JP3228316B2 - Write timing control device for light beam scanning device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a writing timing control device of a light beam scanning device for writing an electrostatic latent image on a photoreceptor and used in a copying machine, a laser beam printer, and the like. The present invention relates to an improvement for improving the adjustment accuracy of an image writing position.

[0002]

2. Description of the Related Art In a digital copying machine, for example, an electrostatic latent image is formed on a photoreceptor by a light beam scanning device based on image information of a document read by an image scanner, and the electrostatic latent image is developed. The formed toner image is transferred to a recording sheet to form an image. The light beam scanning device used for such a purpose modulates a light beam emitted from a laser light source with an image signal, and scans the photosensitive member with the modulated light beam using a polygon mirror rotating at high speed. Each line is configured to be deflected and moved over a predetermined scanning range, whereby an electrostatic latent image corresponding to image information can be written on a photoconductor.

In such a light beam scanning device,
In order to prevent the writing position of the latent image for each scanning line from varying and deteriorating the image quality, the scanning start position of the light beam is detected by the position detection sensor for each scanning line, and the scanning output by this sensor is performed. Start signal (hereinafter, SOS signal)
, An image signal write timing signal (hereinafter, video clock) is synchronized, and thereafter, the electrostatic latent image is written based on the synchronized video clock.

In recent years, yellow, cyan,
There has been proposed a color image forming apparatus in which toner images of magenta and black color components are continuously transferred from a plurality of photoconductors to one recording sheet to increase the image forming speed. In this color image forming apparatus, a light beam scanning device is provided for each photoconductor of each color component. By controlling the writing timing of the electrostatic latent image in each light beam scanning device, the toner of each color component on the recording sheet is controlled. A device has been devised to exactly match the transfer position of the image.

More specifically, a reference pattern is sequentially transferred from a photosensitive member of each color component onto a transfer means such as a belt for transferring a recording sheet, and a transfer position of the reference pattern on the transfer means is determined by an optical sensor. To calculate the amount of deviation of the transfer position of the other toner image from the transfer position of the first color toner image to create correction data for the writing position of the electrostatic latent image, and based on this correction data, form the next image It is configured to control the writing timing of the electrostatic latent image in each light beam scanning device from the operation.

Conventionally, as an apparatus for controlling the write timing of the light beam scanning apparatus based on such write position correction data, a reference clock having a frequency several times higher than that of the video clock is used in response to the input of the SOS signal. There is known a device that counts, outputs a delay timing signal when the count value reaches a predetermined set value, and synchronizes a video clock with the delay timing signal.

In such a device, the video clock is synchronized at a timing delayed by a predetermined time from the input timing of the SOS signal in accordance with the set value of the counter for counting the reference clock. By changing the set value of the counter based on the correction data, the writing timing of the electrostatic latent image could be freely controlled, and the transfer position of the toner image on the recording sheet could be adjusted.

[0008]

However, in order to control the writing timing of the electrostatic latent image with high precision in such a conventional apparatus, a reference clock having a higher frequency is required. However, there is a problem that the circuit design becomes complicated and the cost is increased. In addition, since an electromagnetic wave is easily generated to generate a high-frequency clock, a measure for shielding the electromagnetic wave is required. Further, the technical limit of the frequency of the reference clock is about 150 MHz. Considering that the video clock of the medium-speed color copying machine is about 50 MHz,
No matter how much the writing timing of the electrostatic latent image is controlled, the transfer position of the toner image is at most one pixel of each pixel forming an image.
The adjustment could only be made with an accuracy of about ３, and the transfer position deviation of the toner image smaller than this could not be eliminated.

As a write timing control device which solves such a problem, a plurality of delay circuits are connected in series to an oscillator for oscillating a reference clock, and a plurality of video clocks having different delay times with respect to the reference clock are generated in advance. It has been already proposed that a video clock having a delay time closest to the delay time required by the write position correction data is selected (Japanese Patent Application Laid-Open Nos. 63-296558 and 63-296558). -282954).

