JP3251308B2 - Image forming device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus such as a laser printer, a laser copying machine, a laser facsimile, etc., which performs recording on a recording medium using an electrophotographic system. More specifically, the present invention relates to an image forming apparatus capable of changing a pixel density.

[0002]

2. Description of the Related Art A laser printer, which is one type of image forming apparatus, is a printer device in which an image is formed by a large number of pixels arranged in a matrix, and is modulated so as to be turned on / off according to input information. A latent image composed of pixels is formed on the photoreceptor by the scanning light, and a visible image is obtained by toner development, transferred to a sheet, and then fixed. In particular, laser printers are capable of high-speed modulation of laser light, so that high-speed and high-quality printing and graphic recording can be realized.Thus, as a data processing system using a computer and an output device of an image creation system, Has a wide range of uses.

[0003] Fig. 23 is a conceptual diagram of the mode of use.
When printing information from a word processor or computer,
Printer controller 3 from host device (word processor, computer, etc.) 1 through host interface 2
Then, paper size, image information, and the like are output. here,
Host interface 2 is Centronics or RS2
32C. The image information includes text information such as characters and graphic information such as simple figures, and a PDL (Page Descripp) for specifying these.
Action Language) and NON-PDL.

[0004] Next, the printer controller 3 that has received the image information issues a print command to the printer engine 5 via the video interface 4. The video interface 4 passes information from the host device 1, for example, information such as from which paper feed tray the specified paper is to be fed and at what position on the paper the dots are to be recorded.

In a conventional printer engine, the size (pixel diameter) and pitch (resolution) of the dots are constant and cannot be changed. Therefore, when there are many host devices having different resolutions, printer engines for the number of host devices are required. In recent years, to solve this problem, a printer engine that can change the dot pitch (resolution) has been provided. However, simply changing the dot pitch is not enough. If the pixel diameter is not changed along with the dot pitch, good quality is obtained. Images cannot be obtained.

The reason will be described with reference to the drawing. Now, as shown in FIG. 24, when the pixel diameter is printed at 200 dpi and the dot pitch is similarly printed at 200 dpi, and as shown in FIG. 25, the pixel diameter is 400 dpi and the dot pitch is also changed. Similarly, when printing is performed at 400 dpi, a high-quality image is expected in each case. However, when printing is performed with a pixel diameter of 200 dpi and a dot pitch of 400 dpi, FIG.
As shown in (2), adjacent dots overlap, and the resolution is significantly reduced. Conversely, when printing is performed with a pixel diameter of 400 dpi and a dot pitch of 200 dpi, as shown in FIG. 27, white blank portions are formed, and a solid image cannot be guaranteed. Therefore, it is necessary to adjust both the pixel diameter and the dot pitch according to the pixel density.

[0007]

In a printer capable of changing the pixel density, the linear velocity v of the photosensitive member, the rotational speed Rm of the polygon mirror,
At least two of the pixel clocks W must be changed.

[0008]

In the conventional laser printer, since the pixel density is fixed, the rotation speed of the polygon motor is also fixed. For this reason, when the polygon motor has reached a steady rotation, the lock signal is output from the polygon motor to detect that the rotation is a steady rotation, and then the optical writing is started so that a normal image can be obtained. (If the optical writing is started before the steady rotation, the normal image will not be obtained).

However, in such a configuration, in order to make the pixel density variable, if the rotation speed of the polygon motor is set to be changed in several steps according to the pixel density, each rotation speed is changed. Each outputs a lock signal. For this reason, depending on the set pixel density, a lock signal may be output when a rotation speed corresponding to a different pixel density is reached. For example, a pixel density of 200
The rotation speed of the polygon motor corresponding to dpi is 6000
rpm, and when the rotation speed of the polygon motor corresponding to the pixel density of 400 dpi is preset to 12000 rpm, when the pixel density of 400 dpi is set, the pixel density becomes 20% before reaching 12000 rpm.
When the rotation speed reaches 6000 rpm corresponding to 0 dpi, a lock signal is output, and a normal image cannot be obtained.

[0011] It is an object of the present invention in view of the above problems.
An object of the present invention is to provide an image forming apparatus capable of always forming a normal image even when the pixel density is changed.

