JPH06191084A - Image forming apparatus - Google Patents

Abstract

PURPOSE:To prevent contamination in a body apparatus and a decrease in life of a cleaner due to adhesion of toner to a photosensitive member at the time of altering a pixel density by simple means. CONSTITUTION:A CPU 41 confirms OFF of a main motor 14 for driving a photosensitive drum 15 (stop of a photosensitive member) according to a pixel density alteration command of a controller 30 and designates a frequency of a PM clock corresponding to the designated pixel density to a clock generator 25, a speed alteration to a PM driver 54d and a laser light emission to an LD unit 50. The driver 54d so controls that a polygon motor 54 for driving a rotary deflector rotates in synchronization with a PM clock to be input from the generator 35. Stable speed is sensed by a period of a synchronous signal to be formed upon reception of a laser light reflected by the deflector. Since the drum 15 is stopped during this period, a quantity of toner adhering to a part exposed with the light is extremely small.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical scanning type image forming apparatus having a pixel density varying function.

[0002]

2. Description of the Related Art A laser beam pulse-modulated according to image data (VIDEO signal) output from a laser diode is imaged as a spot on a photosensitive member moving in the sub-scanning direction, and the spot is formed in the sub-scanning direction. There is an optical scanning type image forming apparatus such as a laser printer, a digital copying machine, and a high speed facsimile which forms an image by scanning in a main scanning direction orthogonal to.

Since these image forming apparatuses, such as laser printers, are superior in speed and resolution to other printers, a high-end model has a pixel density variable function capable of changing the pixel density according to the purpose. I have many things.

In order to change the pixel density, if the moving speed of the photoconductor is constant, the scanning speed of the spot, that is, the rotation speed of a rotary deflector such as a polygon mirror for deflecting the laser beam is proportional to the pixel density. Further, it is necessary to change the frequency of the image clock, which is the synchronization reference of the VIDEO signal, in proportion to the square of the pixel density.

Conventionally, even if an instruction to change the pixel density is issued from the host machine, it is not executed during printing, and the rotation speed of the polygon motor for driving the polygon mirror is changed after printing or before printing. At this time, in order to confirm whether or not the synchronization signal in the main scanning direction has a cycle corresponding to the new pixel density, the laser diode is caused to emit light and the reflected light from the polygon mirror is detected.

[0006]

However, when the photosensitive member is moving, the toner adheres to an uncharged portion when passing through the developing unit, and the adhered toner scatters in the main body apparatus. It is necessary to charge the photoconductor because there is a problem that it becomes dirty and the life of the cleaner is shortened.

However, since the exposed portion of the photosensitive member is completely discharged by causing the laser diode to emit light in order to confirm the period of the synchronizing signal, the toner adheres to the exposed portion even when the charging is performed at an angle. It will be.

Therefore, control such as stopping the developing bias applied to the developing roller is performed. As a result, the toner no longer adheres to the exposed area.However, since a part of the toner contains reversal toner charged to the opposite polarity due to agitation, the polarity of the reversal toner should be canceled, so Another problem is that the reversal toner adheres to the charged portion of the photoconductor.

The present invention has been made in view of the above points, and it is possible to prevent the contamination of the inside of the main body apparatus and the reduction of the life of the cleaner due to the adhesion of toner to the photosensitive member, which occurs when the pixel density is changed, by a simple means. To aim.

[0010]

In order to achieve the above-mentioned object, the present invention provides an image forming apparatus for forming an image by deflecting a laser beam by a rotary deflector and scanning the charged and moving photosensitive member. A rotational speed change instruction means for instructing to change the rotational speed of the rotary deflector, and a rotational speed control means for changing the rotational speed of the rotary deflector in response to an instruction from the rotational speed change instructing means. It was done like this.

According to a first aspect of the present invention, a photosensitive member stop detecting means for detecting the movement / stop of the photosensitive member is provided, and when the rotational speed change instructing means gives an instruction to change the rotational speed, the photosensitive body stop detecting means is exposed to light. The rotation speed control means changes the rotation speed of the rotary deflector only when the stop of the body is detected.

A second aspect of the present invention is provided with a photosensitive member stopping means for stopping the photosensitive member when the rotation speed change instructing means gives an instruction to change the rotation speed.

