Image forming apparatus

Abstract

To accurately detect toner concentration, irrespective of variation in light irradiation capability of a concentration sensor while suppressing cost increases.SOLUTION: An image forming apparatus comprises: a control part 100 for adjusting the light quantity of a concentration sensor 130 based on a first pattern and a second pattern; a calculation part 101 for calculating, as light irradiation capability of the concentration sensor 130, a difference between a first output value output from the concentration sensor 130 in the case of the first pattern and a second output value output from the concentration sensor 130 in the case of the second pattern; and a correction part 102 for performing correction to eliminate a change caused by an ambient temperature with respect to an output value from the concentration sensor 130, in accordance with the light irradiation capability on the basis of change rate information indicating a corresponding relation between the light irradiation capability and a change rate in the output value from the concentration sensor 130 caused by the ambient temperature, the light irradiation capability calculated by the calculation part 101 and the ambient temperature,.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a technique for detecting toner concentration in an image forming apparatus. [Background technology]

[0002] Some image forming devices, such as copiers and multifunction peripherals, are equipped with an image forming unit that forms a toner image on recording paper. For example, the image forming unit is a mechanism that includes a photosensitive drum, a charging device, an exposure device, a developing device, and a primary transfer device for each color (e.g., black, yellow, cyan, and magenta), and forms an image on recording paper as a recording medium by secondary transfer via an intermediate transfer belt.

[0003] Furthermore, some image forming devices equipped with such an image forming unit are equipped with a density sensor that detects the density of toner transferred to the intermediate transfer belt (see, for example, Patent Documents 1 and 2 listed below). The density of toner transferred to the intermediate transfer belt is detected in order to ensure that the toner density in the toner image formed on the recording paper reaches a target density, thereby maintaining the quality of the image formed on the recording paper. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2009-008839 [Patent Document 2] Japanese Patent Application Laid-Open No. 2017-053903 Summary of the Invention [Problem to be solved by the invention]

[0005] The density sensor is configured to include, for example, a light-emitting element such as an LED (Light Emitting Diode) and a light-receiving element that receives the reflected light of the light-emitting element. Such an optical density sensor detects the toner density on the intermediate transfer belt by irradiating light from the light-emitting element onto the intermediate transfer belt, receiving the reflected light with the light-receiving element, and outputting a voltage signal corresponding to the received reflected light.

[0006] However, optical density sensors such as those described above are affected by the ambient temperature, which can cause the output value (voltage signal) from the density sensor to fluctuate, potentially making it impossible to accurately detect toner density. For this reason, density sensors sometimes use a light-receiving element (two-receiving type) that has both a light-receiving element that receives specularly reflected light and a light-receiving element that receives diffusely reflected light.

[0007] If a density sensor uses a two-light receiving element, it can obtain two output values, one from specularly reflected light and one from diffusely reflected light, and can calculate the ratio of these two output values. This ratio of the two output values is not affected by the ambient temperature, making it possible to detect toner density with high accuracy.

[0008] However, light receiving units that receive both specular and diffuse reflected light (two-light receiving type) have the problem of being more expensive than light receiving units that receive only either specular or diffuse reflected light (single-light receiving type).In addition, the light irradiation capabilities of the light-emitting elements such as LEDs that make up the concentration sensor vary from product to product, and this variation can cause errors in the output values from the concentration sensor.

[0009] The present invention has been made in view of the above circumstances, and has as its object to make it possible to detect toner concentration with high accuracy while suppressing increases in cost and regardless of variations in the light irradiation capacity of the concentration sensor. [Means for solving the problem]

[0010] According to one aspect of the present invention, there is provided an image forming apparatus including an image carrier that carries a toner image, an intermediate transfer belt onto which the toner image of the image carrier is transferred, a transfer unit that transfers the toner image transferred onto the intermediate transfer belt onto a recording medium, a light emitting unit that irradiates light toward the intermediate transfer belt, and a light receiving unit that receives only specularly reflected light or diffusely reflected light of the light irradiated by the light emitting unit, and further including a density sensor that detects the density of the toner transferred onto the intermediate transfer belt, a temperature sensor that detects the ambient temperature of the density sensor, an adjustment unit that adjusts the amount of light irradiated from the light emitting unit, a first adjustment that controls the adjustment unit to adjust the amount of light of the light emitting unit in a predetermined first pattern, and a second adjustment that controls the adjustment unit to adjust the amount of light different from the predetermined first pattern. a control unit that selects and executes either a first adjustment that adjusts the light intensity of the light-emitting unit in a predetermined second pattern, or a second adjustment that adjusts the light intensity of the light-emitting unit in a predetermined second pattern; a calculation unit that calculates the difference between a first output value output from the concentration sensor during the first adjustment and a second output value output from the concentration sensor during the second adjustment as the light irradiation capacity of the concentration sensor; and a correction unit that corrects the output value from the concentration sensor to eliminate changes caused by the ambient temperature in accordance with the light irradiation capacity, based on the light irradiation capacity calculated by the calculation unit, the ambient temperature detected by the temperature sensor, and change rate information that indicates a correspondence between the light irradiation capacity and the change rate of the output value from the concentration sensor caused by the ambient temperature.

