JP2564126B2 - Image forming device - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates generally to image forming apparatuses, and more particularly to color image formation such as various color printers including, for example, a multicolor electrophotographic copying apparatus having a plurality of developing devices. Regarding the device. In the present specification, a multicolor electrophotographic copying machine as a color image forming apparatus will be described.

TECHNICAL BACKGROUND OF THE INVENTION AND PROBLEMS THEREOF This type of multicolor electrophotographic copying apparatus has a structure such that, for example, color development of two colors or color copying of three or more colors or full-color copying can be obtained. Inside the main body, a photosensitive drum formed to have a considerably large diameter as an image carrier, and three to four disposed along the outer peripheral surface of the photosensitive drum and close to the outer peripheral surface of the photosensitive drum. The image forming unit is composed of various devices such as individual developing devices. Then, in each of the developing units, a developer such as yellow Y, magenta M, cyan C, black BK, etc. is stored, and the developer for each color is formed on each photoconductor drum. The electrostatic latent image of the document image information is displayed as a visible image. In the multicolor electrophotographic copying apparatus having the above-described structure, four developing devices must be arranged in the vicinity of the outer peripheral surface of the photosensitive drum, and therefore, the outer peripheral surface of the photosensitive drum such as a normal black and white copy. Compared with a monochromatic electrophotographic copying machine that requires only one developing device in the vicinity, an internal space for installing the developing device is required to be four times or more, and the diameter of the photosensitive drum is also a monochromatic copying machine. The diameter must be considerably larger than that provided in the device, and the size of the device as a whole and the cost increase due to the size increase are inevitable. Therefore, as a measure for avoiding such an increase in size of the apparatus, a multicolor electrophotographic copying apparatus having a so-called rotary developing apparatus has been proposed (Japanese Patent Publication No. 50-93437). The outline of the proposal is that a rotary developing device, that is, a substantially cylindrical housing that holds four developing devices and is rotatably supported is arranged near the outer peripheral surface of the photosensitive drum to By rotating the housing of the electrostatic latent image formed on the developing device, the developing device is sequentially developed by the developing device located at the developing position facing the outer peripheral surface of the photoconductor drum. Refer to the above publication).

By the way, even in the case of the multicolor electrophotographic copying machine equipped with the rotary developing device having the above-mentioned structure, it is necessary to downsize the housing in order to downsize the entire device and obtain a lower cost device. The miniaturization of the housing inevitably leads to the miniaturization of each developing device. As described above, in a multicolor electrophotographic copying machine in which the rotary developing device is downsized, a developer replenishing device for replenishing the developer to each developing device is required in addition to each developing device. But,
Since the position at which the developer is replenished from the developer replenishing device to each developing device is different from the above-described developing position, depending on the mutual positional relationship between the rotating developing devices, each developing device is Even if an attempt is made to replenish the developer to another developing device that is not in the developing position during development copying, the developing device that does not stop at the developer replenishing position causes the developing process to stop. The developer cannot be supplied to the container.

Therefore, as a method capable of keeping up with the current trend of increasing the speed of image copying and also supplying the developer to the developing device which cannot supply the developer, the developed and copied transfer An image copying sequence may be continuously executed until the number of sheets reaches a predetermined number, and a sequence may be added in which the developer is replenished from the developer replenishing device to the developing device each time the number of sheets reaches the predetermined number. Be considered However, in such a method, when the consumption amount during the execution of image copying for a predetermined number of sheets is larger than the normal consumption amount, the concentration of the developer in the developing device is significantly lowered. Therefore, there arises a problem that only an output image having a reduced density can be obtained.

Therefore, the present invention was devised to solve the above-mentioned problems, and the purpose thereof is to prevent the supply of the developer from the developer supply device during the execution of the image copying sequence. An object of the present invention is to provide an image forming apparatus capable of obtaining a high-quality image at a high speed without significantly reducing the image density of an output image even when a developing device is provided.

