JPH10319331A - Image forming device - Google Patents

Abstract

(57) Abstract: In an image forming apparatus provided with a scanning optical system using a laser light source, an unnecessary exposure line is required when the laser light source is turned on to obtain the first synchronization signal from the stop of the scanning means. To prevent the electrostatic latent image from being visualized. A laser light source (27) and a light intensity control means (2).
6. Scanning means 29, imaging optical system 30, and synchronization detecting means 31
In the image forming apparatus provided with the optical unit 28 having the following configuration, the light intensity of the laser beam controlled by the control unit 26 is set to Pld, and the minimum value for visualizing the latent image formed by the laser beam scanned on the photosensitive member 34 is set. When the light intensity is Pim and the minimum light intensity required to generate a synchronization detection signal by the laser beam scanned by the synchronization detection means is Pdt,
When the laser light source is turned on to obtain the first synchronization signal from the time when the scanning unit is stopped, the laser beam light intensity Pld from the start of lighting to the time when the first synchronization signal is obtained is calculated as follows: Pdt ≦ Pld <Pim
And

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrophotographic image forming apparatus provided with a laser scanning optical system using a laser light source, such as a digital copying machine or a laser printer.

[0002]

2. Description of the Related Art Conventionally, a laser beam emitted from a laser light source such as a laser diode is scanned by a scanning means such as a polygon mirror (rotating polygon mirror) rotated by a polygon motor, and the laser beam is scanned by an imaging optical system. A laser scanning optical system that forms an image as a laser spot on a photosensitive body that is a scanned surface is provided as a writing unit, the photosensitive body is charged by a charging unit, and an electrostatic latent image is formed by optical writing by the laser scanning optical system, The electrostatic latent image is developed by a developer of a developing unit to be visualized, the visualized image is transferred to a transfer material such as transfer paper by a transfer unit, and the transferred image is fixed by a fixing unit to print or copy image. An image forming apparatus using an electrophotographic process is known, and a laser printer,
It has been commercialized as a digital copying machine and the like.

[0003]

In recent years, image forming apparatuses having a laser scanning optical system, such as a laser printer, have been increasingly required to have higher density and higher speed.
In order to meet the demand for higher density and higher speed, it is necessary to increase the number of rotations of a polygon motor that rotates a polygon mirror serving as a scanning unit. Currently, polygon motors that support high-speed rotation are being developed by motor manufacturers, but this high-speed rotation increases the heat generated by bearings, drive circuits, etc., and this heat shortens the life of the motor. It has occurred.

Normally, in an image forming apparatus such as a laser printer, the polygon motor is rotated at the same time that the power of the main body is turned on, and then continuously rotated until the power is turned off. In this case, the life of the polygon motor is shorter than the life of the main body. Possibilities arise. Therefore, a method has recently been developed in which a polygon motor having a fast rise time is used, and the polygon motor is normally stopped and rotated only during image formation. According to this method, the life of the polygon motor can be extended beyond the life of the main body.

Further, in order to form an image with an image forming apparatus having a laser scanning optical system, a synchronization signal for determining a recording start timing is required. This synchronization signal is generated by inputting a laser beam to a synchronization detecting means provided at a predetermined position.

In order to obtain the first synchronization signal from the time when the polygon motor is stopped, first, the polygon motor is rotated to attain a steady rotation state, and then the laser diode is turned on at an arbitrary timing. Wait for the signal.
Once the synchronization signal is detected, a certain time: Tw is counted from the input of the synchronization signal, and then the laser diode is turned on to repeat the synchronization signal. This fixed time: Tw
When the synchronous signal input interval when the polygon motor is in a steady rotation state is Tl, and the laser diode lighting time for detecting the synchronous signal is Td, Tw = Tl-Td.

