JPH1148531A - Laser scan apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce jitters caused by a shift of an image formation position of a laser light in a forward-rearward direction on an optical axis because of a temperature change in a laser scan apparatus which starts outputting of image signals for lines on the basis of a detection time of the laser light by a photodetecting sensor. SOLUTION: The apparatus is provided with a temperature sensor 21 for detecting an environmental temperature and a means for adjusting a position of an image formation lens 10/a position of a photodetecting sensor 11/a sensitivity of the photodetecting sensor 11 in accordance with a detection result of the temperature sensor 21 so as to output detection signals of an equivalent characteristic to that when a laser light entering the photodetecting sensor 11 forms an image correctly to a photodetecting face of the photodetecting sensor 11.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image signal for each scanning line based on a detection time of a laser beam by a light receiving sensor provided at a predetermined position optically equivalent to an extended position of the main scanning line. The present invention relates to a laser scanning device that controls an output start time.

[0002]

2. Description of the Related Art Laser printers, laser facsimile machines,
2. Description of the Related Art A digital image forming apparatus such as a laser type digital copying machine is equipped with a laser scanning device. In this laser scanning device, the output start time of the image signal for each scanning line is set based on the detection time of the laser beam by the light receiving sensor provided at a predetermined position optically equivalent to the position on the extension of the main scanning line. Controlled. This control is SOS (Start of Scan)
It may be called control, and the light receiving sensor may be called an SOS sensor.

In an SOS sensor, a detection signal is output when the intensity of a laser beam applied to a light receiving surface of the SOS sensor exceeds a certain slice level (a dashed line in FIG. 3A). For example, as shown in FIG. 3B, the detection signal falls at a time when the intensity of the laser beam exceeds the slice level, reaches a peak, and then falls below the slice level. The waveform returns to the original level. By binarizing this waveform with a certain threshold value (a dashed line in FIG. 3B), a synchronization signal shown in FIG. 3C is obtained. In the laser scanning device, as shown in FIG. 3D, the output of the image signal for the line starts at a time when a predetermined time τ has elapsed from the detection time of the synchronization signal. That is, writing of the line is started.

For this reason, the intensity of the laser beam fluctuates,
If the time at which the amount of light exceeding the slice level starts to enter the SOS sensor fluctuates from the normal time, for example, because the mounting position of the SOS sensor deviates from a position (optically equivalent position) on the extension of the scanning line. Therefore, the above-mentioned SOS control is hindered. Japanese Patent Application Laid-Open No. 4-168455 discloses a technique for setting a slice level with a margin by adjusting the amount of laser light at a low level. Japanese Patent Application Laid-Open No. 4-88371 discloses a technique in which the beam irradiation position is set to the best position when adjusting the SOS sensor.

[0005]

As shown in FIG. 4A, the imaging lens 10 is adjusted so that a laser beam forms an image on the light receiving surface of the SOS sensor 11 in an environment where the temperature is 25 ° C. In an environment where the temperature is 45 ° C., the optical system cannot focus the laser beam on the light receiving surface of the SOS sensor 11 as shown in FIG. In this case, the laser light is imaged at a virtual position (a two-dot chain line position) behind the SOS sensor 11. Note that the accompanying waveforms show the intensity distribution of the laser light at each position.

When the laser beam is not focused on the light receiving surface of the SOS sensor 11 and the focus position is shifted in the front-back direction on the optical axis, the SO
The time at which the intensity of the laser beam irradiated so as to cross the light receiving surface of the S sensor 11 exceeds the slice level fluctuates back and forth on the time axis as shown in the right column of FIG. As a result, the shift amount of the output start time of the image data for each line increases. That is, the jitter increases.

[0007] In recent years, as the definition of an image forming apparatus based on laser scanning has become higher, the demand for reducing the fluctuation (jitter) of the writing start position of each scanning line has become stricter. SUMMARY OF THE INVENTION It is an object of the present invention to reduce the jitter caused by the image position of a laser beam being shifted in the front-rear direction on the optical axis due to temperature fluctuation.

[0008]

According to the present invention, a charged surface of a photosensitive member, which is moved at a constant speed in a sub-scanning direction, is scanned in a main scanning direction by a laser beam modulated with an image signal to respond to the image signal. A laser scanning device that forms a latent charge image, a light-receiving sensor provided at a predetermined position optically equivalent to a position on the extension of the scanning line so as to detect laser light outside the main scanning range; Control means for starting output of an image signal for each scanning line based on the detection time of the laser beam by the light receiving sensor; a temperature sensor for detecting the environmental temperature of the laser scanning device; and Adjusting means for adjusting so that a detection signal equivalent to the case where the laser light incident on the light receiving sensor forms an image on the light receiving surface of the light receiving sensor is output.

The present invention is a laser scanning device wherein the adjusting means is means for moving an imaging lens for forming an image of laser light on the light receiving sensor on the optical axis. The present invention is the laser scanning device, wherein the adjusting means is means for moving the light receiving sensor on an optical axis. The present invention is the laser scanning device, wherein the adjusting means is means for adjusting an output level of the light receiving sensor.

[0010]

FIG. 1 is a perspective view schematically showing a mechanism of a laser scanning device according to an embodiment. The laser light output from the laser diode 1 is applied to a collimator lens 2,
From the cylindrical lens 3 to a polygon mirror (polyhedral mirror) 4 which is rotating at a high speed, the polygon mirror
4 is deflected so as to scan in the main scanning direction, is refracted by a scanning lens system 5, is reflected by a return mirror 6, is transmitted through a window 7, and is rotated at a constant speed. Is imaged on the surface of the object, and the surface is scanned in the main scanning direction. As a result, a charge latent image corresponding to the image signal used for modulating the laser light is formed on the charged surface of the photosensitive drum 8, and the charge latent image is developed with toner by a known method and then recorded. It is transferred and fixed on paper.

