JPH1035007A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To accurately control a scanner motor and to extend the service life of a photosensitive drum by a method wherein a rotation driving means is controlled in accordance with a beam detection signal in a first mode and it is controlled in accordance with a rotation speed signal in a second mode. SOLUTION: An emitted laser light is scanned in a horizontal direction in response to rotation of a polygon mirror 104 and a part of the light is detected by a beam detection section 4, thereby generating a beam detection signal (BD signal). An FG 3-3 transmits a speed detection signal (FG signal) while a scanner motor 3-2 rotates making one revolution. A switch 8 selects the BD signal or FG signal along an instruction of a CPU 1 to output it to a speed judgment circuit 5 and a speed error detection circuit 7. Therefore, the CPU 1 can drive and control the scanner motor 3-2 by the same speed even when either the BD signal or FG signal is selected. As a result, it is possible to control the scanner motor with high accuracy and to extend the service life of the photosensitive drum.

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, and more particularly, to control of a scanner motor for driving a polygon mirror.

[0002]

2. Description of the Related Art Conventionally, a laser beam is modulated in accordance with input image information and an electrostatic latent image is formed by exposing and scanning a photoreceptor, which is developed with a developer and transferred to recording paper. There is known a so-called laser beam printer that performs printing.
Further, this process is performed for each color of Y (yellow), M (magenta), C (cyan), and BK (black), and the developed images are transferred onto the same recording paper in a superimposed manner, so that color printing is performed. A color laser printer is provided.

FIG. 4 shows an example of this color laser beam printer.

In FIG. 4, reference numeral 101 denotes a photosensitive drum having a semiconductor layer such as selenium or cadmium sulfide on its surface.
Is rotating in the direction of. 102 is a semiconductor laser for emitting laser light, 103 is a beam expander, 104 is a polyhedral mirror having a plurality of mirror surfaces, 105 is an imaging lens, 1
06 is a reflection mirror for beam detection, 107 is a rotary developing device,
108 is a paper cassette, 109 is a folding mirror, 110
Is a fixing device, 111 is a charger, 112 is a transfer drum, 11
Reference numeral 3 denotes a recording paper, and 3-2 denotes a scanner motor. Also, 4
Denotes a beam detection unit, which includes, for example, a photoelectric conversion element such as a photodiode, and a waveform shaping circuit that shapes the waveform of an electric signal output from the photoelectric conversion element. Hereinafter, these operations will be described.

First, a semiconductor laser 10 is used in accordance with image information.
The laser light L emitted from 2 is a beam expander 1
The beam is converted into a predetermined beam diameter by 03 and is incident on a polyhedral mirror 104 having a plurality of mirror surfaces. Polyhedral mirror 10
4 is rotated by the scanner motor 3-2, and the laser light L is scanned substantially in the horizontal direction. The scanned laser beam L passes through the imaging lens 105 and is turned
9 is formed as a spot light on the photosensitive drum 101, which is reflected by the charger 9 and charged to a predetermined polarity by the charger 111, to form an electrostatic latent image.

Here, the laser light L is applied to the polygon mirror 104.
Each time the photosensitive drum 101 is scanned once, the light is reflected by the beam detecting mirror 106, enters the beam detecting unit 4, and is converted into an electric signal. Based on this beam detection signal (hereinafter referred to as a BD signal), the start timing of the modulation operation of the semiconductor laser 102 for obtaining a desired latent image on the photoconductor 101 is determined.

The electrostatic latent image thus formed is visualized in one of Y, M, C, and BK by a rotary developing machine 107, taken out of a paper cassette 108, and transferred to a transfer drum 112. Is transferred onto the recording paper 113 wound around the paper.

By performing the above process for each color of Y, M, C, and BK, a color image is formed on the recording paper 113. Here, the superposition of the respective color images is adjusted by synchronizing with the top position sensor 10 provided on the photosensitive drum 101.

Although not shown here, the visualized image on the photosensitive drum visualized by the developer is transferred to an intermediate transfer body for each color, and the color visualized image formed on the intermediate transfer body is transferred. Similarly, in a device for re-transferring to recording paper, each color image can be synchronized by the top position sensor 10 attached to the photosensitive drum.

[0010] The color image transferred onto the recording paper 113 is fixed by a fixing device 110, and then the recording paper 11 is fixed.
3 is discharged out of the housing H by a discharger (not shown).

In such a laser beam printer,
As a method for controlling the scanner motor 3-2, there is a method using a BD signal. Next, this method will be described with reference to FIG.

