JP2006018005A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming apparatus capable of reducing the banding amount perceived by human eyes.
A rotation fluctuation frequency of a photoreceptor is detected by a frequency characteristic analysis device, and a signal in which a frequency around the fluctuation frequency is randomly changed with a phase is output from a frequency generation device, and this signal is rotated by a motor. Added to the motor drive control signal at the time.
[Selection] Figure 4

Description

  The present invention relates to an image forming apparatus such as a digital copying machine or a printer.

In an image forming apparatus that develops on a photosensitive member using laser light as a light source, the laser light output from the laser light source is scanned in the longitudinal direction of the photosensitive member by a polygon mirror or the like, and data corresponding to one line of print information is stored on the photosensitive member. Development is performed on the photoconductor, and the photoconductor is rotated at a constant measure, whereby development is sequentially performed on the photoconductor to form a printed image on the photoconductor.
Then, the toner is attached to the image information (latent image) formed in the form of electric charges on the photoconductor, and the toner on the photoconductor is transferred to the output paper by using a transfer belt, etc. Fix and perform output image formation.
However, when performing actual writing, the rotation speed of the photoconductor is increased due to the effects of vibration caused by a number of factors, such as the vibration of the machine itself, vibration during paper feeding, and vibration due to contact between the photoconductor drum and transfer drum. Unevenness occurs.
For this reason, the print data developed on the photoreceptor is affected by vibration, and the pitch between the print lines is not uniform. This phenomenon is called banding and contributes to the deterioration of the quality of the printed image. That is, density unevenness appears in the sub-scanning direction in an actual printed image.
As a technique for suppressing this banding, a technique is known in which a member having a large moment of inertia called a flywheel is added on the axis of the photosensitive member to stabilize the rotation of the photosensitive member, thereby suppressing uneven rotation speed. Used in many products. However, to stabilize rotation using a flywheel, a mass of several tens of kg or more is required, which increases the weight of the entire device, and many problems such as safety when removing during maintenance and downsizing of the entire device. There is.
Further, as a technique for stabilizing the rotation of the photosensitive drum without using the flywheel, a technique for detecting the rotational speed of the photosensitive member with a detector and controlling the rotational speed, for example, as disclosed in Patent Document 1, There is a technique for realizing constant-speed rotation by detecting body position information with an encoder and performing position control.
In addition to the rotation control of the photosensitive member, as a method for controlling the optical system, for example, as shown in Patent Document 2, the vibration of the entire optical system is detected and the vibration that eliminates the vibration is applied to the optical system. There is a technique for making the beam writing position constant by giving the beam.
In addition, as a technique for detecting rotation information of the photoconductor, for example, as shown in Patent Document 3, marking was performed on the circumference of the photoconductor at almost regular intervals, and light was irradiated toward the marking. There is a technique for detecting a rotation speed from two different projection images obtained by forming a projection image on a line sensor.
Japanese Patent Laid-Open No. 10-323067 JP 09-033848 A Japanese Patent Laid-Open No. 08-110347

As described above, in the image forming apparatus, uneven rotation of the photosensitive drum occurs due to the vibration of the machine itself or the vibration due to disturbance, and the scanning line pitch of the laser beam is uneven when forming a latent image on the photosensitive member. As a result, density unevenness called banding occurs in the printed image.
As described above, there is a technology for performing rotation control as a technology for suppressing the banding and improving the image print quality. However, in order to perform the control, a processing device such as a DSP is required, or the control is performed for each machine. There may be problems such as the need to change the system.
In addition, a method for measuring the amount of fluctuation in advance and creating data to be corrected to control the photosensitive drum drive system and a technique for detecting fluctuation in real time and correcting the rotational driving by a method such as feedback control are also employed. However, in these control methods, when banding occurs in a high frequency range (a band exceeding 100 Hz), it is considered that phase alignment becomes difficult or control becomes difficult due to the inherent resonance of the mechanism itself. .
An object of the present invention is to provide an image forming apparatus capable of reducing the banding amount perceived by human eyes.

