JP2897320B2 - Image recording device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image recording apparatus for performing two-color or multi-color recording using a plurality of systems of light beams.

2. Description of the Related Art In recent years, in an image recording apparatus that scans a laser beam on a medium to be scanned such as a photosensitive drum and forms an electrostatic latent image to record an image, color recording associated with permeation of a cutter display has been performed. With the demand and the spread of color copying machines, recording in two colors or multicolors has been performed.

By the way, in the conventional image recording apparatus, the distance from the reflection position of the laser beam on the rotary polygon mirror to each exposure position does not exactly match. Also,
The scanning lens is not always processed so that these laser beams have exactly the same optical characteristics. Due to such subtle differences in optical conditions,
The speed at which the two laser beams operate on the photosensitive drum is different, which may cause a shift in the position of the image.

FIG. 5 and FIG. 6 are for explaining such a situation. As shown in FIG.
The speed at which the two laser beams 2, 3 that have passed through the scanning lens 6 after being deflected by the scanning lens 6 scans the photosensitive drum is V ₁ and V ₂ , respectively, which are supposed to have a relationship of V ₁ <V _2. And In this case, assuming that the electrostatic latent image “ABCDE” is formed from the beginning of each scanning line, as shown in FIG. 5, the latent image by the second system laser beam 3 represented by a broken line is represented by a solid line. The width of the latent image formed by the laser beam 2 of the first system is shorter than that of the latent image. In this figure, the formation position of the electrostatic latent image by both laser beams 2 and 3 is
For convenience, the image is displayed shifted in the sub-scanning direction, and the left end of the image portion of the electrostatic latent image is displayed so as to coincide with each other in order to clarify the positional shift of the formed latent image.

Thus, the two laser beams in the main scanning direction
If the irradiation positions of a few are different, when recording is performed with different recording colors, a color shift occurs, and an image that is difficult to see is formed. This is the same when multicolor recording is performed using three or more laser beams.

Therefore, the present applicant has proposed a method for preventing such image displacement based on the difference in the scanning speed of the laser beam.
Image recording which modulates a laser beam for each system and changes the frequency of a clock signal for transferring an image signal to a modulating means in response to a difference in scanning speed between laser beams. The device was proposed earlier (Japanese Patent Application No. 63-23782).

By the way, in this device, it is necessary to use a clock signal generating circuit for generating a plurality of clock signals having different frequencies.

Conventionally, as this clock signal generation circuit, for example, PL
L (Phase Locked Loop) circuit (phase locked loop circuit)
And a horizontal scanning start signal and a horizontal scanning end signal,
There is a configuration in which a clock is oscillated at a time interval from a horizontal scanning start signal to a horizontal scanning end signal at a period equivalent to the divided time.

In this clock signal generation circuit, the frequency of the clock signal can be made to follow the fluctuation of the rotation speed of the drive motor for rotating the rotary polygon mirror, and the scanning speed × the repetition period of the clock signal can be made constant. There is also an effect.

[Problems to be Solved by the Invention] However, in an image recording apparatus using a conventional clock signal generating circuit, light used to output a horizontal scanning start signal and a horizontal scanning end signal as shown in FIG. The positional accuracy of the detectors 4 and 5, i.e., the variation of the time interval from the horizontal scanning start signal to the horizontal scanning end signal, becomes the variation of the absolute value of the frequency. There is a need to increase the position accuracy and mechanically adjust the position, which is extremely troublesome.

The present invention has been made in view of such a problem, and an object thereof is to increase the accuracy of a photodetector or to change the scanning speed of a light beam with a simple configuration without mechanical adjustment. The frequency of the clock signal can be changed accordingly.
It is an object of the present invention to provide an image recording apparatus capable of suppressing misalignment of an image caused by a difference in scanning speed of a plurality of systems of light beams and forming an easily viewable image.

[Means for Solving the Problems] In order to solve the above-described problems, in the present invention, a light beam generating source that generates a plurality of systems of light beams on a medium to be scanned, and an image signal prepared for each system are provided. A modulating means for modulating a light beam for each system as an input, and a clock signal generating section for generating a plurality of clock signals for transferring an image signal to the modulating means, the clock signal generating section having a reference frequency A reference clock oscillation source for outputting a clock pulse, and a first clock signal having a frequency responsive to a scanning speed of a light beam of a reference system among the light beams, using the clock pulse output from the reference clock oscillation source as an input. A first clock signal generating circuit for outputting the first clock signal, and an optical beam receiving the first clock signal output from the first clock signal generating circuit as an input. Of the frequency corresponding to the scanning speed of the light beam of the other system in the system
A second clock signal generating circuit for outputting the clock signal of the second clock signal, and frequency setting means for setting the frequency of the second clock signal output from the second clock signal generating circuit in accordance with the displacement of the image. It is a thing.