The lighting time of the laser diode for detecting the synchronization signal: Td is used to determine the lighting start timing of the laser diode to prevent the deterioration of the photosensitive member which is the surface to be scanned due to unnecessary exposure and the transfer of toner. In general, it is calculated from the geometrical position of the body by the optical system layout, the rotation speed of the polygon motor, and the like, and is set so as to be after passing through the photosensitive body area.

However, when the laser diode is turned on to obtain the first synchronization signal from the stop of the polygon motor, the turn-on angle of the polygon motor (polygon mirror) when the laser diode is stopped is unknown. As a result, there is a possibility that the photoconductor is exposed for a maximum of one line.

In the case of the system in which the polygon motor is rotated at the same time when the power is turned on, it usually takes several tens of seconds from when the power is turned on until a unit other than the optical system such as the fixing unit starts up. Regarding the unnecessary exposure of one line, the transfer of toner can be prevented by turning off the development, and the electrostatic latent image due to the unnecessary exposure can be erased by the static elimination process by rotating the photosensitive member. Since the time required for this operation is at most about several seconds, it is possible to start up the optical system before the other units start up.

However, in the case of a system in which the polygon motor is rotated only during image formation, a time loss of several seconds due to such an operation leads to a decrease in throughput, which is not preferable in terms of function. In addition, if such an operation is not performed, toner adheres to the line due to unnecessary exposure. For example, in the case of an electrophotographic process using a transfer roller as a transfer unit, toner adheres directly to the transfer roller. In addition, there is a possibility that the transfer roller may be stained, and consequently the transfer paper may be stained.

The present invention has been made in view of the above points, and the invention of claim 1 is directed to a method of rotating the polygon motor only during image formation, even if the first synchronization signal is not supplied after the polygon motor is stopped. It is an object of the present invention to provide an image forming apparatus which does not lower the throughput in the operation for obtaining the transfer paper and does not cause the transfer paper to have back stains.

Another object of the present invention is to obtain a stable synchronizing signal during image formation in addition to the object of the first aspect. A third object of the present invention is to prevent deterioration due to unnecessary emission of a light source such as a laser diode in addition to the objects of the first and second embodiments.

[0013]

According to a first aspect of the present invention, there is provided a laser light source, a light intensity control means for controlling a light intensity of a laser beam emitted from the laser light source, and a laser light source. Scanning means for scanning the beam;
An imaging optical system that forms an image of the laser beam as a laser spot on a surface to be scanned, and a synchronization detection unit that is provided at a predetermined position and receives the laser beam and generates a synchronization signal that determines a recording start timing. An image forming apparatus that has a laser scanning optical system having a laser spot and forms an electrostatic latent image formed by a laser spot on the surface to be scanned by an electrophotographic process. Pld, Pim the minimum light intensity for visualizing an electrostatic latent image formed by the laser beam scanned on the surface to be scanned, and generate a synchronization detection signal by the laser beam scanned by the synchronization detection means. Assuming that the minimum light intensity required for the laser light is Pdt, when the laser light source is turned on to obtain the first synchronization signal from when the scanning means is stopped, the light is turned on. The laser beam intensity Pld from start until a first synchronization signal, and Pdt ≦ Pld <Pim. Thereby, even if an electrostatic latent image is formed by unnecessary exposure lines, toner does not adhere to the latent image,
It is possible to eliminate the visualization of the electrostatic latent image due to unnecessary exposure lines.

According to a second aspect of the present invention, in the image forming apparatus according to the first aspect, when the laser light source is turned on to obtain a synchronization signal after the first synchronization signal is obtained from the time when the scanning unit is stopped, the laser beam is emitted. The light intensity is made larger than at the time of lighting for obtaining the first synchronization signal. This makes it possible to obtain a stable synchronization signal during image formation.

According to a third aspect of the present invention, in the image forming apparatus according to the first aspect, when the laser light source is turned on to obtain a synchronization signal after the first synchronization signal is obtained from when the scanning unit is stopped, a laser beam is used. The light intensity is set equal to the maximum intensity during normal image formation. As a result, it is possible to prevent deterioration due to unnecessary emission of the laser light source.

