Image forming apparatus

Abstract

Conventionally, in a method of obtaining information related to a circumference of a transfer belt based on pattern matching of waveform data of a first round and waveform data of a second round of the transfer belt, there is a possibility that a circumference is erroneously detected in a case where there is a periodic fluctuation in both waveform data. To avoid erroneous detection and to suppress an increase in downtime.SOLUTION: In an image forming apparatus in which a laser scanner and a control means are operated by a common power source, when either one of waveform data of a first round of a transfer belt and waveform data of a second round of the transfer belt is acquired, laser light emission control of the laser scanner being a factor of fluctuation is stopped.SELECTED DRAWING: Figure 12

Description

[Technical Field]

[0001] The present invention relates to an electrophotographic image forming apparatus. [Background technology]

[0002] In recent years, electrophotographic image forming apparatuses have been increasing in speed and image quality. In particular, image forming apparatuses capable of color printing generally have a function for automatically controlling image density because accurate color reproducibility and color stability are required.

[0003] Image density control generally involves detecting multiple test toner images (patches) formed on an image carrier under different image-forming conditions using an image density detector installed inside the image forming device, converting this into the amount of toner adhesion, and determining the optimal image-forming conditions based on the conversion results.

[0004] One method of detecting image density is optical image density detection. Optical image density detection uses a light-receiving element to acquire the light reflected from the patch or the image carrier itself in response to light emitted from a light-emitting element, and calculates the amount of toner attached to the patch based on the results. The conversion to the actual amount of toner attached is performed based on the relationship between the output of the light-receiving element when there is no toner attached to the image carrier and the output of the light-receiving element when there is toner attached to the image carrier.

[0005] The reflectance of the image carrier surface varies depending on the position on the image carrier, and in order to accurately calculate the amount of toner adhesion, it is necessary to obtain outputs indicating the presence and absence of toner at the same position on the image carrier.

[0006] Therefore, in general, the background output of the light receiving element when no toner is attached is acquired at a specific position, and then the image carrier is rotated at least once to create a patch at the same position, and the patch output of the light receiving element is acquired. In this way, the background output corresponds to the light reflected from the background of the image carrier, and the patch output corresponds to the light reflected from the patch.

[0007] To identify a specific position on the image carrier, information on the circumferential length of the image carrier is required, because the time required for a specific position on the image carrier to make one revolution can be obtained by dividing the circumferential length by the peripheral speed (process speed) of the image carrier.

[0008] However, the circumferential length of the image carrier changes due to various factors such as variations in parts and the ambient temperature of the image forming apparatus. Treating the circumferential length as a fixed value will result in errors in identifying the position, so it is necessary to measure the circumferential length of the image carrier dynamically.

[0009] According to Patent Document 1, in an image forming apparatus that uses an intermediate transfer method as an image carrier, information related to the actual circumference is obtained from the characteristics of the intermediate transfer body surface based on matching first waveform data of the intermediate transfer body surface with second waveform data that includes part of the first waveform data. [Prior art documents] [Patent documents]

[0010] [Patent Document 1] Japanese Patent Application Laid-Open No. 2009-288351 Summary of the Invention [Problem to be solved by the invention]

[0011] However, if the first waveform data and the second waveform data have periodic fluctuations that are different from the characteristics of the intermediate transfer body surface, this period may be detected as a feature in pattern matching, which could result in an erroneous detection of the circumference. The following factors, for example, may be considered as causes of periodic fluctuations: In a configuration in which a control unit such as a CPU or ASIC that acquires the amount of light received by the light receiving element is powered by the same power supply as the laser scanner that controls the laser emission, the influence of fluctuations in the power supply voltage that occur when the laser emission is controlled periodically may be considered.

[0012] The present invention has been made in view of the above-mentioned problems, and an object of the present invention is to provide a means for suppressing the influence of periodic fluctuation factors when a control means performs pattern matching. [Means for solving the problem]

[0013] In order to achieve the above-mentioned object, the image forming apparatus of the present invention comprises a photosensitive member, an exposure means for emitting laser light to the photosensitive member and exposing the photosensitive member, a development means for developing with toner an electrostatic latent image formed on the photosensitive member exposed by the exposure means, a transfer belt onto which the toner developed on the photosensitive member is transferred, a detection means for irradiating the transfer belt with light and detecting reflected light from the transfer belt, and a control means for acquiring first waveform data about the surface of the transfer belt based on detection by the detection means at a first timing, and acquiring second waveform data about the surface of the transfer belt based on detection by the detection means at a second timing, the second waveform data including at least a part of the first waveform data, and determining information related to the actual circumference of the transfer belt based on matching of the acquired first waveform data and the second waveform data, wherein the control means and the exposure means are supplied with power by the same power source, and the control means acquires the first waveform data while the exposure means stops controlling the emission of laser light, and acquires the second waveform data while the exposure means is controlling the emission of laser light. [Effects of the Invention]

[0014] According to the present invention, even when there is a periodic voltage fluctuation in the power supply voltage, the peripheral length of the transfer belt can be detected with high accuracy. [Brief explanation of the drawings]

