JP2013015620A - Toner charged state detection device and image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a toner charged state detection device and an image forming apparatus that allow detection of a toner charged state with a simple constitution.SOLUTION: A toner charged state detection device includes: density detection means 51 for detecting a density of a toner image transferred on a transfer medium from on an image holding body 26 by transfer means or of a residual transfer toner image remaining on the image holding body; and charged state detection means 100 for, when the toner image held on the image holding body is transferred to the transfer medium by the transfer means, detecting a toner charged state, in which the toner image is formed while a transfer voltage applied to the transfer means is varied into multiple values, on the basis of the relationship between values of the transfer voltage applied to the transfer means and values of the detected density by the density detection means.

Description

  The present invention relates to a toner charge state detection device and an image forming apparatus.

  Conventionally, in the image forming apparatus, an electrostatic latent image formed on a photosensitive drum is visualized using toner charged by a developing device, and the toner image is recorded directly or via an intermediate transfer member. An image is formed by transferring and fixing on a sheet.

  At that time, in the image forming apparatus described above, for example, in a high temperature and high humidity environment due to environmental conditions such as temperature and humidity, or changes over time such as when low density images and high density images are continuously visualized. In contrast, the toner chargeability decreases and the toner charge amount tends to decrease, but conversely, the toner chargeability increases in a low-temperature and low-humidity environment, and the toner charge amount tends to increase. When the image is continuously visualized, the toner in the developing device is hardly consumed, but the toner is excessively charged by friction, and the amount of charge of the toner tends to increase. When the image is visualized, a large amount of toner in the developing device is consumed, and the frictional charging of the toner becomes insufficient, so that the charge amount of the toner tends to decrease.

  As described above, in the image forming apparatus, when the chargeability of the toner is changed, the toner image on the photosensitive drum is transferred to the recording paper or the intermediate transfer body, or the secondary transfer from the intermediate transfer body to the recording paper is performed. The transferability at the time of image transfer fluctuates, causing image quality defects such as a decrease in image density. In particular, when a toner having a small particle diameter is used as the toner to improve the image quality, the influence of the mirror image force cannot be ignored as the electrostatic force acting on the toner particles as will be described later. Variation in transferability becomes apparent.

  In view of this, techniques disclosed in, for example, Japanese Unexamined Patent Application Publication Nos. 2008-292835 and 2005-17337 have already been proposed as techniques that can improve toner image transferability in the image forming apparatus.

The color image forming apparatus according to the above Japanese Patent Application Laid-Open No. 2008-292835 includes a charging unit that charges a photoconductor, an exposure unit that exposes the photoconductor to form an electrostatic latent image, and develops the electrostatic latent image. The toner image is developed as a toner image by applying a developing voltage by means, the toner image is transferred onto the recording material by a transfer means, and a heating rotator having at least a heating source and a pressure rotator that is in pressure contact with the heating rotator A color image forming apparatus having a fixing unit configured to fix the developer on the recording material by a fixing nip portion configured to be in contact with the heating rotating body and the pressure rotating body.
The developing means includes a developing voltage applying means for applying the developing voltage, and a developing voltage control means for controlling an output voltage of the developing voltage applying means,
On the downstream side of the fixing nip portion in the recording material conveyance path of the image forming apparatus,
Irregularly reflected light detecting means for detecting an irregularly reflected light component when irradiating light emitted from the first light source to the first light source and the recording material;
And a second light source different from the light source, and a specular reflection light detecting means for detecting a specular reflection light component when irradiating light emitted from the second light source, the irregular reflection light detection means and the specular reflection light detection means The output value of the developing voltage control means is corrected based on the detection result.

Further, the image forming apparatus according to Japanese Patent Application Laid-Open No. 2005-17337 multiplexes toner images formed on a plurality of image carriers onto a transfer target body by applying a transfer voltage to a transfer unit at a transfer unit. In an image forming apparatus for transferring and forming a multi-color image,
Before a toner image is formed on the image carrier, a predetermined voltage is applied to the transfer unit with respect to the surface of the image carrier charged to a predetermined potential and simultaneously flows through the transfer unit. Detecting a current value to obtain a relationship between a potential difference between the surface of the image carrier and the transfer unit and a current value flowing at that time;
The transfer voltage is determined in accordance with the relationship and the toner charge amount of the color already formed on the transfer target.

JP 2008-292835 A JP 2005-17337 A

  An object of the present invention is to provide a toner charge amount detection device and an image forming apparatus that can detect the charged state of toner with a simple configuration.

In other words, the invention described in claim 1 is a density detecting means for detecting the density of the toner image transferred onto the transfer medium from the image holding member by the transferring means or the transfer residual toner image remaining on the image holding member. When,
When the toner image held on the image carrier is transferred onto the transfer medium by the transfer unit, the transfer voltage applied to the transfer unit is changed to a plurality of values, and the transfer voltage applied to the transfer unit And a charged state detecting means for detecting a charged state of the toner that forms the toner image based on the relationship between the value of the toner density and the detected density value of the density detecting means.

According to a second aspect of the present invention, the image carrier is made of an intermediate transfer member to which a toner image is transferred from a photosensitive drum, and the transfer medium is made of a recording medium.
The charged state detecting means detects the area of the recording medium when transferring the toner image transferred on the intermediate transfer body corresponding to the size of the recording medium onto the recording medium by the transferring means. 2. The apparatus according to claim 1, wherein the intermediate transfer member is divided into a plurality of small regions along a moving direction of the intermediate transfer member, and a transfer voltage applied to the transfer unit is changed to a plurality of values according to the plurality of small regions. The toner charge state detection device described.