In FIG. 5, 1 is a CPU, 2 is a reference clock generation circuit, 3 is a scanner unit, 3-1 is a motor driver for driving the scanner motor 3-2, 4 is a beam detector, 5 is a speed determination circuit, 6 is a charge pump circuit,
Reference numeral 7 denotes a speed error detection circuit.

As described with reference to FIG.
2 is scanned in the horizontal direction by a polyhedral mirror 104, and a part thereof is
And a BD signal is issued. Here, when the polyhedral mirror 104 has six surfaces, the BD signal is emitted six times while the scanner motor 3-2 makes one rotation. This BD signal is input to the speed determination circuit 5.

The speed judging circuit 5 counts the reference clock generated by the reference clock generating circuit 2 during one period of the BD signal and compares the count value with a preset target value to make a judgment. When the count value exceeds the target value, that is, when it is determined that the scanner motor 3-2 has not reached the target speed, a speed-up signal is output to the charge pump circuit 6 to reach the target value. If not, that is, if the target speed is exceeded, a speed down signal is output to the charge pump circuit 6.

The charge pump circuit 6 includes a speed determination circuit 5
The speed difference is converted into a control voltage in accordance with the speed-up signal or the speed-down signal output from the controller, and output to the motor driver 3-1. For example, if the target speed is not reached, a positive voltage is output, and if the target speed is exceeded, a negative voltage is output.

The motor driver 3-1 controls the scanner motor 3-2 according to the control voltage output from the charge pump circuit 6, so that the polygon mirror 104 can rotate at a target speed.

Also, B emitted by the beam detector 4
The D signal is also input to the speed error detection circuit 5, and the speed error detection circuit 5 determines that an abnormality has occurred when the rotation speed of the scanner motor 3-2 greatly deviates from the target speed, that is, when the rotation speed deviates from the allowable range. And sends a speed error signal to CPU1.
Output to When receiving the error signal, the CPU 1 outputs a rotation stop signal to the speed discrimination circuit 5, and stops the rotation of the scanner motor 3-2.

Although the description of the PLL control is omitted here, the phase difference between the reference speed signal and the BD signal is detected, and the PLL control is performed.
L speed control may be added to achieve PLL speed control.

[0019]

However, there are some problems in the method of performing control using the BD signal as described above.

First, the scanner motor 3-2 is activated. When the scanner motor 3-2 is activated,
Since the rotation speed is low, the BD signal hardly appears, and the timing of the appearance cannot be predicted. Therefore, the laser must be constantly turned on. At this time, since the same line on the photosensitive drum is continuously irradiated by the laser, the photosensitive drum 101 is damaged, causing sensitivity unevenness and shortening the life of the photosensitive drum 101.

To prevent this, the scanner motor 3-2
There is also a method in which the laser is turned off at the time of startup, the acceleration is continued for a fixed time by open control not depending on the BD signal, and after a predetermined time elapses, the laser is turned on to switch to the closed control using the BD signal. In this case, for example, even if dust adheres to the BD sensor detection unit 4 and an abnormality occurs in the BD signal, a problem occurs that the abnormality is not detected until a predetermined time elapses.

The second problem is that the BD during printing is
Occurs when the signal is abnormal. For example, B
BD signal is output at times other than when D should be detected,
Immediately stopping the scanner motor and interrupting printing due to the fact that dust or the like has adhered to the BD sensor and the BD signal has not arrived for several times may reduce the reliability of the apparatus.

The present invention has been made in view of the above points, and has as its object to provide a highly reliable image forming apparatus which controls a scanner motor with high precision, extends the life of a photosensitive drum, and provides a highly reliable image forming apparatus. .

[0024]

According to the present invention, there is provided an image forming apparatus comprising: a photosensitive member for carrying image information; a beam emitting means for emitting a beam; and a polyhedral mirror for reflecting the beam emitted by the beam emitting means. An image forming apparatus comprising: a rotation driving unit that rotationally drives the polyhedral mirror so that the beam reflected by the polyhedral mirror is scanned on the photoconductor. A rotation speed detection means for outputting a rotation speed signal, and a beam detection means for detecting the beam and outputting a beam detection signal, and controlling the rotation drive means in the first mode according to the beam detection signal. In the second mode, the rotation driving means is controlled according to the rotation speed signal.

[0025]

BEST MODE FOR CARRYING OUT THE INVENTION

(Embodiment 1) FIG. 1 is a block diagram of an image forming apparatus according to a first embodiment of the present invention.

In FIG. 1, a scanner 3-3 provided in the scanner unit 3 detects a change in magnetic flux generated by rotation of the scanner motor 3-2 by using a coil or a Hall element. An FG (frequency generator) 2 for detecting the rotation speed of -2, 8 is a switch, and 9 is a target value setting register.

