JP4462792B2 - Image forming apparatus - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an image forming apparatus such as a copying machine, a printer, and a facsimile.
[0002]
[Prior art]
In the image forming apparatus, the largest factor that affects the image density of the formed image is the toner density in the developer in the developing device. Therefore, it is desirable to keep the toner density constant in order to maintain a stable image density. However, the toner concentration greatly depends on changes in physical properties of the developer itself over time, and changes in physical properties due to environmental conditions such as temperature and humidity, development conditions, and the like.
[0003]
Therefore, in an image forming apparatus, the image density is usually detected on the photosensitive member by a developing potential which is a difference between a predetermined surface potential of the photosensitive member as the image carrier and an applied voltage (developing bias voltage) of the developing device. A reference image (P pattern) is formed, and the density of the P pattern is detected by a reflective photosensor called a P sensor. Based on the detection result, a magnetic permeability sensor called a T sensor provided in the developing device The control reference value (reference value for toner density control) Vtref is corrected to determine the toner density as the target output value of the T sensor, thereby obtaining a stable image density. For reference, the relationship between the P pattern toner adhesion amount M / A per unit area on the photoreceptor and the P sensor detection value Vsp for the P pattern is generally as shown in FIG.
[0004]
Conventionally used toner density control methods using a T sensor and a P sensor together include the following methods. During the image forming operation, the toner density in the developing device is detected by the T sensor. The toner replenishment amount from the toner replenishing device to the developing device is controlled according to the difference between the output value Vt of the T sensor obtained from the magnetic permeability of the developer as a substitute characteristic value of the toner concentration and the control reference value Vtref. Here, development due to changes in the charge amount of the developer due to changes in the physical properties of the developer itself over time, or changes in physical properties due to environmental conditions such as temperature and humidity, development conditions, etc., although the toner density does not change. Due to the change in the bulk density of the agent, the T sensor outputs a different Vt, which may cause excessive or insufficient supply of toner.
[0005]
Therefore, a P pattern is formed on the photosensitive member when the power of the machine body is turned on or every predetermined time or every predetermined number of times of image formation, and the image density of the P pattern is detected by the P sensor, and the output value of the P sensor Control reference value based on Vsp, which is the difference (Vt−Vtref) between the output values Vt and Vtref of the T sensor obtained at the same time when the machine body is turned on or every predetermined time or every predetermined number of times of image formation. A correction amount ΔVt of Vtref is calculated, a new reference value Vtref ′ (= Vtref + ΔVt) is determined, and this is set as a new control target value (see Japanese Patent Laid-Open No. 8-110700).
[0006]
As an example, FIG. 4 shows a matrix for determining the correction amount ΔVtref. Here, in consideration of variations in the P sensor output value, control is performed based on the ratio value (Vsp / Vsg) and (Vt−Vtref) of the P sensor output values Vsg and Vsp for the non-image portion on the photosensitive member. The correction amount ΔVt of the reference value Vtref is calculated, and the toner replenishment amount is determined from the difference between the corrected T sensor control target value Vtref ′ and the output value Vt of the T sensor output at each image forming operation or at a predetermined timing. Is determined.
[0007]
The toner replenishment amount can be replaced with the rotation time of the toner bottle (toner replenishment clutch on time) if the toner replenishing device is a type that replenishes toner by rotating the toner bottle, for example. In general, the larger the value of (Vt−Vtref), the longer the toner bottle rotation time (toner replenishment clutch on-time), assuming that the toner density is insufficient with respect to the target value.
[0008]
Japanese Patent Laid-Open No. 5-134548 discloses an image forming apparatus that controls toner density by using both a T sensor and a P sensor, and detects the image density with the P sensor every time a certain number of images are formed. Is described.
Japanese Patent Laid-Open No. 8-110700 discloses an image forming apparatus that performs toner density control by using both a T sensor and a P sensor, and the upper and lower limits of the T sensor toner density control reference value correction amount based on the output value of the P sensor. Is set to prevent toner density fluctuations caused by fluctuations in the charging potential or the like.
