JPH0297981A - Image density controller in copying machine or the like - Google Patents

Abstract

PURPOSE:To properly deal with a photosensitive body deterioration by controlling a charging means with an image density. CONSTITUTION:A P sensor 25 of an image density detecting means is provided to be faced to a photosensitive body 1 in a position after a development and before a transfer, and the density after the development of a reference pattern formed on a position between image areas just after is detected continuously to the latent image formation and development of the original image area. Further, an F sensor 30 of an agent concentration detecting means is provided to a developing device 4. A recovered developer is made to pass in a coil arranged in the flow of the developer recovered from the photosensitive body 1 through a developing sleeve 12 into a developing container 9, the change of the transmissivity of the developer at such a time is detected, and a developer concentration is known. In such a way, the developer concentration in the device 4 is captured with the magnetic permeability change of a sensor coil, it is detected as an inductance change, a generation frequency change and further, a voltage change, it is fed back to a toner feeding system, and the concentration is made fixed. In such a way, the toner concentration cannot be abnormally concentrated, and the photosensitive body deterioration, etc., can be dealt with by the variance of a charging potential.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to an image density control device for a copying machine or the like.

Conventional Technology Generally, in copiers, printers, etc. that use electrophotography, in order to improve the copy quality so that the image density remains constant, toner supply is controlled to keep the image density constant. .

For this reason, as shown in, for example, Japanese Patent Laid-Open No. 60-49363, an electrostatic latent image of a reference pattern is formed outside the image area corresponding to the original image on a photoconductor, and after this is developed, the photoconductor is The density of this reference pattern image above is called P
A P sensor method is widely used in which toner replenishment is controlled so that the image density is constant by detecting the toner with a sensor and feeding back the detection result to the toner replenishing section. This requires a simple detection circuit and the like.

Furthermore, as shown in Japanese Patent Application Laid-open No. 57-136667, the toner concentration in the developer in the developing device is controlled by the so-called F.
Some devices detect it with a sensor and control and stabilize toner replenishment according to the density.

The problem to be solved by the invention is that both the P sensor method and the F sensor method use feedback as a toner replenishment amount control signal. The toner density may become abnormally high, resulting in toner scattering, background smearing, etc., or the toner density may be abnormally low, resulting in carrier adhesion on the image.

Means for Solving the Problems A charging means for charging a photoreceptor, an exposure means for forming an electrostatic latent image on the charged photoreceptor, a developing means for developing the electrostatic latent image on the photoreceptor, and a photoreceptor. and image density detection means for detecting the density of an image developed on the body.

A developer concentration detecting means for detecting the developer concentration in the developing means and a replenishing means for replenishing toner into the developing means are provided, and the replenishing means is controlled based on the detection result of the developer concentration detecting means to determine the image density. A control means is provided for controlling the charging means based on the detection result of the detection means.

Functional toner replenishment control is controlled in accordance with the detection result of the developer concentration in the developing means, which is detected by the developer concentration detection means. On the other hand, the image density detection result on the photoreceptor by the image density detection means is fed back to the charging means and used to control the amount of charge. Therefore, for example, toner can be replenished when the image density decreases due to deterioration of the photoreceptor. There is no problem such as abnormally high toner density.

Example An embodiment of the present invention will be described based on the drawings.

