Fixing device temperature measuring device and image forming apparatus

Abstract

To provide a fixing device temperature measurement device capable of preventing measured temperature from being affected by retrieving radiant heat from a member designed to be at a temperature relatively close to that of a thermopile as stray light.SOLUTION: A thermopile sensor 25, acting as a fixing device temperature measurement device, is supported by a substrate 56, and the substrate 56 is provided with a cylindrical member 61 extending to the front of the thermopile sensor 25 and an aperture 63 provided at a tip end of the cylindrical member 61.SELECTED DRAWING: Figure 5

Description

[Technical Field]

[0001] The present invention relates to a temperature measuring device for a fixing device and an image forming apparatus, and more particularly to a temperature measuring device for a fixing device and an image forming apparatus that includes a fixing rotor and a pressure rotor and thermally fixes a toner image formed on a recording medium. [Background technology]

[0002] Thermopile sensors, which have excellent response time, are known as temperature sensors for controlling the fixing temperature. Because thermopile sensors can withstand temperatures below 100°C, they cannot be installed inside fixing devices. However, their narrow light-receiving angle allows measurements to be taken from a distance. An example of such a temperature measurement device for a fixing device is disclosed in Patent Document 1. The temperature measurement device for a fixing device disclosed in Patent Document 1 is a temperature detection device that non-contactly detects the surface temperature of a heated object heated by a heat source. It includes a sensor unit that includes a non-contact temperature sensor (thermopile sensor) that faces the heated object and measures infrared rays emitted from the heated object, a case that houses the non-contact temperature sensor, and an outer case that houses the sensor unit and maintains a uniform ambient temperature around the sensor unit.

[0003] Similarly, Patent Document 2 discloses an example of using a thermopile sensor in a temperature measurement device for a fixing device. In the temperature measurement device for a fixing device in Patent Document 2, a duct member is provided to allow air to flow from the thermopile sensor to the fixing belt, preventing water vapor filling the fixing cover from flowing into the thermopile sensor and condensing on the thermopile sensor lens, which would create a discrepancy between the actual temperature of the fixing belt and the temperature detected by the thermopile sensor. A guide member is also provided to guide the air flowing from the fixing belt, preventing the airflow from the thermopile sensor from directly hitting the fixing belt and causing a local drop in the surface temperature of the fixing belt. The two opposing airflows collide and are diverted in a direction that intersects with the thermopile sensor at the position where they face the fixing belt, preventing them from being affected by each other's airflows. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2003-35601 [Patent Document 2] Japanese Patent Publication No. 2020-13018 Summary of the Invention [Problem to be solved by the invention]

[0005] The technology in Patent Document 1 has problems such as the device becoming larger due to the outer case, and the amount of infrared light received by the thermopile changing with temperature changes of the outer case, resulting in erroneous temperature detection. This occurs because infrared light at an angle wider than the thermopile's acceptance angle unintentionally reaches the thermopile's acceptance surface due to internal reflection of the thermopile's focusing lens barrel. Hereinafter, infrared light received at an angle wider than the thermopile's acceptance angle will be referred to as stray light. Furthermore, because radiant heat from sources other than the measurement target, such as the outer case, can become stray light for the thermopile, radiation received by the thermopile from sources other than the measurement target will be referred to as stray radiation.

[0006] Furthermore, in Patent Document 2, the opposing airflows from the thermopile sensor and the fixing belt are allowed to escape in directions that intersect with each other, but there are cases where these airflows do not escape properly, or where the airflows themselves affect the temperature measurement, resulting in erroneous detection.

[0007] SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a temperature measuring device that can prevent erroneous detection by a thermopile sensor. [Means for solving the problem]

[0008] The temperature measuring device for a fixing device according to the present invention measures the temperature of a temperature detection object in the fixing device through an opening provided in the fixing device using a thermopile sensor provided outside the fixing device. The thermopile sensor is held by a sensor holding member, and the sensor holding member is provided with a cylindrical member extending in front of the thermopile sensor and a narrowed portion provided at the tip of the cylindrical member. A frame and an outer cover of the fixing device are provided in this order in front of the throttling portion, and the opening size of the throttling portion is smaller than the openings of the frame and the outer cover.

[0009] The cylindrical member prevents radiant heat from the outside and receives stray light radiation from the inner wall of the cylindrical member, which has a temperature close to that of the sensor, thereby reducing the impact on the detection temperature, and the narrowed tip allows more stray light to be blocked without interfering with the original light receiving range.

[0010] As a result, it is possible to provide a temperature measuring device that can prevent the thermopile sensor from making erroneous detections.

[0011] Preferably, the cylindrical member is in contact with the thermopile sensor, and the thermopile sensor and the cylindrical member are thermally conductive.

