JPH08110347A - Image forming device with rotary information detector of sensitized body - Google Patents

Abstract

PURPOSE: To form an improved image by an inexpensive method by forming the image of the reflection light from markings which are provided at a certain spacing on the circumferential surface of a sensitized body on a line sensor. CONSTITUTION: Markings 6 are provided at a certain spacing on the circumferential surface of a sensitized body drum 1. Rays from a light source are applied to the markings and the image of the reflection light is formed on a line sensor 8 by an image-forming lens 7. The sensor 8 converts the projection image to an electrical signal and transmits it to a processing unit 3. The processing unit 3 processes the electrical signal to obtain the rotary information of the drum 1 and transmits it to a control circuit 5. The control circuit 5 controls the rotation of a motor 4 based on the rotary information to optimize the rotation of the drum 1. In this case, the rotation of the drum 1 is detected by the move of the images of the markings 6 projected on the sensor 8, thus calculating the amount of travel of the projection image by entirely capturing one period of the markings and hence eliminating the need that the pitch of the markings 6 is uniform.

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 such as an electrophotographic apparatus or a printing apparatus for reproducing an image on a transfer sheet from image information, and more particularly to a detector for detecting rotation information of a photoconductor for image formation. The present invention relates to a provided image forming apparatus.

[0002]

2. Description of the Related Art Conventionally, in the field of image forming apparatuses such as electrophotographic apparatuses and printing apparatuses, it is necessary to form an electrostatic latent image on a photoconductor by a potential difference and to develop the electrostatic latent image with a developer. Is used to form a developer image. As an example, a specific example of the electrophotographic apparatus will be described with reference to the drawings.

In FIG. 4, an automatic document feeder 11 is located on the upper surface of the image recording apparatus body 10. Automatic document feeder
11 automatically feeds the original to the reading position. A reading unit 12 reads the image information of the document conveyed to the reading position by a light receiving element such as a CCD and outputs the image signal as an analog signal. 13 is a processing circuit unit, which is analog /
It includes a digital conversion unit, an image processing unit, a video interface unit, etc., and performs an analog / digital conversion on the image signal output from the reading unit 12 to convert the analog signal into a digital signal, and further by the image processing unit and the video interface unit. An image signal converted into a digital signal is converted and processed into a recording signal suitable for image recording. A laser writing unit 14 includes a laser optical system that emits light according to a recording signal, and optically scans the rotating photosensitive drum 15a to form a latent image. An image forming unit 15 including a photoconductor drum 15a and a charger provided in the peripheral portion thereof, a developing device, and the like is developed into a toner image by developing the latent image with toner that is a developing material,
It is transferred onto the transfer paper fed from the paper feed units 16a and 16b.
The transfer paper is conveyed to the fixing device 17 and fixed while holding the transferred toner image. The transfer paper on which the toner image is fixed and recorded is discharged from the paper discharge unit 18.

In the image forming apparatus having the above structure, the rotation of the photosensitive drum and the optical scanning by the laser writing unit are synchronized, or the rotation of the photosensitive drum and the development by the developing device are synchronized. Finally, the quality of the image finally formed on the transfer paper is greatly affected. That is, the rotation accuracy of the photosensitive drum directly affects the image quality of the image. This is the same as in the case of using a belt-shaped photoreceptor, in that the rotation accuracy of the rotating body that drives the belt affects the image quality of the image. Therefore, it is desirable to take a method for keeping the rotation of the rotating body that drives the photosensitive drum or the belt-like photosensitive body constant.

There are roughly two means which have been conventionally implemented in this field and which improve the rotation accuracy of the photosensitive member. The first means is to add some structure so that the photoconductor physically rotates stably. This is the first one that attaches a flywheel to the photoconductor to increase the inertial force of the photoconductor to reduce uneven rotation.
Belong to the means. The second means detects the rotation information of the photoconductor by a detector and controls the drive source for driving the photoconductor based on the detected information to actively control the rotation of the photoconductor. It is called active control. The first means is relatively inexpensive to implement, but the second
It is impossible to finely control the rotation of the photoconductor such as that by the above means. Further, since a load is applied to the drive system by attaching a flywheel or the like, a drive system with a large output is required, and the entire image forming apparatus is enlarged. Therefore,
In order to realize a more compact image forming apparatus capable of forming an excellent image quality, rotation control of the photoconductor by active control, which is the second means, is essential.

In order to control the rotation of the photoconductor by active control, it is conceivable to detect the rotation information of the photoconductor by a conventional encoder using a point sensor. The mechanism of this encoder will be described with reference to the drawings.