[0009]
Japanese Patent Laid-Open No. 8-202137 discloses an image forming apparatus that performs toner density control using a T sensor and a P sensor together, and changes the correction amount of the control target value based on the output value of the P sensor by the number of copies. By doing so, there is described what prevents toner density fluctuations due to changes in the characteristics of the developer over time.
[0010]
[Problems to be solved by the invention]
As described above, the charge amount (Q / M) per unit mass of the developer varies depending on environmental conditions, leaving conditions, and the like. If the developer agitation time is long, the Q / M increases, the developing ability decreases, and the output value Vsp of the P sensor increases. Even in the same agitation time, the Q / M is lower in the low humidity environment than in the high humidity environment. The rise of is remarkable. In addition, if the developer is left for a long time, Q / M decreases, the developing ability increases, and the output value Vsp of the P sensor decreases. As an example, FIG. 8 shows changes in Q / M and Vsp with respect to the apparatus leaving time in the image forming apparatus. When the toner density TC is 4 wt%, the developer of this apparatus has an output Vsp of the P sensor of 0.4 (V) at Q / M20 (−μC / g) (that is, Vsp / Vsg is about 0.1 (V )), And an ideal image density ID of 1.35 is obtained.
[0011]
It is assumed that the image forming operation is finished in a state where an ideal image density ID 1.35 is obtained. Thereafter, when left in a resting state for a long time, as shown in FIG. 8, the Q / M of the developer is lowered and the developing ability is increased. Here, when the P pattern is detected by the P sensor, the value of Vsp decreases because the toner adhesion amount on the photoreceptor increases. That is, it is determined from the output value of the P sensor that the image density is high, and the control reference value Vtref is changed in a direction in which the image density decreases (ΔVt> 0). In the developer in this image forming apparatus, when the image is not formed for 3 hours or more and left to stand, the drop in Vsp is large.
[0012]
Here, at the end of an image forming operation, TC was 4 wt%, Q / M was 20 (−μC / g), Vtref was 2.50 (V), and image density ID was 1.35. From here, the apparatus was allowed to stand for 10 hours, and then the machine was turned on to continuously perform image formation. The image density and the TC and Q / M of the developer were measured each time the image was formed. In this apparatus, Vtref is corrected by the output value of the P sensor when the power is turned on. At this time, Vsp / Vsg was 0.05 and (Vt−Vtref) was 0.05 (V). According to the table of 4, the correction amount of Vtref was set to ΔVtref = 0.15 (V), and the new control target value was controlled to Vtref ′ = 2.65 (V).
[0013]
Continuous image forming operations were performed in an environment of 23 ° C. and 50%, an environment of 10 ° C. and 155%, and an environment of 23 ° C. and 15%. A reflection densitometer X-Rite was used to measure the image density. As shown in FIGS. 5 to 7, the image density ID was 1.35 at the initial stage in an environment of 23 ° C. and 50%, but the TC of the developer decreased as the number of image forming sheets (number of copies) increased. In addition, the Q / M increased and the image density slightly decreased to 1.30 in the 200th image formation. This is because toner supply is not performed until the output value Vt of the T sensor for each image formation reaches a new control reference value Vtref ′ (= Vtref + ΔVt) during this period, and the target TC is lowered. Further, when image formation is continuously performed after Vt reaches Vtref ', the TC is almost constant and the Q / M increases, and the decrease in image density at the 500th sheet proceeds to 1.26. Such a decrease in ID is a level at which there is no problem in normal use.
[0014]
However, this tendency becomes prominent in low-temperature / low-humidity environments and medium-temperature / low-humidity environments. If the same thing is performed in a low-temperature / low-humidity environment of 10 ° C. and 15%, The image density decreased to 1.27, and in the image formation of the 500th sheet, the image density decreased to 1.18, which was a visually poor level. At this time, TC was 3.5% and Q / M was 30. Similarly, even in the environment of medium temperature and low humidity of 23 ° C. and 15%, the image density decreased to 1.20 in the 500th image formation.
[0015]
In the middle of passing 500 sheets, a reference image is formed on the photosensitive member every predetermined number of times of image formation such as every 5 sheets or every 10 sheets, or every certain time, and the image density is measured by a P sensor. If it is determined that the image density is low from the output value Vsp, the correction amount ΔVt of the control reference value Vtref is recalculated based on the table shown in FIG. It becomes difficult to do.
