JP2012143280A - Capacitive load drive device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent a carrier ripple from being superimposed on a drive signal of a capacitive load.SOLUTION: A drive waveform signal is subjected to pulse modulation to generate a modulation signal, and the generated signal is power-amplified and passes through a smoothing filter to generate a drive signal. The drive signal thus generated is applied to the capacitive load. The drive signal is subjected to phase forwarding compensation to generate a feedback signal, and the generated signal is fed back to the drive waveform signal. A smoothing filter and the capacitive load are connected to each other by a replaceable wiring. Amplitude information about the amplitude of the carrier ripple is obtained between the wiring and the capacitive load, and a carrier frequency is set on the basis of the information, and pulse modulation is performed. Thus, since pulse modulation is executed at a carrier frequency in which the carrier ripple is suppressed, even if the circuit is replaced, the carrier ripple can be prevented from being superimposed on a drive signal.

Description

  The present invention relates to a technique for driving a capacitive load such as a piezoelectric element using a drive signal.

There are many actuators that are configured by a capacitive load such as a piezoelectric element and operate when a drive signal is applied, such as an ejection head mounted on an inkjet printer. When this drive signal is generated using an analog amplifier circuit,
Since a large current flows in the analog amplifier circuit, a large amount of power is consumed. As a result, not only does the power efficiency decrease, but the circuit board becomes larger, and further, since the consumed power changes to heat, a large heat sink is required, and the board becomes larger.

Therefore, instead of directly amplifying the analog drive signal, the drive waveform signal serving as a reference for the drive signal is pulse-modulated and converted into a modulation signal, and the obtained modulation signal is amplified and then passed through a smoothing filter. A technique for obtaining an amplified drive signal has been proposed (Patent Document 1). Amplification of the modulation signal can be realized simply by switching on / off of the switch. Furthermore, since the smoothing filter can be realized by using an LC circuit in which a coil and a capacitor are combined, in principle, power is not consumed. Therefore, according to the proposed technique, it is possible to generate a drive signal without consuming a large amount of power, and it is possible to reduce the size of the circuit board.

In the proposed technique, a smoothing filter is configured by the LC circuit, and therefore a peak appears in the gain at the resonance frequency of the LC circuit. Normally, the output peak is suppressed by the resistance value of the electric load or by separately inserting a damping resistor. However, in this method, power is consumed by the resistor. Therefore, it has been proposed to suppress the output peak by performing feedback from the output stage (Patent Document 2). Further, since the signal passing through the smoothing filter is delayed in phase by 180 degrees at the maximum, there is a possibility that the output oscillates if feedback is applied as it is with the signal of the output stage. Therefore, feedback is performed after phase lead compensation is applied to the signal of the output stage.

Also, when feeding back the signal from the output stage, the resistance of the wiring from the smoothing filter to the capacitive load suppresses the waveform of the drive signal from being gradual (the voltage change of the waveform becomes gentle) Proposal is also made of a technique for applying feedback in consideration of wiring resistance (Patent Document 3), and a technique for switching the carrier frequency for pulse modulation according to the waveform of the drive signal (Patent Document 4) for the purpose of suppressing power consumption. Has been.

JP 2007-168172 A JP 2009-153272 A JP 2005-329710 A JP 2007-190708 A

However, the conventional techniques such as Patent Document 1 to Patent Document 4 described above have a problem that the ripple (carrier ripple) of the carrier frequency that is removed by the smoothing filter may be superimposed on the drive signal. It was. For this reason, there is a problem that an actuator that is a capacitive load cannot be appropriately driven.

The present invention has been made to solve at least a part of the above-described problems of the prior art, and provides a technique capable of avoiding a carrier frequency ripple from being superimposed on a drive signal after a smoothing filter. For the purpose.

In order to solve at least a part of the problems described above, the capacitive load driving circuit of the present invention employs the following configuration. That is,
A capacitive load drive circuit that drives a capacitive load by applying a drive signal to the capacitive load having a capacitive component,
A drive waveform signal generating circuit for generating a drive waveform signal which is a reference of the drive signal;
An arithmetic circuit that outputs an error signal by subtracting a feedback signal generated using the drive signal applied to the capacitive load from the drive waveform signal;
A modulation circuit that generates a modulation signal by pulse-modulating the error signal;
A digital power amplifier that amplifies the modulated signal to generate a pulsed power amplified modulated signal;
A smoothing filter that generates the drive signal by smoothing the pulse-wave-shaped power amplification modulation signal;
A phase lead compensation circuit that performs phase lead compensation on the drive signal and outputs the signal after the phase lead compensation to the arithmetic circuit as the feedback signal;
Connecting the smoothing filter and the capacitive load, wiring provided to be replaceable,
Amplitude information acquisition means for acquiring amplitude information related to the amplitude of the carrier ripple of the drive signal applied to the capacitive load based on the drive signal;
Carrier frequency setting means for setting a carrier frequency at which the modulation circuit performs pulse modulation of the error signal so that the amplitude of the carrier ripple of the drive signal is a predetermined value or less based on the amplitude information. Is the gist.

In such a capacitive load drive circuit of the present invention, a modulation signal is generated by pulse-modulating a drive waveform signal which is a reference of a drive signal to be applied to the capacitive load, and the obtained modulation signal is power amplified. A drive signal is generated by smoothing later. In this way, phase lead compensation is performed on the drive signal applied to the capacitive load to generate a feedback signal, and negative feedback to the drive waveform signal. The smoothing filter and the capacitive load are connected by wiring, and the drive signal output from the smoothing filter is applied to the capacitive load via the wiring. Also,
The wiring is replaceable. Further, information (amplitude information) related to the amplitude of the carrier ripple of the drive signal applied to the capacitive load is acquired from the drive signal between the wiring and the capacitive load. Based on this amplitude information, the carrier frequency is set so that the amplitude of the carrier ripple is equal to or less than a predetermined value, and pulse modulation is performed at the carrier frequency.

