JPH06278321A - Image forming apparatus - Google Patents

Abstract

PURPOSE:To provide a digital delay element suitable for a case performing the gradation expression of an image by a pulse width modulating system. CONSTITUTION:A first delay quantity generating circuit 106 is constituted by employing an element having definite delay quantity as a unit and the delay quantity thereof is changed by a first switching circuit 108. The delay quantity of a second delay quantity generating circuit 107 is changed by a second switching circuit 109. A plurality of digital signals are inputted from an offset delay quantity control signal input terminal 103 and further inputted to an offset delay quantity control circuit 110 through an input circuit 1 (113). A plurality of signals inputted from a unit delay quantity control input terminal 105 are inputted to a unit delay quantity control circuit 112 through an input circuit 3 (115).

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 for expressing gradation of an image by pulse width modulation.

[0002]

2. Description of the Related Art Conventionally, as a method of varying a pulse generation period, a device is provided with a triangular wave generation unit corresponding to each pulse generation period, and each is compared with an analog video signal by using a comparator to obtain a pulse width. Creating a modulated signal. Then, these modulation signals are selected in correspondence with the screen data value in input pixel cycle units, and output as pulse width modulation signals.

The reason why the pulse width modulation of the image signal is performed by switching the period of the triangular wave is that it is particularly effective in the case of controlling the blinking of the laser light by the pulse width modulation signal and performing the image formation by the electrophotographic method. . That is, if the generation period of the triangular wave is lengthened, the gradation is improved, and if it is shortened, the resolution is improved, so that the type of image data (for example,
The reproducibility of the image is improved by properly using the triangular wave according to the character data and the photo data.

[0004]

However, in the above-mentioned conventional method, since the triangular wave is used, when trying to realize high speed, the cycle of the triangular wave becomes short and the amplitude becomes difficult to take, and the linearity is reduced. However, there is a problem in that the reproducibility of the image deteriorates. The present invention has been made in view of the above problems, and an object of the present invention is to provide an image forming apparatus having a digital delay element suitable for performing gradation expression of an image by a pulse width modulation method in a digital copying machine. Is to provide.

[0005]

In order to achieve the above object, the present invention is an image forming apparatus for expressing gradation of an image by pulse width modulation, which is input based on a predetermined reference clock signal. Means for generating an offset delay amount, a delay amount, a unit delay amount, and a reference signal from an image signal, and a predetermined pulse delayed by a delay time set based on the offset delay amount, the delay amount, the unit delay amount, and the reference signal Means for generating first signals Ps, Pr having a width;
And means for generating a second signal having a pulse width corresponding to the phase difference between the signals Ps and Pr, and performing the pulse width modulation according to the second signal.

[0006]

In the above structure, the delay time can be set at high speed.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described in detail below with reference to the accompanying drawings. FIG. 1 is a diagram showing the configuration of an image forming apparatus according to an embodiment of the present invention. The image forming apparatus shown in the figure is a full-color electrophotographic copying machine (hereinafter referred to as a color printer) that employs an electrophotographic recording system in the image forming process.

In FIG. 1, a photosensitive drum 1 having a photosensitive layer on its surface is rotationally driven in the direction of arrow X in the figure. A primary charger 2 is arranged on the left side of the photosensitive drum 1, and a surface potential sensor 3 for measuring the potential on the surface of the photosensitive drum is arranged diagonally below and to the left of the photosensitive drum 1. Further, just below the photosensitive drum 1 is a mixture of toner and carrier.
Multiple developing units 101M, 1 using component developers
01C, 101Y, 101Bk are stacked, and a developing device 100 that is movable in the left-right direction is arranged.