Means for Solving Problems The above object is achieved by the image forming apparatus according to the present invention. In summary, the present invention comprises an image bearing member carrying an electrostatic latent image, and a developing unit having a plurality of developing units for developing developers of the electrostatic latent image on the image bearing member, each of which contains a developer of a different color, A density detecting means for detecting the density of the developer in the developing device, a judging means for judging whether or not the developer is insufficient by comparing the density detected by the density detecting means with a reference value, and this judging means. And a replenishing means for replenishing the developer having a shortage with the developer when it is determined that the developer is insufficient, the developing device to be developed is located at a common developing position during development. To move the development unit,
When a developer is replenished, a developing and forming apparatus that moves the developing unit so that the developing device to be replenished is located at a common replenishing position has a counter that operates when the developer is determined to be insufficient and counts the number of times of development and formation. However, when images are continuously formed because there are developing units that are not located in the replenishment position even though multiple developing units are located in the development position for development, the developing units that are not located in the replenishment position are used for development. When it is judged that the amount of developer is insufficient, the amount of developer is insufficient until the count value of the counter reaches a predetermined value.Compensation for density decrease due to insufficient amount of developer without replenishing the developer by changing the image forming conditions. The image forming apparatus is characterized in that the image forming apparatus continues the image formation, and when the predetermined value is reached, the developing device lacking the developer is moved to the replenishment position to perform the development.

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

FIG. 1 shows an image forming apparatus according to an embodiment of the present invention. An outline of an image forming apparatus according to an embodiment of the present invention is, as will be apparent with reference to FIG. 1, provided from one side of the apparatus main body 100 (right side in FIG. 1) to a substantially central portion of the apparatus main body 100. The transfer material transport system I and the transfer drum 9 that constitutes the transfer material transport system I in the substantially central portion of the apparatus main body 100.
To the latent image forming section II, a developing unit, i.e., a rotary developing device III and a rotary developing device III, which are disposed near the latent image forming part II. It is roughly divided into the developer replenishing means provided, that is, the developer replenishing device 2. The transfer material transport system I described above is based on the apparatus main body 10
Transfer material supply trays 101 and 102 that are detachable from an opening formed on one side of 0 (right side in FIG. 1), and the trays.
Paper feed rollers 103, 104 arranged substantially directly above the 101, 102
And paper feed guides 5a, 5b provided near the paper feed rollers 103, 104 and provided with the paper feed roller 6, and provided near the paper feed guide 5b, in the rotational direction near the outer peripheral surface. The contact roller 8, the gripper 7 transfer material separating charger 14, and the separating claw 15 are arranged from the upstream side to the downstream side, and
A transfer drum 9 in which a transfer charger 10 and a transfer material separating charger 13 are disposed on the inner peripheral side and which is rotatable in the direction of the arrow in FIG.
Conveyor belt means provided close to the separation claw 15
16 and a fixing device 17 which is disposed close to the terminal end of the transport belt means 16 in the transport direction and is adjacent to a discharge tray 10 which is detachable from the device body 100 extending outside the device body 100. It consists of and.

The latent image forming section II is provided with an outer peripheral surface thereof in contact with the outer peripheral surface of the transfer drum 9 and is rotatable in the direction of an arrow in FIG. A charger 1 for static elimination, which is arranged near the outer peripheral surface of the drum 3 from the upstream side to the downstream side in the rotation direction of the photosensitive drum 3.
1, a cleaning means 12, a primary charger 4, and an image exposure means such as a laser beam scanner for forming an electrostatic latent image on the outer peripheral surface of the photosensitive drum 3 and an image exposure reflection means such as a polygon mirror. are doing. The rotary developing device III includes a rotatable housing (hereinafter referred to as "rotary body").
1 and the photosensitive drum 3 mounted in the rotating body 1, respectively.
Of the electrostatic latent image formed on the outer peripheral surface of the photoconductor drum 3 at a position facing the outer peripheral surface of the yellow developing device 1Y, magenta developing device 1M,
It has a cyan developing device 1C and a black developing device 1BK. The developer replenishing device 2 is arranged adjacent to each other and holds a developer for each color supplied from the outside for each color, a yellow hopper 2Y, a magenta hopper 2M, and a cyan hopper.
2C, Black Hopper 2BK.

