JP2788457B2 - Image density control device in copying machines, etc. - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image density control device in a copying machine or the like.

2. Description of the Related Art In general, in copying machines and printers employing an electrophotographic method, in order to improve copy quality so that image density is constant, toner replenishment is controlled to make image density constant. .

For this reason, an electrostatic latent image of a reference pattern is formed on the photoconductor outside the image area corresponding to the original image, and after developing this, the density of the reference pattern image on the photoconductor is detected by a so-called P sensor. A P sensor system is widely used in which the detection result is fed back to a toner replenishing unit to control the toner replenishment so that the image density becomes constant. this is,
The detection circuit is simple.

In this case, for example, as shown in JP-A-60-49363, if a reference pattern is formed outside the image area in the width direction and its density is detected by a P sensor,
The image density can be detected even during copy printing. At this time,
For large-size, center-conveying copiers, etc., in order to deal with copy printing for various transfer paper sizes with different paper widths, set the pattern formation position at the end of the image area outside the maximum width, and The P sensor is arranged at a position on the trajectory that moves.

However, according to the P-sensor system having such an arrangement,
For example, in a case where continuous copy printing is performed on a narrow paper width transfer paper (narrow image), only the toner near the center of the developing unit is consumed more, whereas the toner consumption is small near the P sensor detection position. Therefore, since the reference pattern density hardly changes, a toner supply command is not generated. That is, the toner consumption accompanying the actual copy printing cannot be accurately detected.

In this regard, the reference pattern formation position is not set at the end in the width direction outside the image area on the photoconductor, but is set between image areas in the photoconductor moving direction as shown in, for example, Japanese Patent Application Laid-Open No. 56-128977. For example, the center line can be set on the center line in the center reference system, and detection control not affected by various width sizes can be performed. However, a large-sized copying machine or the like copies an original of an irregular size, and in addition to those of various widths, there are also various lengths of size, especially when an image such as a long original is formed. If there is, the reference pattern image cannot be formed until the development processing up to the rear end is completed. In other words, despite the fact that a large amount of toner is consumed for the formation of an original long image and the toner density is originally reduced, a reference pattern image cannot be created and the density is set to P.
Since the toner cannot be detected by the sensor, the toner supply operation cannot be performed. That is, in this case, inconvenience occurs at the time of copying a long document or the like.

Means for Solving the Problems A charging unit for charging a photoconductor, an exposure unit for forming an electrostatic latent image on the charged photoconductor, a developing unit for developing the electrostatic latent image on the photoconductor, In a copying machine or the like having an image density detecting means for detecting the developed density of a reference pattern formed at a position between image areas immediately after an image area on a body, and a replenishing means for replenishing toner in the developing means. In the image density control device, an agent concentration detecting unit that detects a developer concentration in the developing unit is provided, and a length detecting unit that detects a length of the image area in the photoconductor moving direction is provided. The replenishing means is controlled based on the detection result of the image density detecting means, and when the detection result of the length detecting means exceeds a predetermined length, switching to the agent concentration detecting means is performed at a predetermined timing to detect the agent concentration. means And control means for controlling the replenishing means according to the detection result of the above.

According to the agent concentration detecting means, detection is always possible regardless of the image area on the photoreceptor. By providing such an agent density detecting means together with the image density detecting means, necessary toner replenishment is normally performed by controlling the toner replenishing means in accordance with the detection result of the image density detecting means. On the other hand, when copying long documents,
If it is detected by the length detection means that it is long,
By controlling the toner replenishing unit using the detection result of the agent concentration detecting unit at a predetermined timing, toner replenishment can be effectively performed even when the image density detecting unit cannot detect the density. Accordingly, it is possible to appropriately supply the toner even in the case of a long copy in which the detection by the agent concentration detecting means cannot be performed for a long time.

