JP2011045192A - Load drive circuit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To output a variety of voltage values, while suppressing the number of storage elements connected in series. <P>SOLUTION: A first output voltage is generated by connecting in series the storage elements of a first storage element group and a second output voltage, different from the first output voltage is generated by connecting in series the storage elements of a second storage element group. The first output voltage and the second output voltage are switched and connected to a load. By doing so, since the storage elements in the storage element group are connected in series, the number of storage elements connected in series can be suppressed compared to the total number of whole storage elements. Since a variety of voltages which the second storage element group generates can be applied, in addition to a variety of voltages which the first storage element generates by switching the first storage element group and the second storage element group and connecting them to the load, a variety of voltages can be applied to the load, while the number of storage elements connected in series is suppressed. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a technique for driving a load by applying a voltage waveform.

A technique for driving a load of an electronic element such as a semiconductor element or a dielectric element by applying a voltage is widely used in various apparatuses. For example, in a fluid ejecting apparatus such as an ink jet printer, a fluid is pushed out and ejected from an ejection port by applying a voltage to a piezo element that expands and contracts according to the voltage. In a display device such as a liquid crystal display or an organic EL display, an image is displayed by applying a voltage to the liquid crystal to align liquid crystal molecules, or applying a voltage to the organic EL element to emit light. In addition to electronic devices,
Techniques by applying a voltage to various loads such as a motor or an electromagnet to drive a load are also widely used.

In the devices that drive these various loads, the operation of the load is controlled by controlling the waveform (voltage waveform) of the voltage applied to the load. For this reason, it is important to accurately generate the voltage waveform. . Therefore, a circuit (so-called charge pump circuit) is used that charges multiple capacitors and increases the voltage by connecting them in series and changes the voltage value by changing the number of capacitors connected in series. A technique for generating a voltage waveform has been proposed (Patent Document 1). In this technology, the output voltage value is determined by the number of capacitors connected in series. By providing a large number of capacitors, an accurate voltage waveform can be generated by outputting many types of voltage values. Is possible.

JP-A-7-130484

However, the proposed technique has a problem in that the impedance of the circuit increases because a large number of capacitors are connected in series. That is, when a large number of capacitors are connected in series, the number of wirings, switches, and the like that connect the capacitors to each other increases, so that the circuit impedance increases due to the electrical resistance of the switches and wirings. As a result, power is consumed in the impedance of the circuit and power efficiency deteriorates, or the time constant of the circuit increases as the impedance increases, making it difficult to drive the circuit at high speed, etc. Inconvenience arises.

The present invention has been made to solve the above-described problems of the prior art,
The purpose of the present invention is to provide a technique for suppressing an increase in the impedance of a circuit by suppressing the number of capacitors connected in series while increasing the number of types of voltage values that can be output and outputting an accurate voltage waveform.

In order to solve at least part of the problems described above, the load driving circuit of the present invention employs the following configuration. That is,
A load driving circuit for driving a load by applying a voltage to the load,
A first power storage element group and a second power storage element group comprising a plurality of power storage elements charged by a power source;
A plurality of output voltages that are switched in stages by switching the connection state between the plurality of power storage elements included in the first power storage element group and changing the number of the power storage elements connected in series. First output voltage generating means for generating one output voltage;
By switching the connection state between the plurality of power storage elements included in the second power storage element group and changing the number of the power storage elements connected in series, the voltage is different from the first output voltage. Second output voltage generating means for generating a second output voltage, which is a plurality of output voltages that are switched automatically,
By switching between the first output voltage and the second output voltage and connecting to the load,
And a voltage applying means for applying a voltage to the load.

In the load driving circuit of the present invention, the first output voltage is generated by connecting the storage elements of the first storage element group in series. Moreover, the 2nd output voltage different from a 1st output voltage is generated by connecting the electrical storage element of a 2nd electrical storage element group in series. Then, the voltage is applied to the load by switching between the first output voltage and the second output voltage and connecting to the load.

If a plurality of power storage elements are divided into a first power storage element group and a second power storage element group, and the power storage elements are connected in series in each of the power storage element groups, the number of power storage elements connected in series is reduced to It is possible to suppress it rather than the number. However, since the number of types of voltage that can be generated is limited to the number of power storage elements connected in series, as long as the voltage is generated by connecting the power storage elements in series, the number of types of voltage that can be generated in this case is , less than the total number of the electricity storage device of the first storage element group and the second power storage element group. Therefore, if different voltages are generated in the first storage element group and the second storage element group, and the voltages generated by the respective storage element groups are switched and applied to the load,
In addition to the plurality of types of voltages generated by the first power storage element, a plurality of types of voltages different from the first power storage element group generated by the second power storage element group can be applied. It is possible to apply more types of voltages to the load than the number of elements and the number of storage elements in the second storage element group. Thereby, it is possible to apply various types of voltages to the load while suppressing the number of power storage elements connected in series.

The storage element may be any element as long as it is an element that is charged and generates a voltage. For example, it may be an element that generates a voltage by accumulating electric charge when it is charged and supplied with a charge like a capacitor, or it stores chemical energy inside like a secondary battery. The element which generates a voltage by this may be sufficient.

In the above-described load drive circuit of the present invention, the storage elements of the first storage element group and the storage elements of the second storage element group may be charged to different voltages.

If the voltage of the power storage elements of the first power storage element group and the voltage of the power storage elements of the second power storage element group are made different, the voltages can be made different even when the power storage elements of the respective power storage element groups are connected in series. It is possible to make the first output voltage different from the second output voltage,
As a result, it is possible to apply various types of voltages to the load by switching between the first output voltage and the second output voltage and connecting to the load. In this way, the power storage elements of the first power storage element group and the second
It is only necessary to connect the power storage elements of the power storage element group in series, and it is not necessary to provide a power source for generating a reference voltage for making the first output voltage different from the second output voltage, so that the apparatus configuration is kept simple. It becomes possible.

In the above-described load driving circuit of the present invention, when the first output voltage is output, the power storage elements of the first power storage element group connected in series are connected to the first reference voltage and the second output voltage is output. The second storage element group connected in series is connected to a second reference voltage different from the first reference voltage.
It may be connected to a reference voltage.