The sequence of the entire image forming apparatus configured as described above will first be briefly described by taking the case of the full color mode as an example. When the photoconductor drum 3 described above rotates in the direction of the arrow in FIG. 1, the photoconductor on the photoconductor drum 3 is uniformly charged by the primary charger 4. When the photosensitive member is uniformly charged by the primary charger 4, that is, primary charging is performed, image exposure is performed by the laser light E modulated by the yellow image signal of the document (not shown), and the photosensitive drum 3 is exposed. An electrostatic latent image is formed on the electrostatic latent image, and the electrostatic latent image is developed by the yellow developing device 1Y which is previously set at the developing position by the rotation of the rotating body 1.

On the other hand, the transfer material conveyed through the paper feed guide 5a, the paper feed roller 6, and the paper feed guide 5b is held by the gripper 7 at a predetermined timing, and the contact roller 8 and the corresponding contact roller 8 are held. It is electrostatically wound around the transfer drum 9 by means of the electrodes opposed to. The transfer drum 9 is rotating in the direction of the arrow in FIG. 1 in synchronism with the photoconductor drum 3, and the visible image developed by the yellow developing device Y is transferred to the outer peripheral surface of the photoconductor drum 3 and the transfer drum 9. Transfer is carried out by the transfer charger 10 at the portion in contact with the outer peripheral surface. The transfer drum 9 continues to rotate and is ready for transfer of the next color (magenta in FIG. 1).

On the other hand, the photoconductor drum 3 is decharged by the decharging charger 11 and cleaned by the cleaning means 12, and then again primary-charged by the primary charger 4, and is recharged by the next magenta image signal as described above. Receive a unique image exposure.
The rotary developing device 1 rotates while the electrostatic latent image based on the magenta image signal is formed on the photosensitive drum 3 by the image exposure, and moves the magenta developing device 1M to the predetermined developing position. The fixed magenta development is performed. Subsequently, the above-described process is performed for cyan color and black color respectively, and when the transfer of four colors is completed, the four-color visible image formed on the transfer material is transferred to each charger 13,
The charge is removed by 14, the grip of the transfer material by the gripper 7 is released, and the transfer material is separated from the transfer drum 9 by the separating claw 15 and sent to the fixing device 17 by the conveyor belt 16, and a series of The full color print sequence is complete,
A required full-color print image is formed.

FIG. 2 shows the structure of a developing unit, that is, a rotary developing device according to an embodiment of the present invention, and FIG. 3 shows the structure of a developer (toner) reinforcing device. In FIG.
The structure of the rotary developing device will be described in more detail. Each of the developing devices 1Y, 1M, 1C and 1BK is a magnetic brush developing system using a two-component developer composed of a magnetic powder carrier and toner. Each of the developing devices is a screw 22a, 2c for circulating the developer.
2b, a developing sleeve 21 for forming a magnetic brush, and the like.

The rotating body 1 is provided with a central shaft 27 rotatably supporting the rotating body 1 at the center thereof, and the outer peripheral portion of the central shaft 27 flows from the respective hoppers. An annular space 28 is formed so that the developer can be temporarily stored therein, and a cam 25 fixed to the central shaft 27 is provided in the annular space 28. Further, in the annular space 28, four swingable shutter levers 24 are provided at substantially equal intervals, and these four shutter levers 24 introduce the developer communicating with the above-mentioned developing devices. When the position of the opening 26 of the passage coincides with the position of the cam 25 due to the rotation of the rotating body 1, the cam member 25 is brought into contact with the cam member 25 and the cam member 25.
Thus, the shutter member 23 that closes the opening 26 is released.

As described above, the shutter member 23 opens and closes the opening portion 26 for toner replenishment, and each of the developing devices is located at the toner replenishment position (the magenta developing device 1M in FIG. 2).
When the shutter lever 24 is rotated by the cam 25 fixedly mounted on the central shaft 27, the shutter 23 of the opening 26 is released and the toner can be replenished.

