JPS63189246A - Ink drop position detector - Google Patents

Abstract

PURPOSE:To detect the position of an ink drop in a sagittal direction without providing a circuit for calculating the sum of photocurrents, by reading the relative positional difference in the sagittal direction of two ink drops jetted respectively from two nozzles, from a memory. CONSTITUTION:A controller 101 selects from a data memory 111, a table showing the relationship between the relative positional difference in a sagittal direction Y of two ink droplets jetted respectively from two adjacent nozzles and the difference between maximum values of the absolute values of photocurrent differences outputted respectively from a pair of photo-detectors when the two kinds of ink drops pass over the photo-detectors. Then, information indicative of the relative positional difference in the sagittal direction Y of the ink drops, corresponding to information outputted from a subtracting circuit 110, is read. Thereafter, the controller 101 adds the positional difference information to the information on the position in the sagittal direction of the ink drop jetted from the nozzle 37S, thereby calculating the information on the position in the sagittal direction Y of the ink drop jetted from the nozzle 37A.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an ink drop position detection device, and particularly to an ink drop position detection device for detecting the position of an ink drop ejected from a droplet generating device on a recording sheet in an inkjet printer. The present invention relates to an ink drop position detection device using a drop sensor capable of detecting in a transport direction (direction perpendicular to the nozzle arrangement direction) and a direction perpendicular to the transport direction (nozzle arrangement direction).

(Prior Art) In a charge control type inkjet printer, the flying position of the ink drop is controlled so that the ink drop ejected from the droplet generating device can reach a desired position on the recording paper. In a multi-nozzle head, the conveyance direction of the recording paper is detected in a direction perpendicular to the nozzle arrangement direction (hereinafter referred to as the sagittal direction) and in the nozzle arrangement direction, and the information is fed back to the control device of the inkjet printer. is configured to do so.

Through this feedback, when the flying position of the ink drop is shifted in the nozzle arrangement direction, the amount of charge on the ink drop is adjusted according to the amount, and when it is shifted in the sagittal direction, the amount of charge on the ink drop is adjusted according to the amount. The paper conveyance timing or printing timing is adjusted. As a result, good printing is always performed regardless of manufacturing errors in the nozzle shape, installation errors in the deflection electrodes, and the like.

The same applies to electric field control type inkjet printers.

A drop sensor that detects the position of an ink drop in the nozzle arrangement direction and the sagittal direction will be briefly described below with reference to the drawings.

FIG. 6 is a schematic front view showing a conventional drop sensor applied to a charge control type inkjet printer. In FIG. 6, the nozzles of the inkjet printer are arranged, for example, on the front side of the page of the figure.

An ink drop 2 is ejected from the nozzle in a direction substantially perpendicular to the plane of the paper in FIG. 6, and the ink drop 2 is deflected in the direction of arrow C by a deflection pole 7 (not shown) depending on the amount of electrical charge. be done.

In FIG. 6, near the flight path of an ink drop 2 ejected from a predetermined nozzle of an inkjet printer, light generated by a light source 1 is emitted at a stitch point of the ink drop 2 or an area corresponding to the stitch point. Light emitting optical fibers 3 and 5 are arranged so as to emit light. The stitch points are the ends of the deflection (scanning) area of the ink drop 2 ejected from the nozzle.

7 and 9 are optical fibers for receiving light emitted from the light emitting optical fibers 3 and 5.

The light-receiving optical fibers 7 and 9 are arranged in sets of two, and each fiber is arranged in the nozzle arrangement direction X.

FIG. 7 is an enlarged view of the area shown in FIG. 6, and FIG. 8 is a difference in the amount of light incident on the optical fibers 7B and 7A in FIG. 3 is a graph showing the relationship between the amount of light emitted (amount of light emitted) and the position of an ink drop in the nozzle arrangement direction X.

In FIG. 7, the same reference numerals as in FIG. 6 represent the same or equivalent parts.

First, in FIG. 7, when an ink drop is charged with a predetermined amount of charge and the ink drop is flown onto the optical path of light emitted from the light emitting optical fiber 3, the optical fiber 7A and/or the optical fiber A shadow 10 of the ink drop is formed on the light receiving surface of the optical fiber 7B.
The amount of light incident on A and/or the optical fiber 7B is reduced.

As shown by the reference numeral 2A in FIG. 7, when an ink drop passes through the center of the optical path of the light emitted from the light emitting optical fiber 3, the ink drop is evenly distributed on the optical fiber 7A and the optical fiber 7B. A shadow 10 is formed.

