JP3591177B2 - Method and apparatus for controlling toner density of image forming apparatus - Google Patents

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an image forming apparatus that performs image forming processing by an electrophotographic method such as a laser printer or a copying machine, and when a latent image formed on a photoconductor is visualized with toner, the density of the toner is reduced. The present invention relates to a toner density control method for maintaining a constant toner density, and further relates to a toner density control device mounted on an image forming apparatus for maintaining a constant toner density.
[0002]
[Prior art]
Generally, in an electrophotographic image forming apparatus, an electrostatic latent image on a photoconductor is visualized using a two-component developer composed of a toner and a carrier, but the toner concentration in the developer is always kept constant. For this purpose, the density of the toner patch image (test toner image) formed on the photoreceptor is measured, this is compared with a predetermined target patch density, and the toner density is corrected (controlled) according to the comparison result. It is supposed to do.
However, in the image forming apparatus, usually, the density of the toner patch image is optically measured using a reflection type photoelectric sensor. That is, the reflection type photoelectric sensor detects the reflected light from the toner patch image and the reflected light from the background surface of the photoconductor, and determines the density of the toner patch image based on the amount of each reflected light (reflectance). It is designed to measure.
[0003]
An example of such an image forming apparatus is disclosed in Japanese Patent Application Laid-Open No. HEI 64-25174. In this apparatus, the measurement variation (sampling) of one toner patch image is performed a plurality of times, and the average value is calculated, thereby suppressing the measurement variation.
Further, for example, Japanese Patent Application Laid-Open No. 4-146559 discloses that by detecting reflected light from a toner patch image and reflected light from the background surface at the same position on the photoconductor, dirt and scratches on the photoconductor surface can be prevented. There is disclosed an image forming apparatus which is not affected by these even if it occurs.
Further, as disclosed in, for example, JP-A-4-39679, the number of times of detection of reflected light from the surface of the background on the photoreceptor is made smaller than the number of times of detection of reflected light from the toner patch image. In some cases, statistical processing is performed on light reflected from the surface of the ground to reduce measurement variations.
[0004]
[Problems to be solved by the invention]
By the way, there is a possibility that "unevenness (reflection)" occurs in the reflectance of the surface of the photoreceptor due to the influence of the surface condition, mechanical accuracy and the like. For example, if the photoreceptor has a drum shape and the reflected light from the background surface is detected for one round of the photoreceptor, the output value of the photoelectric sensor has a certain periodical variation as shown in FIG. Would. This is due to the influence of vibration during the rotation of the photoconductor and honing processing on the surface of the photoconductor. Here, the honing process is a process of roughening the surface of the photoconductor in order to prevent the occurrence of interference fringe patterns due to exposure.
The same can be said for the reflectance of the toner patch image.
[0005]
However, in the above-described conventional image forming apparatus, no consideration is given to such a variation of a certain period, that is, the unevenness of the reflectance of the surface of the photoconductor background.
For example, in the apparatus disclosed in Japanese Patent Application Laid-Open No. 64-25174, a time interval when sampling is performed a plurality of times (hereinafter, referred to as a sampling interval) and a period of reflectance unevenness (hereinafter, referred to as a reflectance unevenness period). May be synchronized. In this case, the result obtained by multiple samplings may be biased within a certain range of variation, so that even if the average value is calculated from the result, an accurate result is obtained. You won't get it. Specifically, the sampling result synchronized with the vicinity of the top (A in FIG. 3) of the variation width and the sampling synchronized with the vicinity of the bottom (B in FIG. 3) have different results.
[0006]
This can be avoided if the sampling interval is set short enough, but this is very difficult because other processes required for image formation are performed in parallel. You end up spending time.
The same applies to the devices disclosed in JP-A-4-146559 and JP-A-4-39679.
[0007]
That is, in the conventional image forming apparatus, when the sampling interval and the reflectance unevenness cycle are synchronized, the measurement of the density of the toner patch image may not be performed correctly, and as a result, the toner density may be always kept constant. Would be difficult to do.