[0015] [Figure 1] FIG. 1 is a diagram showing the overall configuration of an image forming apparatus. [Figure 2] FIG. 2 is a diagram showing a mechanism of the image forming apparatus. [Figure 3] FIG. 2 is a block diagram showing an example of a control unit. [Figure 4] FIG. 2 is a diagram illustrating the configuration of a sensor. [Figure 5] 6A and 6B are diagrams illustrating variations in background output and variations in patch output at a plurality of positions on an intermediate transfer belt. [Figure 6] FIG. 3 is a block diagram showing a sensor control unit. [Figure 7] FIG. 10 is a diagram showing an example of the relationship between each sampling point and a reflected light output value. [Figure 8] 10 is a flowchart and timing chart of measuring the peripheral length of an intermediate transfer belt in a comparative example. [Figure 9] FIG. 10 is a diagram showing the relationship between the waveform profiles of the first and second revolutions and the integrated value. [Figure 10] FIG. 2 is a diagram showing a power supply configuration in the first embodiment. [Figure 11] FIG. 4 is a diagram showing power supply voltage fluctuations in the first embodiment. [Figure 12] 4 is a flowchart and timing chart of circumference measurement in the first embodiment. [Figure 13] FIG. 10 is a diagram showing the relationship between the waveform profiles of the first and second rotations and the integrated value in the first embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0016] Hereinafter, exemplary embodiments of the present invention will be described with reference to the drawings. Note that the following embodiments are merely examples, and the present invention is not limited to the contents of the embodiments. Furthermore, in the following drawings, components that are not necessary for explaining the embodiments are omitted from the drawings. [Example]

[0017] <System configuration> 1 is a diagram showing the overall configuration of a system including an image forming apparatus 102 capable of color printing. A host computer 101 transmits image data to the image forming apparatus 102 and instructs it to form an image. Upon receiving the instruction to form an image, the image forming apparatus 102 forms an image on a recording medium. A video controller 103 within the image forming apparatus 102 performs various data processing operations, such as color conversion and halftone processing, on the received image data. The video controller 102 then transmits the processed image data to a printer engine 104 and instructs it to form an image. Upon receiving the instruction to form an image from the video controller 103, the printer engine 104 forms an image on a recording medium according to the received image data.

[0018] <Mechanism of the image forming device> 2 is a schematic cross-sectional view of the image forming apparatus 102. In FIG. 2, the letters Y, M, C, and K at the end of the reference numerals indicate that the colors of the toner images formed by the corresponding members are yellow, magenta, cyan, and black, respectively. In the following description, when it is not necessary to distinguish between colors, the reference numerals without the letters at the end will be used.

[0019] During image formation, the photoconductor 22 is rotated counterclockwise in FIG. 2. The charger 23 charges the surface of the photoconductor 22 to a uniform potential. The laser scanner 24 is a light irradiation means that irradiates the photoconductor 22 with laser light to form an electrostatic latent image. The laser scanner 24 exposes the photoconductor 22, which is charged to a uniform potential, based on image data to form an electrostatic latent image. The developing unit 26 develops the electrostatic latent image formed on the photoconductor 22 with toner and visualizes it as a toner image. The toner image on the photoconductor 22 is transferred to the transfer belt 27. The toner images on each photoconductor 22 are superimposed and transferred to the transfer belt 27, forming a full-color toner image on the transfer belt 27.

[0020] During image formation, the transfer belt 27 is rotated clockwise in the figure by the drive roller 25. As a result, the toner image on the transfer belt 27 is transported to a position opposite the transfer roller 28. The recording medium 11 housed in the cassette 21 is transported to a position opposite the transfer roller 28 in synchronization with the timing at which the toner image on the transfer belt 27 is transported to the position opposite the transfer roller 28. The transfer roller 28 transfers the toner image on the transfer belt 27 to the recording medium 11 transported along the transport path. After the toner image is transferred, the recording medium 11 is transported to the fixing unit 30. The fixing unit 30 applies heat and pressure to the recording medium 11 to fix the toner image to the recording medium 11. After the toner image is fixed, the recording medium 11 is discharged outside the image forming apparatus. A sensor 6 is provided opposite the transfer belt 27 and detects the detection pattern. The sensor 6 is an example of a detection unit that irradiates the transfer belt 27 with light and detects reflected light from the transfer belt 27.

[0021] Figure 3 is a control block diagram according to the first embodiment. A CPU 301 controls each unit of the image forming apparatus using a RAM 303 as a work area based on a program stored in a ROM 302. Various control programs, various data, tables, etc. are stored in the ROM 302. A program load area, a work area for the CPU 301, and a storage area for various data are secured in the RAM 303. The CPU 301 in Figure 3 includes, as characteristic functions, a circumference measurement unit 311, a density control unit 312, and a laser scanner control unit 313.

[0022] A drive control unit 305 controls the motors for driving the photosensitive drum 22, the charger 23, the laser scanner 24, the developer 26, and the transfer belt 27, as well as the charging bias and the developing bias, in accordance with commands from the CPU 301.

[0023] The non-volatile memory 306 is a storage device that stores various data such as light intensity setting data when controlling image density and information about the circumference of the transfer belt 27. Information about the circumference measured in advance (to be described later) and environmental information at the time of measurement are also stored in the non-volatile memory 306.

[0024] The circumference measurement unit 311 measures the circumference of the transfer belt 27 based on data acquired from the transfer belt 27 by the sensor 6. The circumference measurement unit 311 is an example of a calculation unit for obtaining information related to the actual circumference of the transfer belt 27. Here, the information related to the actual circumference refers to information for determining the circumference of the rotating body, which fluctuates for some reason, and is necessary to identify / detect the same position at a certain time later while the transfer belt 27 is rotating. For example, this corresponds to the length of the transfer belt 27 that has expanded or contracted due to changes over time or environmental fluctuations from its nominal circumference (the ideal dimensional value when there are no manufacturing tolerances or environmental fluctuations), or the actual circumference of one revolution of the rotating body. Furthermore, the entity of the information may be digital data representing time or digital data representing length.