When the ink drop moves from the position 2A in the C1 direction, the shadow 10 also moves toward the light-receiving surface side of the optical fiber 7B, and the amount of light incident on the optical fiber 7B is equal to that of the optical fiber 7A.
The amount of light incident on the

Conversely, when the ink drop moves from the position of 2A in the direction C2, the shadow 1o also moves to the light receiving surface side of the optical fiber 7A, and the amount of light incident on the optical fiber 7A changes to the amount of light incident on the optical fiber 7B. It will be less than the amount of light.

That is, the position of the ink drop in the nozzle arrangement direction Assuming that the ink drop is at point E in Fig. 8, the difference in the amount of light incident on the optical fiber 7B and the optical fiber 7A when the ink drop moves from 2A to 01 or C2 direction is shown in Fig. 8. It changes like this.

In this way, the position of the ink drop can be detected by detecting the difference in the amount of light incident on the optical fiber 7B and the optical fiber 7A.

Now, returning to FIG. 6 again, near the flight path of the ink drop 2, a light emitting optical fiber 4 and a light receiving optical fiber 8 are further arranged. The light emitting optical fiber 4
are arranged so that the light generated by the light source 1 is emitted at a predetermined angle with respect to the sagittal direction Y.

The position detection of the ink drop in the sagittal direction Y is performed using the light emitting optical fiber 4 and the light receiving optical fiber 8.
This is done using The method of detecting the position of this ink drop in the sagittal direction Y is well known and will therefore be omitted.

By the way, in the drop sensor shown in FIG. 6, the light emitting surface and the light receiving surface of the optical fiber must be installed on the flight path of the ink drop, but this installation work is difficult because the optical fiber itself is extremely thin. Therefore, it has to be done manually, which is extremely troublesome. Furthermore, it takes time to adjust the position after installation.

This tendency is particularly strong in inkjet printers having multi-nozzle heads because the number of optical fibers increases in accordance with the number of nozzles.

As a result, the drop sensor cannot be mass-produced, and its manufacturing cost increases.

In order to eliminate the above drawbacks, a drop sensor has been proposed that consists of an LED and a photodetector using an A-8i (amorphous silicon) thin film instead of using an optical fiber.

FIG. 9 is a schematic perspective view of a drop sensor consisting of an LED and a photodetector.

In FIG. 9, LEDs 19A to 19C are arranged near the flying path of the ink drop 2 ejected from the droplet generating device of the inkjet printer so that, for example, light is emitted onto the stitch points of the ink drop 2. There is.

The number of LEDs is determined according to the number of ink ejecting nozzles.

The photodetector sets 20 to 22 are connected to the LEDs 19A to 22.
It is arranged on the substrate so that it can receive the light emitted from 19C. Said photodetector set 2
0 to 22 each consist of a pair of a-8t thin films arranged adjacent to each other.

The LEDs 19A to 19C are configured to irradiate light only to the photodetector sets 20 to 22 facing each other. That is, for example, the LED 19B is configured to emit light in a range indicated by Fl, and can irradiate only the photodetector set 21 with the light.

One of the thin films of the photodetector sets 20 to 22 has a signal line 2 printed directly on the substrate on which the thin film is formed.
3, and the other thin film is connected to signal line 2.
Connected to 4.

In the drop sensor having the above configuration, for example, L
When the ink drop 2 passes on the optical path of the light emitted from the ED 19 B, a shadow 1 appears on the photodetector set 21.
1 is formed, and the amount of light incident on each thin film constituting the photodetector set 21 changes. Therefore, if the difference in the amount of light incident on each thin film, that is, the difference in the photocurrent output from each thin film, is detected from the signal lines 23 and 24, the position of the ink drop 2 in the nozzle arrangement direction X can be detected. be able to.

As mentioned above, since the thin films on one side and the thin films on the other side that make up each ink drop are connected to the common signal line 23 and 24, respectively, the nozzle arrangement direction of the ink drops ejected from each nozzle The position of X is detected by sequentially lighting up the LEDs 19A to 19C.

The position of the ink drop in the sagittal direction Y is detected by flying the ink drop onto the stitch point and calculating the sum of photocurrents output from a pair of thin films forming each photodetector set.

That is, when the position of the ink drop in the sagittal direction Y changes, the size of the shadow formed on the photodetector set also changes in accordance with the change. Therefore, if the relationship between the size of the shape, in other words, the sum of the photocurrents output from the pair of thin films, and the position of the ink drop in the sagittal direction Y is determined in advance, The position in Y can be detected.