In FIG. 3, the configuration of the developer replenishing device 2 will be described in more detail. In the developer replenishing device 2 described above, one end side of each of the developer replenishing devices 2 communicates with each of the hoppers 2Y, 2M, 2C, 2BK, and There are provided screws 31Y, 31M, 31C, 31BK whose end sides communicate with the annular space 28. Each of these screws is rotationally driven by a motor (not shown) and the magenta shown in FIG. The developer corresponding to the developing device is fed to the developing device which has reached the position of the developing device 1M.

FIG. 4 shows the structure of the developer concentration detecting means, that is, the developer concentration detecting device according to the embodiment of the present invention.

A developer concentration detecting device according to an embodiment of the present invention is a fourth embodiment.
As is apparent from the figure, the optical / electrical conversion signal processing circuit (a) and the optical signal supply section (b) for supplying an optical signal to the optical / electrical conversion signal processing circuit (a) Become. The optical / electrical conversion signal processing circuit (a) described above is arranged on the apparatus main body 100 side, and the optical signal supply unit (b) is arranged on each developing device 1Y, 1M, 1C, 1BK. It is assigned to. The optical / electrical conversion signal processing circuit (a) includes a lens lamp 402.
A filter 404, 405, an operational amplifier 401, a negative feedback resistor connected to the operational amplifier 401, and a light receiving element sensor 403 such as a photodiode connected to the inverting input terminal side of the operational amplifier 401. On the other hand, the optical signal supply unit (b) is provided with an optical fiber 406, a dichroic mirror 407, an EL glass 408, an EL glass 408 and a dichroic mirror 407 which receives the optical signal given from the lens lamp 402. Development sleeve 21 given via
It comprises a self-locking lens 409 for receiving a light signal scattered by the developer 410 adhering to it, and an optical fiber 411 for receiving the light signal given through the self-locking lens 409 and giving it to the light receiving element sensor 403. In the developer concentration detecting device, each of the developing devices described above has a predetermined developing position (second
When it is placed at the position of the yellow developing device 1Y in the drawing), the optical / electrical conversion signal processing circuit (a) and the optical signal supply section (b) are connected to complete the density detection circuit. In the above-described state, the light beam emitted from the lens lamp 402 is guided to the optical fiber 406, passes through the dichroic mirror 407 and the EL glass 408, and the developing sleeve 21
The developer 410 in the non-developing position at the upper end (FIGS. 2 and 4) is irradiated. Here, of the light emitted from the lens lamp 402, white light is reflected by the dichroic mirror 407, and near-infrared light is reflected by the developer 410 and scattered. A part of the scattered light is condensed on the optical fiber 411 by the self-locking lens 409, and the optical fiber 41
After passing through the filter 404 or 405 through 1, the light is received by a light receiving element sensor 403 such as a photodiode. The filter 404 is a filter that transmits only white light,
The filter 405 is a filter that transmits only near-infrared light, and is switched in synchronization with a predetermined timing by a position disk and a solenoid (not shown), and a reference signal is transmitted by the transmitted light of the filter 404. Also, the filter 405 can obtain a developer concentration signal. The signal obtained by the light-receiving element sensor 403 has its output level adjusted by the operational amplifier 401 and is converted into a digital signal by the analog / digital converter,
It is read by the control means, that is, the control controller 601 (FIG. 6 described later). The density value of the developer can be obtained by calibrating with the reference signal.

In a rotary developing device including a developer concentration detecting device and a developer replenishing device as described above, the developing position of each developing device and the relationship between the developer concentration detecting position and the developer replenishing position are preset. Since it differs depending on the rotational angle position of the developing device with respect to the reference position (home position) of the rotary developing device, it is impossible to measure the concentration of the developer and immediately replenish the developer.

5 (a) to 5 (e) respectively show a rotary developing device 1.
Each stop position with respect to the photosensitive drum 3 is shown. When the reference position is determined as shown in FIG. 5 (a), each rotation angle from the reference position is 45 °, 135 °, 225 ° and The relationship between the developing position of each developing device 1Y, 1M, 1C, 1BK and each developer concentration detecting position and each developer replenishing position at the 315 ° position is shown in FIGS. 5 (b) to 5 (e) and Table 1 respectively. As shown in.

