JPH0410957A - Image forming device - Google Patents

Abstract

PURPOSE:To miniaturize and lighten the device and carry out the reciprocating motion by easy control by employing a piezoelectric element as a driving source for the reciprocating mechanism and displacing the piezoelectric element with electricity charged to and discharged from said element. CONSTITUTION:An LED head 12 is supported against a base 202 with a displacement amplifying device 201 composed of two arms each of which has a narrow part at its root. A piezoelectric element 200 is provided to a point near the root of the displacement amplifying device 201. The piezoelectric element 200 is charged with and discharged of electricity by control with a driving circuit 30a and is driven for expansion and contraction. The extent of amplitude of the LED head 12 is detected with a displacement sensor 203 and the detected values are fed back to the driving circuit 30a, and thereby operation of the piezoelectric element 200 is controlled, making the amplitude of the LED head 12 controlled to be constant.

Description

[Detailed description of the invention] [Table of contents] Overview Industrial field of application Conventional technology Problems to be solved by the invention Means for solving the problems (Fig. 1) Working example (a) First embodiment Explanation (Figures 2 to 8) (b)
Explanation of the second embodiment (Figures 9 to 12) (C) Third
(Fig. 13) (d) Description of other embodiments (Fig. 13)
(Fig. 14) Effects of the Invention [Summary] Regarding an image forming apparatus that reciprocates an image forming head in which a plurality of dot elements are arranged in a row to form a plurality of dots on an image forming medium using one element. The image forming head has n dot elements arranged in at least one row, and an image forming head arranged opposite to the image forming head. It has a forming medium and a reciprocating mechanism that reciprocates the image forming head in the column direction, and drives the n dot elements three times as the image forming head moves in the column direction to form the image forming medium. In an image forming apparatus that forms an image of a-n dots, the reciprocating mechanism includes a piezoelectric element and a displacement magnifying mechanism that magnifies the displacement of the piezoelectric element, and drives the piezoelectric element by charging and discharging it. A drive circuit was provided to do this.

[Industrial application field]

The present invention relates to an image forming apparatus that forms a plurality of dots with one dot element on an image forming medium by reciprocating an image forming head in which a plurality of dot elements are arranged in one row.

Image forming apparatuses that form images using dots include wire dot methods, electrophotographic methods, thermal methods, thermal transfer methods,
There are various methods of ejecting ink.

In this image forming apparatus, there was a one-to-one correspondence between the dots formed and the dot elements of the image forming head, but in recent years, with the aim of improving resolution, the wire dot type has a plurality of wire dot elements arranged in a row at equal intervals. A so-called shuttle system has been developed in which a single wire dot element forms a plurality of dots by reciprocating heads arranged in a row.

In such a device, it is desirable that the reciprocating mechanism be small and easy to control.

[Conventional technology]

The wire dot type used a motor to reciprocate the head.

[Problem to be solved by the invention]

However, the conventional technology has the following problems.

(2) Since a motor or the like is used, the device becomes large and heavy, making it difficult to reduce its size and weight.

■ If a motor or the like is used, the drive circuit will require speed control, etc., making the control more complicated.

■Also, motors etc. tend to generate noise.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide an image forming apparatus that can be made smaller and lighter, and that can reciprocate with easy control.

Another object of the present invention is to provide an image forming apparatus that can reciprocate while keeping the displacement of the head constant using a piezoelectric element.

[Means to solve the problem]

FIG. 1 is a diagram showing the principle of the present invention.

Claim 1 of the present invention provides an image forming head 12 in which n dot elements 120 are arranged in at least one row, an image forming medium 10 provided opposite to the image forming head 12, and the image forming head 12. It has a reciprocating mechanism 20 that reciprocates in the column direction, and drives the n dot elements 120 three times as the image forming head 12 moves in the column direction to form dots a-n on the image forming medium 10. In the image forming apparatus that performs image formation, the reciprocating machine tI20 includes a piezoelectric element 2
00, and a displacement magnifying mechanism 201 that magnifies the displacement of the piezoelectric element 200, and is provided with a drive circuit 30a that charges and discharges the piezoelectric element 20 to drive it.

According to a second aspect of the present invention, in the first aspect, a displacement amount detection section 203 for detecting the displacement amount of the image forming head 12 is provided, and the drive circuit 30a controls the piezoelectric element 200 according to the detected displacement amount. This controls the charging time.