This example is applied to a digital copying machine, and first,
As shown in FIG. 2, a drum-shaped photoreceptor 1 made of an aluminum material coated with OPC is provided. This photoreceptor 1 is driven to rotate in the direction of the arrow, and is surrounded by a charging device 2 as a charging means, an optical writing head 3 as an exposure means, and a developing device 4 as a developing means in accordance with the photographic process. , a transfer/separation charger 5, a cleaning device 6, and a static elimination lamp 7. Here, as the charging device 2, a Scotron charger with a grid electrode is used to uniformly charge the surface of the photoreceptor 1 to a negative potential. The optical writing head 3 has a well-known configuration in laser printers, and is composed of a semiconductor laser, a rotating polygon mirror, a lens, a mirror, etc., and directs a laser beam modulated according to an image signal onto the surface of the photoreceptor 1 after being charged. An electrostatic latent image is formed by irradiating the image with the electrostatic latent image. The developing device 4 is for developing the electrostatic latent image formed on the photoreceptor 1 with l-toner to make it visible.
In this embodiment, a negative-positive two-component magnetic brush development system is used in which toner is attached to the area irradiated with light by the optical writing head 3. Therefore, the developing device 4 includes a toner hopper 8 for replenishing toner to the developing section, and a replenishing roller 10 as a replenishing means for replenishing the toner in the toner hopper 8 into the developing container 9 based on a toner replenishing signal from a control means to be described later. is provided. The replenishment roller 10 has an electromagnetic clutch on its axis that is driven by the replenishment signal. Further, in the developing container 9, a stirring member 11, a magnetic brush developing sleeve 12 facing the photoreceptor 1, and the like are provided.

On the other hand, roll-shaped transfer papers 15a to 15c of different width sizes are mounted on the lower side of the copying machine in three stages, and the paper is selectively fed to the transfer position of the photoreceptor 1 through cutter means 16a to 16c, respectively. It is configured to be In front of the transfer position, a registration roller 17 is provided that temporarily stops the fed transfer paper 15 and synchronizes it to the transfer position so that the leading edge of the paper 15 coincides with the image on the photoreceptor 1. 17a
1 is a registration sensor that detects the passage of the leading and trailing edges of the transfer paper 15 being conveyed toward the photoreceptor 1, and serves to control the timing of the copying operation. Further, on the downstream side of the transfer position, a conveying means 18 for conveying the transferred transfer paper 15 and a fixing device 19 are provided.
, a paper ejection roller 20, etc. are provided, and the paper is set to be ejected to a paper ejection tray 21 at the uppermost position.

Further, a so-called P sensor 25, which serves as image density detection means, is provided opposite the photoreceptor l at a position after development and before transfer. This P sensor 25 is, for example, JP-A-56-1
As in the case of Publication No. 28977, following the formation and development of a latent image in the original image area, the density after development of a reference pattern formed at a position between image areas (on the center line) immediately after that image area is detected. It is something. More specifically, 1
The image density of the standard pattern, which is a halftone dot pattern of about 25% with a size of about 5 x 5 mm, is determined by L as shown in Figure 3.
It is detected by a P sensor 25 which is a reflective photosensor consisting of an ED 26 and a phototransistor 27.

That is, the transistor 28 is turned on by the reference pattern request signal, and the LED 26 is driven. This LED
A variable resistor VR1 and a resistor R1 are connected in series to 26, so that the LED drive current can be variably adjusted. The light from the LED 26 is reflected by the surface of the photoreceptor 1 and enters the phototransistor 27, thereby turning on the phototransistor 27. By connecting a resistor between the emitter output of the transistor 27 and the ground GND to form an emitter follower, an output voltage that is inversely proportional to the amount of toner adhered to the reference pattern on the photoreceptor l is output as a creativity level detection signal. be done.

In this embodiment, in addition to the P sensor 25, a so-called F sensor 30, which serves as a degree of originality detection means, is provided in the developing device 4. The second F sensor 30 is, for example, as shown in Japanese Unexamined Patent Publication No. 136667/1983,
By passing the collected developer through a coil disposed in the flow of the developer collected from the photoreceptor 1 through the developing sleeve 12 and into the developing container 9, and detecting the change in magnetic permeability of the developer at that time. , which detects the developer concentration.

Here, details of the originality detection circuit using the F sensor 30 will be explained with reference to FIG. First, connector CN401-
2. A sensor coil 31 installed in the developer container 9 is connected between CN401-3. This sensor coil 31 constitutes an oscillation circuit 33 together with capacitors C, C, resistors R, and IC32. Similarly, semi-fixed inductor L
1. The capacitor C, the resistor R, and the IC 34 constitute an oscillation circuit 35. The outputs from the IC terminals 6 of the ICs 32 and 34, which are the outputs from these oscillation circuits 33 and 35, are both commonly connected to the resistor R4 and wired OR.
It is said to be composed of Further, an oscillation circuit 37 having an unstable multivibrator configuration consisting of a resistor R5.degree. This IC36-3
When the output from the number terminal is at H level, the oscillation circuit 33
The oscillation circuit 33 is inputted to the 7th terminal of the IC 32 therein as a strobe signal, and oscillates at a frequency fs corresponding to the inductance of the sensor coil 31.

