JP3674386B2 - Inkjet head drive circuit - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a drive circuit for an inkjet head that drives a piezoelectric element of the inkjet head.
[0002]
[Prior art]
Conventionally, as shown in FIG. 11, a piezoelectric element driving circuit 2 having a plurality of piezoelectric elements 4 to 12 connected in parallel and transistors 13 to 21 connected in series to the piezoelectric elements 4 to 12, and this 2. Description of the Related Art There is known an inkjet head drive circuit 1 that includes a power supply drive circuit 3 that feeds power to the piezoelectric elements 4 to 12 of the piezoelectric element drive circuit 2. Each of the transistors 13 to 21 of the drive circuit 1 has a base terminal connected to a print signal generating circuit (not shown) and is turned on by a print signal output from the print signal generating circuit. The corresponding piezoelectric elements 4 to 12 are powered by the power feeding circuit 3 due to the conduction of the transistors 13 to 21. The supplied piezoelectric element is distorted on the pressure generating chamber side (not shown) of the inkjet head, and ink is ejected from a nozzle hole (not shown) by the pressing force due to the distortion.
[0003]
[Problems to be solved by the invention]
By the way, in the drive circuit 1 of the inkjet head, the number of piezoelectric elements to be driven at the time of printing differs depending on the shape of the font to be printed.
[0004]
Here, the capacitance of each of the piezoelectric elements 4 to 12 is C, the internal resistance is R, and when the voltage V ₀ is applied from the feeder circuit 3 to n of the piezoelectric elements 4 to 12, The voltage rises according to a curve of V ₀ × {1-exp (−t / nCR)} (t: time).
[0005]
According to this curve, how the voltage of the piezoelectric element rises varies according to the number n of piezoelectric elements to be driven, as shown in FIG. That is, as the number of nozzles ejecting ink increases, the voltage rises more slowly, and the ink ejection speed decreases. That is, the ink ejection speed varies depending on the number of nozzles. As a result, there is a problem that the ink ejection speed is not constant and the printing quality is deteriorated.
[0006]
The present invention has been made in view of the above problems, and provides an ink jet head drive circuit capable of reducing variations in the rise of the voltage of piezoelectric elements even when the number of driven piezoelectric elements varies. Objective.
[0007]
[Means for Solving the Problems]
In order to solve the above problem, the invention according to claim 1 is a piezoelectric element driving circuit having a plurality of piezoelectric elements connected in parallel and a switching element connected in series to each piezoelectric element, and the piezoelectric element A drive circuit for an inkjet head that discharges ink by applying a voltage of the DC power supply to each piezoelectric element by causing each switching element to conduct,
A Zener diode having a Zener voltage equal to the drive voltage of the piezoelectric element is connected between the power supply output terminals of the power supply circuit;
Compared with the case where the voltage of the DC power supply is equal to the driving voltage, the voltage of the DC power supply is made higher than the driving voltage of the piezoelectric element so that the rising voltage of each piezoelectric element reaches the driving voltage of the piezoelectric element earlier. Characterized by being enlarged.
[0008]
DETAILED DESCRIPTION OF THE INVENTION
DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of an ink jet head drive circuit according to the present invention will be described below with reference to the drawings.
[0009]
As shown in FIG. 1, the ink jet head drive circuit 30 includes a plurality of piezoelectric elements A ₁ , A ₂ ,... A _N-1 , A _N connected in parallel and the piezoelectric elements A _{1 to} A _N. A piezoelectric element driving circuit 31 having transistors (switching elements) B ₁ , B ₂ ,... B _N-1 , B _N connected in series, and a power feeding circuit 32 that feeds power to the piezoelectric element driving circuit 31 Has been.
[0010]
One end of each piezoelectric element A _{1 to} A _N is connected to the collector terminal of the transistors B _{1 to} B _N. The emitter terminals of the transistors B _{1 to} B _N are grounded, and the base terminal is connected to a print signal generating circuit (not shown). The transistors B _{1 to} B _N are turned on when the print signals 1 ^{# to} N ^# output from the print signal generation circuit are input to the base terminal.
[0011]
As shown in FIG. 2, the power feeding circuit 32 is turned on by the Schmitt circuits 41 and 42 for removing noise from the pulse signal D output from the pulse signal generation circuit 40 and the pulse signal D output from the Schmitt circuits 41 and 42. A transistor 43 that conducts while the transistor 43 is conducting, a transistor 44 that applies the voltage V ₂ of the DC power supply 47 to the output terminal 49 via the resistor 52, and a pulse that is output from the Schmitt circuits 41 and 42. A transistor 45 that is turned on by a signal D and a transistor 46 that is turned on when the transistor 45 is turned off and grounds the output terminal 49 via resistors 52 and 53 are provided. The cathode of the Zener diode 51 is connected to the output terminal 49, and the anode of the Zener diode 51 is connected to the grounded output terminal 50. Here, the Zener diode 51 has a Zener voltage equal to the drive voltage V ₁ of the piezoelectric elements A _{1 to} A _N. Further, the voltage V ₂ of the DC power supply 47 is set to be larger than the driving voltage V ₁ of the piezoelectric elements A _{1 to} A _N.
