JPH0378778A - Image forming device - Google Patents

Abstract

PURPOSE:To appropriately adjust image density even when environmental condition or the toner characteristic is varied and to obtain an image of high quality by evaluating the electrified quantity of toner based on the outputs from a magnetic detecting means and an optical detecting means, and providing a condition setting means which sets the developing condition based on he electrified quantity of the toner. CONSTITUTION:The magnetic detecting means 51 which measures the change in the magnetic permeability of the developer, an optical detecting means 52 which detects the reflected light, a condition setting means 50 which evaluates the electrified quantity of the toner based on the outputs from the magnetic detecting means 51 and the optical detecting means 52 and sets the developing condition based on the toner electrified quantity are provided. Then the operat ing condition is set taking into account the toner characteristic related to the image density, especially the electrified quantity. Thus, even when the environ mental condition and the toner characteristic are changed, the image density is appropriately adjusted, and an image of high quality can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an image forming apparatus using a two-component developer consisting of a powder toner and a magnetic carrier, and particularly to image density control thereof.

[Conventional technology]

In image forming devices such as copying machines, printers, and facsimile machines that use a two-component developer containing powder toner and magnetic carrier, the weight mixing ratio of toner to carrier in the developing device (hereinafter referred to as "toner concentration") has an important effect on image density.

For this reason, conventional image forming apparatuses attach a magnetic sensor to the developing device to measure changes in magnetic permeability based on increases and decreases in toner concentration, and adjust the toner concentration based on the measurement results to control image density. Ta.

[Problem to be solved by the invention]

However, the output of the magnetic sensor changes not only depending on the toner concentration (as shown in FIG. 3<a>), but also depending on the amount of toner charge. In other words, as shown in FIG. Even so, the output Vm of the timing sensor changes depending on the toner charge amount.Furthermore, the toner charge amount is closely related to the ambient humidity and the degree of deterioration of the toner.In other words, as shown in FIG. 3(b) As shown in , even if the toner concentration Tc or Tc is the same, the magnetic sensor output ■
m changes depending on the humidity H, and the toner charge amount Q of the developer at the stage when it is newly introduced into the developing device (initial state)
f,,,Qf,. and the stage at which it contributed to the development of a predetermined number of sheets (
Toner charge amount of developer Q f II, Q f
! + indicates a different value.

Therefore, if you control the image density solely by relying on the output of the magnetic sensor, the toner density in the developing device will fluctuate (sometimes there will be an excess supply of toner, and other times there will be a shortage of toner, making it impossible to obtain a stable image density). There was a problem.

Therefore, the present invention has been made to solve the above-mentioned problems, and the basic idea will be explained.

Development in an image forming apparatus such as a copying machine that uses a two-component developer consisting of toner and magnetic carrier electrically cancels out the potential difference (development potential) between the image area potential of the electrostatic latent image and the development bias voltage. This is done by contacting and supplying enough charged toner to the electrostatic latent image.

Therefore, the development potential and the toner charge amount are important factors in determining the image density.

ii. an optical detection means for illuminating the developer and detecting the reflected light; iii. evaluating the amount of charge on the toner based on the outputs from the magnetic detection means and the optical detection means, and determining the amount of charge on the toner. A condition setting means for setting development conditions based on the development condition is provided.

〔Example〕

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

In the copying machine shown in FIG. 1, an original placed on an original platen glass 2 covered with an opening/closing cover 1 is illuminated by an exposure lamp 4 as an image reader unit 3 moves, and the reflected light illuminates a lens array 5. The light is exposed to the line sensor 6 through the light and read as color signals of the three primary colors of R (red), G (green), and B (blue). These R, G, and B color signals are converted by the image processing circuit 7 into Y (yellow), 2M (magenta), C (cyan), or trivalent or quadrivalent signals obtained by adding BK (black) to these signals, Shikokote,
Toner 1 degree can be evaluated from the amount of reflected light by illuminating the developer. The development potential can be determined by the charging potential, exposure amount, and development bias voltage. Further, the output of the magnetic sensor is determined by the toner concentration of the developer and the amount of toner charge.