  Further, the invention described in claim 3 is characterized in that the density detecting means detects the density of the toner image transferred onto the recording medium and fixed. 1 is a toner charge state detection device.

  According to a fourth aspect of the present invention, in the toner charge according to the second or third aspect, the density detecting unit detects a density of a transfer residual toner image remaining on the intermediate transfer member. It is a state detection device.

Furthermore, the invention described in claim 5 is an image holding body for holding a toner image;
Transfer means for transferring the toner image held on the image carrier onto a transfer medium;
Toner charge state detection means for detecting the charge state of the toner forming the toner image,
An image forming apparatus using the toner charged state detecting device according to claim 1 as the toner charged state detecting means.

According to a sixth aspect of the present invention, there are provided a plurality of image holding members for holding toner images of different colors,
A plurality of primary transfer means for transferring each of the toner images held on the plurality of image holders onto the intermediate transfer member in a multiplexed manner;
Secondary transfer means for performing secondary transfer of the toner images, which have been primary-transferred multiple times on the intermediate transfer body, onto a recording medium at once;
Toner charge state detection means for detecting the charge state of the toner forming each toner image;
Control means for controlling transfer conditions in the plurality of primary transfer means based on the charge state of the toner forming each toner image detected by the toner charge state detection means;
An image forming apparatus using the toner charged state detecting device according to claim 1 as the toner charged state detecting means.

  According to the first aspect of the present invention, the charged state of the toner can be detected with a simple configuration.

  According to the second aspect of the present invention, it is possible to detect the charged state of the toner in a short time in an area corresponding to one recording medium.

  Furthermore, according to the third aspect of the present invention, it is possible to detect the charged state of the toner that determines the image quality of the finally obtained image.

  According to the fourth aspect of the present invention, it is possible to detect the charged state of the toner on the intermediate transfer body in which the fluctuation of the charged state of the toner tends to appear.

  Furthermore, according to the fifth aspect of the present invention, it is possible to provide an image forming apparatus capable of detecting the charged state of toner with a simple configuration.

  According to the sixth aspect of the present invention, the image quality can be improved by controlling the primary transfer conditions according to the charged state of the toner.

1 is a configuration diagram illustrating a main part of an image forming apparatus to which a toner charge state detection device according to Embodiment 1 of the present invention is applied. FIG. 1 is an overall configuration diagram illustrating an image forming apparatus to which a toner charge state detection apparatus according to Embodiment 1 of the present invention is applied. It is a block diagram which shows a linter. FIG. 6 is an explanatory diagram showing a mirror image force acting on toner particles. 4 is a graph showing the relationship between the particle diameter of toner particles and the image force. It is a block diagram which shows the other example of a density | concentration detection means. FIG. 6 is an explanatory diagram illustrating a toner image formed on a recording sheet. FIG. 6 is an explanatory diagram illustrating a toner image formed on a recording sheet. It is a graph which shows the transfer voltage applied to a secondary transfer part. It is a schematic diagram which shows the system resistance of a secondary transfer part. It is a graph which shows the relationship between a secondary transfer voltage and the density on a paper. 6 is a graph showing a toner charging state determination unit based on a density difference between secondary transfer voltages. 6 is a chart showing control values of primary transfer current in a charged state of toner. 6 is a graph showing image density on a sheet as a result of controlling a primary transfer current according to a charging state of toner. It is a block diagram which shows the principal part of the image forming apparatus to which the toner charged state detection apparatus which concerns on Embodiment 2 of this invention is applied. 6 is a graph showing a relationship between a secondary transfer voltage and a density on an intermediate transfer belt. 6 is a graph showing a toner charging state determination unit based on a density difference between secondary transfer voltages. 6 is a chart showing control values of primary transfer current in a charged state of toner. 6 is a graph showing image density on a sheet as a result of controlling a primary transfer current according to a charging state of toner.

  Embodiments of the present invention will be described below with reference to the drawings.

Embodiment 1
FIG. 2 is a schematic configuration diagram showing a tandem type digital color printer as an image forming apparatus to which the toner charge state detection apparatus according to Embodiment 1 of the present invention is applied. The tandem type digital color printer includes an image reading device, and functions as a full-color copying machine or a facsimile. Of course, the image forming apparatus may not include an image reading apparatus and may form an image based on image data output from a personal computer (not shown).

  In FIG. 2, reference numeral 1 denotes a main body of the image forming apparatus. The image forming apparatus main body 1 has an image reading device 3 that reads an image of a document 2 on the upper side of one side (left side in the illustrated example). I have. In addition, in the image forming apparatus main body 1, image data output from the image reading device 3, a personal computer (not shown) or the like, or image data sent via a telephone line, a LAN, etc. An image processing device 4 that performs predetermined image processing is arranged, and an image is formed inside the image forming apparatus main body 1 based on image data that has been subjected to predetermined image processing by the image processing device 4. Is output.

  The image reading device 3 opens and closes the document pressing cover 6 to place the document 2 on the platen glass 7. The image reading device 3 is placed on the platen glass 7 to illuminate the document 2 with the light source 8. The reflected light image is scanned and exposed on an image reading element 13 composed of a CCD or the like through a reduction scanning optical system composed of a full-rate mirror 9, half-rate mirrors 10 and 11, and an imaging lens 12. An image of the original 2 is configured to be read at a predetermined dot density.

