Image forming apparatus

Abstract

To improve detection accuracy when detecting toner formed on an intermediate transfer medium having regions with different optical properties using an optical sensor. [Solution] The printer control unit 700 controls the image forming unit to form multiple toner images at different positions on the intermediate transfer belt 205, performs a detection operation for each of the multiple toner images, and determines whether the time during which the voltage value has been continuously below a predetermined value has been longer than a predetermined time, based on a voltage value output when reflected light from the second part or the toner image is detected in the density sensor, which is different from the voltage value when reflected light from the first part is detected, for each of the multiple toner images, and determines that a toner image has been formed on the intermediate transfer belt 205 based on the result of the determination for each of the multiple toner images.

Description

Technical Field

[0001] The present invention relates to an image forming apparatus, for example, to an image forming apparatus such as a printing apparatus, a copier, a laser beam printer, and a facsimile machine.

Background Art

[0002] Conventionally, as an image forming apparatus using an electrophotographic system, there is an image forming apparatus using an endless intermediate transfer member. A toner image is transferred from the intermediate transfer member to a transfer material, but not all of the toner image is transferred to the transfer material. For this reason, it is necessary to remove (clean) the toner remaining on the intermediate transfer member. As a cleaning system, a cleaning system using a blade is widely adopted. For example, Patent Document 1 proposes a technique of providing an uneven shape on the surface of the intermediate transfer member in order to improve the slipperiness between the cleaning blade and the intermediate transfer member.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] Further, Patent Document 1 discloses a surface configuration of an intermediate transfer member in which uneven shapes are provided in an overlapping manner in some regions. Since the surface state differs between the region where the uneven shapes overlap (overlapping region) and the other regions, optical characteristics (for example, reflectance) may also differ due to the influence thereof. For this reason, when performing a step of detecting the presence or absence of a toner image using, for example, an optical sensor, if the toner image is formed without considering the position of the overlapping region, the following problem may occur. That is, depending on the detection result of the optical sensor, it may not be possible to accurately determine whether a region is the overlapping region or a toner image.

[0005] Therefore, the present invention aims to improve detection accuracy when detecting toner formed on an intermediate transfer material having regions with different optical properties using an optical sensor. [Means for solving the problem]

[0006] To solve the above-mentioned problems, the present invention has the following configuration. (1) An endless intermediate transfer body having a first portion in the direction of movement and a second portion having different optical properties from the first portion in the direction of movement; an image forming means for forming a toner image on the intermediate transfer body; a light source for irradiating the surface of the intermediate transfer body or the toner image formed on the intermediate transfer body with light, and a detection means for detecting reflected light reflected by the intermediate transfer body or the toner image formed on the intermediate transfer body by irradiating the intermediate transfer body or the toner image formed on the intermediate transfer body with light from the light source and outputting a voltage value; and a control means for controlling the image forming means to form the toner image on the intermediate transfer body in order to perform a detection operation to determine the presence or absence of the toner image on the intermediate transfer body based on the result detected by the detection means, wherein the detection The toner image formed on the intermediate transfer body in the intelligent operation is a test image used for the detection operation, the control means controls the image forming means to form a plurality of toner images at different positions on the intermediate transfer body, the detection operation is performed for each of the plurality of toner images, the control means determines for each of the plurality of toner images whether the time during which the voltage value has been continuously below a predetermined value is longer than a predetermined time, based on a voltage value output when reflected light from the second part or the toner image is detected by the detection means, which is different from the voltage value when reflected light from the first part is detected, and determines that the toner image has been formed on the intermediate transfer body based on the result of the determination for each of the plurality of toner images. [Effects of the Invention]

[0007] According to the present invention, when detecting toner formed on an intermediate transfer material having regions with different optical properties using an optical sensor, the detection accuracy can be improved. [Brief explanation of the drawing]

[0008] [Figure 1] Schematic diagrams of the image forming apparatus in Examples 1 and 2. [Figure 2] Enlarged schematic diagram of the intermediate transfer belt in Example 1, and diagram showing the polishing apparatus. [Figure 3] Schematic diagrams illustrating the concentration sensors and sensor output voltages of Examples 1 and 2. [Figure 4] Detailed explanatory diagram of the sensor output voltage in Examples 1 and 2 [Figure 5] Detailed explanatory diagram of the sensor output voltage in Examples 1 and 2 [Figure 6] Hardware configuration diagrams for Examples 1 and 2 [Figure 7] Functional block diagrams of Examples 1 and 2 [Figure 8] Flowchart showing the fitting determination process in Example 1 [Figure 9] Diagram illustrating the method for analyzing the output decrease time in Example 1. [Figure 10] Detailed explanatory diagram of the sensor output voltage in Example 1 [Figure 11] A flowchart showing the fitting determination process as a comparative example of Example 1. [Figure 12] Enlarged schematic diagram of the intermediate transfer belt in Example 2, and schematic diagram of the imprinted end. [Figure 13] Flowchart showing the fitting determination process in Example 2 [Modes for carrying out the invention]

[0009] Embodiments of the present invention will be described below. However, unless otherwise specified, the materials, shapes, relative positions, etc., of the components described in the embodiments are not intended to be limiting. [Examples]

[0010] [Description of Configuration of Image Forming Apparatus] FIG. 1 is a schematic configuration diagram of an image forming apparatus 200 according to the first embodiment. The image forming apparatus 200 is, for example, a full-color laser printer adopting an in-line system and an intermediate transfer system. The image forming apparatus 200 forms a full-color image on a recording material 203 in accordance with image information input from a controller 202. The image forming apparatus 200 includes image forming stations SY, SM, SC, and SK for respective colors of yellow (Y), magenta (M), cyan (C), and black (K). Note that suffixes Y, M, C, and K of reference numerals indicating colors may be omitted hereinafter, except when members of specific colors are described.

[0011] An image forming station S includes a cartridge 204, a rotatable intermediate transfer belt 205 (Intermediate Transfer Belt) that is an intermediate transfer member, and a primary transfer roller 206. The intermediate transfer belt 205 is an endless belt, and rotates in a direction of an arrow A (counterclockwise direction) in the drawing. The primary transfer roller 206 is arranged on a side opposite to the cartridge 204 with the intermediate transfer belt 205 interposed therebetween. The image forming stations SY, SM, SC, and SK are arranged side by side in a rotation direction of the intermediate transfer belt 205, and are substantially the same except that colors to be formed are different.

[0012] The cartridge 204 detachably attachable to the image forming apparatus 200 includes a photosensitive drum 301 that is an image bearing member. In other words, the photosensitive drum 301 is detachably mounted to the image forming apparatus 200. The image forming apparatus 200 includes a scanner unit 207 that is an exposure apparatus for exposing the photosensitive drum 301. Note that an exposure apparatus using light emitting diodes (LEDs) can also be used as the exposure apparatus.

[0013] The photosensitive drum 301 is rotated by a drum motor 731 (see Figure 6). The charging roller 302 is uniformly charged on the surface of the photosensitive drum 301 by applying a high voltage from a high-voltage power supply 721 (see Figure 6). For example, a charging voltage of -1200V is applied to the charging roller 302, and the surface of the photosensitive drum 301 is charged to -700V. Next, the scanner unit 207 irradiates the photosensitive drum 301 with laser light based on the image information input to the controller 202, forming an electrostatic latent image on the surface of the photosensitive drum 301. The potential of the area exposed by the laser light on the photosensitive drum 301 (on the image carrier) becomes, for example, -100V.

