JP2007286410A - Color image forming apparatus and switching method of printing mode - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve image quality by switching printing modes at a timing according to developing ability. <P>SOLUTION: When monochrome printing is carried out in a color mode in an image forming apparatus, toner concentration (value Vt) in a plurality of developing apparatuses are acquired by detecting with respective corresponding toner concentration sensors, whether or not switching from the color mode to the monochrome mode is necessary is judged based on each detected value and when necessary, the switching is executed. Otherwise, when printing is carried out in the color mode, acquiring the number of printing pixels and judging whether or not it is a low image area from the mentioned number of printing pixels, detecting the toner concentration in a plurality of developing apparatuses by each corresponding toner concentration sensor, judging whether or not switching from the color mode to the monochrome mode is necessary based on each detected value and executing the switching when necessary. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a color image forming apparatus such as a color printer, a color copying machine, a color multifunction peripheral, and a color facsimile apparatus using an electrophotographic method, and a printing mode switching method in the color image forming apparatus.

  For example, as a color image forming method in a color image forming apparatus using an electrophotographic method, toner images formed in different colors on a plurality of photosensitive members (image carriers) are directly transferred while being superimposed on transfer paper. There is a transfer system and an intermediate transfer system in which toner images of different colors are transferred while being superimposed on an intermediate transfer body (image carrier) and then transferred onto transfer paper (paper) in a lump. These methods are commonly referred to as a tandem method because a plurality of photoconductors are arranged side by side facing a transfer paper or intermediate transfer member. For each photoconductor, yellow (Y), cyan (C), magenta (M ), An electrophotographic process such as formation and development of an electrostatic latent image is executed for each color of black (K), and on the transfer paper in the direct transfer method, the intermediate transfer in the intermediate transfer method Transfer on the body.

Such a color image forming apparatus includes four photoconductor units (hereinafter also referred to as “PCU”) that respectively perform image formation of each color of Y, C, M, and K. Each PCU is provided with a developing device that performs development with toners of different colors and a toner concentration sensor for adjusting the toner concentration in the developing device.
By the way, the Vt value in the developing device of each PCU usually has the following tendency. The Vt value is an output value of the toner density sensor, that is, a value obtained by converting the toner density into a voltage. The voltage is A / D converted and used for control.
(1) When the amount of toner in the developing device is large, the Vt value becomes a low value.
(2) When the toner amount in the developing device is small, the Vt value becomes a high value.

In the color image forming apparatus as described above, when the printing mode is the color mode, the PCUs of all colors are operated, and the toner and developer in the developing device of each PCU are agitated.
When the print mode is the monochrome mode (monochrome single color mode), only the K PCU is operated, and the toner and developer in the developing device of the PCU are agitated.
Further, when the print mode is the full color mode and monochrome printing (monochrome single color printing) is performed, all the PCUs are operated.

At this time, if K toner is used, the inside of the developing device of the K PCU is agitated to consume the toner and replenish the consumed toner (the Vt value increased by toner consumption becomes the reference value). The toner is replenished until it returns. However, in PCU developing devices of colors other than K, only stirring (empty stirring) is performed without consuming toner.
For this reason, the amount of toner in the developing device for colors other than K does not change due to the empty stirring at this time, but the Vt value decreases.
The relationship between the Vt value and the number of printed sheets at that time is shown in FIG. FIG. 10 shows an example of the relationship between the Vt value (output value of the toner density sensor) and the number of printed sheets when idle rotation (empty agitation) is performed in the developing device of a color other than K.

Here, if the air stirring in the developing device continues, the toner charge amount increases, and the Vt value decreases due to the characteristics of the sensor. For this reason, toner replenishment according to toner consumption is not performed. As a result, the developing ability is reduced and the output image becomes light. In addition, the image deteriorates.
Therefore, as can be seen in Patent Documents 1 to 6, there has been proposed one in which the print mode is switched based on the number of printed sheets, the amount of print data of image information, or the data ratio.
Japanese Patent No. 3589998 Japanese Patent Laid-Open No. 11-133697 JP 2000-29266 A JP 2000-318220 A JP 2001-51470 A JP 2003-237191 A

However, in the case of such a printing mode switching method, since the printing mode is switched from the full color mode to the monochrome mode regardless of the developing capability, the time for the empty stirring in the developing device of a color other than K becomes long. There is a problem that the life of the photosensitive member and the developer is adversely affected and the image quality is adversely affected.
The present invention has been made in view of the above points, and an object of the present invention is to improve image quality in a color image forming apparatus by switching a print mode at a timing according to developing ability.

In order to achieve the above object, the present invention provides the following color image forming apparatus and printing mode switching method.
According to a first aspect of the present invention, there is provided a color image forming apparatus that performs monochrome printing or color printing by selectively using a plurality of developing units that use different color toners. Whether or not it is necessary to switch from the color mode to the monochrome mode based on the detection values of the plurality of toner density detecting means when performing monochrome printing in the color mode with a plurality of toner density detecting means that respectively detect the toner density A printing mode switching necessity judging means for judging whether the printing mode switching necessity judging means judges that switching from the color mode to the monochrome mode is necessary. It is a thing.

  A color image forming apparatus according to a second aspect of the present invention is the color image forming apparatus according to the first aspect, wherein the printing mode switching necessity determining means includes the plurality of toner density detecting means when performing monochrome printing in the color mode. Means for calculating a change amount of the average detection value per predetermined number of printed sheets is compared, and the calculated value is compared with a preset value, and switching from the color mode to the monochrome mode is performed based on the comparison result. It is determined whether or not it is necessary.