In this way, the drive signal applied to the capacitive load is negatively fed back with respect to the drive waveform signal serving as a reference for the drive signal, so that the drive signal is prevented from being distorted due to the resonance of the smoothing filter. Can do. Also, when the drive signal is negatively fed back, it is compensated for phase advance compensation (phase advance compensation) and then negatively fed back. Therefore, the drive signal whose phase is delayed by a smoothing filter is driven negatively. The signal output does not become unstable. Furthermore, as will be described in detail later, when the wiring for applying the drive signal to the capacitive load is changed, carrier ripple may be superimposed on the drive signal. However, in the capacitive load drive circuit of the present invention, the wiring and Information (amplitude information) on the amplitude of the carrier ripple is acquired from between the capacitive load and the carrier frequency is set to a frequency at which the amplitude of the carrier ripple is equal to or less than a predetermined value. For this reason, even if the wiring for applying the drive signal to the capacitive load is replaced, the carrier ripple is not superimposed on the drive signal applied to the capacitive load.

The above-described capacitive load driving circuit of the present invention may be configured as follows. First, it is assumed that the carrier frequency can take a frequency range from a predetermined minimum frequency to a predetermined maximum frequency. When setting the carrier frequency, the amplitude of the carrier ripple is acquired at the carrier frequency within the frequency range from the lowest frequency to the highest frequency. Then, the carrier frequency may be set such that the amplitude of the carrier ripple is a predetermined value or less.

This makes it possible to avoid the carrier ripple from being superimposed on the drive signal applied to the capacitive load even when the wiring is replaced. In the frequency range from the lowest frequency to the highest frequency, when there is no carrier frequency at which the amplitude of the carrier ripple is equal to or less than a predetermined value, the carrier frequency having the smallest amplitude may be set.

In the capacitive load drive circuit of the present invention described above, a drive waveform signal is generated such that the duty ratio of the modulation signal is 50% while the amplitude information acquisition means acquires the carrier ripple amplitude. You may do it.

The amplitude of the carrier ripple superimposed on the signal after the smoothing filter becomes the largest when the duty ratio of the signal before passing through the filter is 50%. Therefore, if a drive waveform signal is generated such that the duty ratio of the modulation signal is 50%, the amplitude of the carrier ripple can be acquired with high sensitivity.

In addition, the capacitive load driving circuit of the present invention described above, a supply pump for supplying liquid,
An injection unit having a liquid chamber into which the liquid supplied from the supply pump flows, an actuator that is the capacitive load, and an injection nozzle that injects the liquid that has flowed into the liquid chamber;
With
When the drive signal is applied to the actuator, the liquid that has flowed into the liquid chamber is ejected in a pulse form from the ejection nozzle.
The present invention can also be applied to a liquid ejecting apparatus.

By providing the capacitive load drive circuit of the present invention in the liquid ejecting apparatus, even if the wiring for applying the drive signal to the capacitive load is replaced, carrier ripple is superimposed on the drive signal applied to the capacitive load. Therefore, even when switching to a liquid ejecting apparatus having a different cable length, the actuator can be driven with an intended drive signal.

It is explanatory drawing which showed the structure of the liquid ejecting apparatus carrying the capacitive load drive circuit of a present Example. It is explanatory drawing which showed the circuit structure of the capacitive load drive circuit of a present Example. It is explanatory drawing which showed the mechanism in which a carrier ripple generate | occur | produces under the influence of the induction component (and resistance component) which a wiring cable has. It is the circuit diagram which showed a part of capacitive load drive circuit of a present Example in detail. It is explanatory drawing which showed the detailed structure of the amplitude information acquisition circuit mounted in the capacitive load drive circuit. It is a flowchart of the carrier frequency setting process performed by an amplitude information acquisition circuit. It is the circuit diagram which showed a part of capacitive load drive circuit of the modification in detail. It is explanatory drawing which showed the detailed structure of the amplitude information acquisition circuit of a modification. It is the flowchart which showed a part of carrier frequency setting process of a modification. It is the flowchart which showed the remaining part of the carrier frequency setting process of a modification. It is explanatory drawing which showed the other aspect of the amplitude information acquisition circuit of the modification.

Hereinafter, in order to clarify the contents of the present invention described above, examples will be described in the following order.
A. Device configuration:
B. Circuit configuration of capacitive load drive circuit:
C. Mechanism for generating carrier ripple:
D. Capacitive load driving circuit of this embodiment:
E. Variations:

A. Device configuration :
FIG. 1 is an explanatory diagram showing a configuration of a liquid ejecting apparatus 100 equipped with a capacitive load driving circuit 200 of the present embodiment. As shown in the figure, the liquid ejecting apparatus 100 is roughly divided into an ejecting unit 110 that ejects liquid, a supply pump 120 that supplies the liquid ejected from the ejecting unit 110 toward the ejecting unit 110, and the ejecting unit 110. And a control unit 130 for controlling the operation of the supply pump 120. Liquid ejecting apparatus 10
0 is an example of a water jet knife as a surgical tool used for excising or incising living tissue by ejecting a pulsed liquid from the ejection unit 110.