[0014] The toner container 307 contains toner. The toner in the toner container 307 is supplied to the developing roller 303 by an agitator (not shown). The developing roller 303 is rotated by a developing motor 711 (see Figure 6). The toner coated on the surface of the developing roller 303, for example, a negatively charged toner, adheres along the electrostatic latent image on the surface of the photosensitive drum 301 when a developing voltage of, for example, -350V is applied by a high-voltage power supply 721, and the electrostatic latent image becomes a visible image. Hereinafter, the visible image formed by the toner will be referred to as the toner image. Hereinafter, when we refer to the developing unit, the developing unit includes the toner and the developing roller 303, which is a developing means that develops the electrostatic latent image on the photosensitive drum 301 with the toner to form a toner image. The developing unit is detachable from the image forming apparatus 200, and in Embodiment 1, the developing unit is included in the cartridge 204. That is, when the cartridge 204 is mounted in the image forming apparatus 200, a toner image is formed on the intermediate transfer belt 205 by the image forming operation. On the other hand, if the cartridge 204 is not installed in the image forming apparatus 200, a toner image will not be formed on the intermediate transfer belt 205 even if the image forming operation is performed.

[0015] The base layer of the photosensitive drum 301 is grounded, and the primary transfer roller 206 is subjected to a voltage opposite to the toner polarity, for example, +1000V, by a high-voltage power supply 721. As a result, an electric field is formed at the nip between the primary transfer roller 206 and the photosensitive drum 301, and the toner image is transferred from the photosensitive drum 301 to the intermediate transfer belt 205. Toner that remains on the surface of the photosensitive drum 301 without being transferred onto the intermediate transfer belt 205 is removed from the photosensitive drum 301 by the cleaning blade 304 and collected in the waste toner container 305. The cleaning blade 304 is an elastic blade made of, for example, urethane rubber supported by sheet metal, and contacts the photosensitive drum 301 with a predetermined pressure, in the direction of the counter relative to the rotation direction of the photosensitive drum 301.

[0016] As the intermediate transfer belt 205 rotates in the direction of arrow A in the diagram, the toner images generated at each color image forming station S are sequentially superimposed and transferred onto the intermediate transfer belt 205 (primary transfer), forming a full-color toner image which is then transported. The intermediate transfer belt 205 is driven by a drive roller 217. The rotation axis direction of the drive roller 217 can be called the rotation axis direction of the intermediate transfer belt 205. The image forming unit, which is the image forming means for forming a toner image on the intermediate transfer belt 205 (on the intermediate transfer body), includes a scanner unit 207, a photosensitive drum 301, a developing roller 303, and a primary transfer roller 206.

[0017] The paper feed cassette 208 is loaded with recording material 203. Based on the paper feed start signal, the paper feed roller 209 is driven and the recording material 203 is fed onto the transport path. The recording material 203 is transported via the registration roller pair (hereinafter referred to as the registration roller pair) 210 to the contact nip portion (hereinafter also referred to as the secondary transfer portion) between the secondary transfer roller 211 and the secondary transfer opposing roller 212, which are transfer members, at a predetermined timing. Specifically, the recording material 203 is transported at the timing when the leading edge of the toner image on the intermediate transfer belt 205 and the leading edge of the recording material 203 overlap.

[0018] While the recording material 203 is held and transported between the secondary transfer roller 211 and the secondary transfer opposing roller 212, a voltage opposite in polarity to the toner is applied to the secondary transfer roller 211 from a power supply (not shown). Since the secondary transfer opposing roller 212 is grounded, an electric field is formed between the secondary transfer roller 211 and the secondary transfer opposing roller 212. This electric field transfers the toner image from the intermediate transfer belt 205 to the recording material 203 (secondary transfer).

[0019] After the recording material 203 passes through the nip between the secondary transfer roller 211 and the secondary transfer opposing roller 212, it is heated and pressurized by the fixing device 213. This fixes any unfixed toner image on the recording material 203 to the recording material 203. Subsequently, the recording material 203 is transported from the discharge port 214 to the discharge tray 215, completing the image formation process.

[0020] Meanwhile, toner that was not transferred to the recording material 203 in the secondary transfer section and remains on the intermediate transfer belt 205 is removed from the intermediate transfer belt 205 by the cleaning blade 216, and the intermediate transfer belt 205 is refreshed (cleaned) to a state where it can form an image again. The cleaning blade 216 is, for example, an elastic cleaning blade and is pressed against the intermediate transfer belt 205. Since the intermediate transfer belt 205 is rotating while the cleaning blade 216 is stationary, the contact surface between the cleaning blade 216 and the intermediate transfer belt 205 slides. This sliding action removes any toner remaining on the intermediate transfer belt 205.

[0021] Furthermore, the user can access the cartridge 204 by opening the access door (not shown) of the image forming apparatus 200. The user can remove the cartridge 204 from the image forming apparatus 200 by opening the access door and pulling the cartridge 204 towards the front in Figure 1. The user can also install the cartridge 204 into the image forming apparatus 200. The image forming apparatus 200 detects whether or not the cartridge 204 (or photosensitive drum 301, developing unit) is installed and displays a message on the display unit 230 indicating the installation status. In addition, the image forming apparatus 200 has a density sensor 218, which will be described later.

[0022] [Explanation of the intermediate transfer belt configuration] Here, the intermediate transfer belt 205 will be described in detail. In Example 1, the intermediate transfer belt 205 is, for example, one with a volume resistivity of 1 × 10⁻⁶. 10 Ω cm, surface resistivity 1×10 12 A seamless belt made of thermoplastic polyvinylidene fluoride with a thickness of 75 μm and a resistance of Ω / sq was used. Electrical resistance was measured at a temperature of 23°C and a relative humidity of 50% RH using an Advantest R8340A measuring instrument and a probe with a main electrode outer diameter of 50 mm and a guard electrode of 70 mm, under the conditions of an applied voltage of 100 V and a charge time of 10 seconds. As an intermediate transfer material, thermoplastic resins such as polyethylene terephthalate, polybutylene terephthalate, and polycarbonate may be used. The electrical resistance was measured with a volume resistivity of 1 × 10⁻⁶. 8 ~1 × 10 11 Ω cm, surface resistivity 1×10 11 ~1 × 10 13 Ω / sq is suitable.

[0023] To improve the wear resistance of the cleaning blade 216 surface during long-term use, a fine uneven surface (hereinafter referred to as the fine uneven surface) is formed on the surface of the intermediate transfer belt 205. While polishing, cutting, and imprinting are generally known as methods for processing the fine uneven surface, polishing is adopted in the configuration of Example 1 from the viewpoint of processing cost, productivity, and shape accuracy.

[0024] In Example 1, the 10-point average roughness was set to 0.5 μm in the width direction and 0.3 μm in the circumferential direction of the intermediate transfer belt 205. Here, the width direction of the intermediate transfer belt 205 is the direction of the rotation axis of the photosensitive drum 301, etc., and the circumferential direction is the direction of movement of the intermediate transfer belt 205, which is the direction of arrow A. For the measurement of the 10-point average roughness (as described in the JIS B0601:2001 Annex), a surface roughness measuring instrument SE3500 manufactured by Kosaka Laboratory Co., Ltd. was used, and the measurement was performed under the conditions of a cutoff value of 0.8 mm, a measurement length of 4 mm, and a measurement speed of 0.1 mm / second.

[0025] Figure 2(a) shows a schematic diagram illustrating a magnified portion of the surface of the intermediate transfer belt 205. In the polishing process, the polishing film is pressed against the surface of the intermediate transfer belt 205, and the polishing film and the intermediate transfer belt 205 are moved in the same rotational direction to perform the polishing. On the intermediate transfer belt 205, polishing is started in the H direction from the starting position 226 and continues until the ending position 227. Since the ending position 227 is located beyond the starting position 226, a first non-overlapping polishing portion 229 and a second overlapping polishing portion 228 are formed in the circumferential direction of the intermediate transfer belt 205. Because the overlapping portion 228 undergoes two polishing processes compared to the non-overlapping portion 229, more polishing marks are formed. For these reasons, the amount of specular reflected light decreases in the overlapping portion 228 compared to the non-overlapping portion 229 when light is irradiated from the density sensor 218, which is an optical sensor. In other words, the intermediate transfer belt 205 is an endless belt having a non-overlapping portion 229 which is a first portion in the direction of movement, and an overlapping portion 228 which is a second portion that has different optical properties from the first portion in the direction of movement. However, since the depth of the fine uneven shape formed by polishing is considerably small compared to the layer thickness of the intermediate transfer belt 205, there is no difference in transferability between the overlapping portion 228 and the non-overlapping portion 229.