  According to a third aspect of the present invention, there is provided the color image forming apparatus according to the first aspect, wherein the printing mode switching necessity determining unit is configured to detect the plurality of toner density detecting units when performing monochrome printing in the color mode. There is a means to calculate the amount of change in the average value of the detected values per predetermined time, the calculated value is compared with a preset value, and it is necessary to switch from the color mode to the monochrome mode based on the comparison result Whether or not.

  A color image forming apparatus according to a fourth aspect of the present invention is the color image forming apparatus according to the first aspect, wherein the printing mode switching necessity determining means is configured to detect the plurality of toner density detecting means when performing monochrome printing in the color mode. Means for calculating an average value of the detected values, comparing the calculated value with a preset threshold value, and determining whether or not switching from the color mode to the monochrome mode is necessary based on the comparison result It is.

  A color image forming apparatus according to a fifth aspect of the present invention is the color image forming apparatus according to the first aspect, wherein the printing mode switching necessity determining means includes the plurality of toner density detecting means when performing monochrome printing in the color mode. Is it necessary to calculate the amount of change in the detected value per predetermined number of printed sheets, compare each calculated value with a preset value, and switch from color mode to monochrome mode based on the comparison result? It is to determine whether or not.

  According to a sixth aspect of the present invention, there is provided the color image forming apparatus according to the first aspect, wherein the printing mode switching necessity determining unit is configured to detect the plurality of toner density detecting units when performing monochrome printing in the color mode. A means for calculating a change amount of the detected value per predetermined time, and comparing each calculated value with a preset value, and whether or not switching from the color mode to the monochrome mode is necessary based on the comparison result This is a judgment.

  According to a seventh aspect of the present invention, there is provided the color image forming apparatus according to the first aspect, wherein the print mode switching necessity determining means includes a plurality of toner density detecting means when performing monochrome printing in the color mode. The detected value is compared with a preset threshold value, and it is determined whether or not switching from the color mode to the monochrome mode is necessary based on the comparison result.

  According to an eighth aspect of the present invention, there is provided a color image forming apparatus which performs monochrome printing or color printing by selectively using a plurality of developing units each using different color toners. A plurality of toner density detecting means for detecting the toner density, a print pixel number acquiring means for acquiring the number of print pixels when printing in the color mode, and a lower value than the print pixel number acquired by the print pixel number acquiring means. Switching from the color mode to the monochrome mode based on the detection values of the plurality of toner density detection means only when the image area determination means for determining whether or not the image area is determined and the low image area is determined by the image area determination means A printing mode switching necessity determination unit that determines whether or not printing is necessary, and the printing mode switching necessity determination unit from the color mode. When the switching to Nokuromodo was determined to be necessary, it is provided with a print mode switching execution means for executing the switching.

  A color image forming apparatus according to a ninth aspect of the present invention is the color image forming apparatus according to the eighth aspect, wherein the plurality of print mode switching necessity determining means is only when the image area determining means determines a low image area. Means for calculating a change amount per predetermined number of printed sheets of the average value of the detected values of the toner density detecting means, comparing the calculated value with a preset value, and from the color mode based on the comparison result It is determined whether or not switching to the monochrome mode is necessary.

  A color image forming apparatus according to a tenth aspect of the present invention is the color image forming apparatus according to the eighth aspect, wherein the plurality of print mode switching necessity determining means is only when the image area determining means determines a low image area. Means for calculating a change amount per predetermined time of the average value of the detected values of the toner density detecting means, comparing the calculated value with a preset value, and from the color mode to the monochrome based on the comparison result It is determined whether or not switching to the mode is necessary.

  According to an eleventh aspect of the present invention, in the color image forming apparatus according to the eighth aspect, only when the print mode switching necessity determining unit determines that the image area determining unit determines a low image area, A means for calculating an average value of the detected values of the toner density detecting means, comparing the calculated value with a preset threshold value, and whether switching from the color mode to the monochrome mode is necessary based on the comparison result It is to determine whether or not.

  A color image forming apparatus according to a twelfth aspect of the present invention is the color image forming apparatus according to the eighth aspect, wherein the print mode switching necessity determining means determines that the plurality of image areas only when the image area determining means determines a low image area. Means for calculating a change amount per predetermined print number of the detected value of the toner density detecting means, comparing each calculated value with a preset value, and from the color mode to the monochrome mode based on the comparison result It is determined whether or not switching to is necessary.

  A color image forming apparatus according to a thirteenth aspect of the present invention is the color image forming apparatus according to the eighth aspect, wherein the plurality of print mode switching necessity determining means is only when the image area determining means determines a low image area. A means for calculating a change amount per predetermined time of the detected value of the toner density detecting means, comparing each calculated value with a preset value, and from the color mode to the monochrome mode based on the comparison result It is determined whether or not switching is necessary.

  A color image forming apparatus according to a fourteenth aspect of the present invention is the color image forming apparatus according to the eighth aspect, wherein the plurality of print mode switching necessity determining means is only when the image area determining means determines a low image area. The detected value of the toner density detecting means is compared with a preset threshold value, and it is determined whether or not switching from the color mode to the monochrome mode is necessary based on the comparison result.

  According to a fifteenth aspect of the present invention, there is provided a printing mode switching method in a color image forming apparatus that performs monochrome printing or color printing by selectively using a plurality of developing units that use different color toners. Whether or not it is necessary to switch from the color mode to the monochrome mode based on each detected value when the toner density in the plurality of developing units is detected by the corresponding toner density sensor when performing monochrome printing in the color mode. When the switching is necessary, the switching is executed.