In order to achieve the above object, according to the first aspect of the present invention, the frequency detecting means for detecting the rotational fluctuation frequency of the photosensitive member and the frequency near the fluctuation frequency detected by the frequency detecting means are randomly changed along with the phase. A frequency generating means for generating a signal and an adding means for adding a signal output from the frequency generating means to a motor drive control signal during motor rotation are provided.
According to a second aspect of the present invention, there is provided a frequency detection means for detecting the rotational fluctuation frequency of the photosensitive member, and a frequency generation means for generating a signal in which the frequency near the fluctuation frequency detected by the frequency detection means is changed randomly along with the phase. And means for vibrating the polarization system in the writing optical path by a signal output from the frequency generator.
According to a third aspect of the present invention, in the image forming apparatus according to the first or second aspect, a signal output from the frequency generating unit is set to a predetermined frequency or higher.
According to a fourth aspect of the present invention, in the image forming apparatus according to the first or second aspect, the signal output from the frequency generating means is equal to or higher than a frequency defined by 0.5 × photoreceptor surface speed. It is characterized by that.
According to a fifth aspect of the present invention, in the image forming apparatus according to the first or second aspect of the present invention, the image forming apparatus further comprises a peak value detecting unit that obtains a peak value of the fluctuating frequency detected by the frequency detecting unit, and the peak value detection When the peak value detected by the means is equal to or less than a predetermined value, the adding means adds the signal from the frequency generating means to the motor drive control signal.

  In the present invention, in consideration of the fact that human perception sensitivity increases with respect to regular fluctuations, only the occurrence frequency of banding is detected, the phase of that frequency is shifted and applied to the drive input, and periodic fluctuations are thereby detected. The human perception sensitivity is lowered. This makes it possible to reduce the amount of banding perceived by the human eye.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a basic configuration diagram of an image forming apparatus. An optical system (including a light source) 1 that irradiates writing light corresponding to one line on the surface of the photoconductor to form a latent image on the photoconductor, a controller 2 that controls the light emission timing of the optical system 1, a photoconductor drum 3, and a transfer A drum (intermediate transfer member) 4, a position detector 5, and a motor rotation control device 6 are provided.
In the image forming operation, the photosensitive drum 3 and the transfer drum 4 are driven to rotate at a substantially constant speed by the motor rotation control device 6. In a state where the photosensitive drum 3 is rotating, image information for each line is emitted from the optical system 1 and sequentially irradiated onto the photosensitive drum 3 to form a latent image. Writing is performed for the number of lines corresponding to the output image for each writing line, and a latent image for forming an output image is formed on the surface of the photoreceptor.
Although omitted in FIG. 1, a charging device for forming electric charges on the photosensitive drum 3 around the photosensitive drum 3, a developing machine for attaching toner to a latent image written by the optical system 1, and a toner on a transfer belt There are devices such as a cleaning blade that removes residual toner after an image is transferred.
A toner image obtained by developing the latent image formed on the photosensitive drum 3 by the optical system 1 by the developing machine is transferred to the transfer drum 4, transferred onto the output paper, and further fixed by a fixing device (not shown). By performing such a process, the image information is output on the paper.
As shown in the graph showing the frequency characteristics in FIG. 2, when there is a steep peak at a certain frequency, a banding state in which periodic color shading occurs at a pitch corresponding to that frequency and is most easily perceived by humans. Become. However, as shown in FIG. 3, if the fluctuation amount does not have a steep peak even if a fluctuation occurs in the frequency characteristics, the positional deviation and the color deviation actually occur, but the banding amount perceived by humans is It becomes a low state.

FIG. 4 is a configuration diagram of the image forming apparatus according to the embodiment of the present invention. The image forming apparatus includes a controller 11, an optical system 12, a polarization system 13, a photosensitive drum 14, an intermediate transfer belt 15, a sensor 16, a motor 17, a frequency characteristic analysis device (frequency detection means) 18, a peak frequency detection device 19, A frequency generation device (frequency generation means) 20 and a rotation control device 21 are provided.
FIG. 5 is an operation flowchart in the image forming apparatus according to the embodiment of the present invention.
When printing is started, first, writing is performed on the intermediate transfer belt 15 at regular intervals in the sub-scanning direction by the optical system 12 (S1), and marking is performed on the intermediate transfer belt 15 at regular intervals.
The interval between marks written on the intermediate transfer belt 15 is read by the sensor 16 (S2). Here, if the rotation of the photosensitive drum 14 or the running speed of the intermediate transfer belt 15 is fluctuated, the frequency fluctuates according to the fluctuation, and a sensor in the frequency characteristic analyzer 18 is used as a sensor. The difference value between the counted outputs is converted into a speed fluctuation amount for each frequency by using FFT analysis or the like (S3).
Next, the peak frequency is detected by the peak frequency detection device 19 from the frequency having a large position fluctuation obtained by the frequency characteristic analysis device 18, and the signal and phase near the detected frequency are detected by the frequency generation device 20. It is changed at random and added to the motor command value (S4).
As described above, the signal generated by the frequency generator 20 with respect to the motor command value is added to the motor drive control signal (motor drive command value) output from the rotation control device 21 that attempts to rotate the motor 17 at a constant speed. (Addition means) 22 is added to drive the motor 17. When a signal is not added, a steep fluctuation peak occurs, but in the present invention, by giving a signal around it, fluctuation around the peak increases in frequency analysis, and on the image Periodic fluctuations are less likely to be perceived by humans.

