JPH08166553A - Image recorder - Google Patents

Abstract

PURPOSE: To extremely easily change image density and resolution. CONSTITUTION: A laser beam reflected from the respective reflection surfaces of a polygon mirror 115 is received by an original-point detection sensor S1 and the light receiving signal thereof is inputted to a controller 121. By the controller 121, image data is outputted to a laser driver 123 prescribed time after the respective input timing of the light receiving signals when the resolution is (d) and outputted to the driver 123 the prescribed time after the second or third input timing of the light receiving signal when the resolution is d/2 or d/3. Besides, the mirror 115 is constituted of the plural reflection surfaces whose reflectivity is different and the timing that the image data is outputted from the controller 121 is selected according to the set image density.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image recording device such as a laser beam printer which irradiates a photoconductor with light from a light source reflected by a reflecting surface of a rotary polygon mirror through an optical system to form an electrostatic latent image on the photoconductor surface. .

[0002]

2. Description of the Related Art An image recording apparatus such as a laser beam printer is provided with a rotary polygon mirror that rotates at a constant speed. The rotary polygon mirror reflects light from a light source such as a laser and the reflection angle associated with the rotation of the rotary polygon mirror. Scan the surface of the photoconductor. During the scanning of the surface of the photoconductor, the light source is controlled to be turned on according to the image recording signal, so that an electrostatic latent image is formed on the surface of the photoconductor line by line. Therefore, it is necessary to synchronize the output timing of the image recording signal to the light source with the rotation of the rotary polygon mirror.

Therefore, in the conventional image recording apparatus, as shown in FIG.
, The light source 8 reflected by the rotating polygon mirror 81
An origin detection sensor 83 for receiving the second light outside the image recording range of the photoconductor 84 is provided, and an image recording signal for the light source 82 based on the timing when the origin detection sensor 83 receives the light reflected by the rotary polygon mirror 81. I'm trying to start the output of. That is, the signal control means for outputting the image recording signal is equipped with a soft timer or counter which is activated by the input of the detection signal from the origin detection sensor 83 and measures a fixed time, and the soft timer or counter has timed up. At one time, the output of the image recording signal for one line is started.

[0004]

However, in the conventional image recording apparatus, the density of the image transferred from the surface of the photoconductor onto the paper is changed by changing the bias voltage of the toner or the charging potential of the photoconductor. Since it was performed, fine control such as changing the density for each line could not be performed. Further, when the resolution is changed, the rotation speed of the rotary polygon mirror is changed, so that there is a problem that a motor that stably rotates at a plurality of rotation speeds is required. Further, the rotational speed R of the motor for driving the rotary polygon mirror and the output frequency clk of the image recording signal are R = (D / 25.4) × V ÷ M clk = 4π × f × R × (D / 25.4) ). Here, D is the resolution, V is the sheet conveyance speed, M is the number of reflecting surfaces of the rotary polygon mirror, and f is the characteristic value of the optical system. Here, the characteristic value f of the optical system is f = X ÷, where X is the scanning distance that advances when the mirror rotates by θ (rad) depending on the distance from the reflecting surface of the rotary polygon mirror to the photoconductor and the characteristic of the fθ lens. Defined by 2θ. Therefore, as shown in FIG.
The rotation speed of the rotary polygon mirror and the output frequency of the image recording signal are set independently, and an independent oscillator is required for each of the image data transfer circuit and the polygon motor drive circuit,
There is a problem that the cost will rise in the future.

It is an object of the present invention to change the image density and resolution very easily, and to output the rotation frequency of the rotary polygon mirror and the output frequency of the image recording signal in the signal control means from a single oscillator. It is an object of the present invention to provide an image recording apparatus that can be produced by using a frequency signal according to the present invention and can realize cost reduction.

[0006]

According to a first aspect of the present invention, a rotary polygonal mirror for irradiating a surface of a photosensitive member with reflected light of a light source and an image recording signal synchronized with rotation of the rotary polygonal mirror are used as a light source. In the image recording apparatus provided with the signal control means for outputting, a reflecting surface selecting means for selecting a reflecting surface used for image recording among the reflecting surfaces of the rotating polygon mirror is provided.

