JP2005031378A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus realizing the improvement of reliability by preventing the lowering of detecting accuracy by preventing scattered toner from adhering to the detection surface of a toner concentration sensor at the non-detection time of the sensor. <P>SOLUTION: A developing unit 4 which supplies specified color toner to an electrostatic image corresponding to a chromatic color image formed on a photoreceptor drum 1 so as to make it visible is arranged oppositely at a specified position on the drum 1, and the toner concentration sensor 44 detecting the concentration of the toner as the reflectance of light is provided at a position separate from a developing position where the unit 4 is opposed to the drum 1. A sensor supporting mechanism 50 supporting the sensor 44 is freely displaced to a 1st position where the sensor 44 is opposed to the unit 4 so as to detect the concentration of the toner and a 2nd position where the sensor 44 is separated from the unit 4 so as to protect the detection surface of the sensor 44. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a non-contact reflection optical detection element for detecting a toner density with respect to a developing device provided in an image forming apparatus, and a support mechanism thereof.
[0002]
[Prior art]
In an electrophotographic image forming apparatus, a two-component developing method using a two-component developer in which a toner and a carrier are mixed is widely known. In order to promote downsizing of the entire image forming apparatus, a rotary developing device (hereinafter referred to as a “revolver developing unit”) having a plurality of color developing devices is attached to a photosensitive drum as an image carrier. A configuration is known in which rotation is performed toward an opposing development position.
In particular, in the two-component development system, it is important to always maintain a constant toner density, which is the ratio of developer toner to carrier. For this reason, a toner density detecting element (hereinafter referred to as a toner density sensor) is arranged on the toner sleeve covering the developing drum of each developing device, and the toner layer on the toner sleeve is measured by the toner density sensor. .
[0003]
In [Patent Document 1], in order to stably detect the toner density in the developing device, an optical sensor different from the magnetic sensor is optically opposed to a predetermined position on the outer periphery of the developing roller (developer carrier). A technique for determining the toner concentration is disclosed.
[0004]
[Patent Document 1]
JP-A-3-13978 gazette
[Problems to be solved by the invention]
By the way, in the revolver developing unit, it is necessary to rotate the entire unit by a predetermined angle so that the developing devices of the respective colors are sequentially opposed to the photosensitive drum. It is inevitable that a certain amount of toner scatters from the toner sleeve as the unit rotates. Then, a part of the scattered toner may adhere to the detection surface of the sensor, and the detection accuracy may be lowered.
[0006]
Conventionally, a shutter mechanism is provided for the sensor detection surface. When the toner density is detected, the shutter mechanism is opened, and when it is not detected, the shutter mechanism is closed to reduce the amount of toner adhering to the sensor detection surface. I try to improve.
Since the distance between the sensor and the toner sleeve is extremely small, a plate body having one end rotatably supported as a shutter mechanism is used. However, while the shutter mechanism is opened and the sensor detects the toner density, the sensor detection surface is completely exposed, and thus part of the scattered toner adheres. For this reason, there is a possibility that the detection accuracy may deteriorate with time.
[0007]
Even if scattered toner adheres to the sensor detection surface, there is no problem if the sensor detection surface can be wiped off by some means and the adhered toner can be completely removed. On the other hand, since the distance between the sensor detection surface and the toner sleeve is extremely narrow and the shutter mechanism is already attached, there is no room for providing a means for wiping the sensor detection surface in a space.
[0008]
In addition, it is necessary to perform calibration for correcting the decrease in sensitivity of the sensor at appropriate intervals. At this time, the distance from the sensor detection surface to the correction surface portion to be calibrated must be the same as the distance from the sensor surface to the toner sleeve. The distance is determined by the characteristics of the sensor. For example, if the distance from the sensor detection surface to the toner sleeve surface is 5.7 mm, the distance from the sensor detection surface to the correction surface portion also needs to be the same 5.7 mm.
[0009]
However, as described above, since the shutter mechanism is already interposed between the sensor detection surface and the toner sleeve surface, the correction surface portion to be calibrated cannot be accurately placed at the position of 5.7 mm, and the sensitivity is lowered. It was difficult to maintain the correction accuracy.
[0010]
The present invention has been made paying attention to the above circumstances, and its object is to prevent scattered toner from adhering to the detection surface of the detection element when the toner concentration detection element is not detected, and to detect accuracy. Therefore, it is an object of the present invention to provide an image forming apparatus that prevents the deterioration of the image quality and improves the reliability.