  According to a sixteenth aspect of the present invention, there is provided a printing mode switching method in a color image forming apparatus that performs monochrome printing or color printing by selectively using a plurality of developing units each using different color toners. When printing in the color mode, the number of print pixels is obtained, and it is determined whether or not the image area is low based on the number of print pixels. Only when the image area is low, the toner density in the plurality of developing means is set. Each detection is performed by a corresponding toner density sensor, and it is determined whether or not switching from the color mode to the monochrome mode is necessary based on each detected value. When the switching is necessary, the switching is executed. .

  According to the present invention, when monochrome printing is performed in the color mode, the toner density in the plurality of developing means is detected by the corresponding toner density detecting means (toner density sensor), and the color mode is based on each detected value. It is determined whether or not switching from monochrome mode to monochrome mode is necessary, and when switching is necessary, the switching is executed. Alternatively, when printing in the color mode, the number of print pixels is obtained, and it is determined whether or not the image area is low based on the number of print pixels. When the toner density in the developing means is detected by the corresponding toner density detecting means, it is determined whether or not switching from the color mode to the monochrome mode is necessary based on each detected value, and the switching is necessary Perform the switch.

  Therefore, the idling time in the developing means of colors other than K is not made longer than necessary, and the life of the image carrier and developer is not adversely affected. As a result, image quality, which is one of the printing capabilities, is unlikely to deteriorate, and printing can be executed without reducing the printing speed, thereby improving user convenience.

Hereinafter, the best mode for carrying out the present invention will be specifically described with reference to the drawings.
FIG. 1 is a diagram showing a configuration example of a mechanism portion of a color printer using an electrophotographic system which is a color image forming apparatus embodying the present invention. FIG. 2 is a cross-sectional view showing a configuration example of the PCU (photoreceptor unit) 10K in FIG. In FIG. 1, for the sake of illustration, PCUs 10Y, 10C, and 10M are only partially shown (photosensitive members), but have the same configuration as PCU 10K.

This color printer includes each mechanism for configuring an engine unit, and a control unit (described later) that performs control related to printing (image formation) process processing by each mechanism.
The engine unit includes four PCUs 10Y for generating toner images of four image carriers that are horizontally adjacent to each other, that is, Y (yellow), C (cyan), M (magenta), and K (black). 10C, 10M, and 10K, and an intermediate transfer belt 11 that is an intermediate transfer body that is in contact with and parallel to the Y, C, and M PCUs 10Y, 10C, and 10M other than the K PCU 10K. Is done.

Each of the PCUs 10Y, 10C, 10M, and 10K uses Y, M, C, and K toners of different colors, but the other configurations are the same, and are replaced when the lifetime is reached.
Here, the configuration of the PCU 10K for generating a K toner image will be described as a representative. As shown in FIG. 2, a drum-shaped photoconductor 1K as an image carrier is provided, and a charging device 2K is provided around it. A developing device 3K, a cleaning device 4K, and the like are provided.

The developing device 3K is disposed in the developing roller 31K, the doctor blade 32K that regulates the layer thickness of the developer supplied onto the developing roller 31K, the developer supplying unit 33K of the developing casing, and the toner replenishing unit 34K. A stirring / conveying member 35K and a toner concentration sensor 36K are provided. The toner density sensor 36K is toner density detection means for detecting the toner density in the developing device 3K. Based on the information (detection information) of the detection result, the corresponding motor is controlled by the control unit, and toner replenishment and developer agitation / conveyance are performed, and the printing mode (image forming mode) related to the present invention is switched. Has been made.
The PCU 10K is detachable from the main body of the color printer, so that consumable parts can be exchanged at once (collectively).

The charging device 2K uniformly charges the surface of the photoreceptor 1K that is rotated clockwise in the drawing by a driving unit (not shown). The uniformly charged surface of the photosensitive member 1K is exposed and scanned by the laser beam from the optical writing unit 12, and an electrostatic latent image for K is formed there.
The K electrostatic latent image is developed into a K toner image by the developing device 3K using K toner. The K toner image is intermediately transferred onto the surface of the intermediate transfer belt 11.
The cleaning device 4K removes untransferred toner remaining on the surface of the photoreceptor 1K after the intermediate transfer process.

Thereafter, the residual charge on the surface of the photoreceptor 1K after cleaning is neutralized by a neutralizing device (not shown). This neutralization initializes the surface of the photoreceptor 1 and prepares for the next printing.
The other PCUs 10Y, 10C, and 10M are configured in the same manner. Similarly, Y, C, and M toner images are formed on the surfaces of the photoreceptors 1Y, 1C, and 1M, respectively, and the intermediate transfer belt 11 has an intermediate surface. Transcribed. However, the order of printing (image formation) is not limited to the above-described order of K, M, C, and Y, but the toner characteristics and the effect of finishing the color image that is finally formed on the paper. It is decided accordingly.

  In FIG. 1, below the PCUs 10Y, 10C, 10M, and 10K, an optical writing unit 12 is disposed as a latent image forming unit. The optical writing unit 12 is controlled by an engine main board and an engine sub board which will be described later. That is, these boards modulate and drive the LD light source in the optical writing unit 7 based on image information from the controller board described later, thereby emitting the corresponding laser light from the LD light source, and emitting the laser light. While scanning in the main scanning direction by a polygon mirror that is rotationally driven by a polygon motor, the surfaces of the photoreceptors 1Y, 1C, 1M, and 1K in the PCUs 10Y, 10C, 10M, and 10K are irradiated through a plurality of optical lenses and mirrors. To expose. By this exposure, electrostatic latent images for Y, C, M, and K are formed on the surfaces of the photoreceptors 1Y, 1C, 1M, and 1K, respectively.