[Function] In claim 1 of the present invention, the piezoelectric element 200 is used as the drive source of the reciprocating mechanism to vibrate the image forming head 12.

Therefore, the drive source can be significantly reduced in size and weight.

Furthermore, since the piezoelectric element 200 generates displacement by charging and discharging, it is easy to control and generates almost no noise.

Since the amount of displacement of the piezoelectric element 200 is on the order of 10 microns at most, the necessary stroke amount for the head 12 cannot be obtained.
The head 12 is vibrated by enlarging the displacement.

If the head 12 has a high resolution, a stroke of at most 0.5 liters is sufficient, so the desired stroke can be obtained by these strokes.

Next, in claim 2 of the present invention, the displacement amount sensor 203 is provided to detect the amount of movement of the image forming head 12 and perform feedback control. The amount of displacement of the head 12 can be controlled to be constant.

This improves the positional accuracy of pixels and enables stable, high-quality image formation.

〔Example〕

! 8+ Description of the First Embodiment FIG. 2 is an overall configuration diagram of the first embodiment of the present invention, FIG. 3 is a configuration diagram of its image forming section, and FIG. 4 is a configuration diagram of its main parts. An example will be given of an electrophotographic printer using a photosensitive drum as the forming medium 10 and an LED array as the image forming head 12.

The photoreceptor (drum) 10 is rotated at a constant speed in the direction of the arrow by a motor 17, and an image is formed by a predetermined electrophotographic process.

That is, as shown in the configuration diagram of the image forming section in FIG. 3, a rotating photosensitive drum 10 having a photosensitive layer on its surface is pre-charged by a pre-charger 11, and image-wise exposed by an LED array 12. A latent image is formed on the photosensitive drum 10 and developed by the developing device 13 to obtain a toner image.

The toner image on the photosensitive drum 10 is transferred onto the conveyed paper PP by a transfer charger 14 and thermally fixed by a heat fixing device 16.

On the other hand, the photosensitive drum 10 is neutralized by a static neutralizer/cleaner 15, residual toner on the surface is removed, and the photosensitive drum 10 is prepared for the next cycle.

Returning to FIG. 2, the LED head 12 has a large number of LEDs 120 arranged in one row, and the number of printed dots in one row is a-n.
On the other hand, one in which n dots are provided at an interval of a, or one in which an n dots are provided in a - column is used.

In this case, in the case where a×n LEDs 120 are provided, it is possible to use a good quality ED element provided at least every a number at equal intervals.

As shown in FIGS. 2 and 4(A), the LED head 12 is supported by a displacement amplifying mechanism 201 consisting of a pair of arms having a constriction at the base with respect to a base 202. The base is piezoelectric
An element 200 is provided.

Therefore, by driving the piezo element 200, the piezo element 200
The displacement is expanded and expanded by the displacement magnification mechanism 201 to
The ED head 12 is reciprocated.

The drive circuit 30a controls charging and discharging of the piezo element 200 to drive the piezo element 200 to expand and contract, and the scan conversion circuit 30b converts the serial image signal of one line (a and n dots) into (a-1 ) The control circuit 30c converts the signal into a serial signal of group a of the dot-placed n door) and outputs it to the LED head 12 according to the drive timing of the piezo element 200. The control circuit 30c controls the drive timing of the drive circuit 30a and scan conversion. The scan conversion timing of the circuit 3Qb is synchronously controlled to control the rotation of the motor 17.

FIG. 5 is an explanatory diagram of the operation of one embodiment of the present invention.

Here, as shown in FIG. 4(B), the LED head 1
One LEDi20 of 2 corresponds to the O pixel position,
It is assumed that the LED head 12 is shifted to 11 pixel and +1 pixel positions by reciprocating motion, and one LED 120 is used to expose three pixels.

The control circuit 30c controls the drive circuit 30a to apply a head drive voltage to the piezo element 200 as shown in FIG.

The piezo element 200 is charged by the head drive voltage, expands, and moves the LED head 12 to the left in FIG.
When the head drive voltage is cut off, the LED head 12 is discharged and shrunk, moving the LED head 12 to the right in FIG.

Therefore, the LED head 12 moves back and forth between -1 pixel and +1 pixel, as shown in the head position in FIG.

