JPH11352425A - Optical scanner - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical scanner which can prevent dot deviation from occurring on a printed image even if a linearity characteristic of a lens system varies by temperature change. SOLUTION: A laser drive circuit 13 continuously and forcibly lights up a laser diode of a laser diode assembly 2 over a maximum scanning range including a printing range. A start side photo-sensor 8 outputs a start signal Ss to a control circuit 12 when a laser beam is made incident thereon, and an end side photo-sensor 10 outputs an end signal Se to the control circuit 12 when the laser beam is made incident thereon. The control circuit 12 determines a time difference between an arrival time of the start signal Ss and an arrival time of the end signal Se, and controls a timing to start writing and an exposure frequency by a laser drive circuit 13 based on this time difference.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical scanning device, and more particularly, to an optical scanning device applied to a tandem type color laser printer. The present invention relates to an optical scanning device configured to prevent a dot shift from occurring.

[0002]

2. Description of the Related Art As a conventional optical scanning device, for example, there is one disclosed in Japanese Patent Application Laid-Open No. 6-67103. This optical scanning device has a unit housing, a semiconductor laser for emitting laser light, a polygon mirror for deflecting the laser light emitted from the semiconductor laser, and a laser light deflected by the polygon mirror in the unit housing. And a plastic fθ lens for scanning at a constant linear velocity on the photosensitive member, and the unit housing is supported by a pair of bimetals from a main plate fixed to the apparatus main body.

In the optical scanning device having the above-described configuration, even if the linearity characteristic of the fθ lens changes due to a temperature change and the scanning range changes, the bimetal expands and contracts due to the temperature change, and the position of the unit housing with respect to the main plate is changed. As a result, the scanning range becomes constant on the photosensitive member, and the effect of preventing the occurrence of dot deviation on the printed image can be obtained.

[0004]

However, according to the conventional optical scanning device, if there is a difference in temperature characteristics between the pair of bimetals, a difference occurs in the displacement of the pair of bimetals. There is a problem that a dot shift occurs on a printed image.

Accordingly, an object of the present invention is to provide an optical scanning device capable of preventing a dot shift from occurring on a printed image even if the linearity characteristic of a lens system changes due to a temperature change.

[0006]

According to the present invention, in order to achieve the above object, a photosensitive member is exposed to laser light corresponding to image data emitted from a laser light source, and is exposed on the photosensitive member according to the image data. Detecting means for detecting a scanning width of the laser light in the main scanning direction which fluctuates according to a temperature change, and detecting the laser light in accordance with the scanning width in the main scanning direction. And a control means for controlling a start timing in the main scanning direction for exposing the photosensitive member and an exposure frequency in the main scanning direction.

[0007]

FIG. 1 shows an optical scanning device according to a first embodiment of the present invention. This optical scanning device has a box-shaped optical housing 1, and a laser diode set including a laser diode for emitting laser light and a collimating lens for shaping laser light from the laser diode on the optical housing 1. The solid 2, a lens 3 for condensing the laser light emitted from the laser diode of the laser diode assembly 2, a polyhedral reflecting mirror 4 a for deflecting the laser light condensed by the lens 3, and a reflecting mirror 4 a
And a first and second fθ lenses 5 and 6 made of, for example, plastic for scanning the laser beam deflected by the reflecting mirror 4a on the photosensitive member 8 at a constant linear velocity. , Printing range 1 on photoconductor 8
The print range change detecting unit 7 for detecting the change of 0, the laser drive circuit 13 for driving the laser diode at a predetermined timing, and the polygon motor 4 are controlled so as to rotate at a constant speed. image data,
And the detection signals Ss, Se from the print range fluctuation detecting section 7
Control circuit 12 that controls laser drive circuit 13 based on
And

[0008] The print range fluctuation detecting section 7 has a maximum scanning range 9.
And the start-side slit 70 and the start-side photosensor 71 disposed at a position scanned within the printing range 10 before the start point 10a of the printing range 10, and the end point 10b of the printing range 10 within the maximum scanning range 9. And an end-side slit 72 and an end-side photosensor 73 that are arranged at a position to be scanned later. The start-side photosensor 71 outputs a start signal Ss to the control circuit 12 when the laser beam is incident across the start-side slit 70, and the end-side photosensor 73 outputs the laser beam across the end-side slit 72. When it is incident, it outputs an end signal Se to the control circuit 12.