[0012] The difference between the temperature of the cylindrical member and the temperature of the thermopile sensor can be reduced, thereby suppressing the amount of stray light radiation.

[0013] More preferably, the diameter of the aperture of the diaphragm at the tip of the cylindrical member does not interfere with the original light receiving range of the thermopile sensor.

[0014] It is preferable to provide the inner wall of the cylindrical member with a metal tube having low emissivity, which reduces the emissivity and the amount of stray light radiation.

[0015] The tip of the holder may be covered with a metal cap having low emissivity.

[0016] By doing so, it is possible to suppress the temperature rise of the holding portion due to radiation from the fixing device, and to reduce the temperature difference between the holding portion and the thermopile sensor.

[0017] According to one embodiment of the present invention, the tubular member is provided with a ventilation hole.

[0018] By configuring in this way, it is possible to suppress a rise in temperature of the holding portion.

[0019] According to another embodiment of the present invention, a gap is provided between the opening provided in the fixing device and the throttling portion, and an exhaust fan is included that exhausts the airflow to the outside in order to generate an airflow that does not enter the tubular member from the opening provided in the fixing device.

[0020] According to another aspect of the present invention, an image forming apparatus includes any one of the temperature measuring devices for a fixing device described above. [Effects of the Invention]

[0021] According to this invention, a temperature measuring device for a fixing device can be provided that receives stray light radiation from the cylindrical inner wall, which is close to the sensor temperature, thereby reducing the impact on the detected temperature, and by narrowing the tip, it is possible to block more stray light without interfering with the original light receiving range, thereby preventing the thermopile sensor from making false detections.

[0022] The above and other objects, features and advantages of the present invention will become more apparent from the following detailed description of the preferred embodiments, which proceeds with reference to the accompanying drawings. [Brief explanation of the drawings]

[0023] [Figure 1] 1 is a schematic cross-sectional view showing an internal structure of an image forming apparatus according to an embodiment of the present invention. [Figure 2] FIG. 2 is a schematic cross-sectional view showing a fixing device. [Figure 3] 2 is a cross-sectional view showing the positional relationship between the fixing device and a thermopile sensor that is a device for measuring the temperature of the fixing device. FIG. [Figure 4] 4 is a diagram showing an incident path of infrared rays when the temperature of the fixing device is measured by a thermopile sensor; FIG. [Figure 5] 1 is a diagram showing the positional relationship between infrared light from a measurement object incident on a lens of a thermopile sensor, unintended infrared light (stray light), and a light blocking member. [Figure 6] FIG. 2 is a diagram showing a detailed configuration of a thermopile. [Figure 7A] FIG. 10 is a view showing the inside of the duct cover of the cylindrical member. [Figure 7B] FIG. 10 is a view showing the inside of the duct cover of the cylindrical member. [Figure 8A] FIG. 10 is a view showing the outside of the duct cover of the cylindrical member. [Figure 8B] FIG. 10 is a view showing the outside of the duct cover of the cylindrical member. [Figure 8C] FIG. 10 is a view showing the outside of the duct cover of the cylindrical member. [Figure 9] 1 is a diagram showing a vent hole provided at an opening of a cylindrical member, and FIG. 2 is a cross-sectional view of the vicinity of a thermopile sensor when the image forming apparatus is viewed from above. [Figure 10] 10A and 10B are diagrams illustrating a portion where an opening of a cylindrical member faces an opening of an outer cover of the fixing device. [Figure 11] 2 is a cross-sectional view of the vicinity of a thermopile sensor when the image forming apparatus is viewed from above. FIG. DETAILED DESCRIPTION OF THE INVENTION

[0024] 1, an image forming apparatus 10 according to an embodiment of the present invention is an apparatus that forms a multicolor or monochrome image on paper by electrophotography. As will be described in detail later, image forming apparatus 10 includes a fixing device 46 that thermally fixes a toner image formed on paper (recording medium).

[0025] First, a brief description will be given of the basic configuration of the image forming apparatus 10. In this specification, the front (front face) is defined as the surface facing the user's standing position, i.e., the surface on which an operation unit (not shown) is provided, and the front-to-rear direction (depth direction) of the image forming apparatus 10 and its components is defined. The left-to-right direction (horizontal direction) of the image forming apparatus 10 and its components is defined based on the state in which the image forming apparatus 10 is viewed from the user.

[0026] 1, in this embodiment, image forming apparatus 10 is a multifunction peripheral (MFP) having functions such as a copy function, a printer function, a scanner function, and a facsimile function. Image forming apparatus 10 includes a device main body 12 equipped with an image forming unit 30 and the like, and an image reading device 14 disposed above the device main body 12.