Further, when the output from the No. 3 terminal of the IC 36 is at L level, the oscillation circuit 35
A strobe signal for this oscillation circuit 33 is input to the No. 7 terminal of the IC 34 inside, and it oscillates at a frequency fR corresponding to the inductance of the inductor L1. In this way, sensor oscillation (frequency fs) and reference oscillation (frequency fR) are alternately repeated in accordance with the oscillation of the oscillation circuit 37.

These oscillation frequency signals are output to the next stage through capacitor C1.

At the next stage of this capacitor C2, first, a differential amplifier circuit 41 consisting of an IC40 made up of two transistors, a resistor R+ 01 RI 1, an inductor L, and a capacitor C6 is connected. Here, the tuning frequency by the inductor L2 and the capacitor C is set to a frequency slightly shifted from the sensor oscillation frequency fS and the base (ψ oscillation frequency fR) of the previous stage.
to the output terminal 42 of.

A voltage with an amplitude corresponding to the input frequency is generated.

Capacitor C3, resistor RI 21 Rl! , diode D1, and capacitor C1 detect the output from the differential amplifier circuit 41 and convert it into a DC output. This converted output is given to an emitter follower circuit 44 made up of a transistor IC43 and a resistor R+4, and the output of this emitter follower circuit 44 is sent to the next stage amplifier circuit through a capacitor CI1.

At this time, it is also connected to the stabilized power output by IC46 through FET45. The gate terminal of this FET 45 is connected to the oscillation circuit (unstable multivibrator) 37, and during reference oscillation when the output of the IC 36 is at L level, the FET 45 becomes conductive and is clamped to the reference voltage.

The amplifier circuit located at the next stage of the emitter follower circuit 44 includes a resistor R+s+ R+s+ Rat and a capacitor CI 2
and an IC 47, which inverts and amplifies the detected output from the emitter follower circuit 44 during sensor oscillation, integrates it, and produces a perfect C output.

On the output side of this amplifier circuit 48, there is a resistor RIll R, .

R11+ Roll R'lil Ls+ R,4,R
zs, variable resistor ■R1, switches sw, , sw, and I
A comparator circuit 50 formed by C49 is connected, and the output from the amplifier circuit 48 is connected to a variable resistor VR, a switch SW, and the like.

Switching is performed by comparing it with a reference voltage that can be adjusted by SW2. The output of this comparator circuit 50 is a Zener diode ZD and a resistor R2.

R2+, LET) 51, resistance R2s r RI S +
R++. and is input to an output buffer 52 made up of two stages of transistors Q, , Q.

IC53 is a stabilized power supply IC connected in series with IC46.

With this originality detection circuit configuration, the developer concentration in the developing device 4 is detected as a change in magnetic permeability in the sensor coil 31, and is detected as a change in oscillation frequency based on a change in inductance, and further as a change in voltage. The density is stabilized by feeding back to the toner supply system.

Next, the configuration of the control device 59 which controls the entire digital copying machine shown in FIG. 2 and also serves as the control means of this embodiment will be explained with reference to FIG. First, a CPU 60 is provided to control the entire system. A reset clock element 61 is connected to this CPU 60 and supplies a reset signal and a clock signal to the CPU 60. Here, the clock signal is CP
This is a pulse-like signal of 5 MHz for performing the operation of tJ60. The reset signal is set to CP when the power is turned on.
This is a signal for resetting U60 for several tens of Ins. The CPU 60 also has upper and lower RAMs via upper and lower latch elements 62a and 62b.
63a, 63b and upper and lower ROM44a.