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

This embodiment is applied to a digital copying machine. First, as shown in FIG. 2, a drum-shaped photoconductor 1 formed by applying OPC to an aluminum material is provided. The photosensitive member 1 is driven to rotate in the direction of the arrow. Around the periphery of the photosensitive member 1 is a charging device 2 as a charging device, a light writing head 3 as an exposure device, a developing device 4 as a developing device, and a transfer device. A separation charger 5, a cleaning device 6, and a neutralization lamp 7 are provided. Here, a scotron charger with a grid electrode is used as the charging device 2 in order to uniformly charge the surface of the photosensitive member 1 to a negative potential. The optical writing head 3 has a well-known configuration in a laser printer, and includes a semiconductor laser, a rotating polygon mirror, a lens, a mirror, and the like.
The electrostatic latent image is formed by irradiating the surface of the charged photosensitive member 1 with a laser beam modulated according to an image signal. The developing device 4 develops an electrostatic latent image formed on the photoreceptor 1 with toner to visualize the latent image.
In this embodiment, a negative-positive two-component magnetic brush developing system in which toner adheres to a portion irradiated with light by the optical writing head 3 is used. For this reason, the developing device 4 has a toner hopper 8 for replenishing toner to the developing unit, and a replenishing roller 10 as a replenishing unit for replenishing the toner in the toner hopper 8 into the developing container 9 based on a toner replenishing signal from a control unit described later. Is provided. On the shaft of the supply roller 10, there is provided an electromagnetic clutch driven by the supply signal. Further, a stirring member is provided in the developing container 9.
A magnetic brush developing sleeve 12 and the like facing the photoconductor 1 are provided.

On the other hand, on the lower side of the copying machine, roll-shaped transfer papers 15a to 15c of different widths are mounted in three stages,
The paper is selectively fed toward the transfer position of the photoconductor 1 via a to 16c. Before the transfer position, there is provided a registration roller 17 for temporarily stopping the fed transfer paper 15 and feeding the transfer paper 15 to the transfer position in synchronization with the image on the photoconductor 1 so that the leading end thereof coincides with the image. Further, on the rear side of the transfer position, a conveying means 18 for conveying the transferred transfer paper 15, a fixing device 19, a paper discharge roller 20, and the like are provided, and the paper is set to be discharged to the paper discharge tray 21 at the uppermost position. I have.

Further, a so-called P sensor 25, which is an image density detecting means, is provided opposite to the photoconductor 1 at a position after development and before transfer. This P sensor 25 is disclosed in Japanese Patent Application Laid-Open No. 56-12897.
As in the case of No. 7, the latent image formation of the original image area
Following the development, the density of the reference pattern formed at the position between the image areas (on the center line) immediately after the image area is detected. More specifically, 15 × 5mm
The image density of a reference pattern having a size of about ^{2 and} a halftone dot pattern of about 25% is calculated by using a reflection type photosensor comprising an LED 26 and a phototransistor 27 as shown in FIG.
This is detected by the sensor 25. That is, the transistor 28 is turned on by the reference pattern request signal, and the LED 26
Drive. Variable resistor VR in the LED 26, the resistor R ₁ are connected in series, LED drive current is variable adjustable. The light from the LED 26 is reflected by the surface of the photoreceptor 1 and enters the phototransistor 27, so that the phototransistor 27 is turned on. The emitter output of the transistor 27 is connected to a ground GND to form an emitter follower, so that an output voltage that is inversely proportional to the amount of toner adhering to the reference pattern on the photoconductor 1 is output as an agent concentration detection signal. You.

In the present embodiment, in addition to such a P sensor 25, a so-called F sensor 30, which is a means for detecting agent concentration, is provided in the developing device 4. As shown in, for example, JP-A-57-136667, the F sensor 30 includes a coil disposed in the flow of the developer collected from the photoreceptor 1 via the developing sleeve 12 into the developing container 9. The developer concentration is detected by passing the collected developer and detecting a change in the magnetic permeability of the developer at that time.