  The image of the document 2 read by the image reading device 3 is, for example, the image processing device 4 as document reflectance data of three colors of red (R), green (G), and blue (B) (for example, 8 bits each). In this image processing apparatus 4, shading correction, position shift correction, lightness / color space conversion, gamma correction, frame deletion, color / moving editing, etc. are predetermined for the reflectance data of the document 2. Image processing is performed.

  The image data that has been subjected to the predetermined image processing by the image processing device 4 as described above is similarly processed by the image processing device 4 in yellow (Y), magenta (M), cyan (C), and black (K). It is converted into image data of four colors, and image exposure units (image forming units) 14Y, 14M, 14C, and 14K for each color of yellow (Y), magenta (M), cyan (C), and black (K) are exposed. The image exposure apparatuses 15Y, 15M, 15C, and 15K perform image exposure with the laser beam LB in accordance with the corresponding color image data.

  Meanwhile, as described above, the image forming apparatus main body 1 includes four image forming units 14Y, 14M, 14C, and 14K of yellow (Y), magenta (M), cyan (C), and black (K). Are arranged in parallel at regular intervals in the horizontal direction.

  As shown in FIG. 2, these four image forming units 14Y, 14M, 14C, and 14K are configured in the same manner except for the color of the image to be formed, and are roughly classified in advance along the direction of arrow A. A photosensitive drum 16 as an image carrier that is rotationally driven at a speed (for example, process speed = 440 mm / sec), a scorotron 17 for primary charging that uniformly charges the surface of the photosensitive drum 16, and the photosensitive drum An image exposure device 15 as image writing means for forming an electrostatic latent image by performing image exposure on the surface of the body drum 16 based on image data corresponding to each color, and an electrostatic formed on the photosensitive drum 16 A developing device 18 as developing means for developing the latent image with toner, and a cleaning device 19 for removing toner and the like remaining on the surface of the photosensitive drum 16; It is al configuration.

  As shown in FIG. 2, the image processing device 4 exposes the image forming units 14Y, 14M, 14C, and 14K for the respective colors of yellow (Y), magenta (M), cyan (C), and black (K). Corresponding color image data is sequentially output to the devices 15Y, 15M, 15C, and 15K, and laser beams LB emitted according to the image data from these image exposure devices 15Y, 15M, 15C, and 15K correspond. The surfaces of the photosensitive drums 16Y, 16M, 16C, and 16K are scanned and exposed to form electrostatic latent images. The electrostatic latent images formed on the surfaces of the photosensitive drums 16Y, 16M, 16C, and 16K are respectively yellow (Y), magenta (M), and cyan (C) by the developing devices 18Y, 18M, 18C, and 18K. The toner image is reversely developed as a toner image composed of toner of black (K) color (charged to negative polarity).

  As toners of various colors of yellow (Y), magenta (M), cyan (C), and black (K) used in the developing devices 18Y, 18M, 18C, and 18K, toners having various particle sizes can be used. However, in the image forming apparatus according to this embodiment, in order to improve the image quality, the particle diameter is close to a spherical shape and the particle diameter is relatively small, for example, the number average particle diameter is 4.0 μm or less (this embodiment) In this embodiment, toner of about 3.8 μm) is used. However, the toner of each color of yellow (Y), magenta (M), cyan (C), and black (K) used in the developing devices 18Y, 18M, 18C, and 18K has a number average particle diameter of 4.0 μm or less. Is an example and may be larger.

  Each color of yellow (Y), magenta (M), cyan (C), and black (K) sequentially formed on the photosensitive drums 16Y, 16M, 16C, and 16K of the image forming units 14Y, 14M, 14C, and 14K. As shown in FIG. 2, the toner image is transferred onto the intermediate transfer belt 26 as an endless belt-like intermediate transfer member disposed below each of the image forming units 14Y, 14M, 14C, and 14K at the primary transfer position N1. Multiple transfer is performed by primary transfer rolls 27Y, 27M, 27C, and 27K as primary transfer means. Multiple transfer is performed by the primary transfer rolls 27Y, 27M, 27C, and 27K. The primary transfer rolls 27Y, 27M, 27C, and 27K have a positive polarity voltage that is opposite to the negative polarity that is the charging polarity of the toner, and the metal rotation that constitutes the primary transfer rolls 27Y, 27M, 27C, and 27K. It is applied in a state of constant current control so that the value of the current flowing through the shaft is constant. The intermediate transfer belt 26 functions as an image holding member that holds a toner image on the surface thereof. However, when the toner image is transferred from the photosensitive drums 16Y, 16M, 16C, and 16K as the image holding member. It also functions as a transfer medium. The intermediate transfer belt 26 is wound around the drive roll 28, the tension applying roll 29, the meandering control roll 30, the driven roll 31, the back support roll 32, and the driven roll 33 with a constant tension. And a predetermined moving speed (for example, a process speed that is a rotational speed of the photosensitive drum) along a direction indicated by an arrow B by a drive roll 28 that is rotationally driven by a dedicated drive motor excellent in constant speed (not shown). And approximately 440 mm / sec). As the intermediate transfer belt 26, for example, a flexible synthetic resin film such as polyimide or polyamideimide is formed in a belt shape, and both ends of the synthetic resin film formed in the belt shape are connected by means such as welding. Thus, an endless belt shape or an endless belt shape from the beginning is used.