If the first reference voltage and the second reference voltage are made different, the voltage can be made different even when the first storage element group and the second storage element group are connected to the reference voltage. The second output voltage can be made different, and as a result, various types of voltages can be applied to the load by switching the first output voltage and the second output voltage and connecting them to the load. Further, since the first output voltage changes according to the first reference voltage and the second output voltage changes according to the second reference voltage, the first output voltage can be changed by changing the first reference voltage or the second reference voltage. And the second output voltage can be changed. For example, if the second reference voltage is set to a voltage higher than the maximum voltage of the first output voltage, it is possible to output a voltage in a different range between the first output voltage and the second output voltage, and output is possible. It is also possible to widen the range of voltage values (so-called dynamic range).

In the above-described load drive circuit of the present invention, the second output voltage is connected to the load in the second output voltage.
The power storage elements in the power storage element group may be charged, and the power storage elements in the first power storage element group may be charged with the second output voltage connected to the load.

When outputting a voltage using a charged storage element, the voltage of the storage element drops with the output of the voltage, so it is necessary to interrupt the voltage output and recharge the storage element before long. For example, since the storage element can be charged while the voltage is applied to the load, it is possible to maintain the voltage of the storage element while continuing to apply the voltage. As a result, the load can be maintained without interrupting the voltage. It becomes possible to continue to add to.

It is explanatory drawing which showed the rough structure of the inkjet printer carrying the piezoelectric element drive circuit of a present Example. It is explanatory drawing which showed the mechanism inside an ejection head in detail. It is explanatory drawing which illustrated the voltage waveform (drive voltage waveform) applied to a piezo element. It is explanatory drawing which showed the piezoelectric element drive circuit with which the inkjet printer of the present Example was equipped, and its peripheral circuit structure. It is explanatory drawing which showed the structure of the piezoelectric element drive circuit of a present Example. It is explanatory drawing which showed a mode that several types of voltage values were output using the charge pump circuit (charge pump A) of the piezoelectric element drive circuit of a present Example. It is explanatory drawing which showed a mode that the charge pump B of the piezoelectric element drive circuit of a present Example was operate | moved in the state connected in series with the power supply. It is explanatory drawing which showed notionally the mode that the number of the capacitors connected in series can be suppressed while being able to output many voltage values by the piezoelectric element drive circuit of a present Example. It is explanatory drawing which showed the piezoelectric element drive circuit of the 1st modification which charges a capacitor | condenser while outputting a voltage. It is explanatory drawing which illustrated the charge pump drive circuit of the 2nd modification which made the voltage value of the power supply which charges the capacitor | condenser of the charge pump A, and the voltage value of the power supply which charges the capacitor | condenser of the charge pump B into different voltage values. It is explanatory drawing which showed the piezoelectric element drive circuit of the 3rd modification which shared the power supply for charge in two charge pumps. It is explanatory drawing which showed the piezoelectric element drive circuit of the 4th modification which enabled the direct output of the voltage of a power supply from an output terminal. It is explanatory drawing which showed notionally the mode that the electric power input into the piezo element was collect | recovered by the capacitor | condenser of a piezo element drive circuit. A state in which the capacitor of the charge pump A is maintained in an appropriately charged state by combining the operation of collecting power from the piezo element to the capacitor of the charge pump A and the operation of charging the capacitor of the charge pump A using the charging power source. It is explanatory drawing which illustrated.

Hereinafter, in order to clarify the contents of the present invention described above, examples will be described in the following order.
A. Inkjet printer configuration:
B. Piezo element driving circuit of this embodiment:
C. Variation:
C-1. First modification:
C-2. Second modification:
C-3. Third modification:
C-4. Fourth modification:
C-5. Fifth modification:

A. Inkjet printer device configuration:
FIG. 1 is an explanatory diagram showing a rough configuration of an ink jet printer equipped with the piezo element driving circuit of this embodiment. As shown in the drawing, the inkjet printer 10 includes a carriage 20 that forms ink dots on the print medium 2 while reciprocating in the main scanning direction, a drive mechanism 30 that reciprocates the carriage 20, and paper of the print medium 2. The platen roller 40 is used for feeding. In the carriage 20, an ink cartridge 26 that contains ink, a carriage case 22 in which the ink cartridge 26 is mounted, and an ejection head that is mounted on the bottom surface side (side facing the print medium 2) of the carriage case 22 and ejects ink. 24 and the like, and the ink in the ink cartridge 26 is ejected from the ejection head 2.
4, it is possible to eject an accurate amount of ink from the ejection head 24 toward the print medium 2.

The drive mechanism 30 for reciprocating the carriage 20 includes a guide rail 38 extending in the main scanning direction, a timing belt 32 having a plurality of teeth formed therein, and a timing belt 32.
The driving pulley 34 and the step motor 36 are driven. A part of the timing belt 32 is fixed to the carriage case 22.
By driving the carriage case 22, the carriage case 22 can be accurately moved along the guide rail 38.

Further, the platen roller 40 is driven by a drive motor or a gear mechanism (not shown), and can feed the print medium 2 by a predetermined amount in the sub-scanning direction. Each of these mechanisms is controlled by a printer control circuit 50 mounted on the inkjet printer 10. Under the control of the printer control circuit 50, the platen roller 40 feeds the print medium 2 and the carriage case 22 by ejecting ink from the ejection head 24 while moving in the main scanning direction to print an image on the print medium 2.

FIG. 2 is an explanatory view showing in detail the mechanism inside the ejection head. As shown,
A plurality of ejection ports 200 are provided on the bottom surface (the surface facing the print medium 2) of the ejection head 24, and ink droplets can be ejected from the respective ejection ports 200. Each ejection port 200 is connected to an ink chamber 202, and the ink chamber 202 is filled with ink supplied from the ink cartridge 26. A piezo element 204 (piezoelectric element) is provided on the ink chamber 202, and when a voltage is applied to the piezo element 204, the piezo element is deformed to pressurize the ink chamber 202, thereby causing an ink droplet from the ejection port 200. Can be injected. In addition, since the deformation amount of the piezo element 204 changes according to the voltage value of the applied voltage, if the voltage applied to the piezo element 204 is appropriately controlled, the pressing force and the pressing timing of the ink chamber 202 are adjusted. It is possible to change the size of the ejected ink droplet. For this reason, the inkjet printer 10 applies the following voltage waveform to the piezo element 204.