Below the optical writing unit 12, paper feeding means having a paper feeding cassette 13, a paper feeding roller 14, a registration roller pair 15, and the like are disposed.
A plurality of transfer papers (paper sheets) as recording media are stored in the paper feed cassette 13, and a paper feed roller 14 is in contact with the uppermost transfer paper.
When the paper feeding roller 14 is rotated counterclockwise by a driving means (not shown), the uppermost transfer paper is fed toward the gap (nip) between the registration roller pair 15.

Both rollers of the registration roller pair 15 are driven to rotate so as to sandwich the transfer paper. However, as soon as the registration roller 15 is sandwiched, the rotation is temporarily stopped and the skew of the transfer paper is corrected. Then, the registration roller pair 15 is re-driven at an appropriate timing, and the transfer paper is sent out toward a secondary transfer nip described later.
In the sheet feeding unit having such a configuration, a conveying unit is configured by a combination of the sheet feeding roller 14 and the registration roller pair 15 as a timing roller pair.
This conveying means conveys the transfer paper from a paper feed cassette 13 as a storing means to a secondary transfer nip described later.

  Above the PCUs 10Y, 10C, 10M, and 10K, an intermediate transfer unit 16 that moves the intermediate transfer belt 11 as an intermediate transfer member endlessly while stretching is disposed. In addition to the intermediate transfer belt 11, the intermediate transfer unit 16 includes four primary transfer bias rollers 17Y, 17C, 17M, and 17K, a cleaning device 18, and the like. A secondary transfer backup roller 19, a cleaning backup roller 20, a tension roller 21 and the like are also provided. The intermediate transfer belt 11 is endlessly moved counterclockwise by the rotational drive of at least one of the rollers while being stretched around these three rollers.

The primary transfer bias rollers 17Y, 17C, 17M, and 17K sandwich the intermediate transfer belt 11 that moves endlessly with the photoreceptors 1Y, 1C, 1M, and 1K to form primary transfer nips, respectively. Yes.
In these methods, a transfer bias having a polarity opposite to that of toner (for example, plus) is applied to the back surface (loop inner peripheral surface) of the intermediate transfer belt 11.
All the rollers except the primary transfer bias rollers 17Y, 17C, 17M, and 17K are electrically grounded.

The intermediate transfer belt 11 sequentially passes through the primary transfer nips for Y, C, M, and K along with the endless movement thereof, and Y, C, and M on the photoreceptors 1Y, 1C, 1M, and 1K. , K toner images are superimposed and primarily transferred.
As a result, a four-color superimposed toner image (hereinafter referred to as “four-color toner image”) is formed on the intermediate transfer belt 11.
The secondary transfer backup roller 19 sandwiches the intermediate transfer belt 11 between the secondary transfer roller 22 and forms a secondary transfer nip.

The four-color toner image formed on the intermediate transfer belt 11 is transferred to the transfer paper at the secondary transfer nip.
On the intermediate transfer belt 11 after passing through the secondary transfer nip, untransferred toner that has not been transferred to the transfer paper is adhered. This is cleaned by the cleaning device 18.
In the secondary transfer nip, the transfer paper is sandwiched between the intermediate transfer belt 11 whose surface moves in the forward direction and the secondary transfer roller 22 and is conveyed in the direction opposite to the registration roller pair 15 side.

When the transfer paper fed from the secondary transfer nip passes between the rollers of the fixing device 23, the four-color toner image transferred to the surface is fixed by heat and pressure.
Thereafter, the transfer paper on which the four-color toner image is fixed is discharged outside the apparatus through the pair of paper discharge rollers 24.
A stack unit 25 is formed on the upper surface of the printer main body, and the transfer sheets discharged out of the apparatus by the discharge roller pair 24 are sequentially stacked on the stack unit 25.
Below the stack unit 25, toner bottles 26Y, 26C, 26M, and 26K that supply Y, C, M, and K toners to the developing devices of the PCUs 10Y, 10C, 10M, and 10K are disposed.

FIG. 3 is a block diagram showing a hardware configuration example of the control system of the color printer shown in FIG.
The control unit of the color printer includes a controller board 51, an engine main board 52, an engine sub board 53, a power supply unit (hereinafter referred to as “PSU”) 54, and the like.

  The controller board 51 uses a microcomputer including a CPU, ROM, RAM, and ASIC (described later). A network interface (hereinafter referred to as “interface”) such as a LAN (local area network) from a host computer (not shown) such as a personal computer. (Abbreviated as “I / F”) 71, IEEE1284 / I / F72, IEEE1394 / I / F73, IEEE802.11b / I / F74 It is received, developed, converted into image information (bitmap data) in a format printable by the engine unit, and output to the engine main board 52.

  The engine main board 52 uses the same microcomputer as the controller board 51, exchanges various signals with the engine sub board 53, and based on the image information from the controller board 51 in the optical writing unit 12. The LD light source 101 is modulated and driven, and the high voltage power source 102 is controlled to drive the charging devices and developing devices of the PCUs 10Y, 10C, 10M, and 10K. The engine main board 52 and an engine sub board 53 described later serve as print mode switching necessity determination means, print mode switching execution means, print pixel number acquisition means, and image area determination means.

The engine sub board 53 also uses the same microcomputer as the controller board 51, and exchanges various signals with the engine main board 52 based on signals from the synchronization detection unit 201 in the optical writing unit 12. The polygon motor 203, various other motors 204, and various clutches 205 are controlled based on signals from various sensors 202 including a toner density sensor, and the PSU 54 is controlled based on a thermistor (temperature sensor) 206 in the fixing device 23. To do. The PSU 54 controls on / off of energization to a heater (fixing heater) 207 built in a roller in the fixing device 23.
The operation unit 208 includes an input unit for performing various settings and a display unit for displaying various information.