[0027] The image reading device 14 includes a document table 16 made of a transparent material. A document retaining cover 18 is attached above the document table 16 via a hinge or the like so that it can be opened and closed freely. This document retaining cover 18 is provided with an ADF (automatic document feeder) 24 that automatically feeds documents placed on a document tray 20 one by one to an image reading position 22. In addition, an operation unit (not shown) is provided on the front side of the document table 16 for receiving input operations such as printing instructions from the user. This operation unit is appropriately provided with a display such as a touch panel display and various operation buttons, etc.

[0028] The image reading device 14 also includes a built-in image reading unit 26 that includes a light source, multiple mirrors, an imaging lens, a line sensor, etc. The image reading unit 26 exposes the surface of the document to light, and guides the light reflected from the document surface to the imaging lens using multiple mirrors. The imaging lens then forms an image of the reflected light on the light-receiving elements of the line sensor. The line sensor detects the luminance and chromaticity of the reflected light that forms an image on the light-receiving elements, and generates image data based on the image of the document surface. A CCD (Charge Coupled Device) or a CIS (Contact Image Sensor) is used as the line sensor.

[0029] The device main body 12 incorporates a control unit 28 including a CPU, RAM, and HDD, and an image forming unit 30. The control unit 28 (specifically, the CPU) transmits control signals to each part of the image forming device 10, including the fixing device 46, in response to input operations by a user to an operation unit, causing the image forming device 10 to perform various operations.

[0030] The image forming section 30 includes an exposure unit 32, a developing device 34, a photosensitive drum 36, a cleaner unit 38, a charger 40, an intermediate transfer belt unit 42, a secondary transfer roller 44, and a fixing device 46, and forms an image on paper conveyed from a paper feed tray 43 or a manual paper feed tray 50, and discharges the paper with the image formed on it to a paper discharge tray 52. ​​Image data used to form an image on paper is image data read by the image reading section 26 or image data sent from an external computer.

[0031] The image data handled by the image forming apparatus 10 corresponds to color images of four colors: black (K), cyan (C), magenta (M), and yellow (Y). Therefore, four of each of the developing device 34, photosensitive drum 36, cleaner unit 38, and charger 40 are provided so as to form four types of latent images corresponding to each color, and these constitute four image stations.

[0032] The photosensitive drum 36 is an image carrier having a photosensitive layer formed on the surface of a cylindrical conductive base, and the charger 40 is a member that charges the surface of the photosensitive drum 36 to a predetermined potential. The exposure unit 32 is configured as a laser scanning unit (LSU) equipped with a laser emitter and a reflecting mirror, etc., and exposes the charged surface of the photosensitive drum 36 to light, thereby forming an electrostatic latent image on the surface of the photosensitive drum 36 according to image data. The developer 34 visualizes the electrostatic latent image formed on the surface of the photosensitive drum 36 with four-color (YMCK) toner. The cleaner unit 38 removes toner remaining on the surface of the photosensitive drum 36 after development and image transfer.

[0033] The intermediate transfer belt unit 42 includes an intermediate transfer belt 54, a drive roller 51, a driven roller 53, and four intermediate transfer rollers 55, and is disposed above the photosensitive drums 36. The intermediate transfer belt 54 is a flexible, endless belt that is stretched by a plurality of rollers, including the drive roller 51 and the driven roller 53, and is disposed so that its surface (outer circumferential surface) abuts against the surface of the photosensitive drums 36. The intermediate transfer belt 54 rotates (circularly moves) in a predetermined direction as the drive roller 51 is driven to rotate. The intermediate transfer rollers 55 are disposed at positions facing each of the photosensitive drums 36 across the intermediate transfer belt 54. During image formation, the intermediate transfer rollers 55 are used to sequentially transfer the toner images of each color formed on each photosensitive drum 36 onto the intermediate transfer belt 54, superimposing them one on top of the other, thereby forming a multi-color toner image on the intermediate transfer belt 54.

[0034] The secondary transfer roller 44 is disposed opposite the drive roller 51 with the intermediate transfer belt 54 sandwiched therebetween. When a sheet of paper passes through the secondary transfer nip between the secondary transfer roller 44 and the intermediate transfer belt 54, the toner image formed on the intermediate transfer belt 54 is transferred onto the sheet of paper.

[0035] The fixing device 46 includes a fixing belt 62, a pressure roller 64, and the like, and is disposed above the secondary transfer roller 44 (downstream in the paper transport direction). The fixing belt 62 includes a fixing pad 76, a heat source 82, and the like (see FIG. 2), and the fixing belt 62 is heated by the heat source 82 to a predetermined fixing temperature (e.g., 170°C). The pressure roller 64 is disposed so as to press the fixing belt 62 between itself and the fixing pad 76. When a sheet of paper passes through a fixing nip N (see FIG. 2) between the pressure roller 64 and the fixing belt 62, the toner image transferred to the sheet of paper is melted, mixed, and pressed against the sheet, thereby thermally fixing the toner image to the sheet of paper. The specific configuration of the fixing device 46 will be described later.

