JPH06127089A - Image forming device - Google Patents

Abstract

(57) [Abstract] [Purpose] To provide an image forming apparatus capable of always printing a drawing at a preset intended position even if there is a mechanical deviation or variation in the paper feeding / winding mechanism. [Structure] By rotating the image forming drum on which the recording paper is fed, by moving the paper position detection sensor by the sensor drive means, the winding position of the recording paper in both the vertical and horizontal directions is detected,
The image output position is corrected by controlling the data transmission timing of the image data supply device using the position information.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus,
More specifically, it relates to an image forming apparatus capable of correcting the position of a formed image on a recording sheet.

[0002]

2. Description of the Related Art As means for forming an image in a graphic printing device such as a printer or a copying machine, an electrostatic latent image is formed by scanning a charged photoconductor with a laser beam modulated with an image signal. Various ones have been proposed and put into practical use, such as an electrophotographic system in which the image is formed and then developed, and a thermal transfer system in which a recording ink is melted by a thermal head and transferred to a recording paper. Although a detailed description of the mechanism of these various image forming means is omitted, in the image forming process, a method of feeding the recording paper to the image forming drum to perform the image forming process is often used.

As an example, an outline of an image forming process by a laser exposure electrophotographic system will be described with reference to FIG.

The recording paper is taken out from the recording paper tray 1 by the action of the paper conveying rollers 2 and 3 and wound around the image forming drum 4 rotating in the direction of the arrow. It is assumed that the recording paper has a photosensitive characteristic and is adsorbed to the drum by the function of a drum adsorbing mechanism (not shown). Then, the surface of the photosensitive paper is uniformly given a positive charge by the charger 5. After that, when the laser light emitted from the laser diode 7 driven by the image data supply device 6 is applied to the recording paper wound around the image forming drum 4, the potential of that portion decreases, so that the recording paper remains on the recording paper. An electrostatic latent image is formed. In the illustration,
The laser light is scanned by the polygon mirror 8 to form an image by the so-called raster scan method. The electrostatic latent image on the recording paper is developed by the developing device 9, and then the developed recording paper is separated from the image forming drum 4 by the functions of the paper separating claw 10 and the paper conveying roller 11 and guided to the dry fixing belt 12. . Then, the recording paper is dried and fixed, and then ejected.

The above is a series of image forming processes by the laser exposure electrophotographic system. In order to control the position of the drawing printed on the recording paper in the above process, the following method is used.

First, the drawing position control in the main scanning direction of the printed image, that is, in the direction parallel to the rotation axis of the image forming drum 4,
This is done by setting the delay time from the horizontal synchronizing signal emitted from the laser beam detector (not shown) to an appropriate value when the image data supply device 6 sends each raster line data to the laser diode 7. Further, the drawing position control in the sub-scanning direction of the printed image, that is, the direction along the circumferential surface of the image forming drum 4, is performed based on the rotation angle of the image forming drum 4, the paper conveying rollers 2 and 3, the image data supply. This is done by controlling the device 6. For example, the paper conveying rollers 2 and 3 are driven so that the front end of the recording paper is wound around the point A in FIG. 4, and when the point A reaches the point B in FIG. The image data supply device 6 operates so as to send the raster data of the first line of the image data in response to the vertical synchronizing signal.

[0007]

However, in the conventional image forming apparatus for controlling the position of the formed image as described above, the mechanical deviation of the paper feeding and rewinding mechanism causes the image forming drum to always have an intended image forming drum. The recording paper is not wrapped around the position, so that the position control of the printed image also varies depending on the process. In addition, the material and thickness of the recording paper may differ depending on the purpose, and the dimensions of the recording paper may slightly vary depending on the lot. In that case, the position of the printed image may be different from the desired position. There was a tendency that the problem.

The present invention has been made to solve the above-mentioned problems, and there is a variation in the position where the recording paper is wound around the image forming drum due to mechanical deviation of the paper feeding and feeding mechanism. Even in such a case, the position of the formed image is constant, and it is an object of the present invention to provide an image forming apparatus capable of always printing a drawing at a preset intended position.

[0009]

In order to overcome such a problem, in an image forming apparatus of the present invention, an image forming drum that winds and rotates a fed recording paper and a position of the recording paper are provided. A paper position detection sensor for detecting, a sensor drive means for moving the paper position detection sensor in the vicinity of the surface of the image forming drum in parallel with the rotation axis of the image forming drum, and the recording paper on the image forming drum. An image forming unit that forms an image, an image data supply device that supplies image data to the image forming unit, and a paper position detection sensor that moves while rotating the image forming drum to detect the position of the recording paper. And a control unit that controls the data transmission timing of the image data supply device based on the position information.