Therefore, the present invention provides a toner density control method capable of correctly controlling the toner density by not synchronizing the sampling interval and the reflectance unevenness cycle of the photoconductor surface when measuring the density of the toner patch image. The purpose is to provide.
Still another object of the present invention is to provide a toner density control device capable of correctly controlling the toner density by not synchronizing the sampling interval and the reflectance unevenness cycle of the photoconductor surface.
[0008]
[Means for Solving the Problems]
The present invention is a method devised to achieve the above object, and is used in an image forming apparatus that visualizes a latent image formed on a photoreceptor using toner, and What is claimed is: 1. A toner density control method for maintaining a constant toner density at the time of visualization, wherein prior to visualizing the latent image, non-image forming is performed without performing the visualization. Sometimes, the reflectance of the photoreceptor surface is detected, and from the detection result, the period of the unevenness of the reflectance of the photoreceptor surface that varies at a certain fixed period is analyzed, and a predetermined value or a random value is set as the analyzed period of the unevenness. In addition, the cycle obtained by using the obtained cycle or the random number is determined as a sampling interval of a cycle that is not synchronized with the cycle of the unevenness, and when a mode for executing the toner density correction is set, the latent image on the photoconductor is transferred to the toner. And develop the toner on the photoreceptor. To form a pitch image, the concentration of one of the toner patch image in the determined sampling interval to detect a plurality of times, the latent image based on the concentration of the detected toner patch image toner when a visible image It is characterized in that the density is corrected.
[0009]
According to the toner density control method of the above procedure, before the image forming apparatus visualizes the latent image, first, the period of the unevenness of the reflectance of the photoreceptor surface is analyzed and synchronized with the period of the unevenness. The cycle that does not occur is determined as the sampling interval. When the sampling interval is determined, the density of the toner patch image formed on the photoconductor is detected at the sampling interval.
In other words, if the density of the toner patch image is detected using this toner density control method, the interval for detecting the density of the toner patch image and the period of the unevenness of the reflectance of the photoconductor surface may be synchronized. Absent. Therefore, even if the unevenness of the reflectance occurs on the surface of the photoconductor, the detection result of the density of the toner patch image is not affected, and the correction of the toner density is correctly performed in the image forming apparatus. Become like
[0010]
According to another aspect of the present invention, there is provided an image forming apparatus which visualizes a latent image formed on a photoreceptor using toner, the latent image being formed on a photoreceptor. A toner density control device for maintaining a constant toner density when visualizing the surface of the photosensitive member, wherein the reflectance of the surface of the photosensitive member is detected, and the detection result indicates that the surface of the photosensitive member varies at a certain period. A period analyzing means for analyzing a period of the unevenness of the reflectance of the sample, and a period obtained by adding a predetermined value or a random value to the period of the unevenness analyzed by the period analyzing means or a period obtained by using a random number. Determining means for determining a sampling interval of a cycle not synchronized with the cycle of the image forming apparatus; patch forming means for developing a latent image on the photosensitive member with toner to form a toner patch image on the photosensitive member; and determining the determining means. Sampling made At intervals, for one toner patch images said patch forming means to form, soluble and concentration detection means for detecting a plurality of times the density of the toner patch images, the latent image on the basis of the density of the density detecting means detects Correction means for correcting the toner density at the time of visualization, wherein the analysis of the period of the unevenness of the reflectance by the period analysis means and the determination of the sampling interval by the determination means are performed by the visualization. In a mode in which toner density correction is performed when non-image formation is not performed and the toner density correction is performed, the patch forming means forms the toner patch image, and the density detecting means sets the toner toner at a sampling interval determined by the determining means. It is characterized in that the density of a patch image is detected .
[0011]
According to the toner density control device having the above-described configuration, when the period detecting unit analyzes the period of the unevenness of the reflectance on the surface of the photoconductor, the determining unit determines a period that is not synchronized with the period of the unevenness as the sampling interval. Then, the density detecting means detects the density of the toner patch image formed on the photoconductor by the patch forming means at the sampling interval determined by the determining means.