[0036] Within the device main body 12, a first paper transport path L1 is formed for sending paper from the paper feed tray 43 or manual paper feed tray 50 to the paper output tray 52 via the registration rollers 68, secondary transfer roller 44, and fixing device 46. In addition, when performing double-sided printing on the paper, a second paper transport path L2 is formed for returning the paper, after single-sided printing is completed and the paper has passed through the fixing device 46, to the first paper transport path L1 upstream in the paper transport direction of the secondary transfer roller 44. A plurality of transport rollers 66 for applying auxiliary propulsion force to the paper are appropriately provided on the first paper transport path L1 and the second paper transport path L2.

[0037] Next, the mechanical configuration of the fixing device 46 will be described with reference to Fig. 2. The fixing device 46 includes a fixing belt 62, which is an example of a fixing rotor, and a pressure roller 64, which is an example of a pressure rotor, and fixes a toner image onto the paper by passing the paper through a fixing nip N formed between them.

[0038] 2, the fixing device 46 includes a heater unit 70 having a fixing belt 62 and the like, and a pressure unit 72 having a pressure roller 64 and the like. The members of the heater unit 70 and the pressure unit 72 are integrally held in a predetermined arrangement by a fixing frame (not shown).

[0039] The heater unit 70 includes a fixing belt 62 that is formed in a generally cylindrical shape and extends in the front-to-rear direction (the width direction of the paper). The fixing belt 62 is typically made of a strip-shaped base material made of a synthetic resin such as polyimide or a metal such as nickel, with a release layer provided on the surface. The fixing belt 62 is rotatable about its axis and has an inner diameter of, for example, 30 mm. Inside the fixing belt 62, a fixing pad 76, a support member 78, a reflector 80, a heat source 82, and the like are also provided.

[0040] The fixing pad 76 is a fixed member fixedly provided so as to be in sliding contact with the inner peripheral surface of the fixing belt 62, and is formed in the shape of a long plate extending along the axial direction of the fixing belt 62. The fixing pad 76 has a sliding contact sheet 76a on its outer peripheral surface (at least the surface that comes into sliding contact with the fixing belt 62), and sliding oil is applied to this sliding contact sheet 76a to reduce frictional force with the fixing belt 62. The length of the fixing pad 76 is the same as the axial length (width) of the fixing belt 62.

[0041] The support member 78 supports the fixing pad 76 while pressing it against the inner circumferential surface of the fixing belt 62, and both ends of the support member 78 are fixed to the fixing frame. In this first embodiment, the support member 78 has a generally L-shaped cross section and includes a long plate-like fixing portion 78a to which the fixing pad 76 is fixed, and a long plate-like standing portion 78b standing from the widthwise end of the fixing portion 78a. In addition, a thin plate-like reflecting plate 80 is attached to the support member 78 so as to cover the surface facing the heat source 82.

[0042] The heat source 82 is a member for heating the fixing belt 62, and is provided so as to extend along the axial direction of the fixing belt 62. A lamp heater such as a halogen lamp is used as the heat source 82. In this embodiment, the heat source 82 includes a first lamp heater 82a that heats the axial center portion of the fixing belt 62, and a second lamp heater 82b that heats both axial end portions of the fixing belt 62. The first lamp heater 82a and the second lamp heater 82b are used differently depending on the paper width.

[0043] The pressure unit 72 includes a pressure roller 64 that is disposed in a position facing the fixing pad 76 across the fixing belt 62. The pressure roller 64 is disposed to extend parallel to the axial direction of the fixing belt 62, and presses the fixing belt 62 between itself and the fixing pad 76 to form a fixing nip N between itself and the fixing belt 62.

[0044] Next, the positional relationship between fixing device 46 and thermopile sensor 25 according to this embodiment will be described. Fig. 3 is a diagram showing the positional relationship between fixing device 46 and thermopile sensor 25. Referring to Fig. 3, fixing device 46 is housed in fixing device cover 45, with thermopile sensor 25 disposed in front of it. Specifically, a restrictor portion (opening) 63 is provided in a portion of fixing belt 62 facing thermopile sensor 25.

[0045] The restrictor 63 is provided on a cylindrical member 61 (see FIG. 5) provided on the front surface of the thermopile sensor 25, but details thereof are omitted here.

