bent. At this time, the charging resistance element 2 (Ra) in FIG.
And the resistance value of the discharge resistance element 3 (Rb) is Ra << Rb. Here, when the signal of FIG. 4A is applied to the terminal a at time t1 to turn on the transistor 5, the charge of the piezoelectric element 4 is discharged through the discharge resistance element 3 (Rb). The element 4 returns from the deflected state to the original state, the volume of the pressurizing chamber increases as shown in FIG. 6, and the ink is drawn into the pressurizing chamber. Predetermined time T1
After the lapse of time, the transistor 5 is turned off at the time t2, and at the same time, the signal of FIG.
Is turned on, the piezoelectric element 4 becomes the charging resistance element 2 (R
As a result of rapid charging via a) and instantaneous bending, the volume of the ink pressurizing chamber 10 decreases and ink droplets are ejected from the nozzle 11 as shown in FIG. FIG. 4C shows a drive voltage waveform of the piezoelectric element 4. In this figure, the falling curve is determined by the capacity of the piezoelectric element 4, the discharge resistance element 3 and the energization time (T1) of the transistor 5, and the rising curve is the capacity of the piezoelectric element 4 and the charging resistance element 2 and the transistor 6. It is determined by the energization time (T2). Both are set so that desired ejection characteristics can be obtained.

FIG. 8 shows an example of a multi-nozzle on-demand type ink jet recording head in which a plurality of ink jet recording heads are provided and ink droplets are appropriately ejected according to a printing pattern to perform recording by a dot matrix.
FIG. 9 shows the driving circuit. This is achieved by connecting a plurality of drive circuits shown in FIG. 3 and forming a discharge circuit corresponding to the number of nozzles. However, the charging circuit is common to all nozzles, and diodes 1-1 to 1-n for backflow prevention corresponding to the number of nozzles are added. When a print command is applied to the terminals a1 to an in FIG. 9, the piezoelectric elements 4-1 to 4-n are selectively driven, and ink droplets are ejected. This drive circuit is disclosed in JP-A-5
No. 7-125060, the number of elements can be reduced because the switching element on the charging side can be configured by one even when the number of piezoelectric elements is increased. Therefore, it is extremely useful in the recent inkjet recording apparatus in which the density is increased and the number of nozzles tends to increase.

[0005]

However, there is always some stray capacitance on the circuit board that constitutes the drive circuit, especially for a piezoelectric element drive circuit in which the number of nozzles increases and the circuit pattern becomes longer. The value of its stray capacity cannot be ignored. That is, as shown in FIG.
(Although it is actually distributed everywhere on the substrate, it can be equivalently expressed as seen from the piezoelectric element drive circuit.)
Due to the presence of C1 and the discharge circuit represented by D1 to Dn
A charging circuit represented by is formed. In the multi-nozzle on-demand type inkjet recording device,
Since the piezoelectric elements are selectively driven according to a desired character or pattern, the number of piezoelectric elements simultaneously driven also changes each time. When the number of piezoelectric elements driven at the same time is large, the influence of the stray capacitance 21 is dispersed to a plurality of nozzles and hardly appears. However, when the number of nozzles driven at the same time is small, only a specific path of D1 to Dn is generated. Since it is a discharge circuit, the time constant of charging / discharging of the piezoelectric element largely changes, the falling / rising curve largely changes, and desired ink ejection characteristics cannot be obtained, resulting in deterioration of print quality. This state is shown in FIGS. 11 and 12.
FIG. 11 shows a comparison between the terminal voltage waveform (W1) of the piezoelectric element when there is no influence of the stray capacitance and the terminal voltage waveform (W2) of the piezoelectric element when only one piezoelectric element is driven. FIG. 12 shows a comparison between the terminal voltage waveform (W1) of the piezoelectric element when there is no influence of the stray capacitance and the voltage waveform (W3) of the piezoelectric element when a plurality of (eight) piezoelectric elements are driven. . In the state of W3, there is no problem in ejection characteristics. The time constant of charging / discharging of the piezoelectric element changes depending on the number of piezoelectric elements driven in this way.

The present invention has been conceived in order to solve such a problem, and an object thereof is to stabilize ejection characteristics and prevent deterioration of print quality in an ink jet recording apparatus with a simple structure. And

[0007]

In order to solve such a problem, in a multi-nozzle on-demand type ink jet recording apparatus for ejecting ink droplets from a nozzle by increasing the liquid pressure of an ink pressurizing chamber of the present invention, An ink pressurizing chamber for storing ejected ink, a nozzle communicating with the ink pressurizing chamber, and a plurality of sets of piezoelectric elements for displacing the walls of the ink pressurizing chamber are provided, and a charging switching element for charging and discharging the piezoelectric element and a discharge At least one of the switching elements is provided individually for a plurality of sets of piezoelectric elements, and the other is provided commonly for a plurality of sets of piezoelectric elements, and the piezoelectric elements are charged / discharged according to a print command, and the number of piezoelectric elements to be driven simultaneously is increased. It is characterized in that the drive voltage of the piezoelectric element is changed in accordance with the change.