FIG. 3 is an explanatory diagram illustrating a voltage waveform (drive voltage waveform) applied to the piezo element. As shown in the figure, the drive voltage waveform has a trapezoidal waveform in which the voltage rises with time and then falls back to the original voltage value. Further, the drawing shows how the piezo element 204 expands and contracts according to the drive voltage waveform. As shown in the figure, when the voltage value of the drive voltage waveform increases, the piezo element 204 gradually contracts accordingly. At this time, since the ink chamber 202 is expanded by being pulled by the piezo element 204, ink can be supplied from the ink cartridge 26 into the ink chamber 202. When the voltage value decreases after the voltage value increases and reaches a peak, this time, the piezo element 204 expands, thereby compressing the ink chamber 202 and ejecting ink from the ejection port 200. At this time, the drive voltage waveform is lowered to a voltage value lower than the original voltage value (the voltage value indicated as “initial voltage” in the drawing), and the piezo element 204 is expanded from the initial state so as to expand the ink. Can be fully extruded. After that, the drive voltage waveform returns to the initial voltage, correspondingly,
The piezo element 204 also returns to the initial state.

As described above, the inkjet printer 10 includes the piezo element 204 in the ink chamber 202, and can apply ink droplets from the ejection head 24 by applying an appropriate drive voltage waveform to the piezo element 204. It has become. For this reason, the ink jet printer 10 includes a piezo element drive circuit 100 that generates a drive voltage waveform and applies it to the piezo element 204 in addition to the printer control circuit 50 that controls the operation of each mechanism.

FIG. 4 is an explanatory diagram showing a piezo element driving circuit provided in the ink jet printer of the present embodiment and its peripheral circuit configuration. Although the detailed configuration of the piezo element driving circuit 100 will be described in detail later, the piezo element driving circuit 100 roughly includes a power source for generating a voltage and a waveform for generating a voltage waveform by changing the voltage from the power source. And a generation unit. The operation of the piezo element driving circuit 100 is controlled by the printer control circuit 50, and the printer control circuit 50 controls the piezo element driving circuit 100 so that the target driving voltage waveform is changed to the piezo element 204. It is possible to apply to.

The output of the piezo element driving circuit 100 is connected to the gate unit 300 as shown. The gate unit 300 includes a plurality of gate elements 302 connected in parallel, and a piezo element 204 is connected to the tip of each gate element 302. Each gate element 302 can be individually in a conductive state or a disconnected state, and if only the gate element 302 of the ejection port from which ink is to be ejected is brought into a conductive state,
By applying a driving voltage waveform only to the corresponding piezoelectric element 204, it is possible to eject ink droplets from the ejection port 200.

The printer control circuit 50 prints an image as follows using such a circuit configuration.
First, an ejection port 200 that ejects ink droplets based on image data of an image to be printed.
And the size of the ink droplet to be ejected, and the drive voltage waveform for ejecting the ink droplet of that size is determined according to the size of the ink droplet to be ejected. And the gate unit 30
A command is sent to 0 to make the gate element 302 corresponding to the injection port 200 conductive, and the piezo element drive circuit 100 is operated to generate a target drive voltage waveform. The drive voltage waveform thus generated is applied to the piezo element 204 of the target ejection port 200 via the gate element 302, and as a result, an ink droplet of the desired size is ejected from the target ejection port 200.

Here, such a drive voltage waveform can be generated by using a circuit (charge pump circuit) that changes the voltage by connecting or disconnecting charged capacitors in series as described above. In the charge pump circuit, the voltage value of the output voltage is determined by the number of capacitors connected in series, so if you have many capacitors, you can output many types of voltages and generate highly accurate drive voltage waveforms can do. However, connecting a large number of capacitors in series increases the number of switches and wires that connect the capacitors, so the impedance of the circuit increases due to the resistance of the switches, resulting in a large power consumption. Or the time constant of the circuit increases and the circuit cannot be driven at high speed. Therefore, in the piezo element driving circuit 100 according to the present embodiment, by adopting the following circuit configuration, it is possible to output many kinds of voltages, while suppressing the number of capacitors connected in series and increasing the impedance. Can be suppressed.

B. Piezo element driving circuit of this embodiment:
FIG. 5 is an explanatory diagram showing the configuration of the piezo element driving circuit of this embodiment. As shown in the drawing, the piezo element driving circuit 100 is composed of capacitors C1 to C4 and switches for connecting them. In addition, these capacitors C1 to C4 can be connected in parallel with the power source indicated as “charging power source” in the figure by closing each switch indicated as “a” in the figure. By connecting in parallel with the charging power source, a predetermined voltage value (“E” in the figure)
It is possible to charge to the voltage value indicated as). These switches and power supplies
The printer control circuit 50 controls the printer control circuit 50.
By operating these, it is possible to control the operation of the piezo element driving circuit 100 (see FIG. 4).

Here, in the piezo element driving circuit 100 of the present embodiment, it is possible to connect the capacitor C1 and the capacitor C2 in series by closing the switch indicated by “SW_A” in the drawing, and the capacitor C1 and the capacitor C2 are connected. Can be used as a so-called charge pump circuit (see the portion indicated as “charge pump A” in the figure).
. Similarly, the capacitor C3 and the capacitor C4 can be used as a charge pump circuit by operating a switch indicated by “SW_B” in the drawing (
(Refer to the part indicated as “charge pump B” in the figure). Piezo element driving circuit 10 of this embodiment
At 0, by using such a charge pump circuit, a plurality of types of voltages are output as follows.

FIG. 6 is an explanatory diagram showing a state in which a plurality of types of voltages are output using the charge pump circuit (charge pump A) of the piezo element driving circuit of this embodiment. FIG. 6A shows a state in which the voltage of the capacitor C1 (the voltage value indicated by “E” in the figure) is output by connecting the capacitor C1 of the charge pump A to the output terminal. Yes. As shown, when the switch SW_C is switched to the charge pump A side, the capacitor C1
Is connected to the output terminal, the voltage value of the capacitor C1 (the voltage value indicated as “E” in the figure) can be output from the output terminal. Further, as shown in FIG. 6B, when the switch SW_A is closed, the capacitor C1 can be connected to the output terminal with the capacitor C1 and the capacitor C2 connected in series. In this way, the voltage value “E” of the capacitor C2 is added to the voltage value “E” of the capacitor C1, so that a voltage having the voltage value “2E” can be output from the output terminal.

