JPH11129540A - Image-forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable use of a scanner motor of a different TAC frequency. SOLUTION: In accordance with a rise of a rotational frequency of a scanner motor from a starting time, a time for a laser light to scan an optical sensor photodetecting part is reduced, whereby a pulse width of a synchronous signal is reduced. The pulse width of the synchronous signal at a regulated rotational frequency of the scanner motor is obtained beforehand, which is set as a regulated synchronous pulse width. The regulated synchronous pulse width is compared with an actual synchronous signal pulse width. Whether or not the scanner motor rotates at the regulated rotational frequency is thus detected. Since a rise of the scanner motor is detected from the pulse width of the synchronous signal, the use of the scanner motor of a different TAC frequency which is impossible heretofore is achieved.

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 in which oscillation light from a laser light source is used as a light source for image exposure.

[0002]

2. Description of the Related Art Conventionally, in this type of image forming apparatus, as means for detecting the number of revolutions of a scanner motor, a TAC frequency which is a signal having a frequency proportional to the number of revolutions is normally output from the scanner motor. The number of rotations is detected by monitoring the frequency.

[0003]

However, in the above conventional example, the TAC frequency at the time of the specified rotation of the scanner motor is determined by the specification of the scanner motor to be used.
When a scanner motor having a different TAC frequency is used, there is a problem that the rotation speed cannot be detected and a failure of the scanner motor cannot be detected. Further, when the start-up time of the scanner motor is prolonged due to a change in environmental temperature or the like, it is not possible to wait for the start of image formation until the scanner motor starts up, so that there is a problem that a defective image is output.

For this reason, once a certain TA of a scanner motor
If the image forming apparatus is designed in accordance with the specification of the C frequency, a scanner motor having a different TAC frequency cannot be used as a substitute even if there is a scanner motor having an advantage in cost performance.

An object of the present invention is to solve the above-mentioned problems,
It is an object of the present invention to provide an image forming apparatus that can be used with scanner motors having different TAC frequencies.

[0006]

According to the present invention, there is provided an image forming apparatus comprising: a laser light source for emitting a laser beam as a light source for image exposure; and a polygon for reflecting the laser beam. An image comprising a mirror, a scanner motor for rotating the polygon mirror at a constant speed to deflect and scan the laser light, and an optical sensor on a scanning path of the laser light and generating a horizontal synchronization signal when the laser light is irradiated. In the forming apparatus, a rise from the start of the scanner motor to a predetermined rotation speed is detected based on a pulse width of the horizontal synchronization signal.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail with reference to the illustrated embodiment. FIG. 1 is a configuration diagram of a laser scanner unit which is a main part of an image forming apparatus common to each embodiment of the present invention. In FIG. 1, reference numeral 1 denotes a laser diode. Laser light from the laser diode is incident on a polygon mirror 3 attached to a scanner motor 2, and the laser light deflected by the polygon mirror 3 is transmitted through a scanning lens 4. A spot light is formed on a photoconductor (not shown). A part of the scanned laser light is made to enter the optical sensor 5, the output of the optical sensor 5 is connected to the MPU 6, and the output of the MPU 6 is connected to the laser diode 1 via the scanner motor 2 and the laser driving means 7. Have been.

The scanner motor 2 scans the laser light reflected by the polygon mirror 3 in the horizontal direction at a constant speed by rotating the polygon mirror 3 at a constant rotation speed. The optical sensor 5 outputs a horizontal synchronization signal to the MPU 6 when the laser beam is irradiated, and the MPU 6 controls the scanner motor 2 and controls the laser driving means 7 in synchronization with the horizontal synchronization signal to emit the laser diode 1. Let it.

The MPU 6 rotates the scanner motor 2 when image data is input from an external device such as a personal computer. FIG. 2A shows a change in the number of revolutions from the start of the scanner motor 2. The MPU 6 controls the laser driving means 7 to emit laser light in order to monitor the synchronization signal from the optical sensor 5. The MPU 6 outputs a laser drive signal only while the laser light scans the light receiving section of the optical sensor 5.

Therefore, as the rotation speed of the scanner motor 2 increases from the start, the laser light is generated by the optical sensor 5.
2B, the pulse width of the synchronizing signal becomes smaller as shown in FIG. 2B. For this reason, the synchronization signal pulse width at the specified rotation speed of the scanner motor 2 is determined in advance, and is set as the specified synchronization pulse width, and is compared with the actual synchronization signal pulse width. You know if it is.

According to this embodiment, since the rising of the scanner motor 2 is detected from the pulse width of the synchronizing signal, it is possible to use the scanner motor 2 having a different TAC frequency, which was impossible in the prior art. Further, since the TAC signal line for detecting the rise of the scanner motor 2 which is required conventionally can be omitted, the number of poles of the connector and the electric wire can be reduced, and the cost can be reduced.