[0011] According to one aspect of the present invention, there is provided an image forming apparatus including an image carrier that carries a toner image, an intermediate transfer belt onto which the toner image of the image carrier is transferred, and a transfer unit that transfers the toner image transferred onto the intermediate transfer belt onto a recording medium, the image forming apparatus further including: a light-emitting unit that irradiates light toward the intermediate transfer belt; and a light-receiving unit that receives either specularly reflected light or diffusely reflected light of the light irradiated by the light-emitting unit; a density sensor that detects the density of the toner transferred onto the intermediate transfer belt; a temperature sensor that detects the ambient temperature of the density sensor; an adjustment unit that adjusts the amount of light irradiated from the light-emitting unit; and a first adjustment that adjusts the amount of light irradiated from the light-emitting unit in a predetermined first pattern by controlling the adjustment unit; and a second adjustment that adjusts the amount of light irradiated from the light-emitting unit in a predetermined second pattern different from the first predetermined pattern. a calculation unit that calculates the difference between a first output value output from the concentration sensor during the first adjustment and a second output value output from the concentration sensor during the second adjustment as the light irradiation capacity of the concentration sensor; an identification unit that identifies a capacity rank of the light irradiation capacity based on the light irradiation capacity calculated by the calculation unit; and a correction unit that corrects the output value from the concentration sensor to eliminate a change caused by the ambient temperature in accordance with the capacity rank, based on the capacity rank identified by the identification unit, the ambient temperature detected by the temperature sensor, and change rate information that indicates a correspondence between the capacity rank and a change rate of the output value from the concentration sensor caused by the ambient temperature. [Effects of the Invention]

[0012] According to the present invention, the output value from the density sensor is corrected to eliminate variations due to ambient temperature in accordance with the light irradiation capacity of the density sensor, and this correction can be achieved with a single-light receiving element instead of the conventional two-light receiving element. Therefore, according to the present invention, it is possible to detect toner concentration with high accuracy, regardless of variations in light irradiation capacity, while suppressing increases in cost. [Brief explanation of the drawings]

[0013] [Figure 1] 1 is a front cross-sectional view showing the structure of an image forming apparatus according to a first embodiment of the present invention. [Figure 2] 1 is a functional block diagram illustrating a schematic main internal configuration of an image forming apparatus according to a first embodiment of the present invention. [Figure 3] FIG. 10 is a diagram illustrating an example of the arrangement of a concentration sensor. [Figure 4] 10 is a graph showing an example of optical characteristics of a concentration sensor. [Figure 5] 10 is a performance rank table in which the light irradiation capabilities of a concentration sensor are divided into performance ranks. [Figure 6] 10 is a graph showing an example of temperature characteristics of a concentration sensor. [Figure 7] 10 is a graph showing an example of the temperature characteristics of a concentration sensor, where (A) shows the case where the ambient temperature is 25°C to 60°C, and (B) shows the case where the ambient temperature is 0°C to 25°C. [Figure 8] 10 is a first increase amount table showing an increase amount of the output value change rate for each light irradiation ability rank when the ambient temperature of the concentration sensor rises by 1° C. when the ambient temperature is between 25° C. and 60° C.; [Figure 9] FIG. 4 is a diagram illustrating an example of temperature characteristics of a concentration sensor. [Figure 10] This is a second increase amount table showing the increase (decrease) in the output value change rate when the ambient temperature of the concentration sensor drops by 1°C when the ambient temperature is between 0°C and 25°C, for each performance rank of light irradiation ability. [Figure 11] 6 is a flowchart showing an example of processing performed by a control unit in the image forming apparatus according to the first embodiment. [Figure 12] 6 is a flowchart showing an example of processing performed by a control unit in the image forming apparatus according to the first embodiment. [Figure 13] FIG. 10 is a functional block diagram illustrating a schematic main internal configuration of an image forming apparatus according to a second embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0014] An image forming apparatus according to an embodiment of the present invention will be described below with reference to the drawings. Fig. 1 is a front cross-sectional view showing the structure of the image forming apparatus according to the first embodiment of the present invention. Fig. 2 is a functional block diagram showing the main internal configuration of the image forming apparatus according to the first embodiment of the present invention.

[0015] The image forming apparatus 1 is a multifunction device that combines multiple functions, such as a copy function, a printer function, a scanner function, and a facsimile function. The image forming apparatus 1 includes a control unit 10, a document feeder 6, a document reader 5, an image forming unit 12, a fixing unit 13, a paper feeder 14, an operation unit 47, a network interface unit 91, and a storage unit 8.

[0016] The document feeder 6 is configured to be openable and closable by a hinge or the like (not shown) on the top surface of the document reading unit 5, and functions as a document pressing cover when reading a document placed on a platen glass (not shown). The document feeder 6 is also an ADF (Auto Document Feeder), and includes a document placement tray 61, and supplies documents placed on the document placement tray 61 to the document reading unit 5.

[0017] The document reading unit 5 includes a scanner and the like, and reads a document fed from a document feeding unit 6, or reads a document placed on a platen glass.

[0018] The following describes the case where a document is read by the image forming apparatus 1. The document reading unit 5 optically reads an image of a document supplied to the document reading unit 5 by the document feeding unit 6 or a document placed on the platen glass, and generates image data. The image data generated by the document reading unit 5 is stored in an image memory (not shown) or the like.