Further, a timer is provided which starts when the photoconductor stopping means is actuated, the time from the actuation of the photoconductor stopping means to the actual stop of the photoconductor being set after the preset time of the timer has elapsed. The rotation speed control means may change the rotation speed of the rotary deflector.

A third aspect of the invention provides a light source control means for stopping the emission of a laser light source for outputting a laser beam while the rotation speed control means is changing the rotation speed of the rotary deflector.

Further, the time from the rotation speed change instructing means is instructed to change the rotation speed until the rotation deflector is stabilized at the changed rotation speed is started by the change instruction of the rotation speed change instructing means set in advance. Set up a timer to
The light source control means may stop the light emission of the laser light source during the operation of the timer.

[0016]

In the image forming apparatus according to the present invention, when the pixel density change command is input, the rotation speed change instructing means determines the rotation speed of the rotary deflector according to the pixel density to be changed and gives an instruction to change the rotation speed. Then, according to the instruction, the rotation speed control means controls the rotation speed of the rotary deflector so that the rotation speed becomes the instructed rotation speed.

In the image forming apparatus according to the first aspect of the present invention, when a change in the number of rotations is instructed, the photosensitive member stop detecting means detects the movement / stop of the photosensitive member, and rotates only when the stop of the photosensitive member is detected. Since the number control means controls the rotation speed to the instructed rotation speed, even if the laser diode is made to emit light for a certain period of time in order to confirm the frequency of the synchronizing signal, the exposed portion of the photosensitive member is slightly equivalent to one scanning line. The amount of toner that adheres is extremely small and does not affect the dirt or the life of the cleaner.

In the image forming apparatus according to the second aspect of the present invention, the photosensitive member stopping means stops the photosensitive member when an instruction to change the rotation speed is given. Therefore, the effect obtained when the laser diode is made to emit light for a certain time is as follows. This is similar to the image forming apparatus according to the first invention.

Instead of directly confirming the stop of the photoconductor by the photoconductor stopping means, a timer having a preset time until the photoconductor stops is started when the photoconductor stopping means is actuated, and after the set time of the timer elapses. If the rotation speed control means changes the rotation speed, it is easier than the direct confirmation of the stop.

In the image forming apparatus according to the third aspect of the invention, the light source control means stops the emission of the laser light source while the rotation speed control means is changing the rotation speed by instructing to change the rotation speed. Even if the charged photoreceptor moves, it is not exposed at all. Therefore, the toner does not adhere, and the inside of the main body device does not become dirty and the life of the cleaner does not decrease. However, since the synchronization signal cannot be used to confirm the rotation speed, the rotation speed is confirmed by detecting the synchronous coincidence of the motor driving the rotary deflector.

Alternatively, a timer that presets the time until the rotational deflector stabilizes at the changed rotational speed is started by the change instruction of the rotational speed change instruction means, and the light source control means controls the laser light source while the timer is operating. It is easier if the light emission is stopped.

[0022]

FIG. 2 is a schematic structural view showing the internal mechanism of a laser printer which is an embodiment of the present invention. In this laser printer, a paper 11 is fed by a paper feed roller 12 from one of the upper and lower two paper feed cassettes 10a and 10b, for example, a paper stack 11a on the upper paper feed cassette 10a. After being timed by the pair 13, the sheet is conveyed to the transfer position of the photosensitive drum 15.

The surface of the photosensitive drum 15, which is rotationally driven in the direction of the arrow by the main motor 14, is charged by the charging charger 16, and is scanned by the modulated spot from the optical writing unit 28 to electrostatically charge the surface. A latent image is formed. The formed latent image is made visible by developing unit 17 with toner attached.

The toner image is transferred by the transfer charger 18 onto the sheet 11 conveyed by the registration roller pair 13. The sheet on which the toner image has been transferred is separated from the photoconductor drum 15, then sent to the fixing unit 20 by the conveyor belt 19 and pressed against the fixing roller 20b by the pressure roller 20a, and is heated in advance with the pressure. It is fixed by the temperature of the fixing roller 20b.

The sheet 11 exiting the fixing unit 20 is discharged by a sheet discharge roller 21 to a sheet discharge tray 22 provided on the side surface of the printer. On the other hand, the toner remaining on the photosensitive drum 15 is removed and collected by the cleaning unit 23. A printed circuit board 24 having a controller and an engine driver mounted thereon is arranged above the printer.