[0010]

First, before the image forming process is started, the paper position detecting sensor is placed at the initial position near the center of the image forming drum by the sensor driving means. After the image forming process is started and the image forming drum starts rotating, when the sheet feeding device feeds the recording sheet to the image forming drum, the recording sheet is wound around the image forming drum. At the same time, the paper position detection sensor starts to move outward near the surface of the image forming drum in parallel with the drum rotation axis by the sensor driving means. After that, when the recording paper wound around the image forming drum reaches the position of the paper position detection sensor, the paper position detection sensor detects the leading end position of the recording paper. After a while, when the paper position detection sensor approaches the end of the image forming drum, the paper position detection sensor next detects the side end position of the recording paper.

The image data supply device uses the leading edge position information and the side edge position information of the recording paper obtained from the paper position detection sensor, respectively, and determines the timing of sending the image data to the image forming means with respect to the reference value. to correct. As a result, the position of the formed image in the sub-scanning direction and the main scanning direction on the recording paper is controlled so as to always be a fixed place.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a perspective view showing the structure of the image forming apparatus of this embodiment. The image forming apparatus of the present embodiment is provided with an image forming drum 25 rotatable in the direction of the arrow, a drum drive motor 24 for driving the image forming drum 25 via a gear, and an image forming drum 25 facing each other. Reflective photo sensor 23
And the reflection type photo sensor 2 through the sensor drive gear 22.
3, a sensor drive motor 21 for moving 3; a drum drive motor 24; a motor control device for controlling the sensor drive motor 21; an image data supply device 28; a laser scanning exposure device 29; and a beam detector 30.

In the initial state, the reflection type photo sensor 23 is operated by the sensor driving motor 21 so that the image forming drum 25
It has moved to a position closer to the center of. Also, the image forming drum 2
5 is stationary at a position where the rotation angle from the reference position is 0 degree.

When the image forming process is started,
The motor controller 27 drives the drum drive motor 24,
The image forming drum 25 starts rotating at a constant angular velocity in the direction of the arrow. Then, the motor control device 27 supplies the image data supply device 28 with the image data supply device 28 at time T0 when the drum drive motor 24 is supplied with a motor drive pulse corresponding to the rotation angle of the image forming drum 25 to reach the constant speed.
Send a process start signal to.

Next, a paper feeding device (not shown) is operated to feed the recording paper 26 to the image forming drum 25. At the same time, the motor control device 27 activates the sensor drive motor 21, and the reflection type photo sensor 23 starts to move outward near the surface of the image forming drum 25 at a constant speed in parallel with the drum rotation axis by the sensor drive gear 22. To do.

When the recording paper 26 reaches the image forming drum 25 by the function of the paper feeding device, the recording paper 26 is attracted to the surface of the image forming drum 25 by the function of a drum suction mechanism (not shown). After that, the recording paper 2 around which the image forming drum 25 is rotated and wound.
When 6 reaches the position of the reflection type photo sensor 23, due to the difference in surface reflectance between the recording paper 26 and the image forming drum 25,
The output of the reflective photo sensor 23 changes. Recording paper 26
Is normally white, and in that case, the output of the reflective photosensor 23 becomes large when the leading edge of the recording paper 26 is detected. Since the output of the reflection type photo sensor 23 is guided to the image data supplying device 28, the time T1 at which the output changes.
Are known to the image data supply 28.

During this time, the reflective photosensor 23 is moving at a constant speed toward the outside of the image forming drum 25 by the action of the sensor drive motor 21 and the sensor drive gear 22, but after a while, the reflective photosensor 23 is moved. When the sensor 23 is moved sufficiently outward, it reaches the side edge of the recording paper 26 being fed in the direction along the drum circumference, and for the same reason as described above, the reflection type photo sensor 23 is moved. The output changes. The time T2 at which the output changes is also known to the image data supply device 28. FIG. 2 shows how the output of the reflective photosensor 23 changes with time in the series of operations up to this point.

Now, the output change time points T1 and T2 of the reflection type photosensor 23 obtained as described above are respectively
It can be regarded as position information of the recording paper 26 on the image forming drum 25. That is, (T1-T0) can be converted into a position in the direction along the drum circumference of the recording paper 26, and (T2
-T0) can be converted into the position of the recording paper 26 in the direction along the drum rotation axis. In this embodiment, since the raster scan method using laser scanning exposure is used as the image forming means, T1 and T2 are not converted into position information, but
The data transmission timing of the image data supply device 28 that drives the laser light is corrected based on T1 and T2. The correction method is performed as follows, for example.