  The yellow (Y), magenta (M), cyan (C), and black (K) toner images transferred multiple times on the intermediate transfer belt 26 have the same polarity (negative polarity) as the toner by the back support roll 32. ) Is applied to the recording paper 35 as a recording medium by the electrostatic force at the secondary transfer position N2 by the secondary transfer roll 34 as a secondary transfer means that is grounded and pressed against the back support roll 32. The recording paper 35 that has been secondarily transferred and onto which the toner image corresponding to the color of the image to be formed has been transferred is transported to the fixing device 38 by two transport belts 36 and 37. At this time, the back support roll 32 has a negative voltage having the same polarity as the negative polarity that is the charging polarity of the toner, and a voltage value applied to the metal rotating shaft constituting the back support roll 32. It is applied in a state of constant voltage control so as to be constant. The recording paper 35 onto which the toner images of the respective colors have been transferred undergoes a fixing process with heat and pressure by the fixing device 38 and is discharged onto a discharge tray 39 provided outside the image forming apparatus main body 1.

  As shown in FIG. 2, the recording paper 35 is of a desired size and material from the paper feed tray 40 disposed at the bottom of the image forming apparatus main body 1. The paper is fed one by one by a pair of rolls, and is temporarily transported to a registration roll 46 through a paper transport path 45 in which a plurality of transport rolls 42, 43, and 44 are disposed. The recording paper 35 supplied from the paper feed tray 40 is sent to the secondary transfer position N2 of the intermediate transfer belt 26 by a registration roll 46 that is rotationally driven at a predetermined timing. Although only one paper feed tray 40 is shown, a plurality of paper feed trays having recording papers 35 having different sizes or the same size may be provided.

  Prior to that, in the four image forming units 14Y, 14M, 14C, and 14K of yellow, magenta, cyan, and black, as described above, the yellow, magenta, cyan, and black toner images are respectively stored in advance. They are formed sequentially at a predetermined timing.

  The photosensitive drums 16Y, 16M, 16C, and 16K are prepared for the next image forming process by removing residual toner and the like by the cleaning devices 19Y, 19M, 19C, and 19K after the toner image transfer process is completed. . Further, residual toner, paper dust, and the like are removed from the intermediate transfer belt 26 by a belt cleaner 47 disposed so as to face the driven roll 33.

  By the way, in the image forming apparatus configured as described above, for example, due to environmental conditions such as temperature and humidity, changes over time such as when low-density images and high-density images are continuously visualized, etc. In a high humidity environment, the chargeability of the toner decreases and the charge amount of the toner tends to decrease.On the other hand, in a low temperature and low humidity environment, the chargeability of the toner increases and the charge amount of the toner increases. When it is easy or when low-density images are continuously visualized, the toner in the developing devices 18Y, 18M, 18C, and 18K is hardly consumed, and the toner is excessively frictionally charged to charge the toner. When high density images are continuously visualized, a large amount of toner is consumed in the developing devices 18Y, 18M, 18C, and 18K, and the toner is insufficiently frictionally charged. There tends to decrease.

  As described above, in the image forming apparatus, when the chargeability of the toner changes, the toner images on the photoconductive drums 16Y, 16M, 16C, and 16K are primarily transferred onto the intermediate transfer belt 26, or the intermediate transfer belt 26 is used. Transferability at the time of secondary transfer from above to the recording paper 35 fluctuates, causing image quality defects such as image density reduction.

  In particular, in the image forming apparatus, as described above, a small particle diameter toner having a number average particle diameter of about 3.8 μm is used in the developing devices 18Y, 18M, 18C, and 18K. As described above, the toner having a small particle diameter having a number average particle diameter of about 3.8 μm is compared with a conventionally used toner having a relatively large or medium particle diameter having a number average particle diameter of about 6 μm. When the primary transfer is performed on the photosensitive drums 16Y, 16M, 16C, and 16K onto the intermediate transfer belt 26, or when the secondary transfer is performed from the intermediate transfer belt 26 onto the recording paper 35, the latter is particularly used on the intermediate transfer belt 26. From the research of the present inventors, it has been found that the influence of the mirror image force on the toner forming the toner image at the time of secondary transfer from the toner to the recording paper 35 is relatively large.

  More specifically, when performing primary transfer from the photosensitive drums 16Y, 16M, 16C, and 16K onto the intermediate transfer belt 26, or when performing secondary transfer from the intermediate transfer belt 26 to the recording paper 35, the developing devices 18Y, An electrostatic coulomb force due to a transfer voltage applied to the primary transfer roll 27 and the back support roll 32 is applied to the toner charged within a predetermined charge amount range of negative polarity in 18M, 18C, 18K, In addition to the adhesion force such as van der Waals force caused by the contact of the toner with the intermediate transfer belt 26 and the recording paper 35, the toner particles are applied to the surface of the photosensitive drums 16Y, 16M, 16C, 16K and the intermediate transfer belt 26. An image force acting electrostatically in the attached state acts.

  Here, the mirror image force is known as a force acting on electric charges in electromagnetics, and as shown in FIG. 3, it is negatively charged opposite to the intermediate transfer belt 26 as a conductor. When the toner particle charge is present, it acts as if there is a negative charge and a positive charge in the opposite polarity to the negative charge in the intermediate transfer belt 26 as a conductor. The electrostatic attraction force (Coulomb force). In FIG. 3, for the sake of convenience, only one negative charge is shown on the surface of the toner particles. However, there are many negative charges that are frictionally charged in the developing device 18 on the surface of the toner particles. Of course.

  Since this mirror image force is inversely proportional to the square of the distance between the electric charge and the conductor, the number average particle diameter is about 6 μm, which is conventionally used. In the case of a large toner having a number average particle size of about 6 μm, the change in the mirror image force was almost negligible with respect to the change in the charged state, but with the developing devices 18Y, 18M, 18C and 18K of the present embodiment, In the case of a toner having a small particle diameter of about 3.8 μm, the influence of the change in the mirror image force becomes obvious and cannot be ignored in consideration of the transfer of the toner image.