On the other hand, under the control of the control circuit 30c, the scan conversion circuit 30b receives an image signal for one line of 3n dots from a controller (not shown) during the charging period of the piezo element 200, and (31-2) during the discharging period. Scan conversion is performed into a first group of dot signals, a second group of (31-1) dot signals, and a third group of 31st dot signals, and 11 pixels are sent to the LED head 12. While in the position, give the first group dot signal, n LED1
20 is driven for the first time, and when it reaches the 0 pixel position, a second group of dot signals is applied, and n LEDs 120 are driven for the first time.
is driven for the second time, and when it reaches the position of +1 pixel, the third
The n LEDs 120 are driven for the third time.

Therefore, as shown in FIG. 5, for one line image signal of 3n dots, n LEDs 120 are driven three times, and each
-1 (N) pixels, 0 (N+1) pixels, +l in D120
Exposure of three pixels (N+2) pixels is performed, and exposure of 3n dots and one line is performed.

In this example, one line of data reception and scanning conversion preparation is performed during the charging (or discharging) period of the piezo element 200, and scan conversion and LED driving can be performed during the discharging (or charging) period, and the piezo element 200 is vibrated at high speed. Thus, one line can be exposed without deviation.

In this way, by reciprocating the LED head 12, one LED L 20 can be positioned at a plurality of printing dot positions in the column direction on the photoreceptor 10, and one LED
20 allows exposure of multiple dots.

Therefore, even if not all of the LEDs 120 provided in the LED head 12 are of good quality, and some of them are defective, the photosensitive medium 10 can be exposed to the required number of dots, and conversely, the LEDs
Even if the LEDs 120 of the head 12 are thinned out to a number less than the number of dots required for exposure, the photosensitive medium 10 can be exposed to the required number of dots, and the structure can be made at a low cost.

Furthermore, by changing the amplitude of the reciprocating motion and the number of drives during one reciprocating motion, it is also possible to switch the resolution.

As a result, if each one of the n groups of the a-n 0 LEDs 120 is at least a good item, the photosensitive medium 10
Since the exposure of the an-n dots necessary for the process can be performed and the head 12 that was considered to be a defective product can be used, an inexpensive head can be used.

Conversely, since n LEDs 120 can expose a-n dots on the photosensitive medium 10, only 1/1/2 of the required number of dots can be exposed.
It is only necessary to provide the number a of 0 LEDs 120 on the head 12,
The head price can be reduced to 1/a.

In this way, since the head 12 is driven by the piezoelectric element 200, even if the head 12 is vibrated, the structure does not become large and lightweight.

Furthermore, since the piezoelectric element 200 is displaced by charge/discharge control, control is easy and there is no noise.

Furthermore, since the displacement magnifying mechanism 201 is used, the necessary stroke of the head 12 can be obtained using the piezoelectric element 200 with a small displacement.

Next, the relationship between the vibration frequency and the stroke when the LED head 12 is vibrated will be explained.

FIG. 6 is a model diagram of the drive system of the head, FIG. 7 is a diagram showing the relationship between displacement and generated stress, and FIG. 8 is a diagram showing the relationship between frequency and stroke.

As shown in FIG. 6(A), the piezo element 200 is vibrated, its displacement Δ is magnified via the displacement magnification mechanism 201, and the LE
When the vibration system for obtaining the required stroke δ of the D head 12 is modeled, the head 12 of quality i1Mk that rotates around a fulcrum as shown in FIG.
The system is vibrated at an enlargement rate r at O.

Here, the generated stress P and displacement amount Δ of the piezoelectric element 200 when a voltage is applied are as shown in FIG. The result converted to parts is shown in Fig. 5(B).

From FIG. 7(A), the relationship between the generated stress P and the displacement amount Δ is as follows: (r　・Δo)2 becomes.

From equation (5), the stiffness km at the head section is as follows.

Here, the piezoelectric element stiffness Ke is Ke=PO/Δ0.

Converting this to the head section, where η is the energy efficiency of the enlarging mechanism, Pmo・δ0=77'Δo−P o −=−−−
−(21δo=r·Δ0 −···−(3).

Substituting equations (2) and (3) into equation (4), we get The natural frequency f is becomes.