In FIG. 5, markings M are provided on the surface of the rotating body R at a constant pitch. Rotating body R
The light source S emits light rays at a constant angle toward the surface of the. The irradiated light beam is reflected by the surface of the rotating body R and received by the fixed optical sensor D. The optical sensor D generates an electric signal according to the light intensity of the received reflected light. At this time, since the light beam from the light source S tends to be absorbed in the portion of the marking M provided on the surface of the rotating body R, the electric signal from the optical sensor D has a low voltage as indicated by t2 in FIG. In the state where there is no marking M on the surface of the rotating body R, the electric signal has a high voltage state such as t1 in FIG. Therefore, as a result, the electric signal from the optical sensor D forms a waveform as shown in FIG.

In the encoder having such a structure, the accuracy of the output signal from the encoder is determined by the relationship between the circumferential length of the rotating body in the encoder and the pitch of the marking made on the rotating body. That is, the accuracy of the encoder output signal is improved by enlarging the rotating body or by making the marking pitch fine and highly accurate. However, when the encoder is used in the image forming apparatus, the size of the rotating body is naturally limited due to the size of the apparatus body.
It is necessary to make the marking pitch finer. The image quality that the inventor of the present application considers as a good image in the image forming apparatus is about 300D in terms of the number of pixels in the resolution of the color image.
That is, an image of PI to 400 DPI can be reproduced well. This resolution has a length of 84.7 μm to 63.5 μm per pixel, and if an image to be reproduced deviates by 5% or more of the length of one pixel, the desired good image quality cannot be achieved. That is, in order to achieve good image quality, it is necessary for the encoder to detect the deviation of the photoconductor of at least about 3 μm, and the printing interval of about 10 μm to 50 μm in the marking on the rotary body of the encoder and A marking width error of less than 1% must be obtained. Such an encoder is very expensive and practically impossible to mount on an image forming apparatus.

[0009]

SUMMARY OF THE INVENTION The present invention is equipped with a rotation information detector which can be realized by an inexpensive method with a precision that can be applied to obtain stable rotation of a photoconductor, and therefore a good image can be formed. An object of the present invention is to obtain an image forming apparatus that can be used.

[0010]

In an image forming apparatus according to the present invention for solving the above-mentioned problems, first, markings are made on a circumferential surface of a photoconductor to be rotated at regular intervals, and the markings are irradiated with light rays. Equipped with a light source. Then, the reflected light from the marking thus obtained is imaged on the line sensor by the imaging lens, so that the line sensor receives the projected image of the marking. At this time, the line sensor has a plurality of consecutive pixels, and each pixel outputs an electric signal corresponding to the projected image of the marking received. Further, the electric signal obtained from the line sensor is processed by the processing unit to obtain rotation information of the photoconductor, and the rotation information of the photoconductor is controlled by the control circuit.

[0011]

According to the above-described image forming apparatus of the present invention, since the rotation of the photosensitive member is detected by the movement of the projected image of the marking projected on the line sensor, one cycle of the marking is entirely captured. The amount of movement of the projected image can be calculated. That is, the rotation of the photoconductor can be accurately detected even if the markings provided on the photoconductor are not uniform in pitch. Further, since the imaging lens is used when the projected image of the marking is formed on the line sensor, the size of the marking applied on the photoconductor can be determined by the magnification. Therefore, the marking is not particularly required to be finely processed.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The general operation and specifications of an image forming apparatus equipped with a rotation information detector according to the present invention are the same as those shown in FIG. 4 and its description, except for the rotation control means of the photoconductor described below. Since they are not particularly related to the present invention, description of their general operation and specifications will be omitted.