With the above configuration, according to the image recording apparatus of the present invention, when the scanning speeds of the light beams are different from each other, the first signal having the frequency of the reference clock oscillation source from the clock signal generator is output.
And a second clock signal having a frequency different from that of the first clock signal obtained by adjusting the first clock signal.
Are output, whereby each light beam is modulated, so that the image is not misaligned on the medium to be scanned.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.

FIG. 3 shows a schematic configuration of an image recording apparatus according to one embodiment of the present invention.

This image recording apparatus includes a photosensitive drum 11 for forming an electrostatic latent image. In this apparatus, two photosensitive drums 11
The system laser beams 12 and 13 respectively arrive. The first system laser beam 12 is output from the first semiconductor laser 14 and passes through the first collimating lens 15 to enter one surface of the rotary polygon mirror 16. Rotating polygon mirror
16 rotates at a constant speed by the scanner motor 17,
The reflected light from the rotating polygon mirror 16 passes through the scanning lens 18 and reaches a first exposure point 19 on the photosensitive drum 11.
On the other hand, the laser beam 13 of the second system is output from the second semiconductor laser 20, and is output from the second collimating lens.
The light passes through 21 and enters the aforementioned surface of the rotary polygon mirror 16. Then, the reflected light from the rotating polygon mirror 16 passes through the scanning lens 18 and reaches the second exposure point 22 on the photosensitive drum 11.

Before the first exposure point 19 around the photosensitive drum 11,
A charger (charge corotron) 23 is provided. In the middle between the first exposure location 19 and the second exposure location 22,
A first developing device 24 is provided. Further, behind the second exposure portion 22, a second developing device 25, a static eliminator 26, and a transfer charger (transfer corotron) 27 are arranged in this order. The photosensitive drum 11 rotates clockwise in the drawing at a constant speed.

Therefore, the first semiconductor laser 14 is driven based on the first image information 30 including the binary data input to the first laser driving unit 28, and the modulated first system laser beam 12 is generated. When scanning is performed at the first exposure portion 19, the charge on the photosensitive drum 11 uniformly charged by the charger 23 is selectively removed, and a first electrostatic latent image is formed. This first electrostatic latent image is developed by the first developing device 24, and as a result, a toner image of the first recording color is formed.

On the other hand, the second semiconductor laser 20 is driven on the basis of the second image information 31 similarly composed of binary data input to the second laser drive unit 29, and the modulated second system laser beam 13 is generated. When scanning is performed at the second exposure portion 22, the charge on the photosensitive drum 11 is selectively removed to form a second electrostatic latent image. This second electrostatic latent image is transferred to a second developing device
25, and as a result, a toner image of the second recording color is formed.

The first image information 30 and the second image information 31 are respectively transferred by a first clock signal 55 and a second clock signal 56 generated in a clock signal generation unit 32 described later, and respectively correspond to the first laser signals. The driving unit 28 and the second laser driving unit 29 are supplied.
It should be noted that the first clock signal 55 and the second clock signal 56 are both an aggregate of a large number of clock pulses as shown in FIG. They have different frequencies corresponding to the difference in the scanning speed of the output light.

When the two-color toner image is formed on the photosensitive drum 11, the charge is removed by the charge remover 26, and the two-color toner image is transferred onto the recording paper 33 by the action of the transfer charger 27. These toner images are fixed on the recording paper 33 by a fixing device (not shown). Further, the toner finally left on the photosensitive drum 11 is collected by a cleaning device (not shown). By rotating the photosensitive drum 11 and repeating the above operation, a plurality of recording paper
Two-color recording of various types of image information becomes possible with respect to 33.

FIG. 1 shows a specific configuration of the clock signal generator 32.

In the clock signal generator 32, the first image information 30 is transmitted from the first image memory 41 to the first memory buffer.
The signals are sequentially supplied to the first and second storages 42 and temporarily stored therein, and then input to the first semiconductor laser driving unit 28 in synchronization with the first clock signal 55. Similarly, the second image information
31 is a second image memory 52 to a second memory buffer 53
Are sequentially supplied to the second semiconductor laser driving unit 29 after being temporarily stored therein and then synchronized with the second clock signal 56.