Thus, in the piezo element driving circuit 100 of the present embodiment, by connecting or disconnecting the capacitor of the charge pump A in series, a plurality of types of voltages (in the example of FIG. 6,
It is possible to output a voltage) of the voltage and the voltage value of the voltage value "E", "2E".
Similarly, not only the charge pump A but also the charge pump B constituted by the capacitor C3 and the capacitor C4 can output a plurality of types of voltages by connecting or disconnecting the capacitors in series. Is possible. Then, switch SW_C (
5) is switched to the charge pump A side, the voltage of the charge pump A can be output, and when switched to the charge pump B side, the voltage of the charge pump B can be output. Is possible.

However, when the voltage output from the charge pump A and the voltage output from the charge pump B are the same, the number of types of voltage that can be output is one charge pump even if the two charge pumps are switched and used. And no different. Therefore, the piezoelectric element driving circuit 1 of the present embodiment.
00 has a power supply in addition to the power supply for charging the capacitor (see FIG. 5).
By operating the charge pump B with this power supply connected to the charge pump B, the output voltage of the charge pump B can be made different from the output voltage of the charge pump A, and more types of voltages can be output. . This point will be described with reference to FIG.

FIG. 7 is an explanatory diagram showing a state in which the charge pump B of the piezo element driving circuit of this embodiment is operated in a state where it is connected in series with the power source. FIG. 7A shows a state in which a voltage is output using one of the capacitors of the charge pump B. When outputting a voltage using the capacitor of the charge pump B, as shown in FIG. 7A, the switch SW_C
Is switched to the charge pump B side, and one terminal of the capacitor C3 is connected to the output terminal. Here, since the other terminal of the capacitor C3 is connected to the power source, the capacitor C3 is connected to the output terminal in a state where the capacitor C3 and the power source are connected in series. As a result, the voltage value “2E” of the power source is added to the voltage value “E” of the capacitor C3, and the voltage value “3E” is output from the output terminal. Then, as described above, when a voltage is output using one capacitor in the charge pump A, the voltage value of the output voltage is “E” for one capacitor (see FIG. 6A). As with the charge pump A, the charge pump B can output a voltage different from that of the charge pump A, although the voltage is output using one capacitor.

As shown in FIG. 7B, when the switch SW_B is closed, the capacitor C
3 a and a capacitor C4 while connected in series, it can be connected to these capacitors to the power supply. Then, the voltage value of the power source (the voltage value indicated as “2E” in the figure) is added to the voltage value of the two capacitors C4 and C3 (the voltage value indicated as “E” in the figure). Since the voltage of the voltage value “4E” can be output, when the charge pump A outputs the voltage using two capacitors in the same manner (the voltage value is “2E”).
It is possible to output a voltage different from “)”.

As described above, in the piezo element driving circuit 100 according to the present embodiment, the charge pump B can be operated in a state where the charge pump B is connected in series with the power source, so that the charge pump B can output a voltage different from the charge pump A. It has become. Then, the voltage output by the charge pump A and the charge pump B is made different so that the piezo element driving circuit 100 of the present embodiment is achieved.
Then, while being able to output various types of voltages, it is possible to suppress the number of capacitors connected in series. This point will be described with reference to FIG.

FIG. 8 is an explanatory diagram conceptually showing how the number of capacitors connected in series can be suppressed while a variety of voltages can be output by the piezoelectric element driving circuit of this embodiment. is there. The horizontal axis in the figure shows the voltages output by the charge pump A and the charge pump B of the piezo element driving circuit 100, and on the upper side of the horizontal axis in the figure,
The state in which the charge pump A and the charge pump B output each of these voltages is conceptually shown.

As described above, the charge pump A can output a voltage with only one capacitor connected, or can output a voltage with two capacitors connected in series. one terminal of the capacitor of the charge pump a is connected to GND (see Figure 6). For this reason, the charge pump A operates based on the voltage value of GND (the voltage value indicated as “0” in FIG. 8). When a voltage is output using one capacitor, the voltage value “E” of one capacitor is set with respect to the reference voltage value “0”.
”Is added to output a voltage value“ E ”, and when two capacitors are connected in series to output a voltage, the voltage value of two capacitors with respect to the reference voltage value“ 0 ” "2
E ”is added to output a voltage having a voltage value“ 2E ”.

On the other hand, in the charge pump B, as described above, one terminal of the capacitor is connected to the power source. Value). When one capacitor is connected, the voltage value “E” of one capacitor is added to the reference voltage value “2E”, and the voltage value becomes “
3E "is output, and when two capacitors are connected in series, the voltage value" 2E "for two capacitors is added to the reference voltage value" 2E ", and the voltage value is" 4E
Is output.

As described above, in the piezo element driving circuit of this embodiment, the two charge pumps have different voltage values as the operation reference, and as a result, the two charge pumps output different voltages. Is possible. By switching between two charge pumps that output different voltages, it is possible to output more types of voltages than when using a single charge pump.

In addition, since the two charge pumps are provided in this way, in the piezoelectric element driving circuit 100 of this embodiment, when the capacitors are connected in series, the capacitors of the charge pump A or the capacitors of the charge pump B are connected in series. The capacitor of the charge pump A and the capacitor of the charge pump B need not be connected in series. For this reason, the number of capacitors connected in series is limited to the number of capacitors provided in each charge pump (two in the example of FIG. 8). As a result, in the piezo element driving circuit 100 according to the present embodiment, the number of capacitors connected in series can be suppressed, and as a result, the number of wirings and switches connecting the capacitors can be suppressed. It is possible to suppress an increase in impedance.

The number of types of voltage values that can be output from each charge pump is limited to the number of capacitors provided in each charge pump, but as described above, the voltage values output by the two charge pumps are different. Thus, it is possible to output many kinds of voltage values by using two charge pumps. With this, in the piezo element driving circuit 100 of this embodiment, while suppressing the number of capacitors connected in series. However, it is possible to output a large number of voltage values.