Here, in the above description, the signal generated by the frequency generator 20 is added to the drive command value of the motor 17. However, the optical path of the writing light is changed using the polarization system 13. Thus, by changing the writing position on the intermediate transfer belt 15 and changing the writing position on the photosensitive drum 14 on the output image in accordance with the signal from the frequency generator 20, the banding peak is made inconspicuous. Also good.
As for the banding pitch, when the surface speed of the photoconductor is v (mm / sec) and the repetition period is a (cycle / mm),
Banding generation frequency fb (Hz) is
fb = a × v (Formula 1)
The value can be expressed by the following formula.
For example, assuming that the surface speed during rotation of the photosensitive member is 200 mm / sec, the banding pitch that is easily perceived by the human eye is 0.5 cycle / mm to 2 cycle / mm. From 0.5 × 200 = 100 Hz to 2 × 200 = 400 Hz is the banding period that is most easily perceived by the human eye.
Further, since the position shift amount increases even with the same speed fluctuation amount as the cycle is delayed, in the form of adding a signal as in the present invention, there is a high risk of worsening the color shift in the low frequency band.

Therefore, in the present invention, when the frequency peak detected from the peak frequency detection device 19 shows the frequency characteristic as shown in FIG. In the case of the peak value (the peak value below the range indicated by the arrow in FIG. 7), no signal is generated by the frequency generator 20 or no control value is added to the operating part.
Further, since the speed fluctuation amount has less influence on the positional deviation as the fluctuation frequency increases, the signal added by the frequency generator 20 is not uniform in all frequency bands, but is changed according to the frequency. The signal may be added even when the amount of fluctuation is large (particularly on the high frequency side. The frequency generator 20 considers the weight as shown by the dotted line in FIG. 8).
By the above operation, the amount of fluctuation given to the motor control value rotating at a constant speed is determined, and the printer is in a print standby state.When actual printing is performed, the peak of the banding occurrence frequency is made inconspicuous by noise, and human perception The amount of banding that can be achieved can be reduced.

1 is a basic configuration diagram of an image forming apparatus. It is a figure which shows the frequency characteristic of a mechanical vibration. It is a figure which shows the frequency characteristic of a mechanical vibration. 1 is a configuration diagram of an image forming apparatus according to an embodiment of the present invention. FIG. 6 is an operation flowchart in the image forming apparatus according to the embodiment of the present invention. It is a figure which shows the relationship between a banding generation frequency and a speed error. It is a figure which shows the relationship between a banding generation frequency and a speed error. It is a figure which shows the relationship between a banding generation frequency and a speed error.

Explanation of symbols

DESCRIPTION OF SYMBOLS 11 Controller, 12 Optical system, 13 Polarizing system, 14 Photoconductor drum 15 Intermediate transfer belt, 18 Frequency characteristic analyzer, 19 Peak frequency detector, 20 Frequency generator, 21 Rotation controller, 22 Adder

Claims (5)

  A frequency detecting means for detecting the rotational fluctuation frequency of the photosensitive member; a frequency generating means for generating a signal obtained by randomly changing the frequency in the vicinity of the fluctuation frequency detected by the frequency detecting means along with the phase; and the frequency generating means And an adding means for adding a signal to the motor drive control signal during motor rotation.   A frequency detecting means for detecting a rotational fluctuation frequency of the photosensitive member; a frequency generating means for generating a signal obtained by randomly changing the frequency in the vicinity of the fluctuation frequency detected by the frequency detecting means along with the phase; and a polarization system in the writing optical path. An image forming apparatus comprising: means for vibrating by a signal output from the frequency generator.   3. The image forming apparatus according to claim 1, wherein a signal output from the frequency generating unit has a predetermined frequency or more.   3. The image forming apparatus according to claim 1, wherein a signal output from the frequency generating unit is equal to or higher than a frequency defined by 0.5.times.photosensitive member surface speed.   3. The image forming apparatus according to claim 1, further comprising: a peak value detecting unit that obtains a peak value of the fluctuation frequency detected by the frequency detecting unit, wherein the peak value detected by the peak value detecting unit is a predetermined value. An image forming apparatus characterized in that, when the value is equal to or smaller than the value, the adding means adds a signal from the frequency generating means to the motor drive control signal.

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