The injection unit 110 has a structure in which a metal rear block 114 is overlapped on a metal front block 113 and screwed, and a circular liquid passage pipe 112 is erected on the front surface of the front block 113. The injection nozzle 111 is disposed at the tip of the liquid passage pipe 112.
Is inserted. A thin disk-shaped liquid chamber 115 is formed on the mating surface of the front block 113 and the rear block 114, and the liquid chamber 115 is connected to the ejection nozzle 111 via the liquid passage tube 112. In addition, an actuator 116 composed of a laminated piezoelectric element is provided inside the rear block 114. Injection unit 1
10 and the control unit 130 are connected by a wiring cable 150, and a drive signal is supplied from the capacitive load driving circuit 200 in the control unit 130 to the actuator 116 via the wiring cable 150. Further, one end side of the wiring cable 150 is attached to the injection unit 110 by a connector 152, and the other end side of the wiring cable 150 is attached to the control unit 130 by a connector 154. For this reason, the distribution cable 150 can be replaced with various distribution cables 150 having different lengths and characteristics. The wiring cable 150 corresponds to “wiring” in the present invention, and the actuator 116 corresponds to “capacitive load” in the present invention.

The supply pump 120 sucks the liquid through the tube 121 from the liquid tank 123 in which the liquid (water, physiological saline, chemical solution, etc.) to be ejected is stored, and then the tube 122.
Is supplied into the liquid chamber 115 of the ejection unit 110. For this reason, the liquid chamber 115 is filled with the liquid.

Then, when a drive signal is applied from the control unit 130 to the actuator 116, the actuator 116 extends and the liquid chamber 115 is compressed, and as a result, the liquid chamber 115.
The liquid filled inside is ejected in a pulse form from the ejection nozzle 111. The extension amount of the actuator 116 depends on the voltage applied as the drive signal. Accordingly, in order to eject a pulsed liquid having a desired characteristic, it is necessary to apply an accurate drive signal to the actuator 116. Therefore, in order to generate such a drive signal, the control unit 130
Inside, a capacitive load driving circuit 200 as described below is mounted.

B. Capacitive load drive circuit configuration:
FIG. 2 is an explanatory diagram showing a circuit configuration of the capacitive load driving circuit 200 mounted on the control unit 130. As shown in the figure, the capacitive load drive circuit 200 includes a drive waveform signal generation circuit 210 that outputs a drive waveform signal (hereinafter referred to as WCOM) serving as a reference for the drive signal, and the WCOM received from the drive waveform signal generation circuit 210. An arithmetic circuit 220 that outputs an error signal (hereinafter referred to as dWCOM) based on a feedback signal (hereinafter referred to as dCOM) described later, and an arithmetic circuit 220
Modulation circuit 23 for pulse-modulating dWCOM from the signal and converting it to a modulation signal (hereinafter referred to as MCOM)
0, a digital power amplifier 240 that digitally amplifies the MCOM from the modulation circuit 230 to generate a power amplified modulated signal (hereinafter referred to as ACOM), and after receiving the ACOM from the digital power amplifier 240 and removing the modulation component The smoothing filter 250 supplied to the actuator 116 of the injection unit 110 as a drive signal (hereinafter referred to as “COM”) and the compensation (phase advance compensation) for advancing the phase with respect to the COM output from the smoothing filter 250 are added, and dCOM ( A phase lead compensation circuit 260 for generating a feedback signal).

Of these, the drive waveform signal generation circuit 210 includes a waveform memory storing WCOM data and a D / A converter, and converts data read from the waveform memory into an analog signal by the D / A converter. To generate a WCOM (drive waveform signal). Arithmetic circuit 2
At 20, a signal obtained by subtracting dCOM from WCOM thus output is output as dWCOM (error signal). Conversely, the drive waveform signal generation circuit 210 reads WCOM (drive waveform signal) as digital data from the waveform memory storing the WCOM data,
After dCOM is converted into digital data by the A / D converter, the arithmetic circuit 22 is used by using a signal processing circuit.
It may be configured to generate dWCOM (error signal) as digital data by subtracting dCOM from WCOM by digital calculation at 0. In that case, the modulation circuit 230 is configured by a digital circuit using the signal processing circuit so that dWCOM is handled as digital data.

The modulation circuit 230 generates (pulse modulation) a pulse-like MCOM (modulation signal) by comparing dWCOM with a triangular wave having a fixed period. Here, the base frequency (carrier frequency) of the triangular wave used for pulse modulation can be set by control from the carrier frequency setting means 280. The carrier frequency setting unit 280 sets the carrier frequency based on the amplitude information acquired by the amplitude information acquisition unit 270 (information on the amplitude of the carrier ripple superimposed on the drive signal supplied to the ejection unit 110). Although described later in detail, it is possible to avoid the carrier ripple from being superimposed on COM by setting the carrier frequency for pulse modulation based on the amplitude information. Here, the carrier ripple means a signal component of a carrier signal (triangular wave signal) used for pulse modulation included in the RCOM applied to the actuator 116.

The MCOM obtained by the modulation circuit 230 is input to the digital power amplifier 240. The digital power amplifier 240 includes two switch elements (MOS) connected in a push-pull manner.
FET, etc.), a power source, and a gate driver for driving these switch elements. When MCOM is in the high state, the switch element on the high side is turned on,
The low-side switch element is turned off, and the power supply voltage Vdd is output as ACOM. When the MCOM is in the low state, the high-side switch element is OF.
F state, the low side switch element is turned on, and the ground voltage is ACO
Output as M. As a result, the MCOM that changes in a pulse waveform between the operating voltage of the modulation circuit 230 and the ground changes to A in a pulse waveform between the voltage Vdd of the power supply and the ground.
Power amplified to COM. In this amplification, since only the ON / OFF of the two switch elements connected in a push-pull manner is switched, it is possible to greatly suppress the power loss as compared with the case where the analog waveform is amplified. As a result, not only can the power efficiency be improved, but there is no need to provide a large heat sink for heat dissipation, and the circuit can be miniaturized.