In the above-described embodiment, the voltage value of the power source connected in series with the charge pump B matches the maximum voltage value of the voltage output by the charge pump A (the voltage value indicated as “2E” in the figure). It was explained as being. However, since the voltage value output from the charge pump B and the voltage value output from the charge pump A need only be different from each other by using the power source, the voltage value of the power source is the maximum voltage value of the charge pump A. It is not always necessary to match. For example, it may be larger than the maximum voltage value “2E” of the charge pump A, or conversely, may be smaller than the maximum voltage value “2E” of the charge pump A. Furthermore, the voltage value of the capacitor “
It is also possible to make the voltage value lower than “E”. Even in such a case, if the power source is connected in series with the capacitor of the charge pump B, the voltage value of the power source is added to the voltage value of the capacitor, so that the voltage value of the charge pump A is different from the voltage value of the charge pump B. it is possible to, it is possible to output a plurality of voltage values by using the two charge pumps.

Further, in the piezo element driving circuit 100 according to the present embodiment, the number of capacitors connected in series can be suppressed, so that the piezo element driving circuit 100 can be driven at a higher speed. That is, when multiple capacitors are connected in series, the capacitance of the entire capacitor (synthetic capacitance) is smaller than the capacitance of individual capacitors, so when connecting many capacitors in series. In this case, it is necessary to increase the capacitance of each capacitor in advance. In such a case, it takes a long time to charge the capacitor due to the large capacity of the capacitor, so after the voltage waveform is output and the capacitor charge is consumed, the capacitor is charged again and the voltage waveform is output. Takes time, and it becomes difficult to output the voltage waveform at an early cycle. Alternatively, it takes time to charge the capacitor immediately after the ink jet printer 10 is turned on, and as a result, there is a possibility that it takes time to start printing after the power is turned on. On the other hand, in the piezo element driving circuit 100 according to the present embodiment, the number of capacitors connected in series can be reduced, so that the capacitance of each capacitor can be reduced. It is possible to quickly output the voltage while saving the time required for charging. In addition, since the capacitance of each capacitor can be suppressed, it is possible to use a small capacitor, and thus the device configuration can be reduced in size.

As described above, in the piezo element driving circuit 100 according to the present embodiment, the voltage value output from the charge pump A and the voltage value output from the charge pump B are made different to output many kinds of voltage values. Although it is possible, the number of capacitors connected in series can be reduced. As a result, it is possible to output a large number of types of voltage values and to apply a highly accurate driving voltage waveform to the piezo element 204, but also to suppress the number of switches and the like for connecting capacitors to increase the impedance of the circuit. It is possible to avoid it. As a result, it is possible to increase the power efficiency by suppressing the power consumption caused by the impedance, and avoid the situation where the time constant of the circuit increases due to the impedance, thereby reducing the operation cycle of the piezo element driving circuit 100. It is also possible to maintain high speed. In addition, since the number of capacitors connected in series is suppressed, it is possible to reduce the capacitance of each capacitor. As a result, the time required for charging the capacitors is shortened, and the piezo element drive circuit It is also possible to operate 100 at a higher speed.

C. Modified example:
Hereinafter, a modification of the above-described embodiment will be described. In the modification described below, the same components as those of the above-described embodiment are denoted by the same reference numerals as those of the embodiment, and detailed description thereof is omitted.

C-1. First modification:
In the piezoelectric element driving circuit 100 of the above-described embodiment, it has been described that each capacitor of the charge pump circuit is charged in advance before outputting a voltage (see FIG. 6). But,
Instead of charging the capacitors before outputting the voltage, it is also possible to charge each capacitor while outputting the voltage.

FIG. 9 is an explanatory diagram showing a piezo element driving circuit of a first modified example in which a capacitor is charged while outputting a voltage. As shown in FIG. 9A, in the piezoelectric element driving circuit 100 of the first modification, the charge pump B is connected to the output terminal, and the charge pump A
Connect each capacitor to a power source for charging. In this way, while the voltage is output from the charge pump B, it is possible to supply power from the power source to each capacitor of the charge pump A to charge each capacitor. Similarly, as shown in FIG. 9B, if the capacitor of the charge pump B is connected to the power source for charging while the charge pump A is connected to the output terminal, the voltage from the charge pump A is increased. It is also possible to charge each capacitor of the charge pump B during output.

In general, in a charge pump circuit, if voltage output continues, the charge stored in the capacitor is consumed and the voltage of the capacitor decreases. Therefore, in order to continue voltage output, it is necessary to recharge the capacitor halfway. is there. Then, when charging the capacitor,
Since the capacitor must be connected to the power supply, the charge pump circuit has a restriction that the voltage output is interrupted. On the other hand, if the two charge pump circuits are used while being switched, and the capacitor of the other charge pump circuit is charged while the voltage is being output from one of the charge pump circuits, the voltage can be output most. Since the capacitor can be charged inside, it is possible to keep the voltage of the capacitor while continuing to output the voltage, and as a result, it is possible to continue outputting the voltage without interruption. For this reason, in the piezo element drive circuit of the first modification, it is possible to operate the piezo element drive circuit 100 at a higher speed by omitting the time for interrupting the voltage output.

In general, since a charge pump circuit outputs a voltage from a capacitor, the voltage output is limited depending on the state of charge of the capacitor. For example, the voltage cannot be output when the capacitor is not charged, and the target voltage cannot be output unless the amount of charge is sufficient even when the capacitor is charged. In this regard, if the capacitor of the other charge pump circuit is charged while the voltage is output from one charge pump circuit, the capacitor of one charge pump is not charged (or the charge amount is not enough) ), It is possible to output a voltage, so that it is possible to reduce restrictions due to the state of charge of the capacitor.

Furthermore, since the voltage can be output if the capacitor of one charge pump is charged, the voltage output is started when the charging of the capacitor of one charge pump is completed. And the other charge pump capacitor does not have to be fully charged. For example, when the voltage is output from a state where each capacitor is not charged, such as immediately after the inkjet printer 10 is turned on, voltage output may be started when the charge of the capacitor of one charge pump is completed. It is possible and the other charge pump capacitor may be in the middle of charging or may not be charged at all. For this reason, charging of the capacitor of one charge pump can be omitted or voltage can be output in the middle of charging. As a result, the time required for charging the capacitor can be shortened and voltage output can be performed quickly. It is possible to start on.