According to a second aspect of the present invention, the rotary polygon mirror includes a first reflecting surface having a predetermined reflectance and a second reflecting surface having a reflectance lower than the reflectance of the first reflecting surface. In addition to being arranged alternately, a light amount detecting means for detecting the amount of reflected light on the reflecting surface of the rotary polygon mirror is provided, and the signal control means is configured to detect the amount of light reflected from the first reflecting surface based on the detection result of the light amount detecting means. It is characterized by including data switching means for outputting basic data of the image recording signal and outputting interpolation data of the image recording signal to the second reflecting surface. The invention described in claim 3 is a rotary polygon mirror that reflects light from a light source,
An optical system for irradiating the surface of the photosensitive member with the reflected light of the rotary polygon mirror, and a signal control means for outputting an image recording signal synchronized with the rotation of the rotary polygon mirror to the light source are provided. The output frequency clk of the image recording signal in the signal control means is D = resolution, the conveyance speed of the sheet is V, the number of reflecting surfaces of the rotary polygon mirror is M, and the characteristic value of the optical system is f = R = (D / 25. 4) × V ÷ M clk = 4π × f × R × (D / 25.4), the characteristic value f of the optical system is f = m × 25. It is characterized by being defined by 4 / (4π × D).

[0008]

According to the first aspect of the present invention, the reflecting surface used for image recording is selected by the reflecting surface selecting means from among the plurality of reflecting surfaces that form the rotary polygon mirror. Therefore, by increasing or decreasing the number of reflecting surfaces used for image recording, the resolution changes without changing the rotation speed of the rotary polygon mirror.

According to the second aspect of the invention, the image recording based on the basic data is performed by the light reflected by the reflecting surface having a high reflectance, and the second recording layer has a reflectance lower than that of the first reflecting surface. Image recording based on the interpolation data is performed by the light reflected on the reflecting surface. Therefore,
When forming an image of a curved line or a slanted line, the portion of the basic data in which the intervals of the dots are widened can be supplemented by the interpolation data, and a smooth image is formed for the curved line and the slanted line.

According to the third aspect of the present invention, the characteristic value f of the optical system, which is one of the factors that determines the output frequency of the image recording signal in the signal control means, is set to a natural number m together with the rotation number of the rotary polygon mirror. , F = m × 25.4 / (4π × D). Substituting the characteristic f of the optical system defined in this way into the equation for determining the output frequency clk of the image recording signal, clk = 4π × f × R × (D / 25.4), the output of the image recording signal is output. The frequency clk is an integral multiple of the rotational speed R of the rotary polygon mirror. A frequency signal whose ratio to one reference frequency is an integer can be easily created by a single or a plurality of frequency dividers. Therefore, by setting the characteristic value f of the optical system as described above, the rotation frequency of the rotary polygon mirror and the output frequency of the image recording signal in the signal control means can be created by the frequency signal output from a single oscillator. You can

[0011]

1 is a schematic diagram showing the structure of an image recording apparatus according to an embodiment of the present invention. A laser beam printer 100, which is an image recording apparatus, includes a photosensitive drum 101 rotatably provided at a substantially central portion of the apparatus, and a charging charger 102, a transfer charger 103, and a developing unit facing a peripheral surface of the photosensitive drum 101. A roller 109 is provided. A light beam for image recording is distributed from the optical unit 117 including the polygon mirror 115 to the photosensitive drum 101. Prior to the exposure with the light beam from the optical unit 117, the surface of the photoconductor drum 101 is charged with a single polarity by the charging charger 102. An electrostatic latent image is formed on the surface of the photoconductor drum 101 by irradiation with light rays from the optical unit 117. This electrostatic latent image is visualized by the developing roller 109.

A paper cassette 114 is mounted at the bottom of the laser beam printer 100. Paper cassette 1
The paper 107 stored in 14 is fed by the paper feed roller 108.
The sheets are fed one by one toward the photosensitive drum 101. The fed sheet 107 is guided between the photosensitive drum 101 and the transfer charger 103 in synchronization with the rotation of the photosensitive drum 101, and the transfer charger 103 forms a toner image on the surface of the photosensitive drum 101 by the transfer charger 103. Is transcribed to. The sheet 107 to which the toner image has been transferred is guided to the fixing roller 104, heated and pressed to fix the toner image, and then ejected to the upper sheet ejection tray 112 by the sheet ejection roller 105.