The power-amplified ACOM (power amplification modulation signal) is converted into COM (drive signal) by passing through a smoothing filter 250 constituted by an LC circuit, and is applied to the actuator 116 via the wiring cable 150. COM is the arithmetic circuit 220.
However, the phase of COM is delayed with respect to WCOM by passing through the smoothing filter 250. Therefore, instead of simply negatively feeding back COM, compensation (phase lead compensation) is performed to advance the phase through a phase lead compensation circuit 260 constituted by a capacitor and a resistor, and the obtained signal is set as dCOM and the arithmetic circuit 220. Negative feedback. Note that, as described above, the COM is passed through the phase lead compensation circuit 260 and the arithmetic circuit 2
The purpose of negative feedback to 20 is to suppress the output peak of the smoothing filter formed by the LC circuit. Therefore, when the output peak is suppressed by a resistance component of the circuit or a separately inserted damping resistor, COM need not be negatively fed back. In this case, the arithmetic circuit 220 and the phase lead compensation circuit 260 are not necessary. A detailed configuration of the amplitude information acquisition unit 270 will be described later.

Here, as shown in FIG. 2, the wiring cable 150 also has an inductive component and a resistance component. Therefore, due to this influence, it seems that some deviation occurs between the COM output from the smoothing filter 250 and the signal (hereinafter referred to as RCOM) actually applied to the actuator 116. When actually examined, it has been found that carrier ripple can be superimposed on the RCOM actually applied to the actuator 116 due to the influence of the inductive component (and the resistance component) of the wiring cable 150. Here, the carrier ripple means a signal component of a carrier signal (triangular wave signal) used for pulse modulation included in the RCOM applied to the actuator 116. Hereinafter, this point will be described in detail.

C. Mechanism for generating carrier ripple:
FIG. 3 is an explanatory diagram showing a mechanism in which carrier ripple occurs due to the influence of the inductive component (and resistance component) of the wiring cable 150. In FIG. 3 (a), ACOM to RC
A circuit configuration up to OM is shown. Let Llpf be the inductance of the coil of the smoothing filter 250, and let Clpf be the capacitance of the capacitive component of the smoothing filter 250. Similarly, let Rc and Lc be the resistance value and inductance of the wiring on one side. Furthermore, the capacitance of the capacitive load is Cload.

For convenience, the transfer function of the coil of the smoothing filter 250 is denoted as Z1, and the wiring cable 1
50, the transfer function of the forward side of 50 (the side of sending from the smoothing filter 250 to the actuator 116) is set as Za, and the return side of the wiring cable 150 (the side of returning from the actuator 116 to the ground of the capacitive load driving circuit 200) is added to the actuator 116. If the transfer function of the part is Zb, Z1, Za and Zb are given by the following equations, respectively.
Z1 = s · Llpf
Za = Rc + s · Lc
Zb = 1 / (s.Cload) + (Rc + s.Lc)
Further, in the circuit configuration shown in FIG. 3A, the transfer function of transfer elements (capacitance components of the reciprocating portion of the wiring cable 150 and the actuator 116 and the smoothing filter 250) connected in series to the coil of the smoothing filter 250. Z2 is given by the following equation.
Z2 = {1 / (s · Clpf)} // {2 (Rc + s · Lc) + 1 / (s · Cload)}
Here, s is a Laplace operator, which is an imaginary unit j multiplied by an angular frequency ω. //
This is a parallel composite symbol representing the composite impedance of parallel connection.
Then, the transfer function H between ACOM and RCOM is given by the equation of FIG.

FIG. 3C shows an example of the gain-frequency characteristic of the transfer function H. In addition, FIG.
c), assuming that the resistance per unit length (= 2 × Rc) of the wiring cable 150 is about several hundred milliohms, and the inductance per unit length (= 2 × Lc) is about several μH. The gain-frequency characteristic obtained by the wiring length is illustrated.

The broken line shown in FIG. 3C is the gain-frequency characteristic when the length of the wiring cable 150 is 2 [m (meter)], and the alternate long and short dash line is the gain when the length is 1 [m]. -It is a frequency characteristic, and a dashed-two dotted line is a gain-frequency characteristic in the case of 0.5 [m]. A solid line represents a gain-frequency characteristic when the wiring cable 150 is not provided. As shown in the figure, when the actuator 116 (capacitive load) is connected via the wiring cable 150, resonance due to the inductance of the wiring cable 150 and the capacitive load occurs on the higher frequency side than the resonance frequency f0 of the smoothing filter 250. appear. Further, when the length of the wiring cable 150 is changed, the inductance value of the wiring cable 150 changes, so that the resonance frequency fc changes.
Therefore, depending on the length of the wiring cable 150 to be connected, the resonance peak may approach (or match) the carrier frequency at the time of pulse modulation, and a very large carrier ripple may remain in the drive signal applied to the actuator 116. Can happen.

For example, the power supply voltage of the digital power amplifier 240 is set to 100 V, and the smoothing filter 25
It is assumed that wiring cables 150 that connect 0 and the actuator 116 have various lengths between 0.5 [m] and 2 [m]. If the inductance of the wiring cable 150 is 0 (corresponding to the case where the cable length is 0 [m]), as shown in the solid line gain-frequency characteristics shown in FIG. The gain at is -40 db, and the carrier ripple remaining in the drive signal is 1 Vpp. However, when the cable length of the wiring cable 150 is 0.5 [m], the gain at the carrier frequency fc is −40 db, and when the cable length is 1 [m], it is −20 db, and the cable length is 2
In the case of [m], it is −45 db. The carrier ripple remaining in the drive signal is 1 Vpp each.
10 Vpp and 0.56 Vpp. ACO amplified by digital power amplifier 240
It is considered that the carrier ripple may be superimposed on the drive signal even though M is smoothed through the smoothing filter 250 due to the mechanism described above.