As described above, in the piezo element driving circuit 100, since the number of capacitors connected in series is suppressed, it is possible to reduce the capacitance of each capacitor. Can be charged in a short time. Therefore, even if the time for connecting to one charge pump output terminal is short, the capacitor of the other charge pump can be sufficiently charged.

C-2. Second modification:
In the piezoelectric element driving circuit of the above-described embodiment, the voltage value of the power source that charges the capacitor of the charge pump A and the voltage value of the power source that charges the capacitor of the charge pump B are set to the same voltage value. (See voltage value labeled “E” in FIG. 5). However, the voltage value of the power source for charging the capacitor of the charge pump A may be different from the voltage value of the power source for charging the capacitor of the charge pump B.

FIG. 10 illustrates a charge pump drive circuit according to a second modification in which the voltage value of the power source for charging the capacitor of the charge pump A is different from the voltage value of the power source for charging the capacitor of the charge pump B. FIG. FIG. 10A shows an example in which the voltage of the power source that charges the capacitor of the charge pump B is higher than the voltage of the power source that charges the capacitor of the charge pump A. As shown in the figure, the voltage value of the power source for charging the capacitor of the charge pump B is “2E”, which is higher than the voltage value “E” of the power source for charging the capacitor of the charge pump A. ing. In this case, when the voltage is output using the charge pump B, a larger voltage can be output because the capacitor is charged to a high voltage. On the other hand, when the voltage is output using the charge pump A, since each capacitor of the charge pump A is charged to a voltage smaller than that of the capacitor of the charge pump B, the voltage is changed in small increments. It becomes possible to output a voltage having a more accurate voltage value.

Also, as shown in FIG. 10 (b), the voltage value of the power source of the charge pump A (in the figure "
The voltage value of the power source of the charge pump B can be set to a voltage value having the opposite polarity (the voltage value indicated as “−E” in the drawing) with respect to the voltage value indicated as “E”. In such a case, if the charge pump B is used, a negative voltage can be output. If the charge pump A is used, a positive voltage can be output. Both of these voltages can be used to drive the load (so-called bipolar drive).

In the piezoelectric element drive circuit 100 according to the second modification, the voltage value is different between the capacitor of the charge pump A and the capacitor of the charge pump B, so that the voltage value output from the charge pump A and the charge pump B are output. Different voltage values are also different from each other. For this reason, as in the piezo element driving circuit 100 shown in FIG. 10B, a power supply that generates a reference voltage and makes the voltage value of the charge pump B different from the charge pump A (
It is also possible to omit (see FIG. 7). In such a case, it is possible to output different voltages between the charge pump A and the charge pump B, and the number of capacitors connected in series is limited to the number of capacitors of each charge pump. From
While being able to output various types of voltages, it is possible to reduce the number of capacitors connected in series.

C-3. Third modification:
The piezoelectric element driving circuit 100 of the above-described embodiment has been described as including two charging power sources, that is, a power source for charging the capacitor of the charge pump A and a power source for charging the capacitor of the charge pump B (FIG. 5). See). However, if the power source for charging the capacitor of the charge pump A and the power source for charging the capacitor of the charge pump B are shared, it is possible to provide only one charging power source.

FIG. 11 is an explanatory diagram showing a piezoelectric element driving circuit of a third modification in which a charging power source is shared by two charge pumps. As shown in the drawing, the piezoelectric element driving circuit of the third modification is provided with only one charging power source, and the switch indicated by “a” in the figure is closed and “b” in the figure. By switching from the power supply side to the GND side, the capacitor of the charge pump A (capacitor C1 and capacitor C2),
It is possible to connect a charging power source to both the capacitors (capacitor C3 and capacitor C4) of the charge pump B. In this way, the charge pump capacitors of both the charge pump A and the charge pump B can be charged by a single charge power supply, so that the charge pump A and the charge pump B each have a charge power supply. it is not necessary to put, it is possible to further simplify the apparatus structure by reducing the number of charging power supply.

Further, as described above, since the charge pump B operates in a state where it is connected to a power source that generates a reference voltage (see FIG. 7B), a high voltage is applied to each capacitor of the charge pump B. Sometimes. In such a case, change the switch indicated as “b” in the figure to G
When a capacitor is connected to ND, a capacitor having a high voltage value and a GND having a low voltage value are connected, so that a large voltage is applied to a switch connecting the capacitor and GND, and a large burden may be imposed on the switch. In this respect, in the piezoelectric element driving circuit of the third modified example, “a
Since the capacitor and GND are connected via two switches, the switch indicated by “” and the switch indicated by “b” in the drawing, it is possible to disperse the burden on the individual switches. For this reason, it is not necessary to increase the resistance (withstand voltage) to the voltage of each switch, and the apparatus configuration can be further downsized by using a small switch with a small withstand voltage.

C-4. Fourth modification:
In the piezo element driving circuit 100 of the above-described embodiment, it has been described that the power source for generating the reference voltage is connected in series to the charge pump B (see FIG. 7). However, the power source may be connected to the output terminal instead of the charge pump B. In this way, it is also possible to output the voltage of the power supply directly from the output terminal.

FIG. 12 is an explanatory diagram showing a piezo element driving circuit of a fourth modified example in which the voltage of the power supply can be directly output from the output terminal. As shown in the drawing, the piezoelectric element driving circuit 10 of the fourth modification example.
0, it is possible to connect the power supply to the output terminal via a switch indicated by “c” in the figure, and this allows the voltage of the power supply to be changed to the capacitor (capacitor C3 and capacitor C3) of the charge pump B. It is possible to output directly from the output terminal without going through C4).

Thus, while the voltage is being output from the power source to the output terminal, the capacitor of the charge pump A and the capacitor of the charge pump B do not need to output the voltage. Can be charged. For this reason, even when the voltage of each capacitor is lowered and charging is required, it is not necessary to interrupt the output of the voltage, and the piezo element is driven quickly without the time to interrupt the output of the voltage. It becomes possible. Further, if the power source is connected to the output terminal, the voltage value of the power source can be output in addition to the voltage value output by the charge pump A and the charge pump B. As a result, a more accurate drive voltage waveform can be output.