[0011]
[Means for Solving the Problems]
In order to satisfy the above-described object, the present invention supplies a predetermined color toner to an electrostatic image corresponding to a chromatic image formed on the photosensitive member at a predetermined position on the outer periphery of the photosensitive member holding the latent image. The toner density is detected by detecting the density of the toner contained in the developing device at a predetermined position away from the developing position where the developing device and the photosensitive member face each other. A detection element support mechanism that provides a detection element and supports the toner density detection element has a first position for detecting the toner density in the developing device with the toner density detection element facing the developing device, and developing the toner density detection element. It is possible to displace to a second position that is separated from the apparatus and protects the detection surface of the toner density detection element.
[0012]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a schematic diagram illustrating a printer apparatus which is an example of an image forming apparatus.
The color printer apparatus (image forming apparatus) 101 includes a photosensitive member 1 (hereinafter referred to as a photosensitive drum because it is in a drum shape in this example) that holds an image to be printed or character information.
[0013]
Around the photosensitive drum 1, there are a charging device 2 that applies a predetermined potential to the photosensitive drum 1, a first developing device (for black) 3 that develops an electrostatic image formed on the photosensitive drum 1, A second developing device (for color) 4 that develops an electric image, and a developer image (an image in which an electrostatic image is visualized by the first or second developing device) formed on the photosensitive drum 1 are transferred. An intermediate transfer member (which is in the form of a belt in this example, hereinafter referred to as an intermediate transfer belt) 5 and a photosensitive drum that are temporarily held for transferring to a sheet or the like, and that convey the transferred developer image. A cleaning / static discharge device 6 is disposed to remove the developer remaining on the surface of 1 and to erase the potential distribution on the drum 1.
[0014]
The second developing device (hereinafter referred to as a color developing device) 4 is integrally formed with three developing devices 41, 42, and 43 containing three color developers corresponding to three subtractive primary colors. Revolver method.
For example, the color developing device 4 includes a Y developing device 41 and a C (Cyan, ie, Y) that holds a developer in which Y (Yellow, ie, yellow) toner and a carrier are mixed at a predetermined ratio (toner concentration). Cyan) C developer 42 holding developer in which toner and carrier are mixed at a predetermined ratio (toner density), and M (Magenta) toner and carrier are mixed at a predetermined ratio (toner density) And an M developing device 43 holding the developer.
[0015]
Each of the developing devices 41 to 43 is formed to be rotatable around the central axis 45 of the color developing device 4 and is sequentially positioned at a developing position facing the photosensitive drum 1 in accordance with a request for image output. The Further, at a predetermined position along the outer periphery of the area where the color developing device 4 is rotated, the toner density on the surface of the developing roller (that is, the toner sleeve surface) in the developing devices 41 to 43 containing toner of an arbitrary color is set. A non-contact reflective optical toner density detecting element (hereinafter referred to as a toner density sensor) 44 to be detected is supported by a sensor support mechanism 50 described later, and is provided in common to the developing devices 41 to 43.
[0016]
From the space around the photosensitive drum 1 and between the charging device 2 and the black developing device 3, image light (laser beam) L whose light intensity is changed corresponding to an image to be printed or character information. Is irradiated by the exposure device 7.
A toner image, which is an electrostatic image developed on the photosensitive drum 1, is transferred to the transfer belt 5 at a position inside the intermediate transfer belt 5 where a developer image on the photosensitive drum 1, that is, a toner image can be transferred. There is provided an intermediate transfer device 8 for providing an electric field for transferring the toner image. Note that the transfer belt 5 is in contact with the photosensitive drum 1 at a predetermined position on the outer periphery of the photosensitive drum 1 by the pressure applied by the intermediate transfer device 8.
[0017]
An electric field for transferring the toner image transferred on the transfer belt 5 to a sheet is provided at a predetermined position on the outer periphery of the intermediate transfer belt 5 on the side where the sheet is conveyed through the sheet conveyance system. Provided (output) transfer device 9 is provided.
In an image forming apparatus (color printer apparatus) 101, exposure is intensity-modulated based on image data by supplying image data from an external apparatus (not shown) such as a personal computer or an image scanner (image input apparatus). Light is irradiated from the exposure device 7 to a predetermined position of the photosensitive drum 1. Thereby, a latent image corresponding to the intensity of the exposure light is formed on the photosensitive drum 1.