Here, the relationship between the vibration frequency f and the stroke δ is as follows: S is the beam spot diameter (1 ring), b is the thinning number of LEDI 20 (-a-1), v is the process speed (fi/5ec),
L is the paper length, M is the processing speed (PPM = paper pe
r m1nutes), and l is the interval between forms (fins), then δ=a-3-41・(7)=ae・−・・−・(8).

In this way, the relationship between the vibration frequency f and the stroke δ is obtained.

Here, L-297m, 1 = 531 turtles, V = 23
．． 3.46.7.70.0 m/sec and the thinning number b=1.2.3.4, the relationship between the frequency f and the stroke δ is shown in FIG.

At this time, M = 4.8.12 (PPM), which is A
This corresponds to a printer that processes 4.8.12 sheets of 4-size paper in the portrait direction per minute.

Then, the resolution included in the lower left side of the curve shown in FIG. 8 becomes usable.

For example, under the following conditions, the usable portion is the shaded area in FIG.

Conditions = Head weight 200g Therefore, head mass MK is Mk = 0.2/g = 0.2/9800#2.04
x 10−' Energy efficiency of expansion mechanism: η = 50 (%
) Displacement magnification rate: r = 10~2° From the catalog value of the piezoelectric element used, the piezoelectric element rigidity Ke
From the above, when r=10, substituting these values into the second (7), the natural frequency f is, and the displacement δ at this time is: δ = 0.0135X 1 0 = 0.135
(Praise Seal)

Similarly, when r=15, f =267 (!1z)r=201
71, f = 200- (Hz) When this is plotted on FIG. 8, the shaded area becomes usable, so the specifications of 240 dpi and 300 dpi with decimation number b=2 and 4 PPM are possible.

('b) Description of second embodiment FIG. 9 is a block diagram of a second embodiment of the present invention.

In the figure, the same parts as those shown in FIG. 2 are indicated by the same symbols.

A displacement sensor 203 is provided in the displacement magnification mechanism 201 to detect the displacement amount of the LED head 12 and feed it back to the drive circuit 30a.
An optical position sensor, a magnetic position sensor using a magnet and a coil, etc. can be used.

In this embodiment, the amplitude of the LED head 12 is detected by the displacement sensor 203 and fed back to the drive circuit 30a to control the drive of the piezoelectric element 200. Zu, L
The amplitude of the ED head 12 is controlled to be constant to prevent dot misalignment on each line.

Figure 10 is a configuration diagram of the drive circuit in Figure 9, and Figure 11 is a diagram of the drive circuit in Figure 1.
FIG. 2 is an explanatory diagram of the sensor section in FIG.

In FIG. 10, the AND gate IcI to which the charging/discharging drive signal 3 is input is connected to the base of the driving transistor Q1, and the collector of the driving transistor Q1 is connected to the base of the charging transistor Q8+.

Charge voltage +130■ to the collector of charging transistor Q2
is supplied, and the emitter of the charging transistor Q2 is connected to one end of the piezoelectric element 200 via a charging resistor R4 and a backflow prevention diode D1.

On the other hand, the charge/discharge drive signal ■ is input to the inverter Iv, and the inverter Iv is connected to the normally open AND gate IC2 by +5■ ("1"), and is connected to the discharge transistor Q3.

The collector of the discharge transistor Q9 is connected to one end of the piezoelectric element 200 via the discharge resistor R5, and the emitter side is connected to 0.

R1, R2, and R3 are bias resistors for passing bias current through the transistors Q1 to Q3, respectively, and R6 and R7
is a voltage dividing resistor, connected to both ends of the piezoelectric element 200,
AI is a comparator that detects the charging voltage of the piezoelectric element 200 and lowers the voltage to the input level of a comparator A1, which will be described later. Compare and control AND gate ICI according to the comparison result, R8
is a pull amplifier resistor, which pulls the output of the comparator A1.

FIG. 11(A) shows the output circuit 203a of the sensor unit 203, which inputs the sensor detection voltage proportional to the swing width from the sensor body shown in FIG. 11(B) to the inverting amplifier AMP via the input resistor R1. , is inverted and amplified, half-wave rectified by a diode Di1, and peak held by a peak hold circuit including a capacitor C1 and a resistor R3 connected to a reference potential Vcc to obtain a sensor output (control voltage) Vc.