[0025] The density control unit 312 adjusts the image formation conditions using the amount of reflected light from the patch image for density control acquired using the sensor 6 and information related to the calculated actual circumference of the transfer belt 27.

[0026] The laser scanner control unit 313 controls the emission of a laser light emitting element (hereinafter referred to as LD) on the laser scanner in accordance with image data from the video controller 103 and commands from the CPU 301 .

[0027] In this embodiment, an example will be described in which the CPU 301 performs circumference measurement and density control. However, the present invention is not limited to this. For example, if an application specific integrated circuit (ASIC) or SOC (System On Chip) is implemented in the image forming apparatus, some or all of the processes for circumference measurement and density control may be performed by these. Here, SOC refers to a chip in which a CPU and an ASIC are integrated and provided in the same package. In this way, performing circumference measurement and density control by the ASIC can reduce the processing load on the CPU 301.

[0028] 4A and 4B are explanatory diagrams of the sensor 6 according to this embodiment. As shown in Fig. 4A, the sensor 6 is provided at the end of the transfer belt 27 in a direction perpendicular to the conveyance direction. Fig. 4B is a configuration diagram of the sensor 6. The light-emitting unit 61 is, for example, an LED, and emits light toward the transfer belt 27.

[0029] Light-receiving unit 62 is, for example, a phototransistor, and receives light emitted by light-emitting unit 61 and reflected from the surface (base) of transfer belt 27 and the toner adhering thereon. Light-emitting unit 61 is disposed at an angle A with respect to the normal direction of transfer belt 27, and light-receiving unit 63 is disposed at an angle A in the opposite direction to light-emitting unit 61. As a result, light-receiving unit 63 receives light that is specularly reflected from transfer belt 27 and the toner. Light-receiving unit 62 is disposed at an angle B with respect to the normal direction of transfer belt 27. As a result, light-receiving unit 62 receives light that is diffusely reflected from transfer belt 27 and the detection pattern.

[0030] FIG. 6 shows the control configuration of the sensor 6 according to this embodiment. The sensor control unit 51 is implemented by the CPU 301. However, it may also be implemented by an ASIC or SoC. The drive unit 52 outputs a drive signal for turning the sensor 6 on and off. When the sensor 6 is turned on, the light-emitting unit 61 emits light, and the light-receiving units 62 and 63 output detection signals indicating the intensity or amount of received light. The measurement unit 53 receives the detection signals output by the sensor 6. Based on the amount of reflected light thus obtained, the circumference measurement unit 311 and the density control unit 312 calculate the circumference of the transfer belt 27 and the amount of toner adhesion.

[0031] The light reflected from the patch and the background contains both specular and diffused components. The light receiving element 63 detects both the specular and diffused components, while the light receiving element 62 detects only the diffused component. When toner adheres to the transfer belt 27, the toner blocks light, reducing the specular reflected light, i.e., the output of the light receiving element 63 decreases.

[0032] <Image density control> In the image forming apparatus 102, a sensor 6 serving as an optical detection means is disposed opposite the transfer belt 27. Generally, in electrophotographic color image forming apparatuses, the electrical characteristics of each unit and recording material and the adhesive strength to toner change depending on various conditions such as replacement of consumables, environmental changes (temperature, humidity, device deterioration, etc.), and the number of prints. These changes manifest themselves as fluctuations in image density and color reproducibility. In other words, these fluctuations make it impossible to obtain the original correct color reproducibility.

[0033] Therefore, in this embodiment, in order to always obtain accurate color reproducibility, multiple patches (toner images) are formed on a test basis while changing the image creation conditions in a non-image forming state, and their densities are detected by the optical sensor 6. Note that the non-image forming state here refers to a state in which no images of documents created by a normal user are being formed. Then, based on the detection results, the density control unit 312 executes image density control. Factors that affect image density include the charging bias, development bias, and exposure intensity.

[0034] <Measurement of information related to actual circumference> FIG. 5 is a diagram illustrating the variation in background output at multiple positions on the transfer belt 27 and the variation in patch output for detecting the amount of toner adhesion. Each patch is a toner image formed with the same halftone density. The background output is the amount of reflected light detected by the light receiving element 302 when no patch is formed on the transfer belt 27. The patch output is the amount of reflected light detected by the light receiving element 63 from a patch formed on the transfer belt 27. As shown in FIG. 5, the output of the light receiving element 63 is affected by the surface reflectance of the transfer belt 27, which is the image carrier (rotating body) in this embodiment. Therefore, even though patches are formed with the same density, the patch output values ​​are different. The same is true for the light receiving element 62.

[0035] If image density control is performed while being affected by the reflectance of the substrate of the transfer belt 27, the correlation between the density data of the printed halftone and the output of the light receiving elements 62 and 63 will be weak. This will result in a decrease in the accuracy of image density control. To cancel the effect of the reflectance of the surface of the transfer belt 27, it is necessary to measure the reflected light from the light receiving elements 62 and 63 at the same position on the transfer belt 27, corresponding to the presence and absence of toner.