In the drop sensor shown in FIG. 9, a
Since the -Si thin film can be deposited on the substrate, mass production of the ink drops is possible.

Furthermore, it is easy to attach the substrate inside the inkjet printer.

(Problems to be Solved by the Invention) The above-described conventional techniques had the following problems.

(1) As mentioned above, conventionally, in order to detect the position of an ink drop in the nozzle arrangement direction A circuit is required to detect the difference in the photocurrents generated, and in order to detect the position of the ink drop in the sagittal direction Y, a pair of a
A circuit is required to detect the sum of photocurrents output from the -8i thin film.

As described above, since both a circuit for detecting the difference in photocurrent and a circuit for detecting the sum are required, the configuration of the conventional ink drop position detection device is complicated.

Moreover, the production cost also increases.

(2) In a drop sensor consisting of an LED and a pair of a-3i thin films, the drop sensor is placed in a dark box so that only the illumination light from the LED is incident on the a-8i thin film.

However, since the dark box is provided with an opening so that an ink drop can pass through the dark box, in reality, some light other than the LED illumination light enters the a-8i thin film. .

As shown in Figure 9, if each a-Si thin film is connected to a common output line, the photocurrent will be output from other thin films than the one from which the photocurrent is extracted. , the photocurrent taken out from the output line increases.

When detecting the photocurrent difference, the increase in the photocurrent difference cancels each other out and does not significantly affect the position detection of the ink drop in the nozzle arrangement direction X. However, when detecting the sum of the photocurrents, is doubled, so there is a risk that the position detection of the ink drop in the sagittal direction Y may become inaccurate.

Furthermore, even if noise is mixed into the photocurrent obtained from the output line, the noise will be doubled when detecting the sum of the photocurrents, so the sagittal direction of the ink drop
position detection may become inaccurate.

The present invention has been made to solve the above-mentioned problems.

(Means and operations for solving the problems) In order to solve the above-mentioned problems, the present invention provides a light detection means configured by arranging two photodetectors in the nozzle arrangement direction, and A plurality of drop sensors each consisting of an illumination means arranged to illuminate are provided in the nozzle arrangement direction, and a photocurrent difference detection means is provided for detecting a difference in photocurrent output from a pair of photodetectors of each of the light detection means. In the ink drop position detection device, - the ink drop ejected from the nozzle is located adjacent to the nozzle according to the maximum value of the difference in photocurrent output from the pair of photodetectors when the ink droplet passes over the pair of photodetectors. The difference obtained by subtracting the maximum value of the difference in the photocurrent output from the photodetectors when the ink droplets ejected from the two nozzles pass over the pair of photodetectors, and the difference between the ink droplets ejected from the two nozzles. A memory in which a plurality of types of ink drops are stored in which the relationship of relative positional deviation in the sagittal direction is stored according to the position of the ink drop in the sagittal direction, and a pair of ink drops ejected from one nozzle of two adjacent nozzles. The output from the photodetector when the ink drop ejected from the other nozzle passes over the pair of photodetectors is determined by the maximum value of the difference in the photocurrent output from the photodetector when the ink droplet is ejected from the other nozzle. ejecting from the two nozzles based on the stored contents of the memory using means for calculating a difference by subtracting the maximum value of the difference in photocurrents, and the numerical difference and the position information of one of the ink drops in the sagittal direction. In this embodiment, the position of the ink drop in the sagittal direction can be determined without providing a circuit for calculating the sum of photocurrents. The feature is that it is possible to do this.

(Example) The present invention will be described in detail below with reference to the drawings.

FIG. 3 is a plan view of an ink drop ejection deflection device and a drop sensor of a charge-controlled inkjet blink, which are applied to the first and second embodiments of the present invention, which will be described later;
FIG. 4 is a front view of the drop sensor shown in FIG. 3, viewed from the ink drop jetting direction. In each figure, the same reference numerals refer to the same or equivalent parts. Also, in FIG. 3, only four nozzles are shown.

In FIG. 3, a droplet generating device 39 has a plurality of nozzles 37 formed at equal intervals.

A pair of charging electrodes 40 and a pair of deflection electrodes 38 are arranged in front of each nozzle 37, respectively.

Each of the charging electrodes 40 charges the ink drops ejected from each nozzle 37 according to image information.

A predetermined voltage is applied to each deflection electrode 38. As a result, the ink droplet flying between the pair of deflection electrodes 38 is separated from the band. Deflected according to Kfi.