[0019] An image forming operation performed by the image forming apparatus 1 will be described. The image forming section 12 includes image forming units 12B, 12Y, 12C, and 12M (hereinafter simply referred to as "image forming units 12") for each color (black, yellow, cyan, and magenta). Each image forming unit 12 includes a photosensitive drum 121 as an image carrier that carries a toner image, a charging device, an exposure device, a developing device, and a primary transfer device 120 (primary transfer roller 126). The image forming units 12 are configured to form an image on recording paper as a recording medium by secondary transfer via an intermediate transfer belt 125 stretched between a drive roller 125A and a driven roller 125B. The primary transfer roller 126 is an example of a transfer section in the claims.

[0020] The image forming unit 12 for each color forms a toner image on the photosensitive drum 121 through the processes of charging, exposing, and developing based on an image consisting of each color component, and the toner image is transferred onto the intermediate transfer belt 125 by the primary transfer roller 126.

[0021] Intermediate transfer belt 125 has an image bearing surface on its outer circumferential surface onto which a toner image is transferred, and is driven by drive roller 125A while in contact with the circumferential surfaces of photosensitive drums 121. Intermediate transfer belt 125 travels endlessly between drive roller 125A and driven roller 125B in synchronization with each photosensitive drum 121.

[0022] The toner images of each color transferred onto the intermediate transfer belt 125 are superimposed on each other on the intermediate transfer belt 125 to form a color toner image. The secondary transfer roller 127 transfers the color toner image formed on the surface of the intermediate transfer belt 125 onto the recording paper P conveyed from the paper feed unit 14 by a conveying roller pair 191 provided at an appropriate position on the conveying path 190, at a nip portion N between the secondary transfer roller 127 and the driving roller 125A, with the intermediate transfer belt 125 sandwiched therebetween.

[0023] The image forming unit 12 includes concentration sensors 130A and 130B (hereinafter simply referred to as "concentration sensor 130") that detect the concentration of toner transferred to the intermediate transfer belt 125, and a temperature sensor 140. The concentration sensor 130 is disposed upstream of the secondary transfer roller 127 in the direction of movement of the intermediate transfer belt 125. As shown in FIG. 3, the two concentration sensors 130A and 130B are disposed in parallel in a direction perpendicular to the direction of movement of the intermediate transfer belt 125 (the axial direction of the photosensitive drum 121). The temperature sensor 140 detects the internal temperature of the image forming apparatus 1 to monitor the status of the image forming apparatus 1 and control its operation. The temperature sensor 140 is also used to detect the ambient temperature of the concentration sensor 130.

[0024] The density sensor 130 is an optical sensor. Each of the density sensors 130A and 130B includes a light-emitting unit (not shown) that emits light toward the intermediate transfer belt 125, and a light-receiving unit (not shown) that receives the reflected light of the light emitted by the light-emitting unit. The light-emitting unit is an LED. The light-receiving unit includes a light-receiving element such as a photodiode, and is a single-light-receiving type that receives only either specularly reflected light or diffusely reflected light of the light emitted by the light-emitting unit. The density sensor 130A includes a light-receiving unit that receives only specularly reflected light, and the density sensor 130B includes a light-receiving unit that receives only diffusely reflected light.

[0025] The density sensors 130A and 130B use different types of light receiving elements to broaden the range of densities that can be detected. Also, since the amount of diffusely reflected light received is small for black toner and the amount of specularly reflected light received is small for toners of colors other than black, it is advisable to use different types of light receiving elements to properly receive the light reflected from each color toner.

[0026] The image forming unit 12 is also provided with adjustment units 131A and 131B (hereinafter simply referred to as "adjustment unit 131") for adjusting the amount of light emitted from the light-emitting units of the density sensors 130A and 130B. In this embodiment, an example will be described in which a variable resistor is used for the adjustment unit 131. The cathode side of the LED, which is the light-emitting unit, is grounded via the variable resistor serving as the adjustment unit 131. The control unit 100, which will be described later, adjusts the resistance value of the variable resistor to change the voltage value applied to the LED, and thereby changes the value of the current flowing through the LED, thereby adjusting the amount of light from the LED.

[0027] Here, the concentration sensor 130 will be described in detail. Fig. 4 is a graph showing an example of the optical characteristics of the concentration sensor 130 detected under predetermined conditions (for example, at a temperature of 25°C). In Fig. 4, the horizontal axis represents the applied voltage applied to the concentration sensor 130 (its light-emitting section), and the vertical axis represents the output voltage from the concentration sensor 130. Fig. 4 shows two line segments LS1 and LS2 that indicate the change in the output voltage from the concentration sensor 130 depending on the applied voltage.

[0028] Line segment LS1 indicates the output voltage from the concentration sensor 130 with the highest light irradiation capability. When the applied voltage is 1 V, the output voltage is 0.238 V, and when the applied voltage is 3 V, the output voltage is 2.87 V. Line segment LS2 indicates the output voltage from the concentration sensor 130 with the lowest light irradiation capability. When the applied voltage is 1 V, the output voltage is 0.182 V, and when the applied voltage is 3 V, the output voltage is 2.47 V.