44b is connected. Further, an I10 element 45 is connected to the CPtJ60. Here, ROM44
A control program to be executed by the CPU 60 is written in a and 44b. As a result, the CPU 60
Load the control program from M64a and 64b and store it in RAM.
Read and write necessary information to 63a and 63b, and
External control is performed through the 10 elements 65.

That is, the CPU 60 is the main body, and the RAM 63 and ROM 64 constitute calculation means. Here, latch element 6
2a and 62b are ADO~A output from cpuao
Since the address output and data output of D7 and AD8 to AD15 are time-divided, the address output is latched by the address latch enable signal ALE and the RAM 63 a
, 63 b, ROM64 a.

64b, etc. A decoding element 66 is also connected to the CPU 60. This decoding element 66 decodes the output signals SO to S2 from the CPU 60 and generates an ALE signal, an RD (read) signal, a WR (write) signal, an INTA (indoor acknowledge) signal, and the like.

Further, a timer element 47 is provided. This timer element 67 uses the 2.5 MHz PCLK signal supplied from the reset clock element 61 as a basic clock, and uses the C
0 depending on the mode and data instructed by PU60.
The UTO outputs pulses with various frequency patterns.

68 is an interrupter element.

On the other hand, the I10 element 65 accesses input elements such as sensors and keys, and output elements such as display LEDs and heaters. Here, A of 8 bits each,
It has 3 ports, B and C, and A and B ports are output ports.
C-boats are considered human-powered boats. More specifically,
The lower 4 bits PAO to PA3 of the A boat are connected to the A/D conversion element 69 by a control signal, and the other output boats PA
4-PA7. PBO to PB7 are external chargers,
Developing motor, P sensor LED, toner replenishment clutch,
The reference pattern request signal, laser exposure request signal, and grid 1 to 3 signals are connected to a laser optical system. Input C
Toner replenishment signals from the registration sensor and F sensor are input to the port, and the DATA signal from the A/D conversion element 69 is manually input to the lowest 1 bit of the C port.

Here, the A/D conversion element 69 converts the analog voltage value outputted by the phototransistor 27 of the P sensor 25 into an 8-bit digital value and transmits it to the CPU 60. For this operation, C8 is always kept active (L level) when performing A/D conversion. Also, ADC
LK is a signal for outputting DATA from this A/D conversion element 69. At this time, A used in this example
/D conversion element 69 is based on MB4052, and D
Since there is only one ATA terminal, data is output serially. Therefore, every time a pulse signal is input to ADCLK, the data is output eight times starting from the most significant data. On the other hand, C.P.
U60 outputs I10 element 65 every time it outputs an ADCLK pulse.
The Oth bit of the C port is read, and this operation is repeated eight times to obtain 8-bit data. The remaining Go and C1 are A/D
Since the conversion element 69 includes four A/D conversion circuits, this signal determines which circuit to select.

Next, toner replenishment control based on the F sensor 30 will be explained. During copying, when the developing motor is on, the CPU
checks the toner replenishment signal, and turns on the toner replenishment clutch if the toner replenishment signal is active, and turns off the toner replenishment clutch if it is not active.

If repeat copying is in progress, this operation is repeated. When the toner replenishment signal is active for a certain period of time or more (for example, 20 seconds or more), it is determined that the toner is near end, and when a certain number of copies, for example, 50 or more copies have been made, the machine is determined to be at the toner end and the machine is stopped. After that, when the toner cartridge is replaced and toner is replenished, the developing motor is rotated, the toner replenishment clutch is turned on, and the toner replenishment signal is checked. When the toner replenishment signal becomes inactive, it is determined that the toner concentration (creation degree) in the developing device 4 has returned to an appropriate state, the developing motor and toner replenishment clutch are turned off, the toner end is released, and the copying process is started. Make it possible. In this way,
Toner replenishment is controlled according to the developer concentration detected by the F sensor 30.

Also, the image density detection operation by the P sensor 25 will be explained. Normally, during copying, the CPU 60 is used for the optical writing head 3.
outputs a laser exposure request signal at a predetermined timing.