  Next, when the printing mode of the color printer of this embodiment is the color mode, the engine sub board 53 of FIG. 3 is sent from the host computer via any one of the communication I / F, the controller board 51, and the engine main board 52. A processing operation related to the present invention using the PCU 10 (10Y, 10C, 10M, 10K) executed at the time of printing (image formation) using incoming image information will be described.

FIG. 4 is a flowchart showing an example of the print mode switching process by the engine sub board 53.
The engine sub board 53 uses a phenomenon in which the Vt value decreases when the PCU of colors other than K, that is, Y, C, and M PCUs (hereinafter also referred to as “color PCUs”) is rotated in the developing mode. When monochrome printing is instructed from the host computer, the processing of FIG. 4 is started by an instruction from the engine main board 52, and the Vt value of each color PCU is obtained in step S1, and the Vt value is obtained in step S2. Based on this, it is determined whether or not it is necessary to switch from the color mode to the monochrome mode (monochrome single color mode). If necessary, the print mode is switched from the color mode to the monochrome mode.

  At this time, image forming loads of Y, C, and M colors that are not necessary for the monochrome mode (the toner images formed on the PCUs 10Y, 10C, and 10M and the photoreceptors 1Y, 1C, and 10M described above are applied to the intermediate transfer belt 11. The primary transfer bias rollers 17Y, 17C, 17M, etc. for transferring are lowered. That is, charging, writing, developing, and transfer processing of the Y, C, and M PCUs 10Y, 10C, and 10M that are being used in the color mode are stopped. After these processes are stopped, the PCUs 10Y, 10C, and 10M that are not used for monochrome printing are separated from the intermediate transfer belt 11.

Here, as a method for determining whether or not the engine sub board 53 needs to switch from the color mode to the monochrome mode (hereinafter, also referred to as “mode switching necessity determination”) using the Vt value, the following (1) to (4) are performed. There are four methods.
(1) Method 1: Method of Using Vt Average Change per Predetermined Number of Figures FIG. 5 shows a mode using the Vt average (average value of Vt values of each color PCU) of Vt average per predetermined number of changes. It is a diagram for demonstrating switching necessity determination.
In this case, the change rate of the Vt average is obtained by the following equation.

Vt average rate of change = ΔVt / Δ number of sheets However, Δ number is a predetermined number of sheets (predetermined number of printed sheets) necessary for obtaining the Vt average rate of change, and ΔVt indicates a change amount in the Vt average of Δ number of sheets.
The engine sub board 53 calculates the change rate of the Vt average (or the change amount per predetermined number of Vt averages) obtained by the above calculation formula, and the calculated value falls below a preset value A (the following formula) If it is determined that the toner density sensor corresponding to the color PCU cannot correctly detect the toner density of the color PCU, it is determined that switching from the color mode to the monochrome mode is necessary, and the switching is performed.
Vt average change rate <value A

However, the value A and the Δ number can be arbitrarily set by the operation on the operation unit 208 of FIG. 3 by the user. Similarly, the starting number for measuring (calculating) the rate of change of the Vt average can also be arbitrarily set.
For example, if Δ sheets = 10 [sheets] and ΔVt = −0.5 [V], the average change rate of Vt is −0.5 / 10 = −0.05 [V / sheets]. Also, the value A = −0.025 [V / number of sheets] (Vt value decreases by −0.5 V after printing 20 sheets).

(2) Method 2: Method of Using Vt Average Change per Unit Time Number FIG. 6 is a diagram for explaining mode switching necessity determination using change amount per unit time number of Vt average. is there.
In this case, the change rate of the Vt average is obtained by the following equation.
Vt average change rate = ΔVt / Δt
However, Δt indicates a predetermined time required for obtaining the change rate of Vt average, and ΔVt indicates the amount of change in Δt of Vt average.

The engine sub board 53 calculates the change rate of Vt average (or the change amount of Vt average per predetermined time) obtained by the above calculation formula, and the calculated value falls below a preset value B (the following formula) If it is determined that the toner density sensor corresponding to the color PCU cannot correctly detect the toner density of the color PCU, it is determined that switching from the color mode to the monochrome mode is necessary, and the switching is performed.
Vt average change rate <value B

However, the values B and Δt can be arbitrarily set by an operation on the operation unit 208 of FIG. 3 by the user. Similarly, the start time for measuring the change rate of the Vt average can be arbitrarily set.
For example, when Δt = 10 [min] and ΔVt = −0.5 [V], the change rate of the Vt average is −0.5 / 10 = −0.05 [V / hour]. Further, the value B = −0.025 [V / hour] (Vt value decreases by −0.5 V after 20 minutes).

(3) Method 3: Method Using Vt Average and Threshold Value FIG. 7 is a diagram for explaining mode switching necessity determination using the Vt average and the threshold value.
The engine sub-board 53 determines that the toner density sensor corresponding to the color PCU cannot correctly detect the toner density of the color PCU when the Vt average falls below a preset threshold value C, and needs to switch from the color mode to the monochrome mode. And switch to it.
However, the threshold C can be arbitrarily set by an operation on the operation unit 208 of FIG. 3 by the user. Similarly, the starting number of sheets (or the starting time) for measuring the Vt average can be arbitrarily set. For example, the threshold value C is set to Vt = 2.0 [V].

(4) Method 4: Method in which any of methods 1 to 3 is slightly different The engine sub board 53 uses the Vt average (the average value of Vt values of each color PCU) in the above-described method 1 to method 3. The necessity of mode switching was determined.
In Method 4, the mode switching necessity determination is performed by using the Vt value of each color PCU instead of the Vt average, and any change rate of each Vt value (a predetermined number of Vt values or a change amount per predetermined time). When at least one of them falls below a preset value (judgment criterion), or when any one of the Vt values falls below a preset threshold (judgment criterion), the toner density of the color PCU corresponds. It is determined that the toner density sensor cannot be detected correctly, it is determined that switching from the color mode to the monochrome mode is necessary, and the switching is performed. The print mode switching process is shown in FIG.

