JPH08248336A - Image forming device - Google Patents

Abstract

PURPOSE: To reduce fatigue by preventing a forcedly emitted laser beam from scanning on a photoreceptor when the revolving speed of a polygon mirror is later than a normal state like a starting time. CONSTITUTION: This device is a laser printer controlling the rotation of the polygon mirror 33 based on the detection result of the laser beam by an SOS sensor 42 provided on the position of this side of scanning in the vicinity of a photoreceptor drum 41. The laser printer is provided with a laser drive circuit 22 driving a laser diode 23 based on the image data and the forced light emission data imparted from a drive data generation circuit 21 and outputting the laser beam, operation parts 11, 12 operating a period immediately before detecting an SOS detection signal and control parts 13, 14 deciding the forced light emission data so that laser beam outputted based on the forced light emission data does not scan on the photoreceptor drum 41 based on the period operated by the operation parts 11, 12 and imparting them to the drive data generation circuit 21.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus for forming an image by scanning a photosensitive member with a laser beam. In particular, a light receiving sensor (= SOS (Start of Scan) sensor) provided in the vicinity of the photoconductor before the start of laser scanning detects the laser beam of forced emission, and controls the rotation of the polygon mirror based on the detection signal. Related to the device.

[0002]

2. Description of the Related Art Electrophotographic image forming apparatuses such as laser printers, digital copying machines, and plain paper facsimiles have been provided. In these devices, an electrostatic latent image is formed on the photoconductor by scanning the photoconductor with a laser beam modulated with image data. In the above device, an SOS sensor is provided at a predetermined position near the start of laser scanning near the photoconductor to detect a forced emission laser beam, and the rotation speed of the polygon mirror is controlled based on the detection signal. It is provided. The forced emission laser beam is a laser beam that is output regardless of image data, and is intended to irradiate the SOS sensor. Therefore, the timing of forced light emission is set to the timing at which the laser beam reflected by the polygon mirror passes through the position of the SOS sensor. The polygon mirror is a rotating polygonal reflecting mirror of a regular polygonal column, and is an optical member that scans the photoconductor by reflecting a laser beam output from a laser diode as the polygon mirror rotates.

[0003]

In a device for controlling the rotation speed of a polygon mirror on the basis of a detection signal of an SOS sensor, when the rotation speed of the polygon mirror is slow, the laser beam of forced emission irradiates the photoconductor. There is a problem of fatigue. That is, the timing of the forced light emission is set to the timing at which the laser beam reflected by the polygon mirror passes through the position of the SOS sensor, and the start time is, for example, the previous detection time by the SOS sensor. . Therefore, when the rotation speed of the polygon mirror is slower than the steady state, such as when the device is started, if the laser diode is forced to emit light at a predetermined timing calculated from the previous detection time of the SOS sensor, the area other than the SOS sensor is detected. For example, the photoconductor is irradiated.

Further, since the scanner motor for rotating the polygon mirror takes a longer time to reach steady rotation than the main motor for rotating the photosensitive drum, there is a circumstance that the scanner motor is started first. . For this reason,
In particular, in the initial stage of startup, the laser beam of forced emission may scan the same line of the photoconductor drum over and over again, which causes a problem that the fatigue of the photoconductor becomes more severe.

It is possible that the forced light emission for the SOS sensor is not performed when the apparatus is started, but in that case,
It becomes impossible to control the rotation speed of the polygon mirror based on the detection signal of the SOS sensor, and as a result, problems such as damage to the motor due to excessive rise in the rotation speed and a long time until the rotation speed stabilizes occur. The present invention prevents the laser beam of forced emission from scanning the photoconductor even when the rotation speed (rotation speed) of the polygon mirror is different from the steady speed, such as when the apparatus is started, and The purpose is to reduce fatigue.

[0006]

SUMMARY OF THE INVENTION The present invention achieves the above object by controlling the timing of forced light emission according to the rotation speed of a polygon mirror. That is,
The present invention forms an electrostatic latent image by repeatedly scanning a photoconductor with a laser beam reflected by a rotary reflecting mirror, and detects the laser beam by a light-receiving sensor provided at a position near the photoconductor before the start of scanning. A device for controlling the rotation of the rotary reflecting mirror based on the detection signal, the driving device driving a laser diode according to image data and forced light emission data to output the laser beam, and detecting the detection signal. A calculating means for calculating the immediately preceding cycle; and the forced light emission data is determined based on the cycle calculated by the calculating means so that the laser beam output according to the forced light emission data does not scan the photoconductor. An image forming apparatus including: a control unit that supplies a driving unit. The "cycle immediately before detection" means 1 immediately before detection.
It may be a cycle, or a certain cycle immediately before detection, or an average value thereof. In short, it suffices to represent the rotation speed of the reflecting mirror at each detection time.