  FIG. 4 shows how the magnitude of the image force acting on the toner layer changes according to the amount of charge of the toner by the present inventor and the number average particle size of the toner having a number average particle size of 3.8 μm. It is obtained by calculation for a toner of 5.8 μm.

  As is apparent from FIG. 4, in the case of a toner having a number average particle diameter of 5.8 μm, the gradient of the broken line indicating the magnitude of the mirror image force acting on the toner layer is small even when the charge amount of the toner varies, Even if the charge amount of the toner changes, the change in the mirror image force is small. In contrast, in the case of the toner having a number average particle diameter of 3.8 μm, when the charge amount of the toner changes, the mirror force that acts on the toner layer increases. It can be seen that the slope of the solid line and the value itself vary greatly.

  Therefore, the image forming apparatus configured as described above includes a toner charge state detection device that detects the charge state of the toner that forms the toner image, and controls the primary transfer conditions according to the charge state of the toner. It is configured.

  As shown in FIG. 1, the toner charged state detection device 50 is roughly divided into recording sheets from the intermediate transfer belt 26 by the secondary transfer roll 34 and the back support roll 32 at a predetermined timing other than the time of image formation. A density detecting means 51 for detecting the density of the toner image 53 for toner charge state detection that has been transferred onto the toner 35 and subjected to fixing processing by the fixing device 38, and the toner image 53 held on the intermediate transfer belt 26 are When transferring onto the recording paper 35 by the secondary transfer roll 34, the transfer voltage applied to the secondary transfer roll 34 is changed to a plurality of values, and the value of the transfer voltage applied to the secondary transfer roll 34 and the density detection means 51. And a charged state detecting means 52 for detecting the charged state of the toner forming the toner image from the relationship with the detected density value.

  As shown in FIG. 2, the density detecting means 51 is disposed on the exit side of the fixing device 38 and intersects the conveyance direction of the recording paper 35 for reading the toner image 53 transferred and fixed on the recording paper 35. An in-line sensor composed of image reading elements such as CCDs arranged in a straight line along the direction (perpendicular to the drawing) is used. Further, the density detecting means 51 is not limited to an inline sensor, and as shown in FIG. 5, a light emitting element 54 made of an LED or the like, and a light receiving element 55 for regular reflection or diffuse reflection made of a phototransistor or the like. A combination may be used. However, since the toner image 53 transferred and fixed on the recording paper 35 is composed of yellow, magenta, cyan, and black toners, these yellow, magenta, cyan, and black colors are used. It is desirable to use density detecting means capable of accurately detecting the density of the toner image. In this respect, the in-line sensor 51 including an image reading element such as a CCD arranged in a straight line directly reads the toner image 53 transferred and fixed on the recording paper 34 as density information and position information. This is desirable in that it is possible to accurately detect the density of each of the yellow, magenta, cyan, and black toner images 53. Of course, the detection accuracy may be improved by performing arithmetic processing such as averaging on the density value detected by the inline sensor 51.

  The toner image 53 transferred / fixed on the recording paper 35 is not particularly limited as long as the image density can be detected. For example, as shown in FIG. A solid image having a predetermined density (for example, the highest density Cin = 100%) is used on the entire surface of the recording sheet 35 having a size over substantially the entire recording area 56. However, as the density of the above-described chiner image 53, it is of course possible to use a density other than the maximum density Cin = 100%. In consideration of the detection accuracy of the toner image 53, a larger area of the toner image 53 is desirable. However, considering the amount of toner consumption, the toner image 53 has an area as shown in FIG. Of course, it may be composed of small rectangular patches. In FIG. 6, only one color toner image 53 is shown, but the toner image 53 is formed over the number of colors (usually four colors) of the toner image for detecting the charged state of the toner.

  As the toner charge state detection means 52, as shown in FIG. 1, for example, a control circuit 100 comprising a CPU or the like as a control means for controlling the image forming operation of the image forming apparatus can be used as it is. The control circuit 100 temporarily stores parameters and the like in the RAM 102 based on a program stored in advance in a ROM 101 as a storage unit, and performs process control operations such as an image forming operation and an image density control operation in the image forming apparatus. Is to control.

  As shown in FIG. 1, the control circuit 100 applies a transfer voltage applied to the secondary transfer roll 34, in this embodiment, to the back support roll 32 facing the secondary transfer roll 34 via the intermediate transfer belt 26. Although the transfer voltage is applied, the secondary transfer voltage applied to the back support roll 32 by controlling the high-voltage power supply circuit 103 that applies the secondary transfer voltage to the back support roll 32 is shown in FIG. In addition, for example, it is configured to change and apply a plurality of values (six levels in the illustrated example) every 0.5 kV from a low voltage of about 0.5 kV to a high voltage of about 2.5 kV. . The high-voltage power supply circuit 103 is configured to control the control circuit 100 by switching the transfer current supplied to the primary transfer rolls 27Y, 27M, 27C, and 27K to a predetermined value.

  The toner image is transferred on the intermediate transfer belt 26 as, for example, a solid image having the highest density Cin = 100%, but the transfer voltage at the time of secondary transfer from the intermediate transfer belt 26 to the recording paper 35 is, for example, 0. By switching to a plurality of values every 0.5 kV from a low voltage of about 0.5 kV to a high voltage of about 2.5 kV, the density of the toner image 53 that has been secondarily transferred and fixed onto the recording paper 35 can It changes according to the charged state of the toner forming the image and the transfer voltage.