[0046] Furthermore, the frame 48 and outer cover 47 of the fixing device cover 45 are provided in this order in front of the restrictor 63, and the opening dimensions of the restrictor 63 are smaller than those of the frame 48 and outer cover 47. The shape of these openings is preferably circular, but may be other shapes.

[0047] The opening diameters of frame 48 and outer cover 47 are related to the thickness of the light beam, and the thicker one may be designed to be larger, or the opening of frame 48 may be designed to be larger taking into account the positional deviation of the light beam when thermopile sensor 25 is tilted.

[0048] Next, the infrared light beam incident on thermopile sensor 25 will be described. FIG. 4 is a diagram illustrating the detailed configuration of thermopile sensor 25 and the infrared light beam entering therein, and is a cross-sectional view taken along the optical axis of the infrared light from fixing device 46. Referring to FIG. 4, thermopile sensor 25 includes a substrate 56, an environment temperature measuring element 58 provided on substrate 56, a CAN 59, and a light receiving element 57 provided in the center of substrate 56 of CAN 59. CAN 59 is cylindrical and extends toward fixing device 46, and a lens 60 that focuses infrared light is provided at the center of its tip.

[0049] 4, only the light beam passing through the center of lens 60 is shown inside CAN 59. As shown in Fig. 4, the light beams passing through the center of lens 60 include infrared rays 83 that are incident straight on light receiving element 57 from fixing device 46 through lens 60, and light beam 85 that is infrared rays from an object whose temperature cannot be controlled, such as fixing device cover 45, that enters CAN 59 from diagonally above, is reflected by wall surface 59a inside CAN 59, and then enters light receiving element 57.

[0050] Here, the thermopile sensor 25 measures the temperature of the object using a measurement principle that allows the temperature of the object to be calculated from the infrared energy measured by the thermopile sensor 25 and the environmental temperature.

[0051] The thermopile sensor 25 increases its sensitivity by concentrating infrared rays from the target object with a lens, and the viewing angle 84, which is a guide to the infrared receiving range, is designed to be about 7 degrees.

[0052] On the other hand, as described above, there exists unintended light beam (stray light) 85 that is reflected by the wall surface 59a inside the CAN 59 of the thermopile sensor 25 and reaches the light receiving element 57. Such infrared rays start to increase at angles of 20 to 30 degrees or more with respect to the optical axis, and are most abundant at approximately 45 degrees as shown in Figure 4. Generally, when infrared rays are received from an infinitely large plane with a uniform temperature, approximately 20% of them are unintended infrared rays.

[0053] When measuring the temperature of the fixing device 46 as shown in Figure 4, unintended infrared rays are present, mainly from the outer cover 47 of the fixing device 46, and this stray light reception results in the temperature of the fixing device cover 45, etc. being picked up, which is added to the temperature of the fixing belt and superimposed, which can cause a temperature error.

[0054] Therefore, in this embodiment, the following configuration is adopted to avoid the influence of such stray light. Figure 5 is a diagram showing this configuration and the configuration in the vicinity of outer cover 47, frame 48, etc. In this embodiment, a cylindrical member 61 is attached to the front of CAN 59 of thermopile sensor 25.

[0055] [First embodiment] That is, referring to FIG. 5, the thermopile sensor is held by a CAN 59 (which functions as a "sensor holding member"), and the CAN 59 is provided with a cylindrical member 61 extending in front of the thermopile sensor and a narrowing portion 63 provided at the tip of the cylindrical member 61.

[0056] The cylindrical member 61 prevents radiant heat from the outside, and receives stray light radiation from the inner wall of the cylindrical member 61, which has a temperature close to the sensor temperature, thereby reducing the impact on the detection temperature, and the narrowed portion 63 at the tip blocks more stray light without interfering with the original light receiving range.

[0057] In Figure 5, infrared rays 83 from the fixing device 46 that are incident perpendicularly on the lens 60 of the thermopile sensor 25 are shown by dotted lines, unintended infrared rays (stray light) 83a and 83b are shown by diagonal lines, and frame radiation light 85a and 85b, which are included in the unintended infrared rays (stray light) 83a and 83b but are infrared rays from the frame 48 that are at a higher temperature than the opening, are shown by dashed and dotted lines (this corresponds to the unintended light beam (stray light) 85 shown in Figure 4).

[0058] In this embodiment, thermopile sensor 25 is provided with a cylindrical member 61 so as to receive all infrared rays 83 from fixing device 46 (not shown), eliminate unintended infrared rays (stray light) 83a, 83b as much as possible, and receive frame radiation light 85a, 85b at light receiving element 57 as shown in Fig. 4, and an aperture section 63 is provided at the tip of cylindrical member 61. Here, the opening diameter of aperture section 63 at the tip of the cylindrical member does not interfere with the original light receiving range of thermopile sensor 25.