[0029] As can be seen from the graph shown in Figure 4, the slope of line segment LS1 is greater than that of line segment LS2, so the difference in output value between the two points is greater for line segment LS1 than for line segment LS2. For example, the difference in output voltage between applied voltages of 1V and 3V is 2.632V (=2.87-0.238) for line segment LS1, while it is 2.288V (=2.47-0.182) for line segment LS2.

[0030] In this way, the difference in output values between two points is larger for a concentration sensor with higher light irradiation capability. In other words, the concentration sensor 130 with larger output values between two points has higher light irradiation capability.

[0031] 5 is a performance ranking table in which the light irradiation capacity of the concentration sensor 130 is divided into 11 performance ranks from "-5" to "+5" based on the difference in output voltage from the concentration sensor when applied voltages are 1 V and 3 V. The difference in one rank is 0.0344 V (= (2.632 - 2.288) / 10).

[0032] Fig. 6 is a graph showing an example of the temperature characteristics of concentration sensor 130. In Fig. 6, the horizontal axis represents the ambient temperature (°C) of concentration sensor 130, and the vertical axis represents the rate of change in the output value (output voltage) from concentration sensor 130. Fig. 6 shows three line segments LS11 to LS13 that represent the temperature characteristics of concentration sensors with different light irradiation capabilities. The reference temperature is set to 25°C, and the rate of change in the output value is shown based on the output value when the ambient temperature of concentration sensor 130 is at the reference temperature of 25°C.

[0033] Line segment LS11 shows the temperature characteristics of the density sensor 130 with the highest light irradiation capability, with a rate of change of -8.831% when the ambient temperature is 0°C and 15.792% when the ambient temperature is 60°C. Line segment LS12 shows the temperature characteristics of the density sensor 130 with the middle light irradiation capability, with a rate of change of -10.280% when the ambient temperature is 0°C and 10.845% when the ambient temperature is 60°C. Line segment LS13 shows the temperature characteristics of the density sensor 130 with the lowest light irradiation capability, with a rate of change of -9.467% when the ambient temperature is 0°C and 5.199% when the ambient temperature is 60°C.

[0034] Fig. 7(A) is a graph showing the temperature characteristics of the concentration sensor 130 when the ambient temperature of the concentration sensor 130 is 25°C (reference temperature) to 60°C. Fig. 7(B) is a graph showing the temperature characteristics of the concentration sensor 130 when the ambient temperature of the concentration sensor 130 is 0°C to 25°C (reference temperature).

[0035] As can be seen from the graph shown in Figure 7(A), when the ambient temperature of the concentration sensor 130 is 25°C or higher, differences in light irradiation capacity (capability rank) are significantly reflected in the rate of change of the output value of the concentration sensor 130. However, as can be seen from the graph shown in Figure 7(B), when the ambient temperature is lower than 25°C, differences in light irradiation capacity (capability rank) do not significantly affect the rate of change of the output value of the concentration sensor 130.

[0036] 8 is a first increase amount table showing the increase (% / °C) in the output value change rate for each light irradiation capacity rank when the ambient temperature of the concentration sensor 130 rises by 1°C when the ambient temperature is between 25°C and 60°C. The output value change rate of the concentration sensor 130 with the highest light irradiation capacity rank increases by 15.792% when the ambient temperature rises by 35°C from 25°C to 60°C, so the increase in the output value change rate for a 1°C rise in ambient temperature is 0.4512% (=15.792 / 35).

[0037] On the other hand, the output value change rate of the concentration sensor 130, which has the lowest light irradiation capability, increases by 5.199% when the ambient temperature rises by 35°C from 25°C to 60°C, so the increase in the output value change rate when the ambient temperature rises by 1°C is 0.1485% (=5.199 / 35).

[0038] Furthermore, the difference in one capacity rank of light irradiation capacity is 0.03027 (= (0.4512 - 0.1485) / 10), so for example, for a concentration sensor 130 with a capacity rank of "-4", the increase in the rate of change of the output value when the ambient temperature rises by 1°C is 0.1788% (≒ 0.1485 + 0.03027).

[0039] Fig. 9 is a diagram showing an example of the temperature characteristics of concentration sensor 130. In Fig. 9, the horizontal axis represents the light irradiation capacity of concentration sensor 130, and the vertical axis represents the increase in the rate of change in the output value of concentration sensor 130 when the ambient temperature of concentration sensor 130 rises by 1°C. As explained using Figs. 4 and 5, the light irradiation capacity can be represented by the difference in output voltage between two points at applied voltages of 1V and 3V, for example.

[0040] 9, one end of line segment LS21 represents the output voltage difference of "2.632" and the increase in the output value change rate of "0.4512," while the other end of line segment LS21 represents the output voltage difference of "2.288" and the increase in the output value change rate of "0.1485." If the increase is Y and the difference (light irradiation capacity) is X, then linear interpolation of these two points can be used to determine Equation 1: Y = 0.8798X - 1.8644.