[0018]
The latent image formed on the photosensitive drum 1 is developed (visualized) as a toner image by selectively supplying a corresponding color toner from either the black developing device 3 or the color developing device 4 or each. Is done.
The toner image developed and attached to the photosensitive drum 1 is conveyed to an intermediate transfer position by rotating the photosensitive drum 1, and is transferred to the transfer belt by an intermediate transfer voltage provided from the intermediate transfer device 8. 5 is transferred.
[0019]
The toner image transferred to the transfer belt 5 is conveyed to a transfer region facing the transfer device 9 by movement of the belt surface of the transfer belt 5, and is transferred from the transfer device 9 to a sheet supplied to the transfer region at a predetermined timing. Are transferred by a transfer electric field (transfer bias voltage).
Sheets (materials to be transferred) are taken out one by one from the first and second sheet cassettes 10a or 10b by the pickup rollers 11a or 11b, and are conveyed in advance through the conveyance path 11 to the aligning roller 12. The paper conveyed to the aligning roller 12 collides with the aligning roller 12 whose rotation has been stopped, so that a non-parallel component, that is, an inclination with respect to the transport direction that may occur when the paper is transported on the transport path 11. It is removed and temporarily stopped.
[0020]
The sheet stopped by the aligning roller 12 is conveyed again toward the transfer position at a predetermined timing with respect to the position of the toner image conveyed by the transfer belt 5. By supplying a transfer electric field from the transfer device 9 to the sheet conveyed to the transfer position at a predetermined timing, the toner image conveyed by the transfer belt 5 is transferred. The paper P may be replaced with, for example, a colored paper or a transparent resin sheet according to the user's request.
[0021]
The sheet on which the toner image has been transferred is further conveyed along the conveyance path 11 and guided to the fixing device 13. Predetermined heat is supplied from the fixing device 13 to the paper guided to the fixing device 13, and the toner constituting the toner image is melted and fixed on the paper. The toner (not shown), that is, the paper on which the image output corresponding to the image information is fixed by the fixing device 13 is sequentially conveyed to a paper holding portion (tray) 15 which is a part of the exterior cover of the printer device 101 by the roller 14. .
[0022]
In this way, a printout (image output) is obtained in which the toner image corresponding to the electrostatic image formed on the photosensitive drum 1 is fixed on the paper.
If the supplied image data is color image data, a total of three times until each subtractive color primary toner image is formed for each color component formed on the photosensitive drum 1 by the toner of each color. The image data is developed by the developing devices 41 to 43 of the respective colors of the color developing device 4 and sequentially transferred onto the transfer belt 5 to be superimposed. Further, when black image formation by the black developing device 3 is also instructed for black enhancement, an image is further formed with black toner based on the black image data, developed, and a color image is formed on the transfer belt 5. Superimposed.
[0023]
Further, when an image output of only a black image is instructed by the black developing device 3, the light intensity corresponding to the black image data by the exposure device 7 is applied to the photosensitive drum 1 to which a predetermined potential is applied in advance. Is irradiated with exposure light (laser beam) with continuously changed. As a result, an electrostatic latent image corresponding to the black image data is formed on the photosensitive drum 1.
The latent image formed on the photosensitive drum 1 is developed by selectively supplying toner from the black developing device 3. The black toner image formed on the photosensitive drum 1 is transferred to the transfer belt 5 when the photosensitive drum 1 is rotated, and is conveyed to the transfer position by moving the belt surface of the transfer belt 5. Transfer is performed on a sheet fed at a timing by a transfer voltage provided from the transfer device 9.
[0024]
In the image forming apparatus 101 according to the present embodiment, the black developing device 3 is at a fixed position, and the toner density can be controlled and the toner can be supplied by the magnetic sensor type toner supply control method that is an already-invented technique.
On the other hand, in the color developing device 4, each of the Y developing device 41, the M developing device 42, and the C developing device 43 is rotated around the central axis 45 to a developing position facing the photosensitive drum 1. Therefore, sufficient accuracy cannot be obtained by the toner replenishment control and the toner density control by the magnetic sensor method. For this reason, the color developing device 4 includes an optical density sensor that detects the toner density from the reflectance of each color toner and the carrier, and a method for managing the toner density of each color toner has been proposed.