Here, details of the agent concentration detecting circuit using the F sensor 30 will be described with reference to FIG. First, the connectors CN401-2 and CN40
A sensor coil 31 installed in the developing container 9 is connected between 1-3. This sensor coil 31 includes capacitors C ₁ and C ₂ ,
An oscillation circuit 33 is configured together with the resistor R ₂ and the IC 32. Similarly,
The inductor L ₁ of the semi-fixed capacitor C _3, C _4, resistor R _3, IC3
4 configures the oscillation circuit 35. The output from the IC terminal 6 of IC32,34 to be output from these oscillation circuits 33 and 35 are all connected in common to the resistor R ₄ is a wired-OR configuration. Further, an oscillation circuit 37 having an unstable multivibrator configuration including resistors R ₅ and R ₆ , capacitors C ₅ and C ₆ and IC 36 is provided, and the output is taken out from the third terminal of IC 36.
The output from the third terminal of IC36 oscillates at a frequency f _S according to the inductance of the sensor coil 31 is input as a strobe signal for the oscillator circuit 33 to pin 7 of IC32 in the oscillation circuit 33 is at H level . Also, when the output from the third terminal of the IC 36 is at the L level, the oscillation circuit is connected to the seventh terminal of the IC 34 in the oscillation circuit 35 by an inverter 39 composed of resistors R ₇ , R ₈ , R ₉ and two-stage transistors of the IC 38. It is input as a strobe signal to the 33, oscillates at a frequency f _R in accordance with the inductance of the inductor L _1. In this way, the sensor oscillation (frequency
f _S ) and the reference oscillation (frequency f _R ) are alternately repeated.

These oscillation frequency signal is output to the next stage through the capacitor C _7.

The next stage of the capacitor C _7, firstly, IC 40 with two transistors, resistors R _10, R _11, differential amplifier circuit 41 including the inductor L ₂ and capacitor C ₈ is connected. Here, the tuning frequency due to the inductor L ₂ and capacitor C ₈ is set slightly shifted frequency than the previous stage of the sensor oscillation frequency f _S and the reference oscillation frequency f _R. For this reason,
At the output terminal 42 of the differential amplifier circuit 41, a voltage having an amplitude corresponding to the input frequency is generated. Capacitor C ₉ , resistor
R ₁₂ and R ₁₃ , the diode D ₁ , and the capacitor C ₁₀ detect the output from the differential amplifier circuit 41 and convert it to a DC output. The converted output is applied to Emitsutafuorowa circuit 44 IC 43 by the transistor and the resistor R _14, the output of the Emitsutafuorowa circuit 44 is sent to the next stage of the amplifier circuit through the capacitor C _11. At this time, it is also connected to the stabilized power output by the IC 46 through the FET 45. The gate terminal of the FET 45 is connected to the oscillating circuit (unstable multivibrator) 37, and the FET 45 becomes conductive at the time of reference oscillation when the output of the IC 36 is at the L level, and is clamped to the reference voltage.

An amplification circuit located at the next stage of the emitter follower circuit 44 is an inverting integration amplifier circuit 48 including resistors R ₁₅ , R ₁₆ , R ₁₇ , a capacitor C ₁₂ and an IC 47, which is used when the sensor oscillates during detection output from the emitter follower circuit 44. Is inverted and amplified and integrated to obtain a complete DC output.

Resistors R ₁₈ , R ₁₉ , R ₂₀ , R ₂₁ , R
_{22, R 23, R 24,} R 25, a variable resistor VR _1, switch SW _1, SW ₂ and IC
A comparator circuit 50 is connected, and the output from the amplifier circuit 48 is compared with a reference voltage adjustable by a variable resistor VR ₁ and switches SW ₁ and SW ₂ for switching.
The output of this comparator circuit 50 is
D, resistors R ₂₆ , R ₂₇ , LED 51, resistors R ₂₈ , R ₂₉ , R _30, and an output buffer 52 of two-stage transistors Q ₂ , Q ₃ .