[0036] On the other hand, the transfer belt 27 expands and contracts due to manufacturing tolerances, the environment, and paper feed durability (long-term operation of the device), resulting in fluctuations in its circumference. To measure the reflected light corresponding to the presence and absence of toner at the same position on the transfer belt 27, it is necessary to accurately determine the circumference of the transfer belt 27. If the circumference after expansion or contraction or the amount of expansion or contraction of the transfer belt 27 can be measured, the time it takes for an arbitrary position to make one revolution can be calculated based on the circumference after expansion or contraction or the amount of expansion and contraction and the process speed. The calculated time it takes for an arbitrary position to make one revolution corresponds to the period in which an arbitrary position on the transfer belt 27 passes the detection point of the sensor 6. Therefore, if the period of the transfer belt 27 is measured using a timer, the count value of the timer indicates the absolute position on the transfer belt 27. The detailed mechanism for measuring the circumference in this embodiment will be described later.

[0037] In addition, in this embodiment, an arbitrary position also includes a position where, for example, multiple measurable start timings are predetermined and measurement starts when the closest measurement start timing arrives after the instruction to start measurement is input.

[0038] <Voltage fluctuations due to laser scanner control> Voltage fluctuations in this embodiment will now be described. When control of the laser scanner 24 begins, a drive current flows through the LD based on the operation of the laser drive circuit. The LD emits laser light at a light intensity level corresponding to the drive current. The laser drive circuit is mounted on the printer engine 104 and is a circuit for driving the LD, which is electrically connected to the video controller 103. The laser light emitted by the LD is then scanned in the horizontal direction of the photosensitive drum 22 by a rotating polygon mirror (not shown). The laser scanner control unit 313 also controls the light emission of the LD in accordance with the period of one face of the polygon mirror. Since the light emission of the LD is controlled in accordance with the period of one face of the polygon mirror, a periodic drive current flows through the LD. This causes minute fluctuations in the power supply voltage at the period of one face of the polygon mirror.

[0039] During normal printing, the laser beam emission control is performed in accordance with image data from the video controller 103. However, the laser beam emission control may also be performed for other purposes. Specifically, the laser beam emission control may be performed to equalize the potential on the surface of the photoconductor 22 to improve the cleaning performance of the remaining toner on the photoconductor 22. Another example of laser beam emission control is to reduce the transfer potential contrast as a measure to prevent image distortion due to aerial discharge occurring in the transfer nip. This type of laser beam emission control is called background exposure control. Background exposure control is an example of laser beam emission control by the laser scanner 24. In background exposure control, the laser scanner control unit 313 performs a small amount of LD emission control, which is not used during normal printing, to the extent that it does not cause toner adhesion to the photoconductor.

[0040] To perform density correction with high precision, it is necessary to set the conditions when acquiring the base data to be the same as when forming the patch, and background exposure control is also performed when acquiring the base data.

[0041] <Explanation of circumference measurement method> Next, a circumference measurement (calculation) method will be described. Here, in order to explain the conventional circumference measurement method and its problems, first, a case where there is no influence of periodic power supply voltage fluctuations due to background exposure control will be described, and then the influence of periodic power supply voltage fluctuations due to background exposure control will be described. After that, circumference measurement in Example 1 of the present invention will be described.

[0042] <Comparative example without power supply voltage fluctuation> The object of circumference measurement is the transfer belt 27, which is an example of a rotating body. The circumference of the transfer belt 27 is measured using an optical sensor 6 that is also used for image density control. In this embodiment, as will be described later, multiple waveform data on the surface (image forming surface) of the transfer belt 27 are detected, and information related to the actual circumference of the transfer belt 27 is obtained using each detected pattern.

[0043] 8A is a flowchart showing a process for obtaining information related to the actual circumference of the transfer belt 27 based on a matching process of two waveform data in a typical conventional circumference measurement example without power supply voltage fluctuations. The process described below is executed by loading a control program stored in the ROM 302 into the RAM 303 by the CPU 301.

[0044] The circumference measurement unit 311 of the CPU 301 determines whether or not to perform circumference measurement (S601). The conditions for determining whether or not to perform circumference measurement include the following examples. This corresponds to the determination of whether or not to perform image density control. - When the number of sheets passed since the previous circumference measurement is equal to or greater than the specified number. - When the environmental parameters have changed by more than a specified value since the environment at the time of the previous circumference measurement. - If the time since the last print job is longer than the specified time. When the process cartridge is replaced.

[0045] Next, the circumference measurement unit 311 commands the drive control unit 305 (S602) to drive the transfer belt 27. As a result, the drive of the transfer belt 27 starts.

[0046] The circumference measurement unit 311 causes the light emitting element 61 of the sensor 6 to emit light with the same amount of light as during image density control (S603). The light output from the light emitting element 61 is reflected by the background, and the reflected light is received by the light receiving element 63. The light receiving element 63 outputs a signal according to the amount of reflected light.

[0047] The laser control unit 312 causes the laser to emit a small amount of light to start background exposure (S604).

[0048] The circumference measurement unit 311 performs sampling of the output value of the reflected light received by the light receiving element 63 for the first round (S605). The reflected light output value at each sampling point is stored in the RAM 303 as a waveform profile (first waveform data) for the first round. Note that the waveform profile for the first round is a profile of the reflected light in an arbitrary section on the transfer belt 27, since sampling starts from an arbitrary position. The waveform profile means the characteristics or features of the measured waveform data.

[0049] In this embodiment, sampling is performed at 0.05 mm intervals, acquiring 1,800 data points. This corresponds to 90 mm. If the nominal circumference of the transfer belt 27 is 792 mm, 100 mm is approximately 1 / 9 of the total length. This sampling does not require acquiring data for one revolution of the transfer belt 27, but only requires acquiring data for approximately 1 / 9 of the total length, thereby reducing memory consumption for storing the acquired data. Note that the timing for starting measurement for the first revolution can be arbitrary.