The printing surface 300 of an ink drop, or the printing surface 300
A drop sensor 201 is placed on the surface corresponding to the stitch point of each ink drop or at a position corresponding to the stitch point.
~203 are arranged.

The drop sensors 201 to 203 include a pair of photodetectors 201A, 201B, and 202A arranged adjacent to each other in the nozzle arrangement direction X, as shown in FIG.
and 202B, and 203A and 203B, and illumination means 201C to 203C configured to illuminate only the light detection means.

As each of the photodetectors, for example, an a-3i thin film can be used, and as each of the illumination means, for example, an LED can be used.

Now, in the drop sensor configured in this way, by detecting the difference in photocurrent output from the pair of photodetectors, it is possible to determine whether the ink drop has passed through a stitch point or a position corresponding to the stitch point. (Detection of position of ink drop in nozzle arrangement direction X)
can be done.

First, an ink drop passing between the drop sensor 201 and the drop sensor 202 shown in FIG. 3 is ejected from the nozzle 37A. By gradually changing the voltage applied to the charging electrode 40A for charging the ink drop, the position of the ink drop passing through the printing surface 300 is gradually moved in the direction of arrow U in FIG. 4.

As a result, the photodetector 202A shown in FIG.
The shadow of the ink drop 2U begins to form more gradually, and when the ink drop 2U reaches the stitching point, the shape is formed in the center of the photodetectors 202A and 202B. If the ink drop 2U is further moved in the direction of the arrow U, the shadow of the ink drop 2U will move to the photodetector 202B.

At this time, the difference obtained by subtracting the photocurrent of photodetector 202B from the photocurrent of photodetector 202A first increases in the negative direction, as shown by arrow U in curve P in FIG. 5, and then becomes zero at the stitch point. After that, it increases in the positive direction.

Therefore, if it is detected that the charging current difference changes from negative to positive, it is inferred that the ink drop has passed the stitch point at that time.

Further, the ink drop passing between the drop sensor 202 and the drop sensor 203 shown in FIG. 3 is ejected from the nozzle 37B. If the voltage applied to the charging electrode 40B for charging this ink drop is gradually changed, and the position of the ink drop passing through the printing surface 300 is gradually moved in the direction of the arrow V in FIG. The shadow of the ink drop 2V is gradually formed from the photodetector 202B side in the figure.

At this time, the difference obtained by subtracting the photocurrent of the photodetector 202B from the photocurrent of the photodetector 202A first increases in the positive direction as shown by the arrow V in the curve Q of FIG. 5, and then becomes zero at the stitch point. After that, it increases in the negative direction.

Now, in FIG. 4, when comparing the positions in the sagittal direction Y of the ink drop 2U ejected from the nozzle 37A (FIG. 3) and the ink drop 2V ejected from the nozzle 37B (FIG. 3), the ink The drop 2v is closer to the illumination means 202C than the ink drop 2U. Therefore, the shadow formed by the ink drop 2V on the light detection means consisting of the pair of photodetectors 202A and 202B is larger than that by the ink drop 2U. Therefore, the maximum absolute value of the difference obtained by subtracting the photocurrent output from the photodetector 202B from the photocurrent output from the photodetector 202A is as shown in FIG.
The effect q caused by the ink drop 2 is larger than the effect p caused by the ink drop 2.

In this way, the maximum absolute value of the photocurrent difference output from a pair of photodetectors of any one drop sensor is determined for ink drops ejected from two adjacent nozzles, and the difference between them is detected. By this, the ink droplet ejected from the two nozzles,
A relative positional shift in the sagittal direction Y can be detected.

- Deflecting the ink droplet ejected from the nozzle so that it passes over the photodetector on the nozzle side of the pair of photodetectors, and determining the absolute value of the difference in photocurrent output from the pair of photodetectors. The charging voltage of the ink drop when is maximum,
Similarly, an ink drop ejected from a nozzle disposed adjacent to the nozzle is deflected so as to pass over the photodetector on the nozzle side of the pair of photodetectors, and Find the charging voltage of the ink drop when the absolute value of the difference between the photocurrents output from the photodetector is maximum, and use these charging and charging voltages to simultaneously fly the ink drop from the two nozzles, At this time, the position of the ink drop in the sagittal direction Y can also be detected by determining the difference between the photocurrents output from the pair of photodetectors.