A first clock signal used for writing and reading first image information to and from the first memory buffer 42
55 is output from the clock synchronization circuit 44 as a first clock signal generation circuit. The frequency of the first clock signal 55 is determined, for example, by the oscillation frequency of the reference clock oscillator 43 using a crystal oscillator. The clock synchronization circuit 44 includes a first semiconductor laser.
The first horizontal scanning synchronization circuit 46 is synchronized with the scanning of the
The first horizontal scanning start signal 57 output from the controller is input. In synchronization with the first horizontal scanning start signal 57, the first clock signal 55
Is output.

The first clock signal 55 is supplied to the first memory buffer
At the same time as being input to 42, it is also input to a counting circuit 45. The counting circuit 45 counts a certain number (for example, an integer N) when the first clock signal 55 is input, and then outputs a first count end signal 58 to stop the counting. It repeats every scan of the 14 output lights.

The first count end signal 58 output from the counting circuit 45 is output to the PLL circuit 5 as a second clock signal generating circuit.
Entered in 4. The PLL circuit 54 includes a phase comparator 48, a loop filter (low-pass filter) 49, and a voltage-controlled oscillator 50.
It is composed of Then, from the PLL circuit 54, the second
A second clock signal 56 used for writing and reading the second image information to and from the memory buffer 53 is output. The phase comparator 48 and the loop filter 49 control the output frequency of the voltage controlled oscillator 50 so that the phases of the first horizontal scanning start signal 57 and the second horizontal scanning start signal 59 always coincide. is there. The second horizontal scanning start signal 59 output from the second horizontal scanning synchronization circuit 47 is input to the voltage controlled oscillator 50 in synchronization with the scanning of the output light of the second semiconductor laser 20. The second horizontal scanning start signal 59 triggers the voltage controlled oscillator 50 to start oscillating. The output of the voltage-controlled oscillator 50 is input to the second memory buffer 53 as a second clock signal 56, and is also input to the counting circuit 51 as frequency setting means. The counting circuit 51 counts a predetermined number (for example, an integer M) when the second clock is input, and then outputs a second count end signal 60 to each of the phase comparator 48 and the voltage controlled oscillator 50 to stop. This is repeated for each scan of the output light of the second semiconductor laser 20.

That is, in the clock signal generating section 32 having the above configuration, as shown in each waveform diagram in FIG. 2, a reference clock pulse obtained from the reference clock oscillator 43 is first input to the clock synchronizing circuit 44, Circuit 44
Are output in synchronization with a first horizontal scanning start signal 57 synchronized with the scanning speed of the output light of the first semiconductor laser 14, and this is used as a first clock signal 55. The first clock signal 55 is input to the first memory buffer 42 and also to the counting circuit 45 at the same time, and after being counted N by the counting circuit 45, the first counting end signal 58
Is input to the clock synchronization circuit 44. Thereafter, the same operation is repeated, whereby the first clock signal 55 becomes the first clock signal 55.
Is input to the first memory buffer in response to the scanning of the output light of the semiconductor laser. On the other hand, the first count end signal 58 is also input to the voltage controlled oscillator 50 via the phase comparator 48 and the loop filter 49 of the PLL circuit 54. As a result, the second clock signal 56 is output from the PLL circuit 54 with the second horizontal scan start signal 59 synchronized with the scanning of the output light of the second semiconductor laser 20 as a trigger. This second
Clock signal 56 is also input to the counting circuit 51 at the same time,
The counting circuit 51 counts M times. as a result,
The counting circuit 51 outputs a second count end signal 60 to each of the phase comparator 48 and the voltage controlled oscillator 50.

Here, the oscillation frequency of the reference clock oscillator 43 and f _1, first from the first horizontal scanning start signal 57 is output 1
First output period of the clock signal 55 period or a series of up to output the count end signal 58, ignoring the synchronization accuracy of the clock synchronization circuit 44 can be expressed by N / f _1.

On the other hand, if the difference between the output timings of the first horizontal scan start signal 57 and the second horizontal scan start signal 59 is constant, and if the first horizontal scan start signal 57 is output earlier by Δt, The frequency f2 of the _second clock signal 56 is expressed by the following equation (1).

f ₂ = M / (N / f ₁ −Δt) (1) Therefore, by changing the value of M, which is the count value of the counting circuit 51, by an external access such as a dip switch, the second clock signal 56 is obtained. it is possible to adjust the frequency f _2. As a result, the first semiconductor laser
V ₁ the scanning speed of the output light 14, when the scanning speed of the output light from the second semiconductor laser 20 and V _2, the relationship between the scanning speed V _1, V ₂ and a frequency f _1, f ₂ is the following Equation (2) is obtained.