As is clear from the above-mentioned contents, the developing device located below at a certain angular position in FIG. 5 (for example, the developing device 1Y in FIG. 5B) is the developing device located at the replenishing position and faces the photoconductor drum 3. The developing device at the above position (for example, the developing device 1BK in FIG. 7B) is the developing device at the developing position and the developer concentration detecting position. That is, regarding a certain developing device, the developing position and the developer concentration detection position are
The 90 ° rotation position is the developer supply position.

As is clear from Table 1 described above, the developing devices for four colors
When performing full-color continuous copying using 1Y, 1M, 1C, and 1BK, all developing units 1Y, 1M, 1C, and 1BK always move to the developer replenishing position. However, in the mode where there are developing devices that are not used, for example, developing devices for three colors 1
When performing continuous copying using Y, 1M, and 1C, the developer replenishment position is the time of developing the developing device 1Y for the developing device 1M and the developing device 1M for the developing device 1C. However, with respect to the developing device 1Y, since development by the developing device 1BK is not performed, simply moving the developing devices 1M and 1C to the positions required for development respectively will cause the developing device 1Y to move to the developer replenishment position described above. Since it cannot be stopped, the yellow developer cannot be replenished as it is. Therefore, during the continuous copying sequence in the three-color mode using the developing devices 1Y, 1M, and 1C, after the development by the developing device 1C, the developing device 1Y must be used.
Is stopped at the developer replenishing position described above, the yellow developer is replenished at that position, and then the developing device 1Y is moved to the developing position to generate an electrostatic latent image corresponding to the yellow image signal. Although it is possible to develop the image, the copying speed will be slowed down accordingly. In view of such a fact, in the present invention, a developing device that does not stop at the developer replenishing position while another developing device is developing at the developing position in order to increase the copying speed as much as possible. With regard to the above, regarding the transfer material, even if the developer concentration is lowered to some extent, a minimum number of sheets are continuously copied as they are, and the developer cannot be replenished during the continuous copying. After adding the sequence, it was decided to perform continuous copying again.
In this example, the toner amount in the developer in each developing device, that is, the developer concentration is controlled so as not to be less than 15% at all, and the amount of the developer at this time is 30 g, and the transfer material of A4 size is used. The amount of developer consumed is about 0.3g experimentally per copy.
It is known that the above-mentioned developer replenishment sequence is added once every 10 copies to the transfer material. The number of copies is not limited to the above. For example, the number of copies may be 5 or 20, the number of copies may be changed according to the copy size, and the developer may be replenished after copying all required set numbers. You may make it add a sequence.

FIG. 6 shows the configuration of the control system of the image forming apparatus according to the embodiment of the present invention. In FIG. 6, the developer detection lamps O ₁ , O ₂ , O _3, ..., Om, the developer hopper drive motors, the developer drive motors, and other loads necessary for printer control are controlled by the controller 601. It is driven by a drive command signal provided to the load drive circuit 606 via the input / output port 605. Input means 1 ₁ , 1 ₂ , 1 ₃ , ..., 1m are required for inputting the developer remaining amount detection signal in each of the hoppers 2Y, 2M, 2C, 2BK and other printer control so,
The signal input from each of these input means is adjusted in signal level by the input interface 607, and then input to the controller 601 via the input / output port 605. The display / operation unit 604 is provided with a display, a switch, etc. necessary for the printer and the remaining amount of each developer, and is connected to the controller 601 via the input / output port 605.

The light receiving element sensor 403 described above (Fig. 4 (a) (a))
The output signals of the density signal and the reference signal of each developer detected by the controller 401 are adjusted by the amplifier 401 and converted into a digital signal by the analog / digital converter 608, and then the controller 601 via the input / output port 605. It is supposed to be input to. The controller 601 executes predetermined control while storing and storing necessary data and the like in the RAM 603 according to a program, table data, and the like stored in advance in the storage unit, that is, the ROM 602.