If the carrier ripple is superimposed, the actuator 116 cannot be driven appropriately. However, if a damping resistor is inserted in the wiring, power is consumed by the resistor, so that power efficiency is lowered. Further, if the characteristic of the smoothing filter 250 is changed so that the frequency component of the carrier ripple is further suppressed, the resonance frequency f of the smoothing filter 250 is changed.
Since 0 becomes low, the signal frequency band cannot be secured. On the contrary, if the carrier frequency at the time of pulse modulation is increased, carrier ripple can be suppressed, but this causes an increase in switching loss at the time of pulse modulation or at the time of amplification of the modulation signal. Therefore, in order to apply a drive signal without carrier ripple to the actuator 116 without such problems, the following method is employed.

D. Capacitive load driving circuit of this embodiment:
FIG. 4 is a circuit diagram showing a part of the capacitive load driving circuit 200 of this embodiment in detail. In this embodiment, the smoothing filter 250 and the actuator 116 are connected by a three-wire wiring cable 150. Of these, the line 1 shown in the figure is the smoothing filter 250.
And the upper end of the actuator 116 are connected, and a line 2 shown in the drawing connects the ground of the smoothing filter 250 and the lower end of the actuator 116. The line 3 connects the upper end of the actuator 116 and the amplitude information acquisition unit 270. Accordingly, the drive signal applied to the actuator 116 is input to the amplitude information acquisition unit 270 via the line 3 of the wiring cable 150.

The amplitude information acquisition means 270 includes an A / D conversion circuit 272 and an amplitude information acquisition circuit 2 described later.
74 is provided. The drive signal supplied via the line 3 of the wiring cable 150 is
The voltage is divided by resistors Ra and Rb so as not to exceed the input voltage range of the A / D conversion circuit 272 and then input to the A / D conversion circuit 272. Note that the wire 1, wire 2, and wire 3 constituting the wiring cable 150 are similar in resistance component (Rc) and inductance (Lc).
have. A voltage dividing resistor (so that the wiring component (resistance component and inductance) of the line 3 for extracting the drive signal applied to the actuator 116 does not affect the waveform of the drive signal input to the A / D conversion circuit 272. The resistance values of the resistor Ra and the resistor Rb) are represented by the line 3
Is set to a value sufficiently larger than the resistance component (Rc).

The digital signal (drive signal information) output from the A / D conversion circuit 272 is input to the amplitude information acquisition circuit 274 to extract information (amplitude information) related to the amplitude of the carrier ripple superimposed on the drive signal. .

FIG. 5 is an explanatory diagram showing a detailed configuration of the amplitude information acquisition circuit 274. As illustrated, the amplitude information acquisition circuit 274 includes a carrier ripple amplitude value calculation circuit 274a that calculates the amplitude of the carrier ripple based on the drive signal information received from the A / D conversion circuit 272,
A memory 274b for storing the calculated amplitude, a carrier ripple amplitude value determining circuit 274c for determining whether or not the amplitude stored in the memory 274b is within a predetermined allowable value, a counter 274d, and a modulation signal duty setting circuit 274e Is provided.

By the way, the resonance frequency of the smoothing filter 250 is determined from a necessary signal frequency band, and cannot be lowered further. In other words, the amount of attenuation in the high frequency region cannot be designed to be larger than that. In the characteristic of the smoothing filter 250 determined as described above, the frequency that can satisfy the specification value of the amplitude of the carrier ripple of the application in the ideal state where the wiring cable 150 is not connected is expressed as the minimum frequency fcmin. .
Further, from the viewpoint of suppressing the switching loss, that is, from the viewpoint of preventing destruction due to heat generation of the switch element, a carrier frequency that cannot be increased any more is expressed as a maximum frequency fcmax. The counter 274d counts the number of steps n when the carrier frequency is increased by a predetermined frequency df between the lowest frequency fcmin and the highest frequency fcmax. The count value in the counter 274d is input to the carrier frequency setting unit 280, and the carrier frequency setting unit 280
A triangular wave having an n-th carrier frequency fcn (= fcmin + df × n) is converted into a modulation circuit 230.
This is generated by the triangular wave generation circuit. Also, the modulation signal duty setting circuit 274e causes the drive waveform signal generation circuit 210 to output a constant WCOM. Here, WCOM is set to a constant WCOM such that the duty ratio of the MCOM obtained by the modulation circuit 230 is 50 percent (duty ratio at which the carrier ripple is the largest).
It should be noted that the duty ratio of MCOM does not have to be just 50 percent, and there may be an error of 50 percent to plus or minus several percent.

When the carrier ripple amplitude value calculation circuit 274a receives the count value n from the counter 274d, the carrier ripple amplitude value calculation circuit 274a receives the count value n from the A / D conversion circuit 272 over a period equal to or longer than the time (1 / fcn) corresponding to the reciprocal of the n-th carrier frequency fcn. And the amplitude value of the carrier ripple is calculated based on the minimum value and the maximum value of the drive signal information. The calculated amplitude value is stored in the memory 274b as the amplitude value of the nth step. Further, the carrier ripple amplitude value determination circuit 274c reads the carrier ripple amplitude value stored in the memory 274b, and determines whether or not the carrier ripple amplitude value is within an allowable value. The amplitude information acquisition circuit 274 having such a configuration performs the following processing, thereby performing the modulation circuit 23.
0 determines the carrier frequency for pulse modulation.

FIG. 6 is a flowchart of the carrier frequency setting process performed by the amplitude information acquisition circuit 274. This process is a process executed when the control unit 130 is activated when the wiring cable 150 is connected to the control unit 130 and the ejection unit 110 of the liquid ejecting apparatus 100 shown in FIG. The reason is that if the wiring cable 150 is not replaced, the acquired amplitude information does not change and it is not necessary to newly set a carrier frequency.