Therefore, the conditions for obtaining images with appropriate density,
In other words, the relationship between toner concentration, toner charge amount, and magnetic sensor output is determined in advance through experiments, and these data are stored in a microcomputer, and the toner concentration and magnetic sensor output are measured in the actual image forming apparatus. By evaluating the toner charge amount from these values and determining the development potential based on the obtained toner charge amount, an image with appropriate density can be obtained.

[Means to solve the problem]

The present invention has been made based on the above-mentioned ideas, and provides an image forming apparatus that develops an electrostatic latent image with a two-component developer consisting of toner and carrier. - the optical system 8; Note that the copying machine of this embodiment does not have an image memory for three colors, and the image league unit 3 scans each time when forming an image for each color, and based on this scan, sequentially prints Y, M, C, or Y.

The M, C, and BK signals are transmitted to the laser optical system 8.

The laser optical system 8 includes the above-mentioned Y, M, C or Y, M.

Image forming laser beams for each color based on the C and BK signals are emitted toward the photosensitive drum 12 via the polygon mirror 9, the fθ rereno 10, and the reflective mirror 11.

The photoreceptor drum 12 is charged by the charger 13, and the charged area is exposed to laser light as described above to form an electrostatic latent image corresponding to color information.

As the photoreceptor drum 12 rotates, this electrostatic latent image is formed by the arrow a.
the developing device 14 (14Y).

14, M, 14C, 148K), toner is supplied and developed. The developing device 14 uses a two-component powder developer consisting of toner and carrier; the developing device 14Y uses yellow toner, and the developing device 14M uses yellow toner.
contains magenta toner, the developing device 14C contains cyan toner, and the developing device 14BK contains black toner.The toner replenishing device 15 (15Y) contains toner of the corresponding color in an amount corresponding to the amount consumed by development.
.

15M, 15C, 158K).

The toner image in which the electrostatic latent image is visualized by the developing device 14 is transferred onto paper (not shown) using a transfer material at a portion facing the transfer charger 16 .

The paper is once conveyed from the paper feed cassette 17 or 18 to the timing roller 20, and then
0 and is conveyed to the lower part of the transfer drum 21. Transfer drum 2
The paper conveyed under 1 is held on the outer peripheral surface of the transfer drum 21 with its leading end held by a chuck 22, and as the transfer drum 21 rotates, it passes between the photosensitive drum 12 and the transfer charger 16. To go. Here, the timing between the toner image and the paper is controlled by a transfer drum switch 23 provided on the side of the transfer drum 21, and a developing sleeve 32 is provided in an area facing the chuck 22 and ram 12.

The developing sleeve 32 houses a magnet (not shown) therein, is rotatably supported on the side wall of the developer tank 31 via a support shaft 33, and has rollers 34 provided at both ends of the support shaft 33, 3
4 are brought into contact with the outer circumferential surfaces of both ends of the photoreceptor drum 12, and a predetermined development gap Ds is established between the photoreceptor drum 12 and the photoreceptor drum 12.
is ensured.

The rear space of the developing sleeve 32 is partitioned into front and back by a partition wall 35, and a supply path 36 on the side of the developing sleeve 32 and a conveyance path 37 at the rear of the partition wall are formed.
are connected by passages 38 and 39 provided at both ends of the bulkhead.

Conveying blades 40 are provided in the supply path 36 and the conveying path 37, respectively.
．． 43 is the provision. These conveying blades 40.43 each consist of a support shaft 41.44 and a plurality of blades 42, 45 attached to this at a predetermined interval.
．． Both ends of 44 are rotatably supported on the side walls of developer tank 31, respectively.

is detected and the laser optical system 8 is driven using the detected signal as a reference.

After the surface of the photosensitive drum 12 that has passed through the portion facing the transfer charger 16 has residual toner removed by a cleaning device 24, the residual charge is erased by light irradiation from an eraser lamp 25, and the surface is ready for the next development.

If the image to be created is a multicolor image, the image reader unit 3 scans multiple times, and each time the laser optical system 8 emits laser light to form an electrostatic latent image of the color to be reproduced. The toner image is developed by the developing device 14 of the corresponding color to form a multicolor unfixed color toner image on the paper.

When all development and transfer are completed, the paper is separated from the transfer drum 21 and conveyed by a conveyor 26 to a fixing device 27, where the unfixed color toner image is heat-fixed to the paper and discharged onto a paper discharge tray 28.