Therefore, the sensor output voltage Vc with respect to the amplitude is the 11th
As shown in Figure (C), the reference potential V is the maximum with zero amplitude.
cc, and decreases linearly as the amplitude of vibration increases.

FIG. 12 is a time chart diagram of the configuration shown in FIG.

As shown in FIG. 12, the charging/discharging drive signal (2) repeats 0N10FF at a constant cycle.

The AND gate ICI turns on the charging transistor Q2 via the drive transistor Ql when the charge/discharge drive signal ■ is high (charging instruction) and the output of the comparator A1 is high (that is, the control voltage Vc is higher than the charging voltage ■). and charges the piezoelectric element 200.

When the charging of the piezoelectric element 200 progresses and the charging detection voltage ■ exceeds the control voltage Vc, the output of the comparator A1 becomes low, and the AND gate ICI is closed.

Therefore, the base input of the charging transistor Q2 becomes like the charging control signal (2), and the charging transistor Q2 is turned off. At this time, the discharge transistor Q3 is off because it is driven by the inverted signal ◎ of the charge/discharge drive signal ■, and the piezoelectric element 20
The voltage applied to 0 is held constant because charging and discharging are not performed.

Thereafter, when the charge/discharge drive signal (2) becomes low, the discharge transistor Q3 is turned on and the charge of the piezoelectric element 200 is discharged.

As explained in FIG. 11, this control voltage Vc is obtained by peak-holding the displacement detection signal (detection voltage) of the sensor body, so as shown in FIG. A control voltage Vc inversely proportional to the maximum deflection of the head 12 is applied to the comparator A1 as a reference voltage, and the charging time of the current cycle is controlled.

Therefore, if the amplitude in the previous cycle is large, the control voltage Vc will be low, the charging time of the current cycle will be shortened, and the amplitude will be controlled in the direction of small, so that the amplitude in the previous cycle will be small. If so, the control voltage Vc becomes high, the charging time of the current cycle becomes longer, and the amplitude is controlled in the larger direction.

For this reason, when charging the piezoelectric element with a constant voltage, the power supply voltage is set to 50% to 100% higher than the target voltage, so that it can be charged to a voltage higher than the target voltage. I'll keep it.

In addition, the resistor R4 used for charging should have a value as small as possible so that an excessive current does not flow through the circuit and charging is completed in as short a time as possible.
Here, the resistance value is set to a value that takes a certain amount of time to complete charging.

In this way, conventionally, voltage was applied by repeating two cycles of charging-discharging-charging, but by changing it to three cycles of charging-holding-discharging, and making the charging and holding times variable, Control the voltage applied to the piezoelectric element.

(C) Description of the third embodiment FIG. 13 is a circuit diagram of a second embodiment of the drive circuit.

In the figure, the same components as those shown in FIG. 10 are indicated by the same symbols, TM is a timer circuit, and sensor 2
The pulse width (
This makes the charging time (charging time) variable.

In this embodiment, the time chart is the same as that in FIG. 11, and regardless of the voltage applied to the piezoelectric element 200,
The output directly controls the charging time, that is, the time during which the charging transistor Q2 is turned on.

This also enables control to reduce the charging time when the amplitude of vibration is larger than the target, and to increase the charging time when the amplitude of vibration is smaller than the target.

In this way, by detecting the displacement of the head, performing feedback control based on the amplitude of vibration, and controlling the charging voltage of the piezoelectric element 200 based on the charging time, it is possible to eliminate variations in the piezoelectric element 200 and the head system, as well as the power supply voltage. First, the amount of displacement of the head 12 can be made constant, the positional accuracy of pixels is improved, and it is possible to stably form high-quality images.

+d) Description of other embodiments FIG. 14 is an explanatory diagram of another embodiment of the present invention.

In the figures, the same parts as those shown in FIGS. 2, 3, and 4 are indicated by the same symbols.

As shown in FIG. 14('A), the LED head 12 consists of an LED array main body 12a and an imaging lens 12b. In the above embodiment, the LED array main body 12a and the imaging lens 12b are integrated, I was moving things around in my body back and forth.

In the embodiment shown in FIG. 14(B), the imaging lens 12b is fixed and only the LED array main body 12a is moved back and forth. Even in this case, the same effect is achieved and the mass of the moving head is reduced. It is possible to vibrate at high speed (reciprocating motion).