[0012]
Next, the operation of the inkjet head drive circuit 30 will be described.
[0013]
For example, print signal 1 ^# is the input to the base terminal of the transistor B _1, the transistor B ₁ is conductive. On the other hand, as shown in FIG. 4, when the pulse signal D is output from the pulse signal generation circuit 41, the transistor 43 is turned on and the transistor 44 is turned on, so that only the piezoelectric element A ₁ is driven by the DC power supply 47 of the power feeding circuit 32. Power is supplied. Thereafter, when the pulse signal D is turned off, the transistor 45 is turned off together with the transistor 44 and the transistor 46 is turned on, so that the piezoelectric element A ₁ is discharged, and then the print signal 1 ^# is turned off. Ink is discharged from the nozzle holes corresponding to the piezoelectric element A ₁ in the same manner as conventional by feeding to the piezoelectric element A _1. Similarly, when other print signals 2 ^{# to} N ^# are input to the base terminals of the transistors B _{1 to} B _N , ink is ejected from the nozzle holes corresponding to the piezoelectric elements A _{1 to} A _N to perform printing. .
[0014]
Here, when each of the piezoelectric elements A _{1 to} A _N is supplied with the voltage V _X by the DC power supply 47 of the power supply circuit 32, the rising voltage V of the piezoelectric element is V = V _X × {1−exp (−t / nCR)}. Here, t is time, C is the capacitance of each of the piezoelectric elements A _{1 to} A _N , R is the resistance value of the resistor 52, and n is the number of driving of the piezoelectric elements.
[0015]
As shown in FIG. 3, all the piezoelectric elements A _{1 to} A _N are driven (n = N), and the voltage V _X of the DC power supply 47 is made equal to the driving voltage V ₁ of each piezoelectric element A _{1 to} A _N ( V _X = V ₁ ), as shown by the curve (1), the voltage rise of the piezoelectric element becomes slow, and the rise voltage V of the piezoelectric elements A _{1 to} A _N reaches the drive voltage V ₁ at time t _N. . On the other hand, if the voltage V _X of the DC power supply 47 is a voltage V ₂ higher than the drive voltage V ₁ (V _X = V ₂ ), the voltage V ₂ is higher than the voltage V ₁ , so that the curve (2 As shown in FIG. 4B, the rise is less slow than the curve (1), and the rise voltage V of the piezoelectric elements A _{1 to} A _N reaches the drive voltage V ₁ at a time t _N ′ earlier than t _N.
[0016]
One of the piezoelectric elements A _{1 to} A _N is driven (n = 1), and the voltage V _X of the DC power supply 47 is made equal to the driving voltage V ₁ of each piezoelectric element A _{1 to} A _N (V _X = V ₁ ), the voltage V of the piezoelectric element rises as shown by the curve (3), and the rising voltage V of the piezoelectric element reaches the drive voltage V ₁ at time t ₁ . On the other hand, when the voltage V _X of the DC power supply 47 is V ₂ (V _X = V ₂ ), the voltage V ₂ is higher than the voltage V ₁ , so that the curve (4) becomes the curve (3). The rising voltage V of the piezoelectric element reaches the driving voltage V ₁ at a time t ₁ ′ that rises more rapidly than t ₁ and is earlier than t ₁ .
[0017]
As is apparent from FIG. 3, the time required for the rising voltage V of the N piezoelectric elements to reach the driving voltage V ₁ and the time required for the rising voltage V of one piezoelectric element to reach the driving voltage V _1. in the difference between the time difference (t _N -t ₁₎ time difference than (t _N '-t _1') times more of the shorter. That is, when a high voltage V ₂ than the voltage V _X of the driving voltage V ₁ of the DC power source 47, resulting in the voltage V of the piezoelectric element to alleviate the variation time to reach the driving voltages V _1.
[0018]
In addition, since the Zener diode 51 having the Zener voltage V ₁ is connected between the output terminals 49 and 50 of the power feeding circuit 32, the voltage V _X of the DC power supply 47 is set to V ₂ larger than the drive voltage V ₁ of the piezoelectric element. In addition, a voltage exceeding the driving voltage V ₁ (the dotted line portion of the curves (1) and (3)) is not applied to each of the piezoelectric elements A _{1 to} A _N, and is maintained at the driving voltage V ₁ , and the piezoelectric element fails. Does not occur.
[0019]
Actually, 16 piezoelectric elements having a drive voltage V ₁ of 20 V are driven by the power supply circuit shown in FIG. 2 (n = 16), and the voltage V _X of the DC power supply 47 is 30 V, as shown in FIG. The time t ₁₆ ′ required for the rising voltage V of the piezoelectric element to reach the drive voltage V ₁ (V ₁ = 20 V) was 2.58 usec. When one piezoelectric element is driven (n = 1), the time t ₁ ′ required for the rising voltage V of the piezoelectric element to reach the driving voltage V ₁ (V ₁ = 20 V) as shown in FIG. .26 usec. From these results, the difference between t ₁₆ ′ and t ₁ ′ (t ₁₆ ′ −t ₁ ′) is 2.32 usec. That is, the rise variation time is only 2.32 usec.