Therefore, the toner image 53 that has been secondarily transferred and fixed on the recording paper 35 is elongated in the direction of the axis of the photosensitive drum 16, that is, in the direction intersecting the conveyance direction of the recording paper 35 along the conveyance direction of the recording paper 35. It is divided into six small regions 57 _{1 to} 57 ₆ according to the voltage. Note that the number of the small regions 57 _{1 to} 57 ₆ is not limited to six, and may be smaller or larger, and is determined by the number of transfer voltages to be switched.

Further, the value of the transfer voltage switched to a plurality of values is not limited to every 0.5 kV from 0.5 kV to 2.5 kV, and as shown in FIG. 9, the current value I flowing through the secondary transfer portion and the back support roll 32, the secondary transfer roll 34 is appropriately determined according to the system resistance R _sys of the system constituted by the intermediate transfer belt 26. In addition, since a certain amount of time is required to switch the secondary transfer voltage by the high-voltage power supply circuit 103, the secondary transfer voltage is maintained after the second transfer voltage is maintained for a predetermined time. Can be switched.

  Further, as shown in FIG. 1, an output signal from the inline sensor 51 is input to the control circuit 100, and the control circuit 100 determines the value of the transfer voltage applied to the secondary transfer roll 34 and the inline sensor. The charging state of the toner that forms the toner image is detected from the relationship with the detected density value 51.

  As shown in FIG. 10, the control circuit 100 sets the density value of the toner image 53 on the recording paper 35 with respect to a plurality of secondary transfer voltages applied to the back support roll 32 when the charged state of the toner is a normal state. Is stored in the ROM 101 in advance. Then, the control circuit 100 records the recording paper 35 detected by the inline sensor 51 from the relationship between the values of the plurality of transfer voltages applied to the secondary transfer roll 34 and the detected density values of the inline sensor 51 corresponding thereto. The density value of the upper toner image 53 is smaller than the normal charged state of the toner, and the density is lowered, but the transfer voltage value applied to the secondary transfer roll 34 is 0.5 kV to 2.5 kV. When it is determined that the characteristic when the toner is changed to the extent that the charged state of the toner shows the same tendency as the normal state, it is detected that the charged state of the toner is a low charged state.

  Further, the control circuit 100 detects the recording sheet detected by the inline sensor 51 from the relationship between the transfer voltage value applied to the secondary transfer roll 34 and the detected density value of the inline sensor 51 as shown in FIG. The density value of the toner image 53 on the toner 35 is still smaller than the normal charged state of the toner, but the value of the transfer voltage applied to the secondary transfer roll 34 is changed to about 0.5 kV to 2.5 kV. The toner charge state differs greatly from the normal state, and the density value of the toner image on the recording paper 35 is low until the value of the transfer voltage applied to the secondary transfer roll 34 is about 1.5 kV. When it is determined that the density value of the toner image on the recording paper 35 tends to increase rapidly when the value of the transfer voltage applied to the secondary transfer roll 34 exceeds about 1.5 kV. Detects a charged state of the toner is high charged state.

As shown in FIG. 10, the control circuit 100 detects the charged state of the toner, for example, when the value of the transfer voltage applied to the secondary transfer roll 34 is about 1.5 kV to about 2.0 kV. The transfer voltage value before and after abrupt change when multiple changes are made to about 5 kV is about 1.5 kV, and the predetermined transfer voltage value is about 1.5 kV when multiple changes are made to 2.5 kV. The density difference between the density value of the toner image 53 on the recording paper 35 detected by the in-line sensor 51 between the first value and the second value of about 2.5 kV is a threshold value D _sh as shown in FIG. It is determined whether it is above or below the threshold, and if it is above the threshold, it is detected that the charged state of the toner is a high charged state. Further, the density value of the toner image 53 on the recording paper 35 detected by the in-line sensor 51 when the predetermined transfer voltage value is about 1.5 kV and the second value is about 2.5 kV. 11 is less than the threshold value D _sh as shown in FIG. 11, and the density value of the toner image is a predetermined difference from the density value in the normal state as shown in FIG. If it is smaller than ΔD, it is detected that the charged state of the toner is a low charged state, and if it is within a predetermined difference ΔD from the density value in the normal state, the charged state of the toner is in the normal state. It detects that it is.

  Further, when the control circuit 100 detects whether the charging state of the toner is a normal state, the charging state of the toner is a low charging state, or the charging state of the toner is a high charging state, the control circuit 100 Based on the charged state of the toner that forms the toner image of each color detected by 100, the value of the transfer current supplied to the corresponding primary transfer rolls 27Y, 27M, 27C, and 27K via the high-voltage power supply circuit 103 is controlled. It is configured.

  In the above configuration, according to the image forming apparatus in which the toner charge amount detection device is applied to this embodiment, the toner charge state can be detected with a simple configuration as follows. Accordingly, image quality can be improved by controlling the primary transfer conditions.