FIG. 8 is a flowchart showing another example of the print mode switching process by the engine sub board 53.
When monochrome printing is instructed from the host computer in the color mode, the engine sub board 53 starts the processing of FIG. 8 according to an instruction from the engine main board 52, and first acquires the Vt value of the PCU 10C in step S11.
Next, in step S12, based on the Vt value, it is determined whether or not switching from the color mode to the monochrome mode is necessary as described above. If necessary, the process proceeds to step S17 to change the print mode from the color mode to the monochrome mode. Switch.

If it is determined in step S12 that switching from the color mode to the monochrome mode is not necessary, the process proceeds to step S13, and the Vt value of the PCU 10M is acquired.
Next, in step S14, based on the Vt value, it is determined whether or not it is necessary to switch from the color mode to the monochrome mode as described above. If necessary, the process proceeds to step S17 to change the print mode from the color mode to the monochrome mode. Switch.

If it is determined in step S14 that switching from the color mode to the monochrome mode is not necessary, the process proceeds to step S15, and the Vt value of the PCU 10Y is acquired.
Next, in step S15, based on the Vt value, it is determined whether or not it is necessary to switch from the color mode to the monochrome mode as described above. If necessary, the process proceeds to step S17 to change the print mode from the color mode to the monochrome mode. Switch.
When the process of step S17 is completed, or when it is determined in step S16 that switching from the color mode to the monochrome mode is not necessary, the process of FIG. 8 ends.

The above description describes the processing when monochrome printing is instructed when the print mode is the color mode. Considering that monochrome printing has not been instructed, the mode switching necessity determination is performed based on the number of print pixels. It is also possible to perform this. FIG. 9 shows a printing mode switching process using the mode switching necessity determination.
FIG. 9 is a flowchart showing still another example of the print mode switching process by the engine sub board 53.

The engine sub board 53 starts the process of FIG. 9 in response to an instruction from the engine main board 52 in the color mode. First, in step S21, the number of print pixels of each color Y, C, and M is acquired.
Here, an ASIC for optical writing (for storing image information for emitting the corresponding laser light by modulating and driving the LD light source 101) is provided in the engine main board 52, and after completion of optical writing (FGATE When the image information of each color of Y, C, and M in the ASIC is read out (when is turned off), the number of pixels (the number of print pixels) can be measured and acquired. FGATE is a frame gate signal (maintains ON state during optical writing) and indicates an effective period in the sub-scanning direction (photosensitive member rotation direction) of image information of one page.

The engine sub board 53 determines whether the printing is monochrome printing or color printing in step S22 by acquiring the number of printing pixels of each color of Y, C, and M. At this time, whether or not the image area is low can be determined from the obtained number of pixels of each color. If the image area is low, it is determined that monochrome printing is performed, and if the image area is not low, it is determined that color printing is performed.
Only in the case of monochrome printing, the print mode switching process using any one of methods 1 to 4 is performed in step S23.
Here, Table 1 shows an example of the number of pixels in monochrome printing, and Table 2 shows an example of the number of pixels in full color printing.

As can be seen from these tables, normally, in the case of monochrome printing, the number of used pixels of Y, C, and M is “0”.
However, considering the case of creating a pattern that cannot be recognized by the user, such as a tracking pattern (a machine-specific background pattern that cannot be recognized unless enlarged), all colors used (Y, C, M) When the number of pixels becomes equal to or less than a certain number of pixels, a method of determining that the image area is low and determining monochrome printing is preferable.
Further, a method for determining a threshold value for determining that Y, C, and M are monochrome printing (determining that the area is a low image area) is also conceivable.

For example, as shown in Table 3, a threshold value Jy and a pixel number Dy for determining that monochrome printing is performed for Y are considered. Similarly, a threshold value Jc and a pixel number Dc are considered for C, and a threshold value Jm and a pixel number Dm are considered for M, respectively.
In this case, it is determined whether or not monochrome printing is performed using the inequalities shown in the following (a) to (c).
(A) Dy <Jy
(B) Dc <Jc
(C) Dm <Jm

For example, if the pixel density is 600 [dpi], the size is A4 (210 [mm] × 297 [mm]), and the pixel area ratio is 1 [%], the number of pixels is (210 [mm] /25.4 [mm]. / Inch]) * 600 [dpi] * (297 [mm] /25.4 [mm / inch]) * 600 [dpi] * 0.01 = 348332 [dot].
Therefore, for example, when printing of an image having a pixel area ratio of 1 [%] continues for 10 sheets, when the print mode is switched from the color mode to the monochrome mode, the number of pixels Dy, Dc, and Dm are Dy = Dc = Dm = 348332 [dot].

The engine sub board 53 can determine whether the image area is low using the three inequalities shown in (a) to (c) above. Then, when all the three inequalities are satisfied, it is determined that the image area is low and monochrome printing is determined. Then, print mode switching processing using any one of methods 1 to 4 is performed.
However, each of the Jy, Jc, and Jm values can be arbitrarily set by an operation on the operation unit 208 of FIG. 3 by the user.