FIG. 2 shows a cross section of the developing device 14.

In the developing device 14, the photoreceptor in the developing tank 31 and the conveying blades 40 in the supply path 36 are driven and connected to a motor 46.
The transport blades 40, 43 and the developing tube I7-32 are part of the gear mechanism 4.
7, and the conveying blades 40, 43 and the developing sleeve 32 are rotated in the directions indicated by the arrows based on the rotation of the motor 46.

In the developing device 14 having the above configuration, two-component developer consisting of toner and magnetic carrier is stored in the supply path 36 and the conveyance path 37, respectively. This developer is circulated and conveyed through the supply path 36 and the conveyance path 37 via passages 38 and 39 by conveyance blades 40 and 43 driven by the motor 46, and a part of the developer conveyed through the supply path 36 is transferred to the developing sleeve. 32. Further, the developer is mixed and stirred during the conveyance process, and the toner and carrier are charged to opposite polarities.

The developer supplied to the outer periphery of the developing sleeve 32 is held by the magnetic force of the magnet and is moved to the area facing the photoreceptor drum 12 (hereinafter referred to as "developing") based on the rotation of the developing sleeve 32 and/or the rotation of the magnet. The electrostatic latent image formed on the outer periphery of the photoreceptor drum 12 is supplied with toner in the development area. The development here is based on the potential difference (development potential) ΔV (Vn Vi) between the image area potential Vi of the electrostatic latent image and the development bias voltage 8 applied to the development sleeve 32 from the power source 48. The potential difference △
This is done by supplying enough charged toner to cancel out V.

Next, image density control of the image forming apparatus and devices related thereto will be explained.

In FIG. 2, a magnetic sensor 51 measures changes in magnetic permeability of the developer, and is provided at the bottom of the conveyance path 37 so that its sensor surface is in contact with the developer.

The optical sensor 52 includes a light emitting section 53 and a light receiving section 54, and the light emitting section 53 is
The developer is illuminated with light, and the reflected light is detected by the light receiving section 54.

The magnetic sensor 51 and optical sensor 52 are electrically connected to a microcomputer (hereinafter referred to as rcPUJ) 50, and when the output from each sensor advances to 1 and the copy start switch is pressed, in step S5 A copying operation is performed using the value of the developing bias voltage calculated in step S3, and it is determined in step S6 whether or not the internal timer has expired. Then, when it is determined in step S6 that the internal timer has ended, the process returns to step S1 again.

FIG. 5 shows the contents of the charge amount calculation routine.

In this routine, in step Sll, the magnetic sensor 5
Read the output Vm of 1.

In step S12, the output VS of the optical sensor 52 is read. In step S13, the output Vs of the optical sensor 52
Based on this, the toner concentration Tc is calculated from Table 1 (optical sensor output and toner concentration) below. Note that the output voltage Vs of the optical sensor 52 is not affected by humidity;
The toner concentration Tc is uniquely determined from this value.

The signal is input to the CPU 5Q, and the CPU performs image density control based on the signals from each sensor.

Note that the toner density of the developing device 14 is controlled to approximately a predetermined value for each color developer based on a signal from the magnetic sensor 51. A description of this toner density control will be omitted.

Image density control by the CPU 50 will be described below with reference to the attached flowchart. Note that in the flowchart, only processes necessary for the present invention are described, and other processes are omitted.

FIG. 4 shows the contents of the main routine.

In step S1, an internal timer is set. This internal timer defines the time for executing the following processing.

Next, in step S2, a charge amount calculation routine is executed, and in step S3, a development bias calculation routine is executed.

Next, in step S4, it is detected whether or not the copy start switch has been pressed, and if the copy start switch has not been pressed, step S62 Table 1: Optical sensor output and toner concentration Vs (V) Tc (%) 1.0 or more - less than 1.5 40 1.5 - 2.0 5.0 2.0 - 2.5 5.8 25 - 3.0 6.5 3, O - 3 .5〃7.1 3.5〃 ~4.0 〃7.6 4,O〃~4.5〃8.1 4.5 〃~5.0〃8.5 In step S14, the toner charge amount is Calculate in the following order.