[0016]

Embodiments of the present invention will be described below in detail with reference to the drawings.

First, the configuration and operation of claim 1 will be described. FIG. 1 shows a schematic configuration diagram of a laser scanning optical system of an image forming apparatus according to the present invention. In FIG. 1, a laser beam emitted from a laser diode 10 serving as a laser light source is converted into parallel light by a collimating lens 11 and an extra laser 12 is provided by an aperture 12 having a slit portion corresponding to the size of a dot to be formed. The beam is cut. And the laser beam is given by the first cylinder lens: 13
The light is condensed so as to have a predetermined size on the photosensitive member 19 serving as the surface to be scanned, and the polygon motor 1 serving as the scanning unit 14 is
Scanning is performed in the main scanning direction (the long axis direction of the photoconductor 19) x by the polygon mirror 14b rotated at 4a. Then, the constant-speed scanning imaging lens system: 15 comprising a pair of fθ lenses: 15a and 15b changes the equiangular motion to the constant-velocity motion and corrects the field curvature.

Next, the laser beam angle is changed by the first mirror 16 and the light is condensed in the sub-scanning direction (rotation direction of the photoconductor 19) y by the second cylinder lens 17 so that the laser beam is on the photoconductor 19. To form an image as a minute laser spot. The laser beam reflected by the synchronization detection mirror 18a is synchronized with the synchronization detection cylinder lens 18b.
The optical signal is condensed on the optical fiber 18c, and is subjected to photoelectric conversion by a pin photodiode (PinPD) or the like of a synchronization signal generation circuit provided on a control board (not shown) to become a synchronization signal (FIG. 3A shows a synchronization signal generation circuit). Shows an example).

Although not shown in FIG. 1, the photosensitive member:
Around the laser scanning optical system 19, a charging unit, a developing unit, a transfer unit, a fixing unit, a cleaning unit, a charge removing unit, and the like for forming an image by a known electrophotographic process are arranged in addition to the laser scanning optical system. When the image forming operation is started, the photosensitive member:
9 is charged by the charging unit while rotating in the direction B of FIG. 1, a laser beam is irradiated on the photoconductor 19 as a minute laser spot by the above-described laser scanning optical system, an image is formed, and intensity modulation is performed according to image data. While scanning, the image is written in the main scanning direction x to write an image for each line: 19a, and this optical writing is sequentially repeated in the sub-scanning direction y to form an electrostatic latent image for one page. This electrostatic latent image is developed by a developer of a developing unit, for example, a toner, and is visualized. The visualized toner image on the photoconductor 19 is transferred by a transfer unit onto a transfer material such as transfer paper conveyed from a paper supply unit (not shown) via a conveyance mechanism and a registration roller. The transfer material onto which the toner image for one page has been transferred is conveyed to a fixing unit, where the toner image is fixed on the transfer material by performing a fixing process by applying heat and pressure by a pair of fixing rollers. Further, the photosensitive member 19 after the transfer is cleaned of the residual toner by the cleaning unit, and is discharged by the discharging unit.

FIG. 2 is a block diagram showing a schematic configuration of a laser printer as an example of the image forming apparatus according to the present invention. This laser printer includes a laser scanning optical system having the same configuration as that of FIG. In FIG. 2, image data sent from a host PC 21 such as a personal computer or a word processor to a laser printer 20 via a printer interface (PRINTER I / F) 22 is bit-mapped by a printer controller 23. After being expanded into information, it is sent to the printer engine 24. The transferred image data is synchronized with the synchronization signal: 3 by the engine control unit 25.
ON / OF of laser diode with 2 as start reference signal
The laser beam from the laser diode, which has been converted into an F signal, passes through an optical unit 28 having the same configuration as the laser scanning optical system shown in FIG. 1 having a polygon motor 29, an imaging optical system 30, a synchronization detecting means 31, and the like. Via photoconductor: 34
Is irradiated. Thereafter, as described above, image formation is performed by the electrophotographic process: 33, charging by the charging unit, formation of an electrostatic latent image by the optical unit, development by the developing unit, transfer by the transfer unit, and fixing by the fixing unit. An image is formed on the transfer material through the above steps.