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

With such an agent concentration 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 a change in inductance is detected as a change in oscillation frequency and further a change in voltage. By feeding back the toner to the toner supply system, the density is made constant.

2, a registration sensor 55 is provided near the registration roller 17 to detect the passage of the leading and trailing edges of the transfer paper 15 conveyed toward the photoreceptor 1 and to control the timing of the copying operation. . Here, in this embodiment,
The registration sensor 55 is also used as a length detecting means for detecting the length of the image area in the photoconductor moving direction. That is, the registration sensor 55 detects the transport length from the leading edge of the transfer paper, and determines whether or not the image area length at that time = the transfer paper length is longer than a predetermined length. Make a determination.

Next, the configuration of a control device 59 which controls the entire digital copying machine shown in FIG. 2 and also serves as control means of the present embodiment will be described with reference to FIG. First, a CPU 60 that controls the entire system is provided. A reset clock element 61 is connected to the CPU 60, and supplies a reset signal and a clock signal to the CPU 60. Here, the clock signal is a pulse-like signal of 5 MHz for causing the CPU 60 to operate. The reset signal is a signal for resetting the CPU 60 for several tens of ms when the power is turned on. Also, the upper and lower RAMs 63a and 63b are connected to the CPU 60 via upper and lower latch elements 62a and 62b.
And the upper and lower ROMs 44a and 44b are connected. further,
The I / O element 45 is connected to the CPU 60. Here, ROM44
Control programs to be executed by the CPU 60 are written in a and 44b. Thus, the CPU 60 reads the control program from the ROMs 64a and 64b, reads and writes necessary information from and to the RAMs 63a and 63b, and performs external control via the I / O element 65. That is, the arithmetic means is constituted mainly by the CPU 60 and the RAM 63 and the ROM 64. Here, the latch elements 62a, 62b
In the case of AD0 to AD7 and AD8 to AD15 output from the CPU 60, the address output and the data output are time-division-multiplexed. Used to supply. The decoding element 66 is also connected to the CPU 60. The decoding element 66 decodes the output signals S0 to S2 from the CPU 60, and outputs an ALE signal, an RD (read) signal, and a WR (write)
A signal, an INTA (into acknowledgment) signal and the like are generated.

Further, a timer element 47 is provided. This timer element 67 is supplied from the reset clock element 61.2.
A 5 MHz PCLK signal is used as a basic clock, and pulses of various frequency patterns are output from OUT0 according to the mode and data specified by the CPU 60. 68 is an interrupter element.

On the other hand, the I / O element 65 accesses an input element such as a sensor and a key and an output element such as a display LED and a heater. Here, there are three ports of A, B, and C each having 8 bits, and the A and B ports are output ports, and the C port is an input port. More specifically, the lower four bits PA0 to PA3 of the A port are connected to the A / D conversion element 69 by a control signal, and the other output ports PA4 to PA7 and PB0 to PB7 are connected to an external charging charger, developing motor, P It is connected to sensor LED, toner supply clutch, and laser optical system. Input C
The port is supplied with a toner supply signal from the registration sensor and the F sensor, and the least significant bit of the C port is supplied with the DATA signal from the A / D conversion element 69.

Here, the A / D conversion element 69 converts an analog voltage value output from the phototransistor 27 of the P sensor 25 into an 8-bit digital value and transmits the digital value to the CPU 60.
Due to this operation, ▲ is always active (L level) when performing A / D conversion. ADCLK is the A / D
This is a signal for causing the conversion element 69 to output DATA. At this time, the A / D conversion element 69 used in this embodiment is based on the MB4052, and has only one DATA terminal, so that data is output serially. Therefore, every time a pulse signal is input to ADCLK, the data is output eight times from the most significant data. On the other hand, every time the CPU 60 issues a pulse of ADCLK, the CPU 60 of the I / O element 65
The 0th bit of the port is read, and this operation is repeated eight times.
Get bit data. The remaining C0 and C1 are
Since four A / D conversion circuits are incorporated, this signal is used to determine which circuit is to be selected.