That is, in this toner density control device, the interval at which the density detection unit detects the density of the toner patch image does not synchronize with the period of the unevenness of the reflectance on the surface of the photoconductor. Therefore, even if the unevenness of the reflectance occurs on the surface of the photoreceptor, the detection result by the density detecting means is not affected by the unevenness, and the correction of the toner density by the correcting means can be performed correctly.
[0012]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, a toner density control method and a toner density control device according to the present invention will be described with reference to the drawings. However, here, the case where the present invention is applied to a color copying machine will be described as an example.
FIG. 1 is a flowchart showing a procedure of toner density control in the color copying machine of the present embodiment, and FIG. 2 is an overall configuration diagram of the color copying machine.
[0013]
The color copying machine according to the present embodiment is roughly divided into a scanner unit 1 for reading image data from a document, an image processing unit 2 for processing image data read by the scanner unit 1, as shown in FIG. A ROS (Raster Output Scanner) optical unit 3 for driving a laser beam to irradiate a photoreceptor with a light beam according to the image data processed by the image processing unit 2 and an image forming unit 4 for finally forming an image. Have been.
[0014]
Of these, the image forming unit 4 includes a photoconductor 11, a charging device 12, a rotary developing device 13, a toner dispensing device 14, a paper tray 15, a paper conveying device 16, a transfer drum 17, The apparatus 18, the photoelectric sensor 19, a CPU (Central Processing Unit; not shown) for controlling the entire image forming unit 4, and a RAM (Random Access Memory; not shown) used as a work area of the CPU are provided. Have been.
[0015]
The image forming section 4 forms an image according to a well-known xerographic process. That is, the rotating photoconductor 11 is uniformly negatively charged by the charging device 12, and a latent image is formed by the laser light from the ROS optical unit 3. When the latent image is formed, the rotary developing device 13 receives the first color (Black) toner from the toner dispensing device 14, and develops the latent image on the photoconductor 11 with the toner. The developed image is transported from the paper tray 15 to the paper transport device 16 and is transferred onto the paper wound around the transfer drum 17. After the transfer of the image of the first color is completed, image formation is similarly performed for the second color (Yellow), and this is repeated for the third color (Magenta) and the fourth color (Cyan). When the transfer of all color toners is completed, the fixing device 18 performs a toner fixing process on the paper separated from the transfer drum 17.
In this manner, the image forming section 4 forms a color copy image on a sheet.
[0016]
As shown in FIG. 3, the photoelectric sensor 19 provided in the image forming unit 4 is a reflection type sensor including a light emitting diode 19a and a phototransistor 19b. When specularly reflected by the surface of the photoconductor 11 or a toner image formed on the photoconductor 11, the specularly reflected light is incident on the phototransistor 19b. Then, photoelectric conversion is performed on the amount of reflected light received by the phototransistor 19b, and the result is notified to the CPU. That is, the photoelectric sensor 19 is for measuring the toner density of the toner image formed on the photoconductor 11.
[0017]
In this photoelectric sensor 19, in order to narrow the optical axis of the irradiation light or the specularly reflected light, the diameter of the opening 19c for the light emitting diode 19a or the phototransistor 19b is smaller than the diameter (for example, 3 mm) of these. (For example, 1 mm). The inner surface of the opening 19c is black in order to suppress irregular reflection of light inside the opening 19c. Accordingly, light other than light that directly reaches the phototransistor 19b is absorbed, and improvement in sensor sensitivity can be expected.
[0018]
Further, in FIG. 2, the image forming section 4 corrects the toner density at the time of developing the latent image on the photoconductor 11 in accordance with a well-known toner density control process. That is, in a mode in which the toner density correction is performed, a toner patch image is formed on the photoconductor 11 by exposure from the ROS optical unit 3 and development by the rotary developing device 13. This toner patch image is usually formed on a non-image portion on the photoconductor 11. When the toner patch image is formed, the photoelectric sensor 19 detects the reflectance of the toner patch image and the reflectance of the background surface of the photoconductor 11, respectively, and measures the density of the toner patch image based on the detection results. . Here, the CPU compares the measurement result of the density of the toner patch image with a preset target patch density. Then, according to the comparison result, the CPU instructs the rotary developing device 13 and the toner dispensing device 14 to increase or decrease the toner amount when developing the latent image on the photoconductor 11.