[0026] (polishing equipment) Figure 2(b) shows an example of a polishing device 600 used for polishing the intermediate transfer belt 205. The polishing device 600 is equipped with a polishing film 601 and a polishing head 602. During polishing, the intermediate transfer belt 205 is stretched by three rollers 603, 604, and 605 and rotated in the direction of the arrow. The polishing film 601 is conveyed and recovered by two rollers 606 and 607 via the polishing head 602. The polishing head 602 acts to bring the polishing film 601 and the intermediate transfer belt 205 into contact with a predetermined pressure, and the intermediate transfer belt 205 is polished by the polishing film 601. In Example 1, the polishing conditions were set to a feed rate of 250 mm / sec for the intermediate transfer belt 205, a feed rate of 0.5 mm / sec for the polishing film 601, and a pressing pressure of 5 kg / 400 mm to obtain the desired surface roughness. This polishing process forms polishing marks on the surface of the intermediate transfer belt 205.

[0027] Thus, in Example 1, the intermediate transfer belt 205 is polished on the surface where the toner image is formed. The overlapping portion 228 in the second part is polished more times (e.g., twice) than the non-overlapping portion 229 in the first part (e.g., once), resulting in different optical properties from the first part.

[0028] [Concentration sensor configuration] Figure 3(a) is a schematic diagram of the density sensor 218, which is an optical detection means, and is a cross-sectional view of the position where the density sensor 218 is located, perpendicular to the rotational direction of the intermediate transfer belt 205. The density sensor 218 can optically detect the presence or absence of toner on the intermediate transfer belt 205. The toner image T is transferred to the surface of the intermediate transfer belt 205 by the image forming station S and then transported to the position of the drive roller 217 as the intermediate transfer belt 205 rotates. The density sensor 218 is located on the opposite side of the drive roller 217 via the intermediate transfer belt 205. The density sensor 218 is used in the test image detection process described later. Note that the placement of the density sensor 218 is not limited to this position. The density sensor 218 should be located downstream of the image forming station (SK in Example 1) located furthest downstream in the rotational direction of the intermediate transfer belt 205, and upstream of the secondary transfer section.

[0029] The direction perpendicular to the rotation direction of the intermediate transfer belt 205 is the same as the rotation axis direction of the intermediate transfer belt 205. The configuration of the density sensor 218 is described below. The density sensor 218 has an illumination unit that irradiates light onto the surface of the intermediate transfer belt 205 or the image pattern described later, and a light receiving unit that receives reflected light, and optically detects the surface of the intermediate transfer belt 205 or the image pattern. Optically detecting the surface of the intermediate transfer belt 205 will henceforth be referred to as detecting the intermediate transfer belt 205.

[0030] Specifically, the density sensor 218 mainly consists of an illuminating element 219, which is the illumination part, and a light-receiving element 220 for specular reflection and a light-receiving element 221 for diffuse reflection, which are the light-receiving parts. The illuminating element 219 emits, for example, infrared light, and this light is reflected from the surface of the toner image T. The light-receiving element 220 for specular reflection is positioned in the specular reflection direction relative to the position of the toner image T and detects the specularly reflected light at the position of the toner image T. The light-receiving element 221 for diffuse reflection is positioned in a position other than the specular reflection direction relative to the toner image T and detects the diffusely reflected light at the position of the toner image T. Hereafter, the voltage value received (detected) by the light-receiving element 220 and output from the light-receiving element 220 will be called the specular reflection output, and the voltage value received (detected) by the light-receiving element 221 and output from the light-receiving element 221 will be called the diffuse reflection output.

[0031] As described above, the density sensor 218 has a light-emitting element 219, which is a light source that irradiates light onto the surface of the intermediate transfer belt 205 and the toner image formed on the intermediate transfer belt 205. The density sensor 218 detects the reflected light reflected by the intermediate transfer belt 205 or the toner image formed on the intermediate transfer belt 205 by irradiating light from the light-emitting element 219 onto the intermediate transfer belt 205 or the toner image formed on the intermediate transfer belt 205.

[0032] Figure 3(b) is a schematic diagram illustrating the variation in specular reflection output and diffuse reflection output with respect to concentration, and the variation in output voltage calculated from them. In the graph of Figure 3(b), the horizontal axis represents concentration, and the vertical axis represents the output voltage of the concentration sensor 218 (sensor output voltage). Specular reflection output is shown by the dashed line 401, diffuse reflection output by the dotted line 402, and the output of the concentration sensor 218 by the solid line 403.

[0033] When the amount of toner in the toner image T is small, the density sensor 218 detects a large amount of reflection from the smooth surface of the intermediate transfer belt 205, resulting in a large specular reflection output. As the amount of toner in the toner image T increases, the specular reflection output decreases. When the number of toner layers in the toner image T exceeds one, the specular reflection component from the surface of the intermediate transfer belt 205 is almost eliminated. However, since the specular reflection output includes both specular and diffuse reflection components, the specular reflection output does not decrease monotonically in the high-density region. On the other hand, the diffuse reflection output increases monotonically with respect to the amount of toner, but the amount of change is smaller than that of the specular reflection output. By removing the diffuse reflection component obtained from the diffuse reflection output from the specular reflection output, an output correlated with density (solid line 403) is obtained. Hereinafter, the output of the density sensor 218 obtained in this way (solid line 403) will also be called the sensor output or sensor output voltage. The sensor output of the density sensor 218 is output to the printer control unit 700, which will be described later, and is used by the printer control unit 700 for detecting the presence or absence of toner images and density detection.

[0034] Figure 4(a) is a schematic diagram illustrating the formation of a toner image on the intermediate transfer belt 205 in the image forming apparatus 200. The arrows in Figure 4(a) indicate the position (rotational position) [mm] in the rotational direction (hereinafter also referred to as the rotational direction) of the intermediate transfer belt 205, with the reference position on the intermediate transfer belt 205 (hereinafter referred to as the reference position) being 0 mm. 501 indicates the toner image formed on the intermediate transfer belt 205. Here, in order to show the sensor output for both the toner image 501 and the overlapping portion 228 due to polishing, the toner image 501 was formed so as not to overlap with the overlapping portion 228. In Example 1, the length of the overlapping portion 228 is 20 mm. The toner image 501 is 40 mm, which is longer than the length of the overlapping portion 228. Both lengths are the lengths in the rotational direction of the intermediate transfer belt 205.

[0035] Figure 4(b) shows the sensor output at each position across the entire intermediate transfer belt 205 in the state shown in Figure 4(a). In Figure 4(b), the horizontal axis represents the rotational position [mm] of the intermediate transfer belt 205, and the vertical axis represents the sensor output voltage [V]. The horizontal axis corresponds to the horizontal axis in Figure 4(a). Around 400 mm, where the toner image 501 is formed, the sensor output voltage decreases. Also, around 600 mm, which corresponds to the position of the overlapping portion 228, the sensor output voltage decreases. Excluding these areas, the sensor output voltage around the entire circumference of the intermediate transfer belt 205 is approximately 2.5V. In contrast, at the location of the toner image 501 and the overlapping portion 228, the sensor output voltage drops to approximately 1.3V. That is, when the density sensor 218 detects reflected light from the second portion, the overlapping portion 228 or the toner image 501, it outputs a different voltage than when it detects reflected light from the first portion, the non-overlapping portion 229.