However, in this device, a delay circuit is required for each different delay time. Therefore, if the delay time is subdivided in order to control the writing timing of the electrostatic latent image with high accuracy, the device is also realized. However, there is a problem in that the circuit for this becomes complicated, resulting in an increase in cost.

SUMMARY OF THE INVENTION The present invention has been made in view of the foregoing problems, and has as its object to write a light beam on a photosensitive member without using a high-frequency reference clock and with a simple circuit configuration. An object of the present invention is to provide a writing timing control device of a light beam scanning device capable of adjusting a position with high accuracy.

[0012]

That is, as shown in FIG. 1, a writing timing control device of a light beam scanning device according to the present invention comprises a light beam (Bm) corresponding to an image signal for each scanning line of the photosensitive member 2. ) Is moved and scanned, and the light beam scanning device 1 that writes a latent image corresponding to an image signal on the photosensitive member 2 detects a scanning start position of the light beam (Bm) for each scanning line and outputs a scanning start signal (Bm). The scanning start signal (SOS) is generated in accordance with the scanning start signal generating means 3 for generating the SOS, and the latent image writing position correction data for the photoconductor 2.
S) outputs a delay timing signal (DELAY) after a predetermined delay time from the input of S), and a write timing signal (V) of the image signal at a predetermined timing synchronized with the delay timing signal (DELAY).
CK) and timing signal generating means 5 for generating
The delay time generating means 4 outputs the scanning start signal (SO
S), a ramp voltage generating means 6 for outputting a lamp voltage, a constant voltage generating means 7 for outputting a fixed delay time determining voltage according to the write position correction data, and a ramp voltage and a delay time determining voltage. And when the two voltage values match, the delay timing signal (DELAY)
And a voltage comparing means 8 for outputting the same.

In the above technical means, the ramp voltage generating means 6 constituting the delay time generating means 4 is triggered by the input of the SOS signal as shown by the solid line in the graph of FIG. As long as the lamp voltage generates a lamp voltage in which the magnitude of the voltage V gradually changes in one direction with the passage of time, the specific configuration may be appropriately changed in design. Such a lamp voltage generating means 6 is realized by a circuit in which a capacitor C and a resistor R are connected in parallel to a DC power supply DC as shown in FIG. 3, for example. In this circuit, when the switch a is closed and the switch b is opened to charge the capacitor C, and then the switches a and b are opened and closed in reverse, a lamp voltage can be obtained from the output across the resistor R.

FIG. 2 shows a lamp voltage in which the time T and the voltage V are completely proportional to each other. However, if the voltage V changes linearly with the elapse of the time T, the lamp voltage is changed. The lamp voltage of the present invention is not limited to that of FIG.

Further, as shown by a broken line in the graph of FIG. 2, the constant voltage generating means 7 constituting the delay time generating means 4 has a constant voltage corresponding to the write position correction data within the change range of the ramp voltage. Delay time determination voltage V
_As long as it outputs ₀ , its specific configuration may be appropriately changed in design.

Furthermore, the timing signal generating means 5
As long as a write timing signal, that is, a video clock is generated at a timing synchronized with the delay timing signal output from the delay time generation unit 4, the specific configuration may be appropriately changed in design. A specific configuration for synchronizing the video clock with the input signal in this manner is described in, for example,
No. 9346, JP-A-61-150587, JP-A-1-222568 and the like.

[0017]

According to the above technical means, the lamp voltage generating means generates a lamp voltage which changes with time triggered by the input of the scan start signal (SOS signal), while the constant voltage generating means generates the electrostatic latent voltage with respect to the photosensitive member. A constant delay time determination voltage is output according to write position correction data indicating a correction value of an image write position. The voltage comparing means compares the ramp voltage with the delay time determination voltage, and outputs a delay timing signal when the ramp voltage changed with the passage of time matches the delay time determination voltage. Thereafter, the timing signal generation means generates a write timing signal (video clock) of the image signal at a predetermined timing synchronized with the delay timing signal.