[0059] That is, although the outer cover 47 and the frame 48 block unintended infrared rays (stray light) 83a, 83b, the aperture diameter of the diaphragm section 63 is narrowed to further block stray light from entering the thermopile.

[0060] It is possible to narrow the aperture 63 further so that only infrared rays 83 from the fixing device 46 are incident, but here the aperture 63 is sized to receive frame radiation light, which is infrared rays from the outer cover 47 and the like that are at a higher temperature than the opening, through the aperture 63. In this way, stray light with a temperature close to that of the thermopile sensor 25 is received, reducing its effect on the measured temperature.

[0061] [Second embodiment] Furthermore, the cylindrical member 61 is in contact with the thermopile sensor 25, and thermal conductivity is possible between the thermopile sensor 25 and the cylindrical member 61. This configuration reduces the temperature difference between the cylindrical member 61 and the thermopile sensor 25, thereby reducing the amount of stray light radiation.

[0062] As for specific opening dimensions, for example, the opening diameter of the restrictor portion 63 is 6 mm, the opening diameter of the outer cover 47 is 12 mm, and the opening diameter of the frame 48 is 16 mm.

[0063] Next, the configuration of the cylindrical member 61 of the thermopile sensor 25 will be described in detail. Fig. 6 is a diagram illustrating the configuration of the cylindrical member 61 of the thermopile sensor 25 in detail. Referring to Fig. 6, the cylindrical member 61 of the thermopile sensor 25 (shown by a dotted line in the figure) is configured by integrating a thermopile holding component 88 and a duct cover 89 (see Fig. 11). That is, the cylindrical member 61 includes the thermopile main body 25a attached to the substrate 56 and the thermopile holding component 88, and the thermopile holding component 88 is fixed to the substrate 56 by thermopile holding claws 88a. The thermopile holding component 88 is fixed to the duct cover 89 by pins 90, and the duct cover 89 is attached to the duct 91 (see Fig. 11).

[0064] 6, the duct cover 89 has a recess 89a in the portion facing the lens 60 of the thermopile sensor 25, and an opening 92 for the thermopile sensor 25 in the center of the recess 89a. This opening 92 corresponds to the opening of the diaphragm portion 63.

[0065] Here, the diameter of the opening 92 is preferably in the range of +1 mm to +5 mm greater than the diameter of the lens 60, and more preferably about +3 mm.

[0066] If the diameter of the opening 92 is less than the diameter of the lens 60 + 1 mm, there is a risk of blocking infrared rays from the target object. Also, if the diameter of the opening 92 is more than the diameter of the lens 60 + 3 mm, a lot of stray light from covers other than the fixing device is received, which is likely to cause temperature errors.

[0067] Next, we will explain the distance 93 from the thermopile tip to the opening. The distance is preferably in the range of 2 to 8 mm, and approximately 5 mm is even more preferable. If the distance is less than 2 mm, the aperture effect is weakened, and a lot of stray light from the outer cover 47 and the like is received, making it more likely for temperature errors to occur. If the distance is more than 8 mm, the thermopile tip is too close to the fixing device and is more likely to be heated by radiant heat, causing a temperature difference with the thermopile sensor, increasing the amount of infrared light from the opening, and making it more likely for temperature errors to occur.

[0068] The above can be summarized as follows: The material of the opening 92 (duct cover) is selected from resins such as PC (polycarbonate) and PET (polyethylene terephthalate), and the like, or the above resins containing glass fiber.

[0069] When the diameter of the lens 60 of the thermopile sensor is 4 mm, the diameter of the opening 92 of the thermopile sensor is φ7 mm, and the distance 93 is 5 mm.

[0070] When the diameter of the lens 60 of the thermopile sensor is 6 mm, the diameter of the opening of the thermopile sensor is φ9 mm, and the distance 93 is 5 mm.

[0071] Next, a description will be given of the material of opening 92. Figures 7A, 7B, and 8A to 8C are diagrams showing the specific configuration of opening 92, with Figures 7A and 7B showing details of a case where a metal tube 94 is provided inside opening 92, and Figures 8A to 8C showing a case where a metal cap 97 is provided outside opening 92.

[0072] First, referring to FIG. 7A, a metal tube 94 is fitted into a recess 89a of a duct cover 89 in which the thermopile sensor 25 is disposed, and then the metal tube 94 is fitted in front of a thermopile holding part 88 that houses the CAN 59 of the thermopile sensor 25 (FIG. 7B).

[0073] Here, the metal tube 94 that forms the inner wall of the cylindrical member 61 is made of a metal with low emissivity. By using a metal with low emissivity, radiation can be suppressed, and the amount of stray light radiation can be reduced.