[0016]
On the other hand, in recent machines, a reduction in space and cost is indispensable. For this reason, a form in which the photoconductor and the transfer roller are always in contact with each other without providing a contact / separation mechanism between the photoconductor and the transfer roller is becoming common. The above apparatus is also an example, and there are problems such as a decrease in productivity of an image formed product by securing a transfer roller cleaning time after each P pattern creation when the P pattern adheres to the transfer roller, and deterioration of the transfer roller due to cleaning. appear. From these points, it is difficult to quantitatively determine how many image forming sheets or Vtref correction should be performed with the P sensor output value every time, and it is impossible to solve the above problem. .
SUMMARY OF THE INVENTION An object of the present invention is to provide an image forming apparatus that solves the above problems and can prevent an excessive decrease in image density over time during image formation in a low temperature or low humidity environment.
[0017]
[Means for Solving the Problems]
  In order to achieve the above object, the invention according to claim 1 is directed to developing means for supplying toner to the latent image formed on the image carrier to visualize the latent image, and supplying toner to the developing means. Toner replenishing means, toner density detecting means for detecting the toner concentration of the developer in the developing means, and the toner replenishing means based on the comparison result between the output value Vt of the toner density detecting means and the reference value Vtref. A toner replenishment control means for controlling, an image density detection means for detecting an image density of a reference image for image density detection formed on the image carrier, and the reference value based on an output value of the image density detection means In an image forming apparatus having a reference value correcting unit that corrects Vtref by ΔVtref to obtain (Vtref + ΔVtref), the temperature inside or near the apparatusMeasure degree TA detection unit that knows, and when correcting the reference value Vtref based on the output value of the image density detection unit,The temperature T is set to a predetermined temperature T according to the output value of the detection means. _L The ratio Vsp / Vsg between the output value Vsp of the image density detection means for the reference image and the output value Vsg of the image density detection means for the non-image portion on the image carrier is less than a predetermined value α. ΔVtref when T> T _L Smaller than the value ofIs.
[0018]
  The invention according to claim 2Developing means for supplying toner to the latent image formed on the image carrier to visualize the latent image, toner supplying means for supplying toner to the developing means, and toner for developer in the developing means A toner density detecting means for detecting density, a toner replenishing control means for controlling the toner replenishing means based on a comparison result between an output value Vt of the toner density detecting means and a reference value Vtref, and formed on the image carrier. An image density detecting means for detecting the image density of the reference image for image density detection, and a reference value correction for correcting the reference value Vtref by ΔVtref based on the output value of the image density detecting means to (Vtref + ΔVtref) An image forming apparatus having a detecting means for detecting a humidity H in or near the apparatus, and correcting the reference value Vtref based on an output value of the image density detecting means. The humidity H are predetermined humidity H by the output value of the detection means _L The ratio Vsp / Vsg between the output value Vsp of the image density detection means for the reference image and the output value Vsg of the image density detection means for the non-image portion on the image carrier is equal to or less than a predetermined value β. ΔVtref when H> H _L Smaller than the value ofIs.
[0019]
  The invention according to claim 32. The image forming apparatus according to claim 1, wherein the detecting means detects a temperature T in or near the apparatus every time a predetermined number of images are formed or an image is formed for a predetermined time, and T> T _L When ΔVtref is satisfied, T> T _L Return to the value at the time ofIs.
[0020]
  The invention according to claim 42. The image forming apparatus according to claim 1, wherein the detecting means detects a temperature T in or near the apparatus every time a predetermined number of images are formed or an image is formed for a predetermined time, and T> T _L In this case, the reference value Vtref is corrected again based on the output value of the image density detecting means.Is.
[0021]
  The invention according to claim 53. The image forming apparatus according to claim 2, wherein the detecting means detects a humidity H in or near the apparatus every time a predetermined number of images are formed or an image is formed for a predetermined time, and at that time, H> H _L When ΔVtref is satisfied, H> H _L Return to the value at the time ofIs.