[0007]

The forced light emission data is determined based on the period of the SOS signal immediately before detection, which reflects the rotational speed of the reflecting mirror at the detection time, so that the laser beam for forced light emission does not scan the photoconductor, and the forced light emission is performed. The laser diode is driven according to the data.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a block diagram showing a schematic configuration of a main part of a device of the embodiment, functions and inputs / outputs of a control circuit, and FIG. 2 is a timing chart of each signal for determining a forced light emission time zone.
FIG. 3 is a flow chart showing the processing related to turning on / off the scanner motor, and FIG. 4 is a flow chart showing the processing for setting the timer B for managing the forced light emission time in response to the interrupt of the SOS signal. , FIG. 5 is an explanatory diagram showing the relationship between Ts, Tf and E.

As shown in FIG. 1, this apparatus repeats the surface of the photosensitive drum 41, which is rotated at a constant speed by a main motor (not shown), in the direction of the arrow in the figure by the laser beam reflected by the polygon mirror 33. A laser printer that forms an electrostatic latent image on the surface of the photosensitive drum 41 by scanning, develops the electrostatic latent image with a developing device (not shown) to transfer it onto a sheet, and then fixes and discharges it. Is.

The image data corresponding to the electrostatic latent image is read out from a recording medium such as a CD-ROM, read by an image scanner, or acquired through a communication network to obtain a laser beam. It is given to the drive data generation circuit 21. The laser drive data generation circuit 21
Data for driving the laser diode is created according to the input image data and is given to the laser driving circuit 22.
In response to this, the laser drive circuit 22 drives the laser diode 23 to output the laser beam toward the polygon mirror 33. Thus, the electrostatic latent image is formed as described above.

In this apparatus, a light receiving (SOS (Start of Scan) sensor is provided at a position near the photosensitive drum 41 on the front side of the scanning start, and the scanner motor 32 is based on the signal detected by the SOS sensor 42. That is, the rotation speed of the polygon mirror 33 is calculated by the rotation speed calculation unit 11 based on the detection signal of the SOS sensor 42, and the detection speed as the calculation result is set to a desired speed. The control voltage of the scanner motor 32 required to bring them closer to the rotation control voltage calculation unit
The calculation is performed at 15, and the control voltage signal that is the calculation result is applied to the motor drive circuit 31 to control the rotation speed of the scanner motor 32 to a desired value.

Therefore, as the polygon mirror 33 rotates, the laser beam repeatedly scanned in the direction of the arrow in FIG.
The laser diode 23 is forced to emit light at the timing of passing the position of the OS sensor 42. That is, since there is no image data at this timing, the laser diode 23 should originally be turned off. However, as described above, since the SOS sensor 42 needs to detect a signal to control the rotation speed of the scanner motor 32, the image data is The laser diode 23 is turned on regardless of.

The data for this is the forced light emission ON / OF.
It is supplied from the F control unit 13 to the laser drive data generation circuit 21. In the conventional device, the rotation speed of the polygon mirror 33 is not reflected in the on / off signal for forced light emission. Therefore, when the polygon mirror 33 is rotating at a low speed such as when the apparatus is started, the laser beam of forced emission may irradiate the photoconductor drum 41 as described above. 41 was the cause of fatigue.

In this apparatus, the period Ts immediately before the detection of the laser beam by the SOS sensor 42 is obtained, and the value Tf obtained by multiplying the period Ts by a constant E is set as the elapsed time until the next forced light emission start time. In other words, the problem described above is solved by using Tf as timing data that gives the next forced light emission start time.

Here, E is the time b during which the laser beam scans the photosensitive drum 41 in the steady state, as shown in FIG. 5, and the laser beam in the steady state is the SOS sensor.
A value divided by the period a passing through 42, that is, E = b / a. In other words, E is a value indicating the ratio of the time that the laser beam scans the photosensitive drum 41 during image formation (steady state). On the other hand, the period Ts is a value corresponding to the rotation speed of the polygon mirror 33. To be exact, SO
Polygon mirror just before each detection time by the S sensor 42
It is a value corresponding to the rotation speed of 33.