[0050] When the 1800 samplings of the first cycle are completed, the circumference measurement unit 311 starts to acquire waveform data for density correction for the output value of the reflected light received by the light receiving element 63 (S606).

[0051] The density correction waveform data is acquired from one rotation of the transfer belt 27 including the waveform data for the second rotation, and is stored in the RAM 303 .

[0052] The circumference measurement unit 311 activates a timer to determine the start timing of sampling for the second rotation based on the detection timing of the waveform data for the first rotation (e.g., simultaneously with the start of sampling). Sampling of the waveform data for the second rotation is performed so that the section of the image forming surface of either the first or second rotation waveform data is included in the section of the image forming surface corresponding to the other waveform data. In other words, when the circumference measurement unit 311 acquires two waveform data from RAM 303, the section of the image forming surface corresponding to one waveform data is included in the section of the image forming surface corresponding to the other waveform data. Therefore, based on the detection timing of the waveform data for the first rotation, sampling of the waveform data for the second rotation is performed at a timing adjusted by a predetermined time from a predetermined reference time required for the transfer belt 27 to rotate one rotation, and the sampled waveform data is stored in RAM 303. In the case of FIG. 8A, the timer is set to a value obtained by subtracting half the maximum circumference variation from the nominal one rotation.

[0053] The value subtracted from the nominal circumference when setting the timer is not limited to half the maximum circumference variation. A predetermined value may be set as long as measurement errors do not occur frequently. When the timer reaches the time, the process proceeds to step S607.

[0054] Here, an example of two waveform data acquired from RAM 103 is shown in FIG. 7. FIG. 7 shows a waveform profile of the first rotation and a waveform profile of the second rotation. The reason why the sample values ​​included in the waveform profile of the second rotation are 200 more samples than the sample values ​​included in the waveform profile of the first rotation is because there is a shift area. The shift area is a margin provided to determine the amount of shift from the nominal circumference. The shift area is determined taking into account the maximum circumference fluctuation amount, which is the maximum value of the circumference fluctuation amount (elasticity characteristic) of transfer belt 27.

[0055] The circumference measurement unit 311 performs a second round of sampling (S607) on the output values ​​of the reflected light received by the light receiving element 63. Here, the number of samples taken in the second round is greater than the number of samples taken in the first round, corresponding to a longer detection time.

[0056] 8B is a timing chart for explaining the period from timing t0 when background exposure starts (S604) to timing t6 when sampling for the first cycle ends (S607). Note that t0 indicates the timing when background exposure starts. t1 indicates the timing when sampling for the first cycle starts, and t2 indicates the timing when sampling for the first cycle ends. The timing when background exposure starts may be before or at the same time as the timing when sampling for the first cycle starts. t3 indicates the timing when sampling for the second cycle starts, t4 indicates the timing corresponding to the nominal circumference starting from t1, and t5 indicates the timing when the amount of circumference extension is maximum.

[0057] The time from t1 to t2 indicates the sampling period of the first cycle, and the time from t3 to t6 indicates the sampling period of the second cycle.

[0058] Here, background data for the period from t2 to t6 is also obtained as data for canceling the influence of the reflectance of the surface of the transfer belt 27 when performing the density correction control described above.

[0059] The time from t1 to t3 corresponds to the shortest time required for the transfer belt 27 to make one revolution when the circumference of the transfer belt 27 is at its shortest due to fluctuations. In other words, the time from t1 to t3 is the time obtained by subtracting half of the maximum circumference fluctuation from the nominal circumference of the transfer belt 27 and dividing the result by the process speed. This is intended to ensure that the sampling start point for the first revolution is included in the section in which the waveform profile for the second revolution is acquired. Therefore, if a little extra sampling is performed, the time from t1 to t3 may be further shortened.

[0060] The time from t1 to t4 is obtained by dividing the nominal circumference of the transfer belt 27 by the process speed. That is, the time from t1 to t4 indicates the reference time required for the transfer belt 27 to make one rotation when it has the nominal circumference.

[0061] The sampling interval for the second lap is 0.05 mm, the same as for the first lap. However, the number of samples for the second lap is greater than the number of samples for the first lap by the amount of shift. If the number of samples for the first lap is 1800 points and the amount of shift is 200 points, the number of samples for the second lap will be 2000 points. Here, the maximum circumference variation is set to 10 mm. The waveform profile for the second lap (second waveform data) is also stored in RAM 103. The relationship between each sampling point and the reflected light output value is as shown in Figure 7.

[0062] In the flowchart of FIG. 8A, all sampled data is treated as waveform data, but this is not a limitation. Essentially, it is sufficient to obtain data for the pattern matching calculation described below. For example, sampling may be performed extra at the start and / or end timings described above, and two waveform data necessary for the pattern matching calculation may be obtained from memory. In the following description, a preferred example will be described in which only the amount of sampling used for the pattern matching calculation is performed.

[0063] After the sampling of the first and second rounds is completed, in step S608, a variable X indicating the shift amount is initialized to zero. Note that the circumference measurement unit 311 compares the waveform profile of the first round with multiple waveform profiles (third waveform data) of the same length as the waveform profile of the first round, which are each shifted by a different shift amount within the waveform profile of the second round, as described below. In other words, the third waveform data can be considered a comparison profile of reflected light in multiple sections that are shifted by different shift amounts from a reference position based on the nominal circumference, starting from the detection start position of the section in which the waveform profile of the first round was acquired.