When the recording paper 26 is wound around the correct position of the image forming drum 25, the first output change time T1 of the reflection type photosensor 23 detected by the image data supply device 28 is:
Let T1REF. At this time, when the image data supply device 28 sends the first raster line data of the image data after TvREF seconds from the time T0 when the process start signal is received from the motor control device 27, the image data supply device 28 follows the circumference of the drum on the recording paper 26. The image can be formed at a desired position in any direction. Therefore, assuming that T1 actually detected is T1DET, the image data supply device 28 sends the first raster line data from T0 to (TvREF + (T1DET
-T1)) Correct so that it will be done in seconds.

Similarly, the recording paper 26 is used as the image forming drum 25.
Image data supply device 2 when wound around the correct position of
It is assumed that the second output change time point T2 of the reflective photosensor 23 detected by 8 is T2REF. Then, at this time, when the delay time from the horizontal synchronizing signal generated by the beam detector 30 to the start of sending the first pixel data of one raster line is ThREF seconds, the image data supply device 28 sets the recording paper 2
An image can be formed on the desired position in the direction along the drum rotation axis on 6. So now, T2 actually detected
Is T2DET, the image data supply device 28
The delay time from the horizontal sync signal to the start of sending the first pixel data of one raster line is (ThREF-A (T2DET-T
2)) Correct to seconds. Here, A is a positive constant determined by the ratio of the rotation speed of the image forming drum 25 and the scanning speed of the laser scanning exposure device 29.

The state of the image data transmission timing correction described above is shown in FIG. The mechanism for changing the image data transmission timing in the image data supply device 28 will not be described in detail, but it is easily recalled that it is possible, for example, by changing the count value set in the counter that counts the data transmission start time. Will

Returning to the description of the image forming process, after the second output change time T2 of the reflection type photo sensor 23, the image forming drum 25 is further rotated and the recording paper 26 is emitted by the laser scanning exposure device 29. When reaching the vicinity of the light irradiation scanning line, the image data supply device 28 sends the image data to the laser scanning exposure device 29 at the data sending timing corrected as described above. As a result, the electrostatic latent image is formed on the recording paper 26 at a preset intended position without being affected by the variation in the winding position of the recording paper 26 caused by the mechanical deviation of the paper feeding / winding mechanism. It is formed. After that, the recording paper 26 is developed by a developing device (not shown), but the subsequent steps are not an essential part of the present embodiment, and are omitted.

As can be seen from the above description, in the image forming apparatus described in this embodiment, the recording paper 26 is prevented from passing through the reflective photosensor 23 within (T2-T1) seconds. It is necessary to set the moving speed of the reflective photosensor 23 determined by the sensor drive motor 21 and the sensor drive gear 22.

As described above in detail, according to the image forming apparatus of the present embodiment, the position of the formed image is constant, and the graphic can always be printed at the preset intended position.

The present invention is not limited to the embodiments described in detail above, and modifications can be made without departing from the spirit of the invention. For example, in this embodiment, the sensor drive motor 21 and the sensor drive gear 22 are used as the sensor drive means, but this uses a mechanical drive mechanism that reciprocates in synchronization with the rotation of the image forming drum 25. It is also possible. It can also be implemented when a thermal transfer system using a thermal head is used as the image forming means.

[0027]

As described above in detail, according to the image forming apparatus of the present invention, the position where the recording paper is wound around the image forming drum may vary due to the mechanical deviation of the paper feeding / feeding mechanism. Even in such a case, the position of the formed image is constant, and the drawing can always be printed at a preset intended position.

[Brief description of drawings]

FIG. 1 is a perspective view of an image forming apparatus of this embodiment.

FIG. 2 is a diagram showing a graph showing how the output of a reflective photosensor changes with time.

FIG. 3A and FIG. 3B are explanatory diagrams showing a state of image data transmission timing correction.

FIG. 4 is a configuration diagram illustrating an image forming process by a conventional laser exposure electrophotographic method.

[Explanation of symbols]

 21 sensor drive motor 22 sensor drive gear 23 reflection type photo sensor 24 drum drive motor 25 image forming drum 26 recording paper 27 motor control device 28 image data supply device 29 laser scanning exposure device 30 beam detector

Claims (1)

[Claims] 1. An image forming drum for feeding and rotating a fed recording paper, a paper position detecting sensor for detecting a position of the recording paper, and a portion near a surface of the image forming drum for the image forming drum. Sensor drive means for moving the paper position detection sensor parallel to the rotation axis of the image forming means, image forming means for forming an image on the recording paper on the image forming drum, and image data for supplying image data to the image forming means. A supply device and a control unit that moves the paper position detection sensor while rotating the image forming drum to detect the position of the recording paper, and controls the data transmission timing of the image data supply device based on the position information. An image forming apparatus characterized by the above.