  That is, in the image forming apparatus according to this embodiment, as shown in FIG. 2, image forming units 14Y, 14M, and 14C for each color of yellow (Y), magenta (M), cyan (C), and black (K) are used. , 14K, toner images of corresponding colors are formed on the respective photosensitive drums 16Y, 16M, 16C, 16K according to the color of the image to be formed, and these photosensitive drums 16Y, 16M, 16C, 16K are formed. The formed yellow (Y), magenta (M), cyan (C), and black (K) toner images are subjected to predetermined currents on the primary transfer rolls 27Y, 27M, 27C, and 27K at the primary transfer position N1. A positive transfer current whose current is controlled to a constant value is energized, and multiple primary transfers are performed on the intermediate transfer belt 26. Thereafter, the yellow (Y), magenta (M), cyan (C), and black (K) toner images that have been primary-transferred multiple times onto the intermediate transfer belt 26 are secondary-transferred at the secondary transfer position N2. A negative secondary transfer voltage controlled at a constant voltage to a predetermined voltage value is applied to the back support roll 32 facing the roll 34, and the secondary transfer voltage is collectively transferred onto the recording paper 35. The unfixed toner image is fixed by heat and pressure by the fixing device 38 and is discharged onto the discharge tray 39.

  At this time, in the image forming apparatus, as shown in FIG. 2, the developing devices of the image forming units 14Y, 14M, 14C, and 14K for yellow (Y), magenta (M), cyan (C), and black (K). In 18Y, 18M, 18C, and 18K, a toner having a relatively small particle diameter with a number average particle diameter of about 3.8 μm is used. Therefore, when the toner image made of the toner having the small particle diameter is primarily transferred onto the intermediate transfer belt 26 and then secondarily transferred from the intermediate transfer belt 26 onto the recording paper 35 at a time, As shown in FIG. 3, the mirror image force with respect to the intermediate transfer belt 26 as a conductor greatly changes according to the state of charge of the toner, that is, the amount of charge of the toner, as shown in FIG. Effect.

  More specifically, in the above image forming apparatus, as shown in FIG. 4, when the charged state of the toner is low, that is, when the amount of charge of the toner is small, the mirror image force with respect to the intermediate transfer belt 26 is small. Since the Coulomb force for the secondary transfer acting on the side of the paper 35 is also small, as shown in Example 1 in FIG. 12, the primary transfer current is increased to charge up the toner with a small amount of charge to improve the secondary transfer property. There is a need to improve. On the other hand, when the charged state of the toner is high, that is, when the amount of charge of the toner is large, the mirror image force on the intermediate transfer belt 26 is large as shown in FIG. If the primary transfer current is increased in order to increase the coulomb force for the acting secondary transfer, the toner having a large amount of charge is further charged up, and recording is caused by the influence of the mirror image force on the intermediate transfer belt 26. The density of the toner image that is secondarily transferred onto the paper 35 is instead lowered.

  Therefore, in this embodiment, when the charged state of the toner is high, that is, when the amount of charge of the toner is large, the primary transfer is performed in consideration of the large mirror image force on the intermediate transfer belt 26 as shown in FIG. In order to avoid excessive charge-up of the toner in FIG. 12, the primary transfer current is set relatively low compared to the toner in the normal charge state as shown in Example 2 in FIG. Prevents excessive toner from being charged up in the primary transfer, reduces the influence of the mirror image force on the secondary transfer, and successfully transfers the toner image on the intermediate transfer belt 26 onto the recording paper 35. It is possible to do.

  In FIG. 12, yellow (Y) and cyan (C) and magenta (M) and black (K) in Examples 1 and 2 have different primary transfer current values in the yellow located on the upstream side. This is because (Y) and the like take into account that the number of times of receiving the primary transfer electric field is large and that the black (K) toner has different charging characteristics from other color toners.

  Therefore, according to the image forming apparatus of this embodiment, the charged state of the toner is detected in the normal state by detecting the charged state of the toner and controlling the value of the primary transfer current according to the charged state of the toner. Of course, the toner image on the intermediate transfer belt 26 can be satisfactorily secondary-transferred to the recording paper 35 even when the toner is in a low charge state or a high charge state. A high-quality image can be formed without causing a decrease in density or the like.

  FIG. 13 shows an image forming apparatus configured as shown in the first embodiment, in which the charging state of toner of each color of yellow (Y), magenta (M), cyan (C), and black (K) is normal. The initial state, and the pre-adjustment state in which the charging state of the toner of each color of yellow (Y), magenta (M), cyan (C), and black (K) fluctuates is applied. 6 is a graph showing the result of detecting the density of an image transferred and fixed on the adjusted recording paper 35.

  As is apparent from the graph shown in FIG. 13, in the state before adjustment in which the charging state of the toner of each color of yellow (Y), magenta (M), cyan (C), and black (K) is fluctuating, yellow While the density of toner images of each color of (Y), magenta (M), cyan (C), and black (K) varies, in the state after adjustment using the first embodiment, yellow ( It can be seen that the toners of the respective colors Y), magenta (M), cyan (C), and black (K) have substantially the same density as the initial state, which is the normal state.

  In FIG. 13, plotting is performed with respect to a single color, but it has been confirmed that the same effect can be obtained by managing the density of single color (transfer toner amount) for multiple colors of two or more colors.

Embodiment 2
FIG. 14 shows a second embodiment of the present invention. The same parts as those in the first embodiment will be described with the same reference numerals. In the second embodiment, the image carrier is transferred by a transfer means. Instead of the toner image transferred onto the transfer medium from above, the density of the untransferred toner image remaining on the image carrier is detected by the density detecting means.

  That is, in the second embodiment, as shown in FIG. 14, at the downstream side of the secondary transfer position N2 along the moving direction of the intermediate transfer belt 26, at a position facing the surface of the intermediate transfer belt 26. An in-line sensor 51 serving as a density detecting unit is arranged, and the in-line sensor 51 is configured to detect the density of the transfer residual toner image remaining on the intermediate transfer belt 26.