Therefore, the time Tf, that is, Tf = Ts × E, can be considered to be approximately equal to the time during which the laser beam scans the photosensitive drum 41 at each detection time of the SOS sensor 42. Is. By using such time Tf as timing data for giving the next forced light emission start time, in this device, the laser beam for forced light emission is changed to the photosensitive drum 41.
I try not to irradiate. Note that the above E can be used during acceleration of the scanner motor 32, but cannot be used during deceleration. Therefore, in this device, the laser beam forcibly emitting light is turned off during deceleration.

A description will be given below with reference to the flow chart and timing chart. When the scanner motor 32 is requested to be turned on by issuing a command to start the device by turning on the power (S1
1) On condition that the scanner motor 32 is off
(S21; YES), command to turn on the scanner motor 32 (S22)
And, the laser diode 23 is instructed to be turned on (S23).
. Further, the SOS signal interrupt is permitted (S24). SO
The interruption of the S signal occurs at each edge at which the SOS signal switches from the on state to the off state.

Further, the count of the timer A for period measurement is started (S25). This timer A will be called S
It is reset each time the OS signal is interrupted, and the counting up is restarted (see FIG. 2B). Further, the count value Ts at the time of reset is stored in the buffer and used for the calculation of steps S53 and S54 in FIG. That is, Tf =
It is used for the calculation of Ts × E.

Furthermore, as a trigger for the forced light emission timer B, an edge at which the SOS signal switches from the on state to the off state is selected (S26). The timer B is subsequently subjected to step S53 and step S54 of FIG. 4 each time the SOS signal is interrupted and the count value becomes "0".
The time Tf, which is the result of the calculation at, is read (S55)
The countdown is restarted (see (c) of FIG. 2).

The timer B which counts down in this way
When the count value of is 0, the forced light emission of the laser diode 23 is started each time, as shown in FIG. Further, the forced light emission is continued until the next edge when the SOS signal is switched from the on state to the off state is detected.

As a result of being controlled in this way, in this device,
According to the rotation speed of the polygon mirror 33, it is possible to switch the forced emission timing of the laser diode 23 so that the laser beam does not scan the photosensitive drum 41, and as a result, the laser beam of the forced emission at the time of low speed rotation. Fatigue due to the scanning of the photosensitive drum 41 is prevented.

The branch of steps S31 to S36 in FIG. 3 is the processing when the scanner motor 32 is requested to be turned off by issuing a command to stop the apparatus by turning off the power supply or the like. That is, as described above, the ratio E is effective during the acceleration of the scanner motor 32, but cannot be used during the deceleration. Therefore, when the scanner motor 32 is requested to be turned off, the scanner E The motor 32 and the laser diode 23 are turned off (S32, S33), the interruption of the SOS signal is prohibited (S34), the period measurement timer A and the forced light emission timer B are set.
Is stopped (S35, S36). Further, even if the control is performed in this way, there is no risk of causing a problem in the controlled object.

[0023]

According to the present invention, S is determined according to the forced light emission data.
The forced light emission for the OS sensor is performed, and the forced light emission data is determined as the timing for scanning other than the photoconductor region based on the cycle immediately before the detection of the SOS signal corresponding to the rotation speed of the reflecting mirror. Even when the rotation speed of the polygon mirror deviates from the steady speed, such as when starting up,
The forced emission laser beam is prevented from scanning the photoconductor, thus reducing unnecessary fatigue of the photoconductor.

[Brief description of drawings]

FIG. 1 is a block diagram schematically showing a configuration of a main part of an apparatus according to an embodiment.

FIG. 2 is a timing chart of each signal that determines the forced light emission time zone in the apparatus of the embodiment.

FIG. 3 is a flowchart showing a process related to turning on / off a scanner motor.

FIG. 4 is a flowchart of a process of setting a timer B that manages a forced light emission time in response to an SOS signal interrupt.
To.

FIG. 5 is an explanatory diagram showing a relationship among values Ts, Tf, and E used in the apparatus of the embodiment.

[Explanation of symbols]

 32 Scanner Motor 33 Polygon Mirror 41 Photosensitive Drum 42 SOS Sensor

Claims (1)

[Claims] 1. An electrostatic latent image is formed by repeatedly scanning a photoconductor with a laser beam reflected by a rotary reflecting mirror, and a laser beam is provided by a light receiving sensor provided in a position near the photoconductor before the start of scanning. And a drive means for driving a laser diode according to image data and forced light emission data to output the laser beam; Is calculated based on the cycle calculated by the calculating means so that the laser beam output according to the forced light emission data does not scan the photoconductor. And a control unit that supplies the driving unit with the image forming apparatus.