FIG. 2 is a schematic plan view showing the structure near the optical unit and the photosensitive drum. Optical unit 1
Reference numeral 17 is composed of an fθ lens 110, a polygon mirror 115, and a semiconductor laser 111. The light emitted from the semiconductor laser 111 is the polygon mirror 115.
The light is reflected by the reflection surface of No. 1 and is distributed to the surface of the photoconductor drum 101 via the fθ lens 110. The polygon mirror 115 rotates in the direction of arrow A in the figure, and the fθ lens 110
The laser light transmitted through the photoconductor drum 1 in the direction of arrow B in the figure.
Scan surface 01. An origin detection sensor S1 is provided outside the range of the photosensitive drum 101 in the scanning range of the laser light. The origin detection sensor S1 creates a reference timing for controlling the image start position on the photosensitive drum 101. That is, the origin detection sensor S1
Outputs a light receiving signal when it receives a laser beam, and drives the semiconductor laser 111 by an image signal after a predetermined time has elapsed from this light receiving signal. As a result, the photosensitive drum 10
The image formation start positions of the respective scan lines on 1 are aligned.

The detection signal of the origin detection sensor S1 is input to the controller 121. The controller 121 includes an image memory 122, and a resolution setting unit 13 including an operation panel or a DIP switch in the device.
The setting signal from 1 is also input. A laser driver 123 is connected to the controller 121, and the controller 121 uses the laser driver 12 based on the detection signal of the origin detection sensor S1 and the setting signal of the resolution setting unit 131.
The lighting signal So and the image data Sg are output to 3. The laser driver 123 drives the laser 111 by receiving the lighting signal So or the image data Sg.

FIG. 3 is a flowchart showing the processing procedure of the controller. A print start signal is input to the controller 121 from a print switch on the operation panel or an external terminal device. When this print start signal is input (n1), a drive signal is output to the motor driver 124 to rotate the mirror motor 125 (n2). At the same time, a lighting signal is output to the laser driver 123 (n3). The laser driver 123 drives the semiconductor laser 111 by the output of this lighting signal, and the laser light of the semiconductor laser 111 scans the surface of the photoconductor 101 in the direction of arrow B shown in FIG. 2 by the rotation of the polygon mirror 115. The reflected light of the laser light from the polygon mirror 115 enters the document detection sensor S1,
When a light reception signal is input from the origin detection sensor S1 (n
4), the controller 121 stops the output of the lighting signal (n5).

Next, the controller 121 selects the reflecting surface of the polygon mirror 115 to be used for image recording according to the resolution D set in the resolution setting section 131 (n6 to n11). That is, when the resolution setting unit 131 can select three types of resolutions d, d / 2, and d / 3, which resolution is selected is determined (n
6, n9), if a resolution of 1/3 of the maximum resolution d that can be set is set, n3 to until the content of the counter C that counts the number of times the light receiving signal of the origin detection sensor S1 is input becomes 3 The process of n5 is repeated (n7, n8).
When half the maximum value D of the settable resolution is set, n3 is set until the content of the counter C becomes 2.
The processing from to n5 is repeated (n10, n11).

When the resolution setting unit 131 sets the resolution of the maximum value d, when the resolution of d / 3 is set, the content of the counter C becomes 2, or the resolution of d / 2. When the content of the counter C becomes 1 when is set, the counter C is cleared (n12) and the timer T1 for measuring a fixed time is started (n13). The timer T1 is a time required for moving the laser beam reflected by the polygon mirror 115 to the predetermined image start position on the surface of the photosensitive drum 101 after entering the origin detection sensor S1. When this timer T1 times out (n14),
The controller 121 outputs the image data for one line of the image data stored in the image memory 122 to the laser driver 123 (n15). Laser driver 1
23 is a semiconductor laser 111 according to this image data.
Control lighting. When the output of the image data for one line is completed, it is determined whether or not the output of all the image data stored in the image memory 122 is completed (n1
6) The processes of n3 to n15 are continuously performed until the output of the image data for all lines is completed.

As described above, the controller 121 selects the reflective surface to be used for image recording from among the six reflective surfaces forming the polygon mirror 115 based on the resolution set in the resolution setting section 131. As a result, the image recording interval in the rotation direction on the surface of the photosensitive drum 101 changes, and the resolution of the recorded image can be changed.