When the carrier frequency setting process is started, first, the count value n of the counter 274d is set to “
“0” is set (step S100). Then, the n-th carrier frequency fcn is
After setting to the lowest frequency fcmin (step S102), the value of WCOM is set so that the duty of MCOM is 50% (step S104). Then, in this state (the set WCOM is pulse-modulated with the carrier frequency fcn, the obtained MCOM is converted into the smoothing filter 2.
The drive signal information obtained from the A / D conversion circuit 272 is acquired over a time of 1 / fcn or more (step S106).

By detecting the minimum value and the maximum value of the drive signal information acquired in this way, the amplitude of the carrier ripple superimposed on the drive signal is calculated (step S108), and the obtained amplitude is
Memory 274 as the amplitude value of the carrier ripple at the n-th carrier frequency fcn
b is stored (step S110). Subsequently, it is determined whether or not the amplitude value stored in the memory 274b is within a predetermined allowable value (step S112). For convenience of explanation, it is assumed here that the amplitude value does not fall within the allowable value (step S112: no). In such a case, it is subsequently determined whether or not the carrier frequency fcn at that time has reached the maximum frequency fcmax (step S116). As a result, when the carrier frequency fcn has not yet reached the maximum frequency fcmax (step S116: no), the count value n of the counter 274d is set to “1”.
"Is increased (step S120). Along with this, the carrier frequency fcn is also increased by the predetermined frequency df as a new carrier frequency fcn (step 122), and drive signal information at the carrier frequency fcn is acquired (step S106).

While repeating such processing, whether the amplitude value of the carrier ripple falls within a predetermined allowable value (step S112: yes) or whether the carrier frequency fcn reaches the maximum frequency fcmax (step S116: yes). This condition is satisfied. When the amplitude value of the carrier ripple falls within a predetermined allowable value (step S112: yes), the carrier frequency fcn at that time is set as the carrier frequency used when driving the actuator 116 (step S114). On the other hand, when the carrier ripple amplitude value does not fall within the predetermined allowable value (step S112: no) and the carrier frequency fcn reaches the maximum frequency fcmax (step S116: yes), it is stored in the memory 274b. The carrier frequency fcn corresponding to the smallest amplitude value among the amplitude values is set as the carrier frequency used when driving the actuator 116 (step S118). When the carrier frequency is set in this way, the carrier frequency setting process shown in FIG.

In the amplitude information acquisition circuit 274 shown in FIG. 4 or FIG. 5, the carrier ripple amplitude is obtained by acquiring information related to the carrier ripple amplitude while changing the carrier frequency fcn from the lowest frequency fcmin to the highest frequency fcmax. A carrier frequency that falls within the allowable value is selected. Then, the finally selected carrier frequency is set in the carrier frequency setting means 280. By doing so, it becomes possible to suppress the amplitude of the carrier ripple of the drive signal applied to the actuator 116 to a predetermined value or less regardless of which wiring cable 150 is connected.

E. Modified example:
In the above-described embodiment, the description has been given on the assumption that the amplitude information is acquired and the carrier frequency is set when the control unit 130 of the liquid ejecting apparatus 100 is activated. this is,
If the wiring cable 150 is not replaced, the acquired amplitude information will not change,
Therefore, it is sufficient to set the carrier frequency when the control unit 130 is activated.
However, depending on the application of the liquid ejecting apparatus 100, amplitude information may be acquired and the carrier frequency may be set even after the apparatus is activated. For example, when a so-called ink jet printer ejecting head corresponds to the liquid ejecting apparatus 100, the ejecting head frequently moves during the ejection of the liquid (ink). In addition, since the wiring cable 150 that sends the drive signal to the capacitive load (piezo element) in the ejection head is a flat cable that is easy to bend and has a large number of cores, and is not a twisted pair cable, the state of the wiring cable 150 Depending on the case, the resonance frequency may change. Therefore, in such a case, amplitude information may be acquired in real time and the carrier frequency may be changed. Below, the capacitive load drive circuit 200 of such a modification is demonstrated.

FIG. 7 is an explanatory diagram showing a part of a capacitive load driving circuit 200 according to a modification. As shown in the figure, in the capacitive load driving circuit 200 of the modified example, the amplitude information acquisition unit 270 is provided with a high-pass filter by a capacitor C and a resistor R, and a signal that has passed through the high-pass filter is supplied to the A / D conversion circuit 272. It is designed to be entered. The characteristics of the high pass filter are set so as to suppress frequency components lower than the lowest frequency fcmin. Accordingly, the component corresponding mainly to the carrier ripple in the RCOM is input to the A / D conversion circuit 272, and this component is converted into digital data and then input to the amplitude information acquisition circuit 274 as drive signal information. . When the signal that has passed through the high pass filter exceeds the input voltage range of the A / D conversion circuit 272, a resistor Rd is further provided between the line 3 of the wiring cable 150 and the capacitor C of the high pass filter. A configuration may be adopted in which resistance is divided by Rd and the resistance R of the high pass filter.

FIG. 8 is an explanatory diagram showing a detailed configuration of the amplitude information acquisition circuit 274 mounted on the capacitive load driving circuit 200 of the modification. Similar to the amplitude information acquisition circuit 274 described above with reference to FIG. 5, the amplitude information acquisition circuit 274 of the modified example also includes a carrier ripple amplitude value calculation circuit 274a,
A memory 274b and a carrier ripple amplitude value determination circuit 274c are provided. The amplitude information acquisition circuit 274 of the modified example is also provided with a flag setting circuit 274f described later. The amplitude information acquisition circuit 274 of the modified example having such a configuration performs the following process while outputting the COM and driving the actuator 116 (capacitive load).
The carrier frequency when the modulation circuit 230 performs pulse modulation is determined.