Therefore, by appropriately changing the value of the count value M of the counting circuit 51, the output light of the first semiconductor laser 14 and the second
It is possible to correct the image shift caused by the difference in the scanning speed of the output light of the semiconductor laser 20. In practice, it would be better to adjust while measuring the magnification difference between the two color images on the output print of this recording device.

FIG. 4 corresponding to FIG. 5 shows the state of formation of the electrostatic latent image obtained by this correction.
It can be seen that “ABCDE” matches the position in the main scanning direction with any of the laser beams.

As described above, in the image recording apparatus of the present embodiment, the position shift of the image can be corrected by changing the value of M of the counting circuit 51 in the clock signal generator 32 by external access. It is not necessary to increase the accuracy of the horizontal scanning synchronization circuits 46 and 47 as the detectors or to make mechanical adjustments.

As described above, the present invention has been described with reference to the embodiment. However, the present invention is not limited to the above-described embodiment, and can be variously changed without changing the gist of the present invention. For example, in the above embodiment, two systems of laser beams 12 and 13 are used. However, the present invention can be applied to a case where multicolor recording is performed using three or more systems of laser beams. The circuit having the same configuration as that of the clock signal 56 generator may be added.

Further, in the above embodiment, two types of electrostatic latent images are formed on the same photosensitive drum 11 using one rotating polygon mirror 16, and
Although the case where the image is transferred in one transfer operation has been described, it is needless to say that the present invention can be applied to the case where each laser beam is simultaneously polarized and scanned on a different medium to be scanned.

Furthermore, in the above-described embodiment, an example in which image recording is performed by scanning with a laser beam has been described. However, it is a matter of course that the present invention can be applied to an image recording apparatus that performs scanning with a light beam.

[Effects of the Invention] As described above, according to the image recording apparatus of the present invention, a plurality of clock signals used to correct a position shift of an image due to a difference in scanning speed of a plurality of light beams on a medium to be scanned. As one of them, a first clock signal having a frequency obtained from a reference clock oscillation source such as a crystal oscillator is used, a second clock signal as another clock signal is used, and a first clock signal is used as a PLL. Since the configuration is obtained by adjusting with a circuit, it is possible to suppress the image displacement with a simple configuration without increasing the position accuracy of the photodetector or performing mechanical adjustment, and thus a clear image can be obtained. Obtainable.

[Brief description of the drawings]

FIGS. 1 to 3 each illustrate an embodiment of the present invention. FIG. 1 is a block diagram showing the configuration of a clock signal generator, and FIG. 2 is a block diagram of the clock signal generator. FIG. 3 is a waveform diagram for explaining the operation, FIG. 3 is a schematic configuration diagram showing a main part of the image recording apparatus, and FIGS. 4 and 5 show a state of forming an electrostatic latent image by two kinds of laser beams. FIG. 4 is an explanatory view showing a state after correction by the clock signal generator, FIG. 5 is an explanatory view showing a state before correction, and FIG. 6 is an explanatory view showing a state of polarization scanning of the rotary polygon mirror. It is. 11 photosensitive drum, 12 first-system laser beam, 13 second-system laser beam, 32 clock signal generator, 42 first memory buffer, 43 reference clock oscillator, 44 …… Clock synchronization circuit, 45,51… Counter circuit, 48 …… Phase comparator, 49 …… Loop filter, 50 …… Voltage controlled oscillation, 53 …… Second memory buffer, 54 …… PLL circuit .

Continuation of the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) B41J 2/44 B41J 2/525 G03G 15/04

Claims (1)

(57) [Claims] 1. A light beam generating source for generating a plurality of systems of light beams on a medium to be scanned, a modulating means for receiving an image signal prepared for each system and modulating the light beam for each system, A clock signal generator for generating a plurality of clock signals for transferring a signal to the modulator, the clock signal generator comprising: a reference clock oscillation source for outputting a reference clock pulse; and a reference clock oscillation source. A first clock signal generating circuit for receiving a clock pulse output from the first input and outputting a first clock signal having a frequency corresponding to a scanning speed of a light beam of a reference system among the light beams; Inputting the first clock signal output from the clock signal generation circuit of (1), corresponding to the scanning speed of another type of light beam of the light beam. A second clock signal generating circuit for outputting a second clock signal having a wave number; and a frequency for setting the frequency of the second clock signal output from the second clock signal generating circuit in accordance with the displacement of the image An image recording apparatus comprising: setting means.