[0025]
The toner concentration sensor 44 used here emits, for example, light of a near infrared wavelength, receives light reflected and returned from the measurement object, and corresponds the amount of the received light to the reflectance of the measurement object. Output as an electrical signal. Therefore, the amount of toner in the developer, that is, the toner concentration can be obtained from the output of the toner concentration sensor 44.
[0026]
Next, the sensor support mechanism 50 will be described in detail.
2 is a sectional view of the sensor support mechanism 50, FIG. 3 is a perspective view of the sensor support mechanism 50 as viewed from the front side, FIG. 4 is a perspective view of the sensor support mechanism 50 as viewed from the front side, and FIG. It is the perspective view which looked at from the back side.
[0027]
The substrate 51 is formed by metal sheet metal processing. The substrate 51 has a mounting piece 51a having a horizontal upper end, and is fixed to the apparatus housing. Both side ends of the attachment piece 51a are bent at a substantially right angle to form a first bent piece 51b and a second bent piece 51c extending obliquely downward. The width dimension of the second bent piece 51c is narrower than that of the first bent piece 51b. Each piece 51a, 51b, 51c is appropriately opened in order to reduce the weight within a range in which rigidity is maintained.
[0028]
A support shaft 52 is stretched over substantially the center of the first bent piece portion 51b and the second bent piece portion 51c, and both end portions of the support shaft 52 are attached and fixed to the respective pieces 51b and 51c. The The support shaft 52 is parallel to the central axis 45 of the revolver developing unit 4 described above and parallel to the attachment piece 51a. A housing 53 is rotatably supported between the first bent piece portion 51b and the second bent piece portion 51c in the support shaft 52.
[0029]
The housing 53 is formed of a synthetic resin material and partially opened, and a box-shaped housing main body 53a in which a support piece portion supported by the support shaft 52 via a bearing 54 is integrally provided, and the housing It consists of a closing piece 53b made of a thin metal plate that covers the opening of the main body 53a.
The toner density sensor 44 is attached to one side of the front surface of the housing main body 53a on the side of the developing unit 4, and the detection surface S faces the developing unit 4. The cords connected to the toner concentration sensor 44 protrude outside through a hole a provided in the side surface of the housing 53 opposite to the sensor mounting surface.
[0030]
The closing piece portion 53b has a bent portion b projecting toward the support shaft 52 side (rear), and a hole portion 55 through which the support shaft 52 is inserted is provided. Further, the bent portion b protrudes and engages with an operating rod 57 of a solenoid 56 described later. The solenoid 56 is forcibly pulled in by pulling the operating rod 57, and the urging force to the operating rod 57 is removed when the solenoid 56 is turned off.
[0031]
A bracket 58 made of the same synthetic resin material as that of the housing 53 is fixedly attached to the lower side of the housing 53 extending over the first bent piece portion 51b and the second bent piece portion 51c constituting the substrate 51. The solenoid 56 is attached to the rear side of the bracket 58. The operating rod 57 of the solenoid 56 is provided with a groove c, and a pin 59 is installed. The bent part b of the closing piece part 53b is inserted between the pin 59 and the bottom part of the groove part c, and the bent part b moves as the operating rod 57 advances and retreats, and the closed piece part provided with the bent part b. 53b and the housing 53 are urged to rotate about the support shaft 52 as a fulcrum.
[0032]
A coil spring 60 that is a tension spring is stretched between the lower surface of the housing 53 and the lower end of the bracket 58. One end of the coil spring 60 is hooked on a bracket 58 that is a fixing member, and the other end is hooked on a housing 53 that is a rotating member. Accordingly, the housing 53 is always elastically biased so that the housing 53 is rotated clockwise around the support shaft 52. Two protrusions d are integrally provided at the upper end on the front side of the bracket 58, and receive the housing 53 that is urged to rotate by the tensile elastic force of the coil spring 60 so as to alleviate the impact. .
[0033]
On the other hand, a shutter member 65 formed of a synthetic resin material is attached and fixed to the lower surface side of the attachment piece 51a constituting the substrate 51. In a state where the housing 53 is pulled and urged by the coil spring 60 and the lower surface portion of the housing 53 is stopped by the protruding piece d of the bracket 58, the detection surface S of the toner density sensor 44 is exposed from the shutter member 65. The sensor detection surface S is designed to be covered with the shutter member 65 in a state where the solenoid 56 is excited and the operating rod 57 rotates and urges the housing 53 against the elastic force of the coil spring 60.