[0022]
  The invention according to claim 63. The image forming apparatus according to claim 2, wherein the detecting means detects a humidity H in or near the apparatus every time a predetermined number of images are formed or an image is formed for a predetermined time, and at that time, H> H _L In this case, the reference value Vtref is corrected again based on the output value of the image density detecting means.Is.
[0024]
DETAILED DESCRIPTION OF THE INVENTION
The first embodiment of the present invention will be described below. The first embodiment is an embodiment of an electrophotographic copying machine that is an image forming apparatus.
First, a schematic configuration of the copying machine according to the first embodiment will be described with reference to FIG. A charging roller 2 as charging means for uniformly charging the surface of the photosensitive member 1 by applying a voltage from a power source (not shown) in order around the drum-shaped photosensitive member 1 as an image carrier in the counterclockwise direction. An exposure unit (not shown) that forms an electrostatic latent image by irradiating the surface of the photosensitive member 1 with exposure light 3 based on image information of a document read by an image reading unit (not shown) is formed on the photosensitive member 1. A developing device 4 that visualizes the electrostatic latent image as a toner image, a transfer roller 5 as a transfer unit that transfers the toner image on the photoreceptor 1 onto a sheet P as a recording material, and a photoreceptor after transfer. A cleaning device 6 is provided as a cleaning means for removing toner remaining on the toner 1 and a static eliminator such as a static elimination lamp (not shown) that initializes the surface potential of the photoreceptor 1 after transfer.
[0025]
The photosensitive member 1 is rotationally driven by a driving unit (not shown) and is uniformly charged by a charging roller 2 and irradiated with exposure light 3 based on document image information from an image reading unit (not shown) by an exposure unit (not shown). An electrostatic latent image is formed. The electrostatic latent image on the photoreceptor 1 is visualized as a toner image by the developing device 4, and the toner image on the photoreceptor 1 is transferred onto the paper P by the transfer roller 5. Further, after the transfer, the residual toner is removed by the cleaning device 6 after the transfer, and the surface potential is initialized by a static eliminator (not shown).
[0026]
The developing device 4 includes a developing roller 7 as a developer carrying member that carries the developer and supplies toner to the photosensitive member 1, and a developing screw 8 and 9 as stirring and conveying means for stirring and conveying the developer. A toner density detector for detecting a toner density of a two-component developer composed of a carrier and a negatively charged toner in a developing casing 10 is provided below the conveying screw 9 far from the developing roller 7. A T sensor (permeability sensor) 11 is provided as means. Although not shown, a toner replenishing device as a toner replenishing means for replenishing toner to the two-component developer in the developing casing 10 is provided above the transport screen 9. A negative developing bias is applied to the developing roller 7 from a power source (not shown), and a predetermined developing potential is formed between the photoreceptor 1 and the developing roller 7.
[0027]
The sheets P stored in the sheet feeding cassette 12 are separated one by one from the uppermost one by the sheet feeding roller 13 and the like, and are sent toward the registration roller pair 14. The sheet P is temporarily stopped by the registration roller pair 14, and after the oblique deviation is corrected, the sheet P is sent to the transfer nip portion between the photosensitive member 1 and the transfer roller 5 by the registration roller pair 14 at a predetermined timing. In this transfer nip portion, a transfer bias is applied to the transfer roller 5 from a power source (not shown), and the toner image on the photoreceptor 1 is transferred to the paper P. The sheet P on which the toner image is transferred is sent to a fixing device (not shown) located downstream in the transport direction, and the toner image is fixed by heat and pressure in this fixing device.
[0028]
Between the transfer roller 5 and the developing device 4, a P sensor (reflection photosensor) 15 is provided as an image density detection unit having a light emitting element and a light receiving element. The output value Vt of the T sensor 11 shows a lower value as the toner density TC in the developer is higher, and the output value Vsp of the P sensor 15 shows a lower value as the image density on the photoreceptor 1 is higher.
[0029]
FIG. 1 shows a control unit of the first embodiment. The overall operation of the copying machine according to the first embodiment is controlled by a control unit 16 as control means. The control unit 16 includes an I / O interface 17, a CPU 18, a RAM 19, and a ROM 20. A main motor 23 and a toner supply clutch 24 are connected to the I / O interface 17 through drivers 21 and 22, respectively. An operation display unit (operation panel) 25 is connected to the I / O interface 17. The main motor 23 drives the photoreceptor 1 to rotate.