In addition, in the embodiment shown in FIG. 14(C), the LED array main body 1
2a is fixed, and only the imaging lens 12b is moved back and forth. If a parallel equal-magnification lens is used, the amplitude can be halved, the same effect can be achieved, and the mass of the head vibrating part can be further reduced. High-speed vibration becomes easy.

Similarly, when using the head 12 with a liquid crystal shutter structure or a thermomagnetic shutter structure, the light source is fixed,
Only the shutter portion may be vibrated.

In addition to the embodiments described above, the present invention can be modified as follows.

(2) Although the image forming head has been described using an LED head as an example, it is also possible to use a liquid crystal shutter type head, a thermomagnetic effect shag type head, a thermal head, an ink jet head, or a wire dot head.

(2) It is driven when the head 12 is shifted to the right, but it may be driven when the head 12 is shifted to the left, or it may be driven when the head 12 is shifted to the left or right.

Although the present invention has been described above using examples, the present invention can be modified in various ways according to the gist of the present invention, and these are not excluded from the present invention.

〔Effect of the invention〕

As explained above, according to the present invention, the following effects are achieved.

According to claim 1 of the present invention: a. Since a piezoelectric element is used as the drive source, it is possible to reduce the size and weight.

b. Vibration displacement is obtained by controlling the charging and discharging of the piezoelectric element, so control is easy and noise is low.

Since the C1 displacement magnification mechanism is provided, the stroke necessary for the image forming head can be obtained by the piezoelectric element.

According to claim 2 of the present invention, d. Furthermore, the displacement amount of the image forming head 12 can be controlled to be constant by the piezoelectric element regardless of variations in the piezoelectric element or the head or the power supply voltage, and the positional accuracy of the pixels is improved. , it becomes possible to form stable and high-quality images.

[Brief explanation of drawings]

FIG. 1 is a diagram of the principle of the present invention, FIG. 2 is an overall configuration diagram of the first embodiment of the invention, FIG. 3 is a configuration diagram of the image forming section in FIG. 2, and FIG. 5 is an explanatory diagram of the operation of the first embodiment of the present invention, FIG. 6 is a model diagram of the drive system of the head of the present invention, and FIG. 7 is a displacement diagram of the present invention. Relationship diagram between amount and generated stress,
Fig. 8 is a diagram of the relationship between frequency and stroke of the present invention, Fig. 9 is a block diagram of a second embodiment of the present invention, Fig. 10 is a block diagram of the drive circuit of Fig. 9, and Fig. 11 is a block diagram of the drive circuit of Fig. 10. 12 is a time chart diagram of FIG. 10, FIG. 13 is a circuit diagram of a second embodiment of the drive circuit of FIG. 9, and FIG. 14 is an explanation of another embodiment of the present invention. It is a diagram. O--image forming medium, 2--image forming head, 0--reciprocating mechanism, Oa-- drive circuit, 30--dot element, 00--piezoelectric element, 01--displacement magnifying mechanism . Patent Applicant: Fujitsu Ltd. Representative Patent Attorney Akira Yamatani CB) 7th Embodiment t-portion diagram Figure 4 Trench shape A' II Figure 3 (A) CB) Mk- Head 1 amount Ke 1 pound, Gosho r Emaijimatsu, Ndo guide dynamic system 7 dels 2 roo. rso. #f (Hl) Frequency needle and Ztrok connection a diagram Figure 8 △ CA) (B) Gui Z + Ya H Maro Figure 12 (A) /2o3ct CB) CC) Figure 11

Claims (2)

[Claims] (1) An image forming head (12) in which n dot elements (120) are arranged in at least one row, an image forming medium (10) provided opposite to the image forming head (12), and the image forming It has a reciprocating mechanism (20) that reciprocates the head (12) in the column direction, and drives the n dot elements (120) a times as the image forming head (12) moves in the column direction. In the image forming apparatus that forms an a/n dot image on the image forming medium (10), the reciprocating mechanism (20) includes a piezoelectric element (20).
0) and a displacement magnifying mechanism (201) that magnifies the displacement of the piezoelectric element (200), and a drive circuit (201) that charges and discharges the piezoelectric element (200) to drive it.
30a). (2) A displacement amount detection section (203) for detecting the displacement amount of the image forming head (12) is provided, and the drive circuit (30a
) controls a charging time of the piezoelectric element (200) according to the detected displacement amount.