[0008]

[Function] Since the number of piezoelectric elements that are driven at the same time is detected and the drive voltage is changed according to the detection result, when the number of piezoelectric elements that are driven is small, the amount of change in charge / discharge characteristics due to the effect of stray capacitance of the circuit board Can be corrected, and stable ink ejection characteristics can be obtained.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be specifically described below with reference to the embodiments shown in the drawings.

The ink jet recording head used in the present invention has a structure as shown in FIG. An inkjet recording head having multiple nozzles has a structure shown in FIG. The operation related to ink ejection is as described above.

FIG. 1 is a block diagram showing an embodiment of the present invention. Reference numeral 101 in FIG. 1 is a CPU which is a control unit of the printer.
Further, the ROM 102 storing the control program and the RAM 103 temporarily storing various data are provided together. The print data from the host device 104 is sent to the CPU 101 via the I / F unit (interface unit) 105. The CPU 101 performs a series of printing operations such as carriage motor drive, head drive, and paper feed motor drive in accordance with print data. Reference numeral 106 in FIG. 1 denotes a head drive unit having the circuit configuration shown in FIG. Reference numeral 8 in FIG. 1 denotes a drive power supply unit having the circuit configuration shown in FIG. The operation of one embodiment of the present invention will be described with reference to FIG.
In FIG. 1, the detection unit detects the number of piezoelectric elements that are simultaneously driven from the print signal given to the head drive unit in response to the print command. The CPU 101 detects the detection result of the detection unit via the I / O unit 108, and when the drive voltage needs to be changed, the transistor T of the reference voltage setting unit of the drive power supply unit described above is detected.
The r2, Tr3, and Tr4 are selectively turned on, the reference voltage is changed to change the output voltage VH of the driving power supply unit, and the piezoelectric element is driven by a predetermined driving voltage. The above is a series of operations in one printing (every one printing timing). The detection of the number of driving elements and the change of the driving voltage may be performed from the time when the charging operation is completed to the time when the next discharging operation is started. As for the detecting means, a method using software (CPU) or a method using hardware (counter, etc.) can be considered depending on the method of transferring print data and the configuration of the drive circuit.

IC1 in FIG. 13 is a general-purpose switching regulator controller, and in this embodiment, TL494.
Are using. IC1 has two error amplifiers (EA
1, EA2) is built in, and EA1 is for constant voltage control,
EA2 is used for current limiting control, respectively. IC2
Is a shunt regulator, which stabilizes the voltage at the K terminal. The voltage V4 (shunt regulator output) at the K terminal is the voltage adjustment volume VR1 and R4 and R described later.
The voltage is divided by the combined resistance Rp of 5, R6, R7 and R8, and I
It is connected to the inverting input terminal of the error amplifier EA1 in C1,
It becomes the reference voltage Vref. On the other hand, a voltage obtained by dividing the output voltage VH by R11 and R12 is connected to the non-inverting input terminal of the error amplifier EA1, and the error amplifier EA1 controls the output voltage so that the two input voltages become equal. Therefore, the output voltage VH is

[0013]

[Equation 1]

It is output so as to satisfy the above condition. That is,

[0015]

[Equation 2]

[0016]

The combined resistance Rp will be described below. The combined resistance Rp is R5, R6, R7, R8, Tr2, Tr3, Tr4.
It is set by the reference voltage setting unit configured by. R6, R7, and R8 in FIG. 13 are transistors Tr2, Tr3, and T.
It is inserted in parallel with R5 by selectively turning on and off r4. Rp when all transistors are off
= R5, and when Tr2 is turned on, the combined resistance by parallel connection becomes Rp = R5.R6 / (R5 + R6). The same applies to Tr3 and Tr4. Considering even the setting of the resistance value and the combination of transistors, it is possible to switch to more stages. That is, the output voltage VH can be set in multiple stages.