  As described above, when performing monochrome printing in the color mode, it is necessary to detect the toner density in each of the plurality of developing devices by the corresponding toner density sensor and switch from the color mode to the monochrome mode based on each detected value. Whether the switching is necessary or not is executed. Alternatively, when printing in the color mode, the number of print pixels is obtained, and it is determined whether or not the image area is low based on the number of print pixels. The toner density in the developing means is detected by the corresponding toner density sensor, and it is determined whether or not switching from the color mode to the monochrome mode is necessary based on each detected value. Perform the switch. Therefore, the idling time in the developing devices of colors other than K is not made longer than necessary, and the life of the photosensitive member (image carrier) and developer is not adversely affected. As a result, image quality, which is one of the printing capabilities, is unlikely to deteriorate, and printing can be executed without reducing the printing speed, thereby improving user convenience.

As described above, the embodiment in which the present invention is applied to a color printer using a photosensitive drum and an intermediate transfer belt as a combination of image bearing members for image formation has been described. However, the present invention is not limited thereto, and the photosensitive drum and Of course, other color image forming apparatuses such as color copiers, color multifunction peripherals, and color facsimile machines using an intermediate transfer belt, other combinations of image carriers for image formation, such as a photosensitive belt and an intermediate transfer drum The present invention can also be applied to various color image forming apparatuses using a combination or a combination of a photosensitive drum and a transfer conveyance belt.
That is, an example in which the present invention is applied to a tandem type color image forming apparatus in which a plurality of photosensitive drums are arranged side by side on an intermediate transfer belt has been described. However, a color image forming apparatus to which the present invention can be applied has this configuration. It is not limited to.

In the above-described embodiment, the present invention is applied to an indirect transfer type color image forming apparatus in which toner images of four colors are transferred onto an intermediate transfer belt, the four colors are superimposed, and then transferred onto a transfer sheet at once. Although applied, the present invention can also be applied to a direct transfer type color image forming apparatus that transports transfer paper by a transfer transport belt and sequentially transfers four color toner images from the photosensitive drum onto the transfer paper. .
Furthermore, in the above-described embodiments, laser light is used as the exposure light source, but the present invention is not limited to this, and for example, an LED array or the like may be used as the light source.

  The program relating to the present invention functions as a print mode switching necessity determination unit, a print mode switching execution unit, a print pixel number acquisition unit, and an image area determination unit on the CPU (computer) of the engine main board and the engine sub board. This is a program to be realized, and the above-described effects can be obtained by causing a computer to execute such a program.

Such a program may be stored in a storage means such as a ROM or HDD from the beginning, but a non-volatile recording medium (memory such as a CD-ROM or flexible disk, SRAM, EEPROM, or memory card) that is a recording medium. ) Can be recorded and provided. The program recorded in the memory can be installed in a digital copying machine or an external device and executed by the CPU, or the CPU can read out and execute the program from the memory to execute the above-described procedures. .
Furthermore, it is also possible to download and execute an external device that is connected to a network and includes a recording medium that records the program, or an external device that stores the program in the storage unit.

  As is apparent from the above description, according to the present invention, the print mode is switched at the timing according to the developing ability, so that the image quality can be improved. Therefore, if this invention is used, a color image forming apparatus capable of acquiring a high-quality image regardless of the developing ability can be provided.

1 is a diagram illustrating a configuration example of a mechanism unit of a color printer using an electrophotographic system which is a color image forming apparatus embodying the present invention. It is sectional drawing which shows the structural example of PCU10K of FIG. FIG. 2 is a block diagram illustrating a hardware configuration example of a control system of the color printer illustrated in FIG. 1. FIG. 4 is a flowchart illustrating an example of a print mode switching process by the engine sub board. It is a diagram for explaining mode switching necessity determination using a Vt average change amount per predetermined number of sheets.

It is a diagram for demonstrating mode switching necessity determination using the variation | change_quantity of the Vt average per predetermined time. It is a diagram for demonstrating mode switching necessity determination using Vt average and a threshold value. 6 is a flowchart showing another example of a print mode switching process by the engine sub board of FIG. 3. It is a flowchart which shows another example similarly. FIG. 10 is a diagram illustrating an example of a relationship between a Vt value and the number of printed sheets when idling is performed in a developing device other than K.

Explanation of symbols

1K, 1Y, 1C, 1M: photoconductor 2K: charging device 3K: developing device 4K: cleaning devices 10K, 10Y, 10C, 10M: PCU (photoconductor unit)
11: Intermediate transfer belt 12: Optical writing unit 13: Paper feed cassette 14: Paper feed roller 15: Registration roller pair 16: Intermediate transfer units 17Y, 17C, 17M, 17K: Primary transfer bias roller 18: Cleaning device 19: Secondary transfer backup roller 20: Cleaning backup roller 21: Tension roller 22: Secondary transfer roller 23: Fixing device 24: Paper discharge roller pair 25: Stack unit 26Y, 26C, 26M, 26K: Toner bottle 31K: Development roller 32K: Doctor blade 33K: developer supply unit 34K: toner replenishment unit 35K: stirring / conveying member 35K 36K: toner density sensor 51: controller board 52: engine main board 53: engine sub board 54: PSU (power supply unit)
71: Network I / F 72: IEEE1284 I / F
73: IEEE 1394 I / F 74: IEEE 802.11b I / F
101: LD light source 102: High voltage power supply 201: Synchronization detection unit 202: Various sensors 203: Polygon motor 204: Various motors 205: Various clutches 206: Thermistor 207: Heater

Claims (16)