Here, the light intensity of the laser beam controlled by the light amount control unit 26 as light intensity control means is represented by Pl.
d, Pim is the minimum light intensity for the electrostatic latent image formed by the laser beam scanned on the photoconductor 34 to be visualized by the electrophotographic process 33, and synchronization detection means 31.
Synchronization detection signal: 32 by laser beam scanned in
In the case of the present invention, when the minimum light intensity required for generating the laser beam is Pdt, when the laser diode is turned on to obtain the first synchronization signal from the stop of the scanning means, the first synchronization signal from the start of lighting is applied. The laser beam light intensity Pld until it is obtained is controlled by the light amount control unit 26 so that Pdt ≦ Pld <Pim. Accordingly, even if an electrostatic latent image is formed by an unnecessary exposure line, toner does not adhere to the latent image, and the electrostatic latent image is not visualized by the unnecessary exposure line, thereby lowering the throughput. Nothing. In addition, since extra toner is not attached to the photoconductor, the back surface of the transfer paper and wasteful toner consumption are prevented.

Next, the configuration and operation of claim 2 will be described. In the laser printer 20 having the configuration shown in FIG. 2, after obtaining the first synchronization signal from the stop of the scanning means, the geometrical position of the synchronization detection means 31 of the optical unit 28 and the optical system layout of the photosensitive member 34 is obtained. , Polygon motor: 2
The laser diode for synchronization signal is controlled so as not to irradiate the photoreceptor 34 with the laser diode start timing calculated from the rotation speed and the like of No. 9.

FIG. 3 is a diagram showing a change in the output of the PinPD and a change in the width of the synchronization signal depending on the synchronization signal generation circuit and the light intensity. As shown in FIG. 3, it is generally known that as the light intensity of the laser beam for the synchronization signal increases, the output width of the synchronization signal increases and the synchronization signal is stabilized.
Therefore, in the case of the present invention, when the laser diode is turned on to obtain the synchronization signal after obtaining the first synchronization signal from the stop of the scanning unit, the light amount control unit as the light intensity control unit:
The control by 26 controls the laser beam light intensity for the synchronizing signal to be higher than at the time of lighting for obtaining the first synchronizing signal. By performing such control, a more stable synchronization signal can be obtained during image formation.

Next, the configuration and operation of claim 3 will be described. In the laser printer 20 having the configuration shown in FIG. 2, in the case of the present invention, after the first synchronization signal is obtained from the time when the scanning means is stopped, when the laser diode is turned on to obtain the synchronization signal, the light intensity control means is used. A certain light amount control unit 26 controls the laser beam light intensity to be equal to the maximum intensity during normal image formation. By controlling in this way, it is possible to prevent deterioration due to unnecessary over-emission of the laser diode, and to achieve the most stable synchronization within a range that does not cause deterioration due to unnecessary over-emission of the laser diode. A signal can be obtained.

[0025]

As described above, according to the first aspect of the present invention, the light intensity of the laser beam controlled by the light intensity control means is Pld, and the electrostatic force formed by the laser beam scanned on the surface to be scanned is Pld. When the minimum light intensity for visualizing the latent image is Pim, and the minimum light intensity necessary for generating a synchronization detection signal by the laser beam scanned by the synchronization detection means is Pdt, the first time from when the scanning means is stopped, When the laser light source is turned on in order to obtain the synchronization signal, the laser beam light intensity Pld from the start of lighting until the first synchronization signal is obtained.
By setting Pdt ≦ Pld <Pim, the electrostatic latent image is not visualized by unnecessary exposure lines, so that the throughput is not reduced, and the back stain of the transfer paper and wasteful toner consumption are prevented. An image forming apparatus that does not cause the problem can be provided.