FIG. 9 shows the image density D with respect to the contrast potential V (the surface potential of the photosensitive drum 3 corresponding to the developing bias voltage) applied to the image forming apparatus according to the embodiment of the present invention.
The V-D characteristic value data showing the characteristic of (Macbeth value) is shown. The data shown in FIG. 9 can be obtained in advance by some means such as an experiment. Based on such data, the developer concentration decrease is divided into several ranges in advance, and The correction value of the developing bias voltage or the primary high voltage corresponding to the range is previously described in the ROM 602 (6th
In the figure), the developer is replenished from the positional relationship of the rotation angle when continuous copying is performed without immediately replenishing the developer even if the developer concentration in each developing device decreases. The developing bias voltage or the primary high voltage as described above is corrected when the developing device is used only when the developer concentration in the developing device is lowered.

FIG. 7 is a flow chart showing the processing operation of the control system as shown in FIG. This sequence is basically obtained by counting the pulses from an encoder (not shown) that a counter built in the controller 601 rotates in synchronization with a drive motor for driving the photosensitive drum 3. The reference position of the transfer drum 9 which advances in accordance with the numerical value and rotates in synchronization with the photoconductor drum 3 is such that the shutter member 23 disposed on the transfer drum 9 crosses a photo interrupter (not shown). Is detected by the photo interrupter, the count value is reset by the detection, and the number of rotations of the transfer drum 9 is detected. If these count values match the set values stored in advance in the ROM 602 shown in FIG. 6 (step 701), the processing for the set values,
For example, processing such as turning on the developing drive motor is performed, and the operation sequence described with reference to FIG. 1 proceeds.

FIG. 8 is shown in FIG. 7 when the image forming apparatus according to the embodiment of the present invention described above performs the development in the so-called three-color mode in which the developing devices 1Y, 1M and 1C are used. From step 702, the process of development, detection of developer concentration, and developer (toner) replenishment operation will be described.
In FIG. 8, the controller 601 drives the developing device driving motor via the input / output port 605 and the load driving circuit 606 to cause the developing device 1Y to develop a yellow developer (hereinafter referred to as “Y”).
Move it to the replenishment position (called "toner") (step
801), check the Y toner supply flag to be described later,
It is determined whether Y toner needs to be replenished (step 80
2), when it is judged necessary, input / output port 605,
By driving the developer hopper drive motor via the load drive circuit 606, Y toner is replenished to the developing device 1Y, and the Y toner replenishment flag is reset (step
803). The above steps 801-803 may be omitted depending on the case. When the processing operations of steps 801 to 803 are completed, the developing device driving motor is driven through the input / output port 605 and the load driving circuit 606 to move the developing device 1Y to the developing position as shown in FIG. After moving (step 804), after correcting to a value as described later based on the correction value data relating to the voltage and the primary high voltage created based on the data shown in FIG. 9 and stored in the ROM 602, (Step 805), developing unit 1
At Y, development of the electrostatic latent image corresponding to the yellow image signal formed on the photosensitive drum 3 is started (step 80).
6). At the same time, the controller 601 takes in the signal output from the amplifier 401 and input via the A / D converter 608 and the input / output port 605, and during development in step 806, the developer in the developing device 1Y The density is detected (step 809). As described above, when the developing device 1Y is developing at step 807, since the developing device 1M is at the developer toner replenishment position, the magenta developer (hereinafter referred to as "M toner") is set by the M toner replenishment flag. Therefore, it is determined whether or not the replenishment is necessary (step 808). If it is determined that the replenishment is necessary, the M toner is replenished in the same manner as in step 803 and the M toner replenishment flag is reset (step 808).
809). When the development using the Y toner of the first color by the developing device 1Y started in step 806 is completed (step 81
0), in the same manner as in step 804, the developing device 1M is moved to the developing position in order to perform the development using the M toner of the second color, and the developing bias voltage and the primary charging device 4 are applied with the primary voltage. After returning the grid bias voltage to the normal value when developing with M toner, development with M toner is started to detect the concentration of the developer in the developing device 1M, and also to detect the concentration. If it is determined to be necessary during this time, the cyan developer (hereinafter referred to as "C toner") is replenished to the developing device 1C in the same manner as in steps 803 and 809 (steps 811 to 816).
M of the second color by the developing device 1M started at step 813
When the development using toner is completed (step 817),
The developing device 1C is moved to the developing position in order to perform the development using the C toner of the third color, and the development bias voltage and the primary high voltage are utilized to develop using the C toner as in step 812. After returning to the normal value when
The development with the toner is started to detect the developer concentration in the developing device 1C (steps 818 to 821), and when the development with the third-color cyan C toner by the developing device 1C started in step 820 is completed ( Step 822), controller 601
Determines whether or not the value of the Y toner supply counter, which will be described later, has reached a predetermined reference value (step 823). If the result of the determination is that the value of the Y toner supply counter has not reached the predetermined reference value. When it recognizes, it shifts to step 804,
The sequence for the next image copying is executed, and the processing operations from step 804 to step 823 are repeated.