The image forming apparatus according to the present invention is provided with rotation control means for actively controlling the rotation of the photosensitive drum 1 as shown in FIG. Markings 6 are provided at regular intervals on the circumferential surface of the photosensitive drum 1. At this time, the position where the marking 6 is applied is the photosensitive drum 1
The outer surface, inner surface of the photosensitive drum 1,
Any of the side surfaces may be used, or the marking may be provided by mounting the rotating body coaxially with the rotation axis of the photosensitive drum 1. The marking 6 is irradiated with a light ray from a light source (not shown), and the reflected light is imaged on the line sensor 8 by the imaging lens 7. The line sensor 8 that receives the reflected light including the projected image of the marking 6 converts the projected image into an electric signal and transmits the electric signal to the processing unit 3. Processing unit 3
Then, the rotation information of the photosensitive drum 1 is obtained by the processing described later based on the electric signal sent from the line sensor 8.
Further, the processing unit 3 transmits the acquired rotation information of the photosensitive drum 1 to the control circuit 5. The control circuit 5 controls the rotation of the drive system based on the rotation information sent from the processing unit 3 so that the rotation of the photosensitive drum 1 is optimal for image formation. At this time, the drive system of the photosensitive drum 1 includes the motor 4 and the speed reducer 2, and the driving of the motor 4 rotates the photosensitive drum 1 via the speed reducer 2. In this embodiment, the rotation control of the photosensitive drum 1 uses a control circuit called active control. This is a control that refers to data based on previously registered experience values with respect to the rotation information obtained from the processing unit 3 or predicts data while making corrections for various environmental changes. It is a complicated and highly accurate rotation control. However, the detection of the rotation information itself using the line sensor, which is a feature of the present embodiment, can be applied to even simpler rotation control, and can also be used, for example, in conventional control called feedback control. . In this feedback control, the obtained rotation information of the photosensitive drum 1 is directly sent to the drive system as a control amount of the drive system to control the drive system.

The line sensor 8 used in this embodiment is
It is a CCD element with a maximum number of 5000 pixels, and is generally available at a low cost. The 5000 pixel CCD element used is
The element length is 35 mm and the length of one pixel is about 7 μm. As shown in FIG. 2, the photosensitive drum 1 is rotating in the direction indicated by the arrow at a speed of 15 rpm, and the photosensitive drum 1 having a diameter of 180 mm moves at a peripheral speed of about 141.3 mm / sec. A projected image of the marking 6 provided at the marking cycle T on the circumferential surface of the photosensitive drum 1 is imaged on the line sensor 8 by the imaging lens 7 having a magnification of 1 / M. In the line sensor 8, as shown in FIG. 2, a portion that receives the projected image of the marking 6 and a portion that receives the reflected light from the blank portion where the marking 6 is not applied are represented by diagonal lines and blanks. Pixels that receive reflected light with different light intensities are created.
Therefore, the line sensor 8 generates an electric signal of a voltage (or current) corresponding to the light intensity received by each pixel.

In the present invention, the electrical signal thus obtained by the line sensor 8 is the marking 6 at a temporary point.
Is configured to have information corresponding to one cycle or more. The marking period T of the marking 6 is determined by the relationship between the element length L of the line sensor 8 and the number of pixels N, and the magnification 1 / M of the imaging lens 7. The line sensor 8 has the element length L = 35 mm and the number of pixels N = 5000 as described above,
Since the imaging lens 7 has a magnification of 1/10 (M = 10), the marking cycle T is 3.5 mm from the relational expression of T = L × 1 / M. The processing unit 3 is a line sensor 8
The information of the electric signal sent from is temporarily stored in the storage means, and the information obtained at two different times is compared to detect the rotation information of the photosensitive drum 1. Figure 3
To explain with reference to (a) and 3 (b) as an example, first, at time t, information based on an electric signal sent from the line sensor 8 is stored in the storage means. This stored information is for one cycle or more of the marking 6 due to the above configuration, and is as shown in FIG. Actually, information of 5000 pixels is stored, but in FIG. 3A, it is shown in a simplified manner. Here, the shaded portion is the portion where the projected image from the marking 6 is captured. Further, at time t + α, which is delayed by α from time t, the information based on the electric signal from the line sensor 8 is stored again in the storage means. This stored information also has more than one cycle of the marking 6, as shown in FIG.
It becomes like (b).