According to the second aspect of the present invention, in addition to the configuration and effect of the first aspect, when the laser light source is turned on in order to obtain a synchronization signal after obtaining the first synchronization signal from the stop of the scanning means. By providing a laser beam intensity higher than that at the time of lighting for obtaining the first synchronization signal, a stable synchronization signal can be obtained at the time of image formation. can do.

According to the third aspect of the invention, in addition to the configuration and effect of the first aspect, when the laser light source is turned on in order to obtain a synchronization signal after obtaining the first synchronization signal from the time when the scanning unit is stopped. By making the laser beam light intensity equal to the maximum intensity at the time of normal image formation, it is possible to prevent deterioration due to unnecessary over-emission of the laser light source. An image forming apparatus can be provided that performs image formation with the most stable synchronization signal within a range that does not cause deterioration due to the above.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of a laser scanning optical system of an image forming apparatus according to the present invention.

FIG. 2 is a diagram illustrating an example of an image forming apparatus according to the present invention, and is a block diagram illustrating a schematic configuration of a laser printer.

FIG. 3A illustrates an example of a synchronization signal generation circuit.
(B) is a diagram showing a change in PinPD output depending on light intensity;
(C) is a diagram showing a change in the synchronization signal width depending on the light intensity.

[Explanation of symbols]

 10: Laser diode (laser light source) 11: Collimating lens 12: Aperture 13: First cylinder lens 14: Scanning means 14a: Polygon motor 14b: Polygon mirror 15: Constant speed scanning imaging lens system 15a, 15b: fθ lens 16: First mirror 17: Second cylinder lens 18: Synchronous detection means 18a: Synchronous detection mirror 18b: Synchronous detection cylinder lens 18c: Optical fiber 19: Photoconductor (scanned surface) 20: Laser printer 21: Host PC 22: Printer I / F 23: Printer controller 24: Printer engine 25: Engine control unit 26: Light amount control unit (light intensity control means) 27: Laser diode substrate 28: Optical unit (laser scanning optical system) 29: Polygon motor 30: Imaging optics System 31: Synchronization detection means 33: Electronic photography Process 34: photoreceptor

Claims (3)

[Claims] 1. A laser light source, and light intensity control means for controlling the light intensity of a laser beam emitted from the laser light source;
Scanning means for scanning the laser beam, an imaging optical system for imaging the laser beam as a laser spot on the surface to be scanned, and receiving the laser beam at a predetermined position to determine a recording start timing An image forming apparatus comprising: a laser scanning optical system having a synchronization detection unit that generates a synchronization signal; and an electrostatic latent image formed by a laser spot on the surface to be scanned is visualized by an electrophotographic process. The light intensity of the laser beam controlled by the control means is Pld, the minimum light intensity for visualizing an electrostatic latent image formed by the laser beam scanned on the surface to be scanned is Pim, and the synchronization detection means is scanning. When the minimum light intensity required to generate a synchronization detection signal by the generated laser beam is Pdt, the first synchronization signal is obtained from when the scanning unit is stopped. When the laser light source is turned on, the laser beam light intensity Pld from the start of lighting until the first synchronization signal is obtained is set to Pdt ≦ Pld <Pim. 2. The image forming apparatus according to claim 1, wherein after obtaining the first synchronizing signal from the stop of the scanning means, when turning on the laser light source to obtain the synchronizing signal, the intensity of the laser beam is changed to the initial value. An image forming apparatus characterized in that it is made larger than at the time of lighting for obtaining a synchronization signal. 3. An image forming apparatus according to claim 1, wherein when the laser light source is turned on in order to obtain the synchronization signal after obtaining the first synchronization signal from the stop of the scanning means, the intensity of the laser beam is reduced to a normal value. An image forming apparatus wherein the intensity is made equal to the maximum intensity at the time of image formation.