Assuming that the piezoelectric element driven in FIG. 9 is 4-1 only, the charge of the stray capacitance 21 passes through the diode 1-1, the resistor 2-1, the resistor 3-1, and the transistor 5-1. As described above (FIG. 11), the time constant of the discharge of the piezoelectric element 4-1 is changed by being discharged. In the ink jet recording head used in this example, the ink ejection speed was remarkably reduced due to the change in the discharge time constant. It was also found that the ink ejection speed can be corrected by increasing the drive voltage of the piezoelectric element. The ink ejection speed is corrected by an increase in the displacement amount of the piezoelectric element during discharging and an increase in the actual applied voltage during charging. The terminal voltage waveform of the piezoelectric element at this time is shown in FIG. In this way, the change in the ejection characteristic due to the influence of the stray capacitance can be corrected by changing the drive voltage. The charging / discharging time constant changes according to the number of driven piezoelectric elements,
The drive voltage for correcting the ink ejection speed also changes.

The ink jet recording head used in this embodiment has 48 nozzles, and if the number of simultaneously driven nozzles is 8 or more, the change in ink ejection speed due to the influence of stray capacitance is almost eliminated, so 8 or more. There is no need to correct the driving of. Therefore, in this embodiment, the number of driving piezoelectric elements is divided into four stages of 1, 2 to 3 and 4 to 7, 8 or more, and the optimum driving voltage is set as the output voltage VH in the driving power source section (VH1 , VH
2, VH3, VH4). The setting of each resistance value in this embodiment is V4 = 10 (V), VR1 = 1 (kΩ), R4 = 2 (k).
Ω), R5 = 4 (kΩ), R6 = 36 (kΩ), R7 = 1
8 (kΩ), R8 = 12 (kΩ), R11 = 200 (k
Ω) and R12 = 10 (kΩ). Tr2, Tr3, Tr
The voltage when all 4 are off is VH1 = 120
(V), and the voltage when only Tr2 is on is VH2
= 110 (V), the voltage when only Tr3 is on is VH3 = 100 (V), and the voltage when only Tr4 is on is VH4 = 90 (V).

[0020]

As described above, according to the present invention, the number of driving piezoelectric elements is detected, and the driving voltage of the piezoelectric elements is changed according to the detection result, so that the driving voltage is almost always independent of the number of piezoelectric elements to be driven. Since the same ejection characteristics can be secured, it is possible to reduce the change in ejection characteristics due to stray capacitance when the number of driving piezoelectric elements is small, and it is possible to provide an inkjet recording apparatus with stable print quality.

[Brief description of drawings]

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

FIG. 2 is a structural diagram of an inkjet recording head of the present invention.

FIG. 3 is a drive circuit diagram of the ink jet recording head of the present invention.

FIG. 4 is a drive timing chart of the inkjet recording head of the present invention.

FIG. 5 is a diagram illustrating an ejection operation of the inkjet recording head of the present invention.

FIG. 6 is a diagram illustrating an ejection operation of the inkjet recording head of the present invention.

FIG. 7 is a diagram illustrating an ejection operation of the inkjet recording head of the present invention.

FIG. 8 is a structural diagram of a multi-nozzle on-demand type ink jet recording head of the present invention.

FIG. 9 is a drive circuit diagram of a multi-nozzle on-demand type inkjet recording head of the present invention.

FIG. 10 is a circuit diagram of a conventional inkjet recording head drive circuit.

FIG. 11 is a diagram illustrating charge / discharge characteristics of a conventional piezoelectric element.

FIG. 12 is a diagram illustrating charge / discharge characteristics of a conventional piezoelectric element.

FIG. 13 is a circuit diagram of a driving power supply unit according to an embodiment of the present invention.

FIG. 14 is a diagram illustrating charge / discharge characteristics of an example of the present invention.

[Explanation of symbols]

 1-n diode 2-n resistance element 3-n resistance element 4-n piezoelectric element 5-n transistor 6 transistor 7 transistor 8 drive power supply section 9 recording head 10 ink pressurizing chamber 11-n nozzle 12 vibrating plate 13 ink tank 21 Stray capacitance 101 CPU 102 ROM 103 RAM 104 Host device 105 I / F unit 106 Head drive unit 107 Detection unit 108 I / O unit

Claims (1)

[Claims] 1. A plurality of sets of an ink pressurizing chamber for storing ejected ink, a nozzle communicating with the ink pressurizing chamber, and a piezoelectric element for displacing a wall of the ink pressurizing chamber are provided to charge and discharge the piezoelectric element. At least one of the charge switching element and the discharge switching element is individually provided to the plurality of sets of piezoelectric elements, and the other is commonly provided to the plurality of sets of piezoelectric elements, and the piezoelectric elements are charged / discharged in response to a print command and are simultaneously driven. An inkjet recording apparatus comprising a multi-nozzle on-demand inkjet recording head that changes a driving voltage of the piezoelectric element according to the number of piezoelectric elements.