By the way, even if the difference in the maximum absolute value of the photocurrent difference output from a pair of photodetectors is the same, the difference between two ink droplets ejected from adjacent nozzles will differ depending on whether the ink drop is moving away from the photodetector or approaching it. The relative positional displacement of the ink drops in the sagittal direction Y is different. That is, since the shadow formed on the photodetector when the ink drop is moving away from the photodetector is larger than the shadow formed on the photodetector when the ink drop is approaching the photodetector, two nozzles adjacent to each other Even if the difference in the maximum absolute value of the photocurrent difference determined by the ink drops ejected from the photodetector is the same, the relative difference in the sagittal direction Y of the ink drops when the ink drops are far from the photodetector is The actual displacement is smaller than the displacement when the ink drop approaches the photodetector.

Therefore, in the present invention, first, two adjacently arranged
The relationship between the relative positional deviation in the sagittal direction Y of ink drops ejected from two nozzles and the difference in the maximum absolute value of the photocurrent difference output from a pair of photodetectors is expressed as the position of the ink drop in the sagittal direction. Prepare multiple types in memory in advance as parameters. Furthermore, the position of the ink drop ejected from the - nozzle among the plurality of nozzles in the sagittal direction Y is detected using a conventional method. In the following description, a nozzle that ejects an ink drop whose position in the sagittal direction Y has been detected will be referred to as a reference nozzle.

and the data in the memory corresponding to the position in the sagittal direction Y of the ink drop ejected from the reference nozzle, the reference nozzle, and the ink drop ejected from the nozzle arranged adjacent to the reference nozzle. The sagittal direction Y of the ink drop ejected from the nozzle arranged adjacent to the reference nozzle is determined using the difference between the maximum absolute values of the photocurrent differences detected using the
The position of the object is detected.

FIG. 1 is a schematic block diagram showing the configuration of a first embodiment of the present invention.

In FIG. 1, the same reference numerals as in FIG. 3.4 represent the same or equivalent parts.

In addition, in order to make the diagram easier to read, we have added an ink ejection nozzle (
37, 37A, 37B, 37S), and a drop sensor consisting of an illumination means and a pair of photodetectors (
201, 202, 203...) are shown six each. Further, the drop sensor is shown in a front view as seen from the ink drop ejection direction, and the droplet generator 39, charging electrodes 40, 40A, 40B, 40S, and deflection electrode 38 are shown in a direction perpendicular to the ink drop ejection direction. It is shown in a plan view.

In FIG. 1, lighting means (201C, 202C, 203C, etc.) such as LEDs arranged at the stitch points of each nozzle or at positions corresponding to the stitch points are connected to a power supply device 103 via a switching device 102. has been done. The switching device 102 sequentially turns on each of the lighting means in response to a control signal supplied from the control device 101.

A pair of photodetectors (201A) of light detection means are arranged to face each of the illumination means.

B, 202A, B, 203A, B...) are connected to output lines 111A and 112A, respectively.

The output lines 111A and 112A are connected to an optical TK current difference detection device 105.

The charge current difference detection device 105 calculates the difference between two manually input signals, that is, the difference between the photocurrents output from a pair of photodetectors, and sends the result to the control device 1.
01, the control device 10
1 or output to the maximum value detection device 108.

The maximum value detection device 108 is the charging current difference detection device 1.
The maximum value or the maximum absolute value of the photoelectric field 2 outputted from the photovoltaic generator 05 is detected, and when the maximum value is detected, a signal to that effect is output to the control device 101, and the control device 101
The maximum value is output to the maximum value memory 109 or the subtraction circuit 110 according to the control signal output from the maximum value memory 109 or the subtraction circuit 110.

The maximum value memory 109 is connected to the charge current difference detection device 10.
The maximum value or the maximum absolute value of the photoelectronic plating output from the controller 5 is temporarily stored, and the maximum value is output to the subtraction circuit 110 in response to a control signal output from the controller 101.

The subtraction circuit 110 subtracts the data output from the maximum value detection device 108 from the data output from the maximum value memory 109, or subtracts the data output from the maximum value detection device 108 from the data output from the maximum value detection device 108. memory 1
09 and outputs the result to the control device 101.

A data memory 111 is connected to the control device 101. The data memory 111 stores the relative positional deviation in the sagittal direction Y of ink drops ejected from two adjacent nozzles, and the ink drop ejected from one of the two nozzles. From the maximum value of the difference in photocurrent output from a pair of photodetectors when the photocurrent passes over the photodetectors,
Data representing the relationship between the ink droplet ejected from the other nozzle and the difference obtained by subtracting the maximum value of the difference in photocurrent output from the pair of photodetectors when the ink droplet ejected from the other nozzle passes over the pair of photodetectors, or A plurality of types are stored using positions in the sagittal direction Y as parameters.