[0019]
In this way, the image forming section 4 corrects the toner density so that the toner density is always constant. That is, the image forming section 4 also has a function as a toner density control device in the present invention.
[0020]
By the way, in the color copying machine having the above configuration, the photoelectric sensor 19 measures the density of the toner patch image before correcting the toner density. However, this measurement, that is, sampling, is performed a plurality of times for one toner patch image, and the cycle (sampling interval) is determined by the CPU of the image forming unit 4.
In measuring the density of the toner patch image, the detection position of the reflectance of the toner patch image and the detection position of the reflectance of the background surface of the photoconductor 11 are the same position on the photoconductor 11, Or it may be a different position. Further, the number of times of detecting the reflectance of the toner patch image and the number of times of detecting the reflectance of the background surface of the photoconductor 11 may be the same or different.
[0021]
Here, the procedure for determining the sampling interval in this color copying machine will be described in detail with reference to the flowchart of FIG.
[0022]
In this color copying machine, the CPU determines the sampling interval during non-image formation. The non-image forming time is, for example, immediately after turning on the power of the color copying machine or during a period from when a start button for instructing start of the image forming process is pressed to when the scanner unit 1 starts reading image data. This is when image formation is not being performed.
When the power of the color copier is turned on or the start button is pressed, the CPU determines that a non-image formation is to be performed immediately after that (step 101; hereinafter, step is abbreviated as S), and sets the sampling interval. The process for determining is started.
[0023]
When the CPU starts the process for determining the sampling interval, first, the photoelectric sensor 19 detects the reflectance of the background surface of the photoconductor 11 (S102). The reflectance detection at this time is performed at predetermined intervals set in advance (for example, every 1 msec). This is because the CPU does not need to perform other processing required for image formation at this time, and can cope even with a sufficiently short interval.
[0024]
When the photoelectric sensor 19 detects the reflectance of the ground surface of the photoconductor 11, the RAM sequentially stores the detection results. However, at this time, the CPU determines whether or not the detection result by the photoelectric sensor 19, that is, the output value from the photoelectric sensor 19 is within a normal range (for example, 1.9 ± 0.3V) (S103). If not, an error display and processing stop are performed (S104). If the output value from the photoelectric sensor 19 is within the normal range, it is determined whether or not the reflectance of the background surface has been detected for the entire circumference of the photoconductor 11 (S105), and until the detection for the entire circumference is completed. The above steps (S102 to S105) are repeated.
[0025]
When the detection of the entire circumference of the photoconductor 11 is completed and the detection result is stored in the RAM, the CPU performs a frequency analysis, which is a well-known technique, on the detection result to determine a variation in the detection result. The period is calculated (analyzed), and the result is set as the reflectance unevenness period of the surface of the photoconductor 11 (S106).
[0026]
After calculating the reflectance unevenness cycle of the background surface of the photoconductor 11, the CPU adds a predetermined value to the reflectance unevenness cycle, and determines the result as a sampling interval not synchronized with the reflectance unevenness cycle. (S107). For example, as a result of the frequency analysis, if the reflectance unevenness cycle is every 10 msec, the CPU adds 3 msec to this, and determines a cycle of every 13 msec not synchronized with the reflectance unevenness cycle as a sampling interval. The determined sampling interval is stored in the RAM.
[0027]
In this way, in this color copying machine, the sampling interval for measuring the density of the toner patch image is determined.
Then, after the sampling interval determined by the CPU is stored in the RAM, if the CPU determines that image formation is being performed instead of non-image formation (S101), the CPU performs the following according to the sampling interval stored in the RAM. As described above, the density of the toner patch image is measured (S108), and based on the result, the toner density is corrected so that the toner density is always constant.