[0034]
A brush 66 is implanted at the lower end portion of the shutter member 65, and a hair tip portion of the brush 66 protrudes so as to face the sensor detection surface S. The bristles of the brush 66 are in positions where the sensor detection surface S passes while contacting with the rotating action of the housing 53.
[0035]
Further, a calibration portion 67 is integrally provided on the upper side from the brush 66 mounting portion of the shutter member 65. The calibration unit 67 surrounds the upper and lower portions of the sensor detection surface S and both the left and right sides in a state where the solenoid 56 is excited and the operating rod 57 urges the housing 53 against the elastic force of the coil spring 60. Is formed as a recess.
[0036]
In this state, the concave surface facing the sensor detection surface S is called a calibration surface (correction surface portion) E. The distance between the sensor detection surface S and the calibration surface E is set to be the same as the distance when the sensor detection surface S faces the toner sleeve 70 of the developing devices 41 to 43.
In other words, in order to obtain the maximum characteristic as the toner density sensor 44, it is necessary to match the distance from the sensor detection surface S to the toner sleeve 70 with the reference value. Then, in performing calibration for correcting the sensitivity reduction of the sensor 44, accurate calibration can be performed by matching the distance from the sensor detection surface S to the calibration surface E to the reference value. The shutter member 65 itself is color-tuned according to the characteristics of the toner density sensor 44, and the calibration surface E is textured.
[0037]
The image forming apparatus 101 having the sensor support mechanism 50 configured as described above operates as described below.
FIG. 6 is a sectional view of a part of the sensor support mechanism 50 and the developing device 43, showing a state in which the toner concentration sensor 44 detects the toner concentration with respect to the toner sleeve 70 constituting the C developing device 43, for example. FIG. 6 is a cross-sectional view of the sensor support mechanism 50 and the developing device part 43 in a state where the toner density sensor 44 does not detect.
[0038]
First, the state where the toner density sensor 44 of FIG. 6 detects the toner density will be described. The position of the toner density sensor 44 at this time is referred to as a first position. The solenoid 56 is in a disconnected state, and the operating rod 57 protrudes. The elastic force of the coil spring 60 acts on the housing 53, and the housing 53 is pulled and biased to a position where the lower surface portion of the housing 53 comes into contact with the protrusion d of the bracket 58.
[0039]
The toner density sensor 44 protrudes from the lower end edge of the shutter member 65, and the detection surface S directly faces the toner sleeve 70 constituting the developing device 43. The distance between the sensor detection surface S and the toner sleeve 70 is determined by the characteristics of the sensor 44 used here. As in the prior art, the toner density sensor 44 is used which can exhibit the best characteristics when the predetermined distance f (5.7 mm) is set between the sensor detection surface S and the toner sleeve 70. Under such a configuration, the toner density sensor 44 detects the toner density on the toner sleeve 70 and sends the detection signal to the control unit to perform necessary control.
[0040]
While developing units 41 to 43 of a predetermined color supply and visualize a predetermined color toner on the photosensitive drum 1 with respect to a color image formed on the photosensitive drum 1, the toner density sensor 44 is visualized. Detects the toner density of the toner sleeve 70 in the next developing device.
When these actions are finished, the refolder developing unit 4 rotates 120 ° clockwise with the central shaft 45 as a fulcrum. At this time, an excitation signal is sent to the solenoid 56 and the operating rod 57 is forcibly pulled in against the elastic force of the coil spring 60.
[0041]
The housing 53 is urged to rotate counterclockwise about the support shaft 52, and the sensor detection surface S moves to a position facing the shutter member 65. Along with the movement of the sensor detection surface S, the sensor detection surface S comes into contact with the bristles of the brush 66 provided at the lower end of the shutter member 65 and passes therethrough.
In the state of FIG. 6, that is, while the toner density sensor 44 is in the first position and detects the toner density with respect to the toner sleeve 70, the sensor detection surface S is exposed from the shutter member 65, while the revolver A certain amount of toner scatters and floats around the developing unit 4. Therefore, it is inevitable that a part of the floating toner adheres to the sensor detection surface S that detects the toner density.
[0042]
While the toner concentration sensor 44 moves from the position shown in FIGS. 6 to 7, the sensor detection surface S contacts the bristles of the brush 66. As a result, the toner adhering to the sensor detection surface S is wiped off, and the sensor detection surface S becomes clean.