Here, since the value of the ramp voltage gradually decreases or increases with the passage of time, if the delay time determining voltage output by the constant voltage generating means is changed according to the write position correction data, It is possible to arbitrarily extend or shorten the time from when the output of the lamp voltage is started until the voltage value matches the delay time determination voltage. In addition, since the setting step of the delay time determining voltage can be easily subdivided within the range of decrease or increase of the lamp voltage, the time until the voltage value of the lamp voltage and the delay time determining voltage match with high accuracy. Can be controlled.

That is, it is possible to control the delay time from the input of the scanning start signal to the output of the delay timing signal with high accuracy, and to synchronize the write timing signal of the image signal with the delay timing signal. Thus, a write timing signal delayed by a predetermined time with respect to the scan start signal can be generated.

[0020]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram showing a write timing control device of a light beam device according to the present invention; In this embodiment, the present invention is applied to a digital color copying machine equipped with a light beam scanning device (hereinafter referred to as ROS).

FIG. 4 shows the ROS 10 used in this embodiment.
FIG. In FIG.
Is a photosensitive drum, 12 is a semiconductor laser, 13 is a reflecting surface 13 of a light beam Bm emitted from the semiconductor laser.
a is a scanner motor for rotating the polygon mirror 13;
Denotes an fθ lens, which is configured so that the light beam Bm scans the photosensitive drum 11 over a predetermined scanning range n with the rotation of the polysilicon mirror 13. A mirror 17 is provided in the optical path of the light beam Bm corresponding to the scanning start point of the photosensitive drum 11, and the light beam Bm
A position detection sensor 16 (hereinafter, referred to as an SOS sensor) on which the reflected light of the mirror 17 is incident is disposed outside the scanning range n of m, and the SOS sensor 16 detects the scanning start timing of the light beam Bm. It has become so.

FIG. 5 is an overall block diagram of the image writing control system of the ROS 10. As shown in FIG. In the figure, reference numeral 18 denotes a sensor amplifier for amplifying a scanning start signal (hereinafter referred to as an SOS signal) sent from the SOS sensor 16 to a predetermined level, and reference numeral 19 performs image processing of a read document image and sequentially outputs an image signal IS. Reference numeral 20 denotes a laser control signal LC delayed for a predetermined time from the SOS signal in accordance with the write position correction data.
A video clock generation control circuit that outputs an S write timing signal (hereinafter referred to as a video clock) VCK;
Reference numeral 21 denotes an ROS controller to which an image signal IS and a video clock VCK from the image processing unit 19 are input and outputs a laser control signal LCS based on the image signal IS in synchronization with the video clock VCK.
The laser driver converts the laser control signal LCS from the S controller 21 into a laser drive signal LDS and outputs the laser drive signal LDS to the semiconductor laser 12. In the above configuration, the video clock generation control circuit 20 corresponds to the write timing control device of the present invention.

FIG. 6 shows the video clock generation control circuit 20 described above. This circuit is the main C
A delay time generating circuit 30 that outputs a delay timing signal after a predetermined delay time from the input of the SOS signal based on the electrostatic latent image write position correction data sent from the PU
And a flip-flop 40 for generating a delayed SOS signal synchronized with the delayed timing signal, and a timing signal generating circuit 50 for outputting a video clock VCK synchronized with the delayed SOS signal.