As described above with reference to FIG. 3, in the inkjet printer 10, the piezo element 2 is used.
It applies a pre-fixed voltage value of the voltage (voltage indicated by "Initial voltage" in FIG. 3) to 04. Therefore, if the voltage value of the power supply is matched with the voltage value of the initial voltage, the piezo element 2 is used by using the power supply.
It is also possible to apply an initial voltage to 04, and it is also possible to prepare for output of the drive voltage waveform by charging each capacitor while the initial voltage is applied. In particular, in an inkjet printer, the time during which the initial voltage is applied tends to be longer than the time during which a voltage of another voltage value is applied.Therefore, if the capacitor is charged during application of the initial voltage, the time is reduced. The capacitor can be sufficiently charged over time, which is more preferable. Furthermore, if the initial voltage is output from the power supply, it is not necessary to separately prepare a power supply for applying the initial voltage, so that the apparatus configuration can be simplified.

In the piezo element driving circuit 100 of the fourth modified example, the switch indicated by “d” in FIG. 12 is closed, and the output terminal is connected to GND by switching the switch SW_C to the lower side in FIG. It is possible. In this way, the voltage value of GND (voltage value “0
It is also possible to output “volt”, so that it is possible to further increase the number of types of voltage values that can be output.

C-5. Fifth modification:
In the above-described embodiments and modifications, it has been described that power is supplied from the capacitor to the piezo element 204 by connecting the capacitor of the piezo element driving circuit 100 to the output terminal. However, in these piezo element driving circuits 100, not only power is supplied from the capacitor to the piezo element 204, but also the power supplied to the piezo element 204 can be recovered by the capacitor.

FIG. 13 is an explanatory diagram conceptually showing a state in which the electric power input to the piezo element is collected by the capacitor of the piezo element drive circuit. On the left side of FIG. 13 (a), voltage values output by the charge pump A and the charge pump B are shown, and on the right side of FIG. 13 (a),
The drive voltage waveform applied to the piezo element 204 using these voltage values is illustrated.
As described above, the drive voltage waveform applied to the piezo element 204 is a trapezoidal voltage waveform that drops after the voltage value rises (see FIG. 3). a
) Passes the timing indicated by “t1”, the piezo element drive circuit 100 decreases the voltage applied to the piezo element.

Here, as shown in FIG. 13B, when the charge pump B is connected to the piezo element 204 with the capacitor C3 and the power source of the charge pump B connected in series, the voltage value of the charge pump B Is “3E”, which is the sum of the voltage value “E” of the capacitor C3 and the voltage value “2E” of the power source, and the voltage value “4E” of the piezo element at the time point “t1” in FIG. Therefore, the electric charge stored in the piezo element 204 is reduced by the piezo element 20.
4 flows out toward the charge pump B. As a result, power can be recovered from the piezoelectric element 204 to the capacitor C3 of the charge pump B.

When the electric power is recovered from the piezo element 204 to the capacitor C3, the voltage of the piezo element 204 decreases as the electric power is recovered. When the timing indicated by “t2” in FIG. The voltage value of the element 204 is equal to the voltage value of the charge pump B, and the power recovery is stopped. Therefore, this time, as shown in FIG.
_C is switched to connect the piezo element to the charge pump A. In this state, the voltage value of the charge pump A becomes a voltage value “2E” obtained by adding the voltage value of the capacitor C1 and the voltage value of the capacitor C2, and the piezo at the time indicated by “t2” in FIG. Since the voltage is lower than the voltage “3E” value of the element 204, electric charge flows out from the piezo element 204 toward the capacitor of the charge pump A, and as a result, the electric power of the piezo element 204 can be recovered in the capacitor of the charge pump A. Become.

When the power recovery is continued and the voltage of the piezo element 204 further decreases and the power recovery stops again (refer to the timing indicated by “t3” in FIG. 13A), this time, the charge pump A is connected in series. Disconnect the capacitor and connect only one capacitor to the piezo element.
In this way, the voltage value of the charge pump A can be lowered to the voltage value “E” of one capacitor with respect to the voltage value “2E” of the piezo element 204, so that the power from the piezo element 204 can be recovered. Subsequently, it is possible to sufficiently recover power from the piezo element 204.

As described above, in the piezo element driving circuit 100, it is possible to charge the capacitor using the charging power source. For this reason, it is possible to keep the capacitor of the charge pump properly charged by appropriately combining the operation of collecting power from the piezo element 204 to the capacitor and the operation of charging the capacitor using the charging power source. It becomes possible. This point will be described with reference to FIG.

FIG. 14 shows an operation of recovering electric power from the piezoelectric element to the capacitor of the charge pump A,
It is explanatory drawing which illustrated a mode that the capacitor | condenser of charge pump A is maintained in the state charged appropriately by combining with the operation | movement which charges the capacitor | condenser of charge pump A using the power supply for charge. FIG. 14A illustrates a state in which power is first recovered from the piezo element 204 to the capacitor, and then the capacitor is charged with a charging power source. When a voltage waveform is applied to the piezo element 204, the charge pump B is first connected to the piezo element 204, as indicated by the white arrow below the graph in the figure, and the voltage of the piezo element 204 is applied. To raise. Next, when the timing indicated by “t2” in the drawing is reached, the piezoelectric element 2
04 is switched from charge pump B to charge pump A and connected. Thus, as described above, since the voltage of the charge pump A (voltage value is “2E”) is lower than the voltage of the piezoelectric element (voltage value is “3E”), the piezoelectric element 204 transfers to the capacitor of the charge pump A. Electric power can be recovered (see FIG. 13C). When the voltage of the piezo element 204 is lowered to the minimum voltage “E” while recovering the electric power from the piezo element 204 in this way, the voltage of the piezo element 204 is raised to the initial voltage and the output of the voltage waveform is finished. a
This time, as indicated by the white arrow above, the capacitor of the charge pump A is charged using the charging power source.