[0064] In step S609, in order to perform pattern matching processing on the two waveform data, the circumference measurement unit 311 performs integration of the absolute difference values ​​between the waveform profile of the first round and the waveform profile of the second round (third waveform data). The integration is performed, for example, based on the following equation:

[0065]

number

[0066] Here, I(X) indicates the integrated value when the shift amount is X. V1st lap(i) indicates the reflected light output value at point i on the first lap. V2nd lap(i+X) indicates the reflected light output value at point i+X on the second lap. Note that X=0, 1, 2, ..., 200.

[0067] In step S610, the circumference measurement unit 311 stores the integrated value I(X) in RAM 303. In step S611, the circumference measurement unit 311 increments the value of X by 1. In step S612, the circumference measurement unit 311 determines whether the value of X exceeds the maximum shift. If it does not, the process returns to step S608. If it does exceed the maximum shift, the process proceeds to step S613. In this way, the integrated value I(X) for all X values ​​from X=0 to X=200 is calculated.

[0068] In step S613, the circumference measurement unit 311 determines the minimum value among the calculated multiple integrated values ​​I(X). By determining this minimum integrated value, when one of the two waveform data, V1 cycle (i), is used as the reference waveform data, it is possible to extract waveform data that matches V1 cycle (i). Also in step S613, X corresponding to the minimum integrated value I is extracted. This identified X indicates a deviation (expansion or contraction) from a predetermined nominal circumference, and therefore corresponds to information (interval information) corresponding to the interval between V1 cycle (i) as the reference waveform data and the waveform data corresponding to X when the integrated value I is minimum. In other words, if the interval between the reference waveform data and the waveform data corresponding to X when the integrated value I is minimum increases, the value of X increases; conversely, if the interval decreases, the value of X decreases.

[0069] FIG. 9 shows the relationship between the waveform profiles of the first and second revolutions and the integrated value. Here, it shows that the integrated value is smallest when the correlation between the two waveform profiles is greatest. On the other hand, the correlation is low between different positions, and the waveform profiles are not similar, so the integrated value is relatively large. In this way, by identifying the points where the correlation between the waveforms of the first and second revolutions is high using Equation 1, information related to the circumference of the transfer belt 27 can be calculated.

[0070] In step S614, the circumference measurement unit 311 calculates the actual circumference of the transfer belt 27 and stores the calculated actual circumference in the RAM 303 or non-volatile memory 306, which are examples of storage means for storing information indicating the measured actual circumference. The actual circumference can be calculated, for example, by the following equation using the value of X that gave the smallest integrated value. In the following equation, the actual circumference of the rotating body is calculated from the nominal circumference and the shift amount obtained by comparing the extracted waveform data with the reference waveform data. <Expression 2> Actual perimeter = (X Profile result - XITB ideal) * 0.05 + Nominal perimeter

[0071] Here, "X profile result" refers to the X with the smallest integrated value calculated in step S611. "XITB ideal" refers to the X when the ITB circumference is the nominal value (here, X = 100). Furthermore, "nominal circumference" refers to the ideal dimension value (792 mm for the transfer belt 27 in this embodiment) when the ITB circumference is free of manufacturing tolerances and environmental variations. In Equation 2, "(X profile result - XITB ideal) * 0.05" refers to the deviation (unit: mm) of the measured circumference of the transfer belt 27 from the ideal dimension value when there are no manufacturing tolerances or environmental variations. In the example, sampling is performed at 0.05 mm intervals, so "(X profile result - XITB ideal)" is multiplied by 0.05 in Equation 2. However, if sampling is performed at 0.1 mm intervals, for example, multiplication by 0.1 is sufficient.

[0072] 9A, the integrated value is smallest when X = 114. Therefore, from equation 2, the actual circumference is (114 - 100) * 0.05 + 792 = 792.7 mm.

[0073] When storing information for grasping the obtained actual circumference, the information may be converted into time or may be stored as length.

[0074] The density control unit 312 of the CPU 301 executes image density control using the value calculated by Equation 2 as information related to the actual circumference of the transfer belt 27 determined in step S612. Note that the amount of expansion / contraction may be calculated by subtracting 100 from X, which gives the smallest integrated value, as information related to the actual circumference, and the time it takes for an arbitrary position to make one revolution may be calculated based on the calculated amount of expansion / contraction. In this case, more specifically, the time required for the nominal transfer belt 27 to make one revolution may be added by the time corresponding to the calculated amount of expansion / contraction (or a negative value if the value is negative), thereby enabling accurate image density control.

[0075] After executing the image density control, the CPU 301 returns to step S601 again, and if the circumference measurement condition is met, executes the flowchart shown in FIG. 7A.

[0076] <Explanation of a comparative example affected by periodic power supply voltage fluctuations> Next, we will explain the effect on circumference measurement when there is a power supply voltage fluctuation due to background exposure control. In this example, we will explain an example shown in Figure 11, where the period of one polygon surface is equivalent to 15 samples and the power supply voltage fluctuation has an amplitude of 15 mV.

[0077] 10 shows the power supply configuration of the CPU 301, laser scanner 24, and sensor 6. In this embodiment, the CPU 301 and laser scanner 24 operate on the same 3.3V power supply. That is, the CPU 301, which is an example of a control means, and the laser scanner 24, which is an example of an exposure means, are supplied with power from the same power supply. On the other hand, the sensor 6, which is an example of a detection means, operates on a 24V power supply that is separate from the power supply for the CPU 301 and laser scanner 24.