The reference clock generating circuit 2, the beam detecting section 4, the speed judging circuit 5, the charge pump circuit 6, and the speed error detecting circuit 7 have the same configuration as those described in the conventional example. A CPU 1 controls the entire image forming apparatus.

Hereinafter, these operations will be described.

The laser beam L emitted from the semiconductor laser 102 is scanned in the horizontal direction by the rotation of the polyhedral mirror 104, a part of which is detected by the beam detector 4, and a BD signal is emitted. Here, when the polyhedral mirror has six surfaces, the BD signal is emitted six times while the scanner motor 3-2 makes one rotation.

On the other hand, FG3-3 is a scanner motor 3-.
For example, four times during one rotation of the motor 2, the speed detection signal (hereinafter referred to as F
G signal).

The switch 8 operates according to a command from the CPU 1
The D signal or the FG signal is selected and output to the speed determination circuit 5 and the speed error detection circuit 7.

The speed judging circuit 5 counts the reference clock generated by the reference clock generating circuit 2 during one period of the BD signal or the FG signal, and the count value is set in the target value setting register 9. Compared to the target value N
judge. When the count value exceeds the target value N, that is, when it is determined that the scanner motor 3-2 has not reached the target speed, a speed-up signal is output,
If the target value N has not been reached, that is, if the target speed has been exceeded, a speed down signal is output.

Thereafter, the operations of the charge pump circuit 6 and the motor driver 3-1 are the same as those described in the conventional example.

Here, the CPU 1 and the target value setting register 9 will be described in detail.

In the above operation, for example, the switch 8
It was connected to the BD side and BD signal of the reference clock N _BD
In order to control the scanner motor 3-2 to be generated by the multiple of the period, and has set a target value of the target value setting register 9 to N _BD. Now, from the control based on the BD signal, the FG
When switching to the control based on the signal, the CPU 1 switches the switch 8 from the BD side to the FG side. However, as described above, the BD signal is emitted six times and the FG signal is emitted four times during one rotation of the scanner motor 3-2. Therefore, the CPU 1 sets the scanner motor 3
2, in order to rotate subsequently at the same speed, rewrites the target value N _BD of the target value setting register 9 to N _FG. However,
In this case, N _FG = 1.5 × N _BD .

Similarly, when the control based on the FG signal is switched to the control based on the BD signal, the target value of the target value setting register 9 is similarly rewritten.

Although the configuration in which the BD signal is emitted six times and the FG signal is emitted four times during one rotation of the scanner motor 3-2 has been described, the ratio is different even in the configuration in which these values are different. It is also easy to rewrite in the same way.

As described above, when switching the switch 8, the CPU 1 rewrites the value of the target value setting register 9 according to the selection destination of the switch 8 at the same time, so that the CPU 1 selects either the BD signal or the FG signal. The drive of the scanner motor 3-2 can be controlled at the same speed.

Next, the operation flow will be described.

First, at the time of startup, the CPU 1 sets the switch 8 to the FG side and sets the target value setting register 9 to N.
Set to _FG . Next, when the control of the scanner motor 3-2 is started according to the FG signal, the rotation speed of the scanner motor 3-2 gradually increases. Note that the laser is not turned on during this period.

The speed error detection circuit 7 includes the scanner motor 3
Continue to observe whether -2 has reached the aforementioned tolerance,
Upon reaching the allowable range, CPU 1 switches the switch 8 to the BD side, to simultaneously set the target speed setting register 9 to N _BD, inform that the preparation of the printing operation has been completed to the controller (not shown) by the light emission of the laser Printing starts.

This eliminates the necessity of forcibly turning on the laser when the scanner motor 3-2 is started, so that the photosensitive drum 101 is not damaged and the life of the photosensitive drum 101 is extended. Further, since the control is performed in a closed manner from the time of starting, it is possible to detect an abnormality immediately.

In the first embodiment, the FG
The signal is used until the scanner motor 3-2 reaches the allowable range. Since the accuracy of the FG 3-3 does not affect the formed image, the FG 3-3 does not need to be high-precision and is inexpensive. A low-precision one may be used.

(Embodiment 2) FIG. 2 is a block diagram of an image forming apparatus according to a second embodiment of the present invention, and FIG. 3 is a flowchart showing the operation thereof.

In FIG. 2, reference numeral 10 denotes a top detection sensor for detecting that the leading end of the recording paper 113 has reached a predetermined distance before the transfer position, reference numeral 11 denotes a sub-scanning counter for counting the number of laser scans, and reference numeral 1 denotes this image formation. A CPU that controls the entire apparatus is configured in the same manner as the first embodiment.