In a color image forming apparatus that performs monochrome printing or color printing by selectively using a plurality of developing units that use toners of different colors,
When performing monochrome printing in the color mode with a plurality of toner density detecting units that respectively detect the toner density in the plurality of developing units, the color mode is changed to the monochrome mode based on the detection values of the plurality of toner density detecting units. A printing mode switching necessity determination unit that determines whether or not switching is necessary, and printing that executes the switching when the switching from the color mode to the monochrome mode is determined by the printing mode switching necessity determination unit A color image forming apparatus comprising a mode switching execution unit. The color image forming apparatus according to claim 1.
The print mode switching necessity determining means includes means for calculating a change amount per predetermined print number of an average value of detection values of the plurality of toner density detection means when performing monochrome printing in a color mode. A color image forming apparatus comprising: comparing a calculated value with a preset value and determining whether or not switching from a color mode to a monochrome mode is necessary based on the comparison result. The color image forming apparatus according to claim 1.
The print mode switching necessity determining unit includes a unit that calculates an amount of change per predetermined time of an average value of detection values of the plurality of toner density detection units when performing monochrome printing in a color mode. A color image forming apparatus comprising: comparing a value with a preset value and determining whether switching from a color mode to a monochrome mode is necessary based on the comparison result. The color image forming apparatus according to claim 1.
The print mode switching necessity determining means has means for calculating an average value of detection values of the plurality of toner density detection means when performing monochrome printing in a color mode, and the calculated value and a preset threshold value And determining whether or not it is necessary to switch from the color mode to the monochrome mode based on the comparison result. The color image forming apparatus according to claim 1.
The print mode switching necessity determining unit includes a unit that calculates a change amount per predetermined print number of detection values of the plurality of toner density detection units when performing monochrome printing in a color mode. And a preset value, and based on the comparison result, it is determined whether or not it is necessary to switch from the color mode to the monochrome mode. The color image forming apparatus according to claim 1.
The print mode switching necessity determining means includes means for calculating a change amount per predetermined time of the detection values of the plurality of toner density detection means when performing monochrome printing in a color mode, A color image forming apparatus that compares a preset value and determines whether or not switching from a color mode to a monochrome mode is necessary based on the comparison result. The color image forming apparatus according to claim 1.
The print mode switching necessity determination unit compares the detection values of the plurality of toner density detection units with preset thresholds when performing monochrome printing in the color mode, and determines whether or not the color mode is selected based on the comparison result. A color image forming apparatus that determines whether or not switching to a monochrome mode is necessary. In a color image forming apparatus that performs monochrome printing or color printing by selectively using a plurality of developing units that use toners of different colors,
A plurality of toner density detecting means for detecting the toner density in each of the developing means, a print pixel number acquiring means for acquiring the number of print pixels when printing in the color mode, and the print pixel number acquiring means. Based on the detection values of the plurality of toner density detection means, only when the image area determination means determines whether or not the image area is low based on the acquired number of print pixels, and the image area determination means determines that the image area is low. When it is determined by the print mode switching necessity determination means that the switching from the color mode to the monochrome mode is necessary. A color image forming apparatus, comprising: a printing mode switching execution unit that performs switching. The color image forming apparatus according to claim 8.
The print mode switching necessity determination unit calculates the amount of change per predetermined number of printed sheets of the average value of the detection values of the plurality of toner density detection units only when the image area determination unit determines that the image area is low. A color image forming apparatus characterized by comprising means for comparing the calculated value with a preset value and determining whether or not switching from the color mode to the monochrome mode is necessary based on the comparison result . The color image forming apparatus according to claim 8.
The printing mode switching necessity determining unit calculates a change amount per predetermined time of an average value of the detection values of the plurality of toner density detecting units only when the image area determining unit determines that the image area is low. A color image forming apparatus characterized by comparing the calculated value with a preset value and determining whether or not switching from the color mode to the monochrome mode is necessary based on the comparison result. The color image forming apparatus according to claim 8.
The print mode switching necessity determining unit includes a unit that calculates an average value of detection values of the plurality of toner density detecting units only when the image area determining unit determines that the image area is low. And a preset threshold value, and based on the comparison result, it is determined whether or not switching from the color mode to the monochrome mode is necessary. The color image forming apparatus according to claim 8.
The printing mode switching necessity determining means has means for calculating a change amount per predetermined print number of the detection values of the plurality of toner density detecting means only when the image area determining means determines that the image area is low. Then, each calculated value is compared with a preset value, and it is determined whether or not switching from the color mode to the monochrome mode is necessary based on the comparison result. The color image forming apparatus according to claim 8.
The printing mode switching necessity determining means has means for calculating a change amount per predetermined time of the detection values of the plurality of toner density detecting means only when the image area determining means determines that the image area is low. A color image forming apparatus comprising: comparing each calculated value with a preset value and determining whether or not switching from the color mode to the monochrome mode is necessary based on the comparison result. The color image forming apparatus according to claim 8.
The print mode switching necessity determination unit compares the detection values of the plurality of toner density detection units with preset thresholds only when the image area determination unit determines that the image area is low, and the comparison result A color image forming apparatus that determines whether or not switching from a color mode to a monochrome mode is necessary based on the above. In a method for switching a print mode in a color image forming apparatus that performs monochrome printing or color printing by selectively using a plurality of developing units that use toners of different colors,
Whether or not it is necessary to switch from the color mode to the monochrome mode based on each detected value when the toner density in the plurality of developing units is detected by the corresponding toner density sensor when performing monochrome printing in the color mode. And switching the print mode when it is necessary to switch the print mode. In a method for switching a print mode in a color image forming apparatus that performs monochrome printing or color printing by selectively using a plurality of developing units that use toners of different colors,
When printing in the color mode, the number of print pixels is obtained, and it is determined whether the image area is low based on the number of print pixels. Only when the image area is low, the toner density in the plurality of developing units is set. Detecting by each corresponding toner density sensor, determining whether or not switching from the color mode to the monochrome mode is necessary based on each detected value, and executing the switching when the switching is necessary The print mode switching method.

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