As a result, an electrostatic latent image is formed on the photoreceptor 1 by exposure according to the image data. The laser exposure request signal turns off,
After a certain period of time has elapsed, the reference pattern request signal turns on.
Turns off after a certain period of time. As a result, an electrostatic latent image of a standard pattern of 15 x 15 M'' size is formed and developed on the photoconductor 1 at a position immediately after the image area.This operation is repeated during repeat copying, and a standard pattern is formed between each image area. An image is formed.The LED 26 in the P sensor 25 is turned on when the rear end of the image area passes the position of the P sensor 25, and turned off when the rear end of the reference pattern image passes.

The CPU 60 samples the P sensor output voltage using the A/D conversion element 69 several times at intervals of 10 m5 until the rear end of the image area image passes on the P sensor 25 and the front end of the reference pattern image arrives, and calculates the average value. Calculate and store in the buffer. This is sampling of non-pattern areas. Next, while the reference pattern image passes over the P sensor 25, the P sensor output voltage is similarly sampled several times at loms intervals by the A/D conversion element 69, and the average value is calculated and stored in the buffer. This is sampling of the pattern portion. When the values sampled in this way are converted into voltages, they are around 4■ in the non-pattern area and 1.5 in the pattern area.
The value will be around 5v. When the sampled point is black (dark), the voltage decreases, and when the sampled point is thin, the voltage increases. In this way, the density of the reference pattern image on the photoreceptor 1 is detected. If repeat copying is in progress, the operation is repeated in this manner.

One of the features of this embodiment is that the detection result by the P sensor 25 is used to control the amount of charge of the charging means 2, and the charge control will be explained with reference to the circuit shown in FIG. First, as described above, the charging means 2 of this embodiment uses a Scotron charger with a grid electrode.
As shown in FIG. 6, a corona wire 71 is stretched in a grounded casing 70, and a grid wire 72 is
will be established. Such charging means 2 is connected to a charging power source 73. This charging power source 73 is the corona wire 71
It consists of a charge power supply section 74 that supplies power to the grid wire 72 , and a grid power supply section 75 that supplies power to the grid wire 72 . The grid power supply unit 75 is first provided with a D/A converter 76 to which 3-bit switching signals of grids 1 to 3 are input, and analog signals preset according to the values of grids 1 to 3 are input. is output to the control circuit 77.

A driver circuit 79 for driving a transformer 78 is connected to this control circuit 77 . This driver circuit 79 oscillates at several tens of kHz to excite the transformer 78. In addition to the primary winding N I 1 connected to the driver circuit 79, the transformer 78 has secondary and tertiary windings N
＋! It has IN 13. The secondary winding N + 2 includes a rectifier diode D 3 + and a smoothing capacitor C5.
1, a resistor R31, a voltage detection semi-fixed resistor Rst, and a capacitor C32 are connected and drawn out to a grid output terminal for the grid wire 72. Tertiary winding N I
3 is connected to a winding voltage detection circuit 80. The control circuit 77 receives the analog output from the D/A converter 76, the voltage output fed back from the semi-fixed resistor Riz, and the tertiary winding N1 . The oscillation state of the driver circuit 79 is controlled by performing arithmetic processing based on the voltage and the like. With such a configuration of the grid power supply unit 75,
A negative DC voltage is output from the grid output terminal to the grid wire 72.

Here, in this grid power supply section 75, grid 1
The output voltages are set as shown in the table below according to the signals of 3 to 3.

Further, the charge power supply unit 74 is similarly configured except for the D/A converter 76, and includes a control circuit 81, a transformer 82 (first to third windings N2.

N 1ffil Nas), driver circuit 83
, winding voltage detection circuit 84, rectifier diode Dsx
, a smoothing capacitor C33, a resistor Rss, a voltage detection semi-fixed resistor R34, and a capacitor C34. With such a configuration of the charge power supply section 74, a negative DC voltage is outputted from the charge output terminal to the corona wire 71.