Some conventional image forming apparatuses detect the rising of the scanner motor by monitoring the cycle of the horizontal synchronizing signal. In the conventional example, at least one scanning time by the laser light is required to detect the number of rotations of the scanner motor. However, in this embodiment, it is only necessary to scan the light receiving portion of the optical sensor 5 with the laser light in order to detect the rotation speed of the scanner motor 2. Therefore, the laser emission time for detecting the rising of the scanner motor 2 can be shortened, and the life of the laser diode 1 can be extended.

In the first embodiment, the scanner motor 2
Until the scanner motor 2 reaches the specified number of revolutions after the start of the operation, the laser light is always emitted to monitor the synchronization signal pulse width. However, the scanner motor 2 always takes a certain amount of time until it reaches the specified number of revolutions, and emitting laser light during that time is useless and shortens the life of the laser diode 1. If the laser light is emitted when the rotation speed of the scanner motor 2 is low, the photosensitive drum (not shown) is irradiated with the laser light for a long time, and the life of the photosensitive drum is shortened.

Therefore, the second embodiment employs a scanner motor 2
An appropriate waiting time from the start of the operation to the start of laser light emission is determined in advance from the start characteristics of the scanner motor 2,
During the waiting time, the laser light is not emitted, and the light emission is started after the rotation speed of the scanner motor 2 has sufficiently risen.
The synchronization pulse width is to be monitored. By doing so, the emission time of the laser can be greatly reduced, and the life of the laser diode 1 and the photosensitive drum can be extended.

In the second embodiment, the scanner motor 2
The waiting time from the start of the operation to the start of laser emission is determined in advance from the start characteristics of the scanner motor 2. However, since the start-up time of the scanner motor 2 greatly changes depending on the environmental temperature and the like, it is actually difficult to determine an appropriate waiting time. That is, depending on the external environment, the rise time of the scanner motor 2 becomes longer, and the laser emission starts before the scanner motor 2 rises with the set waiting time, thereby shortening the life of the laser diode 1 and the photosensitive drum. Problems and conversely, the rise time of the scanner motor 2 is shortened, so that although the scanner motor 2 is sufficiently started, wasteful time of waiting for the start of laser light emission occurs, and the first print time is delayed. The problem of becoming inevitable.

Therefore, in the third embodiment, as shown in FIG. 3, after the scanner motor 2 is started, the laser diode 1 is made to emit light periodically for a very short time. Is detected.

In this way, even if the start-up time of the scanner motor 2 changes greatly due to the external environment, the required minimum laser emission time can be obtained and the rise of the scanner motor 2 can be detected early. The printing time can be shortened.

[0018]

As described above, according to the image forming apparatus of the present invention, the rise of the scanner motor is detected from the pulse width of the horizontal synchronizing signal. Can be used. Further, since the TAC signal line for detecting only the rising of the scanner motor, which is conventionally required, can be omitted, the number of poles of the connector and the electric wire can be reduced, and the cost can be reduced.

Further, as compared with the case where the rise of the scanner motor is detected from the period of the synchronization signal, the rise of the scanner motor can be detected in a shorter time and the laser emission time can be shortened. Life can be extended.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of a scanner unit.

FIG. 2 is a graph for explaining the first embodiment.

FIG. 3 is a graph for explaining a third embodiment.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Laser diode 2 Scanner motor 3 Polygon mirror 5 Optical sensor 7 Laser drive means 6 MPU

Claims (4)

[Claims] 1. A laser light source for emitting a laser beam as a light source for image exposure, a polygon mirror for reflecting the laser beam, and a scanner motor for rotating the polygon mirror at a constant speed to deflect and scan the laser beam. And an optical sensor that is on a scanning path of laser light and generates a horizontal synchronization signal when the laser light is irradiated. And an image forming apparatus for detecting by a pulse width of the horizontal synchronizing signal. 2. A method according to claim 1, wherein the rising of the scanner motor is performed by emitting a laser beam from the laser light source after a predetermined waiting time has elapsed from the start of the scanner motor, and determining a pulse width of the horizontal synchronization signal at that time. The image forming apparatus according to claim 1, wherein the detection is performed. 3. The image forming apparatus according to claim 1, wherein the rise of the scanner motor is periodically detected by emitting a laser beam from the laser light source for a short time, and the pulse width of the horizontal synchronization signal at that time is detected. . 4. A laser light is emitted from the laser light source for a short period periodically after a predetermined waiting time has elapsed from the start of the scanner motor, and the horizontal position of the horizontal axis at that time is determined. The image forming apparatus according to claim 1, wherein the detection is performed based on a pulse width of the synchronization signal.