The laser light refracted by the scanning lens system 5 and deviating from the scanning range of the main scanning (developing before the start of the main scanning) is reflected by the mirror 9 for SOS. Is refracted by the SOS imaging lens 10, and
Irradiation reaches the light receiving surface of the sensor 11 and crosses the light receiving surface. Based on this, the output start time of the image data for each line is controlled. That is, as described earlier with reference to FIG. 3, the image data for the line starts from the time when a predetermined time τ has elapsed from the synchronization time (SOS detection time) generated based on the detection signal of the SOS sensor 11. Is started.

In the present laser scanning device, a temperature sensor 21 for detecting an environmental temperature is provided at a predetermined position.
The laser beam radiating across the OS sensor 11 is
When an image is accurately formed on the light receiving surface of the S sensor 11 (FIG. 4A)
Detection signal having the same fall characteristic as that of the S
As output from the OS sensor 11, the temperature sensor 21
Is adjusted based on the detection result.

For example, in the example shown in FIG. 2A, the actuator 23 moves the lens holder 10a forward / backward along the optical axis in accordance with an instruction from the controller 22 based on the detection result of the temperature sensor 21. Thus, the imaging lens 10 integrated with the lens holder 10a is moved to a position shown by a two-dot chain line in the figure. As a result, the laser light
Adjustment is performed so that an image is accurately formed on the light receiving surface of the S sensor 11, and jitter is reduced. Here, the correspondence between the environmental temperature and the movement amount and movement direction of the imaging lens 10 (the drive amount and drive direction of the actuator 23) is stored in the controller 22 in advance as a table created based on the actually measured values. Shall be

In the example shown in FIG. 2B, the actuator 24 moves the sensor holder 11a forward / backward along the optical axis in accordance with an instruction from the controller 22 based on the detection result of the temperature sensor 21. Thus, the SOS sensor 11 integrated with the sensor holder 10a is moved to the position shown by the two-dot chain line in the figure. As a result, the laser light
Adjustment is performed so that an image is accurately formed on the light receiving surface of the S sensor 11, and jitter is reduced. Here, environmental temperature and SOS
The correspondence between the movement amount and the movement direction of the sensor 11 (the drive amount and the drive direction of the actuator 24) is assumed to be stored in the controller 22 in advance as a table created based on the actually measured values.

In the example shown in FIG. 2C, the resistance of the variable resistor 25 provided in series with the power supply circuit to the SOS sensor 11 in response to an instruction from the controller 22 based on the detection result of the temperature sensor 21. The value is adjusted, so that the sensor output waveform detected as the potential difference V between both ends of the SOS sensor 11 is not a waveform having a bad falling characteristic as shown in the right column of FIG. The sensor sensitivity is adjusted so that a waveform with good fall characteristics as shown in the left column of
Thereby, the jitter is reduced. Here, the correspondence between the environmental temperature and the adjustment amount / adjustment direction of the variable resistor 25 is stored in the controller 22 as a table created based on the actually measured values.
In advance.

[0016]

According to the present invention, according to the environmental temperature, S
Since the adjustment is performed so that the detection signal equivalent to the case where the laser light crossing the OS sensor forms an accurate image on the light receiving surface of the SOS sensor is output from the SOS sensor, the image formation position of the laser light varies with temperature. Therefore, it is possible to reduce the jitter caused by the displacement in the front-back direction on the optical axis.

[Brief description of the drawings]

FIG. 1 is a perspective view schematically showing a mechanism of a laser scanning device according to an embodiment.

FIG. 2 is a diagram showing an example of an ambient temperature such that a detection signal having the same characteristics as when a laser beam crossing the SOS sensor 11 of the apparatus shown in FIG. Shows a configuration example of a mechanism that adjusts according to
(A) is for moving the imaging lens 10, (b) is for SO
When the S sensor 11 is moved, FIG.
The case of adjusting the sensitivity of each is shown.

FIG. 3 is an explanatory diagram illustrating the concept of SOS control.

FIG. 4 is an explanatory view showing a state in which an image forming position of a laser beam is shifted on an optical axis due to a temperature change.

FIG. 5 shows an SOS when an image forming position of a laser beam is shifted on an optical axis.
FIG. 4 is an explanatory diagram showing a state in which a detection time of a signal (a time that determines output timing of image data) is shifted.

[Explanation of symbols]

 9 Mirror for SOS 10 Imaging lens for SOS 11 Light receiving sensor (SOS sensor) 21 Temperature sensor

Claims (4)

[Claims] 1. A charged surface of a photosensitive member, which is moved at a constant speed in a sub-scanning direction, is scanned in a main scanning direction by a laser beam modulated by an image signal to form a charge latent image corresponding to the image signal. In a laser scanning device, a light receiving sensor provided at a predetermined position optically equivalent to a position on the extension of the scanning line so as to detect the laser light outside the main scanning range; Control means for starting output of an image signal for each scanning line based on the detection time; a temperature sensor for detecting an environmental temperature of the laser scanning device; and a laser incident on the light receiving sensor based on a detection result of the temperature sensor Adjusting means for adjusting so as to output a detection signal equivalent to the case where light forms an image on the light receiving surface of the light receiving sensor. 2. The laser scanning device according to claim 1, wherein the adjustment unit is a unit that moves an imaging lens that forms a laser beam on the light receiving sensor on an optical axis. 3. The laser scanning device according to claim 2, wherein said adjusting means is means for moving said light receiving sensor on an optical axis. 4. The laser scanning device according to claim 2, wherein said adjusting means is means for adjusting an output level of said light receiving sensor.