  In the second embodiment, when the secondary transfer voltage applied to the back support roll 32 is changed to a plurality of values, the density of the residual toner image remaining on the intermediate transfer belt 26 is the characteristic shown in FIG. However, the tendency itself shows that the charged state of the toner is a normal charged state, the charged state of the toner is a low charged state, and the charged state of the toner is high. This is the same as the detected density of the in-line sensor 51 in the charged state.

  That is, in the second embodiment, as shown in FIGS. 15 and 16, the control circuit 100 sets the values of a plurality of transfer voltages applied to the secondary transfer roll 34 and the detected densities of the inline sensor 51 corresponding thereto. From the relationship with the value, the density value of the toner image 53 on the recording paper 35 detected by the in-line sensor 51 is smaller than the normal state in the charged state of the toner. If the characteristic when the value of the transfer voltage applied to 34 is changed from about 0.5 kV to about 2.5 kV is determined that the charged state of the toner shows the same tendency as the normal state, the charged state of the toner Is detected to be in a low charged state.

  Further, the control circuit 100 detects the recording paper detected by the inline sensor 51 from the relationship between the value of the transfer voltage applied to the secondary transfer roll 34 and the value of the detected density of the inline sensor 51, as shown in FIG. The density value of the toner image 53 on the toner 35 is still smaller than the normal charged state of the toner, but the value of the transfer voltage applied to the secondary transfer roll 34 is changed to about 0.5 kV to 2.5 kV. The toner charge state differs greatly from the normal state, and the density value of the toner image on the recording paper 35 is low until the value of the transfer voltage applied to the secondary transfer roll 34 is about 1.5 kV. When it is determined that the density value of the toner image on the recording paper 35 tends to increase rapidly when the value of the transfer voltage applied to the secondary transfer roll 34 exceeds about 1.5 kV. Detects a charged state of the toner is high charged state.

  Similarly to the first embodiment, as shown in FIG. 17, the primary transfer currents of yellow (Y) and cyan (C) and magenta (M) and black (K) are controlled, as shown in FIG. As described above, in the pre-adjustment state in which the charging state of the toner of each color of yellow (Y), magenta (M), cyan (C), and black (K) varies, yellow (Y), magenta (M), While the density of the toner images of cyan (C) and black (K) varies, in the state after adjustment using the second embodiment, yellow (Y), magenta (M), cyan It can be seen that the charged state of the toner of each color of (C) and black (K) has substantially the same density as the initial state which is a normal state.

  In the second embodiment, paper is unnecessary and desirable, and it is possible to accurately detect the density difference of the toner image 53 on the high transfer voltage side where the amount of toner remaining on the intermediate transfer belt 26 is small.

  Since other configurations and operations are the same as those of the first embodiment, description thereof is omitted.

  In the above-described embodiment, the toner image formed on the photosensitive drum is primarily transferred onto the intermediate transfer belt 26 and then secondarily transferred onto the recording paper from the intermediate transfer belt 26. Of course, the present invention can also be applied to an image forming apparatus configured to directly transfer a toner image formed on a body drum onto a recording sheet conveyed by a sheet conveying belt.

  26: Intermediate transfer belt (image carrier), 34: Secondary transfer roll, 35: Recording paper (transfer medium), 51: Inline sensor (density detection means), 53: Toner image, 100: Control circuit (charged state detection) means).

Claims (6)

Density detecting means for detecting the density of the toner image transferred onto the transfer medium from the image holding member by the transfer means or the transfer residual toner image remaining on the image holding member;
When the toner image held on the image carrier is transferred onto the transfer medium by the transfer unit, the transfer voltage applied to the transfer unit is changed to a plurality of values, and the transfer voltage applied to the transfer unit And a charged state detecting means for detecting a charged state of the toner forming the toner image based on the relationship between the value of the toner and the detected density value of the density detecting means. The image carrier is composed of an intermediate transfer member onto which a toner image is transferred from a photosensitive drum, and the transfer medium is composed of a recording medium.
The charged state detecting means detects the area of the recording medium when transferring the toner image transferred on the intermediate transfer body corresponding to the size of the recording medium onto the recording medium by the transferring means. 2. The apparatus according to claim 1, wherein the intermediate transfer member is divided into a plurality of small regions along a moving direction of the intermediate transfer member, and a transfer voltage applied to the transfer unit is changed to a plurality of values according to the plurality of small regions. The toner charged state detection device according to claim.   The toner charge state detection device according to claim 1, wherein the density detection unit detects a density of a toner image transferred onto the recording medium and fixed.   The toner charge state detection device according to claim 2, wherein the density detection unit detects a density of a transfer residual toner image remaining on the intermediate transfer member. An image carrier for holding a toner image;
Transfer means for transferring the toner image held on the image carrier onto a transfer medium;
Toner charge state detection means for detecting the charge state of the toner forming the toner image,
An image forming apparatus using the toner charged state detecting device according to claim 1 as the toner charged state detecting means. A plurality of image carriers that hold toner images of different colors;
A plurality of primary transfer means for transferring each of the toner images held on the plurality of image holders onto the intermediate transfer member in a multiplexed manner;
Secondary transfer means for performing secondary transfer of the toner images, which have been primary-transferred multiple times on the intermediate transfer body, onto a recording medium at once;
Toner charge state detection means for detecting the charge state of the toner forming each toner image;
Control means for controlling transfer conditions in the plurality of primary transfer means based on the charge state of the toner forming each toner image detected by the toner charge state detection means;
An image forming apparatus using the toner charged state detecting device according to claim 1 as the toner charged state detecting means.

Images