A transfer device 5 is arranged diagonally above and to the right of the photosensitive drum 1, and the adhesion force of the toner remaining on the surface of the photosensitive drum 1 to the drum after the transfer is reduced substantially directly above the photosensitive drum 1. A front static eliminator 6 is provided for facilitating cleaning. Further, a cleaning device 7 is arranged diagonally above and to the left of the photosensitive drum 1. An optical system 10 is arranged above the color printer, and an original image on the platen 28 is exposed to the photosensitive drum 1 by an exposure unit 9 located between the primary charger 2 and the surface potential sensor 3.
Configured to project onto. The optical system 10 includes a first operation mirror 11 and second and third operation mirrors 12, 1 that move in the same direction at a speed half that of the first operation mirror 11.
3, imaging lens 14, CC integrated with R, G, B filters
D15, a laser scanner unit 16, and fixed mirrors 17 and 18.

In the optical system 10, the original illumination source 2 is used.
0 is configured to interlock with the first operation mirror 11. Therefore, the reflected light image of the document scanned by the first to third operation mirrors 11, 12, 13 is always projected on the light receiving surface of the CCD 15 having the RGB three color separation filters after passing through the lens 14. Has become. A fixing device 20 and a paper feeding device 30 are arranged on the right side of the color printer, and transfer paper conveying systems 25 and 35 are arranged between the transfer drum 5 and the fixing device 20 and the paper feeding device 30, respectively. Has been done.

The developing device 100 includes a developing unit 101M (magenta developing unit), a developing unit 101C (cyan developing unit), a developing unit 101Y (yellow developing unit), and a developing unit 101Bk (black) which are removably held on a moving table 120. Each of the color-separated latent images of the respective colors is converted into a toner image by the corresponding developing unit.

The transfer device 5 is composed of a transfer drum 5b having a gripper 5a for holding the transfer paper P on its peripheral surface.
The transfer device 5 includes a transfer paper cassette 31 of the paper supply device 30.
Alternatively, the front end of the transfer paper P fed from the transfer paper cassette 32 through the transfer paper transport system 35 is held by the gripper 5a,
The transfer paper P is attracted to the transfer drum 5b by the action of the attraction charger 4 disposed inside the transfer drum 5b, and is rotated to transfer the toner image of each color on the photosensitive drum 1. In the transfer area, the transfer charger 5c is provided on the transfer drum 5
It is arranged inside b.

The transfer paper P on which the toner images of the respective colors are sequentially transferred is separated from the transfer drum 5b by the separation charger 8 and the separation claw 8'from the gripper 5a. Next, the transfer paper P
Is sent to the fixing device 20 by the transfer paper transport system 25,
Then, the toner image on the transfer paper P is fixed, and then discharged to the paper discharge tray 23. In the color printer having the above configuration, the photosensitive drum 1 is charged, exposed, and exposed by the primary charger 2, the optical system 10, the developing device 100, the transfer device 5, and the cleaning device 7 for each color separated by the CCD 15. Image forming processes of development, transfer and cleaning are performed.

Further, the first to third operation mirrors 11, 12,
The reflected light image of the original scanned by the lens 13 is reflected by the lens 14
After passing through, CCD15 equipped with RGB three color separation filter
Is color-separated and converted into an electric signal, and the original information signal is A / D converted and sent to the image processing unit as a digital image signal. The image processing unit described above is a logarithmic converter, U
Processing such as CR, masking, and gradation correction is performed, and thereafter, the semiconductor laser in the laser scanner unit 16 is modulated and driven. The laser light emitted from the semiconductor laser is the polygon mirror, the lens, and the fixed mirrors 17, 18 in the laser scanner unit 16 as well.
The photosensitive drum 1 is scanned via the to form an electrostatic latent image.

The latent image thus formed is developed by the developing device 100 to form a toner image, and the transfer device 5
After being transferred to a transfer sheet by means of, the sheet is fixed by the fixing device 20 and discharged. As a control system of the color printer having the above configuration, a control unit (not shown) controls the entire printer by a predetermined program, and a CPU, ROM,
It has a configuration in which a RAM, an I / O, an A / D converter and the like are present.