In this embodiment, the polygon mirror 11 is used.
Although the lighting signal is output to all the reflecting surfaces of No. 5 and the detection value of the light receiving signal from the origin detection sensor S1 is changed, the output timing of the image data is changed according to the set resolution. As shown in FIG. 4, the reflecting surface of the polygon mirror 115 used for image recording can also be selected by changing the output timing of the lighting signal. That is, since the rotation speed of the polygon mirror 115 is constant, the time interval t at which the reflected light on each reflecting surface of the polygon mirror 115 enters the origin detection sensor S1.
1 is constant. Therefore, the output timing of the lighting signal is t1, t2 = t1 × according to the set resolution.
By selecting either 2 or t3 = t1 × 3,
By changing the input timing of the light receiving signal of the origin detection sensor S1 according to the resolution and outputting the image data after a lapse of a predetermined time from the input timing of each light receiving signal, the resolution of the photosensitive drum 101 in the sub-scanning direction is changed. You can

Further, although the polygon mirror 115 is used as the rotary polygon mirror in this embodiment, the number of types of resolution that can be selected can be increased or decreased depending on the number of reflection surfaces of the polygon mirror used.

FIG. 5 is a view showing the arrangement of the optical unit of a laser printer according to another embodiment of the present invention. As shown in FIG. 6, the polygon mirror 145 included in the optical system unit has reflecting surfaces 145a to 145a having different reflectances.
It is composed of 45f. Further, a light amount detection sensor S2 is provided together with the origin detection sensor S1 outside the image recording range of the photosensitive drum 101 within the irradiation range of the laser light reflected by each reflection surface of the polygon mirror 145. This light amount detection sensor S2 is a polygon mirror 14
The light amount of the laser light reflected at 5 is detected, and the light amount data is input to the controller 121. By providing the light amount detection sensor S2 at the origin position, the light amount detection sensor S2 and the origin detection sensor S1 can be used together.
Further, a density signal is input to the controller 121 from a density setting unit 132 provided on the operation panel.

FIG. 7 is a flow chart showing the processing procedure of the controller of the optical system unit. The controller 121 waits for the input of the print start signal (n21), and when the print start signal is input, outputs the drive signal of the motor 125 which supplies the rotational force to the polygon mirror 145 (n22). This causes the polygon mirror 145 to start rotating. Then, the laser driver 12
A lighting signal is output to 3 (n23). As a result, laser light is emitted from the semiconductor laser 111, and the laser light reflected by the polygon mirror 145 is received by the light amount sensor S2. The light amount sensor S2 outputs a voltage according to the amount of received light, and this voltage signal is the A / D converter 13
The light amount data is input to the controller 121 via the data No. 3. When the light amount data is input (n24), the controller 121 determines whether or not the light amount corresponds to the light amount corresponding to the density set by the density setting unit 132 (n2).
5). When the light amount data input from the light amount sensor S2 matches the light amount corresponding to the set density, the flag F1 is set (n26), and when they do not match, the flag F1 is reset (n27).

Next, the input of the light receiving signal from the origin detecting sensor S1 is awaited (n28), and when the light receiving signal is input, the output of the lighting signal is stopped (n29). As a result, the driving of the semiconductor laser 111 is stopped. Further, the state of the flag F1 is checked (n30), and when the flag F1 is reset, the timer T2 times out and then the process returns to n23 (n31, n32). This timer T2
Measures a certain period of time after the laser light reflected on one reflecting surface of the polygon mirror 145 enters the origin detection sensor S1 and before the timing of turning on the semiconductor laser 111 for the next reflecting surface. When the flag F1 is set, the image data for one line of the image data stored in the image memory 122 is output after the timer T1 times out (n35). The above n23 to n3
The process of No. 5 is executed for all the image data stored in the image memory 122 (n36).

By the above processing, image recording can be performed using only the reflecting surface that reflects the laser light with the light amount corresponding to the image density set in the density setting section 132.
An image with the set density can be output.