9 and 10 are flowcharts of the carrier frequency setting process performed by the amplitude information acquisition circuit 274. When the carrier frequency setting process is started, first, the control unit 1
30 is started (step S200). Then, the flag provided in the flag setting circuit 274f of the amplitude information acquisition circuit 274 is set to “0” (step S202). Subsequently, after setting the carrier frequency fcn to the minimum frequency fcmin (step S204), the drive waveform signal generation circuit 210 outputs WCOM (step S206). Then, the capacitive load driving circuit 200 performs the series of processes described above with reference to FIG.
OM is output, and RCOM is applied to the actuator 116 via the wiring cable 150.

The RCOM applied to the actuator 116 in this way is the line 3 of the wiring cable 150.
Is input to the amplitude information acquisition means 270. In the amplitude information acquisition means 270 of the modification,
The input signal is passed through a high-pass filter and then converted into digital data by the A / D conversion circuit 272, and this digital data is acquired as drive signal information (step S20).
8). Thereafter, the carrier ripple amplitude value calculation circuit 274a is used to calculate the carrier ripple amplitude value (step S210), and the obtained amplitude value is stored in the memory 274b (step S212).

Then, it is determined whether or not the amplitude value of the carrier ripple is within an allowable value (step S2).
14). As a result, when it is determined that the value is within the allowable value (step S214: yes),
After setting the flag to 0 (step S220 in FIG. 10), it is determined whether or not to end the use of the liquid ejecting apparatus 100 (step S222). If not completed (step S222: n
o) After returning to step S208 and acquiring drive signal information again (step S208)
Then, the following series of processing is repeated.

Thus, while using the liquid ejecting apparatus 100, such processing is repeated every predetermined time. In the processing, first, the carrier frequency fcn is set to the minimum frequency fcmin, it is determined whether or not the amplitude of the carrier ripple at that frequency is within an allowable value, and if it is within the allowable value, the minimum frequency fcmin is set to the carrier. The frequency is fcn. Therefore, as long as the amplitude of the carrier ripple is within the allowable value, the lowest frequency fcmin is continuously set as the carrier frequency fcn.

Of course, there may be a case where the calculated amplitude of the carrier ripple exceeds an allowable value. In such a case, “no” is determined in step S214 of FIG. Next, the flag is 0
Whether or not (step S216). As described above, since the initial state of the flag is set to 0, it is determined as “yes” in step S216, and the current carrier frequency fcn is determined.
Is set to the lowest frequency fcmin (step S228 in FIG. 10).
Since the carrier frequency fcn is normally set to the minimum frequency fcmin, step S228 is performed.
Then, after determining “yes” and changing the carrier frequency fcn to the maximum frequency fcmax (step S230), the flag is changed to 1 (step S234). The meaning of the flag will be described later. If the current carrier frequency fcn is not set to the lowest frequency fcmin (step S228: no), the lowest frequency fcmin is set to the carrier frequency fcn (step S232), and then the flag is changed to 1 (step S234). ).

When the flag is set to 1 (step S234), the process returns to step S208,
Drive signal information is acquired (step S208). And the changed carrier frequency fcn
Is calculated (step S210), and the obtained amplitude value is stored in the memory 274b (step S212). Then, it is determined whether or not the obtained amplitude value is within an allowable value (step S212). Step S214). If the result is within the allowable value (step S
214: yes), the flag is reset to 0 (step S220 in FIG. 10), and the liquid ejecting apparatus 1
It is determined whether or not the use of 00 is finished (step S222). If the use is not finished (step S222)
222: no), it returns to step S208 again and repeats a series of subsequent processes.

As a result of such processing, the carrier frequency fcn is first set to the minimum frequency fcmin to obtain the amplitude value of the carrier ripple. If the amplitude value is within the allowable value, the carrier frequency fcmin is set to the minimum frequency fcmin. Will remain. On the other hand, when the amplitude value exceeds the allowable value, the carrier frequency fcn is changed to the maximum frequency fcmax, and the changed amplitude value of the carrier ripple is calculated. If the new amplitude value is within the allowable value, the carrier frequency fcn is changed to the maximum frequency fcmax.

However, the carrier ripple amplitude value at the maximum frequency fcmax may also exceed the allowable value. In such a case, since “no” is determined in step S214, it is subsequently determined whether or not the flag is 0 (step S216). As mentioned above, the flag is
It is set to 1 when the carrier frequency fcn is changed. Therefore, when the flag is 1, the carrier frequency fcn is changed, and the amplitude values of the carrier ripples at the two carrier frequencies fcn (here, the lowest frequency fcmin and the highest frequency fcmax) are stored in the memory 274b. It shows that. Therefore, when the flag is 1 (step S216:
no), two carrier frequencies fcn (here, the lowest frequency fcmin and the highest frequency fcmax)
The amplitude values of the carrier ripples acquired in step 1 are compared, and the frequency having the smaller amplitude value is set as the carrier frequency fcn (step S218). Thereafter, after setting the flag to 0 (step S220 in FIG. 10), it is determined whether or not to end the use of the liquid ejecting apparatus 100 (step S222). If not completed (step S222: no), step S208
Returning to FIG. 5, after obtaining the drive signal information again (step S208), the following series of processing is repeated.

As described above, while the liquid ejecting apparatus 100 is being used, such processing is repeated every predetermined time, and the carrier frequency fcn is reviewed. If it is determined that the use of the liquid ejecting apparatus 100 is finished (step S222: yes), the output of WCOM from the drive waveform signal generation circuit 210 is stopped (step S224), and the control unit 130 is stopped (
Step S226), the carrier frequency setting process shown in FIGS. 9 and 10 is terminated.

In the capacitive load drive circuit 200 according to the modified example, when the control unit 130 is started, the carrier frequency setting process as described above is executed at predetermined time intervals, and the carrier frequency is reviewed. As a result, even if the resonant load including the wiring cable 150 can change during use, such as the ejection head of an inkjet printer, the carrier ripple is superimposed on the RCOM by reviewing the carrier frequency almost in real time. It becomes possible to avoid doing.