First, the delay time generating circuit 30 includes a ramp voltage generating circuit 31 for generating a ramp voltage as shown in FIG. 2 in accordance with a switch operation, and a constant delay time determining voltage in accordance with write position correction data. The output voltage of the ramp voltage generation circuit 31 and the output voltage of the D / A converter 32 are compared with each other, and a voltage that outputs a delay timing signal when the two voltage values match is obtained. And a comparator 33. The lamp voltage generating circuit 31 includes a pulse generating circuit 34 for generating a trigger signal having a fixed time width from the SOS signal, and a trigger circuit 35 for performing a switch operation of the lamp voltage generating circuit 31 in accordance with the trigger signal. Connected, SOS
The lamp voltage is generated at a predetermined timing synchronized with the input of the signal. On the other hand, a latch circuit 36 is connected to the D / A converter 32 so that write position correction data supplied to the D / A converter 32 is held in accordance with a latch signal.

A reset signal for resetting the ramp voltage generation circuit 31 is input to the trigger circuit 35 from a delay circuit 37. The reset signal is supplied to the trigger circuit 35 from a delay timing from the voltage comparator 33. The signal is generated by applying a signal to the delay circuit 37.

On the other hand, the flip-flop 40 has an SOS
A delay SOS signal is output to the timing signal generation circuit 50 in response to the input of a signal, a trigger signal, and a delay timing signal. The SOS signal is input to an input terminal D of the signal, and the trigger signal is input to a clock terminal CK. Is input, the delayed SOS signal of the output Q switches to a high level, and when the delay timing signal is further input to the reset terminal R, the delayed SOS signal switches to a low level.

The timing signal generation circuit 50
Is an oscillator 51 for generating a reference clock, and a video clock synchronization circuit 52 for synchronizing the reference clock with the delayed SOS signal sent from the flip-flop 40.
It is composed of FIG. 7 shows an example of the timing signal generation circuit 50, in which the oscillation of the video clock can be turned on / off according to the input of the delayed SOS signal.

FIG. 8 is a timing chart showing the output timing of each signal in the video clock generation control circuit 20. Assuming that the light beam Bm starts scanning the photosensitive drum 11 and the SOS signal is switched from a low level (hereinafter, described as L) to a high level (hereinafter, described as H) at time t ₁ , the pulse generation circuit 34 Switches the trigger signal from L to H with a predetermined delay from time t1.
The delay time here is a response delay of the pulse generation circuit 34. As a result, a switch operation of the lamp voltage generation circuit 31 is performed, and the lamp voltage generation circuit 31 outputs a lamp voltage.

The write position correction data is transferred from the main CPU of the copying machine to the latch circuit 36 for each original image or for each scanning line of the light beam Bm. / A converter 32 is set. As a result, the D / A converter 32 outputs a fixed delay time determination voltage according to the write position correction data.

Then, the voltage comparator 33 compares the ramp voltage from the ramp voltage generating circuit 31 with the delay time determining voltage from the D / A converter 32. Switch from L to H. Here, the delay time from the coincidence of the two voltage values to the output of the delay timing signal is determined by the voltage comparator 3
3 is the response delay.

On the other hand, for the flip-flop 40,
Since the SOS signal is input to the input terminal D and the trigger signal is input to the clock terminal CK, when the trigger signal switches from L to H with a slight delay from the SOS signal, the flip-flop 40 outputs from the output terminal Q. Delayed SOS
Switch the signal from L to H. And the reset terminal R
Is switched from L to H at time t2, the delayed SOS signal is switched from H to L with a slight delay. This delay time is an operation delay time in the flip-flop 40.

Therefore, the delayed SOS signal switches from L to H at a timing synchronized with the SOS signal, and switches from H to L at a timing synchronized with the delayed timing signal.

The delay timing signal is also input to the delay circuit 37, and a reset signal slightly delayed from the delay timing signal is input from the delay circuit 37 to the trigger circuit 35. Thereby, the lamp voltage generation circuit 31
Is operated to stop the output of the lamp voltage.