[0030]
Further, the I / O interface 17 converts a PWM controller 26 for supplying a predetermined voltage to the T sensor 11 and the P sensor 15 and an analog signal output from the T sensor 11 and the P sensor 15 into a digital signal. A / D converters 27 and 28 are connected. In addition, between the PWM controller 26 and each of the T sensor 11 and the P sensor 15, a circuit including resistors 29 to 31, 32 to 34, capacitors 35 and 36, and operational amplifiers 37 and 38 is connected.
[0031]
FIG. 9 shows a flow of toner supply control (toner density control) in the first embodiment. When the main switch of the first embodiment is turned on (step S2), the control unit 16 controls each unit of the present embodiment to form a reference image for image density detection on the photosensitive member 1, and is determined in advance, for example. A P pattern as a reference image for detecting image density is formed on the photosensitive member 1 by the developing potential which is the difference between the surface potential of the photosensitive member 1 and the applied voltage (developing bias voltage) of the developing device (step S3). Then, the control unit 16 stores and uses the previous reference value as the reference value Vtref for toner replenishment control (step S4).
[0032]
Next, the control unit 16 takes in the output value Vsp of the P sensor 15 with respect to the reference image on the photosensitive member 1 and the output value Vsg of the P sensor 15 with respect to the non-image portion on the photosensitive member 1, and the ratio value ( Vsp / Vsg) = A is calculated (step S5), and an output value Vt that differs depending on the TC of the developer in the developing device is taken in almost simultaneously from the T sensor 11 to calculate (Vt−Vtref) = B (step S6). .
[0033]
At this time, the control unit 16 takes in an output value of a temperature sensor (not shown) as a detecting means for detecting the temperature T in or near the present embodiment in step S7, and the temperature T is set to a predetermined value from the output value of the temperature sensor. Set value T_LIt is determined whether or not (for example, 10 ° C.) or less, and whether to apply the Vtref correction table for the low temperature environment or the normal Vtref correction table is selected based on the result. These correction tables differ in the correction amount ΔVtref of Vtref.
[0034]
The control unit 16 has T ≦ T_LIn this case, in step S8, it is assumed that the atmosphere in the apparatus is low temperature, that is, the Q / M increase is large due to the stirring of the developer by image formation, and a low temperature Vtref correction table as shown in FIG. > T_LIn this case, the normal Vtref correction table as shown in FIG. 4 is applied on the assumption that the atmosphere in the apparatus is at room temperature, that is, the Q / M rise is not large due to the stirring of the developer by image formation in step S9.
[0035]
Here, especially when Vsp / Vsg is not more than the target value α (here 0.09), that is, when the image density is high, it is obtained by the low-temperature Vtref correction table (Vtref correction table shown in FIG. 10) in step S8. ΔVtref (low) is always a value smaller than ΔVtref (mid) obtained in the normal Vtref correction table (the Vtref correction table shown in FIG. 4) in step S9. That is, in step S8, the correction amount in the direction in which TC decreases. Thus, excessive reduction in image density over time during image formation in a low temperature environment can be prevented.
[0036]
From the B = (Vt−Vtref) value fetched in step S6 and A = (Vsp / Vsg) detected in step S5, the control unit 16 obtains a Vtref correction table as shown in FIG. 10 in step S8 or step S9. A correction amount ΔVtref of the reference value Vtref is calculated with reference to the Vtref correction table as shown in FIG. (Step S10).
[0037]
Thereafter, the control unit 16 controls each unit of this embodiment in step S11 to perform an image forming operation (copying operation), and outputs the output value Vt of the T sensor 11 and the reference value Vtref ′ in step S6. The comparison result (Vt−Vtref ′) determines the ON time τ of the toner supply clutch 24 (step S12), and the toner supply clutch 24 is turned ON for τ seconds to supply toner for τ seconds (step S13). Here, the toner replenishing device is driven by a driving source (not shown) when the toner replenishing clutch 24 is turned on to replenish toner to the developing device.