In the modification described above, instead of the voltage dividing circuit of the amplitude information acquisition unit 270 described above with reference to FIG. 4, a high-pass filter including a capacitor C and a resistor R is inserted, and the signal passing through the high-pass filter is converted to A It has been described that the drive signal information is generated by converting the digital data using the / D conversion circuit 272. However, the signal before passing through the high-pass filter may be converted into digital data using the A / D conversion circuit 272 to generate drive signal information. That is, similar to the above-described embodiment shown in FIG. 4, the RCOM applied to the actuator 116 is acquired via the line 3 of the wiring cable 150, then divided by resistance, and then input to the A / D conversion circuit 272. To generate drive signal information. The drive signal information thus obtained is information including the COM signal component. Therefore, as shown in FIG. 11, a high-pass filter 274g (digital filter) corresponding to the high-pass filter of the modification may be provided on the amplitude information acquisition circuit 274 side.

Although the capacitive load drive circuit of the present embodiment and the modification has been described above, the present invention is not limited to the above-described embodiment or the modification, and may be implemented in various modes without departing from the gist thereof. Is possible. For example, in the above embodiment, the lowest frequency fcmi
Although the carrier frequency is set between n and the maximum frequency fcmax, a configuration without the minimum frequency fcmin and the maximum frequency fcmax may be used. In this case, the change of the carrier frequency is repeated until the amplitude value of the carrier ripple is within the allowable value. In the above embodiment, the drive waveform signal generation circuit 210 generates the drive waveform signal WCOM having a duty ratio of 50%. However, the duty ratio of the WCOM may be a duty ratio that can acquire the amplitude of the carrier ripple. It does not have to be 50 percent.

In addition, by applying the capacitive load driving circuit of this embodiment to various electronic devices including medical devices such as a fluid ejection device used for forming a microcapsule containing a medicine or a nutrient, the power efficiency can be improved. A small-sized electronic device can be provided well. The present invention can also be suitably applied to a capacitive load driving circuit that is mounted on an ink jet printer and drives an ejection nozzle that ejects ink.

DESCRIPTION OF SYMBOLS 100 ... Liquid injection apparatus, 110 ... Injection unit, 111 ... Injection nozzle,
112 ... Liquid passage tube, 113 ... Front block, 114 ... Rear block,
115 ... Liquid chamber, 116 ... Actuator, 120 ... Supply pump,
121 ... Tube, 122 ... Step, 122 ... Tube,
123 ... Liquid tank, 130 ... Control unit, 150 ... Wiring cable,
152 ... Connector, 154 ... Connector, 200 ... Capacitive load drive circuit,
210 ... Driving waveform signal generation circuit, 220 ... Arithmetic circuit,
230: modulation circuit, 240: digital power amplifier, 250: smoothing filter,
260 ... compensation circuit, 270 ... amplitude information acquisition means, 272 ... A / D conversion circuit,
274 ... Amplitude information acquisition circuit, 274a ... Carrier ripple amplitude value calculation circuit,
274b: Memory, 274c: Carrier ripple amplitude value determination circuit,
274d: Counter, 274f: Flag setting circuit,
274g ... high pass filter, 280 ... carrier frequency setting means

Claims (4)

A capacitive load drive circuit that drives a capacitive load by applying a drive signal to the capacitive load having a capacitive component,
A drive waveform signal generating circuit for generating a drive waveform signal which is a reference of the drive signal;
An arithmetic circuit that outputs an error signal by subtracting a feedback signal generated using the drive signal applied to the capacitive load from the drive waveform signal;
A modulation circuit that generates a modulation signal by pulse-modulating the error signal;
A digital power amplifier that amplifies the modulated signal to generate a pulsed power amplified modulated signal;
A smoothing filter that generates the drive signal by smoothing the pulse-wave-shaped power amplification modulation signal;
A phase lead compensation circuit that performs phase lead compensation on the drive signal and outputs the signal after the phase lead compensation to the arithmetic circuit as the feedback signal;
Connecting the smoothing filter and the capacitive load, wiring provided to be replaceable,
Amplitude information acquisition means for acquiring amplitude information related to the amplitude of the carrier ripple of the drive signal applied to the capacitive load based on the drive signal;
A carrier frequency setting unit configured to set a carrier frequency when the modulation circuit performs pulse modulation of the error signal based on the amplitude information so that an amplitude of a carrier ripple of the drive signal is equal to or less than a predetermined value. Load drive circuit. The capacitive load drive circuit according to claim 1,
The modulation circuit is a circuit that performs pulse modulation on the error signal at the carrier frequency included in a range from a predetermined minimum frequency to a predetermined maximum frequency;
The amplitude information acquisition means is means for setting the carrier frequency within a range from the lowest frequency to the highest frequency, and acquiring the amplitude of the carrier ripple,
The carrier frequency setting means is a capacitive load drive circuit which is a means for setting the carrier frequency when the modulation circuit performs pulse modulation to the carrier frequency whose amplitude acquired by the amplitude information acquisition means is not more than the predetermined value. . The capacitive load driving circuit according to claim 2,
The drive waveform signal generation circuit is a circuit that generates the drive waveform signal in which the duty ratio of the modulation signal is 50% while the amplitude information acquisition unit acquires the amplitude of the carrier ripple. Load drive circuit. A capacitive load driving circuit according to any one of claims 1 to 3,
A supply pump for supplying liquid;
An injection unit having a liquid chamber into which the liquid supplied from the supply pump flows, an actuator that is the capacitive load, and an injection nozzle that injects the liquid that has flowed into the liquid chamber;
With
When the drive signal is applied to the actuator, the liquid that has flowed into the liquid chamber is ejected in a pulse form from the ejection nozzle.
Liquid ejector.

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