As described above, if the capacitor is charged with the charging power source after the power is recovered from the piezo element 204, even if the capacitor cannot be sufficiently charged with the power recovered from the piezo element 204, the insufficient power is supplied from the charging power source. The capacitor can be reliably charged by supplying. In addition, since the capacitor is charged by the charging power source after the electric power is recovered from the piezo element 204, the capacitor can be maintained at a constant voltage value after charging regardless of the amount of electric power recovered from the piezo element 204. For this reason, it is possible to avoid a phenomenon (so-called drift phenomenon) in which the voltage value of the capacitor fluctuates due to fluctuations in the amount of power recovered from the piezo element 204.

Further, as shown in FIG. 14B, the capacitor of the charge pump A may be charged with a charging power source before the electric power is recovered from the piezo element 204. In such a case, even when the power recovered from the piezo element 204 is small, the capacitor is charged in advance, so that the capacitor can be sufficiently charged when the power recovery from the piezo element 204 is completed. . As a result, the operation of charging the capacitor after the output of the voltage waveform can be omitted. As a result, the time required for charging can be eliminated and the piezo element 20 can be omitted.
4 can be driven quickly. In particular, in the inkjet printer 10, the power consumed by the piezo element 204 increases when a large number of ink droplets are ejected from the ejection head 24, and the power collected from the piezo element 204 may decrease accordingly. Therefore, in such a case, if the capacitor is charged in advance with the charging power source, the capacitor can be sufficiently charged when power is recovered from the piezo element 204. However, it does not take time to charge the capacitor. Accordingly, it is possible to drive the piezo element 204 at high speed while ejecting a large number of ink droplets, and as a result, it is possible to print an image quickly.

Furthermore, if the capacitor is charged in advance, the voltage of the capacitor rises. Therefore, when recovering power from the piezo element to the capacitor, the power difference is suppressed while keeping the voltage difference between the capacitor and the piezo element 204 small. Can be recovered. If the voltage difference between the piezo element 204 and the capacitor is large, the recovered power may be consumed as heat (so-called Joule heat) due to a large current flowing from the piezo element 204 toward the capacitor. In this way, if the difference between the voltage of the piezo element 204 and the voltage of the capacitor is made small, the current can be suppressed, so that the power consumption due to the current is suppressed and the power of the piezo element 204 is efficiently consumed. It becomes possible to collect.

When recovering power from the piezo element 204 to the capacitor, it is possible to estimate the amount of power recovered from the piezo element 204 to the capacitor based on the voltage value, capacitance, etc. of the piezo element 204 and the capacitor. It is. It is also possible to infer from the estimated amount of power how much the capacitor is charged before the power is recovered and the capacitor can be set to an appropriate voltage value after the power is recovered. Therefore, when the capacitor is charged in advance before collecting the power, the amount of power collected from the piezo element 204 is estimated and the time for charging the capacitor is determined based on the estimated amount of power. Also good. For example, when it is estimated that the amount of power recovered from the piezo element 204 is small, the time for charging the capacitor may be lengthened. Conversely, when the amount of power recovered is large, What is necessary is just to shorten the time to charge the capacitor. By doing so, it is also possible to avoid a situation in which the voltage value of the capacitor after the power is recovered due to the change in the amount of power recovered from the piezo element 204.

In the above, the ink jet printer equipped with the piezoelectric element driving circuit of the present embodiment has been described. However, the present invention is not limited to all the above embodiments, and can be implemented in various modes without departing from the gist thereof. Is possible. For example, the piezo element driving circuit of this embodiment may be mounted on a printing apparatus (so-called line head printer or the like) having a larger ejection head. In such a printing apparatus, since a large number of piezoelectric elements are mounted as the ejection head becomes larger, the circuit configuration for generating the drive voltage waveform tends to become larger.
In this respect, it is preferable to use the piezoelectric element driving circuit of this embodiment because the circuit configuration can be reduced in size.

In the above-described embodiments, the case where the piezo element of the ink jet printer is driven has been described as an example. However, the drive circuit of this embodiment can be applied to various devices that are driven according to the voltage. For example, the present invention can be applied to a display device that can operate with a voltage such as a liquid crystal panel or an organic EL panel. In addition, the present invention can be applied to a surgical instrument for incising or excising a living tissue by ejecting water or saline by driving a piezo element. Even when such an apparatus is driven, various types of voltage values can be output, so that various elements such as a liquid crystal element and an organic EL element can be accurately operated. Of course, not only a display device but also a device that can be driven by voltage can output a large number of types of voltage values, so that the device can be driven accurately.

10 ... inkjet printer, 20 ... carriage,
22 ... Carriage case, 24 ... Ejecting head, 26 ... Ink cartridge,
30 ... Drive mechanism, 32 ... Timing belt, 34 ... Drive pulley,
36 ... Step motor, 38 ... Guide rail, 40 ... Platen roller,
50 ... Printer control circuit, 100 ... Piezo element drive circuit,
200: ejection port, 202 ... ink chamber, 204 ... piezo element,
300 ... Gate unit 302 ... Gate element

Claims (4)

A load driving circuit for driving a load by applying a voltage to the load,
A first power storage element group and a second power storage element group comprising a plurality of power storage elements charged by a power source;
A plurality of output voltages that are switched in stages by switching the connection state between the plurality of power storage elements included in the first power storage element group and changing the number of the power storage elements connected in series. First output voltage generating means for generating one output voltage;
By switching the connection state between the plurality of power storage elements included in the second power storage element group and changing the number of the power storage elements connected in series, the voltage is different from the first output voltage. Second output voltage generating means for generating a second output voltage, which is a plurality of output voltages that are switched automatically,
By switching between the first output voltage and the second output voltage and connecting to the load,
And a voltage applying means for applying a voltage to the load. 2. The load driving circuit according to claim 1, wherein the storage element of the first storage element group and the storage element of the second storage element group are charged to different voltages. The load driving circuit according to claim 1,
The first output voltage generating means is means for generating the first output voltage by connecting the plurality of power storage elements in series to a first reference voltage that is a predetermined reference voltage.
The second output voltage generation means is a load drive that is means for generating the second output voltage by connecting the plurality of power storage elements in series with respect to a second reference voltage different from the first reference voltage. circuit. A load driving circuit according to any one of claims 1 to 3,
The storage elements of the first storage element group are charged with the second output voltage connected to the load, and the storage elements of the second storage element group have the first output voltage connected to the load. Load drive circuit that is charged in a live state.

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