Next, in the configuration of the present embodiment including both the P sensor 25 and the F sensor 30, a toner supply control operation based on the detection result will be described.

First, the basic control of toner supply based on the P sensor 25 will be described. Normally, during copying, the CPU 6
0 outputs a laser exposure request signal at a predetermined timing. Thus, the photosensitive member 1 is exposed according to the image data to form an electrostatic latent image. When the laser exposure request signal is turned off and a predetermined time has elapsed, the reference pattern request signal is turned on and turned off after a certain time. As a result, an electrostatic latent image of a 15 × 15 mm ² size reference pattern is formed on the photoreceptor 1 immediately after the image area, and is developed. This operation is repeated at the time of repeat copying, and a reference pattern image is formed between image areas. The LED 26 in the P sensor 25 turns on when the rear end of the image area passes through the position of the P sensor 25, and turns off when the rear end of the reference pattern image passes. The CPU 60 controls the A / D conversion element 6 several times at 10 ms intervals until the rear end of the image area passes on the P sensor 25 and the front end of the reference pattern image arrives.
The P sensor output voltage is sampled by 9 and the average value is calculated and stored in a buffer. This is sampling of a non-pattern part. Next, while the reference pattern image passes on the P sensor 25, the output voltage of the P sensor is sampled by the A / D conversion element 69 several times at intervals of 10 ms, and the average value is calculated and stored in a buffer. This is sampling of the pattern portion. When the value sampled in this way is converted into a voltage, the value is around 4 V in the non-pattern portion and around 1.5 V in the pattern portion. When the sampling point is black (dark), the voltage decreases, and when the sampling point is light, the voltage increases. Here, if the voltage of the pattern portion is equal to or more than a certain value, for example, 1.5 V or more, it is determined that the toner density is low, and the toner is supplied. When toner is supplied, the toner is supplied according to a predetermined supply rate.
Assuming that the supply rate is 30% and the time until the next sampling is 10 seconds, the toner supply clutch is turned on for 3 seconds. If the detected voltage of the pattern portion is 1.5 V or less, it is determined that the toner density is high, and toner supply is not performed. If a repeat copy is being performed, such an operation is repeated.

Next, basic control of toner supply based on the F sensor 30 will be described. During copying, when the development motor is on, CPU6
A value of 0 checks the toner supply signal. If the toner supply signal is active, the toner supply clutch is turned on. If the toner supply signal is not active, the toner supply clutch is turned off.
Such an operation is repeated during the repeat copy. If the toner supply signal is activated for a certain period of time (for example, 20 seconds or more), the machine is stopped at the toner near end, and if a certain number of copies, for example, 50 sheets or more, have been made, the machine is stopped at the toner end. After this, replace the toner cartridge and replenish the toner.
The developing motor is rotated to turn on the toner supply clutch, and the toner supply signal is checked. When the toner supply signal becomes inactive, it is determined that the toner concentration (agent concentration) in the developing device 4 has returned to an appropriate state, the developing motor and the toner supply clutch are turned off, the toner end is released, and copying is performed. Make it possible.

As described above, the P sensor control and the F sensor control are prepared. In the present embodiment, the toner supply control is normally performed by the P sensor control, and both controls are performed at the time of a long copy of a predetermined length or more. The selection is switched. FIG. 1 shows such a P
5 is a flowchart showing switching between sensor control and F sensor control. First, in the copying operation, the length of time required for the transfer paper 15 to pass through the registration sensor 55 is checked to determine the length of the transfer paper 15 and, accordingly, the length of the image area on the photoreceptor 1 is a predetermined length. It is determined whether or not it is a scale. If the copy is not a long copy of 1 m or more, toner supply is controlled by the above-described P sensor control method.