Here, the digital delay element used in the color printer in this embodiment will be described. Figure 2
FIG. 4 is a circuit diagram showing a configuration of a digital delay element according to this example. In the color printer according to the present exemplary embodiment, as illustrated in FIG.
In the circuit shown in (1), the electric signal input from the controlled signal input terminal 101 is output from the controlled signal output terminal 102 with a predetermined delay amount.

The first delay amount generation circuit 106 is constituted by an element having a constant delay amount as a unit, and the delay is generated by the first switching circuit 108 controlled by the offset delay amount control circuit 110. The amount is changed. Also, the second
The delay amount generating circuit 107 is a unit delay amount generating circuit 107a, 107b, ... Which is an element unit having a predetermined delay amount.
The delay amount is changed by the second switching circuit 109 which is controlled by the delay amount control circuit 111.

The unit delay amount generating circuit 107 described above is used.
are controlled by the unit delay amount control circuit 112 to change the unit delay amount. A plurality of digital signals are input from the offset delay amount control signal input terminal 103, and these signals are input to the offset delay amount control circuit 110 via the input circuit 1 (113). Further, a plurality of signals input from the unit delay amount control signal input terminal 105 are input to the unit delay amount control circuit 112 via the input circuit 3 (115).

The timing control circuit 117 controls the timing of each input / output signal and the internal circuit which constitute the delay circuit based on the reference clock signal input from the reference clock input terminal 116. Next, the laser drive system of the color printer will be described. FIG. 3 is a block diagram showing a laser drive system in the printer according to this embodiment. In the figure, a digital image signal (307)
Is the signal conversion circuit 3 in synchronization with the reference clock (308).
01 is input. The signal conversion circuit 301 uses the reference clock (308) to generate a digital image signal (307).
Therefore, the offset delay amount control signals (315), (31
6), delay amount control signals (317) and (318), unit delay amount control signals (319) and (320), and reference signal t.
r (11) is output.

Digital delay elements (302), (303)
2 is a digital delay element whose configuration is shown in FIG. 2. Offset delay amount control signals (315), (316), delay amount control signals (317), (318), unit delay amount control signals (319), ( 320) and the reference signal tr (31
1) is input, and the pulse signal Ps having a predetermined width is delayed from the reference signal tr (311) by the amount of delay time set by the control signals (315) to (320).
(312) and Pr (313) are output.

The pulse generation circuit 304 inputs the above-mentioned pulse signals Ps (312) and Pr (313), and outputs these two signals.
A pulse signal Pw having a width corresponding to the phase difference between the two pulse signals
(314) is generated. That is, the pulse signal Ps (3
12), the rise of the pulse signal Pw (314) is set, and the fall of the pulse signal Pw (314) is set by the pulse signal Pr (313).

Therefore, the pulse width of the pulse signal Pw (314) becomes equal to the phase difference between the pulse signals Ps (312) and Pr (313). The laser drive circuit 305 inputs the pulse signal Pw (314) and turns on the semiconductor laser 306 for a time equal to the pulse width. A power source V is supplied to the semiconductor laser 306.

FIG. 4 shows the digital image signal (3
7 is a timing chart showing signal timing in each part when (07) is character data. In this case, the pulse signals Ps (312) and Pr (313) are generated within the same cycle of the reference clock (308), and the delay amounts ds and dr are: ds + dr = T _clk (1) Then, T _clk has a relation of time for one cycle of the reference clock (308).

Then, as described above, the pulse signal Ps
The pulse signal Pw (314) is generated so as to be equal to the phase difference between (312) and Pr (313). FIG. 5 is a timing chart showing the signal timing of each part when the digital image signal (307) shown in FIG. 3 is photographic data. In this case, the delay amounts Ps (312) and Pr
(313) is alternately generated in each cycle of the reference clock (308), and the delay amounts ds and dr also satisfy the relationship represented by the above equation (1).