[0012]

According to an image forming apparatus of a first embodiment of the present invention, a light beam is rotated by a polygon motor.
Optical writing on the photoreceptor by scanning with a polygon mirror
At the same time, the rotation speed of the polygon motor is used as pixel density information.
Change the pixel density in the image forming apparatus
Pixel density information before and after pixel density change
The rotation speed of the polygon motor is stable for each combination
Motor stabilization time recording means for recording multiple times before starting
And the pixel density information before and after the pixel density change
The polygon corresponding to the combination with the pixel density information
The time required for the rotation speed of the motor to stabilize
The plurality of polygon models recorded in the stable time recording means
Select from the time until the rotation speed of the
Motor stabilization time setting means to set the pixel density information
When there is a change, set by the motor stabilization time setting means
Optical writing for starting the optical writing after a given time has elapsed
And an embedding control means .

An image forming apparatus according to a second embodiment of the present invention has a light
A polygon mirror whose beam is rotated by a polygon motor
To write light on the photoreceptor by scanning with
Motor rotation speed is variable according to pixel density information
In the image forming apparatus, the rotation speed of the polygon motor
Rotation speed detecting means for detecting the pixel density and the pixel before the pixel density change
Combination of density information and pixel density information after pixel density change
Until the rotation speed of the polygon motor stabilizes
A motor stabilization time recording means for plural recording time, the pixel
Pixel density information before density change and pixel density after pixel density change
Of the polygon motor corresponding to the combination with the information
The time until the rotation speed is stabilized is referred to as the motor stabilization time.
The number of rotations of the plurality of polygon motors recorded in the recording means
Mode to select and set from the time until the rotation speed stabilizes
Data stabilization time setting means and the rotation speed detection means
The rotation speed corresponds to the pixel density information after the pixel density is changed.
The motor stabilization time setting means
Start the optical writing after the time set in
Optical writing means .

In the image forming apparatus according to the second aspect, the rotation
The speed detecting means is one for one surface of the polygon mirror.
The polygon is obtained by the synchronization detection light beam obtained
The rotation speed of the motor can be detected.

[0015]

[0016]

According to the present invention, a predetermined motor stabilization time is set.
After the elapse, optical writing is started.

[0017]

[0018]

[0019]

[0020]

Next, an embodiment of the present invention will be described in detail with reference to the drawings. FIG. 2 shows a partial schematic configuration of a laser printer according to one embodiment of the present invention. The laser light emitted from the laser diode 10 is collimated by a collimator lens 11, and excess light is removed by a variable aperture 12 having a slit portion corresponding to the size of a dot (pixel density) to be formed. The laser light transmitted through the slit is condensed by the first cylinder lens 13 so as to have a predetermined size on the photoreceptor 14, and the polygon motor 1
Scanning is performed in the main scanning direction (axial direction of the photoconductor 14) x by the polygon mirror 16 rotated at 5. Then, the pair of Fθ lenses 17 makes the equiangular motion a uniform motion, and corrects the field curvature. Next, the angle of the laser beam is changed by the first mirror 18, and the light is condensed in the sub-scanning direction (rotation direction of the photoconductor 14) y by the second cylinder lens 19, and the surface of the photoconductor 14 is irradiated.

On the other hand, the laser beam for synchronization detection reflected by the polygon mirror 16 enters the optical fiber 22 through the second mirror 20 and the third cylinder lens 21, and then enters the photodiode on the engine drive board (not shown). 23
, And controls the timing of the start of light emission (start of optical writing) of the laser beam for image formation for each scan.

FIG. 1 shows a schematic configuration of a control system for controlling the dot pitch and the pixel diameter according to the pixel density. When paper size, image information, and the like are sent from the host computer 24 to the printer controller 26 via the host interface 25, the printer controller 26 sends information necessary for printing to the printer engine 28 via the video interface 27. The printer engine 28 has three types of pixel diameters, for example, as shown in FIG.
The three types of dot pitches (1), (2) and (3) can be controlled separately. That is,
The printer engine 28 includes a video interface 27
Discriminating means 29 for discriminating pixel density information, text information and graphic information from the information sent from
A combination setting means 30 for setting a combination of a pixel diameter and a dot pitch based on the discriminated information; and a dot pitch control means 31 and a pixel diameter control means 32 for separately controlling the dot pitch and the pixel diameter according to the setting.
And

In the case of FIG. 3, there are nine combinations of the pixel diameter and the dot pitch. However, it is preferable that the pixel diameter is large for text characters and close to the theoretical value for graphics. Therefore, when the pixel density information has three levels of small, medium, and large, the combination setting unit 30 sets the dot pitch and the pixel diameter to a combination as shown in Table 1, for example. That is, for graphics, (1),
For the dot pitches of (2) and (3),
, And pixel diameter, and for text, (1),
For the dot pitches of (2) and (3),
, Choose the pixel diameter.