[0078] Here, the measurement unit 53 of the sensor control unit 51, which is realized by the CPU 301, measures the detection signal from the sensor 6 using a 3.3V power supply as a reference voltage. In other words, if the 3.3V power supply fluctuates, the detection value also fluctuates accordingly. When sampling is performed to measure the circumference in this state, a waveform profile is obtained in which periodic fluctuations corresponding to the period of one face of the polygon mirror are superimposed on each of the waveform profiles of the first and second revolutions.

[0079] FIG. 9B shows the relationship between the waveform profiles and the integrated value for the first and second rotations when 3.3V fluctuates. When the circumference measurement unit 311 performs pattern matching in the same way as when there is no 3.3V fluctuation, the correlation between the waveform profiles for the first and second rotations increases each time X becomes an integer multiple of 15, because the polygon mirror surface period is 15 samples. As a result, the absolute difference integrated value decreases. Therefore, the absolute difference integrated value decreases every 15 samples, which corresponds to the polygon mirror surface period. This influences the X at which the absolute difference integrated value is minimized. Specifically, when there is no 3.3V fluctuation, the absolute difference integrated value is minimum at X = 114, whereas when there is a 3.3V fluctuation, the absolute difference integrated value is minimum at X = 120. In other words, the actual circumference is calculated from Equation 2 as (120 - 100) * 0.05 + 792 = 793.0 mm.

[0080] As such, if the waveform profiles for both the first and second rotations have periodic fluctuations, such as the period of one polygon mirror face, the resulting information may be incorrect, rather than the actual circumference of the transfer belt 27. One possible solution is to acquire the first and second waveform data for circumference detection while stopping the control that causes the periodic fluctuations. Meanwhile, in image density control, to accurately calculate the amount of toner adhesion, it is necessary to acquire outputs with and without toner at the same position on the transfer body under the same conditions. In other words, even if a control that causes periodic fluctuations in waveform data is necessary for patch formation, it is necessary to acquire waveform data when no toner is attached while the control is in progress. Generally, considering factors such as the memory capacity required to store waveform data and the time required to acquire the waveforms, a single waveform data is used to combine the waveform data for circumference detection and the waveform data for image density control. Therefore, acquiring waveform data for image density control and circumference detection separately can lead to increased downtime and memory usage.

[0081] <Explanation of circumference measurement> Therefore, in this embodiment, the circumference measurement is performed as follows. Fig. 12 shows a flowchart related to the circumference measurement operation. In the circumference measurement of the comparative example described using Fig. 8(B), background exposure control (S604) is performed followed by first-round sampling (S605). On the other hand, in the flowchart shown in Fig. 12 shown in Fig. 7, background exposure is started (S705) after first-round sampling (S704). In other words, in the first-round sampling, background exposure control is not performed, and laser emission control of the laser scanner 24 is stopped.

[0082] Fig. 12(B) shows a timing chart for measuring circumference in this embodiment. As with the circumference measurement of the comparative example described in Fig. 7(B), t1 indicates the start timing of sampling for the first round, and t2 indicates the end timing of sampling for the first round. t3 indicates the start timing of sampling for the second round, t4 indicates the timing corresponding to the nominal circumference from t1, and t5 indicates the timing when the amount of extension of the circumference is maximum. The time from t3 to t6 also indicates the sampling period for the second round, as with conventional circumference measurement.

[0083] 12B, the timing t2 at which sampling ends for the first rotation is set as the timing at which background exposure starts. Background exposure starts at t2, and background data is acquired from t2 to t6 as data for canceling the influence of the reflectance of the surface of the transfer belt 27 when performing the density correction control described above.

[0084] By using this timing, the waveform profile for the first rotation is sampled while laser emission control is stopped. This eliminates the influence of power supply fluctuations at one polygon mirror face period caused by background exposure control. On the other hand, the waveform profile acquired between t2 and t6 includes the influence of power supply fluctuations at one polygon mirror face period caused by background exposure control.

[0085] As mentioned above, to perform density correction with precision, the conditions when acquiring the base data and when forming the patch must be the same, so base data after background exposure is required. In other words, although the waveform data from the first cycle is not affected by power supply fluctuations, it cannot be used for density correction. On the other hand, the waveform data acquired between t2 and t6 is waveform data that is affected by power supply fluctuations, and can be said to be base data that can be used for density correction.

[0086] The relationship between the waveform profiles and the integrated value for the first and second revolutions thus obtained is shown in Figure 13. Although the waveform profile for the second revolution includes fluctuations due to the period of one polygon mirror face, the waveform profile for the first revolution does not include fluctuations due to the period of one polygon mirror face, and therefore the correlation between the waveform profiles for the first and second revolutions is not high for the period of one polygon mirror face. As a result, the absolute difference integrated value is smallest at X=114, which is the actual peripheral length of transfer belt 27, and the actual peripheral length of transfer belt 27 can be determined with high accuracy.

[0087] Furthermore, even if the second waveform data, which includes part of the first waveform data, has periodic fluctuations that are different from the characteristics of the intermediate transfer body surface, the circumference of the transfer belt, which is the image carrier, can be detected with high accuracy without increasing downtime.

[0088] [Other embodiments] The present invention can also be realized by supplying a program that realizes one or more functions of the above-described embodiments to a system or device via a network or a storage medium, and having one or more processors in the computer of the system or device read and execute the program.The present invention can also be realized by a circuit (e.g., ASIC) that realizes one or more functions.

[0089] [Note] The disclosure of the present embodiment also includes the following configuration examples and method examples.