[0074] The emissivity of the PC that constitutes the duct cover 89 is 0.9, and the emissivity of the Ni-plated steel sheet that constitutes the metal tube 94 is 0.2 or less. The emissivity of aluminum is 0.1 or less, and the emissivity of stainless steel is 0.3 to 0.6.

[0075] To reduce the temperature error, it is necessary to reduce the amount of infrared radiation from the opening. To do this, in addition to reducing the temperature difference between the opening and the thermopile sensor, the amount of infrared radiation can be further reduced by using a material with low infrared radiation for the inner wall of the opening.

[0076] As mentioned above, the emissivity of resin is about 0.9, but by using metal materials such as Ni-plated steel (0.2 or less) or aluminum (0.1 or less), the amount of infrared radiation can be reduced to 20% or less. The emissivity of stainless steel is higher than the previous metals, so the effect is smaller than that of the previous metals.

[0077] Therefore, in terms of emissivity, cost, and workability, Ni-plated steel sheet, aluminum, etc. are preferred.

[0078] 8, a protrusion 89b is provided on the outside of recess 89a of duct cover 89 (FIG. 8A), and a metal cap 97 having a recess (or opening) that engages with protrusion 89b is placed over it (FIG. 8B). This configuration suppresses the temperature rise of the holding part due to radiation from the fixing device, and reduces the temperature difference between the holding part and the thermopile sensor.

[0079] This is combined with the metal plate 98 provided on the inside and placed in front of the thermopile sensor 25 (FIG. 8C). The convex portion or concave portion used for this engagement may be provided on either of the members.

[0080] If the temperature rise at the opening is not small, such as when the opening is close to the fixing belt, and a temperature difference occurs between the opening and the thermopile sensor, the temperature rise at the opening can be suppressed by providing a metal cap on the outside of the opening.

[0081] As the metal material, one with high reflectivity and resistance to radiant heat is preferred, and in view of cost and workability, Ni-plated steel sheet, aluminum, etc. are preferred.

[0082] Next, the ventilation holes in the opening 92 will be described. Fig. 9 is a diagram similar to Fig. 6, but showing a ventilation hole 87 provided in the opening 92. The more equal the temperatures of the opening 92 and the thermopile sensor 25 are, the more the stray light receiving energy decreases, and the smaller the measurement error becomes. Therefore, the ventilation hole 87 is provided in the recess 89a of the duct cover 89, which is a cylindrical member, to suppress the temperature rise of the thermopile holding part 88. Note that Fig. 9 shows the recess 89a of the duct cover 89 having the configuration shown in Fig. 6, but the configuration shown in Figs. 7A to 8C may also be used.

[0083] The temperature of opening 92 is increased by the radiant heat of fixing belt 62 and hot air, and the temperature of the air inside opening 92 in particular rises. Therefore, by providing ventilation holes 87 in the side walls of opening 92 to allow the heated air to escape, the temperature inside opening 92 can be reduced.

[0084] The ventilation holes 87 may be provided on the left and right as shown in the figure, or on the top and bottom (front and back in the figure). It is desirable to open a hole with a diameter smaller than the thickness of the opening 92 so as not to receive stray light from outside.

[0085] Next, the effects of such a configuration will be described.

[0086] When the temperature control setting of the fixing belt 62 is 150°C and the ambient temperature is 25°C, the detected temperature of the thermopile sensor when the fixing belt temperature reaches 150°C immediately after the power is turned on is set to 150°C. The detected temperatures 5 minutes and 1 hour after the start of paper feed are shown for each of the following conditions.

[0087] The metal cap is made of nickel-plated steel sheet 0.2 mm thick.

[0088] [Table 1]

[0089] When there was no opening, the temperature difference after one hour was as large as 5.3°C, but with the opening of the present invention, the difference was reduced to 2.6°C, with the metal inside the opening being 1.2°C and the metal outside the opening being 1.0°C.

[0090] For reference, the temperatures (°C) of the components around the thermopile sensor are shown in Table 2.

[0091] [Table 2]

[0092] Next, a method for reducing the influence of air currents when measuring the temperature of thermopile sensor 25 in this embodiment will be described. Fig. 10 is a diagram illustrating air currents in the vicinity of thermopile sensor 25 in this embodiment, and Fig. 11 is a cross-sectional view of fixing device 46, as viewed from above, of image forming apparatus 10, in which a plurality of thermopile sensors 25 shown in Fig. 10 are provided in succession (arranged in a row). In the figure, the left side is the front side of the image forming apparatus, and the right side is the rear side of the image forming apparatus.