The position of the toner density sensor 44 shown in FIG. 7 is referred to as a second position. The operating rod 57 is forcibly retracted, and the upper end surface of the housing 53 comes into contact with the upper surface constituting the calibration portion 67 of the shutter member 65. The detection surface S of the toner density sensor 44 passes through the hair tip of the brush 66 and is at a position facing the calibration surface E. The sensor detection surface S is surrounded by the calibration unit 67 in the vertical and horizontal directions.
[0043]
Thereafter, the refolder developing unit 4 is rotated by 120 °. Even if the toner scatters and floats, the sensor detection surface S is completely surrounded by the calibration portion 67 of the shutter member 65, so that the toner does not adhere to the sensor detection surface S, and the detection surface S is surely secured. Protected.
As described above, at the second position of the toner density sensor 44, the sensor detection surface S and the calibration surface E face each other with a predetermined distance f (5.7 mm). Alternatively, calibration for correcting a decrease in sensitivity of the toner density sensor 44 can be executed every period, and the detection accuracy of the reflective sensor is always kept within a certain range.
[0044]
After the revolver developing unit E is rotated by 120 ° or after the calibration for the toner density sensor 44 is performed, the energization to the solenoid 56 is stopped again. The elastic force of the coil spring 60 acts to rotate the housing and return to the position shown in FIG. Also at this time, the sensor detection surface S comes into contact with the bristles of the brush 66, and the cleanliness of the sensor detection surface S is further increased.
[0045]
The present invention is not limited to the above-described embodiment, and various modifications and changes can be made without departing from the scope of the invention. In addition, the embodiments may be combined as appropriate as possible, and in that case, the effect of the combination can be obtained. For example, in order to explain the above-described embodiment, an example of the operation of the developing device has been described by taking a color printer as an example. However, a color copying machine (color copy) or facsimile in which an image reading unit is integrally formed is described. Needless to say, it can also be used for devices.
[0046]
【The invention's effect】
As described above, according to the present invention, it is possible to prevent scattered toner from adhering to the detection surface of the sensor when the sensor is not detected, and to prevent a decrease in detection accuracy of the sensor, thereby improving reliability. There is an effect.
[Brief description of the drawings]
FIG. 1 is a schematic cross-sectional view of an image forming apparatus according to an embodiment of the present invention.
FIG. 2 is a cross-sectional view of a sensor support mechanism according to the embodiment.
FIG. 3 is a perspective view of the sensor support mechanism according to the embodiment as viewed from the front side.
FIG. 4 is a perspective view of the front side of the sensor support mechanism according to the embodiment.
FIG. 5 is a rear perspective view of the sensor support mechanism according to the embodiment.
6 is a cross-sectional view of the sensor support mechanism and a part of the developing device at the first position of the toner density sensor according to the embodiment; FIG.
FIG. 7 is a cross-sectional view of the sensor support mechanism and a part of the developing device at a second position of the toner density sensor according to the embodiment;
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Photosensitive drum (photosensitive body), 4 ... Color developing device, 44 ... Toner density sensor (toner density detection element), 50 ... Sensor support mechanism (detection element support mechanism), 66 ... Brush (cleaning member), E ... Calibration surface (correction surface).

Claims (3)

A photoreceptor for holding the latent image;
A developing device that is arranged to face a predetermined position on the outer periphery of the photoconductor, and supplies a predetermined color toner to an electrostatic image corresponding to a chromatic image formed on the photoconductor to be visualized;
A toner concentration detecting element provided at a predetermined position apart from a developing position where the developing device and the photosensitive member face each other, and detecting the concentration of toner contained in the developing device as a reflectance of light;
The toner density detecting element is supported, the toner density detecting element is opposed to the developing device, the first position for detecting the toner density in the developing device, and the toner density detecting element is separated from the developing device. An image forming apparatus comprising: a detection element support mechanism that is displaceable to a second position that protects a detection surface of the detection element. 2. The detection element support mechanism includes a cleaning member that wipes a detection surface as the toner density detection element passes between the first position and the second position. Image forming apparatus. Corrects the decrease in sensitivity of the toner density detection element at the second position in the detection element support mechanism and at the same distance as the distance from the detection surface of the toner density detection element to the developing device at the first position. The image forming apparatus according to claim 1, further comprising a correction surface portion for performing calibration.

Images