[0020]
On the other hand, when 16 piezoelectric elements having a driving voltage V ₁ of 20V are driven by a power supply circuit not connected to the Zener diode shown in FIG. 5 (n = 16) and the voltage V _X of the DC power supply 47 is 20V. As shown in FIG. 8, the time t ₁₆ required for the rising voltage V of the piezoelectric element to reach the drive voltage V ₁ (V ₁ = 20 V) was 7.64 usec. When one piezoelectric element is driven (n = 1), the time t ₁ required for the rising voltage V of the piezoelectric element to reach the drive voltage V ₁ (V ₁ = 20 V) as shown in FIG. It was 99 usec. That is, the rise variation time, which is the difference between t ₁₆ and t ₁ (t ₁₆ −t ₁ ), is 6.65 usec.
[0021]
FIG. 10 shows these results. Thus, the voltage V _X of the DC power supply 47 is set higher than the drive voltage V ₁ of the piezoelectric element _{(V 1 = 20V) (V} X = 30V), the drive voltage V ₁ of the piezoelectric element (V ₁ = 20V) By connecting a Zener diode 51 having a Zener voltage equal to the output terminals 49 and 50 of the power feeding circuit 32, the variation time of the rise of the voltage V of the piezoelectric element can be suppressed. Further, the power supply circuit 32 is simply connected to the output terminals 49 and 50 of the power supply circuit 32 with the Zener diode 51 so that the voltage V _X of the DC power supply 47 is higher than the drive voltage V ₁ of the piezoelectric element. It is very simple and the cost can be kept low.
[0022]
【The invention's effect】
As described above, according to the first aspect of the present invention, a piezoelectric element driving circuit having a plurality of piezoelectric elements connected in parallel and a switching element connected in series to each piezoelectric element, and feeding power to the piezoelectric element A drive circuit for an inkjet head that discharges ink by applying a voltage of the DC power supply to each piezoelectric element by causing each switching element to conduct,
A Zener diode having a Zener voltage equal to the drive voltage of the piezoelectric element is connected between the power supply output terminals of the power supply circuit;
Compared with the case where the voltage of the DC power supply is equal to the driving voltage, the voltage of the DC power supply is made higher than the driving voltage of the piezoelectric element so that the rising voltage of each piezoelectric element reaches the driving voltage of the piezoelectric element earlier. Since the size is increased, variations in the voltage rise are alleviated even when the number of driven piezoelectric elements varies, and a decrease in print quality can be suppressed. In addition, a Zener diode is connected between the power supply output terminals of the power supply circuit, and the voltage of the DC power supply is simply made larger than the drive voltage of the piezoelectric element. Can do.
[Brief description of the drawings]
FIG. 1 is a circuit diagram showing a drive circuit of an inkjet head according to the present invention.
FIG. 2 is a detailed circuit diagram of the power feeding circuit in FIG.
FIG. 3 is a graph showing a voltage change of a piezoelectric element when a voltage is applied to the piezoelectric element.
FIG. 4 is an explanatory diagram illustrating timings of a pulse signal D, print signals 1 ^# and 2 ^# , transistors 13 to 16, and piezoelectric elements A ₁ and A ₂ .
FIG. 5 is a circuit diagram showing a conventional power feeding circuit.
6 is a graph showing the voltage V of the piezoelectric element when the number of piezoelectric elements driven by the power feeding circuit 32 is 16. FIG.
7 is a graph showing the voltage V of the piezoelectric element when the number of piezoelectric elements driven by the power feeding circuit 32 is 1. FIG.
8 is a graph showing a voltage V of piezoelectric elements when the number of driven piezoelectric elements is 16 by the conventional power feeding circuit of FIG.
9 is a graph showing a voltage V of a piezoelectric element when the number of driven piezoelectric elements is 1 by the conventional power feeding circuit of FIG.
FIG. 10 is a table showing the results of FIGS.
FIG. 11 is a circuit diagram showing a conventional inkjet head drive circuit.
FIG. 12 is a graph showing a rise in voltage of a piezoelectric element when a voltage is applied to a plurality of piezoelectric elements.
[Explanation of symbols]
A _{1 to} A _N Piezoelectric element 32 Feed circuit 47 DC power supply 51 Zener diode

Claims (1)

A piezoelectric element drive circuit having a plurality of piezoelectric elements connected in parallel and a switching element connected in series to each piezoelectric element; and a power supply circuit having a DC power source for supplying power to the piezoelectric element, A drive circuit for an ink-jet head that discharges ink by applying a voltage of the DC power source to each piezoelectric element by being conducted;
A Zener diode having a Zener voltage equal to the drive voltage of the piezoelectric element is connected between the power supply output terminals of the power supply circuit;
Compared with the case where the voltage of the DC power supply is equal to the driving voltage, the voltage of the DC power supply is made higher than the driving voltage of the piezoelectric element so that the rising voltage of each piezoelectric element reaches the driving voltage of the piezoelectric element earlier. A drive circuit for an inkjet head, characterized in that it is enlarged.

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