FIG. 2 shows a control system of the apparatus. The control circuit 12 includes a reference clock generation circuit 120 for generating a reference clock, a temperature compensation clock generation circuit 121 for generating a dot clock as a temperature compensation clock obtained by multiplying the reference clock from the reference clock generation circuit 120, and a temperature compensation clock. A modulation circuit 122 for modulating the image data stored in the image memory 11 based on the dot clock from the generation circuit 121, and a predetermined operation based on the detection signals Ss and Se from the print range changing unit 7 to perform a temperature compensation clock. An arithmetic circuit 123 controls the generation circuit 121 and controls the laser drive circuit 13.

The arithmetic circuit 123 includes a start-side photosensor 7
The time difference (t ₂ + Δt ₂ ) between the arrival time of the start signal Ss output from the end signal 1 and the arrival time of the end signal Se output from the end side photo sensor 73 is obtained, and this time difference (t ₂ +
Delta] t ₂₎ the following equation (1) based on, (and 2) from the write time t ₁ 'and clock Dc' a and calculates each write timing from the start signal Ss is arrived after writing time t ₁ ' Signal to laser drive circuit 1
3 to control the multiplication rate of the temperature compensation clock generation circuit 121 so that the dot clock Dc ′ is output from the temperature compensation clock generation circuit 121. t ₁ ′ = t ₁ × α (t ₂ + Δt ₂ ) / t ₂ (1) Dc ′ = Dc × β (t ₂ + Δt ₂ ) / t ₂ (2) where α, β: fθ lens 5, 6; etc. t ₁ : preset write time at reference temperature t ₂ : preset time difference between arrival time of start signal Ss and end signal Se at reference temperature Dc: preset time at reference temperature Set dot clock

Next, the operation of the optical scanning device according to the first embodiment configured as described above will be described with reference to the drawings.

FIG. 3A is a timing chart for a reference temperature, and FIG. 3B is a timing chart for a change in temperature. The laser driving circuit 13 controls the maximum scanning range 9 including the printing range 10 under the control of the control circuit 12.
Over, the laser diode 20 of the laser diode assembly 2 is continuously forcibly turned on. The start-side photo sensor 71 of the print range change detection unit 7 outputs a start signal Ss to the control circuit 12 when laser light is incident, and the end-side photo sensor 73 outputs an end signal when laser light is incident. Se is output to the arithmetic circuit 123 of the control circuit 12. The arithmetic circuit 123 calculates the arrival time of the start signal Ss and the end signal Se.
, The time difference (t ₂ + Δt ₂ ) from the arrival time is calculated, and based on the time difference (t ₂ + Δt ₂ ), the writing time t ₁ ′ and the dot clock Dc ′ are calculated from the above (1) and (2). The arithmetic circuit 123 outputs a write start timing signal to the laser drive circuit 13 after a write start time t ₁ ′ from the arrival of the start signal Ss. The arithmetic circuit 12
Reference numeral 3 controls the multiplication rate of the temperature compensation clock generation circuit 121 so that the dot clock Dc 'is output from the temperature compensation clock generation circuit 121. The modulation circuit 122 outputs the dot clock D from the temperature compensation clock generation circuit 121.
The image data stored in the image memory 11 is modulated based on c ′ to generate video data and output to the laser drive circuit 13. The laser drive circuit 13 starts writing time t ₁ ′ after the start-side photo sensor 71 outputs the start signal Ss.
Thereafter, the laser diode 20 is driven to light based on the video data from the modulation circuit 122. The laser light emitted from the laser diode 20 is condensed by the lens 3 and then reflected by the reflecting mirror 4a, so that the first and second f
The light is condensed on the photoconductor 8 by the θ lenses 5 and 6,
An image is formed in the upper print area 10. The image on the photoconductor 8 is transferred onto a sheet, and a print image is formed on the sheet.

According to the above-described first embodiment, fθ
Even if the linearity of the lenses 5 and 6 fluctuates due to a change in temperature, the printing range 10 is constant, so that it is possible to prevent a dot shift from occurring on a printed image.