[0036] Although not shown in the diagram, the sensor output voltage also drops to about 1.3V when the toner image overlaps with the overlapping area 228. In other words, simply by looking at the sensor output voltage value, it is not possible to determine whether the voltage drop is due to the toner image 501, the overlapping area 228, or the region where the toner image and the overlapping area 228 overlap.

[0037] Figure 5(a) is a schematic diagram illustrating the situation in the image forming apparatus 200 when the reflectivity of the intermediate transfer belt 205 decreases due to an unexpected disturbance. The range of rotational position is a part of the non-overlapping area 229 (approximately 100 mm to approximately 500 mm), excluding the overlapping area 228 due to the polishing process. The same reference numerals are used for components similar to those in Figure 4(a). 502 indicates the formed toner image, and its length is 40 mm, the same as the toner image 501 in Figure 4(a).

[0038] Figure 5(b) shows the sensor output voltage [V] for each position within the same range of rotational positions as in Figure 5(a), under the conditions shown in Figure 5(a). The vertical axis, horizontal axis, etc., represent the same as in Figure 4(b). Unexpected disturbance factors include excessive adhesion of toner and external additives to the intermediate transfer belt 205 due to long-term use. Also, for example, since the adhering material does not necessarily adhere uniformly across the entire surface of the intermediate transfer belt 205, the amount of decrease in the sensor output voltage may vary depending on the position on the intermediate transfer belt 205. Here, the toner image 502 and the sensor output voltage in the region where the sensor output voltage has decreased due to unexpected disturbance factors are shown, so the toner image 502 is formed in the region where the decrease in the sensor output voltage is small.

[0039] Around 250mm, where toner image 502 is formed, the sensor output voltage decreases. Furthermore, a decrease in the sensor output voltage due to disturbances is observed peaking around 150mm and 350mm. Around 450mm, where toner image 502 is absent and the decrease in sensor output voltage due to disturbances is minimal, the sensor output voltage is approximately 2.3V. In contrast, at the location of toner image 502, while the output voltage would be approximately 2.3V if toner image 502 were absent (similar to around 450mm), it drops to approximately 1.3V. Additionally, at the peaks of sensor output voltage decrease due to disturbances around 150mm and 350mm, the output voltage drops to approximately 1.5V.

[0040] Let's assume that a decrease in the sensor output voltage is determined when it falls below a predetermined voltage threshold, for example, 1.8V (dashed line in Figure 5(b)). In this case, the decrease in the sensor output voltage due to the toner image 502 and the decrease in the sensor output voltage due to disturbance factors are both similarly judged as regions where the sensor output voltage has decreased. Although not shown in the figure, the sensor output voltage will also drop if the toner image 502 overlaps with a region where the sensor output voltage has decreased due to disturbance factors. In other words, by looking only at the value of the sensor output voltage, it is not possible to distinguish whether the voltage decrease is due to the toner image 502, due to disturbance factors, or due to an overlap of both. In this sense, the region in which the sensor output voltage decreases due to disturbance factors is also included in the second part.

[0041] [Hardware Block Diagram] Figure 6 is a hardware block diagram of the image forming apparatus 200 of Embodiment 1. The printer control unit 700 has circuits such as a CPU 703, ROM 704, RAM 705, and video interface 702, and executes a program to control each device in the image forming apparatus 200. For example, the CPU 703 controls the image forming apparatus 200 while using RAM 705 as a temporary work area according to a program stored in ROM 704.

[0042] The controller 202 is connected to the printer control unit 700 via the video interface 702 and, according to the settings of the host computer 701, issues instructions to the printer control unit 700 to start image formation via a wired or wireless network or printer cable. The controller 202 sends an image formation reservation command to the printer control unit 700 via the video interface 702 in accordance with the print command from the host computer 701. When the controller 202 is ready to form an image, it sends an image formation start command to the printer control unit 700.

[0043] The display unit 230 is capable of communicating with the controller 202 and the printer control unit 700. The display unit 230 displays messages indicated by the printer control unit 700. The display unit 230 may also function as an operation unit, having an input section such as a touch panel or various keys for the user to input information. The printer control unit 700 prepares to execute image formation in the order of the image formation reservation commands from the controller 202 and waits for the image formation start command from the controller 202. When the printer control unit 700 receives the image formation start command, it outputs a / TOP signal to the controller 202, which is the reference timing for the output of the video signal, and starts the printing operation according to the image formation reservation command.

[0044] Next, we will describe each actuator connected to the CPU 703. The CPU 703 is connected to the drive circuit 710 for the developer motor 711, the drive circuit 720 for the high-voltage power supply 721, and the drive circuit 730 for the drum motor 731 via the IO port 706. The CPU 703 is also connected to the drive circuit 740 for the scanner unit 207, the drive circuit 750 for the belt motor 751, and the input / output circuit 760 for the density sensor 218.

[0045] The drive circuit 710 drives the developing motor 711 to rotate the developing roller 303. The drive circuit 720 drives the high-voltage power supply 721 and applies high voltage to the developing roller 303, the charging roller 302, and the primary transfer roller 206 (not shown in Figure 6). The drive circuit 730 drives the drum motor 731 to rotate the photosensitive drum 301 and the charging roller 302. The drive circuit 740 drives the scanner unit 207 to irradiate the surface of the photosensitive drum 301 with laser light. The drive circuit 750 drives the belt motor 751 to rotate the intermediate transfer belt 205.

[0046] The input / output circuit 760 causes the light-emitting element 219 of the density sensor 218 to emit light, and the specularly reflected and diffusely reflected light are received by the light-receiving elements 220 and 221. The received light is converted into voltage values ​​by the input / output circuit 760 and input to the printer control unit 700, specifically the CPU 703, via the IO port 706 as specularly reflected output and diffusely reflected output.

[0047] [Functional Block Diagram] The function of the printer control unit 700 in the detection step for the presence or absence of the cartridge 204, which is one of the toner image (or test image) detection steps, will be explained using the functional block diagram in Figure 7. The functions of the printer control unit 700 are executed by the CPU 703 based on the program stored in the ROM 704 and the data stored in the RAM 705. The details of the functions will be explained in order. The image pattern forming unit 807 controls the cartridge 204 and the scanner unit 207. The image pattern forming unit 807 drives the cartridge 204 and the scanner unit 207 to form a toner image of the image pattern, which will be described later, on the intermediate transfer belt 205. The image pattern forming unit 807 functions as a means for forming an image pattern including at least one toner image on the surface of the intermediate transfer belt 205. The belt control unit 808 rotates the intermediate transfer belt 205. The toner detection unit 809 acquires the sensor output voltage [V] of the density sensor 218. The device determination unit 801, which acts as a means for determining the presence or absence of toner, determines that a toner image is present on the surface of the intermediate transfer belt 205 when the sensor output voltage of the toner detection unit 809 is lower than a predetermined threshold. The display control unit 810 receives the determination result from the device determination unit 801, determines a message as the printer control unit 700, and displays it on the display unit 230.

[0048] [Description of the detection process for the test image in Example 1] The printer control unit 700, which is a control means, controls the image forming unit described above to form a toner image on the intermediate transfer belt 205 in order to perform a detection operation to determine the presence or absence of a toner image on the intermediate transfer belt 205 based on the result detected by the density sensor 218. Note that the toner image formed here is not a toner image to be formed on the recording material 203, but a test image. Note that a toner image to be formed on the recording material 203 may be used as the test image. In the detection operation, the printer control unit 700 controls the formation of the test image such that the first length (L1 described later) in the direction of movement of the test image is longer than the second length (L2 described later) in the direction of movement of the second part (overlapping part 228).

[0049] In this embodiment 1, the printer control unit 700 is controlled to perform a detection step to determine whether or not the cartridge 204 (developing unit) is installed in the image forming apparatus 200. The image forming apparatus 200 performs a test image detection step to confirm whether or not the cartridge 204 is installed, in order to prevent situations where the apparatus is operated without the cartridge 204 installed and image formation is not possible. The test image detection step (detection operation) will be described below.