[0041] 10 is a second increase amount table showing the increase (% / °C) in the output value change rate when the ambient temperature of the concentration sensor 130 drops by 1°C for each light irradiation capacity rank when the ambient temperature is between 0°C and 25°C. The output value change rate of the concentration sensor 130 with the highest light irradiation capacity rank decreases by 8.831% when the ambient temperature drops by 25°C from 25°C to 0°C, so the increase in the output value change rate when the ambient temperature drops by 1°C is -0.3532 (≒-8.831 / 25). In other words, as the ambient temperature drops, the output value change rate decreases.

[0042] On the other hand, the output value change rate of the concentration sensor 130, which has the lowest light irradiation capability, decreases by 9.467% when the ambient temperature drops by 25°C from 25°C to 0°C, so the increase in the output value change rate when the ambient temperature drops by 1°C is -0.3787 (≒-9.467 / 25).

[0043] In addition, the output value change rate of the concentration sensor 130, whose light irradiation capability is ranked in the middle, decreases by 10.280% when the ambient temperature drops by 25°C from 25°C to 0°C, so the increase in the output value change rate when the ambient temperature drops by 1°C is -0.4112 (=-10.280 / 25).

[0044] The difference in one level of light irradiation capability rank from the middle rank to the highest rank is 0.0116 (= (0.4112 - 0.3532) / 5), so for example, for a concentration sensor 130 with a capability rank of "+4", the increase in the rate of change of the output value when the ambient temperature drops by 1°C is -0.3648 (= -0.3532 - 0.0116).

[0045] Furthermore, the difference in one level of light irradiation capability rank from the middle rank to the lowest rank is 0.0065 (= (0.4112 - 0.3787) / 5), so for example, for a concentration sensor 130 with a capability rank of "-4," the increase in the rate of change of the output value when the ambient temperature drops by 1°C is -0.3852 (= -0.3787 - 0.0065).

[0046] The temperature characteristics of the concentration sensor 130 are significantly affected by the light irradiation capacity when the ambient temperature is 25°C or higher, but are less affected by the light irradiation capacity when the ambient temperature is below 25°C. Therefore, when the ambient temperature of the concentration sensor 130 is below 25°C, the increase in the rate of change of the output value of the concentration sensor 130 when the ambient temperature of the concentration sensor 130 drops by 1°C can be expressed as a fixed value without taking into account differences in light irradiation capacity. For example, the average of the highest, lowest, and median ranks of light irradiation capacity, "-0.381 (≒ (-0.3532 - 0.3787 - 0.4112) / 3)," is set as the fixed value.

[0047] Returning to the description of other components of the image forming apparatus 1, the image forming unit 12 forms a toner image on recording paper fed from the paper feed unit 14, based on image data generated by the document reading operation, image data stored in an image memory or the like, image data received from a computer connected via a network, and the like, to create a printed matter.

[0048] The paper feed unit 14 includes a paper feed cassette 141, a pickup roller that picks up recording paper P from the paper feed cassette 141 and feeds it to the image forming unit 12, a transport roller, a transport path, and a rotation drive mechanism for each roller.

[0049] The fixing unit 13 is a fixing device equipped with a heat roller, a pressure roller, and a drive mechanism for rotating these rollers. The fixing unit 13 heats and presses the recording paper on which the toner image has been formed by the image forming unit 12 at the nip between the two rollers, fixing the toner image to the recording paper. The recording paper that has been fixed is then discharged to the discharge tray 151.

[0050] The operation unit 47 includes various hard keys that are operated by the user, and receives instructions from the user, such as an instruction to execute an image forming operation, regarding various operations and processes that the image forming apparatus 1 can execute in response to the operation of the hard keys.

[0051] The operation unit 47 includes a display unit 473 that displays operation guides and the like to the operator. The operation unit 47 also receives input of instructions from the user based on the user's operation (touch operation) on the screen displayed on the display unit 473 via a touch panel that the display unit 473 has.

[0052] The display unit 473 is composed of an LCD (Liquid Crystal Display) or the like. When the operator touches a button or key displayed on the screen, the touch panel receives an instruction associated with the touched position. In this case, the touch panel functions as an operation unit.

[0053] The network interface unit 91 is a communication interface for transmitting and receiving various data to and from an external device (for example, a personal computer) within a local area or on the Internet.

[0054] The storage unit 8 is a large-capacity storage device such as a hard disk drive (HDD) or a solid state drive (SSD), and stores various control programs and the like.

[0055] The control unit 10 includes a processor, a random access memory (RAM), a read only memory (ROM), and a dedicated hardware circuit. The processor is, for example, a central processing unit (CPU), an application specific integrated circuit (ASIC), or a micro processing unit (MPU). The control unit 10 includes a control unit 100, a calculation unit 101, and a correction unit 102.

[0056] The control unit 10 functions as a control unit 100, a calculation unit 101, and a correction unit 102 through operation by the processor in accordance with a control program stored in the storage unit 8. However, the control unit 100 and the like can also be configured by hardware circuits, without relying on operation in accordance with a control program by the control unit 10. Unless otherwise specified below, the same applies to each embodiment.

[0057] The control unit 100 is responsible for overall operational control of the image forming apparatus 1. The control unit 100 is connected to the document feed unit 6, the document reading unit 5, the image forming unit 12, the fixing unit 13, the paper feed unit 14, the operation unit 47, the network interface unit 91, and the storage unit 8, and controls the driving of each of these units. For example, the control unit 100 executes various processes required for image formation by the image forming apparatus 1.