In this embodiment, the polygon mirror 145 is used.
Although the amount of reflected light is measured for all the reflecting surfaces of the polygon mirror 145, since the rotation speed of the polygon mirror 145 is constant, the polygon mirror 145 is detected after detecting the amount of reflected light that matches the amount of light corresponding to the set density. The lighting signal may be output to the laser driver 123 at the timing of one rotation. By doing so, it is not necessary to refer to the reflected light amount of the light amount detection sensor S2 again after once detecting the reflective surface having the reflectance corresponding to the set density, and the processing in the controller 121 can be simplified.

Although the polygon mirror 145 is used as the rotary polygon mirror in this embodiment, the number of selectable image densities can be increased or decreased by changing the number of reflection surfaces of the polygon mirror.

FIG. 8 is a diagram showing the structure of a polygon mirror used in the optical unit of the laser printer according to the second embodiment of the invention. Polygon mirror 15
Reference numeral 5 is configured by alternately arranging first reflecting surfaces having reflectance a and second reflecting surfaces having reflectance b <a. The optical unit of the polygon mirror 155 has the same structure as that shown in FIG. However, the image memory 122 included in the controller 121 is composed of basic data and interpolation data as image data.

FIG. 9 is a flow chart showing the processing procedure of the controller of the optical unit. The controller 121 is waiting for the input of the print start signal (n4
1) When a print start signal is input, a motor drive signal and a lighting signal are output (n42, n43). After that, when the light amount data is input from the light amount detection sensor S2 (n44), the flag F2 is set or reset according to the content of the light amount data (n45 to n47). Flag F
2 stores the state of whether the light amount data input from the light amount detection sensor S2 is the light amount a corresponding to the basic data or the light amount b corresponding to the interpolation data.

Thereafter, when a light receiving signal is input from the origin detecting sensor S (n47), the output of the lighting signal is stopped (n48) and the timer T1 is started (n49).
After the timer T1 times out (n50), basic data or interpolation data is output to the laser driver 124 based on the content of the flag F2 (n51 to n53).
The above processing of n42 to n53 is executed for all the image data stored in the image memory 122 (n5
4).

By the above processing, the image recording of the basic data can be performed with the laser beam of the light amount a, and the image recording of the interpolation data can be performed with the laser beam of the light amount b. As shown in FIG. 9, this interpolated data is data that supplements the space between the basic data 151. By interpolating the gaps in the basic data with the interpolated data 152, the blanks between the dots of the curved line and the diagonal line are interpolated to obtain a smooth image. Can be obtained. In this case, if the interpolation data is recorded with the same laser power as the basic data, the line becomes thick or the image becomes too dark, but in this embodiment, the light amount of the interpolation data is lower than the light amount of the basic data. It is possible to minimize the influence on the density of the entire image.

FIG. 11 is a diagram showing a configuration of a reference signal generating circuit supplied to the controller and the motor driver shown in FIGS. 2 and 5. Controller 121
Output frequency clk of the image data and the rotation speed R of the polygon motor 125 in the motor driver 124
A reference signal W 1 is provided to the controller 121 and the motor driver 124 to determine F, which is one of the factors that determines the output frequency of the image data in the controller 121 together with the rotation speed R of the polygon mirror 115
The characteristic value f of the θ lens 110 is defined by f = m × 25.4 / (4π × D) using a natural number m. Substituting the characteristic f of the optical system defined in this way into an equation for determining the output frequency clk of the image data, clk = 4π × f × R × (D / 25.4), clk = m × R Therefore, the output frequency clk of the image data becomes an integral multiple of the rotation speed R of the polygon mirror 115.

Therefore, the oscillation pulse output from the single crystal oscillator 161 is frequency-divided by the frequency divider 162 and supplied to the controller 121 as a reference signal for determining the output frequency clk of the image data. The frequency is divided by the frequency divider 163, and the motor driver 12 is used as a reference signal for determining the rotation speed R of the polygon motor 125.
4 Here, the frequency division ratio of the frequency divider 162 is m times the frequency division ratio of the frequency divider 163.

With this configuration, the reference signal to be supplied to the controller 121 and the motor driver 124 can be created from the oscillation pulse of the single crystal oscillator 161, and the controller 121 and the motor driver 124 can be supplied with the reference signal. There is no need to provide a separate crystal oscillator.

[0034]

According to the invention described in claim 1, a rotary polygon mirror is constituted by a plurality of reflecting surfaces having a uniform reflectance or a plurality of reflecting surfaces having different reflectances. By selecting the reflective surface used for image recording, there is an advantage that the resolution or the image density can be changed without controlling the rotation speed of the rotary polygon mirror or the light amount of the light source.