Hereinafter, the operation flow will be described with reference to FIGS.
This will be described with reference to FIG.

First, the process starts from S1. Incidentally, at this time, the rotational speed of the scanner motor 3-2 reaches the target speed, and the switch 8 is set to BD side, the target value setting register 9 is assumed that the value of N _BD is set .

In step S 2, the CPU 1 detects the top end of the recording paper 113 from the transfer drum 112
It is determined whether or not the transfer paper has reached a predetermined distance before the upper transfer position. If not, the process waits until the transfer has reached the transfer position. When the transfer paper reaches the predetermined position, the process proceeds to S3.

In S3, one of Y, M, C, and BK
Start the printing operation for the color.

When the BD signal is detected in S4, the speed error detection circuit 7 determines in S5 whether or not the count value of the reference clock is within the allowable range. If the count value is within the allowable range, the process proceeds to S7. On the other hand, if deviating from the allowable range, it is determined that abnormality in the BD signal is generated, the switch 8 switched to the FG side in S6, the process proceeds to S7 rewrites the target value to the N _FG.

At S7, the speed determination circuit 5 compares the counter value with the target value, and if the counter value is larger than the target value, outputs a speed-up signal at S8, and if smaller, outputs a speed-down signal at S9. move on.

In S10, it is determined whether printing for one page has been completed for the color, that is, whether the sub-scanning count has reached the number of scans for one page. If so, proceed to S11.

In S11, it is determined whether or not printing has been completed for all colors of Y, M, C, and BK. If printing has not been completed for all colors, the process returns to S2, and the same applies to the remaining colors. It controls printing and the scanner motor. S
If printing has been completed for all colors at 11, the operation ends.

As described above, in this embodiment, when an abnormality occurs in the BD signal, the rotation speed of the scanner motor 3-2 is controlled in accordance with the FG signal until printing of all colors is completed. The control may be switched to the control by the BD signal immediately when the signal returns to normal, or the control may be switched to the control by the BD signal when the printing of the color is completed.

(Other Embodiments) In the above two embodiments, the FG is used to monitor the rotation speed of the scanner motor 3-2. However, instead of the FG, for example, a DC brushless motor is provided. It is also easy to use a built-in position detector for phase detection or a speed monitor based on a back electromotive voltage of a switching transistor.

[0056]

As described above, according to the present invention, a photosensitive member carrying image information, a beam emitting means for emitting a beam, and a polyhedral mirror for reflecting the beam emitted by the beam emitting means An image forming apparatus comprising: a rotation driving unit that rotationally drives the polyhedral mirror so that the beam reflected by the polyhedral mirror is scanned on the photoconductor. A rotation speed detection means for outputting a rotation speed signal, and a beam detection means for detecting the beam and outputting a beam detection signal, and controlling the rotation drive means in the first mode according to the beam detection signal. In the second mode, by controlling the rotation driving means in accordance with the rotation speed signal, the scanner motor is controlled with high precision, and the photosensitive drum is controlled. Seeking a longer life, it is possible to provide a highly reliable image forming apparatus.

[Brief description of the drawings]

FIG. 1 is a block diagram of an image forming apparatus as a first embodiment.

FIG. 2 is a block diagram of an image forming apparatus as a second embodiment.

FIG. 3 is a flowchart illustrating the operation of an image forming apparatus according to a second embodiment.

FIG. 4 is a schematic view of a conventional image forming apparatus.

FIG. 5 is a block diagram of a conventional image forming apparatus.

[Explanation of symbols]

 104 Polyhedral mirror 3-2 Scanner motor 3-3 FG (frequency generator) 4 Beam detector 5 Speed judgment circuit 9 Target value setting register 1 CPU

Claims (3)

[Claims] 1. A photosensitive member that carries image information, a beam emitting unit that emits a beam, a polyhedral mirror that reflects the beam emitted by the beam emitting unit, and a beam that is reflected by the polyhedral mirror. An image forming apparatus comprising: a rotation driving unit that rotationally drives the polyhedral mirror so as to be scanned on the photoconductor; a rotation speed detection unit that detects a rotation speed of the rotation driving unit and outputs a rotation speed signal; Beam detecting means for detecting the beam and outputting a beam detection signal, controlling the rotation driving means in accordance with the beam detection signal in a first mode, and controlling the rotation speed signal in a second mode. An image forming apparatus, wherein the rotation driving unit is controlled in response to the rotation. 2. The image forming apparatus according to claim 1, wherein the second mode is executed when the rotation drive unit is started. 3. The image forming apparatus according to claim 1, wherein the second mode is executed when an abnormality occurs in the beam detection signal.