FIG. 3 is a block diagram showing an example of a control system of this laser printer. The main part of the controller 30 includes an MPU 31, a ROM 32 that stores programs, constant data, character fonts, etc., a RAM 33 that stores temporary data and dot patterns, and an I / O 34 that controls data input / output. This is an image processing unit.

The controller 30 further includes an operation panel 35 connected to the MPU 31 via the I / O 34, and an internal interface (I / F) 36, which are mutually connected by a data bus, an address bus, and the like. A host machine 38 that outputs a print command, character data, image data, etc. is also connected to the MPU 31 via the I / O 34.

The engine driver 40 includes a CPU 41 and
The ROM 42 stores programs, constant data and the like, the RAM 43 stores temporary data and the like, and the I / O 44 which controls the input / output of data. Connected by.

The I / O 44 is connected to the internal interface 36 of the controller 30. The controller 30 inputs the video signal and the states of various switches on the operation panel 35, and the controller 30 receives status signals such as an image clock and a paper end. Output to.

Further, the I / O 44 is also connected to the optical writing unit 28 and other sequence equipment group 46 constituting the printer engine 45 which is a printing means, and various sensors 47 including a synchronization sensor.

The controller 30 receives a print command, a character code, and image data from the host machine 38,
Edit those codes and data, and if it is a character code, R
The dot pattern necessary for image writing is converted by the character font stored in the OM32, and the dot pattern of those characters and images (collectively referred to as "image" below) is stored in the VRAM (video RAM) area in the RAM33. Put.

When the image clock WCLK is input together with the ready signal from the engine driver 40, the controller 3
0 designates the dot pattern stored in the VRAM area as a video signal synchronized with the image clock WCLK via the internal interface 36 and the engine driver 40.
Output to.

On the operation panel 35, there are switches and indicators (not shown) for controlling data according to instructions from the operator and displaying the information in the engine driver 40.
Or display the printer status on the display.

The engine driver 40 is the controller 3
From the data from 0, the optical writing unit 28 of the printer engine 45, the charger 16, the developing unit 1
The sequence device group 46 such as 7 is controlled, and a video signal necessary for image writing is input from the controller 30 and output to the optical writing unit 28.

The engine driver 40 also inputs signals from the synchronous sensor and other sensors 47 indicating the state of each part of the engine for processing, and outputs necessary information and status signals of error conditions to the controller 30.

FIG. 4 is a perspective view of an essential part of the optical writing unit 28. The optical writing unit 28 includes an LD (laser diode) unit 50, a first cylinder lens 51, a first mirror 52, an image forming lens 53, and a polygon motor 54.
And a rotary deflector 56 composed of a polygon mirror 55 rotated in the direction of arrow A, a second mirror 57, a second cylinder lens 58, a third mirror 60, a condenser lens 61, and a synchronous sensor 62 which is a light receiving element. It has and.

The LD unit 50 has a laser diode (not shown) and a collimator lens for converting a divergent beam emitted from the laser diode into a parallel light beam, which are integrally incorporated therein.

The first cylinder lens 51 is the LD unit 5
0 has a function of shaping the parallel light beam emitted from 0 in the sub-scanning direction on the photoconductor drum 15, and the imaging lens 53 converts the parallel light beam reflected by the first mirror 52 into a convergent beam, Mirror surface 55 of polygon mirror 55
It is incident on a.

The polygon mirror 55 is an R polygon mirror formed by bending each mirror surface 55a, and is a post-object type (a light beam is made to be a convergent light beam) which does not use the fθ lens conventionally arranged between the second mirror 57 and the polygon mirror 55. After that, the rotary deflector 56 of the type in which the deflector is arranged is configured.

The second mirror 57 reflects the light beam reflected and deflected by the rotary deflector 56 toward the photosensitive drum 15. The light beam reflected by the second mirror 57 is
An image is formed as a sharp spot on the main scanning line 15a on the photosensitive drum 15 through the cylinder lens 58.

The third mirror 60 is a rotary deflector 56.
Is arranged outside the scanning area on the photoconductor drum 15 due to the light beam reflected by
Reflect toward 2.