FIG. 4 shows an optical scanning device according to a second embodiment of the present invention. The second embodiment is different from the first embodiment in the arrangement position of the start-side photosensor 71 and the end-side photosensor 73 of the print range fluctuation detecting unit 7, and the other is different from the first embodiment. It is configured similarly. That is, the opening 8 is located at a position within the maximum scanning range 9 of the photoconductor 8 and scanned earlier than the start point 10a of the printing range 10.
a, and the start side photosensor 7 is provided behind the opening 8a.
1, an opening 11b is provided at a position within the maximum scanning range 9 of the photoconductor 8 and scanned after the end point 10b of the printing range 10, and an end-side photosensor 73 is arranged behind the opening 8b. It was done.

According to the second embodiment, as in the first embodiment, even if the linearity of the fθ lenses 5 and 6 fluctuates due to a temperature change, the printing range 10 is constant. It is possible to prevent a dot shift from occurring on a printed image. Further, since the start-side photosensor 71 and the end-side photosensor 73 are arranged inside the photoconductor 8, the size of the apparatus is reduced.

The present invention is not limited to the above embodiment, but can be variously modified. For example, a temperature sensor that detects a temperature change in the apparatus may be used as the print range change detection unit. This makes it possible to easily measure the change in the printing range. Further, the print range change detecting unit may be a linear sensor in which a plurality of optical sensors for detecting laser light are arranged in an array over the entire scanning range of the photoconductor 8. This makes it possible to measure a change in the printing material range with high accuracy.

[0017]

As described above, according to the optical scanning device of the present invention, the scanning width in the main scanning direction of the laser beam which fluctuates according to the temperature change is detected, and the detected scanning width in the main scanning direction is determined. The start timing in the main scanning direction of exposing the photoreceptor with laser light and the exposure frequency in the main scanning direction are controlled accordingly, so that even if the linearity characteristics of the lens system change due to temperature changes, dot misalignment may occur on the printed image. It can be prevented from occurring.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of an optical scanning device according to a first embodiment of the present invention.

FIG. 2 is a block diagram illustrating a control system of the optical scanning device according to the first embodiment of the present invention.

FIGS. 3A and 3B show the operation of the optical scanning device according to the first embodiment, wherein FIG. 3A is a timing chart for a reference temperature, and FIG.
Is a timing chart when a temperature change occurs.

FIG. 4 is a configuration diagram of an optical scanning device according to a second embodiment of the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Optical housing 2 Laser diode assembly 4 Polygon motor 4a Reflecting mirror 5 First fθ lens 6 Second fθ lens 7 Printing range fluctuation detecting section 8 Photoconductor 8a, 8b opening 9 Maximum scanning range 10 Printing range 10a Printing range Start point 10b End point of print range 11 Image memory 12 Control circuit 13 Laser drive circuit 20 Laser diode 70 Start side slit 71 Start side photo sensor 72 End side slit 73 End side photo sensor 120 Reference clock generation circuit 121 Temperature compensation clock generation circuit 122 modulation circuit 123 arithmetic circuit Dc ', Dc dot clock Se end signal Ss start signal t, t _1' write time

Claims (5)

[Claims] 1. An optical scanning device for exposing a photosensitive member with laser light corresponding to image data emitted from a laser light source to form an electrostatic latent image on the photosensitive member according to the image data, comprising: Detecting means for detecting a scanning width in the main scanning direction of the laser light that varies according to the start timing in the main scanning direction of exposing the photoconductor with the laser light according to the scanning width in the main scanning direction, An optical scanning device comprising: a control unit configured to control an exposure frequency in a main scanning direction. 2. The optical scanning device according to claim 1, wherein said detecting means includes a measuring means for measuring a time required for the laser light to pass through two predetermined points set in the main scanning direction. 3. The start-side detection means for detecting the laser beam irradiated outside a predetermined exposure start point in the main scanning direction and outputting a start signal, and a predetermined exposure in the main scanning direction. An end-side detection unit that detects the laser beam irradiated outside the end point and outputs an end signal, and an operation unit that calculates the required time based on the start signal and the end signal. The optical scanning device according to claim 2. 4. The apparatus according to claim 1, wherein said start-side detection means and said end-side detection means include an optical sensor disposed between said photosensitive member and a lens system for focusing said laser beam on said photosensitive member. 3. The optical scanning device according to 3. 5. The photoreceptor has an opening outside a predetermined exposure start point and an exposure end point in the main scanning direction, and the start side detection means includes an opening outside the predetermined exposure start point. 4. The optical scanning device according to claim 3, further comprising: an optical sensor arranged behind the opening, and wherein the end side detection unit includes an optical sensor arranged behind the opening outside the predetermined exposure end point. .