The processing unit 3 compares the thus obtained information at the time point t with the information at the time point t + α, and calculates the amount of movement of the projected image of the marking 6 drawn with diagonal lines in the α time. To detect. That is, this amount of movement is the peripheral speed of the photosensitive drum 1, and by comparing this peripheral speed for each unit time, it is possible to know whether or not the photosensitive drum 1 is rotating at a constant speed. Processing unit 3
In regard to the time for comparing and calculating the information at the two points in time, the peripheral speed of the photosensitive drum 1 is about 141.3 mm / sec, and the marking cycle T is 3.5 mm. It should be within seconds. This time is cheap C
Sufficient time for calculation using PU or the like. Also, it is naturally possible to prepare a dedicated circuit for calculation and perform high-speed processing. Further, even if the calculation speed is slow such that the information of 5000 pixels cannot be calculated within this time even if the information of 5000 pixels is compared one by one, some states expected after α time from the information at the time t are previously calculated. Prepare in storage means,
The peripheral speed of the photosensitive drum 1 can be detected in a shorter time by comparing the information at time t + α with the prepared state and repeating the narrowing operation. The electric signal obtained from the line sensor 8 is output as an analog signal, but when the processing unit 3 uses a digital circuit to compare and calculate the electric signal, the analog signal is converted into a multi-valued digital signal. There must be. At this time, the present invention can be implemented by binarizing, but the precision of the comparison operation can be further improved by A / D converting into a multi-value exceeding binary. For example, when the reflected light from the marking 6 is imaged on the line sensor 8 and one end of the projected image for one cycle is located at an intermediate position of a pixel of the line sensor 8, one end of the projected image is received. The electric signal output from the pixel is different from the output of the pixel receiving the projected image of the marking 6 as a whole. When the electric signal from the line sensor 8 is binarized, one end of this projected image is recognized as 0 or 1 (presence or absence of the image) by the threshold value for judgment, and in any case, the length of the projected image is Will result in an error of one pixel. However, when the electric signal from the line sensor 8 is multi-valued by exceeding two values, the output from the pixel that receives one end of this projected image and the output of the pixel that receives the entire projected image It is possible to distinguish between the two and accurately recognize one end of the projected image of the marking 6. This makes it possible to judge the movement of the marking while accurately capturing the length of the projected image of the marking 6 when performing the comparison calculation.

[0017]

In the conventional encoder using the point sensor, only the marking information at one point of the rotating body can be obtained at a time point, so that the marking and the signal obtained from the optical sensor have a one-to-one relationship. The accuracy of the rotation speed of the rotating body, which the optical sensor detects, depends on the accuracy of marking. However, according to the present invention, by using the line sensor as an optical sensor, the marking sensor
It is now possible to capture information for more than one cycle at a time at the same time, and to grasp the movement of one marking cycle as one unit. That is,
According to the present invention, even if there is a slight error in the marking pitch, one marking period is captured as a set of information, and therefore is not related to the detection accuracy of the rotation speed of the rotating body.

Further, according to the present invention, since the imaging lens is used when the reflected light from the marking provided on the peripheral surface of the photoconductor drum 1 which is the rotating body is imaged on the line sensor 8, the marking cycle is used. T can be determined by the magnification of the imaging lens, and the conventional requirement of 10 μm to 50 μm is now 3.5 mm.

As described above, according to the present invention, the rotation of the photosensitive drum can be controlled with high precision by an inexpensive structure, and a good image can be formed in the image forming apparatus.

[Brief description of drawings]

FIG. 1 is a configuration diagram of a rotation control unit of a photoconductor according to the present invention.

FIG. 2 is a conceptual diagram showing a means for detecting markings on the peripheral surface of a photosensitive drum using a line sensor according to the present invention.

FIG. 3 is a conceptual diagram showing means for detecting the movement of the marking by the projected images of the marking formed on the line sensor at two different times according to the present invention.

FIG. 4 is a configuration diagram showing a configuration of a general image forming apparatus.

FIG. 5 is a configuration diagram showing a configuration of an encoder using a conventional point sensor.

FIG. 6 is a diagram showing a waveform of a signal obtained by a conventional encoder.

[Explanation of symbols]

 1 Photoconductor drum 2 Reduction gear 3 Processing unit 4 Motor 5 Control circuit 6 Marking 7 Imaging lens 8 Line sensor L Element length N Number of pixels T Marking cycle

Claims (3)

[Claims] 1. A rotating body having markings on its circumferential surface at regular intervals, a photoconductor that rotates about the same rotation axis as the rotating body, a drive system that rotates the photoconductor, and the marking. A line sensor in which a plurality of pixels that generate different electrical signals depending on the light intensity of the emitted light are connected, and the reflected light obtained by the light reflected on the marking is the line sensor. An imaging lens for forming an image on a plurality of continuous pixels, a processing unit for detecting rotation information of the photoconductor from the electric signal obtained from the line sensor, and the processing unit based on the rotation information obtained by the processing unit. An image forming apparatus having a control circuit for controlling rotation of the photoconductor by controlling a drive system. 2. The electric signal obtained from the line sensor is converted into a multi-valued digital signal having more than two values and processed by the processing unit.
Image forming apparatus. 3. The image according to claim 1, wherein the marking, the imaging lens, and the line sensor are configured such that the projected image of the marking formed on the line sensor has one cycle or more of the marking. Forming equipment.