[0093] 10, the opening of narrowed portion 63 at the tip of cylindrical member 61 of thermopile sensor 25 faces the openings of outer cover 47 and frame 48 of the fixing device, and the diameter φA of the opening of narrowed portion 63 is smaller than the diameter φB of the opening of frame 48, for example, φA is about 6.5 mm and φB is about 12 mm. Note that the shapes of outer cover 47 and frame 48 here are different from those in FIG. 5.

[0094] If there is an air current between them, it will cause condensation on thermopile sensor 25. Therefore, in this embodiment, φB is set to be greater than φA, and a gap is provided between the openings, making it difficult for the air current from fixing device 46 (indicated by the arrow in the figure) to enter the restrictor portion of thermopile sensor 25.

[0095] 10, the CAN portion of the thermopile sensor (the portion where lens 60 is provided) has no part that is exposed to the outside air except for the front opening (there is no duct member as shown in Patent Document 2). Furthermore, the thermopile CAN is exposed to the outside air only at the front opening. In other words, there is no airflow from the thermopile substrate 56 side to the fixing belt 62 as in Patent Document 2.

[0096] As a result, no air is blown out from the thermopile sensor 25 side, and the fixing belt 62 is not cooled.

[0097] Next, a description will be given of a configuration for generating such an airflow from fixing device 46 to thermopile sensor 25. Referring to Fig. 11, in order to generate an airflow (indicated by the arrow in the figure) that does not enter cylindrical member 61 of thermopile sensor 25 from the opening of fixing device 46, an exhaust fan 96 is provided that exhausts the airflow to the outside via duct 91. By providing exhaust fan 96, a rise in temperature inside the image forming apparatus is suppressed.

[0098] If there is a gap in the thermopile, the airflow 67 from inside the fixing device will be drawn by the exhaust fan 96 and directed toward the thermopile, causing condensation on the thermopile and a rise in the temperature of the CAN.

[0099] Therefore, by ensuring that there are no gaps in the thermopile, the above problem can be prevented.

[0100] The present invention can be implemented in various other forms without departing from the spirit or main features thereof. Therefore, the above-described embodiments are merely examples and should not be interpreted as being limiting. All modifications and variations within the scope of the claims of the present invention are within the scope of the present invention. [Industrial Applicability]

[0101] The present invention is useful when applied to a temperature measurement device for a fixing device, because it receives stray light radiation from the cylindrical inner wall, which is close to the sensor temperature, thereby reducing the impact on the detected temperature, and the narrowed tip does not interfere with the original light receiving range, blocking more stray light and preventing the thermopile sensor from making false detections. [Explanation of symbols]

[0102] 10 Image forming device 12 Device body 25 Thermopile Sensor 46 Fixing device 47 Outer cover 48 frames 56 Circuit Board 57 Photodetector 58 Environmental temperature measuring element 59 CAN 60 lenses 61 Cylindrical member 62 Fixing belt 88 Thermopile holding parts 89 Duct Cover 91 Duct 92 Thermopile sensor opening 94 Metal cylinder 95 Resin cover 96 Exhaust fan

Claims

1. A temperature measuring device that measures the temperature of a temperature detection object in a fixing device through an opening provided in the fixing device by a thermopile sensor provided outside the fixing device, the thermopile sensor is held by a sensor holding member, the sensor holding member is provided with a cylindrical member extending in front of the thermopile sensor and a narrowed portion provided at a tip of the cylindrical member, A temperature measuring device in which a frame of a cover of the fixing device and an outer cover are provided in this order in front of the throttle portion, and the opening size of the throttle portion is smaller than the openings of the frame and the outer cover.

2. 2. The temperature measuring device for a fixing device according to claim 1, wherein the cylindrical member is in contact with a thermopile sensor, and the thermopile sensor and the cylindrical member are thermally conductive.

3. 3. The temperature measuring device for a fixing device according to claim 1, wherein the diameter of the opening of the narrowed portion at the tip of the cylindrical member does not interfere with the original light receiving range of the thermopile sensor.

4. 4. The temperature measuring device for a fixing device according to claim 1, wherein a metal cylinder having low emissivity is provided on an inner wall of the cylindrical member.

5. 5. The temperature measuring device for a fixing device according to claim 1, wherein a metal cap having low emissivity is provided at the tip of the cylindrical member.

6. 6. The temperature measuring device for a fixing device according to claim 1, wherein the cylindrical member is provided with a vent.

7. a gap is provided between the opening provided in the fixing device and the restricting portion; The temperature measuring device for a fixing device according to any one of claims 1 to 6, further comprising an exhaust fan that exhausts airflow to the outside in order to generate an airflow that does not enter the cylindrical member through an opening provided in the fixing device.

8. 8. An image forming apparatus comprising the temperature measuring device for a fixing device according to claim 1.

Images