Nozzles 37° 37A, 3 formed in the droplet generator 39
Charging electrode 40.40A for charging the ink drops flying from 7B and 37S.

40B and 40S are each connected to the high voltage generator 107.

The high voltage generator 107 generates a predetermined voltage according to a control signal supplied from the control device 101, and supplies the voltage to a predetermined selected charging electrode. This changes the amount of charge on the ink drop, that is, the amount of deflection.

In the ink drop position detection device having the above configuration, for example, the charging voltage when the flying ink drop ejected from the nozzle 37A passes both stitch points is determined as described below.

First, the illumination means 201C is selected by the switching device 102, and the illumination means 201C is turned on.
A photodetector 201A arranged to face the
, 201B only.

Next, the ink drop ejected from the nozzle 37A,
A photodetector 20 facing the illumination means 201C
1A, B and the illumination means 201C, that is, the photodetector 201A.
, B such that the photocurrent difference between them becomes zero.
7 adjusts the charging voltage of the ink drop applied to the charging electrode 40A.

In this way, the charging voltage when the ink drop passes through the center of the drop sensor 201 is detected.

That is, the charged electrode is detected by the control device 101 when it is detected by the control signal 101 that the polarity of the photocurrent difference outputted from the charging current difference detection device 105 has changed.

Next, the lighting means 202C is selected by the switching device 102, and the lighting means 202C is turned on.
A photodetector 202 arranged to face C
Light is irradiated only to A and B.

Then, the charging voltage of the ink drop applied to the charging electrode 40A is adjusted by the high voltage generator 107 so that the ink drop passes through the center of the drop sensor 202.

In this way, the charging voltage when the ink drop passes through the center of the drop sensor 202 is detected. In this way, the charging voltage of the ink drop passing through each stitch point is determined for each nozzle.

Thereafter, in the control device 101, the voltage applied to the charging electrode (the charging voltage of the ink drop), which is applied according to the image information, is adjusted by a known method using each of the charging voltages, and the voltage applied to the charging electrode (the charging voltage of the ink drop) is adjusted according to the image information. The area is set. As a result, good printing is performed without missing or overlapping characters.

Detection of the position of the ink drop in the sagittal direction Y is performed as follows.

It is assumed that the position in the sagittal direction of the ink drop ejected from the nozzle 37S (reference nozzle) is determined in advance by a conventional method.

First, the illumination means 201C is selected by the switching device 102, and the illumination means 201C is turned on.
A photodetector 201A arranged to face the
, B is irradiated with light.

Next, the charging voltage of the ink drop applied to the charging electrode 40S is adjusted by the high voltage generator 107 so that the ink drop ejected from the nozzle 37S passes the drop sensor 201.

Charge current difference detection device 105 outputs the photocurrent difference between photodetectors 201A and 201B to maximum value detection device 108 according to a command from control device 101.

When the maximum value detection device 108 detects the maximum value of the absolute value of the photocurrent difference, it sends a signal to that effect to the control device 10.
1, and also outputs the maximum value to the maximum value memory 109 based on the control signal output from the control device 101. The maximum value memory 109 stores the maximum value.

When the maximum value detection device 108 detects the maximum absolute value of the photocurrent difference, the control device 101 performs charging to charge an ink drop ejected from a nozzle 37A disposed adjacent to the nozzle 37S. The charged electrode 40A is selected by the high voltage generator 107 so that the ink drop passes through the drop sensor 201.
Adjust the charging voltage of the ink drop applied to the ink drop.

The charge current difference detection device 105 again detects the photocurrent difference between the photodetectors 201A and 201B by the maximum value detection device 1.
Output on 08.

When the maximum value detection device 108 detects the maximum value of the absolute value of the photocurrent difference, it sends a signal to that effect to the control device 10.
1, and the control device output from the control device 101 outputs the maximum value to the subtraction circuit 110. When the maximum value detection device 108 detects the maximum absolute value of the photocurrent difference, the control device 101 activates the maximum value memory 109 and converts the stored contents of the maximum value memory 109 into a subtraction circuit. 110.

The subtraction circuit 110 calculates the difference between the signals output from the maximum value detection device 108 and the maximum value memory 109, and outputs the result to the control device 101.