[0038]
The control unit 16 takes in the output value Vt of the T sensor 115 for each image formation (step S14). The control unit 16 determines in step S15 whether or not one job (Job), that is, a set number of continuous image forming operations has been completed, and returns to step S11 if it has not been completed, and fetched in step S14. The toner replenishment time τ is determined by the Vt value and the reference value Vtref ′ (step S12). Thereafter, the control unit 16 repeats steps S11 to S15 until one job is completed.
[0039]
In the first embodiment, the temperature T in or near the apparatus is set to the set value T in step S7._LWhen it is determined that the temperature is equal to or lower than (10 ° C.) and a new Vtref ′ is calculated in the low-temperature Vtref correction table, the temperature T is detected every time a predetermined number of images are formed._LIf it is determined that the temperature is higher than (10 ° C.), it is determined that the environment has been controlled so that the increase in Q / M and the decrease in ID during the image formation peculiar to the low temperature and low humidity environment are suppressed. It is also possible to configure so that ΔVtref (low) is switched to the normal ΔVtref (mid) obtained in step S9.
[0040]
The second embodiment of the present invention is an embodiment of the image forming apparatus having such a configuration, and FIG. 11 shows a toner replenishment control flow. In the second embodiment, in the first embodiment, the control unit 16 executes the toner supply control flow shown in FIG. 11 instead of the toner supply control flow shown in FIG. In FIG. 11, steps S16 to S21 are the same as steps S1 to S6 of FIG.
[0041]
Here, the control unit 16 sets the temperature T in or near the present embodiment to T in step S22._LIt is determined that the temperature of the apparatus is lower than (10 ° C.), the temperature of the apparatus is considered to be low, that is, the increase in Q / M due to the stirring of the developer due to image formation is large. Applying the B = (Vt−Vtref) value acquired in step S21 and A = (Vsp / Vsg) detected in step S20, the correction amount of the reference value Vtref with reference to the Vtref correction table as shown in FIG. ΔVtref is calculated (step S23). Steps S24 to S28 are the same as steps S10 to S14 in FIG.
[0042]
In step S29, the control unit 16 determines whether or not one job, that is, the set number of continuous image forming operations has been completed. If not, the control unit 16 proceeds to step S30. Here, the control unit 16 again determines that the temperature T is T from the output value of the temperature sensor._LIt is determined whether or not (10 ° C.) or less, and the temperature T is T_LIf (10 ° C.) or less, the toner replenishment time τ is determined based on the Vt value and the reference value Vtref ′ in the previous step S28 (step S26).
[0043]
The controller 16 has a temperature T of T_LWhen the temperature rises higher than (10 ° C.), it is determined that the environment has been suppressed in which the increase in Q / M and the decrease in the image density ID during the image formation specific to the low-temperature and low-humidity environment are suppressed. ΔVtref (low) for low temperature is switched to normal ΔVtref (mid) in step S31, and the correction amount ΔVtref of the reference value Vtref is referred to with reference to a normal Vtref correction table as shown in FIG. 4 as in step S9 of FIG. Is calculated.
[0044]
In the second embodiment, the temperature in or near the inside is detected at the end of the job. However, the same effect can be obtained by performing the detection in the middle of the job or every predetermined time. Further, in the second embodiment, the temperature T in or near the present apparatus becomes T in step S30 of FIG._LWhen the temperature rises to (10 ° C.) or more, it is judged that the environment has been suppressed in which the increase in Q / M and the decrease in image density ID during the image formation characteristic of low temperature and low humidity environment are suppressed. If a reference image is created and Vsp / Vsg is detected again, it is possible to correct Vtref according to the state of the developer at that time.
[0045]
The third embodiment of the present invention is an embodiment of an image forming apparatus having such a configuration. In the third embodiment, a toner supply control flow as shown in FIG. 12 is executed in place of the toner supply control flow as shown in FIG. 11 in the second embodiment. In FIG. 12, Steps S32 to S45 are the same as Steps S16 to S29 of FIG.