However, the sampling interval stored in the RAM is a value (for example, 13 msec) sufficiently larger than a predetermined interval (for example, 1 msec) for detecting the reflectance of the surface of the photoconductor 11. Therefore, even if sampling is performed at the time of image formation, the load on the CPU is small.
[0028]
As described above, in the color copying machine according to the present embodiment, based on the detection result of the photoelectric sensor 19, the reflectance unevenness cycle of the background surface of the photoconductor 11 is obtained, and the sampling interval not synchronized with the reflectance unevenness cycle is determined by the CPU. Is determined, and the density of the toner patch image formed on the photoconductor 11 is detected at the sampling interval. That is, in this color copying machine, the sampling interval for detecting the density of the toner patch image does not synchronize with the reflectance unevenness cycle of the background surface of the photoconductor 11. Therefore, even if the unevenness of the reflectance occurs on the background surface of the photoconductor 11, the density detection result of the toner patch image is not affected by the unevenness, and as a result, the latent image on the photoconductor 11 is developed. In this case, the toner density is always kept constant.
[0029]
Specifically, when the reflectance unevenness cycle and the sampling interval are synchronized (hereinafter, simply referred to as “synchronous case”) and when they are asynchronous, the detection of the density of the toner patch image is repeatedly performed. It can be seen that the magnitude of the variation in the detection results when the measurement was performed 20 times was significantly different as shown in FIG. This is because, in the case of the asynchronous, the detection result is biased within a certain width as in the case of the synchronization, and there is no need to make a different bias in each detection (see FIG. 6). .
[0030]
In addition, the reflectance unevenness period of the photoconductor 11 usually differs depending on the lot at the time of manufacturing the photoconductor, as shown in FIG. 5A, for example. That is, it is highly possible that the reflectance unevenness cycle has an individual value for each photoconductor 11. Further, as shown in FIG. 5B, the reflectance unevenness cycle varies depending on the diametrical change of the photoconductor 11, for example, the occurrence of scratches and dirt.
On the other hand, in the color copying machine of the present embodiment, before the rotary developing device 13 visualizes the latent image on the photoconductor 11, first, the reflectance unevenness period of the photoconductor 11 is obtained. The sampling interval is determined on the basis of the reflectance unevenness cycle obtained in (1). Therefore, even if the reflectance unevenness cycle of the photoconductor 11 is different for each lot or changes over time, these do not affect the density detection result of the toner patch image.
[0031]
Further, in the color copying machine of the present embodiment, the detection of the reflectance unevenness cycle and the determination of the sampling interval are performed during non-image formation. In other words, in this color copying machine, the reflectance nonuniformity cycle is analyzed when the CPU does not need to perform other processing, so that it is possible to detect the reflectance of the background surface of the photoconductor 11 at sufficiently short intervals. In addition, it is possible to more accurately detect the reflectance unevenness period. In addition, since the sampling interval is already determined at the time of image formation, image formation can be performed quickly.
[0032]
In this embodiment, the case where the sampling interval (for example, every 13 msec) is determined by adding a predetermined value (for example, every 3 msec) to the reflectance unevenness cycle (for every 10 msec) has been described as an example. The invention is not limited to this. For example, a random value (2, 3, 4,... Msec, etc.) may be sequentially added to the reflectance unevenness cycle, and this may be used as a sampling interval (12, 13, 14,... Msec, etc.). Is no longer synchronized with the reflectance unevenness cycle.
[0033]
Further, instead of sequentially adding random values to the reflectance unevenness cycle, it is conceivable to determine the sampling interval using a random number generated within a certain range (for example, 10 to 20 msec). In this case, the sampling intervals become sequentially different values, for example, 15, 18, 13... Msec, so that they are not synchronized with the reflectance unevenness period, and can be handled even if the reflectance unevenness period is not determined in advance. become.
[0034]
Further, in the present embodiment, the case where the present invention is applied to a color copying machine has been described. However, the present invention is not limited to this. It goes without saying that the present invention can be applied to a printer or the like.