Then, in the timing signal generation circuit 50 to which the delayed SOS signal is input, the delayed SOS signal becomes L
Oscillating cutting switched the video clock to H is turned off, the oscillation of the video clock is restarted at the time with a time delay and delay SOS signal is switched from H to L t ₃ from. That is, the video clock is synchronized with the timing at which the delay SOS signal switches from H to L, in other words, the video clock is synchronized with the timing at which the delay timing signal switches from L to H.

[0035] In the video clock generation control circuit 20 of the thus this embodiment, the delay timing signal at a timing t ₂ when the predetermined delay time from the input timing t ₁ of the SOS signal has passed is output, synchronized to the delayed timing signal video clock is generated at the timing t ₃ when the. At this time, if appropriately setting the delay time determining voltage in accordance with the writing position correction data, the time T ₀ until the lamp voltage matches the delay time determined voltage from the occurrence is shortened or extended, for the timing t ₁ delay time of the timing t ₂ would correspond to the writing position correction data.

If the main CPU of the copying machine is assumed to be 8 bits, the write position correction data, that is, the delay time determination voltage can be subdivided into 256 steps, so that the time T ₀ is set to 256 steps. Can be
It can be controlled by that amount the delay time of the timing t ₂ for the timing t ₁ with high accuracy.

Accordingly, in this embodiment, after the SOS sensor 16 detects the start of scanning of the light beam Bm, the video clock is synchronized at a timing after a predetermined delay time according to the write position correction data has elapsed. Since the writing of the electrostatic latent image is performed using the obtained video clock, the writing position of the electrostatic latent image can be adjusted with high accuracy in accordance with the writing position correction data.

[0038]

As described above, according to the write timing control device of the light beam scanning device of the present invention,
The ramp voltage is generated by the ramp voltage generator in synchronization with the scanning start signal, while the constant voltage generator outputs a fixed delay time determination voltage according to the write position correction data, and these are compared by the voltage comparator. Since the write timing signal delayed by a predetermined time with respect to the scan start signal can be generated with high accuracy, the writing of the light beam to the photosensitive member can be performed with a simple circuit configuration without using a high frequency reference clock. The position can be adjusted with high precision.

[Brief description of the drawings]

FIG. 1 is a diagram showing a schematic configuration of a write timing control device of a light beam scanning device according to the present invention.

FIG. 2 is a graph showing a relationship between a lamp voltage and a delay time determining voltage.

FIG. 3 is a circuit diagram illustrating an example of a lamp voltage generation unit.

FIG. 4 is a perspective view showing a light beam scanning device according to the embodiment.

FIG. 5 is a block diagram illustrating a control system of the light beam scanning device according to the embodiment.

FIG. 6 is a block diagram illustrating a video clock generation control circuit according to the embodiment;

FIG. 7 is a circuit diagram illustrating an example of a timing signal generation circuit according to the embodiment;

FIG. 8 is a timing chart showing an operation state of the video clock generation control circuit according to the embodiment.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Light beam scanning device, 2 ... Photoconductor, 3 ... Scan start signal generation means, 4 ... Delay time generation means, 5 ... Timing signal generation means, 6 ... Lamp voltage generation means, 7 ... Constant voltage generation means

Claims (1)

(57) [Claims] 1. A light beam scanning apparatus for moving and scanning a light beam corresponding to an image signal for each scanning line of a photosensitive member and writing a latent image corresponding to the image signal on the photosensitive member. Detect the beam scanning start position,
Scanning start signal generating means for generating a scan start signal; delay time generating means for outputting a delay timing signal after a predetermined delay time from the input of the scan start signal, in accordance with the latent image writing position correction data on the photosensitive member; Timing signal generating means for generating a write timing signal of the image signal at a predetermined timing synchronized with the delay timing signal, wherein the delay time generating means outputs a lamp voltage according to the scanning start signal. A voltage generating unit, a constant voltage generating unit that outputs a fixed delay time determining voltage according to the write position correction data, and a comparison between the ramp voltage and the delay time determining voltage. And a voltage comparing means for outputting the delay timing signal. Timing control device.