[0058] In addition, the control unit 100 controls the adjustment unit 131 to select and execute either a first adjustment that adjusts the light intensity of the light-emitting unit of the density sensor 130 in a predetermined first pattern, or a second adjustment that adjusts the light intensity of the light-emitting unit of the density sensor 130 in a predetermined second pattern that is different from the above-mentioned predetermined first pattern.

[0059] For example, under predetermined conditions (ambient temperature of concentration sensor 130: 25°C), control unit 100 controls variable resistor VR as adjustment unit 131 to set the magnitude of the voltage applied to the light-emitting element of concentration sensor 130 to 1 V as the first adjustment, and to set the magnitude of the voltage applied to the light-emitting element of concentration sensor 130 to 3 V as the second adjustment.

[0060] The calculation unit 101 calculates the difference between the first output value output from the density sensor 130 during the first adjustment and the second output value output from the density sensor 130 during the second adjustment as the light irradiation capability of the density sensor 130.

[0061] For example, when the first output value is 0.22 V and the second output value is 2.74 V, the calculation unit 101 calculates the difference between the two, 2.52 V (=2.74-0.22), as the light irradiation capacity of the concentration sensor 130. Therefore, according to the capacity rank table shown in FIG. 5, which divides the light irradiation capacity into 11 capacity ranks from "-5" to "+5", the capacity rank of the concentration sensor 130 corresponds to "+2".

[0062] The calculation of the light irradiation capacity of the density sensor 130 by the calculation unit 101 is performed at any timing, such as when the image forming apparatus 1 is manufactured or shipped, and information indicating the light irradiation capacity obtained by the calculation by the calculation unit 101 (light irradiation capacity information) is stored in the storage unit 8. The light irradiation capacity information stored in the storage unit 8 may be the difference between the first output value and the second output value (for example, 2.52 V) or a capacity rank (for example, +2).

[0063] The correction unit 102 corrects the output value from the concentration sensor 130 to eliminate changes caused by the ambient temperature in accordance with the light irradiation capacity, based on the light irradiation capacity calculated by the calculation unit 101, the ambient temperature detected by the temperature sensor 140, and change rate information indicating the correspondence between the light irradiation capacity and the change rate of the output value from the concentration sensor 130 caused by the ambient temperature.

[0064] The change rate information is, for example, information indicating the increase or decrease in the rate of change of the output value of the concentration sensor 130 when the ambient temperature of the concentration sensor 130 changes by 1°C. When the ambient temperature is between 25°C and 60°C, it is the above formula 1 (Y=0.8798X-1.8644) or the first increase amount table as shown in Figure 8, and when the ambient temperature is between 0°C and 25°C, it is the above fixed value (-0.381) or the second increase amount table as shown in Figure 10.

[0065] The true value of the output value from the concentration sensor 130 will be explained using an example where the output value from the concentration sensor 130 is 1.56 V, the difference between the first output value and the second output value is 2.52 V (this is the light irradiation capacity, calculated at the time of manufacture or shipment, etc., and stored in the memory unit 8), and the ambient temperature is 27.6°C.

[0066] When the difference between the first output value and the second output value is 2.52 V and the ambient temperature is 27.6°C (>25°C), the increase amount when the ambient temperature rises by 1°C is calculated to be 0.352% / °C (=0.8798*2.52-1.8644) from the above formula 1. On the other hand, when the first increase amount table shown in Fig. 8 is used, the performance rank of the concentration sensor 130 is "+2", so the increase amount when the ambient temperature rises by 1°C is 0.3604% / °C.

[0067] Because the ambient temperature is 2.6°C (=27.6-25) higher than 25°C, the output value change rate is 0.9152% (=0.352*2.6). In other words, the output value from the concentration sensor 130 is 1.009152 times the true value (=100%+0.9152%). Dividing the output value of 1.56V from the concentration sensor 130 by 1.009152 to restore the output value to its true value results in 1.5459V.

[0068] Next, the true value of the output value from the concentration sensor 130 will be explained using an example where the output value from the concentration sensor 130 is 1.42 V, the difference between the first output value and the second output value is 2.43 V, and the ambient temperature is 22.7°C.

[0069] When the difference between the first output value and the second output value is 2.43 V and the ambient temperature is 22.7°C (<25°C), the increase when the ambient temperature rises by 1°C from the fixed value is -0.381% / °C. On the other hand, when the second increase amount table shown in Figure 10 is used, the performance rank of the concentration sensor 130 is "-1", so the increase when the ambient temperature drops by 1°C is -0.4047% / °C.

[0070] Because the ambient temperature is 2.3°C (=25-22.7) lower than 25°C, the output value change rate is -0.9308% (≒-0.4047*2.3). In other words, the output value from the concentration sensor 130 is 0.990692 times the true value (=100%-0.9308%). Dividing the output value of 1.42V from the concentration sensor 130 by 0.990692 to restore the output value to its true value results in 1.4333V.