First, from the toner concentration Tc obtained in step S13, a corresponding toner concentration Qf conversion table is selected according to Table 2 (toner concentration and Qf conversion table). Note that FIG. 6 shows the relationship between the magnetic sensor output Vm, the toner concentration Tc, and the charge amount Qf, and shows that the toner charge amount can be evaluated from the toner concentration and the magnetic sensor output. Also, Qf
Six conversion tables are prepared depending on the size of the toner concentration, and each Qf conversion table sets the toner concentration to a corresponding value.
The relationship between the magnetic sensor output Vm, humidity H, and toner charging IQf was experimentally determined by changing them.

Table-2: Toner concentration and Qf conversion table Tc (%) Conversion table 6.5 or less 0 6.5 or more to less than 7.0 1 7.0 ~ 7.5 2 7.5 ~ 8.0 3 8.0~8.5 4 8.5 or more 5 Next, the output Vm of the magnetic sensor and the average humidity (60~69%
), the toner charge amount is determined using a Qf conversion table. Note that Table 3 below relates to Qf conversion table 3, and the toner density is 7.5 to 8. 5 Table 4 = Charge amount and developing bias voltage 8.0 or less 300 8.0 or more to less than 9.0 300 9, O ~ 10. O〃 350 10, O〃 ~11.0 〃 40011, O〃
~12. O〃 45012, O〃 ~13. O〃
50013, O〃 ~14. O〃 5501
4, O ~ 15. O〃 60015, O〃 ~1
6. O〃 65016.0 〃 ~17.0 〃
70017, O ~ 18. O〃 75018
．． 0 or more 800 Here, Table 4 describes the conditions of the developing bias voltage that can obtain an image with the most appropriate density for the amount of toner charge, and is determined experimentally.

Therefore, in an image forming apparatus with a developing bias voltage under the above conditions, environmental conditions such as humidity and toner Table 3: Qf conversion table 3 14.5 14.0 13.5 30 12.5 12.0 11.5 10 10.5 00 Unit: μc/g Once the toner charge amount is determined by the above operations, in step S6 of the main routine, the developing bias voltage ■
8 is determined, and a voltage of the determined value is applied to the developing sleeve 32 by the power source 48.

1.4～ 1.6～ 1.8～ 2.0～ 2.2~ 2.4~ 2.6~ 2.8~ 30~ 3.2-3.4 6 Good quality images can be obtained regardless of the degree of deterioration.

Note that the above processing is performed on all developing devices 14 (14Y,
14M, 14C, and 14BK), and the developing bias voltage of each color developing device 14 is adjusted appropriately.

Furthermore, in the above description, the toner charge amount Qf is determined and the developing bias voltage (8) is adjusted from that value. The development potential may be adjusted by adjusting.

〔Effect of the invention〕

As is clear from the above description, in the image forming apparatus according to the present invention, the image forming conditions are set to conditions that allow a high quality image to be obtained, taking into account the characteristics of the toner related to image density, especially the amount of charge. .

Therefore, even if environmental conditions and toner characteristics change, the image density of the resulting image can be adjusted appropriately, and a high-quality image can be obtained.

[Brief explanation of drawings]

Figure 1 is a cross-sectional view of the copying machine, Figure 2 is a cross-sectional view of the developing device, Figure 3 (a) is a diagram showing the relationship between the magnetic sensor output and toner concentration, and Figure 3 (b) is a diagram showing the relationship between humidity and The relationship diagram with the magnetic sensor output, Figures 4 and 5 are flowcharts of image density control.
FIG. 4 shows the main routine, FIG. 5 shows the charge amount calculation subroutine, and FIG. 6 shows the relationship between the magnetic sensor output and the toner charge amount. 12... Photosensitive drum (electrostatic latent image carrier) 14... Developing device 50... Microcomputer 51... Magnetic sensor 52... Optical sensor

Claims (1)

[Claims] (1) An image forming apparatus that develops an electrostatic latent image with a two-component developer consisting of toner and carrier, which includes a magnetic detection means for measuring changes in magnetic permeability of the developer, and a magnetic detection means that illuminates the developer and an optical detection means for detecting reflected light; and a condition setting means for evaluating the amount of charge of the toner based on the outputs from the magnetic detection means and the optical detection means and setting developing conditions based on the amount of charge of the toner. An image forming apparatus comprising: