Sensor device and image forming apparatus

Abstract

To suppress changes in the detection results of a sensor device due to changes in the temperature of a light-emitting element without requiring a processing device. [Solution] The sensor device 8 is a sensor device 8 that outputs an output signal Sig2 corresponding to the density of the toner image in the image forming apparatus 100, and comprises a light-emitting element 81, a light-receiving element 82, and an impedance element 84. The light-emitting element 81 irradiates light onto an image carrier that holds the toner image. The light-receiving element 82 receives light reflected by the image carrier. The impedance element 84 changes its impedance according to the temperature. The output signal Sig2 is a signal whose magnitude changes according to the amount of light received by the light-receiving element 82. The impedance element 84 is connected to the light-emitting element 81 or the light-receiving element 82 in order to suppress changes in the magnitude of the output signal Sig2 due to changes in the temperature of the light-emitting element 81.

Description

Technical Field

[0001] The present invention relates to a sensor device and an image forming apparatus.

Background Art

[0002] As related art, an image forming apparatus is known that reads a detection image formed on an image carrier with an optical sensor, and detects the image density of the detection image according to the read result (for example, refer to Patent Document 1). The optical sensor includes a light emitting element that irradiates light to the detection image, a light receiving element that receives reflected light, a temperature detection unit that detects the temperature of the optical sensor, and a current adjustment unit that adjusts the amount of current supplied to the light emitting element based on the temperature of the optical sensor.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of Invention

Problems to be Solved by the Invention

[0004] In the configuration shown in the related art described above, correction processing for keeping the light emission amount of the light emitting element constant is executed in order to suppress changes in the detection result of the optical sensor (sensor device) accompanying temperature changes of the light emitting element. Further, in the configuration shown in the related art described above, not only the temperature detection unit but also a current adjustment unit which is a processing device (processor) such as a CPU (Central Processing Unit) is required to execute the correction processing. For this reason, the configuration shown in the related art described above has a problem that the design including the processing device must be performed, which complicates the design of the sensor device.

[0005] An object of the present invention is to provide a sensor device and an image forming apparatus capable of suppressing changes in the detection result of the sensor device accompanying temperature changes of a light emitting element without being provided with a processing device. [Means for solving the problem]

[0006] A sensor device according to one aspect of the present invention is a sensor device that outputs an output signal corresponding to the density of a toner image in an image forming apparatus, and comprises a light-emitting element, a light-receiving element, and an impedance element. The light-emitting element irradiates light onto an image carrier that holds the toner image. The light-receiving element receives light reflected by the image carrier. The impedance element changes its impedance according to the temperature. The output signal is a signal whose magnitude changes according to the amount of light received by the light-receiving element. The impedance element is connected to the light-emitting element or the light-receiving element in such a way as to suppress changes in the magnitude of the output signal due to changes in the temperature of the light-emitting element.

[0007] An image forming apparatus according to another aspect of the present invention comprises the sensor device, an image forming unit, and an adjustment processing unit. The image forming unit includes the image carrier and forms the toner image. The adjustment processing unit adjusts the density of the toner image based on the output signal output by the sensor device. [Effects of the Invention]

[0008] According to the present invention, it is possible to provide a sensor device and an image forming apparatus that can suppress changes in the detection results of a sensor device due to changes in the temperature of a light-emitting element without requiring a processing device. [Brief explanation of the drawing]

[0009] [Figure 1] Figure 1 is a schematic cross-sectional view showing the configuration of an image forming apparatus according to Embodiment 1. [Figure 2] Figure 2 is a schematic block diagram showing the configuration of the image forming apparatus according to Embodiment 1. [Figure 3] Figure 3 is a schematic diagram showing the arrangement of the sensor device according to Embodiment 1. [Figure 4] Figure 4 is a schematic circuit diagram showing the configuration of the sensor device according to Embodiment 1. [Figure 5]Figure 5 is a schematic diagram showing the change in the magnitude of the output signal in response to a change in temperature of the sensor device according to Embodiment 1. [Figure 6] Figure 6 is a schematic circuit diagram showing the configuration of the sensor device according to Embodiment 2. [Figure 7] Figure 7 is a schematic circuit diagram showing other configurations of the sensor device according to Embodiment 2. [Modes for carrying out the invention]

[0010] (Embodiment 1) The embodiments of the present invention will be described below with reference to the attached drawings. The following embodiments are examples that embody the present invention and are not intended to limit the technical scope of the present invention.

[0011] [1] Overall configuration of the image forming apparatus First, the overall configuration of the image forming apparatus 100 according to this embodiment will be described with reference to Figures 1 and 2.

[0012] For the sake of explanation, the vertical direction is defined as the up-down direction D1 when the image forming apparatus 100 is in a usable installation state (as shown in Figure 1). The front-to-back direction D2 is defined with the left side of the image forming apparatus 100 shown in Figure 1 as the front. The left-to-right direction D3 is defined with the front of the image forming apparatus 100 in the above installation state as the reference point.

[0013] The image forming apparatus 100 is a multifunction device having multiple functions, including a scanning function for reading an image from a document, a printing function for forming an image based on the image data, a fax function, and a copying function. The present invention may also be applied to image forming apparatuses such as printers, fax machines, and copiers capable of forming images using an electrophotographic method.

[0014] As shown in Figures 1 and 2, the image forming apparatus 100 comprises an ADF (Auto Document Feeder) 1, an image reading unit 2, an image forming unit 3, a paper feeding unit 4, an operation display unit 5, a storage unit 6, and a control unit 7.

[0015] ADF1 conveys a document to be read by the scan function. The ADF1 includes a document setting section, a plurality of conveyance rollers, a document presser, and a paper discharge section.

[0016] The image reading section 2 implements the scan function. The image reading section 2 includes a document platen, a light source, a plurality of mirrors, an optical lens, and a CCD (Charge Coupled Device).

[0017] The image forming section 3 implements the print function. Specifically, the image forming section 3 forms a color or monochrome image on a sheet supplied from the paper feed section 4 in accordance with an electrophotographic system. The image forming section 3 forms an image using toner. Further, in the process of forming an image on a sheet, the image forming section 3 forms a toner image on an intermediate transfer belt 22 which is an image carrier to be described later. That is, the image forming section 3 includes the intermediate transfer belt 22 (image carrier), and forms a toner image on the intermediate transfer belt 22.

[0018] The paper feed section 4 supplies sheets to the image forming section 3. The paper feed section 4 includes a paper feed cassette, a manual feed tray, and a plurality of conveyance rollers.

[0019] The operation display section 5 is a user interface of the image forming apparatus 100. The operation display section 5 has a display unit such as a liquid crystal display that displays various types of information in response to control instructions from the control section 7, and an operation unit such as operation keys or a touch panel that inputs various types of information to the control section 7 in response to user operations.

[0020] The storage section 6 is a non-volatile storage device. For example, the storage section 6 is a non-volatile memory such as a flash memory. Note that the storage section 6 may be an SSD (Solid State Drive) or an HDD (Hard Disk Drive).

[0021] The control unit 7 comprehensively controls the image forming apparatus 100. The control unit 7 includes a CPU, ROM (Read Only Memory), and RAM (Random Access Memory). The CPU is a processor that performs various arithmetic operations. The ROM is a non-volatile memory device in which information such as control programs for causing the CPU to perform various operations is pre-stored. The RAM is a volatile or non-volatile memory device used as temporary storage memory (work area) for various operations performed by the CPU. The CPU comprehensively controls the image forming apparatus 100 by executing various control programs pre-stored in the ROM.

[0022] Furthermore, the control unit 7 may be a separate control unit from the main control unit that comprehensively controls the image forming apparatus 100. Also, the control unit 7 may be composed of electronic circuits such as an integrated circuit (ASIC (Application Specific Integrated Circuit)).

[0023] Next, the configuration of the image forming unit 3 will be described with reference to Figures 1 and 2. As shown in Figure 1, the image forming unit 3 comprises four image forming units 20, two optical scanning devices 21, an intermediate transfer belt 22, a secondary transfer roller 23, a fixing device 24, and a paper output tray 25. Also, as shown in Figure 2, the image forming unit 3 comprises a density correction unit 30, a voltage application unit 38, a light source 39, and a sensor device 8.

[0024] The four image forming units 20 each form toner images for yellow (Y), cyan (C), magenta (M), and black (K), respectively. As shown in Figure 1, the four image forming units 20 are arranged along the front-to-back direction D2, in the order of yellow, cyan, magenta, and black from the front side of the image forming apparatus 100.

[0025] As shown in Figure 1, each of the four image forming units 20 includes a photoreceptor drum 31, a charging roller 32, a developing device 33, a primary transfer roller 34, a drum cleaning unit 35, and a toner container 36.

[0026] An electrostatic latent image is formed on the surface of the photoreceptor drum 31. The photoreceptor drum 31 rotates in response to rotational driving force supplied from a motor (not shown). This causes the photoreceptor drum 31 to transport the electrostatic latent image formed on its surface.

[0027] The charging roller 32 charges the surface of the photoreceptor drum 31 by receiving a preset charging voltage. For example, the charging roller 32 charges the surface of the photoreceptor drum 31 in a positive polarity. The surface of the photoreceptor drum 31, which has been charged by the charging roller 32, is irradiated with light based on image data emitted from the optical scanning device 21. As a result, an electrostatic latent image is formed on the surface of the photoreceptor drum 31.

[0028] The developing device 33 develops the electrostatic latent image formed on the surface of the photoreceptor drum 31. The developing device 33 comprises a pair of stirring members, a magnetic roller, and a developing roller 37. The pair of stirring members stir the developer containing toner and carrier housed inside the developing device 33. The magnetic roller draws up the developer stirred by the pair of stirring members and supplies the toner contained in the developer to the developing roller 37. The developing roller 37 transports the toner supplied from the magnetic roller to a position opposite the photoreceptor drum 31. The developing roller 37 also receives a preset developing bias voltage and supplies the toner transported to the opposite position to the photoreceptor drum 31. As a result, toner is selectively supplied to the exposure area on the photoreceptor drum 31 that has been irradiated by light emitted from the light scanning device 21, and the electrostatic latent image formed on the surface of the photoreceptor drum 31 is developed. The developing device 33 is supplied with toner from a toner container 36.

[0029] The voltage application unit 38 is a power supply capable of applying a development bias voltage to the developing roller 37. The voltage application unit 38 is provided in accordance with each of the four image forming units 20.

[0030] The primary transfer roller 34 receives a preset primary transfer current and transfers the toner image formed on the surface of the photoreceptor drum 31 to the outer surface of the intermediate transfer belt 22. The primary transfer roller 34 is positioned opposite the photoreceptor drum 31, with the intermediate transfer belt 22 in between.

[0031] The drum cleaning unit 35 removes toner remaining on the surface of the photoreceptor drum 31 after the toner image has been transferred by the primary transfer roller 34.

[0032] The density correction unit 30 corrects the density of the image data to be formed based on predetermined table data. Specifically, the density correction unit 30 corrects the density of the image data to be formed so that the relationship between the density of the image data input to the image forming unit 3 and the density of the image formed by the image forming unit 3 is linear. In other words, the density correction unit 30 performs so-called gamma correction. The table data mentioned above is data that shows the gamma table used for the gamma correction.

[0033] The density correction unit 30 and the table data described above are provided for each printing color. The density correction unit 30 corresponding to Y (yellow) corrects the density of the Y (yellow) image data based on the first table data, which is the table data corresponding to Y (yellow). The density correction unit 30 corresponding to C (cyan) corrects the density of the C (cyan) image data based on the second table data, which is the table data corresponding to C (cyan). The density correction unit 30 corresponding to M (magenta) corrects the density of the M (magenta) image data based on the third table data, which is the table data corresponding to M (magenta). The density correction unit 30 corresponding to K (black) corrects the density of the K (black) image data based on the fourth table data, which is the table data corresponding to K (black).

[0034] The light source 39 emits light based on the image data after density correction by the density correction unit 30. A separate light source 39 is provided for each printing color.

[0035] The two optical scanning devices 21 emit light based on image data toward the surface of the photosensitive drum 31 of each image forming unit 20. The two optical scanning devices 21 are arranged side by side along the front-to-back direction D2.

[0036] Of the two optical scanning devices 21, the front optical scanning device 21 emits light based on yellow (Y) image data toward the photosensitive drum 31 of the image forming unit 20 corresponding to yellow (Y). The front optical scanning device 21 also emits light based on cyan (C) image data toward the photosensitive drum 31 of the image forming unit 20 corresponding to cyan (C). Of the two optical scanning devices 21, the rear optical scanning device 21 emits light based on magenta (M) image data toward the photosensitive drum 31 of the image forming unit 20 corresponding to magenta (M). The rear optical scanning device 21 also emits light based on black (K) image data toward the photosensitive drum 31 of the image forming unit 20 corresponding to black (K). Each of the two optical scanning devices 21 scans the light emitted from the light source 39 to form an electrostatic latent image on the photosensitive drum 31.

[0037] The intermediate transfer belt 22 is an endless belt member onto which the toner images formed on the surface of each of the four photoreceptor drums 31 of the four image forming units 20 are transferred. The intermediate transfer belt 22 is an example of the image carrier of the present invention. The intermediate transfer belt 22 is stretched at a predetermined tension by a drive roller 221 and a tension roller 222. The intermediate transfer belt 22 rotates in the rotational direction D4 as the drive roller 221 rotates in response to rotational driving force supplied from a motor (not shown). As a result, the intermediate transfer belt 22 transports the toner images transferred from each photoreceptor drum 31 to the transfer position to the sheet by the secondary transfer roller 23. After the toner images have been transferred by the secondary transfer roller 23, the outer surface of the intermediate transfer belt 22 is cleaned by a belt cleaning unit (not shown).

[0038] The secondary transfer roller 23 receives a preset secondary transfer current and transfers the toner image transferred to the outer surface of the intermediate transfer belt 22 to the sheet supplied from the paper feeding unit 4. The secondary transfer roller 23 is positioned opposite the drive roller 40, with the intermediate transfer belt 22 in between.

[0039] Here, the axial size (left-right direction D3) of the secondary transfer roller 23 is smaller than the width (size in the left-right direction D3) of the intermediate transfer belt 22. As a result, a non-contact area A2 is created on the outer surface of the intermediate transfer belt 22 that does not come into contact with the secondary transfer roller 23, as shown in Figure 3. The non-contact area A2 is the area on the outer surface of the intermediate transfer belt 22 that is outside the contact area A1 that comes into contact with the secondary transfer roller 23, and includes the end of the intermediate transfer belt 22 in the width direction.

[0040] The fixing device 24 fixes the toner image transferred to the sheet by the secondary transfer roller 23 to the sheet.

[0041] The output tray 25 receives a sheet on which the toner image has been fixed by the fuser unit 24.

[0042] The sensor device 8 detects the density of the toner image transferred to the non-contact area A2 on the outer circumferential surface of the intermediate transfer belt 22. For example, the sensor device 8 is a reflective type photosensor, and multiple sensor devices are arranged side by side along the left-right direction D3. In this embodiment, as shown in Figure 3, the image forming apparatus 100 is equipped with two sensor devices 8, a first sensor device 8α and a second sensor device 8β, and the two sensor devices 8 are arranged side by side along the left-right direction D3. As shown in Figure 1, the sensor device 8 is positioned downstream in the rotation direction D4 from the toner image transfer position by the secondary transfer roller 23, and opposite the tension roller 222. Note that the sensor device 8 is not limited to being positioned opposite the tension roller 222, but may be positioned at other locations. The sensor device 8 outputs an output signal Sig2 (see Figure 4) corresponding to the density of the toner image to be detected to the control unit 7. The configuration of the sensor device 8 will be described in detail later in "[2] Sensor Device".

[0043] Here, the control unit 7 has an adjustment processing unit 71, as shown in Figure 1. Specifically, the ROM of the control unit 7 has an image quality adjustment program pre-stored in it to allow the CPU to function as the adjustment processing unit 71. The CPU then functions as the adjustment processing unit 71 by executing the image quality adjustment program stored in the ROM.

[0044] The image quality adjustment program may be recorded on a computer-readable recording medium such as a CD, DVD, or flash memory, and may be read from the recording medium and stored in a storage device such as the storage unit 6. The adjustment processing unit 71 may also be composed of electronic circuits. Furthermore, the image quality adjustment program may be a program that causes multiple processors to function as the adjustment processing unit 71.

[0045] The adjustment processing unit 71 adjusts the image quality of the output image produced by the toner-based image formation process while the image formation process using the image formation unit 3 is being executed. The image formation process is a process in which the image formation unit 3 forms an image on a sheet based on image data.

[0046] Specifically, the adjustment processing unit 71 adjusts one of several adjustment targets related to the image quality of the output image, selected in a predetermined order, each time a predetermined adjustment condition is met.

[0047] Here, the multiple adjustment targets include the development bias voltage. When the development bias voltage corresponding to any of the image forming units 20 changes, the density of the toner image formed by that image forming unit 20 changes. In other words, the development bias voltage can be said to be an image forming condition related to the image quality (density) of the output image.

[0048] Furthermore, the multiple adjustment targets include the amount of light emitted from the light source 39. When the amount of light emitted from the light source 39 corresponding to any of the print colors changes, the density of the toner image based on the electrostatic latent image formed by that light source 39 changes. In other words, the amount of light emitted from the light source 39 can be said to be an image formation condition related to the image quality (density) of the output image.

[0049] Furthermore, multiple adjustment targets include table data. When the table data corresponding to any of the print colors changes, the density of the toner image formed using that table data changes. In other words, table data can be said to be data related to the image quality (density) of the output image.

[0050] The adjustment processing unit 71 performs the adjustment process when adjusting one of several adjustment targets. During the adjustment process, for example, a detection toner image of Y (yellow) is formed in the non-contact area A2 of the intermediate transfer belt 22. The adjustment process refers to the output signal Sig2 output by the sensor device 8, which corresponds to the density of the detection toner image. Then, during the adjustment process, the adjustment target for the image forming unit 20 corresponding to Y (yellow) is adjusted based on the detection result of the output signal Sig2, that is, the density of the detection toner image. During the adjustment process, the adjustment targets for the image forming units 20 corresponding to other printing colors are adjusted in the same manner as described above. In other words, the adjustment processing unit 71 adjusts the image quality (density) of the output image (image formed on the intermediate transfer belt 22) based on the output signal Sig2 output by the sensor device 8.

[0051] Incidentally, as a related technology, an image forming apparatus is known that reads a detection image formed on an image carrier using a photosensor and detects the image density of the detection image according to the reading result. The photosensor comprises a light-emitting element that irradiates the detection image with light, a light-receiving element that receives reflected light, a temperature detection unit that detects the temperature of the photosensor, and a current adjustment unit that adjusts the amount of current supplied to the light-emitting element based on the temperature of the photosensor.

[0052] In the configuration shown in the related technologies described above, a correction process is performed to maintain a constant light emission level from the light-emitting element in order to suppress changes in the detection result of the light sensor (sensor device) due to changes in the temperature of the light-emitting element. Furthermore, in the configuration shown in the related technologies described above, a current adjustment unit, which is a processing unit (processor) such as a CPU, is required not only for the temperature detection unit but also for the processing unit, is required to perform the correction process. For this reason, the configuration shown in the related technologies described above has the problem that the design of the sensor device becomes complicated because the processing unit must also be included in the design.

[0053] In contrast, in this embodiment, the sensor device 8 described below enables the realization of a sensor device 8 and an image forming apparatus 100 that can suppress changes in the detection results of the sensor device 8 due to changes in the temperature of the light-emitting element, without the need for a processing device.

[0054] [2] Sensor device The configuration of the sensor device 8 will be described in detail below with reference to Figures 3 and 4. In the following, to distinguish it from the sensor device 8 in Embodiment 2 which will be described later, the sensor device 8 in this embodiment will be referred to as "sensor device 8A," and the sensor device 8 in Embodiment 2 will be referred to as "sensor device 8B."

[0055] In this embodiment, as already described, the image forming apparatus 100 includes two sensor devices 8A, a first sensor device 8α and a second sensor device 8β, as shown in Figure 3.

[0056] The first sensor device 8α includes a first light-emitting element 811 (described later) as a light-emitting element 81 and a first light-receiving element 821 (described later) as a light-receiving element 82. In the first sensor device 8α, the first light-emitting element 811 and the first light-receiving element 821 are arranged such that the first light-receiving element 821 receives light that is specularly reflected in the non-contact region A2 of the image carrier (in this embodiment, the intermediate transfer belt 22). Specifically, in the first sensor device 8α, the first light-emitting element 811 and the first light-receiving element 821 are arranged such that the angle of incidence of light incident from the first light-emitting element 811 to the intermediate transfer belt 22 and the angle of reflection of light reflected from the intermediate transfer belt 22 to the first light-receiving element 821 are roughly the same. In other words, the first sensor device 8α can be described as a specular reflection type photosensor device.

[0057] The second sensor device 8β includes a second light-emitting element 812 as a light-emitting element 81 and a second light-receiving element 822 as a light-receiving element 82. In the second sensor device 8β, the second light-emitting element 812 and the second light-receiving element 822 are arranged such that the second light-receiving element 822 receives light that diffuses and reflects in the non-contact area A2 of the image carrier (in this embodiment, the intermediate transfer belt 22). Specifically, in the second sensor device 8β, the second light-emitting element 812 and the second light-receiving element 822 are arranged such that the angle of incidence of light incident from the second light-emitting element 812 to the intermediate transfer belt 22 and the angle of reflection of light that diffuses and reflects from the intermediate transfer belt 22 to the second light-receiving element 822 are different from each other. In other words, the second sensor device 8β can be described as a diffuse reflection type photosensor device.

[0058] In this embodiment, the density of the detection toner image formed in the non-contact area A2 of the intermediate transfer belt 22 is detected using a first sensor device 8α, which is a specular reflection type photosensor, and a second sensor device 8β, which is a diffuse reflection type photosensor. This makes it possible to detect the density corresponding to the K (black) printing color in the detection toner image with the first sensor device 8α, and to detect the densities corresponding to the relatively bright printing colors Y (yellow), M (magenta), and C (cyan) with the second sensor device 8β.

[0059] As shown in Figures 3 and 4, the sensor device 8A is constructed by mounting multiple circuit elements constituting an electrical circuit 83 on a substrate 80. The electrical circuit 83 includes a light-emitting element 81, a light-receiving element 82, and an impedance element 84. In other words, the sensor device 8A comprises a light-emitting element 81, a light-receiving element 82, an electrical circuit 83, and an impedance element 84.

[0060] In this disclosure, "circuit element" refers to an element having a single function, and may include passive elements such as resistors, capacitors, or coils, or active elements such as diodes or transistors. Therefore, "circuit element" does not include ICs (Integrated Circuits) which are made by combining multiple semiconductor elements having a single function into a single package. Furthermore, "circuit element" does not include processing units (processors) such as CPUs, GPUs (Graphics Processing Units), FPGAs (Field Programmable Gate Arrays), and ASICs (Application Specific Integrated Circuits).

[0061] The light-emitting element 81 emits light in response to power supply, irradiating the image carrier (intermediate transfer belt 22) that holds the toner image in the image forming apparatus 100 with light. In this embodiment, the light-emitting element 81 is composed of an LED (Light Emitting Diode) that emits light of a specific color, such as white. The number of LEDs constituting the light-emitting element 81 may be one or multiple. Note that the light-emitting element 81 is not limited to LEDs, but may also be an organic EL (Electro-Luminescence) element or a semiconductor laser, etc.

[0062] The light-receiving element 82 receives light reflected by the image carrier (intermediate transfer belt 22). In this embodiment, the light-receiving element 82 is composed of a phototransistor. The number of phototransistors constituting the light-receiving element 82 may be one or more. Note that the light-receiving element 82 is not limited to a phototransistor, but may also be a photodiode or the like.

[0063] The electrical circuit 83 has multiple circuit elements, including a light-emitting element 81 and a light-receiving element 82. The electrical circuit 83 outputs an output signal Sig2 according to the density of the toner image (in this embodiment, the detection toner image formed on the intermediate transfer belt 22). In other words, the sensor device 8 outputs an output signal Sig2 according to the density of the toner image in the image forming apparatus 100. In this embodiment, the electrical circuit 83 is a discrete circuit composed of multiple circuit elements, each having a single function.

[0064] The impedance element 84 is included in multiple circuit elements and changes its impedance according to the temperature.

[0065] In this embodiment, the impedance element 84 is a thermistor that changes its resistance value in response to temperature changes. More specifically, the impedance element 84 is an NTC (Negative Temperature Coefficient) thermistor that has the characteristic of decreasing impedance (resistance value) as the temperature rises.

[0066] Here, the impedance element 84 is included in the electrical circuit 83 together with the light-emitting element 81 and is positioned near the light-emitting element 81. Therefore, the temperature of the impedance element 84 is approximately the same as the temperature of the light-emitting element 81. Consequently, the impedance element 84 changes its resistance value in response to changes in the temperature of the light-emitting element 81.

[0067] As shown in Figure 4, the electrical circuit 83 includes a light-emitting circuit 831 containing a light-emitting element 81 and a light-receiving circuit 832 containing a light-receiving element 82. The light-emitting circuit 831 and the light-receiving circuit 832 are spaced apart on the surface of the substrate 80 and are electrically insulated from each other. In this embodiment, the impedance element 84 is included in the light-emitting circuit 831.

[0068] The light-emitting circuit 831 has an amplifying element 85 that amplifies the input current I1 and supplies it to the light-emitting element 81. In this embodiment, the amplifying element 85 is an NPN type bipolar transistor. Therefore, the input current I1 is the base current input to the base of the amplifying element 85. Note that the amplifying element 85 is not limited to an NPN type bipolar transistor, but may be, for example, a FET (Field Effect Transistor).

[0069] The base of the amplification element 85 is connected to the first terminal of the resistor element R1. The second terminal of the resistor element R1 is connected to the anode of the first voltage source S1. The cathode of the first voltage source S1 is grounded. The first voltage source S1 is a constant voltage source that outputs a constant DC voltage of several volts, for example.

[0070] The base of the amplification element 85 and the first terminal of the resistor R1 are connected to the first terminal of the impedance element 84. The second terminal of the impedance element 84 is connected to the first terminal of the resistor R2. The second terminal of the resistor R2 is grounded. In other words, the impedance element 84, together with the resistor R2, forms a series circuit connected to the base of the amplification element 85 and the first terminal of the resistor R1. Note that the order in which the impedance element 84 and the resistor R2 are connected in the series circuit may be reversed.

[0071] The collector of the amplification element 85 is connected to the cathode of the light-emitting element 81. The anode of the light-emitting element 81 is connected to the anode of the second voltage source S2. The cathode of the second voltage source S2 is grounded. The second voltage source S2 is a constant voltage source that outputs a constant DC voltage of several volts, for example. The emitter of the amplification element 85 is connected to the first terminal of the resistor R3. The second terminal of the resistor R3 is grounded.

[0072] The base current (input current I1) of the amplifying element 85 is amplified according to the amplification factor of the amplifying element 85 and supplied to the light-emitting element 81 as collector current. As a result, the light-emitting element 81 emits light with an intensity corresponding to the magnitude of the supplied collector current.

[0073] In the light-emitting circuit 831, each of the resistive elements R1, R2, and R3 may be one or more. Also, the impedance element 84 may be one or more.

[0074] The light-receiving circuit 832 has a light-receiving element 82, which is a phototransistor whose voltage across its terminals changes according to the amount of light received. In this embodiment, the voltage across its terminals represents the collector-emitter voltage of the light-receiving element 82. The collector of the light-receiving element 82 is connected to the anode of the third voltage source S3. The cathode of the third voltage source S3 is grounded. The third voltage source S3 is a constant voltage source that outputs a constant DC voltage of, for example, several volts.

[0075] The emitter of the light-receiving element 82 is connected to the first terminal of the resistor R4. The second terminal of the resistor R4 is grounded. The emitter of the light-receiving element 82 is also connected to the first terminal of the resistor R5. The second terminal of the resistor R5 is connected to the non-inverting input terminal of the amplifier 86. The second terminal of the resistor R5 and the non-inverting input terminal of the amplifier 86 are connected to the first terminal of the capacitor C1. The second terminal of the capacitor C1 is grounded.

[0076] The inverting input terminal of the amplifier 86 is connected to the first end of resistor R6. The second end of resistor R6 is grounded. The inverting input terminal of the amplifier 86 is also connected to the first end of resistor R7. The second end of resistor R7 is connected to the output terminal of the amplifier 86.

[0077] In the light receiving circuit 832, each of the resistive elements R5, R6, and R7 may be one or more.

[0078] [3] Operation of electrical circuits The operation of the electrical circuit 83 is described below. In the light-emitting circuit 831, the light-emitting element 81 emits light when collector current is supplied to it. In the light-receiving circuit 832, the light-receiving element 82 receives reflected light from the image carrier (intermediate transfer belt 22), resulting in a voltage across its terminals (collector-emitter voltage) corresponding to the amount of light received. The charging voltage V1 of the capacitor C1 is input to the non-inverting input terminal of the amplification unit 86. The charging voltage V1 of the capacitor C1 changes according to the collector-emitter voltage of the light-receiving element 82. Specifically, the charging voltage V1 of the capacitor C1 decreases as the collector-emitter voltage of the light-receiving element 82 increases, and increases as the collector-emitter voltage decreases. The amplification unit 86 then amplifies the input voltage of the non-inverting input terminal (charging voltage V1 of the capacitor C1) and outputs it as an output signal Sig2. In other words, the amplification unit 86 amplifies the electrical signal Sig1 (in this case, the charging voltage of capacitor C1), which changes in magnitude according to the amount of light received by the light-receiving element 82, and outputs it as an output signal Sig2. The amplification factor of the amplification unit 86 is the value obtained by dividing the resistance value of resistor R7 by the resistance value of resistor R6.

[0079] In other words, in the electrical circuit 83, when the amount of light emitted by the light-emitting element 81 increases, the amount of light received by the photodetector 82 increases, and the input voltage of the non-inverting input terminal of the amplifier 86 decreases, causing the output signal Sig2 to decrease. On the other hand, when the amount of light emitted by the light-emitting element 81 decreases, the amount of light received by the photodetector 82 decreases, and the input voltage of the non-inverting input terminal of the amplifier 86 increases, causing the output signal Sig2 to increase. In short, the output signal Sig2 is a signal whose magnitude changes according to the amount of light received by the photodetector 82.

[0080] In this embodiment, if the light-emitting circuit 831 does not have an impedance element 84, the magnitude of the base current (input current I1) input to the base of the amplifying element 85 is determined by the output voltage of the first voltage source S1 and the resistance values ​​of the resistors R1, R2, and R3. In this embodiment, the impedance element 84 is connected in series with the resistor R2 as described above. In other words, the impedance element 84 is connected in series with the circuit element (resistor R2) that determines the magnitude of the input current I1 among the multiple circuit elements of the electrical circuit 83. Therefore, in this embodiment, the magnitude of the input current I1 is determined by the output voltage of the first voltage source V1, the resistance values ​​of the resistors R1, R2, and R3, and the impedance of the impedance element 84.

[0081] Furthermore, the impedance (resistance) of the impedance element 84 changes depending on the temperature of the impedance element 84, and consequently, the temperature of the light-emitting element 81. The resistance of the impedance element 84 is one of the factors that determine the magnitude of the input current I1. Therefore, as the resistance of the impedance element 84 changes with the temperature of the light-emitting element 81, the magnitude of the input current I1 also changes with the temperature of the light-emitting element 81.

[0082] Furthermore, the input current I1 decreases as the resistance of the series circuit of the resistive element R2 and the impedance element 84 increases, and increases as the resistance of the series circuit decreases. In this embodiment, the impedance element 84 is an NTC thermistor, which has the characteristic that its resistance decreases as the temperature of the impedance element 84, and consequently the temperature of the light-emitting element 81, rises. Therefore, as the temperature of the light-emitting element 81 rises, the resistance of the series circuit of the resistive element R2 and the impedance element 84 decreases, and the input current I1 increases as the temperature of the light-emitting element 81 rises.

[0083] Here, the light-emitting element 81 has the characteristic that its light emission decreases as its temperature rises. Therefore, if the electrical circuit 83 does not have an impedance element 84, as the temperature of the light-emitting element 81 rises, its light emission decreases compared to the light emission at room temperature (for example, 25 degrees Celsius). When the light emission of the light-emitting element 81 decreases compared to room temperature, the output signal Sig2 becomes larger than at room temperature. In other words, if the electrical circuit 83 does not have an impedance element 84, the magnitude of the output signal Sig2 changes with the temperature of the light-emitting element 81, which leads to a problem in that the accuracy of detecting the density of the detection toner image decreases.

[0084] In contrast, in this embodiment, since the light-emitting circuit 831 has an impedance element 84, the above problem can be resolved. That is, when the temperature of the light-emitting element 81 rises, the impedance (resistance value) of the impedance element 84 decreases, which reduces the resistance value of the series circuit of the resistor element R2 and the impedance element 84. As a result, the base current (input current I1) increases, so the collector current supplied to the light-emitting element 81 also increases, and the light intensity of the light-emitting element 81 increases. In other words, the magnitude of the current (collector current) supplied to the light-emitting element 81 changes according to the impedance of the impedance element 84.

[0085] Thus, in this embodiment, by using the characteristics of the impedance element 84, it is possible to suppress changes in the amount of light emitted by the light-emitting element 81 due to temperature changes. Furthermore, by suppressing changes in the amount of light emitted by the light-emitting element 81, it is possible to suppress changes in the magnitude of the output signal Sig2, thereby suppressing a decrease in the accuracy of detecting the density of the detection toner image. In other words, the impedance element 84 is connected to the light-emitting element 81 or the light-receiving element 82 (in this embodiment, the light-emitting element 81) in such a way as to suppress changes in the magnitude of the output signal Sig2 due to changes in the temperature of the light-emitting element 81.

[0086] Figure 5 shows the effect of the electrical circuit 83 having an impedance element 84. In Figure 5, the vertical axis represents the rate of change of the magnitude of the output signal Sig2, and the horizontal axis represents the temperature of the light-emitting element 81. Also in Figure 5, the solid line graph represents the temperature characteristics of the rate of change when the electrical circuit 83 has an impedance element 84 (hereinafter referred to as "the case of this embodiment"). The dashed line graph represents the temperature characteristics of the rate of change when the electrical circuit 83 does not have an impedance element 84 (hereinafter referred to as "the case of the comparative example"). Also in Figure 5, a rate of change of 0.0% means that the magnitude of the output signal Sig2 is the same as the magnitude of the output signal Sig2 at room temperature.

[0087] As shown in Figure 5, in the comparative example, in the region where the temperature of the light-emitting element 81 is higher than room temperature (here, 25 to 60 degrees Celsius), the rate of change increases to approximately 8.0% as the temperature of the light-emitting element 81 rises. In contrast, in the embodiment, in the region where the temperature of the light-emitting element 81 is higher than room temperature, the rate of change only rises to approximately 3.0% even as the temperature of the light-emitting element 81 rises. Furthermore, in the embodiment, even in the region where the temperature of the light-emitting element 81 is lower than room temperature (here, 10 to 25 degrees Celsius), the increase in the rate of change is suppressed compared to the comparative example.

[0088] As described above, the sensor device 8A according to this embodiment has an impedance element 84, which makes it possible to suppress changes in the detection result (output signal Sig2) of the sensor device 8A due to changes in the temperature of the light-emitting element 81 without requiring a processing device such as a CPU. For this reason, in this embodiment, it is not necessary to design the sensor device 8A to include a processing device as in the configuration shown in the related technology above, and the sensor device 8A can be designed simply. Specifically, in the configuration shown in the related technology above, for example, the temperature of the light-emitting element is detected by a thermistor, and a correction process based on the detected temperature is performed by a processing device. In this case, in addition to the processing device, wiring is required to transmit the detection result of the thermistor to the processing device, but these are unnecessary in this embodiment.

[0089] (Embodiment 2) The configuration of the sensor device 8B according to Embodiment 2 will now be described in detail with reference to Figure 6. The sensor device 8B according to this embodiment differs from the sensor device 8A according to Embodiment 1 in that the impedance element 84 is included in the light receiving circuit 832 instead of the light emitting circuit 831. The impedance element 84 is provided in the light receiving circuit 832, but is located near the light-emitting element 81. Therefore, the impedance (resistance value) of the impedance element 84 changes according to the temperature of the impedance element 84, and consequently the temperature of the light-emitting element 81, similar to Embodiment 1. In the following, configurations common to Embodiment 1 will be omitted from the explanation as appropriate.

[0090] In this embodiment, the impedance element 84 is an NTC thermistor having the characteristic of decreasing impedance (resistance value) as the temperature rises, similar to Embodiment 1. In this embodiment, the first end of the impedance element 84 is connected to the emitter of the photodetector 82 and the first end of the resistor R5, and the second end is connected to the first end of the resistor R4. In other words, the impedance element 84, together with the resistor R4, constitutes a series circuit connected to the emitter of the photodetector 82 and the first end of the resistor R5. Note that the order in which the impedance element 84 and the resistor R4 are connected in the series circuit may be reversed.

[0091] In this case, if the light-receiving circuit 832 does not have an impedance element 84, the magnitude of the output signal Sig2 is determined by the charging voltage V1 of the capacitor C1 input to the non-inverting input terminal of the amplification unit 86. The charging voltage V1 of the capacitor C1 is determined by the collector-emitter voltage of the light-receiving element 82 and the resistance value of the series circuit of the resistor R4 and the impedance element 84. In this embodiment, the impedance element 84 is connected to the resistor R4 as described above. In other words, the magnitude of the output signal Sig2 changes according to the impedance of the impedance element 84.

[0092] Furthermore, the charging voltage V1 of capacitor C1 increases as the resistance of the series circuit of the resistor R4 and impedance element 84 increases, and decreases as the resistance of the series circuit decreases. In this embodiment, since the impedance element 84 is an NTC thermistor, the resistance of the series circuit decreases as the temperature of the light-emitting element 81 rises. Therefore, the charging voltage V1 of capacitor C1 decreases as the temperature of the light-emitting element 81 rises.

[0093] In this case, if the electrical circuit 83 does not have an impedance element 84, the amount of light emitted from the light-emitting element 81 will decrease as the temperature rises compared to the amount of light emitted at room temperature. When the amount of light emitted from the light-emitting element 81 decreases compared to room temperature, the output signal Sig2 will increase compared to room temperature. In contrast, in this embodiment, as the temperature of the light-emitting element 81 rises, the impedance (resistance value) of the impedance element 84 decreases, which lowers the charging voltage V1 of the capacitor C1, causing the output signal Sig2 to decrease.

[0094] Thus, in this embodiment, by using the characteristics of the impedance element 84, it is possible to suppress changes in the magnitude of the output signal Sig2 due to temperature changes, and to suppress a decrease in the accuracy of detecting the density of the detection toner image.

[0095] Incidentally, the impedance element 84 is not limited to being connected to the resistor element R4 as described above. For example, as shown in Figure 7, the impedance element 84 may be connected between the resistor element R6 and the resistor element R7. Specifically, the first end of the impedance element 84 is connected to the inverting input terminal of the amplifier 86 and the first end of the resistor element R6. The second end of the impedance element 84 is connected to the first end of the resistor element R7. In other words, the impedance element 84, together with the resistor element R7, constitutes a series circuit connected to the inverting input terminal of the amplifier 86 and the first end of the resistor element R6. Note that the order in which the impedance element 84 and the resistor element R7 are connected in the series circuit may be reversed.

[0096] Here, if the light receiving circuit 832 does not have an impedance element 84, the magnitude of the output signal Sig2 is determined by the amplification factor determined by the resistance values ​​of the resistors R6 and R7. The impedance element 84 is connected to the resistors R6 and R7 as described above. In other words, the impedance element 84 is connected to the circuit elements (resistors R6 and R7) that determine the amplification factor of the electrical signal Sig1 relative to the output signal Sig2. That is, the amplification factor of the electrical signal Sig1 relative to the output signal Sig2 of the amplifier 86 changes according to the impedance of the impedance element 84.

[0097] Furthermore, the amplification factor increases as the resistance of the series circuit of the resistive element R7 and the impedance element 84 increases, and decreases as the resistance of the series circuit decreases. In this embodiment, since the impedance element 84 is an NTC thermistor, the resistance of the series circuit decreases as the temperature of the light-emitting element 81 rises. Therefore, the amplification factor decreases as the temperature of the light-emitting element 81 rises.

[0098] In this embodiment, as the temperature of the light-emitting element 81 rises, the impedance (resistance value) of the impedance element 84 decreases, resulting in a smaller amplification factor and a decrease in the output signal Sig2. Thus, even in the configuration shown in Figure 7, by utilizing the characteristics of the impedance element 84, it is possible to suppress changes in the magnitude of the output signal Sig2 due to temperature changes, thereby suppressing a decrease in the accuracy of detecting the density of the detection toner image.

[0099] [Differentiation] In embodiments 1 and 2 described above, the impedance element 84 is an NTC thermistor, but it is not limited to this. For example, the impedance element 84 may be a PTC (Positive Temperature Coefficient) thermistor, which increases in resistance as the temperature of the element rises. However, PTC thermistors have the characteristic that their resistance changes sharply when the temperature of the element exceeds a certain temperature, making it difficult to design them to suppress changes in the output signal Sig2 due to temperature changes. In contrast, NTC thermistors have the characteristic that their resistance changes gradually in accordance with changes in the temperature of the element, making it easier to design them to suppress changes in the output signal Sig2 due to temperature changes.

[0100] In the above embodiment 1, the circuit including the impedance element 84 may consist of only the impedance element 84 instead of a series circuit of the resistor R1 and the impedance element 84. However, the circuit including the impedance element 84 is better able to appropriately suppress changes in the output signal Sig2 due to changes in the temperature of the light-emitting element 81 compared to the case in which only the impedance element 84 is used.

[0101] In the configuration shown in Figure 6 of Embodiment 2 described above, the circuit including the impedance element 84 may consist of only the impedance element 84 instead of a series circuit of the resistor element R4 and the impedance element 84. Similarly, in the configuration shown in Figure 7, the circuit including the impedance element 84 may consist of only the impedance element 84 instead of a series circuit of the resistor element R7 and the impedance element 84. In these configurations as well, the series circuit including the impedance element 84 is more effective at suppressing changes in the output signal Sig2 due to temperature changes of the light-emitting element 81 compared to the case where only the impedance element 84 is used.

[0102] In embodiments 1 and 2 described above, the impedance element 84 is included in only one of the light-emitting circuit 831 and the light-receiving circuit 832, but is not limited to this. For example, the impedance element 84 may be included in both the light-emitting circuit 831 and the light-receiving circuit 832.

[0103] In embodiments 1 and 2 described above, the image carrier is an intermediate transfer belt 22, but it is not limited to this. The image carrier only needs to be capable of forming the detection toner image that is the target of detection by the sensor device 8, and may be, for example, a photoreceptor drum 31.

[0104] In embodiments 1 and 2 described above, the image forming unit 3 has a printing function that forms a color or monochrome image on a sheet supplied from the paper feeding unit 4, but it is not limited to this. For example, the image forming unit 3 may have a printing function that forms only a monochrome image on the sheet. In this case, the image carrier may be a photosensitive drum instead of the intermediate transfer belt 22.

[0105] [Notes on the invention] The following is an overview of the invention extracted from the above-described embodiments. Note that each configuration and processing function described below can be selected and combined as desired.

[0106] <Note 1> A sensor device that outputs an output signal corresponding to the density of the toner image in an image forming apparatus, A light-emitting element that irradiates light onto an image carrier that holds the toner image, A light-receiving element that receives light reflected from the image carrier, It has an impedance element that changes impedance according to temperature, The output signal is a signal whose magnitude changes according to the amount of light received by the light-receiving element, The impedance element is connected to the light-emitting element or the light-receiving element to suppress changes in the magnitude of the output signal due to changes in the temperature of the light-emitting element. Sensor device.

[0107] <Note 2> The impedance element has the characteristic that the impedance decreases as the temperature rises. The sensor device described in Appendix 1.

[0108] <Note 3> The light-emitting circuit including the light-emitting element and the light-receiving circuit including the light-receiving element are electrically isolated from each other. The impedance element is included in the light-emitting circuit. The sensor device described in Appendix 1 or 2.

[0109] <Note 4> The magnitude of the current supplied to the light-emitting element changes according to the impedance of the impedance element. The sensor device described in Appendix 3.

[0110] <Note 5> The light-emitting circuit including the light-emitting element and the light-receiving circuit including the light-receiving element are electrically isolated from each other. The impedance element is included in the light receiving circuit. A sensor device as described in any one of the appendices 1 to 4.

[0111] <Note 6> The magnitude of the output signal changes according to the impedance of the impedance element. The sensor device described in Appendix 5.

[0112] <Note 7> The light receiving circuit has an amplification unit that amplifies an electrical signal whose magnitude changes according to the amount of light received by the light receiving element and outputs it as the output signal. The amplification factor of the electrical signal with respect to the output signal of the amplification unit changes according to the impedance of the impedance element. The sensor device described in Appendix 5 or 6.

[0113] <Note 8> A sensor device described in any one of the appendices 1 to 7, The image forming unit includes the image carrier and forms the toner image, The system includes an adjustment processing unit that adjusts the density of the toner image based on the output signal output by the sensor device, Image forming apparatus. [Explanation of Symbols]

[0114] 100 Image forming apparatus 22 Intermediate transfer belt (image carrier) 3 Image forming unit 71 Adjustment Processing Unit 8. Sensor device 81 Light-emitting element 82 Photodetector 831 Light-emitting circuit 832 Light receiving circuit 84 Impedance elements Sig1 Electrical signal Sig2 output signal

Claims

1. A sensor device that outputs an output signal corresponding to the density of the toner image in an image forming apparatus, A light-emitting element that irradiates light onto an image carrier that holds the toner image, A light-receiving element that receives light reflected from the image carrier, It has an impedance element that changes impedance according to temperature, The output signal is a signal whose magnitude changes according to the amount of light received by the light-receiving element, The impedance element is connected to the light-emitting element or the light-receiving element to suppress changes in the magnitude of the output signal due to changes in the temperature of the light-emitting element. Sensor device.

2. The impedance element has the characteristic that the impedance decreases as the temperature rises. The sensor device according to claim 1.

3. The light-emitting circuit including the light-emitting element and the light-receiving circuit including the light-receiving element are electrically isolated from each other. The impedance element is included in the light-emitting circuit. The sensor device according to claim 1 or 2.

4. The magnitude of the current supplied to the light-emitting element changes according to the impedance of the impedance element. The sensor device according to claim 3.

5. The light-emitting circuit including the light-emitting element and the light-receiving circuit including the light-receiving element are electrically isolated from each other. The impedance element is included in the light receiving circuit. The sensor device according to claim 1 or 2.

6. The magnitude of the output signal changes according to the impedance of the impedance element. The sensor device according to claim 5.

7. The light receiving circuit has an amplification unit that amplifies an electrical signal whose magnitude changes according to the amount of light received by the light receiving element and outputs it as the output signal. The amplification factor of the electrical signal with respect to the output signal of the amplification unit changes according to the impedance of the impedance element. The sensor device according to claim 6.

8. A sensor device according to claim 1 or 2, The image forming unit includes the image carrier and forms the toner image, The system includes an adjustment processing unit that adjusts the density of the toner image based on the output signal output by the sensor device, Image forming apparatus.

Images