[0071] That is, when the ambient temperature detected by the temperature sensor 140 is higher than a predetermined reference temperature at which the rate of change is 0, the correction unit 102 performs a predetermined correction to reduce the output value from the concentration sensor 130, and when the ambient temperature is lower than the reference temperature, the correction unit 102 performs a predetermined correction to increase the output value from the concentration sensor 130.

[0072] Next, an example of processing performed by the control unit 10 in the image forming apparatus 1 according to the first embodiment will be described with reference to the flowchart shown in Fig. 11. Note that this processing is performed under predetermined conditions (for example, when the ambient temperature of the density sensor 130 is 25°C) at the time of manufacturing or shipping, and is performed for each of the density sensors 130A and 130B.

[0073] The control unit 100 controls the variable resistor VR as the adjustment unit 131 to set the magnitude of the voltage applied to the light-emitting element of the concentration sensor 130 to 1 V as the first adjustment (S1), and obtains the output value (voltage signal) from the concentration sensor 130 as the first output value (S2).

[0074] Next, the control unit 100 controls the variable resistor VR serving as the adjustment unit 131 to set the magnitude of the voltage applied to the light-emitting element of the concentration sensor 130 to 3 V as the second adjustment (S3), and obtains the output value (voltage signal) from the concentration sensor 130 as the second output value (S4).

[0075] The calculation unit 101 calculates the difference between the first output value output from the concentration sensor 130 during the first adjustment and the second output value output from the concentration sensor 130 during the second adjustment as the light irradiation capacity of the concentration sensor 130 (S5), and the control unit 100 stores information indicating the difference (light irradiation capacity) calculated by the calculation unit 101 in the memory unit 8 (S6), and this processing ends.

[0076] Next, another example of processing performed by the control unit 10 in the image forming apparatus 1 according to the first embodiment will be described with reference to the flowchart shown in Fig. 12. This processing is performed, for example, when the operation unit 47 receives a user operation instructing to correct the toner concentration, and is performed for each of the concentration sensors 130A and 130B.

[0077] The control unit 100 controls the operation of the image forming unit 12 to generate a toner patch on the intermediate transfer belt 125 (S11), and controls the variable resistor VR as the adjustment unit 131 to apply a predetermined voltage (e.g., 2 V) to the light-emitting element of the density sensor 130 (S12), and acquires an output value (voltage signal) from the density sensor 130 (S13).

[0078] Next, the control unit 100 acquires information indicating the ambient temperature T detected by the temperature sensor 140 (S14), and determines whether the ambient temperature T is 25°C or higher (S15). If the control unit 100 determines that the ambient temperature T is 25°C or higher (YES in S15), the correction unit 102 reads out the light irradiation capacity information stored in the storage unit 8 (S16), and calculates the increase Y in the rate of change of the output value when the ambient temperature rises by 1°C based on the above formula 1 and the light irradiation capacity (difference X) indicated by the read light irradiation capacity information (S17). For example, when the difference X is 2.52V, the increase Y when the ambient temperature rises by 1°C is calculated from the above formula 1 to be 0.352% / °C (=0.8798*2.52-1.8644).

[0079] The correction unit 102 calculates the temperature difference ΔT between the ambient temperature T and 25°C (S18), and calculates the rate of change of the output value based on the increase Y calculated in S17 and ΔT (S19). For example, when the ambient temperature T is 2.6°C higher than 25°C, the rate of change of the output value is 0.9152% (=0.352*2.6).

[0080] The correction unit 102 restores the output value from the density sensor 130 to a true value based on the calculated rate of change in the output value (S20), and this process ends.

[0081] On the other hand, if the control unit 100 determines that the ambient temperature T is not equal to or higher than 25°C (NO in S15), the correction unit 102 calculates the temperature difference ΔT between the ambient temperature T and 25°C (S21), and calculates the output value change rate based on the increase in the output value change rate (fixed value, -0.4047% / °C) and ΔT (S22). For example, when the ambient temperature T is 2.3°C lower than 25°C, the output value change rate is -0.9308% (≒-0.4047*2.3).

[0082] The correction unit 102 restores the output value from the density sensor 130 to the true value based on the calculated rate of change of the output value (S20), as described above, and then the process ends.

[0083] According to the first embodiment, the output value from the density sensor 130 is corrected to eliminate variations due to ambient temperature, depending on the light irradiation capacity of the density sensor 130. Furthermore, this correction can be achieved using a single-light-receiving light-receiving unit, rather than the conventional dual-light-receiving type. Therefore, it is possible to accurately detect toner concentration regardless of variations in light irradiation capacity, while suppressing cost increases. Even when the ambient temperature T is lower than 25°C, the increase in the output value change rate may not be fixed, but a new formula may be set for each light irradiation capacity rank based on the data shown in FIG. 10, and the output value change rate may be calculated from the temperature difference ΔT and the formula.

[0084] 13 is a functional block diagram showing a schematic diagram of the main internal configuration of an image forming apparatus according to the second embodiment. In the second embodiment, the control unit 10 functions as a control unit 100, a calculation unit 101, a correction unit 102, and also as an identification unit 103, by the operation of the processor in accordance with the control program stored in the storage unit 8.