[0035]
As another method for eliminating the influence of unevenness, the CPU uses a digital filter, such as a high-pass filter (High Pass Filter) or a low-pass filter (Low Pass Filter), used for performing frequency analysis based on the calculated period. And the like may be corrected.
[0036]
【The invention's effect】
As described above, according to the present invention, the period of the unevenness of the reflectance of the photoconductor surface and the sampling interval for detecting the density of the toner patch image on the photoconductor may be synchronized. Absent. Therefore, even if unevenness of the reflectance occurs on the surface of the photoreceptor, the density detection result of the toner patch image is not affected by the unevenness, and as a result, the toner is not developed when the latent image on the photoreceptor is developed. The concentration will always be kept constant.
[Brief description of the drawings]
FIG. 1 is a flowchart illustrating a procedure of toner density control in a color copying machine to which the present invention is applied.
FIG. 2 is an overall configuration diagram of a color copying machine to which the present invention is applied.
FIG. 3 is a cross-sectional view illustrating a configuration of a photoelectric sensor.
FIG. 4 is an explanatory diagram showing the magnitude of variation in the density detection result of a toner patch image.
FIGS. 5A and 5B are explanatory diagrams showing differences in reflectance unevenness periods in the photoconductor, in which FIG. 5A shows a difference between lots at the time of manufacturing, and FIG. .
FIG. 6 is an explanatory diagram showing unevenness of reflectance on the surface of the photoconductor when light reflected from the surface of the photoconductor is detected by a photoelectric sensor.
[Explanation of symbols]
2 Image processing unit 3 ROS optical unit 4 Image forming unit 11 Photoconductor 12 Charging device 13 Rotary developing device 14 Toner dispensing device 17 Transfer drum 18 Fixing device 19 Photoelectric sensor

Claims (2)

Used in an image forming apparatus that visualizes a latent image formed on a photoreceptor by using toner, and toner density control for maintaining a constant toner density when the latent image is visualized. The method,
Prior to visualizing the latent image, at the time of non-image formation in which the visualization is not performed , the reflectance of the photoconductor surface is detected, and the detection result varies in a certain period. Analyze the period of the unevenness of the reflectance of the photoconductor surface,
A cycle obtained by adding a predetermined value or a random value to the cycle of the analyzed unevenness or a cycle obtained by using a random number is determined as a sampling interval of a cycle not synchronized with the cycle of the unevenness,
In a mode for executing the toner density correction, the latent image on the photoconductor is developed with toner to form a toner patch image on the photoconductor, and the density of one toner patch image is determined at the determined sampling interval. Detect multiple times ,
A toner density control method for an image forming apparatus, comprising: correcting a toner density when the latent image is visualized based on a detected density of the toner patch image. Toner density control mounted on an image forming apparatus that visualizes a latent image formed on a photoreceptor using toner, and for maintaining a constant toner density when the latent image is visualized. A device,
Detecting the reflectance of the photoreceptor surface, from the detection result, a period analyzing means for analyzing a period of unevenness of the reflectance of the photoreceptor surface that varies at a certain period,
Determining means for determining a cycle obtained by adding a predetermined value or a random value to the cycle of unevenness analyzed by the cycle analyzing means or a cycle obtained by using a random number as a sampling interval of a cycle not synchronized with the cycle of unevenness; ,
Patch forming means for developing a latent image on the photoconductor with toner to form a toner patch image on the photoconductor,
Density detecting means for detecting the density of the toner patch image a plurality of times for one toner patch image formed by the patch forming means at the sampling interval determined by the determining means;
Correction means for correcting the density of toner when the latent image is visualized based on the density detected by the density detection means ,
Analysis of the cycle of the unevenness of the reflectance by the cycle analysis unit and determination of the sampling interval by the determination unit are performed at the time of non-image formation in which the visualization is not performed, and the toner density correction is performed. Wherein the patch forming means forms the toner patch image, and the density detecting means detects the density of the toner patch image at a sampling interval determined by the determining means .

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