The light beam reflected by the third mirror 60 and condensed by the condenser lens 61 is a synchronous sensor 62.
Is detected by a light receiving element such as a photodiode, which is included in the above, and is output from the synchronization sensor 62 as a synchronization signal DETP.

FIG. 1 is a block diagram showing the configuration of the first embodiment of the control system relating to the change of the rotation speed of the rotary deflector 56 for changing the pixel density, and the connecting line with an arrow indicates the electric system. , The thick connecting line without an arrow is a mechanical system. In addition,
The same parts as those shown in FIGS. 2 to 4 are designated by the same reference numerals, and the controller 30 and the engine driver 40 shown in FIG. 3 are omitted.

In the first embodiment shown in FIG. 1, the clock generator 25 and the LD unit 50 of the optical writing unit 28 constituting the printer engine 45 are directly connected to each other, and the main motor 14 and the polygon motor 54 are each connected to the MM driver. 14d and the PM driver 54d, it is connected to the I / O 44 of the engine driver 40 and controlled by the CPU 41.

The main motor 14 drives various rollers such as the paper feed roller 12, the registration roller pair 13, the paper discharge roller 21, the transport belt 19, the developing roller in the developing unit 17, the toner agitator, and the like, and also the photoconductor. The drum 15 is rotated (the photoconductor is moved).

When a command to change the pixel density is input from the host machine 38 (FIG. 3) to the controller 30, the controller 30 (the MPU 31 of the controller) immediately outputs the command if it is not executing the print. Hold 1
After printing the pages (completion of paper discharge), the CPU 41 of the engine driver 40 is instructed to change the pixel density to a new pixel density.

The CPU 41, which is both rotation speed change instruction means and photoreceptor stop detection means, determines the image clock WCLK corresponding to the newly instructed pixel density and the frequency of the PM clock for controlling the rotation speed of the polygon motor 54. At the same time, it is detected via the MM driver 14d whether the main motor 14 is rotating, that is, whether the photoconductor is moving or stopped.

When the main motor 14 and the photoreceptor corresponding thereto are stopped, the CPU 41 instructs the clock generator 25 to change the image clock WCLK and PM clock frequencies and the PM driver 54d to change the rotation speed.

The clock generator 25 divides the high frequency pulse stabilized by the crystal unit 25a according to the frequency instruction of the CPU 41, outputs the image clock WCLK, and serves as a rotation speed control means for the PM clock. Output to the PM driver 54d.

The PM driver 54d controls the polygon motor 54 to rotate synchronously with a new PM clock input from the clock generator 25 in response to a rotation speed change instruction from the CPU 41. On the other hand, the CPU 41 instructs the LD unit 50 to forcibly cause the laser diode to continuously emit light in order to confirm whether or not the new rotation speed instructed by the polygon motor 54 has been reached.

As shown in FIG. 4, six mirror surfaces 55
Since the laser beam deflected by the polygon mirror 55 having a is incident on the synchronization sensor 62 for each scanning, the synchronization sensor 62 outputs six synchronization signals DETP for each rotation of the motor. Therefore, by detecting the cycle of the synchronization signal DETP, the polygon motor 54 is set to a new P
It is possible to know whether or not stable synchronous rotation has started with respect to the M clock.

As described in the section of the operation, since the photosensitive drum 15 is stopped, the portion discharged by the continuous light emission of the laser diode is one scanning line.
The amount of toner that adheres is extremely small, and there is no problem with dirt in the device or reduction in the life of the cleaner. Also,
If the developing bias voltage is controlled so that the reverse toner does not adhere to the charged portion of the photoconductor, the amount of adhered toner can be further suppressed.

FIG. 5 is a block diagram showing the configuration of the second embodiment of the control system relating to the change in the number of revolutions. The same parts as those of the first embodiment shown in FIG. Is omitted.

The second embodiment shown in FIG. 5 differs from the first embodiment in that a clutch 26, which is a photosensitive member stopping means, is provided between the main motor 14 and the photosensitive drum 15, and the CPU 4
1 controls the I / O 44 and the CL driver 26d. Further, a pulse generator 27 is provided coaxially with the photosensitive drum 15,
By outputting a pulse having a frequency proportional to the number of revolutions to the CPU 41 via the I / O 44, a reliable photosensitive member stop detecting means is configured.