On the other hand, in the registration sensor 55, the paper size (length) is
If it is determined that the distance is 1 m or more, this is stored, and it is checked whether or not the image has passed the developing unit position on the photoreceptor 1 by 1 m from its leading end. Supply control is performed according to the replenishment rate according to the above, and at the stage of passing the developing unit by 1 m or more, the control at the replenishment rate by the P sensor control is stopped, and instead, the toner replenishment control by the F sensor control method is executed. . Thereafter, when the registration sensor 55 detects the passage of the rear end of the transfer paper 15 and the laser exposure request signal is turned off, a reference pattern image is created at normal timing, and the P sensor 25
Sampling is performed. At this point, the control by the F sensor 30 is stopped, and the control is returned to the control by the P sensor 25.

As described above, at the time of copying a long image (for example, 5 m or more) based on the P sensor control method and the image density detection by the P sensor 25 cannot be performed for a long time, switching to the F sensor control method is performed at a predetermined timing. The toner supply is controlled and the P sensor 25 returns to the P sensor control method from the time when the image density can be detected by the P sensor 25. With the temporary assistance provided by the F sensor control method, The toner supply control is performed, and the toner density control is completed.

As described above, the present invention provides a charging unit for charging a photoconductor, an exposure unit for forming an electrostatic latent image on the charged photoconductor, and a developing unit for developing the electrostatic latent image on the photoconductor. Means, an image density detecting means for detecting a developed density of a reference pattern formed at a position between image areas immediately after the image area on the photoreceptor, and a replenishing means for replenishing toner in the developing means. In an image density control device in a copying machine or the like, an agent concentration detecting unit that detects a developer concentration in the developing unit is provided,
A length detecting means for detecting a length of the image area in the photoconductor moving direction is provided. Basically, the replenishing means is controlled by a detection result by the image density detecting means, and a detection result of the length detecting means is provided. When the length exceeds a predetermined length, the control unit switches to the agent concentration detecting unit at a predetermined timing and controls the replenishing unit based on the detection result by the agent concentration detecting unit. Based on the toner replenishment based on the result, for example, in the case of a long image, if the image density detection becomes long and impossible, the image density control is switched to the toner replenishment control based on the detection result of the agent density detecting means. It is possible to continue, and it is possible to prevent the image density from becoming extremely low in the case of a long image.

[Brief description of the drawings]

FIG. 1 shows an embodiment of the present invention. FIG. 1 is a flow chart showing switching of P sensor control / F sensor control.
The figure is a schematic configuration diagram of the whole, FIG. 3 is a P sensor detection circuit diagram,
FIG. 4 is an F sensor detection circuit diagram, and FIG. 5 is a block diagram of a control device. 1 photoreceptor, 2 charging means, 3 exposure means, 4
... developing means, 10 ... toner replenishing means, 25 ... image density detecting means, 30 ... agent concentration detecting means, 55 ... length detecting means,
59 ... Control means

Continuation of the front page (58) Field surveyed (Int. Cl. ⁶ , DB name) G03G 15/00 303 G03G 21/00 370-540 G03G 15/08 115

Claims (1)

(57) [Claims] A charging unit configured to charge the photosensitive member; an exposure unit configured to form an electrostatic latent image on the charged photosensitive member; a developing unit configured to develop the electrostatic latent image on the photosensitive member; Image density in a copying machine or the like having image density detecting means for detecting the developed density of a reference pattern formed at a position between image areas immediately after the image area, and replenishing means for replenishing toner in the developing means. In the control device, an agent concentration detecting unit for detecting a developer concentration in the developing unit is provided, and a length detecting unit for detecting a length of the image area in the photoconductor moving direction is provided. The replenishing means is controlled based on the detection result of the detecting means, and when the detection result of the length detecting means exceeds a predetermined length, switching is made to the agent concentration detecting means at a predetermined timing, and the agent concentration detecting means is used. Detection result Image density control device in the copying machine or the like, characterized in that a control means for controlling said replenishing means by.