The control device 101 controls the relative positional deviation in the sagittal direction Y of the ink drops ejected from two adjacent nozzles according to the position information in the sagittal direction Y of the ink drop ejected from the nozzle 37S. and,
output from the photodetector when the two types of ink drops pass over the pair of photodetectors;
A table showing the relationship between the absolute value of the photocurrent difference and the difference in the maximum value is selected from the data memory 111. Then, information indicating the relative positional deviation of the ink drop in the sagittal direction Y, which corresponds to the information output from the subtraction port 110, is read from the table. The read data indicates the positional deviation in the sagittal direction Y of the ink drops ejected from the nozzles 37S and 37A.

After that, the control device 101 adds the positional deviation information and the positional information in the sagittal direction Y of the ink drop ejected from the nozzle 37S, and from this, the positional information in the sagittal direction Y of the inkdrop ejected from the nozzle 37A is obtained. is calculated.

In this way, once the position of the ink drop in the sagittal direction Y is detected, the position in the sagittal direction Y of the ink drop ejected from the nozzle adjacent to the nozzle that ejects the ink drop whose position has been detected is sequentially detected. Let's do it.

Once the positions of the ink drops ejected from all the nozzles in the sagittal direction Y are detected, based on that information, for example, the flight timing of the ink drops ejected from each nozzle is adjusted.

FIG. 2 is a schematic block diagram showing the configuration of a second embodiment of the present invention. In Figure 2, the same symbols as in Figure 1 are
Since the same or equivalent parts are referred to, their explanation will be omitted.

In FIG. 2, the charging voltage memory 112 is connected to the control device 1.
01. The charging voltage memory 112 is
The ink drop charging voltage when the absolute value of the photocurrent difference outputted from the maximum value detection device 108 becomes the maximum is stored.

In the ink drop position detecting device having the above configuration, the position detection of the ink drop in the sagittal direction Y is performed as shown below.

It is assumed that the position in the sagittal direction of the ink drop ejected from the nozzle 37S (reference nozzle) is determined in advance by a conventional method.

First, the lighting means 201c is selected by the switching device 102, and the lighting means 201C is turned on.
A photodetector 201A arranged to face the
, B is irradiated with light.

Next, the charging voltage of the ink drop applied to the charging electrode 40S is adjusted by the high voltage generator 107 so that the ink drop ejected from the nozzle 37S passes the drop sensor 201.

When the maximum value detection device 108 detects the maximum value of the difference between the photocurrent outputted from the photodetector 201B and the photocurrent outputted from the photodetector 201A, which is outputted from the charging current difference detection device 105, it detects the difference. The signal is output to the control device 101. The control device 101 controls the charging voltage of the ink drop at this time (charging electrode 40
The voltage applied to S) is output to the charging voltage memory 112 and stored in the charging type press-fitting memory 112.

Next, the charging voltage of the ink drop applied to the charging electrode 40A is adjusted by the high voltage generator 107 so that the ink drop ejected from the nozzle 37A passes the drop sensor 201.

The maximum value detection device 108 is the negative maximum value of the difference obtained by subtracting the photocurrent output from the photodetector 201A from the photocurrent output from the photodetector 201B, which is output from the charging current difference detection device 105, in other words, the photodetector 201A. When the maximum value of the difference obtained by subtracting the photocurrent output from the photodetector 201B from the photocurrent output from the photodetector 201B is detected, a signal to that effect is output to the control device 101. The control device 101 outputs the charging voltage of the ink drop at this time (the voltage applied to the charging electrode 40A) to the charging voltage memory 112, and stores it in the charging voltage memory 112.

Then, the charging electrode 40S, the band Ti, and the electrode 40A are selected, and the charging electrodes 40S and 40A are energized again using the charging voltage stored in the charging voltage memory 112. Then, ink drops are simultaneously ejected from the nozzles 37S and 37A.

At this time, the difference between the photocurrents output from the photodetectors 201A and 201B is output from the charge current difference detection device 105 to the control device 101.

As described above with reference to FIG. 1, the control device 101 controls the position of ink drops ejected from two adjacent nozzles in accordance with the position information in the sagittal direction Y of the ink drop ejected from the nozzle 37S. A table is selected from the data memory 111 that shows the relationship between the relative positional shift in the sagittal direction Y and the difference between the maximum values of photoelectric deposition output from a pair of photodetectors. and,
Based on the difference in photocurrent output from the charge current difference detection device 105, relative positional shift information of the ink drop in the sagittal direction Y is read from the table.

By adding the positional deviation information to the position information in the sagittal direction Y of the ink drop ejected from the nozzle 37S, the position information in the sagittal direction Y of the ink drop ejected from the nozzle 37A is calculated.

In the embodiment described above, the position of the ink drop can be detected even if the ink drop is ejected one drop at a time intermittently or continuously, that is, by using a continuous ejection layer.

When using a continuous ejection layer, in order to reduce fluctuations in the photocurrent output from the photodetection means, the interval between the ink drops should be smaller than the width of the photodetection means in the ink drop flying direction. In other words, it is preferable to have a large number of ink drops formed on the photodetecting means.

Furthermore, in the above description, the photodetecting means is constructed of a pair of a-St thin films, but the present invention is not limited to this, and two other elements are arranged in the X direction. It goes without saying that the light detection means may be constructed by arranging them side by side.

Furthermore, although the illumination means has been described as being an LED, the present invention is not particularly limited to this, and it goes without saying that other illumination means may be used.

Furthermore, in the above description, the drop sensor is applied to a charge control type inkjet printer, but the present invention is not limited to this, and is applicable to an electric field control type inkjet printer. Of course, it may be applied.

(Effects of the Invention) As is clear from the above description, according to the present invention, the following effects are achieved.

(1) Since the position of the ink drop in the sagittal direction Y can be calculated using the charge current difference detection device, there is no need to provide a circuit for detecting the sum of photocurrents. Therefore, the ink drop position detection device can be manufactured at low cost.

(2) The position of the ink drop in the sagittal direction Y can be calculated by detecting the difference in photocurrent.
L facing the photodetector
Even if light other than the illumination light of the ED is incident or electrical noise is mixed into the photocurrent, these are canceled out, so the position can be detected accurately.

[BRIEF DESCRIPTION OF THE DRAWINGS] FIG. 1 is a schematic block diagram showing the structure of a first embodiment of the present invention, FIG. 2 is a schematic block diagram showing the structure of a second embodiment of the present invention, and FIG. 4 is a plan view of an ink drop ejection deflection device and a drop sensor applied to each embodiment of the present invention, FIG. 4 is a front view of the drop sensor shown in FIG. 3, viewed from the ink drop ejection direction, and FIG. Graph showing the relationship between the position of an ink drop passing through the drop sensor in the nozzle arrangement direction X and the difference in photocurrent output from a pair of photodetectors. FIG. The figure is an enlarged view of the area in FIG. 6, and FIG. 8 is a graph showing the relationship between the difference in the amount of light incident on the optical fibers 7B and 7A in FIG. 7 and the position of the ink drop in the nozzle arrangement direction X. FIG. 9 is a schematic perspective view of a drop sensor consisting of an LED and a photodetector. 2.2U, 2V...Ink drop, 37.3
7A, 37B, 37S... Nozzle, 38...
Deflection electrode, 39...droplet generator, 40° 40A, 4
0B, 40S...Charging electrode, 101...Control device,
1α2...Switching device, 103...Power supply device, 105
...Charging current difference detection device, 107...High voltage generator, 108...Maximum value detection device, 109...Maximum value memory, 110...Subtraction circuit, 111...Data memory, 112 ...Charging voltage memo, 201-203
...Drop sensor, 201A, 201B, 202A
, 202B, 203A, 203B... Photodetector, 201C, 202C, 203C... Illumination means, 3
00...Printed surface

Claims (1)

[Claims] (1) A plurality of drop sensors are provided in the nozzle arrangement direction, each consisting of a light detection means configured by arranging two photodetectors in the nozzle arrangement direction, and an illumination means arranged to illuminate the light detection means; An ink drop position detection device equipped with photocurrent difference detection means for detecting a difference between photocurrents output from a pair of photodetectors of each photodetection means, the ink droplet ejected from an arbitrary nozzle is From the maximum value of the difference in photocurrent output from the photodetector when passing over the photodetector, the ink drop ejected from the nozzle disposed adjacent to the nozzle is determined to be , the relationship between the difference obtained by subtracting the maximum value of the difference between the photocurrents output from the photodetector and the relative positional shift in the sagittal direction of the ink drops ejected from the two nozzles is the sagittal position of the ink drop. When an ink drop ejected from one of two adjacent nozzles passes over a pair of photodetectors, the difference in photocurrent output from a pair of photodetectors is stored. means for calculating a difference by subtracting a maximum value of the difference in photocurrent output from the pair of photodetectors when an ink drop ejected from the other nozzle passes over the pair of photodetectors from the maximum value; Using the difference and the sagittal position information of one of the ink drops, the two
An ink drop position detection device comprising: means for reading a relative positional shift in the sagittal direction of ink drops ejected from two nozzles.