[0046]
In step S46, the controller 16 determines that the temperature T is T from the output value of the temperature sensor._LWhen higher than (10 ° C.), step S47 to step S50 similar to step S34 to step S37 are followed, and in step S51, ΔVtref is determined in the same manner as step S31 of FIG. 11 according to the normal Vtref correction table.
[0047]
Thereafter, the control unit 16 corrects the reference value Vtref by the correction amount ΔVtref in step S40 and further determines and stores it as a new reference value Vtref ′ (= Vtref + ΔVtref). In the third embodiment, the temperature T in or near the inside is detected at the end of the job. However, the same effect can be obtained even during the job or every predetermined time.
[0048]
Further, as described above, the developer agitation, that is, continuous image formation, raises the Q / M of the developer, and the environment in which the image density tends to decrease is at low temperature / low humidity and at medium temperature / low humidity. In general, there are many cases of low humidity conditions at low temperatures, but there are medium and low humidity conditions at intermediate temperatures. Therefore, the humidity sensor is more desirable than the temperature sensor in order to sequentially see the Q / M fluctuation of the developer due to the environment. The detection value H of the humidity sensor is H <H_LIn the case of (= 15%), it is considered that the atmosphere of the apparatus is low in temperature, that is, the increase in Q / M is large due to the stirring of the developer by image formation.
[0049]
As an example of the image forming apparatus having such a configuration, in the first embodiment, the determination in step S7 in FIG. 9 is performed by using a humidity sensor as a detection unit that detects the humidity H in or near the image forming apparatus. From output value H ≦ H_L(= 15%), and a low humidity Vtref correction table is used instead of the matrix of FIG. That is, when Vsp / Vsg is less than the target value β, that is, when the image density is high, ΔVtref (low) obtained by the low humidity Vtref correction table is always greater than ΔVtref (mid) obtained by the normal Vtref correction table. In step S8, the Vtref correction amount in the direction in which the TC decreases is reduced, and this has the effect of preventing an excessive decrease in image density over time during image formation in a low humidity environment.
[0050]
Further, in the second embodiment, the determination in step S22 and the determination in step S30 in FIG. 11 are performed based on the output value of the humidity sensor that detects the humidity H in or near the image forming apparatus._L(= 15%) By using the low humidity Vtref correction table instead of the matrix shown in FIG. 10, the same effect as in the second embodiment can be obtained using humidity as a criterion. Can do.
[0051]
In the third embodiment, the determination in step S39 and the determination in step S46 in FIG. 12 are performed based on the output value of the humidity sensor that detects the humidity H in or near the image forming apparatus._L(= 15%) If the Vtref correction table for low humidity is used instead of the matrix shown in FIG. 10, the same effect as in the third embodiment can be obtained using humidity as a criterion. it can.
[0052]
Although these image forming apparatuses detect the humidity in or near the inside at the end of the job, the same effect can be obtained even if it is performed during the job or every predetermined time.
In each of the above embodiments, the correction amount ΔVtref is changed by detecting the temperature or humidity in or near the image forming apparatus. However, the correction amount ΔVtref is detected by detecting the temperature or humidity in or near the image forming apparatus. May be changed.
[0053]
【The invention's effect】
  As described above, according to the present invention, it is possible to prevent an excessive decrease in image density over time during image formation in a low temperature or low humidity environment.
  Claims4, 6According to the invention, it is possible to correct the reference value Vtref according to the developer situation.
[Brief description of the drawings]
FIG. 1 is a block diagram illustrating a control unit according to a first embodiment of the present invention.
FIG. 2 is a characteristic diagram showing a general relationship between a P pattern toner adhesion amount M / A per unit area on a photosensitive member and a P sensor detection value Vsp with respect to the P pattern.
FIG. 3 is a cross-sectional view schematically showing the first embodiment.
FIG. 4 is a diagram illustrating an example of a matrix for determining a correction amount ΔVtref of a control reference value Vtref.
FIG. 5 is a diagram illustrating an example of a relationship between the number of copies of an image forming apparatus and an image density ID.
FIG. 6 is a diagram illustrating an example of a relationship between the number of copies of the image forming apparatus and a toner density TC.
FIG. 7 is a diagram illustrating an example of a relationship between the number of copies of the image forming apparatus and a charge amount Q / M per unit mass of developer.