[0090] (Item 1) A photoreceptor; an exposure unit that emits a laser beam onto the photosensitive member and exposes the photosensitive member; a developing means for developing, with toner, the electrostatic latent image formed on the photosensitive member by exposure by the exposure means; a transfer belt onto which the toner developed on the photosensitive member is transferred; a detecting means for irradiating the transfer belt with light and detecting reflected light from the transfer belt; a control means for acquiring first waveform data about the surface of the transfer belt based on detection by the detection means at a first timing, and acquiring second waveform data about the surface of the transfer belt based on detection by the detection means at a second timing, the second waveform data including at least a part of the first waveform data, and determining information about the actual circumference of the transfer belt based on matching of the acquired first waveform data and the acquired second waveform data; Equipped with the control means and the exposure means are supplied with power by the same power source; The image forming apparatus is characterized in that the control means acquires the first waveform data while stopping the control of the laser light emission by the exposure means, and acquires the second waveform data while performing the control of the laser light emission by the exposure means.

[0091] (Item 2) 2. The image forming apparatus according to item 1, wherein the laser light emission control performed by the exposure unit is a weak light emission control that does not cause toner to adhere to the photosensitive member.

[0092] (Item 3) the control means uses one of the first waveform data and the second waveform data as reference waveform data, and extracts an amount of deviation from the reference waveform data that is determined to match based on a result of integrating an absolute difference between the other waveform data, 3. The image forming apparatus according to item 1 or 2, wherein information on the circumference corresponding to the extracted amount of deviation is obtained as information related to the actual circumference of the transfer belt.

[0093] (Item 4) 4. The image forming apparatus according to any one of items 1 to 3, wherein the detecting unit operates on a power supply different from the power supply.

[0094] (Item 5) 5. The image forming apparatus according to any one of items 1 to 4, wherein the second timing is a timing adjusted by a predetermined time from a reference time for the transfer belt to make one rotation.

[0095] (Item 6) The image forming apparatus described in any one of items 1 to 5, characterized in that the first waveform data is waveform data of the first revolution of the transfer belt when an instruction to start measuring the actual circumference of the transfer belt is issued, and the second waveform data is waveform data of the second revolution of the transfer belt.

[0096] (Item 7) 7. The image forming apparatus according to any one of items 1 to 6, wherein the number of samples of the second waveform data is greater than the number of samples of the first waveform data.

[0097] (Item 8) 8. The image forming apparatus according to any one of items 1 to 7, wherein the control unit adjusts image forming conditions using information relating to the actual circumference of the transfer belt. [Explanation of symbols]

[0098] 6 sensors 21 Cassette 22 Photoreceptor 23 Charger 24 Laser scanner 25 Drive roller 26 Developer 27 Transfer belt 28 Transfer roller 30 Fixing unit 51 Sensor control unit 52 Drive unit 53 Measurement section 55 Arithmetic section 61 Light-emitting part 62, 63 Light receiving section 101 host computer 102 Image forming device 103 Video Controller 104 Printer Engine 301 CPU 302 ROM 303 RAM 305 Drive control unit 306 Non-volatile memory 311 Perimeter measurement section 312 Temperature control unit 313 Laser scanner control unit

Claims

1. A photoreceptor; an exposure unit that emits a laser beam onto the photosensitive member and exposes the photosensitive member; a developing means for developing, with toner, the electrostatic latent image formed on the photosensitive member by exposure by the exposure means; a transfer belt onto which the toner developed on the photosensitive member is transferred; a detecting means for irradiating the transfer belt with light and detecting reflected light from the transfer belt; a control means for acquiring first waveform data about the surface of the transfer belt based on detection by the detection means at a first timing, and acquiring second waveform data about the surface of the transfer belt based on detection by the detection means at a second timing, the second waveform data including at least a part of the first waveform data, and determining information about the actual circumference of the transfer belt based on matching between the acquired first waveform data and the acquired second waveform data; Equipped with the control means and the exposure means are supplied with power by the same power source; The image forming apparatus is characterized in that the control means acquires the first waveform data while stopping the control of the laser light emission by the exposure means, and acquires the second waveform data while performing the control of the laser light emission by the exposure means.

2. 2. The image forming apparatus according to claim 1, wherein the laser light emission control performed by the exposure unit is a weak light emission control that does not cause toner to adhere to the photosensitive member.

3. the control means uses one of the first waveform data and the second waveform data as reference waveform data, and extracts an amount of deviation from the reference waveform data that is determined to match based on a result of integrating absolute differences between the other waveform data, 2. The image forming apparatus according to claim 1, wherein information on the circumference corresponding to the extracted amount of deviation is obtained as information related to the actual circumference of the transfer belt.

4. 2. The image forming apparatus according to claim 1, wherein the detecting means is operated by a second power supply different from the power supply.

5. 2. The image forming apparatus according to claim 1, wherein the second timing is adjusted by a predetermined time from a reference time required for the transfer belt to make one revolution.

6. 2. The image forming apparatus according to claim 1, wherein the first waveform data is waveform data of the first revolution of the transfer belt when an instruction to start measuring the actual circumference of the transfer belt is issued, and the second waveform data is waveform data of the second revolution of the transfer belt.

7. 2. The image forming apparatus according to claim 1, wherein the number of samples of the second waveform data is greater than the number of samples of the first waveform data.

8. 2. The image forming apparatus according to claim 1, wherein the control means adjusts image forming conditions using information relating to the actual circumference of the transfer belt.

Images