The main motor 14 is used as the photosensitive member stopping means.
May be turned off, but since the main motor 14 is not only the photosensitive drum 15 but also the drive source for each part of the mechanism, the inertia of the whole becomes large, and until the photosensitive drum actually stops. It takes a long time.

By providing the clutch 26, the required stop time is greatly shortened, and during printing, the roller after fixing is rotated at the time when the transfer of the toner image is completed without waiting for the completion of paper discharge. If only the photosensitive drum 15 is stopped as it is, the rotation speed can be changed more quickly.

Therefore, when an instruction to change the pixel density is input from the controller 30, the CPU 41 merely confirms that the transfer of the toner image is completed, and immediately activates the clutch 26 and sets the pixel density to the instructed pixel density. Determine the frequencies of the corresponding two clocks.

The clutch 26 is operated to operate the main motor 14
After removing the connection between the photosensitive drum 15 and the photosensitive drum 15,
Detects the output of the pulse generator 27, surely detects the stop of the photosensitive drum 15 by stopping the output, and changes the frequencies of the image clock WCLK and the PM clock in the clock generator 25 and the rotation speed in the PM driver 54d. Each is instructed to change the rotation speed.

Although not particularly shown, a timer having a preset time from the actuation of the clutch 26 to the actual stop of the photosensitive drum 15 is provided in the CPU 41, and the clutch 2
If the CPU 41 instructs the PM driver 54d to change the number of revolutions after the set time has elapsed by starting the operation at the same time as the operation of 6, the pulse generator 27 becomes unnecessary, and the same degree of certainty can be ensured with a simpler configuration. Sex is obtained.

In the second embodiment, as in the first embodiment, since the photoconductor drum 15 is stopped and the laser diode continuously emits light, the same effect can be obtained for toner adhesion.

FIG. 6 is a block diagram showing the configuration of the third embodiment of the control system relating to the change of the rotation speed.
The same parts as those of the first and second embodiments shown in FIG.

The third embodiment shown in FIG. 6 is different from the first embodiment in the control system for stopping the light emission of the laser diode while the rotation number of the rotary deflector 56 is changed. The CPU 41, which is means, has the function.
Further, instead of the polygon motor 54 and the PM driver 54d, a polygon motor 54a having a pulse generator (not shown) and a PM driver 54p having a built-in PLL (phase lock loop) circuit are provided.

The third embodiment differs from the second embodiment in that the rotation speed is not confirmed by the light emission of the laser diode, so that it is not necessary to stop the photosensitive drum 15, and the clutch 26 and the CL driver 26d are not necessary. And that the pulse generator 27 is no longer necessary.

That is, in the third embodiment, when a pixel density change command is input from the controller 30, CP
The U41 simply confirms that one page of optical writing by the optical writing unit 28 is completed, and immediately instructs the clock generator 25 of the frequencies of two clocks respectively corresponding to the instructed pixel density. Along with PM driver 5
4p is instructed to change the number of revolutions, and further is instructed to the LD unit 50 of the optical writing unit 28 as the light source control means to prohibit the laser diode from emitting light.

In the PM driver 54p, the polygon motor 54a is provided with the clock generator 25 by the built-in PLL circuit.
Control is performed so as to rotate in synchronism with the PM clock input from, and a pulse output from a pulse generator (not shown) of the polygon motor 54a is input to perform comparison with the PM clock.

When the synchronous rotation of the polygon motor 54a with respect to the PM clock becomes stable, the PLL circuit outputs a synchronous coincidence signal, so that the PM driver 54p outputs the synchronous coincidence signal to the CPU 41 via the I / O 44 to achieve constant speed rotation. Notify you that you have entered. The CPU 41 immediately releases the emission inhibition of the laser diode when the synchronization coincidence signal is input.

In the third embodiment, as in the second embodiment, a timer for presetting the time from when the rotation speed change is instructed until the rotation deflector 56 stabilizes at the instructed rotation speed is set to C.
If it is provided in the PU 41 and the timer is started at the same time as the instruction to change the rotation speed so that the laser diode is prevented from emitting light while the timer is operating, the pulse generator of the polygon motor 54a and the P of the PM driver 54p are set.
Since the LL circuit is unnecessary and the configuration is exactly the same as that of the first embodiment, there is no increase in cost.