When it is determined that the value of the Y toner replenishment counter has reached the predetermined reference value (step 823), the Y toner replenishment Sequence, that is, the developing device 1Y is moved to the Y toner replenishment position (development position when development is performed by the developing device BK) (step 824), and Y toner is replenished in the manner as described above. After resetting the replenishment flag and the Y toner replenishment counter (step 825), the process proceeds to step 804.

Each developing device 1Y, 1 that is implemented in the processing operation described above
Detecting density of developer in M, 1C (Steps 807, 814, 8
The details of 21) are the same for all the developing devices, and therefore will be described as a representative of the process described in steps 827 to 841. The controller 601 drives the lens lamp 402 for density detection by outputting a drive command signal to the load drive circuit 606 via the input / output port 605, and (step 827) the input interface from the input means 607, The reference signal for density detection provided via the input / output port 605 is read and the RAM 603 (6th
(Figure) to memorize (step 828). After storing the reference signal in the RAM 603 in step 828, the filters 404 and 405 shown in FIG. 4 are moved to the density detecting position (step 829) and the developing position shown in FIG. The developer concentration in the container is read in the same manner as in step 828 and stored in the RAM 603 (step 83).
0). The controller 601 reads the reference signal and the density signal stored in the RAM 603 again in step 828 and step 830 to perform a comparison operation between them (step 831), and a difference value obtained by the comparison operation, If the developer density standard value data set in advance in the ROM 602 for each developing device is compared (step 832), and if it is determined that the difference value is lower than the standard value data, the toner for each developing device is determined. It is confirmed whether or not the toner replenishment flag indicating that replenishment is necessary has already been set (step 833). When the above-mentioned toner replenishment flag is already set at step 833, that is, the developing device requires toner replenishment, but it depends on the rotational positional relationship between the developing device and another developing device. It also shows that when the developing device other than the developing device is in the above-described developing position, the developing device cannot stay in the toner replenishing position and thus the toner cannot be replenished. Therefore, since it is necessary to correct the developing bias voltage and the primary charging voltage in step 805 described above, the correction value data of the developing bias voltage and the primary charging voltage are read from the ROM 602, and the data is transferred to step 831. Obtaining the correction value of the developing bias voltage and the primary charging voltage according to the difference value obtained by
It is stored in the RAM 603 (step 836), and a replenishment counter for counting the number of transfer materials on which an image has been copied when toner cannot be replenished is counted (step 837). As described above, when the replenishment counter reaches an arbitrary set value in step 823, the toner replenishment sequence for the developing device is executed. On the other hand, if it is determined in step 832 that the difference value is higher than the standard value, the supply flag is reset (step 835), and if it is recognized in step 833 that the supply flag is not set, the supply flag is set. A set (step 834) is performed and the process proceeds to step 836. When the above-mentioned step 832 shifts to step 835, it means that the toner supply is normally performed.
The normal values of the developing bias voltage and the primary charging voltage are set (step 838), and the replenishment counter is reset (step 839). Then, the filters 404 and 405 are again moved to the reference signal detecting position (step 840), the driving of the lamp 402 is stopped, and the series of developing density detecting operation is ended.