[0085] The specifying unit 103 specifies the performance rank of the light irradiation performance based on the light irradiation performance calculated by the calculating unit 101. For example, the specifying unit 103 specifies the performance rank of the light irradiation performance of the concentration sensor 130 using a performance rank table such as that shown in FIG.

[0086] The correction unit 102 corrects the output value from the concentration sensor 130 to eliminate changes caused by the ambient temperature according to the performance rank, based on the performance rank identified by the identification unit 103, the ambient temperature detected by the temperature sensor 140, and change rate information indicating the correspondence between the performance rank and the change rate of the output value from the concentration sensor 130 caused by the ambient temperature.

[0087] Furthermore, the storage unit 8 stores, as the change rate information, a first increase amount table such as the example shown in Fig. 8 and a second increase amount table such as the example shown in Fig. 10. The correction unit 102 performs the correction using the first increase amount table and the second increase amount table.

[0088] According to the second embodiment, unlike the first embodiment, a table is used instead of a mathematical formula, and therefore calculation processing using a mathematical formula is not required, thereby simplifying the processing.

[0089] The present invention is not limited to the configuration of the above embodiment, and various modifications are possible. In addition, in the above embodiment, the configuration and processing shown in the above embodiment using Figures 1 to 13 are merely one embodiment of the present invention, and it is not intended that the present invention be limited to these configurations and processing. [Explanation of symbols]

[0090] 1. Image forming device 12 Image forming unit 100 control section 101 Calculation Unit 102 Correction unit 103 Specific part 121 Photosensitive drum 125 Intermediate transfer belt 126 Primary transfer roller 130 Concentration sensor 131 Adjustment section 140 Temperature Sensor

Claims

1. an image carrier that carries a toner image; an intermediate transfer belt onto which the toner image of the image carrier is transferred; a transfer section that transfers the toner image transferred onto the intermediate transfer belt onto a recording medium; a density sensor having a light-emitting unit that irradiates light toward the intermediate transfer belt and a light-receiving unit that receives only either specularly reflected light or diffusely reflected light of the light irradiated by the light-emitting unit, and that detects the density of the toner transferred to the intermediate transfer belt; a temperature sensor for detecting an ambient temperature of the concentration sensor; an adjustment unit that adjusts the amount of light emitted from the light emitting unit; a control unit that controls the adjustment unit to selectively execute either a first adjustment that adjusts the light amount of the light-emitting unit in a predetermined first pattern or a second adjustment that adjusts the light amount of the light-emitting unit in a predetermined second pattern different from the predetermined first pattern; a calculation unit that calculates a difference between a first output value output from the density sensor during the first adjustment and a second output value output from the density sensor during the second adjustment as the light irradiation capability of the density sensor; an image forming apparatus comprising: a correction unit that corrects the output value from the density sensor to eliminate changes caused by the ambient temperature in accordance with the light irradiation capacity, based on the light irradiation capacity calculated by the calculation unit, the ambient temperature detected by the temperature sensor, and change rate information that indicates the correspondence between the light irradiation capacity and the change rate of the output value from the density sensor caused by the ambient temperature.

2. an image carrier that carries a toner image; an intermediate transfer belt onto which the toner image of the image carrier is transferred; a transfer unit that transfers the toner image transferred to the intermediate transfer belt onto a recording medium, a density sensor having a light-emitting unit that irradiates light toward the intermediate transfer belt and a light-receiving unit that receives only either specularly reflected light or diffusely reflected light of the light irradiated by the light-emitting unit, and that detects the density of the toner transferred to the intermediate transfer belt; a temperature sensor for detecting an ambient temperature of the concentration sensor; an adjustment unit that adjusts the amount of light emitted from the light emitting unit; a control unit that controls the adjustment unit to selectively execute either a first adjustment that adjusts the light amount of the light-emitting unit in a predetermined first pattern or a second adjustment that adjusts the light amount of the light-emitting unit in a predetermined second pattern different from the predetermined first pattern; a calculation unit that calculates a difference between a first output value output from the density sensor during the first adjustment and a second output value output from the density sensor during the second adjustment as the light irradiation capability of the density sensor; an identification unit that identifies a performance rank of the light irradiation performance based on the light irradiation performance calculated by the calculation unit; an image forming apparatus comprising: a correction unit that corrects the output value from the density sensor to eliminate changes caused by the ambient temperature in accordance with the performance rank, based on the performance rank identified by the identification unit, the ambient temperature detected by the temperature sensor, and change rate information indicating the correspondence between the performance rank and the change rate of the output value from the density sensor caused by the ambient temperature.

3. The image forming apparatus of claim 1 or claim 2, wherein the correction unit performs a predetermined correction to reduce the output value from the density sensor when the ambient temperature detected by the temperature sensor is higher than a predetermined reference temperature at which the rate of change is 0, and performs a predetermined correction to increase the output value from the density sensor when the ambient temperature is lower than the reference temperature.

4. The image forming apparatus according to claim 3 , wherein the reference temperature is set to a temperature at which the rate of change changes due to a difference in the light irradiation capacity.

5. 5. The image forming apparatus according to claim 4, wherein the correction unit corrects the output value based on the light irradiation capacity when the ambient temperature is higher than the reference temperature, and corrects the output value without based on the light irradiation capacity when the ambient temperature is lower than the reference temperature.

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