FIG. 8 is a diagram illustrating an example of changes in Q / M and Vsp with respect to apparatus leaving time in an image forming apparatus.
FIG. 9 is a flowchart showing a toner replenishment control flow of the control unit in the first embodiment.
FIG. 10 is a view showing a low-temperature Vtref correction table of the first embodiment.
FIG. 11 is a flowchart illustrating a toner replenishment control flow of a control unit according to the second embodiment of the present invention.
FIG. 12 is a flowchart illustrating a toner supply control flow of a control unit according to a third embodiment of the present invention.
[Explanation of symbols]
1 Photoconductor
2 Charging roller
4 Development device
5 Transfer roller
11 T sensor
15 P sensor
16 Control unit
24 Toner supply clutch

Claims (6)

Developing means for supplying toner to the latent image formed on the image carrier to visualize the latent image, toner supplying means for supplying toner to the developing means, and toner for developer in the developing means A toner density detecting means for detecting density, a toner replenishing control means for controlling the toner replenishing means based on a comparison result between an output value Vt of the toner density detecting means and a reference value Vtref, and formed on the image carrier. An image density detecting means for detecting the image density of the reference image for image density detection, and a reference value correction for correcting the reference value Vtref by ΔVtref based on the output value of the image density detecting means to (Vtref + ΔVtref) in the image forming apparatus and means, having a detection means for detection known the temperature T inside or in the vicinity of the device, when performing correction of the reference value Vtref on the basis of the output value of the image density detecting means Wherein said temperature T by an output value of the detection means is equal to or less than a predetermined temperature T _L, and the image density detecting means output value Vsp and for the non-image portion on said image bearing member of the image density detecting means with respect to said reference image An image forming apparatus characterized in that when the ratio Vsp / Vsg to the output value Vsg is equal to or less than a predetermined value α, ΔVtref is set to a smaller value than when T> _TL . Developing means for supplying toner to the latent image formed on the image carrier to visualize the latent image, toner supplying means for supplying toner to the developing means, and toner for developer in the developing means A toner density detecting means for detecting density, a toner replenishing control means for controlling the toner replenishing means based on a comparison result between an output value Vt of the toner density detecting means and a reference value Vtref, and formed on the image carrier. An image density detecting means for detecting the image density of the reference image for image density detection, and a reference value correction for correcting the reference value Vtref by ΔVtref based on the output value of the image density detecting means to (Vtref + ΔVtref) An image forming apparatus having a detecting means for detecting a humidity H in or near the apparatus, and correcting the reference value Vtref based on an output value of the image density detecting means. Wherein the humidity H by the output value of the detection means is equal to or less than a predetermined humidity H _L, and the image density detecting means output value Vsp and for the non-image portion on said image bearing member of the image density detecting means with respect to said reference image An image forming apparatus characterized in that ΔVtref is set to a smaller value than when H> H _L when the ratio Vsp / Vsg to the output value Vsg is equal to or less than a predetermined value β . 2. The image forming apparatus according to claim 1, wherein the detecting means detects a temperature T in or near the apparatus every time a predetermined number of images are formed or an image is formed for a predetermined time, and at that time, T> _TL . In this case, the image forming apparatus returns the ΔVtref to the value when T> _TL . 2. The image forming apparatus according to claim 1, wherein the detecting means detects a temperature T in or near the apparatus every time a predetermined number of images are formed or an image is formed for a predetermined time, and at that time, T> _TL . In this case, the reference value Vtref is corrected again based on the output value of the image density detecting means . 3. The image forming apparatus according to claim 2, wherein the detecting means detects a humidity H in or near the apparatus every time a predetermined number of images are formed or an image is formed for a predetermined time, and at that time, H> _HL . the ΔVtref if it becomes an image forming apparatus and returning the value of the time of H> H _L. 3. The image forming apparatus according to claim 2, wherein the detecting means detects a humidity H in or near the apparatus every time a predetermined number of images are formed or an image is formed for a predetermined time, and at that time, H> _HL . image type forming apparatus, characterized in that the correction of the reference value Vtref based again on the output value of the image density detecting means when it becomes.

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