As described above, according to this embodiment,
When recording with changing the recording density to an integral multiple of the reference clock according to the type of image such as characters and photographs, synchronize the input digital image signal with the reference clock and set the delay amount per unit. By controlling, the delay time setting can be speeded up, and the setting value can be highly accurate and stable. [Modification] FIG. 6 is a block diagram showing the configuration of a digital delay element according to this modification. In the figure, the same components as those of the digital delay circuit according to the embodiment shown in FIG. 2 are designated by the same reference numerals, and the description thereof will be omitted here.

In the delay element according to this modification, when the delay amount of the second delay amount generating circuit 107 is changed in order to increase the accuracy of the set value or change the rate of change, the first element is changed accordingly. The control of the delay amount generation circuit 106 is also changed. In this case, here, the semiconductor memory 601 is provided, that is, a data rewritable storage element is provided, and the first delay amount generation circuit 10 according to the delay amount to be set therein is provided therein.
The control pattern 6 is written. Then, the offset delay amount control circuit 110 reads the control pattern corresponding to the set delay amount from the semiconductor memory 601 which is a storage element, and switches the first switching circuit 108.

Since the control pattern is rewritable, it is possible to cope with a change in the delay amount due to a change in the surrounding environment or a change over time. In the delay element according to the present modification, the semiconductor memory 601 is controlled by the signal line switching circuit 602, and the signal line switching circuit 602 is
The memory control signal (603) is input.

When it is desired to compensate the linearity of the change in the delay amount in this modification, the delay amount is set by the signal from the delay amount control signal input terminal 104 and finely adjusted by the signal from the offset delay amount control signal input terminal 103. Set the delay amount for. Then, the set value of the offset delay amount control signal input terminal 103 is changed while observing the delay amount of the output signal from the controlled signal input terminal 102. When it reaches a predetermined set value, the set value is written in the semiconductor memory 601.
This operation is performed for all set values.

Thereafter, when a value is set from the delay amount control signal input terminal 104, the offset delay amount control circuit 11
For 0, a predetermined control pattern is read from the semiconductor memory 601 and the first delay amount generation circuit 106 is set.

[0030]

As described above, according to the present invention,
The delay time can be set faster, and the set value can be made more accurate and stable.

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration of an image forming apparatus according to an exemplary embodiment of the present invention.

FIG. 2 is a circuit diagram showing a configuration of a digital delay element according to an example.

FIG. 3 is a block diagram showing a laser drive system in the printer according to the embodiment.

FIG. 4 is a signal timing chart of each part when the image signal is character data.

FIG. 5 is a signal timing chart of each part when the image signal is photographic data.

FIG. 6 is a block diagram showing a configuration of a digital delay element according to a modification.

[Description of Reference Signs] 101 controlled signal input terminal 102 controlled signal output terminal 103 offset delay amount control signal input terminal 105 unit delay amount control signal input terminal 106 first delay amount generating circuit 107 second delay amount generating circuit 107a , 107b, ... Unit delay amount generation circuit 108 First switching circuit 109 Second switching circuit 110 Offset delay amount control circuit 111 Delay amount control circuit 112 Unit delay amount control circuit 113-115 Input circuit 117 Timing control circuit

Claims (4)

[Claims] 1. An image forming apparatus for expressing gradation of an image by pulse width modulation, wherein an offset delay amount, a delay amount, a unit delay amount, and a reference from an input image signal based on a predetermined reference clock signal. Means for generating a signal; means for generating a first signal Ps, Pr having a predetermined pulse width delayed by a delay time set based on the offset delay amount, the delay amount, the unit delay amount, and a reference signal; A second signal having a pulse width according to the phase difference between the first signals Ps and Pr, and performing the pulse width modulation according to the second signal. . 2. The image forming apparatus according to claim 1, wherein the offset delay amount, the delay amount, and the unit delay amount can be controlled independently of each other. 3. The image forming apparatus according to claim 1, wherein the offset delay amount changes according to changes in the delay amount and the unit delay amount. 4. The change pattern for the delay amount and the unit delay amount is written in a memory in advance, and the offset delay amount changes according to the pattern read from the memory. The image forming apparatus according to item 3.