[0024]

[Table 1]

When the pixel density information, the text information, and the graphic information are transmitted by serial communication with the paper size information and the like by the video interface 27, for example, FIG.
With such a bit configuration, the information discriminating means 29 can easily discriminate. If pixel density information not supported by the printer engine 28 is sent, an error is generated.

The combination setting means 30 can be implemented by placing it on a ROM, but can be set arbitrarily by reading / writing to a RAM area or an EEPROM or by providing a combination mode setting means 33 which can be manually switched to a large number. The combination can be set arbitrarily, or the automatic mode and the manual mode can be separated, so that a mode in which automatic printing is performed in a predetermined combination and a mode in which the user freely selects can be arbitrarily selected. .

The dot pitch control means 31 may have a structure in which the rotation speed of the polygon motor 15 is variable as described later, or a means in which the frequency of the pixel clock is variable. Examples of the pixel diameter control means 32 include a variable beam diameter, a variable laser power, a variable laser lighting time, and a variable process condition (for example, a variable developing bias potential).

FIG. 5 shows an example in which the beam diameter is varied, and shows an example in which the laser beam from the laser diode 10 passing through the hole 34a of the base frame 34 is adjusted by the variable aperture 12. That is, the variable aperture 12
When the variable aperture 12 is stepped by being slidably mounted on the base plate 35 and rotating the ratchet 37 by the drive solenoid 36, the light transmitting area of the slit 38 of the variable aperture 12 is adjusted. Reference numeral 39 denotes a sensor for detecting the home position of the variable aperture 39.

Next, a description will be given of an embodiment in which the rotation speed of the polygon motor is controlled in accordance with the input pixel density information, and the optical writing is started after the rotation speed is stabilized. FIG. 6 is a block diagram of the control system. 40 is a CPU of a main control unit, 41 is a printer controller, 42 is a ROM, 43 is a timer, 44 is a polygon motor controller, 45 is an I / O port, and 46 is a dip switch ( DIP / SW), 47 is an aperture controller, 4
8 is a write control unit gate array, 49 is its internal register, 50 is a main scanning control unit, and 51 is an automatic power control unit (A
PC) and 52 are video interfaces.

As shown in Table 2, in a table in the ROM 42, for example, 200 dpi, 240 dpi, 300 dpi
The rotation speed of the polygon motor is set to 6000 rpm and 7 for four pixel densities of 400 dpi and 400 dpi, respectively.
Data set to 200 rpm, 9000 rpm, and 12000 rpm are stored in advance. Another table shows that when the pixel density is changed, as shown in Table 3, the time until the rotation speed of the polygon motor stabilizes is determined from the relationship between the previous pixel density and the next pixel density. Data to be set is stored in advance. In Table 3, 240d
Data corresponding to pi is omitted.

[0031]

[Table 2]

[0032]

[Table 3]

In operation, when print data of a certain pixel density is sent from the printer controller 41, the CPU 40 determines this and sends a signal to the polygon motor controller 44 to refer to the table shown in Table 2. To control the rotation speed of the polygon motor to a speed corresponding to the pixel density. Now, after printing at 400 dpi,
When printing at 200 dpi, the rotation speed of the polygon motor is changed from 12000 rpm to 6000 rpm as shown in Table 2.
rpm. When the speed is changed to 300 dpi thereafter, the speed changes from 6000 rpm to 9000 rpm. Here, the time required for the rotation speed of the polygon motor to stabilize is not uniform, but varies depending on the case. Therefore, all of this time is measured in advance, and the polygon motor rotation speed stabilization time is set to t for each change in pixel density.
(M, n), and the data is stored in the ROM 42 as described above.
In advance.

In the flowchart of FIG. 7, when image information is input, the timer 43 is incremented (step 100), and it is determined whether or not there is a pixel density switching command (step 101). If there is, R
From the table shown in Table 3 of OM42, data t (m,
n) is extracted (step 102), and rotation of the polygon motor is started (step 103). And timer 4
3 reaches data t (m, n) (step 10
4) That is, after the rotation speed of the polygon motor is stabilized, the pixel density switching command is terminated (step 105), and optical writing is started (step 106). Step 101
If there is no command to switch the pixel density, the timer 43 is reset (step 107).

Next, a description will be given of an embodiment in which the rotation speed of the polygon motor is controlled in accordance with the inputted pixel density information, and the rotation speed is detected to start the optical writing after the rotation becomes steady. FIG. 8 is a block diagram of the control system. 53 is a host computer, 54 is a printer controller, and 55 is a CPU that performs various controls in accordance with information sent from the host computer 53 via the printer controller 54. The CPU 55 has functions of a pulse generator 56, a counter 57, a comparator 58, a timer 59, and a calculator 60. Reference numeral 61 denotes a polygon motor driver for driving the polygon motor 62; 63, a laser beam synchronization detection unit; and 64, a ROM in which data as shown in Table 2 is stored.

The operation will be described with reference to the flowchart of FIG. 9. When print data having a pixel density of 400 dpi is transmitted from the host computer 53, for example, the CPU
55 determines this and sends a signal to the polygon motor driver 61 to rotate the polygon motor 62 to 1200 rpm.
Start at 0 rpm (Step 20)
0).

Thereafter, when the synchronization detector 63 detects a laser beam for synchronization detection at a certain timing (n-th) (step 201), the synchronization detector 63 sends a signal to the counter 57 to count. The process is started (step 202), and when the synchronization detection unit 63 detects the m-th (n + m) -th laser beam therefrom (step 20).
3) Stop counting (step 204).
Now, the count value at this time is C _1. Since the laser light is detected once for one surface of the polygon mirror, C ₁ is proportional to the rotation speed of the polygon motor 62.

Therefore, the count value corresponding to the rotation speed of the polygon motor 62 is stored in advance in the ROM 64 as a set value corresponding to the pixel density in Table 2, for example. Now, the rotational speed of the polygon motor 62 when the count set value when the 12000rpm and C _2, the magnitude of C ₁ and C ₂ are compared in the comparator 58 (step 205). Here, when C ₁ and C ₂ do not match, because the polygon motor 62 will be not rotating at 12000 rpm, again counts by the counter 57 returns to step 201 is repeated until consistent.

FIG. 10 shows the responsiveness when the rotation speed of the polygon motor 62 is changed. As can be seen from the figure, the operation of the polygon motor 62 includes a time t ₁ required to reach a certain rotation speed and a time t ₂ − required to reach a steady rotation.
There is t ₁ (unstable time). Match point of the C ₁ and C _2, this could be a post t ₁ elapses in the drawing, when the start of optical writing to this point, the optical writing is performed during unstable time, a normal image is obtained Absent. Therefore, unstable time t ₂ -t _1, since previously known by the changing pattern of the pixel density, an unstable time t ₂ -t ₁ in each pattern previously measured, the measured value as a time setting tm ROM 64
In advance.

In FIG. 9, when C ₁ and C ₂ match, the timer 59 starts counting time (step 206). After tm has elapsed, the timer 59 stops counting time (step 207). A start signal is sent to the optical writing system to start optical writing (step 208). By doing so, at the time of optical writing, the polygon motor 62 becomes a steady rotation at a speed corresponding to the pixel density.

Next, an embodiment in which the pixel diameter is adjusted by changing the size of the slit of the aperture will be described. 11 and 12 show a first example. FIG.
In 1, a collimator lens 72, a disc-shaped variable aperture 73, a cylinder lens 74, a polygon mirror 75 of a deflector, an Fθ lens 76, and a mirror 77 are arranged in a laser beam path from a laser light source 70 to a photoconductor 71. ing. In the variable aperture 73, for example, four rectangular light-transmitting holes 78 having different sizes are radially formed with a phase difference of 90 degrees, and are emitted from the laser light source 70 and collected by the collimator lens 72. The laser beam L passes through one light transmitting hole 78 of the variable aperture 73. The transmitted laser beam L passes through the cylinder lens 74 and is reflected by the polygon mirror 75 rotating at a constant high speed, so that it is deflected into scanning light. The scanning light is transmitted through the Fθ lens 76 so as to form an image on the peripheral surface of the photoreceptor 71 in a straight line, the optical path is changed by the mirror 77, and the spot diameter according to the size of the transmitted light transmitting hole 78 is changed. An image is formed on the photoconductor 71 with (pixel diameter).

The variable aperture 73 is rotated around its center 79 by a stepping motor or the like (not shown).
The four light transmitting holes 78 of the variable aperture 73 are provided such that their centers are located on the same arc line R centered on the rotation fulcrum of the variable aperture 73 as shown in FIG. The size of the four light transmitting holes 78 is determined so that the laser beam L passing therethrough forms a spot diameter on the photoreceptor 71 corresponding to four levels of pixel densities to be varied.

As a method of selecting the light transmitting hole 78 of the variable aperture 73, for example, when a signal of a desired pixel density is received for an image to be output next between jobs, the variable aperture 73 is set to a stepping motor or the like. , And one light transmitting hole 78 corresponding to the pixel density is
The rotation of the variable aperture 73 is stopped at the position where the light is transmitted.

FIG. 13 shows a second example. In this example, the variable aperture 80 is a horizontally long rectangular plate, and a plurality of light transmitting holes 81 having different sizes are provided at intervals in the length direction. The variable aperture 80 is urged from one end by a spring 82 so that the other end is pressed against the eccentric cam 83. Then, the eccentric cam 83 is moved by a stepping motor or the like as shown in FIG.
As shown in FIG. 17, the variable aperture 80 is moved linearly by rotating the pin 84 as a fulcrum, and the light transmitting hole 81 through which the laser beam L is transmitted can be selected.

18 to 21 show other examples of driving the variable aperture 80 having a rectangular plate shape. FIG.
Then, a rack 85 is provided integrally with the variable aperture 80, and a pinion 86 is engaged with the rack 85, and the pinion 86
The variable aperture 80 is moved linearly by the rotation of, and the light transmitting hole 81 is switched. In FIG. 19, the bevel gear 8
7, 88 and a pulley 89, and rotate the wire 90
To convert the variable aperture 80 into a linear motion. In FIG. 20, the variable aperture 80 is connected to the electromagnet 91
The variable aperture 80 is switched and moved by the electromagnet 91. In this case, a guide for guiding the variable aperture 80 is provided, and springs 93 are provided at both ends for switching the variable aperture 80.
Concatenate. In FIG. 21, one end 94 of the variable aperture 80 is used as a part of an electromagnet, and the variable aperture 80 is switched and moved by suction and repulsion.

FIG. 22 shows still another example, in which a plurality of variable apertures 96 each having one light-transmitting hole 95 having a different size are sequentially arranged in the direction of the optical path of the laser beam and individually rotated. In this case, only one of the variable apertures 96 can be rotated to an operation position where the transmission of the laser beam is permitted.

[0047]

According to the present invention, the motor safety set in advance is set.
By starting optical writing after a fixed time, the
Gon motor reaches rotation speed corresponding to different pixel density
Output a lock signal and start optical writing
Can be prevented.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a schematic configuration of an example of an image forming apparatus according to the present invention.

FIG. 2 is a perspective view of the optical system.

FIG. 3 is an explanatory diagram showing a relationship between a pixel diameter and a dot pitch.

FIG. 4 is a bit configuration diagram illustrating an example of transmitting pixel density information and the like by serial communication.

FIG. 5 is a perspective view illustrating an example of a case where a pixel diameter is adjusted by a variable aperture.

FIG. 6 is a block diagram of an embodiment in which the rotation speed of a polygon motor is controlled in accordance with input pixel density information, and optical writing is started after the rotation speed is stabilized.

FIG. 7 is a flowchart of the above.

FIG. 8 is a block diagram of an embodiment in which the rotation speed of the polygon motor is controlled in accordance with the input pixel density information, and the rotation speed is detected to start the optical writing after the rotation becomes steady.

FIG. 9 is a flowchart of the above.

FIG. 10 is a graph showing responsiveness when the rotation speed of a polygon motor is changed.

FIG. 11 is a perspective view of a first example of an image forming apparatus that adjusts a pixel diameter by changing the size of a slit of an aperture.

FIG. 12 is a front view of the variable aperture in the above.

FIG. 13 is a perspective view of a second example.

FIG. 14 is an operation explanatory diagram of the second example.

FIG. 15 is an operation explanatory diagram of the second example.

FIG. 16 is an operation explanatory diagram of the second example.

FIG. 17 is an operation explanatory diagram of the second example.

FIG. 18 is a perspective view of another example of driving a rectangular plate-shaped variable aperture.

FIG. 19 is a schematic perspective view of another driving example.

FIG. 20 is a schematic perspective view of another driving example.

FIG. 21 is a schematic perspective view of another driving example.

FIG. 22 is a schematic view of another example of the variable aperture.

FIG. 23 is a conceptual diagram of a usage mode of a laser printer.

FIG. 24 is an explanatory diagram of an example of dot printing.

FIG. 25 is an explanatory diagram of a dot printing example.

FIG. 26 is an explanatory diagram of a dot printing example.

FIG. 27 is an explanatory diagram of an example of dot printing.

[Explanation of symbols]

 Reference Signs List 14 photoconductor 15 polygon motor 16 polygon mirror 29 information discriminating means 30 combination setting means 31 dot pitch control means 32 pixel diameter control means 33 combination mode setting means 80 variable aperture 81 light transmitting hole 86 variable aperture

──────────────────────────────────────────────────続 き Continuation of front page (72) Inventor Kazunori Kobayashi Ricoh Company, Ltd. Ricoh, 1-3-6 Nakamagome, Ota-ku, Tokyo (56) References JP-A-61-277262 (JP, A) JP-A Sho JP-A-58-121145 (JP, A) JP-A-59-117372 (JP, A) JP-A-63-108852 (JP, A) JP-A-62-272584 (JP, A) A) Real opening sho 59-96969 (JP, U) (58) Field surveyed (Int. Cl. ⁷ , DB name) H04N 1/23-1/31

Claims (3)

(57) [Claims] A light beam is rotated by a polygon motor.
Optical writing on the photoreceptor by scanning with a polygon mirror
At the same time, the rotation speed of the polygon motor is used as pixel density information.
In an image forming apparatus that is variable according toPixel density information before and after pixel density change
For each combination with density information, the rotation of the polygon motor is
Motor stabilization that records multiple times until the rotation speed stabilizes
Time recording means; Pixel density information before and after pixel density change
The polygon mode corresponding to the combination with the density information
The time until the rotation speed of the motor stabilizes
A plurality of polygon motors recorded in time recording means
Select from the time until the rotation speed of the Setting
Means for setting the motor stabilization time, and when the pixel density information is changed,SaidMotor stabilization time
The optical writing is performed after the time set by the setting unit has elapsed.
Optical writing control means for starting the operation.
Image forming apparatus. 2. A light beam is rotated by a polygon motor.
Optical writing on the photoreceptor by scanning with a polygon mirror
At the same time, the rotation speed of the polygon motor is used as pixel density information.
In the image forming apparatus, the rotation speed of the polygon motor is detected.
Means,Pixel density information before and after pixel density change
For each combination with density information, the rotation of the polygon motor is
Motor stabilization that records multiple times until the rotation speed stabilizes
Time recording means; Pixel density information before and after pixel density change
The polygon mode corresponding to the combination with the density information
The time until the rotation speed of the motor stabilizes
A plurality of polygon motors recorded in time recording means
Select from the time until the rotation speed of the
Motor stabilization time setting means ,The rotation speed detection The rotation speed detected by the meansPixel density change
AfterAfter reaching the speed corresponding to the pixel density information,further
After the time set by the motor stabilization time setting means elapses
FromOptical writing means for starting the optical writing
An image forming apparatus, comprising: Wherein said rotational speed detecting means, and detects the rotation speed of the polygon motor by a light beam for detecting synchronization obtained once for one surface of the polygon mirror, the claim 3. The image forming apparatus according to 2.