[0050] Figure 8 is a flowchart showing the processing when an operation instruction (hereinafter referred to as an operation instruction) such as printing is received. The circumferential length of the test image is defined as the first length, L1, and the circumferential length of the overlapping portion 228 due to the polishing process is defined as the second length, L2. The length L1 of the test image is set to be longer than the length L2 of the overlapping portion (L1 > L2). In Example 1, the length L1 is 40 mm and the length L2 is 20 mm. The time it takes for the intermediate transfer belt 205 to rotate for a length of L1 is defined as the first time, which is the rotation time of the test image, TL1. The time it takes for the intermediate transfer belt 205 to rotate for a length of L2 is defined as the second time, which is the rotation time of the overlapping portion 228, TL2. In the following, the rotation of the intermediate transfer belt 205 is assumed to be performed at the same speed. Therefore, the relationship between the magnitude of the rotation distance and the rotation time is the same (L1 > L2, TL1 > TL2).

[0051] In the detection operation, the printer control unit 700 determines the presence or absence of a test image on the intermediate transfer belt 205 based on the result detected by the density sensor 218, the first time (TL1), and the second time (TL2). The first time, rotation time TL1, is the time it takes for the test image to pass the density sensor 218 as the intermediate transfer belt 205 moves. The second time, rotation time TL2, is the time it takes for the second overlapping portion 228 to pass the density sensor 218 as the intermediate transfer belt 205 moves.

[0052] When the printer control unit 700 receives an operation instruction from the controller 202, the printer control unit 700 starts processing from step (hereinafter referred to as S) 101 onwards. In S101, the printer control unit 700 determines whether or not the cartridge 204 is installed. For example, if the cartridge 204 has a storage means, such as an IC tag, the printer control unit 700 determines that the cartridge is installed if it can access the IC tag, and determines that the installation status is unknown if it cannot access the IC tag. Note that other known methods may be used to determine whether or not the cartridge 204 is installed.

[0053] If the printer control unit 700 determines in S101 that the cartridge is installed, it proceeds to S102. In S102, the printer control unit 700 moves to the instructed operation and terminates processing. If the printer control unit 700 determines in S101 that it cannot determine whether the cartridge is installed, that is, that the installed state of the cartridge 204 is unknown, it proceeds to the test image detection process from 103 onwards. In S103, the printer control unit 700 starts the belt motor 751, drum motor 731, developer motor 711 and high-voltage power supply 721, and once the rotation speed of each motor has stabilized, it forms a test image.

[0054] Here, the test image is formed as a solid image of a predetermined size by, for example, the image forming station SK. The image forming station SK is located at the downstream end in the rotational direction of the intermediate transfer belt 205, which shortens the time it takes for the formed test image to reach the density sensor 218. Furthermore, by forming the test image using only the image forming station SK, toner consumption can be suppressed. Moreover, by using the image forming station SK, i.e., black toner, for the test image, the decrease in the sensor output voltage can be significantly reduced. Note that the test image may be formed using other image forming stations S, and the size, shape, density, etc. of the test image may be varied as long as the purpose of the test image detection process can be achieved. The test image is developed on the photosensitive drum 301, primary transferred to the intermediate transfer belt 205, and then passes through the opposite section of the density sensor 218. The position where the test image (toner image) on the photosensitive drum 301 is primary transferred to the intermediate transfer belt 205 is called the primary transfer section.

[0055] In S104, the printer control unit 700 acquires the output voltage profile P over a total time of TL1 + 2 × TL2, which is the sum of the rotation time TL1 for the test image to pass from its leading to trailing end and the rotation time TL2 before and after that point. The printer control unit 700 determines the presence or absence of the test image using the detection results from the density sensor 218 from two hours earlier than the timing when the leading end of the test image is detected to two hours later than the timing when the trailing end of the test image is detected. The printer control unit 700 can predict the time from when the formation of the test image begins until the primary transferred test image reaches the density sensor 218. For example, the printer control unit 700 can predict the time it takes for the test image to reach the density sensor 218 based on the / TOP timing, the positional relationship between the primary transfer unit and the density sensor 218, the rotation speed of the photosensitive drum 301 and the intermediate transfer belt 205, etc.

[0056] Here, the output voltage profile P refers to the voltage profile of the sensor output. The printer control unit 700 acquires the sensor output voltage from the density sensor 218 at predetermined time intervals during time TL1 + 2 × TL2, that is, it acquires sampling data at predetermined sampling intervals. In S105, as soon as the printer control unit 700 has finished acquiring the output voltage profile P, it moves to the stop process. That is, the printer control unit 700 stops the belt motor 751, drum motor 731, developer motor 711, etc. The stop process may include the removal of the test image on the intermediate transfer belt 205 by the cleaning blade 216.

[0057] In S106, the printer control unit 700 analyzes the output voltage profile P acquired in S104 and extracts intervals (I = 1 to n) in which the sensor output voltage is below a predetermined value. Here, n is the number of samples of the output voltage profile P and is a positive integer. The time of each interval (I) is defined as the output reduction time Td(I). The output reduction time Td(I) will be described later.

[0058] In S107, the printer control unit 700 determines whether there exists an output reduction time Td(I) within the range of rotation time TL1 or more and time TL1+TL2 or less (TL1≦Td(I)≦(TL1+TL2)). In S107, the printer control unit 700 determines that there exists a time Td(I) such that TL1≦Td(I)≦(TL1+TL2), and proceeds to S108; otherwise, it proceeds to S109. In S108, the printer control unit 700 determines that the test image has been successfully detected by the device determination unit 801 (detection present) and that the cartridge 204 is installed (installed), and proceeds to S102. The printer control unit 700 determines that the test image has been formed on the intermediate transfer belt 205 if the time during which the voltage value output from the density sensor 218 has been continuously below a predetermined value (threshold 1.8V) is within the range of 1 hour or more and less than or equal to the sum of 1 hour and 2 hours.

[0059] In S109, the printer control unit 700 determines that the test image detection result is either "not detected" or "detection unknown" as described later. In S110, the printer control unit 700 notifies the display unit 230 that there is no cartridge 204 (no cartridge) or that detection is unknown, and thereafter ends the process without performing the next step. Note that the start of S106 may be during the operation of S105. Further, the execution timing of this step may be other than when the printer control unit 700 receives an operation instruction.

[0060] (Reason for performing the determination process of S107) The reason for checking in S107 whether any of the output decrease times Td(I) is within a predetermined range (TL1≦Td(I)≦(TL1+TL2)) will be described using Table 1. Table 1 shows the determination content by the apparatus determination unit 801 regarding the presence or absence of test image detection when the output decrease time Td(I) in a specific section is within or outside the predetermined range, respectively. [Table 1] In Table 1, the first column shows the output decrease time Td, the second column shows the division names (R1, R2, R3) assigned to each range, the third column shows the specific range (region), and the fourth column shows the test image detection status (not detected, detected, detection unknown) in each range. Here, the division R1 is defined as the case where Td(I) is in the range less than TL1 (Td<TL1), and the division R2 is defined as the case where Td(I) is in the range from TL1 to "TL1+TL2" (TL1≦Td≦TL1+TL2). The division R3 is defined as the case where Td(I) is in the range greater than TL1+TL2 (TL1+TL2<Td).

[0061] If the output reduction time Td(I) is less than TL1, which is category R1, the device determination unit 801 determines that the output reduction time Td(I) is a disturbance shorter than the test image, specifically a disturbance including the overlapping portion 228, and determines that there is no toner image, resulting in "no detection" (S109). The printer control unit 700 determines that a test image has not been formed on the intermediate transfer belt 205 if the time during which the voltage value output from the density sensor 218 has been continuously below a predetermined value is shorter than the first time.

[0062] If the output reduction time Td(I) is longer than "TL1 + TL2", in category R3, the device determination unit 801 determines that the output reduction time Td(I) is affected by disturbances due to unexpected factors. The device determination unit 801 cannot determine whether or not a test image was formed during the output reduction time Td(I), and therefore determines that it is "undetectable" and cannot determine whether or not a toner image is present (S109). The printer control unit 700 determines that it is unclear whether or not a test image was formed on the intermediate transfer belt 205 if the time during which the voltage value output from the density sensor 218 was continuously below a predetermined value is longer than the sum of the first time and the second time.

[0063] Unexpected factors that may cause a decrease in the reflectivity of the intermediate transfer belt 205 surface include, for example, excessive adhesion of toner, external additives, etc., to the intermediate transfer belt 205 due to long-term use. On the other hand, in category R2 where the output reduction time Td(I) is TL1 ≤ Td(I) ≤ TL1 + TL2, the device judgment unit 801 determines that "detection present" in the test image.

[0064] (Regarding the derivation of the output decay time Td(I)) Next, we will explain the specific method of S106, which involves analyzing the output voltage profile P to derive the output reduction time Td(I). Figure 9(a) shows the sensor output voltage for approximately one full rotation (0mm to 800mm) of the intermediate transfer belt 205. In Figure 9(a), the horizontal axis shows the circumferential position (circumferential position) [mm] relative to a predetermined position on the intermediate transfer belt 205, and the vertical axis shows the sensor output voltage [V] obtained at each circumferential position. The diamonds in the graph indicate sampling data obtained by the concentration sensor 218.

[0065] As mentioned above, the sensor output voltage fluctuates depending on the position of the intermediate transfer belt 205, and the sensor output voltage in the overlapping section 228 decreases significantly in the area within the dashed frame shown in Figure 9(a). Figure 9(b) is a schematic diagram showing an enlarged view of the sensor output voltage near the area indicated by the dashed frame in Figure 9(a), and the area on the intermediate transfer belt 205 corresponding to that circumferential position. In Figure 9(b), the horizontal axis shows the circumferential position [mm] (500mm~600mm) of the intermediate transfer belt 205, and the vertical axis shows the sensor output voltage [V], with the intermediate transfer belt 205 corresponding to that circumferential position shown at the top of the graph. The sensor output voltage [V] is roughly 2.5V in the non-overlapping section 229, while it drops to about 1.3V in the overlapping section 228. The output reduction time Td(I) can be determined by measuring the time it takes for the intermediate transfer belt 205 to rotate while the output voltage falls below a predetermined threshold, for example, 1.8V.

[0066] In S106, the output voltage profile P, i.e., the output reduction time Td(I), is similarly determined within the time period (TL1 + 2 × TL2) mentioned above. For example, if only the overlapping portion 228 is detected by the density sensor 218, the output reduction time Td(I) obtained by analyzing the output voltage profile P will be Td1 as shown in Figure 9(b). The printer control unit 700 then determines that there is "no detection" because Td1 is less than TL1.

[0067] (Test image 'Detection' judgment) Next, the reason for determining that the test image is "detected" when the output decrease time Td(I) satisfies TL1≦Td(I)≦TL1+TL2 in the section R2 will be described. FIG. 10(a) is a schematic explanatory diagram of a region PT for acquiring the output voltage profile P on the intermediate transfer belt 205 when a test image is formed. Reference numeral 503 denotes the formed test image, which has a length of 40 mm. TL1 and TL2 represent times corresponding to the lengths L1 and L2, respectively, which are the aforementioned rotation times. The horizontal axis also indicates the circumferential position [mm] of the intermediate transfer belt 205.

[0068] As described above, the rotation time of the region PT is the time (TL1+2×TL2), which is the sum of the rotation time TL1 during which the test image 503 passes the portion facing the density sensor 218 and the rotation time TL2 before and after that (PT=TL1+2×TL2). FIG. 10(b) shows an output voltage profile P1 as an example for the case of section R2. In this example, Td2 represents the time during which the sensor output voltage continuously falls below the threshold value of 1.8V, and is the output decrease time Td(I) obtained by analyzing the output voltage profile P1. In FIG. 10(b), the horizontal axis represents the circumferential position [mm], and the vertical axis represents the sensor output voltage [V]. In FIG. 10(b), the threshold value of 1.8V is also indicated by a broken line. Furthermore, FIG. 10(b) also shows vertical broken lines corresponding to the circumferential positions in FIG. 10(a).

[0069] Here, the time Td2 is longer than the rotation time TL1 (Td2>TL1), which is presumed to be because the overlapping portion 228 is located at the position shown in FIG. 10(a). In FIG. 10(a), a part of the overlapping portion 228 and a part of the test image 503 overlap. Regarding the positional relationship between the test image 503 and the overlapping portion 228, since TL1<Td2<TL1+TL2 is detected here, it is predicted that the two partially overlap.

[0070] On the other hand, in other situations where Td2=TL1 and Td2=TL1+TL2 are detected, the following inferences can be made. First, when Td2=TL1 is detected, it can be inferred that either the overlapping portion 228 is not within region PT, or the overlapping portion 228 is included in the test image 503 (hidden beneath the test image 503).

[0071] Furthermore, if Td2 = TL1 + TL2 is detected, it can be inferred that the overlapping portion 228 is connected at its ends either before or after the test image 503. Here, being connected at the ends before the test image 503 means that in the circumferential direction (rotational direction) of the intermediate transfer belt 205, the rear end of the overlapping portion 228 is continuous with the front end of the test image 503. Being connected at the ends after the test image 503 means that in the circumferential direction (rotational direction) of the intermediate transfer belt 205, the front end of the overlapping portion 228 is continuous with the rear end of the test image 503. As described above, regardless of the position of the overlapping portion 228 in region PT, if TL1 ≤ Td2 ≤ TL1 + TL2, it can be inferred that the test image 503 has been detected.

[0072] [Explanation of the conventional test image detection process] Next, as a comparative example, the conventional test image detection process will be explained using Figure 11. Figure 11 is a flowchart showing the process by which the conventional test image detection process, as a comparative example, is executed. Note that steps S201 to S203 in Figure 11 are the same as steps S101 to S103 in Figure 8, and therefore the explanation will be omitted.

[0073] During the rotation time TL1 in which the test image is developed, primary transferred, and passes the opposite part of the density sensor 218, the printer control unit 700 acquires the output voltage profile P2 in S204. The process in S205 is the same as the process in S105 in Figure 8, and therefore the explanation is omitted. In S206, the printer control unit 700 analyzes the output voltage profile P2 acquired in S204 and determines whether the sensor output voltage has been continuously decreasing to or below a predetermined value during this time period. If the printer control unit 700 determines in S206 that the sensor output voltage has been continuously decreasing to or below a predetermined value, the process proceeds to S207. The process in S207 is the same as the process in S108 in Figure 8, and therefore the explanation is omitted. On the other hand, if the printer control unit 700 determines in S206 that the sensor output voltage has not been continuously decreasing to or below a predetermined value, the process proceeds to S208. The processes in S208 and S209 are the same as the processes in S109 and S110 in Figure 8, and therefore the explanation is omitted. Note that the processing of S206 may begin while S205 is running.

[0074] [Comparison of accuracy under control between the comparative example and Example 1] Next, we will describe a comparison of the accuracy of the conventional control (Figure 11), which is a comparative example, and the test image detection of Example 1 (Figure 8) when moving on to the test image detection process. Table 2 shows a comparison of the possibility of false detection of test images in the control methods of Example 1 and the conventional example. [Table 2] Table 2 shows the relationship between the length of the test image (test image length) L1 and the length of the overlapping portion 228 (polished overlapping portion length) L2 (L1>L2, L1≦L2) in the first column, and the possibility of false detection of the test image in the second column. In the second column, for each of Example 1 and Comparative Example, the presence or absence of false detection with the overlapping portion 228 (present, absent) and the possibility of false detection with the reflectance change region (high, low) are shown for each of the two relationships between lengths L1 and L2.

[0075] In the control of the comparative example, when L1 ≤ L2, it is impossible to distinguish between the overlapping area 228 and the reflectance change area when the test image overlaps, so the possibility of false detection is high. When L1 > L2, there is no false detection between the test image and the overlapping area 228. However, in the reflectance change area, if the change in reflectance progresses, in other words, if the decrease in the sensor output voltage in the reflectance change area progresses to below the threshold and its length in the circumferential direction becomes longer than length L1, false detection occurs. That is, if any part of the area with a length of L1 or more passes through the time period during which the density sensor 218 acquires the output voltage profile P2, it will be falsely detected as a test image. In other words, the more the change in reflectance progresses, the higher the probability of false detection, and the possibility of false detection is high.

[0076] On the other hand, in Example 1, L1 ≤ L2 is not satisfied, and L1 > L2 is set, so there is no false detection of the test image and the overlapping portion 228. Furthermore, regarding the reflectance change region, false detection only occurs when the change in reflectance progresses and its length falls exactly within the range of section R2 in Table 1, and only when that region passes through the time period during which the output voltage profile P is acquired, so the possibility of false detection is low.

[0077] In summary, compared to the comparative example, the control in Example 1 reduces the probability of false detections and improves the reliability of the test image detection process. While Example 1 shows an example where the presence or absence of cartridge 204 is determined by the test image detection process, the purpose of test image detection is not limited to this, and the presence or absence of detection may be used for other determinations.

[0078] Furthermore, the comparison target for setting the length L1 of the test image described above is not limited to overlapping areas due to the polishing process, but applies to all cases with different reflectances, as long as there are areas on the intermediate transfer belt with different optical properties that occur during manufacturing, etc. Also, it is not limited to areas with different specular reflected light quantities, but also areas with different diffuse reflected light quantities. In other words, it is applicable to areas on the intermediate transfer belt 205 with different optical properties. Also, the change in reflected light quantity is not limited to a decrease, but can also be an increase. Regarding the number of polishing cycles for overlapping areas due to the polishing process, as mentioned above, it is not limited to the difference between 1 and 2 cycles, but any difference is sufficient. Furthermore, although the detection time was set to (TL1 + 2 × TL2) in the above description, it does not have to be exactly this time, and a margin may be given to consider detection errors. For example, a configuration in which a 2 mm margin is given for judgment is also included in the present invention.

[0079] According to the control method of the embodiment described above, even if there are overlapping processing areas or areas with changed reflectivity due to long-term use on the intermediate transfer belt, the probability of false detection of the test toner image can be reduced, and the reliability of test image detection can be improved. The intermediate transfer belt may experience a decrease in reflectivity due to overlapping surface treatment areas, or a decrease in reflectivity over a wide area due to excessive adhesion of toner, etc., due to long-term use. Even when using such an intermediate transfer belt, the probability of false detection of the toner image can be reduced, and the reliability of test image detection can be improved.

[0080] As described above, according to Example 1, when detecting toner formed on an intermediate transfer material having regions with different optical properties using an optical sensor, the detection accuracy can be improved. [Examples]

[0081] In Example 2, a method for further improving the reliability of test image detection is described by clarifying the operation when the test image detection result is unknown during the test image detection process. Note that the same reference numerals are used for the same components as in Example 1, and their explanations are omitted.

[0082] [Explanation of the intermediate transfer belt configuration] Figure 12(a) is an enlarged schematic view of the intermediate transfer belt 205 as seen from the cross-sectional direction. The intermediate transfer belt 205 is endless in shape and consists of a base layer 242 and a surface layer 243. In Example 1, the surface layer 243 is in contact with the cleaning blade 216, and the base layer 242 is in contact with the drive roller 217 and the secondary transfer opposing roller 212. The base layer 242 is made of polyethylene naphthalate resin as the base material and is mixed with a conductive material, with a volume resistivity of 1 × 10⁻⁶ 10 The volume resistivity was adjusted to be Ω·cm. The volume resistivity was obtained using a measurement probe compliant with JIS method K6911, with an ADVANTEST R2340 high-resistivity meter, at a temperature of 25°C, relative humidity of 50%, and with a voltage of 50-100V applied.

[0083] Furthermore, the layer thickness of the intermediate transfer belt 205 is, for example, 70 μm. In the configuration of Example 2, polyethylene naphthalate resin was used as the base material, but it is not limited to this. The base material must have appropriate charge decay characteristics and flexibility to deform to conform to the shape of the contact member, and thermoplastic resins are generally used. Specifically, examples include polyimide, polyester, polycarbonate, polyarylate, acrylonitrile butadiene styrene copolymer (ABS), polyphenylene sulfide (PPS), polyvinylidene fluoride (PVdF), etc., either alone or in mixtures.

[0084] The surface layer 243 is based on acrylic resin, with zinc oxide dispersed as an electrical resistance modifier. The layer thickness is, for example, about 3 μm. From the viewpoint of strength, such as abrasion resistance and crack resistance, a resin material (curable resin) is preferable for the surface layer 243 among curable materials, and in particular, an acrylic resin obtained by curing an unsaturated double bond-containing acrylic copolymer is preferable. To improve the abrasion resistance of the surface of the cleaning blade 216 during long-term use, the surface layer 243 of the intermediate transfer belt 205 is made with a fine uneven surface. In the configuration of Example 2, imprint processing is adopted from the viewpoint of processing cost, productivity, and shape accuracy.

[0085] Figure 12(b) shows a schematic diagram of a magnified portion of the surface of the intermediate transfer belt 205. H indicates the direction of rotation, and I indicates the direction perpendicular to the direction of rotation H. Imprinting is performed by pressing the imprinting die against the surface of the intermediate transfer belt 205, and then moving the intermediate transfer belt 205 in the direction of rotation. As a result, grooves (recesses 245) are formed on the surface of the intermediate transfer belt 205 along the direction of movement of the intermediate transfer belt 205, and the grooves (recesses 245) are spaced at predetermined intervals with respect to the width direction of the intermediate transfer belt 205. In other words, the imprinted intermediate transfer belt 205 has protrusions 244 that are almost uniform with respect to the direction of rotation H and periodic in the direction I, and recesses 245 as regions having grooves. The distance between the protrusions 244 and the protrusions 244 (or between the recesses 245 and the recesses 245) is denoted by w.

[0086] The groove shape (recessed shape) on the intermediate transfer belt 205 is created by starting the imprinting process in the H direction from the starting position 246 and continuing until the end position 247. In other words, according to the imprinting process in this embodiment, grooves (recesses 245) are formed from the starting position 246 to the end position 247 with respect to the movement direction of the intermediate transfer belt 205. Furthermore, as shown in Figure 12(a), by performing the imprinting process to create a recessed shape by pressing a predetermined die against the surface, protrusions 244a are formed on the surface of the intermediate transfer belt 205 at positions adjacent to the recesses 245. These protrusions 244a are formed when the surface layer 243 is raised by pressing the die, and this is the configuration obtained by the imprinting process in this embodiment. The projection 244a is provided at the end of the convex portion 244 adjacent to the concave portion 245 in the width direction of the intermediate transfer belt 205, which is perpendicular to the direction of movement of the intermediate transfer belt 205, and protrudes from the surface of the intermediate transfer belt 205 defined by the height of the center position of the convex portion 244. Here, the dashed line L11 in Figure 12(a) indicates the height position of the surface of the intermediate transfer belt 205 defined by the height of the center position of the convex portion 244.

[0087] Since the end position 247 of the imprint process is located beyond the start position 246, a first non-overlapping portion 249 and a second overlapping portion 248, which is a region with optically different characteristics from the first portion, are formed. The recesses 245 in the overlapping portion 248 are highly likely to be misaligned in the I direction. This is due to the intermediate transfer belt 205 moving in the I direction during the imprint process. When this misalignment occurs, the ratio of the recesses 245 to the entire surface, i.e., the ratio of the groove's occupied area, increases in the overlapping portion 248 compared to the non-overlapping portion 249. Also, since the overlapping portion 248 undergoes two imprint processes, the depth of the recesses 245 becomes greater. For these reasons, the amount of specularly reflected light decreases in the overlapping portion 248 compared to the non-overlapping portion 249 when light is shone on it. However, since the depth is considerably small compared to the layer thickness, there is no difference in transferability between the two.

[0088] Thus, the intermediate transfer belt 205 of Example 2 is subjected to a textured surface on which the toner image is formed, in which recesses 245 and protrusions 244 are formed alternately in a direction perpendicular to the direction of movement. The overlapping portion 248, which is the second portion, has a greater proportion of recesses 245 formed in the direction perpendicular to the direction of movement than the proportion of recesses 245 formed in the overlapping portion 248, which is the first portion, and therefore has different optical properties from the first portion.

[0089] [Description of the test image detection process in Example 2] The following describes the test image detection process in Example 2. Figure 13 is a flowchart of the processing when an operation instruction is received. The circumferential length of the test image is L3, and the circumferential length of the overlapping portion 248 is L4. The length L3 of the test image is set to be longer than the length L4 of the overlapping portion 248 (L3 > L4). In Example 2, length L3 is set to 40 mm, for example, and length L4 is set to 15 mm. The time required for the intermediate transfer belt 205 to rotate by length L3 is defined as rotation time TL3, and the time required to rotate by length L4 is defined as rotation time TL4. The number of times the test image has been detected is defined as the number of retries K1. The number of retries K1 is managed by the printer control unit 700 using a counter (not shown), for example.

[0090] The processes in S301 and S302 in Figure 13 are the same as those in S101 and S102 in Figure 8, and therefore the explanation is omitted. If the printer control unit 700 determines that it cannot confirm whether cartridge 204 is installed, it proceeds to S303. In S303, the printer control unit 700 sets the number of retries K1 to its initial value, i.e., 0. The processes in S304 to S309 are the same as those in S103 to S108 in Figure 8, and therefore the explanation is omitted. However, where rotation time TL1 was used in Figure 8, it should be read as rotation time TL3, where rotation time TL2 was used, it should be read as rotation time TL4, and where output reduction time Td(I) was used, it should be read as output reduction time Td(I2). Also, where output voltage profile P was used in Figure 8, it should be read as output voltage profile P3.

[0091] In S308, the printer control unit 700 determines that there is no output reduction time Td(I2) that is within the range of rotation time TL3 or more and rotation time (TL3+TL4) or less, and proceeds to S310. In S310, the printer control unit 700 determines whether there is an output reduction time Td(I2) that is greater than the rotation time (TL3+TL4). In S310, the printer control unit 700 determines that there is no output reduction time Td(I2) that is greater than the rotation time (TL3+TL4), and proceeds to S311. In S311, the printer control unit 700 determines that no test image has been detected. In S312, the printer control unit 700 notifies the display unit 230 that there is no cartridge and terminates processing.

[0092] In S310, if the printer control unit 700 determines that there is an output reduction time Td(I2) that is greater than the rotation time (TL3+TL4), it proceeds to S313. In S313, the printer control unit 700 determines whether the number of retries K1 is 1 (K1=1) or not. In S313, if the printer control unit 700 determines that the number of retries K1 is 1, it proceeds to S314. In S314, the printer control unit 700 determines that the test image could not be detected. In S315, the printer control unit 700 notifies the display unit 230 that the cartridge could not be detected and terminates processing. In S313, if the printer control unit 700 determines that the number of retries K1 is not 1, it proceeds to S316. In S316, the printer control unit 700 updates the number of retries K1 by adding 1 (K=K+1) and returns to processing S304. In Example 2, the retry count K1 was set to 1 by setting the condition K1=1 in the decision process in S313. Note that the retry count K1 is not limited to 1 and may be set to any other number.

[0093] As described above, the number of retries K1 is set to a predetermined number of times, and if cartridge detection is unclear in the first test image detection step, the test image detection step is executed multiple times. By performing the detection step multiple times, test images are formed at different positions on the intermediate transfer belt 205. This increases the accuracy of test image detection, and more reliable detection results can be obtained when the control shown in Figure 13 is completed. Note that the control of Example 2 may be applied to the intermediate transfer belt 205 that has undergone polishing in Example 1. Also, the control of Example 1 may be applied to the intermediate transfer belt 205 that has undergone imprint processing in Example 2.

[0094] As described above, according to Example 2, when detecting toner formed on an intermediate transfer material having regions with different optical properties using an optical sensor, the detection accuracy can be improved. [Explanation of symbols]

[0095] 205 Intermediate Transfer Belt 207 Scanner Unit 218 Concentration Sensor 301 Photosensitive drum 303 Developing Roller 700 Printer Control Unit

Claims

1. An endless intermediate transfer body having a first portion in the direction of movement and a second portion having different optical properties from the first portion in the direction of movement, Image forming means for forming a toner image on the intermediate transfer body, A detection means having a light source that irradiates light onto the surface of the intermediate transfer body or the toner image formed on the intermediate transfer body, and detecting reflected light reflected by the intermediate transfer body or the toner image formed on the intermediate transfer body by irradiating the intermediate transfer body or the toner image formed on the intermediate transfer body with light from the light source, and outputting a voltage value, A control means controls the image forming means to form the toner image on the intermediate transfer medium in order to perform a detection operation that determines the presence or absence of the toner image on the intermediate transfer medium based on the result detected by the detection means, Equipped with, The toner image formed on the intermediate transfer medium in the detection operation is a test image used for the detection operation. The control means controls the image forming means to form a plurality of toner images at different positions on the intermediate transfer body, and performs the detection operation for each of the plurality of toner images. The control means determines, based on a voltage value output when reflected light from the second portion or the toner image is detected by the detection means, which is different from the voltage value output when reflected light from the first portion is detected, whether the time during which the voltage value has been continuously below a predetermined value is longer than a predetermined time for each of the plurality of toner images, and determines, based on the result of the determination for each of the plurality of toner images, that the toner image is formed on the intermediate transfer body. An image forming apparatus characterized by the following:

2. When the time during which each of the plurality of toner images passes the detection means as the intermediate transfer body moves is defined as the first time, and the time during which the second portion passes the detection means as the intermediate transfer body moves is defined as the second time, The image forming apparatus according to claim 1, characterized in that the control means uses the results detected by the detection means for each of the plurality of toner images between a timing two hours earlier than the timing when the detection means detects reflected light from the leading edge of the toner image and a timing two hours later than the timing when the detection means detects reflected light from the trailing edge of the toner image.

3. An image carrier on which an electrostatic latent image is formed, A developing unit having toner and developing means for developing the electrostatic latent image on the image carrier with the toner to form a toner image, Equipped with, The developing unit is detachable from the image forming apparatus. The image forming apparatus according to claim 1 or 2, characterized in that the control means controls the detection operation to determine whether or not the developing unit is mounted on the image forming apparatus.

4. The intermediate transfer body is subjected to polishing on the surface on which the toner image is formed. The image forming apparatus according to claim 3, characterized in that the second part has different optical properties from the first part because it is subjected to the polishing process more times than the first part.

5. The intermediate transfer body has a surface on which the toner image is formed that is subjected to a textured surface in which recesses and protrusions are formed alternately in a direction perpendicular to the direction of movement. The image forming apparatus according to claim 3, characterized in that the second portion has different optical characteristics from the first portion, in which a larger proportion of the recesses are formed in a direction perpendicular to the direction of movement than the proportion occupied by the recesses formed in the first portion.

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