In such a configuration of the charging power source 73, when the charging signal shown in FIG. 5 is applied to the trigger terminal shown in FIG.
A strobe signal is applied to each control circuit 81, 77. As a result, a charge output of a constant current output is given to the corona wire 71, and corona discharge is performed with a constant current. On the other hand, the grid output is given as a constant voltage output to the grid wire 72 to control the charging potential of the photoreceptor 1. At this time, as shown in the table above, the output voltage is varied according to the grid 1 to 3 signals to the grid power supply section 75, and the standard is 700. And P
According to the image density detection result by the sensor 25, as shown in the flowchart of FIG. 1, the grid voltage is lowered when the image density is higher than the standard value, and when the image density is lower than the standard value Grid 1 to 3 signals are controlled so that the grid voltage becomes high.

For example, the normal output voltage (reference output voltage) of the charging means 2
is 700V, and the reference pattern of the P sensor 25 (normal detection voltage of the P sensor pattern image (P sensor reference voltage) is 1.
5■, and if the detection voltage of the pattern image detected by this P sensor 25 during copying changes to 1.7■,
The interruption output voltage of the charging means 2 is 700VX (1,7/1
．． 5)≠790■, and grids 1 to 3 are 0 and 1, respectively.
It is assumed that the data signal is ゜1. On the other hand, if the voltage detected by the P sensor 25 drops to 1.3■, the charging means 2
The disconnection output voltage is 700VX (1,3/1.5) #61
Since it is 0V, the grid 1-3 signals are 0, 0 .
It is assumed to be a data signal of 0.

In the second embodiment, the charging potential of the photoreceptor I by the charging means 2 is controlled in accordance with the image density detection result of the P sensor 25 in this embodiment. By controlling this charging potential, the image density on the photoreceptor 1 is substantially corrected, and the P sensor 25 detects it as a standard density.

Therefore, even if the density of the reference pattern image changes due to deterioration of the photoreceptor 1, toner will not be replenished, and there will be no problem such as an abnormally high donor density. At this time, according to this embodiment, since the grid voltage of the charging means 2 is variably controlled by the scotron charger, sparks are generated and ozone is increased compared to the case where the corona current (voltage) is variably controlled by the scotron charger. There is also an advantage that there is no such thing.

Effects of the Invention As described above, the present invention provides an image density detection means for detecting the density of an image developed on a photoconductor, a developer concentration detection means for detecting the developer concentration in the developing means, and a division ratio detection method. Since the control means is provided to control the replenishing means according to the detection result of the image density detection means and to control the charging means according to the detection result of the image density detection means, toner replenishment control is performed by controlling the toner replenishment in the developing means detected by the division ratio detection means. The image density is controlled according to the agent concentration detection result to maintain a constant image density, while the image density detection result on the photoreceptor by the image density detection means is fed back to the charging means to control the amount of charge. ,
For example, there is no need to replenish toner due to a decrease in image density due to photoreceptor deterioration, etc., and there is no inconvenience such as abnormally high toner density, and it is possible to cope with photoreceptor deterioration by varying the charging potential. Can be done.

4 is an F sensor detection circuit diagram, FIG. 5 is a block diagram of the control device, and FIG. 6 is a block diagram of the charging power source.

DESCRIPTION OF SYMBOLS 1... Photoreceptor, 2... Charging means, 3... Exposure means, 4... Developing means, 10... Toner replenishing means, 25
. . . Image density detection means, 30 . . . Division degree detection means,
59...control means

[Brief explanation of drawings]

Claims (1)

[Claims] A charging means for charging the photoreceptor, an exposure means for forming an electrostatic latent image on the charged photoreceptor, a developing means for developing the electrostatic latent image on the photoreceptor, and an image developed on the photoreceptor. An image density detection means for detecting the density, a developer concentration detection means for detecting the developer concentration in the development means, and a replenishment means for replenishing toner in the development means are provided, and the detection result of the developer concentration detection means is provided. An image density control device for a copying machine or the like, characterized in that a control means is provided for controlling the replenishing means and controlling the charging means based on the detection result of the image density detection means.