According to the second aspect of the present invention, the image recording of the basic data is performed by the light source light reflected by the first reflecting surface, and the image recording of the interpolation data is performed by the light source light reflected by the second reflecting surface. Thus, the gap of the basic data can be compensated by the interpolation data having a density lower than that of the basic data, and it is possible to obtain an image of a smooth curve or a slanted line, and it is possible to prevent the image density from largely changing.

According to the invention described in claim 3, the reference block of the drive circuit of the motor for driving the rotary polygon mirror and the reference clock in the output circuit of the image data are created from the reference signal transmitted from the same transmitter. Therefore, it is not necessary to provide a separate oscillator for each of the drive circuit of the motor that supplies the rotating force to the rotary polygon mirror and the output circuit of the image data, and the configuration of the device can be simplified to realize cost reduction. There is an advantage that can be.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing a configuration of a laser printer according to an embodiment of the invention described in claim 1.

FIG. 2 is a diagram showing a configuration of an optical unit of the laser printer.

FIG. 3 is a flowchart showing a processing procedure of a controller in the optical unit.

FIG. 4 is a timing chart of signals in an optical unit of a laser printer according to another embodiment of the present invention.

FIG. 5 is a diagram showing a configuration of an optical unit of a laser printer according to still another embodiment of the present invention.

FIG. 6 is a diagram showing a configuration of a polygon mirror of the optical unit.

FIG. 7 is a flowchart showing a processing procedure of a controller of the optical unit.

FIG. 8 is a diagram showing a configuration of a polygon mirror included in a laser printer according to an embodiment of the invention described in claim 2;

FIG. 9 is a flowchart showing a processing procedure of a controller of an optical unit including the polygon mirror.

FIG. 10 is a diagram showing an image forming state by the laser printer.

FIG. 11 is a diagram showing a reference signal generating circuit for a controller and a motor driver in the laser printer of the present invention.

FIG. 12 is a diagram showing a configuration of an optical unit of a conventional laser printer.

FIG. 13 is a diagram showing a reference signal generation circuit for an image data transfer circuit and a polygon motor drive circuit in the conventional laser printer.

[Explanation of symbols]

 100-laser printer (image recording device) 101-photosensitive drum 117-optical unit 115-polygon mirror (rotating polygon mirror) 111-laser (light source) 110-fθ lens S1-origin detection sensor S2-light amount detection sensor (light amount detection) means)

Claims (3)

[Claims] 1. An image recording apparatus comprising: a rotary polygon mirror for irradiating the surface of a photosensitive member with reflected light of a light source; and a signal control means for outputting an image recording signal synchronized with the rotation of the rotary polygon mirror to a light source. In the image recording apparatus, a reflecting surface selecting means for selecting a reflecting surface used for image recording among the reflecting surfaces of the rotary polygon mirror is provided. 2. The rotating polygon mirror is configured by alternately arranging first reflecting surfaces having a predetermined reflectance and second reflecting surfaces having a reflectance lower than the reflectance of the first reflecting surfaces. At the same time, a light amount detecting means for detecting the amount of reflected light on the reflecting surface of the rotary polygon mirror is provided, and the signal control means outputs the basic data of the image recording signal to the first reflecting surface based on the detection result of the light amount detecting means. The image recording apparatus according to claim 1, further comprising a data switching unit that outputs the interpolation data of the image recording signal to the second reflecting surface. 3. A rotating polygonal mirror for reflecting light from a light source, an optical system for irradiating the surface of a photosensitive member with reflected light from the rotating polygonal mirror, and a signal for outputting an image recording signal which is the same as the rotation of the rotating polygonal mirror to a light source. Control means, and the output frequency clk of the image recording signal in the rotational speed R of the rotary polygon mirror and the signal control means.
Where R is (D / 25.4) × V ÷ M clk = 4π × f, where D is the resolution, V is the transport speed of the paper, M is the number of reflecting surfaces of the rotary polygon mirror, and f is the characteristic value of the optical system. In the image recording apparatus defined by × R × (D / 25.4), the characteristic value f of the optical system is defined by f = m × 25.4 / (4π × D) using a natural number m. An image recording device characterized by the above.