The density of each developer and its standard value data are compared with each other. In this embodiment, as described above, first, the difference value between the reference signal and the density signal is obtained, and this difference value is the standard developer. If it is smaller than that, it is determined that the density is low. Alternatively, for example, the density signal may be divided by the reference signal to obtain the quotient, and the value may be used for the determination. It is also possible to read the reference signal and the density signal several times, store them in the RAM 603, and calculate the average value of each of them and compare them.

The contents described above are for the case where the so-called three-color mode development using Y toner, M toner, and C toner is carried out. Toner can be replenished. That is, when the developing device that needs toner replenishment is in the toner replenishing position as described above during the development by another developing device, it is used to replenish the toner,
If not, the output image density is adjusted by correcting the developing bias voltage or the primary charging voltage as described above without replenishing the toner for a minimum number of image copies on the transfer material. After that, the sequence may be performed again for toner replenishment.

As described above, according to the present invention, the detected developer concentration value does not reach the prestored reference concentration value, and the developer is replenished without interrupting the development formation. If there is a developing device that cannot perform the image forming operation, the image forming condition is changed without replenishing the developing device with the developer from the developer replenishing means, and, for example, the developing bias voltage and the image applied to the developing device are changed. Since the primary charging voltage applied to the carrier is corrected to a previously stored correction value to compensate for the decrease in density due to insufficient developer, and the image formation of a predetermined amount is continued, the image formation sequence is Even when there is a developing device that cannot be replenished with the developer from the developer replenishing means during execution, it is possible to obtain a high-quality image at high speed without the image density of the output image being remarkably reduced. Image forming equipment Can be provided.

[Brief description of drawings]

FIG. 1 is an explanatory diagram of the overall configuration of an image forming apparatus according to an embodiment of the present invention. FIG. 2 is a sectional view of a rotary developing device according to an embodiment of the present invention. FIG. 3 is a perspective view of a developer (toner) replenishing device according to an embodiment of the present invention. FIG. 4 is a layout explanatory view of a developer concentration detecting device according to an embodiment of the present invention. 5 (a) to 5 (e) are illustrations of the stop position of the rotary developing device. FIG. 6 is a block diagram of the control system of the image forming apparatus according to the embodiment of the present invention. FIG. 7 is a flow chart of the control sequence in the control system shown in FIG. FIG. 8 is a flow chart showing a developer concentration detection and developer replenishment sequence in the sequence shown in FIG. FIG. 9 shows V- of the image forming apparatus according to the embodiment of the present invention.
It is the figure which showed the D characteristic curve. 1: Rotating developing device 1Y, 1M, 1C, 1BK: Color developing device 2: Developing device (toner) replenishing device 2Y, 2M, 2C, 2BK: Color developing device hopper (external replenishing device) 3: Photosensitive (body) drum 26: Developer replenishment opening 402: Lens trap 403: Light receiving element sensor 601: Controller 602: ROM 603: RAM

Claims (1)

(57) [Claims] 1. A developing unit having an image bearing member carrying an electrostatic latent image, a plurality of developing units for developing developers of electrostatic latent images on the image bearing member, each developer unit containing a different color, and a developing unit. Density detecting means for detecting the density of the developer in the inside, judging means for judging whether or not the developer is insufficient by comparing the density detected by the density detecting means with a reference value, and the judging means for developing And a replenishing means for replenishing developer to the developing device that is short of developer when it is determined that the developer is insufficient, so that the developing device to be developed is located at a common developing position during development. In the development forming device that moves the developing unit and moves the developing unit so that the developing device to be replenished is located at the common replenishment position when replenishing the developer, the device operates when it is determined that the developer is insufficient It has a counter to count When image formation is continuously performed due to the existence of developing devices that are not located at the replenishment position even though the number of developing devices are located at the development position and developing is performed, the developer not located at the replenishment position is short of developer. When it is judged that the count value by the counter reaches a predetermined value, the developer is insufficient and the density decrease due to the developer shortage is compensated by changing the image forming condition without supplying the developer to the developer. An image forming apparatus, characterized in that image formation is continued, and when a predetermined value is reached, a developing device lacking developer is moved to a replenishment position for development.