As described above, in the third embodiment, since the laser diode is not made to emit light while changing the rotation speed, the photosensitive drum 15 remains charged and toner adhesion does not occur. Further, the control of the rotation of the main motor 14 and the photoconductor drum 15 and the control of the developing bias are not necessary, so that the control is simple. Further, since the rotation speed can be changed when the optical writing for one page is completed, the rotation speed can be changed most quickly and the next print can be put on standby as compared with the conventional example and other embodiments. .

[0069]

As described above, in the image forming apparatus according to the present invention, it is possible to prevent the inside of the main body apparatus from being contaminated and the life of the cleaner from being shortened due to the adhesion of the toner to the photosensitive member when the pixel density is changed, by a simple means. You can

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of a first embodiment of a control system related to changing the number of rotations of a rotary deflector for changing the pixel density.

FIG. 2 is a schematic configuration diagram showing an example of an internal mechanism of a laser printer which is an embodiment of the present invention.

3 is a block diagram showing an example of a control system of the laser printer shown in FIG.

FIG. 4 is a perspective view of a main part of the optical writing unit shown in FIG.

FIG. 5 is a block diagram showing a configuration of a second embodiment of a control system relating to a rotation speed change.

FIG. 6 is a block diagram showing a configuration of a third embodiment of a control system relating to a change in rotation speed.

[Explanation of symbols]

14 main motor 14d MM driver 15 photoconductor drum 26 clutch (photoconductor stop means) 26d CL driver 27 pulse generator (photoconductor stop detection means) 30 controller 38 host machine 40 engine driver 41 CPU (rotation speed change instruction means, photoconductor) Stop detection means, light source control means, timer) 50 LD unit (laser light source) 54, 54a
Polygon motor 54d, 54p PM driver (rotation speed control means)

Claims (5)

[Claims] 1. An image forming apparatus for forming an image by scanning a charged and moving photoconductor by deflecting a laser beam by a rotary deflector, wherein a rotational speed for instructing a change in the rotational speed of the rotary deflector. A change instruction means, a rotation speed control means for changing the rotation speed of the rotary deflector according to an instruction of the rotation speed change instruction means, and a photoconductor stop detection means for detecting movement / stop of the photoconductor are provided. When the rotation speed change instructing means gives an instruction to change the rotation speed, the rotation speed control means controls the rotation deflector only when the photoreceptor stop detection means detects the stop of the photoreceptor. An image forming apparatus characterized in that the number of rotations is changed. 2. An image forming apparatus for forming an image by scanning a charged and moving photosensitive member with a laser beam deflected by a rotary deflector, wherein a rotational speed for instructing a change in the rotational speed of the rotary deflector. Change instruction means, rotation speed control means for changing the rotation speed of the rotary deflector in accordance with the instruction of the rotation speed change instruction means, and when the rotation speed change instruction means gives an instruction to change the rotation speed, An image forming apparatus comprising: a photosensitive member stopping unit that stops the photosensitive member. 3. The image forming apparatus according to claim 2, wherein the time from the actuation of the photoconductor stop means to the actual stop of the photoconductor is set in advance, and is started when the photoconductor stop means is actuated. The image forming apparatus is characterized in that a rotation timer is provided, and the rotation speed control means changes the rotation speed of the rotary deflector after a set time of the timer has elapsed. 4. An image forming apparatus for forming an image by scanning a charged and moving photosensitive member with a laser beam deflected by a rotary deflector, wherein a rotational speed for instructing a change in the rotational speed of the rotary deflector. Change instruction means, rotation speed control means for changing the rotation speed of the rotary deflector in response to an instruction from the rotation speed change instruction means, and the rotation speed control means changes the rotation speed of the rotary deflector. The image forming apparatus is provided with a light source control unit that stops the emission of the laser light source that outputs the laser beam. 5. The image forming apparatus according to claim 4, wherein a time period from when the rotation speed change instruction unit gives an instruction to change the rotation speed until the rotation deflector stabilizes at the changed rotation speed is set in advance. An image forming apparatus is provided with a timer that is started by a change instruction of the rotation speed change instruction means, and the light source control means stops the light emission of the laser light source during the operation of the timer.